Epoxy resin powder coating material

Abstract

To provide an epoxy resin powder coating material that reduces fusion of the powder coating material to peripheral equipment even when applied on a heated coating target in electrostatic coating, and exhibits excellent electrostatic coating performance.SOLUTION: An epoxy resin powder coating material comprises mixed particles containing (A) an epoxy resin having a softening point or melting point of 90°C to 150°C and (B) a curing agent, wherein the surfaces of the mixed particles are coated with (C) an inorganic material surface-treated with a tackifier.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an epoxy resin powder coating material, and in particular to an epoxy resin powder coating material suitable for use on an object whose surface is heated during electrostatic coating. [Background technology]

[0002] Epoxy resins are excellent in mechanical properties, chemical resistance, electrical properties, and corrosion resistance, and are widely used as powder paints. Powder paints using epoxy resins (epoxy resin powder paints) have excellent electrical properties, corrosion resistance, and the like, and are used in the field of processed steel materials such as bus bars and steel pipes. In addition, as described in Patent Document 1, they are also used as paints for imparting heat resistance, electrical insulation, and the like as sealing materials for electronic components such as capacitors and transistors, and paints for imparting electrical insulation and corrosion resistance, and the like to in-vehicle components such as starters, wipers, and brake pads.

[0003] Known methods for painting with epoxy resin powder paint include electrostatic painting, preheated electrostatic painting, fluidized bed dipping, hot spray, etc. Of these, electrostatic painting is a painting method in which an electric charge is applied to the powder paint to cause it to adhere to the surface of the object to be painted, and includes electrostatic spraying, electrostatic fluidized bed dipping, etc. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-110805 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, before painting, the object to be painted may be heated and degreased as necessary, and the surface of the object to be painted is heated during this process. Therefore, in the electrostatic painting method, except for the preheating electrostatic painting method that requires preheating especially for thick-film painting, a process of dissipating heat from the preheated surface of the object to be painted and the surrounding equipment of the object to be painted is required. Specifically, when electrostatic painting is performed when the temperature of the object to be painted is high, the temperature of the surrounding equipment of the object to be painted, such as the conveying device (belt conveyor, etc.) that conveys the object to be painted, is also high, and the powder paint applied to the surface of the object to be painted may be heated and melted by the surrounding equipment of the object to be painted, which may make it difficult to use the equipment continuously. Therefore, in the electrostatic painting method, in order to prevent the powder paint from melting to such equipment, it was necessary to cool the object to be painted to a temperature at which the powder paint does not melt before painting. There is a problem that the cost is increased by carrying out such a cooling process and the manufacturing efficiency is reduced.

[0006] In addition, in the past, in order to control the fluidity of powder paint, inorganic materials such as fine silica or surface-treated inorganic materials are blended into paint as fluidity imparting agents. However, the surface treatment of powder paint with conventional fluidity imparting agents affects not only the fluidity of powder paint in air, which uses air as a medium, but also the softening point of powder paint depending on the amount of fluidity imparting agent added. Therefore, although the softening point of inorganic materials such as fine silica or fluidity imparting agents surface-treated with such inorganic materials can be improved by adjusting the amount of addition, as the amount of addition increases, the surface of the object to be painted becomes slippery, which causes problems in electrostatic coating properties.

[0007] The present invention has been made with attention to the above points, and aims to provide an epoxy resin powder coating which has good electrostatic paintability and can suppress the adhesion of the powder coating to surrounding equipment even when used on a heated object to be coated in electrostatic painting. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention is specified as follows (1) to (3). (1) (A) an epoxy resin having a softening point or melting point of 90°C to 150°C; (B) a curing agent; The mixture particles include (C) An epoxy resin powder coating, in which the surfaces of the mixture particles are coated with an inorganic material that has been surface-treated with a tackifier. (2) The epoxy resin powder coating material according to (1) above, wherein the surface coverage of the mixture particles by (C) is 10% or more. (3) The epoxy resin powder coating according to (1) or (2) above, further comprising (D) a filler. Effect of the Invention

[0009] According to an embodiment of the present invention, an epoxy resin powder coating can be provided that has good electrostatic paintability and can suppress the adhesion of the powder coating to surrounding equipment even when used on a heated object to be coated in electrostatic coating. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The following describes an epoxy resin powder coating according to an embodiment of the present invention, but the present invention should not be construed as being limited thereto, and various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art without departing from the scope of the present invention.

