Flow dip coating method and flow dip coating apparatus

Abstract

The present invention relates to a flow dip coating method and a flow dip coating apparatus. The present invention provides a flow dip-based coating method including the steps of: introducing air from a bottom of a flow tank storing a powder coating at an average air velocity of 5 mm / min or more and 20 mm / min or less per unit area of the bottom, so that a floating rate of the powder coating is 5% or more and 20% or less, in a state in which at least a portion of a coated object having a temperature of a softening temperature or more and a melting temperature or less of the powder coating is dipped in the powder coating; removing the coated object from the powder coating; and heating the powder coating adhered to the coated object.

Description

Technical Field

[0001] This invention relates to a fluid impregnation coating method and a fluid impregnation coating apparatus. Background Technology

[0002] The fluidized bed coating method described below is well known. In this method, air is supplied from the bottom of a fluidized bed containing powder coating material, the object to be coated is immersed in the fluidized powder coating material, and after being removed from the powder coating material, the film of powder coating material adhering to the object to be coated is heated to form a coating film.

[0003] For example, Japanese Patent Application Publication No. 2001-234112 discloses "a powder coating for flow impregnation coating, comprising polyolefin resin powder, inorganic powder and metal soap powder, with a median particle size of 90 to 160 μm, a bulk density of 0.35 to 0.50 g / ml and an angle of repose of 20 to 35 degrees". Summary of the Invention

[0004] However, it is difficult to form a thin coating film using the flow dip coating method.

[0005] Therefore, the technical problem to be solved by the present invention is to provide a flow dip coating method that can achieve continuous thin film coating compared with the cases where the average air velocity introduced from the bottom of the flow tank is less than 5 mm / min or greater than 20 mm / min, the floating rate of the powder coating is less than 5% or greater than 20%, and the temperature of the coated object is lower than the softening temperature of the powder coating or higher than the melting temperature.

[0006] According to a first aspect of the present invention, a coating method based on flow impregnation is provided, comprising the following steps:

[0007] Air is introduced from the bottom of the flow tank containing the powder coating at an average air flow rate of 5 mm / min to 20 mm / min per unit area of ​​the bottom, so that the floating rate of the powder coating is 5% to 20%. Under this condition, at least a portion of the object to be coated, with a temperature above the softening temperature and below the melting temperature of the powder coating, is immersed in the powder coating.

[0008] The step of removing the coated material from the powder coating; and

[0009] The step of heating the powder coating that is adhered to the coated object.

[0010] According to a second aspect of the present invention, the object to be coated is preheated in a range of softening temperature +20°C or higher and melting temperature +5°C or lower than that of the powder coating, and then impregnated with the powder coating.

[0011] According to the third aspect of the present invention, the volume average particle size D50v of the powder coating is 5 μm or more and 20 μm or less, and the aeration flow energy AE of the powder coating is 5 mJ or more and less than 100 mJ (here, AE is obtained using a powder rheometer with a cross-sectional area of...). The container was tested under the conditions of a rotating blade tip velocity of 100 mm / s, a rotating blade entry angle of -5°, and an air flow rate of 20 ml / min.

[0012] According to the fourth aspect of the present invention, the volumetric particle size distribution index GSDv of the above-mentioned powder coating is 1.15 or more and 1.40 or less.

[0013] According to the fifth aspect of the present invention, the volumetric particle size distribution index GSDv of the powder coating is 1.15 or more and 1.25 or less.

[0014] According to the sixth aspect of the present invention, the above-mentioned buoyancy rate is more than 10% and less than 20%.

[0015] According to the seventh aspect of the present invention, the powder coating contains powder particles and external additives added to the powder particles.

[0016] According to the eighth aspect of the present invention, the aforementioned external additive is a hydrophobic external additive.

[0017] According to the ninth aspect of the present invention, the volume average particle size of the aforementioned external additive is 5 nm or more and 30 nm or less.

[0018] According to a tenth aspect of the present invention, a coating apparatus based on flow impregnation is provided, comprising the following mechanisms:

[0019] The flow tank stores powder coating, and air is introduced from the bottom at an average air flow rate of 5 mm / min to 20 mm / min per unit area of ​​the bottom.

[0020] The impregnation mechanism impregnates at least a portion of the object to be coated, which is at a temperature above the softening temperature and below the melting temperature of the powder coating, in the powder coating when the floating rate of the powder coating in the flow tank is 5% to 20%.

[0021] The removal mechanism removes the coated material from the powder coating; and

[0022] A heating mechanism heats the powder coating that is attached to the coated material.

[0023] According to the 11th aspect of the present invention, the coating apparatus further includes a preheating mechanism for preheating the object to be coated in a range of softening temperature of the powder coating +20°C or higher and melting temperature of the powder coating +5°C or lower; the impregnation mechanism impregnates the object to be coated, which has been preheated by the preheating mechanism, into the powder coating.

[0024] According to the 12th aspect of the present invention, the volume average particle size D50v of the powder coating is 5 μm or more and 20 μm or less, and the airflow energy AE of the powder coating is 5 mJ or more and less than 100 mJ (here, AE is obtained using a powder rheometer with a cross-sectional area of...). The container was tested under the conditions of a rotating blade tip velocity of 100 mm / s, a rotating blade entry angle of -5°, and an air flow rate of 20 ml / min.

[0025] According to the 13th aspect of the present invention, the volumetric particle size distribution index GSDv of the above-mentioned powder coating is 1.15 or more and 1.40 or less.

[0026] According to the 14th aspect of the present invention, the volumetric particle size distribution index GSDv of the powder coating is 1.15 or more and 1.25 or less.

[0027] According to the 15th aspect of the present invention, the above-mentioned upward floating rate is more than 10% and less than 20%.

[0028] According to the 16th aspect of the present invention, the powder coating contains powder particles and external additives added to the powder particles.

[0029] According to the 17th aspect of the present invention, the aforementioned external additive is a hydrophobic external additive.

[0030] According to the 18th aspect of the present invention, the volume average particle size of the external additive is 5 nm or more and 30 nm or less.

[0031] (Effect)

[0032] According to the first embodiment above, a flow immersion coating method is provided. Compared with cases where the average air velocity introduced from the bottom of the flow tank is less than 5 mm / min or greater than 20 mm / min, the floating rate of the powder coating is less than 5% or greater than 20%, and the temperature of the coated object is lower than the softening temperature of the powder coating or higher than the melting temperature, the flow immersion coating method of this embodiment can achieve continuous thin film coating.

[0033] According to the second scheme mentioned above, a flow impregnation coating method is provided. Compared with the case where the preheating temperature of the object to be coated is lower than the softening temperature of the powder coating by 20°C or higher than the melting temperature by 5°C, the flow impregnation coating method of this scheme can achieve continuous thin film coating.

[0034] According to the above-mentioned schemes 3, 7, 8 or 9, a flow impregnation coating method is provided, which can achieve continuous thin film coating compared with the case where the volume average particle size D50v of powder coating is greater than 20 μm or the gas flow energy is less than 5 mJ or greater than 100 mJ.

[0035] According to the above-mentioned schemes 3, 4 or 5, a flow impregnation coating method is provided, which can achieve continuous thin film coating compared with the case where the volume particle size distribution index GSDv of powder coating is greater than 1.40 or greater than 1.25.

[0036] According to the sixth embodiment above, a flow impregnation coating method is provided, which, compared with the case where the floating rate exceeds 20% when air is introduced from the bottom of the flow tank at a ventilation rate of 5 mm / min to 10 mm / min per unit area of ​​the bottom when the powder coating is stored in the flow tank, the flow impregnation coating method of this embodiment can achieve continuous thin film coating.

[0037] According to the 10th embodiment above, a coating apparatus based on flow impregnation is provided. Compared with cases where the average air velocity introduced from the bottom of the flow tank is less than 5 mm / min or greater than 20 mm / min, the floating rate of the powder coating is less than 5% or greater than 20%, and the temperature of the coated object is lower than the softening temperature of the powder coating or higher than the melting temperature, the apparatus of this embodiment can achieve continuous thin film coating.

[0038] According to the 11th embodiment above, a coating apparatus based on flow impregnation is provided. Compared with the case where the preheating temperature of the object to be coated is lower than the softening temperature of the powder coating by 20°C or higher than the melting temperature by 5°C, the apparatus of this embodiment can achieve continuous thin film coating.

[0039] According to the above-mentioned 12th, 16th, 17th or 18th schemes, a coating apparatus based on flow impregnation is provided, which can achieve continuous thin film coating compared with the case where the volume average particle size D50v of powder coating is greater than 20 μm or the gas flow energy is less than 5 mJ or greater than 100 mJ.

[0040] According to the above-mentioned 12th, 13th or 14th scheme, a coating apparatus based on flow impregnation is provided, which can achieve continuous thin film coating compared with the case where the volumetric particle size distribution index GSDv of powder coating is greater than 1.40 or greater than 1.25.

[0041] According to the 15th embodiment above, a coating apparatus based on flow impregnation is provided, which, compared with the case where the buoyancy rate is greater than 20% when air is introduced from the bottom of the flow tank under the condition that the powder coating is stored in the flow tank and the air flow rate per unit area of ​​the bottom is more than 5 mm / min and less than 10 mm / min, can achieve continuous thin film coating. Attached Figure Description

[0042] Figure 1 This is a diagram illustrating the method for determining flowability energy using a powder rheometer.

[0043] Figure 2 A graph showing the relationship between vertical load and energy gradient obtained using a powder rheometer.

[0044] Figure 3 This is a schematic diagram illustrating the shape of the rotating blades used in a powder rheometer.

[0045] Figure 4 This is a diagram illustrating the preheating temperature conditions for obtaining a thin, continuous coated film on the substrate. Detailed Implementation

[0046] The following describes an embodiment of the present invention.

[0047] It should be noted that, within the numerical range recorded in stages, the upper or lower limit value recorded in a certain numerical range can be replaced with the upper or lower limit value of the numerical range of other stages recorded.

[0048] In addition, within the numerical range, the upper or lower limit value recorded in a certain numerical range can be replaced with the value shown in the embodiment.

[0049] <Flow Dip Coating Method>

[0050] The flow immersion coating method of this embodiment is as follows: air is introduced from the bottom of a flow tank storing powder coating at an average air flow rate of 5 mm / min to 20 mm / min per unit area at the bottom, so that the floating rate of the powder coating is 5% to 20%. Under this condition, at least a portion of the object to be coated, which has been preheated in a range above the softening temperature and below the melting temperature of the powder coating, is immersed in the powder coating. After being removed from the powder coating, the film of powder coating adhering to the object to be coated is heated.

[0051] The flow dip coating method of this embodiment can achieve continuous thin film coating. The reason for this is speculated to be as follows.

[0052] Firstly, for example, in the case of applying a resin-based powder coating to the surface to ensure insulation or rust prevention of the coated object, a uniform coating film with a thickness of 20 μm or more and 30 μm or less can be applied in one coat by using a solvent-based spray coating.

