JP2509724B2 - Method for manufacturing optical disc substrate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for directly producing a disc substrate from unmelted granular polycarbonate to produce a high-quality optical disc substrate having a low foreign matter strength.

[Prior Art] For an optical recording medium such as an audio disc, a laser disc, an optical disc memory or a magneto-optical disc which records and / or reproduces information by using laser light, formability, strength and light transmission Polycarbonate is often used because of its excellent rate and moisture resistance.

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

Therefore, conventionally, the foreign matter in the raw material is reduced by filtering it with a filter in the process of purifying the raw material, the granulation process, etc., for example, Japanese Patent Laid-Open No. 61-90345 or 6-90345.
Techniques such as those described in 3-91231 have been proposed.

However, when reducing the amount of foreign matter, it is not sufficient to remove the foreign matter from the unmelted raw material, and it is necessary to prevent dust from mixing in the pelletizing step of the raw material or to prevent the formation and mixing of carbide during extrusion molding. No. 58-126119 or 61-95.
Techniques such as those described in No. 914 have also been proposed.

[Problems to be Solved] The technique described in JP-A-58-126119 is to mold an optical disk substrate by using pellets obtained by blending polycarbonate flakes with an antioxidant and pelletizing. However, this technique has a problem that the material is thermally deteriorated by melting and heating at the time of pelletizing, and foreign matter cannot be sufficiently prevented from being mixed in the pelletizing step. Therefore, there has been a limit to improving the performance.

In addition, the technique described in JP-A-61-95914 is an optical disc that is injection-molded as it is without pelletizing a transparent acrylic resin in the form of beads obtained by suspension polymerization of methyl methacrylate (MMA). A substrate is manufactured. However, this technology can be applied to acrylic resins with low heat resistance, moisture resistance, and strength. Polycarbonate, which has excellent performance as a material for optical discs, is bead-shaped due to the difference in its polymerization method. There is a problem that a polymer cannot be obtained and it cannot be applied as it is.

The present invention has been made in view of the above circumstances, and has a low foreign matter strength, that is, when a recording medium is used, by reducing the contamination of foreign matter and suppressing thermal decomposition of the resin by reducing the thermal history. An object of the present invention is to provide a method for manufacturing an optical disc substrate with a reduced bit error rate (BER).

[Means for Solving the Problems] In order to achieve the above object, in the method for producing an optical disc substrate of the present invention, an unmelted granular polycarbonate having a viscosity average molecular weight of 10000 to 22000 is injection-molded to have a foreign matter strength of 1 or less.
A disc substrate having a size of × 10 ⁵ μm ² / g or less is manufactured. And, preferably, the granular polycarbonate is a polycarbonate having a particle size of 500 to 2000 μm.
It is designed to be 5 wt.% Or more, and the bulk density of the granular polycarbonate is set to 0.6 to 0.8 g / cm ³ .

Direct injection molding of unmelted granular polycarbonate to manufacture a disk substrate can reduce the foreign material strength of the material itself, and also reduce the thermal decomposition of the resin by minimizing the thermal history of the resin to minimize the inclusion of carbides. Since it can be suppressed, it is possible to easily obtain a high-performance optical disc substrate with a small amount of foreign matter and a small number of bit errors.

Here, the "foreign matter strength" is the sum of the product of the square and the number of each particle diameter of the foreign matter having a particle size of 0.5 μm or more per unit weight. The foreign matter is detected in a solution in which a material to be evaluated (raw material, substrate, etc.) is dissolved in a large excess of an organic solvent (particularly methylene chloride). The foreign matter strength is represented by the formula I = Σ {[1/2 (d _i + d _{i + 1} )] ² × (n _i −n _i ′)} / W. In the formula, I is the foreign matter strength, d _i is the i-th particle size classification value (μm), n _i is less than the particle size d _{i + 1} and more than the particle size d _i , and is detected in the solution. N _i ′ is the number of foreign matters contained in the solution before use, and W is the weight (g) of the material.

