JPS63161191A - Tin-free steel for welded can - Google Patents

Abstract

PURPOSE:To improve the weldability and corrosion resistance of a steel by successively applying a Cr plated layer, a galvanized layer, and a chromate layer at respectively specific amt. to the steel from the surface side. CONSTITUTION:A Cr plated layer at 10-300mg/m<2>, a galvanized layer at 0.1-5g/m<2>, or further a chromate layer at <=25mg/m<2> (expressed in terms of Cr) are applied to the steel sheet surface to obtain the tin-free steel for a welded can. The chromate layer is formed with a Cr oxide or the oxide and metallic Cr. Since inexpensive Zn and Cr are used in the tin-free steel, the cost of the steel is reduced, and the weldability and corrosion resistance are also improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a tin-free steel plate for welded cans that has excellent weldability and corrosion resistance after painting.

<Prior art and its problems> Generally, tin plate and tin-free steel sheet (hereinafter abbreviated as TFS-CT) are mainly used as materials for cans. Tin cans are rapidly transitioning from solder cans to welded cans in order to save resources, reduce costs, and improve appearance, and the tin weight is also decreasing to 2.8g/
Instead of those with a weight of 1.0 g/II+2 or less, thin ones with a basis weight of 1.0 g/II+2 or less have been developed. However, from a cost perspective, even thin tinplate cannot be said to be superior to TFS-CT. That is one of the reasons why the use of TFS-CT is increasing. In this way, cost-effective TF
S-tl:T also has a big problem. TFS-CT is a steel plate with a thin coating of metallic chromium and non-metallic chromium formed on its surface, and is mainly used as an adhesive can. This is due to the inability to solder and the high resistance of its surface coating.
This is to solve the drawback of TFS-GT that it cannot be welded due to its high melting point.

However, with this adhesive can, when the contents of the can are subjected to high temperature sterilization, the adhesive portion may be torn and the can may be plated with copper. Adhesive cans are always associated with such risks, although they have been significantly improved by modification of the hydrated chromium oxide coating on TFS-CT. If weldable TFS-CT were developed, this kind of trouble would not only be eliminated;
The overlap of the joint part is 0.2 to 0 from 5mo+ (adhesive can)
．． Since it is 4 mm, it has the advantage of saving material and preventing the risk of vacuum leakage from the seaming part. Therefore, there are high expectations for the development of weldable TFS-CT.

For example, Japanese Patent Publication No. 57-1°9752 and Japanese Patent Publication No. 57-36986 are already known as providing methods for manufacturing TFS-(:T) that can be welded.

However, all of these attempts to improve weldability by reducing the amount of metallic chromium or non-metallic chromium. In such TFS-(:T, the metal chromium layer has a porous structure, which inevitably leads to a significant loss of corrosion resistance.

In addition, a chromium-plated steel sheet (Japanese Patent Laid-Open No. 55-484
No. 06) is also well known, in which the steel plate is slightly elongated by temper rolling, causing cracks in the chrome plating layer to improve weldability, but cracks in the chrome layer are TFS.
- Corrosion resistance as CT deteriorates.

Furthermore, products with a reduced amount of chromium plating or products with cracks in the chrome plating layer have a considerable amount of iron exposed.
When using TFS- by painting and baking T, there is a problem that iron oxides with high electrical resistance are likely to be generated during baking heat, which has an adverse effect on weldability.

As mentioned above, improving the weldability of TFS-(:T with a single layer of chromium is limited by the physical properties of chromium metal. Therefore, multi-layer plated steel sheets and steel sheets using metals other than chromium are used as materials for welding cans. was suggested.

(1) A multilayer plated steel plate in which a steel plate is plated with three layers of chromium, nickel, and chromate (Japanese Patent Application Laid-Open No. 60-162791, JP-A No. 61-159596).

(2) A multilayer plated steel plate in which a steel plate is coated with chrome, followed by zinc-nickel alloy plating and chromate (Japanese Patent Laid-Open No. 60-211099).

(3) Chrome plating on the steel plate, then tin plating,
Multilayer plated steel sheet for chromating (JP-A-60-190)
No. 597, JP-A-60-262975).

(4) A steel plate characterized in that the steel plate is nickel plated and then chromated (Japanese Patent Publication No. 59-46320, Japanese Patent Publication No. 59-47040).

etc. are provided.

The technical idea for achieving improved weldability using these TFS-CTs is explained as follows.

In (1), (2), and (3), TFS-C
The idea is to use other metals to facilitate the passage of welding current without reducing the corrosion resistance of T. In (4), nickel plating is applied as a substitute for chrome plating, and the purpose is to learn how nickel plating can function as a can due to its corrosion resistance and weldability.

However, nickel is not completely satisfactory in terms of weldability. (+), which is based on the same concept and uses Ni to improve weldability, has the same problem. .

