JPH03165871A - Coating method - Google Patents

Abstract

PURPOSE:To inhibit the dripping of paint between spraying and drying stages by setting the thickness of paint in the spraying stage and the speed of rotation of a body to be coated in the drying stage so that the dripping of paint is prevented and interposing a cooling stage between the spraying and drying stages. CONSTITUTION:In a spraying stage P1, paint is sprayed on an automobile body as a body to be coated in such a thickness that the paint begins to drip from at least the perpendicular surface of the body. In a drying (rotary baking) stage P3, the body is rotated around a nearly horizontal axis before the paint begins to drip from at least the vertical surface of the body and until the paint does not drip any more. The speed of rotation is made higher than the speed at which the body shifts from the vertical state to the horizontal state before the paint begins to drip and lower than the speed at which the paint is allowed to drip by centrifual force due to rotation. A cooling stage P2 is interposed between the spraying and drying stages P1, P3 so that cooling is carried out immediately after spraying.

Description

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

(Prior technology) When spray painting the outer surface of an object to be painted, for example an automobile body, there is a preparation process to remove dust adhering to the object, and a process of spraying and applying the paint to the object. and a drying step of drying the applied paint. This drying process is generally carried out in two stages: a setting process and a baking process. It is carried out in a temperature atmosphere of 60'C (the baking temperature in the baking process is usually 140'C).
(around ℃).

The object to be coated is usually transported by means of transportation such as a trolley through the preparation process, painting process, and drying process, but the posture of the object to be coated is maintained at a predetermined position in each process. It is still being done.

By the way, one of the criteria for evaluating the quality of painted surfaces is:
There is smoothness (flatness), and this smoothness reduces the degree of l"I +'+ of the culm surface, resulting in a good coating. It is already known that this can be achieved by increasing the thickness of the coating film, that is, the thickness of the coated room material.

On the other hand, paint ゜″
This sagging is caused by the large downward flow of the applied paint due to the application of the E force, and the thicker the film of paint applied at one time, the more likely it is that sagging will occur. Since the cause of this sag is ultimately the effect of gravity, it is more likely to occur on surfaces of the object to be coated that extend in the vertical direction, that is, so-called vertical surfaces.

For example, when considering the body of a car as the object to be coated, sagging is less likely to occur on the horizontal hood or trunk lid, but it is more likely to sag on the fender, which is on the vertical side.

Therefore, on the horizontally extending surfaces of the object to be coated, where dripping of the paint is not so much of a problem, that is, the so-called horizontal surfaces, it is possible to apply a larger thickness of paint than on the vertical surfaces. Even if the thickness of the paint film on the surface and the thickness of the paint film on the vertical surface are the same, the unevenness on the horizontal surface will be smaller due to slight flow of the paint that does not cause dripping, and the smoothness on the vertical surface will be smaller. Good smoothness can be obtained.

- From the point of view mentioned above, in the past, in order to prevent the paint from sagging and to obtain a painted surface with as much smoothness as possible,
Painting was done using a paint with as little fluidity (low viscosity) as possible. The so-called ``sag limit'' at which paint sag on the vertical surface was about 40 am at maximum in terms of coating film thickness for conventional thermosetting paints.More specifically, thermosetting Dragging of mold paint 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, and the thickness of the paint applied during the painting process is determined to prevent dripping during this period. , the maximum value of this determined thickness, that is, the sagging limit value, is about 40 μm. Therefore, if you want to obtain a painted surface with even greater absolute smoothness, in the conventional painting method, for example, two coats, etc. , it was necessary to repeat the series of steps from the painting process to the baking process multiple times.

JP-A No. 63-178871 discloses a method that overcomes the sagging limit that is a problem when painting by spraying as described above, and provides a coated surface with better smoothness for the same coating thickness. A coating method is disclosed. In other words, when applying paint by spraying, the thickness of the paint film is set to be above the dripping limit, and the object to be coated is rotated around the approximately horizontal axis until the applied paint is cured to the point where no dripping occurs. We have developed a painting method that rotates the paint. According to this coating method, the rotation of the object to be coated changes the direction of the gravity acting on the paint to prevent dripping, while actively utilizing the paint's great fluidity to achieve the same paint film. If it is thicker, a coated surface with better smoothness can be obtained.

