JP2006231236A - Method and apparatus for collecting water-based paint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for collecting water-based paint in which foaming can be effectively reduced and water-based paint mist can be collected in the case of spray painting using water-based paint. <P>SOLUTION: The method for collecting water-based paint comprises flowing water-based fluid along a member so as to form a liquid film covering a surface of the member and flowing a gas containing water-based paint in a mist form through a gap between the liquid films. The apparatus for collecting water-based paint (20) comprises a flow path (1) in which a gas containing the water-based paint mist (9) moves upward and flows, and a baffle plate (3) disposed in an inclined state is provided in the flow path (1), wherein the water-based fluid (12) is flowed through the flow path (1) while forming the liquid film covering a lower side of the baffle plate (3) inclined, whereby the water-based paint mist (9) in the gas is collected in the water-based fluid (12). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a collection method and apparatus for collecting an aqueous paint, particularly an aqueous paint contained in a mist form in a gas.

  As a general coating method, a spray coating method of spraying (or spraying) a coating material on an object to be coated is widely used (see, for example, Patent Documents 1 to 6). In such a spray coating method, a paint that has not been applied to an object to be coated during coating may exist in a mist state in a gas atmosphere (hereinafter, also referred to as a paint mist in this specification). There is a painting booth that uses a water curtain to collect the paint mist.

  A collecting device provided in a conventional water curtain painting booth will be described with reference to the drawings.

  The collection device 60 shown in FIG. 4 is disposed adjacent to a painting chamber (not shown). During painting, an air flow is formed by a fan or the like as indicated by the arrow in the figure, and the gas atmosphere in the painting chamber is forcibly exhausted through the exhaust passage 61.

  In the collection device 60, the water curtain 71 is formed by flowing water (or booth water) along the wall surface (or flat plate) of the exhaust passage 61 on the painting chamber side. The painting is carried out by spraying the paint toward the object to be coated, but most of the sprayed paint that has not been applied to the object reaches the water curtain 71 and is collected in the water. Is done. The paint mist 69 that may exist in the gas in the paint chamber is a centrifugal force applied to the paint when the gas passes through the water curtain 71 at a high speed from the gap between the wall surface behind the water curtain 71 and the centrifugal plate 65. (Such centrifugal plates are shown in FIGS. 1 and 2 (vortex plate) of Patent Document 2, FIG. 3 of Patent Document 5 and FIG. 1 of Patent Document 6). The collected paint is collected in a booth tank (not shown) in the form of booth water.

  The gas that has passed through the water curtain 71 ascends in the exhaust passage 61, passes through the baffle plates 67 that are alternately inclined as shown in the figure, passes through a filter (not shown), and is discharged to the outside. . At this time, the paint mist 69 (and the water that may be present) remaining in the gas is removed from the gas by the baffle plate 67 and the filter, and the paint mist 69 that collided with the baffle plate 67 is collected in the booth water tank. The baffle plate 67 generally has a size over the entire width of the exhaust passage 61 (length in the direction perpendicular to the paper surface of FIG. 4). When the baffle plate 67 and the filter are washed during painting, water droplets scatter and adversely affect the painting. Therefore, the baffle plate 67 and the filter are spray-washed from the nozzle while not painting. The filter is replaced during maintenance.

JP 05-146727 A Japanese Patent Laid-Open No. 06-142573 Japanese Patent Laid-Open No. 07-1000041 JP 07-299399 A Japanese Patent Application Laid-Open No. 09-10640 JP 2000-126659 A

  In recent years, water-based paints have been used in place of solvent-based paints from the viewpoints of the influence on the environment and the human body and ease of reuse.

  However, the conventional collecting device as described above is not fully satisfactory when a water-based paint is used. Since the air current passes through the water curtain 71 at high speed and the air current and the water collide with the centrifugal plate 65, forced gas-liquid mixing occurs. It is because the bubble that has become overflowing from the booth tank. When using a solvent-type paint, the wind speed of the airflow when passing through the water curtain 71 is about 20 to 35 m / s. However, when using a water-based paint, foaming occurs when the wind speed exceeds 10 m / s. Is an upper limit wind speed of 15 m / s at the maximum, and a sufficient collection rate cannot be obtained if foaming is to be suppressed.