[0011] In this specification, the term "to" indicating a range of values ​​indicates a range including the values ​​given as the upper and lower limits. When a unit is given only for the upper limit of a range of values, it means that the lower limit is expressed in the same unit as the upper limit. In the present specification, in which numerical ranges are described stepwise, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described stepwise. In addition, in the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0012] (Epoxy resin powder coating) The epoxy resin powder coating according to an embodiment of the present invention contains mixture particles including (A) an epoxy resin having a softening point or melting point of 90°C to 150°C and (B) a curing agent, and the surfaces of the mixture particles are coated with (C) an inorganic material that has been surface-treated with a tackifier.

[0013] Hereinafter, each component contained in the epoxy resin powder coating material according to the embodiment of the present invention will be described.

[0014] <(A) Epoxy resin> The epoxy resin (A) used in the embodiment of the present invention is not particularly limited as long as it has a softening point or melting point of 90° C. to 150° C., and examples thereof include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, biphenyl type epoxy resins, alicyclic epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, naphthol novolac type epoxy resins, dicyclopentadiene type epoxy resins, naphthalene type epoxy resins, and epoxy resins modified in various ways such as CTBN modification or halogenation. These may be used alone or in combination of two or more.

[0015] As the epoxy resin (A), bisphenol A type epoxy resin is particularly preferred, and a powder coating material containing such a bisphenol A type epoxy resin exhibits good mechanical properties, chemical resistance, electrical properties, and corrosion resistance of a coating film, which is a cured product formed after application.

[0016] The bisphenol A type epoxy resin preferably has an epoxy equivalent of 875 to 3300 g / eq. By setting the epoxy equivalent of the bisphenol A type epoxy resin to 875 g / eq or more, the softening point of the powder coating material is increased, and defects such as adhesion of the powder coating material to peripheral equipment can be suppressed even when electrostatically coating a heated substrate. In addition, by setting the epoxy equivalent of the bisphenol A type epoxy resin to 3300 g / eq or less, the melt viscosity of the powder coating material is improved, and a uniform and smooth coating film can be obtained even when electrostatically coating a heated substrate. The bisphenol A type epoxy resin may be used in combination with two or more types having different epoxy equivalents so that the epoxy equivalent is in the range of 875 to 3300 g / eq.

[0017] Commercially available bisphenol A type epoxy resins include JER-1004, JER-1007, JER-1009 (all manufactured by Mitsubishi Chemical Corporation), YD-014, YD-017, YD-019, YD-904, YD-907, YD-7910 (all manufactured by Nippon Steel Chemical & Material Co., Ltd.), GESR-904, GESR-907 (all manufactured by Epoxy Base Electronic Material Corporation Limited), and the like.

[0018] The epoxy resin (A) used in the embodiment of the present invention has a softening point or melting point of 90° C. to 150° C. When the epoxy resin (A) has a softening point or melting point of 90° C. to 150° C., it adheres to the surface of the heated object to be coated, but can be prevented from immediately fusing. The softening point or melting point of the epoxy resin (A) can be measured by the softening point test method for epoxy resins (JIS K 7234-1986). The "softening point of the epoxy resin powder coating" will be described in detail later in this specification.

[0019] <(B) Hardener> As the curing agent (B), dicyandiamide, imidazole-based curing agents, amine-based curing agents, phenol-based curing agents, acid anhydride-based curing agents, polyamide compounds, etc. can be used alone or in combination. Among them, it is preferable to use dicyandiamide because it is a component with a high melting point. Also, by using dicyandiamide, the temperature range in which the curing reaction with the epoxy resin starts can be raised, so that a rapid reaction can be suppressed when the dicyandiamide adheres to the surface of the object to be coated, and heat generation due to the curing reaction can be avoided.

