JPS61106800A - Manufacture of zinc compound one side electroplating steel plate - Google Patents

Abstract

PURPOSE:To obtain a one side plating steel plate having a non-plating surface which is excellent in its chemical conversion treating property by performing a zinc compound electroplating to one side, and thereafter, washing a non-plating surface, and executing an anodic oxidation in a water solution containing sulfate or phosphate of a specified metal. CONSTITUTION:A zinc compound electroplating is performed to one side of a steel plate, and thereafter, a non-plating surface is washed, and dried temporarily. Subsequently, a water solution which contains one kind or more of sulfate or phosphate of Na, D, Li, Mg and Al, and whose pH is 1-4 is adjusted. In this water solution, an anodic treatment is executed by setting a relative speed of the steel plate and the liquid, and an anodic current density to <=2.5m/sec and >=20A/dm<2>, respectively, and impurities which have been precipitated by a very small quantity on the non-plating surface are removed. Subsequently, the non-plating surface is polished as necessary. According to this method, a chemical conversion treating property of the non-plating surface in a zinc compound one side electroplating steel plate can be improved by a treatment over a short period.

Description

[Detailed Description of the Invention] <Field of Industrial Application> The present invention provides zinc-based single-sided electroplating:! ! This invention relates to a method for manufacturing steel plates.

<Prior Art and Disadvantages> In recent years, the use of zinc-based electroplated steel sheets has been increasing in order to prevent corrosion of automobile bodies caused by antifreeze agents sprayed on roads. In this case, both sides are plated lol
In I-fu, steel plates plated on only one side are often used due to problems with adhesion and appearance after painting.The non-plated side of single-sided plated steel plates has problems in terms of chemical conversion treatment and paintability.
It is required to be as good as cold-rolled steel sheets.

However, in the V-structure of zinc-based electroplated steel sheets, a sulfuric acid bath or an acidic chloride bath is used as the plating bath.
Corrosion resistance on non-plated surfaces cannot be avoided. For this reason, the non-plated surface often becomes dirty and streaky due to the accumulation of acid-insoluble substances and the precipitation of impurities, and the chemical conversion treatment property deteriorates. Furthermore, precipitation of plating on non-plated surfaces due to diversion of plating current is often a cause of deterioration in chemical conversion treatment properties.

Deterioration in chemical conversion treatment property refers to the fact that uniform phosphorus salt crystals are not formed, and some areas without crystals called stagnation occur, or uneven coarse crystals are formed. This is a serious problem as it may lead to deterioration in corrosion resistance and adhesion, or non-uniform appearance. Therefore,
As a countermeasure for this! ! Afterwards, the non-plated surface is treated as w4J4i and electrolyzed in an acid or salt aqueous solution. So-called electrolytic pickling is performed.

Electrolytic pickling has a chemical effect of H, 504 on the steel plate surface, and a physical effect of the 02 gas generated at the same time. However, in the plating line for steel plate strips, only one or two electrolytic pickling tanks are actually installed, and the time it takes to pass through this tank is several seconds or more. It was difficult to uniformly clean the non-plated surface in such a short period of time.

In other words, in some cases, the removal of dirt was insufficient in general, or in some cases, dirty areas and cleaned areas were mixed in spots.

This phenomenon occurs because when plating alloys such as Zn-Ni and Zn-Fe, elements more harmful than Fs precipitate on the Fe surface during plating, and Fe dissolves violently, causing stains. When this kind of condition occurs on the non-plated surface, which is particularly likely to occur, the chemical conversion treatment properties are inferior to those without electrolytic pickling in terms of uniformity.
This is an extremely big problem.

<Object of the Invention> In view of the current situation as described below, the object of the present invention is to obtain an electrolytically pickled surface that is uniformly cleaned even with a short treatment of a few seconds or less, and thereby to have an excellent chemical conversion treatment property. An object of the present invention is to provide a method for producing a zinc-based single-sided electroplated steel sheet having a non-plated surface.

<Structure of the Invention> According to the present invention, after zinc-based electroplating is applied to one side of a steel sheet, 1. When electrolytically pickling a non-plated surface, plating! !
After washing the steel plate surface with water to remove the plating solution, dry it once, and then add Na, K, Li, M,
Of the sulfates or phosphates of AI.

In an aqueous solution with a pH of 1 or more and 1- and less than 4 containing H of 1 type or 2p or more, the relative velocity between the m slope and the liquid is 2.5 layers/sec or less, and the anode current density is 20 A/d, 2 or more. By anodizing, the purpose listed above can be achieved.

