JPH10626A - Plastic molding method and apparatus - Google Patents

Abstract

(57) [Problem] In a conventional technique of plastic injection molding, transferability differs depending on a distance from a gate. On the other hand, if an attempt is made to ensure the transferability over the entire area of the molded product, molding must be performed at a high mold temperature, and the molded product will be deformed during release and removal. Therefore, the present invention provides a heat insulating portion between the mold cavity surface or the mold cavity surface and the mold cooling path in order to maintain the interface temperature between the molten resin and the mold cavity surface at a high temperature and uniformly. The transfer amount and its uniformity were improved by the molding method in which the heat transfer efficiency was changed depending on the location in the mold cavity. In order to maintain the temperature of a molten resin, which has been completely charged in a non-uniform state in temperature, on the surface of a mold cavity at a high temperature and uniformly, the surface of the mold cavity or the surface from the mold cavity surface to the mold cooling path is cooled. Provide a heat insulation part between,
In addition, the heat transfer efficiency is changed according to the temperature drop of the molten resin, that is, by changing the position in the mold cavity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plastic molding method and a plastic molding method.

[0002]

2. Description of the Related Art In plastic injection molding, as one method for improving mold transferability, a portion of a molten resin filled in a mold cavity in contact with a cavity surface is kept at a high temperature and uniformly over the entire region. Is mentioned. As a specific temperature condition, it is necessary to maintain the boundary surface temperature between the filling resin and the surface of the mold cavity at a temperature equal to or higher than the thermal deformation temperature of the molding resin, and in some cases, equal to or higher than the glass transition temperature.

In forming an optical disk substrate, the most important issue is the precise transfer of information pits and laser guide grooves on the order of submicrons. In general, in injection molding of an optical disk substrate, as shown in FIG. 1, a nickel stamper for forming and transferring information pits and laser guide grooves is mounted in a mold cavity, and molten resin is injected from a gate provided in the center of the cavity. Is injected and filled, cooled and solidified, and then released to complete the molding.

In injection molding, molten resin is cooled by a mold during filling (under the molding conditions described below, about 20
Therefore, in the conventional technology of an optical disc substrate made of a polycarbonate resin, almost no transfer was performed with respect to the groove depth of the stamper as shown in FIG.
Moreover, the amount of transfer tends to decrease as the distance from the gate increases.

In the case of molding an optical disk substrate, techniques for improving transferability without increasing pressure to avoid an increase in optical distortion (birefringence) include (1) high-speed filling of molten resin, and (2) gold. Molded with high mold temperature.

In the high-speed filling molding of the prior art (1), as shown in FIG. 8, transferability is improved to some extent, but complete molding transfer cannot be obtained. In addition, the problem that the transferability decreases as the distance from the gate decreases is not solved. In terms of the performance of the injection molding machine, high-speed filling is possible as compared with the example shown in FIG. 8, but there is a limit to high-speed filling due to generation of burrs and the like.

In the prior art (2), the mold temperature is at most close to the thermal deformation temperature of the molding resin (below the thermal deformation temperature: the thermal deformation temperature of the polycarbonate resin is from the viewpoint of preventing deformation of the molded product at the time of mold release). 126 [deg.] C.), the transferability is not satisfactory as shown in FIG. 8 as described above, and the problem that the transferability decreases as the distance from the gate increases as in the prior art (1) remains. It has been done.

As a method for preventing a decrease in transferability, a method has been proposed in which molding is performed by increasing the mold temperature (cavity temperature) in a portion far from the gate, as described in JP-A-1-278322. ing. However, in this method, even when the substrate is released from the mold, the mold temperature is high (the temperature is set to be equal to or higher than the thermal deformation temperature in order to improve transferability). (Warpage) specification is not satisfied. In addition, a plurality of mold temperature control mechanisms are required in terms of equipment. Further, as one method of solving this problem, a mold temperature cooling / heating cycle method has been developed in which the mold temperature is set to be equal to or higher than the heat deformation temperature when filling the resin, and the mold temperature is equal to or lower than the heat deformation temperature when releasing the mold. I have. However, with this method, the equipment becomes more complicated,
In addition, a new problem that the molding cycle becomes longer occurs.

