JP2001323385A - Chromate treated composition for galvanized steel and chromate treated galvanized steel excellent in chromium elution property and corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide chromate treated galvanized steel excellent in corrosion resistance and blackening resistance and also extremely little or free from the elution of haxavalent chromium which is an environmental polution substance, and to provide a chromate treated composition having industrially sufficient bath stability. SOLUTION: This composition contains partially reduced chromic acid, a phosphoric compound and a nitric compound as essential components, and in which the relations in the following inequalities of (I) to (IV) are satisfied between the chromium reduction ratio (X) of partially reduced chromium acid and the concentration of each component in the bath: 60%<=X<=100%...(I), 0.1<=HNO3/CrO3<=1.0...(II), and, in the case of Y=(HNO3/CrO3)+(H3PO4/CrO3), Y<=0.0002 X2-0.02 X+3.1...(III) and Y>=0.0005 X2-0.05 X+2.6...(IV).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is widely applicable to home appliances, building materials, automobiles and the like, has excellent corrosion resistance and blackening resistance, and has very little elution of hexavalent chromium which is an environmentally hazardous substance. The present invention relates to a chromate-treated galvanized steel material which is zero, and a chromate-treated composition having industrially sufficient bath stability for the galvanized steel material.

[0002]

2. Description of the Related Art Chromate treatment is sometimes applied to galvanized steel sheets for home appliances, building materials and automobile parts for the purpose of improving rust prevention and paintability. For chromate treatment, in addition to the primary function of primary rust prevention,
Top coat paintability, fingerprint resistance, blackening resistance, chromium hardly soluble, etc. are required. Blackening is a phenomenon in which oxygen-deficient zinc oxide is formed on the surface of a galvanized steel sheet during the storage period and during transportation, causing blackening. It is known that it easily occurs when additives such as Al and alloy elements such as Al are contained. The blackening deteriorates the appearance of the galvanized steel sheet, which may impair its commercial value, which is one of the problems to be solved. On the other hand, with increasing interest in environmental issues in recent years, chromium insolubility has been emphasized among the above-mentioned required characteristics, and it has been demanded that elution of hexavalent chromium be reduced to the utmost without deteriorating corrosion resistance.

[0003] As a prior art relating to insolubility of chromate treatment of a zinc-based plated steel sheet, for example, Japanese Patent Application Laid-Open No.
JP-A-7981, JP-A-7-118872 and JP-A-9-3657. Of these,
In Japanese Patent No. 3657, the chromium elution rate is reduced to 20% or less by setting the chromium reduction rate to 30 to 80% and adding resin, phosphoric acid, and metal ions to the bath. Japanese Patent Application Laid-Open No. 4-179881 discloses a chromium reduction rate of 25 to 25.
60%, phosphate ion, silica sol and silane coupling agent are added to the bath, and the chromium elution rate in the film by alkali washing is reduced by several% by network bonding by bonding silanol groups of silica sol and silane coupling agent. It is suppressed below. Also, Japanese Patent Application Laid-Open No. Hei 7-11887
In Japanese Patent Publication No. 2 (KOKAI), the chromium reduction ratio is set to 20 to 80%, and phosphoric acid and a water-soluble glycol ether and / or polyvinyl alcohol are added to a chromate bath.
Hexavalent chromium is further reduced in the bath to reduce the chromium elution rate due to boiling water immersion to about 3%.

On the other hand, JP-A-5-331659 and JP-A-7-54156 disclose a chromate treatment technique which achieves both resistance to blackening and white rust. For improvement of blackening resistance by chromate treatment, see JP-A-59-1773.
It is known that pretreatment by immersion in Ni ²⁺ , Co ²⁺ -containing aqueous solution, which is found in, for example, No. 81, is effective.
Since two steps are required, JP-A-5-331659
In JP-A-7-54156, nitric acid, boric acid and phosphoric acid, and Zn, Ni, Co, Al
It is disclosed that the blackening resistance can be improved in one step by adding one or more metal ions. Further, in JP-A-4-358080, a sol such as silica / titania, a phosphate compound, a fluorine compound, a water-soluble or water-dispersible resin, and a metal ion such as Fe, Ni, and Co are added to a chromate treatment bath. It is disclosed that the blackening resistance can be improved by the addition.

