JPH05302196A - Production of tin plate excellent in appearance of alloy layer for inside non-coating use - Google Patents

Abstract

PURPOSE:To produce a high corrosion resistant tin plate having 'grey color' hue by reducing the quantity of the alloy layer of the tin plate to a specific quantity. CONSTITUTION:It is confirmed that the alloy layer of the tin plate usually exhibits 'black' because a large quantity of columnar iron-tin alloy layer is formed by reflow treating to cause the absorption or irregular reflection of light and as a result of various examinations, the quantity of the formed metallic layer is reduced to 0.11-0.56g/m<2>. As a result, the hue is improved to be 'grey color' and the quantity of the formed alloy layer is reduced by the reflow treating of low temp. and long time baking (at 100-220 deg.C for 20min) and the tin plate excellent in the appearance of the alloy layer and little in the elution speed of tin is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a tin plate having a small tin elution rate and an alloy layer having a good appearance after detinning in tin plates used for uncoated inner surfaces such as bamboo shoots, pineapples and peaches. It is a thing.

[0002]

2. Description of the Related Art Tinplate has been widely used as a canning material. Especially when packing solids such as bamboo shoots, pineapples, peaches, changes in contents during storage,
It is very important to suppress changes in flavor. In order to suppress the discoloration of contents and the change of flavor, it is indispensable to elute tin ions into the contents, and tinplate is used without coating the inner surface for such applications. The tin plate used without coating the inner surface is usually tin-plated at 2.8 to 16.8 g / m ^{2 on} one side of the steel plate,
After tin plating, molten tin treatment (hereinafter referred to as "reflow treatment") is performed to obtain a good tin appearance with metallic luster, and at the same time, an iron-tin alloy layer is formed at the plating interface to ensure good corrosion resistance. There is.

[0003]

In recent years, in a user who uses a tin plate without coating the inner surface, a black material is generated on the inner surface of the can after a relatively short time after the content is filled for a certain period of time. However, it has been pointed out that the product value of tinplate is greatly impaired. This is because the detinning reaction proceeded in a short time during the aging period and the alloy layer was exposed.However, since the tint of the alloy layer of tinplate is usually "black", this is what led to this point. is there. That is, there are the following two problems that must be solved. Even if the detinning reaction proceeds on the inside of the can and the alloy layer is exposed, the tin with an alloy layer with a good appearance that is not "black" but "gray white" must be developed. This is because the tin removal reaction on the inner surface is slow, and a long-life tinplate with a long time until the alloy layer is exposed, that is, a highly corrosion-resistant tinplate with a small tin elution rate must be developed.

[0004]

First of all, the tin alloy layer looks "black" because the reflow treatment after tin plating is a high temperature / short time heat treatment for several seconds at a temperature higher than the melting point of tin (232 ° C). This is because a large amount of columnar iron-tin alloy is generated (see FIG. 1). The alloy layer produced in a large amount by this reflow treatment has a columnar shape and grows in the height direction, so that it absorbs or diffusely reflects light and appears “black”. Therefore, the inventors conducted various studies to improve the color tone of the alloy layer to "gray white". As a result, if the amount of the alloy layer produced by the reflow treatment is reduced, the color tone changes from "black" to "gray white". I found that I could improve. This is because the alloy layer having a columnar shape is generated by the reflow treatment, but since the amount thereof is small, the flat iron surface is exposed, so that the amount of light absorbed is small and diffuse reflection is also small. (See Figure 2)

On the other hand, if the amount of the alloy layer is reduced, its appearance is improved, but if it is reduced too much, the coverage of the alloy layer with respect to the iron surface is lowered, which causes a problem that the elution rate of tin is increased. In other words, the coverage of the alloy layer on the iron surface is poor, so-called ATC (Alloy-Tin Cou).
Since the ple) value becomes large and the corrosion resistance of the tin plate deteriorates, tin is eluted and the alloy layer is exposed in a short time.
Therefore, the inventors have made various investigations in order to develop a tin plate having a gray tone of the alloy layer and having a small tin elution rate and excellent corrosion resistance. As a result, the following conclusions have been reached.

