JPS61103911A - Low-warpage acrylic resin-based disc plate - Google Patents

Abstract

PURPOSE:To provide the titled article of practical value such as low-warpage due to creep, low-level coloring, etc., based on an acrylic copolymer of specific composition made up of methyl methacrylate, o-methylphenyl maleimide, etc. CONSTITUTION:The objective article can be obtained by using as a base, a copolymer made up of (A) 43-95wt% of methyl methacrylate unit, (B) 2.5-40wt% of O-methylphenyl maleimide unit, (C) 0.5-2.5wt% of acrylonitrile unit, and (D) 2-15wt% of methacrylonitrile unit. For pref. the production of said copolymer, the above monomers are subjected, using a polymerization initiator such as azobisisobutylonitrile and chain transfer agent such as butyl mercaptan, to suspension polymerization at -95-50 deg.C.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a self-extensible acrylic resin disc,
More specifically, by using a specific copolymer,
This invention relates to a disc that has excellent practical performance and reduces warping due to creep, which is the biggest drawback of polymethyl methacrylate discs. Recently, discs such as video discs and audio discs for recording and reproducing information have been developed and put into practical use in line with the demands of the information society and other areas. In order to record and reproduce information signs using a semiconductor laser or the like, these discs are made of a base made of transparent resin by injection molding or compression molding, and aluminum is vapor-deposited on the recording surface.
Further, a protective film is formed thereon.

(Prior Art) As such base resins, resins such as polyvinyl chloride, polystyrene, polymethyl methacrylate, and polycarbonate have been proposed. However, all of them have drawbacks in terms of moldability and birefringence, and among them, polymethyl methacrylate can be used for limited purposes. Generally, a substrate molded by injection molding or compression molding has high birefringence depending on the orientation during molding. If birefringence increases, it will have a negative effect on reproduced sound quality and images, so a resin that can provide a substrate with as little birefringence as possible and has good moldability is advantageously used. Polymethyl methacrylate has a lower intrinsic birefringence than other resins and has good moldability, so it is a relatively hard material resin in that molding orientation is suppressed.

(Problem to be solved by the invention) However, when providing a substrate on which information signs are recorded, especially as an audio disc or a DRAW (Direct Read After Write) disc, an anti-phenomenon of deformation into an umbrella shape is observed, making it impossible to put it into practical use. It has certain defects.

The cause of this phenomenon is considered to be warpage due to creep of the resin base of the formed disk.

Providing a base that does not cause such warping is an important technical issue in this technical field, and is also highly desired in order to improve the quality of discs.

(Means and effects for solving the problems) As a means to solve the above problems, the present inventors filed a patent application for a specific acrylic resin with significantly improved heat deformation resistance (Japanese Patent Application
8-149178). Furthermore, the present inventors aimed to find a resin for the base that does not cause troubles caused by solvent-resistant cracks that occur during the manufacturing process of disk disks, and also does not cause surface defects due to thermal decomposition of the resin during disk disk formation. As a result of extensive research, it has been discovered that an acrylic resin with a specific composition provides suitable properties for a disk substrate, and the present invention has been completed.

That is, the present invention provides methyl methacrylate units 43-9
5111%, 0-methylphenylmaleimide units 2.5
-40% by weight, 0.5-2.5% by weight of acrylonitrile units, and 2-15% by weight of methacrylonitrile units.

The copolymer itself consisting of methyl methacrylate and O-methylphenylmaleimide is disclosed in Japanese Patent Publication No. 43-9753. However, this copolymer has 2
．． Contains 0-5.0% by weight of unpolymerized monomer, which causes poor surface appearance (silver), poor coloring, etc. during high-temperature injection molding. For this reason, its use was limited to general use, and it could not be used for optical I-disk discs that require high-temperature injection molding.

The copolymer used for the disc of the present invention has excellent heat deformation resistance, heat decomposition resistance, solvent resistance, and high temperature moldability, and also has good transparency and is an extremely excellent material as a base material for a disc.

