JPH04232280A - Black chromated steel sheet and production thereof - Google Patents

Abstract

PURPOSE:To form a black chromate film having superior blackness and adhesion on a steel sheet in a short time by previously forming a Zn-Ni alloy plating film on the surface of the steel sheet and then carrying out chemical treatment with a chromate bath having a specified compsn. CONSTITUTION:A Zn-Ni alloy plating film consisting of 10-15 wt.% Ni and the balance Zn is formed as an upper layer on at least one side of a steel sheet. A black chromate film is then formed on the surface of the plating film by chemical treatment at about 30 deg.C with a chromate bath of pH <=1.0 contg. 30-250 g/l (expressed in terms of CrO3) Cr<6+> ions, 10-100g/l NO3<-> ions and 10-150g/l SO4<2-> ions. An org. high molecular resin film of 0.1-3mum thickness or 1-1,000 mg/m<2> chromate film is further formed as required. A black chromated steel sheet having superior corrosion resistance and high-grade appearance is obtd.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black chromate-treated steel sheet that has excellent blackness and coating adhesion and corrosion resistance, and a method for producing the same.

0002

[Prior Art] Recently, attempts have been made to continuously and quickly blacken zinc or zinc alloy coated strip steel sheets or to apply a clear coating to them for use in automobile parts, electronic parts, refrigerator parts, etc. There is.

As a blackening treatment method, a black chromate treatment method is disclosed in Japanese Patent Publication No. 61-429, but this method uses a silver salt in the treatment solution, but the treatment time is several minutes to 10 minutes. This is not preferred because it requires several minutes and cannot be processed in a short period of time.

[0004] JP-A No. 56-62996 describes a method of applying a black resin film containing a black pigment such as carbon black as the main component, but this method is not preferred due to problems in film adhesion and processability. do not have.

[0005]Also, there is a cathodic electrolytic treatment method using a bath containing chromic acid and acetic acid as main components, but this method has drawbacks such as the long treatment time, which requires several minutes or more.

[0006] JP-A No. 62-89879 describes a method of treating zinc or zinc alloy plating with an acidic aqueous solution containing metal ions to deposit a black layer on the surface by displacement. poor adhesion,
Not practical. Furthermore, since it is characterized by electrochemically depositing a more noble metal than plating, it has the disadvantage that the corrosion resistance of the black film is inferior to that of the original plating.

[0007] Japanese Patent Publication No. 63-30262 describes a method of chemically dissolving and blackening Zn-Ni alloy plated steel sheets using a nitric acid aqueous solution, but the corrosion resistance of the black coating is lower than that of the original Zn-Ni alloy. It has the disadvantage that it is inferior to Ni alloy plating.

[0008] Japanese Patent Publication No. 63-46158 and Japanese Patent Publication No. 63-46159 describe a method of anodizing a Zn-Ni alloy plated steel sheet in a bath containing NO3- ions. have the same drawbacks.

[0009]

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to provide a black chromate treatment method that can be processed in a short time and is inexpensive, and that also provides uniform blackness, adhesion, and corrosion resistance. An object of the present invention is to provide a black chromate-treated steel sheet having a black coating and a method for manufacturing the same.

0010

[Means for Solving the Problems] In order to achieve the above object, the black chromate-treated steel sheet of the present invention has Ni:10 formed on at least one surface of the steel sheet.
A Zn-Ni alloy plating layer as an upper layer consisting of ~15wt%, balance: Zn, and 30% in terms of CrO3
Cr6+ ions in an amount of ~250 g/l and 10-10
NO3 − ions in an amount of 0 g/l and 10
A black chromate film formed on the surface of the Zn-Ni alloy plating film by chemical treatment with a chromate bath containing SO4 2- ions in an amount of ~150 g/l and having a pH of 1.0 or less. It is characterized by consisting of.

[0011] Furthermore, if necessary, a chromate film in an amount of 1 to 1000 mg/m2, or an organic polymer resin film or an alkali film in a thickness of 0.1 to 3 μm is applied on the surface of the black chromate film. It is characterized by the formation of a silicate film.

Further, a chromate film with a chromium adhesion amount of 1 to 1000 mg/m2 is formed on the surface of the black chromate film, and a chromate film with a thickness of 0.1 to 3 μm is formed on the surface of the chromate film. It is characterized by the formation of an organic polymer resin coating or an alkali silicate coating.

