JPS6210292A - Manufacture of colored galvanized steel sheet - Google Patents

Abstract

PURPOSE:To manufacture a colored galvanized steel sheet of superior quality by electrolyzing a galvanized steel sheet as a cathode under proper conditions in an aqueous soln. contg. specified amounts of Zn, Ni, Fe, V, Mo and Cr ions and by coating the resulting colored film with a protective film. CONSTITUTION:A galvanized steel sheet is electrolyzed as a cathode with 20-200C/dm<2> electricity in an aqueous soln. prepd. by adding 0.01-0.5mol/l ions of one or more among V, Mo and Cr to an aqueous soln. contg. 0.1-1mol/l Zn ions 0.1-1mol/l NI ions and 0.01-0.2mol/l Fe ions. A colored film having satisfactory adhesion is formed on the surface of the galvanized steel sheet in a short time with the least dissolution of zinc. The colored film is then coated with an inorg. or org. protective film. A colored galvanized steel sheet having fine ornamental appearance is obtd. at a low cost with high productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention generally relates to a method for manufacturing colored galvanized steel sheets for use in members requiring decoration in fields where galvanized steel sheets are used.

(Prior Art) Surface-treated steel sheets are used in a wide range of fields because of their general-purpose quality and low cost, and it is certain that their demand will continue to increase due to quality improvements.

Improvements in the quality of galvanized steel sheets have led to the creation of many new products in terms of appearance, rust prevention, processability, and paintability, as well as the high quality of the base material, meeting the demands of automotive steel sheets, home appliances, and building materials. It's here.

In recent years, customer demands have led to the introduction of surface-treated steel sheets that aim to improve product quality, minimize total costs, and simplify treatment processes. In other words, by introducing a pre-coated steel sheet to products that have conventionally been pre-treated and painted after processing a surface-treated steel sheet, the pre-treatment and painting that were performed in the customer process can be omitted, resulting in a low-cost product. One of them is pre-painted steel sheet to obtain high quality products.

Initially, 2 was developed as a pre-painted steel sheet that could meet these demands.
High-grade pre-coated steel sheets of 0 to 30μ have been used,
In pursuit of thorough cost reduction and from the viewpoint of weldability,
There is a demand for colored surface-treated steel sheets. In addition to corrosion resistance and workability, it is important for materials to have uniformity in appearance to meet these demands, and weldability and chemical resistance are also required as necessary. Black-ish colors are preferred.

A known technique for coloring galvanized steel sheets is the method of JP-A-52-45544 (Private) for treating galvanizing in a chromate solution containing silver ions, based on phosphoric acid and silver phosphate. There is a method disclosed in JP-A-5-B-177477 (Kyoto Chromate Industries) which involves treatment in a chromate solution. These methods eutectoid silver oxide on a chromate film to obtain a black appearance. In addition, as a method for blackening treatment by forming sulfides, Japanese Patent Application Laid-Open No. 52-65139
(Foreign) method has been published. In addition, as a method of coloring a chromate film using a dye after forming it, Japanese Patent Application Laid-Open No. 54
-145336 (Mitsui Mining and Mining) Special Publication Showa 52-2873
0 (Mitsui Metal Mining Co., Ltd.) method has been published. All of these methods involve a direct chemical reaction between a solution and galvanizing to obtain a colored surface. In addition, a method of obtaining a black surface by an anodic oxidation method has been disclosed. For example, Ni, Co
, a method disclosed in JP-A-58-151491 for anodizing a Mo and Zn alloy plated steel sheet in an aqueous ammonium sulfate solution;
Typical published techniques include the method disclosed in JP-A-58-151490, which involves anodizing in an alloy plating bath of N1, Co, Mo, and Zn.

(Problems to be Solved by the Invention) Conventional coloring methods are excellent methods, but unfortunately they do not necessarily match the manufacturing equipment owned by steel manufacturers. For example, in terms of high-speed productivity, it is necessary to shorten the processing time. In addition, in the case of blackening treatment of zinc plating using conventional methods, the black film immediately after treatment is gel-like and has poor adhesion, which is a major hindrance to coil production and requires hardening treatment, which makes the process difficult. It's getting complicated.

In any case, we have never experienced a method of uniformly coloring a wide coil product using a method other than painting. The present invention provides a method for obtaining uniform black galvanized steel sheets at high speed and in a short time under current process conditions.

(Means for solving the problem) As mentioned above, one of the problems with coloring galvanized steel sheets is the formation of gel-like substances immediately after blackening treatment and poor adhesion due to corrosion of the underlying zinc. .

Various solutions can be considered to solve this problem, but basically it is effective to suppress the dissolution of the underlying zinc and form an unhydrated, compact film, such as a continuous film such as plating.

