JP2007321222A - Surface treated steel sheet having excellent corrosion resistance and water resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a surface treated steel sheet having excellent corrosion resistance and water resistance. <P>SOLUTION: The surface of a galvanized steel sheet is provided with a surface treatment film with a prescribed coating weight comprising: (A) a tetravalent vanadium compound; (B) a phosphoric acid or a phosphoric acid compound; (C) a bifunctional type silane compound; and (D) a water base organic resin. By the incorporation of the bifunctional type silane compound into the treatment agent, the stability of the treatment liquid improves, and the barrier properties of the surface treatment film and its adhesion with the plating film are strengthened, thus, even in the case of the one treated with the treatment liquid with the lapse of time after preparation, excellent corrosion resistance and water resistance can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface-treated steel sheet that is optimal for use in automobiles, home appliances, and building materials, and relates to an environment-adaptive zinc-based plated steel sheet that does not contain hexavalent chromium in the surface-treated film.

  Steel sheets for home appliances, building materials, and automobiles that have been conventionally chromated with a treatment liquid containing chromic acid, dichromic acid, or salts thereof as the main component for the purpose of improving the corrosion resistance of the surface of galvanized steel sheets. Is widely used. The chromate film exhibits corrosion resistance, adhesion, etc. mainly due to poorly soluble chromium hydroxide, and as a film formation method, a coating method without electrolytic treatment, an electrolytic treatment method, or the like is adopted.

  The chromate treatment uses hexavalent chromium which is a pollution control substance, but this hexavalent chromium can be processed by a closed system in any film forming method, and further by an organic film formed on the upper layer in the coating method. In the sealing and electrolysis methods, the reduction of hexavalent chromium to trivalent chromium by cathodic electrolysis can reduce the elution of chromium from the chromate film to almost zero, so the human body and the environment are substantially contaminated by hexavalent chromium. Never happen. However, with increasing interest in global environmental issues in recent years, not only laws and regulations that emphasize the conventional work environment and wastewater treatment, but also laws and regulations that emphasize environmental load and environmental harmony are beginning. In addition, with the background of the times when manufacturers are evaluated for their environmental contribution, there is an increasing trend to reduce the use of hexavalent chromium.

Against this background, many chromate-free techniques have been proposed as techniques for improving the corrosion resistance of galvanized steel sheets that do not use hexavalent chromium. For chromate-free coatings, as with chromate coatings, film formation with poorly soluble compounds is indispensable for performance.For example, the following method for forming a conversion coating by applying and drying a treatment solution containing vanadium is proposed. Has been.
In Patent Documents 1 to 3, a divalent to tetravalent vanadium compound, a metal compound containing at least one metal selected from Zr, Ti, Mo, W, Mn, and Ce, and a water-soluble organic resin or / In addition, a method of forming a chemical conversion film using a water-dispersible organic resin and a treatment agent containing an etching agent such as phosphoric acid or hydrofluoric acid has been proposed. Patent Document 4 proposes a method of forming a chemical conversion film with a treatment agent containing a tetravalent vanadium compound, a phosphoric acid compound, a Si compound, and a water-soluble organic resin and / or a water-dispersible organic resin. Has been. Further, Patent Documents 5 to 7 disclose a method for forming a chemical conversion film with a treatment agent containing a tetravalent vanadium compound, a phosphoric acid compound, a silane compound, and a water-soluble organic resin or / and a water-dispersible organic resin. Has been proposed.

JP 2001-181860 A JP 2002-30460 A JP 2004-183015 A JP 2005-48199 A JP 2005-290436 A JP 2005-290534 A JP 2005-290535 A

However, in the methods shown in Patent Documents 1 to 3, soluble divalent and trivalent vanadium compounds are inevitably mixed in the chemical conversion film, and sufficient corrosion resistance cannot be obtained. In addition, since the bivalent and trivalent vanadium easily dissolves in a wet environment and the chemical conversion film is colored, the appearance quality is extremely inferior and cannot be used.
Moreover, since the method shown by patent document 4 does not contain the bivalent and trivalent vanadium compound in a chemical conversion film, the above problems do not arise. In particular, by containing a phosphoric acid compound that is an etching agent, the insolubilization of tetravalent vanadium is promoted and an extremely high appearance quality is obtained. However, when the steel sheets are stacked and stored after being manufactured (stacked state), dew condensation water may accumulate between the steel sheets due to temperature and humidity changes, which causes the etching agent in the chemical conversion film to elute and alter the plating film, The appearance may be whitened.

