JP2656610B2 - Painting method - Google Patents

Description

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

(Prior art and its problems) When coating an object to be coated, for example, the outer surface of an automobile body,
The method includes a preparation step of removing dust adhering to the article, a step of applying a paint to the article, and a drying step of drying the applied paint. This drying step is generally performed in two steps of a setting step and a baking step in the case of a thermosetting coating material that is widely used as a coating material. The setting step is a step of slowly evaporating a solvent in the coating material, It volatilizes without generating holes. Therefore, the setting step is performed before the baking step in an atmosphere at a lower temperature than this baking step, for example, at a temperature of 40 ° C. to 60 ° C., which is also called normal temperature or calcination (the baking temperature in the baking step is usually 14 ° C.).
Around 0 ° 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. The term “drip of paint” means that a trace of 1 to 2 mm from the position where the paint is sprayed on the object to be coated is cured by a drying process, and can be visually confirmed on the painted surface. Therefore, the trace is at least
If it exceeds 2mm, it means sagging. Therefore, to have a thickness within the sagging limit means that
It is a thickness that does not cause sagging in the drying process even if it is left as it is after spraying the paint. Conversely, the term "thickness equal to or greater than the sagging limit" means a thickness that causes sagging at least in the drying step if left as it is after spraying the paint.

This dripping of the paint is caused by the flow of the paint applied downward due to the gravity, and "sag" is more likely to occur as the thickness of the paint applied at one time is larger.
The cause of the "sag" is ultimately due to the influence of gravity, so that it is likely to occur on the surface of the object to be coated extending in the vertical direction, that is, the so-called vertical surface. Also, once the sagged painted surface is repaired, even if it is provisionally repaired, it is inevitably inferior to the painted surface where the sagging did not occur. Is an important issue.

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

From the viewpoints described above, in the past, in order to obtain a painted surface with as large a smoothness as possible while preventing "sagging" of the paint, it has been attempted to apply the paint using a paint with low fluidity (small viscosity) as much as possible. I was The so-called "sag limit", in which "sag" of the coating occurs on the vertical surface, was about 40 μm in the thickness of the coating film of the conventional thermosetting coating.
More specifically, the “sag” of the paint is likely to occur at an early stage of the setting process and an early stage of the baking process, particularly at an early stage of the baking process.
The thickness of the coating material to be applied in the coating step is determined so that "sag" does not occur in the magnetism, and the maximum value of the determined thickness, that is, the sag limit value is about 40 μm. Therefore, in order to obtain a coated surface having a much higher degree of smoothness, in the conventional coating method, it is necessary to repeat a series of steps from the coating step to the baking step a plurality of times, for example, twice coating. was there.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a coating method capable of obtaining a coated surface with even greater smoothness if the thickness of the coating film is the same. And

(Means for Solving the Problems, Function) The present invention basically relates to the fluidity of the paint by appropriately changing the direction of gravity acting on the paint applied to the object to be coated. Is positively utilized so as to obtain a painted surface having a higher smoothness if the film thickness is the same. Specifically, the configuration is as follows. That is, in a coating method having a coating step of applying a coating material to an object to be coated and a drying step of interfering with the coating material applied to the object to be coated, at least one of the coating step or the drying step may include a dripping of the coating in at least the drying step. Is applied, and the object to be coated is rotated around a substantially horizontal axis while the paint is dripping.

More specifically, in the coating process, a disturbance that causes dripping is applied to at least one of the coating process and the drying process, and at least before dripping occurs in the coating material, dripping does not occur. By rotating the object to be rotated about a substantially horizontal axis, an object to be coated having a coated surface free from sagging is obtained.

As described above, in the present invention, the direction of gravity acting on the paint applied to the object to be coated is changed by rotating the object to be coated in the horizontal direction. Without drying.

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 if the thickness of the coating film is the same as before,
Utilizing the fluidity of the paint, it is possible to obtain an excellent painted surface having smaller irregularities, that is, a greater smoothness.

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 thickness of the paint to be applied can be made thinner than the conventional one, The amount of paint used can be reduced by the amount that can be made thinner.

