JP3282994B2 - Surface treatment method of steel sheet, surface treated steel sheet, and thermoplastic resin coated steel sheet using the surface treated steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for surface treatment of a steel sheet, a steel sheet subjected to the surface treatment, and a thermoplastic resin-coated steel sheet obtained by coating the surface-treated steel sheet with a thermoplastic resin. More specifically, not only processing into can lids and drawn cans, but also strict drawing ironing cans, cans that have been stretched after drawing, and cans that have been stretched after drawing and then ironed. Suitable for applications where processing is performed, even if the contents are filled into a molded can and subjected to heat sterilization treatment (hereinafter referred to as retort treatment) in steam, the coated thermoplastic resin does not peel off , A surface treatment method suitable for steel sheets where the adhesion of the coating, especially the processing adhesion, and the retort resistance after processing are required, and a steel sheet subjected to the surface treatment, and a thermoplastic resin to the surface-treated steel sheet The present invention relates to a coated thermoplastic resin-coated steel sheet.

[0002]

2. Description of the Related Art Molding applications and contents such as can lids, drawn cans, drawn and ironed cans, cans subjected to stretching after drawing, stretched after drawing, and further ironed A steel sheet coated with a coating such as a coating film or a thermoplastic resin film is used for cans that are to be retorted after filling. The adhesion of these films,
In particular, the working adhesion is greatly affected by the state of the surface treatment of the steel sheet as the base. Therefore, in order to improve the adhesion between the steel sheet and the resin film, an electrolytic chromic acid-treated steel sheet (tin-free steel or TF) in which an electrolytic chromic acid-treated film having excellent adhesion with the organic resin film is formed on the steel sheet.
S (hereinafter, referred to as TFS) is widely used as a base steel sheet for covering an organic resin film (Japanese Patent Laid-Open No. 4-224).
936).

[0003] The above-mentioned TFS is used not only for relatively light processing such as a flat plate, a can lid, and a drawn can, but also for a drawn ironed can, a can that has been subjected to a stretched work after drawing, and a stretched work after drawn. The coating film is excellent in processing adhesion even in applications where severe processing is performed, such as applied and ironed cans. TFS is a coating film that can be applied to flanges to provide a protruding edge around which the can lid is wound on the top of these cans, or to neck-in to reduce the diameter of the can at the top of the can. Although it has extremely excellent processing adhesion without peeling, when filling the contents in a can that has been subjected to these processing and retorting in high-temperature steam, the above-described flange processing and neck The film in the in-processed portion may peel off, and even though TFS has extremely excellent workability, the retort resistance after severe processing has not always been satisfactory.

[0004]

The technical problem to be solved by the present invention is that, after the above-mentioned severe forming process is performed, even if the retort treatment is performed in high-temperature steam, the film of the processed portion has sufficient adhesion. An object of the present invention is to provide a surface treatment method for a steel sheet having strength, a steel sheet subjected to the surface treatment, and a thermoplastic resin-coated steel sheet obtained by coating the surface-treated steel sheet with a thermoplastic resin.

[0005]

