JPS6289879A - Treating solution for blackening zinc or zinc alloy and blackening method - Google Patents

Abstract

PURPOSE:To obtain a uniform film having high blackness, superior corrosion resistance and adhesion in a short time by blackening Zn (alloy) with an acidic aqueous soln. contg. specified amounts of Sb ions and ions of one or more among Ni, Fe and Co and by forming a phosphate film on the resulting black film. CONSTITUTION:Zn (alloy) is blackened with an acidic aqueous soln. of <=6 pH contg. 0.2-5g/l Sb ions (a) and 10-100g/l metallic ions (b) of one or more among Ni, Fe and Co in 5-110 molar ratio of b/a. A phosphate film is then formed on the surface of the resulting black film. The molar ratio of b/a may be regulated to 25-70 and a chromate film by 1-1,000mg/m<2> (expressed in terms of Cr), an alkali silicate film of 0.01-3mum thickness or a resin film may be formed in place of the phosphate film.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is a method of continuously and quickly treating zinc or zinc alloys, particularly zinc or zinc alloy plating strip steel sheets, to form a black film on the entire surface thereof. The present invention relates to a blackening treatment liquid used for things and a method thereof. The zinc or zinc alloy used in the present invention contains AA and Co in the galvanizing bath for the purpose of generating spangles and improving corrosion resistance.
, Cr, Ni + My.

In , ■' + P b + Sn + Mo * F
This also includes those plated with one or more metals selected from e.

[Conventional technology]

Attempts have been made to apply blackening treatment to liquid passing, zinc or zinc alloy plated strip steel sheets in a short period of time, or applying clear coating to automobile parts, troublesome parts, refrigerated NtjA products, etc. .

As a blackening treatment method, the black chromate method was published in JP-A-58
Although disclosed in Japanese Patent No. 193376, this method is undesirable because it uses a silver salt in the processing solution, which is expensive and also makes short-term processing impossible. Matamachi Kosho 45-2769
No. 0 describes a method for producing a black matte plate on the surface of a metal object. This method involves contacting the surface of the gold 4 target with an acidic aqueous solution of a trivalent antimony salt to form a black antimony deposit. The first stage treatment consists of a first stage process of depositing a phosphate protective coating over the surface, and a second stage process of depositing a phosphate protective coating over the surface. Therefore, it is not possible to obtain a good black film even after the second stage treatment, making it impractical.

[Problem that the invention seeks to solve]

The present invention is an improved antimony-containing acidic aqueous solution which can be processed in a short time and is inexpensive, and which provides a blackening treatment solution for producing a highly black coating of zinc or zinc alloy and an excellent coating with no coating unevenness. The purpose is to provide a method.

[Means for solving problems]

The blackening treatment (a) for achieving the purpose of the present invention involves the addition of antimony ions (a) kO, 2 to 5.0 g/l, and metal ions (b) selected from nickel ions, iron ions, and cobalt ions. 1 type or 2m or more gold 10
~100 Vl, and +>71 metal ion (b) / An id antimony ion (a) molar ratio is 5 to 110, preferably 25 to 70, and 1) H is 6
The following is an aqueous solution.

When fluoride ions are added to this aqueous solution, a uniform black film can be formed in a shorter time.

Antimony ion ha, dark stone α antemonyl potassium, 3
It is derived from soluble salts such as antimony chloride and antimony pentachloride, and is used at a concentration of 0.2 to 5.0 g/l.

If it is less than 0.2 g/l, it is not preferable to form a black film in a short time because the opaque content is too thick, and if it exceeds s, o s4, the adhesion of the formed black film will be poor.

The metal ions of nickel + kk + cobalt are nickel carbonate, nickel nitrate, nickel chloride, nickel d, nickel sulfate, ferrous nitrate, and ferric nitrate.

Ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, cobalt carbonate, cobalt chloride, cobalt nitrate.

It is extracted from inorganic salts such as cobalt sulfate and organic compounds such as nickel acetate, ferric ammonium, and cobalt acetate. In order to obtain a coating with a high degree of blackness, the # degree is 10 to 18 g/l as metal ions.
g/1 or more is required, and the molar ratio of the whole ion/antimony ion is 5 to 110, preferably 25 to 70.
is within the range of Considering the economic aspect, the upper limit of the metal ion concentration is 100 so/l or less, preferably 50 g/l.
It should be less than l.

