JPS6251411A - Manufacture of plastic substrate excellent in dimensional stability - Google Patents

Abstract

PURPOSE:To obtain a reliable information recording medium, which does not deform even when it is placed under the environment liable to develop the deformation and warpage therein by a method wherein a thermoplastic resin molded product, which is injection-molded after being heated up to a temperature exceeding its flow temperature, is held at a temperature lower than the heat distortion temperature of the resin under high humidity until the moisture in the molded product reaches a specified state. CONSTITUTION:After thermoplastic resin, which is heated up to a temperature exceeding its flow temperature, is injectioned-molded, the resultant molded product is held at a temperature lower than the heat distortion temperature of the resin by 20 deg.C or more under high humidity until the moisture in the molded product reaches 40% or more of the equilibrium condition. The above-mentioned high temperature means 70% relative humidity and more or preferably 90% relative humidity and more. Under the condition less than 70% relative humidity, the effect of moisture is small and the time for treatment becomes longer and the effect is not enough. A temperature lower than the heat distortion temperature of the resin by 20 deg.C or more is used as an annealing temperature. In case of methyl methacrylate resin, the effective annealing environment is 30-80 deg.C or preferably 40-70 deg.C. The processing temperature exceeding the heat distortion temperature minus 20 deg.C is not preferable, because the deformation develops in the molded product under said temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a plastic substrate by injection molding of a thermoplastic resin having excellent dimensional stability. In particular, the present invention relates to a method of manufacturing a plastic substrate suitable for optical disks.

[Prior Art] As substrates for optical disks, substrates made by injection molding of transparent thermoplastic resin are often used. However, the injection molding method causes a problem in that residual stress that causes post-deformation occurs in the obtained substrate. Conventionally, transparent thermoplastic resins such as polyvinyl chloride, polycarbonate, polymethyl methacrylate, and poly(4-4) have been used as substrates for optical disks.
Methylpentene etc. are used. In particular, polymethyl methacrylate resins are increasingly used in optoelectronic materials due to their excellent optical properties and moldability.

For example, it is used as an optical fiber material or as a recording substrate for optical lenses, optical discs, optical cards, etc. As for the latter optical disk substrate, methyl methacrylate resin is mainly used as an optical video disk substrate.

However, although the heat distortion temperature of methyl methacrylate resin is around 100°C, it has some hygroscopicity, so thin molded products can warp even at fairly low temperatures when placed in a high humidity environment. .

This may result in deformation such as twisting or drooping, which limits its application to writable optical discs that require higher dimensional accuracy.

These characteristics of methyl methacrylate resins vary depending on the molding method, but in the case of injection molding, the above-mentioned deformation is most noticeable because the molding distortion is considerable.

Conventionally, as a solution to the problems mentioned above.

One method proposed is to change the polymer composition to reduce the hygroscopicity itself. This method requires the use of a fairly large amount of a copolymerized monomer that imparts low hygroscopicity, resulting in problems such as loss of characteristics of the methyl methacrylate resin, deterioration of optical properties, and brittle molded products. The number of points has increased, and up until now there has been no decisive factor.

Another known method is to anneal the molded product for 7 times. Usually, the molded product is annealed at a temperature 10 to 20° C. lower than the heat distortion temperature for a certain period of time. Therefore, in the case of methyl methacrylate resin, 90
It is common to process at ~80°C.

[Problems to be Solved by the Invention] However, in the method of annealing a molded product, if the thickness of the molded product is thin, the molded product will be greatly deformed if annealed at the above-mentioned temperature, making it unusable. In addition, if the annealing temperature is lowered, the effect of the 7-mer will not be produced, or a long time treatment will be required to produce the annealing effect.

In view of the technical issues described above, the present inventors have investigated an annealing method that does not involve deformation.

Focusing on the large amount of deformation of molded bodies under high humidity, we separately investigated the effects of moisture and temperature on the annealing effect, and found that there is a synergistic effect that cannot be predicted from the effects of each alone. This invention has been achieved.

[Means for Solving the Problems] That is, the present invention, when manufacturing a substrate by injection molding a thermoplastic resin, involves injection molding the thermoplastic resin heated to a temperature higher than the flow temperature, and then molding the molded product into the resin. A method for producing a plastic substrate with excellent dimensional stability, characterized by maintaining the molded product under high humidity at a temperature 20°C or more lower than the heat distortion temperature of the molded product until the moisture content in the molded product reaches 40% or more of the equilibrium state. It is in.

