JPH04320819A - Injection mold and manufacture for molded item - Google Patents

Abstract

PURPOSE:To obtain a molded item having a fine external surface free from shrinkage, warpage, and flow mark by providing a resin storage space which can be made open to a resin passage. CONSTITUTION:Molten resin is injected into a cavity 13 from a resin nozzle through a resin passage 14 and a resin injection gate 15. At this moment, the periphery of a gas feed gate 16 spaced apart from the gate 15 is covered with the injected resin. And then pressurized gas is fed from the gate 16 into the resin filled in the cavity 13, whereby uncured resin in the central portion of a thick wall formation section in the cavity 13 is pressed to form a hollow in said portion. The resin having been pushed out is returned from the gate 15 to the passage 14, while the resin having increased volume is led to a resin storage space in communication with the passage 14 by retracting a core 171. Thereafter the pressure in the mold 1 is maintained so as to press the resin against the inner surface of the mold 1, while the resin is cooled and cured, and then the mold 1 is opened to take out a molded item.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to an injection mold which can form molded products having thick or uneven thickness parts with good external surface condition and without the occurrence of sink marks, warpage, flow marks, etc.
and a method for manufacturing a molded article using this mold.

0002

[Prior Art] Conventionally, when manufacturing a molded product having a thick wall portion or an uneven thickness portion by injection molding, the cooling time of the resin in the thick wall portion or uneven thickness portion is delayed compared to other parts. As a result, there are problems in that sink marks, warpage, etc. occur on the outer surface, resulting in an unsatisfactory appearance and poor physical properties, which may cause damage.

[0003] However, in the past, for example,
As described in Japanese Patent No. 4968, the mold cavity a
A method has been proposed in which a hollow molded product is manufactured by injecting an insufficient amount of molten synthetic resin into mold cavity a to fill the mold cavity, and then subsequently injecting a gas through the same inlet b (see Figure 4). There is. Furthermore, as described in Japanese Patent Application Laid-Open No. 60-24913, a method has been proposed in which a pressurized gas is directly injected into the resin filled in the cavity to produce a hollow molded product. .

0004

[Problems to be Solved by the Invention] However, in the former method, the injected gas pushes out the resin in the resin injection nozzle and the resin in the sprue and runner, and then fills the mold cavity. Since it enters the resin injected into a, the molding time increases accordingly, and this time results in a large loss during molding. Also,
Because the mold is cooling, the tip of the resin injected into the mold cavity a stays in one place for a long time, and a part of it hardens.
There is a problem in that flow marks are generated on the surface of the hollow molded product at the boundary between this part and the part that is hardened after being moved by the injection of gas.

In addition, in the latter method, even if gas is injected at high pressure into the resin filling the cavity, it is difficult for the gas to enter, and the advantages of the gas injection method cannot be fully utilized. However, there was a problem in that it was difficult to prevent the occurrence of sink marks and the like.

[0006]

[Means for Solving the Problems] According to the present invention, a cavity having an inner surface shape corresponding to the outer surface shape of the molded product is provided between a fixed mold and a movable mold, and a resin flow path is formed from a resin nozzle. A resin injection gate is provided for injecting the resin into the cavity through the resin injection gate, and a gas injection gate for injecting pressurized gas into the cavity is provided at a position away from the resin injection gate, and the resin injection gate can be opened into the resin flow path. An injection mold is provided with a reservoir, and using this mold, a sufficient amount of molten resin is injected into the cavity from a resin nozzle through a resin flow path and a resin injection gate to fill the cavity. , and pressurized gas is injected into the cavity from the gas injection gate to extrude the uncured resin at the center of the resin injected into the cavity to form a hollow part, and the extruded resin is poured into the resin from the resin injection gate. In this method, the molded product is produced by returning the resin to the flow path, guiding the increased amount of resin to an open resin reservoir, and cooling the resin in the cavity while keeping pressure against the inner surface of the mold.

[0007]

[Operation] Uses an injection mold in which a gas injection gate for injecting gas into the cavity is provided at a position separate from the resin injection gate, and a resin reservoir is provided in the resin flow path so that it can be opened. By injecting pressurized gas into the thick part of the resin filling the cavity, the uncured resin inside is pushed out and a hollow part is actively formed in that part, resulting in a good outer surface condition. It is possible to produce hollow molded products.

