JP4796410B2 - Surface coated aluminum-zinc alloy plated steel sheet - Google Patents

Description

  The present invention relates to a surface-coated aluminum-zinc alloy-plated steel sheet having corrosion resistance, alkali resistance, and molding processability and excellent in weather resistance and stain resistance. The surface-coated aluminum-zinc alloy-plated steel sheet, which is the subject of the present invention, can be used in the fields of building material products, home appliances, automobile members, etc., but will be described mainly in the case of application to building material products used outdoors. .

  The aluminum-zinc alloy-plated steel sheet is a steel sheet plated with an alloy containing 4 to 75% by mass of aluminum, most of the remainder being zinc, and further containing a trace amount of a third component such as Si, Mg, Ce-La. In what is currently commercialized, a so-called low aluminum-zinc alloy-plated steel sheet in which 4 to 10% by mass of aluminum, and most of the remainder is alloy-plated with zinc and Ce-La, and 55% of aluminum are used. %, 43.4% by mass of zinc and 1.6% by mass of Si, and so-called high aluminum-zinc alloy plated steel sheet. And when the plating layer has the same thickness as that of the generally used hot dip galvanized steel sheet, the corrosion resistance of the low aluminum-zinc alloy plated steel sheet is 1.5 to 2 times, and the high aluminum-zinc alloy plated steel sheet is 3-6. It has twice as much excellent properties. Moreover, in the case of a high aluminum-zinc alloy plated steel sheet, it is excellent in heat resistance and heat reflectivity.

  This high-aluminum-zinc alloy-plated steel sheet has a composition in which the aluminum non-moving body protective effect and the sacrificial anti-corrosive effect of zinc function in the most balanced manner. Unlike the hot-dip galvanized steel sheet, when the corrosion starts, a dense and stable corrosion product is formed and fills the network space and the corrosion does not proceed further. It is said to be excellent. In addition, because of its excellent heat resistance and heat reflectivity, building materials such as roofing and walls, civil engineering materials such as guardrails, noise barriers, snow fences, and drains, automobiles, home appliances, and industrial equipment Materials such as, and even coated steel plates are rapidly spreading.

  However, even though the plated steel sheet is excellent in corrosion resistance, it means that it takes a long time for red rust to occur due to corrosion of the base iron. And black rust occurs, and the silver-white beautiful appearance of the plated steel sheet is impaired.

  Therefore, in order to prevent the occurrence of white rust and black rust, chromate treatment and hexavalent aqueous resins having an acid value of 10 to 200 as disclosed in Japanese Examined Patent Publication No. 4-2672 (Patent Document 1) are conventionally used. A method of forming a resin film with a chromium-containing composition, or a lubricant-containing silicone resin film treatment containing a trace amount of chromium as disclosed in JP-A-7-251128 (Patent Document 2) is employed. I came.

  However, although the high-aluminum-zinc alloy-plated steel sheet treated with chromate has improved corrosion resistance, since the plating layer contains aluminum, the hardness of the plating layer is high. When forming by pressing, the lubricity between the high-aluminum-zinc alloy-plated steel sheet and the forming roll or press die is poor, the plating layer is destroyed, or the plating layer is broken by frictional heat between the two. As a result, the metal powder emitted from the high-aluminum-zinc alloy-plated steel sheet adheres to the forming roll and the press mold, resulting in a corner portion of the molded product. There is a risk that the appearance of the metal powder may change due to the accumulation of the metal powder and the occurrence of seizure phenomenon or defects such as scratches or abrasion.

  Surface coating aluminum-zinc by coating the plating surface with a resin film using the resin composition described in Japanese Patent Publication No. 4-2672 (Patent Document 1) or JP-A-7-251128 (Patent Document 2). When an alloy-plated steel sheet is formed, it is possible to prevent the occurrence of defects during the forming process as described above, but since the resin film contains hexavalent chromium ions in order to maintain corrosion resistance, If condensation occurs on the aluminum-zinc alloy-plated steel sheet or exposure to rainwater, environmental pollution due to elution from the resin film of hexavalent chromium ions may occur, which is preferable from the viewpoint of using environmentally hazardous substances. It is not a thing. In addition, if left in contact with alkaline foreign matters such as mortar and concrete, the surface of the surface-coated aluminum-zinc alloy-plated steel sheet may undergo a black change (blackening) peculiar to aluminum, which may impair the appearance. It was.

