JPWO2013186832A1 - Powder coating composition and method for producing the same - Google Patents

Abstract

The present invention relates to a layer-separated type powder coating composition having good weather resistance and reducing production costs, and more specifically, a fluororesin containing a hydroxyl group or a carboxyl group and a polyester containing a hydroxyl group or a carboxyl group. Forming a coating film comprising a resin and a curing agent selected from the group consisting of β-hydroxyalkylamide, triglycidyl isocyanurate and an isocyanate compound, and comprising a fluorine coating layer and a polyester coating layer The present invention relates to a powder coating composition that can be used.

Description

  The present invention relates to a powder coating composition and a method for producing the powder coating composition, and in particular, a powder coating composition capable of forming a coating film comprising a fluorine coating layer and a polyester coating layer. It is about. Such a powder coating composition may be referred to as a layer separation type powder coating composition.

  In recent years, global environmental problems such as global warming, ozone depletion, and acid rain have been greatly raised, and international countermeasures against environmental pollution have been called out. Has come to be done. Among them, the release of organic solvents (especially volatile organic compounds VOC) into the atmosphere has become a major problem, and the movement to deorganic solvents (especially de-VOCs) is active along with the trend of strengthening VOC regulations in each industry. It has become. In the paint industry, environmentally friendly paints that do not contain VOC at all, do not require exhaust treatment / wastewater treatment, and can be recovered and reused are required as alternatives to conventional organic solvent paints. Expectations are growing.

  As the powder coating, acrylic resin, polyester resin, or epoxy resin powder coating is mainly used. However, the epoxy resin-based powder coating has a disadvantage that it is inferior in weather resistance.

  As a powder coating to improve such defects, a mixture of a thermosetting acrylic resin powder coating and a thermosetting epoxy resin powder coating is applied, and the mixture is heated and cured, whereby the upper layer is made of acrylic. Powder coatings have been developed that are capable of forming a multilayer coating film that is a resin-based powder coating and the lower layer is an epoxy resin-based powder coating (see, for example, Patent Documents 1 to 3).

  On the other hand, from the viewpoint of improving weather resistance, a thermosetting fluororesin-based powder coating using a fluororesin having better weather resistance than acrylic resins and polyester resins has been developed (for example, see Patent Document 4). However, a powder coating using only a fluororesin as a resin requires a large amount of expensive fluororesin and tends to increase the cost.

JP-A-53-140336 JP 54-105135 A JP 2001-259520 A JP 2008-266361 A

  Accordingly, an object of the present invention is to provide a layer-separated type powder coating composition that has good weather resistance and reduces manufacturing costs. Another object of the present invention is to provide a method for producing such a powder coating composition.

  As a result of intensive studies to achieve the above object, the present inventor uses a powder coating composition comprising a fluororesin excellent in weather resistance, a low-cost polyester resin, and a specific curing agent. As a result, it has been found that a highly weather-resistant coating film comprising a fluorine coating film layer and a polyester coating film layer can be formed at low cost and in a reduced process, and the present invention has been completed.

  That is, the powder coating composition of the present invention comprises a group comprising a fluororesin containing a hydroxyl group or a carboxyl group, a polyester resin containing a hydroxyl group or a carboxyl group, β-hydroxyalkylamide, triglycidyl isocyanurate and an isocyanate compound. It is possible to form a coating film comprising a fluorine coating layer and a polyester coating layer.

  The powder coating composition of the present invention preferably further contains an epoxy resin.

  The powder coating composition of the present invention preferably further contains a luster pigment.

  In a preferred example of the powder coating composition of the present invention, the polyester resin is a hydroxyl group-containing polyester resin, and the hydroxyl group-containing polyester resin has a number average molecular weight of 5,000 or less and a weight average molecular weight of 10,000 to 20,000. .

  In another preferred embodiment of the powder coating composition of the present invention, the polyester resin has a melt viscosity of 3.5 Pa · s (190 ° C.) or less, a measurement start temperature of 200 ° C., and a temperature drop rate of 10 ° C./min. In the Arrhenius plot based on the melt viscosity (Pa · s) measured under the above conditions, the slope in the range of 100 to 120 ° C. is 15000 or more.

  In another preferred embodiment of the powder coating composition of the present invention, the fluororesin is a hydroxyl group-containing fluororesin.

  In another preferable example of the powder coating composition of the present invention, a mass ratio (A / B) of the fluororesin (A) and the polyester resin (B) is 50/50 to 10/90.

  In another preferred embodiment of the powder coating composition of the present invention, the difference in solubility parameter (SP value) between the fluororesin and the polyester resin is 0.6 to 0.9.

  Also, the method for producing the powder coating composition of the present invention comprises melt-kneading a mixture containing the fluororesin, the polyester resin, and the curing agent at 100 to 160 ° C., then pulverizing the mixture after cooling, A body coating composition is prepared.

  According to the present invention, by using a fluorine resin excellent in weather resistance, a low-cost polyester resin, and a specific curing agent, a highly weather-resistant coating film comprising a fluorine coating layer and a polyester coating layer is reduced. It is possible to provide a layer-separated type powder coating composition that can be formed at low cost and in a reduced process. Moreover, the manufacturing method of this powder coating composition can also be provided.

It is the image which mapped the fluorine atom which exists in a coating film cross section.

