JPH0616327B2 - Optical information recording substrate made of methacrylic resin - Google Patents

Description

TECHNICAL FIELD The present invention relates to a methacrylic resin having a low hygroscopic property, which is suitable for an optical recording substrate for optically recording and reproducing information.

(Prior art) A method of detecting recorded information engraved with fine irregularities on a disk substrate by using a laser beam spot, reproducing an image or sound, and further, an optical property of a recording film provided on the substrate surface. Recently, a recording / reproducing system for performing high-density information recording / reproducing has attracted attention.

In addition to being transparent, the disk substrate used in such a recording / reproducing system is required to have characteristics such as good dimensional stability, optical homogeneity, and small birefringence.
Although it is possible to mold a large number of duplicate substrates at low cost by using a resin material as the disc substrate,
It is widely known that molecular orientation occurs in the process of resin flow and cooling during the molding of a disk substrate to cause birefringence, which is a fatal defect in an optical disk substrate due to birefringence.

Since molecular orientation during molding is unavoidable especially in injection molding, the only resin material with low optical anisotropy suitable for optical disk substrate molding is a polymer containing methyl methacrylate as a main component. The current situation.

However, when a conventionally known polymer containing methyl methacrylate as the main component is used for the substrate, the dimensional stability is poor due to its high hygroscopicity, and warping and twisting occur in a humid environment. It has drawbacks. This drawback is described in detail in, for example, Nikkei Electronics (June 7, 1982, p. 138). Therefore, an aromatic polycarbonate resin having a low moisture absorption rate is used as a compact disk material for acoustics. Has been.

On the other hand, since aromatic polycarbonate resin contains a highly anisotropic aromatic ring in its main chain, it is difficult to reduce the birefringence of the molded substrate. However, since the birefringence is due to the material itself, it is not possible to consistently produce a substrate with low birefringence, and the diameter is larger than that of a compact disc for acoustic use. It is extremely difficult to manufacture a substrate by injection molding.

Further, in order to improve the dimensional stability which is a drawback of the polymer mainly containing methyl methacrylate, for example, JP-A-57-3
JP-A-3446, JP-A-57-162135, and JP-A-58-88843 propose a copolymer of methyl methacrylate and an aromatic vinyl monomer. However, a copolymer with a vinyl monomer having an aromatic ring is likely to cause birefringence and is practically unusable.

Further, JP-A-58-5318 and JP-A-58-127.
No. 754 discloses a copolymer with cyclohexyl methacrylate for reducing hygroscopicity without deteriorating birefringence, but cyclohexyl methacrylate is used as an aromatic compound for reducing hygroscopicity. Since it is necessary to carry out a large amount of polymerization as compared with vinyl monomers, there arises a problem that heat resistance and material strength are lowered.

Although further excellent birefringence and dimensional stability are required for a disc substrate capable of not only reproducing information but also recording, a resin material that can sufficiently satisfy these requirements has not yet been found. Absent.

(Problems to be Solved by the Invention) In view of such a problem to be solved by the present invention, that is, the object of the present application, the birefringence is low even by injection molding, compression molding, etc., and heat resistance and mechanical strength are low. Has a good balance of
It is an object of the present invention to provide an optical information recording substrate made of a methacrylic resin having excellent dimensional stability.

(Means for Solving the Problems) The present invention provides (a) phenyl methacrylate alone or phenyl methacrylate and the general formula (In the formula, R represents a linear or branched hydrocarbon group having 8 to 20 carbon atoms or an alicyclic hydrocarbon group having 6 to 12 carbon atoms.)
30 to 90% by weight of a mixture with at least one methacrylic acid ester represented by
The present invention relates to a methacrylic resin optical information recording substrate obtained by copolymerizing 0 to 70% by weight, and (c) 0 to 10% by weight of another unsaturated compound copolymerizable therewith.

The monomer (a) used in the present invention is more hydrophobic than the monomer (b) (methyl methacrylate).

The monomer (a) is phenyl methacrylate alone or a mixture of phenyl methacrylate and a specific methacrylic acid ester represented by the above general formula.

Examples of the specific methacrylic acid ester represented by the above general formula include n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, 2
-Ethylhexyl methacrylate, cyclohexyl methacrylate, methylcyclohexyl methacrylate, adamantyl methacrylate, bornyl methacrylate,
Examples thereof include isobornyl methacrylate, fentyl methacrylate, 1-menthyl methacrylate, tricyclo [5.2.1.0 ^2,6 ] -dec-8-yl methacrylate and the like.

The ratio of the (a) monomer used in the present invention is 30 to 9
It is preferably 0% by weight, more preferably 35 to 70% by weight. If the proportion of the monomer (a) used is less than 30% by weight, the hygroscopicity of the resulting resin will not be sufficiently improved, and if it exceeds 90% by weight, the mechanical strength of the resin will decrease, which is not preferable.

