JP2003211083A - Deposition method for double-layered coating film by powder coating material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for depositing a double-layered coating film while saving time and energy required for heating by using powder coatings and performing baking once or performing stacked coating of the powder coating material to an object to be coated which is heated to a temperature equal to or higher than the baking temperature of the powder coating material. <P>SOLUTION: In the deposition method for the double-layered coating film having at least two coating film layers selected from the group consisting of a primer coating film layer, an intermediate coating film layer, a finish coating film layer, a colored coating film layer and a clear coating film layer respectively formed by using the powder coating materials, the respective powder coating materials forming the respective coating film layers are successively stacked and attached to the object to be coated and the respective stacked and attached powder coating materials are simultaneously baked, or the respective powder coating materials forming the respective coating film layers are successively stacked and coated on the object to be coated held at the temperature equal to or higher than the baking temperature of the powder coating material whose baking temperature is highest among the respective powder coating materials. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multi-layer coating film by powder coating, and more particularly, by using powder coating, 1 bake such as 2 coat 1 bake, 3 coat 1 bake or the like, or The present invention relates to a method for forming a multi-layer coating film by forming a multi-layer coating film by laminating coating of a powder coating material on an object heated to a temperature equal to or higher than the baking temperature of the powder coating material.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of environmental problems and the like, a coating system that does not use an organic solvent, for example, a coating system that uses a powder coating, has been widely adopted in order to prevent the diffusion of the organic solvent into the atmosphere. It has become like. In addition, the powder paints are used in the fields of conventional thick coating such as anticorrosion coating, pipe coating, and structure coating, as well as automobile outer panels, automobile parts, fuel tanks for motorcycles, parts such as frames, light electrical appliances, and decorations. It has come to be used as a powder coating for thin film beauty in a wide range of fields such as products, and further, baking conditions are required to be low temperature and short time.

Conventionally, when a multilayer coating film is formed by using a powder coating material, a lower coating film layer is baked to form a film as in the case of 2 coat 2 bake or 3 coat 3 bake, and then an upper layer is formed. The coating method of coating and baking the coating layer has been practiced. For example, depending on the required properties of each coating layer, a primer powder coating is applied to an object to be coated for a primer layer and baked to form a primer layer, and an intermediate coating powder for an intermediate coating layer. The paint is applied and baked to form the intermediate coating film layer, and similarly, the top coat powder coating, the colored powder coating or the clear powder coating is respectively applied and baked to form each coating layer. It was That is, in order to form a multi-layer coating film having two or more layers, it was necessary to bake as many times as the number of coating film layers.

Conventionally, when a multi-layer coating film is formed by using a solvent type paint, for example, a metallic coating film and a clear coating film are wet-on-wet as in the case of forming a coating film for outer panels of automobiles. 2 coats that are coated with and coated by heating at once
The bake system is adopted. For example, a method of simultaneously forming two layers by adding a fluidity control agent to a solvent-based paint or a clear paint and changing the solvent composition to prevent mixing of the lower metallic base layer and the clear layer has been put into practical use. There is.

Energy saving in the field of powder coating,
Such a system has come to be required due to the reasons such as the process saving. In carrying out the 2-coat 1-bake coating method of powder coating, it is necessary to use a primer powder coating and a top coating powder coating, an intermediate coating powder coating and a colored powder coating, and a colored powder coating and a clear powder coating. It is necessary to apply powder coatings with different functions as separate layers to form a film by heating at the same time. Also, in carrying out the 3-coat 1-bake coating method, each powder coating should be applied as separate layers. It is necessary to form a film by heating at once.

Conventionally, a method of applying one kind of powder coating material in two steps and forming a film by one bake, or applying the same powder coating material twice with two kinds of coating machines and one baking step There was a method of forming a film. These coating methods are effective for sufficiently charging the powder coating material with a small discharge amount and coating it densely to form a smooth coating film, and for improving the coating efficiency of the powder coating material. It was a painting method.

[0007] Also, a mixture of two kinds of powder coating materials is mixed in one to adhere to an object to be coated, and one coating bake 2
A coating method for forming a two-layer coating film separated into layers and a coating method for forming a two-layer coating film by laminating and adhering a water-based coating material and a powder coating material have also been proposed.

The above-mentioned coating method for forming a two-layer coating film separated into two layers is carried out by applying a powder coating mixture (corresponding to two types of powder coating) in which two kinds of resins or polymer alloys are mixed, Although this is an epoch-making method in which a coating film separated into two layers is formed by one baking, in reality, two mixed layers or
A partially incompletely separated coating film is formed, the appearance of the coating film is poor, and a coating film with insufficient gloss or smoothness is formed, which is a step for practical use.

In addition, in the coating method for forming a two-layer coating film using the above water-based paint and powder coating, the water-based paint is applied and preheated and dried in advance to obtain a fixed amount of solvent and water in the water-based paint. It is necessary to deposit the powder coating material after the following (usually 5% or less) state and bake to form a film. If this preheat drying is insufficient, pinholes may be generated in the coating film due to volatile components from the lower coating film during baking, or the gloss of the coating film may be reduced.

[0010]

[Problems to be Solved by the Invention] As described above,
In the prior art, there has been no coating method in which two or more coating layers having different functions such as a primer, an intermediate coating, a top coating, a coloring, and a clear are respectively formed by using a powder coating in one baking.

The present invention uses a powder coating to form two coats.
Multi-layer coating saves time and energy required for heating by one baking such as baking, three coats and one bake, or by laminating coating of powder coating on an object to be coated heated to a temperature higher than the baking temperature of the powder coating. An object is to provide a method for forming a multilayer coating film for forming a film.

[0012]

That is, a method for forming a multilayer coating film using the powder coating material of the present invention is a primer coating layer, an intermediate coating layer and a top coating layer formed by using the powder coating material, respectively. In a method for forming a multilayer coating film having at least two coating layers selected from the group consisting of a coating layer, a colored coating layer and a clear coating layer, each powder coating material forming each coating layer is used. It is characterized in that the powder coating materials are successively laminated and adhered to an object to be coated, and the respective powder coating materials thus laminated and adhered are simultaneously baked.

In the method for forming a multi-layer coating film by the powder coating material of the present invention as described above, each powder coating material forming each coating layer is (1) The temperature below the melt-softening temperature of the powder coating material with the lowest melt-softening temperature, usually at room temperature, can be applied in a layered manner, or (2) the melt-softening temperature of the powder coating material Whether or not the powder softening temperature of the low powder coating material is higher than the melting softening temperature of the powder coating material of each of the powder coating materials, and is successively laminated and adhered to the object to be held at a temperature lower than the melting softening temperature of the powder coating material. Or (3) a powder coating having the highest baking temperature among the powder coatings above the melting and softening temperature of the powder coating having the highest melting softening temperature among the respective powder coatings. Sequentially stacking and adhering to the object to be coated, which is kept at a temperature lower than the baking temperature, and then applying each powder coating It is possible to simultaneously burn.