(2) is a design concept in which Zn-Ni alloy plating is applied on top of the Cr plating layer to improve weldability with Zn-Ni alloy, but since Zn-Ni alloy has poor workability and is easy to break, multi-bead Not suitable for food can materials that are processed or flanged.

Although (3) can no longer be called TFS-CT because it uses expensive soot, it has better weldability than TFS-CT.

However, although the technique of plating tin on chrome is described in the above-mentioned patents, it has a poor appearance and is difficult to manufacture industrially.

<Object of the Invention> The object of the present invention is to provide a welded can that has excellent weldability even after being subjected to heat treatment by paint baking, and has corrosion resistance and paint adhesion similar to conventional TFS-CT. The aim is to provide tin-free steel.

<Structure of the Invention> It has already been mentioned that if conventional TFS-(:T) is to be welded and made after coating and heating, commercially satisfactory welding will not be possible unless the surface film is removed by polishing. (1) Chromium oxide with high electrical resistance is generated on the surface of metal chromium.

(2) The hydrated chromium oxide is dehydrated by heating and changes into a chromium oxide with higher electrical resistance.

(3) Due to the high hardness of metal chromium, it is not compatible with welding electrodes.

Examples include. It was found that (1) and (3) among these causes of deterioration of weldability were particularly large.

However, the chromium oxide film is essential in terms of paint adhesion and cannot be reduced to an extreme degree. In the end, it was found that the most effective method was to reduce the hardness of the surface of the metal chromium layer and improve its compatibility with the welding electrode.

In order to improve the conformability of the TFS-(:T surface to the welding electrode), the hardness of the metal chromium layer can be lowered, but the hardness of the metal chromium alone is harder than that of cold-rolled steel sheets, and weldability deteriorates.

Therefore, by forming a layer of zinc with relatively low hardness on the surface of the chromium metal, it becomes more compatible with the welding electrode. It was discovered that the weldability was improved because the weldability was lower than that of the metal used as a material, and this led to the present invention.

That is, the first aspect of the present invention is a tin-free steel for welded cans, which has a chromium plating layer of 10 to 300 Barn2 per side and a zinc plating layer of 0.1 to 5 gem2 on the surface of the steel plate. provide.

Further, the second aspect of the present invention is to apply 1 per side to the surface of the steel plate.
A chromium plating layer of O~300 mg/m2, a zinc plating layer of 0.1~5g1012 on top of that, and a chromate layer of chromium oxide or metal chromium and chromium oxide of 25 rag/m2 or less on top of that. To provide a tin foot steel for a welded can having the following.

Next, each layer of the tin-free steel for welded cans of the present invention will be explained in more detail.

The amount of metallic chromium in the first layer is 10 to 300 per side.
rng/+2. This metallic chromium layer is a layer for ensuring corrosion resistance. If it is less than 10 mg/m2, the plating layer becomes porous and corrosion resistance cannot be ensured. The thicker the metal chromium layer, the better the corrosion resistance.
/[If it exceeds 112, it will be saturated and the weldability will be poor. More preferably it is 50 to 150 mg/m2.

The second galvanized layer is 0.1 to 5 g/m2 per side.
It is stipulated that

Figure 1 shows the first 0.22+nm thick AQ killed steel plate on the north side.
tOOmg/m2 of metallic chromium is deposited as a layer, zinc is plated as a second layer with varying amounts of deposition from 0 to 2.0 g/m2, and a chromium oxide film (chromate layer) is deposited as a third layer in terms of metallic chromium. This is a graph of the measurement results showing the relationship between the contact resistance value and the amount of zinc plating when 7 mg/+2 was deposited (the measurement method was shown later in the examples).

From the results shown in FIG. 1, it can be seen that when the zinc plating amount is less than 0.1 g/m2, the effect of zinc as an intermediate layer is small, electrode conformity becomes poor, and weldability deteriorates.

FIG. 2 is a graph showing the measurement results of blister resistance when the galvanization of the second layer is 0 to 6.0 g/m2, except that it is similar to FIG. (shown inside).

From the results shown in FIG. 2, it can be seen that when the zinc plating layer exceeds 5 g/ln2, the corrosion resistance and paint adhesion after painting are poor even if chromate is applied.

The third chromate layer of the present invention is preferably formed at a density of 25 rng/m' or less. The chromate layer may include only a chromium oxide film, or may include a chromium oxide film containing metallic chromium. The total amount of chromium in the chromate layer is 25 argoIa
Limited to 2 or less.

The amount of chromate is preferably determined according to the amount of zinc plating, as described below. The total amount of chromium in the chromate layer is 2
If it exceeds 5 mg/m2, the properties of chromium become stronger, leading to deterioration of weldability.

