JPH0957806A - Injection mold for optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an optical disk having small double refraction even at the outer periphery by holding the injection molding temperature of a mold part corresponding to an annular area set out of the outer peripheral area of a cavity from the intermediate area of the disk to be molded in the cavity in a predetermined temperature range. SOLUTION: Temperature regulating means is constituted by providing a plurality of annular passages 3 for passing temperature regulating liquid in the stationary mold part 1 and the movable mold part 2 of an injection mold corresponding to annular area in a flat surface shape set to the area near the outside from the outer peripheral area of a cavity 6 from the intermediate area of an optical disk to be molded in the cavity 6 of the mold. Temperature regulating liquid is supplied to the plurality of passages 3 from a temperature regulating liquid supply source thereby to regulate the temperature of the mold as desired.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for injection molding an optical disc.

[0002]

2. Description of the Related Art A concave portion (pit) corresponding to an information signal to be recorded and reproduced is formed on a signal surface, and a light spot having a minute diameter is irradiated on the signal surface to read the information signal. Such a recorded information recording medium has been practically used as a compact disc, a video disc, a digital audio disc, a write-once disc, or another optical disc. Then, in the case of mass-producing the above-mentioned various optical disks, an injection molding method known as one of the heat and pressure molding methods is used, and the uneven portion corresponding to the information signal to be recorded and reproduced is used. Is performed by transferring the uneven shape of the surface of the stamper formed on the surface of the stamper onto the surface of the disk made of synthetic resin.

That is, a predetermined amount of a particulate thermoplastic resin material in a supply hopper of an injection molding machine is supplied to a heating chamber, and the thermoplastic resin melted in the heating chamber is constituted by an optical disk injection molding die. It is injected into the cavity filled with thermoplastic resin at high speed, and the optical disc in which the uneven shape of the surface of the stamper installed on the wall of the cavity is transferred to the surface of the resin disc is manufactured. I have to. The mold of the injection molding machine is composed of a fixed mold part and a movable mold part, and the cavity is formed between the fixed mold part and the movable mold part.
When the molten thermoplastic resin is filled into the cavity at a high speed, the movable mold part has a mold clamping force that is appropriately opened by the filling pressure of the molten thermoplastic resin injected into the cavity. After the thermoplastic resin of the part is solidified, the mold clamping force is increased so that the uneven shape of the surface of the stamper is satisfactorily transferred to the surface of the disk made of synthetic resin. Then, after the thermoplastic resin in the cavity formed by the mold adjusted to a predetermined low temperature is solidified, the mold is opened and the optical disk substrate in which the stamper pattern is transferred to the mold is molded. Take out from.

By the way, as a substrate material for an optical disk, it has good optical characteristics in the used wavelength range, low hygroscopicity, small warpage due to hygroscopicity, high fluidity in the molding temperature range, and high stampability from the stamper. A thermoplastic resin that can satisfy various conditions such as excellent transferability, excellent heat resistance, good dimensional stability and long-term reliability, good mass productivity, etc. is used. Is desired. In compact discs, the use of a polycarbonate resin that has low hygroscopicity, small warpage due to moisture absorption, excellent heat resistance, good dimensional stability, and high long-term reliability is not adopted. As is well known.

However, the injection-molded product of the polycarbonate resin is liable to cause birefringence due to the molecular orientation of the polymer main chain, and has a problem that it requires high-temperature molding because it has poor fluidity. As the polycarbonate resin for the compact disc, a resin whose molecular weight is reduced to about 14,000 to 17,000 to improve the fluidity is used, and the birefringence is reduced by controlling the molding conditions. That is, in a compact disc using a polycarbonate resin as a substrate, a polycarbonate resin having a molecular weight reduced to about 14,000 to 17,000 is used, and the mold temperature of the injection molding machine and the temperature of the resin are increased, By taking measures such as slowing down the cooling rate, the orientation layer is made smaller and the internal stress of the substrate is made smaller to obtain an optical disc exhibiting a birefringence value within the standard of the compact disc.

