Process for preparing a substrate for optical recording media

A process for preparing a substrate for optical recording media which comprises injection-molding a polyvinylacetal resin resulting from acetalization of polyvinylalcohol to a degree of at least 60 mole % with at least one acetalizing agent selected from the group consisting of aliphatic aldehydes, alicyclic aldehydes, aromatic aldehydes and heterocyclic aldehydes.

The following examples illustrate the present invention more specifically. 
EXAMPLE 1 
(A) Preparation of polyvinylacetal 
One hundred grams of polyvinylalcohol having a degree of saponification of 
99.2 mole % and a degree of polymerization of 2,200 was dissolved in 880 g 
of distilled water, and 57 g of concentrated hydrochloric acid was added. 
While the mixture was maintained at 14.4.degree. C., 57.3 g of 
isobutylaldehyde was added dropwise over 15 minutes. Ten minutes after the 
addition, polyvinylbutyral precipitated. This reaction system was heated 
and maintained at 40.degree. C. for 10 hours. The temperature was then 
lowered, and it was neutralized with sodium bicarbonate. The resulting 
polyvinylbutyral was washed with water, and dried at 70.degree. C. for 48 
hours. The degree of acetalization of this resin was measured. 
(B) Molding of the polyvinylacetal resin and evaluation of its properties 
The resin obtained as described in section (A) was injection-molded at a 
cylinder temperature of 195.degree. C. and a molding temperature of 
60.degree. C. The warpage after water absorption, percentage water 
absorption, total light transmittance, haze value and birefringence of the 
resulting injection-molded plate (1.2 mm.times.120 mm.times.120 mm) were 
measured by the methods shown below. 
The results obtained in Examples 1 to 8 and Comparative Example 1 are 
summarized in Table 1. 
(1) Warpage after water absorption 
Aluminum was vapor deposited on one surface of the molded plate, and a 
protective coating was further applied to shut off intrusion of water from 
the vapor-deposited layer. This sample was immersed in water at 20.degree. 
C., and its warpage at the central portion was measured 72 hours later. 
(2) Water absorption 
The molded plate not subjected to the vapor deposition treatment was 
immersed in water at 20.degree. C., and the weight of the sample after 72 
hours was measured. The percentage of an increase in weight was 
calculated. 
(3) Total light transmittance 
Measured in accordance with the method of ASTM D-1003. 
(4) Haze value 
Measured in accordance with the method of ASTM D-1003. 
(5) Presence or absence of birefringence 
The molded plate not subjected to the vapor deposition treatment was 
interposed between two polarizing plates. Visible light was transmitted 
through it, and the presence or absence of birefringence was examined by 
observing the interference fringe. 
(6) Degree of acetalization 
Measured in accordance with JIS K-6728, 5.5.2. The same method was used in 
Examples 2, 6, 8, 16 and 17 in which the acetalization was effected by 
using a single aldehyde. 
When two or more aldehydes were used as in Examples 3 to 5, 7, 9 to 14, 16 
and 18, the aldehydes were treated with hydroxylamine hydrochloride to 
convert them to the corresponding oximes which were quantitatively 
determined by gas chromatography in accordance with JIS K-6728, 5.5.2. The 
operating conditions for gas chromatography were as follows: 
Gas chromatoigraphic device: GC6AM made by Shimazdu Seisaku Sho, K.K. (FID 
method) 
Column: PEG 6000 
Column temperature: 100.degree.-180.degree. C., fixed temperature method 
(temperatures at which two oximes can be separated differ) 
Carrier gas: nitrogen 
Flame gas: hydrogen/air 
EXAMPLE 2 
Example 1 was repeated except that 69.5 g of isobutylaldehyde was used, and 
the degree of saponification of the polyvinylalcohol was 99.4%. 
EXAMPLE 3 
Example 1 was repeated except that the degree of saponification of the 
polyvinylalcohol was 99.6%, and instead of isobutylaldehyde, 53.1 g of 
n-butylaldehyde and 6.8 g of formaldehyde were used. 
EXAMPLE 4 
Example 1 was repeated except that the degree of saponification of the 
polyvinylalcohol was 98.8%, and instead of isobutylaldehyde, 33.5 g of 
n-butylaldehyde and 29.9 g of acetaldehyde were used. 
EXAMPLE 5 
Example 1 was repeated except that the degree of saponification of the 
polyvinylalcohol was 98.8%, and instead of isobutylaldehyde, 34.9 g of 
acetaldehyde and 35.7 g of 2-ethylhexylaldehyde were used. 
