JPH07910A - Coating method - Google Patents

Abstract

PURPOSE:To excellently form a film in specified thickness or more by rotating a material to be coated at a speed where the material surface is turned from vertical to horizontal and at a low speed where a paint is not dripped before the paint applied on the material surface is dripped by gravity. CONSTITUTION:A material 1 to be coated such as an automobile body is rotatably placed on a truck 4 with the front and rear ends supported respectively by horizontal shafts 2 and 3. Meanwhile, the truck 4 is traveled on the floor 6 of a coating line by means of its wheels 5, engaged with a rod 9 erected on a conveyor chain 8 set in a pit 7 below the floor 6 and conveyed. A driving chain 15 engaged with a sprocket 14 is arranged in the region in the pit 7 where the material 1 is rotated. The material 1 is rotated before the paint applied on the material 1 surface is dripped by gravity, namely, at a speed where the surface of the material 1 is turned from vertical to horizontal and at a low speed where the paint is not dripped.

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 that the coating amount be changed according to the surface to be coated to achieve uniform coating.

On the other hand, when forming a coating film from a coating material containing a solvent for producing gloss on the coated surface of the object to be coated, the coating amount is increased to increase the film thickness of the coating surface. The high smoothness is obtained and the quality is improved.

Further, it is generally known that the viscosity of a paint attached to an object to be coated is lower as the content of a solvent is higher, and the viscosity immediately after being applied to the object to be coated is lower.

[0005]

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 paint is in the up-down direction or in an inclined state, the viscosity of the applied paint loses gravity and flows downward, causing "paint sag", which creates irregularities on the coated surface and impairs smoothness. It will reduce the quality of the membrane.

Whether the coating dripping of the coating film occurs immediately during coating when the film thickness exceeds the limit value in the coating spraying process, or when a predetermined time has elapsed during the setting for volatilizing the solvent after spraying. In addition, since the coating film is baked, it is likely to occur when the temperature is raised in the initial stage of heating in the drying furnace.

[0007] 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 several times. 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, the present invention has a simple method for increasing the coating sag limit film thickness so that a high film thickness can be applied once without causing paint sag on the upper and lower surfaces of an object to be coated. It is an object of the present invention to provide a coating method which is obtained in step 1 above and provides a high-definition image and a high-smooth coating surface by high-smooth finish coating with an increase in film thickness.

[0009]

In order to achieve the above object, the coating method of the present invention is to support an object to be coated rotatably around a substantially horizontal axis, and to move the object in the normal vertical direction on the surface of the object. On the extended surface, a coating step of applying a coating material containing a solvent to a film thickness that causes coating dripping, and a drying step of curing the coating material on the surface of the coating object with a subsequent setting step and baking step, at least Before the paint drip of the paint applied to the surface of the object to be coated is caused by gravity due to gravity in the setting step, the object to be started to rotate about a substantially horizontal axis, and the rotation in this case is at least the paint drip of the applied paint. At a speed such that the surface of the object to be coated transitions from a substantially vertical state to a substantially horizontal state before
In addition, it is characterized in that it is rotated at a speed lower than the speed at which paint drips due to the centrifugal force due to rotation.

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 film thickness. 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 several seconds after exceeding the paint dripping limit film thickness in the coating process. Is the time of occurrence, and the limit of the coating dripping film thickness is about 40 to 45 μm in the normal topcoating. When it does not occur at the time of coating, the second generation time is a state in which dripping of the paint gradually starts after spraying and about 3 to 4 minutes have elapsed at the time of setting in the drying process. Further, immediately after heating the article to be coated and heating it in the furnace, that is, when the temperature of the article to be coated has risen to, for example, about 60 ° C. after 20 to 30 seconds is the third generation timing at which the maximum sag rate is reached.

Then, at least during the setting step, that is, at the second generation time when the above-mentioned paint dripping occurs, the object to be coated is rotated around the horizontal axis to prevent the paint dripping from occurring. The smoothness of the painted surface is obtained.
That is, when the film thickness of the coating film is considerably larger than the limit value, or when the viscosity of the coating material is low and the fluidity is large, paint dripping occurs from the first generation time in the coating process. It is necessary to rotate the coated object for all of the first to third generation times. On the other hand, in the setting step and the baking step, when the coating film thickness is not so large, or the coating material has a high viscosity and a coating film having a predetermined film thickness is formed and paint dripping does not occur at the first generation time, The object to be coated may be rotatably operated in the drying steps of the second and third generation times.

