JP2007007904A - Organic resin coated hot dipping steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an organic resin coated hot dipping steel sheet showing corrosion resistance after coating exceeding that of a phosphate film without requiring chromate treatment heavy in environmental load. <P>SOLUTION: A hot dipping steel sheet having a hot dipping layer with a surface layer concentration of Al of 3 mass% or above is used as a base sheet and coating which contains a π conjugated polymer and a silane coupling agent is applied to the base sheet and baked to provide an organic resin film comprising the π conjugated polymer on a substrate surface. Since the organic resin film is bonded to the hot dipping layer through the silane coupling agent, it is excellent in the adhesion of a coating film and the original corrosion preventing action of the π conjugated polymer can be developed effectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic resin-coated hot-dip steel sheet that is used as an interior material, an exterior material, a cover material, and the like and exhibits excellent post-coating corrosion resistance.

Conductive polymers represented by polyaniline are expected to be applied to coating primers and the like because they exhibit the action of suppressing corrosion under the coating film. For example, a coated metal plate having improved corrosion resistance with a polyaniline film formed by applying a solution containing a soluble polyaniline to a metal surface and drying (Patent Document 1), an anticorrosion paint containing polyaniline and phosphoric acid (Patent Document 2), etc. It has been known.
JP-A-6-128769 Japanese Unexamined Patent Publication No. 11-21505

Although the polyaniline film exhibits excellent properties such as corrosion resistance, it does not have satisfactory results as compared with conventional coating pretreatments such as phosphate treatment and chromate treatment because of insufficient adhesion to the base. When the film adhesion is improved, the excellent characteristics of polyaniline can be utilized, and the coating pretreatment with a large environmental load as in the chromate treatment is not necessary.
The present inventors have investigated and examined various effects on the adhesion of the polyaniline film to the substrate in order to meet such demands. As a result, when using an Al-enriched base on the surface and interposing a silane coupling agent at the interface between the polyaniline film and the base, it is clarified that the film adhesion is improved and the excellent characteristics of polyaniline are imparted. did. The present invention has been completed based on such knowledge, and provides an organic resin-coated hot-dip steel sheet that is excellent in corrosion resistance after painting and is used in a wide range of fields as an interior material, an exterior material, a cover material, and the like. Objective.

  The organic resin-coated hot dip plated steel sheet of the present invention uses a steel sheet provided with a hot dip plating layer having a surface layer enriched with Al as a base, and a silane between the hot dip plating surface and the polyaniline-containing organic resin film. An interfacial layer made of a coupling agent is interposed. The degree of Al concentration needs to be 3% by mass or more (preferably 10% by mass or more) in terms of the Al content on the surface of the hot dipping layer. The silane coupling agent binds to the polyaniline of the organic resin film with one or more organic functional groups selected from an amino group, a cycloalkane, and an atomic group having a π bond.

  Adhesion improvement by a silane coupling agent is not limited to a polyaniline-containing film, but is also effective for an organic resin film containing a similar heterocyclic conjugated system or hetero atom-containing conjugated π-conjugated polymer. The organic resin film may be a film that does not contain a dopant, but becomes a film provided with conductivity by blending the dopant. Heteroatoms contained in the π-conjugated polymer include nitrogen and sulfur.

  Al contained in the hot-dipped layer is an element having a large oxygen affinity, and reacts with oxygen and moisture in the atmosphere to become oxides and hydroxides. As the surface Al becomes an oxide or hydroxide, Al is supplied from the inside of the hot-dip plated layer to the surface layer, and the Al concentration of the surface layer increases. For example, even a hot-dip plated steel sheet provided with a Zn-0.1% by mass Al alloy plating layer detects a surface layer having an Al concentration of 20 to 40% by mass by surface analysis using ESCA, AES, or the like. Incidentally, Zn, which is another typical plating metal, is partially present on the surface of the plating layer.

