JPS6365086A - Black surface-treated steel sheet and its production - Google Patents

Abstract

PURPOSE:To produce the titled high-quality black suface-treated steel sheet at a low cost by carrying out electrolysis with the steel sheet as a cathode in an aq. acidic soln. consisting essentially of metal ions such as Zn<2+> and Fe<2+>, an oxidizing ion, and a condensed phosphate compd. CONSTITUTION:The aq. acidic soln. at about 1.5-3.0pH consisting essentially of Zn<2+>, >=1 kind among Fe<2+>, Co<2+>, and Cr<2+>, an oxidizing ion, and a condensed phosphate compd. is prepared. The concn. of Zn<2+> as the sulfate is controlled to about 50-300g/l, the concn. of other metal ions is adjusted to about 50-300g/l, NO3<-> is most preferably used as the oxidizing ion, the concn. of NO3<-> is regulated to about 1-20g/l, and a condensed phosphate compd. for supplying an ion such as P2O5<4-> is used. The aq. soln. is used, a steel sheet or a galvanized steel sheet is used as a cathode, and electrolysis is carried out at 5-50A/dm<2> current density and 5-100 coulomb/dm<2> quantity of electricity, and a black coated film is formed in 0.1-50g/m<2> deposition quantity on the cathode. By this method, a black surface-treated steel sheet having excellent appearance, workability, and corrosion resistance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to colored steel sheets, particularly black steel sheets, used for members requiring decoration.

[Conventional technology]

The development of low-cost, high-performance surface-treated steel sheets has been consistently required in the fields of automobile anticorrosive steel sheets, household steel sheets, furniture, and building materials. These required standards are lowering costs year by year,
With the shift toward higher quality, steel manufacturers have developed new technologies and products to meet customer demands. In recent years, by introducing bled steel sheets to products that were previously processed from surface-treated steel sheets and then pre-treated and painted, the pre-treatment and painting that were performed in the customer process can be omitted, resulting in lower costs. There is a growing movement toward using prepainted steel sheets to obtain high-quality products. In order to meet these demands, pre-painted steel sheets have traditionally been used, but due to issues such as thorough cost reduction, high-quality appearance, weldability, and handling scratches, there is a strong demand for inorganic colored steel sheets. It has come.

As for the color tone, there is a strong need for a black color, and in addition to the above-mentioned characteristics, the material is required to be resistant to fingerprints, workability, chemical resistance, and corrosion resistance.

Conventional blackening methods commonly use stainless steel, steel plates, and copper, but galvanized steel plates are suitable for this purpose from the viewpoint of cost and corrosion resistance, so the conventional techniques for blackening them are described below. state

A known technique known as a method for blackening zinc-plated or zinc alloy-plated steel sheets is disclosed in Japanese Patent Application Laid-Open No. 52-455 as a black chromate treatment in an aqueous chromate solution containing silver ions.
There is a method described in Publication No. 44, or a technique described in Jitsugyo Surface Technology Journal, Vol. 32, No. 10, p. 541, Table 3, Table 5, etc.

These methods involve eutectoiding silver oxide with a chromate film to obtain a black surface. A method for obtaining a black appearance by forming sulfides is described in JP-A-52-65139. Furthermore, Japanese Patent Laid-Open No. 58-151490 and Japanese Patent Laid-Open No. 58-151491 disclose a method of blackening by anodic electrolytic treatment. The former is Ni", Go"
, Mo” and Zn2+ in an alloy plating bath, the latter being Ni, C
In this method, oxides of Ni, Co, and Mo are formed by anodizing a steel plate coated with an alloy of o, Mo, and Zn in an aqueous ammonium sulfate solution. Also, JP-A-60-12
No. 1275 discloses that Ni-Z is treated with an aqueous solution of nitric acid or chlorate.
discloses a method of chemically dissolving n alloy plated steel sheets to obtain a black appearance.

In addition, Japanese Patent Application Laid-open No. 60-200996 discloses Zn" and Ni"
This patent discloses a method for blackening an alloy galvanized steel sheet containing 15% or more of Ni by cathodic electrolysis in an alloy plating bath.

[Problem that the invention seeks to solve]

The conventional methods described above are not necessarily the best methods and have many problems.For example, the method using silver ions is expensive and has difficulty in high productivity. In addition, anodizing significantly dissolves the plating on the base, which limits the amount of plating on the base, and it is impossible to re-dissolve the plating once deposited.

