JP4124177B2 - Painting method - Google Patents

Description

  The present invention relates to a coating method that is preferably used when, for example, an aqueous topcoat base paint and a clear paint are applied wet-on-wet.

  The painting system of an automobile body is generally composed of an electrodeposition coating as an undercoat, an intermediate coating, and a 3-coat 3-bake of a top coat. Among these, in the top coating of a metallic paint color, a base paint containing a bright pigment and a transparent clear paint containing no pigment are applied wet-on-wet and baked at the same time (Patent Document 1).

  When applying top-coat base paint and clear paint in wet-on-wet, the interval for evaporating the solvent contained in the top-coat base film between applying the top-coat base paint and applying the clear paint ( Hereinafter referred to as flash-off). When this flash-off is short, the solvent in the applied top coat base film evaporates in the drying furnace after the clear paint is applied, and this becomes a crater-like coating defect called “WAKI”.

  By the way, in the case of a conventional organic solvent-based topcoat base paint, a low boiling point solvent was used, so a flash-off time of about 1 to 2 minutes was sufficient. A flash-off time or additional flash-off drying oven is required.

However, since this flash-off is a process provided in one topcoat booth, if the flashoff of the water-based topcoat base paint is lengthened, it is necessary to extend the topcoat booth by that amount. There is a problem of eroding other processes.
Japanese Patent Laid-Open No. 11-57608

An object of this invention is to provide the coating method which can perform flash-off of the water-system topcoat base coating material appropriately.
In order to achieve the above-mentioned object, the coating method of the present invention applies a water-based topcoat base paint and a clear paint to a plurality of objects to be continuously conveyed by wet-on-wet and then baked and cured them simultaneously. In a coating method in which an organic solvent-based topcoat base paint and a clear paint are applied by wet-on-wet and then simultaneously baked and cured, the clear paint is coated with 2-butoxyethanol. It is characterized by adding.

In the present invention, an overcoat base paint that is a water- based paint is applied, and a clear paint is applied wet-on-wet. At this time, the non-evaporated moisture is contained in the coating film by the top coating base paint, but it is absorbed by 2-butoxyethanol contained in the coating film by the clear coating applied thereon. That is, 2-butoxyethanol absorbs and disperses the moisture to be evaporated from the topcoat base coating into the clear coating. The base top coating film and the clear coating film when operated simultaneously bake hardening, since the water dispersed in the clear coating film is gradually evaporated at the same time can prevent the occurrence of popping defects, base top coating material and clear The flash-off between the paints can be omitted or shortened.
In particular, the coating method according to the present invention promotes water evaporation of the water-based topcoat base film by adding a hydrophilic solvent to the clear paint, so that the equipment of the topcoat booth is shared with the case of using the organic solvent base topcoat base paint. can do. In other words, even if a body that coats a water-based topcoat base paint and a body that coats an organic solvent-based topcoat base paint flow in the same topcoat booth, it can be handled without remodeling or adding equipment. it can.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a process diagram showing an embodiment of a coating method according to the present invention, and FIG. 2 is a plan view showing an embodiment of a topcoat booth to which the coating method according to the present invention is applied. In the following, the term “paint” refers to the state before painting on the object to be coated, and what is formed by painting this paint on the object to be coated is called “coating film”, especially before baking and curing. The coating film is called an uncured coating film, and the coating film after baking and curing is called a cured coating film.

  The coating method of this embodiment is a method of forming a top coat base film and a clear coat film as a top coat film, for example, on a steel sheet formed with an electrodeposition coat and an intermediate coat as an undercoat. It is. In FIG. 1, the undercoat film and the intermediate coat film are denoted by reference numeral 1 and are referred to as a base or simply an object to be coated. Either one of the electrodeposition coating film and the intermediate coating film may be omitted.

  The coating method according to the present embodiment is a so-called two-coat one-bake type top coat system in which a top coat base paint and a clear paint are applied by wet-on-wet and then baked and cured at the same time. In particular, the topcoat base paint is not an organic solvent-based paint but a water-based paint, whereas the clear paint is an organic solvent-based paint. The clear paint may be a water-based paint.

