JP2584632B2 - Base material for information recording medium - Google Patents

Description

The present invention relates to a base material for an information recording medium such as a video disk and a memory disk.

[Conventional technology]

The methacrylic resin is used as a resin for a substrate of an information recording medium by taking advantage of its original properties of excellent transparency and weather resistance. JP-A-57-123208 and JP-A-57-138601 have been proposed as methacrylic resins for information recording media. JP-A-57-123208 discloses a copolymer with ethyl acrylate, but the heat distortion temperature is 92 ° C. or less, which is insufficient in heat deformation resistance and mechanical strength. Not enough. JP-A-57-138601 discloses a copolymer with an alkyl acrylate or alkyl methacrylate having an alkyl group having 1 to 12 carbon atoms, but within a range defined by the intrinsic viscosity and the heat distortion temperature. When the heat deformation temperature is increased, the intrinsic viscosity is lowered and the mechanical strength is reduced, and there is a problem that a crack occurs when peeled from the mold, and when the moldability and the mechanical strength are maintained, the heat deformation temperature is reduced.

By the way, when a copolymer containing methyl methacrylate as a main component is used for a disk substrate, there is a drawback that methyl methacrylate has a large hygroscopicity, so that dimensional stability is poor, and warping and twisting occur in a humid environment. For this reason, an aromatic polymer carbonate resin having low hygroscopicity is used as a substrate for an audio disk.
However, it is difficult to reduce the birefringence of the aromatic polycarbonate resin, and it is difficult to stably produce a substrate having a low birefringence, and a low birefringence substrate having a diameter larger than that of an audio disk is formed by injection molding. It is a very difficult situation to manufacture.

Further, copolymers with cyclohexyl methacrylate have been proposed to reduce the hygroscopicity without lowering the birefringence of the methacrylic resin (JP-A-58-5318, JP-A-58-127754).

[Problems to be solved by the invention]

However, in order to sufficiently reduce the hygroscopicity of the above-mentioned copolymer, it is necessary to copolymerize a large amount of cyclohexyl methacrylate. Therefore, there is a problem that heat resistance and mechanical strength are reduced.

On the other hand, there is a strong demand from the market for a substrate having excellent heat resistance, release property, transferability, dimensional stability, and mechanical strength, but at present it has not yet been put on the market.

[Means for solving the problem]

The present inventors have conducted intensive studies in view of such a situation, and as a result, by using a copolymer containing methyl methacrylate, phenyl methacrylate and N-substituted maleimide as main components, a base for an information recording medium free from the above-mentioned problems has been obtained. It has been found that a material can be obtained, and the present invention has been achieved.

That is, the present invention relates to a copolymer having 10 to 85% by weight of methyl methacrylate unit, 10 to 60% by weight of phenyl methacrylate unit, 5 to 60% by weight of N-substituted maleimide unit and 0 to 15% by weight of aromatic vinyl compound unit. The first aspect of the present invention relates to an information recording medium base material comprising:
To 85% by weight, 10 to 60% by weight of a phenyl methacrylate unit, 5 to 60% by weight of an N-substituted maleimide unit and 0 to 15% by weight of an aromatic vinyl compound unit. ₁ COOR ₂ (where R ₁ and R ₂ represent alkyl groups having 5 to 20 carbon atoms) fatty acid monohydric alcohol ester, stearyl alcohol, cetanol, glyceryl stearate ester, oligomer containing perfluoroalkyl group and lipophilic group At least one compound of 0.05
To 2.0 parts by weight of an information recording medium base material.
Invention.

According to the present invention, an information recording medium having heat resistance of 105 ° C. or higher, excellent releasability, transferability, and mechanical strength, and having a saturated water absorption in water at 20 ° C. of 1.8% or less. Substrate can be provided.

10 to 85 of the copolymer methyl methacrylate unit of the present invention
% By weight, preferably 10 to 75% by weight. The methyl methacrylate unit, together with the phenyl methacrylate unit described below, is a component that imparts particularly optical and mechanical properties. If it is less than 10% by weight, the mechanical properties tend to decrease. If it exceeds 85% by weight, it absorbs moisture. And heat resistance become insufficient.

Next, the content of the phenyl methacrylate unit as the second component is 10 to 60% by weight, and if it is less than 10% by weight, it tends to be inferior in optical properties, heat resistance and low moisture absorption.
If the amount is more than 10% by weight, mechanical properties tend to decrease.

