JPH0772358B2 - Method for manufacturing single-sided electroplated steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention stably manufactures a single-sided electroplated steel sheet which is excellent in appearance on the non-plated surface and also has good chemical conversion treatability and which is suitable as an anticorrosive steel sheet for automobiles. On how to do.

<Prior art and its problems> In recent years, in order to improve the durability of automobiles, single-sided electroplated steel sheets such as Zn series have come to be widely used as rustproof steel sheets for automobiles. This is because the one-sided electroplated steel sheet ensures excellent corrosion resistance due to the plated surface, and can utilize good weldability and paintability of the non-plated surface.

However, in producing such a single-sided electroplated steel sheet, there were the following problems.

That is, an acid bath such as a sulfuric acid bath or a chloride bath is used as a plating bath during electroplating. Therefore, corrosion of the non-plated surface due to the plating bath (acid) occurs on the surface, resulting in a corrosion product having a black surface. The resulting stain (acid burn) occurs. Further, due to this phenomenon, not only the non-plated surface of the steel sheet is discolored and the appearance quality is impaired, but also the chemical conversion treatment property is deteriorated and the coating property is deteriorated.

Therefore, in actual work, as a countermeasure against these problems, "a means for mechanically polishing or electrolytically treating the non-plated surface of the plated steel sheet or performing electrolytic treatment to remove metal and other stains deposited on the non-plated surface" Has been taken.

However, with the above-mentioned "means for mechanically polishing the non-plated surface of the steel sheet after plating", the effect of removing stains and blackened portions of the non-plated surface (hereinafter referred to as "black film") is recognized to some extent. However, there is a problem in that the surface roughness is lowered due to the grinding of the base material, and "slip" occurs on the blanking line of the automobile manufacturer.

Therefore, "a means for electrolytically treating the non-plated surface of the steel sheet after plating" is generally adopted, but the following various proposals have been made in order to secure a more stable effect by this method.

a) After subjecting a steel sheet to be plated to one-side plating, the electrolytic treatment is carried out in a mixed solution of sulfate and phosphate having a pH of 5 to 9 and a concentration of 50 to 300 g / (JP-A-62-99494). B) After subjecting a steel sheet to be plated to one-side plating, the electrolytic treatment is carried out in the form of an anodic electrolytic treatment and a cathodic electrolytic treatment in a conductive bath containing a specific sulfur compound (JP-A-62-13).
No. 595), c) One-side thin plating is applied to the steel sheet to be plated, and then indirect electricity is applied in an electrolytic bath containing a pH buffer and an oxidizing agent, with the non-plated surface serving as the anode and the plated surface serving as the cathode. Electrolytic treatment is carried out (Japanese Patent Laid-Open No. 61-163292), d) One-side plating is applied to a steel sheet to be plated, and then the electrolytic treatment is carried out in an aqueous solution of a soluble sulfate containing triethanolamine (Japanese Patent Laid-Open No. Sho 61-163292). 61-117300), e) One-side plating is applied to a steel plate to be plated, and then the electrolytic treatment is performed in a form of anodizing in an aqueous solution containing a sulfate or a phosphate (JP-A-61-106800). , F) After subjecting the steel sheet to be plated to one side plating, the electrolytic treatment is carried out in the form of anodizing in a conductive bath at pH 4 to 10 containing 0.05 to 20% of a surfactant (Japanese Patent Publication No. Sho 61-36597).
issue).

However, in practice, for such electrolytic treatment after plating, it is usual that only one or two treatment tanks can be installed due to cost and installation space. It was difficult to sufficiently clean the non-plated surface within "a short time of several seconds or less" when passing through the bath. In particular, when performing alloy plating of Zn-Ni alloy, etc.
Although the precipitation of elements such as Ni cannot be avoided, it has been more difficult to remove such elements by the above-mentioned short-time electrolytic treatment.