[0009]

As described above, in the prior art, a plurality of mold temperature control mechanisms are required to obtain uniform transferability, and the resulting molded product is inevitably deformed by release and removal. Is done. An object of the present invention is to solve these problems.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a mold for reducing the cooling rate of a molten resin which has been completely filled in a non-uniform temperature state and realizing a uniform cooling rate is provided. A heat insulating portion is provided between the surface of the cavity or the surface of the mold cavity and the mold cooling path, and the heat transfer efficiency is changed depending on the location in the mold cavity, so that the cooling speed is slow and uniform molding is realized.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described below with reference to the drawings, taking an optical disk substrate mold as an example.

Embodiment 1: First, a ceramic heat insulating material 13
FIG. 2 shows an embodiment according to the present invention in which the thickness is changed according to the distance from the gate.

Beforehand, it was simulated how the temperature at the surface of the stamper 4 with the filled resin, which is a main factor that determines the mold transferability, changes depending on the thickness of the heat insulating material. Table 1 shows the specifications used in the simulation, and the results are shown in FIG.

[0014]

[Table 1]

Based on the calculation results shown in FIG. 3, the boundary temperature between the resin immediately after resin filling and the surface of the stamper 4 is set at a resin temperature of 380.degree. C. and a mold temperature of 110.degree. Is 130 ° C. as a temperature higher than the thermal deformation temperature (126 ° C.), the thickness of the heat insulating material at that temperature is 0.13
mm. On the other hand, according to the resin flow analysis, there is a drop of about 30 ° C. from the gate to the outer peripheral portion of the substrate. Therefore, when the resin temperature at the outer peripheral portion is 350 ° C., the thickness of the heat insulating material is 0.6 mm. Based on this result, the thickness of the heat insulating material was increased as the distance from the gate was increased, and was set to 0.13 mm at the inner peripheral portion and 0.6 mm at the outer peripheral portion. The heat insulating material 1
3 is attached to the movable core 5 with an epoxy adhesive.
Fixed. Thereby, even at the outer peripheral portion of the substrate where the molten resin temperature immediately after filling is lower than the inner peripheral portion of the substrate near the gate,
The temperature of the boundary surface between the resin and the stamper immediately after filling with the resin is equal to or higher than the thermal deformation temperature of the resin, and the same temperature is attained between the inner and outer peripheral portions of the substrate. By molding with such a mold,
As shown in FIG. 8, good transferability can be obtained in both the inner and outer peripheral portions. Moreover, since the cooling rate of the resin is slow in this mold, the internal stress of the molded product (birefringence)
Can also be kept small.

In the first embodiment, zirconia is used as a heat insulating material. However, as shown in Table 2, a titania material having a small thermal conductivity may be used. Incidentally, as compared with a resin material generally used as a heat insulating layer, the ceramics employed in the present invention have a much higher hardness than the resin material, do not deform due to injection molding pressure, and do not lower the planar accuracy of the molded product.

Embodiment 2 Next, an embodiment according to the present invention in which the heat conductivity of the heat insulating material layer is changed in accordance with the distance from the gate by combining two kinds of materials having high and low thermal conductivity. Is shown in FIG. In FIG. 2 of the embodiment, since the thickness of the heat insulating material is different between the inner peripheral portion and the outer peripheral portion, the movable core 5 to which the heat insulating material is attached has a conical shape, which causes a processing problem. Therefore, in the embodiment shown in FIG. 4, the thickness ratio of the ceramic material 14 having a large thermal conductivity in the inner peripheral portion is made larger than that of the ceramic heat insulating material 13 having a small thermal conductivity, and vice versa in the outer peripheral portion. And the thickness of the structure is uniform. This makes it possible to attach the heat insulating material without processing the movable core into a conical shape, and furthermore, a heat insulating layer having a high thermal conductivity at the inner peripheral portion of the substrate and a small heat conductivity at the outer peripheral portion is formed. . As a result, the cooling effect of the filled molten resin is the same as that of the above-described embodiment, and a substrate having a uniform transferability at the inner and outer peripheral portions can be obtained in the optical disk substrate molding. In particular, using silicon nitride ceramics (Table 2) having higher thermal conductivity than the movable core material,

