JP2603236B2 - Painting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a coating method.

(Prior art and its problems) When coating an object to be coated, for example, the outer surface of an automobile body,
The method includes a step of applying a paint to an object to be coated and a drying step of drying the applied paint. This drying step is generally
The baking process is performed in two stages, a setting process and a baking process. The setting process is performed before the baking process at a lower temperature than the baking process, for example, at a room temperature or at a temperature of 40 ° C to 60 ° C as also referred to as calcination. (The baking temperature in the baking process is usually around 140 ° C).

In addition, as a method of coating an object to be coated, an intermediate coating and an upper coating are often performed after an undercoat. Therefore,
After the undercoating, an intermediate coating step, an intermediate coating drying step, a top coating step, and a top coating drying step are performed.

By the way, as one criterion for evaluating the quality of a painted surface, there is smoothness (flatness). The greater the smoothness, the smaller the degree of unevenness of the painted surface, and the better the painted surface. It is already known that the smoothness of the painted surface can be improved by increasing the thickness of the coating film, that is, the thickness of the applied paint.

On the other hand, there is a "drip" of the paint as an obstacle to the quality of the painted surface. This dripping occurs when the applied paint flows downward due to gravity and causes 1
The greater the film thickness of the coating applied at a time, the more easily “sagging” occurs. Since the cause of “sagging” is ultimately the effect of gravity, the so-called vertical surface of the object to be coated extends vertically. It is likely to occur.

Therefore, the thickness of the coating material to be applied to the surface extending in the horizontal direction, that is, the so-called horizontal surface, of the object to be coated on which the “sagging” of the coating does not become a problem can be made larger than the vertical surface. Even if the thickness of the coating on the horizontal surface is the same as the thickness of the coating on the vertical surface, the unevenness is reduced by a slight flow of paint that does not cause dripping on the horizontal surface, and the vertical surface is smooth. The degree of smoothness better than the degree is obtained.

From the viewpoints described above, in the past, in order to obtain a painted surface with as large a smoothness as possible while preventing "sagging" of the paint, it has been attempted to apply the paint using a paint with low fluidity (small viscosity) as much as possible. I was The so-called "sagging limit" at which "sagging" of the paint occurs on the vertical surface is about 40 [mu] m in the thickness of the coating film of the conventional painting. More specifically, the “sag” of the paint is likely to occur at the beginning of the setting process and at the beginning of the baking process, particularly during the baking process. Is determined, and the maximum value of the determined thickness, that is, the sag limit value is about 40 μm. Therefore, in order to obtain a coated surface having a much higher degree of smoothness, in the conventional coating method, it is necessary to repeat a series of steps from the coating step to the baking step a plurality of times, for example, twice coating. was there.

As for the smoothness described above, when the middle coat and the top coat are performed, the smoothness after the middle coat has a great influence on the smoothness after the top coat. Conventionally, since there is a limit in improving the smoothness by the top coat, water polishing is performed after the intermediate coating drying step to improve the smoothness of the intermediate coated surface.

However, performing water sharpening after the intermediate coating drying step requires not only the step of performing the water sharpening itself but also a drying step of drying the object coated by the water sharpening, which is a major cause of the increase in the number of steps. Becomes Also, in the case of objects to be coated that have been painted by water sharpening, especially those that have complex shapes and many openings, such as automobile bodies,
It was difficult to completely remove the water, and the residual water had an adverse effect on the subsequent overcoat (the quality of the finally obtained coated surface).

The present invention has been made in view of the above circumstances, and provides a coating method that does not require water sharpening after drying of the intermediate coating, assuming that an overcoat is performed after the intermediate coating. Is to do.

(Means and Actions for Solving the Problems) In order to achieve the above object, the present invention has the following configuration. In other words, of the surface of the substrate having a vertical surface extending in the vertical direction,
In a coating method of applying an intermediate coating to at least the vertical surface and applying a top coating over the intermediate coating, the intermediate coating is applied to at least the vertical surface of the workpiece surface. A middle coat coating step, a middle coat drying step of drying the middle coat paint, a top coat coating step of applying a top coat to at least the vertical surface of the work to be coated to a thickness not less than causing paint dripping; A top coat drying step of drying, and at least in the top coat drying step, before the paint dripping of the paint applied to the surface of the article is caused by gravity, the article to be coated is started to rotate about a substantially horizontal axis, and In this case, the rotation is performed at a speed such that the vertical surface transitions from a substantially vertical state to a substantially horizontal state at least before paint dripping of the applied paint occurs due to gravity, and by centrifugal force due to rotation. Rotate operated at a slower rate than the coating sagging occurs, the intercoat drying without the wet sanding of the paint coating in which are dried by step, there as being migrated, configuration to the overcoating process.