That is, the present invention has succeeded in obtaining a colored film with good adhesion on the surface of a galvanized steel sheet in a short period of time in a state where the length of the zinc plating is short enough to allow dissolution of the zinc plating.

The present invention is comprised of the following components. In other words, zinc ion 0.1-1 mol/l, nickel ion 0.1-1 mol/l
1 d using a galvanized steel plate as a cathode in an aqueous solution containing 0.01 to 0.2 mol/l of iron ions and 0.01 to 0.5 mol of vanadium ions, molybdenum ions, or chromium ions. -To 920
The problem was solved by a method for manufacturing a colored galvanized steel sheet, which is characterized in that it is electrolytically treated at ~200 coulombs and then coated with a protective film.

The present invention will be described below.

The electrolytic bath used in the present invention can be colored by cathodic electrolytic treatment in an aqueous solution containing metal ions as described above. The precipitated colored film is composed of a composite film of an alloy mainly composed of zinc and nickel, and a metal oxide.

In the present invention, it is necessary to eutectoid a colored oxide, particularly a black oxide, into a composite. Therefore, special conditions must be provided to the plating bath and electrolytic conditions for oxide precipitation at the cathode.

In a zinc-only bath, it is difficult to eutectoid oxides and it is difficult to obtain the desired colored film in a short time. Due to the presence of nickel ions and iron ions, oxides co-deposit with metal precipitation. A composite plating of Zn-Ni-Oxides containing zinc plating as the main component is best because hydrogen is generated in a single Ni bath and the potential difference with the underlying zinc plating is large. The oxide of the composite must not be reduced to the metal.

Therefore, a compound that is a transition element and has a high valence is selected, and is precipitated as a low valence oxide in the reduction process. With the exception of T1 ion, which does not reduce to metal in an aqueous solution, both 2.3 and 4 valence can be applied. Composite plating has the disadvantage that a thick film cannot provide sufficient processing adhesion, so a thin film is required.

The present invention will now be explained in detail with respect to the treatment bath, electrolytic conditions, and protective coating.

One of the electrolytic baths used in the present invention contains 0.1 to 1 mol/l of zinc ions, 0.1 to 1 mol/l of nickel ions, and 0.01 to 0.2 mol/l of iron ions, preferably nickel. When the molar concentration ratio of ions and zinc ions (N1/Zn ratio) is set to 0.2 to 2.0, blackening tends to occur. This is an aqueous solution in which 0.01 to 0.5 mol/l of metal ions (described below as colored metal ions) described below are added to a treatment bath containing these ions. The pH of the bath varies depending on the degree of coloring and electrolytic conditions.
In order to obtain a black appearance, a value of 1 to 4 is desirable.

The reasons for determining these conditions are as follows.

If the concentration of zinc ions and nickel ions is less than 0.1 mol/mol, precipitation will be insufficient and a colored appearance will not be obtained.

If it exceeds 1.0 mol/l, zinc and nickel will preferentially precipitate, making it difficult for oxides to co-deposit, making it impossible to obtain a sufficient colored appearance.

When obtaining a black appearance, if the Ni/Zn ratio is less than 0.2, the nickel eutectoid rate is low, and the amount of oxide induced to eutectoid due to nickel precipitation is low, resulting in a low degree of blackness. N1/Z
If the n ratio exceeds 2.0, hydrogen gas is generated due to a decrease in hydrogen overvoltage, resulting in unevenness and insufficient coloring.

In addition, iron ions have the effect of promoting the precipitation of oxides,
Add in a range of 0.01 to 0.2 mol/l. If the amount is less than 0.01 mol/mol, the effect is weak and coloring is difficult. 0.2 mol/
If it exceeds l, the negative effects of iron will occur. That is, problems such as uneven appearance, pale color tone, and formation of precipitates in the bath occur.

The colored metal ions (some abbreviated as Men+) are polyvalent metal ions such as vanadium ions, molybdenum ions, or chromium ions. Vanadium ion is 2.
3.4.5 valence ions Molybdenum ions are 2.3.4 valence ions, and chromium ions are 3.6 valence ions.

These metal ions are difficult to precipitate in a single bath, and are induced by precipitation of zinc, nickel, and iron.

Therefore, the concentration of these metal ions is determined from the viewpoint of the degree of coloring and the mixing ratio of zinc, nickel and iron plating as a vehicle, particularly from the viewpoint of processing adhesion and adhesion immediately after cathodic electrolytic treatment. The concentration is Q, 001-0.5 mol/l. Preferably, the ratio of colored metal ion concentration to the total concentration of vehicle metal ions (Me”/(Zn”+Ni”+
When Fe"+F e" ) is 0.025 to 0.25, good appearance and quality can be easily obtained. The lower limit of the concentration of each coloring metal ion is insufficient coloring due to insufficient eutectoid, and the upper limit is oxide that does not precipitate and tends to have a metallic glossy appearance, and even if a black appearance is obtained, powdering may occur. This is because powder-like flaking called . In terms of powdering (Me”/(Zn”+Fe2++Fe”10F, e
"j)) The ratio is preferably 0025 to 0.25.

