JPH03183799A - Surface treated steel sheet for vessel excellent in rust resistance, corrosion resistance, and printing finish characteristic - Google Patents

Abstract

PURPOSE:To produce the steel sheet excellent in rust resistance, corrosion resistance, and printing finish characteristics by laminating a Zn.Sn plating layer and a chromate film on the surface of one side of a steel sheet under respectively specified conditions and also laminating a chromate film and a thermoplastic resin on the surface of the opposite side under respectively specified conditions. CONSTITUTION:A Zn.Sn plating layer containing >=10% Zn is formed by 1-30g/m<2> coating weight on the surface of one side of the steel sheet, and a chromate film is formed on the above by 0.1-50mg/m<2> expressed in terms of Cr. Further, a chromate film in which metallic Cr and Cr hydrated oxide are regulated to 10-200mg/m<2> and 5-30mg/m<2> expressed in terms of Cr, respectively, is formed on the surface of the opposite side of the steel sheet, and a thermoplastic resin of 10-100mu thickness is stuck on the above. Moreover, it is preferable that cathodic electrolytic treatment is exerted as the chromate treatment, and bath temp. and cathodic electrolytic current density are regulated to about 30-70 deg.C and about 5-100A/dm<2>, respectively. By this method, the surface treated steel sheet for vessel suitable for beverage cans, food cans, etc., can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a surface-treated steel sheet for containers, which is mainly used as a material for beverage cans, food cans, general containers, and the like.

(Prior art) In recent years, there has been a remarkable development in can manufacturing methods using drawing and drawing and ironing processes (for example, DI processing can manufacturing method), mainly for beverage cans, and there is a demand for surface-treated steel sheets for containers with higher performance than ever before. Very strong. Conventionally, tinplate with good DIIfc shape has been used as a surface-treated steel sheet for DI cans, but the following three problems can be cited as major problems with the can surface.

■Mackerel tends to grow on the outside of the can. In particular, when a can is immersed in tap water to cool it, mackerel will form in a short period of time at the damaged parts of the bottom and wall.

- After tinplate is DI-formed, the outer surface of the can becomes glossy, resulting in a dark appearance after printing, which poses a problem that affects the print finish.

■In order to ensure corrosion resistance against the contents during the can manufacturing process and/or after can manufacturing, it is necessary to perform repair coating on the inside of the can (usually 1 to 2 times, sometimes 3 times), increasing can cost. .

Furthermore, tinplate and electrolytic chromic acid treated steel sheets (hereinafter referred to as TFS-CT) are used for can lids such as drawn cans (for example, for DrD processing, easy oven ends (hereinafter referred to as EOE), and ordinary ends). Although it has been used, 01
Similar problems exist with regard to the rust resistance of the outer surface of the can and the corrosion resistance of the inner surface of the can, as described in the case of cans.

As described above, the problem of rust resistance on the outer surface of the can and corrosion resistance on the inner surface of the can can be explained by the potential relationship between the base iron and the plating layer. In other words, in the case of tin plate/TFS-CT, the Sn plating layer and the Cr plating layer are responsible for the potential of the base steel, and there is no sacrificial corrosion protection effect on the base steel. JP-A-62-13594 introduces a Sn-based coated steel sheet for containers that has excellent paintability and corrosion resistance. This steel sheet has the effect of improving the rust resistance of the outer surface by exerting sacrificial corrosion protection of the plating layer by controlling the potential of the base steel by adding other components (for example, chromium) to the base steel. In order to exhibit a sufficient effect, it is necessary to add several percent of other components, which poses a problem in terms of economic efficiency.

Furthermore, with regard to improving the printing finish after shaping DI cans, a surface-treated steel sheet for containers is introduced in Japanese Patent Application Laid-Open No. 1697-1987. This steel plate contains Zn-containing Sn-Z
Although the can is plated with n alloy to improve rust resistance, since Zn content is present on the inner surface of the can, it may be difficult to use from a hygienic point of view (simply Zn = lead of zinc) when containing beverages or food. There is also a theory that the kanji is the problem), which causes users to avoid using it.