<Powder coating composition>
The powder coating composition of the present invention is selected from the group consisting of a fluororesin containing a hydroxyl group or a carboxyl group, a polyester resin containing a hydroxyl group or a carboxyl group, β-hydroxyalkylamide, triglycidyl isocyanurate, and an isocyanate compound. It is possible to form a coating film comprising a fluorine coating layer and a polyester coating layer. Moreover, since the powder coating composition of this invention uses cheap polyester resin other than the fluororesin which is excellent in a weather resistance, it can suppress the manufacturing cost and can form the coating film excellent in a weather resistance. In addition, when the powder coating composition of the present invention is coated on a substrate, two coating layers are formed by one coating, so that the coating film manufacturing process can be omitted. In addition, a fluorine coating layer refers to the coating layer formed based on a fluororesin, and a polyester coating layer refers to the coating layer formed based on a polyester resin.

<Fluorine resin>
In the powder coating composition of the present invention, the fluororesin needs to be a solid resin at room temperature, and its softening point is preferably 50 to 150 ° C. The said fluororesin forms a fluorine coating film layer, and brings a weather resistance to a coating film. In addition, normal temperature is the temperature of the range of 20 degreeC ± 15 degreeC (5-35 degreeC) prescribed | regulated by JISZ8703.

  Moreover, the said fluororesin needs to have a reactive site | part which reacts with a hardening | curing agent etc., and contains a hydroxyl group or a carboxyl group. Therefore, the said fluororesin can be manufactured by copolymerizing a fluorine-containing monomer with the monomer containing a specific reactive group, for example.

  Examples of the fluorine-containing monomer include vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, bromotrifluoroethylene, chlorotrifluoroethylene, pentafluoropropylene, hexafluoropropylene, and (per) fluoroalkyltrifluoro. Vinyl ether [(per) fluoroalkyl group has 1 to 18 carbon atoms. ] Etc. are mentioned.

  On the other hand, the monomer containing a specific reactive group is a polymerizable monomer containing a hydroxyl group or a carboxyl group as a group (reactive group) that reacts with a curing agent or the like.

  Specifically, examples of the hydroxyl group-containing polymerizable monomer include allyl alcohol; hydroxyalkyl vinyl ethers such as 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxycyclohexyl vinyl ether; 2-hydroxy Hydroxyalkyl allyl ethers such as ethyl allyl ether, 3-hydroxypropyl allyl ether, 4-hydroxybutyl allyl ether, 4-hydroxycyclohexyl allyl ether; hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate; Hydroxy vinyl acetate, Hydroxy isobutyrate, Hydroxy propionate, Hydroxy butyrate, Hydroxy valerate, B carboxymethyl esters of hydroxyalkyl carboxylic acids and vinyl alcohol vinyl cyclohexyl carboxylic acid, and the like; hydroxyethyl allyl ester, hydroxypropyl allyl ester, hydroxybutyl allyl ester, hydroxyalkyl allyl esters such as hydroxyethyl isobutyl allyl ester, and the like.

  Examples of the carboxyl group-containing polymerizable monomer include (meth) acrylic acid and carboxyalkyl allyl ester.

  Among these reactive group-containing monomers, a hydroxyl group-containing polymerizable monomer is preferable from the viewpoints of resin stability and control of melt viscosity. In other words, the fluororesin is preferably a hydroxyl group-containing fluororesin.

  For the polymerization of the fluororesin, a polymerizable monomer other than the fluorine-containing monomer and a monomer containing a specific reactive group may be used. Such polymerizable monomers include vinyl ethers, olefins, allyl ethers, vinyl esters, allyl esters, (meth) acrylic acid esters, (meth) acrylic acid amides, cyano group-containing monomers, dienes, etc. And crotonic acid esters.

  Specific examples of the polymerizable monomer other than the fluorine-containing monomer and the monomer containing a specific reactive group include, for example, alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, cyclohexyl vinyl ether, and chloroethyl vinyl ether. Olefins such as ethylene, propylene, 1-butene, isobutylene, cyclohexene, vinyl chloride and vinylidene chloride; styrenic monomers such as styrene and α-methylstyrene; methyl allyl ether, ethyl allyl ether, butyl allyl ether, cyclohexyl allyl Alkyl allyl ethers such as ether; vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl hexanoate, octane Vinyl esters of carboxylic acids (preferably fatty acids) such as vinyl and vinyl versatate; allyl esters of carboxylic acids (preferably fatty acids) such as allyl propionate and allyl acetate; methyl (meth) acrylate, (meth) (Meth) acrylic esters such as ethyl acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate; (meth) acrylic amides such as (meth) acrylic amide; acrylonitrile, 2,4-dicyanobutene Cyano group-containing monomers such as -1; dienes such as isoprene and butadiene; and crotonic acid esters such as 2-hydroxyethyl crotonic acid and 4-hydroxybutyl crotonic acid.

  Furthermore, you may use the polymerizable monomer which has reactive groups other than a hydroxyl group and a carboxyl group for the superposition | polymerization of the said fluororesin. Examples of such reactive groups include functional groups such as amide groups, amino groups, nitrile groups, glycidyl groups, and isocyanate groups.

  Specifically, amino group-containing polymerizable monomers include aminoalkyl vinyl ethers and aminoalkyl allyl ethers, and amide group-containing polymerizable monomers include (meth) acrylamide, N-methyl (meth) acrylamide and the like. Examples of the nitrile group-containing polymerizable monomer include (meth) acrylonitrile, and examples of the glycidyl group-containing polymerizable monomer include glycidyl allyl ether and glycidyl (meth) acrylate, and an isocyanate group-containing polymerizable monomer. Examples thereof include vinyl isocyanate and isocyanatoethyl acrylate.

