JP2018153786A - Electrostatic powder applying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide powdered paint that restrains the occurrence of coating film roughness of a resulting coating film, compared with a case where an attenuation factor in a first sticking layer is less than 30% or exceeds 60%.SOLUTION: An electrostatic powder applying method comprises: a first applying process of discharging first powdered paint to apply a first sticking layer having an attenuation factor of 30%-60%, the attenuation factor being expressed by an absolute value of (Q30-Q300)/Q30, where Q30 is an electric charge amount of a sticking layer after 30 seconds from the finish of application and Q300 is an electric charge amount of the sticking layer after 300 seconds; a second applying process of applying a second sticking layer by discharging second powdered paint onto the first sticking layer; and a seizure process of heating and baking the first sticking layer and the second sticking layer.SELECTED DRAWING: None

Description

  The present invention relates to an electrostatic powder coating method.

  In recent years, powder coating technology using powder coatings has reduced the amount of volatile organic compounds (VOC) emitted in the coating process, and the powder coating that has not adhered to the object after coating has been reduced. Since it can be recovered and reused, it is attracting attention in terms of protecting the global environment. For this reason, various types of powder coating materials have been studied.

  Patent Document 1 describes a thermosetting powder coating material having an average particle size of 5 to 15 microns, a 90% cumulative particle size of 15 to 25 microns, and a spherical particle shape.

  Patent Document 2 discloses a powder paint obtained by mixing a conductive metal oxide fine powder having a volume resistivity of 1 to 100 Ω · cm in a powder paint particle by a melt-kneading method. A powder coating for electrostatic coating is described, characterized in that the metal oxide fine powder is 0.1 to 10.0% by weight in the powder coating.

  Patent Document 3 discloses 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 using a powder coating. In the method of forming a multilayer coating film having a plurality of coating layers, each powder coating material forming each coating film layer is sequentially laminated and adhered to an object to be coated. A method for forming a multilayer coating film by a powder coating is described.

  Patent Document 4 has a core containing a thermosetting resin and a thermosetting agent, a resin coating that covers the surface of the core, and has a volume particle size distribution index GSDv of 1.50 or less, an average A thermosetting powder coating having powder particles having a circularity of 0.96 or more is described.

  Patent Document 5 discloses a toning method in which at least two types of powder coatings having different colors are dry mixed to perform color matching, wherein the powder coating contains powder particles, Describes a toning method comprising a thermosetting resin and a thermosetting agent, having a volume average particle size of 3 μm to 10 μm and a GSDv of 1.3 or less.

  Patent Document 6 describes a thermosetting powder coating containing a thermosetting resin, a thermosetting agent, and a metal salt containing an aliphatic group having 5 to 20 carbon atoms.

  Patent Document 7 discloses a core part having a sea-island structure composed of an island part containing a surface conditioner and a sea part containing a thermosetting resin and a thermosetting agent, and a resin coating part covering the surface of the core part. A thermosetting powder coating is described that includes powder particles having the following:

  In Patent Document 8, the thermosetting resin A having a number average molecular weight of 100,000 or more is contained in the total resin in an amount of 5% by mass to 40% by mass, and the volume particle size distribution index GSDv is 1.50 or less. A thermosetting powder coating containing powder particles is described.

Japanese Patent Laid-Open No. 9-208855 Japanese Patent Application Laid-Open No. 11-100534 JP 2003-211083 A JP, 2015-233203, A JP, 2006-000794, A JP, 2006-006143, A JP, 2006-030785, A JP 2006-056332 A

When obtaining a coated product in which two types of powder coatings (coating films) are laminated, instead of heating (baking) each time an adhesion layer of each powder coating is applied, a coating is obtained. There is an electrostatic powder coating method in which a coating film is obtained by baking once after an adhesion layer of two kinds of powder paints is applied. Such a powder coating method is also called a 2-coat 1-bake method.
When a coating film is formed by a two-coat one-bake method using a conventional powder coating material, coating film roughness may occur in the resulting coating film.

  The present invention provides a powder coating material that suppresses the occurrence of coating film roughness of the obtained coating film as compared with the case where the attenuation rate in the first adhesion layer is less than 30% or exceeds 60%. With the goal.

The above problem is solved by the following means. That is,
The invention according to claim 1
(Q30-Q300) / Q30 when discharging the first powder coating and Q30 is the charge amount of the adhesion layer 30 seconds after the end of the coating, and Q300 is the charge amount of the adhesion layer after 300 seconds. A first application step of applying a first adhesion layer having an attenuation rate represented by an absolute value of 30% or more and 60% or less;
A second coating step of applying a second adhesive layer by discharging a second powder coating on the first adhesive layer;
An electrostatic powder coating method comprising: a baking step of heating and baking the first adhesion layer and the second adhesion layer.
The invention according to claim 2
According to the absolute value of (q30−q300) / q30, where q30 is the charge amount of the adhesion layer 30 seconds after the end of the coating in the second adhesion layer, and q300 is the charge amount of the adhesion layer after 300 seconds. The electrostatic powder coating method according to claim 1, wherein the attenuation rate is 30% or more and 60% or less.
The invention according to claim 3
The electrostatic powder coating method according to claim 2, wherein the second powder coating material includes powder particles and titania particles.
The invention according to claim 4
According to the absolute value of (q30−q300) / q30, where q30 is the charge amount of the adhesion layer 30 seconds after the end of the coating in the second adhesion layer, and q300 is the charge amount of the adhesion layer after 300 seconds. The electrostatic powder coating method according to claim 1, wherein the attenuation rate is less than 30%.
The invention according to claim 5
The electrostatic powder coating method according to claim 4, wherein the second powder coating material includes powder particles and silica particles.

  According to the first aspect of the present invention, the powder that suppresses the occurrence of coating film roughness of the obtained coating film as compared with the case where the attenuation rate in the first adhesion layer is less than 30% or exceeds 60%. Body paint is provided.

  According to the invention of claim 2, the powder that suppresses the occurrence of coating film roughness of the obtained coating film as compared with the case where the attenuation rate in the second adhesion layer is less than 30% or exceeds 60%. Body paint is provided.

  According to the invention of claim 3, there is provided a powder coating material that suppresses the occurrence of coating film roughness of the obtained coating film as compared with a case where the powder coating material includes powder particles and zinc oxide particles. Provided.

  According to the invention which concerns on Claim 4, compared with the case where the attenuation factor in a 2nd adhesion layer exceeds 60%, the powder coating material which suppresses generation | occurrence | production of the coating film roughness of the coating film obtained is provided.

  According to the invention which concerns on Claim 5, compared with the case where a powder coating material contains a powder particle and a titania particle, the powder coating material excellent in the smoothness of the coating film obtained is provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

(Electrostatic powder coating method)
In the electrostatic powder coating method of the present embodiment, the first powder coating material is discharged, the charge amount of the adhesion layer 30 seconds after the end of the coating is Q30, and the charge amount of the adhesion layer after 300 seconds is Q300. A first application step of applying a first adhesion layer having an attenuation rate represented by an absolute value of (Q30-Q300) / Q30 of 30% or more and 60% or less; A second coating step of applying a second adhesive layer by discharging a second powder coating material onto the adhesive layer; heating the first adhesive layer and the second adhesive layer; A baking step of baking.
According to the powder coating material of this embodiment, the occurrence of coating film roughness (also referred to as “defect”) of the coating film obtained after the baking process is suppressed. The reason is not clear, but is presumed as follows.

  Conventionally, powder coatings (powder particles) used for powder coating include binder resins and curing agents for curing the binder resins used as necessary, pigments for coloring, flame retardants, leveling agents, etc. The components are mixed and melted, and then pulverized to a desired particle size. The powder coating material manufactured in this way is applied to the object to be coated by a method such as electrostatic coating. The electrostatic coating method is a method in which powder particles charged by contact charging or corona discharge are discharged using a spray gun to electrostatically adhere the powder particles to a grounded workpiece.

However, when a coating film is formed by a 2-coat 1-bake method using a conventional powder coating, especially when the particle size of the powder particles contained in the first powder coating is small (for example, 10 μm or less) In some cases, the resulting coating film was rough.
Since the coating film roughness increases the total thickness of the adhesion layers by applying two adhesion layers (for example, the total thickness of the application layers is 50 μm or more), the first adhesion layer and the second adhesion layer It is presumed that this is caused by the accumulation of electric charge and the occurrence of electrostatic repulsion.
Electrostatic repulsion means that when the layer of powder particles becomes too thick, a charge opposite to that of the object to be coated is induced and the powder particles repel each other to form a circular (crater-shaped) dent. It means to make it.
Therefore, when the first powder coating material is discharged, the charge amount of the adhesion layer 30 seconds after the end of the coating is Q30, and the charge amount of the adhesion layer after 300 seconds is Q300 (Q30-Q300) / By applying the first adhesion layer having an attenuation rate represented by an absolute value of Q30 (also simply referred to as “attenuation rate”) of 30% or more and 60% or less, the occurrence of the coating film roughness is suppressed. The
When the attenuation rate of the first adhesion layer is 30% or more, charge leakage to the object to be coated (charge leakage) occurs, and accumulation of charge that causes electrostatic repulsion in the adhesion layer is eliminated. It is presumed that
In addition, when the first powder coating and the second powder coating are being discharged, the first adhesion layer includes the first adhesion layer because the attenuation rate of the first adhesion layer is 60% or less. Since the powder coating to be charged has an electric charge, it is excellent in electrostatic adhesion of the first powder coating or the second powder coating, and for example, it is suppressed that the powder particles are blown off by the air flow during application. A coating film is formed.
Hereinafter, details of each process included in the electrostatic powder coating method according to the present embodiment will be described.

<First coating process>
In the first coating step, the charged first powder paint is discharged, and the first powder paint is electrostatically attached to the object to be coated to apply the first adhesion layer.
Specifically, in the first coating step, for example, in a state where an electrostatic field is formed between the discharge port of the electrostatic powder coating machine and the coated surface (surface having conductivity) of the object to be coated, The first powder coating is discharged from the discharge port of the electrostatic powder coating machine, and the first powder coating is electrostatically attached to the surface to be coated. Apply. In other words, for example, a grounded surface to be coated is used as an anode, an electrostatic powder coating machine is used as a cathode, a voltage is applied, an electrostatic field (electrostatic field) is formed on both electrodes, and a charged powder coating is allowed to fly. Then, the powder coating film is formed by electrostatically adhering to the painted surface of the object to be coated.
In addition, you may implement in a coating process, moving relatively the discharge port of an electrostatic powder coating machine, and the coating surface of a to-be-coated object.

  Here, examples of the electrostatic powder coating machine include a corona gun (a coating machine that discharges powder coating charged by corona discharge), a tribo gun (a coating machine that discharges powder coating by friction charging), and a bell gun (corona discharge). Alternatively, a known electrostatic powder coating machine such as a coating machine that discharges powder paint charged by frictional charging by centrifugal spraying is used. The discharge conditions for achieving good coating may be the set range of each gun.

The amount of the powder coating adhered to the coated surface of the object to be coated is 20 g / m ² or more and 100 g / m ² or less (preferably 25 g / m ² or more and 50 g / m ²⁾ from the viewpoint of suppressing fluctuations in the smoothness of the coating film. m ² or less).

