JP2606832B2 - Optical disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polycarbonate used for an optical information recording disk for recording a signal by a laser beam or reading a recorded signal by reflection or transmission of the laser beam. The present invention relates to an optical disk made of a copolymer.

(Prior Art) A DRAW in which a spot beam of a laser beam is applied to a disk and a signal is recorded in fine pits on the disk, or a signal recorded by such a pit is read out by detecting the reflected or transmitted light amount of the laser beam.
(Direct Read After Write), Erasable
-With the DRAW (Eraser Blue Direct Read After Write) type optical information recording / reproducing method, the recording density can be significantly increased. In particular, the Erasable-DRAW type allows erasing and writing of recordings, and has excellent characteristics of images and sound quality reproduced from them. for that reason,
The above optical information recording / reproducing method is expected to be widely used for recording or recording / reproducing images and sound quality, and for recording / reproducing a large amount of information. The disk used in this recording / reproducing method is required to have high optical homogeneity in order to reduce reading errors as well as being transparent because the laser beam passes through the disk body. When the laser beam passes through the disk body, birefringence occurs mainly due to thermal stress, molecular orientation, and residual capacity due to volume change near the glass transition generated during the cooling and flowing processes of the resin during the formation of the disk body. . The large optical non-uniformity caused by the birefringence is a fatal defect for an optical disc. Furthermore, with optical discs,
Durability capable of maintaining excellent recording characteristics for a long time is required.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to achieve high optical homogeneity,
Another object of the present invention is to provide an optical disk having excellent durability.

(Means for solving the problems) The birefringence caused mainly by the thermal stress, molecular orientation, and residual stress generated during the cooling and flowing processes of the resin during the formation of the disk should be considerably reduced by selecting the forming conditions. Can be. However, the birefringence of the disk greatly depends on the inherent birefringence of the molding resin itself, that is, the photoelastic constant.

Birefringence is defined as the product of photoelastic constant and residual stress,
It can be represented by an equation.

n ₁ −n ₂ = C (σ ₁ −σ ₂ ) (1) n ₁ −n ₂ : birefringence σ ₁ −σ ₂ : residual stress C: photoelastic constant From equation (1), decrease the photoelastic constant. Obviously, even if the molding conditions are the same, the birefringence of the obtained disk is reduced.

The present inventors have conducted intensive studies focusing on the above points and found that 1,1-bis- (4-hydroxyphenyl) cyclohexane and 2,2-bis- (4-hydroxy-3-tert-butylphenyl) The present inventors have found out that a resin having a small photoelastic constant can be obtained without impairing the mechanical properties of an aromatic polycarbonate when carbonate is bonded to propane at a specific ratio by a transesterification method, and the present invention has been achieved.

That is, the present invention relates to 95-47 mol% of 1,1-bis- (4-hydroxyphenyl) cyclohexane and 2,2-bis-
(4-hydroxy-3-tert-butylphenyl)
Provided is an optical disk comprising an aromatic polycarbonate copolymer obtained by carbonate bonding of 5 to 53 mol% of propane by a transesterification method.

The 1,1-bis- (4-hydroxyphenyl) cyclohexane and 2,2-bis- (4-bidroxy-3-tert-butylphenyl) propane are represented by the following formulas (I) and (II), respectively.

In the aromatic polycarbonate copolymer, the content of the structural unit represented by the formula (II) is preferably from 10 to 53 mol%.
The viscosity average molecular weight of the aromatic polycarbonate copolymer in the present invention is preferably from 13,000 to 50,000. If the viscosity average molecular weight is less than 13,000, the copolymer becomes brittle and 50,000
If it exceeds, the fluidity of the copolymer becomes poor and the moldability becomes poor.
In the copolymer of the present invention, the third component can be further copolymerized.

In the present invention, the specific proportion of the bisphenols represented by the formulas (I) and (II) is carbonate-bonded by a transesterification method to obtain the polycarbonate copolymer.
For example, the copolymer can be obtained as follows.

A mixture of 1,1-bis- (4-hydroxyphenyl) cyclohexane and 2,2-bis- (4-hydroxy-3-tert-butylphenyl) propane, and a stoichiometric excess of the mixture with respect to the mixture. Is reacted for about 30 minutes in the presence of a conventional carbonate-forming catalyst under the conditions of a temperature of about 160 to 180 ° C., a normal pressure, and an inert gas introduction. Then, the reaction is continued at a temperature of 180 to 220 ° C. while gradually reducing the pressure over about 2 to 3 hours, and finally, the conditions of 10 Torr and 220 ° C. are reached, and the pre-condensation is completed. Then, at 10 Torr, 270 ° C for 30 minutes, 5 Torr,
The reaction is carried out at 270 ° C. for 20 minutes, and then the post-condensation proceeds at 270 ° C. for 1.5 to 2.0 hours under a reduced pressure of 0.5 Torr or less, preferably 0.3 to 0.1 Torr. In addition, as a carbonate formation catalyst for forming a carbonate bond, an alkali metal or alkaline earth metal catalyst such as a lithium catalyst, a potassium catalyst, a sodium catalyst, a calcium catalyst, and a tin catalyst is suitable. Examples of the carbonate catalyst include lithium hydroxide, lithium carbonate, potassium borohydride, potassium hydrogen phosphate, sodium hydroxide, sodium borohydride, calcium hydride, dibutyltin oxide, and stannous oxide. Of these, it is preferable to use a potassium-based catalyst.

