JP2001017904A - Formation of coating film and formation of multiple layer coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forming method of a coating film capable of obtaining the coating film excellent in smoothness and a multiple layer coating film using the same. SOLUTION: The forming method of coating film comprises applying a thermosetting powder coating material composition containing a thermosetting resin and a hardening agent on a material to be coated and heating in 2 stages. The heating temp. in a 1st stage is set to a lower temp. than a hardening setting temp. of the thermosetting powder coating material composition and the heating temp. in a 2nd stage is set to a higher temp. than the heating temp. in the 1st stage. Or the forming method of coating film comprises heating the thermosetting powder coating material composition at the higher temp. than the hardening setting temp. thereof and a heating condition is set so that the time required for the temp. of the material to be coated to reach the temp., at which the thermosetting powder coating material composition shows the lowest melting viscosity, from the start of the heating, is about 15-40 min.

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 using a thermosetting powder coating and a method for forming a multilayer coating film using a coating film obtained thereby.

[0002]

2. Description of the Related Art In recent years, die casting has been widely used as a material for housings of electric products, metal products and the like. The surface of this die-cast is coated with the purpose of improving the appearance and texture. In general, such coating is performed by applying a thick coat of an undercoat putty paint, polishing and smoothing the surface, and then applying an intermediate coat and a top coat. For this reason, as a paint for undercoat putty,
2. Description of the Related Art Solvent-type thermosetting paints that can form a coating film having excellent smoothness and being easily polished are used. However, since the solvent type thermosetting paint contains an organic solvent,
It is pointed out that the impact on the environment is great.

On the other hand, thermosetting powder coatings have attracted attention as environmentally friendly coatings containing no organic solvent, and attempts have been made to use these as coatings for undercoat putty. JP-A-6-279709 and JP-A-10-279709
Japanese Patent No. 147732 discloses a thermosetting powder coating composition which can obtain a coating film which can be easily polished by mixing a pigment such as talc with an epoxy group-containing resin. However, in the case of coating an object to be coated having a myriad of fine holes on its surface, such as die casting, there is a problem that the coating film foams due to the fine holes and the smoothness of the obtained coating film is reduced. Was.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for forming a coating film and a method for forming a multi-layer coating film capable of obtaining a coating film having excellent smoothness, particularly when die-casting is used as an object to be coated. The purpose is to do.

[0005]

According to the present invention, in a coating film forming method in which a thermosetting powder coating composition is applied to an object to be coated and then heated, heating is set in two stages. A coating film forming method, wherein 1) the heating temperature in the first step of heating is set to a temperature lower than the setting temperature of the thermosetting powder coating composition, and 2) the heating in the second step. It is another object of the present invention to provide a method for forming a coating film, wherein the temperature is set to be higher than the first-stage heating temperature. Here, for example, the heating temperature in the second stage is set to be equal to or higher than the curing setting temperature, and the heating temperature in the first stage is a temperature at which the thermosetting powder coating composition exhibits the lowest melt viscosity. It is set above. Further, for example, the thermosetting powder coating composition further contains a wax, and the melting point of the wax is 50 ° C. or more and the heating temperature of the second stage. For example, the melting point of the wax is the first stage. The heating temperature is higher than the heating temperature of the eyes and is equal to or lower than the setting temperature of the thermosetting powder coating composition.

Further, the present invention provides a method for forming a coating film by applying a thermosetting powder coating composition to an object to be coated and then heating the thermosetting powder coating composition at a temperature equal to or higher than a setting temperature of curing. In the method, the heating condition is such that the time from the start of heating to the temperature at which the thermosetting powder coating composition exhibits the lowest melt viscosity after the start of heating is 15 to 40 minutes. It is intended to provide a coating film forming method characterized by being set as described above. Here, the thermosetting powder coating composition further contains, for example, a wax, and the melting point of the wax is 50 ° C. or more and the curing setting temperature of the thermosetting powder coating composition, and The melting point of the wax is higher than the temperature at which the thermosetting powder coating composition exhibits the minimum melt viscosity.

In the method of forming a coating film of the present invention, for example, the thermosetting powder coating composition further contains an extender pigment, and further contains an epoxy group-containing resin and a carboxylic acid group-containing curing agent. In. For example, in the coating film forming method of the present invention, the object to be coated is die-cast.

Further, according to the present invention, the coating film obtained by the coating film forming method of the present invention is polished in the following steps: 1) a step of polishing the surface of the obtained coating film, and 2) a first step. Provided is a method for forming a multilayer coating film comprising a step of forming a top coating film by further applying a top coating material on the surface of the coating film, and a multilayer coating film obtained by the method for forming a multilayer coating film.

