JP2001096567A - Method of manufacture for resin molding and resin molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the weatherability of a resin molding by efficiently and uniformly forming a coating film of acrylic resin on the surface of a resin- molded part. SOLUTION: First, a coating M composed of an acrylic resin and a solvent is poured into a cavity 13 of an opened mold 2, and the mold 2 is closed and further, a vacuum pump 34 is driven to reduce the internal pressure of the cavity 13. Then the solvent contained in the coating M boils and the coating M is efficiently applied to the wall face of the cavity 13 by the increased volume of the coating M and the breaking of bubbles during boiling. In addition, a coating film layer of the acrylic resin is formed on the wall face of the cavity 13 by vaporization of the solvent contained in the coating M. After that, a polypropylene(PP) which is provided with a fluidity by heating and softening process is injected into the cavity 13 to be cured by cooling. Thus it is possible to perform the simultaneous molding of the resin into a back panel and coating thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a resin molded product, which is obtained by applying a coating material in advance to a cavity in a mold and performing injection molding using a resin material in order to simultaneously perform molding and coating of the resin molded product. The present invention relates to a resin molded product.

[0002]

2. Description of the Related Art Conventionally, injection molding of a thermoplastic resin has been employed as a method for mass-producing resin molded products. Specifically, in injection molding of automobile parts, polypropylene (PP) or the like, which is excellent in moldability and lightweight and inexpensive, is used as a molding material.

[0003] However, since PP has poor weather resistance,
In the case of an automobile part resin-molded using this PP, it is necessary to form a coating film having excellent weather resistance on the surface thereof. Therefore, a method has been proposed in which a paint is applied to a cavity in a mold in advance and then the product is molded. Specifically, an acrylic paint solution is applied to the cavity with a spray gun to form a coating layer on the surface of the cavity. After that, the mold is closed and heated and softened to make the fluidized PP.
Is injected into a cavity and cooled and cured in the cavity. Thereby, a coating film having excellent weather resistance is formed on the surface of the product.

[0004]

However, when the coating solution is applied to the cavity by the spray gun as described above, the coating solution is applied to portions other than the cavity of the mold, or is applied to the air without being applied to the mold. Scattering results in poor coating efficiency. Further, paint applied to portions other than the cavities causes burrs after molding, so that a processing step for removing the burrs is required. further,
Paint scattered in the air without being applied not only stains the workplace, but also degrades the surrounding environment.

[0005] Further, in the spray gun application, the coating cannot be applied uniformly. In particular, in the parting line part, it is not possible to sufficiently apply the coating, and the coating layer formed on the cavity surface becomes thin. For this reason, the coating film layer is broken by molding pressure, temperature, and the like during resin molding, and the product yield deteriorates.

The present invention has been made to solve the above problems, and a first object of the present invention is to provide a method for producing a resin molded article capable of efficiently and uniformly forming a coating film of an acrylic resin. To provide. Further, a second object is to provide a resin molded product having excellent weather resistance.

[0007]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 is directed to a resin molded product in which a coating solution is previously applied to a mold cavity in order to simultaneously perform molding and coating. In the manufacturing method, a coating solution containing an acrylic resin and a solvent is boiled in a mold cavity under reduced pressure, and a coating layer is formed in the mold cavity by increasing the volume at the time of boiling and breaking bubbles. The gist of the invention is that a resin material imparted with a property is injected into a mold cavity, and is cooled and cured to be molded.

According to a second aspect of the present invention, in a resin molded product which is injection molded using a predetermined resin material, an acrylic resin coating film is formed on the surface of the injection molded portion with a substantially uniform thickness. The gist of this is to be done.

(Operation) According to the first aspect of the present invention,
Boiling the coating solution in the mold cavity under reduced pressure,
A coating layer of an acrylic resin is formed in the mold cavity due to the increase in volume and the breakage of bubbles at the time of boiling. That is, in the closed mold cavity, the paint is efficiently and uniformly applied to the wall surface. Also, by adjusting the injection amount of the coating solution, since the coating film can be uniformly formed at a desired thickness,
It is possible to uniformly form the acrylic resin coating layer with a desired strength. Therefore, when the resin material which has been softened by heating and has flowability is injected into the cavity and the material is molded in the cavity, the coating pressure formed at the time prevents the coating layer formed in the mold cavity from being broken. Is done.

According to the second aspect of the present invention, the acrylic resin coating film is formed on the surface of the molded portion with a substantially uniform thickness, and the weather resistance of the molded portion is improved. In particular, by forming a coating film having a desired thickness even on a parting line, the weather resistance of that portion is improved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are partial cross-sectional views of an injection molding machine according to the present embodiment, and FIG. 4 is a perspective view of a back panel 1 formed into a plate shape by the injection molding machine. The back panel 1 is a component mounted between the stop lamps at the rear of the vehicle.

