JP6926570B2 - Powder coating and electrostatic powder coating method - Google Patents

Description

The present invention relates to a powder coating method and an electrostatic powder coating method.

In recent years, powder coating technology using powder coatings has been used to produce powder coatings that emit less volatile organic compounds (VOCs) in the coating process and do not adhere to the object to be coated after coating. Since it can be collected and reused, it is attracting attention in terms of protecting the global environment. Therefore, various powder coating materials have been studied.

Patent Document 1 describes a powder coating composition obtained by mixing needle-like conductive titanium oxide fine powder with paint powder by a dry blend method, and the needle-like conductive titanium oxide fine powder is the paint powder 100. A powder coating composition for electrostatic coating, which is 0.1 to 10.0 parts by weight with respect to parts by weight, is described.

^{Patent Document 2 states that conductive zinc oxide fine particles having a volume specific resistance of 1 × 10 4} Ω · cm or less on the surface of powder particles composed of at least a binder resin and a curing agent and having a volume average particle size of 5 to 20 μm. A powder coating material to which powder or conductive titanium oxide fine powder is adhered or fixed is described.

Patent Document 3 has a core portion containing a thermosetting resin and a thermosetting agent, and a resin coating portion that covers the surface of the core portion, and has a volume particle size distribution index GSDv of 1.50 or less, which is an average. A thermosetting powder coating material having powder particles having a circularity of 0.96 or more is described.

Patent Document 4 describes a color matching method in which at least two types of powder coating materials having different colors are dry-mixed and color-matched. The powder coating material contains powder particles, and the powder particles contain powder particles. , A color matching method containing a thermosetting resin and a thermosetting agent, having a volume average particle diameter of 3 μm or more and 10 μm or less, and a GSDv of 1.3 or less is described.

Patent Document 5 describes a thermosetting powder coating material containing a thermosetting resin, a thermosetting agent, and a metal salt containing an aliphatic group having 5 or more and 20 or less carbon atoms.

Patent Document 6 describes a core portion having a sea-island structure composed of an island portion containing a surface conditioner and a sea portion containing a thermosetting resin and a thermosetting agent, and a resin coating portion covering the surface of the core portion. Described are thermosetting powder coatings, including powder particles having.

In Patent Document 7, 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 or more and 40% by mass or less, and the volume particle size distribution index GSDv is 1.50 or less. Thermosetting powder coatings containing powder particles are described.

JP-A-11-106683 Japanese Unexamined Patent Publication No. 8-253711 JP-A-2015-23063 Japanese Unexamined Patent Publication No. 2016-000794 Japanese Unexamined Patent Publication No. 2016-006143 JP-A-2016-030785 Japanese Unexamined Patent Publication No. 2016-0563332

The powder coating material used in the electrostatic powder coating method is charged by contact charging or corona discharge, and then ejected onto the object to be coated to electrostatically adhere to it, and then heated to form a coating film. Is formed. However, in the adhesive layer formed by electrostatically adhering the powder paint on the object to be coated, the powder particles burst from the adhesive layer to generate circular or crater-like dents (pop marks), and then. Even in the coating film formed through the heating step, the dents may remain and the coating film may become rough.

_{An object of the present invention is that the attenuation rate [30-300]} from the load amount Q30 30 seconds after the end of adhesion to the charge amount Q300 300 seconds after the end of adhesion in the adhesion layer adhered to the substrate with the following adhesion amount is 30%. It is an object of the present invention to provide a powder coating material capable of suppressing the occurrence of coating film roughness in a coating film formed by adhering to and heating an object to be coated as compared with the case where the amount is less than or equal to less than.

The above problem is solved by the following means. That is,
< 1 >
Wherein the powder particles, and inorganic particles, and
"(Q30-Q300)" in the case where the charge amount 30 seconds after the end of adhesion is Q30 and the charge amount 300 seconds after the end of adhesion is Q300 in the adhesion layer having an adhesion amount of 100 g / m ^{2 adhered to the substrate.} _{A powder coating material having a decay rate [30-300]} (%) represented by an absolute value of "/ Q30" of 30% or more and 60% or less.

< 2 >
Absolute value by the attenuation rate expressed in "(Q30-Q100) / Q30" when the charge amount after 100 seconds deposition ends before SL deposited layer was Q100 _[30-100] (%) is more than 5% The powder coating according to < 1 > , which is 20% or less.

< 3 >
Before a volume average particle diameter of Kikotai particles is 3μm or more 10μm or less <1> or powder paint according to <2>.

< 4 >
Before SL volume average particle diameter of the inorganic particles is 10nm or more 100nm or less <1> to <3> Powder paint according to any one of.

< 5 >
Before SL aspect ratio of the inorganic particles, 1 to 5 or less <1> to <4> Powder paint according to any one of.

< 6 >
Before SL inorganic particles are titania particles <1> to <5> Powder paint according to any one of.

< 7 >
A step of ejecting a charged powder coating material to adhere the powder coating material to an object to be coated, which is the powder coating material according to any one of < 1 > to < 6 >.
The process of heating the powder paint adhering to the object to be coated to form a coating film,
Electrostatic powder coating method with.

According to the invention according to < 1 > _{, the decay rate [30-300]} from the charge amount Q30 30 seconds after the end of adhesion to the charge amount Q300 300 seconds after the end of adhesion in the adhesion layer adhered to the substrate with the adhesion amount. _] Is less than 30%, a powder coating material capable of suppressing the occurrence of coating film roughness in the coating film formed by adhering to and heating the object to be coated is provided.
According to the invention according to < 2 > _{, the decay rate [30-100]} from the charge amount Q30 30 seconds after the end of adhesion to the charge amount Q100 100 seconds after the end of adhesion in the adhesion layer adhered to the substrate with the adhesion amount. _] Is less than 5%, even when the coating film formed on the object to be coated is thicker and the amount of adhesion is large (for example, the amount of adhesion is 120 g / m ² or more), the coating film is rough. A powder coating material capable of suppressing the generation is provided.
According to the invention according to < 3 > , the coating film formed by adhering to and heating the object to be coated has higher smoothness than the case where the volume average particle diameter of the powder particles exceeds 10 μm. Provided is a powder coating material capable of suppressing the occurrence of coating film roughness.
According to the invention according to < 4 > , the coating film roughened in the coating film formed by adhering to the object to be coated and heating as compared with the case where the volume average particle diameter of the inorganic particles is less than 10 nm or exceeds 100 nm. A powder coating film capable of suppressing the occurrence of
According to the invention according to < 5 > , a powder capable of suppressing the occurrence of coating film roughness in a coating film formed by adhering to and heating an object to be coated, as compared with the case where the aspect ratio of inorganic particles exceeds 5. Paint is provided.
According to the invention according to < 6 > , a powder coating material capable of suppressing the occurrence of coating film roughness in a coating film formed by adhering to and heating an object to be coated, as compared with the case where the inorganic particles are zinc oxide particles. Is provided.

According to the invention according to < 7 > _{, the decay rate [30-300]} from the charge amount Q30 30 seconds after the end of adhesion to the charge amount Q300 300 seconds after the end of adhesion in the adhesion layer adhered to the substrate with the adhesion amount. _] Is less than 30%, an electrostatic powder coating method capable of suppressing the occurrence of coating film roughness in the coating film is provided as compared with the case of using a powder coating material.

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

(Powder paint)
The powder coating material of the present embodiment contains powder particles and inorganic particles. Then, when an adhesive layer having an adhesion amount of 100 g / m ² is attached onto the substrate, the charge amount 30 seconds after the end of adhesion is Q30, and the charge amount 300 seconds after the end of adhesion is Q300. _{The attenuation rate [30-300]} (%) represented by the absolute value of "Q30-Q300) / Q30" is 30% or more and 60% or less.

The powder coating material used for powder coating includes, for example, a binder resin and other components such as a curing agent for curing the binder resin used as needed, a coloring agent such as a pigment, a flame retardant, and a leveling agent. It is produced by adding inorganic particles to the powder particles containing the above. Such a powder coating material is coated on an object to be coated by a method such as an electrostatic powder coating method, and is heated to form a coating film. In the electrostatic powder coating method, for example, powder coating material charged by contact charging, corona discharge, etc. is discharged (spouted) using a spray gun or the like, and the powder coating material is electrostatically applied to a grounded object to be coated. It is a method of adhering to.

However, in the past, when a coating film was formed on an object to be coated using a powder coating material, rough coating film (popping marks) sometimes occurred.
On the other hand, according to the powder coating material of the present embodiment, it is possible to suppress the occurrence of rough coating film (popping marks) in the coating film formed by adhering to and heating the object to be coated.
The reason can be inferred as follows.

Roughening of the coating film is caused by the accumulation of electric charges in the adhesive layer and the generation of electrostatic repulsion when the powder coating is ejected onto the object to be coated and electrostatically adhered to form the adhesive layer. I'm guessing. Electrostatic repulsion means that an electric charge is accumulated in the adhering layer and a charge opposite to that of the object to be coated is induced, so that a repulsive force is generated between the powder particles in the adhering layer. It is considered that due to this electrostatic repulsion, the adhered powder particles are repelled from the adhering layer, so that circular or crater-like dents (splash marks) are generated and the coating film is roughened.