[0009]

A method of forming a coating film DETAILED EMBODIMENTS OF THE INVENTION Coating forming method of the present invention two types. One is to set the heating conditions in two stages, and the other is to set the time to reach the temperature at which the thermosetting powder coating composition to be used exhibits the lowest melt viscosity.

(1) A coating film type in which heating conditions are set in two stages
A first method of forming a coating film of the present invention is a method of forming a coating film in which a thermosetting powder coating composition is applied to an object to be coated and then heated. A coating film forming method that is set, wherein 1) the first stage heating temperature in the heating is set to a temperature lower than a curing set temperature of the thermosetting powder coating composition, and 2) The second
The heating temperature of the first stage is set to be higher than the heating temperature of the first stage.
Hereinafter, this will be described as a first coating film forming method.

In the first method of forming a coating film according to the present invention, first, a thermosetting powder coating composition is applied to an object to be coated. The object to be coated is not particularly limited, and specific examples thereof include plastics and iron plates, steel plates, aluminum plates, various alloys, and those obtained by subjecting them to surface treatment. The present invention is advantageously applied to a metal workpiece used for a housing of a metal product.
Specific examples of the metal workpiece include die cast, and examples include magnesium die cast, thixomolded magnesium alloy, and aluminum die cast.

The method of applying the thermosetting powder coating composition on the object to be coated is not particularly limited. Specifically, a spray coating method, an electrostatic powder coating method, a fluid immersion method, and the like. Coating methods and the like are well known by those skilled in the art, but from the viewpoint of coating efficiency and uniformity of the thickness of the obtained coating film, electrostatic powder coating using a powder coating gun Preferably, it is a method. Specific examples of the powder coating gun include a corona charging coating gun and a friction charging coating gun.

The coating thickness in this coating film forming method is not particularly limited, but is preferably 100 to 400 μm.

According to a first method of forming a coating film of the present invention, an object to be coated on which the above-mentioned thermosetting powder coating composition has been applied is first heated to a first stage heating condition, for example, by heating. It is charged into a furnace and then charged into a heating furnace set to the second stage heating conditions.

Of the heating conditions set in the above two stages,
The first stage heating is for melting the thermosetting powder coating composition to be used, and does not actively promote the curing reaction. From the viewpoint of the smoothness of the obtained coating film, the first-stage heating temperature is set to a temperature lower than the curing setting temperature of the thermosetting powder coating composition, and the thermosetting powder coating composition It is preferable that the temperature is set to a temperature not lower than the lowest melt viscosity of the composition.

The heating time of the first stage is not particularly limited, and can be appropriately set according to the size and shape of the object to be coated, but is preferably 15 to 40 minutes. If the above time is shorter than 15 minutes, the resulting coating film may not be smooth enough. If it is longer than 40 minutes, the time for obtaining the coating film may be too long.

The heating in the second stage is for promoting the curing reaction, and is set at a temperature higher than the heating temperature in the first stage from the viewpoint of the performance and physical properties of the resulting coating film. It is more preferable that the temperature is set to be equal to or higher than the curing setting temperature.

The heating time of the second stage is not particularly limited, and can be appropriately set according to the size and shape of the object to be coated, but is preferably 10 to 30 minutes. When the above-mentioned time is shorter than 10 minutes, the performance and physical properties of the obtained coating film may be insufficient, and when it is longer than 30 minutes, the time for obtaining the coating film may be too long.

In the coating film obtained by the first coating film forming method of the present invention, a coating film having necessary properties and physical properties must be obtained at the end of the second stage heating. Accordingly, it is substantially preferable that the curing reaction of the thermosetting powder coating composition proceeds in the second stage among the heating conditions set in the two stages.

In the first method of forming a coating film according to the present invention,
The total time of the heating in the second stage and the second stage is not particularly limited, but is preferably within 60 minutes.

In the first coating film forming method of the present invention, for example, the object to be coated is put into a heating furnace set at a first stage heating temperature without separately preparing a heating furnace. After the treatment for a predetermined time, the coating temperature can be set again by setting the heating temperature of the heating furnace to the second-stage heating temperature.

Here, the temperature at which the thermosetting powder coating composition of the present invention exhibits the lowest melt viscosity varies depending on the type of the thermosetting powder coating composition described later. The method for measuring the temperature at which the minimum melt viscosity is exhibited is not particularly limited,
Specifically, a method well known by those skilled in the art such as a viscoelasticity measuring device can be used.