The object of the present invention can be achieved by controlling the three locations as described above.

The manufacturing method of the present invention will be described below, but the present invention is not limited to this manufacturing method.

First, a steel plate is degreased and pickled using a conventional method, and then the first metallic chromium layer is coated with a thickness of 10 to 300 m in a known chromium plating bath.
g/II+2 is formed. At this time, a chromium oxide film is also formed at the same time, but since this chromium oxide film impairs the uniform electrodeposition of zinc and the adhesion of plating, it is better to reduce the amount of the chromium oxide film.

To reduce the amount of chromium oxide film, there is a method of after-dipping in a plating solution or rinsing with a high-concentration, high-temperature solution of CrO2. Using this method, the chromium oxide film was deposited at 10 mg/
After reducing the area to less than m2, zinc plating is performed.

A known acidic zinc plating bath is used for zinc plating.

Known acidic zinc plating baths include sulfuric acid bath, zinc chloride bath,
There are boron fluoride baths available, any of which can be used.

The amount of precipitation of zinc plating is 0. l ~ 5 g/+". Precipitation of zinc plating varies depending on the thickness of the oxide film on the surface of the first metal chromium layer. If the oxide film is thick, it will precipitate in granular form, and there will be less oxide film. In some cases, the zinc layer is deposited in the form of a flat plate.Since the zinc layer is a layer for improving weldability, there is no problem as long as it exists almost uniformly even if it does not cover the entire surface of metallic chromium microscopically.

However, if you want to roughly increase the plating coverage, immerse it in a hot solution of NaO+1 or KOH of about 1 to IOM, or immerse it in a hot solution of 08.01M to 5M HCft.
If the oxide film on the surface of metallic chromium is removed by cathodic electrolysis in a strong acid such as , lI2SO4 and then galvanized, a galvanized layer with improved adhesion can be obtained.

Finally, apply chromate if necessary. Chromate is 25 mg in terms of metallic chromium for the purpose of improving paint adhesion.
/m2 or less. The bath used for chromate is usually a dichromic acid bath or an anhydrous chromic acid bath (S
O4'', SiF, '-1F-, etc.) may be used. However, in the case of a dichromic acid bath, only a chromium oxide film is deposited, and in the case of an anhydrous chromic acid bath, metallic chromium and chromium oxide film are deposited at the same time. However, the total amount of adhesion should be 25 mg/1rr2 or less in terms of metal chromium.

<Example> The present invention will be specifically explained below using Examples.

Killed steel plate (0,22
mm thickness) was used.

(Example 1) CrO3250g/I2, H2SO41, 5g/f
l, Na2SiF65g/I! , using a bath with a bath temperature of 50
℃, cathodic electrolytic treatment at a current density of 50 A/dm2,
00 mg/n+2 metal chromium plated. After plating, it was immersed in the bath for 5 seconds.

Immediately after washing with water, ZnSO4410g/l, AILC1
320g/JZ, Na2SO475gait, pH4,
1 by cathodic electrolysis at 30 A/dm2 at 30°C in a bath of 0.
g/m2 galvanizing was carried out. Furthermore, 3
Current density 5 using 0 g/l sodium dichromate bath
Chromate treatment at A/dm2 and an oxide film of 10 m
g/m2 was deposited.

(Example 2) Using a bath of Cr (h 200 g/l, H2SO42 gel), cathode treatment was performed at a bath temperature of 50° C. and a current density of 50 A/dm2, and 60 mg/m2 of metallic chromium was plated.

Thereafter, it was immediately immersed in a solution of CrO390gel1 at a temperature of 70°C for 5 seconds, and then ZnCff1z20
0g1n%NHa to j! 250 g/l,
pH 5.0, bath temperature 50°C, current density 100 A/do+
2, and 0.5 g/ln2 of zinc was plated. Chromate was not performed after that.

(Example 3) Using a bath of 350 g/l of CrO and 4 g/4 of NaF,
Cathode treatment was performed at a bath temperature of 50° C. and a current density of 50 8/dm2 to deposit 250 mg/m2 of metallic chromium. Thereafter, immediately dilute the solution in a 1.5 M HCII solution at a temperature of 30°C.
Cathode electrolysis at 5 A/da+2 was performed. Furthermore, ZnSO4410g/1%AJ2 C11320g
/I1. , Na2SO475g/Il, 9114
．． Zinc plating was performed at 4 g/m2 by cathodic electrolysis at 30 A/dn+2 at 30°C in a bath of 0. Furthermore, Cr0315g/JZ, ) H2SO40, 15g/f
Chromate treatment was carried out in a fi bath at a liquid temperature of 40°C and a current density of 208/dm2, and the amount of metallic chromium was 100+g/m2. 121 oxide film! Ig/l112 was attached.

