GB1603762A - Creation of Inventions and Patents with Artificial Intelligence

GB1603762A – Optical recording medium
– Google Patents

GB1603762A – Optical recording medium
– Google Patents
Optical recording medium

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Info

Publication number
GB1603762A

GB1603762A
GB16729/78A
GB1672978A
GB1603762A
GB 1603762 A
GB1603762 A
GB 1603762A
GB 16729/78 A
GB16729/78 A
GB 16729/78A
GB 1672978 A
GB1672978 A
GB 1672978A
GB 1603762 A
GB1603762 A
GB 1603762A
Authority
GB
United Kingdom
Prior art keywords
layer
recording medium
light
recording
medium according
Prior art date
1977-08-29
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)

Expired

Application number
GB16729/78A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)

RCA Corp

Original Assignee
RCA Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1977-08-29
Filing date
1978-04-27
Publication date
1981-11-25

1978-04-27
Application filed by RCA Corp
filed
Critical
RCA Corp

1981-11-25
Publication of GB1603762A
publication
Critical
patent/GB1603762A/en

Status
Expired
legal-status
Critical
Current

Links

Espacenet

Global Dossier

Discuss

230000003287
optical effect
Effects

0.000
title
description
8

230000004888
barrier function
Effects

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claims
description
43

239000000463
material
Substances

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claims
description
27

VYPSYNLAJGMNEJ-UHFFFAOYSA-N
Silicium dioxide
Chemical compound

O=[Si]=O
VYPSYNLAJGMNEJ-UHFFFAOYSA-N
0.000
claims
description
26

235000012239
silicon dioxide
Nutrition

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claims
description
13

239000000377
silicon dioxide
Substances

0.000
claims
description
13

XAGFODPZIPBFFR-UHFFFAOYSA-N
aluminium
Chemical group

[Al]
XAGFODPZIPBFFR-UHFFFAOYSA-N
0.000
claims
description
11

229910052782
aluminium
Inorganic materials

0.000
claims
description
11

RTAQQCXQSZGOHL-UHFFFAOYSA-N
Titanium
Chemical group

[Ti]
RTAQQCXQSZGOHL-UHFFFAOYSA-N
0.000
claims
description
6

239000010936
titanium
Substances

0.000
claims
description
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229910052719
titanium
Inorganic materials

0.000
claims
description
6

229920005989
resin
Polymers

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claims
description
5

239000011347
resin
Substances

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claims
description
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239000003795
chemical substances by application
Substances

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claims
description
3

125000002887
hydroxy group
Chemical group

[H]O*

0.000
claims
description
3

XUIMIQQOPSSXEZ-UHFFFAOYSA-N
Silicon
Chemical group

[Si]
XUIMIQQOPSSXEZ-UHFFFAOYSA-N
0.000
claims
description
2

CZMRCDWAGMRECN-UGDNZRGBSA-N
Sucrose
Chemical compound

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CZMRCDWAGMRECN-UGDNZRGBSA-N
0.000
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description
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238000002679
ablation
Methods

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description
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ester group
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description
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229910052710
silicon
Inorganic materials

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description
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silicon
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description
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239000005720
sucrose
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description
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239000004411
aluminium
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1

125000000185
sucrose group
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239000000975
dye
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description
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XKRFYHLGVUSROY-UHFFFAOYSA-N
Argon
Chemical compound

[Ar]
XKRFYHLGVUSROY-UHFFFAOYSA-N
0.000
description
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229910052751
metal
Inorganic materials

0.000
description
6

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metal
Substances

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BASFCYQUMIYNBI-UHFFFAOYSA-N
platinum
Chemical compound

[Pt]
BASFCYQUMIYNBI-UHFFFAOYSA-N
0.000
description
6

229920002050
silicone resin
Polymers

0.000
description
6

PCHJSUWPFVWCPO-UHFFFAOYSA-N
gold
Chemical compound

[Au]
PCHJSUWPFVWCPO-UHFFFAOYSA-N
0.000
description
5

239000010931
gold
Substances

0.000
description
5

229910052737
gold
Inorganic materials

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description
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238000002844
melting
Methods

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238000001704
evaporation
Methods

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organic material
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substance
Substances

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description
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239000000758
substrate
Substances

