AU648837B2

AU648837B2 – Anti-reversion coagents for rubber vulcanization
– Google Patents

AU648837B2 – Anti-reversion coagents for rubber vulcanization
– Google Patents
Anti-reversion coagents for rubber vulcanization

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Publication number
AU648837B2

AU648837B2
AU87656/91A
AU8765691A
AU648837B2
AU 648837 B2
AU648837 B2
AU 648837B2
AU 87656/91 A
AU87656/91 A
AU 87656/91A
AU 8765691 A
AU8765691 A
AU 8765691A
AU 648837 B2
AU648837 B2
AU 648837B2
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AU
Australia
Prior art keywords
sulfur
vulcanization
rubber
reversion
coagent
Prior art date
1990-10-29
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AU87656/91A
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AU8765691A
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Inventor
Rabindra Nath Datta
Rudolf Frank De Block
Andreas Herman Hogt
Auke Gerardus Talma
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Flexsys America LP

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Akzo NV
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1990-10-29
Filing date
1991-10-29
Publication date
1994-05-05

1991-10-29
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Akzo NV

1992-05-26
Publication of AU8765691A
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patent/AU8765691A/en

1994-05-05
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1994-05-05
Publication of AU648837B2
publication
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patent/AU648837B2/en

2007-09-13
Assigned to FLEXSYS AMERICA L.P.
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FLEXSYS AMERICA L.P.
Alteration of Name(s) in Register under S187
Assignors: AKZO N.V.

2011-10-29
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C—CHEMISTRY; METALLURGY

C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON

C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS

C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons

B—PERFORMING OPERATIONS; TRANSPORTING

B60—VEHICLES IN GENERAL

B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES

B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition

C—CHEMISTRY; METALLURGY

C07—ORGANIC CHEMISTRY

C07D—HETEROCYCLIC COMPOUNDS

C07D207/00—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom

C07D207/02—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom

C07D207/44—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having three double bonds between ring members or between ring members and non-ring members

C07D207/444—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having three double bonds between ring members or between ring members and non-ring members having two doubly-bound oxygen atoms directly attached in positions 2 and 5

C07D207/448—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having three double bonds between ring members or between ring members and non-ring members having two doubly-bound oxygen atoms directly attached in positions 2 and 5 with only hydrogen atoms or radicals containing only hydrogen and carbon atoms directly attached to other ring carbon atoms, e.g. maleimide

C07D207/452—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having three double bonds between ring members or between ring members and non-ring members having two doubly-bound oxygen atoms directly attached in positions 2 and 5 with only hydrogen atoms or radicals containing only hydrogen and carbon atoms directly attached to other ring carbon atoms, e.g. maleimide with hydrocarbon radicals, substituted by hetero atoms, directly attached to the ring nitrogen atom

C—CHEMISTRY; METALLURGY

C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON

C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients

C08K5/00—Use of organic ingredients

C08K5/16—Nitrogen-containing compounds

C08K5/34—Heterocyclic compounds having nitrogen in the ring

C08K5/3412—Heterocyclic compounds having nitrogen in the ring having one nitrogen atom in the ring

