JP5585483B2 - Zinc-based plated steel with excellent blackening resistance - Google Patents

Description

The present invention relates to a zinc-based plated steel material excellent in blackening resistance.

  Since zinc (Zn) -based plated steel has excellent corrosion resistance, it is widely used in automobile materials, building materials, electrical products, and the like. When zinc-based plated steel is stored in a coiled state for a long period of time, especially when stored in a high-temperature and high-humidity environment, the so-called blackening phenomenon that inevitably occurs is the blackening phenomenon that the plating surface loses its gloss over time and turns black. There is. The commercial value of the zinc-based plated steel material that has turned black is reduced in appearance. Further, the zinc-based plated steel is generally subjected to chemical conversion treatment such as chromate treatment or chromate-free treatment for the purpose of suppressing white rust of zinc-based plating. However, when the chemical conversion treatment is performed, the Zn-based plating tends to cause a blackening phenomenon.

  In recent years, the chemical conversion treatment has been switched from a chromate treatment with a large environmental load to a chromate-free chemical conversion treatment.

  As a technique for improving the blackening resistance of a Zn-based plated steel sheet, for example, as described in Patent Document 1, one or more selected from Ni, Co, or In in an electroplating layer mainly composed of Zn. The method of containing these metal elements is mentioned. However, the technique described in Patent Document 1 must suppress impurities during plating, and must add an expensive element such as Ni, Co, In, etc. There is a problem.

  Further, in Patent Document 2, an aqueous solution containing a cobalt salt or an iron salt or both is sprayed on the surface of a zinc-aluminum alloy hot-plated layer to thermally decompose the salt, thereby oxidizing cobalt or iron or both. A hot-dip galvanized steel sheet on which a physical film is formed is described. However, the technique described in Patent Document 2 has a lower corrosion resistance because a noble metal than Zn exists on the surface of the plating layer. Further, the use of cobalt salt or iron salt increases the cost, and the disposal cost when the treatment liquid containing the metal ions deteriorates becomes a problem.

  Furthermore, in Patent Document 3, in a continuous hot-dip Zn plating line, after plating using a plating bath having a plating bath temperature of 410 to 470 ° C., when the plated steel plate is cooled, the plate temperature is 400 ° C. to 380 ° C. Describes a method for producing a hot-dip Zn-Al-plated steel sheet having a cooling rate of 15 to 100 ° C./second while the temperature is lowered. Patent Document 4 discloses a method for performing dal skin pass rolling after plating. In addition, a method for producing a hot-dip Zn-Al alloy-plated steel sheet is described in which a heat treatment is performed in an oxidizing atmosphere to form an oxide film on the plating surface. However, the techniques of Patent Documents 3 and 4 both have a small blackening suppression effect, and Patent Documents 3 and 4 both improve blackening when chromate treatment is performed, and are chromate-free. No consideration is given to the blackening suppression effect of the zinc-based plated steel sheet on which the chemical conversion film is formed.

  Furthermore, in Patent Document 5, the content of Al and Pb in the plating layer is limited, and after the remelting of the plated layer of the Zn-plated steel sheet, the hot dip galvanizing is immediately cooled at a cooling rate of 20 ° C./s or more. A method for manufacturing a steel sheet is described. However, the method described in Patent Document 5 evaluates blackening resistance in a galvanized steel sheet that does not form a chemical conversion film, and particularly in the case of a galvanized steel sheet that forms a chromate-free chemical conversion film. No consideration is given to the blackening suppression effect.

JP 2000-355790 A JP-A-1-129978 Japanese Patent Laid-Open No. 5-125515 JP-A-9-20974 JP-A-8-27557

  The object of the present invention has been developed in view of the above-mentioned present circumstances, and is excellent in blackening resistance while maintaining good corrosion resistance, particularly in a zinc-based plated steel material having a chromate-free chemical conversion film on the surface of a zinc-based plating layer. It is to provide a zinc-based plated steel material.

  The present inventors performed a chromate-free chemical conversion treatment by containing a specific element in the chromate-free chemical conversion film and by causing the specific element contained in the chemical conversion film to exist in a predetermined amount or more as a heteropolyacid. It has been found that the blackening resistance can be remarkably improved without deteriorating the corrosion resistance of the galvanized steel sheet.