(Problems to be Solved by the Invention) However, when such a coating method is employed, there is a risk that dripping may occur during the transfer process from the paint spraying process to the drying process. That is, in the coating method described in the above publication,
Since the thickness of the paint film is increased or the amount of solvent contained in the paint is increased to increase the thickness of the paint film beyond the dripping limit, such painting methods involve spraying the paint onto the object to be coated. There is an inherent risk that paint will drip immediately after the paint is applied. Therefore, if a predetermined time is required for transfer to the spraying process, it is necessary to suppress the occurrence of sagging during this transfer process.

On the other hand, even if the thickness of the paint film exceeds the dripping limit, it should be at least thick enough to prevent dripping during the transfer process, or reduce the amount of solvent, etc. contained in the paint so that the paint itself Possible solutions include reducing the liquidity of

However, when such a method is adopted, certain restrictions are placed on the coating conditions, and the meaning of removing the major restriction of the sag limit from the conventional coating conditions by using the coating method described in the above publication is diluted. This will result in

Therefore, the purpose of the present invention is to make it difficult for the paint sprayed on the object to physically flow, without imposing restrictions on the coating conditions, and to suppress the occurrence of dripping between the spraying process and the drying process. The object of the present invention is to provide a coating method that achieves this.

Means for Solving Problem C) In order to achieve this technical problem, in the present invention, painting the object to be coated includes a spraying step of spraying the paint and drying the sprayed paint. In the spraying culm, the paint is sprayed to a thickness of -L so that the paint drips on at least the vertical surface of the object to be coated, and in the drying step, the paint is sprayed to a thickness of at least +iii. Before the paint starts to drip on the vertical surface of the object and until the paint stops dripping, the object to be painted is rotated about a substantially horizontal axis, and the rotation speed of the object is determined by gravity. Set as a range that is greater than the rotational speed at which the vertical state changes from a vertical state to at least a horizontal state before the paint starts to drip, and smaller than the rotational speed that causes paint to drip due to centrifugal force caused by rotation. Between the spraying step and the drying step, a cooling step for cooling the sprayed paint is provided immediately after the spraying step.

(Operation, Effect) With the above configuration, the direction of gravity acting on the paint applied to the object to be coated is changed by rotating the object to be coated around a substantially horizontal axis, so that the paint is "Sauce"
It will dry without causing any damage.

This means that the film thickness of the paint applied per coat can be made much thicker than conventionally, and it is possible to obtain an extremely good coated surface whose smoothness far exceeds the level conventionally considered to be the limit. Furthermore, even when the coating film has the same thickness as conventional coatings, the fluidity of the coating material can be utilized to produce an excellent coated surface with fewer irregularities, that is, greater smoothness. Furthermore, if you want to obtain a painted surface with the same level of smoothness, for example, the same level of smoothness as that obtained with conventional painting methods, you can reduce the film thickness of the paint, and use only the amount that can be made thinner. The amount of paint used can be reduced.

Here, the paint may be sprayed by static 'I'Ii painting. In addition, paint dripping refers to the movement of paint that can be visually confirmed when the paint is left in a sprayed state (it appears as an i'i'h shape when the paint hardens). Generally, dripping is considered to have occurred when paint movement of about 2 mm is confirmed. therefore,
Spraying paint to a thickness that exceeds the dripping limit means that the thickness must be such that if 1 liter of paint is left as it is, it will move at least 2 mm, and the more fluid the paint used, the higher the dripping limit. becomes smaller.

To achieve a thickness that exceeds the sag limit, it may be done by one spraying (1-stage spraying), or it may be sprayed two or three times or more to achieve a final thickness that exceeds the sag limit ( multiple stage blowing). Furthermore, since the rotation of the object to be coated around the approximately horizontal axis should be such that the paint does not move significantly due to the action of gravity, until the paint no longer has a large flow state that would cause dripping, That is, until the paint hardens, rotation may be performed continuously or intermittently in the predetermined -R direction, or forward and reverse rotation may be performed continuously or intermittently. As for the rotation angle range of the object to be coated, it is sufficient that the direction in which gravity acts is reversed for any part where the paint is sprayed to a thickness above the dripping limit, and 270 degrees is sufficient. .

