JPS61287923A - Optical disc - Google Patents

Abstract

PURPOSE:An optical disc which does not adversely affect a recording film applied thereto, has good double refraction and is low in a decrease in the SN ratio, obtained by injection-molding a specified bis(hydroxyphenyl)alkane polycarbonate resin and applying a recording film to the injection molding. CONSTITUTION:A polycarbonate resin of bis(hydroxyphenyl)alkane [e.g., 2,2-bis(4- hydroxyphenyl)propane] having an average MW of 13,000-22,000 and containing no antioxidant is injection-molded to obtain an optical disc base of a thickness of about 1.2mm. A recording film is applied to this base.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical disc for recording signals by reflection or transmission of laser light and for reading recorded signals.

2. Description of the Related Art Digital audio discs (compact discs) and optical video discs are currently commercially available as optical discs. These are read-only optical discs.
Information is already stored on the disc. As these read-only optical discs have come into practical use, write-once or rewritable optical discs for recording information are also being actively developed. This write-once type, rewritable type optical disk has a high possibility of becoming a promising memory medium for information such as images, documents, and data.

Glass or transparent resin is used as the substrate material for these optical discs, and in the case of resin, the following performance is generally required.

(1) Good moldability and good mold transferability (11) High light transmittance (iiD) Small optical anisotropy (hereinafter referred to as birefringence) (iv) Mechanical strength (■) Must have excellent weather resistance and retain its initial special physical properties for as long as possible (VD) Must have good adhesion to the recording material.Resins for optical discs include acrylic resin, polycarbonate resin, etc. A resin with excellent optical properties is used.

On the other hand, regarding vapor deposition materials, in the case of read-only optical disks, aluminum is vapor-deposited on the disk substrate. For recordable and rewritable optical discs, there are melting type and phase change type.

Various materials have been developed for each magneto-optical type.

As described above, the optical disk substrate does not chemically react with these recording films and have no adverse effects such as corrosion. That is, it is necessary that the material has high bleeding properties and volatility, and does not contain anything that promotes deterioration of the recording film.

Problems that the invention seeks to solve Polycarbonate resins usually suffer from thermal deterioration during molding (
Phosphorus-based antioxidants are added to suppress thermal decomposition. However, this antioxidant itself has an adverse effect on the recording film. Particularly in a high-temperature atmosphere, the antioxidant reacts with moisture in the air and turns into an acidic substance, and this acidic substance is thought to promote deterioration of the recording film. The present invention solves the problem that polycarbonate resin has an adverse effect on the recording film on the disc substrate, and it is an optical disc that does not have any adverse effects such as chemical reaction and corrosion on the recording film. The present invention provides an optical disc using polycarbonate resin.

Means for Solving the Problems The optical disc of the present invention is made by injection molding a bis(hydroxyphenyl)alkane-based polycarbonate resin having an average molecular weight of 13,000 to 22,000, without adding any antioxidant, and then forming a recording film thereon. obtained by As bis(hydroxyphenyl) alkanes, 2
．． 2-bis(4-hydroxyphenyl)propane (hereinafter abbreviated as bisphenol A), 2.2-bis(4-hydroxyphenyl)butane, 2.2-bis(4-hydroxyphenyl)pentane, 2.2-bis( Examples include 4-hydroxyphenyl)octane and 1,1-bis(4-hydroxyphenyl)ethane. Moreover, the average molecular weight of the polycarbonate resin needs to be 13,000 to 22,000. Note that the average molecular weight is a value calculated by a normal viscosity method. When attempting to make an optical disk substrate by injection molding a polycarbonate resin having an average molecular weight of 22,000 or more, the birefringence of the optical disk substrate becomes large due to high melt viscosity and reduced fluidity. On the other hand, when the average molecular weight is less than 1300Q, the mechanical properties are significantly reduced and the material cannot be used as an optical disk substrate.

Incidentally, in conventional polycarbonate resins, an antioxidant is usually added to ensure stability in a high-temperature molten state during molding. Therefore, using common sense, we obtained an optical disk substrate by injection molding a polycarbonate resin to which no antioxidant was added, and measured the error rate of the optical disk obtained by applying a recording film on this substrate.
It is thought that the number of large defects that cannot be corrected will increase. However, when the purity of the polycarbonate resin itself becomes good, the number of these large defects is drastically reduced to less than the number of replacement tracks, even without adding a preservative antioxidant, and it becomes usable as an optical disk. Note that the purity of the polycarbonate resin can be determined by measuring the electrical conductivity of the extract, as described in the practical column.

Furthermore, when injection molding polycarbonate resin that does not contain antioxidants to make optical disk substrates, care must be taken to minimize molding defects such as black spots and silver formation due to thermal deterioration. . for that purpose,
The thickness of the optical disk substrate is usually about 1.2 mm, and the cooling time is relatively short, so the molding cycle is shortened as much as possible, and the resin temperature is set low enough to prevent birefringence from worsening. Methods can be taken such as suppressing thermal decomposition of the resin by drying the resin sufficiently, and removing water by thoroughly drying the resin.

Function The present invention prevents corrosion of the recording film and prevents deterioration of the recording film by not adding an antioxidant.

Example Hereinafter, implementation sequences of the present invention will be described.

Implementation F1 A tellurium-based oxide, which is a phase change type recording material, was deposited on a clean glass plate, and the sample was left in an atmosphere of 4o'Ce5%RH to examine the deterioration of the recording film. . For comparison, tri-n-octyl phosphite was selected from among the phosphorus compounds commonly used as antioxidants for polycarbonate resins.

