JPH0620800B2 - Injection mold - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mold used for injection molding, and more particularly to a mold with improved gas release properties in a cavity during injection.

[Prior Art] In the case of injection molding, if gas such as air remains in the cavity, a gas pool is generated and the appearance of the product is impaired. Therefore, as a method of venting the gas in the cavity, conventionally, a die is provided with a gas vent hole formed by a minute slit or through hole having a diameter of 3 to 50 μm that communicates the cavity with the outside. Specifically, a method of providing a slit in the mold split surface, a method of forming a part of the mold surface with a porous sintered alloy, and a method of providing a through hole for communicating the sintered alloy with the outside, a knock pin and a pin hole. Known methods are to provide a gap between them, or to form a nested structure having fine through holes.

[Problems to be Solved by the Invention] In the above-described conventional injection mold, the gas vent holes are fine slits or through holes through which the molding material does not pass but the gas passes. However, in such a mold, the gas vent hole is clogged, and it is unavoidable to perform regular cleaning or conversion. Further, since the diameter of the gas vent hole is very small, there is a problem that the ventilation resistance is large and the gas escape rate is slow.

The present invention has been made in view of such circumstances,
The object is to increase the diameter of the gas vent hole and prevent the molding material from entering the gas vent hole.

[Means for Solving the Problems] In the case of injection molding, the air in the cavity is pressed by the injected molding material. Therefore, there is no air in the portion of the molding material filled in the cavity, and the air exists in a compressed state on the front side of the advancing molding material. Moreover, the injected molding material has a large internal pressure.

Therefore, the inventors of the present invention have completed the present invention as a result of diligent research, remembering that the gas is released in front of the advancing molding material and the gas vent hole is closed by utilizing the internal pressure of the molding material.

That is, the injection molding die of the present invention includes a through hole that opens to the molding cavity and communicates with the outside, and a slide that is movable in a direction that the tip is inserted into the through hole and protrudes into the molding cavity and that is inserted into the through hole. One of the split molds has a member and holding means for holding the slide member with the tip protruding into the molding cavity when the molding cavity is not filled with the molding material. The head has a tapered surface that slopes in the opposite direction and closes the opening of the through hole when it is inserted into the through hole, and the side peripheral surface that is spaced from the tapered surface is formed. It is characterized in that it has a groove portion that opens to the front side in the material flow direction and that communicates the molding cavity with the outside.

A general thermoplastic resin is mainly used as the molding material, but rubber, ceramics, or the like may be used depending on the case.

The greatest feature of the present invention is that it has a slide member. This slide member has a taper surface whose tip is inclined so as to face the direction of flow of the molding material. When the head slides into the through hole, it closes the opening of the through hole, and in the front of the direction of flow of the molding material. And a groove portion that opens to the outside and communicates the molding cavity with the outside. The groove portion is provided on the side peripheral surface spaced apart from the tapered surface. That is, at the position where the slide member projects into the cavity, the groove is exposed in the cavity. At the position where the slide member is recessed in the split mold, the head portion closes the opening of the through hole so that the groove portion is not exposed. This slide member may be specially provided, but it is also preferably used also as a push-up pin or the like. Further, the width and depth of the groove can be arbitrarily selected. For example, the depth can be increased to 0.5 mm or more.

The retaining means retains the slide member in a state of protruding into the molding cavity when the molding material is not filled, and uses a spring, a sliding resistance, or a push-up, as shown in Examples described later. You can use pins, etc.

[Operation] In the injection molding die of the present invention, the tip of the slide member projects into the cavity by the holding means before the injection of the molding material. When the molding material is injected into the cavity in that state, the molding material advances in the cavity and the air in the cavity is pressed by the molding material and becomes compressed.
At this time, since the groove of the slide member is exposed in the cavity, the air in the cavity is discharged to the outside through the groove. Further, since the groove portion is open to the front side in the flowing direction of the molding material, the molten resin cannot enter the groove portion unless it exceeds the slide member.

However, when the molding material reaches the position of the slide member, the internal pressure of the molding material is transmitted to the slide member, and the slide member is subjected to a force in the direction of immersing in the split mold due to the tapered surface of the head. Therefore, as the molding material advances, the slide member sinks into the mold, and when the molding material reaches the position of the groove, the head of the slide member closes the opening of the through hole and the groove does not appear.

