JPH01315371A - Painting method - Google Patents

Abstract

PURPOSE:To form a painted surface having high smoothness by applying such disturbance which causes the sag of a paint in at least either of a painting stage or drying stage and rotating the work approximately around the horizontal axial line during the state when the paint sags. CONSTITUTION:A painting stage P2 for coating the paint on the work W and a drying stage for drying the paint coated on the work W are provided. Such disturbance (e.g., heating, vibration) which causes the sag of the paint in at least either of the painting stage P2 or the drying stage is applied to the work and the work W is rotated approximately around the horizontal axial line (l) during the state when the paint sags. As a result, the painted surface having the higher smoothness than heretofore and high quality with the same thickness of the paint is formed by utilizing the flowability of the paint and rotation. Since the large flowability is given to the paint by applying the disturbance, thereto, the components of the paint, the painting conditions, etc., are not largely restricted and have wide versatility.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a coating method.

(Prior art and its problems) When painting the outer surface of an object to be painted, such as an automobile body, there are a preparation process for removing dust adhering to the object, a process for applying paint to the object, and a coating process. and a drying step of drying the painted paint. This drying process is generally carried out in two stages, a setting process and a baking process, in the case of thermosetting paints, which are commonly used as paints. In other words, the setting process is performed before the baking process at a temperature lower than that of the baking process, such as room temperature or 40° to 60°C (also called calcination). °
It is carried out in a temperature atmosphere of C (the baking temperature in the baking process is usually around 140°C).

The object to be coated is usually conveyed by means of transportation such as a trolley while going through the above preparation process, painting process, and drying process. It is still being done.

By the way, one of the criteria for evaluating the quality of painted surfaces is:
It has smoothness (flatness), and the higher the smoothness, the smaller the degree of unevenness on the painted surface, resulting in a better painted surface. It is already known that in order to improve the smoothness of the painted surface, it is sufficient to increase the thickness of the paint film, that is, the film thickness of the applied paint.

On the other hand, paint sag is a factor that impairs the quality of painted surfaces. Paint sag refers to traces of paint sprayed on an object being moved by lrnm to 2 mm from the position of adhesion that can be visually confirmed on the painted surface before it hardens through the drying process. Therefore, if the above-mentioned trace exceeds at least 2 mm, it is considered that sagging has occurred.

Therefore, a film thickness within the sag limit means a thickness that does not cause sag during the drying process even if the paint is left as is after being sprayed. On the other hand, making the film thicker than the sag limit means that if the paint is left as is after being sprayed, it will be small (this refers to a thickness that would cause sag during the drying process).

This paint sag occurs when the applied paint flows downward under the influence of gravity, and the thicker the paint that is applied at one time, the more likely it is that "sag" will occur (this °° sag). The cause of this is, after all, the effect of gravity, so it is more likely to occur on surfaces that extend in the vertical direction of the object to be painted, that is, so-called vertical surfaces.Also, even if a painted surface that has sagged is repaired by sheet metal, , the smoothness is inevitably inferior to that of a painted surface that does not sag,
Preventing sag is an important issue in obtaining a highly smooth painted surface.

Therefore, on surfaces extending in the horizontal direction of the object to be coated, that is, so-called lateral surfaces, where the amount of sagging of the paint is not a problem, it is possible to apply a thicker coating than on the vertical surfaces. Even if the thickness of the paint film on the vertical side is the same as the thickness of the paint film on the vertical side, the unevenness on the horizontal side will be reduced due to slight flow of the paint that does not cause sagging.
This results in better smoothness than in the vertical plane.

From the above-mentioned point of view, conventionally, in order to prevent the paint from "sagging" and obtain a painted surface with as much smoothness as possible, painting was done using a paint with as little fluidity (low viscosity) as possible. was. The so-called ``sag limit'' at which paint sag occurs on the vertical surface is a maximum coating film thickness of about 40 μm for conventional thermosetting paints.

More specifically, paint sag tends to occur at the beginning of the setting process and the beginning of the baking process, especially at the beginning of the baking process (in order to prevent sagging during this period, the paint applied during the painting process is The maximum value of this determined thickness, that is, the sagging limit value, is about 40 μm.Therefore, if you want to obtain a coated surface with even greater absolute smoothness, the conventional coating method For example, it was necessary to repeat a series of steps from the painting process to the baking process multiple times, such as applying two coats.

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a coating method that can provide a coated surface with even greater smoothness if the thickness of the coating film is the same. purpose.

(Means and actions for solving interlayer points) The present invention basically consists of 1! i By appropriately changing the direction of the gravity that acts on the paint applied to the coating, the fluidity of the paint can be actively utilized, resulting in smoother coatings with the same thickness. This is to ensure a large painted surface. Specifically, the configuration is as follows. That is, in a coating method that includes a coating process of applying paint to an object to be coated and a drying process of drying the paint applied to the object, it is possible to prevent the paint from dripping in at least one of the painting process or the drying process. The structure is such that the object to be coated is rotated around a substantially horizontal axis during conditions that cause the paint to sag.

