JPH01184297A - Method for plating partially tinned steel sheet with chromium - Google Patents

Abstract

PURPOSE:To obtain a surface treated steel sheet for a welded can having superior weldability, adhesion to paint and corrosion resistance by depositing metallic Cr on only the untinned part of a partially tinned steel sheet and further depositing metallic Cr on the entire surface to carry out Cr plating. CONSTITUTION:The surface of a steel sheet 1 is partially tinned 2 and the partially tinned surface is plated with Cr at low current density to deposit metallic Cr 3 on only the untinned part and Cr oxide hydrate 3a on the entire surface. Cr plating is then carried out at high current density to deposit metallic Cr 4 and Cr oxide hydrate 4a on the entire surface. The untinned part has a larger amt. of metallic Cr than the tinned part and a low-cost material for a welded can having superior high-speed seam weldability, adhesion to paint and corrosion resistance is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a new surface-treated steel sheet for welded cans suitable for filling and storing various foods, beverages, and other liquids.

BACKGROUND ART Solder cans, adhesive cans, and welded cans are used as metal three-piece cans used as storage containers for foods, beverages, and the like. A tin-plated steel plate is used for the solder can, and tin-free steel (hereinafter abbreviated as TFS-CT) is used for the adhesive can. However, the tin-plated steel sheet itself for solder cans is expensive, and the lead in the solder poses a food hygiene problem.
In recent years, the production volume has been drastically decreasing due to insufficient paint adhesion, the large area of material used for can exit, and limited can manufacturing speed.

On the other hand, the production volume of adhesive cans using TFS-CT, which has a chromium water-conserving oxide film on the upper layer and metallic chromium on the lower layer, is cheaper than Furisa and has superior paint adhesion and corrosion resistance, and the production volume is still increasing. There is.

However, TFS is a material for welded cans that has higher productivity and requires less material area when exiting the can.
CT is inappropriate. The reason for this is mainly that the electrical resistance of the upper layer chromium water-conserving oxide film is high, and the TF
This is because it is necessary to mechanically or chemically remove this film in order to weld S-CT at high speed. This is not only troublesome in terms of can manufacturing technology, but also deteriorates paint adhesion and corrosion resistance in the vicinity of the weld, and requires sufficient correction painting.

Currently, there are three main types of materials used for welded cans.

■For example, as described in JP-A No. 53-23833, the amount of expensive tin plating is reduced to the lower limit that is satisfactory from the viewpoint of weldability and corrosion resistance. nickel, so-called thin tin-plated steel sheet, as the lower layer of tin in the thin tin-plated steel sheet.
Corrosion resistance and weldability are improved by providing a base layer such as a nickel-iron alloy layer, and the tin weight is 0.8g/rn'
This is a so-called ultra-thin tin-plated steel sheet that aims to lower the price by reducing the cost to a very low level. ■Although it lacks versatility in the contents that can be filled because its corrosion resistance and weldability are not at a fully satisfactory level, it is used as a tin-free steel sheet for coffee drinks, etc. This is a nickel-plated steel sheet.

It is difficult to say that these three materials are fully satisfactory in terms of achieving the characteristics required for materials for welded cans: excellent corrosion resistance, paint adhesion, weldability, and low price. is the current situation.

The inventors developed a striped tin-plated tin-free steel sheet as a material for welded cans that has weldability comparable to that of #25 tin, corrosion resistance comparable to TFS-CT, and economic efficiency (Japanese Patent Application Laid-Open No. 1981-1999). 213:395). The steel plate is plated with tin to the same level as #25 tin only on the parts to be welded in the can-making process, and coated with metallic chromium and chromium hydrated oxide on the other parts and the tin-plated parts. .

The role of this metallic chromium and chromium water-conserving oxide film is to
In the non-tin-plated parts, we aim to provide paint adhesion and corrosion resistance comparable to that of regular TFS-CT, but in the tin-plated parts, we aim to improve paint adhesion and corrosion resistance, and we also provide superior welding properties that have been painstakingly added. There should be no obstruction or deterioration of sexuality. Therefore, the amount of metallic chromium and chromium water-conserving oxide film to be applied on the non-tin-plated area and the tin-plated area is as follows:
It is necessary to control each to an independent optimum value.

