JP5665845B2 - Coated galvanized steel sheet with excellent white rust resistance - Google Patents

Description

  The present invention relates to a coating-formed galvanized steel sheet having a multilayer coating film formed on both the front and back surfaces, which is excellent in rust prevention by a non-chromic coating composition, and more particularly, white rust resistance of processed parts and end face parts. The present invention relates to a galvanized steel sheet with excellent coating properties.

  Conventionally, coating-formed galvanized steel sheets such as pre-coated steel sheets painted by coil coating, etc. are used for building materials such as roofs, walls, shutters, garages, various home appliances, switchboards, refrigerated showcases, steel furniture and Widely used as housing-related products such as kitchen appliances.

  In order to manufacture these housing-related products from a coating-formed galvanized steel sheet, the coating-formed galvanized steel sheet such as a pre-coated steel sheet 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 exposed metal part and crack generating part are less likely to have corrosion resistance than other parts. Therefore, in order to improve the corrosion resistance, chrome-based rust preventive pigment should be included in the undercoat film of the galvanized steel sheet. However, chromium-based anti-corrosion pigments contain or produce hexavalent chromium with excellent anti-rust properties, and this hexavalent chromium is good for human health and environmental protection. It is a problem from the point of view.

  Until now, various coating compositions that combine non-chromium pigments and various metal materials having good corrosion resistance in which a coating film is formed by applying the coating composition have been proposed.

  For example, Patent Document 1 describes a coating composition in which a specific amount of a specific vanadium compound, a specific metal silicate, and a specific metal hydrogen phosphate are blended as a rust preventive pigment in a hydroxyl group-containing film-forming resin. Has been.

  Patent Document 2 discloses an anticorrosive coating composition containing a predetermined amount of a specific vanadium compound, a specific silicon-containing material, and a phosphate calcium salt as a rust preventive pigment in a hydroxyl group-containing film-forming resin. A coating-forming metal material in which a rust coating film is formed on both front and back surfaces of a metal material is described.

However, although the metal material on which the coating film by the coating composition described in Patent Documents 1 and 2 is formed has generally good corrosion resistance, particularly when the metal material is a galvanized steel sheet, a chromium-based pigment Compared with a metal material on which a coating film is formed by a coating composition using, white rust is conspicuous at the initial use, and the suppression thereof is insufficient.

JP 2008-291160 A JP 2000-266444 A

  The object of the present invention is that a coating film made of a non-chrome coating composition is formed on both the front and back surfaces, and not only the corrosion resistance of the flat portion, but also the outstanding white rust resistance of the processed portion and the end surface portion, which is particularly noticeable in the initial stage of use. It is to provide a coating-formed galvanized steel sheet.

  As a result of earnest research to solve the above problems, the present inventors have formed a coating film on both the front and back surfaces, and at least one lowermost layer on the front and back surfaces, a rust preventive pigment is added to the hydroxyl group-containing film forming resin. In a coating film-forming galvanized steel sheet in which a coating film is formed from a coating composition containing a predetermined amount, at least one uppermost layer on the front and back surfaces, a hydroxyl group-containing coating film-forming resin, a metal silicate and a metal ion exchange silica At least one compound selected from the group consisting of: at least one resin selected from the group consisting of a phosphate group-containing film-forming resin and a phosphate group-containing film-forming resin; and / or an azole compound. It has been found that the above-mentioned problems can be solved by forming a coating film with a coating composition containing a predetermined amount, and the present invention has been completed.

That is, the present invention provides the following items:
Item 1. A coating film-formed galvanized steel sheet in which a multilayer coating film is formed on the surface of a galvanized steel sheet and a single layer or multilayer coating film is formed on the back surface,
A coating layer formed of the following coating composition (I) is formed on at least one lowermost layer of the front and back surfaces, and a coating layer of the following coating composition (II) is formed on at least one uppermost layer of the front and back surfaces. Film-formed galvanized steel sheet.

Coating composition (I) : A coating composition containing (A) a hydroxyl group-containing film-forming resin, (B) a crosslinking agent, and (C) a rust preventive pigment, wherein the resin (A) and the crosslinking agent ( The coating composition whose quantity of a rust preventive pigment (C) is 10-150 mass parts with respect to 100 mass parts of total solid content of B).

Coating composition (II) : A coating composition comprising (A) a hydroxyl group-containing film-forming resin and (B) a crosslinking agent,
Further, (Da) contains at least one compound selected from the group consisting of metal silicates and metal ion exchanged silica, and the total solid content of 100 parts by mass of the resin (A) and the crosslinking agent (B) On the other hand, the amount of the compound (Da) is 3 to 50 parts by mass,
(Db) containing at least one resin selected from the group consisting of a phosphate group-containing film-forming resin and a phosphate group-containing film-forming resin, and the resin (A) and the crosslinking agent (B ) To 100 parts by mass of the total solid content, the amount of the resin (Db) is 5 to 30 parts by mass, or (Dc) contains an azole compound and the resin (A) and the crosslinking agent (B The coating composition whose amount of azole compound (Dc) is 2 to 30 parts by mass with respect to 100 parts by mass of the total solid content.

  Item 2. Item 2. The coating film-formed galvanized steel sheet according to item 1, wherein the zinc content in the galvanized steel sheet is 10% by mass or more.

  Item 3. Item 3. The coating film-formed galvanized steel sheet according to Item 1 or 2, wherein the hydroxyl group-containing coating film-forming resin (A) is at least one selected from the group consisting of a hydroxyl group-containing polyester resin and a hydroxyl group-containing epoxy resin.

  Item 4. Item 4. The coating film-formed galvanized steel sheet according to Item 3, wherein the hydroxyl group-containing coating film-forming resin (A) of the coating composition (II) is a hydroxyl group-containing polyester resin.

  Item 5. Item 5. The crosslinking agent according to any one of Items 1 to 4, wherein the crosslinking agent (B) is at least one crosslinking agent selected from the group consisting of an amino resin, a phenol resin, and an optionally blocked polyisocyanate compound. Film-formed galvanized steel sheet.

  Item 6. The rust preventive pigment (C) is (1) at least one vanadium compound selected from the group consisting of vanadium pentoxide, calcium vanadate, ammonium metavanadate and magnesium vanadate, (2) a silicon-containing compound, and (3) Item 6. The coating film-formed galvanized steel sheet according to any one of Items 1 to 5, which is a phosphate metal salt.

  Item 7. The phosphate metal salt (3) is at least selected from the group consisting of calcium phosphate, calcium monohydrogen phosphate, calcium dihydrogen phosphate, and a tripolyphosphate metal salt whose metal element is magnesium, aluminum, zinc, or calcium. Item 7. The coating film-formed galvanized steel sheet according to Item 6, which is one type.

  Item 8. 1 part by weight of the compound (Da) is added to 100 parts by weight of a 5% strength by weight sodium chloride aqueous solution at 25 ° C., stirred at 25 ° C. for 6 hours, and then allowed to stand at 25 ° C. for 24 hours. Item 8. The coating film-formed galvanized steel sheet according to any one of Items 1 to 7, wherein the pH of the filtrate obtained by filtering is 10 to 13.

  Item 9. Item 10. The coating film-formed galvanized steel sheet according to any one of Items 1 to 8, wherein the resin (Db) has a molecular weight distribution and a mass fraction of a component having a molecular weight of 1000 or less is 5 to 30% by mass.

  Item 10. 1 part by weight of resin (Db) is added to 100 parts by weight of a 5% strength by weight sodium chloride aqueous solution at 25 ° C., stirred at 25 ° C. for 6 hours, and then allowed to stand at 25 ° C. for 24 hours. Item 10. The coating film-formed galvanized steel sheet according to any one of Items 1 to 9, wherein the pH of the filtrate obtained by filtering the solution is 3 to 7.

  Item 11. Item 11. The coating film-formed galvanized steel sheet according to any one of Items 1 to 10, wherein the azole compound (Dc) is an azole compound having a triazole group or a thiadiazole group.

  Item 12. Item 12. The coating-formed galvanized steel sheet according to any one of Items 1 to 11, wherein the coating composition (I) further contains at least one pigment selected from the group consisting of titanium dioxide and extender pigments.

  Item 13. Item 1-12, wherein the coating composition (II) further contains at least one pigment selected from the group consisting of rust preventive pigments other than the compound (Da), titanium dioxide, and extender pigments. The coating film-formed galvanized steel sheet.

  Item 14. A coating layer of the coating composition (I) is formed on the lowermost layer of the surface (surface used outward), and a coating layer of the coating composition (II) is formed on the uppermost layer of the reverse side. Item 8. The coating film-formed galvanized steel sheet according to Item 6 or 7.

  Item 15. Item 14: A coating film layer formed of the coating composition (I) is formed on the lowermost layer on both the front and back surfaces, and a coating film layer formed of the coating composition (II) is formed on the uppermost layer on the back surface (the surface used inward). The film-forming galvanized steel sheet according to 1.

Item 16. Coating the following coating composition (I) on the lowermost layer of at least one of the front and back surfaces of the galvanized steel sheet,
Curing the coating film obtained by coating the coating composition (I),
A step of coating the following coating composition (II) on at least one uppermost layer of the front and back surfaces, and a step of curing the coating film obtained by coating the coating composition (II);
A method of forming a multilayer coating film on the surface of a galvanized steel sheet and forming a single layer or multilayer coating film on the back surface:
Coating composition (I) : A coating composition containing (A) a hydroxyl group-containing film-forming resin, (B) a crosslinking agent, and (C) a rust preventive pigment, wherein the resin (A) and the crosslinking agent ( The coating composition whose quantity of a rust preventive pigment (C) is 10-150 mass parts with respect to 100 mass parts of total solid content of B).

Coating composition (II) : A coating composition comprising (A) a hydroxyl group-containing film-forming resin and (B) a crosslinking agent,
Further, (Da) contains at least one compound selected from the group consisting of metal silicates and metal ion exchanged silica, and the total solid content of 100 parts by mass of the resin (A) and the crosslinking agent (B) On the other hand, the amount of the compound (Da) is 3 to 50 parts by mass,
(Db) containing at least one resin selected from the group consisting of a phosphate group-containing film-forming resin and a phosphate group-containing film-forming resin, and the resin (A) and the crosslinking agent (B ) To 100 parts by mass of the total solid content, the amount of the resin (Db) is 5 to 30 parts by mass, or (Dc) contains an azole compound and the resin (A) and the crosslinking agent (B The coating composition whose amount of azole compound (Dc) is 2 to 30 parts by mass with respect to 100 parts by mass of the total solid content.

  The coating film-formed galvanized steel sheet of the present invention is formed by forming a coating film by a non-chrome coating composition advantageous in terms of environmental hygiene on both surfaces of the galvanized steel sheet, not only excellent in corrosion resistance of the flat part, In the coated galvanized steel sheet, which has been difficult to achieve with non-chromium anticorrosive paints so far, the effect of being able to form a coating film with excellent white rust resistance at the processed part and end face part, which is particularly noticeable in the initial stage of use.

  In the coating film-formed galvanized steel sheet of the present invention, the anticorrosion property of the flat surface is that of the coating layer formed by the coating composition (I) containing the anticorrosive pigment formed in at least one lowermost layer of the front and back surfaces. At least one compound selected from the group consisting of metal silicate and metal ion-exchanged silica formed on the uppermost layer of at least one of the front and back surfaces is achieved by the anticorrosion effect, and the white rust resistance of the processed part and the end face part It is achieved by the rust prevention effect of the coating layer formed by the coating composition (II) containing

  White rust in a galvanized steel sheet is generated when zinc (ions) in plating becomes zinc oxide. White rust is a state in which a bulky zinc oxide is formed on the surface of the galvanized surface, with white or white with some light brown spots, and the appearance is such that white powder is attached. In particular, when the plating layer is exposed to an environment where it does not dry easily due to rain, dew, etc., or when the plating layer is unevenly wet due to rain or dew, it tends to occur. And the end face part is a part where white rust is likely to occur. Since white rust is bulky zinc oxide, the actual corrosion appears to be significantly corroded even if it is slight, and is very conspicuous.