According to a first aspect of the present invention, there is provided a method for treating a surface of a steel sheet, comprising: a drawn ironing can, a can which has been subjected to stretching after drawing, or a stretch which has been subjected to stretching after drawing and further subjected to ironing. A method for surface treatment of a steel sheet to be a substrate of a resin-coated steel sheet for forming a can that has been made,
At least one side of the steel plate is subjected to electrolytic chromic acid treatment, and then a silane coupling agent is immersed in a treatment solution mixed under the following conditions to obtain 0.3 to 10 mg / silicon as silicon.
and characterized by applying silane treatment in the range of m ^2. Concentration of silane coupling agent to solvent: 0.5-20
%, A mixed solution obtained by mixing solvent = ethanol: water at a ratio of 1: 4 to 4: 1, the surface treatment method for a steel sheet according to claim 2, wherein at least one surface of the steel sheet is subjected to the electrolytic chromic acid treatment. It is characterized in that two layers comprising a lower metal chromium layer and an upper chromium hydrated oxide layer are formed. The method for surface treating a steel sheet according to claim 3 is characterized in that the lower metal chromium layer is formed in an amount of 30 to 300 mg / m ² . The surface treatment method for a steel sheet according to claim 4 is characterized in that the chromium hydrated oxide layer to be the upper layer is formed as chromium in an amount exceeding 0 and not more than 20 mg / m ² . The method for treating a surface of a steel sheet according to claim 5 is characterized in that the chromium hydrated oxide layer serving as the upper layer is formed as chromium in excess of 0 and 10 mg / m ² or less. The surface-treated steel sheet according to claim 6 is,
5. A method for forming a metal sheet on at least one side of a steel sheet, a chromium hydrated oxide layer on the upper layer, and a silane-treated film on the upper layer, using the method for treating a steel sheet according to any one of the above items 5. Features. A thermoplastic resin-coated steel sheet according to a seventh aspect is characterized in that at least one surface of the surface-treated steel sheet according to the sixth aspect is coated with a thermoplastic resin film.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a steel sheet is subjected to electrolytic chromic acid treatment, and then subjected to silane treatment using a silane coupling agent, thereby achieving excellent processing adhesion of a film suitable for the purpose of the present invention. It was found that retort resistance after processing was obtained. That is, in the present invention, the processing adhesion and the retort resistance after processing of the coating for the purpose of further improving the amount of chromium metal and chromium hydrated oxide in the coating formed by electrolytic chromic acid treatment, Further, it depends on the amount of the film formed by the silane treatment. If the base steel sheet is insufficiently covered with the metal chromium and the exposed area of the steel is large, the retort resistance after processing becomes poor. Also, the larger the amount of hydrated oxide formed on metallic chromium, the greater the amount of silane-treated film formed on the upper layer.However, if the amount of chromium hydrated oxide is reduced by adjusting the surface treatment conditions, The amount of the coating does not significantly affect the retort resistance after processing. On the other hand, when the amount of chromium hydrated oxide is large, the retort resistance after processing becomes poor if the amount of the silane treatment film is small.

Based on the above facts, the present invention will be described in detail below. First, the steel sheet used in the present invention is subjected to severe forming processing such as a drawn ironing can, a can that has been subjected to stretching after drawing, a can that has been subjected to stretching after drawing, and further subjected to ironing. There is no particular limitation as long as it is a possible steel sheet, but a low carbon cold rolled steel sheet having a thickness of 0.15 to 0.30 mm, which is widely used for forming cans, is preferable from the viewpoint of cost and formability.

Next, the surface treatment method for a steel sheet according to the present invention will be described. The steel sheet of the present invention is characterized in that it is subjected to electrolytic chromic acid treatment, a lower layer is formed of chromium metal, and an upper layer is formed of two layers of chromium hydrated oxide, and then subjected to silane treatment using a silane coupling agent. I do. First, the surface of the steel sheet is degreased and pickled using a known method, and then mainly contains chromic anhydride and a small amount of sulfuric acid, sulfate, hydrofluoric acid, fluoride, silicon fluoride or borofluoride as an auxiliary agent. Electrolytic treatment is performed using a steel plate as a cathode in a known treatment bath containing at least one species to obtain a metal chromium layer.

On this metal chromium layer, chromium hydrated oxide, which is an intermediate reduction product in the chromium precipitation process, is inevitably formed. In the present invention, unlike ordinary TFS, it is indispensable to keep the chromium hydrated oxide content at 20 mg / m ² or less in order to maintain excellent processing adhesion and retort resistance. 20m of hydrated chromium oxide
If the amount exceeds g / m ² , as described above, unless the amount of the silane-treated film is increased according to the amount of chromium hydrated oxide, stretching is performed after drawing, followed by flange processing and neck-in processing. When severe processing is performed and further retort treatment is performed in high-temperature steam, sufficient adhesion of the film cannot be obtained, and many expensive silane treatment agents are required, which is not economical. Preferably 10 mg / m
² or less, more preferably 5 mg / m ² or less. The amount of hydrated chromium oxide is measured as the amount of chromium metal for convenience of measurement. As a precipitation method for suppressing the formation of chromium hydrated oxide, the following techniques are known empirically and can be easily implemented. (1) Bath composition 1) Concentration of chromic anhydride In the preparation of ordinary TFS, it is carried out at 50 to 300 g / l. The generation of products is low. 2) Type and concentration of auxiliary agent Sulfuric acid is a typical auxiliary agent in the preparation of ordinary TFS. In addition, hydrofluoric acid, fluoride, silicofluoric acid, borofluoric acid, and their alkali metal salts may be added alone or in combination with sulfuric acid. Generally, a fluorine-based auxiliary is a sulfuric acid-based auxiliary. The formation of chromium hydrated oxide is smaller than that. The amount of the auxiliary agent varies somewhat depending on the type, but is about 1 to 5% of the chromic anhydride concentration. (2) Bath temperature TFS is usually prepared at 30 to 60 ° C., but when the bath temperature is high, such as at 50 to 60 ° C., the generation of hydrated chromium oxide tends to be small. (3) Cathode current density In the preparation of a normal TFS, 10 to 100 A / dm ²
However, as in the case of 30 to 100 A / dm ² , the higher the cathode current density, the smaller the generation of chromium hydrated oxide.