Of course, paints that cause "sags" even with thin coatings
It may be obtained by reducing a component that inhibits fluidity from a conventional paint by a predetermined ratio (in a conventional paint,
In order to improve the sag limit, an anti-sagging agent for reducing the fluidity is mixed).

In particular, in the present invention, a disturbance that causes dripping of the paint is applied in the coating step or the drying step.In other words, it is possible to use a paint that does not droop unless disturbance is applied. Thus, the coating material can be provided with a large fluidity such that dripping occurs only when necessary. This means that there is no need to be restricted by the components of the paint or the coating method (for example, the interval time in the case of one-time spraying, two-time blowing, and two-time blowing), and the degree of necessity is large. More specifically, for example, even in a case where sagging does not occur in the drying process due to a thin film thickness, it is possible to provide a large fluidity that causes sagging in the drying process. Improvement of smoothness utilizing large fluidity and rotation can be easily obtained even in the case of a thin film thickness. (Of course, even in this thin film thickness, dripping is caused in a drying process without giving disturbance. You can also
In this case, there are great restrictions on the paint components and the like).

Disturbances that cause the paint to sag include heating and vibration. For example, in the case of heating, the setting process is much lower than the baking process in the thermosetting paint,
For example, this is done in a normal temperature atmosphere, but by heating in this setting step in the same way as in the baking step, even if the coating does not cause dripping in the setting step or baking step, it can easily cause dripping in the setting step. Can be. In addition, since the paint has sufficient fluidity, no problem such as generation of pinholes will occur even if heating is performed in the setting step.

The rotation axis of the object to be coated may be in a range inclined about 10 degrees with respect to the horizontal axis. The rotation may be continuous rotation in one direction, or may be reversal (forward / reverse rotation) such that the object is rotated in one direction by a predetermined angle and then rotated in the opposite direction.

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 P4.

First, the body W, for which undercoating has been completed as is known by electrodeposition coating, is sent to the preparation process P1 while being held by the carriage D. In the preparation step P1, dust inside and outside the body W is removed by, for example, air blow or vacuum suction. Thereafter, in step P2, paint is sprayed on the body W. Then, the paint is dried in the setting step P4 and the baking step P5.

When the processes P1 to P4 are for intermediate coating, after the process P4, the body W is sent to the process for top coating. In addition, steps P1 to P4
Is for overcoating, the body W is transported to the assembly line in a known manner.

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

As described above, by removing the dust while rotating the body W, the dust adhered to the inside of the closed section such as the inner corner of the roof panel or the side sill of the body W, that is, the body W must be rotated. It is possible to completely remove dust that does not fall.

The rotation range of the body W is 36 as shown in FIG.
The rotation may be 0 °, but may be rotated in the range of 180 ° (in the range of FIGS. 2A and 2E) in accordance with the rotation of the body W in the drying process described later. Things.

Spraying and drying of paint First, spraying of paint at P2 is performed so that the thickness of the coating film is within the sag limit. In other words, in the case of a thermosetting paint generally used in the past, the maximum thickness of the paint that does not cause “sag”, that is, the sag limit value is about 40 μm, but in the process P2, the coating thickness is thinner than the sag limit of 40 μm. The paint is sprayed so as to form a film (for example, 35 μm).

After P2, the process proceeds to the setting step of P3. In this setting step P3, as shown by the α line in FIG. 16,
The body W is heated in the same manner as the heating in the printing step p4 indicated by β rays. The heating in the setting step P3 becomes a disturbance for giving the paint a large fluidity that causes dripping. That is, when the setting step P3 is performed at normal temperature (20 ° C.) and heating is performed only in the baking step P4 after the setting step P3, there is no fluidity of the paint at 35 μm, and the setting is performed at 45 μm. It has such a large fluidity that sagging occurs in both the process P3 and the baking process P4. Thus, 35μ
Even in a state in which the paint does not sag as a thin film thickness such as m, the paint can have a large fluidity by heating as a disturbance. Note that the paint conditions for obtaining the data shown in FIG. 16 are the same as those in FIGS. 3 and 4 described later for each thickness.

In the setting step P3 where this disturbance is given, the second
As shown in FIGS. (A) to (i), the body W is rotated in the horizontal direction.

