JPS5844459B2 - In-mold painting method - Google Patents

Description

[Detailed description of the invention] The present invention relates to an in-mold coating method.

In-mold coating is a process in which a coating film is formed in the mold and pressed together with the resin component during hot press molding of the resin component, thereby covering the surface of the resin molded product with the coating film.
The coating film is used to prevent air bubbles generated within the molded product during press molding of resin parts from swelling due to heat expansion during the baking drying process, etc., and to simplify the painting finishing process. Generally widely adopted.

Conventionally, the methods for forming a coating film in the above mold include spraying liquid paint or electrostatic powder paint onto the molding surface of the upper mold with a spray gun before press molding, and A generally known method is to slightly float the mold and inject liquid paint between the upper mold and the resin member.

However, with the former one-way spray method, the amount of paint that adheres to sloped surfaces is smaller than that to surfaces perpendicular to the spray direction, and the thickness of the paint film becomes uneven, especially on molded surfaces with complex shapes. easy.

This one-spray method cannot sufficiently suppress the expansion of air bubbles in areas where the coating film is thin.
It is difficult to achieve the intended purpose of preventing blistering of molded products, the paint is likely to scatter around and cause a deterioration of the working environment, and it is difficult to collect unapplied powder paint. There is also the problem that film formation takes time.

On the other hand, with the latter injection method, when the injected paint is spread by a separate vehicle, the heat of the mold hardens the paint, which tends to cause a decrease in flowability.Especially when the shape is complex, a uniform coating film cannot be obtained. In addition to being difficult to obtain, striped patterns are likely to occur on the surface of the coating film during spreading.

Furthermore, in the above-mentioned injection method, paints mainly composed of polyurethane are often used from the viewpoint of fluidity, but because the curing time is short, not only does the problem of flowability occur, but the paint also sticks around the injection nozzle. There is also the problem of clogging of the nozzle.

In view of the above, the present invention has been developed to form a complex shape in a short time by suspending the powder coating with an additional gas and adhering it to the molding surface of the upper die before press-molding the resin member. An object of the present invention is to provide an in-mold coating method that forms a coating film with a uniform thickness on a surface and makes it possible to recover unapplied paint, thereby solving the above-mentioned conventional problems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below based on embodiments with reference to the drawings.

1 is an upper mold, 2 is a lower mold, 3 is a paint tank with an open upper end that is fitted into the upper mold 1 from below the molding surface 4, 5 is a perforated plate provided inside the paint tank 3, and 6 is a paint A separate pipe with an outlet at the bottom of the tank 3 for sending gas, 7 an on-off valve interposed in the middle of the vibro, 8 a powder coating, and 9 a resin member.

The paint tank 3 moves up and down together with the vibro, and is horizontally rotatable using the vibro as an arm so that it can be retracted from below the upper mold.

Thus, the in-mold coating method of the present invention consists of a first step of forming a coating film and a second step of hot press molding.

In the first step, first, the upper mold 1 and the lower mold 2 are heated to 155°C and 150°C, respectively, which are the temperatures of hot press molding.
It is heated to.

Powder paint 8 is stored above the perforated plate 5 of the paint tank 3, and the paint tank 3 is rotated together with the vibro to be positioned below the molding surface 4 of the upper mold 1, and the paint is removed. The tank 3 is attached to the upper mold 1, and the paint tank 3 and the upper mold 1 form a floating chamber.

Subsequently, the on-off valve 7 is opened and pressurized gas, in this example 0.08
Kg/'cTt of air is blown into the paint tank 3 from the bottom.

This pressurized gas is blown upward from each through hole of the perforated plate 5.
The powder coating 8 is made to float.

A part of the powder coating 8 adheres to the heated molding surface 4 of the upper mold 1 and hardens, forming a coating film 10 having a uniform thickness over the entire molding surface 4.

In this example, the additional gas supply time is 8 seconds, and when the on-off valve 7 is closed to stop the pressurized gas supply, the remaining floating powder coating 8 falls onto the perforated plate 5. , collected without scattering to the surrounding area.

After forming the coating film 10 as described above, the paint tank 3 is lowered together with the vibro to separate it from the upper mold 1, and the vibro is used as an arm to rotate the paint tank 3 like a water wheel, and from the bottom of the upper mold 1 to the outside. evacuate to.

Note that the supply time of the pressurized gas varies somewhat depending on the thickness of the coating film 10 to be formed or the area of the molding surface 4, but may be about 30 seconds at most.