  The problem of foaming can be dealt with by adding antifoaming agents and using antifoaming equipment, but these require additional costs, and in the case of concentrating and reusing booth water that collects paint mist. Addition of a large amount of antifoaming agent is not desirable because the composition of the recovered paint changes.

  In addition, in the conventional painting booth, the internal structure is complicated, so the cleaning performance is poor, and it is necessary to lengthen the cleaning time when performing color change. Moreover, since the amount of contamination is large, usable paint colors are limited.

  Furthermore, in the conventional painting booth, water-based paint adheres to the inside of the exhaust passage (more specifically, a filter and a baffle plate), and it is necessary to frequently perform maintenance, which is expensive.

  The object of the present invention is to effectively reduce and preferably prevent foaming even in the case of spray coating using a water-based paint, to collect paint mist while improving cleanability and reducing maintenance frequency. It is an object of the present invention to provide a collection method and apparatus that can be used.

According to one aspect of the present invention, a method for collecting a water-based paint comprising:
There is provided a method comprising flowing an aqueous fluid along a member to form a liquid film covering the surface of the member, and flowing a gas containing a mist-like aqueous paint through a gap in the liquid film.

  According to such a collection method of the present invention, the aqueous fluid flows while forming a liquid film covering the surface of the member, and the gas flows through the liquid film, so that the aqueous fluid and the gas are vigorously mixed. Therefore, foaming can be effectively reduced and preferably prevented. Further, the water-based paint can be quickly collected by the aqueous fluid without being fixed to the member, and the member can be kept relatively clean (in other words, the cleaning property is high). As a result, the maintenance frequency of the flow path through which the gas passes can be reduced. In addition, since the pressure loss during passing through the flow path is small, noise can be further reduced.

According to another aspect of the present invention, a collecting device for collecting a water-based paint,
A flow path in which a gas containing a mist-like water-based paint rises and flows;
A baffle plate (or elimine plate) placed in the flow path,
The baffle plate is disposed in an inclined manner, and the aqueous fluid flows through the flow path while forming a liquid film covering the inclined lower surface of the baffle plate, whereby the water-based paint contained in the mist form in the gas is contained in the aqueous fluid. A collection device is provided for collecting. The aqueous fluid in which the aqueous coating material is collected can be collected along an inner wall surface of the channel, for example, and collected in a suitable tank such as a booth water tank.

  Such a collection device of the present invention uses an inclined baffle plate as a member in the collection method of the present invention, and has the same effect as the collection method of the present invention.

  Throughout the present invention, “aqueous fluid” means water or a liquid fluid containing water as a main component. The “water-based paint” may be a general water-based paint, that is, a water-based paint containing a nonvolatile content and an aqueous solvent. Nonvolatile components constituting the water-based paint are paint resin and pigment. Further, the aqueous solvent constituting the aqueous paint may contain a hydrophilic organic solvent in addition to water.

  In one aspect of the present invention, a plurality of baffle plates may be arranged in a staggered multi-stage, at least two or more stages, for example, 3 to 6 stages in the flow path. By arranging in a staggered manner in this manner, it can be removed one by one, and the size and weight of one baffle plate can be reduced, thus facilitating maintenance.

  In order for the aqueous fluid to cover the lower surface of the baffle plate to form a liquid film, it is important that the aqueous fluid exhibits good wettability with respect to the lower surface. The wettability can be evaluated by the contact angle of the aqueous fluid with respect to the lower surface of the baffle plate. When such a contact angle is exhibited, the liquid film can be formed to cover the entire lower surface of the baffle plate without the film being interrupted or the liquid being scattered.