The third component, an N-substituted maleimide unit, is an essential component for improving heat resistance.
Cycloalkyl maleimide, N-alkyl maleimide,
N-benzylmaleimide, N-arylmaleimide and derivatives thereof. Representative examples are N-cyclohexylmaleimide, N-methylmaleimide, N-ethylmaleimide, Nn-butylmaleimide, Nt-butylmaleimide, N- Benzylmaleimide, N-phenylmaleimide, N- (2-chlorophenyl) maleimide, N-
(4-chlorophenyl) maleimide, N- (4-bromophenyl) maleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N
-(2-methoxyphenyl) maleimide, N- (2,4,6
-Trimethylphenyl) maleimide, N- (4-benzylphenyl) maleimide, and the like. N-cyclohexylmaleimide, Nt-butylmaleimide, and N-arylmaleimide are considered in consideration of the balance between hygroscopicity and heat resistance. preferable. In particular, when N-arylmaleimide is selected, the following formula It is desirable to use at least one selected from the group consisting of:

In the present invention, the content of the N-substituted maleimide unit in the copolymer is in the range of 5 to 60% by weight, preferably 5 to 20% by weight. On the other hand, if it exceeds 60% by weight, the copolymerizability decreases, the amount of unreacted monomer increases, and the ratio of improvement in heat resistance tends to decrease, and the mechanical properties of the obtained base material decrease. Come.

Further, an aromatic vinyl compound can be copolymerized in the copolymer of the present invention in a range of up to 15% by weight. As the aromatic vinyl compound that can be used in the present invention, styrene, o-, m-, p-methylstyrene, 1,3-dimethylstyrene, 2,4-dimethylstyrene, pt-butylstyrene, α-methyl Monovinylidene aromatic hydrocarbons such as styrene, α-ethylstyrene, α-methyl-p-methylstyrene, o-, m-, p-chlorostyrene, 2,4-dibromostyrene, and 2-methyl-4-chlorostyrene Alhalomonovinylidene aromatic hydrocarbons and the like. Among them, at least one selected from the group consisting of styrene, vinyltoluene, and α-methylstyrene is preferable, and α-methylstyrene having a large effect of improving heat resistance is particularly preferable. The aromatic vinyl compound is preferably used in a molar ratio of 2 or less to the N-substituted maleimide, more preferably 1.5 or less.

The copolymer of the present invention can be easily obtained by copolymerizing the above-mentioned monomer components. As the polymerization, any method such as solution polymerization and bulk polymerization can be adopted, but bulk polymerization is particularly suitable.

As a polymerization initiator for producing the copolymer of the present invention, a polymerization initiator used for ordinary radical polymerization is used. For example, azobisisobutyronitrile, 2,
An azo-based initiator such as 2'-azobis (2,4-dimethylvaleronitrile), benzoyl peroxide, t-butyl peroxy 2-ethylhexanoate, lauroyl peroxyside, decanoyl peroxyside, etc. An oxide or the like can be used. When lauroyl peroxide or decanoyl peroxide is used, the obtained copolymer is excellent in transparency, hot water whitening property, and the like, and is particularly preferable.

In addition, it is preferable to use a chain transfer agent during the copolymerization, and examples thereof include alkyl mercaptans such as butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, and t-dotesyl mercaptan.

Further, a preferred method for producing the copolymer of the present invention is a cast polymerization method. For example, two cast endless stainless steel endless belts running opposite to each other and an integrated continuous soft vinyl chloride gasket running at the same speed on both side portions of the endless belt are used to obtain the cast polymer. After forming the molding space so as to make the thickness constant, and continuously injecting the monomer or partial polymer of the above-mentioned component subjected to the defoaming treatment and passing through the first polymer region at 40 to 90 ° C. , 110-135
A colorless and transparent plate can be obtained by passing through a second polymerization zone and a slow cooling zone at ° C. If necessary, the plate can be pulverized, and a beret can be obtained while removing volatile components with a vented extruder.

Further, as a particularly preferred method of obtaining a copolymer having excellent transparency, a continuous bulk polymerization method of uniformly polymerizing at a constant temperature in the range of 50 to 150 ° C. and then removing volatile components using a degassing extruder is used. Can be adopted.

Although the present invention is not limited thereto, it is preferable that the residual monomer is 1% by weight or less, particularly preferably 0.5% by weight or less, in the copolymer obtained as described above. If the amount of the residual monomer exceeds 1% by weight, silver-like defects are likely to occur depending on molding conditions. N
When the remaining monomer of the substituted maleimide is further supplemented, the content is preferably 0.5% by weight or less, more preferably 0.3% by weight.
If the content is less than 0.5% by weight, contamination of the mold is likely to occur, and the obtained base material tends to have poor long-term storage stability.

