JP3230907B2 - Method for producing blackened steel sheet excellent in productivity and blackening - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a blackened steel sheet having a blackened layer having a uniform appearance and used in the fields of building materials, home appliances, automobiles and the like.

[0002]

2. Description of the Related Art At present, steel sheets having a blackened surface are widely used for home appliances, copying machines, information communication devices, automobile parts, interior building materials and the like. As a method for producing this black steel sheet,
There are (1) black coating, (2) chemical treatment, (3) black chromate, (4) anodizing, and (5) cathodic. Above all, the anodizing method is an industrial production method disclosed in JP-B-61-60915 and JP-B-63-46158.
And JP-B-63-46159.

The anodizing method is industrially disadvantageous in comparison with the cathodic method because a part of the alloy component is eluted into the electrolytic solution from the zinc alloy plating layer once formed on the steel sheet and colored. The top adhesion and the uniformity of appearance are advantageous over other methods. In order to provide a method for producing a black-treated steel sheet having a uniform colored layer without being affected by the conditions of the base plating, the present inventors have proposed a new method for producing a colored-treated steel sheet (Japanese Unexamined Patent Publication No. 04-143293). Gazette).

[0004] However, when production on a commercial scale was started under these conditions, the following problems occurred. Generation of metal hydroxides such as zinc during production Dropout of substances formed on the cathode, etc. Generation of spark marks

[0005] As the production increases, Zn accumulates in the electrolyte due to anodization. On the cathode side, the pH of the electrolyte rises due to the generation of hydrogen, so that pH adjustment is required. The pH is adjusted when the electrolytic solution returns from the electrolytic tank to the storage tank, so that a time delay occurs, and the pH of the electrolytic tank becomes higher than that of the storage tank. Therefore, as the amount of Zn accumulates, in the electrolytic cell, a hydroxide of Zn is formed due to a rise in the pH, and floats in the liquid without gradually disappearing, adheres to the roll, and causes the generation of defect scratches due to foreign matter biting. Becomes At this time, what adheres to the cathode and the like in a state where the alloy component is not completely reduced to the metal may fall off and adhere to the roll, thereby damaging the steel sheet.

[0006] In the horizontal electrolytic cell, conductor rolls are arranged on the entrance side and the exit side to supply electricity. However, when electricity is supplied to both sides during the blackening treatment, small metallic glossy defects due to spark marks are generated on the steel sheet surface on the exit side of the electrolytic cell. When the entire current is supplied to the input-side conductor roll, the steel sheet generates heat due to Joule heat, which becomes remarkable particularly when the sheet thickness is reduced, and also increases the temperature of the electrolytic solution, which adversely affects the black appearance. Therefore, in order to produce while maintaining a good black appearance, the production speed is forced to half the capacity.

[0007] In order to ensure a certain level of quality, such a problem is solved. When the Zn concentration in the solution exceeds a certain value, the electrolyte is replaced with a new one. Measures were taken to reduce the capacity to half of its capacity. With such measures, the downtime of production was large and the operating speed could not be increased, and it was difficult to improve productivity.

In order to solve such a problem, it is conceivable to provide facilities such as adding a Zn removing device and an electrolytic cell, but this is not economically easy such as capital investment. Japanese Patent Application Laid-Open No. 04-17695 has been proposed, but it is difficult to maintain and manage the steel sheet indirectly by spraying an acid or alkali onto an energizing roll, and it is easy to cause unevenness in the width direction due to decolorization. There were problems such as becoming.

As described above, on the cathode side, the pH in the electrolyte rises due to the generation of hydrogen gas, and the eluted zinc forms a hydroxide, which floats in the electrolyte and bites as foreign matter on the roll. Defects such as intrusion occur. To this problem
On the other hand, it is conceivable to lower the pH of the electrolytic solution.
However, when the pH is lowered, the surface roughness after electrolysis becomes coarse due to the influence of etching, and the gloss is lost. In addition, the blackening layer is scraped off by the etching, the black coating is decolorized, and the appearance defect factors such as the problem of nonuniform appearance in the width direction increase. It was difficult to solve these problems.

