JPH0549448B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an injection molding method in which a plurality of colors or types of materials are used simultaneously to obtain an integrally molded product made of a plurality of colors or types of materials. In particular, using an injection molding machine each equipped with a plurality of molds for forming a cavity and a slide core that slides and reciprocates with respect to the mold,
In the state in which the slide core is reciprocated, a first injection molding is performed by a first injection into a first cavity formed by the mold for molding and the slide core.
molded product, and then in a state where the slide core is moved back, this back movement causes the first molded product to be molded.
forming a second molded product by secondary injection in a second cavity that is formed in series with the cavity;
This invention relates to an injection molding method in which the first molded product and the second molded product are integrally molded with each other.

[Conventional technology]

First, an example will be described in which the conventional injection molding method described above is applied to integrally mold the upper half of a tape cassette for a video tape recorder and a transparent window.

Fig. 2 shows a tape cassette for a video tape recorder.A cassette housing 1 consists of upper and lower halves 2 and 3 molded from synthetic resin (for example, black resin) that are fitted from above and below with screws or the like. It is combined into one piece. And cassette case 1
A front lid 4 molded from the same synthetic resin as the upper and lower halves 2 and 3 is rotatably attached to the front end of the housing. A substantially rectangular transparent window 5 is integrally formed on the upper surface of the upper half 2 at substantially the center thereof, as will be described later. The transparent window 5 is molded from transparent resin, and is configured so that the inside of the cassette housing 1 can be seen through the transparent window 5 and the remaining amount of tape can be checked.

FIG. 3 shows a molding process of an injection molding method in which the above-mentioned upper half 2 and transparent window 5 are molded integrally with each other. A step-by-step explanation will be given with reference to the injection molding machine shown in FIGS. 4 to 6.

First, FIG. 4 shows a state in which the movable mold 8 and the fixed mold 9 of the injection molding machine 7 are opened. The movable mold 8 is moved in the direction indicated by the arrow a through a link type toggle mechanism 12 by a mold clamping cylinder 11 fixed to a base 10.
It is being moved back in the direction. Further, the slide core 13 in the movable mold 8 is moved back in the direction of arrow b by a core drive cylinder 14 fixed to the movable mold 8. Note that the distance between the circumferential surface of the sliding hole 19 of the movable mold 8 and the circumferential surface of the slide core 13 is about 3/100 mm.

Next, as shown in FIG. 5, the movable mold 8 is moved forward in the direction of arrow c by the mold clamping cylinder 11, and the movable mold 8 is closed with the fixed mold 9. At this time, the slide core 13 is moved forward in the direction of arrow d by the core drive cylinder 14, and the tip surface of the slide core 13 is in close contact with the surface of the fixed mold 9 that includes the secondary injection gate 15. There is. In this state, further pressure is applied to the mold clamping cylinder 11,
Since the link-type toggle mechanism 12 applies a clamping force F of about 20 to 30 tons to the movable mold 8, the movable mold 8 and the fixed mold 9 are clamped together.

Next, the primary injection gate 17 is inserted into the first cavity 16 formed by the movable mold 8, the fixed mold 9, and the slide core 13 by the mold clamping described above.
The molten black resin is injected and filled into the first cavity 16. This filled black resin is cooled for about 2 seconds and solidified, thereby forming the upper half 2.

Next, when the molding of the upper half 2 is completed, the movable mold 8 and the fixed mold 9 remain in the mold clamping state intermittently due to the mold clamping force F, and as shown in FIG. 13 is moved back in the direction of arrow e by an amount corresponding to the thickness of the transparent window 5 by the core drive cylinder 14. The state shown in FIG. 6 is substantially the same as the state shown in FIG. 5 except for the parts shown. When the slide core 13 moves back as described above, the second cavity 18 is formed in series with the first cavity 16.
The molten transparent resin is injected from the secondary injection gate 15 into the molten resin. At this time, due to the heat of the transparent resin and the injection pressure, the part of the already solidified black resin that comes into contact with the transparent resin becomes a semi-molten state. Therefore, when the transparent resin is cooled and solidified, the black resin and the transparent resin are welded to each other at their contact portions, and as a result, the transparent window 5 is integrally molded into the upper half 2.

Next, the movable mold 8 is moved back in the direction of arrow f by the mold clamping cylinder 11 via the link-type toggle mechanism 12, and the movable mold 8 and the fixed mold 9 are opened. This state is substantially the same as that shown in FIG. 4, except that the upper half 2 with the transparent window 5 integrally molded thereon is on the movable mold 8, and then the transparent window 5 The upper half 2 integrally molded is taken out from the movable mold 8.