_{The powder coating material of the present embodiment has a charge amount attenuation rate [30-300]} of 30% from 30 seconds to 300 seconds after the completion of adhesion in the adhesion layer adhered (coated) on the substrate with a specific adhesion amount. More than 60% or less. The above-mentioned _{powder coating material having an attenuation rate [30-300]} of 30% or more causes charge leakage (charge leakage) when it is ejected to an object to be coated or after being electrostatically adhered to the object to be coated. It indicates that it is a powder coating that is easily generated. As a result, the accumulation of electric charge in the adhesive layer is reduced, the generation of electrostatic repulsion is suppressed, and the powder particles are prevented from popping from the adhesive layer to generate dents (pop marks) and roughening the coating film. It is presumed to be.
Further, the powder coating material having the attenuation factor _[30-300] of 60% or less means that the amount of charge in the adhesive layer does not decrease too much even after the charge leakage (charge leakage) occurs. ing. As a result, even in the powder coating material being ejected (discharged) to the object to be coated, the electric charge does not drop too much and electrostatic adhesion is obtained. Therefore, for example, due to the influence of the air flow at the time of ejection. It is possible to prevent the powder coating material from being blown off and not adhering to the intended location on the object to be coated. Further, even in the powder coating material electrostatically adhered to the object to be coated, the electric charge does not drop too much, and it is suppressed that the powder coating material is removed (peeled off) from the adhering layer due to insufficient electric charge. From these, it is presumed that the coating film has excellent film forming property.

If the particle size of the powder particles contained in the powder coating material is small (for example, the volume average particle size is 10 μm or less), a coating film having better smoothness can be formed, while the powder coating material as a whole can be formed. Since the surface area of the coating material is larger than that of the case where the particle size is larger, the influence of the accumulation of charge is larger, and the coating film is more likely to be roughened (popping marks). However, according to the present embodiment, as described above, the accumulation of electric charges in the adhesive layer is reduced, and the occurrence of coating film roughness (popping marks) is suppressed.

In addition, when the coating film formed on the object to be coated becomes thicker, that is, the amount of adhesion increases (for example, the amount of adhesion is 120 g / m ² or more), electric charges are more likely to be accumulated, so that the coating film becomes rough (splash marks). It becomes easier to do. However, according to the present embodiment, as described above, the accumulation of electric charges in the adhesive layer is reduced, and the occurrence of coating film roughness (popping marks) is suppressed.

Next, the powder coating material according to this embodiment will be described in detail.

≪Attenuation rate≫
-Attenuation rate from 30 seconds to 300 seconds after the end of adhesion _[30-300]
The powder coating material according to the present embodiment has a charge amount Q30 30 seconds after the end of adhesion and a charge amount Q30 300 seconds after the end of adhesion in the adhesion layer adhered (coated) on the substrate at an adhesion amount of 100 g / m ^2. _{The attenuation rate [30-300]} (%) represented by the absolute value of "(Q30-Q300) / Q30" with the amount of electric charge Q300 is 30% or more and 60% or less.
When the attenuation rate _[30-300] is 30% or more, it is possible to prevent the powder particles from popping from the adhesion layer to generate dents (splash marks) and causing the coating film to become rough. On the other hand, when the attenuation factor _[30-300] is 60% or less, the film forming property of the coating film is excellent.

The value of the attenuation factor _[30-300] 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.

-Attenuation rate from 30 seconds to 100 seconds after the end of adhesion _[30-100]
Further, in the present embodiment, the charge amount Q30 30 seconds after the end of adhesion and the charge amount Q100 100 seconds after the end of adhesion in the adhesion layer adhered (coated) on the substrate with the adhesion amount. _{The attenuation rate [30-100]} (%) represented by the absolute value of "(Q30-Q100) / Q30" is preferably 5% or more and 20% or less.
A powder coating material having an attenuation rate _[30-100] of 5% or more means that charge leakage (charge leakage) is likely to occur quickly, that is, when it is ejected onto an object to be coated or on the object to be coated. This indicates that the powder coating material is likely to cause a charge leakage (charge leakage) quickly after being electrostatically adhered to the coating material. As a result, even when the coating film formed on the object to be coated becomes thick and the amount of adhesion is large (for example, the amount of adhesion is 120 g / m ² or more), the powder particles are repelled from the adhering layer and dented (splash marks). Is likely to occur and roughening of the coating film in the coating film is easily suppressed.
On the other hand, when the damping factor _[30-100] is 20% or less, the amount of charge does not drop too sharply, and in the powder coating material being ejected (discharged) to the object to be coated, for example, the ejection occurs. It becomes easy to prevent the powder coating material from being blown off due to the influence of the air flow at the time and not adhering to the intended portion on the object to be coated. Further, even in the powder coating material electrostatically adhered to the object to be coated, the electric charge does not drop too much, and it becomes easy to prevent the powder coating material from coming off (peeling off) from the adhering layer due to insufficient electric charge. As a result, it becomes easy to obtain an excellent film forming property of the coating film.

The value of the attenuation factor _[30-100] is preferably 5% or more and 20% or less, more preferably 7% or more and 18% or less, and further preferably 9% or more and 15% or less.

-Attenuation rate from 30 seconds to 200 seconds after the end of adhesion _[30-200]
Further, in the present embodiment, the charge amount Q30 30 seconds after the end of adhesion and the charge amount Q200 200 seconds after the end of adhesion in the adhesion layer adhered (coated) on the substrate with the adhesion amount. _{The attenuation rate [30-200]} (%) represented by the absolute value of "(Q30-Q200) / Q30" is preferably 15% or more and 30% or less.
When the attenuation rate _[30-200] is 15% or more, it is possible to prevent the powder particles from popping from the adhesion layer to generate dents (splash marks) and causing the coating film to become rough. On the other hand, when the attenuation factor _[30-200] is 30% or less, it becomes easy to obtain excellent film forming property of the coating film.
The value of the attenuation factor _[30-200] is preferably 15% or more and 30% or less, more preferably 17% or more and 28% or less, and further preferably 20% or more and 25% or less.

-Method of measuring the amount of charge in the adhering layer The above-mentioned amount of charge Q30 and amount of charge Q300 are measured by the following methods.
First, an adhesive layer is formed using Asahi Sanac Corona Gun XR4-110C by the following method. Prepare a mirror-finished aluminum plate (30 cm x 30 cm) as the substrate, and slide the corona gun up, down, left and right at a distance of 20 cm from the front (distance between the substrate and the discharge port of the corona gun) to the powder paint. Is electrostatically adhered to the substrate to obtain an adhering layer having an adhering amount of 100 g / m ^2. If this time 98 g / ^{m 2} or more 102 g / ^{m 2} or less of the adhesive layer is regarded as 100 g / ^{m 2.} The applied voltage of the corona gun is 100 kV, the input air pressure is 0.55 MPa, and the discharge rate is 100 g / min.
Next, the amount of charge is measured. The amount of charge in the adhering layer is measured using a faraday gauge, and is measured using a small suction type charge measuring device (charge amount measuring device EA02 system manufactured by U-Tech Co., Ltd.). From the adhesion layer 30 seconds after the end of adhesion and the adhesion layer 300 seconds after the end of adhesion, the powder particles contained in the adhesion layer are directly taken into the filter in the Faraday gauge by the suction nozzle, and the amount of charge and mass are measured to measure the powder. Find the amount of charge per unit mass of body particles. The amount of electric charge per unit mass of the powder particles is measured at any 10 points of the adhesive layer, and the arithmetic mean value thereof is taken as the amount of electric charge of the adhesive layer.

The measurement of the charge amount Q100 100 seconds after the end of adhesion and the charge amount Q200 200 seconds after the end of adhesion is also the measurement other than taking powder particles into the filter in the faraday gauge from the adhesion layer 100 seconds or 200 seconds after the end of adhesion. The amount of electric charge is measured according to the above method.

-Method of controlling the damping factor The damping factor _[30-300] , the damping factor _[30-200] , and the damping factor _[30-100] are indexes of the susceptibility to charge leakage (charge leakage) in the powder coating material. be. Each attenuation factor can be controlled by, for example, the composition of the powder particles, the method for producing the powder particles, the composition of the inorganic particles, the surface treatment, and the like.
For example, as an example, as the inorganic particles externally attached to the surface of the powder particles, the more inorganic particles having a low degree of attenuation treatment (more preferably, the inorganic particles not attenuating treatment) are used, the more each of the above It becomes easy to reduce the attenuation rate.

From the viewpoint of facilitating control of each of the above attenuation rates within the above range, it is preferable that the dielectric loss factor of the powder coating material is within the following range.

− Dielectric loss rate −
The powder coating material according to this embodiment preferably has a dielectric loss ratio of 40 × 10 ^-3 or more and 150 × 10 ^-3 or less, and ^{more preferably 50 × 10 -3} or more and 100 × 10 ^-3 or less. , 50 × 10 ^-3 or more and 80 × 10 ^-3 or less is more preferable.
The dielectric loss rate of the powder coating material is measured by the following method.
First, 5 g of powder coating material is molded into pellets, set between electrodes [SE-71 type solid electrode, manufactured by Ando Electric Co. Ltd.] at 20 ° C. and 60% relative humidity, and LCR meter (4274A type). , Yokogawa Hulett Packard), 5V, frequency 100kHz.
The dielectric loss ratio is calculated by the following formula (1).
(14.39 / (W × D ² )) × Gx × Tx × 10 ¹² ... Equation (1)
Here, W = 2πf (f: measurement frequency 100 kHz), D: electrode diameter (cm), Gx: conductivity (S), Tx: sample thickness (cm).

The dielectric loss rate of the powder coating material can be controlled by, for example, the composition of the powder particles, the method for producing the powder particles, the composition of the inorganic particles, the surface treatment, and the like. For example, as the inorganic particles externally added to the surface of the powder particles, the more the inorganic particles having a low degree of hydrophobization treatment (more preferably, the inorganic particles not hydrophobizing treatment) are used, the more easily the dielectric loss rate is lowered. ..

[Inorganic particles]
The powder coating material according to this embodiment includes powder particles and inorganic particles.
The inorganic particles are externally added to the surface of the powder particles (hereinafter, also simply referred to as "external addition").
The external addition method is not particularly limited, and an external addition method known in the field of powder coating can be used.