For example, the determination of the temperature at which the minimum melt viscosity of Powders H100 (a polyester / epoxy resin powder coating manufactured by Nippon Paint Co., Ltd.) is determined will be described as an example. M
The melt viscosity of this paint was measured using an R-300 liquid meter (viscoelasticity meter manufactured by Rheology Co., Ltd.), and from the relationship between the obtained temperature and the melt viscosity, the lowest melt viscosity was in the range of 135 to 145 ° C. It can be seen that there is a temperature at which From this, the intermediate value of 140 ° C. in the temperature range was determined as the temperature at which the coating material exhibited the lowest melt viscosity.

Further, the curing set temperature in the present invention is:
Means the temperature necessary to sufficiently obtain the performance and physical properties of the obtained coating film. After heating at that temperature for 25 minutes, the surface of the coating film is wiped off with gauze dipped in xylene, and there is no abnormality on the surface It means the lowest temperature at which a coating can be obtained.

For example, the setting of the curing temperature of Powderx H100 (polyester / epoxy resin powder paint manufactured by Nippon Paint Co., Ltd.) will be described as an example. This paint is applied to an iron plate, and the heating condition is changed from 140 ° C to 200 ° C in steps of 10 ° C.
The coating film obtained by baking for 25 minutes in each of the heating furnaces set at a temperature level of up to 200 ° C was wiped off with gauze soaked in xylene, and no abnormality was found on the surface of the coating film obtained under heating conditions of 180 ° C or higher. . From this, 180 ° C., the lowest temperature at which no abnormality was observed on the coating film surface, was determined as the curing set temperature of this paint.

(2) Reaching the temperature at which the lowest melt viscosity is exhibited
The second method of the coating film forming method of forming a coating film Method for setting the time, the thermosetting powder coating composition was applied against the object to be coated, the thermosetting powder coating composition A coating film forming method of heating at a temperature equal to or higher than a curing setting temperature of an object, wherein the heating condition is such that the temperature of the object to be coated after starting heating is the minimum of the thermosetting powder coating composition. The time required to reach the temperature at which the melt viscosity is exhibited is set to be 15 to 40 minutes. Hereinafter, this will be described as a second coating film forming method.

The second method for forming a coating film of the present invention is the same as the first method.
First, a thermosetting powder coating composition is applied to an object to be coated in the same manner as in the method of forming a film. As for the application of the thermosetting powder coating composition on the object to be coated, the method described in the first method is applied as it is.

In the second method for forming a coating film according to the present invention, specifically, the above-mentioned object to be coated with the thermosetting powder coating composition is set at a temperature equal to or higher than a set curing temperature. Was
For example, it is put into a heating furnace and heated. The temperature of the charged object to be coated gradually rises, first reaches a temperature at which the thermosetting powder coating composition exhibits the lowest melt viscosity, and then reaches a set curing temperature, whereby a curing reaction proceeds. . At this time, in the second coating film forming method, the time required to reach the temperature at which the minimum melt viscosity is exhibited is 15 to 4 hours.
It is set to be 0 minutes. The curing setting temperature and the temperature at which the minimum melt viscosity is exhibited are the same as those described above.

When the time required to reach the temperature at which the above-mentioned minimum melt viscosity is reached is shorter than 15 minutes, the smoothness of the obtained coating film is reduced, and when it is longer than 40 minutes, the time for obtaining the coating film is longer. It takes too much. The time required to reach this temperature is preferably set so as to be within the above range depending on the heating temperature, the air volume, the wind speed and the amount of the object to be coated.

The temperature change of the object to be coated until the temperature at which the minimum melt viscosity is exhibited is not particularly limited, and may be linear or non-linear. If the time to reach the temperature at which the melt viscosity is exhibited is within the above range, the heating temperature may or may not be changed during heating of the object to be coated, but the workability and the resulting coating film From the viewpoint of smoothness, it is preferable that the heating temperature is not changed during the heating of the object to be coated.

The total heating time in the second coating film forming method of the present invention is not particularly limited, but is preferably within 60 minutes.

The thermosetting powder coating composition used in the coating film forming method of the present invention contains a thermosetting resin and a curing agent. Specific examples of the thermosetting resin include an acrylic resin, a polyester resin, and an epoxy resin having a curing functional group.

Specific examples of the acrylic resin having a curable functional group include those obtained by polymerizing at least one curable functional group monomer and, if necessary, other neutral monomers according to a conventional method. Can be. Examples of the curable functional group-containing monomer include a carboxylic acid group-containing monomer such as (meth) acrylic acid, a hydroxyl group-containing monomer such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate and hydroxybutyl acrylate, and glycidyl (meth) acrylate. ) Acrylate, 2-
An epoxy group-containing monomer such as methyl glycidyl methacrylate can be exemplified. Further, as the neutral monomer, for example, methyl (meth) acrylate,
Examples thereof include ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, styrene, vinyltoluene, and p-chlorostyrene. .