  On the other hand, the silane coupling agent has a silanol group that is easily bonded to a metal oxide or hydroxide, and an organic functional group such as an amino group, a cycloalkane, or an atomic group having a π bond. Although it adheres firmly to the surface of the hot-dip plating layer containing Al oxide and hydroxide via the silanol group, the adhesion force due to the silanol bond increases with the Al concentration on the surface of the plating layer. Since the organic resin film is laminated on the underlying hot-dip plated steel sheet through the interface layer made of the silane coupling agent, the adhesion of the organic resin film is improved and excellent post-coating corrosion resistance is imparted.

The organic functional group of the silane coupling agent has a binding force to the conductive polymer constituting the organic resin film. For example, in the case of a silane coupling agent having an amino group, a strong hydrogen bond is generated between the hetero atom of the conductive polymer and the amino group, and in the case of an atomic group having a cycloalkane or a π bond, between the π-conjugated group. The organic resin film has improved adhesion to the underlying hot-dip steel sheet.
Since the organic resin film containing the heterocyclic conjugated system or hetero atom-containing conjugated π-conjugated polymer is formed on the underlying hot-dip plated steel sheet with good adhesion, corrosion under the coating film is also suppressed. The suppression mechanism of under-coating corrosion by the organic resin film can be explained as follows. In the following description, polyaniline is taken as an example, but the same can be said for π-conjugated polymers other than polyaniline.

When the corrosive factor penetrates the organic resin film and reaches the surface of the hot-dip plated steel sheet, the metal on the base surface is oxidized, but polyaniline is reduced during the oxidation reaction. Reduced polyaniline becomes the original polyaniline by air oxidation, and the metal oxide becomes a higher-order oxide. The higher-order oxide reacts with OH ⁻ generated by oxygen reduction, and finally becomes an oxide film. In the hot-dip plating layer with a high surface Al concentration, oxidation and reduction of polyaniline are frequently repeated to promote Al oxidation, resulting in the formation of a dense and stable oxide film, in other words, a barrier layer with a high environmental barrier. . Therefore, further progress of corrosion of the base is suppressed.

[Hot-plated steel sheet]
The hot dip plated steel sheet targeted by the present invention does not impose any particular restrictions on the composition of the hot dip coating layer as long as the Al concentration in the surface layer region from the surface of the hot dip plating layer to a depth of 100 nm: 3% by mass or more is satisfied. Various plated steel sheets such as Zn—Al, Zn—Al—Mg, Zn—Al—Mg—Si, and Al—Si are used. Further, it may be a hot-dip plated layer containing Ti, B, Fe or the like as necessary. Since the plating layer composition substantially reflects the bath composition, the hot plating layer can be adjusted to the target composition by managing the composition of the hot plating bath.

  When manufacturing Zn-Al plated steel sheets with a relatively low Al content of about 0.1% by mass, by controlling the cooling rate and cooling conditions (air cooling, water cooling, etc.) of the steel strip pulled up from the hot dipping bath In addition, Al can be concentrated to 3% by mass or more on the surface layer of the hot dipping layer. The surface layer Al concentration is a value obtained by scanning and analyzing an area of 1000 μm square by AES analysis, and repeatedly analyzing from the surface layer to a depth of 100 nm by Ar sputtering.

[Interface layer]
The organic resin-coated hot-dip steel sheet of the present invention forms an interface layer made of a silane coupling agent between the underlying hot-dip steel sheet and the organic resin film. The interfacial layer is formed by applying and baking a coating containing a silane coupling agent and a π-conjugated polymer on a hot-dip plated steel sheet, but it is formed by previously applying a silane coupling agent-containing liquid to the hot-dip plated steel sheet and drying it. What you did is fine. The interface layer can be confirmed by analyzing the element distribution state in the depth direction of the organic resin-coated hot-dip plated steel sheet using ESCA, AES, or the like.

  The silane coupling agent contains silanol groups that exhibit strong bonds to Al oxides and hydroxides on the surface of the hot-dip plating layer, and organic functional groups that exhibit strong bonds to the conductive polymer of the organic resin film. Have. The organic functional group includes an amino group, a cycloalkane, and an atomic group having a π bond.

