JPS6183213A - Disk base and its production - Google Patents

Abstract

PURPOSE:To produce an information recording disk having a low double refractive index and excellent mechanical strength, moisture resistance and solvent resistance, by curing a specified meethacrylate prepolymer in a mold. CONSTITUTION:A homogeneous methacrylate prepolymer (of a viscosity at 25 deg.C of 5-200 P) is formed by polymerizing 10-80 wt.% methyl methacrylate (a), 20-80 wt.% specified alkyl methacrylate (b), 0.3-10 wt.% crosslinking monomer (c) and 0-10 wt.% other monoethylenically unsaturated monomers (d) in the presence of a radical polymerization initiator and a chain transfer agent and stopping the reaction by cooling in the midst of the reaction. Said prepolymer and, if necessary, a radical polymerization initiator are poured into a mold and cured by post-polymerization by application of heat and pressure (about 40-100 deg.C, about 10-200 kg, about 5-30 min).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disk substrate and a method for manufacturing the same.

[Conventional technology]

Methacrylic resin is used as the substrate material for playback-only optical video discs for general home and business use, and polycarbonate resin is used as the substrate material for digital audio discs. Optical disks for large-capacity image files and large-capacity computer memories are being developed, and the industry's greatest concern is what is suitable for their substrate materials. Methacrylic resin, polycarbonate resin, and glass are considered likely. Among them, methacrylic resin is attracting particular attention because of its optical properties such as birefringence, mechanical strength, and moldability. Optical video discs for home use, etc. are for playback only, and the stamper inside the mold is made using the injection molding method.
Since the signal is directly transferred from the disc and two discs are bonded together with adhesive, problems such as dimensional changes and warpage due to moisture absorption are alleviated, and the birefringence is well within the allowable range. Methacrylic resin molding material is used as the substrate material because it has a value that falls within the range of On the other hand, optical discs for information recording are capable of recording, reproducing, and rewritable information, and require a lower birefringence because they are required to record and display signals with higher precision. Injection molded products made from methacrylic resin molding materials also have a modern feel, and include the vapor deposition and sputtering process of recording thin films on disk substrates, and the coating process of low moisture absorption films to prevent moisture absorption of substrates. It is necessary to improve the solvent resistance of the disk substrate because of the fact that the surface of the disk substrate must be cleaned with an organic solvent such as dust, dirt, and oil prior to the application of a coating solution of an organic recording material. Furthermore, the above-mentioned problem of hygroscopicity of methacrylic resin is fundamentally caused by the chemical structure of the monomers that make up the polymer. Improvements have been attempted, such as methyl methacrylate-cyclohexyl methacrylate copolymer (JP-A-58-5318, JP-A-58-12775).
No. 4), methyl methacrylate-benzyl methacrylate copolymer (JP 1185B-104939),
In both cases, the improvement has not been so great as to eliminate the coating process with a low hygroscopic film, and it is necessary to improve the solvent resistance, and the mechanical strength of the injection molded product obtained is reduced. The birefringence tends to increase, and improvements in heat resistance remain.

[Problem that the invention seeks to solve]

The present invention improves the drawbacks of the conventional methacrylic resins mentioned above, and uses methacrylic resins that have a low birefringence (maintains mechanical strength, and has improved moisture absorption resistance, properties, and solvent resistance) for information recording. The present invention aims to provide a disk substrate and a method for manufacturing the same.

[Means for solving problems]

For these purposes, 10 to 80% by weight of methyl methacrylate,
Specific methacrylic acid alkyl ester (mu) 20-80
Weight%, crosslinkable monomer (B) 0.3 to 10% by weight and monoethylenically unsaturated single stitched body θ which can be copolymerized with these
It consists of 10% by weight and has a viscosity of 5 to 200 boids (at 25°C).
, type B viscometer) is a homogeneous methacrylic partial polymer (
The problem is solved by a disk substrate characterized in that it is obtained by curing I).

Furthermore, these purposes are methyl methacrylate lO~80f
it%, specific methacrylic acid alkyl ester (A)2
0 to 80% by weight, 0.3 to 10% by weight of the crosslinkable monomer (B), and 0 to 10% by weight of a monoethylenically unsaturated monomer copolymerizable with these, and has a viscosity of 5 to 200% by weight. A disk substrate characterized in that a homogeneous methacrylic partial polymer (I) of BOYS (25° C., B-type viscometer) is cured in a mold under pressure and heat in the presence of a radical polymerization initiator. The problem is solved by the manufacturing method.