As described above, in the present invention, since the direction of gravity acting on the top coat applied to the object to be coated is changed by rotating the object to be coated in the horizontal direction, it is applied thicker than the dripping limit. The top coat will be dried without "sagging". In other words, by applying the top coat over the sagging limit and the subsequent rotation of the object to be coated, it is possible to obtain a coated surface with even more excellent smoothness than before as long as the same top coat is the same thickness. It is possible to make the thickness of the paint itself much larger than the level which has been conventionally limited. Thus, even if the top coat is performed without water sharpening after the middle coat drying step, the poor smoothness of the coated surface after the middle coat drying step can of course be compensated for by improving the smooth surface by the top coat. In addition, by making the thickness of the top coat sufficiently thick, it is possible to finally obtain a coated surface having better smoothness than before even without performing water sharpening.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

Overview of Overall FIG. 1 shows the overall steps in the case of coating an automobile body W as an object to be coated, and the steps are indicated by P1 to P8.

First, the body W, for which undercoating has been completed as is known by electrodeposition coating, is sent to the preparation process P1 while being held by the carriage D. In the preparation process P1, dust inside and outside the body W is removed by, for example, vacuum suction. After this, process P2
In the above, an intermediate paint is sprayed on the body W. The drying of the intermediate coating is the setting process.
This is performed in P3 and the printing step P4. Such P1 ~
The process of P4 is exactly the same as before.

After the baking step P4 for the intermediate coating, the coating passes through the steps P5 to P8 for the top coating without performing the conventional water sharpening and drying associated with the water sharpening. The steps P5 to P8 for overcoating correspond to the steps P1 to P4 for intermediate coating, but have the following features.

First, the spraying of the paint (for overcoating) at P6 is performed so that the thickness of the coating film is not less than the sag limit. In other words, in the paint generally used in the past, the maximum thickness of the paint that does not cause “sag”, that is, the sag limit value is about 40 μm, but in step P10, the coating film is much thicker than the sag limit of 40 μm. (For example, 65 μm).

In the setting step P7, FIGS.
As shown in (i), the body W is rotated in the horizontal direction. That is, the rotation axis l where the body W extends in the horizontal direction
, And in the embodiment, the rotation axis l
Extend in the front-rear direction of the body W. The temperature atmosphere in the setting step P7 is normal temperature in the embodiment, but may be set to an appropriate temperature in a range of a temperature lower than the temperature atmosphere in the next baking step P8, such as 40 ° C. to 60 ° C. Of course, this setting step P7 is to volatilize the low-boiling components in the paint in advance, so that pinholes are generated on the painted surface due to rapid volatilization of the low-boiling components in the next baking step P8. Is prevented.

In the baking step P8, baking of the top coat is performed, for example, in a temperature atmosphere of 140 ° C. Also at this P8, the body W is rotated in the horizontal direction as shown in FIGS. 2 (a) to 2 (i), similarly to the setting step of P7.

Due to the horizontal rotation of the body W at P7 and P8 described above, even if the top coat is sprayed to a thickness greater than the sag limit at P6,
The paint is dried without dripping. This allows
Even if the thickness of the top coat is the same, a high quality coated surface with extremely high smoothness, which cannot be obtained by the conventional coating method, can be obtained.

Note that, in the overcoat drying step, the body W can be rotated only in the baking step P8.

Then, by applying the top coat paint beyond the sagging limit and rotating thereafter, the poor smoothness of the middle coat painted surface, which was not subjected to water sharpening after the middle coat, is compensated for, and the smoothness or the same as the conventional one Excellent smoothness is obtained.