The axis of rotation of the object to be coated is 3
It may be tilted within a range of about 0 degrees, and the axis of rotation may also be swung.

! O In addition, the cooling of the paint performed in the cooling step may be at least as long as it increases the viscosity of the paint applied to the corrugated object.

As a result, the paint sprayed onto the object to be coated is immediately cooled down and its coating viscosity is increased, resulting in a decrease in fluidity of the paint.

Therefore, the fluidity of the paint decreases due to this cooling, making it physically difficult for the paint to sag, and the IR function makes it possible to suppress the occurrence of sag between the spraying process and the drying process.

(Embodiments) Hereinafter, embodiments of the present invention will be described based on the attached drawings.

Figure 1 shows the overall process for painting an automobile body as an object to be coated, and each process is designated by P1 to P3.

First, a body that has been undercoated by electrocoating in a known manner is conveyed to a painting process P1 while being held on a truck. In this painting step P1, paint of a desired color is applied to the entire outer surface of the body by spraying. After this, after passing through the cooling process P2 described later, in the drying process P3, by setting and subsequent baking,
Allow the paint to dry thoroughly.

In the coating process Pl, the thickness of the paint applied is greater than the dripping limit. Then, in the drying process P3,
Until the paint dries until it no longer drips, the body W is rotated approximately around the water axis f, as shown in FIG. 2, for example.

The rotational speed of the object to be coated, such as the body W, varies depending on the film thickness and viscosity of the sprayed paint, but basically the rotational speed is within the range between the lower limit and upper limit as shown below. is set to 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 due to weight and causes dripping. In addition, the upper limit is set at a rotation speed of 1 at which no sagging occurs due to the centrifugal force generated by rotation.
The maximum value of 2 degrees is 38 degrees at the rotation tip position.
The rotation speed is preferably 0 cm/sec or less. Note that when the object to be coated is rotated around a substantially horizontal axis, the rotation axis is
Although it may be inclined by about 30' with respect to the water f axis, it is preferable that this inclination is within 10'.

The period of time during which the object to be coated is rotated approximately around the water axis may be at least in the drying step, from before sag occurs on the coated surface until it hardens 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 the 1-h direction, forward/reverse rotation in which forward rotation and reverse rotation are alternately performed, or intermittent simultaneous rotation with a simultaneous rotation stop period Ehi in the middle.

Unusual body coating (11 Undercoat cationic electrodeposition baking = 170℃ x 30 minutes Film thickness: 20±2μm l3 (2) Topcoat (1) Normal viscosity 0.6 poise a. Paint: Alkyd melamine high Solid thermosetting paint (main resin average molecular weight: 2800. Hue: black) b. Paint viscosity (coating viscosity): Q. 6poiseC.
Non-volatile content = 48% by weight d. Solvent: Toluene = 25 parts by weight/Solbetsuso 1 0
0: 25 parts by weight/Solbetsuso 150: 50 parts by weight e. Anti-sagging agent: Liang Chian acrylic resin powder; 3% based on non-volatile content) r. Paint coater: Mini bell (bell diameter 6, Omm: manufactured by Ransburg Japan) Mini bell rotation speed: l 6000 rpm Shaving pressure: 3 kg/cm2 Voltage: -90 KV Gun distance: 30 cm For two sprays, 5 minute interval g. Spraying atmosphere: Temperature 20℃±2℃ 1 4 hours. 1. J ・ Booth wind speed 0.3 degrees 0.1/sec (push, pull, down flow) Setting conditions: Setting starting temperature 20℃±2℃
/Setting time: 7 minutes Baking conditions: Temperature: 140°C/Time: 25 minutes Heating rate = 8
(20° C.→140° C.) Rotation Conditions Waveform The object to be coated was rotated about a horizontal axis 75 cm away from the center axis of the object so that both end surfaces were parallel to each other. The rotation speed is 6 rpm.