COMATIVE EXAMPLE 1 
Poly(methyl methacrylate) resin (APET F1000, a product of Kyowa Gas 
Chemical Co., Ltd.) generally used for an optical disc was molded and 
evaluated in the same way as in Example 1. 
TABLE 1 
__________________________________________________________________________ 
Polyvinylalcohol Degree 
Amount of of Properties of the molded article 
residual acetali- Water Total light 
acetyl groups zation 
Warpage 
absorption 
transmittance 
Example 
D. P. 
(mole %) 
Aldehyde (mole %) 
(mm) (%) (%) Haze value 
Birefringence 
__________________________________________________________________________ 
1 2200 
0.8 Isobutylaldehyde 
69.5 0.6 0.8 92.3 0.6 None 
2 2200 
0.6 Isobutylaldehyde 
78.4 0.3 0.5 92.8 0.6 None 
3 2200 
0.4 n-Butylaldehyde 
62.0 0.4 0.7 91.7 0.8 None 
Formaldehyde 
12.0 
4 2200 
1.2 n-Butylaldehyde 
40.0 0.5 0.6 92.4 0.6 None 
Acetaldehyde 
42.0 
5 2200 
1.2 Acetaldehyde 
60.0 0.6 0.5 92.4 0.6 None 
2-Ethylhexylaldehyde 
21.0 
6 500 
0.95 Isobutylaldehyde 
69.1 0.7 0.8 92.1 0.4 None 
7 500 
0.95 Isobutylaldehyde 
30.2 0.5 0.6 92.2 0.7 None 
2-Ethylhexylaldehyde 
31.0 
8 500 
0.95 Trimethylaldehyde 
60.5 0.4 0.5 92.4 0.8 None 
Comp. 
-- -- -- -- 2.1 1.2 91.9 0.8 None 
Ex. 1 
__________________________________________________________________________ 
EXAMPLE 6 
Example 1 was repeated except that polyvinylalcohol having a degree of 
polymerization of 500 and containing 0.95% of residual acetyl groups was 
used instead of the polyvinylalcohol used in Example 1. 
EXAMPLE 7 
Example 1 was repeated except that the polyvinylalcohol used in Example 6 
was used, and 28 g of isobutylaldehyde and 35.8 g of 2-ethylhexylaldehyde 
were used instead of 57.3 g of isobutylaldehyde. 
EXAMPLE 8 
Example 1 was repeated except that the polyvinylalcohol used in Example 6 
was used, and instead of isobutylaldehyde, 61.5 g of trimethylacetaldehyde 
was used. 
EXAMPLE 9 
(A) Preparation of polyvinylacetal 
One hundred grams of polyvinylalcohol having adegree of saponification of 
99.2 mole % and a degree of polymerization of 1,500 was dissolved in 880 g 
of distilled water. Concentrated hydrochloric acid (57 g) was added, and 
while the mixture was maintained at 14.4.degree. C., 28,8 g of 
isobutylaldehyde was added dropwise over 15 minutes. Ten minutes after the 
addition, a precipitate of polyvinylbutyral formed. Cyclohexanealdehyde 
(63.5 g) was further added, and the reaction mixture was heated and 
maintained at 40.degree. C. for 10 hours. The temperature was then 
lowered, and the reaction mixture was neutralized with sodium bicarbonate. 
The resulting polyvinylacetal was washed with water, and dried at 
70.degree. C. for 48 hours. 
(B) MoIding of polyvinylacetal and evaluation of its properties 
The resin obtained in (A) was injection-molded at a cylinder temperature of 
255.degree. C. and a die temperature of 75.degree. C. The warpage after 
water absorption, percent water absorption, total light transmittance, 
haze value, birefringence and heat distortion temperature of the resulting 
injection molded plate (1.2 mm.times.120 mm.times.120 mm in size) were 
measured. 
The results obtained in Examples 9 to 14 and Comparative Examples 2 and 3 
are summarized in Table 2. The heat distortion temperature was measured by 
the method of ASTM D-648 (18.6 kg/cm.sup.2), and the other properties were 
measured in the same way as in Example 1. 
