JPH045510B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a novel paint masking method,
More specifically, the present invention relates to a novel paint masking method that provides a beautiful appearance to the parting portions when color-coding automobiles and the like. Conventional technology In recent years, in the fields of automobiles, motorcycles, etc.
For example, the bumper part, the body line of the car,
Stripes, motorcycle tanks, motorcycle windshields, etc. are painted in multiple colors when a new vehicle is manufactured or when repaired, which is called color-coded painting. During color separation painting, it is important in order to increase product value that the colors do not mix together at the boundaries between colors, that is, at the separation areas, and that the lines at the separation areas are finished sharply. Therefore, conventionally, in color-coded painting, areas other than the target area to be painted are covered with masking tape.
Or cover with newspaper, film, etc., apply masking tape to the parting area, paint, and then,
The method used was to peel off masking tape, etc. Problems to be Solved by the Invention However, the method using masking tape has problems such as the difficulty of applying the masking tape directly to the eyelids, and the fact that the masking tape may partially float up after being applied and the paint may get into that area. For some reason, there was a problem where the parting section was not finished beautifully as expected. Therefore, the present inventor applied strippable paint to the object to be painted, dried the strippable paint, cut the resulting film with a suitable cutting tool, and then peeled off the unnecessary parts of the film. We conducted research from various angles on methods of painting the peeled areas. As a result, when using a knife as a cutting tool, the accuracy of the finish varies depending on the skill level, it is difficult to cut only the film, and the base material or substrate to be coated may be damaged, and the knife edge may wear out. It turned out that it is not very desirable that the blade becomes sharp and stops cutting quickly. Therefore, we researched a method using laser beams, which is commonly used as a cutting method in the past.
With a CO ₂ laser, the finish at the parting section is generally beautiful, but it is extremely difficult to reach the base material and selectively cut only the upper layer of film. When we conducted an experiment using a lower-power YAG laser, which is mainly used for optical communications, drilling, welding, etc., we were unable to cut not only the base material but also the desired film. Therefore,
The inventor studied the types of film and coated the film with a strippable paint containing 1 to 20% by weight (relative to resin) of carbon black. Only the film layer can be cut,
In addition, we have discovered a cutting method that allows beautiful parting parts to be obtained. However, it has been found that this method has limited tolerance, as the film may not be cut due to variations in the thickness of the strippable film layer, laser output, etc., or may even damage the underlying layer. Therefore, the present invention involves forming a lower layer of adhesive as an undercoat before applying a masking paint to the surface, and then applying a flexible top coat with film-forming ability on the upper layer. It has been discovered that a more beautiful parting part can be obtained, the permissible width of the laser beam is increased, and operational stability can be obtained. Means for Solving the Problems That is, the present invention provides a removable coating composition containing 1 to 20% by weight (based on resin) of carbon black as a layer in contact with the object to be coated,
Apply a paint with adhesive strength, then add 1 to 20% by weight of carbon black into the coating as a surface layer.
(resin content), is flexible, and has a film-forming ability, and forms a two-layered coating film that both contains carbon black.