[0053] However, in spray coating, the object to be coated is fixed to a bracket or similar fixture, and the solvent-based coating is diffused into the space from a distance of 200mm to 300mm. Therefore, the coating efficiency is poor for small objects, below 10%. Consequently, to coat the entire surface of the object, at least two coats (one on the surface and one on the back) are applied. Furthermore, to perform these two coats, the object must be remounted on the bracket, requiring significant time spent repeatedly fixing the object to the bracket.

[0054] On the other hand, in the flow dip coating method using powder coatings, air is supplied from the bottom of a flow tank storing powder coatings, the workpiece to be coated is immersed in the flowing powder coating, and after being removed from the powder coating, the film of powder coating adhering to the workpiece is heated to form a coating film. Therefore, the coating efficiency reaches approximately 100%. Furthermore, if flow dip coating is performed in a contactless manner, a coating film can be formed on the entire surface of the workpiece in one pass without fixing the workpiece to a support. From this perspective, the flow dip coating method based on powder coatings is advantageous. Even with solvent-based coatings, coating by such dip coating methods based on powder coatings can be considered, but generally, solvent-containing coatings have excessively high fluidity, resulting in sags or extremely thin edges, which is unsuitable for precision coating.

[0055] On the other hand, existing powder coatings require a minimum film thickness of 100 μm or more to achieve a continuous film. If the coating is to be thinner than this, the surface will exhibit noticeable unevenness or numerous discontinuities, making it extremely difficult to achieve a thin film coating. Especially for small objects used in assembly, dimensional deviations due to coating thickness directly impact assembly accuracy. Currently, it is difficult to obtain coatings using flow dip coating in applications requiring high performance.

[0056] To obtain a thin and continuous coating film, at least 2 to 3 layers of particles need to be adsorbed onto the substrate. The powder coatings used in existing flow dip coating methods have large particle sizes; if 2 to 3 layers of particles are adsorbed, a thick film with a thickness of at least 50 μm, typically 100 μm or more, will be formed. Furthermore, such large-particle-size powder coatings have high heat capacity; therefore, for them to adsorb onto the substrate, the surface temperature of the substrate needs to be above the melting temperature Tm of the powder coating (or its resin). On the other hand, to achieve a thin film and adsorb small-particle-size powder coatings, for example, to obtain a continuous film with a thickness of approximately 50 μm, particles of approximately 20 μm or less are required. With such small-particle-size powder coatings, if they come into contact with a substrate at a temperature much higher than the melting temperature Tm of the powder coating (or its resin), they melt rapidly due to their low heat capacity, forming molten droplets and hindering the formation of a continuous film.

[0057] The inventors conducted in-depth research and, assuming that the reason hindering the formation of the coating film is due to the aforementioned reasons, investigated the temperature conditions of the coated object. Until now, in order to melt the powder coating for coating, the coated object has been heated to a temperature higher than the melting temperature Tm of the powder coating (and its resin). However, the inventors have instead set it at a temperature lower than this melting temperature Tm. Furthermore, in order to soften the 2-3 particle layers of the powder coating within an appropriate time, although this varies slightly depending on the resin properties, it is necessary to maintain the powder coating near the coated area under softening conditions above the softening temperature Tg for at least 5 seconds. To meet this condition, it is necessary to adjust the temperature of the coated object and the airflow used for coating fluidization, which affects the temperature reduction of the coated object.

[0058] Therefore, in the flow impregnation coating method of this embodiment, the average air velocity from the bottom of the flow tank is reduced to 5 mm / min to 20 mm / min and the powder coating float rate is reduced to 5% to 20%, thus making the powder coating flow. As a result, the powder coating maintains a high bulk density while remaining in a flow state. When a workpiece at a temperature above the softening temperature and below the melting temperature of the powder coating is immersed in this flow-state powder coating, the powder coating is absorbed by the workpiece in a softened state, forming a dense and continuous film. The workpiece is then removed from the powder coating while maintaining this film state.

[0059] Afterward, the object to be coated is removed from the powder coating, and the powder coating film is heated, thereby melting the powder coating and continuously forming a thin coating film (for example, continuously forming a coating film with a thickness of more than 20 μm and less than 50 μm).

[0060] It is speculated that, for the reasons mentioned above, the flow dip coating method of this embodiment can achieve continuous thin film coating.

[0061] The following is a detailed description of the flow impregnation coating method of this embodiment.

[0062] In the flow immersion coating method of this embodiment, as a method for immersing the object to be coated in powder coating and then removing it from the powder coating, the following known methods can be used: immersing the object to be coated in powder coating stored in a flow tank while holding the object in the state, and then pulling it up; dropping the object to be coated into powder coating stored in a flow tank, and then conveying the object to be coated by vibration; and so on.

[0063] The powder coating may be vibrated before or during the immersion of the material in the powder coating.

[0064] During the period when the object is immersed in the powder coating, the object can be stationary or moved in a manner that draws straight lines or arcs at, for example, 10 to 20 mm / s.

[0065] The object to be coated can be partially or completely immersed in the powder coating, depending on the area where the coating film will be formed.

[0066] The average air flow rate introduced from the bottom of the flow tank is 5 mm / min or more and 20 mm / min or less, and from the perspective of achieving continuous thin film coating, it is preferably 5 mm / min or more and 10 mm / min or less.

[0067] If the average air velocity is too low, the flowability of the powder coating cannot be ensured, and the powder coating will not adhere discontinuously to the substrate, resulting in a non-continuous coating film. On the other hand, if the average air velocity is too high, the necessary bulk density (approximately 80% or higher) cannot be ensured, the adhesive film will soften and lose its compactness, resulting in significant unevenness or defects, and the quality of the molten coating film will deteriorate.

[0068] It should be noted that the average ventilation velocity is obtained by dividing the volume of air introduced from the bottom of the flow channel per unit time (min) by the area of ​​the bottom of the flow channel (the air introduction surface).

[0069] The float rate of the powder coating is between 5% and 20%, and from the perspective of achieving continuous film coating, it is preferably between 10% and 15%.

[0070] If the float ratio is too low, the flowability of the powder coating cannot be ensured, and the powder coating will not adhere discontinuously to the coated object, resulting in a non-continuous coating film. On the other hand, if the float ratio is too high, the necessary bulk density (approximately 80% or more) cannot be ensured, the adhesive film will soften and lose its density, resulting in significant unevenness or defects, and the quality of the molten coating film will deteriorate.

[0071] It should be noted that the buoyancy rate is calculated using formula H, which will be described later.

[0072] The temperature of the object to be coated is above the softening temperature and below the melting temperature of the powder coating. From the perspective of achieving continuous film coating, the preferred temperatures are: above the softening temperature of the powder coating +5°C and below the melting temperature; above the softening temperature of the powder coating +10°C and below the melting temperature; or above the softening temperature of the powder coating +20°C and below the melting temperature.

[0073] By maintaining the temperature of the object to be coated within the aforementioned range, the necessary softening and adhesion of the powder coating is achieved, enabling continuous thin-film coating.

[0074] In particular, it is preferable that after immersing the object in the powder coating, the surface temperature of the object be coated is maintained for at least 5 seconds within a range above the softening temperature and below the melting temperature of the powder coating.

[0075] It should be noted that the temperature of the object to be coated refers to the surface temperature of the object when it is immersed in the powder coating.

[0076] From the perspective of achieving continuous thin film coating, the preheating temperature of the coated material is preferably in the range of softening temperature of the powder coating +20°C or more and melting temperature +5°C or less, more preferably softening temperature of the powder coating +25°C or more and melting temperature of the powder coating +5°C or less, and even more preferably softening temperature of the powder coating +30°C or more and melting temperature of the powder coating or less.

[0077] If the preheating temperature is too low and no reheating is performed, such as Figure 4 As shown, if the temperature of the substrate drops excessively without allowing the necessary softening and bonding time for the powder coating, insufficient coating may occur. Similarly, if the preheating temperature is too high, molten droplets may form on the surface of the substrate at the start of impregnation. Therefore, it is difficult to obtain a continuous coating film.

[0078] It should be noted that the methods for determining the softening temperature and melting temperature of powder coatings are described below.

[0079] Here, the preheating temperature of the object to be coated is the temperature at which it is removed from the heating device. When at least a portion of the object to be coated is immersed in the powder coating, the surface temperature of the immersed portion of the object decreases by approximately 5°C. Furthermore, the time for forming the softening adhesive film of the powder coating is approximately 10 seconds, during which time the temperature of the object to be coated decreases by approximately 10°C. In addition, during the softening and bonding of the powder coating, it is necessary to soften the powder coating on the outer surface of the powder coating directly adsorbed by the object to be coated to the extent that two particle layers also occur; preferably, this is at least 20°C higher than the softening temperature, and more preferably at least 25°C higher. This helps to mitigate the temperature drop of the object to be coated when using an object with a large heat capacity. Especially when performing precision coating on small parts, the preheating temperature needs to be determined considering the empty feed before immersion and the temperature drop caused by heat conduction with the contact particles during immersion.

[0080] From the perspective of achieving productivity and continuous film coating, the immersion time of the coated object is preferably 5 seconds to 20 seconds, more preferably 5 seconds to 10 seconds.

[0081] The temperature at which the powder coating film adhering to the coated object is heated (hereinafter also referred to as "baking temperature") is preferably 90°C to 250°C, more preferably 100°C to 220°C. The heating time (baking time) is adjusted according to the heating temperature (baking temperature).

[0082] The thickness of the powder coating film is preferably 10 μm or more and 50 μm or less, more preferably 10 μm or more and 30 μm or less, and even more preferably 15 μm or more and 25 μm or less.

[0083] There are no particular limitations on the objects to be coated with powder coatings; various metal parts, ceramic parts, resin parts, etc., can be included. These objects can be unformed products such as sheet-like or wire-like items before being molded into various articles, or they can be molded products for use in electronic components, road vehicles, building interior and exterior decoration materials, etc. In addition, objects can be items whose surfaces have been pre-treated with a base coat, plating, electrodeposition coating, or other surface treatments.

[0084] Next, an example of a powder coating suitable for use in the flow impregnation coating method of this embodiment (hereinafter also referred to as "the powder coating of this embodiment") will be described.

[0085] The powder coating for flow impregnation coating (hereinafter also referred to as "powder coating") of this embodiment has a center particle size D50v of 5 μm or more and 20 μm or less. The air flow energy AE measured using a powder rheometer under the conditions of a blade tip velocity of 100 mm / s, a blade entry angle of -5°, and an air flow rate of 10 ml / min is 10 mJ or more and less than 100 mJ.

[0086] The powder coating of this embodiment utilizes a flow dip coating method to more easily form a thin coating film. In particular, it is easier to form a smooth and continuous coating film. The reason for this is presumably as follows.

