JPS62279910A - Molding method of plastic board - Google Patents

Abstract

PURPOSE:To improve characteristics of an optical disk base by preventing a deterioration in life of a recording film by lowering a water absorbtion of the board, by heating the plastic board obtained through radical polymerization of multifunctional acrylate in specific expression at a temperature of at least 150 deg.C or more as a post cure temperature. CONSTITUTION:This board is released from a mold at the time when the glass transistion temperature (Tg) of a plastic board obtained through application of radical polymercation to a multifunctional acrylate compound to be expressed by a general formula (I) has arrived at 10-100 deg.C. As cure is insufficient at the temperature of less than 10 deg.C, a deformation is generated on the plastic transperent board and when the temperature exceeds 100 deg.C, it follows that mold release is hard and that a crack and break are apt to be generated on the board. The plastic board which has been released from the mold is placed on a flat place and postcure is applied to the plastic board until the Tg becomes 110 deg.. It is desirable that the temperature and a quantity of irradiation are performed stepwise for the postcure and that heating is performed at a temperature of at least 150 deg.C or more as the postcure temperature. It is desirable further that the plastic transparent board is obtained by curing within a vacuous or inactive gaseous atmosphere under the temperature of 200 deg.C or more.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a method for molding a plastic transparent substrate, and is used, for example, as a disk substrate for a disk that performs recording and reproduction using light (optical disk, magneto-optical disk, etc.). The present invention relates to a method for molding a plastic transparent substrate.

Conventional technology Plastic transparent substrates have been gaining popularity in recent years due to their excellent low birefringence, which can be said to be a fundamental optical property.
It is attracting attention.

Generally, this plastic transparent substrate is made by injecting a polymerizable liquid material such as polyallyl carbonate, polyol poly(meth)acrylate, or epoxy acrylate into the cavity of a mold, and then radically polymerizing it within the mold to obtain a transparent substrate. A molding method is used (Japanese Patent Application Laid-Open No. 1983-13
No. 0450, No. 58-137150).

In addition, a method of photopolymerization in a double-sided glass mold (Japanese Patent Application Laid-open No. 1983-
202557), and a method in which the liquid resin is thermally polymerized by applying pressure after vacuum casting or liquid injection is completed (Japanese Patent Laid-Open No. 60-2
03414).

Conventional casting molding methods for plastic transparent substrates require about 24 hours for the mold used to complete molding of the plastic transparent substrate from the time of injecting the reactive liquid material, resulting in extremely poor utilization efficiency of the mold and poor signal generation in the grooves. Stamper to transfer etc.
This increases the number of plastic transparent substrates and poses a major obstacle to the productivity of plastic transparent substrates.

Furthermore, if the radical polymerization by light energy is completed in the mold, the shrinkage rate of the curing reaction is large, resulting in the problem that the substrate cracks and a molded product cannot be obtained.

In order to solve this problem, the present inventors developed polyfunctional (meta)
In a method of obtaining a plastic transparent substrate by radically polymerizing an acrylate compound using a cast molding method, when the glass transition temperature (Tg) of the plastic substrate obtained by radical polymerization in a mold reaches 10 to 100°C. After releasing this substrate, the substrate is further post-cured to have a Tg of 11.
We have developed a method for molding plastic substrates that is characterized by the ability to obtain substrates with a temperature of 0°C or higher, and have proposed an extremely productive molding method that uses molds with high efficiency and is less prone to damage to the resulting substrates. (Patent Application No. 156494, Showa 60).

Problems to be Solved by the Invention However, the present inventors' proposal (Japanese Patent Application No. 60-156)
494), although it was possible to improve the productivity of crack-free plastic substrates, when viewed as a disk substrate, the amount of residual double bonds was large, increasing the water absorption rate of the substrate and reducing heat resistance. There was a problem. This problem reduced the lifetime of the recording film, especially when the water absorption rate was high.

The present invention provides a molding method that solves the problem that a plastic transparent substrate obtained by radical polymerization has a high water absorption rate, which reduces the life of the recording film of an optical disk.

Means to Solve the Problems The present invention uses a cast molding method to radically polymerize a polyfunctional (meth)acrylate compound in a mold. When this temperature is reached, the substrate is released from the mold, and then the substrate is further post-cured to obtain a substrate with a Tg of 110°C or higher.In the plastic substrate molding method, the final curing temperature is set to 150°C or higher, IIIk4< The object of the present invention is to provide a molding method for obtaining an excellent plastic substrate that is cured at high temperature, has a small amount of residual double bonds, and has a low ratio of ÷←←, so that the life of the recording film is less reduced.

The above polyfunctional acrylate compound has the following general formula (
1) % Formula % (1) [In the formula, R1 is an alcohol residue having 2 to 50 carbon atoms, R is H or CH3, and n is a number from 2 to 6.

] A compound represented by the following is used, and the cured product obtained by radical polymerization thereof has a glass transition temperature of 100° C. or higher.