  Examples of silane coupling agents having amino groups include γ-(-aminoethyl) aminopropyltrimethoxysilane, aminosilane, γ-ureidopropyltriethoxysilane, trimethoxysilane, γ-aminopropyltriethoxysilane, and γ-aminopropyl. Examples include trimethoxysilane and methyldimethoxysilane. Among them, a silane coupling agent containing only a primary amino group as an amino group, such as γ-aminopropyltrimethoxysilane, exhibits a great effect of improving adhesion.

  Cycloalkane or silane coupling agents with π bond include N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, 3-anilinopropyltrimethoxysilane, cyclohexylmethyldimethoxysilane, phenyltri Methoxysilane, diphenyldimethoxysilane 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, N- [2- (vinylbenzylamino) ethyl] -3-aminopropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane , 3-acryloxypropyltrimethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane.

[Organic resin film]
The π-conjugated polymer that is the main component of the organic resin film has a heterocyclic conjugated system or a heteroatom-containing conjugated system, and specifically, the following compounds are used.
Heterocyclic conjugated system: polypyrrole, polyfuran, polythiophene, polyselenophene heteroatom-containing conjugated system: poly (paraphenylene sulfide), poly (paraphenylene oxide), polyaniline Especially, poly (paraphenylene sulfide) having heteroatom S When polyaniline having N is used for the π-conjugated polymer, the adhesion of the organic resin film is further improved.

[Preparation and painting of paint]
A paint for forming an organic resin film is prepared by dissolving a silane coupling agent and a π-conjugated polymer in a solvent. Solvents that can be used are not particularly limited as long as silane coupling agents and π-conjugated polymers are stably dissolved. Water, alcohols such as methanol, methyl ethyl ketone, xylene, acetone, acetonitrile, N-methyl There are organic solvents such as -2-pyrrolidone.

The π-conjugated polymer is preferably blended at 1 to 30% by mass. When the amount of the π-conjugated polymer is less than 1% by mass, the π-conjugated polymer in the coating is insufficient, and it is difficult to form a uniform organic resin film. On the other hand, when the amount exceeds 30% by mass, the stability of the paint is deteriorated and the renewal time of the paint is also advanced.
The silane coupling agent is preferably added at a ratio of 0.1 to 30% by mass with respect to the π-conjugated polymer. If the addition amount is less than 0.1% by mass, a sufficient adhesion improving effect cannot be obtained. Conversely, if the addition amount exceeds 30% by mass, the property imparting by the π-conjugated polymer tends to be adversely affected.

  A target organic resin film is formed by applying a paint to the original plate by roll coating, spraying, dipping, etc., baking and drying. Baking / drying does not impose any particular restrictions on the temperature conditions as long as the solvent is volatilized while preventing decomposition of the π-conjugated polymer, but the baking / drying temperature is in the range of 50 to 300 ° C. from an industrial viewpoint. It is preferable to select. If the temperature does not reach 50 ° C., baking and drying for a long time is required, and if the temperature exceeds 300 ° C., there is a concern that the quality may be deteriorated due to decomposition of the π-conjugated polymer.

The organic resin film has excellent post-coating corrosion resistance and can be used for both the undercoat film and the surface film, and is preferably adjusted to a dry film thickness of 0.1 to 10 μm. With a thin film of less than 0.1 μm, sufficient corrosion resistance is not ensured. The thicker the organic resin film, the better the quality such as corrosion resistance. However, even if the film thickness exceeds 10 μm, a further quality improvement effect cannot be obtained, which is economically disadvantageous.
When used as an undercoat film, if the film thickness is less than 0.1 μm, the progress of the undercoat corrosion inhibition from the buttocks is insufficient, and if it exceeds 10 μm, the corrosion resistance improving effect is saturated. There is a possibility that the organic resin film may crack at a site where the processed shape is severe, and there are concerns that characteristics such as appearance and corrosion resistance are not sufficient.