As shown in FIG. 1 to FIG.
And a cover 4 in a box 5. Specifically, the lower die 8 of the mold 2 is fixed to the frame 3 and the lid 4
The upper die 9 of the die 2 is fixed to the upper part. In addition, a seal member 10 is provided at a joint of the lid 4 and the frame 3. Then, the frame 3 and the lower mold 8 are moved upward from the state in which the mold 2 is opened as shown in FIG.
The mold 2 is closed and clamped as shown in FIG. At this time, a box 5 is formed by the frame 3 and the lid 4,
The inside of the box 5 is sealed by the seal member 10.

The lower die 8 and the upper die 9 are formed with concave portions 11 and 12, and the concave portions 11 and 12 become cavities 13 for forming a molded product shape. A discharge hole 14 (for example, a cross-sectional area = 4 mm ² ) is formed in the concave portion 12 of the upper die 9, and the cavity 13 is formed by the discharge hole 14.
It is communicated with the hollow part 21 inside. The discharge hole 14 is also formed at a position corresponding to the corner 1a of the back panel 1 shown in FIG.

An injection nozzle 22 is provided on one side wall (the right side wall in the figure) of the frame 3, and polypropylene (PP) from an injection device main body (not shown) receives the injection nozzle 22.
Is injected into the cavity 13 through the gate 23.
A discharge pipe 31 is provided on the other side wall (the left side wall in the figure) of the frame 3, and the discharge pipe 31 is connected to a vacuum pump 34 via a pipe 32 and a valve 33. When the vacuum pump 34 is driven, the air in the box 5 is discharged from the discharge pipe 31, and the pressure in the box 5 is reduced.

Next, the back panel 1 in the present embodiment
The resin molding method will be described with reference to FIGS. First,
As shown in FIG. 1, the mold 2 is opened, and a mold release agent is applied to the wall surfaces of the cavity 13 (the concave portion 11 of the lower die 8 and the concave portion 12 of the upper die 9). This release agent is made of wax, silicone oil, etc., and prevents the molded product from sticking to the mold 2,
It is applied for the purpose of facilitating removal of the molded product.

Next, the liquid paint M is poured into the concave portion 11 of the lower die 8 while keeping the die 2 horizontal. The solution of the coating material M in the present embodiment contains methyl ethyl ketone (MEK) as a solvent and an acrylic resin as a solid content. Then, the frame 3 and the lower mold 8 are moved upward, and the mold 2 is closed and clamped as shown in FIG. At this time, the frame 3 and the lid 4 are joined via the seal member 10, and the inside of the box 5 is in a sealed state.

Thereafter, the vacuum pump 34 is driven to drive the discharge pipe 3
By discharging the air in box 5 from box 1, box 5
Reduce the pressure inside. At this time, the air in the cavity 13 is sucked into the hollow portion 21 in the box 5 through the discharge hole 14, and the pressure in the cavity 13 is also reduced. When the pressure in the cavity 13 is reduced, the boiling point of the solvent (MEK) of the coating material M decreases. As a result, the paint M boils and breaks bubbles with an increase in volume. Specifically, the temperature of the mold 2 is room temperature (about 20
° C) and the cavity 13 has a pressure of 70 torr.
When the pressure is reduced below, the solvent boils. The paint M is applied to the wall surface of the cavity 13 due to the increase in volume and the breakage of bubbles at the time of boiling.

Then, the solvent of the coating material M evaporates, and the acrylic resin is applied to the wall surface of the cavity 13. The vaporized solvent is supplied from the discharge hole 14 to the vacuum pump 34 via the hollow portion 21 in the box 5 and the discharge pipe 31.
It is exhausted from.

Next, polypropylene which has been heated and softened by an injection device body (not shown) and given fluidity is injected into the cavity 13 from the injection nozzle 22 through the gate 23, and cooled in the cavity 13 as shown in FIG. To cure. Thereby, resin molding and painting of the back panel 1 are performed simultaneously. That is, a coating film of the acrylic resin A1 having excellent weather resistance is formed with a substantially uniform thickness on the surface of the polypropylene P1 formed by injection molding.

Thereafter, the mold 2 is opened, the back panel 1 shown in FIG. 4 is taken out, and the molding process is completed. Incidentally, when it is applied by a spray gun, it is not possible to apply the paint accurately, and in particular, the application to the parting line becomes insufficient. As a result, the coating film in the part of the parting line becomes thin, and polypropylene (PP)
When resin molding is performed using a resin, the coating pressure at that time breaks the coating film at the parting line, and the product yield is deteriorated. However, according to the above-mentioned molding method, it is possible to form a coating layer of the acrylic resin A1 with an appropriate thickness also on the parting line by adjusting the injection amount of the coating material M. Therefore, the coating layer formed on the wall surface of the cavity 13 due to the pressure during molding is prevented from being broken.

