JP5612280B2 - Method for forming layer-separated coating film - Google Patents

Description

  The present invention is a powder coating material containing a fluororesin having good weather resistance and a low-cost polyester resin, and can form a multilayer coating film that is separated into two layers by one-coat coating. The present invention relates to a method for forming a layer-separated coating film using a layer-separated powder coating that can form a highly weather-resistant coating film at a lower cost and in a process that is less expensive than a powder coating material.

  In recent years, global environmental destruction problems such as global warming, ozone layer destruction, and acid rain have been greatly highlighted, and global environmental pollution countermeasures have been screamed internationally. Has come to be done. Among them, the release of organic solvents (VOC) into the atmosphere has become a big problem, and in each industry, the movement to remove organic solvents (de-VOC) has become active along with the trend of strengthening VOC regulations. In the paint industry, as an alternative to conventional organic solvent-type paints, expectations for powder paints are growing as environmentally friendly paints that do not contain VOC at all, do not require exhaust treatment / wastewater treatment, and can be recovered and reused. Yes.

  As the powder coating, acrylic resin-based, polyester resin-based, and epoxy resin-based powder coatings are 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 drawbacks, a mixture of a thermosetting acrylic resin powder coating and a thermosetting epoxy resin powder coating is applied and cured by heating, so that the upper layer is an acrylic resin powder. Powder coatings have been developed in which a body coating and a lower layer form a multilayer coating with an epoxy resin powder coating (see, for example, Patent Documents 1 to 3).

  On the other hand, a fluororesin-based thermosetting powder coating using a fluororesin that is more excellent in weather resistance than an acrylic resin or a polyester resin has been developed (see, for example, Patent Document 4).

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

  The object of the present invention is to provide a weather-resistant layer-separated powder coating that has good weather resistance and is excellent in cost, can form a multi-layer coating film that can be separated into two layers by one-coat coating, and is low in cost and low in process. It is to provide a method for forming the layer separation coating used.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved with the following configuration, and have reached the present invention.

According to the present invention, a mixture containing (A) 10 to 50% by mass of a fluororesin, (B) 10 to 80 % by mass of a polyester resin, and (C) 10 to 50% by mass of a pigment is melt-kneaded and pulverized after cooling. A process of obtaining a powder coating by
Coating the powder coating on a substrate and melting and curing at a temperature of 170 to 210 ° C. to form a coating film;
A method for forming a layer-separated coating film, wherein the formed coating film is separated into (A) a fluororesin layer and (B) a polyester resin layer to form a multilayer coating film Is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the multilayer coating film which carries out layer separation into two layers by 1 coat coating can be formed, and the formation method of the low weather and a highly weather resistant layer separation coating film can be provided.

It is an electron micrograph of the coat section which carried out layer separation. It is a fluorine atom mapping figure of a coat section.

  Hereafter, the formation method of the layer separation coating film of this invention is demonstrated in detail. First, each component of the powder coating composition used in the present invention will be described.

(A) Fluororesin The fluororesin used in the present invention is a solid resin at room temperature, and preferably has a softening point of 50 to 150 ° C.

  The fluororesin is a fluorine-containing copolymer obtained by polymerizing (or copolymerizing) a fluorine-containing monomer, and the following fluorine-containing monomer is used.

  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. ] And the like are typical examples.

  The fluororesin may be obtained by copolymerizing a polymerizable monomer other than the above-mentioned fluorine-containing monomer. Examples of the polymerizable monomer include vinyl ethers, olefins, allyl ethers, vinyl esters, allyl esters, (meta ) Acrylic acid esters, crotonic acid esters and the like.

  Specific examples of the polymerizable monomer include the following compounds.

For example,
Alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, cyclohexyl vinyl ether, chloroethyl vinyl ether;
Olefins such as ethylene, propylene, 1-butene, isobutylene, cyclohexene, vinyl chloride, vinylidene chloride;
Styrene monomers such as styrene and α-methylstyrene;
Alkyl allyl ethers such as methyl allyl ether, ethyl allyl ether, butyl allyl ether, cyclohexyl allyl ether;
Fatty acid vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl hexanoate, vinyl octoate, vinyl versatate;
Fatty acid allyl esters such as allyl propionate and allyl acetate; (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate;
(Meth) acrylic acid amides such as (meth) acrylic acid amide;
Cyano group-containing monomers such as acrylonitrile and 2,4-dicyanobutene-1;
Examples thereof include polymerizable monomers such as dienes such as isoprene and butadiene.