If the above conditions are selected, and if necessary, after the completion of electrolysis for precipitating metallic chromium, the chromium hydrated oxide is dissolved when immersed and held in a treatment bath, the chromium hydrated oxide amount is 20 mg / mg. it is m ² or less can be easily achieved. In this manner, chromium metal is deposited on the steel sheet while suppressing the formation of hydrated oxides as much as possible.
The chromium metal is deposited in an amount of 30 to 300 mg / m ² . If the amount of metallic chromium is less than 30 mg / m ^2, the exposed area of the base steel sheet becomes large, and after drawing, stretch processing is performed, followed by flange processing and neck-in processing. When the film is retorted in steam, sufficient film adhesion cannot be obtained. On the other hand, even if chromium metal is deposited in an amount exceeding 300 mg / m ² , the effects of improving the work adhesion and the retort resistance are saturated, which is not economical. Preferably 50
To 200 mg / m ² , more preferably 70 to 15 mg / m ^2.
0 mg / m ² .

After forming the metal chromium layer and the chromium hydrated oxide layer as described above, a silane treatment layer is formed thereon. In the silane treatment of the present invention, a commercially available silane coupling agent is diluted in a solvent, applied to a steel sheet, and dried. Although water alone can be used as the solvent, it is preferable to use a mixed solvent of ethanol and water. For example, the mixing ratio of water and ethanol is water: ethanol = 1: 1
Good results are obtained with a mixed solvent of 4 to 4: 1, preferably 1: 2 to 2: 1. When the mixing ratio of ethanol to water is more than 1: 4, the silane coupling agent is sufficiently uniformly dispersed in the mixed solution, but ethanol is expensive and is not advantageous in cost. On the other hand, the mixing ratio is 4:
If it is less than 1, the silane coupling agent will not be sufficiently uniformly dispersed in the mixed solution, and it will take a long time to dry after being applied to the steel sheet surface. The concentration of the silane coupling agent is preferably in the range of 0.5 to 20% with respect to the mixed solution, and more preferably in the range of 1 to 10%. If it is less than 0.5%, the coating state after drying tends to be non-uniform, and sufficient adhesion cannot be obtained. If it exceeds 20%, the effect of improving the adhesion is saturated, and the cost is not advantageous. The temperature of the treatment liquid is preferably in the range of room temperature to 60 ° C, more preferably in the range of room temperature to 40 ° C. As a processing method, after immersing the steel sheet in the processing liquid, excess liquid is squeezed with a roll and then dried. An immersion time of 1 to 15 seconds is sufficient, and a range of 3 to 10 seconds is more preferable. Although the amount of treatment depends on the amount of chromium hydrate oxide generated by electrolytic chromic acid treatment prior to silane treatment, the range of 0.3 to 10 mg / m ² as silicon is considered from the viewpoint of retort resistance and economical efficiency after processing. Preferably 1
The range is more preferably from 5 to 5 mg / m ² .

In the present invention, when the above-mentioned surface-treated steel sheet is coated with a thermoplastic resin, the thermoplastic resin to be coated may be polyethylene, polypropylene, polyester, polyamide, polycarbonate, polyvinyl chloride, polyvinylidene chloride. And one or more copolymer resins of acrylic resin, or a composite resin in which two or more are blended. These thermoplastics have heat resistance,
Although they have different properties such as corrosion resistance, workability, and adhesion, they should be selected according to the intended use. For example, for the use of cans that are subjected to particularly severe forming such as stretching after drawing and further ironing, polyesters, especially polyethylene terephthalate, copolymerized polyester mainly composed of ethylene terephthalate units, butylene terephthalate It is preferable to coat a film composed of polyester mainly composed of units and a composite resin in which these are blended, and it is more preferable to use a biaxially oriented film of these resins. Furthermore, if impact resistance is required,
A film of a composite resin in which bisphenol A polycarbonate is blended with the above polyester, or a two-layer film in which the above composite resin is an upper layer, and the above polyester is a lower layer, or further, the above polyester is an upper layer, and a lower layer, It is preferable to use a three-layer film having bisphenol A polycarbonate as an intermediate layer.

