JPS63234009A - Methacrylic resin composition - Google Patents

Abstract

PURPOSE:To obtain the titled composition outstanding in transparency, heat resistance and molding processability, useful for disc substrates, etc., by polymerization between methyl methacrylate, substituted phenyl maleimide monomer and another copolymerizable vinyl monomer in specified proportion. CONSTITUTION:The objective composition can be obtained by polymerization at 50-95 deg.C in the presence of generally a radical polymerization initiator, between (A) 55-98(pref. 65-90)wt.% of methyl methacrylate, (B) 2-45(pref. 10-30)wt.% of a substituted phenyl maleimide monomer of formula (R1 and R2 are each 1-3C alkyl) (e.g., N-2,6-diethylphenyl maleimide, N-ethyl-6- methylphenyl maleimide) and (C) 0-40(pref. 0-20)wt.% of another vinyl monomer copolymerizable therewith (e.g. acrylic acid, styrene).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a methacrylic resin that has excellent transparency, heat resistance and moldability and is extremely useful as a disk substrate and an optical lens.

(Prior art) Generally, polymethyl methacrylate resin or methacrylic resin containing methyl methacrylate as a main component has a transparency of 9.
Surface Glossiness 9 Due to its excellent properties such as mechanical strength and moldability, demand for it as a material for optical elements such as optical fibers, optical lenses, and optical disks has been increasing in recent years. However, due to its poor heat resistance, as represented by its heat distortion temperature, its use is limited in applications that require shape stability at high temperatures, and research has been widely conducted to improve the heat resistance of methacrylic resins. For example, an optical disk substrate made of a copolymer with improved heat resistance by copolymerizing methyl methacrylate with a maleimide monomer (Japanese Patent Laid-Open No. 61-950)
No. 11).

(Problems to be Solved by the Invention) The copolymer obtained according to the above publication maintains the excellent properties originally possessed by methacrylic resin and has improved heat resistance, but the resulting base exhibits a yellow color. Furthermore, increasing the maleimide content certainly improves heat resistance, but it also has the disadvantage of increasing coloration and extremely poor light transmittance and birefringence. It is not fully satisfactory for applications that require excellent light transmittance and birefringence, such as optical disk substrates and optical lenses in optical disk memory systems such as optical video disks, digital audio disks, and image file disks. There wasn't.

(Means for Solving the Problem) In view of the current situation, the present inventors have attempted to solve the problem immediately (as a result of extensive research, they have developed a resin composition consisting of methyl methacrylate and a specific substituted phenylmaleimide). However, it is possible to maintain the mechanical properties, light transmittance, birefringence, and transparency that methacrylic resin alone has, and to increase heat resistance, and this substituted phenylmaleimide is also excellent in safety. They discovered this and completed the present invention.

That is, the present invention comprises 55 to 98% by weight of methyl methacrylate and 2 to 45% by weight of a substituted phenylmaleimide monomer represented by the general formula (wherein Rr and Rz each represent an alkyl group having 1 to 3 carbon atoms). This is a methacrylic resin composition obtained by polymerizing 0 to 40% by weight of another vinyl monomer copolymerizable with these monomers.

The method for producing a copolymer obtained by copolymerizing methyl methacrylate and a maleimide monomer used in the present invention was disclosed in the Japanese Patent Publication No. 4
It is known from Japanese Patent No. 3-9753.

Specifically, the substituted phenylmaleimide monomer represented by the general formula (1) of the present invention includes, for example, N-2,6-dimethylphenylmaleimide, N-2゜6-dinitylphenylmaleimide, Examples include N-2-ethyl-6-methylphenylmaleimide and N-2゜6-dipropylphenylmaleimide, and among them, 2,6-dinitylphenylmaleimide is suitable for workability and physical properties of molded products. Examples of copolymerizable vinyl monomers that are particularly preferred and excellent in terms of stability include acrylic acid, methacrylic acid, methyl acrylate, ethyl methacrylate, styrene, α-methylstyrene, and P-methyl styrene. Examples include methylstyrene and acrylonitrile.

The copolymer used in the present invention is methyl methacrylate 5
It is necessary to contain 5 to 98% by weight, preferably 65 to 90% by weight. 55% by weight of methyl methacrylate
If the amount is less than 2 to 45% by weight, preferably 10 to 45% by weight, the substituted phenylmaleimide monomer represented by general formula (1) is undesirable because transparency, birefringence, and mechanical strength decrease.
It is necessary to contain 30% by weight. 'When the amount of substituted phenylmaleimide monomer is less than 2% by weight, heat resistance decreases,
When the content exceeds 45% by weight, there is a practical problem because mechanical strength and high temperature moldability decrease. In addition, other vinyl monomers that can be copolymerized with these monomers range from 0 to 40
If the vinyl monomer is contained in an amount of more than 40% by weight, problems with transparency and coloring may occur, which is undesirable. It can contain a light stabilizer such as an absorber and a heat stabilizer such as an antioxidant.

