JP6915699B2 - Pre-coated steel sheet - Google Patents

Description

The present invention relates to a precoated steel sheet.
The present application claims priority based on Japanese Patent Application No. 2017-243736 filed in Japan on December 20, 2017, the contents of which are incorporated herein by reference.

As exterior materials for home appliances, building materials, automobiles, etc., painted products that are painted after processing and pre-coated steel sheets that are coated with a paint film are used.

Until now, pre-coated steel sheets have generally been coated with a plurality of coating films having shared functions. This coating film is often composed of at least two layers, a primer layer that imparts corrosion resistance and a top layer that imparts designability, solvent resistance, and the like. For example, Patent Document 1 discloses a coated steel sheet having a coating film containing a plurality of rust preventive pigments on a Zn plating layer.

In recent years, a colored steel sheet that can be manufactured at low cost has been studied from the viewpoint of manufacturability and economy. For example, Patent Document 2 discloses a chromate-free black-coated metal plate on which a black coating film based on a resin having a thickness of 2 to 10 μm is formed. Similar to the conventional precoated steel sheet having a two-layer coating film, these steel sheets are also required to have scratch resistance, sweat resistance, corrosion resistance of processed parts, adhesion, and end face coagulation peeling resistance.

Japanese Patent Application Laid-Open No. 2008-291160 International Publication No. 2010/137726 International Publication No. 2012/133671

The chromate-free black-coated metal plate described in Patent Document 2 has a problem that the coating film is scratched until or during the processing, and the scratches are conspicuous due to the scratches on the steel sheet. Further, when the chemical conversion treatment is not performed between the coating film and the metal plate, there is a problem that the adhesion is remarkably inferior.

For example, Patent Document 3 discloses a steel sheet having a plating layer containing Zn and V and having a coating film coated immediately above the plating layer. Since the plating layer containing Zn and V is hard, it is difficult for flaws to occur, and because it is black, the flaws are not noticeable, so that it is excellent in flaw resistance.

However, as a result of examination by the inventors, a steel sheet having a coating film containing an organic resin on a plating layer containing Zn and V described in Patent Document 3 may be inferior in sweat resistance and corrosion resistance in a processed portion. I understood. Here, the sweat resistance refers to a phenomenon in which, after sweat adheres to a steel sheet, the sweat permeates the coating film to discolor the coating film, or the sweat dissolves the base of the coating film. In particular, when the coating film contains a water-dispersed resin containing a sulfonic acid group, a water-dispersed urethane resin, or the like, it is known that the sweat resistance is inferior.

Further, it was found that the plating layer containing Zn and V is easily cracked during processing, and at the same time, the coating film is also cracked, so that the corrosion resistance of the processed portion is also inferior. On the other hand, a coating film having excellent elongation is hard to crack, but there is a problem that the coating film coagulates and peels off when the cut end face is slid when the coated steel sheet is pressed (cohesive peeling of the end face coating film). "End face coating film coagulation peeling" is a phenomenon in which the coating film at the cut end is peeled off due to the cohesive fracture of the coating film itself caused by the ironing process. Conventionally, it has been difficult to achieve both corrosion resistance of a processed portion and cohesive peeling resistance of an end face coating film at a high level.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a precoated steel sheet having excellent scratch resistance, sweat resistance, corrosion resistance of processed parts, and end face coagulation peeling resistance.

The present inventor has studied diligently in order to solve the above problems. With the conventional coated steel sheet, excellent scratch resistance, sweat resistance, etc. could not be obtained unless a base treatment and a primer layer were used between the steel sheet and the coating film. However, as a result of research, surprisingly, a binder resin having a butylated melamine resin and an OH group directly above a plating layer containing one or more of vanadium and zirconium and zinc without using a base treatment and a primer layer. It was found that excellent scratch resistance, sweat resistance, end face coating coagulation peeling resistance, and corrosion resistance of processed parts can be obtained by forming a coating film having a predetermined glass transition temperature by curing reaction with and. rice field. Here, "directly above" means that they are in contact with each other without sandwiching another layer.

The gist of the present invention is as follows.
(1) The precoated steel sheet according to one aspect of the present invention is formed on the steel sheet, a plating layer containing one or more of vanadium and zirconium and zinc on at least one surface of the steel sheet, and directly above the plating layer. A coating film having a glass transition temperature of 25 ° C. to 80 ° C. and containing a cured product composed of a binder resin having an OH group and a butylated melamine resin is provided.
(2) The precoated steel sheet according to (1) is zinc when the zinc concentration and the carbon concentration are measured by the glow discharge emission analysis method in the measurement range starting from the surface of the coating film and ending at the steel sheet. Starting from the depth position A where the concentration is the maximum value in the measurement range, the zinc concentration is 5% of the maximum value, and the end point is the depth position B located on the steel plate side of the depth position A. The carbon concentration may always be 1 atomic% or more, and the ratio of the carbon concentration to the zinc concentration at the depth position A may be 8% or more.
(3) In the precoated steel sheet according to (1) or (2), in the butylated melamine resin, one or more of the structural units R1 to R6 represented by the following formula (1) have −CH2OC3H7. You may.