[0020] Examples of imidazole-based hardeners include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1,2-dimethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and triazine compounds having an imidazole ring. Examples of triazine compounds having an imidazole ring include 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine. Two or more types of imidazole-based hardeners may be used in combination. Among them, it is preferable to use 2-phenyl-4,5-dihydroxymethylimidazole because it is a component with a high melting point. Commercially available imidazole curing agents include Curesol (registered trademark) 2MZ-A and 2PHZ-PW (both manufactured by Shikoku Chemical Industry Co., Ltd.).

[0021] Examples of the amine-based curing agent include aliphatic amines, aromatic amines, modified amines, etc. Among them, it is preferable to use diaminodiphenylsulfone from the viewpoint of increasing the temperature at which the curing reaction with the epoxy resin starts.

[0022] The softening point of the phenol-based curing agent is preferably 90° C. to 140° C. For example, orthocresol novolac resin can be used.

[0023] The acid anhydride curing agent preferably has a softening point or melting point of 90° C. or higher. For example, benzophenone tetracarboxylic dianhydride can be used.

[0024] The polyamide compound preferably has a softening point or melting point of 100° C. or higher. For example, a polycondensation product of a dimer acid and a polyamine can be mentioned.

[0025] The softening point or melting point of the hardener (B) can be measured by the ring and ball method or a melting point measuring apparatus.

[0026] The amount of the curing agent (B) blended is not particularly limited as long as it is within a range that does not impair the effects of the present invention. When the epoxy equivalent relative to the total amount of epoxy resin is taken as 1, the amount of the curing agent in terms of the reactive group equivalent is preferably within a range of 0.7 to 1.3.

[0027] The epoxy resin powder coating according to the embodiment of the present invention contains a mixture particle containing the above-mentioned epoxy resin (A) and a curing agent (B). The mixture particle may contain various components described below in addition to (A) and (B).

[0028] <(C) Inorganic material surface-treated with a tackifier> In the epoxy resin powder coating according to an embodiment of the present invention, the surface of a mixture particle containing the above-mentioned epoxy resin (A) and hardener (B) is coated with an inorganic material that has been surface-treated with a tackifier (C). The inorganic material that has been surface-treated with a tackifier may be used in the form of particles that have been crushed using a dispersing machine such as a Disper.

[0029] Here, the powder coating containing the mixture particles containing the epoxy resin (A) and the hardener (B) coated with a conventional flowability imparting agent obtained by surface-treating an inorganic material such as fine silica, etc., slides easily on the surface of the object to be coated even when electrostatically coated on the heated object to be coated, and further, the friction between the mixture particles on the surface is reduced, and the surface of the adhering mixture particles also slides easily. Therefore, the amount of the powder coating applied to the surface of the object to be coated tends to be reduced, and there is a problem that it is difficult to form a coating film on the object to be coated. In particular, when the flowability imparting agent is contained in the epoxy resin powder coating at a high compounding rate in order to increase the flowability, the surface of the object to be coated tends to slide easily, and it is difficult to form a coating film on the object to be coated. In contrast, the powder coating containing the mixture particles containing the epoxy resin (A) and the hardener (B) coated with an inorganic material surface-treated by a tackifier can increase the softening point of the powder coating, and even when electrostatically coated on a heated object to be coated, the tackifier on the surface of the inorganic material can firmly adhere to the surface of the object to be coated. Therefore, even if an epoxy resin powder paint contains a high content of inorganic material that has been surface-treated with a tackifier, not only can the paint adhere firmly to the surface of the object to be coated, but the softening point of the powder paint is also increased. This allows the epoxy resin powder paint to adhere well to the surface of the object to be coated, and even when the epoxy resin powder paint is used on a heated object to be coated, it is possible to suppress the paint from fusing to surrounding equipment.