〔Attenuation rate〕
The attenuation rate in the first adhesion layer is 30% or more and 60% or less, preferably 30% or more and 55% or less, and more preferably 32% or more and 50% or less.
In this embodiment, the attenuation rate of the adhesion layer is (Q30-Q300) / Q30 when the charge amount of the adhesion layer 30 seconds after the end of coating is Q30 and the charge amount of the adhesion layer after 300 seconds is Q300. Expressed by the absolute value of Q30.
Q30 and Q300 are measured by the following method.

The charge amount of the adhesion layer is measured using a Faraday gauge, and is measured using a suction type small charge measuring device (a charge amount measuring device EA02 system manufactured by U-Tech Co., Ltd.).
The powder particles contained in the adhesion layer are directly taken into the Faraday gauge filter by a suction nozzle, and the charge amount and mass are measured to determine the charge amount per unit mass of the powder particles. The amount of charge per unit mass of the powder particles is measured at any 10 locations of the adhesion layer, and the arithmetic average value is taken as the amount of charge of the adhesion layer.

[First powder coating]
The first powder paint preferably contains powder particles and inorganic particles. Details of the preferred embodiment of the powder particles and the method for producing the first powder coating will be described later.

-Inorganic particles-
The first powder coating according to the present embodiment preferably includes powder particles and inorganic particles.
The inorganic particles are externally added to the surface of the powder particles.
The external addition method is not particularly limited, and a known external addition method can be used in the field of powder coating. Examples of inorganic particles include SiO ₂ , TiO ₂ , Al ₂ O ₃ , CuO, ZnO, and SnO. _{2, CeO 2, Fe 2 O} 3, MgO, BaO, CaO, K 2 O, Na 2 O, ZrO 2, CaO · SiO 2, K 2 O · (TiO 2) n, Al 2 O 3 · 2SiO 2, _{CaCO 3, MgCO 3, BaSO 4} , particles containing MgSO ₄ is preferred.
As the inorganic particles used in the present embodiment, titania particles or zinc oxide particles are preferable, and titania particles are more preferable from the viewpoint of suppressing coating film roughness of the coating film obtained by the powder coating.
As the crystal form of the titania particles, rutile type and anatase type are mainly known, and any of them can be used in this embodiment, but from the viewpoint of light resistance of the coating film, rutile. A mold is preferred.
In the present embodiment, the inorganic particles may be used alone or in combination of two or more.

<< particle size >>
The volume average particle size of the inorganic particles is preferably 10 nm to 100 nm, more preferably 15 nm to 90 nm, and still more preferably 20 nm to 80 nm.
When the volume average particle diameter of the inorganic particles is in the above range, the adhesion to the powder particles is excellent, and the coating film roughness of the coating film obtained by the powder coating is suppressed.
The volume average particle diameter of the inorganic particles is measured by the following method.
First, the powder coating material to be measured is observed with a scanning electron microscope (SEM). Then, the equivalent circle diameter of each of the 100 inorganic particles to be measured is obtained by image analysis, and the equivalent circle diameter of 50% on the volume basis from the small diameter side in the volume basis distribution is defined as the volume average particle diameter.
Image analysis for obtaining the equivalent circle diameter of 100 inorganic particles to be measured is performed by taking a two-dimensional image with a magnification of 10,000 times using an analysis apparatus (ERA-8900: manufactured by Elionix), and image analysis software WinROOF. (Mitani Corporation) is used to determine the projected area under the condition of 0.010000 μm / pixel, and the equivalent circle diameter is determined by the formula: equivalent circle diameter = 2 × (projected area / π) ^1/2 .
In order to measure the volume average particle diameter of a plurality of types of external additives from a powder coating material, it is necessary to distinguish each external additive. Specifically, each type of external additive corresponds to an element derived from each type of external additive by performing element mapping by SEM-EDX (scanning electron microscope with an energy dispersive X-ray analyzer). Distinguish by associating with external additives.

<< Aspect ratio >>
The aspect ratio of the inorganic particles is preferably 1 or more and 10 or less.
When the aspect ratio is in the above range, the inorganic particles are hardly released from the powder particles, and the coating film obtained is more suppressed from being rough.
The aspect ratio is preferably 1 or more and less than 2 and more preferably 1 or more and 1.5 or less from the viewpoint of further suppressing the coating film roughness of the powder particles.
The aspect ratio is preferably 2 or more and 5 or less, and more preferably 2.5 or more and 4.5 or less from the viewpoint of preventing the inorganic particles from being separated from the powder particles.
For the above aspect ratio, the image of the scanning electron microscope (SEM, manufactured by Hitachi High-Technologies Corporation, product name: SU8010) is applied to the inorganic particles on the powder particles, and the image analysis software (manufactured by Mitani Corp., product) By measuring the particle shape using a name: WinROOF, the ratio (L / S) of the major axis (L) to the minor axis (S) is measured.

<< Hydrophobic treatment >>
The surface of the inorganic particles used in the present embodiment may be previously hydrophobized, but is not excessively hydrophobized from the viewpoint of suppressing coating film roughness of the coating film obtained by the powder paint. It is preferable.
The hydrophobizing treatment can be performed by immersing the inorganic oxide particles in a hydrophobizing agent. Although there is no restriction | limiting in particular as said hydrophobic treatment agent, For example, a silane coupling agent, a silicone oil, a titanate coupling agent, an aluminum coupling agent etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together.

<< Volume resistivity >>
The inorganic particles used in this embodiment preferably have a volume resistivity of 1 × 10 ⁵ Ω · cm to 1 × 10 ¹³ Ω · cm, and preferably 1 × 10 ⁶ Ω · cm to 1 × 10 ¹² Ω · cm. It is more preferable that it is cm or less, and it is still more preferable that it is 1 × 10 ⁷ Ω · cm or more and 1 × 10 ¹¹ Ω · cm or less.
If the volume resistivity is within the above range, the coating film obtained by the powder coating is preferably prevented from being rough.
The volume resistivity of the inorganic particles is measured by the following method.
First, inorganic particles are separated from powder particles. Then, on the surface of a circular jig arranged 20 cm ² of the electrode plate, placing a discrete inorganic particles to be measured to a thickness on the order more than 3mm less 1 mm, to form the inorganic particle layer. A 20 cm ² electrode plate similar to the above is placed thereon, and an inorganic layer is sandwiched therebetween. In order to eliminate voids between the inorganic particles, a load of 4 kg is applied on the electrode plate placed on the inorganic particle layer, and then the thickness (cm) of the inorganic particle layer is measured. Both electrodes above and below the inorganic layer are connected to an electrometer and a high-voltage power generator. A high voltage is applied to both electrodes, and the current value (A) flowing at this time is read to calculate the volume resistivity (Ω · cm) of the inorganic particles. The above measurement is performed under conditions of a temperature of 20 ° C. and a relative humidity of 50%. The calculation formula of the volume resistivity (Ω · cm) of the inorganic particles is as shown in the following formula.
In the formula, ρ is the volume resistivity (Ω · cm) of the inorganic particles, E is the applied voltage (V), I is the current value (A), I ₀ is the current value (A) at an applied voltage of 0 V, and L is Represents the thickness (cm) of the inorganic particle layer. In this embodiment, the volume resistivity when the applied voltage is 1000 V is used.
Formula: ρ = E × 20 / (I−I ₀ ) / L

<< Content >>
The content of the inorganic particles is preferably 0.1% by mass or more and 3% by mass or less, and preferably 0.3% by mass or more with respect to the total mass of the powder particles, from the viewpoint of suppressing coating film roughness of the obtained coating film. 1.5 mass% or less is more preferable.

<Second coating process>
In the first coating step, the charged second powder coating material is discharged, and the second powder coating material is electrostatically attached onto the first adhesion layer to apply the second adhesion layer. .
As a method for discharging the second powder coating in the second coating step, a method similar to the method for attaching the first powder coating in the first coating step can be used, and the preferred embodiment is also the same. It is.

〔Attenuation rate〕
In the electrostatic powder coating method of the present embodiment, the attenuation rate in the second adhesion layer is preferably 60% or less, more preferably 30% or more and 60% or less, and 30% or more and 55% or less. More preferably, it is 30% or more and 50% or less.
If the attenuation rate in the second adhesion layer is 60% or less, the second powder coating is excellent in electrostatic adhesion while the second powder coating is being discharged. The powder particles are prevented from being blown off by the air current, and a coating film is easily formed.
Moreover, if the attenuation rate in a 2nd adhesion layer is 30% or more, coating-film roughness will be suppressed further. This is considered to be because the electrostatic repulsion between the second powder coating materials is suppressed.
In the electrostatic powder coating method of the present embodiment, since the surface of the first adhesion layer becomes almost flat, the second adhesion layer having an attenuation factor of less than 30% was applied. Even in this case, the occurrence of coating film roughness is suppressed.
When the attenuation rate in the second adhesion layer is less than 30%, the effect of suppressing the occurrence of coating film roughness is that the adhesion amount of the second powder coating material in the second adhesion layer is 20 g / m ² or more and 50 g. / M ² or less, particularly easily obtained.

[Second powder paint]
The second powder paint preferably contains powder particles and inorganic particles.
The second powder paint is preferably a clear paint.
Therefore, the powder particles contained in the second powder coating material preferably have a colorant content described below of less than 25% by mass and less than 20% by mass with respect to the total mass of the powder particles. More preferably, it is more preferably less than 10% by mass, particularly preferably less than 5% by mass, and most preferably less than 1% by mass. The minimum of content of the said coloring agent is not specifically limited, 0 mass% may be sufficient.
The powder particles contained in the second powder coating are synonymous with the powder particles contained in the first powder coating except for the content of the colorant, and the preferred embodiments are also the same. .
Moreover, the manufacturing method of a 2nd powder coating material is synonymous with the manufacturing method of a 1st powder coating material except content of the coloring agent in a powder particle being the said range, and its preferable aspect is also the same. .

-Inorganic particles-
The second powder paint according to this embodiment preferably contains inorganic particles. The inorganic particles are externally added to the surface of the powder particles.
When the attenuation rate in the second adhesion layer is 30% or more and 60% or less, the inorganic particles contained in the second powder coating are synonymous with the inorganic particles in the first powder coating described above, which is preferable. The aspect is also the same.
In addition, when the attenuation rate in the second adhesion layer is 30% or more and 60% or less, from the viewpoint of reducing coating unevenness, the inorganic particles contained in the first powder coating and the second powder coating It is preferable that the inorganic particles contained in are the same inorganic particles.

When the attenuation rate in the second adhesion layer is less than 30%, the inorganic particles contained in the second powder coating are not particularly limited, and SiO ₂ , TiO ₂ , Al ₂ O ₃ , CuO, ZnO, _{SnO 2, CeO 2, Fe 2} O 3, MgO, BaO, CaO, K 2 O, Na 2 O, ZrO 2, CaO · SiO 2, K 2 O · (TiO 2) n, Al 2 O 3 · 2SiO 2 , CaCO ₃ , MgCO ₃ , BaSO ₄ , MgSO _{4 and the} like, and silica particles (SiO ₂ particles) are preferable.
When the inorganic particles contain silica particles, the smoothness of the resulting coating film is excellent. This is presumably because the fluidity of the second powder coating is improved. The effect that the smoothness of the coating film is excellent is particularly easily obtained when the adhesion amount of the second powder coating material in the second adhesion layer is 20 g / m ² or more and 50 g / m ² or less.

