JP2545434B2 - Painting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) 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 preparation step of removing dust adhering to the object to be coated, a step of applying a coating material to the object to be coated, and a drying step of drying (curing) the applied coating material. In the case of a thermosetting coating that is generally used, this drying step is performed in two steps, a setting step and a baking step (the setting step is lower than the baking step, for example, at room temperature or around 60 ° C). Slowly evaporate the solvent in the paint at low temperature). When the coating material is a powder coating material, it is performed in only one step of baking process. And the object to be coated is usually
Although the preparation process, the coating process, and the drying process are performed while being transported by a transporting means such as a carriage, the posture of the object to be coated is maintained in a predetermined posture in each process.

By the way, smoothness (flatness) is one of the criteria for evaluating the quality of the coated surface. The higher the smoothness, the smaller the degree of unevenness of the coated surface, and the better the coated surface. It is already known that in order to improve the smoothness of the coated surface, the thickness of the coating film, that is, the thickness of the applied coating material may be increased.

On the other hand, there is "drip" of the paint that hinders 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 horizontal surface of the object to be coated, which is a so-called horizontal surface, in which the "drip" of the coating material does not cause a problem, can be made thicker than the vertical surface. Even if the thickness of the coating film on the horizontal surface is the same as the thickness of the coating film on the vertical surface, the unevenness is reduced by the slight flow of the paint that does not cause sagging on the horizontal surface, resulting in smoothness on the vertical surface. The smoothness is better than the degree.

In view of the above, conventionally, in order to obtain a painted surface with as large a smoothness as possible while preventing "sagging" of the paint, painting has been performed using a paint with as low fluidity as possible. In other words, in order to obtain a coated surface with even greater smoothness, in the conventional coating method, for example, a series of steps from the coating step to the baking step, such as two-time coating, is repeated multiple times. I had to do it.

The above-mentioned dripping of the coating material occurs in both the setting step and the baking step in the conventional thermosetting coating material, and in the baking step in the case of the powder coating material. And, conventionally, the range in which sagging does not occur during such a drying step, more specifically, the film thickness such that the sagging speed of the paint is within an allowable range of 2 mm per minute or less is the maximum of the paint film thickness obtained. Had become thick.

(Object of the Invention) The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a coating method capable of obtaining a coated surface having more excellent smoothness with the same film thickness. And

(Structure and Action of the Invention) In order to achieve the above-mentioned object, the present invention has the following structure. That is, in a coating method including a coating step of applying a coating material to an object to be coated, and a baking step of baking and curing the applied coating material, the object to be coated is rotatably supported about a substantially horizontal axis, In the coating step, at least the surface extending in the vertical direction of the object to be coated is applied to the object to be coated with a paint that causes paint sag only by the heating action in the baking step, and in the step of baking, the object to be coated is applied. Before the paint sagging of the applied paint is caused by gravity, the object to be rotated is started to rotate about the horizontal axis, and in this case, at least the surface of the object to be applied is rotated before the paint sag of the applied paint is caused by the gravity. It is configured to be rotated at a speed at which it shifts from a substantially vertical state to a substantially horizontal state, and at a speed slower than the speed at which paint dripping occurs due to the centrifugal force caused by the rotation.

As described above, in the present invention, the direction of gravity acting on the coating material applied to the object to be coated is changed by rotating the object to be coated in the horizontal direction, so that the coating material "drips" during the baking process. It will be dried and cured without causing.

According to the present invention, it is possible to obtain a very good painted surface whose smoothness far exceeds the level which has been conventionally regarded as the limit by making the thickness of the coating applied at one time much thicker than before. it can.

Also, even when the thickness of the coating film is the same as the conventional one,
By utilizing the fluidity of the coating material, it is possible to obtain an excellent coated surface having a smaller unevenness, that is, a higher smoothness.

Furthermore, if it is desired to obtain a coated surface having the same smoothness, for example, a smoothness equivalent to that obtained by a conventional coating method, it is possible to make the coating film to be applied thinner than the conventional one. The amount of paint used can be reduced only by the amount that can be thinned.

Further, in the present invention, since the coating material that causes sagging only in the baking step is used, the time for rotating the object to be coated can be made as short as possible, and the coating material remains until it is heated by the baking step. Since there is no sagging, there is no need to worry about sagging during the process transition from the painting process to the baking process.