  The fluororesin may have a reactive site that reacts with a curing agent or the like, and may be a copolymer with a reactive group-containing monomer together with the above-mentioned fluorine-containing monomer or polymerizable monomer.

  Examples of the reactive group include functional groups such as a hydroxyl group, a carboxyl group, an amide group, an amino group, a nitrile group, a glycidyl group, and an isocyanate group. Specific examples of the reactive group-containing monomer include the following compounds.

Examples of the hydroxyl group-containing 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;
Hydroxyalkyl allyl ethers such as 2-hydroxyethyl allyl ether, 3-hydroxypropyl allyl ether, 4-hydroxybutyl allyl ether, 4-hydroxycyclohexyl allyl ether;
Hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate;
Esters of hydroxyalkyl carboxylic acids such as vinyl hydroxyacetate, vinyl hydroxyisobutyrate, vinyl hydroxypropionate, vinyl hydroxybutyrate, vinyl hydroxyvalerate, vinyl hydroxycyclohexylcarboxylate and vinyl alcohol;
Examples thereof include hydroxyalkyl allyl esters such as hydroxyethyl allyl ester, hydroxypropyl allyl ester, hydroxybutyl allyl ester, and hydroxyisobutyl allyl ester.

Also,
Examples of the carboxyl group-containing monomer include (meth) acrylic acid and carboxyalkyl allyl ester.
Examples of amino group-containing monomers include aminoalkyl vinyl ethers and aminoalkyl allyl ethers.
Examples of the amide group-containing monomer include (meth) acrylamide, N-methyl (meth) acrylamide, and the like.
Examples of nitrile group-containing monomers include (meth) acrylonitrile,
Examples of the glycidyl group-containing monomer include glycidyl allyl ether and glycidyl (meth) acrylate.
Examples of the isocyanate group-containing monomer include vinyl isocyanate and isocyanate ethyl acrylate.

  Among these, it is preferable to use a hydroxyl group-containing fluororesin using a hydroxyl group-containing monomer.

  The fluororesin used in the present invention preferably has a fluorine content of 10 to 70% by mass. The hydroxyl value is preferably 10 to 100 mgKOH / g, more preferably 30 to 70 mgKOH / g.

(B) Polyester resin The polyester resin used in the present invention is a resin obtained by reacting a carboxylic acid and a polyhydric alcohol by a known method, and is a solid resin at room temperature. The softening point is preferably 100 to 150 ° C.

  Examples of carboxylic acid components that can be used in the production of polyester resins 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 polyvalent carboxylic acids and their anhydrides, or hydroxy such as malic acid, tartaric acid, 1,2-hydroxystearic acid, paraoxybenzoic acid, etc. Carboxylic acid can be mentioned .

  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, , 4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, spiroglycol, 1,10-decanediol, 1, 4-Cyclohexanedimethanol, trimethylolethane, trimethylolpropane, glycerin, pentaerythritol and the like can be mentioned.

  The polyester resin can be produced by a conventional method for producing a polyester resin for powder coating, using the carboxylic acid component and the 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. Then, a depolymerization reaction can be performed with an alcohol component to obtain a polyester resin.

  The polyester resin thus obtained is preferably a hydroxyl group-containing polyester resin, preferably having a number average molecular weight of 5,000 or less and a weight average molecular weight of 10,000 to 20,000.

  The hydroxyl value of the polyester resin is preferably 20 to 100 mgKOH / g, more preferably 30 to 80 mgKOH / g. The acid value is preferably 1 to 80 mgKOH / g, more preferably 3 to 50 mgKOH / g.

  The polyester resin has a melt viscosity of 3.5 Pa · s (190 ° C.) or less and a melt viscosity measured at 100 to 120 ° C. when the rheometer measures the melt viscosity from 200 ° C. at a temperature drop rate of 10 ° C./min. The slope determined from the Arrhenius plot of temperature and viscosity is preferably 15000 or more. The measurement at this time is a 40 mm diameter parallel plate, a gap width of 1.0 mm, a frequency of 9.42 rad / s, and a strain of 1.0%, using a rheometer ARES manufactured by TA Instruments. Performed under conditions. The obtained measurement results are plotted on the graph with the inverse 1 / T of temperature T (K) on the horizontal axis and the logarithmic lnV of viscosity V on the vertical axis (Arrhenius plot), and the slope of the straight line at 100 to 120 ° C. Asked.

