JPH11216744A - Resin molded body, injection mold and injection molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the surface of a resin molded body just after the removal of the body from a mold from having a gate part mark thereon by a method wherein a block having a surface movable parallel to at least some surface of a mating part is provided so as to shut off a gate part, which is provided parallel to the mating part surface, through the forward and backward motions of this block. SOLUTION: At a mating part A made by a fixed retainer plate 1 and a movable retainer plate 2, a cavity 3, which corresponds to the shape and dimensions of a resin molded body, a runner 4 and a gate 5 are formed. To the movable retainer plate 2, a plurality of ejector pins 6 and 7, which are arranged slidably and reciprocated by a driving means are equipped. To the fixed retainer plate 1, a block 8, which moves parallel to the mating part A so as to cut off the gate, and a spring 9 for pushing back to the block 8 are equipped. Thus, through the reciprocating motion of an ejector rod, the block 8 can be moved so as to cut off the gate 5. Through a molding, in which the above-mentioned constitution is employed, the surface of a discharged resin molded body has no gate part mark.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin molded article injection-molded by an overlap gate method, a mold for injection molding thereof, and an injection molding method.

[0002]

2. Description of the Related Art A resin molded product such as a disk-shaped roller is required to have a high precision in its outer peripheral surface in terms of function. When such a resin molded body is injection-molded, if a gate is installed on the outer peripheral surface of the injection molding die, that is, a surface that is perpendicular to the parting line, a gate mark or the like remains and the accuracy of the outer peripheral surface is reduced. . For this reason, the gate is provided on the width end surface, that is, the surface which is parallel to the parting line. In this case, a pin point gate method or an overlap gate method is applied as the gate method. In general, a resin molded body injection-molded from a pinpoint gate type mold has a recess called gate escape in the gate portion, and the gate rest fits in this recess and does not protrude to the surface of the molded body. I have. However, in molding of a nylon resin or polyurethane resin having a large tensile elongation at break, the gate portion is pulled at the time of release from the mold, so that a large amount of the gate residue is generated. For this reason, when the thickness of the gate installation surface of the resin molded body is small, the recess cannot be made large, and the gate portion must be finished after the molding. Furthermore, when a resin having poor fluidity is used, it is necessary to increase the gate cross-sectional area. For example, in a resin having a very large tensile elongation at break such as a molten fluororesin, the gate causes stringing and cannot be molded without being cut. In particular, there is a problem that the resin is restricted.

[0003] For this reason, an overlap gate system, which is much less restricted by the product shape and resin than the pinpoint gate system, is used for a mold for molding a resin molding such as a disk-shaped roller. The overlap gate method is also called a straight top gate, and a gate is installed in parallel with a width end surface of a disk-shaped roller or the like. For this reason, similarly to the side gate method, the resin molded product injection-molded from the mold of this method is taken out of the mold with the gate attached to the product part (cavity part). Processing must be performed.

[0004]

However, for a resin molded body such as a disk-shaped roller, whose outer surface is required to have high accuracy in function, an overlap gate method is preferable, but gate cutting in a mold by injection molding is difficult. There is a problem that is. Therefore, if gate cutting is performed after the gate is removed from the mold, equipment and processing costs required for the gate cutting increase, and the manufacturing cost of the resin molded article increases.

The present invention has been made in order to address such a problem, and has provided a resin molded article having no gate mark on the surface immediately after removal of the mold, a mold for injection molding thereof, and the use of the same. An object of the present invention is to provide an injection molding method.

[0006]

Means for Solving the Problems The resin molded article of the present invention comprises:
A resin molded article that is injection-molded by an overlap gate method having a gate portion in parallel with the molded body end face portion,
It is characterized by having no gate mark on the surface immediately after removing the mold. Here, having no gate mark means that the surface of the resin molded body is smooth and has no gate mark without performing gate cutting or polishing after molding.

The injection mold of the present invention has a fixed mold plate and a movable mold plate for forming a cavity at an abutting portion with the fixed mold plate, wherein the cavity is movable. A block provided on the template and having a surface that is movable back and forth in parallel with at least a part of the abutment portion, and a gate portion provided in parallel with the abutment portion surface is blocked by the forward / backward movement of the block. It is characterized by.

According to the injection molding method of the present invention, there is provided a step of forming a cavity by abutting a fixed mold plate and a movable mold plate, and melting the cavity into the cavity from a gate portion formed in parallel with the abutting surface. It is characterized by including a step of injecting and filling a resin, and a step of blocking a gate portion by advancing and retreating a block having a surface capable of moving back and forth in parallel with the abutting surface after filling the molten resin.