To be more specific, 1. In the painting process, a disturbance that causes sagging is applied to the object to be coated at least in the painting process or the drying process, and at least the sag is caused to occur before the sag occurs on the object to be coated. The object to be coated is rotated about a substantially horizontal axis until no sag occurs, thereby obtaining a coated object having a coated surface free from sagging.

In this way, 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 in the horizontal direction, so that the paint does not "sag". It will be dried without drying.

According to the present invention, the film thickness of the paint applied per coat can be made much thicker than before, and an extremely good painted surface with smoothness that far exceeds the level conventionally considered to be the limit can be obtained. can.

Further, even when the thickness of the coating film is the same as that of the conventional coating, the fluidity of the coating material can be utilized to obtain an excellent coated surface with smaller irregularities, that is, greater smoothness.

Furthermore, if you try to obtain a painted surface with the same smoothness, for example, the same level of smoothness as that obtained with conventional painting methods,
The film thickness of the paint to be applied can be made thinner than in the conventional method, and the amount of paint used can be reduced by the amount that can be made thinner.

Of course, paints that cause sag even in thin films can be obtained by reducing the components that inhibit fluidity in conventional paints by a predetermined percentage. Therefore, anti-sagging agents are mixed in to reduce fluidity).

In particular, in the present invention, a disturbance that causes the paint to sag during the painting or drying process is applied, so in other words, it is possible to use a paint that does not sag unless a disturbance is applied. This allows the paint to have great fluidity so that it does not sag only when necessary. This means that there is no need to be constrained by the components of the paint or the coating method (for example, the interval time in the case of one-time spraying, two-time spraying, two-time spraying, etc.). More specifically, even if it is necessary to avoid sagging during the drying process due to the thin film thickness, it is possible to provide a large fluidity during the drying process that would cause sagging. Improvement in smoothness using this large fluidity and rotation can be easily obtained even in the case of a thin film (of course, even with this thin film thickness, it is necessary to ensure that sagging occurs during the drying process without causing disturbances). Although it is possible,
In this case, there are major restrictions on paint components, etc.).

Disturbances that cause paint to sag include heating and vibration. For example, in the case of heating, with thermosetting paints, the setting process is done at a much lower temperature than the baking process, for example in a room temperature atmosphere, but by heating in this setting process in the same way as the baking process, the setting Even if the paint does not sag at all during the printing or baking process, it can easily sag during the setting process. Since the paint has sufficient fluidity, even if it is heated during the setting process, problems such as pinholes will not occur.

The axis of rotation of the object to be coated may be tilted by about 10 degrees with respect to the horizontal axis. Further, the rotation may be continuous rotation in one direction, or may be reversed (forward and reverse rotation), such as rotating the object to be coated by a predetermined angle in one direction and then rotating it in the opposite direction.

(Example) Hereinafter, an example of the present invention will be described based on the attached drawings.

Overall Overview FIG. 1 shows the overall process for painting an automobile body W as an object to be coated, and each process is indicated by PI-P4.

First, the body W, which has been undercoated by electrodeposition coating in a known manner, is sent to the preparation step PI while being held on a trolley. In this preparation step Pi, dust inside and outside the body W is removed by, for example, air blowing or vacuum suction. After that, in step P2, paint is sprayed onto the body W. Then, the paint is dried in a setting step P4 and a baking step P5. ,
If step PL-P4 is for intermediate coating, the body W is sent to the top coating step after step P4. Also, process P
If I-P4 is for topcoating, the body W is transported to an assembly line in a known manner.

Dust removal in the dust removal step PI is performed while rotating the body W around the horizontal axis β, as shown in FIG. That is, for example, first, the rotation of the body W is stopped in the state shown in FIG. 2(a) to remove dust, and then the dust is removed as shown in FIG. 2(b).
The posture of the body W is changed to the state shown in FIG. In this way, dust is removed while the body W is intermittently rotated as shown in (c), (d), . . . (i) in FIG.

In this way, by removing dust while rotating the body W, it is possible to remove dust adhering to closed sections such as the inside corners of the roof panel and side sills of the body W, i.e., if the body W is not rotated. It becomes possible to completely remove even the garbage that does not fall.

The rotation range of the body W is 36 degrees as shown in FIG.
Although it may be rotated by 0°, it may be rotated by 180' (the range shown in Fig. 2 (a) and (e)) as appropriate, in accordance with the rotation of the body W in the drying process, which will be explained later. It can be made into

Spraying and Drying of Paint Film First, the paint is sprayed in P2 so that the thickness of the paint film is within the sag limit. In other words, in conventional thermosetting paints, the maximum thickness of the paint that does not cause sag, that is, the sag limit value, is about 40 μm, but in process P2, the coating is thinner than this sag limit of 40 μm. The paint is sprayed so as to form a film (for example, 35 μm).

After this P2, the process moves to P3, a setting process.