The surface of the inorganic particles as the external additive is preferably subjected to a hydrophobic treatment. The hydrophobic treatment is performed, for example, by immersing inorganic particles in a hydrophobic treatment agent. The hydrophobizing agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, aluminum coupling agents and the like. These may be used individually by 1 type and may use 2 or more types together.
The amount of the hydrophobizing agent is usually 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles, for example.

  The volume average particle size of the inorganic particles is preferably 5 nm to 200 nm, more preferably 7 nm to 100 nm, and still more preferably 10 nm to 50 nm.

<Baking process>
In the baking step, the first adhesion layer and the second adhesion layer are heated to form a coating film (paint film). Specifically, the coating film is formed by melting and curing the powder particles of the powder coating film by heating.
The heating temperature (baking temperature) is selected according to the type of powder paint. As an example, the heating temperature (baking temperature) is preferably 90 ° C. or higher and 250 ° C. or lower, more preferably 100 ° C. or higher and 220 ° C. or lower, and still more preferably 120 ° C. or higher and 200 ° C. or lower. The heating time (baking time) is adjusted according to the heating temperature (baking temperature).

<To be painted>
Here, the object to be coated which is an object to be coated with the powder coating is not particularly limited, and examples thereof include various metal parts, ceramic parts, resin parts, and the like. These target articles may be unmolded articles before being molded into each article such as a plate-shaped article and a linear article, or molded for electronic parts, road vehicles, building interior / exterior materials, etc. It may be a product. In addition, the target article may be an article in which a surface to be coated is previously subjected to a surface treatment such as primer treatment, plating treatment, or electrodeposition coating.

  Hereinafter, the powder particles contained in the first powder coating material and the second powder coating material, and the manufacturing method of each powder coating material will be described.

<Powder particles>
The powder particles contained in the first powder coating and the second powder coating preferably contain a thermosetting resin and a thermosetting agent. The powder particles may contain a colorant and other additives as necessary.
The powder particles contained in the first powder paint are preferably colored powder paints in which the content of the colorant is 25% by mass or more based on the total mass of the powder particles.
The powder particles contained in the second powder coating material are preferably clear powder coating materials in which the content of the colorant is less than 25% by mass with respect to the total mass of the powder particles.
Further, from the viewpoint of suppressing color unevenness of the coating film, the thermosetting resin in the first powder coating and the thermosetting resin in the second powder coating are preferably the same resin.

[Thermosetting resin]
The thermosetting resin is a resin having a thermosetting reactive group. Examples of thermosetting resins include various types of resins conventionally used as powder particles in powder coatings.
The thermosetting resin is preferably a water-insoluble (hydrophobic) resin. When a water-insoluble (hydrophobic) resin is applied as the thermosetting resin, the environmental dependency of the charging characteristics of the powder coating material (powder particles) is reduced. Further, when the powder particles are produced by an aggregation and coalescence method, the thermosetting resin is preferably a water-insoluble (hydrophobic) resin from the viewpoint of realizing emulsification and dispersion in an aqueous medium. In addition, water-insoluble (hydrophobic) means that the amount of the target substance dissolved in 100 parts by mass of water at 25 ° C. is less than 5 parts by mass.

Examples of the thermosetting resin include thermosetting (meth) acrylic resin, thermosetting polyester resin, thermosetting fluorine-based resin (for example, fluoroethylene-vinyl ether (FEVE) copolymer resin), thermosetting epoxy, and the like. Examples thereof include at least one selected from the group consisting of a resin and a thermosetting epoxy-polyester resin. Among thermosetting resins, thermosetting polyester resins are preferred from the viewpoints of easy control of the charge train during coating, the strength of the coating film, and the beauty of the finish.
Examples of the thermosetting reactive group contained in the thermosetting polyester resin include an epoxy group, a carboxyl group, a hydroxyl group, an amide group, an amino group, an acid anhydride group, and a blocked isocyanate group. From the viewpoint, a carboxyl group and a hydroxyl group are preferable.

-Thermosetting polyester resin-
The thermosetting polyester resin is a polyester resin having a curing reactive group. Examples of the thermosetting reactive group contained in the thermosetting polyester resin include an epoxy group, a carboxyl group, a hydroxyl group, an amide group, an amino group, an acid anhydride group, and a blocked isocyanate group, from the viewpoint of easy synthesis. , Carboxyl group and hydroxyl group are preferred.

The thermosetting polyester resin is, for example, a polycondensate obtained by polycondensation of a polybasic acid and a polyhydric alcohol.
Introduction of the thermosetting reactive group of the thermosetting polyester resin is carried out by adjusting the amount of polybasic acid and polyhydric alcohol used when synthesizing the polyester resin. By this adjustment, a thermosetting polyester resin having at least one of a carboxyl group and a hydroxyl group as a thermosetting reactive group is obtained.
Moreover, after synthesizing the polyester resin, a thermosetting reactive group may be introduced to obtain a thermosetting polyester resin.

  Examples of polybasic acids include terephthalic acid, isophthalic acid, phthalic acid, methyl terephthalic acid, trimellitic acid, pyromellitic acid, anhydrides of these acids; succinic acid, adipic acid, azelaic acid, sebacic acid, Maleic acid, itaconic acid, anhydrides of these acids; fumaric acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid hexahydrophthalic acid, methylhexahydrophthalic acid, anhydrides of these acids; cyclohexanedicarboxylic acid, 2,6 -Naphthalene dicarboxylic acid etc. are mentioned.

  Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and neopentyl. Glycol, triethylene glycol, bis- (hydroxyethyl) terephthalate, cyclohexanedimethanol, octanediol, diethylpropanediol, butylethylpropanediol, 2-methyl-1,3-propanediol, 2,2,4-trimethylpentanediol Hydrogenated bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A, propylene oxide adduct of hydrogenated bisphenol A, trimethylolethane, trimethylolpropane, glycerin Pentaerythritol, tris-hydroxyethyl isocyanurate, hydroxypivalic valyl hydroxy pivalate and the like.

In the thermosetting polyester resin, monomers other than the polybasic acid and the polyhydric alcohol may be polycondensed.
Examples of other monomers include compounds having both a carboxyl group and a hydroxyl group in one molecule (for example, dimethanolpropionic acid, hydroxypivalate, etc.), monoepoxy compounds (for example, “Cardura E10 (manufactured by Shell)”) Etc.), various monohydric alcohols (for example, methanol, propanol, butanol, benzyl alcohol, etc.), various monovalent basic acids (for example, benzoic acid, p-tert-butylbenzoic acid). Acid), various fatty acids (for example, castor oil fatty acid, coconut oil fatty acid, soybean oil fatty acid, etc.) and the like.

  The thermosetting polyester resin may have a branched structure or a linear structure.

The thermosetting polyester resin is preferably a polyester resin having a total acid value and hydroxyl value of 10 mgKOH / g or more and 250 mgKOH / g or less and a number average molecular weight of 1000 or more and 100,000 or less.
When the sum of the acid value and the hydroxyl value is within the above range, the smoothness and mechanical properties of the coating film are easily improved. When the number average molecular weight is within the above range, the smoothness and mechanical properties of the coating film are improved, and the storage stability of the powder coating is easily improved.

  The acid value and hydroxyl value of the thermosetting polyester resin are measured in accordance with JIS K-0070-1992. Moreover, the measurement of the number average molecular weight of a thermosetting polyester resin is the same as the measurement of the number average molecular weight of the thermosetting (meth) acrylic resin mentioned later.

-Thermosetting (meth) acrylic resin-
The thermosetting (meth) acrylic resin is a (meth) acrylic resin having a thermosetting reactive group. For the introduction of the thermosetting reactive group into the thermosetting (meth) acrylic resin, a vinyl monomer having a thermosetting reactive group is preferably used. The vinyl monomer having a thermosetting reactive group may be a (meth) acrylic monomer (a monomer having a (meth) acryloyl group) or a vinyl monomer other than a (meth) acrylic monomer. It may be a mer.

  Here, examples of the thermosetting reactive group of the thermosetting (meth) acrylic resin include an epoxy group, a carboxyl group, a hydroxyl group, an amide group, an amino group, an acid anhydride group, and a (block) isocyanate group. . Among these, the thermosetting reactive group of the (meth) acrylic resin is at least one selected from the group consisting of an epoxy group, a carboxyl group, and a hydroxyl group from the viewpoint of easy production of the (meth) acrylic resin. Is preferred. In particular, it is more preferable that at least one of the thermosetting reactive groups is an epoxy group from the viewpoint of excellent storage stability and coating film appearance of the powder coating material.

  Examples of the vinyl monomer having an epoxy group as a curable reactive group include various chain epoxy group-containing monomers (for example, glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, glycidyl vinyl ether, allyl). Glycidyl ether), various (2-oxo-1,3-oxolane) group-containing vinyl monomers (for example, (2-oxo-1,3-oxolane) methyl (meth) acrylate, etc.), various alicyclics Examples thereof include an epoxy group-containing vinyl monomer (for example, 3,4-epoxycyclohexyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate, etc.)).

  Examples of the vinyl monomer having a carboxyl group as a curable reactive group include various carboxyl group-containing monomers (for example, (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, etc.), various types Monoesters of α, β-unsaturated dicarboxylic acid and monohydric alcohol having 1 to 18 carbon atoms (for example, monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monoisobutyl fumarate, mono tert-butyl fumarate) Monohexyl fumarate, monooctyl fumarate, mono 2-ethylhexyl fumarate, monomethyl maleate, monoethyl maleate, monobutyl maleate, monoisobutyl maleate, mono tert-butyl maleate, monohexyl maleate, monooctyl maleate, Mono-2-ethylhexyl maleate Itaconic acid monoalkyl ester (for example, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate, monoisobutyl itaconate, monohexyl itaconate, monooctyl itaconate, mono-2-ethylhexyl itaconate, etc.).

  Examples of the vinyl monomer having a hydroxyl group as a curable reactive group include various hydroxyl group-containing (meth) acrylates (for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxy Propyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, etc.) Addition reaction products of the above various hydroxyl group-containing (meth) acrylates and ε-caprolactone, various hydroxyl group-containing vinyl ethers (for example, 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxy Loxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 3-hydroxybutyl vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl vinyl ether, etc.), various hydroxyl group-containing vinyl ethers and ε-caprolactone Addition reaction products with various hydroxyl group-containing allyl ethers (for example, 2-hydroxyethyl (meth) allyl ether, 3-hydroxypropyl (meth) allyl ether, 2-hydroxypropyl (meth) allyl ether, 4-hydroxybutyl) (Meth) allyl ether, 3-hydroxybutyl (meth) allyl ether, 2-hydroxy-2-methylpropyl (meth) allyl ether, 5-hydroxypentyl (meth) allyl ether Ether, 6-hydroxyhexyl (meth) allyl ether), and addition reaction products of the various hydroxyl group-containing allyl ether and ε- caprolactone.

