WO2015152848A2

WO2015152848A2 - Coating method with elektrostatic powder paint

Info

Publication number: WO2015152848A2
Application number: PCT/TR2015/000133
Authority: WO
Inventors: Ömer Hakan OKUTAN; Ahmet Ozcan
Original assignee: Pulver Kimya Sanve Ticas
Current assignee: Pulver Kimya Sanve Ticas
Priority date: 2014-03-31
Filing date: 2015-03-31
Publication date: 2015-10-08
Anticipated expiration: 2016-09-30
Also published as: WO2015152848A3; EP3126063A2

Abstract

The present invention relates to a powder paint coating method developed for being able to coat the applied surfaces with powder paint of equal thickness and to achieve smooth surface after coating.

Description

DESCRIPTION

COATING METHOD WITH ELEKTROSTATIC POWDER PAINT

Technical Field The present invention relates to a powder paint coating method developed for being able to coat the applied surfaces with powder paint of equal thickness and to achieve smooth surface after coating .

Prior Art

Paint is a coating material that adheres to the applied surface thus protecting the same from mechanical and chemical impacts, and granting an aesthetic appearance to the surface it is applied.

Painting operation is not an operation that is completed only upon application of the paint to the material surface, but is a combination of long processes that consist of steps with different procedures. The application area formed by all such steps represents the painting systems.

Various paint application methods are employed in the prior art for coating the surfaces, which are;

• Brush Painting Method: The oldest and the easiest painting method. It is performed manually and is completely dependent on the skill of the operator.

• Immersion Method: The piece to be painted is immersed into a tank wherein the paint is continuously circulated; after being removed from the tank, the piece is allowed to rest awhile in order to ensure that the paint accumulated on the product leaks back into the tank.

• Curtain Method: This method is generally employed for painting smooth surfaces. The paint flowing like a curtain paints the piece passing thereunder.

• Spray Method: In general, powder paints are used for painting applications performed using the spray method. Powder paints are the paints not containing any liquid, which is applied to metal or other conductive surfaces and are solvent-free. The paint is applied to the metal furniture, window frames, radiators, pipes, automotive parts, computers, wooden and glass surfaces by means of a sprayer .

Spraying method is the most frequently used method for painting conductive surfaces, and one of the other most preferred methods for coating with powder paint is the coating with electrostatic method .

In the electrostatic method, generally the powder paints are readily applied to the metallic and similar surfaces with electrical conductivity. Coating powder paint on materials with electrical conductivity occurs by means of electrostatic forces.

The powder paint is transferred to the sprayer by means of an air stream and sprayed onto the surface to be painted in the form of a dust cloud. Said powder paint is electrified when passing through the sprayer and adheres onto the pre-grounded material. In order to achieve a good adherence of powder paint to the material to be coated, the material surface must be grounded in the best manner possible. The material on which the powder paint is sprayed is then subjected to firing operation in a furnace. The heat ensures that the powder paint adheres on the product through melting and chemical hardening through polymerization on the product.

The solvent-free structure, surface quality, robustness, paint recovery system, cost-effectiveness, low labor costs and environmental sensitivity render electrostatic powder paints more advantageous compared to the wet paints.

Extremely advantageous in terms of its use and other properties, electrostatic powder paints can be used directly only on the products with electrical conductivity. If intended for use on other dielectric materials, electrical conductivity must be provided to such materials. In order to give electrical conductivity to mostly non-conductive surfaces (dielectric) such as composite materials such as wood, chipboards or plastics and then coat the same with powder paint, several methods such as pre-heating or coating with an electrolyte primary fluid (undercoat) or dampening the surfaces are applied to the surface in the prior art .

In the patent application No. TR 2012/07395, electric conductivity is provided to the products intended to be coated with powder paint by means of an undercoat mixture. The undercoat paint mixture of the invention consists of conductive metal powder, undercoat, epoxy resin and accelerator agents. The electrical conductivity feature of the undercoat comes from, the conductive metal powder contained in the mixture. Said undercoat paint mixture is in liquid form and applied to the product by means of paint gun or manually. The material achieving electrical conductivity by applying undercoat is then grounded and in this manner the static electric charged powder paint adheres to the material. The material is then put into a furnace for enabling the paint to be tightly adhered onto the material.

In aforementioned invention, coating the material to be paint- coated with an electrostatic undercoat prior to painting operation provides an electrical conductivity to the surface. The need for a lot of materials so as to prepare the undercoat of the invention leads to extra costs in coating operation. Another problem encountered at the surfaces on which electrical field is formed using primary fluid (undercoat) is that, when the undercoat is not applied evenly on the surface to be coated, the powder paint accumulates on the surface unevenly as the coated powder paint cannot ensure a smooth and proportional coating and that the powder paint is weakly adhered on the substrate. Weak adherence leads to shedding, stripping and dislocation of the applied powder coat from the surface in time.