In this setting step P3, the body W is heated as shown by the alpha line in FIG. 16 in the same manner as the heating in the baking step p4 shown by the beta line. This setting process P
The heating at step 3 acts as a disturbance to give the paint enough fluidity to cause sag. In other words, if the setting process P3 is performed at room temperature (20°C) and heating is performed only in the baking process P4 after this setting process P3,
In the case of μm, total (there is no fluidity of paint, 45
In the case of μm, it has such a large fluidity that it causes sag in both the setting process P3 and the baking process P4. In this way, even if the coating film is as thin as 35 μm and would not normally cause the coating to sag, it is possible to impart great fluidity to the coating by heating as a disturbance. The paint conditions for obtaining the data shown in Figure 16 are as follows for each thickness:
This is the same as in FIGS. 3 and 4, which will be described later.

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

At this rotation speed, the fluidity of the paint improves due to disturbance (overheating of the painted surface), and the gravity applied to the paint exceeds the viscosity of the paint on the painted surface, causing the paint to move in the direction of gravity, resulting in sagging. This is the speed at which the painted surface is brought from a vertical state to a horizontal state.
The rotational speed is limited to a range where the paint, which has improved fluidity and texture due to overheating of the painted surface, does not sag due to the centrifugal force generated by rotation. Preferably, the maximum sagging speed of the paint can be determined in advance through experiments, so the rotational speed may be determined in accordance with this maximum sagging speed.

That is, the body W is rotated around a rotation axis β that extends in the horizontal direction, and in the embodiment, this rotation axis β extends in the front-rear direction of the body W. Note that when the body W is rotated around a substantially horizontal axis, the rotation axis may be inclined by about 30 degrees with respect to the horizontal axis.
Preferably, this inclination is within 10''.

In the baking step P4, the paint is baked in an atmosphere at a temperature of, for example, 140°C. In this P4,
Since the paint is sufficiently cured, it is no longer necessary to rotate the body W, but from the viewpoint of uniformly heating the body W, the body W may be rotated even at this P4.

Further, the period for rotating the body W around the approximately horizontal axis may be any period from before sagging occurs on the painted surface until it hardens until no sagging occurs (at least in the drying process).Of course, equipment etc. Due to this relationship, the body W may be rotated throughout the drying process.

The rotational speed of the body W varies depending on the film thickness and viscosity of the sprayed paint, but is basically set to a rotational speed within a range between the following lower limit and upper limit. That is, the lower limit of the rotational speed is the minimum value of the rotational speeds at which the painted surface can be brought from at least a vertical state to a horizontal state before the paint on the painted surface moves by gravity and sag.

Further, the upper limit value is the maximum value among the rotational speeds at which sagging does not occur due to centrifugal force generated by rotation.

Note that when the body W is rotated around a substantially horizontal axis, the rotation axis may be inclined at an angle of about 30 degrees with respect to the horizontal axis, but it is preferable that this inclination is within 10 degrees.

The period during which the body W is rotated around the approximately horizontal axis is as follows:
At least in the drying step, it may be from before sagging occurs on the coated surface until it is cured until no sagging occurs. Of course, the object to be coated may be rotated throughout the drying process depending on the equipment and the like.

Further, this rotation may be continuous rotation in one direction, forward/reverse rotation that alternately performs forward rotation and reverse rotation, or intermittent rotation with a rotation stop period in between.

As the paint used in the present invention, any paint that is commonly used for coating objects can be used, such as thermosetting paints, two-component mixed paints, powder paints, etc. Examples include paint and the like. The paint should be selected appropriately depending on the application means, type of disturbance, rotational speed of the object to be coated, etc. For example, the amounts of the anti-sag agent and the solvent can be increased or decreased as needed.

Number average molecular weight of 2000-2000 for automobile paint
The reason why it is preferable to set the range to 0 is as follows.

Those with a coefficient of less than 2,000 correspond to paints that are cured by electron beams or ultraviolet rays, and these paints have a high crosslinking density (they are brittle, so they are not durable (2 to 3 years)) and are not very desirable for use on automobile exterior panels. In addition, if it exceeds 20,000, the viscosity becomes high, requiring a large amount of solvent, and a large amount of solvent is discharged, which is undesirable.
Latex polymers with a viscosity exceeding 0 are undesirable because their viscosity increases immediately after spraying, making it difficult to improve smoothness.

(Hereinafter in the margin) In the coating method according to the present invention, the upper limit and lower limit rotation speed are determined for each coating film thickness. That is, the lower limit of the rotational speed is the minimum value of the rotational speeds at which the painted surface can be brought from at least a vertical state to a horizontal state before the paint on the painted surface moves by gravity and sag. Further, the upper limit value is the maximum value among the rotational speeds at which sagging does not occur due to centrifugal force generated by rotation.

In this way, the lower limit of the rotational speed is the minimum value for preventing sagging, and increases as the film thickness increases, and the upper limit is the maximum value for centrifugal force generation, and increases as the film thickness increases. The upper limit coating thickness is the thickness at which the lower limit and upper limit rotation speed match.

As shown in FIG. 20, as a result of a coating experiment conducted under the same coating conditions as described above, it was found that the upper limit coating thickness in this case was approximately 185 μm. Note that the above results were obtained with a rotation distance of 30 cm, but the coating film thickness and rotation speed change when this rotation distance changes, that is, when the tip speed of the rotating object changes, the rotation speed changes. The relationship with them will also change.

