JP6509604B2 - Painted galvanized steel sheet - Google Patents

Description

  The present invention relates to a chromate-free coated zinc-based plated steel sheet which is excellent in corrosion resistance, particularly corrosion resistance at a processed portion such as bending or the like and at a cut end surface.

  A coated zinc-based coating on which a chemical conversion treatment film and a primer coating film are formed on the surface of a steel plate plated with zinc or an alloy containing zinc (hereinafter abbreviated as "zinc-based plated steel plate") and various coating films formed thereon Plated steel sheet has many merits such as stability of quality and rationalization by omission of coating process at the customer, so interior materials such as exterior materials such as roof and wall of building and partitions, members of electrical equipment products , Etc. are widely used. Usually, such a coated zinc-based plated steel sheet is subjected to various processing including press bending, roll forming, or embossing, including 90 degree bending or 180 degree bending, and long-term film durability performance after use Required

  In order to meet these requirements, zinc-plated steel sheet is subjected to conversion treatment containing chromate, chromate-based rust preventive pigment is contained in primer coating film, and thermosetting type polyester resin as top coat film on it In general, a coated zinc-plated steel sheet on which a fluorine-based resin coating film is formed is applied to a coating film or a request for higher weather resistance.

  However, with regard to such a coated zinc-based plated steel sheet in recent years, the use of chromate, which is an environmentally harmful substance, is regarded as a problem, and a chromate-free coated zinc-based plated steel sheet containing no chromate is strongly desired. Patent Literatures 1 to 4 are proposed as techniques corresponding to these needs.

JP, 2008-291162, A JP, 2009-127057, A JP, 2014-214315, A JP, 2005-169765, A

  Patent Document 1 describes a coated zinc-coated steel sheet in which a coating composition in which a non-chromate rust preventive pigment such as a molybdenum compound is mixed with a primer coating film is applied to a galvanized steel sheet via a chemical conversion treatment film. However, since the galvanized steel sheet to be applied is limited to one containing 94% or more of zinc and a chromate type is applied as the chemical conversion film, it can not be said to be a coated zinc-based galvanized steel sheet with chromate free. The

  Patent Document 2 relates to a surface treatment agent (chemical conversion treatment film) comprising a resin and a chromate-free rust preventive pigment. Patent Document 2 is a technique for primary anticorrosion that does not apply coating, and when it is applied as a chemical conversion treatment film of a coated zinc-based plated steel sheet, sufficient corrosion resistance can not be obtained.

  Patent Document 3 relates to a coated zinc-based plated steel sheet using a surface treatment agent (chemical conversion treatment film) comprising a resin and a chromate-free rust preventive pigment. Patent Document 3 proposes a total anticorrosion design including a primer, but it can not be said that the corrosion resistance of the machined part is particularly sufficient.

  Patent Document 4 is a coated zinc-based plated steel sheet on which a specific chemical conversion treatment film and a primer coating film each containing a non-chromate-based rust-preventing pigment, and a technology aimed at improving the total corrosion resistance is described ing. However, a sufficient effect can not be obtained particularly on the corrosion resistance of the processed portion.

  As described above, the conventional chromate-free coated zinc-based plated steel sheet is inferior in corrosion resistance to the coated zinc-based plated steel sheet containing chromate, or the thickness of the primer coating film compared to the coated zinc-based plated steel sheet containing chromate Needs to be extremely thick, which is not economical.

  Then, in view of the said subject, an object of this invention is to provide the chromate-free coated zinc-based galvanized steel sheet excellent in corrosion resistance, especially corrosion resistance in process parts, such as bending etc., and a cutting end.

  The present inventors have found that the problem can be solved by forming a chemical conversion treatment film and a primer coating film containing specific common elements, as described below, and reached the present invention. That is, the gist configuration of the present invention is as follows.

