JP2022130780A - Water-based paint film formation method and water-based paint film formation device - Google Patents

Abstract

To provide a technique of eliminating necessity of a flash-off process for evaporating moisture in a paint film by a predetermined amount from a surface after painting when wet-on-wet painting is performed with a water-based paint.SOLUTION: A technique eliminates necessity of a flash-off process by performing spray painting and drying in the same work zone alternately in multiple times until a predetermined paint film thickness is achieved with a water-based paint, while irradiating a painted surface with an infrared ray to evaporate moisture in a painting film by a predetermined amount for drying.SELECTED DRAWING: Figure 1

Description

The present invention relates to the formation and pre-drying of a coating film using a water-based paint, in particular a method of forming a coating film and pre-drying an object to be coated at the same time, thereby making it possible to control the solid content of the applied paint. Regarding the device.

Conventionally, intermediate coating with a water-based paint required pre-drying called flash-off, even if the subsequent top coating was performed wet-on-wet. In addition, pre-drying called flash-off is required whether the metallic base coating is performed using water-based paint or the subsequent clear coating is performed wet-on-wet. When switching the process from solvent paint to water-based paint, or when installing equipment for applying water-based paint, it was necessary to add this flash-off process after the water-based paint coating process.

JP-A-2003-251250 Japanese Patent Application Laid-Open No. 2007-319762 JP-A-2005-305231 JP 2008-178773 A

Fiscal 2003 Minister of Economy, Trade and Industry Prize New Machinery Promotion Award Winner Achievement Summary Mazda Motor Corporation Development of Environmentally Friendly Three-Wet-On Painting Technology

Since the solvent of the solvent-based paint evaporates quickly, so-called wet-on-wet painting can be achieved relatively easily. However, as shown in the upper diagram of FIG. 6, water as a solvent for water-based paint evaporates extremely slowly. A process for evaporating a predetermined amount of moisture from the surface was required. For this reason, a dedicated process for pre-drying using infrared rays or hot air is called a flash-off process, which requires a process time of about 3 minutes. Since the flash-off process controls the temperature and humidity while supplying and exhausting air, the energy consumed for air conditioning is enormous. Furthermore, when the existing process is switched from solvent paint to water-based paint, a new flash-off process must be added to the existing line, but in many cases there is no space for this. Adding a process was a big space problem.

As in Patent Document 1, "When applying a thermosetting water-based paint, the sprayed particles of the paint come in contact with the pattern around the coating pattern from behind the paint ejection port in almost the same direction as they move to the surface to be coated. A method of forming a coating film characterized by controlling the solid content of the applied paint by a method of injecting air whose temperature and/or humidity are controlled as described above, in which a large amount of warm air is ejected from the rear of the paint spray gun. A technique has been proposed in which coating and drying are performed at the same time. As a result, even if the flash-off process can be made unnecessary, the hot air disturbs the flying flow of the sprayed paint particles, resulting in a large decrease in the transfer efficiency, not only wasting the paint, Due to the fact that the moisture content of the paint particles in flight before being applied is lowered by the hot air, the viscosity of the paint particles increases, and the proper viscosity cannot be secured when the paint particles adhere to the surface to be coated. I didn't. As a result, the smoothness of the coating surface is greatly hindered, and there is a problem in obtaining normal coating quality.

For that purpose, as in Patent Document 2, a flash-off is installed in the same painting booth as the painting process, and "a process of applying a water-based paint to a work and irradiating infrared rays while rotating the work coated with the water-based paint A method for forming a coating film of a water-based paint, characterized by comprising a step of increasing the solid content ratio of the applied paint. Although this eliminates the need for a dedicated flash-off process, it replaces the flash process with the process of rotating the workpiece while irradiating it with infrared rays to increase the solid content of the applied paint. It was decided to add a new one, and the space problem was not solved.

In addition, as in Patent Document 3, "a preheating step of preheating the object to be coated to a temperature range higher than normal temperature that can accelerate the drying of the paint, and maintaining the object to be coated after the preheating process in the temperature range In the paint application step of sequentially applying one or more paints to the object to be coated in a state where it is being coated, and the preheating step, the object to be coated is irradiated with far infrared rays to heat the object. method” is proposed. Such heating of the object to be coated before painting is effective for relatively simple workpieces, but it may be difficult to apply heat to objects with partially different thicknesses or objects with complex irregularities such as holes. In the method, the amount of heat transferred from the residual heat to the surface of the object to be coated is not uniform, and there have been cases where partial drying is insufficient or excessive.

The present invention eliminates the flash-off process while ensuring stable coating quality without enlarging the coating booth regardless of the shape of the object to be coated. An object of the present invention is to provide a technique that eliminates the need for a flash-off process for evaporating a predetermined amount of water in a coating film from the surface after coating in wet-on-wet coating with water-based paint.

