Optical disc

An optical disc wherein a transparent base plate is made from a special light-curable resin composition comprising at least one compound of the formula: ##STR1## wherein R.sub.1 =H or methyl and n=0-5, and a photopolymerization initiator, is excellent in heat resistance, mechanical strength, moisture resistance, etc.

BACKGROUND OF THE INVENTION 
This invention relates to an optically readable information disc (or simply 
optical disc) for storing, recording and reproducing voices, images, 
information, and the like, characterized in its base plate. 
A base plate for optical discs used in digital audio discs, video discs, 
optical disc recording media, magneto-optical disc recording media 
comprises a transparent plate of about 1 mm thick having an information 
pattern of groove-like and hole-like depressions and protuberances on a 
surface thereof. 
Such an optical disc base plate can be formed by the following three 
methods: 
(1) In a mold installed with a metal-made stamper having an information 
pattern such as grooves and pits (or holes), a melt of polymer material 
such as polycarbonate, polymethyl methacrylate, or the like, is injected, 
cooled and molded to give a transparent plate having an information 
pattern [Nikkei Mechanical, page 34, Feb. 1, 1982; Nikkei Electronics, 
page 133, June 7, 1982]. 
(2) A thin liquid layer of light-curable resin is interposed between a 
metal-made stamper having an information pattern and a transparent 
supporting plate made from plastics or glass, and exposed to light from 
the transparent supporting plate side to cure the resin, followed by 
separation of the cured resin from the stamper while maintaining the 
adhesion between the transparent supporting plate and the cured resin to 
give a transparent plate having an information pattern [Japanese Patent 
Unexamined Publication Nos. 53-86756 and 55-152028]. 
(3) After pouring a light-curable resin into a space formed by placing a 
stamper having an information pattern and a light-transmissible flat plate 
in parallel, light is irradiated from the light-transmissible flat plate 
side to cure the resin, followed by removal of the stamper and the 
light-transmissible flat plate to give a transparent plate having an 
information pattern [Japanese Patent Unexamined Publication No. 
55-160338]. 
But these methods have the following problems. 
The method (1) is good in workability, but it is difficult to completely 
remove molecular orientation at the time of flowing and solidification of 
the polymer material. Thus, optical anisotropy is generated in the base 
plate, resulting in causing noises at the time of reading or writing 
information signals. The optical anisotropy in the base plate becomes 
particularly remarkable when a heat distortion temperature of the base 
plate is raised in order to obtain a heat resistant base plate, which 
results in making optically practical use impossible. Further, the base 
plate obtained by the method (1) has a tendency to make it difficult to 
precisely transfer the shape of information pattern from the stamper to 
the base plate. 
The method (2) is good in transfer properties of the information pattern, 
but is complicated in working steps and has a tendency to make the 
production cost higher since the transparent supporting plate should be 
produced previously. Further since it is difficult to maintain sufficient 
adhesiveness between the transparent supporting plate and the 
light-curable resin, there is a tendency to make it difficult to maintain 
reliability for a long period of time under high temperatures and high 
humidity. 
The method (3) is good in workability, but is difficult to select 
light-curable resins and molding conditions. Thus, it is difficult to 
produce the base plate having excellent mechanical strength, heat 
resistance and moisture resistance and small optical anisotropy. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an optical disc overcoming the 
disadvantages of the prior art mentioned above, and having small optical 
anisotropy, a high heat distortion temperature, excellent stability under 
high temperatures and high humidity and low production cost. 
This invention provides an optical disc comprising a transparent base plate 
having a relief structure corresponding to information signals to be 
carried, and a recording film layer formed thereon, characterized in that 
the transparent base plate is made from a light-curable resin composition 
comprising 100 parts by weight of at least one acrylic group- or 
methacrylic group-containing compound including a compound of the formula: 
##STR2## 
wherein R.sub.1 is hydrogen or a methyl group; and n is zero or an integer 
of 1 to 5, in an amount of 30 to 100% by weight, and 
0.5 to 10 parts by weight of a photopolymerization initiator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The term "base plate" used in this invention means both a substrate 3 shown 
in FIG. 2(d), and a transparent support 2 and an undercoating layer 8 
shown in FIG. 1(d). Optical discs can be constructed in a conventional 
manner by using these base plates, that is, as one example, a transparent 
substrate 3 made from the special light-curable resin composition and 
having a relief structure corresponding to information signals to be 
carried and a metal-made recording film 5 formed on the relief structure 
as shown in FIG. 2(d), and as another example, a transparent support 2, a 
transparent undercoating layer 8 formed on the transparent support and 
made from the special light-curable resin composition and having a relief 
structure corresponding to information signals to be carried, and a 
metal-made recording film 5 formed on the relief structure as shown in 
FIG. 1(d). 
The special light-curable resin composition used for forming the 
transparent substrate or the transparent undercoating layer comprises: 
100 parts by weight of at least one acrylic group- or methacrylic 
group-containing compound including a compound of the formula: 
##STR3## 
wherein R.sub.1 is hydrogen or a methyl group; and n is zero or an integer 
of 1 to 5, in an amount of 30 to 100% by weight, and 
0.5 to 10 parts by weight of a photopolymerization initiator. 