(1) Zinc-based plated steel sheet,
A chemical conversion treatment film which does not contain a chromate compound and is formed on at least one surface of the galvanized steel sheet;
A primer coating film containing no chromate compound and formed on the chemical conversion film;
A top coat formed on the primer coat,
A coated zinc-based plated steel sheet having
The chemical conversion coating is a composite of a resin component and an inorganic component, and as the resin component, 30 to 50 mass% in total of an anionic urethane resin (a) having an ester bond and an epoxy resin (b) having a bisphenol skeleton And the compounding ratio of (a) to (b) is in the range of 3:97 to 60:40 by mass%, and the vanadium compound is 2 to 10% by mass, and the zirconium compound is the inorganic component. 40 to 60% by mass, and 0.5 to 5% by mass of a fluorine compound,
The primer coating film is mainly composed of a polyester resin having a urethane bond, contains a vanadium compound, a phosphoric acid compound, and magnesium oxide, and the breaking elongation of the primer coating film at 25 ° C. is 20% or more, and 25 A coated zinc-based plated steel sheet having a tensile strength at 20 ° C. of 20 MPa or more.

  (2) 40 to 88% by mass of the polyester resin, 4 to 20% by mass of the vanadium compound, 4 to 20% by mass of the phosphoric acid compound, and 4 to 20% by mass of the magnesium oxide in the primer coating film The coated zinc-based plated steel sheet according to the above (1), which is contained.

(3) The coated zinc system according to the above (1) or (2), wherein the adhesion amount of the chemical conversion coating is 0.025 to 0.5 g / m ² and the thickness of the primer coating is 1.5 μm or more. Plated steel plate.

  The coated zinc-based plated steel sheet according to the present invention can obtain excellent corrosion resistance particularly in a processed portion such as bending or a cut end surface while being chromate-free advantageous in terms of environmental safety. Therefore, when the coated zinc-based plated steel sheet of the present invention is applied to the building materials field, long-term corrosion can be suppressed in the bent portion of the roof molded product, the embossed portion of the wall material, and the square span bent portion. Maintenance costs such as repairs can be reduced significantly.

  The coated zinc-based plated steel sheet according to one embodiment of the present invention comprises a zinc-based plated steel sheet, a chemical conversion treatment film formed on at least one surface of the zinc-based plating steel sheet and containing no chromate compound, and the chemical conversion treatment film. It has the primer coating film which does not contain the chromate type compound formed, and the top coat film formed on this primer coating film.

(Zinc-based plated steel sheet)
In the present invention, the zinc-based plated steel sheet to be a base may be a steel sheet containing zinc in the plating layer, and there is no particular limitation. However, hot-dip galvanized steel sheet (GI) or alloyed alloy thereof Galvanized steel plate (GA), Galvanized steel plate such as electrogalvanized steel plate (EG), Zn-Ni plated steel plate, Zn-Al plated steel plate (for example, Zn-5 mass% Al alloy plated steel sheet, Zn-55 mass% It is possible to use an Al alloy plated steel sheet), a Zn-Al-Mg plated steel sheet, or the like.

  In addition, the zinc plating layer contains a small amount of a foreign metal element or one or more of nickel, cobalt, manganese, iron, molybdenum, tungsten, titanium, chromium, aluminum, magnesium, lead, antimony, tin and copper as impurities. You may In addition, two or more layers of the same or different types of the above-mentioned zinc plating layers may be plated.

(Chemical conversion film)
The chemical conversion film is a composite of a resin component and an inorganic component, and contains an anion urethane resin (a) having an ester bond and an epoxy resin (b) having a bisphenol skeleton as the resin component, and a vanadium compound as the inorganic component , Zirconium compounds, and fluorine compounds.

  As the anionic urethane resin (a) having an ester bond, a resin obtained by reacting a polyester polyol with diisocyanate or polyisocyanate having two or more isocyanate groups and copolymerizing dimethylol alkyl acid can be applied. A chemical conversion treatment liquid can be obtained by dispersing in a liquid such as water by a known method.

