JPH04193980A - Manufacture of tinned steel sheet for welded can - Google Patents

Abstract

PURPOSE:To form a metallic tinned layer into a discontinuous island state by specifying heating conditions for a tinned layer. CONSTITUTION:In the stage of heating treatment, the temp. rising rate at the time when the melting and heating temp. of a tinned layer exceeds the m.p. of tin is regulated to <=70 deg.C/sec, and the final heating temp. is regulated to the range exceeding the m.p. of tin to <=260 deg.C. Then, heating conditions are defined so that the coating weight of tin in the tinned layer shall be regulated to the range of 0.6 to 1.5g/m<2> and Y>=0.02X-0.3 (shown in caption) shall be satisfied. If required, after the completion of the tinning and before executing heating treatment, flux treatment is furthermore executed in hot water contg. a prescribed amt. of flux, e.g. <=0.1g/l PSA. Moreover, by combining resistance heating and high-frequency heating, heating treatment is executed to the tinned layer.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing tin-plated steel sheets (thin tin plate) suitable for welding during can manufacturing. an alloy layer consisting of; a discontinuous island-shaped metal tin layer formed on the surface of the alloy layer; and a chromium hydrated oxide formed on the surfaces of the metal tin layer and the alloy layer; The present invention relates to a method for producing, at high yield and at low cost, a tin-plated steel sheet for welded cans on which a chromate coating layer consisting of metallic chromium and chromium hydrated oxide is formed.

[Conventional technology]

Tin-plated steel sheet, which is a steel sheet plated with tin by electroplating (
Electroplated tin (electroplated tin) has excellent properties such as good corrosion resistance and ease of processing, and is widely used as a material for food cans, but tin, the plating raw material, is expensive and manufacturing technology is difficult. In recent years, materials with reduced amounts of tin have been put into practical use due to advances in technology.

It is generally known that when the amount of tin deposited is reduced to #10 (approximately 1.0 g/m), paint baking causes problems in later weldability and corrosion resistance called thread rust resistance.

As one method for solving these problems, a method is known in which metal tin is deposited non-uniformly, such as in the form of islands. In terms of weldability, this method allows the tin to adhere unevenly, such as in the form of islands, so that even after the paint is baked, the tin does not completely alloy. It remains and can maintain good weldability.

In addition, regarding corrosion resistance, the progression of filamentous rust is suppressed by areas where tin is coarse and alloyed, and areas where metallic tin is significantly enriched, resulting in the formation of island-like and uneven metallic tin layers. By doing so, good filamentous rust resistance can be maintained.

At present, we have reduced the amount of tin adhesion to #10 (approximately 1.0g/m3) and at the same time made the metal tin layer on the surface into a non-uniform form such as an island shape, so that the surface layer after baking the paint is mixed with the alloyed part and the metal tin layer. Materials consisting of an enriched portion of

By the way, as a method of forming a metal tin layer on the surface in a non-uniform form such as an island shape, there has been a method of performing an inert treatment such as Ni plating before tin plating (Japanese Patent Application Laid-Open No. 61-2231
97), a method using a steel plate subjected to Ni diffusion treatment (Japanese Patent Application Laid-Open No. 60-208494), a method of eliminating flux treatment after tin plating, a method of unevenly plating tin (Japanese Patent Application Laid-Open No. 60-208494), Publication No. 184688/1983) and the like are disclosed.

However, increasing the number of manufacturing steps as in the case of inert treatment is undesirable in terms of cost. In addition, methods that eliminate flux treatment after tin plating and methods that plate tin nonuniformly have difficulty controlling the surface tin morphology, and are also problematic in terms of yield and cost.

Furthermore, from research on the surface defects of tinplate,
A description of the shape of the partially heterogeneous metallic tin layer (Pr
oceedingoflst[nter, Tinpla
teCon fe, 1976), but these do not form a non-uniform metallic tin layer on the front surface of the steel sheet.

