JPH04232279A - Black chromate treated steel plate and its manufacture - Google Patents

Abstract

PURPOSE:To form a uniform chromate film excellent in blackness and adhesiveness to a steel plate by executing a chemical treatment to the steel plate forming Zn-Ni alloy plating film on the surface with the specific composition of chromate bath. CONSTITUTION:At least on one side of surface of the steel plate, Zn-Ni alloy plating layer composed of 10-15wt.% Ni and the balance Zn is formed as an upper layer. Successively, on the surface of this Zn-Ni alloy plating layer, by using the chromate bath incorporating 0.1-5.0g/l Cr<6+> ion expressed in terms of CrO3, 1-50g/l NO3<-> ion and 1-50g/l SO4<2-> ion and having <=2.0pH, the chemical treatment is executed at 30-80 deg.C to form the black chromate film. Further, as necessary, the chromate film having 1-1000mg/m<2> or organic polymer resin coating film having 0.1-3mum thickness is formed. By this method, the black chromate treated steel plate having corrosion resistance is obtd. with the low concn. of the black chromate treated solution.

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, zinc or zinc alloy plated steel sheets are used as materials for automobile parts, electronic parts, refrigerator parts, etc., by applying a blackening treatment, or by applying a clear coating after the blackening treatment. Attempts have been made to use a steel plate with a black coating formed on its surface. Hereinafter, conventionally known methods of forming a black film and their problems will be described.

[0003] Japanese Patent Publication No. 61-429 discloses a method comprising subjecting a steel plate to black chromate treatment using a silver salt as a treatment liquid. However, this method requires a processing time of several minutes to several tens of minutes, and therefore has the problem that short-term processing is impossible.

[0004] JP-A-56-62996 discloses a method comprising coating a steel plate with a black resin coating containing a black pigment such as carbon black as a main component. However, this method has the problem of poor film adhesion and processability. Another known method is to subject steel plates to cathodic electrolytic treatment in a bath containing chromic acid and acetic acid as the main components, but this method requires a treatment time of several minutes or more, so It has a problem that cannot be treated.

[0005] Japanese Patent Application Laid-Open No. 62-89879 discloses that a zinc or zinc alloy coated steel sheet, in which a zinc or zinc alloy plating film is formed on the surface of the steel sheet, is treated with an acidic aqueous solution containing metal ions to remove the plating film. A method is disclosed which consists in displacement depositing a black film on the surface of. However, this method is characterized by electrochemically depositing a nobler metal than the plating film, so the corrosion resistance of the black film is inferior to the original zinc or zinc alloy plating film, and the adhesion of the black film is poor. They have problems with poor sexuality.

[0006] In Japanese Patent Publication No. 63-30262, Z
For n-Ni alloy plated steel sheet, using nitric acid aqueous solution etc.
A method is disclosed which consists of applying a chemical dissolution treatment to achieve blackening. However, this method has a problem in that the corrosion resistance of the black film is inferior to that of the original Zn-Ni alloy plating film.

[0007] Japanese Patent Publication No. 63-46158 and Japanese Patent Publication No. 63-46159 disclose a method comprising anodizing a Zn-Ni alloy plated steel sheet in a bath containing NO3- ions. There is. However, like the above, this method has the problem that the corrosion resistance of the black film is inferior to that of the original Zn-Ni alloy plating film.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a coating with excellent blackness and film adhesion on the surface thereof.
Further, a black chromate-treated steel sheet on which a uniform black chromate film with good corrosion resistance and fingerprint resistance is formed, and a black chromate-treated steel sheet that allows such a black chromate-treated steel sheet to be manufactured in a short time and economically. An object of the present invention is to provide a method for manufacturing treated steel sheets.

[0009]

[Means for Solving the Problems] The present inventors have solved the above-mentioned problems, and have provided a processing solution that has a shorter processing time, superior blackness and film adhesion, and is inexpensive compared to conventional methods. We conducted intensive research to develop a black chromate-treated steel sheet that could be economically manufactured using the following methods. As a result, a specific range of amounts of Cr6+, NO3 − and SO
By chemically treating the surface of the Zn-Ni alloy plating film with a black chromate treatment solution containing 42-, a uniform coating with excellent blackness and film adhesion, as well as good corrosion resistance and fingerprint resistance is formed on the surface of the Zn-Ni alloy plating film. It has been discovered that a black chromate coating can be formed in a short time and economically.