[0013] Further, in the method for manufacturing a black chromate-treated steel sheet of the present invention, on at least one surface thereof, an upper layer containing Ni: 10 to 15 wt%, balance: Zn.
Cr6+ ions in an amount of 30 to 250 g/l in terms of CrO3 and N in an amount of 10 to 100 g/l in terms of CrO
The Zn-Ni alloy plating film is chemically treated with a chromate bath containing O3 - ions and SO4 2- ions in an amount of 10 to 150 g/l and having a pH of 1.0 or less. It is characterized by the formation of a black chromate film on the surface. The chemical treatment for the steel sheet on which the Zn--Ni alloy plating film is formed includes treatment by immersion in the chromate bath.

Furthermore, if necessary, the amount of chromium deposited on the surface of the black chromate film is 1 to 1000.
chromate coating in an amount of mg/m2 or 0.
It is characterized by forming an organic polymer resin coating or an alkali silicate coating with a thickness of 1 to 3 μm.

[0015] Further, a chromate film with a chromium adhesion amount of 1 to 1000 mg/m2 is formed on the surface of the black chromate film, and then an organic film with a thickness of 0.1 to 3 μm is formed on the surface of the chromate film. It is characterized by forming a polymer resin coating or an alkali silicate coating.

[0016] In other words, the present invention has the following advantages: compared with conventional black coating methods for zinc or zinc alloys, the corrosion resistance of the black film is particularly excellent; the black chromate treatment can be carried out in a short time (within 5 seconds); As a result of our efforts to invent an unprecedented black processing method that satisfies conditions such as the processing liquid being inexpensive and containing no expensive Ag ions, we have developed Zn-Ni.
Alloy plating is Cr6+ (CrO 3 ), NO3 −
We have invented a novel black chromate treatment method that satisfactorily satisfies the purpose by chemically treating in a bath containing three main components: , SO4 2-. As a method for chemically treating the material in the bath, the immersion method is mainly preferred, but it is also possible to perform the treatment using a fluidized bath and an anodic treatment.

Cr6+, NO3 − and SO4 2
All three components - are essential components, and if one of them is insufficient, a black chromate film will be formed, but the film will not have a black color.

Cr6+ is dissolved in a solvent (water) as a water-bathable hexavalent chromium compound such as CrO3, chromate, dichromate, etc. The concentration of each main component in the black chromate treatment bath of the present invention is 3 Cr6+ in terms of CrO 3 .
0-250g/l (l is liter), NO3
- is 10-100 g/l, SO4 2- is 10-1
50g/l, preferably Cr6+ is CrO
3 Converted to 60 to 220 g/l, NO3 − is 20
~60g/l, SO4 2- 15-80g/l
It is.

[0019] Cr6+ is 30g/in terms of CrO3
If it is less than 220 g, the blackness is insufficient.
If it exceeds 250g/l, the blackness will decrease, especially if it exceeds 250g/l.
If it exceeds , it is inappropriate both from the viewpoint of blackness and from the viewpoint of chemical cost.

[0020] NO3 − includes HNO3 as well as Na
It is derived from water-soluble nitrates such as NO3, KNO3, and metal salts, but HNO3 is preferred. NO3-
is less than 20g/l, especially less than 10g/l,
Unfavorable due to insufficient blackness. On the other hand, 60g
If it exceeds 100g/l, the blackness will decrease, especially if it exceeds 100g/l.
Exceeding this is not preferable because the Zn--Ni alloy plating will be significantly leached.

SO 4 2- is derived as H2 SO4 or a water-soluble sulfate such as Na2 SO4, (NH4)2 SO4, metal salt, etc., but H2 SO
4 is desirable. If the SO 4 2- is less than 15 g/l, particularly less than 10 g/l, the degree of blackness is insufficient, which is not preferable. On the other hand, when it exceeds 80 g/l, the blackness decreases, and especially when it exceeds 150 g/l, Zn-
This is not preferable because the Ni alloy plating is significantly eluted.

The pH of the black chromate treatment bath is 1.0.
The following shall apply. When the pH exceeds 1.0, the reaction rate between the plating and the treatment bath is slow, and a good black film cannot be obtained in a short time. The lower limit is not particularly determined because it is difficult to actually measure an accurate pH when the pH becomes a negative value, but an excessively low pH is not preferable because it causes significant elution of the plating.

