JPS61217225A - Mold for injection molding - Google Patents

Abstract

PURPOSE:To permit to mold high-qualitied discs continuously and stably without generating faulty molding by a method wherein the thickness of a gate, provided in a resin flow path between a spool and a cavity, is made same as the thickness of a runner to provide the resin flow path widely. CONSTITUTION:The gate is provided widely so as to have the same width as the runner 7. Molten resin passes through the heated spool 6 and is filled into the cavity 9 through the widely provided gate from the runner 7. The spool 6 is heated upon injecting and filling the resin, therefore, deterioration of the molten resin due to cooling upon passing through the spool may be prevented. Further, the gate is designed so as to be wide, therefore, heat generation due to compression of the resin may be restrained, generation of void such as graphitization of the molten resin, silver streak or the like may be prevented, delicate adjustment of gate clearance for filling the molten resin uniformly and radially becomes unnecessary and whereby the discs of high quality may be molded continuously and stably.

Description

DETAILED DESCRIPTION OF THE INVENTION 2.\- Industrial Application Field The present invention relates to an injection mold for molding disc-shaped record carriers such as video discs and optical memory discs.

BACKGROUND OF THE INVENTION In recent years, injection molding has become mainstream in the production of video discs, CDs, optical memory discs, etc., and the injection mold has a great influence on the characteristics of the molded product.

An example of a conventional injection mold will be described below with reference to the drawings.

FIG. 3 shows a cross-sectional view of a conventional injection mold.

In FIG. 3, 1 is a stationary die plate, and 2 is a movable die plate. 3 is a fixed side core, 4 is a movable side core, and is fixed to the fixed side die plate 1 and the movable side die plate 2 with bolts 61 and 5i2, respectively. 5a
is a sprue.

It slides perpendicularly to the surface of the fixed core 3.

6 is a sprue, 7 is a runner, and 8 is a gate, which is a flow path for molten resin. 9 forms a molded product with a cavity. 10
is a stamper, which forms the focus and grooves necessary for a disk-shaped record carrier. The stamper 10 is fixed to the movable core 4 by a center bin 11 and an outer circumferential holding ring 12. 13 is an ejector ring that ejects the molded product. 1
4 is a center hole punch to form a center hole in the molded product.

15 is a sprue lock pin that pushes out the cooled and solidified resin from a part of the sprue when taking out the product. 16 and 17 are cooling waterways that keep the mold temperature constant and cool and solidify the molded product. 1
Reference numeral 8 denotes a parting surface, which is a surface where the movable die plate 2 and the fixed die plate 1 form a cavity 9 and join together. 19 is an injection cylinder.

The operation of the mold configured as described above will be explained below.

First, by the mold clamping mechanism, the movable die plate 2 and the fixed die plate 1 form a cavity 9, are joined at the parting surface 18, and are clamped under high pressure.

Next, a high temperature molten resin such as acrylic resin or polycarbonate resin is injected from the injection cylinder 19. At this time, the temperature of the acrylic resin is 220°C to 260°C, and the temperature of the polycarbonate resin is 320°C to 36°C.

Next, the injected molten resin passes from the sprue 6 through the runner and is filled into the cavity 9 through the gate 8. Since the sprue 6 and the runner 7 are formed at the center of the stationary core 3, and the gate 8 is formed in a circular shape, the molten resin is uniformly filled radially into the cavity 9.

Further, the thickness of the gate 8 is formed to be as narrow as 0.4 mm or less, so that the solidification of the molten resin is accelerated at the gate 8, and when the molten resin filled in the cavity 9 is solidified, it is prevented from flowing back. In order to prevent the backflow of molten resin, it is necessary to speed up the cooling and solidification of the gate 8, and the thinner the gate 8 is, the more effective it is.

The molten resin filled in the cavity 9 is transferred to the cooling water channel 16.
Heat exchange is performed by the cooling water flowing through 17, and the material is cooled and solidified. Cooling and solidification is completed in several seconds to several tens of seconds, and a molded article is formed within the cavity 9.

During this time, the center hole of the molded product is formed using the center hole punch 14. After that, the mold is opened, and the resin that has cooled and solidified in the molded product and part of the sprue comes to the movable side. The molded product is ejected by the ejector ring 13, and the resin that is still cooled and solidified in a portion of the sprue is ejected by the sprue lock pin 15, and is taken out of the mold by the molded product removal mechanism.

