JP2586575B2 - Optical disk substrate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical disc substrate, and more particularly, to an optical disc substrate comprising a polyvinylcyclohexane-based resin containing a specific heat stabilizer and having excellent heat processing stability. The present invention relates to an optical disk substrate.

[Prior Art] Optical recording using a laser is capable of high-density information recording, storage, and reproduction, and has been actively developed in recent years. An example of such optical recording is an optical disk. Generally, an optical disc is basically composed of a transparent substrate and various recording media coated thereon.

In many cases, a transparent substrate of an optical disc is made of a colorless and transparent synthetic resin, and a typical example thereof is polycarbonate (hereinafter, abbreviated as “PC”) or polymethyl methacrylate (hereinafter, abbreviated as “PMMA”). ). Although these resins excel in colorless transparency, they also have excellent properties unique to each,
It does not have all the requirements for an optical material, particularly for an optical disc substrate, but has problems to be solved. For example, PC has a problem of birefringence caused by the aromatic ring, and also has a problem of water absorption or water permeability. On the other hand, problems in heat resistance, absorbency, and toughness have been pointed out in PMMA.

As described above, each of these resins is used with inherent problems inherent therein. However, in practice, the relationship with a recording medium coated on a transparent substrate made of these resins is further increased. , A new problem as described below has arisen.

On the other hand, a wide variety of recording media have been conventionally developed according to the use of optical disks. For example, a write-once type for recording / reproduction only is a drilling type, and an erasable type for recording-reproduction-erasing-re-recording is a phase transition type utilizing a crystal transition phenomenon. And a magneto-optical type utilizing the magneto-optical effect are known. These recording medium materials include tellurium or its oxide or alloy compound in the write-once type, and Gd / Fe in the erasable type.
/ TbFe, rare earth-transition metal amorphous alloy compounds such as Gd.Fe.Co/Tb.FeCo and other inorganic materials are predominant.Generally, dry processing such as sputtering under a high vacuum is applied to a transparent substrate. It is formed by forming a film.

By the way, the hygroscopicity and water permeability of PC and PMMA cause, on the one hand, a problem of warpage due to expansion of the substrate itself upon absorption of moisture, while on the other hand, the permeation of moisture through the substrate causes corrosion of the recording medium, causing Cause a shortening of the life of the battery.

Further, if further mentioning the heat resistance of the substrate resin,
There are the following problems. That is, in an optical disk, particularly in a write-once type, an erasable type or the like, the temperature of the recording medium at the time of writing and erasing the recording is 200 ° C.
That's all. For this reason, even if this heat is not directly applied to the disk substrate, it is expected that the substrate will become extremely hot at the time of writing or erasing the recording. Problems can occur.

On the other hand, in the optical disk production process, a heat treatment process is often adopted for the purpose of preventing the substrate or the recording medium from changing over time. However, in order to improve the productivity, the process is performed by processing at the highest possible processing temperature. It is desired to reduce the time. From such a viewpoint, if the heat resistance of the resin is low, a high processing temperature cannot be adopted, and there is a problem that productivity cannot be increased.

For these reasons, PMMA with low heat resistance is not enough to withstand the high temperatures of the optical disc production process or usage conditions. Conventionally, PCs with higher heat resistance are exclusively considered as transparent substrate materials. Have been. However, PC is not always evaluated as having sufficient heat resistance, and the appearance of a resin material having higher heat resistance is desired.

To compensate for the drawbacks of conventional resins such as PC and PMMA, Japanese Patent Application Laid-Open No. 63-43910 proposes a method using a polyvinylcyclohexane resin as an optical disk substrate.

[Problems to be Solved by the Invention] However, even when a polyvinylcyclohexane-based resin is used, a high-performance optical disc substrate is not always obtained, and a satisfactory result in some points is not obtained. It is the current situation.

The present inventors have studied in detail the moldability and the like of an optical disk substrate using a polyvinylcyclohexane-based resin proposed in the above patent application, and have obtained the following knowledge.

