JPS6345291B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to reaction injection molding (RIM).
Injection Molding) products, especially thick-walled RIM products, with a method of applying a paint film. [Prior Art] In recent years, there has been a trend for automobile parts to shift to synthetic resin products that are lightweight and have excellent designs, and the types of these products vary depending on the purpose. Among these, urethane RIM products have minute air bubbles and are highly elastic, so compared to, for example, polypropylene molded products, they have higher impact resistance and elastic recovery rate, making them excellent as bumpers. Unlike molded products, there is no need to provide reinforcing ribs on the back side, which is preferable from a design standpoint as it gives a high-grade feel. Initially, these products were installed on vehicles as unpainted or molded products, but due to the market demand for a sense of unity with the vehicle and the resulting sense of luxury, they were changed to the same color as the exterior of the vehicle. Painting began to be applied. Normally, RIM products removed from the mold are thoroughly cleaned using a solvent or hot water to remove the mold release agent.
After that, an undercoat is applied, heat treated, and a topcoat is applied, followed by further heat treatment to harden the coating. Conventional RIM products that have been painted in this way have the cross section shown in Figure 5, and regardless of the wall thickness, they usually have an integral skin layer A with a thickness of several tens to hundreds of microns and a foam layer. An undercoat film 2 and a topcoat film 3 are formed on the surface of the foamed molded product 1 consisting of layer B. However, as shown in FIG. 6, air bubbles 4 existing inside the skin layer A or in the outermost layer cause defects in the appearance quality (pinholes) 5 of the coating film, and how can these be suppressed to the minimum number? This was the key to improving finishing quality and productivity. By the way, for RIM products with relatively thin walls (2 to 5 mm) such as bumpers, it is possible to flow the monomer in a film shape along the surface of the cavity by adjusting the mold temperature, injection speed of the raw material monomer, shape of the injection port, etc. However, the wall thickness was thick (approximately 50 mm) and
For molded products with complex shapes that require reinforcing material to be inserted into the foam layer, the injected monomer tends to cause turbulent flow, causing air bubbles to flow into the skin layer. hole) could not be resolved. Figure 7 shows a cross-sectional view of a thick-walled RIM product as described above, which has been removed from the mold and then coated with an undercoat and a topcoat. It can be seen that this is the cause of the occurrence of pinhole 5. [Object of the Invention] An object of the present invention is to provide a method for coating thick-walled RIM products to solve the above-mentioned pinhole problem. [Structure of the Invention] Prior to molding, the present inventors coated the inner surface of a foam mold with an undercoat paint, and applied this coating layer to RIM.
RIM by suppressing air bubbles that are generated near the skin layer by being transferred to the molded product during molding.
It has been discovered that the number of air bubbles appearing on the surface of a molded product can be reduced, and by sufficiently curing the undercoat film during post-curing after molding, the undercoat film can be cured by the solvent used when removing the mold release agent. It was confirmed that there was no damage to the In other words, the coating method for thick-walled RIM products of the present invention is to apply a release agent to the inner surface of the mold, then apply an undercoat paint, and after drying, perform reaction injection molding to transfer the above-mentioned undercoat film to the molded product. After curing the coating film by post-curing after demolding, the release agent adhering to the undercoat film is washed with an organic solvent, dried, and then another undercoat and topcoat are applied. It is characterized by applying a coating. The undercoating paint used in the present invention is preferably a urethane paint of the same quality as the foam layer from the viewpoint of adhesive strength with the internal foam layer. Among urethane paints, two-component type urethane paints have the disadvantage of short pot life, but on the other hand, this shortens the setting time from painting one side to forming RIM, so in the present invention, two-component type urethane paints are used. However, it is not limited to this. When these undercoat films are dried or semi-cured and then injection molded, the unreacted groups in the paint film and the unreacted groups in the foam layer cause a urethane reaction.
Adheres by chemical bonding. Because the metal mold has a large heat capacity, it is constantly heated at 40 to 60 degrees Celsius.
Normally, after drying the undercoat film, it is directly put into the molding process, but if the mold is cooled, it is necessary to heat it to the above temperature in advance. The undercoat film transferred to the molded product during molding has the effect of suppressing air bubbles from entering near the skin layer, but it is difficult to suppress them 100%, and depending on changes in molding conditions, pinholes may be formed after the topcoat. There remains a risk that this may occur. On the other hand, if the film thickness of the above-mentioned mold coating is set to a sufficient thickness, for example, 50 to 60 μm, and the mold is closed and injection molding is performed after sufficiently promoting the curing of the coating film, the pinholes will disappear, but the coating film will harden. It takes too much time and becomes a problem in terms of productivity. Therefore, the purpose of the second undercoat in the present invention is to correct small pinholes that could not be eliminated by the first undercoat (1). Therefore, before applying the second undercoat, it is necessary to wash and remove the mold release agent using a solvent. This can be done by placing the molded product in the solvent vapor for several minutes and removing it along with the vapor, or by wiping it off with gauze soaked in the solvent.
At this time, if the undercoat (1) coating film is not sufficiently cured, wrinkles will occur in the coating film. The undercoat (1) coating film has already been cured to a certain extent in the dry state before molding, but the method of the present invention is characterized in that post-curing is further performed on the molded product that has been demolded after molding. As shown in the examples below, the degree of post-curing is 80% based on the uncured state of the paint.
to 100%, preferably 90 to 100%. Next, the solvent used for cleaning the mold release agent on the cured undercoat (1) coating film is appropriately selected from trichloroethane, trichloroethylene, xylene, alcohol, thinner, etc., depending on the type of mold release agent. Since the solvent is adsorbed on the surface of the molded product after cleaning, if you apply the undercoat (2) as it is, the undercoat will be removed.
(2) Solvent may remain in the paint film, and this solvent may evaporate, causing blistering in the undercoat (2) paint film. Therefore, by heating the molded product again at 80 to 120°C for 15 to 60 minutes after cleaning,
Let the solvent evaporate and dry. In this way, after washing and drying, apply the undercoat (2)
Paint and top coat. [Examples] Hereinafter, the present invention will be specifically explained using Examples and Comparative Examples. Example After spraying a _mold release agent on the surface of the mold 6 for spoiler molding shown in FIG. It was applied to a surface of 30 μm to 30 μm and left to dry for 2 minutes. Next, after inserting a steel plate reinforcing material with a thickness of 1 mm into the mold 6, using a liquid mixture with the following mixing ratio, the material was heated to 32°C using a mold equipped with a mixing head.
℃, the mold temperature was 60℃, and the injection pressure was 170Kg/cm ² . Ingredient blending ratio Part A polypropylene glycol 90 parts Polyethylene glycol 20 parts Dibutyl laurate (catalyst) 0.2 parts Freon R-11 (blowing agent) 5 parts B part Isocyanate 115 parts After keeping the mold temperature above for several minutes, mold 4 was opened and demolded, and the distortion of the product was corrected by applying heat, and post-curing was performed at 120°C for 30 minutes to accelerate the curing of the undercoat (1) coating. Undercoat (1) The degree of cure of the coating film is as shown in the table below.
80 to 100% is necessary; if curing is insufficient, wrinkles will appear in the paint film. The curing conditions for obtaining the following samples are a temperature of 80 to 120℃ and a time of 30℃.
Remaining in the paint film by changing the range between 60 minutes and 60 minutes
The amount of NCO was measured, and four samples having the amount of NCO shown in the table were placed in 1.1.1-trichloroethane vapor for 2 minutes and the degree of wrinkles in the coating film was observed.