In order to improve the color tone of the alloy layer, it is necessary to reduce the amount of the alloy layer produced by the reflow treatment, but there is a problem that the tin elution rate increases because of the high ATC value. In order to solve this problem, that is, to reduce the elution rate of tin with a small metal layer (reduce the ATC value), it was found that low temperature-long baking is extremely effective. This is because a dense alloy layer is formed on the iron surface where the alloy layer was not formed by the reflow treatment by baking at low temperature for a long time, and the coverage of the alloy layer is dramatically improved, so that the ATC value can be greatly reduced. To do. Further, the color tone of the alloy layer formed by baking at low temperature for a long time is "gray white", and the reason for this can be explained as follows. The shape of the alloy layer formed by baking at low temperature for a long time is different from the columnar shape of the alloy layer formed by the reflow treatment, and has a spherical shape, which causes specular reflection even for reflection that is difficult to absorb light. is there. (See Figure 3)

The present invention was made on the basis of the findings, and the gist thereof is as follows: (1) 2.8 to 16.8 g / m ² per surface of a steel plate surface
After the tin plating is applied, reflow treatment is performed and the alloy layer is reduced to 0.
11 to 0.56 g / m ^{2 A} method for producing a tin plate having an excellent appearance of an alloy layer for the purpose of not coating the inner surface (2) 2.8 to 16.8 g / m ² per surface of the steel sheet
After the tin plating is performed, a reflow treatment is performed to form an alloy layer of 0.11 to 0.56 g / m ² , and then a temperature of 10
Another object of the present invention is to provide a method for producing a tin plate having an excellent appearance of an alloy layer for internal unpainted use, which is characterized by baking at 0 to 220 ° C. for 1 to 20 minutes.

[0008]

The present invention will be described in detail below. In the present invention, the original plating plate is not particularly limited, and a steel plate usually used as a container material is used. There is no particular restriction on the manufacturing method, material, etc. of the plated original plate, and it is manufactured from the ordinary billet manufacturing process through processes such as hot rolling, pickling, cold rolling, annealing and tempering. Further, this plated original plate is annealed after cold rolling according to the required can strength and plate thickness, and then re-cold rolled (that is, 2C).
R method). After all the degreasing and pickling treatments, tin plating is applied, followed by reflow treatment. Conditions for degreasing, pickling, and tin plating are not particularly limited. For tin plating, a ferrostane bath, a halogen bath or the like which is usually performed may be applied. Similarly, the reflow processing conditions are not particularly limited, and either one of the conduction reflow and the induction reflow or a combination of both may be used.
The purpose of the reflow treatment is to produce a beautiful tin plate having metallic luster by melting the tin-plated white plated surface with molten tin. At the same time, an alloy layer is formed at the iron / tin interface to ensure good corrosion resistance. When the inner surface is not coated, the tin plating amount is usually 2.8 to 16.8 g / m ² per one side of the steel plate, and is used depending on the corrosiveness of the contents.

First, an appropriate amount of alloy layer that determines the color tone of the alloy layer will be described. The iron-tin alloy layer formed by the reflow treatment has a columnar shape and grows in the height direction with respect to the iron surface, and a large amount of such an alloy layer is formed so as to cover the entire iron surface. When such an alloy layer is formed, when the light hits it, the light is mostly absorbed in the alloy layer.
Alternatively, even if reflection occurs, the reflection is diffuse reflection and does not become specular reflection, and therefore the human eye recognizes the alloy layer formed by the reflow process as “black”. That is, in order for the human eye to recognize the color tone of the alloy layer as "gray white", it is necessary to generate a metal layer having a smooth surface which does not absorb much light or causes specular reflection.