As for the rotation speed, the fluidity of the paint is improved by disturbance (overheating of the paint surface), the gravity applied to the paint is more than the viscosity of the paint on the paint surface, and the dripping occurs due to the paint moving in the direction of gravity. First, the speed at which the painted surface is changed from a vertical state to a horizontal state at least. In addition, the upper limit value is limited to a rotation speed in a range in which the paint having improved fluidity due to disturbance (paint surface overheating) does not cause dripping due to centrifugal force generated by rotation. Preferably, the maximum sagging speed of the paint is determined in advance by an experiment, and the rotational speed may be determined in accordance with the maximum sagging speed.

That is, the body W is rotated around the rotation axis l extending in the horizontal direction. In the embodiment, the rotation axis l is
It extends in the front-back direction of the body W. In addition,
When rotating the body W about a substantially horizontal axis, the rotation axis may be inclined by about 30 ° with respect to the horizontal axis.
Preferably, the inclination is within 10 °.

In the baking step P4, for example, the paint is baked in a 140 ° C. temperature atmosphere. In P4, since the paint is sufficiently cured, the rotation of the body W is no longer necessary, but from the viewpoint of uniform heating of the body W, the body W may also be rotated in P4.

In addition, the period during which the body W is rotated about the substantially horizontal axis may be at least in the drying step from before the coating surface is dripped until it is cured until the coating surface is not dripped. Of course, the body W may be rotated throughout the entire drying process from the viewpoint of equipment and the like.

The rotation speed of the body W changes depending on the thickness and viscosity of the sprayed paint, but is basically set to a rotation speed in the range between the lower limit and the upper limit as described below. In other words, the lower limit of the rotation speed is the minimum value of the rotation speeds at which the coating surface can be changed from at least the vertical state to the horizontal state before the paint on the coating surface moves due to gravity and sags. The upper limit value is a maximum value among rotation speeds at which no dripping occurs due to centrifugal force generated by rotation. When the body W is rotated about a substantially horizontal axis, the rotation axis may be inclined by about 30 ° with respect to the horizontal axis, but it is preferable that the inclination be within 10 °.

The period during which the body W is rotated about the substantially horizontal axis may be at least as long as the coating surface is cured until no dripping occurs on the coating surface in the drying step. Of course, the object to be coated may be rotated over the entire drying process from the viewpoint of equipment and the like.

In addition, this rotation may be any of continuous rotation in one direction, forward / reverse rotation alternately performing forward rotation and reverse rotation, and intermittent rotation in the middle of a rotation stop period.

As the paint used in the present invention, any paint can be used as long as it is a paint that is usually used for applying to an object to be coated. For example, a thermosetting paint, a two-pack type paint, a powder Paints and the like. The paint may be appropriately selected depending on the application means, the type of disturbance, the rotation speed of the object to be coated, and the like. If necessary, for example, the used amount of the anti-sagging agent and the solvent can be increased or decreased.

The reason why the number average molecular weight is preferably in the range of 2,000 to 20,000 as a paint for automobiles is that if it is less than 2,000, it is a paint that cures with an electron beam or ultraviolet light, and this paint has a high crosslinking density and is durable because of its brittleness (2 to 3 years), which is not very suitable for use in automobile outer panels. Also, 20000
If the viscosity exceeds the above, a large amount of solvent is required because the viscosity becomes high, and it is not preferable because a large amount of solvent is discharged.Moreover, for latex polymers having a number average molecular weight of more than 20,000, the viscosity becomes high immediately after spraying, so that the It is not preferable because it is difficult to improve the properties.

Coating upper limit film thickness In the coating method according to the present invention, the upper and lower limit rotation speeds are determined for each coating film thickness. In other words, the lower limit of the rotation speed is the minimum value of the rotation speeds at which the coating surface can be changed from at least the vertical state to the horizontal state before the paint on the coating surface moves due to gravity and sags. The upper limit value is a maximum value among the rotation speeds not generated by the centrifugal force generated by the rotation.

As described above, the lower limit of the rotation speed is the minimum value for suppressing dripping, and is increased as the film thickness increases, and the upper limit is the maximum value of the occurrence of centrifugal force, and The upper limit film thickness of the coating is a film thickness at which the lower limit and the upper limit rotational speed coincide with each other.

