JP2002316086A - Coating method with water based coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method, by which an inner plate part is finished with a water based coating material in an intermediate coating process without generating a vapor wash phenomenon. SOLUTION: The water based coating material is applied on a material to be coated so that the relation among a solid portion NV (wt.%) in a wet coating film, water content WT (wt.%) in the wet coating material and a film thickness (t) (μm) of a based coating film is NV/(WT.t)>=0.10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method for spraying a coating on an object such as an automobile body, and more particularly to a coating method suitable for spraying a water-based coating on an inner plate portion of an automobile body.

[0002]

2. Description of the Related Art In general, the coating of an automobile body is mainly performed with an undercoating for the purpose of rust prevention, an intermediate coating for the purpose of rustproofing and improvement of the finish of the topcoating, and mainly for the finish of the appearance. 3 coats 3 with top coat
It is performed in a bake method. Of these, a paint having a desired color is used for the top coat, which is applied to a portion that is exposed when the vehicle is completed. Conventionally, not only the outer plate but also the inner plate around the engine room, the door opening, the back door opening, the trunk opening, and the like have been coated with the top coating.

However, when an overcoat is applied to such an inner plate in the overcoat process, the engine hood, door, back door, trunk lid, etc. must be opened and closed each time. become. Further, when such an inner plate portion and an outer plate portion subsequent to the inner plate portion are coated by wet-on-wet in the overcoating step, there is a problem that paint dust when the inner plate portion is coated lowers the finished skin of the overcoat. Furthermore, the inner plate does not need to have the weather resistance required for the outer plate.

[0004] For this reason, an inner coating portion such as an engine room, around a door, around a back door, etc. has an intermediate coating having the same system color as the outer plate in the intermediate coating process (hereinafter also referred to as an inner coating). Is applied with an intermediate gray paint and wet-on-wet (for example, see
2-63233).

[0005]

However, when the inner plate such as around the opening of the back door is coated with a water-based inner plate color paint and then put into an intermediate coating drying oven with the back door closed, the inner plate is dried. When the color paint is baked, the evaporated water fills the narrow part of the opening of the back door without diffusing into the furnace, and this water vapor causes the inner plate color paint to be washed away, so-called vapor wash.
A phenomenon occurs. That is, there has been a problem that the undercoat film is exposed at the portion where the inner plate color paint is applied due to the vapor wash phenomenon.

However, Japanese Unexamined Patent Publication (Kokai) No. 2-115081 discloses a two-coat, one-bake topcoat coating method using a water-based paint. Is removed, and a clear paint is applied thereon.However, since the inner plate portion is also coated with the water-based outer plate color paint, the lid is removed as in the case of using the solvent-based paint described above. The load on the overcoating step, such as opening and closing, is large. The publication also discloses that the inner plate portion is finished with an inner plate color paint in an intermediate coating process, but this inner plate color paint is a solvent-based paint and not a water-based paint.

The present invention has been made in view of such problems of the prior art. In particular, it is possible to finish an inner plate portion by an intermediate coating process using a water-based paint without causing a vapor wash phenomenon. The purpose is to provide a coating method that can be performed.

[0008]

(1) In order to achieve the above object, according to the present invention, a solid content NV of a wet coating film is provided.
(Wt%), the moisture WT (wt%) of the wet coating and the thickness t (μm) of the baked coating are NV / (WT
(T) A coating method characterized by applying a water-based paint to an object to be coated such that ≧ 0.10 is provided.

The present inventor pays attention to the solid content of the wet coating film, the moisture content of the wet coating film, and the thickness of the baked coating film, and if these are coated so as to have a predetermined relationship, there is no vapor wash phenomenon. It has been found that a coating film having a suitable appearance finish can be obtained. That is, the larger the solid content of the wet coating film, the smaller the moisture of the wet coating film, the thinner the thickness of the baked coating film, the better the conditions for suppressing the vapor wash phenomenon. t cannot be reduced to a certain value or less depending on the quality of an object to be coated, and a certain film thickness is required. Therefore, the ratio NV / WT between the solid content and the moisture of the wet coating film is constant. With the above, the water-based paint can be applied to narrow portions without causing the vapor wash phenomenon.

