JP5585484B2 - 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 the zinc-based plated steel material is stored in a coil state for a long period of time or stored in a high-temperature and high-humidity environment, there is a problem that a so-called blackening phenomenon is unavoidably caused that the plating surface loses its gloss over time and turns black. 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 was developed in view of the above-mentioned present situation, and has a chromate-free chemical conversion film on the surface of the zinc-based plating layer via a specific intermediate film, while maintaining good corrosion resistance, An object of the present invention is to provide a zinc-based plated steel material excellent in blackening resistance.

  The inventors of the present invention form a specific intermediate film between a zinc-based plating layer and a chromate-free chemical film, containing a specific element and having a specific element as a heteropoly acid in a predetermined ratio or more. Thus, it has been found that the blackening resistance can be remarkably improved without deteriorating the corrosion resistance of the zinc-based plated steel sheet subjected to the chromate-free chemical conversion treatment.

  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, the surface of the zinc-based plating layer, Si, P, and at least one first element or we selected B, Mo, W, and contains at least one second element V or we selected, and chromate via an intermediate coating said second element is present at 0.40 × 10 ^-5 mol / m ² or more deposition amount as a heteropolyacid A zinc-based plated steel material having a free chemical conversion film, wherein the heteropolyacid contains the first element as a heteroelement.

  According to the present invention, by having a chromate-free chemical conversion film through a specific intermediate film on the surface of the zinc-based plating layer, a zinc-based plated steel material excellent in blackening resistance while maintaining good corrosion resistance is provided. It became possible to do.

Next, embodiments of the present invention will be described in detail below.
Examples of the zinc-based plated steel material (steel plate) of the present invention include a galvanized steel plate, a Zn—Ni plated steel plate, a Zn—Fe plated steel plate (electroplating, alloyed hot dip galvanizing), a Zn—Cr plated steel plate, and a 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.

  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.

The zinc-based plated steel material of the present invention has a zinc-based plating layer on the surface of the plated steel material, the surface of the zinc-based plating layer, Si, P, and at least one of either et selected B a first element X, Mo, W, and contains at least one second element M V or we selected, and said second element is 0.40 × 10 ^-5 mol / m ² or more as a heteropolyacid It has a chromate-free chemical conversion film through an intermediate film present in an amount of adhesion, and the heteropolyacid contains the first element as a hetero element .

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, between the chemical conversion coating of zinc-based plating layer and the chromate-free, Si, and P, and B or al least one first element selected (hetero element) X, Mo, W, and V It contains at least one second element (poly element) M is selected pressurized et al, ^{and, 0.40 × 10 -5 mol / m} 2 or more deposition amount as a second element heteropolyacid contained in the chemical conversion film in It is necessary to form an intermediate film existing in (3) in that the blackening resistance is remarkably improved without deteriorating the corrosion resistance.

In addition, the mechanism by which the blackening resistance is improved by the presence of the second element in the intermediate coating as a heteropolyacid in an amount of 0.40 × 10 ^-5 mol / m ² or more is not clear, but our investigation As a result, when there is more heteropoly acid than the above adhesion amount, under the blackening environment, 1) production of ZnO, which is the cause of blackening, is suppressed, and 2) the heteropolyacid is reduced. It was found that it exists on the plating surface together with the plating 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. Are presumed to combine on the plating surface. Thus, 1) the results of oxygen reduction reaction is inhibited, OH causing substances ZnO generation ^- generation of ZnO for the generation of ions is suppressed is suppressed, 2) a compound of the plating metal ions and heteropoly acid 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 contained in the intermediate film is limited to the amount of deposit of 0.40 × 10 ⁻⁵ mol / m ² or more as the heteropolyacid is that the amount of the second element present as the heteropolyacid is limited. However, if it 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 intermediate 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 intermediate film is preferably 0.6 × 10 ⁻⁵ mol / m ² or more. If the adhesion amount of the first element X in the intermediate 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.

Further, the second element M in the intermediate 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 intermediate film is preferably 1.2 × 10 ⁻⁵ mol / m ² or more. When the adhesion amount of the second element M in the intermediate film is less than 1.2 × 10 ⁻⁵ mol / m 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 added directly as a heteropolyacid powder or a heteropolyacid aqueous solution, it is not limited to the above, and the adhesion amount of the second element contained in the heteropolyacid is 0.40 × 10 ⁻⁵ mol / m ² or more. If it is good.

In addition, the adhesion amount of the 2nd element M which exists as heteropoly acid in an intermediate film 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) Intermediate film (hereinafter referred to as C).
2) A compound (hereinafter referred to as G1) that is added to the intermediate coating solution as a raw material and serves as a supply source of the second element M. Generally, it is an oxo acid compound of element M.
3) M oxide constituting heteropolyacid containing 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 MO _3.
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 intermediate film, for example, the heteropolyacid powder is used by dispersing in water, or the heteropolyacid aqueous solution is used as it is or diluted with water, or the first element An example is a method in which a mixed solution in which an oxo acid of X and an oxo acid of the second element M are added 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 oxo acid source of the second element M 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

  In order to make a treatment liquid for forming an intermediate film using the oxo acid, it is easy to use an aqueous solution, for example, while maintaining water at about pH 1 to 5 with an acid such as hydrochloric acid, nitric acid, sulfuric acid, An aqueous solution prepared by dissolving equimolar amounts of the oxo acid of the first element X and the second element M can be mentioned.