The ratio of methyl methacrylate used in the present invention is 10 to 80
% by weight, more preferably 30-70% by weight, and 10% by weight.
If % by weight is left ungrooved, the mechanical strength and thermal deformation temperature of the final disk substrate will decrease, which is undesirable.
If it exceeds 0% by weight, the moisture absorption resistance decreases, which is not preferable.

As the specific methacrylic acid alkyl ester (A),
At least one of ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate and isobornyl methacrylate, and the proportion of these methacrylic acid alkyl esters (A) used is preferably 20 to 80% by weight, more preferably is 30 to 70% by weight. If it is less than 20% by weight, moisture absorption resistance decreases, and 8
If it exceeds 0% by weight, mechanical strength and heat distortion temperature will decrease, which is not preferable.

Examples of the crosslinkable monomer (B) include polyethylene glycol di(meth)acrylate (polyethylene glycol has a molecular weight of 170 to 1020), neopentyl glycol di(
meth)acrylate, pentaerythritol(meth)acrylate and trimethylolpropane tri(meth)
It is necessary to use at least one type of acrylate, and the usage ratio is 0.3 to 10% by weight, more preferably 1 to 7% by weight. The type of crosslinking monomer greatly influences the mechanical strength and heat distortion temperature of the disc substrate obtained, and even in polyethylene glycol dimethacrylate, the molecular weight of polyethylene glycol is 17.
If the molecular weight of polyethylene glycol exceeds 1020, the resulting disk substrate will be easily cracked (mechanical strength will decrease significantly, and divinylbenzene and allyl methacrylate will show a similar tendency. If the molecular weight of polyethylene glycol exceeds 1020, the heat resistance of the disk substrate will decrease. This is undesirable because it makes it difficult to deposit a recording thin film onto the substrate.Furthermore, a crosslinkable monomer containing a phenyl group is undesirable because it increases the birefringence (the above-mentioned crosslinkable monomer (B)). If the usage rate is less than 0.3% by weight, the solvent resistance will not be improved, and cracks will easily occur in the disk substrate due to organic solvents.If it exceeds 10% by weight, the solvent resistance and heat resistance will be good, but there will be no improvement in solvent resistance. The resulting substrate has a high birefringence (which is not desirable as a substrate for the intended disk).

In addition, in the present invention, a monoethylenically unsaturated monomer copolymerizable with the above-mentioned monomers is optionally added in an amount of 0 to 1O 1ilt.
% may be used. These monoethylenically unsaturated monomers include methacrylic acid esters such as n-propyl methacrylate, n-7'thyl methacrylate, phenyl methacrylate, benzyl methacrylate, and cyclohexyl methacrylate, methyl acrylate, and acrylic acid. Acrylic acid esters such as ethyl, n-propyl acrylate, n-butyl acrylate, and cyclohexyl acrylate, aromatic vinyls such as styrene, α-methylstyrene, and p-methylstyrene, or acleantolyl, and methacrylic acid. ) vinyl cyanides such as lyl.

The method for manufacturing the disk substrate of the present invention includes methyl methacrylate, a specific alkyl methacrylate ester (A)
, a homogeneous methacrylic partial polymer (I) consisting of a crosslinkable monomer (B) and a monoethylenically unsaturated monomer copolymerizable with these monomers (I) is once produced; ) may be a partial polymer obtained by dissolving a monomer-soluble polymer in a monomer containing a crosslinking monomer, or a partial polymer obtained by stopping the reaction during polymerization, but Limited to partial polymers in which the polymer is uniformly dissolved in the monomer. Disk substrates obtained from partial polymers containing swollen polymers copolymerized with crosslinkable monomers or partial polymers in which polymers are non-uniformly dissolved have extremely high birefringence. In addition to this, the haze is also high, making it impossible to use it as a target disc substrate. The viscosity of the methacrylic partial polymer (I) is preferably 5 to 200 voids (25° C., B-type viscometer), more preferably 30 to 150 voids. If it is less than 5 poise, when it is cured in a mold for forming a disk substrate, sink marks and cracks occur, making it difficult to obtain a plate of a constant thickness, and bubbles tend to occur (unpreferably).