Among the metal ions of nickel, iron, and cobalt, nickel ions are most preferred from the viewpoint of film reactivity.

Fluoride ions are hydrogen fluoride modified, hydrogen silicofluoride compensated,
It is derived from hydroxide, etc., and its concentration is 1 to 60.
It is used in v/l, but it changes when I L<H3~309/l. If it is less than I V1, the uniformity of the film will be poor and the weight will be less than 60 g.
If it exceeds /l, the adhesion of the black film formed will be reduced, equipment corrosion will be severe, and the working environment will be poor.

The pH of the blackening treatment liquid is adjusted using hydrochloric acid, (flowing liquid,
acid, fluorinated acid, hydrofluorosilicic acid, flIitl
An inorganic acid such as hydrogen acetate septate fR or an M-organic acid such as -cough may also be used.

In the blackening treatment liquid, the treatment liquid does not settle and handle the processed material.
In order to prevent layering of sludge, a complexing agent such as tartaric acid, citric acid, 1 g malic acid, succinic acid or its salts can be added. The addition '1 requires 0.1 to 40 g of the complexing agent, taking into consideration the effects and advantages of the addition.
/l.

The blackening treatment liquid of the present invention contains fffi! of the primitive material to be treated, antimony, nickel, iron, and cobalt! Since it uses a reaction, it is greatly influenced by processing time and liquid temperature.

The higher the solution temperature, the faster the reaction rate, so it is preferably room temperature or higher. In particular, if strip-plated plates are treated continuously, the treatment time will be less than 10 seconds, so in that case it is preferably 30°C or higher. The upper limit of liquid temperature is the evaporation of water,
In consideration of safety, energy saving, etc., the temperature is preferably 80°C or less.

The black coating formed by the blackening treatment solution of the present invention has insufficient corrosion resistance and adhesion. In order to improve this corrosion resistance and adhesion, a chromate film, a phosphate film, an alkali silicate film, or a resin film is applied after the blackening treatment and washing with water.

Applying a phosphate film after blackening treatment increases the degree of blackness. Improvement in fingerprint resistance can be achieved by applying a resin film or a film containing an alkali silicate as a main component to the surface of the film.

The resin film in the present invention is a known film formed by treatment with a water-soluble, emulsion-type or dispersion-type M machine polymer resin aqueous liquid, and is disclosed, for example, in Japanese Patent Publication No. 60-33192 +J. Examples of resins used in this film include currently used vinyl-based resins such as vinyl acetate, vinyl chloride, and vinylidene chloride, as well as their copolymers, acrylic acid, methacrylic acid, acrylic esters, methacrylic esters, and hydroxyacrylic resins. acid,
Acrylic systems and their copolymers such as hydroxyacrylic modified esters, alkyd systems, epoxy threads, urea systems, fluorine threads, urethane systems, ester threads, styrene threads, olefin systems and their copolymers, and synthetic rubber systems such as butadiene. and resins such as natural molecules are required. If necessary, inorganic substances such as chromium compounds and silica can be added to this engineered polymer solution.

Preferably, the chromate film is formed using a partially reduced chromium bath coat, such as the films disclosed in JP-A-50-28444 and JP-A-60-218483. Depending on the requirements, silica particles (silica sol, fumed silica) having a f number of 10 to several 1000 times may be included. cr3+ in chromic acid aqueous solution
/Cr6+ **The ratio is preferably 1/1 to 1/3 by reducing with a Miso arresting agent such as Sequos or alcohols or an inorganic reducing agent, and the pH of the aqueous solution is 1.5 to 4. A range of 0 is good.

If the amount of chromate film is too large, the black film will be hidden and the blackness will be weakened, and if it is too small, the effect of the chromate film will be weakened.
'm', preferably 10 to 2001 ny/.2.

Films containing alkali silicate as the main component are, for example,
There is one disclosed in Publication No. 7-2274, and the general formula M
It can be obtained by treatment with an aqueous solution containing as a main component an alkali silicate represented by 20% nsi02 (M: Na, K% Li, ammonium or amine, n: 2-20), but this can be used as needed. Furthermore, chromium compounds such as chromic acid are added to. The amount of alkali silicate film is
For the same reason as applying the chromate film, the thickness of the film is 0.01 to 3 μm.