゛・Relationship between film 6, sag lever, 1' slip P, and ゛' rotation Figure 3 shows the influence of coating film thickness on the sag limit. In this Figure 3, the coating film thickness is 40
Three cases are shown: um, 53 μm, and 65 μm. It is understood that for any of these thicknesses, peak sag occurs both at the beginning of the setting process and at the beginning of the baking process. Also, the sag limit is usually 1 to 2 mm per minute. The maximum coating thickness that can be obtained within this sag limit is the value at which sag occurs (visually inspected and the painted surface is judged to be defective if it sag at a rate of 2 mm/min or more). The diameter of this paint is approximately 40 μm.

On the other hand, FIG. 4 shows H given to the smoothness when the body W is rotated in the horizontal direction and when it is not rotated. A in FIG. 4 shows a state in which the body W is not rotated (conventional painting method). FIG. 4B shows the case where the body W is rotated 90 degrees and then reversed (second
Forward/reverse rotation between figures (a) and (c)). FIG. 4C shows a case where the body W is rotated by 135 degrees and then reversed (forward and reverse rotation between FIG. 2(a) and FIG. 2(d)). Fourth
The figure shows the case where the body W is rotated 180 degrees and then reversed (forward and reverse rotation between FIG. 2(a) and FIG. 2(e)). FIG. 4E shows the case where the body W is continuously rotated in the same direction (FIGS. 2(a), (b), (c)
)... Take the posture in the order of (i) and return to (a) again).

As is clear from Fig. 4, if the thickness of the coating is the same, it is better to rotate the body W (Fig. 4 B, C, D, E).
), thicker smoothness can be obtained than in the case of no rotation (Figure 4A).Also, it is understood that even if the rotation is the same, it is preferable to rotate 360° in the same direction in order to increase the smoothness. Of course, if the body W does not rotate, there is a limit to the thickness of the coating film, so there is a limit to how much smoothness can be increased.

By the way, assuming the thickness of the coating film is 65 μm, the body W is 3
When rotated by 60 degrees, the obtained smoothness is equal to the image sharpness of 1. G is r87J (lower limit of PGD value of 1.0). In addition, when the thickness of the coating film is 40 gm, the case where the body W does not rotate is 1. "58" in G (P
The lower limit of GD value is 0.7), whereas when the body W is rotated 360 degrees, it is 1. r68J in G (PG
The lower limit of D value is 0.8).

As is known, IG (image cross) in the mapping sharpness indicates the ratio of the sharpness to the mirror surface (black glass) as lOO, and PGD indicates the discrimination degree of the reflected image as 1. This is a value at which the smoothness of the painted surface decreases as it decreases from 0.

The test conditions for the data shown in FIGS. 3 and 4 are as follows, and these test conditions indicate the conditions for performing an upward φ rotation at P2.

a, l material: melamine alkyd (black) viscosity: 22 seconds/20'C in Ford cup #4 b, coating surface: Minibell (16, OOOr pm) shaping air 0.2, Okg/am2 C3 discharge rate: 2 Spraying is divided into several times, the first time...
10occ/min 2nd time+, 150-200cc/min, Setting time: 10 minutes x room temperature e, Baking conditions: 140°C x 25 molecules, Base smoothness: 0.6 (PGD value) (Intermediate coating, (on PE tape) g1 Rotation or reversal operating range: Setting (10 minutes) to baking (10 minutes) h, Painted on the side of a rectangular cylinder with a knee side of 30 cm, rotatably supported in the center i, coated Object rotation speed: 6rpm, 30rpm, 60r
pm, but there were no significant differences due to differences in rotational speed. The value was measured.

In addition, the sagging limit value for each coating film thickness was also measured (without rotation).

The results are shown in each drawing.

Specific Example 1 (1) Treatment of the object to be coated and undercoat/intermediate coating A cold-rolled steel sheet, which is commonly used for automatic tank bodies, was treated with zinc phosphate by a conventional method, and then subjected to cationic electrodeposition at 175°C for 30 minutes. An undercoat layer with a thickness of 30 um was formed. Then,
After spraying a black oil-free polyester intermediate coat, bake it at 140℃ for 25 minutes to form a 35μm coat.
An intermediate coating layer was formed.

(2) Topcoating A solvent-diluted paint having the following composition was used as the topcoat, and the topcoat was applied under the following conditions so as to have a divine film thickness as shown in Table 2 below.

(a) Paint Alkyd melamine high solid thermosetting paint C main resin content average molecule @: 2800; Hue Niblack) (b) Spraying viscosity: 20 seconds (Ford Cup #4/20
℃) (c) Non-volatile content: 48% by weight (d) Solvent ditoluene: 25 parts by weight/Tsurupez 100
: 25 parts by weight / Tsurupetz 150 : 50 parts by weight (e) Anti-sagging agent: Cross-linked acrylic resin powder; % triple rings based on non-volatile content) (3) Top coating conditions (a) Coating coater: Minibell (bell diameter) 0n+s: Made by Japan Unsberg) 1 stage spraying is mini bell rotation speed: 160 Qrp.

