Powder coating composition and coated body

Abstract

To provide a powder coating composition capable of forming a coating film having quick curability in which a coating film is quickly cured, excellent defoaming properties in which an air bubble easily escapes from a coating film and excellent adhesion and impact resistance and to provide a coated body coated with the powder coating composition.SOLUTION: There is provided a powder coating composition which comprises a resin (A) and a curing agent (B), wherein the powder coating composition has a gel time of 30 seconds or less at 200°C and when a pellet, which is a molded product obtained by pressing and compacting the powder coating composition, is melted by heating from 100°C to 200°C at the rate of temperature rise of 5.6°C / minute, the time from the point where the viscosity reaches the lowest melt viscosity to the point where the viscosity increases tenfold is 3.0 minutes or more and 9.0 minutes or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a powder coating composition and a coated body.

Background Art

[0002] Conventionally, many metal products and parts have been used as structural materials for building materials, home appliances, automobiles, etc. Since these metal products are required to have aesthetics and corrosion resistance, coated bodies obtained by coating their surfaces with a powder coating composition have been used. Recently, it has become common to apply a powder coating composition to metal members used in infrastructure such as water pipes. In addition, the powder coating composition is required to have rapid curing properties that allow curing in a short time from the viewpoints of further improving productivity and reducing environmental impact. However, when the powder coating composition is usually cured in a short time, there is a problem that bubbles easily remain in the coating film during curing, and coating film properties such as impact resistance, adhesion, and corrosion resistance of the coating film deteriorate.

[0003] As powder coatings for metal members, Patent Document 1 and Patent Document 2 disclose epoxy resin powder coating compositions containing an epoxy resin and a curing agent. These epoxy resin powder coating compositions improve the corrosion resistance of metal members. However, Patent Document 1 and Patent Document 2 do not disclose that the epoxy resin powder coating composition has rapid curing properties or the above-described problems caused by curing in a short time. Further, Patent Document 3 discloses a powder coating composition that cures at a low coating temperature. Thereby, the corrosion protection of metal members is improved and it has rapid curing properties. However, in Patent Document 3, the powder coating of Example 1, which is the only example, uses sebacic acid dihydrazide as a curing agent, and sebacic acid dihydrazide has a problem that bubbles easily remain in the coating film when cured in a short time.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] Therefore, the inventions described in Patent Documents 1 to 3 have the problem that a powder coating composition can not be obtained that has rapid curing properties while also having good coating film characteristics such as defoaming properties that do not leave air bubbles in the coating film, adhesion, and impact resistance.

[0006] The object of the present invention has been made in view of the above problems, and is to provide a powder coating composition that can form a coating film that has excellent rapid curing properties, which allow the coating film to harden quickly, excellent defoaming properties which allow air bubbles to escape easily from the coating film, and excellent adhesion and impact resistance, as well as a coated body coated with this powder coating composition. [Means for solving the problem]

[0007] The objective of the present invention was achieved as follows. (1) A powder coating composition comprising a resin (A) and a curing agent (B), The aforementioned powder coating composition has a gel time of 30 seconds or less at 200°C, and A powder coating composition in which, when pellets, which are molded bodies formed by compressing the aforementioned powder coating composition, are heated from 100°C to 200°C at a heating rate of 5.6°C / min to melt, the time it takes for the viscosity to increase tenfold from the point where the minimum melt viscosity is reached is in the range of 3.0 minutes to 9.0 minutes. (2) The powder coating composition according to (1), wherein the minimum melt viscosity is in the range of 500 Pa·s or more and 5000 Pa·s or less. (3) The powder coating composition according to (1) or (2), wherein the resin (A) is an epoxy resin. (4) The powder coating composition according to (1), (2), or (3), wherein the curing agent (B) comprises both an imidazole compound and an imidazoline compound. (5) A coated body having a base material and a coating film formed on the surface of the base material using any one of the powder coating compositions described in (1) to (4). [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a powder coating composition that can form a coating film that exhibits excellent rapid curing (quick drying) properties, excellent defoaming properties that allow air bubbles to escape easily from the coating film, and also excellent adhesion and impact resistance, as well as a coated body coated with this powder coating composition. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows one embodiment of the coated body of the present invention. [Figure 2] This figure shows one embodiment of the coated body of the present invention. [Modes for carrying out the invention]

[0010] The powder coating compositions and coated bodies of the present invention will be described in detail below, but are not limited thereto.