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description
4

IICHURGZQPGTRD-UHFFFAOYSA-N
4-phenyldiazenylnaphthalen-1-amine
Chemical compound

C12=CC=CC=C2C(N)=CC=C1N=NC1=CC=CC=C1
IICHURGZQPGTRD-UHFFFAOYSA-N
0.000
description
3

RSWGJHLUYNHPMX-UHFFFAOYSA-N
Abietic-Saeure
Natural products

C12CCC(C(C)C)=CC2=CCC2C1(C)CCCC2(C)C(O)=O
RSWGJHLUYNHPMX-UHFFFAOYSA-N
0.000
description
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239000011358
absorbing material
Substances

0.000
description
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229910052786
argon
Inorganic materials

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description
3

238000000576
coating method
Methods

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description
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defect
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239000000428
dust
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evaporation
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interaction
Effects

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239000003960
organic solvent
Substances

0.000
description
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229910052697
platinum
Inorganic materials

0.000
description
3

SYDJVRWZOWPNNO-UHFFFAOYSA-N
sucrose-benzoate
Natural products

OCC1OC(OC2(COC(=O)c3ccccc3)OC(CO)C(O)C2O)C(O)C(O)C1O
SYDJVRWZOWPNNO-UHFFFAOYSA-N
0.000
description
3

IJGRMHOSHXDMSA-UHFFFAOYSA-N
Atomic nitrogen
Chemical compound

N#N
IJGRMHOSHXDMSA-UHFFFAOYSA-N
0.000
description
2

KHPCPRHQVVSZAH-HUOMCSJISA-N
Rosin
Natural products

O(C/C=C/c1ccccc1)[C@H]1[C@H](O)[C@@H](O)[C@@H](O)[C@@H](CO)O1
KHPCPRHQVVSZAH-HUOMCSJISA-N
0.000
description
2

BLRPTPMANUNPDV-UHFFFAOYSA-N
Silane
Chemical compound

[SiH4]
BLRPTPMANUNPDV-UHFFFAOYSA-N
0.000
description
2

239000002253
acid
Substances

0.000
description
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150000007513
acids
Chemical class

0.000
description
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125000001231
benzoyloxy group
Chemical group

C(C1=CC=CC=C1)(=O)O*

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230000015572
biosynthetic process
Effects

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description
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239000003054
catalyst
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239000011248
coating agent
Substances

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239000006059
cover glass
Substances

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description
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239000003989
dielectric material
Substances

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description
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238000009792
diffusion process
Methods

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electron-beam-induced deposition
Methods

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description
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229910010272
inorganic material
Inorganic materials

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description
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239000011147
inorganic material
Substances

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239000000178
monomer
Substances

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description
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239000002245
particle
Substances

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description
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WXZMFSXDPGVJKK-UHFFFAOYSA-N
pentaerythritol
Chemical class

OCC(CO)(CO)CO
WXZMFSXDPGVJKK-UHFFFAOYSA-N
0.000
description
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229920000642
polymer
Polymers

0.000
description
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229910000077
silane
Inorganic materials

0.000
description
2

YCUVUDODLRLVIC-VPHDGDOJSA-N
sudan black b
Chemical compound

C1=CC(=C23)NC(C)(C)NC2=CC=CC3=C1\N=N\C(C1=CC=CC=C11)=CC=C1\N=N\C1=CC=CC=C1
YCUVUDODLRLVIC-VPHDGDOJSA-N
0.000
description
2

KHPCPRHQVVSZAH-UHFFFAOYSA-N
trans-cinnamyl beta-D-glucopyranoside
Natural products

OC1C(O)C(O)C(CO)OC1OCC=CC1=CC=CC=C1
KHPCPRHQVVSZAH-UHFFFAOYSA-N
0.000
description
2

QIROQPWSJUXOJC-UHFFFAOYSA-N
1,1,2,2,3,3,4,4,5,5,6-undecafluoro-6-(trifluoromethyl)cyclohexane
Chemical compound

FC(F)(F)C1(F)C(F)(F)C(F)(F)C(F)(F)C(F)(F)C1(F)F
QIROQPWSJUXOJC-UHFFFAOYSA-N
0.000
description
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BTXXTMOWISPQSJ-UHFFFAOYSA-N
4,4,4-trifluorobutan-2-one
Chemical group

CC(=O)CC(F)(F)F
BTXXTMOWISPQSJ-UHFFFAOYSA-N
0.000
description
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BQACOLQNOUYJCE-FYZZASKESA-N
Abietic acid
Natural products