The copolymer used in the present invention must contain 43-95% by weight, preferably 60-90% by weight of methyl methacrylate units. 43 methyl methacrylate units
When the amount is less than % by weight, the transparency and mechanical strength are significantly reduced, which is a practical problem.

The 0-methylphenylmaleimide unit, which is a copolymerization component, is 2.5-40! It is necessary that it be contained in an amount of i%, preferably 10-30% by weight. If the content of 0-methylphenylmaleimide units is less than 2.5% by weight, one of the effects of the present invention, which is improvement in heat deformation resistance, cannot be achieved;
If it is used in excess of this amount by weight, it becomes very difficult to reduce the residual monoyar, resulting in problems such as inability to perform high-temperature molding and significant discoloration, making it impossible to put it to practical use.

Acrylonitrile and methacrylonitrile, which are other components of the copolymer, must be used in combination, with the acrylonitrile unit being 0.5-2.5% by weight, and the methacrylonitrile unit being 2-15% by weight, preferably an acrylonitrile unit. The content of methacrylonitrile units is 1-2% by weight, and 5-10% by weight of methacrylonitrile units. If the acrylonitrile unit content is less than 0.5% by weight, one of the effects of the present invention, which is improved solvent resistance and improved mechanical properties, cannot be achieved even if the metaxolonitrile unit contains 15% by weight. However, if it is used in an amount exceeding 2.5% by weight, coloration due to the nitrile group will be severe and it cannot be put to practical use.

The copolymer component methacrylonitrile unit is 2% by weight.
If the amount is less than 2.5% by weight, even if 2.5% by weight of acrylonitrile units are used, one of the effects of the present invention is improved solvent resistance.
cannot be exerted, and if it is used in excess of 15% by weight←
is undesirable because mechanical properties deteriorate and the polymerization rate slows down, resulting in a decrease in productivity.

Furthermore, it is desirable that the copolymer used in the present invention generates less silver during disk molding and that the resulting disk has less coloring.

As such a copolymer, a copolymer with a small amount of residual monomer in the pellet during disk molding is desirable.

Copolymers that can be used in the disc of the present invention include:
Methyl methacrylate, 0-methylphenylmaleimide,
It is a copolymer of acrylonitrile and methacrylonitrile, and it is desirable that the residual monomer in the pellet before making the disk disk is 0.6% by weight or less, and 0.6% by weight.
If it exceeds 0.8% by weight, the surface appearance of the disc tends to be impaired (silver generation), and the residual monomer in the obtained disc exceeds 0.8% by weight, which is not preferable. In particular, residual acrylonitrile and 0-methylphenylmaleimide are undesirable because they cause polymer coloring.

When copolymerizing with butylphenylmaleimide, chlorophenylmaleimide, nitrophenylmaleimide, etc. instead of 0-methylphenylmaleimide, copolymerization is poor and residual monomer increases, causing problems such as yellowish coloration. . It also has the fatal defect of not being able to be molded at high temperatures.

In the copolymer of the present invention, a copolymerizable monomer such as acrylic ester or styrene may be used as a third component within a range that does not deteriorate the properties of the disc.

As the polymerization initiator for producing the resin according to the present invention, polymerization initiators used in ordinary radical polymerization can be used. For example, azobisisobutyronitrile, 2.
Azo initiators such as 2-azobis(2,4-dimethylvaleronitrile), peroxides such as benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, etc. can be used. Further, in the copolymerization, it is preferable to use a chain transfer agent, and examples thereof include alkyl mercaptans such as butyl mercaptan and octyl mercaptan.

Preferred methods of the production method of the present invention include suspension polymerization, emulsion polymerization, solution polymerization, and bulk polymerization. Particularly preferred is a suspension polymerization method, at 50-95°C.
The desired copolymer can be obtained by polymerization using the above-mentioned initiator, chain transfer agent, and conventional suspending agents and auxiliary agents at a temperature in the range of .

(Example) Hereinafter, the details of the invention will be specifically explained with reference to Examples.

Melt index (MI) is ASTM-D123
8. Is the tensile strength ASTM-D? 90, heat deformation resistance (
HDT) was measured according to ASTM-D648.