[0030] As the tackifier, known tackifiers can be used, such as rosin-based tackifiers (rosin resin, rosin derivatives), terpene-based tackifiers (terpene resin, terpene phenol resin, aromatic modified terpene resin, hydrogenated terpene resin), petroleum resin-based tackifiers (aliphatic, aromatic, copolymer, alicyclic), and other tackifiers (phenolic resin, xylene resin, chroman-indene resin, ketone resin), etc.

[0031] The inorganic material to be surface-treated by the tackifier may be any of the materials conventionally known as fillers for epoxy resin powder coatings, such as silica, alumina, heavy calcium carbonate, precipitated calcium carbonate, calcium silicate, magnesium silicate, aluminum silicate, wollastonite, talc, zeolite, clay, and compounds containing these.

[0032] Commercially available inorganic materials that have been surface-treated with a tackifier (C) include Homocal D (rosin acid-treated light calcium carbonate), Hakuenka O (rosin acid-treated light calcium carbonate), and Viscoexcel 30 (fatty acid-treated synthetic calcium carbonate) (all manufactured by Shiraishi Kogyo Co., Ltd.).

[0033] The primary particle diameter of the inorganic material that has been surface-treated with the tackifier (C) is preferably 1 nm to 1000 nm, and more preferably 5 nm to 500 nm. With this configuration, the surface of the mixture particles can be well coated. The primary particle diameter of the inorganic material that has been surface-treated with the tackifier (C) can be measured by a scanning electron microscope.

[0034] The inorganic material that has been surface-treated with a tackifier (C) may be in a state where the tackifier is attached to the surface of the inorganic material, or may be in a state where the tackifier is chemically bonded to a functional group on the surface of the inorganic material. In addition, it is preferable that the entire surface of the inorganic material is surface-treated with a tackifier, or it may be that only a part of the surface is surface-treated with a tackifier.

[0035] The mixture particles containing the epoxy resin (A) and the curing agent (B) are preferably completely covered with the inorganic material that has been surface-treated with the tackifier (C), but may be partially covered. Specifically, the surface coverage of the mixture particles with the inorganic material that has been surface-treated with the tackifier (C) is preferably 10% or more. When the surface coverage is 10% or more, the epoxy resin powder coating can be more firmly attached to the surface of the substrate, and the softening point of the powder coating increases. The surface coverage is more preferably 50% or more, more preferably 70% or more, and more preferably 100% or more. The surface coverage is a value measured by the method described below, and may exceed 100%.

[0036] The surface coverage of the mixture particles by the tackifier of the inorganic material can be calculated by the following method. The surface coverage (%) of the mixture particles by the tackifier of the inorganic material is expressed as a percentage obtained by dividing the specific surface area of ​​the mixture particles by the cross-sectional area of ​​the inorganic material that has been surface-treated with the tackifier. The specific surface area of ​​the mixture particles is calculated using the particle size distribution measured by a laser diffraction / scattering method (JIS Z8825). The cross-sectional area of ​​the inorganic material that has been surface-treated with a tackifier is calculated using the particle diameter measured by a scanning electron microscope.

[0037] <(D) Filler> The epoxy resin powder coating according to the embodiment of the present invention preferably further contains a filler (D). Examples of the filler (D) include oxides such as silica, alumina, zirconium dioxide, magnesium oxide, zinc oxide, iron oxide, barium titanate, and silica-alumina composite oxide; nitrides such as silicon nitride, titanium nitride, boron nitride, and aluminum nitride; poorly soluble ion crystals such as calcium fluoride, barium fluoride, calcium sulfate, and barium sulfate; covalent crystals such as graphite, silicon, and silicon dioxide; calcium carbonate, aluminum sulfate, aluminum hydroxide, magnesium hydroxide, potassium titanate, calcium silicate, magnesium silicate, talc, kaolinite, montmorillonite, sericite, mica, bentonite, zeolite, boehmite, and mullite, and compounds containing these. Among these, aluminum hydroxide and magnesium hydroxide are particularly preferred because they can improve the flame retardancy of the epoxy resin powder coating by generating water when heated.