【table】

〔Effect of the invention〕

As is clear from the above description, the thick wall of the present invention
RIM products suppress air bubbles from entering the skin layer with the undercoat (1) coating film, and the undercoat (1) above.
Since small pinholes that could not be eliminated with undercoat (2) can be corrected with undercoat (1), the thickness of the undercoat (1) film can be made thinner, and post-curing does not require a long time. And since the paint film is sufficiently cured,
The coating film is not damaged even by the organic solvent used in the subsequent mold release agent removal process. As described above, the method of the present invention makes it possible to provide a thick-walled RIM product with no defects in appearance and can be used for automobile parts such as the aforementioned spoiler.

[Brief explanation of drawings]

Figure 1 shows a cross-sectional view of the undercoating (1) process, and the second
The figure shows a cross-sectional view of the spoiler according to the example, FIG. 3 shows an external view of a product of a comparative example, FIG. 4 shows a cross-sectional view of a product of a comparative example, and FIG. 5 shows a conventional thin-walled RIM product. Figure 6 shows a schematic cross-sectional view of a pinhole that occurred in a thin-walled RIM product, and Figure 7 shows a cross-sectional view of a pinhole that occurred in a conventional thick-walled RIM product. represent In the figure, 1... foam molded body, 2... undercoat film, 3...
Top coat film, 4... Air bubbles, 5... Pinhole, 6... Mold, 7... Undercoat (1) paint, 8... Spoiler, 9... Reinforcement material, 10... Urethane foam resin, 11... Undercoat (1) paint film, 12... Undercoat (2) coating film, 13... Topcoat coating film, 1
4...Mounting surface.

Claims (1)

[Scope of Claims] 1 After applying a mold release agent to the inner surface of the mold, an undercoat paint is applied, and after drying, reaction injection molding is performed to transfer the undercoat film to the molded product, and post-cure after demolding. After curing the above coating film, the release agent adhering to the undercoat film is washed with an organic solvent, dried, and another undercoat and topcoat are applied. A method for painting thick-walled RIM products. 2 Post-cure the undercoat film to 80% or more.
The method according to claim 1, which results in 100% curing.