Conventionally, for chromium plating on steel sheets, there are the so-called 1-step method and 2-step method as TFS-CT manufacturing techniques. The former is a relatively dilute chromic acid of less than 100 g/liter of chromic anhydride, sulfuric acid and/or hydrofluoric acid,
This is a method in which metallic chromium and hydrated chromium oxide are simultaneously precipitated from a plating bath containing additives, etc. The latter is a method in which chromium metal and hydrated chromium oxide are precipitated simultaneously after chromium plating using a high concentration chromic acid bath containing auxiliary agents such as sulfuric acid and additives. , followed by the addition of a smaller amount of the same auxiliary agent,
This method consists of forming a chromium hydrated oxide film using a low concentration chromic acid bath.

Even if the steel plate to be plated is not steel (Fe) as the base material, but Sn-plated or Ni-plated steel plate is used, the method is basically the same, and it is included in the technology of the above one-step method or two-step method. It is.

On the other hand, there is a known technology for manufacturing special ultra-thin tin-plated steel sheets as materials for welded cans by controlling not only the composition of the plating solution but also the potential or current during cathodic electrolysis during thin chromium plating. Yes (Japanese Patent Application Laid-Open No. 82-124296
). This method is applied to a steel plate that is non-uniformly tin-plated so that the exposed parts of the steel plate are scattered in a microscopically discontinuous manner (this can be called a microscopically partially tin-plated steel plate). This is a method to precipitate both uniformly and simultaneously.

As mentioned above, in the conventional thin chrome plating technology, there is no method that deals with partially tin-plated steel sheets as the material to be plated.
There was no technology to control the amount of metallic chromium in tin-plated parts.

Problems to be Solved by the Invention As a material for welded cans that satisfies weldability, paint adhesion, and corrosion resistance at the same time, partially tin-plated TFS, in which only the welded area is tin-plated, exhibits excellent performance. To this end, the tin-plated parts must have a sufficient tin plating layer (approximately 1.0 g/rn' or more) to ensure high-speed seam weldability, and a length that improves paint adhesion and corrosion resistance without impairing weldability. It is necessary to provide a metallic chromium amount to the non-tin plated parts (portions that are not welded) so as to exhibit paint adhesion and corrosion resistance equivalent to that of conventional TFS-CT.

An object of the present invention is to advantageously provide a manufacturing technology for a steel plate having the above-mentioned characteristics that could not be achieved using conventional thin chromium-plated steel sheet manufacturing technology.

Means for Solving the Problems In the present invention, when chromium plating is applied to a partially tin-plated steel sheet, metallic chromium is first deposited only on the non-silver plated area and then on the entire surface, and the tin-plated area is more concentrated in the non-silver plated area. This is a chromium plating method for partially tin-plated steel sheets, which is characterized by reducing the amount of metallic chromium.

It is necessary to have the best weldability, paint adhesion, and corrosion resistance as a working part tin-plated steel plate TFS.

The partial tin-plated parts to be welded are usually coated with a seam weld diameter correction coating during the can manufacturing process, but the tin-plated layer is insufficient in paint adhesion and corrosion resistance. For this reason 5-8
0 g/rn', preferably 15-50 rag/rIf
It is preferable to provide a metallic chromium layer of about 100%. 5mg/rr?
If it is less than 8, the improvement in paint adhesion and corrosion resistance is insufficient.
If the layer exceeds 0 g/rn', the paint adhesion will be poor even if more than that is applied.
This is because not only the corrosion resistance improvement effect is saturated, but also the weldability decreases markedly.

On the other hand, the non-silver plated parts require the same paint adhesion and corrosion resistance as conventional TFS-CT, so approximately 60II1g/r
A metallic chromium layer with a concentration of If or more, preferably 100 mg/rn' or more is required. The reason for this need not be stated again, but it is determined by the amount of metallic chromium required to exhibit sufficient resistance to contents.

In order to apply more metallic chromium to the non-silver plated areas and less to the tin-plated areas, chromium plating is carried out by first depositing metallic chromium only on the non-silver plated areas and then on the entire surface. It is valid.

To explain using Figure 1, Gr03180g/JL, H
2So40.7g/l, Na2S iF65 g/liter,
In a solution at a temperature of 45°C, a steel plate (corresponding to the non-silver plated part), a tin-plated steel plate with a plating amount of 2.8 g/ml, and a tin plate are
The graph shows a cathode polarization curve obtained when electrolysis was carried out at a constant rate of mV/s while moving the potential to a base value.