The polyvinylcyclohexane-based resin is usually obtained by hydrogenating an aromatic ring of a vinyl aromatic polymer, and is generally known as a brittle polymer similar to polystyrene.

As described above, optical disks of the write-once type, erasable type and the like receive a considerable heat history in their use and production process, and therefore require high heat resistance to the resin substrate. Further, the resin material for the disk substrate is required to have toughness at least not to be damaged at the time of mold release during injection molding.

In order to satisfy such demands, to obtain a polyvinylcyclohexane-based polymer with excellent heat resistance and a certain degree of toughness, the hydrogenation rate of the aromatic ring should be increased and the molecular weight should be kept at a certain level during synthesis. There is a need to.

On the other hand, the optical disc substrate needs to have good warp and distortion and good group transferability. From such a viewpoint, it is preferable that the fluidity of the resin during injection molding is as good as possible. In addition, in order to prevent silver streaks and coloration, while reducing the amount of moisture absorbed by the resin,
It is necessary to prevent deterioration of the resin as much as possible.

By the way, regarding polyvinylcyclohexane-based resin having a molecular weight that maintains a certain degree of toughness, in injection molding at a low temperature that can prevent the deterioration of the resin, the fluidity becomes insufficient, so it is necessary to increase the molding temperature. . Such a molding temperature is 270-330 ° C, further 280-320 ° C
Is preferable.

However, in the above temperature range, deterioration of the polyvinylcyclohexane-based resin is inevitable, and the use of a stabilizer is indispensable.

An object of the present invention is to provide a high-performance optical disc substrate made of a polyvinylcyclohexane-based resin having improved properties such as heat resistance, toughness, fluidity, hygroscopicity, and transparency by adding a stabilizer.

[Means and Actions for Solving the Problems] The optical disk substrate of the present invention has a 5%
It is characterized by comprising a polyvinylcyclohexane-based resin blended with a hindered phenol-based heat stabilizer and a phosphorus-based heat stabilizer having a weight loss temperature of 295 ° C. or higher.

That is, the present inventors have intensively studied a stabilizer that effectively prevents the above-described thermal degradation of the polyvinylcyclohexane-based resin, and as a result, the stabilizer was measured using a thermogravimeter.
By using a hindered phenol-based heat stabilizer and a phosphorus-based heat stabilizer having a% weight reduction temperature of 295 ° C. or higher, the deterioration of the resin is effectively prevented, and the problems of silver streaks and coloring are eliminated. The inventors have found that the present invention has been achieved.

In the present invention, as the hindered phenol-based heat stabilizer, those having four or more hindered phenol groups in one molecule are preferable.

In addition, tetrakis (2,4-
Di-tert-butylphenyl) -4,4'-biphenylenephosphonite and / or bis (2,6-di-tert-butyl-4)
-Methylphenyl) pentaerythritol di-phosphite is preferred.

Further, the number average molecular weight of the polyvinylcyclohexane-based resin is preferably from 40,000 to 300,000.

 Hereinafter, the present invention will be described in detail.

The polyvinylcyclohexane-based resin used in the present invention is preferably obtained by nucleating a styrene-based resin (styrene-based polymer).

Examples of the raw material styrene-based polymer include a vinyl aromatic hydrocarbon polymer and a vinyl aromatic hydrocarbon block copolymer. The latter vinyl aromatic hydrocarbon block copolymer includes a vinyl aromatic hydrocarbon polymer segment (hereinafter abbreviated as “A segment”) and at least one or more conjugated diene polymer segments (hereinafter “B”).
Segment ”. ).

Examples of the vinyl aromatic hydrocarbon used as a monomer include styrene, p-methylstyrene, α-methylstyrene, and the like, and styrene is particularly typical.

Examples of the vinyl aromatic hydrocarbon polymer include a homopolymer or a copolymer of two or more of these vinyl aromatic hydrocarbons. In particular, when adhesiveness or the like is required, the vinyl aromatic hydrocarbon and an unsaturated monomer having a polar group copolymerizable therewith lose the properties of the vinyl aromatic hydrocarbon polymer. It is preferable to use a copolymer obtained by copolymerization within a range not to be restricted.

