JP2006265622A - Surface treated steel sheet having excellent corrosion resistance and scratch resistance and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a chromium-free surface treated steel sheet exhibiting excellent corrosion resistance and scratch resistance. <P>SOLUTION: As a first layer film, an organic-inorganic composite layer in which the surface layer of a plating film is made inactive by a surface treatment composition containing a water base resin, a phosphoric compound and a silane coupling agent is formed as a second layer film, an organic film combining firm adhesion and lubricity in between the first layer film is formed by a coating material film composition containing a water soluble or water dispersible urethane modified resin, a curing agent, silica and wax in specified ratios, and, by the two layer film structure, excellent corrosion resistance and scratch resistance are realized. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface-treated steel sheet that does not contain hexavalent chromium in the film, and is related to a surface-treated steel sheet that provides excellent corrosion resistance and scratch resistance in applications such as automobiles, home appliances, and building materials.

  Steel plates for home appliances, steel plates for building materials, and steel plates for automobiles have traditionally been made with chromic acid, for the purpose of improving corrosion resistance (white rust resistance, red rust resistance) on the surface of zinc-plated steel sheets or aluminum-based plated steel sheets. Steel plates subjected to chromate treatment with a treatment liquid containing hexavalent chromium containing dichromic acid or a salt thereof as a main component are widely used. This chromate treatment is an economical treatment method that provides excellent corrosion resistance and can be performed relatively easily.

However, since the film by chromate treatment contains hexavalent chromium which is a pollution-controlling substance, a surface-treated steel sheet that does not use hexavalent chromium is desired.
In addition, especially in the home appliance industry, in order to improve the working environment, the lubricating oil application and degreasing processes are omitted, and the molding process is often performed without painting. Therefore, surface-treated steel sheets having an organic resin film having good lubricity and wear resistance, and surface-treated steel sheets in which wax is further added to the organic resin film have been developed.

Specifically, the following can be mentioned.
(1) A method of forming a film in which a wax is dispersed in a urethane-based, acrylic-based, or polyester-based resin (for example, Patent Document 1 and Patent Document 2)
(2) A method of forming a film on the upper layer of the two-layer film using two types of solvent-based thermosetting resins having different glass transition temperatures (for example, Patent Document 3)
(3) A method of forming an organic resin film containing a polyolefin wax dispersion as an upper layer using a film containing an aqueous resin, a silane coupling agent and a phosphoric acid compound as a lower layer component (for example, Patent Document 4)
(4) A method of forming a film with an aqueous metal surface treatment composition containing a urethane resin, a curing agent, silica, and a polyolefin wax (for example, Patent Document 5)

Japanese Patent Laid-Open No. 10-23747 JP 2000-52478 A Japanese Patent Laid-Open No. 2003-239081 Japanese Patent No. 3464652 JP 2000-239690 A

However, these conventional techniques have the following problems.
Since the method (1) is based on the premise that a chromate film is formed on the galvanized surface, the condition that hexavalent chromium is not contained in the film is not satisfied.
In the above method (2), the effect of reducing the peeling of the film and the blackening of the peeled part at the time of processing (particularly press processing) can be obtained as the scratch resistance, but since the solvent-based resin is used, the paint is formed into a coating film. Occasionally, volatile organic substances (VOC) are volatilized, which is unfavorable for the environment and work.

The above method (3) aims to improve the scratch resistance by using a polyolefin wax dispersion, but the effect of the organic resin covering the entire surface is great for the scratch resistance. Since the effect of the scattered polyolefin wax is small, sufficient scratch resistance cannot be obtained.
The method (4) has a great effect on the scratch resistance by using a urethane resin having excellent abrasion resistance in addition to the polyolefin wax, but the urethane resin, silica and polyolefin wax have a rust prevention effect. Almost no corrosion resistance is obtained.

As described above, in the prior art, a chromium-free surface-treated steel sheet having both corrosion resistance and scratch resistance has not been obtained.
Accordingly, an object of the present invention is to solve such problems of the prior art and to provide a surface-treated steel sheet having excellent corrosion resistance and scratch resistance without containing hexavalent chromium in the film.

  As a result of intensive studies by the present inventors in order to solve the above problems, in order to achieve both excellent corrosion resistance and scratch resistance, an organic / inorganic in which the plating film surface layer is inactivated as the first layer film It has been found that a two-layer film structure in which an organic film having a strong adhesion and lubricity between the first layer film and the composite layer as a second layer film is formed is the most effective. That is, the first layer film is formed of a surface treatment composition containing an aqueous resin, a phosphoric acid compound, and a silane coupling agent, and the second layer film is formed of a water-soluble or water-dispersible urethane-modified acrylic resin, a curing agent, and silica. It has been found that by forming the coating composition containing the wax in a specific ratio, the above-described combined functions are exhibited, and excellent corrosion resistance and scratch resistance can be obtained. It was also found that by adding a Co metal compound to the first layer coating, the corrosion resistance was further improved and blackening (a kind of oxidation phenomenon on the plating surface) in a wet environment was suppressed. It was.