[0011] <Powder coating composition> The powder coating composition of the present invention is characterized by comprising at least a resin (A) and a curing agent (B).

[0012] <Resin (A)> Resin (A) can be either a thermosetting resin or a thermoplastic resin, but a thermosetting resin is preferred. It hardens when heat is applied, allowing for easy formation of a coating film. As resin (A), commonly used resins can be used, such as acrylic resin, silicone resin, acrylic silicone resin, styrene-acrylic copolymer resin, polyester resin, fluororesin, rosin resin, petroleum resin, coumarone resin, phenolic resin, urethane resin, melamine resin, urea resin, epoxy resin, cellulose resin, xylene resin, alkyd resin, aliphatic hydrocarbon resin, butyral resin, maleic acid resin, fumaric acid resin, vinyl resin, amine resin, ketimine resin, etc., with epoxy resin being particularly preferred. These resins may be used individually or in combination of two or more types.

[0013] Furthermore, the resin (A) contained in the powder coating composition of the present invention can be modified to improve the effect of the curing agent. Examples of modified resins include those that have been modified by alkyl modification, alkyl ether modification, alkylphenol novolac modification, acrylic modification, fatty acid modification, urethane modification, amino modification, isocyanate modification, silicone modification, or other graft modification utilizing allyl groups (preferably epoxy resins, resins containing hydroxyl groups, etc.). Examples of resins containing hydroxyl groups include hydroxyl group-containing acrylic resins, hydroxyl group-containing acrylic silicone resins, and hydroxyl group-containing fluororesins.

[0014] <Epoxy resin> Epoxy resins are suitable for use as resin (A) contained in the powder coating composition in order to impart adhesion to the substrate. Examples of the epoxy resins used in the present invention include bisphenol type epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, novolak type epoxy resin, cycloaliphatic epoxy resin, glycidylamine type resin, heterocyclic epoxy resin, polyfunctional epoxy resin, and the like. These can be used alone or in combination. Specifically, solid epoxy resins synthesized from bisphenol A and epihalohydrin, epichlorohydrin, solid epoxy resins obtained by the elongation reaction of an epoxy resin derived from bisphenol A, a dihydric phenol, and epihalohydrin with bisphenol A, and the like are preferred.

[0015] Examples of such epoxy resins include jER1004, jER1004F, jER1007, jER4005P manufactured by Mitsubishi Chemical Corporation, EPICLON3050, EPICLON4050 manufactured by DIC Corporation, Epotote YD014D manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., EPONANYANPES-904 manufactured by Nan Ya Plastics Corporation, and the like, which are available.

[0016] Resin (A) can be used by mixing a plurality of epoxy resins having different epoxy equivalent weights. The epoxy equivalent weight is not particularly limited, but is preferably 400 to 3000. Further, it is preferable to combine those having an epoxy equivalent weight of 1000 or less and those having an epoxy equivalent weight of 1000 or more, and the difference in the epoxy equivalent weight between the epoxy resin having the minimum epoxy equivalent weight and the epoxy resin having the maximum epoxy equivalent weight is 300 or more, preferably 500 or more.

[0017] The epoxy resin preferably has a number average molecular weight (in terms of polystyrene conversion by SEC) of 200 to 5000, more preferably 300 to 2000, from the viewpoints of coating film properties and coating workability. The softening point of the epoxy resin is not particularly limited, but a range of 60 to 150°C is preferred, and more preferably a range of 90 to 120°C. If the softening point is less than 60°C, the storage stability is insufficient and the workability in coating decreases. If it exceeds 150°C, the rapid curing property and defoaming property decrease.

[0018] <Hardener (B)> The hardener (B) contained in the powder coating composition of the present invention can be appropriately selected according to the type of resin used, and a commonly used hardener (B) can be used. For example, amide compounds, acid anhydrides, dibasic acids, glycidyl compounds, aminoplast resins, isocyanate compounds, hydroxyalkylamides, etc. can be mentioned. These hardeners (B) may be used alone or in combination of two or more. The content of the hardener (B) is appropriately adjusted according to the amount of reactive groups with the hardener (B) contained in the resin.