The phosphate film is the first phosphorus rg! Lead, calcium zinc phosphate, aluminum phosphate, manganese monophosphate, i
A phosphate aqueous solution with a pH of 2.5 to 5 containing Xl phosphate powder and diammonium phosphate as the main components is used, but to form a strong film with the best adhesion, a lead phosphate aqueous solution is used. Kei is preferred. For example, the phosphate aqueous solution described in Japanese Patent Publication No. 12130/1984 is used.

In the present invention, a corrosion-resistant film is formed by the first stage black film and the second stage chromate film, phosphate film, alkali silicate film or resin film, but a third stage treatment is further added. That is, black film → coated chromate film → resin film or alkali silicate film, dotted color film → phosphate film → resin film, coating 1114 of coated chromate film or alkali silicate film on the surface of zinc or zinc alloy. By applying the coating to the surface, an even more highly erodible film can be obtained.

An example of the treatment steps of the blackening treatment method of the present invention is as follows. (Degreasing → Water washing) → 1st stage treatment → Water washing → [Surface with titanium colloid aqueous solution: A leveling] → 2nd stage treatment → Water washing → [3rd stage treatment] → Drying Do this as necessary.

It is treated under the conditions of the first stage, second stage, and third stage treatment by spraying, dipping, roll coating, etc. at room temperature to 90° C. for an arbitrary period of time.

In addition to the above, known treatment water bath agents such as tannic acid aqueous solution and phytic acid aqueous solution may be used for the second stage and .pi.3 stage treatments.

[Effect]

When a lead alloy or lead alloy is brought into contact with the blackening treatment solution of the present invention, ions of Sb%Nl s Co + Fe in the treatment solution precipitate on the surface of zinc or zinc alloy due to a substitution reaction with Zn of the material. However, during the reaction, Sb, Ni, Co
Alternatively, the precipitation and dissolution reactions of Fe proceed selectively and stepwise due to the difference in standard electrode potential of Zn. Body, Sb%N
i (or C01Fe), easily precipitates in 1 m of zn,
zn %Nl (or ico, Fe) and Sb are easily dissolved in this order. The TiL conversion reaction results in the precipitation of only Sb and the precipitation of Zn.
Rather than just dissolving, the metals Sb%Ni (or C01Fe) and Zn repeatedly precipitate and dissolve, and as a result, a film with a structure that absorbs the original material is created.

Black residence J! l! When setting the conditions of a, the whiteness of the film and W
(Lab)) The degree of blackness was determined by measuring using a color computer manufactured by Zensuga Test Instruments Co., Ltd. The whiteness is W (Lab) ~ 100-((100
-L)"+a"+b"]172, and the smaller the W value, the closer to black the color becomes.

i@50”C Ni”1 with varying Sb3+ concentration
The whiteness of the film formed by immersing a zinc-coated t209/z galvanized steel sheet in an acidic hydrochloric acid solution containing 5 g/6% s t Fe” -4!j/l for 10 seconds was
As shown in the figure.

As can be seen from this figure, in order to obtain a black film, Sb3+
A concentration of 0.29/1 or more, preferably 1.3 g/1 or more is required.

s b of board temperature 50℃ with CorA degree Mk changed
3 +1,5 Vl, siF, ”-49/1 Miya salt r: IN acidic water am, zinc adhesion ii 20 gi
Figure 2 shows the whiteness of the film formed by spraying Zeng's lead-plated steel plate for 5 seconds. As can be seen from this figure, in order to obtain a black film, it is necessary to use C02+10v1 or more, preferably 18&/1 or more. Also N1
s Fe also shows almost the same value as C02+.

Sb” 1.5M with a liquid temperature of 50°C with various changes in pif gold
Figure 3 shows the whiteness of the film formed by spraying a galvanized steel plate with a zinc coverage of 20 I//m+ for 5 seconds using an aqueous solution containing 209/ef. It can be seen that it is best to adjust the pH of the solution in the treated water to 6 or less in order to obtain the following.

s b 3 + concentration and Ni2+, C02+, Fe 3
"5iFa with a liquid temperature of 50℃ with various changes in #I!"
- Zinc adhesion at 4 g/l rich hydrochloric acid acidic water solution t 20
Ni in the treated aqueous solution on the whiteness of the film formed by treating a galvanized steel sheet of g/,' for 5 seconds with tin spray.
Figure 4 shows the relationship between the molar ratio of CO and Sb.
Figure 5 shows the relationship between the molar ratio of Fe and Sb, and Figure 6 shows the relationship between the molar ratio of Fe and Sb.
It can be seen that a metal ion/Sb3+ molar ratio of 5 to 110, preferably 25 to 70, is sufficient to obtain a black film.

