JPH01317728A - Production of optical disk substrate made of polyvinyl cyclohexane resin - Google Patents

Abstract

PURPOSE:To obtain an optical disk substrate excellent in transparency, heat resistance and toughness and reduced in optical strain by subjected a polyvinyl cyclohexane resin specified in its MW and the nuclear hydrogenation rate of an aromatic ring to injection molding under a specific condition. CONSTITUTION:A polyvinyl cyclohexane resin having a number average MW of 40,000-300,000 and a nucleus hydrogenation rate of 90% or more obtained by hydrogenating the aromatic ring of a styrenic resin is subjected to injection molding under such a condition that the temp. of the resin is 270-350 deg.C and that of a mold is 30-120 deg.C to prepare an optical disk substrate. It is necessary that the number average MW is large than 4,000 from the aspect of toughness and, when said MW exceeds 300,000, no good moldability is obtained. When the nucleus hydrogenation rate is below 90%, the heat resistance of the resin is lowered and double diffraction is increased. When the temp. of the resin exceeds 350 deg.C, coloration and a silver streak are generated and toughness is lowered and, when said temp. is below 270 deg.C, the flowability of the resin is lowered and a group transfer property becomes inferior and optical strain is increased. When the temp. of the mold exceeds 120 deg.C, deformation becomes large and, when said temp. is below 30 deg.C, a molded product reduced in optical strain is not obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an optical disk substrate made of polyvinylcyclohexane resin, and more specifically, to a method for manufacturing an optical disk substrate made of polyvinylcyclohexane resin, which has a specific molecular weight and has excellent heat resistance and toughness. The present invention relates to a method of manufacturing a high-performance optical disk substrate.

[Conventional technology] Optical recording using lasers is capable of high-density information recording, storage,
Since it can be recycled and regenerated, its development has been actively carried out in recent years. An optical disk can be cited as an example of such optical recording. In general, an optical disk basically consists of a transparent substrate and various recording media coated thereon.

Colorless and transparent synthetic resins are often used for the transparent substrates of optical discs, and typical examples include polycarbonate (hereinafter abbreviated as rPCJ) and polymethyl methacrylate (hereinafter abbreviated as rPMMAJ). I can do it. Although these resins are colorless and transparent and have unique and excellent properties, they do not meet all the requirements for optical materials, especially optical disk substrates, and there are problems that need to be solved. For example, PC has the problem of birefringence due to its aromatic ring, and also has problems with water absorption or water permeability. On the other hand, problems with PMMA in terms of heat resistance, water absorption, and toughness have been pointed out for some time.

In this way, these resins are used with their own inherent problems, but in reality, there are also
In relation to recording media coated on transparent substrates made of these resins, new problems have arisen as described below.

On the other hand, regarding recording media, a wide variety of developments have been carried out depending on the use of optical discs.
The write-once type, which is only for recording and playback, is a hole-drilling type, and the erasable type, which is used for recording, playback, erasing, and re-recording, is a double-drilling type that utilizes the crystalline phenomenon. Magneto-optical types that utilize magnetic effects are known. The materials for these recording media are tellurium or its oxide, alloy compound, etc. for the write-once type, and Gd for the erasable type.
Fe, TbFe%GdFeCo.

Inorganic materials such as rare earth-transition metal amorphous alloy compounds such as TbFeCo are mainstream, and are generally formed by forming a film on a transparent substrate by a dry process such as sputtering under a high vacuum.

By the way, the hygroscopicity and water permeability of PC and PMMA, on the one hand, cause the problem of warpage due to the expansion of the substrate itself when it absorbs moisture, but on the other hand, the permeation of moisture through the substrate causes corrosion of the recording medium, and the optical disc This causes a shortened lifespan.

Further, regarding the heat resistance of the substrate resin, there are the following problems. That is, optical discs, especially light discs,
For optical discs such as once type and erasable type,
The temperature of the recording medium during writing and erasing of records reaches 200° C. or more. For this reason, even though this heat is not directly applied to the disk substrate, it is expected that the substrate will reach a considerably high temperature when writing and erasing records, and resins with low heat resistance may cause deformation of the substrate or group formation. Problems such as deformation may occur.

On the other hand, in the production process of optical discs, a heat treatment process is often incorporated in order to prevent aging of the substrate or recording medium. It is desirable to shorten the time.

From this point of view as well, if the heat resistance of the resin is low, a high treatment temperature cannot be used and productivity cannot be increased.

