JP2001219117A - Method for coating water-based coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method by using a water-based coating material capable of efficiently recovering uncoated coating material with a small amount of water, yet capable of refining the recovered coating material to utilize it again as it is in coating. SOLUTION: An object to be coated is coated by spraying the water-base coating material 12 in a coating material circulation tank 4 through an air atomizing coater 2, and simultaneously, the water-based coating material 12 is transported to an ultrafilter 5 with a pump 20 to perform an ultrafiltration, while the filtered water is transported to a running water tank 22 and the solid content is sent back to the coating material circultion tank 4. The overflowed water from the running water tank 22 is supplied to the upper portion of a running water board 3 and flows down along the surface of the running water board 3. Consequently, the uncoated coating material collected at the running water tank 3 flows down accompanied with water which flows down, and then recovered at a recovering gutter 11. The recovered uncoated coating material is sent to a filtering device 25 to remove dust included during the recovering cycle, and after that, is sent back to the coating circulation tank 4 for reutilization as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method using a water-based paint, and more particularly to a coating method for recovering and reusing an uncoated paint generated when atomizing a water-based paint.

[0002]

2. Description of the Related Art Atomization coating is one of the most widely used coating methods because of its excellent coating properties. However, since the atomization coating sprays the paint in a mist state, only a part thereof adheres to the object to be coated, and the coating efficiency is usually 30 to 70%.
Uncoated paint that has not been applied to the object to be painted, which is so low, is usually discarded as paint waste. In order to reduce such paint waste and to effectively use paint, it is desired to efficiently collect and reuse uncoated paint.

[0003] In recent years, the replacement of solvent type paints having a large environmental load with water-based paints having a small environmental load has been advanced. In water-based paints, the diluent used is water, and the rate of evaporation of the diluent is slower than the organic solvent used in general solvent-based paints, so the amount of diluent that evaporates during atomization coating is small. Therefore, the composition of the uncoated paint is close to the original paint composition. Further, even if the uncoated paint is recovered with water, it is easily dissolved or dispersed in water, and there is no problem such as agglomeration as in the solvent type paint.

[0004] Since the water-based paint has the above-mentioned characteristics, the recovery and reuse of the uncoated paint are widely performed as compared with the solvent-based paint. For example, JP-A-51-69541,
Japanese Patent Application Laid-Open No. Hei 8-71488 proposes a method of recovering and reusing an uncoated paint without using water. JP-A-51-5
0949, JP-A-9-24333, JP-A-9-66
No. 256 proposes a method in which a collecting unit is kept wet with a small amount of water such as dew condensation water to collect and reuse uncoated paint. JP-A-50-80321, JP-A-56-14
No. 1875 and Japanese Patent Application Laid-Open No. 9-1014 propose a method of recovering and reusing an uncoated paint by using a large amount of water.

[0005]

However, the conventional methods for collecting and reusing non-coated paint have the following problems.
In other words, the method that does not use water for the recovery of uncoated paint,
There is a problem in that the fluidity of the non-coated paint is small and it takes a long time to collect the paint, and the collecting part is contaminated with the paint because the collecting part is not washed with water. The method of using a small amount of water for collecting the non-coated paint can reduce the above problem, but has a problem that the solid content of the collected non-coated paint varies depending on the amount of water used. In the method in which a large amount of water is used for recovering the non-coated paint, the solid content of the recovered non-coated paint is significantly reduced and cannot be directly reused for coating. For this reason, the recovered uncoated paint is reused as a diluent or is concentrated and reused.However, the method of reusing as a diluent limits the amount of reusable paint and concentrates and reuses. The method used has problems that the quality of the paint is deteriorated and complicated readjustment is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide an unpainted paint which can be efficiently recovered with a small amount of water, and that the recovered paint can be easily purified and reused for painting. Is to propose a method.

[0007]

Means for Solving the Problems The present inventor has conducted intensive studies in order to solve the above-mentioned problems. As a result, water was extracted from the aqueous paint in the paint circulation tank and supplied to the flowing water surface. We found a way to collect the uncoated paint with water, return it to the paint circulation tank and reuse it for painting. According to this method, the unpainted paint is collected using the water extracted from the paint. Therefore, even if the collected paint is returned directly to the paint circulation tank, the solid content of the paint can be obtained regardless of the amount of water used for the collection. There is almost no change in concentration. Therefore, the non-coated paint can be efficiently recovered using water, and can be reused for coating without requiring complicated paint readjustment.