[0010] This invention was made based on the above-mentioned knowledge, and the present invention is based on the above-mentioned findings. 0.1 to 5.0 in terms of CrO3 for the steel plate on which the alloy plating film is formed.
Cr6+ ions in an amount of 0 g/l and 1 to 50 g/l
with an amount of NO3 − ions, and 1 to 50 g
/l of SO4 2- ions, and the pH is 2.
．． The present invention is characterized in that a black chromate film is formed on the surface of the Zn-Ni alloy plating film by performing chemical treatment using a chromate bath having a concentration of 0 or less. In this invention, if necessary, a chromate coating in an amount of 1 to 1000 mg/m2 as the amount of chromium deposited on the surface of the black chromate coating,
Alternatively, an organic polymer resin film or alkali silicate film with a thickness of 0.1 to 3 μm is formed, or a chromium adhesion amount of 1 to 1000 mg/m 2 is formed on the surface of the black chromate film. and on the surface of said chromate coating in an amount of 0.1 to 3
An organic polymer resin coating or an alkali silicate coating with a thickness of .mu.m may be formed.

[0011] In this invention, a predetermined amount of Cr6+, NO3 - and SO4 2- is used as a chromate bath.
Use a black chromate treatment solution containing Cr6+, NO3 − and SO4 in black chromate treatment solution
2- are all essential components, and even if any one of them is missing, a chromate film having a black color cannot be formed.

Cr6+ is CrO3, chromate,
It is dissolved in a solvent (water) as a water-bathable hexavalent chromium compound such as dichromate. The concentration of Cr6+ is CrO3
Converted from 0.1 to 5.0g/l (l is liter)
should be limited within the range of Cr6+ is CrO3
If it is less than 0.1 g/l, NO3 − and S
Although it is possible to blacken the film to some extent due to the etching effect of O4 2-, the degree of blackness is insufficient and the anticorrosive effect of the chlorite film cannot be obtained. On the other hand, when Cr6+ exceeds 5.0 g/l in terms of CrO 3 , a chromate film is formed more than necessary, and Z
Since elution of the n-Ni alloy plating film is suppressed, the degree of blackness is reduced. The preferred concentration of Cr6+ is CrO
It is within the range of 0.3 to 4.0 g/l in terms of 3.

[0013] NO3 − is HNO3, NaNO
3, derived from water-soluble nitrates such as KNO3 and metal salts. Preferable NO3 − is HNO
It is 3. The concentration of NO3 − is 1 to 50 g/l
should be limited within the range of 1g of NO3 −
If it is less than /l, the degree of blackness is insufficient. On the other hand, NO3
- If it exceeds 50 g/l, the Zn--Ni alloy plating film will be significantly leached and the degree of blackness will decrease. N
The preferred concentration of O3 − is within the range of 5 to 40 g/l.

SO 4 2- is H 2 SO 4 , N
It is derived as water-soluble sulfuric acid such as a2SO4, (NH4)2SO4, and metal salts. A preferred SO 4 2- is H2 SO4. The concentration of SO42- should be limited to within the range 1-50 g/l. The concentration of SO 4 2- is 1 g.
If it is less than /l, the degree of blackness is insufficient. On the other hand, S.O.
When the concentration of 4 2- exceeds 50 g/l, Zn-
The elution of Ni alloy plating becomes significant and the degree of blackness decreases. The preferred concentration of SO42- is 3-30g/
It is l.

The pH value of the black chromate treatment solution is 2.
Should be limited to 0 or less. If the pH value exceeds 2.0, the reaction rate between the Zn--Ni alloy plating film and the treatment solution becomes slow, making it impossible to form a good black film in a short time. There is no particular lower limit to the pH value because it becomes difficult to measure accurate pH when the pH value becomes negative, but if the pH value becomes too low, Z
This is not preferable because the elution of the n-Ni alloy plating film becomes significant.

