JPH0359996B2 - - Google Patents

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. [Prior Art] The development of low-cost, high-performance surface-treated steel sheets has been consistently required in the fields of automobile rust-proofing steel sheets, household steel sheets, furniture, and building materials. These requirements have shifted to lower costs and higher quality year by year, and steel manufacturers have developed new technologies and products to meet the demands of customers. In recent years, by introducing pre-coated steel sheets to products that were conventionally 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. There is a growing movement towards the use of pre-painted steel sheets to obtain high-quality products at low cost. In order to meet these demands, pre-painted steel sheets have been used in the past, but due to cost reduction, high quality appearance, weldability and handling scratches, there is a growing demand for inorganic colored steel sheets. I've become stronger. 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.
The conventional technology related to the blackening will be described below. Known techniques for blackening zinc-plated or zinc-alloy plated steel sheets include the method described in Japanese Patent Application Laid-Open No. 52-45544, or the method described in Jitsugyo Surface Technology 32, in which black chromate is treated in an aqueous chromate solution containing silver ions. There are techniques described in Vol. 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. or,
JP-A-58-151490 and JP-A-58-151491
The publication discloses a method of blackening by anodic electrolytic treatment. The former is Ni ²⁺ , Co ²⁺ , Mo ²⁺ and Zn ²⁺
The latter method involves forming oxides of Ni, Co, and Mo by anodizing a Ni, Co, Mo, and Zn alloy plated steel sheet in an aqueous ammonium sulfate solution. Furthermore, Japanese Patent Application Laid-Open No. 121275/1983 discloses a method for obtaining a black appearance by chemically dissolving a Ni--Zn alloy plated steel sheet in an aqueous solution of nitric acid or chlorate. Furthermore, JP-A-60-200996 discloses a method of blackening an alloy galvanized steel sheet containing 15% or more of Ni by cathodic electrolysis in an alloy plating melt of Zn ²⁺ and Ni ²⁺ . . [Problems to be Solved by the Invention] The conventional methods described above are not necessarily the best methods and have many problems. For example, methods using silver ions are expensive and have difficulty in achieving high productivity. In addition, anodizing significantly dissolves the plating on the substrate, which limits the plating on the substrate, and it is difficult to re-dissolve the plating once deposited. In addition, in the method of JP-A-60-200996, the resulting film is a black alloy plating film of Ni and Zn, so in order to obtain a black color, the current density must be limited, the bath temperature, and the base plating must be zinc or zinc. This method is difficult to produce as it is limited to plating based on alloys. 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) It is characterized by having a black film with a coating weight of 0.1-5.0 g/m ² mainly composed of Zn and an oxide consisting of one or more of Fe, Co, Ni, and Cr and an amorphous condensed phosphoric acid compound. Black surface treated steel sheet. (2) The upper layer of a black film with a coating weight of 0.1-5.0 g/m ² mainly composed of Zn and an oxide consisting of one or more of Fe, Co, Ni, and Cr and an amorphous condensed phosphoric acid compound. A black surface-treated steel sheet characterized by having a guard coat of ^m2 or less. (3) Zn ²⁺ 50−300g/, Fe ²⁺ ,
The total amount of one or more types of Co ²⁺ , Ni ²⁺ Cr ²⁺ is 50-300 g/in terms of sulfate, and the oxidizing ion is 1-20
g/ and Na ₅ P ₃ O ₁₀ /NaNO ₃ conversion ratio of 1-
3 g/m 2 or less when electrolyzed at a current density of 5-100 clones/dm ² at a current density of 5-50 A/dm ² using a steel plate or a plated steel plate as a cathode in an acidic aqueous solution containing a condensed phosphoric acid compound as a ^main component. A method for producing a black surface-treated steel sheet, the method comprising coating a steel sheet with a guard coat. (4) Oxidizing ions are NO ₃ ^- , NO ^2- , ClO ₄ ^- ,
ClO ₃ ^- , condensed phosphoric acid compounds are P ₂ O ₇ ^4- , P ₃ O ₁₀ ^5- ,
A method for producing a black surface-treated steel sheet, characterized in that the compound is a compound that supplies condensed phosphate ions represented by P ₄ O ₁₃ ^6- and P ₆ O ₁₉ ^8- . The invention is based on a method of blackening by a coating deposited on the cathode from an aqueous solution, the resulting black coating consisting of a metal oxide and a condensed phosphate compound of pumorphus. The black film is a smooth film with fine irregularities, and has an L value (lightness;
A black appearance with JIS Z 8370) of 20 or less can be obtained extremely easily. Figure 2 shows ZnSO 4 7H 2 O/ZnSO ₄ 7H ₂ O/
NiSO ₄・7H ₂ O／NaNO ₃ ／Na ₅ P ₃ O ₁₀ = 200／