When the pH of the bath is low, the blackness is low, and when the pH is high, the blackness is high. If it is less than 1, it tends to peel off immediately after cathodic electrolytic treatment due to etching of the zinc surface, so the electrolytic conditions should be adjusted. More than 4 will cause precipitation, but these can be overcome by adding complexing agents such as citric acid, gDTA, tartaric acid, etc. However, since the vehicle metal is difficult to precipitate, it is preferable to carry out the reaction at pH'1 to 4. Further, in order to lower the electrolytic voltage, a bath to which a conductive additive is added is also within the scope of the present invention.

By adding all the brighteners to the treatment bath of the present invention, a smooth colored galvanized steel sheet with a high degree of blackness can be obtained.

Examples of brighteners include water-soluble cationic and nonionic polymer compounds such as amines having secondary to tertiary amines in their side chains, polymers and their copolymers, polyacrylamide, dextrin, and the like. The amount added varies depending on the compound and is 0.
It is in the range of 01 to 1 l/l. Polyacrylamide is effective in brightening at low concentrations. In the case of polyamine sulfone compounds, amine polymers are highly effective in brightening and blackening over a wide range of areas.

In addition, starches and sugars such as dextrin have a greater glossing effect at higher concentrations. These additives smooth the deposited composite plating and give it a transparent color tone. Furthermore, it provides a film with uniform deposition and fewer pinholes on the irregularities of the plating base. Amine polymers are particularly effective in blackening treatment.

The electrolysis conditions will be described. As described above, the present invention requires conditions for eutectoiding the vehicle metal and the oxide, and it is necessary to set the coulomb amount as the electrolytic conditions. The present invention uses cathodic electrolysis in the range of 20 to 200 coulombs per ldi. Outside this range, it is difficult to obtain blackish coloring.

The current density is preferably 5 to 50 A)/dff11, but it varies depending on the electrometx cell conditions. The bath temperature may be within the range of 20 to 60°C under normal electrolytic conditions.

The protective film will be explained in detail below.

By further coating a protective film on the colored film formed by cathodic electrolytic treatment, it provides a more excellent appearance as well as corrosion resistance, workability, and scratch resistance.

These coatings can be classified into three types: inorganic, organic, and organic thermal MA.

Inorganic types include chromate film, phosphate film, silicate film, and zirconate film. These films are finished by applying an aqueous solution onto the colored surface, controlling the film thickness, and then drying or baking. Alternatively, coating is performed by electrolytic treatment in these aqueous solutions. Moreover, layered coating, in which a chromate film is treated and then an organic film is applied, is the most excellent method for improving quality. In these cases, inorganic coatings are preferable as the lower layer coating.

As organic systems, chelate compounds, tannic acid, phytic acid compounds, water-soluble polymers, or water-dispersible emulsions are applied together with a hardening agent onto a colored plated steel plate, the film thickness is controlled, and the coating is finished by drying or baking. Alternatively, it is coated by electrolytic treatment. Organic/inorganic systems are created by adding inorganic polymers (e.g. silica, silica, alumina, zirconia), etc., or chromate, condensed phosphoric acid, zirconic acid, silane compounds to water-soluble or water-dispersed organic polymer compounds. The resulting aqueous solution or emulsion is applied onto a colored plated steel plate, the film thickness is controlled, and the coating is then dried, baked, or electrolytically treated.

By coating these protective films on the black plating, the above-mentioned properties are added, and a more practical pre-coated steel sheet can be obtained. Wax finishing and the like can also be used from the viewpoint of improving appearance and processability. The film thickness is preferably 3μ or less for organic and organic-inorganic systems, and 1μ for inorganic systems.
The following is desirable.

One application method is roll coating or a conventional method of controlling the film thickness using a squeeze roll or an air knife after application. The baking temperature is preferably a board temperature of 60 to 150°C.

The second method is to apply the coating by electrolytic treatment, wash it with water or squeeze it with a roll, or squeeze it with an air knife if necessary, and then dry it.

(Example) The present invention will be described in detail below with reference to Examples.

Example 1 Zinc sulfate (ZnSO4-7H20) 100 liters (0,3
4 mol), nickel sulfate (NiSO4.6H20) 1
00 y (o, 35 mol) ferrous sulfate (Fe50.
7H20) 50f (0.17 mol) was dissolved in water. (1 in Ni/Zn). Furthermore, Panaji sulfate/l/ (
VO30, 6H20), ammonium metavanadate (NH4VO3) 101 (o, o 6 mo#, 0.0
Electrolytic treatment was carried out in a treatment bath (pH=3.0) to which 8 mol) was added separately, using an electrogalvanized steel plate (fabric weight 20 y/rr?) as a cathode. Bath temperature 50℃, current density 20A
/dTr? , 50 coulombs/d.