The polycarbonate copolymer obtained in this way is useful for a DRAW, Erasable-DRAW optical information recording disc for recording a signal by a laser beam, or reading a signal recorded by reflection or transmission of a laser beam. .

(Examples) Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Incidentally, the viscosity average molecular weight shown in the following examples, 20 ° C. obtained by measuring using a methylene chloride solution
The following relational expression [E. Miiller & O. Bay] between the intrinsic viscosity [η] of bisphenol A / polycarbonate and the molecular weight M
er; USP 2,999,844 (1961)], and calculated from the measured value of the intrinsic viscosity in terms of bisphenol A / polycarbonate.

[Η] = 1.11 × 10 ⁻⁴ M ^0.82 Example 161 parts by weight (50 mol%) of 1,1-bis- (4-hydroxyphenyl) cyclohexane and 2,2-bis- (4-hydroxy-3-tert-butyl) Phenyl) propane 204
Parts by weight (50 mol%) and 264 parts by weight of diphenyl carbonate are put into a 3 L three-necked flask, and after degassing and N ₂ purging are repeated 5 times, melting is performed using a silicon bath at 160 ° C. while introducing nitrogen. I let it. After melting, a solution prepared by dissolving potassium borohydride as a carbonate catalyst in phenol in advance (10 ^-3 mol% based on the total amount of bisphenol charged)
), And the mixture was stirred at 160 ° C for 30 minutes under an N ₂ atmosphere to brew. Next, the pressure was reduced to 100 Torr at the same temperature, and the mixture was stirred for 30 minutes. Next, the temperature was gradually raised to 220 ° C., and the reaction was performed for 60 minutes. In the reaction so far, 80% of the theoretical amount of phenol was distilled off.

Thereafter, the pressure was reduced to 10 Torr at the same temperature, and the reaction was performed for 30 minutes. The temperature was gradually raised to 270 ° C., and the reaction was performed for 30 minutes. Further, at the same temperature, the pressure was reduced to 5 Torr, and the reaction was carried out for 30 minutes.

Next, post-condensation was performed at the same temperature at 0.1 to 0.3 Torr for 2 hours. Under a nitrogen atmosphere, the product polymer was taken out and cooled, and then the solution viscosity was measured at 20 ° C. using dichloromethane as a solvent. The viscosity average molecular weight calculated from this value is
v = 20,800. In addition, DSC (Differential Scanning Calorimeter; Perkin-Elmer2C)
Mold), the glass transition point was found to be Tg = 137 ° C. Further, when the photoelastic constant was determined, it was found that C = 39 Brewsters ( ^10-12 m ² / N). In addition, the photoelastic constant (C) is the test piece (50 mm × 10
A tensile stress is applied in the length direction (mm × 1 mm), the birefringence value is measured, and the magnitude of the tensile stress and the birefringence value are calculated as (σ ₁ −σ ₂ ) and (n ₁ ) −n ₂ ). Incidentally, the photoelastic constant of polycarbonate obtained from 2,2-bis- (4-hydroxyphenyl) propane is C = 82 Brewsters, 10
^-12 m ² / N).

(Evaluation of Recording Characteristics) A recording film was attached to the polycarbonate copolymer produced as described above, and the optical recording characteristics were evaluated. That is,
The polycarbonate copolymer described in the examples was 130 m in diameter using an injection molding machine (manufactured by Meiki Seisakusho, Dynamelter).
m, formed on a disk-shaped substrate with a thickness of 1.2 mm.
_{Using a 23.5} Fe _64.2 Co _12.3 (atomic%) alloy target, a magneto-optical recording film having a film thickness of 1000 angstroms was formed in a sputtering apparatus (RF sputtering apparatus, manufactured by Japan Vacuum Corporation). On this recording film, a protective film (thickness: 1000 Å) of inorganic glass described in Japanese Patent Application Laid-Open No. 60-177449 filed by the present applicant was formed using the same sputtering apparatus as described above. The performance of the obtained magneto-optical disk was evaluated based on the CN ratio, BER (bit error rate), and the CN ratio change rate under the conditions of 60 ° C. and 90 RH%. The results were as shown in Table 1.

As is clear from the results shown in Table 1, the magneto-optical disk comprising the specific polycarbonate copolymer of the present invention has a significantly improved CN ratio and excellent durability due to a decrease in the birefringence value. Also, unlike the case of using phosgene, the bisphenol compound is carbonate-bonded by transesterification, so that Cl ^- ions do not remain on the disk, so that the recording film is not corroded and excellent recording characteristics are maintained for a long time. it can.

Claims (1)

(57) [Claims] (1) 1,1-bis- (4-hydroxyphenyl)
95-47 mol% of cyclohexane and 2,2-bis- (4-hydroxy-3-tert-butylphenyl) propane 5
An optical disc made of an aromatic polycarbonate copolymer obtained by carbonate-bonding with 5353 mol% by a transesterification method.