JP5086288B2 - Chromium-free painted metal sheet coating method and painted metal sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chrome-free coated metal sheet having excellent external appearance of a coating film, hardness of the coating film, workability, weather resistance and corrosion resistance. <P>SOLUTION: A method for forming the coating film on the chrome-free coated metal sheet comprises the steps of: applying a chrome-free primer coating material (A) to one or both surfaces of a metal sheet whose surfaces can be treated chemically, to form a primer-hardened coating film having 1-10 &mu;m dry film thickness; applying a specific final coating material (B) to at least one surface of the primer-hardened coating film; and heating/hardening the applied coating material to form a hardened final coating film having 5-30 &mu;m dry film thickness. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a coating film forming method and a coated metal plate of a chromium-free coated metal plate excellent in coating film appearance, coating film hardness, workability, weather resistance, and corrosion resistance, and more specifically, even in a chromium-free painted metal plate The present invention relates to a method for forming a coating film of a chromium-free painted metal plate and a coated metal plate that have good corrosion resistance not only in the corrosion resistance but also in the processed portion and end face portion.

  Conventionally, pre-coated metal sheets such as pre-coated steel sheets painted by coil coating, etc., building materials such as roofs, walls, shutters, garages, various household appliances, switchboards, refrigerated showcases, steel furniture, kitchen appliances, etc. Widely used as a housing related product.

  In order to manufacture these housing-related products from a pre-coated metal plate, the pre-coated steel plate is usually cut, press-molded and joined. Therefore, these housing-related products often have a metal exposed portion that is a cut surface and a crack generating portion due to press working. The above metal exposed part and crack generation part are likely to have a corrosion resistance lower than other parts, so in order to improve the corrosion resistance, it is common to include a chromium-based anticorrosive pigment in the primer coating of the pre-coated steel sheet Has been done.

However, chromium-based rust preventive pigments contain or produce hexavalent chromium having excellent rust prevention properties, and the use of this hexavalent chromium has been restricted from the viewpoint of human health and environmental protection. ing. To date, many non-chromium anticorrosive pigments such as zinc phosphate, aluminum tripolyphosphate, and zinc molybdate have been put on the market, and various primers have been proposed as a combination of non-chromium pigments. ing.
On the other hand, a highly durable coated metal plate that has been conventionally coated with, for example, coil coating, using a paint that contains at least 50 mol% of hexahydrophthalic acid as an acid component and further uses polyester using neopentyl alcohol. Has been disclosed (Patent Document 1).

  However, when the coated metal plate according to Patent Document 1 is a multi-layer coating without a primer coating and is a chromium-free coating, the corrosion resistance at the processed or end surface of the coated metal plate, in particular the exposure Corrosion resistance was insufficient.

In addition, a primer coating and a hue coating are provided on a metal plate, and a multilayer coating on which a clear coating including a polyester resin containing hexahydrophthalic anhydride and neopentyl glycol is provided on the hue coating. A coated metal plate is disclosed (Patent Document 2).
However, when the primer coating film is made chromium-free on the coated metal plate according to Patent Document 2, simply using a polyester resin containing hexahydrophthalic anhydride and neopentyl glycol, Corrosion resistance and endurance corrosion resistance at the end face were insufficient.

JP-A-5-239196 JP 2007-55137 A

  The problem to be solved by the present invention is to find a method for forming a coating film of a chromium-free coated metal sheet excellent in coating film appearance, coating film hardness, workability, weather resistance, and corrosion resistance, and to provide a coated metal sheet excellent in the above performances. That is.

  As a result of intensive studies, the present inventors have found that a chromium-free primer coating material that does not contain a chromium-based rust preventive component on one or both surfaces of a metal plate that may be subjected to chemical conversion treatment on the surface ( A primer cured film having a dry film thickness of 1 to 10 μm according to A) is formed, and a specific topcoat paint (B) is applied on at least one surface of the primer cured film and heat-cured, and a dry film thickness of 5 to 30 μm is formed. By the method of forming a coating film on a chromium-free coated metal sheet, which is characterized by forming a top-coated cured coating film, a chrome-free coated metal sheet having excellent coating film appearance, coating film hardness, workability, weather resistance and corrosion resistance has been obtained. It was.

That is, the present invention
1. A primer having a dry film thickness of 1 to 10 μm by a chromium-free primer coating (A), which does not contain a chromium-based rust preventive component on one or both surfaces of a metal plate which may be subjected to chemical conversion treatment on the surface A cured coating film is formed, and an overcoat paint (B) having the following characteristics is applied to at least one surface of the primer cured coating film and heat-cured to form a top-coated cured film having a dry film thickness of 5 to 30 μm. It is the coating-film formation method of the chromium-free paint metal plate which makes it.
Top coat (B):
A hydroxyl group-containing polyester resin (B1) comprising the polybasic acid component (b1) and the polyhydric alcohol component (b2) as constituent components, i) based on the total mass of the polybasic acid component (b1),
The total proportion of polybasic acid selected from hexahydrophthalic anhydride, hexahydroisophthalic acid, tetrahydrophthalic anhydride is 90 to 100% by mass, and (ii) based on the total mass of the polyhydric alcohol component (b2), A polyhydric alcohol component having a total ratio of polyhydric alcohol selected from neopentyl glycol, 1,4-cyclohexanedimethanol and hydrogenated bisphenol A of 50 to 100% by mass, the polybasic acid component (b1) and A hydroxyl group-containing polyester resin (B1) obtained by reacting with the polyhydric alcohol component (b2), a crosslinking agent (B2) containing a blocked aliphatic polyisocyanate and / or a blocked alicyclic polyisocyanate compound, and The pigment component (B3) is added to 100 parts by mass of the solid content of the resin (B1) and the crosslinking agent (B2). Topcoat 2 containing 120 parts by weight. The polyhydric alcohol component (b2) contains at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A,
And the coating-film formation method of the chromium-free paint metal plate of 1 characterized by including the at least 1 sort (s) of compound chosen from trimethylol propane and glycerol,
3. The method for forming a coating film on a chromium-free coated metal sheet according to 1 or 2, wherein the crosslinking agent (B2) is a blocked product of hexamethylene diisocyanate.
4). Chromium-free primer paint (A) is an aliphatic polybasic acid (a11) having 4 to 36 carbon atoms, an acrylic resin (a12) having a glass transition temperature of -20 to 50 ° C, and a polyester resin having a glass transition temperature of -20 to 50 ° C. It is a chromium-free primer coating containing a bisphenol-type epoxy resin (A1) modified with at least one soft organic component of (a13), a crosslinking agent (A2), and a chromium-free rust preventive component (A3). 4. The method for forming a coating film on a chromium-free painted metal sheet according to any one of items 3 to 4.
5. The chromium-free rust preventive component (A3) is at least one vanadium compound (1) of vanadium pentoxide, calcium vanadate and ammonium metavanadate (1), metal phosphate (2), metal silicate and silica fine particles 5. The method for forming a coating film on a chromium-free coated metal sheet according to any one of items 1 to 4, which contains at least one silicon-containing compound (3).
It is related with the coating metal obtained by the coating-film formation method of the chromium-free coating metal plate of any one of 6.1-5.

  A composite coating obtained by coating a specific topcoat (B) on a coating obtained by coating a chromium-free primer coating characterized by not containing a chromium-based anticorrosive component. The layer coating film can provide a chromium-free coated metal plate excellent in coating film appearance, coating film hardness, processability, weather resistance and corrosion resistance.

  The top coating (B) comprising a combination of a specific polyester resin (B1) and a specific cross-linking agent (B2) has an excellent balance between workability and coating film hardness, and is deteriorated by resin or acidity due to light irradiation or the like. Since hydrolysis due to rain or the like can be suppressed, specifically, it is possible to prevent cracking, fading and gloss deterioration of the coating film due to outdoor bakuro. Because of this, it is suitable as a top coating for precoated steel sheets.

  Further, a chromium-free primer coating (A) containing a bisphenol type epoxy resin (A1) modified with a soft organic component, a curing agent (A2), and a chromium-free rust preventive component (A3) in the chromium-free primer coating (A) By making the coating film using a lower layer, workability can be further imparted to the coating film. Furthermore, a multilayer coating film excellent in corrosion resistance can be formed not only in the corrosion resistance of the flat portion but also in the processed portion and the end surface portion of the coated metal plate. A coated metal plate excellent in the above-mentioned various properties can be obtained without using chromium.

  The present invention forms a primer-cured coating film having a dry film thickness of 1 to 10 μm with a chromium-free primer coating (A) on one or both surfaces of a metal plate whose surface may be subjected to chemical conversion treatment, and is cured by primer. A coating film of a chromium-free painted metal sheet, characterized in that a specific topcoat paint (B) is applied on at least one surface of the coating film and cured by heating to form a topcoat cured film having a dry film thickness of 5 to 30 μm. A forming method and a chromium-free painted metal plate. Details will be described below.

[Metal coating]
The metal plate to be coated is iron, aluminum alloy, brass, copper plate, stainless steel plate, tin plate, galvanized steel plate, alloyed zinc (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel plate, aluminum Metal plates such as plated steel plates; surface-treated metal plates obtained by subjecting the surfaces of these metal plates to chemical conversion treatment such as phosphate treatment and chromate treatment. In addition to the above metal plate, a metal resin composite plate having a layer configuration of “metal plate / adhesive layer / resin layer / adhesive layer / metal plate” having a metal plate on the outermost layer on one or both sides is used. it can.
In addition, a metal resin composite plate in which the surface of a non-metallic substance such as resin is coated with a metal layer by vapor deposition or the like can also be used as an object to be coated. Further, by melting the resin and sandwiching it between the metal resin composite plates, What is referred to as “plate / resin layer / metal plate” can also be used as an object to be coated.

  From the viewpoint of lightness and durability, a metal resin composite plate having a layer configuration of “metal plate / adhesive layer / resin layer / adhesive layer / metal plate” having a metal plate on the outermost layer on one or both sides is provided. Preferably, aluminum is more preferable as the metal plate from the viewpoint of workability and corrosion resistance.

