JP2000280304A - Injection molding machine for resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of gloss nonuniformity by defective mold transfer in the boundary place between a main body part (general part) and a projected part (thick wall part) such as a boss and a rib without deteriorating the functions of resin injection molding when the projected part molded to be integrated with the main body part of a resin molding. SOLUTION: In a molding machine, a recessed part 21 is formed in a place on the molding surface on the product surface side of a product surface side mold 3 opposite to the recessed molding surface (gas channel 5) of a product back side mold 6 forming a projected part (thick wall part), a gas permeable mold material 20 is arranged in the recessed part 21, a suction hole 22 communicating with the hole of the mold material 20 is formed in the mold 3, and a vacuum device 23 connected with the suction hole 22 is actuated. In this way, a molten resin injected into a mold cavity 9 can be sucked to the mold molding surface (area K) on the product surface side of a cavity 8 for molding the thick wall part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin injection molding apparatus for integrally molding a protrusion such as a boss or a rib on a resin molded product body.

[0002]

2. Description of the Related Art When manufacturing a resin molded product in which a protruding portion (ie, a thick portion) such as a boss or a rib is integrally formed on a main body, gas-assisted injection molding (a kind of resin injection molding) is used. Gas injection molding) has been implemented conventionally. In this gas-assisted injection molding, after injecting the molten resin into the mold cavity,
The gas is selectively passed only through the inside of the thick portion in the molten state, thereby hollowing the inside of the thick portion.

FIG. 3 shows a conventional resin injection molding apparatus for performing gas assist injection molding. A mold 1 used in this resin injection molding apparatus includes a product surface side mold 3 having a mold molding surface 2 for molding a surface (for example, a flat external surface) of a resin molded product main body, and a molding surface 2. A mold forming surface 4 which is arranged to face the back surface of the resin molded product body and is formed at a position on a part of the mold forming surface 4 so as to be depressed toward the side opposite to the mold forming surface 2. A product backside mold 6 having a channel (concave molding surface for forming a thick portion) 5. Thus, the product surface side mold 3
A cavity 9 composed of a main body molding cavity 7 and a thick portion (projection) molding cavity 8 is formed between the metal mold 6 and the product back side mold 6. Specifically, the main body molding cavity 7 for molding the main body of the resin molded product is formed by the mold molding surface 2 of the product front mold 3 and the mold molding surface 4 of the product back mold 6. Is formed, and the mold surface 2 of the product front side mold 3 and the gas channel 5 of the product back side mold 6 have a projection having a protrusion projecting from a part of the back surface of the main body. A thick part forming cavity 8 for forming a thick part is formed.

By injecting the molten resin into the cavity 9 of the mold 1 with a required pressure by an injection machine (not shown), a resin molded product having a projecting portion on the back surface of the main body is integrally formed. It has become so. In addition, at the time of such injection molding, an operation is performed in which a gas is selectively passed through a molten resin in a thick portion of a molding portion of a projecting portion to hollow the inside of the thick portion, Thereby, the rigidity of the resin molded product is improved, the amount of the molded resin material is reduced, and the weight of the resin molded product is reduced.

[0005]

However, the conventional resin injection molding apparatus for performing the above-described gas-assisted injection molding has the following problems. That is, according to the gas-assisted injection molding, the inside of the thick portion that becomes thicker as the boss portion, the rib portion, and the like are integrally formed is hollow, so that the surface portion of the formation portion of the thick portion is formed. It is possible to some extent to suppress the occurrence of sink marks peculiar to resin molding (so-called sink marks and rib sink marks).
In fact, the suppression effect is not sufficient. When resin molding is performed by gas-assisted injection molding, a predetermined portion on the surface of the resin molded product, that is, a general portion of the main body molded in the main body molding cavity 7 (a product excluding a location where the protruding portion is provided). Boundary point between a general surface) and a portion corresponding to the thick portion formed by the thick portion forming cavity 8 including the gas channel 5 (a protruding portion corresponding surface corresponding to a location where the protruding portion is disposed). 3, that is, the symbol S in FIG.
There is a problem that sinks occur in the surface of the resin molded product corresponding to the portions indicated by, and an appearance surface having uneven gloss is exhibited.
When the gloss unevenness occurs remarkably, it appears that a streak is formed at the above-described boundary portion and the vicinity thereof, resulting in poor appearance.

The cause of sink or uneven gloss is caused by the mold 1
Insufficient adhesion force of the molten resin filled in the cavity 9 to the mold surface, double transfer (contact with the mold surface twice during molten resin filling and gas filling), and so on This may result in poor mold transfer. So, at present,
In order to prevent the occurrence of uneven gloss as described above, the size of the gas channel 5 may be reduced, or the width W at the boundary between the gas channel 5 and the surrounding general portion 10 (see FIG. 3).
We are trying to take measures such as gradual changes.