Since the gas injection gate is provided at a position away from the resin injection gate, the pressurized gas can be reliably injected into the resin of the thick-walled portion where the hollow portion is to be formed. Since the cavity is filled with resin, the area around the gas injection gate outlet is covered with resin. By injecting pressurized gas into the cavity through the gas injection gate, high-pressure gas is injected into the thick part of the resin filling the cavity, and the uncured resin in the center is pushed out into the resin flow path. At the same time, a hollow part is actively formed in that part. The extruded resin is returned to the resin channel through the resin injection gate, and the increased amount of resin in the resin channel is guided to the resin reservoir opened by retracting the core. Therefore, it is possible to easily extrude the uncured resin in the thick part and easily form a hollow part in that part. Subsequently,
By cooling the resin while pressing it against the inner surface of the mold, it is possible to produce a hollow molded product without sink marks, warpage, flow marks, etc. on the thick surface.

Here, the position where the gas injection gate is located away from the resin injection gate differs depending on the size and shape of the molded product to be molded, but it is necessary to inject enough resin into the cavity to fill the cavity. When manufacturing a hollow molded product using the so-called full shot gas injection injection molding method, there is a thick-walled part forming part that should be hollow between the resin injection gate and the gas injection gate. A position that exists.

0010

[Examples] The present invention will be explained below with reference to Examples. Figure 1
FIG. 1 is a vertical cross-sectional view showing a mold according to an embodiment of the present invention.

The mold 1 consists of a fixed mold 11 and a movable mold 12. Between the fixed mold 11 and the movable mold 12, there is formed a thick part 22 with a rib part 21 formed thereon.
A resin flow path 14 is provided which includes a cavity 13 having an inner surface shape having a thick-walled portion molded portion 131 corresponding to that shown in FIG. Further, a resin injection gate 15 is provided, through which molten resin is introduced into the cavity 13 through a resin flow path 14 from a resin nozzle (not shown).
It can be injected into the body. Further, a gas injection gate 16 is provided at the part of the thick-walled portion forming portion 131 that is farthest from the resin injection gate 13, so that pressurized gas can be pressurized into the resin filled in the cavity 13. has been done.

It should be noted that it is better to provide the gas injection gate 16 at a position farthest from the resin injection gate 15 so that the uncured resin in the center of the thick-walled part molded part 131 can be pushed out and a hollow part formed in that part. Although it is easy to form and is the most suitable, since the injection of high pressure gas also pushes out the uncured resin on the opposite side of the resin injection gate 15 around the gas injection gate to form a hollow part, it is not necessarily the farthest position. There is no need to provide it.

[0013] In addition, the resin flow path 14 has a resin reservoir 1.
7 is provided. The resin reservoir portion 17 is formed by a core 171 having a surface portion that is flush with the resin flow path 14 when moving forward.
It is formed by retracting the

Next, with reference to FIGS. 2 and 3, a method for manufacturing the molded product 2 having the thick portion 22 using the mold shown in FIG. 1 will be described. First, as shown in FIG. 2, the fixed mold 1 of the mold 1
1 and the movable mold 12 are closed. At this time, the core 171 is moved forward so that its surface is flush with the resin flow path 14, and the resin reservoir 17 is not opened to the surface of the resin flow path 14. Molten resin is injected into the cavity 13 from a resin nozzle (not shown) through a resin flow path 14 and a resin injection gate 15. The amount of resin is cavity 1
Fill with enough amount to fill 3. At this time, the area around the exit of the gas injection gate 16 which is remote from the resin injection gate 15 is covered with the filled resin.

Subsequently, as shown in FIG. 3, pressurized gas is injected into the resin filled in the cavity 13 through the gas injection gate 16. While extruding the uncured resin at the center of the thick-walled molded part 131 in the cavity 13, a hollow part is formed in that part. The extruded resin is returned to the resin flow path 14 through the resin injection gate 15, and the increased amount of resin is guided to the resin reservoir 17 opened to the resin flow path 14 by retracting the core 171. Subsequently, the resin is cooled while being pressed against the inner surface of the mold 1, and after the resin has hardened, the mold 1 is opened and the molded product 2 is taken out, thereby obtaining a hollow molded product.

