JP2002096352A - In-mold coating method - Google Patents

Abstract

[PROBLEMS] An in-mold coat that can form a film on a surface of an injection-molded product on which a film is to be formed accurately during a thermoplastic resin injection molding process using a mold having a simple structure. Provide a way. A thermoplastic resin (4) is injected and filled into a cavity (2) of a mold (1) in a state in which a mold (1) including an upper mold (1a) and a lower mold (1b) is clamped. Mold 1a
While the lower mold 1b is kept at a low temperature, the lower mold 1
The b side is solidified and contracted, and then the mold temperature of the upper mold 1a is lowered to solidify the upper mold 1a side of the resin 4, and then the surface of the upper mold 1a side of the resin 4 and the upper mold 1a The coating material 6 is injected into a gap 7a created by supplying a compressed gas between the cavity inner surface 2a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-mold coating method for forming a film on the surface of an injection-molded article made of a thermoplastic resin during an injection molding process.

[0002]

2. Description of the Related Art Conventionally, according to Japanese Patent Application Laid-Open No. Hei 7-112450, a gap is formed between the surface of a thermoplastic resin and the inner surface of the cavity while the mold is being clamped after the thermoplastic resin is injected and filled into the cavity. There is known an in-mold coating method in which a film material is injected into the gap to form a film during an injection molding process. In the first embodiment, the coating material is injected into a gap generated between the resin surface and the cavity inner surface due to a reduction in volume when the resin filled in the mold cavity cools and solidifies. However, it is uncertain which side of the resin surface with respect to the inner surface of the cavity, that is, which side of the movable mold or the fixed mold that forms the cavity, and the resin on the side where film formation is required. The surface may be unevenly formed due to uneven shrinkage due to uneven shrinkage during shrinkage due to solidification, and may be formed in an uneven shape. There is a problem with the shape accuracy of the film. For this reason,
In the second aspect, a movable core portion is provided on the movable mold of the mold, and at the time of solidification of the resin, only the core portion is retracted while the mold is closed, and the surface of the resin on the movable mold side is removed. A gap is mechanically formed between the core and the core, and the coating material is injected into the gap. Further, in the third aspect, the fixed mold and the movable mold that constitute the mold are formed in a nested structure, and a cavity structure is employed in which the resin is fixed to the movable mold when the resin is solidified. By moving the movable mold back a little, a gap is mechanically formed between the surface of the fixed mold side of the resin and the inner surface of the cavity of the fixed mold, and the film material is injected into this gap.

[0003]

In the above method, in order to improve the first aspect in which the position where the gap is formed with respect to the resin surface is uncertain, in the second aspect, a movable core is used as a movable mold. In the third embodiment, the fixed mold and the movable mold constituting the mold are engaged with each other in a nested structure. Becomes

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a method for forming a film on a surface of an injection-molded article on which a film is to be formed with high accuracy during a thermoplastic resin injection molding process using a mold having a simple structure. An object of the present invention is to provide an in-mold coating method that can be obtained.

[0005]

In order to solve the above-mentioned problems, the present invention provides an in-mold coating method for forming a film on the surface of an injection-molded article made of a thermoplastic resin in a cavity of the mold. After the thermoplastic resin is injected and filled into the cavity of the mold with the mold clamped, the mold is clamped while the mold is closed. While keeping the other mold at a lower temperature than the one mold located, the other mold side of the resin is solidified, and then the temperature of the one mold is lowered to reduce the temperature of the one mold to the one mold of the resin. After that, the coating material is injected between the surface of the one mold side of the resin and the inner surface of the cavity of the one mold.

According to the present invention, when the other mold side of the resin is solidified, a gap is formed between the surface of the other mold side of the resin and the inner surface of the cavity of the other mold due to the resin shrinkage accompanying the solidification. Next, when one mold side of the resin is solidified,
A resin surface located on one mold side and requiring film formation is formed by transferring the shape of the cavity inner surface of one mold,
Further, the adhesive state between the surface of the resin on the one mold side and the inner surface of the cavity of the one mold is eliminated. Therefore, when the solidification of the resin on one mold side is completed, the resin surface on which the shape of the cavity inner surface of one mold is transferred can be separated from the cavity inner surface of one mold by the action of a slight external force. As described above, since there is a gap between the surface of the other mold side of the resin and the inner surface of the cavity of the other mold as described above, and the resin is not supported on the other mold side, The resin is easily released from one mold. Therefore, after that, the coating material can be injected between the surface on the one mold side of the resin and the inner surface of the cavity of the one mold, and in this way, the coating can be accurately formed on the surface of the injection molded product. .