The thickness of the above-mentioned thermoplastic resin layer should be selected based on the required properties,
A range of 50 μm is preferable, and a range of 10 to 25 μm is more preferable. If the thickness is less than 5 μm, the coating work on the surface-treated steel sheet becomes extremely difficult, and pinholes easily occur after coating or after forming,
Sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 50 μm, it is not advantageous in terms of cost as compared with a coated film.

If necessary, additives such as stabilizers, antioxidants, antistatic agents, pigments, lubricants, and corrosion inhibitors may be added to the thermoplastic resin.

If the adhesion of the thermoplastic resin to the steel sheet, especially after the severe processing described above, is not sufficient, or if the thermoplastic resin layer alone cannot ensure sufficient corrosion resistance, An adhesive composed of a curable resin, for example, an epoxy-phenol adhesive is coated on a steel sheet after applying a thermoplastic resin, or the adhesive is applied in advance to a bonding surface of the coated thermoplastic resin with the steel sheet. Every
It may be coated on a steel plate.

The above-mentioned thermoplastic resin is heated and melted, and is extruded directly onto a steel sheet by extrusion. Alternatively, a biaxially oriented film of the thermoplastic resin is brought into contact with a steel sheet heated to a temperature not lower than the melting point of the resin. The film can be coated by any method of a film lamination method in which the two are sandwiched and laminated by a pair of rolls.

Hereinafter, the present invention will be described in more detail with reference to examples. (Example) Both sides of a cold-rolled steel sheet having a thickness of 0.18 mm shown in Tables 1 to 8 were subjected to degreasing treatment and pickling treatment by a conventional method.
Thereafter, a surface treatment comprising electrolytic chromic acid treatment and silane treatment was performed under the conditions shown in Tables 1 to 4. In the table, the adhesion amount of chromium hydrated oxide is a value obtained by measuring the amount of metal chromium for convenience of measurement.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

The steel sheet subjected to these surface treatments is 240
℃, polyethylene terephthalate 8 on both sides
A film obtained by biaxially stretching a copolyester consisting of 8 mol% and 12 mol% of polyethylene isophthalate and heat setting (the surface to be the inner surface of the can after molding into a can described later: 25 μm in thickness, outer surface of the can) (A surface having a thickness of 15 μm) was simultaneously abutted, a film and a steel plate were sandwiched between a pair of rolls, laminated, immediately immersed in water, rapidly cooled, and then dried.

A paraffin wax is applied to both sides of the polyester film-coated steel sheet obtained as described above for about 50 minutes.
mg / m ^2, and the following molding process was performed. First, after punching into a blank having a diameter of 160 mm, a drawn can having a can diameter of 100 mm was formed by drawing. Next, it was formed into a redrawn can having a can diameter of 80 mm by redrawing. The redrawn can was formed into a drawn and ironed can having a can diameter of 66 mm by a composite process in which stretching and ironing were simultaneously performed. This composite processing was performed under the following conditions. Spacing between redrawing and ironing at the top of the can:
20mm Shoulder radius of redrawing die: 1.5 times the plate thickness Clearance between redrawing die and punch: 1.0 times the plate thickness Clearance of ironed part: 50% of the original plate thickness Next, the upper end of the can is trimmed by a standard method After the neck-in processing and the flange processing were performed, and the contents were filled, a drawn and ironed can covered with a polyester film in a state in which the lid could be tightly wound was obtained.

[0024] The presence or absence of film peeling at the neck-in processed portion and the flange processed portion of the drawn and wrought iron can coated with a polyester film obtained as described above was visually observed and judged according to the following criteria to evaluate the processing adhesion. . ：: No peeling X: Peeling off The evaluation results are shown in Table 5.