  If the inclination is 15000 or more, it is preferable because the raw material can be smoothly melted and kneaded during the production of the powder coating material, and the inclination is preferably 16000 to 20000.

(C) Pigment As for the pigment, color pigments, extender pigments, luster pigments and the like used in general powder paints can be used.

  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. Examples of extender pigments include barium sulfate, barium carbonate, calcium carbonate, clay, silica powder, diatomaceous earth, talc, basic magnesium carbonate, and alumina white.

  As bright pigments, for example, aluminum powder pigment, nickel powder pigment, stainless powder pigment, copper powder, bronze powder, gold powder, silver powder, mica pigment, graphite pigment, glass flake pigment, flaky plastic pigment, scaly iron oxide A pigment etc. can be mentioned.

  Moreover, an antirust pigment can be used with respect to the base material which needs antirust 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 can be contained alone or in combination of two or more.

(D) About Epoxy Resin The powder coating used in the present invention can further contain (D) an epoxy resin in addition to the components of (A) fluororesin, (B) polyester resin, and (C) pigment. . This epoxy resin is preferably added in an amount of 1 to 5 % by mass in order to improve the adhesion to the substrate. (However, the total content of (A) fluororesin, (B) polyester resin, (C) pigment and (D) epoxy resin does not exceed 100% by mass).

  The epoxy resin used in the present invention is a resin that is solid at room temperature, and the softening point of the resin is preferably 50 to 150 ° C. As such an epoxy resin, an epoxy resin conventionally used for producing an epoxy resin powder coating can be used without particular limitation.

  Specifically, 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., or those in which substituents of these resins are replaced with other ones, for example, CTBN or esterification Those subjected to modification such as can be used without limitation.

  As the epoxy resin, an epoxy resin having an epoxy equivalent of preferably 300 to 1200, particularly preferably 400 to 1000 is suitable.

(E) Curing Agent The curing agent used in the present invention is particularly limited as long as it reacts with the (A) fluororesin, (B) polyester resin, and (D) epoxy resin to form a crosslink. The various hardening | curing agents conventionally used can be used, without being carried out. In particular, the curing agent is preferably an isocyanate compound from the viewpoint of coating film properties such as coating film hardness and hydrolysis resistance, and more preferably a blocked isocyanate compound.

  In the present invention, the preferred blocked isocyanate as a curing agent is solid at room temperature. Examples of the isocyanate include polyisocyanate obtained by reacting an aliphatic, aromatic, and araliphatic diisocyanate with a low-molecular compound having active hydrogen, by reacting with a blocking agent and masking. It is manufactured and its manufacture is easy. Examples of the diisocyanate used here include tolylene diisocyanate, 4,4′-diphenylmethane isocyanate, xylylene diisocyanate, hexamethylene diisocyanate, 4,4′-methylene bis (cyclohexyl isocyanate), methylcyclohexane diisocyanate, bis (isocyanate). Methyl) cyclohexane, isophorone diisocyanate, dimer acid diisocyanate, lysine diisocyanate and the like.

  Examples of low molecular weight compounds having active hydrogen include water, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, ethanolamine, diethanolamine, hexamethylenediamine, and isocyanurate. Uretidione, low molecular weight polyesters containing hydroxyl groups, 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. .

  These blocked isocyanates preferably have a softening temperature of 10 ° C to 120 ° C, particularly preferably 40 to 100 ° C. When the softening temperature is less than 10 ° C., the powder coating is hardened in an environment of about room temperature or a granular lump is formed, which is not preferable. On the other hand, when the temperature exceeds 120 ° C., it becomes difficult to uniformly disperse the blocked isocyanate in the coating when the powder coating is produced by melt-kneading, and the smoothness, coating strength, and moisture resistance of the resulting coating are obtained. The performance of such as is impaired. These blocked isocyanates are preferably blended so that the isocyanate groups are preferably 0.05 to 1.5 equivalents, particularly 0.8 to 1.2 equivalents, relative to the hydroxyl groups in the resin component. The reason for this limitation is that when the isocyanate group is less than 0.05 equivalent, the degree of curing of the paint is insufficient, and the coating performance such as adhesion, coating hardness, chemical resistance is lowered, and 1.5 equivalent. If it exceeds 1, the coating film becomes brittle, and the heat resistance, chemical resistance, moisture resistance and the like are inferior due to the influence of the excess isocyanate compound, and the block isocyanate itself is expensive, which is disadvantageous in terms of cost.