[Chrome-free primer paint (A)]
A coating film of a chromium-free primer coating (A) characterized by not containing a chromium-based rust preventive component is formed on the metal coating as necessary. Examples of the chromium-free primer coating (A) include primer coatings such as polyester resin and epoxy resin. Among these, from the viewpoint of improving workability, corrosion resistance, and corrosion resistance, it is possible to react the soft organic component (a1) with the bisphenol-type epoxy resin (a2), and to modify the soft organic component-modified bisphenol-type epoxy resin (A1) ( Hereinafter, a chromium-free primer coating (A) using “modified resin (A1)” may be abbreviated.

Bisphenol type epoxy resin (A1):
The soft organic component (a1) in the production of the bisphenol type epoxy resin (A1) is an organic component having a functional group that reacts with the bisphenol type epoxy resin and capable of plasticizing the bisphenol type epoxy resin (a2). -36 aliphatic polybasic acid (a11), an acrylic resin (a12) having a glass transition temperature of -20 to 50 ° C, and a polyester resin (a13) having a glass transition temperature of -20 to 50 ° C. .

  The aliphatic polybasic acid having 4 to 36 carbon atoms (a11) is a saturated or unsaturated aliphatic polybasic acid having 4 to 36 carbon atoms, preferably 8 to 36, including alicyclic polybasic acids. For example, hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, methylhexahydroterephthalic acid, 1-tetrahydrophthalic acid, 2-tetrahydrophthalic acid, 3-tetrahydrophthalic acid, 4-tetrahydrophthalic acid, 3-tetrahydroisophthalic acid, 4-tetrahydroisophthalic acid, 1-tetrahydroterephthalic acid, 2-tetrahydroterephthalic acid, methyltetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid, hexachloroendo Methylenetetrahydrophthal Alicyclic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dodecanedicarboxylic acid, suberic acid, pimelic acid, maleic acid, fumaric acid, itaconic acid, Aliphatic dicarboxylic acids such as brassic acid, citraconic acid, chloromaleic acid and dimer acid and their anhydrides; trivalent or higher aliphatic polybasic acids such as hexahydrotrimellitic acid; methyl esters and ethyl esters of these acids And lower alkyl esters.

  Examples of the acrylic resin (a12) that can be used as the soft organic component in the production of the modified resin (A1) include an acrylic resin (a12) having a reactive group that reacts with the epoxy group of the bisphenol-type epoxy resin. The acrylic resin (a12) includes a modified acrylic resin such as a urethane-modified acrylic resin. Examples of the reactive group include a carboxyl group, an amino group, a hydroxyl group, and the like. Among the acrylic resins, an acrylic resin having a carboxyl group is preferably used.

  The acrylic resin having a carboxyl group is obtained by copolymerizing a polymerizable unsaturated monomer having a carboxyl group and other polymerizable unsaturated monomers by a known method such as a solution polymerization method, a suspension polymerization method, or a bulk polymerization method. Among them, the solution polymerization method is preferable because of easy control of polymerization. The other polymerizable unsaturated monomer contains a (meth) acrylic acid ester. It is preferable that the amount of (meth) acrylic ester used is in the range of 30 to 98% by mass based on the total amount of copolymerization monomer components constituting the modified resin (A). Examples of the polymerizable unsaturated monomer having a carboxyl group include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, and itaconic acid.

  Examples of the other polymerizable unsaturated monomers include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, and ε-caprolactone modified. Tetrahydrofurfuryl (meth) acrylate, ε-caprolactone modified hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- Hydroxyl group-containing polymerizable unsaturated monomers such as hydroxy-3-butoxypropyl (meth) acrylate and monohydroxyethyl (meth) acrylate phthalate; methyl (meth) acrylate , Ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, stearyl (meth) acrylate , Alkyl (meth) acrylates such as tridecyl (meth) acrylate; cycloalkyl (meth) acrylates such as cyclohexyl (meth) acrylate; benzyl (meth) acrylate, phenyl (meth) acrylate; dimethylaminoethyl (meth) acrylate, diethylamino Di (alkyl) aminoalkyl (meth) acrylates such as ethyl (meth) acrylate; glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, allyl glycidyl ether Epoxy group-containing polymerizable unsaturated monomers such as styrene, α-methylstyrene, vinyl toluene, and other vinyl aromatic compounds; acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, methylolacrylamide, methylolmethacrylamide , Diacetone acrylamide, acryloyl morroline, N-vinyl-2-pyrrolidone, γ-acryloxypropyltrimethoxylane, γ-methacryloxypropyltrimethoxylane, vinyl chloride, propylene, ethylene, C4-C20 α-olefin Etc. These can be used alone or in combination of two or more. In the present specification, “(meth) acrylate” means “acrylate or methacrylate”.

The number average molecular weight of the acrylic resin (a12) is 2,000 to 40,000, particularly 3,000, when it is synthesized by solution polymerization from the viewpoint of compatibility with the bisphenol type epoxy resin and reactivity. Within the range of ~ 30,000 is preferred.
In the present specification, the average molecular weight of the resin is a value calculated based on the molecular weight of standard polystyrene from the chromatogram measured by gel permeation chromatography. As the gel permeation chromatograph, “HLC8120GPC” (manufactured by Tosoh Corporation) was used. As the columns, four columns of “TSKgel G-4000HXL”, “TSKgel G-3000HXL”, “TSKgel G-2500HXL”, “TSKgel G-2000HXL” (both manufactured by Tosoh Corporation, trade name) were used, Mobile phase: Tetrahydrofuran, measurement temperature: 40 ° C., flow rate: 1 ml / min, detector: under the conditions of RI.

  The acrylic resin (a12) preferably has an acid value of 3 to 50 mgKOH / g, particularly 5 to 40 mgKOH / g, from the viewpoints of reactivity and adhesion to the bisphenol type epoxy resin (a2). Further, the hydroxyl value of the acrylic resin (a12) is preferably 10 to 300 mgKOH / g, particularly preferably 30 to 250 mgKOH / g, from the viewpoint of the curability and water resistance of the coating film. Furthermore, the glass transition temperature (Tg) of the acrylic resin (a12) is in the range of −20 ° C. to 50 ° C., preferably −20 ° C. to 40 ° C., from the viewpoint of the balance between processability and hardness of the resulting coating film. Is preferred. In the present specification, the glass transition temperature (Tg) of the resin is determined by scanning differential thermal analysis (DSC).

  Examples of the polyester resin that can be used as the soft organic component (a1) in the production of the bisphenol type epoxy resin (A1) include a polyester resin (a13) having a reactive group that reacts with the epoxy group of the bisphenol type epoxy resin. The polyester resin (a13) includes both oil-free polyester resins and oil-modified polyester resins, and may be modified polyester resins such as silicon-modified polyester resins and urethane-modified polyester resins. Examples of the reactive group include a carboxyl group, an amino group, a hydroxyl group, and the like, and a polyester resin having a carboxyl group is particularly preferably used as the polyester resin.

  Of the polyester resin (a13), the oil-free polyester resin can be produced using a known method such as a direct esterification method, a transesterification method, or a ring-opening polymerization method. Specific examples of the direct esterification method include a method of polycondensation of a polybasic acid and a polyhydric alcohol.

  As the polybasic acid, one or more dibasic acids selected from phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, fumaric acid, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, etc .; Tribasic acid or more polybasic acid such as trimellitic anhydride, methylcyclohexylic carboxylic acid, pyromellitic anhydride, etc. is used, and benzoic acid, crotonic acid, p-tertbutylbenzoic acid, etc. are used as the acid component as required. Monobasic acids can also be used. As the polyhydric alcohol, dihydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, butanediol, neopentyl glycol, hexanediol and 1,6-hexanediol are mainly used. A trihydric or higher polyhydric alcohol such as methylolethane, trimethylolpropane and pentaerythritol can also be used in combination.

  The production of the polyester resin (a13) can be carried out by a known method in a compounding ratio in which the acid group is excessive with respect to the hydroxyl group of the polybasic acid and the polyhydric alcohol. It can also be carried out by post-adding a polybasic acid such as trimellitic anhydride or phthalic anhydride to the hydroxyl group.

  The oil-free polyester resin can also be produced by polycondensation by transesterification between a polybasic acid lower alkyl ester and a polyhydric alcohol. Furthermore, the oil-free polyester resin can also be produced by ring-opening polymerization of lactones such as δ-valerolactone and ε-caprolactone.

  Of the polyester resin (a13), an oil-modified polyester resin is obtained by reacting an oil fatty acid with the oil-free polyester resin. Examples of the oil fatty acid include coconut oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, Flower oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, tung oil fatty acid and the like can be mentioned. The reaction between the polyester resin and the oil fatty acid can also be carried out by a known method, and the oil length is usually preferably 30% or less. .

  The number average molecular weight of the polyester resin (a13) may be in the range of 1,000 to 30,000, particularly 2,000 to 20,000, from the viewpoint of compatibility with the bisphenol-type epoxy resin and reactivity. Is preferred. The acid value of the polyester resin is preferably from 3 to 100 mgKOH / g, particularly preferably from 5 to 70 mgKOH / g, from the viewpoints of reactivity and adhesion with the bisphenol-type epoxy resin. Moreover, the glass transition temperature (Tg) of the polyester resin (a13) is in the range of −20 ° C. to 50 ° C., preferably −20 ° C. to 40 ° C. from the viewpoint of compatibility between the workability of the obtained coating film and the coating film hardness. Preferably it is.

  The bisphenol-type epoxy resin (a2) used in the production of the bisphenol-type epoxy resin (A1) modified with a soft organic component is a bisphenol-type epoxy resin having one or more, preferably two or more epoxy groups in one molecule. Yes, for example, a resin obtained by condensing epichlorohydrin and bisphenol up to a high molecular weight in the presence of a catalyst such as an alkali catalyst, if necessary, epichlorohydrin and bisphenol, if necessary, in the presence of a catalyst such as an alkali catalyst. Any of resins obtained by condensation to form a low molecular weight epoxy resin and a polyaddition reaction of the low molecular weight epoxy resin and bisphenol may be used.

  The bisphenol type epoxy resin (a2) usually has a number average molecular weight of 350 to 5,000, preferably 400 to 4,000, and an epoxy group content of 0.5 to 15.4 mmol / g, preferably 0.8-10 mmol / g is preferred.