C08K5/3415—Five-membered rings

C—CHEMISTRY; METALLURGY

C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON

C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients

C08K5/00—Use of organic ingredients

C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds

C08K5/37—Thiols

C08K5/378—Thiols containing heterocyclic rings

C—CHEMISTRY; METALLURGY

C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON

C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients

C08K5/00—Use of organic ingredients

C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds

C08K5/39—Thiocarbamic acids; Derivatives thereof, e.g. dithiocarbamates

C—CHEMISTRY; METALLURGY

C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON

C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients

C08K5/00—Use of organic ingredients

C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds

C08K5/41—Compounds containing sulfur bound to oxygen

C—CHEMISTRY; METALLURGY

C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON

C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS

C08L7/00—Compositions of natural rubber

C—CHEMISTRY; METALLURGY

C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON

C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS

C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons

C08L9/06—Copolymers with styrene

Description

0PI DATE 26/05/92 AOJP DATE 09/07/92 APPLN. ID 87656 91 PCT NUMBER PCT/EP91/02048 TREATY (PCT) (51) International Patent Classification 5 International Publication Number: WO 92/07904 C08K 5/3415, C08J 3/24 Al C08L 21/0 0 (43) International Publication Date: 14 May 1992 (14.05.92) (21) International Application Number: PCT/EP91/02048 (74) Agent: SCHALKWIJK, Pieter, Cornelis; Akzo Velperweg 76, Postbus 9300, NL-6800 SB Arnhem (NL).
(22) International Filing Date: 29 October 1991 (29.10.91) (81) Designated States: AT (European patent), AU, BE (Euro- Priority data: pe1 patent), BR, CA, CH (European patent), CS, DE 90202864.6 29 October 1990 (29.10.90) EP (European patent), DK (European patent), ES (Euro- (34) Countriesfor which the regional pean patent), Fl, FR (European patent), GB (European or international application patent), GR (European patent), HU, IT (European pawas filed: NL et al. tent), JP, KR, LU (European patent), NL (European patent), PL, SE (European patent), SU US.
(71) Applicant (for all designated States except US): AKZO N.V.
[NL/NL]; Velperweg 76, NL-6824 BM Arnhem Published With international search report.
(72) inventors; and Inventors/Applicants (for US only) HOGT, Andreas, Herman [NL/NL]; Deurningerstraat 58, NL-7514 BJ Eaischede TALMA, Auke, Gerardus [NL/NL]; Polakstraat 34, NL-7437 AT Bathmen DE BLOCK, 4 Rudolf, Frank [NL/NL]; Vonderstraat 80, NL-7419 BR Deventer DATTA, Rabindra, Nath [IN/NL]; Slauerhoffgaarde 2, NL-7414 XK Deventer (NL).
(54) Title: ANTI-REVERSION COAGENTS FOR RUBBER VULCANIZATION (57) Abstract A rubber composition which is the vulcanization reaction product of a rubber, sulfur or a sulfur donor and particular antireversion coagents, is disclosed. The anti-reversion coagents only partially react under sulfur-vulcanization reaction conditions up to optimum cure, and, after optimum cure, form cross-links bonded to the sulfur cross-linked rubbers by carbon-carbon linkages.
Also disclosed are a vulcanization process carried out in the presence of the anti-reversion coagents and the use of these antireverFson coagents in the sulfur-vulcanization of rubbers. The anti-reversion coagents of the disclosure pro-ide sulfur-vulcanized rubbers having significantly improved physical properties.
See back of page WO 92/07904 PCT/EP91/02048 Anti-Reversion Coagents for Rubber Vulcanization This invention relates to a rubber composition having improved physical properties. More particularly, it relates to a sulfur-vulcanized rubber composition which is vulcanized in the presence of particular anti-reversion coagents. The invention also relates to a sulfur-vulcanization process which is carried out in the presence of particular anti-reversion coagents and the use of particular anti-reversion coagents in the sulfur-vulcanization of rubber. Finally, the invention also relates to rubber products comprising rubber vulcanized with sulfur in the presence of particular anti-reversion coagents.
In the tire and belt industries, among others, better mcchanical ar’ heat resistance properties are being demanded. It has long been known that the mechanical properties of rubber can be improved by using a large amount of sulfur as a cross-linking agent to increase the crosslink density in vulcanized rubbers. However, the use of large amounts of sulfur suffers from the disadvantage that it produces reversion and leads to a marked decrease in heat resistance and resistance to flex cracking, among other properties, in the final product. The fact that reversion is a continuing problem can be seen from, «Rubber Microstructure and Reversion,» Nordsiek, Dr. Rubber World, 197 pp. 30-38, 1987, and, «Physikalische und Chemische Aspekte der Reversion,» Kautschuk Gummi Kunstoffe, 34, No. 9, 1981.
In order to eliminate the foregoing disadvantage, it has been proposed to add coagents to sulfur-vulcanization systems. One known type of coagent are the maleimides. Such vulcanization systems are disclosed in, «Vulcanization With Maleimides,» Journal of Applied Polymer Science, Vol. 8, pp. 2281-2298 (1964).
U.S. patent 3,297,713 suggests the use of dithiobis .(N-phenylmaleimides) as vulcanizing agents for rubber. However, this system does not employ .sulfur as a vulcanization agent and thus suffers from several disadvantages which result from the absence of sulfur cross-links in the rubber product.
SUBSTITUTE
SHEET
WO 92/07904 PC/EP91/02048 2 Japanese patent publication J6 1014-238 discloses sulfur-vulcanization systems wherein maleimides are used as coagents and which also contain either dibenzothiazyl disulfide or tetramethylthiuram disulfide.
However, this solution is of limited application since only vulcanization accelerators having relatively short scorch times can be used with the bis-maleimides.
European patent application 0 191 931 suggests that the use of a bismaleimide compound in combination with a sulfenamide and a dithiophosphoric acid leads to further improvements in the mechanical and anti-reversion properties of sulfur-vulcanized rubbers. The patent specification claims that these rubbers exhibit improved resistance to reversion, resistance to heat ageing and resistance to flex cracking. However, this system is limited to vulcanization carried out in the presence of a sulfenamide accelerator in combination with a dithiophosphoric acid accelerator and is thus of limited utility in actual practice.
In the article, «Change in the Structure and Properties of Vulcanizates Based on Natural Rubber Under Prolonged Vulcanization in the Presence of Vulcanizing Systems Containing Sulfur and Bismaleimides,» Chavchich, et al., Kauchuk i Rezina, vol. 4, pp. 20-3, 1981, there is disclosed that vulcanization uf natural rubber tread stocks with sulfur in the presence of m-phenylenebismaleimide at 143 0 C over a 600-minute period gave vulcanizates with enhanced physiomechanical properties and resistance to reversion.
Other articles relating to the sulfur-vulcanization of rubbers using bismaleimides as coagents include, «Vulcanization of cis-1,4-isoprene rubber by derivatives of maleimide under the action of high temperatures and radiation,» Kauchuk i Rezina, vol. 3, pp. 10-12, 1974; «High-temperature Vulcanization of Unsaturated Rubbers by Thio Derivatives of Maleimide,» Kauchuk i Rezina, vol. 3, pp. 16-19, 1975; and, «Influence of the Type and Concentration of Crosslinking Agent on the Effectiveness of a Combined System of Bismaleimide and Sulfur,» Kauchuk i Rezina, No. 10, pp. 15-19, 1985.
C(I nczTrrI I–jr qLJEur= WO 92/07904 PCT/EP91/02048 3 Even more recently, Japanese patent applications Jb 3286-445 and J6 3312-333 disclosed the vulcanization of rubber with sulfur and an aliphatic bis-maleimide or N,N’-toluene bis-maleimide. These particular bis-maleimides are said to improve the heat resistance and adhesion properties of the rubbers.
Further, European patent applications 345 825 and 410 152 also relate to the use of bismaleimides as coagents in sulfur-vulcanization of rubber. These two patents are directed to vulcanization systems which contain a second coagent, presumably to improve upon the bismaleimide system.
However, despite the fact that some of the above patents claim to reduce reversion by addition of a bismaleimide, in actual practice th2 reduction in reversion achieved with the bismaleimides is insufficient. Accordingly, although the reversion and the heat resistance are slightly improved, the problem remains that there is no generally applicable anti-reversion agent which may be used in combination with a number of different rubber accelerators during the vulcanization process and which satisfactorily solves the reversion problem while at the same time significantly improving the heat resistance of sulfurvulcanized rubbers without having an adverse affect on other rubber properties.
Another type of curing system used to inhibit reversion in rubbers is disclosed in, «Latest Developments in the Urethane Crosslinking of Natural Rubber,» Kautschuk Gummi Kunstoffe 36, pp. 677-684, 1983.
However, this so-called NOVOR system also suffers from several disadvantages including very limited applicability to particular vulcaniza.
tion processes.
Further, in Canadian Patent no. 738,500 the vulcanization of rubbers in the absence of sulfur, with either bis-maleimides and biscitraconimides, is disclosed. This process had, for its purpose, to be an alternative to sulfur-vulcanization processes. However, the SUBs,1*TITLJt E 9ET WO 92/07904 PCT/EP91/02048 4 rubber products made by the process of this patent suffer from the usual disadvantages of peroxide-cured rubbers such as low tensile strength and significant reductions irn other important properties.
This patent does not disclose the use of the bis-maleimides or biscitraconimides in the sulfur-vulcanization of rubber.
The present invention provides a solution to the above problems by the use of a novel class of anti-reversion coagents in the sulfurvulcanization of rubbers. More particularly, in a first aspect, the present invent’on relates to a sulfur-vulcanized rubber composition which comprises the vulcanization reaction product of: 100 parts by weight of at least one natural or synthetic rubber; 0.1 to 25 parts by weight of sulfur and/or a sufficient amount of a sulfur donor to provide the equivalent ot 0.1 to 25 parts by weight of sulfur; and 0.1 to parts by weight of a coagent which only partially reacts under sulfur-vulcanization reaction conditions up to optimum cure, and which, after optimum cure, forms cross-links bonded to the sulfur cross-linked rubber by a carbon-carbon linkage at a rate sufficient to compensate for from 10 to 200 percent of the reversion in said rubber composition.
In addition, the present invention relates to a vulcanization process carried out in the presence of the anti-reversion coagents and the use of these anti-reversion coagents in the sulfur-vulcanization of rubbers. Further, the invention also encompasses rubber products which comprise at least some rubber which has been vulcanized with sulfur in the presence of said anti-reversion coagents.
The present invention provides an excellent anti-reversion effect as well as improvements in several rubber properties without having a significant adverse effect on the remaining properties, when compared with similar sulfur-vulcanization systems using other coagents.
SUBSTITUTE
SHEET
WO 92/07904 PCT/EP91/02048 The present invention is applicable to all natural and synthetic rubbers. Examples of such rubbers include, but are not limited to, natural rubber, styrene-butadiene rubber, butadiene rubber, isoprene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, isopreneisobutylene rubber, brominated isoprene-isobutylene rubber, chlorinated isoprene-isobutylene rubber, ethylene-propylene-diene terpolymers, as well as combinations of two or more of these rubbers and combinations of one or more of these rubbers with other rubbers and/or thermoplastics.
Examples of sulfur which may be used in the present invention include various types of sulfur such as powdered sulfur, precipitated sulfur and insoluble sulfur. Also, sulfur donors may be used in place of, or in addition to sulfur in order to provide the required level of sulfur during the vulcanization process. Examples of such sulfur donors include, but are not limited to, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, dipentamethylene thiuram hexasulfide, dipentamethylene thiuram tet-asulfide, dithiodimorpholine and mixtures thereof.
In tilis text, references to sulfur shall include sulfur donors and mixtures of sulfur and sulfur donors. Further, references to the quantity of sulfur employed in the vulcanization, when applied to sulfur donors, refer to a quantity of sulfur donor which is required to provide the equivalent amount of sulfur that is specified.
The anti-reversion coagents of the present invention are characterized by the fact that they must be capable of forming cross-links bonded to the rubber oy a carbon-carbon linkage. This type of cross-link is known in the rubber literature from, for example, «High-temperature vulcanization of unsaturated rubbers by thio derivatives of maleimide,» Krashennikov et al., Kauchuk i Rezina, No. 3, pp. 16-20, 1975. Such cross-links bonded to the rubber by a carbon-carbon linkage are highly desirable in rubbers, and parviularly sulfurvulcanized rubbers since such cross-links are thermally stable.
SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 6 Accordingly, we have found that it is desirable, in sulfurvulcanization, to proC-ue cross-links bonded to the rubber by carboncarbon linkages. For the purposes of this patent application, these cross-links will be hereinafter referred to as, «carbon-carbon» crosslinks. In order to make a thermally stable rubber composition which still possesses the advantageous properties of sulfur-vulcanization, however, it remains necessary to combine the formation of carboncarbon linkages with the formation of the stable monosulfidic crosslinks which result from sulfur-vulcanization.
While it is possible to obtain a significant number of carbon-carbon cross-links by sulfur-vulcanizing rubber in the presence of bismaleimides, we have found that such rubbers still suffer from significant reversion (reduction in the cross-link density) upon thermal loading of the rubber after vulcanization. This leads to a corresponding decrease in some of the imrortant properties of such rubber compositions during their use in, for example, tires.
While not wishing to be bound by any particular theory, it is thought that the anti-reversion coagents of the present invention solve this long-standing problem since they are sufficiently unreactive under sulfur-vulcanization conditions such that, at optimum cure, a substantial portion of the coagent remains in the rubber composition in a form in which it is still capable of reacting with the sulfurvulcanizea rubber to form additional cross-links, which cross-links are bonded to the rubber by a carbon-carbon linkage.
One possible measure of the reactivity of the anti-reversion coagents under sulfur-vulcanization conditions up to optimum cure is crosslinking efficiency. Cross-linking efficiency, in the context of this patent application, refers to a measure of the percentage increase or decrease in shear modulus of the vulcanized rubber, per millimole of anti-reversion coagent, per 100 grams of rubber, as compared with the same rubber composition vulcanized under the same reaction conditions in the absence of the anti-reversion coagent. The shear modulus SUBSTiTu iE SHEET WO 92/07904 PCT/EP91/02048 7 measurements for determining the cross-linking efficiency are made on a rubber composition at optimum cure. For a definition of optimum cure see, W. Hofmann, «Rubber Technology Handbook.» For example, if 1 millimole of anti-reversion coagent, when compared to the t 90 control, gives an increase in the shear modulus (as measured in accordance with the procedure of the examples hereafter) of 0.5% at optimum cure, then the cross-linking efficiency for that anti-reversion coagent is With t 90 control is meant the optimum cure time of a rubber composition vulcanized without anti-reversion coagent. In addition, if for the same amount of coagent, 0.3% less crosslinks are formed, then the cross-linking efficiency is The cross-linking efficiency gives an indication of the influence of the coagent on the sulfur-vulcanization up to optimum cure and thereby an indication of the cross-linking reactivity of the coagent under sulfur-vulcanization conditions. In general, the anti-reversion coagents of the present invention exert little influence on the sulfur-vulcanized rubber up to optimum cure.
We have found that the preferred anti-reversion coagents of the present invention generally exhibit a cross-linking efficiency of between and More preferred coagents have a cross-linking efficiency of 1.0 to and most preferred coagents have a cross-linking efficiency of 0.5 to However, it should be noted that the cross-linking efficiency is only an inidication of the reactivity of the coagent up to optimum cure, and does not directly measure what is thought to be the important feature of the coagents of the present invention, namely that some of the coagent is still present at optimum cure in a form capable of reacting with the sulfur-vulcanized rubber to form additional cross-links. Yhus, some useful coagents may have a higher or lower cross-linking efficiency but still fall within the scope of the present invention if they meet all of the other criteria.
SUBSTITUTE
SHEET
WO 92/07904 PCT/EP91/02048 8 The final characterizing feature of the coagents of the present invention is that they must form stable carbon-carbon cross-links at a rate sufficient to compensate for 10-200% of the reversion in that rubber composition. It is this final feature of the present coagents which prevents significant reversion of the sulfur-vulcanized rubber since, the degraded polysul:ide cross-links are simply replaced by the thermally stable carbon-carbon cross-links formed by the anti-reversion coagents, thereby holding the torque at a relatively constant level.
The rate of formation of carbon-carbon cross-links after optimum cure can vary within a particular range depending upon how much reversion or marching can be tolerated in the particular rubber composition.
Marching is when the compensation of the coagent exceeds the reversion such that, after optimum cure, a further increase in the cross-link density occurs. It is preferred that the coagent exhibit a reactivity which compensates for at least 10% of the reversion in the rubber composition and not more than 200% of the reversion. More preferably, the coagent compensates for from 40-150% of the reversion and most preferably for 70-120% of the reversion. Of course, the amount of anti-reversion compensation which is desired and/or acceptable depends to a great extent on the particular rubber composition, the application in which the rubber is used and the conditions to which the rubber will be exposed during its lifetime.
Anti-reversion coagents of the present invention include, but are not limited to compounds represented by the general formula A: Q1-D-(Q2)n wherein D, optionally containing one or more heteroatoms or groups selected from nitrogen, oxygen, silicon, phosphorus, boron, sulphone and sulphoxy, is a monomeric or oligomeric divalent, trivalent or tetravalent group, n is an integer selected from 1, 2 or 3, Q1 and Q2 are independently selected from the formulas I and II: 01 Inc-r C7rl ITF= qHPFT WO 92/07904 PCT/EP91/02048 9 B R 1 -N R2 (I) 3
II
BI
and; B RI II -N
R
2 (II) 3 B, H wherein R 1
R
2 and R 3 are independently selected from hydrogen, C 1
-C
18 alkyl groups, C 3
-C
18 cycloalkyl groups, C 6
-C
18 aryl groups, C 7
-C
30 aralkyl groups and C 7
-C
30 alkaryl groups and R 2 and R 3 may combine to form a ring when R 1 is hydrogen; B and B, are independently selected from the following hetero atoms: oxygen and sulfur.
The imides of the present invention are, in general, known compounds and may be prepared by the methods disclosed in, «The synthesis of Biscitraconimides and Polybiscitraconimides,» Galanti, A.V. and Scola, Journ. of Poly. Sci.: Polymer Chemistry Edition, Vol. 19, pp.
451-475, (1981); and «The Synthesis of Bisitaconamic Acids, Isomeric Bisimide Monomers,» Galanti, A.V. et al., Journ. Poly. Sci.: Polymer Chemistry Edition, Vol. 20, pp. 233-239 (1982) and Hartford, S.L., Subramanian, S. and Parker, Journ. Poly. Sci.: Polymer Chemistry Edition, Vol. 16, p. 137, 1982, the disclosures of which are hereby incorporated by reference.
The imide compounds useful in the present invention and represented by the formula A include, but are not limited to, the biscitraconimides wherein Q1 and Q2 are of the formula I, R 1
=R
2 =Rj=H, n=l and B=Bl=oxygen; the bis-itaconimides wherein Qi and Q2 are of the formula q1 Mcz- i-ri i-r= ct-ir- r WO 92/07904 PCF/EP9I /02048 I I, Rl=R 2
=R
3 n=1 and B=B’~oxygen; the mixed citraconimide and itaconimide wherein Q1 is of the formula I, Q2 is of the formula II, Rl=R 2
=R
3 n=1 and B=Bl=oxygen; and mixtures of the above-mentioned compounds.
More specifically, the group 0 mentioned in the formula A can be a monomeric divalent, trivalent or tetravalent linear or branched radical chosen from a Cl.-CI 8 alkyl, C 2
-C
18 alkenyl, C 2
-C
18 alkynyl,
C
3
-C
18 cycloalkyl, C 3
-C
18 polycycloalkyl, C 6
-C
18 aryl, C 6
-C
30 polyaryl, C 7
-C
30 aralkyl, C 7
-C
30 alkaryl, oligomers of one or more of these radicals, and which radicals may optionally contain one or more of oxygen, nitrogen, silicon, phosphorus, sulphone, sulfoxy and boron, all of which radicals may also be optionally substituted at one or more of the atoms in the radical with a substituent selected from oxygen, nitrogen, silicon, Si0 2 sulfoxy, boron, phosphorus, amido, imino, azo, diazo, hydrazo, azoxy, alkoxy, hydroxy, iodine, fluorine, bromine, chlorine, carbonyl, carboxy, ester, carboxylate, S0 2 S03, sulphonamido, SiO 3 nitro, imido, thiocarbonyl cyano, and epoxy groups.
More specific examples of some of the imide compounds useful in the present invention includr-, but are not limited to, the following: N,NI-ethylene-bis-citraconic imide (BCI-C2); N,N’-hexamethylene-bis-citraconic imide (BCI-C6); N,N’-tetramethylene-bis-citraconic imide; N,N’-2-methyl-pentamethylene-bis-citraconic imide; N,N’-.(i,3-propylene)-bis-citraconic imide; N,N’-(3,3′-oxydipropylene)-bis-citraconic imide; N,N’-(aminodiethylene)-bis-citraconic imide; N,N’-(aminodipropylene)-bis-citraconic imide; N,N’-(1,10-(4,7-dioxa)-decanediyl )-bis-citraconic imide; N,N’-(4,4′-(di-(2-methylcyclohexyl)methylene)-bis-citraconic imide; N,N’-(4,41-dicyclohexy1-isopropylene)bis-citraconic imide; N.M’ -(4,4′-dicyclohexyloxy)-bis-citraconic imide; N,N’ -(4,4′-dicyclohexylene)-bis-citraconic imide; SUBSTITUTE SHEET WO 92/07904 WO 9207904PCT/EP9I /02048 I1I N,N’-o-phenylene-bis–citraconic imide; N,NI-m-phenylene-bis-citraconic imide(BCI-MP); N,Ni-m-phenylene-bis-itaconic imide (BII-MP); N,N’-p-phenylene-bis-citraconic imide; NN’-(5-chloro-1,3-phenylene)-bis-citraconic imide; i,N’l-(5-hydroxy-1,3-phenylene)-bis-citraconic imide; N,N’-(5-methoxy-1,3-phenylene)-bis-citraconic imide; N,N’ -(a,a’-(1,3-dimethylphenylr ne))-bis-citraconic imide; N,N’ -(4,4′-(1JCr-decanediol -dibenzoate) )-bis-citi-aconic imide (BCI-BAEIO); N,N’-(4,4′-diphenyl-bisphenol-A-ether)-bis-citraconic imide; N,N’-(4,4′-biphenylene)-bis-citraconic imide; N,N’-(4,4′-diphenylmethylene)-bis-citraconic imide (BCI-DPM); N,N’-(4,4′-diphenylmethylene)-bis-itaconic i mi de (BII-DPM); N,Ni-rn-xylylene-bis-citraconic imide (BCI-MX); N,N ‘-(4,4′-diphenyl isopropylene)-bi s-citraconic imide N,N’ -(.3′-dimethyl-4,4′-biphenylene)-bis-citraconic imide: N,N -(3,3-dichloro-4,4′-biphenylene-bis-citraconic imide; N,N’ -di fluoro-4,4′-biphenylene)-bis-citraconic imide; N,N’-(4,4′-oxydiphenylene)-bis-citraconic imide; N,N’ -(4,4′-diphenylsul fone)-bis-citraconic imide; N,N’7(4,4′-diphenylcarboxy)-bis-citracoiic irnide; N,N’-(4,4′-(1,1-diphenylpropylene))-bis-citraconic imide; N,N’ -3,5-(1,2,4-triazole)-bis-citraconic imide; N,N’-dodecamethylene-bis-citraconic imide; N,N’-(2,2,4-trime~chylhexamethylene)-bis-citraconic imide; N,N’-(1,11-(4,6-.dioxa-undecanediy1 ))-bis-citraconic imide; N,N’-(4,4′-benzophenonediyl)-bis-citr-aconic imide; N,N’-(1,4-anthraquinonediyl)-bis-citIraconic imide; N,N’-(1,3-naphthalenediyl)-bis-citraconic imide; N,N’-(1,4-naphthalenediyl)-bis-citraconic imide; imide; N,N’-(1,3-cyc1oh~xylefle)-bis-citracoflic imide; N,N’i(1,4-cyclohexylene)-bis-citraconic imide; N,N’-(5-methyl-1,3-phenylene)-bis-citraconic imide; N,N’ -(a,a’-(1,3-dinmethylcyclohexylene))-bi s-citracon~lc imide (BC 1-BAC); SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 12 N,N’ -(a,3-(1,1,5,5-tetramethyl -cyclohexylene))-bis-citraconic imide; N,N’-(isophiorony/l)-bis-citraconic imide; N,N ‘-(dimeth’-itricyclododecylene)-bis-citraconic imide; N,N’-octamethylene-bis-citraconic imide; N,N’ -(1,2-propyl ene)-bis-citraconic imide; N,N’-decamethylene-bis-citraconic imide; N,N’-heptamethylene-bis-citraconic imide; N.N’-(5-bromo-1,3-phenylene)-bis-citraconic imide; N,N’-(1,13-(7-aza-tridecanediyl ))-bis-citraconic imide; N,N’ -(1,7-(4-aza-heptanediyl ))-bis-citraconic iie N,N’-(1,11-(3,6,9-triaza-undecanediyl ))-bis-citraconic imide; N,N’-(1,8-(3,6-diaza-octanediyl )-bis-citraconic imide; N,N’-(N,N’-di-2-ethylpiperazinyl )-bis-citraconic imide; N,N’-(2-hydroxy-1,3-propylene)-bis-citraconic imide; N,N’,N»-(2,4,6-trihexamethylene-isocyanuratetriyl)-tris-citraconic imide (TCI-AA33); N,N’-(3,5-benzoic aciddiyl)-bis-citraconic imide; N,N’-pentamethylene-bis-citraconic imide; N,N’-undecamethylene-bis-ci~raconic imide; N,N’-(4-(N-methylene-citraconic imide)-octamethylene-bis-citraconic imide (TCI-C9v); N,N’-nonamethylene-bis-citraconic imide; N,N’-(2-butyl-2-ethylpentamethylene)-bis-citraconic imide; N,N’-polytetrahydrofuryl-bis-citraconic imide; N,N’-(Jeffamine D230a)-bis-citraconic imide; N,N ‘-(Jeffamine D2000a)-bis-citraconic imide; and ~N-(Jeffamine ED600em)-bis-citraconic imide.
Jeffamine D2300 Jeffamine D2000 0 and Jeffamine ED6009 are registered tradenames of the Texaco company. The biscitraconic imides based on these amines have the following general structure:
QI-CH(CH
3
)-CH
2 (0kOCH 2
-C(CH
3
>CH
2
CH(CH
3
)-Q
2 Q1 and Q2 are as defined above. m represents from 1 up to 1000.
In addition, the bis-, tris- and tetra- itaconi mi des of the present invention may be the same as mentioned above, except that all SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 13 citraconimide groups are exchanged for itaconimide groups. The same materials as mentioned above may be mixed imides if some of the citraconimide groups are exchanged for itaconimide groups.
The amount of sulfur to be compounded with the rubber is, based on 100 parts of rubber, usually 0.1 to 25 parts by weight, and more preferably 0.2 to 8 parts by weight. The amount of sulfur donor to be compounded with the rubber is an amount sufficient to provide an equivalent amount of sulfur which is the same as if sulfur itself were used.
