JPH0312837A - Production of optical disk substrate - Google Patents

Abstract

PURPOSE:To decrease the amt. of the unreacted monomer included in a surface part by irradiating the specific optical disk substrate with UV rays in an inert gaseous atmosphere to increase the degree of polymn. of the optical disk substrate. CONSTITUTION:The multifunctional (meth)acrylate compd. expressed by formula I is subjected to radical polymn. and the polymer is formed as a plate body or worked to the plate body. The resulted optical disk substrate is irradiated with UV rays in the inert gaseous atmosphere to increase the degree of polymn. of the optical disk surface. In the formula I, R1 and R2 may be the same or different and are respectively hydrogen or methyl group; n is 0 or 1 integer. The remaining rate of the unreacted monomer of the surface is decreased in this way and the corrosion of a thin metallic film, such as recording film, is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION Field of Industrial Application The present invention relates to optical disc substrates, particularly to substrates for optical discs on which information can be written and erased. More specifically, the present invention relates to a method for manufacturing an optical disc substrate that is excellent in birefringence, heat resistance, transparency, and protection of recording films and the like.

<Prior Art> Typical resins used for optical disc substrates are polymethyl methacrylate resin and polycarbonate resin. However, while the former has excellent optical properties such as birefringence, it has poor heat resistance, water absorption, and especially shape retention during water absorption.
Although it has excellent water absorption, it still has problems such as optical properties that need improvement.

Various proposals have been made to solve the essential problems of the above-mentioned resins, and among them, a superior method of casting a thermosetting resin having multiple polymerizable functional groups in the molecule has been proposed. A substrate with characteristics has been obtained (Japanese Patent Application Laid-open No. 6
No. 1-174208, JP-A-61-27531-2,
JP-A No. 61-28791, No. 3, JP-A No. 62-2255
08 publications, etc.).

By the way, a system using a compound having a polyfunctional radically polymerizable group is one of the technologies that should be noted as it can overcome the low productivity in cast polymerization (Japanese Patent Application Laid-Open No.
No. 2-18223 and Japanese Unexamined Patent Publication No. 62-279910': 5).

However, as is generally known, it is extremely difficult to react all of the radically polymerizable groups during cast polymerization of compounds having polyfunctional radically polymerizable groups, and in many cases, these radically polymerizable groups are The monomers remain in the polymer as unreacted monomers (those in which at least one radically polymerizable group is present in an unpolymerized state are collectively referred to as unreacted monomers). This unreacted monomer causes deterioration of the J law constant when water is absorbed, and corrosion of metal thin films such as recording films.
(I) (R and R2 may be the same or different, and each is hydrogen or a methyl group. n is an integer of 0 or 1.) <Effects of the Invention> By using the method of the present invention, when producing an optical disk substrate, the degree of polymerization, especially the surface (approximately 1), can be extremely easily controlled in the cast polymerization of a polyfunctional (meth)acrylic acid ester compound. It is possible to increase the reaction rate of acrylic acid or methacrylic acid ester residues.Furthermore, by reducing the residual rate of unreacted monomers on the surface, corrosion of metal thin films such as recording films can be suppressed. can be expected.

[Detailed description of the invention]

[I] Monomer and its polymerizable monomer> When specifying the compound of the above formula (I) used in the present invention, there is an urgent need for a number of groups with a low content of unreacted monomers. It is.

[Summary of the invention]

<Problems to be Solved by the Invention> The present invention aims to eliminate undesirable substances contained in the substrate, especially in the surface area, by cast-polymerizing a compound having a polyfunctional radically polymerizable group. The purpose is to reduce the amount of reactive monomers.

Means for Solving the Problems> As a means for solving the above problems, the method for manufacturing an optical disk substrate according to the present invention comprises radically polymerizing a polyfunctional (meth)acrylic acid ester compound represented by the following formula (I). In a method for manufacturing an optical disk substrate that involves obtaining or processing a polymer into a plate-like body, the degree of polymerization on the surface of the optical disk substrate is determined by irradiating the obtained optical disk substrate with ultraviolet rays in an inert gas atmosphere. It is characterized by enhancing.