Further, a flaw reaching the steel plate was formed on the inner and outer surfaces of the neck-in processed portion of the drawn and ironed can coated with a polyester film using a cutter in the circumferential direction of the can, and a film cut portion was provided. In the container for 1 hour. The can after retorting was visually observed, and the length in the circumferential direction of the film peeling portion generated from the film cut portion was determined based on the following criteria, and the retort resistance after the forming process was evaluated. ：: Peeling length 0 mm ○: Peeling length exceeding 0 mm and less than 2 mm Δ: Peeling length exceeding 2 mm and less than 5 mm ×: Peeling length 5 mm or more The evaluation results are shown in Table 5.

[0026]

[Table 5]

Sample Nos. 3 to 12 and 17 to 20 (Examples) are obtained by drawing a film-coated steel sheet coated with a polyester film on the surface-treated steel sheet of the present invention and forming it into an iron can. Shows excellent processing adhesion and retort resistance after processing. On the other hand, sample numbers 1 to
Sample No. 2 (Comparative Example) has an adhesion amount of the metal chromium smaller than the preferred range, and has poor adhesion of the film after forming. Sample Nos. 13 to 14 (Comparative Examples) are cases where the amount of chromium hydrated oxide adhered was much larger than the amount of the silane-treated film, and the adhesion of the film after molding was excellent, but the retort resistance was high. Poor. Sample Nos. 15 to 16 (Comparative Examples) are examples in which the amount of the silane-treated film is smaller than the preferred range, and the retort resistance is poor. Sample No. 21 (Comparative Example) has a large amount of the silane-treated film, but has a larger amount of chromium hydrated oxide attached than the amount of the silane-treated film, and thus has poor retortability. Sample No. 22 (Comparative Example) is a normal TFS, and has excellent adhesion of the formed film, but poor retort resistance.

[0028]

The steel sheet which has been subjected to the surface treatment of the present invention has excellent processing adhesion of the coating. Thermoplastic resin coated steel sheet coated with a thermoplastic resin on the steel sheet subjected to the surface treatment of the present invention,
The film does not peel off even after being formed into a particularly severely formed can which is subjected to stretching after drawing and further ironing, and exhibits excellent workability. Furthermore, even after the contents are filled into a molded can and subjected to a heat sterilization treatment in high-temperature steam, peeling of the film does not occur, and excellent retort resistance is exhibited.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-156499 (JP, A) JP-A-9-1054 (JP, A) JP-A-57-19398 (JP, A) 74176 (JP, B2) JP-B-51-44094 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) C25D 11/38

Claims (7)

(57) [Claims] Claims: 1. A drawn ironing can, stretched after drawing
Processed cans or stretched after drawing
Resin coating for forming ironed cans
A steel surface treatment method of the substrate of the steel sheet, on at least one surface of the steel sheet, subjected to an electrolytic chromic acid treatment, following
The silane coupling agent was mixed under the following conditions.
Immersed in a physical solution to obtain 0.3-10 mg /
and characterized by applying silane treatment in the range of m ^2, the surface treatment method of a steel sheet. Of silane coupling agent to solvent
Concentration: 0.5 to 20%, solvent = ethanol: water mixed at a ratio of 1: 4 to 4: 1
Mixed liquid, 2. The method according to claim 1, wherein the electrolytic chromic acid treatment forms at least one surface of the steel sheet with two layers including a lower metal chromium layer and an upper chromium hydrated oxide layer. 2. The method for surface treating a steel sheet according to item 1. 3. The method according to claim 1, wherein the lower metal chromium layer is 30 to
The surface treatment method for a steel sheet according to claim 1, wherein the steel sheet is formed at 300 mg / m ² . 4. The chromium hydrated oxide layer serving as the upper layer,
Characterized in that to form 20 mg / m ² or less than 0 as chromium, a surface treatment method of steel sheet according to claim 1. 5. The chromium hydrated oxide layer serving as the upper layer,
Characterized in that to form 10 mg / m ² or less than 0 as chromium, a surface treatment method of steel sheet according to claim 4. 6. A metal chromium layer on at least one side of the steel sheet, a chromium hydrated oxide layer on the metal chromium layer, and a silane hydrate layer on the metal chromium layer on the steel sheet, using the method for surface treatment of a steel sheet according to claim 1. Surface treated steel sheet with a treated film formed. 7. A thermoplastic resin-coated steel sheet obtained by coating at least one surface of the surface-treated steel sheet according to claim 6 with a thermoplastic resin film.