[Example 1] An electrolytic galvanized steel sheet was prepared, antimonyl potassium tartrate was converted to Sb, and cobalt acetate was converted to C.

Contains 10 &/1 in terms of conversion, and has a pH of 1.5
It was immersed for 10 seconds in an acidic solution of hydrochloric acid heated to 50-60°C to form a black film, washed with water, and then heated to 55-60°C.
It was immersed for 10 seconds in an aqueous solution containing zinc phosphate as the main component (Bonderite 3300° Nippon Barcalizing Shafi) with a total acidity of 20 points heated to 5'C, and washed with water.
After drying, appearance evaluation and film adhesion test were performed, and the results are shown in Table 1.

[Example 2] Electrolytic galvanized temples were treated with antimony trichloride at an amount of 0.5 s/g in terms of Sb and 25.0 s/g in terms of ferrous sulfate fFe. Zo/
Hydrochloric acid Llambda ice water solution containing 1.3 and heated to 55 to 65 °C, immersed for 7 seconds to form a black film, washed with water, and soaked at 55 to 65 °C. Immerse for 7 seconds in an aqueous solution (Bonderite 3300° Nippon Barcalizing Co., Ltd.) containing sulfuric acid with a total acidity of 25 points for 7 seconds, then rinse with water.
．． Table 1 shows the results of immersion in a 1 so/j chromic acid aqueous solution for 3 seconds, cutting into d-cuts, drying, and performing appearance evaluation and film adhesion test.

[Example 3] - 1 t of aluminum-plated steel plate and alloying bath fusion lead-plated sokari, I, antimonyl potassium phosphate in terms of Sb, i, s
y/l, nickel chloride is 30g/l in terms of Ni,
Contains about 10% of silicon fluoride in terms of F, and... is 1.5
Dip in an acidic hydrochloric acid solution heated to 60-70°C for 5 seconds (for Tunqing lead-plated steel sheets) to 10 seconds (for alloyed hot-dip galvanized steel sheets) to form a black film, and then rinse with water. Then, an aqueous solution (Bonderite 3300° manufactured by Nippon Bar Riki Rising Co., Ltd.) containing phosphorous rfl submk for zinc with a total acidity of 15 points was heated to 60 to 70°C.
Table 1 shows the Yuatsu a fruit that was immersed for 0 seconds, washed with water, dried, and subjected to appearance evaluation and Vfi adhesion test.

[Comparative Example 1] Low-temperature zinc oxide: 1 = Steel plate containing 1 &/l of antimonyl potassium tartrate calculated as 1 sbs, and 1.5 and 5
It was immersed in an acidic solution of hydrochloric acid heated to 0 to 60°C for 10 seconds to form a black film, washed with water, and then heated to 55 to 60°C.
An aqueous solution mainly composed of zinc phosphate for zinc with a total acidity of 20 points heated to ℃ (Bonderite 3300° B2E)
(manufactured by Parriki Rising) for 10 seconds. Table 1 shows the results of appearance evaluation and adhesion test.

[Comparative Example 2] Table 1 shows the results of performing only the first stage treatment of Example 1, washing with water, drying, and performing appearance evaluation and adhesion test.

Table 1 (Blackness of film) (Uniformity of film) [Judgment method] ◎True black ◎Uniform ■Black 　　　　○Slightly uneven △ Non-uniform to gray-black (Adhesion test method) Adhere cellophane tape to the surface of the sample. When this is suddenly torn off. The degree of peeling of the black surface film was observed.

◎ No peeling 0 Less than 10% peeling @ 10 inches or more, less than 30 inches peeling △ 30% or more, less than 60% peeling x 50% or more peeling [Example 4] Add antemonyl potassium tartrate to an aqueous hydrochloric acid solution at 39/l in terms of Sb , nickel nitrate is about 30 in terms of Ni, silicon is 7
A blackening treatment solution was prepared by dissolving 5 fi/l of tutric acid in terms of F and adjusting the Ni''/Sb'+ molar ratio of the aqueous solution to 21 and - to 1.7, and heated to 50 to 55°C. It was heated to

The galvanized plate A was soaked in this treatment solution for 10 seconds to form a black film, washed with water, and then dried.