Japanese Patent Application Laid-Open No. 4-107274 discloses another technique for improving the performance by adding the above-mentioned additives to a chromate bath. This is because phosphate ions, in a chromate bath having a chromium reduction ratio of 20 to 58%,
One or more of sulfuric acid, nitric acid and hydrofluoric acid ions, Co,
By adding one or more of Ni, Sn, Cu, Fe, and Pb and forming a chromate film on the substitutionally precipitated additive metal ions, the electrodeposition coatability of galvanized steel sheets was improved. Things.

[0006]

However, there are problems with these prior arts. The chromate disclosed in Japanese Patent Application Laid-Open No. 9-3657 has a maximum elution rate of chromium in boiling water of nearly 20%, which is not sufficient with respect to the recently required level of chromium insolubilization. Also, since it contains a large amount of resin, it is inferior in blackening resistance. In the case of Japanese Patent Application Laid-Open No. 4-179881, the chromium elution rate is low with alkali washing at a liquid temperature of 60 ° C. for 2 minutes, but the chromium hardly soluble in boiling water is still insufficient. On the other hand, in the case of JP-A-7-118872, although the chromate film is hardly soluble in chromium, the reduction proceeds quickly in a chromate bath, and the bath changes with time, so that the performance is not stable. The service life is not enough from an industrial level.

JP-A-5-33165 having improved resistance to blackening
No. 9 and Japanese Patent Application Laid-Open No. 7-54156 also have sufficient blackening resistance, but the elution rate of chromium exceeds 10% even at the best, which is insufficient. JP-A-4-358080 and JP-A-4-107274 also have a problem in that chromium is hardly soluble. That is, in the prior art, while securing corrosion resistance, chromium hardly soluble in accordance with the recently required level, industrially sufficient bath stability,
None of them satisfy the blackening resistance under high temperature and high humidity conditions.

An object of the present invention is to widely apply to applications such as home appliances, building materials, and automobiles, and has excellent corrosion resistance and blackening resistance, and extremely little or no elution of hexavalent chromium, which is an environmentally hazardous substance. An object of the present invention is to provide a chromate-treated galvanized steel material and a chromate-treated composition having industrially sufficient bath stability for the galvanized steel material. More specifically, a chromate-treated galvanized steel material having a chromium elution rate of 10% or less when immersed in boiling water for 30 minutes, and a chromate treatment in which the film performance does not change even when the bath is aged at a bath temperature of 40 ° C. for 3 days or more. It is to provide a composition.

[0009]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems. As a result, regarding the elution suppression of hexavalent chromium, first, by using a partially reduced chromic acid having a chromium reduction rate of 60% or more,
With regard to bath stability, a target that could be solved by adding a phosphate compound and a nitrate compound to the bath in a specific ratio according to the reduction rate and the amount of chromic acid was obtained. In addition, among the above, it was also found that a nitric acid compound has an effect of improving corrosion resistance. It has been found that blackening resistance can be solved by adding a specific ratio of Ni ions and / or Co ions to the amount of nitrate compound in the bath.