  Water-based paints are superior to organic solvent-based paints in that the waste water treatment of paints is easy and the impact on the environment is extremely small. In particular, the topcoat base paint has a solvent dilution ratio of about 50% (clear paint and topcoat solid paint are 20 to 30%), so the effect when water-based paint is used is great. Is often adopted. However, in the 2-coat 1-bake type top coat system, it is necessary to increase the solid content of the top coat base film to 80% or more immediately before the clear paint is applied. Since the water has a high boiling point, it is necessary to devise a flash-off process. This point will be described later.

  In the coating method of this embodiment, as shown in FIG. 1, it has the process A2 which applies a water-based topcoat base paint, and in this process A2, the water-based topcoat base paint is applied to the surface of the base 1, and the topcoat base coating film 2 is formed. Form. The film thickness of the top coat base coating film 2 is, for example, 15 to 20 μm.

  In the painting booth 12 shown in FIG. 2, the top coating base painting process A2 is provided following the preparation process A1 provided at the entrance of the painting booth 12, and the body 11 is mainly processed by the painting robot 13 or hand-blow painting. It comprises a process A21 in which the top coat base paint is applied to the inner plate and a process A22 in which the top coat base paint is applied mainly to the outer plate of the body 11 by the coating machine 14. The preparation process A1 is a process for wiping and cleaning dust and the like adhering to the body 11.

  Next, the solvent contained in the uncured topcoat base coating film 2, that is, moisture is naturally evaporated. This is the flash-off step A3 shown in FIG. 1, but in the present invention, this flash-off step can be omitted. Further, the flash-off process A3 according to the present embodiment is born from securing space on equipment such as an automatic machine and a robot formed between the top coat base coating process A2 and the clear coating process A4 as shown in FIG. It can also be done with inevitable intervals.

  After the flash-off step A3, there is a clear coating step A4. In this step A4, the clear coating is applied to the surface of the uncured topcoat base coating 2 to form the clear coating 3. The film thickness of the clear coating film 3 is, for example, 30 to 45 μm.

  Explaining in the painting booth 12 shown in FIG. 2, this clear painting process A4 is provided following the above-described flash-off process A3, and the clear paint is applied mainly to the inner plate of the body 11 by the painting robot 15 or the hand spray painting. Step A41, a step A42 in which a clear paint is mainly applied to the outer plate of the body 11 by the coating machine 16, and a finishing step A43 in which finish coating is performed. This finishing step A43 may or may not be appropriately performed depending on the object to be coated and conditions.

  Particularly in this embodiment, 2-butoxyethanol (butyl cellosolve) as a hydrophilic solvent is added to the organic solvent-based clear coating. 2-Butoxyethanol is a solvent that is soluble in water and organic solvents and has a boiling point as high as 170 ° C. To get. When this 2-butoxyethanol is added to the clear paint, it is soluble in water, so that the moisture to be evaporated from the uncured top coat base film 2 is absorbed and dispersed in the clear paint film 3. Present. Therefore, even if the top coat base coating 2 contains a large amount of water, the 2-butoxyethanol contained in the clear coat 3 takes it into the clear coat 3 and disperses it. The occurrence of armpits from can be prevented.

  The amount of 2-butoxyethanol added is desirably 2 to 15% by weight of the solvent contained in the clear paint. If the amount is less than this, the moisture absorption / dispersion action is insufficient, and the surface from the top coat base film 2 is generated. On the other hand, if the amount is larger than this, the evaporation rate of the entire solvent component decreases, and there is a risk of problems such as sagging. A hydrophilic solvent such as 2-butoxyethanol can be added to the coating stock solution, or can be added when the coating stock solution is diluted with a diluted thinner.

  After applying the clear paint, the previously applied top coat base film 2 and clear paint film 3 are baked and cured simultaneously. The bake curing temperature is, for example, 140 ° C. for 20 minutes.

  In the layout shown in FIG. 2, a setting chamber 17 is provided at the exit of the top coat booth 12, and the body 11 that has finished the clear coating passes through the setting chamber 17 so that the solvent is pre-evaporated from the clear coating film. Become. The setting process B takes several minutes. Then, a top coat drying furnace 18 is provided following the setting chamber 17, and this top coat drying furnace 18 is the top coat drying process C.

  Next, the operation of this example will be described with reference to the right diagram of FIG.

  First, when the top coat base coat 2 is formed on the surface of the base 1, a part of the water contained in the top coat base coat 2 is evaporated in the flash-off step A3. This is indicated by the arrow X1 in FIG. Water other than this remains in the top coat base coating film 2.