Next, A in the vinyl aromatic hydrocarbon block copolymer
Examples of the segment include those similar to the above-mentioned vinyl aromatic hydrocarbon polymer. The conjugated diene of the B segment in the block copolymer includes 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,
Examples thereof include 3-pentadiene and 1,3-hexadiene, and 1,3-butadiene and isoprene are particularly common. A
The block copolymer composed of the segment and the B segment can be easily prepared by a known method called so-called living anionic polymerization, for example, a method of polymerizing in a hydrocarbon solvent such as hexane or heptane using an organolithium compound as an initiator. Can be obtained. Incidentally, the content of the A segment in such a block copolymer is 80% by weight or more,
It is preferably at least 90% by weight, more preferably at least 93% by weight. When the content of the A segment is less than 80% by weight, the heat resistance of the resin obtained after hydrogenation is reduced, and the resin becomes invincible as an optical disk substrate.

In the present invention, such a raw material styrene-based polymer preferably has a number average molecular weight of 50,000 or more. If the molecular weight of the styrene copolymer is too low, the heat resistance and toughness of the resin obtained after hydrogenation will decrease.

The decrease in the toughness accompanying the decrease in the molecular weight is more remarkable as the content of the diene polymer in the polymer is smaller. Therefore, for polymers containing no diene polymer, the number average molecular weight is
Preferably it is greater than 80,000. On the other hand, the upper limit of the molecular weight is not particularly limited, but usually, 400,000
The following is preferred.

The polyvinylcyclohexane-based resin can be obtained by hydrogenating such a styrene-based polymer in the presence of a hydrogenation catalyst having an aromatic hydrogenation ability. As the hydrogenation catalyst used here, for example, nickel, cobalt,
Examples thereof include metals such as ruthenium, rhodium, platinum, and palladium, and oxides, salts, and complexes thereof, and those in which these are supported on a carrier such as activated carbon, diatomaceous earth, and alumina.
Among these, Raney nickel, Raney cobalt,
Stabilized nickel and ruthenium, rhodium or platinum carbon or alumina supported catalysts are preferred in terms of reactivity.

The nuclear hydrogenation reaction uses a saturated hydrocarbon solvent such as cyclohexane, methylcyclohexane, n-octane, decalin, tetralin, or naphtha as a solvent at a pressure of 50 to 250 kg / cm ² and a temperature of 100 to 200 ° C. It is preferable to carry out.

Incidentally, usually, in the nuclear hydrogenation of the styrene polymer,
As a side reaction, the molecular chain of the polymer is cut. In order to prevent this molecular chain scission, it is preferable to carry out the hydrogenation at as high a hydrogen pressure as possible and in a short time.

The nuclear hydrogenation rate of aromatic nuclei by nuclear hydrogenation reaction is 90% or more, especially
It is preferably at least 95%. Low nuclear hydrogenation rate, 90%
If it is less than this, there are problems such as a decrease in heat resistance of the obtained resin and an increase in birefringence, which is not preferred. In the present invention, as the heat resistance of the resin, it is preferable that the softening point measured by a thermomechanical analyzer is 150 ° C. or more, and when molded as an optical disc substrate, the value of Δn _5.5 described below is obtained. Those having a thickness of 30 nm or less are preferred.

In the present invention, the molecular weight of the polyvinylcyclohexane-based resin thus obtained depends on the composition, molecular weight, hydrogenation (hydrogenation) conditions and the like of the styrene-based polymer as a raw material, and the appropriate range also depends on the composition. Different, but usually
The number average molecular weight is greater than 30,000, preferably greater than 50,000. From the viewpoint of toughness, the smaller the content of the diene-based polymer, the higher the molecular weight is required.For those containing no diene-based polymer, the molecular weight is 40,0.
It needs to be greater than 00, preferably greater than 60,000. The upper limit of the molecular weight is defined from the viewpoint of moldability, but is usually 300,000 or less in number average molecular weight.