The compound of the formula [I] is an important component of the 
light-curable resin composition and can satisfy a plurality of 
requirements such as to maintain the viscosity during working relatively 
low, to ensure the heat distortion temperature of a cured article, to 
improve moisture resistance, to reduce optical strain, and the like 
simultaneously. These requirements cannot be satisfied at the same time 
according to known materials. 
These excellent properties of the compound of the formula [I] seem to be 
derived from the special chemical structure thereof. That is, complicated 
cyclo rings constituting the skeleton of the compound of the formula [I] 
weaken the intermolecular attraction and help to reduce the viscosity of 
the liquid compound. Thus, the workability of the resin composition using 
the compound of the formula [I] is improved. Further, a cured article of 
the light-curable resin composition has a higher heat distortion 
temperature due to rigidity of the cyclo rings of the compound of the 
formula [I], a lower moisture absorption property due to small polar 
groups, and little optical strain due to small refractive index anisotropy 
at the time of molecular orientation. Further, since the compound of the 
formula [I] has two acrylic groups or methacrylic groups in one molecule, 
the resin composition including it has excellent curing properties, large 
crosslinking density, and is effective for maintaining the high heat 
distortion temperature. Further, in the compound of the formula [I], the 
larger the value of n becomes, the more difficult it is to absorb water, 
resulting in imparting the resulting optical disc with a more preferable 
resistance to circumstances (or humidity). But when n is larger than 5, 
the viscosity of the compound of the formula [I] increases so high that 
there is a tendency to lower the workability. Therefore, from the 
viewpoint of the resistance to circumstances, the preferable value of n is 
1 to 5. 
The compound of the formula [I] can be produced, for example, as follows: 
Polymerization of cyclopentadiene can be carried out by a process 
described, for example, in Von K. Alder, G. Stein: Justus Liebigs Aunalen 
der Chemic 485, 223-246 (1931) as follows: 
##STR4## 
Modification of polycyclopentadiene with a diol can be carried out by a 
process described, for example, in Von B. Connils, R. Payer: 
Chemiker-Zeitung 98, 70-76 (1974), Report of Prefectural Industrial 
Research Institute of Hokkaido 74-82 (1968) as follows: 
##STR5## 
Modification of the resulting diol with an acrylate or methacrylate can be 
carried out by a process described, for example, in "Polymer Data 
Handbook" pp. 105, 121, (1986), published by Baifu-kan as follows: 
##STR6## 
The compound of the formula [I] alone or as a mixture thereof can be used 
in an amount of 30 to 100% by weight as the acrylic group- or methacrylic 
group-containing compound. It is possible to use one or more other acrylic 
group- or methacrylic group-containing compounds, in order to adjust the 
viscosity and the degree of curing so long as the properties of the 
compound of the formula [I] are not damaged, in amounts up to 70% by 
weight. Further, by admixing one or more compounds having special acrylic 
or methacrylic groups as shown in the working examples mentioned below, 
the optical properties and mechanical properties of the compound of the 
formula [I] can be improved remarkably. Such compounds include (i) 
monofunctional monomers and (ii) polyfunctional monomers, these monomers 
being compatible with the compound of the formula [I] and able to bring 
about copolymerization by radical polymerization. 
Examples of the monofunctional and polyfunctional monomers are as follows: 
(i) Monofunctional Monomers: 
A compound of the formula: 
##STR7## 
wherein R.sub.1 is hydrogen or a methyl group; and R.sub.5 is a 
hydrocarbon group having 6 to 16 carbon atoms, e.g., 
##STR8## 
Among these groups, 
##STR9## 
are more preferable. 
Examples of the compound of the formula [II] are cyclohexyl acrylate, 
cyclohexy methacrylate, bornyl acrylate, bornyl methacrylate, isobornyl 
acrylate, isobornyl methacrylate, dicyclopentenyl acrylate, 
dicyclopentenyl methacrylate, tricyclodecanyl acrylate, tricyclodecanyl 
methacrylate, n-hexyl acrylate, n-hexyl methacrylate, 2-ethylhexyl 
acrylate, 2-ethylhexyl methacrylate, n-decyl acrylate, n-decyl 
methacrylate, lauryl acrylate, lauryl methacrylate, tridecyl acrylate, 
tridecyl methacrylate, etc. These compounds can be used alone or as a 
mixture thereof. 
