JPS6389530A - Optical disc - Google Patents

Abstract

PURPOSE:To obtain an optical disc having a low double refractive index, a large CN ratio and excellent durability, by using a copolymer obtained by bonding 4,4'-dihydroxy-2,2,2-triphenylethane to 1,1'-bis(4-hydroxyphenyl)-m- diisopropylbenzene through a carbonate bond. CONSTITUTION:A mixture of 97-3mol% 4,4'-dihydroxy-2,2,2-triphenylethane of formula with 3-97mol% 1,1'-bis(4-hydroxyphenyl)-m-diisopropylbenzene of formula II is mixed with diphenyl carbonate in an amount slightly excess of the stoichiometric amount. The obtained mixture is precondensed at 160-220 deg.C and a pressure of normal pressure to 10Torr in the presence of a carbonation catalyst (e.g., KBH4) in an inert gas and postcondensed at about 270 deg.C while the pressure is gradually diminished to obtain an aromatic polycarbonate copolymer of a viscosity-average MW of 13,000-50,000. An optical disc is made by using this copolymer.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to a polycarbonate copolymer used in optical information recording disks that record signals using laser beams or read out recorded signals by reflection or transmission of laser beams. Concerning an optical disc consisting of a combination.

(Prior art) DRAW (DRAW) is a method in which a spot beam of a laser beam is applied to a disk, and signals are recorded on the disk using minute pits, and the signals recorded by the pits are read out by detecting the amount of reflected or transmitted light of the laser beam. Direct Read After Write), Erasab
le-DRAW (Erasable Direct Read)
The after-write (after-write) type optical information recording and reproducing system can significantly increase the recording density, especially in Erasable-D.
The RAW type allows erasing and writing of records, and the images and sound quality reproduced from them have excellent characteristics, so it is widely used for recording and reproducing images and sound quality, recording and reproducing large amounts of information, etc. It is expected that. The disks used in this recording/reproducing system are required not only to be transparent because the laser beam passes through the disk body, but also to have optical homogeneity to reduce reading errors. Birefringence occurs when the laser beam passes through the disk body, mainly due to thermal stress generated during the cooling and flow process of the resin during disk body formation, residual stress due to bimolecular orientation and volume change near the glass transition point. This large optical non-uniformity caused by birefringence is a fatal defect for optical discs.

(Problem to be solved by the invention) As described above, birefringence, which is mainly caused by the thermal stress bimolecular orientation and residual stress generated during the cooling and flow process of the resin during disk molding, can be obtained by selecting the forming conditions. Although the birefringence of the disk can be made considerably small, it is highly dependent on the inherent birefringence of the molding resin itself, that is, the photoelastic constant.

(Means for solving the problem) Birefringence can be expressed by the following equation (1) as a product of a photoelastic constant and a residual stress.

nl-n2=C(a□-a2) (1)
nl-n2: birefringence σ1-02=residual stress C: photoelastic constant From equation (1), it is clear that if the photoelastic constant is made smaller, the birefringence of the disc obtained will be smaller even if the molding conditions are the same. Therefore, the inventors developed 4,4-dihydroxy-2
,2,2-triphenylethane and 1,1'-bis-(4
-Hydroxyphenyl)-m-diisopropylbenzene was discovered by copolymerizing with carbonate bonds to obtain a resin with a small photoelastic constant without impairing the mechanical properties of aromatic polycarbonate, leading to the present invention. It is.

(Structure of the Invention) The present invention combines 97 to 3 mol% of 4,4-dihydroxy-2,2,2-triphenylethane (I) and 1,1-bis-(4
The present invention relates to an optical disc made of an aromatic polycarbonate copolymer obtained by carbonate bonding with 3 to 97 mol% of -hydroxyphenyl)-m-diisopropylbenzene (II). Thus, according to the present invention, there is provided an aromatic polycarbonate copolymer obtained by copolymerizing bisphenols represented by the following formulas (I) and (II) through carbonate bonds.