The present inventors conducted various experiments and found that the amount of the alloy layer had the greatest influence on the color tone of the alloy layer. That is, the color tone of the alloy layer changes from "black" to "gray white" when the amount of alloy layer is 0.56 g / m.
^{From 2} or less, and when an alloy layer exceeding 0.56 g / m ² is formed, the alloy layer exhibits a “black” color tone due to light absorption and diffuse reflection. However, 0.56 g / m
^{When the} amount of alloy layer is ² or less, the columnar alloy layer does not grow so much in the height direction with respect to the iron surface, and since the amount of alloy layer is small, the iron surface is not entirely covered. The absorption does not occur so much in the alloy layer, and the reflection is not diffuse reflection but mainly close to specular reflection on the iron surface. For these reasons, the color tone of the alloy layer becomes “gray white”. From the above, the upper limit of the amount of alloy layer is determined to be 0.56 g / m ² .

Further, the lower limit of the appropriate amount of alloy layer is determined from the reflow treatment as follows. The reflow process is applied to produce a beautiful tin plate having a metallic luster, but the degree of the reflow process is mainly controlled by voltage. That is, the reflow process is performed at a high voltage when increasing the alloy layer amount, and at a low voltage when decreasing the alloy layer amount. The amount of alloy layer that is inevitably generated when the tin plating layer is completely melted to obtain a tin plate with a beautiful appearance and the minimum necessary reflow treatment to obtain a metallic luster is performed is
It is 0.11 g / m ² . From the above, an appropriate amount of alloy layer having a “gray white” color tone is 0.11 to 0.56 g / m 2.
Determined as ² .

On the other hand, when the amount of the alloy layer is reduced in this way, the coverage of the alloy layer on the iron surface is lowered, so that the ATC value is increased and the elution rate of tin is increased. This is because a large couple current flows in a direction in which a local battery is formed between the iron surface where the alloy layer is not formed and the tin-plated layer, and tin is dissolved. On the other hand, when the coverage of the alloy layer on the iron surface is high, since a local battery is formed between the alloy layer and the tin-plated layer, a couple current flows in the direction in which tin dissolves, but the value becomes extremely small ( That is, the ATC value decreases and the tin elution rate decreases. The present inventors have studied a method of reducing the amount of alloy layer generated in the reflow treatment as much as possible and reducing the ATC value (reducing the dissolution rate of tin), and as a result, baking at low temperature for a long time is extremely excellent. It was found that the effect was obtained.

This is because a very dense spherical alloy layer is uniformly formed in a small amount by baking at a low temperature for a long time, so that the coverage of the alloy layer is dramatically improved. That is, in the reflow treatment, a heat treatment is performed at a temperature higher than the melting point of tin for a short time, but in that case, the alloying reaction of iron-tin proceeds extremely quickly, so that the alloy layer is a columnar alloy layer locally. The color tone is black and the coverage is poor. On the other hand, when baking is performed for a long time at a temperature lower than the melting point of tin after the reflow treatment, the alloying reaction proceeds slowly, so that an alloy layer is formed on the entire surface of the iron-tin interface, and its form becomes a spherical form. .. The color tone of the spherical alloy layer is “gray white” because it is difficult to absorb light and specular reflection occurs even when reflection occurs. That is, by baking at low temperature for a long time after the reflow treatment, a dense alloy layer is uniformly formed, and an alloy layer having a good color tone and an excellent covering property is formed.

Next, appropriate low temperature and long time baking conditions will be described. A suitable temperature for low temperature long time baking is 100 to 220 ° C. This is because the iron-tin alloying reaction rate is extremely slow at 100 ° C. or less and almost no alloy layer is formed, so that the effect of improving the coating property of the alloy layer is not recognized. Further, at 220 ° C. or higher, the alloying reaction rapidly progresses, so that the formed alloy layer has a columnar shape and the color tone becomes “black”, impairing the appearance of the alloy layer. Furthermore, a baking time of 1 to 20 minutes is appropriate. If the baking time is 1 minute or less, the alloy layer is not sufficiently formed and the improvement of the covering property is not recognized. Further, if the baking time is 20 minutes or more, the effect that the spherical alloy layer is uniformly formed is saturated, and an economical demerit occurs from the viewpoint of productivity. From the above, an appropriate low temperature and long time baking condition can be determined to be 1 to 20 minutes at 100 to 220 ° C. The baking process at low temperature and for a long time is not specified, and it may be carried out by a steel manufacturer or a can manufacturing manufacturer. For example, it is sufficiently possible to utilize baking at the time of external coating at a can manufacturing maker.