[0023] The pH of the black chromate treatment solution is as follows:
HNO3 is used as NO3 −, and SO3
When using H2SO4 as 2-, the pH at the time of bath preparation is naturally within an appropriate range, but when using other salts, or when using HNO3, H2SO
Even if the acid No. 4 is used, if the pH of the bath increases with continuous treatment, it is necessary to adjust the pH. For pH adjustment in that case, HNO3 and H2SO4 are desirable, but other inorganic acids may also be used.

The black chromate treatment liquid used in this invention utilizes local elution of Zn-Ni alloy plating and precipitation of hydrated chromium oxide, and is greatly affected by treatment time and liquid temperature. . The higher the liquid temperature, the faster the reaction rate, so it is preferably room temperature or higher. In particular, if strip-plated steel sheets are treated continuously, the treatment time will be 10 seconds or less, so in that case it is preferably 30° C. or higher. The upper limit of the liquid temperature is preferably 80° C. or lower in consideration of moisture evaporation, safety, energy saving, etc. In addition, in order to suppress the reaction of black chromate treatment, chinoline ethiodide,
Known reaction inhibitors such as tolylthiourea, propylsulfide dialmine, formaldehyde, para-thiocresol, glycols, alcohol, and glycerin may be added.

The black chromate coating formed by the black chromate treatment of the present invention has superior corrosion resistance in terms of resistance to red rust compared to the conventional black coating formed by etching, but in order to further improve the corrosion resistance, Furthermore, in order to improve fingerprint resistance, after the black chromate treatment and washing with water, a chromate coating, an organic polymer resin coating, or an alkali silicate coating is further applied.

Regarding corrosion resistance, since the black chromate coating according to the present invention has superior corrosion resistance compared to the conventional black coating formed by etching, the same protective coating is applied to the surface of each black coating. For example, when applying an organic polymer resin film with a thickness of 1.0 μm, using a black chromate film as the base can provide better corrosion resistance than using a black film formed by conventional etching as the base.

Therefore, in the case of conventional etching, for example, in order to satisfy the corrosion resistance specifications for home appliances, two protective coatings are required: "blackening treatment (etching) → chromate treatment → organic polymer resin coating". be. According to this invention, since the black chromate film can have the function of both the blackening treatment and the chromate treatment in the above step,
It has the same corrosion resistance as "black chromate treatment → organic polymer resin coating", but has the great advantage of being able to omit one step.

[0028] Fingerprint resistance (resistance to fingerprints when touching the surface of a steel plate with a finger) can be improved by applying a resin coating or a coating mainly composed of an alkali silicate to the surface of the coating.

The resin coating in this invention is a known coating formed by treatment with a water-soluble, emulsifying, or dispersible organic polymer resin or a solvent-based organic polymer compound, such as Special Public Service 1986-
In the coating disclosed in Publication No. 33192, examples of the resin include currently used vinyl-based resins such as vinyl acetate, vinyl chloride, vinylidene chloride, copolymers thereof, acrylic acid, methacrylic acid, and acrylic esters. , methacrylic acid ester, hydroxyacrylic acid, acrylic type and its copolymers such as hydroxyacrylic acid ester, alkyd type, epoxy type, urea type, fluorine type,
Examples include urethane-based, ester-based, styrene-based, olefin-based and copolymers thereof, synthetic rubber-based resins such as butadiene, and natural polymer resins. If necessary, an inorganic substance such as a chromium compound or silica can be added to this organic polymer resin aqueous solution.

[0030] The chromate film is disclosed in, for example, Japanese Patent Application Laid-Open No. 1983-2
This film is disclosed in Japanese Patent Application Laid-open No. 8444 and Japanese Patent Application Laid-open No. 60-218483, and is preferably formed using a partially reduced chromic acid aqueous solution. Particles (silica sol, fumed silica) may also be included. The Cr3+/Cr6+ weight ratio in the chromic acid aqueous solution is reduced to 1/1 by reducing it with an organic or inorganic reducing agent such as sugars or alcohols.
~1/3 is best, and the pH of the aqueous solution is 1.5.
A range of ~4.0 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.
The amount of adhesion is 1 to 1000 mg/m 2 , preferably 10 to 200 mg/m 2 .