Moreover, if the non-plated surface is subjected to polishing treatment with an abrasive after the electrolytic treatment described above, the chemical conversion treatment properties can be made uniform and good.

In order to achieve the above-mentioned purpose, the present inventors have already filed an application with the same subject matter as in the above (Japanese Patent Application No. 59-16).
6H3), the present invention was completed after further investigation and finding that good effects can be obtained even with an electrolytic bath having a lower pH.

The method for electrolytic pickling of zinc-based single-sided electroplated steel sheets of the present invention will be described in detail below.

In the case of electrolytic pickling in the uninvention, after plating, the non-plated surface must be washed with water and once dried. This is because washing with water alone will not completely remove the M# acid in the plating solution that has adsorbed onto the surface of the steel sheet. This is because a passive film is not formed in the portions that are not removed and free resist remains, and therefore over-etching may occur in some cases due to electrolytic pickling.

This phenomenon is particularly likely to occur with phosphorous-added steel, which is susceptible to etching.After washing with water, the surface is once dried, and in the process, residual Atam reacts with the steel plate surface, forming a uniform passive film over the entire surface. Therefore, uniform etching can be performed in the subsequent electrolytic pickling.

The electrolytic pickling solution contains at least one of Na, Li, A1 sulfate or phosphate as a main component.

Since the deposition potential of the metal ion H is higher than the actual level of hydrogen content, metal deposition does not occur in electrolysis of an aqueous solution. For this reason, it is easy to maintain the total ion concentration in the bath and maintain the cathode, and the alkali produced at the anode and the alkali produced at the cathode are separated depending on the relationship, and the bath pH is
This is because it is also suitable for maintaining.

Also, I chose sulfate or phosphate.

These aqueous solutions 1; no harmful gases were generated in the solution.

This is also because the Fe surface has a strong cleaning power. Chlorides, fluorides, nitrates, etc. may generate toxic gases such as halogen gas and NOl, and carbonates, silicate, organic acids, etc. have poor acid dissolving power.

Not preferred, but it is permissible to add carbonate, borium salt, and acetate for pH adjustment of the electrolytic solution or for other purposes.

The pH of the electrolytic bath is defined as 1 or more and less than H4. +1) If 1 is less than 1, the etching of the Fe surface will be severe, resulting in O/H etching and not 4t.For 4 or more, it has already been specified in Japanese Patent Application No. 1988-+8H93 (・
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, the present invention. However, when the pi of the electrolytic bath is less than 4, dissolution of Zn on the plated surface tends to occur. This can be prevented by shortening or sole plated surfaces.

Furthermore, in the present invention, the relative velocity between the steel plate and the electrolyte is
．． It is defined as 5s/sea or less. The reason for this is that if the relative speed is too high, the acid generated on the non-plated surface will quickly separate from the Fe surface, reducing the pickling power and cleaning the Fe surface uniformly within tV Be. This is because it becomes difficult.

As mentioned in v1 above, an uneven surface is something that must be avoided as it will definitely cause unevenness in the chemical conversion treatment, and for this purpose, controlling the relative speed of the steel plate and the liquid is extremely important.

In addition, in the present invention, the electrolytic treatment must be performed at a current density of 2 OA/dm2 or higher.
This is because if it is less than /dm2, the surface cleaning ability will decrease, which may be due to uneven destruction of the oxide film or a decrease in the agitation force at the interface of the 02 gas.

The chemical conversion treatment Fl property of the non-plated surface treated under the following conditions is excellent in itself, but it becomes even better by polishing with an abrasive material afterwards. This is because polishing makes the surface more active. As the abrasive material, a brush containing abrasive grains such as SiG or Al703, Scotchbrite, or a grinding belt can be used.

Also, after anodizing or polishing, Xi, Sn:j? It is also possible to further improve chemical conversion treatment properties by flash plating.

Zinc-based electroplating in the present invention refers to Zn and Zn-
This includes Ni, Zn-Fe alloy plating, and even those with other elements such as Cr6Go added to them! & Acid bath Plating is performed with acidic liquid in a chloride bath or a mixed bath. The electrolytic pickling tank is of horizontal type, vertical type or radial cell type.