  The polyester polyol includes a polyester obtained by dehydration condensation reaction from a glycol component and an acid component such as an ester-forming derivative of hydroxyl carboxylic acid, a polyester obtained by ring-opening polymerization reaction of a cyclic ester compound such as ε-caprolactone, Copolymerized polyester is mentioned. As polyisocyanate, aromatic polyisocyanate, aliphatic polyisocyanate, alicyclic polyisocyanate etc. are mentioned. Examples of the aromatic polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-xylene diisocyanate, diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2-diphenylmethane diisocyanate and triphenyl. Methanetriisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, and derivatives thereof (for example, prepolymers obtained by reaction with polyols, modified polyisocyanates such as carbodiimide compound of diphenylmethane diisocyanate, etc.) and the like can be mentioned. . Specifically, a mixture in which a part of diphenylmethane diisocyanate is carbodiimidized is mentioned. When the polyester polyol is reacted with a diisocyanate or polyisocyanate to synthesize a urethane, the ester bond used in the present invention is obtained by copolymerizing dimethylol alkyl acid, self-emulsifying and water-solubilizing it. The anionic urethane resin (a) which has these can be obtained.

  A well-known resin can be used for the epoxy resin (b) which has a bisphenol skeleton, and a chemical conversion treatment liquid can be obtained by disperse | distributing to liquids, such as water, by a well-known method.

  The resin component acts as a binder for the chemical conversion film, and since the anionic urethane resin (a) having an ester bond is flexible, it has the effect of making the chemical conversion film difficult to break (peel off) when it is processed. The epoxy resin (b) has the effect of improving the adhesion to the underlying galvanized steel sheet and the primer coating film on the upper layer. The resin component is contained in a total of 30 to 50% by mass in the chemical conversion film. When the amount is less than 30% by mass, the binder effect of the chemical conversion treatment film is reduced. When the amount is more than 50% by mass, the function of the inorganic components shown below, for example, the inhibitor action is reduced.

  The compounding ratio of the anionic urethane resin (a) having an ester bond and the epoxy resin (b) having a bisphenol skeleton is in the range of 3:97 to 60:40 by mass%, assuming that the entire resin is 100. Outside this range, the adhesion decreases as the flexibility of the chemical conversion film decreases.

  The vanadium compound is added to the chemical conversion treatment solution to act as a rust inhibitor (inhibitor). Examples of the vanadium compound include vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, vanadium acetylacetonate and the like. Particularly preferred are tetravalent vanadium compounds, or tetravalent vanadium compounds obtained by reduction or oxidation.

  It is preferable that content of the vanadium compound in a chemical conversion treatment film is 2-10 mass%. If the amount is less than 2% by mass, the inhibitor effect is reduced to cause a decrease in corrosion resistance, and if the amount is more than 10% by mass, the moisture resistance of the chemical conversion treatment film is reduced.

  The zirconium compound is added to the chemical conversion solution, and the reaction with the plating metal and the coexistence with the resin component can be expected to improve the strength and the corrosion resistance as a chemical conversion film, and further the chemical conversion film is dense with the zirconium compound itself. It can be expected to have a barrier effect because it contributes to the formation of Examples of the zirconium compound include neutralized salts such as zirconium sulfate, zirconium carbonate, zirconium nitrate, zirconium lactate, zirconium acetate, zirconium chloride and the like.

  It is preferable that content of the zirconium compound in a chemical conversion treatment film is 40-60 mass%. If it is less than 40% by mass, the strength and corrosion resistance as a chemical conversion treatment film will be lowered, and if it exceeds 60% by mass, the chemical conversion treatment film will become embrittled and fracture and peeling of the chemical conversion treatment film will occur when subjected to severe processing. is there.

  A fluorine compound is added in a chemical conversion treatment liquid, and acts as an adhesion imparting agent with a zinc-based plated steel sheet. As the fluorine compound, for example, a fluoride salt such as ammonium salt, sodium salt, potassium salt or the like, or a fluorine compound such as ferrous fluoride or ferric fluoride can be used. Particularly preferred are ammonium fluoride and fluoride salts such as sodium fluoride and potassium fluoride.