(4) In the precoated steel sheet according to any one of (1) to (3), the binder resin is a polyester resin having an OH group, a polyol-added epoxy resin, a polyol-added polyurethane resin, a polyol-added olefin resin, or a polyol. It may be one or more selected from the group consisting of the added acrylic resin.
(5) In the precoated steel sheet according to any one of (1) to (4), the binder resin may not contain a sulfonic acid group.
(6) The precoated steel sheet according to any one of (1) to (5) may have a glass transition temperature of the binder resin of 7 ° C. or higher and 71 ° C. or lower.
(7) The precoated steel sheet according to any one of (1) to (6) may have a hydroxyl value of 5 to 50 KOHmg / g of the binder resin.
(8) In the precoated steel sheet according to any one of (1) to (7), the coating film may further contain a methylated melamine resin.
(9) The precoated steel sheet according to any one of (1) to (8) may contain an adduct of a silane coupling agent in the coating film.
(10) In the precoated steel sheet according to any one of (1) to (9), the film thickness of the coating film may be more than 5 μm and 20 μm or less.
(11) In the precoated steel sheet according to any one of (1) to (10), the coating film may further contain an epoxy resin.

According to the above aspect, unlike the conventional coated steel sheet, even if a base treatment and a primer layer are not used between the steel sheet and the coating film, scratch resistance, sweat resistance, corrosion resistance of the processed portion, and end face cohesive peeling are performed. It is possible to provide a precoated steel sheet having excellent properties.

It is sectional drawing of the precoated steel sheet which concerns on embodiment of this invention. It is a figure which shows the density | concentration of V, Zn and C in the depth direction obtained by measuring the precoated steel sheet which concerns on embodiment of this invention by a glow discharge light emission method.

Hereinafter, preferred embodiments of the present invention will be described in detail.

Hereinafter, the precoated steel sheet according to the embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a precoated steel sheet 10 according to an embodiment of the present invention.
The precoated steel sheet 10 of the present invention contains zinc (Zn) and vanadium (V) or Zn and zirconium (Zr) on at least one surface of the steel sheet 1 (that is, one surface or both sides of the steel sheet 1) by a cathode electrolysis treatment. It is a precoated steel sheet 10 in which a coating film 3 is formed by forming a plating layer 2, applying a coating material containing a binder resin or the like on the plating layer 2, and heating the coating layer 2.
For precoated steel sheets in which the glass dislocation temperature of the coating film and the dynamic surface tension of the paint are not sufficiently controlled, the resin may not sufficiently penetrate into the plating layer and sufficient adhesion may not be obtained (Table 6). -2).

(Steel plate)
In the present embodiment, the steel plate 1 is not particularly limited. For example, ultra-low C type, Al-k type, two-phase structure type (for example, structure containing martensite in ferrite), work-induced transformation type (structure containing retained austenite in ferrite), fine crystal type (mainly ferrite). Any type of steel plate such as (texture) may be used as the steel plate 1.

(Plating layer)
The plating layer 2 contains one or more of V and Zr and Zn ions as elements. Specifically, the plating layer 2 contains any one or more of V and Zr metals, oxides and hydroxides, and one or more of Zn metals, oxides and hydroxides. The plating layer 2 is produced from an electrolytic treatment bath composed of a solution containing one or more of V and Zr and Zn ions.

The plating layer 2 can be produced by subjecting the steel sheet 1 to cathodic electrolysis using a solution containing one or more of V ions and Zr ions and Zn ions. A solution containing one or more of V ions and Zr ions and Zn ions can be prepared by a conventionally known method. Specifically, it can be obtained by dissolving Zn sulfate, vanadyl oxide or zirconyl nitrate in, for example, an inorganic acid, for example, sulfuric acid.

The pH of the solution containing one or more of V ions and Zr ions and Zn ions is preferably 1.0 to 4.0. If the pH is lower than 1.0, one or more of V and Zr may not be incorporated into the plating layer 2. When the pH is higher than 4.0, V ions or Zr ions are precipitated as oxides in a solution containing one or more of V and Zr and Zn ions, and are not incorporated into the plating layer 2.

Mass ratio of one or more V ions and Zr ions in a solution containing one or more V ions and Zr ions and Zn ions to Zn ions ((one or more V ions and Zr ions) / Zn Ions) are preferably 0.25 to 0.90. If it is smaller than 0.20 or larger than 0.90, one or more of V ions and Zr ions may not be incorporated into the plating layer 2.

The component composition of the metal ion or the plating layer 2 in the solution containing one or more of V ion and Zr ion and Zn ion is a known method such as ICP (Inductively Coupled Plasma) emission spectroscopic analysis or fluorescent X-ray spectroscopic analysis. Can be analyzed. When the component composition of the plating layer 2 is analyzed by ICP emission spectroscopic analysis, the plating layer 2 is dissolved in a solution prepared by adding an inhibitor to hydrochloric acid or the like so that the steel plate 1 is not dissolved, and the measurement is performed.

The lower limit of the amount of Zn adhered to the plating layer 2 ^{is preferably 1.5 g / m 2} or more. This is because when the amount of Zn adhered is 1.5 g / m ² or more, the scratch resistance is improved. The upper limit of the amount of Zn adhered ^{is preferably 9 g / m 2} or less. This is because when the amount of Zn adhered is 9 g / m ² or less, the adhesion between the plating layer 2 and the steel sheet 1 is improved, and the end face coating film coagulation peeling property is improved.