  This invention is made | formed based on such knowledge, Comprising: The summary structure is as follows.

(1) has a zinc-based plating layer on the surface of the processed steel, has a chromate-free conversion coating on the surface of the zinc-based plating layer, said chemical conversion coating is, Si, is selected or al P, and B contains at least one of the first element, Mo, W, and at least one second element V or we selected, and, 0.40 × 10 as the second element heteropolyacid contained in the chemical conversion film in A zinc-based plated steel material which is present in an adhesion amount of ⁻⁵ mol / m ² or more , and wherein the heteropolyacid contains the first element as a heteroelement.

  According to the present invention, it is possible to provide a zinc-based plated steel material having a chromate-free chemical conversion film on the surface of a zinc-based plated layer, particularly a zinc-based plated steel material excellent in blackening resistance while maintaining good corrosion resistance. became.

Next, embodiments of the present invention will be described in detail below.
Examples of the zinc-based plated layer constituting the zinc-based plated steel material of the present invention include Al: 20% by mass or less, Ni: 20% by mass or less, Si: 10% by mass or less, Fe: 15% by mass or less, Mg: 10 Satisfying mass% or less, Cr: 20 mass% or less, Co: 2 mass% or less, and Mn: 40 mass% or less (including any case where the content is 0 mass%), with the balance being Zn This zinc-based plating layer is coated by an electroplating method (electrolytic method), a hot dipping method (including the case of alloying plating that has been subjected to an alloying treatment after hot dipping), a vapor phase method, or the like. By forming on the surface of the plated steel material, the zinc-based plated steel material of the present invention can be manufactured. In addition, it does not specifically limit about the to-be-plated process steel material used as the base material of zinc-type plated steel material.

As the zinc-based plated steel material (steel plate) as a base, galvanized steel plate, Zn-Ni plated steel plate, Zn-Fe plated steel plate (electroplating, alloyed hot dip galvanizing), Zn-Cr plated steel plate, Zn-Mn plated steel plate Zn-Co plated steel sheet, Zn-Co-Cr alloy plated steel sheet, Zn-Cr-Ni plated steel sheet, Zn-Cr-Fe plated steel sheet, Zn-Al plated steel sheet (for example, Zn-5% Al alloy plated steel sheet, Zn −55% Al alloy-plated steel sheet), and zinc-based composite plated steel sheets (for example, Zn—SiO ₂ dispersed plating) in which metal oxides, polymers, and the like are dispersed in these platings can be used. 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.

And the zinc-based plated steel material of the present invention has a zinc-based plated layer on the surface of the steel material to be plated, and has a chromate-free chemical film on the surface of the zinc-based plated layer. P, and comprises at least one first element X or we selected B, Mo, W, and at least one second element M V or we selected, and, contained in the chemical conversion film in The second element is present as a heteropolyacid in an amount of 0.40 × 10 ⁻⁵ mol / m ² or more, and the heteropolyacid contains the first element as a heteroelement .

Adhesion amount of the zinc-based plating layer is preferably in the range of 0.5~1000g / m ^2. This is because if the adhesion amount of the zinc-based plating layer is less than 0.5 g / m ² , it tends to be difficult to maintain good corrosion resistance, and the adhesion amount of the zinc-based plating layer exceeds 1000 g / m ^2. This is because it only increases the plating cost.

In the present invention, conversion coating, Si, P, and at least one first element (hetero element) B or al selected X and, Mo, W, and the second at least one of V or we selected The corrosion resistance is improved by containing the element (poly element) M and the second element contained in the chemical conversion film as a heteropoly acid in an amount of 0.40 × 10 ⁻⁵ mol / m ² or more. This is necessary in terms of significantly improving blackening resistance without deteriorating.