The amount of anti-reversion coagent to be compounded with the rubber is, based on 100 parte of rubber, 0.1 to 5 parts by weight, and more preferably 0.2 to 3.0 parts by weight. These ingredients may be employed as a pre-mix, or added simultaneously or separately, and they may be added togeth.r with other rubber compounding ingredients as well.
In most circumstances it is also desirable to have a vulcanization accelerator in the rubber compound. Conventional, known vulcanization accelerators may be employed. The preferred vulcanization accelerators include mercaptobenzothiazole, 2,2′-mercaptobenzothiazole disulfide, sulfenamide accelerators including N-cyclohexyl-2-benzothiazole sulfenamide.
N-tertiary-butyl-2-benzothiazole sulfenamide, N,N’-dicyclohexyl-2-benzothiazole sulfenamide, and 2-(morpholinothio)benzothiazole; thiophosphoric acid derivative accelerators, thiurams, dithiocarbamates, diphenyl guanidine, diorthotolyl guanidine, dithiocarbamylsulfenamides, xanthates, triazine accelerators and mixtures thereof.
When the vulcanization accelerator is employed, quantities of from 0.1 to 8 parts by weight, based on 100 parts by weight of rubber composition, are used. More preferably, the vulcanization accelerator comprises 0.3 to 4.0 parts by weight, based on 100 parts by weight of rubber.
SUBSTITUTE
SHEET
WO 92/07904 WO 92/07904 PCT/EP91/02048 14 Other conventional rubber additives may also be employed in their usual amounts. For example, reinforcing agents ;uch as carbon black, silica, clay, whiting and other mineral fillers, as well as mixtures of fillers, may be included in the rubber composition. Other additives such as process oils, tackifiers, waxes, antioxidants, antiozonants, pigments, resins, plasticizers, process aids, factice, compounding agents and activators such as stearic acid and zinc oxide may be included in conventional, known amounts. For a more complete listing of rubber additives which may be used in combination with the present invention see, W. Hofmann, «Rubber Technology Handbook, Chapter 4, Rubber Chemicals and Additives, pp. 217-353, Hanser Publishers, Munich 1989.
Further, scorch retarders such as phthalic anhydride, pyromellitic anhydride, benzene hexacarboxylic trianhydride, 4-methylphthalic anhydride, trimellitic anhydride, 4-chlorophthalic anhydride, Ncyclohexyl-thiophthalimide, salicylic acid, benzoic acid, maleic anhydride and N-nitrosodiphenylamine may also be included in the rubber composition in conventional, known amounts: Finally, in specific applications it may also be desirable to include steel-cord adhesion promoters such as cobalt salts and dithiosulfates in conventional, known quantities.
The present invention also relates to a vulcanization process which comprises the step of vulcanizing at least one natural or synthetic rubber in the presence of 0.1 to 25 parts by weight of sulfur or a sulfur donor per 100 parts by weight of rubber, characterized in that said process is carried out in the presence of an effective amount of a coagent which only partially reacts under sulfur-vulcanization reaction conditions up to optimum cure, and which, after optimum cure, forms cross-links bonded to the sulfur cross-linked rubber by a carbon-carbon linkage at a rate sufficient to compensate for from to 200 percent of the reversion in said rubber composition.
SUBSTITUTE SHIEET WO 92/07904 P(rEP91/02048 The process is carried out at a temperature of 110-220 0 C over a period of up to 24 hours. More preferably, the process is carried out at a temperature of 120-190°C over a period of up to 8 hours in the presence of 0.1 to 5.0 parts by weight of anti-reversion coagent. Even more preferable is the use of 0.2-3.0 parts by weight of antireversion coagent. All of the additives mentioned above with respect to the rubber composition may also be present during the vulcarization process of the invention.
In a more preferred embodiment of the vulcanization process, the vulcanization is carried out at a temperature of 120-190°C over a period of up to 8 hours and in the presence of 0.1 to 8.0 parts by weight, based on 100 parts by weight of rubber, of at least one vulcanization accelerator.
In another preferred embodiment of the vulcanization process, the anti-reversion coagent is selected from a compound of the formula A.
The present invention also comprises the use of an anti-rcversion coagent which only partially reacts under sulfur-vulcanization reaction conditions up to optimum cure, and which, after optimum cure, forms cross-links bonded to the sulfur cross-linked rubber by a carbon-carbon linkage at a rate sufficient to compensate for from to 200 percent of the reversion in said rubber composition, in a process for the sulfur-vulcanization of rubber.
Finally, the present invention also includes articles of manufacture, such as tires, which comprise sulfur-vulcanized rubber which is vulcanized in the presence of the anti-reversion coagents of the present invention.
The invention is further illustrated by the following examples which are not to be construed as limiting the invention in any way. The scope of the invention is to be determined from the claims appended hereto.
c IPTITI ITP SHET WO 92/07904 PCT/EP91/02048 16 EXPERIMENTAL METHODS USED IN THE EXAMPLES Structural characterization of the rubber network The crosslink density and the distr» ution of poly-, di- and monosulfidic and non-sulfidic crosslinks has been determined in a rubber compound based on a natural rubber (NR) gum recipe (NR SMR CV5 100 parts, stearic acid 2 phr, ZnO RS 5 phr, Perkacit® CBS 0.6 phr, sulfur 2.3 phr), all amounts being related to the amount of rubber, which recipe was mixed on a two-roll mill and vulcanized as described below.
The density of crosslinks was determined from the elastic constant (J.
Mullins, J. Appl. Polym. Sci. 2, 1, 1959; J. Mooney et al., J. Appl.
Physics, 11, 100, 1940) following the procedure given by Saville and Watson (Rubber Chem. Technol. 40, 100, 1967). The proportions of the sulfidic crosslinks were determined by thiol-amine chemical probes Campbell et al., J. Appl. Polym. Sci. 13, 1201, 1969 and Proc.
Int. Conf. 5th, 1, 1967, 1968), and the proportions of non-sulfidic, carbon-carbon, crosslinks by methyl iodide treatment Moore et al., J. Polym. Sci. 19, 237, 1956 and 32, 503, 1958; M.L. Selker et al., Ind. Eng. Chem. 36, 20, 1944).
Compounding, Vulcanization and Characterization of Compounds In the following examples, rubber compounding, vulcanization and testing was carried out according to standard methods except as otherwise stated: Base compounds were mixed in a Farrel Bridge BR 1.6 liter Banbury type internal mixer (preheating at 50 0 C, rotor speed 77 rpm, mixing time 6 min with full cooling).
SUBSTITUTE SHPT WO 92/07904 PCT/EP91/02048 Vulcanization ingredients a Schwabenthan Polymix temperature 70 0 C, 3 min).
and coagents were addded 150L two-roll mill to the compounds on (friction 1:1.22, Mooney viscosity was determined using a Mooney viscosimeter MV at 100 0 C according to ASTM 01646-89.
Scorch times were determined using a Mooney viscosimeter MV 121°C as time to until an increase of 5 Mooney units was ASTM 01646-89).
2000E at observed Cure characteristics were determined using a Goettfert elastograph or Monsanto rheometer ODR (arc or MDR 2000E (arc 0.50): delta torque or extent of crosslinking (Ro) is the maximum torque (MH, also denoted as initial torque maximum, Ti) minus the minimum torque Scorch safety (ts2) is the time to 2% of delta torque above minimum torque optimum cure time (t 90 is the time to 90% of delta torque above minimum, reversion time (trp) is the time to 2% of delta torque below maximum torque. Final torque (Tf) is the torque measured after the overcure time.
Sheets and test specimens were vulcanized by compression molding in a Fontyne TP-400 press.
Tensile tester 412-87, measurements were carried out using a Zwick 1445 tensile (ISO-2 dumbbells, tensile properties according to ASTM D tear strength according to ASTM 0 624-86).
Hardness was determined according to DIN 53505, and ISO 48 (IRHD).
Rebound resilience was measured at room temperature (RT) or at 100 0
C
according to ASTM D 1054-87.
Compression set was determined after 24 h at 70 0 C or 72 h at 23 0
C
according to ASTM D 395-89.
SUBSTITUTE
SHFFT
WO 92/07904 PCI/EP91/02048 18 Heat build-up and compression set after dynamic loading were determined using a Goodrich Flexometer (load 1 MPa, stroke 0.445 cm, frequency 30 Hz, start temperature 100 0 C, running time 30 min or till blow out; ASTM D 623-78).
Fatigue to failure was determined using a Monsanto FTFT tester (cam 24; ASTM D 4482).
Abrasion was determined using a Zwick abrasion tester as volume loss per 40 m path travelled (DIN 53516).
Dynamic mechanical analysis was carried out using an Eplexor Dynamic Mechanical Analyzer (prestrain 10%, frequency 15 Hz, ASTM D 2231) Examples 1-5 and Comparative Examples A and B Five different imide anti-reversion agents in accordance with the present invention were prepared and tested in the sulfur vulcanization process according to the present invention. The imides employed were the following: 1. N,N’-m-phenylene-bis-citraconic imide (BCI-MP); 2. N,N’-ethylene-bis-citraconic imide (BCI-C2); 3. N,N’-hexamethylene-bis-citraconic imide (BCI-C6); 4. N,N’-1,3-dimethyl-cyclohexyl-bis-citraconic imide (BCI-BAC); 5. N,N’-m-xylylene-bis-citraconic imide (BCI-MX);and A. N,N’-m-phenylene-bis-maleimide (HVA-2®) (ex. Du Pont); The accelerator employed was n-cyclohexyl-2-benzothiazole sulfenamide (CBS). Comparative example B was a control example with no antireversion additive. Natural rubber was vulcanized in the presence of the foregoing compounds using the formulations listed in Table 1.
~I IR~TRTJ ITF RHET WO 92/07904 PCI’/EP9I /02048 19 TABLE 1 Example No. 1 2 13 4 5 A- B Compound Natural Rubber 100 100 100 100 100 100 100 Carbon Black 50 50 50 50 50 50 Zinc Oxide 5 5 5 5 5 5 Stearic Acid 2 2 2 2 2 2 2 CBS 1 1 1 1 1 1 1 Sulfur 2.3 2.3 2.3 2.3 2.3 2.3 2.3 BCI-11P 1.5 BCI-C2 1.2 BCI-C6– 1.5 BOI-BAC 1.6 BCI-MX 1.6 I 1 1.3 The vulcanized rubbers listed in Table 1 were then tested for antireversion and other physical properties upon overcure. The results are given in Table 2.
SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 TABLE 2 Evaluation of bis-citraconimides for improvement of mechanical properties relative to bis-maleimide upon (over)cure at 180°C for minutes.
Example No. 1 2 3 4 5 A B Mechanical property Hardness (Sh A) 70 68 69 68 69 67 62 Modulus 300%(MPa) 13.3 13.2 13.8 18.4 19.4 10.5 Tensile strength 17.4 19.8 23.0 21.4 21.4 18.3 17.4 (MPa) Compression set 9.8 8.0 8.9 12.1 11.0 Reversion -3 -2 -13 -4 -6 22 Reversion= [Mod.300%, at 180°C, to 0 ]-[Mod.300%, at 180 0 C 60 min.] (x100) [Mod.300%, at 150°C, t 90 g not tested These results show that with the known bis-maleimide anti-reversion agent a reduced reversion was observed No reversion is represented by All of the anti-reversion agents of the present invention were significantly superior to the bis-maleimide, as can be seen from the observed physical properties wherein the bis-citraconimides gave higher 300% modulus values than the bis-maleimide. The agents of the present invention gave satisfactory properties due to their anti-reversion effect.
Example 6 and Comparative Examples C-F The effects of several materials on the vulcanization curve of natural rubber vulcanized at 180 0 C were determined. In addition to HVA-2® and BCI-MP, the following materials were employed: D. Phenyl-maleimide (PMI) (ex. Janssen Chimica);and E. Phenyl-citraconimide (PCI).
SUSTITUTE
SHEET
WO 92/07904 PCT/EP91/02048 21 The accelerators employed were 2,2′-mercaptobenzothiazole disulfide (MBTS). Comparative example F was a anti-reversion additive. The rubber formu are given in Table 3.
control example with no lations which were employed TABLE 3 Example 6 C D E F Compound Natural Rubber 100 100 100 100 100 Carbon Black 50 50 50 50 S Zinc Oxide 5 5 5 5 S Stearic Acid 2 2 2 2 2 MBTS 1 1 1 1 1 Sulfur 2.25 2.25 2.25 2.25 2.25 HVA-2 2.0 PMI 2.6 PCI 2.8 Vulcanization curves were measured with a G6ttfert Elastograph at 180 0 C for a period up to 60 minutes. The anti-reversion effect can be seen by comparing the final torque (Tf) with the initial torque maximum (Ti).
TABLE 4 Torque (Nm) Ti Tf Example 6 0.96 1.13 C 1.14 0.89 D 0.90 0.72 E 0.82 0.38 F 0.88 0.55 As in the previous examples, the BCI-MP anti-reversion agent slightly over-compensated for the reversion thereby providing a rubber with satisfactory physical properties. The PCI enhanced the reversion effect on the contol example. The HVA-2® increased the viscosity during the vulcanization more than the PMI did but neither of these agents compensated as much for the reversion effect as did the BCI-MP.
4 1 I WO 92/07904 PCT/EP91/02048 22 Examples 7-14 and Comparative Example G In these examples four different accelerators were used in combination with the anti-reversion agents of the present invention in order to demonstrate that the anti-reversion effect is independent of the accelerator employed. The rubber formulations shown in table 4 were vulcanized in accordance with the present invention.
The accelerators employed for these tests included MBTS, N,N’-dicyclohexyl-2-benzothiazole sulfenamide (DCBS) and MBS.
TABLE
CBS,
Example 7 8 9 10 11 12 13 14 Compound Natural Rubber 100 100 100 100 100 100 100 100 Carbon Black 50 50 50 50 50 50 50 Zinc Oxide 5 5 5 5 5 5 5 Stearic Acid 2 2 2 2 2 2 2 2 MBTS 1 1 CBS 1 MBS 1 DCBS 1 1 Sulfur 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 BCI-MP 1.5 1.5 1.5 1.5 BCI-C6 1.5 1.5 1.5 All of the formulations superior torque retention without BCI. Mathematical that the anti-reversion vulcanization accelerator gave similar vulcanization curves with upon overcure as compared with the controls analysis of the vulcanization curves showed effect was not influenced by the type of used.