The present invention has been made based on such findings, and the gist thereof is as follows.
(1) A surface treatment composition containing an aqueous resin, a phosphoric acid compound and a silane coupling agent (but not containing hexavalent chromium) is applied to the surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet and dried. A first layer film formed thereon, and (a) a water-soluble urethane-modified acrylic resin or / and a water-dispersible urethane-modified acrylic resin, (b) a curing agent, (c) silica, , (D) containing wax, and (a) + (b), (c), (d) solid content mass ratio to the total solid content mass of these (a) to (d), respectively (a) + (B): 50 to 95% by mass, (c): 3 to 40% by mass, (d): 2 to 20% by mass, and the solid content mass ratio of (a) and (b) is (a) / (B) = 4 to 49, a coating composition (however, containing no hexavalent chromium) is applied and dried. A surface excellent in corrosion resistance and scratch resistance, characterized in that it has a formed second layer film and the total film thickness of the first layer film and the second layer film is 0.1 to 5 μm Treated steel sheet.

(2) In the surface-treated steel sheet according to (1) above, the surface treatment composition for forming the first layer film contains 1 to 300 parts by mass of silane coupling agent with respect to 100 parts by mass of the solid content of the aqueous resin, phosphorus A surface-treated steel sheet excellent in corrosion resistance and scratch resistance, characterized by containing 0.1 to 50 parts by mass of an acid compound.
(3) In the surface-treated steel sheet according to (1) or (2), the surface treatment composition for forming the first layer film further contains Co metal compound with respect to 100 parts by mass of the solid content of the aqueous resin. A surface-treated steel sheet excellent in corrosion resistance and scratch resistance, characterized by containing 0.01 to 50 parts by mass.
(4) In the surface-treated steel sheet according to any one of (1) to (3), the reactive functional group of the silane coupling agent contained in the surface treatment composition for forming the first layer film is an amino group. A surface-treated steel sheet with excellent corrosion resistance and scratch resistance.
(5) The surface-treated steel sheet according to any one of (1) to (4) above, wherein at least a part of the aqueous resin contained in the surface treatment composition for forming the first layer film is an epoxy resin. A surface-treated steel sheet with excellent corrosion resistance and scratch resistance.
(6) In the surface-treated steel sheet according to any one of the above (1) to (5), the Ni content in the plating film of the galvanized steel sheet is 20 to 1000 ppm. Excellent surface-treated steel sheet.

(7) A surface treatment composition containing an aqueous resin, a phosphoric acid compound, and a silane coupling agent (but not containing hexavalent chromium) is applied to the surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet, and a reaching plate A first layer film is formed by drying at a temperature of 30 to 300 ° C., and (a) a water-soluble urethane-modified acrylic resin and / or a water-dispersible urethane-modified acrylic resin, (b) It contains a curing agent, (c) silica, and (d) wax, and (a) + (b), (c), (d) with respect to the total solid mass of these (a) to (d) (A) + (b): 50-95% by mass, (c): 3-40% by mass, (d): 2-20% by mass, and (a) and (b) Coating composition whose solid content mass ratio is (a) / (b) = 4 to 49 (however, it does not contain hexavalent chromium) ) And drying at a temperature at which the ultimate plate temperature is 50 to 350 ° C., and a total film thickness of the first layer film and the second layer film is 0.1 to 5 μm. A method for producing a surface-treated steel sheet having excellent corrosion resistance and scratch resistance, wherein the surface treatment composition and the coating composition are applied so that
(8) In the production method of (7) above, the surface treatment composition for forming the first layer film further contains 0.01 to 50 mass parts of the Co metal compound with respect to 100 mass parts of the solid content of the aqueous resin. A method for producing a surface-treated steel sheet excellent in corrosion resistance and scratch resistance, characterized by containing a part.

  The surface-treated steel sheet of the present invention has excellent corrosion resistance and scratch resistance without containing hexavalent chromium in the film.