EXAMPLE 10 
(A) Preparation of polyvinylacetal 
One hundred grams of polyvinylalcohol having a degree of saponification of 
99.2 mole % and a degree of polymerization of 1,500 was dispersed in a 
mixture of 100 g of distilled water and 700 g of isopropanol. Concentrated 
hydrochloric acid (57 g) was added. With stirring at 65.degree. C., 28.8 g 
of isobutylaldehyde and 95.8 g of 2,2,6-trimethylcyclohexanealdehyde were 
added. The mixture was maintained at 65.degree. C. for 15 hours. The 
reaction mixture was neutrallized, and then a large amount of water was 
added to precipitate the resin. The resulting polyvinylacetal resin was 
washed with water, and dried at 70.degree. C. for 48 hours. 
(B) Molding of the polyvinylacetal resin, and the evaluation of its 
properties were carried out in the same way as in Example 9. 
EXAMPLE 11 
(A) Preparation of polyvinylacetal 
Example 1 was repeated except that 86.2 g of phellandral was added instead 
of the cyclohexanealdehyde. 
(B) Molding of the polyvinylacetal resin and the evaluation of its 
properties were carried out in the same way as in Example 9. 
EXAMPLE 12 
(A) Preparation of polyvinylacetal 
Example 9 was repeated except that the amount of isobutylaldehyde was 
changed to 61.3 g, and the amount of cyclohexanealdehyde was changed to 
12.7 g. 
(B) Molding of the polyvinylacetal resin and the evaluation of its 
properties were carried out in the same way as in Example 9. 
EXAMPLE 13 
(A) Preparation of polyvinylacetal 
Example 1 was repeated except that 54.4 g of benzaldehyde was used instead 
of cyclohexanealdehyde. 
(B) Molding of the polyvinylacetal and the evaluation of its properties 
were carried out in the same way as in Example 9. 
EXAMPLE 14 
(A) Preparation of polyvinylacetal 
Example 9 was repeated except that the amount of isobutylaldehyde was 
changed to 61.3 g, and 21.8 g of furfural was used instead of the 
cyclohexanealdehyde. (B) Molding of the polyvinylacetal and the evaluation 
of its properties were carried out in the same way as in Example 9. 
EXAMPLE 15 
(A) Preparation of polyvinylacetal 
Example 9 was repeated except that the amount of isobutylaldehyde was 
changed to 57.3 g, and the cyclohexanealdehyde was not used. 
(B) Molding of the polyvinylacetal and the evaluation of its properties 
were carried out in the same way as in Example 9. 
COMATIVE EXAMPLE 2 
Poly(methyl methacrylate) resin (APET F1000, a product of Kyowa Gas 
Chemical Co., Ltd.) generally used for an optical disc was molded and 
evaluated in the same way as in Example 9. 
TABLE 2 
__________________________________________________________________________ 
Properties of the molded article 
Degree of Water Total light 
acetalization absorption 
transmittance 
Haze Bire- 
Heat distortion 
Example 
Aldehyde (mole %) 
Warpage (mm) 
(%) (%) value 
fringence 
temperature 
(.degree.C.) 
__________________________________________________________________________ 
9 Isobutylaldehyde 
35 0.4 0.6 92.3 0.9 None 83 
Cyclohexanealdehyde 
50 
10 Isobutylaldehyde 
35 0.2 0.3 92.4 1.0 None 91 
2,2,6-Trimethyl 
50 
cyclohexanealdehyde 
11 Isobutylaldehyde 
35 0.2 0.3 92.6 0.8 None 84 
Phellandral 
50 
12 Iaobutylaldehyde 
75 0.6 0.5 92.8 0.9 None 74 
Cyclohexanealdehyde 
10 
13 Isobutylaldehyde 
35 0.5 0.5 91.8 1.1 None 78 
Benzaldehyde 
50 
14 Isobutylaldehyde 
75 0.6 0.6 92.4 0.8 None 73 
Furfural 10 
Comp. 
Isobutylaldehyde 
70 0.6 0.8 92.3 0.6 None 61 
Ex.15 
Ex.15 
-- -- 2.1 1.2 91.9 0.8 None 82 
__________________________________________________________________________ 
EXAMPLE 16 
(A) Preparation of polyvinylacetal 
Example 9 was repeated except that polyvinylalcohol having a degree of 
polymerization of 500 and a degree of saponification of 99.2 mole % was 
used. 
(B) Molding of the polyvinylacetal and the evaluation of its properties 
were carried out in the same way as in Example 9. 
The results obtained in Examples 16 to 19 are summarized in Table 3. 
EXAMPLE 17 
(A) Preparation of polyvinylacetal 
Example 9 was repeated except that the same polyvinylalcohol as used in 
Example 16 was used, and 90 g of cyclohexanealdehyde was used instead of 
the isobutylaldehyde. 