  Examples of the bisphenol include bis (4-hydroxyphenyl) methane [bisphenol F], 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) propane [bisphenol A], 2, 2-bis (4-hydroxyphenyl) butane [bisphenol B], bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-tert-butyl-phenyl) -2,2-propane, bis ( 2-hydroxy-tert-butyl-phenyl) -2-hydroxy-1,3-oxy-propane, p- (4-hydroxyphenyl) phenol, oxybis (4-hydroxyphenyl), sulfonylbis (4-hydroxyphenyl), 4,4'-dihydroxybenzophenone, bis (2-hydroxynaphth Le), etc. can be mentioned methane, bisphenol A, bisphenol F are preferably used among others. The bisphenols can be used alone or as a mixture of two or more.

  As a commercial product of bisphenol type epoxy resin, for example, manufactured by Japan Epoxy Resin, jER828, jER812, jER815, jER820, jER834, jER1001, jER1004, jER1007, jER1009, jER1010, jER4004P, jER4007P, jER4210; Araldite AER6099; and Epomic R-309 manufactured by Mitsui Chemicals, Inc. can be used.

  The method for producing the modified resin (A) by reacting the soft organic component (a1) with the bisphenol type epoxy resin (a2) is not particularly limited. For example, when two types of soft organic component (a1) are used, a method in which two types of soft organic component (a1) and bisphenol-type epoxy resin (a2) are simultaneously reacted together, a soft organic component ( a1) After reacting 1 type and bisphenol type epoxy resin (a2), the method of making the remaining soft organic component react can be mentioned.

  The above reaction can be suitably carried out, for example, by reacting usually at 100 to 150 ° C. for 1 to 5 hours in the presence of a reaction catalyst as necessary in a solvent capable of dissolving these components.

Examples of the reaction catalyst include quaternary salt catalysts such as tetraethylammonium bromide, tetrabutylammonium bromide, tetraethylammonium chloride, tetrabutylphosphonium bromide and triphenylbenzylphosphonium chloride; amines such as triethylamine and tributylamine Etc.
In the above reaction, when the reactive group of the soft organic component (a1) is a carboxyl group, the equivalent ratio of (epoxy group in the bisphenol type epoxy resin) / (carboxyl group in the soft organic component) is 10 / It is suitable to be in the range of 1-1 / 1, preferably 5/1 to 2/1.

  When the acrylic resin (a12) has a reactive group that reacts with an epoxy group other than a carboxyl group in the synthesis reaction of the modified resin (A1), the ratio of each reactive group is “in the soft organic component” It is preferable to be within the range of the formula in which “the carboxyl group of” is replaced with “a reactive group that reacts with an epoxy group other than the carboxyl group”.

  The blending ratio of the soft organic component (a1) and the bisphenol type epoxy resin (a2) when producing the modified resin (A1) is within the following range based on a total of 100 parts by mass of both. Soft organic component (a1): 5 to 50 parts by mass, preferably 10 to 40 parts by mass, bisphenol type epoxy resin (a2): 50 to 95 parts by mass, preferably 60 to 90 parts by mass.

  Further, the modified resin (A1) is composed of benzoic acid, salicylic acid, or a secondary grade, because when the epoxy group remains after the soft organic component (a1) and the bisphenol type epoxy resin (a2) are reacted, the epoxy group is blocked. It may be obtained by reacting a blocking agent such as an amine compound. Moreover, depending on the case, a blocking agent can also be made to react at the time of reaction of a soft organic component (a1) and a bisphenol-type epoxy resin (a2). It is considered that the modified resin (A1) has a soft component in the structure, thereby contributing to the development of stress relaxation ability of the crosslinked coating film and contributing to improvement of workability and corrosion resistance.

Cross-linking agent (A2):
The cross-linking agent (A2) reacts with the modified resin (A1) to form a cured coating film, and is particularly limited as long as it can be cured by reacting with the modified resin (A1) by heating or the like. Among them, amino resins, phenol resins and polyisocyanate compounds which may be blocked are suitable. These crosslinking agents can be used alone or in combination of two or more. Examples of the amino resin include amino resins obtained by the reaction of amino components such as melamine, urea, benzoguanamine, acetogranamamine, steroguanamine, spiroguanamine, and dicyandiamide with aldehyde, and among these, melamine resin is preferable from the viewpoint of processability. .

  The melamine resin is a monohydric alcohol having 1 to 8 carbon atoms, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i, part or all of the methylol group of methylolated melamine. Examples thereof include partially etherified or fully etherified melamine resins etherified with butyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like.

  These may be used in which all methylol groups are etherified or partially etherified so that methylol groups or imino groups remain. Examples include alkyl etherified melamines such as methyl etherified melamine, ethyl etherified melamine, and butyl etherified melamine, and only one kind may be used or two or more kinds may be used in combination. Of these, methyl etherified melamine resin in which at least a part of methylol group is alkyl etherified is preferable.

  Examples of such commercially available melamine resins include Cymel 202, Cymel 232, Cymel 235, Cymel 238, Cymel 254, Cymel 266, Cymel 267, Cymel 272, Cymel 285, Cymel 301, Cymel 303, Cymel 325, Cymel 327. Cymel 350, Cymel 370, Cymel 701, Cymel 703, Cymel 1141 (manufactured by Nihon Cytec Industries, Inc.), Uban 20SE60 (manufactured by Mitsui Chemicals, trade name, average polymerization degree exceeding 3) and the like are commercially available.

  The phenol resin that can be used as the crosslinking agent (A2) crosslinks with the modified resin (A) and introduces a methylol group by heating and condensing the phenol component and formaldehyde in the presence of a reaction catalyst. And a resol type phenol resin obtained by alkylating a part or all of the methylol group of the methylolated phenol resin obtained with the alcohol with an alcohol.

  In the production of a resol-type phenol resin, a bifunctional phenol compound, a trifunctional phenol compound, a tetrafunctional or higher functional phenol compound, or the like can be used as the phenol component as a starting material.

  Examples of the phenol compound include, for example, bifunctional phenol compounds such as o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, and 2,5-xylenol. Examples of the trifunctional phenol compound include carboxylic acid, m-cresol, m-ethylphenol, 3,5-xylenol, and m-methoxyphenol. Examples of the tetrafunctional phenol compound include bisphenol A and bisphenol F. Can be mentioned. Among them, in order to improve scratch resistance, it is preferable to use a trifunctional or higher functional phenol compound, in particular, carboxylic acid and / or m-cresol. These phenol compounds may be used alone or in combination of two or more.

  Examples of formaldehydes used in the production of phenol resins include formaldehyde, paraformaldehyde, trioxane, and the like, which can be used alone or in combination of two or more.

  As the alcohol used for alkyl etherifying a part of the methylol group of the methylolated phenol resin, a monohydric alcohol having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, can be suitably used. Suitable monohydric alcohols include methanol, ethanol, n-propanol, n-butanol, isobutanol and the like.

  A phenol resin having an average of 0.5 or more, preferably 0.6 to 3.0, alkoxymethyl groups per benzene nucleus is suitable from the viewpoint of reactivity with the modified resin (A1). Yes.

  Examples of the unblocked polyisocyanate compound that can be used as the curing agent as the curing agent include aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate; hydrogenated xylylene diisocyanate or Cycloaliphatic diisocyanates such as isophorone diisocyanate; organic diisocyanates themselves such as tolylene diisocyanate, xylylene diisocyanate or 4,4'-diphenylmethane diisocyanate, aromatic diisocyanates such as crude MDI, or each of these organic diisocyanates and polyvalent Adducts with alcohol, low molecular weight polyester resin or water, or as described above Cyclic polymerization of an organic diisocyanate comrades, further include isocyanate-biuret, or the like.

  The blocked polyisocyanate compound is obtained by blocking free isocyanate groups of the polyisocyanate compound with a blocking agent. Examples of the blocking agent include phenols such as phenol, cresol and xylenol; ε-caprolactam; lactones such as δ-valerolactam and γ-butyrolactam; methanol, ethanol, n-, i- or t-butyl alcohol, ethylene Alcohols such as glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and benzyl alcohol; oximes such as formamidoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime System: Active methylene such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, acetylacetone It can be suitably used blocking agent, such as. By mixing the polyisocyanate compound and the blocking agent, free isocyanate groups of the polyisocyanate compound can be easily blocked.

  The blending ratio of the bisphenol type epoxy resin (A1) and the cross-linking agent (A2) is based on 100 parts by mass of the total solid content of the components (A1) and (A2), and the bisphenol type epoxy resin (A1) is 55 to 55 parts. It is 95 mass parts, Furthermore, it is 60-95 mass parts, Comprising: It is sclerosis | hardenability, workability, corrosion resistance, etc. that a crosslinking agent (A2) exists in the range of 5-45 mass parts, and also 5-40 mass parts. From the point of view, it is preferable.

  In addition, in order to raise the sclerosis | hardenability of chromium free primer coating material (A), a curing catalyst can be mix | blended as needed. When the crosslinking agent (A2) contains an amino resin, particularly a low molecular weight, methyl etherified or mixed etherified melamine resin of methyl ether and butyl ether, sulfonic acid compound or amine neutralization of sulfonic acid compound as a curing catalyst A thing is used suitably. Representative examples of the sulfonic acid compound include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, and the like.

  The amine in the amine neutralized product of the sulfonic acid compound may be any of primary amine, secondary amine, and tertiary amine. Among these, the amine neutralized product of p-toluenesulfonic acid and / or the amine neutralized product of dodecylbenzenesulfonic acid is preferable from the viewpoints of the stability of the coating, the reaction promoting effect, and the physical properties of the obtained coating film. .

  When the crosslinking agent (A2) is a phenol resin, the sulfonic acid compound or an amine neutralized product of the sulfonic acid compound is preferably used as the curing catalyst.

  When the crosslinking agent (A2) is a blocked polyisocyanate compound, a curing catalyst that promotes dissociation of the blocking agent of the blocked polyisocyanate compound, which is a curing agent, is suitable. As a suitable curing catalyst, for example, octyl Tin oxide, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, lead 2-ethylhexanoate And organometallic catalysts such as When the crosslinking agent (A2) combines two or more kinds of crosslinking agents, an effective curing catalyst can be used in combination with each crosslinking agent.