The details of the present invention and the reasons for limitation will be described below.
Examples of the zinc-based plated steel sheet used as the base of the surface-treated steel sheet of the present invention include galvanized steel sheet, Zn-Ni alloy-plated steel sheet, Zn-Fe alloy-plated steel sheet (electroplated steel sheet, galvannealed steel sheet), Zn-Cr. Alloy-plated steel sheet, Zn-Mn alloy-plated steel sheet, Zn-Co alloy-plated steel sheet, Zn-Co-Cr alloy-plated steel sheet, Zn-Cr-Ni alloy-plated steel sheet, Zn-Cr-Fe alloy-plated steel sheet, Zn-Al-Mg Alloy-plated steel sheet (for example, Zn-6% Al-3% Mg alloy-plated steel sheet, Zn-11% Al-3% Mg alloy-plated steel sheet), Zn-Al alloy-plated steel sheet (for example, Zn-5% Al-alloy plated steel sheet) Zn-55% Al alloy-plated steel sheet) or the like can be used. Further, one or two of nickel, cobalt, manganese, iron, molybdenum, tungsten, titanium, chromium, aluminum, magnesium, lead, antimony, tin, copper as a small amount of different metal elements or impurities in the plated layer of these plated steel sheets It is also possible to use a plated steel sheet containing seeds and / or a plated steel sheet (for example, Zn—SiO ₂ dispersed plated steel sheet) in which a metal oxide such as silica, a polymer, or the like is dispersed.

Moreover, the multilayer plating steel plate which plated two or more layers of the same kind or different kind among the above plating can also be used.
Moreover, it is desirable that the plating film of the galvanized steel sheet contains 20 to 1000 ppm, more preferably about 25 to 800 ppm of Ni. Here, when the Ni content is less than 20 ppm, the blackening resistance is not sufficient. On the other hand, when the Ni content exceeds 1000 ppm, the color tone (L value) after the formation of the first layer and the second layer film is lowered, so that it is used without coating. If you do, it will not be suitable.

As the aluminum-based plated steel sheet used as the base of the surface-treated steel sheet of the present invention, an aluminum-plated steel sheet or an Al—Si alloy-plated steel sheet can be used.
Moreover, as a plated steel plate, the steel plate surface may be plated in advance with a thin plate such as Ni, and the above-described various types of plating may be performed thereon.
As a plating method, any feasible method among an electrolytic method (electrolysis in an aqueous solution, electrolysis in a non-aqueous solvent), a melting method, and a gas phase method can be employed.
In addition, when the surface treatment film is formed on the surface of the plating film, alkali degreasing, solvent degreasing, surface conditioning treatment (alkaline surface conditioning) is performed on the surface of the plating film as necessary in order to prevent film defects and unevenness from occurring. Treatment, acidic surface conditioning treatment) and the like can be performed.

In addition, iron group metal ions (Ni ions, Co ions, Fe ions) are preliminarily applied to the plating surface for the purpose of preventing blackening (a kind of oxidation phenomenon on the plating surface) under the usage environment of the surface-treated steel sheet. Surface conditioning treatment with an acidic or alkaline aqueous solution containing can also be performed.
When using an electrogalvanized steel sheet as the base steel sheet, iron group metal ions (one or more of Ni ions, Co ions, Fe ions) are added to the electroplating bath for the purpose of preventing blackening, and the plating film These metals can be contained in an amount of 1 ppm or more. In this case, there is no particular limitation on the upper limit of the iron group metal concentration in the plating film.

Next, the surface treatment film (first layer film) formed on the surface of the zinc-based plated steel sheet or the aluminum-based plated steel sheet will be described.
In the surface-treated steel sheet of the present invention, the first layer film formed on the surface of the zinc-based plated steel sheet or the aluminum-based plated steel sheet contains an aqueous resin, a phosphoric acid compound, and a silane coupling agent, preferably these are the main components. A surface treatment film formed by applying and drying the surface treatment composition. This surface treatment composition for the first layer film does not contain hexavalent chromium.

  Here, the aqueous resin includes, in addition to the water-soluble resin, a water-dispersible resin in which a water-insoluble resin is dispersed in water, such as an emulsion or a dispersion. There are no particular restrictions on the water-based resin that can be used. For example, epoxy resin, urethane resin, acrylic resin, acrylic silicon resin, acrylic-ethylene copolymer, acrylic-styrene copolymer, alkyd resin, polyester resin, ethylene resin, fluorine resin 1 type, or 2 or more types can be used. However, from the viewpoint of corrosion resistance, it is preferable to use an organic polymer resin having an OH group and / or a COOH group, and among them, the epoxy resin can remarkably improve the adhesion between the base metal and the upper film, Particularly preferred.

  Examples of the silane coupling agent include vinyl methoxy silane, vinyl ethoxy silane, vinyl trichloro silane, vinyl trimethoxy silane, vinyl triethoxy silane, β- (3,4 epoxy cyclohexyl) ethyl trimethoxy silane, and γ-glycidoxy. Propyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-β (aminoethyl) γ- Aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-metac Lilooxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, p-styryltrimethoxysilane, γ -Acryloxypropyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, γ-chloropropyltrimethoxysilane, bis (triethoxysilylpropyl) tetrasulfide, γ-isocyanatopropyl Triethoxysilane, γ-triethoxysilyl-N- (1,3-dimethyl-butylidene) propylamine, N- (vinylbenzylamine) -β-aminoethyl-γ-aminopropyltrimeth Etc. can be mentioned Shishiran, can be used one or two or more thereof. The reason why the film containing these silane coupling agents is excellent in corrosion resistance is that silanol groups (Si-OH) generated by hydrolysis of the silane coupling agent in the aqueous solution hydrogen bond with the surface of the plating film, Is considered to impart excellent adhesion by a dehydration condensation reaction.