As the polyester resin having a cured functional group, for example, an acid component containing a polyvalent carboxylic acid as a main component and an alcohol component containing a polyhydric alcohol as a main component are compressed by a usual method. Polymerized products can be exemplified. The acid component is not particularly limited, and examples thereof include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid and anhydrides thereof, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, and the like. , Succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, saturated aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and anhydrides thereof, lactones such as γ-butyrolactone and ε-caprolactone And aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid, and corresponding hydroxycarboxylic acids and the like. These may be two or more kinds.

The alcohol component is not particularly restricted but includes, for example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,5-hexanediol, diethylene glycol, triethylene glycol, Ethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol,
Bisphenol A alkylene oxide adduct, bisphenol S alkylene oxide adduct, 1,2-propanediol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 2,3- Pentanediol, 1,4-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, 1,2-dodecanediol, 1,2-octadecanediol, etc. Examples thereof include aliphatic glycols having a side chain, trihydric or higher polyhydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol. These may be two or more kinds.

Further, specific examples of the epoxy resin having a cured functional group include an epoxy group-containing resin having two or more epoxy groups in one molecule, such as glycidyl ester resin and novolak. Reaction product between type phenol resin and epichlorohydrin, reaction product between bisphenol resin (A type, B type, F type, etc.) and epichlorohydrin, novolak type phenol resin and bisphenol resin (A type, B type, F type, etc.) Glycidyl ether type such as a reaction product of a novolak type phenol resin and a bisphenol resin (A type, B type, F type, etc.), a reaction product of a cresol compound such as cresol novolak and epichlorohydrin, Resin, alicyclic epoxy resin, linear aliphatic epoxy resin, bromine containing Epoxy resins, phenol novolak type epoxy resin, cresol novolak type epoxy resin, and the like can be exemplified epoxy group-containing acrylic resin.

The Tg of the thermosetting resin is not particularly limited, but is preferably from 20 to 100 ° C.
In the present invention, Tg is a differential scanning calorimeter (DS).
In the case where the thermosetting resin is an acrylic resin, it can also be obtained from the monomer ratio having a known Tg constituting the copolymer.

The thermosetting powder coating composition used in the coating film forming method of the present invention contains a curing agent in addition to the thermosetting resin. The melting point of the curing agent is not particularly limited, but is preferably from 50 to 150 ° C. from the viewpoint of storage stability and smoothness of the obtained coating film.

The curing agent is not particularly limited, and is selected according to the type of the curing functional group of the thermosetting resin. As the curing agent, when the curing functional group of the thermosetting resin is an epoxy group, specifically, aliphatic polycarboxylic acids such as decanedicarboxylic acid and sebacic acid, and polycarboxylic acid anhydrides Dicyandiamide, blocked isocyanate, amine-based curing agent, carboxylic acid group-containing acrylic resin, polyamide-based curing agent, phenolic resin, imidazole compounds and imidazoline compounds.

When the curing functional group of the thermosetting resin is a hydroxyl group, specifically, an aliphatic polycarboxylic acid, an aliphatic acid anhydride, an aminoplast resin, an epoxy group-containing resin or a triglycidyl Polyepoxy compound such as isocyanurate, blocked isocyanate, glycoluril curing agent, further, when the curing functional group of the thermosetting resin is a carboxylic acid group, an epoxy group-containing resin,
Examples thereof include polyepoxy compounds such as triglycidyl isocyanurate, polyhydroxy compounds, and hydroxyalkylamides. The curing agent may be of two or more types.

In the case where the thermosetting resin and the curing agent are used in the thermosetting powder coating composition used in the method for forming a coating film of the present invention, the ratio of the thermosetting resin to the curing agent is determined as follows. Is not particularly limited, but generally, the molar ratio of the curing functional group of the thermosetting resin / the curing functional group of the curing agent is preferably set to 1 / 0.5 to 1/2. . If the above molar ratio is outside the above range, the performance and physical properties of the obtained coating film may be reduced.

The thermosetting powder coating composition used in the method for forming a coating film of the present invention is a thermosetting powder coating composition from the viewpoints of adhesion to an object to be coated, coating film performance, and easy industrial availability of raw materials. It is preferable to use an epoxy group-containing resin as the resin and a carboxylic acid group-containing compound as the curing agent.

Specific examples of the carboxylic acid group-containing compound include the above-mentioned aliphatic polycarboxylic acids, polycarboxylic anhydrides, and carboxylic acid group-containing acrylic resins.