For these reasons, PMMA, which has low heat resistance, is completely insufficient to handle the high temperatures encountered in the production process or usage conditions of optical discs, and conventionally, PC, which has higher heat resistance, has been used exclusively as a transparent substrate material. It is being considered. However, even PC is not necessarily evaluated as having sufficient heat resistance, and the emergence of resin materials with higher heat resistance is desired.

To compensate for the drawbacks of conventional resins such as PC%PMMA, Japanese Patent Application Laid-Open No. 63-43910, Japanese Patent Application No. 62-157324
A method of using a polyvinylcyclohexane resin as an optical disk substrate has been proposed in .

[Problems to be Solved by the Invention] However, even when polyvinylcyclohexane resin is used, it is not always possible to obtain a high-performance optical disc substrate, and satisfactory results have not been obtained in several respects. This is the current situation.

The present inventors conducted a detailed study on the moldability of the optical disc substrate using the polyvinylcyclohexane resin proposed in the patent application, and as a result, the following findings were obtained.

Polyvinylcyclohexane resin is usually obtained by hydrogenating the aromatic ring of a vinyl aromatic polymer, and is generally known as a brittle polymer similar to polystyrene.

As mentioned above, optical disks such as write-once type and erasable type are subjected to considerable heat history during their use and production process, so high heat resistance is required of the resin substrate.

Further, the resin material for the disk substrate is required to have at least a degree of toughness that will not cause damage during mold release during injection molding.

In order to meet these demands and obtain a polyvinylcyclohexane polymer with excellent heat resistance and a certain degree of toughness, it is necessary to increase the hydrogenation rate of the aromatic ring during synthesis and to increase the molecular weight above the window. need to be retained.

On the other hand, as an optical disk substrate, it is necessary to have good group transferability with little warpage or distortion, and from this point of view, it is preferable that the fluidity of the resin during injection molding be as good as possible.

By the way, in injection molding of polyvinylcyclohexane resin having a molecular weight that maintains a certain degree of toughness, if the molding temperature is too low, the fluidity will be insufficient for molding optical disk substrates; If it is too high, the fluidity will be good, but the resin will deteriorate, causing problems such as insufficient toughness of the molded product, coloring, and silver streaks.

Because of this, it has excellent transparency, heat resistance, toughness, etc.
Moreover, it is extremely difficult to obtain an optical disc substrate with low optical distortion, and conventionally, there has been no optical disc substrate that can fully satisfy all of these characteristics.

It is an object of the present invention to solve these conventional problems and provide a high-performance optical disk substrate made of a polyvinylcyclohexane resin that has significantly improved the above-mentioned properties.

[Means and effects for solving the problems] The method for producing an optical disk substrate made of polyvinylcyclohexane resin of the present invention is obtained by hydrogenating an aromatic ring of a styrene resin.
A polyvinylcyclohexane resin having a number average molecular weight of 40,000 to 300,000 and a nuclear hydrogenation rate of 90% or more is injection molded at a resin temperature of 270 to 350°C and a mold temperature of 30 to 120°C.

That is, in view of the above-mentioned conventional circumstances, the present inventors have conducted intensive studies on a method for obtaining an optical disk substrate with excellent transparency, heat resistance, toughness, and small optical distortion. We discovered that by injection molding a polyvinylcyclohexane resin with a specified nuclear hydrogenation rate under specific molding conditions, it was possible to produce an optical disk substrate with excellent transparency, heat resistance, and toughness, and low optical distortion. The invention has been achieved.

The present invention will be explained in detail below.

The polyvinylcyclohexane resin used in the present invention is obtained by nuclear hydrogenation of a styrene resin (styrene polymer).

Examples of the raw material styrenic polymer include vinyl aromatic hydrocarbon polymers and vinyl aromatic hydrocarbon block copolymers. The latter vinyl aromatic hydrocarbon block copolymer includes a vinyl aromatic hydrocarbon polymer segment (hereinafter referred to as "A segment") and at least one conjugated diene polymer segment (hereinafter referred to as "B segment").
abbreviated as "segment". ).

Examples of the vinyl aromatic hydrocarbon used as a monomer include styrene, p-methylstyrene, and a-methylstyrene, with styrene being a particularly representative example.

