JPH07304069A - Injection molding method and injection mold - Google Patents

Abstract

PURPOSE:To eliminate the weld line of an injection molded product or to make the same inconspicuous. CONSTITUTION:A wall thickness changing mechanism 200 (200a, 200b, 200c, 200d) is supported at a region where the molten resins injected into a cavity 100 from gates 100a must meet each other by at least one of the templates 110, 120 constituting the cavity 100 and allowed to penetrate in the region at the injection start initial period. The wall thickness changing mechanism 200 is retracted from the cavity 100 so that two flows meet with each other at an acute angle after the molten resins reach the wall thickness changing mechanism 200 to suppress the generation of a weld line at the confluent part.

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 and a mold for injection molding in which a weld is eliminated or made inconspicuous in injection molding.

[0002]

2. Description of the Related Art When a thermoplastic resin is injection-molded, a multi-point gate is used for facilitating the molding up to the end, or there is a hole (= a protrusion in a cavity) on the design of a molded product, By shunting even from a single gate,
Weld occurs when the two flow tips meet. As a technique to prevent welds, control the thickness of the molded product.
A method of raising the temperature of the resin during molding by heating the mold, a method of making a weld once generated to make a resin reservoir to cause a secondary flow to be inconspicuous, and the like are used. However, if the uneven thickness structure is provided and the thin wall portion is provided, the fluidity becomes insufficient and surface defects are likely to occur. Therefore, the method of heating the mold requires a long molding cycle and a large amount of capital investment. In addition, when a resin reservoir is formed, post-processing after taking out is required, and there are problems and limitations in any of the methods, and there is no simple method that can improve the effect.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent or make inconspicuous welds with a simple structure. Another object of the present invention is to prevent the weld from occurring or make it inconspicuous without lengthening the molding cycle or causing surface defects.

[0004]

According to a first aspect of the present invention, when a thermoplastic resin is injection-molded, a movable member of a variable thickness mechanism provided in a portion near the weld generating portion reduces the thickness of that portion. By thinning or eliminating it, it obstructs the flow of the molten resin and dams it, and by causing hesitation, a weld is temporarily generated at a place where no weld originally occurs, and then the flow is changed by retracting the movable member. This is an injection molding method for improving the appearance and strength of the weld portion by moving the weld. By retreating the movable member, the wall thickness at that position becomes thicker than usual, becomes normal, or becomes thicker than before retreating but thinner than usual. The invention of claim 2 is
When a thermoplastic resin is injection molded, the movable member of the variable thickness mechanism, which is originally provided at the position where the weld is generated, reduces or eliminates the thickness of that portion so that the molten resin flows around the variable thickness mechanism. And then the movable member is retracted so that the flow merges in a state where the flow is maintained at an acute angle, thereby preventing the occurrence of welds. By retreating the movable member, the wall thickness at that position becomes thicker than usual, becomes normal, or becomes thicker than before retreating but thinner than usual. The angle at which the flows merge is defined as the angle formed by the vectors of the forces that cause the two flows to advance. That is, according to this definition, when the two flows are parallel, the merging angle is 0 °. Further, when the two flows collide with each other from the front, the merging angle is 180 °. The acute angle is desirably 48 ° or less. The invention of claim 3 is a mold capable of carrying out the method of claim 1. The invention of claim 4 is
A mold capable of carrying out the method of claim 2.

[0005]

According to the first and third aspects of the present invention, the weld does not occur in the portion where the weld originally occurs, and the weld line due to the hesitation that temporarily occurs in the other portion is the movable member of the variable thickness mechanism. When is retracted, it is washed away to the downstream side. Therefore, no weld occurs in that portion.
In the inventions of claims 2 and 4, the merging at the portion where the weld originally occurs is temporarily hindered, and the merging is performed after the merging angle becomes an acute angle. Therefore, the occurrence of welds is prevented.

