JPH082546B2 - Injection molding method - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an injection molding method,
Specifically, it relates to an injection molding method for forming a molded body having a weld portion.

[0002]

2. Description of the Related Art In the automobile industry, low fuel consumption,
For the purpose of cost reduction and the like, the need for weight reduction is increasing, and various parts are being switched to resin parts. For example, the wheel cap was previously formed from sheet metal, but in recent years, it is manufactured from a resin material such as PP or nylon by a molding method such as injection molding. Since resin alone lacks in strength, it is usually formed from a composite material containing a filler such as glass fiber.

[0003]

By the way, the wheel cap is provided with a valve hole for exposing the tire valve. In addition, in order to avoid the deterioration of the designability due to the valve hole, there are many cases in which a plurality of design hole portions are formed and one of them is used as the valve hole. However, when a wheel cap having a hole on the surface is formed by injection molding, the molding material merges at a part of the peripheral edge of the hole to inevitably form a weld.
However, when molded with a molding material containing fillers such as glass fiber, talc, and mica, the surface of the weld bulges more convexly than other parts, and quality such as appearance, dimensional accuracy, and tactile feel often deteriorates. It was happening. Therefore, the number of man-hours such as inspection after molding and correction by machining is large.

The present invention has been made in view of such circumstances, and an object of the present invention is to form a molded body in which the weld portion does not rise.

[0005]

The injection molding method of the present invention, which has solved the above-mentioned problems, uses a molding material containing an oriented filler, and a weld part in which the flow of one molding material merges with the flow of the other molding material. In the injection molding method for forming a molded body having the above-mentioned, the weld part is molded so that one molding material enters into the other molding material to form a three-layer structure.

In the injection molding method of the present invention, a molding material containing an oriented filler is used. Oriented fillers are those having the characteristic that the molding material is oriented in a certain direction during flow, and materials in the form of fibers, scales, etc. are applicable. Specific examples include glass fiber, talc powder, and mica powder. A resin is used as the matrix, and a thermoplastic resin is generally used.

The greatest feature of the present invention resides in that, in the weld portion, one molding material enters into the other molding material to form a three-layer structure. For molding in this way, there is a method in which the pressure of the molding material is different on both sides of the weld portion. In this case, the high-pressure molding material having a high pressure enters the low-pressure molding material having a low pressure to form a three-layer structure in which the high-pressure molding material is sandwiched between the low-pressure molding materials.

The temperature of the molding material may be different on both sides of the weld portion. In this case, the high temperature molding material enters inside the low temperature molding material. Further, the molding materials on both sides may reach the weld portion with a time lag. In this case, since the outer surface of the molding material that reaches the outer surface in contact with the mold surface is deprived of heat by the mold to cool, the viscosity of the outer material is higher than that of the inner material. Therefore, when the other molding material arrives there after, the molding material that arrives later enters the inside of the molding material that arrives earlier with low viscosity.

By thus forming the weld portion with a three-layer structure, it is possible to prevent the weld portion from rising.

[0010]

When the weld portion is formed of the molding material containing the orientation filler, the molding materials on both sides collide with each other in the welding portion, so that the orientation of the orientation filler is different from that of the other portions. For example, what has been oriented in the flow direction until then may be oriented in the direction perpendicular to the flow direction. Therefore, it is presumed that the degree of shrinkage in that portion during cooling is different from that in other portions, and that swelling occurs.

However, according to 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. That is, since the orienting filler oriented in the flow direction maintains the same orientation state, it is considered that there is no difference from other portions and no swelling occurs. Therefore, according to the manufacturing method of the present invention, it is possible to reliably form a molded body having excellent appearance, dimensional accuracy, and tactile sensation of the welded portion, and reduce the number of man-hours required for inspection and correction after molding.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples. An injection molding machine having two barrels and capable of controlling each independently was used to inject two kinds of molding materials of different colors from each barrel so that the condition of the weld portion can be visually confirmed. As the molding material, both PP and 30% by weight of glass fiber were used, and the uncolored natural color molding material A and the gray color molding material B were used.

A mold having a cavity 10 having a substantially U-shaped cross section as shown in FIG. 1 and having three gates 1, 2 and 3 is prepared.
The molding material B was injected from No. 3 to perform molding. Here, the length of the cavity 10 is 1470 mm, the gate 1 and the gate 2
Is 600 mm, and the distance between gate 2 and gate 3 is 24
It is 2 mm. Then, the injection pressure of the two barrels was adjusted and molding was performed. At this time, the internal pressure difference near the weld 20 is 30
A ~50kgf / cm ^2, towards the molding material A has a pressure higher than the molding material B.

The welded portion 20 of the obtained molded body was cut and its cross section was observed. The cross-sectional view is shown in FIG. 2 and the CC cross-sectional view of FIG. 2 is shown in FIG. As shown in FIGS. 2 and 3,
In the weld portion 20, the molding material A entered the inside of the molding material B and was sandwiched between the molding materials B to form a three-layer structure, and no swelling occurred on the surface of the molding, and the appearance, dimensional accuracy, and tactile sensation were excellent.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a cavity of a molding die used in an example.

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

FIG. 3 is a sectional view taken along line CC of FIG.

[Explanation of Codes] 1, 2, 3: Gate 10: Cavity 20:
Weld part A, B: molding material

Claims (4)

[Claims] 1. An injection molding method for forming a molded article having a weld portion in which a flow of one molding material and a flow of another molding material are combined with each other by using a molding material containing an oriented filler. 2. The injection molding method, characterized in that the molding material of (1) enters into the other molding material and is molded so as to form a three-layer structure. 2. The injection molding method according to claim 1, wherein molding is performed so that 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 molding is performed so 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 molding is performed so that the one molding material reaches the weld portion later than the other molding material.