JPH06134816A - Injection mold - Google Patents

Abstract

(57) [Summary] [Construction] An injection molding die including a fixed-side die 11, a movable-side die 12 that moves relative to the fixed-side die 11, and a sprue 20 formed on the fixed-side die 12. A mold for injection molding, characterized in that the movable mold 12 is provided with a protrusion 15 that is inserted into the sprue 20 of the fixed mold 11 when the mold is closed. [Effect] Even if the molding cycle is shortened, the sprue part of the molded product does not stretch or break when the molded product is released, and vacuum bubbles are generated in the thick part at the end of the sprue part of the molded product. Never.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an injection molding die,
More specifically, the present invention relates to an injection molding die suitably used for molding an optical disk substrate.

[0002]

BACKGROUND OF THE INVENTION In an injection molding method, a heated and melt-plasticized resin is injected into a cavity through a sprue of a mold, and this is cooled and solidified to produce a molded body.
When a molded product such as an optical disk substrate is molded by the injection molding method, a mold as shown in FIGS. 4 and 5 is usually used as follows. 4 is a schematic cross-sectional view showing an example of a conventional optical disk substrate molding die, and FIG. 5 is an enlarged cross-sectional view of a main part of the optical disk substrate molding die shown in FIG.

First, the stamper 16 is attached to the movable side mold 12, the mold is closed, and the mold is clamped. Then the injection mechanism 1
Resin melt-plasticized from 9 sprue 20, runner 2
5, injected through the gate 26 into the cavity 21,
The optical disk substrate is formed by transferring pits and the like from the stamper 16 and cooling and solidifying the resin inside the mold. After that, the movable side mold 12 is moved to open the mold, and the molded optical disk substrate is released from the mold.

By the way, the mold sprue 20 used in the injection molding spreads toward the movable mold 12 side so that the sprue part of the molded product is smoothly separated from the fixed mold 11 when the mold is opened. Therefore, the radial thickness of the sprue end portion 27, which is the end portion of the sprue 20 on the movable mold 12 side, is equal to the thickness (1.2 mm) of the disk substrate formed in the cavity 21. It is getting bigger. Therefore, in the molding process of the optical disk substrate, the resin immediately solidifies in the cavity 21, but it takes time to solidify the resin at the sprue end 27. Therefore, if the molding cycle is shortened, the cooling time is shortened and the resin at the sprue end portion 27 is insufficiently solidified, which causes a problem that the sprue portion of the molded product is stretched or broken when the molded product is released from the mold. Further, since the sprue end portion 27 has a large wall thickness, vacuum bubbles easily occur due to volume contraction when the resin is cooled and solidified, which also causes sprue breakage.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can shorten the molding cycle in the production of a molded product by injection molding, for example, the manufacturing process of an optical disk substrate, and further, can improve sprue elongation and sprue. It is an object of the present invention to provide an injection molding die that can prevent breakage problems.

[0006]

SUMMARY OF THE INVENTION An injection molding die according to the present invention comprises an injection molding die having a stationary die, a movable die moving relative to the stationary die, and a sprue formed on the stationary die. The mold for use is characterized in that the movable mold is provided with a protrusion that is inserted into the sprue of the fixed mold when the mold is closed.

In the injection molding die of the present invention, since the radial thickness of the sprue end portion is small, the solidification speed of the resin at the sprue end portion can be increased as compared with the conventional die. Therefore, even if the molding cycle is shortened, the sprue does not stretch or break when the molded product is released, and vacuum bubbles do not occur at the end of the sprue. Such an injection molding die is particularly suitable for molding an optical disk substrate.

[0008]

DETAILED DESCRIPTION OF THE INVENTION An injection molding die according to the present invention will be described below with reference to the drawings by taking an optical disk substrate molding die as an example.