In addition, in the method of JP-A-60-200996, since the obtained film is a black alloy plating film of Ni and Zn,
This method is difficult to produce because it requires limited current density and bath temperature to obtain a black color, and the base plating is limited to zinc or zinc-based alloy plating.

The present invention solves these problems and provides a black surface-treated steel sheet manufactured based on a blackening method that is capable of high-speed, short-time processing and does not depend on the underlying metal.

(Means for Solving the Problems) The present invention is a black surface-treated steel sheet obtained by cathodic treatment as described below, and a method for manufacturing the same.

(1) Deposition amount of Zn and oxide consisting of one or more of Fe, Cot Ni, and Cr and phosphate as main components 0.1
A black surface-treated steel sheet characterized by having a black coating of ~5,0 g/rd.

(2) Deposit amount of Zn and oxides and phosphates consisting of one or more of Fe, Co, Ni, and Cr as main components 0.1~
A black surface-treated steel sheet characterized by having a guard coat of 3 g/m or less on the upper layer of a black film of 5.0 g/m.

(3) Zn” and F e”, Co”, N i”.

A method for producing a black surface-treated steel sheet, which comprises electrolyzing a steel sheet or a plated steel sheet as a cathode in an acidic aqueous solution containing one or more types of Cr''+, oxidizing ions, and condensed phosphoric acid compounds as main components.

(4) The oxidizing ions are NO, -, NO2-.

CQO9-,CQO,-fused phosphoric acid compound P2o,'
−.

P , 01a' -+ P 40 x s' -+
4. The method for producing a black surface-treated steel sheet according to item 3, wherein the compound is a compound that supplies condensed phosphate ions represented by PsOxs''-TE.

(5) The current density is 50A/dirr or less and the amount of current is 10
The third characterized in that it is less than or equal to 0 coulomb/drrf.
A method for producing a black surface-treated steel sheet as described in .

The invention is based on a method of blackening by a coating deposited on the cathode from an aqueous solution, the resulting black coating being composed of metal oxides and phosphate chlorides. The black film has a smooth film shape with minute irregularities, and has an L value (lightness; J
A black appearance with an IS Z 8370) of 20 or less can be obtained very easily. Figure 2 shows Zn5O, -7H, O/N after 3μ electrolytic galvanizing on the surface of the steel plate.
iSO4-7H,O/NaNO3/Na5P30. ,”
200/100/40/16 g/Q, pH=1.8
(7) This is a scanning electron microscope (SEM) photograph of the surface of a black surface-treated steel sheet obtained by performing cathodic electrolytic treatment at a current density of 10 A/drrr and 50 coulombs/dbo in an aqueous solution and then washing with water. Figure 3 shows Na, P, and O□ for comparison. This is an SEM photograph of a black surface-treated steel sheet obtained under the same conditions from a bath without adding. Na5P, O. Additive-free materials have a rod-like rough structure, whereas Na, P, and O. It is clear that the additive material has a fine and dense structure.

The black film composition is Zn, an oxide of one or more of Fe, Co, Ni, and Cr, and a phosphate. Phosphate is a condensed phosphate and differs from the crystalline nature of conventional phosphate coatings. In order to obtain sufficient blackness (L value 20 or less), it is necessary to apply electrogalvanizing, Ni-Zn alloy electroplating, and cold-rolled steel sheets, which vary depending on the surface condition of the metal to be treated. This can be achieved by controlling the amount of the deposited film to be 0.1 g/m or more. If the amount of adhesion is too large, the film becomes powdery and adhesion becomes poor. The practical upper limit of adhesion is 5g/
It is rd. The most preferable coating amount is 0.5 to 2.
It is 0g/bo.

FIG. 1 is a configuration diagram of a colored surface-treated steel sheet. S is the base metal material, such as thin steel plate, stainless steel plate, plated steel plate,
Examples include zinc and zinc alloy plated steel sheets, aluminum and aluminum alloy plated steel sheets, tin and lead plated steel sheets. B is a black film layer formed according to the present invention, G is a guard coat, Gc is a chromate film within the guard coat, and Z is a plating layer.

FIG. 1(a) shows an example in which a steel plate is directly colored.

The same figure (b) is an example of colored plated steel plate, the same figure (c) is B
An example is shown in which chromate treatment is performed on the top and a guard coat is applied.