  When the clear coating 3 is formed on this surface, moisture X2 to be evaporated from the top coat base coating 2 is absorbed into the clear coating 3 by the 2-butoxyethanol which is a hydrophilic solvent contained in the clear coating 3 And disperse. When the top coat base film 2 and the clear coat film 3 are baked at the same time, the moisture X3 absorbed from the top coat base coat 2 in addition to the organic solvent contained in the clear coat film 3 also evaporates out of the coat film. become.

  In this way, the moisture contained in the uncured topcoat base coating 2 is absorbed by the clear coating 3 immediately above it and further gradually evaporates from the clear coating 3 to the outside. It does not evaporate after being cured, and the occurrence of cracking problems is prevented.

  In addition, in the coating method of this example, the water evaporation of the water-based topcoat base coating film is promoted by adding a hydrophilic solvent to the clear paint, so that the equipment of the topcoat booth 12 is shared with the case of using the organic solvent base topcoat base paint. can do. In other words, even if the body 11 that coats the water-based topcoat base paint and the body 11 that coats the organic solvent-based topcoat base paint flow in the same topcoat booth 12, it can be handled without modifying or adding equipment. can do.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  Hereinafter, the present invention will be described more specifically.

Example 1
An electrodeposition coating film having a film thickness of 15 μm was formed and baked on a steel sheet having a thickness of 0.8 mm, and an intermediate coating film having a film thickness of 25 μm formed thereon and baked thereon was used as a coating original plate.

  In a painting booth at a temperature of 23 ° C. and a humidity of 73% RH, a water-based topcoat base paint (Aqua BC-3 BKL0 manufactured by Nippon Oil & Fats Co., Ltd.) is applied to the surface of this coating original plate using a bell-type coating machine. The coating was performed in two stages at intervals of 3 minutes under the conditions of 000 rpm, shaping air 600 Nl / min, discharge rate 150 cc / min, applied voltage -60 kV, gun distance 20 cm.

  After flash-off for 3 minutes at room temperature in the painting booth, 5% of the solvent content of the organic solvent-based clear paint (Nippon Yushi Co., Ltd. Bellcoat No. 7300) was replaced with 2-butoxyethanol. Was applied in a single stage under the conditions of 25,000 rpm, shaping air 300 Nl / min, discharge rate 200 cc / min, applied voltage -80 kV, gun distance 20 cm.

  This was baked at 140 ° C. for 20 minutes. When the obtained sample was visually observed to evaluate the presence or absence of the occurrence of the armpit, no armpit was found.

Comparative Example 1
In Example 1, the sample was prepared under the same conditions as Example 1 except that the solvent component of the clear coating did not contain a hydrophilic solvent such as 2-butoxyethanol.

Reference example 1
The same clear paint as in Comparative Example 1 was used, but the top coat base coating was heated at 80 ° C. for 3 minutes between the application of the top coat and the clear paint. When the sample was prepared under the same conditions as in Comparative Example 1 except for the above, no occurrence of cracks was observed.

  As described above, when the clear paint to which a hydrophilic solvent is added as in Example 1 is applied on the water-based topcoat base coating, the occurrence of cracks can be prevented without preheating in the flash-off process.

It is process drawing which shows embodiment of the coating method which concerns on this invention. It is a top view which shows embodiment of the top coat booth to which the coating method which concerns on this invention is applied.

Explanation of symbols

A ... Top coating process A1 ... Preparatory process A2 ... Top coating base coating process A3 ... Flash-off process A4 ... Clear coating process B ... Setting process C ... Top coating drying process 1 ... Intermediate coating film (coating material)
2 ... top coat base film 3 ... clear paint film 11 ... body 12 ... top coat booths 13 and 15 ... painting robots 14 and 16 ... painting machines

Claims (2)

For multiple coated article to be conveyed continuously, and specifications for baking and curing them simultaneously after the water-based base top coating material and an organic solvent-based clear paint was painted in a wet-on-wet manner, an organic solvent-based base top coating material and organic In the painting method in which the solvent-based clear paint is applied in wet-on-wet and then the specifications for baking and curing these at the same time are performed in any order.
A coating method comprising adding 2-butoxyethanol to the organic solvent-based clear paint. 2. The coating method according to claim 1, wherein the 2-butoxyethanol is contained in an amount of 2 to 15 wt% with respect to the solvent component of the organic solvent-based clear paint.

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