Since the resin molded article of the present invention is manufactured by the overlap gate method and the gate cut method in the mold, there is no gate mark on its surface. In addition, in the injection molding die, the cavity is provided on the movable mold plate side, and the block having a surface that can be advanced and retracted in parallel with at least a part of the die abutting portion is parallel to the abutting portion surface by advancing and retreating movement. Since the gate portion provided in the above is shut off, an injection-molded article excellent in appearance and dimensional accuracy can be obtained as compared with the pinpoint gate method. Furthermore, since the injection molding method of the present invention performs injection molding using the above-described injection molding die,
An injection molded body that does not require post-gate processing can be obtained, and equipment required for gate processing and processing costs can be reduced, and stable production can be performed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A mold for injection molding of a resin molded article according to the present invention and a method for molding a resin molded article molded using the same will be described with reference to the drawings. FIG. 1 is a diagram showing a cross section of a main part of a mold showing one embodiment of the present invention. A fixed die 1 and a movable die 2 movable forward and backward with respect to the fixed die 1 constitute a main part of a mold. A cavity 3 corresponding to the shape and dimensions of a resin molded body, for example, a disk-shaped roller, a runner 4 as a resin flow path, and a gate 5 as an entrance of the resin into the cavity 3 are formed in the joint portion A. The cavity 3 provided on the movable mold plate 2 side is injection-filled with a molding resin composition via a runner 4 and a gate 5. The movable mold plate 2 includes a plurality of ejector pins 6 and an ejector rod 7 which are slidably arranged, and these are reciprocally driven by driving means such as a hydraulic cylinder (not shown). The fixed side template 3 is provided with a block 8 for cutting the gate, which moves in parallel with the abutting portion A, and an urging force for pushing it back, for example, a spring 9. Can move to shut off gate 5. In addition, the block 8 has a surface that can advance and retreat in parallel to at least a part of the abutting portion A.

An embodiment of the injection molding method of the present invention will be described with reference to FIGS. 2 to 8 using the mold shown in FIG. 2 to 5 show the injection molding process, FIG. 6 shows a supplementary view of FIG. 2, FIG. 7 shows a supplementary view of FIG. 3, and FIG. 8 shows a supplementary view of FIG. These supplementary figures are provided for better understanding of the present invention. First, the fixed mold plate 1 and the movable mold plate 2 are abutted, and the molding resin composition P is injected and filled into the cavity 3 via the runner 4 and the gate portion 5 (FIGS. 2 and 6). . After the filling step of the molding resin composition P into the cavity 3 is completed, the block 8 is moved to the gate portion 5 when the molding resin composition P is not completely cured during the pressure-holding step or the cooling step. To advance.
Thereby, the gate is completely cut in the mold. The resin pressed by the block 8 has some fluidity at this time, and thus flows into the resin molded body or is pushed back from the gate portion 5 to the runner 4. Thereafter, the molding resin composition P is completely cured (FIGS. 3 and 7).

After the molding resin composition P is cured, the ejector rod 7 is returned in the direction of the movable mold plate 2 to return the block 8 for cutting the gate by the force of the spring 9 (FIGS. 4 and 8). Thereafter, the movable mold plate 2 is moved to open the mold, and the resin molded body 10 and the runner 4 are ejected from the injection mold by the ejector pins 6 (FIG. 5).
By the above-described molding method, the discharged resin molded body 10 becomes a resin molded body having no gate mark on the surface.

According to the present invention, the ejector rod 7 is driven so as to be able to move forward and backward perpendicular to the abutting surface A of the mold.
The block 8 is moved parallel to the abutment plane A. This parallel movement cuts the gate. For this reason, the injection molding machine which can use the injection mold of the present invention has a mechanism capable of independently controlling the ejector pin 6 and capable of driving the ejector rod 7 to move back and forth with respect to the abutment surface A when the mold is closed. Any injection molding machine can be used without particular limitation. Examples of the function of such an injection molding machine include a pre-ejector manufactured by FANUC, and a press α manufactured by Sumitomo Heavy Industries, Ltd.

In the resin molded article of the present invention, the gate is completely cut in the mold in the injection molding step. Therefore, when applied to a resin composition having a large tensile elongation at break, which tends to cause stringing at the time of gate cutting, the effect is large. Particularly preferred resins constituting the resin composition include resins having a tensile elongation at break of 100% or more at room temperature.
As such a resin, a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PF)
A), tetrafluoroethylene-ethylene copolymer (E
TFE), molten fluororesin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP), thermoplastic elastomers such as urethane elastomer, polyester elastomer, polyamide elastomer, vinyl chloride elastomer, polybutadiene elastomer, polyurethane resin, polyamide resin, polyethylene Resins, polypropylene resins, polyacetal resins and the like can be mentioned.

