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(11) | EP 2 497 845 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 153(4) EPC |
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| (54) | METHOD FOR PRODUCING SURFACE-TREATED STEEL SHEET |
| (57) Provided is a method for manufacturing a surface treated steel sheet for a resin
coated steel sheet having excellent working adhesiveness even at the time of rigorous
forming working. In a method for manufacturing a surface-treated steel sheet, an area
ratio of tin covering a surface of a steel sheet is set to 5% to 95% by adjusting
the Sn concentration in a tin sulfate plating bath containing a sulfuric acid and
tin sulfate to a value which falls within a range of 30 to 120 g/L, a temperature
of the tin sulfate plating bath is set to a value which falls within a range of 20
to 60°C, and current density in tin sulfate plating to a value which falls within
a range of 2 to 50 A/dm2, whereby the surface of the steel sheet is coated with metallic tin such that some
of iron on the surface of the steel sheet is exposed. |
TECHNICAL FIELD
[0001] The present invention relates to a method for manufacturing a surface-treated steel sheet for a resin-coated steel sheet having excellent working adhesiveness.
BACKGROUND ART
[0002] Recently, there has been manufactured a can where a top plate is seamed to a can body which is an integral body formed of a can barrel portion and a can bottom portion by working. The can body is formed by making a steel sheet covered with a resin subjected to rigorous working such as drawing, further stretching after drawing, further ironing after drawing or working in which both stretching and ironing are further performed after drawing. Such a can body is, to prevent peeling or breaking of a coated resin during the rigorous forming working and after such forming working, required to have excellent adhesiveness of a resin to the steel sheet. Accordingly, as a raw material for such a can body, there has been used a resin coated chromate treated steel sheet where chromate treated steel sheet such as a tin free steel (TFS) having a surface on which a chromate film having excellent working adhesiveness is formed is covered with an organic resin.
[0003] However, in the can body manufactured using the resin coated chromate treated steel sheet, when a minute hole or crack which reaches a surface of a steel sheet is formed in the resin layer, due to the insufficient corrosion resistance of the chromate treated steel sheet, there exists a drawback that, the corrosion of the steel sheet is liable to rapidly progress particularly when the content filled in the can body has a lot of acidity.
In view of the above, to cope with such a drawback, an attempt has been made to use a resin-coated tin-plated steel sheet which is manufactured by applying a resin to a tin-plated steel sheet which exhibits excellent corrosion resistance even when a content having large acidity is filled in a can. However, the adhesiveness of resin to a tin-plated layer, particularly, the film working adhesiveness at the time of can body working is insufficient and hence, there has been a demand for the development of a material having excellent film working adhesiveness even when the material is subjected to the above-mentioned rigorous working. Particularly, a tin plate has a drawback that the tin plate is inferior to a TFS in film adhesiveness due to the presence of a tin oxide film and the low temperature of the steel sheet at the time of coating a resin film.
In general, as a plated steel sheet used for manufacturing beverage cans, a tin sheet (tin plated steel sheet) and a TFS (electrolytic chromium plated steel sheet) are mainly named. In filling a beverage can with a content having high corrosiveness, a tin sheet which can make use of a sacrificial corrosion prevention effect of tin has more excellent corrosion resistance than TFS. Due to the presence of a tin oxide film (impeding the adhesiveness of the tin sheet with an organic resin film) and the difficulty in coating the film at a temperature equal to or above a melting point of tin (232°C) (that is, tin acquires fluidity when melted and adheres to a heating facility) and hence, the coating of the film at a melting point or above is difficult whereby the tin sheet is inferior to the TFS in film adhesiveness after manufacturing cans currently.
On the other hand, although the TFS is inferior to the tin sheet in corrosion resistance, a chromium oxide film having excellent film adhesiveness is present on a surface layer, and also coating of the film at a temperature of 232°C or above is possible (melting point of chromium: approximately 1800°C) and hence, the TFS has more excellent film adhesiveness after manufacturing cans than the tin sheet.
[0004] To overcome the above-mentioned drawbacks, patent document 1 describes a resin-coated tin plated steel sheet which is formed such that a silane coupling agent coating layer is formed on a non-reflow tin plated sheet steel (tin plated steel sheet to which tin melting treatment is not applied) or a reflow tin plated sheet steel (tin plated steel sheet to which tinmelting treatment is applied), and an organic resin film is laminated to the silane coupling agent coating layer.
Prior Art Document
Patent Document
SUMMARY OF THE INVENTION
PROBLEMS THAT THE INVENTION IS TO SOLVE
[0006] However, the treatment of the resin-coated tin-plated steel sheet described in patent document 1 requires the addition of new treatment and hence, a manufacturing cost of a tin plate is being pushed up. Further, when a can body is formed by working by further using both stretching and ironing after drawing, there is a case where a resin peels off at an upper portion of the can body in the midst of forming working thus giving rise to a drawback in working adhesiveness of the resin at the time of performing can body working.
It is an object of the present invention to overcome the above-mentioned drawbacks and to provide a method for manufacturing a surface treated steel sheet for a resin coated steel sheet having excellent working adhesiveness even at the time of rigorous forming working and a resin coated steel sheet where the surface treated steel sheet is coated with a resin.
MEANS FOR SOLVING THE PROBLEMS
[0007]
- (1) A method for manufacturing a surface-treated steel sheet according to the present invention, wherein an area ratio of tin covering a surface of a steel sheet is set to 5% to 95% by adjusting the Sn concentration in a tin sulfate plating bath containing a sulfuric acid and tin sulfate to a value which falls within a range of 30 to 120 g/L, a temperature of the tin sulfate plating bath is set to a value which falls within a range of 20 to 60°C, and current density in tin sulfate plating to a value which falls within a range of 2 to 50 A/dm2, whereby the surface of the steel sheet is coated with metallic tin such that some of iron on the surface of the steel sheet is exposed.
- (2) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 30 to 50 g/L, the temperature of the tin sulfate plating bath is set to a value which falls within a range of 30 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 A/dm2 or less.
- (3) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 30 to 50 g/L, the temperature of the tin sulfate plating bath is set to a value which falls within a range of 40 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 to 5 A/dm2.
- (4) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 50 to 70g/L, the temperature of the tin sulfate plating bath is set to a value which falls within a range of 20 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 to 5 A/dm2.
- (5) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 50 to 70g/L, the temperature of the tin sulfate plating bath to a value which falls within a range of 30 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 to 7 A/dm2.
- (6) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 50 to 70g/L, the temperature of the tin sulfate plating bath is set to a value which falls within a range of 50 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 to 10 A/dm2.
- (7) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 70 to 90g/L, the temperature of the tin sulfate plating bath is set to a value which falls within a range of 20 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 to 7 A/dm2.