As shown in FIG. 20, as a result of a coating experiment performed under the same conditions as the above-mentioned coating conditions, it was found that the coating upper limit film thickness in this case was approximately 185 μm. The above results are obtained at a rotation distance of 30 cm.However, when the coating film thickness and the rotation speed change, that is, when the rotation distance changes, that is, when the tip speed of the rotating coating object changes, the rotation speed and the rotation speed change. The relationship also changes.

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

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

As is apparent from FIG. 4, if the thickness of the coating film is the same, the method in which the body W is rotated is used (see FIGS. 4B, 4C, 4D, and 4C).
E) In the case where no rotation is performed (FIG. 4A), an image having a higher 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 is not rotated, the thickness of the coating film is limited, and 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” (the lower limit of 0.7 in the PGD value) when the body W is not rotated. IG "68"
(Lower limit of 0.8 in PGD value).

As is known, IG (image gloss) in the image sharpness indicates the ratio of sharpness to a mirror surface (black glass) of 100, and PGD indicates the degree of discrimination of a reflected image by 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 / 22 ° C with Ford cup # 4 b. Coating machine: Minibell (16,000 rpm) Shaping air: ^{2, 0} kg / cm ² c. Spraying two times, 1st time: 100 cc / min 2nd time: 150-200 cc / min d. Setting time: 10 minutes x normal temperature e. Baking conditions: 140 ° C x 25 minutes f. Substrate smoothness: 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: 30 cm square cylinder Coating on the side, 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 (specific example) In the method, various paints were applied to different film thicknesses, and the PGD values of the obtained painted surfaces were measured.
Also, the sag limit value at each coating film thickness was measured (however, no rotation was applied), and the results are shown in the respective drawings.

Specific Example 1 (1) Treatment of an object to be coated and undercoat / intermediate coating A cold-rolled steel sheet usually used for an automobile body is subjected to a zinc phosphate treatment by a conventional method, and then subjected to cationic electrodeposition at 175 ° C. for 30 minutes. Thus, an undercoat layer having a thickness of 30 μm was formed. Subsequently, a hue black oil-free polyester type intermediate coating was sprayed and baked at 140 ° C. for 25 minutes to form a 35 μm intermediate coating.

(2) Top Coating A solvent diluting coating having the following composition was used as a top coating, and was coated under the following conditions so as to have various film thicknesses shown in Table 2 below.

(A) Paint alkyd melanmin high solid thermosetting paint (average molecular weight of main resin: 2800; (hue: black)) (b) Spraying viscosity: 20 seconds (Ford cup # 4/20 ° C) (c) Non-volatile Min .: 48% by weight (d) Solvent: 25 parts by weight of toluene / 100: 25 parts by weight of Solvesso / 150: 50 parts by weight of Solvesso (e) Anti-sagging agent: Crosslinked acrylic resin powder; 3% by weight based on nonvolatile content) (3) Top coating conditions (a) Coating coater: Mini bell (bell diameter 60 mm: manufactured by Ransburg Japan) 1 stage spray Mini-benyl rotation speed: 1600 rpm Shaping pressure: 3 kg / cm ² Voltage: 90 KV Gun distance: 30 cm (b) Spray Atmosphere: Temperature 20 ℃ ± 2 ℃ Booth air velocity 0.3 ± 0.1m / sec) Push / pull down flow) (c) Setting conditions: Setting start temperature 20 ℃ ±
2 ° C / setting time 10 minutes (d) Baking condition: temperature 140 ° C / time 25 minutes Heating rate: 8 minutes (20 ° C → 140 ° C) (4) Rotation conditions A distance of 75 cm away from the central axis of the object to be coated The object was rotated about a horizontal axis so that both end surfaces of the object were parallel.

The top-coated steel sheet is transported to the setting process under the above coating conditions, and in the setting process,
Using a device equipped with a high-frequency induction coil as shown in Fig. 18, heating was started three minutes after the start of the setting process, and the temperature was raised from 20 ° C to 60 ° C in 30 seconds. Heating was maintained for 1.5 minutes. During the heating, the substrate was rotated at a rate of 30 rpm. In the baking step, neither heating by high-frequency induction nor rotation was applied.

