JPH0557741A - Injection molding of thermoplastic resin - Google Patents

Abstract

PURPOSE:To provide a molding method imparting excellent reinforcing effect to a weld part and also imparting excellent appearance and moldability. CONSTITUTION:In the injection molding of a thermoplastic resin using a mold forming a molded product having an annular shape or a mold having a plurality of resin injection ports (resin gates), an inert fluid is introduced into a part where the molten resins injected in the cavity of the mold from the resin gates meet with each other to stop under pressure to move the uncured part in the resins from a weld part to the other part and the lowering of the strength of the weld part is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for housings, chassis, frames, machine cases, automobile parts, etc. of electronic / electrical products using a thermoplastic resin.

[0002]

2. Description of the Related Art Thermoplastic resins, so-called plastics materials, are widely used for housings, cases, chassis, mechanical parts and the like in all industrial fields. Injection molding, extrusion molding, thermoforming after sheet / film processing, and other molding methods are used to put the thermoplastic resin into actual use. Among these, the injection molding method is particularly important for productivity. In addition to being excellent, it has excellent appearance, shape and dimensional accuracy, and is currently the mainstream of processing methods. On the other hand, the form of plastic products can be a combination of complex irregularities and structures unlike metal processing, and in the housings of electrical products, the product exterior part, the internal mechanism, and the part built-in structure are integrated. Things are also molded.

On the other hand, a plastic product has a display window,
Many of them have openings for ventilation, and when such a product is injection-molded with plastic, the material injected into the mold cavity is divided by the ring-shaped part and joins again. Will have. In addition, for large products or products with partial shape changes, multiple resin injection ports (resin gates) are arranged to facilitate the injection of resin material, but even in that case, the resin flow from each gate merges. Therefore, a weld portion is generated. In the weld part, when the merged material continues to flow to other parts,
There is a case where it stops at the place where it joins, and if the joining point is the same as the stopping point and that part is a relatively narrow part or the final filling part, both the molten resin temperature and the pressure at the time of joining and stopping will be This lowers the weld strength at the merging point, leading to a decrease in so-called weld strength.

In order to solve such a problem, a resin gate position is selected so that the weld portion does not become a relatively narrow portion or the final filling portion, and if the resin gate position cannot be changed, the weld portion cannot be changed. It is reinforced by increasing the wall thickness and increasing the welding area. Generally, reinforced grades containing glass fiber, carbon fiber, metal whiskers, etc. are used to supplement the strength and rigidity of plastics for metal products substitution, large-scale products, mechanical parts, etc. The strengthening effect is small in the weld part, and the difference in strength from other parts than the weld part is large
The weld part may become a defective part of the product. Also,
Many blends of different materials and alloyed materials have been developed in order to complement the characteristics of each plastic material and to exhibit excellent performance, but there is a problem that the strength of the welded part deteriorates like the reinforced material.

The state of the weld portion when a fiber reinforced material is used is schematically shown in the state of FIG. 1, and the reinforced fibers and whiskers compounded inside the resin have a flow direction especially in the flow surface layer of the material. Although it is easy to orient in the same direction, it is known that the weld portion where the resin flows merge is oriented in the thickness direction, and only the base resin is present at the merging interface. For this reason, in the fiber-reinforced material system, the reinforcing effect is weakened in the weld portion, and the strength difference from the portion other than the weld portion, which is reinforced by the fiber orientation, becomes large. Therefore, when the molded product receives a load, the weld portion becomes a weak point, and the weld portion is vulnerable to damage by stress concentration at a value considerably lower than the original material strength.

As a means for preventing the strength of the weld portion from decreasing, a device for repeatedly applying a plurality of resin injection pressures to a plurality of resin gates, which is disclosed in Japanese Patent Laid-Open No. 61-179715, is combined, and each pressure load is repeated. An injection molding method has been proposed in which the internal molten resin is moved and solidified by carrying out. However, in this case, since the resin in the weld portion is moved while delaying the solidification of the resin,
In order to enhance the reinforcing effect, it is necessary to make the weld wall thickness of the product thicker than in the general molding method, and the molding cycle tends to be longer, so it cannot be applied to any product form and the productivity is improved. However, there is a disadvantage.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a molding method which is excellent in the effect of reinforcing the welded portion and which is excellent in appearance and productivity.

[0008]

Means for Solving the Problems As a result of intensive investigations by the present inventors, gas injection molding has been used as a technique for solving the problem of sink and warp, which are molding defects of plastics, and for weight reduction by imparting rigidity and hollowing. By applying the method, it has been found that it becomes possible to easily reinforce the weld portion, which could not be solved by the conventional injection molding method, and the present invention has been completed. That is, the present invention is an injection molding method of a thermoplastic resin using a mold having a ring shape as a molded product or a mold having a plurality of resin injection ports (resin gates). The inert fluid is forced into the cavity where the molten resin injected into the cavity merges and stops (weld) to move the uncured resin inside the resin from the weld section to another section. It is an invention relating to a thermoplastic resin injection molding method for improving strength reduction.

