JPS608028A - Injection molding method of box-shaped product - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a sink mark in a molding by a method in which when molten resin in molds is being hardened by cooling, compressed air is sent into the through holes of a porous part by an air controller to press the corner portions of the molding. CONSTITUTION:When molten resin in molds 3 is being hardened by cooling, compressed air is sent into the through holes 5 of a porous part 6 by an air controller and blown onto the corners 1C of a molding 1 in such a way as to form an air trap 9 until the molten resin is hardened. The inside of the corners 1C of the molding is pressed outwards by the air trap 9 to prevent the occurrence of sink mark in the molding 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of injection molding a box-shaped molded product using a synthetic resin.

Generally, in order to mold a box-shaped product, as shown in Figure 1 (21), the cavity of a mold a is filled with molten resin using an injection machine, and the molten resin is cooled and hardened to form a box-shaped product. Molded product c' (i7 molded. However,
Molded product C has its own molding shrinkage rate, and shrinkage in areas where cooling is slow, such as the center and thick parts, causes the surface to become depressed and cause so-called sink marks. Dashed line X
There is a risk that it will be molded into a shape like this. d is a cooling mechanism.

Therefore, in the past, the cavity shape of mold a was formed as shown by the chain line Y shown in FIGS. When sinkage occurs in the molded product C, the molded product C can assume the desired shape.However, since the molded product C that will become the product and the cavity shape of the mold a are different,
In reality, it is difficult to obtain a desired shape, and some molded products C are defective.

In view of the above circumstances, the present invention aims to provide an injection molding method for box-shaped molded products that can be molded into a desired shape while preventing sink marks.

-3? Y Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 3 to 5.

In this embodiment, a mold 3 is filled with molten resin constituting a molded product 1 using an injection machine 2, and the molten resin is cooled and hardened by a cooling mechanism 4 provided in the mold 3, thereby forming a box shape. Product 1 is being molded.

Specifically, the box-shaped molded product 1 has a main body 1a and a side plate 1b around the main body 1a to form a square box shape. The mold 3 is composed of a fixed part 31 forming the surface of the molded product 1 and a movable part 32 forming the inside of the molded product 1.
A protruding bottle 33 is provided for releasing the molded product 1 when it is molded. Further, porous members 6 each having a through hole 5 are embedded in the mold 3 at a position corresponding to the inner side of a part of the IC at a corner of the molded product 1. The porous member 6 is embedded at the tip of the mold movable part 32 at a position where 1 ci of each corner of the molded product 1 is formed, and is made of a material that is heat resistant to molten resin, such as metal or ceramics. Karanatsumata is here. Although not shown in detail, the through hole 5ta has a size of about 5 to 30 μm to prevent the molten resin from entering when it is filled into the mold 3, and the porous member 6
There are multiple formations inside. The through hole 5 has one end facing toward the molded product corner part]C, and has an air control means 8 provided at the other end via an air passage 7.

Each of the air passages 7 has one end connected to the through hole 5 of the porous member 6.
The movable portion 32 is formed through the movable portion 32 so that the other end thereof communicates with the movable portion 32 and opens to the outside of the movable portion 32 . The air control means 8 includes W
, as clearly shown in FIG. 3, an air pump 81, an air filter 82, a directional switching valve 83, a pressure regulating valve 84, and a connecting portion 85 that connects the pressure regulating valve 84 and the air passage 7.
, an injection machine signal 86 that outputs a signal in synchronization with the timing of the injection machine 2 , and a timer 87 that switches and controls the direction switching valve 83 based on the output from the injection machine signal 86 . This air control means 8 is configured such that when the injection machine 2 fills the mold 3 with molten resin, the timer 87 is input by the output of the injection machine signal 86, and the molten resin in the mold 3 is cooled and hardened. By switching the directional control valve 83 from the position A to the position 1r while the air pump is in the open position, the compressed air from the air pump 31 can be sent into the through hole 5 of the porous member 6 through the air path 7. It is now possible to do so. Then, when compressed air is sent 9 into the through hole 5 by the air control means 8, the compressed air presses a corner IC of the molded product l from the through hole 5, causing a sink mark on the molded product l. It is now possible to prevent this.