- (8) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 70 to 90g/L, the temperature of the tin sulfate plating bath is set to a value which falls within a range of 30 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 to 10 A/dm2.
- (9) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 70 to 90g/L, the temperature of the tin sulfate plating bath is set to a value which falls within a range of 50 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 to 15 A/dm2.
- (10) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 90 to 120g/L, the temperature of the tin sulfate plating bath is set to a value which falls within a range of 20 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 to 10 A/dm2.
- (11) In the method for manufacturing a surface-treated steel sheet according to the present invention having the above-mentioned constitution (1), the Sn concentration in the tin sulfate plating bath is set to a value which falls within a range of 90 to 120g/L, the temperature of the tin sulfate plating bath is set to a value which falls within a range of 40 to 60°C, and the current density in the tin sulfate plating is set to a value which falls within a range of 2 to 15 A/dm2.
- (12) In the method for manufacturing a resin-coated steel sheet according to the present invention, a resin is applied by coating to the surface treated steel sheet manufactured by the method for manufacturing a surface-treated steel sheet according to any one of the above-mentioned constitutions (1) to (11).
- (13) In the method for manufacturing a resin-coated steel sheet according to the present invention having the above-mentioned constitution (12), the resin coating is performed at a temperature equal to or above a melting point of tin.
ADVANTAGEOUS EFFECTS OF THE INVENTION
[0008] According to the present invention, the surface of the steel sheet is coated with tin such that some of iron on the surface of the steel sheet is exposed and hence, a resin-coated steel sheet where the resin layer is laminated to the surface of the steel sheet exhibits the excellent working adhesiveness compared to the prior art.
Further, the surface of the steel sheet is coated with tin such that some of iron on the surface of the steel sheet is exposed and hence, the resin layer which is laminated to the surface of the steel sheet adheres to the iron surface having favorable adhesiveness and, at the same time, due to an anchoring effect acquired by the unevenness of the surface of the tin layer formed on the steel sheet by granular precipitation, the adhesiveness of the steel sheet with the resin layer can be largely enhanced compared to a conventional tin-plated steel sheet having a flat surface.
Further, with respect to the surface treated steel sheet where the surface of the steel sheet is coated with tin such that some of iron is exposed, resin coating can be performed at a temperature equal to or above a melting point of tin (232°C) and hence, the resin layer after manufacturing a can exhibits excellent adhesiveness equivalent to the adhesiveness of the resin layer of a TFS.
That is, in a conventional tin-plated steel sheet, tin is present over the whole surface of the steel sheet and hence, when resin coating is performed at a melting point of tin or above, tinmelted at the time of tinmelting treatment has fluidity thus giving rise to drawbacks that the appearance of the steel sheet becomes non-uniform and, at the same time, tin adheres to a heating facility at the time of resin coating whereby resin coating at a temperature of a melting point of tin or above is difficult. With respect to the surface treated steel sheet which is formed by the manufacturing method of the present invention where the surface of the steel sheet is coated with tin such that some of iron is exposed, even when the steel sheet is heated at a temperature of a melting point of tin or above, portions of tin in a molten state are not bonded to each other so that tin does not have fluidity whereby resin coating at a melting point of tin or above can be performed.
Further, in the method for manufacturing a surface treated steel sheet according to the present invention, the tin sulfate plating bath can be used. This bath uses an inexpensive sulfuric acid instead of a conventional PSA (phenolsulfonic acid) which is component of a conventional Ferrostan tin plating bath leading to the reduction in a cost of a plating bath and also the reduction in a COD.
Brief Description of the Drawings
[0009]
Fig. 1 is a photograph (SEM image) where a cross section of a surface treated steel sheet is observed at an inclination of 45°, wherein (a) is an observation photograph of a cross section of an example 1 according to the present invention, and (b) is an observation photograph of a cross section of a comparison example 1.
Fig. 2 is a plan view showing a shape of a specimen for measuring S peel strength.
Fig. 3 is a plan view showing a state where a cut is formed in a surface of a coated resin film of a specimen for measuring S peel strength.
Fig. 4 is a plan view showing a state where a score is formed in a specimen for measuring S peel strength.
Fig. 5 is a cross-sectional view of a part of the specimen for measuring S peel strength in which the score is formed.
Fig. 6 is a schematic perspective view showing a state where S peel strength is measured by putting a specimen for measuring S peel strength in a specimen holder.
Mode for Carrying Out the Invention
[Steel sheet]
[0011] With respect to a steel sheet used as a material sheet for a surface treated steel sheet of the present invention, depending on usage, a cold-rolled steel sheet having a sheet thickness of 0.15 to 0. 3mm which is produced by applying temper rolling after annealing a low-carbon aluminum-killed hot-rolled sheet used for cans in general; a cold-rolled steel sheet whose strength is increased by further applying cold rolling after annealing or the like is used. Further, a cold-rolled steel sheet which is manufactured from non-aging ultra low carbon steel to which niobium and titanium are added can be also used as the material sheet for the surface treated steel sheet of the present invention. The cold-rolled steel sheet is subjected to electrolytic degreasing and pickling and, thereafter, a tin plating layer is formed on the steel sheet thus manufacturing a surface treated steel sheet.
[Plating bath]
[0012] In manufacturing the surface treated steel sheet, according to the present invention, a tin sulfate plating bath is used.
With respect to the composition of the tin sulfate plating bath, the concentration of tin sulfate (in terms of Sn concentration) is set to a value which falls within a range of 30 to 120 g/L, and a surfactant, an anti-oxidizing agent or the like can be also added to the tin sulfate plating bath besides tin sulfate.
With respect to plating condition, plating current density is set to a value which falls within a range of 2 to 50 A/dm2, and a plating bath temperature is set to a value which falls within a range of 20 to 60°C.
When the concentration of tin sulfate is less than 30 g/L in terms of the Sn concentration, even when the current density is lowered, a precipitation state of Sn is not brought into a state where base iron is exposed (exposure of base iron) and hence, when the surface of the steel sheet is coated with a resin, the adhesiveness of the resin is not enhanced.
On the other hand, when the concentration of tin sulfate (in terms of Sn concentration) exceeds 120 g/L, the concentration is liable to be changed and hence, there may be a case where an accurate plating operation becomes difficult. Further, pH becomes excessively low so that corrosiveness of a plating liquid is increased thus giving rise to a possibility that the plating liquid becomes contaminated.
The reason the plating current density is set to a value which falls within a range of 2 to 50 A/dm2 is that when the plating current density is less than 2A/dm2, it takes a long time before plating treatment is finished thus giving rise to a case where an accurate plating operation becomes difficult due to a change in the composition of a plating liquid or the like.