Further, the method for forming a multilayer coating film by the powder coating material of the present invention includes a primer coating layer, an intermediate coating layer, an overcoat coating layer and a colored coating layer which are respectively formed by using the powder coating. In the method for forming a multilayer coating film having at least two coating layers selected from the group consisting of layers and clear coating layers,
Each powder coating forming each coating layer is sequentially laminated and coated on an object to be coated which is maintained at a temperature equal to or higher than the baking temperature of the powder coating having the highest baking temperature among the powder coatings. It is characterized by doing.

Further, the method for forming a multi-layer coating film by the powder coating material of the present invention includes a primer coating layer, an intermediate coating layer, a top coating layer and a colored coating layer which are respectively formed by using the powder coating. In the method for forming a multilayer coating film having at least two coating layers selected from the group consisting of layers and clear coating layers,
Each powder coating material forming each coating layer is sequentially laminated and adhered to an object to be coated, and then the coating object is heated to the baking temperature of the powder coating material having the highest baking temperature among the respective powder coating materials. It is characterized in that the remaining powder coating material is laminated and coated by heating to the above temperature.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below in various embodiments. <Each powder coating that forms each coating layer with different functions,
Among the powder coating materials, the powder coating material having the lowest melting and softening temperature is successively laminated and adhered to the object having a temperature lower than the melting and softening temperature of the powder coating material, and the powder coating materials thus laminated and laminated are simultaneously baked to form a multilayer. Method of forming coating film (hereinafter referred to as embodiment A)>

In the method for forming a multilayer coating film of the embodiment A, each powder coating material forming each coating layer having a different function is a powder having the lowest melting and softening temperature among the powder coating materials. Laminate and adhere to the object to be coated at a temperature lower than the melting and softening temperature of the body paint, usually the object to be coated at room temperature, in the same manner as the normal coating method of powder paint (at this stage, all powder paint The powder coating remains as a powder), and then each of the powder coatings adhered in layers is baked at a temperature higher than the baking temperature of the powder coating having the highest baking temperature among the powder coatings to form a multilayer. Form a coating film.

The method for forming a multilayer coating film of Embodiment A has the following constraint conditions, but is most preferable in terms of energy and process, and ideally meets environmental and social requirements. It is a possible method for forming a multilayer coating film. In the method for forming a multilayer coating film of Embodiment A, when the resin particles of the powder coating material as the lower layer and the resin particles of the powder coating material as the upper layer are preferably the same resin system and a curing agent is used. A combination in which the curing agents are the same is preferable. Therefore, for example,
It is preferable to combine two layers or multiple layers only with an epoxy resin system, two layers or multiple layers only with a polyester resin system, or two layers or multiple layers only with an acrylic resin system.

However, the lower layer is an epoxy resin type and the upper layer is an epoxy / polyester resin type, the lower layer is an epoxy / polyester resin type and the upper layer is a polyester resin type, the lower layer is an epoxy / acrylic resin type and the upper layer is an acrylic layer. A multi-layer coating film can be formed by baking once, such as a combination of resin systems, a combination of lower layers of acrylic resin systems and upper layers of acrylic modified fluororesin systems, and combinations of mutually soluble resin particles.

In the method for forming a multilayer coating film of the embodiment A, in the case of heating from the coating film side of the lower layer to melt and form a film as a baking method such as high frequency induction heating of metal, a hot air drying furnace is used. Compared to the case of heating and melting from the coating layer side of the upper layer to form a film, the allowable range of the combination of the types of resin particles of each powder coating forming each coating layer having a different function becomes wider. .

For example, in the case of producing a precoated steel sheet using an apparatus having a high energy of high frequency induction heating, the temperature of an object to be coated rapidly rises to a high temperature by a thin plate, the melting time of the powder coating material is short, and soon. In the case of forming a coating film, the melting and softening by heating starts from the lower layer side, and before the heat transferred from the object to be coated reaches the upper layer, most of the lower layer coating film melts and softens and the resin particles Are connected to each other,
Since the coating film has been formed until it does not move freely,
A wide variety of combinations of resin types and compositions of the lower layer and the upper layer can be used.For example, even if the resin particles of the powder coatings forming the coating layers having different functions are completely different resin systems, or the upper layer side is It is possible to form a high quality coating film even with a combination of a resin having a lower melting point and faster curing than the lower layer side.

<Each powder coating for forming each coating layer,
Within the melting and softening temperature of the powder coating material with the lowest melting and softening temperature among the powder coating materials and below the melting and softening temperature of the powder coating material with the highest melting and softening temperature among the powder coating materials. A method of sequentially laminating and adhering to an object to be coated which is kept at a temperature and simultaneously baking each of the laminating and adhering powder coating materials to form a multilayer coating film (hereinafter, referred to as embodiment B)>

In the method for forming a multilayer coating film according to the embodiment B, each powder coating material forming each coating layer having a different function is a powder having the lowest melting and softening temperature among the powder coating materials. When the temperature is higher than the melting softening temperature of the body paint and the temperature is lower than the melting softening temperature of the powder paint having the highest melting softening temperature among the respective powder paints, In the same manner as the coating method, the layers are successively laminated and adhered, and at least a layer of the powder coating material having the lowest melting and softening temperature in the coated powder coating material, preferably at least the resin particles of the lowermost layer are fused at least partially ( At this stage, at least one layer other than the powder coating material having the highest melt softening temperature, preferably at least the lowermost layer powder coating material is at least partially fused,
The rest of the layers remain powdery), and the powder coatings with the highest baking temperature among the respective powder coatings that have been laminated and deposited in a state where the resin particles are difficult to move. Baking at a temperature equal to or higher than the baking temperature of 1 to form a multilayer coating film.

In the method for forming a multilayer coating film of Embodiment B, when the powder coating material having the lowest melt softening temperature among the powder coating materials is used for the lowermost layer, the powder coating material for the lowermost layer is used. Since the powder coating of the upper layer is applied in a state where the resin particles of are fused and fixed at least partially, the coating efficiency of the powder coating of the upper layer is improved, and The coating film can be easily formed even if the resin particles of the powder coating material of the lower layer and the resin particles of the powder coating material of the upper layer are different types of resin-based powder coating material.

When baking of the lower coating film starts and shrinks after the baking of the upper coating film is finished and fluidity is lost, unevenness occurs on the surface of the coating film. When the gloss of the coating film is reduced and this phenomenon is severe, there is a problem that a coating film in a matte state or a coating film with fine irregularities on the surface tends to be formed. When using the powder coating with the lowest melting and softening temperature among the powder coatings for the lowermost layer, the lower layer powder coating starts to burn and the upper layer powder coating burns after a short delay. Such a problem does not occur because the film formation is started and started.

The baking method in the method for forming a multilayer coating film of Embodiment B is substantially the same as the baking method described in the method for forming a multilayer coating film of Embodiment A, and is substantially the same. The action and effect are achieved.

<Each powder coating forming each coating layer,
A temperature above the melting and softening temperature of the powder coating material with the highest melting and softening temperature among the powder coating materials and below the baking temperature of the powder coating material with the highest baking temperature among the powder coating materials. A method of sequentially laminating and adhering to the held object to be coated, and simultaneously baking each of the laminating and adhering powder coating materials to form a multilayer coating film (hereinafter, referred to as embodiment C)>

In the method for forming a multilayer coating film of embodiment C, each powder coating material forming each coating layer having a different function is powder having the highest melting and softening temperature among the powder coating materials. Above the melting and softening temperature of the body paint, the baking temperature of the powder paint having the highest baking temperature among the respective powder paints (the baking of each powder paint is higher than the melting and softening temperature of each powder paint). It is carried out at a high temperature) and the resin particles of the respective powder coatings are applied at least partially on the object to be coated, which is kept at a temperature lower than the above, in the same manner as the normal coating method for powder coatings. (At this stage, all the powder coating materials are at least partially fused, and the temperature of the object to be coated is that of the powder coating material with the lowest baking temperature among the powder coating materials. (If the temperature is higher than the baking temperature, some layers may have been baked at this stage.) In a state in which each resin particle does not easily peel off or move, each powder coating adhered to the laminate is heated to a temperature not lower than the baking temperature of the powder coating having the highest baking temperature among the powder coatings. Bake at temperature to form a multilayer coating.

In the method for forming a multilayer coating film of embodiment C, the powder coating material for the upper layer is applied in a state where the resin particles of the powder coating material for the lowermost layer are at least partially fused and fixed. Therefore, the coating efficiency of the powder coating of the upper layer is improved, and the resin particles of the powder coating of the lower layer and the resin particles of the powder coating of the upper layer are different resin types. A coating film can be easily formed even with the above powder coating material. By repeating this operation, the powder paints of the third and fourth layers can be applied. Each of the powder coatings laminated and adhered is then baked at a temperature equal to or higher than the baking temperature of the powder coating having the highest baking temperature among the powder coatings to form a coating film.

In the method for forming a multilayer coating film of the embodiment C, it is easy to use different kinds of powder coatings in which the resin particles of the powder coating forming each layer are resin systems of different types from each other. A coating film can be formed, but in order to form a uniform and smooth coating film, it is desirable to adjust the start timing of baking of the coating film of at least each layer. That is, in baking, it is preferable that the powder coating of the lower layer starts baking and the powder coating of the upper layer starts baking a little later to form a film.

When baking of the lower coating film starts and shrinks in a state where the baking of the upper coating film is finished and fluidity is lost, unevenness occurs on the coating surface, and when this phenomenon is remarkable, it is formed. When the gloss of the coating film is reduced and this phenomenon is severe, there is a problem that a coating film in a matte state or a coating film with fine irregularities on the surface tends to be formed. Since the powder coating material starts baking and the upper layer powder coating material starts baking to form a film after a short delay, such a problem does not occur.

In the method for forming a multilayer coating film of the embodiment C, for example, an epoxy resin-based anticorrosive powder coating material is applied to an object kept at 120 ° C., and then an epoxy / polyester resin-based top coating powder coating material is applied. Paint and bake at 180 ° C,
It is possible to form a uniform coating film.

In the case of the combination of the powder coating materials as described above, the properties of the resin particles, especially the compatibility, are good by the common resin called the epoxy resin, and even if the coating film is formed by two coats and one bake, the unevenness is obtained. There are few, and it is easy to form a uniform coating film. However, because of good compatibility, mixing is likely to occur between the two layers when forming a coating film by two coats and one bake.

Therefore, when an aluminum pigment is blended with the lower layer epoxy resin powder coating material to form a coating film with the upper layer being a clear powder coating material, a single layer film consisting only of the lower layer will give a metallic coating film. Although it can be formed, when a coating film is formed by two coats and one bake, the aluminum pigment also moves to the upper clear coating film layer, the orientation of the aluminum pigment is disturbed, and the metallic feeling is remarkably reduced. Tend.

Further, an acrylic resin using a blocked isocyanate resin having a reaction temperature of 170 ° C. as a cross-linking agent in the combination of the above-mentioned epoxy resin type anticorrosion powder coating material and epoxy / polyester resin type top coating powder coating material It is also possible to apply a powder type powder coating and bake three layers simultaneously at 180 ° C to form a film. As described above, it is possible to simultaneously cross-link and form a multilayer coating film even if the baking temperature is slightly different.

A method for forming a multilayer coating film according to the above embodiment A,
In both the method for forming the multilayer coating film of Embodiment B and the method for forming the multilayer coating film of Embodiment C, the resin particles of the oversprayed powder coating are almost unaffected by the temperature of the object to be coated. Since it passes through and falls in a short time without receiving it, operations such as cooling are not particularly required.

<At least two layers selected from the group consisting of a primer coating layer, an intermediate coating layer, a top coating layer, a colored coating layer and a clear coating layer, each of which is formed by using a powder coating material. In the method for forming a multi-layer coating film having a film layer, each powder paint forming each coating film layer is heated to a temperature higher than the baking temperature of the powder paint having the highest baking temperature among the powder paints. A method of forming a multi-layer coating film by sequentially laminating coating on the object to be coated (hereinafter, referred to as embodiment D)>

In the method for forming a multilayer coating film of Embodiment D, the powder coatings forming the coating layers having different functions are powders having the highest baking temperature among the powder coatings. The powder coating material is kept laminated at a temperature higher than the baking temperature of the coating material in the same manner as a normal coating method for powder coating materials (overcoating), and each coating layer is baked by the heat of the coating material. To form a multilayer coating film. In this case, the coated powder coating material is immediately melted to form a uniform coating film.

When the resin particles of the powder coating material applied first are melted and the powder coating material of the upper layer is applied in a state after the stage where the fusion is started, the resin particles of the powder coating material of the lower layer are already present. Since the surface area is reduced by fusion to start the formation of the coating film interface, the influence of surface tension and shrinkage stress on the powder coating applied on it is very small, and it is extremely uniform and is divided into two layers. A coating film can be formed. By repeating this operation, a three-layer or four-layer coating film can be easily formed.

In particular, by keeping the time interval between the coating of the lower layer and the coating of the upper layer of the powder coating relatively long, the coating film formed is finished in the same manner as the two-coat, two-bake coating film. Also, by keeping the heating temperature of the object to be coated high, the baking reaction starts simultaneously with the melting of the resin particles of the powder coating, and the coating loses its fluidity, so a clearer interface with the layer above it is created. A coating layer having the same is formed.

In the method for forming a multilayer coating film of Embodiment D, for example, an epoxy resin-based anticorrosive powder coating material is applied to an object to be coated kept at 200 ° C., and the resin particles of the powder coating material are melted and softened. At the same time, apply the polyester resin-based intermediate coating powder coating, and further apply the acrylic resin-based top coating powder coating, and
After holding for 0 minutes, it can be cooled to form a uniform and smooth three-layer coating film.

In this way, the coating film obtained by sequentially coating the pre-heated object with each powder coating material coating time interval kept as long as several tens of seconds to several minutes, and each coating film separately. When compared with a coating film which was sequentially applied by coating on a low-temperature coated object, heating, melting, and baking, no difference was observed in the formation of the coating film or the coating film quality.

However, since the resin particles of the oversprayed powder coating material pass through the heated atmosphere in the high temperature environment of the object to be coated and fall, the resin particles tend to be fused to some extent. It was unfavorable for powder coatings and clear powder coatings with low melt softening temperature. However, after collecting each powder coating material at each booth, immediately mixing and cooling with a large amount of low-temperature air and collecting it, it prevents fusion and deterioration of fluidity due to progress of crosslinking reaction inside the resin particles. It was ready and could be collected and reused.

In the method for forming a multilayer coating film of the embodiment D, even if different kinds of powder coatings in which the resin particles of the powder coating forming each layer are different resin systems from each other are used. The coating film can be easily formed without being significantly affected by the properties of. However, in the case of an object to be coated having a small heat capacity, the temperature of the object to be coated may drop during coating, and the formation of a coating film may be insufficient. Therefore,
The method for forming the multilayer coating film of Embodiment D is generally a method for forming a coating film suitable for an object to be coated having a large heat capacity such as cast parts and iron structures.

In particular, in recent years, the control technology for high frequency induction heating has been remarkably improved, so that even for an object to be coated whose temperature changes greatly, for example, a thin steel plate, while measuring the temperature of the thin plate with a radiation type temperature measuring device, the high frequency induction heating is performed. By controlling the output energy of heating, it becomes possible to control the temperature of the object to be coated while coating, and it has been put to practical use.

<At least two layers selected from the group consisting of a primer coating layer, an intermediate coating layer, a top coating layer, a colored coating layer and a clear coating layer, each of which is formed by using a powder coating material. In the method for forming a multilayer coating film having a film layer, each powder coating material forming each coating film layer is sequentially laminated and adhered to an object to be coated, and then the coating object is applied to each of the powder coating materials. A method of forming a multilayer coating film by heating the powder coating material having the highest baking temperature to a temperature equal to or higher than the baking temperature and coating the remaining powder coating material in layers (hereinafter, referred to as embodiment E)>

In the method for forming a multilayer coating film of embodiment E, at least one of the powder coating materials forming the coating film layers having different functions is used to form the multilayer coating film of embodiment A above. Method, method of forming multilayer coating film of Embodiment B or Embodiment C
In accordance with the method for forming a multi-layer coating film, the coating materials are successively laminated and adhered to an object to be coated, and then the object to be coated is heated to a temperature higher than the baking temperature of the powder coating material having the highest baking temperature among the powder coating materials. After heating to a temperature, the remaining powder coating is laminated and coated according to the method for forming a multilayer coating film of Embodiment D above to form a multilayer coating film.

In the method for forming a multilayer coating film of the embodiment E, for example, the temperature of the coating object which is increasing in temperature is 120 ° C.
When it reaches the vicinity, the epoxy resin-based anticorrosive powder paint is applied to the object to be coated, and when the temperature of the object reaches to around 180 ° C, the epoxy / polyester resin top coat powder paint is applied to the object. Can be applied to form a uniform coating film.

A method for forming a multilayer coating film of Embodiment A, a method for forming a multilayer coating film of Embodiment B, a method for forming a multilayer coating film of Embodiment C, and a multilayer coating film of Embodiment D of the present invention. In any of the forming methods, the lower the melting and softening temperature of the resin that constitutes the resin particles of the powder coating material, the greater the decrease in viscosity at the baking addition temperature, the more the particles of the resin particles that constitute The smaller the diameter, the smoother and more uniformly the finished coating film is formed even at low temperatures. Further, the smaller the particle diameter of the resin particles constituting the powder coating material, the smoother and more uniformly the coating film formed by coating and heating is, even if the coating film thickness is thin.

The melting and softening temperature of the resin particles of the powder coating material used in the present invention is limited by the storage temperature of the powder coating material and the transportation environment temperature, and the range may be satisfied, but is not particularly limited. Melt softening temperature of resin particles of powder coating is 40
If it is ℃ or more, it can be used as a powder coating even at an ambient temperature of about 40 ℃ in summer. However, in consideration of the production and pulverization efficiency of the powder coating material, the melting and softening temperature of the resin particles of the powder coating material is preferably 45 ° C. or higher. In the case of thin film beauty powder coating, the melting and softening temperature of the resin particles is 40 ° C to 60 ° C.
By setting the temperature to a low temperature of ° C, a smooth coating film can be formed with a coating film thickness of 2 to 5 times the average particle diameter of the resin particles. Although the upper limit of the melting and softening temperature of resin particles is not limited at all, the recent demand for low-temperature baking powder coatings, the energy required to form a coating film during baking, and the reduction of the amount of carbon dioxide released to the environment Considering the above, it is desirable that the temperature is 250 ° C. or lower, preferably 200 ° C. or lower.

Regarding the average particle diameter of the resin particles of the powder coating material used in the method for forming a multilayer coating film of the present invention, in order to reduce the amount of the powder coating material required for coating, the thin film beauty powder is used. Since it can be used as a paint, the average particle size of the resin particles of the powder paint is preferably 40 μm or less by the volume method. Further, in order to form a smooth coating film with a coating film thickness similar to that of the solvent-based paint, it is more preferable that the average particle diameter is 25 μm or less.

Furthermore, in the forming method of the present invention for forming a multi-layer coating film, the upper layer coating film resulting from the accumulation of charges of the charged particles deposited as the lower layer coating film on the object to be coated is electrostatically charged. In order to reduce the electrostatic repulsion during coating, it is preferable to reduce the coating film thickness of each layer and finish it smooth. Further, since the multiple layers are baked at one time, it is preferable that the stacked multiple layer coating film is thin as a measure for preventing pinholes in the coating film and preventing sagging of the coating film. For this purpose, it is better that the average particle size of the resin particles of the powder coating is smaller,
For the coating workability, particularly for supplying the powder coating material to the coating machine and atomizing and coating from the coating machine, the average particle diameter of the resin particles is preferably 5 μm to 25 μm.

Even in the case of coating with powder paint for products such as automobile skins, automobile parts, fuel tanks for motorcycles, parts such as frames, light electric appliances, ornaments, etc., which have been conventionally coated with solvent-based paint, solvent is used. It is now required to have the same finished appearance as the coating film of the mold paint, or an even smoother finished appearance. In the method for forming a multilayer coating film of the present invention, the average particle diameter of the resin particles of the powder coating material is set to about 10 μm to 25 μm, and the coating film thickness is set to 30 μm to 6 μm.
By setting the thickness to about 0 μm, it is possible to form a smooth and uniform coating film like the coating film of a solvent type paint.

Raw material composition for powder coating used as primer powder coating, intermediate coating powder coating, top coating powder coating, colored powder coating, clear powder coating in the method for forming a multilayer coating film of the present invention Is composed of a resin, a curing agent, a pigment and additives which are added as necessary, which are generally used in the production of powder coatings.

Examples of the resin include alkyd resin, acrylic resin, polyester resin, epoxy resin, melamine resin, blocked isocyanate resin, fluorine resin, silicone resin, amide resin, ABS resin, novolac resin, ketone resin, butyral resin, and phenoxy resin. , A polyolefin resin or the like can be used alone or in combination of two or more kinds at any mixing ratio.

In order to form a uniform and smooth coating film by using a powder coating material in which different resin particles are mixed, in order to melt and soften each resin particle, change the viscosity, surface tension at the time of melt softening, coating by cross-linking reaction. It is necessary that the properties such as film strain and shrinkage stress are the same or very close.

If desired, polybasic acids, acid anhydrides, amino compounds, glycidyl group-containing compounds, aminoblast resins, which are crosslinking agents used in ordinary powder coatings,
Dicyandiamide, blocked isocyanate resin, acid hydrazide, etc. can be used.

Acrylic resin which is a resin raw material of resin particles,
The main examples of polyester resin, epoxy resin, blocked isocyanate resin, etc. are illustrated below. Methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, sec-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate are used as the acrylic monomers constituting the acrylic resin. , Lauryl acrylate, tridecyl acrylate, stearyl acrylate, cyclohexyl acrylate, benzyl acrylate, tetrahydrofurfuryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl Acrylate, 2-phenoxyethyl acrylate, ethyl carbitol acrylate, allyl Acrylate, glycidyl acrylate, dimethylaminoethyl acrylate, acrylic acid, sodium acrylate, trimethylolpropane acrylate,
Mention may be made of acrylic acid such as 1,4-butanediol diacrylate, 1,6-hexanediol acrylate, neopentyl glycol diacrylate, pentaerythritol triacrylate, acrylic acid ester and acrylate monomers.

Further, as acrylic monomers constituting the acrylic resin, methyl methacrylate, ethyl methacrylate, butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, cyclohexyl are used. Methacrylate, propyl methacrylate, benzyl methacrylate, i-propyl methacrylate,
sec-Butyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, allyl methacrylate, ethylene glycol methacrylate, triethylene glycol methacrylate, tetraethylene glycol methacrylate , 1,3-butylene glycol methacrylate, trimethylolpropane methacrylate, 2-ethoxyethyl methacrylate, 2-methoxyethyl methacrylate, dimethylaminoethyl methyl chloride salt methacrylate, methacrylic acid, methacrylic acid such as sodium methacrylic acid, methacrylic acid ester and methacrylic acid Acid salt It can be mentioned mer.

Further, in addition to the above-mentioned acrylic monomer component, as a copolymerization component, vinyl monomers such as acrylamide, acrylonitrile, vinyl acetate, ethylene, propylene, isobutylene, butadiene, isoprene and chloroprene, glycidyl (meth) acrylate, methyl. Epoxy group-containing ethylenically unsaturated monomers such as glycidyl (meth) acrylate, allyl glycidyl ether, 3,4-epoxycyclohexylmethyl (meth) acrylate, (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, etc. The carboxyl group-containing ethylenically unsaturated monomer, the hydroxyl group-containing ethylenically unsaturated monomer such as hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate can be used.

As a method for preparing a resin by polymerizing the above-mentioned acrylic monomer component, a high molecular weight resin is synthesized by an ordinary solution polymerization method, and then the solvent is removed and recovered by a thin film heating decompression method or the like to obtain a solid resin. There is a method or a method of synthesizing a resin by a suspension polymerization method and then removing water by a spray drying method or the like to obtain a solid resin.

As the curing agent for the acrylic resin, when the reactive polar group in the acrylic resin is a glycidyl group, a polyfunctional carboxyl group-containing compound such as sebacic acid or dodecanedicarboxylic acid, or a polyfunctional acid anhydride is used. Can be used. When the reactive polar group of the acrylic resin is a hydroxyl group or both a hydroxyl group and a carboxyl group, a blocked isocyanate resin, a melamine resin or the like can be used.

As the blocked isocyanate resin, an isocyanate resin such as hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated xylene diisocyanate, toluene diisocyanate and the like, which is resinified by the addition reaction of trimethylolpropane, or a polyfunctionalized isocyanate resin, A blocked isocyanate resin obtained by blocking a hydrogenated and polyfunctionalized isocyanate resin with caprolactone or an oxime can be mentioned. With regard to these blocked isocyanate resins, a resin that becomes solid even when the blocked isocyanate resin is a simple substance is preferable, and a blocked isocyanate resin obtained by blocking a resin from isophorone diisocyanate with ε-caprolactam is preferable. However, even a liquid curing agent can be used depending on the addition amount, the addition amount of the pigment, or the combination with an acrylic resin or a polyester resin having a high glass transition temperature.

Examples of the carboxylic acid component that can be used for producing the polyester resin include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, Sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,2-octadecanedicarboxylic acid, isacosanedicarboxylic acid, maleic acid, fumaric acid, cyclohexanedicarboxylic acid, Hexahydrophthalic acid, tetrahydrophthalic acid, trimellitic acid, pyromellitic acid and other polyvalent carboxylic acids, lower alkyl esters and anhydrides of these polyvalent carboxylic acids, or malic acid,
Examples thereof include hydroxycarboxylic acids such as tartaric acid, 1,2-hydroxystearic acid, and paraoxybenzoic acid.

Examples of the alcohol component that can be used for producing the polyester resin include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,3-butanediol. 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, spiroglycol, 1,10-decanediol, 1,4-cyclohexanedimethanol, 2,2,4-trimethylpentane-
Examples thereof include 1,3-diol, trimethylolethane, trimethylolpropane, glycerin and pentaerythritol.

The polyester resin can be produced by a conventional method for producing a polyester resin for powder coating, using the above-mentioned acid component and alcohol component as raw materials. For example, after using the above-mentioned raw materials in an appropriate combination and mixing ratio and carrying out an esterification or transesterification reaction at a temperature of 200 to 280 ° C. according to a conventional method, the pressure is reduced to 500 Pa or less and
A polycondensation reaction may be performed at 30 to 290 ° C. in the presence of a catalyst to give a resin having a high degree of polymerization, and then a depolymerization reaction may be performed with an alcohol component to give a polyester resin.