(Problems to be Solved by the Invention) The present invention was made to deal with these problems, and in terms of performance, it exhibits excellent rust resistance on the outer surface of the can, and good can manufacturing processability ( In particular, DIFti, shape), ■D
The printing finish after the Itc shape is also good, and in addition, it is possible to avoid contact between the Zn and the contents on the inner surface of the can, and it is also rust resistant, which makes it possible to reduce the number of times of repainting to compensate for the corrosion resistance of the plating layer. The object of the present invention is to provide a surface-treated steel sheet for containers that has excellent hardness, corrosion resistance, and print finish.

(Means for Solving the Problems) That is, the gist of the present invention is to apply a Zn/Sn plating layer containing 10% or more of Zn to one surface of a steel plate at a rate of 1 to 30 g/rr.
T and a chromate film on it with a Cr equivalent amount of 0.1~
50■/Po is applied, and the opposite surface is coated with metal CrlO.
~200mg/rri and hydrated oxidized Cr of 5~ in terms of Cr
10-1 on top of a chromate coating of 30■/rrr
00. This is a surface-treated steel sheet for containers that has excellent rust resistance, corrosion resistance, and print finish, and is coated with μm thermoplastic resin.

(for production) The present invention will be explained in detail below.

As the container trimming plate of the present invention, a plating base plate having a material suitable for the purpose is used. In addition, there are no particular restrictions on the manufacturing method of the plated original sheet, and it includes the normal billet manufacturing process, hot rolling, pickling, and cold rolling.

It is manufactured through processes such as annealing and rolling. The plated original plate manufactured in this way has 5n-2n on one side surface.
An electrolytic chromate coating is applied to the main surface, and an electrolytic chromic acid treatment coating is applied to the opposite surface, and then a thermoplastic resin is pasted on top.

The purpose of applying 5nZn plating to one surface is to improve the rust resistance and printing finish on the outer surface side. The composition and amount of plating of the 5n-Zn plating layer have a large influence on the effect of improving rust resistance and print finish. However, if the Zn content in the 5n-Zn plating layer is low, less than 10%, almost no effect on improving the external rust resistance is observed, and the rust resistance is only comparable to that of tinplate. This means that when Zn is less than 10%, 5n-Zn
The potential of the plating layer is responsible for the base steel, and when it is exposed to a corrosive environment, especially when the plating layer is damaged by DI processing, etc., or when there is a plating defect such as a pinhole in the plating layer. As with tinplate, it is not possible to sacrificially protect the base metal from corrosion.On the contrary, when the amount of Zn in the Sn/Zn plating layer exceeds 10%, the effect of Zμm, which is a base metal, will cause the corrosion of the 5n-Zn plating layer. The potential changes to a base metal, and it begins to exhibit sacrificial corrosion protection against the base steel.

In other words, a plated steel sheet having a 5n-Zn plating layer in which the amount of Zn in the 5n-Zn plating layer is 10% or more is exposed to a corrosive environment where there is sufficient moisture or oxygen, and the plating layer has machining damage or pinholes. Even if there were, mackerel outbreaks from subway lines are not recognized.

Furthermore, regarding the printing finish of the plating layer, Sn/Zn
If the Znl content in the plating layer is less than 10%, the appearance of the plating layer will hardly change, and the outer appearance after DII processing will have a gloss similar to that of tinplate, and the printing finish will be dark and not good. When the amount of Zn in the plating layer becomes 10% or more, the appearance of the plating layer becomes white, the outer appearance after DI stamping loses its luster, and the appearance after printing becomes whitish compared to that of tinplate. Good finish quality. In other words, the appropriate amount of Zn in the 5n-Zn plating layer to ensure good rust resistance and print finish on the outer surface side of 01 cans, DrD cans, and can lids is 10% or more.