Shaving pressure: 3 kg/cm" Voltage: 90 KV Gun distance: 30 cm (b) Blowing atmosphere: Temperature 20°C ± 2°C Booth wind speed 0.3 ± 0.1 m/shaft (butshu pull down flow) (C) Setting conditions: Setting start temperature 20℃
±2℃/Setting time 10 minutes (dJ baking conditions: Temperature 140℃/Time 25 minutes Rising speed: 8 minutes (20℃→140℃) (4) Rotation conditions 75cm distance from the center axis of the object to be coated The object to be coated was rotated about a horizontal axis so that both end surfaces of the object were parallel to each other.

The steel plate coated with the top coat under the above coating conditions is transported to the setting process, and in the setting process, the first
Using a device equipped with a high-frequency induction coil as shown in Figure 8, heating was started 3 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 at that temperature for 1.5 minutes. During this heating, the object to be coated was rotated at a rate of 30 rpm. In addition, during the baking process, neither heating by high-frequency induction nor rotation was applied.

Table 2 below shows the relationship between the thickness of the topcoat layer and the rotation speed by rotating the topcoat layer having various thicknesses coated under the above conditions while applying disturbance due to heating. The values in the table mean PGD values. In addition, the values in parentheses for the film thickness tank in the table below are obtained without rotating the object to be coated.
PG of the top coat layer with a film thickness of 40 μm obtained without applying ultrasonic waves.
It means D value.

FIG. 21(a) shows the relationship between the sag rate of the top coat layer due to the application of ultrasonic waves as a disturbance and the time of the drying process (setting process and baking process). In the figure, the chain line indicates the sagging speed when neither disturbance nor rotation is applied for reference.

(Hereinafter referred to as Ito et al.) Table 2 Specific Example 2 The cold rolled steel sheet coated with the intermediate coating layer obtained in Specific Example 1 was top coated in the same manner as in Specific Example 1 to have the film thickness shown in Table 3 below. Painted. In this specific example, in the setting step, instead of the high-frequency induction coil used in specific example 1, a device equipped with a far-infrared lamp as shown in FIG. 17 was used to perform heating with the far-infrared lamp. The heating conditions were such that heating was started 1 minute after the start of the setting process, the temperature was raised from 20°C to 60°C over 1 minute, and the temperature was maintained for 3 minutes. During this heating, the object to be coated was rotated at a rate of 15 rpm. In this specific example, disturbance and rotation were applied only during one setting process, and neither was applied during the baking process.

Table 3 shows the relationship between film thickness and 1 rotation speed.

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

Table 3 Specific Example 3 The cold-rolled steel sheet coated with the intermediate coat layer obtained in Specific Example 1 was coated with a top coat in the same manner as in Specific Example 1 to have the film thickness shown in Table 4 below. In this example, in place of the high-frequency induction coil used in Example 1, a conveying device equipped with a heating device as shown in FIG. It was heated. The heating conditions were such that heating was started 1 minute after the start of the setting process, the temperature was raised from 20°C to 60°C over 3 minutes, and the temperature was maintained for 1 minute. Further, during this heating, the object to be coated was rotated at a rate of 10 rpm.

In this specific example, disturbance and rotation were applied only during the setting process, and neither were applied during the baking process.

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

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

Table 4 Specific Example 4 The cold rolled steel sheet provided with the intermediate coat layer obtained in Specific Example 1 was top coated in the same manner as in Specific Example 1 except for the following conditions.

(1) Top coat: 2-component thermal urethane paint (hue black) (Al main ingredient Niacrylic resin (average molecular FFI: 1500) (b) Curing agent: Polyisocyanate (c) Mixing ratio: Main ingredient/curing agent = 7/ 1 (d) Spraying viscosity: 16 paper/foed cup #4 (20℃
) (excluding anti-sag agent) (e) Nonvolatile content: 54% by weight (f) Solvent: Ethyl acetate 15 parts Butyl acetate 55 parts Cellosolve acetate 30 parts (2) Baking conditions 90°C for 725 minutes Interfacial temperature speed: 5 minutes ( (20℃→90℃) (3) Sag limit film thickness: 45μm The object coated with the top coat as described above is transported to the setting process, and the disturbance caused by the high frequency induction coil is carried out in the same manner as in Example 1. and rotation, and the following 4th
An overcoat layer having a thickness as shown in the table was formed.

Table 5 shows the relationship between film thickness and rotation speed. In addition, the value between 0 in the film thickness column in the table indicates the PGD value when neither disturbance nor rotation was applied to the overcoat layer.

FIG. 22(a) shows the relationship between the paint sag rate and the film thickness when a disturbance is applied without rotating the object to be coated. In addition, the dashed line in the figure shows the sagging rate for reference when the topcoat layer with a thickness of 45 μm obtained by applying the topcoat under the above conditions is not subjected to any disturbance.