In the present invention, a hindered phenol-based heat stabilizer having a 5% weight loss temperature of 295 ° C. or higher as measured in a thermogravimeter under an air stream is used as a stabilizer for such a polyvinylcyclohexane-based resin. At least one is combined with at least one phosphorus-based heat stabilizer having a 5% weight loss temperature of 295 ° C. or higher.

In the present invention, the 5% weight loss temperature measured in a thermogravimeter under an air stream is the air flow rate.
The weight loss when heated at a heating rate of 20 ° C./min under a flow rate of 100 ml / min is measured, and the temperature at which the weight loss reaches 5.0% by weight.

Examples of the hindered phenol-based heat stabilizer employed in the present invention 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) propionyloxydiethyl] -2,4,8,10-tetraoxaspiro [5,5] undecane, 1,3,5-tris (3,5-di- t
-Butyl-4-hydroxybenzine-s-triazine-
2,4,6 (1H, 3H, 5H) -trione, 1,3,5-trimethyl-2,
4,6-tris (3,5, -di-t-butyl-4-hydroxybenzyl) benzene and the like.

In addition, tetrakis (2,4-
Di-t-butylphenyl) -4,4'-biphenylenephosphanite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol-di-phosphite and the like.

Among these stabilizers, the best effect is obtained when a hindered phenol-based stabilizer having four or more hindered phenol groups in one molecule is used.

A suitable amount of these stabilizers is 0.01 to 3 parts by weight of a hindered phenol-based heat stabilizer and 0.01 to 3 parts by weight of a phosphorus-based stabilizer with respect to 100 parts by weight of a polyvinylcyclohexane-based resin.
Preferably it is 0.05 to 1 part by weight. If the added amount of the stabilizer is less than this range, the effect of preventing deterioration is insufficient, and if the added amount exceeds this range, problems such as bleeding and reduction in transparency required as an optical disk substrate may occur. .

There is no particular limitation on the method of mixing these stabilizers with the polyvinylcyclohexane-based resin, but usually the resin and the stabilizer are blended with a ribbon blender, a tumbler blender,
The mixture is mixed with a Henschel mixer or the like, and then melt-kneaded with a Banbury mixer, a single-screw extruder, a twin-screw extruder, or the like, and mixed in a pellet form. Then, using the pellets obtained in this manner, at a molding temperature of 270 to 330
By performing the injection molding at a temperature of 280 ° C., particularly 280 to 320 ° C., it is possible to obtain an optical disk substrate which is excellent in transparency, heat resistance and the like, has no coloring, and has extremely small optical distortion.

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

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.

In addition, various physical properties in the following Examples and Comparative Examples,
It was measured by the following method.

Number average molecular weight: gel permeation chromatography (GP
According to C), the same measurement as in polystyrene was performed using THF as a solvent, and the number average molecular weight in terms of polysterene was determined.

Nuclear hydrogenation rate (%): A polyvinylcyclohexane-based resin was dissolved in tetrahydrofuran (THF) and measured by UV absorption.

Softening temperature (° C): Using a Dupont thermomechanical analyzer,
The softening temperature was measured at a heating rate of 5 ° C./min.

 Light transmittance (%) of optical disk substrate: Measured according to JIS K6714.

Birefringence (nm) of optical disc substrate: From the center of a molded 1.2mm thick, 130mm diameter disc
Birefringence at 5.5 cm position (hereinafter abbreviated as “Δn _5.5 ”)
Was evaluated. The birefringence was measured with a polarizing microscope manufactured by Nippon Kogaku.

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

Appearance of optical disk substrate: Coloring, generation of silver streaks, and the like were visually inspected for an optical disk substrate formed by a method described later.

Example 1 Polyvinylcyclohexane having a number average molecular weight of 70,000 and a nucleus hydrogenation rate of 99% obtained by hydrogenating a styrene homopolymer.
100 parts by weight of tetrakis [methylene-3- (3,5-di-
0.2 parts by weight of t-butyl-4-hydroxyphenyl) propionate methane ("Irganox1010" manufactured by Ciba Geiger Japan), tetrakis (2,4-di-t-butylphenyl) -4,
4'-biphenylenephosphonite (Irgaphos P
-EPQ ”), and melt-kneaded at 260 ° C. using an extruder to form pellets.