When one or more of V and Zr ions and one or more of Zr ions are present together with Zn ions in a solution containing one or more of V and Zr ions and Zn ions, one or more of V and Zr and Zn are dendrite-like. It precipitates on the steel plate or the outermost surface of the previously deposited plating to form a plating layer. Therefore, many irregularities are formed on the surface of the plating layer 2 formed by performing the cathode electrolysis treatment in the coexistence of one or more of Zn ions, V ions, and Zr ions. By the resin entering the unevenness, a sufficient anchor effect can be obtained between the coating film 3 and the plating layer 2, and the end face coating film coagulation peeling property is improved. The total amount of adhesion of one or more of V and Zr ^{is preferably 0.35 g / m 2} or more and 1.00 g / m ² or less in terms of V or Zr. When the total adhesion amount of one or more of V and Zr is 0.35 g / m ² or more, one or more of Zn and V and Zr grow in a dendrite shape, so that the end face coating film coagulation peeling property is improved. Therefore, it is preferable. If the total amount of adhesion of one or more of V and Zr exceeds 1.00 g / m ² , the effect of improving the cohesive peeling property of the end face coating film due to the plating surface shape is saturated, which is not preferable. In the solution containing one or more of V ion and Zr ion and Zn ion, either V ion or Zr ion may be present alone, or both V ion and Zr ion are present. You may be.

The mass ratio of one or more of V and Zr in the plating layer 2 to Zn is the mass ratio of the content of one or more of V and Zr and the content of Zn in terms of metal ((1 of V and Zr). The seed or higher) / Zn) is preferably 0.05 to 0.50. If it is less than 0.05, the scratch resistance is inferior, which is not preferable. If it exceeds 0.50, the adhesion between the plating layer 2 and the steel sheet 1 is inferior, and the end face coating film coagulation peeling property is inferior, which is not preferable.

(Coating film)
The glass transition temperature (Tg) of the coating film 3 formed directly above the plating layer 2 is 25 ° C. or higher and 80 ° C. or lower. Tg is preferably 50 ° C. or higher and 80 ° C. or lower. If the Tg is less than 25 ° C., the cohesive force of the coating film 3 is small, and the sweat resistance and the end face coating film cohesive peeling property are inferior, which is not preferable. If the temperature exceeds 80 ° C., the cohesive force of the coating film 3 is large and the coating film 3 is hard, so that large coating film cracks occur with plating and the corrosion resistance of the processed portion is inferior, which is not preferable.

The Tg of the coating film 3 can be measured using a rigid pendulum tester according to ISO 12013-2: the method for measuring the thermal properties (Tg, hardness) of the coating film.

The coating film 3 is excellent in sweat resistance and end face coating film coagulation peeling property by containing a butylated melamine resin and a binder resin having an OH group. Here, the components of sweat include sodium chloride, lactic acid, amino acids, urea and the like, but here, attention was paid particularly to the resistance to sodium chloride and lactic acid (artificial sweat). By the curing reaction between the butylated melamine resin and the binder resin having an OH group, a cured product of the binder resin having an OH group and the butylated melamine resin is formed in the coating film. The OH group is necessary for the curing reaction of cross-linking the binder resin having an OH group and the butylated melamine resin. Conventionally, it has been considered difficult to achieve both corrosion resistance of a processed portion of a coating film and cross-sectional cohesive peeling at a high level only by controlling Tg. In the present application, a precoated steel sheet 10 having excellent corrosion resistance at a processed portion and cohesive peeling property at an end surface coating film 10 was obtained by controlling the Tg of the coating film 3 using a butylated melamine resin and a binder resin having an OH group. .. The details of the reason why the excellent corrosion resistance of the processed portion and the cohesive peeling property of the end face coating film were obtained are unknown, but the butylated melamine resin is crosslinked with the OH group and the butylated melamine resin has high self-condensation property. It is considered that this is due to the fact that the cohesive force is increased. As for the sweat resistance of the butylated melamine resin, since the sweat component permeates the coating film 3, compatibility between the melamine resin and the sweat component is also important, and in this respect, butylation is used to improve the sweat resistance. It is considered that the melamine resin was suitable.

Examples of the binder resin having an OH group that can be used for the coating film 3 include a polyester resin having an OH group, an epoxy resin (polyol-added epoxy resin) reacted with a polyol, and a polyurethane resin (polyurethane-added polyurethane resin). , Olefin resin (polyurethane-added olefin resin), acrylic resin (polyurethane-added acrylic resin) and other resins. The OH group-containing binder resin may be only one type selected from the group of these resins, or may be two or more types. The binder resin having an OH group preferably does not contain a sulfonic acid group. If the binder resin having an OH group contains a sulfonic acid group, the sweat resistance of the coating film 3 becomes unsuitable, which is not preferable.

The hydroxyl value of the binder resin having an OH group is preferably 50 or less. More preferably, it is 30 or less. The lower limit of the hydroxyl value of the binder resin having an OH group is preferably 5 or more. More preferably, it is 7 or more. If the hydroxyl value is more than 50, the corrosion resistance of the processed portion may be lowered, which is not preferable. Further, the Tg of the coating film 3 may exceed 80 ° C., which is not preferable. If the hydroxyl value is less than 5, the reaction with butylated melamine does not proceed sufficiently, which is not preferable. In addition, Tg may be less than 25 ° C, which is not preferable. The unit of the hydroxyl value is KOHmg / g.