For example, bis(oxymethyl)tricyclo[5゜2.
1.02"] ] Decane-diacrylate-1, bis(oxymethyl)tricyclo[5,2,1°02°6] Decane-dimethacrylate, bis(oxymethyl)tricyclo[5,2,1,02" ) Decanenia acrylate methacrylate and mixtures thereof, bis(oxymethyl)pentacyclo[6°3.62.709.13]pentadecane 5.1.1. 0°=diacrylate, bis(oxymethyl)pentacyclo[6,5,1,1,3°6o, 2,709.13]
Pentadecane diacrylate, bis(oxymethyl)
Pentacyclo (6,5,1,1,3"o, 2'709
゛13) Pentadecane = acrylate methacrylate -1.
and mixtures thereof. Two or more of these tricyclodecane compounds and pentacyclopentadecane compounds may be used in combination within or between groups.

As a polymerization target in the present invention! l''-mers are those consisting primarily of compounds of formula (I) above.

Here, "mainly" means that 0 to 20 parts by weight of the copolymerizable monomer may be used in combination with 100 parts by weight of the compound of formula (I).

That is, in the present invention, a radically polymerizable compound can be added to the compound of formula (I) within a range that does not impair the object of the present invention.

Specific examples of such comonomers include monofunctional acrylic and methacrylic esters such as methyl acrylate and methyl methacrylate-1, aromatic vinyl compounds such as styrene, and bisphenol-A. To difunctional acrylic acid and methacrylic acid esters such as diacrylate and dimethacrylate of ethylene oxite adducts.
Can be mentioned. The amount of these radically polymerizable compounds used is 20 parts by weight or less per 100 parts by weight of the compound of formula (I).

[I[] Various proposals have already been published regarding methods for manufacturing optical disc substrates by polymerizing the compound of polymerization formula (I). A common method is to mix the peroxide and/or photoinitiator necessary for radical polymerization of the compound of formula (I), pour it into a casting mold, and then use heat and/or ultraviolet rays to form a substrate. The present invention can also follow this principle.

Examples of peroxides used here include benzoyl peroxide, diisopropyl peroxycarbonate, lauroyl peroxide, tertiary-butyl peroxypivalate, dicumyl peroxide, azoisobutyronitrile, and the like. Specific examples of photoinitiators include sulfur compounds such as benzophenone, benzoin ethyl ether, benzyl, acetophenone, anthraquinone, diphenyl sulfide, and thiocarbamate.

The amounts of these peroxides and photoinitiators to be used are based on the formula (I
) is in the range of 0.01 to 20 parts by weight, preferably 0.1 to 10 parts by weight, per 100 parts by weight of the compound.

In the method of polymerizing the compound of formula (I) in a mold using heat and/or ultraviolet rays, and simultaneously forming and molding the polymer to form a substrate, optical distortion due to shrinkage during polymerization, It is necessary to suppress as much as possible the occurrence of shape distortions in appearance, such as flatness and surface roughness. As a way to solve this problem, a two-step precure/post-cure method is proposed, namely heat and/or
Alternatively, it is preferable to use ultraviolet rays to polymerize the substrate to the extent that it can maintain its shape in the mold, then remove it from the mold, and perform post-curing by heating.

Precure can be carried out in air or inert gas at temperatures from room temperature to 100°C. After demolding is performed in an inert gas, the substrate is seeded into a post-cure mold consisting of two glass plates and a spacer. Post-cure conditions can be carried out at 150°C to 200°C in air or inert gas.

In this way, the polymer can be directly applied to a plate (not necessarily in its final form, but also includes cases where surface finishing is further performed).
Instead of obtaining the polymer as a final plate-like body, it is also possible to obtain the polymer in a shape other than the final plate-like body and process it to obtain the optical disk substrate as the final plate-like body.

It is possible to manufacture an optical disc substrate with excellent shape, optical properties, heat resistance, etc. by the above method, but
As mentioned above, it is difficult for the degree of polymerization of this substrate, that is, the reaction rate of the (meth)acrylic acid ester compound of formula (I), to exceed 95%, and unreacted monomers remain.

[m1 Surface Polymerization The method for producing an optical disk substrate of the present invention is a method of increasing the reaction rate of the (meth)acrylic acid ester compound near the surface of the substrate obtained above and reducing the amount of residual unreacted monomer. .

