CA1211407A - Process for producing a thin tin and zinc plated steel sheet - Google Patents
Process for producing a thin tin and zinc plated steel sheetInfo
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- CA1211407A CA1211407A CA000412070A CA412070A CA1211407A CA 1211407 A CA1211407 A CA 1211407A CA 000412070 A CA000412070 A CA 000412070A CA 412070 A CA412070 A CA 412070A CA 1211407 A CA1211407 A CA 1211407A
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- zinc
- bath
- stannous
- tin
- tinplating
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Abstract
PROCESS FOR PRODUCING A THIN TIN AND
ZINC PLATED STEEL SHEET
ABSTRACT OF THE DISCLOSURE
A process for producing a thin tin and zinc plated steel sheet which comprises electroplating zinc on a steel sheet from a zinc electroplating bath containing zinc ions followed by tin-plating the zinc plated steel sheet by immersion or by immersion followed by electroplating in a tinplating bath containing stannous ions, whereby zinc ions from the zinc plated steel sheet replace the stannous ions in the tinplating solution during the immersion tinplating. The resultant solution from the tinplating which contains zinc ions is recycled to make up the zinc electroplating bath.
ZINC PLATED STEEL SHEET
ABSTRACT OF THE DISCLOSURE
A process for producing a thin tin and zinc plated steel sheet which comprises electroplating zinc on a steel sheet from a zinc electroplating bath containing zinc ions followed by tin-plating the zinc plated steel sheet by immersion or by immersion followed by electroplating in a tinplating bath containing stannous ions, whereby zinc ions from the zinc plated steel sheet replace the stannous ions in the tinplating solution during the immersion tinplating. The resultant solution from the tinplating which contains zinc ions is recycled to make up the zinc electroplating bath.
Description
FIELD OF THE INVENTION
The present invention relates to a process for produeing a thin tin and zinc plated steel sheet by thin tin-plating by an immersion or by an eleetroplatin~ after an immersion into an aeidie tinplating bath after eleetro-plating of zine on a steel sheet by using a zine plating bath produeed by the substitution of stannous ion for zine ion in said tinplating bath whieh is used for said tinplating.
DESCRIPTION OF T~IE INVENTION
Eleetrotinplated materials have been previously used for manufaeturing eans sueh as food eans, five gallon eans and paint eans. Recently the ehangeover from expensive eleetrotinplated materials to cheaper tin free steel (TFS) eonsisting of metallie ehromium and hydrated ehromium oxide as well as a decrease in the weight of the tin eoating in eleetrotinplated materials has rapidly oeeured in the can manufaeturing field beeause the tin used for the production of tin-~lated materials is very expensive and there is coneern about possible exhaustion of tin resources throughout the world.
An ordinàry metal can eonsists of two pieces of can ends and one pieee of can body. As a method of seaming a TFS can body, electric welding is well known. Further, a methocl ~,rployinc3 a nylon adhesive is widely used for bevera~3e can bodies. In this ele~ctric welding of the TFS ean body, however, the mec}lanical or chemieal removal of TFS film consisting of metallic chroillium layer and hydrated ehro.iu:~
~L2~ 7 oxide layer is indispensable for satisfaction welding.
Therefore, the welded parts must 'be sufficiently coated by lacquer in order to prevent the corrosion.
On the other hand, the seaming of the tinplate can body is generally carried out by soldering. In the field of food cans, the use of expensive pure tin solder for the seam-ing of the tinplate can body increases because the lead content in the canned food is regulated by the FI~A. Thus, it is difficult to decrease the tin co~ting weight in tinplates to below 1.0 g/m , because stable operation of the soldering at high speed becomes difficult.
Furthermore, as a method of seaming the tinplate can body, the employment of an organic adhesive such as nylon adhesive has been also proposed, for instance, in Japanese Laid-Open Patent Application No. Sho ~9-37829 filed August 11, 1972 in the name of Kozo Yoshizaki, entitled "Tin Plated Steel Sheet Having E~cellent Adhesive Strength", and in Japanese Patent Publication No. Sho 48-18929 filed December 4, 1969 in the name of Kozo Yoshizaki, entitled "Process for Adhering Tin Plated Steel Sheet with Organic Adhesive".
However, the tinplate can body seamed by an organic adhesive may be broken when a beverage such as fruit juice is hot packed, because the bonding strength in the seam becomes remarkably low. Presently, such method is not considered practical.
Recently, a lap seam welding method, for instance the SOUDRONIC (trade mark) process, has become widely used for the seaming of a tinplate can body such as an aerosol can and a dry fill can, instead of soldering.
As described above, both tinplate and TFS present certain problems as materials for welded cans. Narnely, ?, - ' '.
~2~14~
tinplate is expensive although it is easily welded at high speed and TFS is not satisfactorily welded without scraping off the TFS film.
- 3a -In view of the background as described above, light tin coated steel sheets shown in United States Patent No. 4,113,5~0 and United States Patent No. 4,145,263 were developed several years ago.
However, these light tin coated steel sheets also present certain problems. Namely, these sheets can not be welded without splashing under welding at high speeds such as 40 m/min.. Furthermore, the filiform corrosion in these sheets coated by lacquer may appear after aging in an atmosphere having high humidity.
SUMMAR~ OF THE INVENTION
It is an object of the present invention to provide a process for producing a thin tin and zinc plated steel sheet having an excellent weldability and an excellent filiform corrosion resistance.
This object can be accomplished by electroplating zinc on a steel sheet ~rom a zinc electroplating bath containing zinc ions followed by tin-plating the zinc plated steel sheet by immersion or by immersion followed by electroplating in a tinplating bath containing stannous ions, whereby zinc ions from the zinc plated steel sheet substantially replace the stannous ions in the tinplating solution during the immersion tinplating. ~he rcsultant solution from the tinplating which contains zinc ions is employed to make up the zinc electro-plating. The resultant coating on steel sheet, after the tin-plating, contains 0.005 - 0.2 g/m2 zinc and 0.05 to 1.0 5/m2 tin.