After cutting only the surface coating film using a laser beam and peeling off the unwanted parts of the film along with the adhesive layer, the main coating is applied to the peeled area, and then the remaining removable coating film is peeled off. This is a new painting method that produces a beautiful finish on the parting section. This will be explained in detail below. Function The present invention is a coating method that uses a special coating film having a two-layer structure, and the substrate, which is the object to be coated, is coated with a surface paint for protection through an adhesive layer. Typical examples of underground materials include plastic molded products such as polypropylene, polyethylene, PVC resin, polystyrene, ABS, and polycarbonate, metal plates such as stainless steel plates, aluminum plates, and steel plates, coated plates such as paint steel plates, and decorative plywood. and is not particularly limited. Strippable paint is a paint that forms a two-layer structure, that is, a lower layer of adhesive and an upper layer of top coat, and is a removable coating used to temporarily protect the surface of the object being painted. Examples include water-based paints such as acrylic emulsion, vinyl acetate emulsion, and EVA, and solvent-based paints such as vinyl chloride sol, polyvinyl butyral, and vinyl acetate. In the present invention, an adhesive containing 1 to 20 wt % of carbon black is applied to the lower layer of the strippable paint to a dry film thickness of 10 to 100 μm. The adhesive layer, which is the lower layer, serves as a buffer to prevent the laser beam from reaching the substrate and has peeling properties, so even when there are variations in the intensity of the laser beam or operation, the laser beam can easily remove the substrate. prevent being hurt. This increases operational stability. Furthermore, it has been found that a more beautiful parting portion can be obtained. The adhesive is preferably one with weak adhesiveness, and for example, acrylic, vinyl acetate, or EVA-based aqueous emulsions can be used. Since it contains carbon black as mentioned above, laser light is absorbed and does not damage the underground. Therefore, the film thickness after drying needs to be 10μ or more, but 100μ is sufficient. In the present invention, a top coat having flexibility and film-forming ability is applied as a top coat via an adhesive layer. In the present invention, carbon black is contained in the top coat in an amount of 1 to 20 wt% based on the resin content. By incorporating carbon black, by YAG laser beam described later,
The paint film can be easily cut. carbon black
If the content exceeds 20 wt%, the film becomes hard and the carbon black becomes powdery and easily falls off from the film, which is not preferable. As a strippable paint, it is preferable that the upper layer film has flexibility so that the lower layer and the upper layer can be peeled off as one piece. Also, if the lower and upper layers have similar paint compositions and are painted together, the lower and upper layers will have better adhesion and will be easier to peel off as a single film. The adhesive and top coat may be applied by any of the usual methods, such as spraying, curtain flow coating, roll coating, brush coating, and dipping, and it is desirable to apply them as uniformly as possible. The film thickness of the strippable paint should be strong enough to be peeled off as a film, and there should be no holes or pinholes that would expose the underground. Generally, a dry film thickness of 20 to 300 microns is appropriate for the combined upper and lower layers. Films with a diameter of less than 20μ are generally weak and may tear easily and be difficult to remove when peeled, and are also prone to pinholes and small pores. If the dry film thickness exceeds 100μ, cracks and shrinkage occur during drying, making it difficult to obtain a film with a smooth surface. Also, 300 μm is sufficient for masking, and it is unnecessary to use a larger amount of material, and it takes time to dry, which is wasteful. The drying may be carried out by drying the adhesive layer and then drying the top coat, or by drying the upper and lower layers simultaneously after the upper and lower layers have been coated. The applied strippable paint may be dried to form a film, and the drying conditions may be determined depending on the type of strippable paint. Generally, the temperature is between room temperature and about 200°C. The present invention uses a laser as a means for cutting the film thus produced. As a laser, a laser oscillator with a wavelength ranging from the visible region to the near-infrared region is preferable. Has a wavelength in the red region
