JP2666984B2 - Painting method - Google Patents

Description

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

(Prior Art) When an object to be coated, for example, an outer surface of an automobile body is applied by spraying, a preparation step for removing dust adhering to the object to be coated, and a step of spray-coating the object with the coating, Drying the applied paint. This drying step is generally performed in two stages, a setting step and a baking step, and the setting step is performed before the baking step at a lower temperature than the baking step, for example, at room temperature or 40 ° C. It is performed in a temperature atmosphere of 60 ° C. (the baking temperature in the baking process is usually around 140 ° C.).

The object to be coated usually undergoes the above-described preparation step, coating step, and drying step while being conveyed by a conveying means such as a cart, but the posture of the object to be coated is maintained at a predetermined position in each step. It is being done as it is.

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 is caused by a large downward flow of the applied paint due to gravity, so that the greater the thickness of the paint applied at one time, the more easily the "sagging" occurs. The cause of the "sagging" is as follows. After all, because of the influence of gravity, the surface of the object to be coated tends to occur on a surface extending in the vertical direction, that is, a so-called vertical surface. For example, when considering the body of an automobile as an object to be coated, sagging is not likely to occur on a hood or a trunk lid serving as a lateral surface, but sagging tends to occur on a fender serving as an upright surface.

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 viewpoint as described above, conventionally, in order to obtain a painted surface with as large a smoothness as possible while preventing "sagging" of the paint, the painting is performed 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 was about 40 [mu] m in the thickness of the coating film of the conventional thermosetting paint. More specifically, the “sag” of the thermosetting paint is likely to occur at the beginning of the setting step and at the beginning of the baking step, particularly at the beginning of the baking step, and is applied in the painting step so that “sag” does not occur at this time. The thickness of the paint 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 greater smoothness absolutely, the conventional coating method requires, for example, two coatings.
A series of steps from the painting step to the baking step had to be repeated a plurality of times.

On the other hand, recently, an object to be coated is applied in two colors. For example, in the case of an automobile body, a so-called two-tone type in which the lower color and the upper color are different from each other is increasing. In order to obtain such a two-tone color, conventionally, a first color top coat is sprayed on a part of the surface of the intermediate coat surface, that is, for example, as a lower color, which is dried and then left. Part 1
Is performed by, for example, spraying an overcoat paint of a second color different from the above color as an upper color and drying it.

(Problems to be Solved by the Invention) Overcoming the sagging limit, which is a problem when coating by spraying as described above, a coated surface with better smoothness can be obtained if the coating thickness is the same. Applicants have developed a coating method that can be obtained. That is, while the thickness of the coating film when applying the paint by spraying is set to a thickness equal to or more than the sagging limit, the object to be applied is rotated about a substantially horizontal axis until the applied paint is cured until sagging does not occur. We developed a painting method that can be rotated. According to this painting method,
The direction of gravity acting on the paint is changed by the rotation of the object to prevent dripping, while actively utilizing the large fluidity of the paint, making it smoother if the thickness of the coating is the same An excellent painted surface can be obtained.

By the way, it is desired to classify the color of the object to be finally obtained into two colors, and to improve the smoothness of one of the two colors. For example, when an automobile body is color-coded into a lower color and an upper color, it is desired to improve the smoothness of the upper color, which is particularly required to look good.
In other words, it is desired to improve the smoothness of only a desired portion, that is, a painted surface of a desired color, while minimizing the amount of the top coat used as a whole.

Therefore, an object of the present invention is to provide a coating film of one color that has the same film thickness so that the smoothness of the coating surface of one color can be sufficiently improved when the color of the finally obtained coating surface is classified into two colors. It is to provide a coating method.

(Means and Actions for Solving the Problems) In order to achieve the above object, the present invention has the following configuration.

Undercoating, a first topcoating step of partially applying the first topcoating by spraying to the workpiece to which the intermediate coating has been completed, and a first drying step of drying the first topcoating, A second color different from the first topcoat is applied to the remaining portion of the object to which the first topcoat is not applied.
A second overcoating step of applying the overcoating by spraying, and a second drying step of drying the second overcoating, wherein the thickness of the second overcoating applied in the second overcoating step is In the second drying step, the object to be coated is rotated around a substantially horizontal axis until the second overcoating material is dried until no dripping occurs, in the second drying step. .

With such a configuration, the paint surface finally obtained is color-coded into two colors, that is, the color of the first top coat and the color of the second top coat.

Of course, since the direction of gravity acting on the second topcoat applied to the object is changed by rotating the object around a substantially horizontal axis, the second topcoat is
It will be dried without causing "sag".

