JP2571787B2 - Method for producing molded article with improved releasability - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a molded article including a disk substrate from a methacrylic partial polymer having remarkably improved releasability.

(Prior art) Methacrylic resin utilizes its excellent optical properties to make optical video discs, digital audio discs,
It is being used or developed as a substrate material for information recording disks for computers. However, a methacrylic resin containing methyl methacrylate as a main component has a large hygroscopic property and involves problems such as dimensional change and warpage of a molded article. However, there is a problem such as an increase in birefringence due to the distortion, and no satisfactory material has been proposed as a substrate material of an information recording disk requiring high quality. The inventors of the present invention have conducted intensive studies in view of the above-mentioned drawbacks, and as a result, have found that a methacrylic partial polymer composed of a monoethylenically unsaturated monomer having an alkyl methacrylate as a main component and a polyfunctional crosslinking monomer has been obtained. By hardening under pressure and heating conditions in a molding die, monoethylenically unsaturated monomers that could not be used in the conventional injection molding due to their birefringence can be used. You've got the foundation. (JP-A-60-258219, JP-A-61-83213)
And JP-A-61-142546. However, in the above-described method for manufacturing a disk substrate, the improvement of the releasability is required to reduce the defect rate and improve the productivity because the presence of a very small mold release defect or cracking of the substrate leads to the possibility of use as a disk substrate. It has emerged as an indispensable issue for improvement.

(Problems to be Solved by the Invention) In the stage of studying and solving the above problems, the present inventors have not only improved the releasability in the manufacture of disk substrates, but also the releasability of other molded products. The inventors have found that the composition has remarkably hardening for improvement, and have come to propose the present invention.

(Means for Solving the Problems) That is, the present invention provides a methacrylic partial polymerization comprising an ethylenically unsaturated monomer containing an alkyl methacrylate as a main component and having a viscosity at 25 ° C. of 1 to 1000 poise. Stuff
To 100 parts by weight of the general formula _{(C n H 2n + 1 O} ) m P (O) (OH) 3-m (A) A molded product having improved releasability, comprising adding 0.001 to 1.0 part by weight of an alkyl acid phosphate represented by the formula (1), and curing in a molding die under pressure and heating conditions in the presence of a radical polymerization initiator. It is a manufacturing method of.

(Action) As the alkyl methacrylate in the present invention, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, iso-propyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate Phenyl methacrylate, 2,4,6-trichlorophenyl methacrylate, 2,4,6-tribromophenyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate and isobornyl methacrylate, and the like. A superior amount is necessary in order to improve the polymerization rate and improve the releasability. Examples of ethylenically unsaturated monomers other than alkyl methacrylate include acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, and n-butyl acrylate, styrene, α-methylstyrene, and p-methyl acrylate. Examples include aromatic vinyls such as methylstyrene, vinyl cyanides such as acrylonitrile and methacrylonitrile, and maleimides such as phenylmaleimide, O-chlorophenylmaleimide and cyclohexylmaleimide. Examples of the polyfunctional crosslinking monomer include (poly) ethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) acrylate, divinylbenzene, alkyldiol di (meth) acrylate, Methylolpropane tri (meth) acrylate and the like are used, and the use ratio is 20% by weight or less, more preferably 1 to 10% by weight in the ethylenically unsaturated monomer.

The viscosity of the methacrylic partial polymer is 1 to 1000 poise (25
C. B type viscometer), more preferably 20 to 400 poise. If it is less than 1 poise, when it is cured in a molding die, the amount of heat generated by polymerization and the amount of polymerization shrinkage are large, so that bubbles are easily generated and the curing time is undesirably long. If the viscosity exceeds 1000 poise, it becomes difficult to handle, making it difficult to uniformly mix the radical polymerization initiator and shortening the pot life of the methacrylic partial polymer, which is not preferable.

The compounds of general formula _{(C n H 2n + 1 O} ) m P (O) (OH)
_The alkyl acid phosphate represented by _3-m (A) has n = 8 to 13 and m = 1. n ≦
When 7 and n ≧ 14, the effect of improving the releasability is sufficient but not sufficient, and partial peeling failure is likely to occur, and fatty acids, aliphatic alcohols or anionic surfactants generally used in methacrylic resins are generally used. It is necessary to use it in combination with a mold release agent. When n = 3, no effect of improving the releasability is recognized. Among these alkyl acid phosphates, (C ₈ H ₁₇ O) P of general formula (A) wherein n = 8 and m = 1
(O) (OH) ₂ is preferred.

The amount of addition is 0.001 to 1.0 part by weight, more preferably 0.01 to 0.2 part by weight, based on 100 parts by weight of the partial polymer. If the amount is less than 0.001 part by weight, the effect of improving the releasability is poor. If the amount is more than 1.0 part by weight, the effect of improving the releasability is very remarkable.

The alkyl acid phosphate of the present invention may be used in combination of two or more, or may be used in combination with a commonly used release agent.