[0016] The pH of the black chromate treatment solution is determined by NO3 during the blackening treatment within the scope of the claims of the present invention.
- When using HNO3 as SO3 and H2 SO4 as SO3 2-, the pH at the time of bath preparation
is naturally within an appropriate range, but even if other salts are used or acids such as HNO3 and H2SO4 are used, if the pH of the bath increases with continuous treatment, the pH must be adjusted. There is a need. For pH adjustment in that case, HNO3 and H2SO4 are desirable, but other inorganic acids may also be used.

[0017] The black chromate treatment in this invention is as follows:
It utilizes the local elution of the Zn-Ni alloy plating film and the precipitation of hydrated chromium oxide, and is greatly affected by the treatment time and the temperature of the black chromate treatment solution. Since the higher the liquid temperature, the faster the reaction rate becomes, the liquid temperature is preferably at least room temperature. In particular, when strip-plated steel sheets are subjected to continuous black chromate treatment, the treatment time is 10 seconds or less, so it is preferable that the temperature of the black chromate treatment liquid be 30° C. or higher. Note that the upper limit of the liquid temperature is preferably 80° C. or lower in consideration of moisture evaporation, safety, energy saving, etc.

Known reaction inhibitors such as quinoline ethiodide, tolylthiourea, propyl sulfide diamylamine, formaldehyde, para-thiocresol, glycols, alcohol, and glycerin may be added to the black chromate treatment solution. .

The corrosion resistance of the black chromate coating formed by the method of the present invention is superior to that of the black coating formed by conventional etching treatment in terms of red rust resistance. Furthermore, on top of such a black chromate film,
By forming a chromate film and/or an organic polymer film or an alkali silicate film, corrosion resistance and fingerprint resistance can be further improved. For example, when an organic polymer resin film with a thickness of 1.0 μm is formed on a black chromate film formed by the method of the present invention, the black film formed by the conventional etching process is , same as above 1.0 μm
Excellent corrosion resistance is exhibited compared to when an organic polymer resin film is formed with a thickness of .

Therefore, for example, in order to satisfy the corrosion resistance specifications of a black chromate-treated steel sheet for home appliances, in the case of the conventional method, a black coating is formed, then chromate treatment is applied, and then an organic coating is applied. While three steps are required to form a polymer resin film, according to the present invention, the black chromate treatment serves as both the above-mentioned blackening film formation process and chromate treatment. After that, through the two steps of forming an organic polymer resin film, corrosion resistance superior to that of the conventional method can be obtained.

[0021] Fingerprint resistance (resistance to fingerprints when touching the surface of a steel plate with a finger) can be improved by forming a resin film or a film mainly composed of an alkali silicate on the surface of the black chromate film. achieved by.

In the present invention, the resin film formed on the surface of the black chromate film is treated with a water-soluble, emulsifying, or dispersible organic polymer resin, or a solvent-based organic polymer compound. For example, a known resin coating disclosed in Japanese Patent Publication No. 60-33192 may be used. Examples of resins include vinyl-based resins such as vinyl acetate, vinyl chloride, and vinylidene chloride, and their copolymers, acrylic acid, methacrylic acid,
Acrylic and its copolymers such as acrylic ester, methacrylic ester, hydroxyacrylic acid, hydroxyacrylic ester, alkyd, epoxy, urea, fluorine, urethane, ester, styrene, olefin, and Examples include copolymers thereof, synthetic rubbers such as butadiene, and resins such as natural polymers. An inorganic substance such as a chromium compound or silica can be added to such an aqueous organic polymer resin solution as necessary.

As the chromate film formed on the surface of the black chromate film, for example, Japanese Patent Application Laid-Open No. 50-2844
4, JP-A No. 60-218483, etc., and it is preferable to form the coating using a partially reduced chromic acid aqueous solution. If necessary, a resin or silica particles (silica sol, fumed silica) having a size of several tens to several thousand angstroms may be included in the chromate film. The Cr3+/Cr6+ weight ratio in the chromic acid aqueous solution is preferably reduced to 1/1 to 1/3 by reducing with an organic or inorganic reducing agent such as sugar or alcohol.
The pH value of the aqueous solution is preferably in the range of 1.5 to 4.0. If the amount of chromate coating is too large, the black coating will be hidden and the degree of blackness will be weakened, and if it is too small, the effect of the chromate coating will be weakened. Therefore, the amount of chromium deposited is 1 to 1000
mg/m 2 , preferably 10-200 m
g/m2.