FIG. 1 is a schematic sectional view of an optical disk substrate molding die according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a main part of the optical disk substrate molding die shown in FIG. . FIG. 3 is an explanatory view showing a method for manufacturing an optical disk substrate using the injection molding die of the present invention. This optical disk substrate molding die includes a pair of dies 11 and 12, and the die 11 is a fixed side die and the die 12 is a movable side die. These fixed side mold 11 and movable side mold 12
Are attached to the fixed-side mold plate 13 and the movable-side mold plate 14 of the injection molding machine (not shown), respectively.

An injection mechanism 19 for injecting the melted resin is provided on the fixed side mold plate 13 side, and a sprue which is a flow path through which the melted resin passes is provided substantially at the center of the fixed side mold 11. 20 are formed. Molten resin is supplied into the cavity 21 through the sprue 20. The sprue 20 is used to facilitate the drawing of the solidified molded product.
The taper is tapered by 4 ° and is formed so as to expand toward the movable-side mold 12 side.

A concave portion 28 having an opening and having a substantially circular cross-section is formed at a substantially central portion of the movable die 12 so as to face the opening of the sprue 20 on the movable die 12 side. . The bottom surface of the recess 28 is provided with a protrusion 15 into which the tip is inserted into the sprue 20 of the stationary mold 11 when the mold is closed. The protrusion 15 is a cone, a truncated cone, a polygonal pyramid, or the like in order to facilitate the pulling out of the solidified molded product.
The shape is preferably a truncated pyramid. The protrusion 15 is preferably shaped so that the maximum radial thickness of the sprue 20 is 4 mm or less when the mold is closed. More specifically, the radial thickness is preferably in the range of 1 to 3 mm and the axial length is preferably in the range of 5 to 15 mm.

A stamper 16 which is a mold plate of an optical disk substrate is attached to the movable mold 12. The stamper 16 is supported by a mounting member 17 and a moving ring 18.

The fixed-side mold 11 and the movable-side mold 12 are provided with abutting surfaces 22 and 23, respectively, and these abutting surfaces 22 and 23 are brought into contact with each other when both the molds are closed. There is. A cavity 21 is formed in a portion where the fixed mold 11 and the stamper 16 face each other, and a fixing ring 24 is provided so as to define the cavity 21. In the figure, 25 is a runner and 26 is a gate.

The injection molding die of the present invention and the protruding portion 15
The material of is not particularly limited, and the same material as the material of the mold can be used. For example, stainless steel is used. Next, a method for molding an optical disk substrate using the injection molding die of the present invention will be described. First, as shown in FIG. 3 (A), the stamper 16 is attached to the movable side mold 12, the mold is closed, and the mold is clamped. Next, the heated and melted and plasticized resin is injected from the injection mechanism 19 into the cavity 21 through the sprue 20, and the groove from the stamper 16
The optical disk substrate is formed by transferring the pits, the mirror portion, etc., and cooling and solidifying the resin inside the mold. Subsequently, as shown in FIG. 3B, the movable side mold 12 is moved to open the mold, and the molded optical disk substrate 10 is released from the mold. That is, when the mold is opened, the molded optical disk substrate 10 is separated from the fixed-side mold 11 by the fixed-side mold release mechanism attached to the mold, and the movable-side mold is attached with the optical disk substrate 10 in close contact with the stamper 16. 12
Is moved, and then the optical disk substrate 10 is separated from the stamper 16 by a movable-side mold release mechanism attached to the mold. The optical disk substrate 10 molded in this way is
Robots stock them in disc magazines or stack poles.

In the present invention, the movable mold 12 is provided with the protrusion 15 which is inserted into the sprue 20 of the fixed mold 11 when the mold is closed. The radial thickness of the sprue end portion 27 becomes thin. When the resin is molded using such a mold, the time required for cooling and solidifying the resin at the sprue end portion 27 can be shortened as compared with the conventional mold. Therefore, even if the molding cycle is shortened, the solidification of the resin at the sprue end portion 27 is sufficient, and there is no problem that the sprue portion extends or breaks when the molded product is released from the mold. Further, since it is possible to prevent vacuum bubbles from being generated at the sprue end portion 27 due to volume contraction when the resin is cooled and solidified, it is also possible to prevent sprue breakage due to generation of vacuum bubbles.