Relationship between coating film thickness, sag limit, smoothness, and horizontal rotation FIG. 3 shows the effect of the film thickness on the sag limit. In FIG. 3, the coating thickness is 40
The three cases of μm, 53 μm and 65 μm are shown. It is understood that, in any of these thicknesses, a "drip" peak occurs both at the beginning of the setting step and at the beginning of the printing step. Also, the dripping limit is usually 1 per minute.
~ 2mm is the value when sagging occurs (2mm /
If the sagging of more than a minute occurs, the coated surface is considered to be defective), and the maximum coating thickness obtained in the range below the sagging limit is about 40 μm with a conventional paint.

On the other hand, FIG. 4 shows the influence on the smoothness when the body W is rotated in the horizontal direction and when it is not. A in FIG. 4 shows a state in which the body W is not rotated (conventional coating method). FIG. 4B shows a case where the body W is rotated by 90 ° and then reversed (forward and reverse rotation between FIGS. 2 (a) and (c)). FIG. 4C shows
The case where the body W is rotated by 135 ° and then reversely rotated (forward and reverse rotation between FIGS. 2 (a) and (d)) is shown. 4th
FIG. D shows a case in which the body W is rotated 180 ° and then reversed (forward and reverse rotation between FIGS. 2 (a) and (e)). FIG. 4E shows a case where the body W is continuously rotated in the same direction (FIGS. 2 (a), (b),
(C)... (I) are taken in this order, and the process returns to (a) again).

As is apparent from FIG. 4, if the thickness of the coating film is the same, it is better to rotate the body W (FIG. 4, B, C, D,
E) When the rotation is not performed (FIG. 4A), a greater smoothness can be obtained. Further, it is understood that even in the same rotation, it is preferable to rotate in the same direction by 360 ° in order to increase the smoothness. Of course, when the body W does not rotate,
Since the thickness of the coating film is limited, there is a limit in increasing the smoothness.

By the way, the body W is 360
゜ When rotating, the resulting smoothness is
It is "87" (lower limit of 1.0 in PGD value) in IG. When the thickness of the coating film is 40 μm, the IG is “58” (lower limit of 0.7 in the PGD value) when the body W is not rotated. If the IG is "68"
(Lower limit of 0.8 in PGD value).

As is known, IG (image gloss) in the image sharpness indicates the ratio of the sharpness to the mirror surface (black glass) as 100, and the PGD indicates the degree of discrimination of the reflected image as 1.0. Is a value at which the smoothness of the painted surface decreases as the value decreases.

The test conditions of the data shown in FIG. 3 and FIG. 4 are as follows. These test conditions show the conditions when the overcoat is performed at P6.

a. Coating: Melamine alkyd (black) Viscosity: 22 seconds / 20 ° C with Ford cup # 4 b. Coating machine: Minibell (16,000 rpm) Shaping air ^{2 0} kg / cm ² c. The first time ... 100cc / min The second time ... 150-200cc / min d. Setting time: 10 minutes × normal temperature e. Baking conditions: 140 ° C × 25 minutes f. Substrate Smoothness: 0.6 (PGD value) (Medium coating, on PE tape) g. Rotating or reversing operation range: Setting (10 minutes) to baking (10 minutes) h. Coating object: Painted on the side of a 30 cm square cylinder , Supported rotatably at the center. I. Rotation speed of the object to be coated: three rotations of 6 rpm, 30 rpm, and 60 rpm, but there was virtually no difference due to the difference in rotation speed. A specific example of a jig used to support the trolley D so as to be rotatable in the horizontal direction will be described.

FIG. 5 shows a front jig attached to the front of the body W.
Shows 1F. The jig 1F includes a pair of left and right mounting brackets 2, a pair of left and right stays 3 welded to the left and right brackets 2, a connecting bar 4 for connecting the pair of left and right stays 3, and a connecting bar 4. And an integrated rotation shaft 5. In such a jig 1F, the bracket 2 is
It is fixed to a front strength member of the body W, for example, a front end of the front side frame 11. That is, since a bracket 12 for mounting a bumper (not shown) is usually welded to the front side frame 11, the bracket 2 is bolted (not shown) to the bracket 12 on the body W side.
Use to fix.

On the other hand, the rear jig 1R attached to the rear of the body W
Is shown in FIG. The rear jig 1R has the same configuration as the front jig 1F, and the components corresponding to the front jig 1F are denoted by the same reference numerals. This rear jig
To attach the 1R to the body W, the bracket 2 is attached to the floor frame 13 as a strength member at the rear end of the body W.
By fixing with bolts. Of course, at the rear end of the floor frame 13, a bumper mounting bracket is welded in advance because the bumper is generally mounted, so that the rear jig 1R is Mounting can also be performed.

