JPH0390593A - Production of no-reflow tinplate excellent in rust resistance - Google Patents

Abstract

PURPOSE:To reduce the amt. of tin to be deposited and to produce a no-reflow tinplate excellent in rust resistance without deteriorating its DI workability by successively applying degreasing, continuous annealing and temper-rolling to a steel sheet and then plating the sheet without itself being previously pickled. CONSTITUTION:The surface of a cold-rolled steel sheet is degreased, and the sheet is continuously annealed and then temper-rolled in a dry state. The sheet is then immediately plated with tin without itself being previously pickled. Alternatively, the sheet is degreased, continuously annealed, temper-rolled in a wet state, degreased and then immediately plated with tin without itself being previously pickled. Consequently, sufficient rust resistance can be obtained even if the tin plating amt. is reduced to <2.8g/m<2> per one side, and the cost of the tinplate for the DI can is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a no-reflow tinplate with excellent rust resistance, which is a surface-treated steel sheet for can manufacturing.

<Conventional technology> Tinplate has been used as a material for making cans for a long time.
Because soldering has excellent properties and weldability, it has been used for a variety of purposes, including the bodies of three-piece cans such as solder cans and welded cans, and can lids.

In recent years, two-piece DI cans have made significant inroads into the field of beverage cans for beer, carbonated drinks, sports drinks, etc., but tinplate has a tin-plated layer that provides excellent lubricity during drawing and ironing, so it is not suitable for DI cans. It is also used as

By the way, in the manufacturing process of -182 tinplate, a heat treatment called reflow is performed after tin plating.

The tin plating layer immediately after plating does not have sufficient adhesion to the base steel, has many pinholes, and has a white appearance. During reflow, a part of the tin-plated layer is alloyed with the base steel, forming a dense alloy layer between the iron and tin, which improves corrosion resistance and gives the tin-plated layer a bright metallic luster after melting. become.

As described above, since reflow improves both corrosion resistance and appearance, it has great advantages in applications such as 3-piece can bodies and can lids.

However, when used for DI cans, the situation is different. In other words, the iron-tin alloy layer formed by reflow is hard and brittle, and is easily destroyed during DI processing, which not only cannot be expected to improve corrosion resistance, but also shortens the life of the mold for DI processing. There are disadvantages. As described above, the iron-tin alloy layer, which has been useful in conventional applications, is not harmful when used with caution in 01 cans.

Therefore, currently, no-reflow tinplate, which is not subjected to reflow treatment after tin plating, is usually used for DI cans.

In the DI can manufacturing process, after DI processing, the outer surface of the can is coated with a base coat followed by printing, and the inner surface of the can is spray painted.

In the can body, the tin plating layer is significantly destroyed during processing, so the anticorrosion effect of the tin plating layer cannot be expected, and corrosion resistance must depend on the organic coating film. As for the effect of the tin plating layer, it is thought that the lubricity during DI processing is rather important.

However, the tin plating layer on the bottom of the can is not subjected to DI processing and remains intact, so an anticorrosive effect can be expected.

Currently, for DI cans, the amount of tin deposited on one side is 2.8.
A so-called E2.8 tinplate non-reflow material with a rating of 1.5 g/m2 is used, but in order to reduce costs, it is necessary to reduce the amount of expensive tin attached. However, as mentioned above, in no-reflow tinplate, there is no MI-dense iron-tin alloy layer, so when the amount of tin deposited is reduced, the degree of exposure of the base steel plate on the tinplate surface increases due to pinholes in the tin plating layer. .

As is well known, tin has a higher potential than iron in the atmosphere, so it cannot be expected to have a sacrificial anticorrosion effect, and as the degree of exposure of the base steel sheet increases, the risk of red rust occurring increases. In order to solve such problems in the corrosion resistance of non-reflow tinplate, Japanese Patent Publication No. 57-35276 and Japanese Patent Application Laid-Open No. 51-614
0 etc. has been proposed.

In Tokuko Sho 57-35276, iron was added to the lower layer of the tin plating layer.
Corrosion resistance is improved by forming a nickel alloy layer.

In addition, in JP-A-51-6140, the surface roughness is regulated and the amount of tin is O by heating at a temperature below the melting point of tin.
An iron-tin alloy layer of 14~0°01g7m2 is formed.

<Problems to be Solved by the Invention> Regarding Japanese Patent Publication No. 57-35276, as is well known, tin and nickel diffuse very quickly even at room temperature and are easily alloyed. Therefore, when an iron-nickel alloy layer is formed as the base of the tin plating layer, the tin-nickel alloying progresses during the DI processing at the can manufacturer after the tinplate is manufactured.
As a result of the formation of a hard and brittle alloy layer, the life of the mold for DI processing is shortened.

Regarding JP-A-51-6140, even if the alloy layer is formed at a temperature below the melting point of tin, it cannot be denied that the presence of the iron-tin alloy layer has an adverse effect on DI processability.