  It is preferable that content of the fluorine compound in a chemical conversion treatment film is 0.5-5 mass%. When the amount is less than 0.5% by mass, the adhesion at the processed portion is not sufficiently obtained. When the amount is more than 5% by mass, the moisture resistance of the chemical conversion treatment film is lowered.

The preferable adhesion amount of the chemical conversion film is 0.025 to 0.5 g / m ² . If the amount is less than 0.025 g / m ² , the adhesion to the underlying zinc-based plated steel plate and the primer coating film as the upper layer may be reduced, and the corrosion resistance may be reduced. If it exceeds 0.5 g / m ² , the chemical conversion coating tends to break (peel) when subjected to severe bending, and the corrosion resistance may also decrease.

  The chemical conversion film is formed by continuously coating a chemical conversion solution on a zinc-based plated steel plate using a roll coater or the like, and then using hot air or induction heating to reach a plate temperature of about 60 ° C. to 200 ° C. (Peak Metal Temperature: It is obtained by drying with PMT).

(Primer coating film)
The primer coating film is mainly composed of a polyester resin having a urethane bond, and contains a vanadium compound, a phosphoric acid compound, and magnesium oxide. In addition, a "main component" here means that it is a component with most content in each component in a primer coating film.

  As polyester resin which has a urethane bond, well-known things, such as resin obtained by reaction with polyester polyol and 2 or more of isocyanate groups, and diisocyanate or polyisocyanate, can be used. In addition, a resin obtained by curing a resin (urethane-modified polyester resin) obtained by reacting a polyester polyol with diisocyanate or polyisocyanate having two or more isocyanate groups in an excess of hydroxyl groups (blocked polyisocyanate) can also be used.

  The polyester polyol can be obtained by a known method utilizing the dehydration condensation reaction of a polyhydric alcohol component and a polybasic acid component.

  Examples of polyhydric alcohols include glycol and polyhydric alcohols having a valency of 3 or more. As glycol, for example, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexylene glycol, 1,3-butanediol, 1,4-butanediol Butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, methylpropanediol, cyclohexanedimethanol, 3,3-diethyl-1,5- A pentanediol etc. are mentioned. Further, examples of trivalent or higher polyhydric alcohols include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol and the like. These polyhydric alcohols can be used alone or in combination of two or more.

  As polybasic acids, polyvalent carboxylic acids are usually used, but if necessary, monovalent fatty acids can be used in combination. As polyvalent carboxylic acid, for example, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 4-methylhexahydrophthalic acid, bicyclo [2,2,1] heptane-2,3-dicarboxylic acid, trimellitic acid, adipine Acid, sebacic acid, succinic acid, azelaic acid, fumaric acid, maleic acid, itaconic acid, pyromellitic acid, dimer acid etc., and their acid anhydrides, and 1,4-cyclohexanedicarboxylic acid, isophthalic acid, tetrahydroisophthalic acid , Hexahydroisophthalic acid, hexahydroterephthalic acid and the like. These polybasic acids can be used alone or in combination of two or more.

  Examples of polyisocyanate compounds include aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and xylylene diisocyanate (XDI), metaxylylene diisocyanate, tolylene diisocyanate (TDI), 4,4. -Aromatic diisocyanates such as diphenylmethane diisocyanate (MDI), isophorone diisocyanate, hydrogenated XDI, hydrogenated TDI, cyclic aliphatic diisocyanates such as hydrogenated MDI, adducts thereof, biuret bodies, isocyanurate bodies, etc. Be These polyisocyanate compounds can be used alone or in combination of two or more.

  The hydroxyl value of the polyester resin having a urethane bond is preferably 5 to 120 mg KOH / g, more preferably 7 to 100 mg KOH / g, and still more preferably 10 to 80 mg KOH, from the viewpoint of solvent resistance, processability, etc. It is / g.

  The number average molecular weight of the polyester resin having a urethane bond is preferably 500 to 15,000, more preferably 700 to 12,000, and still more preferably 800 to 15,000, from the viewpoint of solvent resistance, processability, etc. It is 10,000.