[0006]

By the way, as described above, in the manufacture of an optical disc by an injection molding machine, a thermoplastic resin melted in a heating chamber is injected into a cavity formed by an injection molding die. The cavity is filled with thermoplastic resin at high speed, and after the thermoplastic resin is solidified in the cavity of the mold adjusted to a predetermined low temperature, the mold is opened and the stamper pattern is transferred to the surface. The substrate of the optical disc in the state is taken out from the mold,
The temperature of the mold is adjusted by circulating a temperature adjusting liquid through a liquid passage provided in the mold (see FIG. 4). In FIG. 4 showing a cross-sectional view of the mold, 7 is a mold (fixed mold part or movable mold part) 8 is a part constituting a cavity, 3, 3 ...
Is a liquid passage (temperature adjusting groove, cooling groove, temperature adjusting hole, cooling hole) provided in the mold.

The display of the temperature shown in FIG. 4 is the temperature value of each isothermal curve shown in the figure. Conventionally, the temperature difference on the surface of the mold becomes small in consideration of the thermal diffusivity. The arrangement mode of the temperature control grooves 3, 3 ... Is determined so as to be in such a state. However, depending on the arrangement of the temperature control grooves 3, 3, ... As described above, the temperature of the mold in the portion corresponding to the outer peripheral portion of the optical disc corresponds to the middle peripheral portion of the optical disc due to heat radiation from the mold. Is lower than the temperature of
The resin injected into the cavity is blocked by the outer peripheral ring (member indicated by reference numeral 5 in FIGS. 1 and 2) to increase the internal stress of the resin. growing. As a means for solving the above-mentioned problems, it is conceivable to provide a temperature control groove in the outer peripheral space of the mold as disclosed in JP-A-62-275729. 27574
In the temperature adjusting groove provided in the outer peripheral space of the mold as shown in Japanese Patent Publication No. 9, the temperature variation on the outer peripheral surface of the mold becomes large, and the birefringence value on the circumference of the outer peripheral part of the optical disk is increased. Has the drawback that it varies widely.

[0008]

According to the present invention, a molten thermoplastic resin is injected into a cavity formed by a mold for injection molding of an optical disc, and the uneven shape of the surface of a stamper provided on the wall surface of the cavity is reduced. A mold for injection molding of an optical disk used when manufacturing an optical disk in a state of being transferred onto the surface of a resin disk, which is an intermediate region of the optical disk molded in the cavity of the injection molding mold described above. To the region outside the outer peripheral region of the cavity, the temperature at the time of injection molding of the portion of the injection molding die corresponding to the annular region in the planar shape set in the predetermined temperature range. Injection molding die for an optical disc having a temperature adjusting means for holding the molten thermoplastic resin and a molten thermoplastic resin are injected into a cavity formed by the injection molding die for the optical disc. An injection-molding die for an optical disc used in producing an optical disc in which the uneven shape of the surface of the stamper provided on the wall surface of the cavity is transferred to the surface of the disc made of resin. An injection molding die corresponding to an annular area in a planar shape set from the intermediate area of the optical disk molded in the cavity of the molding die to the area outside the outer peripheral area of the cavity. There is provided a mold for injection molding of an optical disc, in which a plurality of annular passages through which a liquid for temperature control is circulated is provided in the section.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The concrete contents of an optical disk injection molding die of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a vertical cross-sectional view of a part of a mold for injection molding of an optical disc of the present invention, in which 1 is a fixed mold part, 2 is a movable mold part, and 4 is a recording / reproducing target. This is a stamper in which uneven portions corresponding to information signals are formed on the surface. The inner peripheral portion of the stamper 4 is held by a retainer (not shown), and the outer peripheral portion of the stamper 4 is held by an outer peripheral ring 5. The inner peripheral surface 5a of the outer peripheral ring 5 has the fixed mold portion 1 described above.
And an outer peripheral wall of the cavity 6 formed between the movable mold part 2 and the inner peripheral surface 5 a of the outer peripheral ring 5.
Forms the outer peripheral surface of an optical disk made of thermoplastic resin having a diameter of 120 mm, which is molded in the cavity 4.