In the present invention, the stccl shcct dc~reased and picklcd by ordinary methods is firstly clectroplated ~y ~Z~14~7 a suitable arnount of zinc with due consideration of the dissolved amount of zinc and the amount of tin to be plated during imrnersion tinplating.
After that, the zinc plated steel sheet is further plated by tin by the immersion into the tinplating bath.
The deposition of tin from the tinplating bath occurs with the dissolution of the plated zinc into said tinplating bath.
Namely, both the reaction for the deposition of tin and the dissolution of the plated zinc occur simultaneously by the chemical substitution reaction between zinc and stannous ion.
Therefore, the tinplating bath gradually is converted to a zinc plating bath due to the substitution of stannous ions by zinc ions in said tinplating bath. In spite of the increase of zinc ion in said tinplating bath, tin is deposited on said zinc plated steel sheet due to the presence of stannous ion in said tinplating bath, because the standard electrode potential of zinc is less than that of tin. Namely, the tinplating bath can be used ror tinplating until stannous ion in the tinplating bath is almost exhausted and after that this bath can be used ac~ain for the electroplating of zinc on the steel sheet in the present invention.
Furthermorc, the e~hausted solution consisting of a dilute tinplating bath in the conventional tinplating process is also used for producing a thin tin and zinc plated steel sheet according to the present invention with the recovery of stannous ion from the evhausted solution.
Therefore, the process according to the present invention is very economical method for produciny a thin tin and zinc plated stecl sheet.
~Z1~4~7 DETAILE~ DESCRIPTION OF THE INV~NTION
A thin tin and zinc plated steel sheet having an excellent weldability and an excellent filiform corrosion resistance which is the object of -~he present invention is ohtained by an imrnersion plating or by an electroplating after an irnmersion plating of 0.05 - 1.0 g/m2 of tin after electroplating 0.005 - 0.2 g/m2 of zinc, by measurement after said tin-plating on a zinc plated steel sheet, according to the present invention.
In this tin and zinc plated steel sheet, the presence of zinc in the range of 0.005 - 0.2 g/m2 by measurement after said tinplating is indispensable in order to improve weldability and prevent filiform corrosion.
If the amount of zinc is below 0.005 g/m2, the weldability at high speed is not improved and the filiform corrosion is not prevented. ~t above 0.2 g/m2 of zinc, the weldability at high speed is not also improved and the white rust due to the corrosion of zinc appears although the filiform corrosion is prevented.
If the amount of the plated tin is below 0.05 g/m2, welding at high speed becomes very difficult and white rust due to the corrosion of zinc is not prevented. ~n increase in the amount to above 1.0 g/m2 of tin is not economical, although the weldability does not deteriorate.
For an industrial operation, the present invcntion is carried ou~ according to the following process: degreasing with an alkali solution and pickliny with an acid solution ~ water rinsing - -~ electroplating of zinc ~watcr 4C~7 rinsing ~ tin-plating by immersion or by electroplating after immersion into tinplating bath--~ water rinsing >post-treatment for example by sodium dichromate used for conventional electrotinplating--~ water rinsing ~ drying -__~ oiling, for example with dioctyl sebacate or cotton seed oil.
In this process, the bath containing the same anion and the same additives as those in the tinplating bath, besides zinc ion is, in principle, used for zinc plating. The additi-ves are organic additive agents such as gelatine, peptone, di-hydroxy diphenyl sulphone, monobutyl phenyl phenol, sodiummonosulphonate, ethoxylated ~-naphthol and ethoxylated c~-naphthol sulfonic acid used for tinplating bath. For the tinplating in the present invention, the known acidic tinplat-ing bath for conventional electrotinplating is used, namely, an acidic bath such as a stannous su~fate bath, a stannous phenol-sulfonate bath and a stannous halogenide bath and solutions prepared by reconstituting such exh~usted solutions.
However, it is necessary in the present invention that a pH of the tinplating bath be below 1.7 in the stannous sulfate bath and the stannous phenolsulfonate bath and be below 4.0 in the stannous halogenide bath. Further, the concentration of stannous ion in these tinplating baths should preferably be above 2 g/l.
If the pH of the tinplating bath is not below 1.7 or 4.0 tinplating by the immersion method is impossible because stannous ion is precipitated. If the concentration of stannous ion in these tinplating baths is below 2 g/l, a continuous operation for producing the thin tin and zinc plated steel sheet according to the present invention is difficult because stannous ion is consumed in a short time by the deposition of tin and is not supplied from anywhere~ Although an increase in the amount of stannous ion in these tinplating baths does not adversely _7-~2~
affect the immersion tinplating, it is desirable to limit the amount of stannous ion below 70 g/l from an economical view-point.
-7a-An increase in the amount o~ zinc ion in the tinplating bath is not limited in the present invention, because it does not affect the immersion tinplating, although the amount of zinc ion in the tinplating bath increases with a decrease of stannous ion. It is preferable to control the temperature of the tinplating bath in the ran~e of 20 - 60C
from the industrial and economical viewpoints.
At a temperature of tinplating bath above 60C, some additives such as ethoxylated ~-naphthol sulfonic acid used in conventional electrotinplating bath may be decomposed.
Furthermore, the immersion time of the zinc plated steel sheet into the tinplating bath is preferably 0.1 - 5 seconds.
If the immersion time is below 0.1 seconds, the amount of tin re~uired in the present invention is not dcposited by the substitution reaction between stannous ion and the plated zinc.