  In recent years, as the need for global environmental protection has increased, a surface-treated aluminum / zinc-based alloy-plated steel sheet that does not contain chromium, described in Japanese Patent Application Laid-Open No. 2003-201578 (Patent Document 3), as a technique for solving the above-described problem. And an aqueous resin composition for aluminum-zinc alloy plating treatment, a coating method, and an aluminum-zinc alloy plated steel sheet described in JP-A-2004-204333 (Patent Document 4).

Japanese Patent Application Laid-Open No. 2003-201578 (Patent Document 3) and Japanese Patent Application Laid-Open No. 2004-204333 (Patent Document 4) coat an aluminum-zinc alloy plated steel sheet with a urethane resin film in which a silane coupling agent and a zirconium compound are blended. This gives lubricity and improves defects such as scratches and abrasion. However, in Japanese Patent Application Laid-Open No. 2003-201578 (Patent Document 3), there is a concern about the decomposition of the urethane resin film by ultraviolet rays. Application to the building materials field that is used outdoors for a long period of time may result in the coating of steel sheets with coloring of the film caused by the decomposition of the urethane resin and carbon stains that are caused by inorganic carbon components floating in the atmosphere. This is not preferable from the viewpoint of design. JP 2004-204333 A (Patent Document 4), in addition to the above-mentioned concerns, when the glass transition temperature (Tg) of the urethane resin to be blended is low, the film is missing at the time of molding. Softening occurs, reducing the corrosion resistance and alkali resistance.
Japanese Patent Publication No.4-2672 JP 7-251128 A JP 2003-151578 A JP 2004-204333 A

  The present invention has been made in view of the above points, and the appearance is not impaired by molding, etc., has excellent corrosion resistance and alkali resistance, and has good weather resistance and stain resistance. An object of the present invention is to provide a surface-coated aluminum-zinc alloy-plated steel sheet that does not contain the steel.

The surface-coated aluminum-zinc alloy-plated steel sheet according to claim 1 of the present invention contains a water-dispersible polyester-based urethane resin (a) having a glass transition temperature (Tg) of 80 ° C. or higher, a carboxyl group, and a glycidyl group. A water-dispersible acrylic resin (b) having an acid value of 10 to 60 containing no styrol group, a zirconium compound (c) and hindered amines (d) are blended as components, and the ratio of each component is expressed as a solid content mass ratio ( The blending ratio of a) / (b) is 99/1 to 70/30, and the content of (c) is Zr / ((a) + (b)) blending ratio of 1/10 to 1/500 in terms of zirconium. The surface coating composition in which the blending amount of (d) is in the range of 5/100 to 1/1000 in the blending ratio of (d) / ((a) + (b)) and the pH is in the range of 7-10. Aluminum as the plating composition The containing from 25 to 75 wt% of aluminum - dried after application to the surface of the zinc alloy coated steel sheet, the coating layer is in the range dry film weight of 0.5 to 5.0 g / m ² per surface It is characterized by being formed.

  The invention according to claim 2 is the glycidyl methacrylate according to claim 1, wherein the monomer composition for synthesizing the water-dispersible acrylic resin (b) having an acid value of 10 to 60 which contains a carboxyl group and a glycidyl group but does not contain a styrol group. And at least one selected from acrylic acid and methacrylic acid, and at least two selected from n-butyl acrylate (methacrylate), methyl acrylate (methacrylate), ethyl acrylate (methacrylate), and acrylonitrile. Is.

  The invention according to claim 3 is that in claim 1 or 2, the temperature at which the surface coating composition is applied to the surface of the aluminum-zinc alloy plated steel sheet and then dried is 40 to 250 ° C. as the ultimate plate temperature. It is a feature.

  According to the surface-coated aluminum-zinc alloy-plated steel sheet according to claim 1 of the present invention, it is possible to obtain high corrosion resistance, alkali resistance, molding processability, weather resistance, and contamination resistance, and further, chromium is added. Since it is not used at all, the environmental and industrial utility value is extremely high.

  According to the invention which concerns on Claim 2, a weather resistance and contamination | pollution resistance can be obtained further higher.

  According to the invention which concerns on Claim 3, corrosion resistance and alkali resistance can be obtained further higher.

  Embodiments of the present invention will be described below.