  The fluororesin preferably has a fluorine content of 5 to 80% by mass, and more preferably 10 to 70% by mass. If the fluorine content of the fluororesin is 5% by mass or more, sufficient weather resistance can be imparted to the coating film obtained from the powder coating composition of the present invention, and the fluorine content of the fluororesin is 80% by mass. When it is below, sufficient chemical resistance can be imparted to the coating film. Further, when the fluororesin is a hydroxyl group-containing fluororesin, the hydroxyl value of the fluororesin is preferably 100 mgKOH / g or less from the viewpoint of maintaining the flexibility of the coating film. From the viewpoint of imparting impact properties, it is preferably 10 mgKOH / g or more. In particular, the hydroxyl value of the fluororesin is preferably 30 to 70 mgKOH / g.

<Polyester resin>
In the powder coating composition of the present invention, the polyester resin can be produced by reacting a carboxylic acid component and a polyhydric alcohol component by a known method, and must have a reactive site that reacts with a curing agent or the like. It needs to be a resin that contains a hydroxyl group or a carboxyl group and is solid at room temperature, and its softening point is preferably 100 to 150 ° C. The polyester resin forms a polyester coating layer and constitutes a part of the coating. Thereby, compared with the coating film which consists only of a fluorine coating-film layer, the external appearance and workability of a coating film can improve, and also manufacturing cost can be reduced.

  Examples of carboxylic acid components that can be used in the production of the polyester resin include phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,2-octadecanedicarboxylic acid, maleic acid, fumaric acid, cyclohexanedicarboxylic acid, hexahydrophthalic acid, tetrahydrophthalic acid , Polycarboxylic acids such as trimellitic acid and pyromellitic acid, lower alkyl esters of these polycarboxylic acids and acid anhydrides thereof, and malic acid, tartaric acid, 1,2-hydroxystearic acid, p-hydroxybenzoic acid, etc. And hydroxycarboxylic acid.

  Examples of the polyhydric alcohol component that can be used in the production of the polyester resin include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, and 1,4. -Butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, spiroglycol, 1,10-decanediol, 1,4- Examples include cyclohexanedimethanol, trimethylolethane, trimethylolpropane, glycerin, pentaerythritol and the like.

  As described above, the polyester resin can be produced by a conventional method known for producing a polyester resin for a powder coating composition using a carboxylic acid component and a polyhydric alcohol component as raw materials. For example, the above raw materials are used in an appropriate combination and mixing ratio, and after esterification or transesterification at 200 to 280 ° C. according to a conventional method, a catalyst is used under reduced pressure and a polycondensation reaction at 230 to 290 ° C. In some cases, a polyester resin can be produced by performing a depolymerization reaction with a polyhydric alcohol.

  The polyester resin may have a reactive group other than a hydroxyl group and a carboxyl group. Examples of such reactive sites include functional groups such as amide groups, amino groups, nitrile groups, glycidyl groups, and isocyanate groups.

  The polyester resin is preferably a hydroxyl group-containing polyester resin from the viewpoint of cross-linking reaction and control of coating film properties. From the viewpoint of controlling the melt viscosity, the polyester resin preferably has a number average molecular weight of 5000 or less and a weight average molecular weight of 10,000 to 20,000. Here, the number average molecular weight and the weight average molecular weight can be determined using polystyrene as a standard substance by gel permeation chromatography (GPC).

  When the polyester resin is a hydroxyl group-containing polyester resin, the hydroxyl value of the polyester resin is preferably 20 to 100 mgKOH / g, and more preferably 30 to 80 mgKOH / g. When the hydroxyl value of the polyester resin is less than 20 mgKOH / g, it is difficult to obtain sufficient mechanical properties and solvent resistance of the coating film. On the other hand, when the polyester resin exceeds 100 mgKOH / g, an amount of curing agent suitable for the hydroxyl value (for example, isocyanate) Compound), which is expensive. Moreover, 20-80 mgKOH / g is preferable and the acid value of the said polyester resin has more preferable 30-80 mgKOH / g. When the acid value of the polyester resin is less than 20 mgKOH / g, it is difficult to obtain sufficient mechanical properties and solvent resistance of the coating film. On the other hand, when it exceeds 100 mgKOH / g, a curing agent in an amount suitable for the acid value (for example, β-hydroxyalkylamide and triglycidyl isocyanurate) are required and expensive.

  The polyester resin preferably has a melt viscosity of 3.5 Pa · s (190 ° C.) or less. When the melt viscosity of the polyester resin exceeds 3.5 Pa · s (190 ° C.), layer separation of the coating film is difficult to occur. The polyester resin has an Arrhenius plot based on the melt viscosity (Pa · s) measured under the conditions of a measurement start temperature of 200 ° C. and a temperature drop rate of 10 ° C./min, and a slope in the range of 100 to 120 ° C. is 15000. The above is preferable. The melt viscosity is measured by using a rheometer such as a rheometer ARES manufactured by TA Instruments Inc. The conditions other than the measurement start temperature and the temperature lowering speed are as follows: a parallel plate with a diameter of 40 mm, a gap width of 1. 0 mm, frequency 9.42 rad / s, distortion 1.0%. In addition, the measurement result of the obtained melt viscosity is plotted on a graph in which the horizontal axis is the reciprocal 1 / T of the temperature T (K) and the vertical axis is the logarithm lnV of the melt viscosity V (Pa · s), and Arrhenius By creating a plot, the slope of a straight line at 100 to 120 ° C. can be obtained. If the inclination of the straight line is 15000 or more, it is preferable because layer separation of the coating film is easily formed, and more preferably, the inclination is 16000 to 20000.