Chrome-free rust preventive component (A3):
The chromium-free primer coating (A) uses a chromium-free rust-preventing component (A3) from the viewpoint of health for the human body and environmental protection. Examples of the chromium-free rust preventive component (A3) include zinc phosphate, aluminum tripolyphosphate, calcium molybdate silicate, vanadium pentoxide, calcium vanadate, ammonium metavanadate, phosphorus vanadate, aluminum phosphate, calcium phosphate, Silica fine particles having magnesium phosphate, calcined product of manganese oxide and vanadium oxide, calcined product of calcium phosphate and vanadium oxide, oil absorption of 30 to 200 ml / 100 g, and pore volume of 0.05 to 1.2 ml / g , Etc. These rust preventive components (A3) can be used alone or in combination of two or more.

  The chromium-free rust preventive component (A3) of the chromium-free primer coating (A) is preferably a combination of the following vanadium compound (1), phosphate metal salt (2) and silicon-containing compound (3). Can be used.

Vanadium compound (1)
The vanadium compound (1) is at least one vanadium compound selected from vanadium pentoxide, calcium vanadate, and ammonium metavanadate. Vanadium pentoxide, calcium vanadate and ammonium metavanadate are excellent in elution of pentavalent vanadium ions into water, and the pentavalent vanadium ions released from the vanadium compound (1) react with the material metal, It works effectively to improve corrosion resistance by reacting with ions from other antirust pigment mixtures.

Phosphate metal salts (2)
The phosphoric acid metal salt (2) is at least one of a phosphoric acid metal salt, a hydrogen phosphate metal salt, and a tripolyphosphate metal salt. The metal of the phosphate metal salt is not particularly limited, and examples of suitable metals include Ca, Zn, Al, and Mg. Among these, Ca is particularly suitable.

  Examples of the phosphate metal salt include calcium phosphate, calcium ammonium phosphate, calcium monohydrogen phosphate, calcium dihydrogen phosphate, calcium phosphate phosphate, zinc phosphate, aluminum phosphate, magnesium phosphate, hydrogen phosphate Examples thereof include zinc, aluminum phosphate, magnesium phosphate, aluminum hydrogen phosphate, magnesium hydrogen phosphate, magnesium ammonium phosphate, and aluminum dihydrogen triphosphate. Of these, calcium phosphate, calcium monohydrogen phosphate, and calcium dihydrogen phosphate are particularly preferred from the viewpoint of corrosion resistance. Phosphate ions released from the phosphate metal salt (2), metal ions such as Ca, Zn, Al, or Mg effectively work to improve corrosion resistance.

Silicon-containing compound (3)
The silicon-containing compound (3) is at least one of metal silicate and silica fine particles. The metal silicate is a salt made of silicon dioxide and a metal oxide, and may be any of orthosilicate, polysilicate, and the like. Examples of the silicate include zinc silicate, aluminum silicate, aluminum orthosilicate, aluminum hydroxide silicate, aluminum calcium silicate, sodium aluminum silicate, beryllium aluminum silicate, sodium silicate, calcium orthosilicate, calcium metasilicate, sodium calcium silicate, and silicic acid. Zirconium, magnesium orthosilicate, magnesium metasilicate, magnesium calcium silicate, manganese silicate, barium silicate, olivine, garnet, tortovite, cyllite, benitoite, neptunite, nymphite, turquoise, quartzite, barracite, tosen Stones, zonotorite, talc, gyoganite, aluminosilicate, borosilicate, beryllosilicate, cholite, fluorite and the like. Among them, calcium orthosilicate and calcium metasilicate are preferable as the metal silicate.

  The silica fine particles can be used without any limitation as long as they are silica fine particles. For example, silica fine powder whose surface is not treated, silica fine powder whose surface is treated with organic matter, calcium ion-exchanged silica fine particles, organic solvent-dispersible colloidal silica And so on.

  Examples of the silica fine particles whose surface is not treated or treated with an organic substance include silica fine powder having an average particle size of 0.5 to 15 μm, preferably 1 to 10 μm, and organic solvent-dispersible colloidal silica. As the fine silica powder, those having an oil absorption of 30 to 350 ml / 100 g, preferably 30 to 150 ml / 100 g can be suitably used, and as commercially available products, silicia 710, silicia 740, silicia 550, Examples include Aerosil R972 (all of which are manufactured by Fuji Silysia Chemical Co., Ltd.), Mizukacil P-73 (manufactured by Mizusawa Chemical Industry Co., Ltd.), Gasil 200DF (manufactured by Crossfield).

  Calcium ion exchanged silica is silica fine particles in which calcium ions are introduced into a fine porous silica carrier by ion exchange. Examples of commercially available calcium ion exchanged silica include SHIELDEX (Shielddex, registered trademark) C303, AC-3, AC-5 (all of which are manufactured by WR Grace & Co.). it can.

  Calcium ions released from calcium ion exchanged silica are involved in electrochemical action and various salt forming actions, and effectively work to improve corrosion resistance. Moreover, the silica fixed in the coating film effectively works to suppress peeling of the coating film in a corrosive atmosphere. The organic solvent-dispersible colloidal silica is also called an organosilica sol, in which silica fine particles having a particle size of about 5 to 120 nm are stably dispersed in an organic solvent such as alcohols, glycols, and ethers. Examples of commercially available products include the OSCAL series (manufactured by Catalyst Kasei Co., Ltd.) and organosols (manufactured by Nissan Chemical Co., Ltd.). Of these, calcium ion exchanged silica fine particles are preferred. Each metal silicate and each silica fine particle can be used as a silicon-containing compound (3) by 1 type or in combination of 2 or more types.

  In the chromium-free primer coating (A), the amount of the chromium-free rust preventive component (A3) is 10 to 150 masses with respect to 100 mass parts of the total solid content of the bisphenol type epoxy resin (A1) and the crosslinking agent (A2). Part, preferably 15 to 90 parts by weight, from the viewpoint of corrosion resistance. Among them, as the chromium-free rust preventive component (A3), the vanadium compound (1), the silicon-containing compound (2) and the phosphate metal salt (3) is preferably within the following range from the viewpoint of improving the corrosion resistance.

Vanadium compound (1): 3 to 50 parts by mass, preferably 5 to 30 parts by mass,
Phosphate metal salt (2): 3 to 50 parts by mass, preferably 5 to 30 parts by mass,
Silicon-containing compound (3): 3 to 50 parts by mass, preferably 5 to 30 parts by mass,
In the coating composition of the present invention, as a rust-preventive pigment mixture, a combination of these (1), (2) and (3) in a predetermined amount can synergistically improve the corrosion resistance, in particular, the corrosion resistance of the blackboard. It is.

  In addition to the bisphenol-type epoxy resin (A1), the crosslinking agent (A2), the chromium-free rust preventive component (A3), and a curing catalyst blended as necessary, the chromium-free primer coating (A) includes an adhesion-imparting agent, Additives such as coloring pigments, extender pigments, organic solvents, anti-settling agents, antifoaming agents, coating surface modifiers, and the like that can be used in the paint field can be blended as necessary.

  Examples of the adhesion-imparting agent include epoxy resins having secondary or tertiary amino groups, and acrylic resins having secondary or tertiary amino groups. The resol type phenol resin described in the section of the crosslinking agent (A2) also has a function as an adhesion imparting agent.

  The epoxy resin having a secondary or tertiary amino group is a resin having an epoxy resin skeleton and a secondary or tertiary amino group. Examples of the epoxy resin skeleton include a bisphenol type epoxy resin skeleton and a novolac epoxy resin. Examples include skeletons.

  The epoxy resin having a secondary or tertiary amino group is, for example, a secondary compound obtained by adding an amine compound to an epoxy group such as a glycidyl group in an epoxy resin such as a bisphenol type epoxy resin, a novolac epoxy resin or a urethane-modified epoxy resin. Alternatively, it can be obtained by introducing a tertiary amino group. As an epoxy resin, it is usually preferable that the epoxy equivalent is 200 to 1,000 from the viewpoint of reactivity with an amine compound, and among them, a bisphenol type epoxy resin and a novolac epoxy resin are preferable.

  When a bisphenol type epoxy resin is used, a secondary or tertiary amino group is usually present in the resin skeleton or at the end by reacting a bisphenol type epoxy resin having an epoxy equivalent of about 400 to 1000 with a primary or secondary amine compound. Can be obtained. When a novolac epoxy resin is used, a novolac epoxy resin having an epoxy equivalent of about 200 to 500 is usually used. However, if it is reacted with a primary amine compound, it is easily gelled in production, and therefore a secondary or tertiary amine having a high amine concentration. When obtaining a novolak type epoxy resin having an amino group, it is usually preferable to react a secondary amine compound such as N-methylethanolamine or diethanolamine with a novolak epoxy resin.

  The acrylic resin having an amino group can be obtained, for example, by reacting an acrylic resin copolymerized with an acrylic monomer having an epoxy group such as glycidyl methacrylate and a primary or secondary amine compound. Moreover, the acrylic resin which copolymerized the acrylate or methacrylate monomer which has tertiary amino groups like N, N- dimethylamino ethyl (meth) acrylate and N, N- dimethylaminopropyl (meth) acrylate may be sufficient.

  Of the adhesion-imparting agents, an epoxy resin system is preferable from the viewpoint of the toughness of the coating film required for scratch resistance and the like, and an acrylic resin system is preferable from the viewpoint of water resistance and chemical resistance. If necessary, two or more kinds of adhesion imparting resins can be used in combination.

  Examples of the colored pigment include organic colored pigments such as cyanine blue, cyanine green, organic red pigments such as azo and quinacridone; and inorganic colored pigments such as titanium white, titanium yellow, bengara, carbon black, and various fired pigments. Among them, titanium white can be preferably used. Examples of the extender pigment include talc, clay, mica, alumina, calcium carbonate, barium sulfate and the like.

  The said organic solvent which can be mix | blended with a chromium free primer coating material (A) is mix | blended as needed, and melt | dissolves thru | or disperse | distributes the bisphenol type | mold epoxy resin (A1) and crosslinking agent (A2) which were modified | denatured with the soft organic component. Specifically, for example, hydrocarbon solvents such as toluene, xylene, high boiling petroleum hydrocarbons, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl acetate , Ester solvents such as ethylene glycol monoethyl ether acetate and diethylene glycol monoethyl ether acetate, alcohol solvents such as methanol, ethanol, isopropanol and butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl Ether, diethylene glycol and ether alcohol-based solvents such as monobutyl ether can be exemplified, which may be used alone or in combination of two or more.

