JPH1177778A - Reduction of deformation of disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the deformation of a disk substrate by holding the inner and outer peripheral parts of the disk substrate made of plastic produced by injection molding under a temp. condition satisfying a plurality of specific formulae at the same time. SOLUTION: The inner and outer peripheral parts of the disk substrate made of plastic produced by injection molding are held under a temp. condition simultaneously satisfying a formula (1); Tin -Tout >=50 deg.C and formula (2); Tp +30 deg.C>=Tin >=Tp -50 deg.C [wherein Tin is the temp. ( deg.C) of the inner periphery part of the disk substrate; Tout is the temp. ( deg.C) of the outer peripheral part of the disk substrate; and Tp is the thermal deformation temp. (1) of the disk substrate]. A holding time is usually set to 3 sec or more and heat treatment is pref. performed so that the inner peripheral part is present in a region within 1/3 a radius when the center of the disk substrate is set to a start point and the outer peripheral part is present in the region outside 1/3 the radius.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for reducing deformation of a plastic disk substrate used for an optical disk or the like.

[0002]

2. Description of the Related Art In recent years, optical recording media have attracted attention as large-capacity, high-speed memory media. As optical recording media, read-only optical disks (CD, CD-ROM, DVD-RO
M, LD, etc.), recording / reproducing optical discs (WO, CD-
R, DVD-R, etc.), recordable, reproduced, erased, and rewritable optical discs (CD-RW, PD, MO, DVD-RA)
M) are known. As a substrate of these optical recording media, a plastic substrate such as a polycarbonate resin or an acrylic resin is generally used.

[0003] These disk substrates are usually manufactured by a so-called injection molding method including an injection compression molding method. According to this method, an annular flat stamper having preformat information is mounted in a cavity formed between a fixed mold and a movable mold, and a molten resin material is introduced into the cavity to form a stamper. This is a method of molding a disk substrate on which preformat information such as signals (pits) and laser guide grooves is transferred.

[0004]

However, there is a problem that the disk substrate manufactured by this molding method is deformed. It is considered that this is mainly due to molecular orientation distortion due to shear stress during molding and distortion due to thermal stress. The degree of deformation depends on the molding conditions. Generally, when the molding cycle is shortened or the mold temperature is increased to improve productivity, the deformation increases. Further, even if the thickness of the disk substrate is reduced, the deformation increases. As a method of reducing deformation, heat treatment of a disk substrate has been conventionally proposed. However, the conventional heat treatment has a small effect, and further improvement is desired. The present invention addresses this need.

[0005]

According to the present invention, a plastic disk substrate manufactured by injection molding is provided.
By maintaining the inner peripheral portion and the outer peripheral portion under temperature conditions that simultaneously satisfy the following expressions (1) and (2), deformation of the disk substrate can be reduced.

[0006]

Embedded image _{T in -T out ≧ 50 ℃ ...} (1) T p + 30 ℃ ≧ T in ≧ T p -50 ℃ ... (2) where T _in: the inner peripheral portion temperature of the disk substrate (° C.) T _out : Outer peripheral temperature of disk substrate (° C) T _p : Thermal deformation temperature of disk substrate (° C)

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail. In the present invention, a plastic disc substrate manufactured by injection molding is prepared by setting an inner peripheral portion to a high temperature and an outer peripheral portion to a low temperature, and reducing a temperature difference between the two. And heat treatment. This allows
It is considered that since the residual stress is eliminated, the deformation of the disk substrate is also reduced. In the present invention, a plastic disk substrate manufactured by injection molding using a polycarbonate resin, an acrylic resin, or the like is subjected to a heat treatment. The size of the disk substrate varies depending on the standard, but is usually about 50 to 300 mm in diameter, particularly about 80 to 135 mm, and about 0.5 to 1.5 mm in thickness. In the present invention, the inner peripheral portion and the outer peripheral portion of the disk substrate hold the disk substrate under a temperature condition that simultaneously satisfies the following expressions (1) and (2).

[0008]

Embedded image _{T in -T out ≧ 50 ℃ ...} (1) T p + 30 ℃ ≧ T in ≧ T p -50 ℃ ... (2) Here T _in: the inner peripheral portion temperature of the disk substrate (° C.) T _out : Outer peripheral temperature of disk substrate (° C) T _p : Thermal deformation temperature of disk substrate (° C)

If the temperature difference between the inner peripheral portion and the outer peripheral portion is less than 50 ° C., a sufficient deformation reduction effect cannot be obtained as in the conventional method for uniformly heat treating the entire disk substrate. When the temperature of the inner peripheral portion is lower than the thermal deformation temperature of the disk by 50 ° C., the effect of reducing the deformation is poor, probably because the stress relaxation by the heat treatment does not proceed sufficiently. Conversely, if the temperature of the inner peripheral portion is higher than the thermal deformation temperature of the disk by more than 30 ° C., there is a risk that the disk substrate is deformed by the action of gravity or the like during the heat treatment. Preferably, the disk substrate is heat-treated under a temperature condition that satisfies the following equations (3) and (4) simultaneously.