The residual monomer was measured by gas chromatography according to a conventional method.

Solvent resistance test Physical property test piece obtained using a 3 oz injection molding machine (L6
QXL9×3m) was conditioned in an atmosphere of 23° C. and 50% relative humidity. The moisture content of the test piece was 0.5% by weight. Soaked in isopropyl alcohol at 23°C for 2 hours,
The state of crank occurrence was observed.

The percentages in the table are by weight. .

Example 1 83 parts by weight of methyl methacrylate, 10 parts by weight of 0-methylphenylmaleimide, 2 parts by weight of acrylonitrile, 5 parts by weight of methacrylotrile, 0.20 parts by weight of azobisisobutyronitrile, 0.26 parts by weight of octyl mercaptan. A monomer solution consisting of
The mixture was suspended in a suspension phase consisting of 50 parts by weight and 1 part by weight of potassium polymethacrylate, heated water was passed through the jacket, and polymerization was started at a polymerization temperature of 80°C. 180 minutes after the start of polymerization, the polymerization temperature was raised to 95°C. The mixture was warmed and the reaction was continued for an additional 300 minutes to complete the reaction. The obtained polymer is cooled, washed, dried,
Beads with a diameter of 0.3n were obtained. These beads were extruded using a 30 mm diameter extruder with a vent at a temperature of 305°C and a vacuum degree of 30°C.
It was pelletized under conditions of mlg. The obtained pellet was injection molded using an injection molding machine (M-200/8000M manufactured by Meiki Seisakusho), and a 30 (
A base having a diameter of 1.2 m and a thickness of 1.2 m was obtained. The injection molding temperature was 290° C., and the injection pressure and speed were high pressure and high speed. This substrate was fixed to a vapor deposition apparatus, and aluminum vapor deposition was performed under a vacuum of IQ-'mHg.

After the vapor deposition was completed, a protective film was applied using a conventional method, and the two substrates were bonded together using an adhesive.

The disc test was conducted at a temperature of 50° C. and a relative humidity of 90% for 10 hours. To measure the reversal, the distance from the center of the disk to a plane passing through at least two points on the outer periphery of the disk was measured every time, and the maximum amount of reversal was taken as the reversal.

Tensile test and HDT measurement Using the obtained pellet, 3 oz injection molding was performed to prepare a physical property test piece. (160x19x3mm). It was measured according to a conventional method.

The results are shown in the table.

Example 2-7, Comparative Example 1-6 Copolymers having various heptad compositions shown in the table were produced in the same manner as in Example 1. In this way, discs of a copolymer according to the present invention (Example 2-7) and a copolymer different from the present invention (Comparative Examples 1-6) were obtained in the same manner as in Example 1. The physical properties of the copolymer and the characteristics of the disk are shown in the table.

Example 8 In Example 1, polymerization was carried out at 95° C. for 60 minutes to complete the reaction. The obtained beads were formed into pellets using a 30 mψ vented extruder. The usual extrusion conditions were that the degree of vacuum in the vent was 150 n+Hg and the extrusion temperature was 240°C. The residual monomer content of the obtained pellet was 1.1% by weight. A disk was produced by injection molding in the same manner as in Example 1.

The solvent resistance and crankability of the disc were good, and the resistance was 300μ. The remaining upper limit of the disc is 1.
It was 65% by weight, and some silver generation was observed.

Comparative Example 7 - 70 parts by weight of methyl methacrylate, 2 parts of methacrylonitrile
Polymerization was carried out in the same manner as in Example 1, except that 0 parts by weight and 10 parts by weight of O-methylphenylmaleimide were used as monomers. Polymerization was carried out at 80°C for 12 hours and at 95°C for 1 hour. The results obtained are shown in the table.
1 or less margin

Claims (1)

[Claims] A copolymer consisting of 43-95% by weight of methyl methacrylate units, 2.5-40% by weight of O-methylphenylmaleimide units, 0.5-2.5% by weight of acrylonitrile units, and 2-15% by weight of methacrylonitrile units. A disc that serves as the base.