[0008] Also, the research on the structure of the flowing water surface,
It has been found that the amount of water supplied to the flowing water surface can be greatly reduced when the flowing water surface is formed in a groove or grid shape. The present invention has been achieved based on the above research results.

That is, the present invention is a coating method using the following water-based paint. (1) In a method of spraying a water-based paint supplied from a paint circulation tank and spraying the object to be coated, a flowing water surface is disposed behind the object to be coated, and water is extracted from the water-based paint in the paint circulation tank. Then, this water is supplied to the upper part of the flowing water surface, the flowing water surface is caused to flow down, and the water-based paint sprayed on the flowing water surface is collected together with the flowing water, and the collected water-based paint is transferred to the paint circulation tank. A coating method using a water-based paint, which is returned and reused. (2) The method according to the above (1), wherein the flowing water surface is formed in a groove shape or a grid shape.

The water-based paint to which the coating method of the present invention can be applied is not particularly limited as long as it uses water as a diluent (solvent or dispersant), such as a water-soluble paint, a water-dispersible paint or an emulsion paint. Can be used without limitation. Specific examples include alkyd resin paints, acrylic resin paints, polyester resin paints, vinyl resin paints, melamine resin paints, epoxy resin paints, and urethane resin paints.

[0011] The coating method of the present invention is a method of atomizing such a water-based paint to coat an object to be coated. The method of atomizing and coating is not particularly limited, and examples thereof include airless atomizing coating, air atomizing coating, rotary atomizing coating, and electrostatic atomizing coating. These coatings are usually, but not exclusively, performed in a coating booth. The painting booth may be either a wet booth or a dry booth.

In the coating method according to the present invention, the flowing water surface is arranged behind the object to be coated, that is, at a position opposite to the atomizing coating apparatus. By arranging the running surface in the painting direction,
Applicable to any painting direction. Here, the back includes a back surface, a side surface, a bottom surface, and the like. The flowing water surface can be arranged perpendicular to the spray direction of the water-based paint, or can be arranged at an angle.

The flowing water surface used in the present invention may have any shape such as a flat surface, a curved surface, a cylindrical surface, and a combination thereof. The material of the running surface is
Any material may be used as long as it does not transmit water, does not denature or deform depending on the aqueous paint and coating conditions, and does not adversely affect the aqueous resin, and examples thereof include metals and resins. In the case of a lattice shape, it is preferable that a weir lower than the groove is provided in a groove through which water flows down, and the whole is in a lattice shape.

The flowing water surface may be flat, groove-shaped or grid-shaped. The grooves are preferably provided in parallel with the direction in which the water flows down. It is preferable that the flowing water surface is groove-shaped or lattice-shaped since the amount of water used for collecting the uncoated paint can be significantly reduced as compared with the case where the flowing water surface is flat. For example, the amount of water to be used is 1 compared to the case where a flat running surface is used.
Even at / 10, the same degree of cleaning can be secured.

When the water flow surface is formed in a groove shape or a grid shape, the depth of the concave portion is 0.1 to 10 m.
m, preferably 1 to 5 mm, the width of the concave portion is 1 to 100 m
m, preferably 2 to 50 mm. When the shape of the groove or the lattice is in the above range, the amount of water supplied to the flowing water surface can be effectively reduced, and the uncoated paint can be more efficiently recovered.

The flowing water surface is located at a portion where the atomized paint that has not adhered to the object to be applied collides or falls. In this case, the area of the flowing water surface affects the recovery rate of the uncoated paint, and is set to a size that can obtain the target recovery rate. Regarding the relationship between the area of the flowing water surface and the recovery rate of the uncoated paint, the higher the area, the higher the recovery rate can be obtained, but it is necessary to supply more water to the flowing water surface. On the other hand, if the area is reduced, the recovery rate decreases.

According to the coating method of the present invention, the sprayed water-based paint is collected on the above-mentioned flowing water surface, and the collected paint is recovered by accompanying the water flowing down the flowing water surface. In the coating method of the present invention, water extracted from a water-based paint used for coating is used as water used for recovery.