After the substrate in the mold, which has undergone the above-mentioned post-curing, is maintained at a predetermined temperature, ultraviolet rays are irradiated through the glass constituting the mold. The ultraviolet rays used in the present invention are 0.1 to 60
0 nm, preferably 190 to 430 nm, or an appropriate wavelength of 1 to 30 nm on the surface of the irradiated object.
A total light amount of 0 mJ/c, preferably 5 to 200 mJ/c♂ is irradiated. Less than 5 mJ/c/ has little effect;
If it exceeds 00 mJ/cn〒, it is uneconomical. The temperature of the object to be irradiated, that is, the disk substrate in the glass mold, when irradiated with ultraviolet rays may be in the range of room temperature to 200°C. Increasing the temperature reduces the amount of ultraviolet irradiation and shortens the working time, but at high temperatures, the resulting optical disc substrate becomes markedly colored and the transmittance of the laser light used for recording/erasing/reading decreases. However, this poses a big problem in practice. The method of irradiating ultraviolet rays is to perform post-curing as described above, then demold under an inert gas atmosphere, and then without using a glass mold or spacer.
Ultraviolet irradiation may be performed in a similar atmosphere.

[IV] Reference Example (Manufacturing Example of Optical Disc Substrate) Bis(oxymethyl)tricyclo(5,2,1°02.
8] Decane = acrylate methacrylate-1 (mixture consisting of 16% diacrylate, 36% dimethacrylate and 48% acrylate/methacrylate cross-body) to 100 parts of 1-hydroxycyclohexyl phenyl ketone (1) After adding 0.1 part of Irgacure 184J (Ciba Geigy product) and 1.0 part of dicumyl peroxide (all parts by weight) and stirring uniformly, defoaming was performed.Then, this liquid was placed on a glass plate and It was injected into a mold made of silicone rubber with a diameter of 13 cm and a thickness of 1.5 mm.Using a high-pressure mercury lamp with an output of 80 W/cm, the glass plate surface was irradiated with ultraviolet rays for 15 seconds, and it was cured without any liquid part. This cured product was further heated in an air oven at 11,150° C. for 2 hours to obtain a colorless and transparent cured product in the form of an optical disc substrate.

The surface reactivity of the optical disk substrate can be measured using the multiple reflection method (ATR-FT method) in infrared absorption spectrum analysis (Di
gilab FTS-]5CFTIR device KR8-5
The degree of reactivity was estimated from the change in peaks derived from carbon-carbon double bonds in the spectrum.

The reduction rate (α) of carbon-carbon double bonds was determined from the following formula.

α-100X (I-γI/γ0) γ and γ1 indicate the residual rate of the double bond after irradiation and 1 2- irradiation, respectively. γ1/γ. can be calculated from the absorption intensity ratio of the absorption peak (810 cm') derived from the double bond and the absorption peak (I730 cm-1) derived from the carboxyl group in each infrared absorption spectrum.

Examples 1 to 5 Optical disk substrates obtained by the method shown in Reference Examples were inserted into a mold made of a glass plate and a silicone rubber spacer under nitrogen, and heated to a predetermined temperature (listed in Table 1). After that, ultraviolet rays were irradiated from the glass plate surface using a high-pressure mercury lamp with an output of 80 W/cm so as to provide a predetermined total light intensity (listed in Table 1). The reduction rate of carbon-carbon double bonds on the surface of the irradiated surface and the results of appearance evaluation are summarized in Table 1.

Comparative Example 1 An optical disc substrate obtained by the method shown in Production Example was heated at 240° C. for 1 hour in an air oven.

The 1υ substrate was significantly colored, and although it was confirmed that the carbon-carbon double bond had disappeared on the surface, the +l+ of each absorption band in the infrared absorption spectrum was broadened, indicating that it was not caused by bonds other than those mentioned above. This showed that a crosslinking reaction was occurring. The results are shown in Table-1.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are surface infrared absorption spectra of optical disk substrates obtained in Reference Example, Example 5, and Comparative Example 1, respectively.

Claims (1)

[Scope of Claims] Mainly consisting of a polyfunctional (meth)acrylic acid ester compound represented by the following formula (I), the polymer is obtained in the form of a plate by radical polymerization of the polymer, or the polymer is obtained in the form of a plate. A method for producing an optical disc substrate comprising processing the optical disc substrate, the method comprising: irradiating the obtained optical disc substrate with ultraviolet rays in an inert gas atmosphere to increase the degree of polymerization on the surface of the optical disc substrate. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (R_1 and R_2 may be the same or different,
Each is hydrogen or methyl group. n is an integer of 0 or 1. )