[0087] The volume average particle size D50v is between 5 μm and 20 μm.

[0088] Using the cross-sectional area of ​​a powder rheometer The ventilated flow energy AE of the container was measured under the conditions of a blade tip velocity of 100 mm / s, a blade entry angle of -5°, and a flow rate of 20 ml / min, and was greater than 5 mJ and less than 100 mJ.

[0089] The powder coating of this embodiment can form a thin coating film using a flow dip coating method. In particular, it is easy to form a smooth and continuous coating film. The reason for this is speculated to be as follows.

[0090] Firstly, for example, in the case of applying a resin-based coating to the surface to ensure insulation or rust prevention of the coated object, a uniform coating film with a thickness of 20 μm or more and 30 μm or less can be applied in one coat by using a solvent-based coating spray.

[0091] However, in spray coating, the object to be coated is fixed to a bracket or similar fixture, and the solvent-based coating is diffused into the space from a distance of 200mm to 300mm. Therefore, the coating efficiency is poor for small objects, below 10%. Consequently, to coat the entire surface of the object, at least two coats (one on the surface and one on the back) are applied. Furthermore, to perform these two coats, the object must be remounted on the bracket, requiring significant time spent repeatedly fixing the object to the bracket.

[0092] On the other hand, in the flow dip coating method using powder coatings, air is supplied from the bottom of a flow tank storing powder coatings, the workpiece to be coated is immersed in the flowing powder coating, and after being removed from the powder coating, the film of powder coating adhering to the workpiece is heated to form a coating film. Therefore, the coating efficiency reaches approximately 100%. Furthermore, if flow dip coating is performed in a contactless manner, a coating film can be formed on the entire surface of the workpiece in one pass without fixing the workpiece to a support. From this perspective, the flow dip coating method based on powder coatings is advantageous. Even with solvent-based coatings, coating by such dip coating methods based on powder coatings can be considered, but generally, solvent-containing coatings have excessively high fluidity, resulting in sags or extremely thin edges, which is unsuitable for precision coating.

[0093] On the other hand, existing powder coatings require a minimum film thickness of 100 μm or more to achieve a continuous coating film. If the coating is to be thinner than this, the surface will exhibit noticeable unevenness or numerous discontinuities, making it very difficult to achieve a thin film coating. Especially for small objects used in assembly, dimensional deviations due to coating thickness directly impact assembly accuracy. Currently, it is difficult to obtain coatings using flow dip coating in applications requiring high performance.

[0094] The reason for this is believed to be due to the large volume average particle size (e.g., above 50 μm) and poor flowability of the powder coating.

[0095] The powder coating of this embodiment has a small volume average particle size D50v, which is more than 5 μm and less than 20 μm, and the air flow energy AE is more than 5 mJ and less than 100 mJ, and has high fluidity.

[0096] Therefore, when air is introduced into the powder coating stored in the flow tank, the powder coating forms a flowing state with a low buoyancy while maintaining a high bulk density. If a preheated substrate is immersed in this flowing powder coating, the powder coating forms a dense and continuous film after being adsorbed onto the substrate in a softened state. The substrate is then removed from the powder coating while maintaining this film state.

[0097] Afterward, the object to be coated is removed from the powder coating, and the powder coating film is heated, thereby melting the powder coating and continuously forming a thin coating film (for example, continuously forming a coating film with a thickness of more than 20 μm and less than 50 μm).

[0098] It is speculated that, for the reasons mentioned above, the powder coating of this embodiment can form a thin coating film using a flow dip coating method.

[0099] The details of the powder coating in this embodiment will be described below.

[0100] (Volume average particle size)

[0101] The volume average particle size D50v of the powder coating in this embodiment is 5 μm or more and 20 μm or less.

[0102] By making the volume average D50v of the powder coating less than 20 μm, a thin coating film can be formed using the flow dip coating method. On the other hand, when the volume average particle size D50v of the powder coating is less than 5 μm, particles flying in the airflow are not easy to settle, making it difficult to ensure a stable flow (fluidization) state of the powder coating and making it difficult to continuously perform flow dip coating.

[0103] The volume average particle size D50v of the powder coating is preferably 5 μm or more and 15 μm or less, more preferably 7 μm or more and 12 μm or less.

[0104] The method for determining the volume average particle size of powder coatings is carried out using the method described later.

[0105] (Aerodynamic Energy)

[0106] The airflow energy AE of the powder coating in this embodiment is 5 mJ or more and less than 100 mJ.

[0107] By making the air flow energy AE of the powder coating less than 100mJ, the powder coating has high fluidity and a dense mobile phase, forming a thin and dense adsorption layer, which can form a smooth and thin continuous coating film.

[0108] On the other hand, when the air flow energy AE of the powder coating is below 5mJ, the powder coating has too high fluidity, the mobile phase of the powder coating becomes too thin, the amount of adhesion on the coated object is reduced, so it cannot form a dense adsorption layer, and after calcination it is too thin, forming a discontinuous and rough coating film.

[0109] The air flow energy AE of the powder coating is preferably 7mJ or more and 80mJ or less, more preferably 7mJ or more and 60mJ or less, and even more preferably 10mJ or more and 50mJ or less.

[0110] The airflow energy (AE) of powder coatings can be adjusted by the particle size and shape of the powder particles, as well as the type and particle size of external additives.

[0111] The method for measuring ventilation flow energy (AE) is as follows.

[0112] The ventilation flow energy (AE) was measured using a powder rheometer under the conditions of a rotating blade tip velocity of 100 mm / s, a rotating blade entry angle of -5°, and a ventilation flow rate of 10 ml / min.

[0113] A powder rheometer is a flowability measuring device that directly determines flowability by simultaneously measuring the rotational torque and vertical load obtained by rotating a paddle in a helical manner within a filled powder. By measuring both the rotational torque and vertical load, flowability, including the effects of the powder's inherent properties and the external environment, can be detected with high sensitivity. Furthermore, since the measurement is performed after the particle filling state has been kept constant, data with excellent reproducibility can be obtained.

[0114] The powder rheometer used was the FT4 manufactured by Freeman Technology. It should be noted that, to avoid the influence of temperature and humidity, the powder coating was placed at 25°C and 45% RH for at least 8 hours before use.

[0115] First, fill the powder coating with a volume of 160mL or more into a cylindrical split container with a grid-shaped air inlet structure at the bottom, an inner diameter of 50mm, and a height (132mm overall and 81mm for the folding section).

[0116] After the powder coating is applied, the sample is homogenized by gently stirring the applied powder coating. This process is referred to below as conditioning.

[0117] During conditioning, the rotating blades are slowly stirred in a direction that does not exert a load on the powder coating while it is in a filled state, so as to remove most of the excess air and local stress and make the sample homogeneous. Regarding the specific conditioning conditions, stirring is carried out in the container at a height of 100 mm to 10 mm from the bottom, an entry angle of 5°, and a blade tip speed of 60 mm / s.

[0118] At this time, the spiral-shaped rotating blades move downwards while rotating, so the blade tips trace a spiral shape. The angle of the path traced by the spiral blade tips at this time is called the entry angle.

[0119] After repeating the conditioning process four times, gently move the top of the split container to a height of 81mm and level the powder coating inside, resulting in a 160mL container filled with powder coating. The conditioning process is performed because consistently obtaining a powder with a constant volume is crucial for accurately determining flowability energy.

[0120] After performing one more conditioning operation, move the container with the height from the bottom surface from 100mm to 10mm, moving it at an entry angle of -5° while simultaneously rotating it at a blade tip speed of 100mm / second. At this point, measure the rotational torque and vertical load. The direction of the screw rotation at this time is opposite to the conditioning direction (clockwise when viewed from above).

[0121] The relationship between rotational torque or vertical load and height H from the bottom surface is as follows: Figure 1 (A) Figure 1 As shown in (B), the energy gradient (mJ / mm) relative to height H is calculated from the rotational torque and vertical load, and the resulting graph is shown below. Figure 2 .Will Figure 2 The area obtained by integrating the energy gradient ( Figure 2 The slanted portion represents the fluid energy (mJ). The fluid energy (fluidity energy) is calculated by integrating the interval from 10mm to 100mm above the bottom surface.

[0122] In addition, to reduce the impact of errors, the conditioning and energy measurement operation was repeated 5 times, and the average value obtained was taken as the flow energy (mJ).

[0123] The rotating blades were manufactured by Freeman Technology. Figure 3 The double-bladed spiral shown has a diameter of

[0124] Furthermore, when measuring the rotational torque and vertical load of the aforementioned rotating blades, the flow energy measured simultaneously when air flows in from the bottom of the container at the target ventilation flow rate (ml / min) is termed "ventilation flow energy." It should be noted that in the FT4 manufactured by Freeman Technology, the inflow of air is controlled.

[0125] (Upward fluctuation rate)

[0126] In this embodiment, the floating rate of the powder coating is preferably 20% or less.

[0127] By reducing the buoyancy, a high packing density can be easily maintained even when the powder coating in the flow tank is in a flowing state due to the introduction of air. Therefore, a dense and thin film of powder coating can easily adhere to the substrate. As a result, thin and continuous coating films can be easily formed using the flow dip coating method.

[0128] On the other hand, if the floatation rate is too low, it will be difficult to make the powder coating in the flow tank flow through the introduction of air. Therefore, the lower limit of the floatation rate is preferably 5% or more, more preferably 7% or more, further preferably 10% or more, and even more preferably 15% or more.

[0129] In particular, the upward floating rate is preferably 10% to 20%, and more preferably 15% to 20%.

[0130] The flotation rate of powder coatings can be adjusted based on the average air velocity, the particle size and shape of the powder particles, and the type and particle size of external additives.

[0131] The flotation rate is the rate of change in the bulkiness of the fluidized bed when the powder coating is stored in a flow tank and aeration is introduced from the bottom of the flow tank.

[0132] The buoyancy rate is the value when the powder coating is stored in a flow tank and air is introduced from the bottom of the flow tank at an average air flow rate of 5 mm / min to 10 mm / min per unit area of ​​the bottom.

[0133] Furthermore, the buoyancy rate is calculated using the following formula H.

[0134] Formula H: Upward buoyancy (%) = (H2 - H1) / H1 × 100

[0135] In formula H, H1 represents the height of the powder coating surface stored in the flow tank when no air is introduced (i.e., the height from the bottom of the flow tank to the powder coating surface).

[0136] H2 represents the height of the powder coating stored in the flow tank after air is introduced (i.e., the height from the bottom of the flow tank to the surface of the powder coating).

[0137] It should be noted that the average ventilation velocity is the value obtained by dividing the volume of air introduced from the bottom of the flow tank per unit time (min) by the area of ​​the bottom of the flow tank (its air inlet surface). In flow impregnation coating, the cross-sectional area of ​​the flow tank is arbitrary, so the average ventilation velocity is used when expressing the impregnation conditions.