(ii) Polyfunctional Monomers: 
Ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene 
glycol diacrylate, propylene glycol dimethacrylate, neopentyl glycol 
diacrylate, neopentyl glycol dimethacrylate, 1,6-hexanediol diacrylate, 
1,6-hexanediol dimethacrylate 1,10-decanediol diacrylate, 1,10-decanediol 
dimethacrylate; epoxy acrylates and methacrylates such as bisphenol A 
diglycidyl ether acrylate, bisphenol A diglycidyl ether methacrylate, 
hydrogenated bisphenol A diglycidyl ether acrylate, hydrogenated bisphenol 
A diglycidyl ether methacrylate, etc.; ether acrylates and methacrylates 
such as bisphenol A ethylene glycol adduct diacrylate, bisphenol A 
ethylene glycol adduct dimethacrylate, hydrogenated bisphenol A ethylene 
glycol adduct diacrylate, hydrogenated bisphenol A ethylene glycol adduct 
dimethacrylate, etc.; urethane acrylates and methacrylates of the formula: 
##STR10## 
wherein R.sub.1 is hydrogen or a methyl group; R.sub.2 is hydrogen, an 
alkyl group having 1 to 5 carbon atoms or 
##STR11## 
and R.sub.3 is a hydrocarbon group having 6 to 16 carbon atoms, such as a 
reaction product of 1 mole of isophorone diisocyanate and 2 moles of 
2-hydroxyethyl acrylate or 2-hydroxyethyl methacrylate, a reaction product 
of 1 mole of methylenebis(4-cyclohexyl isocyanate) and 2 moles of 
2-hydroxypropyl acrylate or 2-hydroxypropyl methacrylate, etc.; 
trimethylolethane triacrylate, trimethylolethane trimethacrylate, 
trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 
pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, 
dipentaerythritol hexaacrylate, dipentaerythritol hexamethacrylate; and a 
compound of the formula: 
##STR12## 
wherein R.sub.1 is hydrogen or a methyl group; R.sub.2 is an alkyl group 
having 1 to 5 carbon atoms or 
##STR13## 
R.sub.3 is a hydrocarbon group having 6 to 16 carbon atoms, 
##STR14## 
and R.sub.4 is a hydrocarbon group having 2 to 100 carbon atoms, 
preferably 6 to 16 carbon atoms, e.g. 
##STR15## 
These polyfunctional monomers can be used alone or as a mixture thereof. 
The compound of the formula [IV] can be synthesized, for example, by 
reacting 1 mole of a diol with 2 moles of a diisocyanate, followed by a 
reaction of residual isocyanate group with 2 moles of monohydroxylated 
acrylate or methacrylate. These compounds can be reacted as they are. If 
necessary, the reaction can be carried out in an organic solvent such as 
toluene, xylene, or the like which is inert to the isocyanate. It is 
possible to carry out the reaction by using a tin compound catalyst such 
as di-n-butyl tin dilaurate, or the like as a reaction accelerator. If 
necessary, the reaction can be carried out at 50.degree. to 70.degree. C. 
As the diol, there can be used ethylene glycol, propylene glycol, 
1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, 
1,12-dodecanediol, 1,14-tetradecanediol, 1,4-cyclohexyldimethanol, 
hydrogenated butanediol, etc. 
As the diisocyanate, there can be used 2,4-tolylene diisocyanate, 
4,4'-diphenylmethane diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 
1-methylcyclohexane-2,4-diisocyanate, methylenebis(4-cyclohexyl 
isocyanate), 2,2'-propylenebis(4-cyclohexyl isocyanate), isophorone 
diisocyanate 1,6-hexamethylene diisocyanate, 1,16-hexadecamethylene 
diisocyanate, etc. 
As the monohydroxylated acrylate or methacrylate, there can be used 
2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl 
acrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, 
2-hydroxybutyl methacrylate, 2-hydroxypentyl acrylate, 2-hydroxypentyl 
methacrylate, 2-hydroxy-3-phenoxypropyl acrylate, 
2-hydroxy-3-phenoxypropyl methacrylate, etc. 
Useful examples of the compounds of the formula [IV] are as follows: 
a reaction product obtained by reacting 1 mole of 1,6-hexanediol and 2 
moles of isophorone diisocyanate, followed by addition of 2 moles of 
2-hydroxyethyl acrylate or methacrylate, 
a reaction product obtained by reacting 1 mole of 1,10-decanediol and 2 
moles of isophorone diisocyanate, followed by addition of 2 moles of 
2-hydroxyethyl acrylate or methacrylate, 
a reaction product obtained by reacting 1 mole of 1,12-dodecanediol and 2 
moles of isophorone diisocyanate, followed by addition of 2 moles of 
2-hydroxybutyl acrylate or methacrylate, 
a reaction product obtained by reacting 1 mole of 1,14-tetradecanediol and 
2 moles of isophorone diisocyanate, followed by addition of 2 moles of 
2-hydroxyethyl acrylate or methacrylate, 
a reaction product obtained by reacting 1 mole of 1,4-cyclohexyldimethanol 
and 2 moles of isophorone diisocyanate followed by addition of 2 moles of 
2-hydroxyethyl acrylate or methacrylate, 
a reaction product obtained by reacting 1 mole of 1,6-hexanediol and 2 
moles of methylenebis(4-cyclohexyl isocyanate), followed by addition of 2 
moles of 2-hydroxypropyl acrylate or methacrylate, 
a reaction product obtained by reacting 1 mole of 1,4-cyclohexyldimethanol 
and 2 moles of 1-methylcyclohexane-2,4-diisocyanate, followed by addition 
of 2 moles of 2-hydroxybutyl acrylate or methacrylate, 
a reaction product obtained by reacting 1 mole of 1,10-decanediol and 2 
moles of 2,2'-propylenebis(4-cyclohexyl isocyanate), followed by addition 
of 2 moles of 2-hydroxy-3-phenoxypropyl acrylate or methacrylate, 
a reaction product obtained by reacting 1 mole of 1,10-decanediol and 2 
moles of isophorone diisocyanate, followed by addition of 2 moles of 
2-hydroxytubyl acrylate or methacrylate, etc. 