(a) The content ratio of phenyl methacrylate in the monomer is 30.
It is preferably ˜100% by weight. When the content of phenyl methacrylate as the monomer (a) is less than 30% by weight, the heat resistance and mechanical strength of the obtained resin are lowered, which is not preferable.

(a) As the monomer, when a combination of phenyl methacrylate and the specific methacrylate represented by the above general formula is used, a glass of a polymer obtained from the monomer excluding phenyl methacrylate from the combination. Transition temperature is 8
It is preferable to select the combination so that the temperature is 0 ° C. or higher.

In the present invention, the proportion of the monomer (b), methyl methacrylate, used is preferably 10 to 70% by weight.

If the proportion of the monomer (b) used is less than 10% by weight, the mechanical strength of the obtained resin is low, and if it exceeds 70% by weight, the proportion of the relatively hydrophobic monomer (a) is reduced. However, the hygroscopicity of the obtained resin is not sufficiently improved, which is not preferable.

In the present invention, the monomers (a) and (b) and the other unsaturated compound (c) copolymerizable therewith may be mixed and used within a range that does not reduce the effects of the present invention. The proportion of the monomer (c) used is preferably 10% by weight or less. Examples of the monomer (c) include alkyl acrylates such as methyl acrylate, ethyl acrylate and butyl acrylate; vinyl compounds such as styrene and acrylonitrile. Methyl acrylate, ethyl acrylate, butyl acrylate and the like are particularly preferable as those which improve the thermal decomposition resistance of the methacrylic resin.

The method for producing the low hygroscopic methacrylic resin of the present invention may be any polymerization method such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization. When the resin is obtained as a sheet material, the bulk polymerization by a casting method is carried out, and when the molding material is intended, the bulk polymerization, suspension polymerization or emulsion polymerization method is preferable from the viewpoint of workability and productivity. It is preferable that no foreign matter is mixed into the polymer, and if necessary, it is desirable to remove dust and the like from the monomer in advance by filtration, distillation or the like and then carry out the polymerization. In the post-treatment after the polymerization, it is preferable to avoid mixing of foreign matters. From this point, the bulk polymerization and the suspension polymerization are particularly preferable as the polymerization method.

When the suspension polymerization method or the emulsion polymerization method is adopted, the radical polymerization initiator and the monomer mixture to which a chain transfer agent is added for controlling the molecular weight are dispersed in water in which a suspension dispersant or an emulsifier is dissolved. Polymerize. In the case of the bulk polymerization method by the casting method, a partial polymer is first prepared from a monomer mixture mixed in a predetermined ratio, poured into a glass or stainless cell, and polymerization is carried out for several hours.

Examples of the radical polymerization initiator include 2,2′-azobis (isobutyronitrile), 1,1′-azobis (cyclohexanecarbonitrile), 2,2′-azobis (2,4-dimethylvaleronitrile) and azo. Azo compounds such as bisisobutanol diacetate, and lauroyl peroxide, di-tert-butyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, di-tert-butyl perphthalate, di-tert-butyl peracetate, di- Organic peroxides such as tert-amyl peroxide may be mentioned.

In producing the methacrylic resin of the present invention for a molding material, it is necessary to adjust the molecular weight so that the melt index value at a melting temperature of 230 ° C. and a load of 3.8 kg is 1.5 to 30 g / 10 g. preferable. In this case, when the melt index value is 1.5 or less, the birefringence cannot be sufficiently low when molding the information recording medium substrate, and when the melt index value exceeds 30, the mechanical strength decreases. Not preferable.

Further, when the sheet material is obtained by the casting method, there is no molecular orientation at the time of molding and there is no fear of birefringence, so that the melt index value may be 30 or less.

The molecular weight is controlled by adding a chain transfer agent to the polymerization system. Examples of the chain transfer agent include n-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan and the like.

In the case of the casting method, as described above, there is no fear of birefringence, and therefore a method in which no chain transfer agent is used is preferable in order to obtain a resin having a molecular weight as high as possible and mechanical strength as high as possible.

If necessary, other polymers may be mixed with the methacrylic resin obtained by the method of the present invention, and an oxidative stabilizer, a weather resistance stabilizer, a coloring agent, a release agent, etc. may be added. You may add and use an agent.

(Examples) Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Among the physical property measuring methods in Examples, the total light transmittance and the haze value are ASTM D1003 for a sample having a thickness of 3 mm, the bending strength is ASTM D790, and the heat distortion temperature is ASTM D64.
It measured according to 8. The water absorption rate was measured according to ASTM D570 by measuring the water absorption rate in 60 ° C. distilled water for 24 hours. Also, the melt index is 23 according to ASTM D1238.
It was measured at 0 ° C. and a load of 3.8 kg.

For birefringence, retardation was measured by a Senarmont compensator method at 546 nm using a polarization microscope.