On the other hand, when the plating current density exceeds 50A/dm2, the plating covers the whole surface of the steel sheet and hence, the exposure of base iron does not take place.
The reason the plating bath temperature is set to a value which falls within a range of 20 to 60°C is that when the plating bath temperature is below 20°C, an area ratio of tin covering a surface of a steel sheet becomes 95% or more and hence, a state substantially equal to the whole surface coating (base iron being not exposed) is brought about whereby a film adhesive force is remarkably lowered.
On the other hand, when the plating bath temperature exceeds 60°C, the concentration of the composition in the plating liquid is liable to be changed thus making accurate plating difficult.
[Area ratio of tin covering a surface of a steel sheet]
[0013] It is desirable that an area which metallic tin precipitated on a steel sheet in a dispersed manner occupies on the steel sheet, that is, an area ratio of tin covering a surface of a steel sheet (tin area ratio) is set to a value which falls within a range of 5 to 95%.
When the area ratio of tin covering a surface of a steel sheet is less than 5%, corrosion resistance and workability remarkably deteriorate and hence, it is necessary to set the area ratio of tin covering a surface of a steel sheet to at least 5% or more.
When the area ratio of tin covering a surface of a steel sheet exceeds 95%, the iron exposure area becomes small and therefore the exposure of iron does not contribute to the enhancement of the adhesiveness of the resin layer. This is because the iron exposure area of at least 5% or more is necessary for enhancing the adhesiveness of the steel sheet with the resin layer.
The area ratio of tin covering a surface of a steel sheet can be obtained by adopting an image of a surface observed by an electron microscope as a first image, by adopting an image of the surface observed again by the electron microscope after chemically removing tin present on the surface of the steel sheet in a dispersed manner as a second image, and by comparing both images obtained in this manner by computer image processing.
[Coating weight of metallic tin]
[0014] A coating weight of metallic tin on a surface of a steel sheet is desirably set to a value which falls within a range of 0.1 to 13 g/m2 from a viewpoint of exposing a iron surface with a tin area ratio of 5% or more.
The coating weight of metallic tin is desirably set to a value which falls within a range of 0.5 to 5.6 g/m2. When the coating weight of tin is less than 0.1 g/m2, corrosion resistance becomes insufficient. Accordingly, the coating weight in such a range is not preferable. Particularly, when melting of tin (reflow) treatment is performed, all plated tin is transformed into a Fe-Sn alloy so that not only corrosion resistance but also workability are remarkably deteriorated. Accordingly, the coating weight of at least 0.1g/m2 or more is necessary.
On the other hand, when the coating weight exceeds 13 g/m2, iron is not exposed to the surface of the steel sheet and hence, such setting of the coating weight does not contribute to the enhancement of the adhesiveness of the resin layer.
[Tin coating with exposed iron surface]
[0015] The reason that tin plated onto a steel sheet is brought into a state where the iron surface is exposed is not sufficiently clarified yet. It is considered, however, that when a small amount of tin plating is applied to the iron surface where an oxide film is formed, wettability of tin differs among parts of an iron oxide film and hence, a tin plating layer having the uniform thickness is hardly formed.
Further, average particle size (an average size of particle diameters as viewed in a plan view) of metallic tin is desirably set to a value which falls within a range of 0.5 to 50µm.
It is more preferable to set the average particle size of metallic tin to a value which falls within a range of 2 to 20µm.
When the average particle size of metallic tin is less than 0.5µm, the particle size of metallic tin is excessively small and hence, an anchoring effect of anchoring the resin layer due to the unevenness of the tin layer formed on the steel sheet cannot be sufficiently acquired and thereby such setting of the average particle size does not contribute to the enhancement of the adhesiveness of the resin layer.
On the other hand, when the average particle size exceeds 50µm, the electrolytic deposition of tin becomes difficult in view of the restriction imposed on electrolytic processing.
[Lamination of resin layer]
[0016] A resin film which becomes a resin layer is laminated on one surface or both surfaces of the surface treated steel sheet manufactured as described above. The resin layer may preferably be formed using a thermoplastic resin having excellent workability even after heating. That is, the resin layer may be a single-layered resin layer made of: a polyester resin such as polyethylene terephthalate, polybutylene terephthalate, polyethylenenaphthalate, ethylene terephthalate ethylene isophthalate copolymer or butylene terephthalate butylene isophthalate copolymer; a resin which is formed by mixing two or more kinds of these polyester resins; polyethylene, polypropylene, ethylene propylene copolymer or these resins modified with a malaic acid; a polyolefin resin such as ethylene vinyl acetate copolymer or ethylene acrylic acid copolymer; a polyamide resin such as 6-nylon, 6, 6-nylon or 6, 10-nylon; polycarbonate; polymethylpentene; or a mixture of the above-mentioned polyester resin and ionomer, a multi-layered resin layer which is made of two or more kinds of resins selected from the above-mentioned resins or the like.
[0017] A thickness of the resin layer is preferably set to a value which falls within a range of 10 to 100µm from viewpoints of easiness of a resin layer laminating operation, the adhesive strength between the resin layer and the surface treated steel sheet of a formed body (can or the like) after performing the forming working of the resin coated steel sheet, corrosion resistance, economic efficiency and the like.
The resin layer is formed in such a manner that resin pellets are melted by heating, and a melted body is extruded from a T die of an extruder thus forming a film having a desired thickness, and the film is laminated to a surface treated steel sheet on which metallic tin is formed in a state where a iron surface is exposed.
As a method for laminating the resin layer, for example, a thermal bonding method is named. In this method, a resin film is brought into contact with a surface treated steel sheet which is heated to a temperature which falls within a predetermined temperature range, and the surface treated steel sheet and the resin film are sandwiched and pressurized from both surfaces by a pair of pressurizing rollers and hence, the surface treated steel sheet and the resin film are bonded to each other.
To the surface treated steel sheet manufactured by the manufacturingmethod of the present invention, even when a formed resin film is a resin film having the biaxial alignment due to stretching, the resin film can be thermally bonded at a temperature higher than a melting point temperature of tin (250°C, for example).
Examples
[0018] Hereinafter, the present invention is specifically explained in conj unction with examples and comparison examples.
A low carbon cold rolled steel sheet is subjected to electrolytic degreasing in alkali aqueous solution and washing with water. Then, the steel sheet is subjected to sulfuric acid pickling and washing with water. Thereafter, the steel sheet is subjected to tin plating using a sulfate tin plating bath under the following tin plating conditions and conditions shown in Tables 1 to 6 thus forming metallic tin on a surface of the steel sheet such that a iron surface is exposed.
