JPS609721A - Assembly of mold for injection molding for plastic disc for carrier of high density informaton record - Google Patents

Abstract

PURPOSE:To mold effectively a disc for a high density information record having a highly accurate central opening, by forming a flat annular molding cavity by a stationary side split mold and a moving side split mold. CONSTITUTION:Molten resin entered through a nozzle touch part 19 of an assembly of a mold is throttled by a narrow flush gate 21 provided between an annular sprue 20 and a molding cavity 15, turned into a uniform flow and injected into the molding cavity 15. The tip 21' of the annular fush gate 21 formed between the outer surface 22 of a central core 5 of a right circular cylinder and an annular protrusion 23 is extended beyond a plane of a flat surface 16 of the molding cavity 15 and up to the central part of the molding cavity 15. With this formation, marks of the gate to be remained on a molded article when the sprue has been cut off from the molded article at the time of mold opening can be prevented from protruding from the flat surface. Then a central opening of a disc can be formed very accurately by the outer surface 22 of the central core 5 of the right circular cylinder fixed firmly to a movable assembly of the mold.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for molding plastic moldings with a central opening, in particular high-density information carrier substrates such as video disc optical discs. In particular, the present invention relates to an improvement in a mold used when injection molding a disk as described above using a synthetic resin.

Precision molding technology is required to mold the discs as described above, and strict precision is required in the dimensions of the discs. Within this disc dimensional standard, the disc is formed at the center in order to fit the disc into the center bin of the turntable and to place the concentric or snobbery information tracks on the disc precisely concentrically on the turntable. 15m
Eccentricity tolerance of center opening of m1~35iiu is maximum 30μ
It must be of a certain degree.

Known methods for forming such central openings in disks include U.S. Pat.
There is a center punching method as described in Japanese Patent No. 139940. In this method, a punch for forming the center opening is built into the mold assembly, and after injecting molten resin into the molding cavity, the punch is pushed out with the cavity closed to punch out the center opening. It looks like this.

However, this method has some drawbacks.

First of all, this disk molded product is made of transparent plastic material.
In particular, PMMA resin is used, which has a small refractive index, but since this material is brittle at around room temperature, cracks may occur around the opening if the cutting is not carried out before it is completely cooled.

Next, the mold is opened in two stages, and cutting is performed in the half-open state of the first stage, but in this state, the fixed side and movable side of the mold are released from clamping by the mold clamping mechanism of the molding machine. There is a possibility that they may shift relative to each other within the clearance of the guide pins of the mold. Generally, the clearance between the guide pin and the bushing is about 100'', and this increases as the mold wears out due to long-term use.

If cutting is performed with this deviation, the eccentricity of the center hole of the formed disc will naturally increase.

Furthermore, the structure of the mold assembly becomes complicated, increasing the cost of manufacturing the mold.

A method for forming a hole at the center of a disk without using the center punching method as described above is disclosed in Japanese Patent Application Laid-open No. 57-2.
No. 03517 and Japanese Unexamined Patent Publication No. 58-57931, these methods require the use of a hot runner, and if the hot runner is used frequently, the molded product cannot be extracted from the mold. A more serious drawback is that extremely critical injection conditions are required for molded products that require a high degree of precision, such as the high-density information storage carriers that are the subject of the present invention. The problem lies in the fact that runners are not available. Furthermore, if a hot runner is used, an extra factor is added to the condition setting, making it susceptible to disturbances, resulting in poor fractionation and making the mold itself complicated.

An object of the present invention is to provide an injection mold assembly which eliminates the drawbacks of the above-mentioned known injection molding machines and can mold extremely simple plastic disks for high-density information storage carriers by boiling.

A feature of the injection mold assembly of the present invention is that a flat annular molding cavity is formed by a stationary split mold having a center hole and a movable split mold having a right cylindrical central core at the center. The tip of the core is inserted into the center hole of the fixed side split type through a continuous annular gap with this center hole, and this continuous annular gap is used as a flan yugate.

Another feature of the injection mold assembly of the present invention is that in the mold assembly, the tip of the annular flash gate that opens into the mold cavity is connected to the flat surface of the mold cavity through which the flash gate opens. The point is that it penetrates deeper into the molding cavity than the surface.