(2) In the above invention, although not particularly limited, preferably, the paint is applied to a paint for coating an inner plate of an automobile body, more preferably to a narrow inner plate portion of an automobile body, more preferably an intermediate coat. It is applied in the process.

The coating method of the present invention can be applied to all parts as long as it is a water-based coating, and can be applied in any of the intermediate coating step and the top coating step. When applied to the inner plate portion of the body, especially the narrow inner plate portion, the vapor wash phenomenon can be prevented, and high quality coating can be obtained at low cost. Further, by applying the paint for coating the inner plate in the intermediate coating step, the load of the top coating step can be reduced, and the productivity is improved.

(3) Although not particularly limited in the above invention, the solids content of the wet coating film is controlled by the coating conditions of a coating machine that sprays the coating material on the object to be coated, in addition to the composition or preparation conditions of the coating material. Can be.

The coating conditions in this case include the particle size of the coating particles sprayed from the coating machine, more specifically, when the coating machine is a rotary atomizing type coating machine, the number of rotations of a bell cup, the coating machine, Is an air atomizing type coating machine, and is the atomizing air pressure and / or the pattern air pressure.

When the particle size of the coating particles sprayed from the coating machine is reduced, the solid content of the wet coating film can be increased,
As for the coating conditions of the coating machine, increasing the number of rotations of the bell cup of the rotary atomizing type coating machine or increasing the atomizing air pressure and / or the pattern air pressure of the air atomizing type coating machine will increase the wet coating. Solid content can be increased.

As described above, in the relational expression of NV / (WT · t) ≧ 0.10, which is the coating condition of the present invention, the minimum thickness is determined from the relation with the coating quality. It cannot be thinned below the value. The moisture WT of the wet coating film is a value uniquely determined from the solid content NV of the wet coating film and the coating composition. Therefore, if the solid content NV of the wet coating film is increased, coating satisfying the above relational expression can be performed.

[0016]

According to the first aspect of the present invention, it is possible to obtain a coating film having good finish without a vapor wash phenomenon.

In addition to the above, according to the second and third aspects of the present invention, a coating film having a good finish without a vapor wash phenomenon can be obtained even in a part where the vapor wash phenomenon is particularly likely to occur. According to the fourth aspect of the present invention, the load of the overcoating step can be reduced, and the productivity is improved.

According to the invention of claims 5 to 8,
Since the solid content of the wet coating is controlled by the coating conditions of the coating machine, it is difficult to increase the solid content of the wet coating due to the small solid content of the coating and the solvent that hardly evaporates the moisture. Even if it is difficult to increase the solid content of the film, the coating satisfying the above relational expression according to the present invention can be performed.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a process diagram of the entire coating process showing an embodiment of the coating method of the present invention. The white body assembled in the vehicle body process is carried into the undercoat coating process 1. In the undercoating process 1, after the oil and iron powder attached to the white body are washed, the surface is adjusted and a chemical conversion treatment is performed, and further, the electrodeposition coating forming the undercoating film is performed. The body coated with the electrodeposition paint is carried into an electrodeposition drying oven, and an electrodeposition coating film is formed on the inner and outer plates and the bag structure of the body.

The body on which the electrodeposition coating film is formed is sent to a sealing step and a step of applying an anti-chipping material (not shown), and the steel sheet joints and the edges of the steel sheet are treated with chloride for the purpose of rust prevention or sealing. A vinyl resin-based sealing material is applied. In the step of applying a chipping-resistant material, a vinyl chloride resin-based chipping-resistant material is applied to a tire house or a floor. The sealing material and the chipping-resistant material are cured in a dedicated drying furnace or an intermediate coating drying furnace 5 described below.

The body on which the sealing material and the chipping-resistant material are applied and the inner and outer plates have the electrodeposited coating film formed thereon is then carried into the intermediate coating booth 2. In the intermediate coating booth 2, first, an inner panel coating material corresponding to the outer panel color of the vehicle is applied to the inner panel of the body (inner panel intermediate coating 3), and the outer panel is wet-on-wet. Is applied with an intermediate coating (external coating 4).