The prefecture temperature can be arbitrarily selected from room temperature to 70°C. The cleaning efficiency of the non-plated surface varies slightly depending on the type of storage agent used, and the electrical conductivity varies.
Although it cannot be determined exactly, it is desirable that it be approximately 50 g/Q or less.

Further, even if the electrolysis time is as short as several seconds or less, for example, one second, it is possible to clean the non-plated surface.

After electrolytic treatment or further polishing, the steel plate is washed with water and dried.

It is considered a product.

Example of implementation Examples of the present invention will be specifically described below.

Phosphorus-added WI board with board thickness 0.7++u+ (P content 0.1%
) using a horizontal layer plating bath, one-sided Zn-Ni was coated under the following conditions.
Alloy plated.

(1) Bath composition N15Oa 8) 170250
gelZnSO47) 170 130 gelNa
2SOa 40 g/11 (2) Bath pH
L, 5 (3) Bath temperature 60 ℃ (4) Current density 50A/d Port 2 (5) Plating lNM&'l 15 5ec (6
) Plating weight 9 20 g/m' Next, wash with water and dry M! After that, the non-plated surface was electrolytically pickled under the conditions shown in Table 1, followed by ice washing and drying.

In addition, some of the samples were subjected to Scotchbrite polishing after electrolytic pickling, and then washed with water and dried.

After this, the presence or absence of dirt or unevenness on the non-plated surface is visually determined, and as an index of surface cleanliness, the whiteness (CW) is determined using a color difference meter and the Nl addition is determined by chemical analysis. # We analyzed the hot water. In addition, the presence or absence of stains and unevenness on the plated surface was visually determined in Comparison 1.

After this 1. Phosphate treatment JI made by Nippon Barker Rising
Using liquid Bonderite 53030.

Chemical conversion treatment was performed using a dip method. The chemical conversion coating was evaluated visually and by scanning N and @ observation in terms of uniformity, crystal density, presence of scratches, etc., and the chemical conversion adhesion zone was also measured for the non-plated surface. These results are shown in Table 1.

1+- After the plate shown in Comparative Example 5: 4, 'I: No solution treatment &... (In the case, the non-plated surface has a low degree of whiteness due to dirt, a large amount of Ni4F deposited, and is not chemically treated. Also inferior.

However, as shown in the electrolytic treatment shown in the example of the present invention, the cleanliness of the surface was improved as shown by the significant decrease in whiteness, increase, and RQ with Ni, and the chemical conversion treatment property was also excellent. There is.

On the other hand, in Comparative Example 1 in which the pH of the bath exceeded the range of the present invention, F
The e-plane was excessively dissolved and the chemical conversion treatment properties were poor. Furthermore, the chemical formation property of the plating surface is also poor.

In addition, Comparative Examples 2 to 3 are outside the scope of the present invention due to the relative speed of the steel plate and the bath, current density, plating, drying after water washing, and drying before electrolysis, etc.
All of No. 4 had poor chemical conversion treatment properties on the non-plated surface. It should be noted that the reason why the chemical conversion adhesion in these comparative examples is greater than that in the examples is due to the fact that the chemical conversion coating crystals have become coarser.

<Effects of the Invention> From the following, it can be seen that the method of the present invention very effectively improves the chemical conversion treatability of non-plated surfaces in a short treatment time of 1 to 1.5 seconds. .

Furthermore, if a polishing treatment is performed after the electrolytic pickling treatment mentioned above, even better chemical conversion treatment property of the non-plated surface can be obtained.

Claims (2)

[Claims] (1) After applying a zinc-based electroplated steel sheet to one side of the steel sheet, when electrolytically pickling the non-plated side, after plating, the steel sheet surface is washed with water to remove the plating solution, dried once, and then Na In an aqueous solution containing one or more of sulfates or phosphates of K, Li, Mg, and Al with a pH of 1 or more and less than 4, the relative velocity between the steel plate and the liquid was set at 2.5 m/min.
sec or less, and the anode current density is 20A/dm^2
A method for manufacturing a zinc-based single-sided electroplated steel sheet, which is characterized in that it is anodized as described above. (2) After applying zinc-based electroplating to one side of a steel plate, when electrolytically pickling the non-plated side, after plating, the steel plate surface is washed with water to remove the plating solution, dried once, and then Na In an aqueous solution containing one or more of the following sulfates or phosphates:
/sec or less, and the anode current density is 20A/dm^
1. A method for manufacturing a zinc-based single-sided electroplated steel sheet, which comprises polishing the non-plated surface after anodizing with 2 or more.