<Epoxy resin>
The powder coating composition of the present invention preferably further contains an epoxy resin in order to improve the adhesion to the substrate.

  In the powder coating composition of the present invention, the epoxy resin needs to be a solid resin at room temperature, and its softening point is preferably 50 to 150 ° C. It does not specifically limit as said epoxy resin, The epoxy resin conventionally used in manufacture of an epoxy resin type powder coating composition can be used.

  Specifically, as the epoxy resin, for example, bisphenol A type diglycidyl ether resin, bisphenol F type diglycidyl ether resin, aminoglycidyl ether resin, bisphenol AD type diglycidyl ether resin, bisphenol Z type diglycidyl ether resin, O -Cresol novolac epoxy resin, phenol novolac epoxy resin, biphenol glycidyl ether resin, cyclopentadiene skeleton epoxy resin, naphthalene skeleton epoxy resin, GMA acrylic resin, etc., and other substituents other than the epoxy group of these resins are replaced with other substituents Examples thereof include resins obtained by a modification reaction using carboxyl group-terminated polybutadiene-acrylonitrile (CTBN) or a modification reaction such as esterification. The epoxy resin preferably has an epoxy equivalent of 300 to 1200, particularly preferably 400 to 1000.

<Curing agent>
In the powder coating composition of the present invention, the curing agent needs to be a curing agent selected from the group consisting of β-hydroxyalkylamide, triglycidyl isocyanurate and isocyanate compound, and a hydroxyl group or carboxyl group-containing fluororesin It can react with a hydroxyl group or carboxyl group-containing polyester resin and an epoxy resin to form a cross-linked bond.

<< β-hydroxyalkylamide >>
When the resin used in the powder coating composition of the present invention has a carboxyl group, it is preferable to use β-hydroxyalkylamide as a curing agent. As β-hydroxyalkylamide, those having two or more functional groups per molecule are particularly preferred from the viewpoint of low-temperature curability and the water resistance of a coating film obtained by coating. Examples of β-hydroxyalkylamide include N, N-di (β-hydroxyethyl) acetamide, bis (β-hydroxyethyl) adipamide, bis (β-hydroxypropyl) adipamide, bis [N, N-di (β-hydroxy). Ethyl)] adipamide and bis [N, N-di (β-hydroxypropyl)] adipamide are particularly preferred. In the β-hydroxyalkylamide, the hydroxylamide group is preferably 0.5 to 1.5 equivalents relative to the carboxyl group in the resin.

<< Triglycidyl isocyanurate >>
When the resin used in the powder coating composition of the present invention has a carboxyl group, it is preferable to use triglycidyl isocyanurate (TGIC) as a curing agent. Examples of triglycidyl isocyanurate include Araldite (registered trademark) PT 710, Araldite (registered trademark) PT 810, Araldite (registered trademark) PT 910, Araldite (registered trademark) PT 912 (all manufactured by Huntsman) Etc.

<< Isocyanate compound >>
In addition, the powder coating composition of the present invention can be blended with an isocyanate compound as a curing agent from the viewpoint of coating film properties such as coating film hardness and hydrolysis resistance. Is more preferable. The isocyanate compound is preferably solid at room temperature.

  The blocked isocyanate compound may be masked by reacting, for example, a polyisocyanate obtained by reacting an aliphatic, aromatic or araliphatic diisocyanate with a low molecular weight compound having active hydrogen with a blocking agent. Therefore, manufacturing is also easy. Examples of the diisocyanate include tolylene diisocyanate, 4,4′-diphenylmethane isocyanate, xylylene diisocyanate, hexamethylene diisocyanate, 4,4′-methylene bis (cyclohexyl isocyanate), methylcyclohexane diisocyanate, bis (isocyanatomethyl) cyclohexane, and isophorone. Diisocyanate, dimer acid diisocyanate, lysine diisocyanate, etc. can be mentioned. Examples of the low molecular weight compound having active hydrogen include water, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, ethanolamine, diethanolamine, hexamethylenediamine. Etc., isocyanurate, uretidione, hydroxyl group Low molecular weight polyesters having, polycaprolactone and the like. Specific examples of the blocking agent include alcohols such as methanol, ethanol and benzyl alcohol, phenols such as phenol and crezone, lactams such as caprolactam and butyrolactam, and oximes such as cyclohexanone, oxime and methyl ethyl ketoxime. . For example, specific examples of the blocked isocyanate include isophorone diisocyanate blocked with ε-caprolactam (Vestagon B1530 manufactured by Evonik, Clelan UI manufactured by Bayer) and the like.

  In the powder coating composition of the present invention, the isocyanate compound preferably has a softening point of 10 to 120 ° C, particularly preferably 40 to 100 ° C. A softening point of less than 10 ° C. is not preferable because the powder coating composition is cured in a room temperature environment or a granular lump is formed. On the other hand, when the softening point exceeds 120 ° C., it becomes difficult to uniformly disperse the isocyanate compound in the powder coating composition when the powder coating composition is produced by melt kneading. Performances such as smoothness, coating strength, and moisture resistance may be impaired. In the isocyanate compound, the isocyanate group is preferably 0.05 to 1.5 equivalents, particularly preferably 0.8 to 1.2 equivalents, based on the hydroxyl groups in the resin. If the isocyanate group is less than 0.05 equivalent, the degree of cure of the powder coating composition may be insufficient, and coating performance such as adhesion, coating hardness, and chemical resistance may be lowered. Moreover, when this isocyanate group exceeds 1.5 equivalent, there exists a possibility that a coating film may become weak, heat resistance, chemical resistance, moisture resistance, etc. may be inferior. Furthermore, since the blocked isocyanate is expensive, the cost is increased if an excess of blocked isocyanate is used.