As the photopolymerization initiator, there can be used benzils such as 
benzil, etc.; benzoins such as benzoin, benzoin methyl ethyl, benzoin 
ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 
.alpha.-methylbenzoin, etc.; benzophenones such as benzophenone, 
4-methoxybenzophenone, 1-hydroxycyclohexyl benzophenone, etc.; 
acetophenones such as acetophenone, 2,2-diethoxyacetophenone, 
.alpha.,.alpha.,.alpha.-tribromoacetophenone, etc.; thioxanthones such as 
2-chlorothioxanthone, 2-methylthioxanthone, etc.; anthraquinones such as 
2-ethylanthraquinone, 2-methylanthraquinone, etc.; benzyl methyl ketal, 
1-hydroxycyclohexyl phenyl ketone, 
2-hydroxy-2-methyl-1-phenylpropane-1-one, 
1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, etc. These 
photopolymerization initiators can be used alone or as a mixture thereof. 
Among the light-curable resin compositions, preferable ones comprise a 
compound of the formula [I], a compound of the formula [II], a compound of 
the formula [IV], and a photopolymerization initiator, the amounts of the 
compounds [I], [II] and [IV] being in the range enclosed by the line 
A-B-C-D-E-A in the triangular diagram shown by FIG. 4 and the amount of 
the photopolymerization initiator being 0.5 to 10 parts by weight, 
preferably 0.5 to 5 parts by weight, more preferably 0.7 to 3 parts by 
weight based on 100 parts by weight of the total of the compounds [I], 
[II] and [IV], and individual points A, B, C, D and E in FIG. 4 having the 
following values in percents by weight. 
______________________________________ 
Compound Compound Compound 
[I] [IV] [II] 
Point wt % wt % wt % 
______________________________________ 
A 75 20 5 
B 25 70 5 
C 10 70 20 
D 10 40 50 
E 30 20 50 
______________________________________ 
As mentioned above, the compound of the formula [I] is used in an amount of 
10 to 75% by weight based on the total amounts of the resin components. 
When the amount is less than 10% by weight, the effects of the compound of 
the formula [I] become insufficient, whereas when the amount is more than 
75% by weight, the cured product has lower in mechanical strength and 
increased optical strain. 
The compound of the formula [IV] is effective for ensuring necessary 
mechanical strength of the cured product. The compound of the formula [IV] 
is used in an amount of 20 to 70% by weight based on the total amounts of 
the resin components. When the amount is less than 20% by weight, the 
effect mentioned above becomes insufficient, whereas when the amount is 
more than 70% by weight, the viscosity of the resin before curing becomes 
higher to make the workability worse and at the same time heat resistance 
of the cured article is lowered. 
The compound of the formula [II] is effective for lowering the viscosity so 
as to make the working easy and to lower optical strain and absorption 
properties of the cured article. The compound of the formula [II] is used 
in an amount of 5 to 50% by weight based on the total amounts of the resin 
components. When the amount is less than 5% by weight, the effects 
mentioned above become insufficient, whereas when the amount is more than 
50% by weight, there is a tendency to lower the mechanical strength of the 
cured article. 
The photopolymerization initiator is effective for producing radicals by 
irradiation of light in the light-curable resin composition and making the 
acryl group and the methacryl group in the light-curable resin composition 
bring about radical polymerization. When the amount of the 
photopolymerization initiator is less than 0.5 part by weight based on 100 
parts by weight of the total of the compounds [I], [II] and [IV], the 
curing by light becomes insufficient. On the other hand, when the amount 
is more than 10 parts by weight, there is a tendency to lower the 
mechanical strength of the cured article. 
The light-curable resin composition may further contain a silane coupling 
agent such as .gamma.-acryloxypropyltrimethoxysilane, 
.gamma.-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, 
vinyltriethoxysilane, etc., alone or as a mixture thereof, in an amount of 
preferably upto 6 parts by weight based on 100 parts by weight of the 
light-curable resin composition in order to further stabilize the adhesive 
properties of the light-curable resin composition at the time of absorbing 
moisture. 
Using the light-curable resin composition, plastic information-recording 
media such as optical discs can be produced according to conventional 
processes. 
For example, the light-curable resin composition 8' is inserted into a 
space formed between a stamper 1 of, e.g., nickel having grooves and pits 
thereon and a transparent support 2 made of, e.g., glass plate, plastic 
plate, etc., as shown in FIG. 1(a) and pressed at a pressure of 2 to 20 
g/cm.sup.2, preferably 5 to 15 g/cm.sup.2 and exposed to ultraviolet 
irradiation at 50 to 400 mW/cm.sup.2, preferably 100 to 250 mW/cm.sup.2, 
using a high-pressure mercury lamp 4, xenone lamp, or the like to cure the 
resin composition (FIG. 1(b)). 