Table 2 below shows the relationship between the thickness of the overcoat layer and the rotation speed by rotating the overcoat layer having various thicknesses applied under the above conditions while applying disturbance by heating. The values in the table mean PGD values. The values in parentheses in the film thickness column in the table below indicate the PG of the overcoat layer having a film thickness of 40 μm obtained without rotating the object to be coated and without applying ultrasonic waves.
Means the D value.

FIG. 21 (a) shows the relationship between the sagging speed of the overcoat layer due to the application of ultrasonic waves as a disturbance and the time of the drying step (setting step and baking step). In the drawing, the chain line shows the sag speed when neither disturbance nor rotation is applied.

Specific Example 2 The cold-rolled steel sheet provided with the intermediate coating layer obtained in Specific Example 1 was subjected to a top coating in the same manner as in Specific Example 1 so as to have a film thickness shown in Table 3 below. In this specific example, in the setting step, instead of the high-frequency induction coil in the specific example 1, a device equipped with a far-infrared lamp as shown in FIG. 17 was used to heat with the far-infrared lamp. The heating conditions were such that the heating was started one minute after the start of the setting step, the temperature was raised from 20 ° C. to 60 ° C. over one minute, and maintained at that temperature for three minutes. During the heating, the substrate was rotated at a rate of 15 rpm. In this example, the disturbance and rotation are applied only during the setting process.
None was applied in the baking step.

 Table 3 shows the relationship between the film thickness and the rotation speed.

FIG. 21 (b) shows the relationship between the coating sag speed and the film thickness when a disturbance is applied without rotating the object to be coated.

Specific Example 3 The cold-rolled steel sheet provided with the intermediate coating layer obtained in Specific Example 1 was subjected to a top coating in the same manner as in Specific Example 1 so as to have a film thickness shown in Table 4 below. In this embodiment, in the setting step, instead of using the high-frequency induction coil of the first embodiment, a transfer device equipped with a heating device as shown in FIG. Did. The heating conditions were such that the heating was started one minute after the start of the setting step, the temperature was raised from 20 ° C. to 60 ° C. in three minutes, and maintained at that temperature for one minute. During the heating, the substrate was rotated at a rate of 10 rpm. In this specific example, the disturbance and the rotation were applied only during the setting step, but were not applied during the printing step.

 Table 4 shows the relationship between the film thickness and the rotation speed.

FIG. 21 (c) shows the relationship between the coating sag speed and the film thickness when a disturbance is applied without rotating the object to be coated.

Example 4 The cold-rolled steel sheet provided with the intermediate coating layer obtained in Example 1 was overcoated in the same manner as in Example 1 except for the following conditions.

(1) Topcoat paint: two-pack type urethane paint (hue black) (a) Main ingredient: acrylic resin (average molecular weight: 1500) (b) Hardener: polyisocyanate (c) Mixing ratio: main ingredient / hardener = 7 / 1 (d) Spraying viscosity: 16 seconds / Ford cup # 4 (20 ° C)
(Not including anti-sagging agent) (e) Non-volatile content: 54% by weight (f) Solvent: 15 parts of ethyl acetate 55 parts of butyl acetate 30 parts of cellosolve acetate 30 parts (2) Baking conditions 90 ° C./25 minutes Heating rate: 5 minutes ( (20 ° C. → 90 ° C.) (3) Sagging limit film thickness: 45 μm The object coated with the top coat as described above is transported to the setting step, and the disturbance by the high-frequency induction coil and the By applying rotation, an overcoat layer having a film thickness as shown in Table 4 below was formed.

Table 5 shows the relationship between the film thickness and the rotation speed. The values in parentheses in the film thickness column in the table indicate PGD values when no disturbance or rotation was applied to the overcoat layer.

FIG. 22 (a) shows the relationship between the coating dripping speed and the film thickness when a disturbance is applied without rotating the object to be coated. In addition, what is indicated by a chain line in the drawing is a value obtained by referring to the sag speed when the top coat layer obtained by applying the top coat under the above conditions and the top coat layer having a thickness of 45 μm is not subjected to disturbance.