[0038] The filler (D) preferably has an average particle size D50 of 0.5 μm to 40 μm. When the average particle size D50 is 0.5 μm to 40 μm, the powder coating has a good melt viscosity. From the viewpoint of imparting an appropriate flowability to the epoxy resin powder coating when melted, the filler (D) is preferably contained in an amount of 10 parts by mass to 150 parts by mass, and more preferably 20 parts by mass to 100 parts by mass, when the total amount of the epoxy resin is taken as 100 parts by mass.

[0039] The average particle size D50 of the filler is the 50% cumulative volume particle size (also called the median size) measured by the laser diffraction / scattering method (JIS Z8825). The average particle size D50 can be measured using a laser diffraction particle size distribution measuring device or the like.

[0040] In the epoxy resin powder coating according to the embodiment of the present invention, the total epoxy equivalent of all epoxy resins is preferably 200g / eq to 2500g / eq. By appropriately adjusting the total epoxy equivalent of all epoxy resins within the range of 200g / eq to 2500g / eq, the coating amount on the surface of the coated object becomes good, and even when used on a heated coated object, the coating material can be prevented from fusing to surrounding equipment. In the epoxy resin powder coating according to the embodiment of the present invention, the total epoxy equivalent of all epoxy resins is more preferably 500g / eq to 2200g / eq.

[0041] <Other ingredients> In the epoxy resin powder coating according to the embodiment of the present invention, conventional auxiliary components such as thermosetting resins, thermoplastic resins, curing accelerators, flame retardants, colorants, surface modifiers, thixotropic agents, anti-settling agents, coupling agents, defoamers, and release agents may be appropriately blended in addition to the above-mentioned components, so long as the effects of the present invention are not impaired. Examples of the flame retardant include phosphorus compounds, halogen compounds, antimony compounds such as antimony trioxide, and metal hydroxides. Examples of the surface modifier include (meth)acrylic acid alkyl ester polymers. Examples of colorants include titanium dioxide, ferric oxide, carbon black, and phthalocyanine blue.

[0042] <Softening point> The epoxy resin powder coating according to the embodiment of the present invention preferably has a softening point of 100°C or higher. Generally, the object to be coated may be heated and degreased before coating as necessary. If electrostatic coating is performed when the temperature of the object to be coated is high, the temperature of the peripheral equipment of the object to be coated, such as the conveying device (belt conveyor, etc.) that conveys the object to be coated, is also high, and the powder coating applied to the surface of the object to be coated may be heated and fused in the peripheral equipment of the object to be coated, which may make it difficult to use the equipment continuously. In contrast, if the softening point of the epoxy resin powder coating is 100°C or higher, even if electrostatic coating is performed on the object to be coated that is placed on the conveying device (belt conveyor, etc.) that conveys the object to be coated and has a high temperature after heat degreasing, it is possible to suppress fusion to the peripheral equipment. At this time, the epoxy resin powder coating adheres to the peripheral equipment, but is not fused, so it can be easily removed, making it easy to use the equipment continuously. In addition, since it is not necessary to cool the object to be coated to a temperature at which the powder coating does not fuse before coating, it is advantageous in terms of cost and further improves production efficiency. The epoxy resin powder coating material according to the embodiment of the present invention preferably has a softening point of 105° C. or higher. The upper limit of the softening point is not particularly limited, but may be 200° C. or lower, or 150° C. or lower.