After curing the resin composition for the undercoating layer 8, the 
stamper 1 is removed as shown in FIG. 1(c). Then, a recording film 5 made 
of a metallic material such as Al, Bi, In, Te, Te alloys, As, Pb, Sn, TbFe 
alloys, TbCo alloys, or the like with almost uniform thickness is formed 
on the surface of the undercoating layer 8 to give an optical disc base 
plate integrally formed of the recording film 5, the undercoating layer 8 
and the transparent support 1 as shown in FIG. 1(d). 
Finally, two optical disc base plates are placed in parallel so as to face 
the primer layer resin sides to each other and bonded via spacers with a 
predetermined space to give an air sandwich type optical disc. 
A base plate for optical discs comprising a transparent substrate 3 and a 
recording film 5 can be produced by a process shown by FIGS. 2(a) to 2(d), 
wherein numeral 1 denotes a stamper, numeral 2 a transparent support, 
numeral 4 a high-pressure mercury lamp, numeral 6 a space and numeral 7 an 
inlet for pouring a light-curable resin composition. 
Using these base plates as shown in FIG. 1(d) and FIG. 2(d), it is possible 
to produce optical disc by a so-called cast method by placing a pair of 
the base plates facing the recording film sides to each other and bonding 
them via an adhesive. 
The thus produced optical discs according to this invention are stable and 
hardly cause softening and expansion of the base plates even if allowed to 
stand under a wide range of temperatures from as low as -40.degree. C. or 
lower to as high as 120.degree. C. or higher, or under high temperatures 
and high humidity (60.degree. C. or higher and 95% RH or higher), so that 
no extreme stress is given to the attached film, resulting in causing no 
cracks on and no peeling of the attached film. 
This invention is illustrated by way of the following Examples, in which 
all percents and parts are by weight unless otherwise specified. 
EXAMPLES 1 TO 13, COMATIVE EXAMPLES 1 TO 5 
Light-curable resin compositions were prepared by uniformly mixing 
compounds of the formulae (A) and (B) belonging to the compound of the 
formula [I], generally used acrylates and methacrylates of the formulae 
(U) to (Z) with a photopolymerization initiator and a silane coupling 
agent as listed in Table 1. 
##STR16## 
The compounds of the formulae (A) and (B) were liquid with relatively high 
viscosities at room temperature. 
##STR17## 
The compounds of the formulae (U) to (Z) were liquid at room temperature. 
As the silane coupling agent, .gamma.-methacryloxypropyltrimethoxysilane 
was used. 
TABLE 1 
__________________________________________________________________________ 
(Parts) 
Comparative 
Example No. Example No. 
Composition 
1 2 3 4 5 6 7 8 9 10 
11 
12 
13 
1 2 3 4 5 
__________________________________________________________________________ 
Compound [I] 
A 98 
-- 
78 
48 
48 
30 
48 
48 
-- 
-- 
-- 
24 
24 
-- 
-- 
-- 
-- -- 
B -- 
98 
-- 
-- 
-- 
-- 
-- 
-- 
48 
48 
48 
24 
24 
-- 
-- 
-- 
-- -- 
Generally used 
U -- 
-- 
20 
-- 
-- 
-- 
25 
25 
20 
-- 
-- 
25 
25 
-- 
-- 
-- 
-- -- 
acrylates or 
V -- 
-- 
-- 
50 
-- 
-- 
25 
-- 
-- 
50 
-- 
25 
-- 
-- 
-- 
50 
50 -- 
methacrylates 
W -- 
-- 
-- 
-- 
50 
68 
-- 
25 
-- 
-- 
50 
-- 
25 
-- 
-- 
-- 
-- -- 
X -- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
98 
-- 
48 
-- -- 
Y -- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
98 
-- 
48 -- 
Z -- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 98 
Silane coupling 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
-- 
1 1 -- 
-- 
-- 
-- -- 
agent 
Photopolymeriza- 
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 
tion initiator 
__________________________________________________________________________ 
As the photopolymerization initiator, 
2-hydroxy-2-methyl-1-phenylpropane-1-one was used. 
A stamper 1 as shown in FIG. 1(a) made of nickel having an outer diameter 
of 300 mm with grooves (depth 0.09 .mu.m, width 0.40 .mu.m) and pits 
(depth 0.16 .mu.m, width 0.60 .mu.m) was prepared. 
A light-curable resin composition 8' was interposed between a transparent 
support 2 (thickness 1.2 mm) made of glass, having an outer diameter of 
300 mm and treated with a silane coupling agent 
(.gamma.-methacryloxypropyltrimethoxysilane) by baking at 110.degree. C. 
for 30 minutes and the stamper 1. The transparent support 2 was pressed to 
the stamper 1 so as to make the thickness of the light-curable resin 
composition layer about 80 .mu.m as shown in FIG. 1(b). Then, the 
light-curable resin composition 8' was cured by irradiating energy beams 
having a wavelength of 320 to 400 nm and light intensity of 150 
mw/cm.sup.3 from a high-pressure mercury lamp 4 for 30 seconds from the 
transparent support 2 side. 