As vinyl aromatic hydrocarbon polymers, these vinyl aromatic hydrocarbons 1f! Examples include a homopolymer or a copolymer of two or more. In particular, when adhesive properties are required, the above-mentioned vinyl aromatic hydrocarbon and an unsaturated monomer having a polar group that can be copolymerized with the vinyl aromatic hydrocarbon may be used to remove the properties of the vinyl aromatic hydrocarbon polymer. It is preferable to use a copolymer obtained by copolymerization within a range that does not occur.

Next, examples of the A segment in the vinyl aromatic hydrocarbon block copolymer include those similar to those of the vinyl aromatic hydrocarbon polymer described above. In addition, the conjugated diene of the B segment in the block copolymer includes 1,3-butadiene, isoprene, 2,3-dimethyl-183-butadiene, 1,3-pentadiene, 1,3-hexadiene, etc. In particular, 1,3-butadiene and isoprene are common. A block copolymer consisting of an A segment and a B segment can be easily produced by a known method called living anionic polymerization, such as a method in which polymerization is performed using an organic lithium compound as an initiator in a hydrocarbon solvent such as hexane or hebutane. can be obtained. The content of the A segment in such a block copolymer is 80% by weight or more, preferably 90% by weight or more, and more preferably 93% by weight or more. When the content of the A segment is less than 801i% by weight, the heat resistance of the resin obtained after hydrogenation decreases, making it unsuitable for use as an optical disc substrate.

In the present invention, the molecular weight of such raw material styrenic polymer is preferably 50,000 or more in terms of number average molecular weight.If the molecular weight of the styrenic polymer is too low, the heat resistance of the resin after hydrogenation will be affected. , the toughness decreases.

The lower the content of the diene polymer in the polymer, the more remarkable the decrease in toughness accompanying the decrease in molecular weight.

Therefore, regarding polymers that do not contain diene polymers,
It is preferable that the number average molecular weight is larger than ao or ooo, while there is no particular restriction on the upper limit of the molecular weight,
In normal cases, it is preferably 400.000 or less.

Polyvinylcyclohexane resin can be obtained by nuclear hydrogenating such a styrene polymer in the presence of a hydrogenation catalyst capable of aromatic hydrogenation. Examples of hydrogenation catalysts used here include metals such as nickel, cobalt, 5-nium, rhodium, platinum, and baladicum, or their oxides, salts, and complexes, and these on carriers such as activated carbon, diatomaceous earth, and alumina. Examples include those that are supported. Among these, Raney nickel, Raney cobalt, stabilized nickel and ruthenium, rhodium or platinum supported catalysts on carbon or alumina are particularly preferred from the viewpoint of reactivity.

The nuclear hydrogenation reaction is carried out at a pressure of 50 to 250 kg/c and a temperature of 100 to 200 °C using a saturated hydrocarbon solvent such as cyclohexane, methylcyclohexane, n-octane, decalin, tetralin, or naphtha as a solvent. It is preferable to use . In addition, ether solvents such as tetrahydrofuran can also be used.

Normally, nuclear hydrogenation of styrenic polymers involves scission of the molecular chain of the polymer as a side reaction.In order to prevent this molecular chain scission, hydrogenation is carried out at as high a hydrogen pressure as possible.
It is also preferable to carry out the process in a short period of time.

In the present invention, aromatic nuclei (aromatic rings) due to nuclear hydrogenation reaction
The nuclear hydrogenation rate is 90% or more, preferably 95% or more. If the nuclear hydrogenation rate is low and is less than 90%, there are problems such as a decrease in the heat resistance of the resulting resin and an increase in birefringence, which is undesirable.In addition, in the present invention, the heat resistance of the resin is as follows:
The softening point measured with a thermomechanical analyzer is 15
The temperature is preferably 0° C. or higher, and the birefringence is Δn s, which will be described later, when molded as an optical disk substrate.
It is preferable that the value of s is 30 nm or less.

In the present invention, the molecular weight of the polyvinylcyclohexane resin thus obtained depends on the composition, molecular weight, hydrogenation conditions, etc. of the styrene polymer as a raw material, and its appropriate range also depends on the composition. Although the number average molecular weight is different, the number average molecular weight is 40,000 to 300,000. From the viewpoint of toughness, the lower the diene polymer content, the higher the molecular weight is required, and for those containing no diene polymer, the molecular weight is preferably greater than 40,000. must be greater than 6o,ooo. The upper limit of the molecular weight is determined from the viewpoint of moldability; if the number average molecular weight exceeds 300,000, good moldability cannot be obtained.

In the present invention, an optical disc substrate is manufactured by injection molding such a polyvinylcyclohexane resin under the following specific conditions.