The purpose of the guard coat is to improve quality. For example, applying a guard coat improves the uniformity of the appearance.
The degree of coloring also becomes stronger. Depending on the type and thickness of the guard coat, a steel plate with an appearance ranging from semi-gloss to gloss can be obtained. Also, resistance to scratches is improved. Particularly effective against press, handling, and contact scratches. The effect of improving corrosion resistance is particularly large.

The guard coat of the present invention includes (1) a chemical conversion coating, for example, a coating formed through a chemical reaction such as a chromate coating, a phosphate coating, a chelate coating, (2) a resin coating, (3) an inorganic polymer coating, ( 4) a composite film of resin and inorganic polymer, and (5) oil, oil, fat, wax, etc., and the film is composed of a single film or a multilayer film of these.

Care must be taken to ensure that the amount of guard coat deposited does not harm the appearance or weldability, etc., and the amount of deposit is 3 g /
m or less, preferably 1.5 g/n (or less).

Resin (organic polymer) is a coating made by coating a water-soluble or water-dispersible solvent-soluble organic polymer compound with a curing agent and hardening it by baking, etc., a coating film cured by ultraviolet rays, or a composite film with an inorganic organic compound. This is a film made by coating a composite polymer with a hardening agent if necessary and hardening it by baking or the like. Compounds include chromium compounds, oxides such as silica, titania, alumina, and zirconia, inorganic compounds such as mica, talc, phosphates, and borates, fatty acid soaps, carbon, fatty acid esters,
These are organic compounds for plastic particles, and organometallic compounds such as silane coupling agents and titanium coupling agents.

Examples of inorganic polymers include silicate compounds and sols of sodium silicate and lithium silicate, condensed phosphoric acid polymers, biphosphates, and zirconic acid polymers.

Known oils and oil waxes may be used.

Further, since the black surface-treated steel sheet of the present invention has a thin colored composite plating film and a guard coat, it has the characteristic that it can obtain an appearance and quality that takes advantage of the surface condition of the base metal, such as gloss and roughness.

Hereinafter, the method for manufacturing the black surface-treated steel sheet of the present invention will be described. The components of the treatment bath used in the present invention will be described. The treatment bath of the present invention contains Zn"+ as an essential component, and further contains F s",
It is an aqueous solution containing metal ions selected from Go", Ni", and Cr3+, and further containing oxidizing ions and condensed phosphoric acid compounds as main components. Metal ions are supplied in the form of sulfates, chlorides, sulfamates or metal and oxides, carbonates.

The concentration is 50 g/Q~30 of Zn”+ as sulfate.
0 g/Q, other metal ions also 50 g/Q
The higher the concentration of s Z n ”+, which is ~300 g/Q, the lower the L value can be obtained.The preferred range is Zn” 100 to 200 g/Q, and other metal ions such as Ni8+, 50 to 200 g/fl. , 20-200 g/Q for Fa"+, 20-200 g/Q for Co"'t
2oOg/Q + Cr 3” Te is 5~50g/f
l is preferred.

The ratio of Zn'''' to added second metal ions influences blackness and quality. The sum of all ions of the second metal ions is M
If it is shown as "e", M e"' / Z n "+ ratio is 0.
．． A value of 3 to 1.0 is preferable. If it is less than 0.3, it is likely to be discolored in a subsequent process, for example, due to guard coating or chromate. On the other hand, if it exceeds 2.0, appearance unevenness tends to occur.

The oxidizing ions are NO, -, NO, -.

CQO,- and CQO,- are preferred, and Konouchi NO,- is the most stable and a black film can be easily obtained. The concentration is 1~
20 g/Q is preferred. If it is less than Ig/Q, the blackness is insufficient, and if it exceeds 20 g/Ω, white compounds tend to precipitate on the surface, which tends to cause uneven appearance and poor adhesion, which is not preferable.

Condensed phosphoric acid compounds are P, OS' in which two or more Ps are bonded.
-, P, o, --, P4013'-j p, 012'''
Compounds that supply ions such as sodium salts, potassium salts, calcium salts, magnesium salts, metal salts (Zn,
(Fe, Co, Ni, Cr), the amount added is related to oxidizing ions, NaN0°(A) and VaSP)01
0 In the example of (B), (B)/(A)=1-2 is preferable.

The condensed phosphoric acid compound in the present invention has the effect of smoothing the deposited black film. Figures 2 and 3 mentioned above
A comparison of the figures shows that condensed phosphoric acid has a large effect. The condensed phosphoric acid compound makes the black film smooth and dense, resulting in a semi-glossy surface that improves the appearance and significantly improves adhesion and corrosion resistance. In addition, it co-integrates in the coating as a phosphate and has the effect of strengthening the adhesion with the guard coat.