(I) (II) Moreover, the structural unit of formula (II) is preferably 10 to 90 mol%. This is because if the content of the structural unit of formula (II) is less than 10 mol%, the fluidity of the resulting aromatic polycarbonate will be significantly poor, and if the content of the structural unit of formula (II) exceeds 90 mol%, The glass transition point of the resulting aromatic polycarbonate is significantly lowered. In addition, the viscosity average molecular weight of the copolymer of the present invention is 13,000 to 50,0
00 is preferred. If it is less than 13,000, the copolymer will become brittle, and if it exceeds 50,000, the copolymer will have poor flow and poor moldability.

Furthermore, it is also possible to copolymerize the third component.

The method for producing the polycarbonate copolymer of the present invention includes:
There are two methods:

■Transesterification method 4.4-dihydroxy-2,2,2-triphenylethane and 1,1-bis-(4-hydroxyphenyl)-m-
A slight excess of diphenyl carbonate than the stoichiometric equivalent to a mixture of diisopropylbenzene is added in the presence of a conventional carbonation catalyst, at a temperature of about 160 to 180°C, under normal pressure, and under conditions where an inert gas is introduced. Let it react for about 30 minutes at 180℃ while gradually reducing the pressure for about 2 to 3 hours.
Finally at 10 Torr, 220 at a temperature of ~220°C
The precondensation is completed under °C. After that, 10Torr, 2
30 minutes at 70°C, 20 minutes at 5 Torr, 2706C
0.5 Torr or less, preferably 0.3 Torr.
Torr~0. 1 at 270°C under reduced pressure of ITorr.
．． After 5 to 2.0 hours, proceed with the condensation. For carbonate bonding, alkali metal or alkaline earth metal catalysts such as lithium-based catalysts, potassium-based catalysts, sodium-based catalysts, calcium-based catalysts, and tin-based catalysts are suitable as carbonation catalysts, such as lithium hydroxide, carbonate, etc. lithium,
Examples include potassium borohydride, potassium hydrogen phosphate, sodium hydroxide, sodium borohydride, calcium hydride, dibutyltin oxide, and stannous oxide. Among these, it is preferable to use a potassium catalyst.

■Phosgene method Attach a stirrer, thermometer, gas inlet pipe, and exhaust pipe to the three-bottle flask. A mixture of 4,4-dihydroxy-2,2,2-triphenylethane and 1,1-his,(4-hydroxyphenyl)-m-diisopropylbenzene is dissolved in pyridine, and phosgene gas is introduced while stirring the mixture vigorously. However, since phosgene is extremely poisonous, it must be operated in a strong fume hood. Additionally, a unit is installed at the exhaust end to decompose and detoxify excess phosgene with a 10% sodium hydroxide aqueous solution. For phosgene, use air washing bottles from cylinders,
Introduce the paraffin into the flask through the air washing bottle (count the number of ponds) and the empty air washing bottle. The glass introduction tube should be inserted into the top of the stirrer, and the tip should be widened into a funnel shape to prevent it from becoming clogged by precipitated pyridine salt. As gas is introduced, pyridine hydrochloride precipitates and the contents become cloudy. Water cooling is performed so that the reaction temperature is 30°C or less. As condensation progresses, it becomes viscous. Phosgene is passed through the mixture until the yellow color of the phosgene-hydrogen chloride complex no longer disappears. After the reaction is completed, methanol is added to precipitate the polymer, which is then filtered and dried. Since the polycarbonate produced is soluble in methylene chloride, pyridine, chloroform, tetrahydrofuran, etc., it is purified by reprecipitation from these solutions with methanol. The polycarbonate copolymer thus obtained is used in DRAW, which records signals using a laser beam or reads out signals recorded by reflection or transmission of the laser beam.

It is useful for erasable-DRAW optical information recording discs. EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 4 parts by weight (50 mo 1%) of 4.4-dihydroxy-2,2,2-)diphenylethane and 1,1'-bis=(
20,812 tft parts (50 mo 1%) of 4-hydroxyphenyl)-m-diisopropylbenzene and 264 parts by weight of diphenyl carbonate were placed in a three-necked flask, degassed, and subjected to N2 purge 5 times. It was melted while introducing ``cm'' element. Once melted, add a solution of potassium borohydride, which is a carbonation catalyst, dissolved in phenol (10-3 mo1% amount based on the total amount of bisphenol charged), and heat at 170°.
The mixture was stirred and incubated under C2N2 for 30 minutes. Next, at the same temperature,
After stirring at 1 QQ Torr for 30 minutes, the pressure was further reduced to 5 Q Torr at the same temperature and reaction was carried out for 30 minutes. Next, the temperature was gradually raised to 220°C, and the reaction was continued for 60 minutes, with 80% of the theoretical amount of phenol being distilled out.