[0019] When an epoxy resin is used in the powder coating composition of the present invention, the hardener (B) is not particularly limited as long as it is a commonly used hardener (B). In particular, imidazole compounds, imidazoline compounds, dicyandiamide, acid anhydrides, polycarboxylic acid hydrazides and their derivatives, phenol compounds and their derivatives, etc. can be mentioned. Examples of the polycarboxylic acid hydrazide include adipic acid dihydrazide, sebacic acid dihydrazide, dodecanedione dihydrazide, isophthalic acid dihydrazide, salicylic acid hydrazide, etc.

[0020] In particular, the curing agent (B) preferably contains both imidazole compounds and imidazoline compounds. In addition, at least one selected from the group of polycarboxylic acid hydrazides and their derivatives can be used. Imidazole compounds contribute significantly to the rapid curing properties in the powder coating composition. Imidazolin compounds improve the reactivity at low temperatures in the powder coating composition and contribute to defoaming. These curing agents (B) are preferably contained in an amount of 0.5 to 10 parts by mass per 100 parts by mass of epoxy resin. If the amount of curing agent (B) is less than 0.5 parts by mass, the rapid curing properties decrease. If the amount of curing agent (B) exceeds 10 parts by mass, the defoaming properties decrease.

[0021] <Pigments> The powder coating composition of the present invention may contain a pigment (C) in addition to a resin (A) and a curing agent (B). Examples of pigments (C) include coloring pigments (C1) and extender pigments (C2). Other pigments that may be included include rust-preventive pigments (C3) and luminous pigments (C4).

[0022] <<Coloring Pigment (C1)>> Coloring pigments are broadly classified into inorganic pigments and organic pigments based on their composition. Examples of inorganic pigments include titanium dioxide, red iron oxide, yellow iron oxide, and carbon black, while examples of organic pigments include phthalocyanine blue, phthalocyanine green, naphthol red, quinacridone red, benzimidazolone yellow, Hansa yellow, benzimidazolone orange, and dioxazine violet.

[0023] <<Extender Pigment (C2)>> Extender pigments (C2) are white or colorless pigments. Because of their low refractive index, they have little effect on opacity when mixed with binders, and are used as fillers to reduce costs in paints, coatings, and cosmetics, and to adjust color strength, gloss, strength, and feel. Extender pigments (C2) can be made from known materials, such as precipitated barium sulfate, silica, cristobalite, calcium carbonate, alumina, alum, white clay, magnesium hydroxide, and magnesium oxide. Furthermore, extender pigments (C2) may also be in the form of thin, flat pigments like foil (flak-like pigments), with specific examples including glass flakes, talc, mica, and kaolin clay.

[0024] <<Rust-preventive pigment (C3)>> As the rust-preventive pigment (C3), known materials can be used, including zinc powder, zinc oxide, barium metaborate, calcium silicate, aluminum phosphate, condensed aluminum phosphate, aluminum tripolyphosphate, zinc phosphate, zinc phosphite, potassium phosphite, calcium phosphite, aluminum phosphite, calcium zinc phosphate, aluminum zinc phosphate, zinc phosphomolybdate, aluminum phosphomolybdate, magnesium phosphate, vanadic acid / phosphate mixed pigment, etc.

[0025] <<Glitter pigment (C4)>> Known materials can be used as luminous pigments, and specific examples include flaky metallic pigments made from metals such as zinc, nickel, chromium, tin, copper, silver, platinum, gold, and aluminum, which are thin and flat like foil, and pearl pigments made by surface-treating talc or mica with metal oxides such as titanium dioxide. Furthermore, flaky metallic pigments also include pigments made from alloys such as stainless steel. These luminous pigments may be used individually or in combination of two or more types.

[0026] Furthermore, in the powder coating composition of the present invention, the pigment content in the solid content is preferably 5% by mass or more and 25% by mass or less. These pigments may be used individually or in combination of two or more.