[Example 5] A galvanized copper plate was subjected to the treatment of Example 4 except for the drying process, and then the solid content concentration was 20Vl, Cr3n (r6+
The weight ratio of 2/3, pl (xi-g to 2.5 with KOH)
It was coated with a coating-type chromate treatment aqueous solution and dried after a roll bath.

[Example 6] A galvanized steel sheet was subjected to the treatment of Example 4 excluding the drying step, and then treated with an aqueous acrylic resin solution (Watersol 574).
4...Dry film (manufactured by Dainippon Ink Co., Ltd.) of 1 μm
Dry the fallen cloth so that it becomes K.

[Example 7] A galvanized steel sheet was subjected to the treatment of Example 4 except for the drying process, and then a specific lithium silicate (Li2O 4.88i) which was adjusted to a concentration of 50 g/l by SiO
n,) An aqueous solution was applied using a roll coater and dried.

[Example 8] I galvanized steel sheet except for the drying process (Process 4 of Example 4)
'C, and then immersed for 10 seconds in a phosphate film treatment aqueous solution (Bonderite 3300...manufactured by Nippon Parriki Rising Co., Ltd.) containing zinc phosphate as the main component and heated to 60 to 65°C. After that, it was washed with water and dried.

[Example 9] A galvanized steel sheet was subjected to the treatment of Example 5, and then coated with the acrylic resin aqueous solution of Example 6 and dried.

[Example 10] A galvanized steel sheet was coated with the lithium silicate aqueous solution of Example 7, and then dried.

[Example 11] A galvanized steel sheet was subjected to all the treatments of Example 8 except for drying, and then coated with the aqueous acrylic resin solution of Example 6 and dried.

[Example 12] Galvanized & 48! After performing the treatment of Example 8 except for drying, the treatment of Example 5 of gluing with a coating-type chromate treatment aqueous solution and drying was performed.

[Example 13] A galvanized steel sheet was coated with the lithium silicate aqueous solution of Example 7 after being subjected to the treatment of Example 8, excluding drying.
Let's do the drying.

[Comparative Example 3] A galvanized steel sheet was treated in the same manner as in Example 4, except that the blackening treatment solution did not contain nickel nitrate.

[Comparative Example 4] Nickel nitrate α degree of blackening treatment liquid was 5 g/l in terms of Ni
A galvanized steel sheet was treated in the same manner as in Example 4, except that the Ni''/Sb3+ molar ratio was 10.

[Comparison row 5] The blackening treatment solution contains about 1 sl of antimonyl potassium izoite in terms of tSb, 60 s of nickel nitrate in terms of N1, and Ni
A zinc-plated i-sheet was treated in the same manner as in Example 4, except that the 2+/Sb3+ molar ratio was 120.

[Comparative Example 6] The same procedure was carried out except that in the blackening treatment liquid, antimonyl potassium tartrate was 4.69/l in terms of Sb count, nickel nitrate was set to about 10 in N1 count, and N]2+/Sb3+ molar ratio was 4.5. A continuous plated steel plate was treated in the same manner as in Example 4.

Said Example 4.5.6.7.8.9.10.11.12
．． Regarding the lead-plated plates treated in Comparative Example 3.13 and Comparative Example 3.4.5.6, the results of the fingerprint resistance test are shown in the second coat, and the results of the film adhesion test are shown in the third coat. The results of the whiteness measurement are shown in Table 4, and the results of the salt spray wiping test are shown in FIG.

Table 2 Table 3 Table 4 (Total) Whiteness determination method...○ indicates whiteness (W (Lab))
× less than 20 means white U (W (Lab) ) 20 or more [Effects of the invention] The present invention can form a black film on the surface of zinc or zinc alloy in a short time, and does not use silver salt in the treatment solution. ,
It can be applied at a lower cost than the conventional dot chromate method. Also, the black matte color described in Japanese Patent Publication No. 45-27690? It is possible to form a blacker and more uniform film on the lead or zinc alloy surface than with methods that produce a coating.