Among the silane coupling agents, a silane coupling agent having an amino group is particularly preferable than a silane coupling agent having a mercapto group or a glycidyl group as a reactive functional group. The reason for this is considered that the amino group is more adsorbable with the plating metal than the other functional groups.
Examples of the silane coupling agent having an amino group include N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, and N-β (aminoethyl). γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and the like can be mentioned. Specifically, “KBM-903” and “KBE-903” manufactured by Shin-Etsu Chemical Co., Ltd. , “KBM-603”, “KBE-602”, “KBE-603” (all are trade names), and the like.
The compounding amount of the silane coupling agent is preferably 1 to 300 parts by mass, more preferably 5 to 100 parts by mass, and further preferably 15 to 50 parts by mass with respect to 100 parts by mass of the solid content of the aqueous resin. Is appropriate. If the blending amount of the silane coupling agent is less than 1 part by mass, the corrosion resistance is inferior. On the other hand, if it exceeds 300 parts by mass, a sufficient film cannot be formed. descend.

There is no restriction | limiting regarding the skeleton of a phosphate ion, a condensation degree, etc. as a phosphoric acid compound, For example, hypophosphorous acid, phosphorous acid, orthophosphoric acid, polyphosphoric acid, and those salts can be used. This phosphoric acid compound has the effect | action which acts on the surface of an inactive plating film and activates a metal surface. And it is thought that corrosion resistance improves notably as a result of the adhesiveness of the plating metal surface and film formation resin activated in this way improving remarkably via a silane coupling agent.
The blending amount of the phosphoric acid compound is preferably 0.1 to 50 parts by mass, more preferably 1 to 40 parts by mass, and further preferably 5 to 30 parts by mass with respect to 100 parts by mass of the solid content of the aqueous resin. Is appropriate. When the blending amount of the phosphoric acid compound is less than 0.1 parts by mass, the corrosion resistance is inferior. On the other hand, when it exceeds 50 parts by mass, the appearance unevenness after film formation tends to occur.

In order to improve corrosion resistance and blackening resistance, the surface treatment composition preferably further contains a Co metal compound. Examples of the metal compound of Co include metal salts such as Co nitrate, Co sulfate, and Co chloride, and one or more of these can be used. The amount of the Co metal compound is 0.01 to 50 parts by weight, preferably 0.5 to 40 parts by weight, and more preferably 1 to 30 parts by weight with respect to 100 parts by weight of the solid content of the aqueous resin. Is appropriate. If the blending amount of the Co metal compound is less than 0.01 parts by mass, the effect of improving the corrosion resistance is not sufficient. On the other hand, if it exceeds 50 parts by mass, the reactivity with the treatment liquid becomes strong and uneven appearance tends to occur.
The dry film thickness of the first layer film is preferably 0.01 μm or more and less than 5 μm, more preferably 0.1 to 3 μm, and still more preferably 0.3 to 2 μm. If the dry film thickness is less than 0.01 μm, the corrosion resistance tends to be insufficient, while if it is 5 μm or more, the conductivity is lowered.

Next, the second layer film (organic film) formed on the first layer film will be described.
This second layer film comprises (a) a water-soluble urethane-modified acrylic resin and / or a water-dispersible urethane-modified acrylic resin, (b) a curing agent, (c) silica, and (d) a wax in a specific ratio. It is a film formed by applying a coating composition containing these as a main component and drying. The coating composition for the second layer film does not contain hexavalent chromium.
The urethane-modified acrylic resin that is the base resin of the film may be either water-soluble or water-dispersible, or both resins may be used in combination.
The method for modifying the acrylic resin with urethane is not particularly limited. For example, the acrylic polyol is synthesized by the method shown in (I) below, and the urethane-modified acrylic is synthesized by the method shown in (II) below using the synthesized acrylic polyol. Resins can be synthesized.

(I) Synthesis of acrylic polyol An acrylic polyol which is an acrylic copolymer of an acrylic monomer having a hydroxyl group and an acrylic monomer having no hydroxyl group is prepared. Examples of the acrylic monomer having a hydroxyl group include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and the like, and one or more of these can be used. Examples of the acrylic monomer having no hydroxyl group include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, butyacrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, Examples include isopropyl methacrylate, butyl methacrylate, N-hexyl methacrylate, lauryl methacrylate, acrylamide, N-methylol acrylamide, diacetone acrylamide, and glycidyl methacrylate, and one or more of these can be used.