[0027] <Other additives (D)> The powder coating composition of the present invention may contain, as appropriate, other additives such as other resins, matting agents, flexibility agents, surface modifiers, wetting agents, dispersants, emulsifiers, thickeners, anti-settling agents, anti-skinning agents, anti-sagging agents, defoaming agents, anti-color separation agents, leveling agents, drying agents, plasticizers, film-forming aids, antifungal agents, antibacterial agents, insecticides, light stabilizers, UV absorbers, electrostatic lubricants, antistatic agents, and conductivity agents, depending on the purpose. Commercially available products can be suitably used for these components.

[0028] <Method for manufacturing powder coating composition> The present invention provides a method for producing a powder coating composition, which involves melt-kneading a mixture containing a resin (A) such as epoxy resin, a curing agent (B), a pigment (C), and an additive (D) at 100 to 160°C, then cooling and pulverizing the mixture to prepare the powder coating composition. Preferably, the mixture is dry-blended using a Henschel mixer or the like, then melt-kneaded at 120 to 140°C using a kneader or the like, cooled and pulverized, and then classified using a mesh of a desired size, such as a 180-mesh (96 μm) wire mesh, to obtain the powder coating composition.

[0029] <Viscosity behavior of powder coating compositions> The powder coating composition of the present invention is characterized in that, when a pellet, which is a molded body formed by compressing the powder coating composition, is heated from 100°C to 200°C at a heating rate of 5.6°C / min to melt it, the time from the point where the minimum melt viscosity is reached to when the viscosity increases to 10 times that amount is in the range of 3.0 minutes to 9.0 minutes.

[0030] <Geltime> The powder coating composition of the present invention has a gel time (curing time) of 30 seconds or less at 200°C, preferably 28.5 seconds or less. However, it is preferable that the gel time be at least 20 seconds or more. When coating the surface of a substrate such as a water pipe preheated to around 200°C, if the gel time is too short, the coating will harden before the coating film melts and becomes smooth on the substrate, impairing fluidity and causing irregularities on the coating film surface. Also, because the coating film hardens too quickly, air bubbles in the coating film may not be able to escape to the outside and may remain. Furthermore, if the coating film is subjected to impact, there is a risk that the areas containing air bubbles in the coating film may crack, resulting in reduced impact resistance. In addition, the adhesion of the coating body may decrease due to contact between the substrate and air bubbles. Conversely, if the gel time is too long, it will take time for the paint film to harden after painting is complete, which can cause dripping at the ends of water pipes, etc., and result in an uneven film thickness. Therefore, if the paint does not have fast-curing properties, it will take a considerable amount of time to obtain the paint film, or a reheating process may be required after painting to make the film thickness uniform. Therefore, the powder coating composition of the present invention can produce a good coating film by setting the gel time (curing time) at 200°C to 30 seconds or less.

[0031] <Method for measuring gel time> To measure the gel time, place 0.7g of powder coating on a hot plate heated to 200°C, stir it with a 1mm diameter wire from the moment it begins to melt, and measure the time it takes until it stops stringing to determine the gel time.

[0032] <Minimum melt viscosity> Furthermore, the powder coating composition of the present invention preferably has a minimum melt viscosity in the temperature range of 100°C to 200°C, which is the minimum viscosity at which it becomes molten, in the range of 500 Pa·s to 5000 Pa·s. If the minimum melt viscosity is less than 500 Pa·s, the viscosity is insufficient, resulting in excessive fluidity. When forming a coating along the surface of a substrate such as a water pipe, the coating spills off the substrate surface, resulting in a coating of uneven thickness. If the minimum melt viscosity exceeds 5000 Pa·s, the fluidity is insufficient, preventing the coating from spreading along the shape of the substrate surface such as a water pipe. As a result, the formed coating has an uneven surface with irregularities. Even with a flat substrate, insufficient fluidity causes irregularities on the coating surface, making it difficult to form a uniform coating. Furthermore, air bubbles in the coating cannot be sufficiently de-aeration, leaving bubbles behind and reducing de-aeration performance. In addition, air bubbles in the coating may burst when the coating is subjected to impact, resulting in reduced impact resistance. Moreover, contact between the substrate and air bubbles may reduce the adhesion of the coated object.