In the immersion tinplating, the immersion time above 5 seconds is meaningless for producing at high speed a thin tin and zinc plated steel sheet according to the present invention, because the surface of the plated zinc is gradually covered by thc deposited tin and then the rate of the deposition of tin becomes low. For instance, the rate of the deposition of tin becomes remarkably 10W at above o.~ y/m2 of deposited tin, even if the plated zinc is present in a sufficient amount rcquired for the deposition of 1.0 c~/m2 of tin. In this case, elcctroplating should be carried out after the immcrsion tinplating in order to supplcment thc deficiency of tin. In tilc prcscnt invcntion, electrotinplatinc3 aftcr the immersion tinplatinc~ is carried out under thc same conditions as in conventional tinplating. It is desirable that the tempera-ture of tinplating bath be 20 - 60C and the current density be 5 - 50 A/dm2. Generally, lower current density is applied for the formation of a uniform tin layer at lower bath tempera-ture and lower concentration of stannous ion. On the contrary, at higher bath temperature and high concentration of stannous ion, a higher current density is applied. Furthermare, in the case where the concentration of stannous ion below 2 g/l, the electrical resistance of the bath increases and the current efficiency for tinplating becomes very low, and therefore, such low concentration of stannous ion is not suitable for industrial production of the thin tin and zinc plated steel sheet according to the present invention.
The composition of the zinc plating bath used in ~he present invention is naturally regulated because the zinc ions therein substantially replace the stannous ions during the tin-plating. For instance, if a stannous sulfate bath is used for tinplating, a zinc sulfate bath containing the same anion and the same additives is used for zinc plating on the steel sheet in the present invention.
The concentration of zinc ion in the zinc plating bath should be controlled in the range of 10 - 100 g/l. If the concentration of zinc ion is below 10 g/l, it is not suitable for industrial production of the thin tin and zinc ---platcd stccl sheet accordiny to thc present invention, bccause the electrical resistance of the ZillC plating bath is high and a rectifier having a large capacity is necessary. The use of a zinc plating bath having above 100 g/l of zinc ion is not econo3nical.
In the case of zinc plating by using the zinc plating bath obtained from the tinplating bath having a small amount of stannous ion, therefore, zinc i.on should be supplied by the addition of a zinc salt having the same anion as in the tinplating bath, zinc hydroxide or the dissolution of zinc.
For instance, if the tinplating bath having 2 g/l of stannous ion is used for tinplating, at least about 9.9 g/l of zinc ion should be supplied to the zinc plating bath obtained from this tinplating bath, even if 2 g/l of stannous ion is completely 10 replaced by zinc ion. '.
The concentration of stannous ion in the zinc plating bath should be kept below 1 g/l, desirably almost zero, because the excess amount of tin is preferentially deposited during electroplating zinc of the amount required in the present invention.
When a small amount of stannous ion is present in the zinc plating bath~ the pH of the zinc plating bath should be kept below 1.7 in zinc sulfate bath or zinc phenolsulfonate bath and below ~.0 in zinc halogenide bath, because stannous 20 ion is precipi-tated in zinc plating bath at above the pH
described above and gives a bad appearance in the thin tin and zinc plated steel sheet according to the present invention.
In the absence of stannous ion in the zinc plating bath, the pH of the zinc plating bath may be raised to about 7 by the addition of al]sali hydroxide, alkali oxide or zinc hydroxide.
In this case, however, water rinsing should be preferably carried out after zinc plating in order to prevent the rise of pH in the tinplating bath, although it may be 30 omitted in the ~se of a.zinc plating bath beiny below 1.7 or 4.0 of pH.
~LZ11407 In zinc plating, it is preferable to control the temperature of the zinc plating bath in the range of 20 - 60C
from the industrial and economical viewpoints. At a tempera-ture of the zinc plating bath above 60C, some additives such as ethoxylated a-naphthol used in the tinplating bath may be decomposed.
Furthermore, the cathodic current density for zinc plating is 0.1 - 100 A/dm2, preferably 1 - 70 A/dm2 in the present invention. A lower current density below 0.1 A/dm2 is not suitable for the continuous production of the thin tin and zinc plated steel sheet at high speed. A higher current density above 100 A/dm2 is not also suitable because a rectifier having a large capacity is necessary.
In the process according to the present invention, it is very important to control the amount of the electroplated zinc, because the arnount of the plated tin dep~nds on the amount of the dissolved zinc in the immersion tinplating.
Namely, 1 mole/dm2 of tin is theoretically plated by the dissolution of 1 mole/dm2 of the plated zinc. Therefore, for the deposition of 0.05 - 1.0 g/m2 of tin, the dissolution of 0.028 - 0.55 g/m2 of the platcd zinc is necessary. In the clctcrmination of th~ ~mount o the zinc rclllaininc3 a~ter tinplating, the amount of the electroplated zinc is calculated by the follo~ing equation:
The amount of the plated zinc (g/rn2) = the amount of the plated tin ~ 58- 639 + 0.005 ~ 0.2 ~lowevcr, it lS difficult from a practical standpoint to deposit a'aove 0.4 y/m2 of tin by thc immcrsion tinplatinc~
I,ccau-: thc sur1acc of thc platcc'i zinc is yraduall~ COVClCCi ~y the clc~)ositc~i tin anci then thc ratc in thc cieposition of tin ~eCO;ilC,5 relil~r~;a~lv low.
_ 1 1 _ 14~
Therefore, it is desirable in the present invention that the amount of the electroplated zinc be below 0.42 g/m2 for producing the thin tin and zinc plated s-teel sheet at high speed.
In some cases, heating the thin tin and zinc plated steel sheet at a temperature above melting point of tin and quenching are carried out, in order to improve lacquer adhesion, although the weldability at hiyh speed becomes slightly poorer. In the case of a light tin coating weight, such as 0.10 g/m , the plated tin is sufficiently converted to an iron-tin alloy by heating at a somewhat higher tempera-ture (about 250C) than the melting point of tin. However, for a heavy tin coating weight, such as 0.8 g/m2, heating at a considerably higher temperature (300 - 400C) than the melting point of tin is necessary. Generally, it is necessary that the temperature during formation of the iron-tin alloy be maintained in the range of 232 - 4aooc for 0.5 - 10 seconds.
In this case, heating is carried out by a known method such as resistance heating and/or induction heating which is generally used in the manufacturing process of conventional clectrotinplated materials.
Furthermore, the thin tin and zinc plated steel sheet according to the present invention is subjected to a cathodic treatment Ol^ an immersion treatment in a known solution containing hexavalent chromium ion such as a sodium dichromate solution or chromic acid solution which is generally used for the post-treatment of conventional electrotinplated materials.
phosphate treatment or sodium carbonate treatment can be used for the post-treatrnent of the thin tin and zinc plated steel sheet instcad of chromate treatmenk.