The ratio of the epoxy group-containing resin to the carboxylic acid group-containing curing agent is not particularly limited.
From the viewpoint of the performance and physical properties of the obtained coating film, the molar ratio of the epoxy group of the epoxy group-containing resin to the carboxylic acid group of the carboxylic acid group-containing curing agent may be 1/1 to 1 / 0.5. More preferably, it is 1 / 0.8 to 1 / 0.6. If the molar ratio of the epoxy group is less than 1/1, the performance and physical properties of the resulting coating film may be reduced, and the molar ratio of the epoxy group may be 1 / 0.5.
If the amount is larger, the water resistance of the obtained coating film may be reduced.

The thermosetting powder coating composition used in the method for forming a coating film of the present invention preferably further contains a wax. When the above-mentioned wax is contained in the thermosetting powder coating composition in the first coating film forming method, the melting point thereof is not particularly limited.
It is preferable that the heating temperature is equal to or lower than the heating temperature of the first
It is further preferable that the heating temperature is higher than the heating temperature at the stage and is equal to or lower than the setting temperature of the thermosetting powder coating composition. If the melting point is lower than 50 ° C., the blocking resistance may decrease. If the melting point is higher than the second stage heating temperature, the wax may not melt and the smoothness of the coating film may decrease. .

When the wax is contained in the thermosetting powder coating composition in the second coating film forming method, the melting point thereof is not particularly limited. The temperature is preferably equal to or lower than the curing setting temperature of the composition, and more preferably higher than the temperature at which the thermosetting powder coating composition exhibits the minimum melt viscosity. When the melting point is lower than 50 ° C., the blocking resistance may be reduced. When the melting point is higher than the setting temperature of the thermosetting powder coating composition, the wax does not melt and the smoothness of the coating film is reduced. May drop.

Specific examples of such a wax include a synthetic wax and a natural wax. Examples of the synthetic wax include an ester compound of a higher alcohol and a higher fatty acid, for example, a long-chain alcohol having 16 to 36 carbon atoms such as cetyl alcohol, palmityl alcohol or stearyl alcohol and stearic acid, palmitic acid or myristic acid. Reaction products with acids, glycerides of fatty acids such as stearic acid, glycol esters or polyethylene glycol, glycol esters and synthetic beeswax, aliphatic amine waxes obtained by the reaction of hydrogenated castor oil with monoethanolamine, Examples thereof include a molecular weight aliphatic amide. Natural waxes include vegetable, animal or mineral natural waxes. Examples of the natural wax include montan wax, carnauba wax,
Examples include beeswax, shrub wax, paraffin wax, ceresin, and Japanese wax.

As the shape of the synthetic wax and the natural wax, various shapes such as a solid mass, a flake, and a powder can be used.

When the thermosetting powder coating composition used in the method for forming a coating film of the present invention contains the above wax, the content of the wax is preferably 1 to the total of the above thermosetting resin and the above curing agent.
The amount is preferably 0.5 to 8 parts by weight, more preferably 1 to 5 parts by weight, from the viewpoint of smoothness and blocking resistance of the obtained coating film. When the amount of the wax is less than 0.5 part by weight, the resulting coating film has low smoothness. If the amount is more than 8 parts by weight, the blocking resistance and the performance and physical properties of the obtained coating film are reduced.

The thermosetting powder coating composition used in the method of forming a coating film of the present invention may contain an extender pigment in addition to the above components. The extender is not particularly limited, and specific examples thereof include talc, clay, calcium carbonate, barium sulfate, silica, and the like.

The extender preferably contains talc from the viewpoints of smoothness and easiness of polishing of the obtained coating film. Specific examples of the talc include known ones such as S talc and PS talc.

The content of the extender is not particularly limited, but is preferably 100 parts by weight of the total of the thermosetting resin and the curing agent from the viewpoint of smoothness and easiness of polishing of the resulting coating film. , Preferably 15 to 40 parts by weight, more preferably 20 to 35 parts by weight. The extender may be of two or more types.

The thermosetting powder coating composition used in the method for forming a coating film of the present invention may further comprise, if necessary, a surface conditioner, a pigment other than the extender, a curing accelerator,
Other additives such as a curing catalyst, a plasticizer, a pigment dispersant, and benzoin may be included.

Examples of the surface modifier include silicones such as dimethyl silicone and methyl silicone, and acrylic oligomers.

The pigment other than the above-mentioned extender is not particularly limited, and examples thereof include titanium dioxide, red iron oxide, iron oxide,
Examples thereof include coloring pigments such as carbon black, NL Fast Yellow, phthalocyanine blue, phthalocyanine green, quinadone pigments, and azo pigments.

