JPH0239951B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to so-called reinforced reaction injection molding, R-RIM (Reinforced
This relates to a method of painting molded products using Reaction Injection Molding. [Prior art] Polyurethane used in automobile parts such as bumpers is generally produced by RIM molding, in which two or more chemically active liquid components with relatively low viscosity that react with each other are molded into a sealed mold using a high-pressure injection machine. Although the mixture is injected into the mold to cause a chemical reaction and is then molded at the same time, it has the disadvantage of large dimensional changes due to heat and water absorption. Therefore, outer panel parts such as pumpers, which have become larger in recent years, and fenders, which are being made of resin to reduce body weight, are required to have dimensional stability close to that of steel. For this reason, R-RIM molded products that contain reinforcing materials such as glass fiber and mica are gaining attention, but the problem with R-RIM molded products is that when two coats of conventional RIM molded products are applied, On the surface of the top coat, fine irregularities (hereinafter referred to as dusty skin) due to the incorporation of the above-mentioned reinforcing agent occur, resulting in a deterioration in appearance. [Problems to be Solved by the Invention] The problem faced by the present invention is to provide a method for coating R-RIM molded products that does not cause the above-mentioned dusty skin. [Means for Solving the Problems] When painting an R-RIM molded product, the present invention uses an undercoat film or an intermediate coat that is applied directly to the R-RIM molded product as a raw material, and has a Young's modulus of 180 or more.
It is characterized by providing a coating film with a high Young's modulus of 4000Kg/cm ² and then applying a topcoat. The physical properties of polyurethanes vary greatly depending on the proportions and properties of the starting materials. The present inventors selected polyurethane paints from commercially available polyurethane paints that form coating films with different Young's moduli,
By using these paints and prototype paints with different mixing ratios of the main agent and curing agent of commercially available paints as undercoats or intermediate coats, the Young's modulus can be improved.
Those that can form a coating film of 180 to 400 kg/cm ² are
It has been found to be effective in eliminating flaky skin.
Examples of such paints include paints prepared by mixing 1 or more parts of isocyanate resin or melamine resin with 5 parts of polyester resin or acrylic resin. [Function] In general, RIM molded products are removed from the mold, washed to remove the mold release agent, coated with an undercoat (so-called primer coating), heated and dried to harden the coating, coated with a topcoat, and then subjected to further heat treatment. to harden the coating. Urethane paints are mainly used for the above-mentioned primers (conventional undercoat paints) because they are the same as the material, have good adhesion, and can be cured at low temperatures. The Young's modulus of the membrane is approximately 16Kg/cm ²
Because of this, the paint spreads easily and RIM
When applied to a molded product, the unevenness caused by the reinforcing material on the surface of the material during heating and drying of the topcoat film is directly transmitted to the topcoat surface, resulting in unevenness in the topcoat film. Young's modulus as a base coat or intermediate coat
By forming a coating film of 180 to 4000Kg/ ^cm2 ,
Since these paints do not spread easily, they do not transmit the unevenness of the reinforcing material to the surface of the top coat, and are effective in eliminating dusty skin. Furthermore, as described in the later examples, 180Kg/cm ²
There is no effect if it is less than 4000Kg/cm2, and the effect remains the same even if it exceeds 4000Kg/ ^cm2 . [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. Example 1 Add 10 parts of short glass fiber reinforcement to 90% polyurethane raw material consisting of polyol, organic isocyanate, chain extender, and catalyst, mix with a high-pressure injection machine, and inject into a flat plate type closed mold to form polyurethane. I got the item. After removing the mold release agent from the obtained molded product, it was cut into small pieces of 10 cm in length, 10 cm in width, and 0.3 cm in thickness. The 11 types of paints shown in Table 4 below selected from commercially available two-component urethane paints - XI were used with a film thickness of 20 to
It was applied to a thickness of 25 μm and baked at 100°C for 30 minutes.

