JPH04236209A - Methacrylic resin for optical information recording unit - Google Patents

Abstract

PURPOSE:To provide a methacrylic resin useful as an information recording unit. CONSTITUTION:A methacrylic resin is composed of 80-99.5wt.% methyl methacrylate unit and 20-0.5wt.% benzyl acrylate unit and useful as an information recording unit. The objective methacrylic resin, excellent in heat resistance and fluidity and useful as the information recording unit is obtained while holding improved optical characteristics essentially possessed by the methacrylic resin.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a methacrylic resin useful for optical information recording media such as video discs.

0002

[Prior Art] Methacrylic resin has excellent moldability and transparency, and exhibits useful optical properties, so it is known that it can be used in various optical devices.Recently, its excellent properties have been used to make video discs, etc. Used as a substrate for optical information recording media.

Substrates for optical information recording media are required to have low optical distortion, excellent heat resistance, and moldability, and in recent years, there has been a strong desire to improve the productivity of video discs, that is, to shorten the molding cycle. desired.

A copolymer of methyl methacrylate and ethyl methacrylate (Japanese Unexamined Patent Publication No. 123208/1983) has been proposed as a methacrylic resin for optical information recording media.

[0005]

[Problems to be Solved by the Invention] However, when the fluidity of the above-mentioned copolymer is improved, the optical distortion decreases;
On the other hand, it has been difficult to improve productivity because of the disadvantages of decreased heat resistance and decreased mechanical strength.

Currently, optical information recording substrates, especially video disks and audio disks, are mainly manufactured by injection molding, but when considering the productivity, the heat resistance and fluidity of the resin make it difficult to The molding cycle has been determined. In order to improve productivity in injection molding, optical distortion is small, excellent transparency, and heat resistance is improved to reduce resin fluidity and cooling time during injection molding without sacrificing mechanical strength. It is necessary to let
Existing molding materials have a problem in that improving their heat resistance is accompanied by a decrease in fluidity and mechanical strength.

[0007]

[Means for Solving the Problems] In view of the current situation, the inventors of the present invention have conducted intensive studies to provide a material for optical information recording media that does not have the above-mentioned problems.
We have arrived at the present invention.

That is, the present invention is a methacrylic resin for information recording media comprising 80 to 99.5% by weight of methyl methacrylate units and 20 to 0.5% by weight of benzyl acrylate units.

The copolymerization ratio of the methacrylic resin of the present invention is as described above, and outside this range, the mechanical strength of the molded article
It is not possible to combine this with productivity during mass production. That is, if the content of methyl methacrylate units exceeds 99.5% by weight, the molecular weight must be lowered in order to maintain the fluidity of the resin, resulting in a decrease in mechanical strength. On the other hand, if the benzyl acrylate unit content exceeds 20% by weight, the mechanical strength will be significantly inferior.

[0010] Furthermore, the heat deformation temperature of the methacrylic resin of the present invention is AS
The temperature is preferably 70°C or higher, more preferably 80°C or higher, as measured under a load of 18.56 kg based on TM-D648. If the heat distortion temperature is lower than 70°C, the heat resistance of the molded product will be poor, and in particular, heat distortion during molding and use will become large, which may be undesirable.

For producing the methacrylic resin of the present invention, conventional methods for producing methacrylic resins such as suspension polymerization, bulk polymerization, and solution polymerization can be used. Stabilizers, mold release agents, lubricants, plasticizers, dyes, etc. may be added to the methacrylic resin of the present invention as required.The methacrylic resin of the present invention thus obtained can be used for injection molding, compression Molding The substrate can be formed by any method.

0012

[Examples] The present invention will be specifically explained below with reference to Examples. Note that "%" and "parts" in the examples indicate "% by weight" and "parts by weight", respectively. In addition, the measurement of each physical property value is
It was done in the following way. 1) Heat distortion temperature (HDT) Measured under a load of 18.56 kg according to ASTM-D648. 2) Melt flow rate (MFR) ASTM-D123
Measurement was performed with a load of 3.8 kg according to 8. 3) Tensile strength, tensile elongation injection molding machine (Nissei Plastics, PS
-60E), a dumbbell type A test piece was injection molded, and A
Measured according to STM-D638. 4) Light transmittance injection molding machine (M-200 manufactured by Meiki Seisakusho)
φ300mm disc (1.2
mmt) was injection molded at a cylinder temperature of 260°C, and the transmittance at a point 7 cm from the center of the obtained disc molded product was measured using UV-160A manufactured by Shimadzu Corporation.
It was measured in the area of m. 5) Birefringence 7 from the center of the disc molded product obtained in 4)
The birefringence at the cm point was measured using a polarizing microscope (Nikon, OPT
IPHOT-POL, SENARMONT COMP
ENSATOR: Usage wavelength 546nm, single
pass).