The mechanism by which the blackening resistance is improved by the presence of the second element in the chemical conversion film as a heteropolyacid in an amount of 0.40 × 10 ^-5 mol / m ² or more is not clear, As a result, when there is more heteropolyacid than the above adhesion amount, under the blackening environment, 1) production of ZnO, which causes blackening, is suppressed, and 2) the heteropolyacid is reduced and plated. It has been found that the plating surface is concentrated together with metal ions. From the above, when a heteropolyacid is present in the chemical conversion film, 1) the cathode reaction associated with the ionization of the plating metal changes from an oxygen reduction reaction to a reduction reaction of the heteropolyacid, and 2) the ionized plating metal and the heteropolyacid. It is presumed that they combine and concentrate on the plating surface. As described above, 1) As a result of suppressing the reduction reaction of oxygen, the generation of ZnO, which is the causative substance of ZnO generation, is suppressed, so that the formation of ZnO is suppressed. 2) The compound of plating metal ion and heteropolyacid It is presumed that a mechanism such as concentration of zinc on the plating surface exhibits a passivating action and suppresses the formation of ZnO.

The reason why the second element is present in the chemical conversion film as a heteropolyacid in an amount of 0.40 × 10 ⁻⁵ mol / m ² or more is as follows:
This is because, when the adhesion amount of the second element existing as the heteropolyacid is less than 0.40 × 10 ⁻⁵ mol / m ² , the above effect is not sufficiently exhibited, and as a result, blackening resistance cannot be sufficiently improved.

The first element X in the chemical conversion film may be contained as a single component or may be contained as two or more components. The adhesion amount of the first element X in the chemical conversion film is preferably 0.6 × 10 ⁻⁵ mol / m ² or more. When the adhesion amount of the first element X in the chemical conversion film is less than 0.6 × 10 ⁻⁵ mol / m ² , there is a problem that a sufficient amount of heteropolyacid is not formed with the element M. There is no particular upper limit on the amount of the first element X deposited, but it is sufficient that the first element X is deposited within a range that does not affect various necessary characteristics.

Moreover, the 2nd element M in a chemical conversion film may be contained as a single component, or may be contained as two or more components. The adhesion amount of the second element M in the chemical conversion film is preferably 1.2 × 10 ⁻⁵ mol / m ² or more. When the adhesion amount of the second element M in the chemical conversion film is less than 1.2 × 10 ⁻⁵ molm ⁻² , there is a problem that a sufficient amount of heteropolyacid for suppressing blackening is not generated. There is no particular upper limit on the amount of adhesion of the second element M, but it may be added in a range that does not affect various necessary characteristics.
When the heteropolyacid is directly added to the chemical conversion film, the amount of adhesion in terms of the second element M, which is a poly element, may be 0.4 × 10 ⁻⁵ mol / m ² or more. If the amount is less than this, the blackening suppression is not sufficient.

In addition, the adhesion amount of the 2nd element M which exists as heteropoly acid is determined using the X-ray absorption near edge structure (XANES: X-ray Absorption Near Edge Structure) of an X-ray absorption spectrum. Specifically, the XANES spectrum of the second element M present in the following three substances is measured.
1) Chemical conversion film (hereinafter referred to as “C”).
2) A compound that is added as a raw material to the chemical conversion coating solution and serves as a supply source of the second element M (hereinafter referred to as “G1”). Generally, it is an oxo acid compound of element M.
3) An oxide of M constituting a heteropolyacid containing the element M (hereinafter referred to as “G2”). For example, taking the Keggin structure that is the most basic heteropolyacid represented by [XM ₁₂ O ₄₀ ] ^{n- as an} example, when expressed by the oxide unit constituting the substance, [XO ₄ · 12MO ₃ ] ^{n -} since the measures XANES spectrum of MO3.
Next, by fitting the XAMES spectrum of C with the XANES spectra of G1 and G2, among the elements M contained in C, the ratio of the element M present in the G1 state and the element M present in the G2 state is I want. Since the adhesion amount of the element M contained in C is known, the adhesion amount of the element M present in the state of G2 is obtained. Here, the adhesion amount of the element M present in the state of G2 is defined as the adhesion amount of the element M present as the heteropolyacid.
When the heteropolyacid is directly added as a heteropolyacid powder or a heteropolyacid aqueous solution, the amount of the element M attached is calculated from the known addition amount.