[0010]

## STR00005 ## _{80 ℃ ≧ T in -T out ≧} 60 ℃ ... (3) T p + 20 ℃ ≧ T in ≧ T p -30 ℃ ... (4)

The disk substrate is replaced by the above formula (1) and (2)
The time during which the temperature is preferably maintained under the temperature condition that simultaneously satisfies the expression, preferably the expression (3) and the expression (4), varies depending on the molding conditions of the substrate, the thickness of the substrate, and the like.
It is preferably for at least seconds. If the holding time is too short, of course, a sufficient deformation reducing effect cannot be obtained. A longer holding time is acceptable in terms of reducing deformation, but reduces productivity. Usually at most 3
It is preferable to keep the time to 0 seconds, especially 20 seconds or less.

In the present invention, it is preferable that the heat treatment is performed such that the inner peripheral portion is located in a region inside a radius of 1/3 and the outer peripheral portion is located in a region outside the radius, starting from the center of the disk substrate. Normally, it is preferable that almost the entire area inside one-third is the inner peripheral part. However, in some cases, the inner peripheral portion may extend beyond one third of the radius to the outside. However, it should not exceed 1/2 of the radius in any case, and is preferably within 2/5 of the radius.

Also, the outer peripheral portion does not need to be the entire region outside the radius of 1/3, but at least the entire region outside the radius of 2/3 is preferably the peripheral region. Normally, as long as the means for generating a temperature difference between the outer peripheral portion and the inner peripheral portion allow,
It is preferable that the inner peripheral portion and the outer peripheral portion are close to each other. Means for generating a predetermined temperature difference between the inner peripheral portion and the outer peripheral portion is arbitrary. For example, the entire disk substrate is heated to a predetermined inner peripheral part temperature or slightly higher than it, and then is contacted only with the outer peripheral part with a low-temperature conductive object such as a low-temperature metal to rapidly cool to a predetermined temperature difference. Or a predetermined temperature difference can be generated by rapidly cooling and then gradually cooling the whole. As this deformation, while preventing the temperature from dropping by bringing only the inner peripheral portion of the disk substrate entirely heated to a high temperature into a high-temperature object, the outer peripheral portion is air-cooled to generate a predetermined temperature difference, Alternatively, a predetermined temperature difference can be generated by removing the high-temperature object and lowering the temperature of the whole after the temperature is reduced to such an extent that the outer peripheral portion is formed by air cooling. If this method is applied to, for example, a high-temperature disk substrate immediately after molding, it can be performed with high productivity.

As another method, a method may be employed in which a high-temperature metal or the like is brought into contact with only the inner peripheral portion of a low-temperature disk substrate and heated to generate a predetermined temperature difference. Although it is not clear why the method of the present invention reduces the deformation of the disk substrate, during injection molding, relatively large stress remains in the inner peripheral portion of the disk substrate, but the inner peripheral portion is heated to a high temperature. It is considered that this stress is released by this, and the residual stress of the disk substrate is reduced as a whole and made uniform.

Example 1 An optical disk substrate having an outer diameter of 120 mm, an inner diameter of 15 mm, and a thickness of 0.6 mm was produced by injection molding using a polycarbonate resin (heat deformation temperature: 120 ° C.). Injection molding was performed at a mold temperature of 130 ° C. and a molten resin temperature of 380 ° C.
After cooling the obtained disk substrate to normal temperature,
The disk substrate was concentrically placed on a metal thick plate having a diameter of 30 mm heated to ° C. for 10 seconds. At this time, the portion 7.5 to 15 mm from the center of the disk substrate is heated to 120 ° C.
The temperature from 0 to 50 mm was raised to 40 ° C. When the disk substrate was removed from the metal thick plate and allowed to stand at room temperature, it took about 5 seconds for the portion 7.5 to 15 mm from the center to cool to 100 ° C. FIG. 1 shows the average values of the amounts of deformation in the circumferential direction and the radial direction of a region of 23 to 58 mm from the center of the disk substrate that has undergone this heat treatment. The measurement was performed using a rotary stage and a displacement measuring device equipped with a non-contact type laser displacement meter that moves parallel to the rotation surface with the rotation center of the stage as the origin. When the measurement position is determined by moving the laser displacement meter in the radial direction, and the disk substrate is mounted on the rotary stage and rotated, an average value of the amount of deformation in the circumferential direction at the radial position is obtained.