The present invention comprises the following (1) to (6). (1) Partially reduced chromic acid, a phosphoric acid compound, and a nitric acid compound are essential components, and the chromium reduction rate of partially reduced chromic acid (X), the total chromium concentration in the bath of partially reduced chromic acid (in terms of CrO ₃ , g / l), concentration of phosphate compound in bath (H ₃ PO ₄ equivalent, g /
l), the concentration of nitric acid in the bath (HNO ₃ equivalent, g / l)
A chromate treatment composition for galvanized steel, characterized by having the following formulas (I) to (IV). 60% ≦ X ≦ 100% (I) 0.1 ≦ HNO ₃ / CrO ₃ ≦ 1.0 (II) When Y = (HNO ₃ / CrO ₃ ) + (H ₃ PO ₄ / CrO ₃ ) Y ≦ 0.0002 X ² − 0.02 X + 3.1 (III) Y ≧ 0.0005 X ² −0.05 X + 2.6 (IV) (2) The bath further contains Ni ions and / or Co ions, and the concentration (in terms of metal Ni and Co) is expressed by the following formula (V The chromate treatment composition for galvanized steel according to the above (1), characterized by satisfying (1). 0.1 ≦ (Ni + Co) / CrO ₃ ≦ 0.4 (V) (3) One or two kinds of inorganic dispersion, water-soluble or water-dispersible resin, water-soluble or water-dispersible lubricant in the bath. The chromate treatment composition for galvanized steel according to the above (2), which contains the above. (4) Cr, P, and N are contained as essential components on the surface of a zinc-based plated steel material, and the amount of Cr attached (Cr, mg / m ² ), the amount of P attached (P, mg / m ² ), N The following formula (VI)-between the adhesion amount (N, mg / m ² ) and the chromium reduction rate (D,%) before and after immersion in boiling water
A chromate-treated galvanized steel material having excellent chromium insolubility and corrosion resistance, characterized in that the chromate film having the relationship of (VIII) has a Cr adhesion amount of 5 to 300 mg / m ² . 0.04 ≦ (N / Cr) ≦ 0.43 (VI) 0.8 ≦ (P / Cr) + (N / Cr) ≦ 1.74 (VII) D ≦ 10 (VIII) (5) Further Ni and / or Co in the chromate film The chromium hardly soluble according to the above (4), wherein the chromium content thereof (Ni, Co mg / m ² ) satisfies the following formula (IX):
Chromate treated galvanized steel with excellent corrosion resistance. 0.2 ≦ (Ni + Co) /Cr≦0.8 (IX) (6) One or more of colloidal silica, a water-soluble or water-dispersible resin, and a water-soluble or water-dispersible lubricant are further added to the chromate film. The chromate-treated galvanized steel material having excellent chromium insolubility and corrosion resistance according to claim 5, which is contained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. First,
The above (1) defines the bath composition of the chromate treatment composition of the present invention. The formula (I) defines the range of the chromium reduction rate of the partially reduced chromic acid, which is an essential component. If the chromium reduction rate is less than 60%, the chromium elution rate is too high. Equation (II) defines the ratio of nitric acid compound to partially reduced chromic acid in the bath. If this ratio is less than 0.1, the corrosion resistance is insufficient, and the blackening resistance due to the composite with Ni and Co is also insufficient. If it exceeds 1.0, the bath stability will rapidly deteriorate. Formulas (III) and (IV) define the range of the chromium reduction ratio X and the sum of the ratios of the nitrate compound and the phosphate compound in the bath to the partially reduced chromic acid, and are hardly soluble in chromium.
It defines the bath composition range in which bath stability and corrosion resistance are all good. If the formula (III) is not satisfied, the bath stability of the composition is good but the corrosion resistance of the chromate-treated steel sheet is poor. If the formula (IV) is not satisfied, on the contrary, the corrosion resistance is good but the bath stability is insufficient. FIG. 1 illustrates the relationship between the expressions (I) to (IV). The bath composition of the present invention is within the range shown by the thick line in FIG.

The above (2) is necessary for suppressing blackening when the galvanized steel sheet subjected to the chromate treatment is easily plated with black, for example, hot-dip galvanized steel sheet to which Sb is added to form spangles. Na, Co and / or Ni
Is defined. If the ratio is less than 0.1, the effect of suppressing blackening is insufficient.
Corrosion resistance and secondary adhesion of paint deteriorate. Co and Ni can be added in the form of nitrates, carbonates, sulfates, etc., but when added as nitrates, of all the nitrates in the bath, those added as Co nitrate and / or Ni nitrate are used. After subtraction, the above formulas (II), (III) and (IV) must be applied.

The above (3) specifies an additive in a bath that can further enhance the performance of a chromate-treated steel sheet. Examples of the inorganic dispersion include silica, alumina, titania, and inorganic sols such as zirconia.
Addition of silica is effective in improving corrosion resistance.

