JP2525703B2 - Painting method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating the surface of an article to be coated such as the body of an automobile.

[0002]

2. Description of the Related Art Conventionally, a method of applying a coating from the lateral direction to the surface of an object to be coated such as an automobile body, particularly a vertical surface, and performing the coating is disclosed in, for example, Japanese Patent Laid-Open No. 59-4471. Is known. It has also been proposed to change the amount of paint applied in accordance with the surface to be painted and to perform uniform painting.

On the other hand, when the coating amount of the coating is increased to increase the film thickness of the coating film, high smoothness of the surface is obtained and the quality is improved.

[0004]

However, when a large amount of paint is applied at one time when the film thickness of the paint film is increased to improve the quality of the paint as described above, the painted surface of the object to be coated If the coating is in the up-down direction or in an inclined state, the applied coating flows downward in the baking process and "paint dripping" occurs, forming unevenness on the coated surface and impairing the smoothness of the coating. Will be lowered.

[0005] The paint dripping of the coating film occurs immediately during coating when the film thickness exceeds the limit value in the coating spraying process, or even after a lapse of a predetermined time during the setting for volatilizing the solvent after spraying. However, in particular, since the coating film is baked, it is likely to occur when the temperature is raised in the initial stage of heating in a drying furnace.

[0006] Conventionally, since there is a problem of the above-mentioned paint dripping, there is a limit to apply a large amount of paint at one time to thicken the coating film, and the application and drying are repeated in several steps. Although it is possible to increase the final film thickness, there is the problem that the coating time will be long due to complicated processes, and multiple coating facilities will be required, and the film thickness per coating is limited. It was not possible to obtain a highly smooth coated surface due to the increase in the sagging limit film thickness.

In view of the above circumstances, therefore, the present invention increases the coating sag limit film thickness by a simple method so that a high film pressure can be achieved even on the upper and lower surfaces of an object to be coated without causing paint sag in the baking process. It is an object of the present invention to provide a coating method which can obtain a high-definition image and a high-smooth coating surface by a high-smooth finish coating with an increase in film thickness.

[0008]

In order to achieve the above object, the coating method of the present invention comprises spray coating a paint containing a solvent with a film thickness not less than that which causes paint dripping on at least the surface of an article to be vertically extended. And a drying process including a setting process and a baking process thereafter,
In the baking step, the paint dripping of the painted paint is faster than the speed at which the surface of the object to be coated moves from a substantially vertical state to a substantially horizontal state before the dripping occurs due to gravity, and more than the speed at which paint dripping occurs due to centrifugal force. It is characterized in that the object to be coated is rotated around a substantially horizontal axis at a low speed.

The coating step comprises, for example, a first spraying zone and a second spraying zone, and spray-coats the surface of the object to be coated with a predetermined thickness of the coating. When the surface is in the up-down direction, the paint is usually applied to a film thickness that causes a paint dripping. Also,
The drying step includes a setting step of leaving the coated surface as it is after coating the coating material to volatilize the solvent, and a baking step of carrying it into a drying furnace and heating and baking it.

In the coating and drying process as described above, the paint dripping of the coating film is apt to occur when the coating is applied for a few seconds after the paint dripping limit film thickness is exceeded. Is the time of occurrence, and the limit of the coating dripping film thickness is about 40 to 45 μm in the normal topcoating. In addition, when the drying process is set, the second generation time is a state in which dripping of the paint is gradually started after spraying and about 3 to 4 minutes have passed. Further, immediately after the object to be coated is placed in a furnace and heated, that is, when the temperature of the object to be coated has risen to, for example, about 60 ° C. after 20 to 30 seconds, the maximum dripping speed is obtained.
Is the time of occurrence of.

During the baking step, that is, at the third generation time of the above-mentioned paint dripping, the object to be coated is rotated around the horizontal axis to prevent the paint dripping from occurring, and the coating is performed. The surface smoothness is obtained. That is, even if a coating film having a predetermined film thickness is formed, even if the coating dripping does not occur at the first generation timing in the coating process and the second generation timing in the setting process, the coating material does not occur at the third generation timing in the baking process. Since dripping may occur, the object to be coated is rotated at the third generation time.

The rotation operation is a continuous rotation operation, a reversal operation in which normal rotation and a reverse rotation are alternately repeated at a predetermined angle, and a continuous rotation or a reversal operation while stopping at a constant angle. It is performed in various rotation modes such as a rotation type. In addition, the rotation speed is such that the coating surface is in a horizontal state or an inverted state by the time the paint drips, and the speed at which the paint dripping does not occur due to the centrifugal force accompanying the rotation, that is, The speed is set to a speed higher than the speed at which the surface of the object to be coated in the portion changes from a substantially vertical state to a substantially horizontal state before the paint drips due to gravity, and a speed lower than the speed at which the paint drips due to the centrifugal force.