  Other additives include plasticizers, curing accelerators, crosslinking accelerators, surface conditioners, ultraviolet light absorbers, light stabilizers, antioxidants, fluidity modifiers, anti-sagging agents, and anti-foaming agents that are additives for general paints. A foaming agent etc. can be used.

"About paint formulation"
The powder coating material used in the present invention is obtained by melt-kneading a mixture containing (A) a fluororesin 10 to 50 % by mass, (B) a polyester resin 10 to 80 % by mass, and (C) a pigment 10 to 50 % by mass. And obtained by grinding after cooling. (A) When the amount of the fluororesin is less than 10 % by mass, the weather resistance tends to be inferior, and when it exceeds 50 % by mass, the amount of the expensive fluororesin used increases, resulting in an increase in cost. (B) If the polyester resin is less than 10 % by mass, the cost becomes expensive and the layer separation tends to decrease. If the polyester resin exceeds 80 % by mass, the weather resistance of the coating film decreases, and layer separation occurs. Tend to decrease. When the amount of the pigment (C) is less than 10 % by mass, the concealability to the lower layer tends to be inferior, and when it exceeds 50 % by mass, the coating film tends to be hard and brittle.

Furthermore, it is preferable to contain 1-5 mass % of (D) epoxy resin as a resin component, in order to improve adhesiveness with a base material. (However, the total content of (A) fluororesin, (B) polyester resin, (C) pigment and (D) epoxy resin does not exceed 100% by mass).

Furthermore, it is preferable from the point of a coating-film physical property to contain 5-20 mass % of (E) isocyanate compounds as a hardening | curing agent. (However, the total content of (A) fluororesin, (B) polyester resin, (C) pigment and (E) isocyanate compound does not exceed 100% by mass.)

  The powder coating used in the present invention has a weather resistance and low cost that the blending ratio of (A) fluororesin and (B) polyester resin is A / B = 50/50 to 10/90 by mass ratio. It is preferable from the viewpoint. (A) If the mass ratio of the fluororesin exceeds 50, the amount of high-cost fluororesin used is increased, resulting in an increase in cost. On the other hand, if the mass ratio is less than 10, the weather resistance tends to be inferior.

  Moreover, it is preferable that the difference of the solubility parameter (SP value) of (A) fluororesin and (B) polyester resin is 0.6-0.9.

Calculation of SP value of resin was performed as follows. And 10 wt% solution by dissolving the resin in tetrahydrofuran (THF), and _{V THF} was separated a certain amount of the solution, it performs each titrated with hexane (Hexane) and deionized water (Water), the cloudy point The drop amounts (ml) of V _Hexane and V _Water were substituted into the following formulas (1) and (2), respectively, to calculate SPn and SPh, respectively. Next, the SP value obtained by substituting the obtained SPn and SPh into the equation (3) was obtained.

_{SPn = (SP THF × V THF} + SP Hexane × V Hexane) / (V THF + V Hexane) ··· (1)
_{SPh = (SP THF × V THF} + SP Water × V Water) / (V THF + V Water) ···· (2)
SP = 10 ^ ((logSPn + logSPh) / 2) (3)
(However, SP _THF = 9.1, SP _Hexane = 7.3, SP _Water = 23.4)

  When the difference in SP value of each resin is less than 0.6, when the melt value is cured and a coating film is formed, (A) the fluororesin and (B) the polyester resin tend to become compatible. Layer separation is unlikely to occur in the upper and lower layers, and if the difference in SP value exceeds 0.9, delamination may occur between the upper and lower layers where layer separation occurs.

  The powder coating used in the present invention has (B) a polyester resin and (E) a reaction with an isocyanate compound as a curing agent, and a melt viscosity is increased by 80 ° C. to 200 ° C. at a heating rate of 10 ° C./min. The temperature difference from the start of melting to the start of curing at the time of measurement is preferably 50 ° C. or more, and if it is outside this range, the flowability of the powder coating at the time of coating film formation tends to decrease, and the coating film The sharpness of the image tends to deteriorate. Furthermore, the temperature difference is more preferably 80 to 100 ° C.

