JP3379408B2 - Electrodeposition method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel electrodeposition coating method. More specifically, the coating liquid remaining in the steel sheet joints of the car body or automobile parts such as automobile parts may boil out after the car body enters the baking oven in the baking process after electrodeposition coating. The present invention relates to an electrodeposition coating method for preventing sagging on a coating film during curing to prevent rough skin after baking.

[0002]

2. Description of the Related Art Conventionally, an automobile body (so-called white body) that has been subjected to a welding process is subjected to electrodeposition coating in a coating process to form an electrodeposition coating film to ensure corrosion resistance quality. There is. That is, as an example of cationic electrodeposition coating that has become the mainstream in recent electrodeposition coating, the car body is immersed in the cationic electrodeposition paint, the car body side as the cathode, the in-tank electrode as the anode, This is based on a method of depositing an electrodeposition coating film on the surface of a steel plate of an automobile body by electrophoresis. In such an electrodeposition coating method, since the vehicle body is completely immersed in the electrodeposition tank containing the coating liquid and soaked, that is, the so-called dipping method is used to perform the electrodeposition coating, so that the inside of the vehicle body cannot be coated by the spray coating method. Since the coating film can be distributed around the plate, the bag structure part, or the inner surface of the seam of the steel plate, it is widely used as an effective method for ensuring the corrosion resistance of the part.

In the above electrodeposition coating method, an automobile body, which is the object to be coated, is immersed in an electrodeposition tank to perform electrodeposition coating (electrodeposition coating step), and then immediately after the electrodeposition tank is discharged. Since the coating liquid remains inside and outside the vehicle body, a setting zone and a washing zone are appropriately provided after the electrodeposition tank according to the purpose, and the sag is cut off before moving to the washing or baking step in the setting zone (setting step). During this time, reduce and dry the paint liquid and cleaning water that have adhered to the vehicle surface,
In the rinsing zone, clean water or circulating rinsing water is sprayed or dip rinsing is performed (rinsing process) to wash away the paint liquid adhering to the vehicle body (for example, setting zones and rinsing zones are provided in multiple stages as shown in Fig. 2 and set Process,
The first washing step, the second washing step, and the setting step are performed in this order.) After the paint liquid and washing water adhering to the vehicle body surface are removed before baking, the vehicle body is put into a baking oven and baked (baking). Process), to form an electrodeposition coating film (see FIG. 2).

However, in the above electrodeposition coating method, most of the coating liquid is washed off with water before baking.
The washing water is dropped due to the sagging, but the washing water locally collects and remains in places where it is difficult to drop due to the sagging. Then, during baking, non-volatile components (residues of dust and coating liquid) contained in the residual liquid were locally abnormally deposited on the coated surface, which caused defective coating.

In order to reduce such problems, the process conditions from the electrodeposition coating to the baking are devised. For example, take a long time so that the sagging can be sufficiently cut in the setting process, or preheat (preheat) zone is provided to perform preheat drying (preheat process) so that the liquid adhering to the vehicle body surface will not locally collect and remain. As described above, you can dry or reduce the amount as much as possible, or in the washing process, dip washing to strengthen the agitation by the washing water during washing, and replace the liquid adhering to the vehicle body surface with more clean water. It is usually done to reduce coating defects due to residual liquid. Furthermore, as a method for reliably removing the wash water that adheres to the vehicle body surface before baking, multiple air nozzles are provided in the preheating zone before baking and drying, and high-pressure air is blown onto the vehicle body to remove the cleaning water that adheres to the vehicle body. Blow-off and one that prevents coating failure in a baking oven (see, for example, Japanese Patent Laid-Open No. 6-228794), or a vehicle body that has undergone a water-washing process is tilted backward together with a hanger to drain the wash water, and before the baking oven. In the preheating zone of No. 6, there is proposed such one that is inclined forward to reduce the amount of cleaning water remaining at the time of inserting the baking furnace to prevent coating failure in the baking furnace (for example, refer to JP-A-6-235094). There is.

[0006] These are effective in reducing the amount of paint liquid or cleaning water that has adhered to or remains on the general surface or floor surface of the vehicle body inner and outer plates or the bag structure, and is effective as a measure for preventing the appearance failure due to it. .

