JPS6195011A - Optical disk substrate - Google Patents

Abstract

PURPOSE:The titled substrate useful as video disk, etc., having improved heat resistance, transparency, and small refractive index, obtained by copolymerizing methyl methacrylate with a specific maleimide monomer and another vinyl monomer copolymerizable with these monomers in a specific ratio. CONSTITUTION:55-98wt%, preferably 75-95wt% methyl methacrylate is copolymerized with 2-25wt%, preferably 5-20wt% maleimide monomer shown by the formula (R is H, 1-20C alkyl, or aryl) and 0-40wt%, preferably 0-20wt% monomer mixture (preferably acrylic acid), to give the aimed substrate.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to an optical disc substrate.

More specifically, the present invention relates to an optical disk substrate that has excellent heat resistance and transparency, and low birefringence.

<Conventional technology> In general, plastic materials are lightweight, have excellent impact resistance, processability, and mass productivity, so in recent years optical fibers,
Demand for materials for optical elements such as optical lenses and optical discs is increasing. Currently, transparent resins such as polymethyl methacrylate, polystyrene, and polycarbonate are mainly used as plastic materials for these optical elements (Japanese Patent Publication No. 8978/1989).

<Problems to be Solved by the Invention> However, polymethyl methacrylate and polystyrene have poor heat resistance, typified by heat distortion temperature, and therefore have the problem of not being able to withstand use under high temperature conditions. Further, although polycarbonate has excellent heat resistance, it has poor melt flowability, resulting in poor moldability and high birefringence due to molding distortion.

In particular, extremely high precision is required for optical disk substrates in optical disk memory systems such as optical video disks, digital audio disks, and image file disks, so the disk substrate materials must have higher heat resistance and transparency. In particular, it is required that the birefringence be sufficiently small.

However, a substrate material that satisfactorily satisfies these requirements has not yet been found, and therefore no optical disc substrate that satisfactorily satisfies these requirements has been found.

As a result of intensive studies aimed at providing a high-precision optical disc substrate that satisfies the above requirements, the present inventors found that an optical disc made of a copolymer of a specific composition obtained from methyl methacrylate and a specific maleimide monomer. It was discovered that the substrate material has excellent heat resistance and transparency, and low birefringence, and the present invention was achieved.

Means and operation for solving the problem> That is, the present invention provides methyl methacrylate 55 to 98:1 liffi%
, below (maleimide monomers 2 to 2 represented by formula 11)
The present invention provides an optical disc substrate made of a copolymer obtained by polymerizing a monomer mixture consisting of 5% by weight and 0 to 40% by weight of other vinyl monomers copolymerizable with these monomers. .

(2) (In formula (I), R represents a hydrogen atom, a substituted or unsubstituted alkyl group or aryl group having 1 to 20 carbon atoms.

) In the present invention, an optical disc is a memory device that records and/or reproduces information using light.

Specific examples include optical video discs, digital audio discs, and image file discs. This also includes magneto-optical disks.

The copolymer obtained by copolymerizing methyl methacrylate and maleimide spinning wheel used in the present invention is known (for example, Japanese Patent Publication No. 43-9753).

The copolymer used in the present invention (hereinafter referred to as a maleimide copolymer) contains 55 to 98% by weight of methyl methacrylate, preferably 75 to 95% by weight, and a maleimide monomer represented by the following formula (I). 2-25% by weight, preferably 5
It is a copolymer obtained by polymerizing a monomer mixture consisting of ~20 MFk% and 0 to 40% by weight, preferably 0 to 20% by weight of other vinyl monomers copolymerizable with these monomers.

CH2=CH2 In the formula (1), R represents a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, or an aryl group.

Therefore, the leimide copolymer used in the present invention has 55
-98% by weight of methyl methacrylate units, 2-25% by weight of N-unsubstituted or substituted maleimide units represented by the above formula (I), and 0-40% by weight of the other vinyl monomers. It is a copolymer containing units derived from.

The maleimide monomer is not particularly limited as long as it satisfies formula (I), but preferred specific examples include maleimide, N-methylmaleimide, N-ethylmaleimide,
Examples include N-t-butylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, and the like. The vinyl monomer is not particularly limited as long as it can be copolymerized with methyl methacrylate and/or the above maleimide monomer, but preferred specific examples include acrylic acid, methacrylic acid, (Meth)acrylic acid (ester) spinning wheel ffi, such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, and cyclohexyl methacrylate
Examples include aromatic vinyl-based single flHEs such as styrene, α-methylstyrene, and p-methylstyrene, maleic anhydride, and acrylonitrile.

The proportions of methyl methacrylate and maleimide monomers in the monomer mixture are as described above.

If the content of methyl methacrylate is less than 55% by weight or the content of the maleimide monomer exceeds 25% by weight, transparency will be poor and birefringence will be large, which is not preferred. Methyl methacrylate exceeds 98% by weight or maleimide monomer
If it is less than % by weight, the heat resistance will be poor, which is not preferable. If the amount of other vinyl monomers exceeds 40% by weight, the effects of the present invention will not be sufficiently exhibited, which is not preferable.

