JPS5933035B2 - How to paint a car body - Google Patents

Description

[Detailed Description of the Invention] Currently, the most commonly used coating method for automobile bodies is to use an automatic machine (air spray gun, electrostatic coating machine, etc.) in a fixed or moving manner. The method used is to paint the relatively flat parts of the exterior of the car body using a machine that sprays the surface of the vehicle, and then manually paints the parts that cannot be painted by the automatic machine (hereinafter referred to as hand-blown correction painting). .

On the other hand, this method is often used for topcoating, but with this method, relatively flat areas that are coated with an automatic machine can be coated with the required thickness uniformly, but it is possible to apply the required film thickness manually. The areas to be sprayed with correction paint have complex shapes and many edges, making it easy for paint to escape and sag.

Therefore, the film thickness tends to be thin and non-uniform. In this method of painting the body of an automobile, the middle paint is applied with a single color paint such as gray or rust red using an automatic machine or by hand-blown correction, but in this case, the top paint completely matches the color of the middle paint. It is necessary to paint until it is covered.

As mentioned above, there is no particular problem with relatively flat areas that can be coated with an automatic machine as they can be coated sufficiently, but areas that are hand-blown with correction coating have complex shapes and shadow areas cannot be coated sufficiently, so it is necessary to apply intermediate coats. It is not possible to hide the color of the material, causing problems with the gradation. Also, if you try to paint this part sufficiently, other parts will become thicker than necessary, causing problems such as sagging. Therefore, when it comes to designing a top coat that does not cause problems such as sagging and sagging, there are restrictions on the pigments that can be used, making it difficult to obtain a desired color that meets market needs. In addition, in order to improve the hiding power with the same pigment, it is necessary to increase the pigment/resin ratio, but this tends to cause a decrease in quality such as appearance (gloss, etc.) and durability, and also increases the pigment content. This leads to an increase in paint costs. As a way to cover up these shortcomings, some luxury cars use an intermediate coating device for the purpose of improving the appearance quality. There is a method of applying a top coat, and it is possible to use this first top coat as an intermediate coat, but in this case it is necessary to install an automatic machine with multiple colors and a color changing device, which requires a large amount of equipment cost. It takes. Moreover, the paint also uses more expensive pigments than those for gray or rust-red colors, resulting in an increase in cost. The present invention aims to eliminate these drawbacks. In other words, in the intermediate paint coating method, automatic machines paint all car bodies with a single color paint made of oil-free alkyd melamine resin with pigments, while hand-blown correction paint coats each car body with the oil-free alkyd melamine resin. Paint with a pigment that is the same or almost the same color as the top coat. In other words, the middle paint is made of oil-free alkyd melamine resin with pigments, and is the same or almost the same color as the top coat.The automatic machine paints all cars with one of the colors, and the hand-blown correction coat is matched to the color of the top coat. and paint. By using this method, there is no need for an expensive color changing device in an automatic machine, and areas that are likely to suffer from scratching when applying the top coat are painted with the same or almost the same color as the top coat during the intermediate coating process. Even if the top coat is not applied sufficiently, problems such as sagging will not occur and problems such as sagging will be eliminated.

In the present invention, an oil-free alkyd melamine resin is used for the intermediate coating material, but if oil-modified alkyd melamine resins or epoxy-modified alkyd melamine resins, which are currently commonly used, are used instead, the coating film formed with these resins will be has poor weather resistance, so if the top coat is thin and does not sufficiently block sunlight (mainly ultraviolet rays), the sunlight that reaches the middle coat will cause the film to deteriorate, causing damage between the middle coat and top coat. The adhesion strength decreases, causing serious defects such as blistering (paint blistering) and delamination.

On the other hand, since the oil-free alkyd melamine resin has excellent weather resistance, it will not cause serious defects even if the top coat is not coated to the point where it blocks sunlight, that is, even if it is coated thinly. do not have. Furthermore, since hand-blown correction coating is applied with a paint that is the same or almost the same color as the top coat, it is also possible to paint the inside of the vehicle body, such as the engine compartment and trunk compartment, in the intermediate coating process.

That is, although it has conventionally been customary to paint the interior of the vehicle body with a top coat, there is nothing wrong with this even if a middle coat is used. However, the mist of the top coat that circulates during the top coat appears in spots and the appearance is significantly inferior, lowering the product value. Further, in order to prevent the adhesion of this paint mist, masking may be applied before applying the top coat, but for reasons such as requiring a large amount of time, the top paint has been applied during the top coat. Therefore, if the middle paint is the same or almost the same color as the top paint, the paint mist that has entered this area during the top coat will be hardly noticeable and will not reduce the product value. If the interior parts of the car body can be painted during the intermediate coating process, it will be easier to balance the intermediate coating process and the top coating process, and the process organization (personnel allocation, length of equipment such as spray booths, etc.) will be easier. Next, examples of oil-free alkyd melamine resin paints used in the present invention will be described.

Oil-free alkyd resin varnish is synthesized from polyhydric alcohol components (neopentyl alcohol, trimethylolpropane, propylene glycol, pentaerythritol, etc.) and acid components (isophthalic acid, terephthalic acid, phthalic anhydride, adipic acid, etc.). Acid value 15 or less, hydroxyl value 100-200, number average molecular weight 1500-500
Use 0. Film thickness of top coat when using the above oil-free alkyd melamine resin intermediate coating (hereinafter referred to as A paint) and the currently commonly used oil-modified alkyd melamine resin intermediate coat (hereinafter referred to as B paint). Experimental data on differences in coating film performance due to differences, or in other words, differences in sunlight transmittance, are shown below.

Claims (1)

[Claims] 1 In a system that continuously paints automobile bodies, an automatic machine applies a base coat or intermediate paint to the exterior of the car body, and areas that cannot be painted by the automatic machine are hand-sprayed to correct the coating. All car bodies are painted with a single color paint consisting of a melamine resin with a pigment, and for the hand-blown correction coating, the oil-free alkyd melamine resin is coated with a pigment that is the same or almost the same color as the top coat of each car body. An automobile body painting method characterized by painting with a coated paint.