Subsequently, after the reflow treatment, a chromate treatment is carried out for the purpose of improving the coating adhesion or the rust resistance. The chromate treatment is usually performed by electrolytic treatment in sodium dichromate, but the amount of chromate film is controlled by the electrolytic treatment conditions and the amount of the chromate film is usually 2 to 12 in terms of chromium.
g / m ² . The chromate treatment is also not particularly limited, but a mild treatment is preferable for the chromate treatment in order to prevent local detinning on the inner surface of the can, and the chromate film amount is ² to 6 mg / m ^{2 in} terms of chromium.
Is desirable.

[0016]

【Example】

Example 1 Examples of the present invention are described below, and the results are shown in Table 1. A plating base plate adjusted to a predetermined thickness and strength by cold rolling or twice rolling after annealing is electrolytically degreased in 5% caustic soda, washed with water, electrolytically pickled in 10% sulfuric acid, surface activated, and then plated with tin. gave. The tin plating was performed under the conditions shown in (1), and the tin plating amount was adjusted under the electrolytic conditions. The reflow treatment was performed by appropriately combining conduction reflow and induction reflow, and controlling the alloy layer amount by the reflow voltage. Subsequently, the chromate treatment was carried out under the condition shown in (2), and the chromate adhesion amount was adjusted under the electrolytic condition.

(1) Tin plating conditions Plating bath composition Tin sulfate 20 to 30 g / l Phenolsulfonic acid 25 to 35 g / l (65% solution) Bath temperature 45 ° C. Current density 15 to 25 A / dm ² (electrolysis time is tin (Adjust by plating amount)

(2) Chromate treatment conditions Bath composition Sodium dichromate 25 g / l pH 4.5 Bath temperature 50 ° C. Current density 4 A / dm ² (electrolysis time is adjusted by chromium deposition amount)

Regarding the above-mentioned treated materials, the following (A) to
The item (D) was evaluated and its performance was evaluated. (A) Measurement of tin plating amount and alloy layer amount The amount of metallic tin and the amount of alloy tin were calculated by the electrolytic stripping method in 1N hydrochloric acid. (B) Chromium Adhesion Amount Tin was immersed in an aqueous solution of hydrochloric acid: water = 1: 2, the chromium layer on the surface was dissolved, and then the solution was measured by an atomic absorption method to calculate the amount of surface chromium. (C) Color Tone of Alloy Layer The untinned metal tin layer was removed by electrolytic stripping in 5% caustic soda, the alloy layer was exposed, and the color tone was visually observed. The evaluation criteria are as follows. ◯: Alloy layer color tone is gray white Δ: Alloy layer color tone is gray black ×: Alloy layer color tone is black

(D) Actual Can Test Welding cans were prepared with a seam welder, filled with bamboo shoots and stored at 38 ° C. for 6 months and 12 months, and the degree of exposure of the alloy layer and the color tone of the exposed alloy layer were visually observed. did. The evaluation criteria are as follows. ◎: The exposed area of the alloy layer is small and its color tone is gray white. ○: The exposed area of the alloy layer is large, but its color tone is gray white. △: The exposed area of the alloy layer is small, but its color tone is black. Large area, black color

[0021]

[Table 1]

Example 2 Another example of the present invention will be described below, and the results are shown in Table 2. A plating base plate adjusted to a predetermined thickness and strength by cold rolling or twice rolling after annealing is electrolytically degreased in 5% caustic soda, washed with water, electrolytically pickled in 10% sulfuric acid, surface activated, and then plated with tin. gave. The tin plating was performed under the conditions shown in (1), and the tin plating amount was adjusted under the electrolytic conditions. The reflow treatment was performed by appropriately combining conduction reflow and induction reflow, and controlling the alloy layer amount by the reflow voltage. Subsequently, chromate treatment was performed under the condition shown in (2), and the amount of chromate adhered was adjusted under electrolytic conditions. Furthermore, baking was performed at low temperature for a long time.

