JPH02276040A - Production of optical disk substrate - Google Patents

Abstract

PURPOSE:To decrease the intrusion of foreign matter into the above disk substrate, to lessen heat history so as to suppress the thermal decomposition of a resin and to lower a bit error rate by injection molding unmolten granular polycarbonate having a specific viscosity average mol.wt., and thereby producing a disk substrate. CONSTITUTION:The unmolten granular polycarbonate having 10,000 to 22,000 viscosity average mol.wt. is injection-molded to produce the disk substrate. The foreign matter strength of the material itself is, therefore, lowered to <=10,000mum<2>/g and the heat history of the resin is lessened to just one time, by which the thermal decomposition of the resin is decreased and the intrusion of the carbide is minimized. The high-performance optical disk substrate which contains the foreign matter at a lower ratio and has less bit errors is easily obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for directly manufacturing a disk substrate from unmelted granular polycarbonate to produce a high-quality optical disk substrate with low foreign object strength.

[Prior Art] Optical recording media that record and/or reproduce information using laser light, such as audio discs, laser discs, optical disc memories, and magneto-optical discs, have a moldability of 9. Polycarbonate is often used because it has excellent transmittance and moisture resistance.

In this case, it is known that foreign matter (dust, carbide, etc.) contained in the transparent substrate has a great influence on the occurrence of bit errors.

Conventionally, efforts have been made to reduce foreign substances by filtering them during the raw material refining process or granulation process. A technique such as that described in has been proposed.

However, in order to reduce the amount of foreign matter, it is insufficient to remove foreign matter from unmelted raw materials, and it is necessary to prevent dust from entering the raw material during the pelletizing process, or to prevent the formation and contamination of carbides during extrusion molding. Since it is necessary to do so, it is necessary to do so in Japanese Patent Application Laid-open No. 58-126119 or No. 61. A technique as described in Japanese Patent Application No.-95914 has also been proposed.

[Problems to be Solved] The technology described in JP-A-58-1.25119 is to mold an optical disk substrate using a pellet made by blending an antioxidant with polycarbonate flakes. be. However, this technique has problems in that it causes thermal deterioration of the material due to melting and heating during pelletizing, and it is not possible to sufficiently prevent contamination of foreign matter during the pelletizing process. Therefore, there was naturally a limit to improving performance.

In addition, the technology described in JP-A No. 61-95914 involves injection molding bead-shaped transparent acrylic resin obtained by suspension polymerization of methyl methacrylate (MMA) as it is without pelletizing it to form an optical disc. It manufactures substrates. However, this technology can be applied to acrylic resins that have low heat resistance and 1IiFf humidity 9 strength.
Polycarbonate, which has excellent performance as a material for optical discs, has the problem that bead-shaped polymers cannot be obtained due to differences in polymerization methods, and it cannot be used as is.

The present invention has been made in view of the above circumstances, and it is possible to reduce foreign matter contamination, reduce thermal history, and suppress thermal decomposition of the resin. The object of the present invention is to provide a method for manufacturing an optical disk substrate with reduced bit error rate (BER).

[Means for Solving the Problems] In order to achieve the above object, the method for manufacturing an optical disk substrate of the present invention provides
The unmelted granular polycarbonate is injection molded to produce a disk substrate having a foreign material strength of IXIO5p-m2/g or less. Preferably, the granular polycarbonate has a particle size of 500 to 2,000 Ii.m, and the bulk density of the granular polycarbonate is 0.6 to 0.8 g/cm'. It's Toshide.

Manufacturing disk substrates by direct injection molding from unmelted granular polycarbonate reduces the foreign material resistance of the material itself, and also allows the resin to undergo only one thermal history, reducing thermal decomposition of the resin and minimizing carbide contamination. Since it is possible to suppress the amount of foreign matter, it is possible to easily obtain a high-performance optical disk substrate with less foreign matter content and fewer bit errors.

Here, the "foreign material strength" is the sum of the product of the square of each particle size and the number of foreign particles per unit weight having a particle size of 0.5 lumen or more. Foreign substances are detected in a solution in which a material to be evaluated (such as a raw material or a substrate) is dissolved in a large excess of an organic solvent (particularly methylene chloride). The foreign material strength is expressed by Formula 1 (%)] An example of setting the particle size classification value is as follows: d, = 1
．． 1 (gm) a9 =25.0 (gm) d5
= 2.5 (μm) If foreign matter with a particle size exceeding 25.0 pm is detected, set d□ to an appropriate value. , d1□, etc. are used.