That is, air flows smoothly from the groove until the molding material moves on the tapered surface of the slide member and reaches the position of the groove. When the molding material reaches the position of the groove, the groove is not exposed, so that the molding material is prevented from entering the groove.

[Effects of the Invention] Therefore, according to the injection molding die of the present invention, the size of the groove can be increased to, for example, 0.5 mm because the molding material is prevented from entering the groove. As a result, the ventilation resistance is reduced, so that the air in the cavity can be smoothly discharged and the air accumulation can be reliably prevented. Further, there is no need to wash or replace the slits or the like as in the conventional case, and the cost can be reduced.

[Examples] Specific examples will be described below.

(Embodiment 1) FIG. 1 shows a main part of an injection molding die according to an embodiment of the present invention. This mold basically comprises a fixed mold 1, a movable mold 2 clamped to the fixed mold 1, and a slide member 3 slidably held by the movable mold 2.

The slide member 3 has a substantially columnar shape, and is slidably held in the through hole 20 of the movable die 2. Slide member 3
Is a columnar shaft portion 30 having a diameter of 20 mm, a head portion 32 having a tapered surface 31 formed on the tip of the shaft portion 30 and facing the flowing direction of the molding material on the end surface, and a side opposite to the head portion 32. And a locking portion 33 having a large diameter formed at the end of the. Further, the shaft portion 30 is provided with a groove portion 34 having a depth of 1.0 mm and extending in the axial direction from a position 0.5 mm away from the head portion 32 on the front side in the flowing direction of the molten resin. As shown in FIG. 3, the groove portion 34 is formed wide on an arc having a central angle of 120 ° in the circumferential direction of the shaft portion 30. The groove 34 is also formed on the surface of the locking portion 33.

The movable die 2 has a through hole 20 opening to the cavity 10 and a locking hole 21 provided continuously to the through hole 20, and a fixed plate 22 is fixed by closing the opening of the locking hole 21. . Then, the slide member 31 moves from the head 32 to the locking hole 2
The movement of the slide member 3 is restricted by being inserted into the inside of the sliding member 1 and contacting the locking portion 33 with the inner wall of the locking hole 21 or the fixed plate 22.

The spring 4 is interposed between the locking portion 33 of the slide member 3 and the fixed plate 22, and biases the head 32 of the slide member 3 so as to project into the cavity 10. The spring force of the spring 4 causes the slide member 3 to move to the cavity 1
It is weak enough to project into 0 and is easily compressed by the internal pressure of the injected molten resin. That is, the spring 4 constitutes a holding means.
The locking hole 2 is provided between the movable die 2 and the fixed plate 22.
An exhaust passage 23 that communicates 1 with the outside is formed.

The operation of the mold of this embodiment configured as described above will be described below. First, before injecting the molten resin, the head portion 32 of the slide member 3 is in a state of protruding into the cavity 10 by the urging force of the spring 4. The tapered surface 31 of the head 32 is inclined so as to face the direction in which the molten resin flows. That is, the cavity 1 is located further forward in the traveling direction of the molten resin.
The amount of protrusion into 0 is large. Second in this state
As shown in the figure, the groove 34 is exposed to the cavity 10 on the front side of the direction in which the molten resin flows.

Next, when the molten resin is injected into the cavity 10, the air in the cavity 10 is pressed as the molten resin advances. The pressed air is smoothly discharged to the outside from the exhaust passage 23 through the groove 34 and the locking hole 21. Groove 3 here
The depth of 4 is 1.0 mm, which is 2 compared to conventional slits.
Since it is larger than 0 times, the air in the cavity 10 is discharged very smoothly.

When the molten resin reaches the position of the slide member 3, the taper surface 31 of the slide member 3 receives the internal pressure of the molten resin, and the slide member 3 receives a force in the direction in which the slide member 3 is retracted into the movable die 2. Since the internal pressure of the molten resin is extremely larger than the spring force of the spring 4, the slide member 3 is pressed against the urging force of the spring 4 and retracts into the movable mold 2. As a result, when the molten resin reaches the position of the groove 34, the head 32 closes the opening of the through hole 20, and the groove 34 does not appear in the cavity 10. Therefore, the molten resin is prevented from entering the groove portion 10, and is cooled and solidified in a state of being in contact with the tapered surface 31 as shown in FIG.