  In the coating film-formed galvanized steel sheet of the present invention, the coating layer formed by the coating composition (II) containing the component (Da), (Db) and / or (Dc) is at least one of the front and back surfaces. Before the zinc oxide which is formed in the uppermost layer and causes white rust is generated, the zinc ions generated in the processed part and the end face part are converted to silicate ions of metal silicate and metal ion-exchanged silica; The zinc ion can be efficiently trapped by reacting with the phosphate group and / or phosphate group of the coating film-forming resin and / or the phosphate group-containing coating film-forming resin; and / or the azole compound. Since the production of zinc oxide can be suppressed, the white rust resistance of the processed part and the end face part is very excellent.

  The coating film-formed galvanized steel sheet of the present invention has a multilayer coating film on the surface and one or more coating films on the back surface, and a hydroxyl group-containing coating film-forming resin (A ), A coating layer by the coating composition (I) containing the crosslinking agent (B) and the rust preventive pigment (C) is formed, and the hydroxyl group-containing coating-forming resin (A) is formed on at least one uppermost layer of the front and back surfaces. , Crosslinking agent (B) and metal silicate and / or metal ion exchange silica (Da), phosphate group-containing film-forming resin and / or phosphate group-containing film-forming resin (Db) and / or azole compound It is a coating film-forming galvanized steel sheet in which a coating film layer is formed from the coating composition (II) containing (Dc).

  Hereinafter, the coating film-formed galvanized steel sheet of the present invention (hereinafter sometimes referred to as “the plated steel sheet of the present invention”) will be described in detail.

Coating composition (I)
The coating composition (I) is a coating composition containing a hydroxyl group-containing film-forming resin (A), a crosslinking agent (B), and a rust preventive pigment (C).

Hydroxyl-containing film-forming resin (A)
As the hydroxyl group-containing coating film-forming resin used in the coating composition (I), it can be used without particular limitation as long as it is a hydroxyl group-containing resin having a coating film-forming ability that can be normally used in the paint field. One type or two or more types of mixed resins such as a polyester resin, an epoxy resin, an acrylic resin, a fluororesin, and a vinyl chloride resin containing a hydroxyl group can be exemplified. As the film-forming resin, among them, at least one organic resin selected from a hydroxyl group-containing polyester resin and a hydroxyl group-containing epoxy resin can be preferably used.

  Examples of the hydroxyl group-containing polyester resin include oil-free polyester resins, oil-modified alkyd resins, and modified products of these resins, such as urethane-modified polyester resins, urethane-modified alkyd resins, epoxy-modified polyester resins, and acrylic-modified polyester resins. Is done. The hydroxyl group-containing polyester resin has a number average molecular weight of 1500 to 35000, preferably 2000 to 25000, a glass transition temperature (Tg) of 10 to 100 ° C., preferably 20 to 80 ° C., and a hydroxyl value of 2 to 100 mgKOH / g, preferably 5 Those having ˜80 mg KOH / g are preferred.

  In this specification, the number average molecular weight and the weight average molecular weight are the retention time (retention capacity) measured using a gel permeation chromatograph (GPC), the retention time (retention capacity) of a standard polystyrene having a known molecular weight measured under the same conditions. ) To obtain the molecular weight of polystyrene.

Specifically, for example, “HLC-8120GPC” (trade name, manufactured by Tosoh Corporation) is used as a gel permeation chromatograph, and one “TSKgel G4000HXL” and two “TSKgel G3000HXL” are used as columns. , And one “TSKgel G2000HXL” (trade name, all manufactured by Tosoh Corporation), using a differential refractometer as the detector, mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., The flow rate can be measured under the condition of 1 mL / min.
Moreover, in this specification, the glass transition temperature (Tg) of resin is based on a differential thermal analysis (DSC).

  The oil-free polyester resin is an esterified product of a polybasic acid component and a polyhydric alcohol component. Examples of the polybasic acid component include one or more selected from phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, fumaric acid, adipic acid, sebacic acid, maleic anhydride, and the like. Dibasic acids and lower alkyl esterified products of these acids are mainly used, and if necessary, monobasic acids such as benzoic acid, crotonic acid, pt-butylbenzoic acid, trimellitic anhydride, methylcyclohexericarboxylic acid , Tribasic or higher polybasic acids such as pyromellitic anhydride are used in combination. These polybasic acids can be used alone or in admixture of two or more. As the acid component, isophthalic acid, terephthalic acid, and lower alkyl esterified products of these acids are particularly preferable. Examples of the polyhydric alcohol component include divalents such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, 1,6-hexanediol, and the like. Alcohol is mainly used, and a trihydric or higher polyhydric alcohol such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol can be used in combination as necessary. These polyhydric alcohols can be used alone or in admixture of two or more. The esterification or transesterification reaction of both components can be carried out by a method known per se.

  In addition to the acid component and alcohol component of the oil-free polyester resin, the alkyd resin is obtained by reacting an oil fatty acid by a method known per se. Examples of the oil fatty acid include coconut oil fatty acid, soybean oil fatty acid, Examples thereof include linseed oil fatty acid, safflower oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, and kiri oil fatty acid. The oil length of the alkyd resin is preferably 30% or less, particularly about 5 to 20%.

  As the urethane-modified polyester resin, the oil-free polyester resin or the low-molecular weight oil-free polyester resin obtained by reacting an acid component and an alcohol component used in the production of the oil-free polyester resin, a polyisocyanate compound and Examples thereof include those reacted by a method known per se. The urethane-modified alkyd resin is obtained by reacting the alkyd resin or a low molecular weight alkyd resin obtained by reacting each component used in the production of the alkyd resin with a polyisocyanate compound by a method known per se. Things are included. Polyisocyanate compounds that can be used in the production of urethane-modified polyester resins and urethane-modified alkyd resins include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4 ′. -Methylenebis (cyclohexyl isocyanate), 2,4,6-triisocyanatotoluene and the like. In general, as the urethane-modified resin, those having a modification degree such that the amount of the polyisocyanate compound forming the urethane-modified resin is 30% by weight or less with respect to the urethane-modified resin can be preferably used.

  As the epoxy-modified polyester resin, a reaction product obtained by reacting a carboxyl group of this resin fat with an epoxy group-containing resin using a polyester resin produced from each component used for the production of the polyester resin; The reaction product by reaction, such as addition of a polyester resin and an epoxy resin, condensation, grafting, etc., such as the product which combined the hydroxyl group of this and the hydroxyl group in an epoxy resin through a polyisocyanate compound can be mentioned. In general, the degree of modification in the epoxy-modified polyester resin is preferably such that the amount of the epoxy resin is 0.1 to 30% by weight with respect to the epoxy-modified polyester resin.

  As the acrylic-modified polyester resin, a polyester resin produced from each component used in the production of the polyester resin is used, and a group having reactivity with these groups on the carboxyl group or hydroxyl group of the resin, for example, carboxyl group, hydroxyl group or epoxy. A reaction product obtained by reacting a group-containing acrylic resin; a reaction product obtained by graft-polymerizing a polyester resin with (meth) acrylic acid, (meth) acrylic acid ester or the like using a polymerization initiator Etc. In general, the degree of modification in the acrylic-modified polyester resin is preferably such that the amount of the acrylic resin is 0.1 to 50% by weight with respect to the acrylic-modified polyester resin.

  Among the polyester resins described above, among them, oil-free polyester resins and epoxy-modified polyester resins are preferable from the viewpoint of balance between processability and corrosion resistance.

  Examples of the epoxy resin suitable as the hydroxyl group-containing film-forming resin include, for example, bisphenol type epoxy resins, novolac type epoxy resins; modified epoxy resins in which various modifiers are reacted with epoxy groups or hydroxyl groups in these epoxy resins. Etc. In the production of the modified epoxy resin, the modification time with the modifier is not particularly limited, and it may be modified in the middle of the epoxy resin production or in the final stage of the epoxy resin production.

  The bisphenol-type epoxy resin is, for example, a resin obtained by condensing epichlorohydrin and a bisphenol compound to a high molecular weight in the presence of a catalyst such as a basic catalyst, if necessary, and epichlorohydrin and bisphenol as basic. Any of resins obtained by condensation in the presence of a catalyst such as a catalyst to form a low molecular weight epoxy resin and a polyaddition reaction of the low molecular weight epoxy resin and bisphenol may be used.

  Examples of the bisphenol compound 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, p -(4-hydroxyphenyl) phenol, oxybis (4-hydroxyphenyl), sulfonylbis (4-hydroxyphenyl), 4,4'-dihydroxybenzophenone, bis (2-hydroxynaphthyl) methane, etc. But bisphenol A and bisphenol F are preferred It is. The bisphenols can be used alone or in combination of two or more.

  As commercial products of bisphenol type epoxy resins, for example, Epicoat 828, 812, 815, 820, 834, 1001, 1004, 1007, 1009, 1010 manufactured by Japan Epoxy Resin; Asahi Ciba Examples include Araldite AER6099 manufactured by the company, and Epomic R-309 manufactured by Mitsui Chemicals.

  Examples of the novolac type epoxy resin that is an epoxy resin suitable as a hydroxyl group-containing film-forming resin include, for example, phenol novolac type epoxy resins, cresol novolac type epoxy resins, and phenol glyoxal types having a large number of epoxy groups in the molecule. Various novolak-type epoxy resins, such as an epoxy resin, can be mentioned.

  Examples of the modified epoxy resin include an epoxy ester resin obtained by reacting, for example, a dry oil fatty acid with the bisphenol type epoxy resin or the novolac type epoxy resin; and a polymerizable unsaturated monomer component containing acrylic acid or methacrylic acid. Epoxy acrylate resin; Urethane-modified epoxy resin reacted with isocyanate compound; Amino group or quaternary by reacting amine compound with epoxy group in bisphenol type epoxy resin, novolac type epoxy resin or various modified epoxy resins An amine-modified epoxy resin obtained by introducing an ammonium salt can be used.

Cross-linking agent (B)
The crosslinking agent (B) reacts with the hydroxyl group-containing coating film-forming resin (A) to form a cured coating film, and reacts with the hydroxyl group-containing coating film-forming resin (A) by heating or the like. As long as it can be cured, it can be used without particular limitation. 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 methylolated amino resins obtained by reacting an amino component such as melamine, urea, benzoguanamine, acetogranamamine, steroguanamine, spiroguanamine, and dicyandiamide with an aldehyde. Examples of the aldehyde used in the reaction include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. Moreover, what etherified the said methylolated amino resin with suitable alcohol can also be used as an amino resin. Examples of alcohols used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol, 2-ethylhexanol and the like.

  The phenol resin that can be used as the cross-linking agent is one that undergoes a cross-linking reaction with the hydroxyl group-containing coating film-forming resin (A), and a phenol component and formaldehyde are heated in the presence of a catalyst to undergo a condensation reaction to form a methylol group. A resol type phenol resin obtained by alkyl etherifying a part or all of the methylol group of a methylolated phenol resin obtained by introducing an alcohol with 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 that is a starting material.

  Examples of the phenol compound include o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, and 2,5-xylenol as bifunctional phenol compounds. Examples of the trifunctional phenol compound include coalic 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 these, from the viewpoint of improving 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 can be used alone or in combination of two or more.

  Examples of formaldehydes used in the production of the phenol resin include formaldehyde, paraformaldehyde, trioxane and the like, and these 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.

  The phenol resin has an average of 0.5 or more, preferably 0.6 to 3.0, alkoxymethyl groups per benzene nucleus in terms of reactivity with the hydroxyl group-containing film-forming resin (A). What you have is suitable.

  Examples of the non-blocked polyisocyanate compound that can be used as the crosslinking agent as the crosslinking 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 Adducts with polyhydric alcohols, low molecular weight polyester resins 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 phenol blocking agents such as phenol, cresol and xylenol; ε-caprolactam; lactam blocking agents such as δ-valerolactam and γ-butyrolactam; methanol, ethanol, n-, i- or Alcohol blocking agents such as t-butyl alcohol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, benzyl alcohol; formamidoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl mono Oxime-based blocking agents such as oxime, benzophenone oxime, cyclohexane oxime; dimethyl malonate, diethyl malonate, acetoacetic acid Chill, it can be suitably used blocking agent such as active methylene blocking agent such as acetylacetone. By mixing the polyisocyanate compound and the blocking agent, free isocyanate groups of the polyisocyanate compound can be easily blocked.