<Bright pigment>
The powder coating composition of the present invention can further contain a luster pigment. There are also scaly pigments. Bright pigments include, for example, aluminum powder pigment, nickel powder pigment, gold powder, silver powder, bronze powder, copper powder, stainless steel powder pigment, mica pigment, graphite pigment, glass flake pigment, metal-coated glass powder, metal coating Mica powder, metal-coated plastic powder, and scaly iron oxide pigment. The content of the bright pigment in the powder coating composition of the present invention is preferably 0.1 to 30% by mass, and more preferably 0.5 to 20% by mass. When the content of the glitter pigment is less than 0.1% by mass, it is difficult to obtain the brightness of the coating film. On the other hand, when it exceeds 30% by mass, the layer separation property of the coating film and the glitter pigment on the coating film surface are difficult to obtain. There is a possibility that the chemical resistance, moisture resistance, etc. of the coating film due to the exposure of the film are inferior. Further, since bright pigments are expensive, the cost increases when using excessive bright pigments.

<Coloring pigments, extenders and antirust pigments>
The powder coating composition of the present invention can contain pigments commonly used, such as colored pigments and extender pigments, in addition to the luster pigment. Examples of the color pigment include inorganic pigments such as titanium oxide, yellow iron oxide, titanium yellow, bengara, lithopone, and antimony oxide, Hansa Yellow 5G, Permanent Yellow FGL, Phthalocyanine Blue, Indanthrene Blue RS, Permanent Red F5RK, And organic pigments such as Brilliant First Scarlet G. On the other hand, examples of extender pigments include barium sulfate, barium carbonate, calcium carbonate, clay, silica powder, diatomaceous earth, talc, basic magnesium carbonate, and alumina white. Moreover, the powder coating composition of this invention may contain a rust preventive pigment, when the base material which should be coated needs rust prevention property. Examples of rust preventive pigments include condensed calcium phosphate, aluminum phosphate, condensed aluminum phosphate, zinc phosphate, aluminum phosphite, zinc phosphite, calcium phosphite, zinc molybdate, calcium molybdate, and manganese molybdate. Can be mentioned. These pigments may be used alone or in combination of two or more.

<Other additives>
The powder coating composition of the present invention includes plasticizers, curing accelerators, crosslinking accelerators, surface conditioners, ultraviolet absorbers, light stabilizers, antioxidants, fluidity adjustments as additives for general paints. You may mix | blend an agent, a dripping prevention agent, an antifoamer, etc. as needed.

<Mass ratio of fluororesin and polyester resin>
The powder coating composition of the present invention has a mass ratio (A / B) of the fluororesin (A) and the polyester resin (B) of 50/50 to 10/90 from the viewpoint of weather resistance and low cost. preferable. If the ratio of the fluororesin to the total of the fluororesin and the polyester resin exceeds 50% by mass, the amount of expensive fluororesin is increased, which increases the cost. On the other hand, the fluororesin accounts for the total of the fluororesin and the polyester resin. If the ratio is less than 10% by mass, sufficient weather resistance may not be obtained.

<Solubility parameters of fluororesin and polyester resin>
In the powder coating composition of the present invention, the difference in solubility parameter (SP value) between the fluororesin and the polyester resin is preferably 0.6 to 0.9. If the SP value difference between the fluororesin and the polyester resin is less than 0.6, the fluororesin and the polyester resin may become compatible when melted and cured to form a coating film. On the other hand, when the difference between the SP values exceeds 0.9, layer separation occurs, but there is a concern about delamination between the upper layer and the lower layer. The SP value, which is a resin solubility parameter, is calculated as follows. By dissolving the resin in tetrahydrofuran (THF) to prepare a 10 wt% solution, it was separated a certain amount of the solution to the volume (ml) and _{V THF.} Moreover, hexane (Hexane) and ion-exchange water (Water) are each dripped at the fractionated solution, and titration is performed. The dripping amount (ml) at the time of cloudiness is defined as V _Hexane and V _Water , respectively. The obtained values are substituted into the following formulas (1) and (2) to calculate SPn and SPh. Next, the SP value obtained by substituting the obtained SP _n and SP _h into the equation (3).
SP _n = (SP _THF × V _THF + SP _Hexane × V _Hexane ) / (V _THF + V _Hexane ) (1)
_{SP h = (SP THF × V} THF + SP Water × V Water) / (V THF + V Water) ···· (2)
SP = 10 ^ ((logSP _n + logSP _h ) / 2) (3)
(However, SP _THF = 9.1, SP _Hexane = 7.3, SP _Water = 23.4)

<Curing>
In the case of reacting the polyester resin and the curing agent, the temperature difference from the start of melting to the start of curing under the temperature rising rate of 10 ° C./min is preferably 50 ° C. or more, and is 80 to 100 ° C. More preferably it is. When the temperature difference is less than 50 ° C., when the coating film is formed from the powder coating composition of the present invention, the flowability of the powder coating composition tends to decrease, and the sharpness of the coating film decreases. There is. The melting start temperature (° C.) is the temperature when the elastic modulus of the mixture of the polyester resin and the curing agent starts to decrease, and the curing start temperature (° C.) is when the elastic modulus of the mixture starts to increase. Temperature. Therefore, in order to measure the temperature difference, it is necessary to measure the change in elastic modulus of the mixture of the polyester resin and the curing agent. For measuring the elastic modulus, a rheometer such as a rheometer ARES manufactured by T.A. Instruments Inc. is used. Conditions other than the rate of temperature increase are a parallel plate with a diameter of 40 mm, a gap width of 1.0 mm, and a frequency of 9. 42 rad / s, strain 1.0%, temperature range 80-200 ° C.