When the jigs 1F and 1R are attached to the body W, the rotating shafts 5 are positioned on the same straight line extending in the front-rear direction of the body W. This same straight line becomes the rotation axis l of the body W. Preferably, this rotation axis l is the center of gravity G of the body W (see FIG. 7).
Through. It should be noted that the rotation axis l passes through the center of gravity G, thereby preventing a large fluctuation in the rotation speed when the body W rotates. This prevents the body W from receiving an impact due to the rotation fluctuation, which is more preferable for preventing dripping.

The front and rear jigs 1F and 1R are for the type of vehicle (the type of body W)
A special one is prepared in advance in accordance with.

Dolly A dolly used at least in P7 and P8 and having a function of rotating the body W. In FIG. 7, a truck D has a base 21, and wheels 22 mounted on the base 21 travel on a road surface 23. The base 21 is composed of one front support 24, two intermediate supports 25, 26 and one rear support extending in the running direction from the front side to the rear side (from right to left in FIG. 7). It has a strut 27, an intermediate strut 25, 26 and a rear strut 27
The space between them is a support space 28 which is largely spaced in the front-rear direction.

The body W is disposed in the support space 28, and its front portion is rotatably supported on the intermediate support 26 using the front jig 1F, while its rear portion uses the rear jig 1R. Then, it is rotatably supported by the rear column 27.

The front and rear jigs 1F and 1R (the rotating shaft 5) can be freely disengaged from the columns 26 and 27 from above and below, and the rear jig is also provided.
1R is immovably engaged in the direction of the rotation axis l. For this reason, the notch 26a which opens in the upper end surface is formed in the intermediate support | pillar 26 (refer FIG. 10-12), The notch 27a which opens in the upper support surface is formed in the rear support | pillar 27. (First
FIG. 0, FIG. 14, FIG. 15). These two notches 26a, 27a
Is large enough to fit the rotating shafts 5 of the jigs 1F and 1R. The flange 5a is attached to the rotating shaft 5 of the rear jig 1R.
On the other hand, a notch 27b having a shape corresponding to the flange portion 5a communicating with the notch 27a is formed in the rear support column 27. As a result, the rear jig 1R has the notch
It is disengaged from the vertical direction with respect to 27a, 27b, and is immovable in the front-rear direction with respect to the rear support column 27 by the stopper action of the flange portion 5a. The application of the rotational force to the body W is performed via the rotary shaft 5 of the front jig 1F.
(See also FIG. 5).

A stay 29 protrudes downward from the base 21, and a tow wire 30 is connected to a lower end of the stay 29. The wire 30 is of an endless type and is driven in one direction by a motor (not shown), whereby the carriage D is driven in a predetermined transport direction. Of course, the motor is installed at a safe place from the viewpoint of explosion protection.

The rotation of the body W is performed using the movement of the bogie D, that is, using the displacement of the bogie D with respect to the traveling road surface 23. The rotation take-out mechanism 31 for taking out the displacement of the cart D as a rotation is configured as follows. That is, the rotation take-out mechanism 31 includes a rotation shaft 32 extended vertically in the base 21 and supported rotatably, a sprocket 33 fixed to a lower end of the rotation shaft 32, and a chain 34 meshed with the sprocket 33. And is composed of This chain 34
Is disposed in parallel with the wire 30 and in a stationary state with respect to the traveling road surface 23. Thus, when the trolley D is pulled through the wire 30, the chain 34 is immovable, and the sprocket 33 meshing with the chain 34 and thus the rotating shaft
32 is rotated.

A transmission mechanism 35 for transmitting the rotation of the rotation shaft 32 to (the rotation shaft 5 of) the front jig 1F is configured as follows. That is, the transmission mechanism 35 includes a casing 36 fixed to the rear surface of the front support 24 and a rotating shaft 37 that extends in the lateral direction (front-rear direction) and is rotatably supported by the casing 36.
A pair of bevel gears 38 and 39 for interlocking the rotation shaft 37 and the upper rotation shaft 32, and a connection shaft 40 held rotatably and slidably in the front-rear direction with respect to the intermediate support 25. Have. The connecting shaft 40 is spline-coupled to the rotating shaft 37 (the connecting portion is indicated by reference numeral 41 in FIG. 7). When the rotating shaft 32 is rotated, the connecting shaft 40 is also rotated. Become. Of course, the rotation shaft 37 and the connection shaft 40 are installed so as to be located on the rotation axis l.