In order to extract water from the water-based paint, any method capable of separating or extracting a part of the water incorporated as a diluent (solvent) from the water-based paint can be adopted without limitation. It can be performed by a membrane separation method such as filtration. For the ultrafiltration, an ultrafiltration membrane having a hollow fiber shape or a flat membrane shape can be used.

The water extracted from the water-based paint is supplied to the upper part of the flowing water surface disposed behind the object to be coated, and flows down the flowing water surface. As a result, the water-based paint sprayed on the surface of the flowing water is collected together with the flowing water. Water may be allowed to flow continuously or intermittently, but is preferably made to flow continuously.

The amount of water supplied to the flowing water surface is 0.1 to 5 as the amount of water supplied per minute per 1 m ² of the area of the flowing water surface.
liter / min / m ² , preferably 0.2 to 2 liter / min / m
^It is desirable to set it to ² . In particular, when the flowing water surface is flat, it is 1 to 5 liter / min / m ² , preferably 1.2 to ² liter.
/ Min / m ² , 0.1 to 2 lite for grooves or grids
r / min / m ² , preferably 0.1 to 1 liter / min / m ² . If the amount of water to be supplied is less than the above range, the washing performance of the running water surface is insufficient, and the running water surface is easily stained with paint. On the other hand, in order to supply water beyond this range, the paint circulation tank and the equipment for extracting water become large, and the equipment cost and operating cost increase.

The uncoated paint collected on the flowing water surface easily flows down along with the water. It is preferable to install a gutter or the like for collecting water flowing down at the lower end of the flowing water surface. The uncoated paint thus collected can be reused by returning it to the paint circulation tank. In order to remove dust and the like mixed in the coating booth, it is preferable to perform purification by filtration or the like before returning to the paint circulation tank. In this case, since the paint is recovered in a state diluted in flowing water, purification by filtration or the like can be easily performed.

In the present invention, as described above, the water extracted from the water-based paint used for coating is used for the recovery of the uncoated paint. Therefore, even if the recovered paint is returned to the paint circulation tank, the recovered paint can be recovered. Regardless of the amount of water used, the fluctuations in the solids concentration in the paint circulation tank are extremely small, so there is no need for complicated readjustment such as adjusting the solids concentration when reusing the recovered paint. ,
The recovered paint can be reused for painting as it is. In addition, when the flow surface is formed in a groove shape or a grid shape, the amount of water used for collecting the uncoated paint can be significantly reduced.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a coating apparatus according to an embodiment for implementing a coating method for collecting and reusing uncoated paint according to the present invention. In FIG. 1, B is a painting booth, which is configured to paint a painting object 1 with a paint atomized by an air atomizing painting machine 2. Numeral 3 denotes a flowing water plate having a flowing water surface formed on the coating object 1 side. Reference numeral 4 denotes a paint circulation tank, and 5 denotes an ultrafilter, which are attached to a coating booth B. The painting booth B is a wet booth having a water tank 6.

In the coating apparatus shown in FIG. 1, the object to be coated 1 is suspended on a conveyor 10 and is carried into the booth from one side of the booth (perpendicular to the direction of coating), and then to the other side. The coating target 1 is configured to be coated by the air atomizing coating machine 2 while being carried out. A stainless steel flush plate 3 having a flat surface structure is vertically arranged behind the object 1 to be coated, and a collecting gutter 11 is provided at a lower end of the flush plate 3. A water-based paint 12 is stored in the paint circulation tank 4, and a stirring device 13 is provided therein.
Is attached.

In the coating apparatus shown in FIG. 1, the water-based paint 12 in the paint circulation tank 4 is sent to the air atomizing coater 2 from the communication path 15 by the pump 14, and
To paint the object 1 to be coated. The unpainted paint that has not adhered to the painting object 1 is collected by the running water plate 3. The exhaust gas is exhausted from the exhaust port 16.