In this case, if a compressed gas is supplied between the surface of the resin on the one mold side and the inner surface of the cavity of the one mold before injecting the coating material, one of the resins is supplied as described above. The resin is released from one mold while maintaining the resin surface formed by transferring the shape of the inner surface of the cavity of the mold, and a gap is formed between the resin surface and the inner surface of the cavity of the one mold. And the subsequent injection of the coating material becomes easy.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A to 1D show an in-mold coating process using a vertical injection molding machine. FIG.
Reference numeral 1 denotes a main part of a mold of a vertical injection molding machine, and a mold 1 includes a movable mold upper mold 1a and a fixed mold lower mold 1b.
The upper die 1a is clamped to the lower die 1b to form a cavity 2 having a required product shape between the upper die 1a and the lower die 1b. A resin supply path 3 is provided substantially at the center of the cavity inner surface 2b of the lower mold 1b.
And a resin supply port 3b connected to the upper mold 1a is provided so that a molten resin composed of a thermoplastic resin 4 is injected into the cavity 2 through the resin supply path 3 by an injection machine (not shown). An injection port 5a connected to the injection path 5 is provided on the surface 2a, and one of a compressor (not shown) and an injection machine (not shown) can be selectively connected to the injection path 5, so that the injection path 5 and A compressed gas such as compressed air or nitrogen gas in a compressor and a coating material 6 in a coating material injection machine are selectively injected into the cavity 2 via the inlet 5a.

At the time of injection molding, first, as shown in FIG. 1A, the upper die 1a and the lower die 1b of the mold 1 are brought into contact with each other and closed, and the injection pressure at the time of injection filling can be withstood. Then, the mold 1 is clamped by a mold clamping device (not shown). In this state, the molten thermoplastic resin 4 is supplied from the injection machine (not shown) via the resin supply port 3b of the supply path 3 to the cavity 2 of the mold 1. Injection filling. Then, when the cavity 2 is filled with the resin, the resin supply path 3 is shut off by an appropriate shut-off means to complete the injection filling step. The injection port 5a is closed by a suitable closing means until injection of a compressed gas or a coating material described later is performed.

Next, with the mold 1 clamped, the upper mold 1a
And the mold temperature of the lower mold 1b is lowered.
As shown in (b), the upper mold 1a is kept at the mold temperature during the above-described injection filling step, and only the mold temperature of the lower mold 1b is lowered to reach a predetermined temperature during the cooling step. Thereafter, the mold temperature of the upper mold 1a is lowered so that the upper mold 1a also reaches a predetermined temperature during the cooling step.

In this case, when the temperature of the lower mold 1b is decreasing, the upper mold 1a of the resin 4 is kept in a molten state by the upper mold 1a maintained at the high mold temperature in the injection filling step. On the other hand, the lower mold 1b of the resin 4 having a relatively low temperature
The side starts to solidify by cooling. At this time, the volume of the molten resin 4 decreases while solidifying in a direction from the relatively low temperature lower mold 1b side to the relatively high temperature upper mold 1a side. As shown in FIG. 1C, a gap 7 is formed between the surface of the resin 4 on the lower mold 1b side and the cavity inner surface 2b of the lower mold 1b.
b occurs. Then, when the mold temperature of the upper mold 1a is lowered after the lower mold 1b, the upper mold 1a side of the resin 4 starts to solidify by cooling.

At the start of the solidification of the upper mold 1a side of the resin 4, the solidification of the resin 4 has already progressed sequentially from the lower mold 1b side to the upper mold 1a side due to the lower mold temperature of the preceding lower mold 1b. The start of solidification is most delayed in the vicinity of the surface of the resin 4 on the upper mold 1a side. Therefore, on the upper mold 1a side of the resin 4, the resin 4 solidifies without the resin shrinkage unlike the lower mold 1b side, and the surface of the upper mold 1a side of the resin 4 becomes the upper mold 1a.
a from the cavity inner surface 2a. When the upper mold 1a side of the resin 4 solidifies, the surface of the upper mold 1a side of the resin 4 accurately transfers and forms the shape of the cavity inner surface 2a, while being in close contact with the cavity inner surface 2a of the upper mold 1a. Is done. Further, when the mold temperature of the upper mold 1a decreases to a predetermined temperature in the cooling step and the solidification of the upper mold 1a side of the resin 4 is completed, the surface of the upper mold 1a side of the resin 4 and the cavity of the upper mold 1a are removed. The adhesive state between the lower mold 1b and the surface 2a is eliminated, and a gap 7b is formed between the lower mold 1b side surface of the resin 4 and the cavity inner surface 2b of the lower mold 1b. Side, the surface of the upper mold 1a side of the resin 4 can be separated from the inner surface 2a of the upper mold 1a by the action of a slight external force. Thus, the resin 4 is separated from the upper mold 1a. The mold is easily released.