[0006]

EXAMPLES Examples of the present invention will be described below. (1) Example 1 FIG. 2 is a schematic view showing the cavity of the mold of Example 1,
(A) is an AA cross section of (b), (b) is BB of (a).
It is a cross section. 1 (b) and 1 (c) show the progress of the flow front in the mold of the first embodiment. As shown in the figure, a protrusion 12 a is integrally provided at a substantially central portion of the lower mold 12 so as to protrude into the cavity 10. The protrusion 12a is a portion that becomes a through hole (hole) in the molded product. A recess 11a is formed in the upper mold 11, and a movable member 20 having a circular cross section (movable member of the variable thickness mechanism) 20 is vertically displaced in this recess 11a via a spring 20s. It is supported. Due to the urging force of the spring 20s, the tip surface (bottom surface) side of the movable member 20 is in contact with the cavity surface of the lower mold 12 in a normal state. The installation position of the movable member 20 in a top view is a position adjacent to the protrusion 12a. In the case of the conventional mold shown in FIG. 1 (a), when the molten resin is injected from the gate 10a into the cavity 10 as indicated by the two-dot chain line arrow, the flow front end thereof is the protrusion 12a. It is divided into two. Therefore,
The two split streams are merged again on the downstream side, and a weld W is generated at that portion. On the other hand, FIG.
In the case of the mold of the present embodiment shown in (c), since the movable member 20 of the variable thickness mechanism is inserted into one side of the divided flow, it is temporarily blocked at that portion, whereby Hesitation W is generated. In addition, since there is no variable thickness mechanism on the other side of the split flow, the flow proceeds as it is.
It wraps around from behind the protrusion 12a and reaches the rear side of the variable thickness mechanism 20. Further, when the flow front on the other side reaches the rear side of the thickness varying mechanism 20, the movable member 20 of the thickness varying mechanism is retracted upward (see (c) in FIG. 1). That is, the movable member
20 is housed in the recess 11a of the upper mold 11. In this mold, the force for this is given by the pressure of the molten resin overcoming the biasing force of the spring 20s. Also, the retracted height is
The height is determined by a stopper provided as a step in 11a, which is the height at which the tip surface of the movable member 20 is the same as the cavity surface of the upper mold 11. It should be noted that they may not be the same but may be thick or thin. When the movable member 20 of the variable thickness mechanism is retracted into the recess 11a, the blocked flow end of the one side starts to move again. As a result, the flow front end on the other side that wraps around behind the movable member 20 is also swept away to the downstream side, and
The hesitation W is also washed away downstream (see W1). Therefore, the weld that is about to occur at the position of the variable thickness mechanism 20 is also eliminated. As described above, in the first embodiment, the hedation is generated not at the position behind the protrusion 12a (see (a) of FIG. 1) but at the lateral position where the protrusion 12a can be swept to the downstream side. It prevents the occurrence.

(2) Second Embodiment Description of parts having the same principle as the first embodiment will be simplified or omitted. 3A and 3B are schematic views showing the cavity of the mold of Example 2, where FIG. 3A is a sectional view taken along the line AA of FIG. 3B, FIG. 3B is a sectional view taken along the line BB of FIG. It is a modification 200 ′ of the movable member of the variable mechanism. 4 (a) and 4 (b) show the progress of the flow front in the mold of the second embodiment. As shown in the figure, at the center of the lower mold 120, the protrusion 120a is
It is provided integrally so as to project into 100. Upper mold 11
A recess 110a is formed in 0, and in this recess 110a,
A movable member 200 of a variable thickness mechanism having a semicircular cross section is supported via a spring 200s so as to be vertically displaceable. The installation position of this movable member 200 in a top view is the protrusion 12
Behind 0a. From the gate 100a into the cavity 100,
When the molten resin is injected as indicated by the two-dot chain line arrow, the flow front thereof advances as shown in FIG. That is, initially,
What was one flow is split into two at the protrusion 120a. Since each branch channel is narrower than that in the first embodiment, when two branch streams meet behind the protrusion 120a, their traveling directions are opposite to each other. In other words, the two diverted streams meet so as to collide head-on, and a weld will occur if they are left as they are. For this reason, in this embodiment, a variable thickness mechanism is provided behind the protrusion 120a, and the movable member 200 thereof changes the direction of the two split streams to the downstream side. In addition, after the two split flows are directed to the substantially downstream side, the movable member 200 of the variable thickness mechanism is pressed by the upper mold 11 by the resin pressure.
It is retracted into the 0 recessed portion 110a. After that, the two split flows integrally proceed to the downstream side (see FIG. 4B).
Further, since the angle formed by the advancing directions of the two split flows (see (c) of FIG. 6) at the time of merging is an acute angle (preferably 48 ° or less), the occurrence of welds at the merging portion is prevented. In the above, the case where the movable member 200 of the variable thickness mechanism is an integral member has been described.
As shown by broken lines in FIG. 3, for example, four members 200a, 2
It is possible to make the angle formed by the advancing directions of the two diverted flows even more acute by constructing 00b, 200c, and 200d and retracting in order from 200a. Further, although the case where the tip end surface of the movable member 200 of the variable thickness mechanism is flat has been described above, the movable member may be any one that can temporarily stop the progress of the molten resin. As shown in FIG. 3 (c), an internal void may be provided, or a taper may be used. In addition, such a modification is similarly established in the above-described first embodiment and each of the later-described embodiments.