CC(C)C1=CC2=CC[C@]3(C)[C@](C)(CCC[C@@]3(C)C(=O)O)[C@H]2CC1
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0.000
description
1

241000206607
Porphyra umbilicalis
Species

0.000
description
1

ZIJKGAXBCRWEOL-SAXBRCJISA-N
Sucrose octaacetate
Chemical compound

CC(=O)O[C@H]1[C@H](OC(C)=O)[C@@H](COC(=O)C)O[C@@]1(COC(C)=O)O[C@@H]1[C@H](OC(C)=O)[C@@H](OC(C)=O)[C@H](OC(C)=O)[C@@H](COC(C)=O)O1
ZIJKGAXBCRWEOL-SAXBRCJISA-N
0.000
description
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239000001344
[(2S,3S,4R,5R)-4-acetyloxy-2,5-bis(acetyloxymethyl)-2-[(2R,3R,4S,5R,6R)-3,4,5-triacetyloxy-6-(acetyloxymethyl)oxan-2-yl]oxyoxolan-3-yl] acetate
Substances

0.000
description
1

RSWGJHLUYNHPMX-ONCXSQPRSA-N
abietic acid
Chemical compound

C([C@@H]12)CC(C(C)C)=CC1=CC[C@@H]1[C@]2(C)CCC[C@@]1(C)C(O)=O
RSWGJHLUYNHPMX-ONCXSQPRSA-N
0.000
description
1

125000003668
acetyloxy group
Chemical group

[H]C([H])([H])C(=O)O[*]

0.000
description
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230000001464
adherent effect
Effects

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230000002411
adverse
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230000032683
aging
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HSFWRNGVRCDJHI-UHFFFAOYSA-N
alpha-acetylene
Natural products

C#C
HSFWRNGVRCDJHI-UHFFFAOYSA-N
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150000001412
amines
Chemical class

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239000012159
carrier gas
Substances

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238000006243
chemical reaction
Methods

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coherent effect
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contaminant
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cross link polymer
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decreasing effect
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ethynyl group
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239000011521
glass
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in-situ storage
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nitrogen
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sucrose octaacetate
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Classifications

G—PHYSICS

G11—INFORMATION STORAGE

G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER

G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor

G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material

G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material

G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers

G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only

G11B7/246—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing dyes

G—PHYSICS

G11—INFORMATION STORAGE

G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER

G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material

G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material

G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers

G11B7/257—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers

G11B7/2578—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials

G—PHYSICS

G11—INFORMATION STORAGE

G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER

G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material

G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material

G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers

G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers

G11B2007/24302—Metals or metalloids

G11B2007/24306—Metals or metalloids transition metal elements of groups 3-10

G—PHYSICS

G11—INFORMATION STORAGE

G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER

G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material

G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material

G11B2007/25705—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials

G11B2007/2571—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials containing group 14 elements except carbon (Si, Ge, Sn, Pb)

G—PHYSICS

G11—INFORMATION STORAGE

G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER

G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material

G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material

G11B2007/25715—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers consisting essentially of inorganic materials containing oxygen

G—PHYSICS

G11—INFORMATION STORAGE

G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER

G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material

G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material

G11B7/254—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of protective topcoat layers

G11B7/2542—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of protective topcoat layers consisting essentially of organic resins

G—PHYSICS

G11—INFORMATION STORAGE

G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER

G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material

G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material

G11B7/258—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of reflective layers

G11B7/2585—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of reflective layers based on aluminium

G—PHYSICS

G11—INFORMATION STORAGE

G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER

G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material

G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material

G11B7/2595—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of reflective layers based on gold