In addition, - in the above embodiment, the perforated plate 5 was provided in the paint tank 3 in order to make the pressurized gas act uniformly over the entire surface of the molding surface 4, thereby making the thickness of the coating film 10 uniform. It is possible to further improve the

Next, in the second step of hot press molding, first, the resin member 9 is placed on the substantially central portion of the molding surface 11 of the lower mold 2 .

The resin member 9 of this example is made of a material (unsaturated polyester resin containing glass fiber) in the form of a thick sheet, and weighs 2
．． 5 to 9, the area of each of the upper and lower surfaces is the molding surface 4.
Alternatively, it is about 45% of the area of the molding surface 11.

After the resin member 9 is placed on the lower mold 2 as described above, the upper mold 1 is lowered and hot press molding is performed.

In this hot press molding, the molded ball weighs 7 s kg/f
fl, pressurization speed is 14 seconds/10 seconds, application (mo time is 3
It is 0 minutes.

Through this hot press molding, the resin member 9 is heated and softened, spreads over the entire region of the cavity formed by the upper mold 1 and the lower mold 2, and is plastically deformed according to the shape of the cavity to become the resin molded product 12. .

At the same time as this plastic deformation, the resin molded product 12
The upper surface is covered with the coating film 10 formed in the process.

As described above, the press-molded product 13, which is formed by coating the resin molded product 12 with the coating film 10, is released from the upper mold 1 and the lower mold 2, and then the alkali which removes stains from the mold release agent etc. from the surface. Degreasing is performed, and if necessary, a finishing coat is applied on the coating film 10.

Table 1 and Table 1 show the data for Test A-, in which the above in-mold coating method was applied to the primer coating of a sliding roof for a passenger car, and Test t-H, in which the above coating method was applied to the bumper color finish coating for a passenger car. It is shown in Table 2.

That is, Table 1 does not show the composition and particle size of the powder coating used in the test.

Table 2 shows the test results regarding the physical and chemical properties of the coating film coated on the resin molded article.

In Table 2, each test item from gloss to gasoline resistance is tested using oil-modified alkyd resin, oil-modified alkyd resin,
These are the test results for a product that was finished with a paint consisting of a melamine resin hardener, white pigment, etc. and baked at 140°C for 30 minutes.For test B, the finish was applied using an in-mold coating method. alms, 1
These are test results for those baked at 50° C. for 20 minutes.

In addition to the paint used in the above test, the powder coating may also be a powder coating whose main component is thermoplastic or thermosetting polyester resin or a powder coating whose main component is polyurethane resin. Furthermore, by causing static electricity to accumulate in such a powder coating, the thickness of the coating film may be made uniform and the time required for forming the coating film may be further shortened.

Furthermore, as the separate gas, nitrogen gas may be used instead of air.

As described above, according to the present invention, since the powder coating is suspended by a separate gas and attached to the molding surface of the upper mold, the molding surface has a complicated uneven shape. It is possible to form a coating film of uniform thickness in a short time, and since it is a powder coating, it is also possible to form a thick coating film, which further demonstrates the effect of preventing blistering on molded products. Furthermore, the excellent effect of making it possible to recover unapplied paint can be obtained.

[Brief explanation of the drawing]

The drawings illustrate the embodiments of the present invention; FIG. 1 shows the step of forming a coating film, FIG. 2 shows the step of leaving the paint tank, and FIG. 3 shows the step of hot press forming. FIG. 3 is a central vertical cross-sectional view of the mold coating device. 1...Top mold, 2...Bottom mold, 3...
...Paint tank, 4...Molding surface of upper mold, 5...
...Perforated plate, 6...Pipe, 7...Opening/closing valve, 3...Powder coating, 9...Resin member, 10... ... Paint film, 11 ... Molding surface of lower mold, 12 ... Resin molded product, 13 ...
Press molded product.

Claims (1)

[Claims] 1. Place the paint tank containing the powder paint below the molding surface of the heated upper mold for hot press molding, and use the additional gas to float and adhere the powder paint to the molding surface of the upper mold to form a coating film. After forming, the paint tank and the upper mold are separated, and the resin member is hot-press molded using the upper mold and the lower mold on which the paint film has been formed, thereby forming a resin molded product of a predetermined shape from the resin member. An in-mold coating method characterized by coating the resin molded article with the coating film.