Example 1 3000 g of pure water was placed in 5 reactors equipped with a stirrer, and 2 g of polyvinyl alcohol as a suspension stabilizer was added and dissolved. Separately, 970 g of methyl methacrylate, 580 g of cyclohexyl methacrylate, 44 of phenyl methacrylate
A solution prepared by dissolving 4 g of n-dodecyl mercaptan as a chain transfer agent and 6 g of lauroyl peroxide as an initiator in a monomer mixture of 0 g and 60 g of ethyl acrylate was added to a reactor, and polymerization was performed while stirring at a temperature of 80 ° C. went. After about 1.5 hours, an increase in reaction temperature was observed, and then polymerization was carried out at 98 ° C for 3 hours. The obtained polymer was dehydrated, washed with water and dried, and then pelletized at a cylinder temperature of 240 ° C.

Physical property test pieces were prepared using these pellets, and the results shown in Table 2 were obtained. Cylinder temperature 270 ° C, mold temperature 6
Injection molding was performed at 0 ° C. to prepare a disc-shaped test piece having a diameter of 120 mm and a thickness of 1.2 mm. 30 from the center of the obtained molded product
The birefringence at the position of mm and the water absorption of the disk were measured.

Comparative Examples 1 to 8 Polymerization was carried out in the same manner as in Example 1 except that the monomer composition was changed as shown in Table 1 to obtain a methyl methacrylate copolymer. Physical properties were measured in the same manner as in Example 1, and the results are shown in Table 2.

Example 2 Methyl methacrylate 970 was prepared in the same manner as in Example 1.
g, bolinyl methacrylate 388 g, phenyl methacrylate 582 g, and ethyl acrylate 60 g were polymerized to obtain a copolymer. The physical property values are shown in Table 3.

Example 3 Methyl methacrylate 780 was prepared in the same manner as in Example 1.
g, tricyclomethacrylate [5.2.1.0 ^2,6 ]
-Deca-8-yl, 660 g, phenyl methacrylate 5
A monomer mixture of 00 g and butyl acrylate 60 g was polymerized to obtain a copolymer. The physical property values are shown in Table 3.

Example 4 A three-separable flask equipped with a stirrer was charged with a monomer mixture of 350 g of methyl methacrylate and 650 g of phenyl methacrylate, and 0.1 g of azobisisobutyronitrile was dissolved as an initiator, and the mixture was heated at 80 ° C. for 1 hour. Polymerization gave a partially polymerized product. 3 g of lauroyl peroxide was dissolved as an initiator in this partially polymerized product, and the mixture was degassed and poured into a mirror-finished stainless steel cell, which was then heated at 80 ° C. for 1 hour at 120 ° C.
Was reacted for 2 hours to obtain a sheet polymer having a thickness of 1.2 mm.

The total light transmittance of this sheet was 92%, the haze value was 0.9, the water absorption rate was 0.64%, and the birefringence was 3 nm or less.

Comparative Example 4 In the same manner as in Example 4, 350 g of methyl methacrylate,
Polymerization was carried out by injecting a monomer mixture of 650 g of cyclohexyl methacrylate into a stainless cell.
The strength was weak because a phenomenon that it was easily damaged was observed during cooling or after taking out the sheet.

(Effects of the Invention) According to the method of the present invention, low moisture absorption, good dimensional stability,
A transparent resin having a good balance of heat resistance and mechanical strength can be obtained, and the birefringence is low even by injection molding, and a good molded product can be obtained.

In particular, the inventors of the present invention have diligently studied the relationship between the birefringence of the substrate obtained by molding the resin material and the structure of the resin material used, and as a result, the specific polymer using phenyl methacrylate was found to be polystyrene or the like. Like polystyrene, which has a large photoelastic constant in the glass state and is likely to cause birefringence during molding, it is possible to obtain a substrate with low birefringence by injection molding, unlike polystyrene. Moreover, the copolymer using phenyl methacrylate is superior in mechanical strength to the conventionally known copolymer using a methacrylic acid ester having an alicyclic hydrocarbon group, such as cyclohexyl methacrylate. Found.
The resin obtained by the method of the present invention can be suitably used as a substrate for recording optical information.

Continuation of front page (56) Reference JP-A-59-182408 (JP, A) JP-A-56-69625 (JP, A) JP-A-54-11950 (JP, A) JP-A-49-66789 (JP , A) Actual development Sho 58-5318 (JP, U) Actual development Sho 58-127754 (JP, U)

Claims (1)

[Claims] 1. (a) Phenyl methacrylate alone, or phenyl methacrylate and the general formula (In the formula, R represents a linear or branched hydrocarbon group having 3 to 20 carbon atoms, or an aliphatic hydrocarbon group having 6 to 12 carbon atoms.) Mixture 30 with at least one methacrylic acid ester To 90% by weight, (b) 10 to 70% by weight of methyl methacrylate, and (c) 0 to 10% by weight of another unsaturated compound copolymerizable with them, made of a methacrylic resin obtained by copolymerization Optical information recording substrate.