Therefore, the object of the present invention is to eliminate the above-mentioned problems during production of a single-sided electroplated steel sheet and to secure a non-plated surface having an excellent appearance and also a good chemical conversion treatment property. The purpose of the present invention is to provide a means capable of stably producing a plated steel sheet without requiring a special increase in equipment.

<Means for Solving the Problem> The inventors of the present invention have obtained the following findings as a result of repeated studies while repeating many experiments in order to achieve the above object. In other words, (a) In consideration of the actual equipment, etc., "the means for removing the black film formed on the non-plated surface by mechanical grinding or electrolytic treatment after the plating treatment" is the appearance of the non-plated surface. And can not be the fundamental means of improving chemical conversion treatability,
In order to completely eliminate the various problems found in the conventional method, it is necessary to apply "a means to prevent the phenomenon (acid burn) itself that the non-plated surface of the steel sheet discolors due to corrosion by the plating solution (acid)". To be.

(B) As such a means, it is extremely effective to add an organic inhibitor of adsorbed film formation type to the plating solution at a specific concentration, whereby the organic inhibitor is adsorbed on the active surface of the steel sheet. , The acid stain on the non-plated surface in the plating solution is effectively suppressed, and a sufficiently cleaned non-plated surface can be obtained, and the chemical conversion treatability does not have any particular adverse effect.

(C) In addition to the method of adding an organic inhibitor to the plating solution, a "pickling solution" which is a pretreatment solution for plating
It is even more effective to add an adsorbed film-forming type organic inhibitor in a specific concentration to the “washing solution after pickling”. By this means also, the organic inhibitor is added to the active surface of the steel sheet. It will be adsorbed, and the subsequent acid burns on the non-plated surface and deterioration of chemical conversion treatment in the plating solution will be further effectively suppressed.

The present invention has been made on the basis of the above-mentioned findings and the like, "When manufacturing a single-sided electroplated steel sheet, an adsorption film forming type organic inhibitor of 1 ppm or more is added to the plating solution to be adsorbed on the active surface of the steel sheet. Alternatively, by adding 1 ppm or more of an adsorption film forming type organic inhibitor in the pickling solution which is a pretreatment solution for plating or the washing solution after pickling, and adsorbing it on the active surface of the steel sheet, By adding the amount of inhibitor to each 0.1ppm or more, and by using both of them together, it effectively suppresses acid burns on the non-plating surface and deterioration of chemical conversion treatment in the plating solution, and the appearance and chemical conversion of the non-plating surface. It is characterized in that a single-sided electroplated steel sheet excellent in processability can be easily and stably manufactured. "

Here, the adsorption film forming type organic inhibitor applied in the present invention is not particularly limited in its type, and examples thereof include mercaptans, thiocyanates,
Thioureas, thiazoles and amines, diamines,
Typical examples are hydrazines and amides, and these are added singly or in combination of two or more to "plating solution" or "pickling solution used before plating or washing solution after pickling". To do. Low pH of chloride or sulfuric acid plating bath
The organic inhibitor used for pickling can be used for this purpose since it is in the acidic region of.

<Action> In general, as one of the methods for preventing corrosion of metals, it has been performed for a long time to suppress corrosion by adding a small amount of a substance (inhibitor) to the corrosive environment. It is known and classified from various viewpoints as described below.

Classification by compound form Inorganic inhibitors: Chromate, nitrite, etc. Organic inhibitors: amine, amide, acetylene, mercaptan, etc. Classification by mechanism of action Anode inhibitors: Phosphate, silicate, chromate, etc. Cathode inhibitor: magnesium salt, zinc salt, etc. Adsorption inhibitor: amine, amide, etc.

Of these, organic inhibitors are polar organic compounds and are said to suppress corrosion by adsorbing to active sites (anode region or cathode region) on the metal surface. It is said that lone pair electrons such as N, S, O atoms in the inhibitor molecule, π electrons of unsaturated bonds, etc. move to the metal side and are adsorbed. Alternatively, it is adsorbed to both of them and stops the reaction occurring in each region, or enhances the effect of suppressing the reaction rate.