There are no particular limitations on the method of polymerizing the maleimide copolymer, and the polymerization can be carried out by a commonly known method (for example, the method described in Japanese Patent Publication No. 43-9753). That is,
Polymerization can be carried out by maintaining the above monomer mixture at a predetermined temperature condition in the presence or absence of a radical-generating initiator. Various methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization can be used.

There is no particular restriction on the degree of polymerization of the maleimide copolymer of the present invention, but when molding a disk substrate by injection molding, it is necessary to have good melt flowability, and in that case, dimethyl formaldehyde is used in 1. The intrinsic viscosity ([η]) measured at 30°C is preferably 0.15 to 0.50.

The optical disc substrate of the present invention can be manufactured by a conventional method. That is, the maleimide copolymer of the present invention can be used to mold disc substrates of predetermined shapes and dimensions according to purposes such as video discs, audio discs, and image file discs by methods such as injection molding and compression molding. be able to. Alternatively, it can also be manufactured using the cast 1 method. By subjecting the substrate to predetermined processing and treatment, the desired optical disc can be manufactured.

Injection molding is usually used as a molding method for the disk substrate. That is, molding can be carried out using an injection molding machine with a cylinder temperature of 180 to 300°C, preferably 200 to 280°C, and a mold temperature of 30 to 120°C, preferably 50 to 95°C.

The optical disc substrate of the present invention can contain light stabilizers such as ultraviolet absorbers, heat stabilizers such as antioxidants, and the like. Further, other combinations may be contained in a mixed state within a range that does not impair the effects of the present invention.

<Examples> Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Hereinafter, heat distortion temperature, light transmittance, refractive index and birefringence used in Examples and Comparative Examples were measured according to the following methods.

Heat Distortion Temperature: Measured according to ASTM D-648-56.

Light transmittance: Measured using an integrating sphere type light transmittance measuring device in accordance with JIS K6714 using a 3.0H thick test piece.

Refractive index (no): Measured using an Atsube refractometer according to ASTM D542 50+c.

Birefringence: Diameter 1200, thickness L2ff by injection molding
A disk substrate was molded using a center gate mold having the shape of , and the birefringence at a position 200 degrees from the center of the disk substrate was measured using a Toshiba Precision Strainmeter 5VP-30 manufactured by Toshiba Glass Co., Ltd.

Example (Manufacture of maleimide copolymer) 0.5 parts by weight of azobisisobutyronitrile was added to 100 parts by weight of the monomer mixture having the composition shown in Table 1, dissolved, and 6 parts by weight were added at 75°C. Maleimide copolymers (M-1 to M-7) were obtained by polymerizing for 2 hours at 95°C.
Manufactured by gamma.

Table 1 (Measurement of physical properties using molded products) Maleimide copolymers thus produced (M-1 to M-
5) was injection molded to form each test piece and disk substrate, and each physical property was measured. The results are shown in Table 2.

Injection molding was carried out by setting the cylinder temperature of the molding machine to 260'C1 and the mold temperature to 60°C.

Comparative example (comparison with other polymers) M-6, M-7, “Stylon 666 (Asahi Kasei Corporation)
ff polystyrene), “Acryvet VH” (acrylic resin manufactured by Mitsubishi Rayon Co., Ltd.) and Kneepilon H400
0 (Ho II carbonate manufactured by Mitsubishi Gas Chemical Co., Ltd.) was also measured for each physical property in the same manner as in the examples.

Only the molding of UPIO:/H4000 was carried out at a cylinder temperature of 320°C and a mold temperature of 80°C.

From the results of Examples and Comparative Examples, the following is clear. That is, the maleimide copolymers of the present invention (M-1 to M
-5) has excellent heat deformation temperature, excellent transparency, and low birefringence. On the other hand, a disk substrate made of polymethyl methacrylate (M-6, Akrivet VH) has a low heat distortion temperature. Polystyrene (Styron 6
66) has poor thermal deformation temperature and birefringence. A disk substrate made of polycarbonate (Nipilon H4000) has a high heat deformation temperature, but has a large birefringence. Furthermore, a maleimide copolymer having a maleimide monomer content of more than 25% by weight is not preferred because of poor transparency and birefringence.

<Effects of the Invention> As explained above, the optical disc substrate made of the maleimide copolymer of the present invention has excellent heat deformation temperature and transparency.
At the same time, birefringence is small, and the balance between these is superior to that of conventional optical plastic disk substrates.

Claims (1)

[Claims] 55 to 98% by weight of methyl methacrylate, 2 to 25% by weight of a maleimide monomer represented by the following formula (I), and other vinyl monomers copolymerizable with these monomers. Body 0~
An optical disc substrate made of a copolymer obtained by polymerizing a monomer mixture containing 40% by weight. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) (In formula (I), R represents a hydrogen atom, a substituted or unsubstituted alkyl group or aryl group having 1 to 20 carbon atoms.)