The uncoated paint collected by the running water plate 3 is recovered as follows. That is, the water-based paint 12 in the paint circulation tank 4 is continuously sent to the ultrafilter 5 by the pump 20, and is continuously ultrafiltered by the ultrafiltration membrane 5a. The water extracted from the water-based paint 12 by the ultrafiltration is continuously sent from the running water supply path 21 to the running water tank 22, and the concentrated paint is continuously returned to the paint circulation tank 4 from the communication path 23. The water overflowing the flowing water tank 22 is continuously supplied to the upper part of the flowing water plate 3, and the flowing water plate 3 is caused to continuously flow down by gravity drop. At this time, the uncoated paint collected by the flowing water plate 3 flows down along with the flowing water and is collected by the collecting gutter 11. The uncoated paint thus collected is sent from the communication path 24 to the filtration device 25, where impurities such as dust mixed in the recovery process are removed and purified, and then returned to the paint circulation tank 4 and reused as it is. . In this case, since the recovered paint is diluted with flowing water, purification by filtration is easily performed.

In the apparatus shown in FIG. 1, the volume of the aqueous paint 12 in the paint circulation tank 4 is at least 50 times the volume of water extracted per minute, preferably 75 to 50 times.
Desirably, it is set to 0 times the capacity. Ultrafilter 5 for water extraction
When the water-based paint 12 is used, the amount of the water-based paint 12 is usually required to be 25 times or more larger than the amount of the water to be extracted. can do.

In order to increase the temperature during the paint circulation and to keep the temperature of water extracted from the paint low, the paint circulation tank 4, the flowing water plate 3, the ultrafilter 5, and cooling devices are provided in each pipe. You can also.

In FIG. 1, a flush plate 3 having a flat surface is used. Instead of the flush plate 3, a plate formed in a groove shape as shown in FIG. 2 or a grid as shown in FIG. What is formed in the shape can also be used. In FIG. 2, grooves 27 are formed by bank-shaped convex portions 26 that are parallel to the vertical direction, and a water supply port 28 is provided above each groove 27 and communicates with the flowing water tank 22. In FIG. 3, a weir 29 is provided in the groove 27 shown in FIG. 2, and has a lattice shape as a whole. In the case of the flowing water plate 3 in FIGS. 2 and 3, the water is supplied by discharging the water in the flowing water tank 22 from the water supply port 28 on the upper part of the flowing water plate 3. In the case of using the flowing water plate 3 formed in a groove shape or a grid shape, the amount of supplied water can be effectively reduced, and the uncoated paint can be more efficiently recovered.

When the flowing water plate 3 is formed in a groove shape or a lattice shape, the water film on the surface is less likely to be cut as compared with a flat shape. The portion not covered with the water film is liable to be stained because the uncoated paint is not washed, and the recovery rate of the uncoated paint is reduced. However, the flowing water plate 3 formed in a groove or grid shape has a water film on the surface. Since the cuts are less likely to occur, the amount of water flowing down can be significantly reduced as compared with the flat water flowing plate 3. This is presumed to be due to the following reasons. That is, the presence of the convex portion 26 or the weir 29 of the flowing water plate 3 prevents water from flowing intensively to a specific portion, and the flow is averaged. This is presumed to be because the interfacial tension between the surface of the plate 3 and water increases, the flow rate of water decreases, and the water film is stabilized even with a thin film.

In the case of using the flowing water plate 3 formed in a groove shape or a lattice shape, the amount of water used for recovery can be reduced, so that the capacity of the water-based paint 12 in the paint circulation tank 4 is also reduced. be able to. Even when the water-flowing plate 3 formed in a groove shape or a lattice shape is used, the capacity of the water-based paint 12 in the paint circulation tank 4 is as follows.
For the same reason as described above, it is desirable to make the volume of water extracted per minute the same as that described above.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.
The examples show preferred examples for carrying out the present invention, and do not limit the present invention.

Example 1 A paint recovery test was conducted using the apparatus shown in FIG. The water flowing plate 3 used had an area of 1 m ² (length 1 m, width 1 m). In 200 liter paint circulation tank 4,
As the water-based paint 12, Aqua No. 8500 (trademark, manufactured by NOF Corporation) was charged in 150 liters. Next, after filling the running water tank 22 with deionized water, the amount and pressure of the aqueous paint 12 to be sent to the ultrafilter 5 by the pump 20 are adjusted,
2 liter / min / m ² of water per 1 m ² of area of the water flow plate 3 was continuously supplied to the water flow plate 3. Ultrafilter 5
V-85 (trademark, manufactured by AS Engineering Co., Ltd.) was used as the ultrafiltration membrane.