  On the other hand, the methods shown in Patent Documents 5 to 7 contain a silane compound having an epoxy group or / and an amino group as a Si compound, so that the appearance quality (water resistance) is excellent even when stored in the stacked state. Is obtained. The alkoxysilane in the silane compound is hydrolyzed into a silanol (Si—OH) group in the treatment solution, and when applied on the plating film, hydrogen bonds to the plating film by hydrogen bonding. Furthermore, when a film is formed, a dehydration condensation reaction occurs by drying, and chemical bonding results in strong adhesion. For this reason, even if the etching agent is eluted from the chemical conversion film in a stacked state, it cannot reach the plating film, and good water resistance is obtained. However, since the silanol group obtained from the silane compound is unstable, there is a disadvantage that the treatment liquid stability is poor. That is, silanol groups in the treatment liquid undergo a self-condensation reaction over time, resulting in a siloxane bond. Even if the chemical conversion film obtained from the treatment liquid that is not prepared has good corrosion resistance and water resistance, In the case of a treatment solution that has been aged for several days, gelation occurs and it becomes difficult to apply, or even if it can be applied, the corrosion resistance and water resistance are significantly reduced. For this reason, although a relatively expensive silane compound is contained, the treatment liquid cannot be reused, leading to an increase in cost.

  Accordingly, an object of the present invention is to provide a surface-treated steel sheet that can provide excellent corrosion resistance and water resistance even if it is treated with a treatment solution that has been aged since preparation.

The surface-treated steel sheet of the present invention for solving the above-mentioned problems is a vanadium compound (A) having a tetravalent valence on the surface of a zinc-based plated steel sheet, phosphoric acid or / and a phosphoric acid compound (B), A bifunctional silane compound (C) and a water-soluble organic resin or / and a water-dispersible organic resin (D) are contained, and the amount of the vanadium compound (A) attached is 1 to 100 mg / m ^{2 in} terms of metal V, The adhesion amount of the phosphoric acid or / and phosphoric acid compound (B) was 5 to 200 mg / m ^{2 in} terms of P, and the adhesion amount of the bifunctional silane compound (C) was 5 to 300 mg / m ^{2 in} terms of Si. The surface-treated steel sheet is excellent in corrosion resistance and water resistance, characterized in that a surface-treated film having a film thickness of 0.2 to 3 μm is formed.

  The surface-treated steel sheet of the present invention contains a bifunctional silane compound in the treatment agent, so that the stability of the treatment solution is improved, and the barrier property of the surface treatment film and the adhesion with the plating film are enhanced. Even if it is processed with a processing solution that has passed over time, excellent corrosion resistance and water resistance can be obtained.

  According to the present invention, a vanadium compound (A) having a tetravalent valence, phosphoric acid or / and a phosphoric acid compound (B), and a bifunctional silane compound (C) are formed on the surface of a zinc-based plated steel sheet. By forming a surface-treated film containing a water-soluble organic resin and / or water-dispersible organic resin (D), the barrier property of the surface-treated film and the adhesion with the plating film are strengthened, and excellent corrosion resistance and water resistance It is possible to form a chromate-free film that exhibits its properties.