[0031] A film containing an alkali silicate as a main component is disclosed, for example, in Japanese Patent Publication No. 57-2274, and has the general formula M2O.nSiO2 (M: Na, K
, Li, ammonium or amine, n: 2 to 20
), and a chromium compound such as chromic acid is further added thereto as required. The amount of the alkali silicate coating is set to 0.01 to 3 μm for the same reason as the chromate coating.

[0032]

[Operation] When a Zn--Ni alloy plated steel sheet is treated in a black chromate treatment bath containing CrO3, NO3-, and SO4 2- as in the present invention, a dissolution reaction of the plating occurs first. That is, Zn → Zn 2++2e Ni → Ni 2++2e At this time, the dissolution reaction progresses microscopically non-uniformly due to local differences in standard electrode potential of the plating. On the other hand, Cr6+ in the bath gains electrons and is reduced to Cr3+. That is, Cr6+ +3e → Cr3+ At this time, Cr3+ is deposited on the surface as an oxide film. In addition to Cr3+, this chromium oxide also contains zinc, nickel, hexavalent chromium, others, NO3 -, SO4 2
It is a complex complex oxide consisting of various elements supplied from -, and it is not clear what kind of structure the compound has.

The black chromate-treated steel sheet of the present invention consists of a chemical dissolution reaction and a chromium oxide film forming reaction, and the synergistic effect of both provides excellent blackness. In other words, the effect of the microscopically non-uniform dissolution reaction and the effect of the extremely fine chromium oxide film create a black film with a very deep and excellent blackness. Furthermore, since this black film has a chromium oxide film formed on the outermost layer, it has an excellent anticorrosion effect.

There is a close relationship between the composition of the black chromate treatment bath of the present invention and the blackness after treatment. In the case of immersion treatment, C
The color tone does not change with rO 3 alone or a combination of CrO3 and NO3. Also, CrO 3 and S
In combination with O4 2-, a deep brown color is obtained, but not a good black color. CrO3, NO3-, S
A good black color can only be obtained by the combination of O4 2-. In addition, pure Zn and CrO 3 , HNO 3 ,
Colored chromate treatment using a H2SO4 bath has been known as a known technique for a long time, but it does not produce a black surface. That is, Zn-Ni alloy and CrO 3 , NO
A good black color can be obtained by the combination of 3- and SO4 2-.

FIG. 1 shows the concentration of NO3 − at 30 g/
l (added as HNO 3 ), SO4 2- concentration was kept constant at 30 g/l (added as H 2 SO4 ), and the concentration of CrO3 was varied (
20g/m2 of Zn-12%Ni alloy plating was immersed for 5 seconds at a liquid temperature of 30°C), and the blackness (indicating the L value) of the film formed was shown. L
The smaller the value, the closer it becomes to black. As can be seen from Figure 1, L
To obtain a black coating of ≦20, the concentration of CrO 3 is 30
~250g/l, 60 to obtain a black film with L≦15
It can be seen that it is necessary to be in the range of ~220 g/l. Furthermore, the concentration of CrO 3 is 100 to 180 g/
1, an extremely good blackness of L≦11 is obtained.

FIG. 2 shows that the concentration of CrO 3 is 120 g/
l, the concentration of SO4 2- is 30g/l (H2S
Aqueous solutions (added as HNO 3 at a liquid temperature of 30
℃), 20g of Zn-12%Ni alloy plating
/ m2 for 5 seconds and shows the degree of blackness of the film formed. As can be seen from Figure 2, L≦2
To obtain a black film of NO3, the concentration of NO3 is 10 to 100.
g/l, 20-60g to obtain a black film with L≦15
It can be seen that a range of /l is required. Furthermore, N
An extremely good blackness of L≦11 can be obtained at an O3 − concentration of 27 to 40 g/l.

FIG. 3 shows that the concentration of CrO 3 is 120 g/
1, the concentration of NO3 − was set at 30 g/l (HNO
(added as 3) and constant, the concentration of SO4 2-
2 Aqueous solutions of various changes as SO4 (liquid temperature 30℃
), Zn-12%Ni alloy plating 20g
/ m2 was immersed for 5 seconds, and the blackness of the film formed is shown. As can be seen from FIG. 3, in order to obtain a black film with L≦20, the concentration of SO4 2− is 10 to 150.
g/l, 15-80g to obtain a black film with L≦15
It can be seen that a range of /l is required. Furthermore, S
An extremely good blackness of L≦11 is obtained at an O4 2- concentration of 17 to 50 g/l.