(hereinafter /iP, f3) Table 5 Specific Example 5 The cold rolled steel sheet coated with the intermediate coating layer obtained in Specific Example 1 was treated in the same manner as in Specific Example 4 to have a film thickness shown in Table 6 below. A top coat was applied to the surface. In this specific example, in the setting process, instead of the high frequency induction coil of Example 4,
The object to be coated was heated in the same manner as in Example 2 using a far-infrared lamp. In this specific example, disturbance and rotation were applied only during the setting process, and neither were applied during the baking process.

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

Figure 22 (bJ) shows the relationship between the paint sag rate and the film thickness when a disturbance is applied without rotating the object to be coated.

(Table 6 Specific Example 6 The cold rolled steel sheet coated with the intermediate coating layer obtained in Specific Example 1 is coated with a top coat in the same manner as in Specific Example 4 to have the film thickness shown in Table 7 below. In this example, in the setting process, instead of the high frequency induction coil of Example 4,
In the same manner as in Example 3, the object to be coated was heated by internal heating using hot air. In this specific example, disturbance and rotation were applied only during the setting process, and neither were applied during the baking process.

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

FIG. 22(b) shows the relationship between the paint sag rate and the film thickness when a disturbance is applied without rotating the object to be coated.

CLA Lower Margin Table 7 Next, a device for applying disturbance and rotation in the coating method according to the present invention will be specifically explained.

Figures 17 and 18 show a preferred example of the drying oven 60, which can be used in both the setting process P3 (when heating is performed as a disturbance) and the baking process P4 described above.

In the one shown in FIG. 17, a large number of infrared panels 61 are arranged to cover the left and right side surfaces and the top surface of the body W. In addition, the one in Fig. 18 is the infrared panel 6.
1 is replaced by a high frequency induction coil 62. Both of these embodiments are preferable in that the upper part of the drying oven 60 is kept at a sufficiently high temperature to prevent air convection and to prevent the generation of floating dust as much as possible. In addition, in the case shown in FIG. 18, the magnetic field can be kept constant in response to the change in the distance between the body W and the coil 62 as the body W rotates, and the body W can be made uniform. This is more preferable in terms of heating. That is, the coil 62 is energized via the rectifier 66 and the inverter 67, and the control unit 68 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 the drying ovens shown in FIGS. 17 and 18, as well as any of the known drying ovens. That is, the body W
A heating cylinder 71 having a large number of small holes on its surface is disposed inside the heating cylinder 71, and each end of the heating cylinder 71 is connected to a pair of front and rear rotating jigs IF.
, and is connected to the IR (the hollow rotating shaft portion). Heated air is then supplied into the heating cylinder 71 via the hose 72 and a rotary joint (not shown). Thereby, the body W is sufficiently heated not only from the outside but also from the inside.

Rotation Jig Next, a specific example of a jig used for rotatably supporting the body W in the horizontal direction with respect to the trolley will be described.

Figure 5 shows the front jig I attached to the front of the body W.
Indicates F. This jig IF includes a pair of left and right mounting brackets 2, a pair of left and right stays 3 welded to each of the left and right brackets 2, a connecting bar 4 that connects the left and right pair of stays 3, and a connecting bar 4. It has a rotating shaft 5 integrated with. The bracket 2 portion of such a jig IF is fixed to the front strength member of the body W, for example, to the front end of the front side frame 11. That is, since the front side frame 11 is usually welded with a bracket 12 for mounting a bumper (path shown), the bracket 2 is attached to the bracket 12 on the front side of the body using bolts (path shown). Fix it.

On the other hand, the rear jig IR attached to the rear part of the body W is shown in FIG. The rear jig IR has a similar configuration to the front jig IF, and the same reference numerals are given to the components corresponding to the front jig IF. The rear jig IR 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, at the rear end of the floor frame 13,
Since the bumper mounting bracket is generally welded for mounting the bumper, it is also possible to use the bumper mounting bracket to install the rear side jig P-IH.

When the front and rear jigs IF and IR are attached to the body W, their 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 rotational axis 2 of the body W, and preferably, this rotational axis 2 is the center of gravity G of the body W (see Fig. 7).
It is made to pass through. Note that the rotation axis 1i [is the center of gravity G
By passing through, large fluctuations in rotational speed are prevented when the body W rotates. As a result, body W has
This prevents impact from occurring due to rotational fluctuations, which is more preferable in terms of preventing sagging.

Note that the front and rear jigs IF and IR are specially prepared in advance according to the vehicle type (type of body W).

It is a trolley that is used in P3 and has the function of rotating the body W.

In FIG. 7, the trolley has a base 21, and this base 2
Wheels 22 attached to the vehicle 1 are run on a road surface 23. This base 21 has one front support 24, two intermediate supports 25, 26, and one rear support that extend upward in sequence from the front side in the running direction to the rear side (from the right side to the left side in FIG. 7). It has a support column 27, and a support space 28 is provided between the intermediate column 25, 26 and the rear column 27 with a large gap in the front-rear direction.

The body W is disposed in the support space 28, and its front part is rotatably supported with respect to the intermediate support 26 using the front jig IF, while its rear part is supported using the rear jig IR. It is rotatably supported by the rear support 27.