The galvanized steel sheet used as the original sheet of the surface-treated steel sheet of the present invention includes a galvanized steel sheet, a Zn—Ni alloy plated steel sheet, a Zn—Fe alloy plated steel sheet (electroplated steel sheet, galvannealed steel sheet), and 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 alloy plated steel sheet (For example, Zn-5% Al alloy-plated steel sheet), Zn-Mg alloy-plated steel sheet, Zn-Al-Mg alloy-plated steel sheet, and zinc-based composite plating in which metal oxides, polymers, etc. are dispersed in these plating films A steel plate (for example, a Zn—SiO ₂ dispersion-plated steel plate) can be used. However, the zinc-based plated steel sheet containing Al as an alloy plating component is limited to those in which the Al content in the plating film is less than 25 mass%.

Moreover, the multilayer plating steel plate which plated two or more layers of the same kind or different kind among the above plating can be used.
Moreover, as a plated steel plate, the steel plate surface may be pre-plated with light-weight plating such as Ni and the above-described various plating may be performed thereon.
As a plating method, any feasible method among an electrolytic method (electrolysis in an aqueous solution or electrolysis in a non-aqueous solvent), a melting method, and a gas phase method can be adopted.

In addition, for the purpose of preventing blackening in the usage environment (a kind of oxidation phenomenon on the plating surface), an iron group metal ion (one or more of Ni ion, Co ion, Fe ion) is previously applied to the plating surface as necessary. Surface adjustment 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 formed on the surface of the galvanized steel sheet will be described.
This surface treatment film is composed of a vanadium compound (A) having a tetravalent valence, phosphoric acid or / and a phosphoric acid compound (B), a bifunctional silane compound (C), a water-soluble organic resin, and / or It contains the water-dispersible organic resin (D) (preferably mainly).
Among the vanadium compounds, a typical pentavalent vanadium compound is reduced by vanadium itself due to its oxidizing action, and a film is formed on the surface of the plating layer as an oxide or hydroxide. At that time, it is considered that divalent to tetravalent compounds are mixed due to a difference in local pH increase during film formation (difference in local pH increase due to hydrogen ion consumption during vanadium compound reduction). That is, a readily soluble divalent or trivalent vanadium compound also exists, and that portion becomes a starting point of corrosion. On the other hand, the tetravalent vanadium compound used in the present invention does not have an oxidizing action unlike the pentavalent vanadium compound. Therefore, the divalent and trivalent vanadium compounds are hardly formed, and the film is chemically stable tetravalent vanadium. Formed with compounds. As a result, it is estimated that high corrosion resistance is exhibited.

Examples of the tetravalent vanadium compound (A) include vanadium oxides, hydroxides, sulfides, sulfates, carbonates, halides, nitrides, fluorides, carbides, cyanides, and salts thereof. . In addition, the pentavalent vanadium compound was reduced by adding one or more of alcohols such as methanol, aldehyde compounds such as formaldehyde, organic acids such as tartaric acid, monosaccharides such as glucose, polysaccharides such as sucrose, and the like 4 A valent vanadium compound may be used. Such a supply source of vanadium is not particularly limited, and one or more of these can be used. However, among the tetravalent vanadium compounds, reduced products of vanadium sulfate oxide and vanadium pentoxide are preferable because they can easily achieve both corrosion resistance and blackening resistance and are easily soluble in water.
The adhesion amount of the vanadium compound (A) in the surface treatment film is 1 to 100 mg / m ^{2 in} terms of V. If the adhesion amount in terms of V is less than 1 mg / m ² , the effect of improving corrosion resistance is not sufficiently obtained. On the other hand, if the adhesion amount exceeds 100 mg / m ² , the effect of improving corrosion resistance commensurate with the adhesion amount cannot be obtained. Disadvantageous.

By adding the phosphoric acid and / or the phosphoric acid compound (B) to the tetravalent vanadium compound (A), the corrosion resistance can be drastically improved. When the etching action of the plating film is promoted by the addition of phosphoric acid or phosphoric acid compound, the plating metal taken into the surface treatment film increases, and the physical analysis shows that the symmetry of the molecular structure of the tetravalent vanadium compound increases. As a result, it is estimated that poor solubility is promoted.
The phosphoric acid and phosphoric acid compound are not particularly limited as long as they are soluble, and phosphoric acid, primary phosphate, secondary phosphate, tertiary phosphate, pyrophosphoric acid, pyrophosphate, tripolyphosphoric acid, Examples include condensed phosphates such as tripolyphosphate, phosphorous acid, phosphite, hypophosphorous acid, hypophosphite, and the like, and one or more of these can be used.
The adhesion amount of phosphoric acid and / or phosphoric acid compound (B) in the surface treatment film is 5 to 200 mg / m ^{2 in} terms of P. When the adhesion amount in terms of P is less than 5 mg / m ² , the effect of improving the corrosion resistance is small, whereas when the adhesion amount exceeds 200 mg / m ² , the water resistance is remarkably lowered.