  In the present invention, the water-dispersible polyester-based urethane resin (a) has a glass transition temperature (Tg) having a resin physical property of 80 ° C. or higher. When the glass transition temperature (Tg) is less than 80 ° C., the coating (coating layer) is not durable due to severe molding, and plating wear may occur and the film may easily turn black. Moreover, when the glass transition temperature (Tg) is low, water or water containing an alkali component is likely to permeate and the plating discoloration rate is increased. Therefore, the glass transition temperature (Tg) is 80 ° C. or higher, preferably in the range of 80 ° C. to 150 ° C., and more preferably in the range of 100 ° C. to 130 ° C. However, if the glass transition temperature (Tg) exceeds 150 ° C., the film becomes too hard, so that the adhesion to the base material with the metal material is lowered, and the film cannot follow the molding process, and the moldability may be lowered. is there.

  The water-dispersible polyester-based urethane resin (a) is obtained by a general synthesis method using a diisocyanate or polyisocyanate having two or more isocyanate groups, a diol or polyol, a diamine or polyamine, and an acid component as a raw material, It is the polyester-type urethane resin which is the polyester polyol of the said diol or a polyol component. The synthesis method is not particularly limited.

  At the time of making the aqueous system, dimethylol alkyl acid is copolymerized at the time of synthesizing urethane with polyester polyol and hydrogenated isocyanate, and self-emulsified to make it aqueous (water dispersion). This eliminates the use of an emulsifier at the time of forming an aqueous system, so that film performance excellent in water resistance can be obtained, leading to improvement in corrosion resistance and alkali resistance.

  Examples of the polyester polyol include a polyester obtained by a dehydration condensation reaction from a glycol component and an acid component such as an acid component and an ester-forming derivative of a hydroxycarboxylic acid, in addition to a ring-opening polymerization reaction of a cyclic ester compound such as ε-caprolactone. Examples thereof include polyesters obtained and copolymerized polyesters thereof. Examples of the glycol component include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, and 1,6-hexane. Diol, neopentyl glycol, butyl ethyl propane diol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol (molecular weight 300-6,000), dipropylene glycol, tripropylene glycol, bishydroxyethoxybenzene, 1,4-cyclohexane Examples include diol, 1,4-cyclohexanedimethanol, bisphenol A, hydrogenated bisphenol A, hydroquinone, and alkylene oxide adducts thereof.

  Examples of the acid component include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, maleic anhydride, fumaric acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid. Acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, 1,2-bis (phenoxy) ethane-p , P′-dicarboxylic acid and anhydrides or ester-forming derivatives of these dicarboxylic acids; p-hydroxybenzoic acid, p- (2-hydroxyethoxy) benzoic acid, and the like.

  Examples of the isocyanate include aliphatic, alicyclic or aromatic polyisocyanates. For example, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate ester, hydrogenated xylylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4, 4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 2 , 4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylme Down diisocyanate, phenylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, and the like. Among these, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate ester, hydrogenated xylylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate When an aliphatic or alicyclic polyisocyanate compound such as the above is used, a film excellent in weather resistance as well as alkali resistance and corrosion resistance can be obtained.

  The water dispersible polyester urethane resin (a) may be silane-modified using a silane coupling agent at the stage of synthesis. There are no particular limitations on the type of silane coupling agent and the amount of modification when the silane is modified, but as examples, the types of silane coupling agents include vinyltrichlorosilane, vinyltris (2-methoxyethoxysilane), Vinyltriethoxysilane, vinyltrimethoxysilane, 3- (methacryloyloxypropyl) trimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycid Xylpropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, N- (2-aminoethyl) 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) 3-aminopropylmethyldimethoxysilane, 3 -Aminopropyl Trimethoxysilane, 3-aminopropyl triethoxysilane, N- phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-chloropropyl trimethoxy silane, and the like ureidopropyltriethoxysilane.

  The water-dispersible polyester-based urethane resin (a) can be blended with an organic solvent in order to enhance the stability during resin synthesis and the film-forming property during low-temperature drying. Examples of the organic solvent include butyl cellosolve, N-methyl-2-pyrrolidone, butyl carbitol, and texanol.

  In the present invention, by using a water-dispersible acrylic resin (b) having an acid value of 10 to 60 which contains a carboxyl group and a glycidyl group but does not contain a styrol group, the surface-coated aluminum-zinc alloy plated steel sheet has weather resistance and Contamination resistance can be imparted.