Examples of the inorganic particles include 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. particles comprising _{SiO 2, K 2 O · (} TiO 2) n, Al 2 O 3 · 2SiO 2, CaCO 3, MgCO 3, BaSO 4, MgSO 4 may preferably be mentioned.
As the inorganic particles used in the present embodiment, titania particles and zinc oxide particles are preferable, and titania particles are more preferable, from the viewpoint of suppressing the coating film roughness of the coating film obtained by the powder coating.
As the crystal morphology of the titania particles, rutile type and anatase type are mainly known, and any of them can be used in the present embodiment, but from the viewpoint of light resistance of the coating film, rutile type is used. The mold is preferred.
In the present embodiment, one type of inorganic particles may be used alone, or two or more types may be used in combination.

− Grain size −
The volume average particle size (average primary particle size) of the inorganic particles is preferably 10 nm or more and 100 nm or less, more preferably 15 nm or more and 90 nm or less, and further preferably 20 nm or more and 80 nm or less.
When the volume average particle diameter of the inorganic particles is within the above range, the adhesion to the powder particles is excellent, and the coating film roughness obtained by the powder coating film 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 circle-equivalent diameter of each of the 100 inorganic particles to be measured is obtained by image analysis, and the volume-based particle diameter is defined as the volume-based cumulative 50% circle-equivalent diameter from the small diameter side in the volume-based distribution.
For image analysis to obtain the equivalent circle diameter of 100 inorganic particles to be measured, a two-dimensional image with a magnification of 10,000 times is taken using an analysis device (ERA-8900: manufactured by Elionix Inc.), and image analysis software WinROOF. Using (manufactured by Mitani Shoji Co., Ltd.), the projected area is calculated under the condition of 0.010000 μm / pixel, and the equivalent circle diameter is calculated by the formula: circle equivalent 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, for each type of external additive, element mapping is performed by SEM-EDX (scanning electron microscope equipped with an energy dispersive X-ray analyzer), and the element derived from each type of external additive is applicable. Distinguish by associating with an external additive.

− 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 less likely to be released from the powder particles, and the coating film roughness of the obtained coating film is further suppressed.
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 roughness of the coating film 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 release of the inorganic particles from the powder particles.

The above aspect ratio is the image analysis software (Mitani Shoji Co., Ltd., product, manufactured by SEM, Hitachi High-Technologies, Inc., product name: SU8010) attached to the inorganic particles on the powder particles. By performing particle shape analysis by name: WinROOF), it is measured as the ratio (L / S) of the major axis (L) to the minor axis (S).

-Hydrophobic treatment-
The surface of the inorganic particles used in the present embodiment may be hydrophobized in advance. However, from the viewpoint of facilitating the attenuation of the charge in the powder coating material, and as a result, the above-mentioned attenuation rate _[30-300] , attenuation rate _[30-200] , and attenuation rate _[30-100] can be easily controlled within the above range. Therefore, it is preferable to use inorganic particles having a low degree of attenuation treatment (more preferably, inorganic particles that have not been attenuated). That is, from the viewpoint of suppressing the coating film roughness of the coating film obtained by the powder coating, it is preferable that the coating film is not excessively hydrophobized.

The hydrophobizing treatment can be performed by immersing the inorganic oxide particles in the hydrophobizing agent. The hydrophobizing agent is not particularly limited, and examples thereof include a silane coupling agent, a silicone oil, a titanate-based coupling agent, and an aluminum-based coupling agent. These may be used alone or in combination of two or more.

− Volume resistivity −
The inorganic particles used in the present embodiment preferably have a volume resistivity of 1 × 10 ⁵ Ω · cm or more and 1 × 10 ¹³ Ω · cm or less, and 1 × 10 ⁶ Ω · cm or more and 1 × 10 ¹² Ω ·. It is more preferably cm or less, and further preferably 1 × 10 ⁷ Ω · cm or more and 1 × 10 ¹¹ Ω · cm or less.
When the volume resistivity is within the above range, the roughness of the coating film obtained by the powder coating film is easily suppressed, which is preferable.

The volume resistivity of the inorganic particles is measured by the following method.
First, the inorganic particles are separated from the powder particles. Then, the ^{separated inorganic particles to be measured are placed on the surface of a circular jig on which a 20 cm 2} electrode plate is arranged so as to have a thickness of about 1 mm or more and 3 mm or less to form an inorganic particle layer. ^{The same 20 cm 2} electrode plate as described above is placed on this, and the inorganic particle layer is sandwiched. In order to eliminate the voids between the inorganic particles, a load of 4 kg is applied on the electrode plate installed on the inorganic particle layer, and then the thickness (cm) of the inorganic particle layer is measured. Both electrodes above and below the inorganic particle layer are connected to an electrometer and a high-voltage power generator. A high voltage is applied to both electrodes, and the volume resistivity (Ω · cm) of the inorganic particles is calculated by reading the current value (A) flowing at this time. The above measurement is performed under the conditions of a temperature of 20 ° C. and a relative humidity of 50%. The formula for calculating the volume resistivity (Ω · cm) of inorganic particles is as shown in the formula below.
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 the applied voltage 0 V, and L is the current value (A). Each 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 of inorganic particles-
The content of the inorganic particles is preferably 0.1% by mass or more and 3% by mass or less, preferably 0.3% by mass, based on the total mass of the powder particles from the viewpoint of further suppressing the roughness of the coating film of the obtained coating film. More preferably 1.5% by mass or less.

[Powder particles]
The powder particles contained in the powder coating material preferably contain a thermosetting resin and a thermosetting agent. The powder particles may contain a colorant and other additives, if necessary.

-Thermosetting resin-
The thermosetting resin is a resin having a thermosetting reactive group. Examples of the thermosetting resin include various types of resins conventionally used as powder particles of powder coating materials.
The thermosetting resin is preferably a water-insoluble (hydrophobic) resin. When a water-insoluble (hydrophobic) resin is applied as the thermosetting resin, the environmental dependence of the charging characteristics of the powder coating material (powder particles) is reduced. Further, when the powder particles are produced by the 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. The 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 a thermosetting polyester resin, a thermosetting (meth) acrylic resin, a thermosetting fluororesin (for example, a fluoroethylene-vinyl ether (FEVE) copolymer resin, etc.), and a thermosetting polyethylene resin. , At least one selected from the group consisting of thermosetting epoxy resin, and thermosetting epoxy-polyester resin. Among the thermosetting resins, the thermosetting polyester resin is preferable from the viewpoints that the charge train is easily controlled at the time of painting, the strength of the coating film, the beauty of the finish, and the like.
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, a blocked isocyanate group and the like, but the synthesis is easy. From the point of view, carboxyl groups and hydroxyl groups 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, a blocked isocyanate group, and the like, but from the viewpoint of easy synthesis. , Carboxyl groups, and hydroxyl groups are preferred.

The thermosetting polyester resin is, for example, a polycondensate obtained by at least polycondensing a polybasic acid and a polyhydric alcohol.
The thermosetting reactive group of the thermosetting polyester resin is introduced by adjusting the amount of the polybasic acid and the polyhydric alcohol used in synthesizing the polyester resin. By this adjustment, a thermosetting polyester resin having at least one of a carboxyl group and a hydroxyl group can be obtained as a thermosetting reactive group.
Further, 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, methylterephthalic acid, trimellitic acid, pyromellitic acid, and anhydrides of these acids; succinic acid, adipic acid, azelaic acid, sebatic acid, and these acids. Anhydrous; 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 -Naphthalenedicarboxylic acid and the like can be 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. Glycer, 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, trishydroxyethylisocyanurate, hydroxypivalylhydroxypi Valeate and the like can be mentioned.

The thermosetting polyester resin may be polycondensed with monomers other than the polybasic acid and the polyhydric alcohol.
Examples of other monomers include a compound having both a carboxyl group and a fatty acid in one molecule (for example, dimethanol propionic acid, hydroxypivalate, etc.) and a monoepoxy compound (for example, "Cadura E10 (manufactured by Shell)". (Glysidyl ester of branched aliphatic carboxylic acid, etc.), various monohydric alcohols (eg, methanol, propanol, butanol, benzyl alcohol, etc.), various monovalent basic acids (eg, benzoic acid, p-tert-butylbenzoic acid, etc.) Acids, etc.), various fatty acids (for example, castor oil fatty acid, coconut oil fatty acid, soybean oil fatty acid, etc.) and the like.

The structure of the thermosetting polyester resin may be 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 total of the acid value and the hydroxyl value is within the above range, the smoothness and mechanical properties of the coating film are likely to be 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 material is also likely to be improved.

The measurement of the acid value and the hydroxyl value of the thermosetting polyester resin conforms to JIS K-0070-1992. Further, the measurement of the number average molecular weight of the thermosetting polyester resin is the same as the measurement of the number average molecular weight of the thermosetting (meth) acrylic resin described 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, it is preferable to use a vinyl monomer having a thermosetting reactive group. 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 the (meth) acrylic monomer. It may be a monomer.

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 preferable. In particular, it is more preferable that at least one thermosetting reactive group is an epoxy group from the viewpoint of excellent storage stability of the powder coating material and the appearance of the coating film.

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, and allyl). (Glysidyl ether, etc.), various (2-oxo-1,3-oxolane) group-containing vinyl monomers (for example, (2-oxo-1,3-oxolane) methyl (meth) acrylate, etc.), various alicyclic types Examples thereof include an epoxy group-containing vinyl monomer (for example, 3,4-epoxide cyclohexyl (meth) acrylate, 3,4-epoxide cyclohexylmethyl (meth) acrylate, 3,4-epoxide cyclohexylethyl (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.). Monoesters of α, β-unsaturated dicarboxylic acid and monovalent alcohol having 1 or more and 18 or less carbon atoms (for example, monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monoisobutyl fumarate, monotert-butyl fumarate) , Monohexyl fumarate, monooctyl fumarate, mono2-ethylhexyl fumarate, monomethyl maleate, monoethyl maleate, monobutyl maleate, monoisobutyl maleate, monotert-butyl maleate, monohexyl maleate, monooctyl maleate, Mono2-ethylhexyl maleate, etc.), Itaconic acid monoalkyl ester (eg, monomethyl itaconic acid, monoethyl itaconic acid, monobutyl itaconic acid, monoisobutyl itaconic acid, monohexyl itaconic acid, monooctyl itaconic acid, mono2-ethylhexyl itaconic acid, etc.) And so on.

