JPS61100425A - Mold for molding plastic - Google Patents

Abstract

PURPOSE:To improve the surface smoothness of a product, by using a ceramic material to constitute at least part of the molding surface constituting a cavity. CONSTITUTION:When a stationary mold 10 and a movable mold 20 are closed, a flat cavity 30 for molding is definded between auxiliary plates 13, 23. In view of the durability, etc., the auxiliary plates 13, 23 preferably have a thickness of 100 microns or more, and as a material therefor can be mentioned desirably a material high in dielectric and absorption of high-frequency, particularly silicon carbide, SiC. If high surface smoothness is required, a signal crystal is used. The movable mold 10 is closed to the stationary mold 10, and a resin is injected. The resin flows from a sprue 14 via a runner 15 to fill the cavity 30. As a result, a disk A is molded. The disk A can have high surface smoothness, since the auxiliary plates 13, 23 has high surface smoothness, and are heated previously to or over the resin deformation temperature.

Description

Detailed Description of the Invention The present invention relates to a mold for molding plastic products with excellent surface smoothness. Its applications are expanding and it is used in various products, but along with this, high surface smoothness is sometimes required.For example, in substrates for optical disks and magnetic λ disks, the center line average roughness Ra In order to mold a substrate with the above-mentioned surface smoothness, it is necessary to suppress the illumination to 0.015 microns or about 0°003 microns in some cases. However, even if the mold material is cut and polished, the above-mentioned high surface smoothness cannot be achieved due to the material and the difficulty of machining.

Therefore, as seen in Japanese Unexamined Patent Publication No. 59-135133, a technology to form a metal film of chromium, rhodium, etc. on the molding surface of a mold using a metal surface film method (vacuum deposition or sputtering) has been studied. has been done.

(Problem to be solved by the invention) However, with the above technology, even if Ra of the molding surface can be reduced by covering the mold material with a large center line average roughness Ra with a film, the surface of the mold material It is not possible to reduce the waviness Rw. Moreover, since the film cannot be made thick, the durability of the film is poor.

i'' W Roasted (Means for Solving the Problems) Since the present invention has been made to solve the above problems,
The gist thereof is to provide a molding metal for plastic molding in which at least a part of the molding surface constituting the cavity is made of a ceramic material.

(Function) In the present invention, since a ceramic material that can achieve high surface smoothness by cutting and polishing is used for at least a part of the molding surface, the plastic product that is molded in contact with this molding surface is Surface smoothness can be improved.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. The illustrated injection mold is for molding a plastic magnetic disk or optical disk.

The molds include a fixed mold 10 and a movable mold 20 that are opened and closed with each other.
It is made up of. A circular recess 11 is formed in the fixed mold 10, and an auxiliary plate 12 made of metal is attached to the center of the recess 11, and an annular auxiliary plate 13 made of a ceramic material is attached around the periphery. Ikegata: A recess 21 is also formed in the movable mold 20, and a metal auxiliary plate 22 is placed in the center of this recess 21, and an annular auxiliary plate 23 made of a ceramic material is placed around the periphery.
are pasted on each.

When the fixed type 10 and mobile type 20 are closed, the auxiliary platform
A flat molding cavity 30 is formed between the trays 13 and 23. The surface of the auxiliary plate 13.degree. 23 becomes the molding surface 13a, 23a. The molding surfaces 13a, 23a have extremely high surface smoothness due to surface cutting and polishing. From the viewpoint of durability, it is desirable that the auxiliary plates 13, 23 have a thickness of 100 microns or more.

As the ceramic material in 13.23 (auxiliary play) above, it is desirable to use a material with high dielectricity and high frequency absorption ability;
Silicon carbide SiC is preferable.

A sintered body is usually used as the ceramic material, but a single crystal body is used when higher surface smoothness is required.

A sprue 14 is formed on the fixed mold 10.

A runner 15 is formed between the opposing auxiliary plays) 12 and 22. Also, mobile type 20 auxiliary play)
An ejector pin 24 is inserted into 22 and 23.

In the above configuration, first, with the fixed mold 10 and the movable mold 2.O open, each auxiliary plate 13, 23 is heated by high frequency dielectric using a high frequency generator (not shown). At this time, the high frequency is a fixed type 10 made of metal material. Mobile type 2
Since the light is reflected at 0 and absorbed only by the auxiliary plate 13.23 made of a highly dielectric ceramic material, the auxiliary plate 13.23 can be efficiently heated to a temperature higher than the resin deformation temperature in a short time. Auxiliary plate 13
When SiC is used as the material of ゜23, the required high frequency is about 2450±50 MHz. Note that the above-mentioned high-frequency dielectric heating can also be performed by inserting a transmitting element into the cavity 30 while the mold is closed.

Next, the movable mold 20 is closed to the fixed mold 10, and the lubricant is injected. The lubricant rises from the sprue 14 to the runner 15 and fills the cavity 30 through a thin gate (not shown).As a result, Disc A is molded. Disc A
Since auxiliary play) 13.23 has high surface smoothness, high surface smoothness can be obtained. Moreover, since the auxiliary plates 13, 23 are heated in advance to a temperature higher than the resin deformation temperature, good transfer to the resin can be achieved, so that higher surface smoothness can be obtained.

Next, after the resin has cooled and solidified, the movable mold 20 is moved back and opened, and the ejector pin 24 is activated to release the disk A from the mold and separate the disk A from the sprue part B and the runner part C. .

The present invention is not limited to the above-mentioned embodiments, and various embodiments are possible.For example, the present invention is not limited to the above-mentioned injection mold,
It can also be applied to compression molding molds and injection compression molding molds.

Cooking 1 and Cooking 1- As explained above, in the present invention, cutting is performed.

Since a ceramic material that can achieve high surface smoothness by polishing is used for at least a portion of the molding surface, the surface smoothness of the plastic product that is molded in contact with this molding surface can be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a mold according to an embodiment of the present invention in an open state, and FIG. 2 is a cross-sectional view of the mold in a closed state. 10...Fixed type, 20...Movable type, 13.23...
・Auxiliary plate made of ceramic material, +3a, 2
3a... Molding surface, 30... Cavity, A... Disc (plastic product)

Claims (6)

[Claims] (1) A mold for plastic molding, characterized in that at least a part of the molding surface constituting the cavity is formed of a ceramic material. (2) The plastic mold according to claim 1, wherein the ceramic material is a sintered body. (3) The plastic molding die according to claim 1, wherein the ceramic material is a single crystal. (4) The plastic molding die according to claim 1, wherein the ceramic material has high dielectricity. (5) The plastic mold according to claim 4, wherein the ceramic material is silicon carbide. (6) The plastic molding die according to claim 1, wherein the ceramic material has a thickness of 100 microns or more.