【table】

[Table] Note: After the patent application for the present invention, paints and paints are respectively Kansai Paint/Solution.
Letkus 100T〓,〓Nippon B Chemical/
R〓206〓 and〓Nippon B Chemical/R〓
It was marketed as 278〓. Paint XI is a top coat paint.
Next, apply a topcoat white paint (polyester paint, manufactured by Nippon B Chemical Co., Ltd./Flexene 101), which is usually used for painting polyurethane molded products, to a film thickness of 3.
After coating from 0 to 35 μm, baking was performed at 120° C. for 40 minutes. For these test pieces, a gloss tester TRDC-2 manufactured by Toyota Chuobi Research Institute was used.
The gloss value was measured using a 2000-2000 and visual evaluation was performed. Separately, Young's modulus was measured under the following test conditions for a prepared coating film with a thickness of 50 to 60 μm obtained by pouring the above 11 types of paint onto a flat plate and peeling it off after curing. Shown in the table. Young’s modulus measurement conditions Measuring device…Tensilon UTM-2-SS-105D-B
(Manufactured by Toyo Baldwin Co., Ltd.) Sample length...10mm x 40mm Sample film thickness...50-60μm Tensile speed...50mm/min Measurement temperature...20℃

【table】

[Table] Note: ○: Smooth coating film △: Coating film that is not completely smooth ×: Coating film with scratchy skin From the above results, the material surface of the R-RIM molded product can be directly coated with a Young's modulus of 180 to 4000 Kg/cm ² . It has been found that by forming a coating film with a high Young's modulus, it is possible to eliminate the dusty skin from the top coating film. FIG. 1 shows a schematic cross-sectional view of such a two-coat film, where 1 shows the R-RIM material, 2 shows the high Young's modulus film, and 3 shows the top coat film. Example 2 The surface of the same test pieces (Nos. 12 to 22) as obtained in Example 1 was coated with a conventionally used urethane paint for brimers (Brexen 600, manufactured by Nippon B Chemical Co., Ltd.) to a thickness of 20 to 20 mm. Apply to 25μm,
After baking at 100° C. for 30 minutes, a two-coat coating similar to that in Example 1 was applied to obtain a three-coat coating as shown in FIG. A test similar to that of Example 1 was conducted on this three-coat film, and the results were summarized in the second example.
Shown in the table. Note that 4 indicates a primer coating film.

【table】

[Table] From the above results, it can be seen that there is no difference in the effect even if the primer coating film 4 is provided under the high Young's modulus coating film 2. Example 3 Example 2 except that the order of stacking the primer coating film 4 and the high Young's modulus coating film 2 in Example 2 was changed.
In the same manner as above, test pieces (No. 23 to No. 33) were coated with 3 coats, and the same tests as in Example 2 were conducted. The results are shown in Table 3.

〔Effect of the invention〕

As mentioned above, when painting R-RIM molded products, the Young's modulus between the top coat and the material is 180 to 4000.
By providing a coating film of Kg/cm ² , it is possible to eliminate the dusty skin of the top coat film and improve the appearance quality. Furthermore, if the above-mentioned high Young's modulus coating is provided in place of the conventional primer coating, a high-quality product can be obtained with the same two-coat coating as in the conventional method, which is advantageous in terms of manufacturing costs.

[Brief explanation of drawings]

FIG. 1 shows a schematic cross-sectional view of the coating film of Example 1, FIG. 2 shows a film-type cross-sectional view of the coating film of Example 2, and FIG. 3 shows a schematic cross-sectional view of the coating film of Example 3. FIG. 4 is a graph showing the relationship between the Young's modulus of the high Young's modulus coating film and the gloss value and visual evaluation of the top coating film. In the figure, 1...Material, 2...High Young's modulus coating, 3
...Top coat film, 4...Primer film.

Claims (1)

[Claims] 1. By providing a high Young's modulus coating film with a Young's modulus of 180 to 4000 Kg/cm ² as an undercoat film or intermediate coating film that is applied directly to the material, and then applying a top coat, it is possible to eliminate the dusty skin in the top coat film. A method for coating reinforced reaction injection molded products characterized by preventing the occurrence of such occurrence.