The pH of the aqueous solution is preferably 1.5 to 3.0. In the present invention, a black surface can be obtained in an extremely wide range (pH 0.7 to 4.0), but the quality of the obtained black film, such as the adhesion In consideration of this, the above-mentioned PI range is preferable.As for the bath temperature, attempts were made in the range of 20 to 60°C, and good black coatings were obtained in all cases.

In the case of the present invention, other compounds may be added if necessary for the following purposes. Various supporting salts to increase the conductivity of solutions, borates, phosphates, and phthalates as pH buffering agents, polymers to improve adhesion processability, and rust prevention and to increase adhesive strength with guard coats. phosphate and chromic acid,
These include inorganic sol compounds, cationic polymers, chelating agents to prevent precipitation, chlorides and fluorine compounds that provide smoothness to the zinc composite plating film to be formed.

The electrolysis conditions will be described below.

The present invention is an extremely superior method that allows selection of conditions over a wide range of blackening areas in a shorter time than conventional methods. The current density is preferably 5 to 50 A/drrr.

If it is less than 5A/drd, coloring is difficult, and if it is less than 50A/d
If it exceeds rd, hydrogen gas will be generated and there is a high risk of unevenness or peeling off of the formed film.0 Current flow is 5 to 100 coulombs/dr
A high quality black film can be obtained with &.

If it is less than 5 coulombs/drr, coloring is difficult and tends to result in an uneven appearance, and if it exceeds 100 coulombs/drrr, a whitish film tends to eutectoid and become uneven.

The surfaces to be treated were cold-rolled steel sheets, zinc alloy-plated steel sheets, galvanized steel sheets, bright galvanized steel sheets, tin-plated steel sheets, etc. As a result, all of them were colored, and in the case of black, cold-rolled steel sheets and zinc alloy-plated steel sheets were black. It was excellent in terms of scratch resistance and scratch resistance.

Coating methods for Guard Coat include well-known roll coating, roll drawing, spraying, air knife drawing,
After applying by dip painting, electrolytic treatment method, electrostatic coating method,
If necessary, heating (hot air, infrared rays, combustion furnace, electric heat) or ultraviolet curing can be employed.

Example 1 Cold rolled steel sheet (symbol S), electrogalvanized steel sheet (symbol E),
Ni (12%)-Zn alloy plated steel plate (symbol NZ),
Fe (20%) -Zn alloy plated steel plate (symbol FZ)
Using Funabashi as a cathode and Funabashi as a counter electrode, electrolytic treatment was carried out in the aqueous solution shown in Table 1, and the quality was evaluated by chemical conversion treatment and coating with an organic polymer film if necessary in a water washer.

N o and l indicate examples outside the scope of the present invention, and Z
This is an example of a black film obtained from a bath in which components C and D are added to the n''+ single bath.If the guard coat is not treated, a uniform appearance with a low value (12) is obtained, but if the guard coat is treated, , the L value increases to 25.

No. 002 is an example outside the scope of the present invention that does not contain component D and has insufficient adhesion. No, 3 to 10 are Z n” and N
In the examples of the present invention in which the concentrations of the C and D components were varied in the i2+ bath and the Dk was varied, black surface-treated steel sheets of good quality were obtained. NO, 11.12 is an example of pH=1.5.

No. 13.14 is an example in which a cold-rolled steel sheet was subjected to black treatment. When the adhesion amount is 5.5 for No. 14, the adhesion is deteriorated. No. 1' 5 to 17 are examples of electrogalvanized steel sheets subjected to blackening treatment. Good results were obtained in all cases.

As shown in N0117, a black color with an L value of 13 can be obtained at 12 coulombs/drrr, and the fact that the amount of current required for blackening is small is a plus. No. 18 is an example of a blackened iron-zinc alloy plated steel sheet.

Example 2 A 12% Ni-Zn alloy plated steel sheet was electrolyzed in the aqueous solution shown in Table 2 in the same manner as in Example 1, coated with a guard coat if necessary, and evaluated.