12~ 7 The present invention is illustrated by the following Exampl.es-A eold redueed steel sheet having a thickness of0.22 mm was eleetrolyticall.y degreased in a solution of 70 g/l sodium hydroxide and then cathodieally piekled in a solution of 30 g/1 of sulfurie acid. The steel sheet, after rinsing with water, was electroplated with zine under the following plating conditions:
L0 Conditions of electroplating of zine:
Composition of bath ZnS0~-7H20 50 g/l Ethoxylated a-naphthol 2 g/l pH 1.6 Bath temperature 40C
Cathodie current density 10 A/dm2 Amount of plated zinc 0.32 g~m2 ~fter rinsing with water, the zinc plated steel sheet was plated with tin by immersion into the tinplating bath consistiny of 5 g/l of SnS04, 3 g/l of H2S0~ and 2 g/l of ethoxylated ~-naphthol and having a pH of 1.1, for 3 seeonds at a bath temperature ~f 40C.
Aftcr rinsing with water, the tin and zinc plated steel sheet ~as eathodically treated in 30 9/l of sodiurn diehromate under 5 ~/clm2 at a bath temperature of 50C and was rinsed with water, dried and coated ~ith dioctyl scbaeat~
of 4 mo/m2 by thc ordirlary mcthocl used in convcntional elcc~l-o-platinc~ ijrocc~sscs.
- \
~z~
ExAMæLE 2 A steel sheet pretreated as in Example 1 was electroplated with zinc under the following plating conditions:
Conditions of electroplating of zinc:
Composition of bath znS04 7H2Q 50 g/l Phenolsulfonic acid ( 60% aqueous solution) 50 g/l Ethoxylated a-naphthol sulfonic acid 4 g/1 pH 0.9 sath temperature 50C
Cathodic current density 15 A/c~12 Amount of plated zinc 0.41 g/m2 Without rinsing with water, the zinc plated steel sheet was plated with tin by the immersion into the tinplating bath consisting of 6~ g/l of SnS04, 50 g/l of phenolsulfonic acid ( 60~o aqueous solution) and 4 g/l of ethoxylated ~-naphthol sulfonic acid and having a pH of 0.6, for 1 second at a bath temperature of 50C and then electroplated with tin by using thc same tinplating bath under a current density of 8 A/dm2.
After rinsing with water, t.he thin tin and zinc plated steel sheet was trcated in the same manner as mentioncd in Example 1.
E~i~-iPLE 3 A steel shcet pretreated as in E:~ample 1 was clcctroplated t~itil zinc under the follo~inc~ conditions:
Conditions of electroplating of zinc:
Composition of bath znC12 .300 g/l NaCl 45 g/l NaF 25 g/l ICHF2 50 g/l pH 1.8 Bath temperature 55C
Cathodic current density 20 A/dm2 Amount of plated zinc 0.24 g/m2 After rinsing with water, the zinc plated steel sheet was electroplated with tin by immersion into the tinplating bath consisting of 75 g/l of SnC12-2H20, 45 g/l of NaCl, 25 g/l of NaF and 50 g/l of KHF2 and having a pH of 1.8, for 0.7 seconds at a bath temperature of 55C.
After rinsing with water, the thin tin and zinc plated steel sheet was immersed in 50 g/l of sodium dichromate solution for 3 seconds at a bath temperature of 40~C and was rinsed with water, dried. After that, dioctyl sebacate is 20 coated as in Example 1.
EX~MPLE 4 A steel sheet pretreated as in Example 1 was clcctroplatcd with zinc under thc followin~ conditions:
. _ ~2~4Q7 Conditions oE electroplating of zinc:
Composition of bath znC12 .200 g/l SnC12 2H2 0.4 g/l NaCl 30 g/l NaF 15 g/l KHF2 35 g~l pH (controlled by addition of NaOH) 3.5 Bath temperature 40~C
Cathodic current density 5 A/dm2 Amount of plated zinc 0.15 g/m2 After rinsing with water, the zinc plated steel slleet was plated with tin by immersion into the tinplating bath used in Example 3 for 0.5 seconds at a bath temperature of 55C.
After rinsing with water, the thin tin and zinc plated steel sheet was treated in the same manner as mentioned in Example 1.
EX~MPLE 5 A steel sheet pretreated as in Example 1 was plated with zinc and tin under the same conditions as in Example 3.
After rinsing with water and drying, the thin tin ànd zinc plated steel sheet was kept at a temperature of 232 - 250C for 2 seconds by resistance heating, and then was immediately quenched. This treated steel sheet was cathodically treatcd in thc samc manncr as mcntioncd in E~ample 1.
~2~
COMPARATIVE EX~PLE 1 -A steel sheet pretreated as in Example 1 was electroplated with tin by using the tinplating bath used in Example 2 under a current density of 10 A/dm2 at a bath temperature of 50C.
After rinsing with water, the tin plated steel sheet was treated in the same manner as mentioned in Example 1.
The characteristics of the resultant tin and zinc plated steel sheet were evaluated by the following testing methods, after the measuremen~ of the coating weight on the resultant sheet by the X-ray fluorescent method, the results of which are shown in the attached Table.
(1) WELDABILITY
The weldability of the resultant sheet was evaluated b~ using a wire seam welding machine having a copper wire as an intermediate electrode under the following welding conditions:
Welding conditions:
Power supply frequency 250 Hz Welding speed 30 m/min.
Overlap of sheet 0.45 mm Addcd pressure 45 kg The weldability was shown as an available range of sccondary curl-cl-t in wcldillc~. Thc uppcr limit in the availablc sccondary current rang~- corrcsl~oncls to thc wcldinc3 condi~iolls in which soi;le defect such as splashing is found and the lower limit corresponds to the welding conditions in which the breaka~3e occurx in tllc parcnt metal or weldccl part by tcarin~
tests. Thc wicicr thc scconc-~ary currcnt ranclc in weldiny, thc better the weldability.