Specific examples of such polyfunctional acrylate compounds include:
2.2'-bis[4-(β-methachyyloxy)cyclohexylupropane, 2.2'-bis[4-(β-methacryloyloxyjetoxy)cyclohexylupropane, bis(oxymethyl)tricyclo[ 5, 2, 1, 0
2.5] Decane dimethacrylate, 1,4-bis(methacloyloxymethyl)cyclohexane, trimethylolpropane tri(meth)acrylate, neobentyl glycol di(meth)acrylate, 1,6-hexanethiol di(meth) Acrylate, 1,3-butanediol di(meth)acrylate, diethylene glycol di(
Examples include methacrylic esters such as meth)acrylate, 2,2'-hisC4-(methacryloyljethoxy)phenylpropane, and acrylic ester compounds alone and mixtures thereof, but from the viewpoint of optical properties, 2, 2'-bis[:4-(β-methacroyloxyethoxy)cyclohexyl]furopane, bis(oxymethyl)tricycloC5,2,1,02"5]decane dimethacrylate, 1,4-bis(methacroyloxymethyl) )
Cyclohexane is available. Here, (meth)acrylate refers to both acrylate and methacrylate.

Furthermore, in addition to the compound of general formula (■) as described above, it is possible to use a radically polymerizable monomer generally used as a viscosity modifier in an amount of 10% by weight or less.

Examples of such other polymerizable monomers include styrene,
Chlorstyrene, dichlorostyrene, vinyltoluene,
Vinyl compounds such as divinylbenzene, vinyl acetate, vinyl chloride, methyl methacrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, cyclohexyl (
Examples include (meth)acrylic compounds such as meth)acrylate, glycidyl (meth)acrylate, epoxy (meth)azilylate, and urethane (meth)acrylate, and allyl compounds such as diethylene glycol bisallyl carbonate and diallyl phthalate.

The radical initiators used in the polymerization of these seven polymers are not particularly limited, and include peroxides such as benzoyl peroxide, diisopropyl peroxycarbonate, lauroyl peroxide, and tert-butyl peroxybivalate; Known radical initiators include azo compounds such as isobutyronitrile, photosensitizers such as benzophenone, benzoin ethyl ether, benzyl, acetophenone, and anthraquinone, and sulfur compounds such as diphenyl sulfite and thiocarbamates.

Further, the radical polymerization conditions in the mold can be general radical polymerization conditions (heating, light irradiation, electron beam irradiation, etc.). The amount of radical initiator added is 0.01 to 100 parts by weight of the polyfunctional acrylate compound.
10 parts by weight, and the polymerization temperature is 10 to 20°C, preferably 30 to 160°C. The polymerization atmosphere can be in air or in an inert gas.

The glass transition temperature of the plastic transparent substrate obtained by radical polymerization of the above polyfunctional acrylate by a cast molding method is 10 to 100°C when released from the mold.

If the temperature is less than 10°C, curing will be insufficient, causing deformation of the plastic transparent substrate, and if it exceeds 100°C, it will be difficult to release from the mold, making the substrate more likely to crack or chip, which is unsuitable. The Tg range of the substrate resin during mold release is 10~
The temperature is 10Q°C, preferably 20 to 80°C. In this case, the radical polymerization time of the polyfunctional acrylate in the mold can be set to 2 hours or less, preferably 1 hour or less.

The released plastic substrate is placed on a flat surface and T
Post-curing is performed until g becomes 11C)C or more.

Means for in-mold curing and post-curing include heating, ultraviolet irradiation, electron beam irradiation, and the like.

It is preferable to carry out post-curing in stages by adjusting the temperature, irradiation amount, etc. It is preferable to heat at least at a post-curing temperature of 160°C or higher, and furthermore, at a temperature of 200°C or higher, vacuum or nitrogen or inert It is preferable to obtain a plastic transparent substrate by curing in a gas atmosphere.

Function The present invention achieves a glass transition temperature of 1 through radical polymerization within a mold.
By demolding in an incomplete radical polymerization state below the glass transition temperature of the final cured plastic substrate (0°C to 100°C), mechanical distortion and optical distortion caused by reaction curing shrinkage can be minimized, and post-curing can be demolded. By performing this later, there was an effect of eliminating the difference in mechanical strain between the surface and the inside due to the restraint of the outer peripheral surface of the plastic substrate. This post-curing is performed because the glass transition temperature of the plastic substrate obtained by in-mold polymerization is 1Q℃ to 100℃, and the temperature is rapidly increased to 15℃ to maintain the shape.
The temperature cannot be raised to 0°C.

Furthermore, a low post-curing temperature increases the number of residual double bonds, but post-curing at a temperature of 150°C or higher promotes radical polymerization of the remaining double bonds, reducing the number of double bonds. Ta.

Examples are shown below. In the examples, "part" means part by weight, and "chi" means % by weight.