Description

PATENT SPECIFICATION ( 11) 1603 762
( 21) Application No 16729/78 ( 22) Filed 27 April 1978 C ( 31) Convention Application No 828 847 ( 19) ( 32) Filed 29 Aug 1977 in a ( 33) United States of America (US) i ( 44) Complete Specification published 25 Nov 1981 -1 ( 51) INT CL 3 G 11 B 7/24 ( 52) Index at acceptance G 5 R B 21 B 265 B 361 B 36 Y B 571 B 57 X B 675 B 701 B 711 B 713 B 714 B 71 X B 734 B 784 B 789 ( 54) OPTICAL RECORDING MEDIUM ( 71) We, RCA CORPORATION, a corporation organised under the laws of the State of Delaware, United States of America, of 30 Rockefeller Plaza, City and State of New York, 10020, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following 5
statement:-
This invention relates to an optical recording medium More particularly, this invention relates to an optical recording medium comprising a light reflecting material coated with a light absorbing layer which is coated with a thin, hard, inert.
thermally insulating transparent layer and overcoated with a thick transparent,10 layer.
Our Specification 1560245 describes an ablative recording system whereby a focussed modulated light beam, such as a laser beam, is directed at an ablative recording medium The recording medium comprises a light reflecting material coated with a light absorbing material on a substrate The thickness of the light 15 absorbing layer is chosen to reduce the reflectivity to a minimum value so that a maximum of light energy impinging on it is retained therein and is converted to thermal energy This thermal energy causes the light absorbing material in the area struck by the light to ablate, thereby exposing selected portions of the light reflecting layer During readout, the contrast between the light reflected from the 20 absorbing layer, which is at the reflection minimum, and the light reflecting layer is detected.
Ongoing work in this area has resulted in the improved performance of the materials employed Thus, in an illustrative embodiment of this recording medium, a substrate which is a flat, smooth, non-conductor of heat is coated with a thin layer 25 of a light reflecting material, such as aluminum The aluminum layer is passivated e.g as described in our Specification 1576279 The passivated aluminum layer is in turn coated with a layer of an organic light absorbing material, such as 4phenylazo-l-naphthylamine, as described in Bloom et al, “Ablative Optical Recording Medium”, U S Patent No 4,023,185 30 Alternatively, as proposed in our Application 52944/77) (Serial No 1590296) the light reflecting layer is coated with a transparent dielectric material, such as silicon dioxide A thin layer of a metal is coated thereon to serve as the light absorbing layer Titanium is the metal most frequently used for this light absorbing layer 35 In order to eliminate or reduce signal defects or dropouts caused by surface dust which precipitates onto the medium from the environment, an overcoat from about 0 05 to 1 millimeter thick is applied to the light absorbing layer in our Application 16730/78 (Serial No 1603763) Dust particles and other surface contaminants which settle on the upper surface of the overcoat layer are so far 40 removed from the focal plane of the recording lens that their effect on the recording or playback signal is considerably reduced and no defects are noticeable on the playback monitor.
Silicone resin is a good overcoat material However, the preferred silicone resin system uses a platinum catalyst to promote curing of the resin Platinum can 45 react with amines present in the light absorbing layer, thereby adversely affecting curing of the resin and attacking the surface of the light absorbing layer This reaction, which increases the number of signal defects or dropouts, can be mitigated but not eliminated by baking or ageing the dye-coated disc before applying the silicone overcoat In addition, organic dyes dissolve in most organic solvents, thereby limiting the number of materials suitable for use as overcoats.
When a metal light absorbing layer is used, it must have a low melting point to avoid damage to or optical distortion of the overcoat layer during recording Thus.
high-melting metals which form otherwise excellent light absorbing layers cannot 5 be used effectively for recording through the overcoat layer An improved recording medium would make it possible to protect the overcoat layer from thermal or chemical interaction with the light absorbing layer.
According to the present invention there is provided recording medium for use with a recording laser beam providing light of a given frequency, said recording 10 medium comprising a layer which reflects light of said given frequency with a layer which absorbs light of said given frequency thereon, an overcoat layer thereover; and a barrier layer substantially transparent to light of said given frequency situated between the light absorbing layer and the overcoat layer; wherein 15 said barrier layer is of a material and of a thickness such that it is thermally insulating and chemically unreactive with respect to the light absorbing layer and the overcoat layer.