FIG. 4 shows that the concentration of CrO 3 is 120 g/
1, the concentration of NO3 − was set at 30 g/l (HNO
3), the concentration of SO4 2- was 30 g/l
(Added as H2SO4) When adding NaOH to change the pH, Zn
-12 wt% Ni alloy plating is immersed for 5 seconds to form a film, and this represents the blackness (L value). From FIG. 4, it can be seen that in order to obtain a black film with L≦20, pH≦1 is essential.

[0039]

[Example] Next, the present invention will be explained with reference to an example. [Example Nos. 1 to 13] Area weight (plating amount) 20g
/m 2 of Zn-12wt%Ni alloy plated steel sheet, as shown in Table 1, the concentration of Cr6+ was 30 to 25.
0g/l (added as CrO3), NO3 −
The concentration of SO4 2- was 10-100 g/l (added as HNO 3 ), and the concentration of SO4 2- was 10-150 g/l (added as HNO 3 ).
After being immersed in an aqueous solution with a pH of -0.2 and a bath temperature of 30° C. containing H 2 SO 4 (added as H 2 SO 4 ) varied within the range of this invention for a treatment time of 5 seconds, washed with water, and then dried, Examples No. 1 to No. 13 were prepared.

[Example No. 14] A Zn-12w%Ni alloy plated steel sheet with a coating weight (coating amount) of 20 g/m 2 was subjected to the same treatment as in Example No. 1, and then a solid content concentration of 20 g/l and a Cr3+ A coated chromate treatment solution with a /Cr6+ weight ratio of 2/3 and a pH adjusted to 2.5 with KOH was applied with a roll coater and dried.
A film with a chromium adhesion amount of 50 mg/m3 was formed.

[Example No. 15] A Zn-12w%Ni alloy plated steel sheet with a coating weight (coating amount) of 20 g/m 2 was subjected to the same treatment as in Example No. 3, and then treated with an aqueous acrylic resin solution (trade name: Watersol S744). (Registered trademark) / Dainippon Ink Co., Ltd.) and dry it.
A film of μm was formed.

[Example No. 16] A Zn-12w%Ni alloy plated steel sheet with a coating weight (coating amount) of 20 g/m 2 was subjected to the same treatment as in Example No. 7, and then Si
A lithium silicate (LiO 4,8SiO2) aqueous solution adjusted to a concentration of 50 g/l in terms of O2 was applied and dried using a roll coater, and the concentration was 0 in terms of SiO2.
．． A coating of 3 g/m2 was formed.

[Example No. 17] A Zn-12w%Ni alloy plated steel sheet with a coating weight (coating amount) of 20 g/m 2 was subjected to the same treatment as in Example No. 14, and then treated with an acrylic resin aqueous solution (trade name Watersol S744). (registered trademark) manufactured by Dainippon Ink Co., Ltd.) and dry it.
A film of 1 μm was formed.

[Example No. 18] A Zn-12w%Ni alloy plated steel sheet with a coating weight (coating amount) of 20 g/m 2 was subjected to the same treatment as in Example No. 14, and then Si
A lithium silicate (LiO 4,8SiO2) aqueous solution adjusted to a concentration of 50 g/l in terms of O 2 was applied using a roll coater and dried to form a film of 0.3 g/m 2 in terms of SiO 2 .

[Comparative Example No. 1] NO3 − in aqueous solution
The same treatment as in Example 1 was performed except that SO4 2- was not contained.

[Comparative Example No. 2] NO3 − in aqueous solution
The same treatment as in Example 1 was performed except that .

[Comparative Example No. 3] SO4 2 in aqueous solution
The same treatment as in Example 1 was performed except that - was not included.

[Comparative Example No. 4] CrO 3 in aqueous solution
The same treatment as in Example 1 was performed except that .

[Comparative Example No. 5] An electrogalvanized steel sheet (Zn-plated steel sheet) was subjected to the same treatment as in Example 1.

[Comparative Example No. 6] The same treatment as in Example 1 was carried out except that the pH was set to 7.0.

[Comparative Example No. 7] Zn-12wt%N
The i-alloy plated steel sheet was immersed in a 5 wt % nitric acid aqueous solution for 5 seconds, washed with water, and dried.