  As the carboxyl group-containing monomer for producing the water-dispersible acrylic resin (b) having an acid value of 10 to 60, acrylic acid, methacrylic acid, maleic acid, itaconic acid and the like can be used, and a glycidyl group can be used. As the containing monomer, glycidyl acrylate, glycidyl methacrylate, or the like can be used. The method for synthesizing the acrylic polymer resin emulsion is not particularly limited, but an anionic activator such as polyoxyethylene alkyl sodium salt and alkylbenzene sulfonic acid sodium salt, polyoxyethylene alkylphenyl ether, Using one or more emulsifiers selected from nonionic active agents such as oxyethylene alkyl esters and sorbitan alkyl esters, reactive emulsifiers having a functional group capable of radical polymerization at a hydrophobic group, etc. Can be synthesized by radical polymerization.

  Here, if the acid value of the water-dispersible acrylic resin (b) is less than 10, the adhesion between the aluminum-zinc alloy-plated steel sheet and the resin film (coating layer) is lowered, leading to a reduction in molding processability. Moreover, when the said acid value exceeds 60, the alkali resistance of a resin film will fall.

  The water-dispersible acrylic resin (b) having an acid value of 10 to 60 does not contain styrene as a monomer component and does not contain a styrol group. The presence of a styrol group promotes oxidative degradation of the resin film because it has a property of generating a peroxide in the air, and when it is irradiated with ultraviolet rays, it is colored and the weather resistance is lowered. Furthermore, contaminants such as inorganic carbon having high hydrophobicity are easily adsorbed, and contamination resistance is reduced.

  In the present invention, the blending amount of the water-dispersible acrylic resin (b) having an acid value of 10 to 60 which contains a carboxyl group and a glycidyl group but does not contain a styrol group is the same as that of the water-dispersible polyester urethane resin (a). The solid content weight ratio (a) / (b) is in the range of 99/1 to 70/30, preferably in the range of 98/2 to 80/20, and more preferably in the range of 95/5 to 85/15.

  Here, when (a) / (b) exceeds 99/1, sufficient weather resistance and contamination resistance cannot be imparted, and when it is less than 70/30, corrosion resistance and alkali resistance are deteriorated.

  In the present invention, the zirconium compound (c) is not limited, but zirconium acetate, zirconium nitrate, zirconium sulfate, ammonium zirconium carbonate, sodium zirconium carbonate, potassium zirconium carbonate, zirconium lactate, zirconium chloride, zircon hydrofluoric acid and The ammonium salt can be used.

  Among these, it is more preferable to use sodium zirconium carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, and zirconium lactate.

  By containing the zirconium compound (c), it becomes possible to react with the metal material and to undergo a crosslinking reaction with the polar group present in the urethane resin skeleton, thereby improving the corrosion resistance. The compounding ratio of the zirconium compound (c) is the solid content mass conversion ratio of the water-dispersible polyester urethane resin (a) and the water-dispersible acrylic resin (b) having an acid value of 10 to 60 in terms of zirconium, Zr / ((a) + (b)) is in the range of 1/10 to 1/500, and preferably in the range of 1/20 to 1/200. If it exceeds 1/10, the resin component ((a) + (b)) will be insufficient, and the moldability will deteriorate. On the other hand, if it is less than 1/500, the zirconium compound may be insufficient, and the alkali resistance may be lowered.

  In the present invention, the hindered amines (d) are not limited, but 2,2,6,6-tetramethyl-4-piperidyl, (1,2,2,6,6-pentamethyl-4-piperidyl)- 1,2,3,4-butanetetracarboxylate, tetrakis (2,2,6,6-tetramethyl-4-piperidyl) -1,2,3,4-butanetetracarboxylate, tridecyl-1,2, 3,4-butanetetracarboxylate, bis (1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-methyl-2,2,6,6-tetramethyl-4) -Piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis- (1,2,2,6,6-pentamethyl-4-piperidyl) sebake 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonic acid (1,2,2,6,6-pentamethyl-4-piperidyl), poly [{6 -(1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethyl {(2,2,6,6-tetramethyl-4-piperidyl) imino}], dimethyl succinate-1- (2-hydroxylethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine heavy Condensate, poly {[6-morpholino-2,4-diyl] [4- (2,2,6,6-tetramethylpiperidyl) iminohexamethylene] [4- (2,2,6,6-tetramethyl Piperidyl) imino]} and the like can be used.

