KR960001036B1 - Method for making zine-chromium alloy plated steel sheet - Google Patents

Abstract

No content.

Description

Manufacturing method of zinc chromium alloy plated steel sheet

The present invention relates to a method for producing a zinc chromium-based alloy plated steel sheet excellent in all properties such as corrosion resistance, corrosion resistance after coating, plating adhesion, and weldability using a specific electroplating bath.

Zn-coated steel sheet is widely used as anti-rust steel sheet for automobiles, home appliances, and building materials required for corrosion resistance. This is because the pure zinc layer is more easily oxidized than iron in the steel sheet, so there is a sacrificial effect that zinc is first corroded to the exposed parts of the ground iron caused by plating bonding or processing such as pinholes. This is because it prevents the occurrence of red rust. However, since pure zinc is active, there is a drawback that corrosion of zinc plating itself proceeds significantly in a corrosion environment such as salt spraying. In addition, pure zinc is likely to produce conductive ZnO as a corrosion product, and the lack of a protective effect by the corrosion product present on the surface is considered to be a factor that is not sufficient in corrosion resistance. Therefore, an improved plating method such as Zn-Ni, Zn-Fe, etc. has been proposed in place of pure zinc plated steel sheets, and in recent years, Zn-Cr alloy plating and its manufacturing method have been proposed.

As a manufacturing method of the electroplating steel plate containing chromium in a plating layer, Unexamined-Japanese-Patent No. 57-67188, Unexamined-Japanese-Patent No. 64-55398, Unexamined-Japanese-Patent No. 1-303298, etc. are mentioned.

The method described in Japanese Patent Application Laid-Open No. 57-67188 discloses electroplating containing 70 to 370 g / l sulfate ion, 45 to 60 g / l nickel ion, 0.5 to 13 g / l chromium ion, and 10 to 80 g / l boric acid. It is a method of electroplating, maintaining a bath at pH 1.4-2. The amount of chromium contained in the plating layer obtained by this method is only 1.0 wt%, and the effect of chromium on corrosion resistance can hardly be expected. That is, in order to improve corrosion resistance, it is necessary to further improve chromium content rate.

Japanese Unexamined Patent Publication No. 64-55398 is characterized by plating at a current density of 50 A / dm 2 or more using an acid plating bath containing zinc ions, trivalent chromium ions and 0.01 to 20 g / l polyoxyalkylene derivatives. do. A method for producing a zinc chromium plated steel sheet having excellent surface quality and corrosion resistance is described. According to the above method, the Cr content contained in the plating layer can be increased to about 40 wt%, but the adhesion of the obtained film is inferior, and the reverse OT adhesion test (after attaching the cellophane tape to the surface of the plating film, the plated steel sheet is applied to the cellophane tape shaft 180). ° Fold and return to the original, then peel off the cellophane tape and check the peeling degree of the plating layer from the weight of the plating component adhered to the surface, not to mention the usual cellophane tape peeling test (attaching the cellophane tape to the plating layer) Then, it peels off finely, and peels easily also in the method of checking the peeling degree of a plating layer from the weight of the plating component adhering to the surface. In addition, in the high current density region of 60 A / dm 2 or more, segregation of Cr occurs and streaks in the plating layer are not necessarily sufficient plating methods.

Japanese Patent Laid-Open No. 1-303298 discloses corrosion resistance characterized by electroplating using an acid plating bath containing Cr ions and a cationic polymer and having a Cr ⁶⁺ ion / Cr ⁵⁺ ion ratio of 0.1 or less. Described is an electroplated steel sheet with excellent surface gloss. The use of quaternary amine polymers as cationic polymers is also described here. Although it is possible to produce Zn-Cr alloy plated steel sheet by this method, it is difficult to keep constant the concentration of polymer with high amount of bath because the cationic polymer easily enters the film. / dm < 2 >), there is a problem that the adhesion of the plated film obtained only by plating with a current density of more than that is sharply lowered. In addition, Japanese Unexamined Patent Publications No. 64-55398 and Japanese Unexamined Patent Publication No. Hei 1-303298 only have problems with the amount of Cr precipitated, but the improvement of adhesion is also an important problem as well as corrosion resistance. However, neither of the above-mentioned publications mentions that.