[0138] As an example, in cross-sectional area In the flow channel, the bottom area is approximately 2000 mm². 2 Air volume 20ml / min 2 This is equivalent to an average ventilation rate of 10 mm / min.

[0139] (Other features)

[0140] From the perspective of forming a thin coating film using the flow dip coating method, the volumetric particle size distribution index (GSDv) of the powder coating is preferably 1.15 to 1.40, more preferably 1.15 to 1.30, and even more preferably 1.15 to 1.25. Even with poor particle size distribution, the initial coating quality will not deteriorate significantly. However, in the case of continuous coating, the residual particle size distribution sometimes changes slowly, resulting in unstable quality.

[0141] From the perspective of forming a thin coating film using the flow dip coating method, the average roundness of the powder coating is preferably 0.9 or more and 0.995 or less, more preferably 0.93 or more and 0.995 or less, and even more preferably 0.96 or more and 0.995 or less.

[0142] The volume average particle size D50v and volumetric particle size distribution index GSDv of the powder coating were measured using a Coulter Multisizer II (Beckman Coulter), and the electrolyte was measured using an ISOTON-II (Beckman Coulter).

[0143] During the determination, 0.5 mg to 50 mg of the test sample is added to 2 ml of a 5% aqueous solution of the surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is then added to 100 ml to 150 ml of electrolyte.

[0144] The electrolyte containing the suspended sample was dispersed using an ultrasonic disperser for 1 minute. The particle size distribution of particles ranging from 1 μm to 30 μm was determined using a Coulter Multisizer II with a 50 μm pore size. 50,000 particles were sampled.

[0145] Relative to the particle size ranges (segments) defined by the measured particle size distribution, the cumulative distribution of the volumetric reference is depicted from the smallest diameter side. The particle size at the cumulative 16% point is defined as the volume average particle size D16v, the particle size at the cumulative 50% point is defined as the volume average particle size D50v, and the particle size at the cumulative 84% point is defined as the volumetric particle size D84v. The volumetric particle size distribution index GSDv is calculated as (D84v / D16v).

[0146] The average roundness of the powder coating was determined using a flow cytometry particle image analyzer (FPIA-3000, Sysmex). Specifically, 0.1 ml to 0.5 ml of a surfactant (alkylbenzene sulfonate) as a dispersant was added to 100 ml to 150 ml of water (after removing impurities), and 0.1 g to 0.5 g of the test sample was added. The suspension containing the test sample was dispersed using an ultrasonic disperser for 1 to 3 minutes to achieve a dispersion concentration of 3000 particles / μl to 10,000 particles / μl. The average roundness of the powder particles in this dispersion was then determined using a flow cytometry particle image analyzer.

[0147] The average roundness of the powder particles is calculated by the following formula to obtain the roundness (Ci) of each of the n powder particles measured. In the following formula, Ci represents the roundness (= circumference of a circle with the same projected area as the particle / circumference of the particle's projected image), and fi represents the frequency of the powder particles.

[0148] Average roundness

[0149] To ensure preservation as a coating and smoothness during firing, the softening temperature Tg of the powder coating in this embodiment is preferably 45°C or higher and 70°C or lower, more preferably 50°C or higher and 65°C or lower.

[0150] The softening temperature of powder coatings is the glass transition temperature, which is determined as follows. The glass transition temperature is obtained from the DSC curve obtained by differential scanning calorimetry (DSC), or more specifically, it is determined by extrapolating the glass transition onset temperature as described in the method for determining the glass transition temperature in JIS K7121-1987 "Method for determination of transition temperature of plastics".

[0151] From the perspectives of ensuring the tolerance of preheating temperature, the versatility of the coated object, and energy saving, the melting temperature Tm of the powder coating in this embodiment is preferably 80°C or higher and 180°C or lower, more preferably 90°C or higher and 160°C or lower.

[0152] The method for determining the melting temperature of powder coatings is as follows.

[0153] Regarding the melting temperature, a high-performance rheometer CFT-500 (manufactured by Shimadzu Corporation) was used, with a die orifice diameter of 0.5 mm and a pressure load of 0.98 MPa (10 kgf / cm²). 2 Given a heating rate of 1℃ / min, calculate the temperature that makes 1cm³... 3 The temperature at which the sample begins to flow out as it melts is taken as the melting temperature.

[0154] (constitute)

[0155] The powder coating of this embodiment has, for example, powder particles and external additives.

[0156] -Powder Particles-

[0157] Powder particles contain resin. Powder particles may also contain colorants and other additives.

[0158] --Resin--

[0159] The resin can be any of the thermoplastic resins and thermosetting resins.

[0160] On the other hand, from the perspective of improving the strength of the coated film, a thermosetting resin is preferred. When using a thermosetting resin, a thermoplastic resin can be used in combination. For example, from the perspective of improving the curing density (crosslinking density) of the coated film, the proportion of thermoplastic resin in the total resin is preferably 5% by mass or less, more preferably 1% by mass or less, and preferably substantially free of thermoplastic resin. That is, the resin contained in the powder particles is preferably only a thermosetting resin. When using both a thermosetting resin and a thermoplastic resin, it is preferable that both resins are of the same type.

[0161] It should be noted that when thermosetting resins are used as resins, the powder particles also contain thermosetting agents.

[0162] Examples of thermoplastic resins include vinyl resins formed from homopolymers of monomers or copolymers of two or more of these monomers, such as: styrene (e.g., styrene, p-chlorostyrene, α-methylstyrene, etc.), (meth)acrylates (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), olefinic unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropylene ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.).

[0163] Examples of thermoplastic resins include epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, modified rosin, and other non-vinyl resins, mixtures of these non-vinyl resins with the aforementioned vinyl resins, or graft polymers obtained by polymerizing vinyl monomers in their coexistence.

[0164] These thermoplastic resins can be used alone or in combination of two or more.

[0165] Thermosetting resins are resins that have thermosetting reactive groups. Examples of thermosetting resins include various types of resins that have been used in powder particles for powder coatings.

[0166] Examples of thermosetting resins include thermosetting epoxy resins, thermosetting (meth)acrylic resins, thermosetting silicone resins, thermosetting phenolic resins, thermosetting polyimide resins, thermosetting polyurethane resins, thermosetting melamine resins, and thermosetting urea resins.

[0167] It should be noted that thermosetting resins can also be water-insoluble (hydrophobic) resins. When water-insoluble (hydrophobic) resins are used as thermosetting resins, the environmental dependence of powder coatings (powder particles) is reduced. Furthermore, when producing powder particles via agglomeration (agglomeration-based method), water-insoluble (hydrophobic) resins are also suitable for thermosetting in aqueous media from the perspective of achieving emulsification and dispersion. Water-insoluble (hydrophobic) means that the solubility of the target substance in water at 25°C is less than 5 parts by mass per 100 parts by mass.

[0168] As a thermosetting resin, it is preferably at least one selected from the group consisting of thermosetting (meth)acrylic resins and thermosetting polyester resins.

[0169] Thermosetting (meth)acrylic resins

[0170] Thermosetting (meth)acrylic resins are (meth)acrylic resins having thermosetting reactive groups. The introduction of thermosetting reactive groups into thermosetting (meth)acrylic resins can be achieved using vinyl monomers having thermosetting reactive groups. These vinyl monomers can be (meth)acrylic monomers (monomers having (meth)acryloyl groups) or vinyl monomers other than (meth)acrylic monomers.

[0171] Examples of thermosetting reactive groups in thermosetting (meth)acrylic resins include epoxy, carboxyl, hydroxyl, amide, amino, anhydride, and (terminated) isocyanate groups. Among these, from the perspective of ease of manufacturing (meth)acrylic resins, at least one group selected from the group consisting of epoxy, carboxyl, and hydroxyl groups is preferred as the thermosetting reactive group. From the perspective of excellent storage stability and coating appearance of powder coatings, at least one epoxy group is preferred.

[0172] Regarding vinyl monomers with epoxy groups as thermosetting reactive groups, examples include various chain-type epoxy-containing monomers (e.g., glycidyl acrylate, β-methyl glycidyl acrylate, glycidyl vinyl ether, allyl glycidyl ether, etc.), various vinyl monomers containing (2-oxo-1,3-dioxopentyl) groups (e.g., methyl (2-oxo-1,3-dioxopentyl) acrylate, etc.), and various alicyclic vinyl monomers containing epoxy groups (e.g., 3,4-epoxycyclohexyl acrylate, 3,4-epoxy(cyclohexyl) methyl acrylate, 3,4-epoxy(cyclohexyl) ethyl acrylate, etc.).

[0173] Regarding vinyl monomers with carboxyl groups as curing reactive groups, examples include various carboxyl-containing monomers (e.g., (meth)acrylic acid, butenoic acid, itaconic acid, maleic acid, fumaric acid, etc.), and monoesters of various α,β-unsaturated dicarboxylic acids and monohydric alcohols with 1 to 18 carbon atoms (e.g., monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monoisobutyl fumarate, monotert-butyl fumarate, monohexyl fumarate, monooctyl fumarate). Esters, such as mono-2-ethylhexyl fumarate, monomethyl maleate, monoethyl maleate, monobutyl maleate, monoisobutyl maleate, monotert-butyl maleate, monohexyl maleate, monooctyl maleate, mono-2-ethylhexyl maleate, etc.), and various monoalkyl itaconic acid esters (such as monomethyl itaconic acid, monoethyl itaconic acid, monobutyl itaconic acid, monoisobutyl itaconic acid, monohexyl itaconic acid, monooctyl itaconic acid, mono-2-ethylhexyl itaconic acid, etc.).

[0174] Regarding vinyl monomers having hydroxyl groups as curable reactive groups, examples include various hydroxyl-containing (meth)acrylates (e.g., 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (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.), the addition reaction products of the above-mentioned hydroxyl-containing (meth)acrylates with ε-caprolactone, and various hydroxyl-containing vinyl ethers (e.g., 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-mentioned hydroxyl-containing vinyl ethers with ε-caprolactone, various hydroxyl-containing allyl ethers (e.g., 2-hydroxyethyl(methyl)allyl ether, 3-hydroxypropyl(methyl)allyl ether, 2-hydroxypropyl(methyl)allyl ether, 4-hydroxybutyl(methyl)allyl ether, 3-hydroxybutyl(methyl)allyl ether, 2-hydroxy-2-methylpropyl(methyl)allyl ether, 5-hydroxypentyl(methyl)allyl ether, 6-hydroxyhexyl(methyl)allyl ether, etc.), addition reaction products of the above-mentioned hydroxyl-containing allyl ethers with ε-caprolactone, etc.