[0033] <Time taken from the point where the minimum melt viscosity is reached until the viscosity increases tenfold> The powder coating composition of the present invention, when a pellet formed by compressing the powder coating composition is heated and melted from 100°C to 200°C at a heating rate of 5.6°C / min, has a viscosity that increases tenfold from the point where it reaches its minimum melt viscosity in a range of 3.0 minutes to 9.0 minutes. By optimizing the gradient of viscosity increase under the condition of heating and melting from 100°C to 200°C at a heating rate of 5.6°C / min, it is possible to degas the coating without leaving air bubbles and cure it in a short time. When heated at a constant heating rate, the viscosity increases tenfold in a short time, between 3.0 and 9.0 minutes, from the point where it reaches its minimum melt viscosity. This allows the powder to easily melt after being applied to the surface of the substrate, and also improves defoaming properties, expelling any remaining air bubbles from the coating surface. Furthermore, conversely, a coating applied at a high temperature can be cured rapidly by quickly increasing its melt viscosity from a low state to a high minimum melt viscosity state in a short time, thereby improving its rapid curing properties. Therefore, in order for the painted coating to have both rapid curing properties that allow it to dry quickly and degassing properties that prevent air bubbles from remaining, it is preferable that the time from the point where the minimum melt viscosity is reached to the point where the viscosity increases to 10 times that amount is in the range of 3.0 minutes to 9.0 minutes.

[0034] <Method for measuring the minimum melt viscosity and the time it takes for the viscosity to increase tenfold from the point where the minimum melt viscosity is reached> A MARS40 (rotational rheometer) manufactured by Thermo Fisher Scientific Co., Ltd. was used as the measuring device. 1.0 g of powder coating composition was weighed out, placed in a mold with an inner diameter of 16 mm, and pressed with a hydraulic press at 20 MPa for 1 minute to form a pellet. The pellet was placed in the measuring section of the MARS40, which had been preheated to 100°C, and the viscosity change was measured from 100°C to 200°C with a gap of 1.0 mm, a frequency of 1.5 Hz, a jig rotation speed of 9.4 rad / s, and a heating rate of 5.6°C / min.

[0035] <Painted body> Figure 1 shows one embodiment of the coated body of the present invention. In the present invention, the coated body 1 has a coating film 12 formed on a substrate 11.

[0036] <Base material> The base material 11 constituting the coated body 1 of the present invention is not particularly limited, but its shape may be, for example, plate-shaped, sheet-shaped, foil-shaped, etc. The material of the base material may be a metal or alloy such as cast iron or cast steel, carbon steel, galvanized steel, stainless steel, magnesium alloy, aluminum, or aluminum alloy.

[0037] <coating film> A coating film 12 made of a powder coating composition is formed on the uppermost layer of the coated body 1 of the present invention. The thickness of the coating film 12 is 50 μm or more and 1500 μm or less, preferably 100 to 1200 μm, and more preferably 200 μm or more and 800 μm or less.

[0038] Figure 2 shows one embodiment of the coated body of the present invention. In the coated body 1 of the present invention, a chemical conversion treatment layer 13 is formed between the substrate 11 and the coating film 12, as shown in Figure 2.

[0039] <Chemical treatment layer> Furthermore, a chemical conversion treatment layer 13 can be provided between the substrate 11 and the coating film 12 for purposes such as improving adhesion and bonding. The chemical conversion treatment layer 13 may be subjected to oxidation treatment, for example. As an example, a substrate 11 made of aluminum that has been oxidized by methods such as anodizing, phosphate treatment, chromate treatment, or non-chromate treatment can be used. It may also be formed by a pretreatment aqueous solution containing a silane coupling agent. It may also be treated with a resin different from that of the coating film 12.

[0040] <Painting Method> The coating method for a coated body 1 using the powder coating composition of the present invention allows for coating a preheated cast iron water pipe, for example, with a coating film 12 applied by spray coating, electrostatic spray coating, or the like, to a base material 11. Furthermore, if the base material 11 is a cast iron pipe, coating can be applied while the pipe is stationary or while it is rotating. Additionally, heating methods can include indirect heating using preheating furnaces such as hot air furnaces, electric furnaces, and far-infrared furnaces, and direct heating methods such as electromagnetic induction heating, high-frequency heating, and burner heating.