  The hindered amines (d) are blended in order to keep the film in a stable state for a long time by capturing radicals generated in the process of decomposing the resin by ultraviolet rays or the like. However, if the amount added is too large, the properties of the resin film are deteriorated, and if it is small, sufficient effects cannot be obtained and the resin film is decomposed or colored. Therefore, the blending ratio of (d) is a solid content mass conversion ratio of the water-dispersible polyester urethane resin (a) and the water-dispersible acrylic resin (b) having an acid value of 10 to 60 (d) / The mixing ratio of ((a) + (b)) is in the range of 5/100 to 1/1000, and preferably in the range of 5/100 to 1/100. If it exceeds 5/100, the alkali resistance is lowered, and if it is less than 1/1000, sufficient effects cannot be obtained for weather resistance and stain resistance.

The surface coating composition for forming the coating layer of the surface-coated aluminum-zinc alloy-plated steel sheet of the present invention can be obtained by blending the components (a) to (d) in the above blending amounts. The pH of this surface coating composition is in the range of 7-10. If it deviates, the passive layer of aluminum on the surface of the aluminum-zinc alloy plated steel sheet will be destroyed, and the performance of the alloy plating itself will be greatly reduced. Further, if the dry film mass per side is less than 0.5 g / m ² , a sufficient effect of the resin film cannot be obtained, and excellent corrosion resistance, alkali resistance, etc. cannot be imparted, and 5.0 g / m ² is reduced. When exceeding, in order not to produce the poor film formation of the resin film, a long drying time is required, and the performance is saturated, resulting in productivity and economic loss.

  Basically, when a resin having a high glass transition temperature (Tg) is used, the corrosion resistance and chemical resistance are often excellent as the characteristics of the resin film. However, the resin film obtained by baking and drying is liable to cause poor film-forming properties and may not exhibit excellent processability. Therefore, baking at a temperature higher than the glass transition temperature (Tg) is preferable. Therefore, the temperature when the surface coating composition is applied to the surface of the aluminum-zinc alloy plated steel sheet and then dried is preferably 40 to 250 ° C, more preferably 60 to 200 ° C, and more preferably 80 to 150 ° C as the ultimate plate temperature. Further preferred. Further, if the ultimate plate temperature is less than 40 ° C, the corrosion resistance and alkali resistance may be lowered. If the ultimate plate temperature exceeds 250 ° C, the water-dispersible polyester-based urethane resin (a) and the acid value However, a part of the water-dispersible acrylic resin (b) having a molecular weight of 10 to 60 may be decomposed and the corrosion resistance and alkali resistance may be lowered.

  As a method for obtaining the surface-coated aluminum-zinc alloy plated steel sheet of the present invention, any method can be used. For example, regarding the coating method of the surface coating composition, a roll coating method, a spray method, a dipping method, a shower ringer method, an air knife method and the like can be mentioned. In order to form a coating layer after coating, moisture may be volatilized by natural drying, or it may be forcibly dried using a heating device such as an electric furnace, hot air furnace, induction heating furnace, etc., and the method is limited. Not what you want.

  Applying the surface coating composition having the above composition to the surface of an aluminum-zinc alloy-plated steel sheet containing aluminum in a range of 25 to 75% by mass as a plating composition, followed by drying to form a resin film The surface-coated aluminum-zinc alloy-plated steel sheet of the present invention is manufactured by performing a surface treatment. Even if aluminum is less than 25% by mass or more than 75% by mass as the plating composition, desired corrosion resistance cannot be obtained.

  Hereinafter, the present invention will be specifically described by way of examples.

(1) Test material A 55% aluminum-zinc alloy-plated steel sheet, in which the improvement effect according to the present invention is most easily exhibited, was used as the metal material.

(2) Degreasing treatment As a pretreatment of the metal material, a clean surface state was obtained by alkali degreasing. Specifically, a silicate alkali degreasing agent Fine Cleaner N364S (manufactured by Nippon Parkerizing Co., Ltd.) was adjusted to a concentration of 2% and a temperature of 60 ° C., and sprayed for 10 seconds. Then, after wash | cleaning with a tap water, it squeezed with the draining roll and heat-dried at 50 degreeC for 30 second.

(3) Surface treatment agent for metal material (3) -1 Urethane resin (a)
The urethane resin (a) shown in Table 1 was obtained by the synthesis method shown below.