The connecting shaft 40 is disengaged from the rotating shaft 5 of the front jig 1F. That is, as shown in FIGS. 10 to 12, a cross-shaped connecting portion 5b is formed at the tip of the rotary shaft 5 for the front jig 1F, while the connecting shaft 40 has As shown in FIGS. 10 and 13, a box portion 40a having an engagement recess 40c into which the connecting portion 5b is fitted without play is formed. Thus, for example, the rod 43 is
By sliding the connecting shaft 40 through the connector, the box portion 40a (engaging recess 40c) and the connecting portion 5b are disengaged, and the connecting shaft 40 and the rotating shaft 5 can be integrally rotated during the engagement. It is said. As shown in FIG. 10, the rod 43 is fitted into an annular groove 40b formed on the outer periphery of the box 40a so as not to hinder the rotation of the connecting shaft 40.

With the above configuration, the body W is lowered with respect to the bogie D while the connecting shaft 40 is displaced to the right in FIG. 7, so that the rotary shafts 5 of the front and rear jigs 1F and 1R are It is rotatably supported by the columns 26 and 27 and is immovable in the front-rear direction. Thereafter, the connecting shaft 40 (locking recess 40c) is engaged with (the connection portion 5b of) the rotating shaft 5 in the front jig 1F.
Thus, if the trolley D is pulled through the wire 30, the body W will be rotated about the predetermined horizontal axis l. The removal of the body W from the carriage D may be performed in a procedure reverse to the procedure described above.

FIG. 16, FIG. 17, FIG. 18, and FIG. 19 each show a modified example of a joint portion between the rotation shaft 5 of the front jig 1F and the connection shaft 40.

16 and 17, first, the intermediate support 26
The notch 26a is formed in a semicircular shape so as to rotatably support the box portion 40a. The connecting portion 5b-1 of the rotating shaft 5 is formed in an L-shape, while the engagement recess 40c-1 formed in the box portion 40a is formed in the L-shaped connecting portion 5b-1.
Are shaped so as to be engaged so that they cannot rotate relative to each other. The engaging recess 40c-1 is opened on one side surface of the box portion 40a, and when the opening is directed upward, the connecting portion 5b-1 is moved with respect to the engaging recess 40c-1. The connection shaft 40 is disengaged from the vertical direction (no sliding of the connection shaft 40).

FIGS. 18 and 19 show the rotation of the front jig 1F only when the engaging recess 40c-2 formed in the box portion 40a faces upward, as in FIGS. 17 and 18. The connecting portion 5b-2 formed on the shaft 5 can be engaged and disengaged.
FIG. 16 and FIG. 16 show that 5c-2 has a square cross-section while engagement recess 40c-2 has a shape corresponding to this square.
It is different from the case shown in FIG.

Of course, in the case of FIGS. 16 to 19, the connection shaft 40 and the front jig 1F can be disengaged (engagement recesses 40c-1, 40c).
In a state where -2 faces upward), the body W is in the upright position (a state in which the roof panel of the body W shown in FIG. 7 is upward).

Supplementary Explanation Next, supplementary explanations related to the present invention will be sequentially described.

First, the dust removal in the process P5 is preferably performed while rotating the body W about the rotation axis l (see FIGS. 2A to 2I). Thereby, the inner surface of the body W,
In particular, in the erect position, dust adhering to a downward surface or the like falls downward due to gravity, so that dust can be more reliably removed. This means that dust does not fall during the rotation of the body W in the setting step or the printing step, which is important for obtaining a high quality painted surface.

In the middle coat, as in the case of the top coat, paint application (P2) exceeding the dripping limit and rotation of the object to be coated (P3, P4) may be performed.

In the case where the body W is rotated with the top coat and a thin coating film is formed with a top coat having a small sag limit, a so-called color middle coat may be performed. As a result, even if the intermediate paint can be seen through the top paint,
There is no bearing in terms of hue.