(II) Synthesis of urethane-modified acrylic resin The method for synthesizing the urethane-modified acrylic resin is not particularly limited, and examples thereof include the following methods. Here, the urethane-modified acrylic resin refers to a polymer of an acrylic polyol, a low molecular polyolefin polyol, and an isocyanate compound.
Isocyanate compounds include aliphatic, alicyclic and aromatic polyisocyanates. Specifically, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate ester, hydrogenated xylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, 3, 3′-dimethoxy-4,4′biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4′-biphenylmethane Polyisocyanates such as diisocyanate, phenylene diisocyanate, xylene diisocyanate, and tetramethylxylene diisocyanate, or these Include derivatives obtained from polyisocyanate, may be used alone or two or more thereof.

  The isocyanate compound can be masked to protect the isocyanate group as necessary. Examples of the blocking agent include malonic acid diester (such as diethyl malonate), acetylacetone, acetoacetate (acetoacetate). Active methylene compounds such as ethyl acetate; oxime compounds such as acetoxime, methyl ethyl ketoxime (MEK oxime), methyl isobutyl ketoxime (MIBK oxime); methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, heptyl alcohol, hexyl alcohol , Monohydric alcohols such as octyl alcohol, 2-ethylhexyl alcohol, isononyl alcohol, stearyl alcohol or isomers thereof; methyl glycol, ethyl glycol, Chill diglycol, ethyl triglycol, butyl glycol, glycol derivatives such as butyl diglycol; and amine compounds such as dicyclohexylamine and the like, may be used alone or two or more thereof.

The blocking reaction for obtaining the blocked isocyanate is performed by a known reaction method. The addition amount of the blocking agent is usually 1.0 to 2.0 equivalents, preferably 1.05 to 1.5 equivalents, relative to the free isocyanate group.
In the usual isocyanate compound blocking reaction, a blocking agent is added in the final reaction. Further, when the polyurethane is subjected to a blocking reaction, the blocking agent can be added and reacted at any stage to obtain a blocked polyisocyanate.

  The water-soluble or water-dispersible urethane-modified acrylic resin (a) desirably has a solid content mass ratio of the urethane component in the resin solid content of 10 to 50 mass%, more preferably 10 to 30 mass%. When the solid content mass ratio of the urethane component is less than 10 mass%, it is difficult to obtain excellent wear resistance unique to the urethane resin. On the other hand, if it exceeds 50% by mass, the amount of the isocyanate compound that is indispensable for the synthesis of the urethane resin is increased, and this isocyanate compound is expensive and thus not economical.

  The curing agent (b) is added in order to sufficiently crosslink the film, and excellent corrosion resistance and solvent resistance can be obtained by the crosslinking. There are no particular restrictions on the type of curing agent used, but there are epoxy groups and oxazolines which are not hydrophilic groups, such as amines having a hydrophilic group such as amino groups, hydroxyl groups and carboxyl groups, polyhydric alcohols and polybasic acids. It is particularly preferable to use a compound having at least one functional group selected from a group, an isocyanate group, and an aziridinyl group.

  In addition, when an epoxy compound is used as the curing agent, the chemical resistance of the resulting resin (chemical resistance to acids, alkalis, solvents, etc.) and adhesion improve the chemical resistance and paint adhesion of the resulting film. To do. Furthermore, in the case where an epoxy resin is contained in the first layer coating, it is possible to drastically improve the adhesion by including an epoxy compound as a curing agent in the second layer coating. Further, by strengthening the adhesion between the first layer film and the second layer film as well as the adhesion with the base plating metal, the shielding effect of the corrosion factor is exhibited, which contributes to the improvement of the corrosion resistance.

  Total solid content mass of water-soluble urethane-modified acrylic resin and / or water-dispersible urethane-modified acrylic resin (a) + curing agent (b) + silica (c) + wax (d) (hereinafter referred to as “(a) to (d The total solid content mass ratio of the water-soluble urethane-modified acrylic resin and / or the water-dispersible urethane-modified acrylic resin (a) and the curing agent (b) is 50 to 95 mass). %, Preferably 55 to 75% by mass. If the mass ratio is less than 50 mass%, the target corrosion resistance cannot be obtained because the binder effect is insufficient. Moreover, the target corrosion resistance is not obtained also when it exceeds 95 mass%.

  Further, the curing agent (b) is such that the solid content mass ratio with the water-soluble urethane-modified acrylic resin and / or the water-dispersible urethane-modified acrylic resin (a) is (a) / (b) = 4 to 49. Blend. When the solid content mass ratio is less than 4, the characteristics of the water-soluble or water-dispersible urethane-modified acrylic resin (a) that is the base resin cannot be sufficiently exhibited, and the base resin and the unreacted curing agent are not present. Since it remains and acts as a plasticizer, the corrosion resistance and paint adhesion deteriorate. On the other hand, when the solid content mass ratio exceeds 49, the effect of blending the curing agent becomes poor.