COMPARATIVE EXAMPLE 1 The average value of the amount of deformation was measured in the same manner as in Example 1 for the disk substrate which was manufactured by injection molding in Example 1 and was not heat-treated. The results are shown in FIG.

Comparative Example 2 The disk substrate manufactured by injection molding in Example 1 was replaced with 1
After heating to 20 ° C. for 30 seconds, it was allowed to cool. The average value of the amount of deformation was measured in the same manner as in Example 1.
The results are shown in FIG.

Example 2 The disk substrate manufactured by injection molding in Example 1 was replaced with 1
After heating to 20 ° C. for 30 seconds, it was concentrically mounted on a 30 mm diameter metal plate heated to 120 ° C. After about 20 seconds, the area from 7.5 to 15 mm from the center of the disk substrate remained at about 120 ° C., but was 40 to 50 m from the center.
In the area of m, the temperature dropped to about 50 ° C. At this point, when the disk substrate was removed from the metal plate and left at room temperature, the area from the center to 7.5 to 15 mm from the center was 100 ° C in about 5 seconds.
The temperature dropped. FIG. 2 shows the measurement results of the amount of deformation in the circumferential direction at a position 58 mm from the center of the disk substrate that has undergone this heat treatment.
Shown in

COMPARATIVE EXAMPLE 3 With respect to the disk substrate manufactured by injection molding in Example 1 and not heat-treated, the amount of deformation in the circumferential direction at a position 58 mm from the center was measured in the same manner as in Example 2.
The results are shown in FIG.

[Brief description of the drawings]

FIG. 1 is a graph showing the average value of the amount of deformation in the circumferential direction of a polycarbonate resin disk substrate (inner diameter 15 mm, outer diameter 120 mm, thickness 0.6 mm) manufactured by injection molding.

FIG. 2 is a graph showing the amount of circumferential deformation of a polycarbonate resin disk substrate (inner diameter 15 mm, outer diameter 120 mm, thickness 0.6 mm) manufactured by injection molding at a position 58 mm from the center.

Claims (8)

[Claims] 1. A plastic disk substrate manufactured by injection molding is maintained under a temperature condition in which an inner peripheral portion and an outer peripheral portion simultaneously satisfy the following expressions (1) and (2). To reduce the deformation of the disk substrate. ## STR1 ## _{T in -T out ≧ 50 ℃ ...} (1) T p + 30 ℃ ≧ T in ≧ T p -50 ℃ ... (2) where T _in: the inner peripheral portion temperature of the disk substrate (° C.) T _out : Outer peripheral temperature of disk substrate (° C) T _p : Thermal deformation temperature of disk substrate (° C) 2. The method for reducing deformation of a disk substrate according to claim 1, wherein the plastic disk substrate is held for at least 3 seconds under a temperature condition that simultaneously satisfies the expressions (1) and (2). 3. A plastic disk substrate manufactured by injection molding is maintained under such a temperature condition that an inner peripheral portion and an outer peripheral portion simultaneously satisfy the following expressions (3) and (4). To reduce the deformation of the disk substrate. ## STR2 ## _{80 ℃ ≧ T in -T out ≧} 60 ℃ ... (3) T p + 20 ℃ ≧ T in ≧ T p -30 ℃ ... (4) where T _in: the inner peripheral portion temperature of the disk substrate (℃ ) T _out : Outer peripheral temperature of disk substrate (° C) T _p : Thermal deformation temperature of disk substrate (° C) 4. The method for reducing deformation of a disk substrate according to claim 3, wherein the plastic disk substrate is held for at least 3 seconds under a temperature condition that simultaneously satisfies the expressions (3) and (4). 5. Starting from the center of the substrate, the inner peripheral portion is a region inside one third of the radius of the substrate, and the outer peripheral portion is a region outside one third of the radius of the substrate. The method for reducing deformation of a disk substrate according to any one of claims 1 to 4, wherein: 6. The method for reducing deformation of a disk substrate according to claim 1, wherein the plastic disk substrate is made of polycarbonate. 7. The method according to claim 1, wherein only the inner peripheral portion of the plastic disk substrate is brought into contact with a hot plate heated to a high temperature to selectively heat the inner peripheral portion. 3. The method for reducing deformation of a disk substrate according to item 1. 8. The method according to claim 1, wherein only the outer peripheral portion of the plastic disk substrate heated to a high temperature is brought into contact with a low-temperature object to selectively cool the outer peripheral portion. 3. The method for reducing deformation of a disk substrate according to item 1.