  As a means for causing the heteropolyacid to be present in the chemical conversion film, for example, a mixed solution obtained by directly adding a heteropolyacid powder or a heteropolyacid aqueous solution to the chromate-free treatment solution is used, or an oxoacid of the first element X is used. And a mixed solution to which the oxo acid of the second element M is added, and this mixed solution is applied to the surface of the zinc-based plating layer and then dried by heating.

  Examples of the heteropolyacid include phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, phosphovanadomolybdic acid, phosphotungstomolybdic acid, phosphotungstic acid aqueous solution, phosphomolybdic acid aqueous solution, and silicotungstic acid aqueous solution.

  Examples of the oxo acid source of the first element X include the following compounds. In addition to the compounds shown below, any compound containing the first element can be used as the oxo acid source.

Record
Si: Silane coupling agent, silicic acid, silicate P: phosphoric acid, phosphate
As: arsenic acid, arsenate S: sulfuric acid, sulfate
Fe: Iron oxide, iron chloride
Co: Cobalt sulfate, alum B: Boric acid, borate
Ge: Sodium orthogermanate
Mn: Potassium permanganate
Cu: Copper sulfate, copper chloride, copper nitrate
Zn: Zinc chloride, zinc sulfate

  Examples of the second element oxo acid source include the following compounds. In addition to the compounds shown below, any compound containing the second element oxo acid can be used as the oxo acid source.

Record
Mo: molybdate W: tungstate V: vanadate
Nb: Niobate

  The base material of the chemical conversion film is not particularly limited, but is an aqueous solution containing water-dispersible silica, an alkyd resin, and a trialkoxysilane compound, a water-soluble resin comprising a hydroxypyrone compound derivative, an aqueous resin, colloidal silica, and ammonium vanadate. A treating agent comprising an organic resin and a thiocarbonyl group-containing compound, a treating agent containing an organic resin, a silane coupling agent and a solid lubricant in an aqueous lithium silicate solution, a carboxyl group-containing polyurethane resin and ethylene- Resin aqueous solution containing unsaturated carboxylic acid copolymer aqueous dispersion, silica particles and silane coupling agent in specific ratio, urethane resin, lubricant, treatment agent comprising inorganic colloidal compound and silane coupling agent, silane cup Table adjusted to pH 2.5-4.5 by mixing ring agent and urethane resin Surface treatment liquid, treatment agent containing aqueous dispersion resin, silica particles and organic titanate in specific ratio, aqueous epoxy resin dispersion, urethane resin dispersion, silane coupling agent, phosphoric acid and / or phosphoric acid compound and one molecule Examples thereof include a treating agent containing a compound having 1 to 5 fluorine atoms.

  The chromate-free treatment liquid that is the base of the chemical conversion treatment for forming the chemical conversion film is not particularly limited. However, as the chemical conversion treatment method, the treatment liquid is applied to the surface of the zinc-based plating layer, for example, a coating method or a dipping method. A so-called coating-type treatment method is preferred, in which the surface of a zinc-based plated steel sheet is treated with a treatment liquid by a spray method and then dried by heating. As a coating method, any method such as a roll coater (for example, a 3-roll system, a 2-roll system), a squeeze coater, a bar coater, or a spray coater may be used. In addition, after the coating process using a squeeze coater or the like, or the dipping process or the spray process, the coating amount may be adjusted, the appearance may be made uniform, or the film thickness may be made uniform by an air knife method or a roll drawing method. The heating means for performing heat drying is not particularly limited, and a dryer, a hot air furnace, a high frequency induction heating furnace, an infrared furnace, or the like can be used. The drying temperature is preferably 50 to 250 ° C. at the ultimate plate temperature. Generally, when it exceeds 250 degreeC, a crack will enter in a chemical conversion film, and there exists a tendency for corrosion resistance to fall. On the other hand, when the temperature is lower than 50 ° C., moisture remains in the chemical conversion film, and the corrosion resistance tends to decrease. From such a point of view, the temperature for heat drying is preferably in the range of 50 to 250 ° C, more preferably in the range of 60 to 200 ° C, and particularly preferably in the range of 60 to 180 ° C.

  What has been described above is merely an example of an embodiment of the present invention, and various modifications can be made within the scope of the claims.