[0043] The softening point of the epoxy resin powder coating can be measured by a conventionally known method. It can be measured as follows based on the test method for powder coatings for electrical insulation (JIS C 2161:2010). First, prepare a softening point measuring device (Kofler hot bench) consisting of a hot plate with a temperature gradient from one side to the other and a scale plate indicating the softening point of the sample. The Kofler hot bench is then pre-warmed to allow the temperature of the hot plate to reach equilibrium, and the temperature indication is adjusted using a standard material close to the melting point of the sample. Next, place a small amount of powder in a band so that the expected melting point is in the middle of the 20°C temperature range, and after about 1 minute, brush the powder off with a soft brush toward the low temperature side of the temperature gradient. The position where the powder shows signs of being baked is taken as the softening point, and the temperature indication at that point is read. The same sample is measured three times, the average value is calculated, and this is the softening point of the sample.

[0044] <Average particle size D50 and specific surface area> In the epoxy resin powder coating according to the embodiment of the present invention, the smaller the particle size, the larger the specific surface area. The softening point of the epoxy resin powder coating is measured using a Kofler hot bench as described above, but since the sample is evaluated about one minute after being placed on the Kofler hot bench, if the particle size is large, it takes time for heat to be transmitted to the entire particle. For this reason, the softening point tends to rise. In this way, the softening point of the epoxy resin powder coating is affected by the particle size.

[0045] The epoxy resin powder coating according to the embodiment of the present invention preferably has an average particle size D50 of 10 μm to 50 μm. By controlling the average particle size D50 of the epoxy resin powder coating within the range of 10 μm to 50 μm, it becomes easier to control the softening point of the epoxy resin powder coating to 100° C. or higher. The average particle size D50 of the epoxy resin powder coating can be measured by a method similar to the method for measuring the average particle size D50 of the filler (D) described above.

[0046] The epoxy resin powder coating according to the embodiment of the present invention has a specific surface area of ​​900 cm 2 / g~3500cm 2 / g. The specific surface area of ​​the epoxy resin powder coating is preferably 900 cm 2 / g~3500cm 2 / g, it becomes easier to control the softening point of the epoxy resin powder coating to 100° C. or higher. The specific surface area of ​​the epoxy resin powder coating can be measured by a method similar to the method for measuring the specific surface area of ​​the mixture particles containing the epoxy resin (A) and the hardener (B) described above.

[0047] <Electrostatic paintability> Electrostatic paintability indicates the coating efficiency when applied to the surface of a substrate by electrostatic painting. The epoxy resin powder paint according to the embodiment of the present invention can be well applied to a substrate by electrostatic painting. In other words, the electrostatic paintability to the substrate is good.

[0048] <Application> The epoxy resin powder paint according to the embodiment of the present invention, like general epoxy resin powder paints, can be used as a paint for imparting electrical insulation, heat resistance, corrosion resistance, etc. to processed steel materials such as bus bars and steel pipes, electronic components such as capacitors and transistors, and in-vehicle components such as starters, wipers and brake pads.

[0049] The method of coating with the epoxy resin powder coating according to the embodiment of the present invention is not particularly limited, and known coating methods can be applied.Specific examples include electrostatic coating, fluidized bed immersion, and hot spray methods.Among these, the electrostatic coating is particularly effective in suppressing the coating from fusing to surrounding equipment even when used on a heated object to be coated, and in providing good adhesion to the object to be coated, which is a feature of the epoxy resin powder coating according to the embodiment of the present invention.