(Example 4) Cr03150 g/fl, l+2SO41 g/fl
Cathode treatment was performed using a bath at a bath temperature of 50°C and a current density of 70 A/dm2 to deposit 75 mg/m2 of metallic chromium. After that, it was immersed in the plating solution for 3 seconds, and after washing with water, ZnSO4240g/fl, Nt1401 15
g/fl, A n 2 (504) 330 g/4
2, 25°C in a pH 4.2 bath, current density 10 A/d
Cathode electrolysis was carried out at 0.2 g/m2 of lead plating. Furthermore, (:r0315g/n, NaF
Ig/42 liquid temperature 40°C current density 308/dm2. Chromate treatment was carried out to deposit metallic chromium at 7 mg/l112 and oxide film at 12 mg/m2.

(Comparative Example 1) Zn5O for chromium plating, 410g/l, 8l
C1s 20g/l, Na2S0. 7
5g/1. Zinc plating of 1 gem2 was carried out by cathodic electrolysis at 30° C. and 30 8/dm2 in a pH 4.0 bath. Subsequently, chromate treatment was performed using a 30 g/l sodium dichromate bath at a current density of 58/dm2 to obtain an oxide film of 10 UJg/m2.

(Comparative Example 2) Cr03 200 g#, It□5o40.3g/Q,
Using a bath of Na2SiF65g/ffi, bath temperature 50℃
, cathodic electrolysis treatment was carried out at a current density of 508/dm2, and 10
Plated with 0 ig/m2 of metallic chromium. Plating (f
i 5 A in a solution at 50°C adjusted to pH 1.0 with sulfuric acid
/dm2 cathode electrolysis ivy (7)? ) Direct? )
Ni50.200 g/fl, N1CQ230
g/Q, tlJOi in a bath of 30 g/l, bath temperature 50°C, current density 108/dm2, 100 m
Nickel plating of g/m2 was applied. Finally Cry360
g/n, +I □S O.

Chromate treatment was performed at 0.6 g, l, and the amount of metallic chromium was 10 mg/m2. The oxide film was set at 7 mg/m2.

(Comparative Example 3) (:r03200 g/11, H2SO40,3g/
1, using a bath of 65 g/2 NaSiF, cathodic electrolytic treatment was performed at a bath temperature of 50 °C and a current density of 50 A/dm2,
Plated with rng/m2 metallic chromium. Cr after plating
y360g/l, 11□504 0.1g/j2, Na
Chromate treatment was performed using a bath containing 60.5 g/Q of 2SiF at a bath temperature of 40° C. and a current density of 10 A/dm2 to obtain a chromium oxide film of 15 mg/m2.

The test materials produced as described above were tested for contact resistance and post-painting corrosion resistance as values that indicate electrode compatibility.

(1) Contact resistance The test material was heat-treated at 210° C. for 20 minutes and then pressed with a spot welding electrode tip with a force of 100 N to measure it.

(2) Corrosion resistance after painting I (IJ (:G test)) Epoxyphenol-based can inner surface paint was applied to the sample material at 70 mg/dm2?f
After printing, make cross cuts with a knife. NaC
A corrosive liquid consisting of 115 g/l of citric acid and 15 g/l of citric acid was degassed, and the test material was immersed. After being left at 50°C for one week, the corrosion width was examined.

(3) Corrosion resistance after painting ■ (Blister test) After baking the same paint as in (2), it was degassed without causing any damage and then placed in a tomato juice solution.

After being left at 50°C for 3 weeks, the occurrence of blisters was observed.

Number of points Number of blisters 4 1-10 3 10-20 2　　　　20~(local) 1　Full surface Table 1 shows the test results.

Table 1 All examples had low contact resistance and good corrosion resistance. Comparative example 1 where only chromate treatment was applied to zinc plating
had low contact resistance but poor corrosion resistance. Comparative example 2.3
Both had good corrosion resistance, but had high contact resistance and poor weldability.

<Effects of the Invention> The tin-free steel for welded cans of the present invention uses zinc and chromium, which are cheaper than tin, so it is a low-cost can material with good weldability and corrosion resistance.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the amount of zinc deposited and the contact resistance value. FIG. 2 is a graph showing the relationship between the amount of zinc plating and the blister resistance index.

Claims (2)

[Claims] (1) On the surface of the steel plate, 10 to 300 mg/m^ per side
2 chrome plating layer and 0.1~5g/m^2 on top
Tin-free steel for welding cans with galvanized layer. (2) 10 to 300 mg/m^2 per side on the steel plate surface
a chromium plating layer, a zinc plating layer of 0.1 to 5 g/m^2 on top of it, and a chromate layer of chromium oxide or chromium oxide and metal chromium on top of it of 25 mg/m^2 or less. Tin-free steel for welding cans with.