[0007] However, when the size of the gas channel 5 is reduced, the glossiness is reduced. However, the main purpose of the gas assist injection molding, ie, “molding of the hollow portion in the gas channel 5 by gas” is reversed. It is disadvantageous for fulfilling the main purpose. Further, if the change in the width W at the boundary between the gas channel 5 and the general part 10 around the gas channel 5 is gentle, another gas leakage (permeation) from the gas channel 5 to the surface of the general part 10 may occur. Failure may occur.

[0008] Not only in the case of the gas-assisted injection molding apparatus as described above, but also in the case of using a conventional general resin injection molding apparatus, there is a problem that uneven gloss due to generation of sink marks occurs. For example, as shown in FIG. 4, a product surface side mold 11 for molding the surface of the main body of the resin molded product.
And a product back side mold 12 for integrally forming a rib on the back surface of the main body of the resin molded product and a rib on the back surface.
When molding a resin molded product with ribs using No. 3,
In FIG. 4, sink marks (so-called rib sink marks) are generated at portions indicated by broken lines R, that is, at surface portions of the main body portion of the resin molded product corresponding to the rib forming recesses 14, and accordingly, the sink portions are glossy. There is a problem that goes wrong.

The present invention has been made in view of such circumstances, and has as its object to form a protrusion (thick portion) such as a boss or a rib on a main body of a resin molded product. ,
Resin injection molding that does not impair the function of resin injection molding and that can effectively prevent the occurrence of gloss unevenness due to poor mold transfer at the boundary between the main body (general part) and the projection. It is to provide a device.

[0010]

In order to achieve the above object, the present invention provides a cavity for molding a main body of a resin molded product, and a back side of the main body of the resin molded product. The body is integrally provided with the protrusion by injecting a molten resin into a cavity of a mold comprising a thick part molding cavity for forming a thick part having a protrusion having a protruding part. In a resin injection molding apparatus configured to integrally mold a resin molded product, a recess is formed at a molding surface location on a product surface side of the mold opposite to a concave molding surface of the mold for molding the protrusion. Then, while arranging the permeable mold material in the recessed portion, forming an intake hole communicating with the hole of the permeable mold material in the mold, and operating a decompression device connected to the intake hole. Is injected into the mold cavity. The molten resin so that Suiyoseru on the mold surface of the product surface side of the thick portion molding cavity.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 and 2
In FIG. 6, the same parts as those in FIGS. 3 and 4 are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 shows a resin injection molding apparatus according to a first embodiment of the present invention. This device is for producing a resin molded product having a protruding portion (thicker portion thicker than the main body portion) whose interior is made hollow by performing gas-assisted injection molding. The mold 1 includes a side mold 3 and a product backside mold 6.

As shown in FIG. 1, a mold 3 for molding the front surface (product surface) of a resin molded product has a gas permeable portion at a position opposed to a gas channel 5 of a mold 6 for a product rear surface. The mold material 20 is arranged. More specifically,
A gas channel corresponding area P1 corresponding to a specific portion of the mold molding surface 2 of the product front mold 3, that is, the entire gas channel 5 of the product back mold 6 (the entire length in the flowing direction of the molten resin), and , P2, P near the upstream and downstream sides of the gas channel corresponding region P1.
3 are formed from the mold molding surface 2 of the product surface side mold 3 toward the inside thereof, that is, toward the side opposite to the gas channel 5. The air-permeable mold material 20 having a large number of holes is incorporated in the portion 21. Then, one side 20a of the air-permeable mold material 20 exposed and arranged on the side of the opening of the recess 21 is set so as to be flush with the mold molding surface 2 of the product surface side mold 3, whereby One side 2 of breathable mold material 20
Oa constitutes a part of the mold molding surface 2.

Further, the product surface side mold 3 is provided with an air inlet 22 communicating with the recess 21 and the air hole of the air permeable mold material 20, and a vacuum installed outside the mold 1. A pressure reducing device (suction device) 23 such as a pump is
2 are connected. When the decompression device 23 is operated, the air in the cavity 9 near one surface 20a of the permeable mold material 20 is divided into the holes in the permeable mold material 20 and the branch port portions 22a and 22b of the intake hole 22. , 22
c, the pressure is sequentially discharged to the outside of the mold 1, and the pressure in the cavity 9 near one surface 20a of the air-permeable mold material 20 is reduced (reduced) accordingly.