Next, in order to ensure these good properties, 5n-
Not only the amount of Zn in the Zn plating layer but also the amount of plating has a large influence. In order to exhibit good rust resistance and print finish on the outer surface of the can lid for 01 cans and DrD cans, 5.
It is necessary to regulate the plating amount of n-Zn plating to 1 to 30 g/%.

In other words, if the amount of 5n-Zn plating is less than 1 g/m, there will be many pinholes in the plating layer, and the effect of improving rust resistance will be small.Furthermore, the lubricity of the plating layer will be insufficient, and galling will easily occur during DI forming. Deteriorates Dltc morphology. Furthermore, if the amount of plating exceeds 30 g/rd, the effects of improving rust resistance, DII workability, etc. will be saturated, which will be economically disadvantageous.

The plating bath that forms the 5n-Zn plating layer with such excellent properties is not particularly regulated, but
A pyrophosphoric acid bath, a cyanide bath, a sulfuric acid bath, and a chloride bath are used, and the amount of Zn in the 5n-Zn plating layer can be controlled mainly by the balance of the amount of metal ions in each bath.
The amount of plating can be controlled by the number of coulombs required for electrolysis.

The chromate treatment performed on the top surface of the 5n-Zn plating layer is -
(a) is subjected to an immersion treatment in an aqueous solution of chromic acid sodium salt, potassium salt, ammonium salt, etc. This is because the chromate film formed by electrolysis has poor lubricity and deteriorates the DI rectangularity. therefore,
In order to prevent discoloration of the plating layer due to air oxidation without impairing the good formability of the 5n-Zn plating layer, immersion chromate treatment may be performed. The amount of chromate deposited can be controlled by the bath concentration, but discoloration due to air oxidation can be prevented if the amount of chromate deposited is 0.1 /nf or more in terms of the amount of metallic chromium. Furthermore, in the case of 01 can use, chromate treatment or phosphoric acid treatment is performed after the DI form to improve coating performance and post-painting corrosion resistance, but in the present invention, these treatment methods and treatments after the DII form are applied. There are no particular restrictions on the conditions, and commonly used processing methods are applied.

Further, chromate treatment for uses other than 01 cans is performed by electrolytic treatment. The chromate film formed during the electrolytic treatment is very effective in improving the rust resistance of filamentous rust, so-called filiform corrosion, which occurs under the coating on the outer surface of the can during storage.

By forming the romate film in this manner, rust resistance is maintained over a long period of time.

As described above, the chromate film has a great effect on improving performance, especially when it is used after being painted, but if too much is attached, BO[! Cracks may occur in the chromate coating layer in areas that have been subjected to severe processing such as R/D processing, which may actually impair rust resistance. The chromate coating referred to here includes two types: one is a single coating of hydrated chromium oxide, that is, the original chromate coating, and the other is a coating consisting of two layers: a metallic chromium layer on the bottom layer and a hydrated chromium oxide layer on the top layer. is pointing to.

In this way, the amount of ROM deposited is 0.1 to 501 Ig/r, which has good paintability and does not deteriorate the rust resistance of processed parts.
rr is selected.

That is, if the amount of chromium deposited is less than 0.1 .mu./po, the effect of improving paint adhesion cannot be obtained, so the amount of chromium deposited is set to be 0.1 .mu./po or more. On the other hand, if it exceeds 50■/nl, EO
B. Rust resistance of processed parts deteriorates in areas that have undergone severe processing such as DrD processing. Therefore, the amount of chromium deposited is 50m
g/m2 or less.

The chromate treatment may be carried out by any method such as immersion treatment with aqueous solutions of various sodium salts, potassium salts, and ammonium salts of chromic acid, spray treatment, electrolytic treatment, etc., but cathodic electrolytic treatment is particularly excellent. In particular, 5o4- ions and F- ions (including complex ions) in chromic acid.
Alternatively, cathodic electrolytic treatment in an aqueous solution to which a mixture thereof is added is most excellent. The concentration of chromic acid is not particularly regulated, but it is 20 to 200 g//! is sufficient.