Low viscosity Q. For 2 poise Paint: Same as above (1) Paint viscosity (coating viscosity): 0.2 poise Non-volatile content: 3
5% by weight Solvent: Toluene = 35 parts by weight/Solbetsuso 100:
25 parts by weight/Solbetsuso l50: 50 parts by weight 15 Other e - j are the same as in the case of 0.6 poise in (1) above.

1 scoop 1” 24i day The intermediate coat and top coat are the same paint.

a. Paint: Polyester urethane paint white (
Manufactured by Nippon B Chemical Co., Ltd., product name P-263) Main resin: Polyester polyol white Hardening agent:
Hexamethylene diisocyanate mixing ratio (weight ratio): ratio of 1 part curing agent to 4 parts main resin b. Painting machine: Pressure-feeding air spray gun (Iwata Painting Machine)
Co., Ltd., product name Wider W71) C. Coating viscosity: 0.6 poise and 0.2 poised. Paint discharge amount: 350cc/min e. Atomization air pressure: 4. Okg/am2f. Spraying distance: 30cm l 6 g. For two coats, the interval is 5 minutes h. Drying conditions:
Setting 7 minutes (room temperature) 90°C x 25 minutes (heating rate 5 minutes (20°C-90°C)) i. Rotation speed: same heating speed as for thermosetting paint 2
i Pruning (1) Intermediate coating a. Paint: Thermosetting oil-free polyester paint (
gray) b. Application viscosity: 0.6poise and 0.2poiseC. Painting
: Mini bell (bell diameter 60mm) rotation speed 2200Orpm Voltage -90KV Shaving air pressure 3.0kg/cm2 Gun distance 30cm d. Drying conditions: 140℃ after setting for 7 minutes (room temperature)
x 25 minutes 7 (2) Top coat a. Paint: Thermosetting acrylic melamine paint (black) b. Coating viscosity: 0.6poise and 0.2poiseC non-volatile content = 4
2% by weight (0.6poise) 33% by weight (0.2poise)
i se) d. Solvent: ■For 0.6 poise: Toluene 50% by weight/Solbetsuso 10050% by weight ■For 0.2 poise: Toluene 55% by weight/Solbetsuso 100% by weight e. Anti-sag agent: Cross-linked acrylic resin powder (= 6% based on non-volatile content) Other coating conditions for the coating calculation are the same as for the alkyd melamine high solid thermosetting paint described in 1r11.

l 8 A suitable coating for the body Here, automatic f is preferred.

The number average molecular peak is 2000 to 2000 for automobile paint.
The reason why it is preferable to set it in the range of 0 is that if it is less than 2000, it corresponds to a paint that is cured by electron beam or ultraviolet light, and this paint has a high Kurihashi density and is brittle, so it is not durable (2~
3 years), is not very desirable for use as an outer panel for automatic tunnels.

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.Furthermore, latex volima with a number average molecular weight exceeding 20,000 has a high viscosity immediately after spraying. This makes it difficult to improve smoothness, which is undesirable.

(The following is a blank space) l 9 The third diagram of Hyosen-nuri Satatare and and is as follows.
This paper uses a thermosetting paint as an example to illustrate the influence of coating film thickness on the sagging limit. FIG. 3 shows three cases of coating film thickness: 40 μm, 53 μm, and 65 μm. It is understood that for any of these thicknesses, a sagging peak occurs both at the beginning of the setting process and at the beginning of the baking process. In addition, the sag limit is normally the value when sagging occurs at a rate of 1 to 2 mm per minute. The maximum film thickness obtainable in the range is around 40 um with conventional paints.

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 painting method). Figure 4B shows the body W
The case is shown in which the rotation is performed by 90 degrees and then reversed (forward and reverse rotation is the same between Figure 2 18) and (c). FIG. 4C shows a case where the body 21W is rotated by 135 degrees and then reversed (forward and reverse rotation between FIGS. 2(a) and (d)). Figure 4D
shows the case where the body W is rotated by l80 degrees and then reversed (forward and reverse rotation between Figure 2 (a) and (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 film is the same, it is better to rotate the body W (Fig. 4 B.C, D.E.
), a higher degree of smoothness can be obtained than in the case of no rotation (Fig. 4A). Furthermore, it is understood that even if the rotation is the same, it is preferable to rotate 360 degrees in the same direction in order to improve 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 65μm, the body W is 36mm.
When rotating by 0", the obtained !Y slide 2 2 degrees is "8.7J. (P G D
The value is 1, the lower limit of O). In addition, the thickness of the coating film was increased to 40
In the case of um, if the body W does not rotate, I.
G is r58J (lower limit of PGD value 0.7), whereas when body W is rotated 360°, I. G
and r68J (lower limit of PGD value of 0.8).