  The coating film formation with the chrome-free primer coating (A) is usually performed by coating the chrome-free primer coating (A) on a metal plate with a roll coater so that the dry film thickness is 1 to 10 μm, preferably 2 to 8 μm. Then, a cured coating film is formed by baking and drying at a material attainable maximum temperature (PMT) of 160 to 250 ° C. for 15 to 180 seconds, particularly PMT of 180 to 230 ° C. for 20 to 120 seconds.

[Top coat (B)]
The method for forming a coating film on a chromium-free coated metal sheet according to the present invention comprises applying a top coating (B) on at least one surface of a cured coating with the chromium-free primer coating (A) and curing it by heating. It is characterized by forming.
The top coating (B) includes a specific hydroxyl group-containing polyester resin (B1), a crosslinking agent (B2) containing a blocked aliphatic isocyanate compound, and a solid content of the resin (B1) and the crosslinking agent (B2). 5 to 120 parts by mass of the pigment component (B3) is contained with respect to 100 parts by mass in total. Hereinafter, each component will be described in detail.

Hydroxyl group-containing polyester resin (B1):
The hydroxyl group-containing polyester resin (B1) used in the present invention comprises the polybasic acid component (b1) and the polyhydric alcohol component (b2) as constituent components, and is based on the total mass of (i) the polybasic acid component (b1). The ratio of at least one polybasic acid selected from hexahydrophthalic anhydride, hexahydroisophthalic acid, and tetrahydrophthalic anhydride is 90 to 100% by mass, preferably 92 to 100% by mass, and further 95 to 100% by mass To do.

  And (ii) 50 to 100 masses of at least one polyhydric alcohol selected from neopentyl glycol, 1,4-cyclohexanedimethanol and hydrogenated bisphenol A, based on the total mass of the polyhydric alcohol component (b2). %, Preferably 70 to 100% by mass, more preferably 85 to 100% by mass. By reacting these specific polybasic acid component (b1) and polyhydric alcohol component (b2), a coating film having particularly excellent coating film hardness, workability, weather resistance and corrosion resistance can be obtained.

  In addition, polybasic acid components (b1) other than hexahydrophthalic anhydride, hexahydroisophthalic acid, and tetrahydrophthalic anhydride are, for example, phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, 1 such as diphenylmethane-4,4′-dicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, het acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid, and anhydrides thereof Examples include compounds having two or more carboxyl groups in the molecule.

  On the other hand, polyhydric alcohol components (b2) other than neopentyl glycol, 1,4-cyclohexanedimethanol and hydrogenated bisphenol A are, for example, ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol. , Dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol, 1,2-pentanediol 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,5-pentanediol, 2,2, 4-trimethyl-1,3- Glycols such as tantalenediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, hydroxypivalic acid neopentyl glycol ester, and the like Lactones such as ε-caprolactone and polyester diols such as bis (hydroxyethyl) terephthalate; glycerin, trimethylolpropane, trimethylolethane, diglycerin, triglycerin, 1,2,6- Examples include hexanetriol, pentaerythritol, dipentaerythritol, dipentaerythritol, sorbitol, mannitol and the like.

  Here, when using at least one polyhydric alcohol component (b2) selected from neopentyl glycol, 1,4-cyclohexanedimethanol and hydrogenated bisphenol A as an essential component, and further using other polyhydric alcohol components, Trimethylolpropane and / or glycerin is also preferable in order to obtain a coating film excellent in coating film hardness, processability, weather resistance and corrosion resistance.

  The number average molecular weight (Note 1) of the hydroxyl group-containing polyester resin (B1) is 1,000 to 35,000, preferably 2,000 to 25,000, hydroxyl value 5 to 80 mgKOH / g, preferably 10 to 70 mgKOH / g. g is preferred. Furthermore, the glass transition temperature (Note 2) of the polyester resin (B) is 5 ° C to 50 ° C, preferably 10 ° C to 40 ° C. By being the said range, the coating film excellent in coating-film hardness, workability, a weather resistance, and corrosion resistance can be obtained.

  (Note 1) Number average molecular weight: Measured by gel permeation chromatography (GPC) using a standard polystyrene calibration curve as described above for the chromium-free primer coating (A).

  (Note 2) Glass transition temperature: Determined by differential scanning thermal analysis (DSC) in the same manner as described above for the chromium-free primer coating (A).

Cross-linking agent (B2) containing a blocked aliphatic polyisocyanate compound and / or a blocked alicyclic polyisocyanate compound:
The top coat (B) of the present invention may be abbreviated as a cross-linking agent (B2) containing a blocked aliphatic polyisocyanate compound and / or a blocked alicyclic polyisocyanate compound (hereinafter referred to as “cross-linking agent (B2)”. The blocked polyisocyanate compound is an addition reaction product of a polyisocyanate compound and a blocking agent.
Here, examples of the aliphatic polyisocyanate compound include ethylene diisocyanate, tetramethylene diisocyanate, and hexamethylene diisocyanate (HDI). Examples of the alicyclic polyisocyanate compound include isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI), and cyclohexylene diisocyanate. Among these, it is preferable to use a blocked product of hexamethylene isocyanate (HDI) as the crosslinking agent (B2) in terms of coating film hardness, workability, weather resistance, and corrosion resistance.

The blocking agent is added to the isocyanate group of the polyisocyanate compound to block, and the blocked polyisocyanate compound produced by the addition is stable at normal temperature, but the baking temperature of the coating film (usually 100 to 200 ° C. It is desirable that the blocking agent can be dissociated to regenerate free isocyanate groups when heated to).
Examples of the blocking agent used in the blocked aliphatic isocyanate compound include oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime; phenol compounds such as phenol, para-t-butylphenol and cresol; n-butanol, 2- Aliphatic alcohols such as ethyl hexanol; Aromatic alkyl alcohols such as phenyl carbinol and methyl phenyl carbinol; Ether alcohol compounds such as ethylene glycol monobutyl ether and diethylene glycol monoethyl ether; ε-caprolactam, γ-butyrolactam, etc. Lactam compounds; and the like.

The ratio of the blocked aliphatic isocyanate compound in the crosslinking agent (B2) is 50 to 100% by mass, preferably 60 to 100% by mass, more preferably 70 to 70% by mass, based on the resin solid content of the crosslinking agent (B2). 100% by mass is also preferable for obtaining a coating film excellent in coating film hardness, workability, weather resistance and corrosion resistance in combination with the specific hydroxyl group-containing polyester resin (B1). Furthermore, a conventionally known blocked polyisocyanate compound, melamine resin, benzoguanamine resin, urea resin and the like can be used in combination with the crosslinking agent (B2).
As a conventionally known blocked polyisocyanate compound, for example, a blocked polyisocyanate compound blocked with an aromatic polyisocyanate by the blocking agent can be used.

  Aromatic polyisocyanates include 1,3- and / or 1,4-phenylene diisocyanate, 2,4- and / or 2,6-tolylene diisocyanate (TDI), 2,4'- and / or 4,4. '-Diphenylmethane diisocyanate (MDI), 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanato Examples include diphenylmethane, 1,5-naphthylene diisocyanate, 4,4 ′, 4 ″ -triphenylmethane triisocyanate, m- and p-isocyanatophenylsulfonyl isocyanate.

Moreover, as a melamine resin which can be used together, some or all of the methylol groups of methylolated melamine are monohydric alcohols having 1 to 8 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n- Examples include partially etherified or fully etherified melamine resins etherified with butyl alcohol, i-butyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like.
These may be used in which all methylol groups are etherified or partially etherified so that methylol groups or imino groups remain.
Examples include alkyl etherified melamines such as methyl etherified melamine, ethyl etherified melamine, and butyl etherified melamine, and only one kind may be used or two or more kinds may be used in combination. Of these, methyl etherified melamine resin in which at least a part of methylol group is alkyl etherified is preferable.

  Examples of such commercially available melamine resins include Cymel 202, Cymel 232, Cymel 235, Cymel 238, Cymel 254, Cymel 266, Cymel 267, Cymel 272, Cymel 285, Cymel 301, Cymel 303, Cymel 325, Cymel 327. Cymel 350, Cymel 370, Cymel 701, Cymel 703, Cymel 1141 (manufactured by Nihon Cytec Industries, Inc.), Uban 20SE60 (manufactured by Mitsui Chemicals, trade name, average polymerization degree exceeding 3) and the like are commercially available. Among these, a melamine resin in which a hydrophilic group (for example, imino group) does not remain is preferable for improving corrosion resistance. For example, a combined use of a methyl etherified melamine resin is good for improving corrosion resistance.

  Here, as a blending ratio of the hydroxyl group-containing polyester resin (B1) and the crosslinking agent (B2), 65 to 95 parts by mass of the hydroxyl group-containing polyester resin (B1), preferably based on 100 parts by mass of the total solid content of both components, preferably Is 70 to 90 parts by mass, 5 to 35 parts by mass, preferably 10 to 30 parts by mass of the crosslinking agent (B2).

Moreover, the ratio of the blocked aliphatic polyisocyanate compound and / or the blocked alicyclic polyisocyanate compound in the crosslinking agent (B2) is preferably 50 to 100% by mass, based on the solid content of the crosslinking agent (B2). Is preferably from 100 to 100% by mass from the viewpoints of coating stability, coating film hardness, processability, weather resistance and corrosion resistance.
The top coat (B) used in the coating film forming method of the present invention contains a pigment component (B3) in addition to the hydroxyl group-containing polyester resin (B1) and the crosslinking agent (B2).

The pigment component (B3) is usually used in the paint field, for example, white pigments such as titanium white and zinc white; blue pigments such as cyanine blue and indanthrene blue; green pigments such as cyanine green and patina; azo Organic red pigments such as quinacridone and red pigments such as Bengala; organic yellow pigments such as benzimidazolone, isoindolinone, isoindoline and quinophthalone, yellow pigments such as titanium yellow and yellow lead; carbon black Black pigments such as graphite, pine smoke; Luminous pigments such as aluminum powder, copper powder, nickel powder, titanium oxide-coated mica powder, iron oxide-coated mica powder and glittering graphite. And extender pigments such as clay, talc, barita, calcium carbonate, silica;
The blending amount of the pigment component (B3) is 5 to 120 parts by mass from the viewpoint of weather resistance, workability, and corrosion resistance with respect to 100 parts by mass of the solid content of the hydroxyl group-containing polyester resin (B1) and the crosslinking agent (B2). Preferably it is used in the range of 10-100 parts by mass, more preferably 20-80 parts by mass.

