JPS61104099A - Surface-treated steel sheet and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the titled surface-treated steel sheet having excellent characteristics such as wettability to a paint and smudge resistance by treating cathodically a tinplate after reflow treatment in an alkaline salt, anodizing with an alkaline salt or a chromate treating liq., and then treating cathodically with chromate. CONSTITUTION:A layer consisting of >=60vol% SnO2 in the tin oxide at <=2.0mc/cm<2> tin oxide amt. is coated on the surface of a thin steel strip. A tinplate after reflow treatment is cathodically treated in an alkaline salt soln. such as an aq. sodium carbonate soln., and the oxides in the tinplate are reduced and removed. Or the tinplate is pickled. Then the tinplate is anodized in an alkaline salt or a chromate treating liq. to form tin oxide on the surface of metallic tin. The tinplate is successively rinsed, and treated with chromate by treating cathodically in a bichromate or chromate soln. The coated amt. of the chromate-treated film is regulated to about 1.0-15.0mg/m<2>, expressed in terms of chromium, and the coating rate is preferably regulated to 20-70%.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to a surface-treated steel sheet with excellent surface properties such as paint wettability, smudge resistance, paint adhesion, and stain resistance, and a method for manufacturing the same. It is.

(Prior art) In general, tinplate is required to have excellent corrosion resistance and good appearance, but in particular, tinplate used for food mortars, beverage cans, etc. has the following surface properties in addition to the above. There are four characteristics required to do this.

(1) The paint should have good wettability during painting, since the paint will sag on beverage cans and the like.

(2) Good adhesion of the applied paint.

(3) There is little occurrence of surface stains called smudges that tend to occur on the tinplate surface during manufacturing. A material with poor scratch resistance generally has poor slip resistance and is easily scratched.

(4) It must have excellent sulfidation resistance so that it will not be eroded by contents such as fish meat or corned beef.

However, a bumper that satisfies all of these four characteristics has not been obtained to date.

(Problems to be Solved by this Invention) This invention advantageously solves the above problems. C1 Surface treatment with excellent surface properties that fully satisfies all of the above four properties, as well as corrosion resistance and aesthetics. The purpose is to propose steel plates and their manufacturing methods.

(Means for Solving the Problem) In order to solve the above-mentioned problem, the inventors focused on the influence of the tin oxide layer and the surface chromium on the above-mentioned surface properties and developed various methods. As a result of repeated experiments and studies, we obtained the findings described below.

(1) In order to improve the wettability of paint, it is possible to increase the surface free energy of tin.In this regard, tin oxide has a larger surface free energy than chromium oxide, so tin oxide has a higher surface free energy than chromium oxide. To ensure wettability, it is necessary to reduce the coverage of surface chromium and increase the exposed area of tin oxide.

(2) Paint adhesion When the paint is peeled off with tape, the peeled surface is! Since it is tin oxide, the quality of adhesion is thought to depend on the peel strength of tin oxide, but the peel strength is different for SnO type and S
The S nQ Z type tin oxide is larger than the nO type. Therefore, in order to improve the adhesion, it is necessary to reduce the amount of tin oxide and to change its type to SnO2 type.

(3) Smudge Resistance The cause of smudge is tin oxide produced by So70 treatment, and is generated by cathodic treatment of this tin oxide in sodium dichromate. The smudge resistance exhibits the same tendency as the paint adhesion, and the higher the tin oxide releasability-strength, the better. Therefore, to improve the smudge resistance, tin oxide produced by reflow treatment is treated with dichromate cathode.

It is necessary to first remove the poles, change the shape to SnO2 type, and uniformly form a chromate-treated BIN film.

(4) The cause of flow-resistant sulfide black discoloration is SnS, and its generation point is mainly SnQ.
Therefore, in order to improve the sulfidation resistance, it is necessary to change the tin oxide to the SnO2 type and increase the coverage of the chromate treatment film.δ This invention is based on the above knowledge. .