As the epoxy resin, polyurethane resin, olefin resin, and acrylic resin, generally known resins can be used. As the epoxy resin, "jER (registered trademark)" manufactured by Japan Epoxy Resin Co., Ltd., "EPICLON (registered trademark) series" manufactured by DIC Corporation, or the like can be used. Urethane resins include "Bihydrour (registered trademark) series" manufactured by Sumika Bayer Urethane, "Cosmonate (registered trademark) series" manufactured by Mitsui Chemicals, "Hisel (registered trademark) series" manufactured by Toho Chemical Industry Co., Ltd., and DIC. The "Bondic (registered trademark) series" manufactured by the company can be used. As the olefin resin, "Hi-Tech (registered trademark) series" manufactured by Toho Chemical Industry Co., Ltd. can be used. As the acrylic resin, "Acrydic (registered trademark) series" manufactured by DIC Corporation, "Acryset (registered trademark) series" manufactured by Nippon Shokubai Co., Ltd., and the like can be used.

It is preferable that the binder resin having an OH group used for the coating film 3 is a polyester resin because the corrosion resistance of the processed portion is more excellent. This is because the polyester resin has excellent ductility and workability.

As the polyester resin having an OH group, an alkyd resin, an unsaturated polyester resin, a modified alkyd resin and the like are used. The alkyd resin is a resin in which a condensate of a polybasic acid such as phthalic anhydride and a polyhydric alcohol such as glycerin is used as a skeleton and modified with fatty acid fats and oils. The alkyd resin is classified into a short oil alkyd resin, a medium oil alkyd resin, a long oil alkyd resin and an ultra long oil alkyd resin according to the type and content of the fat and oil used. Unsaturated polyester resins are synthesized by esterifying unsaturated polybasic acids or saturated polybasic acids with glycols. Examples of polybasic acids include phthalic anhydride, isophthalic acid, terephthalic acid and adipic acid, and examples of glycols include propylene glycol. As the modified alkyd resin, a resin modified with a polymerizable monomer such as a natural resin, a phenol resin or styrene can be used. As the polyester resin having an OH group, a generally known polyester resin can be used.

Examples of polyester resins other than the above include ^{commercially available "Byron TM} " manufactured by Toyobo Co., Ltd. (registered trademark of Toyobo Co., Ltd.) and "Desmophen ^TM " manufactured by Sumika Bayer Urethane Co., Ltd. (registered trademark of Sumika Bayer Urethane Co., Ltd.). Goods can be used.

When the Tg of the binder resin having an OH group used for the coating film 3 is 7 ° C. or higher and 71 ° C. or lower, the sweat resistance, the end face coating film coagulation peeling property, and the corrosion resistance of the processed portion of the obtained coating film 3 are more excellent. Suitable. If the temperature is lower than 7 ° C., the cohesive force of the obtained coating film 3 is insufficient, and the sweat resistance and the end face coating film cohesive peeling property are lowered, which is not preferable. If the temperature exceeds 71 ° C., large cracks may occur in the processed portion of the coating film 3 and the corrosion resistance of the processed portion may decrease, which is not preferable. The Tg of the coating film 3 can be controlled by reacting the butylated melamine resin in the range of Tg with the binder resin having an OH group at a predetermined temperature and a predetermined amount.

When the Tg of the polyester resin used for the coating film 3 is 7 ° C. or higher and 71 ° C. or lower, the sweat resistance, the end face coating film coagulation peeling property, and the corrosion resistance of the processed portion of the obtained coating film 3 are more excellent, which is preferable. If the temperature is lower than 7 ° C., the cohesive force of the obtained coating film 3 is insufficient, and the sweat resistance and the end face coating film cohesive peeling property are inferior. If the temperature exceeds 71 ° C., large cracks are formed in the processed portion of the coating film 3 and the corrosion resistance of the processed portion is inferior. The Tg of the coating film 3 can be controlled by reacting the butylated melamine resin in the range of Tg with the polyester resin at a predetermined temperature and a predetermined amount.

The proportion of the binder resin having an OH group in the coating film 3 is preferably 50% by mass or more and 95% by mass or less with respect to the total resin constituting the coating film 3. When the binder resin having an OH group is 50% by mass or more, the reaction between the binder resin having an OH group and the butylated melamine resin proceeds, and the coating film 3 is hard to peel off, which is preferable. Further, when the binder resin having an OH group is 50% by mass or more, the Tg of the coating film 3 can be adjusted to 25 ° C. or more, which is preferable. By setting the proportion of the binder resin having an OH group to 95% by mass or less, the corrosion resistance of the processed portion is improved. Further, by setting the proportion of the binder resin having an OH group to 95% by mass or less, the Tg of the coating film 3 can be adjusted to 80 ° C. or less.

The proportion of the polyester resin having an OH group in the coating film 3 is preferably 50% by mass or more and 95% by mass or less with respect to the total resin constituting the coating film 3.

As the butylated melamine resin that can be used for the coating film 3, one or more of the constituent units R1 to R6 represented by the following formula (1) are −CH ₂ OC ₃ H ₇ . In the formula, R, which is not _{−CH 2} OC ₃ H ₇ , can be a group selected from _{H, CH 2} OH, CH ₂ OCH _3. As the butylated melamine resin, a commercially available butylated melamine resin or the like can be used. Since the butylated melamine resin is usually insoluble in water, it is used as a coating material using an organic solvent as a solvent.

The butylated melamine resin in the coating film 3 is preferably 5% by mass or more and 50% by mass or less with respect to the total resin constituting the coating film 3. When the butylated melamine resin is 5% by mass or more, the reaction between the butylated melamine resin and the binder resin having an OH group proceeds, the coating film 3 is less likely to be peeled off, and the corrosion resistance of the processed portion is improved, which is preferable. When the butylated melamine resin is 50% by mass or less, the corrosion resistance of the processed portion is improved, which is preferable.