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, and 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-hydroxypropyl 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.), addition reaction products of the above various hydroxyl group-containing vinyl ethers and ε-caprolactone, various Hydroxy hydroxyl-containing allyl ethers (eg, 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, 6-hydroxyhexyl (meth) allyl ether, etc.), various hydroxyl group-containing alleles described above Examples thereof include addition reaction products of ether and ε-caprolactone.

In addition to the (meth) acrylic monomer, the thermosetting (meth) acrylic resin may be copolymerized with another vinyl monomer having no thermosetting reactive group.
Other vinyl monomers include various α-olefins (eg ethylene, propylene, butene-1, etc.), various halogenated olefins other than fluoroolefins (eg vinyl chloride, vinylidene chloride, etc.), and various aromatic vinyls. Diesters of monomers (eg, styrene, α-methylstyrene, vinyltoluene, etc.), various unsaturated dicarboxylic acids and monovalent alcohols with 1 to 18 carbon atoms (eg, 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, (meth) acrylic acid, tetrahydrophthalic anhydride, etc.), various steric phosphate group-containing monomers (eg, diethyl-2- (meth) acryloyloxyethyl phosphate). , Dibutyl-2- (meth) acryloyloxybutyl phosphate, dioctyl-2- (maecryloyloxyethyl phosphate, diphenyl-2- (meth) acryloyloxyethyl phosphate, etc.), various hydrolyzable silyl group-containing singles Metrics (eg, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, etc.), various aliphatic vinyl carboxylates ( For example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, branched aliphatic carboxylate vinyl having 9 or more and 11 or less 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-butyl benzoate, etc.) and the like.

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, the thermosetting (meth) acrylic resin 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 ester (for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and (meth). ) Isopropyl acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, (meth) acrylic 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.), various (meth) acrylic acid aryl esters (eg, benzyl (meth) acrylate, phenyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc.), various alkyl carbs Thor (meth) acrylates (eg ethylcarbitol (meth) acrylates, etc.), various other (meth) acrylic acid esters (eg, isobornyl (meth) acrylates, dicyclopentanyl (meth) acrylates, dicyclopentenyl (meth)) Acrylate, dicyclopentenyloxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, etc.), various amino group-containing amide-based unsaturated monomers (for example, N-dimethylaminoethyl (meth) acrylamide, N- Diethylaminoethyl (meth) acrylamide, N-dimethylaminopropyl (meth) acrylamide, N-diethylaminopropyl (meth) acrylamide, etc.), various dialkylaminoalkyl (meth) acrylates (eg, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (eg, dimethylaminoethyl (meth) acrylate) (Meta) acrylate, etc.), various amino group-containing monomers (for example, tert-butylaminoethyl (meth) acrylate, tert-butylaminopropyl (meth) acrylate, aziridinyl ethyl (meth) acrylate, pyrrolidinyl ethyl (eg. Meta) acrylate, piperidinyl ethyl (meth) acrylate, etc.).

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

The weight average molecular weight and the 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 by using GPC / HLC-8120GPC manufactured by Tosoh Corporation as a measuring device and column / TSKgel SuperHM-M (15 cm) manufactured by Tosoh Corporation in a THF solvent. The weight average molecular weight and the number average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared from a monodisperse polystyrene standard sample.

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

The content of the thermosetting resin is preferably 20% by mass or more and 99% by mass or less, and preferably 30% by mass or more and 95% by mass or less with respect to the entire powder particles.
As will be described later, when the powder particles are core-shell type particles and a thermosetting resin is applied as the resin of the resin coating portion, the content of the thermosetting resin is the core portion. And the content of the total thermosetting resin in the resin coating part.

-Thermosetting agent-
The thermosetting agent is selected according to the type of thermosetting reactive group of the thermosetting resin.
Here, the thermosetting agent means a compound having a functional group capable of reacting with a thermosetting reactive group which is a terminal group of a thermosetting resin.

When the thermosetting reactive group of the thermosetting resin is a carboxyl group, the thermosetting agent includes, for example, various epoxy resins (for example, polyglycidyl ether of bisphenol A) and epoxy group-containing acrylic resin (for example, glycidyl group-containing acrylic). Resins, etc.), polyglycidyl ethers of various polyvalent alcohols (eg, 1,6-hexanediol, trimethylolpropane, trimethylolethane, etc.), various polyvalent carboxylic 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 (eg, bis (3,4-epoxycyclohexyl) methyladipate, etc.), hydroxy Examples thereof include amides (for example, triglycidyl isocyanurate, β-hydroxyalkylamide, etc.).

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, trimethylhexamethylene diisocyanate, etc.), various cyclic aliphatic diisocyanates (for example, xylylene diisocyanate, isophorone diisocyanate, etc.), and various aromatic diisocyanates (for example, xylylene diisocyanate, isophorone diisocyanate, etc.). Organic diisocyanates such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, etc .; adducts of these organic diisocyanates with polyhydric alcohol, low molecular weight polyester resin (for example, polyester polyol), water, etc .; Polymers (polymers also containing isocyanurate-type polyisocyanate compounds); various polyisocyanate compounds such as isocyanate biuret compounds blocked with a known and commonly used blocking agent; self-blocking having a uretdione bond as a structural unit Examples include polyisocyanate compounds.

When the thermosetting reactive group of the thermosetting resin is an epoxy group, the thermosetting agents include, for example, succinic acid, glutaric acid, adipic acid, pimelli acid, suberic acid, azelaic acid, sebatic acid, dodecanedioic acid, and aikosan. 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, pyromerit Acids such as acids; anhydrides of these acids; urethane modified products of these acids and the like can be mentioned. Among these, as the thermosetting agent, an aliphatic dibasic acid is preferable from the viewpoint of the physical properties of the coating film and storage stability, and dodecane diic acid is particularly preferable from the viewpoint of the physical properties of the coating film.

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

The content of the thermosetting agent is preferably 1% by mass or more and 30% by mass or less, and preferably 3% by mass or more and 20% by mass or less, based on the thermosetting resin.
As will be described later, when the powder particles are core-shell type particles and a thermosetting resin is applied as the resin of the resin coating portion, the content of the above thermosetting agent is the core portion and the content of the thermosetting agent. It means the content of the resin coating part with respect to the total thermosetting resin.

-Colorant-
Examples of the colorant include pigments. As the colorant, a dye may be used in combination with the pigment.
Pigments include, for example, inorganic pigments such as iron oxide (for example, red iron oxide), titanium oxide, titanium yellow, zinc white, lead white, zinc sulfide, lithopone, antimony oxide, cobalt blue, carbon black; quinacridone red, phthalocyanine blue, etc. Examples thereof include organic pigments such as phthalocyanine green, permanent red, Hansa yellow, indanslen blue, brilliant first scarlet, and benzimidazolone yellow.
Other examples of pigments include brilliant pigments. Examples of the brilliant pigment include metal powders such as pearl pigments, aluminum powders, and stainless steel powders; metal flakes; glass beads; glass flakes; mica; phosphorescent iron oxide (MIO) and the like.

The colorant 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, lightness, depth and the like 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 with respect to the total resin constituting the powder particles.

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

-Metal ions with a valence of -2 or more-
The powder particles may contain divalent or higher valent metal ions (hereinafter, also simply referred to as “metal ions”). As will be described later, this metal ion is a component contained in both the core portion and the resin coating portion of the powder particles when the powder particles are core-shell type particles.
When the powder particles contain a metal ion having a valence of 2 or more, the powder particles form an ion bridge with the metal ions. For example, the functional group of the thermosetting resin (for example, when the thermosetting polyester resin is used as the thermosetting resin, the carboxyl group or the hydroxyl group of the thermosetting polyester resin) and the metal ion interact with each other to crosslink the ions. To form. Due to this ion cross-linking, inclusions of powder particles (thermosetting agent, colorant added as needed in addition to the thermosetting agent, other additives, etc.) are deposited on the surface of the powder particles (so-called). , Bleed) is suppressed, and the storability is likely to be improved. Further, in this ion cross-linking, after coating the powder coating material, the bond of the ion cross-linking is broken by heating during thermosetting, so that the melt viscosity of the powder particles is lowered and a highly smooth coating film is formed. It will be easier to do.

Examples of the metal ion include a metal ion having a divalent value or more and a tetravalent value or less. 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 source of the metal ion (compound contained in the powder particles as an additive) include a metal salt, an inorganic metal salt polymer, a metal complex, and the like. This metal salt and the inorganic metal salt polymer are added to the powder particles as a coagulant, for example, when the powder particles are produced by the coagulation 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 (II) sulfate, and calcium polysulfide.
Examples of the metal complex include a metal salt of an aminocarboxylic acid. Specific examples of the metal complex include known chelate-based metal salts such as ethylenediaminetetraacetic acid, propanediaminetetraacetic acid, nitrile triacetic acid, triethylenetetramine 6 acetic acid, and diethylenetriamine 5 acetic acid (eg, calcium salt, etc.). Magnesium salt, iron salt, aluminum salt, etc.) and the like.

The source of these metal ions may be added as a mere additive, not as a flocculant.