[0007]

However, there is a stagnation of the coating liquid due to the surface tension inside the steel sheet seam of the automobile body immediately after leaving the electrodeposition tank through the electrodeposition coating process. It is not a method of reducing the liquid (residual liquid) before entering the baking furnace. Therefore, the poor appearance due to the liquid sagging in the vicinity of the steel sheet joint has not been solved.
That is, the preheating that the coating liquid (residual liquid) that stays inside the steel sheet joint is preheated while performing the setting process in the subsequent setting zone, the rinsing process in the rinsing zone, and the high pressure air blowing in the preheating zone. Even after passing through the steps, the car body does not come out, and in the subsequent baking step, the automobile body enters the baking oven and
When it enters a high temperature of ℃ or more, the coating liquid is boiled out from the steel sheet joint of the vehicle body. The coating liquid that has come out by bumping flows down on the coating film in the middle of curing, resulting in rough skin after baking. Then, this rough surface impairs the appearance of the finished coating near the seam of the steel sheet, and it takes a lot of man-hours to correct the appearance. For example, as shown in FIG. 3 (A), the connecting portion B between the side sill 50 and the center pillar 60 has a side sill outer panel 51 and a center pillar outer panel 61, as shown in FIG. 3 (B) and FIG. It is a so-called "sticky" structure, and the coating liquid that has entered the gap of the sticking surface D due to surface tension spouts in the baking furnace,
This flows down to the sill outer and hardens. One like this
If "electrodeposition sagging" (secondary sagging) failure, which is a kind of rough skin, occurs, there is a problem in that the quality of the final finish deteriorates, and a lot of man-hours are required for correction work.

Therefore, the object of the present invention was made in view of such problems of the prior art, and the sagging flow due to the coating liquid penetrating into the steel sheet joint of the object to be coated causes the sag flow from the steel sheet joint. It is intended to provide an electrodeposition coating method capable of preventing a defective appearance in the vicinity of a seam of a steel plate without dripping.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the inventors of the present invention have made earnest studies on a method of preventing liquid sagging in the steel sheet seam portion of an article to be coated, which has not been studied so far from a new viewpoint. The present invention has been completed as a method for preventing the appearance defects near the steel sheet seams.

That is, the above object of the present invention is achieved by the electrodeposition coating methods for automobile bodies shown in the following ( 2 ) to (5).

(1) In an electrodeposition coating method in which an object to be coated is dipped in an electrodeposition coating material and the object to be coated is baked, the object to be coated is heated and baked before baking the object to be coated. A method for electrodeposition coating, characterized in that the coating liquid is dried while avoiding dripping of the coating liquid remaining in the steel sheet seams.

(2) In an electrodeposition coating method in which an object to be coated is dipped in an electrodeposition coating material and the object to be coated is baked, a preheating step is provided before baking the object to be coated, and in the preheating step, the object to be coated is An electrodeposition coating method, wherein an object is heated to a predetermined temperature range at a temperature rising rate of 6 to 8 ° C./minute.

(3) In the preheating step, the article to be coated is heated to a predetermined temperature range at a temperature rising rate of 6 to 8 ° C./minute, and then, the temperature rising rate is set to 8 ° C./minute or less within the predetermined temperature range. The electrodeposition coating method according to (2) above, which is held for 1 to 10 minutes.

(4) The predetermined temperature range is 60 to 95 ° C.
The electrodeposition coating method according to (2) or (3) above, wherein

(5) In the preheating step, the entire article is heated.
The electrodeposition coating method according to any one of (4).

[0016]

[0017]

Further, in the electrodeposition coating method which is another means for solving the problems of the present invention, in the electrodeposition coating method of immersing an object to be coated in the electrodeposition coating material and baking the object to be coated, A preheating step is provided before baking the object, and in the preheating step, the article to be coated is heated to a predetermined temperature range at a temperature rising rate of 6 to 8 ° C./minute.

In the above electrodeposition coating method, the coating liquid is heated in order to dry the coating liquid while avoiding sag flow due to boiling of the coating liquid remaining in the steel sheet seam of the coating product. Before baking the coated material, a preheating step which will be described in detail below is provided.