The front and rear jigs IF and 1R (rotary shafts 5 of them) can be freely engaged with and disengaged from the columns 26 and 27 from the vertical direction, and the rear jig IR is immovably engaged in the direction of the rotation axis β. Ru.

For this reason, the intermediate support 26 is formed with a notch 26a that opens at its upper end surface (see FIGS. 10 to 12).
, a notch 27a is formed in the upper end surface of the rear strut 27 (see FIGS. 10, 14, and 15).
. The notches 26a, 27a are sized to fit the rotating shafts 5 of the jigs IF, IR. A flange portion 5a is formed on the rotating shaft 5 of the rear jig IR, and a notch 27b having a shape corresponding to the flange portion 5a communicating with the notch 27a is formed in the rear support 27. . As a result, the rear jig IR can be inserted into the notch 2 of the rear column 27.
7a, 27b from above and below, and is immovable from front to back with respect to rear support 27 due to the stopper action of flange portion 5a. Note that the rotational force is applied to the body W via the rotation shaft 5 of the front jig IF, and for this reason, a connection portion 5b (see FIG. 5), which will be described later, is provided at the tip of the rotation shaft 5 of the front jig IF. (see also) is formed.

A stay 29 is provided to protrude downward from the base 21,
A traction wire 30 is connected to the lower end of this stay 29. This wire 30 is of an endless type,
It is driven in one direction by a motor (not shown), and thereby the trolley is driven in a predetermined transport direction. Of course, the motor is installed in a safe location from an explosion-proof point of view.

The rotation of the body W is performed by using the movement of the truck, that is, by using the displacement of the truck with respect to the running road surface 23. A rotation extraction mechanism 31 for extracting the displacement of the truck as rotation is configured as follows. In other words, the one-rotation take-out mechanism 31 includes a rotating shaft 32 extended vertically and rotatably supported on a base 21, a sprocket 33 fixed to the lower end of the rotating shaft 32, and a sprocket 33 fixed to the lower end of the rotating shaft 32.
The chain 34 is meshed with the chain 34. This chain 34 is disposed in parallel with the wire 30 in an immovable state with respect to the running road surface 23. This results in
When the trolley is pulled through the wire 30, the chain 3
Since the chain 4 is stationary, the sprocket 33 meshing with the chain 34 rotates the rotating shaft 32.

The rotation of the rotation shaft 32 is controlled by the rotation shaft 5 of the front jig IF.
The transmission mechanism 35 for transmitting the signal is configured as follows. That is, the transmission mechanism 35
The casing 36 fixed to the rear surface of 4 and the casing 3
6, a rotating shaft 37 extending laterally (back and forth) and rotatably supported, a pair of bevel gears 38 and 39 that interlock this rotating shaft 37 and the upper rotating shaft 32, and The connecting shaft 40 is held rotatably and slidably in the front-rear direction. This connecting shaft 40 is
It is spline-coupled to the rotating shaft 37 (this engaging portion is indicated by the number 41 in FIG. 7), so that when the rotating shaft 32 is rotated, the connecting shaft 40 is also rotated. Of course, the rotation shaft 37 and the connection shaft 40 are installed so as to be located on the rotation axis β.

The connecting shaft 40 is connected to the rotating shaft 5 of the front jig IF.
be disengaged. That is, as shown in FIGS. 10 to 12, a cross-shaped connecting portion 5b is formed at the tip of the front jig IF rotating shaft 5.

As shown in FIGS. 10 and 13, the end of the connecting shaft 40 is provided with an engaging recess 4 into which the connecting portion 5b is fitted without play.
A box portion 40a having a diameter of 0c is formed. Therefore, for example, by sliding the connecting shaft 40 via the rod 43 by a pneumatic cylinder 42, the box portion 40a (engaging recess 40c) and the connecting portion 5b are engaged and disengaged, and when they are engaged, they are connected. The shaft 40 and the rotating shaft 5 are allowed to rotate together. Note that the rod 43 is the tenth rod.
As shown in the figure, it is fitted into an annular groove 40b formed on the outer periphery of the box portion 40a so as not to inhibit the rotation of the connecting shaft 40.

With the above configuration, the front and rear jigs IF are moved by lowering the body W relative to the trolley while the connecting shaft 40 is displaced to the right in FIG.

Each rotating shaft 5 of the IR is rotatably and immovably supported in the front-rear direction by intermediate struts 26 and 27. Thereafter, the connecting shaft 40 (locking recess 40c) is engaged with (the connecting portion sb of) the rotating shaft 5 in the front jig IF. As a result, when the trolley is pulled via the wire 30, the body W is rotated about the predetermined horizontal axis β. In addition, the removal of the body W from the trolley may be performed in the reverse order to the above-described procedure.

Supplementary explanation and old examples Next, supplementary explanation and cart related to the present invention,
Modifications of the painting method, etc. will be explained in sequence.

■When applying the top coat after the intermediate coat, the wet sanding after the intermediate coat baking process can be eliminated. In this case, the body W may be rotated only during either the intermediate coating process or the top coating process. In other words, the quality of the final painted surface obtained after the top coating is determined by the quality of the intermediate coating, but when the body W is rotated during the intermediate coating, the finish level of this intermediate coating is This eliminates the need for wet sanding, which was conventionally done.Also, if you rotate the body W with the top coat, you can eliminate the need for wet sanding with the middle coat. It can be covered with a good topcoat.