In the present invention, one or more of these organic inhibitors are added to the "plating solution" or the "pickling solution used before plating or the washing solution after pickling" at a concentration of 1 ppm or more. As a result, the organic inhibitor is adsorbed on the surface of the steel sheet to prevent the discharge of H ⁺ ions and suppress the elution of Fe ions in the plating solution. As a result, formation of a black film in the plating solution is prevented, and deterioration of appearance and deterioration of chemical conversion treatability are suppressed.

As described above, the compound acting as the organic inhibitor has one or more polar groups which are convenient for the molecule of the compound to be adsorbed on the metal surface. As such a polar group, there are lone atoms such as lone atom, unsaturated bond π atom, etc., but depending on the size, orientation, shape and charge of the inhibitor molecule, the adsorption ability to the steel sheet and its bond Strength changes. Further, the anion in the plating solution is also related to the structure of the adsorption film and the electric double layer, and therefore, even if the same organic inhibitor is used, the effect is different in hydrochloric acid and sulfuric acid. That is, in the case of a sulfuric acid bath-based plating bath, it is preferable to use an inhibitor having a particularly strong adsorption force, but it goes without saying that an inhibitor having and may be used. In addition, an inhibitor having a chloride bath-based plating bath is preferable, but the inhibitor is not limited to this, and other ones also exhibit a sufficient effect.

Specific examples of the organic inhibitor having the lone electron pair are those shown in Table 1.

Examples of the organic inhibitor having the lone electron pair include those shown in FIG. Further, examples of the organic inhibitor having a lone electron include aldehyde.

When an inhibitor is added to the plating bath to produce a single-sided plated steel sheet, the type and amount of the organic inhibitor to be added should be appropriately selected according to the type of plating solution and the plating conditions, if possible. However, in the range of about 1 to 10 ppm, a generally good effect can be obtained.

However, when an organic inhibitor is added to the plating solution, for example, in Zn electroplating, the crystal orientation of Zn changes, which tends to cause a problem that the plating appearance becomes grayish black. Zn-Fe, Zn-Ni-Co, Zn-Mn and other alloy electroplating problems such as alloy composition fluctuations (eg Ni
There is a concern that the content rate and Fe content rate will decrease), but water or an acid added with an organic inhibitor at the stage before plating (for example, degreasing-washing after pickling, or the step of pickling). A means for immersing at least the non-plated surface of the steel sheet with a solution, that is, "means for adding an organic inhibitor to a pickling solution or a washing solution after pickling" does not have such a problem, and is therefore more preferable. In this way, by adding the organic inhibitor to the pickling solution prior to plating or the water washing solution after pickling, and dipping at least the non-plating surface of the steel plate into the organic inhibitor film adsorbed on the non-plating surface As a result, "corrosion of the non-plated surface by the plating solution in the plating process" is effectively prevented, and acid burn is sufficiently suppressed.

In any case, the addition amount of the organic inhibitor should be 1 ppm or more, and if the addition amount is less than 1 ppm, the desired acid burn suppressing effect cannot be obtained.

Furthermore, the combined use of “means for adding an organic inhibitor to a pickling solution or an aqueous solution after pickling” and “means for adding an organic inhibitor to a plating solution” more effectively prevents acid burn. This is preferable for the purpose. And
In this case, the amount of organic inhibitor added is 0.1 ppm each.
If it is above, a sufficient effect can be obtained.

Next, the present invention will be specifically described with reference to examples.

<Example> Example 1 First, a plating solution under the following conditions was prepared.

Bath composition _{ZnSO 4 · 7H 2 O: 130g} /, NiSO 4 · 6H 2 O: 260g /, Na 2 SO 4: 75g /, pH: 1.8, bath temperature: 50 ° C..

Then, after adding the organic inhibitors shown in Table 2, current density: 60 A / dm ₂ , plating coverage: 20 g / m ₂ .