An example of the setting of the particle size classification value setting is as follows.

d ₁ = 0.5 (μm) d ₆ = 5.0 (μm) d ₂ = 0.6 (μm) d ₇ = 10.0 (μm) d ₃ = 0.7 (μm) d ₈ = 20.0 (μm) d ₄ = 1.1 (μm) d ₉ = 25.0 (μm) d ₅ = 2.5 (μm) When foreign particles with a particle size exceeding 25.0 μm are detected,
Use d ₁₀ and d ₁₁ etc. of appropriate numerical values.

As used herein, the term "foreign matter" means a contaminant that originally enters the optical disk substrate from various ways, such as impurities, dust, or carbide of the raw material resin, but is a "foreign matter" that is a methylene chloride insoluble component. It is possible to accurately evaluate the bit error rate of the optical disk substrate by using the foreign matter strength calculated from the above.

When the foreign matter strength is 1 × 10 ⁵ μm ² / g or less, a sufficiently reliable optical disc substrate for an optical information recording medium can be obtained.

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

In this manufacturing method, a polycarbonate resin is used as the material of the disk substrate. At this time, the polycarbonate resin has a viscosity average molecular weight of 10000 to 22000, preferably 12000 to 20000, and is not melt-pelletized as conventionally used, but is in an unmelted granular form.

The viscosity average molecular weight is set to 10000 to 22000 in order to secure good molding properties for improving optical properties such as strength, transparency and birefringence of the disc substrate and for obtaining uniformity.

The polycarbonate resin here is not particularly limited, for example, a viscosity average molecular weight of 10000 to 22000, preferably 12000 to 20000, by a reaction of a dihydric phenol and a carbonic acid ester such as phosgene or diphenyl carbonate. It is manufactured. Examples of dihydric phenols include hydroquinone, 4,4′-dioxyphenyl, bis (hydroxyphenyl) alkane, bis (hydroxyphenyl) cycloalkane, bis (hydroxyphenyl) ether, bis (hydroxyphenyl) ketone, bis (hydroxy). Examples thereof include phenyl) sulfide, bis (hydroxyphenyl) sulfone, and their lower alkyl and halogen substitution products.
2'-bis (4-hydroxyphenyl) propane (hereinafter referred to as bisphenol A), 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) -hexafluoropropane, etc. Preferably.

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

Further, 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 an end terminating agent such as pt-butylphenol during the production of the polycarbonate. If the viscosity average molecular weight is less than 10,000, the strength of the disk substrate cannot be put to practical use, and if it exceeds 22,000, a disk substrate having sufficient performance in terms of moldability and optical properties cannot be obtained.

The viscosity average molecular weight [M _v ] is determined by measuring the specific viscosity η _sp of the polycarbonate resin in a methylene chloride solution at 20 ° C. and using the formula η _sp /C=[η](1+0.28 η _sp ), where C is Polycarbonate resin concentration (g /)] and [η] = 1.23 × 10 ⁻⁵ M _v ^0.83 .

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

If necessary, it is possible to add additives such as phosphorus-based antioxidants.

Furthermore, the particle size distribution in granular polycarbonate is
It is preferable that the particles having a particle size of 500 to 2000 μm be 95 wt.% Or more. This is because when the viscosity average molecular weight is 22000 or less, it generally becomes a fine powder polymer, and it is difficult or difficult to perform degassing and uniform feeding at the time of melting, and stable injection molding cannot be performed to form a good disk substrate. Since it cannot be obtained, it is preferable to set the particle size distribution as described above.

Therefore, the particle size distribution is more preferably 95 wt.% Or more when the particle size is 700 to 1400 μm. In this case, the particle size distribution is narrow, and the plasticization of the screw during injection molding can be stably performed as if it were a molten pellet.

Furthermore, the bulk density of the above-mentioned granular polycarbonate is 0.6 to 0.8 g / cm ^{3 in} order to improve the meltability, degassing property, and metering property.
It is preferable that

An injection molding machine (including an injection compression molding machine) when manufacturing an optical disc substrate from the above polycarbonate resin
To use. A generally used injection molding machine may be used, but from the viewpoint of reducing the generation of carbides and improving the reliability of the disk substrate,
C _o -N _i -M _o -C consisting _r alloy (e.g. C _o 5~80%, N _i 5~
80%, M _o 0.1~10%, performs a C _r 1 to 20% of an alloy) linings, it is preferable to use those subjected to two-layer coating of T _i C and T _i N to the screw surface.