100/10/16 g/, scanning electron scanning of the surface of a black surface-treated steel plate obtained by performing cathodic electrolysis treatment at a current density of 10 A/dm ² and 50 coulombs/dm ² in an aqueous solution of PH = 1.8, followed by washing with water. This is a microscopic (SEM) photograph. 3 is a SEM photograph of a black surface-treated steel sheet obtained under the same conditions from a bath without adding Na ₅ P ₃ O ₁₀ as in FIG. 3. It is clear that the Na ₅ P ₃ O ₁₀ -added material has a rod-like rough structure, while the Na ₅ P ₃ O ₁₀ -added material has a fine and dense structure. The composition of the black coating is Zn and one or more oxides of Fe, Co, Ni, and Cr, and an amorphous condensed phosphate, which is different from the crystalline structure of conventional phosphate coatings. In order to obtain a sufficient degree of blackness (L value 20 or less), it is necessary to use conventional electrolytic galvanizing, Ni-Zn alloy plating, and cold-rolled steel sheets, although this varies depending on the surface condition of the metal to be treated. This can be achieved by increasing the amount of the deposited film to 0.1 g/m ² 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 5 g/m ² . The most preferable coating amount is 0.5 to 2.0 g/m ² . FIG. 1 is a configuration diagram of a colored surface-treated steel sheet. S
is the base metal substrate, such as thin steel plate, stainless steel plate, plated steel plate, such as zinc and zinc alloy plated steel plate, aluminum and aluminum alloy plated steel plate, tin, and lead plated steel plate. B is a black film layer formed according to the present invention, G is a guard coat, and Gc
indicates the inner chromate coating of the guard coat, and Z indicates the plating layer. Figure 1a shows an example in which a steel plate is directly colored. Figure b shows an example in which a plated steel plate is colored, and figure c shows an example in which B is subjected to chromate treatment and coated with a guard coat. The purpose of the guard coat is to improve quality. For example, by applying a guard coat, the uniformity of the appearance improves and the degree of coloration 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 chemical conversion coatings, such as chromate coatings, phosphate coatings, chelate coatings, etc. that are formed through chemical reactions, 2 resin coatings, 3 inorganic polymer coatings, and 4 composites of resin and inorganic polymers. These are coatings, 5 oils, fats and waxes, and are composed of single or multi-layered coatings of these. It is necessary to consider the amount of guard coat deposited so as not to harm the appearance, weldability, etc., and the deposit amount is 3 g/m ² or less, preferably 1.5 g/m ² 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., or a coating film cured by ultraviolet rays, or an inorganic organic compound. It is a film made by coating a composite polymer together 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, and organic compounds such as plastic particles. , silane coupling agents, titanium coupling agents, and other organometallic compounds. 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 fat waxes may be used. In addition, since the black surface-treated steel sheet of the present invention has a thin colored composite plating film and a thin guard coat,
It has the characteristic of being able to 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 processing bath components used in the present invention will be described. The treatment bath of the present invention contains Zn ²⁺ as an essential component, further contains metal ions selected from Fe ²⁺ , Co ²⁺ , Ni ²⁺ , and Cr ³⁺ , and further contains oxidizing ions and condensed phosphate compounds. This is water welding whose main component is Metal ions are supplied in the form of sulfates, chlorides, sulfamates or metal and oxides, carbonates. The concentration is 50g/~300g/Zn ²⁺ as sulfate.
, other metal ions are also 50g/~300g/. A higher Zn ²⁺ concentration results in a surface with a lower L value. The preferred region is Zn ²⁺ 100-200
g/, other metal ions such as Ni ²⁺
50 to 200 g/l, 20 to 200 g/l for Fe ²⁺ , 20 to 200 g/l for Co ²⁺ , and 5 to 50 g/l for Cr ³⁺ are preferable. The ratio of Zn ²⁺ and added second metal ions affects blackness and quality. When the sum of all second metal ions is expressed as Me ⁿ⁺ , the Me ⁿ⁺¹ /Zn ²⁺ ratio is 0.3.
~1.0 is preferred. If it is less than 0.3, discoloration is likely to occur in the subsequent process. For example, the color changes due to guard coat or chromate. On the other hand, if it exceeds 2.0, appearance unevenness tends to occur. Oxidizing ions include NO ₃ ^- , NO ₂ ^- , ClO ₄ ^- ,
ClO ₃ ⁻ is preferable, and among these, NO ₃ ⁻ is the most stable and can easily form a black film. The concentration is 1-20g/
is preferred. If it is less than 1 g/l, the blackness is insufficient, and if it exceeds 20 g/l, white compounds tend to precipitate on the surface, resulting in uneven appearance and poor adhesion, which is not preferable. Condensed phosphoric acid compounds have two or more P bonded together.
Compounds that supply ions of P ₂ O ₅ ^4- , P ₃ O ₁₀ ^5- , P ₄ O ₁₃ ^6- , P ₆ O ₁₃ ^8- such as sodium salts, potassium salts, calcium salts, magnesium salts, metal salts (Zn , Fe, Co, Ni, Cr). The amount added is related to the oxidizing ions, NaNO ₃ (A) and Na ₅ P ₃ O ₁₀