<Example 1>
[0019]
[Formation of surface treated steel sheet]
Composition of tin sulfate plating
Concentration of tin sulfate (In terms of Sn): 50g/L
Plating condition
Plating current density: 5A/dm2
Plating bath temperature: 40°C
Tin coating weight: 2.8
[Formation of resin coated steel sheet]
[0020] Next, on one surface of the surface treated steel sheet (a surface which constitutes an inner surface side of a can), a transparent non-stretched film having a thickness of 28µm which is made of ethylene terephthalate ethylene iso phthalate copolymer (PETI) is laminated, while on the other surface of the surface treated steel sheet (a surface which constitutes an outer surface side of the can), a white non-stretched film having a thickness of 16µm which is made of a white material formed by adding 20 mass% of titanium based white pigment to ethylene terephthalate ethylene isophthalate copolymer (PETI) is laminated at a laminating temperature of 230°C. After the resin films are laminated to the respective surfaces of the surface treated steel sheet, the steel sheet is immediately cooled thus forming a resin coated steel sheet.
<Example 2>
[0021]
[Formation of surface treated steel sheet]
Composition of tin sulfate plating
Concentration of tin sulfate (In terms of Sn): 70g/L
Plating condition
Plating current density: 7A/dm2
Plating bath temperature: 40°C
Tin coating weight: 2.8
[Formation of resin coated steel sheet]
<Example 3>
[0023]
[Formation of surface treated steel sheet]
Composition of tin sulfate plating
Concentration of tin sulfate (in terms of Sn): 90g/L
Plating condition
Plating current density: 10A/dm2
Plating bath temperature: 40°C
Tin coating weight: 2.8
[Formation of resin coated steel sheet]
<Evaluation>
[0025] The evaluation of the surface treated steel sheets of the examples 1 to 3 is described hereinafter.
[Surface observation]
[0026] Fig. 1(a) is a surface observation photograph (SEM image) of the surface treated steel sheet of the example 1 of the present invention in a state where tin is precipitated on a surface of the steel sheet where iron is exposed, and Fig. 1(b) is a surface observation photograph of a surface treated steel sheet of a comparison example 1.
As shown in Fig. 1 (a), with respect to the surface treated steel sheet of the example 1, it is understood that a tin plating layer having an average particle size of 10µm is precipitated on the steel sheet in a dispersed manner in a state where the iron surface is exposed on the steel sheet where an iron base is partially exposed (the exposure of base iron).
On the other hand, with respect to the surface treated steel sheet of the comparison example 1 shown in Fig. 1(b), small metallic tin particles are precipitated on the steel sheet in a matted manner and there is no exposure of base iron.
<Evaluation of adhesiveness>
[Manufacture of 1st cup]
[0027] Next, specimens for evaluating adhesiveness are prepared from resin coated steel sheets which are formed by laminating a resin film to the surface treated steel sheets of the present invention and the comparison example in the following manner.
A blank having a diameter of 151mm is punched out and, thereafter, in such a manner that a surface of the blank which is coated with a transparent non-stretched film forms a cup inner surface side (in a state where a surface coated with a white non-stretched film forms an outer surface of the can), first-stage drawing is applied to the blank with a drawing ratio of 1.64 thus forming a 1st cup, a B/M can and a CHS can, wherein the transparent non-stretched film coated surface becomes a measuring surface.
These specimens are set to a tensile tester and S peel strengths of the specimens are measured.
Further, the presence or the non-presence of the delamination (peeling of film) at a cup distal end is observed with respect to the 1st cup, the B/M can and the CHS can.
Still further, the S peel strength is measured also with respect to the resin-coated steel sheet per se, and the appearance of the resin-coated steel sheet after lamination is observed with naked eyes (delamination observation).
Here, the 1st cup is a cup which is manufactured by drawing a sheet, the B/M can is a can having a small can diameter and a large side wall height which is formed by further drawing and ironing the 1st cup, and the CHS can is a can which is manufactured by further trimming, flanging and necking the B/M can.
The result of the above-mentioned evaluation is shown in a column "evaluation of adhesiveness" in Tables 1 to 6.
[0028] The cups which are manufactured using the resin-coated steel sheets prepared from the surface treated steel sheets of the examples 1 to 3 exhibit the S peel strength of 0.25g/15mm or more, the S peel strength of 0.35g/15mm or more and the S peel strength of 0.5g/15mm or more respectively with respect to the 1st cup so that these cups are excellent in the working adhesiveness of the resin film at the time of cup forming working.
Further, no delamination is observed at the distal end of the cup with respect to the 1st cup, the B/M can and the CHS can (mark "good").
To the contrary, with respect to the cup which is manufactured using the resin-coated steel sheet prepared from the surface treated steel sheets of the comparison example 1, when the forming working is applied to the 1st cup, the adhesiveness between the resin film at the distal end portion of the cup and the surface treated steel sheet becomes defective so that the delamination occurs at the distal end portion of the cup.
[0029] In the present invention, the following are considered as factors which bring about the enhancement of the adhesiveness.
That is, in the evaluation of the adhesiveness in a state of the 1st cup, for example, to compare the example 1 (see Table 2) and the comparison example 1 (see Table 1), although both examples exhibit the same values with respect to a tin coating weight (Sn = 2.8g/m2) and a surface treated steel sheet heating temperature (lamination temperature = 230°C) at the time of coating, the S peel strength of the 1st cup of the example 1 and the S peel strength of the 1st cup of the comparison example 1 are 0.25kg/15mm and 0.05kg/15mm respectively so that the significant difference of 50 times is recognized.
[0030] Further, to compare the appearance of the surface treated steel sheet after tin plating in Fig. 1(a) (example 1) and the appearance of the surface treated steel sheet after tin plating in Fig. 1(b) (comparison example 1) which correspond to each other, the example 1 and the comparison example 1 differ from each other in a tin electrodeposition mode. In the surface treated steel sheet of the example 1 where tin is formed in such a manner that the iron surface is exposed, an area ratio of tin covering a surface of a steel sheet is 88% and an average tin particle size is 5µm so that tin particles are large in size whereby it is understood that the tin layer formed on the surface treated steel sheet has a large uneven surface. To the contrary, in the surface treated steel sheet of the comparison example 1 which is manufactured by a conventional manufacturing method, an area ratio of tin covering a surface of a steel sheet is 98% and an average tin particle size is 0.3µm so that it is understood that the surface treated steel sheet has a small uneven surface. The same goes for other examples and comparison examples.
[0031] Further, to observe the can wall of the 1st cup (surface of the surface treated steel sheet after S peel strength test) where the large difference is observed in the adhesiveness (S peel strength) of the resin film between the example 1 and the comparison example 1, with respect to the surface of the surface treated steel sheet where tin plating is applied such that the iron surface is exposed, it is observed that a trace of the resin film adhered to a plating recessed portion (a portion where there is no electrodeposition of tin so that the iron surface is exposed) is formed into a shrunken state.