Examples 15-17 These examples compare the effects of different concentrations of N,N’-hexamethylene-bis-citraconimide. The results of vulcanization with three different concentrations of anti-reversion agents are given in Table 6.
SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 23 To obtain the results given in Table 6, vulcanization was carried out at 180 0 C over a period of 60 minutes.
TABLE 6 Example 15 16 17 G Compouna Natural Rubber 100 100 100 100 Carbon Black 50 50 50 Zinc Oxide 5 5 5 Stearic Acid 2 2 2 2 CBS 1 1 1 1 Sulfur 2.3 2.3 2.3 2.3 BCI-C6 0.75 1.5 2.25 Hardness (Shore A) 63 65 67 58 Modulus (MPa) 100% 3.3 3.8 4.5 2.1 300% 15.9 18.6 20.5 10.7 These results composition of and modulus at demonstrate that at varying concentrations the the present invention gave generally superior hardness all concentrations.
Examples 18-20 and Comparative Examples H and I These examples demonstrate that the rubbers in accordance with the present invention exhibit significantly better properties after ageing than prior art rubbers do. More particularly, the compositions shown in Table 7 were vulcanized under three different sets of vulcanization conditions, and then subjected to ageing for 48 hours at 100 0
C.
The results given in Table 7 were obtained from vulcanization at 150 0
C
for a period of 7-11 minutes. The results given in Table 8, in which similarly numbered and lettered examples employed the same quantities of all ingredients, were obtained from vulcanization at 180°C for a period of 2 minutes, and the results given in Table 9 were obtained from vulcanization at 180 0 C for a period of 60 minutes.
SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 24 TABLE 7 Example H1 11 18a 19a Natural Rubber 100 100 100 100 100 Carbon Black 50 50 50 50 Zinc Oxide 5 5 5 5 Stearic Acid 2 2 2 2 2 CBS 1 1 1 1 1 Sulfur 2.3 2.3 2.3 2.3 2.3 HVA-2® 1.3 BCI-MP 1.5 BCI-C2 1.2 BCI-C6 I Ageing Properties Hardness (Shore A) Modulus (MPa)100% Tensile Strength (MPa) 60 69 66 64 3.2 4.2 3,7 3.7 7.2 5.9 7.9 8.4 8.7 TABLE 8 Example H2 12 18b 19b Ageing Properties Hardness (Shore A) 62 62 66 65 64 Modulus (MPa)100% 3.4 3.4 4.3 3.9 3.8 Tensile Strength (MPa) 6.6 6.4 7.7 8.3 TABLE 9 Example H3 13 18c 19c Ageing Properties Hardness (Shore A) 52 60 63 59 63 Modulus (MPa)100% 2.3 2.4 3.0 3.1 Tensile Strength (MPa) 6.4 6.7 8.1 9.3 8.7 These results show that, in general, the rubbers of the present invention exhibit superior properties after ageing as compared with comparable prior art rubber compositions.
SUBSTITUTE
SHEET
WO 92/07904 PCT/EP91/02048 Examples 21-22 and Comparative Example J The effect of two anti-reversion agents of the present invention was tested in three different CBS/sulfur vulcanization systems: conventional semi-efficient (semi-E.V.) and efficient In addition to BCI-MP and BCI-C6 a comparative HVA-2®-containing example was employed.
The rubber formulations which were employed with C.V. are given in Table 10. Similarly lettered examples employed the same quantities of all the ingredients except for the vulcanization accelerator and sulfur contents. The amounts of vulcanization accelerator and sulfur in the rubber formulations considered to be semi-E.V. are given in Table 11. The amounts of vulcanization accelerator and sulfur in the rubber formulations considered to be E.V. are given in Table 12.
TABLE Example 21a 22a Ja Compound Natural Rubber 100 100 100 Carbon Black 50 50 Zinc Oxide 5 5 Resin Pine Tar 2 2 2 BCI-MP 1.5 BCI-C 1.5 HVA-2 1.3 CBS 0.6 0.6 0.6 Sulfur 2.3 2.3 2,3 TABLE 11 SUBSTIUTI SHEET WO 92/07904 PCT/EP91/02048 26 TABLE 12 To obtain the results given in Table 13, vulcanization was carried out at 180 0 C over a period of 60 minutes. The anti-reversion effect can be seen by comparing the final torque (Tf) with the initial torque maximum (Ti).
TABLE 13 torque (dNm) Ti Tf Example 21a 16.25 19 22a 16.25 18.8 Ja 19.5 15.0 ‘lb 17.8 18.8 22b 17.5 18.0 Jb 21.6 16.0 21c 13.7 17.5 22c 13.0 13.5 Jc 16 13.5 The compensation effects of the anti-reversion agents according to the present invention were quite similar in C.V. and semi-E.V., but decreased for the efficient cure system. HVA-2® showed vulcanization curves initially reflecting high reactivity, but due to reversion a low final torque resulted. Compared with the anti-reversion agents of the present invention the contribution of HVA-2® to thE cure curves 3 was relatively less dependent on the efficiency of the cure system.
BCI-MP and BCI-C6 have a significant anti-reversion effect in C.V. and semi- E.V. NR-based formulations. The effect on E.V compounds is smaller, but also less relevant in E.V compounds. The anti-reversion SUBSTITUTE
SHEET
WO 92/07904 PCT/EP91/02048 27 effect of BCI’s is probably a synergistic effect with sulfur. HVA-2® shows inferior anti-reversion effects in the cure curves as compared with the anti-reversion agents of the present invention.
Examples 23-27 The effect of mixed itaconimide and citraconimide groups was tested for hexamethylene bisimide derivatives (BI-C6). Also the bis-itaconimide of diphenylmethane (BII-DPM) was compared with the bis-citracon imide thereof (BCI-DPM). The rubber formulations which were employed are given in Table 14.
TABLE 14 Example No. 23 24 25 26 27 Compound Natural Rubber 100 100 100 100 100 Carbon Black 50 50 50 50 Stearic Acid 2 2 2 2 2 Zinc Oxide 5 5 5 5 Resin Pine Tar 3 3 3 3 3 S CBS 0.6 0.6 0.6 0.6 0.6 Sulphur 2.3 2.3 2.3 2.3 2.3 BI(97,5/2.5)2-C6 BI(70/30),-C6 BI(37/63)i-C6 BCI-DPM 1.9 BII-DPM 1.9 1 The relative citraconimide/itaconimide content (mole%/mole%) is given in parentheses.
To obtain the results given in Table 15, vulcanization was carried out at 180 0 C over a period of 60 minutes. The anti-reversion effect can be seen by comparing Tf with Ti.
Ottl IRTI’Fi ITP WO 92/07904 PCT/EP91/02048 TABLE torque (dNm) Ti Tf Example 23 16 17.6 24 16 17.6 16 17.6 26 16.3 20.5 27 17.4 18.5 The different hexamethylene citraconimide derivatives with itaconimide contents of 2.5% (BCI-C6), 30% and 63%, respectively, gave similar vulcanization curves. The diphenylmethane derivatives of BCI and BII showed anti-reversion effects close to those of BCI-MP. The BII-DMP showed an improved modulus after vulcanization at 1800C.
Examples 28-35 The effects of BCI-MP on the physical properties of natural rubber, styrene-butadiene rubber (SBR) and different rubber blends e.g NR-BR and SBR-BR, NR being natural rubber and BR being butadiene rubber) were investigated.
The formulations of the NR and SBR compounds are listed in Table 16.
CZ1 I-TITI ITI= qHIFFT WO 92/07904 PCT/EP91/02048 2 9 TABLE 16 Example No. 28 29 30 31 Compounds NR 100 100 SBR 100 100 Carbon Black 50 50 50 Stearic acid 2 2 2 2 Zinc Oxide 5 5 5 Aromatic oil A2 3 3 Aromatic oil B2 3 3 BCI-MP 1.5 CBS 0.6 0.6 0.6 0.6 Sulfur 2.3 2.3 2.3 2.3 -=aromatic oil Dutrex 729 HP® 2=aromatic oil Enerflex 72® The formulations of the NR-BR and SBR-BR blends are listed in Table 17.
TABLE 17 Example No. 32 33 34 Compounds NR 80 80 SBR 55 BR 20 20 45 Carbon Black 50 50 50 Stearic Acid 2 2 2 2 Zinc Oxide 5 5 5 Aromatic oil A 3 3 3 3 BCI-MP 1.5 CBS 0.6 0.6 0.6 0.6 Sulfur 2.3 2.3 2.3 2.3 Mixing procedure for the blend In a banbury mixer separate rubber masterbatches were mixed to ensure homogeneous carbon dispersion.
The additional ingredients, including BCI-MP, were added to the masterbatch according to the formulations of Table 17 and mixed. After SUBSTITUTE SHE WO 92/07904 PCT/EP91/02048 24 hours the masterbatches were cross-blended in the 3 minutes. After an additional 24 hours, the batches a mill on addition of sulfur and accelerators.
banbury mixer for were finalized on The cure characteristics of the examples obtained at 150°C are listed in Table 18 and the values obtained at 180 0 C are presented in Table 19, At the optimum cure time (opt. cure time (tg 0 the torque was at its maximum. At the reversion time the torque started to decrease.
TABLE 18 Characteristics Cross-linking Scorch safety Opt.cure Reversion R»,dNm ts2,min time,min time,min Example 28a 18.5 4.1 11.0 24.3 29a 18.7 4.2 12.4 20.7 10.1 24.1 31a 22.6 10.4 24.3 32a 20.4 4.9 12.8 28.8 33a 20.1 4.8 13.0 34a 23.6 9.4 26.2 23.7 9.7 26.0 TABLE 19 28b 15.3 0.6 1.6 2.3 29b 15.2 0.6 1.7 20.5 1.2 4.3 12.5 31b 22.8 1.2 27 32b 17.1 0.6 1.9 3.1 33b 16.4 0.6 7.9 34b 27.1 1.0 4.0 20.2 22.5 1.1 5.5 indicates no reversion Tables 20 and 21 give the resulting properties of the cured products obtained, a-indices referring to curing at 150°C up to optimal cure, tgo and b-indices referring to curing at 180 0 C over a period of minutes.
SUBSTITUTE SHEiT WO 92/07904 PCr/EP91/02048 31 TABLE Example No. 28a 28b 29a 29b 30a 30b 31a 31b Properties Hardness, Shore A,MPa 61 42 53 51 67 66 69 69 Modulus, MPa 0.95 0.64 0.97 0.96 1.86 1.65 1.89 1.96 100% 1.63 0.96 1.66 1.68 3.66 2.92 3.53 4.01 300% 8.33 4.59 8.45 8.76 20.1 16.1 18.9 21.5 Tensile Strength,MPa 25.6 13.5 24.8 15.8 29.5 21.4 26.6 22.9 Elongation at break, 590 545 595 429 423 387 379 294 TABLE 21 Example No 32a 32b 33a ’33b 34a 34b 35a Properties Hardness, Shore A, MPa 67 61 67 69 67 64 67 69 Modulus, MPa 1.61 1.29 1.49 1.75 1.53 1.47 1.56 1.75 100% 3.09 2.22 2.67 3.29 2.49 2.40 2.51 3.06 300% 15.4 11.1 13.5 15.9 12.9 12.5 12.4 16.2 Tensile Strength,MPa 27.2 17.4 29.7 20.5 22.0 20.9 20.9 19.0 Elongation at break,% 503 417 513 389 454 458 442 313 As already shown in previous examples, BCI-MP has a remarkable effect by counteracting the reversion phenomenon in NR formulations. This is also true for SBR, NR-BR and SBR-BR formulations. The mechanical properties of the SBR, NR-BR and SBR-BR vulcanizates with BCI-MP are well retained, especially on over-cure.
SUBSTITUTE
SHEET
WO 92/07904 PCT/EP91/02048 Examples 36-41 Tire formulations with common ingredients were prepared various BCI-MP contents. A truck tire tread compound recipe to Baker Elastomerics, July 1989, pp 20-25″ is Table 22, example 36. Various BCI-contents were added to employing according listed in this composition (examples 37-41).
obtained by vulcanization at Table 23, the ones obtained by minutes, in Table 24.
The resulting mechanical properties 150°C up to optimum cure, are given in vulcanization at 180°C overcured for TABLE 22 Example No. 36 37 38 39 40 141 Compound NR 80 80 80 80 80 BR 20 20 20 20 20 Carbon Black 55 55 55 55 55 Stearic Acid 2 2 2 2 2 2 Zinc Oxide 4 4 4 4 4 4 Aromatic oil A 8 8 8 8 8 8 Permanax 6PPD® 2 2 2 2 2 2 BCI-MP 0.5 0.75 1.00 1.25 1.50 CBS 1.2 1.2 1.2 1.2 1.2 1.2 Sulfur 1.2 1.2 1.2 1.2 1.2 1.2 TABLE 23 Example No 36a 37a 33a 39a 40a 41a Properties Hardness,Sh A 60 62 62 63 63 64 Modulus 50% 1.17 1.14 1.15 1.14 1.20 1.14 100% 2.05 1.92 1.91 1.88 2.04 1.95 300% 10.8 10.3 10.6 10.4 10.8 10.8 Tensile Strength,MPa 24.0 25.1 24.7 24.2 24.0 23.2 Elongation at break,% 556 600 571 574 568 535 Tear strength, N/mm 119 107 114 110 110 111 SUBSTITUTE
SHEET
WO 92/07904 PCT/EP91/02048 33 TABLE 24 Example No 36b 37b 38b 39b 40b 41b Properties Hardness,Sh A 55 60 62 64 63 66 Modulus 50% 1.02 1.07 1.19 1.33 1.35 1.32 100% 1.65 1.71 1.82 2.37 2.37 2.30 300% 8.5 8.8 10.0 11.9 12.0 11.5 Tensile Strength,MPa 16.5 18.3 20,4 20.7 20.6 20.4 Elongation at break,% 482 502 501 489 461 460 Tear strength, N/mm 41 60 64 66 66 68 These experiments show that BCI-MP can be used in various quantities to improve the reversion resistance of tire compounds.
Example 42 Structural characterization of rubber networks NR gum stocks (NR 100 parts, zinc oxide 5 phr, stearic acid 2 phr, CBS 0.6 phr and sulfur 2.3 phr) were compounded with various coagents: phenylmaleimide (PMI), HVA-2®, phenylcitraconimide (PCI) and BCI-MX (all 1.5 phr). The compounds were vulcanized at 150 0 C until optimum cure (tg 0 and at 170 0 C for 30 min. The number and distribution of types of crosslinks were determined as described above and presented in TABLES 25 and 26.
SUBSTITUTE
SHEET
WO 92/07904 WO 9207904PCT/EP91/02048 Di stributicn to tgo.
TABLE of crosslinks in vulcanizates obtained at 150 0 C cured up Cobmpound Toa Pol1y Di Mono- C-C crosslinks* Sulfidic sulfidic sulfidic Crosslinks X 10*5 X 10*5 X 10*5 X 10*5 X 10*5 Control 5.05 3.18 1.87 3% HVA-2®D 6.30 2.91 1.64 0.17 1.57 2 PM1 5.42 3,20 1.96 0.26 36%) PCI 4.92 3.18 1.75 BCI-MX 5.04 2.94 2.10 *Concentration of crosslinks are expressed in terms of Gram mole per gram of RH.
SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 TABLE 26 Distribution of crosslinks of vulcanizates obtained at 170 0 C and overcured for 30 minutes Compound Total Poly Di- Mono- C-C crosslinks* Sulfidic sulfidic sulfidic Crosslinks X 10*5 X 10*5 X 10*5 X 10*5 X 10*5 Control 2.05 0.04 0.06 1.94 (93%) HVA-2® 2.2 0.11 0.11 1.32 0.67 PMI 2.12 0.008 0.03 1.93 0.15 PCI 1.86 0.05 0.10 1.71 (92%) S BCI-MX 2.54 0.03 0.10 0.88 1.53 Concentration gram of RH.
of crosslinks are expressed in terms of Gram mole per After optimum cure at 150 0 C only PMI and BMI-MP gave an increased number of total crosslinks as compared to the control which consisted besides sulfidic also of non-sulfidic carbon-carbon type crossli-,ks.
Similarly cured compounds with PCI and BCI-MX showed no additional contribution to the total crosslinks and no C-C type crosslinks.
These results indicate that coagents such as biscitraconimides have substantially no influence on the total crosslink density up to optimal cure in contrast to bismaleimides.