The higher the valence of the metal ion, the easier it is to form a mesh-like ion crosslink, which is preferable in terms of the smoothness of the coating film and the storability of the powder coating material. Therefore, Al ion is preferable as the metal ion. That is, as a source of metal ions, aluminum salts (for example, aluminum sulfate, aluminum chloride, etc.) and aluminum salt polymers (for example, polyaluminum chloride, polyaluminum hydroxide, etc.) are preferable. Further, in terms of the smoothness of the coating film and the storability of the powder coating material, even if the valences of the metal ions are the same among the sources of the metal ions, the inorganic metal salt polymer is compared with the metal salt. preferable. Therefore, as a source of metal ions, an aluminum salt polymer (for example, polyaluminum chloride, polyaluminum hydroxide, etc.) is particularly preferable.

The content of the metal ion is preferably 0.002% by mass or more and 0.2% by mass or less, preferably 0.005% by mass, based on the total amount of the powder particles, in terms of the smoothness of the coating film and the storage property of the powder coating material. % Or more and 0.15% by mass or less is more preferable.
When the content of the metal ion is 0.002% by mass or more, appropriate ion cross-linking by the metal ion is formed, bleeding of the powder particles is suppressed, and the storability of the coating paint is easily improved. On the other hand, when the content of the metal ion is 0.2% by mass or less, the formation of excessive ion crosslinks due to the metal ion is suppressed, and the smoothness of the coating film is likely to be improved.

Here, when the powder particles are produced by the aggregation and coalescence method, the source of metal ions (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. do.

Specifically, the higher the valence of the metal ion, the more suitable it is to obtain a narrower particle size distribution. Further, in terms of obtaining a narrow particle size distribution, a metal salt polymer is preferable to a metal salt even if the valences of the metal ions are the same. Therefore, from these points as well, aluminum salts (for example, aluminum sulfate, aluminum chloride, etc.) and aluminum salt polymers (for example, polyaluminum chloride, polyaluminum hydroxide, etc.) are preferable as the source of metal ions, and the aluminum salt weight is preferable. Coalescence (eg polyaluminum chloride, polyaluminum hydroxide, etc.) is particularly preferred.

Further, when the aggregating agent is added so that the content of the metal ion is 0.002% by mass or more, the agglomeration of the resin particles in the aqueous medium proceeds, which contributes to the realization of a narrow particle size distribution. Further, the agglomeration of the resin particles to be the resin coating portion proceeds with respect to the agglomerated particles to be the core portion, which contributes to the realization of the formation of the resin coating portion on the entire surface of the core portion. On the other hand, when a flocculant is added so that the content of metal ions is 0.2% by mass or less, excessive formation of ionic crosslinks in the agglomerated particles is suppressed, and the powder produced when fusion and coalescence are performed. The shape of the particles tends to approach a spherical shape. Therefore, from these points as well, the content of the metal ion 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 source of metal ions are mixed to obtain a resin mixture having a known concentration of metal ions. A pellet sample of 200 mg of this resin mixture is obtained using a tablet molding machine having a diameter of 13 mm. The mass of this pellet sample is precisely weighed, and the fluorescence X-ray intensity of the pellet sample is measured to obtain the peak intensity. Similarly, the pellet sample in which the amount of the metal ion source added is changed is also measured, and a calibration curve is prepared from these results. Then, using this calibration curve, the content of metal ions in the powder particles to be measured is quantitatively analyzed.

As a method for adjusting the content of the metal ion, for example, 1) a method for adjusting the addition amount of the metal ion source, and 2) when the powder particles are produced by the aggregation and coalescence method, the metal ion content is adjusted in the aggregation step. After adding a flocculant (eg, a metal salt or metal salt polymer) as a source, a chelating agent (eg, EDTA (ethylenediamine tetraacetic acid), DTPA (diethylenetriamine pentaacetic acid), NTA (Nitrilotriacetic acid)) is added at the end of the flocculation step. Etc.) is added, a complex is formed with the metal ion by a chelating agent, and the complex salt formed in the subsequent washing step or the like is removed to adjust the content of the metal ion.

-Other additives-
Other additives include various additives used in powder coatings.
Specifically, as other additives, for example, foaming (armpit) inhibitor (for example, benzoin, benzoin derivative, etc.), curing accelerator (amine compound, imidazole compound, cationic polymerization catalyst, etc.), surface conditioner (for example) Leveling agents), plasticizers, charge control agents, antioxidants, pigment dispersants, flame retardants, fluidizers 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 that covers the surface of the core portion. ..
At this time, in addition to the thermosetting resin and the thermosetting agent, the core portion may contain the above-mentioned other additives of the colorant, if necessary.

Further, the resin coating portion of the core-shell type particles will be described below.
The resin coating portion may be composed of only the resin, or may contain other components (thermosetting agent, other additives, etc. described as the components constituting the core portion).
However, from the viewpoint of reducing bleeding, the resin coating portion is preferably made of only resin. Even when the resin coating portion contains components other than the resin, the resin may occupy 90% by mass or more (preferably 95% by mass or more) of the entire resin coating portion.

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. That is good.
When a thermosetting resin is applied as the resin of the resin coating portion, examples of the thermosetting resin are the same as those of the thermosetting resin of the core portion, and preferred examples thereof 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.
When a non-curable resin is applied as the resin of the resin coating portion, at least one selected from the group consisting of an acrylic resin and a polyester resin is preferably used as the non-curable 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 suppressing bleeding.

The coverage of the resin coating is a value obtained by XPS (X-ray photoelectron spectroscopy) measurement for the coverage of the resin coating on the surface of the powder particles.
Specifically, XPS measurement is carried out by using JPS-9000MX manufactured by JEOL Ltd. as a measuring device, using MgKα ray as an X-ray source, setting an acceleration voltage of 10 kV and an emission current of 30 mA. ..
From the spectrum obtained under the above conditions, the coverage of the resin coating on the surface of the powder particles is achieved by peak-separating the component caused by the material of the core on the surface of the powder particles and the component caused by the material of the coating resin. Quantify. Peak separation separates the measured spectrum into components using curve fitting by the least squares method.
As the component spectrum that is the basis of separation, the spectrum obtained by independently measuring the thermosetting resin, the curing agent, the pigment, the additive, and the coating resin used for producing the powder particles is used. Then, the coating ratio is obtained from the ratio of the spectral intensities caused by the coating resin to the total of the total spectral intensities obtained from the powder particles.

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 or the like and cutting them with a diamond knife or the like. This thin section is observed with a transmission electron microscope (TEM) or the like, and cross-sectional images of a plurality of powder particles are taken. The thickness of the resin coating portion is measured at 20 points from the cross-sectional image of the powder particles, and the average value is adopted. When it is difficult to observe the resin coating portion in the cross-sectional image with a clear powder coating material or the like, it is possible to facilitate the measurement by observing the resin coating portion by dyeing.

-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 more preferably 1.30 or less in terms of the smoothness of the coating film and the storability of the powder coating. Is even more preferable. When the volume particle size distribution index GSDv is 1.40 or less, deterioration of the smoothness of the coating film is suppressed.

-Volume average particle size D50v
The volume average particle size 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 having high smoothness with a small amount.
If the particle size of the powder particles contained in the powder coating material is small (for example, the volume average particle size is 10 μm or less), a coating film having better smoothness can be formed, while the powder coating material as a whole can be formed. Since the surface area of the coating material is larger than that of the case where the particle size is larger, the influence of the accumulation of charge is larger, and the coating film is more likely to be roughened (popping marks). However, according to the present embodiment, as described above, the accumulation of electric charges in the adhesive layer is reduced, and the occurrence of coating film roughness (popping marks) is suppressed. From this point of view, the volume average particle size D50v of the powder particles is preferably in the range of 3 μm or more and 10 μm or less.

-Average circularity Further, the average circularity of the powder particles is preferably 0.97 or more, more preferably 0.98 or more, still more preferably 0.99 or more.
When the average circularity of the powder particles is 0.97 or more, it is possible to obtain a powder coating material in which the occurrence of coating film roughness is suppressed.
The details of the mechanism for obtaining a powder coating material in which the occurrence of coating film roughness is suppressed are unknown, but if the average circularity of the powder particles is 0.97 or more, the powder in the coating film is formed when the coating film is formed. Since the density of the body particles is high and the surface area of the powder particles per unit mass is small, the amount of charge retained by the powder particles in the coating film is also small, so that electrostatic repulsion between the powder particles is suppressed. It is presumed that the occurrence of rough coating is suppressed.

Here, the volume average particle size D50v of the powder particles and the volume particle size distribution index GSDv use Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolyte uses ISOTON-II (manufactured by Beckman Coulter). Is measured.
At the time of measurement, 0.5 mg or more and 50 mg or less of the measurement sample is added to 2 ml of a 5% aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is added to 100 ml or more and 150 ml or less of the electrolytic solution.
The electrolyte solution 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 or more and 60 μm or less is obtained by using a Coulter Multisizer II with an aperture of 100 μm. taking measurement. The number of particles to be sampled is 50,000.
A cumulative distribution is drawn from the small diameter side for each volume for the particle size range (channel) divided based on the measured particle size distribution, and the particle size with a cumulative total of 16% is the volume particle size D16v and the cumulative 50%. The particle size is defined as the volume average particle size D50v, and the particle size with a cumulative total of 84% is defined as the volume particle size D84v.
Then, the volume particle size distribution index (GSDv) is calculated as ^{(D84v / D16v) 1/2.}

Further, the average circularity of the powder particles is measured by using a flow type particle image analyzer "FPIA-3000 (manufactured by Sysmex Corporation)". Specifically, 0.1 ml or more and 0.5 ml or less of a surfactant (alkylbenzene sulfonate) as a dispersant is added to 100 ml or more and 150 ml or less of water from which the impure solid matter has been removed in advance, and the measurement sample is further added to 0. 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 to bring the dispersion liquid concentration to 3,000 pieces / μl or more and 10,000 pieces / μl or less. The average circularity of the powder particles is measured with respect to this dispersion using a flow-type particle image analyzer.