By using the mold assembly of the present invention, a disk for a high-density information recording carrier having a high-precision center opening can be efficiently molded with an extremely simple structure, and can be used with any type of resin. I can do it.

Furthermore, it is possible to make in one step a disc that does not have gate marks protruding on the surface of the disc that would make the disc uncomfortable to sit on when it is placed on a turntable.

Hereinafter, the present invention will be explained using the accompanying drawings.

FIG. 1 is a conceptual sectional view showing the principle of a mold assembly used in the molding method of the present invention, and in order to facilitate understanding, parts that are not characteristic of the present invention are omitted from the figure. Therefore, for example, a tie rod for aligning both split molds, a drive cylinder for the split molds, a mold clamping mechanism, heating and cooling means, etc. are not shown. It will also be appreciated that the relative dimensions of each member may differ from the actual dimensions.

In the drawing, a flat annular molding cavity 15 defined by a stationary split mold 1 and a movable split mold 2 having a right cylindrical central core 5 has a diameter of 76 to 300+ m and a thickness of -6=E depending on the desired disc size. A stamper 10 having an information pattern of micron to submicron order is held on one side of the stamper 15 by a stamper holder 7.8. This stand bar
10 is attached only to the movable side split mold 2 in the figure, but it can also be attached to the stationary side split mold 1. Centering and fixing of the stamper 10 can be effected by adjusting bolts 9. In the figure, an ejector sleeve 11 is provided for ejecting the molded product, but a compressed air ejector can be used instead.Furthermore, the ejector can be moved by using vacuum suction to separate the molded product from the mold. It can also be omitted.

According to a first feature of the invention, molten resin is injected into mold cavity 15 through an annular flash gate. That is, the molten resin entering the nozzle touch part 19 of the mold assembly with which the injection cylinder comes into contact is injected into the molding cavity 15 through the annular sprue 2o. A narrow annular flash gate 21 is provided between the annular sprue 20 and the molding cavity 15, and the molten resin is squeezed by the flash gate 21 to form a uniform flow and injected into the molding cavity 15. Ru. As shown in FIG. 1.2, the annular flush gate 21 is formed by connecting the right cylindrical surface 22 of the central core 5 fixed to the movable mold assembly to which the movable mold 2 is attached and the fixed mold 1. It is formed by a gap between the ring-shaped projection 23 formed at the end of the molding cavity flat surface 16 and penetrates into the inside of the molding cavity 15 due to the second feature. That is,
The outer surface 22 of the right cylindrical central core 5 and the ring-shaped protrusion 2
The tip 21'' of the annular flush gate 21 formed between the molding cavity 15 and the molding cavity 15 extends to the middle of the molding cavity 15 beyond the plane of the flat surface 16 of the molding cavity 15. By extending the gate into the inside of the molding cavity in this manner, it is possible to prevent gate marks remaining on the molded product from protruding from the flat surface of the molded product when the molded product and the sprue are cut when the mold is opened. The ring-shaped protrusion 23 is not limited to the trapezoidal cross-section shown in FIG. 2, but may be triangular in cross-section as shown in FIG. 3. In short, the tip 21° of the annular flash gate is formed at the same time as the disk is formed by injection into the forming capite mold. That is, the central core 5Ω right circular cylinder surface 22 is firmly fixed to the movable mold assembly.
This allows the center opening of the disk to be formed with extremely high precision. The upper end of the central core 5 is preferably frustoconically shaped to form a sprue 20.

4A to 40 show the mold opening order when a disk is molded using the mold assembly of FIG. 1. First, with the stationary split mold 1, the movable split mold 2, and the first and second sprue plates 3.4 closed, that is, in the state shown in FIG. 1, acrylic resin, polycarbonate 9-resin, etc. The resin material is injected and filled into the molding cavity 15 through the sprue 20 and the flash gate 21. After that, after cooling the resin, the first and second sprue plates 3 are separated with the two split molds 1.2 in a closed state.
．． The sprue 31 is separated from the molded disk 30 by separating the sprue 31 from the fixed side mold 1 (Fig. 4A).
. Next, the movable mold assembly to which the movable mold split 2 is attached is moved back to open the mold split 1.2 (FIG. 4B). lastly,
The ejector sleeve 11 is driven to eject the formed disc 30.