Further, the glass transition temperature (TCI) and residual double bond content (x) obtained in the examples and the method of forming a recording film on a substrate and examining the influence on the recording film were measured by the following test method.

O Glass transition temperature (Tcy): Differential scanning calorimeter (D
Measured at SC).

0Residual double bond amount (%): Measured by IR analysis16
60-1660cm and 2600-86ω(7)-
Fill in the baseline for one peak, set the respective peak areas as 31 and 32, then n = 51/S2, set n of liquid resin as 100%, set ○ when 51 = o as a calibration curve, and calculate each sample. n of
was determined, and Chi was calculated from the calibration curve.

0 Effect on the recording film: Observation of morphology after immersion in water As shown in the drawing, the recording film 2 was sputter-linked onto the obtained substrate 1 and sealed with a quartz plate 3 via a Teflon spacer 4 and paraffin wax 5. , and are sealed with clamps 6.

This was immersed in a constant temperature bath 7 filled with pure water 8, and taken out when the saturated water absorption rate was reached, and changes in morphology were observed using a microscope.

Comparative Example 1: 2.2'-bis(4-(β-methacroyloxyethoxy)cyclohexyl)propane 1Q○ part of photosensitizer (Irgacure 651 (manufactured by Ciba Geigy))
Add parts O and S and parts O and S of benzoyl peroxide, heat to 60°C and stir uniformly.

After mixing, defoaming, the liquid was injected into a molded cavity consisting of a glass plate with a diameter of 120, silicone rubber, and a metal stambar, and an 80W/Crn UV lamp was heated at 200W.
After irradiation with ultraviolet rays and demolding, a plastic disk substrate with no cracks or chips was obtained.The Tg of this substrate was cured at 80°C for 2 hours, and the Tg was 1.
At 48°C, residual double bonds were 38%.

Example 1: The unpost-cured substrate obtained in Comparative Example 1 was post-cured at 150° C. for 2 hours. The remaining double bonds of the substrate were 32, and the saturated water absorption rate of this substrate was 1.6. It was Chi.

Comparative Example 2: In Example 1, bis(oxymethyl)tricyclo(5,2,1,02
・5] A plastic disk substrate free from cracks and chips was obtained using tecan dimethacrylate.

The Tg of the plastic disk substrate was measured and found to be 38°C.

Thereafter, this substrate was placed on a flat plate and further post-cured at IOOO DEG C. to obtain a plastic disk substrate with a final Tg of 261 DEG C. and good transferability of standby signals.

Example 2: This plastic substrate was post-cured at 150° C. for 2 hours, and the amount of residual double bonds was 28.

Example 3: This plastic substrate was post-cured at 200° C. for 2 hours, and the amount of residual double bonds was 17.

Example 4: A plastic substrate where the substrate was post-cured in N2 for 30,002 hours. The amount of remaining double bonds was 8%.

Comparative Example 3: In Example 1, post-curing was carried out only by UV irradiation, and even after 50 passes of the UV lamp, 191
At 20°C, the final Tg of 148°C was not reached, and the amount of remaining double bonds was about 43 to 45.

Example 5: In Example 1, the curing reaction was carried out at a polymerization temperature of 80° C. instead of using ultraviolet or radiation without adding a photosensitizer. 30
After a few minutes, the mold was released to obtain a disk substrate with no cracks or chips at Tgss°C.

When post-curing was carried out in the same manner as in Example 1, the amount of residual double bonds was reduced to 28%.

Table 1 shows the water absorption rates and effects on recording films of the above Examples and Comparative Examples.

Table 1 Effects of the Invention According to the present invention, by heating a plastic substrate obtained by radical polymerization of a polyfunctional acrylate at a post-curing temperature of at least 150 tl or more, the amount of residual double bonds in the final plastic substrate can be reduced. The water absorption rate decreased to 30% or less, the water absorption rate of the substrate also decreased, the influence on the recording film was reduced, and the effect of improving the characteristics of the optical disk substrate was obtained.

[Brief explanation of the drawing]

The drawing is an explanatory diagram showing an experimental method for examining the correlation between water absorption of a recording film and a plastic substrate.

Claims (2)

[Claims] (1) A polyfunctional acrylate compound is cast using a cast molding method.
In the method of obtaining a plastic substrate by radical polymerization, the glass transition temperature of the plastic substrate obtained by radically polymerizing a polyfunctional acrylate composition in a mold is 10 to 100.
When the temperature reaches ℃, this substrate is released from the mold, and then this substrate is further post-cured to obtain a substrate with a Tg of 110℃ or higher, and this substrate is post-cured at a temperature of 150℃ or higher to obtain a substrate. A method for molding a plastic substrate, characterized by: (2) The polyfunctional acrylate compound has the following general formula (
I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼・・・・・・・・・
(I) [In the formula, R_1 is an alcohol residue having 2 to 50 carbon atoms, R_2 is H or CH_3, and n is a number from 2 to 6. ] The method for molding a plastic substrate according to claim 1, wherein the compound is a compound represented by: