JP2002192071A - Method for forming coating film to wooden base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a coating film having decreased pitting surfaces (traces of foaming) in a method of forming the coating film by coating the surface of a wooden base material with a powder coating material. SOLUTION: The wooden base material is subjected to idle baking before coating of the powder coating material and is preferably precoated with the powder coating material to form a primer coating film and thereafter the surface of the primer coating film is subjected to regular coating with the powder coating material so as to attain a prescribed film thickness.

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 coating film by applying a powder paint on a woody base material such as wood or flooring material.

[0002]

2. Description of the Related Art In order to enhance the durability and aesthetics of wood and a flooring material, a coating film such as a clear coating film may be formed on the surface thereof.
Wood substrates such as wood and flooring materials are inferior in heat resistance and cannot be heated to a high temperature. Therefore, such a clear coating film is formed using a room-temperature-curable urethane paint. When a clear coating film having a large thickness is formed, the clear coating film is formed by overcoating.

[0003] When a large number of coatings are performed as described above, there is a problem that the manufacturing process is complicated. In recent years,
A powder coating material that does not use a solvent such as an organic solvent has attracted attention as being environmentally preferable. If a coating film can be formed on a wooden substrate using such a powder coating, a thick coating film can be formed at a time, and it is considered preferable from the viewpoint of environmental hygiene.

However, since the wood base material contains a large amount of water and has irregularities on the surface, when a powder coating is applied to form a coating film, foaming occurs during heating and melting, There was a problem that a large number of so-called wedges (foaming marks) were generated, and a coating film that could withstand practical use could not be formed.

An object of the present invention is to provide a coating film forming method capable of reducing the occurrence of foaming traces when a powder coating material is applied on a wooden substrate to form a coating film.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for applying a powder coating on a wooden substrate to form a coating film. Before applying the powder coating, the wooden substrate is baked. It is characterized by doing.

[0007] By baking the wooden base material before applying the powder coating, it is possible to reduce the wrinkles (foam marks) generated when the powder coating is applied and heated and melted. Therefore, it is possible to suppress the occurrence of foam (trace of foaming) in the formed coating film.

In the present invention, the baking temperature may be any temperature as long as it can remove moisture and the like that cause traces of foaming from the woody base material. Preferably, it is in the range of 110 to 130 ° C. The heating time can be appropriately selected depending on the heating temperature, and for example, can be selected from the range of 5 to 240 minutes. Preferably, it is 20 to 60 minutes.

Further, in the present invention, it is preferable that the powder coating applied on the wooden substrate is melted and attached by utilizing the heat of the wooden substrate after baking. Since the wooden substrate is insulative, if it is applied by electrostatic coating or the like, the powder coating repels electrostatically on the wooden substrate, and a sufficient coating rate cannot be obtained. When the powder coating is applied on a wooden substrate with a high temperature after baking, the powder coating melts due to the heat of the wooden substrate,
The powder coating can be adhered without causing electrostatic repulsion. Therefore, it is preferable to apply the powder coating in a state where the temperature of the wooden substrate is high after the baking.

Further, in the present invention, after baking, a powder coating is preliminarily coated, heated and melted to form an undercoat, and then the powder is coated on the undercoat so as to have a predetermined thickness. It is preferable to apply the paint completely. When the pre-coated powder coating is heated and melted to form a base coat, moisture and air, etc. are generated from the wooden base material, and these do not cause a wrinkle (foaming marks) on the base coat and Will be released. Therefore, in the subsequent main coating, almost no moisture, air, or the like is generated from the woody base material, and it is thought that generation of a wobble (foaming trace) in the coating film of the main coating can be suppressed. Therefore, it is preferable that the undercoating film allows moisture, air, and the like to pass through without leaving any trace of foaming. From such a viewpoint, the undercoating film is preferably a discontinuous coating film in which, for example, the coating film is scattered. Further, it is preferable that the coating film is a continuous coating film having an average film thickness of 80 μm or less, preferably 30 μm or less.

In the case where a small amount of the undercoat is generated in the base coat, the undercoat may be polished and removed with sandpaper or the like, and then the powder coating may be applied. In addition, preliminary painting,
The undercoating is not limited to one time, and the preliminary coating may be repeated a plurality of times to form the base coat.

In the present invention, the main coating is a step of applying a relatively large amount of powder coating so as to have a film thickness necessary for imparting smoothness. The powder coating used in the present invention is not particularly limited, and may be any of ultraviolet curable, thermosetting, and thermoplastic, but is preferably an ultraviolet curable powder coating or a thermosetting powder. Body paint is used.

In the present invention, when the powder coating is an ultraviolet-curable powder coating, the temperature of the wooden base material is lowered by UV (ultraviolet) irradiation in the preliminary coating. Preferably, the substrate is preheated. The temperature and time of the preheating are preferably about the same as the temperature and time of the above-mentioned empty baking, and are preferably about 10 to 120 minutes in a temperature range of 80 to 150 ° C. More preferably, it is 20 to 60 minutes. Note that the heating time can be appropriately selected depending on the heating temperature.

[0014] After the preliminary heating, similarly to after the baking,
It is preferable to use the heat of the wooden substrate to melt and adhere the powder coating that has been finally applied onto the wooden substrate. In the case of using an ultraviolet-curable powder coating, it is preferable to heat and melt the powder coating and then irradiate ultraviolet rays to cure the base coating when forming the base coating. However, the ultraviolet ray may be irradiated while the powder coating is heated and melted.

The resin used in the UV-curable powder coating material is not particularly limited as long as it is a resin which can be cured by ultraviolet rays, but it is preferable that the main component is a polyester resin or an acrylic resin. For example, the following (1)
To (5).

(1) A methacrylate group-containing polyester resin in which a carboxylic acid group contained in the polyester resin is reacted with glycidyl methacrylate (GMA) to give a polymerizable functional group.

(2) A resin comprising two components, a polyester resin having a double bond introduced by an unsaturated monomer, and a polyfunctional acrylate oligomer. (3) An acrylic resin in which acrylic acid is added to a glycidyl methacrylate (GMA) -containing acrylic resin to make the acrylic group a crosslinkable functional group.

(4) An epoxy resin having an acrylic group as a crosslinkable functional group by adding acrylic acid to the epoxy resin. (5) A resin in which a hydroxyl group-containing methacrylate is introduced into a polyfunctional alcohol via a diisocyanate.

Further, a photopolymerization initiator and other additives are added to the resin. As the photopolymerization initiator, photopolymerization initiators generally used for ultraviolet curable resins can be used alone or in combination of two or more. Specific examples include an aromatic carbonyl compound, anthraquinone and its derivatives, thioxanthone and its derivatives, benzoin ether and its derivatives, alphageon and its derivatives, benzylalkyl acetal and its derivatives, acetophenone derivatives, and phosphine oxides. If necessary, a photosensitizer can also be used.

As other additives, additives required for powder coatings such as pigments, surface conditioners, and flow agents can be added. In the present invention, when the powder coating is a thermosetting powder coating, it is preferable to heat and melt the powder coating and then form the base coating film by thermosetting. Further, it is preferable that after the base coat film is formed, the powder coating material is subsequently applied, heated and melted, and then heat-cured. Here, the temperature at the time of heat-melting and thermosetting is 100 to 180 ° C, preferably 110 to 170 ° C, and the time is 10 minutes to 12 minutes.
0 minutes, preferably 20 to 60 minutes.

As the resin of the thermosetting powder coating, polyester resin, acrylic resin, epoxy resin and the like can be used. The curing system is a block isocyanate curing system, an acid epoxy curing system, a phenol epoxy curing system, a β
Conventionally known curing systems such as a hydroxyalkylamide curing system, a hydrazide epoxy curing system, and an amine epoxy curing system can be used. Preferably, an acid epoxy curing system of an acrylic resin is preferred. That is, it is a thermosetting powder coating composed of an epoxy group-containing acrylic resin and dicarboxylic acid.