The thermosetting (meth) acrylic resin may be copolymerized with other vinyl monomers having no thermosetting reactive group, in addition to the (meth) acrylic monomer.
Examples of other vinyl monomers include various α-olefins (for example, ethylene, propylene, butene-1, etc.), various halogenated olefins other than fluoroolefins (for example, vinyl chloride, vinylidene chloride, etc.), and various aromatic vinyls. Monomers (for example, styrene, α-methylstyrene, vinyltoluene, etc.), diesters of various unsaturated dicarboxylic acids and monohydric alcohols having 1 to 18 carbon atoms (for example, dimethyl fumarate, diethyl fumarate, dibutyl fumarate) , Dioctyl fumarate, dimethyl maleate, diethyl maleate, dibutyl maleate, dioctyl maleate, dimethyl itaconate, diethyl itaconate, dibutyl itaconate, dioctyl itaconate, etc.), various acid anhydride group-containing monomers ( For example, maleic anhydride, itaconic anhydride, citraconic anhydride Acid, anhydrous (meth) acrylic acid, tetrahydrophthalic anhydride, etc.), various phosphate ester group-containing monomers (eg diethyl-2- (meth) acryloyloxyethyl phosphate, dibutyl-2- (meth) acryloyloxy) Butyl phosphate, dioctyl-2- (methacryloyloxyethyl phosphate, diphenyl-2- (meth) acryloyloxyethyl phosphate, etc.), various hydrolyzable silyl group-containing monomers (for example, γ- (meth) acryloyl) Oxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane), various aliphatic vinyl carboxylates (eg vinyl acetate, vinyl propionate, vinyl butyrate) , Vinyl isobutyrate, Vinyl pronate, vinyl caprylate, vinyl caprate, vinyl laurate, branched aliphatic vinyl carboxylate having 9 to 11 carbon atoms, vinyl stearate, etc.), various vinyl esters of carboxylic acids having a cyclic structure ( For example, vinyl cyclohexanecarboxylate, vinyl methylcyclohexanecarboxylate, vinyl benzoate, vinyl p-tert-butylbenzoate and the like.

In addition, in the thermosetting (meth) acrylic resin, when a vinyl monomer other than the (meth) acrylic monomer is used as the vinyl monomer having a thermosetting reactive group, it has a curable reactive group. Do not use acrylic monomers.
Examples of the acrylic monomer having no curable reactive group include (meth) acrylic acid alkyl esters (for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, (meth ) Isopropyl acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, (meth) acryl 2-ethylhexyl acid, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethyloctyl (meth) acrylate, dodecyl (meth) acrylate, isodecyl (meth) acrylate, (meth) acrylic acid Lauryl, stearyl (meth) acrylate, etc.) and various aryl esters of (meth) acrylate (For example, benzyl (meth) acrylate, phenyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc.), various alkyl carbitol (meth) acrylates (for example, ethyl carbitol (meth) acrylate, etc.), other various types (Meth) acrylic acid esters (for example, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate), (meth) acrylic acid tetrahydrofur Furyl etc.), various amino group-containing amide unsaturated monomers (for example, N-dimethylaminoethyl (meth) acrylamide, N-diethylaminoethyl (meth) acrylamide, N-dimethylaminopropyl (meth) acrylamide, N-diethylamino). Propyl (meth) acrylamide etc.), various dialkylaminoalkyl (meth) acrylates (eg dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate etc.), various amino group-containing monomers (eg tert-butylamino) Ethyl (meth) acrylate, tert-butylaminopropyl (meth) acrylate, aziridinylethyl (meth) acrylate, pyrrolidinylethyl (meth) acrylate, piperidinylethyl (meth) acrylate, and the like.

The thermosetting (meth) acrylic resin is preferably an acrylic resin having a number average molecular weight of 1,000 to 20,000 (preferably 1,500 to 15,000).
When the number average molecular weight is within the above range, the smoothness and mechanical properties of the coating film are easily improved.

  The weight average molecular weight and number average molecular weight of the thermosetting (meth) acrylic resin are measured by gel permeation chromatography (GPC). The molecular weight measurement by GPC is carried out with a THF solvent using a GPC / HLC-8120GPC manufactured by Tosoh Co., Ltd. and a column / TSKgel SuperHM-M (15 cm) manufactured by Tosoh Co., Ltd. as a measuring device. The weight average molecular weight and the number average molecular weight are calculated using a molecular weight calibration curve prepared from a monodisperse polystyrene standard sample from this measurement result.

  Thermosetting resins may be used alone or in combination of two or more.

20 mass% or more and 99 mass% or less are preferable with respect to the whole powder particle, and, as for content of a thermosetting resin, 30 mass% or more and 95 mass% or less are preferable.
As will be described later, when the thermosetting resin is applied as the resin of the resin coating portion when the powder particles are core / shell type particles, the content of the thermosetting resin is the core portion. And the total thermosetting resin content of the resin coating.

[Thermosetting agent]
A thermosetting agent is selected according to the kind of thermosetting reactive group of a thermosetting resin.
Here, a thermosetting agent means the compound which has a functional group which can react with respect to the thermosetting reactive group which is the terminal group of a thermosetting resin.

  When the thermosetting reactive group of the thermosetting resin is a carboxyl group, examples of the thermosetting agent include various epoxy resins (for example, polyglycidyl ether of bisphenol A), epoxy group-containing acrylic resins (for example, glycidyl group-containing acrylics). Resin), polyglycidyl ethers of various polyhydric alcohols (eg 1,6-hexanediol, trimethylolpropane, trimethylolethane, etc.), various polycarboxylic acids (eg phthalic acid, terephthalic acid, isophthalic acid, hexa Polyglycidyl esters of hydrophthalic acid, methylhexahydrophthalic acid, trimellitic acid, pyromellitic acid, etc., various alicyclic epoxy group-containing compounds (for example, bis (3,4-epoxycyclohexyl) methyl adipate), hydroxy Amides (eg triglycidyl isocyanate) Isocyanurate, beta-hydroxyalkyl amide) and the like.

  When the thermosetting reactive group of the thermosetting resin is a hydroxyl group, examples of the thermosetting agent include polyblock isocyanate and aminoplast. Examples of the polyblock polyisocyanate include various aliphatic diisocyanates (for example, hexamethylene diisocyanate and trimethylhexamethylene diisocyanate), various cyclic aliphatic diisocyanates (for example, xylylene diisocyanate and isophorone diisocyanate), and various aromatic diisocyanates (for example). For example, organic diisocyanates such as tolylene diisocyanate and 4,4′-diphenylmethane diisocyanate); adducts of these organic diisocyanates with polyhydric alcohols, low molecular weight polyester resins (for example, polyester polyols) or water; Polymers (polymers including isocyanurate type polyisocyanate compounds); various polyisotopes such as isocyanate and biuret bodies The Aneto Compound those that have been blocked with blocking agents known customary; and self-blocked polyisocyanate compound containing uretdione bond as a structural unit thereof.

  When the thermosetting reactive group of the thermosetting resin is an epoxy group, examples of the thermosetting agent include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, and eicosane. Diacid, maleic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, trimellitic acid, pyromellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexene-1,2-dicarboxylic acid, trimellitic acid, pyromellitic Acids such as acids; anhydrides of these acids; urethane modified products of these acids, and the like. Among these, as the thermosetting agent, an aliphatic dibasic acid is preferable from the viewpoint of coating film physical properties and storage stability, and dodecanedioic acid is particularly preferable from the viewpoint of coating film physical properties.

  A thermosetting agent may be used individually or in combination of 2 or more types.

1 mass% or more and 30 mass% or less are preferable with respect to thermosetting resin, and, as for content of a thermosetting agent, 3 mass% or more and 20 mass% or less are preferable.
As will be described later, when the thermosetting resin is applied as the resin of the resin coating portion when the powder particle is a core / shell type particle, the content of the thermosetting agent is as follows: It means content with respect to the total thermosetting resin of a resin coating part.

[Colorant]
Examples of the colorant include pigments. The colorant may use a dye together with the pigment.
Examples of the pigment include inorganic pigments such as iron oxide (eg, Bengala), titanium oxide, titanium yellow, zinc white, lead white, zinc sulfide, lithopone, antimony oxide, cobalt blue, and carbon black; quinacridone red, phthalocyanine blue, Organic pigments such as phthalocyanine green, permanent red, Hansa yellow, indanthrene blue, brilliant first scarlet, and benzimidazolone yellow are listed.
Other examples of pigments include glitter pigments. Examples of glitter pigments include metal powders such as pearl pigments, aluminum powder, and stainless steel powder; metal flakes; glass beads; glass flakes; mica; flake iron oxide (MIO).

  The colorants may be used alone or in combination of two or more.

The content of the colorant is selected according to the type of pigment and the color, brightness, depth, etc. required for the coating film.
For example, the content of the colorant is preferably 1% by mass or more and 70% by mass or less, and more preferably 2% by mass or more and 60% by mass or less based on the total resin constituting the powder particles.
In particular, in the powder particles in the first powder paint, the content of the colorant is preferably 25% by mass or more, and 25% by mass or more and 70% by mass with respect to the total mass of the powder particles. It is more preferable that the content is 30% by mass or more and 60% by mass or less.

  Here, the powder particles may contain a color pigment other than the white pigment as a colorant together with the white pigment. When the powder particles contain the white pigment together with the color pigment, the color of the surface of the object to be coated is concealed by the coating film, and the color developability of the color pigment is improved. Examples of the white pigment include well-known white pigments such as titanium oxide, barium sulfate, zinc oxide, and calcium carbonate. Titanium oxide is preferable in terms of high whiteness (that is, high concealability).

[Divalent or higher metal ions]
The powder particles preferably contain a divalent or higher valent metal ion (hereinafter also simply referred to as “metal ion”). As will be described later, this metal ion is a component contained in both the core of the powder particle and the resin coating when the powder particle is a core-shell type particle.
If the powder particles contain metal ions having a valence of 2 or more, the powder particles form ionic crosslinks by metal ions. For example, a functional group of a thermosetting resin (for example, when a thermosetting polyester resin is used as the thermosetting resin, a carboxyl group or a hydroxyl group of the thermosetting polyester resin) interacts with a metal ion, and ion crosslinking Form. A phenomenon (so-called phenomenon) in which the inclusion of powder particles (a thermosetting agent, a colorant added as necessary in addition to the thermosetting agent, other additives, etc.) precipitates on the surface of the powder particles due to this ionic crosslinking. , Bleeding) is suppressed, and the storability is easily increased. In addition, this ion cross-linking causes the melt viscosity of the powder particles to be lowered and the coating film with high smoothness to be formed by cutting the bond of the ion cross-links by heating during the heat curing after the powder coating is applied. It becomes easy to do.

  Examples of the metal ion include divalent to tetravalent metal ions. Specifically, examples of the metal ion include at least one metal ion selected from the group consisting of aluminum ion, magnesium ion, iron ion, zinc ion, and calcium ion.