The silane compound is an organic alkyl compound having an alkoxysilane (Si (OR) ₃ , R is a methyl group, an ethyl group) that hydrolyzes to generate a silanol (Si—OH) group. A monofunctional silane compound having three alkoxy groups bonded to Si at one end of an alkyl group and having an organic functional group such as an amino group, a glycidyl group, a vinyl group, or a mercapto group at the other end is referred to as a monofunctional silane compound. On the other hand, those having no organic functional group and having an alkoxysilane at both ends of the alkyl group (including those having an amino group or S bond in the middle) are referred to as bifunctional silane compounds.

  The silane compound is dissolved in water, and the alkoxysilane is hydrolyzed to a silanol (Si—OH) group. When this solution is applied to the surface of a galvanized steel sheet and heated, the silanol group hydrogen bonds with the OH group on the surface of the plated metal or vanadium, which is a metal component in the coating, to exhibit adhesion, and the dehydration condensation reaction results in a polymer. To form a polysiloxane film and exhibit barrier properties. However, silanol groups obtained by hydrolysis from alkoxysilanes are unstable, and a self-condensation reaction occurs in an aqueous solution over time. For this reason, even if sufficient corrosion resistance and water resistance are obtained by the above action in the surface treatment film obtained from the treatment liquid that is not prepared, the surface treatment film obtained from the time-treated treatment liquid has corrosion resistance. The water resistance is remarkably inferior. As a result of various investigations, by applying a bifunctional silane compound as a silane compound, even with a surface treatment film obtained from a time-treated treatment liquid, there is no deterioration in corrosion resistance and water resistance, and extremely stable performance Was found to be obtained.

  The reason for this is not always clear, but (1) the bifunctional silane compound has a very slow self-condensation reaction compared to the monofunctional silane compound, and (2) the bifunctional silane compound is an alkoxy contained per molecule. Since the number of silanes is twice that of monofunctional silane compounds, the resulting film can effectively exhibit the above adhesion and barrier properties. (3) Bifunctional silane compounds are crosslinked in organic resins. It can also act as an agent, contributing to the toughening of the surface treatment film, etc., and as a result of combining these actions, even if the etching agent elutes in the stack state, the surface treatment film acts as a barrier. It is thought that it can prevent the deterioration of the plating film due to the high adhesion between the plating film and the surface treatment film and the barrier effect of the polysiloxane film while acting to suppress the penetration.

Examples of the bifunctional silane compound (C) include bis-1,2- [triethoxysilyl] ethane (hereinafter referred to as “BTSE”), bis-1,2- [triethoxysilylpropyl] amine (hereinafter referred to as “BTSPA”), bis -1,2- [triethoxysilylpropyl] tetrasulfide (hereinafter referred to as “BTSPS”), and the like can be used alone or in combination of two or more. However, among these bifunctional silane compounds, BTSE is particularly preferable from the viewpoint of processing solution stability.
The adhesion amount of the bifunctional silane compound (C) in the surface treatment film is 5 to 300 mg / m ^{2 in} terms of Si. If the adhesion amount in terms of Si is less than 5 mg / m ² , the effect of improving the water resistance is hardly obtained, whereas if the adhesion amount exceeds 300 mg / m ² , the corrosion resistance is lowered. Moreover, the range of the more preferable adhesion amount from the above viewpoint is 10-60 mg / m < ² >.