In this specification, "foreign matter" essentially refers to contaminants that enter the optical disk substrate through various means, such as impurities,
The bit error rate of an optical disk substrate can be accurately evaluated using the above-mentioned foreign material strength calculated from "particles, which are dust or carbides of raw resin, which are insoluble components in methylene chloride."

And when the foreign material strength is 1xlO5μm2/g or less,
An optical disc substrate that is sufficiently reliable for use in optical information recording media can be obtained.

Hereinafter, a preferred specific example of the method for manufacturing an optical disc substrate of the present invention will be described.

In this manufacturing method, polycarbonate resin is used as the material for the disk substrate. At this time, the polycarbonate resin has a viscosity average molecular weight of 10,000 to 22,000,
It is preferably 12,000 to 20,000, and is in the form of unmelted granules rather than the molten pellets commonly used in the past.

The viscosity average molecular weight was set to 10,000 to 22,000 because
This is to ensure good moldability in order to obtain uniformity and good optical properties such as strength, transparency, and birefringence of the disk substrate.

There are no particular restrictions on the polycarbonate resin, for example, a viscosity average molecular weight of 10,000 to 22,000.
, preferably from 12,000 to 20,000, and is produced by reacting a dihydric phenol with a carbonic ester such as phosgene or diphenyl carbonate. As dihydric phenols, hydroquinone, 4
, 4'-dioxyphenyl, bis(hydroxyphenyl)alkane, bis(hydroxyphenyl)cycloalkane, bis(hydroxyphenyl)ether, bis(hydroxyphenyl)ketone, bis(hydroxyphenyl)
Examples include sulfide, bis(hydroxyphenyl)sulfone, and substituted products thereof such as lower alkyl and halogen, such as 2,2'-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A), 1
．． 1-bis(4-hydroxyphenyl)ethane, 2.2
-Bis(4-hydroxyphenyl)-hexafluoropropane and the like are preferably used.

Further, these dihydric phenols can be used alone or in combination.

Furthermore, the polycarbonate used in the present invention may have a partially branched structure.

The viscosity average molecular weight of 10,000 to 22,000 can be controlled by adding a terminal capping agent such as pt-tutylphenol during the production of polycarbonate. If the viscosity average molecular weight is less than 10,000, the strength of the disk substrate will not be suitable for practical use, and if it exceeds 22,000, it will not be possible to obtain a disk substrate with sufficient performance in terms of moldability and optical properties.

Note that the viscosity average molecular weight [Mv] is the specific viscosity η of the polycarbonate resin in a methylene chloride solution at 20°C. and [η] = 1.23X 10-'Mv. ” can be calculated.

The raw material polycarbonate used for injection molding is produced by a conventionally known method and then filtered in a solution state, or the granular raw material is washed with a poor solvent such as acetone under heating conditions to remove low molecular weight components. It is preferable to remove impurities and foreign substances such as and unreacted components. In any case, it is necessary to keep the content of foreign substances, impurities, solvents, etc. in the raw material before injection molding as low as possible.

Furthermore, if necessary, it is also possible to add additives such as phosphorus-based antioxidants.

Furthermore, the particle size distribution of the granular polycarbonate is preferably such that the particle size is 500 to 2000 gm at 95 wt% or more. This has a viscosity average molecular weight of 220
00 or less, it generally becomes a fine powder polymer,
Since degassing and uniform feeding during melting are impossible or difficult, stable injection molding cannot be performed and it becomes impossible to obtain a good disk substrate, so it is preferable to have the particle size distribution as described above.

Therefore, the particle size distribution is from 700 to 14007 h.
It is more preferable that m is 95wt% or more. In this way, the particle size distribution is narrow, and screw plasticization during injection molding can be stably performed as if it were a molten pellet.

Furthermore, the bulk density of the granular polycarbonate is set to 0, 6 to 0, in order to improve melting properties, degassing properties, weighability, etc.
It is preferable to set it to 8 g/cm3.