Urethane resin (a1)
In a reaction vessel, 100 parts by mass of a polyester polyol having a number average molecular weight of 1500 obtained from 1,4-butanediol and adipic acid, 5 parts by mass of 2,2-dimethyl-1,3-propanediol, and 2,2-dimethylolpropion 15 parts by weight of acid, 100 parts by weight of 4,4-dicyclohexylmethane diisocyanate, and 100 parts by weight of N-methyl-2-pyrrolidone are reacted to obtain a urethane prepolymer having a free isocyanate group content of 5% based on the nonvolatile content. It was. Next, 16 parts by mass of piperazine and 10 parts by mass of triethylamine are added to 500 parts by mass of ion-exchanged water, and while stirring with a homomixer, a urethane prepolymer is added and emulsified and dispersed to obtain a water-dispersible urethane resin having a nonvolatile content of 35% by mass. Got.

Urethane resin (a2)
In a reaction vessel, 100 parts by mass of a polyester polyol having a number average molecular weight of 2000 obtained from 1,6-hexanediol, neopentyl glycol and adipic acid, 5 parts by mass of 2,2-dimethyl-1,3-propanediol, 2,2 -Urethane having a free isocyanate group content of 5% based on the nonvolatile content by adding 20 parts by mass of dimethylolpropionic acid, 100 parts by mass of 4,4-dicyclohexylmethane diisocyanate, and 100 parts by mass of N-methyl-2-pyrrolidone. A prepolymer was obtained. Next, 16 parts by mass of ethylenediamine and 10 parts by mass of triethylamine are added to 500 parts by mass of ion-exchanged water, and while stirring with a homomixer, a urethane prepolymer is added and emulsified to disperse and a water-dispersible urethane resin having a nonvolatile content of 35% by mass. Got.

Urethane resin (a3)
In a reaction vessel, 100 parts by mass of a polyester polyol having a number average molecular weight of 2000 obtained from 1,6-hexanediol and adipic acid, 5 parts by mass of 2,2-dimethyl-1,3-propanediol, and 2,2-dimethylolpropion 20 parts by weight of acid, 100 parts by weight of 4,4-dicyclohexylmethane diisocyanate, 1 part by weight of 3-aminopropyltriethoxysilane, and 100 parts by weight of N-methyl-2-pyrrolidone are reacted to form a free isocyanate group with respect to the nonvolatile content. A water dispersible urethane prepolymer having a content of 5% was obtained. Next, 16 parts by mass of tetramethylenediamine and 10 parts by mass of triethylamine are added to 500 parts by mass of ion-exchanged water and stirred with a homomixer. A urethane resin was obtained.

Urethane resin (a4)
In a reaction vessel, 100 parts by mass of a polyester polyol having a number average molecular weight of 20000 obtained from 1,6-hexanediol, neopentyl glycol and adipic acid, 5 parts by mass of 2,2-dimethyl-1,3-propanediol, 2,2 -20 parts by mass of dimethylolpropionic acid, 100 parts by mass of hexamethylene diisocyanate, and 100 parts by mass of N-methyl-2-pyrrolidone were reacted to obtain a urethane prepolymer having a free isocyanate group content of 5% based on the nonvolatile content. It was. Next, 16 parts by mass of ethylenediamine and 10 parts by mass of triethylamine are added to 500 parts by mass of ion-exchanged water, and while stirring with a homomixer, a urethane prepolymer is added and emulsified to disperse and a water-dispersible urethane resin having a nonvolatile content of 35% by mass. Got.

Urethane resin (a5)
In a reaction vessel, 100 parts by mass of a polyether polyol having a number average molecular weight of 2000 obtained from ethylene glycol and propylene glycol, 5 parts by mass of 2,2-dimethyl-1,3-propanediol, and 20 parts by mass of 2,2-dimethylolpropionic acid. Part, 4,4-dicyclohexylmethane diisocyanate 100 parts by mass and N-methyl-2-pyrrolidone 100 parts by mass were reacted to obtain a urethane prepolymer having a free isocyanate group content of 5% based on the nonvolatile content. Next, 16 parts by mass of ethylenediamine and 10 parts by mass of triethylamine are added to 500 parts by mass of ion-exchanged water, and while stirring with a homomixer, a urethane prepolymer is added and emulsified to disperse and a water-dispersible urethane resin having a nonvolatile content of 35% by mass. Got.