In the example of (B), (B)/(A)=1 to 2 is preferable. The condensed phosphoric acid compound in the present invention has the effect of smoothing the deposited black film. From the comparison of FIGS. 2 and 3 described above, it can be seen that the effect of condensed phosphoric acid is large. The condensed phosphoric acid compound makes the black film smooth and dense, resulting in a semi-glossy surface that improves the appearance value and significantly improves adhesion and corrosion resistance. In addition, it is co-contained as a phosphate in the coating and has the effect of strengthening the adhesion with the guard coat. The pH of the aqueous solution is preferably 15 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 in consideration of the quality of the obtained black film, such as adhesion, the above-mentioned PH 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 buffers, polymers to improve adhesion processability, and rust prevention and to increase adhesive strength with guard coats. These include phosphates, chromic acid, 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/dm ² .
Coloring is difficult at less than 5 A/dm ² . Also, 50A/
If the temperature exceeds dm ² , hydrogen gas will be generated, and there is a high risk that the film will become uneven and come off. A high-quality black film can be obtained when the amount of current is 5 to 100 coulombs/dm ² . 5
If it is less than coulomb/dm ² , coloring is difficult and tends to give an uneven appearance. Also, at over 100 coulombs/ ^dm2 ,
The whitish film tends to eutectoid and becomes uneven. As a result of attempts to treat cold rolled steel plates, zinc alloy plated steel plates, galvanized steel plates, bright galvanized steel plates, tin plated steel plates, etc., all surfaces were colored, and in the case of black,
Cold-rolled steel sheets and zinc alloy plated steel sheets were superior in terms of blackness and scratch resistance. Guard coat coating methods include roll coating, roll squeezing, spraying, air knife squeezing, dipping, electrolytic treatment, and electrostatic coating, followed by heating (hot air, infrared rays, incineration furnace, Electric heating) or ultraviolet curing can be used. Example 1 Cold rolled steel sheet (symbol S), electrogalvanized steel sheet (symbol E), Ni (12%)-Zn alloy plated steel sheet (symbol
NZ), Fe (20%)-Zn alloy plated steel sheet (symbol FZ)
Using a lead electrode as a cathode and a lead electrode as a counter electrode, electrolytic treatment was carried out in the aqueous solution shown in Table 1, and after washing with water, chemical conversion treatment and organic polymer coating were applied as necessary to evaluate the quality. No. 1 shows an example outside the scope of the present invention.
This is an example of a black film obtained from a bath in which C and D components were added to a Zn ²⁺ bath alone. Without guard coat treatment, a uniform, low L value (12) appearance is obtained, but with guard coat treatment, the L value increases to 25. No. 2 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 C and D in Zn ²⁺ and Ni ²⁺ baths.
In the examples of the present invention in which the concentrations of components and Dk were varied, black surface-treated steel sheets of good quality were obtained. Nos. 11 and 12 are examples of PH=1.5. Nos. 13 and 14 are examples of cold-rolled steel sheets subjected to black treatment. When the adhesion amount is 5.5 for No. 14, the adhesion has deteriorated. No.15〜
17 is an example of an electrogalvanized steel sheet that has been blackened. Good results were obtained in all cases. As shown in No. 17, a black color with an L value of 13 can be obtained at 12 coulombs/dm ^{2 ,} and the fact that the amount of current required for blackening is small is a plus. No. 18 is an example of blackened iron-zinc alloy plated steel sheet. Example 2 A 12% Ni-Zn alloy plated steel plate 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 contains F (NaNO ₃ ) and H in Zn ²⁺ and Ni ²⁺ baths.
(Na ₅ P ₃ O ₁₀ ) was added to the bath.
No. 20 is a bath with F and H added to Zn ²⁺ and Fe ²⁺ , No. 21
No. 22 is an example in which Co ²⁺ is added to Zn ²⁺ and Ni ²⁺ , and No. 22 is an example in which Cr ³⁺ is added. Nos. 19 to 22 all showed good quality black surface treatment coating performance. No. 23 is an example of using NaNO ₃ and KClO ₄ together as oxidizing ions, No. 24
No. 25 shows an example of the present invention in which Na ₈ P ₆ O ₁₉ was used as condensed phosphoric acid, and No. 25 shows an example in which Ni ²⁺ and Fe ²⁺ were coexisting.
Nos. 23 to 25 were obtained with excellent quality. No.26
is an example of a high pH, resulting in poor adhesion and uniformity. No. 27 with lower pH is good. No.28 is
In the example where Dk was set to 70A/dm ² , the appearance was uneven.
Nos. 29 to 31 are examples in which the Ni ²⁺ /Zn ²⁺ ratio was changed from 0.33 to 2.0, and No. 29 showed slightly inferior results in uniformity of appearance. Example 3 The surface of a cold-rolled steel sheet was electrolytically galvanized (basis weight 20 g/m ² ) from a sulfuric acid bath, and then subjected to cathodic electrolytic treatment in baths A and B shown below to form a black film. The chemical treatment of Example 1 was carried out, and the organic and silica composite resins of Example 1 were applied at a target of 1, 3 and 5 g/m ² and baked to obtain a black surface-treated steel sheet. Bath A (ZnSO ₄ 7H ₂ O/NiSO ₄ 7H ₂ O/NaNO ₃ = 200/100/5 g/, PH = 1.8) Bath B (Bath with Na ₅ P ₃ O ₁₀ 10 g/added to Bath A, PH =
1.8) Electrolytic conditions: 10 A/dm ² , 50 coulombs/dm ² Chemical: Total chromium deposition amount 20 mg/m ² The A bath material had a slightly white finish with an L value of 19 to 25 after guard coating, while the B bath material obtained a semi-gloss appearance with an L value of 12-15. The spot weldability was greatly affected by the organic silica composite resin, and the 5 g/m ² material could not be welded, while the 1 g/m ² material could be continuously spot welded. 3g/m ² had a defective rate of 20%.