[0013]

In the coating method as described above, the coating object is rotated around the horizontal axis at a predetermined speed at the time of the baking process in which paint dripping occurs, and the film thickness exceeding the paint dripping limit film thickness is obtained. Even if a coating film having the above is formed, the phenomenon of paint dripping is prevented from occurring in the coating film, and a coating film having a high surface smoothness due to a large film thickness is formed.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a front view of an article transfer device used for carrying out the method of the present invention, and FIG. 2 is a plan view of a bottom transfer mechanism.

The article 1 to be coated with the body of an automobile is rotatably mounted on a carriage 4 with front and rear ends fastened to horizontal shafts 2 and 3. This trolley 4 is provided so that it can travel on the floor 6 of the coating line by means of the wheels 5 at the bottom, and the trolley 4 is mounted on a rod 9 that is erected upward from a conveyor chain 8 installed in a pit 7 below the floor 6. Are engaged and transported along the coating line.

Further, a gear box 10 is provided on the horizontal shaft 2.
Bevel gear 11 inside is fixed and bevel gear that meshes with this bevel gear 11
The vertical shaft 13 is fixed to the upper end of the vertical shaft 13, the vertical shaft 13 is supported by the base 4a of the carriage 4, and the sprocket 14 is fixed to the lower end of the vertical shaft 13 which penetrates the carriage 4 and faces the pit 7. A drive chain 15 is arranged in the pit 7 in a region where the work 1 to be rotated is engaged with the sprocket 14.

In the coating process, the vertical surface 1a (both side surfaces), the horizontal surface 1b (roof portion), etc. of the article 1 are coated, and the sprayed zones in the first zone and the second zone are coated with the article to be coated. 1, a mini-bell, that is, a rotary atomizing electrostatic coating machine (not shown) is provided above and on both sides of the coating material 1 to spray the coating material onto the coating object 1. Spray paint to a film thickness that exceeds.

On the other hand, in the drying step, the coated object 1 after coating is
It has a setting step of holding for about 15 minutes and a baking step of heating the coating object 1 in a drying furnace (not shown) to bake the coating film.

Further, in this embodiment, a drive chain 15 for rotatably driving the article 1 is arranged along the baking process of the drying process, and the drive chain 15 is for carrying the carriage 4. A drive system is provided separately from the drive of the conveyor chain 8 so that the function of rotating the article to be coated 1 can be obtained even when the conveyance is stopped. The drive chain 15 can be driven continuously in one direction to continuously rotate the article 1 to be coated, or to drive the article 1 to be reversed by switching the driving rotation direction at predetermined intervals. Can be set to. Also, the drive rotation speed can be arbitrarily set according to various conditions.

Next, the experimental data for confirming the effect on the image clarity of the coated surface by the rotating operation about the horizontal axes 2 and 3 when the object 1 (sample) is actually coated is shown in FIG. 3 shows.

The coating conditions in this data are: a. Paint melamine alkyd (black) Viscosity ... Ford cup # 4 22 seconds / 20 ° C b. Painting machine Minibell (16,000rpm) Shaping air ... 2.0kg / cm ² c. Discharge rate 1st zone: 100cc / min 2nd zone: 150-200cc / min d. Setting time 10 minutes e. Baking conditions 140 ° C x 25 minutes f. Ground smoothness (PGD value) 0.6 (intermediate coating, on PE tape) g. Rotation or reversal operating area Baking (10 minutes) h. Object to be coated Painted on the side of a 30 cm square tube, rotatably supported at the center As can be seen from Fig. 3, when the coating surface is in the vertical state, as shown in A, the top coating film thickness is about 45 µm. Paint dripping occurs and the smoothness is good.

On the other hand, when reversing at an angle of 90 °, 135 °, 180 ° (the reversing speed is equivalent to 6 rpm), B,
As shown in C and D, the larger the reversal angle, the larger the film thickness at which paint drips occur, and the smoothness is improved from good to excellent. It should be noted that when the reversal angle becomes large, the time for the paint flow to flow in the opposite direction due to reversal increases,
The effect of preventing paint dripping is further increased, and the film thickness can be increased.

On the other hand, when continuously rotated, the effect of preventing paint dripping is greatest as shown by E, and the smoothness is excellent due to the increase in the film thickness. The rotation speed in this continuous rotation was 6, 30, and 60 rpm, respectively, but there was no difference due to the speed, and good results were obtained even at 6 rpm. However, it is necessary to set a relatively high rotation speed depending on the type of paint, the film thickness, and the like.

The IG (image gloss) in the image clarity is a ratio of the image clarity to the mirror surface (black glass) being 100, and the PGD lowers the identification degree of the reflected image from 1.0. The value is such that the surface condition of the coating film decreases as

If the rotating speed of the object 1 to be continuously rotated or reversed is slow, there is no effect of preventing paint dripping. On the other hand, if the rotating speed is fast, the centrifugal force causes the coating film to flow to the outside of the rotation, which is similar to paint dripping. The above phenomenon occurs and is set according to the paint dripping speed of the coating film. In setting the rotation speed, for example, as shown in FIG. 4, the paint dripping speed in each zone is obtained, and the rotation speed is set so that the paint dripping does not occur at the maximum speed of the baking process. .