[0032] With respect to the examples and the comparison examples shown in Table 1 to Table 6, the examples where indication of plating appearance is described as "base iron exposed" and the surface treatment is performed under conditions within the range of the present invention exhibit a tin area ratio of 90% or less and S peel strength of 0.2kg/15mm or more.
With respect to examples where the surface treatment is performed under conditions which fall outside the range of the present invention, the plating appearance is described as "base iron exposed", "whole surface coated", "dendrite precipitated" or "dendrite". The comparison examples are explained hereinafter.
With respect to the example where the surface treatment is performed under conditions which fall outside the range of the present invention although the indication of the plating appearance is described as "base iron exposed", a tin area ratio is 98% and S peel strength is 0.05kg/15mm (comparison example-1).
With respect to the example where the surface treatment is performed under conditions which fall outside the range of the present invention although the indication of the plating appearance is described as "whole surface coated", a tin area ratio is 100% and S peel strength is 0.02kg/15mm.
With respect to the examples where the surface treatment is performed under conditions which fall outside the range of the present invention although the indication of the plating appearance is described as "dendrite precipitate" or "dendrite" (dendritic precipitation), the example is in a plated state exceeding a proper current density range and exhibits a black tone due to the precipitation of metallic Sn powder on a plating surface so that the example has no product value. A tin area ratio is 100% and S peel strength is 0.01kg/15mm.
In the Tables, the expression of an upward arrow (↑) means that a state described in one column is equal to a state in another column above one column.
<Evaluation of corrosion resistance after making can>
[0033] In the evaluation of corrosion resistance, a side wall portion of a can is cut out after can making, and corrosiveness of a cross-cut portion (a cut having a size of 20mmx20mm being formed by a cutter knife) is compared among cans.
The manner of performing the test is described hereinafter.
(1) Resin coating treatment
[0034] A PET film having a thickness of 16µm and made of polyethylene terephthalate/isophthalate (12mol%) which contains approximately 20% of a Ti pigment is thermally bonded to a surface of the surface treated steel sheet which becomes a can outer surface by way of laminate rolls and a PET film having a thickness of 16µm and made of polyethylene terephthalate/isophthalate (12mol%) which contains approximately 20% of a Ti pigment is thermally bonded to a surface of the surface treated steel sheet which becomes a can inner surface by way of laminate rolls thus manufacturing a resin coated steel sheet.
(2) Can making step
[0035] A blank having a diameter of 154mm is punched out from the resin-coated steel sheet, and drawing of a first stage is applied to the blank at a drawing ratio of 1.64 thus forming a drawn cup having a diameter of 96mm and a height of 42mm (1st cup). The cup is subjected to further drawing and ironing thus forming a drawn and ironed cup having a diameter of 52mm and a height of 138mm (2nd cup).
[0036] Then, to remove strains of the resin film, the second cup is subjected to heat treatment where the second cup is held at a temperature of 220° for approximately 1 minute thus manufacturing a final formed can (Fi can).
(3) Preparation of corrosion specimens
[0037] A can wall of the final formed can is cut out in a square shape having a size of 40mmx40mm, and a cruciform cross cut (a cut having a size of 20mm×20mm) is formed in the cut-out can wall from a center portion on a can inner surface side by a cutter knife, a cylindrical glass cell having an inner diameter of 35mm, a height of 40mm and an outer diameter of 38mm is set on the cross-cut surface, and upper and lower portions of the cell are fixed to vinyl chloride sheets having a size of 80mmx80mm and a thickness of 5mm (four corners being fixed by bolts).
(4) Filling of corrosion liquid
[0038] 100mL of corrosion test liquid is filled in the cell and, after the cell is hermetically sealed, the cell is held in a thermostatic chamber at a temperature of 37° for one week.
(5) Evaluation of corrosion
[0039] The cell is taken out from the thermostatic chamber, and amounts of iron and tin which are dissolved in a corrosion liquid are measured by an atomic absorption spectrometry, and a corrosion state (corrosion width) of a cross cut portion is compared among the examples.
[Table 1]
| Sn concentration | bath temperature | current density | tin coating weight | plating appearance | area ratio of tin on surface layer | lamination temperature | adhesiveness evaluation | corrosion resistance evaluation | ||
| (g/L) | (°C) | (A/dm2) | (g/m2) | (%) | (°C) | delamination | S peel | (after can making) | ||
| 10 | 30 | 2 | 28 | base iron exposed | 98 | 230 | fair | 0 05 | good | comparison example-1 |
| 5 | whole surface coated | 100 | ↑ | bad | 0 02 | good | comparison example | |||
| 7 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 10 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 15 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 20 | dendnte precipitated | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 30 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 001 | bad | ↑ | |||
| 10 | 50 | 2 | 28 | base iron exposed | 98 | 230 | fair | 0.05 | good | ↑ |
| 5 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 7 | whole surface coated | 100 | ↑ | bad | 0 02 | good | ↑ | |||
| 10 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 15 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 20 | dendnte precipitated | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 30 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 001 | bad | ↑ |
[Table 2]
| Sn concentration | bath temperature | current density | tin coating weight | plating appearance | area ratio of tin on surface layer | lamination temperature | adhesiveness evaluation | corrosion resistance evaluation | ||
| (g/L) | (°C) | (A/dm2) | (g/m2) | (%) | (°C) | delamination | S peel | (after can making) | ||
| 30 | 20 | 2 | 28 | base iron exposed | 98 | 230 | fair | 0 05 | good | comparison example |