This means that the thickness of the second top coat applied at one time can be made much thicker than in the past, and a very good painted surface with a smoothness far exceeding the level which has been conventionally regarded as the limit can be obtained. Can be. In addition, even when the second top coat has the same thickness as that of the conventional paint, it is possible to obtain an excellent coated surface having smaller irregularities, that is, a larger smoothness, by using the fluidity of the paint. Furthermore, if it is intended to obtain a coated surface having the same smoothness, for example, the same smoothness as that obtained by a conventional coating method, the film thickness of the second overcoating material can be reduced, and this thinning can be achieved. The amount of paint used can be reduced.

Here, the spraying of the paint may be spraying by electrostatic painting. In addition, the dripping of the paint refers to the movement of the paint that can be visually confirmed when the paint is left in a sprayed state (appears as a streak when the paint is cured),
Generally, it is assumed that dripping occurs when the movement of the paint by about 2 mm is confirmed. Therefore, spraying paint to a thickness greater than the sag limit means that the paint will move at least about 2 mm if left as it is, and the greater the fluidity of the paint used, the greater the sag The marginal thickness becomes smaller. In order to make the thickness equal to or more than the sagging limit, the spraying may be performed by one spraying (one stage blowing), and the thickness may be finally equal to or more than the sagging limit by two or three or more sprayings ( Multistage blowing). Furthermore, the rotation of the object to be coated about the substantially horizontal axis is
Since it is only necessary to prevent a large movement of the paint due to the action of gravity, the paint is continuously moved in a predetermined direction until the paint does not have a large flow state that causes dripping, that is, until the paint is hardened. The rotation may be performed continuously or intermittently, or the forward and reverse rotations may be performed continuously or intermittently. As the rotation angle range of the object to be coated, it is sufficient that the direction in which gravity acts on any part where the paint is sprayed to the thickness above the sag limit is reversed, and 270 ° is sufficient. . The rotation axis of the object to be coated may be inclined at an angle of about 30 degrees with respect to the true horizontal axis, and the rotation axis may be swung.

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 the undercoating has been completed and the intermediate coating has been completed by electrodeposition coating, is sent to the masking step P1 while being held by the carriage D. In this masking step P1, for example, as shown in FIG.
Is divided into two upper and lower colors, the upper color portion is masked. After this, the first topcoat process P2
In the above, the overcoat paint corresponding to the lower color of the body W is applied by spraying. The thickness of the first top coat is set to be within the sag limit as in the prior art. Thereafter, in a masking removing step P3, the masking in the step P1 is removed. Then, in the first drying step P4,
Drying of the first top coat, that is, when the first top coat is a general thermosetting coating, the first top coat is sufficiently dried by setting and subsequent baking.

After the process P4, in a masking process P5, as shown in FIG. 16, masking is performed on the lower portion of the body W (the hatched portion in the drawing and the portion where the first overcoat exists). Thereafter, in a second topcoating step P6, a second topcoat as a top color different from the first topcoat is applied to the upper portion of the body W by spraying. Thereafter, after the masking in the step P5 is removed in the masking removing step P7, in the second drying step P8, the second topcoat paint is sufficiently dried by setting and subsequent baking.

In the second overcoating step P6, the thickness of the applied second overcoat is set to a thickness equal to or larger than the sag limit. Then, in the second drying step P8, the second top coat is sufficiently dried by setting and subsequent baking. In the second drying step P8, as shown in FIG. 2, the body W
Is rotated about a horizontal axis.

In addition, since the applied thickness of the second top coat in the process P2 is set to be within the sagging limit, the body W is not rotated in the drying process in the process P4.

Here, FIG. 17 shows a cross section of the entire coating film layer after the above-described steps P1 to P8. In both figures, C1
Is an undercoat layer, and C2 is an intermediate coat layer. Further, C3 forms the first overcoat layer, that is, the lower color of the body W, and C4 forms the second overcoat layer, that is, the upper color of the body W. Of course, the thickness l1 of the second top coating layer C4 is set to a thickness not less than the sag limit.

Specific Examples of Coating Conditions Next, specific examples for obtaining a coating film as shown in FIG. 17 will be described.