After leaving the water flowing on the water-flowing plate 3 for 5 minutes, the air-atomizing coating machine 2 is directed toward the water-flowing plate 3 for 120 minutes at a paint discharge rate of 250 cm ³ / min without the object 1 to be coated. The air atomization coating of the water-based paint 12 was continued. Further, the coating liquid level in the coating circulation tank 4 was recorded at the start of coating. After the coating was completed, the supply of water from the ultrafilter 5 to the flowing water plate 3 was continued for another 10 minutes, and then the operation of the pump 20 was stopped.

After the operation of the pump 20, the coating liquid level in the coating circulation tank 4 was recorded. From the liquid level in the paint circulation tank 4, the tank 4
The paint amount in the inside was calculated, and the paint reduction amount from the start of coating to the end of operation of the pump 20 was obtained. The paint recovery rate was calculated from the total amount of paint reduction and the amount of paint discharged from the air atomizing coating machine 2. The aqueous paint 12 in the paint circulation tank 4 was extracted, and the solid content concentration was measured. In addition, dirt on the flowing water plate 3 was visually determined. Table 1 shows the results.

Example 2 In the apparatus shown in FIG. 1, a water flow plate 3 formed in a groove shape as shown in FIG. The size of the groove is 2 mm for the portion A in the figure, 5 mm for the portion B, and 2 m for the portion C in the drawing.
m. The length D of the water supply port 28 is 5 mm. Example 1 was repeated except that the amount of paint and the pressure fed to the ultrafilter 5 were adjusted so that 0.2 liter / min / m ² of water was supplied to the water plate 3 using the water plate 3. The test was performed in the same manner. Table 1 shows the results.

Example 3 In the apparatus shown in FIG. 1, a flowing water plate 3 formed in a lattice shape as shown in FIG. The size of the grid in the figure is 2 mm for portion A, 5 mm for portion B, 2 mm for portion C, 1 mm for portion E, and 10 mm for portion F in the drawing. The length D of the water supply port 28 is 5 mm. A test was performed in the same manner as in Example 2 except that the grid-like running water plate 3 was used. Table 1 shows the results.

[0038]

[Table 1] * 1 Paint recovery rate (% by weight) was determined from the following formula. 100-the amount of paint decrease / the total amount of paint discharge × 100 * 2 The degree of contamination of the running water plate was visually determined according to the following criteria. ○: No dirt ×: Dirt

[0039]

According to the method for coating with a water-based paint of the present invention, the non-painted paint is recovered using water extracted from the water-based paint. In addition, the recovered water-based paint can be easily purified and reused for coating without re-adjusting the concentration. In addition, by forming the running water surface in a groove or grid shape, the amount of water supplied to the running water surface can be significantly reduced, and in this case also, good cleaning properties can be obtained and contamination of the running water surface can be prevented. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a coating apparatus for performing a coating method of the present invention.

FIG. 2 is a partial perspective view schematically illustrating a structure of a water plate according to another embodiment.

FIG. 3 is a partial perspective view schematically showing a structure of a water plate according to still another embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 coating object 2 air atomizing coating machine 3 running water plate 4 paint circulation tank 5 ultrafiltration device 5a ultrafiltration membrane 6 water tank 10 transfer conveyor 11 collection gutter 12 waterborne paint 13 stirrer 14, 20 pump 15, 23, 24 Communication path 16 Exhaust port 21 Running water supply path 22 Running water tank 25 Filtration device 26 Convex part 27 Groove 28 Water supply port 29 Weir

Claims (2)

[Claims] 1. A method for atomizing a water-based paint supplied from a paint circulation tank to coat an object to be painted, wherein a flowing water surface is disposed behind the object to be painted, and water is supplied from the water-based paint in the paint circulation tank. And supplying the water to the upper part of the flowing water surface, causing the flowing water surface to flow down, collecting the water-based paint sprayed on the flowing water surface by accompanying the flowing water, and collecting the recovered water-based paint by the paint circulation. A method of coating with a water-based paint, which is returned to a tank and reused. 2. The method according to claim 1, wherein the flowing water surface is formed in a groove shape or a grid shape.