A CO ₂ gas laser is not preferred because it has a high possibility of cutting not only the strippable paint on the surface but also most of the underlying plastic and painted surfaces. Preferably a YAG laser (near infrared wavelength)
Alternatively, a dye laser (wavelength in the visible region) is preferable. Particularly preferred is a YAG laser. For YAG, the output is single mode and 1 to 20 Watts is sufficient. Dye lasers have a small output, but because they have wavelengths in the visible region, they can efficiently absorb energy into the paint film, and it is sufficient to have an output that can melt the strippable film. It is even more desirable to have a YAG laser equipped with a Q-switch, and a pulse frequency of 500 Hz to 30 KHz, preferably 1 to 20 KHz, cuts most beautifully.
The film can be cut beautifully even with a pulse frequency of over 30 KHz to 50 KHz, but if the focus of the laser beam is not moved quickly, it will often damage not only the film but also the plastic underground.
This is because many of the underground plastic molded products often have increased performance and contain carbon black, so this is not the case with plastics that do not contain carbon black, and the pulse oscillation number is over 30 KHz.
Even at 50KHz, beautiful cutouts can be created. If the pulse oscillation frequency is less than 500Hz, the film will not cut if the focus of the laser beam is moved too quickly. It's fine if you move the laser light slowly, but it's not suitable for creating a parting line for paint masking. In this way, the film is cut with a laser beam, unnecessary parts of the film are peeled off, and then the main coating is applied to those parts. The paint used for main painting is selected according to each application. When applying solvent-based paints, water-based (especially emulsion polymerized) strippable paints for paint masking are preferred. Conversely, when applying a water-based paint, the strippable paint for paint masking may be water-based or solvent-based. In any case, the strippable paint for paint masking is preferably one that is resistant to the paint applied over it, but it is not particularly important as long as it can function as a paint masking. When removing the film as a paint masking after applying the main coating, it is better to remove it after applying the main coating and before the paint has hardened, so that the parting area will be cleaner. After the main paint has dried, remove the film.
The parting part may become jagged. Especially when the paint is hard (hard enough to crack at room temperature)
is likely to lead to this result. This will be explained below using examples. The symbols used in Examples and Comparative Examples are as follows. PP...polypropylene, 2EHA...2 ethylhexyl acrylate, BA...butyl acrylate, AN...acrylonitrile, AA...acrylic acid, MMA...methyl methacrylate,
DVB...divinylbenzene, MAc...methacrylic acid, BMA...butyl methacrylate. Parts in the examples are parts by weight. Example 1 On a PP test panel (100 x 100 x 3 mm),
First, water-based acrylic emulsion (50 parts of 2EHA,
Composition of 40 parts BA, 7 parts AN, and 3 parts AA. ) was coated with an adhesive containing 3 parts of carbon black and dried. (Average film thickness 40-50μ). On top of this, a top coat of water-based acrylic emulsion (composition of 10 parts MMA, 55 parts BA, 33 parts AN, 2 parts AA) with 5 parts of carbon black added was applied, dried (average film thickness 50-70μ), 2
A layered film was created. This, YAG laser (manufactured by NEC, SL-114F)
The Q switch (SL-231B) was linked to change the oscillation conditions and disconnection was performed. The condition of the strippable paint after cutting,
We observed the degree of damage to the underground PP panels. (1) Painting conditions (a) Spray painting (b) Drying 80℃ x 5 minutes (for lower and upper layers each) (2) Laser cutting conditions (a) Laser NEC SL-144F (output 20W)
and SL-231B (b) Excitation lamp input 17A (average output 2.9W at modulation pulse 3KHz) (c) Mode single mode (d) Cutting speed 50mm/sec