The water-soluble or water-dispersible resin is not particularly limited, but an acrylic resin, a urethane resin, an epoxy resin, a polyester resin, a phenol resin, a melamine resin or the like, or a mixture or copolymer thereof can be used. With respect to the water-dispersible resin, it is necessary to appropriately select an emulsifier, a protective colloid, and the like in order to stably disperse in a chromic acid aqueous solution. When using a water-dispersible resin,
The particle size may be small as compared with the desired film thickness and large enough not to easily aggregate in a bath, but is usually 50 to 30.
It is about 0 nm.

Examples of the water-soluble or water-dispersible lubricant include organic lubricants such as polyethylene wax, polyolefin wax, paraffin wax, micro wax,
Fluorocarbons, montan wax, carnauba wax, stearic acid and compounds thereof, or inorganic lubricants such as graphite, MoS, BN and the like can be used, but preferably polyethylene wax, polyolefin wax, paraffin wax, microwax, fluorocarbon And organic lubricants.
Usually, a lubricant having a particle size of about 0.05 to 6 microns is suitable. In order to stably disperse the lubricant in the chromic acid aqueous solution, it is effective to coat the particle surface with a surfactant or a protective colloid, and in particular, a nonionic or anionic surfactant or a protective colloid is effective. . Examples include polyalkylene glycol-based activators, alkylphenol-based activators, alkylbenzene sulfonates, cellulose, polyethylene glycol, polyvinyl alcohol, fatty acid soaps, sulfonic acid-based activators, and phosphoric acid-based activators.

The above (4) to (6) correspond to the above (1) to
This defines the film structure and film performance of the chromate-treated galvanized steel sheet manufactured by the method (3). Cr
Adhesion amount is insufficient in corrosion resistance is less than 5mg / m ^2, 300mg /
Saturation occurs above m ² . First, (4) will be described. The formula (VI) defines the composition range of the chromate film produced in the bath composition range of the formula (II). The value of N / Cr is determined by surface analysis of the film, and is accurately determined by depth analysis by Auger electron spectroscopy. The formula (VII) defines the composition range of the chromate film produced in the bath composition range of the above formulas (I) to (IV). Here, N / Cr and P / Cr are determined by a surface analysis method, for example, the above-mentioned Auger electron spectroscopy (depth analysis).

The formula (VIII) defines the range of the chromium elution rate of the chromate film produced in the bath composition range of the above formulas (I) to (IV). The method for measuring the chromium adhesion amount and the chromium elution rate will be described below. First, the amount of Cr attached to the test material was measured by analyzing a test material punched out to a diameter of 50 mm with a fluorescent X-ray analyzer (RIX2000, manufactured by Rigaku Corporation). The target of the X-ray tube was Rh, and the application conditions were 50 kV and 50 mA. The calibration curve for quantitative analysis is as follows: After measuring the strength of Cr with a galvanized steel sheet sample of 10 levels in which the amount of deposited Cr was changed, the chromate film was dissolved in a 5% HCl aqueous solution, and the chromate film was dissolved in the aqueous solution. By analyzing the Cr concentration of

The Cr reduction rate (D,%) was determined by the following procedure. Samples of 50 mm in diameter were punched out from the test material by n = 5 each, and the amount of Cr attached was measured by the X-ray fluorescence method. Then, the samples were immersed in boiling water, taking care not to overlap the samples. Remove after 30 minutes. After thoroughly washing the surface with water and wiping off the water sufficiently, use fluorescent X-ray again.
The amount of Cr adhering was measured, and the difference from the amount adhering before the test was defined as the amount of Cr eluted. D = (Cr reduction rate) = (Cr elution amount / initial Cr adhesion amount) × 100 (%). When the elution amount of Cr is extremely small and there is only a measurement error of the fluorescent X-ray, D <0 may be satisfied. In this case, the average value of n = 5 sheets is directly calculated, and the average value itself is calculated. When it became a negative value, it was treated as D = 0. FIG. 2 illustrates the relationship between the expressions (VI) to (VIII). The chromate-treated steel sheet of the present invention has a composition and performance within the range shown by the thick line in FIG.

