JPS61188120A - Manufacture of substrate for magneto-optical disc - Google Patents

Abstract

PURPOSE:To obtain a high quality substrate for magneto-optical disc by a method wherein the end of a compression member is moved so as to reduce the internal volume of a cavity by means of driving means, after raw material for a molded body is filled in the cavity for injection molding. CONSTITUTION:Firstly, raw material 7 injected through a sprue 3 in a cavity, which is set for injecting raw material. In this case, the injection pressure is allowed to be so low that a little air space 8 is produced at the peripheral part of the cavity. Secondly, before the injected raw material 7 solidifies, a compression ring 4 is moved by means of a driving source 5 so as to reduce the internal volume of the cavity in order to apply pressure by the end of the ring to the raw material in the peripheral part of the cavity, resulting in trimming the external shape of a molded body or substrate by vanishing the air space 8. In such a manner as a described above, the sinkage at the portion of the cavity, to which the injection pressure is most hard to be transmitted, is eliminated by applying pressure to the raw material in said portion. In addition, because the molded body can be molded at very low injection pressure, the molded body with little internal strain is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an injection molding method that is effective for manufacturing plastic molded bodies without sink marks or internal distortion, particularly plastic substrates such as magneto-optical disks.

[Conventional technology]

□ Conventionally, the pull steel substrate of a magneto-optical disk has generally been manufactured by injection molding or injection compression molding. When manufacturing such a disk-shaped substrate,
The gate for filling the raw material into the cavity formed by the mold is designed to fill the raw material into the disc-shaped cavity as uniformly and quickly as possible.
Generally located in the center of the disk.

[Problem that the invention seeks to solve]

However, in the case of injection molding, the pressure from the injection of the raw material is difficult to transmit to the resin raw material filled around the periphery of the disc-shaped cavity, so there are two sinks around the periphery of the molded disc-shaped substrate. This often occurred.

In order to prevent the occurrence of such sink marks, when the injection pressure of the raw material is increased, the difference in pressure applied to the resin at the center of the substrate near the gate □ and the resin at the periphery of the substrate also increases. This has the disadvantage that the distortion caused by the pressure difference remains on the molded substrate, which does not satisfy the birefringence properties of a disk substrate, and the substrate is easily deformed or damaged.

On the other hand, the conventional injection compression molding method has the above drawbacks.
However, since the entire surface of the substrate, which is a molded object, is compressed after the molded material is completely filled into the cavity, the molding accuracy of the information side of the substrate, which requires high molding accuracy, decreases. Or.

This surface was often damaged.

The above-mentioned problems exist not only in the above-mentioned disk-shaped substrates but also in the manufacture of products requiring high molding accuracy, and have remained unsolved.

The present invention has been made to solve the above problems, and its purpose is to prevent sink marks even in areas where sink marks are likely to occur in the conventional injection molding method, and to prevent sink marks from occurring inside the interior. An object of the present invention is to provide an injection molding method that can produce molded bodies with reduced distortion, particularly high-quality substrates for magneto-optical disks.

[Means for solving problems]

In the injection molding method of the present invention, each surface constituting the cavity of the mold, and a drive means installed in the mold so that the end surface is exposed at a desired portion within the cavity constituting surface of the mold, After setting a cavity with the end face of the compression member movable within the mold, the molded body material is filled into the cavity, and then the end face of the compression member is moved by the drive means to reduce the internal volume of the cavity. The molded body raw material is locally pressurized by moving the molded body raw material so as to decrease the pressure, thereby uniformizing the internal pressure of the molded body raw material within the cavity.

〔Example〕

Hereinafter, the injection molding method of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a portion for setting a cavity in an example of an apparatus used in the method of the present invention. The apparatus in this example is for molding a substrate for a magneto-optical disk.

1 and 2 are molds, 3 is a sprue portion, and 6 is a portion for forming an information surface of the substrate. A compression ring 4 is installed inside the mold 2, and the end surface of the compression ring 4 is a mold.

It is exposed in a part of the plane that constitutes the cavity of No. 2. That is, this end face exists as an annular shape in the periphery of the circular plane constituting the cavity of the mold 2. The compression ring 4 can be moved within the mold 2 by an attached driving source 5.

FIGS. 2 and 3 are schematic diagrams showing the steps of carrying out the method of the present invention using the above-mentioned apparatus.

First, the mold bodies 1 and 2 are clamped, while the compression ring 4 is not 11i! 1. Set the cavity for raw material injection. Raw material 7 is injected from sprue 3. At this time, the injection pressure does not need to be high enough to apply sufficient pressure to the raw material 7 existing in the peripheral area of the cavity, but may be sufficient to create some voids 8 in the peripheral area (FIG. 2).

Next, before the raw material 7 solidifies, the compression ring 4 is moved by a driving source 5 using, for example, hydraulic pressure so as to reduce the internal volume of the cavity, and the raw material 7 existing around the cavity is removed by this end face. Pressure is applied (FIG. 3). By doing so, the voids 8 are eliminated and the outer shape of the substrate on which the molded product is formed is adjusted, and sink marks are not generated on the periphery and sides of the molded product. The pressure and the driving pressure of the compression ring 4 are determined with consideration given to preventing strain from being caused in the periphery of the substrate due to too much pressure being applied to the raw material 7 in the periphery of the cavity.

After the raw material 7 is cooled and solidified, the molded body is taken out.

According to the method of the present invention as described above, even if the injection pressure of the raw material is lowered, it is possible to mold a molded article without sink marks even in the peripheral area of a disk-shaped substrate. Note that the method of the present invention can be applied not only to disc-shaped molded bodies but also to molded bodies of any other shape. That is, the effects of the present invention can be obtained by applying pressure to the molded body portion where sink marks are likely to occur locally using a compression member corresponding to the compression ring of the above embodiment.

〔Effect of the invention〕

As described above, in the method of the present invention, after the injection of the raw material is completed, the compression member is used to pressurize the raw material present in a part of the cavity where injection pressure is most difficult to transmit, thereby eliminating sink marks in that part. As a result, it is possible to mold a molded article with a very low injection pressure, so that a molded article with less internal distortion can be obtained. The method of the present invention is particularly effective when molding substrates for magneto-optical disks, molded bodies of complex shapes, etc. that require high molding accuracy.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the cavity setting part of an example of the apparatus used in the method of the present invention, and FIGS. 2 and 3 are schematic diagrams showing an example of the implementation steps of the method of the present invention. be. 1.2: Mold 3 Varnish pull 4: Compression ring 5: Drive source 6: Information surface forming part 7: Raw material Figure 1 Figure 3

Claims (1)

[Scope of Claims] 1) Each surface constituting the cavity of the mold, and a driving means installed in the mold so that the end surface is exposed at a desired portion within the cavity constituting surface of the mold; After setting a cavity with the end face of the compression member movable within the mold, the molded body material is filled into the cavity, and then the end face of the compression member is moved by the drive means to reduce the internal volume of the cavity. An injection molding method characterized in that the raw material for the molded body is locally pressurized by moving so as to reduce the internal pressure of the raw material for the molded body within the cavity. 2) A mold having a circular cavity forming surface is used to set a cavity for molding the magneto-optical disk substrate, and an annular mold which is exposed at the periphery of the cavity forming surface is used as the compression member. An injection molding method as claimed in claim 1, in which a compression ring having end faces is used.