In the present embodiment, the resin supply path 3 is closed after the injection and filling step, and the process shifts to the cooling step without going through the pressure-holding step. Even when the volume of the resin 4 is reduced due to solidification, the resin 4 is replenished from the injection machine side. As a result, when the lower mold 1b side of the resin 4 solidifies, the surface of the lower mold 1b side of the resin 4 and the cavity of the lower mold 1b are formed. Surface 2
This is because a gap 7b cannot be formed between the upper mold 1a and the resin 4 and the resin 4 may be prevented from being easily released from the upper mold 1a as described above.

Next, while the mold 1 is clamped, the injection path 5
Is opened, and a compressed gas is injected from a compressor (not shown) between the surface of the upper mold 1a side of the resin 4 and the inner surface 2a of the cavity of the upper mold 1a. In this case, while the surface accuracy of the upper mold 1a side of the resin 4 to which the shape of the cavity inner surface 2a is transferred is maintained, the surface of the upper mold 1a side of the resin 4 is separated from the cavity inner surface 2a of the upper mold 1a. The resin 4 is released from the upper mold 1a, and a space shown as a gap 7a in FIG. 1D is created between the surface of the resin 4 on the upper mold 1a side and the cavity inner surface 2a of the upper mold 1a. At this time, the gap 7
The volume b decreases by the newly generated gap 7a.

Further, while the mold 1 is clamped, FIG.
As shown in (d), the coating material 6 is injected into the gap 7a from the coating material injection machine (not shown) through the injection port 5a and filled. In this case, when the coating material 6 contains a thermosetting resin as a main component, the coating material 6 is kept while keeping the upper mold 1a and the lower mold 1b at a low temperature so that the fluidity of the coating material 6 can be maintained at the time of injection. Is filled in a liquid state, and after filling, the mold temperature of the upper mold 1a is increased, and the coating material 6 is thermally cured to form a coating. When the coating material 6 is mainly composed of a thermoplastic resin, the upper die 1a is kept at a high temperature while the lower mold 1b is kept at a low temperature so that the fluidity of the coating material 6 is maintained at the time of injection. After filling and filling in a molten state, the upper mold 1a
Is reduced, and the coating material 6 is solidified to form a coating. Regardless of whether the coating raw material 6 is a thermosetting resin or a thermoplastic resin, the coating raw material 6 is formed by accurately transferring the shape of the cavity inner surface 2a to the surface of the injection-molded article formed as described above. Since it is filled between the cavity inner surface 2a and the cavity surface 1a, a film having good shape accuracy is formed by solidifying the film raw material 6. For example, when a molded product having a smooth surface is obtained, a molded product excellent in smoothness without unevenness due to sink marks or the like can be obtained.

In these cases, the coating material 6 is filled in the gap 7a formed between the upper mold 1a side surface of the injection molded product made of the thermoplastic resin 4 and the cavity inner surface 2a of the upper mold 1a. Therefore, even if the mold temperature of the upper mold 1a is raised, the heat generated thereby is not directly transmitted to the injection molded product, and the heat causes the injection molded product to be in a molten state again. The formation of the coating by the coating material 6 is not hindered.

[0017]

As is apparent from the above description, according to the present invention, the surface of the injection-molded article on which the film is to be formed during the injection molding process of the thermoplastic resin using the mold having a simple structure. A film can be formed accurately and reliably.

[Brief description of the drawings]

FIG. 1 (a) to (d) Process charts of in-mold coating using a vertical injection molding machine

[Explanation of symbols]

Reference Signs List 1 mold 2 cavity 4 thermoplastic resin 6 coating material 7a gap

Claims (2)

[Claims] In an in-mold coating method for forming a film on the surface of an injection-molded article made of a thermoplastic resin in a cavity of a mold, the thermoplastic resin is filled in the cavity of the mold while the mold is clamped. After injection filling, the other mold was kept at a lower temperature than one of the pair of molds constituting the mold, which was located on the surface side on which the film of the injection molded article was to be formed, while the mold was clamped. In the state, the other mold side of the resin is solidified, and then the temperature of the one mold is reduced to solidify the one mold side of the resin, and then the one mold side of the resin is solidified. An in-mold coating method characterized by injecting a coating material between the surface of the mold and the inner surface of the cavity of the one mold. 2. The method according to claim 1, wherein a gap is formed by supplying a compressed gas between the surface of the one mold side and the inner surface of the cavity of the one mold before injecting the coating material. The in-mold coating method according to claim 1.