  The contact angle is determined by a combination of the composition of the aqueous fluid for forming the liquid film and the material constituting the lower surface of the baffle plate. As the aqueous fluid, an aqueous fluid having a small surface tension is preferable. For example, a mixed liquid containing water as a main component and an appropriate amount of a hydrophilic solvent can be used. This hydrophilic solvent may be the same as the hydrophilic solvent that can be included in the aqueous paint, and the aqueous fluid (booth water) collected in the booth water tank may be reused. Booth water contains the hydrophilic solvent contained in the water-based paint, has an advantage that it has a small surface tension and can easily form a liquid film. On the other hand, the material constituting the lower surface of the baffle plate is preferably a material having a hydrophilic surface. For example, a material subjected to hydrophilic treatment by coating or surface modification can be used. Moreover, it is preferable that the inner wall surface is smooth and smooth.

  Further, in order to avoid gas-liquid mixing, it is preferable that the aqueous fluid that covers the lower surface of the baffle plate and forms a liquid film does not drip off the lower surface. For this reason, the inclination angle of the lower surface of the baffle plate can be limited in consideration of the above-mentioned wettability, the gas passing wind speed, the flow rate of the aqueous fluid, and the like. The lower surface of the baffle plate is inclined with respect to the horizontal plane at an angle in the range of about 120 to 165 °, for example. This angle (also referred to as an inclination angle in the present specification) is an angle between the lower surface and the horizontal plane, and means an angle on the exposed side (side in contact with the aqueous fluid) of the lower surface.

  According to the present invention, there is provided a collection method and apparatus capable of effectively reducing and preferably preventing foaming and collecting paint mist even when spray coating is performed using an aqueous paint. The Furthermore, the collection method and apparatus of the present invention have higher cleaning properties, less frequent maintenance, and lower noise than conventional collection devices.

  As shown in FIG. 1A, the collection device 20 in this embodiment includes a flow path 1 in which a gas containing an aqueous paint mist 9 rises and a baffle plate that is disposed in an inclined manner in the flow path 1. 3. The aqueous fluid 12 is supplied so as to form a liquid film covering the inclined lower surface of the baffle plate 3. Further, as shown in FIGS. 1A and 2, in the painting booth 30 in which the collection device 20 is integrally formed, the water curtain 11 causes the aqueous fluid to flow along the wall surface on the painting chamber 21 side of the flow path 1. May be formed.

  As shown in FIG. 1A, the baffle plate 3 extends from one wall of the flow path 1 to the other wall facing the flow path 1, and is provided in multiple stages of at least two stages, for example, three to six stages. (FIGS. 1A and 1B show the case of four stages). Further, the baffle plates 3 are arranged in a staggered manner so that a gap between the baffle plates in a certain step is covered by the baffle plate in the upper step (see FIGS. 1B and 1C). Note that FIG. 1 (c) typically shows three baffles, a total of eight baffle plates 3).

  The contact angle of the aqueous fluid 12 with respect to the lower surface of the baffle plate 3 is, for example, within about 60 ° (0-60 °), and preferably within about 30 ° (0-30 °). The aqueous fluid 12 preferably has a low surface tension. The booth water collected in the booth water tank 23 (FIG. 2) may be supplied into the flow path 1 as the aqueous fluid 12 and circulated for use. Booth water contains a suitable amount of a hydrophilic solvent derived from an aqueous paint, such as diethylene glycol monobutyl ether (BDG), in water, and has a low surface tension. On the other hand, the lower surface of the baffle plate 3 may be made of a material such as stainless steel as long as the surface tension of the aqueous fluid 12 is small. For example, the surface of the baffle plate 3 may be formed by coating the surface with a hydrophilizing agent made of silicate. More preferred.

  As shown in FIG. 3, the inclination angle of the lower surface of the baffle plate 3 with respect to the horizontal plane is, for example, about 120 to 165 °, preferably about 135 to 150 °, depending on the magnitude of the contact angle. When the inclination angle is close to 90 °, it is difficult to extend the baffle plate 3 across the opposing walls of the flow path 1. On the other hand, if the inclination angle is too large, the aqueous fluid 12 drops from the lower surface of the baffle plate 3 and a liquid film cannot be formed.

  It is preferable that the lower surface of the baffle plate 3 is smooth and smooth.

  Next, operation | movement and an effect | action of the collection apparatus 20 of this embodiment and the coating booth 30 provided with this are demonstrated.