The amount of anion added is 1/300-1/25 of Cr0.
Preferably, the best chromate coating is obtained when the ratio is 1/200-1150. The amount of anion is 1/30 of Cr6+
If it is less than 0, it will not be possible to obtain a high quality chromate film which will have a significant effect on homogeneous and uniform OO coating performance. On the other hand, if it exceeds 1/25, the amount of anions incorporated into the formed chromate film will increase, and the coating performance, especially the secondary adhesion of the paint, will deteriorate.

The added anions are added to the chromic acid bath in the form of compounds of sulfur, chromium sulfate, sodium fluoride, and the like.

There are no particular regulations regarding the bath temperature, but it should be between 30 and 7
A temperature range of 0°C is appropriate from the viewpoint of workability.

A cathode electrolysis current density of 5 to 100 A/drf is sufficient. The treatment time is such that, in any combination of the treatment conditions, the amount of chromium deposited is O, 1 to 50 mg as shown above.
/m2.

In addition, the amount of the hydrated chromium oxide layer can be adjusted by adjusting the immersion time in an aqueous solution after electrolytic treatment or by dissolving it in a chromic acid-anion treatment bath with different concentrations in a separate treatment tank. .

The purpose of applying electrolytic chromic acid plating to the opposite side of the 5n-2n plating and pasting the thermoplastic resin film is to apply electrolytic chromic acid plating to the opposite side of the 5n-2n plating. This is to cover the back side of the component Zμm, and to provide a composite surface-treated steel sheet with excellent corrosion resistance at low cost by omitting repair painting on the inner surface of cans by can manufacturers. For this purpose, a thermoplastic resin film that can withstand processing into DI cans, DrD cans, can lids, etc. is attached to a steel plate using this electrolytic chromic acid plating layer as a binder.

Thermoplastic films with such characteristics include:
Although not particularly restricted, carbonyls based on free carboxylic acids, carboxylates, carboxylic esters, carboxylic acid amides, carboxylic acid anhydrides, carbonic esters, urethanes, and urea (urea) may be present in the main chain or side chain. It is preferable to use a thermoplastic resin film containing groups, a thermoplastic polyester resin film in which 45 mol% or more of the dicarboxylic acid component is terephthalic acid, and 55 mol% or more of the diol component is 1,4-butanediol.

In order to withstand the processing of DI cans, DrD cans, can lids, etc., and to exhibit corrosion resistance, the thickness of the thermoplastic resin film must be 10 to 100 nm. If the thickness of the thermoplastic resin film is less than Ion, defects such as pinholes will easily occur in the film when it is processed into DI cans, DrD cans, can lids, etc., and therefore corrosion resistance will not be sufficient. If the thickness exceeds 100 nm, the economical efficiency will be significantly reduced.

The amount of romming necessary to fully exhibit the adhesion of the thermoplastic resin film is 10 to 200 metal Cr on the surface side of the steel plate.
■/po, 5 to 30 ■/po when hydrated oxidized Cr is Cr. The chromate coating is composed of metallic chromium and a chromium oxide coating mainly composed of hydrated chromium oxide formed on its surface. If the amount of metallic chromium is less than 10 μ/Po, the adhesion of the thermoplastic resin film will decrease, and the thermoplastic resin film and the electrolytic chromic acid treated steel sheet may peel off during processing of the steel sheet or during hot water treatment such as retort treatment. more likely to occur.

Corrosion resistance is also insufficient, and even when a thermoplastic resin film is attached, so-called under-film corrosion, such as undercutting corrosion, in which the contents of the can pass through the film and corrosion progresses under the film, is likely to occur. . If the hydrated chromium oxide is less than 5 μ/Po as chromium, the thermoplastic resin film and the electrolytic chromic acid treated steel sheet may peel off during processing of the steel sheet or during hot water treatment such as retort treatment, as in the case of metal chromium. will occur easily.