  The polyester resin having a urethane bond has both flexibility and strength, and when processed, it is possible to obtain the effect that a crack is less likely to occur in the primer coating film. Further, the affinity with the chemical conversion film containing a urethane resin is high, and in particular, contributes to the improvement of the corrosion resistance of the processed portion.

  It is preferable that 40-88 mass% of polyester resins are included in a primer coating film. If the amount is less than 40% by mass, the binder function as a primer coating film may be reduced, and if it exceeds 88% by mass, the function by inorganic substances shown below, for example, the inhibitor action may be reduced.

  Vanadium compounds act as inhibitors. Examples of the vanadium compound include vanadium pentoxide, metavanadic acid, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, magnesium vanadate, vanadyl acetylacetonate, vanadium acetylacetonate and the like. Particularly preferred are tetravalent vanadium compounds, or tetravalent vanadium compounds obtained by reduction or oxidation. The vanadium compound to be added to the primer coating film may be the same as or different from the vanadium compound to be added to the chemical conversion film. The vanadate compound reacts with water which invades from the outside, and the vanadate ion and ions on the surface of the zinc-based plated steel plate react with each other to form a passive film with good adhesion, thereby protecting the exposed metal part and preventing it. It is believed that a rust effect appears.

  It is preferable that content of the vanadium compound in a primer coating film is 4-20 mass%. If the amount is less than 4% by mass, the inhibitor effect is reduced to cause a reduction in corrosion resistance, and if it exceeds 20% by mass, the moisture resistance of the primer coating film is reduced.

  The phosphoric acid compounds act as inhibitors, and for example, phosphoric acid, ammonium salts of phosphoric acid, alkali metal salts of phosphoric acid, alkaline earth metal salts of phosphoric acid and the like can be used. In particular, alkali metal salts of phosphoric acid such as calcium phosphate are preferred.

  It is preferable that content of the phosphoric acid compound in a primer coating film is 4-20 mass%. If the amount is less than 4% by mass, the inhibitor effect is reduced to cause a reduction in corrosion resistance, and if it exceeds 20% by mass, the moisture resistance of the primer coating film is reduced.

  Magnesium oxide has the effect of stabilizing the product produced by the initial corrosion as a poorly soluble magnesium salt. It is preferable that the addition amount of magnesium oxide in a primer coating film is 4-20 mass%. If the amount is less than 4% by mass, the above-mentioned effect is reduced to cause a reduction in corrosion resistance, and if it exceeds 20% by mass, the flexibility of the primer coating may be reduced to thereby particularly reduce the corrosion resistance of the processed portion.

  The crosslinking agent used when forming a primer coating film reacts with the polyester resin which has a urethane bond, and forms a crosslinked coating film, and the block formation polyisocyanate compound is preferable. Examples of blocked polyisocyanates include isocyanate groups of polyisocyanate compounds, for example, alcohols such as butanol, oximes such as methyl ethyl ketoxime, lactams such as .epsilon.-caprolactam, diketones such as acetoacetic acid diester, imidazole And those blocked with imidazoles such as 2-ethylimidazole or phenols such as m-cresol.

  The elongation at break of the primer coating film at 25 ° C. is 20% or more. As a result, it is possible to suppress the occurrence of cracks in the primer coating film due to the deformation of the primer coating film that occurs when forming and processing for various uses, and the corrosion resistance of the processed portion is improved. In addition, the tensile strength at 25 ° C. of the primer coating film is 20 MPa or more. If the pressure is less than 20 MPa, the strength of the primer coating may be reduced, and the primer coating may be peeled off when a shearing force is applied during molding or the like.

  The breaking elongation and tensile strength of the primer coating can be measured by the following method. The primer coating was coated on a tin plate with a cured coating film to a thickness of about 10 μm and baked for 40 seconds so that the maximum achieved temperature would be 230 ° C. The coating film was peeled off from the tin plate by amalgam method. Prepare test samples for Next, using a tensile tester, the tensile test is conducted 5 times under the conditions of 25 ° C., tensile speed 4 mm / min, distance between chucks 40 mm, full scale setting 2 kg, and the average elongations obtained in 5 tests The value is taken as the elongation at break, and the average value of the tensile strengths obtained in 5 tests is taken as the tensile strength.