[Comparative Example No. 8] Zn-12wt%N
The i-alloy plated steel sheet was subjected to the same treatment as in Comparative Example 7, and then an aqueous acrylic resin solution (trade name Watersol S74) was applied.
4 (registered trademark) manufactured by Dainippon Ink Co., Ltd.),
It was dried to form a 1 μm film.

[Comparative Example No. 9] Zn-12wt%N
The i-alloy plated steel sheet was subjected to the same treatment as in Comparative Example 7, and then the solid content concentration was 20 g/l, Cr3+/Cr6+
A coated chromate treatment solution with a weight ratio of 2/3 and a pH adjusted to 2.5 with KOH was applied using a roll coater and dried to form a film with a chromium adhesion amount of 50 mg/m3. Next, an aqueous acrylic resin solution (trade name: Watersol S744 (registered trademark), manufactured by Dainippon Ink Co., Ltd.)
was applied and dried to form a 1 μm film. Table 1 shows the results of a test similar to that of Example No. 17 performed on this steel plate.

[0054] The following tests (1) to (5) were conducted for each of Examples Nos. 1 to 18 and Comparative Examples Nos. 1 to 9, and the results are also shown in Table 1.

(1) Blackness test: The chromaticity was evaluated by measuring the lightness (L value) of the coating using a color computer manufactured by Suga Test Instruments Co., Ltd. The evaluation criteria are as follows. Those with an L value of 15 or less; ◎ Those with an L value of 20 or less; ○ Those with an L value of more than 20; ×.

(2) Fingerprint resistance test: Fingerprints were placed on the surface of the test material, and the conspicuousness of the attached fingerprints was visually evaluated. The evaluation criteria are as follows. Fingerprints are not conspicuous; ○ Fingerprints are slightly conspicuous; △ Fingerprints are conspicuous; ×.

(3) Adhesion test: A cellophane tape was adhered to the surface of the test material, and when the tape was rapidly peeled off, the degree of peeling of the film was visually judged. The evaluation criteria are as follows. No peeling; ◎ Less than 10% peeling; ○ Less than 10 to 30% peeling; △ 31% or more peeling; ×.

(4) Corrosion resistance test ■ A 5% salt spray test was conducted on the test material, and the red rust was 5%.
The evaluation was based on the time taken to generate %. The evaluation criteria are as follows. 2000 hours or more; ◎ 1000 hours or more; ○ 500 hours or more; △ 100 hours or more; ×.

(5) Corrosion resistance test ■ A 5% salt spray test was conducted on the test material, and white rust was found to be 5%.
The evaluation was based on the time taken to occur. The evaluation criteria are as follows. 500 hours or more; ◎ 200 hours or more; ○ 50 hours or more; △ 10 hours or more; ×.

[0060]

[Table 1]

As is clear from Table 1, Example No. 1
It can be seen that samples 1 to 18 had good evaluations of blackness and adhesion, and had excellent corrosion resistance. Furthermore, Example No. 1
It can be seen that samples Nos. 5 to 18 are also excellent in fingerprint resistance.

On the other hand, Comparative Examples Nos. 1 to 4 were all inferior in blackness.

Example No. 1 exhibited better corrosion resistance than Comparative Example No. 7.

Example No. 17 exhibited better corrosion resistance than Comparative Example No. 8.

Example No. 17 has almost the same corrosion resistance as Comparative Example No. 9. In other words, the steel sheet coated with an acrylic resin film without the applied chromate treatment as in Example No. 17 has the same corrosion resistance as Comparative Example No. 9, which was subjected to both the applied chromate treatment and the acrylic resin coating. This shows that the black chromate treatment of the present invention can also omit post-treatment steps.

[Example No. 19] Fabric weight (plating amount) 2
Zn-12wt%Ni electrolytic zinc alloy plated steel sheet of 0g/m2 was coated with 120g/l of CrO3, N
The concentration of O3 − was 30 g/l (added as HNO 3 ), and the concentration of SO4 2− was 30 g/l (added as HNO 3 ).
The relationship between treatment time and blackness (L value) was investigated by immersing the sample in an aqueous solution containing 2 SO4 (added as SO4). Figure 5
is a graph showing the results.

[Comparative Example 10] As a comparative example, 15 g/l of CrO 3 , H as disclosed in Japanese Patent Publication No. 61-429 was used as a black chromate treated aqueous solution.
2 SO4 6g/l, H3 PO6 0.6g/l
, containing 1g/l of Ag3PO4, pH 0.7
The degree of blackness was evaluated in the same manner as in Example 17, except that an aqueous solution adjusted to . The results are also shown in FIG.