(3) -2 Acrylic resin (b)
A mixture of deionized water and polyoxyethylene octylphenyl ether with acrylic acid, methacrylic acid, glycidyl methacrylate, butyl acrylate, methyl methacrylate, and acrylonitrile in the composition (mass%) shown in Table 2 and ammonium persulfate as a polymerization catalyst Was reacted at 80 to 85 ° C. for several hours, and then pH adjustment and concentration adjustment were performed with ammonia water and deionized water to obtain a water-dispersible acrylic resin having a solid content concentration of 40%.

  The zirconium compound (c) used in this example is shown in Table 3 below.

  The hindered amines (d) used in this example are shown in Table 4 below.

  Table 5 shows the composition (mass ratio) of the surface treatment agent (surface coating composition) containing the components shown in Tables 1 to 4 above. In addition, in each surface treating agent, the density | concentration adjustment was finally carried out using deionized water so that solid content concentration might be 30%.

(4) Coating method The amount of wet coating was controlled by changing the type of bar coater so that a predetermined coating amount was obtained. Then, it dried so that it might become predetermined | prescribed ultimate board temperature in 280 degreeC atmosphere, produced the surface coating aluminum-zinc alloy plating steel plate which formed the coating layer, and this was made into the process board.

(5) Measuring method of glass transition temperature (Tg) of polyester-type urethane resin (a) It measured using the dynamic viscoelasticity measuring apparatus.

(6) Method for measuring acid value of water-dispersible acrylic resin (b) Potassium hydroxide required per gram of solid content of the acrylic resin to neutralize the carboxylic acid contained in the water-dispersible acrylic resin (b) The number of mg was determined.

(7) Evaluation method Table 6 shows treated plates of Examples and Comparative Examples prepared using the surface coating composition of Table 5. The following tests were carried out on these treated plates and judged according to the evaluation criteria.

(7) -1 Corrosion resistance Based on the salt spray test method JIS-Z-2371, the white rust generation area after 500 hours of salt spray was visually determined and evaluated according to the following evaluation criteria.

Evaluation criteria: White rust generation area ratio ◎; Less than 5% ○; 5% or more and less than 15% △; 15% or more and less than 50% ×; 50% or more (7) -2 Alkali resistance 1% strength sodium hydroxide aqueous solution It was immersed for 5 hours at 25 ° C., washed with deionized water and then dried with a dryer. The state of the treated plate was evaluated by the following evaluation criteria by visual judgment.

Evaluation criteria: Degree of discoloration to black or brown ◎; Less than 5% ○; 5% or more and less than 15% △; 15% or more and less than 50% ×; 50% or more (7) -3 Molding workability A bead with a tip of 5 mmR is used. A test of pulling the treated plate upward was carried out while pressing the surface with 300 kgf (2942N), and the appearance of the treated plate was visually judged and evaluated according to the following evaluation criteria.

Evaluation criteria: Degree of color change to black ◎; Less than 1% ○; 1% or more and less than 5% △; 5% or more and less than 50% ×; 50% or more (7) -4 Contamination resistance 250 g / 20 ° C and 60 ° C An L carbon black suspension was prepared and immersed for 30 seconds. Then, after washing with deionized water, after drying the dryer, the difference in brightness before and after immersion was measured with a color difference meter (Color Meter ZE2000, manufactured by Nippon Denshoku Industries Co., Ltd.), and evaluated according to the following evaluation criteria.

Evaluation criteria: degree of change of L value ◎; 0 or more and less than 2 ○; 2 or more and less than 5 △; 5 or more and less than 10 ×; 10 or more (7) -5 Weather resistance Outdoor exposure test for 12 months in Funabashi City, Chiba Prefecture The L value and b value difference before and after the test were evaluated with a color difference meter (Color Meter ZE2000, Nippon Denshoku Industries Co., Ltd.).

Evaluation standard: L value change degree ◎; 0 or more and less than 2 ○; 2 or more and less than 5 △; 5 or more and less than 10 ×; 10 or more Evaluation standard: b value change degree ◎; 0 or more and less than 2 ○; Δ: 4 or more and less than 7 ×: 7 or more Table 6 shows the above evaluation results.