Problems to be Solved by the Invention However, with the above configuration, when the molten resin is filled into the cavity 9 from the gate 8, the molten resin is compressed at the gate 8 and the temperature rises rapidly, causing silver streaks and resin. In view of the above-mentioned drawbacks, the present invention has been developed to improve the gate 8 of the mold. The thickness is set to suppress the rapid temperature rise of the molten resin during injection filling, eliminate defects such as blackening and silver streaks, and ensure uniform filling and injection without requiring delicate adjustments to the gate 8 of the mold. By preventing the molten resin from solidifying in some parts of the sprue during the process, it is easy to set the molding strip, and the injection molding mold can continuously and stably mold high-quality discs without molding defects. It provides:

Means for Solving the Problems In order to solve the above-mentioned problems, the injection mold of the present invention has a cavity in which a stamper is disposed on one side of the core, and a mold for injecting outward from the center of the cavity. The sprue bushing is provided with a sprue bush provided as shown in FIG. According to the invention, with the above configuration, the molten resin
The heated sprue is passed from the searunner through a wide gate and filled into the cavity. During injection filling,
Since the sprue is heated, deterioration due to cooling of the molten resin while passing through the sprue can be prevented.

Furthermore, since the gate is set wide, heat generation due to resin compression is suppressed, and defects such as blackening of the molten resin and silver streaks can be prevented.

After the injection filling is completed, the sprue is forcibly cooled down rapidly to prevent the injection filled molten resin from flowing back.

Since the gate is set widely, there is no need to make delicate adjustments to the gap between the gates to uniformly and radially fill the molten resin, making maintenance of the mold and setting of molding conditions easier.

In this way, high quality disks can be continuously and stably molded without any defects.

EXAMPLE Hereinafter, an injection molding mold according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of an injection mold according to a first embodiment of the present invention. In FIG. 1, 1 is a fixed die plate, 2 is a movable die plate, 3 is a fixed core, 4 is a movable core, 5a is a sprue bushing, 5b is a sprue bushing outer ring, 6 is a sprue, and 7 is a sprue bushing. is the runner, 9 is the cavity, 1o is the stamper, 11 is the center pin, 1
2 is an outer valve ring, 13 is an ejector ring, 14 is a center hole punch, 16 is a sprue lock pin, 1
6.17 is a cooling channel, 18 is a parting surface, 19 is an injection cylinder, 51, 52, 53 is a bolt, 3o is a heating and cooling medium flow path, and 31 is a pipe.

The operation of the injection mold constructed as described above will be described below.

Sprue bushing 5a and sprue bushing outer ring 5
A heating and cooling medium flow path is provided between b and connected to an external heating and cooling medium supply section through a pipe 31 and an external hose. For example, steam and water are used as the heating and cooling medium, and the heating and cooling medium flows alternately through the heating and cooling medium flow path 30 by switching a valve.
Sprue-6 is heated or cooled. The gate part is set wide and has the same width as the runner 7.

First, the movable die plate 2 and the fixed die plate 1 form a cavity 9 by a mold clamping mechanism, are joined at the parting surface 18, and are clamped under high pressure.

Next, the acrylic resin melted at 220° C. to 260° C. is injected onto the sprue 6 from the tip of the injection cylinder 19. At this time, the area around the sprue 6 is heated to 170 to 180° C. by high pressure steam flowing through the heating and cooling medium channel 3o, thereby preventing the surface of the injected acrylic resin from cooling and solidifying.

Next, the acrylic resin passes from the sprue 6 through the runner 7 and is filled into the cavity 9. At the same time as injection filling is completed,
Cooling water flows through the heating and cooling medium flow path 30, and the sprue 6
The acrylic resin is rapidly cooled and injected into the cavity 9.
Prevent backflow from.

After that, the filled acrylic resin is added to the cooling channel 16.1.
Heat exchange is performed by the cooling water flowing through 7, and the product is cooled and solidified. Cooling and solidification are completed in several seconds to several tens of seconds, and a molded product is formed within the cavity 9. During this time, a hole is formed in the center of the molded product using a center hole punch 14.