As is known, IG (Image Cross) in mapping 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 to 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 when overcoating is performed at P2.

a. Paint: Melamine alkyd (black) Viscosity: 22 seconds/20”C with Ford cup #4 b. Shaving machine: Minibell (+6, OOOrpm) 2 3 Shaving air.. 2.0 kg/cm2 C. Discharge amount: 2 times The first time was sprayed in several parts...
．． I OOcc/min 2nd time. ．． 150-200cc/min. Setting time = 10 minutes x room temperature e. Baking conditions = 140°C x 25 minutes f. Base smoothness: 0.6 (PGD value) (Intermediate coating, I) on E-dep) g. Rotation or reversal operating range: Setting (10 minutes) to baking (10 minutes) h. w1 Coating: Painted on the sides of a rectangular tube with sides of 30 cm, rotatably supported at the center i. Rotation speed of the object to be coated: 6 rpm, 30 rpm. 60r
The experiment was carried out at three different pm values, but virtually no difference occurred due to the difference in rotational speed.

(Left blank) 2 4 Painting process (Figure 5 (a) shows the painting process PI in which spray painting is performed on the body W, which is the object to be painted, and the cooling process P2 that immediately follows.
shows.

In FIG. 5(A), reference numeral 12 denotes a truck for transporting the body W along the painting line, and the truck 12 can run on a floor surface 16 by means of wheels 14 provided at its bottom. A transport chain 20 driven by an appropriate drive stage is installed inside the bit l8 provided below the floor surface l6, and is engaged with a rod 22 fixed to the transport chain 20. By doing so, the trolley 12 is transported.
sent.

The bogie l2 has a pair of front and rear car body holding shafts 2 extending in the horizontal direction.
4 and 25 are held rotatably. Front barrel holding shaft 2
A bevel gear 28 housed inside the gear box 26 can be seen at the front end of the body W. It meshes with a bevel gear 32 fixed to the upper end. Further, a sprocket wheel 34 is fixed to the lower end of the vertical rotation/rotation shaft 30, and this sprocket wheel 34 is engaged with a rotation chain 36 installed inside the bit 18. 30 rotates as the rotating chain 36 is driven, and connects to the front vehicle body holding shaft 24 via bevel gears 28 and 32.
In turn, the body W is rotated.

In the painting process P1, painting machines (minibells) 38, 38 spray top coat paint onto the body W at appropriate locations above and on the left and right sides of the body W, which is placed on the trolley 12 and passes through the painting process PI. is located.

Please illustrate. The body W is coated with an undercoat by known electrodeposition in the undercoat painting process, and after dust inside and outside the body W is removed by cleaning or other means such as air blowing, the body W is transferred to the painting process P1 by a trolley 12. In this painting process P1, the paint is applied by the paint machine 38 from the front to the rear while moving the body.
It is sprayed for about 3 minutes.

2 6 A cooling process P2 is provided adjacent to the vehicle body exit portion of the painting process PI, and this cooling process P2 is provided with a cooling dome 40 that opens in the front and rear. A cold air supply duct 42 is disposed in the upper part of the cooling dome 40, and the cold air supply duct 42 is provided with a plurality of cold air outlets 42a that open downward. The cold air supply duct 42 includes:
The air cooled by the heat exchanger 43 is forcibly supplied by the blower 44, and the cold air is sent to the duct 42.
The cold air is discharged into the dome 40 through the cold air outlet 42a.

As a result, the body W that has left the painting process PI is transferred from the front side into the cooling dome 40, and the paint applied to the surface of the body W is cooled by the cold air discharged from the cold air outlet 42a. The viscosity is upper bound.