A water-based paint is applied to the object to be coated in multiple times, and between the first spray coating and the subsequent spray coating, infrared drying is performed in multiple times. Repeat until a film thickness of in that way,
By alternately repeating the formation of the coating film and the drying of the coating film, a predetermined amount of water in the coating film can be evaporated from the surface when the coating film formation is completed. As shown in FIG. 4, on the surface of the object 50 to be coated, film formation begins at A and proceeds in the order of B, C, D, E, and F. As shown in FIG. In A, C, and D, the paint particles 51 applied by spray coating contain a large amount of water and are hemispherical. evaporates and shrinks in the thickness direction. Needless to say, the speed of water evaporation can be sufficiently controlled by appropriately selecting the type and intensity of infrared rays.

As an indicator of the intensity of infrared rays, the infrared rays striking the surface of the object to be coated are measured in kilowatts per unit area. In FIG. 5, the irradiation range is defined as the entire range 21a, the partial range 21b, and the range 22 where the coating was sprayed. Since the object to be coated rotates continuously, it goes without saying that each range rotates continuously. When the entire object to be coated is irradiated with infrared rays, the water inside the sprayed paint particles is overheated before coating, causing an increase in the viscosity of the paint, and a smooth painted surface cannot be obtained. In addition, since the infrared irradiation time is limited, even if the intensity of the infrared rays is too low, the moisture is not sufficiently evaporated. Also, even if the intensity of the infrared ray was too strong, a pinhole defect occurred due to the gasification of moisture due to a partial temperature rise in the applied paint. Condition 5, in which the intensity of infrared rays was 10 Kw per square meter, and repeated partial coating and partial drying, gave the best coating finish.

According to the present invention, it is possible to complete the formation of the water-based paint film on the surface of the object to be coated in the coating zone, and at the same time, evaporate a predetermined amount of water in the coating film from the surface. As described above, the flash-off process can be made unnecessary in wet-on-wet painting with water-based paint.

FIG. 2 is a plan view showing the first embodiment; It is a top view which shows a 2nd Example. It is the front view and top view which show the principal part of the infrared irradiation apparatus of an Example. It is sectional drawing explaining the coating-film formation process. It is explanatory drawing of a coating part and a drying part. It is an explanatory view showing the difference in the process between the conventional technology and the technology of the present invention. It is a figure which shows the installation method of the infrared lamp in a 3rd Example.

In this embodiment, the coating of an aluminum wheel will be described as an example. In FIG. 1, an aluminum wheel material as an object to be coated is washed, electrodeposition coated, and then powder-coated as a primer, and then set in a top coating jig. The tact time is about 30 seconds. When the object to be coated 3 is conveyed in front of the coating robot 4 by the conveyor 2 for conveying the object to be coated 3 into the coating booth 1, it is engaged with the object rotating device 6 and rotates at a speed of 30 to 60 revolutions per minute. Now, start spinning. The coating robot 4 aims at a portion of the object 3 to be coated, and sprays a water-based metallic base paint (trade name AQUACRON manufactured by PPG) from the spray gun 7 onto the 22 parts in FIG. The object 3 to be coated continues to rotate. At the same time, the portion of the object 3 being coated by the coating robot 4 that is to be rotated 180 degrees is coated with the paint at a heat quantity of about 10 kilowatts per square meter by the near-infrared heater 5 side of FIG. The surface is heated. The infrared lamp 11 is a T3-type near-infrared quartz tube, and a pseudo-parabolic reflecting plate 12 irradiates near-infrared rays toward the object to be coated in a substantially parallel manner. Infrared wavelengths are near-infrared in the range of 1 to 2 microns, which are mainly absorbed by moisture and do not promote overheating of materials. An air discharge nozzle 13 is attached to the upper portion of the infrared lamp 11 to cool the lamp and prevent contamination of the lamp surface. This air becomes hot air, which slightly accelerates the drying of the coating film, but an excessive amount of air disturbs the spray coating pattern, which is not preferable. With these configurations, by performing painting and drying at the same time for about 30 seconds, painting and drying are alternately repeated 15 to 30 times, and the paint film is continuously formed, and the paint immediately after application is NV50%. What used to be before and after is secured at NV75% or more to complete the coating film formation, and after that, as a wet-on-wet process, sufficient pre-drying is performed to overlay another layer of clear coating (PPG's product name SPECTRACRON). Got. The coating conditions were set so that the dry film thickness of the aqueous metallic base was 15 microns. Moreover, the energy actually consumed by the near-infrared heater was 1 Kw at most, which was 1/50 of the energy consumed for the air conditioning in the flash-off process.