  In addition to the hydroxyl group-containing polyester resin (B1), the cross-linking agent (B2), and the pigment component (B3), the top coating material (B) includes a curing catalyst, an antifoaming agent, a surface conditioner, and organic resin fine particles as necessary. Further, additives such as a solvent, an ultraviolet absorber and a light stabilizer may be contained.

The organic resin fine particles blended in the top coat (B) are not completely melted by baking at the time of coating film formation, and do not contain a color pigment in the resin fine particles. Examples of the resin species include fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyamides, acrylic resins, polyurethanes, phenol resins, silicone resins, polypropylene, and polyamides such as nylon 11 and nylon 12. .
Specifically, Techpolymer MBX-12 (manufactured by Sekisui Plastics Co., Ltd., average particle size 12 μm, acrylic resin), Techpolymer MBX-15 (manufactured by Sekisui Plastics Kogyo Co., Ltd., average particle size 15 μm, acrylic resin) , Techpolymer MBX-20 (manufactured by Sekisui Plastics Co., Ltd., average particle size 20 μm, acrylic resin), techpolymer MB30X-20 (manufactured by Sekisui Plastics Co., Ltd., average particle size 20 μm, acrylic resin), techpolymer BM30X -20 (manufactured by Sekisui Plastics Co., Ltd., average particle size 20 μm, acrylic resin), Diasphere MPB-X10 (manufactured by KOLON, trade name, average particle size 10 μm, acrylic resin).

  The compounding amount of the organic resin fine particles in the top coat (B) is 1 to 40 parts by mass, preferably 2 to 15 parts by mass, based on 100 parts by mass in total of the solid content of the hydroxyl group-containing polyester resin (B1) and the crosslinking agent (B2). It is suitable from the viewpoint of paint stability and workability.

  The solvent blended in the top coat (B) is blended as necessary for improving paintability, and can be used to dissolve or disperse the film-forming resin component. Specifically, For example, hydrocarbon solvents such as toluene, xylene, high boiling petroleum hydrocarbons, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, diethylene glycol mono Ester solvents such as ethyl ether acetate, alcohol solvents such as methanol, ethanol and butanol, ether alcohol systems such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether and diethylene glycol monobutyl ether Agents, etc. can be mentioned water, which may be used alone or in combination of two or more.

  The curing catalyst is blended as necessary to accelerate the curing reaction with the hydroxyl group-containing polyester resin (B1) and the crosslinking agent (B2), and is appropriately selected according to the type of the crosslinking agent (B2). Can be used.

  When a melamine resin is used in combination with the cross-linking agent (B2), an acid catalyst such as sulfone is used as a curing catalyst, particularly in the case of a low molecular weight methyl etherated or mixed etherified melamine resin of methyl ether and butyl ether. An amine neutralized product of an acid compound or a sulfonic acid compound is preferably used. Representative examples of the sulfonic acid compound include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, and the like. The amine in the amine neutralized product of the sulfonic acid compound may be any of primary amine, secondary amine, and tertiary amine. Among these, the amine neutralized product of p-toluenesulfonic acid and / or the amine neutralized product of dodecylbenzenesulfonic acid is preferable from the viewpoints of the stability of the coating, the reaction promoting effect, and the physical properties of the resulting coating film. For the crosslinking agent (B2) containing the blocked aliphatic polyisocyanate compound and / or the blocked alicyclic polyisocyanate compound, a curing catalyst that promotes dissociation of the blocking agent can be suitably used. For example, octyl Tin oxide, dibutyltin di (2-ethylhexanoate), dioctyltin di (2-ethylhexanoate), dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, tetra-n-butyl-1,3-di And organometallic catalysts such as acetoxy distanoxane. Among these, tetra-n-butyl-1,3-diasecitodistanoxane is preferable from the viewpoints of curability and corrosion resistance.

  The curing catalyst is 0.1 to 5.0 parts by mass, preferably 0.2 to 1.5 parts by mass, based on 100 parts by mass of the total solid content of the hydroxyl group-containing polyester resin (B1) and the crosslinking agent (B2). Is suitable from the viewpoint of improving the stability of the paint and the hardness of the coating film.

Moreover, in order to improve a weather resistance, in order to improve a weather resistance, either one or both of an ultraviolet absorber and a light stabilizer can be added to a top coating material (B) to a coating composition.
Examples of such ultraviolet absorbers include benzotriazole, triazine, anilide, benzophenone, oxalate anilide, and cyanoacrylate. Commercially available products include “Tinuvin 1130” and “Tinuvin 400” (above, Ciba Specialty). Chemicals), “CYASORBUV-1164L” (Nippon Cytec Industries), “SANDUVOR3206” (Clariant). As a light stabilizer, a hindered amine type is suitable, and as commercially available products, “Tinuvin 123”, “Tinuvin 144” (above, manufactured by Ciba Specialty Chemicals), “Sanol LS-292” (manufactured by Sankyo Lifetech) ) Can be exemplified.

  The top coating (B) is applied by coating the top coating (B) on the cured coating of the chromium-free primer coating (A) by a curtain coating method or a roll coating method, and a cured film thickness of 5 to 30 μm, preferably 10 It is coated to be ~ 20 μm, and within the range of 15 to 180 seconds at a material maximum temperature (PMT) 160 to 250 ° C., particularly within a range of 20 to 120 seconds at a material maximum temperature (PMT) 180 to 230 ° C. A dry coating film is formed by baking and drying under conditions. By the above process, a multilayer coating film in which the coating film of the top coating (B) is formed on the coating film of the chromium-free primer coating (A) is obtained.

The Young's modulus of the single film of the top coat (B) is 20,000 kgf / cm ² or more, preferably 22,000 to 30,000 kgf / cm ² , and the elongation is 4% or more, preferably 5% or more. It is considered that no coating film physical properties are obtained, which contributes to the improvement of the coating film performance.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited at all by the following examples, unless the summary is exceeded. Hereinafter, both “parts” and “%” are based on mass.

[Production example of chromium-free primer coating (A)]
Synthesis Example 1 Production of acrylic resin AC1 solution (acrylic resin (a12))
65.0 parts of Swazol 1000 (manufactured by Maruzen Petrochemical Co., Ltd., high-boiling aromatic petroleum solvent) was added to a flask equipped with a stirrer, condenser, thermometer, nitrogen inlet tube and dropping device, and reacted while stirring. The temperature in the container was raised to 110 ° C., and a mixture of raw materials such as monomers shown below was added dropwise over 3 hours while maintaining the temperature at 110 ° C.

Styrene 18.4 parts Methyl methacrylate 31.2 parts N-butyl acrylate 37.5 parts 2-hydroxyethyl acrylate 11.0 parts Acrylic acid 1.9 parts 2,2'-Azobisisobutyronitrile 7 parts After the completion of dropping, 0.5 parts of 2,2′-azobisisobutyronitrile was further added, and the reaction was further continued for 2 hours at the same temperature. Then, 35.0 parts of cyclohexanone was added, and the solid content was 50%. A soft acrylic resin AC1 solution was obtained. The acrylic resin AC1 had an acid value of 15 mgKOH / g, a hydroxyl value of 53 mgKOH / g, a glass transition temperature of 5 ° C., and a number average molecular weight of about 10,000.

Synthesis Example 2 Polyester resin PE1 solution (Polyester resin (a13))
The following raw material mixture was put into a reactor equipped with a stirrer, a heating device, a thermometer, a separation device, and a distillate storage tank, and heating was started.

Neopentyl glycol 729 parts Hexahydrophthalic anhydride 704 parts After stirring, when stirring became possible, stirring was started, the temperature was raised to 240 ° C while removing condensed water, and the reaction was continued at the same temperature. When the outflow of water stopped after about 1.5 hours, 40 parts of xylene was added to promote the reaction, dehydration condensation was continued, and the reaction was carried out until the acid value reached 51 mgKOH / g. Next, the mixture was cooled, and 417 parts of cyclohexanone was added for dilution to obtain a polyester resin PE1 solution having a solid content of 70%. The obtained polyester resin PE2 had a glass transition temperature of 30 ° C. and a number average molecular weight of 2,200.

Synthesis Example 3 Production of Modified Bisphenol Type Epoxy Resin ME1 Solution In a flask equipped with a stirrer, a condenser, and a thermometer, 43 parts of cyclohexanone and 70 parts of jER1004 (Note 3) (solid content) were blended and heated to a temperature of 130 ° C. After confirming that the epoxy resin was dissolved, 15.0 parts of dimer acid, 30 parts of the 50% soft acrylic resin AC1 solution obtained in Synthesis Example 1 (15 parts in solid content) and 0.5 part of tetraethylammonium bromide were added. In addition, the temperature was maintained at 130 ° C. and reacted for 3 to 4 hours. Confirming that the resin acid value is 1 mgKOH / g or less, mixed solvent 1 [cyclohexanone / swazol 1000 (manufactured by Maruzen Petrochemical Co., Ltd., high boiling aromatic petroleum solvent) = 1/2 (mass ratio)] In addition, a resin solution ME1 having a solid content of 40% was obtained.

  (Note 3) jER1004: bisphenol A type epoxy resin manufactured by Japan Epoxy Resin, epoxy equivalent of about 925.

Synthesis Example 4 Production of Modified Bisphenol Type Epoxy Resin ME2 Solution In a flask equipped with a stirrer, a condenser and a thermometer, 60 parts of cyclohexanone and 70 parts of jER4004P (Note 4) (solid content) were blended and heated to a temperature of 130 ° C. The epoxy resin was dissolved. After confirming that the epoxy resin was completely dissolved, 15.0 parts of dimer acid, 21.4 parts of a polyester resin PE1 solution with a solid content of 70% obtained in Synthesis Example 2 (solid content 15 parts) and tetraethyl bromide 0.5 part of ammonium was added, and the temperature was maintained at 130 ° C. and reacted for 3 to 4 hours. Confirming that the resin acid value is 1 mgKOH / g or less, mixed solvent 1 [cyclohexanone / swazol 1000 (manufactured by Maruzen Petrochemical Co., Ltd., high boiling aromatic petroleum solvent) = 1/2 (mass ratio)] In addition, a resin solution ME2 having a solid content of 40% was obtained.