| 5 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 7 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 10 | ↑ | ↑ | ↑ | bad | 0 02 | good | ↑ | |||
| 15 | ↑ | ↑ | ↑ | bad | 0.02 | good | ↑ | |||
| 20 | dendnte precipitated | ↑ | ↑ | bad | 0.01 | bad | ↑ | |||
| 30 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 9 01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 30 | 30 | 2 | 28 | base iron exposed | 90 | 230 | good | 0.2 | good | present invention |
| 5 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 7 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 10 | whole surface coated | 100 | ↑ | bad | 0 02 | good | ↑ | |||
| 15 | ↑ | ↑ | ↑ | bad | 0 02 | good | ↑ | |||
| 20 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 30 | dendrite | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 001 | bad | ↑ | |||
| 30 | 40 | 2 | 28 | base iron exposed | 88 | 230 | good | 025 | good | present invention |
| 5 | ↑ | 90 | ↑ | good | 0 2 | good | ↑ | |||
| 7 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 10 | whole surface coated | 100 | ↑ | bad | 0 02 | good | ↑ | |||
| 15 | ↑ | ↑ | ↑ | bad | 0 02 | good | ↑ | |||
| 20 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 30 | dendnte | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 30 | 50 | 2 | 28 | base iron exposed | 88 | 230 | good | 0 25 | good | present invention |
| 5 | ↑ | 90 | ↑ | good | 0 2 | good | ↑ | |||
| 7 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 10 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 15 | whole surface coated | 100 | ↑ | bad | 0 02 | good | ↑ | |||
| 20 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 30 | dendnte | ↑ | ↑ | bad | 001 | bad | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 30 | 60 | 2 | 2.8 | base iron exposed | 85 | 230 | good | 0 3 | good | present invention |
| 5 | ↑ | 88 | ↑ | good | 025 | good | ↑ | |||
| 7 | ↑ | 90 | ↑ | good | 0 2 | good | ↑ | |||
| 10 | base iron exposed | 98 | ↑ | fair | 0.05 | good | comparison example | |||
| 15 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 20 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 30 | dendrite | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 0.01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ |
[Table 3]
| Sn concentration | bath temperature | current density | tin coating weight | plating appearance | area ratio of tin on surface layer | lamination temperature | adhesiveness evaluation | corrosion resistance evaluation | ||
| (g/L) | (°C) | (A/dm2) | (g/m2) | (%) | (°C) | delamination | S peel | (after can making) | ||
| 50 | 20 | 2 | 28 | base iron exposed | 88 | 230 | good | 0.25 | good | present invention |
| 5 | ↑ | 90 | ↑ | good | 0.2 | good | ↑ | |||
| 7 | base iron exposed | 98 | ↑ | fair | 0.05 | good | comparison example | |||
| 10 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 15 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 20 | ↑ | ↑ | ↑ | bad | 0.02 | good | ↑ | |||
| 30 | ↑ | ↑ | ↑ | bad | 0.02 | good | ↑ | |||
| 40 | dendnte | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | 30 | 2 | 2.8 | base iron exposed | 85 | 230 | good | 0.3 | good | present invention |
| 5 | ↑ | 88 | ↑ | good | 0 25 | good | ↑ | |||
| 7 | ↑ | 90 | ↑ | good | 0 2 | good | ↑ | |||
| 10 | base iron exposed | 98 | ↑ | fair | 005 | good | comparison example | |||
| 15 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 20 | whole surface coated | 100 | ↑ | bad | 0 02 | good | ↑ | |||
| 30 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 40 | dendrite | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | 40 | 2 | 28 | base iron exposed | 85 | 230 | good | 0 3 | good | present invention |
| 5 | ↑ | 88 | ↑ | good | 0 25 | good | example-1 | |||
| 7 | ↑ | 90 | ↑ | good | 0 2 | good | present invention | |||
| 10 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 15 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 20 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 30 | whole surface coated | 100 | ↑ | bad | 0 02 | good | ↑ | |||
| 40 | dendrite | ↑ | ↑ | bad | 0.01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 50 | 50 | 2 | 28 | base iron exposed | 80 | 230 | good | 0 35 | good | present invention |
| 5 | ↑ | 85 | ↑ | good | 03 | good | ↑ | |||
| 7 | ↑ | 88 | ↑ | good | 0 25 | good | ↑ | |||
| 10 | ↑ | 90 | ↑ | good | 0 2 | good | ↑ | |||
| 15 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 20 | ↑ | ↑ | ↑ | fair | 005 | good | ↑ | |||
| 30 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 40 | dendrite | ↑ | ↑ | bad | 0.01 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 001 | bad | ↑ | |||
| 50 | 60 | 2 | 28 | base iron exposed | 75 | 230 | good | 04 | good | present invention |
| 5 | ↑ | 80 | ↑ | good | 035 | good | ↑ | |||
| 7 | ↑ | 85 | ↑ | good | 03 | good | ↑ | |||
| 10 | ↑ | 88 | ↑ | good | 025 | good | ↑ | |||
| 15 | ↑ | 90 | ↑ | good | 0 2 | good | ↑ | |||
| 20 | base iron exposed | 98 | ↑ | fair | 005 | good | comparison example | |||
| 30 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 40 | dendnte | ↑ | ↑ | bad | 001 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 001 | bad | ↑ |
[Table 4]
| Sn concentration | bath temperature | current density | tin coating weight | plating appearance | area ratio of tin on surface layer | lamination temperature | adhesiveness evaluation | corrosion resistance evaluation | ||
| (g/L) | (°C) | (A/dm2) | (g/m2) | (%) | (°C) | delamination | S peel | (after can making) | ||
| 70 | 20 | 2 | 28 | base iron exposed | 80 | 230 | good | 035 | good | |
| 5 | ↑ | 85 | ↑ | good | 03 | good | present invention | |||
| 7 | ↑ | 88 | ↑ | good | 0.25 | good | ↑ | |||
| 10 | base iron exposed | 98 | ↑ | fair | 005 | good | comparison example | |||
| 15 | ↑ | ↑ | ↑ | fair | 005 | good | ↑ | |||
| 20 | whole surface coated | 100 | ↑ | bad | 0.02 | good | ↑ | |||
| 30 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 40 | dendrite | ↑ | ↑ | bad | 001 | bad | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 0.01 | bad | ↑ | |||
| 70 | 30 | 2 | 2.8 | base iron exposed | 75 | 230 | good | 0 4 | good | present invention |
| 5 | ↑ | 80 | ↑ | good | 0 35 | good | ↑ | |||
| 7 | ↑ | 85 | ↑ | good | 0.3 | good | ↑ | |||
| 30 | ↑ | 90 | ↑ | good | 0 2 | good | ↑ | |||
| 15 | base iron exposed | 98 | ↑ | fair | 0 05 | good | companson example | |||
| 20 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 30 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 50 | dendrite | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 70 | 40 | 2 | 28 | base iron exposed | 70 | 230 | good | 0 5 | good | present invention |