[0010]

SUMMARY OF THE INVENTION Accordingly, the present invention solves the above-mentioned various problems, improves the production rate by lowering the pH of the electrolyte, and increases the metal hydroxide and spark generated in the production. Blackening-treated steel sheet of the same or better quality than conventional ones by reducing the factor of plating defects due to marks etc. and remarkably reducing the amount of power consumption, while compensating for the deterioration of the surface appearance due to pH drop with resin chromate coating An object of the present invention is to provide a method for producing the same.

[0011]

That is, according to the present invention, a zinc-based alloy-coated steel sheet is prepared by adding 5 to 100 g / l of chlorate ion (ClO ₃ ⁻ ) and 10 to 300 g / l of SO ₄ ²⁻ ion.
1 and anodized in a solution having a pH of 0.5 to 2.5 at a temperature of 30 to 75 ° C. and a quantity of electricity of 10 to 300 coulombs / dm ² , and further disperse an aqueous acrylic resin on an anodized steel sheet. An object of the present invention is to provide a method for producing a blackened steel sheet having excellent chromatographic properties, in which a chromate layer is formed in a thickness of 0.3 to 2.5 μm.

Here, the above-mentioned solution is further used as an additive aid in Cl ⁻ , NO ₃ ⁻ , H ₂ O ₂ , Ni ²⁺ , Co ²⁺ , F 2.
It is preferable that at least one selected from the group consisting of e ²⁺ and Mn ²⁺ be contained in a total amount of 5 to 100 g / l. Further, it is preferable that the ratio of the acrylic resin to Cr in the aqueous acrylic resin-dispersed chromate layer is 2 to 10 parts by weight of Cr based on 100 parts by weight (dry weight) of the acrylic resin.

[0013]

The present invention is characterized in that, while accepting an increase in external disturbance factors due to a drop in pH, a purpose is found for solving the production problems. That is, if the pH is lowered, the roughness and gloss change, which is rejected as a conventional user complaint, and the responsibility for supplying products of the same quality is required. However, it is necessary to make full use of production capacity to reduce costs. Therefore, as a result of intensive research, it was found that the problem of appearance due to a decrease in pH could be solved by forming a resin chromate layer on the upper layer of the anodized steel sheet, and this was greatly promoted. The specific configuration will be described below.

In the present invention, a blackened steel sheet is manufactured by anodizing a zinc-based alloy-plated steel sheet in an electrolytic solution. After anodizing, a resin chromate layer is formed. Examples of the zinc-based alloy plating include Zn-Ni, Zn-Fe, Zn
-Co, Zn-Mn or other binary alloy plating, or Z
n-Ni-Co, Zn-Ni-Fe, Zn-Co-F
e, Zn-Fe-P, Zn-Ni-P of any and ternary alloy plating Ru can be mentioned typically.

The electrolytic solution used for the anodization contains 5 to 100 g / l of chlorate ions (ClO ₃ ⁻ ) and 10 to 300 g / l of SO ₄ ^2- ions, and the pH is 0.5 to 2.5 g / l.
It is as follows. Conditions for electrolysis using this electrolytic solution are as follows: the temperature of the electrolytic solution is 30 to 75 ° C., and the amount of electrolytic electricity is 10 to 300 coulombs / dm ² . This electrolyte solution is Cl
^{_{-, NO 3 -, H 2}} O 2, Ni 2+, Co 2+, 5 in total of one or more selected from the group consisting of Fe ²⁺ and Mn ²⁺
It is preferred that it contains 〜100 g / l.

On a steel plate blackened by anodic electrolysis,
It is preferable to form a water-based acrylic resin dispersion chromate layer. The ratio of the acrylic resin to Cr in the resin chromate layer was such that Cr was 2-1 to 100 parts by weight of the acrylic resin.
It is preferably 0 parts by weight.

The water-based acrylic resin-dispersed chromate layer in the present invention means, for example, a layer formed by applying an aqueous solution obtained by mixing an aqueous solution of an acrylic resin and an aqueous solution of chromic acid to a steel plate and drying.

Next, the reasons for limiting the respective constituent requirements will be described. 5 g / l of ClO ₃ ^- ions in the electrolyte
If it is less than 100 g / l, the contribution of the blackening treatment is small, and if it is more than 100 g / l, drag-out (carrying out the chemical solution by the steel plate) is not economical in continuous treatment of the steel strip. When used as a halide, Na, K, NH ₄ , Ca, M
The use of g or the like alone or in combination of two or more does not affect the blackening effect, but it is preferable to use the Na salt because the Na salt has high solubility and is inexpensive.