Thereafter, the pressure was reduced to 1 Q Torr at the same temperature, and the reaction was carried out for 30 minutes.The temperature was gradually raised to 270°C, and the reaction was carried out for 30 minutes. Further, at the same temperature, the pressure was reduced to 5 Torr and the reaction was allowed to proceed for 30 minutes, and almost all of the theoretical amount of phenol was distilled out to complete the precondensation. Next, under the same temperature, 0.1 to Q, 2 at 3 Torr.
The time edges were aligned. After taking out the product polymer under nitrogen and cooling it, it was heated to 20°C using dichloromethane as a solvent.
The solution viscosity was measured. The viscosity average molecular weight calculated from this value was Mv=19,500. DSC (differential scanning calorimetry) revealed that the glass transition point was Tg=131°C. When measuring the photoelastic constant, C=51B
rewsters (10-12 m2/N).

Example 2 A three-hole flask is equipped with a stirrer, a thermometer, a gas inlet pipe, and an exhaust pipe. 4,4-dihydroxy- in dichloromethane
174 parts by weight of 2,2,2-triphenylethane and 1,I
208 parts by weight of bis-(4-hydroxyphenyl)-m-diisopropylbenzene were dissolved, a 10% by weight aqueous solution of sodium hydroxide was added thereto, and while stirring the mixture vigorously, phosgene gas was introduced. Phosgene was introduced from the cylinder into the flask through an empty air wash bottle, a water filled air wash bottle, and an empty air wash bottle.

The reaction temperature during introduction of phosgene gas was water-cooled to 25°C or less. As the condensation progresses, the solution becomes viscous. Further, phosgene was passed through the mixture until the yellow color of the phosgene-hydrogen chloride complex no longer disappeared. After the reaction was completed, the reaction solution was poured into methanol, filtered, and washed with water repeatedly. Furthermore, the produced polycarbonate was purified by reprecipitation with methanol from a dichloromethane solution. After purification and thorough drying, the solution viscosity was measured at 20°C using dichloromethane as a solvent. The viscosity calculated from this value was measured. The viscosity average molecular weight calculated from this value was Mv=22,000.

(Evaluation of recording properties) A recording film was attached to the polycarbonate copolymer produced as described above, and the optical recording properties were evaluated. That is, Example 1
, 2, using an injection molding machine (
Diameter 130m using Guina Melter (manufactured by each machine factory)
A sputtering device (RF sputtering device, manufactured by Japan Vacuum Co., Ltd.) was formed using an alloy target of Tb23.5Fe64゜2CO12,3 (atomic %) on this substrate. A magneto-optical recording film was formed in the chamber. On this recording film, a protective film of 1,000 inorganic glasses as described in JP-A-60-177449 by the present applicant was formed using the same sputtering apparatus as above. The performance of the obtained magneto-optical disk was evaluated by the CN ratio, BER, and CN ratio change rate under the conditions of 60° C. and 90 RH%. The results are shown in Table 1.

Table 1 Note 1) CN ratio = Write power 7 mW (milliwatt input read power 1 mW, carrier frequency IMHz, measured at 30 KHz in the resolution band (Note 2) CN change rate (%) = 60 with respect to the initial CN ratio
Comparative example of degree of decrease in CN ratio after 30 days at 290 RH% (°C) = Magneto-optical disk was prepared using the same procedure as above using a conventionally known polycarbonate (AD-5503, manufactured by Ondai Kasei Co., Ltd.) substrate. It's something I made.

As is clear from the results in Table 1, the polycarbonate copolymer according to the present invention has a significantly improved CN ratio due to a decrease in birefringence value, and is also found to have excellent durability.

Claims (1)

[Claims] Carbonate bonding of 97 to 3 mol% of 4,4'-dihydroxy-2,2,2-triphenylethane and 3 to 97 mol% of 1,1-bis-(4-hydroxyphenyl)-m-diisopropylbenzene Optical disc made of aromatic polycarbonate copolymer obtained by