  Silica (c) is added to improve corrosion resistance. There is no restriction | limiting in particular in the kind of silica, For example, 1 or more types, such as colloidal silica and a fumed silica, can be used. The compounding amount of silica (c) is 3 to 40% by mass in terms of the solid mass ratio relative to the total solid mass of (a) to (d). When the blending ratio of silica is less than 3% by mass, the effect of improving the corrosion resistance is small. On the other hand, when the silica content exceeds 40% by mass, the binder effect of the resin is small, and in this case, the corrosion resistance is lowered. The particle size and type of silica are not particularly limited in the present invention.

Wax (d) improves the scratch resistance as a lubricating component. There are no particular restrictions on the type of wax, such as carnauba wax, rice wax, lanolin wax, montan wax, paraffin wax, microcrystalline wax, fatty acid ester wax, fatty acid amide wax or partially saponified products thereof, polyethylene wax, polyolefin wax. Chlorinated hydrocarbon, fluorinated hydrocarbon, ethylene acrylic copolymer wax, and the like, and one or more of these can be used.
The average particle size of the wax is preferably 0.05 to 3.0 μm. If the average particle size is less than 0.05 μm, the processability tends to be insufficient, whereas if it exceeds 3.0 μm, the distribution of the solidified wax tends to be uneven.

The melting point of the wax is preferably 50 to 160 ° C. If the melting point of the wax is less than 50 ° C., the wax itself melts in the summer working environment, and the inherent lubricity of the wax is not exhibited, so that the scratch resistance is lowered. On the other hand, if the melting point of the wax exceeds 160 ° C., the lubricity of the wax itself is not exhibited, so that the scratch resistance also decreases in this case. In addition, as a shape of a wax particle, a spherical shape is more preferable in order to obtain high processability.
The compounding quantity of wax (d) is 2-20 mass% in the solid content mass ratio with respect to the total solid mass of (a)-(d), Preferably you may be 5-15 mass%. If the blending ratio of the wax is less than 2% by mass, the effect of improving the molding processability is small. On the other hand, if it exceeds 20% by mass, the wax is scattered in the press apparatus and its surroundings during the molding process. .

The surface treatment composition for the first layer coating and the coating composition for the second layer coating used in the present invention are surfactants called wettability improvers for forming a uniform coating on the coated surface. A thickener, a conductive material for improving conductivity, a color pigment for improving design properties, a solvent for improving film forming property, and the like may be added as necessary.
The dry film thickness of the second layer film is preferably 0.01 μm or more and less than 5 μm, more preferably 0.1 to 0.3 μm, and still more preferably 0.3 to 2 μm. If the dry film thickness is less than 0.01 μm, the scratch resistance tends to be insufficient, whereas if it is 5 μm or more, the conductivity decreases.
In the present invention, the total film thickness (dry film thickness) of the first layer film and the second layer film is 0.1 to 5 μm. If the total film thickness is less than 0.1 μm, either corrosion resistance or wrinkle resistance tends to be insufficient, while if it exceeds 5 μm, the conductivity decreases.

Next, the manufacturing method of the surface treatment steel plate of this invention is demonstrated.
In the production method of the present invention, the surface treatment composition (treatment liquid) for forming the first layer film described above is applied to the surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet, and the ultimate plate temperature is 30 to 300. The first layer film is formed by drying at a temperature of ℃, and the above-mentioned coating composition for forming the second layer film is applied to the upper part, and the ultimate plate temperature is 50 to 350 ° C. The surface treatment composition and the coating composition are applied so that the second layer film is formed by drying at a temperature, and the total film thickness of the first layer film and the second layer film is 0.1 to 5 μm. To do.

The surface of the plated steel sheet can be subjected to an alkali degreasing treatment as necessary before applying the surface treatment composition, and further subjected to a pretreatment such as a surface adjustment treatment in order to improve adhesion and corrosion resistance.
A surface treatment composition for forming the first layer film is applied to the surface of the plated steel sheet in a predetermined range of film thickness (dry film thickness, preferably 0.01 μm or more and less than 5 μm, more preferably 0.1 to 3 μm, still more preferably 0. 3 to 2 μm). It is desirable to adjust the surface treatment composition (treatment liquid) to pH 0.5-6, preferably 1-4. If the pH of the surface treatment composition is less than 0.5, the reactivity of the treatment liquid is too strong and uneven appearance tends to occur. On the other hand, if the pH exceeds 6, the reactivity of the treatment liquid becomes low, and the plating metal and film Bonding is insufficient and corrosion resistance tends to decrease.