  The mixing ratio of the hydroxyl group-containing coating film-forming resin (A) and the crosslinking agent (B) is based on the total solid content of 100 parts by mass of the components (A) and (B), and the hydroxyl group-containing coating film-forming resin. (A) is 55 to 95 parts by mass, more preferably 60 to 95 parts by mass, and the crosslinking agent (B) is in the range of 5 to 45 parts by mass, and further 5 to 40 parts by mass. It is suitable in terms of boiling water, processability, curability and the like.

  A curing catalyst can be blended as necessary to improve the curability of the coating composition (I). When the crosslinking agent (B) 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 viewpoint of the stability of the coating, the reaction promoting effect, the physical properties of the obtained coating film, and the like. .

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

  When the crosslinking agent (B) is a blocked polyisocyanate compound, a curing catalyst that promotes dissociation of the blocking agent is suitable. Examples of suitable curing catalysts include tin octylate and dibutyltin di (2-ethyl). Hexanoates), dioctyltin di (2-ethylhexanoate), dioctyltin diacetate, dibutyltin dilaurate, dibutyltin oxide, dioctyltin oxide, organometallic catalysts such as lead 2-ethylhexanoate, etc. it can.

  When the crosslinking agent (B) is a combination of two or more kinds of crosslinking agents, an effective curing catalyst can be used in combination with each crosslinking agent.

Antirust pigment (C)
As the anti-corrosion pigment (C), any chromium-based pigment or non-chromium pigment can be used as long as it has anti-rust properties. However, it is non-chromium from the viewpoint of human health and environmental protection. It is suitable that it is a rust preventive pigment.

  Examples of chromium anticorrosive pigments include strontium chromate, zinc chromate, potassium potassium chromate, barium chromate, anhydrous chromic acid, chromium chromate, and chromium phosphate.

  Non-chromium anticorrosive pigments include vanadium compounds such as vanadium pentoxide, calcium vanadate, ammonium metavanadate and phosphorus vanadate; silicon-containing compounds such as metal silicates and silica fine particles; zinc phosphate, aluminum phosphate, calcium phosphate, Examples thereof include phosphoric acid-based metal salts such as magnesium diphosphate and aluminum tripolyphosphate; calcined products of zinc molybdate, manganese oxide and vanadium oxide, calcined products of calcium phosphate and vanadium oxide, and the like. These rust preventive pigments can be used alone or in combination of two or more.

  In the coating composition (I), a combination of the following (1) vanadium compound, (2) silicon-containing compound and (3) phosphate metal salt can be suitably used as the anticorrosive pigment (C). .

Vanadium compound (1)
The vanadium compound (1) is at least one vanadium compound selected from the group consisting of vanadium pentoxide, calcium vanadate, ammonium metavanadate and magnesium vanadate. Vanadium pentoxide, calcium vanadate, ammonium metavanadate and magnesium vanadate 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 pigments.

Silicon-containing compound (2)
The silicon-containing compound (2) is at least one selected from the group consisting of metal silicates 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 silicates include calcium silicate, magnesium silicate, zinc silicate, aluminum silicate, aluminum orthosilicate, hydrated aluminum silicate, aluminum calcium silicate, sodium aluminum silicate, aluminum beryllium silicate, sodium silicate, calcium orthosilicate, calcium metasilicate. , Calcium sodium silicate, Zirconium silicate, Magnesium orthosilicate, Magnesium metasilicate, Calcium magnesium silicate, Manganese silicate, Barium silicate, Olivine, Pomegranate, Tortite, Oysterite, Benitoite, Neptunite, Ryokuchuite, Toriishi, Kaikai List stones, barra stones, dolomite, zonotorite, talc, gyoganite, aluminosilicates, borosilicates, beryllosilicates, cholite, fluorite, etc. It can be. Among them, calcium silicate, 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 Etc.

  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 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-exchange 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 referred to as 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 JGC Catalysts & Chemicals Co., Ltd.), organosol (manufactured by Nissan Chemical Co., Ltd.), and the like. Of these, calcium ion exchanged silica fine particles are preferred.

  The said silicon containing compound (2) can be used by 1 type or in combination of 2 or more types.

Phosphate metal salt (3)
The phosphoric acid metal salt (3) is at least one selected from the group consisting of a metal phosphate, a metal hydrogen phosphate, and a metal tripolyphosphate. 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, dibasic phosphorus Magnesium phosphate, zinc hydrogen phosphate, aluminum phosphate, magnesium phosphate, aluminum hydrogen phosphate, magnesium hydrogen phosphate, magnesium ammonium phosphate; metal elements such as aluminum tripolyphosphate and aluminum dihydrogen triphosphate are magnesium, aluminum and zinc Or a metal salt of tripolyphosphate which is calcium. Among these, calcium phosphate, calcium monohydrogen phosphate, calcium dihydrogen phosphate, and tripolyphosphate metal salt whose metal element is magnesium, aluminum, zinc, or calcium are particularly preferable from the viewpoint of corrosion resistance. Phosphate ions released from the phosphoric acid metal salt (3), metal ions such as Ca, Zn, Al or Mg effectively work to improve the corrosion resistance.

  In the coating composition (I), the amount of the anticorrosive pigment (C) is 10 to 150 parts by mass with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing film-forming resin (A) and the crosslinking agent (B). From the viewpoint of corrosion resistance, it is preferably 15 to 90 parts by mass. Among them, as the anticorrosive pigment (C), the vanadium compound (1), the silicon-containing compound (2) and the phosphate metal salt (3) are preferable. Is within the following range from the viewpoint of improving corrosion resistance.

Vanadium compound (1): 3 to 50 parts by mass, preferably 5 to 30 parts by mass,
Silicon-containing compound (2): 3 to 50 parts by mass, preferably 5 to 30 parts by mass,
Phosphate metal salt (3): 3 to 50 parts by mass, preferably 5 to 30 parts by mass.

  In the coating composition (I), the corrosion resistance can be synergistically improved by combining a predetermined amount of the above (1), (2) and (3) as the anticorrosive pigment (C).

  Moreover, when using said (1), (2) and (3) combining predetermined amount as a rust preventive pigment (C), it is in each quantitative range of said (1), (2) and (3). 1 part by weight of a mixture of part by weight with respect to 100 parts by weight of a 5% strength by weight sodium chloride aqueous solution at 25 ° C., stirred at 25 ° C. for 6 hours, and then allowed to stand at 25 ° C. for 48 hours. The pH of the filtrate obtained by filtering the liquid is 3 to 10, preferably 5 to 9, and the above-mentioned (1), (2) and (3) water solubility and rust preventive pigment solution, metal plate, From the viewpoint of the reactivity, it is more preferable to be in this range from the viewpoint of corrosion resistance.

  In addition to the hydroxyl group-containing film-forming resin (A), the crosslinking agent (B), the rust preventive pigment (C), and a curing catalyst blended as necessary, the coating composition (I) is used in the coatings field. Usable coloring pigments, extender pigments, UV absorbers, UV stabilizers, organic solvents; additives such as antisettling agents, antifoaming agents, coating surface modifiers, and the like can be blended as necessary. The form of the coating composition (I) may be any of organic solvent-type coatings, water-based coatings, and powder coatings.

  Examples of the colored pigment include organic colored pigments such as organic red pigments such as cyanine blue, cyanine green, azo pigments, and quinacridone pigments; 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, silica, mica, alumina, calcium carbonate, barium sulfate and the like.

  Examples of the ultraviolet absorber include 2- (2-hydroxy-3,5-di-t-amylphenyl) -2H-benzotriazole, isooctyl-3- (3- (2H-benzotriazol-2-yl)- 5-t-butyl-4-hydroxyphenylpropionate, 2- [2-hydroxy-3,5-di (1,1-dimethylbenzidine) phenyl] -2H-benzotriazole, 2- [2-hydroxy-3- Dimethylbenzyl-5- (1,1,3,3-tetramethylbutyl) phenyl] -2H-benzotriazole, methyl-3- [3-t-butyl-5- (2H-benzotriazol-2-yl)- Benzotriazole compounds such as condensates with 4-hydroxyphenyl] propionate / polyethylene glycol 300; 2- [4- (2-hydroxy- -Dodecyloxypropyl) oxy] -2-triazine compounds such as hydroxyphenyl-4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine; ethanediamide-N- (2-ethoxyphenyl)- Succinic acid anilide compounds such as N ′-(2-ethylphenyl)-(oxalic amide), ethanediamide-N- (2-ethoxyphenyl) -N ′-(4-isododecylphenyl)-(oxalic amide), etc. Can be mentioned.

  Examples of the UV stabilizer include hindered amine compounds, hindered phenol compounds; CHIMASORB 944, TINUVIN 144, TINUVIN 292, TINUVIN 770, IRGANOX 1010, IRGANOX 1098 (all of these products are products of Ciba Specialty Chemicals) And the like.

  By blending a UV absorber and / or UV stabilizer into the paint, the paint composition (I) by light that has passed through the upper coating film and reached the coating film surface formed by the paint composition (I). Since deterioration of the formed coating film surface can be suppressed, delamination between the coating film formed from the coating composition (I) and the upper coating film can be prevented, and excellent corrosion resistance can be maintained.

  The organic solvent that can be blended in the coating composition (I) is blended as necessary for improving the coating properties of the coating composition (I), and includes a hydroxyl group-containing film-forming resin (A) and Those which can dissolve or disperse the crosslinking agent (B) can be used. Specifically, for example, hydrocarbon solvents such as toluene, xylene, high boiling point petroleum hydrocarbons, ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and isophorone. Solvents, ethyl acetate, butyl acetate, ester solvents such as ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, alcohol solvents such as methanol, ethanol, isopropanol, butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether Diethylene glycol It can be mentioned ether alcohol solvents such as mono butyl ether, which may be used alone or in combination of two or more.

  In the coating composition (I), the cured coating film obtained from the coating composition (I) has a glass transition temperature of 40 to 115 ° C., preferably 50 to 105 ° C., corrosion resistance, acid resistance and processability of the coating film. From the point of view, it is preferable. In this specification, the glass transition temperature of the coating film is a DINAMIC VISCOELASTOMETER MODEL VIBRON (dynamic viscoelastometer model vibron) DDV-IIEA type (manufactured by Toyo Baldwin, automatic dynamic viscoelasticity measuring machine) at a frequency of 110 Hz. This is the maximum temperature obtained from the change in tan δ by temperature dispersion measurement.

In the coating composition (I), when the rust preventive pigment (C) is a combination of the above (1) vanadium compound, (2) silicon-containing compound and (3) phosphoric acid metal salt, the coating composition (I ) Is coated on a galvanized steel sheet, and the formed coating film exhibits excellent corrosion resistance. The reason for this is that the present inventors have developed metal ions and pentavalent vanadium ions (vanadate ions such as VO ₃ ⁻ , VO ₄ ^3−, etc.) generated by dissolution of the raw material metal by chloride ions or the like in a corrosive environment. Direct precipitation of salt without oxidation-reduction reaction with trivalent vanadium ions and material metal ions generated by oxidation-reduction reaction of pentavalent vanadium ions and material metals effectively precipitates with silicate ions In order to effectively cover the exposed surface of the material by forming a salt or compound of the above, and further, the corrosion progressing site and its surroundings are formed between the pentavalent vanadium ion and the material metal by phosphoric acid ions eluting at the same time. This is considered to be because the pH is adjusted to a suitable pH range for the oxidation-reduction reaction to proceed. In particular, in galvanized steel sheets with a low alloy content of metals such as aluminum that have a strong deconducting effect, they elute from anticorrosive pigments in zinc and iron dissimilar metal battery forming parts such as edges and deep cut parts. It is desirable for the component to become non-conductive due to film formation as soon as possible, and it is considered that metal hydrogen phosphate as a component that strongly stabilizes the atmosphere pH eluted at this point to the acidic side plays an important role. Further, as the anticorrosive pigment (C), by using the (1), (2) and (3) in combination, the acid resistance, alkali resistance and the (1), (2) and (3) respectively have The weak water resistance can be effectively canceled out. It is considered that the synergistic effect of the action based on these rust preventive pigments worked greatly and achieved excellent corrosion resistance.