As described above, all of the conventional methods aimed at improving corrosion resistance involve the formation of an iron-tin alloy layer, which is a contradiction in terms as it inevitably impedes DI workability. It was accompanied by

An object of the present invention is to provide a method for producing a no-reflow tinplate that can reduce the amount of tin deposited, dramatically reduce can cost, and have excellent rust resistance without impairing DI workability.

Means for Solving the Problems> The present inventors believe that in order to avoid the above-mentioned contradiction and improve corrosion resistance without impairing DI workability, it would be better to rely on a dense iron-tin alloy layer. Based on the recognition that it is important to improve the coverage of the base steel by reducing pinholes in the tin plating layer itself, we have studied the conditions for obtaining a tin plating layer with few pinholes over many years. As a result, we finally arrived at the present invention.

That is, according to the present invention, in order to achieve the above object,
After continuous degreasing and continuous annealing of a thin steel plate, followed by skin pass rolling in a dry state, without pickling,
Provided is a method for producing a no-reflow tinplate with excellent rust resistance, which is characterized by immediately carrying out tin plating.

Further, according to the present invention, after a thin steel sheet is continuously degreased, continuously annealed, and then temper rolled in a wet state, tin plating is performed immediately without pickling after degreasing. Provided is a method for producing a no-reflow tin plate with excellent rust resistance.

The present invention will be explained in more detail below.

In the conventional tinplate manufacturing process, the plated original plate after cold rolling is degreased and then annealed on a batch annealing or continuous annealing line, followed by skin pass rolling, and then degreased and pickled on an electro-tin plating line. After pretreatment, tin plating is performed, and each of these steps is performed on an independent line. For this reason, it is inevitable that the surface of the coil of the tinplate original plate will be subject to oil adhesion and oxidation during the processing period after annealing and before being transported to the electrolytic tin plating line. Therefore, in order to obtain a tin plating layer with good adhesion, it was necessary to perform degreasing and pickling as a pretreatment for the original plating treatment. In general, pickling treatment as a pre-plating treatment consists of immersion or electric field treatment at a cathode, anode, etc. performed either singly or alternately in an aqueous solution of an inorganic acid such as sulfuric acid or hydrochloric acid, depending on the oxidation state of the steel sheet surface. This is an important treatment for activating the steel plate surface.

When the oxidation state of the steel sheet surface is extremely severe, it is impossible to perform tin plating with good adhesion without pickling. However, although the detailed mechanism is unknown,
If the surface is sufficiently clean, pickling is not only unnecessary in order to obtain a tin plating layer with good adhesion, but in fact pickling is harmful in order to obtain a tin plating layer with few pinholes. The present inventors have discovered that.

Generally, annealing is performed in a reducing atmosphere, so the surface of the plated blank immediately after coming out of the continuous annealing line is in an activated state. Therefore, in the first invention of the present application, temper rolling is performed in a dry state while the surface is in such a state, and tin plating is performed immediately without pickling. This makes it possible to obtain a tin plating layer with fewer pinholes than when tin plating is performed.

Also, in the second invention of the present application, pickling is omitted by immediately following the continuous annealing of the degreasing material, which is essential when wet rolling using rolling oil is performed as skin pass rolling. By performing tin plating all at once while the surface is in an active state, tin plating with fewer pinholes can be performed.

In the present invention, it is important to carry out tin plating after continuous annealing while the surface of the steel sheet is still in an active state. This can be achieved by doing it on line. Furthermore, there are no restrictions on the conditions for tin plating itself, and commonly used baths such as halogen baths and ferrostane baths can be used.

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

In the description of each example and comparative example, the contents of each condition indicated by the symbols (■) to (■) are as follows.

■Annealing conditions ■Tin-plated strips (halogen valley) ■Tin plating conditions (ferrostane bath) ■Pickling conditions (Example 1) A low-carbon cold-rolled steel sheet was electrolytically degreased according to a conventional method, washed with water, dried, and then subjected to ■ It was annealed under the conditions shown, followed by dry temper rolling at a rolling reduction of 1%, immediately followed by tin plating under the conditions shown in (2), washed with water, and dried to obtain a test material. During this time, the steps from annealing to tin plating were completed within 1 minute.

(Example 2) A low carbon cold rolled steel sheet was electrolytically degreased according to a conventional method, washed with water, dried, annealed under the conditions shown in Immediately after degreasing and washing with water, tin plating was performed under the conditions shown in (2), followed by washing with water and drying to obtain a test material. During this time, the steps from annealing to tin plating were completed within 1 minute.

(Example 3) A low carbon cold rolled steel sheet was electrolytically degreased in accordance with a conventional method, washed with water, dried, annealed under the conditions shown in ■, followed by dry temper rolling at a rolling reduction of 1%, and then immediately under the conditions shown in ■. After tin plating, the sample was washed with water and dried. During this time, the steps from annealing to tin plating were completed within 1 minute.

(Example 4) A low carbon cold rolled steel sheet was electrolytically degreased according to the conventional method, washed with water, dried, annealed under the conditions shown in Immediately after degreasing and washing with water, tin plating was performed under the conditions shown in (2), followed by washing with water and drying to obtain a test material. During this time, the steps from annealing to tin plating were completed within 1 minute.