For steel plate 1, tin-plated steel plate 2, and tin plate 3, a cathode film is generated and dissolved at a potential that is -1,OV relative to a saturated calomel electrode (hereinafter, the expression "relative to a saturated calomel electrode" is omitted). occurs, and precipitation of metallic chromium occurs at potentials less base than about -1.0 .

Further, the current flowing through the tin-plated steel plate at a potential of -0.8 to -1.OV is significantly larger than the current flowing through the steel plate. Even if the potential is fixed at 10.8 V and low-potential electrolysis is performed on steel plates and tin-plated steel plates, no precipitation of metallic chromium is observed, and only the formation of water-containing chromium oxides is observed. Furthermore, −1,6
V, and when the potential was fixed at a more base potential, precipitation of metallic chromium was observed on both the plate and the tin-plated steel plate.

On the other hand, actual industrial resin plating is generally performed by constant current electrolysis. As is clear from Fig. 1, for example, when constant current electrolysis is performed at 30 A/dm2, the potential on the steel plate is around -1.7 V, and metallic chromium should easily precipitate. The potential is around -0.8V, and metallic chromium should not be deposited.

In the same liquid as the one actually used for the measurement in Figure 1,
When a cathode current of 2.2 dm was applied, the precipitation efficiency of metallic chromium was 23% on the steel plate, whereas the formation of hydrated chromium oxide was observed on the tin-plated steel plate; It was confirmed that no reduction occurred.

Next, in the same liquid, 12OA/dPeng2, 0.5
When a cathode current of seconds was applied, the precipitation efficiency of metallic chromium was 22% on the steel plate and 20% on the tin-plated steel plate.

At least, it can be considered from FIG. 1 that in order to precipitate metallic chromium in this plating solution, 10 A/dm2 or more is required on a steel plate, and 50 A/dm2 or more on a tin plating.

In order to manufacture the steel sheet of the present invention, it is necessary to be able to independently control the amount of metallic chromium deposited in non-silver plated areas and smaller in tin plated areas. Therefore, in the same solution as in Fig. 1, plating is first carried out in current density area B (metallic chromium deposited only on the steel plate) in Fig. 1, and then in current density area A (on both the steel plate and the tin-plated plate). There may be a method of plating with metal chromium precipitation) or, conversely, a method of plating in area A and then plating in area B.

When chrome plating is applied to a partially tin-plated (tin amount 2.8 g/rn') steel plate, 0.
2 seconds, 1 second at 30A/d+s2 as region B, rest time between two energizations (time immersed in electrolyte)
was set to 0.5 seconds. Interestingly, in the method (B+A) in which plating is performed first at a low current density and then at a high current density, 1001 g/rr of metallic chromium was deposited on the non-silver plated area and 40 mg/rrf on the tin plated area, whereas the opposite Method (A-+
B)-c was deposited at 10 hg/rrf on the non-silver plated area and 40 mg/rn' on the tin plated area, whereas in the reverse method, it was 110 mg/m' on the non-silver plated area and 11 on the tin plated area.
Metallic chromium of 0.05 trr/rrf was precipitated and the objective could not be achieved.

Although the detailed reason is unknown, in A+B, metallic chromium precipitates on the tin plating after the first pass (before the second pass), resulting in a cathode film corresponding to the intermediate state of the so-called reduction reaction to Cr0. Since chromium is present on the metallic chromium layer, it is thought that even if current is applied at castle B, where reduction from Cr+6 to Cr0 should not occur in a pure anchoring case, the precipitation of metallic chromium will occur efficiently.

Therefore, if for some reason it is necessary to plate at Castle A first, before plating at Castle B, remove the cathode film deposited on the iron by electrochemical dissolution such as reverse electrolysis, mechanical Unless it is completely and uniformly removed by some method such as manual polishing, the amount of metallic chromium in the tin-plated area will be lower than that of the non-silver-plated area, and it will be impossible to control the amount of metallic chromium in each area independently. It's not impossible, but it's extremely difficult.

On the other hand, in the method of B area → A area, for example, ll
hg/m', if you want to add 30+wg/rn' metallic chromium to the trowel part, basically 80mg to the non-tin part in area B.
It is sufficient to apply 30 mg/rn'' of metallic chromium to both the non-tin portion and the tin-plated portion, that is, the entire surface of the steel plate.