On the other hand, in recent years, resin molded articles pursuing high functionality and high accuracy are often obtained by molding a resin composition having a high compounding ratio of a filler and a high melt viscosity. Injection molding using the mold for injection molding of the present invention enables molding with those resin compositions, and can produce a highly functional and highly accurate resin molded body. Particularly preferred resins constituting the resin composition include polyamide imide resin, thermoplastic polyimide resin, and polyphenylene sulfide resin containing fluorine fiber.

[0016]

Examples and Comparative Examples Disc-shaped rollers (outer diameter D: 12 mm, inner diameter d: 8 mm, thickness t: 8 mm) having the shape shown in FIG. 9 were mixed with a polyimide resin composition containing 30% by weight of carbon fibers. Injection molding was performed using the injection mold described above and a conventional injection mold using a pinpoint gate method as a comparative example. The outer peripheral surface 10a of the disk-shaped roller serves as a functional surface, and precision on the outer peripheral surface is particularly required, so that a gate portion cannot be provided on the outer peripheral surface. In the above-described injection mold, a semicircular gate portion 10c is provided on a part of the side surface 10b adjacent to the outer peripheral surface 10a in parallel with the abutment surface A. Gate section 10c
Has a length L of about 2 mm. Note that the pinpoint gate in the comparative example has a diameter of
There are three locations in b.

In the comparative example, the resin molded body remained on the fixed side mold plate in the first injection molding, and the injection molding could not be continuously performed. In contrast, the example was able to injection-mold 1,000 continuous disc-shaped rollers without stopping production. Table 1 shows a comparison of the characteristics of the disc-shaped rollers obtained in the examples and comparative examples.

[0018]

[Table 1]

As shown in Table 1, in the example, there was no convex portion of the gate mark, and no post-gate processing was required. On the other hand, in the comparative example, a convex portion of the gate mark was observed, and post-gate processing was required. In addition, the appearance characteristics of the resin molded article, such as gloss and sink, were excellent. Further, the roundness of the outer peripheral surface was also excellent.

[0020]

The resin molded article of the present invention has no gate mark on the surface immediately after removal of the mold, so that post-gate processing is not required.

In the injection mold of the present invention, the cavity is provided on the movable mold plate side, and the gate portion is shut off by the advance / retreat movement of a block having a surface which can advance and retreat in parallel with at least a part of the abutting portion. Therefore, gate cutting in the mold can be easily performed on the abutting surface of the mold, and an injection molded article excellent in appearance and dimensional accuracy can be obtained.

According to the injection molding method of the present invention, since the injection molding is performed by using the above-described injection mold, an injection molded body that does not require post-gate processing can be obtained, and equipment and processing cost required for gate processing can be reduced. In addition, stable production can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section of a main part of a mold showing one embodiment of the present invention.

FIG. 2 is a view showing a resin composition filling step in the injection molding step.

FIG. 3 is a view showing a gate cutting step in a mold in the injection molding step.

FIG. 4 is a diagram showing a state in which a block returns in an injection molding process.

FIG. 5 is a diagram showing a state in which the resin molded body is discharged.

FIG. 6 is a supplementary diagram of FIG. 2;

FIG. 7 is a supplementary diagram of FIG. 3;

FIG. 8 is a supplementary diagram of FIG. 4;

FIG. 9 shows a disk-shaped roller used for injection molding.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixed side template 2 Movable side template 3 Cavity 4 Runner 5 Gate 6 Ejector pin 7 Ejector rod 8 Block 9 Spring 10 Resin molding

Claims (3)

[Claims] 1. A resin molded article injection-molded by an overlap gate method having a gate section parallel to an end face of a molded article, wherein the molded article has no gate mark on the surface immediately after taking out a mold. Resin molded body. 2. An injection molding die having a fixed mold plate and a movable mold plate for forming a cavity at an abutting portion with the fixed mold plate, wherein the cavity is provided on the movable side. A block provided on the template and having a surface that is movable back and forth in parallel with at least a part of the abutment portion, and a gate portion provided in parallel with the abutment portion surface is shut off by the forward / backward movement of the block. A mold for injection molding, characterized in that: 3. A step of forming a cavity by abutting a fixed mold plate and a movable mold plate, and injecting and filling a molten resin into the cavity from a gate portion formed parallel to the abutting surface. And a step of shutting off the gate portion by moving a block having a surface which can be moved back and forth in parallel with the abutting surface after filling the molten resin. .