Example 43 Extraction Experiments Sheets of NR gum stock with 1.5 phr HVA-20 or BCI-MP vulcanized at SUBSTITUTE SHEiE WO 92/07904 PCT/EP91/02048 36 150 0 C until optimum cure were extracted with chloroform in a Soxhlet apparatur over a 24 hour period. The extract was evaporated, dissolved in deuterated chloroform and examined with H-NMR. The extract from the HVA-2® containing sheet did not show a detectable quantity of bismaleimide, whereas BCI-MP was successfully extracted from the sheet containing BCI-MP. This indicates that unreacted BCI-MP was present in the vulcanizate.
Example 44 Compounding BCI with rubber on a two-roll mill and in a Banbury internal mixer BCI-MP was compounded with a NR rubber recipe (NR SMR CV5: 100 parts, carbon black N-330 50 phr, stearic acid 2 phr, zinc oxide RS 5 phr, aromatic oil (Dutrex 729 HP®)3 phr, Perkacit® CBS 0.6 phr and sulfur 2.3 phr) by different procedures; a. The ingredients, excepting CBS, sulfur and BCI-MP, were mixed in a Banbury internal mixer at 135-140 0 C stepwise for 6 minutes. Then, the vulcanization agents and the BCI-MP (1.5 phr) were mixed on a two-roll mill at 60-70 0
C.
b. The ingredients including 1.5 phr BCI-MP and excepting sulfur and CBS, were mixed in the Banbury and the CBS and sulfur were added on a two-roll mill.
Then, the cure characteristics of these compounds and a control compound containing no BCI-MP were determined using a Monsanto rheometer MDR 2000E at 180 0 C during a 60 minute period.
Monsanto rheometer data obtained at 150 0 C (data in parenthesis are obtained at 1800C) SUSTITI1r.– ou=- WO 92/07904 PCr/EP91/02048 37 There was no difference in anti-reversion effect according to the cure characteristics after either following the two-roll mill or Banbury procedure for compounding.
TABLE 27 Control Procedure Procedure a) b) Scorch safety, ts2 11.0 12.4 12.5 (min) (1.6) Cure time, tgo (min) 4.1 4.2 4,2 (0.6) Extent of crosslinking, 18.5 18.7 19.3 Rm(dNm) Monsanto rheometer cure curve at 180°C,60 min (dNm): Ti 17.3 17.3 17.4 Tf 11.5 19.0 19.0 Example Properties of NR/SBR and NR compounds with BCI-MP A carbon black-filled NR compound with conventional amounts of activators, processing oil, antidegradants and a C.V. curing system with 1.8 phr sulfur, and an NR/SBR (75/25) blend with conventional amounts of activators, oils, antidegradants, wax and a semi-E.V.
curing system with 1.5 phr sulfur were mixed with 0.5 or 1.0 phr BCI-MP according to a standard procedure as described above. In control compounds, BCI-MP was omitted.
Tables 28 and 29 show that there is slight or no influence of BCI-MP on scorch and cure characteristics of the NR/SBR and NR compounds.
The reversion time at 170 0 C is always increased. A Monsanto rheometer ODR was used for the determination of cure characteristics.
SUBSTITUTE SHEET WO 92/07904 PCT/EP9I /02048 38 TABLE 28 Scorch and Cure characteristics* of NR-SBR compounds.
Compound 1 2 3 (control) (BCI-MP (BCI-MP 0.5 phr) _1.0 phr) Mooney scorch time 43 42 413 min Cure at 15 0
C,,
Extent of crosslinking, 2.53 2.50 2.45 RcP, Nm Scorch safety, ts2, min. 8.0 8.0 Optimum curetime, t 90 14.5 14.0 14.0 min.
Reversion tCime, tr 2 min.
Cure at 170*C: Extent of crosslinking, 2.25 2.25 2.25 Rco, Nm Scorch safety, ts2, min. 2.5 2.j Optimum cure time, t 90 min. 5.0 5.0 Reversion time, tr 2 23.0 )C) mi indicates no reversion Monsanto rheometer ONR SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 39 TABLE 29 Scorch and Cure* characteristics of NR compounds.
Compound 4 5 6 (control) (BCI-MP (BCI-MP phr) 1.0 phr) Mooney scorch time 41 41 42 min Cure at 150OC: Extent of crosslinking, 2.77 2.70 2.70 Ro, Nm Scorch safety, ts2, min. 5.8 6.3 6.2 Optimum cure time, t 90 min. 13.8 14.0 14.0 Cure at 170OC: Extent of crosslinking, 2.4 2.3 2.4 Rc, Nm Scorch safety, ts2, min. 1.6 1.7 1.9 Optimum cure time, t 90 min. 4.1 3.9 4.3 Reversion time, tr 2 10.5 16.4 min., indicates no reversion Monsanto rneometer ODR TABLES 30 and compounds with tear strength, 31 show improvements obtained in the NR/SBR and NR BCI-MP regarding hardness, modulus, tensile strength, compression set, and abrasion.
SUBSTITUTF
AHFI’
WO 92/07904 WO 9207904PCT/EP91/02048 TABLE Mechanical properties of the vulcanizates cured at 150 0 C for t 90 and at 170 0 C tYor 30 min. (o~ercured shown between parenthesis).
Compound 1 2 13 Hardness, Shore A 57.0 60.0 60.0 (54.5) (59.5) (60.0) Modulus 50%, MPa 1.20 1.15 1.20 (0.90) (1.15) (1.20) 100%, MPa 1.90 1.85 1.80 (1.35) (1.81) (1.90) 300%, MPa 9.30 9.45 (6.51) (8.90) (9.95) Tensile strength, MPa 23.2 23.1 23.3 (15.5) (19.0) (20.1) Tear strength, KN/m I89.0 86.5 82.5 I(46.5) (61.5) (58.5) Compression set, 24h/70 0 C 21 23 22 (26) (25) (24) 72h/23 0 C 15 14 12 (17) (17) Abrasion (volume loss mm 3 /40m path travelled) 102 103 105 (201) 1(131) 1(117) qI IRCZTIr; ITP qWF=PT WO 92/07904 PCT/EP91/0204 41 TABLE 31 Mechanical properties of the vulcanizates cured at 150 0
C
at 170°C for 30 min. (overcured shown in parenthesis).
for t 90 and Compound 4 5 6 Hardness, Shore A 60 62 64 (52) (57) Modulus 50%, MPa 1.15 1.20 1.20 (0.88) (1.04) (1.20) 100%, MPa 2.06 2.15 2.10 (1 30) (1.65) (2.00) 300%, MPa 11.8 11.4 11.4 (10.7) Tensile strength, MPa 27.2 28.0 28.5 (18.2) (21.3) (21.3) Tear strength, KN/m 101 119 136 (25.5) (39.0) (58.0) Compression set, 24h/70 0 C 21 23 23 (33) (28) (24) 72h/23 0 C 9 10 23 (17) (13) (12) Abrasion (volume loss mm 3 /40m path travelled) 122 121 122 (214) (172) (145) TABLES 32 and 33 show substantial reduction of heat build up (temperature rise) and permanent set in the Goodrich flexometer test and improved fatigue resistance of the compounds containing BCI-MP cured at 170°C for 30 min.
,ql JRRTTI JTtF UE WO 92/07904 PCT/EP91/02048 42 TABLE 32 Heat build up and permanent set properties of overcured (170 0 C, 30 minutes) vulcanizates a) NR/SBR Compounds Temperature rise, At,°C Permanent set,% b) NR Compounds Temperature rise, At, C 1 (control) 42 12.0 4 (control) 52 2
(BCI-MP
phr) 30 8.1 5
(BCI-MP
phr) 31 3
(BCI-MP
1.0 phr) 26 5.4 6 (BC 1-MP 1.0 phr) 24 Permanent set.% 17.2 TABLE 33 Fatigue to Failure properties of overcured vulcanizates (170°C, minutes) a) NR/SBR Compounds 1 2 3 (control) (BCI-MP (BCI-MP phr) 1.0 phr) Number of Kilo cycles 37.5 38.1 41.2 to Failure NR-Compounds 4 5 6 (control) (BCI-MP (BCI-MP phr) 1.0 phr) Number of Kilo cycles 50.1 53.7 55.4 to Failure_ Increased loss modulus as measured by dynamic mechanical analysis of the NR/SBR blend with BCI-MP as shown in TABLE 34 can contribute to the improvement of tire properties such as wet grip or skid resistance Grosch, Nature, 197, 858, 1963).
‘SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 43 TABLE 34 Dynamic-mechanical data (at 150°C/t9o.
20°C) of NR/SBR vulcanizates cured at Compound E’ E» E* tan6 MPa MPa MPa 1(Control) 18.3 2.8 18.5 0.152 2(BCI-MP 0.5 phr) 22.2 3.2 22.4 0.145 3(BCI-MP 1.0 phr) 24.4 3.6 24.7 0.148 Increased storage modulus and decreased loss tangent (tan6) measured at 60C as shown in TABLE 35 imply a lower loss compliance (tan6/E’) which can contribute to improved tire properties such as reduced rolling resistance Collins et al., Trans. Inst. Rubber Ind. 40, T239, 1964), which by consequence leads to fuel savings during service.
TABLE Dynamic-mechanical data (at min.
60°C) of NR-vulcanizates cured at 170 0 Compound E’ E» E* tan6 MPa MPa MPa 4 (Control) 8.2 1.3 8.3 0.160 6(+BCI-MP 1.0 phr) 9.3 1.1 9.4 0.119 Example 46 NR/BR compound with various BCI’s An NR/BR recipe (see Example 36), useful as truck tire tread compound Baker Elastomerics, July 1989, pp.20-25) has been used to test the effects of various BCI’s. Compounding was done with phr BCI-MP, BCI-DPM and BCI-MX as described above (Example 36).
Vulcanization was done by compression moulding at 150 0 C (tgo and min) and 170°C (t90 and 30 min).
SUBSTITUTE
SHEET
WO 92/079C4 PC/E P91/02048 TABLE 36 shows that BCI’s have slight or viscosity, scorch time and cure characteristics.
no effect on Mooney TABLE 36 Control BCI- BCI- BCI- MP DPM MX Mooney viscosity (MU) 46.4 42.6 45.2 45.3 Mooney Scorch time (min) 36.1 36.1 36.4 35.5 Monsanto rheometer cure data (150°C) ts2 5.0 5.2 5.5 5.2 t t 8.3 8.4 8.7 8.6 Delta torque (Nm) 1.5 1.5 1.5 Monsanto rheometer cure data (170°C) ts2 1.5 1.6 1.7 1.7 tg 0 2.6 2.6 2.7 2.7 Delta torque (Nm) 1.4 1.4 1.4 1.4 TABLE 37 gives Monsanto rheometer torque data obtained at total cure time of 8 hours that show that antireversion also obtained under these conditions with the BCI’s.
140 0 C with a effects are TABLE 37 *Final torque after 8 hours, 140°C.
TABLES 38 and 39 show improvement of the following properties of vulcanisates after overcure at 150 0 C for 60 minutes and especially at 170°C for 30 minutes: hardness, tensile strength, modulus, abrasion, CI IRqTITI ITP q4P:FT WO 92/07904 PCT/EP91/02048 compression set, tear strength, and both permanent set and heat build up.
TABLE 38 Physical and mechanical properties of the vulcanizates cured at 150°C/t90 and 150°C/60 min. (between paranthesis): Compound 01 02 04 control BCI-MP BCI-DPM BCI-MX Hardness IRHD 70 71 74 71 (67) (72) (72) Tensile strength MPa 25.5 25.4 24.9 26.3 (21.9) (22.8) (22.9) (23.0) Modulus 50% MPa 1.2 1.3 1.3 1.3 (1.3) Modulus 100% MPa 2.4 2.2 2.2 2.3 (2.1) Modulus 300% MPa 12.5 12.0 11.3 12.4 (10.5) (12.5) (11.2) (11.2) Abrasion mm 3 93 86 117 96 (128) (76) (78) Tear strength kN/m 115 106 114 113 (88) (92) (87) Permanent set 13.1 10.6 12.5 9.4 (13.9) (9.9) Heat build up 0 C +40 +29 +33 +27 R1 1 R.qfiT1 WO 92/07904 PCT/EP91/02048 TABLE 39 Physical and mechanical properties of the vulcanizates 170°C/t 90 cured at Compound 01 02 04 Scontrol BCI-MP BCI-DPM BCI-MX Hardness IRHD Rebound Tensile stren Modulus 50% Modulue 100% Modulus 300% Abrasion Tear strength
FTFT
gth MPa MPa MPa MPa MPa mm3 kN/m kcycl
°C
69 (63) 34 (31) 25.1 (16.8) 1.2 (1.0) 2.1 (1.5) 11.2 (7.6) 83 (126) 105 (43) 45.2 (47.9) 14.0 (17.9) +39 (+58) 11 (18 69 (70) 33 (32) 24.5 (20.9) 1.2 (1.3) 2.0 (2.1) 10.8 (10.7) 86 (113) 104 (68) 46.2 (39.2) 15.7 (5.4) +36 (+29) 12 (15) 72 (69) 31 (32) 24.0 (20.8) 1.2 (1.2) 2.0 (2.0) 10.7 (9.8) 93 (100) 102 (70) 44.0 (41.9) 14.6 (8.7) +35 (+35) 14 (16) 69 (68) 33 (31) 23.8 (19.7) 1.2 2.J 11.0 (10.2) 92 110 (67) 47.7 (38.5) 12.4 (7.1) (+31) 14 (15) Permanent set Heat build up Compression set %(72h..23 0
C)
U ‘L U .A A 1 0 The data in the parentheses are the values vulcanizates cured at 170 0 C/30 minutes.
obtained for the The compound containing 1 phr BCI-MX (and control without BCI) vulcanized at 170 0 C for 30 min was subjected to a blow out test in the Goodrich flexometer.
SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 47 TABLE Blow out test results.
Blow out time Temp. rise (hrs) (C Control 1.5 92 BCI-MX 10 43 The results show that the blow out time is substantially lengthened and the heat build up and temperature rise are substantially lowered by BCI-MX.
Example 47 l,10-Bis(4-citraconimidobenzoyloxy)decane Tris(6-citraconimidohexyl)isocyanurate (TCI-AA33) and 1,8-bis(citraconimido)-4-citraconimidomethyloctane (TCI-C6v) were compounded in an NR recipe (see Example 44) and their effects on the Monsanto rheometer cure curves at 170 or 180 0 C up to 30 min determined (Table 41): SUBSTITLME SHEET WO 92/07904 PT/EP91/02048 48 TABLE 41 Coagent BCI-BAE10 TCI-AA33 TCI-C9V Concentration (phr) 3.0 1.0 Test temperature (OC) 180 170 170 Scorch safety, ts2 0.8 1.0 0.9 (min) (0.9) Optimal cure time, 1.7 3.1 2.9 t 9 0 (min) (2.9) Torque retention after 109 86 91 min (68) (73) (73) Monsanto rheometer MDR 2000E; Values between parenthesis: control without BCI or TCI BCI-BAE10, TCI-AA33 and TCI-C9V had slight or no effect on scorch and cure time, but improved reversion resistance of the compound.
Example 48 NR c’ompound vulcanized with higher amount of sulfur A black-filled NR compound (NR SMR CV 100, Carbon black N-326 Stearic acid 0.5,ZnO 8, Permanax 6PPD® 2, Dutrex 729 HP® 3, Crystex OT 20® 5, Perkacit CBS® 0.7 phr) containing a high amount of (insoluble) sulfur, useful as steel cord skim stock in tire compounding Piertoh and R. Schubart, Kautsch. Gummi, Kunstst.
43, 385, 1990), was compounded with 1.0 phr BCI-MP or BCI-MX.
The BCI’s had practically no influence on cure characteristics at n, 170 0 C (Table 42): SUBSTITUTE
SHEET
WO 92/07904 PCT/EP91/02048 49 TABLE 42 Cure characteristics at 170°C Compound 1 2 3 Coagent BCI-MP BCI-MX Scorch safety, t 2 (min) 0.7 0.7 0.7 Cure time, tg (min) 2.6 2.8 2.7 Delta torque _Nm) _1.8 1.8 1.9 Compounds containing BCI-MP and BCI-MX showed properties after overcure at 170 0 C for 30 min control without BCI: improved hardness, modulus, 43): improved mechanical as compared to the tear strength (Table TABLE 43 Mechanical properties after cure at 170 0 C, t 90 (between parenthesis) and 170°C, 30 min Compound 1 2 3 Coagent BC1-MP BCI-MX 2 Hardness, Shore A 59 (53) 59 (58) 60 57) Modulus (MPa) 50% 1.5 1.5 (1.6 1.5 1.7) 100% 2.7 2.7 2.7 2.8 300% 11.6 12.0 (10.7) 11.8 (12.1) Tear strength, KN/m 107 (35) 115 (42) 103 (42) Example 49 The contribution of different coagents to the cross-inking reaction of a conventionally cured carbon-black filled NR compound (see Example 44) was tested at 150°C to 180 0 C up to optimum cure. Table 44 shows the cross-linking reaction of BCI-C6, HVA-2® and BCI-MP, expressed as the percentage change in torque at optimum cure per mmole coagent.
SUBSTITUTE SHEET WO 92/07904 PCT/EP9 1/02048 TABLE 44.
Crosslinking reaction of coagents* Coagent Concn. -Temp.—-torque torque (phr) 0 C change at changF at t 90 %/mmole BCI-C6 1.5 150 -3.0 -0.6 180 -3.0 -0.6 HVA-2″ 1.5 170 +13.2 +2.4 170 +112 170 +249 +6.7 BCi-MP 1.5 170 -4.0 -0.8 170 -1.3 -0.1 10 170 1-3.3 J-0-.
*Monsanto rheometer MIDR 2000E.
Both BCI-C6 and BCI-MP exerted no cross-linking reaction in the conv -,tionally cured carbon-black filled NR compound as measured by torque change optimum cure, whereas the bismaleimide and HVA-28~ exerted a substantil cross-linking reaction.
SUBSTITUTE SHEET