Next, examples of the present invention will be described below.
Zinc-based plated steel materials include hot-dip Zn-5mass% Al-0.5mass% Mg alloy-plated steel sheet (cold-rolled steel sheet with a thickness of 0.8mm, double-sided plating, coating weight per side: 90g / m ² ), and electrozinc Two types of plated steel sheets (cold-rolled steel sheets with a thickness of 0.8 mm, double-sided plating, plating adhesion amount per side: 20 g / m ² ) were used. After these galvanized steel sheets are subjected to alkaline degreasing treatment, washed with water and dried, the base liquid shown in Table 1 and the mixed liquid mixed in the ratio of the base liquid shown in Table 2 and additives 1 to 3 are stirred with a stirrer. Then, apply the chemical conversion treatment solution prepared with a bar coater, then immediately heat it by induction heating method so that the steel sheet surface temperature becomes 140 ° C in several seconds to tens of seconds, then hold and dry for 5 seconds, zinc plating A chromate-free chemical conversion film having the composition shown in Table 3 was formed on the surface of the steel plate. The film thickness (adhesion amount) of this chemical conversion film was adjusted by the concentration of the aqueous surface treatment solution, the P adhesion amount in the chemical conversion film was quantified with a fluorescent X-ray analyzer, and the film adhesion amount was calculated therefrom. About the adhesion amount of the element M which exists as heteropoly acid, it calculated | required using the X-ray absorption near edge structure (XANES: X-ray Absorption Near Edge Structure) of the X-ray absorption spectrum mentioned above. Table 4 shows the types of Additive 2 (heteropolyacid source) used in the treatment liquids Nos. 21 to 32 shown in Table 2.

  The test material (zinc-based plated steel sheet) obtained as described above was evaluated. The evaluation method is shown below, and the evaluation results are shown in Table 3.

(Evaluation method)
(1) Corrosion resistance Corrosion resistance is 120 for each sample material when the salt spray test (JIS-Z-2371) is performed in the state of a flat plate and the base is a molten Zn-5mass% Al-0.5mass% Mg alloy-plated steel sheet. In the case of an electrogalvanized steel sheet, the test was carried out for 48 hours, and the case where the area ratio of white rust generated on the surface of the test material was maintained at 5% or less was evaluated as an acceptable level. A case where the area ratio of rust is maintained at 5% or less is indicated by “◯”, and a case where the area ratio of white rust exceeds 5% is indicated by “x”.

(2) Blacking resistance Blacking resistance is the color difference ΔL before and after each specimen was held at 80 ° C. and 98% RH for 24 hours (in the L, a and b display systems defined in JIS-Z-8729). The difference in CIE 1976 brightness L between the two object colors was measured and evaluated. The evaluation criteria are as follows.

In the case where the zinc-based plated steel sheet on which the chemical conversion film is formed is a molten Zn-5 mass% Al-0.5 mass% Mg alloy-plated steel sheet,
A: -9 <△ L
○: −12 <ΔL ≦ −9
×: ΔL ≦ −12
It was evaluated as follows.

When the galvanized steel sheet on which the chemical conversion film is formed is an electrogalvanized steel sheet,
◎: -2 <△ L
○: −3 <ΔL ≦ −2
×: ΔL ≦ −3
It was evaluated as follows.

  From the evaluation results shown in Table 3, it can be seen that the inventive examples are superior in blackening resistance while securing the same level of corrosion resistance as compared to the comparative examples.

  According to the present invention, it is possible to provide a zinc-based plated steel material having a chromate-free chemical conversion film on the surface of a zinc-based plated layer, particularly a zinc-based plated steel material excellent in blackening resistance while maintaining good corrosion resistance. became.

Claims (1)

Has a zinc-based plating layer on the surface of the steel material to be treated,
Has a chromate-free conversion coating on the surface of the zinc-based plating layer, said chemical conversion coating is, Si, and at least one first element selected P, and B or al, Mo, W, and V or al Containing at least one selected second element ;
The second element is present at 0.40 × 10 ^-5 mol / m ² or more deposition amount as a heteropoly acid containing prior Symbol conversion coating in,
The zinc-based plated steel material, wherein the heteropolyacid contains the first element as a heteroelement.