One-sided Zn-Ni alloy plating was applied to the steel plate under the plating conditions of.

After that, the appearance of the non-plated surface of the single-sided plated steel sheet, the amount of Ni remaining was measured by fluorescent X-rays, and the zinc phosphate treatability was evaluated.

The zinc phosphate treatment is evaluated visually and by running. Uniformity of the chemical conversion coating produced on the non-plated surface by査型electron microscopy, as well as evaluating the compactness, phosphophyllite by X-ray diffraction _{[Zn 2 Fe (PO 4) 2} · 4H 2 O ] and hopeite [Zn ₃ to measure the peak of the _{(PO 4) 2 · 4H 2} O ], was determined P value is alkali resistance and an indication of coating adhesion according to the following equation.

On the Zn-Ni alloy plated surface, the Ni content of the coating was measured by fluorescent X-rays, and the phase structure of the plated coating was identified by X-ray diffraction.

The results of these investigations are also shown in Table 2.

As is clear from the results shown in Table 2, according to the method of the present invention in which the organic inhibitor is added in an amount of 1 ppm or more in the plating solution, no acid burn film is formed on the non-plated surface and the chemical conversion treatment is improved. I understand.

However, from Test No. 6, the Ni content of the plating film decreases as the amount of organic inhibitor added increases, and the phase structure changes from γ to γ + η. It is also conjectured that this causes deterioration of the corrosion resistance of the plating.

Example 2 A plating solution having the following conditions was prepared.

Bath composition _{ZnCl 2: 250g /, KCl:} 320g /, NiCl 2 · 6H 2 O: 100g /, pH: 4.5, bath temperature: 55 ° C..

Next, the organic inhibitors shown in Table 3 were added to this, and then the current density was 60 A / dm ² , and the coating weight was 20 g / m ² .

One-sided Zn-Ni alloy plating was applied to the steel plate under the plating conditions of.

Then, the same evaluation as in Example 1 was performed, and the result was evaluated as the third.
It is also shown in the table.

From the results shown in Table 3, according to the present invention, it is possible to obtain a non-plated surface having a good appearance and good chemical conversion treatment property. It can be seen that a single-sided plated steel sheet that can be obtained is stably obtained.

In this example, the single-sided Zn-Ni electroplated steel sheet was described, but the single-sided Zn electroplated steel sheet, the single-sided Zn-Fe plated steel sheet, the single-sided Zn-Ni-Co plated steel sheet, the single-sided Zn-Mn plated steel sheet, etc. It was also confirmed that similar results were obtained for the single-sided electroplated steel sheet.

Example 3 The surface of the steel sheet to be treated was alkali degreased with a caustic soda-based electrolytic degreasing solution, electrolyzed in H ₂ SO ₄ , and then washed with washing water containing thiourea at various concentrations shown in Table 4. Then, Zn-Ni alloy plating on one side was performed under the following conditions.

Plating bath composition ZnSO ₄ / 7H ₂ O: 120g /, NiSO ₄ / 6H ₂ O: 250g /, Glauber's salt: 75g /, pH: 2, Bath temperature: 55 ℃, Current density: 60A / dm ² , Plating weight: 20 g / m ² .

After that, the appearance of the non-plated surface of the single-sided plated steel sheet, the amount of Ni remaining was measured by fluorescent X-rays, and the zinc phosphate treatability was evaluated. The zinc phosphate treatability was evaluated in the same manner as in Example 1.

The results are also shown in Table 4.

As is clear from the results shown in Table 4, according to the method of the present invention which is carried out by adding 1 ppm or more of thiourea to the wash water, acid scorching does not occur on the non-plated surface of the obtained single-sided steel sheet, It can be seen that the chemical conversion processability is also improved. Further, it is presumed that the addition amount of thiourea is preferably 5 ppm or more.