Then, the stamper 1 was separated from the cured product of light-curable 
resin composition (an undercoating layer 8) as shown in FIG. 1(c) to give 
a transparent base plate having an information pattern thereon. 
Subsequently, Te-Sn-Pb alloy recording film 5 with 30 nm thick was formed 
on the information pattern surface by vacuum deposition as shown in FIG. 
1(d). Finally, optical discs were constructed according to a conventional 
method. 
The thus constructed optical discs were subjected to the following tests. 
(1) Heat Resistance 
An optical disc was allowed to stand at 100.degree. C. for 4 hours and 
evaluated as follows: 
o: Relief grooves on which a recording film had been vapor deposited were 
excellent in thermal stability without changing the depth and shape of 
grooves and without causing cracks on or peeling of the recording film. 
x: The above-mentioned changes were brought about and an optical disc was 
unbearable for practical use. 
(2) Moisture Resistance 
An optical disc was allowed to stand at 60.degree. C. and 95% RH for 100 
hours and evaluated as follows: 
o: No change was caused in the relief of grooves on which a recording film 
had been vapor deposited, no cracks were generated in the recording film, 
no peeling of an undercoating layer took place, no oxidation of the 
recording film or no change in light transmittance were brought about by 
corrosive substances released from a cured resin by the moisture 
absorption of the light-curable resin, and the optical disc was bearable 
for practical use. 
x: The above-mentioned changes were brought about and an optical disc was 
unbearable for practical use. 
TABLE 2 
__________________________________________________________________________ 
Comparative 
Example No. Example No. 
Properties 
1 2 3 4 5 6 7 8 9 10 
11 
12 
13 
1 2 3 4 5 
__________________________________________________________________________ 
Heat resistance 
o o o o o o o o o o o o o x x x x x 
Moisture 
o o o o o o o o o o o o o x x x x x 
resistance 
__________________________________________________________________________ 
As is clear from Table 2, the optical discs of Examples 1 to 13 are 
excellent in the heat resistance and the moisture resistance and bearable 
for practical use. On the other hand, the optical discs of Comparative 
Examples 1 to 5 wherein generally used acrylates or methacrylates are used 
cause the deformation of information patterns, cracks on the recording 
films and peeling of the recording films and are unbearable for practical 
use. 
Further, the optical discs of Examples 1 to 13 were operated normally, when 
writing and reading properties by using a semiconductor laser light of 830 
nm were evaluated. 
EXAMPLE 14 
A stamper 1 as shown in FIG. 2(a) made of nickel having an effective 
diameter of 120 mm with grooves (depth 0.09 .mu.m, width 0.40 .mu.m) and 
pits (depth 0.16 .mu.m, width 0.60 .mu.m) was prepared. 
A transparent support 2 (thickness 10 mm) of glass circular plate having an 
outer diameter of 200 mm and baked with a dimethylsilicone mold release 
agent was placed opposite to the stamper to form a space 6 with 1.3 mm. 
From an inlet 7, the same light-curable resin compositions 8' used in 
Examples 1 to 13 and Comparative Examples 1 to 5 were poured under vacuum 
as shown in FIG. 2(b), respectively. 
Then, the light-curable resin composition was cured by irradiating energy 
beams having a wavelength of 320 to 400 nm and light intensity of 30 
mw/cm.sup.3 from a high-pressure mercury lamp 4 for 90 seconds from the 
transparent support 2 side. The cured article 3 (substrate) obtained from 
the light-curable resin composition was separated from the stamper 1 and 
the transparent support 2 as shown in FIG. 2(c) to give the transparent 
substrate 3 having a thickness of about 1.2 mm together with grooves and 
pits. 
Optical anisotropy of the transparent substrate was measured by using a 
light with a wavelength of 830 nm and evaluated as retardation 
[R=d(n.sub.1 -n.sub.2), wherein d is the thickness of the transparent 
support; and n.sub.1 and n.sub.2 are refractive indexes at main stress 
directions 1 and 2]. The retardation of 10 nm or less was evaluated as 
good. 
The results are shown in Table 3. 
TABLE 3 
______________________________________ 
Resin Composition 
Retardation (nm) 
______________________________________ 
Example 
1 10 
2 10 
3 5 
4 10 
5 10 
6 10 
7 5 
8 5 
9 5 
10 10 
11 10 
12 5 
13 5 
Compartive 
Example 
1 10 
2 20 
3 20 
4 20 
5 20 
______________________________________ 
As is clear from Table 3, the retardation of the substrates obtained from 
the resin compositions of Examples 1 to 13 was satisfactory but almost 
substrates obtained from Comparative Examples 1 to 5 were unsatisfactory. 