The melt flow rate of the copolymer is ASTM-D1238
It is preferably in the range of 1 to 40 g / 10 minutes as measured at a load of 3.8 kg based on the above. If the melt flow rate is less than 1 g / 10 minutes, the transferability of information from the mold is poor, and the birefringence tends to increase. On the other hand, if it is larger than 40 g / 10, the mechanical strength tends to decrease.

Further, the heat resistance of the copolymer of the present invention is preferably 105 ° C. or more as measured at a load of 18.56 kg based on ASTM-D648. One of the reasons is that, when aluminum is deposited in the disk manufacturing process, heat is required because heat is applied, and heat resistance is required in practical use if the heat resistance is lower than 105 ° C. This is because there is a concern that the body may be deformed when exposed to high temperatures, and therefore, better body heat resistance is required.

Further, the copolymer of the present invention preferably has a water absorption in water at 20 ° C. of less than 1.8%. When the water absorption is 1.8% or more, the amount of warpage due to moisture absorption of the base material tends to increase.

Further, in the present invention, a general formula R ₁ COOR ₂ (R ₁ , R ₂ has 5 to 20 carbon atoms) as a releasing agent in 100 parts by weight of the copolymer described above.
At least one of fatty acid monohydric alcohol ester, stearyl alcohol, cetanol and glyceryl stearate represented by the formula:
It is preferable to add from 0.05 to 2.0 parts by weight. If the amount of the release agent is less than 0.05 parts by weight, the releasability is poor, and if it is more than 2.0 parts by weight, the heat distortion temperature tends to decrease. More preferably, it is 0.1 to 0.5 part by weight. General formula R ₁ COOR ₂ (R ₁ , R ₂
Represents an alkyl group having 5 to 20 carbon atoms). Specific examples of the fatty acid monohydric alcohol ester represented by the formula include stearyl stearate, lauryl stearate, isotridecyl stearate, stearyl palmitate, myristyl myristate, and the like. The acid glycerin ester includes a monoester, a diester and a triester.

As a method of mixing the above-described release agent, for example, a method of adding the above-mentioned monomer mixture or a partial polymer thereof and polymerizing it favorably in the presence of a polymerization initiator or blending with a copolymer And the like, but in the present invention, the former is preferred.

If necessary, a stabilizer, a lubricant, a plasticizer, a dye, and the like can be added to the copolymer of the present invention.

〔Example〕

Hereinafter, the present invention will be described specifically with reference to examples. In each example, “parts” indicates “parts by weight”. In addition, the measurement of each characteristic value was performed by the following method.

Heat distortion temperature (HDT) Measured under a load of 18.56 kg (264 psi) according to ASTM-D648.

 Melt flow rate (MFR) Measured under a load of 3.8 kg according to ASTM-D1238.

Tensile strength / tensile elongation Measured using a dumbbell A-type test piece according to ASTM-D638.

Thermal decomposition resistance Using a Nikko V17-65 injection molding machine, cylinder temperature 280
A 2 mm × 110 mm × 110 mm plate was formed at 50 ° C. and a cycle of 50 seconds, and silver strips were visually judged.

Releasability Using a famous machine Dynamelter injection molding machine, use
1.2mm, diameter 300mm, track spacing 1.6mm, track width 0.5
μm, using a disk with a track groove depth of 0.3μm, molding at a cylinder temperature of 290 ° C, a mold temperature of 85 ° C, and a cycle of 45 seconds, the number of disk defects (cracks, etc.) in 20 shots It was checked and evaluated.

Light transmittance The transmittance in the wavelength region from 500 nm to 900 nm was measured with a Hitachi spectrometer 330.

Birefringence The birefringence (single pass) was measured at a distance of 75 mm from the center of the same disk used for the releasability evaluation.

The test piece used for the water absorption was immersed in water at 20 ° C., and the saturated water absorption was measured.

The base material prototyped in the warpage measurement was fixed to a vapor deposition apparatus, and aluminum was vapor-deposited under a high vacuum by a conventional method to cover the protective film. Then, the two substrates were bonded together with an adhesive to produce a disk.
Using this disk, the maximum amount of warpage between the central portion and the outer peripheral portion was measured under the conditions of 50 ° C. and 80% RH.

Residual monomer amount Residual monomer in the pellet was measured by gas chromatography using a conventional method.