(B) Molding of the polyvinylacetal and the evaluation of its properties 
were carried out in the same way as in Example 9. 
EXAMPLE 18 
(A) Preparation of polyvinylacetal 
Example 9 was repeated except that polyvinylalcohol having a degree of 
polymerization of 800 and a degree of saponification of 99.5 mole % was 
used, and 101 g of 3-methylcyclohexanealdehyde was used instead of 
isobutylaldehyde. 
(B) Molding of the polyvinylacetal and the evaluation of its properties 
were carried out in the same way as in Example 9. 
EXAMPLE 19 
(A) Preparation of polyvinylacetal 
Example 9 was repeated except that 45 g of cyclohexanealdehyde and 51 g of 
3-methylcyclohexanealdehyde were used instead of isobutylaldehyde. 
(B) Molding of the polyvinylacetal and the evaluation of its properties 
were carried out in the same way as in Example 9. 
TABLE 3 
__________________________________________________________________________ 
Polyvinylalcohol Properties of the molded article 
Amount of Degree Total Heat 
residual of Water 
light distor- 
acetyl acetali- absorp- 
trans- tion tem- 
Ex- groups zation 
Warpage 
tion 
mittance 
Haze 
Bire- 
perature 
ample 
D. P. 
(mole %) 
Aldehyde (mole %) 
(mm) (%) (%) value 
fringence 
(.degree.C.) 
__________________________________________________________________________ 
16 500 99.2 Isobutylaldehyde 
34 0.7 0.6 91.1 0.6 None 81 
Cyclohexanealdehyde 
49 
17 500 99.2 Cyclohexanealdehyde 
61 0.5 0.9 90.2 0.9 None 86 
18 800 99.5 3-Methylcyclohexane- 
61.5 0.5 0.8 91.2 1.0 None 82 
aldehyde 
19 800 99.5 3-Methylcyclohexane- 
30.5 0.5 0.8 91.4 1.1 None 84 
aldehyde 
Cyclohexanealdehyde 
31 
__________________________________________________________________________ 
EXAMPLE 20 
(A) Synthesis of polyvinyl acetal 
One hundred kilograms of polyvinyl alcohol having a degree of 
saponification of 99.2% and a degree of polymerization of 1500 was 
dissolved in 880 kg of distilled water. 5.7 kg of concentrated 
hydrochloric acid was added to this solution and then 44.8 kg of 
cyclohexanealdehyde was added dropwise over 15 minutes with maintaining 
the temperature of the solution at 14.4.degree. C. In 10 minutes after the 
addition, polyvinyl butyral precipitated. 63.5 kg of cyclohexanealdehyde 
was further added, and this reaction system was heated and maintained at 
40.degree. C. for 10 hours. The temperature was then lowered and the 
reaction system was neutralized by sodium bicarbonate. The resulting 
polyvinyl acetal resin was washed with water and dried at 70.degree. C. 
for 48 hours. 
(B) Molding of polyvinyl acetal resin and evaluation of its properties 
The resin obtained above was molded into optical discs substrate by a 
toggle type injection molding machine Model S165/75 made by Sumitomo Heavy 
Ind., Ltd. Actually, this molding machine was equipped with a stamper in 
which a certain music sound signals were stored and compact disks for 
music reproduction were molded. 
The molding conditions are as follows. 
Injection temperature: 260.degree. C. to 320.degree. C. 
Charge time: 0.3 to 05 second 
Mold temperature: 70.degree. C. to 80.degree. C. 
Dwell pressure: 3.6 to 12.4 kg/cm.sup.2 
Shape and properties of disks 
Outer diameter of disk: 120.phi. 
Inner diameter of disk: 15.phi. 
Thickness of disc: 1.2 mm 
Track pitch: 1.67.mu. 
Depth of pit: 0.11.mu. 
Length of pit: 0.9 to 3.3.mu. 
Width of pit: 0.5.mu. 
This relationship between the injection molding temperatures and 
birefringence for the resin of this Example is shown in FIG. 1. In 
addition, the disc substrate molded at 310.degree. C. showed slight 
coloring and flaws. However, these did not occur in the disc substrates 
molded at temperatures of not higher than 300.degree. C. 
(C) Method of measurement of birefringence 
The measurement of birefringence in this Example was carried out in the 
following method. The same was also done in the following Examples. 