The coating film 3 of the present invention may further contain a methylated melamine resin. It is more preferable to use the methylated melamine resin in combination with the butylated melamine resin because the solvent resistance is excellent. Here, in the methylated melamine resin, one or more of the structural units R1 to R6 represented by the following formula (2) are −CH ₂ OCH ₃ . In the formula, R other than _{−CH 2} OCH ₃ can be a group selected from _{H and CH 2 OH.}

Carbon black may be contained in the coating film 3 in an amount of 1% by mass to 20% by mass based on the total solid content of the coating film 3. Carbon black is preferable because the design of the coating film is better when it contains carbon black than when it does not contain carbon black.

The carbon black that can be used is not particularly limited, and for example, known carbon blacks such as furnace black, ketjen black, acetylene black, and channel black can be used. Further, known carbon blacks that have been subjected to ozone treatment, plasma treatment, or liquid phase oxidation treatment can also be used.

A silane coupling agent may be contained in the paint used for producing the coating film 3. When a silane coupling agent is added, the siloxane oligomer generated by the decomposition of the silane coupling agent improves the adhesion between the plating layer 2 and the coating film 3, which is preferable. The siloxane oligomer generated by the decomposition reacts with the hydroxyl groups on the surface of the plating layer 2 and the resin in the coating film 3. That is, an adduct of a silane coupling agent, which is a reaction product of the siloxane oligomer and the hydroxyl group on the surface of the plating layer 2 and the resin in the coating film 3, is formed. The amount of the silane coupling agent in the coating material is preferably 1% by mass to 20% by mass based on the mass of the coating material.

As the silane coupling agent, a general silane coupling agent can be used. Examples of the silane coupling agent include γ-aminopropyltrimethoxysilane, γ-aminopropylethoxysilane, N- [2- (vinylbenzylamino) ethyl] -3-aminopropyltrimethoxysilane, 2- (3, 4-Epoxycyclohexyl) ethyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltriethoxysilane, N-β- (aminoethyl) -Γ-Aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercabutpropyltrimethoxysilane, γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-amino Ethyl) Aminopropylmethyldimethoxysilane, γ- (2-aminoethyl) aminopropyltriethoxysilane, γ- (2-aminoethyl) aminopropylmethyldiethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane , Γ-Methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, N-β- (N-vinylbenzylaminoethyl) -Γ-Aminopropyltrimethoxysilane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropylmethyldimethoxysilane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltriethoxysilane , N-β- (N-vinylbenzylaminoethyl) -γ-aminopropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltri Ethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, methyltrimethoxy Silane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltriethoxysilane, γ-chloropropyl Methyldiethoxysilane, hexamethyldisilazane, γ-anilinopropyltrimethoxysilane, γ-anilinopropylmethyldimethoxysilane, γ-anilinopropyltriethoxysilane, γ-anilinopropylmethyldiethoxysilane, vinyltrimethoxy Silane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride, octadecyldimethyl [3- (methyldimethoxysilyl) propyl] ammonium chloride, octadecyldimethyl [3- (Triethoxysilyl) propyl] ammonium chloride, octadecyldimethyl [3- (methyldiethoxysilyl) propyl] ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyl Dichlorosilane, trimethylchlorosilane and the like can be used.

The film thickness of the coating film 3 is preferably more than 5 μm and 20 μm or less, and this range is suitable because the coating film 3 is excellent in sweat resistance and end face coating film coagulation peeling property. If it is 5 μm or less, the barrier property becomes small and the sweat resistance is inferior, which is not preferable. Further, if it exceeds 20 μm, the internal stress becomes large, the adhesion to the plating layer 2 is inferior, and the end face coating film coagulation peeling property is inferior, which is not preferable. The film thickness of the coating film 3 can be obtained by observing the cross section with an electron microscope at a magnification of 2000 and dividing the area of the coating film portion by the length of the coating film in the longitudinal direction. The area of the coating film portion can be obtained by analyzing the image obtained by observing the cross section with commercially available image analysis software.

The coating film 3 may further contain an epoxy resin in addition to the binder resin having an OH group. It is preferable to use an epoxy resin because the epoxy group is bonded to the surface of the plating layer 2 and the sweat resistance and adhesion are more excellent.

As the epoxy resin, a known epoxy resin can be used. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolak type epoxy resin and the like can be mentioned.

The coating film 3 may contain a rust preventive pigment. As the rust preventive pigment, a known pigment generally applied to zinc-based plating can be used. For example, phosphorus-based, silica-based, vanadium-based and the like can be mentioned.