Next, the operation when performing gas-assisted injection molding using the resin injection molding apparatus having the above-described configuration will be described below. First, the molten resin is supplied from the injection machine (not shown) to the cavity 9 of the mold 1 with a required pressure.
When the gas is injected into the gas channel 5, the gas flows into the gas channel 5 through the general portion 10 on the upstream side as shown by an arrow A in FIG. The pressure (flow pressure) acting on the molten resin decreases in accordance with the width change or the product thickness change (change in the flow cross-sectional area) in the above, so that the die of the product surface side die 3, which is the product side die. The adhesive strength of the molten resin to the molding surface 2 is reduced, and mold transfer failure occurs. But,
By providing the air-permeable mold material 20, the intake hole 22, and the pressure reducing device 23 and performing the following operation procedure as in the present embodiment, the occurrence of the mold transfer failure as described above is prevented.

That is, in performing gas-assisted injection molding, if the pressure reducing device 23 is operated before filling (injection) of the molten resin into the cavity 9 of the mold 1, the mold on the product surface side is accompanied. 3 corresponding to the gas channels in the molding surface 2 (regions P1, P2, P3 shown in FIG. 1).
Is discharged to the outside of the mold 1 sequentially through the many holes and the intake holes 22 of the air-permeable mold material 20, and the above-described gas channel-corresponding portions are depressurized. Then, when the molten resin flows into the gas channel corresponding portion where such a reduced pressure state is maintained,
The molten resin that has reached the location where the permeable mold material 20 is disposed is reduced in FIG. 1 by the depressurizing effect in the region near the permeable mold material 20, and the molten resin portion in the cavity 9 flowing on the opposite side of the gas channel 5 in FIG. As shown by the arrow B, the air is sucked toward the one surface 20a of the air-permeable mold material 20. Therefore, the molten resin is supplied to the gas channel 5 in the cavity 9.
Irrespective of the resin pressure drop caused by the width change (product thickness change) in the above, it is attracted to one side 20a of the permeable mold material 20 and adheres to the one side 20a by the absorbing force at that time. The surface of the melted resin becomes the product surface of the resin molded product. In this case, one side 2 of the air-permeable mold material 20 is used.
Since the adhesive force of the molten resin adhered to 0a does not decrease while the depressurized state is maintained by the depressurizing device 23, if the depressurizing device 23 is kept operating until the mold release, a stable mold can be obtained. Transfer will be performed.

Therefore, according to the resin injection molding apparatus having such a configuration, by operating the pressure reducing device 23 immediately before the molten resin reaches the gas channel 5, it is possible to prevent occurrence of mold transfer failure. Can be. That is,
In the case of the conventional apparatus, the molten metal flows from the general portion 10 of the cavity 9 to the gas channel 5 at the location where the gas channel 5 is disposed.
Although the adhesive force of the molten resin to one side 20a of the air-permeable mold material 20 which constitutes a part of the mold molding surface 2 of the above will be reduced, the resin injection molding apparatus of the present embodiment reduces the pressure. Due to the function of the pressure reducing mechanism composed of the device 23, the vent 22 and the permeable mold material 20, the cavity area K on the side of the product surface side mold 3 corresponding to the gas channel 5 in the mold 1 (FIG.
) Can be brought into a reduced pressure state. In response to this, the air remaining in the cavity 9 at the gas channel installation location of the mold 1 due to the decrease in the adhesive strength of the molten resin is permeable to the air-permeable mold material. It can be discharged to the outside of the mold 1 through the holes 20 and the suction holes 22. Therefore, the product surface side mold 3
The adhesive strength of the molten resin to one side 20a of the air-permeable mold material 20 which constitutes a part of the mold molding surface 2 can be sufficiently obtained, and the resin molding at the boundary between the general portion 10 and the gas channel 5 can be achieved. It is possible to prevent sink or uneven gloss on the surface of the product (product surface).

FIG. 2 shows a resin injection molding apparatus according to a second embodiment of the present invention. This apparatus integrally forms a rib (or boss) on the back surface of the main body of the resin molded product. It is used for This apparatus is not of the type for performing the gas-assisted injection molding described above, but of the type for simply injecting a molten resin into the mold 1 and simply filling the cavity 9. In FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals.

In the resin injection molding apparatus of the present embodiment, as shown in FIG. 2, the product front side mold 3 is provided with a rib forming concave portion (concave molding surface) 30 of the product back side mold 6. A depression 21 is formed at a corresponding position, and the depression 2
The air-permeable mold material 20 is incorporated in the air-permeable mold material 20.
Is arranged so as to constitute a part of the mold molding surface 2 of the product surface side mold 3 (a portion facing the concave portion for rib molding). The above-mentioned product surface side mold 3 is provided with an intake hole 22 having one end communicating with the recess 21, and is provided with a decompression device 2 arranged outside the product surface side mold 3.
3 is connected to the other end of the intake hole 22.