The above-mentioned β-hydroxyalkylamide curing system is a curing system obtained by reacting a carboxyl group with a β-hydroxyalkylamide curing agent represented by the following formula.

[0023]

Embedded image

Wherein R ¹ is a hydrogen atom, a methyl group or an ethyl group, R ² is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or HOCH (R ¹ ) CH ₂ —, and A is a divalent In the present invention, the baking and preliminary heating of the wooden base material, the heating and melting of the powder coating, and the like can be performed by heating with infrared irradiation, heating with hot air, or the like.

[0025] The wood substrate used in the present invention is not particularly limited, and examples thereof include wood, flooring material, and wood chips. The volume average particle diameter of the powder coating used in the present invention is preferably 5 to 50 μm, more preferably 5 to 40 μm,
More preferably, it is 5 to 30 μm.

The powder coating used in the present invention comprises:
Generally, it is preferable to use a clear paint in order to make use of the appearance pattern of the wooden substrate. Therefore, a paint containing no pigment is preferable.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples, and may be modified as appropriate without departing from the scope of the invention. It can be implemented by

(Examples 1 to 6 and Comparative Example 1) As a powder coating, an ultraviolet curable powder coating having the composition shown in Table 1 below was prepared and used.

The powder coating was produced by premixing the raw materials according to a conventional method, kneading the mixture using a mixer, finely pulverizing and sieving. The raw materials used in Table 1 are as follows.

-Unsaturated polyester resin: trade name "UV
ECOAT 2000 ", manufactured by UCB Chemicals Inc.-Photoinitiator: trade name" Irgacure 2959 ", manufactured by Ciba Specialty Chemicals Inc.-Flow regulator: trade name" Acronal 4F ", BASF
Company

[0031]

[Table 1]

As a wood substrate, 80 mm × 130 mm
X A 5 mm-thick flat wood plate was used. About Examples 1-6, after baking under the conditions shown in Table 2, the powder coating was applied. In Example 1, the main coating was performed after baking. In Examples 2 to 4, after pre-coating after baking, main coating was performed. In Example 5, after preliminary firing, preliminary coating was performed twice, and then main coating was performed. In Example 6, after preliminary baking, pre-coating was performed, the undercoating film was cured by irradiation with ultraviolet light, and the generated wedges were removed by polishing, followed by main coating. Curing of the coating film by UV (ultraviolet) irradiation was performed under the condition of 500 mJ.

In Table 2, "Dust" is indicated as the film thickness of the preliminary coating because the coating is performed in a state where the powder coating is scattered, and the undercoating is discontinuous. It is considered that the surface of the base material is exposed.

In Comparative Example 1, the main coating was performed without performing the empty baking. The appearance of the coating film formed on wood as described above was evaluated according to the following criteria.

×: Many armpits were observed on the surface of the coating film,
The coating is cloudy. ：: The coating film surface has few wrinkles and the coating film is transparent. ：: Very little or almost no cracks on the surface of the coating film were observed, and the coating film was transparent.

Table 2 shows the evaluation results.

[0037]

[Table 2]

As is evident from the results shown in Table 2, baking is carried out before applying the powder coating according to the present invention, whereby it is possible to suppress the occurrence of wrinkles in the coating film. .

(Examples 7 to 10 and Comparative Example 2) As a powder coating material, a thermosetting powder coating material was prepared using the raw materials and formulations shown in Table 3 and used.

The raw materials shown in Table 3 are as follows. -Epoxy group-containing acrylic resin: trade name "FINEDIC A207S", manufactured by Dainippon Ink Co., Ltd.-Epoxy resin: trade name "Epototo NT114", manufactured by Toto Kasei Co., Ltd.-Flow regulator: trade name "Leveler P", acrylic ester, Nippon Paint Co., Ltd.