The reason for containing SO ₄ ^2- in an amount of 10 to 300 g / l is to promote the dissolution of the Zn-based alloy plating and to facilitate the elution of alloy components such as Ni, Co, Fe and Mn which are particularly necessary for blackening. It is mentioned. If it is less than 10 g / l, no effect on dissolution can be expected, and the pH buffering property is poor and the pH fluctuation is large. On the other hand, if it exceeds 300 g / l, dragging out in continuous treatment of steel strip is large and it is not economical, and piping and the like are clogged due to a decrease in temperature in winter, which is not preferable.
As the SO ₄ ^- ion source, Na ₂ SO ₄ , K ₂ S
O ₄ , (NH ₄ ) ₂ SO ₄ , CaSO ₄ , and MgSO ₄ are preferred because of their high solubility.

The pH is preferably in the range of 0.5 to 2.5. More preferably, the pH is from 1 to 2.0. If the pH is less than 0.5, etching with an acid is strong and proceeds more than necessary, causing uneven coloring, and even if a resin chromate layer is formed on the upper layer, it is not preferable because the restoration becomes impossible. In addition, pH 2.5
When it becomes excessive, as shown in FIG. 1, the amount of electricity for obtaining the same L value sharply increases, which is a factor of productivity hindrance.
That is, in order to obtain the same appearance, a small amount of electricity is required on the low pH side, so that the production speed can be improved in proportion to the amount of electricity. This is because pH 2.5
This is because, when the value exceeds 2, the effect of dissolution of zinc by etching is extremely reduced, and dissolution by electrolysis becomes dominant. The Zn-based alloy-plated steel sheet used in FIG.
% Ni alloy plated steel sheet, and the composition of the electrolytic solution is ClO ₃
^- 50 g / l, a SO ₄ ^2- 100g / l. The bath temperature is 50 ° C.

Further, a complex compound of zinc and a sulfate and hydroxide of an alloy component is formed on the surface of the blackening treatment. When this layer is thick, it has a white appearance and does not become a black film. This composite compound is an electrical insulator,
It causes spark marks. Metal complex compound in FIG. 2 ((Zn, Ni) · (SO 4) x · (OH) y · zH 2
Looking at the transition of S, which is an element in O), it can be seen that S decreases on the low pH side when compared with the same amount of electricity. From this result, by setting the pH of the electrolytic solution to 2.5 or less, more preferably 2.0 or less, the amount of the metal composite compound attached to the steel sheet surface is reduced, and a spark mark is generated on the exit side of the electrolytic cell. , And electricity can be supplied to both sides of the electrolytic cell on the inlet and outlet sides, that is, the production speed can be greatly increased. The Zn-based alloy-plated steel sheet used in FIG.
-12% Ni alloy plated steel sheet, the composition of the electrolyte is C
lO ₃ ^- 50g / l, a SO ₄ ^2- 100g / l. The bath temperature is 50 ° C., and the quantity of electricity is 100 C / dm ² .

The pH is adjusted by H ₂ SO ₄ , HCl, HNO
₃ , can be carried out using a mineral acid such as HClO ₃ , a halogen acid or the like, but is not limited thereto as long as the object of the present invention is achieved.

The solution used for anodizing is the above-mentioned ClO
₃ ^- in addition to Cl as an additive aids ^{_{-, NO 3 -, H 2}} O
₂ , one of Ni ²⁺ , Co ²⁺ , Fe ²⁺ , and Mn ²⁺
Species or two or more, more preferably, Ni ²⁺ , Co ²⁺ ,
Fe ^2+, Mn ^2+, and one or two of H ₂ O ₂
It is preferable to use, as a auxiliaries, those containing a total of 5 to 100 g / l of at least seeds in order to improve blackness. However, if it is less than 5 g / l, the contribution of the blackening treatment is small, and if it exceeds 100 g / l, drag-out is large in continuous treatment of the steel strip, which is not economical. Further, the contribution of the blackening process is small and the L value is large. The reason why these are effective as an auxiliary agent for improving the degree of blackening is that Zn-based alloy plating layers are easily eluted as Zn, Ni, Co, Fe, and Mn ions, and metal ions required for the blackening layer are blackened. It is considered that it is supplied to the interface of the treated steel sheet. Cl ^-, NO ₃ ^- as a source of acid or their Na salts, Ka salts, ammonium salts and the like, but is not limited thereto. Examples of the source of Ni ²⁺ , Co ²⁺ , Fe ²⁺ , and Mn ²⁺ include, but are not limited to, sulfates, chlorides, and nitrates.