In the present invention, the molded product with the weld portion reinforced is a molded product in which the weld defects of the conventional injection molded products as shown in FIGS. 2 and 3 are improved. That is,
At the weld part where the resin flow stops at the confluence point, which could not be solved by the conventional injection molding method, the inert fluid is pressed into the molten resin part at the same time as before or after the injection of the resin is adjusted, This is a method of obtaining a molded product in which the welded part is reinforced by moving the molten resin in the welded part where merging is stopped, and after the molten resin has solidified, the inert fluid is discharged to take out the molded product. By this method, a molded product having a welded portion reinforced as shown in FIG. 2 is obtained.

The injected inert fluid (for example, nitrogen gas) does not solidify, the pressure is hardly reduced to the reaching end, and the pressure is transmitted to the molten resin, so that it is effective even at a relatively low pressure. Since the pressure can be maintained until it solidifies, it is not necessary to increase the thickness other than the weld portion to transmit the resin pressure from the resin gate port as in the prior art, and as a result, the molding cycle is not extended. , Leading to reduction of material cost and production cost.
The inlet of the inert fluid is not limited to the vicinity of the weld, but in order to promptly generate a new flow in the molten resin before solidifying, it is better to place the inlet as close to the weld as possible.

If a plurality of inert fluid inlets are provided across the weld portion and injection and discharge or pressure load fluctuations are repeated, a resin flow reciprocating in the weld portion can be generated. As a result, an injection molded product as shown in FIG. 3 is obtained, and the reinforcement can be performed more effectively. Especially in the case of material systems such as fiber reinforced materials and liquid crystal polymers, where the reinforcing effect is greatly enhanced by orienting the filling fibers and the molecular orientation of the polymer, the surface layer (gold Since it can be solidified while sequentially orienting from the contact surface with the mold) to the inner layer, a remarkable effect is obtained. The molding method of the present invention will be described below based on examples.

[0012]

EXAMPLE A flat plate-shaped molded product having vertical rib structures at both ends shown in FIG. 4, which has three points of resin gates on the upper surface of the flat plate and is provided on the back surface so as to connect the vertical ribs at both ends. On the surface of the reinforcing rib opposite to the central resin gate portion, as shown in FIG.
Injection using a glass fiber reinforced polycarbonate resin (trade name: Iupilon GS2020M, glass fiber content 20% by weight, manufactured by Mitsubishi Gas Chemical Co., Inc.) in an injection mold with an inert gas injection port at each point. Molded. First, from the three resin gates, the molding temperature 31
The glass fiber reinforced polycarbonate resin was injected under the conditions of 0 ° C., injection pressure of 157 MPa, and mold temperature of 80 ° C. At the same time as the resin flow merges at the center between the resin gates and the other parts are also filled with the molten resin, the pressure on the injection molding machine side is reduced almost at the same time, as an inert gas,
Pressure of nitrogen gas from the gas gate inside the resin is 9.8 MPa.
Then, the resin in the molten state inside the reinforcing ribs connecting the vertical ribs at both ends was moved from the gas injection side to the opposite side, and the pressure was maintained until the entire resin solidified.

After solidification of the molten resin, nitrogen gas was discharged from the gas gate to bring the internal pressure to atmospheric pressure, the mold was opened, and the molded product was taken out. For comparison, the gas gate portion of the mold was shielded, and the same molded product was molded by a general injection molding method under the same material and molding temperature, injection pressure and holding pressure of 98 MPa. A test piece was cut out from each of the molded products so that the weld-occurring portion was located at the center, and a bending test in which both ends of the welded portion were supported and a load was applied to the center / weld portion was performed to compare the breaking strength. As a result, the breaking load is 131 for normal products.
In contrast to N, the molded product molded by the molding method of the present invention was 172N, which was a reinforcing effect of more than 30% as compared with the normal product.

[0014]

EFFECTS OF THE INVENTION The weld reinforcement effect of the present invention can improve the resin joining in injection molding and the strength reduction at the stopping point, and depending on the shape, the weight reduction effect by hollowing can be obtained. Since it is possible to solve the constraint of the shape as well as the constraint of the existence of the opening and the gate of the other point, the product design has a wide range. Further, since the thick portion can be hollowed, the molding cycle can be shortened, and the productivity can be improved and the cost can be reduced.

[0015]

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a state of a weld portion when a fiber reinforced material is used.

FIG. 2 is a schematic view showing a state in which an inert fluid is press-fitted toward the weld portion to move the resin in the weld portion to another portion.

FIG. 3 is a schematic diagram showing a state in which an inert fluid is press-fitted into the weld portion from two inert fluid inlets to reciprocate and the resin in the weld portion is moved to another portion. It is a figure.

FIG. 4 is a perspective view showing a flat plate-shaped molded product having a rib structure at both ends, which is used in the embodiment.

FIG. 5 is a schematic cross-sectional view in the rib direction of a molded product obtained in an example.

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Claims (2)

[Claims] 1. A thermoplastic resin injection molding method using a mold having a ring shape or a mold having a plurality of resin injection ports (resin gates), wherein the molded product is a mold cavity from the resin gate. Inert fluid is pressed into the portion where the molten resin injected inside joins and stops (weld) to move the uncured resin inside the resin from the weld portion to another portion, and the strength of the weld portion Thermoplastic injection molding method to improve the deterioration. 2. The thermoplastic resin injection molding method according to claim 1, wherein an inert fluid is press-fitted to move the uncured resin inside the resin from the weld portion to another portion. A thermoplastic resin injection molding method, which is a method of moving from a weld portion to another portion by a plurality of reciprocating motions until the injected molten resin is solidified.