Examples of the metal ion supply source (compound to be included in the powder particles as an additive) include metal salts, inorganic metal salt polymers, metal complexes, and the like. The metal salt and the inorganic metal salt polymer are added to the powder particles as a flocculant, for example, when the powder particles are produced by an aggregation coalescence method.
Examples of the metal salt include aluminum sulfate, aluminum chloride, magnesium chloride, magnesium sulfate, iron (II) chloride, zinc chloride, calcium chloride, calcium sulfate and the like.
Examples of the inorganic metal salt polymer include polyaluminum chloride, polyaluminum hydroxide, polyiron sulfate (II), and calcium polysulfide.
Examples of the metal complex include a metal salt of aminocarboxylic acid. Specific examples of the metal complex include metal salts based on known chelates such as ethylenediaminetetraacetic acid, propanediaminetetraacetic acid, nitriletriacetic acid, triethylenetetraminehexaacetic acid, diethylenetriaminepentaacetic acid (for example, calcium salts, Magnesium salt, iron salt, aluminum salt, etc.).

  In addition, you may add these metal ion supply sources not only as a flocculant use but as a mere additive.

  The higher the valence of the metal ions, the easier it is to form a network ion bridge, which is preferable in terms of the smoothness of the coating film and the storage property of the powder paint. For this reason, Al ion is preferable as the metal ion. That is, as a metal ion supply source, an aluminum salt (for example, aluminum sulfate, aluminum chloride or the like) or an aluminum salt polymer (for example, polyaluminum chloride or polyaluminum hydroxide) is preferable. Furthermore, in terms of the smoothness of the coating film and the storability of the powder coating, the inorganic metal salt polymer compared to the metal salt, even if the metal ion valence is the same among the metal ion supply sources. preferable. For this reason, as a metal ion supply source, an aluminum salt polymer (for example, polyaluminum chloride, polyaluminum hydroxide, etc.) is particularly preferable.

The content of the metal ions is preferably 0.002% by mass or more and 0.2% by mass or less, and 0.005% by mass with respect to the entire powder particles in terms of the smoothness of the coating film and the storage property of the powder coating. % To 0.15% by mass is more preferable.
When the content of metal ions is 0.002% by mass or more, moderate ionic cross-linking by metal ions is formed, bleed of the powder particles is suppressed, and the storability of the paint coating is easily increased. On the other hand, when the content of metal ions is 0.2% by mass or less, the formation of excessive ion crosslinking due to metal ions is suppressed, and the smoothness of the coating film is likely to be enhanced.

  Here, when powder particles are produced by an aggregation coalescence method, the metal ion supply source (metal salt, metal salt polymer) added as an aggregating agent contributes to the control of the particle size distribution and shape of the powder particles. To do.

  Specifically, the higher the valence of the metal ion, the better in obtaining a narrow particle size distribution. Further, in terms of obtaining a narrow particle size distribution, a metal salt polymer is preferable compared to a metal salt even if the valences of the metal ions are the same. Therefore, also from these points, the supply source of metal ions is preferably an aluminum salt (eg, aluminum sulfate, aluminum chloride, etc.) or an aluminum salt polymer (eg, polyaluminum chloride, polyaluminum hydroxide, etc.). A coalescence (for example, polyaluminum chloride, polyaluminum hydroxide, etc.) is particularly preferred.

  Further, when the flocculant is added so that the content of metal ions is 0.002% by mass or more, the aggregation of the resin particles in the aqueous medium proceeds and contributes to the realization of a narrow particle size distribution. Further, the aggregation of the resin particles serving as the resin coating portion proceeds with respect to the aggregated particles serving as the core portion, which contributes to the realization of the formation of the resin coating portion on the entire core surface. On the other hand, when a flocculant is added so that the content of metal ions is 0.2% by mass or less, excessive generation of ionic crosslinks in the agglomerated particles is suppressed, and the powder produced when coalescing and coalescing. The shape of the particles tends to approach a sphere. Therefore, also from these points, the content of metal ions is preferably 0.002% by mass or more and 0.2% by mass or less, and more preferably 0.005% by mass or more and 0.15% by mass or less.

  The content of metal ions is measured by quantitatively analyzing the fluorescent X-ray intensity of the powder particles. Specifically, for example, first, a resin and a metal ion supply source are mixed to obtain a resin mixture having a known metal ion concentration. A pellet sample is obtained from 200 mg of this resin mixture using a tableting machine having a diameter of 13 mm. The mass of the pellet sample is precisely weighed, and the fluorescent intensity of the pellet sample is measured to determine the peak intensity. Similarly, measurement is also performed on a pellet sample in which the addition amount of the metal ion supply source is changed, and a calibration curve is created from these results. Then, using this calibration curve, the metal ion content in the powder particles to be measured is quantitatively analyzed.

  As a method for adjusting the content of metal ions, for example, 1) a method of adjusting the addition amount of a source of metal ions, and 2) when powder particles are produced by an aggregation coalescence method, After adding a flocculant (eg, metal salt or metal salt polymer) as a source, at the end of the agglomeration step, a chelating agent (eg, EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), NTA (nitrilotriacetic acid) Etc.), a complex with a metal ion is formed by a chelating agent, a complex salt formed in a subsequent washing step or the like is removed, and the content of the metal ion is adjusted.

[Other additives]
Examples of other additives include various additives used in powder coatings.
Specifically, other additives include, for example, foaming inhibitors (eg, benzoin, benzoin derivatives, etc.), curing accelerators (amine compounds, imidazole compounds, cationic polymerization catalysts, etc.), surface conditioners ( Leveling agents), plasticizers, charge control agents, antioxidants, pigment dispersants, flame retardants, fluidizing agents, and the like.

[Core-shell type particles]
In the present embodiment, the powder particles may be core-shell type particles having a core portion containing a thermosetting resin and a thermosetting agent and a resin coating portion covering the surface of the core portion. .
Under the present circumstances, the core part may contain the other additive of the coloring agent mentioned above other than a thermosetting resin and a thermosetting agent as needed.

Moreover, the resin coating part in a core-shell type particle | grain is demonstrated below.
The resin coating part may be comprised only with resin, and may contain the other component (The thermosetting agent demonstrated as a component which comprises a core part, another additive, etc.).
However, from the viewpoint of reducing bleed, the resin coating portion is preferably made of only resin. In addition, even when a resin coating part contains other components other than resin, it is good that resin occupies 90 mass% or more (preferably 95 mass% or more) of the whole resin coating part.

The resin constituting the resin coating portion may be a non-curable resin or a thermosetting resin, but is a thermosetting resin from the viewpoint of improving the curing density (crosslinking density) of the coating film. It is good.
When a thermosetting resin is applied as the resin of the resin coating portion, examples of the thermosetting resin include the same ones as the thermosetting resin of the core portion, and preferred examples are also the same. However, the thermosetting resin of the resin coating portion may be the same type of resin as the thermosetting resin of the core portion, or may be a different resin.
In addition, when applying non-hardening resin as resin of a resin coating part, at least 1 sort (s) selected from the group which consists of an acrylic resin and a polyester resin is mentioned suitably as non-hardening resin.

  The coverage of the resin coating portion is preferably 30% or more and 100% or less, and more preferably 50% or more and 100% or less from the viewpoint of suppression of bleeding.

The coverage of the resin coating portion is a value obtained by XPS (X-ray photoelectron spectroscopy) measurement of the coverage of the resin coating portion on the powder particle surface.
Specifically, XPS measurement is performed by using JPS-9000MX manufactured by JEOL Ltd. as a measuring device, using MgKα ray as an X-ray source, setting acceleration voltage to 10 kV, and emission current to 30 mA. .
From the spectrum obtained under the above conditions, the coverage of the resin-coated part on the powder particle surface is determined by peak-separating the component resulting from the core material on the powder particle surface and the component resulting from the coating resin part material. Quantify. In peak separation, the measured spectrum is separated into each component using curve fitting by the least square method.
The component spectrum that is the base of separation is a spectrum obtained by independently measuring the thermosetting resin, the curing agent, the pigment, the additive, and the coating resin used for the production of the powder particles. And a coverage is calculated | required from the ratio of the spectrum intensity resulting from the resin for coating | cover with respect to the sum total of all the spectrum intensity | strengths obtained with the powder particle.

The thickness of the resin coating portion is preferably 0.2 μm or more and 4 μm or less, and more preferably 0.3 μm or more and 3 μm or less from the viewpoint of suppressing bleeding.
The thickness of the resin coating portion is a value measured by the following method. Thin sections are prepared by embedding powder particles in epoxy resin and cutting with a diamond knife. The thin slice is observed with a transmission electron microscope (TEM) or the like, and cross-sectional images of a plurality of powder particles are taken. From the cross-sectional image of the powder particles, the thickness of the resin coating portion is measured at 20 locations, and the average value is adopted. When it is difficult to observe the resin-coated portion in the cross-sectional image with a clear powder paint or the like, the measurement can be facilitated by observing after dyeing.

[Preferred characteristics of powder particles]
-Volume particle size distribution index GSDv-
The volume particle size distribution index GSDv of the powder particles is preferably 1.50 or less, more preferably 1.40 or less, and 1.30 or less in terms of the smoothness of the coating film and the storage property of the powder paint. Is more preferable. If volume particle size distribution parameter | index GSDv is 1.40 or less, the deterioration of the smoothness of a coating film will be suppressed.

-Volume average particle diameter D50v-
Further, the volume average particle diameter D50v of the powder particles is preferably 1 μm or more and 25 μm or less, more preferably 2 μm or more and 20 μm or less, and further preferably 3 μm or more and 15 μm or less from the viewpoint of forming a coating film with a small amount and high smoothness.

-Average circularity-
Furthermore, the average circularity of the powder particles is preferably 0.97 or more, more preferably 0.98 or more, and even more preferably 0.99 or more.
If the average circularity of the powder particles is 0.97 or more, it is possible to obtain a powder paint in which the occurrence of coating film roughness is suppressed.
Although the details of the mechanism for obtaining a powder coating material in which the occurrence of coating film roughness is suppressed are unknown, if the average circularity of the powder particles is 0.97 or more, the powder in the coating film is formed during the formation of the coating film. Since the density of the body particles is increased and the surface area per unit mass of the powder particles is reduced, the amount of charge retention of the powder particles in the coating film is also reduced, so that electrostatic repulsion between the powder particles is suppressed, It is estimated that the occurrence of coating film roughness is suppressed.

Here, the volume average particle diameter D50v and the volume particle size distribution index GSDv of the powder particles use Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolyte uses ISOTON-II (manufactured by Beckman Coulter). Measured.
In the measurement, 0.5 mg to 50 mg of a measurement sample is added as a dispersant to 2 ml of a 5% aqueous solution of a surfactant (preferably sodium alkylbenzenesulfonate). This is added to 100 ml or more and 150 ml or less of the electrolytic solution.
The electrolyte in which the sample is suspended is dispersed for 1 minute with an ultrasonic disperser, and the particle size distribution of particles having a particle size in the range of 2 μm to 60 μm is measured using a 100 μm aperture with a Coulter Multisizer II. taking measurement. The number of particles to be sampled is 50,000.
For the particle size range (channel) divided based on the measured particle size distribution, the cumulative distribution of the volume is drawn from the small diameter side, and the particle size that becomes 16% is the volume particle size D16v and the accumulation is 50%. The particle diameter is defined as a volume average particle diameter D50v, and the particle diameter at a cumulative 84% is defined as a volume particle diameter D84v.
The volume particle size distribution index (GSDv) is calculated as (D84v / D16v) ^1/2 .