In the present invention, high humidity refers to a relative humidity of 70% or more, preferably 90% or more. If it is less than 70%, the effect of moisture is small, the processing time becomes long, and the effect is not sufficient.

As the annealing temperature, a temperature that is 20° C. or more lower than the thermal deformation temperature of the resin is used. In the case of methyl methacrylate resin, it is effective to keep it in an environment of 30 to 80°C, preferably 40 to 70°C.

If the treatment temperature exceeds the heat distortion temperature -20°C, the molded product will be deformed, which is not preferable.

The method of the present invention may be applied to a flat plate, or to a flat plate with grooves or bits formed thereon.

The method of the present invention utilizes the property of a molded article to absorb a small amount of water, and is effective for not only methyl methacrylate resin but also various thermoplastic resins as long as the material absorbs a small amount of water. Furthermore, since the diffusion coefficient of moisture inside the molded product is small, this effect cannot be expected for thick molded products.

When processing molded products, it is necessary to consider the method of holding the product. If the thickness of the molded product is thin, it may deform in the direction of 1 gravity due to its own weight under high humidity conditions, so if the molded product is disc-shaped,
When processing large quantities of molded discs, where it is necessary to hold the disc surface perpendicular to gravity and it is preferable to rotate it, various methods can be considered. Attach the rotating shaft, attach the molded product to it,
If necessary, fix it through the center hole of the spacer,
We also use continuous processing methods, such as rotating at a constant speed, or placing the molded products on a conveyor that holds them perpendicular to 1 gravity without touching each other, and passing them through a tunnel with controlled temperature and humidity. be able to.

Optical disk plates using substrates treated in this way do not deform even when placed in environments where ordinary polymethyl methacrylate substrates would deform or warp, making them reliable information recording media. Become.

Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. In Examples and Comparative Examples, all humidity refers to relative humidity.

[Example] Example 1 Using Acryvet vH (trade name manufactured by Mitsubishi Rayon Co., Ltd.) as a commercially available methyl methacrylate resin pellet, a disk substrate with a pre-group having a diameter of 300 mm and a thickness of 1.2+im was injected using the famous Guina Melta injection method. Injection molding was performed using a molding machine at a cylinder temperature of 285°C and a mold temperature of 60°C. The two substrates were treated for 2 hours in a constant temperature and humidity chamber adjusted to 60° C. and 90% relative humidity. The water absorption rate after treatment was 1.2%. Note that the substrate was fixed to a rotating shaft so as to be perpendicular to gravity, and the shaft was rotated at a speed of Brp-.

One of the treated substrates and the untreated substrate were placed in a constant temperature and humidity chamber at 45°C and 90% using a fixing jig, and after a certain period of time, they were taken out and the amount of deformation due to their own weight was measured using a micrometer. It was measured using

Figure 1(a) is a side view of the fixture for measuring deformation and the board;
FIG. 1(b) is an explanatory diagram of the deformation measurement position.

(1) shows a fixture, and (2) shows a substrate to be measured.

3-1 to 3-8 are deformation measurement positions, and ΔH is the deformation amount at the edge of the substrate.

Separately, untreated substrates and remaining treated substrates were vacuum evaporated, and changes in the group surface were observed by tracking the disk group using a disk inspection machine and converting changes in reflectance into electrical signals. The reflected signal of the processing board is
No significant difference was observed compared to the untreated substrate. 1st
The table shows changes in deformation amount over time. Processing conditions are 45
It is an average value of n=8 conducted in an atmosphere of 90% Celsius.

Fig. 1 Comparative Example 1 A disk substrate with a diameter of 300 cm attached to the same rotating jig as in Example 1 was processed in an oven at 80°C for 30 minutes, and processed at 60°C for 2 hours - h-AI Q
kh -7" /-1m x I J-Jvf Tsume h44/T'+ 1t, B514 HL+ +(-
4- Listen, it could not be used for the following tests.