In the fixed mold part 1 and the movable mold part 2 of the injection molding die of the optical disk shown in FIG. 1, the outer periphery of the cavity 6 from the intermediate area of the optical disk molded in the cavity 6 of the injection molding die. The temperature at which the temperature at the time of the injection molding operation of the portion of the injection molding die corresponding to the annular area in the planar shape set up to the area outside the area is maintained within the predetermined temperature range. Adjustment means are provided.
The temperature adjusting means in the configuration example shown in FIG. 1 is set from the intermediate region of the optical disk molded in the cavity 6 of the injection molding die to a region near the outside of the outer peripheral region of the cavity 6. Fixed mold portion 1 of the injection molding die corresponding to the annular region in the formed planar shape
And the movable mold part 2 are provided with a plurality of annular passages 3, 3 ... (temperature adjusting groove, cooling groove, temperature adjusting hole, cooling hole) through which the temperature adjusting liquid is circulated, By supplying the temperature adjusting liquid to the plurality of annular passages 3, 3 ... (Temperature adjusting grooves 3, 3 ...) from the temperature adjusting liquid supply source (not shown), The temperature of the injection mold is adjusted as desired.

FIG. 1 shows an example of the structure of an injection molding die for an optical disk used when a substrate for an optical disk having a diameter of 120 mm is produced in a cavity 6 of the injection molding die. 1, the position of the inner peripheral surface 5a of the outer peripheral ring 5 forming the outer peripheral wall of the cavity 6 is indicated by an arrow φ1.
It is indicated by 20. In the fixed mold part 1 and the movable mold part 2 in FIG. 1, the temperature adjusting grooves 3, 3, ... Shown on the left side of the position of the inner peripheral surface 5a of the outer peripheral ring 5 are cavities from the intermediate region of the optical disk. 6 are temperature control grooves 3, 3 ... Provided in an annular region in a plan view corresponding to the outer peripheral region of 6, and in the fixed mold part 1 and the movable mold part 2 in FIG. Inner peripheral surface 5a of outer peripheral ring 5
The temperature adjusting groove 3 shown on the right side of the position of is the temperature adjusting groove 3 provided in the annular region in the planar shape corresponding to the region near the outside of the outer peripheral region of the cavity 6.
It is. In the configuration example shown in FIG. 1, the temperature control groove 3 illustrated on the right side of the position of the inner peripheral surface 5a of the outer peripheral ring 5 described above has an outer peripheral ring 5 indicated by an arrow φ120.
The center is located at a position shown by an arrow φ130 in FIG.

In the plane shape set from the intermediate area of the optical disk molded in the cavity 6 of the injection molding die to the area outside the outer peripheral area of the cavity 6, the area corresponding to the annular area. In order to keep the temperature of the injection molding die part during the injection molding operation within a predetermined temperature range, temperature adjusting means provided in the fixed mold part 1 and the movable mold part 2 of the injection molding mold of the optical disk. In addition to the structure in which the temperature adjusting liquid is circulated in the temperature adjusting groove as described above, the intermediate region of the optical disk molded in the cavity 6 of the injection molding die to the outer peripheral region of the cavity 6 can be used. A heating wire for temperature control is provided on the fixed mold part 1 and the movable mold part 2 of the injection molding die corresponding to the annular area in the plane shape set up to the area closer to the outside than the area. You may make it arrange.