Coating composition (II)
The coating composition (II) comprises a hydroxyl group-containing film-forming resin (A), a crosslinking agent (B) and a metal silicate and / or metal ion-exchanged silica (Da); Alternatively, it is a coating composition containing a phosphate group-containing film-forming resin (Db); and / or an azole compound (Dc) in a specific ratio.

Hydroxyl-containing film-forming resin (A)
The hydroxyl group-containing coating film-forming resin used in the coating composition (II) is not particularly limited as long as it is a hydroxyl group-containing resin having a coating film-forming ability that can be normally used in the paint field, as in the coating composition (I). Typical examples include one or two or more mixed resins such as polyester resin, epoxy resin, acrylic resin, fluororesin, and vinyl chloride resin that contain a hydroxyl group. As the film-forming resin, among them, at least one organic resin selected from a hydroxyl group-containing polyester resin and a hydroxyl group-containing epoxy resin can be preferably used.

  Examples of the hydroxyl group-containing polyester resin include oil-free polyester resins, oil-modified alkyd resins, and modified products of these resins, such as urethane-modified polyester resins, urethane-modified alkyd resins, epoxy-modified polyester resins, and acrylic-modified polyester resins. Is done. The hydroxyl group-containing polyester resin has a number average molecular weight of 2000 to 20000, particularly 3000 to 15000, a glass transition temperature (Tg) of 0 to 70 ° C., particularly 10 ° C. to 50 ° C., and a hydroxyl value of 5 to 80 mgKOH / g, particularly 10 It is preferable to be within the range of ˜50 mg KOH / g.

  Examples of the oil-free polyester resin, alkyd resin, urethane-modified polyester resin, urethane-modified alkyd resin, epoxy-modified polyester resin, and acrylic-modified polyester resin include those exemplified in the coating composition (I). Of these polyester resins, among them, oil-free polyester resins and epoxy-modified polyester resins are preferable from the viewpoint of balance between processability and corrosion resistance.

  Examples of the epoxy resin suitable as the hydroxyl group-containing film-forming resin include bisphenol type epoxy resins, novolac type epoxy resins; modified epoxy resins in which various modifiers are reacted with epoxy groups or hydroxyl groups in these epoxy resins, and the like. Can be mentioned. In the production of the modified epoxy resin, the modification time with the modifier is not particularly limited, and it may be modified in the middle of the epoxy resin production or in the final stage of the epoxy resin production.

  Examples of the bisphenol-type epoxy resin, novolac-type epoxy resin, and modified epoxy resin include those exemplified for the coating composition (I).

Cross-linking agent (B)
Like the coating composition (I), the crosslinking agent (B) reacts with the hydroxyl group-containing coating film-forming resin (A) to form a cured coating film. The hydroxyl group-containing coating film is formed by heating or the like. As long as it can be cured by reacting with the functional resin (A), it can be used without particular limitation. 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, the phenol resin and the polyisocyanate compound which may be blocked include those exemplified for the coating composition (I).

  The mixing ratio of the hydroxyl group-containing coating film-forming resin (A) and the crosslinking agent (B) is based on the total solid content of 100 parts by mass of the components (A) and (B), and the hydroxyl group-containing coating film-forming resin. (A) is 50 to 95 parts by weight, particularly 70 to 90 parts by weight, and the crosslinking agent (B) is in the range of 5 to 50 parts by weight, particularly 10 to 30 parts by weight, corrosion resistance and boiling water resistance. From the viewpoints of processability and curability.

  A curing catalyst can be blended as necessary to improve the curability of the coating composition (II). Examples of the curing catalyst include those exemplified for the coating composition (I).

  When the crosslinking agent (B) is a combination of two or more kinds of crosslinking agents, an effective curing catalyst can be used in combination with each crosslinking agent.

Compound (Da)
The compound (Da) is at least one selected from the group consisting of metal silicates and metal ion exchange silica.

Metal silicate Metal silicate is a salt composed of silicon dioxide and metal oxide, and may be any of orthosilicate, polysilicate and the like. Examples of silicates include calcium silicate, magnesium silicate, zinc silicate, aluminum silicate, aluminum orthosilicate, hydrated aluminum silicate, aluminum calcium silicate, sodium aluminum silicate, aluminum beryllium silicate, sodium silicate, calcium orthosilicate, calcium metasilicate. , Calcium sodium silicate, Zirconium silicate, Magnesium orthosilicate, Magnesium metasilicate, Calcium magnesium silicate, Manganese silicate, Barium silicate, Olivine, Pomegranate, Tortite, Oysterite, Benitoite, Neptunite, Ryokuchuite, Toriishi, Kaikai List stones, barra stones, dolomite, zonotorite, talc, gyoganite, aluminosilicates, borosilicates, beryllosilicates, cholite, fluorite, etc. It can be. As a metal silicate, what contains calcium or magnesium is suitable. These metal silicates can be used alone or in combination of two or more.

Metal ion exchange silica Metal ion exchange silica is fine silica particles in which metal cations such as calcium ions are introduced into a fine porous silica carrier by ion exchange. Examples of the metal ion exchange silica include calcium ion exchange silica, magnesium ion exchange silica, and cobalt ion exchange silica.

  As the metal ion exchange silica, silica fine powder having an average particle diameter of 0.5 to 15 μm, preferably 1 to 10 μm, and an oil absorption of 30 to 300 ml / 100 g, preferably 30 to 150 ml / 100 g. It can be preferably used.

  Among them, calcium ion exchange silica can be preferably used as the metal ion exchange silica. Examples of commercially available calcium ion-exchange silica include SHIELDEX (Shielddex, registered trademark) C303, AC-3, AC-5 (all of which are manufactured by WR Grace & Co.). it can.

  Metal cations such as calcium ions released from metal ion-exchanged silica are involved in electrochemical action and various salt forming actions, and effectively work to improve corrosion resistance. Silicate ions released from metal ion-exchanged silica effectively work to improve the white rust resistance of the multilayer coating film and to suppress peeling.

  The said metal ion exchange silica can be used by 1 type or in combination of 2 or more types.

  In the coating composition (II), the amount of the compound (Da) is preferably 3 to 50 parts by mass, preferably 100 parts by mass of the total solid content of the hydroxyl group-containing film-forming resin (A) and the crosslinking agent (B). Is preferably from 5 to 30 parts by mass from the viewpoint of white rust resistance. When the amount of the compound (Da) exceeds 50 parts by mass, the white rust resistance tends to decrease, but when the amount of the compound (Da) is excessive, the water resistance of the coating film decreases. it is conceivable that.

  Further, 1 part by mass of the compound (Da) was added to 100 parts by mass of a 5% by mass sodium chloride aqueous solution at 25 ° C., and the mixture was stirred at 25 ° C. for 6 hours, and then allowed to stand for 24 hours. The pH of the filtered filtrate is preferably 10 to 13 from the viewpoint of the solubility of the compound (Da) by moisture and the reactivity between the dissolved solution of the compound (Da) and the metal plate, and should be within this range. This is more preferable from the viewpoint of white rust resistance.

Phosphate group-containing film-forming resin and / or phosphate group-containing film-forming resin (Db)
Of the phosphoric acid (salt) group-containing film-forming resin (Db), the phosphoric acid group-containing film-forming resin is a phosphoric acid group [—OPO (OH) (OR ¹ )] (where R ¹ is hydrogen. An atom, a phenyl group, or an alkyl group having 1 to 20 carbon atoms, particularly preferably a hydrogen atom or an alkyl group having 2 to 10 carbon atoms). It is not particularly limited as long as it is compatible with (A) and the crosslinking agent (B), and examples thereof include acrylic resins, epoxy resins, and polyester resins.

  The phosphoric acid group-containing acrylic resin can be obtained, for example, by copolymerizing a phosphoric acid group-containing unsaturated monomer and another polymerizable unsaturated monomer.

  Examples of the phosphate group-containing unsaturated monomer include (2-acryloyloxyethyl) acid phosphate, (2-methacryloyloxyethyl) acid phosphate, (2-acryloyloxypropyl) acid phosphate, (2-methacryloyloxypropyl) Acid phosphate, 10-acryloyloxydecyl acid phosphate, (meth) acryloyloxyalkyl (2-20 carbon atoms) acid phosphate such as 10-methacryloyloxydecyl acid phosphate; orthophosphoric acid or acidic phosphate (1-20 carbon atoms) To which is added an equimolar amount of an epoxy group-containing unsaturated monomer such as glycidyl (meth) acrylate; Kayamar PM-2, PM-21 (Nippon Kayaku Co., Ltd., trade name) and the like. Examples of the acidic phosphate ester include methyl acid phosphate, butyl acid phosphate, 2-ethylhexyl acid phosphate, isodecyl acid phosphate, lauryl acid phosphate, isotridecyl acid phosphate, oleyl acid phosphate, and phenyl acid phosphate. It is done.

  Examples of the other polymerizable unsaturated monomer that copolymerizes with the phosphoric acid group-containing unsaturated monomer constituting the phosphoric acid group-containing acrylic resin include, for example, 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl. Hydroxyl group-containing unsaturated monomers such as (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 2-hydroxyethyl allyl ether; acrylic acid, methacrylic acid; styrene, Vinyl aromatic compounds such as α-methylstyrene, vinyltoluene, α-chlorostyrene; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, (n- I-, t-) butyl (meth) acrylate, Hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, isobornyl (meth) C1-C24 alkyl ester or cycloalkyl ester of acrylic acid or methacrylic acid such as acrylate; vinyl acetate, vinyl chloride, vinyl ether, acrylonitrile, methacrylonitrile and the like. In the present invention, “(meth) acrylate” means “acrylate or methacrylate”.

  The phosphoric acid group-containing acrylic resin adds a phosphoric acid compound to a copolymer resin of an unsaturated monomer having an epoxy group, such as glycidyl (meth) acrylate, and the other polymerizable unsaturated monomer. It can also be obtained by a method. As the phosphoric acid compound to be added, orthophosphoric acid, acidic phosphoric acid ester and the like are suitable, and examples of the acidic phosphoric acid ester include those exemplified as the acidic phosphoric acid ester.

  The phosphoric acid group-containing epoxy resin can be obtained by adding a phosphoric acid compound to an epoxy resin. Examples of the epoxy resin to which the phosphoric acid compound is added include bisphenol type epoxy resins, novolak type epoxy resins, and modified epoxy resins in which various modifiers are reacted with epoxy groups or hydroxyl groups in these epoxy resins. it can. The type of phosphoric acid compound to be added is the phosphoric acid compound added to the copolymer resin of an unsaturated monomer having an epoxy group and another polymerizable unsaturated monomer in the description of the phosphoric acid group-containing acrylic resin. Can be used in the same manner.

  The phosphoric acid group-containing polyester resin can be obtained, for example, by reacting a phosphoric acid compound with the hydroxyl group of the polyester resin. As the kind of the phosphoric acid compound to be reacted, those mentioned as the phosphoric acid compound in the description of the phosphoric acid group-containing acrylic resin can be used similarly.

  Of the phosphoric acid group-containing coating film-forming resin or the phosphate group-containing coating film-forming resin (Db), the phosphate group-containing coating film-forming resin is phosphoric acid in the phosphoric acid group-containing coating film-forming resin. It can be obtained by reacting a group with a metal compound to form a phosphate. Examples of the metal compound to be reacted with the phosphate group include calcium oxide, magnesium oxide, cobalt oxide, nickel oxide, zinc oxide, cerium oxide, and lanthanum oxide.

  The phosphate group-containing film-forming resin and / or phosphate group-containing film-forming resin has a number average molecular weight of 1000 to 20000, in particular 3000 to 15000, and a glass transition temperature (Tg) of 0 to 100 ° C. Particularly, those having a temperature of 20 to 60 ° C., an acid value of 20 to 120 mgKOH / g, particularly 30 to 100 mgKOH / g, and a hydroxyl value of 0 to 50 mgKOH / g, particularly 5 to 30 mgKOH / g are preferred. Can be used.