The polymerization initiator used in the present invention is not particularly limited, but lauroyl peroxide, benzoyl peroxide, tert-butyl peroxypivalate,
tert-butylperoxy neodecanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxyisobutyrate, di-iso-propylperoxydicarbonate, di-2-ethylhexylperoxydi Organic peroxide initiators such as carbonates, 2,2 ′
-Azobisisobutyrate, dimethyl-2,2'-azobisisobutyrate, 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile) Azo initiators such as 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) and benzoyl peroxide with N, N-di (2-hydroxypropyl) -P-toluidine, N, N -Dimethyl-toluidine,
A redox initiator obtained by using a tertiary amine such as N, N-dimethylaniline in combination may be used.

Although the method of manufacturing a molded article according to the present invention differs depending on the shape of the molded article, a disk substrate will be described as an example. The curing conditions vary depending on the type and amount of the methacrylic partial polymer and the radical polymerization initiator.However, the pressure may be increased gradually with the curing, or the pressure may be increased at the stage where the curing is accelerated before the heat generation peak of the polymerization. There are methods, finally 5~200Kg / cm ^2, more preferably pressure conditions 30~150Kg / cm ² is suitable. Similarly, the temperature condition is 40 to 100
C., more preferably 50-90 C., and in some cases 10
It may be copolymerized at 0 to 150 ° C. The curing time is about 5 to 30 minutes.

The material of the molding die used in the present invention is not particularly limited as long as it is a steel material used for an injection molding die or a press molding die, a casting die such as stainless steel, and a disk. Of course, it is also possible to use a nickel stamper which is usually used as a stamper.

In the present invention, if necessary, mercaptans, dyes, pigments, ultraviolet absorbers, lubricants and the like can be used in combination as a chain transfer agent.

(Examples of the Invention) Hereinafter, the present invention will be described specifically with reference to examples.

The following abbreviations are used for ethylenically unsaturated monomers and general release agents used in the examples. [] Is an abbreviation.

Methyl methacrylate [MMA], tert-butyl methacrylate [t-BMA], cyclohexyl methacrylate (CHM
A], 2,4,6-Tribromophenyl methacrylate [TBPM
A], styrene [ST], phenylmaleimide [PMI], cyclohexylmaleimide [CHMI], neopentyl glycol dimethacrylate [NPG], polyethylene glycol dimethacrylate (the number of moles of ethylene glycol added is 4) [PEG4].

Stearic acid [SA], stearyl alcohol [SOH] The following abbreviations are used for the alkyl acid phosphate and the alkyl phosphate used in the examples.

_{(C n H 2n + 1 O} ) m P (O) (OH) 3-m Abbreviations: [A-n-m].

Examples 1 to 6 A methacrylic partial polymer (NPG) obtained by stopping a reaction during polymerization of an ethylenically unsaturated monomer having a different composition containing alkyl methacrylate as a main component.
A-8-1 0.03 based on 100 weight
Parts by weight and 0.3 parts by weight of 2,2'-azobis- (2,4-dimethylvaleronitrile) are added and mixed.
Molding mold for square tray of 4mm thickness (150W × 7
(0D × 35Hmm) and kept under pressure for 15 minutes to obtain a square tray after cooling. Table 1 shows the results.

Examples 7 to 9, Comparative Examples 1 to 6 75% by weight of methyl methacrylate and 20% by weight of monoethylenically unsaturated monomers other than methyl methacrylate of a different kind
The syrup obtained by stopping the reaction during the polymerization of the monomer mixture consisting of
By weight, a methacrylic partial polymer was obtained. 0.5 parts by weight of tert-butyl peroxypivalate and 100 parts by weight of this partial polymer were mixed with varying amounts and types of alkyl acid phosphate or other release agents, and after degassing, a predetermined amount was brought to 85 ° C. The mixture was poured into a 30-cm diameter disk-shaped molding die that had been adjusted in temperature, and was cured by holding it under pressure for 10 minutes. After cooling, a disk substrate having a thickness of 1.2 mm was obtained. Table 2 shows these results including the comparative examples.

(Effects of the Invention) According to the method of the present invention, a molded article press-molded under heating is released from a mold, that is, the releasing operation is extremely easily performed, and the molded article is released with the mold release. Sink on the surface of the
There is almost no cracking or cracking of the molded product. Furthermore, if the method of the present invention is applied to the production of discs for information recording carriers, high-quality discs can be produced easily in operation and at a high yield.

Claims (1)

(57) [Claims] 1. A methacrylic partial polymer having a viscosity of 1 to 1000 poise at 25.degree. (C _n H _{2n + 1} O) _m P (O) (OH) _3-m (A) A molded product having improved releasability, comprising adding 0.001 to 1.0 part by weight of an alkyl acid phosphate represented by the formula (1), and curing in a molding die under pressure and heating conditions in the presence of a radical polymerization initiator. Manufacturing method.