Using an injection molding machine ("M140A" manufactured by each machine company), the pellet was attached to a movable mold side with a grooved stand bar, and a disc-shaped optical disc substrate having a thickness of 1.2 mm and a diameter of 130 mm was formed at a resin temperature of 300 ° C. .

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

Example 2 A hydrogenated styrene-butadiene-styrene block copolymer (butadiene content 5% by weight) obtained by anionic polymerization was obtained by hydrogenating a 100% by weight polyvinylcyclohexane-based resin having a number average molecular weight of 60,000 and a nuclear hydrogen rate of 99%. 9-bis [1,
1-dimethyl-2- {β- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy} ethyl] -2,4,8,10-tetraoxyspiro [5,5] undecane (ADEKA・ Argus “Mark Aφ-80”) 0.2 parts by weight, tetrakis (2,4-di-t-butylphenyl-4,
4'-biphenylenephosphonite (Nippon Ciba Geigy I
(rgaphos P-EPQ) 0.2 part by weight was added, and pelletization and injection molding were carried out in the same manner as in Example 1.

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

Comparative Example 1 Example 1 was repeated except that 0.2 parts by weight of butylhydroxytoluene was used as a stabilizer and the injection molding temperature was 260 ° C.
An optical disk substrate was obtained in the same manner as described above.

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

Comparative Example 2 An optical disk substrate was obtained in the same manner as in Example 1 except that 0.2 parts by weight of distearyl thiopropionate was added instead of “Irgaphos P-EPQ”.

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

As is clear from Table 1, by using a polyvinylcyclohexane-based resin containing a specific hindered phenol-based heat stabilizer and a phosphorus-based heat stabilizer, excellent heat resistance, transparency, optical properties, and shape stability are obtained. Thus, a high-performance optical disk substrate free of silver streaks and coloring can be obtained.
On the other hand, in the case of Comparative Example 1, although there was no change in the softening temperature, transparency and the like of the disk, slight coloring and silver streak occurred, the warpage was 0.5 mm, and the birefringence Δn _5.5 = 8 nm. And high. Further, in the case of Comparative Example 2, coloring (yellow) was observed, and generation of some silver streaks was observed.

[Effects of the Invention] As described in detail above, according to the present invention, stable production of a high-performance polyvinylcyclohexane resin having excellent heat resistance, transparency, etc., low hygroscopicity, and low birefringence without deterioration of the resin is achieved. An optical disk substrate is provided.

In the present invention, in particular, as a hindered phenol-based heat stabilizer, one having four or more hindered phenol groups in one molecule, and as a phosphorus-based heat stabilizer, tetrakis (2,4-di-t-butylphenyl) ) -4,4'-biphenylenephosphonite and / or bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol-di-phosphite; When the number average molecular weight is from 40,000 to 300,000, an extremely excellent effect can be obtained.

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location // (C08K 5/00 5:13 5:49)

Claims (4)

(57) [Claims] (1) The 5% weight loss temperature measured by a thermogravimeter is 29.
An optical disc substrate comprising a polyvinylcyclohexane-based resin blended with a hindered phenol-based heat stabilizer and a phosphorus-based heat stabilizer at a temperature of 5 ° C. or higher. 2. The optical disc substrate according to claim 1, wherein the hindered phenol-based heat stabilizer has four or more hindered phenol groups in one molecule. 3. The method according to claim 1, wherein the phosphorus heat stabilizer is tetrakis (2,4-di-t-butylphenyl) -4,4'-biphenylenephosphonite and / or bis (2,6-di-t-butyl-butyl). 4-
3. The optical disk substrate according to claim 1, wherein the substrate is methylphenyl) pentaerythritol di-phosphite. 4. The optical disk substrate according to claim 1, wherein the number average molecular weight of the polyvinyl cyclohsan resin is from 40,000 to 300,000.