An embodiment comprising an optical recording medium of a light reflecting layer coated with a light absorbing layer and overcoated with a relatively thick 20 transparent layer, wherein a thermal and chemical barrier layer is situate between the light absorbing layer and the overcoat layer The barrier layer insulates the light absorbing layer and the overcoat layer from chemical and thermal interactions which might result in a decreased signal-to-noise ratio of recorded information.
The relatively thick overcoat layer of material tends to suspend any surface dust 25 particles out of focus of the recording laser beam In order to insulate the light absorbing layer and the overcoat layer from chemical and thermal interactions, the barrier layer is coated on the light absorbing layer prior to application of the overcoat layer If desired, the barrier and overcoat layers can be applied after recording, provided the light absorbing layer is kept clean 30 The light reflecting material can for instance be coated on a substrate with an optionally smooth, flat surface to which the subsequently applied light reflective layer is adherent A glass or plastic plate or disc is suitable The reflecting layer should reflect light at the wavelength employed for recording A gold layer about 800 angstroms thick forms a good, non-reactive reflecting layer An aluminum 35 layer from about 250 to 500 angstroms thick is also suitable The aluminum layer can be oxidized to a depth of about 30 angstroms in order to passivate the surface.
The light absorbing layer must be absorbing at the wavelength used for recording In addition it should form an amorphous, coherent film of a thickness that minimizes light reflection Further, the light absorbing layer should be readily 40 ablatable at low temperatures to form clearly defined, regularly shaped holes A layer of 4-phenylazo-l-naphthylamine, obtained by evaporating the dyestuff Sudan Black B in a vacuum chamber, forms an excellent coating Another good light absorbing arrangement is provided by coating the light reflecting layer with a transparent dielectric layer of silicon dioxide which, in turn, is coated with a thin 45 layer of titanium as the light absorbing layer.
The overcoat layer should be transparent and non-scattering at the wavelength used for recording and readout In addition it should be stable to ambient conditions When the signal is recorded through the overcoat, the overcoat should allow formation of the signal elements beneath it and readout through it without 50 substantially affecting picture quality Silicone resins such as General Electric’s RTV 615 and RTV 602 and Dow Corning’s Sylgard 184 form suitable overcoat materials.
Preferably, materials for the barrier layer will be amorphous and nonscattering at the recording and readout wavelength In addition they should be 55 thermally insulating and chemically unreactive with respect to the light absorbing layer and the overcoat layer It is desirable that materials for barrier layers be capable of application without chemically, physically or thermally disturbing the light absorbing layer For example, when organic dyes are used for the light absorbing layer, since they are readily soluble in most organic solvents, a desired 60 characteristic of a suitable barrier layer material is the capability of forming an amorphous layer by a non-solvent deposition process.
As with the overcoat material, the barrier layer should allow formation of the Registered Trade Marks 1,603,762 signal elements beneath it and readout through it without substantially affecting picture quality, and therefore, should have a sufficiently high melting point and hardness to resist rupture during readout When a metal light absorbing layer is used, the signal-to-noise ratio of recorded information is increased about 5 decibels (d B) by choosing a barrier layer which does not soften when heated during 5 recording.
Both organic and inorganic materials are suitable for use as barrier layers in the present invention Inorganic dielectric materials have higher melting points and provide harder films than organic materials These characteristics reduce the likelihood of rupture during recording and provide a barrier layer which can be 10 used effectively with metal light absorbing layers having high melting points In addition, inorganic materials are not attacked by most organic solvents which are used in applying certain overcoat materials Therefore, they are somewhat more versatile materials for barrier layers than organic materials.
In a preferred embodiment, a silicon dioxide (Si O 2) barrier layer of an 15 appropriate thickness is applied to a disc previously coated with light reflecting and light absorbing layers Electron-beam deposition under high vacuum or reactive glow discharge from gaseous monomers such as silane are the preferred methods of forming the Si O 2 laver There is no noticeable difference between Si O 2 layers formed using these two methods Resistance heating yields an averaged formula of 20 Si Ox, where x is some value between 1 and 2, which is somewhat less durable than Si O 2 but is also suitable.