That is, in this invention, the amount of tin oxide in the metal tin surface layer on the surface of the thin steel strip is 2. OmC/- or less, and s in the tin oxide
This is a surface-treated steel sheet comprising a chromate treatment film on a tin plate whose o vot% or more is occupied by SnO2, and the chromate treatment film has a coating amount of 1.0 to 15.0 cm/cm in terms of chromium. I? +2 and the coverage is preferably 20 to 70%.

The present invention also provides a method in which the tinplate after reflow treatment is subjected to cathodic treatment in an alkali salt, or after pickling, cathodic treatment is performed in an alkali salt or chromate treatment solution, and then cathode treatment is performed in a chromate treatment solution. Kotokuri's characteristic surface treatment IIl! This is a method for manufacturing steel plates.

(effect) This invention will be explained in detail below.

(a) The amount of tin oxide in the metallic tin surface layer of the tin plate is 2
The reason for setting the value to be less than -Ome/c- and the method for quantifying the amount of tin oxide will be explained first. Tin oxide covers only the surface of metal tin, and it is difficult to directly measure the amount. Therefore, a constant current of, for example, 2 mAl 1 degree is applied to the surface to reduce the tin oxide, and the time required for this is determined and expressed as the value obtained by dividing the amount of electricity flowing by the treated area.

As a result, it was found that when the amount of tin oxide exceeds 2.0 no/cW2y2, not only the smudge resistance deteriorates, but also the adhesion and sulfidation resistance.

[Yes]) The proportion of SnO in the above tin oxide is 60
Reason for setting VO to 1% or more: Electrode potential was used to quantify SnO. Tin oxides are represented by SnO and SnO2, and some other 5
n20. It is thought that these are mixed in. Therefore, using silver as a reference electrode, we selected a large number of bumps at random from a large number of bumps created under various manufacturing conditions, and set the one with the largest absolute value of the electrode potential as 100% SnO composition, while the one with the smallest Assume that SnO□ occupies 100% of the material, and for those with an intermediate potential, S will be proportionally distributed.
The proportion of nO was determined. ◇ As a result, if the amount of SnO in the acetylation pot was less than 60 voj%, paint adhesion deteriorated, and it also had a negative effect on sulfidation resistance and smudge resistance. There was found.

Above, we have explained the appropriate amount of tin oxide and SnO2 in it, which are essential conditions for the steel sheet of this invention.In this invention, the following (0) It is more desirable to satisfy the following conditions in order to achieve the intended purpose.

(C) The amount of chromate film covered is 1.0 to 1.0 in terms of chromium.
15.0 mg/m22 and coverage rate of 20-70%.

In order to increase sulfidation resistance, the greater the amount of chromate treated film, the better. However, if too much chromate treatment film is applied, the wettability of the paint will deteriorate, so the amount of chromate treated film coated should be 1.0 to 1 in terms of chromium.
It is desirable to set it to about 5.0"9/m. Also, regarding the coverage rate, if the coverage rate' is less than 20%, the sulfurization resistance will be poor, while if it exceeds 70%, the paint wettability will tend to deteriorate. Therefore, it is preferable to set the coating amount to about 20 to 70%.0 It has been confirmed that if the amount and coverage of the chromate treatment film are within the above range, there is almost no effect on paint adhesion and smudge resistance. ing.

Next, the manufacturing method of this invention will be explained.

Generally, the surface of tinplate that comes out of the plating bath is porous, so reflow treatment is performed to make it denser and improve its surface gloss. The surface of the bump that has been melted and solidified by this reflow treatment is covered with SnO over the entire area, but the amount of nitrogen covered is quite large, and therefore, before the chromate treatment (see later), tin oxide is formed. It is difficult to control the quantity and quality of

Therefore, in this invention method, the SnOr
After the Ili tin oxide film is removed by reduction by cathodic treatment in an alkali salt or by washing with sulfuric acid spray or dipping, it is anodized in a dichromate or chromic acid solution before the tin plate is exposed to the atmosphere. The surface of the metal tin is treated or anodized in an alkali salt.
This allows a thin tin oxide film to be produced.