  The measurement was performed as follows. Using a rheometer ARES manufactured by TA Instruments Inc., measurement was performed with a parallel plate having a diameter of 40 mm, a gap width of 1.0 mm, a frequency of 9.42 rad / s, and a strain of 1.0%. The change in elastic modulus was measured when the temperature was raised from 80 to 200 ° C. at a rate of 10 ° C./min. The temperature at which the elastic modulus began to decrease was defined as the melting start temperature (° C.), and the elastic modulus began to increase. The temperature at the time was defined as the curing start temperature (° C.). At this time, the reaction between the (B) polyester resin and the (E) isocyanate compound was carried out with the molar ratio of the OH group and the NCO group contained in each as a mixing ratio of 1: 1.

The powder coating composition used in the present invention comprises (A) a curing start temperature T _R (A) of a fluororesin and (E) an isocyanate compound, (B) a curing start of a polyester resin and (E) an isocyanate compound. tend temperature _T the temperature difference between _{R (B) T R (B} ) -T R (a) is preferably at 20 ° C. or higher, is outside this range, the layer separation at the time of film formation decreases There is.

  When the powder coating composition used in the present invention is melted and cured at a temperature of 170 to 210 ° C., each resin component of (A) fluororesin and (B) polyester resin causes layer separation, and a multilayer coating film is formed. The multilayer coating film is preferably formed such that (A) fluororesin is segregated in the upper layer and (B) polyester resin is segregated in the lower layer. FIG. 1 shows an electron micrograph of the cross-section of the separated coating film. In the coating film configuration of FIG. 1, the base material is white from the bottom, the thin layer above it is the surface treatment layer of the base material, the layer on which the polyester resin is segregated, and the fluororesin is segregated. Is a layer.

  In the present invention, the powder coating is baked at a temperature of 170 to 210 ° C. and melted / cured. However, if it falls outside this range, the physical properties of the coating film will deteriorate, the coating film will turn yellow, the layer separation will decrease, etc. is there. Preferably it is 175-200 degreeC, and 190 degreeC is especially preferable.

  Examples of powder coating methods include corona charging electrostatic powder coating, friction charging electrostatic powder coating, fluid immersion powder coating, electrostatic fluid immersion powder coating, electric field cloud powder coating, etc. In the present invention, corona charging electrostatic powder coating is preferable from the viewpoint of controlling coating efficiency and coating film thickness.

  This makes it possible to form a multi-layer coating that separates into two layers by one-coat coating, and because the fluororesin component segregates in the upper layer, it becomes a coating with excellent weather resistance, and it is a highly weather-resistant coating with low cost and reduced processes. Can be formed.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. In the examples and comparative examples, “part” and “%” are based on mass.

<Preparation of powder coating>
About Examples 1-9 and Comparative Examples 1-9, the raw materials shown in Table 1 are blended as shown in Tables 2 and 4, mixed well, melt-kneaded, classified through fine pulverization, and each powder. A body paint was obtained.

<Preparation of test plate>
In the powder coating materials prepared in Examples 1 to 8 and Comparative Examples 1 to 8, a chromate-chromate-treated aluminum plate having a thickness of 1.5 mm was suspended in the vertical direction, and a corona charging electrostatic powder coating machine (Asahi) PG-1 type manufactured by Sunac Co.) was applied electrostatically to a film thickness of 60 μm at a voltage of −60 KV, baked in an electric furnace at 190 ° C. for 20 minutes, melted and cured, and left at room temperature. The test plate was produced by allowing to cool. A test plate was prepared in the same manner as above except that Example 9 was baked at 200 ° C. for 15 minutes, and Comparative Example 9 was baked at 230 ° C. for 15 minutes.

  Thereafter, various evaluation tests described below were performed, and the results are shown in Tables 3 and 5.

<State of coating film>
The state of the coating film surface after coating plate preparation is determined visually.

<Layer separation>
The cross section of the cut coating film is observed using a microscope (Keyence Corporation), and it is evaluated whether or not the inside of the coating film is separated into upper and lower layers. Similarly, observe the cross section of the coating film using a scanning electron microscope (Hitachi High-Technologies Corporation super-high resolution analytical scanning electron microscope SU-70), and confirm the distribution of the fluorine element (fluororesin) in the cross section of the coating film by elemental analysis. did. A fluorine atom mapping diagram of the coating film cross section is shown in FIG. It can be seen that dark portions in the figure are portions having a large amount of fluorine components, and the upper layer is unevenly distributed.