[Problem to be solved by the invention]

As mentioned above, the tin adhesion amount is 110 (approximately 1.0
g/m3) tin-plated steel sheets, it is necessary to make the metallic tin layer on the surface into a non-uniform form such as an island shape from the viewpoint of later weldability and corrosion resistance, but with conventional methods,
This results in an increase in plating processes and a decrease in yield (therefore, an increase in costs is inevitable.

Therefore, the present invention was made to solve this problem, and #6
~15 (approximately 0.6 to 1.5 g/bo) tin-plated steel plate, a method for producing an unrestricted tin-plated steel plate for welded cans, in which the metal tin layer on the surface of the steel plate has a non-uniform form such as an island shape on the entire surface The purpose is to provide.

[Means to solve the problem]

In order to solve the above-mentioned problems, the inventors conducted extensive research, focused on the amount of tin plating and the heating temperature raising process of the heat treatment process (reflow process), and developed the present invention.

In order to achieve the above object, in the present invention, a steel plate is passed through a tin plating bath containing a tin plating solution to form a tin plating layer on at least one surface of the steel plate, and then,
A steel plate having a tin plating layer formed on at least one surface of the steel plate is heat-treated to form an iron-tin alloy plating layer as a lower layer and a metal tin plating layer as an upper layer on the surface of the steel plate. Then, the steel plate on which the iron-tin alloy plating layer as the lower layer and the metal tin plating layer as the upper layer are formed is subjected to chromate treatment to form chromium hydrate on the metal tin plating layer. A method for producing a tin-plated steel sheet for welding cans, which comprises forming a chromate layer consisting of any one of oxide, metallic chromium, and hydrated chromium oxide, on at least one surface of the steel sheet. In the heat treatment process for the steel plate on which the tin plating layer is formed, the heating rate when the melting heating temperature of the tin plating layer exceeds the melting point of tin is set to 70°C/see or less, and the final heating temperature is set to the melting point of tin. Temperatures exceeding ~26
The temperature should be 0°C or lower, and the amount of tin deposited on the tin plating layer should be 0.
In the range of 6 to 1.5 g/m, and Y≧0.0
2X -0.3, where Y: Adhesive amount of tin (g/m3)
, X: temperature increase rate ("C/see"), heating conditions are determined so as to satisfy the following, and the metal tin plating layer is thus formed in a discontinuous island shape.

Furthermore, if necessary, after tin plating is completed and before heat treatment, a predetermined amount of flux, for example 0.1 g/l, is added.
The present invention is characterized in that flux treatment is performed in hot water containing the following PSA, and in that the partial plating layer is heat treated by combining resistance heating and high-frequency heating.

[Effect]

To maintain the weldability of tin-plated steel sheets for welded cans, the melting point of tin (
0.1g of metallic tin remains on the surface even after the reflow process, which involves melting at temperatures exceeding 231.8°C), and the heat treatment of paint baking at temperatures below the melting point of tin.
It is necessary that more than m remain.

Tin adhesion amount is 0.6g/rr! If it is less than that, all of the metal tin will be alloyed during reflow and paint baking, making it impossible to maintain weldability. The corrosion resistance (stringy rust resistance) of tin-plated steel sheets for welded cans is determined by the fact that the areas where metallic tin is loosely adhered are completely alloyed without any residual metallic tin after heat treatment for reflow and paint baking. is necessary. The amount of tin attached is 1.5g
If /l+f is exceeded, a trace amount of metallic tin, which should originally be completely alloyed, remains even after heat treatment, resulting in poor thread rust resistance.

Final heating temperature (final temperature reached) during reflow is 260℃
Exceeding this value causes alloying to proceed rapidly, making it difficult to control the amount of metallic tin after heat treatment, resulting in deterioration of weldability.