Specific Example 5 The cold-rolled steel sheet provided with the intermediate coating layer obtained in Specific Example 1 was overcoated with a film thickness shown in Table 6 in the same manner as in Specific Example 4. In this specific example, in the setting step, a far-infrared lamp is used in the same manner as in the specific example 2 instead of the high-frequency induction coil of the fourth embodiment.
The substrate was heated. In this specific example, the disturbance and the rotation were applied only during the setting step, but were not applied during the printing step.

 Table 6 shows the relationship between the film thickness and the rotation speed.

FIG. 22 (b) shows the relationship between the coating sag speed and the film thickness when a disturbance is applied without rotating the object.

Specific Example 6 The cold-rolled steel sheet provided with the intermediate coating layer obtained in Specific Example 1 was subjected to a top coating in the same manner as in Specific Example 4 so as to have a film thickness shown in Table 7 below. In this example, in the setting step, the object to be coated was heated by internal heating using warm air in the same manner as in Example 3 instead of the high-frequency induction coil of Example 4. In this specific example, the disturbance and the rotation were applied only during the setting step, but were not applied during the printing step.

 Table 7 shows the relationship between the film thickness and the rotation speed.

FIG. 22 (b) shows the relationship between the coating sag speed and the film thickness when a disturbance is applied without rotating the object.

Next, an apparatus for imparting disturbance and rotation in the coating method according to the present invention will be specifically described.

Drying Furnace FIGS. 17 and 18 show a preferred example of the drying furnace 60, and can be used in any of the above-described setting step P3 (when heating as a disturbance) and baking step P4.

In FIG. 17, a large number of infrared panels 61 are provided so as to cover the left, right, side and top surfaces of the body W. In FIG. 18, a high-frequency induction coil 62 is used in place of the infrared panel 61. In both of these embodiments, the convection of air is prevented by setting the upper part of the drying furnace 60 to a sufficiently high temperature, which is preferable in preventing the generation of floating dust as much as possible. In addition to this, in Fig. 18,
The magnetic field can always be kept constant in response to a change in the distance between the body W and the coil 62 accompanying the rotation of the body W, which is more preferable in terms of uniform heating of the body W. In other words, the coil 62 is energized through the rectifier 66 and the inverter 67, but the control unit 88
Controls the inverter 67 to keep the magnetic field constant as described above.

FIG. 19 shows an example in which the body W is heated from the inside, and can be used in combination with any of the drying furnaces shown in FIGS. 17 and 18 and known drying furnaces. That is, in the body W, the heating cylinder 71 having a large number of small holes on the surface is disposed,
Each end of the heating cylinder 71 is connected to a pair of front and rear rotating jigs 1F and 1R (a hollow rotating shaft portion). Then, the heating air is supplied into the heating cylinder 71 via a hose 72 and a rotary joint (not shown). As a result, the body W is sufficiently heated not only from the outside but also from the inside.

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
The 1R is attached to the body W by fixing the bracket 2 to the floor frame 13 as a strength member at the rear end of the body W with bolts.
Of course, since a bumper mounting bracket is welded in advance to the rear end of the floor frame 13 because a general bumper is mounted, the rear jig 1R is utilized by using the bumper mounting bracket. Can also be mounted.

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

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

Dolly This is a dolly that is used in at least P3 and has a function of rotating the body W.

In FIG. 7, the trolley D has a base 21, and this base 21
The wheels 22 attached to the vehicle run 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 supports 25, 26, and one rear support 27, and a space between the intermediate supports 25, 26 and the rear support 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 rotation shaft 5 thereof) can be freely disengaged from the columns 26 and 27 from above and below, and the rear jig is also provided.
1R is immovably engaged in the direction of the rotation axis l. For this reason, the notch 26a which opens in the upper end surface is formed in the intermediate support | pillar 26 (refer FIG. 10-12), The notch 27a which opens in the upper support surface is formed in the rear support | pillar 27. (First
FIG. 0, FIG. 14, FIG. 15). These two notches 26a, 27a
Is large enough to fit the rotating shafts 5 of the jigs 1F and 1R. The flange 5a is attached to the rotating shaft 5 of the rear jig 1R.
On the other hand, a notch 27b having a shape corresponding to the flange portion 5a communicating with the notch 27a is formed in the rear support column 27. As a result, the rear jig 1R has the notch
It is disengaged from the vertical direction with respect to 27a, 27b, and is immovable in the front-rear direction with respect to the rear support column 27 by the stopper action of the flange portion 5a. The application of the rotational force to the body W is performed via the rotary shaft 5 of the front jig 1F.
(See also FIG. 5).