Electrolytic chromic acid treatment as a protective film (30% as total chromium)
η/-) After applying 1μ of a composite bath of acrylic emulsion and silica, the plate was baked for a short time with hot air at a temperature of 120°C. The quality of the obtained colored plated steel sheet is that it has a black glossy appearance with an L value (value representing brightness) of 12 to 13, and a salt spray test (hereinafter referred to as S).
S, T, and abbreviations: 1 in JISZ 2371 continuous method)
No rust was observed for 20 hours. Further, no peeling was observed even after press working to a depth of 30+13 was performed.

Also, when an aqueous solution of sodium silicate is applied as a protective coat instead of acrylic emulsion and silica, L
The value was 12 to 13, and no rust was observed at SS'r of 72 hours.

Example 2 Zinc sulfate 5 o y/l (0.17 mol/l), nickel sulfate 70 y/l (0.25 mol/l), ferrous sulfate 2
0 g,/l (0,0'i'mol/l), ammonium sulfate 5o y/! .

Ammonium molybdate 5 (0,02 mol/l), 10 (o, 04 mol/4) ta/l in an aqueous solution of
(1 in Ni/Zn) at pH = 3.5 with addition of
, 4), the electrogalvanized steel sheet was subjected to cathodic electrolysis treatment (current density 15 A/am', coulomb amount 100 coulombs/drr?).

Next, an aqueous solution of colloidal silica and chromic acid is applied, dried with hot air, and chromated (total chromium: 25~//
rr? ) After that, an ammonia aqueous solution of polyacrylic acid and zirconic acid, pH=6, was applied and baked at a board temperature of 120°C. A black appearance with an L value of 12 was obtained, and the diameter was 3 with no rust after 120 hours of 5ST! No peeling was observed when Eaφ was bent at 180°C.

Example 3 In place of ammonium molybdate in Example 2, colored metal ions shown in Table 1 were added and the same treatments and evaluations were carried out.

Table 1 Examples of the present invention Example 4 A galvanized steel sheet was subjected to cathodic treatment under the same conditions in a treatment bath in which 10 parts of polyamine sulfone polymer was added to the treatment bath of Example 1.

A protective film of 05μ of acrylic emulsion, ammonium chromate, and silica was applied onto the treated steel plate and baked at a plate temperature of 100°C. The L value was 12 to 11, and the corrosion resistance showed no white rust after 120 hours of salt water spraying.

Example 5 Aqueous solution of zinc sulfate 100 y/l (0.34 mol/l) nickel sulfate 100 y/l (0.35 mol/l) ferrous sulfate 50 f/l (0.17 mol/l) Sodium molybdate 20 y/1 (0.1 mol/
l) and then polyacrylamide lOOppm
A hot-dip galvanized steel sheet was heated in an aqueous solution of pH = 2.5 at a current density of 30 A/d m' and 150 coulombs/drr? After cathodic electrolytic treatment of
Apply 1μ of a solution consisting of an emulsion of polyethyleneimine and silica gel and a silane coupling agent, and the plate temperature is 12t1.
Baked at °C. L value is 13, black appearance, color fastness is 90'
There was no rust on the bent part for 48 hours.

Furthermore, instead of applying chromate, a commercially available phosphate treatment was applied for 1/4 hour (30 seconds) of the normal treatment (2 minute spray), and then the same application evaluation was performed. L value is 14, corrosion resistance is 90
There was only 2% rust at the bent part.

(Effects of the Invention) The present invention is a decorative steel plate made from a galvanized steel plate that is relatively inexpensive and has anti-corrosion properties.It has an appearance similar to a conventional coated steel plate, and has inorganic features such as hardness and eaveability. Quality effects such as The biggest advantage is that low-cost mass production is possible.

In order to pre-coat conventional boss coat materials, it is necessary to have characteristics that incorporate various operations in the customer process, and there are limitations with aerobic coating alone, and the present invention is one of the advances in this field. .

Claims (1)

[Claims] Zinc ion 0.1-1 mol/l, nickel ion 0.1
~1 mol/l, an aqueous solution containing 0.01-0.2 mol/l of iron ions and 0.01-0.5 mol/l of one or more of vanadium ions, molybdenum ions, and chromium ions. Inside, a galvanized steel plate is used as a cathode, 1 dm^
1. A method for producing a colored galvanized steel sheet, which comprises applying a protective film after electrolytic treatment at 20 to 200 coul per 2.