Meanwhile, the sprue 31 is released by separating the first and second sprue plates (FIG. 4C). Although the illustration shows first and second sprue plates 3.4 used to release sprue 31, other known sprue release means can be used, such as sprue ejectors. Further, although the ejector sleeve 11 is used in the figure, a known ejector turbine, ejector gas (compressed air), or the like may be used instead. Furthermore, when a vacuum suction type mold release means is used, the ejector can be omitted, and in this case, the structure of the mold assembly can be further simplified and it can be made stronger. can.

Center opening surface 32 of disk 30 molded according to the invention
(FIG. 5) is a transcription of the right cylindrical surface 22 of the central core 5, so it is extremely flat and has high dimensional accuracy.

In the present invention, when separating the sprue 31 from the molded disk 30 (FIG. 4A), the disk center opening surface 32
A beard 33 is generated near the top edge of the disc 30, but since this beard 33 is on a plane lower than the surface 34 of the disc 30, it does not affect the centering of the disc, and when the disc 30 is placed on the turntable of a playback device, the disc It does not make sitting uncomfortable.

This whisker 33 does not substantially affect the performance of the disc, but if necessary, it can be removed by any suitable method, such as with an electric trowel or by cutting, after the disc 30 has been removed from the mold after molding. , suitable hair removal means may also be incorporated into the mold assembly.

In FIG. 6, a porous nozzle 40 for blowing heated air is fitted onto the surface of the center core 5 facing the flash gate 21, and compressed air or By blowing out heated air from the porous nozzle, the formation of whiskers 33 can be prevented or flattened.

Although the present invention has been described above using special embodiments, the present invention is not limited thereto. For example, the center core 5 is made separately from the movable side split mold 2 in FIG.
You can also make both together.

[Brief explanation of drawings]

FIG. 1 is a conceptual cross-sectional view of a mold assembly used in the injection molding method for a high-density information recording carrier base according to the present invention. FIG. 2 is an enlarged view of the vicinity of the flash gate in FIG. 1. FIG. 3 is a diagram showing a modified embodiment within the circle indicated by ■ in FIG. 2. FIGS. 4A, 4B, and 40 are explanatory diagrams showing the mold opening order when molding is performed using the mold assembly shown in FIG. 1. FIG. FIG. 5 is a conceptual enlarged view of the vicinity of the center opening of a disk molded according to the present invention. FIG. 6 is a view showing heated air supply means incorporated into the central core used when cutting the flash gate, with the left half being a side view and the right half being a sectional view. (Symbols in the figure) 1: Fixed side split mold, 2: Movable side split mold, 3.4 Varnish pull plate, 5: Center core, 7.8 Nistamper holder, 10 Nistamper 111: Ejector sleeve, 15: Molding cavity Tee, 16: Molding surface,
19: Nozzle touch part, 20 Varnish blue, 21: Flash gate, 23: Ring-shaped projection, 30: Molded disk, 33: Beard. Patent applicant Daicel Chemical Industries, Ltd.-13 = 1!5 Figure 33 Procedural amendment (voluntary) Showa et al. 1939? Kazuo Wakasugi, Commissioner of the Japan Patent Office, January 1st, 16 Indication of the case Patent Application No. 115900 of 1982 Title of the invention Mold assembly for injection molding of plastic disks for high-density information recording carriers 3 Related Patent Applicant Address 1-5 Teppocho, Sakai City, Osaka Prefecture Contents of Amendment

Claims (1)

[Scope of Claims] 1) A fixed side split mold having a center hole and a movable side split mold having a right cylindrical center core at the center, and the tip of the right cylindrical center core is connected to the center hole of the fixed side split mold. When inserted, a flat annular molding cavity is formed between the stationary split mold and the movable split mold, and an annular flush gate is formed between the center hole and the right cylindrical central core. A mold assembly for injection molding of a plastic disk for a high-density information recording carrier, characterized by: 2) A feature in that the tip of the annular flash gate opening into the mold cavity extends a certain distance further into the mold cavity than the flat surface of the mold cavity to which the annular flash gate is connected. A mold assembly according to claim 1.