Regardless of the traveling or stopping of the cart D, the switching of the rotation and the stop of the body W and the switching of the change of the rotating direction can be performed as follows, for example. First, in the example of FIG. 7, a pair of first and second chains (corresponding to the chain 34) meshing with the sprocket 33 from opposite sides in the radial direction are provided, and each of the chains can be appropriately driven. I will do it. With such a configuration, the rotation of the body W is controlled according to the following driving mode.

The first chain is stopped and the second chain is free: In this case, the body W is rotated in one direction as the bogie D travels.

First chain free and second chain stop: In this case, the body W is rotated in the opposite direction as the bogie D travels.

Both chains are free: In this case, the body W is not rotated with the carriage D traveling.

Driving the first chain in one direction and freeing the second chain: In this case, the body W is rotated in one direction even when the carriage D is stopped.

Driving the first chain in the other direction and freeing the second chain (the same applies when the first chain is free and the second chain is driven in the other direction): In this case, even when the bogie D is stopped, the body W It is rotated in the opposite direction.

Note that the above is the same even when a rack bar is used instead of the chain. When the rack bar is always arranged in a fixed state (in this case, the traveling of the bogie D is a prerequisite for the rotation of the body W), the rack bar is intermittently arranged, or the position at which the rack bar is arranged is left and right By setting arbitrarily, the body W can be rotated in an arbitrary direction according to the traveling position of the cart D, and the rotation of the body W can be stopped at an arbitrary position.

(Effects of the Invention) As is apparent from the above description, the present invention can improve the smoothness of the finally obtained coated surface without performing water sharpening after the intermediate coating when performing the intermediate coating and the top coating. Things.

[Brief description of the drawings]

FIG. 1 is an overall process diagram showing one embodiment of the present invention. FIG. 2 is a view showing a state of a posture change accompanying rotation of an automobile body as an object to be coated. FIG. 3 and FIG. 4 are graphs showing the relationship among paint thickness, sag, smoothness of the painted surface, and rotation. 5 and 6 are perspective views showing examples of jigs used for rotating the body. FIG. 7 is a side view showing an example of a bogie for body transportation in which the body is rotated. FIG. 8 is a partially cutaway plan view showing a state of the bogie below the traveling path. FIG. 9 is a sectional view taken along line X9-X9 in FIG. FIG. 10 is a side cross-sectional view showing a connecting portion between the rotating jig and the bogie. FIG. 11 is a sectional view taken along the line X11-X11 in FIG. FIG. 12 is a plan view of FIG. FIG. 13 is a sectional view taken along line X13-X13 of FIG. FIG. 14 is a sectional view taken along line X14-X14 of FIG. FIG. 15 is a plan view of FIG. FIG. 16 and FIG. 17 show a modification of the connecting portion between the rotating jig and the bogie, and FIG. 16 is a cross-sectional view taken along line X16-X16 of FIG.
FIG. 17 is a side sectional view. 18 and 19 show still another modified example of the connecting portion between the rotating jig and the bogie, and FIG. 18 shows X18-X18 in FIG.
19 is a side sectional view. P1 to P8: Process W: Body l: Rotation axis D: Transport cart 1F, 1R: Rotating jig

Continuation of the front page (56) References JP-A-54-61933 (JP, A) JP-A-57-100939 (JP, A) JP-B-61-53112 (JP, B2)

Claims (1)

(57) [Claims] 1. A coating method in which an intermediate coating is applied to at least the vertical surface of a surface of a coating object having a vertical surface extending in a vertical direction, and a top coating is applied from above the intermediate coating. An intermediate coating step of applying an intermediate coating to at least the vertical surface of the object surface, an intermediate coating drying step of drying the intermediate coating, and at least the vertical surface of the object surface A topcoat coating step of applying a topcoat paint to a film thickness greater than or equal to the thickness at which paint dripping occurs; and a topcoat drying step of drying the topcoat paint. At least in the topcoat drying step, the paint dripping of the paint applied to the surface of the workpiece is performed. Begins to rotate around the substantially horizontal axis before the gravity occurs due to gravity, and in this case, the rotation is performed so that at least the vertical surface is in a substantially vertical state before the paint dripping of the applied paint occurs due to gravity. At such a speed as to shift to a substantially horizontal state, and rotated at a speed lower than the speed at which paint sag occurs due to centrifugal force due to rotation, without performing water sharpening of the intermediate coating paint dried by the intermediate coating drying step, A coating method characterized by shifting to a top coating process.