~LZ~ 7
The present invention relates to a process for produeing a thin tin and zinc plated steel sheet by thin tin-plating by an immersion or by an eleetroplatin~ after an immersion into an aeidie tinplating bath after eleetro-plating of zine on a steel sheet by using a zine plating bath produeed by the substitution of stannous ion for zine ion in said tinplating bath whieh is used for said tinplating.
DESCRIPTION OF T~IE INVENTION
Eleetrotinplated materials have been previously used for manufaeturing eans sueh as food eans, five gallon eans and paint eans. Recently the ehangeover from expensive eleetrotinplated materials to cheaper tin free steel (TFS) eonsisting of metallie ehromium and hydrated ehromium oxide as well as a decrease in the weight of the tin eoating in eleetrotinplated materials has rapidly oeeured in the can manufaeturing field beeause the tin used for the production of tin-~lated materials is very expensive and there is coneern about possible exhaustion of tin resources throughout the world.
An ordinàry metal can eonsists of two pieces of can ends and one pieee of can body. As a method of seaming a TFS can body, electric welding is well known. Further, a methocl ~,rployinc3 a nylon adhesive is widely used for bevera~3e can bodies. In this ele~ctric welding of the TFS ean body, however, the mec}lanical or chemieal removal of TFS film consisting of metallic chroillium layer and hydrated ehro.iu:~
~L2~ 7 oxide layer is indispensable for satisfaction welding.
Therefore, the welded parts must 'be sufficiently coated by lacquer in order to prevent the corrosion.
On the other hand, the seaming of the tinplate can body is generally carried out by soldering. In the field of food cans, the use of expensive pure tin solder for the seam-ing of the tinplate can body increases because the lead content in the canned food is regulated by the FI~A. Thus, it is difficult to decrease the tin co~ting weight in tinplates to below 1.0 g/m , because stable operation of the soldering at high speed becomes difficult.
Furthermore, as a method of seaming the tinplate can body, the employment of an organic adhesive such as nylon adhesive has been also proposed, for instance, in Japanese Laid-Open Patent Application No. Sho ~9-37829 filed August 11, 1972 in the name of Kozo Yoshizaki, entitled "Tin Plated Steel Sheet Having E~cellent Adhesive Strength", and in Japanese Patent Publication No. Sho 48-18929 filed December 4, 1969 in the name of Kozo Yoshizaki, entitled "Process for Adhering Tin Plated Steel Sheet with Organic Adhesive".
However, the tinplate can body seamed by an organic adhesive may be broken when a beverage such as fruit juice is hot packed, because the bonding strength in the seam becomes remarkably low. Presently, such method is not considered practical.
Recently, a lap seam welding method, for instance the SOUDRONIC (trade mark) process, has become widely used for the seaming of a tinplate can body such as an aerosol can and a dry fill can, instead of soldering.
As described above, both tinplate and TFS present certain problems as materials for welded cans. Narnely, ?, - ' '.
~2~14~
tinplate is expensive although it is easily welded at high speed and TFS is not satisfactorily welded without scraping off the TFS film.
- 3a -In view of the background as described above, light tin coated steel sheets shown in United States Patent No. 4,113,5~0 and United States Patent No. 4,145,263 were developed several years ago.
However, these light tin coated steel sheets also present certain problems. Namely, these sheets can not be welded without splashing under welding at high speeds such as 40 m/min.. Furthermore, the filiform corrosion in these sheets coated by lacquer may appear after aging in an atmosphere having high humidity.
SUMMAR~ OF THE INVENTION
It is an object of the present invention to provide a process for producing a thin tin and zinc plated steel sheet having an excellent weldability and an excellent filiform corrosion resistance.
This object can be accomplished by electroplating zinc on a steel sheet ~rom a zinc electroplating bath containing zinc ions followed by tin-plating the zinc plated steel sheet by immersion or by immersion followed by electroplating in a tinplating bath containing stannous ions, whereby zinc ions from the zinc plated steel sheet substantially replace the stannous ions in the tinplating solution during the immersion tinplating. ~he rcsultant solution from the tinplating which contains zinc ions is employed to make up the zinc electro-plating. The resultant coating on steel sheet, after the tin-plating, contains 0.005 - 0.2 g/m2 zinc and 0.05 to 1.0 5/m2 tin.
In the present invention, the stccl shcct dc~reased and picklcd by ordinary methods is firstly clectroplated ~y ~Z~14~7 a suitable arnount of zinc with due consideration of the dissolved amount of zinc and the amount of tin to be plated during imrnersion tinplating.
After that, the zinc plated steel sheet is further plated by tin by the immersion into the tinplating bath.
The deposition of tin from the tinplating bath occurs with the dissolution of the plated zinc into said tinplating bath.
Namely, both the reaction for the deposition of tin and the dissolution of the plated zinc occur simultaneously by the chemical substitution reaction between zinc and stannous ion.
Therefore, the tinplating bath gradually is converted to a zinc plating bath due to the substitution of stannous ions by zinc ions in said tinplating bath. In spite of the increase of zinc ion in said tinplating bath, tin is deposited on said zinc plated steel sheet due to the presence of stannous ion in said tinplating bath, because the standard electrode potential of zinc is less than that of tin. Namely, the tinplating bath can be used ror tinplating until stannous ion in the tinplating bath is almost exhausted and after that this bath can be used ac~ain for the electroplating of zinc on the steel sheet in the present invention.
Furthermorc, the e~hausted solution consisting of a dilute tinplating bath in the conventional tinplating process is also used for producing a thin tin and zinc plated steel sheet according to the present invention with the recovery of stannous ion from the evhausted solution.
Therefore, the process according to the present invention is very economical method for produciny a thin tin and zinc plated stecl sheet.
~Z1~4~7 DETAILE~ DESCRIPTION OF THE INV~NTION
A thin tin and zinc plated steel sheet having an excellent weldability and an excellent filiform corrosion resistance which is the object of -~he present invention is ohtained by an imrnersion plating or by an electroplating after an irnmersion plating of 0.05 - 1.0 g/m2 of tin after electroplating 0.005 - 0.2 g/m2 of zinc, by measurement after said tin-plating on a zinc plated steel sheet, according to the present invention.