(2) If the body W is to be rotated during topcoating and a thin coating film is to be formed using a topcoat with a small sag limit, it is recommended to use a so-called color intermediate coating. As a result, even if the intermediate coat paint is seen through the top coat paint, there is no equal support in terms of color tone.

■Regardless of whether the bogie is running or stopping, switching the rotation and stopping of the body W and changing the rotation direction can be done by using a separate dedicated actuator such as an air motor, but it can also be done as follows, for example. I can do it. First, in the example shown in FIG. 7, a pair of first and second chains (
(equivalent to chain 34), and each chain is provided so that it can be driven as appropriate. With such a configuration, the body W
rotation control will be performed.

■ Stopping the first chain and freeing the second chain: In this case, the body W is rotated in one direction as the platform @D moves.

■First chain free and second chain stopped: In this case, the body W is rotated in the opposite direction to the above (■) as the single bogie travels.

◎Both chains are free: In this case, the body W is not rotated as the platform iD moves.

(1) Driving the first chain in one direction and freeing the second chain: In this case, even if the stand iD is stopped, the body W is rotated in one direction.

■Drive the first chain in the other direction and make the second chain free (same as if the first chain is free and the second chain is driven in the other direction): In this case, even if the bogie is stopped,
The body W is rotated in the opposite direction to that in the case (2) above.

Note that the above description also applies when a rack bar is used instead of the chain. If this rack bar is always placed in a fixed state (in this case, the traveling of the trolley is a prerequisite for the rotation of the body W), the rack bar may be placed intermittently, or the position of the rack bar may be changed from left to right. By setting it arbitrarily, the body W can be rotated in any direction depending on the traveling position of the trolley, and the rotation of the body W can be stopped at any position.

(2) In addition to heating, vibration may be used as a disturbance to impart large fluidity to the paint that causes sag. In this case, for example, the rails 23 of the trolley may be made uneven, or acoustic vibrations may be applied using a speaker.

(2) A disturbance for imparting a large fluidity that causes sag to the paint may be applied in the coating process P2. In this case, it is advisable to heat the material so that it has substantially greater fluidity, especially in the subsequent setting step. In addition, if there is enough fluidity to cause sagging during the painting process P2, this painting process P2
But all you have to do is rotate the body W.

(Effects of the Invention) As is clear from the above description, the present invention utilizes the fluidity of the paint and the rotation of the object to be coated to achieve a high level of smoothness that is higher than that of conventional paints with the same paint thickness. You can get a quality painted surface.

In addition, since the paint is designed to have great fluidity by applying disturbances, there are no major restrictions on the components of the paint or its coating conditions in order to provide this great fluidity, making it highly versatile. Become something.

[Brief explanation of the drawing]

FIG. 1 is an overall process diagram showing one embodiment of the present invention. FIG. 2 is a diagram showing a state in which the posture of an automobile body as an object to be coated changes as it rotates. Figures 3 and 4 are graphs showing the relationship between paint thickness and sag, smoothness of the painted surface, and rotation. FIGS. 5 and 6 are perspective views showing examples of jigs used to rotate the body. FIG. 7 is a side view showing an example of a body transport trolley in which the body can be rotated. FIG. 8 is a partially cutaway plan view showing the state below the running path of the bogie. FIG. 9 is a sectional view taken along the line X9-X9 in FIG. FIG. 10 is a side cross-sectional view showing the joint portion between the rotating jig and the truck. FIG. 11 is a sectional view taken along line X1l-Xllil in FIG. 1O. FIG. 12 is a plan view of FIG. 11. FIG. 13 is a sectional view taken along the line X13-X13 in FIG. 10 (7). FIG. 14 is a sectional view taken along line X14-X14 in FIG. 10 (7). FIG. 15 is a plan view of FIG. 14. FIG. 16 is a diagram showing the relationship between paint thickness, sagging characteristics, and heating. FIG. 17 and FIG. 18 are diagrams showing preferred examples of the drying oven. FIG. 19 is a diagram showing a preferred method of drying the object to be coated. FIG. 20 is a graph showing the relationship between the upper and lower limits of coating thickness and the number of rotations. FIGS. 21(a) to 21(c) are graphs showing the sag limit values during the drying process when disturbance is applied to the overcoat layer (but no rotation is applied). 22(a) to 22(c) are graphs showing the sag limiting device during the drying process when disturbance is applied to the overcoat layer (but no rotation is applied). P1 to P4: Process W: Body e: Rotation axis D = Transfer platform 1F, 1R: Rotation jig

Claims (1)

[Claims] (1) In a coating method having a coating process of applying paint to an object to be coated, and a drying process of drying the paint applied to the object, at least one of the painting process or the drying process includes removing the paint during at least the drying process. A painting method characterized by applying a disturbance that causes paint to sag, and rotating the object to be coated around a substantially horizontal axis during a state in which paint sag.