[0024] As a film mainly composed of an alkali silicate formed on the surface of a black chromate film, there is a film disclosed in Japanese Patent Publication No. 57-2274, which has the general formula M2O.nSiO2 (M: Na, K, L
i, ammonium or amine, and n: 2 to 20). If necessary, a chromium compound such as chromic acid may be further added thereto. The amount of alkali silicate coating should be limited to within the range of 0.01 to 3 .mu.m for the same reasons as for the chromate coating discussed above.

In the present invention, it is preferable that the chemical treatment with the black chromate treatment liquid described above on the steel plate on which the Zn--Ni alloy plating film is formed is carried out by spraying the black chromate treatment liquid. Note that the above chemical treatment can also be performed using a fluidized bath or cathodic electrolysis treatment.

[0026]

[Operation] When a Zn-Ni alloy plated steel sheet is treated with a black chromate solution containing CrO3, NO3 -, SO4 2- as in the present invention, the following effects occur:
A dissolution reaction of the Zn-Ni alloy plating film occurs. 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 film. on the other hand,
Cr6+ in the bath gains electrons and becomes Cr3+ as shown below.
will be reduced to Cr6+ +3e → Cr3+ At this time, Cr3+ is deposited on the surface as a chromium oxide film. In addition to Cr3+, this chromium oxide contains zinc, nickel, hexavalent chromium, others, NO3 -, S
It is a complex complex oxide consisting of various elements supplied from O4 2-, and it is not clear what kind of structure the compound has.

[0027] The black chromate coating in this invention is
It is produced by a chemical dissolution reaction and a chromium oxide film forming reaction. Therefore, due to the synergistic effect of the two,
Excellent blackness can be obtained. In other words, the effect of the microscopically non-uniform dissolution reaction and the effect of the very fine chromium oxide film create a film with a very deep and excellent black color. Moreover, since this black chromate coating has a chromium oxide coating formed on the outermost layer, it has an excellent anticorrosion effect.

There is a close relationship between the composition of the black chromate solution used in this invention and the blackness after treatment. In the case of immersion treatment, CrO 3 only or CrO 3
The combination of NO3 and NO3 alone does not change the color tone. Also,
The combination of CrO 3 and SO4 2- produces a deep brown color, but not a good black color. CrO3,
A good black color can only be obtained by the combination of NO3 − and SO4 2−. In addition, Zn and CrO 3 ,
Colored chromate treatment of HNO 3 and H2 SO4 has been known as a known technique for a long time, but it does not result in black color. That is, Zn-Ni alloy and CrO 3 , N
A good black color can be obtained in combination with O3 − and SO42 −.

FIG. 1 shows that Zn in an amount of 20 g/m2
- Zn-N with 12% Ni alloy plating film formed
NO3 − (HNO3
The concentration of SO4 2-(
The degree of blackness ( It is a graph showing L value). The smaller the L value, the closer to black the color becomes. From FIG. 1, in order to obtain a black film with L≦20, the concentration of CrO 3 must be set to 0.1.
In order to obtain a black film with L≦15, the concentration of CrO 3 should be within the range of 0.3 to 4.
It is clear that it needs to be within the range of g/l.

FIG. 2 shows the Zn--Ni alloy plated steel sheet with a CrO 3 concentration of 1 g/l and an SO 4 2-
(added as H 2 SO4) at a concentration of 5 g/l
Graph showing the blackness (L value) of a chromate film formed by spraying for 5 seconds an aqueous solution (liquid temperature 30 ° C.) with various concentrations of NO3 − (added as HNO 3 ) while keeping the concentration constant. It is. From FIG. 2, in order to obtain a black film with L≦20, NO3
The concentration of is within the range of 1 to 50 g / l, and further,
It is clear that in order to obtain a black coating with L≦15, the concentration of NO3 must be in the range of 5 to 40 g/l.