That, and an alloy lining consisting of C _o -N _i -M _o -C _r on the inner wall surface of the cylinder, when coating the T _i C and T _i N into two layers on the surface of the screw, non-adherent to the resin and the surface Due to its corrosion resistance, it is possible to prevent the generation of carbides even at high temperatures (400 ° C).

The resin temperature during injection molding is 300 to 400 ° C, and the mold temperature is 50 to 140 ° C, preferably 80 to 130 ° C.

In this case, only the mold surface may be heated to a glass transition temperature or higher by using a high frequency wave or the like, and cooled to a temperature at which the disk substrate can be taken out after the resin injection molding. Thereby, an optically excellent substrate can be obtained.

Most optical disc substrates manufactured by this manufacturing method have a radius of 40 to 170 mm and a thickness of 1 to 3 mm.
In addition, the foreign matter strength of the optical disc substrate is 1 × 10 ⁵ μm ² / g
In order to further reduce the bit error rate and obtain more reliable reliability, it is preferably set to 5 × 10 ⁴ μm ² / g or less.

In order to reduce the strength of foreign matter as described above, an injection molding machine in which the inner wall surface of the cylinder and the screw surface are processed is used, and / or in the production process of the granular polymer, sufficient washing in a molten state, pickling, Repeated alkali washing, granulating with water or warm water, and further washing with poor solvent such as acetone (heating if necessary), 5 wt.% Or less of low molecular weight components (molecular weight 3000 or less), unreacted bisphenol A
20ppm or less of impurities such as
It is effective to use granular polycarbonate having a particle size of pm or less.

[Examples] Next, the performances of the optical disk substrate manufactured by the manufacturing method of the present invention and the optical disk substrate manufactured by the conventional method will be compared.

Examples 1 to 3 As raw materials, unmelted polycarbonate shown in Table 1 [viscosity average molecular weight 15600, particle size distribution 700 to 1400 μm 96.5 wt.
%, Bulk density 0.68 g / cm ³ ], molding temperature of 360 ℃, mold temperature of 120 ℃, using an injection molding machine with the treatment shown in Table 1 130 mmφ × 1.2 mm optical type A disk substrate was molded.

Next, a Tb-Fe-Co recording film was formed on this substrate by sputtering, and the bit error was measured.

Table 1 shows the results of the foreign matter strength of the disk substrate and the bit error rate.

Comparative Examples 1 and 2 Instead of unmelted polycarbonate, melt-molded polycarbonate pellets [viscosity average molecular weight 15400, size
3 mmφ × 3 mm] was used, and the same procedure as in Example 1 was performed. Table 1 shows the results.

As a result, it has been found that the optical disc substrate manufactured by the manufacturing method of the present invention is superior in terms of foreign matter strength and bit error. That is, according to the method of the present invention,
It is clear that a high-performance disk substrate with a foreign matter strength of 10,000 μm ² / g or less can be obtained.

[Effects of the Invention] As described above, according to the method for producing an optical disc substrate of the present invention, the disc substrate is produced by direct injection molding from unmelted granular polycarbonate. In addition, the thermal history of the resin can be reduced only once to minimize the thermal decomposition of the resin and minimize the inclusion of carbides, making it easy to create a high-performance optical disk substrate with a low foreign matter content and few bit errors. can get.

Claims (3)

(57) [Claims] 1. An unmelted granular polycarbonate having a viscosity average molecular weight of 10,000 to 22000 is injection-molded to have a foreign matter strength of 1 × 10.
^A method of manufacturing an optical disk substrate, which comprises manufacturing a disk substrate of ⁵ μm ² / g or less. 2. The granular polycarbonate is 500 to 2000.
The method for producing an optical disk substrate according to claim 1, wherein the polycarbonate having a particle size of μm is 95 wt.% or more. 3. The bulk density of the granular polycarbonate is 0.
The method for producing an optical disc substrate according to claim 1, wherein the optical disc substrate has a weight of 6 to 0.8 g / cm ³ .