  Further, the temperature (° C.) at which the fluororesin and the curing agent start to react is set as a curing start temperature TR (A), and the temperature (° C.) at which the polyester resin and the curing agent start to react is set at a curing start temperature TR In the case of B), the temperature difference TR (B) −TR (A) between the curing start temperature TR (A) and the curing start temperature TR (B) is preferably 15 ° C. or higher, and is 20 ° C. or higher. Is more preferable. When the temperature difference TR (B) −TR (A) is less than 20 ° C., the layer separation property may be lowered when a coating film is formed from the powder coating composition of the present invention.

<Method for producing powder coating composition>
The method for producing a powder coating composition of the present invention is a method for preparing the above-mentioned powder coating composition. Specifically, the mixture containing the fluororesin, polyester resin and curing agent is at 100 to 160 ° C. It is characterized by melt-kneading and then pulverizing the mixture after cooling to prepare a powder coating composition. Preferably, the mixture containing the fluororesin, polyester resin and curing agent is dry blended with a Henschel mixer or the like, melt-kneaded at 120-140 ° C. using a co-kneader, etc., cooled, pulverized, and then 180 mesh (96 μm). ) To obtain a powder coating composition.

<Coating film>
The powder coating composition of the present invention is made of a steel material such as an aluminum alloy such as a building sash or a building panel, a carbon steel such as a railway bridge, a road bridge, a gas tank, a petroleum tank, and a steel tower by a usual method. A coating film is formed by coating on the surface of the substrate and then melting and curing at a temperature preferably in the range of 170 to 250 ° C, more preferably in the range of 170 to 210 ° C. Here, the powder coating composition of the present invention can form a coating film including a fluorine coating layer and a polyester coating layer because the fluororesin and the polyester resin are not compatible and cause layer separation. Due to segregation of the fluororesin and the polyester resin, the lower layer side (that is, the side closer to the substrate surface) is the polyester coating layer, and the upper layer side (that is, the side far from the substrate surface) is the fluorine coating layer. In addition, when using an epoxy resin for the powder coating composition of this invention, an epoxy resin is located in a lower layer side. Moreover, an additive orientates to the upper layer side of a coating film.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

<Preparation of polyester resin A>
A stirrer, a heating device, a thermometer, a fractionation device, and a nitrogen gas were used as an alcohol component of the polyester resin with 2652 g of neopentyl glycol, 3966 g of isophthalic acid as the carboxylic acid component, and 4.7 g of tetra-n-butyl titanate as the reaction catalyst. The reaction vessel was charged into a stainless steel reaction vessel equipped with an introduction tube and subjected to a polycondensation reaction at 250 ° C. for 16 hours with stirring in a nitrogen atmosphere. When the predetermined hydroxyl value was reached, the polyester resin A was obtained.

<Preparation of polyester resin B>
2496 g of neopentyl glycol as the alcohol component of the polyester resin, 4233 g of isophthalic acid as the carboxylic acid component, and 4.7 g of tetra-n-butyl titanate as the reaction catalyst, stirring device, heating device, thermometer, fractionating device and nitrogen gas The reaction vessel was charged into a stainless steel reaction vessel equipped with an introduction tube and subjected to a polycondensation reaction at 250 ° C. for 16 hours while stirring in a nitrogen atmosphere. When the predetermined acid value was reached, the reaction was terminated, and polyester resin B was obtained.

<Preparation and Evaluation of Powder Coating Composition>
In accordance with the formulation shown in Tables 1 to 3, the raw materials were mixed, melted and kneaded at 130 ° C., and the resulting mixture was pulverized after cooling to prepare a powder coating composition.

<Evaluation of powder coating composition>
Various evaluation tests were performed on the powder coating composition. The results are shown in Tables 4-6.

<Preparation of test plate>
First, a test plate was prepared in order to perform an evaluation test of the powder coating composition. First, a 1.5 mm thick chromate-chromate-treated aluminum plate is suspended in the vertical direction so that the film thickness becomes 60 μm using a corona charging type electrostatic powder coating machine (PG-1 type manufactured by Asahi Sunac Co., Ltd.). The aluminum plate was electrostatically coated at a voltage of −60 kV, then baked in an electric furnace under the condition of 190 ° C. × 20 minutes, and allowed to cool to room temperature as it was to prepare a test plate.

<60 ° specular gloss>
Based on JIS K 5600-4-7, it is measured using a gloss meter (micro-TRI-gloss manufactured by BYK: incident reflection angle 60 °).