The rotation of the article to be coated about the horizontal axis may take any appropriate rotation mode such as continuous rotation in one direction, intermittent rotation at predetermined angles, or even inversion with rotation in the opposite direction. That is, the permissible speed of the paint is 2 m / min.
The rotation direction and the number of rotations may be set within the range of m or less.

As the paint used in the present invention, it is possible to use a powder paint which originally does not have the possibility of causing a sag only in the baking step because it does not contain a solvent, and it is also possible to use a thermosetting paint which is generally used conventionally. You can In this case, as the thermosetting paint, the content, viscosity, etc. of the anti-dripping agent are adjusted, and the above-mentioned paint components are adjusted in each stage when the paint is sprayed in two stages. This makes it possible to cause sagging only in the baking process.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

Overview of Overall FIG. 1 shows the overall steps of coating an automobile body W as an object to be coated with a powder coating material, and each step is indicated by P1 to P3.

First, the body W, whose undercoating has been completed by known electrodeposition coating, is sent to the preparatory step P1 while being held by the carriage D. In this preparation step P1, dust inside and outside the body W is removed by, for example, air blow or vacuum suction. Next, in step P2, after the powder coating material is sprayed onto the body W, the coating material is dried or cured in the baking step P3.

Dust Removal The dust removal in the process P1 may be performed while rotating the body W around the horizontal axis l, as shown in FIG. That is, for example, first, after the rotation of the body W is stopped in the state shown in FIG. 2A to remove dust, the posture of the body W is changed to the state shown in FIG. It stops at the position and the dust is removed again. In this way,
As shown in (c), (d), (i) of FIG. 2, dust is removed while the body W is intermittently rotated.

In this way, by removing dust while rotating the body W, for example, dust that adheres to the inner surface corners of the body W or the closed cross section of the side sill, that is, the body W must be rotated. It is possible to completely remove dust that does not fall.

Spraying and drying of paint First, spraying of paint at P2 is performed so that the thickness of the coating film is equal to or greater than the sag limit. That is, in the conventional powder coating material generally used, the maximum thickness of the coating material that does not cause "sag", that is, the sag limit value is about 80 μm, but in the process P2, it is much thicker than the sagging limit of 80 μm. The paint is sprayed so as to form a coating film (for example, 100 μm).

After this P2, the printing process of P3 is immediately started.
In this baking process P3, the body W is rotated in the horizontal direction as shown in FIGS. 2 (a) to (i). That is, the body W is rotated around the rotation axis l extending in the horizontal direction, and in the embodiment, the rotation axis l extends in the front-rear direction of the body W. The temperature atmosphere in this baking step P3 is set to 150 ° C., for example. At the time of this baking, the powder coating material has fluidity due to heat, but the fluidity becomes small due to the acceleration of curing, and eventually it is completely cured. And
The rotation of the body W is performed only while the powder coating material has fluidity (it is not necessary to rotate the body W for the entire baking process).

Due to the horizontal rotation of the body W in the baking process P3 described above, even if the paint is sprayed to a thickness exceeding the sagging limit in P2, the paint is dried without sagging. As a result, a high-quality coated surface with extremely high smoothness, which cannot be obtained by the conventional coating method, can be obtained. Further, in FIG. 1, the setting process between the P2 coating process and the P3 baking process is omitted, but it goes without saying that there may be a setting process.

Relationship between coating thickness, sag limit and horizontal rotation FIG. 3 shows the influence of the coating thickness on the sagging limit. In Fig. 3, the coating thickness is 10
Two cases of 0 μm and 120 μm are shown. It is understood that in any of these thicknesses, heat flow occurs within 5 to 10 minutes after the start of baking. The sagging limit is a value at which a sagging of 1 to 2 mm is usually generated in 1 minute (when the sagging of 2 mm / min or more is visually observed, the coated surface is considered defective).

The rotation of the body W may be continuously rotated in the same direction, or may be reversed at a predetermined angle. Further, the rotation speed is, for example, 3 rpm to 60 rpm, which causes sagging due to centrifugal force. It may be appropriately described within a range in which the direction of gravity acting on the paint is reversed before the sagging occurs without causing the sag.

The test conditions for the data shown in FIG. 3 are as follows. The rotation axis of the body W may be tilted about 10 ° with respect to the horizontal axis.