  As a treatment method for forming the intermediate film, any method such as an immersion method or a spray method may be used. Further, after the coating process with a squeeze coater or the like, or the dipping process and the spray process, the coating amount may be adjusted and the adhesion amount may be made uniform by an air knife method or a roll drawing method. Thereafter, the treatment liquid is dried and solidified using a dryer or the like. In order to increase the drying speed, hot air of 50 to 100 ° C. may be used as a dryer.

  The base material of the chemical conversion film includes an aqueous solution containing water-dispersible silica, an alkyd resin, and a trialkoxysilane compound, a water-soluble resin comprising a hydroxypyrone compound derivative, a treatment agent comprising an aqueous resin, colloidal silica, and ammonium vanadate, an organic Treatment agent containing resin and thiocarbonyl group-containing compound, treatment agent containing organic resin, silane coupling agent, solid lubricant in lithium silicate aqueous solution, carboxyl group-containing polyurethane resin and ethylene-unsaturated carboxylic acid copolymer A resin aqueous liquid containing a combined aqueous dispersion, silica particles and a silane coupling agent in a specific ratio, a urethane resin, a lubricant, a treatment agent comprising an inorganic colloidal compound and a silane coupling agent, a silane coupling agent and a urethane resin. Surface treatment liquid mixed and adjusted to pH 2.5-4.5, aqueous dispersion tree Treatment agent containing fat, 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 fluorine in 1 molecule A treating agent containing a compound having 5 is mentioned.

  There is no particular limitation on the chromate-free treatment liquid that is the base of the chemical conversion treatment for forming the chemical conversion film, but as the chemical conversion treatment method, the chemical conversion treatment liquid is applied to the surface of the intermediate film, for example, coating method, dipping method, A so-called coating-type treatment method is preferred, in which heat treatment is performed after the treatment by the spray method. 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 temperature of the heat drying is preferably 300 ° C. or less, more preferably 250 ° C. or less in terms of the ultimate plate temperature. When the temperature of heat drying exceeds 300 ° C., not only is it uneconomical, but there is a tendency that the chemical conversion film cracks and the corrosion resistance decreases. Moreover, in this invention, it is also possible to form the coating layer with a film thickness of 0.01-5 micrometers which consists of an organic type surface treatment composition further on the surface of the said chemical conversion film.

  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. These galvanized steel sheets are subjected to alkaline degreasing treatment, washed with water and dried, and then applied with a water treatment solution shown in Table 1 using a bar coater, and then hot air is applied so that the steel sheet surface temperature immediately reaches 60 ° C. in 20 seconds. It dried and solidified the process liquid and formed the intermediate film. The adhesion amount of the intermediate film was adjusted by the concentration of the aqueous treatment liquid shown in Table 1, and the adhesion amounts of the first element X and the second element M in the intermediate film were quantified with a fluorescent X-ray analyzer. Next, 70 g of water-dispersible epoxy resin (solid content 20 mass%), 2 g of phosphoric acid (solid content 85 mass%), and 28 g of water were stirred and mixed on the surface of the formed intermediate film with a stirrer. A total of 100 g of the chemical conversion treatment solution was applied with a bar coater, and then immediately dried with an induction heater so that the steel sheet surface temperature was 140 ° C. in 5 seconds to form a chromate-free chemical conversion film. The film thickness (adhesion amount) of this chemical conversion film was adjusted by the concentration of the aqueous surface treatment solution, and the film adhesion amount was converted from the P adhesion amount obtained with a fluorescent X-ray analyzer. The adhesion amount of the second element M present as the heteropolyacid in the intermediate film was determined using the X-ray absorption near edge structure (XANES) of the X-ray absorption spectrum described above. The details of the type of additive 2 (heteropolyacid source) used in the treatment liquids Nos. 25 to 38 shown in Table 1 are 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 hours when the base material is a salt spray test (JIS-Z-2371) 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. The case where the area ratio is maintained at 5% or less is indicated by “◯”, and the 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 to the blackening resistance while the corrosion resistance is equal to or higher than the comparative examples.

  According to the present invention, by having a chromate-free chemical conversion film through a specific intermediate film on the surface of the zinc-based plating layer, a zinc-based plated steel material excellent in blackening resistance while maintaining good corrosion resistance is provided. It became possible to do.

Claims (1)

Has a zinc-based plating layer on the surface of the steel material to be treated,
On the surface of the galvanized layer contains Si, P, and at least one first element or we selected B, Mo, W, and at least one second element V or selected And the second element has a chromate-free chemical film through an intermediate film present as a heteropolyacid in an amount of 0.40 × 10 ⁻⁵ mol / m ² or more,
The zinc-based plated steel material, wherein the heteropolyacid contains the first element as a heteroelement.