Using the precoated steel sheet 10 according to the embodiment of the present invention, the Zn concentration and the carbon (C) concentration are measured by using the glow discharge emission analysis method (GDS) in the measurement range starting from the surface of the coating film 3 and ending at the steel plate 1. Then, starting from the depth position A where the Zn concentration is the maximum value in the above-mentioned measurement range, the Zn concentration is 5% of the maximum value, and the depth is located closer to the steel plate side than the depth position A. In the range with position B as the end point, the C concentration is always 1 atomic% or more (in the elements that can be detected by GDS (C, Fe, H, N, Na, Ni, O, P, S, Si, Ti, V, Zn). The ratio of the C concentration to the Zn concentration at the depth position A is 8% or more.
FIG. 2 is a diagram showing the concentration distributions of V, Zn and C in the depth direction obtained by measuring the precoated steel sheet 10 according to the embodiment of the present invention by the glow discharge emission method. The horizontal axis shows the depth from the surface of the coating film 3, and the vertical axis shows the change in the concentration of each element. As shown in FIG. 2, the precoated steel sheet 10 always has a C concentration of 1 atomic% or more in the range where the depth position A is the starting point and the depth position B is the ending point, and the C concentration with respect to the Zn concentration at the depth position A is Satisfy the relationship that the concentration ratio is 8% or more. Satisfying this relationship indicates that the binder resin having an OH group and the melamine resin have penetrated into the plating layer 2 without any voids. When the binder resin having an OH group and the melamine resin penetrate into the plating layer 2, a sufficient anchoring effect is obtained, and the adhesion between the coating film 3 and the plating layer 2 is greatly improved.

(Film formation method)
As a method for applying the paint used for producing the coating film 3, for example, a well-known method such as a bar coater method, a roll coating method, a ringer roll coating method, an air spray method, an airless spray method, or a dipping method can be used. After the plating layer 2 is formed, washed and dried, the paint is applied. It is preferable to apply the paint within 120 seconds after the plating layer 2 is dried. Generally, when the plating layer 2 is not applied immediately after drying, it is often applied after being oiled and stored for rust prevention and degreased. However, in the case of degreasing, the surface activity is lower than immediately after the formation of the plating layer 2, and the resin of the coating film 3 may be difficult to penetrate into the plating layer 2. Further, even if 120 seconds have passed after the plating layer 2 is dried, the surface activity is low and the resin of the coating film 3 may not easily enter the plating layer 2. If the time from forming the plating layer 2 to drying and applying the paint is 120 seconds or less, the adhesion between the plating layer 2 and the coating film 3 is excellent, so that the coating film between the plating layer 2 and the coating film 3 is coated. It is possible to suppress the interfacial peeling of 3. In particular, when the end face of the precoated steel sheet 10 is squeezed, the interface peeling between the coating film 3 and the plating layer 2 may occur instead of the coating film peeling due to cohesive fracture, which can be suppressed.

The dynamic surface tension of the paint is adjusted to 15 mN / m or more and 30 mN / m or less. When the dynamic surface tension of the paint is less than 15 mN / m and more than 30 mN / m, the paint cannot penetrate into the unevenness of the plating layer 2, which is not preferable.

It is preferable to use a surfactant (including a defoaming agent and a leveling agent) for adjusting the dynamic surface tension of the paint. Known surfactants can be used as the surfactants, and commercially available surfactants include BYK-333 and BYK-307 from BYK, Ermagen from Kao, and Surfinol from Nissin Chemicals. However, there are many others, and they can be added as appropriate depending on the paint used. Further, an adjustment method other than using a surfactant such as dilution or mixing with another solvent may be used.

The method for drying the paint used to produce the coating film 3 is not particularly limited, and hot air, induction heating, near infrared rays, direct flame, and the like can be used alone or in combination.

The paint is cured by heating, and those skilled in the art can adjust the Tg by appropriately controlling the heating temperature and the holding time. The paint is heated at a heating temperature (reaching plate temperature) of 150 ° C. or higher and 250 ° C. or lower. If it is less than 150 ° C., the coating film is insufficiently cured and the solvent resistance is inferior, and if it is more than 250 ° C., the coating film is decomposed and the solvent resistance is inferior. The holding time is 8 seconds to 120 seconds. The holding time is the time for holding the heating after reaching the set temperature. If the holding time exceeds 120 seconds, the Tg of the coating film 3 may exceed 80 ° C., which is not preferable. If the holding time is less than 8 seconds, the Tg of the coating film 3 may be less than 25 ° C., which is not preferable.

Details of the examples of the present invention will be described below.
[Example 1]
1. 1. Steel plate As the steel plate, a steel plate having a thickness of 0.8 mm was used as the SPCD for drawing the general cold-rolled steel sheet described in JIS G 3141.
2. Plating layer Solution A containing Zn ions and V ions and solution B containing Zn ions and Zr ions were prepared. Solution A was prepared by mixing Zn sulfate and vanadyl oxide in sulfuric acid, and solution B was prepared by mixing Zn sulfate and zirconyl nitrate in sulfuric acid. The components of the plating layer were adjusted according to the amount of these solution components. The pH was adjusted by the amount of sulfuric acid and the amount of sodium hydroxide. Using this solution, a plating layer was formed on the steel sheet by cathode electrolysis treatment (current density 20 to 150 A / dm ^2). Each component in the formed plating layer was identified and confirmed by ICP emission spectroscopic analysis.
The components of the prepared solution are shown in Table 1, and the components of the plating layer are shown in Table 2. In Table 1, the mass (g / L) of each ion was converted from the mass of Zn sulfate, vanadyl oxide, and zirconyl nitrate used.

3. 3. The coating film coating material was prepared by mixing and stirring the resins shown in Tables 3-1 and 3-2 and 3-3 and, in some cases, the inorganic pigments shown in Table 4 using Solbesso 150 as a solvent (solid content). 30%). In Table 3-2, Cymel 327 and Cymel 325 are methylated melamine resins, and Mycoat 506 is a butylated melamine resin. The prepared paints are shown in Table 5. (The amount of the solid content excluding the surfinol 104 is described.) The paints 32 and 33 are water-based paints in which 95% or more of the solvent is water (solid content 30%).