In this tin and zinc plated steel sheet, the presence of zinc in the range of 0.005 - 0.2 g/m2 by measurement after said tinplating is indispensable in order to improve weldability and prevent filiform corrosion.
If the amount of zinc is below 0.005 g/m2, the weldability at high speed is not improved and the filiform corrosion is not prevented. ~t above 0.2 g/m2 of zinc, the weldability at high speed is not also improved and the white rust due to the corrosion of zinc appears although the filiform corrosion is prevented.
If the amount of the plated tin is below 0.05 g/m2, welding at high speed becomes very difficult and white rust due to the corrosion of zinc is not prevented. ~n increase in the amount to above 1.0 g/m2 of tin is not economical, although the weldability does not deteriorate.
For an industrial operation, the present invcntion is carried ou~ according to the following process: degreasing with an alkali solution and pickliny with an acid solution ~ water rinsing - -~ electroplating of zinc ~watcr 4C~7 rinsing ~ tin-plating by immersion or by electroplating after immersion into tinplating bath--~ water rinsing >post-treatment for example by sodium dichromate used for conventional electrotinplating--~ water rinsing ~ drying -__~ oiling, for example with dioctyl sebacate or cotton seed oil.
In this process, the bath containing the same anion and the same additives as those in the tinplating bath, besides zinc ion is, in principle, used for zinc plating. The additi-ves are organic additive agents such as gelatine, peptone, di-hydroxy diphenyl sulphone, monobutyl phenyl phenol, sodiummonosulphonate, ethoxylated ~-naphthol and ethoxylated c~-naphthol sulfonic acid used for tinplating bath. For the tinplating in the present invention, the known acidic tinplat-ing bath for conventional electrotinplating is used, namely, an acidic bath such as a stannous su~fate bath, a stannous phenol-sulfonate bath and a stannous halogenide bath and solutions prepared by reconstituting such exh~usted solutions.
However, it is necessary in the present invention that a pH of the tinplating bath be below 1.7 in the stannous sulfate bath and the stannous phenolsulfonate bath and be below 4.0 in the stannous halogenide bath. Further, the concentration of stannous ion in these tinplating baths should preferably be above 2 g/l.
If the pH of the tinplating bath is not below 1.7 or 4.0 tinplating by the immersion method is impossible because stannous ion is precipitated. If the concentration of stannous ion in these tinplating baths is below 2 g/l, a continuous operation for producing the thin tin and zinc plated steel sheet according to the present invention is difficult because stannous ion is consumed in a short time by the deposition of tin and is not supplied from anywhere~ Although an increase in the amount of stannous ion in these tinplating baths does not adversely _7-~2~
affect the immersion tinplating, it is desirable to limit the amount of stannous ion below 70 g/l from an economical view-point.
-7a-An increase in the amount o~ zinc ion in the tinplating bath is not limited in the present invention, because it does not affect the immersion tinplating, although the amount of zinc ion in the tinplating bath increases with a decrease of stannous ion. It is preferable to control the temperature of the tinplating bath in the ran~e of 20 - 60C
from the industrial and economical viewpoints.
At a temperature of tinplating bath above 60C, some additives such as ethoxylated ~-naphthol sulfonic acid used in conventional electrotinplating bath may be decomposed.
Furthermore, the immersion time of the zinc plated steel sheet into the tinplating bath is preferably 0.1 - 5 seconds.
If the immersion time is below 0.1 seconds, the amount of tin re~uired in the present invention is not dcposited by the substitution reaction between stannous ion and the plated zinc.
In the immersion tinplating, the immersion time above 5 seconds is meaningless for producing at high speed a thin tin and zinc plated steel sheet according to the present invention, because the surface of the plated zinc is gradually covered by thc deposited tin and then the rate of the deposition of tin becomes low. For instance, the rate of the deposition of tin becomes remarkably 10W at above o.~ y/m2 of deposited tin, even if the plated zinc is present in a sufficient amount rcquired for the deposition of 1.0 c~/m2 of tin. In this case, elcctroplating should be carried out after the immcrsion tinplating in order to supplcment thc deficiency of tin. In tilc prcscnt invcntion, electrotinplatinc3 aftcr the immersion tinplatinc~ is carried out under thc same conditions as in conventional tinplating. It is desirable that the tempera-ture of tinplating bath be 20 - 60C and the current density be 5 - 50 A/dm2. Generally, lower current density is applied for the formation of a uniform tin layer at lower bath tempera-ture and lower concentration of stannous ion. On the contrary, at higher bath temperature and high concentration of stannous ion, a higher current density is applied. Furthermare, in the case where the concentration of stannous ion below 2 g/l, the electrical resistance of the bath increases and the current efficiency for tinplating becomes very low, and therefore, such low concentration of stannous ion is not suitable for industrial production of the thin tin and zinc plated steel sheet according to the present invention.
The composition of the zinc plating bath used in ~he present invention is naturally regulated because the zinc ions therein substantially replace the stannous ions during the tin-plating. For instance, if a stannous sulfate bath is used for tinplating, a zinc sulfate bath containing the same anion and the same additives is used for zinc plating on the steel sheet in the present invention.
The concentration of zinc ion in the zinc plating bath should be controlled in the range of 10 - 100 g/l. If the concentration of zinc ion is below 10 g/l, it is not suitable for industrial production of the thin tin and zinc ---platcd stccl sheet accordiny to thc present invention, bccause the electrical resistance of the ZillC plating bath is high and a rectifier having a large capacity is necessary. The use of a zinc plating bath having above 100 g/l of zinc ion is not econo3nical.
In the case of zinc plating by using the zinc plating bath obtained from the tinplating bath having a small amount of stannous ion, therefore, zinc i.on should be supplied by the addition of a zinc salt having the same anion as in the tinplating bath, zinc hydroxide or the dissolution of zinc.