Here, the average circularity of the powder particles is a value calculated by obtaining the circularity (Ci) of each of the n particles measured for the powder particles and then calculating by the following formula. However, in the following formula, Ci indicates circularity (= perimeter of a circle equal to the projected area of particles / perimeter of a projected particle image), and fi indicates the frequency of powder particles.

(Manufacturing method of powder paint)
Next, a method for producing the powder coating material according to the present embodiment will be described.
The powder coating material according to the present embodiment can be obtained by externally adding an external additive containing inorganic particles to the powder particles after producing the powder particles.

The powder particles may be produced by any of a dry production method (for example, a kneading and pulverizing method, etc.) and a wet production method (for example, an agglomeration coalescence method, a suspension polymerization method, a dissolution suspension method, etc.). The manufacturing method of the powder particles is not particularly limited to these manufacturing methods, and a well-known manufacturing method is adopted.

For example, in the dry manufacturing method, 1) a kneading crushing method in which a thermosetting resin and other raw materials are kneaded, crushed, and classified, and particles obtained by the kneading crushing method are changed in shape by mechanical impact force or thermal energy. There is a dry manufacturing method to make it.
On the other hand, in the wet production method, for example, 1) a dispersion liquid obtained by emulsion polymerization of a polymerizable monomer for obtaining a thermosetting resin and a dispersion liquid of other raw materials are mixed, aggregated and heat-fused. , Aggregation coalescence method to obtain powder particles, 2) 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, 3. ) There is a dissolution-suspension method in which a thermosetting resin and a solution of another raw material are suspended in an aqueous solvent for granulation. The wet method can be preferably used because it has a smaller thermal effect.
Further, the powder particles obtained by the above-mentioned production method may be used as a core, and resin particles may be further adhered and heat-fused to obtain powder particles which are core-shell type particles.

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

Hereinafter, the aggregation and coalescence method for producing powder particles, which are core-shell type particles, will be described as an example.
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 agent are heat-cured. A step of aggregating the composite particles to form the first agglomerated particles (first agglomerated particle forming step) in a dispersion liquid in which the composite particles containing the agent are dispersed.
The first agglomerated particle dispersion liquid in which the first agglomerated particles are dispersed and the second resin particle dispersion liquid in which the second resin particles containing a resin are dispersed are mixed, and the second agglomerated particles are surfaced on the surface of the first agglomerated particles. A step of aggregating the resin particles and forming the second agglomerated particles in which the second resin particles adhere to the surface of the first agglomerated particles (second agglomerated particle forming step).
A step of heating the second agglomerated particle dispersion liquid in which the second agglomerated particles are dispersed to fuse and coalesce the second agglomerated particles (fusion coalescence step).
It is preferable to produce powder particles through the above.
In the powder particles produced by this agglomeration and coalescence method, the portion where the first agglomerated particles are fused and coalesced becomes the core portion, and the portion where the second resin particles adhering to the surface of the first agglomerated particles are fused and coalesced. Is the resin coating part.
Therefore, if the first agglomerated particles formed in the first agglomerated particle forming step are subjected to the fusion and coalescence step without going through the second agglomerated particle forming step, and fused and coalesced instead of the second agglomerated particles, Powder particles having a single layer structure can be obtained.

The details of each step will be described below.
In the following description, a method for producing powder particles containing a colorant will be described, but the colorant is contained as needed.

<Preparation process for each dispersion>
First, each dispersion used in the aggregation and coalescence method is prepared.
Specifically, a first resin particle dispersion liquid in which first resin particles containing a thermosetting resin in the core are dispersed, a thermosetting agent dispersion liquid in which a thermosetting agent is dispersed, and a colorant in which a colorant is dispersed. Prepare a dispersion liquid and a second resin particle dispersion liquid in which the second resin particles containing the resin of the resin coating portion are dispersed.
Further, instead of the first resin particle dispersion liquid and the thermosetting agent dispersion liquid, a thermosetting resin for the core portion and a composite particle dispersion liquid in which composite particles containing the thermosetting agent are dispersed are prepared.
In each step of the method for producing a powder coating material, the first resin particles, the second resin particles, and the composite particles are generally referred to as "resin particles", and the dispersion liquid of these resin particles is referred to as "resin particle dispersion liquid". It will be described as.

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

Examples of the dispersion medium used in the resin particle dispersion liquid include an aqueous medium.
Examples of the aqueous medium include water such as distilled water and ion-exchanged water; alcohols and the like. These may be used alone or in combination of two or more.

Examples of the surfactant include anionic surfactants such as sulfate ester type, sulfonate type, phosphoric acid ester type and soap type; cationic surfactants such as amine salt type and quaternary ammonium salt type; Examples thereof include nonionic surfactants such as polyethylene glycol-based, alkylphenol ethylene oxide adduct-based, and polyhydric alcohol-based. 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.
The surfactant may be used alone or in combination of two or more. It is possible to adjust the charge of the powder coating material by using two or more kinds of surfactants and leaving a small amount of some surfactants due to the difference in solubility in water.

Examples of the method for dispersing the resin particles in the dispersion medium in the resin particle dispersion liquid include general dispersion methods such as a rotary shear homogenizer, a ball mill having a medium, a sand mill, and a dyno mill. Further, depending on the type of the resin particles, the resin particles may be dispersed in the resin particle dispersion liquid by using, for example, a phase inversion emulsification method.
In the phase inversion emulsification method, a resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, and a base is added to the organic continuous phase (O phase) to neutralize the resin, and then an aqueous medium is used. By adding (W phase), the resin is converted from W / O to O / W (so-called phase inversion) to make it discontinuous, and the resin is dispersed in an aqueous medium in the form of particles. be.

Specifically, there are the following methods as a method for preparing the resin particle dispersion liquid.
For example, when the resin particle dispersion liquid is a polyester resin particle dispersion liquid in which polyester resin particles are dispersed, the polyester resin particle dispersion liquid is obtained by heating and melting the raw material monomer and polycondensing it under reduced pressure. The condensate is dissolved by adding a solvent (for example, ethyl acetate), and further, stirring and phase inversion emulsification are performed while adding a weakly alkaline aqueous solution to the obtained solution.

When the resin particle dispersion liquid is a composite particle dispersion liquid, the thermosetting resin and the thermosetting agent are mixed and dispersed in a dispersion medium (for example, emulsification such as phase inversion emulsification) to disperse the composite particles. Get the 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.
The volume average particle size of the resin particles is determined by using the particle size distribution obtained by the measurement of a laser diffraction type particle size distribution measuring device (for example, manufactured by Horiba Seisakusho, LA-700) with respect to the divided particle size range (channel). , The cumulative distribution is subtracted from the small particle size side for the volume, and the particle size that is cumulatively 50% of all particles is measured as the volume average particle size D50v. The volume average particle diameter of the particles in the other dispersion is also measured in the same manner.

Here, a known emulsification method can be used to prepare the resin particle dispersion liquid, 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). ) Is effective in the phase inversion emulsification method.

In the phase inversion emulsification method, the resin is dissolved in an organic solvent that dissolves the resin, or an amphipathic organic solvent alone or in a mixed solvent to obtain an oil phase. A small amount of the basic compound is added dropwise while stirring the oil phase, and water is gradually added dropwise while further stirring, and water droplets are incorporated into the oil phase. Next, when the amount of water dropped exceeds a certain amount, the oil phase and the water phase are reversed and the oil phase becomes oil droplets. After that, the aqueous dispersion is obtained through the solvent removal step of reducing the pressure.

The amphipathic 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. If the solubility is less than 5 g / L, the effect of accelerating the aqueous treatment rate is poor, and the obtained aqueous dispersion is also inferior in storage stability. Examples of the amphoteric 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, ethyl propionate, diethyl carbonate, etc. Esters such as 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 Glycol derivatives such as 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 methyl ether acetate, dipropylene glycol monobutyl ether, and further. , 3-methoxy-3-methylbutanol, 3-methoxybutanol, acetonitrile, dimethylformamide, dimethylacetamide, diacetone alcohol, ethyl acetoacetate and the like. These solvents can be used alone or in admixture of two or more.

The thermosetting polyester resin as the thermosetting resin is neutralized with a basic compound when it is dispersed in an aqueous medium. The neutralization reaction of the thermosetting polyester resin with the carboxyl group is the starting force for making it water-based, and the electric repulsive force between the generated carboxyl anions makes it easier to suppress the aggregation between the particles.
Examples of the basic compound include ammonia and an organic amine compound having a boiling point of 250 ° C. or lower. Examples of preferred organic amine compounds are 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 thereof include triethanolamine, morpholin, N-methylmorpholin, N-ethylmorpholin and the like.
The basic compound is added in an amount capable of at least partially neutralizing, that is, 0.2 times equivalent or more and 9.0 times equivalent or less with respect to the carboxyl group, depending on the carboxyl group contained in the thermosetting polyester resin. It is preferable, and it is more preferable to add 0.6 times equivalent or more and 2.0 times equivalent or less. If the equivalent is 0.2 times or more, the effect of adding the basic compound is likely to be recognized. If the equivalent is 9.0 times or less, it is considered that the hydrophilicity of the oil phase is suppressed from being excessively increased, but the particle size distribution is difficult to be widened and a good dispersion can be easily obtained.

The content of the resin particles contained in the resin particle dispersion is, for example, preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less.

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

<First agglomerated particle forming step>
Next, the first resin particle dispersion liquid, the thermosetting agent dispersion liquid, and the colorant dispersion liquid are mixed.
Then, in the mixed dispersion, the first resin particles, the thermosetting agent, and the colorant are heteroaggregated, and the first resin particles, the thermosetting agent, and the colorant have a diameter close to the diameter of the target powder particles. The first agglomerated particles containing and are formed.