As described above, the present embodiment has the following advantages. (1) Since the coating material M is applied in the closed mold 2, the coating efficiency can be increased as compared with the case where the coating material M is applied by a spray gun, and the material cost of the coating material M can be reduced. . In addition, the coating material M is not applied to the outside of the cavity 13, so that the occurrence of burrs during molding can be prevented.
Therefore, a processing step for removing burrs, which is required in the related art, becomes unnecessary. As a result, manufacturing costs can be kept low. Further, the paint M is prevented from scattering to the outside, the work place can be kept clean, and the deterioration of the surrounding environment can be prevented.

(2) The coating material M is uniformly applied to the wall surface of the cavity 13 as the solvent boils and the volume increases and bubbles are broken. That is, the coating of the acrylic resin A1 having excellent weather resistance is formed with a substantially uniform thickness on the surface of the back panel 1 after molding without coating unevenness. Therefore, weather resistance can be uniformly obtained at any place, and deterioration of product performance can be prevented. Further, since the coating film can be formed uniformly, there is no color unevenness on the product surface and the appearance defect can be reduced.

(3) Thick coating can be performed in a short time as compared with the case where the coating is performed by a spray gun, and when the coating solution is poured into the cavity 13, the desired thickness can be obtained simply by adjusting the amount of the coating solution. Can be formed. That is, it is difficult to thicken the coating film on the parting line (PL section) when the coating material is applied by a spray gun as in the related art, but in the back panel 1 of the present embodiment,
A coating film having an appropriate thickness can be formed at the parting line. Therefore, when the resin is molded by injecting polypropylene (PP), it is possible to prevent the coating film of the acrylic resin A1 from being broken even if the molding pressure at that time increases.

The above embodiment may be implemented in the following manner. In the above embodiment, the paint M is injected with the mold 2 opened. However, a separate paint injecting device is provided, and the mold 1 is closed from the paint injecting device with the mold 2 closed.
3 may be configured to inject the paint M. In this way, the paint M can be injected into the cavity 13 under reduced pressure, and the resin molding can be performed in a short time.

In the above embodiment, the polypropylene (P
Although molded using P), injection molded using another thermoplastic resin material, for example, ABS resin or the like may be used.
Further, the molded product is not limited to the back panel 1, and includes, for example, a steering wheel, an instrument panel,
The present invention can be applied to other parts such as a console box, a glow box, a door cover, an air spoiler, and a bumper.
Of course, the present invention may be applied to molded articles such as home electric appliances in addition to automobile parts.

In the above embodiment, the solvent of the coating material M is methyl ethyl ketone (MEK). However, the solvent is not limited to this, and may be any solution that can dissolve the acrylic resin. For example, acetone, methyl isobutyl ketone,
Ethyl acetate or the like may be used, or a mixture of two or more of them may be used.

Further, technical ideas other than the claims grasped by the above embodiment will be described below together with their effects. (A) In a resin molded product manufactured by injection molding of a thermoplastic resin after forming a coating layer in a mold cavity in advance so as to simultaneously perform molding and painting, an acrylic resin is formed on the surface of the molded portion by the injection molding. A resin molded article characterized in that the coating film of (1) is formed with a substantially uniform thickness. In this case, the weather resistance of the resin molded product can be improved.

[0028]

As described in detail above, according to the present invention,
An acrylic resin coating film can be efficiently and uniformly formed. In addition, since a coating film having a desired thickness is uniformly formed on the surface of the resin molded product, the weather resistance can be improved.

[Brief description of the drawings]

FIG. 1 is a view for explaining a method of forming a back panel according to an embodiment.

FIG. 2 is a view for explaining a method of forming a back panel according to the embodiment.

FIG. 3 is a view for explaining a method of forming the back panel according to the embodiment.

FIG. 4 is an exemplary perspective view of a back panel according to the embodiment;

[Explanation of symbols]

1 ... Back panel, 2 ... Mold, 13 ... Cavity, M ...
Paint, A1: acrylic resin as a coating film, P1: polypropylene as a resin material.

Continued on front page F term (reference) 4F206 AA11 AA13 AD01 AD05 AD11 AD34 AG03 AH17 JA07 JB11 JF05 JL02 JQ81 JQ87

Claims (2)

[Claims] 1. A method for manufacturing a resin molded product, in which a coating solution is previously applied to a mold cavity in order to simultaneously perform molding and coating, wherein a coating solution comprising an acrylic resin and a solvent is placed in the mold cavity in a reduced pressure state. After forming a coating layer in the mold cavity by volume increase and foam breakage at the time of boiling, heat-softened resin material with fluidity is injected into the mold cavity, cooled and hardened to form a mold. A method for producing a resin molded product, characterized in that: 2. A resin molded product which is injection-molded using a predetermined resin material, characterized in that an acrylic resin coating film is formed with a substantially uniform thickness on a surface of a molded portion to be injection-molded. Resin molded products.