Several organic materials also have been identified as suitable for use as barrier layers Derivatives of sucrose in which the hydroxyl groups are replaced by ester groups, such as acetyloxy or benzoyloxy groups, form good barrier layers In 25 an illustrative embodiment, a layer of sucrose benzoate, formed from sucrose in which six or more hydroxyl groups have been replaced by benzoyloxy groups, is evaporated onto the organic dye light absorbing layer of the recording medium prior to application of the overcoat layer Sucrose octaacetate also can be applied by evaporation to form a good barrier layer 30 Another class of materials which form suitable barrier layers are pentaerythritol derivatives of rosin acids These materials are low molecular weight ( 3,0 Q 0-7,000) thermoplastics which can be applied by evaporation Pentaerythritol esters of partially or fully hydrogenated rosin acids, where the principle rosin acid component is abietic acid and the softening point is about 1040 C, form good 35 barrier layers.
Highly crosslinked films prepared in situ by glow discharge or by polymerization of a reactive monomer deposited on the surface are also good barrier layer materials Suitable films include those prepared by exposing to glow discharge either a mixture of acetylene and nitrogen ( 1:3 ratio) or 40 perfluoromethylcyclohexane in an argon carrier gas Using the method described in U S Patent No 3,342,754, issued to Gorham and entitled “Para-xylylene Polymers”, highly crosslinked polymeric conformal coatings can also be prepared having repeating units of the general formula:
R 2 CHH<$ 45 where N indicates the number of repeating units in the polymer, and R and R' can be H or Cl. The initial antireflection, light absorbing condition of the light absorbing layer can be preserved if the thickness of the barrier layer is carefully controlled. Q Optimally, the thickness of an optically passive, non-reflecting barrier layer will be 50 equal to m A/2 n, where m is an integer, A is the wavelength of the recording or readout light from the laser, and N is the refractive index of the barrier layer material at the recording or readout wavelength Thus, when using silicon dioxide as the barrier layer, with a refractive index of about 1 46 at a recording wavelength of 4880 angstroms from an argon laser, the optimum thickness is about 1670 55 angstroms when m is 1 and 3340 angstroms when m is 2. The optimum thickness of the barrier layer is also determined by the thermal properties of the material used This thickness should be such that the heat generated during recording does not diffuse through the barrier layer to the 1,603,762 4 1,603,762 4 boundary of the overcoat layer during the time it takes to record an information pit The thermal diffusion length, 1, of a material is: where K is the thermal diffusivity of the material and t is the recording time For silicion dioxide, K is 6 x 10-3 centimeters squared per second Using a time of 30 5 nanoseconds, during which a given area of the medium is exposed to the recording laser beam, the thermal diffusion length is about 1400 angstroms Thus, the thickness of a silicon dioxide barrier layer should be greater than 1400 angstroms in order to form a thermal barrier Although a barrier layer thickness of 1670 angstroms for silicon dioxide will preserve the optical passivity of the barrier layer 10 and adequately prevent thermal damage to the overcoat layer, a thickness of 3340 angstroms would be preferred. The invention will be further explained by reference to the drawings, in which the three Figures show a recording medium prior to and after recording, and a system for its recording and playback 15 FIG 1 shows a recording medium 24 of the invention prior to exposure to a recording light beam comprising a substrate 110, a light reflecting layer 112 with a transparent layer 114 thereon, a light absorbing layer 116, a barrier layer 118 and an overcoat layer 120. FIG 2 shows a recording medium of the invention after exposure to a 20 recording light beam wherein the light absorbing layer 116 has been ablated to leave a pit 122, exposing the transparent passivating layer 114 to light while leaving the barrier layer 118 and the overcoat layer 120 intact It will be understood that the recording medium after recording contains a plurality of pits 122 rather than the single one shown in FIG 2 25 The use of the present recording medium can be explained in greater detail by referring to FIG 3 For recording, the light emitted by a laser 10 is fed to a modulator 12 which modulates the light in response to an input electrical signal source 14 The modulated light is enlarged by recording optics 16 to increase the diameter of the intensity modulated laser beam so that it will fill the desired 30 aperture of a cover glass corrected objective lens 18 The enlarged modulated laser beam is totally reflected by a polarizing beam splitter 20 and passes through a beam-rotating 1/4 wave plate 22 to the objective lens 18 The modulated recording beam then impinges upon a recording medium 24 as described in FIG I and ablates a portion of the light absorbing layer to expose a portion of the reflecting 35 layer The recording medium 24 is rotated by the turntable drive 26 at about 1800 rpm and may comprise disc having a spiral recording track A focus servo 28 maintains a constant distance between the cover glass corrected objective lens 18 and the surface of the recording medium 24. For readout, an unmodulated and less intense laser beam, which will not cause 40 ablation in the recording