  First, the coating object 27 is coated with a water-based paint in the coating chamber 21 by a spray coating method, and a gas containing the water-based paint mist 9 enters the collecting device 20 from the coating chamber 21 and flows up through the flow path 1. At this time, the water-based paint mist 9 may be partially collected by the water curtain 11.

  Then, when the gas flows up through the flow path 1, the aqueous paint mist contained in the gas can be collected in the aqueous fluid 12. This is because when the gas rises, the aqueous paint mist 9 contained in the gas collides with or contacts the aqueous fluid 12 covering the lower surface of the baffle plate 3.

  By setting the wind velocity of the gas passing between the baffle plates 3 to about 3 to 8 m / s, for example, the water-based paint mist can be efficiently collected in the fluid 22, but is not limited thereto.

  The gas that has passed between the baffle plates 3 in the flow path 1 passes through the filter 25 (FIG. 2) as necessary, and is preferably discharged to the outside of the painting booth in a state substantially free of water-based paint mist. Is done.

  Although it is preferable to always supply the aqueous fluid 12 during coating, it may be intermittently supplied in some cases.

  The aqueous fluid 12 that has collected the aqueous paint in this way then flows down along the inner wall surface of the flow path 1 and is collected in the booth water tank 23 (FIG. 2). The collected aqueous fluid 12 may be used in a circulating manner, and may be discarded after subjecting to a general wastewater treatment method such as sedimentation separation and flotation separation, if necessary.

  According to the collection method and the collection device 20 of the present embodiment as described above, since the aqueous fluid is not vigorously mixed with the gas, the aqueous coating material is contained in the aqueous fluid while effectively suppressing and preferably preventing foaming. Can be collected. As a result, when the recovered aqueous fluid is subjected to a general wastewater treatment method such as sedimentation separation and flotation separation, it is not necessary to add a large amount of antifoaming agent as in the past, reducing the amount of antifoaming agent, Preferably, it can be made unnecessary.

  Further, the aqueous paint can be quickly collected by the aqueous fluid 12 without being fixed to the lower surface of the baffle plate, and the flow path can be kept relatively clean. As a result, the interior of the flow path 1 can be cleaned with a smaller amount of cleaning water (or cleaning agent) to sufficiently remove the water-based paint. Therefore, the frequency of maintenance of the collection device can be reduced. For example, in the past, it was performed four times per year, but according to the present embodiment, it can be performed once.

  In addition, since the pressure loss while passing through the flow path 1 is smaller than the pressure loss used for passing the gas through the water curtain 71 at a sufficient wind speed in the conventional collecting device 60 shown in FIG. Can be made smaller.

  Furthermore, according to the present embodiment, the baffle plates 3 can be removed one by one, and the size and weight of one baffle plate 3 can be reduced, so that maintenance is facilitated. For example, a baffle plate provided in an exhaust passage of a conventional painting booth generally occupies an area of 800 mm × 600 mm or more and weighs 6 kg or more. According to this embodiment, the baffle plate is less than 800 × 300 mm. The area and weight can be about 3-5 kg.

  This embodiment can be variously modified. For example, the recovered aqueous fluid 12 may be separated into a concentrated portion where the aqueous paint concentration is increased and a remaining portion where the aqueous paint concentration is decreased by a concentration separation device. Here, “water-based paint concentration” means, more strictly, the concentration of the non-volatile content of the water-based paint. Generally, a cross-flow filter, preferably an ultrafilter, can be used for the concentration and separation device. The non-volatile component that is a component of the water-based paint has a molecular weight larger than the molecular weight cut off of the filter (filter material), so it remains upstream without passing through the filter, while the component having a molecular weight smaller than this molecular weight cut-off is Since it moves to the filtrate side through the filter, the non-volatile content contained in the water-based paint can thereby be concentrated. The obtained concentrating part may be supplied again to the concentrating device and circulated and concentrated. The concentrated part thus obtained may be used for reusing the water-based paint or may be subjected to an appropriate treatment and discarded. On the other hand, the remaining portion (for example, filtrate) whose aqueous paint concentration has decreased may be reused as an aqueous fluid or discarded as it is.

