JP4233004B2 - In-mold coating method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-mold coating method for forming a film on the surface of an injection molded product made of a thermoplastic resin during an injection molding process.
[0002]
[Prior art]
Conventionally, according to Japanese Patent Laid-Open No. 7-112450, a gap is generated between the surface of the thermoplastic resin and the inner surface of the cavity while the mold is clamped after injection filling the thermoplastic resin into the cavity. An in-mold coating method is known in which a film raw material is injected to form a film during an injection molding process. In the first aspect of this, the coating material is injected into the gap formed between the resin surface and the cavity inner surface due to the volume reduction when the resin filled in the mold cavity is cooled and solidified. However, since it is not certain which side of the resin surface with respect to the inner surface of the cavity, that is, on which side of the movable mold and the stationary mold forming the cavity, in the second aspect, the mold is movable. A movable core part is provided in the mold, and when the resin is solidified, only the core part is retracted while the mold is closed, and a mechanical gap is formed between the surface of the movable mold side of the resin and the core part. The film raw material is injected into this gap. Furthermore, in the third aspect, the stationary mold and the movable mold constituting the mold are configured in a nested structure, and a cavity structure is employed in which the resin is fixed to the movable mold side when the resin is solidified. By moving the movable mold back slightly, a gap is mechanically generated between the surface of the fixed mold side of the resin and the inner surface of the cavity of the fixed mold, and the coating material is injected into this gap.
[0003]
[Problems to be solved by the invention]
In the above method, in order to improve the first mode in which the position where the gap is generated with respect to the resin surface is uncertain, in the second mode, the movable core portion is provided in the movable mold of the mold, and the third mode In the aspect, the fixed mold and the movable mold constituting the mold are engaged with each other by a telescopic structure. However, in both aspects, the mold structure is complicated and causes an increase in cost.
[0004]
In view of the above-mentioned problems, the present invention is designed so that a film can be formed on the surface on which a film of an injection molded product is to be formed during the injection molding process of a thermoplastic resin using a mold having a simple structure. It is an object to provide a mold coating method.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides an in-mold coating method for forming a film on the surface of an injection-molded product made of a thermoplastic resin in a mold cavity. After injection-filling the thermoplastic resin in the mold, one mold located on the surface side on which the film of the injection molded product is to be formed is replaced with the other mold among the pair of molds constituting the mold with the mold clamped The resin is solidified while being kept at a lower temperature, and a film material is injected into a gap formed between the surface of the resin and the inner surface of the cavity of the one mold.
[0006]
According to the present invention, a temperature difference is applied between a pair of molds of the mold, and the resin surface on which one of the molds having a relatively low temperature is to be formed and the cavity inner surface of the mold A gap is surely formed between the two. Thus, a film can be accurately formed on the surface of the injection-molded product with the film material injected into the gap.
[0007]
In this case, if the above-mentioned mold is a vertical type having an upper mold and a lower mold, and the upper mold constitutes the one mold, in addition to the shrinkage caused by the solidification of the resin, The mold side surface peels from the upper mold side of the cavity inner surface due to its own weight and contracts to the lower mold side, so that the film surface between the upper mold side resin surface to be coated with the upper mold cavity inner surface is formed. A gap is surely generated, and further, the shrinkage of the resin is uniformly performed by gravity, and a gap for forming a film is formed in a desired shape. Therefore, a film raw material is injected into this gap to obtain an injection molded product with a film. Can be molded with high accuracy.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
1A to 1D show an in-mold coating process using a vertical injection molding machine. Referring to FIG. 1, reference numeral 1 denotes a main part of a mold of a vertical injection molding machine. The mold 1 includes an upper mold 1a that is a movable mold and a lower mold 1b that is a fixed mold, and the upper mold 1a is a lower mold. A cavity 2 having a required product shape is formed between the upper die 1a and the lower die 1b by clamping the die 1b. In addition, a resin supply port 3b connected to the resin supply path 3 is provided at substantially the center of the cavity inner surface 2b of the lower mold 1b, and a molten resin made of thermoplastic resin 4 is injected into the cavity through the resin supply path 3 from an unillustrated injection machine. Further, a coating material injection port 5a connected to the coating material injection path 5 is provided at a portion of the cavity inner surface 2a of the upper mold 1a so as to be used for forming a coating on the surface of the injection molded product. The raw material 6 is configured to be injected into the cavity 2 from a coating material injection machine (not shown) through a coating material injection path 5 and a coating material injection port 5a.