On the other hand, each multi-layer recording film 5 [SiO+Te-Fe alloy+SiO 
layers with thicknesses of 1000 .ANG.+500 .ANG.+1000 .ANG.] was vapor 
deposited on each transparent substrate having grooves and pits thereon, 
followed by the construction to give an optical disc. 
The heat resistance and moisture resistance of the resulting optical discs 
were evaluated in the same manner as described in Examples 1 to 13. Those 
obtained from the resin compositions of Examples 1 to 13 were excellent 
both in the heat resistance and moisture resistance as in Examples 1 to 
13, but those obtained from the resin compositions of Comparative Examples 
1 to 5 were poor in heat resistance and moisture resistance as in 
Comparative Examples 1 to 5. 
Further, the optical discs obtained by using the resin compositions of 
Examples 1 to 13 were operated normally, when writing, reading and erasing 
properties by using a semiconductor laser light of 830 nm were evaluated. 
EXAMPLE 15 
Resin plates of 1 mm thick, 5 mm wide and 50 mm long were produced by using 
the resin compositions of Examples 1 and 5, and Comparative Examples 1, 2 
and 5 and curing by using a high-pressure mercury lamp (light intensity of 
150 mw/cm.sup.3 at a wavelength of 320-400 nm). 
One end of each resin plate at the lengthwise direction was fixed and 
maintained horizontally, while the other end was loaded with a load of 10 
g. Such a sample was placed in a constant temperature bath and the 
temperature was raised with an interval of 10.degree. C. while maintaining 
at each temperature for 1 hour. 
Change of deformation rate of each sample at each temperature was measured 
and shown in FIG. 3, wherein the curve (i) is the plates obtained from the 
resin compositions of Examples 1 and 5, the curve (ii) is the plate 
obtained from the resin composition of Comparative Example 5, the curve 
(iii) is the plate obtained from the resin composition of Comparative 
Example 2, and the curve (iv) is the plate obtained from the resin 
composition of Comparative Example 1. 
##EQU1## 
Further, the optical discs obtained in Example 14 by using the resin 
compositions of Examples 1 and 5, and Comparative Examples 1, 2 and 5 were 
also placed in the constant temperature bath and subjected to the 
temperature rise with an internal of 10.degree. C. to measure the 
temperature of generating cracks on recording films. The optical discs 
obtained by using the resin compositions of Examples 1 and 5 produced no 
cracks even at 120.degree. C. On the other hand, cracks were generated at 
30.degree. C. in the case of the optical disc obtained by using the resin 
composition of Comparative Example 1, at 40.degree. C. in the case of that 
obtained by using the resin composition of Comparative Example 2, and at 
70.degree. C. in the case of that obtained by using the resin composition 
of Comparative Example 5. 
EXAMPLES 16 TO 39 
Light-curable resin compositions were prepared by using the compounds [I], 
[II], and [IV] and the photopolymerization initiator as listed in Table 4. 
Using these resin compositions, transparent substrates were produced in the 
same manner as described in Example 14 except for using a nickel-made 
stamper having an outer diameter of 300 mm, and a transparent support 
having an outer diameter of 300 mm and changing the intensity of energy 
beams from 30 mw/cm.sup.2 to 150 mw/cm.sup.2 and the irradiation time from 
90 seconds to 40 seconds. 
The thus produced transparent substrates with grooves and pits were 
subjected to the following tests. 
(1) Workability 
When the viscosity of a liquid light-curable resin composition was too high 
at the time of pouring the resin composition into the space 6 formed by 
the stamper 1 and the transparent glass support 2, it was difficult to 
pour the resin composition into the space and the workability was lowered 
remarkably. Since working became remarkably difficult when the viscosity 
at 25.degree. C. was higher than 200 poises, such a viscosity was regarded 
as standard for judging the workability. 
(2) Curing Properties 
Curing state of a transparent substrate formed was judged from a surface 
appearance. 
(3) Retardation 
Retardation of a single pass at a wavelength of 830 nm [R=d(n.sub.1 
-n.sub.2), wherein d is the thickness of a transparent support; and 
n.sub.1 and n.sub.2 are refractive indexes at main stress directions 1 and 
2]. 
(4) Heat Resistance 
A flat plate of 45 mm long and 5 mm wide was cut from a transparent 
support. One end of the flat plate at the lengthwise direction was fixed 
and the other end was loaded with a load of 10 g, while the temperature 
was raised at a rate of 10.degree. C./min to measure the temperature 
beginning deformation. 
(5) Tensile Strength 
A dumbbell specimen was cut from a transparent substrate obtained and 
measured according to JIS-K6745. 
The test results are shown in Table 4. 
Desirable transparent substrates with grooves and pits are good in curing 
properties, have the retardation of 10 nm or less, the heat resistance of 
70.degree. C. or higher, and the tensile strength of 500 kg/cm.sup.2 or 
more. Further, in the case of using for erasable magneto-optical discs, it 
is necessary to make the retardation particularly 5 nm or less, since the 
information signals are readily influenced by optical strain of the base 
plate (or substrate). If the above-mentioned requirements are not 
satisfied, various disadvantages occur such as an increase of signal 
noises for optical disc recording mediums, warpage under a high 
temperature atmosphere, and destruction during the operation. 