Among zinc-based alloy-plated steel sheets, Zn
-Ni alloy plated steel sheet is suitable for obtaining a low-cost base material because the production amount is large and the quality is stable. The Ni content supplied to automobiles falls within the range of 10 to 15%, and in this range, it is excellent in corrosion resistance, plating adhesion, and workability, so it is suitable as a target steel plate for blackening treatment. is there. In addition, Zn-Fe alloy plated steel sheet, Zn-
Co alloy-plated steel sheets, Zn-Mn alloy-plated steel sheets and the like are also used.

At the time of the anodic treatment, it is necessary to determine the optimum amount of electricity with respect to the basis weight of the underlying plating. The basis weight of a Zn—Ni alloy plated steel sheet usually produced for an automobile is 20 to 40 g / m ² per one side of the steel sheet, and when this is used, the optimal quantity of electricity is 10 to 300 C / dm ² .
If it is less than 10 C / dm ² , the change in the L value with the base material is small and there is no effect. Zn-Ni remaining at more than 300 C / dm ²
The alloy plating layer becomes thin, the plating adhesion is poor, and the quality is poor. Although a Zn-Ni alloy-plated steel sheet having a basis weight of 40 g / m ² or more can partially cope with this quantity of electricity, a thick basis weight is not preferable because the cost increases. Also,
The same applies to other Zn-based alloy platings.

In the case of electrolysis on the low pH side, the etching proceeds, the roughness increases, and the gloss decreases. Further, when the variation of the L value was examined, it was found that at pH 3.0, σ = 0.15 (L value 1
0n number = 20) whereas at pH 1.5 σ =
When it is 0.27 (same as above), color unevenness is likely to occur, and the appearance deteriorates. In addition, poor appearance means that color unevenness occurs.

The temperature of the processing solution is 30 to 75 ° C., preferably 40 to 60 ° C. If the temperature is lower than 30 ° C., there is a problem that a sufficient degree of blackening cannot be obtained due to poor reactivity, and that components in the treatment liquid are liable to precipitate. If the temperature exceeds 75 ° C., the reactivity is too high, and in this case, the formed film does not sufficiently exhibit the degree of blackening.

Conventionally, after blackening treatment, chromate is applied to secure corrosion resistance and protect the appearance, and the resin is coated. Low p
Examination of the restoration of the appearance by H conversion revealed that applying chromate and resin in one coat was the most effective. The resins that can be used stably as resin chromate are limited, but when the acrylic resin is mixed with chromic acid, a stable aqueous solution can be obtained, and the dispersion of the L value can be adjusted to pH 3 by using the aqueous acrylic resin dispersed chromate layer. Σ = 0.10 at 0, σ = 0.13 at pH 1.5
And reached almost the same level. Although the reason is not clear, it is speculated that the irregularities on the surface were filled with the resin, and that chromium in the chromate worked to lower the L value. When the aqueous acrylic resin-dispersed chromate layer has a dry film thickness of less than 0.3 μm, there is no effect on the improvement of the appearance,
If it exceeds m, the surface resistance increases, which is not preferable in terms of weldability, conductivity and the like.

The ratio of the acrylic resin to Cr in the aqueous acrylic resin-dispersed chromate layer is preferably 2 to 10 parts by weight of Cr based on 100 parts by weight of the acrylic resin. When Cr is less than 2 parts by weight, the effect of reducing the variation in L value is small,
Poor corrosion resistance. If the content of Cr is more than 10 parts by weight, the electrical insulation property is reduced and the spot weldability of the product is poor.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. (Example) Table 1 was prepared using the following Zn-based alloy-plated steel sheets.
Anodizing was carried out in the baths and conditions shown in Tables 2 and 3. After the blackening treatment, a resin chromate (aqueous acrylic resin Paltop 3966AX + BY: manufactured by Nippon Parker Co., Ltd.) was applied to the blackened surface, and the L value was measured with a color computer (manufactured by Suga Test Instruments Co., Ltd.). Tables 1 and 2 show the results.
Shown in In the present invention, the L value is calculated based on the R.I. S. A hunter diagram proposed by Hunter (1948) showing the lightness of the color space. When the L value is 15 or less (after applying the resin chromate), it is assumed that the degree of blackening is excellent. The amount of SO ₄ ^2- ,
The pH was adjusted using Na ₂ SO ₄ and H ₂ SO ₄ .