[Problem that the invention seeks to solve]

However, when molding the upper half 2 in which the transparent window 5 is integrally molded by the above-mentioned injection molding method, it takes about 200 to 300 continuous moldings to make the slide when molding the transparent window 5. The reciprocating movement of the core 13 was no longer performed smoothly, and it became impossible to perform any more continuous molding unless the slide core 13 was replaced.

As a result of investigating the cause of not being able to perform continuous molding for a long period of time, the present inventor found that the reason for not being able to perform continuous molding for a long time as described above is that the upper half 2 After molding, the slide core 13 is moved back in order to mold the transparent window 5 by secondary injection of transparent resin, but at this time, as shown in FIG. 6, the movable mold 8 and the fixed mold It has been found that 9 is a point where the mold clamping state is continued by the mold clamping force F. That is, this mold clamping force F is approximately 20
Since it is a very large force of ~30t, mold distortion occurs in the movable mold 8 due to this mold clamping force F, the movable mold 8 is bent, and the slide core 13 inside the movable mold 8 is bent.
will be tightened with extremely strong force from the surrounding area. Therefore, if the slide core 13 is moved back in this tightened state, the circumferential surface of the slide core 13 will be significantly damaged after about 200 to 300 continuous molding operations, a so-called "galling" phenomenon. occurs, making further continuous molding impossible.

In order to prevent mold distortion of the movable mold 8, it is possible to improve the strength by changing the mold structure, but changing the mold structure is very large-scale, and the upper half 2, This is not preferable because it imposes restrictions on the shape design of the transparent window 5 and the like.

Therefore, it is an object of the present invention to improve the return motion of the slide core and to enable continuous molding for a long period of time without changing the mold structure at all.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention first closes a plurality of molds to each other and clamps the plurality of molds to each other, and then closes the molds to each other while maintaining the clamped state. performing primary injection, releasing the mold clamping while maintaining the mold closed state after the primary injection, and moving the slide core back with the mold clamping being released and the mold closing being maintained; Next, the mold clamping is performed again and a second injection is performed, and then the mold clamping is released and the plurality of molds are opened.

[Effect]

According to the present invention, after the first injection, the mold clamping is released while the mold is kept closed, the slide core is moved back in a state where the mold clamping is released and the mold closing is maintained, and then the mold clamping is performed. After that, the second injection was performed again. Therefore, mold distortion of the molding die is eliminated, so the slide core is not tightened by the molding die, and for this reason,
The return movement of the slide core after the primary ejection can be performed extremely smoothly. In addition, even when the molding mold is unclamped after the first injection, the closed state of the molding mold is maintained, so there is no sliding between the first injection and the second injection. The operation of re-clamping the mold by moving the core back can be easily and quickly performed. Moreover, it is only necessary to add the process of releasing and re-clamping the mold while maintaining the closed state of the mold before and after moving the slide core back, and there is no need to change the structure of the mold. Therefore, a conventional injection molding machine can be used as is by simply changing the sequence slightly.

〔Example〕

Hereinafter, an embodiment in which the present invention is applied to the integral molding of the upper half of a tape cassette for a video tape recorder and a transparent window will be described with reference to FIGS. 1 and 4 to 6. Note that the same parts as those of the conventional example explained in the above [Prior Art] section are given the same reference numerals, and the explanation thereof will be omitted.

In the injection molding method of the present invention, as shown in FIG. 1, the steps of releasing and reclamping the movable mold 8 and the fixed mold 9 are performed before and after the step of moving the slide core 13 backwards. It was added.

That is, as shown in FIG.
When pressure is applied to 1, the link type toggle mechanism 1
A clamping force F is applied to the movable mold 8 by 2,
The movable mold 8 and the fixed mold 9 are clamped together. Then, the molten black resin is injected into the first cavity 16 from the primary injection gate 17,
The upper half 2 is formed by cooling and solidifying this black resin.

After the upper half 2 is molded, the pressure in the mold clamping cylinder 11 is released, and the mold clamping force F applied to the movable mold 8 by the link type toggle mechanism 12 is reduced to the fifth.
It is temporarily released as shown by arrow F' in the figure. In other words, the movable mold 8 and the fixed mold 9 are temporarily changed from a clamped state to a closed state.

Next, as shown in FIG. 6, in the mold closed state where the mold clamping force F is temporarily released, the slide core 13 is moved by the core driving cylinder 14 to the transparent window 5.
It is moved back in the direction of arrow e by an amount equivalent to the thickness of . After the slide core 13 moves back, the mold clamping cylinder 1
Pressure is applied again to the movable mold 8 and the mold clamping force F is applied to the movable mold 8 by the link-type toggle mechanism 12, so that the movable mold 8 and the fixed mold 9 are clamped together again. Then, in this mold-clamped state, the molten transparent resin is injected from the secondary injection gate 15 into the second cavity 18, so that the upper half 2
A transparent window 5 is integrally molded therein.