On the other hand, if the metallic chromium content exceeds 200 μ/Po, the economical efficiency will be greatly reduced. In addition, if the hydrated chromium oxide exceeds 30 μ/Po as chromium, the thermoplastic resin film and the electrolytic chromic acid treated steel sheet will easily separate during processing of the steel sheet or during hot water treatment such as retort treatment. .

The conditions for forming the chromium plating on the lower layer of the thermoplastic resin film are not particularly limited, but cathodic electrolytic treatment for applications other than 01 cans may be used among the chromate treatments performed on the upper surface of the 5n-Zn plating layer.

The bath conditions, amount of anions added, bath temperature, cathode electrolysis current density, etc. may be the same as those for cathode electrolysis treatment for uses other than 01 cans. Furthermore, the coating amount of the hydrated chromium oxide layer is adjusted in the same manner as in the cathodic electrolytic treatment for uses other than 01 cans.

(Example) Examples of the present invention will be described below, and the results are shown in Tables 1 and 2.

By cold rolling and annealing process, the plated original plate was adjusted to the material and thickness according to 01 can use, DrD can use, and can lid use, and after electrolytic degreasing and water washing in 1 to 15% caustic soda, 5 to 15%
After surface activation by electrolytic pickling in sulfuric acid, the surfaces corresponding to the inside and outside of the can were plated with Sn under the conditions shown in (1), (2)-(a),
5n-Zn plating under the conditions shown in (B), chromate treatment under the conditions shown in (3)-(A), (B), and (C), and further conditions shown in (4)-(A), and (B). It was created by arbitrarily combining ξnates.

(1) Sn plating conditions Plating bath composition Tin sulfate 20-40 g/It additive
2 to 10 g/Pi Plating bath temperature 40 to 55°C Current density 15 to 25 A/d Bo (electrolysis time is adjusted according to the amount of Sn plating) (2) 5n-Zn plating conditions (a) Birophosphoric acid bath plating bath Composition: Tin-pyrophosphate 10-50g/l
(Adjusted according to the plating composition) Zinc sulfate 20 to 100 g/l (Adjusted according to the plating composition) Potassium birophosphate 250 g/l Plating bath temperature 50°C Current density 1O to 30 A/drd (electrolysis time is S
(Adjusted according to the amount of n-Zn plating) (b) Sulfuric acid bath Plating bath composition Stannous sulfate 10-60 g/l (adjusted according to the alloy composition) Zinc sulfate 30-150 g/j! (Adjusted according to alloy composition) Sodium sulfate 300 g/l.

Plating bath temperature: 55°C Current density: 10 to 30 A/d (electrolysis time: 5n
-Adjusted according to the amount of Zn plating) (3) Chromate treatment conditions (a) Bath composition Na, Cr, Ot 24 g /
1 pH 4,5 Bath temperature 45°C Treatment conditions Immersion treatment (B) Bath set rIi, Cr (h 100 g/lSO
4"-1,0g/1 Bath temperature 50"C Current density 5-3QA/dbo (electrolysis time is adjusted according to the amount of chromium deposited) (c) Bath composition Cr0580g/l 5Oa"-0,05g/i! NazSiFi 2.5 g/12N old F0.5
g/l Bath temperature: 45°C Current density: 5 to 60 A/d (electrolysis time is adjusted according to the amount of chromium deposited) (4) Umonate conditions (a) Thickness: 40 μm (b) Thickness: 25 μm Regarding the above treated materials, The following items (A) to (C) were tested and their performance was evaluated.

(8) DI moldability Using a water-soluble emulsion type coolant, DI cans were molded from a blank size of 136 mφ to a can diameter of 65.9 mm at a molding speed of 110 cans/lll 1 μm, and various processed materials were molded. DI moldability was evaluated. The evaluation criteria were as follows.