In the manufacture of similar single-sided Zn-Ni alloy electroplated steel sheet as in Example 4 Example 3, after electrolytic degreasing, a 5% H mercaptan in ₂ SO ₄ in H ₂ SO ₄ electrolyte was added, the H ₂ SO ₄ After electrolytic pickling in it, it was washed with water and then Zn-Ni alloy electroplated on one side.

Then, after that, the non-plated surface of the single-sided plated steel sheet was evaluated in the same manner as in Example 3.

The results are shown in Table 5.

As is clear from the results shown in Table 5, according to the present invention, a single-sided plated steel sheet with good quality can be obtained.

Example 5 The surface of the steel sheet to be treated was alkali degreased with a caustic soda-based electrolytic degreasing solution, then immersion degreasing was performed with a 10% HCl solution containing benzylamine, followed by washing with water and plating on one side with a chloride bath Zn plating bath. did. The plating conditions were as follows.

Plating bath composition ZnCl ₂ : 250g /, KCl: 300g /, pH: 4, Bath temperature: 60 ° C, current density: 60A / dm ² , coating weight: 20g / m ² .

Then, after that, the non-plated surface of the single-sided plated steel sheet was evaluated in the same manner as in Example 3.

The results are shown in Table 6.

As is clear from the results shown in Table 6, according to the present invention, it is found that a good quality single-sided plated steel sheet can be obtained.

Example 6 Similar to Example 3, the surface of the steel sheet to be treated was alkali degreased with a caustic soda-based electrolytic degreasing solution, electrolyzed in H ₂ SO ₄ , and then washing water containing various organic inhibitors shown in Table 7 was used. After rinsing with water, various organic inhibitors (also listed in Table 7) are added to the following plating solution to perform one-sided Zn-Ni alloy plating, and then the appearance evaluation of the non-plated surface, Ni residual amount and zinc phosphate treatment The sex was evaluated. The plating conditions were as follows.

Plating bath composition _{ZnSO 4 · 7H 2 O: 120g} /, NiSO 4 · 6H 2 O: 250g /, Na ₂ SO ₄ : 75 g /, pH: 2, Bath temperature: 55 ° C, Current density: 60 A / dm ² , Plating weight: 20 g / m ² .

The results are also shown in Table 7.

As is clear from the results shown in Table 7, when the means for adding the organic inhibitor to the aqueous solution after pickling and the means for adding the organic inhibitor to the plating solution are used in combination, the organic inhibitor by each of the independent means is A good effect is obtained even with an addition amount smaller than the amount, and it can be seen that this is a means for more effectively preventing acid burn.

<Summary of Effects> As described above, according to the present invention, it becomes possible to manufacture a single-sided plated steel sheet having good appearance and chemical conversion treatability at a low cost by an extremely simple means. This brings about a very useful effect.

[Brief description of drawings]

FIG. 1 is a drawing showing an organic inhibitor having a lone pair of electrons.

Claims (3)

[Claims] 1. When producing a single-sided electroplated steel sheet, 1 p of an adsorption film forming type organic inhibitor is added to the plating solution.
By adding more than pm and adsorbing on the active surface of the steel sheet,
A method for producing a single-sided electroplated steel sheet, which comprises suppressing acid burn on the non-plated surface in a plating solution. 2. When manufacturing a single-sided electroplated steel sheet, an active surface of the steel sheet is prepared by adding 1 ppm or more of an adsorption film forming type organic inhibitor to a pickling solution which is a pretreatment solution for plating or a washing solution after pickling. A method for producing a single-sided electroplated steel sheet, characterized in that acid burn on the non-plated surface in the plating solution after that is suppressed by adsorbing it on. 3. When producing a single-sided electroplated steel sheet, after pretreating the steel sheet with a pickling solution containing 0.1 ppm or more of an adsorption film forming type organic inhibitor or a washing solution after pickling, the steel sheet is further adsorbed. No film-forming organic inhibitor.
A method for producing a single-sided electroplated steel sheet, characterized in that acid plating on a non-plated surface in a plating solution is suppressed by performing one-side plating in a plating solution containing 1 ppm or more.