The temperature increase rate from just below the melting point of tin to the final heating temperature is also related to the morphology of the metallic tin on the surface. The lower the amount of tin deposited or the higher the temperature increase rate, the more difficult it becomes to obtain a non-uniform metallic tin layer such as an island shape. When tin adhesion amount: Y (g/m3) and heating rate: X (''C/see), Y <
In the region of 0.02X -0.3, a non-uniform metallic tin layer such as an island shape cannot be obtained. However, if the temperature increase rate from just below the melting point to 260° C. exceeds 70° C./see, a non-uniform metallic tin layer such as an island shape cannot be obtained regardless of the amount of metallic tin deposited.

Also, if the morphology of the non-uniform tin layer is partially different,
The color tone becomes uneven, the yield decreases, and the cost increases.

In order to generate a non-uniform metallic tin layer evenly over the entire surface of the steel plate, that is, to improve yield, it is better to raise the temperature by using a combination of a resistance heater and a high-frequency heater than by using a resistance heater alone. Warm water is more effective.

After tin plating, apply a certain amount of flux before reflowing.
For example, 0.001~OAg/I! When flux treatment is performed in hot water containing PSA, it is possible to generate a uniform and uneven metal tin layer over the entire surface, which is effective in improving the yield.

If a larger amount of flux is used than this, specifically, if the flux amount exceeds 0.1 g/l, a non-uniform metallic tin layer will not be formed and corrosion resistance and weldability will deteriorate. Heating temperature: 260℃, flux amount: 0.1g
It is a graph showing the claimed scope of the present invention when it is less than /l.

(*Please also briefly explain the chromate layer.) 〔Example〕 Next, the present invention will be explained by examples.

A steel plate with a thickness of 0.2 mm is pretreated by degreasing and pickling, and the line speed is 150 to 850 mp using a ferrostane bath.
m (Plating conditions are ferrostane bath composition: tin; 30g
/l, free acid; 20g/i in terms of H, SO4, additives: 10g/J! , temperature: 40-50℃, current density: 30
~35A/di'), and the tin adhesion amount was 0.5~1.
Tin plating was performed on the surface of the steel plate by varying the temperature up to 6 ttf, and then, after tin plating, reflow treatment was performed by varying the temperature increase rate from below the melting point of tin to above the melting point.

Next, after reflow treatment, hydrated chromic acid is 3.0 to 23 mg/rrf in terms of chromium, and metallic chromium is 2.0 to 2.
Chromate treatment consisting of 0 mg/d was performed. Then, the surface morphology, surface uniformity, corrosion resistance, and weldability of the steel plate (specimen) subjected to such treatment were investigated. The results are shown in Table 1.

The test methods used to obtain these quality performances are as follows.

■Surface morphology: The surface of the specimen after reflow was examined using a SEM and an optical microscope. The evaluation criteria are as follows.

O: The metal tin is uneven, such as in the form of islands. ×: The metal tin is not uneven, such as in the form of islands.

■Surface uniformity: The surface of the specimen after reflow treatment was visually observed to observe unevenness in color tone and gloss. The evaluation criteria for the degree of unevenness are as follows.

◎: Even O: Slightly uneven ×: Much unevenness.

■ Weldability: After tin plating, reflow, and chromate treatment, weldability was investigated by measuring the contact resistance between the coatings of the specimens after dry baking at 210°C for 13 minutes with the paint baking condition as a condition. The evaluation criteria for good or bad weldability are as follows.

○: Good weldability (less than 10 ohms, which is the normal contact resistance range of tin-plated steel sheets) ×: Poor weldability (same as above, 10 ohms or more).

■ Corrosion resistance: A filament resistance test was conducted as a corrosion resistance test on the chromate-treated specimen used in the test (①). In the filament resistance test, 5θmg of epoxyphenol paint was applied to the specimen.
/m3 painted and baked at 210℃ for 13 minutes,
After cutting 60X 90mm and making a cross-shaped cut reaching the surface of the specimen with a razor,
1 extrusion, immersion machine washing in 1.5% citric acid and 1.5% NaCl aqueous solution at 38℃ for 96 hours, and leaving it in a room at 25℃ and 80% relative humidity for 2 weeks, observing changes in the surface appearance. did. The evaluation criteria are as follows.