Claims (14)

1. A sulfur-vulcanized rubber composition which comprises the vulcanization reaction product of: A) 100 parts by weight of at least one natural or synthetic rubber; B) 0.1 to 25 parts by weight of sulfur and/or a sufficient amount of a sulfur donor to provide the equivalent of 0.1 to 25 parts by weight of sulfur; and C) 0.1 to 5.0 parts by weight of a coagent which only partially reacts under sulfur-vulcanization reaction conditions up to optimum cure, and which, after optimum cure, forms cross-links bonded to the sulfur croes-linked rubber by a carbon-carbon linkage at a rate sufficient to compensate for from 10 to 200 percent of the reversion in said rubber composition.

2. A sulfur-vulcanized rubber composition as claimed in claim 1 wherein said rubber composition further comprises 0.1 to 8.0 parts by weight of a vulcanization accelerator.

3. A sulfur-vulcanized rubber composition as claimed in any one of claims 1-2 wherein said coagent has a cross- linking efficiency of -2.0 to 2.0% per millimola under sulfur-vulcanization conditions up to optimum cure.

4. A sulfur-vulcanized rubber composition as claimed in 25 any one of claims 1-3 wherein caid coagent forms cross- links at a rate sufficient to compensate for from 40-150% of the reversion in said rubber composition.

6. 0 5. A sulfur-vulcanized rubber composition as claimed in 00,. any one of claims 1-4 which, immediately after optimum cure, still comprises, in unreacted form, a substantial amount of the 0.1 to 5 parts by weight of coagent which was originally present in the composition. WO 92/07904 PCT/EP91/02048 52 6. A sulfur-vulcanized rubber composition as claimed in any one of claims 1-5 wherein said coagent comprises at least one compound of the formula A: Q1-D-(Q2)n wherein D, optionally containing one or more heteroatoms selected from nitrogen, oxygen, silicon, phosphorus, boron, sulphone and sulphoxy, is a monomeric or oligomeric divalent, trivalent or tetravalent group, n is an integer selected from 1, 2 or 3, Q1 and Q2 are independently selected from the formulas I and II: B R1 I -N R 2 (1) 3 II B’ and; B R 1 II -N R2 (II) II I B’ H wherein R1, R2 ‘nd R 3 are independently selected from hydrogen, C 1 -Cq alkyl groups, C 3 -C 18 cycloalkyl groups, C 6 -C 18 aryl groups, C 7 -C3 0 aralkyl groups and C7-C 3 0 alkaryl groups and R 2 and R 3 may combine to form a ring when RI is hydrogen; B and B’ are independently selected from the following hetero atoms: oxygen and sulfur. SUBSTfITUTr WO 92/07904 PCT/EP91/02048 53

7. A lbber composition according to any one of claims 1-6 wherein said coagent comprises at least one compound selected from a bis- or triscitraconimide and a bis- or trisitaconimide and mixtures thereof.

8. A process for the vulcanization, at a temperature of from 110 to 220 0 C for up to 24 hours, of a vulcanizable composition comprising at lea., one natural or synthetic rubber in the presence of 0.1 to parts by weight of sulfur or a sufficient amount of a sulfur donor to provide the equivalent of 0.1 to 25 parts by weight of sulfur, characterized in that said process is carried out in the presence of an effective amount of an anti-reversion coagent which only partially reacts under sulfur-vulcanization reaction conditions up to optimum cure, and which, after optimum cure, forms cross-links bonded to the sulfur cross-linked rubber by a carbon-carbon linkage at a rate sufficient to compensate for from to 200 percent of the reversion in said rubber composition.

9. A vulcanization process as claimed in claim 8, wherein said rubber is vulcanized in the further presence of 0.1 to 8.0 parts by weight of a vulcanization accelerator. A vulcanization process as claimed in any one of claims 8-9 wnetein said coagent has a cross-linking efficiency of -2.0 to per millimole under sulfur-vulcanization conditions up to optimum cure.

11. A vulcanization process as claimed in any one of claims 8-10 wherein said coagent forms cross-links at a rate sufficient to compensate for from 40-150% of the reversion in said rubber composition.

12. A vulcanization process as claimed in any one of claims 8-11 wherein said coagent comprises at least one compound of the formula A: SJRSTITUTE §4-rffft WO 92/07904 PCT/EP91/02048 54 Q1-D-(Q 2 )n wherein D, optionally containing one or more heteroatoms selected from nitrogen, oxygen, silicon, phosphorus, boron, sulphone and sulphoxy, is a monomeric or )ligomeric divalent, trivalent or tetravalent group, n is an integer selected from 1, 2 or 3, Q1 and Q2 are independently selected from the formulas I and II: B R 1 -N K -N R2 (I) 3 II BI and; B RI II -N R 2 (II) 3 11 I 81 H wherein R 1 R 2 and R 3 are independently selected from hydrogen, C 1 -C 18 alkyl groups, C 3 -C 18 cycloalkyl groups, C 6 -C 18 aryl groups, C 7 -C 30 aralkyl groups and C 7 -C3 0 alkaryl groups and R2 and R 3 may combine to form a ring when R 1 is hydrogen; B and B, are independently selected from the following hetero atoms: oxygen and sulfur.

13. A vulcanization process according to any one of claims 8-12 wherein said coagent comprises at least one compound selected from a bis- or triscitraconimide and a bis- or trisitaconimide and mixtures thereof. SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048

14. The use of an anti-reversion coagent selected from compounds which only partially react under sulfur-vulcanization reaction con- ditions up to optimum cure, and which, after optimum cure, form cross-links bonded to the sulfur cross-linked rubber by a carbon- carbon linkage at a rate sufficient to compensate for from 10 to 200 percent of the reversion in said rubber composition, in the sulfur-vulcanization of rubber. The use as claimed in claim 14 wherein said coagent has a cross- linking efficiency of -2.0 to 2.0% per millimole under sulfur- vulcanization conditions up to optimum cure.