Accordingly, an object of the present invention is to provide a method for producing a zinc chromium-based alloy plated steel sheet having excellent plating adhesion and corrosion resistance after processing.

The present inventors have diligently studied to solve the above problems, and find that a zinc-chromium alloy plated steel sheet having excellent plating adhesion and corrosion resistance after processing is obtained by using a specific plating bath and using a specific plating condition. Will be reached.

That is, according to the first aspect of the present invention, the zinc ions (Zn ²⁺ ) and chromium ions (Cr ³⁺ ) are summed on the surface of the steel sheet in a molar concentration ratio of 0.1 ≦ Cr ³⁺ / (Zn ²⁺ + Cr ³⁺ ) ≦ 0.9. At an acidic plating bath containing not less than 0.5 mol / l, not more than 0.5 mol / l, and at least one type of nonionic organic additive having a triple bond as an additive, from 0.1 to 30 g / l, the bath temperature is 70 ° C., 70 ° C., and pH 1.0-1.0. It is to provide a method for producing a zinc-chromium alloy plated steel sheet having excellent plating adhesion, characterized in that the plating in the range of 4.0, 200A / dm 2 at a current density of 50A / dm 2.

The nonionic organic additive having the triple bond

R ¹ , R ² , R ³ and R ⁴ represent a phenyl group, naphthalene group, anthracene group, phenol group, naphthol group, anthranol group, or At least one or more selected from those alkyl group adducts and / or alkylene group adducts and / or alkylene group adducts and / or sulfonic acid group adducts, hydrogen, hydroxyl groups, alkyl groups, alkylene groups, arkokines or polymers thereof, and sulfonic acid groups And R is at least one kind selected from hydrogen, an alkokine group, or a polymer thereof.

Moreover, it is preferable that the nonionic organic additive which has the said triple bond is ace- chelene alcohol, acetylene glycol, or derivatives thereof.

Hereinafter, the manufacturing method of the zinc chromium plated steel sheet of this invention is demonstrated in detail.

The plating bath for Zn-Cr alloy plating of the present invention mainly comprises Zn ²⁺ ions and Cr ³⁺ ions as metal ions, and these are produced and supplied by dissolving sulfates or metals. The concentration is within 0.5 mol / l or more of the solubility limit in total of Zn ²⁺ ions and Cr ³⁺ ions. In other words, if the total concentration is less than 0.5 mol / L, soot tends to be generated on the surface. On the other hand, if the solubility limit is exceeded, solids are only generated, and the improvement of the effect is not recognized for the appearance color tone, uniform electrodeposition property, and the like.

In addition, the Zn content in the plating layer is controlled to 60 wt% or more and 95 wt% or less, and the Cr ³⁺ / (Zn ²⁺ + Cr ³⁺ ) ratio of the plating bath is 0.1 to 0.9 in order to obtain the effect of the present invention. That is, if it is less than 0.1, the amount of chromium contained in the obtained plating layer cannot be increased and as a result, a film excellent in corrosion resistance is not obtained. On the contrary, when it exceeds 0.9, it will become difficult to make Zn content rate in a plating layer 60weight% or more, and adhesiveness with the steel plate of a film will fall.

One or more types selected from K ₂ SO ₄ , Na ₂ SO ₄ , (NH ₄ ) ₂ SO ₄ , and MgSO ₄ may be added to the plating bath. In that case, it is preferable to contain 10 g / L or more.

The current density is 50 to 200 A / dm 2, and more preferably 70 to 150 A / dm 2. It is because precipitation of Cr is hardly recognized below 50 A / dm <2>, and when it exceeds 200 A / dm <2>, it is easy to generate | occur | produce soot on the surface, and also because adhesiveness of a film falls. 25-70 degreeC of bath temperature is preferable. It is because the adhesiveness of the plated layer and steel plate obtained below 25 degreeC falls, and when it exceeds 70 degreeC on the contrary, it is easy to potter with black appearance.

As for pH, 1.0-4.0 are preferable. Less than 1.0 is not preferable because not only the cathode deposition efficiency is lowered but also the corrosion of the device is remarkable. On the other hand, if it exceeds 4.0, oxidation precipitation of zinc hydroxide occurs severely, which is not preferable.