Note that the air control means 8 operates when the molten resin is cured.
By switching the timer 87 from the position port of the directional control valve 83 to the position A, the compressed air in the direction switch valve 83 can be discharged to the outside. For this reason, when the timer 87 is cooling and hardening the molten resin in the mold 3 or when it is completely hardened, the directional control valve 83
It is set so that it can be switched to the desired position. The feathers are pressure gauges.

When molding the molded product 1, the mold 3 is filled with molten resin, and at that time, the temperature of the mold 3 varies depending on the position of each part of the molded product 1. That is, as shown in FIG.
On page 6 of molded product 1, mark the inside part of the IC as A, and mark the inside part of the molded product main body 1a as B.
, the surface side of the molded product body 1a is C1 molded product corner part I
If the outer part of C is −iD, the temperature height is A) B) C
)D, therefore, when it is cooled, it contracts depending on the temperature, so the shape of the molded product 1 tends to deform as shown by the chain line in the same figure.

However, in the present invention, when the molten resin in the mold 3 is cooling and hardening, compressed air is sent into the through hole 5 of the porous member 60 by the air control means 8, and the compressed air is passed through the through hole 5. As shown in FIG. 5, until the molten resin hardens, compressed air is sprayed onto the corner part of the IC of the molded product 1 to create an air pocket 9. Since the inside is pressed outward, it is possible to prevent sink marks from occurring in the molded product 1. Moreover, even if some corner ICs are dented by the pressure of compressed air, the molded product 10
Since there are no dents on the surface, the appearance will not be impaired. Further, since the through-holes 5 of the porous member 60 are of a size that does not allow molten resin to flow into them, there is no clogging when the mold 3 is filled with molten resin, and compressed air can be sent normally.

As described above, when the molten resin filled in the mold is cooling and hardening, compressed air is sent into the through holes of the porous member by the air control means, and the compressed air penetrates through the through holes. By pressing a part of the corner of the molded product with holes, it is possible to completely prevent sink marks from occurring on the molded product, and therefore the molded product can be reliably molded into the desired shape and Since there are no more defective products, the amount of material used can be saved accordingly.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the general molding state of a box-shaped molded product, FIGS. 2(a) and (b) are an explanatory front view and an explanatory side sectional view showing a conventional box-shaped molded product, and FIG. The figure is an overall view showing one embodiment of the injection molding method according to the present invention, and FIG.
An enlarged cross-sectional view of a part of the figure, FIG. 5 is an explanatory cross-sectional view showing the suppressed state of compressed air for a box-shaped molded product, and FIG. 6 is an explanatory cross-sectional view showing the molding state of a general box-shaped molded product. be. 1...Box-shaped molded product, LC...Part of the corner, 3...
Mold, 6... Porous member, 5... Through hole, 8... Air control means. Patent Applicant Ichimoto Kogyo Co., Ltd. Agent Patent Attorney Tadashi Akimoto Laughter

Claims (1)

[Claims] In the injection molding method for box-shaped molded products, which is formed by filling a mold with molten resin and cooling it to harden, the mold has a corner of the box-shaped molded product, which corresponds to the inside of a part of the box-shaped molded product. A porous member having a plurality of through holes facing a part of the corner is disposed at the position, and an air control means for sending compressed air into the through holes of the porous member is provided to fill the mold. When the molten resin is cooling and hardening, compressed air is sent into the through hole of the porous member by the air control means, and the compressed air presses the inside of a part of the corner of the box-shaped molded product through the through hole. An injection molding method for box-shaped molded products characterized by preventing sink marks from occurring on the surface of the box-shaped molded products.