FIG. 3 shows the Zn--Ni alloy plated steel sheet with a CrO 3 concentration of 1 g/l and NO 3 −
(added as HNO 3 ) at a concentration of 10 g/l
Aqueous solutions with various concentrations of SO4 2- (added as H 2 SO 4 ) held constant (liquid temperature 30°C)
) is a graph showing the blackness (L value) of a chromate film formed by spraying for 5 seconds. From FIG. 3, in order to obtain a black film with L≦20, SO4
In order to set the concentration of SO4 2- in the range of 1 to 50 g/l and obtain a black film with L≦15, SO4 2-
It is clear that the concentration of - should be in the range 3 to 30 g/l.

FIG. 4 shows the Zn--Ni alloy plated steel sheet with a CrO3 concentration of 1.0 g/l and NO3 -
(added as HNO 3 ) at a concentration of 10 g/l
, the blackness (L value) of the chromate film formed by spraying an aqueous solution whose pH was changed by adding NaOH for 5 seconds with the concentration of SO42- (added as H2SO4) set to 5 g / l. This is a graph showing. From FIG. 4, in order to obtain a black film with L≦20,
It is clear that the pH value needs to be 2 or less.

Next, the present invention will be explained in more detail by way of examples and in comparison with comparative examples.

[Example 1] Zn with a Zn-12%Ni alloy plating film formed on its surface in an amount of 20 g/m 2
-Ni alloy plated steel sheets were subjected to black chromate treatment by spraying under the conditions within the scope of the present invention shown in Table 1, then washed with water, and then dried. In this way, Z
Test specimen No. 1 of the black chromate-treated steel sheet of the present invention (hereinafter referred to as the specimen of the present invention) in which a black chromate film was formed on the n-Ni alloy plating film. 1 to 18 were prepared. Invention specimen No. Samples 1 to 13 are specimens in which a black chromate film was formed on the surface of a Zn-Ni alloy plating film.

[0034] Test specimen No. of the present invention. Sample No. 14 of the present invention is specimen No. 14 of the present invention except that no drying treatment is performed. For a steel plate on which a black chromate film was formed by the same treatment as in 1.
A coated chromate treatment solution with a solid content concentration of 20 g/l, a Cr3+/Cr6+ weight ratio of 2/3, and a pH value adjusted to 2.5 with KOH is applied using a roll coater and then dried to coat the surface of the black chromate film. On top, 50mg/
This is a specimen on which a chromate film was formed with a chromium coating amount of m3.

[0035] Test specimen No. of the present invention. Sample No. 15 is the sample of the present invention, except that no drying treatment is performed. For a steel plate on which a black chromate film was formed by the same treatment as in 3.
Acrylic resin aqueous solution (trade name Watersol S744)
(registered trademark) manufactured by Dainippon Ink Co., Ltd.) and then dried to form an organic polymer resin film with a thickness of 1 μm on the surface of the black chromate film.

[0036] Test specimen No. of the present invention. Sample No. 16 of the present invention is the sample of the present invention, except that no drying treatment is performed. For a steel plate on which a black chromate film was formed by the same treatment as in 7.
A lithium silicate (LiO 4,8SiO2) aqueous solution adjusted to a concentration of 50 g/l in terms of SiO2 was applied using a roll coater, dried, and coated onto the surface of the black chromate film at a concentration of 0.3 g/m in terms of SiO2.
This is a specimen on which an alkali silicate film was formed in an amount of 2.

[0037] Test specimen No. of the present invention. Sample No. 17 is the present invention specimen No. 17, except that no drying treatment is performed. An aqueous acrylic resin solution (trade name: Watersol S744 (registered trademark), manufactured by Dainippon Ink Co., Ltd.) was applied to the steel plate on which a chromate film was formed on the surface of the black chromate film by the same process as in step 14, and then dried. This is a specimen on which an organic polymer resin coating with a thickness of 1 μm was formed.

Invention specimen No. Sample No. 18 is the sample of the present invention, except that no drying treatment is performed. 14 A steel plate on which a chromate film was formed on the surface of the black chromate film was subjected to the same treatment as in 14, and 50 g in terms of SiO 2 was added to the steel plate.
Lithium silicate (LiO
・4,8SiO2) aqueous solution was applied using a roll coater and then dried to give 0.3 g/SiO2 equivalent.
This is a specimen on which an alkali silicate film was formed in an amount of m2.

For comparison, a comparative treated steel sheet specimen (hereinafter referred to as comparative specimen ) No. 1 to 9 were prepared.