Example 1 50 parts of methyl methacrylate, phenyl methacrylate
30 parts, N-cyclohexylmaleimide 20 parts, n-octylmercaptan 0.3 part and azobisisobutyronitrile
A mixture consisting of 0.1 part by weight of methyl methacrylate and 2 parts
-Sulfoethyl methacrylic acid sodium salt copolymer
0.005 parts, mixed with 150 parts of pure water in which 0.5 parts of sodium sulfate were dissolved, charged in a pressure-resistant polymerization kettle equipped with a jacket, stirrer, and thermometer and polymerized at 80 ° C. After the internal temperature reached a peak, 120
After cooling at 30 ° C. for 30 minutes, cooling, washing with water, washing with methanol, and drying.After blending 100 parts of the obtained bead polymer and 0.5 part of monoglycerol stearate, 250 parts were extruded with a PCM-30 extruder manufactured by Ikegai Iron Works. After shaping at 10 ° C and 10 mmHgabs pressure, pelletization was performed. When various evaluations were performed using the obtained pellets, the results shown in Table 1 were obtained. The amount of residual monomer in the pellet was 0.35%. Further, the light transmittance was 91% or more over all wavelengths, and the heat decomposition resistance was good without any silver strip defect.

Comparative Example 1 98 parts of methyl methacrylate, methyl acrylate 2
Parts, a mixture consisting of 100 parts of a mixture consisting of 0.3 parts of n-octylmercaptan and 0.1 part of azobisisobutyronitrile was used, and the resulting polymer had a water absorption of 2.2 parts. The warpage in% was 1350μ.

Example 2 Example 2 was carried out in the same manner as in Example 1 except that the amount of n-octyl mercaptan was changed to 0.2 part. MFR of the obtained polymer
Was 0.7, and the releasability was almost good, with 2 defectives out of 20 shots.

Example 3 It carried out like Example 1 except having added 0.02 part of monoglycerin stearate. The releasability was almost good, with 3 defectives out of 20 shots.

Examples 4-6, Comparative Examples 2-3 The monomer charge composition of Example 1 and the type of release agent
The results were as shown in Table 2 when carried out in exactly the same manner as in Example 1 except that the types and proportions shown in the table were used. The birefringence was 25 nm or less in each of Examples 4 to 6. The light transmittance of Examples 4 to 6 was 90% or more in all measured wavelength regions. Further, the residual monomer content in any of the pellets of Examples 4 to 6 was less than 0.3%, and the residual monomer content in the base material was less than 0.6%.

Reference Example 1 A pellet was obtained in exactly the same manner as in Example 5 except that 1.0 part of stearic acid was used as a release agent. This pellet
When 10 g was put into a weighing bottle together with a test piece of HPM-17, a general steel material for molds manufactured by Hitachi Metals, Ltd., and heated in a gear oven at 250 ° C. for 1 hour, corrosion of the steel material was observed.

〔The invention's effect〕

The information recording medium substrate of the present invention has high heat resistance, low hygroscopicity, low dimensional stability, excellent mechanical strength, optical properties, heat decomposition resistance, and mold release properties, especially optical type. It can be suitably used as a base material for an information recording medium, and has excellent industrial effects.

Claims (4)

(57) [Claims] 1. A methyl methacrylate unit of 10 to 85% by weight,
An information recording medium base material comprising a copolymer having 10 to 60% by weight of phenyl methacrylate unit, 5 to 60% by weight of N-substituted maleimide unit and 0 to 15% by weight of aromatic vinyl compound unit. 2. The information recording medium according to claim 1, wherein the N-substituted maleimide is at least one selected from the group consisting of Nt-butylmaleimide, N-cyclohexylmaleimide, and N-arylmaleimide. Substrate. 3. Methyl methacrylate unit 10-85% by weight,
For 100 parts by weight of a copolymer having 10 to 60% by weight of a phenyl methacrylate unit, 5 to 60% by weight of an N-substituted maleimide unit and 0 to 15% by weight of an aromatic vinyl compound unit, the general formula R ₁ COOR ₂ (R ₁ , R ₂ represents an alkyl group having 5 to 20 carbon atoms) at least one compound selected from the group consisting of fatty acid monohydric alcohol ester, stearyl alcohol, cetanol and glyceryl stearate represented by the following formula: Base material for information recording medium. 4. The information recording medium according to claim 3, which is at least one member selected from the group consisting of N-substituted maleimidoga Nt-butylmaleimide, N-cyclohexylmaleimide, and N-arylmaleimide. Base material.