Next, (5) defines the coating composition of the chromate-treated steel sheet having excellent resistance to blackening produced by the method of (2). The above (6) is a chromate treated steel sheet having a higher performance and manufactured by the method of the above (4).

Next, raw materials and materials usable in the present invention will be described. As partially reduced chromic acid, chromic anhydride,
Potassium (bi) chromate, sodium (bi) chromate,
Chromic acid such as ammonium (bi) chromate, barium chromate, strontium chromate, etc., chromate, bichromate can be used as a starting material, and chromic acid partially reduced with starch, alcohol, hydrogen peroxide, etc. can be used. . As the phosphate compound in the present invention, orthophosphoric acid,
Nitric acid is preferred as the polyphosphoric acid and nitric acid compound.

The chromate treatment composition of the present invention can be obtained only by mixing essential components and additives at a predetermined ratio. The order of mixing is not particularly specified, but in order to obtain a composition stably on a large scale, partially reduced chromic acid, a phosphate compound, and a nitrate compound are mixed in advance and stored, and when necessary, It may be mixed with an inorganic dispersion, a water-soluble or water-dispersible resin, a water-soluble or water-dispersible lubricant.

The method of chromate treatment on the metal surface is not particularly limited, and ordinary methods such as application by a roll coater, spray application + ringer roll squeezing, spray application + air knife squeezing, application by a bar coater, and brush application can be used. It is. As for the drying after the application, a usual method such as hot air drying, drying in an open fire furnace, drying by induction heating, etc. can be applied.

Examples of the metal to which the present invention can be applied include various types of galvanized steel sheets prepared by methods such as electroplating, hot-dip plating, vapor deposition plating, electroless plating, and hot-dip electrolytic plating. For example, galvanized steel sheets, alloy-plated steel sheets of one or more metals such as zinc and nickel, iron, aluminum, chromium, titanium, magnesium, manganese, cobalt, tin, lead, and the like. Plated steel sheet containing metal and / or inorganic substance such as silica, alumina, titania, zirconia, and / or organic compound intentionally, or containing as an impurity, and further, has a multi-layer of two or more types of plating described above. There are plated steel sheets and the like.

[0024]

The present invention will now be described by way of non-limiting examples. Example 1 (1) Tested metal plates The following two types of galvanized steel plates were used. GI (hot-dip galvanized steel sheet): A steel sheet with a thickness of 0.8 mm and hot-dip galvanized at 60 g / m ² per side EG (Electro-galvanized steel sheet): A mild steel sheet with a thickness of 0.8 mm and 20 g / side the m ² of zinc plating was electrodeposited steel plate (2) that of the bath symbol A~Z shown in chromate treatment composition Table 1 were prepared using a bath concentration and additives shown in Table 2. "Silica" as an additive
Is described as colloidal silica in the solid content ratio
For those described as "silica, resin", 50% of an acrylic resin emulsion was added at a solid content ratio and 20% of colloidal silica was added at a solid content ratio. (3) Chromate treatment Apply the treatment solution shown in Table 2 to one side of the test plate using a roll coater.
It was dried in a hot air drying oven to reach a plate temperature of 90 ° C. The amount of Cr attached to the dried film was measured by X-ray fluorescence.