(1) Undercoat paint Cathodic electrodeposition Baking: 170 ° C x 30 minutes Film thickness: 20 ± 2 µm (2) Intermediate resin: Thermosetting oil-free polyester Pigment: Gray (hue) Spraying viscosity: 22-25 seconds / 20 ° C ( Ford cup No.4) Electrostatic coating: Mini bell 22,000rpm Shaping air pressure 2.0kg / cm ² Voltage 90KV Gun distance 30cm One stage blowing Body W transfer speed 5.5m / min Film thickness: 35 ± 5μm Setting: 8 minutes (Normal temperature) Baking: 140 ° C x 25 minutes (3) First top coat Base paint (lower layer) Resin: Acrylic melasin (silver) Pigment: Aluminum powder (20.0% by weight) Spraying viscosity: 13 seconds / 20 ° C (Ford cup No. .4) Electrostatic coating: Air atomization Atomization air pressure 4.0kg / cm ² Voltage 60KV Gun distance 30cm 2 stage blowing (3 minutes interval) Film thickness: 20 ± 4μm Clear paint (upper layer) Interval after spraying base paint: 5 minutes Resin: Acrylic melamine Spraying viscosity: 24 seconds / 20 ° C ( Equid cup No.4) Electrostatic coating: Same conditions as intermediate coating Thickness: 35 ± 5μm Setting: 12 minutes (normal temperature) Baking: 140 ° C x 25 minutes Body W transfer speed: 3m / min (4) Second top coating resin : Solid white Spraying viscosity: 22 seconds / 20 ° C (Ford Cup No. 4) Electrostatic coating: Same conditions as for intermediate coating Body W transport speed: 2.5 m / min Film thickness: 60 ± 5 μm Setting: 15 minutes (normal temperature) Baking: 140 ° C x 30 minutes Rotation of body W: whole setting period and initial baking 10
3. Relationship between coating film thickness, sag limit, smoothness, and horizontal rotation FIG. 3 shows the effect of the film thickness on the sag limit, taking a thermosetting paint as an example. FIG. 3 shows three cases of the coating film thickness: 40 μm, 53 μm, and 65 μm. For both thicknesses, both at the beginning of the setting process and at the beginning of the baking process,
It is understood that a "drip" peak occurs. In addition, the sag limit usually means a value when a sag of 1 to 2 mm is generated in one minute (a paint surface is defective if sag of 2 mm / min or more is visually observed). The maximum coating thickness obtained in the range is about 40 μm for the 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 clear from FIG. 4, if the thickness of the coating film is the same, it is better to rotate the body W (FIGS. 4B, 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 overcoating is performed at P2.

a. Paint: 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. Discharge amount: 2 times 1st ・ ・ ・ 100cc / min 2nd ・ ・ 150-200cc / min d. Setting time: 10 minutes × normal temperature e. Baking conditions: 140 ° C × 25 minutes f. Base smoothing Degree: 0.6 (PGD value) (Medium coating, on PE tape) g. Rotating or reversing operating area: Setting (10 minutes) to baking (10 minutes) h. Coating object: Paint on the side of a 30 cm square cylinder, Rotatably supported 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.

Next, a specific example of a jig used to support the body W so as to be rotatable in the horizontal direction with respect to the carriage D 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.

The trolley is a trolley having a function of rotating the body W.

In FIG. 7, the trolley D has a base 21, and this base 21
Is mounted on the road surface 23. The base 21 has a single front support extending sequentially upward from the front side to the rear side (from right to left in FIG. 7) in the traveling direction.
24, two intermediate struts 25, 26 and one rear strut 27, and a space between the intermediate struts 25, 26 and the rear strut 27 is a support space 28 with a large space 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 next 1R is the notch 27
It is disengaged from the vertical direction with respect to a and 27b, and is immovable in the front and 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 engaging 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.

(Effects of the Invention) As is apparent from the above description, the present invention provides a desired color, that is, a desired portion while minimizing the amount of the top coat used as a whole in order to obtain a painted surface colored in two colors. It is possible to obtain a product having excellent smoothness.

[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 is a diagram showing a state of body color coding. Figure 17 shows Figure 16
XX sectional drawing of the figure. P1 to P8: Process W: Body (object to be coated) l: Rotation axis D: Carriage 1F, 1R: Rotating jig C1: Undercoat layer C2: Intermediate layer C3: First overcoat layer C4: Second top coat layer

Claims (1)

(57) [Claims] 1. A first overcoating step of partially applying a first overcoating by spraying to an object to which undercoating and intermediate coating have been completed, and a first overcoating step of drying the first overcoating. (1) a drying step; and a second topcoating in which a second topcoat having a color different from the first topcoat is applied by spraying to a remaining portion of the object to which the first topcoat has not been applied. And a second drying step of drying the second top coat, wherein the thickness of the second top coat applied in the second top coat step is equal to or greater than the sag limit, and the second drying In the step, the object to be coated is rotated around a substantially horizontal axis until the second top coating is dried until no dripping occurs.