<State of coating film>
The state of the coating film surface after the test plate is prepared is visually determined.
◎ ・ ・ ・ No abnormality ○ ・ ・ ・ Yuzu skin △ ・ ・ ・ Rough skin × ・ ・ ・

<Layer separation>
The coating film on the test plate is cut, and the coating film cross section is observed with a microscope (Keyence Co.) to evaluate whether the inside of the coating film is separated into an upper layer and a lower layer. Moreover, this coating film cross section is observed with a scanning electron microscope (Hitachi High-Technologies super high resolution analytical scanning electron microscope SU-70), and the elemental analysis confirms the distribution of the fluorine element (fluororesin) in the coating film cross section. . The image which mapped the fluorine atom which exists in the coating film cross section about Example 8 is shown in FIG. It can be seen that the dark part in the figure is a part with a large amount of fluorine element (fluororesin) and is unevenly distributed in the upper layer.
・ Layer separation (microscopic observation)
○ ... Complete two-layer separation occurs.
Δ: Partial two-layer separation occurs. That is, although two-layer separation occurs, there is a portion having a film thickness of less than ½ as compared with the film thickness of complete two-layer separation fluorine.
X: The polyester resin is exposed on the surface of the upper layer.
・ Layer separation (elemental analysis)
○ ... The fluorine element is unevenly distributed in the upper layer.
Δ ... Although fluorine element is unevenly distributed in the upper layer, fluorine element is also present in the lower layer.
X ... Fluorine element exists in the whole coating film.

<Adhesion>
In accordance with JIS K 5600-5-6 (cross-cut method), the coating film is cut into a grid pattern with an interval of 100 mm at intervals of 1 mm, and whether or not the coating film is peeled off after the adhesive tape is applied is evaluated. . In the table, the denominator represents the number of squares cut in a grid pattern (100), and the numerator represents the number of squares of the coating film remaining on the test plate after tape peeling.

<Weight drop resistance>
In accordance with JIS K5600-5-3 (DuPont type), in order to evaluate the resistance of the coating film to a drop height of 50 cm, the cracking and peeling of the coating film were observed using a striker of 1/2 mm and a weight of 500 g. To do.

<Boiling water resistance>
The test plate is immersed in ion-exchanged water (95 ± 5 ° C.) for 24 hours, cooled with water, dried, and the adhesion of the coating film is evaluated by a method in accordance with JIS K 5600-5-6 (cross cut method). In the table, the denominator represents the number of squares cut in a grid pattern (100), and the numerator represents the number of squares of the coating film remaining on the test plate after tape peeling.

<Mortar resistance>
Apply the mortar paste on the coating surface of the test plate, leave it in a high humidity environment of 50 ° C. and 95RH% for 24 hours, peel off the mortar mass from the test plate, and wash with ion-exchanged water. Thereafter, the state of the coating film is visually evaluated.

<Nitric acid resistance>
A test plate is placed on the glass bottle so as to cover the glass bottle containing 70% by mass nitric acid solution, and the coating film surface of the test plate is exposed to steam for 60 minutes, and then washed with ion-exchanged water. The color difference ΔE with respect to the coating film surface before being exposed to the vapor of the dried coating film surface is measured with a color difference meter (CR-300 manufactured by Minolta).

<Hydrochloric acid resistance>
10 drops of 10% by weight hydrochloric acid aqueous solution is dropped on the surface of the coating film on the test plate, covered with a watch glass, covered with water, and after 15 minutes, washed with ion-exchanged water and then dried. The condition is evaluated visually.

<Moisture resistance>
The test plate is placed in a high humidity environment of 50 ° C. and 95 RH% for 3000 hours, washed with ion-exchanged water, then allowed to cool and dry, and the state of the coating film is visually evaluated.

<Salt water spray resistance>
The test plate is allowed to stand for 3000 hours in a 35 ° C. salt spray environment, washed with ion-exchanged water, then allowed to cool and dry, and the state of the coating film is visually evaluated.

<Accelerated weather resistance>
Using an accelerated weathering tester compliant with JIS B 7753 (Sunshine weatherometer method), the test time is 3000 hours, the 60 ° specular gloss value retention before the test is 100%, and the 60 ° mirror surface after the test Gloss value retention rate was measured with a gloss meter (micro-TRI- gloss BYK, Inc .: incident reflection angle 60 °), and color difference ΔE before and after the test was measured with a color difference meter (Minolta, CR-300). To do.