From FIG. 5, it can be seen that Comparative Example 10
The conventional black chromate treatment of Zn according to Publication No. 9 is as follows:
While it is impossible to process in a short time, Example No.
The black chromate treatment of No. 19 of this invention has a target value (L≦
20) shows that short-time processing within 5 seconds is possible.

[0069]

[Effects of the Invention] Since the present invention is constructed as described above, it produces the following useful effects. ■ Conventional A
Compared to g-ion-containing black chromate treatment, it is possible to form a stable black film with a luxurious appearance on the Zn-Ni alloy plating surface in a shorter time, that is, from several seconds to several tens of seconds. ■ Zn− using conventional nitric acid aqueous solution
It is possible to form a black chromate film that has excellent corrosion resistance up to the occurrence of red rust compared to a black chemical conversion film of Ni alloy. - Since a chromate film, an alkali silicate film, and a resin film are applied on top of the black chromate film, it also has excellent fingerprint resistance, film adhesion, and corrosion resistance up to white rust.

[Brief explanation of the drawing]

[Figure 1] Graph showing the relationship between CrO3 concentration and film blackness (L value)

[Figure 2] Graph showing the relationship between NO3 − concentration and film blackness (L value)

[Figure 3] Graph showing the relationship between SO4 2- concentration and film blackness (L value)

[Figure 4] Graph showing the relationship between the pH value of the aqueous solution and the blackness (L value) of the film

[Figure 5] Graph showing the relationship between aqueous solution immersion treatment time and film blackness (L value)

[Table 1]

[Table 1]

Claims (9)

[Claims] 1. A Zn-Ni alloy plating layer as an upper layer formed on at least one surface of a steel plate and consisting of 10 to 15 wt% Ni and the balance Zn;
Cr6+ in an amount of 30 to 250 g/l in terms of CrO3
ions, NO3 − ions in an amount of 10-100 g/l, and SO4 in an amount of 10-150 g/l.
The Zn-Ni
A black chromate-treated steel sheet comprising a black chromate film formed on the surface of an alloy plating film. 2. On the surface of the black chromate coating,
The black chromate-treated steel sheet according to claim 1, wherein a chromate film is formed in an amount of 1 to 1000 mg/m2. 3. On the surface of the black chromate coating,
The black chromate-treated steel sheet according to claim 1, wherein an organic polymer resin coating or an alkali silicate coating with a thickness of 0.1 to 3 μm is formed. 4. On the surface of the black chromate coating,
A chromate film is formed in an amount of 1 to 1000 mg/m2, and on the surface of the chromate film, an amount of 0.
The black chromate-treated steel sheet according to claim 1, wherein an organic polymer resin coating or an alkali silicate coating with a thickness of 1 to 3 μm is formed. 5. A Zn-Ni alloy plating film consisting of 10 to 15 wt% Ni and the balance Zn is formed as an upper layer on at least one surface of the steel plate, and the coating is 30 to 250 g/l in terms of CrO3. amount of C
r6+ ions and an amount of NO3 − from 10 to 100 g/l.
ions and an amount of 10-150 g/l SO
A black chromate film is formed on the surface of the Zn-Ni alloy plating film by chemically treating it with a chromate bath containing 4 2-ions and having a pH of 1.0 or less. A method for producing black chromate-treated steel sheets. 6. On the surface of the black chromate film,
6. The method for producing a chromate-treated steel sheet according to claim 5, wherein the chromate coating is formed in an amount of 1 to 1000 mg/m2. 7. On the surface of the black chromate coating,
The method for producing a chromate-treated steel sheet according to claim 5, wherein an organic polymer resin coating or an alkali silicate coating having a thickness of 0.1 to 3 μm is formed. 8. On the surface of the black chromate coating,
Form a chromate film in an amount of 1 to 1000 mg/m2, and then add 0.1 mg/m2 on the surface of the chromate film.
6. The method for producing a chromate-treated steel sheet according to claim 5, wherein an organic polymer resin coating or an alkali silicate coating with a thickness of ~3 μm is formed. 9. Any one of claims 5 to 8, wherein the chemical treatment of the steel plate on which the Zn-N alloy plating film is formed is performed by immersion treatment in the chromate bath.
The method for producing a chromate-treated steel sheet described in .