Incidentally, FIG. 6 shows the relationship between paint lag (unit: 2° C.) and paint viscosity (poise) in an alkyd melamine high solid thermosetting paint. As shown in FIG. 6, the viscosity of the paint is approximately 0.6 poise at room temperature of 227 O°C, whereas the viscosity of the paint increases to approximately 2 poise at a temperature of 5°C. Therefore, the temperature of the cold air blown onto the body W in the cooling process P2 is not limited to 5.
It can be understood that approximately ℃ is preferable.

In this embodiment, as a preferable example, the stage is set such that the application of the paint to the rear part is completed and the body W has escaped from the painting-f culm P1, that is, the body W is almost entirely transferred to the cold air duct 42. At this stage, the body W is attached to the vehicle body holding shafts 24, 2.
5, it is rotated approximately around the water axis. This rotation of the body W is performed for uniform cooling of the body W,
As a result, the paint applied to the surface of the body W is uniformly cooled, and the viscosity of the paint is uniformly increased.

As described above, the body W is transferred to the cooling process P2 immediately after being painted in the painting process PI, and the paint is cooled in the cooling process P2 and its viscosity reaches its upper limit, so that dripping of the paint immediately after painting is reliably prevented. Marketed 2 8 .

FIG. 5(b) shows a setting step in which the solvent is evaporated from the paint applied to the body W in the baking step P3. In this setting process, as described above, the body W transferred from the cooling process P2 is rotated around the horizontal axis at room temperature, and the paint on the surface of the body W is removed by approximately 7.
Allow to dry for a minute. In addition, in the setting process described above, the melting temperature is set at room temperature. Although the case where the solvent is volatilized is excluded, instead of this, the solvent may be volatilized while heating the painted surface.

FIG. 5(C) shows the baking step P3 which is carried out after the setting process. This baking process P3 is equipped with a tunnel-shaped drying oven 44 having an appropriate heating means, and the painted surface of the body W transferred from the setting culm is
For example, baking is performed in an atmosphere at a temperature of 140°C. In this baking zone, since the paint has already hardened, there is no need to rotate the body W, but from the viewpoint of uniformly heating the painted surface, baking is performed while rotating the body W around the water axis. good.

Fig. 7 corresponds to Fig. 3 above, and shows that an alkyd melamine high solid thermosetting paint was used as the paint, and the initial coating viscosity was adjusted to 0.6 poise, and the film thickness of the painted surface was 65 μm. , the relationship between the passage of time (unit: min) and the paint dripping speed (mm/min) in each case of performing the cooling process P2, setting process, and baking process P3 after applying a top coat to have a thickness of 53 μm and 40 μm This shows that.

As is clear from these Figures 3 and 7, if the painted surface is not cooled immediately after topcoating (the case shown in Figure 3), the paint will drip immediately after the completion of painting, for example, 2 to 3 minutes after the completion of painting. Although the speed increases, if the painted surface is cooled immediately after painting (as shown in Figure 7), the viscosity of the paint has increased, so the speed will increase even after painting is completed, for example, 3 to 4 minutes after painting is completed. , the paint dripping speed is still not very high. In other words,
By adding the cooling step P2, it is possible to delay the timing at which paint drips occur.

3 0 In addition, the paint dripping limit is the thickness of the paint film at which traces of paint movement can be visually observed on the dried paint film surface due to movement of 1 to 2 mm from the position where the paint adhered during the drying process. When the coating thickness is 2 mm or more, it is generally said that the coating is defective. Therefore, as shown in Figure 7, the paint dripping limit is reached approximately 7 minutes after painting for a film thickness of 40 μm, 5 and 6 minutes after painting for a film thickness of 53 μm, and 4 and 5 minutes after painting for a film thickness of 65 μm. Therefore, if settings involving rotation around the horizontal axis are performed before these times, paint dripping can be reliably prevented.

Similarly, data regarding an alkyd melamine high solid thermosetting paint having an initial coating viscosity of 0.2 poise is shown in FIG. Furthermore, FIG. 9 shows data regarding changes in the coating viscosity of these paints.

Incidentally, the same results were obtained for polyester melamine and acrylic melamine type paints.