Thus, also in this case, by operating the pressure reducing device 23, the one side 20a
Molten resin (filled resin)
Can be attracted to a place on the one surface 20a side, that is, a place where a surface sink (rib sink) easily occurs in the product surface, and by maintaining such a state until the mold release, the rib forming recess 30 is formed. A sufficiently large adhesion force of the molten resin to the product surface side mold 3 at the corresponding location can be ensured, and the molten resin is applied to the mold surface 2 of the product surface side mold 3 (specifically, the mold molding The one-sided surface 20a) of the air-permeable mold material 20 that forms a part of the surface 2 can be securely adhered. As a result, it is possible to prevent the occurrence of rib sink marks on the surface of the thick part of the resin product in which the ribs are integrally formed, and to avoid the occurrence of poor appearance (uneven gloss) of the resin molded article due to the occurrence of the rib sink marks. .

The air-permeable mold material 20 used in the resin injection molding apparatus of the first and second embodiments described above includes:
Any material may be used as long as it is made of a material that can withstand the temperature of the molten resin sufficiently. For example, “Poceracs II” (trade name of Nippon Die & Mold Co., Ltd.) is an example. It is listed as. It is made of a material obtained by pressing and compressing ferrite-based stainless steel powder and sintering it at a high temperature. For example, there is a material having pores of about 3 to 20 μm. In the resin injection molding apparatus according to the present invention,
It is preferable to use a permeable mold material having pores of 20 μm or less, and it is particularly desirable to use a permeable mold material of 3 to 10 μm from the surface appearance.

Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment.
Various modifications and changes are possible based on the technical concept of the present invention. For example, the area in which the gas permeable mold material 20 is disposed with respect to the gas channel 5 or the rib forming recess 30 is not limited to the area shown in FIG. 1 or 2, and corresponds to the gas channel 5 or the rib forming recess 30. As long as it is a region, it can be appropriately set as needed. Further, the present invention is not limited to the case where the boss and the rib are integrally molded, but is also applicable to a resin injection molding apparatus used for integrally molding various thick portions with the main body of the resin molded product.

[0023]

As described above, according to the present invention, a dent is formed at a location on the molding surface on the product surface side of the mold opposite to the concave molding surface of the mold for molding the protruding portion. In addition to arranging a permeable mold material in the part, forming an intake hole communicating with the hole of the permeable mold material in the mold, and injecting into the mold cavity by operating the pressure reducing device connected to the intake hole Since the melted resin is sucked to the mold forming surface on the product surface side of the cavity for forming the thick part, the function of the decompression device, the suction hole and the decompression mechanism composed of the permeable mold material allows the ventilation to be performed. At the side of the conductive mold material, that is, at the surface of the product (where the adhesion of the molten resin to the mold molding surface is the lowest) where sinking is likely to occur when a thick part having a protruding part is integrally molded. The pressure inside the mold cavity can be reduced Along with this, the molten resin is attracted to the mold forming surface on the side of the product surface, so that the adhesive force of the molten resin to the mold molding surface at the product surface where the sink is likely to occur is sufficiently secured, It is possible to prevent the occurrence of sink marks on the surface portion of the resin molded product (product) corresponding to the protruding portion, thereby preventing the occurrence of gloss unevenness, and further, it is possible to eliminate a defect that impairs the appearance of the resin molded product.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a resin injection molding apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating a configuration of a resin injection molding apparatus according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a configuration of a conventional gas assist injection molding device.

FIG. 4 is a configuration diagram showing a configuration of a general resin injection molding apparatus generally used conventionally.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Mold forming surface 3 Product surface side mold 4 Mold forming surface 5 Gas channel (concave molding surface) 6 Product back side mold 7 Main part molding cavity 8 Thick part (projection part) molding Cavity 9 Cavity 10 General part 20 Air-permeable mold material 20a One side 21 Depressed part 22 Intake hole 23 Decompression device 30 Rib forming recess (concave forming surface) K region

Claims (1)

[Claims] 1. A thick portion for forming a thick portion having a cavity for molding a main body portion for molding a main body portion of a resin molded product, and a protruding portion projecting from a back surface side of the main body portion of the resin molded product. In a resin injection molding apparatus, a molten resin is injected into a cavity of a mold composed of a molding cavity to integrally mold a resin molded product integrally including the projecting portion in the main body. Forming a recess at a molding surface location on the product surface side of the mold opposite to the concave molding surface of the mold for forming the protrusion, and arranging a gas-permeable mold material in the recess, An air inlet communicating with the air hole of the air-permeable mold material is formed in the mold, and a pressure reducing device connected to the air inlet is operated to reduce the thickness of the molten resin injected into the mold cavity. Gold on the product surface side of the part forming cavity A resin injection molding device characterized in that it is drawn to a molding surface.