[0041] Furthermore, as a method for curing the coating film 12, cooling by air using the heat of the preheated workpiece is preferred. If cooling by air is insufficient and the coating does not cure sufficiently, it is preferable to bake the coating film 12 by heating it at 150-200°C for about 10-30 minutes using a hot air furnace or the like. The coating using the powder coating composition of the present invention can be applied not only to water pipes made of cast iron, but also to coated parts such as fittings and valves. [Examples]

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the examples described below. In the descriptions of examples and comparative examples, "parts" and "%" are based on mass.

[0043] <1. Preparation of powder coating compositions 1-9> The raw materials listed in Table 1 were combined and mixed in a high-speed mixer for 1 minute. Then, the mixture was kneaded using a single-screw mixer (manufactured by BUSS) with the temperature adjusted to 120°C. The extruded mixture was cold-rolled with a cooling roll, then pulverized using a pin mill, and classified using a 150-mesh screen to obtain each of the powder coating compositions 1 to 9 (50% volume average particle size: approximately 35 μm). The raw materials listed in Table 1 are as follows: (A-1) Epoxy resin 1 (epoxy equivalent 200-220, softening point 80-90°C, polyfunctional epoxy resin) (A-2) Epoxy resin 2 (epoxy equivalent 450-500, softening point 80-90°C, polyfunctional epoxy resin) (A-3) Epoxy resin 3 (epoxy equivalent 600-700, softening point: 83-91°C, bisphenol A type epoxy resin) (A-4) Epoxy resin 4 (epoxy equivalent 700-750, softening point 90-98°C, bisphenol A type epoxy resin) (A-5) Epoxy resin 5 (epoxy equivalent 875-975, softening point 95-100°C, bisphenol A type epoxy resin) (A-6) Epoxy resin 6 (epoxy equivalent 900-1000, softening point 90-100°C, modified epoxy resin) (A-7) Epoxy resin 7 (epoxy equivalent 1200-1300, softening point 109-120°C, bisphenol A type epoxy resin) (B-1) Hardener 1 (softening point 93-98°C, novolac-type phenolic resin) (B-2) Hardener 2 (Bisphenol A / Epichlorohydrin polycondensate (phenol compound)) (B-3) Hardener 3 (Epoxy-amine Adduct) (B-4) Hardener 4 (dicyandiamide) (B-5) Hardener 5 (Dihydrazide adipate) (B-6) Hardener 6 (2-methylimidazole) (B-7) Hardener 7 (2-phenylimidazoline) (C1-1) Coloring Pigment 1 (Titanium Dioxide) (C1-2) Coloring Pigment 2 (Carbon Black) (C1-3) Coloring Pigment 3 (Yellow Iron Oxide) (C2-1) Extender Pigment 1 (Precipitating Barium Sulfate) (C2-2) Extender pigment 2 (silica, average particle size 8 μm) (D-1) Additive 1 (Acrylic-based flexibility enhancer, secondary particle size 15-21 μm) (D-2) Additive 2 (Leveling agent) (D-3) Additive 3 (Lubricant, hydrophilic alumina particles, primary particle size 13 nm)

[0044] [Table 1]

[0045] <2. Preparation of the test panel> ≪2-1. Preparation of the test plate for Example 1≫ A cold-rolled steel sheet (SPCC-SB, 70mm x 180mm x 1.6mm thick), which was a substrate heated to 240°C on a hot plate, was placed on its upper surface. The powder coating was then quickly smoothed using an applicator (groove width 40mm, groove depth 1mm), and heated for 1 minute to form a coating film (film thickness: 500-700μm) on the substrate surface, thus producing the test plate of Example 1. Furthermore, the test plates of Examples 2-4 and Comparative Examples 1-5 were prepared in the same manner as in Example 1, except that powder coating compositions 2-9 were placed on the upper surface of the cold-rolled steel sheet heated to 240°C on a hot plate, instead of powder coating composition 1.