If the viscosity exceeds 200 poise, not only the addition and mixing of the radical polymerization initiator becomes difficult, but also the birefringence becomes high, which is not preferable.

Another feature of the method for manufacturing a disk substrate of the present invention is that after adding a radical polymerization initiator to the methacrylic partial polymer (I) and mixing uniformly, a predetermined amount is injected into a mold for forming a disk substrate. This method directly obtains a disk substrate by curing it under pressure and heating conditions in a short period of time, which is clearly different from the method of cutting from a cast plate or extrusion plate, and eliminates dust, chips, scratches, and It is freed from the drawbacks of a substrate for cutting-excellent disks. Curing conditions vary depending on the type and amount of the methacrylic partial polymer and radical polymerization initiator used, and the pressure is gradually increased with curing to a final pressure of 10 to 200kl. /7
A pressure condition of 50 to 150 Iq/dG is more suitable. In addition, as for the temperature condition, 50 to 90°C is more suitable than 40 to 100°C, and in some cases post-polymerization may be performed at 90 to 120°C (curing time is 5 to 30°C).
It takes about 0 minutes.

The radical polymerization initiator used in the present invention is not particularly limited, and includes lauryl peroxide, benzoyl peroxide, tert-butyl peroxyvivalate, tert-butyl peroxyneodecanoate, and tert-butyl peroxide. Oxy-2-ethylhexanoate, tert-butyl peroxyisobutyrate,
Organic peroxide initiators such as Shiitsubu pyruvar oxydicarbonate, di-2-ethylhexyl peroxydicarbonate, 2,2'-azobisisobutynitrile,
Dimethyl-2,2'-azobisisobutyrate, 2.2
'-Azobis(2-methylbutylnitrile), 2.2'
-azobis(2,4-dimethylvaleronitrile), 2.
An azo initiator such as 2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and benzoyl peroxide and N,N-di(2-human ρxibupyl)-P
-1 luidine, N%N-dimethyl-P-) luidine, N
Examples include redox initiators in combination with tertiary amines such as 1N-dimethylanline.

The disk substrate obtained by this method has a higher molecular weight than injection molding materials and is moderately crosslinked, so it has excellent heat resistance. It is of course possible to attach groups to a disc substrate with pre-grooves by attaching it to the substrate, but it is also possible to attach groups after applying an ultraviolet curing resin on the substrate.

In addition, mercaptans as chain transfer agents, dyes, ultraviolet absorbers, mold release agents, etc. may be added to the methacrylic partial polymer (I) of the present invention, if necessary.

〔Example〕

The present invention will be specifically explained below with reference to Examples.

The methacrylic acid alkyl ester, crosslinking monomer, monoethylenically unsaturated monomer, and organic solvent used in the examples are represented by the following abbreviations.

Methyl methacrylate (MMA), ethyl methacrylate (
EMA), isobu-pvir methacrylate [i-PMA]
, inbutyl methacrylate (i-HMA), tert-butyl methacrylate (t-HMA), isobornyl methacrylate (i-BoMA), polyethylene glycol dimethacrylate (molecule i of polyethylene glycol) C
PEGDM (molecule ik>), neopentyl glycol dimethacrylate [:NPGDMA), trimethylpropane trimethacrylate CTMPTMA), dichloromethane (DCM), tetrachlorodic IfR ethane (TCDFE), inpropyl alcohol [IPA:
l.

The evaluation of the birefringence in Examples is the value of the optical path difference at a location 1 Oca from the center of the 30 cm disk substrate.

The water absorption rate is 2x for the obtained disk substrate with a thickness of 1.2u.
A test piece cut into 3-inch pieces was heated at 40°C in a constant temperature and humidity chamber.
This is the value of weight change after being left for 30 days under the condition of 0% RH.

In addition, the solvent resistance in the examples was evaluated by placing a disk substrate in a glass petri dish, covering the substrate with flannel cloth impregnated with each organic solvent, covering the petri dish, and observing the change in appearance after leaving it for 5 minutes. I judged it.