In Table 4, Examples 20 to 24, 26 and 27 are Comparative Examples wherein 
the compound of the formula [I] is not used or used in too small an 
amount. In Examples 16 to 19 and 25, the compound of the formula [I] is 
used, but the compounds of the formula [II] and/or [IV] are not used, as 
that the test results are not so satisfactory as those of Examples 28 to 
39. 
3 TABLE 4 
Example 16 17 18 19 20 21 22 23 24 25 26 27 28 
Compound[I] 
##STR18## 
100 80 60 30 0 0 0 0 0 50 10 10 75 
Compound[IV] 
##STR19## 
0 20 40 70 100 70 40 20 0 0 85 20 20 
Compound[II] 
##STR20## 
0 0 0 0 0 30 60 80 100 50 5 70 5 Photo-polymeri-zationinitiator 
##STR21## 
2 2 2 2 2 2 2 2 2 2 2 2 2 Properties Workability G G P P P G G G G G P 
G G Curing properties G G G G G G I I I G G I G Retardation (nm) (830 
nm, 1 mm thick) 10 7 6 5 3 2 -- -- -- 2 3 -- 3 Heat resistance (.degree. 
C.) 120 120 100 60 50 45 -- -- -- 100 70 -- 115 Tensile strength 
(kg/cm.sup.2) 200 250 300 550 800 600 -- -- -- 100 700 -- 520 
Example 29 30 31 32 33 34 35 36 37 38 39 
Compound[I] 
##STR22## 
55 25 10 10 30 60 40 30 30 30 20 
Compound[IV] 
##STR23## 
40 70 70 40 20 20 40 60 50 30 40 
Compound[II] 
##STR24## 
5 5 20 50 50 20 20 10 20 40 40 
Photo-polymeri-zationinitiator 
##STR25## 
2 2 2 2 2 2 2 2 2 2 2 Properties Workability G G G G G G G G G G G 
Curing properties G G G G G G G G G G G Retardation (nm) (830 nm, 1 mm 
thick) 3 3 2 1 1 2 2 2 2 1 1 Heat resistance (.degree.C.) 110 75 75 80 
90 115 110 90 100 80 90 Tensile strength (kg/cm.sup.2) 600 550 600 550 
560 510 700 750 600 550 600 
Note 
G: Good 
P: Poor 
I: Insufficient 
EXAMPLES 40 TO 45, COMATIVE EXAMPLES 6 AND 7 
Light-curable resin compositions were prepared by mixing the compounds in 
amounts as listed in Table 5. Using these resin compositions, transparent 
substrates with grooves and pits were produced and evaluated in the same 
manner as described in Examples 16 to 39. 
The result are shown in Table 5. 
As is clear from Table 5, the transparent substrates of Comparative 
Examples 6 and 7 are poor in retardation, heat resistance and tensile 
strength, while those of Examples 40 to 45 are satisfactory in all 
properties. 
Further, the substrates of Examples 28 to 45 had the light transmittance of 
95% or more when measured by using a light of 830 nm. 
3 TABLE 5 
Comparative Example Example 6 7 40 41 42 43 44 45 
Generallyusedacrylateandmethacrylate 
##STR26## 
100 
##STR27## 
100 
Compound[I] 
##STR28## 
40 40 40 40 40 
##STR29## 
35 
Compound[IV] 
##STR30## 
40 40 
##STR31## 
40 
##STR32## 
35 
##STR33## 
40 40 
Compound[II] 
##STR34## 
20 
##STR35## 
20 20 25 25 Photopoly- 1-Hydroxycyclohexyl phenyl ketone 2 2 
2 2 2 2 2 2 merization initiator Properties Workability G G G G G G 
G G Curing properties G G G G G G G G Retardation (nm) (830 nm, 1 mm 
thick) 20 70 2 2 2 2 2 2 Heat resistance (.degree.C.) 50 80 
125 125 122 120 120 124 Tensile strength (kg/cm.sup.2) 470 220 600 630 
650 700 700 600 
(Note) 
G: Good 
EXAMPLE 46 
On each transparent substrate having grooves and pits thereon obtained in 
Examples 28 to 39 an enhance film made of SiO with 100 nm thick, a Te-Fe 
alloy magnetic film with 100 nm thick, and a SiO protective film were 
vapor deposited in this order. Further, a polycarbonate plate of 1 mm 
thick was bonded to the SiO protective film by using an epoxy resin 
adhesive to form a magneto-optical disc recording medium. Writing and 
erasing of information were conducted from the transparent substrate side 
by using a semiconductor laser light of 830 nm and a magnet. The state of 
the writing and erasing were measured by using a semiconductor laser light 
to determine that these magneto-optical disc operated normally. 
According to this invention, there can be produced optical discs with high 
productivity and low production cost due to the use of the base plates for 
optical discs having little optical strain, high heat resistance, 
excellent mechanical strength and precision and high transparency.