Furthermore, on top of the black film, a chromate film, phosphate film, alkali silicate film, or resin film is applied.
It also has excellent fingerprint resistance, film adhesion, and corrosion resistance.

[Brief explanation of drawings]

Figure 1 is a graph of the relationship between Sb''#fij and whiteness, Figure 2 is a graph of the relationship between CO concentration and whiteness, Figure 3 is a graph of the relationship between pH and whiteness, and No. 41 is a graph of the relationship between Ni2+/Sb3+ molar ratio and whiteness. Figure 5 is a graph of the relationship between C02+/Sb3+ molar ratio and whiteness, Figure 6 is the graph of the relationship between Fe 3+ /Sb
A graph showing the relationship between the 3+ molar ratio and whiteness, and FIG. 7 is a graph showing the relationship between the salt spray time and the degree of surface rust formation. Figure 7 Salt water fountain n hours rhr''1 - White MW (Lab) White MW (Lab) Procedural amendment July 26, 1985

Claims (8)

[Claims] (1) Antimony ion (a) at 0.2 to 5 g/l,
One or more metal ions (b) selected from nickel ions, iron ions, and cobalt ions are combined into one
0 to 100 g/l, and the metal ion (b
)/antimony ion (a) molar ratio of 5 to 110, and a pH of 6 or less. A blackening treatment solution for zinc or zinc alloy. (2) The metal ion (b)/antimony ion (a)
The blackening treatment liquid for zinc or zinc alloy according to claim 1, wherein the molar ratio is from 25 to 70. (3) Zinc or zinc alloy containing one or more types selected from 0.2 to 5 g/l of antimony ions (a) and metal ions (b) consisting of nickel ions, iron ions, and cobalt ions. 10 to 100 g/l, and the metal ion (b)/the antimony ion (a)
Black zinc or zinc alloy, characterized in that it is treated with an acidic aqueous solution having a molar ratio of 5 to 110 and a pH of 6 or less to form a black film, and then a phosphate film is applied to the surface thereof. processing method. (4) Said metal ion (b)/antimony ion (a)
The method for blackening zinc or zinc alloy according to claim 3, wherein the molar ratio is 25 to 70. (5) Zinc or zinc alloy, containing 0.2 to 5 g/l of antimony ions (a) and one or more types selected from metal ions (b) consisting of nickel ions, iron ions, and cobalt ions. 10 to 100 g/l, and the metal ion (b)/the antimony ion (a)
After forming a black film by treating with an acidic aqueous solution having a molar ratio of 25 to 70 and a pH of 6 or less, a chromate film with a Cr film amount of 1 to 1000 mg/m^2 is applied to the surface. A method for blackening zinc or zinc alloy, characterized by: (6) Zinc or zinc alloy, containing 0.2 to 5 g/l of antimony ion (a) and one or more types selected from metal ions (b) consisting of nickel ion, iron ion, and cobalt ion. 10 to 100 g/l, and the metal ion (b)/the antimony ion (a)
After forming a black film by treating with an acidic aqueous solution having a molar ratio of 25 to 70 and a pH of 6 or less, an alkali silicate film with a film thickness of 0.01 to 3 μm is applied to the surface. Features: A method for blackening zinc or zinc alloy. (7) Zinc or zinc alloy, containing 0.2 to 5 g/l of antimony ions (a) and one or more types selected from metal ions (b) consisting of nickel ions, iron ions, and cobalt ions. 10 to 100 g/l, and the metal ion (b)/the antimony ion (a)
A blackening treatment for zinc or zinc alloy, characterized by forming a black film by treating with an acidic aqueous solution having a molar ratio of 25 to 70 and a pH of 6 or less, and then applying a resin film to the surface of the black film. Method. (8) Zinc or zinc alloy, containing 0.2 to 5 g/l of antimony ions (a) and one or more types selected from metal ions (b) consisting of nickel ions, iron ions, and cobalt ions. 10 to 100 g/l, and the metal ion (b)/the antimony ion (a)
After forming a black film by treating with an acidic aqueous solution having a molar ratio of 25 to 70 and a pH of 6 or less, a chromate film with a Cr film amount of 1 to 1000 mg/m^2 is applied to the surface, A method for blackening zinc or zinc alloy, which further comprises applying a resin film thereon.