(1) Tin plating conditions Plating bath composition Tin sulfate 20 to 30 g / l Phenolsulfonic acid 25 to 35 g / l (65% solution) Bath temperature 45 ° C. Current density 15 to 25 A / dm ² (electrolysis time is tin (Adjust by plating amount)

(2) Chromate treatment conditions Bath composition Sodium dichromate 25 g / l pH 4.5 Bath temperature 50 ° C. Current density 4 A / dm ² (electrolysis time is adjusted by the amount of chromium deposited)

Regarding the above-mentioned treated material, the following (A) to
It carried out about the item of (E), and evaluated the performance. (A) Measurement of tin plating amount and alloy layer amount The amount of metallic tin and the amount of alloy tin were calculated by the electrolytic stripping method in 1N hydrochloric acid. (B) Chromium Adhesion Amount Tin was immersed in an aqueous solution of hydrochloric acid: water = 1: 2, the chromium layer on the surface was dissolved, and then the solution was measured by an atomic absorption method to calculate the amount of surface chromium. (C) Color Tone of Alloy Layer The untinned metal tin layer was removed by electrolytic stripping in 5% caustic soda, the alloy layer was exposed, and the color tone was visually observed. The evaluation criteria are as follows. ◯: Alloy layer color tone is gray white Δ: Alloy layer color tone is gray black ×: Alloy layer color tone is black

(D) Measurement of ATC In a test liquid prepared by adding 100 ppm of tin ions to degassed tomato juice, flow was made between tin plate (test area: 2.38 cm ² ) with the alloy layer exposed and metallic tin. Couple current was measured at room temperature. (E) Actual Can Test Welding cans were prepared with a seam welder, filled with bamboo shoots and stored at 38 ° C. for 6 months and 12 months, and the exposed degree of the alloy layer and the color tone of the exposed alloy layer were visually observed and evaluated. The evaluation criteria are as follows. ◎: The exposed area of the alloy layer is small and its color tone is gray white. ○: The exposed area of the alloy layer is large, but its color tone is gray white. △: The exposed area of the alloy layer is small, but its color tone is black. Large area, black color

From the above test results, the steel sheet obtained by the method of the present invention has a smaller ATC value than the steel sheet of the comparative example deviating from the manufacturing conditions of the method of the present invention, and the color tone of the alloy layer and the result of the actual can test are stable. Is excellent.

[0028]

[Table 2]

[0029]

As described above, the color tone of the steel sheet obtained according to the present invention can be improved to grayish white, and a tin plate having a low tin elution rate and excellent appearance of the alloy layer can be stably obtained. It has an excellent effect.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a micrograph showing a state where a large amount of columnar iron-tin alloy layers are formed.

FIG. 2 is a schematic diagram of a micrograph showing a state in which there are few iron-tin alloy layers having a columnar shape and a flat iron surface is exposed.

FIG. 3 is a schematic view of a micrograph showing an iron-tin alloy layer having a spherical morphology.

Claims (2)

[Claims] 1. A steel plate surface having 2.8 to 16.8 per surface.
It was subjected to tin plating g / m ^2, excellent appearance of the alloy layer on the inner surface unpainted applications which comprises bringing the alloy layer by performing a reflow process 0.11~0.56g / m ² produced Tin manufacturing method. 2. A steel plate surface having 2.8 to 16.8 per surface.
After the tin plating of g / m ² is applied, a reflow treatment is performed to form an alloy layer of 0.11 to 0.56 g / m ² , followed by baking at a temperature of 100 to 220 ° C. for 1 to 20 minutes. A method of manufacturing tinplate that has an excellent appearance of the alloy layer for internal unpainted applications.