An injection molding machine (including an injection compression molding machine) is used to manufacture an optical disc substrate from the polycarbonate resin. This injection molding machine may be one that is commonly used, but from the viewpoint of reducing the generation of carbides and increasing the reliability of the disk substrate, it is necessary to
, -N, -M, -Cr (e.g. C85-8
0%, 8.5~80L M, 0°1~tox, cr
~20X alloy) along with lining,
It is preferable to use a screw whose surface is coated with two layers of T and C and T and N.

That is, C6-N, -Mo-C,
By coating the screw surface with two layers of T, C and T, N, the formation of carbides is prevented even at high temperatures (400'C) due to non-adhesion with resin and corrosion resistance of the surface. can be prevented.

The resin temperature during injection molding is 300 to 400°C,
Mold temperature is 50-140℃, preferably 80-130℃
And so.

In this case, only the surface of the mold may be heated to a temperature higher than the glass transition temperature using high frequency waves or the like, and then cooled to a temperature at which the disk substrate can be taken out after resin injection molding.

This makes it possible to obtain an optically excellent substrate.

The size of the optical disc substrate manufactured by this manufacturing method is often 40 to 170 mm in radius and 1 to 3 mm in thickness. In addition, the foreign matter strength of the optical disc substrate is lX1
05gm2/g or less to further reduce the bit error rate and obtain more reliable reliability.
It is preferable that the weight is 10'p, m27g or less.

In order to reduce the foreign material strength in this way, it is possible to use an injection molding machine in which the inner wall surface of the cylinder and the screw surface have been processed, and/or in the process of manufacturing the granular polymer.
Rinse thoroughly with water while molten.

5 wt.
, less than 20% of impurities such as unreacted bisphenol A.
It is effective to use granular polycarbonate containing a solvent such as methylene chloride of 20 ppm or less.

[Example] Next, the performance of an optical disk substrate manufactured by the manufacturing method of the present invention and an optical disk substrate manufactured by a conventional method will be compared.

Examples 1 to 3 Unmelted polycarbonate shown in Table 1 as a raw material [viscosity average molecular weight 15600. Particle size distribution 700-1400#1.
m is 96.5 wt, %, bulk density 0.68 g/cm3], using an injection molding machine subjected to the processing shown in Table 1 under conditions of a molding temperature of 360 ° C. and a mold temperature of 120 ° C.
An optical disc substrate measuring mmφ×1.2 mm was molded.

Next, a Tb-Fe-Go recording film was formed on this substrate by sputtering, and bit errors were measured.

Table 1 shows the results of the foreign material strength and bit error rate of the disk substrate.
Shown below.

Comparative Examples 1 and 2 Except for using melt-molded polycarbonate pellets [viscosity average molecular weight 15400, size 3 mmφ x 3 mm] instead of unmelted polycarbonate,
It was carried out according to Example 1. The results are shown in Table 1.

[Margin below] As a result, it was found that the optical disk substrate manufactured by the manufacturing method of the present invention was superior in terms of foreign matter strength and bit error. That is, it is clear that according to the method of the present invention, a high-performance disk substrate with a foreign material strength of 1,010,000 B/g or less can be obtained.

[Effects of the Invention] As described above, according to the method for manufacturing an optical disk substrate of the present invention, since the disk substrate is manufactured by direct injection molding from unmelted granular polycarbonate, the foreign material strength of the material itself can be reduced. At the same time, the thermal history of the resin is limited to one time, which reduces the thermal decomposition of the resin and minimizes the inclusion of carbides, making it easy to create high-performance optical disk substrates with less foreign matter and fewer bit errors. can be obtained.

Claims (3)

[Claims] (1) Injection molding of unmelted granular polycarbonate with a viscosity average molecular weight of 10,000 to 22,000 has a foreign matter strength of 1.
A method for manufacturing an optical disk substrate, characterized by manufacturing a disk substrate of x10^5 μm^2/g or less. (2) The above granular polycarbonate has a molecular weight of 500 to 2000
Polycarbonate with a particle size of 95wt. % or more, the method for manufacturing an optical disc substrate according to claim 1. (3) The bulk density of the granular polycarbonate is 0.6 to
The method for manufacturing an optical disc substrate according to claim 1, wherein the thickness is 0.8 g/cm^3.