That is, in FIG. 4, the result of measurement of the sagging speed in the course of the setting time (10 minutes) after coating was increased by increasing the film thickness in three stages using the top coating (viscosity Ford Cobb for about 20 seconds). , And the results of measuring the sagging speed during the elapse of the baking time due to heating after the above setting.

As a result of the above FIG. 4, the coating dripping limit film thickness is 40 to
The thickness is 45 μm, and at a film thickness smaller than this, a large sag rate does not occur in the setting process. Then, in the baking step, 20 to 30 seconds after starting the heating by putting the article to be coated 1 in a drying furnace (the article to be coated at a temperature of 60 ° C.), the sagging speed becomes larger than that at the time of setting and becomes maximum for 2 to 5 minutes. It will stop later.

With respect to the occurrence of paint dripping as described above, the paint dripping phenomenon which is easily found by visual observation is 1 to 2 mm, and if such paint dripping occurs, it will be a defective product due to surface defects. In order to suppress the paint dripping phenomenon, the coating surface may be rotated from the vertical state to the horizontal state or the inverted state until the flow of the coating film starts to flow by 1 to 2 mm. On the other hand, when the article to be coated 1 is rotated at high speed, centrifugal force acts on the coating film to cause artificial paint dripping,
Since this occurred when reversing in 0.25 seconds with a radius of 30 cm, the rotation speed is lower than this, but since the reversing or the rotation speed does not have to be constant, the tip speed is
If it is set to 380 cm / sec or less, the occurrence of paint dripping due to centrifugal force can be prevented. Further, as the radius of rotation of the article to be coated 1 increases, the allowable rotation speed decreases.

From the above, in the case of FIG. 4, the object to be coated is turned up to 180 ° or horizontal in the baking step.
The time required to rotate 90 ° can be set to 0.25 seconds to 10 minutes. That is, if it is less than 0.25 seconds, the rotation will be too fast and paint dripping will occur due to centrifugal force, and it will correspond to the sag speed at the paint dripping limit film thickness (40 to 45 μm).
The time should be set to about 10 minutes.

The rotating mechanism of the article to be coated 1 is not limited to the gearbox structure using bevel gears as in the above-mentioned embodiment, and a conventionally known drive mechanism is used depending on the size, weight, etc. of the article to be coated. Can be appropriately adopted.

[0031]

According to the present invention as described above, the article to be coated is rotated around the horizontal axis in the baking step of the drying step at the time when paint dripping occurs due to spray coating on the surface of the article to be coated. It is rotated, and its rotation speed is faster than the speed at which the surface of the object to be coated moves from a substantially vertical state to a substantially horizontal state before paint dripping occurs due to gravity, and more than the speed at which paint dripping occurs due to centrifugal force. By setting a slow speed, even when coating with a film thickness above the paint dripping limit film thickness, it is possible to prevent the paint dripping phenomenon from occurring, and it is possible to paint with a large film thickness and high surface smoothness. The coating that has can be performed.

Since the coating dripping limit film thickness of the object to be coated is greatly increased, it is possible to make the film thickness equal to that of the horizontal coating surface, and the vertical coating surface is mirror-finished like the horizontal coating surface. It can be applied to a highly smooth finished surface.

[Brief description of drawings]

FIG. 1 is a front view showing an article conveying device used in a coating method of the present invention.

FIG. 2 is a cross-sectional plan view of an essential part showing the internal structure of a pit on the floor.

FIG. 3 is a graph showing the relationship between the coating film thickness on the coated surface and the image clarity as the coated object rotates.

FIG. 4 is a graph showing the relationship between the coating processing time and the paint dripping speed when the coating film thickness is changed.

[Explanation of symbols]

 1 Object to be coated 1a Vertical surface 2,3 Horizontal axis 4 Bogie 14 Sprocket 15 Drive chain

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadamitsu Nakahama 3-1, Shinchi Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Takakazu Yamane 3-1-1 Shinchu, Fuchu-cho, Hiroshima Prefecture (56) References JP-A-57-30581 (JP, A) JP-B-59-39179 (JP, B2) British patent 584432 (GB, A)

Claims (1)

(57) [Claims] 1. A method of applying a solvent-containing paint to the surface of an article to be coated, which comprises spray-applying the paint to a film thickness that causes at least a paint dripping on the surface of the article to be vertically extended. And a subsequent drying step including a setting step and a baking step. In the baking step, before the paint dripping of the painted paint occurs due to gravity, the surface of the article to be coated is changed from a substantially vertical state. A coating method in which an object to be coated is rotated around a substantially horizontal axis at a speed higher than a speed at which the paint is dripping due to a centrifugal force, and a speed lower than a speed at which the paint drips due to a centrifugal force.