Comparative specimen No. 1 is NO3 in the bath
- and SO4 2- are not included,
Invention specimen No. This is a specimen subjected to the same treatment as No. 1. Comparative specimen No. 2 is NO3 − in the bath
Sample No. of the present invention except that it does not contain This is a specimen subjected to the same treatment as No. 1. Comparative specimen No. Sample No. 3 is the sample of the present invention, except that SO4 2- is not contained in the bath. This is a specimen subjected to the same treatment as No. 1. Comparative specimen No. 4 is
Inventive specimen No. 1 except that CrO 3 was not contained in the bath. This is a specimen subjected to the same treatment as No. 1. Comparative specimen No. 5 is for electrogalvanized steel sheet,
Invention specimen No. This is a specimen subjected to the same treatment as No. 1. Comparative specimen No. Sample No. 6 is the sample of the present invention, except that the pH value of the bath is higher than the range of the present invention. 1
This is a specimen that underwent the same treatment as .

Comparative specimen No. In No. 7, a Zn-Ni alloy plated steel sheet on which a Zn-12% Ni alloy plating film was formed in an amount of 20 g/m 2 was immersed for 5 seconds in a treatment bath consisting of a 5 wt% nitric acid aqueous solution. By applying, then washing with water and drying,
Except for forming a black film on the surface of the Zn-Ni alloy plating film, specimen No. 1 of the present invention was used. This is a specimen subjected to the same treatment as No. 1. Comparative specimen No. 8 is comparative specimen No. 7, a black film is formed by nitric acid on the surface of the Zn-Ni alloy plating film by immersion treatment, and then an acrylic resin aqueous solution (trade name Watersol S744 (registered trademark), Dainippon Ink Co., Ltd. This is a test piece in which a 1 μm thick organic polymer resin coating was formed by coating the sample with a 1 μm thick organic polymer resin coating. Comparative specimen No. 9 is comparative specimen No. The same treatment as in 7 was performed, and then the solid content concentration was 20 g/l, Cr3+
/Cr6+ weight ratio is 2/3, pH is 2.5 with KOH
A coating-type chromate treatment solution adjusted to 100% was applied using a roll coater and then dried to form a chromate film with a chromium coverage of 50 mg/m3.
(manufactured by Dainippon Ink Co., Ltd.) and then dried to 1μ
This is a specimen on which an organic polymer resin coating with a thickness of m is formed.

[0042] Specimen No. of the present invention prepared in this way
．． 1 to 18 and comparative specimen example No. For each of Nos. 1 to 9, blackness, film adhesion, fingerprint resistance, and corrosion resistance were investigated by performance tests shown in (1) to (5) below. The test results are also shown in Table 1.

(1) Blackness test: The blackness 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 specimen, 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 extremely conspicuous: ×.

(3) Film adhesion test: Cellophane tape was attached to the surface of the specimen, and then
The degree of peeling of the film was visually determined when the film was rapidly peeled off. The evaluation criteria are as follows. No peeling: ◎ Peeling amount less than 10%: ○ Peeling amount 10-30%: △ Peeling amount 31% or more: ×.

(4) Corrosion resistance test ■ A 5% salt spray test was performed on the specimen, 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 performed on the specimen, 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: ×.

0048]

[Table 1]

As is clear from Table 1, the present invention specimen No. All of Nos. 1 to 18 had excellent blackness and film adhesion, and also had good corrosion resistance. and,
Invention specimen No. Samples Nos. 12 to 18 were also excellent in fingerprint resistance.

On the other hand, the chemical composition and pH of the bath
Comparative specimen No. whose value is outside the range of the present invention. Nos. 1 to 6 were all inferior in blackness. Comparative specimen No. 1 had a black film formed with nitric acid on the surface of the Zn-Ni alloy plating film. No. 7 had excellent blackness but poor corrosion resistance. Comparative specimen No. 1, in which a black film made of nitric acid and an organic polymer resin film were formed on the surface of the Zn-Ni alloy plating film. 8 is the present invention specimen No. 8 in which a black chromate film and an organic polymer resin film are formed on the surface of a Zn-Ni alloy plating film. It was inferior in corrosion resistance compared to No. 17.