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

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

A transmission mechanism 35 for transmitting the rotation of the rotation shaft 32 to (the rotation shaft 5 of) the front jig 1F is configured as follows. That is, the transmission mechanism 35 includes a casing 36 fixed to the rear surface of the front support 24 and a rotating shaft 37 that extends in the lateral direction (front-rear direction) and is rotatably supported by the casing 36.
A pair of bevel gears 38 and 39 for interlocking the rotation shaft 37 and the upper rotation shaft 32, and a connection shaft 40 held rotatably and slidably in the front-rear direction with respect to the intermediate support 25. Have. The connecting shaft 40 is spline-coupled to the rotating shaft 37 (the 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 truck D is indexed via 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.

Supplementary Explanation and Modifications Next, a supplementary explanation and modification examples of a bogie, a painting method, and the like related to the present invention will be sequentially described.

When performing overcoating after intermediate coating, water sharpening after the intermediate coating baking step can be eliminated. In this case, the body W may be rotated only in one of the intermediate coating step and the top coating step. That is, the quality of the final painted surface obtained after the top coat is determined by the quality of the middle coat, but when the body W is rotated with the middle coat, the finish level of the middle coat is reduced. Since the height can be increased, the conventional water sharpening is unnecessary. In addition, if the body W is rotated with the top coat, the poor finish of the middle coat can be covered with the good top coat without performing water sharpening with the middle coat.

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

Regardless of the traveling or stopping of the cart D, the switching of the rotation and the stop of the body W and the switching of the rotation direction can be performed by using a special actuator such as an air motor, for example. it can. First, the seventh
In the example shown in the figure, a first and second pair of chains (corresponding to the chain 34) are provided on the sprocket 33 so as to mesh with each other from the radially opposite side, and each of the chains can be appropriately driven. deep. With such a configuration, the rotation of the body W is controlled according to the following driving mode.

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

First chain free and second chain stop: In this case, the body W is rotated in the opposite direction as the 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 a direction opposite to that of the 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.

As a disturbance for imparting large fluidity that causes dripping to the paint, vibration may be used in addition to heating. In this case, for example, the rails 23 of the carriage D may be provided with irregularities, or the speaker may be acoustically vibrated.

Disturbance for imparting large fluidity that causes dripping to the paint may be given in the painting process P2. In this case, it is preferable to heat so as to have substantially large fluidity particularly in the subsequent setting step.
In the case where the coating W has sufficient fluidity to cause dripping during the coating process P2, the body W may be rotated also in the coating process P2.

(Effects of the Invention) As is apparent from the above description, the present invention utilizes the fluidity of the paint and the rotation of the object to be coated, and has a higher smoothness than the conventional one if the thickness of the paint is the same. A quality painted surface can be obtained.

In addition, since the paint is given a large fluidity by applying disturbance, it is not versatile to the paint components and its coating conditions, etc. Becomes

[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 view showing the relationship between the thickness of a paint, sagging characteristics and heating. 17 and 18 are diagrams showing a preferred example of a drying oven. FIG. 19 is a diagram showing a preferred method of drying an object to be coated. FIG. 20 is a graph showing the relationship between the upper and lower coating thickness limits and the number of rotations. FIGS. 21 (a) to 21 (c) are graphs showing the sag limit value during the drying step when disturbance is applied to the overcoat layer (however, no rotation is applied). FIGS. 22 (a) to 22 (c) are graphs showing the dripping limit during the drying step when disturbance is applied to the overcoat layer (but no rotation is applied). P1 to P4: Process W: Body l: Rotation axis D: Transport cart 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 drying step of drying the coating material applied to the object to be coated, wherein at least one of the coating step or the drying step is performed in at least a drying step. A coating method characterized by applying a disturbance that causes dripping of the paint, and rotating the object to be rotated about a substantially horizontal axis while the paint is dripping.