  The average circularity of the powder particles is measured by using a flow type particle image analyzer “FPIA-3000 (manufactured by Sysmex Corporation)”. Specifically, a surfactant (alkylbenzene sulfonate) is added as a dispersant in an amount of 0.1 ml to 0.5 ml in 100 ml to 150 ml of water from which impure solids have been removed in advance. Add 1 g or more and 0.5 g or less. The suspension in which the measurement sample is dispersed is subjected to a dispersion treatment for 1 minute or more and 3 minutes or less with an ultrasonic disperser, and the dispersion concentration is adjusted to 3,000 / μl or more and 10,000 / μl or less. For this dispersion, the average circularity of the powder particles is measured using a flow particle image analyzer.

  Here, the average circularity of the powder particles is a value obtained by calculating the circularity (Ci) of each of the n particles measured for the powder particles and then calculating the following equation. In the following formula, Ci represents circularity (= peripheral length of a circle equal to the projected area of the particle / perimeter of the projected particle image), and fi represents the frequency of the powder particles.

(Production method of powder paint)
Next, the manufacturing method of the 1st powder coating material and 2nd powder coating material which concern on this embodiment is demonstrated.
The first powder coating and the second powder coating according to the present embodiment are obtained by externally adding an external additive to the powder particles after manufacturing the powder particles.

  The powder particles may be produced by any of a dry production method (for example, a kneading pulverization method) and a wet production method (for example, an aggregation coalescence method, a suspension polymerization method, a dissolution suspension method, etc.). The production method of the powder particles is not particularly limited, and a known production method is adopted.

For example, in the dry production method, 1) kneading, pulverizing, and classifying the thermosetting resin and other raw materials, and the shape of the particles obtained by kneading and pulverizing is changed by mechanical impact force or thermal energy. There are dry manufacturing methods.
On the other hand, in the wet manufacturing method, for example, 1) A dispersion obtained by emulsion polymerization of a polymerizable monomer for obtaining a thermosetting resin and a dispersion of other raw materials are mixed, and are aggregated and heat-sealed. Agglomeration and coalescence method for obtaining powder particles, 2) a suspension polymerization method in which a polymerizable monomer for obtaining a thermosetting resin and a solution of another raw material are suspended in an aqueous solvent for polymerization. There is a solution suspension method in which a thermosetting resin and a solution of another raw material are suspended in an aqueous solvent and granulated. The wet manufacturing method can be preferably used because it has a smaller thermal effect.
Alternatively, powder particles obtained by the above production method may be used as cores (cores), and resin particles may be further adhered and heat-fused to obtain powder particles that are core-shell type particles.

  Among these, it is preferable to obtain powder particles by the aggregation coalescence method from the viewpoint that the volume particle size distribution index GSDv, the volume average particle diameter D50v, and the average circularity can be easily controlled within the above preferable ranges.

Hereinafter, an example of an aggregation and coalescence method for producing powder particles that are core-shell type particles will be described.
In particular,
In the dispersion liquid in which the first resin particles containing the thermosetting resin and the thermosetting agent are dispersed, the first resin particles and the thermosetting agent are aggregated, or the thermosetting resin and the thermosetting are combined. A step of aggregating the composite particles in a dispersion in which composite particles containing an agent are dispersed to form first aggregated particles (first aggregated particle forming step);
The first aggregated particle dispersion in which the first aggregated particles are dispersed and the second resin particle dispersion in which the second resin particles containing a resin are dispersed are mixed, and the second aggregated particles are formed on the surface of the first aggregated particles. A step of aggregating resin particles to form second agglomerated particles in which the second resin particles adhere to the surface of the first agglomerated particles (second agglomerated particle forming step);
Heating the second aggregated particle dispersion in which the second aggregated particles are dispersed, and fusing and coalescing the second aggregated particles (fusion coalescence process);
Through this process, it is preferable to produce powder particles.
In the powder particles produced by this aggregation and coalescence method, the portion where the first aggregated particles are fused and united becomes the core, and the portion where the second resin particles attached to the surface of the first aggregated particles are fused and united Is the resin coating.
Therefore, if the first aggregated particles formed in the first aggregated particle formation step are not subjected to the second aggregated particle formation step, they are subjected to the fusion coalescence step, and instead of the second aggregated particles, fusion and coalescence are performed. Powder particles having a single layer structure are obtained.

Details of each step will be described below.
In addition, although the following description demonstrates the manufacturing method of the powder particle containing a coloring agent, a coloring agent is contained as needed.

<Each dispersion preparation step>
First, each dispersion used in the aggregation coalescence method is prepared.
Specifically, the first resin particle dispersion in which the first resin particles containing the thermosetting resin in the core are dispersed, the thermosetting agent dispersion in which the thermosetting agent is dispersed, and the colorant in which the colorant is dispersed. A second resin particle dispersion in which the second resin particles including the dispersion and the resin of the resin coating portion are dispersed is prepared.
Moreover, it replaces with a 1st resin particle dispersion and a thermosetting agent dispersion, and prepares the composite particle dispersion in which the composite particle containing the thermosetting resin for core parts and the thermosetting agent was disperse | distributed.
In each step of the powder coating production method, the first resin particles, the second resin particles, and the composite particles are generally referred to as “resin particles”, and a dispersion of these resin particles is referred to as a “resin particle dispersion”. Will be described.

  Here, the resin particle dispersion is prepared, for example, by dispersing resin particles in a dispersion medium using a surfactant.

Examples of the dispersion medium used for the resin particle dispersion include an aqueous medium.
Examples of the aqueous medium include water such as distilled water and ion exchange water; alcohols and the like. These may be used individually by 1 type and may use 2 or more types together.

Examples of the surfactant include anionic surfactants such as sulfate ester, sulfonate, phosphate, and soap; cationic surfactants such as amine salt type and quaternary ammonium salt type; Nonionic surfactants such as polyethylene glycol, alkylphenol ethylene oxide adducts, and polyhydric alcohols can be used. Among these, anionic surfactants and cationic surfactants are particularly mentioned. The nonionic surfactant may be used in combination with an anionic surfactant or a cationic surfactant.
Surfactant may be used individually by 1 type and may use 2 or more types together. Two or more kinds of surfactants are used, and the charge of the powder coating can be adjusted by slightly leaving a part of the surfactant due to the difference in solubility in water. In particular, the charge can be adjusted more by making the amount and type of the surfactant contained in the first powder coating and the second powder coating different.

Examples of the method for dispersing the resin particles in the dispersion medium in the resin particle dispersion include a general dispersion method such as a rotary shear homogenizer, a ball mill having media, a sand mill, and a dyno mill. Depending on the type of resin particles, the resin particles may be dispersed in the resin particle dispersion using, for example, a phase inversion emulsification method.
The phase inversion emulsification method is a method in which a resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, a base is added to the organic continuous phase (O phase), and the aqueous medium is neutralized. By introducing (W phase), conversion of the resin from W / O to O / W (so-called phase inversion) is performed to form a discontinuous phase, and the resin is dispersed in an aqueous medium in the form of particles. is there.

Specific methods for preparing the resin particle dispersion include the following methods.
For example, when the resin particle dispersion is a polyester resin particle dispersion in which polyester resin particles are dispersed, the polyester resin particle dispersion is obtained by heat-melting the raw material monomer and polycondensing under reduced pressure, and The condensate is dissolved by adding a solvent (for example, ethyl acetate or the like), and further, stirring and phase-inversion emulsification while adding a weak alkaline aqueous solution to the resulting solution.

  When the resin particle dispersion is a composite particle dispersion, the composite particle dispersion is obtained by mixing a thermosetting resin and a thermosetting agent and dispersing the mixture in a dispersion medium (for example, emulsification such as phase inversion emulsification). Get liquid

The volume average particle diameter of the resin particles dispersed in the resin particle dispersion is, for example, preferably 1 μm or less, preferably 0.01 μm or more and 1 μm or less, more preferably 0.08 μm or more and 0.8 μm or less, and 0.1 μm or more. 0.6 μm is more preferable.
In addition, the volume average particle diameter of the resin particles is based on the particle size range (channel) divided by using the particle size distribution obtained by measurement with a laser diffraction particle size distribution measuring apparatus (for example, LA-700 manufactured by Horiba, Ltd.). The cumulative distribution is subtracted from the small particle diameter side with respect to the volume, and the particle diameter that becomes 50% cumulative with respect to all the particles is measured as the volume average particle diameter D50v. The volume average particle size of particles in other dispersions is also measured in the same manner.

  Here, in order to prepare the resin particle dispersion, a known emulsification method can be used, but the obtained particle size distribution is narrow and the volume average particle size is 1 μm or less (particularly 0.08 μm or more and 0.40 μm or less). The phase inversion emulsification method, which is easy to be in the range of

  In the phase inversion emulsification method, the resin is dissolved in an organic solvent that dissolves the resin, an amphiphilic organic solvent alone, or a mixed solvent to obtain an oil phase. A small amount of a basic compound is dropped while stirring the oil phase, and water is dropped little by little while stirring, and water droplets are taken into the oil phase. Next, when the dripping amount of water exceeds a certain amount, the oil phase and the water phase are reversed and the oil phase becomes oil droplets. Thereafter, an aqueous dispersion is obtained through a desolvation step of depressurization.

  The amphiphilic organic solvent means a solvent having a solubility in water at 20 ° C. of at least 5 g / L or more, preferably 10 g / L or more. When the solubility is less than 5 g / L, the effect of accelerating the aqueous treatment rate is poor, and the resulting aqueous dispersion is also inferior in storage stability. Examples of the amphiphilic organic solvent include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol, and tert-amyl. Alcohols, alcohols such as 1-ethyl-1-propanol, 2-methyl-1-butanol, n-hexanol, cyclohexanol, ketones such as methyl ethyl ketone, methyl isobutyl ketone, ethyl butyl ketone, cyclohexanone, isophorone, tetrahydrofuran, dioxane Ethers such as ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, 3-methoxybutyl acetate, methyl propionate , Esters such as ethyl propionate, diethyl carbonate, dimethyl carbonate, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol ethyl ether acetate, diethylene glycol, diethylene glycol monomethyl Ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol ethyl ether acetate, propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene Glycol derivatives such as glycol methyl ether acetate and dipropylene glycol monobutyl ether, as well as 3-methoxy-3-methylbutanol, 3-methoxybutanol, acetonitrile, dimethylformamide, dimethylacetamide, diacetone alcohol, ethyl acetoacetate, etc. It is done. These solvents can be used singly or in combination of two or more.