16. The use as claimed in any one of claims 14-15 wherein said coagent forms cross-links at a rate sufficient to compensate for from

40-150% of the reversion in said rubber composition. 17. The use as claimed in any one of claims 14-16 wherein said coagent comprises at least one compound of the formula A: Ql-D-(Q2)n wherein D, optionally containing one or more heteroatoms selected from nitrogen, oxygen, silicon, phosphorus, boron, sulphone and sulphoxy, is a monomeric or oligomeric divalent, trivalent or tetravalent group, n is an integer selected from 1, 2 or 3, QI and Q2 are independently selected from the formulas I and II: B R1 II I I I -N 2 (I) 3 11 B’ and; SUBSTITUTE SHEET WO 92/07904 PCT/EP91/02048 56 B R 1 II -N R 2 (II) 3 11 BI H wherein R 1 R 2 and R 3 are independently selected from hydrogen, C 1 -C 18 alkyl groups, C 3 -C 18 cycloalkyl groups, C 6 -C 18 aryl groups, C 7 -C 30 aralkyl groups and C 7 -C 30 alkaryl groups and R 2 and R 3 may combine to form a ring when R 1 is hydrogen; B and BI are independently selected from the following hetero atoms: oxygen and sulfur. 18. The use according to any one of claims 14-17 wherein said coagent comprises at least one compound selected from a bis- or triscitraconimide and a bis- or trisitaconimide and mixtures thereof. 19. An article of manufacture comprising a rubber vulcanized by any of the processes of claims 8-13. A tire comprising a rubber vulcanized by any of the processes of claims 8-13. SUBSTITUTE SHEET INTERNATIONAL SEARCH REPORT Internationa.l Application No PCT/EP 91/02048 1. CLASSIFICATION OF SUBJECT’ MATTER Oif several classification symbols apply, Indicate all)’ Acc~rding to Internationul Patent Classification IQC or to both NZaItina Classification and IPC Int.Cl. 5 C08K5/3415; C08’J3/24; C08L21/0O U. FIELDS SEARCHED Minimum Documentation Smrdsed Clussification Syrian Classification Symbols Int.Cl. 5 C08K ;C08J Documentatica Searched other than Minimum Documentation to the Extent th’tt such Documents are Included In the Fields Searchedl HI. DOCUMENTS CONSEIERED To BE RELEVANT9 Category Citation of Document, 1 t with Indication, whate appropriate, of the relevat passages 12 Relent to Clairn No.L7 X EP,A,0 345 825 (SUMITOMO CHEMICAL COMPANY LIMITED) 13 December 1989 8-11, cited in the application 14-16, 19-20 see page 2, line 35 page 2, line 38; claim 1 X INTERNATIONAL POLYMER SCIENCE AND TECHNOLOGY. vol. 4, no. 12, 1977, SHAWBURY GB 8-11, pages 48 50; 14-16, A.S.PRASHCHIKINA ET AL.: ‘HIGH-TEMPERATURE 19-20 CURING OF GENERAL-PURPOSE RUBBERS WITH A CURING SYSTEM COMPRISING A BISMALEIMIDE AND SULPHUR’ see page T48, column 1, line 1 -page T48, column 1, line 29 see page T48, column 2, line 10 -page T48, column 2, line o S pedial categories of dited documents 10I later document published after the international filing date WA dcumnt efinng he eneal sateof he a whch s ~or priority date and not in conflict with the application but W dcnsidefinn to e b eta teoof a hc Is o died to understand the principle or theory underlying the consderd t beof prtiula MoacoInvention Er earlier document but published on or after the International document of prilareloince; the claimed Invention filing date cannot be consdre ovel or cannot be considered to ‘V document which may throw doubts on ptlority claim(s) or involve an Inventive stop ithich Is cited to establish the publication date f aother Or document of particular relevance; the claimed Invention Citation or other special reason (as specified) cannot be considered to Involve an Inventive step when the document referring to an oral disclosur, use, exhibidtio or £ocs-‘ z combined with ane or morm other such docu- other momn ments, such combination being obvious to a pawsn skilled P document published prior to the international filing date but in the amt later than the priority date dlaimed WA document memher of the same patint family IV. CERTIFICATION Date of the Actual Completion of the International Search Date of MaLI’ng of Nhs International Search Report 24 JANUARY 1992 0 6. O2. 92 International Searching Authority Signaure of Authorizsd Officer EUROPEAN PATENT OFFCE VAN HUMBEECK V.u PCTI.SAM0I twe &best lJuwry IMPS PCT/EP 9 1/02048 Internlationld Application No IDl. DOCUMFNTS CONSIDERED TO BE RELEVANT (CONTINUED FROM THE SECOND SHEET) Categoy 0 Citaion of Document, with indication, where appropriate, of the reWeat pmap Relevant to 03aim No. X PATENT ABSTRACTS OF JAPAN vol. 12, no. 462 (C-549)(3309) 5 December 1988 8-11, JP,A,63 182 355 BRIDGESTONE CORPORATION 27 14-16, July 1988 19-20 see abstract A PATENT ABSTRACTS OF JAPAN 1 vol. 13, no. 111 (C-577)(3459) 16 March 1989 JP,A,63 284 445 BRIDGESTONE CORPORATION )24 November 1988 cited in the application see abstract A US,A,3 974 163 (A.Y.CORAN) 10 August 1976 1 see column 2, line 46 column 2, line 53 s,,e column 5, line 12 column 5, line 19 sfve column 17, line 42 column 17, line 42 A FR,A,1 257 913 (UNITED STATES RUBBER COMPANY) 27 6 February 1961 Abstract, point A.1 YPer Ttu2 to=1~ Ad 1jjm 7 MnS ANNF TO THE INTERNATIONAL SEARCH REPORT ON 1’4’t ERNATIONAL PATENT APPLICATION No. EP SA 9102048 5~2459 This annex lists the patent family members relating to the patent documents cited in the above-mentioned international search report. The members are as contained in the European Patent Office EDP Ille on The European Patent Office is in no way liable for these particulars which are merely given for the purpose of information. 24/0 1/92 Patent document Publication Patent familly Publication cited in search report I date Imember(s) Idate EP-A-03 45825 13- 12-89 JP-A- JP-A- CA-A- EP-A, B U S-A- US-A- 61166844 61168642 1248272 0191931 4803250 4960833 28-07-86 30-07-86 03-01-89 27-08-86 07-02-89 02- 10-90 US-A-3974163 10-08-76 US-A- 3862051 21-01-75 US-A- 3775428 27-11-73 FR-A-1257913 None 13 For more details about ths annx ee Official Journal of the European Patent Mfie 1 No. 12182

AU87656/91A
1990-10-29
1991-10-29
Anti-reversion coagents for rubber vulcanization

Expired

AU648837B2
(en)

Applications Claiming Priority (3)

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Priority Date
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EP90202864

1990-10-29

EP90202864

1990-10-29

PCT/EP1991/002048

WO1992007904A1
(en)

1990-10-29
1991-10-29
Anti-reversion coagents for rubber vulcanization

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AU8765691A

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1992-05-26

AU648837B2
true

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1994-05-05

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AU87656/91A
Expired

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1990-10-29
1991-10-29
Anti-reversion coagents for rubber vulcanization

AU87458/91A
Ceased

AU650692B2
(en)

1990-10-29
1991-10-29
(Poly)sulfide containing polycitraconimides and polyitaconimides

AU16565/92A
Abandoned

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1990-10-29
1992-05-07
Tire and belt compositions

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AU650692B2
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1990-10-29
1991-10-29
(Poly)sulfide containing polycitraconimides and polyitaconimides

AU16565/92A
Abandoned

AU1656592A
(en)

1990-10-29
1992-05-07
Tire and belt compositions

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ZA
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AU
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not_active
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AR
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CN
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Expired – Lifetime

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DE
DE69120428T
patent/DE69120428T2/en
not_active
Expired – Lifetime

1991-10-29
KR
KR1019930701310A
patent/KR100192077B1/en
not_active
IP Right Cessation

1991-10-29
KR
KR1019930701254A
patent/KR930702295A/en
not_active
Application Discontinuation

1991-10-29
AU
AU87458/91A
patent/AU650692B2/en
not_active
Ceased

1991-10-29
ES
ES91918766T
patent/ES2088505T3/en
not_active
Expired – Lifetime

1991-10-29
WO
PCT/EP1991/002049
patent/WO1992007828A1/en
not_active
Application Discontinuation

1991-10-29
HU
HU9301231A
patent/HU214150B/en
unknown

1991-10-29
BR
BR919107013A
patent/BR9107013A/en
not_active
IP Right Cessation

1991-10-29
PL
PL91300609A
patent/PL169601B1/en
unknown

1991-10-29
DE
DE69113810T
patent/DE69113810T2/en
not_active
Expired – Fee Related

1991-10-29
AT
AT91918766T
patent/ATE139550T1/en
not_active
IP Right Cessation

1991-10-29
EP
EP91918766A
patent/EP0555288B1/en
not_active
Expired – Lifetime

1991-10-29
RU
RU9193004897A
patent/RU2067974C1/en
active

1991-10-29
HU
HU9301230A
patent/HUT65508A/en
unknown

1991-10-29
ES
ES91918041T
patent/ES2077869T3/en
not_active
Expired – Lifetime

1991-10-29
DK
DK91918766.6T
patent/DK0555288T3/en
active

1991-10-29
SK
SK40493A
patent/SK40493A3/en
unknown

1991-10-29
CA
CA002095135A
patent/CA2095135A1/en
not_active
Abandoned

1991-10-29
JP
JP3517059A
patent/JPH06502150A/en
active
Pending

1991-10-29
ZA
ZA918605A
patent/ZA918605B/en
unknown

1991-10-29
PL
PL91300612A
patent/PL169822B1/en
unknown

1991-10-29
US
US08/050,108
patent/US5405918A/en
not_active
Expired – Fee Related

1991-10-29
DK
DK91918041.4T
patent/DK0556203T3/en
active

1992

1992-05-07
AU
AU16565/92A
patent/AU1656592A/en
not_active
Abandoned

1993

1993-04-29
FI
FI931936A
patent/FI931936A/en
not_active
Application Discontinuation

1993-04-29
FI
FI931937A
patent/FI114803B/en
not_active
IP Right Cessation

1995

1995-03-30
US
US08/413,567
patent/US5610240A/en
not_active
Expired – Lifetime

1995-11-29
GR
GR950403332T
patent/GR3018216T3/en
unknown

1996

1996-06-27
GR
GR960401754T
patent/GR3020382T3/en
unknown

Patent Citations (1)

* Cited by examiner, † Cited by third party

Publication number
Priority date
Publication date
Assignee
Title

EP0345825A1
(en)

*

1985-01-19
1989-12-13
Sumitomo Chemical Company, Limited
Rubber composition

Also Published As

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ES2088505T3
(en)

1996-08-16

RU2118333C1
(en)

1998-08-27

HU9301231D0
(en)

1993-09-28

HU214150B
(en)

1998-01-28

WO1992007904A1
(en)

1992-05-14

ZA918607B
(en)

1992-08-26

EP0556203B1
(en)

1995-10-11

CZ77893A3
(en)

1994-01-19

GR3020382T3
(en)

1996-09-30

JP3176367B2
(en)

2001-06-18

DK0556203T3
(en)

1996-02-05

FI931936A0
(en)

1993-04-29

SK279467B6
(en)

1998-11-04

HU9301230D0
(en)

1993-09-28

DE69120428T2
(en)

1997-01-16

CA2095136C
(en)

2002-01-08

DE69113810D1
(en)

1995-11-16

ZA918605B
(en)

1992-08-26

AR247412A1
(en)

1994-12-29

ATE139550T1
(en)

1996-07-15

PL300609A1
(en)

1994-03-21

WO1992007828A1
(en)

1992-05-14

BR9107014A
(en)

1993-09-28

PL300612A1
(en)

1994-03-21

KR930702295A
(en)

1993-09-08

AU650692B2
(en)

1994-06-30

SK40493A3
(en)

1993-10-06

DK0555288T3
(en)

1996-07-15

CA2095135A1
(en)

1992-04-30

CA2095136A1
(en)

1992-04-30

FI114803B
(en)

2004-12-31

PL169601B1
(en)

1996-08-30

CZ289800B6
(en)

2002-04-17

KR100192077B1
(en)

1999-06-15

JPH06502208A
(en)

1994-03-10

GR3018216T3
(en)

1996-02-29

TW209231B
(en)

1993-07-11

FI931936A
(en)

1993-04-29

CN1061230A
(en)

1992-05-20

DE69113810T2
(en)

1996-05-23

EP0555288A1
(en)

1993-08-18

EP0556203A1
(en)

1993-08-25

ATE128967T1
(en)

1995-10-15

SK40593A3
(en)

1993-10-06

HUT64991A
(en)

1994-03-28

HUT65508A
(en)

1994-06-28

KR930702440A
(en)

1993-09-09

RU2067974C1
(en)

1996-10-20

FI931937A0
(en)

1993-04-29

US5610240A
(en)

1997-03-11

AU8745891A
(en)

1992-05-26

CN1042734C
(en)

1999-03-31

US5426155A
(en)

1995-06-20

PL169822B1
(en)

1996-09-30

ES2077869T3
(en)

1995-12-01

BR9107013A
(en)

1993-09-28

US5405918A
(en)

1995-04-11

EP0555288B1
(en)

1996-06-19

FI931937A
(en)

1993-04-29

AU8765691A
(en)

1992-05-26

DE69120428D1
(en)

1996-07-25

JPH06502150A
(en)

1994-03-10

AU1656592A
(en)

1993-06-07

CN1061229A
(en)

1992-05-20

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