The content of the pigment other than the extender is preferably 10 parts by weight or less based on 100 parts by weight of the thermosetting powder coating composition. If the content of the pigment other than the above-mentioned extender is more than 10 parts by weight, the resulting coating film may have poor polishing properties.

The method for producing the thermosetting powder coating composition used in the method for forming a coating film of the present invention is not particularly limited, and any known method in the field of powder coatings can be used. After the raw materials such as the curable resin and the curing agent are dry-mixed with a Henschel mixer or the like, the mixture is melt-kneaded at a temperature at which the thermosetting resin and the curing agent do not react with a buscon kneader or the like, cooled, and then pulverized and classified. Examples can be given.

Method for Forming a Multi-Layer Coating Film The method for forming a multi-layer coating film of the present invention comprises the steps of: 1) polishing the surface of the coating film obtained above with respect to the coating film obtained by the above-mentioned coating film forming method. 2) a step of further applying a topcoat to the surface of the coating film polished in the first step to form a topcoat film. It imparts texture and design to the object.

The first step in the method for forming a multilayer coating film of the present invention is a step of polishing the surface of the coating film obtained by the above-mentioned method for forming a coating film. In this step, the surface of the coating film obtained by the above-mentioned coating film forming method is smoothed by polishing. The polishing method is not particularly limited, and examples thereof include polishing using a machine such as a sander, and manual polishing using polishing paper or the like. The abrasive paper is not particularly limited, and examples thereof include water-resistant abrasive paper and sandpaper. The sander is not particularly limited, and for example, MODEL
Air sander such as 300 (NATIONAL-DETROIT), STUHR (FISHINGPRODUCT)
And the like). The polishing method may use one kind of method or two or more kinds of methods. However, at the end of the first step, polishing using the above-mentioned polishing paper may be performed. preferable.

The second step in the method for forming a multi-layer coating film of the present invention is a step of further applying a top coating material to the surface of the coating film polished in the first step to form a top coating film.

The form of the top coat is not particularly limited, and may be any of a thermosetting paint such as a solvent type, an aqueous type and a powder type, or a normal dry type paint. As the thermosetting paint and the air-drying paint, various paints such as acrylic resin, polyester resin, and epoxy resin can be used depending on required coating film performance.

The method for applying the top coat is not particularly limited, but when a solvent-type or water-based paint is used, it is preferable to use an atomizing coating method. Specific examples of the spray coating include an air spray coating, an airless spray coating, an air atomization type, and a rotary atomization type electrostatic coating machine. The film thickness when applying the above top coating material is 20 to 10 as a dried or cured film thickness.
0 μm. If the thickness of the dried or cured film of the top coat is less than 20 μm, the coating performance and design of the resulting multilayered coating may be reduced, and the
When the thickness is larger than m, the coating performance, texture and design of the multilayer coating film cannot be obtained in proportion to the thickness, which is not economical.

In the method of forming a multi-layer coating film of the present invention, when a normal-dry paint is used as the top coat, after application, the paint is dried at room temperature or forcibly to obtain a top coat. The drying time varies depending on the coating environment conditions and the like, but is preferably performed at room temperature for one day or more.

On the other hand, when a thermosetting paint is used as the above-mentioned top coat, after application, heating is performed to obtain a top coat. The heating conditions are not particularly limited, and the temperature and time can be appropriately set according to the type of the overcoat paint used.

As described above, a multilayer coating film can be obtained by the first step and the second step.

[0066]

EXAMPLES Production Example 1 Preparation of thermosetting powder coating composition 1 Epicoat 1004 50.0 parts by weight (Epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd.) Upicoat GV230 50.0 parts by weight (Polyester resin manufactured by Nippon Yupika Co., Ltd.) Cerafloor 961 3.0 parts by weight (modified polyethylene wax manufactured by BYK, melting point 140 ° C) 15.0 parts by weight of Neolite TPS (calcium carbonate manufactured by Takehara Chemical Co.) Benzoin B 1.0 part by weight (manufactured by Wako Pure Chemical Industries) CF -1056 0.3 parts by weight (surface preparation agent manufactured by Toshiba Silicone Co.) CR-90 5.0 parts by weight (titanium dioxide manufactured by Ishihara Sangyo Co.) Then, the mixture was melted and kneaded at about 100 ° C. by a co-kneader (manufactured by Bus). The obtained melt-kneaded product was cooled to room temperature, coarsely pulverized, then pulverized with an atomizer (manufactured by Fuji Paudal Co.), and then classified with a 150-mesh sieve. The volume average particle diameter was 40 μm, and the temperature at which the lowest melt viscosity was 14 was obtained.
A thermosetting powder coating composition 1 having a setting temperature of 0 ° C. and a setting temperature of 180 ° C. was obtained.