Preheating step: In this step, the article to be coated is heated to a predetermined temperature range at a temperature rising rate of 6 to 8 ° C./minute. As a result, the water content (including volatile matter) of the coating liquid remaining in the steel sheet seam of the automobile body gradually evaporates, so that the inside of the steel sheet seam is dried without causing sag flow due to boiling. The coating liquid can be contained in the steel sheet seam of the object to be coated. Therefore, after that, the object to be coated enters the baking oven and
Even if it enters at a high temperature of 00 ° C. or higher, there is no sagging flow due to the residual coating liquid, and it is possible to prevent the appearance defect in the vicinity of the steel sheet seams after baking. Here, when the temperature rising rate is less than 6 ° C./minute, the water evaporation of the coating liquid does not proceed, and as the temperature rises, bumping is caused and secondary sagging is induced. This is because the volatile components escape from the surface of the coating liquid that faces the outside at the seam of the steel plates, and only the surface is initially hardened to form a thin film, which prevents evaporation of water in the internal coating liquid. Seem. In this case, in the baking process of the next step, the coating liquid boiled and boiled, broke through the above film and blew out from the seam of the steel plate, and flowed out on the coating film (scattered in severe cases). It hardens and induces secondary sagging. On the other hand, if the rate of temperature increase exceeds 8 ° C./minute, the viscosity of the coating liquid may decrease due to a rapid temperature rise, and
The next sauce is triggered. That is, in the case of a sudden temperature rise,
The surface tension and the fluidization rate due to the decrease in viscosity become more dominant than the drying and curing rate due to the evaporation of water in the coating liquid, and as a result, the coating liquid flows out from the steel sheet seam and hardens on the coating film to cause secondary sagging. Will be triggered.

In this preheating step, the intended purpose can be achieved by heating to the predetermined temperature range at the above temperature rising rate. Here, the predetermined temperature range is 60 to 95 ° C, preferably 80 to 95 ° C.
Is desirable. That is, when the temperature is lower than 60 ° C., the water evaporation of the coating liquid inside the steel sheet joint is not promoted, and the coating liquid flows out from the inside of the steel sheet joint and hardens in the baking process as a subsequent step, which induces secondary sagging. However, this leads to poor appearance in the vicinity of the steel sheet seams. On the other hand, when the temperature exceeds 95 ° C., the coating liquid bumps from the steel sheet seam, and the high-concentration coating liquid scatters over a wide range, causing secondary sagging. On the other hand, 80
When the temperature is set to ~ 95 ° C, in order to achieve the intended purpose,
It can be said that it is preferable because it is possible to more surely promote the evaporation of the water content of the coating liquid in the steel sheet seam and to suppress the induction rate of the secondary sag as low as possible.

Further, in this preheating step, the article to be coated is heated at the above-mentioned temperature rising rate to the above-mentioned predetermined temperature region, and thereafter,
If the temperature rising rate is 8 ° C./minute or less, 1 to
It is desirable to maintain the temperature for 10 minutes, preferably within a temperature range of 80 to 95 ° C., which is particularly preferable in the predetermined temperature range, for 5 to 10 minutes, which is a preferable embodiment of the means for solving the above problems.

In the preheating step, after heating to the above-mentioned predetermined temperature range, by keeping the temperature within the predetermined temperature range for a certain period of time, the evaporation of the water content of the coating liquid in the steel sheet seam is promoted and the secondary sagging reduction effect is obtained. It can contribute effectively. Here, if the holding time in the predetermined temperature region is less than 1 minute, there is an effect of promoting the water evaporation of the coating liquid in the steel sheet joint, but the water evaporation amount gradually decreases in proportion to the holding time. The tendency of the present invention is 2
Although it has the effect of reducing the induction of next sauce, the effect cannot be made more prominent. Also, holding time is 1
If it exceeds 0 minutes, the water content of the coating liquid in the steel sheet joint is almost evaporated, and there is little or no effect of promoting water evaporation commensurate with maintaining the heating state, and 10 minutes is not obtained. Even if it goes beyond the above range, the effect of the present invention cannot be made more remarkable. Also, it is not desirable to heat for a long time from the viewpoint of productivity and economy. On the other hand, 80 to 9 which is particularly preferable in the above predetermined temperature range
When the temperature is kept in the temperature range of 5 ° C for 5 to 10 minutes, it is preferable in that the evaporation of the water content of the coating liquid in the steel sheet joint can be promoted more reliably in achieving the intended purpose. However, the secondary sagging induction reducing effect of the present invention can be made more remarkable.