medium, follows the same path as the recording beam to the recording medium 24 The recorded reflection-antireflection pattern modulates the reflected light back through the objective lens 18 and the 1/4 wave plate 22 The light, now rotated by 900 in polarization by each of the two passes through the 1/4 wave plate 22 making 1800 rotation in all, passes through the polarizing beam 45 splitter 20 and is directed by playback optics 30 to a photodetector 32 The photodetector 32 converts the reflected light beam to an electrical output signal which is delivered to terminal 34 and which has amplitude variations corresponding to the input signal A tracking servo 36 monitors the light through the playback optics 30 to ensure that the beam does not wander from the track during playback 50 The present recording media can produce high quality recordings with signalto-noise ratios in the range of about 44 46 decibels (d B) for the 4phenylazo-lnaphthylamine dye light absorbing layer and about 49-52 d B for the titanium light absorbing layer. Light induced thermal recording on the organic dye layer through the barrier 55 and overcoat layers is possible without reducing the signal-to-noise ratio more than 6 d B When a titanium light absorbing layer is covered with a silicon dioxide barrier layer and a silicone resin overcoat layer, the signal-to-noise ratio increases 8-9 d B. The above signal-to-noise ratios are within the range of broadcast standards. Recording media with lower signal-to-noise ratios are useful for consumer video 60 disc or digitally encoded information records. The invention will be further illustrated by the following examples, but the invention is not meant to be limited by the details described therein. Example 1. About 100 discs 12 inches ( 30 5 centimeters) in diameter were coated with light reflecting layers of gold about 800 angstroms thick or aluminum about 300 angstroms thick The aluminum light reflecting layers were oxidized to a depth of about 30 angstroms in order to passivate the surface The light reflecting layers 5 were then coated with light absorbing layers of 4-phenylazo 1 naphthylamine about 400 angstroms thick on the gold layers and about 525 angstroms thick on the passivated aluminum layers The 4-phenylazo-I-naphthylamine was formed by the evaporation and thermal decomposition of Sudan Black B dyestuff. A representative sample of 20 of the resultant recording media was exposed to 10 nanosecond pulses of light having a wavelength of 4880 angstroms from an argon laser as in FIG 3 The best recordings were obtained at a power setting of about milliwatts from the laser and had signal-to-noise ratios in the range of about 46-52 d B. Ten of the sample recording media tested above, were then baked at 500 C 15 overnight and spin coated with overcoat layers about 0 1 millimeter thick of General Electric's RTV 615, a room temperature vulcanizable silicone resin This material is a highly crosslinked polymer formed by mixing a resin having the general formula: CH 3 CH 3 CH 3 I CH 2 = CH -Si -{ O -Si U 0-Si CH = CH 2 20 CH 3 CH 3 CH 3 wherein x is an integer, with a curing agent having the general formula: CH 3 CH 3 CH 3 CH 3-Si Si -O Si CH 3 CH 3 R CH 3 wherein y is an integer and R can be H or CH 3 with the proviso that at least one R is H, in the presence of a platinum catalyst The resin was cured by baking at 50 C. overnight 25 Recording on the resultant recording media was carried out as described above with a laser power setting of about 300 milliwatts The signal-tonoise ratios obtained were in the range of about 38-42 d B. The remaining ten sample recording media were coated with silicon dioxide barrier layers about 1670 angstroms thick using either electron-beam deposition 30 under high vacuum or reactive glow discharge from silane The silicon dioxide layers were then overcoated with a 0 1 millimeter layer of the RTV 615 silicone resin and cured at 50 C overnight. Recording was carried out on the resultant recording media as described above with a laser power setting of about 300 milliwatts The signal-tonoise ratios 35 obtained were in the range of about 44-47 d B. Example 2. About 50 discs 12 inches ( 30 5 centimeters) in diameter were coated with a light reflecting layer of aluminum about 500 angstroms thick The aluminum layers were coated with a layer of silicon dioxide about 800 angstroms thick The silicon 40 dioxide layers were then coated with a titanium layer about 75 angstroms thick. Recording on a representative sample of 12 of the resulting recording media was carried out as described in Example 1 The laser power setting for the best recording was about 350 milliwatts, at which the signal-to-noise ratios were in the range of about 40-44 d B At a power setting of about 300 milliwatts a signal-to 45 noise ratio of about 42 d B was obtained for a representative disc. Two of the sample recording media were overcoated with General Electric's RTV 615 as described in Example 1 Recording was carried out on the resultant recording media as in Example 1 The laser power setting for the best recording was about 250 milliwatts at which a signal-to-noise ratio of about 39 was obtained At a 50 power setting of about 300 milliwatts the signal-to-noise ratio for the representative disc was