[0046] <3. Evaluation of Viscous Behavior> The viscous behavior of the powder coating compositions of Examples 1-4 and Comparative Examples 1-5 was evaluated. A MARS40 (rotational rheometer) manufactured by Thermo Fisher Scientific Co., Ltd. was used as the measuring device. 1.0 g of powder coating composition was weighed out, placed in a mold with an inner diameter of 16 mm, and pressed with a hydraulic press at 20 MPa for 1 minute to form a pellet. The pellet was placed in the measuring section of the MARS40, which had been preheated to 100°C, and the viscosity change was measured from 100°C to 200°C with a gap of 1.0 mm, a frequency of 1.5 Hz, a jig rotation speed of 9.4 rad / s, and a heating rate of 5.6°C / min. From the measurement data, we determined the minimum melt viscosity, the temperature at which the minimum melt viscosity was reached, and the time required for the viscosity to reach 10 times the minimum melt viscosity. Furthermore, 0.7g of powder coating was placed on a hot plate heated to 200°C, and from the moment it began to melt, it was stirred with a 1mm diameter wire. The time required until the stringing stopped was measured, and the gel time was determined. The evaluation results are shown in Table 2.

[0047] <4. Evaluation of coating film properties> The coating properties of the test panels (coated bodies) of Examples 1-4 and Comparative Examples 1-5, namely degassing properties, rapid curing properties (fast drying properties), adhesion, and impact resistance, were evaluated using the methods described below. ≪4-1. Defoaming property≫ The surface appearance and cross-section of the coating film were visually observed, and the degassing properties were evaluated in two stages according to the following criteria. ○: The surface appearance of the coating film is good, and the coating film has few air bubbles in its cross-section. ×: The degassing process during coating formation is insufficient, resulting in a poor appearance or a coating with many air bubbles in the cross-section. ≪4-2. Fast curing≫ Rapid curing properties were evaluated by placing 0.7g of powder coating on a hot plate heated to 200°C, stirring it with a 1mm diameter wire within 30 seconds of it beginning to melt, and measuring the time required until it stopped stringing (gel time). A shorter gel time indicates better rapid curing properties. ○: If the gel time is 30 seconds or less ×: If the gel time exceeds 30 seconds ≪4-3.Adhesion≫ Adhesion was evaluated in two stages according to the following criteria. A dolly (diameter: 20 mm) was attached to the coating on each test plate using adhesive, and the adhesion force was measured when the coating was peeled vertically from the substrate (cold-rolled steel sheet) using an automatic pull-off adhesion tester (elcometer 510 from elcometer). The measured adhesion force was then evaluated. ○: Adhesion strength of 3.0 MPa or higher ×: Adhesion force less than 3.0 MPa ≪4-4. Impact Resistance≫ Impact resistance was evaluated by placing each test plate between the striking die and the support base of a DuPont impact tester (weight 500g, impact core 6.35mm (1 / 4 inch)) as specified in JIS K 5600-5-3:1999, with the coated surface facing upwards. The weight was then dropped onto the striking die, and the presence or absence of cracks or peeling in the coated film was evaluated by visual observation. Impact resistance was performed at a total of four locations, with the position of the coated surface of each test plate shifted, and evaluated according to the following criteria. ○: If no cracking or peeling of the paint film is observed in any of the four locations. ×: If cracking or peeling of the paint film is observed in even one of the four locations.

[0048] [Table 2]

[0049] As shown in Table 2, the powder coating compositions 1 to 4 of Examples 1 to 4 all had a time range of 3.0 minutes to 9.0 minutes from the point where they reached their minimum melt viscosity until their viscosity increased tenfold, and their gel time at 200°C was 30 seconds or less. Therefore, the coating film properties of defoaming, rapid curing, adhesion, and impact resistance were all "○" and met the passing level.

[0050] In particular, the powder coating compositions 1 and 3 of Examples 1 and 3, through the combination of a hydrazide compound and an imidazole compound, exhibit rapid curing at temperatures above 120°C, resulting in fast curing properties. Furthermore, the addition of an imidazoline compound allows for good defoaming even during rapid temperature-raising and baking. Furthermore, the powder coating composition 2 of Example 2, through the combination of a novolac-type phenolic resin curing agent and an imidazole compound, and a hydrazide compound and an imidazole compound, allows for rapid curing at temperatures of 120°C or higher, resulting in fast curing. In addition, the addition of an imidazoline compound improves defoaming even during rapid temperature rise and baking. Moreover, the addition of a small amount of adipic acid dihydrazide can suppress discoloration of the coating film during baking. Furthermore, the powder coating composition 4 of Example 4, through the combination of dicyandiamide, epoxy-amine adduct, and imidazole compound, allows for rapid curing at temperatures of 120°C or higher, resulting in fast curing properties. Additionally, the addition of an imidazoline compound provides good defoaming properties even during rapid temperature rise and baking.