  The preferred thickness of the primer coating is 1.5 μm or more. If the thickness is smaller than this range, the corrosion resistance is lowered and the adhesion to the chemical conversion film and the top coat film is lowered.

  The resin composition for primer coating films can contain known various components usually used in the field of paints, if necessary. Specifically, for example, various surface conditioners such as leveling agents and antifoaming agents, dispersing agents, antisettling agents, ultraviolet light absorbers, light stabilizers, silane coupling agents, various additives such as titanate coupling agents, Examples include various pigments such as color pigments and extender pigments, glitter materials, curing catalysts, organic solvents and the like.

  Although there is no restriction | limiting in particular in the coating method of the coating composition for forming a primer coating film, It is preferable to apply a coating composition by methods, such as roll-coater coating and curtain flow coating, preferably. After the coating composition is applied, it is baked by heating means such as hot air heating, infrared heating, induction heating and the like to obtain a primer coating film. The baking treatment is usually carried out at a maximum reaching plate temperature of about 180 to 270 ° C. and for about 30 seconds to 3 minutes in this temperature range.

(Top coat)
In the production of a coated zinc-based plated steel sheet, a top coating is generally applied onto a primer coating. By applying the top coat, it is possible to impart an aesthetic appearance, and various properties such as processability, weather resistance, chemical resistance, contamination resistance, water resistance, corrosion resistance, etc. required of a coated zinc-based plated steel sheet. It can be enhanced.

  Examples of the top-coating paint used in the present embodiment include polyester resin paints, silicone polyester resin paints, polyurethane resin paints, acrylic resin paints, and fluorine resin paints.

  The thickness of the topcoat film is preferably 5 to 30 μm. If it is less than 5 μm, it is difficult to stabilize the color tone appearance, and if it exceeds 30 μm, the processability is reduced (the occurrence of cracks in the top coat film).

  The top coating film may be titanium dioxide, red iron oxide, mica, carbon black, various other color pigments, metallic pigments such as aluminum powder or mica, or body pigments consisting of carbonates or sulfates, depending on the purpose and application. Alternatively, various kinds of fine particles such as silica fine particles, nylon resin beads, acrylic resin beads, curing catalyst such as p-toluenesulfonic acid, dibutyltin dilaurate, wax and other additives can be blended in appropriate amounts.

  Although there is no restriction | limiting in particular in the coating method of the coating composition for forming a top coat film, It is preferable to apply a coating composition by methods, such as roll coater coating and curtain flow coating, preferably. After the coating composition is applied, it is baked by heating means such as hot air heating, infrared heating, induction heating and the like to obtain a top coat film. The baking treatment is usually carried out at a maximum reaching plate temperature of about 180 to 270 ° C. and for about 30 seconds to 3 minutes in this temperature range.

(Zinc-based plated steel sheet)
The zinc-based plated steel plates used in each test example shown in Table 1 are as follows.
1: Hot-dip 55 mass% aluminum-zinc alloy plated steel plate (JIS G3321, AZ150) with a thickness of 0.35 mm and a plating adhesion amount of 80 g / m ² per side
2: Hot-dip zinc-5% aluminum alloy-plated steel plate (JIS G3317, Y25) with a plating adhesion amount of plate thickness 0.35 mm and 130 g / m ² per side
3: Hot-dip galvanized steel sheet with a thickness of 0.35 mm and a plating adhesion of 130 g / m ² per side (JIS G3312, Z25)

  In each of the test examples, a chemical conversion treatment solution was applied to the surface of the zinc-based plated steel sheet shown in Table 1 by a roll coater and dried to form various chemical conversion treatment films shown in Table 1. At that time, it was dried at a final plate temperature of 90 ° C. using a hot air drying furnace to form a chemical conversion film.