The above-mentioned means for solving the problem is, as described above, carried out from the viewpoint of accelerating the evaporation of the water content of the coating liquid by maintaining the temperature within the predetermined temperature region for a certain period of time. It is desirable that the heating rate be 8 ° C./minute or less. When the rate of temperature increase exceeds 8 ° C./minute, as described above, the viscosity of the coating liquid decreases due to a rapid temperature rise, and secondary sagging is induced. On the other hand, if the rate of temperature increase is 8 ° C./minute or less, the temperature change during this period is not particularly limited, and it is possible to maintain a constant temperature without increasing the temperature, and the temperature decreases within a predetermined temperature range. There is no particular problem even if you do. That is, within the above-mentioned predetermined temperature range, that is, the temperature range of 60 to 95 ° C., even if the temperature is lowered, the temperature is sufficient to accelerate the evaporation of water, and thus the intended purpose can be sufficiently achieved. This is because.

Furthermore, in the preheating step, it is desirable to heat the entire article to be coated, which can be said to be another preferred embodiment of the above means for solving problems.

By heating the entire article to be coated, more uniform heating can be performed in the subsequent baking step, and the electrodeposition coating film on the entire article can be baked and cured without variation. The baking time can also be shortened, which is effective in terms of productivity and economy.

In the present invention, the temperature raising means in the preheating step is not particularly limited,
In the case of heating the entire object to be coated, a conventionally known drying oven (oven), for example, a dark infrared oven or a hot air circulating oven that can be used in a conventional baking process is appropriately used (combined as necessary. In the case of locally heating the vicinity of the steel plate joint of the object to be coated, for example, in the conventional baking process, for small-scale production or repair in the conventional baking process. An infrared furnace or the like that can be used for the purpose can be appropriately installed and is not particularly limited.

The object to be coated in the electrodeposition coating method of the present invention is not particularly limited as long as it has a steel plate seam. Therefore, the invention can be applied not only to automobile bodies but also to automobile parts. Further, the electrodeposition paint is not limited to the cation type and may be the anion type. Further, a conventionally known process can be arranged between the electrodeposition coating process and the preheating process. For example, one or more setting steps and one or more water washing steps can be appropriately provided.

[0029]

EFFECTS OF THE INVENTION According to the electrodeposition coating method of the present invention, it is possible to prevent the roughening of the skin by allowing the coating liquid that has penetrated into the steel sheet seams and stayed to be dried and hardened in the steel sheet seams before baking. it can. As a result, it is possible to improve the quality of the painted surface and reduce the number of repair work steps.

[0030]

Embodiments of the present invention will now be described in more detail with reference to the drawings.

Sample: An unpainted car body (manufactured by Nissan Motor Co., Ltd., R11 type, trade name Presea) was used. The number of samples was 5 in each of the examples and comparative examples. In addition, when the gap between the steel sheet seam surfaces of the lower part of the center pillar of the unpainted vehicle body of these samples was measured, the average was 200 μm in all cases.

Evaluation method: As shown in FIG. 5, the evaluation was carried out by measuring the area of the sagging marks generated from the opening of the steel plate seam in the lower part of the center pillar of the automobile body, which is a sample that has been baked. The area was calculated based on the ratio of the area of the sagging trace of 1 as 100 (= the sagging trace area ratio (%)). Also,
The rough skin condition of the sagging marks was visually evaluated, and the degree was evaluated as ○ (= small skin roughness), △ (= medium skin roughness), ×
(= Severe rough skin). Furthermore, the presence or absence of long (30 mm or more) sagging marks requiring a particularly large number of correction steps was visually evaluated.