Paint: Acrylic powder paint (Nippon Paint Co., Ltd., trade name Powdax A) b. Coating machine: Electrostatic powder coating device (Onoda Cement Co., Ltd., trade name GX101) c. Applied voltage: −60KV d. Paint discharge rate: 180gr / min e. Paint conveying air pressure: 2.0kg / cm ² f. Spraying distance: 25cm Figure 15 shows the case of using thermosetting paint as the paint used in process P2. It is a figure which shows the sag characteristic of a thermosetting coating material. When this thermosetting coating material is used, a setting step is included before the baking step P3. The setting step was performed at a temperature of 20 ° C. for 10 minutes. In the baking step, the temperature is raised from 20 ° C. to 140 ° C. over 8 minutes, and the state at 140 ° C. is maintained for 25 minutes.

FIG. 15 shows a total of four test examples a to d, that is, examples of thermosetting paints that can be used in the present invention. Specific test conditions for obtaining such data are as follows. Is the street. In the following description, Test Example a
Those that do not distinguish between ~ d are common matters.

(1) Paint • Solvent diluted thermosetting melamine kid (hue black) • Diluted solvent Triol 4% (% by weight) Solvesso 100 3% (% by weight) (Made by Esso) Solvet 200 3% (% by weight) (Esso) (Anti-sagging agent) An already cross-linked acrylic resin, and all the numerical values showing the amount added are shown in Table 1 together with the viscosity in terms of% by weight with respect to the nonvolatile content.

-Viscosity All numerical values are indicated by Ford Cup # 4/20 ° C and are shown in Table 1 together with the content of the anti-sagging agent.

(2) Coating conditions Table 2 shows the results after two-stage spraying.

The setting and baking are as described above.

(3) Test plate ・ Cold rolled steel sheet treated with zinc phosphate ・ Undercoat Cathodic electrodeposition 170 ° C × 25 minutes baking thickness 25μm ・ Intermediate coating 140 ° C × 25 minutes baking thickness 40μm ・ Intermediate water sharpening (4) Evaluation method With the test plate of (3) set vertically, the topcoat paint was applied with various changes in the paint viscosity and the content of the anti-sagging agent under the above-mentioned coating conditions. The paints that did not sag in the subsequent setting process and sagging in the baking process are shown in FIG. 15 as Test Examples a to d. In addition,
For these test examples a to d, the PGD value when the test plate was rotated at a speed of 10 rpm around the horizontal axis was measured with a resolution gloss meter until sagging did not occur during the baking process. Only the example c obtained a slightly good PGD value of "0.7", but the other test examples a, b and d obtained extremely excellent results with a PGD value of "1.0".

In each of the above test examples, [viscosity, anti-sagging agent] is [2
[2,3] are the standard ones used in conventional coating methods. Then, in the test example a, the viscosity for the second stage was as standard and the content ratio of the anti-dripping agent was increased while the viscosity was unchanged for the first stage. It is Test Example d that the content ratio of is increased, and Test Example b is that the viscosity and the content of the anti-sagging agent are both increased. On the other hand, in the test example c, the viscosity for the first stage was set as standard and the viscosity for the second stage was increased compared to the standard. In each of the test examples a to d, sagging does not occur in the setting process (dripping speed is 2 mm or less per minute), and sagging occurs only in the baking process.

It should be noted that while the standard for two stages is [22,3], the one for one stage is [22,3], [15,0], [22,0],
Each of [30,0], [15,3], [30,0], and [15,6] was tested, and in each case, sagging occurred in the setting process.

Also, while the standard for one stage is [22,3], the two stages are [22,3], [15,0], [22,0], [3
In the test with 0,0], [15,3], and [15,6], sagging occurred in the setting process, and [22,6],
In the test [30,6], no sagging occurred in the baking process.

Furthermore, for the 1st stage and the 2nd stage, we tested the following 4 cases as combinations without sticking to the standard [22, 3], but in both cases, in the setting process It caused dripping.

1st stage 2nd stage [20,6] [20,0] [20,6] [15,0] [20,6] [15,2] [30,6] [20,0] Rotating jig Next, a specific example of a jig used for supporting the body W so as to be rotatable in the horizontal direction with respect to the carriage D will be described.