In this way, the amount of tin oxide produced is 2. Ome /
- and below, and SnO2 tin oxide is the 6 Q V
Tinplate containing more than Ot% is completed. So, I decided to use this tin as a heavy chrome rj! Chromate treatment is carried out by cathodic treatment in I or chromic acid solution, and thus a surface-treated steel sheet with a desired chromate treatment film is obtained.

(Example) Example 1 The reflow-treated tin was passed through the equipment shown in Figures 1, 2, and 8, respectively, to obtain surface-treated steel plates exhibiting the surface properties shown in Table 1. .

The results of investigating the surface properties of each obtained steel plate were
It is also shown in the table.

In addition, in the apparatus shown in Fig. 1, carbonic acid) IJum 10
In a solution containing ~20 l/l, the quantity of electricity is 1~5 C/dm
After applying a cathode treatment to reduce and remove the tin oxide produced by the tinplate treatment, the amount of electricity used to draw the wire was 0.
1~1c 74m2 to anodize the metal tin surface
After generating O2 tin oxide and rinsing, Ha, Or
, 0.30-409/l, I) A pmate treatment consisting of a cathodic treatment with an electrical quantity o of 1-80/dm in a solution of E (3.5-5.5) was performed.

In addition, in the apparatus shown in Fig. 2, 10 to 2
After applying cathodic treatment with an air volume of 1 to 5 c/dm2 to reduce and remove tin oxide, a rinsing treatment was performed, and then Ha, 0r20730 to 40 g/1% was applied.
Electricity 0.1-1 in a solution with pH f11.5-5.5
C/dm2 cathodic treatment was applied.

In the apparatus roughly shown in Fig. 8, tin oxide is removed by spraying and dipping with 15 to 26 l/l of sulfuric acid, followed by rinsing treatment, and then Ha2Cr, 0780
~40 liters/t, pH 3.5 to 5.0 solution, anodized with an electrical quantity of 0.1 to 1 c/dm2, and then cathodized with an electrical quantity of 0.1 to sc/dm2.

As is clear from the results shown in Table 1, the comparative material (sample number 1) in which the amount of tin oxide exceeds the upper limit of this invention has poor smudge resistance, and even if the amount of tin oxide is suitable, the SnOz occupancy is below this level. In the sample below the lower limit of the invention (sample number 2), the adhesion of the paint was poor.

On the other hand, all of the surface-treated steel sheets according to the present invention have good sulfidation resistance, paint wettability, paint adhesion, and smudge resistance, and in particular, the amount and coverage of the chromate treatment film fall within the preferred range of the present invention. When satisfied, particularly good results were obtained.

(Effects of the Invention) Thus, according to the present invention, the surface properties required for food cans and beverage cans, such as not only corrosion resistance and aesthetics, but also paint wettability, smudge resistance, paint adhesion, and sulfurization resistance, can be achieved. It is possible to obtain a surface-treated steel sheet that has all of the following.

[Brief explanation of drawings]

1 to 3 are all schematic diagrams of processing equipment suitable for use in carrying out the method of this invention.

Claims (1)

[Claims] 1. The amount of tin oxide in the metallic tin surface layer coated on the surface of the thin steel strip is 2.
0 mc/cm^2 or less, and 60 vol% in the tin oxide
A surface-treated steel sheet comprising a tin plate made up of SnO_2 and provided with a chromate treatment film. 2. The amount of chromate treatment film is 1.
2. The surface-treated steel sheet according to claim 1, wherein the coating has a coating rate of 0 to 15.0 mg/m^2 and a coverage rate of 20 to 70%. 3. The tinplate after reflow treatment is cathodically treated in an alkali salt or pickled, then anodized in an alkali salt or a chromate treatment solution, and then cathodized in a chromate treatment solution. A method for manufacturing surface-treated steel sheets.