A molten thermoplastic resin is rapidly filled in a cavity 6 formed between a fixed mold portion 1 and a movable mold portion 2 of an injection molding die for an optical disk shown in FIG. As an example, a polycarbonate resin having an average molecular weight of 15,000 is used as a thermoplastic resin, the polycarbonate resin is melted at 340 degrees Celsius, and the temperature is adjusted to 115 degrees Celsius. The inside of the cavity 6 is filled at high speed. When the above-mentioned molten thermoplastic resin is solidified, the substrate of the optical disk having a diameter of 120 mm is taken out from the mold in a state where the uneven shape of the surface of the stamper 4 is well transferred to the surface of the thermoplastic resin disk. be able to.

Then, with respect to the optical disc manufactured by using the substrate of the optical disc obtained by injection molding using the optical disc injection molding die shown in FIG. When the average value of the birefringence values at 12 points on the circumference was measured, the results shown by the white circles in FIG. 5 were obtained. In addition, regarding an optical disc manufactured by using an optical disc substrate obtained by injection molding using the optical disc injection molding die shown in FIG. 1, on each circumference at a plurality of specific discrete positions in the radial direction. The difference between the maximum value and the minimum value of the birefringence values at the 12 points was calculated as the birefringence variation, and the result is shown by the white bar graph in FIG. The horizontal axis in FIG. 5 represents the distance from the center of the optical disc in the radial direction.

FIGS. 2 and 3 are views showing the construction of an injection molding die used as a comparison with the injection molding die of the optical disk of the present invention described with reference to FIG. A mold for injection molding of an optical disk, which is shown in FIG.
Inside the cavity 6 of the injection mold, the diameter is 120 mm
2 is an injection-molding die for an optical disc used to manufacture a substrate for the optical disc, and the position of the inner peripheral surface 5a of the outer peripheral ring 5 forming the outer peripheral wall of the cavity 6 is indicated by an arrow φ120 in FIG. There is. In the fixed mold part 1 and the movable mold part 2 in FIG. 2, the temperature adjusting grooves 3, 3 ... Are not provided on the right side of the position of the inner peripheral surface 5a of the outer peripheral ring 5 described above. The temperature control grooves 3, 3 ... Of the injection molding die of the optical disk shown in FIG. 2 are provided in an annular area in a plan view corresponding to the intermediate area of the optical disk and the outer peripheral area of the cavity 6. The temperature control groove 3 located on the outermost side of the is centered at a position indicated by an arrow φ109.

The injection molding die of the optical disk shown in the plan view of FIG. 3 has the following features in the cavity 6 of the injection molding die:
It is a mold for injection molding of an optical disk used when manufacturing a substrate of an optical disk having a diameter of 120 mm.
The position of the inner peripheral surface of the outer peripheral ring forming the outer peripheral wall of the cavity 6 is indicated by an arrow φ120. Further, the temperature control grooves 3, 3, ... Are located on the outermost side of the inner peripheral surface of the outer peripheral ring on the left side thereof.
Is provided so that its center is located at a position indicated by an arrow φ109, and on the right side of the position of the inner peripheral surface of the outer peripheral ring, a substantially linear temperature control groove 9,
9 are provided.

Polycarbonate resin having an average molecular weight of 15000 is used as a thermoplastic resin in the cavity 6 of the injection molding die of the optical disk of each comparative example having the structure shown in each of FIGS. 2 and 3 described above. Using the above-mentioned polycarbonate resin in a molten state at 340 degrees Celsius, the inside of the cavity 6 of the injection molding die of the optical disc, which is kept at 115 degrees Celsius by the temperature control means, is filled at high speed, When is solidified, the substrate of the optical disk having a diameter of 120 mm is taken out from the mold in a state where the uneven shape of the surface of the stamper 4 is transferred to the surface of the disk made of thermoplastic resin, and each of the substrates manufactured using the substrate is manufactured. For optical discs, the birefringence value of 12 points on each circumference at specific discrete radial positions is calculated. When the values were measured, the optical disc manufactured by using the substrate of the optical disc injection-molded by using the injection-molding die for the optical disc of the comparative example shown in FIG. 2 is as shown by a black circle in FIG. The result is obtained,
Further, an optical disc manufactured by using the substrate of the optical disc obtained by injection molding using the injection molding die for the optical disc of the comparative example shown in FIG. 3 is shown by a circle hatched with diagonal lines in FIG. The result is as follows.