(Comparative Example 1) A low-carbon cold-rolled steel sheet was electrolytically degreased in accordance with a conventional method, washed with water, dried, and then annealed under the conditions shown in (■) and dry skin-pass rolled at a rolling reduction rate of 1% the next day using a plated original sheet. Two days later, tin plating was performed under the conditions shown in (2) without degreasing or pickling, followed by washing with water and drying to obtain a test material. During this time, it took three days to complete the tin plating process after annealing.

(Comparative Example 2) A low-carbon cold-rolled steel sheet was electrolytically degreased according to a conventional method, washed with water, dried, and then annealed under the conditions shown in (■) using a plated original sheet.The next day, wet temper rolling was performed at a reduction rate of 15%. Two days later, the sample was degreased and washed with water according to a conventional method, and then tin-plated under the conditions shown in (2) without acid washing, washed with water, and dried to obtain a test material. During this time, it took three days to complete the tin plating process after annealing.

(Comparative Example 3) A low-carbon cold-rolled steel sheet was electrolytically degreased according to a conventional method, washed with water, dried, and then annealed under the conditions shown in (■) using a plated original sheet.The next day, dry skin pass rolling was performed at a reduction rate of 1%. , After 2 days, perform pickling under the conditions shown in ■, then wash with water and continue ■
After tin plating was carried out under the conditions shown below, the sample material was washed with water and dried. During this time, it took three days to complete the tin plating process after annealing.

(Comparative Example 4) A low-carbon cold-rolled steel sheet was electrolytically degreased in accordance with a conventional method, washed with water, dried, and then subjected to wet temper rolling at a reduction rate of 15% the next day using a toughened original sheet annealed under the conditions shown in (■). Two days later, it was electrolytically degreased according to a conventional method, washed with water, pickled under the conditions shown in (1), washed with water, tin-plated under the conditions shown in (2), washed with water, and dried to obtain a test material. During this time, it took three days to complete the tin plating process after annealing.

(Comparative Example 5) A low carbon cold rolled steel sheet was electrolytically degreased according to a conventional method, washed with water, dried, annealed under the conditions shown in ■, followed by dry skin pass rolling at a rolling reduction of 1%, and then continued under the conditions shown in ■. After pickling and washing with water, tin plating was performed under the conditions shown in (2), followed by washing with water and drying to obtain a sample material.

The following plating adhesion test and rust resistance test were conducted using each of the test materials produced as described above.

[Plating Adhesion] The adhesion of the tin plating layer was determined by peeling off cellophane tape.

○...No peeling △...Slight peeling ×...Almost peeling [Rust resistance] A 12-hour salt water spray test was carried out according to the method specified in JIS Z 2371. The test was conducted and judged based on the occurrence of red rust.

O: No red rust occurred Δ: A small amount of red rust occurred ×: Red rust occurred over the entire surface The results are summarized in Table 1. Comparative Example 3 and Comparative Example 4 represent quality evaluations of no-reflow tinplate manufactured according to the conventional tinplate manufacturing process.

If the amount of tin plating is thicker than 2.8 g/m', there is no problem in rust resistance, but if the amount of tin plating is further reduced, the occurrence of red rust will suddenly become noticeable.

On the other hand, in Examples 1 and 2, by carrying out tin plating without pickling, it is possible to suppress the occurrence of red rust even with a light area weight of less than 2.8 g/m2. Moreover, as is clear compared to Comparative Examples 1 and 2, this was made possible because plating was carried out immediately after annealing. In other words, in Comparative Examples 1 and 2, the work in progress after annealing is tin-plated after a period of time, so even if pickling is omitted, it is impossible to achieve plating with sufficient adhesion. It has become.・This tendency is especially evident in thick-grained materials. Comparative Example 5 shows that although the process from annealing to plating was carried out quickly, the red rust resistance could not be improved due to pickling.

Moreover, from Example 3 and Example 4, the effects of the present invention are as follows:
This shows that it does not depend on the tin plating conditions themselves.

<Effects of the Invention> Since the present invention is configured as described above, the present invention provides a thin tin plate with a tin plating amount of less than 2.8 g/m2 per one side in a no-reflow tin plate that does not form an iron-tin alloy layer. It has now become possible to obtain sufficient rust resistance even after aging. This makes it possible to reduce the weight of tinplate for DI cans, which can greatly contribute to reducing can costs.

Claims (2)

[Claims] (1) Excellent rust resistance characterized by continuous degreasing, continuous annealing, and subsequent temper rolling of thin steel sheets in a dry state, followed by tin plating immediately without pickling. A method for manufacturing no-reflow tinplate. (2) Rust resistance characterized by continuous degreasing and continuous annealing of a thin steel sheet, followed by skin pass rolling in a wet state, and then tin plating immediately without pickling after degreasing. A method of manufacturing excellent no-reflow tinplate.