For crosslinking baking of these polyester resins,
It is preferable to use the above-mentioned blocked isocyanate resin, and in that case, the ratio of the hydroxyl group of the polyester resin to the latent isocyanate group which contributes to the reaction of the blocked isocyanate resin is 0.6 to 1.2 in NCO / OH ratio.
Is more preferable, and it is further preferable that it is 0.8-1.0.

As for the resin particles, resin particles for clear paint containing no pigment content are changed to resin particles for color paint containing a color pigment or resin particles for matte paint containing a matte pigment, or magnetic particles are used. A pigment can be optionally added such as resin particles for a magnetic coating material containing a pigment or resin particles for a conductive coating material containing a conductive pigment.

It is effective to add a coloring pigment, an anticorrosive pigment, and other additives for imparting other functions as coating film components to these resins and curing agents. As these coloring pigments, inorganic pigments such as yellow iron oxide, titanium yellow, red iron oxide, titanium oxide, zinc white, lithopone, lead white, zinc sulfide, antimony oxide, and Hansa Yellow 5G, permanent yellow FGL, phthalocyanine blue, Dunslen Blue RS, Permanent Red F5RK, Brilliant Fast Scarlet G, Paliogen Red 39
Examples thereof include organic pigments such as 10.

The amount of these color pigments added to the resin particles is usually about 0.5% to 60% by PWC, but it may not be added at all, as in clear paint. Where P
WC is Pigment Weight Concentration and is calculated by the following formula. PWC = [(containing pigment mass%) / (total coating solids mass%)] × 100

In addition, barium sulfate, barium carbonate, calcium carbonate, clay, silica powder, fine silicic acid, as extender pigments for the purpose of adjusting the gloss value of the coating film and adjusting the hardness of the coating film. It is also possible to add diatomaceous earth, talc, basic magnesium carbonate, alumina white and the like.

Further, a surface conditioner for adjusting the surface tension of the powder coating material, an ultraviolet absorber for adjusting the transmission and absorption of ultraviolet rays, an antioxidant for the resin, a baking promoting catalyst for adjusting the baking reaction, etc. Can be contained in the resin particles, or the charge control agent can be added by post-processing after the resin particles are formed.

As a method of adjusting the gloss of the coating film, it is possible to add a matting pigment to the resin particles. It is also possible to mix two or more kinds of resin particles and adjust the gloss by the compatibility between the resin particles and the difference in reaction rate. Also, acrylic resin,
Fine particles of fluororesin and the like can be added for the purpose of adjusting the gloss and imparting the function of lowering the frictional resistance in the same manner as the matting pigment.

When the lower layer coating film and the upper layer coating film are baked at the same time, a cellulose resin is added to the lower layer powder coating material or the upper layer powder coating material so that mixing does not occur between the two layers. It is also preferable to add a silicon-based surface modifier or a surfactant to prevent mixing of the resin layer.

The technique of adding the cellulose resin is not limited to the powder coating, but the two coats of solvent type coating.
This is a technique often used in the bake painting method. In addition, as a similar technique, in the case of solvent-based paint, resin gel particles may be added as a fluidity control agent, which is a technique that can also be applied to the technique of powder paint. It is not a technology that can be used as effectively as solvent-based paints, as it affects the flowability of the paint.

The method for producing the powder coating material is not different from the ordinary method for producing the powder coating material, and may be a dry melt-kneading method or a solvent type coating material may be desolvated to form resin particles. good. It is also possible to prepare a powder coating by forming resin particles as an emulsion resin by emulsion polymerization of acrylic monomers like a clear powder coating and drying the emulsion resin particles by a spray drying method or the like to form resin particles. .

The production and coating of this powder coating material will be described based on the following steps. (1) A step of blending and mixing constituent raw materials of resin particles,
(2) A step of melting and kneading the blended and mixed raw materials of the resin particles at a temperature equal to or higher than the melting and softening temperature thereof to homogenize the dispersion.
(3) A step of crushing the melt-kneaded and homogenized product into resin pellets, storing, transporting, and storing, (4) a step of crushing the crushed resin pellets into resin particles, (5) a predetermined process A step of classifying to a particle size distribution, (6) a step of adjusting the characteristics of the resin particle surface to form a powder coating, and (7) a step of sending the powder coating to a coating machine for coating.

Among these steps, the powder coating material is manufactured in the steps (1) to (6) and applied in the step (7). Also,
The overspray powder generated by painting can be used at the same time for the next painting.

In the step (1) of mixing and blending the constituent raw materials of the resin particles, the solid resin raw material is mainly used as the coloring pigment, the curing agent, the additives, and if necessary, a part of the liquid raw material is made as uniform as possible. Mix. As a device for this purpose, a flash mixer, a screw mixer, a conical blender, a V mixer, a tumbling mixer, a jet mixer, a kneader, a ribbon mixer or the like which is a usual device for mixing powder raw materials can be used. It is preferable to mix and blend with these devices to make the mixture as uniform as possible.

Next, the step (2) of melting and kneading the mixed and blended raw material of the resin particles at a temperature equal to or higher than the melting and softening temperature thereof is carried out. In this step, a solid resin raw material which is a raw material of resin particles, a coloring pigment, a curing agent, an additive, etc. are added in a few μm
The purpose is to mix uniformly in the following degree. The resin raw material and the curing agent are processed into pellets of about several mm for the purpose of facilitating the handling at the time of transportation and compounding and for preventing the rise of dust. Raw materials obtained by crushing the pellets into a mixture of several hundreds of μm are heated to a temperature above the melting and softening temperature and mechanically kneaded. As a device for this,
A roll mill, screw kneader, muller, kneader, etc. can be used. Particularly preferred devices include workability,
A roll mill and a screw kneader are suitable because they are easy to handle. This is because after the melt-kneading, the kneaded product can be quickly discharged from the device and cooled.

This is because, particularly in the case of a cross-linking type powder coating, a curing agent is contained in the resin particles, and when uniformly mixed in this step, a residence time at the time of kneading by heating above the melt softening temperature is kneaded. When the length becomes long, a part of the resin reacts, and when the coating film is formed, it is not smooth, and defects such as insufficient gloss are likely to occur. Therefore, a device that supplies from one direction and continuously discharges from the other direction is suitable.

Next, the step (3) of entering the step of roughly crushing the melt-kneaded and homogenized product into resin pellets is started. The product produced in the melt-kneading step is a lump as it is, and thus, in order to facilitate the subsequent crushing step and classification step, it is roughly crushed into resin pellets in this step. Examples of equipment for this purpose include ring roll mills, edge runners, roll crushers, disintegrators, hammer crushers, impeller breakers, gyre trek crushers, jaw crushers and the like.

Usually, the roughly crushed resin pellets are supplied to a crusher, and the crushing step (4) and the classification step (5) are started.
An apparatus for crushing the roughly crushed resin pellets into resin particles includes a hammer crusher, a turbo crusher, an air jet mill and the like. As a classifier for classifying a powder coating material composed only of resin particles in a predetermined particle size distribution range, there are a sieving device with a net and a classifier with an air flow.