In industrial production, in addition to the liquid composition and current density, the deposition efficiency of chromium plating is determined by the bath temperature, the relative flow rate at the liquid-steel plate interface, and in the case of multi-pass plating, the immersion in the plating solution between the current passes. It is not that simple because it is affected by time and other factors, but for the reasons mentioned above, the low current density B
An effective method is to precipitate metallic chromium on the non-silver-plated parts in the case of iron and then on the entire surface in the high radio wave density region A, and the detailed optimum manufacturing conditions can be established through several trial experiments.

The cathodic polarization curve shown in Figure 1 changes slightly depending on the plating solution composition, bath temperature, and potential scanning speed (actually, the speed at the steel plate-plating solution interface), but the basic idea when applying the present invention is remains unchanged.

Also, whether or not the tin-plated parts are ladle-treated is not a difference in wood quality. Furthermore, it does not matter whether the chromium plating solution is a two-step solution using a high concentration of chromic acid or a one-step solution with a relatively low concentration.

Incidentally, in the case of 2 steps, the chemical treatment after chromium plating is Cr0380g/mm, N&FO,1g/
In the bath, ll0A/d layer 2, the amount of hydrated chromium oxide film on the non-tin area after cathodic electrolysis treatment for 0.1 seconds is IEiOmg/rn', and the amount of hydrated chromium oxide on the tin-plated area is IEiOmg/rn'. The coating amount was 15 g/rn'. Since several tens of mg/m' of metallic chromium is present on the tin-plated area, there is no difference in chemical treatment resistance from the non-silver-plated area in terms of wood quality.

The method of the present invention described above is schematically shown in FIG.
As shown in (a), the surface of the steel plate 1 is partially plated with tin 2, and then, as shown in (b), metal chromium 3 is deposited on the surface of the steel plate 1 (non-silver plated part) at a low current density, and at the same time, the entire surface is oxidized with water-containing chromium. Then, as shown in (c), metal chromium 3a and hydrated chromium oxide 4 are deposited on the entire surface at high current density.
It precipitates a.

According to the present invention, an inexpensive material for welded cans with excellent high-speed seam weldability, paint adhesion, and corrosion resistance is obtained by chromium-plating a partially tin-plated steel plate and further adding a chromium hydrated oxide film. can get.

By controlling the current density during plating on a steel plate with tin plating of approximately 1.0 g/rrf or more only on the parts to be welded, first depositing metallic chromium only on the non-silver plated parts and then on the entire surface, More metallic chromium is applied to non-silver plating and less to tin-plated areas.

The tin-plated part has high-speed seam welding properties equivalent to #25ET, and its adhesion and corrosion resistance are even better. The non-silver plated part is exactly the same as the conventional TFS-CT.

Tinplate, thin tin-plated steel sheets, ultra-thin tin-plated steel sheets with a nickel-based surface treatment layer, nickel-plated steel sheets, etc., which have been conventionally used as materials for welded cans, are all materials with excellent weldability, paint adhesion, corrosion resistance, and low cost. It was difficult to say that it satisfied all of the required characteristics. However, as a result of the present invention, an excellent new plated steel sheet for welded cans having only the advantages of tinplate and TFS-CT can be obtained.

EXAMPLES Next, examples of the present invention will be specifically described together with comparative examples.

A mild steel plate with a thickness of 0.21 mm that has been cold rolled, continuously annealed and temper rolled by a conventional method is electrolytically degreased (N
aOH70g/l, temperature 70℃, electrolytic conditions IOA/
2.2 seconds) and pickling (H2SO470g/text, temperature 25℃, immersion 3 seconds), then 200m perpendicular to the rolling direction.
■Tin plating with a width of 15 mm at intervals (tin amount 2-8 g/rn'
), samples of Examples 1 to 3 and Comparative Examples 1 to 3 were prepared under the conditions shown in Table 1, and the basic characteristics of the non-silver-plated parts and tin-plated parts after treatment were evaluated. .

In Examples 1 to 3, after the first treatment, cathodic electrolysis treatment was performed under current density and electrolysis time conditions that allowed metal chromium to be deposited only on non-silver plated areas, metal chromium was applied to the entire surface of the non-silver plated areas and tin-plated areas. This is an example of cathodic electrolytic treatment using the current density and current application time for deposition.