(3) Third Embodiment Descriptions of parts having the same principle as the above-described embodiments will be simplified or omitted. FIG. 5 is a schematic view showing a cavity portion of a mold of Example 3, (a) is a cross section taken along line AA of (b),
(B) is a BB cross section of (a). 6 (a) and 6 (b) show the progress of the flow front in the mold of the third embodiment. In the cavity 101 of the illustrated mold, the first embodiment is provided.
Unlike No. 2 and No. 2, the projecting portion for dividing the molten resin is not provided in the design, but since the gates 101a are provided at two locations, the molten resin joins in the cavity 101.
At this merging position, a movable member 201 of a variable thickness mechanism having a triangular cross section is supported by an upper mold 111 via a spring 201s so as to be vertically displaceable. Two gates 101a
When the molten resin is injected from the inside into the cavity 101 as indicated by the two-dot chain line arrow, the flow front thereof advances as shown in FIG. When these two flow fronts meet, their traveling directions are opposite to each other, and a weld occurs if they are left as they are. For this reason, in this embodiment, the movable member 201 of the variable thickness mechanism is provided at the confluence position and the directions are aligned so that the advancing directions of the two flow tips form an acute angle θ. Further, after the two flow tips are substantially aligned with each other, the movable member 201 is retracted into the recess 110a of the upper mold 110 by the pressure of the resin. After that, the two flow fronts proceed integrally (see FIG. 6 (b)).

(4) Embodiments 4 and 5 Descriptions of parts having the same principle as the above-described embodiments will be simplified or omitted. FIG. 7A shows a fourth embodiment, which is different from the first embodiment in that it is not the side of the protrusion 12a but the protrusion.
This is the case where a movable member of a variable thickness mechanism having a sharp downstream side is provided behind 12a. Further, FIG. 7B shows the fifth embodiment.
This is the case where a movable member having a sharpened downstream side, not the upstream side, is provided behind the protrusion 120a. In any of Examples 4 and 5, the angle formed by the advancing directions of the two flow tips can be made to be an acute angle at the portion where the two flow tips meet, as in the case of the above-mentioned Example 3, so that the occurrence of welds at the merging portion. It can be prevented.

(5) Experimental Example Experimental Example 1 The mold of Example 1 (the mold of FIG. 2) and the conventional mold without the variable thickness mechanism in FIG. 2 were made of ABS resin and ABS resin made of glass. Each test was conducted on a material containing 20% by weight of fibers. The length of the mold in the longitudinal direction (resin advancing direction) is 200 mm, the length in the lateral direction is 50 mm, and the wall thickness is 2.
It is 4 mm. The injection molding pressure is 150 tons, the maximum injection pressure is 1400 Kg / cm ² , and the holding pressure is 400.
It is Kg / cm ² . In the mold of Example 1, no weld was visually observed in any of the ABS resin and the material in which 20% by weight of glass fiber was mixed with the ABS resin.
On the other hand, in the conventional mold, both of the ABS resin and the material in which 20% by weight of glass fiber was mixed with the ABS resin, a noticeable weld was visually observed behind the protrusion 12a. Experimental Example 2 The mold of Example 5 (the mold of FIG. 7 (b)) and the mold of FIG. 7 (b).
In the conventional mold having no thickness variable mechanism, the ABS resin and the material in which 20% by weight of the glass fiber is mixed with the ABS resin were tested. The length of the mold in the vertical direction (the resin advancing direction) is 200 mm, and the length in the horizontal direction is 20 mm.
The thickness is 0 mm and the thickness is 2.4 mm. Further, in the mold of the fifth embodiment, when the movable member 205 of the variable thickness mechanism is maximally projected into the cavity 100, the gap between the lower mold cavity surface and the mold is 0.5 to 1.0 mm. That is, a taper for expanding the gap in the resin advancing direction is attached to the front end surface of the movable member 205. The injection molding pressure and the like are the same as those in Experimental Example 1.
Is the same as. In the mold of Example 5, no weld was visually observed in either the ABS resin or the material in which 20% by weight of glass fiber was mixed with the ABS resin. on the other hand,
In the conventional mold, it was visually observed that both the ABS resin and the material containing 20% by weight of glass fiber in the ABS resin had a conspicuous weld on the back side of the protrusion 120a.