The volume average particle diameter was measured using Microtrac HRA X-100 (manufactured by Nikkiso Co., Ltd.).

The temperature at which the minimum melt viscosity is exhibited is determined by applying 0.1 g of the pelletized powder coating to an MR-300 solid liquid meter (manufactured by Rheology, measurement conditions; frequency: 0.1).
The temperature was raised from 105 ° C. to 230 ° C. using a temperature rise rate of 20 ° C./min.

On the other hand, the curing setting temperature was set at 7 temperature levels from 140 ° C. to 200 ° C. in increments of 10 ° C. by applying the obtained powder coating to an iron plate by electrostatic coating.
After baking for 5 minutes to obtain a coating film, the surface of the obtained coating film is wiped 10 times with gauze soaked in xylene, and the minimum heating temperature of the coating film having no abnormality such as dissolution on the surface is set. Temperature was determined.

Example 1 Powderx H100 (polyester / epoxy resin powder paint manufactured by Nippon Paint Co., Ltd.) was 0.8 × 70 × 150 m
m on an iron plate and a 10 × 200 × 300 mm thixomolded magnesium alloy plate.
Electrostatic powder coating to a thickness of 30 μm.
The coating was obtained by heating in a heating furnace set at 40 ° C. for 30 minutes and the second stage at 180 ° C. for 20 minutes.

The coating film obtained on the magnesium alloy plate was polished using a water-resistant abrasive paper # 180 in accordance with the easiness of water sharpening specified in 6.6.1 of JIS K5400. After the polished coating film surface was evaluated by the polishing property described below, a solvent-type thermosetting topcoat paint (trade name “Super Rack O-100 Clear”, a melamine-curable acrylic resin paint manufactured by Nippon Paint Co., Ltd.) The dry film thickness is 20 to 3
It was electrostatically coated to 0 μm and heated at 160 ° C. for 20 minutes to obtain a multilayer coating film on the magnesium alloy plate.

The temperature at which the lowest melt viscosity was exhibited and the set temperature for curing were measured in the same manner as in Example 1, and found to be 140 ° C. and 180 ° C., respectively.

Example 2 A coating film and a multilayer coating film were formed on the magnesium alloy plate in the same manner as in Example 1 except that the thermosetting powder coating composition 1 obtained in Production Example 1 was used. I got

Example 3 A coating film and a multi-layer coating film were formed on the magnesium alloy plate in the same manner as in Example 2 except that a coating film was obtained by heating in a heating furnace set at 180 ° C. for 50 minutes. I got The time from when the temperature of the object to be coated reached 140 ° C. after the start of heating was 22 minutes.

Comparative Example 1 A coating film and a multi-layer coating film were obtained in the same manner as in Example 1 except that the heating conditions were not divided into two stages but at 180 ° C. for 50 minutes. The time from when the temperature of the object to be coated reached 140 ° C. after the start of heating was 10 minutes.

Comparative Example 2 A coating film and a multi-layer coating film were obtained in the same manner as in Example 2 except that the heating conditions were not divided into two stages but at 180 ° C. for 50 minutes. The time from when the temperature of the object to be coated reached 140 ° C. after the start of heating was 10 minutes.

Evaluation Test The following items were evaluated for each of the coating films and multilayer coating films obtained in Examples 1 to 3 and Comparative Examples 1 and 2. The evaluation results are shown in Table 1.

<Smoothness> The appearance of each coating film was visually evaluated. The evaluation criteria were as follows. ◎: Good without unevenness ○: Slight unevenness △: Notable unevenness ×: Many unevenness

<Abrasiveness> Examples 1 to 3 and Comparative Examples 1 to
2 was evaluated for abrasiveness. The evaluation criteria were as follows. ：: easy to polish ×: difficult to polish

<Appearance after Overcoating> The appearance of the coating film was visually evaluated. The evaluation criteria were as follows. ◎: Good without unevenness ○: Slight unevenness △: Notable unevenness ×: Many unevenness

[0081]

[Table 1]

As is clear from the evaluation results shown in Table 1, the method for forming a coating film in which heating was set in two stages was performed.
The heating temperature at the stage is set to a temperature lower than the curing setting temperature of the thermosetting powder coating composition used, and
A coating film forming method in which the heating temperature of the first stage is set to a temperature higher than the heating temperature of the first stage (Examples 1 to 3)
2) Or, if the heating conditions are such that the temperature of the object to be coated is
The time from the start of heating to the temperature at which the thermosetting powder coating composition used exhibits the lowest melt viscosity is 15 to 4 hours.
By using the coating film forming method (Example 3) set to be 0 minutes, the smoothness of the coating film obtained on the die cast can be improved. Further, by using the coating film forming method in which the thermosetting powder coating composition contains wax (Example 2), the smoothness of the coating film obtained on die casting can be further improved.