An optical disc substrate was divided into five equal portions and five 
points (23, 30, 45, 50 and 57 cm apart from the center) in each portion, 
totalling 25 points, were selected as points of measurement and the 
measurements were made in these points of measurement by an automatic 
birefringence measuring device (made by Mizojiri Optical Co., Ltd.). 
Measured values were indicated by + or -. Accordingly, when all the 25 
points were indicated singly by either + or -, its maximum value was taken 
as the maximum birefringence, and when + and - were indicated mixedly, the 
difference between + maximum value and - minimum value was taken as the 
maximum birefringence. 
The maximum birefringence value allowable in rerecordable optical discs is 
not particularly standardized, the maximum birefringence of not higher 
than about 10, measured at double pass, is said to be allowable. 
Accordingly, the above results show that substrates can be suitably molded 
for rerecordable use in the range of 270.degree. C. to 300.degree. C. 
(D) Preparation of optical discs 
Aluminum was vacuum-deposited in a thickness of 1500 .ANG. on the surface 
having music sound reproduction signal pits in the resulting optical disc 
substrates under the condition of 10.sup.-5 Torr to give optical discs. 
(E) Thermal resistance test 
Regarding the resulting optical disc, the disc subjected to a heat 
resistance test (50.degree. C., 40% RH) and the disc subjected to a 
moisture resistance test (40.degree. C., 100% RH), the flatness was 
measured and music sound information was detected, and the results are 
shown in Table 4. 
TABLE 4 
______________________________________ 
Flatness* Music information** 
______________________________________ 
Prior to thermal 
+0.16 mm, -0.22 mm 
61 minutes 
resistance test 
6 months passed 
+0.21 mm, -0.22 mm 
61 minutes 
in thermal 
resistance test 
______________________________________ 
*The measurement of flatness was carried out according to the method of 
optical interference by a flatness measuring machine model FT3C made by 
Nidk Co., Ltd. The values indicate each maximum value on the + side and - 
side of one disc. The v alue slightly increased on the + side, which, 
however, is at the level of no significance. (The + side indicates a 
convex state from the recording surface and the - side a concave state 
from the recording surface.) 
**The music sound information was measured as follows. The above disc was 
inserted into an audio compact disc player (made by Nippon Electric Co., 
Ltd., model CD5803) to reproduce music. Generally when the disc is 
subjected to a thermal resistance test or moisture resistance test, it 
warps to a greated extent (especially in the outer area), which thus 
causes a focus error and it becomes impossible to reproduce music sound 
information. 
Accordingly, whether the sound information can be picked up at the initial 
stage (or in the inner area), the focus error is hardly modified as the 
warp becomes larger. The above table shows that even if a compact disc in 
which a 61 minutes long sound information is input is stored under the 
conditions of 50.degree. C. and 40% RH, the original sound information can 
be correctly reproduced. 
An audio compact disc is taken up as an example here for simplification. 
However, as far as a video disc having a disc diameter of 300.phi., a DRAW 
type disc of which severity on an information error is rquired and a 
record-erasable disc are concerned, these subjects are more significant. 
(F) Moisture resistance test 
While the above optical discs were maintained under the conditions of 
40.degree. C. and 100% RH, the flatness was measured and the music sound 
information was detected. The results are shown in Table 5. 
TABLE 5 
______________________________________ 
Flatness Music information 
______________________________________ 
Prior to moisture 
+0.15 mm, -0.21 mm 
61 minutes 
resistance test 
6 months passed 
+0.22 mm, -0.23 mm 
61 minutes 
in moisture 
resistance test 
______________________________________ 
The values found in the above test are a little greater than those found in 
the thermal resistance test, but scarcely affect the picking-up of the 
sound information. 
EXAMPLE 21 
The acetalization of Example 20 was carried out by the use of 50.4 kg of 
4-methylcyclohexanealdehyde in place of 44.8 kg of cyclohexanealdehyde 
added at its earlier step and 71.4 kg of 4-methylcyclohexanealdehyde in 
place of 63.5 kg of cyclohexanealdehyde added at its later step. The 
injection molding, vacuum vapor deposition, thermal resistance test and 
moisture resistance test were carried out under the same conditions as in 
Example 20. The results are shown in Table 6. 