FIG. 4 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. It has the integrated rotating shaft 5. Such a jig 1F, the bracket 2 part,
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 part of the body W
Is shown in FIG. The rear jig 1R has the same structure as the front jig 1F, and the components corresponding to the front jig 1F are designated by the same reference numerals. This rear jig
1R is attached to the body W by mounting the bracket 2 on the floor frame 13 as a strength member at the rear end of the body W.
It is carried out by fixing with bolts. Of course, the rear end of the floor frame 13 is generally pre-welded with a bumper mounting bracket because the bumper is generally mounted, so that the rear jig 1R can be mounted using the bumper mounting bracket. You can do it.

The above-mentioned front and rear jigs 1F and 1R are arranged such that the rotating shafts 5 of the front and rear jigs 1F and 1R are located on the same straight line extending in the front-rear direction of the body W when attached to the body W. This collinear line serves as the rotation axis l of the body W, and this rotation axis l is preferably the center of gravity G of the body W (see FIG. 6).
It is supposed to pass through. Since the rotation axis l passes through the center of gravity G, when the body W rotates, large fluctuations in the rotation speed are prevented. As a result, it is possible to prevent the body W from being impacted by the rotation fluctuation, which is more preferable in terms of preventing sagging.

In addition, the front and rear jigs 1F and 1R are for vehicle type (type of body W)
Special items are prepared in advance according to the requirements.

Truck A truck having a function of rotating the body W.

In FIG. 6, the dolly D has a base 21, and the base 21
Wheels 22 attached to the vehicle are run on a road surface 23. The base 21 is a front support column that extends upward from the front side to the rear side (from the right side to the left side in FIG. 6) in the traveling direction.
24, two intermediate columns 25 and 26, and one rear column 27 are provided, and a space between the intermediate columns 25 and 26 and the rear column 27 is a support space 28 that is largely spaced in the front-rear direction. .

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

The front and rear jigs 1F and 1R (rotating shaft 5) are known from the vertical direction.
It can be engaged and disengaged with 26 and 27, and the rear jig 1R
Are immovably engaged in the direction of the rotation axis l. For this reason,
The middle strut 26 has a notch 26a opening at its upper end surface (see FIGS. 9 to 11), while the rear strut 27 has a notch 27a opening at its upper end surface (see FIG. 9). 9th
(See FIGS. 13, 13 and 14). These notches 26a and 27a are
The size is such that the rotating shaft 5 of the jigs 1F and 1R can be fitted. A flange 5a is formed on the rotary shaft 5 of the rear jig 1R, while a notch 27b having a shape corresponding to the flange 5a communicating with the notch 27a is formed on the rear support column 27. . As a result, the rear jig 1R has 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 rotational force is applied to the body W via the rotary shaft 5 of the front jig 1F. Therefore, the tip of the rotary shaft 5 of the front jig 1F has a connecting portion 5b to be described later.
(See also FIG. 4) are formed.

A stay 29 projects downward from the base 21, and an indexing wire 30 is connected to the 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), which drives the carriage D in a predetermined transport direction. Of course, the motor is installed in a safe place from the viewpoint of explosion protection.

The rotation of the body W is performed by using the movement of the carriage D, that is, the displacement of the carriage D with respect to the traveling road surface 23. A rotation take-out mechanism 31 for taking out the displacement of the carriage D as a rotation is configured as follows. That is, the rotary take-out mechanism 31 includes a rotary shaft 32 that is vertically extended on the base 21 and is rotatably supported, a sprocket 33 fixed to a lower end of the rotary shaft 32, and a chain 34 that is meshed with the sprocket 33. It consists of and. This chain 34
Are arranged in parallel with the wire 30 in a stationary state with respect to the traveling road surface 23. As a result, when the carriage D is indexed through the wire 30, the chain 34 is immovable, so that the sprocket 33 that meshes with the chain 34, and thus the rotary 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 column 24 and a rotation shaft 37 rotatably supported on the casing 36 by extending in the lateral direction (front-back direction).
A pair of bevel gears 38 and 39 that interlock the rotating shaft 37 and the upper rotating shaft 32, and a connecting shaft 40 that is held rotatably and slidably in the front-rear direction with respect to the intermediate column 25. Have. The connecting shaft 40 is spline-connected to the rotating shaft 37 (this engaging portion is shown by reference numeral 41 in FIG. 6), and when the rotating shaft 32 is rotated by this, the connecting shaft 40 is also rotated. become. Of course, the rotary shaft 37 and the connecting shaft 40 are installed so as to be located on the rotary axis l.