After the molded body 5 is solidified, the movable mold 2 and the fixed mold 1 are opened, and when the molded body 5 is taken out, the slide member 3 projects again into the cavity 10 by the urging force of the spring 4 and the next molding is performed. Done.

(Embodiment 2) FIG. 5 shows a main part of an injection molding die according to a second embodiment of the present invention. This mold uses the slide member 3 as an extrusion pin. The configuration is the same as that of the first embodiment except that the diameter of the through hole 20 is partially increased to reduce the sliding resistance between the slide member 3 and the movable die 2 and that no spring is used.

In this mold, the slide member 3 maintains a state in which it protrudes into the cavity 10 due to the sliding resistance with the movable mold 2 when the molten resin is not injected. Then, at the time of injection, the internal pressure of the molten resin overcomes the sliding resistance, the slide member 3 sinks into the movable mold 2, and the molten resin does not enter the groove 34 as in the first embodiment. When the molded body is released from the mold, the push-up rod 6 presses the slide member 3 to release the molded body, and at the same time, the slide member 3 projects into the cavity 10 and slides even if the push-up rod 6 retracts. The resistance keeps the slide member 3 protruding into the cavity 10. In this case, the push-up bar 6 and the sliding resistance form a holding means.

In the case of the present embodiment, the slide member 3 can be projected into the cavity 10 without using the push-up rod 6.
That is, for example, as shown in FIGS. 7 and 8, an undercut convex portion 35 or concave portion 36 is formed on the tapered surface 31. By doing so, the molded body and the slide member 3 are temporarily coupled by the undercut portion, so that the slide member 3 projects into the cavity 10 at the same time as the molded body is released from the movable mold 2. When the locking portion 33 is locked in the locking hole 21, the molded body is released from the undercut portion. In this case, the convex portion 35 and the concave portion 36 form a holding means.

Third Embodiment In the above-described embodiment, in order to prevent the molten resin from entering the groove 34 more reliably, it is effective to increase the length of the tapered surface 31 in the flowing direction of the molten resin. However, if the diameter of the slide member 3 is simply increased, the weight becomes heavier, which requires a large force for movement. In view of this, in this embodiment, a flange portion 37 is provided in a part of the head portion 32 of the slide member 3 so as to extend in the direction perpendicular to the axial direction so as to face the direction in which the molten resin flows, and the flange portion 37 is provided.
Is provided with a tapered surface 31. In this way, when the molten resin reaches the tip of the collar 37, the tip of the collar 37 senses the internal pressure of the molten resin and the tapered surface 31
As a result, the slide member 3 is immersed. Since the distance from the tip of the flange portion 37 to the groove portion 34 is long, it is possible to more reliably prevent the molten resin from entering the groove portion 34 as compared with the above embodiment.

[Brief description of drawings]

1 to 4 relate to an injection mold of one embodiment of the present invention. FIG. 1 is a sectional view of an essential part thereof, FIG. 2 is an enlarged sectional view of an essential part of FIG. 1, and FIG. 2 is a sectional view taken along the line AA in FIG. 2, and FIG. 4 is an enlarged sectional view of an essential part showing a state after the molded body is molded. FIG. 5 is an enlarged cross-sectional view of the essential parts of the injection molding die of the second embodiment of the present invention. 7 and 8 show another mode of the holding means, and are enlarged sectional views of the main part of the head portion of the slide member. FIG. 6 is an enlarged sectional view of a main part of an injection molding die of a third embodiment of the present invention. 1 ... Fixed type, 2 ... Movable type 3 ... Slide member, 5 ... Molded body 4 ... Spring (holding means), 6 ... Push-up rod 10 ... Cavity, 20 ... Through hole 31 ... Tapered surface, 32 ... Head part 33 ... Locking part, 34 ... Groove part

Claims (1)

[Claims] 1. A through hole that opens to a molding cavity and communicates with the outside, and a slide member that is inserted into the through hole and is movable in a direction in which a tip projects into the molding cavity and a direction in which the tip is retracted. Holding means for holding the slide member with the tip protruding into the molding cavity when the molding cavity is not filled with the molding material is provided in one of the split molds, and the slide member has the molding material at the tip. And a molding cavity provided on a side peripheral surface spaced apart from the tapered surface, the head having a tapered surface facing the flowing direction of the head and closing the opening of the through hole when immersed in the through hole. And a groove portion that opens to the front side in the direction of flow of the molding material and that communicates the molding cavity with the outside when the molding die projects.