[0016] The volume of the hollow part 23 in the molded product 2 is
The volume corresponds to the sum of the volume of the resin extruded into the resin flow path 14 and guided into the resin reservoir 17 and the volume of the resin shrinkage due to cooling of the resin.

A gas injection gate 15 is provided in the cavity 13.
There is no problem in injecting a small amount of resin into the cavity 13 from the resin injection gate 16 at the same time when pressurized gas is injected from the resin injection gate 16.

The material of the resin is not particularly limited as long as it can be injection molded. In addition to thermoplastic resins, thermosetting resins can also be used. The gas used is preferably an inert gas, for example nitrogen gas.

The injection molding mold and the method for manufacturing molded products of the present invention can be used, for example, for various containers, handles for plastic buckets, etc., and for various household industries having thick or uneven thickness parts such as automobile bumpers. It can be applied to the production of injection molded products.

Using the mold and manufacturing method shown in FIGS. 1 to 3 above, an experiment was conducted to manufacture a molded product having a thick wall portion under the following conditions. That is, polypropylene (PP) was used as the molding resin, the resin temperature was 230°C, and the mold temperature was 40°C.
℃. In addition, the gas injection conditions include gas pressure of 1
The dose was 20 Kg/cm2, the injection time was 30 seconds, and the injection timing was 0 seconds.

[0021] As a result, the obtained molded product having a thick wall part had no sink marks, warpage, or flow marks, and had a good appearance. In addition, when a molding experiment was conducted under the same conditions as above except that pressurized gas was injected into the cavity without opening the resin reservoir, a sufficient hollow space was not formed in the thick part of the molded product. However, only a molded product with poor appearance was obtained, with sink marks, warpage, and flow marks occurring on the surface of the thick part.

[0022]

Effects of the Invention Since the injection mold of the present invention has the above-described structure, pressurized gas is injected into the thick part of the resin filling the cavity to form a hollow part therein. do,
It can be applied to a so-called full shot molding method to produce a hollow molded product with a good outer surface condition.

[0023] Since the method for manufacturing a molded article of the present invention has the above-described configuration, pressurized gas is injected into the thick wall of the resin filled in the cavity to actively push out the uncured resin. To manufacture a hollow molded product without sink marks, warpage, flow marks, etc. on the outer surface of the thick part by forming a hollow part in the mold and cooling the resin while pressing it against the inner surface of the mold. Can be done.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing a mold according to an embodiment of the present invention.

FIG. 2 is a longitudinal cross-sectional view illustrating steps of a manufacturing method using the mold of the embodiment shown in FIG. 1;

3 is a longitudinal sectional view illustrating the steps of a manufacturing method using the mold of the embodiment shown in FIG. 1. FIG.

FIG. 4 is a partially cutaway front view illustrating the prior art.

[Explanation of symbols]

1 Mold 11 Fixed type 12 Mobile type 13 Cavity 14 Resin flow path 15 Resin injection gate 16 Gas injection gate 17 Resin reservoir part 171 core

Claims (2)

[Claims] Claim 1: A cavity having an inner surface shape corresponding to the outer surface shape of the molded product is provided between a fixed mold and a movable mold, and a resin is injected into the cavity from a resin nozzle through a resin flow path. An injection gate is provided, a gas injection gate for injecting pressurized gas into the cavity is provided at a position away from the resin injection gate, and a resin reservoir is provided in the resin flow path so as to be openable. An injection mold featuring: 2. Using the mold according to claim 1, a sufficient amount of molten resin is injected into the cavity from a resin nozzle through a resin flow path and a resin injection gate, and a gas is injected into the cavity. Pressurized gas is injected through the injection gate to extrude the uncured resin in the center of the resin injected into the cavity to form a hollow part, and the extruded resin is returned to the resin flow path through the resin injection gate to increase its volume. A method for manufacturing a molded product, which comprises guiding the resin into an open resin reservoir, and cooling the resin in the cavity while holding pressure so as to press it against the inner surface of a mold.