Thereafter, a treatment step (6) for adjusting the surface characteristics of the resin particles may be carried out by adding a surface adjusting agent or the like.
In this surface treatment, it is also possible to use fine polyolefin powder as a fluidity modifier, waxes, alumina sol, silica sol, or the like. It is also possible to treat the surface of the resin particles with an amine salt as a charge-improving agent, aminosilane-treated silica sol, or the like.

The powder coating material thus produced can be coated by a conventional coating method using an electrostatic coating apparatus, a fluidized-bed coating apparatus, a triboelectrification coating apparatus, etc. which are ordinary coating apparatuses. In the method for forming a multilayer coating film of the present invention,
It is preferable to apply multiple layers using an electrostatic coating machine or a triboelectric coating machine. It is also preferable to apply the coating by changing the charging voltage of the electrostatic coating machine between the coating layers in order to reduce repulsive peeling of the resin particles due to static electricity.

[0086]

EXAMPLES The present invention will be specifically described below based on examples. All "parts" in the examples are "parts by mass". <Example 1> Melt softening temperature 110 ° C, 32 parts of polyester resin having acid value = 45, 32 parts of bisphenol A type epoxy resin having epoxy equivalent = 560, titanium pigment 20
Parts, 5 parts of phthalocyanine blue, 6 parts of a surface conditioning agent, 3 parts of an ultraviolet absorber, 1 part of an antioxidant and 1 part of a baking accelerator were mixed with a screw mixer, and further mixed uniformly with a flash mixer.

As a melt kneader, a twin-screw kneader was heated to 125 ° C., a two-roll cooler was provided at the exit end of the melt kneader so that it could be rolled and cooled, and a hammer crusher was installed ahead of it. Then, kneading and crushing were performed to prepare resin pellets. 100 parts of this pellet was mixed with 0.3 part of fine silica, pulverized with a pulverizer, and further resin particles having an average particle diameter of 20 μm were produced with a classifier to obtain an epoxy / polyester resin-based top coat powder coating material.

On the other hand, 60 parts of a bisphenol A type epoxy resin having an epoxy equivalent of 970, 5 parts of an imidazole type curing agent, 10 parts of a titanium pigment, 2 parts of carbon black,
Using 15 parts of pulverized silica pigment, 3 parts of surface conditioner and 5 parts of defoaming agent, the same treatment as in the preparation of the epoxy / polyester resin-based topcoat powder coating material was carried out, and the average particle diameter was 25 μm.
The resin particles of No. 1 were prepared to obtain an epoxy resin-based undercoat powder coating material.

A thin mild steel sheet surface-treated with zinc phosphate was prepared, and an epoxy resin-based undercoating powder coating material was applied by a corona charging type electrostatic coating machine to a film thickness of 50 μm. An epoxy / polyester resin-based top coat powder coating material was applied with a coating machine to a film thickness of 50 μm.

The article to be coated was baked for 15 minutes in a baking oven preheated to 200 ° C. The surface of the object to be coated has the same finish appearance as the coating color of the object to be coated on which the epoxy / polyester resin-based top coat powder coating is applied in advance to a film thickness of 50 μm, and the gloss value is also 85 (60 degree gloss value).

Further, the two-coat / one-bake coating object and the coating object coated with only the top coating film were cut with a knife to reach the base material, and a corrosion resistance test was carried out for 500 hours using a salt spray tester. . As a result, a blister with a width of 5 mm on one side was generated from the cut on the coated object coated with only one coat of the top coat, but a slight blister of 1 mm or less was generated on the coated object coated with two coats and one bake. No abnormality was found in the coating film.

<Example 2> 60 parts of methylmethacrylate,
Butyl acrylate 6 parts, glycidyl methacrylate 33
Parts and 1 part of azoisobutyronitrile are uniformly dissolved,
100 parts of xylol was dropped from the dropping tank in 1 hour to the reaction tank which was heated to 120 ° C. and stirred, and then kept for 2 hours. After that, azoisobutyronitrile 0.3
A portion thereof was added and the mixture was kept at 150 ° C. for about 4 hours to cause a polymerization reaction to obtain a resin solution. A thin film and a solvent were removed from this resin solution with a vacuum dryer to obtain a solid acrylic resin. This acrylic resin had a melt softening temperature of about 65 ° C., an epoxy equivalent of 430, and a molecular weight of about 7,000.

66 parts of this acrylic resin, 16 parts of dodecanedicarboxylic acid, 1 part of surface conditioner, 3 parts of flowability imparting agent, 3 parts of phthalocyanine blue, 6 parts of surface conditioner, 3 parts of ultraviolet absorber, 1 of antioxidant Parts and a baking accelerator of 1 part were mixed with a screw mixer, and then melt-kneaded in the same manner as in Example 1, followed by rolling, cooling and crushing to prepare acrylic resin powder paint pellets. To 100 parts of this resin pellet, 0.5 part of fine alumina pigment was added, and the mixture was supplied to an air jet mill which is a crushing classifier, and was classified by a rotary classifier at the same time as crushing to obtain an acrylic resin powder paint having an average particle diameter of 15 μm. Resin particles were obtained.

Resin particles 97 of this acrylic resin powder coating material
Parts and 3 parts of a normal pearl pigment were uniformly mixed to prepare an acrylic resin-based blue metallic powder coating material. The iron cast coated object whose surface was shot blasted was preheated to 190 ° C. in a preheating furnace.

As in the case of Example 1, an epoxy resin-based undercoating powder coating material was applied to this coating object by a corona charging type electrostatic coating machine so as to have a film thickness of 40 μm. The powder coating composition was heat-melted almost simultaneously with the coating to form a uniform coating film. Immediately after applying the epoxy resin-based undercoating powder coating material, the epoxy / polyester resin-based overcoating powder coating material of Example 1 was applied by an electrostatic coating machine of the same system so as to have a film thickness of 40 μm. Further, an acrylic resin-based blue metallic powder coating material was applied by a triboelectrification coating machine to a film thickness of 40 μm, and after cooling for 10 minutes, cold water was sprayed and cooled to room temperature.

When this coating object is coated one layer by a conventional method and heated to form a film, a good coating film appearance cannot be obtained due to foaming from the hole of the casting which is the base material. When painted by the method of, there is an extremely good metallic feeling,
The coated object has no defects such as foaming.

<Example 3> In the method for producing the acrylic resin powder coating material described in Example 2, phthalocyanine blue 3 was used.
An acrylic resin powder coating material (clear powder coating material) was produced in the same manner as in Example 2 except that no parts were used.

95 parts of resin particles of this acrylic resin clear powder coating material and 5 parts of resin-coated aluminum pigment for powder coating material (nonvolatile content 100%, average particle diameter 13 μm) were uniformly mixed to obtain acrylic resin metallic powder. Body paint was made. Non-chromate treated aluminum wheels (15 x
6JJ) was placed on the high-frequency induction heating coil of the high-frequency induction heating machine, and heated to 150 ° C. for 4 minutes with an output of 10 KW.