For instance, if the tinplating bath having 2 g/l of stannous ion is used for tinplating, at least about 9.9 g/l of zinc ion should be supplied to the zinc plating bath obtained from this tinplating bath, even if 2 g/l of stannous ion is completely 10 replaced by zinc ion. '.
The concentration of stannous ion in the zinc plating bath should be kept below 1 g/l, desirably almost zero, because the excess amount of tin is preferentially deposited during electroplating zinc of the amount required in the present invention.
When a small amount of stannous ion is present in the zinc plating bath~ the pH of the zinc plating bath should be kept below 1.7 in zinc sulfate bath or zinc phenolsulfonate bath and below ~.0 in zinc halogenide bath, because stannous 20 ion is precipi-tated in zinc plating bath at above the pH
described above and gives a bad appearance in the thin tin and zinc plated steel sheet according to the present invention.
In the absence of stannous ion in the zinc plating bath, the pH of the zinc plating bath may be raised to about 7 by the addition of al]sali hydroxide, alkali oxide or zinc hydroxide.
In this case, however, water rinsing should be preferably carried out after zinc plating in order to prevent the rise of pH in the tinplating bath, although it may be 30 omitted in the ~se of a.zinc plating bath beiny below 1.7 or 4.0 of pH.
~LZ11407 In zinc plating, it is preferable to control the temperature of the zinc plating bath in the range of 20 - 60C
from the industrial and economical viewpoints. At a tempera-ture of the zinc plating bath above 60C, some additives such as ethoxylated a-naphthol used in the tinplating bath may be decomposed.
Furthermore, the cathodic current density for zinc plating is 0.1 - 100 A/dm2, preferably 1 - 70 A/dm2 in the present invention. A lower current density below 0.1 A/dm2 is not suitable for the continuous production of the thin tin and zinc plated steel sheet at high speed. A higher current density above 100 A/dm2 is not also suitable because a rectifier having a large capacity is necessary.
In the process according to the present invention, it is very important to control the amount of the electroplated zinc, because the arnount of the plated tin dep~nds on the amount of the dissolved zinc in the immersion tinplating.
Namely, 1 mole/dm2 of tin is theoretically plated by the dissolution of 1 mole/dm2 of the plated zinc. Therefore, for the deposition of 0.05 - 1.0 g/m2 of tin, the dissolution of 0.028 - 0.55 g/m2 of the platcd zinc is necessary. In the clctcrmination of th~ ~mount o the zinc rclllaininc3 a~ter tinplating, the amount of the electroplated zinc is calculated by the follo~ing equation:
The amount of the plated zinc (g/rn2) = the amount of the plated tin ~ 58- 639 + 0.005 ~ 0.2 ~lowevcr, it lS difficult from a practical standpoint to deposit a'aove 0.4 y/m2 of tin by thc immcrsion tinplatinc~
I,ccau-: thc sur1acc of thc platcc'i zinc is yraduall~ COVClCCi ~y the clc~)ositc~i tin anci then thc ratc in thc cieposition of tin ~eCO;ilC,5 relil~r~;a~lv low.
_ 1 1 _ 14~
Therefore, it is desirable in the present invention that the amount of the electroplated zinc be below 0.42 g/m2 for producing the thin tin and zinc plated s-teel sheet at high speed.
In some cases, heating the thin tin and zinc plated steel sheet at a temperature above melting point of tin and quenching are carried out, in order to improve lacquer adhesion, although the weldability at hiyh speed becomes slightly poorer. In the case of a light tin coating weight, such as 0.10 g/m , the plated tin is sufficiently converted to an iron-tin alloy by heating at a somewhat higher tempera-ture (about 250C) than the melting point of tin. However, for a heavy tin coating weight, such as 0.8 g/m2, heating at a considerably higher temperature (300 - 400C) than the melting point of tin is necessary. Generally, it is necessary that the temperature during formation of the iron-tin alloy be maintained in the range of 232 - 4aooc for 0.5 - 10 seconds.
In this case, heating is carried out by a known method such as resistance heating and/or induction heating which is generally used in the manufacturing process of conventional clectrotinplated materials.
Furthermore, the thin tin and zinc plated steel sheet according to the present invention is subjected to a cathodic treatment Ol^ an immersion treatment in a known solution containing hexavalent chromium ion such as a sodium dichromate solution or chromic acid solution which is generally used for the post-treatment of conventional electrotinplated materials.
phosphate treatment or sodium carbonate treatment can be used for the post-treatrnent of the thin tin and zinc plated steel sheet instcad of chromate treatmenk.
12~ 7 The present invention is illustrated by the following Exampl.es-A eold redueed steel sheet having a thickness of0.22 mm was eleetrolyticall.y degreased in a solution of 70 g/l sodium hydroxide and then cathodieally piekled in a solution of 30 g/1 of sulfurie acid. The steel sheet, after rinsing with water, was electroplated with zine under the following plating conditions:
L0 Conditions of electroplating of zine:
Composition of bath ZnS0~-7H20 50 g/l Ethoxylated a-naphthol 2 g/l pH 1.6 Bath temperature 40C
Cathodie current density 10 A/dm2 Amount of plated zinc 0.32 g~m2 ~fter rinsing with water, the zinc plated steel sheet was plated with tin by immersion into the tinplating bath consistiny of 5 g/l of SnS04, 3 g/l of H2S0~ and 2 g/l of ethoxylated ~-naphthol and having a pH of 1.1, for 3 seeonds at a bath temperature ~f 40C.
Aftcr rinsing with water, the tin and zinc plated steel sheet ~as eathodically treated in 30 9/l of sodiurn diehromate under 5 ~/clm2 at a bath temperature of 50C and was rinsed with water, dried and coated ~ith dioctyl scbaeat~
of 4 mo/m2 by thc ordirlary mcthocl used in convcntional elcc~l-o-platinc~ ijrocc~sscs.