The mold is then opened, and the resin that has cooled and solidified in the product and part of the sprue comes to the movable side. 10. In the \-/'' shaped product, the resin cooled and solidified at a part of the sprue is pushed out by the sprue lock pin 15 by the rainbow lid ring 13, and taken out of the mold by an external product take-out mechanism.

As described above, according to this embodiment, by forming the gate thickly, providing a wide resin flow path, and providing a heating and cooling medium flow path around the sprue of the mold, blackening of the molten resin can be prevented. There are no molding defects such as streaks or insufficient filling due to resin backflow, there is no deterioration of the molten resin due to heating of a part of the sprue during injection, and there is no need for delicate gate clearance adjustments, resulting in high quality and no molding defects. The second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a partial sectional view of a sprue heating and cooling structure of an injection molding die showing a second embodiment of the present invention.

In Fig. 2, 1 is a stationary die plate, 3 is a stationary core, 5a is a sprue bushing, 6b is a sprue bushing outer ring, 6 is a sprue, 7 is a runner, 9 is a cavity, 11 is a center bin, 13 is an ejector ring, 14 is a center hole punch, 15 is a sprue lock bin, 19 is an injection cylinder, 4o is a sprue cooling channel, and 41 is an electric heater δ Regarding the injection mold configured as above, the following is Let's explain its operation.

The molten resin injected from the injection cylinder 19 passes through the sprue 6 heated by the electric heater 41, passes through the runner 7, and fills the cavity 9. After injection and filling is completed, the electric heater 41 is turned off, cooling water is allowed to flow through the cooling channel 4o, and the sprue 6 is rapidly cooled. After the cooling and solidification is completed, the mold is opened, and the resin that has cooled and solidified in the molded product and part of the sprue is taken out to the outside by an external takeout mechanism. As mentioned above, by using an electric heater to heat the sprue, the temperature setting can be changed freely and easily.
It has the advantage that when the injected molten resin passes through the sprue 6, the cooling of the resin and the prevention of assimilation can be completely and easily controlled.

In the description of the operation of the first embodiment, acrylic resin was used in the explanation, but any resin such as polycarbonate resin that can be injection molded may be used.

Also, 1st. Although water is used for sprue cooling in the second embodiment, other cooling media may be used.

Effects of the Invention As described above, according to the present invention, a structure capable of heating and cooling is provided around the sprue, the thickness of the gate is made the same as that of the runner, and a wide resin flow path to the cavity is provided, thereby improving injection efficiency. This eliminates molding defects caused by deterioration of the molten resin during molding, allows for easy mold adjustment and molding condition settings, and enables stable continuous molding.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an injection mold according to a first embodiment of the present invention, and FIG. 2 is a partial cross-sectional view of a sprue heating and cooling structure of an injection mold according to a second embodiment of the present invention. FIG. 3 is a sectional view of a conventional injection mold. 1...Fixed side Goui plate, 2...Movable side Goui plate, 3...Fixed side core, 4...
...Movable side core, 5a...Sprue bushing, 5b...Sprue bushing outer ring, 6.
...Sprue, 7...Runner, 8...
...Gate, 9...Cavity, 1o...
... Stamper, 11 ... Center bin, 1
2...Outer circumference holding ring, 13...Ejector ring, 14...Center hole punch, 15...Sprue lock bin, 16.17...
... Cooling water channel, 18 ... Parting surface,
19...Injection cylinder, 3o...Heating and cooling medium flow path, 31...Pipe, 4o...
・Sprue cooling waterway, 41...Electric heater, 50
,51゜52...Volt. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
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Claims (1)

[Claims] first and second cores constituting a cavity; a stamper fixed to a main surface of the first core; and a stamper fixed to the second core such that the molten resin is injected outward from the center of the cavity. a sprue bush provided at the center of the sprue, a sprue provided at the center of the sprue bush, a cooling circuit for cooling the first and second cores, an ejector ring for ejecting the molded product, and a sprue provided for the sprue. a sprue lock pin for taking out the cooled and solidified resin, a means for heating the sprue and a means for cooling the sprue are provided near the sprue, and a resin flow path between the sprue and the cavity. An injection molding mold characterized in that the thickness of the provided gate is the same as the thickness of the runner, and the resin flow path is provided widely.