After that, the output of the high frequency induction heating is maintained at 2 KW, and at the same time as this holding, the above acrylic resin-based metallic powder coating material is applied by a corona charging type electrostatic coating device to a film thickness of 40 μm. did. The powder coating composition was heat-melted almost simultaneously with the coating to form a uniform coating film. However, since this coating film was not completely cured yet, it adhered when it came into contact with it, and since the fluidity remained, after a while, the irregularities of the contact part were uniformly smoothed.

One minute after the completion of this coating, the above acrylic resin clear powder coating material was coated with an electrostatic coating machine of the same system to a film thickness of 50 μm, and after holding for 10 minutes, high frequency induction heating was stopped. I let it cool. In this case, the individual resin particles of the powder coating material are immediately melted at the same time as the coating to form a coating film, and the film is formed by stacking, and the metallic feeling of the coating film is high, and the coating film is smooth. It's finished.

With respect to the obtained coating film, the glossiness of the coating film, metallic feeling and blistering from the substrate were measured. A metallic feeling measuring device ALCOPE LMR-200 manufactured by Kansai Paint Co., Ltd. was used for measuring the metallic feeling. The measurement results are shown in Table 1.

<Comparative Example 1> The same powder coating material and object to be coated as those used in Example 3 were used for coating by a usual coating method. That is, as the first layer, an acrylic resin-based metallic powder coating material was applied by a corona charging type electrostatic coating machine so as to have a film thickness of 40 μm, and put in a baking oven at 150 ° C. for baking. Since the heating efficiency was poor, it took 25 minutes to reach 150 ° C., which is necessary for curing the coating film, and it was further held in a baking oven for 10 minutes and then left to cool. Thus, it took a long time to print.

The metallic feel of this coating film was slightly inferior to that of the coating film before coating with the acrylic resin clear powder coating material of Example 3, but the whiteness of the coating film and the arrangement of the aluminum pigments were at an acceptable level. However, some blisters were generated due to bubbles generated from the holes of the base material.

On the coating film obtained above, an acrylic resin clear powder coating material having a thickness of 50 μm was applied by a corona charging type electrostatic coating machine.
It was applied so as to have a thickness of m, then put in a baking oven at 150 ° C. again and baked. The whiteness and metallic feeling of the obtained coating film were slightly inferior to those of the coating film obtained in Example 3, but they were somehow acceptable as a metallic coating film. However, the blisters caused by bubbles generated from the holes of the base material became larger than in the case of the metallic coating film, resulting in a coating film defect. With respect to the obtained coating film, the glossiness, metallic feeling and blistering from the substrate were measured in the same manner as in Example 3. The measurement results are shown in Table 1.

[0105]

[Table 1]

[0106]

EFFECT OF THE INVENTION According to the method for forming a multilayer coating film by the powder coating material of the present invention, two coats and one bake using the powder coating material,
Multi-layer coating can be performed by saving the time and energy required for heating by one baking such as three coats and one bake, or by laminating coating of the powder coating on the object heated to a temperature higher than the baking temperature of the powder coating. Can be formed.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akiko Tagami             878 Nishinomon, Mitsubuchi, Komaki, Aichi Japan             Paint Co., Ltd. Komaki factory (72) Inventor Tetsuro Kodama             878 Nishinomon, Mitsubuchi, Komaki, Aichi Japan             Paint Co., Ltd. Komaki factory F-term (reference) 4D075 AE12 BB23X BB26Z BB93X                       BB93Z CA33 CA48 DA04                       DA06 DB02 DB07 DC10 DC12                       DC13 DC18 DC38 EA02 EA41                       EA43 EB12 EB13 EB14 EB16                       EB19 EB20 EB22 EB32 EB33                       EB35 EB36 EB38 EB39 EB42                       EB45 EC11

Claims (7)

[Claims] 1. At least two layers selected from the group consisting of a primer coating layer, an intermediate coating layer, a top coating layer, a colored coating layer and a clear coating layer each formed by using a powder coating. In the method for forming a multilayer coating film having a coating layer,
A multi-layer coating film made of a powder coating material, characterized in that each powder coating material forming each coating film layer is sequentially laminated and adhered to an object to be coated, and each powder coating material thus laminated and adhered is simultaneously baked. Forming method. 2. A powder coating material forming each coating layer is applied to an object to be coated having a temperature lower than the melt softening temperature of the powder coating material having the lowest melt softening temperature among the powder coating materials. The method for forming a multi-layer coating film by the powder coating material according to claim 1, wherein the powder coating materials are sequentially laminated and adhered, and the powder coating materials thus laminated and adhered are simultaneously baked. 3. Each of the powder coating materials forming each coating layer, when the powder coating material having the lowest melt softening temperature among the powder coating materials has a melting softening temperature or higher. The powder coating composition having the highest melting and softening temperature among the coating materials is successively laminated and adhered to an object to be coated which is maintained at a temperature lower than the melting and softening temperature of the coating material, and the powder coating materials thus laminated and laminated are simultaneously baked. A method for forming a multi-layer coating film by the powder coating material as described above. 4. Each of the powder coating materials forming each coating layer, when the powder coating material of each powder coating material has the highest melt softening temperature of the powder coating material or higher, The powder coating composition having the highest baking temperature among the coating materials is successively laminated and adhered to an object to be coated which is maintained at a temperature lower than the baking temperature of the powder coating material, and the powder coating materials thus laminated and laminated are simultaneously baked. A method for forming a multilayer coating film by powder coating. 5. At least two layers selected from the group consisting of a primer coating layer, an intermediate coating layer, a top coating layer, a colored coating layer and a clear coating layer each formed by using a powder coating material. In the method for forming a multilayer coating film having a coating layer,
Each powder coating forming each coating layer is sequentially laminated and coated on an object to be coated which is maintained at a temperature equal to or higher than the baking temperature of the powder coating having the highest baking temperature among the powder coatings. A method for forming a multi-layer coating film by a powder coating material, comprising: 6. At least two layers selected from the group consisting of a primer coating layer, an intermediate coating layer, a top coating layer, a colored coating layer and a clear coating layer each formed by using a powder coating. In the method for forming a multilayer coating film having a coating layer,
Each powder coating material forming each coating layer is sequentially laminated and adhered to an object to be coated, and then the coating object is heated to the baking temperature of the powder coating material having the highest baking temperature among the respective powder coating materials. A method for forming a multilayer coating film by powder coating, which comprises heating to the above temperature and coating the remaining powder coating in layers. 7. The melting and softening temperature of each powder coating forming a primer coating layer, an intermediate coating layer, a top coating layer, a colored coating layer or a clear coating layer is 40 ° C. to 250 ° C. A method for forming a multilayer coating film using the powder coating material according to claim 1.