Above 2. After preparing the plating layer under the conditions shown in Table 6 and drying the plating layer under the drying conditions shown in Table 6 (time from preparation of plating to drying and drying temperature), the paint shown in Table 5 was coated with a bar coater to a thickness of 10 μm. Then, it was heated in a hot air furnace so that the heating temperature (reaching plate temperature) became 200 ° C. in 30 seconds and held for 8 to 120 seconds. Then, it was immersed in water and cooled to form a coating film. A surfactant "Surfinol 104 (manufactured by Nissin Chemical Co., Ltd.)" was used to adjust the dynamic surface tension of the paint. Table 6 shows the coating film of the prepared precoated steel sheet.

The Tg of the coating film was measured using a rigid pendulum tester according to ISO 12013-2: the method for measuring the thermal properties (Tg, hardness) of the coating film. The evaluation results are shown in Table 6.

The dynamic surface tension of the paint was measured by BP-D5 (maximum foam pressure method) manufactured by Kyowa Interface Science Co., Ltd., and the time from the minimum foam pressure to the maximum foam pressure was 100 ms. The evaluation results are shown in Table 6.

For the GDS measurement of the coating film, GD-PROFILER2 manufactured by Horiba Seisakusho Co., Ltd. was used, and the spectral intensity in the depth direction was measured with the surface of the coating film as the starting point and the steel plate as the ending point under the conditions of a discharge power of 35 W and an argon pressure of 600 Pa. Starting from the depth position A where the Zn concentration is the maximum value in this measurement range, the end point is the depth position B where the Zn concentration is 5% of the maximum value and is located on the steel plate side of the depth position A. The case where the C concentration was always 1 atomic% or more and the ratio of the C concentration to the Zn concentration at the depth position A was 8% or more was Good, and the case where it was less than 8% was Bad. The evaluation results are shown in Tables 6-1 and 6-2.

Test 1. Sweat resistance 0.05 ml of artificial sweat solution (Method D) (JIS L 0848) was added dropwise to a test piece obtained by cutting a precoated steel sheet prepared under the conditions shown in Tables 6-1 and 6-2 to a size of 50 × 100 mm. After being left for 24 hours under the condition of 40 degrees and 98% relative humidity, the state of the dripping marks was evaluated according to the following evaluation criteria. The pass was 3 or more according to the following evaluation criteria.
5: No trace left.
4: Very slight traces are left (level at which traces can be discerned when viewed from an angle)
3: Slight marks are left (level at which the marks can be discerned when viewed from the front)
2: There is a clear mark. (Level at which traces can be identified instantly)
1: The steel plate is exposed.

Test 2. Scratch resistance A test piece obtained by cutting a pre-coated steel sheet prepared under the conditions shown in Tables 6-1 and 6-2 into a size of 50 x 100 mm is installed on a rubbing tester, and then the tip of the sliding jig of the rubbing tester is attached to the right river rubber factory. A columnar eraser manufactured by the company was attached, and the film state after rubbing 100 times with a load of 16 N was evaluated according to the following evaluation criteria. The pass was 3 or more according to the following evaluation criteria.
5: The steel plate is not exposed.
4: The exposed width of the steel plate is less than 1 mm.
3: The exposed width of the steel plate is 1 mm or more and less than 2 mm.
2: The exposed width of the steel plate is 2 mm or more and less than 3 mm.
1: The exposed width of the steel plate is 4 mm or more.

Test 3. Corrosion resistance of processed parts A test plate prepared by cutting a precoated steel sheet prepared under the conditions shown in Tables 6-1 and 6-2 to 50 × 50 mm was extruded by 7 mm with an Eriksen tester, and the edge and back surface of the test plate were tape-sealed. A salt spray test (SST) (JIS-Z-2371) was performed. The white rust generation after 24 hours was observed and evaluated according to the following criteria. The pass was 3 or more according to the following evaluation criteria.
5: No rust.
4: Rust generation area is less than 1%.
3: The rust generation area is 1% or more and less than 5%.
2: The rust generation area is 5% or more and less than 10%.
1: The rust generation area is 10% or more.

Test 4. End face coating film coagulation peeling property The precoated steel sheet prepared under the conditions shown in Tables 6-1 and 6-2 is cut, and the lower burr portion formed on the lower side of the cut steel sheet is further burred using a mold. After processing in (the direction of the burr that occurs when cut), the tape was firmly attached to the coating film on the end face, and after the tape was peeled off, the presence or absence of peeling of the coating film was examined. The pass was 3 or more according to the following evaluation criteria.
5: The coating film has not peeled off at all.
4: The peeling of the coating film is less than 10% of the area where the tape is attached.
3: The peeling of the coating film is 10% or more and less than 30% of the area where the tape is attached.
2: The peeling of the coating film is 30% or more and less than 50% of the area where the tape is attached.
1: The peeling of the coating film is 50% or more of the area where the tape is attached.

Test 5. Solvent resistance A test plate obtained by cutting a precoated steel sheet prepared under the conditions shown in Tables 6-1 and 6-2 into a size of 50 × 50 mm is placed on a rubbing tester, and then cotton wool impregnated with ethanol is applied at 49.03 kPa (0.5 kgf). The state of the coating film after rubbing 10 times with a load of / cm ^{2) was evaluated according to the following evaluation criteria.} The pass was 3 or more according to the following evaluation criteria.
5: No marks are left on the rubbing surface.
4: Very slight marks are left on the rubbing surface (a level at which the rubbing marks can be discerned by squinting).
3: Slight marks are left on the rubbing surface (a level at which the rubbing marks can be easily identified by squinting).
2: A clear mark is left on the rubbing surface (a level at which the rubbing mark can be instantly identified).
1: The coating film melts on the rubbing surface and the base is exposed.