In this invention, in order to obtain the Zn-Cr type alloy plating layer which is excellent in adhesiveness and has a favorable alloy composition, one or more types of nonionic rain additives which have a triple bond are added. The nonionic organic additive which has a triple bond is a compound represented with the following structural formula.

Wherein R ¹ , R ² , R ³ and R ⁴ are a phenyl group, naphthalene group, anthracene group, phenol group, naphthol group, anthranol group, or an alkyl group adduct and / or an alkylene group adduct and / or an alkylene group addition At least one selected from water and / or sulfonic acid adducts, hydrogen, hydroxyl groups, alkyl groups, alkylene groups, alkoxy groups, or polymers thereof, sulfonic acid groups, and R is at least one selected from hydrogen, alkokine groups, or polymers thereof It shows more than a class.

In the nonionic organic additive, the number of carbon atoms constituting one molecule is preferably in the range of 10 to 800, and preferably 10 to 250. That is, if less than 10, it is difficult to deposit both metal ions at the same time by unstable complexion and complex formation in the plating bath and greatly polarization. On the contrary, if it exceeds 800, the steric hindrance near the triple bond increases and the adsorption capacity to the surface of the steel sheet is remarkably lowered, so that it is difficult to obtain gloss plating. If the number of carbon atoms is 250 or less, the adsorption capacity on the surface of the steel sheet is improved, and as a result, the glossiness of the plating is increased. In particular, acetylene alcohols, acetylene glycols, or derivatives thereof are preferable. The following can be illustrated as a typical thing of the nonionic organic additive which has a triple bond.

By adding at least one compound having these triple bonds, the crystals in the Zn-Cr alloy plating layer are refined and the gloss and uniform electrodeposition are remarkably improved. Although it is not certain about the effect of these additives, it is thought to be due to the supporting effect on the metal surface by both triple bond? Electrons and hydrogen bonds and the complex formation effect with Zn ²⁺ ions. The appropriate range of addition amount is 0.1-30 g / l. If it is less than 0.1 g / l, it is difficult to increase the deposition of metal (Cr) and at the same time obtain a plating film of good alloy composition. Not desirable

The plating layer obtained by the above manufacturing method has a Zn content of 60 wt% or more and 95 wt% or less and exhibits a uniform color tone of white gray to silver white, no stripe shape, and good plating adhesion.

In addition, Zn-Cr alloy plating obtained in the present invention is not limited to Zn-Cr binary alloy electroplating, alloy electroplating mainly Zn-Cr, for example Zn-Cr-P, Zn-Cr-Ni, Zn Melting is also possible for -Cr-Ti and Zn-Cr-Fe alloy plating.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

[Examples 1-37, Comparative Examples 1-29]

The powdering resistance and the post-processing corrosion resistance of the zinc chromium alloy plated steel plate produced by the processing process shown below were evaluated. The experimental conditions and the results of the expansion are shown in Tables 1a to 1f and Tables 2a to 2d.

In particular, when the number of tancer atoms constituting one molecule of the nonionic organic additive is greatly increased, the results shown in Tables 3-1 to 3-2 are obtained.

1. Notice

Annealed steel sheet for three persons: 0.7mm thickness

2. Process

After degreasing → water washing → pickling → plating → washing → drying → powdering resistance, corrosion resistance was evaluated after processing.

3. Conditions

(1) degreasing

In an aqueous solution containing 30 g / l of sodium hydroxide and 1 g / l of surfactant, the temperature was 60 ° C., and the steel sheet was used as an anode for 10 seconds at 20 A / dm 2.

(2) Pickling

Pickling was carried out with an aqueous solution of 10 g / l sulfuric acid at an immersion time of 5 sec at a temperature of 30 ° C.

(3) plating equipment

Anticorrosion Fluid Cell

Anode Zn

10mm gap

Plating liquid flow rate 1m / sec

(4) plating bath

Zn ²⁺ 0.5 to 1.50 mol / l

Cr ³⁺ 0.1 to 2.50 mol / l

Cr ³⁺ / (Zn ²⁺ + Cr ³⁺ ) 0.143∼0.909

0 to 28 g / l of organic additive

(5) Plating condition

Bath temperature 35 ~ 80 ℃

Current density 40 ~ 180A / dm

5.56-25.0 sec.