Tris (nonylphenyl) phosphite and triphenyl phosphite were selected, and each of these three types was brought into contact with the vapor deposition sample at 40°C, 95% RH in the same manner as above.
A similar experiment was conducted by leaving it in an atmosphere of The spectral transmittance of the glass plate on which tellurium oxide was vapor-deposited and the sample brought into contact with three types of antioxidants as comparative examples was measured initially and after a predetermined time, and the transmittance at a wavelength of 830 nm was determined. The results are shown in Table 1.

(Left below) Example 2 Using polycarbonate resin pellets made from bisphenol A with an average molecular weight of 15,000 and different purity without adding antioxidants, a 1.2 mm thick and 120 mm diameter polycarbonate resin with spiral pre-groups was prepared. An optical disk substrate for a data file was injection molded, and a tellurium-based oxide was further deposited on the pregroup surface to a thickness of 300 to 500 mm to obtain an optical disk.

The number of disc defects having a length of 30 μm or more along the circumferential direction of this optical disc was examined on the entire disc surface using a measurement and evaluation deck. Furthermore, the obtained optical disk was left in an atmosphere of 80'C8o% RH, and the ON ratio was measured after a predetermined period of time. These results are shown in Table 2.

Here, the purity of the polycarbonate resin was measured by the following method. The pellets were pulverized, 1 g of each was collected in powder form, and extracted with 50 M1 of pure water at boiling for 1 hour, and the conductivity of this extract was measured using a conductivity meter. In the case of polycarbonate resin with poor purity, the electrical conductivity becomes high.

Table 2 Implementation [ff1J3~5 Average molecular weight is 15,000.17,000.

2,000,003 kinds of polycarbonate resin pellets from bisphenol, all of which do not contain any antioxidants, are used to injection mold an optical disk substrate for data files with a spiral pre-group thickness of 1.2 ff+ and a diameter of 120 mm. Then, the birefringence of this substrate was measured. The conductivity of the pellets used was 1.0 μS.
/an. Furthermore, a tellurium-based oxide was deposited on this optical disk substrate to a thickness of 300 to 500 mm to obtain an optical disk. 30/30 along the circumferential direction of this optical disc.
Check the number of defects with a length of jm or more using a measurement and evaluation deck. Furthermore, the obtained optical disc is 80'080
%RH and measure the CN ratio after a predetermined period of time. These results are shown in Table 3.

For comparison, pellets of polycarbonate resin from bisphenol with an average molecular weight of 25,000 and no antioxidants and bisphenol with an average molecular weight of 15,000 and the addition of tris(nonylphenyl) phosphite in an amount of 0.01% by weight. An optical disk was obtained in exactly the same manner using polycarbonate resin pellets obtained from humans, and the birefringence and CN ratio were measured. The results are also listed in Table 3. In addition, birefringence is Nippon Kogaku Co., Ltd. M
A portion of the optical disk substrate having a diameter of 11 oN'lK was measured using a polarizing microscope equipped with a Senarmon convencator.

(Left below) Example 6 Conductivity measured in the same manner as Example 2 was 1μS/1y
tt, using pellets of polycarbonate resin from bisphenols without added antioxidants with an average molecular weight of 15,000, a thickness of 1.271 ff and a diameter of 120'InI with helical pre-groups! An optical disk substrate for a data file was injection molded, and a GdTbFa-based recording material was formed on the pregroup surface by the all-recording material method to obtain an optical disk. The number of disk defects having a length of 30 μm or more along the circumferential direction of this optical disk was investigated and found to be 40. Furthermore, when the obtained optical disc was left in an atmosphere of 80'080% RH and the CN ratio was measured after 2000 hours, it was found that the CN ratio was o, compared to the initial CN ratio.
It decreased by 4aB.

For comparison, an optical disc was obtained using a polycarbonate resin containing 0.01% by weight of tri(nonylphenyl) phosphite added in Example 6 in the same manner as in Example 6, and the same measurements were performed. As a result, although the number of large defects was 6, the CN ratio after 2000 hours in an atmosphere of 80'080% RH was +5 dB lower than the initial value.

Although the above embodiments mainly describe the structures and effects of tellurium-based oxides and magneto-optical recording films, they are of course also effective for compact discs with aluminum evaporation and the CD-120M developed from this compact disc.

Effects of the Invention As is clear from the above explanation, a highly purified bis(hydroxyphenyl)alkane-based polycarbonate resin containing no antioxidant and having an average molecular weight of 13,000 to 22,000 is injection molded, and recording is performed on the resin. By applying the film, there is no adverse effect on the recording film, the birefringence is good, and C
It is possible to obtain an optical disc of excellent quality with little decrease in N ratio. Furthermore, when we forcibly peeled off the recording film of the optical disks in Example 3 and Comparison, and observed the damage to the substrates after irradiation with the semiconductor laser, we found that the grooves in Comparison 13'lJ7 were deformed. Optical discs obtained using polycarbonate resins that do not contain any carbonate have the effect of significantly improving heat resistance.

Claims (1)

[Claims] Bis(hydroxyphenyl) containing no antioxidant and having an average molecular weight of 13,000 to 22,000.
An optical disc obtained by injection molding alkane-based polycarbonate resin and applying a recording film on top of the injection molding.