According to the above injection molding method, the slide core 1
When the movable mold 8 and the fixed mold 9 are moved back, the mold clamping between the movable mold 8 and the fixed mold 9 is released and the mold is in a closed state, so the mold clamping state continues due to a very large mold clamping force. There is no mold distortion in the movable mold 8 unlike in the case where the movable mold 8 is closed, and therefore the slide core 13 within the movable mold 8 is not tightened from the surroundings. Therefore, the so-called "galling" impression, in which the circumferential surface of the slide core 13 is significantly damaged during the return movement of the slide core 13, does not occur at all, and the recovery of the slide core 13 does not occur even during long-term continuous molding. The movement is extremely smooth. In addition, even when the mold clamping of the molds 8 and 9 is released after the first injection, the closed state of both molds is maintained, so there is no sliding between the first injection and the second injection. The operation of moving the core 13 back and clamping the molds 8 and 9 again can be easily and quickly performed.

Although one embodiment of the present invention has been described above, various effective modifications can be made based on the technical idea of the present invention. For example, in this embodiment, a single mold clamping cylinder was used for moving the movable mold and clamping the mold, but these may be performed by separate mechanisms, and the mechanism is also limited to cylinders. isn't it.

Furthermore, although mold clamping was performed using a link type toggle mechanism in this embodiment, a direct pressure type or other various types of mechanisms may be used.

〔Effect of the invention〕

As described above, according to the present invention, the slide core is moved back after the mold clamping of the mold is released after the first injection. There is no mold distortion at all, and the slide core can be moved back extremely smoothly without being damaged.
Therefore, continuous molding can be performed for an extremely long time, and the life of the injection molding machine is significantly improved.

Furthermore, even when the mold is unclamped after the first injection, the closed state of the mold remains, so there is no sliding between the first and second injections. The operation of re-clamping the mold by moving the core back can be easily and quickly performed.

Moreover, according to the present invention, it is only necessary to perform the steps of releasing the mold clamping and reclamping the mold while maintaining the closed state of the mold before and after moving the slide core back, and the process of releasing the mold clamping and reclamping the mold is sufficient. Since there is no need to change the structure at all, a conventional injection molding machine can be used as is with only slight changes in the sequence.

[Brief explanation of the drawing]

Fig. 1 shows the molding process of an embodiment in which the present invention is applied to the integral molding of the upper half of a tape cassette for a video tape recorder and a transparent window, and Fig. 2 shows the molding process of a conventional tape cassette for a video tape recorder. The perspective view and FIG. 3 are views showing the molding process of a conventional injection molding method in which the upper half of the tape cassette for a video tape recorder shown in FIG. 2 and the transparent window are integrally molded. Figures 4 to 6 are the first
An example of an injection molding machine used to carry out the injection molding method according to the present invention shown in the figure and the conventional injection molding method shown in Fig. 3, and Fig. 4 shows the mold opening state before molding. FIG. 5 is a cross-sectional view of the injection molding machine to explain the state in which the first injection is performed, and FIG. 6 is a cross-sectional view to explain the state in which the second injection is performed. FIG. In addition, in the symbols used in the drawings, 2... Upper half (first molded product), 5... Transparent window (second molded product), 7... Injection molding machine, 8... Movable mold (molding mold), 9...Fixed mold (molding mold), 13
... slide core, 15 ... secondary injection gate, 16 ... first cavity, 17 ... primary injection gate, 18 ... second cavity.

Claims (1)

[Claims] 1. Using an injection molding machine each equipped with a plurality of molds for forming cavities and a slide core that slides and reciprocates with respect to the mold, the slide core is In the state of forward movement,
A first molded product is molded by first injection into a first cavity formed by the molding die and the slide core, and then, when the slide core is moved back, by this back movement, A second molded product is molded by secondary injection into a second cavity that is formed in series with the first cavity, thereby forming the first molded product and the second molded product. In an injection molding method in which the plurality of molds are integrally molded, the plurality of molds are closed to each other, and the plurality of molds are clamped to each other, and then the molds are kept in the clamped state. The above-mentioned first injection is performed, and after this first injection, the above-mentioned mold clamping is released while the above-mentioned mold closed state is maintained, and the above-mentioned slide core is restored with this mold clamping being released and the mold closed state being maintained. and then performs the second injection after performing the mold clamping again, and then releasing the mold clamping and opening the plurality of molds. Molding method.