[0175] Regarding (meth)acrylic monomers that do not possess curable reactive groups and serve as structural units in thermosetting (meth)acrylic resins, examples include alkyl (meth)acrylates (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethyloctyl (meth)acrylate, dodecyl (meth)acrylate, isodecanyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, etc.), various aryl (meth)acrylates (e.g., benzyl (meth)acrylate, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc.), and various alkyl carbitol (meth)acrylates. Examples include ethyl carbitol (meth)acrylate, various other (meth)acrylates (e.g., isobornyl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, etc.), various amino amide-containing unsaturated monomers (e.g., N-dimethylaminoethyl (meth)acrylamide, N-diethylaminoethyl (meth)acrylamide, N-dimethylaminopropyl (meth)acrylamide, N-diethylaminopropyl (meth)acrylamide, etc.), various dialkylaminoalkyl (meth)acrylates (e.g., dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, etc.), various amino-containing monomers (e.g., tert-butylaminoethyl (meth)acrylate, tert-butylaminopropyl (meth)acrylate, aziridinyl ethyl (meth)acrylate, pyrrolyl ethyl (meth)acrylate, piperidinyl ethyl (meth)acrylate, etc.), etc.

[0176] In thermosetting (meth)acrylic resins, in addition to (meth)acrylic acid monomers, other vinyl monomers that do not have curing reactive groups can also be copolymerized.

[0177] Other vinyl monomers include various α-olefins (e.g., ethylene, propylene, 1-butene), various halogenated olefins (excluding fluorinated olefins, such as vinyl chloride, vinylidene chloride, etc.), various aromatic vinyl monomers (e.g., styrene, α-methylstyrene, vinyltoluene, etc.), diesters of various unsaturated dicarboxylic acids and monohydric alcohols with 1 to 18 carbon atoms (e.g., dimethyl fumarate, diethyl fumarate, dibutyl fumarate, dioctyl fumarate, dimethyl maleate, diethyl maleate, dibutyl maleate, dioctyl maleate, dimethyl itaconic acid, diethyl itaconic acid, dibutyl itaconic acid, dioctyl itaconic acid, etc.), various monomers containing anhydride groups (e.g., maleic anhydride, itaconic anhydride, citraconic anhydride, (meth)acrylic anhydride, tetrahydrophthalic anhydride, etc.), and various monomers containing phosphate ester groups (e.g., diethyl-2-(meth)acryloyloxyethyl phosphate, dibutyl phosphate, etc.). γ-2-(meth)acryloyloxybutyl phosphate, dioctyl-2-(meth)acryloyloxyethyl phosphate, diphenyl-2-(meth)acryloyloxyethyl phosphate, etc.), various hydrolyzable silyl monomers (e.g., γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, γ-(meth)acryloyloxypropylmethyldimethoxysilane, etc.), various aliphatic carboxylic acid vinyl esters (e.g., vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl hexanoate, vinyl octanoate, vinyl decanoate, vinyl laurate, branched aliphatic carboxylic acid vinyl esters with 9 to 11 carbon atoms, vinyl stearate, etc.), and various vinyl esters of carboxylic acids with cyclic structures (e.g., cyclohexane vinyl carboxylate, methylcyclohexane vinyl carboxylate, vinyl benzoate, vinyl p-tert-butylbenzoate, etc.).

[0178] From the perspective of excellent smoothness of the coating film, the number average molecular weight of the thermosetting (meth)acrylic resin is preferably 1,000 to 20,000, more preferably 1,500 to 15,000.

[0179] The weight-average molecular weight and number-average molecular weight of the thermosetting (meth)acrylic resin were determined by gel permeation chromatography (GPC). For the molecular weight determination using GPC, a Tosoh GPC HLC-8120 GPC was used, along with a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent was employed. The weight-average molecular weight and number-average molecular weight were calculated from these results using a molecular weight calibration curve prepared using monodisperse polystyrene standard samples.

[0180] Thermosetting polyester resin

[0181] Thermosetting polyester resins are, for example, condensation polymers formed by at least polycondensation of a polyacid and a polyol. The introduction of thermosetting reactive groups into the thermosetting polyester resin is achieved by adjusting the amounts of the polyacid and polyol. This adjustment yields a thermosetting polyester resin having at least one of carboxyl or hydroxyl groups as thermosetting reactive groups.

[0182] Examples of polybasic acids include, for example, terephthalic acid, isophthalic acid, phthalic acid, methylterephthalic acid, trimellitic acid, benzopyrene, and the anhydrides of these acids; succinic acid, adipic acid, azelaic acid, sebacic acid, and the anhydrides of these acids; maleic acid, itaconic acid, and the anhydrides of these acids; fumaric acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, and the anhydrides of these acids; cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid; and so on.

[0183] Examples of polyols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentanediol, triethylene glycol, bis(hydroxyethyl) terephthalate, cyclohexanediol, octanediol, diethylpropylene glycol, butylethylpropylene glycol, 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, glycerol, pentaerythritol, trihydroxyethyl isocyanurate, hydroxyneopentyl hydroxyneopentyl ester, etc.

[0184] Thermosetting polyester resins can also be polycondensed with monomers other than polybasic acids and polyols.

[0185] Other monomers include compounds that simultaneously contain both carboxyl and hydroxyl groups in one molecule (such as dimethyl propionic acid, hydroxypentanoate, etc.), monoepoxides (such as glycidyl esters of branched aliphatic carboxylic acids such as "Cardura E10 (Shell Company)"), various monohydric alcohols (such as methanol, propanol, butanol, benzyl alcohol, etc.), various monobasic acids (such as benzoic acid, p-tert-butylbenzoic acid, etc.), and various fatty acids (such as castor oil fatty acids, coconut oil fatty acids, soybean oil fatty acids, etc.).

[0186] The structure of thermosetting polyester resin can be either branched or linear.

[0187] Among thermosetting polyester resins, those with a combined acid value and hydroxyl value of 10 mg KOH / g or more and 250 mg KOH / g or less, and a number average molecular weight of 1,000 or more and 10,000 or less are preferred, considering the excellent smoothness of the coated film.

[0188] Glass transition temperature of thermosetting resins

[0189] In thermosetting resins, from the perspective of excellent smoothness of the coating film even at low-temperature calcination, the glass transition temperature (Tg) is preferably 65°C or lower, more preferably 60°C or lower. Furthermore, from the perspective of storage stability such as agglomeration, the glass transition temperature is preferably 40°C or higher.

[0190] • Content of thermosetting resin

[0191] Thermosetting resins can be used alone or in combination with two or more.

[0192] The content of thermosetting resin relative to the total amount of powder particles is preferably 20% to 99% by mass, more preferably 30% to 95% by mass.

[0193] It should be noted that, as described below, when the powder particles are core / shell type particles, and a thermosetting resin is used as the resin coating, the content of the aforementioned thermosetting resin refers to the total content of all thermosetting resins in the core and the resin coating.

[0194] --Thermosetting Agent--

[0195] The thermosetting agent is selected based on the type of thermosetting reactive groups of the thermosetting resin.

[0196] Specifically, when the thermosetting reactive group of the thermosetting resin is an epoxy group, examples of thermosetting agents include: succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, eicosanoic acid, maleic acid, citracic acid, itaconic acid, pentenic acid, phthalic acid, trimellitic acid, benzoyltetracarboxylic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexene-1,2-dicarboxylic acid, trimellitic acid, benzoyltetracarboxylic acid, etc.; anhydrides of these acids; carbamate-modified forms of these acids; etc. Among these, aliphatic dicarboxylic acids are preferred as thermosetting agents from the perspective of coating film properties and storage stability, and dodecanoic acid is particularly preferred from the perspective of coating film properties.

[0197] When the thermosetting reactive group of a thermosetting resin is a carboxyl group, examples of thermosetting agents include various epoxy resins (such as polyglycidyl ether of bisphenol A), acrylic resins containing epoxy groups (such as acrylic resins containing glycidyl groups), polyglycidyl ethers of various polyols (such as 1,6-hexanediol, trimethylolpropane, trimethylolethane, etc.), polyglycidyl esters of various polycarboxylic acids (such as phthalic acid, terephthalic acid, isophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, trimellitic acid, benzopyrene, etc.), various alicyclic epoxy-containing compounds (such as bis(3,4-epoxycyclohexyl)methyl adipate), and hydroxyamides (such as triglycidyl isocyanurate, β-hydroxyalkylamide, etc.).

[0198] When the thermosetting reactive group of a thermosetting resin is a hydroxyl group, examples of thermosetting agents include end-capped isocyanates and amino plastics. Examples of isocyanate compounds constituting end-capped isocyanates include organic diisocyanates, polymers of organic diisocyanates (including isocyanurate-type polyisocyanate compounds), polyol adducts of organic diisocyanates, low molecular weight polyester resin (e.g., polyester polyol) adducts of organic diisocyanates, and aqueous adducts of organic diisocyanates. Here, examples of organic diisocyanates include various aliphatic diisocyanates (e.g., hexamethylene diisocyanate, trimethylhexamethylene diisocyanate), various cyclic aliphatic diisocyanates (e.g., phenylenediamine diisocyanate, isophorone diisocyanate), and various aromatic diisocyanates (e.g., toluene diisocyanate, 4,4'-diphenylmethane diisocyanate). Examples of isocyanate group-capping agents include formaldehyde oxime, acetaldehyde oxime, acetyl oxime, methyl ethyl ketone oxime, methyl isobutyl ketone oxime, and cyclohexanone oxime.

[0199] Thermosetting agents can be used alone or in combination of two or more.

[0200] The content of the thermosetting agent is preferably 1% to 30% by mass and more preferably 3% to 20% by mass relative to the thermosetting resin contained in the powder particles.

[0201] It should be noted that, as described below, when the powder particles are core / shell type particles and a thermosetting resin is used as the resin coating, the content of the aforementioned thermosetting agent refers to the content of all thermosetting resin relative to the core and the resin coating.

[0202] --Coloring agent--

[0203] Pigments are an example of coloring agents. Coloring agents can be used in combination with pigments and dyes.

[0204] Examples of organic pigments include iron oxide (such as iron oxide red), titanium oxide, titanium yellow, zinc white, lead white, zinc sulfide, zinc barium white, antimony oxide, cobalt blue, and carbon black; quinacridone red, phthalocyanine blue, phthalocyanine green, permanent red, Hansa yellow, indanthrene blue, strong bright scarlet, benzimidazole yellow, and so on.

[0205] In addition to pigments, glossy pigments can also be cited. Examples of glossy pigments include pearl pigments, aluminum powder, stainless steel powder and other metal powders; metal flakes; glass beads; glass flakes; mica; flaky iron oxide (MIO); and so on.

[0206] Colorants can be used alone or in combination of two or more.

[0207] The content of the colorant is selected based on the type of pigment, the required color, brightness, and depth of the coating film. For example, the content of the colorant relative to the total amount of resin constituting the powder particles is preferably 1% to 70% by mass, more preferably 2% to 60% by mass.

