JPH04254928A - Methacrylic resin for optical information recording medium - Google Patents

Abstract

PURPOSE:To enhance the heat resistance, flowability and productivity of the resin for a substrate without deteriorating the optical characteristic by using a methacrylic resin consisting of methyl methacrylate and isobornyl acrylate. CONSTITUTION:This resin consists of 80-99.5wt.% of a methyl methacrylate unit (A) and 20-0.5wt.% of an isobornyl acrylate unit (B). When the unit A is controlled to >99.5%, the mol.wt. has to be lowered to maintain its flowability, and hence the mechanical strength is reduced. Meanwhile, when the unit B exceeds 20%, the mechanical strength is remarkably lowered. Besides, the melt flow rate and heat-deflection temp. of the resin are preferably specified.

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 reduced heat resistance and reduced 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 isobornyl 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 isobornyl acrylate unit content exceeds 20% by weight, the mechanical strength will be significantly inferior.

Further, the melt flow rate (MFR) of the methacrylic resin of the present invention is preferably in the range of 0.5 to 50 g/10 min as measured under a load of 3.8 kg based on ASTM-D1238. MFR is 0.5g/10
If it is smaller than 50 g/10 min, the transferability of information from the mold will be poor and the optical distortion of the molded product will increase, while if it is larger than 50 g/10 min, the mechanical strength will tend to decrease.

[0011] 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. can also be added to the methacrylic resin of the present invention, if necessary.

The methacrylic resin of the present invention thus obtained can be molded into a substrate by either injection molding or compression molding.

[0014]

[Examples] The present invention will be specifically explained below with reference to Examples. Note that "parts" in the examples indicate "parts by weight." In addition, the measurement of each physical property value was performed by the following method. ■Heat distortion temperature (HDT) Measured under a load of 18.56 kg according to ASTM-D648. ■Melt flow rate (MFR) Measured under a load of 3.8 kg according to ASTM-D1238. (2) Tensile strength and tensile elongation A dumbbell type test piece was injection molded using an injection molding machine (PS-60E, manufactured by Nissei Plastics Co., Ltd.), and measured according to ASTM-D638. ■Light transmittance injection molding machine (M-200 Dynamelta, manufactured by Meiki Seisakusho)
A φ300 mm disk (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 disk molded product was measured using Shimadzu Corporation;
It was measured in the region of 500 to 900 nm using UV-160A. ■Birefringence■ Birefringence at a point 7 cm from the center of the disc molded product obtained using a polarizing microscope (Nikon, OPTIPHOT-
POL, SENARMONT COMPENSATO
R: Usage wavelength 546nm, single pass)
It was measured by

Examples 1 to 4 0.35 parts of n-octyl mercaptan was dissolved in 100 parts of a monomer mixture of methyl methacrylate and isobornyl acrylate in the proportions shown in Table 1, and 0.35 parts of lauroyl peroxide was added as a polymerization catalyst. 44 parts, stearyl alcohol 0.1 part as a mold release agent, 0.01 part copolymer of methyl methacrylate and potassium 3-methacryloyloxypropanesulfonate as a suspension polymerization dispersant, 0.15 part sodium sulfate, dispersion medium 145 parts of water was mixed into a glass flask polymerization apparatus equipped with a stirrer and a thermometer, and 80
After polymerization was carried out at 95° C. and the internal temperature reached a peak, the mixture was kept at 95° C. for 30 minutes, cooled, filtered, washed with water, and dried to obtain a bead-like copolymer.

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.

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

Comparative Examples 1 to 4 Experiments were carried out 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 isobornyl 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. The results are shown in Table 1.

[0019] The copolymer obtained by copolymerizing 30 parts of isobornyl acrylate and 70 parts of methyl methacrylate (Comparative Example 3) lacks practicality due to its weak mechanical strength. The polymer obtained by polymerizing the part (Comparative Example 4) had an MFR of 22.5 g/1
0 minutes, and the fluidity was almost the same as in Example 2, but the tensile strength was less than half, and it lacked practicality.

From the results of Examples 1 to 4 and Comparative Examples 1 to 2, the relationship between MFR and HDT is as shown in FIG.
When trying to obtain a copolymer with an FR of 20 g/10 min,
It can be seen that the copolymer of methyl methacrylate and isobornyl acrylate exhibits an approximately 7° C. improvement in HDT than the copolymer of methyl methacrylate and ethyl acrylate.

Furthermore, when trying to obtain a copolymer with an HDT of 85°C, the copolymer of methyl methacrylate and isobornyl acrylate has a MFR of about 12 g/10 compared to the copolymer of methyl methacrylate and ethyl acrylate.
It can be said that the copolymer of methyl methacrylate and isobornyl acrylate has better moldability than the copolymer of methyl methacrylate and ethyl acrylate in terms of productivity.

[0022]

[Table 1]

[0023]

[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 MFR.

Claims (1)

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