Regarding the two-component reactive paint, as in the case 3I above, when the initial coating viscosity is 0.6 poise (No.
As a result of concrete experiments with the case of 0.2 poise (Fig. 1) and the case of 0.2 poise (Fig. 11), we found that the effect of providing the cooling process P2 in both cases is that it is possible to delay the timing at which paint drips. confirmed.

Table 2 below shows how to apply high solid top coat paint to the body W.
The film thickness is 50 to 55 μm for the bonnet and door of
The I.I. G. Value (sharpness value)
and the PGD value (sharpness). As is clear from this Table 2, I. G. There is almost no difference in the PGD value between the case where the cooling step is added and the case where the cooling step is not added. Therefore, it can be seen that even if the top coat is cooled immediately after being applied to the object, the finish of the painted surface is not affected at all. Table 332 shows the results of examining the finishing results of various paints by varying the initial coating viscosity.

(The following is a blank space) 3 3 3da In FIG. 1, a process P2' indicated by a virtual line indicates the second embodiment.

That is, in this embodiment, a process P2' for replacing the trolley 12 is added after the cooling process P2, and in this trolley replacement process P2', the body W is transferred to the rotary baking process P3.
Transfer will be made to a special trolley. By adding this process P2', the paint attached to the trolley 12 is removed from the rotary baking process P2'.
It is possible to avoid an accident in which the paint is scattered during step 3 and the scattered paint adheres to the painted surface of the body W. Of course, this bogie replacement process P2' is performed after the cooling process P2, so the effect of cooling the paint on the body W, that is, the timing at which paint drips occur, is delayed. It can be added based on the fact that

[Brief explanation of the drawing]

FIG. 1 is an overall process diagram showing an example 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. 3 6 Figures 3 and 4 are graphs showing the relationship between the thickness and dripping of paint, the smoothness of the painted surface, and rotation. Figure 5 (a) is a cross-sectional view showing the spraying process and cooling process in the painting line, Figure 5 (b) is a cross-sectional view showing the setting process in the painting line, and Figure 5 (c) is a cross-sectional view of the painting line. Figure 6 is a characteristic diagram showing the relationship between paint knitting and coating viscosity; Figure 7 is an alkyd melamine high solid thermosetting paint (initial coating viscosity: 0.6poi). Figure 8 is a characteristic diagram showing the relationship between the passage of time and the paint dripping rate after the completion of painting using SE). Figure 9 is a characteristic diagram showing the relationship between the passage of time and the paint dripping rate after the completion of the coating using the alkyd melamine high solid thermosetting paint (initial coating viscosity 20.6 and 0.2p37o). Figure 10 is a characteristic diagram showing the relationship between the passage of time and coating viscosity after the completion of coating using a two-component reactive paint (initial coating viscosity: 0.6 po).
Figure 11 is a characteristic diagram showing the relationship between the passage of time and the rate of paint dripping after the completion of painting using a 2-component reactive paint (initial coating viscosity: 0.2 poise). A characteristic diagram showing the relationship between the passage of time and the paint dripping speed after completion. W: 1 2 = 38: 40: 4 2 = 44: Pl: P2: P3: P2': Car body (object to be coated) Trolley coating machine cooling dome Cold air duct Drying oven Spraying process Cooling process Baking process (setting (Including process) Platform weight replacement process 3 8 Ward 0 -512- N O (Y) (Y)

Claims (1)

[Claims] (1) Coating an object to be coated includes a spraying step of spraying the paint and a drying step of drying the sprayed paint, and in the spraying step, the paint is removed at least on the vertical surface of the object. The paint is sprayed to a thickness greater than that at which dripping occurs, and in the drying step, the paint is sprayed at least until the paint begins to drip on the vertical surface of the coated object and until the paint no longer drips. an object is rotated about a substantially horizontal axis, the rotation of the object is greater than the rotational speed at which the paint changes from a vertical position to at least a horizontal position before gravity begins to cause the paint to sag, and The rotational speed is set as a range smaller than the rotational speed that causes paint to drip due to centrifugal force caused by rotation, and a cooling step for cooling the sprayed paint is provided between the spraying step and the drying step. A coating method, which is provided immediately after the spraying step.