(4) Performance Evaluation Test (4-1) Bath Stability The treatment solutions in Table 2 were kept at 40 ° C., and the number of days until abnormalities such as gelation and sedimentation were recorded. ◎ 7 days or more ○ 5 days or more and less than 7 days △ 3 days or more and less than 5 days × less than 3 days (4-2) Measurement of Cr reduction rate (D,%) Fluorescent X-ray After immersion in boiling water for 30 minutes, the residual Cr content was again measured by X-ray fluorescence, and the Cr reduction rate (elution rate) due to boiling water immersion was determined by the following equation. Cr reduction rate (D,%) = 100 × (Cr elution amount by immersion in boiling water) / (initial Cr adhesion amount) (4-3) Flat plate corrosion resistance After the end face and the back face of the sample were tape-sealed, a salt spray test was performed. The following ranking was made according to the time until the occurrence of white rust. ◎: 240 hours or more until white rust occurs ○: 168 hours or more and less than 240 hours until white rust occurs Δ: 120 hours or more and less than 168 hours until white rust occurs ×: less than 120 hours until white rust occurs (4-4) Processing Corrosion resistance After sealing the end and back of the sample with tape, the center of the sample is extruded from the back by Erichsen to a height of 6 m.
m, and a salt spray test was performed to evaluate the rusting state in the processed portion after 120 hours. ：: No white rust occurred ○: White rust occurrence rate 5% or less △: White rust occurrence rate 5% or more, 10% or less ×: White rust occurrence rate 10% or more (4-5) Coating durability Melamine was used for the test material. Apply alkyd paint 25μm, 130 ℃
And then immersed in boiling water for 30 minutes. This is subjected to a so-called Erichsen extrusion process to a height of 6 mm by pressing a steel hemispherical protrusion with a diameter of 15 mm from the back surface, and the coated film of the processed portion is peeled off with Cellotape (registered trademark), and the peeling area ratio is examined. Was. ◎: No peeling of coating film ○: Peeling rate of coating film <5% △: 5% ≦ Peeling rate of coating film <20% ×: 20% ≦ Peeling rate of coating film

The results are shown in Table 2. The chromate-treated composition of the present invention has a stable bath if the composition satisfies the above-mentioned (I) to (IV), and the resulting chromate-treated galvanized steel sheet has the formulas (VI) to (VI). It can be seen that the film composition and the chromium dissolution rate satisfy VIII).

Example 2 (1) Tested metal sheet GI (Sb): (Hot-dip galvanized steel sheet): Mild steel sheet having a thickness of 0.8 mm and hot-dip galvanization of 60 g / m ² per side. Those containing a trace amount of antimony in plating. (2) Chromate treatment composition Bath symbols J, C, Q, E, and Y shown in Table 1 were prepared using the bath concentrations and additives shown in Table 3. Those described as “silica” as an additive are those in which colloidal silica is added at a solid content ratio of 20%, and those described as “silica, resin” are acrylic resin emulsions at a solid content ratio of 50%,
Colloidal silica was added at a solid content of 20%. Co,
With respect to Ni, cobalt carbonate and nickel nitrate were used.
Up to 2, cobalt carbonate alone, and up to numbers 43 to 50,
Both were added so as to be 1: 1 in terms of metal Ni and Co. In addition, in the numbers 31 to 39 to which nickel nitrate was added,
The HNO ₃ / CrO ₃ ratio in the bath was calculated by subtracting nitric acid from nickel nitrate. (3) Chromate treatment Apply the treatment solution shown in Table 3 to one side of the test plate using a roll coater.
It was dried in a hot air drying oven to reach a plate temperature of 90 ° C. The amount of Cr attached to the dried film was measured by X-ray fluorescence.

(4) Performance Evaluation Test (4-1) Bath Stability Evaluation was performed in the same manner as in Example 1. (4-2) Measurement of Cr Reduction Rate (D,%) Evaluation was performed in the same manner as in Example 1. (4-3) Blackening Resistance The lightness (L value) of the sample was measured, and after tape-sealing the back surface, the sample was placed in a high-temperature and high-humidity tester at 70 ° C. and 85% rh.
It was left for a week, taken out, and measured for lightness (L value) again.
When the change in brightness was ΔL, the following ranking was performed. △: ΔL <2 ○: 2 ≦ ΔL <3 Δ: 3 ≦ ΔL <5 ×: 5 ≦ ΔL (4-4) Flat Plate Corrosion Resistance Evaluation was made in the same manner as in Example 1. (4-5) Coating durability Evaluation was made in the same manner as in Example 1.