Inventive specimen No. 1 in which only a black chromate film and an organic polymer resin film were formed on the surface of a Zn-Ni alloy plating film. Comparative specimen No. 17 has a black film made of nitric acid, a chromate film, and an organic polymer resin film formed on the surface of a Zn-Ni alloy plating film. It had almost the same corrosion resistance as No. 9. From this, it is clear that the black chromate coating according to the present invention has better corrosion resistance than the conventional black coating made with nitric acid.

[Example 2] On the surface, 20 g/m
For Zn-Ni alloy plated steel sheet on which Zn-12%Ni alloy plating film was formed in an amount of 1.0 g/
l of CrO 3 , 10 g/l of NO3 − (
(added as HNO 3 ) and 5 g/l S
A black chromate treatment solution containing O4 2- (added as H2 SO4) was used to perform black chromate treatment by spraying, and the relationship between treatment time and blackness (L value) was investigated. FIG. 5 is a graph showing the results. For comparison, 15 g/l CrO 3 , 6 g/l H2 SO4 , 0.6 g/l H3 PO6 disclosed in Japanese Patent Publication No. 61-429
, and containing 1 g/l Ag3 PO4 and p
Using a treatment solution whose H value was adjusted to 0.7, black chromate treatment was performed by spraying, and the treatment time and blackness (L
We investigated the relationship between The results are also shown in FIG.

[0053] As is clear from Fig. 5, the
In the case of the conventional method according to Publication No. 29, the processing time is 1
Even if the processing time is 5 seconds, the blackness (L value) is about 35, whereas in the case of the method of this invention, the processing time is within 5 seconds,
The degree of blackness (L value) was below the target value of 10, and became below 10 within 10 seconds. As described above, according to the method of the present invention, an excellent black chromate film could be formed by a short treatment time of 10 seconds or less.

[0054]

[Effects of the Invention] As described above, according to the present invention,
The following industrially useful effects are brought about. (2) A black chromate-treated steel sheet having a uniform black chromate film with excellent blackness and film adhesion can be economically produced using a low-concentration black chromate treatment liquid. ■ Compared to the conventional black chromate treatment using Ag ion-containing treatment liquid, it takes a shorter time, from several seconds to several tens of thousands of seconds.
It is possible to stably form a black film with a luxurious appearance on the surface of the Zn-Ni alloy plating film in 0 seconds. (2) A black coating with excellent corrosion resistance can be formed compared to the conventional case where a black chemical conversion coating is formed on the surface of a Zn-Ni alloy plating coating using an aqueous nitric acid solution. ■ When a chromate film, an alkali silicate film, or a resin film is further applied on the surface of the black chromate film, excellent fingerprint resistance can be obtained, and the anti-corrosion effect of the black chromate film provides even better resistance. It provides excellent corrosion resistance. ■ In the case of a conventional black film formed by etching, the corrosion resistance that can be obtained only by forming a two-layer protective film, for example, a coated chromate film and a resin film, on the surface of the black film can be achieved with this invention. can be obtained by simply forming a resin film on a black chromate film. Therefore, processing steps can be omitted, and manufacturing costs can be reduced.

[0055]

[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 pH value and film blackness (L value)

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; and Cr.
Cr6+ in an amount of 0.1 to 5.0 g/l in terms of O3
ions, NO3 − ions in an amount of 1 to 50 g/l, and SO4 2− in an amount of 1 to 50 g/l.
and a black chromate film formed on the surface of the Zn-Ni alloy plating film by chemical treatment with a chromate bath containing ions and having a pH of 2.0 or less. Treated steel plate. 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 Zn-Ni alloy plating film is 0.1 to 5 in terms of CrO3. Cr6+ ions in an amount of .0 g/l and NO3 in an amount of 1-50 g/l
- ions and S in an amount of 1 to 50 g/l
By chemically treating with a chromate bath containing O4 2- ions and having a pH of 2.0 or less,
A method for manufacturing a black chromate-treated steel sheet, comprising forming a black chromate film on the surface of the Zn-Ni alloy plating film. 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. The production of a chromate-treated steel sheet according to claim 5, wherein the chemical treatment of the steel sheet on which the Zn-Ni alloy plating film is formed is performed by spraying the chromate bath. Method.