In Comparative Example 1, the first treatment conditions were the same as in Example 1, but
This is an example in which the second process is performed under the same conditions as the first process. No metallic chromium precipitation was observed on the tin-plated area.

Comparative Example 2 is an example in which both the first and second electrolytic treatments were carried out at high current density, and it was impossible to reduce the amount of metallic chromium in the tin-plated area compared to that in the non-silver-plated area.

Comparative Example 3 is an example in which the current density of the first treatment was high and the current density of the second treatment was low. It is presumed that this is because the influence of the metallic chromium on the tin-plated part generated during the first treatment and the cathode film on this layer also extends to the second processing, but the metallic chromium on the tin-plated part The layer was approximately equivalent to that on the non-silver plated area.

Although omitted in Table 1, in order to perform quality evaluation for all cases, after chrome plating, Or0380g/piece, NLP
IOA/dm2.2 in a liquid consisting of 0.1g/jj
A second cathodic electrolytic treatment was performed. The amount of metallic chromium in all cases was measured by anodic electrolysis in a neutral sodium phosphate solution, and the amount of hydrated chromium oxide film (as chromium) was calculated from the total chromium amount determined by the fluorescent X-ray method. I subtracted it. Furthermore, the weldability, paint adhesion, and paint corrosion resistance of each sample were evaluated using the following methods.

Weldability: Seam weldability was evaluated using a seam welder using a copper wire as an intermediate electrode. The test material was heated to 210℃ in advance.
, and was subjected to dry firing for 20 minutes. The welding conditions are lap thickness 0.6
■, Pressure force 45kgF, speed 50mpm, current frequency 400H2, evaluation criteria determined by the width of the appropriate current range. The lower limit was determined by the strength of the welded part, and the upper limit was determined by the occurrence of dust (molten iron protruding in the form of a splash) (the appropriate current range was 200 A or more, which was considered to be practically acceptable).

Paint adhesion: An epoxyphenol paint was applied to one side of the sample at a dry weight of 50 mg/dm2 and baked at 210°C for 12 minutes. This sample was cut into intestines with a width of 5 ml and a length of 150 layers. 11001L between the painted surfaces of the two specimens
Sandwich the nylon film and use a hot press to
Pressure bonding was carried out at 200° C. for 30 seconds with a pressure of kg/cm2. This adhesive specimen was peeled off using a tensile tester, and its adhesive strength was expressed in kg15mm.

Paint corrosion resistance: Baked 50wg/dm2 of epoxy phenol can paint on one side of the test material, sealed the end surface,
Scratch that reaches the substrate with a cutter knife (5c fat x 5
After adding 1.5% citric acid and 100cc of 1.5z salt solution at 50℃ for 3 days, the sample material was washed with water, dried, and the coating was removed using cellophane tape. was measured (less than 0.1 mm during peeling O10,1~0.2
Penguin Δ, 0.2 m or more x).

(Blank below) Effects of the Invention As explained in detail above, metallic chromium is first deposited on the non-tin plating portion of a partially tin-plated steel sheet at a low current density in a chromic acid anhydride plating bath, and then the non-tin plating is applied. By depositing metallic chromium at high current density on the entire surface of tin-plated parts and tin-plated parts, it is possible to independently control and apply more metallic chromium to non-tin-plated parts and less to tin-plated parts. be.

The partially tin-plated TFS manufactured by this method combines only the advantages of tinplate and TFS-CT, and a new surface-treated steel sheet for welded cans having excellent weldability, paint adhesion, and corrosion resistance can be obtained.

[Brief explanation of the drawing]

FIG. 1 shows cathodic polarization curves obtained when a steel plate, a tin-plated steel plate, and a tin plate are electrolyzed in a chromic acid bath while the potential is moved at a constant rate. FIG. 2 is a diagram schematically showing the precipitation process of metallic chromium in the electrolytic treatment of the present invention. 1-...Steel plate, 2...Tin, 3...Metal chromium, 4...
...Hydrated chromium oxide, 3a...metallic chromium, 4a.
...Hydrated chromium oxide.

Claims (1)

[Claims] When applying chromium plating to a selectively tin-plated steel sheet, first deposit metallic chromium only on the non-tin-plated areas and then on the entire surface, and make sure that the amount of metallic chromium is higher in the non-tin-plated areas and smaller in the tin-plated areas. Features a chrome plating method for partially tin-plated steel sheets.