As a method for applying the surface treatment composition to the surface of the plated steel plate, any method such as a so-called application method, dipping method, spray method or the like can be adopted. As a coating method, any method such as a roll coater (3-roll method, 2-roll method, etc.), a squeeze coater, or a die coater may be used. In addition, after the coating process, dipping process or spraying process using a squeeze coater or the like, the coating amount can be adjusted, the appearance can be made uniform, and the film thickness can be made uniform by an air knife method or roll drawing method.
After applying the surface treatment composition, it is dried by heating without washing with water. As the heating and drying means, a dryer, a hot air furnace, a high frequency induction heating furnace, an infrared furnace or the like can be used. It is appropriate to perform the heat treatment in the range of 30 ° C. to 300 ° C., preferably 40 ° C. to 250 ° C., at the ultimate plate temperature. If this heating temperature is less than 30 ° C., a large amount of moisture remains in the film, resulting in insufficient corrosion resistance. Moreover, when it exceeds 300 degreeC, not only is it uneconomical, but there exists a possibility that a defect may arise in a film | membrane and corrosion resistance may fall.

  After the first layer film is formed as described above, a coating composition (treatment liquid) for forming the second layer film is formed thereon with a predetermined film thickness (dry film thickness, preferably 0.01 μm or more and 0). The coating composition is applied so as to be less than 0.5 μm, more preferably 0.1 to 3 μm, and still more preferably 0.3 to 2 μm. Any method such as a roll coater (3-roll method, 2-roll method, etc.), a squeeze coater, a die coater, etc. may be used as the coating method. After the dipping treatment or spray treatment, the coating amount can be adjusted, the appearance can be made uniform, and the film thickness can be made uniform by an air knife method or a roll drawing method.

After applying the coating composition, it is usually heated and dried without washing with water, but a washing process may be carried out after applying the coating composition.
As the heating and drying means, a dryer, a hot air furnace, a high frequency induction heating furnace, an infrared furnace or the like can be used. It is appropriate that the heat treatment is performed in the range of 50 to 350 ° C., preferably 80 to 250 ° C., at the ultimate plate temperature. If this heating temperature is less than 50 ° C., a large amount of moisture remains in the film, resulting in insufficient corrosion resistance. Further, if it exceeds 350 ° C., not only is it uneconomical, but there is a possibility that defects occur in the film and the corrosion resistance is lowered.
The first layer film + second layer film described above may be formed only on one side of the plated steel sheet or on both sides.

  For the formation of the first layer film, a surface treatment liquid (aqueous solution) was prepared by appropriately blending the aqueous resin shown in Table 1, the silane coupling agent shown in Table 2, the phosphoric acid compound shown in Table 3, and the metal compound shown in Table 4. did. Moreover, the coating composition which mix | blended suitably the water resin shown in Table 5, the hardening | curing agent shown in Table 6, the silica shown in Table 7, and the wax shown in Table 8 was prepared for 2nd layer membrane | film | coat formation. Moreover, the various plated steel plates shown in Table 9 were used as the processing original plate.

After the surface of the plated steel sheet was subjected to alkaline degreasing treatment, washed with water and dried, it was treated (applied) with the treatment liquid for forming the first layer film and dried at various temperatures. Subsequently, the coating composition for forming the second layer film was applied to the upper portion and dried at various temperatures to obtain surface-treated steel sheets of invention examples and comparative examples. In addition, the film thickness of the 1st layer and the 2nd layer membrane | film | coat was adjusted with the solid content (heating residue), processing time, etc. of the membrane | film | coat composition.
The results of evaluating the white rust resistance, wrinkle resistance and paint adhesion of the obtained surface-treated steel sheets are shown in Tables 10 to 17 together with the coating composition. The measurement and evaluation methods for each quality performance are as follows.

(1) White rust resistance About each sample, the salt spray test (JIS-Z-2371) was given and it evaluated by the white rust area rate after progress for 120 hours and 240 hours. The evaluation criteria are as follows.
◎: White rust area ratio less than 5% ○: White rust area ratio 5% or more and less than 10% ○-: White rust area ratio 10% or more and less than 25% △: White rust area ratio 25% or more and less than 50% × : White rust area ratio 50% or more

(2) Scratch resistance After rubbing the test piece with corrugated board using a rubbing tester (produced by Taihei Rika Kogyo Co., Ltd.), the surface of the test piece was visually observed and evaluated according to the following evaluation criteria. The test was performed with a pressing load of 500 g, a sliding distance of 60 mm, a speed of 120 mm / s, and a rubbing number of 1000 times.
◎: The number of cocoons is 0. ○: The number of cocoons is 1-2. △: The number of cocoons is 3-10. X: The number of cocoons is 11 or more.