The resin temperature during molding is 270 to 350°C, preferably 2
The temperature shall be 80-320°C. Resin temperature is too high, 350
If the temperature exceeds ℃, decomposition of the resin becomes inevitable, causing coloring and
Problems such as the occurrence of silver streaks and a decrease in toughness occur, which is undesirable. On the other hand, the resin temperature is excessively low and 270
If the temperature is less than 0.degree. C., the fluidity of the resin decreases, leading to problems such as poor group transferability or increased optical distortion.

In addition, the mold temperature is 30 to 120°C, preferably 50 to 120°C.
The temperature shall be 115°C. If the mold temperature is too high and exceeds 120°C, the deformation during mold release will be large and a molded product with small warpage will not be obtained.On the other hand, if the mold temperature is too low and it is less than 30°C, a molded product with small optical distortion will not be obtained. do not have.

Note that, prior to injection molding, it is preferable to add a stabilizer to the resin in order to prevent thermal deterioration of the resin.

There are no particular limitations on the type of stabilizer used, but since the molding temperature is high, it is preferable to use a stabilizer that itself has high heat resistance. It is preferred to use a heat stabilizer whose % weight loss temperature is 295°C or higher.

In addition, in the present invention, the 5% weight loss temperature measured under air flow with a thermogravimeter means
00mj! The weight loss was measured when heated at a temperature increase rate of 20° C./minute under a flow of 20° C./minute, and this was the temperature at which the weight loss became 5.0% by weight.

Examples of such heat stabilizers include hindered phenol heat stabilizers, phosphorus heat stabilizers, and sulfur heat stabilizers as exemplified below.

Examples of the hindered phenol heat stabilizer include tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)]propionate methane, 3,9-bis[1,1-dimethyl- 2-(β-(3-t-butyl-
4-hydroxy-5-methylphenyl)propionyloxy)ethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, 1,3,5-tris(3,5
-di-t-butyl-4-hydroxybenzyl-5-)-
Lyazine-2,4,6 (IH.

3H,5H)-trione, 1,3.5-trimethyl-2
, 4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene and the like.

In addition, as a phosphorus-based heat stabilizer, tetrakis (2,4-
di-t-butylphenyl)-4,4'-biphenylenephosphonite, bis(2,6-di-t-butyl-4-
(methylphenyl) pentaerythritol di-phosphite and the like.

As a sulfur stabilizer, tetrakis[methylene-3-
(dodecylthio)propionate comethane and the like.

The suitable amount of these stabilizers to be added is 0.01 to 3 parts by weight per 100 parts by weight of the polyvinylcyclohexane resin;
Preferably it is 0.05 to 1 part by weight.

There are no particular restrictions on the method of mixing these stabilizers with the polyvinylcyclohexane resin, but the resin and stabilizer are usually mixed using a ribbon blender, tumbler blender, Henschel mixer, etc., and then a Banbury mixer with one shaft. The mixture is melt-kneaded using an extruder, twin-screw extruder, etc., and formed into a pellet shape. The pellet thus obtained is then used as an injection molding material.

According to the method of the present invention, it is possible to obtain an optical disk substrate that has excellent transparency, heat resistance, toughness, etc., is free from coloration, and has extremely low optical distortion.

When manufacturing an optical disc using the optical disc substrate of the present invention, a film of the above-mentioned recording medium is formed on the surface of the substrate by metal vapor deposition or the like, or a film of an organic dye material is provided by a method such as coating, A method such as further covering these with a protective film can be adopted.

[Examples] The present invention will be explained in more detail by referring to Examples and Comparative Examples. However, unless it exceeds the gist of the present invention,
The present invention is not limited to this embodiment.

In addition, various physical properties in the following Examples and Comparative Examples were measured by the following methods.

■ Number average molecular weight Nigel permeation chromatography (GPC)
) was measured in the same manner as polystyrene using THF as a solvent, and the number average molecular weight in terms of polystyrene was determined.

■ Nuclear hydrogenation* (%): Polyvinylcyclohexane resin was dissolved in tetrahydrofuran (THF) and measured by UV absorption.

■ Softening temperature (°C): 1) Using a thermomechanical analyzer manufactured by Upont, the softening temperature was measured at a heating rate of 5°C/min.

■ Light transmittance (%) of optical disc substrate: JIS K
Measured in accordance with 8714.