[0041]

[Table 3]

A powder coating was produced in the same manner as in the above example. In addition, the same wood material as in the above example was used as the wood base material. In Examples 7 to 10, after baking under the conditions shown in Table 4, powder coating was applied. In Example 7, the main coating was performed after baking. In Examples 8 and 9, the main coating was performed after preliminary firing after baking. In Example 9, after the preliminary coating, the wool generated on the base coating film was polished and removed with sandpaper, and then the main coating was performed. In Example 10, after the preliminary firing, the preliminary coating was performed twice, and then the main coating was performed.

In Comparative Example 2, the powder coating was completely applied without baking. The appearance of the coating film obtained as described above was evaluated according to the same criteria as in Example 1. Table 4 shows the evaluation results.

[0044]

[Table 4]

As shown in Table 4, in Examples 7 to 10 in which the powder coating was applied after baking in accordance with the present invention,
It can be seen that the occurrence of armpits is suppressed as compared with Comparative Example 2.

[0046]

According to the present invention, it is possible to form a coating film with a small number of foams (foaming marks) on a wooden substrate by applying a powder coating.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B05D 7/24 301 B05D 7/24 301T 301R B27K 5/00 B27K 5/00 F B27M 3/00 B27M 3 / 00 M 3/04 3/04 F term (reference) 2B230 AA13 AA22 BA18 EA30 EB05 EB12 2B250 AA05 BA03 FA33 FA35 FA37 GA03 HA01 4D075 AE05 AE16 AE17 BB24X BB26Z BB46Z DB21 EA02 EA19 EA19 EA21

Claims (13)

[Claims] 1. A method for forming a coating film by applying a powder coating on a wooden substrate, wherein the wooden substrate is baked before applying the powder coating. A method for forming a coating film on a substrate. 2. The wood substrate according to claim 1, wherein the powder coating applied to the wood substrate is melted and adhered by utilizing the heat of the wood substrate after baking. Film formation method for 3. After baking, pre-coat the powder coating, heat and melt it to form a base coat, and then apply the powder paint on the base coat to a predetermined thickness. The method for forming a coating film on a wooden substrate according to claim 1 or 2, wherein the coating method is performed. 4. The method according to claim 3, wherein the undercoating is a discontinuous coating. 5. The method according to claim 3, wherein the undercoating film is a continuous coating film having a thickness of 80 μm or less. 6. The coating on a wooden substrate according to claim 3, wherein the powder coating is completely applied after polishing and removing the wedges generated on the base coating film. Film formation method. 7. The method according to claim 3, wherein the preliminary coating is repeated a plurality of times to form a base coating. 8. The powder coating according to claim 3, wherein the powder coating is an ultraviolet-curable powder coating, and the wood substrate is preheated before the main coating. A method for forming a coating film on a wooden substrate. 9. Utilizing the heat of the wooden base material after preheating,
9. The method for forming a coating film on a wooden substrate according to claim 8, wherein the powder coating applied on the wooden substrate is melted and adhered. 10. The method for forming a coating film on a wooden substrate according to claim 8, wherein the powder coating material is heated and melted and then irradiated with ultraviolet rays to cure the base coating film. 11. The powder coating material according to claim 3, wherein the powder coating material is a thermosetting powder coating material, and after the powder coating material is heated and melted, a base coating film is formed by thermosetting. 3. The method for forming a coating film on a wood substrate according to claim 1. 12. The method for forming a coating film on a wooden substrate according to claim 11, wherein a powder coating material is continuously applied after the formation of the base coating film, and the coating material is heated and melted and thermally cured. 13. The wooden base material is wood, flooring material,
The method for forming a coating film on a wooden substrate according to any one of claims 1 to 12, wherein the method is a piece of wood.