  Then, in each test example, a primer coating was applied on a chemical conversion treated film by a bar coater, and baked at a final temperature of 230 ° C. of a steel plate and a baking time of 35 seconds to form various primer coated films shown in Table 1. Furthermore, the top coating composition shown in Table 1 is applied thereon with a bar coater so as to obtain the dry film thickness shown in Table 1, and baked at a final temperature of 230 ° C. to 260 ° C. of the steel plate for 40 seconds. A film was formed. Thus, various coated zinc-based plated steel plates were obtained.

(Chemical conversion film)
As a resin component (A) in the chemical conversion film, Super Flex 210, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., as an anionic urethane resin (a) having an ester bond, and Yoshimura oil chemistry as an epoxy resin (b) having a bisphenol skeleton A mixture of Yuka Resin RE-1050 manufactured by Co., Ltd. and the weight ratio of resin shown in Table 1 was used. On the other hand, acrylic resin (B) and polyester resin (C) which are outside this invention were used as a comparison.

  As the vanadium compound, an organic vanadium compound chelated with acetylacetone was used, as the zirconium compound, zirconium ammonium carbonate was used, and as the fluorine compound, ammonium fluoride was used.

  These raw materials were mixed to obtain a chemical conversion treatment solution. The pH of the chemical conversion solution was 8-10. The content of each component in the chemical conversion film was as shown in Table 1. However, in Comparative Examples 13 and 14, the galvanized steel sheet was subjected to chromate conversion treatment (silica-containing coated chromate).

(Primer coating film)
The paint for forming a primer coating film was produced by the following method.
As polyester resin (alpha) which has a urethane bond which is a main component, what hardened urethane modified polyester resin by blocking isocyanate was used. The urethane-modified polyester resin was obtained by reacting 455 parts by mass of the polyester resin and 45 parts by mass of isophorone diisocyanate. The resin acid value of the urethane-modified polyester resin was 3, the number average molecular weight was 5,600, and the hydroxyl value was 36.

  In addition, the polyester resin used when manufacturing the said urethane modified polyester resin was manufactured as follows. In a flask equipped with a stirrer, rectification column, water separator, condenser and thermometer, 320 parts by mass of isophthalic acid, 200 parts by mass of adipic acid, 60 parts by mass of trimethylolpropane, and 420 parts by mass of cyclohexane dimethanol The mixture was heated and stirred, and the temperature was raised from 160 ° C. to 230 ° C. at a constant speed over 4 hours while distilling off generated condensation water out of the system. When the temperature was raised to 230 ° C., 20 parts by mass of xylene was gradually added, and the temperature was maintained at 230 ° C. to continue the condensation reaction. The reaction is terminated when the acid value is 5 or less, and after cooling to 100 ° C., add 120 parts by mass of Solvesso 100 (manufactured by Exxon Mobil, trade name, high-boiling aromatic hydrocarbon solvent) and 100 parts by mass of butyl cellosolve. , A solution of polyester resin was obtained.

  On the other hand, as a comparison, a urethane cured polyester resin (β) whose elongation at break is outside the present invention, a melamine cured polyester resin (γ) which is a resin outside the present invention, and a urethane cured epoxy resin (δ) were used.

  Magnesium vanadate was used as the vanadium compound, and calcium phosphate was used as the phosphoric acid compound.

  After mixing these raw materials, they were stirred for about 1 hour by a ball mill to obtain a primer paint. The content of each component in the primer coating was as shown in Table 1. However, in Comparative Examples 13 and 14, a urethane-cured epoxy resin primer film containing 25% by mass of strontium chromate was used.

  In each test example, the primer coating was measured for breaking elongation at 25 ° C. and tensile strength by the method described above. The results are shown in Table 1.

(Top coat)
Resins for top coats shown in Table 1 are as follows.
I: Melamine cured polyester paint "pre-color HD 0030 HR" (manufactured by BASF Japan Ltd.)
II: Organosol-based stoving-type fluorocarbon resin-based paint "Pre-color No. 8800 HR" (manufactured by BASF Japan Ltd.) having a weight ratio of polyvinylidene fluoride to acrylic resin of 80:20

  With respect to the coated zinc-based plated steel sheets of the invention examples and comparative examples described above, the corrosion resistance, the adhesion in a bending portion, and the scratch resistance were evaluated by the evaluation methods described below. The results are shown in Table 2.