There is no restriction | limiting in particular about water-soluble organic resin or / and water-dispersible organic resin (D), For example, 1 type (s) or 2 or more types, such as an acrylic resin, a urethane resin, an epoxy resin, a phenol resin, can be used, A lubricant may be mixed with this.
Moreover, a rust preventive additive and oxide sol can also be added in a surface treatment film as needed. Further, from the viewpoint of reactivity control, it is possible to add an inorganic acid such as hydrofluoric acid and a salt thereof, an organic acid such as a carboxylic acid and a salt thereof, and the like. In addition, addition of a monofunctional silane compound or the like is possible from the viewpoint of improving adhesion as long as there is no problem. One or more of the above components can be added.
The film thickness of the surface treatment film is preferably 0.2 to 3 μm. If the film thickness is less than 0.2 μm, sufficient corrosion resistance cannot be obtained. On the other hand, when the film thickness exceeds 3 μm, the film is colored and the appearance is inferior.

  As a method of forming the surface treatment film on the surface of the zinc-based plated steel sheet, a commonly applied coating treatment method can be used. For example, the surface treatment composition (treatment liquid) is applied by a coating method, a dipping method, a spray method, or the like, and then dried by heating. In the case of the coating method, any method such as a roll coater (3-roll method, 2-roll method, etc.), a squeeze coater, etc. may be used. In addition, after the coating process with a squeeze coater or the like, or the dipping process or the spray process, 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. 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 300 ° C. or less, preferably 250 ° C. or less at the ultimate plate temperature. When the heating temperature exceeds 300 ° C., not only is it uneconomical, but cracks occur in the film, and the corrosion resistance decreases.

After electrogalvanized steel sheet (plating adhesion amount per side: 20 g / m ² ) is subjected to alkaline degreasing treatment, washed with water and dried, treatment liquids having the compositions shown in Table 1 and Table 2 are prepared immediately after preparation and one month after preparation. It was applied and dried at 140 ° C. The film thickness of the film was adjusted to 1.5 μm by adjusting the solid content (heating residue) of the film composition, the treatment time, and the like. Tables 3 and 4 show the quality performance of the obtained surface-treated steel sheets. The quality performance evaluation method is as follows.
(1) Appearance after wetting test The specimen was allowed to stand for 24 hours in a thermostatic oven controlled at a temperature of 80 ° C. and a relative humidity of 98% RH, and then the surface of the specimen was visually evaluated. The evaluation criteria are as follows.
○: No coloring or discoloration (no difference from before test)
Δ: Very thin color that can be confirmed when viewed from an angle ×: Clear coloration and discoloration

(2) Appearance after wet test in a stacked state (water resistance)
The test material was put in a stacked state and left in a wet testing machine (HCT) for 4 weeks, and then the surface of the test material was visually evaluated. The evaluation criteria are as follows.
○: No whitening (no difference from before test)
△: Very thin whitening that can be confirmed from an angle ×: Clear whitening (3) Corrosion resistance JIS Z 2371 salt spray test was performed on the specimen with the end and back tape sealed, and after 312 hours The white rust area ratio was measured. The evaluation criteria are as follows.
◎: White rust area ratio of less than 5% ○: White rust area ratio of 5% or more and less than 10% △: White rust area ratio of 10% or more and less than 50% ×: White rust area ratio of 50% or more

Claims (1)

On the surface of the galvanized steel sheet, a vanadium compound (A) having a tetravalent valence, phosphoric acid or / and a phosphoric acid compound (B), a bifunctional silane compound (C), a water-soluble organic resin or / And a water-dispersible organic resin (D), the adhesion amount of the vanadium compound (A) is 1 to 100 mg / m ^{2 in} terms of V, and the adhesion amount of the phosphoric acid or / and the phosphoric acid compound (B) is 5 to 200 mg / m ^{2 in} terms of P, the amount of the bifunctional silane compound (C) attached is 5 to 300 mg / m ² in terms of Si, and a coating film thickness of 0.2 to 3 μm is formed. A surface-treated steel sheet excellent in corrosion resistance and water resistance, characterized in that