Zn-Ni alloy plated steel sheet (Inventive Examples 1-1)
2, 16, 17) (Comparative Examples 1 to 11, 14) Adhesion amount 20 g / m ² , Ni content 12% by weight Steel plate Plate thickness 0.7 mm (SPCD) Zn-Fe alloy plated steel plate (Invention Example 13) (Comparative Example 1
3) Adhesion amount: 20 g / m ² , Fe content: 10% by weight Steel plate: 0.7 mm (SPCD) Zn-Co alloy plated steel plate (Invention Example 14) (Comparative Example 1)
2) Adhesion amount 20 g / m ² , Co content 5% by weight Steel sheet Thickness 0.7 mm (SPCD) Zn-Mn alloy plated steel sheet (Inventive Example 15) (Comparative Example 1)
5) Adhesion amount 20 g / m ² , Mn content 10% by weight Steel plate Sheet thickness 0.7 mm (SPCD) Adhesion amount of Cr in resin chromate 50 ± 10 (mg / m
² )

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

According to the present invention, the production rate can be doubled by lowering the pH of the electrolytic solution, the factor of plating defects such as metal hydroxide and spark marks generated during production can be reduced, and the power consumption can be reduced. The effect of reducing the amount by half was obtained. In addition, it is possible to manufacture a blackened steel sheet having a quality equal to or higher than that of a conventional steel sheet by resin chromate treatment, which makes it difficult to compensate for the tendency of deterioration of the surface appearance due to a decrease in pH.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the quantity of electricity and pH required to obtain the same appearance of a blackened surface.

FIG. 2 is a graph showing the relationship between the amount of complex sulfate compound formed on a black film and pH.

Continuing from the front page (72) Inventor Takao Kurisu 351 Naganumacho, Inage-ku, Chiba-shi, Chiba Prefecture Inside Steel Structure Research Laboratory Kawasaki Steel Corp. (72) Inventor Keizo Okuno 1 Kawasakicho, Chuo-ku, Chiba City, Chiba Prefecture No. Kawasaki Steel Engineering Co., Ltd. (72) Inventor Yoshihiro Naruse 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Kawasaki Steel Co., Ltd. Technical Research Headquarters (56) References JP-A-4-143293 (JP, A) JP-A-4-17695 (JP, A) JP-A-7-173686 (JP, A) JP-B-63-46159 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) C25D 11/34 303

Claims (4)

(57) [Claims] 1. A zinc-based alloy-coated steel sheet containing 5 to 100 g / l of chlorate ion (ClO ₃ ⁻ ) and 10 to 300 g / l of SO ₄ ^2- ion and having a pH of 0.5 or more and 2.5 or less. In the above solution, anodize at a temperature of 30 to 75 ° C. and an amount of electricity of 10 to 300 coulombs / dm ² , and further form an aqueous acrylic resin-dispersed chromate layer
A method for producing a blackened steel sheet excellent in productivity and blackening properties, characterized by being formed at 2.5 μm. 2. The above solution further comprises Cl as an additive.
^{_{-, NO 3 -, H 2}} O 2, Ni 2+, Co 2+, Fe 2+, and at least one selected from the group consisting of Mn ²⁺ to claim 1 comprising 5 to 100 g / l in total A method for producing the blackened steel sheet according to the above. 3. The above solution further comprises H ₂ as an additive.
5 to 100 g in total of at least one selected from the group consisting of O ₂ , Ni ²⁺ , Co ²⁺ , Fe ²⁺ , and Mn ²⁺
The method for producing a blackened steel sheet according to claim 1, wherein / l is contained. 4. The water-based acrylic resin-dispersed chromate layer according to claim 1, wherein the ratio of the acrylic resin to Cr is 2 to 10 parts by weight based on 100 parts by weight (dry weight) of the acrylic resin. The method for producing a blackened steel sheet according to any of the claims.