  In addition, in this embodiment, although the case where it applied to a water curtain type painting booth was explained, the collection device of the present invention is not limited to this, for collection of water-based paint, any other device, For example, it can be applied to a painting booth of a venturi type or other forms.

  In this example, the influence of the contact angle and the inclination angle on the liquid film forming property and the cleaning property was examined.

  First, booth water was placed as an aqueous fluid on a sample made of the same material as the lower surface of the baffle plate, and the contact angle was examined. Booth water is a water-based paint added to water and contains a hydrophilic organic solvent (diethylene glycol monobutyl ether (BDG)) derived from the water-based paint. The combinations showing the contact angles in Table 1 were selected by varying the amount of the material for the lower surface of the baffle plate and the amount of water-based paint (more specifically, a hydrophilic solvent).

  Then, an aqueous fluid was allowed to flow along the sample on the lower surface of the baffle plate arranged at a predetermined inclination angle (see FIG. 3), and it was visually observed whether the membrane was interrupted and / or the liquid was dropped. . At this time, the flow rate of the booth water was about 7 liters / minute per 0.3 m of the sample width.

  The evaluation criteria for the liquid film formation are: ○ when the film breakage and / or dripping of the liquid did not occur in the descending order of evaluation, △ when it occurred slightly but acceptable, and when it occurred clearly Was marked with x.

  Further, an aqueous fluid was circulated in a circulating manner, and thereafter, it was visually observed whether or not the aqueous paint was attached to the sample on the lower surface of the baffle plate. At this time, the flow rate of the aqueous fluid (booth water) was the same as described above.

  The evaluation criteria for detergency were ◯ when the water-based paint did not adhere in the descending order of evaluation, △ when it was slightly occurring but acceptable, and x when it was apparent.

  Then, the evaluation results of the liquid film forming property and the cleaning property were integrated, and the lower of the two evaluations was adopted. The results are shown in Table 1.

  From the viewpoints of liquid film formability and cleanability, it was found that the contact angle and tilt angle conditions indicated by ○ in Table 1 are preferable. For example, when stainless steel is coated with a hydrophilizing agent made of silicate on the bottom surface of the baffle plate and the aqueous fluid is a mixed solution having a water: BDG weight ratio of 95: 5, the contact angle is about 20 °, which is acceptable. The possible tilt angle range was about 90-170 °, preferably about 90-150 °. On the other hand, for example, when the lower surface of the baffle plate is made of stainless steel and the aqueous fluid is simply water, the contact angle is about 90 °, and the allowable inclination angle range is about 90 to 120 °. In the latter case, it is necessary to make the flow rate of the aqueous fluid relatively large so that the membrane is not interrupted, but it should be considered that dripping of the liquid can occur if the flow rate is increased at an inclination angle larger than 90 °. is there. It should be noted that the inclination angle is preferably somewhat larger than 90 °, for example, 120 ° or more, from the viewpoint of the apparatus configuration, apart from the liquid film forming property and cleaning property.

  In this example, a coating booth test machine equipped with a collection device was operated to examine collection and foaming properties.

  First, the coating booth 30 in which the collection device 20 described above with reference to FIGS. 1 and 2 was integrally formed was configured as an implementation test machine having a water curtain width of about 1.5 m. In this test machine, a filter 25 was provided above the baffle plate 3 in the flow path 1 in order to completely remove the aqueous paint mist from the gas.

Then, the water-based paint was sprayed for about 30 minutes while circulating the booth water collected in the booth water tank 23 as an aqueous fluid without any work, assuming painting with the water-based paint. An air spray gun was used for coating, the air pressure was about 0.2 MPa, and the water-based paint 9 was sprayed at about 2-3 g / m ³ . Moreover, the exhaust air volume per 1 m of water curtain width was set to about 70 m ³ / min. The concentration of the aqueous paint mist content in the gas exhausted through the filter and the exhaust fan was about 2 to ³ g / m ³ . The concentration of the non-volatile content of the water-based paint in the booth water was about 2% by weight before the application, but increased to about 5% immediately after the application.