(6) powdering resistance

Inverse OT test (fold the irradiation surface with the cellophane tape inward and fold it at an angle of 180 degrees (then fold it so that the gap between the bends is eliminated), and then bend it back to become substantially flat, and then put the plated layer on the surface of the cellophane tape. The peeling amount was measured and evaluated by fluorescent X-ray, and the peeling amount was 10 mg / m 2 or less, and the peeling amount was 10 ~ 100 mg / m 2, The thing of / m <2> or more was set to x * k.

(7) corrosion resistance

After cutting the zinc-chromium alloy plated steel plate into 74 × 150㎜ size and converting it into chemical treatment, coating and middle coating, and painting, 4 hours of salt spray-drying 60 ℃ × 2 hours Wetting 50 ℃ × 2 hours The time until the occurrence of red rust was examined by the corrosion test (CCT). Red rust occurs more than 100 days ˝ ◎ ˝. The thing of 50-100 days was evaluated as ˝ ○ ˝, and the thing of 20-50 days was ˝ △ ˝ and the thing within 20 days was ˝ × ˝.

(8) surface gloss

The obtained zinc-chromium alloy plating steel plate was visually evaluated. When there was a white-sec-white gloss, it was set as ˝ (circle), and when it was grey, it had ˝ (triangle | delta), black, or two or more types of color tone.

TABLE 1a

TABLE 1b

TABLE 1c

TABLE 1d

TABLE 1e

TABLE 1f

TABLE 2a

TABLE 2b

TABLE 2c

TABLE 2d

TABLE 3a

TABLE 3b

[Examples 38 to 43]

As shown in Tables 4a to 4b and 5a to 5b, zinc-chromium-based alloy plated steel sheets were produced in the same manner as in Examples 1 to 37 above under the same process and conditions. However, zinc-chromium containing Fe ²⁺ , Ni ²⁺ , Co ²⁺ , Al ₂ O ₃ , SiO _2, or TiO ₂ in the amounts shown in Tables 4a to 4b and 5a to 5b is added to the plating bath. The results are shown in Tables 4a to 4b and 5a to 5b to prepare the alloy-plated steel sheet and to evaluate the powdering resistance and the corrosion resistance after processing under the above conditions. In the table, TMDD represents 2,4,7,9-tetramethyl-5-decine-4,7-diol, and TMDDE represents an ethylene oxide adduct of TMDD.

TABLE 4a

TABLE 4b

TABLE 5a

TABLE 5b

As described above, a zinc-chromium alloy plated steel sheet having excellent plating adhesion and high corrosion resistance can be obtained by using the organic additive disclosed in the present invention. Moreover, since this invention is excellent in stability of a plating bath, it is possible to carry out manufacture on industrial scale stably. According to the method of the present invention, a zinc-chromium alloy plated steel sheet having excellent plating adhesion and high corrosion resistance can be manufactured industrially.

Claims (4)

Zinc ions (Zn ²⁺ ) and chromium ions (Cr ³⁺ ) are dissolved on the surface of the steel sheet within a molar concentration ratio of 0.1≤Cr ³⁺ / (Zn ²⁺ + Cr ³⁺ ) In addition, using an acidic plating bath containing 0.1-30 g / l of at least one nonionic organic additive having a triple bond as an additive, the bath temperature is 25 ° C. to 70 ° C., pH: 1.0 to 4.0, and current density is 50 to 200 A / d. Method for producing a zinc-chromium-based alloy plated steel sheet characterized in that the plating in the range of ㎡. According to claim 1, wherein the nonionic organic additive having a triple bond, R ¹ , R ² , R ³ and R ⁴ represent a phenyl group, naphthalene group, anthracene group, phenol group, naphthol group, anthranol group or their alkyl group At least one kind of adducts and alkylene group adducts and at least one kind of sulfonic acid group adducts, at least one kind selected from hydrogen, hydroxyl groups, alkyl groups, alkylene groups, alkoxy groups or polymers thereof, sulfonic acid groups and R is At least one or more selected from hydrogen, an alkoxy group or a polymer thereof. The method for producing a zinc chromium-based alloy plated steel sheet according to claim 2, wherein the nonionic organic additive having a triple bond is acequilene alcohol, acetylene glycol or derivatives thereof. The method of manufacturing a zinc chromium-based alloy plated steel sheet according to claim 2, wherein the number of carbon atoms is in the range of 10 to 250.