O: Good thread rust resistance ×: Poor filamentous rust resistance.

As shown in Table 1, from comparative examples Nα1.2 and 3,
It can be seen that weldability deteriorates when the amount of tin deposited is less than 0.6 g/m3, which is outside the range of the present invention.

From Comparative Example Nα16.17, it can be seen that corrosion resistance deteriorates when the tin adhesion amount exceeds 1.5 g/rd, which is outside the range of the present invention.

A comparison between Example Nα10 and Comparative Inversion 8.12 shows that when the final heating temperature exceeds 260'C, which is outside the range of the present invention, the surface morphology and weldability deteriorate.

A comparison between the comparison side skin 15 and the practical side skin 14 shows that an appropriate surface morphology cannot be obtained when the heating rate exceeds 70°C, which is outside the range of the present invention.

From comparative example Nα4.5.6.7.9.10.13, Y<
In the region of 0.02 I know that I can't.

A comparison between Comparative Example Nα11.14 and Example Nα7.12.13 shows that a proper surface morphology cannot be obtained when the flux exceeds 0.1 g/i in PSA concentration.

From the comparison between Example Side Stone 14 and Example Nα16, we found that although there is no problem in terms of performance with the reflow method when resistance heating is used alone, yield (surface uniformity and ) is more advantageous.

A comparison between Example NQ5 and Example Nα6 shows that addition of a very small amount of flux is advantageous in terms of yield (surface uniformity).

〔Effect of the invention〕

As explained above, according to the manufacturing method of the present invention, a tin-plated steel sheet for welded cans having a non-uniform metal tin layer such as an island shape on the entire surface, which is suitable for welding during can manufacturing, can be produced with a non-uniform coating such as N1 plating. It does not require an activation treatment step and can be manufactured at low cost, resulting in industrially useful effects.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the claimed scope of the present invention when the final heating temperature for reflow is 260° C. and the amount of flux is 0.1 g/i or less.

Claims (1)

[Claims] 1. A steel plate is passed through a tin plating tank containing a tin plating solution to form a tin plating layer on at least one surface of the steel plate, and then a tin plating layer is formed on at least one surface of the steel plate. A steel plate on which a tin plating layer has been formed is subjected to heat treatment to form an iron-tin alloy plating layer as a lower layer and a metal tin plating layer as an upper layer on the surface of the steel plate, and then as the lower layer. A steel plate on which an iron-tin alloy plating layer and a metal tin plating layer are formed is subjected to chromate treatment, and chromium hydrated oxide, metal chromium, and chromium are formed on the metal tin plating layer. A method for manufacturing a tin-plated steel sheet for welded cans, which comprises forming a chromate layer made of any one of hydrated oxides, wherein the steel sheet has a tin-plated layer formed on at least one surface of the steel sheet. The temperature increase rate when the melting heating temperature of the tin plating layer in the heat treatment process exceeds the melting point of tin is 7
0°C/sec or less, and the final heating temperature is from a temperature exceeding the melting point of tin to 260°C or less, and the amount of tin deposited on the tin plating layer is in the range of 0.6 to 1.5 g/m^3. and Y≧0.02X-0.3, provided that Y:
Amount of tin attached (g/m^3), X: Temperature increase rate (℃/sec
) A method for producing a tin-plated steel sheet for a welded can, characterized in that heating conditions are determined so as to satisfy the following conditions, and thus the metal tin plating layer is formed into a discontinuous island shape. 2. The method for manufacturing a tin-plated steel sheet for welded cans according to claim 1 or 2, wherein after tin plating and before heat treatment, flux treatment is performed in hot water containing a predetermined amount of flux. 3. The method for manufacturing a tin-plated steel sheet for welded cans according to claim 2, wherein the flux contains PSA at a content of 0.1 g/l or less. 4. The method for manufacturing a tin-plated steel sheet for welded cans according to claim 1 or 2, wherein the heat treatment of the tin-plated layer is performed by a combination of resistance heating and high-frequency heating.