As a resin used when molding a molded article using the injection molding die of the present invention, a resin conventionally used in injection molding can be used. For example, as a resin for an optical disk substrate. Are polycarbonate, polymethylmethacrylate, polymer alloys of polycarbonate and polystyrene, polyolefins, or ethylene-cyclic olefin copolymers such as those shown in U.S. Pat. No. 4,614,778, such as ethylene and 1,4,5. ,
Copolymer with 8-dimethano-1,2,3,4,4a, 5,8,8a-octahydronaphthalene (tetracyclododecene), ethylene and
Copolymer with 2-methyl-1,4,5,8-dimethano-1,2,3,4,4a, 5,8,8a-octahydronaphthalene (methyltetracyclododecene), ethylene and 2- Ethyl-1,4,5,8-dimethano-1,2,
3,4,4a, 5,8,8a-copolymer with octahydronaphthalene,
Hydrogenated homopolymers of tetracyclododecenes and ring-opening copolymers with norbornenes as disclosed in JP-A-60-26024, and thermoplastics such as poly-4-methyl-1-pentene Resins can be used.

The injection molding die of the present invention has been specifically described above by taking the optical disk substrate molding die as an example, but the present invention is not limited to the optical disk substrate molding die and other injection molding die. Needless to say, it can be applied to a mold, for example, a molding mold for a general-purpose injection molded product.

[0018]

According to the present invention, an injection molding die including a fixed side die, a movable side die that moves relative to the fixed side die, and a sprue formed on the fixed side die, The movable mold is provided with a protrusion that is inserted into the sprue of the fixed mold when the mold is closed. Such a mold is
Since the thickness of the sprue end portion is thin, the sprue portion can be cooled and solidified in a short time as compared with the conventional mold. Therefore, even if the molding cycle is shortened, the sprue part of the molded product does not extend or break when the molded product is released from the mold, and vacuum bubbles do not occur in the thick part at the end of the sprue part.

[0019]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples.

[0020]

Example 1 Using a mold for molding an optical disk substrate as shown in FIG. 1, injection of an optical disk substrate having a diameter of 130 mm using a polycarbonate resin at a resin temperature of 340 ° C., a mold temperature of 100 ° C. and a molding cycle of 15 seconds. Molded.

As a result, sprue elongation, sprue breakage did not occur, and vacuum bubbles did not occur even after 1000 shots of molding were continued.

[0022]

Comparative Example 1 A conventional optical disk substrate molding die as shown in FIG. 3 was used, and the diameter was 130 mm in the same manner as in Example 1.
The optical disk substrate of was injection-molded.

As a result, sprue elongation occurred at about 50 shots and sprue breakage occurred at about 100 shots. Also, vacuum bubbles were generated at the sprue end of the molded product with a probability of about 50%.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a mold for molding an optical disk substrate according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of an essential part of the optical disk substrate molding die shown in FIG.

FIG. 3 is an explanatory view showing a method for manufacturing an optical disc substrate using the injection molding die of the present invention.

FIG. 4 is a schematic cross-sectional view showing an example of a conventional optical disk substrate molding die.

5 is an enlarged cross-sectional view of a main part of the optical disk substrate molding die shown in FIG.

[Explanation of symbols]

 11 Fixed-side mold 12 Movable-side mold 15 Projection 20 Sprue

Claims (2)

[Claims] 1. A mold for injection molding, comprising: a fixed-side mold; a movable-side mold that moves relative to the fixed-side mold; and a sprue formed on the fixed-side mold. The mold is closed. A mold for injection molding, characterized in that the movable mold is provided with a protrusion that is sometimes inserted into the sprue of the fixed mold. 2. An injection molding die for optical disk substrate molding, comprising: a fixed-side die; a movable-side die that moves relative to the fixed-side die; and a sprue formed on the fixed-side die. An injection mold for an optical disk substrate, characterized in that the movable mold is provided with a protrusion that is inserted into the sprue of the fixed mold when the mold is closed.