Examples 1 to 3 0.35 parts of n-octyl mercaptan was dissolved in 100 parts of a monomer mixture of methyl methacrylate and benzyl acrylate in the proportions shown in Table 1, and 0.44 parts of lauroyl peroxide was added as a polymerization catalyst. , 0.1 part of stearyl alcohol as a mold release agent, 0.01 part of a copolymer of methyl methacrylate and potassium 3-methacryloyloxypropanesulfonate as a suspension polymerization dispersant, and 0.01 part of sodium sulfate.
15 parts and 145 parts of water as a dispersion medium were mixed into a glass flask polymerization apparatus equipped with a stirrer and a thermometer, and polymerized at 80°C. After the internal temperature reached a peak, it was held at 95°C for 30 minutes and then cooled. A bead-like copolymer was obtained by filtration, washing with water, and drying.

The obtained copolymer was kneaded and pelletized at 240° C. using a 40 mm extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.). When the obtained pellets were used for various evaluations, the results shown in Table 1 were obtained.

[0015] In all Examples, the light transmittance was 91% or more in the wavelength range of 500 to 900 nm, and the birefringence was 20 nm or less, which was good.

Comparative Examples 1 to 4 Experiments were conducted in exactly the same manner as in Example 1, except that 100 parts by weight of a monomer mixture of methyl methacrylate and ethyl acrylate or benzyl acrylate in the proportions shown in Table 1 was used. In Comparative Example 4, the amount of n-octyl mercaptan used was 0.62 parts. Table 1 shows the results.
Shown below.

[0017] The copolymer obtained by copolymerizing 30 parts of benzyl acrylate and 70 parts of methyl methacrylate (Comparative Example 3) lacks practicality due to its weak mechanical strength.
In addition, a polymer obtained by polymerizing 100 parts of methyl methacrylate (Comparative Example 4) has an MRF of 22.5 g/10 minutes, and has almost the same fluidity as Example 2, but has half the tensile strength. It was below and lacked practicality.

From the results of Examples 1 to 4 and Comparative Examples 1 to 2, the relationship between MRF and HDT is as shown in FIG.
When trying to obtain a copolymer with an RF of 30 g/10 min,
It can be seen that the copolymer of methyl methacrylate and benzyl acrylate exhibits an approximately 4° C. improvement in HDT than the copolymer of methyl methacrylate and ethyl acrylate.

In addition, when trying to obtain a copolymer with an HDT of 80°C, the copolymer of methyl methacrylate and benzyl acrylate has a higher MRF rate of about 10 g/10 minutes than the copolymer of methyl methacrylate and ethyl acrylate. Improvement was observed, and it can be said that the copolymer of methyl methacrylate and benzyl acrylate has better moldability than the copolymer of methyl methacrylate and ethyl acrylate in terms of productivity.

[0020]

[Table 1] MMA: Methyl methacrylate BA: Benzyl acrylate EA: Ethyl acrylate

[0021]

[Effects of the Invention] The methacrylic resin for optical information recording media of the present invention is a molding material with excellent heat resistance, good fluidity, and productivity while retaining the excellent optical properties inherent to methacrylic resin. Because it can be suitably used as
It has excellent industrial effects.

[Brief explanation of the drawing]

FIG. 1: HD of the methacrylic resin of the present invention and the conventional copolymer of methyl methacrylate and ethyl acrylate.
It shows the relationship between T and MRF.

Claims (1)

[Claims] [Claim 1] Methyl methacrylate units 80-99
．． 5% by weight and 20 to 0.5% by weight of benzyl acrylate units.
Methacrylic resin for information recording media consisting of 5% by weight.