【table】

【table】

〔Effect of the invention〕

The colored zinc composite plated steel sheet according to the present invention has excellent appearance, workability, and corrosion resistance, and can be used as a new steel sheet with strong resistance to scratches in the field of conventional coated steel sheets, resulting in higher quality products and lower costs. To contribute. 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. 1a, 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.

Claims (1)

[Claims] 1. A black film with a coating weight of 0.1 to 5.0 g/m ² mainly composed of Zn and an oxide of one or more of Fe, Co, Ni, and Cr and an amorphous condensed phosphoric acid compound. A black surface-treated steel sheet having the following features. 2. On the upper layer of a black film with a coating weight of 0.1-5.0 g/ ^m2, the main components are an oxide consisting of Zn and one or more of Fe, Co, Ni, and Cr, and an amorphous condensed phosphoric acid compound.
A black surface-treated steel sheet characterized by having a guard coat of g/m ² or less. 3 Zn ²⁺ 50-300g/, Fe ²⁺ ,
The total amount of one or more of Co ²⁺ , Ni ²⁺ Cr ²⁺ is 50-300g/in terms of sulfate, and the oxidizing ion is 1-20g/
and a current density of 5 using a steel plate or a plated steel plate as a cathode in an acidic aqueous solution mainly composed of a condensed phosphoric acid compound with a Na ₅ P ₃ O ₁₀ /NaNO ₃ conversion ratio of 1-2.
- A method for producing a black surface-treated steel sheet, which comprises electrolyzing 5-100 clones/dm ² at 50 A/dm ² and coating it with a guard coat of 3 g/m ² or less. 4 Oxidizing ions are NO ₃ ^- , NO ₂ ^- , ClO ₄ ^- ,
ClO ₃ ^- , condensed phosphoric acid compounds are P ₂ O ₇ ^4- , P ₃ O ₁₀ ^5- ,
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 P ₄ O ₁₃ ^6- and P ₆ O ₁₉ ^8- .