[0050] (Manufacturing method of epoxy resin powder coating) The epoxy resin powder coating according to the embodiment of the present invention can be produced, for example, by the following method. First, the above-mentioned (A) epoxy resin and (B) curing agent are blended, and, if necessary, conventional auxiliary components such as a (D) filler, a thermosetting resin other than the above-mentioned components, a thermoplastic resin, a curing accelerator, a flame retardant, a colorant, a surface modifier, a thixotropic agent, an anti-settling agent, a coupling agent, an antifoaming agent, and a mold release agent are added to prepare a composition. Next, the composition is melt-kneaded. The melt-kneading is preferably completed in a short time using an extruder or the like. Thereafter, the obtained mixture is cooled and solidified, and the solidified mixture (molten kneaded product) is pulverized to obtain a powder (mixture particles) composed of mixture particles containing at least the epoxy resin (A) and the curing agent (B). Separately, (C) an inorganic material that has been surface-treated with a tackifier is prepared. Here, the inorganic material surface-treated with the tackifier (C) can be prepared by adding the tackifier to an aqueous dispersion of the inorganic material, stirring, and then dehydrating. The aqueous dispersion can be appropriately adjusted in consideration of the dispersibility and dehydration of the inorganic material, and is preferably prepared by adding water so that the solid content is 2 to 30 mass %. The temperature of the water for preparing the aqueous dispersion is preferably 30 to 100°C. The surface coverage of the inorganic material by the tackifier can be controlled by the primary particle size of the inorganic material. The primary particle size of the inorganic material is preferably 1 nm to 1000 nm, and the desired surface coverage of the inorganic material by the tackifier can be obtained by appropriately adjusting the primary particle size of the inorganic material within this range. Here, by increasing the primary particle size of the inorganic material, the surface coverage of the inorganic material by the tackifier can be reduced, and by decreasing the primary particle size of the inorganic material, the surface coverage of the inorganic material by the tackifier can be increased. Next, the inorganic material surface-treated with the tackifier (C) is added to and mixed with the powder composed of the mixture particles containing at least the epoxy resin (A) and the hardener (B) described above. This results in an epoxy resin powder coating according to the embodiment of the present invention, in which the surfaces of the mixture particles are coated with the inorganic material surface-treated with the tackifier (C). EXAMPLES

[0051] The following examples of the present invention are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0052] 1. Preparation of Epoxy Resin Powder Coating <Examples 1 to 20 and Comparative Examples 1 to 12> A composition was prepared by mixing all materials for each experimental example in the compounding ratios shown in Tables 1 to 4. The raw materials for each component shown in Tables 1 to 4 are shown below. In this specification, "compounding ratio" refers to mass ratio unless otherwise specified. The average particle size D50 of the epoxy resin powder coating was measured using a laser diffraction particle size distribution measuring device (SYMPATEC, HELOS and RODOS, analysis software: WINDOX5).

[0053] (A) Epoxy resin (a1) Bisphenol A type epoxy resin (softening point: 97°C, epoxy equivalent: 875g / eq to 975g / eq) (a2) Bisphenol A type epoxy resin (softening point: 128°C, epoxy equivalent: 1750g / eq to 2200g / eq) (a3) Bisphenol A type epoxy resin (softening point: 144°C, epoxy equivalent: 2400g / eq to 3300g / eq) (a4) Novolac type epoxy resin (softening point: 92°C, epoxy equivalent: 200g / eq~220g / eq) (B) Hardener (b1) Dicyandiamide (b2) Phenol novolac resin (softening point: 100°C) (b3) 2-phenyl-4,5-dihydroxymethylimidazole (b4) 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine (C) Treatment agent (c1) Inorganic material: Aluminum oxide (c2) Inorganic material surface-treated with a tackifier: Rosin acid-treated light calcium carbonate (primary particle size: 80 nm) (c3) Inorganic material surface-treated with a tackifier: Rosin acid-treated light calcium carbonate (primary particle size: 30 nm) (D) Filler (d1) Aluminum hydroxide (average particle size D50: 1 μm) (d2) Calcium carbonate (average particle size D50: 1.25 μm)

[0054] Next, each composition was melt-kneaded using an extruder. The mixture was then cooled and solidified, and the solidified mixture (melted and kneaded product) was pulverized to obtain a powder (mixture particles) composed of mixture particles containing at least the epoxy resin (A) and the hardener (B). The obtained powder was then mixed with an inorganic material (C) that had been surface-treated with a tackifier to obtain an epoxy resin powder coating. The surface coverage of the mixture particles containing the epoxy resin (A) and the hardener (B) by the inorganic material (C) that had been surface-treated with a tackifier was as shown in Tables 1 to 4.

[0055] 2. Evaluation The epoxy resin powder coating samples obtained in each experimental example were evaluated for average particle size D50, specific surface area, electrostatic paintability, and softening point by the methods described below.