Specifically, for example, a flocculant is added to the mixed dispersion, 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 dispersed in a mixed dispersion liquid heated to a temperature of the glass transition temperature of the first resin particles (specifically, for example, the glass transition temperature of the first resin particles is -30 ° C or higher and the glass transition temperature is -10 ° C or lower). To agglomerate to form first agglomerated particles.

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

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

Examples of the flocculant include a surfactant having the opposite polarity to the surfactant used as the dispersant added to the mixed dispersion, a metal salt, a metal salt polymer, and a metal complex. When a metal complex is used as the flocculant, the amount of the surfactant used is reduced and the charging characteristics are improved.
After the completion of aggregation, an additive that forms a complex or a similar bond with the metal ion of the flocculant may be used, if necessary. As this additive, a chelating agent is preferably used. By adding this chelating agent, when the flocculant is added excessively, the content of metal ions in the powder particles can be adjusted.

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

<Second agglomerated particle forming step>
Next, the first agglomerated particle dispersion liquid in which the obtained first agglomerated particles are dispersed and the second resin particle dispersion liquid are mixed.
The second resin particles may be of the same type as the first resin particles or may be of different types.

Then, in the mixed dispersion liquid in which the first agglomerated particles and the second resin particles are dispersed, the second resin particles are agglomerated so as to adhere to the surface of the first agglomerated particles, and the first agglomerated particles are attached to the surface of the first agglomerated particles. 2 Form second agglomerated particles to which resin particles are attached.

Specifically, for example, in the first agglomerated particle forming step, when the first agglomerated particles reach the target particle size, the second resin particle dispersion liquid is mixed with the first agglomerated particle dispersion liquid, and this The mixed dispersion is heated below the glass transition temperature of the second resin particles.
Then, by setting the pH of the mixed dispersion liquid in the range of, for example, 6.5 or more and 8.5 or less, the progress of aggregation is stopped.

As a result, the second agglomerated particles that are agglomerated so that the second resin particles adhere to the surface of the first agglomerated particles can be obtained. The charge of the powder coating material can be adjusted by controlling the amount and pH of the second resin particles.

<Fusion union process>
Next, with respect to the second agglomerated particle dispersion liquid in which the second agglomerated particles are dispersed, for example, 10 than the glass transition temperature of the first and second resin particles (for example, 10 from the glass transition temperature of the first and second resin particles). The second agglomerated particles are fused and coalesced to form powder particles by heating to a temperature higher than 30 ° C.).

Through the above steps, powder particles are obtained.

Here, after the fusion and coalescence step is completed, the powder particles formed in the dispersion liquid are subjected to a known washing step, solid-liquid separation step, and drying step to obtain powder particles in a dried state.
In the cleaning step, it is preferable to sufficiently perform replacement cleaning with ion-exchanged water from the viewpoint of chargeability. The solid-liquid separation step is not particularly limited, but suction filtration, pressure filtration, or the like may be performed from the viewpoint of productivity. The drying step is also not particularly limited, but from the viewpoint of productivity, freeze-drying, air-flow drying, fluid drying, vibration-type fluid drying and the like may be performed.

The powder coating material according to the present embodiment is produced by adding inorganic particles to the obtained dry powder particles and mixing them.
The above mixing may be performed by, for example, a V blender, a Henschel mixer, a Reedige mixer or the like.
Further, if necessary, coarse particles of powder particles may be removed by 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 above-mentioned powder coating material according to the present embodiment, in which a charged powder coating material is ejected and the powder coating material is attached (coated) to an object to be coated. It has a step of causing the coating film to be formed (hereinafter, also referred to as a “coating step”) and a step of heating the powder coating material adhering to the object to be coated to form a coating film (hereinafter, also referred to as a “baking step”).
Hereinafter, each step will be described.

<Painting process>
In the coating step, the charged powder coating material is discharged, and the powder coating material is electrostatically adhered (coated) to the object to be coated to form an adhesive 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 coated surface (the surface having conductivity) of the object to be coated. The charged powder coating material is discharged from the discharge port of the body coating machine, and the powder coating material is electrostatically adhered to the surface to be coated to coat the adhered layer. That is, for example, a voltage is applied by using the surface to be coated of the grounded object to be coated as an anode and an electrostatic powder coating machine as a cathode to form an electrostatic field (electrostatic field) on both poles to cause the charged powder coating material to fly. Then, it electrostatically adheres to the coated surface of the object to be coated to form a film of powder coating material.
The coating step may be performed while relatively moving the discharge port of the electrostatic powder coating machine and the coated surface of the object to be coated.

Here, examples of the electrostatic powder coating machine include a corona gun (a coating machine that discharges powder coating charged by corona discharge), a tribogan (a coating machine that discharges powder coating by triboelectric charging), and a bergan (a coating machine that discharges powder coating by triboelectric charging). Alternatively, a well-known electrostatic powder coating machine such as a coating machine that centrifuges and discharges powder coating material charged by triboelectric charging is used. The discharge condition for good coating may be in the setting range of each gun.

The amount of 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 / g / m) from the viewpoint of suppressing fluctuations in the smoothness of the coating film. m ² or less) is good.
On the other hand, when the coating film formed on the object to be coated becomes thicker, that is, the amount of adhesion increases (for example, the amount of adhesion is 120 g / m ² or more), electric charges are more likely to be accumulated, so that the coating film becomes rough (popping marks). It becomes easy to occur. However, according to the present embodiment, as described above, the accumulation of electric charges in the adhesive layer is reduced, and the occurrence of coating film roughness (popping marks) is suppressed.

<Baking process>
In the baking step, the adhesive layer is heated to form a coating film (coating 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 coating material. As an example, the heating temperature (baking temperature) is, for example, 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).

<Painted object>
Here, the object to be coated, which is the object to be coated with the powder coating material, 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 such as plate-shaped articles and linear articles before being molded, or molded for electronic parts, road vehicles, building interior / exterior materials, and the like. It may be a product. Further, the target article may be an article in which the surface to be coated is previously subjected to surface treatment such as primer treatment, plating treatment, electrodeposition coating and the like.

Hereinafter, the present embodiment will be described in detail with reference to Examples, but the present embodiment is not limited to these Examples. In the following description, unless otherwise specified, "parts" and "%" are all based on mass.

(Preparation of powder particles)
<Preparation of white pigment dispersion liquid (W1)>
-Titanium oxide (A-220 manufactured by Ishihara Sangyo Co., Ltd.): 100 parts-Anionic surfactant (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd .: Neogen RK): 15 parts-Nonion surfactant (manufactured by Nippon Emulsifier Co., Ltd .: Newcol 2310): 0 .2 parts ・ Ion exchanged water: 400 parts ・ 0.3 mol / l nitrate: 4 parts or more are mixed and dissolved, and 3 using a high-pressure impact disperser Ultimateizer (manufactured by Sugino Machine Co., Ltd., HJP30006) A white pigment dispersion was prepared by dispersing titanium oxide over time. When measured using a laser diffraction particle size measuring device, the volume average particle size 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)>
A 3-liter reaction tank with a jacket (manufactured by Tokyo Rika Kikai Co., Ltd .: BJ-30N) equipped with a condenser, a thermometer, a water dripping device, and an anchor blade is maintained at 40 ° C. in a water circulation type constant temperature bath. A mixed solvent of 180 parts of ethyl acetate and 80 parts of isopropyl alcohol was added thereto, and the following composition was added thereto.
Polyester resin (PES1) [polycondensate of terephthalic acid / ethylene glycol / neopentyl glycol / trimethylolpropane (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 ・ Block isocyanate curing agent VESTAGONB1530 (EVONIK) (Manufactured by): 60 parts ・ Benzoin: 1.5 parts ・ Acrylic oligomer (Acronal 4F, BASF): 3 parts

After charging, the mixture was stirred at 150 rpm using a three-one motor and dissolved to obtain an oil phase. A mixed solution of 1 part of a 10 mass% aqueous ammonia solution and 47 parts of a 5 mass% sodium hydroxide aqueous solution was added dropwise to the stirred oil phase in 5 minutes, mixed for 10 minutes, and then ion-exchanged water 900. The portions were added dropwise at a rate of 5 parts per minute to invert the phase, and an emulsion was obtained.
Immediately, 800 parts of the obtained emulsion and 700 parts of ion-exchanged water were placed in a 2 liter eggplant flask and set in an evaporator (manufactured by Tokyo Rika Kikai Co., Ltd.) equipped with a vacuum control unit via a trap ball. .. 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 amount of solvent recovered reached 1100 parts, the pressure was returned to normal pressure (1 atm), and the eggplant flask was water-cooled to obtain a dispersion liquid. The obtained dispersion had no solvent odor. The volume average particle diameter of the resin particles in this dispersion was 145 nm. Then, an anionic surfactant (Dowfax2A1, manufactured by Dow Chemical Co., Ltd., active ingredient amount 45% by mass) was added and mixed as an active ingredient with respect to the resin content in the dispersion liquid, and ion-exchanged water was added to add the solid content. The concentration was adjusted to 25% by mass. This was used as a polyester resin / curing agent composite dispersion (E1).

<Preparation of white powder particles (PC1)>
-Agglomeration process-
-Polyester resin / curing agent composite dispersion (E1): 180 parts (solid content 45 parts)
-White pigment dispersion liquid (W1): 160 parts (solid content 40 parts)
-Ion-exchanged water: 200 parts or more were mixed and dispersed in a round stainless steel flask using a homogenizer (Ultratarax T50 manufactured by IKA). Then, a 1.0 mass% nitric acid aqueous solution was used to adjust the pH to 3.5. To this, 0.40 part of a 10 mass% polyaluminum chloride aqueous solution was added, and the dispersion operation was continued with Ultratarax.
A stirrer and a mantle heater are installed, the temperature is raised to 50 ° C. while adjusting the stirring rotation speed so that the slurry is sufficiently stirred, and the mixture is held at 50 ° C. for 15 minutes, and then the 10 mass% polyaluminum chloride aqueous solution 0. .10 parts were added. The particle size of the agglomerated particles was measured with a Coulter counter [Multisizer-II] type (aperture diameter: 50 μm, manufactured by Beckman-Coulter), and when the volume average particle size became 5.5 μm, a polyester resin was used as the shell. 60 parts of the curing agent composite dispersion liquid (E1) was slowly added.