Examples 1 to 7, Comparative Examples 1 to 4, Methyl methacrylate and methacrylic acid alkyl ester (
By changing the composition of A), polymerizing in the presence of a radical polymerization initiator and a chain transfer agent, and cooling during the polymerization to stop the reaction, the type and amount of crosslinkable monomers added to the resulting sillage are changed. The mixture was added and mixed to obtain a uniform methacrylic partial polymer. 0.3 parts by weight of tert-butyl peroxypivalate was added to and mixed with 100 parts of this partially polymerized product, and a predetermined amount was heated to 80°C.
The mixture was injected into a disk-shaped mold and held under pressure for 10 minutes to harden, and after cooling, a disk substrate with a thickness of 1.21 m was obtained.

The evaluation results of the obtained disk substrates are shown in Table 1, including comparative examples.

Comparative Examples 5-6, methyl methacrylate, alkyl methacrylate ester (
polymerization of monomer mixtures having different compositions of crosslinkable monomers (m) and crosslinkable monomers in the presence of a radical polymerization initiator and a chain transfer agent,
To 100 parts by weight of the methacrylic partial polymer obtained by cooling during the polymerization to stop the reaction, 0.3 parts by weight of tertiary butyl baroxypivalet was added and mixed, and the same procedure as in Example 1 was carried out. Depending on the method, diameter 30W, plate thickness 1
A substrate for a disk with a diameter of 2 m was obtained. Table 1 shows the evaluation results of the obtained disk substrate.

Examples 8 to 12, Comparative Examples 7 to 9, Methyl methacrylate and alkyl methacrylate (
Polymer beads were obtained by suspension polymerization in the presence of a radical polymerization initiator and a chain transfer agent while changing the composition of ^). These polymer beads were completely dissolved in a monomer mixture of different compositions consisting of methyl methacrylate, alkyl methacrylate (A), and crosslinkable monomers to form a uniform methacrylic partial polymer. 0.3 parts by weight of Raulyl peroxide was added to 100 parts by weight of this partially polymerized product, and the same method as in Example 1 was used to obtain a disk substrate having a diameter of 30α and a thickness of 1.2 mm.

The evaluation results of the obtained disk substrates are shown in Table 2.

Comparative Examples 10-11 Substrate for a disk with a diameter of 301 cut from a roseglass 1.2iuI plate (manufactured by Kyowa Gas Chemical Industry ■, methacrylic resin casting plate) and rosette F-1000 (manufactured by Kyowa Gas Chemical Industry ■, methacrylic resin molded) The evaluation results of disk substrates having a thickness of 1.2 mm and a diameter of 30 mm (111 mm) are shown in Table 2 as Comparative Examples 1O and 11, respectively, by injection molding of the same material.

−17=

Claims (4)

[Claims] (1) Methyl methacrylate 10-80% by weight, specific methacrylic acid alkyl ester (A) 20-80% by weight,
Consists of 0.3 to 10% by weight of crosslinkable monomer (B) and 0 to 10% by weight of monoethylenically unsaturated monomer copolymerizable with these, and has a viscosity of 5 to 200 poise (25°C) A disk substrate characterized in that it is obtained by curing a uniform methacrylic partial polymer (I). (2) A patent claim characterized in that the specific methacrylic acid alkyl ester (A) is at least one of ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, and isobornyl methacrylate. The disk substrate according to scope 1. (3) The crosslinkable monomer (B) is polyethylene glycol di(meth)acrylate (the molecular weight of polyethylene glycol is 170 to 1020), neopentyl glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, and trimethylol Propantry (
The disk substrate according to claim 1, characterized in that the disk substrate is at least one type of meth)acrylate. (4) Methyl methacrylate 10 to 80% by weight, specific methacrylic acid alkyl ester (A) 20 to 80% by weight,
Consists of 0.3 to 10% by weight of crosslinkable monomer (B) and 0 to 10% by weight of monoethylenically unsaturated monomer copolymerizable with these, and has a viscosity of 5 to 200 poise (25°C) A method for producing a disk substrate, which comprises curing a uniform methacrylic partial polymer (I) in a mold under pressure and heating conditions in the presence of a radical polymerization initiator.