[0056] <2-1: Average particle size D50> The average particle size D50 of the epoxy resin powder coating was measured using a laser diffraction particle size distribution measuring device (SYMPATEC, HELOS and RODOS, analysis software: WINDOX5). The evaluation results are shown in Tables 1 to 4.

[0057] <2-2:Specific surface area> The specific surface area of ​​the epoxy resin powder coating was calculated using the particle size distribution measured by the laser diffraction / scattering method (JIS Z8825) using a laser diffraction particle size distribution analyzer (SYMPATEC, HELOS and RODOS, analysis software: WINDOX5). The evaluation results are shown in Tables 1 to 4.

[0058] <2-3: Electrostatic paintability> The electrostatic paintability of the epoxy resin powder coating was evaluated by the following procedure. First, the epoxy resin powder paint obtained in each experimental example was applied to the surface of the workpiece (steel plate: length x width x thickness = 100 mm x 25 mm x 1.6 mm) heated to a surface temperature of 125°C using a friction-charged paint gun. Next, the adhesion state of the powder paint to the surface of the workpiece was observed. The evaluation criteria were as follows: The evaluation results are shown in Tables 1 to 4. (a) Very good: The coating adhered to the surface of the workpiece without melting, and the coating was applied evenly and smoothly. (b) Good: The paint adhered to the surface of the workpiece without fusing, and although there were some irregularities, the paint was able to be applied to a usable area. (c) Poor: Did not adhere to the surface.

[0059] <2-4: Softening point> The softening point of the epoxy resin powder coating was measured as follows based on the test method for powder coating for electrical insulation (JIS C 2161:2010). First, a softening point measuring device (Kofler hot bench) was prepared, which consisted of a hot plate with a temperature gradient from one side to the other and a scale plate indicating the softening point of the sample. The Kofler hot bench was then pre-warmed to allow the temperature of the hot plate to reach equilibrium, and the temperature indication was adjusted using a standard close to the melting point of the sample. Next, a small amount of epoxy resin powder paint was spread in a band so that the predicted melting point was in the middle of the 20°C temperature range, and after about one minute the powder was brushed off toward the low temperature side of the temperature gradient with a soft brush. The position where the powder showed traces of being baked was taken as the softening point, and the temperature indication at that time was read. The same sample was measured three times, and the average value was calculated and used as the softening point of the sample. The evaluation results are shown in Tables 1 to 4.

[0060] [Table 1]

[0061] [Table 2]

[0062] [Table 3]

[0063] [Table 4]

[0064] 3. Discussion As shown in Tables 1 to 4, the epoxy resin powder coatings according to Examples 1 to 20, which have mixture particles containing at least the above-mentioned (A) and (B) as components and have the surfaces of the mixture particles coated with the treatment agent (C), had good electrostatic paintability. That is, in the epoxy resin powder coatings according to Examples 1 to 20, a coating film that adheres well to the surface of the substrate was formed by electrostatic coating. In addition, the softening point was 100°C or higher, and it is considered that the coating can be prevented from fusing to surrounding equipment even when used on a heated substrate. In Comparative Examples 1 to 6 and 11 to 12, the mixture particles were not surface-treated with the treatment agent (C), and therefore the softening point was less than 100°C. Therefore, it is considered that there is a risk of the paint fusing to surrounding equipment if used on a heated object to be coated. In Comparative Examples 7 to 10, the electrostatic coatability was poor because the treating agent (C) was not an inorganic material that had been surface-treated with a tackifier.

Claims

1. (A) an epoxy resin having a softening point or melting point of 90°C to 150°C; (B) a curing agent; The mixture particles include (C) An epoxy resin powder coating material in which the surfaces of the mixture particles are coated with an inorganic material that has been surface-treated with a tackifier.

2. 2. The epoxy resin powder coating material according to claim 1, wherein the surface coverage of the mixture particles with (C) is 10% or more.

3. The epoxy resin powder coating according to claim 1 or 2, further comprising (D) a filler.

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