  The phosphate group-containing coating film-forming resin or phosphate group-containing coating film-forming resin (Db) is from the viewpoint of coating film performance such as white rust resistance (capturing zinc ions) and water resistance of the resulting coating film. In the molecular weight distribution, the mass fraction of the component having a molecular weight of 1000 or less is in the range of 5 to 30% by mass, and particularly in the range of 5 to 20% by mass. From the viewpoint of

  The phosphoric acid group or phosphate group of the phosphoric acid (salt) group-containing coating film-forming resin (Db) is effective not only for capturing zinc ions but also for improving adhesion imparting property and corrosion resistance in an acidic atmosphere. To work.

  In the coating composition (II), the phosphoric acid group-containing film-forming resin and / or phosphoric acid with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing film-forming resin (A) and the crosslinking agent (B). The solid content of the base-containing coating film-forming resin (Db) is 5 to 30 parts by mass, and particularly preferably 10 to 20 parts by mass from the viewpoint of compatibility between the water resistance and white rust resistance of the coating film.

  Further, the phosphate group-containing coating film-forming resin and / or the phosphate group-containing coating film-forming resin (Db) is used as a solid content with respect to 100 parts by mass of a 5% by mass sodium chloride aqueous solution at 25 ° C. After adding 1 part by mass and stirring at 25 ° C. for 6 hours, the pH of the filtrate obtained by filtering the supernatant liquid that was allowed to stand for 24 hours is 3 to 7, in particular, 3 to 6. It is suitable from the viewpoint of the solubility of the forming resin and / or phosphate group-containing coating film-forming resin (Db) by moisture and the reactivity between the resin (Db) solution and the metal plate, and is in this range. Is more preferable in terms of white rust resistance.

Azole compound (Dc)
An azole compound is a compound having a hetero 5-membered ring containing one or more nitrogen atoms.

  Examples of the azole compound include thiazole group, pyrazole group, triazole group, thiadiazole group, tetrazole group, benzotriazole group, imidazole group, oxazole group, selenazole group, isoxazole group, isothiazole group, oxadiazole group, oxatriazole. And compounds having a group, a thiatriazole group, a benzazole group, an indazole group, a benzimidazole group, and the like.

  Examples of the compound having a thiazole group include 2-N, N-diethylthiobenzothiazole, 2-mercaptobenzothiazole and the like.

  Examples of the compound having a pyrazole group include pyrazole, 3,5-dimethylpyrazole, 3-methyl-5-pyrazolone, and 3-amino-5-methylpyrazole.

  Examples of the compound having a triazole group include 1,2,4-triazole, 3-amino-1,2,4-triazole, 3-mercapto-1,2,4-triazole, 5-amino-3-mercapto- Examples include 1,2,4-triazole and 2,3-dihydro-3-oxo-1,2,4-triazole.

  Examples of the compound having a thiadiazole group include 5-amino-2-mercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole and the like.

  Examples of the compound having a tetrazole group include 5-phenyl-1,2,3,4-tetrazole and 5-mercapto-1-phenyl-1,2,3,4-tetrazole.

  Examples of the compound having a benzotriazole group include 1H-benzotriazole, 1-hydroxybenzotriazole (monohydrate) and the like.

  Among the above, from the viewpoint of white rust resistance, in particular, an azole compound having a triazole group or a thiadiazole group can be preferably used.

  In the coating composition (II), the amount of the azole compound (Dc) is 2 to 30 parts by mass with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing film-forming resin (A) and the crosslinking agent (B). In particular, the content of 3 to 20 parts by mass is preferable from the viewpoint of achieving both the water resistance and the white rust resistance of the coating film.

  Moreover, the said azole compound (Dc) can also be used in combination of 2 or more types.

  In addition, 1 part by mass of the azole compound (Dc) was added to 100 parts by mass of a 5% by mass sodium chloride aqueous solution at 25 ° C., and the mixture was stirred at 25 ° C. for 6 hours, and then allowed to stand at 25 ° C. for 24 hours. The pH of the filtrate obtained by filtering the supernatant liquid is 3 to 8, particularly 4 to 7, so that the solubility of the azole compound (Dc) by water and the reactivity of the solution of the azole compound (Dc) and the metal plate From the standpoint of white rust resistance, it is more preferable that it is in this range.

  The components (Da) to (Dc) may be used alone or in combination of two or more. For example, the component (Db) and the component (Dc) can be combined, or the component (Da) and the component (Dc) can be combined.

  In the coating composition (II), in addition to the hydroxyl group-containing film-forming resin (A), the crosslinking agent (B), the components (Da) to (Dc), and a curing catalyst blended as necessary, Antirust pigments (other than (Da)), coloring pigments, extender pigments, UV absorbers, UV stabilizers, organic solvents; additives such as antisettling agents, antifoaming agents, and coating surface conditioners that can be used in the paint field Etc. can be blended as required. The form of the coating composition (II) may be any of organic solvent-type coatings, water-based coatings, and powder coatings.

  Examples of the color pigment, extender pigment, ultraviolet absorber and ultraviolet stabilizer include those exemplified for the coating composition (I).

  Deterioration of the coating film formed by the coating composition (II) due to the light reaching the surface of the coating film formed by the coating composition (II) by blending the ultraviolet absorber and / or ultraviolet stabilizer in the coating composition It is possible to suppress the delamination between the coating film formed from the coating composition (II) and the lower coating film, and maintain excellent corrosion resistance.

  The organic solvent that can be blended in the coating composition (II) is blended as necessary for improving the paintability of the coating composition (II), and includes a hydroxyl group-containing film-forming resin (A), What can melt | dissolve thru | or disperse | distribute a crosslinking agent (B) and component (Da) (Db) and / or (Dc) can be used, Specifically, what was illustrated by coating composition (I) is mentioned similarly. They can be used alone or in admixture of two or more.

  The coating composition (II) has a cured coating film obtained from the coating composition (II) having a glass transition temperature of 10 to 80 ° C., particularly 20 to 50 ° C., such as corrosion resistance, acid resistance and workability of the coating film. From the point of view, it is preferable.

  In a galvanized steel sheet with a multi-layer coating film, the galvanized steel sheet with a coating layer formed of the coating composition (II) as the uppermost layer exhibits excellent white rust resistance. . The reason for this is considered by the inventors as follows.

  The white rust in the galvanized steel sheet is particularly likely to occur in the processed part and the end face part, and is due to the formation of zinc oxide.

In order to prevent the occurrence of white rust, zinc ions in the galvanizing may be suppressed from becoming zinc oxide. When the component (Da) is used, the coating film-formed galvanized steel sheet of the present invention contains at least one compound selected from the group consisting of metal silicate that is a source of silicate ions and metal ion-exchanged silica. Since the coating film layer formed of the composition (II) is formed on at least one uppermost layer on the front and back surfaces, silicate ions can be more effectively generated from the multilayer coating film. Since the formation of zinc oxide can be suppressed by reacting the silicate ions and zinc ions to produce zinc silicate (ZnSiO ₃ , Zn ₂ SiO _4, etc.), the coating film-forming zinc plating of the present invention It is considered that the steel plate is very excellent in white rust resistance.

  When the component (Db) is used, the coating film-forming galvanized steel sheet of the present invention contains a phosphate group-containing coating film-forming resin and / or a phosphate group-containing coating film-forming resin, which is a source of phosphate ions. The coating layer formed by the coating composition (II) is formed on at least one uppermost layer on the front and back surfaces, so the resin component with phosphoric acid (salt) group is more effective from the multilayer coating. Can be generated. The formation of zinc oxide can be suppressed by reacting the phosphoric acid (salt) group-containing resin component with zinc ions to produce a resin component having a zinc phosphate group. The film-formed galvanized steel sheet is considered to be very excellent in white rust resistance.

  When the component (Dc) is used, the coating film-formed galvanized steel sheet of the present invention has a coating layer formed of the coating composition (II) containing an azole compound formed on at least one uppermost layer on the front and back surfaces. Therefore, the azole compound can be generated more effectively from the multilayer coating film. Since the formation of zinc oxide can be suppressed by reacting the azole compound with zinc ions to form a chelate compound, the coating film-formed galvanized steel sheet of the present invention is extremely resistant to white rust. It is considered excellent.

Coating film-forming galvanized steel sheet and coating film forming method of the present invention The coating film-forming galvanized steel sheet of the present invention is a coating in which a multilayer coating film is formed on the surface of the galvanized steel sheet and one or more coating films are formed on the back surface. A film-formed galvanized steel sheet,
It is obtained by forming a coating layer by the coating composition (I) on at least one lowermost layer of the front and back surfaces and forming a coating layer by the coating composition (II) on at least one uppermost layer of the front and rear surfaces. be able to.

For example, a step of applying the coating composition (I) to the lowermost layer of at least one of the front and back surfaces of the galvanized steel sheet,
Curing the coating film obtained by coating the coating composition (I),
Applying the coating composition (II) to the uppermost layer on at least one of the front and back surfaces, and curing the coating film obtained by coating the coating composition (II);
By the method including, a multilayer coating film can be formed on the surface of a galvanized steel sheet, and one layer or a multilayer coating film can be formed in a back surface.

  The galvanized steel sheet is a galvanized steel sheet in which the zinc content in the plating layer is 10% by mass or more, such as a hot dip galvanized steel sheet, an electrogalvanized steel sheet, and an aluminum-zinc alloy containing about 5% aluminum in the alloy. Galvanized steel such as galvanized steel (for example, “Galfan” (registered trademark)), galvanized steel molded parts, etc .; iron-zinc alloy-plated steel (galvanyl steel), aluminum-zinc alloy-plated steel (about 55% of aluminum in the alloy) Galvanium steel sheet containing about 5%, “galfan” containing about 5% aluminum in the alloy, etc.), zinc alloy plated steel materials such as molded parts made of zinc alloy plated steel, and the like. May have been made. Examples of the chemical conversion treatment include phosphate treatment such as zinc phosphate treatment and iron phosphate treatment, composite oxide film treatment comprising zirconium salt, chromium phosphate treatment, chromate treatment and the like.

  In the coating film-formed galvanized steel sheet of the present invention, first, at least one of the front and back surfaces of the galvanized steel sheet is coated with the coating composition (I) to form the lowermost coating layer. The coating composition (I) can also be applied to both the front and back surfaces. When coating the coating composition (I) only on one side, the coating composition (I) is preferably coated on the surface (surface to be used outward) from the viewpoint of outdoor durability of the coated steel sheet.

  When the coating composition (I) is applied to only one side, an arbitrary (undercoat) coating can be applied to the other side. Examples of (priming) coatings other than the coating composition (I) include (priming) coatings such as polyester resin-based coating compositions, alkyd resin-based coating compositions, and acrylic resin-based coating compositions.

  After the formation of the lowermost coating layer, one or more coating layers can be formed on the lowermost coating layer in addition to the uppermost coating layer. Examples of the coating material for forming this arbitrary coating layer include arbitrary coating materials such as a polyester resin coating composition, an alkyd resin coating composition, and an acrylic resin coating composition.

  After forming the lowermost coating layer (or forming one or more coating layers on the lowermost coating layer), the uppermost coating layer is formed on the coating layer. Let it form. On the back surface, the uppermost coating layer may be only one layer.

  When the coating composition (II) contains the component (Da) or the component (Db), a coating film-formed galvanized steel sheet in which a multilayer coating film is formed on both front and back surfaces of the galvanized steel sheet is preferable. Therefore, in the preferable embodiment, after the lowermost coating layer is formed on both the front and back surfaces (or more than one coating layer is further formed on the lowermost coating layer), An uppermost coating layer is formed on both coating layers.

  At least one of the front and back surfaces is formed with the uppermost coating layer by the coating composition (II). The uppermost coating layer can also be formed on the front and back surfaces by the coating composition (II). When only one layer is formed with the coating composition (II), the coating layer formed with the coating composition (II) is formed on the back surface (the surface used inward). It is preferable from the viewpoint of the weather resistance of the coated steel sheet surface.

  When coating the coating composition (II) only on one side, a coating layer can be formed on the other side with an optional top coating.

  Examples of the top coating include polyester resin-based coating compositions, alkyd resin-based coating compositions, acrylic resin-based coating compositions, silicon-modified polyester resin-based coating compositions, silicon-modified acrylic resin-based coating compositions, and fluororesin-based coatings. And the like. When workability such as pre-coated steel sheet is particularly important, a coating-formed galvanized steel sheet with particularly excellent workability can be obtained by using a polyester-based top coating for advanced processing.