  By including a dopant in the organic resin film, the conductivity and corrosion resistance can be improved. As the dopant, halogen, proton, Lewis acid, organic acid or the like can be used. Specifically, halogens such as chlorine, bromine and iodine, hydrochloric acids, sulfuric acid, perchloric acid, tetramethylammonium perchlorate, tetrafluoroboric acid, hexafluorophosphoric acid and other protonic acids, phosphorus pentafluoride and trifluoride. Examples thereof include Lewis acids such as boron fluoride, and organic acids such as benzenesulfonic acid, toluenesulfonic acid, and naphthalenesulfonic acid.

  The film containing the dopant is a one-step treatment in which a π-conjugated polymer, a silane coupling agent, and a coating containing the dopant are applied and baked on the original plate, or after forming an organic resin film containing the π-conjugated polymer and the silane coupling agent. It is formed by a two-step process of applying a dopant solution. Since the organic resin film doped with the π-conjugated polymer exhibits high conductivity, it can be applied to applications requiring grounding properties, and a surface-treated steel sheet effective as an antistatic material, an electromagnetic wave shielding material, or the like can be obtained.

The relationship between the surface Al concentration and the coating film adhesion was investigated using the hot-dip galvanized steel sheets (1) to (7) as the coating original sheet. Each hot dip plated steel sheet was controlled for cooling rate and cooling conditions after being pulled out of the hot dip bath so that the surface layer Al concentration was 10% by mass or more. Table 1 shows the Al concentration and the surface layer Al concentration in the plating layer.
(1) Hot-dip galvanized steel sheet on which a Zn-0.1 mass% Al alloy plating layer having an adhesion amount of 60 g / m ² and a plate thickness of 0.8 mm is formed.
(2) Zn-Fe-Al alloy-plated steel sheet obtained by alloying the hot-dip plated steel sheet (1)

(3) Hot-dip galvanized steel sheet on which an alloy plating layer of Zn-4 mass% Al with an adhesion amount of 60 g / m ² and a plate thickness of 0.8 mm is formed.
(4) Hot-dip galvanized steel sheet on which an alloy plating layer of Zn-3 mass% Mg-6 mass% Al-0.1 mass% Si having an adhesion amount of 60 g / m ² and a plate thickness of 0.8 mm was formed.
(5) Hot-dip galvanized steel sheet on which an alloy plating layer of Zn-3 mass% Mg-11 mass% Al-0.1 mass% Si having an adhesion amount of 60 g / m ² and a plate thickness of 0.8 mm was formed.

(6) Hot-dip galvanized steel sheet on which an alloy plating layer of Zn-55 mass% Al-1 mass% Si having an adhesion amount of 60 g / m ² and a plate thickness of 0.8 mm is formed.
(7) Hot-dip galvanized steel sheet on which an alloy plating layer of 91 mass% Al-9 mass% Si having an adhesion amount of 60 g / m ² and a plate thickness of 0.8 mm is formed.
(8) Electrogalvanized steel sheet with a coating weight of 20 g / m ² and a plate thickness of 0.8 mm (comparative material)

The paint for forming the organic resin film was prepared by the following procedure.
An aqueous solution in which 40 g of concentrated sulfuric acid was dissolved in 150 g of water was mixed with a solution obtained by adding 600 g of water and 40 g of concentrated hydrochloric acid to 42 g of aniline to prepare a monomer solution. While maintaining the monomer solution at a temperature of 0 ° C. or lower, an oxidant solution in which 130 g of ammonium persulfate was dissolved in 220 g of water was added dropwise to the monomer solution. After dropping, polyaniline was synthesized by carrying out a polymerization reaction with stirring for 5 hours. Next, after dedoping with concentrated aqueous ammonia, washing with water and methanol were repeated, a polyaniline powder in a dedope state was obtained by vacuum drying.
A paint was prepared by dissolving polyaniline powder in methylpyrrolidone at a mass ratio of 1:10 and further blending the silane coupling agent listed in Table 2 at a ratio of 3.0 mass%.