  For comparison, a painting booth (not shown in its entirety) integrally formed with a conventional collecting device 60 'as shown in FIG. 4 is configured as a comparative test machine having a water curtain width of about 0.5 m. Then, using this comparative test machine, coating was performed under the same conditions as the test machine. At this time, the wind speed of the airflow when passing through the water curtain 71 was about 15 m / s. During the painting, booth water was not supplied into the exhaust passage 61.

(Catchability)
After the completion of painting, the collection property of the water-based paint of the collection device was evaluated.

  First, the solid content weight of the water-based paint used for coating in the test machine and the comparative test machine was determined by measuring the amount of water-based paint reduced in a paint tank (not shown).

  The filter after the coating (not washed) was dried and weighed, and this was compared with the weight before the coating, and the increase was taken as the solid weight of the water-based paint captured by the filter.

And the collection rate of the filter was calculated | required by the following formula (I).

  The collection rate with the filter was 0.3% for the test machine and 0.9% for the comparative test machine. The collection rate by the collector is 100% because the water exhausted from the exhaust fan does not contain water-based paint mist and all water-based paint can be regarded as being collected in the paint booth. It can be estimated by subtracting the collection rate (0.3% and 0.9%, respectively). The total collection rate by the collection device of the test machine, more specifically the water curtain and the four-stage inclined baffle plate, is estimated as 99.7%. The total collection rate by the collection device of the comparative test machine, more specifically by the water curtain, centrifuge plate and baffle plate, is estimated as 99.1%.

  From the above results, it was confirmed that the water-based paint contained in the gas can be collected at a high collection rate by the collection device of the test machine.

(Foaming)
Booth water was used as an aqueous fluid, and the foaming degree was evaluated by examining the degree of foaming during the coating while circulating the water. No antifoaming agent was used throughout the painting and filtrate washing operations.

The foams present in the booth tank and the volume of the booth water were examined, and the foaming rate was determined by the following formula (II).

  In the test machine, the foaming rate was 10% or less, while in the comparative test machine, the foaming rate was 30% or more. From this result, when using an implementation test machine equipped with the collection device of the present embodiment, the foaming rate is sufficiently smaller than when using a comparative test machine equipped with a conventional collection device, effectively suppressing foaming. It was confirmed that it was possible.

FIG. 1A is a schematic cross-sectional view for explaining a collection device according to one embodiment of the present invention, and FIG. 1B is a view of a baffle plate of the collection device of FIG. FIG. 1C is a schematic cross-sectional view, and FIG. 1C is a schematic perspective view of a baffle plate of the collection device of FIG. It is a schematic sectional drawing of the coating booth provided with the collection apparatus in embodiment of FIG. It is a figure explaining the inclination-angle of the baffle plate of the flow path in embodiment of FIG. It is a schematic sectional drawing explaining the conventional collection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flow path 3 Baffle board 9 Water-based paint mist 11 Water curtain 12 Aqueous fluid 20 Collection apparatus 21 Coating room 23 Booth tank 25 Filter 27 Coating object 30 Coating booth

Claims (5)

A method for collecting a water-based paint comprising:
A method comprising flowing an aqueous fluid along a member to form a liquid film covering the surface of the member, and flowing a gas containing a mist-like aqueous paint through a gap in the liquid film. A collection device for collecting water-based paint,
A flow path in which a gas containing a mist-like water-based paint rises and flows;
Baffle plates arranged in the flow path;
The baffle plate is disposed in an inclined manner, and the aqueous fluid flows through the flow path while forming a liquid film covering the inclined lower surface of the baffle plate, whereby the water-based paint contained in the mist form in the gas is contained in the aqueous fluid. Collecting device to collect.   The collection device according to claim 2, wherein the plurality of baffle plates are arranged in a staggered manner in the flow path.   The collection apparatus of Claim 2 or 3 whose contact angle of the aqueous fluid with respect to the lower surface of a baffle plate is less than 60 degrees.   The lower surface of a baffle plate is a collection apparatus in any one of Claims 2-4 which inclines at an angle of 120-165 degrees with respect to a horizontal surface.

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