  Each of the coating layers is formed by a known method such as a roll coating method, a curtain flow coating method, a spray method, a brush coating method, or a dipping method for each coating material including the coating composition (I) and the coating composition (II). It can be carried out by coating and curing by the method described above.

  In the formation of each coating layer, after coating and curing only on one side, it can be applied by either the method of coating and curing on the other side, or the method of simultaneously curing both the front and back sides after coating on both sides. A film layer may be formed.

  The cured film thickness of each coating layer is not particularly limited, but the cured film thickness of the coating layer by the coating composition (II) is preferably in the range of 2 to 20 μm, more preferably in the range of 3 to 10 μm. The cured film thickness of the coating layer by any undercoat paint is preferably in the range of 2 to 20 μm, more preferably 3 to 7 μm, and the cured film thickness of the coating film layer by any top coating is preferably It is in the range of 8-30 μm, more preferably 10-25 μm.

  The cured film thickness of the coating layer by the coating composition (I) is preferably 2 to 20 μm, more preferably when metal silicate and / or metal ion exchange silica (Da) is used as the raw material of the coating composition (II). Is in the range of 3-7 μm. When a phosphate group-containing film-forming resin and / or a phosphate group-containing film-forming resin (Db) or an azole compound (Dc) is used as a raw material for the coating composition (II), it depends on the coating composition (I). The cured film thickness of the coating layer is preferably in the range of 2 to 10 μm, more preferably 3 to 7 μm.

  The curing of the coating film may be appropriately set according to the type of resin used in each of the above-mentioned paints. Baking is performed for 15 to 60 seconds under a condition that the temperature is 160 to 250 ° C, preferably 180 to 230 ° C. When baking by a batch type, it can carry out by baking for 10 to 30 minutes normally at 80-200 degreeC.

  In the curing of the coating film, depending on the type of resin used in the coating, etc., when heating is not particularly required for the crosslinking reaction in the coating film forming process, it can be cured at room temperature according to a conventional method. .

  In the coating film-formed galvanized steel sheet of the present invention, examples of the coating film-forming galvanized steel sheet having a preferable coating film structure include the following two.

  1. A coating layer of the coating composition (I) is formed on the lowermost layer of the surface (surface used outward), and a coating layer of the coating composition (II) is formed on the uppermost layer of the reverse side. Film-formed galvanized steel sheet.

  In the above 1, a coating layer of an arbitrary undercoat paint is formed on the lowermost layer of the back surface (the surface used inward). If necessary, one or more coating film layers may be further formed on at least one of the front and back surfaces by any paint.

  After forming the lowermost coating layer on both sides (further, one or more coating layers were formed on at least one of the front and back sides with an arbitrary coating), and then the coating composition (II ), And a coating layer of any top coating composition containing the coating composition (II) is formed on the uppermost layer on the surface.

  In the above 1, the back surface may be only the coating layer made of the coating composition (II).

  2. Coating film with coating composition (I) is formed on the bottom layer on both front and back sides, and coating layer with coating composition (II) is formed on the top layer on the back side (surface used inward) Formed galvanized steel sheet.

  In the above 2, after forming the lowermost coating film, if necessary, one or more coating film layers may be further formed on at least one of the front and back surfaces with any paint.

  After forming the lowermost coating layer on both sides (further, one or more coating layers were formed on at least one of the front and back sides with an arbitrary coating), and then the coating composition (II ), And a coating layer of any top coating composition containing the coating composition (II) is formed on the uppermost layer on the surface.

  Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. However, the present invention is not limited to these. In each example, “parts” and “%” are based on mass unless otherwise specified. Moreover, the film thickness of a coating film is based on a cured coating film.

Manufacture of polyester resin 1
Production Example a1 Synthesis of Polyester Resin Aa1 Solution The following raw material mixture was placed in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, etc., and heated from 160 ° C. to 230 ° C. over 3 hours to produce water. Was distilled off through a rectification column. After maintaining at 230 ° C. for 1 hour, xylene was added, and dehydration was performed while refluxing xylene at 230 ° C. to perform an esterification reaction.
Ethylene glycol 0.9 mol Neopentyl glycol 0.1 mol Isophthalic acid 0.95 mol

  When the acid value becomes almost zero, cool to 140 ° C. and hold for 2 hours. After cooling, add Swazol 1500 (manufactured by Maruzen Petrochemical Co., Ltd., high-boiling aromatic petroleum solvent) to a solid content of 35%. A polyester resin Aa1 solution was obtained. The obtained resin had a number average molecular weight of 3800, a glass transition temperature of 45 ° C., a hydroxyl value of 30 mgKOH / g, and an acid value of about 0 mgKOH / g.

Production of phenolic resin 1
Production Example a2 Production of resol type phenolic resin Ba1 solution In a reaction vessel, 100 parts of bisphenol A, 178 parts of a 37% aqueous formaldehyde solution and 1 part of sodium hydroxide were blended and reacted at 60 ° C. for 3 hours, and then at 50 ° C. under reduced pressure. And dehydrated for 1 hour. Then, 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 resulting solution was filtered to remove sodium phosphate, which was obtained to obtain a resol type phenolic resin Ba1 solution having a solid content of 50%. 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.

Production of coating composition (I) 1
Production Example a3
90 parts of Epicoat # 1009 (Japan Epoxy Resin, bisphenol A type epoxy resin, hydroxyl group-containing resin) mixed solvent 1 [cyclohexanone / ethylene glycol monobutyl ether / solvesso 150 (Esso Petroleum, high boiling point aromatic hydrocarbon solvent) ) = 3/1/1 (mass ratio)] Into 225 parts of the epoxy resin solution dissolved in 135 parts, 20 parts of vanadium pentoxide, 20 parts of calcium phosphate, 20 parts of calcium silicate, 20 parts of titanium dioxide, 20 parts of barita and mixed solvent 2 [Solvesso 150 (manufactured by Esso Petroleum Corporation, high-boiling aromatic hydrocarbon solvent) / cyclohexanone = 1/1 (mass ratio)] were mixed in an appropriate amount, and the tube (particle diameter of the coarse pigment particles) was 20 μm or less. The pigment was dispersed until Next, Desmodur BL-3175 (manufactured by Sumika Bayer Urethane Co., Ltd., HDI isocyanurate type polyisocyanate compound solution blocked with methyl ethyl ketoxime, solid content of about 75%) was added to this dispersion at 13.3 parts (solid content of 10 parts) ) And Takenate TK-1 (manufactured by Takeda Pharmaceutical Co., Ltd., organotin blocking agent dissociation catalyst, solid content: about 10%) 1 part (0.1 part in solid content) and mixed uniformly, and further mixed solvent 2 Was added to adjust the viscosity to about 80 seconds (Ford Cup # 4/25 ° C.) to obtain a coating composition (I-1a).

Production examples a4 to a10
In Production Example a3, except that the hydroxyl group-containing resin, the crosslinking agent, the rust preventive pigment, other pigments and the catalyst are as shown in Table 1 below, the same procedure as in Production Example a3 was performed, and each coating composition (I-2a) to (I-8a) was obtained. The amounts of each component in Table 1 are all expressed by solid mass.

  In Table 1 and Table 2, (note) in a table | surface has the following meaning, respectively.

(Note 1) Cymel 303: Product name, methyl etherified melamine resin, manufactured by Nippon Cytec Industries Co., Ltd .;
(Note 2) K-White G105: manufactured by Teika Co., Ltd., trade name, magnesium oxide treated product of aluminum dihydrogen tripolyphosphate;
(Note 3) Shieldex C303: W.W. R. Grace & Co. Product name, calcium ion exchanged silica;
(Note 4) Co ion exchange silica: Cobalt ion exchange silica, 10 parts by mass of Silicia 710 (product name, silica fine particles, oil absorption amount in 10000 parts by mass of 5% by weight cobalt chloride aqueous solution, manufactured by Fuji Silysia Chemical Ltd.) About 105 ml / 100 g) was stirred and mixed for 5 hours and then filtered to remove the solid content. The solid content was washed thoroughly with water and dried to obtain Co ion-exchanged silica;
(Note 5) Nacure 5225: manufactured by King Industries, trade name, neutralized amine of dodecylbenzenesulfonic acid;
(Note 6) Mg ion exchanged silica: Magnesium ion exchanged silica, 10 parts by mass of Silicia 710 (made by Fuji Silysia Chemical Co., Ltd., trade name, silica fine particles, oil absorption in 10000 parts by mass of magnesium fluoride aqueous solution having a concentration of 5% by mass The amount of about 105 ml / 100 g) was stirred and mixed for 5 hours and then filtered to remove the solid content. The solid content was washed thoroughly with water and dried to obtain Mg ion-exchanged silica.

  The coating composition (I-8a) is a coating composition containing a conventional chromium-based rust preventive pigment, and is used for a reference example.

Production of coating composition (II) 1
Production Example a11
Appropriate amounts of 154.3 parts of calcium silicate, 30 parts of titanium dioxide, 40 parts of varita and mixed solvent 2 (same as in Production Example a3) to 214.3 parts of the polyester resin Aa1 solution produced in Production Example a1 (75 parts of resin solids) And the pigment was dispersed until the tube (particle diameter of the coarse pigment particles) became 20 μm or less.

  Next, 25 parts of Cymel 303 (Note 1) was added to the dispersion and mixed uniformly. Then, 3 parts of Nacure 5225 (Note 6; see above) and 1 part of the above-mentioned mixed solvent 2 were added and the viscosity was about 80. The coating composition (II-1a) was obtained by adjusting to seconds (Ford Cup # 4/25 ° C.).

Production examples a12 to a20
In Production Example a11, except that the hydroxyl group-containing resin, the crosslinking agent, the compound (Da), the rust preventive pigment, other pigments and the catalyst are as shown in Table 2 below, the same procedure as in Production Example a11 was carried out, and each coating composition ( II-2a) to (II-10a) were obtained. The amounts of each component in Table 2 are all expressed by solid mass.

  In Table 2, 1 part of the compound (Da) of each coating composition (II) was added to 100 parts by weight of a 5% by weight sodium chloride aqueous solution at 25 ° C. and stirred at 25 ° C. for 6 hours. The pH of the filtrate obtained by filtering the supernatant liquid allowed to stand for 24 hours (pH of the compound (Da) solution) is also shown.

  The coating compositions (II-8a) and (II-9a) are for comparative examples.

  The coating composition (II-10a) is a coating composition containing a conventional chromium-based rust preventive pigment, and is used for a reference example.

Production of coating composition (III) 1
Production Example a21
An appropriate amount of 30 parts of titanium dioxide, 40 parts of varita and mixed solvent 2 (same as in Production Example a3) is mixed with 214.3 parts of the polyester resin Aa1 solution produced in Production Example a1 (75 parts of resin solids), and The pigment was dispersed until the (particle diameter of the coarse pigment particles) was 20 μm or less.

  Next, 25 parts of Cymel 303 (Note 1) was added to the dispersion and mixed uniformly. Then, 3 parts of Nacure 5225 (Note 6; see above) and 1 part of the above-mentioned mixed solvent 2 were added and the viscosity was about 80. The coating composition (III-1a) was obtained by adjusting to seconds (Ford Cup # 4/25 ° C.).

Manufacture of coated galvanized steel sheet 1
Example a1
The coating composition obtained in Production Example a3 on a galvalume steel sheet (0.4 mm thick, aluminum-zinc alloy-plated steel sheet, containing about 55% aluminum in the alloy, and an alloy plating basis weight of 150 g / m ² ) subjected to chemical conversion treatment The product (I-1a) was applied with a bar coater so as to have a dry film thickness of 5 μm, and baked for 30 seconds so that the maximum material arrival temperature was 180 ° C. to form a lower layer back coating film. A bar coater is applied so that the coating composition (I-1a) obtained in Production Example a3 has a dry film thickness of 5 μm on the surface of the steel sheet opposite to the lower layer back surface coating film of the coated plate on which the lower layer back surface coating film is formed. Then, the lower layer surface coating film was formed by baking for 40 seconds so that the maximum material reaching temperature was 220 ° C.