[0208] [Other Additives]

[0209] Other additives include various additives used in powder coatings. Specifically, other additives include surface conditioners (silicone oils, acrylic oligomers, etc.), antifoaming agents (e.g., benzoin, benzoin derivatives, etc.), curing accelerators (amine compounds, imidazole compounds, cationic polymerization catalysts, etc.), plasticizers, charge control agents, antioxidants, pigment dispersants, flame retardants, flow promoters, etc.

[0210] -Characteristics of powder particles-

[0211] From the perspective of improving the uniformity of powder coating adhesion to the coated surface and thus further enhancing the reflectivity of the coating film, the volume average particle size D50v of the powder particles is preferably 5 μm or more and 20 μm or less, more preferably 5 μm or more and 15 μm or less, and even more preferably 7 μm or more and 12 μm or less.

[0212] -Core / shell type particles-

[0213] The powder particles can be core / shell type particles having a core and a resin-coated portion covering the surface of the core. In this case, in addition to resin, the core may also contain other additives such as the aforementioned colorants, as needed.

[0214] In addition, the resin coating in the core / shell type particles will be explained below.

[0215] The resin-coated portion may consist of resin alone or may contain other components (thermosetting agents, other additives, etc., as described as components of the core).

[0216] From the perspective of reducing exudation, the resin-coated portion can be composed of only resin. It should be noted that even if the resin-coated portion contains other components besides resin, the resin only needs to account for 90% or more (preferably 95% or more) of the total resin-coated portion.

[0217] The resin constituting the resin coating can be either a thermoplastic resin or a thermosetting resin. From the perspective of increasing the curing density (crosslinking density) of the coating film, a thermosetting resin is more suitable.

[0218] When a thermosetting resin is used as the resin coating, the same thermosetting resin as the thermosetting resin of the core can be used, and the preferred examples are also the same. The thermosetting resin of the resin coating can be the same type of resin as the thermosetting resin of the core, or it can be a different resin.

[0219] From the perspective of suppressing exudation, the coverage rate of the resin-coated portion is preferably 30% to 100%, more preferably 50% to 100%.

[0220] Regarding the resin coating rate, the resin coating rate on the surface of powder particles is determined by XPS (X-ray photoelectron spectroscopy).

[0221] Specifically, in the XPS measurement, the JPS-9000MX manufactured by Nippon Electronics Co., Ltd. was used as the measuring device, and MgKα rays were used as the X-ray source. The accelerating voltage was set to 10kV and the radiation current was set to 30mA.

[0222] Based on the spectra obtained under the above conditions, peak separation was performed on the components originating from the core material and the components originating from the coated resin material on the surface of the powder particles to quantify the resin coating rate on the surface of the powder particles. In the peak separation, the measured spectra were separated into individual components using curve fitting based on the least squares method.

[0223] The component spectra used as the basis for separation were obtained by individually measuring the spectra of the thermosetting resin, curing agent, pigments, additives, and coating resin used in the production of the powder particles. The coating ratio was then calculated based on the ratio of the spectral intensity derived from the coating resin to the sum of all spectral intensities obtained from the powder particles.

[0224] From the perspective of suppressing exudation, the thickness of the resin coating is preferably 0.2 μm or more and 4 μm or less, more preferably 0.3 μm or more and 3 μm or less.

[0225] The thickness of the resin coating is determined by the following method: Powder particles are embedded in epoxy resin or similar materials, and thin sections are prepared by cutting with a diamond tool or similar means. These thin sections are observed using a transmission electron microscope (TEM) or similar means, and cross-sectional images of at least two powder particles are captured. The thickness of the resin coating is measured at 20 points based on the cross-sectional images of the powder particles, and the average value is used. In cases where it is difficult to observe the resin coating in the cross-sectional images using transparent powder coatings or similar materials, staining can be used for observation, thus facilitating the measurement.

[0226] [External Additives]

[0227] As an external additive, inorganic particles can be cited as an example. Examples of inorganic particles include SiO2, TiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, K2O·(TiO2)n, Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, and MgSO4.

[0228] Among these, silica particles are preferred as an external additive. The silica particles can be particles with SiO2 as the main component, and can be crystalline or amorphous. Furthermore, the silica particles can be particles manufactured from silicon compounds such as water glass or alkoxysilanes, or particles obtained by crushing quartz.

[0229] Specifically, examples of silica particles include sol-gel silica particles, aqueous colloidal silica particles, alcohol silica particles, fumed silica particles obtained by the gas phase method, and fused silica particles.

[0230] The external additive is preferably a hydrophobic external additive. When using a hydrophobic external additive, it is easier to control the above-mentioned airflow energy and the above-mentioned buoyancy rate within the above-mentioned ranges.

[0231] The surface of the hydrophobic external additive is subjected to a hydrophobic treatment. This hydrophobic treatment can be performed, for example, by impregnating the external additive (inorganic particles, etc.) in a hydrophobic treatment agent. There are no particular limitations on the hydrophobic treatment agent; examples include silane coupling agents, silanes, silicone oils, titanate-based coupling agents, and aluminum-based coupling agents. These agents can be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is, for example, between 1 and 10 parts by mass relative to 100 parts by mass of the inorganic particles.

[0232] Here, from the perspective of controlling the above-mentioned ventilation flow energy and the above-mentioned buoyancy rate within the above-mentioned range, the degree of hydrophobicity of the hydrophobic external additive is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more.

[0233] Regarding the degree of hydrophobicity of external additives, 0.2% by mass of silica particles (as the sample) was added to 50 ml of ion-exchanged water. While stirring with a magnetic stirrer, methanol was added dropwise from a burette. The mass fraction of methanol in the methanol-water mixture at the titration endpoint, where all the sample had settled, was determined as the degree of hydrophobicity.

[0234] The volume average particle size of the external additive is preferably 5 nm to 30 nm, more preferably 5 nm to 20 nm, even more preferably 5 nm to 10 nm, and particularly preferably 5 nm to 9 nm. When the volume average particle size of the external additive is within the above range, it is easy to control the above-mentioned aeration flow energy and the above-mentioned buoyancy rate within the above range.

[0235] The volume average particle size of the external additives was determined as follows.

[0236] Powder coatings with external additives were imaged using a scanning electron microscope (SEM) (Hitachi High-Technologies S-4700, Inc.) at 40,000x magnification, under conditions of accelerating voltage 15kV, radiation current 20μA, and WD 15mm. For identified external additives, the equivalent circular diameter was determined using WinRoof image processing software (Mitani Corporation). The particle size (equivalent circular diameter) of at least 200 particles was measured, and the particle size at the cumulative 50% point from the smallest diameter side in the volumetric reference particle size distribution was used as the volume average particle size.

[0237] The amount of external additive added is preferably 0.01% to 10% by mass and more preferably 0.1% to 7.0% by mass relative to the powder particles.

[0238] <Methods for manufacturing powder coatings>

[0239] Next, the method for manufacturing the powder coating according to this embodiment will be described.

[0240] The powder coating of this embodiment is obtained by adding external additives to the powder particles as needed after manufacturing the powder particles.

[0241] Powder particles can be manufactured by any of the following methods: dry manufacturing (e.g., mixing and pulverizing) or wet manufacturing (e.g., agglomeration and coalescence (agglomeration-1), suspension polymerization, dissolution suspension, etc.). There are no particular limitations on these methods, and well-known methods can be used. Among these, agglomeration and coalescence can be used to obtain powder particles, as it allows for easy control of the aforementioned aeration flow energy and buoyancy rate within the aforementioned ranges.

[0242] Specifically, the powder particles are preferably manufactured through the following steps:

[0243] The first agglomeration step involves agglomerating the composite particles in a dispersion containing resin-containing composite particles to form the first agglomerated particles.

[0244] In the second agglomeration step, a first agglomerate dispersion containing the first agglomerate particles and a second resin particle dispersion containing second resin particles containing resin are mixed, causing the second resin particles to agglomerate on the surface of the first agglomerate particles, forming second agglomerate particles with the second resin particles attached to the surface of the first agglomerate particles; and

[0245] The step of heating the dispersion of the second aggregated particles containing the above-mentioned second aggregated particles to fuse and merge the above-mentioned second aggregated particles.

[0246] In the powder particles manufactured by this agglomeration and merging method, the portion of the first agglomerated particles that has been fused and merged becomes the core, and the portion of the second resin particles attached to the surface of the first agglomerated particles that has been fused and merged (merged into one) becomes the resin-coated portion. Furthermore, when a thermosetting resin is used as the resin, a thermosetting agent may also be included in each dispersion, and a dispersion containing a thermosetting agent may also be used separately.

[0247] It should be noted that the second agglomeration step can also be omitted to produce single-layer powder particles.

[0248] The details of each step are explained below. The following description focuses on the manufacturing method of powder particles containing a colorant and using a thermosetting resin as the resin.

[0249] -Dispersion Preparation Steps-

[0250] First, prepare the dispersions used in the coagulation and aggregation method. Specifically, prepare a first resin particle dispersion containing first resin particles with a core resin, a thermosetting agent dispersion containing a thermosetting agent, a colorant dispersion containing a colorant, and a second resin particle dispersion containing second resin particles with a resin coating resin.

[0251] In the following text, the first resin particles, the second resin particles, and the composite particles will be collectively referred to as "resin particles".

[0252] Resin particle dispersions are prepared, for example, by dispersing resin particles in a dispersion medium using a surfactant.

[0253] Examples of dispersion media used in resin particle dispersions include aqueous media.

[0254] Examples of aqueous media include distilled water, ion-exchanged water, and alcohols. These aqueous media can be used individually or in combination of two or more.

[0255] Examples of surfactants include anionic surfactants such as sulfate esters, sulfonates, phosphate esters, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; and nonionic surfactants such as polyethylene glycols, alkylphenol ethylene oxide adducts, and polyols. Among these, anionic and cationic surfactants are particularly noteworthy. Nonionic surfactants can also be used in combination with anionic or cationic surfactants.

[0256] Surfactants can be used alone or in combination of two or more.

[0257] In resin particle dispersions, common methods for dispersing resin particles in a dispersion medium include using a rotary shear homogenizer or ball mills, sand mills, bead mills, etc., which contain a medium. Alternatively, depending on the type of resin particles, phase inversion emulsification can also be used to disperse resin particles in the resin particle dispersion.

[0258] The phase inversion emulsification method is as follows: the resin to be dispersed is dissolved in a hydrophobic organic solvent that can dissolve the resin, an alkali is added to the organic continuous phase (O phase) for neutralization, and then an aqueous medium (W phase) is introduced, thereby performing a resin conversion from W / O to O / W (so-called phase inversion) to form a discontinuous phase, so that the resin is dispersed in the aqueous medium in particulate form.

[0259] Specifically, in the case of a (meth)acrylic acid resin particle dispersion, the monomers constituting the (meth)acrylic acid resin are emulsified in an aqueous medium, and a water-soluble initiator and chain transfer agent are added and heated to carry out emulsion polymerization, thereby obtaining a resin particle dispersion containing (meth)acrylic acid resin particles.