[0051] In Comparative Example 1, powder coating composition 5 showed a short time of 2.5 minutes for the viscosity to increase tenfold from the point where it reached its minimum melt viscosity, and a long gel time of 32.5 seconds. As a result, the coating film characteristics of defoaming, rapid curing, adhesion, and impact resistance all received a "×" rating and were unsatisfactory.

[0052] In Comparative Example 2, powder coating composition 6 had a gel time of 29.1 seconds, which is less than 30 seconds, so its rapid curing properties were at an acceptable level. However, the time it took for the viscosity to increase tenfold from the point where it reached its minimum melt viscosity was only 2.8 minutes, so the coating film properties of defoaming, adhesion, and impact resistance all failed ("×").

[0053] In Comparative Example 3, powder coating composition 7 had a gel time of 25.6 seconds, which is less than 30 seconds, so its rapid curing properties were at an acceptable level. However, the time it took for the viscosity to increase tenfold from the point where it reached its minimum melt viscosity was only 2.6 minutes, so the coating film properties of defoaming, adhesion, and impact resistance all failed ("×").

[0054] In Comparative Example 4, powder coating composition 8 had a gel time of 23.5 seconds, which is less than 30 seconds, so its rapid curing properties were at an acceptable level. However, the time it took for the viscosity to increase tenfold from the point where it reached its minimum melt viscosity was only 2.2 minutes, so the coating film properties of defoaming, adhesion, and impact resistance all failed ("×").

[0055] In Comparative Example 5, the powder coating composition 9 took 5.6 minutes to increase in viscosity from the point where it reached its minimum melt viscosity, which was within the appropriate range. Therefore, its coating properties, including defoaming, adhesion, and impact resistance, all passed with a "○" rating. However, its gel time was a long 37.5 seconds, resulting in a "×" rating for rapid curing, which was unacceptable.

[0056] From the results of Examples 1-4 and Comparative Examples 1-5, it was found that by keeping the time from the point of lowest melt viscosity to a 10-fold increase in viscosity within the range of 3.0 to 9.0 minutes, and keeping the gel time at 200°C to 30 seconds or less, it is possible to achieve a "○ (passing level)" evaluation for all of the coating film characteristics, including defoaming, rapid curing, adhesion, and impact resistance. [Explanation of symbols]

[0057] 1 Painted body 11 Base material 12. Coating film 13. Chemical treatment layer

Claims

1. A powder coating composition comprising a resin (A) and a curing agent (B), The resin (A) is a bisphenol A type epoxy resin with an epoxy equivalent of 400 to 3000. The curing agent (B) comprises both an imidazole compound and an imidazoline compound. The aforementioned powder coating composition is The gel time at 200°C is 30 seconds or less, and, A powder coating composition in which, when a pellet (1 g, 16 mm in diameter), which is a molded body obtained by compressing the powder coating composition, is heated and melted from 100°C to 200°C at a heating rate of 5.6°C / min using a rotary rheometer with a gap of 1.0 mm and a frequency of 1.5 Hz, the time from the point where the minimum melt viscosity is reached to 10 times that viscosity is in the range of 3.0 minutes to 9.0 minutes.

2. The powder coating composition according to claim 1, wherein the minimum melt viscosity is in the range of 500 Pa·s or more and 5000 Pa·s or less.

3. The powder coating composition according to claim 1 or 2, wherein the imidazoline compound is 2-phenylimidazoline.

4. The powder coating composition according to claim 1 or 2, wherein the imidazole compound and the imidazoline compound are contained in the coating composition in an amount of 0.6% by mass or more and 5.0% by mass or less.

5. The powder coating composition according to claim 1 or 2, wherein the ratio of the imidazole compound to the imidazoline compound (imidazole compound / imidazoline compound) is 0.12 or more and 0.79 or less.

6. A coated body comprising a base material and a coating film formed on the surface of the base material using the powder coating composition described in claim 1 or 2.

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