about 38 d B. 1,603,762 6 1,603,762 6 The remaining ten sample recording media were coated with a layer of silicon dioxide about 1670 angstroms thick as in Example 1 The samples were then overcoated with the RTV 615 as in Example 1. Recording was carried out on these recording media as described in Example 1 The laser power setting for the best recording was about 250 milliwatts, and the 5 signal-to-noise ratios obtained were in the range of about 49-52 d B At a power setting of about 300 milliwatts the signal-to-noise ratio for a representative sample disc was about 50 d B. Example 3. A disc about 12 inches ( 30 5 centimeters) in diameter was coated with a gold 10 layer about 800 angstroms thick The gold layer was coated with a layer of 4phenyl-azo-l-naphthylamine dye about 400 angstroms thick as described in Example 1. Recording on the resultant recording medium was carried out as described in Example 1 The laser power setting for the best recording was about 150 milliwatts 15 at which a signal-to-noise ratio of about 44 d B was obtained At a power setting of 250 milliwatts a signal-to-noise ratio of 43 d B was obtained. A layer of sucrose benzoate (about 1630 angstroms thick) with about 75 percent or more of the -OH groups replaced by 0 11-Pl 20 -0C-Ph groups was then evaporated onto the dye layer of the recording medium The sucrose benzoate layer was coated with a layer of General Electric's RTV 615 about 0 1 millimeters thick as described in Example 1. Recording was carried out on the resultant recording medium as in Example I The laser power setting for the best recording was 250 milliwatts from the laser, at 25 which a signal-to-noise ratio of about 41 d B was obtained. Attention is drawn to our copending Applications (Serial No 1603761) and 1603763) 16728178 and 16730178 which are directed to closely similar subject matter. Claims (1) WHAT WE CLAIM IS: 30 1 A recording medium for use with a recording laser beam providing light of a given frequency, said recording medium comprising a layer which reflects light of said given frequency with a layer which absorbs light of said given frequency thereon, an overcoat layer thereover; and a barrier layer substantially transparent to light of said given frequency 35 situated between the light absorbing layer and the overcoat layer; wherein said barrier layer is of a material and of a thickness such that it is thermally insulating and chemically unreactive with respect to the light absorbing layer and the overcoat layer. 2 A recording medium according to claim 1 in which by the barrier layer is of 40 silicon dioxide. 3 A recording medium according to claim 1 in which the barrier layer is a derivative of sucrose in which the hydroxyl groups of the sucrose are replaced by ester groups. 4 A recording medium according to claim 1 comprising a layer of dielectric 45 material substantially transparent to light of said given frequency and situated between said light reflecting layer and said light absorbing layer. A recording medium according to both claim 2 and claim 4 wherein the reflecting layer is aluminium, the dielectric layer is silicon dioxide, the absorbing layer is titanium and the overcoat layer is a silicon resin 50 6 A recording medium according to any preceding claim and having information already recorded by ablation thereon as a series of pits in said light absorbing layer. 7 A recording medium according to claim 6 wherein said overcoat and said barrier layers have been applied after information has been recorded in said 55 absorbing layer. 8 A recording medium according to any preceding claim wherein the thickness of the barrier layer is m X 2 N where m is an integer, A is the wavelength 7 1,603,762 7 corresponding to said given frequency, and N is the refractive index of the barrier layer material, at said given frequency. 9 A recording medium according to claim I and arranged substantially as any of the examples hereinbefore described. A recording medium substantially as hereinbefore described with reference to Figure 1 or Figure 2 5 JOHN A DOUGLAS, Chartered Patent Agent, Curzon Street, London WIY 8 EU. Agent for the Applicant. Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained. 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US4995028A (en) 1991-02-19 Coated media for optical recording, with soft/hard overcoat US4218689A (en) 1980-08-19 Ablatable medium for optical recording US4242689A (en) 1980-12-30 Ablative optical recording medium US4913949A (en) 1990-04-03 Planar, multilayered, laser-optical recording material GB1603761A (en) 1981-11-25 Protective overcoat layer for optical video disc US4478782A (en) 1984-10-23 Erasable recording medium comprising a dimer acid polyamide resin JPS60253036A (en) 1985-12-13 Light recording layer US4622261A (en) 1986-11-11 Laser recording material GB2066489A (en) 1981-07-08 Ablative optical recording medium US4093684A (en) 1978-06-06 Solid solderable polyurethane data signal recording medium US4522846A (en) 1985-06-11 Spiral-coated media for optical recording Legal Events Date Code Title Description 1982-02-17 PS Patent sealed [section 19, patents act 1949] 1998-05-20 PE20 Patent expired after termination of 20 years Effective date: 19980426
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