The methacrylic resin composition of the present invention can be polymerized according to a commonly known method.

For example, various methods such as suspension polymerization, bulk polymerization, emulsion polymerization, and solution polymerization of the polymerization components can be used in the presence of a radical polymerization initiator in a temperature range of 50 to 95°C. At this time, in addition to the initiator, a chain transfer agent, a usual suspending agent, an auxiliary agent, etc. can also be used. Furthermore, the methacrylic resin composition thus obtained is injection molded into discs and optical lenses having shapes and sizes depending on the purpose.

It can be molded by a method such as compression molding.

(Effects) By selecting 2,6-dialkyl-substituted phenylmaleimide as a monomer to be copolymerized with methyl methacrylate, the present invention achieves the mechanical strength, moldability, light transmittance, and birefringence that methacrylic resin alone has. Furthermore, this 2゜6-dialkyl-substituted phenylmaleimide can maintain its transparency and improve its heat resistance.
−.

-It has extremely low toxicity compared to methylphenylmaleimide and the like, and is also superior in handling safety.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 90 parts of methyl methacrylate, 10 parts of N-2,6-diethylphenylmaleimide and 0.5 part of azobisisobutyronitrile were mixed and heated in a container. A resin composition was obtained by filling a cell with two glass plates (distance: 0.32 cm) with the produced syrup and keeping it at 75°C for 6 hours and then at 95°C for 2 hours.

Examples 2-6. Comparative Examples 1 to 4 Resin compositions having the type of maleimide and the proportion of each monomer of Example 1 shown in Table 1 were manufactured.

(Physical properties of molded articles) Obtained in Examples 1 to 6 and Comparative Examples 1 to 4. A methacrylic resin composition was injection molded, and its physical properties were measured according to the following methods. The results are shown in Table-1.

○Heat deformation resistance (HDT) Measured according to ASTM-D648.

○Light transmittance Measured according to JIS-6714.

○Birefringence injection molding (cylinder temperature 260℃, mold temperature 60℃)
The measurement was carried out using a precision strain meter using a plate with a thickness of 1.2 mm+ obtained by the above method.

Example 7 70 parts by weight of methyl methacrylate, 30 parts by weight of N-2,6-diethylphenylmaleimide, and 1 part by weight of azobisisobutyronitrile were charged with 65 parts by weight of benzene as a solvent in a polymerization can, and the polymerization temperature was set at 60%. Polymerization was carried out at ℃ for 13 hours.

The obtained polymer solution was vacuum dried to remove the solvent, and then extruded using an extruder with a vacuum vent at an extrusion temperature of 305° C. and a vent vacuum degree of IQ+u+Hg to obtain pellets. Example 8. Comparative Examples 5 to 6 Pellets were obtained in the same manner as in Example 4, using various substituted phenylmaleimides shown in Table 2 instead of N-2,6-dinitylphenylmaleimide used in Example 4.

(Physical properties of molded products) The pellets obtained in Examples 7 and 8 and Comparative Examples 5 and 6 were injection molded to prepare methyl methacrylate resin test pieces, and each physical property was measured according to the following method. Display the results -
Shown in 2.

○HDT (heat deformation resistance) Measured according to ASTM-D648.

○MFI (melt flow index) JIS-ni-7
Measured according to 210, but at a temperature of 250℃ and a load of 5kg.
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○Without creating yellowness pellets, a polymerized powder obtained by pouring the polymerization solution into methanol was used as a sample. This was heated at 280"C for 5 minutes using a press molding machine, and then molded into a flat plate of [l thickness]. Using this, measurement was carried out according to JIS-7103.The measurement was carried out by the reflection measurement method, and a standard white plate was placed on the flat plate.

Claims (1)

[Claims] Methyl methacrylate 55 to 98% by weight, represented by the general formula ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, R_1 and R_2 each represent an alkyl group having 1 to 3 carbon atoms.) A methacrylic resin composition obtained by polymerizing 2 to 45% by weight of a substituted phenylmaleimide monomer and 0 to 40% by weight of another vinyl monomer copolymerizable with these monomers.