The thermosetting polyester resin as the thermosetting resin is neutralized with a basic compound when dispersed in an aqueous medium. The neutralization reaction with the carboxyl group of the thermosetting polyester resin is the starting force for making the aqueous solution, and the electric repulsion between the generated carboxyl anions makes it easy to suppress aggregation between particles.
Examples of the basic compound include ammonia and organic amine compounds having a boiling point of 250 ° C. or lower. Examples of preferred organic amine compounds include triethylamine, N, N-diethylethanolamine, N, N-dimethylethanolamine, aminoethanolamine, N-methyl-N, N-diethanolamine, isopropylamine, iminobispropylamine, ethylamine , Diethylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, methylaminopropylamine, dimethylaminopropylamine, methyliminobispropylamine, 3-methoxypropylamine, monoethanolamine, diethanolamine, Examples include triethanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine and the like.
The basic compound is added in an amount that can be at least partially neutralized according to the carboxyl group contained in the thermosetting polyester resin, that is, 0.2 to 9.0 equivalents to the carboxyl group. It is preferable to add 0.6 equivalents or more and 2.0 equivalents or less. If it is 0.2 times equivalent or more, the effect of adding a basic compound is easily recognized. If it is 9.0 times equivalent or less, it is thought that excessive increase in the hydrophilicity of the oil phase is suppressed, but it is difficult to obtain a good dispersion because the particle size distribution is hardly widened.

  As content of the resin particle contained in a resin particle dispersion liquid, 5 to 50 mass% is preferable, for example, and 10 to 40 mass% is more preferable.

  Similar to the resin particle dispersion, for example, a thermosetting agent dispersion and a colorant dispersion are also prepared. That is, regarding the volume average particle diameter, dispersion medium, dispersion method, and particle content of the resin particles in the resin particle dispersion, the colorant particles dispersed in the colorant dispersion and the curing agent dispersion are dispersed. The same applies to the particles of the curing agent.

<First Aggregated Particle Formation Step>
Next, the first resin particle dispersion, the thermosetting agent dispersion, and the colorant dispersion are mixed.
Then, the first resin particles, the thermosetting agent, and the colorant having a diameter close to the diameter of the target powder particles are obtained by heteroaggregating the first resin particles, the thermosetting agent, and the colorant in the mixed dispersion. First agglomerated particles are formed.

  Specifically, for example, the flocculant is added to the mixed dispersion, and the pH of the mixed dispersion is adjusted to acidic (for example, the pH is 2 or more and 5 or less), and a dispersion stabilizer is added as necessary. Particles heated to the glass transition temperature of the first resin particles (specifically, for example, the glass transition temperature of the first resin particles −30 ° C. or more and the glass transition temperature −10 ° C. or less) and dispersed in the mixed dispersion liquid Are aggregated to form first aggregated particles.

  In the first aggregated particle forming step, a composite particle dispersion containing a thermosetting resin and a thermosetting agent and a colorant dispersion are mixed, and the composite particles and the colorant are mixed in the mixed dispersion. May be heteroaggregated to form first aggregated particles.

  In the first aggregated particle forming step, for example, the above-mentioned flocculant is added at room temperature (for example, 25 ° C.) while stirring the mixed dispersion with a rotary shearing homogenizer, and the pH of the mixed dispersion is acidic (for example, pH is 2 or more). 5 or less) and, if necessary, after adding a dispersion stabilizer, the heating may be performed.

Examples of the flocculant include surfactants having a polarity opposite to that of the surfactant used as the dispersant added to the mixed dispersion, metal salts, metal salt polymers, and metal complexes. When a metal complex is used as the aggregating agent, the amount of the surfactant used is reduced and the charging characteristics are improved.
In addition, after completion | finish of aggregation, you may use the additive which forms a complex or a similar bond with the metal ion of an aggregating agent as needed. As this additive, a chelating agent is preferably used. By adding this chelating agent, when the flocculant is added excessively, the adjustment of the metal ion content of the powder particles is realized.

  Here, the metal salt, metal salt polymer, and metal complex as the flocculant are used as a source of metal ions. These examples are as described above.

Examples of the chelating agent include water-soluble chelating agents. Specific examples of the chelating agent include oxycarboxylic acids such as tartaric acid, citric acid, and gluconic acid, iminodiacid (IDA), nitrilotriacetic acid (NTA), and ethylenediaminetetraacetic acid (EDTA).
The addition amount of the chelating agent is, for example, preferably 0.01 parts by mass or more and 5.0 parts by mass or less, and preferably 0.1 parts by mass or more and less than 3.0 parts by mass with respect to 100 parts by mass of the resin particles.

<Second Aggregated Particle Formation Step>
Next, the first aggregated particle dispersion in which the obtained first aggregated particles are dispersed is mixed with the second resin particle dispersion.
The second resin particles may be the same type as the first resin particles or different types.

  Then, in the mixed dispersion liquid in which the first aggregated particles and the second resin particles are dispersed, the aggregates so that the second resin particles adhere to the surface of the first aggregated particles, 2nd aggregated particles to which 2 resin particles are attached are formed.

Specifically, for example, in the first aggregated particle forming step, when the first aggregated particle reaches a target particle size, the second aggregated particle dispersion is mixed with the second resin particle dispersion, The mixed dispersion is heated below the glass transition temperature of the second resin particles.
Then, the progress of aggregation is stopped by setting the pH of the mixed dispersion to a range of, for example, about 6.5 to 8.5.

  Thereby, the second aggregated particles aggregated so that the second resin particles adhere to the surface of the first aggregated particles are obtained. The charge can be adjusted by the amount and pH of the second resin particles.

<Fusion coalescence process>
Next, with respect to the second agglomerated particle dispersion in which the second agglomerated particles are dispersed, for example, the glass transition temperature of the first and second resin particles is higher than the glass transition temperature (for example, 10 from the glass transition temperature of the first and second resin particles). To 30 ° C. or higher temperature), the second aggregated particles are fused and united to form powder particles.

  Through the above steps, powder particles are obtained.

Here, after the fusion and coalescence process is completed, the powder particles formed in the dispersion are obtained through a known washing process, solid-liquid separation process, and drying process to obtain powder particles.
In the washing step, it is preferable to sufficiently carry out substitution washing with ion-exchanged water from the viewpoint of chargeability. The solid-liquid separation step is not particularly limited, but suction filtration, pressure filtration, and the like are preferably performed from the viewpoint of productivity. In addition, the drying process is not particularly limited, but from the viewpoint of productivity, freeze drying, airflow drying, fluidized drying, vibration fluidized drying, or the like is preferably performed.

And the powder coating material which concerns on this embodiment is manufactured by adding an inorganic particle to the obtained powder particle of the dried state, and mixing.
In addition, it is good to perform said mixing with a V blender, a Henschel mixer, a Ladige mixer, etc., for example.
Furthermore, if necessary, coarse particles of the powder particles may be removed using a vibration sieving machine, a wind sieving machine, or the like.

(Electrostatic powder coating method)
The electrostatic powder coating method according to the present embodiment is the powder coating according to the above-described present embodiment, in which the charged powder coating is ejected and the powder coating is adhered to the object to be coated (coating). And a step of heating the powder coating material adhered to the object to be coated to form a coating film (hereinafter also referred to as “baking step”).
Hereinafter, each step will be described.

<Coating process>
In the coating step, the charged first powder coating is discharged, and the powder coating is electrostatically attached (coated) to the object to be coated to form an adhesion layer.
Specifically, in the coating process, for example, electrostatic powder is formed in a state where an electrostatic field is formed between the discharge port of the electrostatic powder coating machine and the coating surface (surface having conductivity) of the object to be coated. The charged powder coating is discharged from the discharge port of the body coating machine, and the powder coating is electrostatically attached to the surface to be coated of the object to be coated, and the adhesion layer is applied. In other words, for example, a grounded surface to be coated is used as an anode, an electrostatic powder coating machine is used as a cathode, a voltage is applied, an electrostatic field (electrostatic field) is formed on both electrodes, and a charged powder coating is allowed to fly. Then, the powder coating film is formed by electrostatically adhering to the painted surface of the object to be coated.
Thereafter, the second first powder coating material is discharged, and the second powder coating material is discharged onto the adhesion layer of the first powder coating material to apply the second adhesion layer. The conditions for forming the electrostatic field are preferably the same as those for discharging the first powder coating material, but can be changed depending on the difference in the charge of the powder.
In addition, you may implement in a coating process, moving relatively the discharge port of an electrostatic powder coating machine, and the coating surface of a to-be-coated object.

  Here, examples of the electrostatic powder coating machine include a corona gun (a coating machine that discharges powder coating charged by corona discharge), a tribo gun (a coating machine that discharges powder coating by friction charging), and a bell gun (corona discharge). Alternatively, a known electrostatic powder coating machine such as a coating machine that discharges powder paint charged by frictional charging by centrifugal ejection is used. The discharge conditions for achieving good coating may be the set range of each gun.

The total amount of the powder coating to be applied to the coated surface of the object to be coated is 20 g / m ² or more and 100 g / m ² or less (preferably 25 g / m ² or more and 50 g from the viewpoint of suppressing fluctuations in the smoothness of the coating film. / M ² or less).
On the other hand, if the coating film formed on the object to be coated is thick, that is, the amount of adhesion increases (for example, the amount of adhesion is 120 g / m ² or more), the charge is more likely to accumulate, so It tends to occur. However, according to the present embodiment, as described above, charge accumulation in the adhesion layer is reduced, and the occurrence of coating film roughness (scratch marks) is suppressed.

<Baking process>
In the baking process, the adhesion layer is heated to form a paint film (paint film). Specifically, the coating film is formed by melting and curing the powder particles of the powder coating film by heating.
The heating temperature (baking temperature) is selected according to the type of powder paint. As an example, the heating temperature (baking temperature) is preferably 90 ° C. or higher and 250 ° C. or lower, more preferably 100 ° C. or higher and 220 ° C. or lower, and further preferably 120 ° C. or higher and 200 ° C. or lower. The heating time (baking time) is adjusted according to the heating temperature (baking temperature).

<To be painted>
Here, the object to be coated which is an object to be coated with the powder coating is not particularly limited, and examples thereof include various metal parts, ceramic parts, resin parts, and the like. These target articles may be unmolded articles before being molded into each article such as a plate-shaped article and a linear article, or molded for electronic parts, road vehicles, building interior / exterior materials, etc. It may be a product. In addition, the target article may be an article in which a surface to be coated is previously subjected to a surface treatment such as primer treatment, plating treatment, or electrodeposition coating.

  Hereinafter, although an embodiment explains this embodiment in detail, this embodiment is not limited to these examples at all. In the following description, “part” and “%” are all based on mass unless otherwise specified.

(Preparation of powder paint)
<Preparation of white pigment dispersion (W1)>
-Titanium oxide (A-220 manufactured by Ishihara Sangyo): 100 parts by mass-Anionic surfactant (Daiichi Kogyo Seiyaku Co., Ltd .: Neogen RK): 15 parts by mass-Nonionic surfactant (Nippon Emulsifier Co., Ltd .: New Coal 2310) : 0.2 parts ・ Ion-exchanged water: 400 parts by mass ・ 0.3 mol / l nitric acid: 4 parts by mass The above is mixed and dissolved, and a high-pressure impact disperser optimizer (manufactured by Sugino Machine Co., Ltd., HJP30006). Was used for 3 hours to prepare a white pigment dispersion liquid in which titanium oxide was dispersed. When measured using a laser diffraction particle size measuring instrument, the volume average particle diameter of titanium oxide in the pigment dispersion was 0.25 μm, and the solid content ratio of the white pigment dispersion was 25%.