[0260] In the case of a polyester resin particle dispersion, the monomers constituting the polyester resin are heated and melted, and then polycondensed under reduced pressure. A solvent (such as ethyl acetate) is added to the obtained polycondensate to dissolve it. An alkaline aqueous solution is then added and stirred simultaneously to perform phase inversion emulsification, thereby obtaining a resin particle dispersion containing polyester resin particles.

[0261] It should be noted that the polyester resin is neutralized using an alkaline compound when dispersed in an aqueous medium. The neutralization reaction with the carboxyl groups of the thermosetting polyester resin is the driving force for water-based conversion, and the electrostatic repulsion between the generated carboxyl anions easily inhibits particle aggregation.

[0262] Examples of alkaline compounds include ammonia and organic amine compounds with a boiling point below 250°C. Ammonia is preferably 10 mol% or more, more preferably 25 mol% or more, and even more preferably 50 mol% or more, relative to the total amount of alkaline compound used. By using ammonia to perform the above-mentioned neutralization reaction, the amount of ammonium ions in the powder coating can be adjusted. Examples of preferred organic amine compounds include triethylamine, N,N-diethylethanolamine, N,N-dimethylethanolamine, aminoethanolamine, N-methyl-N,N-diethanolamine, isopropylamine, iminodipropylamine, ethylamine, diethylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, methylaminopropylamine, dimethylaminopropylamine, methyliminodipropylamine, 3-methoxypropylamine, monoethanolamine, diethanolamine, triethanolamine, morpholine, N-methylmorpholine, and N-ethylmorpholine.

[0263] The alkaline compound is preferably added in an amount that at least partially neutralizes the carboxyl groups contained in the thermosetting polyester resin, i.e., 0.2 to 9.0 equivalents relative to the carboxyl groups, more preferably 0.6 to 2.0 equivalents. It is believed that if the amount is 0.2 equivalents or more, the effect of the alkaline compound addition is easily confirmed. If the amount is 9.0 equivalents or less, excessive increase in the hydrophilicity of the oil phase can be suppressed, thus preventing particle size expansion and easily obtaining a good dispersion.

[0264] Regarding composite particle dispersions, resin and thermosetting agent are mixed and dispersed in a dispersion medium (e.g., emulsification such as phase inversion emulsification) to obtain composite particle dispersions.

[0265] The volume average particle size of the resin particles dispersed in the resin particle dispersion is preferably 1 μm or less, more 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 even more preferably 0.1 μm or more and 0.6 μm or less.

[0266] Regarding the volume average particle size of resin particles, the particle size distribution obtained by laser diffraction particle size distribution measurement device (e.g., LA-700, Horiba Seisakusho) was used. For the divided particle size range (segment), the cumulative distribution of volume was plotted from the smallest particle size side, and the particle size at the point with 50% of the total volume of all particles was measured and taken as the volume average particle size D50v. The volume average particle size of particles in other dispersions was measured in the same way.

[0267] The resin particle dispersion contains, for example, 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less.

[0268] Thermosetting agent dispersions and colorant dispersions are prepared in the same manner as resin particle dispersions. That is, the dispersion medium, surfactant, dispersion method, volume average particle size, and particle content of the thermosetting agent dispersions and colorant dispersions are the same as those of the resin particle dispersions.

[0269] -First Agglomeration Step-

[0270] Next, the first resin particle dispersion, the thermosetting agent dispersion, and the colorant dispersion are mixed.

[0271] Subsequently, the first resin particles, thermosetting agent, and colorant are heterogeneously aggregated in the mixed dispersion to form first aggregated particles with a diameter similar to that of the target powder particles and containing the first resin particles, thermosetting agent, and colorant.

[0272] Specifically, for example, a flocculant is added to the mixed dispersion, and the pH of the mixed dispersion is adjusted to acidic (e.g., pH above 2 and below 5). A dispersion stabilizer is added as needed, and then the mixture is heated to a temperature close to the glass transition temperature of the first resin particles (specifically, for example, above and below the glass transition temperature of the first resin particles), causing the particles dispersed in the mixed dispersion to agglomerate and form the first agglomerated particles.

[0273] In the first agglomeration step, a composite particle dispersion containing a thermosetting resin and a thermosetting agent can be mixed with a colorant dispersion, and the composite particles and colorant can be heterogeneously agglomerated in the mixed dispersion to form the first agglomerated particles.

[0274] In the first coagulation step, for example, the mixed dispersion can be stirred using a rotary shear homogenizer, and a coagulant can be added at room temperature (e.g., 25°C) to adjust the pH of the mixed dispersion to acidic (e.g., pH above 2 and below 5). A dispersion stabilizer can be added as needed, and then heating can be performed.

[0275] Examples of flocculants include surfactants with polarity opposite to that of the surfactant contained in the mixed dispersion, metal salts, inorganic metal salt polymers, and metal complexes. When metal complexes are used as flocculants, the amount of surfactant required is reduced, and the charging characteristics are improved.

[0276] Metal salts, inorganic metal salt polymers, and metal complexes, acting as flocculants, serve as a source of metal ions for powder coatings. Examples of metal salts, inorganic metal salt polymers, and metal complexes are described above.

[0277] -Second aggregation step-

[0278] Next, the dispersion of the first aggregated particles obtained from the dispersion is mixed with the dispersion of the second resin particles. The second resin particles and the first resin particles can be of the same type or different types.

[0279] Subsequently, the first aggregated particles and the second resin particles are aggregated in a mixed dispersion in such a way that the second resin particles are attached to the surface of the first aggregated particles, forming a second aggregated particle with the second resin particles attached to the surface of the first aggregated particle.

[0280] Specifically, for example, in the first agglomeration step, after the first agglomerated particles reach the target particle size, a second resin particle dispersion is mixed into the first agglomerated particle dispersion. At this time, in order to promote the agglomeration of the second resin particles relative to the surface of the first agglomerated particles, the second resin particle dispersion can be mixed while the first agglomerated particle dispersion is continued to be heated. Then, the pH of the mixed dispersion is adjusted to, for example, a range of 6.5 to 10.0 to stop the agglomeration process.

[0281] The pH was adjusted by adding ammonia, thereby adjusting the concentration of ammonium ions in the powder particles.

[0282] The ammonia mentioned above is preferably added in the form of ammonia water.

[0283] Regarding the amount of ammonia added, it is preferable to add it in such a way that the concentration of ammonium ions in the mixed dispersion is more than 0.0001% by mass and less than 0.005% by mass.

[0284] This results in a second aggregated particle formed by agglomerating the second resin particles onto the surface of the first aggregated particle.

[0285] To stop aggregation, chelating agents can be added. Examples of chelating agents include hydroxycarboxylic acids such as EDTA, tartaric acid, citric acid, and gluconic acid; aminocarboxylic acids such as iminodiacetic acid and hyponitrotriacetic acid; and so on. The total amount of chelating agent added relative to all resin particles is preferably 0.01% by mass or more and 3.0% by mass or less.

[0286] -Merge / Merge Steps-

[0287] Next, the dispersion of the second aggregated particles containing the second aggregated particles is heated to, for example, above the glass transition temperature of the first and second resin particles (for example, at a temperature 10°C to 30°C higher than the glass transition temperature of the first and second resin particles) to cause the second aggregated particles to fuse and merge, forming powder particles.

[0288] In the fusion step, it is preferable to have a pH of 8.0 or higher before heating. The pH is preferably 8.5 or higher, and more preferably 9.0 or higher.

[0289] After the above steps, powder particles are obtained.

[0290] The concentration of ammonium ions in the powder particles was adjusted by adding ammonia to the solution containing the obtained powder particles.

[0291] The ammonia mentioned above is preferably added in the form of ammonia water.

[0292] Regarding the amount of ammonia added, it is preferable to add it in such a way that the concentration of ammonium ions in the solution containing the powder particles is more than 0.0001% by mass and less than 0.005% by mass.

[0293] After the fusion and merging step, the powder particles formed in the dispersion are subjected to known washing, solid-liquid separation, and drying steps to obtain dried powder particles. Regarding the washing step, from a power efficiency perspective, displacement washing using ion-exchange water can be fully implemented. Regarding the solid-liquid separation step, from a productivity perspective, methods such as vacuum filtration and pressure filtration can be implemented. Regarding the drying step, from a productivity perspective, methods such as freeze drying, airflow drying, fluidized bed drying, and vibrating fluidized bed drying can be implemented.

[0294] The powder coating of this embodiment is manufactured by adding external additives to the dried powder particles and mixing them as needed. Mixing can be carried out using, for example, a V-type mixer, a Henschel mixer, or a Loedige mixer. Furthermore, coarse particles of the powder coating can be removed as needed using a vibrating screen, a pneumatic screen, or the like.

[0295] Example

[0296] The following examples and comparative examples illustrate this embodiment in more detail, but this embodiment is not limited to the following examples. It should be noted that, unless otherwise stated, "parts" and "%" are mass measurements.

[0297] <Transparent powder coating made of acrylic resin (PCA1)>

[0298] (Preparation of thermosetting acrylic resin particle dispersion (A1))

[0299] Styrene: 160 parts by weight

[0300] Methyl methacrylate: 200 parts by weight

[0301] • n-Butyl acrylate: 140 parts by weight

[0302] Acrylic acid: 12 parts by weight

[0303] • Glycidyl methacrylate: 100 parts by weight

[0304] • Dodecanthiol: 12 parts by weight

[0305] Prepare monomer solution A by mixing and dissolving the above components.

[0306] In addition, 12 parts by mass of an anionic surfactant (manufactured by Dow Chemical Company, DOWFAX) were dissolved in 280 parts by mass of ion-exchanged water, and the above monomer solution A was added to it and dispersed in a flask to obtain an emulsion solution (monomer emulsion A).

[0307] Next, 1 part by weight of anionic surfactant (manufactured by Dow Chemical, DOWFAX) was dissolved in 555 parts by weight of deionized water and added to the polymerization flask. The polymerization flask was then stoppered, a reflux tube was installed, nitrogen gas was injected while stirring slowly, and the polymerization flask was heated to 75°C using a water bath and maintained at that temperature.

[0308] In this state, a solution obtained by dissolving 9 parts by mass of ammonium persulfate in 43 parts by mass of ion-exchanged water was added dropwise to the polymerization flask over 20 minutes using a metering pump. Then, monomer emulsion A was added dropwise over 200 minutes using a metering pump. After the addition was completed, the polymerization flask was kept at 75°C for 3 hours while continuing to stir slowly to end the polymerization, resulting in an anionic thermosetting acrylic resin particle dispersion (A1) with a solid content of 42%.

[0309] The anionic thermosetting acrylic resin particle dispersion (A1) contains thermosetting acrylic resin particles with a volume average particle size of 220 nm, a glass transition temperature of 55 °C, and a weight average molecular weight of 24,000.