  Thereafter, the coating composition (II-1a) obtained in Production Example a10 is applied on the lower back coating film with a bar coater so as to have a dry film thickness of 10 μm, so that the maximum material reaching temperature becomes 200 ° C. The upper layer back coating film was formed by baking for 30 seconds.

  After cooling, KP color 1580B40 (trade name, polyester-based top coating, blue, glass transition temperature of cured coating about 70 ° C.) is dried on the lower surface coating film with a bar coater. Coating is performed to a thickness of about 15 μm, and baking is performed for 40 seconds so that the maximum material temperature reaches 220 ° C. 1a was obtained.

Examples a2 to a17, comparative examples a1 to a2 and reference example a1
In Example a1, the same operation as in Example a1 was performed except that the coating compositions used on the front and back surfaces were as shown in Table 3 below. 2a-20a were obtained.

  In Table 3, it means that a coating composition marked with a circle is applied to each of the front and back layers.

Coating film performance test 1
Each of the coating film-formed galvanized steel sheets No. 1 obtained in Examples a1 to a17, Comparative Examples a1 to a2 and Reference Example a1. Each coating film performance test was conducted according to Test Method 1 below using 1a to 20a as test plates. The test results are shown in Table 3 below.

Test method 1
Preparation of test pieces Each test plate is 6 cm × 12 cm in size so that the burrs of the edge part on the long side are directed to the front surface side on the right side and to the back surface side on the left side toward the coating film surface on the front side. Disconnected. Each test piece was obtained by putting a cross cut with a narrow angle of 30 degrees and a line width of 0.5 mm reaching the substrate using the back of the cutter knife in the center of the cut surface of each test plate.

For each specimen, a combined corrosion test (CCT: JIS K5621) was performed 200 cycles, and the degree of corrosion was evaluated according to the following criteria;
Edge rust appearance: visually evaluated according to the following criteria;
A: Almost no white rust is observed. B: The same level as the reference example containing chromium. C: White rust is slightly observed. D: White rust is significantly generated or slightly recognized. The occurrence of red rust is also observed.

Edge blister evaluation: Judgment was made based on the average value of the bulge width that progressed from the front, back, left and right edges as follows:
A: Less than 5 mm B: 5 mm or more and less than 10 mm C: 10 mm or more and less than 20 mm D: More than 20 mm.

Cut portion: The ratio of the white rust generation length in the substrate exposed portion having a cut width of 0.5 mm and the swelling width spreading on both sides across the cut portion were evaluated according to the following criteria;
A: White rust generation length ratio in the substrate exposed portion is less than 50% and the bulge width is less than 3 mm B: White rust generation length ratio in the substrate exposed portion is 50% or more and the bulge width is less than 3 mm, or white rust in the substrate exposed portion Generation ratio of less than 50% and expansion width of 3 mm or more and less than 5 mm C: White rust generation length ratio of 50% or more in exposed substrate area and expansion width of 5 mm or more and less than 10 mm D: White rust generation length in exposed area of substrate The ratio is 50% or more and the swelling width is 10 mm or more.

A moisture resistance test (50 ° C., relative humidity 98%, 500 hours) was performed, and the degree of corrosion was evaluated according to the following criteria;
Edge rust appearance: visually evaluated according to the following criteria;
A: Almost no white rust is observed. B: The same level as the reference example containing chromium. C: White rust is slightly observed. D: White rust is significantly generated or slightly recognized. The occurrence of red rust is also observed.

Edge blistering evaluation: Evaluation was made based on the following criteria from the maximum value of the bulge width progressed from the front, back, left and right edges;
A: Less than 2 mm B: 2 mm or more and less than 4 mm C: 4 mm or more and less than 7 mm D: More than 7 mm.

Comprehensive evaluation: In the coating-formed galvanized steel sheet, it is important that all the white rust resistance of the processed part and the end face part is high. Therefore, a comprehensive evaluation was performed based on the following criteria:
A: The evaluation of the edge rust appearance, the edge blister appearance, and the cut portion after the composite corrosion test, and the evaluation of the edge rust appearance and edge blister appearance after the moisture resistance test are all A or B, and at least one is A B: all 5 items are B C; all 5 items are A, B or C, and at least one is C D; at least one of the 5 items is D.

Manufacture of polyester resin 2
Production Example b1 Synthesis of Polyester Resin Ab1 Solution Polyester resin Aa1 obtained in Production Example a1 was used as polyester resin Ab1 in the following Examples.

Production of phenolic resin 2
Production Example b2 Production of Resol Type Phenolic Resin Bb1 Solution Resole type phenolic resin Ba1 obtained in Production Example a2 was used as resol type phenolic resin Bb1 in the following Examples.

Production of phosphoric acid (salt) group-containing resin 1
Production Example b3 Production of Phosphoric Acid Group-Containing Acrylic Resin Db1 In a reaction vessel, 100 parts of butanol was charged, and while maintaining the temperature in the reaction vessel at 110 ° C., a mixture of the following composition in which the monomer raw materials were mixed in advance over 3 hours Dripped;
Styrene 50 parts 2-ethylhexyl methacrylate 35 parts glycidyl methacrylate 15 parts 2,2'-azobisisobutyronitrile 3 parts Then, 2,2'-azobisisobutyronitrile 0.5 part is further added, Furthermore, reaction was performed at 110 degreeC for 2 hours. Next, the temperature in the reaction vessel is set to 80 ° C., 12.2 parts of orthophosphoric acid having a concentration of 85% and 10.4 parts of butanol are gradually added, and the reaction is carried out for 1 hour until the reaction vessel is free of turbidity. % Phosphoric acid group-containing acrylic resin Db1 solution was obtained. The obtained phosphoric acid group-containing acrylic resin Db1 had an acid value of 54 mgKOH / g (phosphoric acid group concentration of 0.096 equivalent / 100 g resin), and the molecular weight distribution of the component having a molecular weight of 1000 or less was 20%. (Calculated from the area ratio of the GPC chart. The same applies hereinafter).

Production Example b4 Production of Phosphoric Acid Group-Containing Acrylic Resin Db2 Into a reaction vessel, 100 parts of butanol was charged, and while maintaining the temperature in the reaction vessel at 110 ° C., a mixture of the following composition mixed in advance with monomer raw materials was added dropwise over 3 hours. did;
Styrene 40 parts 2-ethylhexyl methacrylate 30 parts glycidyl methacrylate 30 parts 2,2'-azobisisobutyronitrile 3 parts Then, 2,2'-azobisisobutyronitrile 0.5 part is further added, Reaction was performed at 110 degreeC for 2 hours. Next, the temperature in the reaction vessel is set to 80 ° C., 25 parts of orthophosphoric acid having a concentration of 85% and 17 parts of butanol are gradually added, and the reaction is performed for 1 hour until the reaction vessel is free of turbidity. A group-containing acrylic resin Db2 solution was obtained. The obtained phosphoric acid group-containing acrylic resin Db2 has an acid value of 98 mgKOH / g (the phosphoric acid group concentration is 0.17 equivalent / 100 g resin), and in the molecular weight distribution, the mass fraction of components having a molecular weight of 1000 or less was 27%. It was.

Production Example b5 Production of phosphate group-containing acrylic resin Db3 In a sturdy glass container, 100 parts of the phosphoric acid group-containing acrylic resin Db1 solution with a solid content of 50% obtained in Production Example b3 (50 parts in solid content) and a mortar The mixture was mixed with 5 parts of ground calcium oxide, filled with glass beads, and dispersed with a scan dix until the resin solution became transparent. Then, it was left at room temperature for 48 hours. Thereafter, the glass beads were removed to obtain a phosphate (calcium salt) group-containing acrylic resin Db3 solution having a solid content of 53%.

Production of coating composition (I) 2
Production Example b6
The coating composition (I-1a) produced in Production Example a3 was used as the coating composition (I-1b) in the following Examples.

Production Examples b7 to b13
In Production Example b6, except that the hydroxyl group-containing resin, the crosslinking agent, the rust preventive pigment, other pigments and the catalyst are as shown in Table 4 below, the same procedure as in Production Example b6 was conducted, and each coating composition (I-2b) to (I-8b) was obtained. The amounts of each component in Table 4 are all expressed by solid mass.

  In Table 4 and Table 5, (Note) in the table is as described for Tables 1 and 2 above.

  The coating composition (I-8b) is a coating composition containing a conventional chromium-based rust preventive pigment, and is used for a reference example.

Production of coating composition (II) 2
Production Example b14
Titanium dioxide 30 was added to 214.3 parts (resin solid content 75 parts) of the polyester resin Ab1 solution produced in Production Example b1 and 20 parts (resin solid content 10 parts) of the phosphoric acid group-containing acrylic resin Db1 solution produced in Production Example b3. Part, 40 parts of a variator and an appropriate amount of mixed solvent 2 (same as Production Example b6) were mixed, and pigment dispersion was carried out until the tube (particle diameter of the pigment coarse particles) became 20 μm or less.

  Next, 25 parts of Cymel 303 (Note 1) was added to this dispersion and mixed uniformly. Further, 3 parts of Nacure 5225 (Note 6) (1 part in terms of solid content) and an appropriate amount of the above mixed solvent 2 were added to obtain a viscosity of about 80. The coating composition (II-1b) was obtained by adjusting to second (Ford Cup # 4/25 ° C.).

Production Examples b15 to b23
In Production Example b14, except that the hydroxyl group-containing resin, phosphoric acid (salt) group-containing resin, crosslinking agent, rust preventive pigment, other pigments and catalyst are as shown in Table 5 below, the same procedure as in Production Example b14 was performed. Coating compositions (II-2b) to (II-10b) were obtained. The amounts of each component in Table 5 are all expressed by solid mass.

  In Table 5, 1 part of phosphoric acid (salt) group-containing resin (Db) of each coating composition (II) is added to 100 parts by weight of a 5% strength by weight sodium chloride aqueous solution at 25 ° C., and 6 parts at 25 ° C. The pH of the filtrate (pH of the resin (Db) solution) obtained by filtering the supernatant liquid that was allowed to stand for 24 hours at 25 ° C. after stirring for the time is also shown.

  The coating compositions (II-8b) and (II-9b) are for comparative examples.

  The coating composition (II-10b) is a coating composition containing a conventional chromium-based rust preventive pigment, and is used for a reference example.

Production of coating composition (III) 2
Production Example b24
The coating composition (III-1a) produced in Production Example a20 was used as the coating composition (III-1b) in the following Examples.

Manufacture of coated galvanized steel sheet 2
Example b1
The same operation as in Example a1 was performed except that the coating composition (II-1b) obtained in Production Example b14 was used instead of the coating composition (II-1a), and the coating film-formed galvanized steel sheet No. 1b was obtained.

Examples b2 to b17, comparative examples b1 to b2 and reference example b1
In Example b1, the same operation as in Example b1 was carried out except that the coating compositions used on the front and back surfaces were as shown in Table 6 below. 2b-20b were obtained.

  In Table 6, it means that a coating composition marked with a circle is applied to each of the front and back layers.

Coating film performance test 2
Each of the coating film-formed galvanized steel sheets No. 1 obtained in Examples b1 to b17, Comparative Examples b1 to b2 and Reference Example b1. A coating film performance test was conducted in the same manner as in Test Method 1 except that 1b to 20b were used as test plates. The test results are shown in Table 6 below.

Manufacture of polyester resin 3
Production Example c1 Synthesis of Polyester Resin Ac1 Solution Polyester resin Aa1 obtained in Production Example a1 was used as polyester resin Ac1 in the following Examples.

Production of phenolic resin 3
Production Example c2 Production of Resol Type Phenolic Resin Bc1 Solution Resol type phenolic resin Ba1 obtained in Production Example a2 was used as resol type phenolic resin Bc1 in the following Examples.

Production of phosphate group-containing resin 2
Production Example c3 Production of phosphoric acid group-containing acrylic resin Db1 The phosphoric acid group-containing acrylic resin Db1 produced in Production Example b3 was used as the phosphoric acid group-containing acrylic resin.

Production of coating composition (I) 3
Production Example c4
The coating composition (I-1a) produced in Production Example a3 was used as the coating composition (I-1c) in the following Examples.