The patent application No. EP1330393B1 also available in the prior art mentions subjecting the non-conductive materials to a pre-heating process in advance in order to coat the same with powder paint. In said invention, the surface to be coated is subjected to vapor and heat at a temperature from 70°C to 140 °C for a period from 5 seconds to 10 minutes and then coated with electrostatic paint. The pre-heating operation undertaken enables dampening of the surface. The moisture content of the non-conductive material comes out from the surface as water vapor. The water vapor generated around the surface forms an electrical field, thus ensuring adherence of the powder paint to be applied to the surface. Although the process of dampening the surface through heating is a successful method for creating an electrical field, it is necessary to dampen the entire surface evenly. However, even dampening cannot be achieved on the surface due to various reasons such as failure in heating the entire surface of the non-conductive material evenly each time through the pre-heating method, or the fact that some part of the surface got wet previously due to a certain reason. Moreover, as is the case for the method of the invention, the damp sprayed from the surface during heating process after forming an electrical field on a surface completely dampened and coating this surface with powder paint, might lead to blisters on the paint surface or rough surface .

Another problem encountered in the prior art is occurrence of distortions on the surface due to thermal stress variations at the time of subjecting the paint-coated surface to heat. In order to avoid distortions arising from stress variations, the humidity rate must be reduced to 5% or below. In this case, on the other hand, water or primary electrolyte fluids must be sprayed onto the surface once more. The basic problem experienced during such operation is that the amount of the fluid to evaporate and mix with the air after being absorbed by the non- conductive surface remains unknown. Therefore, it is extremely challenging to balance the amount of water to be applied to the surface externally and the amount of evaporating water vapor. One of the most frequently encountered problems is the failure to coat the edges of the coated surfaces due to this problem.

The Problems that the Invention Aims to Solve The object of the invention is to improve the quality of the process of coating the wooden surfaces with powder paint. Another object of the invention is to avoid low-quality painting operations that might arise due to uneven moisture distribution on the wooden surfaces to be coated with powder paint.

Another object of the invention is to ensure that the entire wooden surface to be coated with powder paint is dampened evenly.

Another object of the invention is to avoid blistering and visual defects that might arise due to evaporation of excessive moisture on the surface during thermal processes applied after painting operation .

Another object of the invention is to prevent release of hazardous gases that might be released during heating process applied for ensuring adhesion of the paint to the surface.

Another object of the invention is to prevent distortions that might arise during thermal processes applied after coating process to the paint-coated wooden surfaces due to uneven moisture distribution.

Another object of the invention is to eliminate the need for the undercoating operation applied before the painting process.

Description of the Figures

Figure 1. Forced Cooling Process of the Material Figure 2. Process for Forming Dew on the Material Surface

Figure 3. Process for Spraying the Powder Paint on the Material

Figure 4. Process for Heating the Material on which Powder Paint is sprayed

Description of References in the Figures

The parts illustrated in the figures are enumerated individually and the part names corresponding to such numbers are as follows:

1. Material 2. Dew Layer

3. Water vapor

4. Electrostatic powder paint

5. Heater

Description of the Invention

The invention relates to an electrostatic powder paint (4) coating method developed for coating the wooden materials (1) with electrostatic powder paint (4) as properly as possible.

The method of the invention is based on forming a properly distributed electrical field on the surface in order to ensure adherence of the electrostatic powder paint (4) to the application surface in the best manner possible. In order to form a smooth electrical field on the wooden material (1) to be coated with electrostatic powder paint (4), it is ensured that every point of the material (1) surface is dampened with equal amount of water mass and a homogenous water vapor (3) mass is formed around the material (1).

In order to ensure an even distribution of water mass at each point on the surface to be coated with electrostatic powder paint (4), the material (1) to be coated is first cooled. The cooling process applied to the material (1) might vary depending on preferences. The cooling method can be forced cooling; but cooling via allowing the material (1) to be painted to remain in a controlled climate conditions is also possible. Values such as surface temperature of the part, ambient temperature, ambient relative humidity rate, etc. are used in order to identify the most ideal cooling temperature for forced cooling operation. The process of identifying the cooling temperature is performed via a microcontroller employing electronic stoichiometric spreadsheet technique.

The material (1) , the temperature of which is reduced through cooling, is then allowed to rest in a moisture-saturated environment under atmospheric conditions with a temperature higher than the material temperature. The material (1) with a temperature lower than the ambient temperature absorbs heat from the air around the material and the excessive water vapor {3} that the air cannot carry anymore due to loss of heat condenses on the material (1), thus forming a dew layer (2) . As a result of dew layer (2) formation, the water molecules homogeneously positioned on the material (1) surface and the water vapor (3) surrounding the dew layer (2) enables formation of an electrical field evenly distributed on the entire surface. Even if the dew layer (2) deteriorates due to any reason such as any intervention or air current, the layer replenishes itself in short time due to ambient conditions and homogenous distribution of the water molecules is reestablished. The thickness of the dew layer (2) achieved at the end of the process is between 0.5 pm and 1 pm, which is the ideal thickness range for such method. The sufficiency of the dew layer (2) is measured with caliper having Eiddy current sensor.