[0009]
At the time of injection molding, first, as shown in FIG. 1 (a), the upper mold 1a and the lower mold 1b of the mold 1 are closed in contact with each other and are closed so as to resist the injection pressure at the time of injection filling. 1 is clamped by a mold clamping device (not shown), and in this state, a molten thermoplastic resin 4 is injected from the injection machine (not shown) into the cavity 2 of the mold 1 through the resin supply port 3b of the supply path 3. Fill. Then, when the cavity 2 is filled with resin, the resin supply path 3 is blocked by an appropriate blocking means to complete the injection filling process. The coating material inlet 5a is blocked by a suitable blocking means until the coating material injection step.
[0010]
Next, both the mold temperatures of the upper mold 1a and the lower mold 1b are lowered. At this time, as shown in FIG. 1 (b), the lower mold 1b is preceded by a temperature drop of the upper mold 1a. During the lowering, the upper mold 1a and the lower mold 1b are finally made to reach a predetermined temperature during the cooling process so as to always exceed the mold temperature of the upper mold 1a.
[0011]
In this way, when the mold temperature of the upper mold 1a is lowered to the predetermined temperature in the cooling process first, the solidification of the resin 4 due to cooling is higher than the lower mold 1b side on the upper mold 1a side where the temperature is relatively low. As a result, the resin 4 starts to shrink first on the upper mold 1a side, and coupled with the fact that the surface of the solidified resin 4 on the upper mold 1a side settles by its own weight, As shown in FIG. 1C, a gap 7 is generated between the surface of the resin 4 on the upper mold 1a side and the cavity inner surface 2a of the upper mold 1a with high accuracy.
[0012]
In this embodiment, the pressure holding step after the injection filling step is omitted. This is because the resin 4 is solidified from the injection machine side even if the resin 4 is solidified and the volume is reduced during the pressure holding step. This is because the volume is recovered by replenishing, and there is a possibility that the gap 7 as described above is prevented from being generated. In other words, in the present embodiment, the volume of the resin 4 is prevented from recovering in the pressure-holding step, and the gap 7 is sufficiently secured by reducing the volume when the resin 4 is solidified by cooling.
[0013]
Next, with the mold 1 clamped, the coating material injection port 5a is opened, and the coating material 6 is injected and filled into the gap 7 from the coating material injection channel 5 as shown in FIG. 1 (d). In this case, when the film raw material 6 is mainly composed of a thermosetting resin, the film raw material 6 is maintained with the upper mold 1a and the lower mold 1b kept at a low temperature so that the film raw material 6 can maintain fluidity during injection. After filling and filling in a liquid phase state, the temperature of the upper mold 1a is raised, and the film raw material 6 is thermally cured to form a film. In the case where the film material 6 is mainly composed of a thermoplastic resin, the film material 6 is kept at a high temperature while keeping the lower mold 1b at a low temperature so that the film material 6 can maintain fluidity during injection. Is injected in a molten state and filled, and then the temperature of the upper die 1a is lowered to solidify the film raw material 6 to form a film.
[0014]
Note that, regardless of whether the film raw material 6 is a thermosetting resin or a thermoplastic resin, it is generated between the surface on the upper mold 1a side of the injection molded product made of the thermoplastic resin 4 and the inner cavity surface 2a of the upper mold 1a. Since the film material 6 is filled in the gap 7, even if the temperature of the upper mold 1a is raised, the heat generated by the upper mold 1a is not directly conducted to the injection molded product, and this heat causes the injection molding. The product is not melted again and the formation of the film by the film raw material 6 is not hindered.
[0015]
【The invention's effect】
As is clear from the above description, according to the present invention, a film having a simple structure is used to accurately form a film on the surface on which the film of the injection molded product is to be formed during the injection molding process of the thermoplastic resin. Can be formed.
[Brief description of the drawings]
FIG. 1 (a) to (d)
In-mold coating process diagram using vertical injection molding machine 【Explanation of symbols】
1 Mold 1a Upper mold 1b Lower mold 2 Cavity 4 Thermoplastic resin 6 Film material 7 Crevice

Claims (2)

In the in-mold coating method in which a film is formed on the surface of an injection molded product made of a thermoplastic resin in a mold cavity, after the mold is clamped, the thermoplastic resin is injected and filled into the mold cavity. Of the pair of molds constituting the mold while the mold is clamped, the resin is solidified in a state where one mold located on the surface side where the film of the injection molded product is to be formed is kept at a lower temperature than the other mold. And a coating material is injected into a gap formed between the surface of the resin and the inner surface of the cavity of the one mold. The in-mold coating method according to claim 1, wherein the mold includes an upper mold and a lower mold, and the upper mold constitutes the one mold.

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