TABLE 6 
______________________________________ 
Flatness Music information 
______________________________________ 
Prior to thermal 
+0.15 mm, -0.21 mm 
61 minutes 
resistance test 
6 months passed 
+0.16 mm, -0.21 mm 
61 minutes 
in thermal 
resistance test 
Prior to moisture 
+0.17 mm, -0.22 mm 
61 minutes 
resistance test 
6 months passed 
+0.19 mm, -0.25 mm 
61 minutes 
in moisture 
resistance test 
______________________________________ 
The relationship between injection molding temperature, maximum 
birefringence and appearance for this resin is as shown in FIG. 2. Disc 
molded at 310.degree. C. took on color to some extent and recognizable 
flows were there. 
The above results show that the flatness did not change through both the 
thermal resistance test and the moisture resistance test and the 
reproductions of music sound information were correctly made from the 
initial stage to the last. 
With regard to the maximum birefringence, it is also seen that substrates 
for rerecordable optical discs can be molded at temperatures from 
280.degree. C. to 300.degree. C. 
The thermal weight loss of the resins obtained in Examples 20 and 21, 
polymethylmethacrylate (Comparative Example 3) and polycarbonate 
(Comparative Example 4) were respectively measured by the use of a thermal 
microbalance analyzer (at the rate of temperature increase of 6.degree. C. 
per minute). 
According to the results of the above measurements, the thermal weight loss 
of the resins in Examples 21 and 22 was not more than 1% at a temperature 
of not higher than 300.degree. C. Namely, the injection molding 
temperature ranges are as shown in Table 7. 
TABLE 7 
______________________________________ 
Temperature at which 
thermal weight loss is 
Resin not higher than 1% 
______________________________________ 
Example 20 not higher than 300.degree. C. 
Example 21 not higher than 300.degree. C. 
PMMA (Comp. Ex 3) not higher than 280.degree. C. 
PC (Comp. Ex. 4 not higher than 400.degree. C. 
______________________________________ 
COMATIVE EXAMPLE 3 
By the use of polymethylmethacrylate commercially graded for optical discs 
(a product of Kyowa Gaschemical Co., Ltd., parapet F1000), Example 20 was 
repeated except for the injection molding temperature range indicated in 
FIG. 4 for the measurement of maximum birefringence, preparation of 
optical discs by vacuum deposition and measurement of thermal resistance 
and moisture resistance. The results are shown in Table 8 and FIG. 4. 
TABLE 8 
______________________________________ 
Flatness Music information 
______________________________________ 
Prior to thermal 
+0.15 mm, -0.19 mm 
61 minutes 
resistance test 
6 months passed 
+0.22 mm, -0.35 mm 
61 minutes 
in thermal 
resistance test 
Prior to moisture 
+0.14 mm, -0.21 mm 
61 minutes 
resistance test 
20 days passed 
+0.96 mm, -2.26 mm 
12 minutes 
in moisture 
resistance test 
______________________________________ 
FIG. 4 shows the relationship of this resin between the maximum 
birefringence and the molding temperature for this resin. Low values of 
birefringence were found at each temperature. Each sample is applicable to 
discs for rerecordable discs. 
In the thermal resistance test, the warpage of the disks prepared in this 
Example was a little larger than that in Examples 19 and 20, which, 
however, can be judged to be at the level at which the picking-up of music 
sound information is not affected. However, in the moisture resistance 
test, since the flatness changed to a great extent when 20 days passed, 
music sound information could not be reproduced in 12 minutes from the 
time reproduction started. 
COMATIVE EXAMPLE 4 
By the use of polycarbonate (PANLITE AD5503, a product of Teijin Kasei 
K.K.) commercially graded for optical discs, Example 20 was repeated 
except for the injection molding temperature range indicated in FIG. 4 for 
the measurement of maximum birefringence, preparation of optical discs by 
vacuum deposition and measurement of thermal resistance and moisture 
resistance. The results are shown in Table 9 and FIG. 5. 
TABLE 9 
______________________________________ 
Flatness Music information 
______________________________________ 
Prior to thermal 
+0.16 mm, -0.20 mm 
61 minutes 
resistance test 
6 months passed 
+0.17 mm, -0.24 mm 
61 minutes 
in thermal 
resistance test 
Prior to moisture 
+0.14 mm, -0.18 mm 
61 minutes 
resistance test 
6 months passed 
+0.13 mm, -0.21 mm 
61 minutes 
in moisture 
resistance test 
______________________________________ 
FIG. 5 shows the relations of this resin between the birefringence and 
injection molding temperature. The reulsts showed a high birefringence of 
around 18. Substrates cannot be used for rerecordable discs. 
The thermal resistance test nd moisture resistance test all showed good 
results.