The raw materials described in Tables 1 to 3 will be described below.
・ Fluorine resin Asahi Glass Co., Ltd., trade name: Lumiflon LF710F (hydroxyl group-containing fluorine resin), solubility parameter (SP value) 9.16
・ Polyester resin A
Hydroxyl-containing polyester resin, hydroxyl value 45 mgKOH / g, number average molecular weight 3200, weight average molecular weight 13200, solubility parameter (SP value) 9.99, melt viscosity 3.1 Pa · s (190 ° C), measurement start temperature 200 ° C and temperature drop Slope 18425 in the range of 100 to 120 ° C. in an Arrhenius plot based on melt viscosity (Pa · s) measured at a rate of 10 ° C./min.
・ Polyester resin B
Carboxyl group-containing polyester resin, acid value 48 mg KOH / g, number average molecular weight 3900, weight average molecular weight 12300, solubility parameter (SP value) 9.84, melt viscosity 2.5 Pa · s (190 ° C.), measurement start temperature 200 ° C. and Slope 15346 in the range of 100 to 120 ° C. in the Arrhenius plot based on the melt viscosity (Pa · s) measured at a temperature decrease rate of 10 ° C./min.
・ Acrylic resin A
Toa Gosei Co., Ltd. ARUFON UH-2170, hydroxyl group-containing acrylic resin, number average molecular weight 4600, weight average molecular weight 14000, solubility parameter (SP value) 9.19, melt viscosity 4.3 Pa · s (190 ° C), start of measurement Slope 12739 in the range of 100 to 120 ° C. in an Arrhenius plot based on melt viscosity (Pa · s) measured at a temperature of 200 ° C. and a cooling rate of 10 ° C./min.
・ Acrylic resin B
ARUFON UC-3920 manufactured by Toa Gosei Co., Ltd., carboxyl group-containing acrylic resin, number average molecular weight 5800, weight average molecular weight 15500, solubility parameter 9.32, melt viscosity 4.8 Pa · s (190 ° C.), measurement start temperature 200 ° C. And a slope 10498 in the range of 100 to 120 ° C. in the Arrhenius plot based on the melt viscosity (Pa · s) measured at a temperature drop rate of 10 ° C./min.
-Bright pigment, aluminum flake powder, manufactured by Toyo Aluminum Co., Ltd., trade name: PCF7620A
-Color pigment Titanium oxide, manufactured by DuPont, trade name: TI-PURE R-960
・ Epoxy resin, manufactured by Toto Kasei Co., Ltd., trade name: Epototo DT-112
Ε-caprolactam block isocyanate isocyanate compound, manufactured by Evonik Degussa, Inc., trade name: Vestagon B1530
・ Β-Hydroxyalkylamide, manufactured by EMS Grilltec Co., Ltd., trade name: PRIMID XL-552
Triglycidyl isocyanurate Huntsman's product name: ARALDITE PT-810
・ Surface conditioner BYK-Chemie, trade name: BYK-360P
・ Temperature difference from the start of melting to the start of curing under the temperature rising rate of 10 ° C./min In the reaction between the polyester resin A and ε-caprolactam block isocyanate (isocyanate compound), the temperature rising rate is 10 ° C./min. The melting start temperature (softening point) was 95 ° C., and the curing start temperature was 183 ° C.
-Temperature difference TR (B) between curing start temperature TR (A) and curing start temperature TR (B)
Curing start temperature TR (A) at which the fluororesin and ε-caprolactam blocked isocyanate (isocyanate compound) start the reaction is 167 ° C., and the curing start at which polyester resin A and ε-caprolactam blocked isocyanate (isocyanate compound) start the reaction The temperature TR (B) was 182 ° C., and the temperature difference TR (B) −TR (A) was 15 ° C.

<Layer separation>
The coating film on the test plate is cut, and the coating film cross section is observed with a microscope (Keyence Co.) to evaluate whether the inside of the coating film is separated into an upper layer and a lower layer. Moreover, this coating film cross section is observed with a scanning electron microscope (Hitachi High-Technologies super high resolution analytical scanning electron microscope SU-70), and the elemental analysis confirms the distribution of the fluorine element (fluororesin) in the coating film cross section. . The image which mapped the fluorine atom which exists in the coating film cross section about the reference example 8 is shown in FIG. It can be seen that the dark part in the figure is a part with a large amount of fluorine element (fluororesin) and is unevenly distributed in the upper layer.
・ Layer separation (microscopic observation)
○ ... Complete two-layer separation occurs.
Δ: Partial two-layer separation occurs. That is, although two-layer separation occurs, there is a portion having a film thickness of less than ½ as compared with the film thickness of complete two-layer separation fluorine.
X: The polyester resin is exposed on the surface of the upper layer.
・ Layer separation (elemental analysis)
○ ... The fluorine element is unevenly distributed in the upper layer.
Δ ... Although fluorine element is unevenly distributed in the upper layer, fluorine element is also present in the lower layer.
X ... Fluorine element exists in the whole coating film.

Claims (9)

  A fluororesin containing a hydroxyl group or a carboxyl group, a polyester resin containing a hydroxyl group or a carboxyl group, and a curing agent selected from the group consisting of β-hydroxyalkylamide, triglycidyl isocyanurate and an isocyanate compound. A powder coating composition capable of forming a coating film comprising a fluorine coating layer and a polyester coating layer.   The powder coating composition according to claim 1, further comprising an epoxy resin.   The powder coating composition according to claim 1, further comprising a bright pigment.   2. The powder coating material according to claim 1, wherein the polyester resin is a hydroxyl group-containing polyester resin, and the hydroxyl group-containing polyester resin has a number average molecular weight of 5000 or less and a weight average molecular weight of 10,000 to 20,000. Composition.   The polyester resin has a melt viscosity of 3.5 Pa · s (190 ° C.) or less and a melt viscosity (Pa · s) measured under a measurement start temperature of 200 ° C. and a temperature drop rate of 10 ° C./min. 2. The powder coating composition according to claim 1, wherein a slope in a range of 100 to 120 ° C. is 15000 or more in an Arrhenius plot based thereon.   The powder coating composition according to claim 1, wherein the fluororesin is a hydroxyl group-containing fluororesin.   The powder coating composition according to claim 1, wherein a mass ratio (A / B) of the fluororesin (A) to the polyester resin (B) is 50/50 to 10/90.   The powder coating composition according to claim 1, wherein a difference in solubility parameter (SP value) between the fluororesin and the polyester resin is 0.6 to 0.9.   2. A powder coating composition is prepared by melt-kneading a mixture containing the fluororesin, the polyester resin and the curing agent at 100 to 160 ° C., and then pulverizing the mixture after cooling. The manufacturing method of the powder coating composition in any one of -8.

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