  As can be seen from the evaluation results in Table 6, the surface-coated aluminum-zinc alloy-plated steel sheets of the present invention shown in Examples 1 to 38 are excellent in corrosion resistance, alkali resistance, molding processability, weather resistance, and stain resistance. Met. Among these, as can be seen from Examples 1 to 4 and Examples 8 to 10, when the blending amount of the water-dispersible acrylic resin (b) and the blending amount of the hindered amines are increased, the weather resistance and stain resistance are increased. The tendency to improve the nature was recognized. On the other hand, in Comparative Example 1 in which no urethane resin was blended, all the evaluation items other than the contamination resistance were lowered. Moreover, in Comparative Example 2 using urethane whose glass transition temperature (Tg) is less than 80 ° C., the corrosion resistance and alkali resistance are lowered, and in Process 3 using polyether-based urethane, molding processability is lowered. It was.

  In Comparative Example 4 where no acrylic resin was added, the weather resistance and stain resistance were lowered. In Comparative Example 5 using an acrylic resin having an acid value of less than 10, molding processability was lowered, and in Comparative Example 6 using an acrylic resin having an acid value of more than 60, alkali resistance was lowered.

  Further, in Comparative Example 7 using a resin blended with styrene, the weather resistance and stain resistance are lowered, and in Comparative Example 8 using an acrylic resin not containing a glycidyl group, the corrosion resistance, alkali resistance, and stain resistance are low. Declined.

  In Comparative Example 9 where the blending ratio of (a) / (b) is less than 70/30, the alkali resistance and molding processability are lowered, and in Comparative Example 10 exceeding 99/1, the weather resistance and stain resistance are insufficient. Met.

  In Comparative Example 11 in which no zirconium compound was blended, the corrosion resistance, alkali resistance, and weather resistance were lowered.

  Further, in Comparative Example 12 in which the blending ratio of Zr / ((a) + (b)) is less than 1/500 in terms of zirconium, the alkali resistance is lowered, and Comparative Example 13 in which the compounding ratio exceeds 1/10 has molding processability. Declined.

  In Comparative Example 14 in which hindered amines are not blended, the weather resistance and stain resistance are lowered, and Comparative Example 15 in which the blending ratio of (d) / ((a) + (b)) is less than 1/1000 has the same result. In Comparative Example 16 exceeding 5/100, the alkali resistance was lowered.

  Moreover, the comparative example 17 and the comparative example 18 in which the pH of the surface coating composition formed on the aluminum-zinc alloy plated steel sheet is outside the range of 7 to 10 have deteriorated alkali resistance, weather resistance and stain resistance.

On the other hand, Comparative Example 19, Comparative Example 20, and Comparative Example 21 in which the dry film mass per one surface formed on the aluminum-zinc alloy plated steel sheet was less than 0.5 g / m ^{2 provided} sufficient performance in all evaluation items. Not shown.

Claims (3)

A water-dispersible polyester-based urethane resin (a) having a glass transition temperature (Tg) of 80 ° C. or higher, a water-dispersible acrylic resin having a carboxyl group and a glycidyl group but not containing a styrol group and having an acid value of 10 to 60 ( b), the zirconium compound (c) and the hindered amines (d) are blended as components, and the ratio of each component is 99/1 to 70/30 in terms of the solid content mass ratio (a) / (b). The content of (c) is Zr / ((a) + (b)) in terms of zirconium and is 1/10 to 1/500, and the amount of (d) is (d) / ((a) + ( The surface coating composition having a blending ratio of b)) of 5/100 to 1/1000 and a pH of 7 to 10 is contained in the range of 25 to 75% by mass of aluminum as a plating composition. Aluminum-zinc alloy plated steel Of dried after application to the surface, the surface-coated aluminum dry film mass per one surface, characterized in that by forming a coating layer is in the range of 0.5 to 5.0 g / m ² - zinc alloy plated steel sheet .   The monomer composition for synthesizing the water-dispersible acrylic resin (b) having an acid value of 10 to 60 containing a carboxyl group and a glycidyl group but not containing a styrol group is at least one selected from glycidyl methacrylate, acrylic acid and methacrylic acid 2. The surface-coated aluminum-zinc alloy plating according to claim 1, wherein n-butyl acrylate (methacrylate), methyl acrylate (methacrylate), ethyl acrylate (methacrylate) and acrylonitrile are used. steel sheet.   The surface-coated aluminum according to claim 1 or 2, wherein the temperature at which the surface-coating composition is applied to the surface of the aluminum-zinc alloy-plated steel sheet and then dried is 40 to 250 ° C as the ultimate plate temperature. Zinc alloy plated steel sheet.