The connecting shaft 40 is engaged with and disengaged from the rotary shaft 5 of the front jig 1F. That is, as shown in FIGS. 9 to 11, a cross-shaped connecting portion 5b is formed at the tip of the rotary shaft 5 for the front jig 1F, while at the end of the connecting shaft 40, As shown in FIGS. 9 and 12, a box portion 40a having an engaging recess 40c into which the connecting portion 5b is fitted without rattling is formed. Thus, for example, a pneumatic cylinder 42 may provide a rod 43
By sliding the connecting shaft 40 via the box part 40a (engaging recess 40c) and the connecting part 5b, the connecting shaft 40 and the rotary shaft 5 can be integrally rotated when engaged. It is said that The rod 43 is fitted in an annular groove 40b formed on the outer periphery of the box portion 40a so as not to hinder the rotation of the connecting shaft 40, as shown in FIG.

With the above configuration, the body W is lowered with respect to the carriage D in a state where the connecting shaft 40 is displaced to the right in FIG. 6, so that the rotary shafts 5 of the front and rear jigs 1F and 1R are moved to the middle. The columns 26 and 27 are rotatably supported in the front-rear direction in an immovable state. Then, the connecting shaft 40 (locking recess 40c) is engaged with (the connecting portion 5b of) the rotating shaft 5 in the front jig 1F.
Accordingly, when the carriage D is pulled through the wire 30, the body W is rotated about the predetermined horizontal axis l. It should be noted that the body W can be removed from the dolly D in the reverse order of the procedure described above.

Supplementary explanation Regardless of whether the carriage D is running or stopped, the body W can be switched between rotation and stop, and the rotation direction can be changed by using a separate dedicated actuator such as an air motor. Can be done. First, in the example of FIG. 6, the sprocket 33 is provided with a pair of first and second chains (corresponding to the chain 34) that mesh with each other from the radial opposite sides, and each chain can be driven appropriately. I will do so. With such a configuration, the rotation of the body W is controlled according to the following driving mode.

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

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

Both chains are free: in this case, the body W is not rotated with the movement of the truck D.

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 if the bogie D is stopped,
The body W is rotated in the direction opposite to the above case.

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 clear from the above description, the present invention makes it possible to obtain a high-quality coated surface having a higher smoothness than conventional ones if the same coating thickness is used.

Further, the object to be coated can be rotated only by the baking process, and the process of rotating the object can be minimized and the rotation time can be minimized.

[Brief description of drawings]

FIG. 1 is an overall process diagram showing an embodiment of the present invention. FIG. 2 is a view showing a state in which the posture of the automobile body as an object to be coated is changed as the automobile body rotates. FIG. 3 is a graph showing the relationship between paint thickness and sag. 4 and 5 are perspective views showing an example of a jig used for rotating the body. FIG. 6 is a side view showing an example of a trolley for carrying a body in which the body is rotated. FIG. 7 is a partially cutaway plan view showing a state below the traveling path of the carriage. FIG. 8 is a sectional view taken along line X9-X9 in FIG. FIG. 9 is a side sectional view showing a connecting portion between the rotating jig and the carriage. FIG. 10 is a sectional view taken along line X11-X11 of FIG. FIG. 11 is a plan view of FIG. FIG. 12 is a sectional view taken along line X13-X13 of FIG. 13 is a sectional view taken along line X14-X14 in FIG. FIG. 14 is a plan view of FIG. FIG. 15 is a diagram showing the dripping characteristics of the thermosetting coating material that can be used in the present invention. P1 to P3: Process W: Body (object to be coated) l: Rotation axis D: Transport carriage 1F, 1R: Rotating jig

Claims (1)

(57) [Claims] 1. A coating method comprising a coating step of applying a coating material to an object to be coated and a baking step of baking and curing the applied coating material, wherein the object to be coated is rotatable about a horizontal axis. Supported, in the coating step, at least the surface extending in the up-and-down direction of the object to be coated is coated with a paint that causes paint sag only by the heating action in the baking step, and in the baking step, the object to be coated is Before the paint drip of the paint applied to the object is caused by gravity, the object to be coated starts to rotate about the horizontal axis, and the rotation in this case is at least before the paint drip of the applied paint is caused by the gravity. The coating method is characterized in that the object surface is rotated at a speed at which the surface changes from a substantially vertical state to a substantially horizontal state, and at a speed slower than a speed at which paint sags due to centrifugal force caused by rotation.