| 5 | ↑ | 75 | ↑ | good | 0 4 | good | ↑ | |||
| 7 | ↑ | 80 | ↑ | good | 0 35 | good | example-2 | |||
| 10 | ↑ | 88 | ↑ | good | 0.25 | good | present invention | |||
| 15 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 20 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 30 | whole surface coated | 100 | ↑ | bad | 0 02 | good | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 0 02 | good | ↑ | |||
| 50 | dendrite | ↑ | ↑ | bad | 001 | bad | ↑ | |||
| 70 | 50 | 2 | 28 | base iron exposed | 65 | 230 | good | 0 55 | good | present invention |
| 5 | ↑ | 70 | ↑ | good | 0 5 | good | ↑ | |||
| 7 | ↑ | 75 | ↑ | good | 04 | good | ↑ | |||
| 10 | ↑ | 80 | ↑ | good | 0 35 | good | ↑ | |||
| 15 | ↑ | 90 | ↑ | good | 0 2 | good | ↑ | |||
| 20 | base iron exposed | 98 | ↑ | fair | 0.05 | good | comparison example | |||
| 30 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 40 | whole surface coated | 100 | ↑ | bad | 0.02 | good | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 70 | 60 | 2 | 2.8 | base iron exposed | 60 | 230 | good | 0 55 | good | present invention |
| 5 | ↑ | 65 | ↑ | good | 0 5 | good | ↑ | |||
| 7 | ↑ | 70 | ↑ | good | 0 4 | good | ↑ | |||
| 10 | ↑ | 75 | ↑ | good | 0 3 | good | ↑ | |||
| 15 | ↑ | 85 | ↑ | good | 025 | good | ↑ | |||
| 20 | base iron exposed | 98 | ↑ | fair | 005 | good | comparison example | |||
| 30 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 40 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ |
[Table 5]
| Sn concentration | bath temperature | current density | tin coating weight | plating appearance | area ratio of tin on surface layer | lamination temperature | adhesiveness evaluation | corrosion resistance evaluation | ||
| (g/L) | (°C) | (A/dm2) | (g/m2) | (%) | (°C) | delamination | S peel | (after can making) | ||
| 90 | 20 | 2 | 28 | base iron exposed | 50 | 230 | good | 07 | good | present invention |
| 5 | ↑ | 60 | ↑ | good | 0.6 | good | ↑ | |||
| 7 | ↑ | 70 | ↑ | good | 0 5 | good | ↑ | |||
| 10 | ↑ | 80 | ↑ | good | 0 35 | good | ↑ | |||
| 15 | base iron exposed | 98 | ↑ | fair | 0.05 | good | comparison example | |||
| 20 | ↑ | ↑ | ↑ | fair | 005 | good | ↑ | |||
| 30 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 50 | dendrite | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 90 | 30 | 2 | 2.8 | base iron exposed | 45 | 230 | good | 0 75 | good | present invention |
| 5 | ↑ | 55 | ↑ | good | 0 65 | good | ↑ | |||
| 7 | ↑ | 65 | ↑ | good | 0 55 | good | ↑ | |||
| 10 | ↑ | 75 | ↑ | good | 0 4 | good | ↑ | |||
| 15 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 20 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 30 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 50 | dendrite | ↑ | ↑ | bad | 0 01 | bad | ↑ | |||
| 90 | 40 | 2 | 28 | base iron exposed | 40 | 230 | good | 0 8 | good | present invention |
| 5 | ↑ | 50 | ↑ | good | 0 7 | good | ↑ | |||
| 7 | ↑ | 60 | ↑ | good | 0 6 | good | ↑ | |||
| 10 | ↑ | 70 | ↑ | good | 0 5 | good | example-3 | |||
| 15 | ↑ | 80 | ↑ | good | 0 35 | good | present invention | |||
| 20 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 30 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 40 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 0 02 | good | ↑ | |||
| 90 | 50 | 2 | 28 | base iron exposed | 35 | 230 | good | 085 | good | present invention |
| 5 | ↑ | 45 | ↑ | good | 0 75 | good | ↑ | |||
| 7 | ↑ | 55 | ↑ | good | 0 65 | good | ↑ | |||
| 10 | ↑ | 65 | ↑ | good | 0 55 | good | ↑ | |||
| 15 | ↑ | 75 | ↑ | good | 0 4 | good | ↑ | |||
| 20 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 30 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 40 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 90 | 60 | 2 | 28 | base iron exposed | 30 | 230 | good | 0 9 | good | present invention |
| 5 | ↑ | 40 | ↑ | good | 0 8 | good | ↑ | |||
| 7 | ↑ | 50 | ↑ | good | 0 7 | good | ↑ | |||
| 10 | ↑ | 60 | ↑ | good | 0 6 | good | ↑ | |||
| 15 | ↑ | 70 | ↑ | good | 0 5 | good | ↑ | |||
| 20 | ↑ | 85 | ↑ | good | 0 3 | good | ↑ | |||
| 30 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 40 | ↑ | ↑ | ↑ | fair | 0 05 | good | ↑ | |||
| 50 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ |
[Table 6]
| Sn concentration | bath temperature | cunent density | tin coating weight | plating appearance | area ratio of tin on surface layer | laimnation temperature | adhesiveness evaluation | corrosion resistance evaluation | ||
| (g/L) | (°C) | (A/dm2) | (g/m2) | (%) | (°C) | delamination | S peel | (after can making) | ||
| 120 | 30 | 2 | 2 8 | base iron exposed | 40 | 230 | good | 0 8 | good | present invention |
| 5 | ↑ | 50 | ↑ | good | 0 7 | good | ↑ | |||
| 7 | ↑ | 60 | ↑ | good | 0 6 | good | ↑ | |||
| 10 | ↑ | 70 | ↑ | good | 0 5 | good | ↑ | |||
| 15 | ↑ | 85 | ↑ | good | 0.3 | good | ↑ | |||
| 20 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 30 | whole surface coated | 100 | ↑ | bad | 0.02 | good | ↑ | |||
| 40 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ | |||
| 120 | 50 | 2 | 28 | base iron exposed | 30 | 230 | good | 0 9 | good | present invention |
| 5 | ↑ | 40 | ↑ | good | 0 8 | good | ↑ | |||
| 7 | ↑ | 50 | ↑ | good | 0 7 | good | ↑ | |||
| 10 | ↑ | 60 | ↑ | good | 0 6 | good | ↑ | |||
| 15 | ↑ | 70 | ↑ | good | 0 5 | good | ↑ | |||
| 20 | ↑ | 85 | ↑ | good | 0 3 | good | ↑ | |||
| 30 | base iron exposed | 98 | ↑ | fair | 0 05 | good | comparison example | |||
| 40 | whole surface coated | 100 | ↑ | bad | 002 | good | ↑ | |||
| 50 | ↑ | ↑ | ↑ | bad | 002 | good | ↑ |
[0040] As has been explained heretofore, with respect to a resin coated steel sheet manufactured using a surface treated steel sheet manufactured by the manufacturing method of the present invention, even when any working such as drawing, further stretching after drawing, or further ironing after drawing is applied to the resin coated steel sheet, there is no possibility that a resin film is peeled off at the time of forming working so that the resin-coated steel sheet exhibits the stable and excellent working adhesiveness. Further, also at the time of performing can body forming working where both stretching and ironing are applied to a can body after more rigorous drawing, there is no possibility that a resin film is peeled off so that the resin-coated steel sheet exhibits the stable and excellent working adhesiveness.