The water vapor (3) mass formed around the dew layer (2) as a result of dew formation ensures generation of a smooth electrical field as the water molecules therein conducts electricity. Electrostatic powder paint (4) is applied onto the surface to be painted by using the smooth electrical field obtained. The electrostatic powder paint (4) is adhered to the surface by virtue of the electrical field formed around the material (1) surface and the surface is homogeneously coated with electrostatic powder paint (4) layer. The ideal electrostatic powder paint (4) layer thickness identified for a high-quality painting operation is between 50 μπι and 250 urn. By heating the air spraying the electrostatic powder paint (4) to the optimum temperature, evaporation of the dew layer is also ensured during electrostatic powder paint (4) spraying process. By virtue of the dew layer which is evaporated through the air set to the optimum temperature, not only the smooth electrical field becomes continuous, but also entrapment and adherence of water molecules between electrostatic powder paint (4) particles is avoided. The impact level of the moisture on the electrostatic powder paint (4) particles is minimized by virtue of evaporation of the dew layer (2) .

Following the processes of spraying the electrostatic powder paint (4) with hot air and evaporating the dew layer (2), the electrostatic powder paint (4) coated surfaces are heated through any of the heating methods of the prior art, preferably through infrared and ultraviolet rays, in order to ensure melting, and adherence to the material (1) surface, of electrostatic powder paint (4) particles. Through this process, the electrostatic powder paint (4) is adhered to the surface through melting, thus achieving a robust adherence.

As the material (1) to be painted is not subjected to pre-heating operation in the method of the invention, the temperature of the material (1) does not exceed 50°C at the end of the process of heating the coated surfaces. As the temperature of the painted material (1) does not reach high values, the possibility of any deformation to occur on the coating surfaces is minimized. Furthermore, the thermal distortion risk of the material (1) is also reduced as the duration of the thermal process applied to the wooden material (1) in order to ensure adherence of sprayed electrostatic powder paint (4) to the surface is low.

The electrostatic powder paint (4) coated material (1) subjected to thermal process is then allowed to rest in an optimized environment with controlled climate conditions in order to complete the coating process and the temperature thereof is reduced. When considered necessary, the electrostatic powder paint (4) coated material (1) subjected to thermal process can also be cooled rapidly by employing the method used for cooling the material (1) before painting.

As the material (1) is cooled before being subjected to heat in the method of the invention, the internal part of the material (1) remains cool even during the process of heating the surface, thus the amount of moisture released towards surface from the internal part of the material (1) is reduced. This reduces the amount of blistering on the electrostatic powder paint (4) layer applied to the surface. The method of the invention enables even electrostatic powder paint (4) layer thickness adhered to the material (1) surface at all points by virtue of the smooth electrical field formed with dew formation. By virtue of the homogeneously formed electrical field, the formation of different layer thicknesses at various points of electrostatic powder paint (4) layer is avoided. Moreover, by virtue of the electrical field formed by the dew layer (2), the electrostatic powder paint (4) layer coating the material {1} surface is strongly adhered to the material (1) surface as a result of the thermal process applied for short periods. Reduced thermal process time not only prevents thermal distortions likely to occur on the material (1) surface, but also reduces thermal power consumption.

Claims

1. An electrostatic powder paint (4) coating method developed for being able to coat the applied surfaces with electrostatic powder paint (4) layer of equal thickness and to achieve smooth surface after coating characterized in comprising the process steps of reducing the temperature of the material (1) to be coated with electrostatic powder paint (4), - forming a dew layer (2) and water vapor (3) mass on the surface of the material (1) to be coated by condensing the water vapor in the air on the material (1) by allowing the cooled material (1) to rest under atmospheric conditions and in an environment with a temperature lower than the material temperature, applying electrostatic powder paint (4) on the material (1) by utilizing the smooth electrical field generated by virtue of the dew layer (2) and water vapor (3) mass formed on the material (1) surface, - adhering the electrostatic powder paint (4), which is applied on the material (1) and. attached onto the material (1) surface by virtue of the electrical field, to the material (1) through melting with thermal process,

- cooling the material (1) , on which the electrostatic powder paint (4) is adhered through heating, by means of forced cooling.

2. The cooling process applied to the material (1) before the formation of dew layer (2) as mentioned in Claim 1, characterized in that the material (1) is force-cooled at the optimum cooling temperature determined as a result of the calculation made by using values such as surface temperature of the material (1) to be coated with electrostatic powder paint (4), ambient temperature, ambient relative humidity rate, etc. in a microcontroller employing electronic stoichiometric spreadsheet method.

3. The heating process of the material (1) coated with electrostatic powder paint (4) with the impact of the electrical field as mentioned in Claim 1, characterized in being applied using infrared and ultraviolet rays.