Although a small deformation of less than 0.3 on occurred in the latter,
One sheet was left as it was in a constant temperature and humidity chamber at 45° C. and 90% as in Example 1, and the amount of deformation was measured. The amount of deformation after 24 hours was 0.75 mm on average, and after 7 days it was l, 3
It was mm. We attached an aluminum reflective film to another processing board and observed the reflected signal on the group surface, but it was difficult to track, and even in the areas where tracking was applied, the waveform was disturbed and it was presumed that some deformation occurred in the group. Ta.

Figure 2 is a diagram showing the waveform of the reflected signal on the group plane.
(a) shows the waveform of an untreated substrate, and (b) shows the waveform of a substrate treated at 60° C. for 2 hours.

Comparative Example 2 A disk substrate with a diameter of 300 m was immersed in a constant temperature water bath at 25±0.5° C. for 72 hours. The water absorption rate at this time was 1.4%. This substrate was placed in a constant temperature and humidity chamber at 45° C. and 90% as in Example 1, and the amount of deformation was measured. The change in the amount of deformation over time was not significantly different from that of the untreated substrate.

Example 2 As in Example 1, a polymethyl methacrylate molded substrate with a diameter of 300 μl was placed in a constant temperature and humidity chamber at 45° C. and 90%, and the amount of deformation was measured. The amount of deformation after 7 days was 0.5 mm.

Comparative Example 3 The entire process was carried out in the same manner as in Example 2 except that the processing time of the substrate was changed to 5 hours, and the amount of deformation was measured. The amount of water absorption after treatment is 0.6%, and the amount of deformation after 7 days is 2.1
It was am.

Example 3 Using the same resin material as used in Example 1, a diameter of 200+
sm pre-grouped disc substrate was molded and heated at 70℃, 9
It was treated in a 5% environment for 1 hour. (The treatment method was carried out according to Example 1.) The treated substrate was heated at 55°C.
When the amount of deformation was measured after being fixed in a 90% constant temperature and humidity chamber, the amount of deformation after 7 days was 0.5 degrees. The amount of deformation of the untreated substrate, which was similarly measured for comparison, was 2.6 layers.

Example 4 Polycarbonate resin (Tubarex 7020AD2 manufactured by Mitsubishi Chemical Industries, Ltd.) was heated to a cylinder temperature of 355°C and a total mold temperature of 9.
A disk substrate with a pregroup having a diameter of 200 mm was molded at 0°C.

This substrate was treated at 75° C. and 90% for 5 hours.

This treated substrate was fixed and left in an atmosphere of 80° C. and 90%, and the amount of deformation was measured. The amount of deformation of the treated substrate every 24 hours was 0.3■■ or less, but the untreated substrate became hazy by 0.9 m.

[Effect of the invention] As can be seen from the above examples and comparative examples, a substrate with excellent dimensional stability can be manufactured by processing an injection molded plastic substrate under high humidity and at a relatively low temperature. .

[Brief explanation of the drawing]

Figure 1(a) is a side view of the fixture for measuring deformation and the board;
FIG. 1(b) is an explanatory diagram of the deformation measurement position. FIG. 2 is a drawing showing the waveform of the reflected signal on the group plane. In the figure, 1 indicates a fixing jig, and 2 indicates a measurement board. Figure 1 (a) Figure 1 (b).

Claims (1)

[Scope of Claims] 1) When producing a substrate by injection molding a thermoplastic resin, after injection molding the thermoplastic resin heated above the flow temperature, the molded product is heated to 20°C above the heat distortion temperature of the resin. When the moisture in the molded product is in an equilibrium state at a temperature lower than 40% and under high humidity,
A method for producing a plastic substrate with excellent dimensional stability, which is characterized by holding the substrate until it reaches % or more. 2) When holding the molded substrate under high humidity, rotate the molded substrate attached to the rotating shaft, the molded substrate, or the molded substrate assembly so that the radial direction of the substrate is perpendicular to the plane. A method for manufacturing a plastic substrate with excellent dimensional stability as set forth in claim 1. 3) The method for producing a plastic substrate with excellent dimensional stability according to claim 1 or 2, wherein the thermoplastic resin is polymethyl methacrylate or a methyl methacrylate resin containing 70% by weight or more of methyl methacrylate units. . 4) The method for producing a plastic substrate with excellent dimensional stability according to claim 1 or 2, wherein the thermoplastic resin is a polycarbonate resin.