[Example 1] As shown in FIG. 1, first, in an electrodeposition coating process, an unpainted vehicle body was completely immersed in an electrodeposition tank containing a coating liquid to perform cationic electrodeposition coating. After that, it is pulled up and set in the setting step for 5 minutes to drain the coating liquid, then washed for 5 minutes in the first washing step, and then for 5 minutes in the second washing step. Then, the coating liquid adhering to the surface coating film of the vehicle body which is the object to be coated was washed away. After that, in the setting step, after setting for 10 minutes to drain the washing water, in the preheating step,
The entire body of the article to be coated is introduced into a mountain heating furnace apparatus for painting and baking, heated to 60 ° C. at a temperature rising rate of 6 ° C./min, and held at that temperature (60 ° C.) for 1 minute (hereinafter, this constant The temperature kept at the temperature is called "holding temperature", and the time kept at this constant temperature is called "holding time"). Finally, in the baking process, the car body is put into the baking oven and 170 ° C x 2
Baking was performed under the condition of 0 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method. The results are shown in Table 1.

[Example 2] The steps from the electrodeposition coating step to the baking step were sequentially performed in the same manner as in Example 1 except that the holding temperature in the preheating step of Example 1 was changed to 80 ° C. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method. The results are shown in Table 1.

[Example 3] The steps from the electrodeposition coating step to the baking step were sequentially performed in the same manner as in Example 1 except that the holding temperature in the preheating step of Example 1 was changed to 95 ° C. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method. The results are shown in Table 1.

[Example 4] The steps from the electrodeposition coating step to the baking step were sequentially performed in the same manner as in Example 1 except that the temperature rising rate in the preheating step of Example 1 was changed to 8 ° C / min. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

Example 5 The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 2 except that the temperature rising rate in the preheating step of Example 2 was changed to 8 ° C./minute. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

Example 6 The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 3 except that the temperature rising rate in the preheating step of Example 3 was changed to 8 ° C./minute. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

Example 7 The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 4 except that the holding time in the preheating step of Example 4 was changed to 5 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Embodiment 8] The steps from the electrodeposition coating step to the baking step were sequentially carried out in the same manner as in Example 5 except that the holding time in the preheating step of Example 5 was changed to 5 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Example 9] The steps from the electrodeposition coating step to the baking step were sequentially performed in the same manner as in Example 5 except that the holding time in the preheating step of Example 6 was changed to 5 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Example 10] The steps from the electrodeposition coating step to the baking step were sequentially performed in the same manner as in Example 1 except that the holding time in the preheating step of Example 1 was changed to 10 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Embodiment 11] The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 2 except that the holding time in the preheating step in Example 2 was changed to 10 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Example 12] The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 3 except that the holding time in the preheating step of Example 3 was changed to 10 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Example 13] The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 4 except that the holding time in the preheating step of Example 4 was changed to 10 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Example 14] The steps from the electrodeposition coating step to the baking step were sequentially performed in the same manner as in Example 5 except that the holding time in the preheating step of Example 5 was changed to 10 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Example 15] The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 6 except that the holding time in the preheating step of Example 6 was changed to 10 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

Comparative Example 1 As shown in FIG. 6, the electrodeposition coating process to the baking process were sequentially performed in the same manner as in Example 1 except that the preheating process was omitted. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method. The results are shown in Table 1.

[Comparative Example 2] The procedure from Example 1 was repeated, except that the holding temperature in the preheating step of Example 1 was changed to 55 ° C, from the electrodeposition coating step to the baking step. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method. The results are shown in Table 1.

[Comparative Example 3] The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 1 except that the holding time in the preheating step in Example 1 was changed to 0.9 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Comparative Example 4] The steps from the electrodeposition coating step to the baking step were sequentially carried out in the same manner as in Example 4 except that the holding temperature in the preheating step of Example 4 was changed to 55 ° C. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method. The results are shown in Table 1.

[Comparative Example 5] The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 4, except that the holding time in the preheating step in Example 4 was changed to 0.9 minutes. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Comparative Example 6] The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 1 except that the temperature rising rate in the preheating step in Example 1 was changed to 5 ° C / min. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Comparative Example 7] The steps from the electrodeposition coating step to the baking step were carried out in the same manner as in Example 1 except that the temperature rising rate in the preheating step of Example 1 was changed to 9 ° C / min. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.

[Comparative Example 8] Example 10 was repeated except that the holding temperature in the preheating step of Example 10 was changed to 100 ° C.
Similarly to the above, the process from the electrodeposition coating process to the baking process was sequentially performed. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.
The results are shown in Table 1.

[Comparative Example 9] Example 13 was repeated except that the holding temperature in the preheating step of Example 13 was changed to 100 ° C.
Similarly to the above, the process from the electrodeposition coating process to the baking process was sequentially performed. Then, the area ratio of the sagging marks, the rough surface of the sagging marks, and the presence or absence of long sagging marks were evaluated by the above evaluation method.
The results are shown in Table 1.

As described above, Examples 1 to 15 and Comparative Examples 1 to 9
The following can be understood from the results of.

First, from the results of Examples 1 to 6 and Comparative Examples 1, 6, and 7, within the range of 6 to 8 ° C./min in the temperature rising rate in the preheating step, the heating rate was slightly higher. However, it was also confirmed that the ratio of the area of sagging traces tends to decrease, and that within the range, it has an effect of preventing rough skin. On the other hand,
If the rate of temperature rise is out of the above range, the effect of preventing rough skin cannot be sufficiently expressed, and if the rate of temperature rise is slow, including when the process of the present invention is omitted, the sagging trace area ratio may deteriorate. confirmed.

Further, Examples 1 to 15 and Comparative Examples 1 to 1
From the results of 5, 8, and 9, the holding temperature and the holding time within a predetermined temperature range (60 to 95 ° C.) for 1 to 10 minutes were as follows:
On the high temperature side of the predetermined temperature range and holding for a long time,
The ratio of the area of sagging traces tends to decrease, especially at 80 to 95 ° C.
Within the range of 10 minutes, the ratio of the area of sagging marks is smaller, which is preferable. In addition, it was confirmed that within the range, it has an effect of preventing rough skin. On the other hand, when the holding temperature and the holding time are out of the above ranges, the sagging trace area ratio is significantly deteriorated, including the case where the step of the present invention is omitted, and the effect of preventing rough skin cannot be sufficiently exhibited. Was confirmed.

It should be noted that the embodiments described above are described for facilitating the understanding of the present invention, and not for limiting the present invention. Therefore, each element disclosed in the above-described embodiments is intended to include all design changes and equivalents within the technical scope of the present invention.

[0061]

[Table 1]

[Brief description of drawings]

1 is a process chart showing a specific embodiment of an electrodeposition coating method of the present invention, showing the method performed in Example 1. FIG.

FIG. 2 is a process chart showing a conventional representative electrodeposition coating method.

FIG. 3 (A) is a perspective view showing an automobile body as an object to be coated, and FIG. 3 (B) is an enlarged view of a circled area B in FIG. 3 (A). .

FIG. 4 is a schematic cross-sectional view taken along the line CC of FIG.

FIG. 5 is a view taken in the direction of arrow E in FIG. 4, and is a schematic diagram schematically showing the sagging marks after baking due to the coating liquid flowing out from the steel plate seam (the seam between the center pillar and the side sill) on the vehicle body side. It is a figure.

FIG. 6 is a process chart showing a specific embodiment of a conventional representative electrodeposition coating method and showing the method performed in Comparative Example 1.

[Explanation of symbols]

50 ... Sill, 51 ... Sill outer panel, 60 ... Center pillar, 61 ... Center pillar outer panel, D ... Steel plate mating surface.

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C25D 13/00 307

Claims (4)

(57) [Claims] 1. An electrodeposition coating method in which an article to be coated is immersed in an electrodeposition coating material and the article to be coated is baked, in which a preheating step is provided before baking the article to be coated, and in the preheating step, the article to be coated is provided. Heating rate 6
An electrodeposition coating method characterized by heating to a predetermined temperature range at 8 ° C / min. 2. In the preheating step, the article to be coated is heated to a predetermined temperature range at a temperature rising rate of 6 to 8 ° C./minute, and then heated to within the predetermined temperature range at a temperature rising rate of 8 ° C./minute or less. The electrodeposition coating method according to claim 1, which is held for 1 to 10 minutes. Wherein electrodeposition coating process according to claim 1 or 2, wherein the predetermined temperature range is characterized in that it is a 60 to 95 ° C.. 4. A said pre-heating step, electrodeposition coating process according to any one of claims 1 to 3, characterized in that warming the entire object to be coated.