(3) Paint adhesion For each sample, after applying a melamine-based baking paint (film thickness of 30 μm), immerse it in boiling water for 2 hours, and immediately cut a grid (10 × 10, 1 mm interval). Adhesion and peeling with an adhesive tape were performed, and the peeled area ratio of the coating film was measured. The evaluation criteria are as follows.
◎: No peeling ○: Peeling area ratio less than 5% △: Peeling area ratio of 5% or more and less than 20% ×: Peeling area ratio of 20% or more

In Tables 10 to 17, * 1 to * 10 indicate the following contents.
* 1: Plated steel plate No. in Table 9
* 2: Aqueous resin Nos. Listed in Table 1
* 3: Silane coupling agent No. described in Table 2
* 4: Phosphate compound Nos. Listed in Table 3
* 5: Metal compound Nos. Listed in Table 4
* 6: Aqueous resin Nos. Listed in Table 5
* 7: Curing agent No. described in Table 6
* 8: Silica No. described in Table 7
* 9: Wax no.
* 10: parts by mass (however, "water-based resin" is solid part by mass)
* 11: Mass% of solid content

Claims (8)

  Formed by applying a surface treatment composition containing an aqueous resin, a phosphoric acid compound, and a silane coupling agent (but not containing hexavalent chromium) to the surface of a zinc-based plated steel sheet or aluminum-based plated steel sheet, and drying. The first layer film is formed, and (a) a water-soluble urethane-modified acrylic resin or / and a water-dispersible urethane-modified acrylic resin, (b) a curing agent, (c) silica, and (d ) Containing wax, and the solid content mass ratio of (a) + (b), (c), (d) to the total solid mass of these (a) to (d) is (a) + (b ): 50 to 95% by mass, (c): 3 to 40% by mass, (d): 2 to 20% by mass, and the solid content mass ratio of (a) and (b) is (a) / (b ) = 4 ~ 49 coating composition (however, hexavalent chromium is not included) A surface-treated steel sheet having excellent corrosion resistance and scratch resistance, wherein the second layer film is formed and the total film thickness of the first layer film and the second layer film is 0.1 to 5 μm .   The surface treatment composition for forming the first layer film contains 1 to 300 parts by mass of the silane coupling agent and 0.1 to 50 parts by mass of the phosphoric acid compound with respect to 100 parts by mass of the solid content of the aqueous resin. The surface-treated steel sheet excellent in corrosion resistance and wrinkle resistance according to claim 1.   The surface treatment composition for forming the first layer film further contains 0.01 to 50 parts by mass of a Co metal compound with respect to 100 parts by mass of the solid content of the aqueous resin. 2. A surface-treated steel sheet having excellent corrosion resistance and scratch resistance according to 2.   The reactive functional group of the silane coupling agent contained in the surface treatment composition for forming the first layer film is an amino group, and the corrosion resistance and wrinkle resistance according to any one of claims 1 to 3 Excellent surface-treated steel sheet.   At least a part of the aqueous resin contained in the surface treatment composition for forming the first layer film is an epoxy resin, and is excellent in corrosion resistance and scratch resistance according to any one of claims 1 to 4. Surface treated steel sheet.   The surface-treated steel sheet having excellent corrosion resistance and scratch resistance according to any one of claims 1 to 5, wherein the Ni content in the plating film of the zinc-based plated steel sheet is 20 to 1000 ppm.   A surface treatment composition containing an aqueous resin, a phosphoric acid compound, and a silane coupling agent (but not containing hexavalent chromium) is applied to the surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet, and the ultimate plate temperature is 30. A first layer film is formed by drying at a temperature of ˜300 ° C., and (a) a water-soluble urethane-modified acrylic resin or / and a water-dispersible urethane-modified acrylic resin, (b) a curing agent, , (C) silica and (d) wax, and (a) + (b), (c), (d) solid content mass with respect to the total solid content mass of these (a) to (d) The proportions are (a) + (b): 50 to 95% by mass, (c): 3 to 40% by mass, (d): 2 to 20% by mass, and the solid contents of (a) and (b) A coating composition having a mass ratio of (a) / (b) = 4 to 49 (but not containing hexavalent chromium) And the second layer film is formed by drying at a temperature at which the ultimate plate temperature is 50 to 350 ° C., and the total film thickness of the first layer film and the second layer film is 0.1 to 5 μm. Thus, the manufacturing method of the surface-treated steel plate excellent in corrosion resistance and wrinkle resistance characterized by apply | coating a surface treatment composition and a coating composition.   The surface treatment composition for forming the first layer film further contains 0.01 to 50 parts by mass of a Co metal compound with respect to 100 parts by mass of the solid content of the aqueous resin. A method for producing a surface-treated steel sheet having excellent corrosion resistance and scratch resistance as described.