(6) Modifications In each of the above embodiments, the movable member of the variable thickness mechanism is provided so as to be supported by the upper mold, but this may be provided in the lower mold, or both. May be provided. Further, in each of the above embodiments, the movable member of the variable thickness mechanism is moved back and forth by the biasing force of the spring and the pressure of the resin, but this may be performed by the elastic force of rubber, hydraulic pressure, or pneumatic pressure. Further, it may be controlled by a mechanical mechanism to move back and forth.

[0012]

As described above, according to the present invention, the occurrence of welds can be prevented or made inconspicuous by a simple structure in which the variable thickness mechanism is moved in and out of a predetermined portion.
Moreover, since the mold is not heated, the molding cycle does not become long. In addition, since the thickness of the molded product is not changed to be thin, surface defects due to it are not generated.

[Brief description of drawings]

1A and 1B are explanatory views showing a flow front end, in which FIG. 1A shows a state where a weld is generated at a confluence portion, and FIG. It shows how to stop it and let the other shunt flow around the back of the protrusion.
(C) shows a state in which the movable member blocked in (b) is removed and the weld once generated is pushed downstream.

2A and 2B are schematic views showing a cavity portion of the mold of Example 1, where FIG. 2A is a cross-sectional view taken along line AA of FIG. 2B, and FIG.
3 shows a cross section taken along line BB of FIG.

3A and 3B are schematic diagrams showing a cavity portion of a mold of Example 2, where FIG. 3A is a sectional view taken along line AA of FIG. 3B, and FIG.
3B is a cross-sectional view taken along line BB of FIG.

4A and 4B are explanatory views showing a flow front in a mold of Example 2, where FIG. 4A shows a state in which the direction of the flow front is changed by a wall thickness varying mechanism, and FIG. 4B shows the wall thickness in FIG. It shows that the flow front advances without causing a weld by removing the movable member of the variable mechanism.

5A and 5B are schematic diagrams showing a cavity portion of a mold of Example 3, where FIG. 5A is a sectional view taken along line AA of FIG. 5B, and FIG.
3 shows a cross section taken along line BB of FIG.

6A and 6B are explanatory views showing a flow front in a mold of Example 3, where FIG. 6A is a state in which the direction of the flow front is changed by a wall thickness variable mechanism, and FIG. 6B is a wall thickness variable mechanism in FIG. (C) shows an angle θ formed by a vector of forces for advancing the two flow tips of the molten resin, by removing the movable member of (1) to move the flow tips without forming a weld line.

7 (a) is an explanatory view showing a flow front in a mold of Example 4, and (b) is an explanatory view showing a flow front in a mold of Example 5. FIG.

[Explanation of symbols]

10, 100, 101 Cavities 10a, 100a, 101a Gates 11, 110, 111 Upper molds 12, 120, 121 Lower molds 12a, 120a, 121a Projections 20, 200, 201, 25, 205 Movable thickness variable mechanism Member 20s, 200s, 201s Spring

Claims (4)

[Claims] 1. When a thermoplastic resin is injection-molded, a movable member of a variable-thickness mechanism provided in a portion in the vicinity of the weld generation portion reduces or eliminates the thickness of the portion to obstruct the flow of the molten resin. The appearance of the weld part is temporarily stopped at the place where the weld does not occur by causing restraint and hesitation, and then the weld is moved by retracting the movable member to change the flow and move the weld. Injection molding method to improve the strength and strength. 2. When a thermoplastic resin is injection-molded, a movable member of a wall thickness varying mechanism originally provided at a position where a weld is generated reduces or eliminates the wall thickness of that portion so that the molten resin has a wall thickness varying mechanism. Injection molding method in which the occurrence of welds is prevented by causing the movable member to retract so that the flow merges in a state where the flow is maintained at an acute angle. 3. A movable member is provided in a portion near the position where the weld originally occurs, and in the initial state, the movable member is present at a position where the wall thickness is thinned or eliminated, and the molten resin flow is blocked by the movable member. An injection molding mold having a variable thickness mechanism in which a movable member is retracted to a position where a molten resin flow is changed so that a temporary weld due to hesitation is moved when hesitation occurs. 4. The movable member is originally provided at a position where a weld is generated, and in the initial state, the movable member is present at a position where the wall thickness is thinned or eliminated, and when the molten resin flow flows around the movable member, An injection molding die having a variable thickness mechanism in which the movable member is retracted to a position where the flows are merged while maintaining an acute angle.