Production Examples c5 to c11
In Production Example c4, except that the hydroxyl group-containing resin, the crosslinking agent, the rust preventive pigment, other pigments and the catalyst are as shown in Table 7 below, the same procedure as in Production Example c4 was conducted, and each coating composition (I-2c) to (I-8c) was obtained. The amount of each component in Table 7 is indicated by solid mass.

  In Tables 7 and 8, (Note) in the tables are as described for Tables 1 and 2, respectively.

  The coating composition (I-8c) is a coating composition containing a conventional chromium-based rust preventive pigment and is used for a reference example.

Production of coating composition (II) 3
Production Example c12
Polyester resin Ac1 solution 214.3 parts (resin solid content 75 parts) produced in Production Example c1 was added to 3-amino-1,2,4-triazole 10 parts, titanium dioxide 30 parts, barita 40 parts and mixed solvent 2 ( An appropriate amount of the same as in Production Example c4) was mixed, and the pigment was dispersed until the tub (particle diameter of the coarse pigment particles) became 20 μm or less.

  Next, 25 parts of Cymel 303 (Note 1) was added to this dispersion and mixed uniformly. Further, 3 parts of Nacure 5225 (Note 6) (1 part in terms of solid content) and an appropriate amount of the above mixed solvent 2 were added to obtain a viscosity of about 80. The coating composition (II-1c) was obtained by adjusting to second (Ford Cup # 4/25 ° C.).

Production Examples c13 to c23
In Production Example c12, except that the hydroxyl group-containing resin, the azole compound, the cross-linking agent, the rust preventive pigment, other pigments and the catalyst (further blended with a phosphate group-containing resin as necessary) are as shown in Table 8 below, It carried out like manufacture example c12 and obtained each coating composition (II-2c)-(II-12c). The amount of each component in Table 8 is indicated by solid mass.

  In Table 8, 1 part of the azole compound (Dc) of each coating composition (II) was added to 100 parts by weight of a 5% by weight sodium chloride aqueous solution at 25 ° C. and stirred at 25 ° C. for 6 hours. The pH of the filtrate obtained by filtering the supernatant liquid that was allowed to stand at 24 ° C. for 24 hours (pH of the azole compound (Dc) solution) is also shown.

  The coating compositions (II-10c) and (II-11c) are for comparative examples.

  The coating composition (II-12c) is a coating composition containing a conventional chromium-based rust preventive pigment and is used for a reference example.

Production of coating composition (III) 3
Production Example c24
The coating composition (III-1a) produced in Production Example a20 was used as the coating composition (III-1c) in the following Examples.

Manufacture of coated galvanized steel sheet 3
Example c1
A coating composition obtained in Production Example c4 on a galvalume steel plate (0.4 mm thick, aluminum-zinc alloy plated steel plate, containing about 55% aluminum in the alloy, and an alloy plating basis weight of 150 g / m ² ) subjected to chemical conversion treatment The product (I-1c) was applied with a bar coater so as to have a dry film thickness of 5 μm, and baked for 30 seconds so that the maximum material temperature reached 180 ° C. to form a lower layer back coating film. A bar coater is applied so that the coating composition (I-1c) obtained in Production Example c4 has a dry film thickness of 5 μm on the surface of the steel sheet opposite to the lower layer back surface coating film of the coated plate on which the lower layer back surface coating film is formed. Then, the lower layer surface coating film was formed by baking for 40 seconds so that the maximum material reaching temperature was 220 ° C.

  Thereafter, the coating composition (II-1c) obtained in Production Example c12 is applied on the lower layer back surface coating film with a bar coater so as to have a dry film thickness of 10 μm, so that the maximum material temperature reaches 200 ° C. The upper layer back coating film was formed by baking for 30 seconds.

  After cooling, KP color 1580B40 (trade name, polyester-based top coating, blue, glass transition temperature of cured coating about 70 ° C.) is dried on the lower surface coating film with a bar coater. Coating is performed to a thickness of about 15 μm, and baking is performed for 40 seconds so that the maximum material temperature reaches 220 ° C. 1c was obtained.

Examples c2 to c20, comparative examples c1 to c3 and reference example c1
In Example c1, the same operations as in Example c1 were performed except that the coating compositions used on the front and back surfaces were as shown in Table 9 below. 2c to 24c were obtained.

  In Table 9, it means that a coating composition marked with a circle is applied to each of the front and back layers.

Coating film performance test 3
Each of the coating film-formed galvanized steel sheets No. 1 obtained in Examples c1 to c20, Comparative Examples c1 to c3 and Reference Example c1. A coating film performance test was conducted in the same manner as in Test Method 1 except that 1c to 24c were used as test plates. The test results are shown in Table 9 below.

Claims (16)

A coating film-formed galvanized steel sheet in which a multilayer coating film is formed on the surface of a galvanized steel sheet and a single layer or multilayer coating film is formed on the back surface,
A coating layer formed of the following coating composition (I) is formed on at least one lowermost layer of the front and back surfaces, and a coating layer of the following coating composition (II) is formed on at least one uppermost layer of the front and back surfaces. Film-formed galvanized steel sheet.
Coating composition (I) : A coating composition containing (A) a hydroxyl group-containing film-forming resin, (B) a crosslinking agent, and (C) a rust preventive pigment, wherein the resin (A) and the crosslinking agent ( The coating composition whose quantity of a rust preventive pigment (C) is 10-150 mass parts with respect to 100 mass parts of total solid content of B).
Coating composition (II) : A coating composition comprising (A) a hydroxyl group-containing film-forming resin and (B) a crosslinking agent,
And (Db) containing at least one resin selected from the group consisting of a phosphate group-containing film-forming resin and a phosphate group-containing film-forming resin, and the resin (A) and the crosslinking agent Whether the amount of the resin (Db) is 5 to 30 parts by mass with respect to 100 parts by mass of the total solid content of (B),
(Dc) It contains an azole compound having a triazole group or a thiadiazole group , and the amount of the azole compound (Dc) is 2 to 100 parts by mass of the total solid content of the resin (A) and the crosslinking agent (B). 30 parts by mass, or (Da) containing at least one compound selected from the group consisting of metal silicates and metal ion exchanged silica, and the total of the resin (A) and the crosslinking agent (B) The coating composition whose quantity of a compound (Da) is 3-50 mass parts with respect to 100 mass parts of solid content.
However, when the coating composition (II) does not contain the compound (Db) and the azole compound (Dc) and contains the compound (Da), the rust preventive pigment (C) in the coating composition (I) is ( 1) at least one vanadium compound selected from the group consisting of vanadium pentoxide, calcium vanadate, ammonium metavanadate and magnesium vanadate, (2) a silicon-containing compound and (3) a phosphate metal salt, and A coating layer of the coating composition (I) is formed on the lowermost layer on both the front and back surfaces, and a coating layer of the coating composition (II) is formed on the uppermost layer of the back surface (the surface used inward).   The coating film-formed galvanized steel sheet according to claim 1, wherein the zinc content during plating of the galvanized steel sheet is 10% by mass or more.   The coating film-forming galvanized steel sheet according to claim 1, wherein the hydroxyl group-containing coating film-forming resin (A) is at least one selected from the group consisting of a hydroxyl group-containing polyester resin and a hydroxyl group-containing epoxy resin.   The coating film-forming galvanized steel sheet according to claim 3, wherein the hydroxyl group-containing coating film-forming resin (A) of the coating composition (II) is a hydroxyl group-containing polyester resin.   The coating film-formed galvanized steel sheet according to claim 1, wherein the crosslinking agent (B) is at least one crosslinking agent selected from the group consisting of an amino resin, a phenol resin and a polyisocyanate compound which may be blocked. .   The rust preventive pigment (C) is (1) at least one vanadium compound selected from the group consisting of vanadium pentoxide, calcium vanadate, ammonium metavanadate and magnesium vanadate, (2) a silicon-containing compound, and (3) The coating-formed galvanized steel sheet according to claim 1, which is a phosphate metal salt.   The phosphate metal salt (3) is at least selected from the group consisting of calcium phosphate, calcium monohydrogen phosphate, calcium dihydrogen phosphate, and a tripolyphosphate metal salt whose metal element is magnesium, aluminum, zinc, or calcium. It is 1 type, The coating-film formation galvanized steel plate of Claim 6.   The coating film-formed galvanized steel sheet according to claim 1, wherein the resin (Db) has a molecular weight distribution and a mass fraction of a component having a molecular weight of 1000 or less is 5 to 30% by mass.   1 part by weight of resin (Db) is added to 100 parts by weight of a 5% strength by weight sodium chloride aqueous solution at 25 ° C., stirred at 25 ° C. for 6 hours, and then allowed to stand at 25 ° C. for 24 hours. The coating film-formed galvanized steel sheet according to claim 1, wherein the pH of the filtrate obtained by filtering is 3-7.   The coating film-formed galvanized steel sheet according to claim 1, wherein the azole compound (Dc) is an azole compound having a triazole group or a thiadiazole group.   1 part by weight of the compound (Da) is added to 100 parts by weight of a 5% strength by weight sodium chloride aqueous solution at 25 ° C., stirred at 25 ° C. for 6 hours, and then allowed to stand at 25 ° C. for 24 hours. The coating film-formed galvanized steel sheet according to claim 1, wherein the filtrate has a pH of 10 to 13.   The coating film-formed galvanized steel sheet according to claim 1, wherein the coating composition (I) further contains at least one pigment selected from the group consisting of titanium dioxide and extender pigments.   The coating film-forming zinc according to claim 1, wherein the coating composition (II) further contains at least one pigment selected from the group consisting of rust preventive pigments other than the compound (Da), titanium dioxide and extender pigments. Plated steel sheet.   A coating layer of the coating composition (I) is formed on the lowermost layer of the surface (surface used outward), and a coating layer of the coating composition (II) is formed on the uppermost layer of the reverse side. The coating film-formed galvanized steel sheet according to claim 6.   A coating layer made of the coating composition (I) is formed on the lowermost layer on both the front and back sides, and a coating layer made of the coating composition (II) is formed on the uppermost layer on the back side (the surface used inward). 14. The coating film-formed galvanized steel sheet according to 14. Coating the following coating composition (I) on the lowermost layer of at least one of the front and back surfaces of the galvanized steel sheet,
Curing the coating film obtained by coating the coating composition (I),
A step of coating the following coating composition (II) on at least one uppermost layer of the front and back surfaces, and a step of curing the coating film obtained by coating the coating composition (II);
A method of forming a multilayer coating film on the surface of a galvanized steel sheet and forming a single layer or multilayer coating film on the back surface:
Coating composition (I) : A coating composition containing (A) a hydroxyl group-containing film-forming resin, (B) a crosslinking agent, and (C) a rust preventive pigment, wherein the resin (A) and the crosslinking agent ( The coating composition whose quantity of a rust preventive pigment (C) is 10-150 mass parts with respect to 100 mass parts of total solid content of B).
Coating composition (II) : A coating composition comprising (A) a hydroxyl group-containing film-forming resin and (B) a crosslinking agent,
And (Db) containing at least one resin selected from the group consisting of a phosphate group-containing film-forming resin and a phosphate group-containing film-forming resin, and the resin (A) and the crosslinking agent Whether the amount of the resin (Db) is 5 to 30 parts by mass with respect to 100 parts by mass of the total solid content of (B),
(Dc) It contains an azole compound having a triazole group or a thiadiazole group , and the amount of the azole compound (Dc) is 2 to 100 parts by mass of the total solid content of the resin (A) and the crosslinking agent (B). 30 parts by mass, or (Da) containing at least one compound selected from the group consisting of metal silicates and metal ion exchanged silica, and the total of the resin (A) and the crosslinking agent (B) The coating composition whose quantity of a compound (Da) is 3-50 mass parts with respect to 100 mass parts of solid content.
However, when the coating composition (II) does not contain the compound (Db) and the azole compound (Dc) and contains the compound (Da), the rust preventive pigment (C) in the coating composition (I) is ( 1) at least one vanadium compound selected from the group consisting of vanadium pentoxide, calcium vanadate, ammonium metavanadate and magnesium vanadate, (2) a silicon-containing compound and (3) a phosphate metal salt, and A coating layer of the coating composition (I) is formed on the lowermost layer on both the front and back surfaces, and a coating layer of the coating composition (II) is formed on the uppermost layer of the back surface (the surface used inward).