<Preparation of polyester resin / curing agent composite dispersion (E1)>
While maintaining a jacketed reactor equipped with a condenser, thermometer, water dropping device and anchor blade (Tokyo Rika Kikai Co., Ltd .: BJ-30N) at 40 ° C. in a water circulating thermostatic chamber, acetic acid was added to the reactor. A mixed solvent of 180 parts by mass of ethyl and 80 parts by mass of isopropyl alcohol was added, and the following composition was added thereto.
Polyester resin (PES1) [terephthalic acid / ethylene glycol / neopentyl glycol / trimethylolpropane polycondensate (molar ratio = 100/60/38/2 (mol%), glass transition temperature = 62 ° C., acid value ( Av) = 12 mgKOH / g, hydroxyl value (OHv) = 55 mgKOH / g, weight average molecular weight (Mw) = 12,000, number average molecular weight (Mn) = 4,000]: 240 parts by mass Blocked isocyanate curing agent VESTAGONB 1530 ( EVONIK Co.): 60 parts by mass Benzoin: 1.5 parts by mass Acrylic oligomer (Acronal 4F BASF): 3 parts by mass

After the addition, the mixture was stirred at 150 rpm using a three-one motor and dissolved to obtain an oil phase. A mixture of 1 part by mass of a 10% by mass aqueous ammonia solution and 47 parts by mass of a 5% by mass aqueous sodium hydroxide solution was added dropwise to the stirred oil phase in 5 minutes, followed by mixing for 10 minutes, and further ion exchange. 900 parts by mass of water was added dropwise at a rate of 5 parts by mass to invert the phase to obtain an emulsion.
Immediately, 800 parts by mass of the obtained emulsion and 700 parts by mass of ion-exchanged water were placed in a 2-liter eggplant flask, and placed in an evaporator (manufactured by Tokyo Rika Kikai Co., Ltd.) equipped with a vacuum control unit via a trap ball. I set it. While rotating the eggplant flask, it was heated in a hot water bath at 60 ° C., and the pressure was reduced to 7 kPa while paying attention to bumping to remove the solvent. When the solvent recovery amount reached 1100 parts by mass, the pressure was returned to normal pressure, and the eggplant flask was cooled with water to obtain a dispersion. There was no solvent odor in the obtained dispersion. The volume average particle diameter of the resin particles in this dispersion was 145 nm. Then, 2% by mass of an anionic surfactant (Dow Chemical, Dowfax 2A1, effective component amount 45% by mass) is added and mixed as an active component with respect to the resin component in the dispersion. The concentration was adjusted to 25% by mass. This was designated as a polyester resin / curing agent composite dispersion (E1).

<Preparation of white powder particles (1)>
-Aggregation process-
Polyester resin / curing agent composite dispersion (E1): 180 parts by mass (solid content 45 parts by mass)
White pigment dispersion (W1): 160 parts by mass (solid content 40 parts by mass)
-Ion-exchanged water: 200 parts by mass The above was mixed and dispersed in a round stainless steel flask using a homogenizer (manufactured by IKA, Ultra Turrax T50). Subsequently, pH was adjusted to 3.5 using 1.0 mass% nitric acid aqueous solution. To this, 0.50 part by mass of a 10% by mass aqueous polyaluminum chloride solution was added, and the dispersion operation was continued with an ultra turrax.
A stirrer and a mantle heater were installed, the temperature was raised to 50 ° C. while adjusting the number of revolutions of stirring so that the slurry was sufficiently stirred, and held at 50 ° C. for 15 minutes. 10 parts were added. The particle diameter of the aggregated particles was measured with a Coulter counter [Multisizer-II] type (aperture diameter: 50 μm, manufactured by Beckman-Coulter). When the volume average particle diameter became 5.5 μm, a polyester resin 60 parts by mass of the curing agent composite dispersion (E1) was slowly added. .

-Fusion integration process-
After holding for 30 minutes, the pH was adjusted to 7.0 using a 5% aqueous sodium hydroxide solution. Then, it heated up to 85 degreeC and hold | maintained for 2 hours.

-Filtration, washing, drying process-
After completion of the reaction, the solution in the flask was cooled and filtered to obtain a solid content. Next, this solid content was washed with ion-exchanged water and then solid-liquid separated by Nutsche suction filtration to obtain a solid content again.
Next, this solid content was redispersed in 3 liters of ion-exchanged water at 40 ° C., and stirred and washed at 300 rpm for 15 minutes. This washing operation was repeated 5 times, and the solid content obtained by solid-liquid separation by Nutsche suction filtration was vacuum-dried for 12 hours to obtain white powder particles (1).

  When the particle diameter of the white powder particles (1) was measured, the volume average particle diameter D50v was 6.1 μm, and the volume average particle size distribution index GSDv was 1.24. The average circularity was 0.98.

<Preparation of clear powder particles (1)>
Clear powder particles (1) were produced by the same method as the production of white powder particles (1) except that the white pigment powder particles were not added in the above-described aggregation step.
When the particle size of the clear powder particles (1) was measured, the volume average particle size D50v was 6.4 μm, and the volume average particle size distribution index GSDv was 1.24. The average circularity was 0.97.

<Preparation of white colored powder particles (2)>
Titanium oxide (A-220 manufactured by Ishihara Sangyo): 200 parts by mass Polyester resin (PES1) [terephthalic acid / ethylene glycol / neopentyl glycol / trimethylolpropane polycondensate (molar ratio = 100/60/38/2) (Mol%), glass transition temperature = 62 ° C., acid value (Av) = 12 mgKOH / g, hydroxyl value (OHv) = 55 mgKOH / g, weight average molecular weight (Mw) = 12,000, number average molecular weight (Mn) = 4,000]: 240 parts by mass Blocked isocyanate curing agent VESTAGON 1530 (manufactured by EVONIK): 60 parts by mass Benzoin: 1.5 parts by mass Acrylic oligomer (Acronal 4F BASF): 3 parts by mass or more in a mixer Mix and then knead while heating to 100 ° C with an extruder. After roughly pulverizing to make flakes, the mixture was finely pulverized with a turbo mill to a particle size of 6 μm and classified to obtain a kneaded pulverized white powder coating material.
When the particle size of the white powder particles (2) was measured, the volume average particle size D50v was 6.81 μm, and the volume average particle size distribution index GSDv was 1.13.

  Details of the inorganic particles used in the examples are shown in Table 1 below.

(Preparation of white powder paint (PCC1))
White powder particles (1): 100 parts by mass, inorganic particles M1: 1.2 parts by mass, hydrophobic silica particles having a volume average particle size of 12 nm (R974, manufactured by Nippon Aerosil Co., Ltd.): 0.5 parts by mass Were mixed at a peripheral speed of 32 m / s for 10 minutes using a Henschel mixer, and then coarse particles were removed using a sieve of 45 μm mesh to obtain a white powder coating material (PCC1).

Hereinafter, it is PCC2-PCC9 which is a colored powder paint, and a clear powder paint in the same manner as in Example 1 except that the blue powder particles and inorganic particles used are changed as shown in Table 2 below. PCCL1 to PCCL9 were obtained.
In addition, in PCCL9, the addition of the inorganic particles corresponding to M1 to M8 described above was not performed, and the addition amount of the hydrophobic silica particles was changed from 0.5 parts by mass to 0.6 parts by mass.

(Examples 1 to 12, Comparative Examples 1 to 6)
Each powder coating was used and electrostatic powder coating was performed as follows.

<Electrostatic powder coating>
Each powder coating material was loaded into a corona gun XR4-110C manufactured by Asahi Sunac.
Asahi Sunac Corona Gun XR4-110C is moved up and down at a distance of 30 cm from the front of the panel (distance between the panel and the corona gun discharge port) against a 30 cm x 30 cm square test panel (coated object) of a mirror-finished aluminum plate. By sliding left and right, the first powder coating material shown in Table 3 was discharged and electrostatically adhered to the panel to obtain a first adhesion layer. The applied voltage of the corona gun is 80 kV, the input air pressure is 0.55 MPa, the discharge amount is 200 g / min, and the adhesion amount of the powder paint to be adhered to the panel is 25 g / m ² , 45 g / m ² , 90 g / m ² , or Four coatings with 110 g / m ² were performed.
In Comparative Example 1 and Comparative Example 4, the second powder coating material is not discharged, and the amount of the first powder coating material applied is 50 g / m ² , 90 g / m ² , 180 g / m ² , or 220 g / m ² .
Then, the second powder coating is discharged to the panel to which the first powder coating is electrostatically attached so that the second powder coating is equivalent to the first powder coating under the same conditions. Got.
Thereafter, each panel was placed in a high temperature chamber set at 180 ° C. and heated (baked) for 30 minutes.

<Evaluation of coating roughness>
The surface of the coating film after being baked by the above method for each adhesion amount was observed and evaluated by the following four-stage evaluation. The evaluation results are shown in Table 3.
1: Coating film roughness is not recognized on the coating film surface.
2: Slight coating film roughness is recognized.
3: Coating film roughness is recognized.
4: On the coated surface, a coating film cannot be formed, and there is a place where the square test panel is visually recognized.

<Evaluation of light resistance>
Was prepared in the evaluation of rough coating, the panel adhering amount of the powder coating is 50.0 g / ^{m 2,} 500 hours, the light irradiation (light source: xenon lamp, irradiance: 540W ^/ m 2 = 100k lux , Without UV cut filter).
After the light irradiation, the surface of the coating film was wiped off with a cloth containing water, and the coating film was evaluated in the same manner as described above. The evaluation results are shown in Table 3.

Claims (5)

(Q30-Q300) / Q30 when discharging the first powder coating and Q30 is the charge amount of the adhesion layer 30 seconds after the end of the coating, and Q300 is the charge amount of the adhesion layer after 300 seconds. A first application step of applying a first adhesion layer having an attenuation rate represented by an absolute value of 30% or more and 60% or less;
A second coating step of applying a second adhesive layer by discharging a second powder coating on the first adhesive layer;
An electrostatic powder coating method comprising: a baking step of heating and baking the first adhesion layer and the second adhesion layer.   According to the absolute value of (q30−q300) / q30, where q30 is the charge amount of the adhesion layer 30 seconds after the end of the coating in the second adhesion layer, and q300 is the charge amount of the adhesion layer after 300 seconds. The electrostatic powder coating method according to claim 1, wherein the attenuation rate is 30% or more and 60% or less.   The electrostatic powder coating method according to claim 2, wherein the second powder coating material includes powder particles and titania particles.   According to the absolute value of (q30−q300) / q30, where q30 is the charge amount of the adhesion layer 30 seconds after the end of the coating in the second adhesion layer, and q300 is the charge amount of the adhesion layer after 300 seconds. The electrostatic powder coating method according to claim 1, wherein the attenuation rate is less than 30%.   The electrostatic powder coating method according to claim 4, wherein the second powder coating material includes powder particles and silica particles.