◎, DI moldability is extremely good.

o: Slight galling occurs on the outer surface during ironing, but D
I Good moldability.

Δ: DI shape is molded, but strong galling occurs on the outer surface during ironing, and DItc shapeability is poor.

The material broke during the X1DI preforming process, making DI molding impossible.

(B) Printing finish quality of DI molding (01 cans were prepared under the conditions of ^>, red, white, and yellow inks for the outside of the can were printed at a film thickness of 5 μm, and the print finish was visually judged. The judgment criteria are as follows.

○: The appearance after printing is whitish, and the printing finish is extremely good.

Δ: Slight gloss was observed in the appearance after printing, and the print finish was slightly inferior.

×: Appearance after printing has the same level of gloss as tinplate,
Poor print finish.

(C) Rust resistance on the outer surface side Created under the conditions of (A) and (B). i-printing can, Dr.
The rust resistance of the outer surface side of the D printing printing table and the evaluation material which was subjected to EOE processing after painting was evaluated by the following evaluation test.

In addition, the scratched part and the bottom part of the DI printing can and the DrD printing plate were evaluated, and the score part and the rivet part of the HOE processed material were evaluated.

■Tap water immersion test The evaluation materials were immersed in tap water at room temperature for 3 days, and the rusting rate of the evaluation part was measured.

■ Refrigeration cycle test evaluation The material is kept in a freezer at -15°C for 30ml, then immediately placed in a humidity chamber at 49°C and relative humidity of 98% or higher for 60ml, and then left indoors at room temperature for 22 hours.One cycle is 15 The cycle test was continued and the rusting rate of the relevant parts was measured.

■Humidity tank test: Store in a humidity chamber at 49℃ and relative humidity of 98% or higher for two weeks.
The rusting rate of the relevant parts was measured. The evaluation criteria for rust resistance in each test are as follows.

◎: No rust was observed at all, and the rust resistance was extremely good.

○: Rust resistance is good with a rust occurrence rate of less than 5%.

Δ: Rust resistance is slightly inferior with a rust occurrence rate of 5 to 30%.

×; The rust resistance is inferior to that of tinplate with a mackerel growth rate of over 30%.

(D) Corrosion resistance on the inner surface side (A), DI printed can made under the conditions of (B), Dr.
The corrosion resistance of the inner surface of the evaluation material that was subjected to EOE processing after painting and the printing table was evaluated by filling it with the following four types of solutions and heating it at 55°C.
After 14 weeks, evaluation was made based on the amount of Fe and Zμm eluted into the solution.

■Sprite ■Coca Cola ■Beer ■Tomato juice The evaluation criteria for corrosion resistance in each test are as follows.

O; Elution amount O O; Elution amount 1 ppm or less Δ; Elution amount more than 1 ppm and 10 ppm or less ×; Elution amount 10
ppm or more (effects of the invention) According to the present invention, in terms of performance, the outer surface of the can exhibits excellent ■ rust resistance, ■ good can forming processability (particularly DI shapeability), and ■ DI It has a good finish after printing after stamping, and also has a high resistance to - avoid contact between the Zn and the contents on the inner surface of the can, and can reduce the number of times of repainting to compensate for the corrosion resistance of the plating layer. It is possible to provide a surface-treated steel sheet for containers that has excellent rust resistance, corrosion resistance, and print finish.

Claims (1)

[Claims] Zn・containing 10% or more of Zn on one surface of the steel plate
A Sn plating layer of 1 to 30 g/m^2 is applied, and a chromate film is applied on top of this to a Cr equivalent amount of 0.1 to 50 mg/m^2, and the opposite surface is coated with metal Cr of 10 to 200 mg/m.
^2 and hydrated oxidized Cr at 5 to 30 mg/m^2 in terms of Cr.
A surface-treated steel sheet for containers with excellent rust resistance, corrosion resistance, and printing finish, characterized by having a chromate film applied thereto and a thermoplastic resin of 10 to 100 μm attached thereon.