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 further, 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 be higher than the speed at which the surface of the object to be coated shifts from the substantially vertical state to the substantially horizontal state before the paint dripping occurs due to gravity, and slower than the speed at which the paint dripping occurs due to the centrifugal force due to the rotation.

[0014]

In the coating method as described above, at least during the setting step in which paint dripping occurs, the object to be coated is rotated around the horizontal axis at the above-mentioned predetermined speed so that the paint dripping limit film thickness or more is exceeded. Even if a coating film having a thickness of 2 is formed, it is possible to prevent the phenomenon of paint dripping occurring during coating and drying, and to form a coating film having high surface smoothness due to a large thickness. I have to.

[0015]

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 which 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, and the vertical shaft 13 is supported by the base portion 4a of the carriage 4, and the sprocket 14 is fixed to the lower end portion 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 painted, and the sprayed zones of 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, in the range from the second zone of the coating process to the middle of the drying process,
A drive chain 15 for rotatably driving the article to be coated 1 is arranged, and this drive chain 15 has a drive system separately from the drive of the conveyor chain 8 for transporting the carriage 4, and when the transport is stopped. Also, the rotation actuating function of the article to be coated 1 is obtained. 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 rotation operation about the horizontal axes 2 and 3 when the coating 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. Rotating or reversing operating range setting (10
Min) -baking (10 min) h. Object to be coated Painted on the side of a 30 cm square cylinder, 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. In addition, when the reversal angle becomes large, the flow time of the paint flows in the opposite direction due to reversal, and
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) of 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 rotation speed of the object 1 to be continuously rotated or reversed is slow, the effect of preventing paint dripping is not obtained. On the other hand, if the speed of rotation is fast, the centrifugal force causes the coating film to flow to the outer side of 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 even at the maximum speed.

That is, in FIG. 4, the result of measurement of the dripping speed in the course of the setting time (10 minutes) after coating is increased by increasing the film thickness in three stages by using the top coating material (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
It is 45 μm, and at a film thickness smaller than this, a large sag rate does not occur. Then, when the coating dripping exceeds the above-mentioned limit film thickness, it occurs after a few seconds and reaches the maximum dripping speed 3 to 4 minutes after coating. In addition, 20 to 30 seconds after starting the heating of the object to be coated 1 in a drying oven (object temperature of 60 ° C.)
The sagging speed becomes larger than that at the time of setting and reaches the maximum, and stops after 2 to 5 minutes.

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 becomes a defective product due to surface defects. In order to suppress the phenomenon, it is sufficient to rotate the coating surface 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, which is the radius of 30
Since it occurred when reversing in cm for 0.25 seconds, the rotation speed is lower than this, but since the reversal or the rotation speed does not have to be constant, it is recommended that the tip speed be 380 cm / sec or less. For example, it is possible to prevent paint dripping due to centrifugal force. 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 180 ° inverted or 90 ° to the horizontal state.
The time required for rotation should 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. Also, in each zone for about 10 minutes corresponding to the sag speed at the paint dripping limit film thickness (40 to 45 μm), It should be set.

The rotating mechanism of the article to be coated 1 is not limited to the gear box structure using the bevel gear 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.

[0032]

According to the present invention as described above, the object to be coated is rotated around the horizontal axis at least in the setting step of the drying step at the time when paint dripping occurs due to spray coating on the surface of the object to be coated. The rotation speed is higher 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 paint drips due to gravity, and is slower than the speed at which the paint drips due to centrifugal force. By setting to 1, it is possible to prevent the phenomenon of paint dripping during coating and drying even when coating with a film thickness above the paint dripping limit film thickness, and it becomes possible to coat large thicknesses. A coating having surface smoothness can be applied.

Since the coating sag 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

Front page continued (72) Inventor Tadamitsu Nakahama 3-1, Fuchu-cho Shinchi, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Takakazu Yamane 3-3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd.

Claims (1)

[Claims] 1. A method of applying a solvent-containing paint to the surface of an article to be coated, wherein the article to be coated is rotatably supported about a substantially horizontal axis, and the surface of the article to be coated is ordinarily rotated vertically. On the surface extending to, there is a coating step of applying the coating to a thickness greater than that of the coating dripping, and a drying step of curing the coating material on the surface of the coated object, which includes a subsequent setting step and a baking step, and at least the setting step described above. Before the paint drip of the paint applied to the surface of the coated object is caused by gravity, the coated object starts rotating about a horizontal axis, and in this case, at least before the paint drip of the applied paint is generated by gravity. In addition, the coating is characterized in that it is rotated at a speed such that the surface of the object to be coated changes 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 centrifugal force due to rotation. How to wear.