[0310] (Preparation of thermosetting agent dispersion (D1))

[0311] • Dodecanoic acid: 50 parts by weight

[0312] Benzoin: 1 part by weight

[0313] • Acrylic oligomer (Acronal 4F, BASF): 1 part by weight

[0314] • Anionic surfactant (manufactured by Dow Chemical, Dow Fax): 5 parts by weight

[0315] • Ion-exchanged water: 200 parts by weight

[0316] The above components were heated to 140°C in a pressure vessel, dispersed using a homogenizer (IKA Corporation: ULTRA-TURRAXT50), and then dispersed using a Manton Gaulin high-pressure homogenizer (Gaulin Corporation) to prepare a thermosetting agent dispersion (D1) containing a curing agent with an average particle size of 0.24 μm and other additives (curing agent concentration: 23%).

[0317] (Manufacturing of transparent powder coating (PCA1))

[0318] -Agglomeration Steps-

[0319] • Thermosetting acrylic resin particle dispersion (A1): 200 parts by weight (84 parts by weight of resin)

[0320] • Thermosetting agent dispersion (D1): 91 parts by weight (21 parts by weight of curing agent)

[0321] • 10% Polyaluminum Chloride: 1 part by weight

[0322] After thoroughly mixing / dispersing the above components in a round stainless steel flask using a homogenizer (IKA, ULTRA-TURRAX T50), the flask was heated to 48°C with stirring using an oil bath and maintained at 48°C for 60 minutes to allow the aggregated particles to grow to 8.8 μm. Then, 68 parts by weight of thermosetting acrylic resin particle dispersion (A1) (28.56 parts by weight of resin) as the shell component was added and the mixture was stirred slowly.

[0323] -Fusion Steps-

[0324] Subsequently, the pH in the flask was adjusted to 5.0 using a 0.5 mol / L sodium hydroxide aqueous solution, and then heated to 95°C while continuing to stir. After heating the flask to 95°C, this state was maintained for 4 hours. The pH was maintained at approximately 4.0 at 95°C.

[0325] -Filtration, washing, and drying steps-

[0326] After the reaction was complete, the solution in the flask was cooled and filtered to obtain the solid component. Next, the solid component was thoroughly washed with deionized water and then separated into solid and liquid components by Buchner funnel filtration to obtain the solid component again.

[0327] Next, the solid component was redispersed in 3 liters of ion-exchanged water at 40°C, and stirred and washed at 300 rpm for 15 minutes. This washing operation was repeated 5 times. Solid-liquid separation was performed using Buchner funnel filtration, and the obtained solid component was vacuum dried for 12 hours.

[0328] Subsequently, 0.5 parts by mass of hydrophobic silica particles (volume average particle size 8 nm) as an external additive were mixed with 100 parts by mass of the powder particles as solid components to obtain a transparent powder coating (PCA1) made of acrylic resin.

[0329] The transparent powder coating has a volume average particle size D50v of 10.6 μm, a volume average particle size distribution index GSDv of 1.21, and an average roundness Ca of 0.97.

[0330] After the transparent powder coating was embedded in epoxy resin, it was cut and the cross-sectional image of the particles was observed using a transmission electron microscope. The results confirmed that the surface of the powder particles was coated with resin.

[0331] Add 0.51 parts of hydrophobic silica particles with an average volume diameter of 8 nm to 100 parts of dried powder particles to obtain a powder coating.

[0332] Commercially available pulverized and graded transparent powder coating (PCA2) made from polyester resin.

[0333] Commercially available polyester powder coating (trade name "783-900 transparent powder particles (Clear powder particles)", manufactured by Takashi Kubo Co., Ltd.) produced by a mixing and pulverizing method was processed using a turbomill R-type T400-4RS110 (manufactured by Freund-Turbo Co., Ltd.) at a rotation speed of 2500 min. -1 The particles were pulverized and classified using a curved-tube jet classifier (LABO, manufactured by Nippon Steel Mining Co., Ltd.) to separate the medium-diameter components, resulting in powder particles with a volume average particle size of 11.5 μm, a GSDv of 1.37, and an average roundness Ca of 0.93.

[0334] For 100 parts of the obtained powder particles, 0.61 parts of hydrophobic silica particles with a volume average particle size of 8 nm were added to obtain a transparent powder coating (PCA2).

[0335] <Transparent powder coating made of acrylic resin (PCA3)>

[0336] After growing to 5 μm using the same method as powder coating (PCA1), shell-based components were added, fused, filtered, and dried to obtain powder particles with a volume average particle size of 6.1 μm, a GSDv of 1.24, and an average roundness Ca of 0.99.

[0337] To obtain a transparent powder coating (PCA3), 0.61 parts of hydrophobic silica particles with a volume average particle size of 8 nm were added to 100 parts of the obtained powder particles.

[0338] Commercially available pulverized and graded transparent powder coating (PCA4) made from polyester resin.

[0339] Using the same operation as powder coating (PCA2) and setting the speed of the bent-tube jet classifier to 1800 min... -1 Further classification yielded powder particles with a volume average particle size of 18.9 μm, a GSDv of 1.20, and an average roundness Ca of 0.90.

[0340] To obtain a transparent powder coating (PCA4), 0.70 parts of hydrophobic silica particles with a volume average particle size of 8 nm were added to 100 parts of the obtained powder particles.

[0341] (Various properties of powder coatings)

[0342] The various properties of powder coatings were studied using the methods described above. The results are shown in the table.

[0343] • Center particle size D50v

[0344] • Volumetric particle size distribution index GSDv

[0345] · Average roundness Ca

[0346] Ventilation flow energy (AE)

[0347] • Increase rate

[0348] It should be noted that the table also shows the volume average particle size of the external additives (abbreviated as "particle size" in the table).

[0349] <Experiments A-D>

[0350] (Formation of a coating film using flow dip coating)

[0351] Prepare a metal clamp consisting of a stainless steel air inlet surface with a 2,300-mesh (5μm aperture) upper surface forming a disc shape at the bottom, and an inner diameter Φ of 50mm (cross-sectional area approximately 2,000mm²) for the sides. 2 A flow channel made of a glass tube (3mm thick).

[0352] Next, powder coating is added to the flow tank with a volume of 80 mL.

[0353] Next, air is introduced from the bottom of the flow tank in a manner that achieves the buoyancy of the powder coating at the average airflow rates according to Tables 1 and 2, thus creating a flowing state for the powder coating. At this time, the flow tank is subjected to a vibration of 100 Hz.

[0354] Next, the aluminum substrate (35mm long × 75mm wide × 3mm thick) is immersed in the powder coating after being heated by a heating plate. Specifically, in the embodiment, when immersing in the powder coating, the aluminum substrate is heated to the preheating temperatures in Tables 1 and 2 so that the surface temperature of the aluminum substrate is within the range of "above the softening temperature and below the melting temperature" before being immersed in the powder coating. On the other hand, in the comparative example, when immersing in the powder coating, the aluminum substrate is heated to the preheating temperatures in Tables 1 and 2 so that the surface temperature of the aluminum substrate is outside the range of "above the softening temperature and below the melting temperature" before being immersed in the powder coating.

[0355] In addition, the aluminum substrate is moved slowly in an arc at a rate of 10 to 20 mm / second while being immersed in the powder coating.

[0356] Next, after 10 seconds of immersion, the aluminum substrate is pulled out of the powder coating.

[0357] Then, the powder coating film attached to the aluminum substrate is heated at 180°C for 30 minutes to form a coating film.

[0358] The evaluation was then conducted according to the following criteria. The results are shown in the table.

[0359] A: The coated film is a continuous, smooth thin film with a thickness of 20μm or more and 50μm or less.

[0360] B: Despite slight unevenness, a continuous film with a thickness of 10 μm to 50 μm was formed.

[0361] C: The coated film is a discontinuous film in which the substrate is visible.

[0362] D: Almost uncoated.

[0363] E: The coated film is a continuous film with a thickness of 100μm or more.

[0364]

[0365]

[0366] As can be seen from the above results, compared with the flow dip coating method of the comparative example, the flow dip coating method of this embodiment can form a continuous thin coating film with a film thickness of 10 μm or more and 50 μm or less.

[0367] Furthermore, the flow dip coating method of this embodiment can well form a continuous thin coating film, so it can be inferred that the coated object maintains an appropriate surface temperature from the start of dip coating until the time required to form the coating.

Claims

1. A coating method based on flow impregnation, comprising the following steps: In the impregnation step, air is introduced from the bottom of the flow tank containing the powder coating at an average air flow rate of 5 mm / min to 20 mm / min per unit area of ​​the bottom, so that the floating rate of the powder coating is 5% to 20%, and at least a portion of the object to be coated is impregnated with the powder coating. The removal step involves removing the coated material from the powder coating; and The heating step involves heating the powder coating adhered to the coated material. in, When at least a portion of the object to be coated is immersed in the powder coating, due to the air feeding prior to immersion and the heat conduction to the contact particles of the powder coating during immersion, the surface temperature of the immersed portion of the object decreases from the preheating temperature by 5°C, and then remains in the range of above the softening temperature and below the melting temperature of the powder coating for more than 5 seconds after immersion. The softening temperature of the powder coating is the glass transition temperature of the powder coating, and is between 45°C and 70°C; the melting temperature of the powder coating is between 80°C and 180°C. The volume average particle size D50v of the aforementioned powder coating is between 5 μm and 20 μm. The coated material is preheated to the preheating temperature before the air feeding and impregnation, and the preheating temperature is in the range of softening temperature of the powder coating +20°C and melting temperature +5°C.

2. The coating method based on flow impregnation as described in claim 1, wherein, The immersion time for at least a portion of the coated material is more than 5 seconds and less than 10 seconds.

3. The coating method based on flow impregnation as described in claim 1, wherein, The airflow energy (AE) of the above-mentioned powder coating is above 5mJ and less than 100mJ. Here, AE is measured using a powder rheometer with a container with a cross-sectional area of ​​50mmφ, under the conditions of a blade tip velocity of 100mm / second, a blade entry angle of -5°, and an airflow rate of 20ml / min.

4. The coating method based on flow impregnation as described in claim 1, wherein, The volumetric particle size distribution index (GSDv) of the above-mentioned powder coating is above 1.15 and below 1.

40.

5. The coating method based on flow impregnation as described in claim 4, wherein, The volumetric particle size distribution index (GSDv) of the above-mentioned powder coating is above 1.15 and below 1.

25.

6. The coating method based on flow impregnation as described in claim 1, wherein, The above-mentioned upward fluctuation rate is between 10% and 20%.

7. The coating method based on flow impregnation as described in claim 1, wherein, The powder coatings described above contain powder particles and external additives added to the powder particles.

8. The coating method based on flow impregnation as described in claim 7, wherein, The aforementioned external additives are hydrophobic external additives.

9. The coating method based on flow impregnation as described in claim 7, wherein, The volume average particle size of the aforementioned external additives is between 5 nm and 30 nm.

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