  (Note 4) jER4004P: manufactured by Japan Epoxy Resin Co., Ltd., trade name, bisphenol F type epoxy resin, epoxy equivalent of about 880.

Synthesis Example 5 Production of acrylic resin AC2 solution
100 parts of propylene glycol monomethyl ether was put into a reaction vessel equipped with a stirrer, a thermometer and a cooler, and the temperature in the reaction vessel was raised to 80 ° C. while stirring. While maintaining the temperature at 80 ° C., a mixture of raw materials such as monomers shown below was added dropwise over 3 hours, and the mixture was further aged at the same temperature for 3 hours to obtain an acrylic resin AC2 solution having a solid content of 35%.
The acrylic resin AC2 had an acid value of 0 mgKOH / g, a hydroxyl value of 120 mgKOH / g, a glass transition temperature of 11 ° C., and a number average molecular weight of about 10,000.

2-hydroxyethyl acrylate 15.0 parts 2-hydroxyethyl methacrylate 11.0 parts styrene 20.0 parts methyl methacrylate 27.0 parts n-butyl acrylate 27.2 parts 2,2'-azobisisobutyronitrile 1 .5 parts 85.7 parts propylene glycol monomethyl ether.

Synthesis Example 6 Synthesis of Polyester Resin PE2 Solution The following raw material mixture was placed in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, etc., heated from 160 ° C. to 230 ° C. over 3 hours, and produced water. Was distilled off through a rectification column. After maintaining at 230 ° C. for 1 hour, xylol was added and dehydration was performed while refluxing the xylol at 230 ° C. to conduct an esterification reaction.

Ethylene glycol 55.8 parts Neopentyl glycol 10.5 parts Isophthalic acid 157.7 parts When the acid value reached about 0 mg KOH / g, it was cooled to 140 ° C and held for 2 hours. After cooling, Swazol 1500 (Maruzen Petrochemical ( Co., Ltd., high-boiling aromatic petroleum solvent) was added to obtain a polyester resin PE2 solution having a solid content of 35%. The obtained resin had a number average molecular weight of 3,800, a glass transition temperature of 45 ° C., and a hydroxyl value of 30 mgKOH / g.

Synthesis Example 7 Production of resol type phenol resin D solution
In a reaction vessel, 100 parts of p-cresol, 178 parts of a 37% aqueous formaldehyde solution and 1 part of sodium hydroxide were blended and reacted at 60 ° C for an hour, and then dehydrated at 50 ° C for 1 hour under reduced pressure.
Subsequently, 100 parts of n-butanol and 3 parts of phosphoric acid were added and reacted at 110 to 120 ° C. for 2 hours. After completion of the reaction, the sodium phosphate produced by filtering the resulting solution was filtered off to obtain a resol type phenolic resin D solution having a solid content of 50% by mass. The obtained resin had a number average molecular weight of 880, an average number of methylol groups per benzene nucleus of 0.4, and an average number of alkoxymethyl groups of 1.0.

Synthesis Example 8 Production of amino group-containing epoxy resin D solution In a reaction vessel equipped with a stirrer and a heating / temperature control device, 65 parts by weight of methoxybutyl acetate solvent, 35 parts of jER1002 (Note 5), 1.09 of 2-aminoethanol The reaction was carried out for 2 hours with stirring and stirring at 90 ° C. under a nitrogen atmosphere. Next, 1.89 parts of diethanolamine was added, and the reaction was further carried out at 90 ° C. for 1 hour, followed by dilution with a methoxybutyl acetate solvent to obtain an amino group-containing epoxy resin D solution having a solid content of 35%.

  (Note 5) jER1002: bisphenol A type epoxy resin manufactured by Japan Epoxy Resin Co., Ltd., trade name, epoxy equivalent 650.

Production Example A Production of backside paint
jER1009F (Note 6) 80 parts mixed solvent 2 [cyclohexanone / ethylene glycol monobutyl ether / swazol 1500 (manufactured by Maruzen Petrochemical Co., Ltd., high boiling aromatic hydrocarbon solvent) = 3/1/1 (mass ratio)] An appropriate amount of 40 parts of titanium white, 40 parts of varita and mixed solvent 2 [Swazole 1500 / cyclohexanone = 1/1 (mass ratio)] was mixed with 200 parts of the epoxy resin solution dissolved in 120 parts, and a tube (pigment coarse particles The pigment dispersion was carried out until the particle diameter of the particle was 20 μm or less.
Next, 26.7 parts of Sumidur BL-3175 (Note 7) (20 parts in solid content) and 2 parts of Formate TK-1 (Note 8) were added to this dispersion and mixed uniformly. Further, the above mixed solvent 2 was added to adjust the viscosity to about 80 seconds (Ford Cup # 4/25 ° C.) to obtain a paint for the back surface.

  (Note 6) jER1009F: manufactured by Japan Epoxy Resin Co., Ltd., bisphenol A type epoxy resin, epoxy equivalent of about 2,000.

Production example of chromium-free primer paint A Production example 1 (corresponding to Example)
To 80 parts (solid content) of a bisphenol-type epoxy resin ME1 modified with the soft organic component obtained in Synthesis Example 3, 20 parts of vanadium pentoxide, 20 parts of calcium phosphate, 20 parts of calcium metasilicate, 20 parts of titanium white, and barita 20 Part and mixed solvent 3 [swazol 1500 / cyclohexanone = 1/1 (mass ratio)] were mixed in an appropriate amount, and pigment dispersion was performed until the tub (particle diameter of the coarse pigment particles) became 20 μm or less.
Next, 20 parts (solid content) of Sumidur BL-3175 (Note 7) in this dispersion, 5 parts (solid content) of the resol type phenol resin D obtained in Synthesis Example 7, and the amino group content obtained in Synthesis Example 8 25 parts of epoxy resin D (solid content) and 2 parts of formate TK-1 (Note 8) were added and mixed uniformly. Further, the above mixed solvent 3 was added and the viscosity was about 80 seconds (Ford Cup # 4/25 ° C. ) Primer paint No. 1 was obtained.

Production Examples 2 to 12 (equivalent to Examples)
Production Example 1 was carried out in the same manner as Production Example 1 except that it was as shown in Table 1. 2-No. 7 was obtained.

Comparative production example 1
Production Example 1 was carried out in the same manner as Production Example 1 except that it was as shown in Table 1. 8 was obtained.

  (Note 7) Sumidur BL-3175: Sumika Bayer Urethane, trade name, blocked hexamethylene diisocyanate.

  (Note 8) Formate TK-1: manufactured by Mitsui Chemicals Polyurethanes, trade name, organotin blocking agent dissociation catalyst, solid content of about 10%.

  (Note 9) jER1007: manufactured by Japan Epoxy Resin Co., Ltd., bisphenol A type epoxy resin, epoxy equivalent of about 1,800.

  (Note 10) Ca ion exchange silica: R. Grace & Co. SHIELDEX (Shielddex, registered trademark) C303 manufactured by the company.

[Production example of top coat (B)]
Synthesis Example 9 Hydroxyl-containing polyester resin 1 Synthesis Example To a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser and water separator,
The following “monomer mixture” was charged, and the temperature was raised from 160 ° C. to 230 ° C. over 3 hours. Then, the condensed water was distilled off with a water separator and maintained at 230 ° C. for 1 hour, and then xylene was refluxed. While dehydrating, the esterification reaction was carried out.
Hexahydrophthalic anhydride 146.3 parts Neopentyl glycol 105.0 parts When the acid value reached about 0, it was cooled to 140 ° C and held for 2 hours. After cooling, the solid content was adjusted with cyclohexanone to obtain a solid content of 55 % Hydroxyl group-containing polyester resin No. 1 1 was obtained.
The obtained hydroxyl group-containing polyester resin No. The hydroxyl value of 1 was 24.0 mgKOH / g, the glass transition temperature was 22.0 ° C., and the number average molecular weight was 2,300.

Synthesis Examples 10-19 Hydroxyl-containing polyester resin solution No. 2-No. 11 synthesis examples (equivalent to examples)
A polyester resin solution No. 1 was prepared in the same manner as in Synthesis Example 9 except that the content of the monomer mixture shown in Tables 2 and 3 was used. 2-No. 11 was obtained.

Synthesis Examples 20 to 26 Hydroxyl-containing polyester resin solution No. 12-No. 18 synthesis examples (equivalent to comparative examples)
A hydroxyl group-containing polyester resin solution No. 1 was prepared in the same manner as in Synthesis Example 9 except that the content of the monomer mixture shown in Table 4 was used. 12-No. 18 was obtained.

[Manufacture of top coat]
Production Example 8 Topcoat No. 1 production (equivalent to Example)
Hydroxyl-containing polyester resin No. 1 obtained in Synthesis Example 9 1 solution 80 parts (solid content), CR-93 (note 16) 24 parts, Mitsubishi carbon MA-100 (note 17) 0.2 parts, Todacolor KN-V (note 18) 2.6 parts, No. 700 -10FG CYBLUE (Note 19) 5.5 parts, LIONOL GREEN 8930 (Note 20) 2.7 parts and an organic solvent (swazol 1500 / cyclohexanone = 40/60 mixed solvent) are mixed in an appropriate amount, and The pigment dispersion was performed until the particle diameter was 10 μm or less.
Next, 20 parts (solid content) of Sumidur BL3175 (Note 7) and 0.2 part of Formate TK-1 (Note 8) were added to this dispersion and mixed uniformly to obtain an organic solvent (Swazole 1500 / cyclohexanone = 40). / 60 mixed solvent) and diluted, and the top coating No. of viscosity 80 seconds (Ford Cup # 4, 25 ° C.). 1 was obtained.

Production Examples 9 to 23 2-No. 16 production (equivalent to the example)
Except for the contents of Table 5 and Table 6, the top coat paint No. 2-No. 16 was obtained.

  (Note 11) Takenate B830: Mitsui Chemicals Polyurethanes, trade name, tolylene diisocyanate blocked isocyanate.

  (Note 12) Takenate B870N: Mitsui Chemicals Polyurethanes, trade name, isophorone diisocyanate-based blocked isocyanate.

  (Note 13) Takenate B842N: trade name, xylylene diisocyanate-based blocked isocyanate, manufactured by Mitsui Chemicals Polyurethanes, Inc.