NO, 19 is F (NaN
In the example of the present invention obtained from a bath containing O, ) and H (NasP30), N o , 20 is F in Zn2+ and Fe''.
, H is added to the bath, NO, 21 is Zn'', Ni'' + C
No. 22 is an example in which o"+ is added. No. 22 is an example in which Cr"+ is added. All of No. 19 to No. 22 showed good quality black surface treatment coating performance. NO, 23 is NaN0.23 as an oxidizing ion. Example of using KCQO4 in combination with NO, 24 is Na, P as condensed phosphoric acid.

In the present invention example using 0□, NO, 25 is Ni24''.

NO, 23 to 25, which are examples in which Fe''+ was present, were excellent in quality. NO, 26 is an example in which the pH was increased, resulting in poor adhesion and uniformity. No. 27 with lowered pH is good.

N'o, 28 was an example in which the Dk was rated at 70 A/d, and the appearance was uneven. NO, 29-31 are N iN + /
N0029 is an example in which the Z n” ratio is changed from 0.33 to 2.0.
However, the uniformity of appearance was slightly inferior.

Example 3 Electrolytic zinc plating (fabric weight 20
g/m2), cathodic electrolytic treatment was performed in baths A and B shown below to form a black film, and then the chemical treatment of Example 1 was performed to form the organic and silica composite resin 1 of Example 1.
, 3 and 5 g/m and baked to obtain black surface-treated steel sheets.

A bath (h Shu, ・7H20/N handle, ・Han0/N seaweed=2■/
10015g/Q, PH=1.8) B bath (l'1 in A bath
asp3oID Log/' R added bath, PH=1
．． 8) Electrolysis conditions: IOA/di”, 50 coulombs/
d♂ Chemical: Total chromium deposition amount 20mg/♂A bath material had a slightly white finish with an L value of 19 to 25 after guard coating, whereas B bath material had an L value of 12 to 15 and a semi-gloss appearance. Ta. In terms of spot weldability, the organic silica composite resin has a large effect, and 5 g/rd material cannot be welded, while 1 glr
Continuous spot welding was possible for the rr material. 3g/rr
f had a defective rate of 20%.

〔Effect of the invention〕

The colored zinc composite plated steel sheet according to the present invention has a quality appearance,
As a new steel sheet with excellent workability, corrosion resistance, and strong resistance to scratches, it can be used in the field of conventional coated steel sheets, contributing to higher quality products and lower costs.

In addition, a wide range of processing conditions can be applied to manufacturing, and high-speed, short-time processing is possible, so processing can be performed within a conventional electroplating line, and manufacturing can be performed at low cost.

In particular, the present invention is advantageous over conventional alloy plating or alloy melting methods in that blackening does not depend on the base metal and a wide range of surfaces can be easily blackened with a small amount of current.

[Brief explanation of drawings]

FIGS. 1(a), (b), and (C) are diagrams showing the structure of the black surface-treated steel sheet of the present invention. FIG. 2 shows a surface micrograph of the black surface-treated steel sheet of the present invention, and FIG. 3 shows a surface micrograph of the surface treated using a bath to which no condensed phosphoric acid was added. Arithmetic 1 Kyou (α) (b) (C)n
L figure Me35o et al. 3 circles, 350°

Claims (5)

[Claims] (1) Deposit amount of Zn and oxides and phosphates consisting of one or more of Fe, Co, Ni, and Cr as main components 0.1~
A black surface-treated steel sheet characterized by having a black coating of 5.0 g/m^2. (2) Deposit amount of Zn and oxides and phosphates consisting of one or more of Fe, Co, Ni, and Cr as main components 0.1~
A black surface-treated steel sheet characterized by having a guard coat of 3 g/m^2 or less on the upper layer of a black film of 5.0 g/m^2. (3) Zn^2^+ and Fe^2^+, Co^2^+, N
A black surface-treated steel sheet characterized by electrolysis using a steel sheet or plated steel sheet as a cathode in an acidic aqueous solution containing as main components one or more of i^2^+, Cr^3^+, oxidizing ions, and a condensed phosphoric acid compound. manufacturing method. (4) Oxidizing ions are NO_3^-, NO_2^-, C
lO_4^-, ClO_3^- condensed phosphoric acid compound is P_
2O_7^4^-, P_3O_1_0^5^-, P_4
The method for producing a black surface-treated steel sheet according to claim 3, wherein the compound is a compound that supplies condensed phosphate ions represented by O_1_3^6^- and P_6O_1_9^8^-. (5) The current density is 50A/dm^2 or less and the amount of current is 10
4. The method for producing a black surface-treated steel sheet according to claim 3, characterized in that it is 0 coulomb/dm^2 or less.