[0083]

The first method of the present invention for forming a coating film comprises:
Since the heating temperature is set in two stages and defines the first stage heating temperature and the second stage heating temperature, it is possible to improve the smoothness of the obtained coating film. This is the first
Melting the thermosetting powder coating used by the second stage heating, spreading the coating to the recesses on the surface of the object to be coated, eliminating the portion where air accumulates, and curing the coating by the second stage heating It is thought that it depends.

The second method of forming a coating film according to the present invention is characterized in that the temperature of the object to be coated is from the start of heating to the temperature at which the thermosetting powder coating composition used exhibits the minimum melt viscosity. , The smoothness of the coating film can be improved. This allows the powder coating to be sufficiently melted by stipulating the time until the temperature at which the thermosetting powder coating composition to be used exhibits the minimum melt viscosity is used. It is considered that this is because the paint spreads to the concave portions to eliminate the portion where air is accumulated, and thereafter, the temperature reaches the curing setting temperature due to the temperature rise over time, and the curing proceeds.

Furthermore, the smoothness of the coating film obtained by adding a wax to the thermosetting powder coating used in the coating film forming method of the present invention can be further improved. This is thought to be due to the melting of the wax when heated.

Further, by adding an extender to the thermosetting powder coating used in the coating forming method of the present invention, a coating which can be easily polished can be obtained. It is considered that this is because the extender increases the brittleness of the coating film.

The coating film forming method of the present invention can exert the above-mentioned effects particularly when a die-cast having an infinite number of minute holes on the surface is used as the object to be coated.

Accordingly, a multilayer coating film having excellent design properties and texture can be formed by further forming a top coating film on the coating film obtained by the present coating film forming method.

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Claims (13)

[Claims] 1. A coating film forming method in which a thermosetting powder coating composition is applied to an object to be coated and then heated, wherein the heating is set in two stages. ,
1) The first stage heating temperature in the heating is set to a temperature lower than the curing set temperature of the thermosetting powder coating composition, and 2) the second stage heating temperature is the second stage heating temperature. A method for forming a coating film, wherein the temperature is set to be higher than the first stage heating temperature. 2. The coating film forming method according to claim 1, wherein the second-stage heating temperature is set to be equal to or higher than the curing set temperature. 3. The coating film forming method according to claim 1, wherein the heating temperature in the first step is set to a temperature at which the thermosetting powder coating composition exhibits a minimum melt viscosity. 4. The thermosetting powder coating composition according to claim 1, further comprising a wax, wherein the melting point of the wax is not lower than 50 ° C. and not higher than the second stage heating temperature. The method for forming a coating film according to any one of the first to third aspects. 5. The coating film forming method according to claim 4, wherein the melting point of the wax is higher than the heating temperature in the first stage and is equal to or lower than a setting temperature of the thermosetting powder coating composition. . 6. A method for forming a coating film, comprising applying a thermosetting powder coating composition to an object to be coated, and then heating the thermosetting powder coating composition at a temperature equal to or higher than a setting temperature for curing the thermosetting powder coating composition. The heating condition is such that the temperature of the object to be coated is 15 to 40 minutes from the start of heating to the temperature at which the thermosetting powder coating composition reaches the minimum melt viscosity. A coating film forming method characterized by being set as follows. 7. The thermosetting powder coating composition further contains a wax, and the melting point of the wax is not lower than 50 ° C. and not higher than a setting temperature of the thermosetting powder coating composition. 7. The method for forming a coating film according to item 6. 8. The method according to claim 7, wherein the melting point of the wax is higher than a temperature at which the thermosetting powder coating composition exhibits a minimum melt viscosity. 9. The method according to claim 1, wherein the thermosetting powder coating composition further comprises an extender pigment. 10. The method according to claim 1, wherein said thermosetting powder coating composition contains an epoxy group-containing resin and a carboxylic acid group-containing curing agent. 11. The method according to claim 1, wherein the object to be coated is die-cast. 12. A coating film obtained by the coating film forming method according to any one of claims 1 to 11; 1) a step of polishing the surface of the obtained coating film; A) forming a top coat by further applying a top coat to the surface of the coat polished in the first step. 13. A multilayer coating film obtained by the method for forming a multilayer coating film according to claim 12.