Next, regarding an optical disc manufactured by using a substrate of the optical disc obtained by injection molding using the optical disc injection molding die shown in FIG. 2, the optical disc is formed at a plurality of discrete discrete positions in the radial direction. The difference between the maximum value and the minimum value of the birefringence values at 12 points on the circumference of is obtained as the birefringence variation, and the result is shown by the black bar graph in FIG. 5, which is shown in FIG. Regarding an optical disc manufactured by using an optical disc substrate obtained by injection molding using an optical disc injection molding die, 12 birefringences on each circumference at specific discrete radial positions The result of obtaining the difference between the maximum value and the minimum value of the above as the variation of the birefringence is shown by a bar graph hatched with diagonal lines in FIG. As is clear from the measurement results shown in FIG. 5, in the optical disc manufactured by using the substrate of the optical disc obtained by injection molding using the optical disc injection molding die of the present invention, the outermost peripheral portion of the optical disc is Can prevent birefringence from becoming a problem.

[0019]

As is clear from the above description, in the injection molding die for an optical disk of the present invention, the molten thermoplastic resin is injected into the cavity formed by the injection molding die for the optical disk. Then, the unevenness of the surface of the stamper provided on the wall surface of the cavity is transferred to the surface of the resin disk and is molded in the cavity of the injection mold of the optical disk used when manufacturing the optical disk. During the injection molding work of the portion of the injection molding die corresponding to the annular area in the planar shape set from the intermediate area of the optical disc to the area outside the outer peripheral area of the cavity By providing the temperature adjusting means for keeping the temperature within the predetermined temperature range, it is possible to prevent the birefringence from becoming a problem even in the outermost peripheral portion of the optical disc. Ri can be favorably solve the conventional problems by the present invention.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a part of a mold for injection molding of an optical disc of the present invention.

FIG. 2 is a longitudinal sectional view of a part of a mold for injection molding of an optical disc of a comparative example.

FIG. 3 is a plan view of a mold for injection molding an optical disc of a comparative example.

FIG. 4 is a diagram showing a temperature distribution in a cross section of an injection molding die.

FIG. 5 is a graph of measured values of the birefringence value in the radial direction of the optical disc.

[Explanation of symbols]

1 ... Fixed mold part, 2 ... Movable mold part, 3, 9 ... Temperature control groove, 4
... Stamper, 5 ... Outer ring, 6 ... Cavity, 1 ...

Claims (2)

[Claims] 1. A molten thermoplastic resin is injected into a cavity formed by an injection-molding die for an optical disk, and the uneven shape of the surface of a stamper provided on the wall surface of the cavity is applied to the surface of the resin disk. An injection-molding die for an optical disc used in producing an optical disc in a transferred state, which is from an intermediate region of the optical disc formed in the cavity of the above-mentioned injection-molding die to a peripheral region of the cavity. Temperature control means for maintaining the temperature of the portion of the injection molding die corresponding to the annular area in the plane shape set up to the area near the outside during the injection molding operation within a predetermined temperature range. A mold for injection molding of an optical disk, which is characterized by being provided. 2. A molten thermoplastic resin is injected into a cavity formed by an injection molding die for an optical disk, and the unevenness of the surface of a stamper provided on the wall surface of the cavity is applied to the surface of the resin disk. An injection-molding die for an optical disc used in producing an optical disc in a transferred state, which is from an intermediate region of the optical disc formed in the cavity of the above-mentioned injection-molding die to a peripheral region of the cavity. A plurality of annular passages for circulating a liquid for temperature control are provided in the portion of the injection molding die corresponding to the annular area in the planar shape set up to the area near the outside. Injection mold for optical disk.