■ Birefringence of optical disk substrate (nm): molded thickness 1
．． 2mm, 5.5 from the center of a 130mm diameter disc
Birefringence at cm position (hereinafter abbreviated as Δns, sJ).

) was evaluated. Birefringence was measured using a polarizing microscope manufactured by Nippon Kogaku Co., Ltd.

(2) Amount of warpage (mm) of optical disc substrate: Measured using a flat tester FT-7 manufactured by N1DEK.

■ Appearance of optical disc substrate: Optical disc substrates molded by the method described below were visually inspected for coloring, occurrence of silver streaks, etc.

Example 1 Tetrakis[methylene-3-(
3,5-di-t-butyl-4-hydroxyphenyl)]
Propionate methane (manufactured by Ciba Geigy Japan)
ganoxlolo J) O 12 parts by weight, tetrakis (2
,4-di-t-butylphenyl)-4,4°-biphenylenephosphonite (rI rgaphosP-EP
Add 0.2 parts by weight of QJ) and use an extruder to
The mixture was melt-kneaded at ℃ to form pellets.

The pellets are then molded using an injection molding machine ("Ml 40AJ" manufactured by Nashusha Co., Ltd.).
), attach a stanbar with a group to the movable mold side, and set the resin temperature to 300°C and the mold temperature to 70°C to a thickness of 1.
A disc-shaped optical disc substrate having a diameter of 2 mm and a diameter of 130 mm was molded.

Table 1 shows the physical properties of the optical disc substrate obtained.

Example 2 In Example 1, the resin was obtained by hydrogenating a styrene-butadiene-styrene block copolymer (butadiene content 5% by weight) by anionic polymerization, with a number average molecular weight of 60,000 and a nuclear hydrogenation rate of 99%. Injection molding was carried out in the same manner as in Example 1, except that the polyvinylcyclohexane resin was used.

Table 1 shows the physical properties of the optical disc substrate obtained.

Example 3 Molding was carried out in the same manner as in Example 1 except that the molding conditions were a resin temperature of 290°C and a mold temperature of 40°C.

Table 1 shows the physical properties of the optical disc substrate obtained.

Example 4 In Example 1, polyvinylcyclohexane with a number average molecular weight of 90,000 and nuclear hydrogenation of 98% obtained by hydrogenating a styrene homopolymer was used, and the molding conditions were changed to a resin temperature of 3.
Molding was carried out in the same manner as in Example 1 except that the mold temperature was 20°C and the mold temperature was 60°C.

Table 1 shows the physical properties of the optical disc substrate obtained.

Comparative Example 1 Molding was carried out in the same manner as in Example 1 except that the molding conditions were a resin temperature of 260°C.

Table 1 shows the physical properties of the optical disc substrate obtained.

Comparative Example 2 Molding was carried out in the same manner as in Example 1 except that the molding conditions were set to a resin temperature of 370°C.

Table 1 shows the physical properties of the optical disc substrate obtained.

Comparative Example 3 Molding was carried out in the same manner as in Example 1 except that the molding conditions were set to a mold temperature of 140°C.

Table 1 shows the physical properties of the optical disc substrate obtained.

Comparative Example 4 In Example 1, the resin was obtained by hydrogenating a styrene homopolymer and had a number average molecular weight of 35.000. When molding was carried out in the same manner as in Example 1 except that polyvinylcyclohexane with a nuclear hydrogenation rate of 98% was used, the resin was brittle and cracks appeared in the molded piece.

Table 1 shows the physical properties of the optical disc substrate obtained.

As is clear from Table 1, according to the present invention, heat resistance,
A high-performance optical disk substrate with excellent transparency, optical properties, and shape stability, and no silver streaks or coloring can be obtained.

[Effects of the Invention] As detailed above, according to the present invention, a high-performance polyvinyl cyclohexane resin having excellent heat resistance, transparency, etc., low moisture absorption, low birefringence, and good toughness can be used to prevent resin deterioration. It is possible to stably produce high-performance optical disc substrates with excellent optical properties without any problems.

Agent: Patent attorney Tsuyoshi Shigeno

Claims (1)

[Claims] (1) A polyvinylcyclohexane resin with a number average molecular weight of 40,000 to 300,000 and a nuclear hydrogenation rate of 90% or more, which is obtained by hydrogenating the aromatic ring of a styrene resin.
A method for manufacturing an optical disk substrate made of a polyvinylcyclohexane resin, characterized by injection molding at a resin temperature of 270 to 350°C and a mold temperature of 30 to 120°C.