[0018]

[Table 2]

If the above-mentioned zirconia is used as the heat insulating material 13 having a small heat conductivity, the thickness specification of the zirconia heat insulating material can be the same as that of the embodiment from the calculated value of the heat conduction. Further, a titania-based heat insulating material 13 having a low thermal conductivity may be used. Also by molding with such a mold, good transferability can be obtained at both the inner and outer peripheral portions as shown in FIG.

Embodiment 3 Next, FIG. 5 shows an embodiment in which an air heat insulating portion is provided as a heat insulating layer. As shown in FIG. 5, an air insulation section is provided between the cavity surface and the cooling circuit,
In addition, the size of the heat insulating portion is increased in accordance with the distance from the gate, thereby increasing the heat insulating effect up to the mold cooling passage. Thus, the same effect as that of the first embodiment shown in FIG. 1 can be obtained.

Embodiment 4 FIG. 6 shows an embodiment using a sintered metal having a void as a heat insulating material. As shown in Example 1, the thickness of the sintered metal is increased in accordance with the distance from the gate.

Embodiment 5: Further, as shown in FIG. 7, the porosity of the sintered alloy is increased according to the distance from the gate to enhance the heat insulating effect.

Thus, the same effects as those of the first embodiment can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a conventional plastic mold.

FIG. 2 is a sectional view of a movable mold core of a plastic molding die according to a first embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the thickness of the heat insulating material and the stamper surface temperature, which are the basis of the first embodiment of the present invention.

FIG. 4 is a sectional view of a movable mold core of a plastic molding die according to a second embodiment of the present invention.

FIG. 5 is a sectional view of a movable mold core of a plastic molding die according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a movable mold core of a plastic molding die according to a fourth embodiment of the present invention.

FIG. 7 is a sectional view of a movable core portion of a plastic molding die according to a fifth embodiment of the present invention.

FIG. 8 is a diagram showing the mold transferability of an optical disc substrate according to the related art and the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, ... Optical disk board molding type, 2 ... fixed type, 3 ... movable type, 4 ... stamper, 5 ... movable type core, 6 ... optical disk substrate, 7 ... stamper inner peripheral holder, 8 ... stamper outer peripheral holder, 9 ... center hole Forming punch, 10 ... ejector, 11 ...
Information pit and laser light guide groove, 12 cooling circuit, 13
... Ceramic insulation material, 14 ... Ceramic material, 15 ...
Air insulation, 16, 16 '... Sintered metal insulation

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazuhiro Fujikawa 1-88 Ushitora 1-chome, Ibaraki-shi, Osaka Inside Hitachi Maxell, Ltd.

Claims (6)

[Claims] 1. A heat insulating portion or a heat insulating layer is provided between a cavity surface or a cavity surface and a mold cooling passage,
A plastic molding method, wherein molding is performed by changing the heat insulating effect of the heat insulating portion or the heat insulating layer depending on the position in the cavity. 2. The plastic molding method according to claim 1, wherein the thickness of the member forming the heat insulating portion is changed depending on the position in the cavity. 3. The heat-insulating part according to claim 1, wherein a plurality of materials having different thermal conductivities are combined to form the heat-insulating part, and the heat-insulating part is formed by changing the heat conductivity according to the position in the cavity. Plastic molding method. 4. A plastic molding method according to claim 1, wherein an air insulating portion is provided between the cavity surface and the mold cooling passage, and the ratio of the air insulating portion is changed depending on the position in the cavity. Method. 5. The plastic molding method according to claim 1, wherein a member made of sintered metal is used as the heat insulating member, and the porosity of the member is changed according to the position in the cavity. 6. A plastic molding method and apparatus for molding an optical disk substrate, wherein the molding is performed by providing a heat insulating portion / layer according to claim 1, 2, 3, 4, 5 on the lower surface of the stamper.