Here, the inner plate portion of the body refers to the inside of the engine room (body side) and the back of the engine hood, around the door opening (body side and door side), around the back door opening (body side and back door side). ), The inside of the trunk room (on the body side), the back of the trunk lid, and the like, which are appropriately selected according to the vehicle type and the like. When applying the paint for coating the inner plate to the inner plate portion, lids such as a hood, a door, a back door, and a trunk lid are opened, and the lids are closed after the application.

FIGS. 2A and 2B are a perspective view of an automobile body V and a sectional view taken along line BB for explaining an example of an automobile inner plate. As shown in FIG. 3B, the application range of the paint for coating the inner plate around the opening of the back door BD is the rain gutter groove 11 on the body side 10 of the back door opening and the outer periphery of the back surface of the back door BD. It becomes the part 12.

[0024] Such an inner plate portion is (1) because it is less likely to receive direct sunlight in a completed vehicle state, the use of an outer plate paint having excellent weather resistance results in excessive quality and excessive cost. (2) Strictly Even if the same paint is not used, there is no sense of incongruity in the difference in hue from the outer panel, etc. (3) When the outer panel color paint is applied wet-on-wet in the top coat booth, paint dust when the inner panel is applied is reduced Adheres to the outer plate,
In this example, the intermediate coating booth 2 has a large load on the inner coating portion and the outer panel portion in the upper coating booth, which causes a large load on the upper coating process. In addition, the paint for the inner plate is to be applied wet-on-wet with the intermediate paint.

In particular, a water-based paint is used as the paint for coating the inner plate and the intermediate paint in this embodiment. After applying the water-based inner plate coating paint and the water-based intermediate coating paint to the inner and outer plate portions of the body in a wet-on-wet manner, the body is carried into the intermediate coating drying furnace 5, where the inner-plate coating paint and the intermediate coating are applied. Bake the paint.

At this time, when applying the coating material for coating the inner plate to the inner plate portion, the solid content of the wet coating film is NV (% by weight), the moisture of the wet coating film is WT (% by weight), and Coating is performed so that these relationships when the film thickness is t (μm) satisfy NV / (WT · t) ≧ 0.10. Specifically, in addition to the material side such as the paint composition of the paint for the inner plate coating and the preparation conditions, it is difficult to increase the solid content of the wet coating film because the solid content of the paint is small, and it is difficult to evaporate the moisture. For paints that contain a solvent and make it difficult to increase the solids content of the wet coating,
The coating satisfying the above relational expression can be performed by considering the coating conditions by the coating machine.

For example, when the particle size of the coating particles sprayed from the coating machine becomes small, the solid content of the wet coating film becomes large. Therefore, when the coating material for the inner plate coating is applied using a rotary atomizing type coating machine. It is advisable to increase the rotation speed of the bell cup.
When the paint for inner plate coating is applied using an air atomizing type coating machine, it is preferable to increase the atomizing air pressure and the pattern air pressure of the coating gun. According to the experiment of the inventor, it was confirmed that when the rotation speed of the bell cup was increased by 10,000 rpm, the solid content of the wet coating film increased by several weight%.

By applying the paint for coating the inner plate so as to satisfy this relational expression, the solid content in the wet coating film increases and the water content decreases. Therefore, since the amount of water that evaporates in the intermediate coating drying furnace 5 is reduced, when the back door BD is closed, the surroundings are substantially closed and the evaporated water vapor is removed, as in the case of the back door opening shown in FIG. Even in an environment where diffusion into the intermediate coating drying furnace is difficult (see the space S in FIG. 2), the occurrence of the vapor wash phenomenon can be suppressed.

