JPH04334413A - Injection molding method - Google Patents

Abstract

PURPOSE:To form a molded body without a swollen weld section in the injection molding method in which a molding material containing an orienting filler is used and a molded body with a weld section where the flow of one molding material joins the flow of the other molding material. CONSTITUTION:Molding is carried out in a manner that one molding material A infiltrates into the other molding material B at a weld section 20 to form a three-layer structure.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an injection molding method,
More specifically, the present invention relates to an injection molding method for forming a molded article having a weld portion.

0002

[Prior art] In the automobile industry, etc., there is a need to improve fuel efficiency,
Due to the increasing need for weight reduction in order to lower prices, various parts are being replaced with resin parts. For example, wheel caps were previously formed from sheet metal, but in recent years they have been manufactured from resin materials such as PP and nylon using molding methods such as injection molding. Note that resin alone does not have enough strength, so it is usually made of a composite material containing a filler such as glass fiber.

0003

By the way, the hubcap is provided with a valve hole for exposing the tire valve. In addition, in order to avoid deterioration of the design due to the valve hole, many of the valve holes are configured to form a plurality of design holes and use one of them as the valve hole. However, when a wheel cap having a hole on its surface is formed by injection molding, the molding material joins together at a part of the periphery of the hole, inevitably forming a weld. However, when molded with a molding material containing fillers such as glass fiber, talc, or mica, the surface of the weld part becomes more convex than other parts, often resulting in a decline in quality such as appearance, dimensional accuracy, and feel. was occurring. Therefore, the number of man-hours required for inspection after molding and correction by machining was large.

The present invention has been made in view of the above circumstances, and an object of the present invention is to form a molded article without swelling of the weld portion.

[0005]

[Means for Solving the Problems] The injection molding method of the present invention, which solves the above problems, uses a molding material containing an oriented filler and uses a weld portion where one flow of molding material merges with the flow of another molding material. In the injection molding method for forming a molded article having the above-mentioned weld part, one molding material enters into the inside of the other molding material to form a three-layer structure.

[0006] In the injection molding method of the present invention, a molding material containing an oriented filler is used. The oriented filler refers to a material that has the property of orienting the molding material in a certain direction during flow, and includes materials in the shape of fibers, scales, etc. Specific examples include glass fiber, talc powder, and mica powder. Further, a resin is used as the matrix, and a thermoplastic resin is generally used.

The greatest feature of the present invention is that in the weld portion, one molding material enters the inside of the other molding material to form a three-layer structure. In order to perform such molding, there is a method in which the pressure of the molding material is varied on both sides of the weld part. In this case, the high-pressure molding material with high pressure enters the inside of the low-pressure molding material with low pressure, resulting in a three-layer structure in which the high-pressure molding material is sandwiched between the low-pressure molding materials.

[0008] Furthermore, the temperature of the molding material may be made different on both sides of the weld portion. In this case, the high-temperature molding material enters the interior of the low-temperature molding material. Furthermore, it is also possible to configure the molding material on both sides to reach the weld portion with a time difference. In this case, the outer surface of the molding material that arrives first in contact with the mold surface receives heat from the mold and cools down, so that the outside has a higher viscosity than the inside. Therefore, when the other molding material arrives there later, the molding material that arrives later enters the lower viscosity interior of the molding material that arrived earlier.

By forming the weld portion into a three-layer structure in this manner, it is possible to prevent the weld portion from swelling.

0010

[Operations and effects of the invention] When a weld part is formed using a molding material containing an oriented filler, the molding materials on both sides collide in the weld part, so the orientation of the oriented filler becomes different from other parts. For example, what was previously oriented in the flow direction may become oriented perpendicular to the flow direction. Therefore, it is presumed that the degree of shrinkage in that part during cooling is different from that in other parts, causing swelling.

However, in the manufacturing method of the present invention, the weld portion has a three-layer structure in which one molding material penetrates into the other molding material. In other words, since the oriented filler oriented in the flow direction maintains its oriented state, it is considered that there is no difference from other parts and no swelling occurs. Therefore, according to the manufacturing method of the present invention, it is possible to reliably form a molded article with excellent appearance, dimensional accuracy, and feel of the weld portion, and it is possible to reduce the number of steps for inspection and correction after molding.

0012

[Examples] Hereinafter, the present invention will be explained in detail using examples. An injection molding machine with two barrels that can be controlled independently was used, and two types of molding materials with different colors were injected from each barrel, so that the condition of the weld part could be visually confirmed. Both molding materials were PP with 30% by weight of glass fiber added, and molding material A was uncolored and had a natural color, and molding material B was colored gray.

A mold having a cavity 10 having a substantially U-shaped cross section and three gates 1, 2, and 3 as shown in FIG.
Molding was performed by injecting molding material B from step 3. Here, the length of cavity 10 is 1470 mm, gate 1 and gate 2.
The distance between gates 2 and 3 is 600mm, and the distance between gates 2 and 3 is 24mm.
It is 2mm. Then, the injection pressure of the two barrels was adjusted and molded. At this time, the internal pressure difference near the weld part 20 is 30
~50 kgf/cm2, and molding material A has a higher pressure than molding material B.

The weld portion 20 of the obtained molded body was cut and its cross section was observed. A cross-sectional view thereof is shown in FIG. 2, and a cross-sectional view taken along the line CC in FIG. 2 is shown in FIG. As shown in Figures 2 and 3,
In the weld portion 20, the molding material A entered the inside of the molding material B to form a three-layer structure sandwiched between the molding materials B, and there was no bulge on the surface of the molded product, which was excellent in appearance, dimensional accuracy, and feel.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the structure of a cavity of a molding die used in Examples.

FIG. 2 is a sectional view of a weld portion of a molded body formed in an example.

FIG. 3 is a sectional view taken along line CC in FIG. 2;

[Explanation of symbols]

1, 2, 3: Gate 10: Cavity
20: Weld parts A, B: Molding material

Claims (4)

[Claims] 1. In an injection molding method for forming a molded article using a molding material containing an oriented filler and having a weld portion where a flow of one molding material merges with a flow of the other molding material, in the weld portion, one An injection molding method characterized in that one molding material enters the other molding material to form a three-layer structure. 2. The injection molding method according to claim 1, wherein the pressure of the one molding material is higher than the pressure of the other molding material in the weld portion. 3. The injection molding method according to claim 1, wherein the molding is performed such that the temperature of the one molding material is higher than the temperature of the other molding material in the weld portion. 4. The injection molding method according to claim 1, wherein the one molding material reaches the weld portion later than the other molding material.