[0041] Conventionally, as a method for evaluating adhesiveness of a coated resin, T peel strength is measured in a state of a flat plate before working. However, it is considered that this measurement does not always accurately reflect working adhesiveness. Accordingly, in the present invention, S peel strength is adopted as peeling strength. That is, S peel strength is adopted as an evaluation method which accurately reflects adhesiveness (working adhesiveness) during working and after working when rigorous forming working where steel sheet is formed into a can body by further applying both stretching and ironing after drawing is applied to the steel sheet.
S peel strength is strength by which working adhesive strength is evaluated based on peeling strength of a resin film of a specimen which is cut out from a side wall of a cup formed by applying drawing to a resin coated steel sheet.
[0042] A specific measuringmethod of S peel strength is explained hereinafter.
Firstly, a blank having a diameter of 154mm is punched out from a resin coated steel sheet, and drawing of a first stage is applied to the blank at a drawing ratio of 1.64 thus forming a drawn cup having a diameter of 96mm and a height of 42mm. A side wall portion of the drawn cup having a size of 30mm in the cup height direction and 120mm in the cup circumferential direction is cut out from the cup, the cut-out side wall portion is bent back to a planar shape and, thereafter, a T-shaped specimen 71 having a size shown in Fig. 2 which is a plan view is punched out from the cut-out side wall portion by a press mold.
Then, as shown in Fig. 3, a cut 72 is formed in a coated resin on a side opposite to an adhesive strength measuring surface (a viewer's side surface in the drawing) of a one-side (right) end portion 71a of the specimen 71 (a back-side surface in the drawing) using a cutter knife such that the cut 72 reaches a surface of the surface treated steel sheet.
Further, as shown in Fig. 4 and Fig. 5, a score 73 is formed in the surface opposite to the adhesive strength measuring surface (the surface in which the cut 72 is formed) using a score forming die set and, thereafter, the score portion is folded and only the surface treated steel sheet is cut. Here, the coated resin is not cut on the adhesive strength measuring surface, and the coated resin remains on both sides of surface treated steel sheets separated by cutting in a connected state.
Next, as shown in Fig. 6, one end portion 71a is inserted into a specimen insertion portion 74a of a specimen holder 74, thus fixing the specimen 71 in the specimen holder 74 and, thereafter, an upper portion 74b of the specimen holder 74 and the other end portion 71b of the specimen 71 are pulled from each other while being clamped by both chuck portions of a tensile tester, and the coated resin is forcibly peeled off from the surface treated steel sheet, and tensile strength is measured, and this value is set as S peel strength.
[0043] The S peel strength measured as described above is preferably set to 0.2kg/15mm or more when a specimen has a width of 15mm. When the S peel strength is less than 0.2kg/15mm, it is impossible to acquire the stable and favorable working adhesiveness in rigorous forming working such as can making working where both stretching and ironing are performed after drawing.
Industrial applicability
[0044] According to the present invention, by enhancing the adhesiveness of a steel sheet with a resin which has been insufficient in a conventional surface treated steel sheet, a surface treated steel sheet which enhances the corrosion resistance without lowering workability of a resin-coated steel sheet can be manufactured stably. Accordingly, the industrial value of the present invention is extremely large.
Explanation of symbols
1. A method for manufacturing a surface-treated steel sheet, wherein an area ratio of
tin covering a surface of a steel sheet is set to 5% to 95% by adjusting the Sn concentration
in a tin sulfate plating bath containing a sulfuric acid and tin sulfate to a value
which falls within a range of 30 to 120 g/L, a temperature of the tin sulfate plating
bath is set to a value which falls within a range of 20 to 60°C, and current density
in tin sulfate plating to a value which falls within a range of 2 to 50 A/dm2, whereby the surface of the steel sheet is coated with metallic tin such that some
of iron on the surface of the steel sheet is exposed.
2. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 30 to 50 g/L, the temperature of the tin sulfate plating bath is
set to a value which falls within a range of 30 to 60°C, and the current density in
the tin sulfate plating is set to a value which falls within a range of 2 A/dm2 or less.
3. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 30 to 50 g/L, the temperature of the tin sulfate plating bath is
set to a value which falls within a range of 40 to 60°C, and the current density in
the tin sulfate plating is set to a value which falls within a range of 2 to 5 A/dm2.
4. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 50 to 70g/L, the temperature of the tin sulfate plating bath is
set to a value which falls within a range of 20 to 60°C, and the current density in
the tin sulfate plating is set to a value which falls within a range of 2 to 5 A/dm2.
5. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 50 to 70g/L, the temperature of the tin sulfate plating bath to
a value which falls within a range of 30 to 60°C, and the current density in the tin
sulfate plating is set to a value which falls within a range of 2 to 7 A/dm2.
6. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 50 to 70g/L, the temperature of the tin sulfate plating bath is
set to a value which falls within a range of 50 to 60°C, and the current density in
the tin sulfate plating is set to a value which falls within a range of 2 to 10 A/dm2.
7. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 70 to 90g/L, the temperature of the tin sulfate plating bath is
set to a value which falls within a range of 20 to 60°C, and the current density in
the tin sulfate plating is set to a value which falls within a range of 2 to 7 A/dm2.
8. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 70 to 90g/L, the temperature of the tin sulfate plating bath is
set to a value which falls within a range of 30 to 60°C, and the current density in
the tin sulfate plating is set to a value which falls within a range of 2 to 10 A/dm2.
9. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 70 to 90g/L, the temperature of the tin sulfate plating bath is
set to a value which falls within a range of 50 to 60°C, and the current density in
the tin sulfate plating is set to a value which falls within a range of 2 to 15 A/dm2.
10. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 90 to 120g/L, the temperature of the tin sulfate plating bath is
set to a value which falls within a range of 20 to 60°C, and the current density in
the tin sulfate plating is set to a value which falls within a range of 2 to 10 A/dm2.
11. The method for manufacturing a surface-treated steel sheet according to claim 1, wherein
the Sn concentration in the tin sulfate plating bath is set to a value which falls
within a range of 90 to 120g/L, the temperature of the tin sulfate plating bath is
set to a value which falls within a range of 40 to 60°C, and the current density in
the tin sulfate plating is set to a value which falls within a range of 2 to 15 A/dm2.
12. A method for manufacturing a resin-coated steel sheet wherein, a resin is applied
by coating to the surface treated steel sheet manufactured by the method for manufacturing
a surface-treated steel sheet according to any one claims 1 to 11.
13. The method for manufacturing a resin-coated steel sheet according to claim 12, the
resin coating is performed at a temperature equal to or above a melting point of tin.
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description