After passing through the drying oven 5, the intermediate coating film is formed on the outer plate portion and the coating film for coating the inner plate is formed on the inner plate portion. In the case of a metallic outer panel color, the base paint (base paint 7) and the clear paint (clear paint 8) are applied wet-on-wet. In the case of a solid outer panel color, a solid paint is applied in the step of clear coating 8. In the coating method of this example, as described above, since the inner plate portion of the body has already been formed with the inner plate coating film having a paint color similar to the outer plate color, the base paint, the clear paint, and the solid paint are used. Need only be applied to the outer plate. Therefore, the work load in the overcoating step is reduced particularly for the metallic outer panel color. In addition, even in the case of the solid outer panel color, the coating operation on the inner panel can be leveled between the overcoating step and the intermediate coating step.

Finally, the body to which the top coat has been applied is conveyed to a top coat drying furnace 9 where it is baked to form a top coat.

Next, the coating method of the present invention will be described with reference to a more specific example. However, the numerical values and the like in the following examples do not limit the present invention at all.

Fifteen white bodies were continuously flown in the same undercoating process, and were subjected to electrodeposition coating under the same conditions. A water-based inner plate coating material (Nippon Yushi BASF Coatings Co., Ltd., Aqua GX Sealer color) was applied under various conditions around the back door openings of the 15 bodies on which the electrodeposition coating film was formed. Then, with the back door closed, it was put into an intermediate coating drying oven and baked while being kept at 140 ° C. for 20 minutes.

The coating quality around the opening of the back door on which the coating film for inner plate coating was formed was visually evaluated, and the presence or absence of the vapor wash phenomenon was evaluated by the symbol “○”.
"」 "Is observed slightly," △ "is observed," △ ~ "
"X" was clearly observed, and "X" was evaluated on a five-point scale that vapor wash was remarkable.

The weight of the coating film in the wet state was measured during the coating of the coating material for the inner plate, and the weight of the coating film after baking was measured. Solid content (% by weight). The water content (% by weight) was determined by calculation from the solid content of the wet coating film determined above and the composition ratio of the coating material for coating the inner plate. Further, the thickness of the dried coating film was measured using a contact-type electromagnetic film thickness meter. Table 1 shows the results.

[0035]

[Table 1]

As is clear from the results of Examples 1 to 5 and Comparative Examples 1 to 10, the value of NV / (WT · t) was 0.1.
In the above cases, a very good finished coating film in which no vapor wash phenomenon was observed was obtained. On the other hand, as the value of NV / (WT · t) becomes smaller than 0.1, the frequency of occurrence of the vapor wash phenomenon increases, and a favorable intermediate coating film cannot be obtained.

The embodiments described above are described for facilitating the understanding of the present invention, and are 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.

[Brief description of the drawings]

FIG. 1 is an overall process diagram showing an embodiment of a coating method of the present invention.

FIGS. 2A and 2B are a perspective view and a cross-sectional view for explaining a coating portion when coating around a back door opening of an automobile body by the coating method of the present invention.

[Explanation of symbols]

 1: Undercoating 2: Middle coating booth 3: Middle coating in inner plate 4: Middle coating in outer plate 5: Middle coating drying furnace

Claims (8)

[Claims] The relationship between the solid content NV (wt%) of the wet coating film, the moisture WT (wt%) of the wet coating film, and the thickness t (μm) of the baked coating film is expressed by the following equation: NV / (WT) A coating method characterized by applying a water-based paint to an object to be coated such that t) ≧ 0.10. 2. The coating method according to claim 1, wherein said paint is a paint for coating an inner plate of an automobile body. 3. The coating method according to claim 2, wherein the paint is applied to a narrow inner plate portion of the automobile body. 4. The coating method according to claim 1, wherein said paint is applied in an intermediate coating step. 5. The coating method according to claim 1, wherein the solid content of the wet coating film is controlled by a coating condition of a coating machine which sprays the coating material on a workpiece. 6. The coating method according to claim 5, wherein said coating condition is a particle diameter of a coating particle sprayed from a coating machine. 7. A coating machine according to claim 5, wherein said coating machine is a rotary atomizing type coating machine, and said coating condition is a rotation speed of a bell cup.
The painting method described. 8. The coating machine is an air atomizing type coating machine,
The coating method according to claim 5, wherein the coating condition is atomization air pressure and / or pattern air pressure.