The results are shown in Table 3. The chromate treatment composition of the present invention can be prepared by using a composition having a bath composition satisfying the above-mentioned formula (V), even if it is applied to an antimony-added hot-dip galvanized steel sheet in which blackening easily occurs (IX). It can be seen that the coating composition satisfies the formula (1) and excellent blackening resistance, corrosion resistance, and coating durability.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

Industrial Applicability According to the present invention, hexavalent chromium, which is widely applicable to home appliances, building materials, automobiles, and the like, has excellent corrosion resistance and blackening resistance, and has very little or no elution of environmentally hazardous substances. And a chromate-treated composition having industrially sufficient bath stability for the zinc-based plated steel material. Therefore, it can be said that the invention is extremely valuable industrially.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 19, 2000 (2005.1.
9)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Added

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a chromium reduction ratio and a bath composition of a chromate treatment composition.

FIG. 2 is a graph showing a relationship between a chromate film composition and a chromium bath rate.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Satoshi Hayakawa 62-1, Kochino, Tachibanacho, Anan-shi, Tokushima Prefecture Nippon Denko Corporation (72) Inventor Seiji Fujimori 62-1, Konochi, Tachibanacho, Anan-shi, Tokushima Pref. F term (reference) 4K026 AA02 AA07 AA12 AA13 AA22 BA06 BB04 BB06 BB08 BB10 CA16 CA18 CA19 CA20 CA23 CA32 CA39 CA41 DA15 DA16

Claims (6)

[Claims] Claims 1. A partially reduced chromic acid, a phosphoric acid compound, and a nitric acid compound are essential components, and a chromium reduction ratio (X) of the partially reduced chromic acid, a total chromium concentration in a bath of the partially reduced chromic acid (in terms of CrO ₃ , g / l), the concentration of the phosphate compound in the bath (H ₃ PO ₄ equivalent, g / l), and the concentration of the nitrate compound in the bath (HNO ₃ equivalent, g / l). A chromate treatment composition for galvanized steel, characterized by having the relationship of (IV). 60% ≦ X ≦ 100% (I) 0.1 ≦ HNO ₃ / CrO ₃ ≦ 1.0 (II) When Y = (HNO ₃ / CrO ₃ ) + (H ₃ PO ₄ / CrO ₃ ) Y ≦ 0.0002 X ² − 0.02 X + 3.1 (III) Y ≧ 0.0005 X 2 - 0.05 X + 2.6 (IV) 2. The method further comprises adding Ni ions and / or Co in the bath.
The chromate treatment composition for galvanized steel according to claim 1, wherein the composition contains ions and the concentration (in terms of metal Ni, Co) satisfies the following formula (V). 0.1 ≤ (Ni + Co) / CrO ₃ ≤ 0.4 (V) 3. The bath further comprises one of an inorganic dispersion, a water-soluble or water-dispersible resin, and a water-soluble or water-dispersible lubricant.
3. The composition according to claim 2, wherein the composition contains at least two species.
A chromate treatment composition for a galvanized steel material according to the above. 4. The method according to claim 1, wherein the surface of the galvanized steel material is Cr, P, N
As an essential component, and the amount of Cr attached (Cr, mg /
(VI) between m ² ), P adhesion (P, mg / m ² ), N adhesion (N, mg / m ² ), and chromium reduction rate (D,%) before and after immersion in boiling water. ~ (VIII) chromate film
And having 5 to 300 mg / m ² as Cr deposition amount, chromium sparingly soluble, excellent chromated galvanized steel in corrosion resistance. 0.04 ≤ (N / Cr) ≤ 0.43 (VI) 0.8 ≤ (P / Cr) + (N / Cr) ≤ 1.74 (VII) D ≤ 10 (VIII) 5. The chromate film further contains Ni and / or Co, and the adhesion amount (Ni, Co mg / m ² ) of the following formula (I
The chromate-treated galvanized steel material having excellent chromium insolubility and corrosion resistance according to claim 4, which satisfies X). 0.2 ≤ (Ni + Co) / Cr ≤ 0.8 (IX) 6. The chromate film according to claim 5, further comprising one or more of colloidal silica, a water-soluble or water-dispersible resin, and a water-soluble or water-dispersible lubricant. Chromate-treated galvanized steel with excellent chromium insolubility and corrosion resistance.