(1) Corrosion resistance A test of 120 cycles (total 960 hours) was conducted according to the combined cycle corrosion test (JIS H8502 8.1).

(1-1) Corrosion resistance of the bent portion In the bent portion of 6T (6 sheets of the same plate as the test piece are pinched inside and 180 degree close contact bending is carried out), surface observation after the test is carried out, and the top coating is performed according to the following criteria. It evaluated by the generation | occurrence | production area rate of the swelling of a coating film, or white rust.
:: No occurrence of blistering and rust is observed ○: Occurrence of blistering and / or rusting is 10% or less in total 膨: Occurrence of blistering and / or rusting is 10% or more and 50% or less in total The occurrence of swelling and / or rust is over 50% in total

(1-2) Corrosion resistance of cut end face The maximum occurrence width of blister or white rust was measured at the end face where the burrs at the time of cutting were on the top (so-called upper burrs), and evaluated according to the following criteria.
:: less than 3 mm ○: 3 mm or more, less than 5 mm Δ: 5 mm or more, less than 10 mm ×: 10 mm or more

(2) Adhesiveness at the Bending Section The portion subjected to 2T bending (180 in which the same plate as the test piece is pinched) is subjected to a film peeling test forcibly with cellophane tape (manufactured by Nichiban Co., Ltd.) The Evaluation was evaluated by the peeling area of the coating film.
○: no peeling Δ: less than 10% of peeled area ×: 10% or more of peeled area

(3) Scratch resistance adhesion property The coating film was scratched in a fixed direction at the outer peripheral part of a 10 yen coin, and the peeling state of the coating film was evaluated according to the following criteria.
○: no peeling at the interface between the top coat and the primer coating, the interface between the primer coating and the chemical conversion coating, or the chemical conversion coating and the plating interface x: the interface between the top coat and the primer coating, the primer coating and the conversion Peeling occurs at either the interface of the treatment film or the interface of the chemical conversion treatment film and the plating

  INDUSTRIAL APPLICABILITY The coated zinc-based plated steel sheet of the present invention is suitable for applications such as household appliances such as outdoor units of air conditioners as well as interior and exterior materials of building materials such as roofs, walls and shutters.

Claims (2)

Zinc-based plated steel sheet,
A chemical conversion treatment film which does not contain a chromate compound and is formed on at least one surface of the galvanized steel sheet;
A primer coating film containing no chromate compound and formed on the chemical conversion film;
A top coat formed on the primer coat,
A coated zinc-based plated steel sheet having
The chemical conversion coating is a composite of a resin component and an inorganic component, and as the resin component, 30 to 50 mass% in total of an anionic urethane resin (a) having an ester bond and an epoxy resin (b) having a bisphenol skeleton And the compounding ratio of (a) to (b) is in the range of 3:97 to 60:40 by mass%, and the inorganic component is 2 to 10 mass% of the vanadium compound, zirconium sulfate, 40 to 60% by mass of a zirconium compound which is a neutralized salt of one or more of zirconium carbonate, zirconium nitrate, zirconium lactate, zirconium acetate, and zirconium chloride , and ammonium fluoride, sodium fluoride, potassium fluoride, fluoride fluoride 0.5 to 5% by mass of a fluorine compound which is one or more of ferrous iron and ferric fluoride ,
40 to 88 wt% wherein the primer coating is a main component a polyester resin having a urethane bond, a vanadium compound 4-20 wt%, the phosphoric acid compound 4-20 wt%, and magnesium oxide 4-20 wt% A coated zinc-based plated steel sheet, which contains the primer coating and has a breaking elongation at 25 ° C. of 20% to 60% and a tensile strength at 25 ° C. of 20 MPa or more. The coated zinc-based plated steel sheet according to claim 1, wherein the adhesion amount of the chemical conversion coating is 0.025 to 0.5 g / m ² and the thickness of the primer coating is 1.5 μm or more.