A coating was applied to the degreased and washed various coating original plates with a bar coater and heated and dried at an ultimate plate temperature of 150 ° C. to form an organic resin film (undercoat film) having a dry film thickness of 2 μm. The hot-dip plated steel sheet after coating exhibited a high brown color tone derived from polyaniline even though the organic resin film was a thin film. In the case of doping, a 0.1 mol / l aqueous solution using p-toluenesulfonic acid and phosphoric acid as dopants was applied to the organic resin-coated steel sheet at a coating amount of 5 ml / m ² . For comparison, a polyaniline-coated steel sheet and a phosphate-treated steel sheet with no silane coupling agent added were prepared.

Next, an acrylic overcoating paint was applied to the surface-treated plated steel sheet and baked to form an overcoating film having a dry film thickness of 20 μm.
The distribution of elements in the depth direction of Zn-0.1 mass% Al alloy-plated steel plate (original plate No. 1 in Table 1) coated with a paint containing silane coupling agent No. A (Table 2) added to polyaniline. FIG. 1 shows the result of AES analysis at a SiO ₂ equivalent sputter rate of 2 nm / second. In the figure, N is a polyaniline and Si is an element of a silane coupling agent. From FIG. 1, it can be confirmed that the silane coupling agent added to the coating is concentrated on the original plate side to form an interface layer. Similar results are obtained even when other silane coupling agents or original plates are used.

  Moreover, the crosscut was put into the flat part of the sample cut out from the coated steel plate, and the corrosion under coating was investigated after spraying a 35% 5% NaCl aqueous solution for 240 hours. The cross-section after spraying with salt water was observed, and the corrosion resistance after coating was evaluated with bulge width: 2 mm or less as ◎, bulge width: 2-4 mm as ◯, bulge width: 4-6 mm as Δ, bulge width: more than 6 mm as x.

As seen in the survey results in Table 3, when using a hot-dip plated steel sheet with concentrated Al on the surface of the plating layer as the coating base plate and providing an undercoat with a paint containing a π-conjugated polymer and a silane coupling agent, All the coated steel sheets exhibited excellent post-coating corrosion resistance that surpassed the phosphate treatment.
In a coated steel sheet using an electrogalvanized steel sheet whose surface layer is not Al-concentrated as an original sheet, the corrosion resistance after coating was not sufficient even when an undercoat film was formed using the same paint. Further, when the undercoat film was formed from a paint containing no silane coupling agent, the post-coating corrosion resistance was further inferior.

  As explained above, when using a hot-dip plated steel sheet with concentrated Al on the surface layer as an original plate, and forming an organic resin film mainly composed of a π-conjugated polymer through an interface layer made of a silane coupling agent, A coated steel sheet that is resistant to undercoat corrosion even when left in a corrosive environment for a long time because a barrier layer with a high environmental barrier is formed on the surface of the hot-dip plated layer by the action of a conjugated polymer that repeats oxidation and reduction. It becomes. Therefore, a healthy coating film surface is maintained over a long period of time, and it is used in a wide range of fields as an interior material, exterior material, cover material, and the like.

Graph showing the distribution of elements in the depth direction of organic resin-coated hot-dip galvanized steel sheets

Claims (2)

  Surface layer Al concentration: Heterocyclic conjugated system or heterogeneous via an interface layer composed of a silane coupling agent having a silanol group and an organic functional group on the basis of a hot dip plated steel sheet provided with a hot dip plated layer of 3% by mass or more An organic resin-coated hot-dip galvanized steel sheet provided with an organic resin film containing an atom-containing conjugated π-conjugated polymer.   The organic resin-coated hot dip plated steel sheet according to claim 1, wherein one or more selected from an amino group, a cycloalkane, and an atomic group having a π bond are used as the organic functional group of the silane coupling agent.

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