【table】

[Table] Modulated pulses below 500Hz resulted in poor cutting, while those above 30KHz caused excessive cutting and damaged the underground panels. With a modulation pulse of 1KHz to 20KHz, I was able to cut the film beautifully without damaging the base material at all, and the line at the parting edge came off cleanly. Example 2 Example 1 was carried out in the same manner as in Example 1, except that the adhesive in the lower layer and the paint in the upper layer were changed as follows. Lower layer adhesive paint: 93 parts of 2EHA, 2 parts of DVB , 2 parts of MAc, 100 parts (resin content 50%) To the above emulsion, 5% apparent carbon black pigment (Dainichiseika, EP510) was added (addition of 3.8% resin content). Upper layer paint MMA 22 parts BA 50 parts AN 25 parts AA 3 parts 100 parts (resin content 50%) Carbon black pigment EP510 was added at an apparent 5% to the above emulsion (resin content 3.8% added).

【table】

[Table] Example 3 The same procedure as in Example 1 was carried out except that the lower layer adhesive and the upper layer paint were changed as follows. Lower layer adhesive paint BMA 42 parts BA 55 parts AA 3 parts Carbon black pigment 3 parts (post-addition) 103 parts (resin content 47.5%) Upper layer paint PVC sol 100 parts Carbon black pigment 3 parts 103 parts

[Table] In the modulated pulse range of 1 to 20KHz, it was possible to cut cleanly without damaging the underground. Comparative Example 1 Example 1 was carried out in the same manner as in Example 1, except that the lower adhesive layer was a clear layer in which no carbon black was mixed. In other words, lower layer adhesive paint 2EHA 50 parts BA 40 parts AN 7 parts AA 3 parts 100 parts (resin content 50%) Upper layer paint MMA 22 parts BA 50 parts AN 25 parts AA 3 parts Carbon black 5 parts (post addition) 105 parts (resin) minute 50%)

[Table] If carbon black is not included in the lower layer,
When the upper film was cut to some extent, the underground PP was also scratched by the laser. In other words, the adhesive layer does not serve as a buffer. The parting section is clean. Comparative Example 2 Example 1 was carried out in the same manner as in Example 1, except that the upper coating layer was a clear layer containing no carbon black. In other words, lower layer adhesive paint 2EHA 50 parts BA 40 parts AN 7 parts AA 3 parts Carbon black 3 parts (post-addition) 100 parts (resin content 50%) Upper layer paint MMA 22 parts BA 50 parts AN 25 parts AA 3 parts 105 parts (resin) minute 50%)

[Table] (1) Since the upper layer film cannot be cut at all, the film cannot be peeled off along the cutting line, and the entire film is 1
It remains connected as a single piece of film. (2) The lower layer was cut at a modulation pulse of 3 to 5 KHz, but re-fused at 20 KHz (however, the carbon disappeared and was recognized as a transparent streak.) (3) The underlying PP was separated from the upper and lower layers. When I looked through the combined adhesive film, I noticed that the base was damaged where the carbon content had disappeared. That is, if the upper film layer could no longer block the laser light, the base would be damaged. Moreover, even though the film layer is refused on the high modulation pulse side,
The base was damaged. Comparative Example 3 The same procedure as in Example 1 was carried out, except that the lower layer was coated with a paint having the same film forming ability and film strength as the upper layer paint. That is, lower layer paint: MMA 22 parts BA 50 parts AN 25 parts AA 3 parts Carbon Black 5 parts (post-added) 105 parts (resin content 50%) Upper layer paint SP 7032 (Mitsui Toatsu) 100 parts Carbon Black (Dainichiseika) 3 Part 103

[Table] (1) Even if the upper layer film breaks, if the lower layer film does not break, it will not be possible to peel it off, and the film will have poor peeling properties. (2) In areas where both the upper and lower layers can be cut, the base is damaged by the laser beam, and the area that can be cut without damaging the underground is narrow. Comparative Example 4 A water-based acrylic strippable paint (Mitsui Toatsu SP7032) with an apparent addition of 5% carbon black pigment (Dainichiseika EP510) was applied to the same test panel as in Example 1 and dried (average film thickness
60-80μ). Under the same conditions as Example 1, YAG
Cut with a laser. (1) Coating conditions (a) Spray coating (b) Drying 80℃ x 5 minutes (c) Average film thickness 60-80μ (2) Laser cutting conditions Same as Example 1

[Table] (1) The range that can be cut without damaging the substrate at all is limited to a modulation pulse number of 1 to 5KHz, and its tolerance is narrow. Effects of the Invention As detailed above, according to the method of the present invention, masking was easy and it was possible to stably perform main coating with a beautiful finish on the parting portion without damaging the base.

Claims (1)

[Claims] 1 In a removable coating composition, 1 to 10% of carbon black is added to the coating film as a layer in contact with the object to be coated.
A coating containing 20% by weight (relative to resin) and adhesive strength is applied, and then 1 to 20% by weight (relative to resin) of carbon black is added to the coating film as a surface layer to improve flexibility. A coating film with carbon black and a film-forming ability is applied to form a two-layer coating film, and only the surface coating film is cut using a laser beam. A new coating method that produces a beautiful finish on the parting part, which is characterized by peeling off the unnecessary part of the film cut with the adhesive layer, applying the main coating to the peeled part, and then peeling off the remaining removable coating film. .