<Adhesion>
In accordance with JIS K 5600-5-6 (cross-cut method), the coating film is cut into a grid at 100 mm intervals of 1 mm, and it is evaluated whether or not the coating film is peeled off by tape peeling after sticking the adhesive tape.

<Weight drop resistance>
Based on JIS K5600-5-3 (DuPont type), the cracking / peeling of the coating film is evaluated for the resistance of the coating film to a drop height of 50 cm with a weight of 1/2 mm φ and a weight of 500 g.

<Boiling water resistance>
The coated 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).

<Mortar resistance>
A mortar paste is applied on the coated surface, left in a humidity resistant environment of 50 ° C. and 95 RH% for 24 hours, the mortar mass is peeled off, and the state of the coating film after water washing is visually evaluated using ion-exchanged water. .

<Nitric acid resistance>
The coated surface is exposed to steam for 60 minutes so as to cover a glass bottle containing a 70% nitric acid aqueous solution, washed with water using ion-exchanged water, and dried to measure the color difference from before the test.

<Hydrochloric acid resistance>
Ten drops of 10% hydrochloric acid aqueous solution is placed on the coated surface, covered with a watch glass, and after 15 minutes, the state of the coating film washed with ion-exchanged water and dried is visually evaluated.

<Moisture resistance>
The coated plate is placed in a humidity resistant environment of 50 ° C. and 95 RH% for 3000 hours, and the state of the coating film is visually evaluated after washing, allowing to cool, and drying using ion exchange water.

<Salt water spray resistance>
The coated plate is allowed to stand for 3000 hours in a 35 ° C. salt water spray environment, and the state of the coating film is visually evaluated after washing, allowing to cool, and drying using ion exchange water.

<Accelerated weather resistance>
Use an accelerated weathering tester that conforms to JIS B 7753 (Sunshine weatherometer method) and measure the 60 ° specular gloss value retention and color difference with a test time of 3000 hours and 100% before the test. .

Fluororesin made by Asahi Glass Co., Ltd., trade name: Lumiflon LF710F
Polyester resin 1 Dainippon Paint Co., Ltd. Self-made product, Polyester resin A
Polyester resin 2 Dai Nippon Paint Co., Ltd. Self-made product, Polyester resin B
Polyester resin 3 Product name: Krill Coat 4642-3 manufactured by Daicel Cytec Co., Ltd.
Polyester resin 4 Product name: Krill Coat 2890-0 manufactured by Daicel Cytec Co., Ltd.
Polyester Resin 5 Made by Nippon Iupika Co., Ltd., trade name: Iupika Coat GV560
Polyester resin 6 Made by Nippon Iupika Co., Ltd., trade name: Iupika Coat GV130
Pigment (titanium oxide), manufactured by DuPont, trade name: TI-PURE R-960
Epoxy resin Toto Kasei Co., Ltd., trade name: Epototo DT-112
ε-Caprolactam block isocyanate, manufactured by Evonik Degussa, trade name: Vestagon B1530
Product name: Primid XL552, manufactured by EMS
* As the isocyanate, Vestagon B1530 was used, and the reaction was carried out so that the molar ratio of NCO and OH group (resin) was 1: 1.

Claims (4)

(A) 10-50% by mass of a fluororesin, (B) 10-80% by mass of a polyester resin, and (C) a mixture containing 10-50% by mass of a pigment is melt-kneaded, cooled, and then pulverized to form a powder coating material Obtaining a step,
Coating the powder coating on a substrate and melting and curing at a temperature of 170 to 210 ° C. to form a coating film;
A method for forming a layer-separated coating film, wherein the formed coating film is separated into (A) a fluororesin layer and (B) a polyester resin layer to form a multilayer coating film .   2. The layer-separated coating film according to claim 1, wherein the layer-separated multilayer coating film is separated into two layers, the (A) fluororesin layer being an upper layer and the (B) polyester resin layer being a lower layer. Method. The method for forming a layer-separated coating film according to claim 1 or 2 , wherein the blend of the (A) fluororesin and the (B) polyester resin is A / B = 50/50 to 10/90 in mass ratio. The method for forming a layer-separated coating film according to any one of claims 1 to 3 , wherein the coating method of the powder coating is by corona charging electrostatic coating.