-Fusion union process-
After holding for 30 minutes after charging, the pH was adjusted to 7.0 using a 5% aqueous sodium hydroxide solution. Then, the temperature was raised to 85 ° C. and maintained for 2 hours.

-Filtration, cleaning and drying processes-
After completion of the reaction, the solution in the flask was cooled at 3 ° C./min and filtered to obtain a solid content. Next, this solid content was washed with ion-exchanged water and then solid-liquid separated by Nutche-type suction filtration to obtain a solid content again.
Next, this solid content was redistributed in 3 liters of ion-exchanged water at 40 ° C., and the mixture was 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 Nucci type suction filtration was vacuum-dried for 12 hours to obtain white powder particles (PC1).

When the particle size of the white powder particles (PC1) was measured, the volume average particle size D50v was 6.1 μm, and the volume particle size distribution index GSDv was 1.24. The average circularity was 0.98.

<Preparation of clear powder particles (PC2)>
White powder except that no white pigment was added in the above-mentioned aggregation step, that is, only the polyester resin / curing agent composite dispersion (E1) and ion-exchanged water were used without using the white pigment dispersion (W1). Clear powder particles (1) were produced by the same method as for producing the particles (1).
When the particle size of the clear powder particles (PC2) was measured, the volume average particle size D50v was 6.4 μm, and the volume particle size distribution index GSDv was 1.24. The average circularity was 0.97.

<Preparation of kneaded and crushed white colored powder particles (PC3)>
-Titanium oxide (A-220 manufactured by Ishihara Sangyo): 200 parts-Polyester resin (PES1) [Polycondensate of terephthalic acid / ethylene glycol / neopentyl glycol / trimethylolpropane (molecular ratio = 100/60/38/2 (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 ・ Block isocyanate hardener VESTAGON B1530 (manufactured by EVONIK): 60 parts ・ Benzoin: 1.5 parts ・ Acrylic oligomer (Acronal 4F, BASF): 3 parts or more are premixed with a mixer. Next, kneading is performed while heating to 100 ° C. with an extruder, coarsely pulverized and placed on flakes. Next, fine pulverization is performed using a turbo mill aiming at a particle size of 6 μm, classification is carried out, and kneaded pulverized white powder. A paint (PC3) was obtained.
When the particle size of the kneaded and pulverized white powder particles (PC3) was measured, the volume average particle size D50v was 6.8 μm, and the volume particle size distribution index GSDv was 1.33.

<Preparation of fluorine-based resin-containing powder particles (PC4)>
(Preparation of oil phase 1)
-Fluorine resin Lumiflon (registered trademark) LF710F (manufactured by Asahi Glass Co., Ltd., glass transition temperature = 51 ° C., hydroxyl value (OHv) = 46 mgKOH / g): 100.0 parts-Block isocyanate curing agent VESTAGONB1530 (manufactured by EVONIK): 20 Part-Ethyl acetate: 100 parts The above material was placed in a beaker and stirred at 3000 rpm for 1 minute using a disper (manufactured by Primix Corporation) to prepare an oil phase 1.

(Preparation of aqueous phase 1)
・ 50% aqueous solution of sodium dodecyldiphenyl ether disulfonate (eleminol MON-7, manufactured by Sanyo Kasei Kogyo): 30.0 parts ・ 1% aqueous solution of carboxymethyl cellulose: 100.0 parts ・ Ion-exchanged water: 400.0 parts Container The aqueous phase 1 was prepared by stirring with a TK homomixer (manufactured by Primix Corporation) at 5000 rpm for 1 minute.

The oil phase 1 was put into the aqueous phase 1, the rotation speed of the TK homomixer was increased to 10000 rpm, and stirring was continued for 1 minute, and the oil phase 1 was suspended in the aqueous phase 1 to obtain a particle dispersion liquid. Then, the solvent was removed at 30 ° C. under a reduced pressure of 50 mmHg, and the operations of filtration and redispersion in ion-exchanged water were repeated to remove the surfactant remaining in the slurry to obtain a filtered cake. After drying, classification was carried out to obtain fluorine-based resin-containing powder particles (PC4).

When the particle size of the fluororesin-containing powder particles (PC4) was measured, the volume average particle size D50v was 6.55 μm, and the volume particle size distribution index GSDv was 1.19. The average circularity was 0.96.

(Preparation of inorganic particles)
The details of the inorganic particles used in the examples are shown in Table 1 below.

[Example 1]
White powder particles (PC1): 100 parts, inorganic particles (M1): 1.2 parts, and hydrophobic silica particles (R974, manufactured by Nippon Aerosil Co., Ltd.) with a volume average particle size of 12 nm: 0.5 parts. After mixing at a peripheral speed of 32 m / s for 10 minutes using a Henshell mixer, coarse particles were removed using a 45 μm mesh sieve to obtain a white powder coating material.

[Examples 2 to 9, Comparative Examples 1 to 2]
A powder coating material was obtained in the same manner as in Example 1 except that the powder particles and inorganic particles used were changed as shown in Table 2 below.

<Electrostatic powder coating>
Each powder paint was loaded into Asahi Sanac Corona Gun XR4-110C.
Asahi Sanac Corona Gun XR4-110C is moved up and down at a distance of 20 cm from the front of the panel (distance between the panel and the discharge port of the corona gun) with respect to a 30 cm x 30 cm square test panel (painted object) of a mirror-finished aluminum plate. By sliding it to the left and right, the powder coating was discharged and electrostatically adhered to the panel to obtain an adhesion layer. The applied voltage of the corona gun is 80 kV, the input air pressure is 0.55 MPa, the discharge rate is 100 g / min, and the amount of powder paint adhered to the panel is 50 g / m ² , 90 g / m ² , 180 g / m ² , or Four coatings at 220 g / m ² were carried out.
Then, each panel was placed in a high temperature chamber set at 180 ° C. and heated (baked) for 30 minutes.

<Measurement of attenuation factor>
"(Q30-Q300) / Q30" of the charge amount Q30 30 seconds after the end of adhesion and the charge amount Q300 300 seconds after the end of adhesion in the adhesion layer adhered (coated) at an adhesion amount of 100 g / m ^2. _{The decay rate [30-300]} (%) represented by the absolute value of was measured by the method described above.
_{Further, the decay rate [30-200]} (%) represented by the absolute value of "(Q30-Q200) / Q30" of the charge amount Q30 30 seconds after the end of adhesion and the charge amount Q200 200 seconds after the end of adhesion. _{), Attenuation rate [30-300]} (%) represented by the absolute value of "(Q30-Q100) / Q30" of the charge amount Q30 30 seconds after the end of adhesion and the charge amount Q100 100 seconds after the end of adhesion. ) Was measured by the method described above.

<Evaluation of coating film roughness>
An adhesion layer was formed with each adhesion amount, and the surface of the coating film after baking by the above method was observed and evaluated by the following four-step evaluation. If the evaluation is "1" or "2", it can withstand practical use. The evaluation results are shown in Table 2.
-Evaluation criteria-
1: No rough coating film (popping marks) is observed on the surface of the coating film.
2: Slight roughening of the coating film (popping marks) is observed.
3: Rough coating film (popping marks, uneven coating) is observed.
4: On the coated surface, there is a part where the coating film cannot be formed, and therefore there is a part where the square test panel can be 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,} 200 hours, the light irradiation (light source: xenon lamp, irradiance: 540W ^/ m 2 = 100k lux , Without UV cut filter).
After the light irradiation was completed, the surface of the coating film was wiped off with a cloth containing water, and then the coating film roughness was evaluated in the same manner as described above. The evaluation results are shown in Table 2.

As shown in Table 2, in _{each example using the powder coating film having a damping factor [30-300] in} the range of 30% or more and 60% or less, the powder having a damping factor _[30-300] outside the above range. It can be seen that the occurrence of coating film roughness in the formed coating film is suppressed as compared with each comparative example using the body paint.

Claims (6)

Including powder particles and inorganic particles,
The volume average particle diameter of the powder particles is 3 μm or more and 10 μm or less.
"(Q30-Q300)" in the case where the charge amount 30 seconds after the end of adhesion is Q30 and the charge amount 300 seconds after the end of adhesion is Q300 in the adhesion layer having an adhesion amount of 100 g / m ^{2 adhered to the substrate.} _{A powder coating material having a decay rate [30-300]} (%) represented by an absolute value of "/ Q30" of 30% or more and 60% or less. _{The attenuation factor [30-100]} (%) represented by the absolute value of "(Q30-Q100) / Q30" when the amount of charge 100 seconds after the end of adhesion in the adhesion layer is Q100 is 5% or more 20. The powder coating according to claim 1, which is less than or equal to%. The powder coating material according to claim 1 or 2, wherein the volume average particle diameter of the inorganic particles is 10 nm or more and 100 nm or less. The powder coating material according to any one of claims 1 to 3 , wherein the inorganic particles have an aspect ratio of 1 or more and 5 or less. The powder coating material according to any one of claims 1 to 4 , wherein the inorganic particles are titania particles. The step of ejecting the charged powder coating material according to any one of claims 1 to 5 to attach the powder coating material to the object to be coated.
The process of heating the powder paint adhering to the object to be coated to form a coating film,
Electrostatic powder coating method with.