  (Note 14) Cymel 303: Nippon Cytec Industries, trade name, methyl etherified melamine resin.

  (Note 15) Cymel 701: Product name, methylol / imino group melamine resin, manufactured by Nippon Cytec Industries, Ltd.

  (Note 16) CR-93: manufactured by Ishihara Sangyo Co., Ltd., trade name, titanium white.

  (Note 17) Mitsubishi Carbon MA-100: trade name, carbon black, manufactured by Mitsubishi Chemical Corporation.

  (Note 18) Toda Color KN-V: Toda Kogyo Co., Ltd., trade name, iron oxide bengara.

  (Note 19) No. 700-10FG CYBLUE: manufactured by Toyo Ink Manufacturing Co., Ltd., trade name, blue organic pigment.

  (Note 20) LIONOL GREEN 8930: Toyo Ink Manufacturing Co., Ltd., trade name, green organic pigment.

  (Note 21) Necure 5225: King Industries, Inc. (USA), trade name, amine-neutralized solution of dodecylbenzenesulfonic acid.

  (Note 22) Tinuvin 400: manufactured by Ciba Specialty Chemicals, trade name, UV absorber.

  (Note 23) Sanol LS292: Sankyo Life Tech Co., Ltd., trade name, light stabilizer.

Comparative Production Examples 2 to 15 17-No. Production of 30 (equivalent to comparative example)
Except for the contents of Table 7 and Table 8, the top coat No. 17-No. 30 was obtained.

Example 1 Painted metal plate No. 1 Create 1
The primer paint No. obtained in Production Example 1 was applied on a hot-dip galvanized steel sheet having a thickness of 0.5 mm × 70 mm × 150 mm subjected to zinc phosphate treatment. No. 1 was coated so that the dry film thickness was about 5 μm, and baked for 30 seconds so that the maximum material reached temperature was 220 ° C. to obtain a primer-coated metal plate.
On the above-mentioned primer-coated metal plate, the top coating paint No. obtained in Production Example 8 was used. No. 1 was coated with a roll coater to a dry film thickness of 20 μm and baked for 60 seconds at a maximum material reaching temperature of 190 ° C. 1 was obtained.

Examples 2 to 22 Painted metal plate No. 2-No. No. 22 The coated metal plate No. 22 was prepared in the same manner as in Example 1 except that the paint contents and heat curing conditions in Table 9 and Table 10 were used. 2-No. 22 was obtained. Since the test according to the following test conditions was conducted, the results are also shown.

Comparative Examples 1-14
A coated metal plate No. 1 was prepared in the same manner as in Example 1 except that the coating contents and heat curing conditions in Tables 11 and 12 were used. 23-No. 36 was obtained. Since the test according to the following test conditions was conducted, the results are also shown.

（注２４）加工性：２０℃の室内において、塗装板の塗膜表面を外側にして折曲げ、その内側に何も挟まずに上記塗装板を万力にて１８０度折曲する４Ｔ折曲げ加工（塗装板の表面側を外側にして折り曲げ、その内側に塗装板と同じ厚さの板を４枚挟み、上記塗装板を万力にて１８０度折り曲げする加工）を行ったときの折曲げ部の塗膜状態を下記基準にて評価した。
◎は、加工部に、塗膜の異常が全く認められない、
○は、加工部に塗膜のワレの発生及び塗膜の剥がれの両方又は一方がわずかに認められる、
△は、加工部に塗膜のワレの発生及び塗膜の剥がれの両方又は一方がかなり認められる、
×は、加工部に塗膜のワレの発生及び塗膜の剥がれの両方又は一方が著しく認められる。

(Note 24) Workability: In a room at 20 ° C., 4T bending in which the coating plate surface of the painted plate is folded outward and the coated plate is folded 180 degrees in a vise without interposing anything inside. Bending when processing (processing to bend with the front side of the coated plate on the outside, sandwiching four plates with the same thickness as the painted plate inside and bending the painted plate 180 degrees in a vise) The coating state of the part was evaluated according to the following criteria.
◎ indicates that no abnormality of the coating film is observed in the processed part.
○, both or one of the occurrence of cracking of the coating film and peeling of the coating film is slightly observed in the processed part,
△ indicates that both or one of the occurrence of cracking of the coating film and peeling of the coating film is considerably observed in the processed part.
In the case of x, both or one of occurrence of cracking of the coating film and peeling of the coating film is remarkably observed in the processed part.

(Note 25) Accelerated weather resistance:
Long-term durability of paint film specified in JIS K 5600 7.7 60 degree mirror surface of paint film tested based on accelerated weathering (xenon lamp method) A method until irradiation time reaches 2,000 hours The gloss retention (%) with respect to the initial gloss measured by glossiness was examined.
◎: Gloss retention exceeds 70% ○: Gloss retention exceeds 50% and 70% or less △: Gloss retention exceeds 30% and 50% or less ×: Gloss retention is less than 30%.

(Note 26) Weather and corrosion resistance test:
Based on A method of the long-term durability accelerated weather resistance (xenon lamp method) test specified in JIS K 5600 7.7 on a test paint plate cut to a size of 5 cm × 10 cm (wet for 18 minutes) Xenon weatherometer was continuously irradiated for 500 hours under the repeated cycle conditions (drying for 102 minutes).
Next, a cross cut with a narrow angle of 30 degrees and a line width of 0.5 mm reaching the substrate is put in the center of the surface side of each test paint plate using the back of the cutter knife, and JASO M609-91 (automobile material corrosion test) 1991), a combined cycle corrosion test (CCT test) was conducted by the following formula: “(35 ° C., 5% saline spray 2 hours) — (60 ° C., 4 hours, relative humidity 95%) — (50 ° C., wet 2 hours) The test was performed for 150 cycles (total of 1200 hours), with "humidity 95%)" as one cycle.
・ Plane part (B rank or higher is accepted)
A: No blistering, etc. No abnormality B: Small blister (less than 3 mm in diameter) is less than 1 to 10 points and no blistering is 3 mm or more in diameter C: Small blister (less than 3 mm in diameter) is 10 or more points Or, one or more bulges with a diameter of 3 mm or more
The average value of the edge creep width on the left and right sides of the long side of the painted plate was determined and evaluated according to the following criteria. ◎ is less than 5mm,
○ is 5 mm or more and less than 10 mm,
Δ is 10 mm or more and less than 20 mm,
X is 20 mm or more.
・ Cross cut part The corrosion state of the cross cut part is determined by the average ratio of the white rust occurrence length in the bare metal exposed part of 0.5 mm cut width and the left and right swelling width (sum of both sides) of the cut part. Evaluation based on the criteria.
◎ indicates that the white rust generation length ratio in the bare metal exposed portion is less than 50% and the swelling width is less than 3 mm,
○ is a white rust occurrence length ratio of 50% or more at the bare metal exposed portion and less than 3 mm in the bulge width, or a white rust occurrence length ratio of less than 50% in the bare metal exposed portion and the bulge width of 3 mm or more and less than 5 mm,
Δ is a white rust occurrence length ratio of 50% or more in the bare metal exposed part and a swelling width of 5 mm or more and less than 10 mm,
X indicates a white rust generation length ratio of 50% or more in the bare metal exposed portion and a swelling width of 10 mm or more.

  It is possible to provide a chromium-free coated metal plate having excellent coating film appearance, coating film hardness, workability, weather resistance, and corrosion resistance.

Claims (6)

A primer having a dry film thickness of 1 to 10 μm by a chromium-free primer coating (A), which does not contain a chromium-based rust preventive component on one or both surfaces of a metal plate which may be subjected to chemical conversion treatment on the surface A cured coating film is formed, and an overcoat paint (B) having the following characteristics is applied to at least one surface of the primer cured coating film and heat-cured to form a top-coated cured film having a dry film thickness of 5 to 30 μm. A method for forming a coating film on a chromium-free painted metal sheet.
Top coat (B):
A hydroxyl group-containing polyester resin (B1) comprising the polybasic acid component (b1) and the polyhydric alcohol component (b2) as constituent components, i) based on the total mass of the polybasic acid component (b1),
The total proportion of polybasic acid selected from hexahydrophthalic anhydride, hexahydroisophthalic acid, tetrahydrophthalic anhydride is 90 to 100% by mass, and (ii) based on the total mass of the polyhydric alcohol component (b2), A polyhydric alcohol component having a total ratio of polyhydric alcohol selected from neopentyl glycol, 1,4-cyclohexanedimethanol and hydrogenated bisphenol A of 50 to 100% by mass, the polybasic acid component (b1) and A hydroxyl group-containing polyester resin (B1) obtained by reacting with the polyhydric alcohol component (b2), a crosslinking agent (B2) containing a blocked aliphatic polyisocyanate and / or a blocked alicyclic polyisocyanate compound, and The pigment component (B3) is added to 100 parts by mass of the solid content of the resin (B1) and the crosslinking agent (B2). 120 parts by topcoating containing paint The polyhydric alcohol component (b2) contains at least one compound selected from neopentyl glycol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, and at least one compound selected from trimethylolpropane and glycerin. It contains, The coating-film formation method of the chromium free coating metal plate of Claim 1 characterized by the above-mentioned. The method for forming a coating film on a chromium-free coated metal sheet according to claim 1 or 2, wherein the crosslinking agent (B2) is a blocked product of hexamethylene diisocyanate. Chromium-free primer paint (A) is an aliphatic polybasic acid (a11) having 4 to 36 carbon atoms, an acrylic resin (a12) having a glass transition temperature of -20 to 50 ° C, and a polyester resin having a glass transition temperature of -20 to 50 ° C. A chromium-free primer coating containing a bisphenol-type epoxy resin (A1) modified with at least one soft organic component of (a13), a crosslinking agent (A2), and a chromium-free rust preventive component (A3). The coating-film formation method of the chromium free coating metal plate of any one of 1-3. The chromium-free rust preventive component (A3) is at least one vanadium compound (1) of vanadium pentoxide, calcium vanadate and ammonium metavanadate (1), metal phosphate (2), metal silicate and silica fine particles The method for forming a coating film on a chromium-free coated metal sheet according to any one of claims 1 to 4, comprising at least one silicon-containing compound (3). The coating metal plate obtained by the coating-film formation method of the chromium free coating metal plate of any one of Claims 1-5.