Test 6. Adhesion A test piece obtained by cutting a precoated steel sheet prepared under the conditions shown in Tables 6-1 and 6-2 to a width of 5 cm was prepared according to JIS. 2T bending was performed in an atmosphere of 20 ° C. by a test method according to G3312. A tape peeling test (tape used: tape manufactured by Nichiban Co., Ltd.) was carried out on the processed part, and the state of occurrence of coating film peeling was observed. The pass was 3 or more according to the following evaluation criteria.
5: No peeling 4: The peeled coating film is less than 5% of the area where the tape is attached.
3: The peeled coating film is 5% or more and less than 20% of the area to which the tape is attached.
2: The peeled coating film is 20% or more and less than 50% of the area to which the tape is attached.
1: The peeled coating film is 50% or more and less than 70% of the area to which the tape is attached.

The evaluation results of the above tests are summarized in Tables 7-1 and 7-2. As can be seen from Tables 7-1 and 7-2, all of the examples (invention examples) of the present invention were excellent in sweat resistance, scratch resistance, corrosion resistance of the processed portion, solvent resistance, and adhesion.

In Comparative Examples 1 to 5, since V and Zr were not contained in the plating layer, the scratch resistance and the corrosion resistance of the processed portion were inferior.
In Comparative Example 6, since the coating film did not contain a binder resin having an OH group, the sweat resistance and the end face coating film coagulation peeling property were inferior.
In Comparative Examples 7 and 9, since the Tg of the coating film was low, the sweat resistance and the end face coating film coagulation peeling property were inferior. The paint 2 used in Comparative Example 7 has the same composition as the paint 3 used in Example 15. The Tg of Comparative Example 7 is lower than that of Example 15 by adjusting the heating conditions.
In Comparative Examples 8 and 10, since the Tg of the coating film was high, the corrosion resistance of the processed portion was inferior.
In Comparative Example 11, since the butylated melamine resin was not contained in the coating film, the corrosion resistance of the processed portion and the cohesive peeling property of the end face coating film were inferior.
In Comparative Examples 12 and 13, since the Tg of the coating film was low, the result was that the end face coating film coagulation peeling property was inferior.
In Comparative Examples 14 and 15, since the butylated melamine resin was not contained in the coating film, the corrosion resistance of the processed portion, the cohesive peeling property of the end face coating film, and the adhesion were inferior.
Since Comparative Example 16 does not contain a melamine resin, the result is that the corrosion resistance of the processed portion, the cohesive peeling property of the end face coating film, and the adhesion are inferior.

Since the pre-coated steel sheet of the present invention is excellent in scratch resistance, sweat resistance, corrosion resistance of processed parts, and end face coagulation peeling resistance, it is used for automobiles, home appliances, building materials, civil engineering, machinery, furniture, and containers. It is extremely useful for applications.

1 Steel sheet 2 Plating layer 3 Coating film 10 Pre-coated steel sheet

Claims (11)

Steel plate and
A plating layer containing one or more of vanadium and zirconium and zinc on at least one surface of the steel sheet.
A coating film formed directly above the plating layer, having a glass transition temperature of 25 ° C. to 80 ° C., and containing a cured product composed of a butylated melamine resin and a binder resin having an OH group.
Pre-coated steel sheet with. When the zinc concentration and carbon concentration are measured using the glow discharge emission analysis method in the measurement range starting from the surface of the coating film and ending at the steel sheet.
Starting from the depth position A where the zinc concentration is the maximum value in the measurement range, the depth position B where the zinc concentration is 5% of the maximum value and is located on the steel plate side of the depth position A is set. In the range of the end point, the carbon concentration is always 1 atomic% or more,
The precoated steel sheet according to claim 1, wherein the ratio of the carbon concentration to the zinc concentration at the depth position A is 8% or more. The precoated steel sheet according to claim 1 or 2, wherein in the butylated melamine resin, at least one or more of the constituent units R1 to R6 represented by the following formula (1) have −CH ₂ OC ₃ H _7.

The binder resin is one or more selected from the group consisting of a polyester resin having an OH group, a polyol-added epoxy resin, a polyol-added polyurethane resin, a polyol-added olefin resin, and a polyol-added acrylic resin, according to claims 1 to 3. The precoated steel plate according to any one of the items. The precoated steel sheet according to any one of claims 1 to 4, wherein the binder resin does not contain a sulfonic acid group. The precoated steel sheet according to any one of claims 1 to 5, wherein the glass transition temperature of the binder resin is 7 ° C. or higher and 71 ° C. or lower. The precoated steel sheet according to any one of claims 1 to 6, wherein the binder resin has a hydroxyl value of 5 to 50 KOH mg / g. The precoated steel sheet according to any one of claims 1 to 7, wherein the coating film further contains a methylated melamine resin. The coating contains an adduct of a silane coupling agent, precoated steel sheet according to claim 1 1 wherein either Re 8 noise. The precoated steel sheet according to any one of claims 1 to 9, wherein the film thickness of the coating film is more than 5 μm and 20 μm or less. The precoated steel sheet according to any one of claims 1 to 10, wherein the coating film further contains an epoxy resin.

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