As a second embodiment, an example of application to a method widely known as spindle coating will be described. In FIG. 2, objects 3a to be coated with a conductive primer in the same manner as in Example 1 are set in the vicinity of the tips of rotating jigs 3b having six arms. The tact time is about 30 seconds. When the rotary jig 3b3 is conveyed in front of the coating robot 4 by the conveyor 2 that conveys the rotary jig 3b into the coating booth 1, it is engaged with the object rotating device 6 to rotate at a speed of 30 to 60 revolutions per minute. Now, start spinning. The painting robot 4 sprays a water-based primer paint (manufactured by PPG under the trade name of Optiprime 3) from the spray gun 7, aiming at the object 3a to be painted near the painting robot side, while the rotating jig 3b continues to rotate. At the same time, the object to be coated 3a farthest from the coating robot 4 is heated by the near-infrared heater 5 with a heat quantity of about 10 kilowatts per square meter. The infrared lamp 11 is a T3-type near-infrared quartz tube, and a pseudo-parabolic reflecting plate 12 irradiates near-infrared rays toward the object to be coated in a substantially parallel manner. Infrared wavelengths are near-infrared in the range of 1 to 2 microns, which are mainly absorbed by moisture and do not promote overheating of materials. An air discharge nozzle 13 is attached to the upper portion of the infrared lamp 11 to cool the lamp and prevent contamination of the lamp surface. This air turns into hot air, which slightly enhances the impression of the coating film, but an excessive air volume disturbs the spray coating pattern, which is not preferable. With these configurations, by performing painting and drying at the same time for about 30 seconds, painting and drying are alternately repeated 15 to 30 times, and the paint film is continuously formed, and the paint immediately after application is NV50%. What was before and after is secured to NV 75% or more to complete the coating film formation, and after that, as a wet-on-wet process, sufficient pre-drying is performed to overlay another top coat (PPG's product name SPECTRACRON). Got. The coating conditions were set so that the dry film thickness of the water-based primer was 20 microns. Moreover, the energy actually consumed by the near-infrared heater was 1 Kw at most, which was 1/50 of the energy consumed for the air conditioning in the flash-off process.

In the third embodiment, clear coating of aluminum wheels will be described as an example. For clear coating, it was necessary to use water-based clear and solvent clear depending on the combination of materials with the base paint. Therefore, explosion-proof equipment specifications are required in the coating booth. As in the first embodiment, the aluminum wheel material as the object to be coated was washed and electrodeposition coated, and then the primer coating of the powder coating was baked, followed by coating with a water-based metallic base, and then clear coating. gone. The tact time is approximately 90 seconds. As in the first embodiment, when the object to be coated 3 is conveyed to the front of the coating robot 4 by the conveyor 2 that conveys the object to be coated 3 into the clear coating booth 1, the object to be coated rotating device 6 is engaged. , start rotating at a speed of 30 to 60 revolutions per minute. The coating robot 4 aims at a part of the object 3 to be coated and sprays a water-based clear coating (product name: EC520 clearcoat manufactured by PPG) from the spray gun 7 onto 22 parts in FIG. The object 3 to be coated continues to rotate. At the same time, the part of the object 3 being coated by the coating robot 4 that is to be rotated 180 degrees is the part heated by the near-infrared heater 5 in FIG. The coating surface is heated with a heat quantity of . The infrared lamp 11 is a T3-type near-infrared quartz tube, and a pseudo-parabolic reflecting plate 12 irradiates near-infrared rays toward the object to be coated in a substantially parallel manner. This infrared heater is covered with a chamber 8 having an opening outside the coating booth, and a transparent heat-resistant glass (quartz glass) is mounted on the surface facing the object to be coated. Infrared wavelengths are near-infrared in the range of 1 to 2 microns, which are mainly absorbed by moisture and do not promote overheating of materials. With these configurations, by performing painting and drying at the same time for about 90 seconds, painting and drying are alternately repeated 45 to 90 times, and the paint film is continuously formed, and the paint immediately after application is NV50%. When the coating film formation was completed, NV75% or more was secured, and the coating film thickness was also secured at 50 microns or more. In addition, although the infrared lamp 11 is non-explosion proof, it is located outside the painting booth, so it is possible to safely alternately paint with solvent-based paint and water-based paint.

This invention can be used in industrial painting such as aluminum wheel painting, exterior mirror cover painting for automobiles, and exterior painting of small home appliances. There is a growing need to reduce energy consumption by eliminating the flash-off process while reducing

1 Coating booth 2 Conveyor 3 Object to be coated 3a Object to be coated 3b Rotating jig 4 Coating robot 5 Near-infrared heater 6 Object rotating device 7 Spray gun 8 Chamber 11 Infrared lamp 12 Reflector 13 Air discharge nozzle 21a Irradiation range ( whole)
21b Irradiation range (partial)
22 spray coating area 50 surface to be coated 51 applied paint particles 52 dried paint particles

Claims (3)

In the method of applying a water-based paint to a surface to be coated with a paint gun, spray coating and drying are performed in the same work zone several times until a predetermined coating film thickness is reached, while infrared rays are applied to the surface to be coated. 1. A method of applying a water-based paint, characterized by evaporating a predetermined amount of water in the paint film by irradiating. In a method of applying a water-based paint to a surface of an object to be coated with a paint gun, the surface to be coated is intermittently rotated and moved between the paint spray range and outside the paint spray range while the water-based paint is being applied. A method of coating a water-based paint, characterized in that the solid content of the applied paint is controlled by repeating a plurality of times of forming a thickness and irradiating with infrared rays outside the spray range of the paint. An infrared heating device for heating an object to be coated placed on a rotatable coating jig in a coating zone provided on a conveying route of the object to be conveyed; and an object to be coated. A coating machine equipped with a coating gun that sprays water-based paint is placed opposite to the surface, and is arranged so that while rotating the work to be coated, water-based paint can be sprayed and the surface to be coated can be pre-dried at the same time. A coating device that is installed.

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