- \
~z~
ExAMæLE 2 A steel sheet pretreated as in Example 1 was electroplated with zinc under the following plating conditions:
Conditions of electroplating of zinc:
Composition of bath znS04 7H2Q 50 g/l Phenolsulfonic acid ( 60% aqueous solution) 50 g/l Ethoxylated a-naphthol sulfonic acid 4 g/1 pH 0.9 sath temperature 50C
Cathodic current density 15 A/c~12 Amount of plated zinc 0.41 g/m2 Without rinsing with water, the zinc plated steel sheet was plated with tin by the immersion into the tinplating bath consisting of 6~ g/l of SnS04, 50 g/l of phenolsulfonic acid ( 60~o aqueous solution) and 4 g/l of ethoxylated ~-naphthol sulfonic acid and having a pH of 0.6, for 1 second at a bath temperature of 50C and then electroplated with tin by using thc same tinplating bath under a current density of 8 A/dm2.
After rinsing with water, t.he thin tin and zinc plated steel sheet was trcated in the same manner as mentioncd in Example 1.
E~i~-iPLE 3 A steel shcet pretreated as in E:~ample 1 was clcctroplated t~itil zinc under the follo~inc~ conditions:
Conditions of electroplating of zinc:
Composition of bath znC12 .300 g/l NaCl 45 g/l NaF 25 g/l ICHF2 50 g/l pH 1.8 Bath temperature 55C
Cathodic current density 20 A/dm2 Amount of plated zinc 0.24 g/m2 After rinsing with water, the zinc plated steel sheet was electroplated with tin by immersion into the tinplating bath consisting of 75 g/l of SnC12-2H20, 45 g/l of NaCl, 25 g/l of NaF and 50 g/l of KHF2 and having a pH of 1.8, for 0.7 seconds at a bath temperature of 55C.
After rinsing with water, the thin tin and zinc plated steel sheet was immersed in 50 g/l of sodium dichromate solution for 3 seconds at a bath temperature of 40~C and was rinsed with water, dried. After that, dioctyl sebacate is 20 coated as in Example 1.
EX~MPLE 4 A steel sheet pretreated as in Example 1 was clcctroplatcd with zinc under thc followin~ conditions:
. _ ~2~4Q7 Conditions oE electroplating of zinc:
Composition of bath znC12 .200 g/l SnC12 2H2 0.4 g/l NaCl 30 g/l NaF 15 g/l KHF2 35 g~l pH (controlled by addition of NaOH) 3.5 Bath temperature 40~C
Cathodic current density 5 A/dm2 Amount of plated zinc 0.15 g/m2 After rinsing with water, the zinc plated steel slleet was plated with tin by immersion into the tinplating bath used in Example 3 for 0.5 seconds at a bath temperature of 55C.
After rinsing with water, the thin tin and zinc plated steel sheet was treated in the same manner as mentioned in Example 1.
EX~MPLE 5 A steel sheet pretreated as in Example 1 was plated with zinc and tin under the same conditions as in Example 3.
After rinsing with water and drying, the thin tin ànd zinc plated steel sheet was kept at a temperature of 232 - 250C for 2 seconds by resistance heating, and then was immediately quenched. This treated steel sheet was cathodically treatcd in thc samc manncr as mcntioncd in E~ample 1.
~2~
COMPARATIVE EX~PLE 1 -A steel sheet pretreated as in Example 1 was electroplated with tin by using the tinplating bath used in Example 2 under a current density of 10 A/dm2 at a bath temperature of 50C.
After rinsing with water, the tin plated steel sheet was treated in the same manner as mentioned in Example 1.
The characteristics of the resultant tin and zinc plated steel sheet were evaluated by the following testing methods, after the measuremen~ of the coating weight on the resultant sheet by the X-ray fluorescent method, the results of which are shown in the attached Table.
(1) WELDABILITY
The weldability of the resultant sheet was evaluated b~ using a wire seam welding machine having a copper wire as an intermediate electrode under the following welding conditions:
Welding conditions:
Power supply frequency 250 Hz Welding speed 30 m/min.
Overlap of sheet 0.45 mm Addcd pressure 45 kg The weldability was shown as an available range of sccondary curl-cl-t in wcldillc~. Thc uppcr limit in the availablc sccondary current rang~- corrcsl~oncls to thc wcldinc3 condi~iolls in which soi;le defect such as splashing is found and the lower limit corresponds to the welding conditions in which the breaka~3e occurx in tllc parcnt metal or weldccl part by tcarin~
tests. Thc wicicr thc scconc-~ary currcnt ranclc in weldiny, thc better the weldability.
~LZ~ 7
(2) FILIFORM COR~OSIO~ RESISTANCE
The resultant sheet was baked at 200C for 10 minutes after coating with 70 mg/dm of vinyl type organosol SJ-9434-003 (trade mark; Kansai Paint Co., Ltd., Japan).
The coated sample was cut to a size of 9 cm x 9 cm, and the coated side was cut crosswise with a razor. After 5 mm of the sample was extruded by using a conventional ERICHSEN
(trade mark) testing machine, the formed sample was set in a chamber into which 5% sodium chloride solution heated to 38C
was sprayed for one hour.
After rinsing with water, the formed sample was set under the relative humidity of 85% at 25C for weeks.
After that, the degree of filiform corrosion was divided into 5 ranks by the naked eye, namely, 5 was excellent, 4 was good, 3 was fair, 2 was poor and 1 was bad.
As apparent from the Table, the thin tin and zinc plated steel sheet according to the present invention has an excellent weldability and an excellent filiform corrosion resistance.
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The resultant sheet was baked at 200C for 10 minutes after coating with 70 mg/dm of vinyl type organosol SJ-9434-003 (trade mark; Kansai Paint Co., Ltd., Japan).
The coated sample was cut to a size of 9 cm x 9 cm, and the coated side was cut crosswise with a razor. After 5 mm of the sample was extruded by using a conventional ERICHSEN
(trade mark) testing machine, the formed sample was set in a chamber into which 5% sodium chloride solution heated to 38C
was sprayed for one hour.
After rinsing with water, the formed sample was set under the relative humidity of 85% at 25C for weeks.
After that, the degree of filiform corrosion was divided into 5 ranks by the naked eye, namely, 5 was excellent, 4 was good, 3 was fair, 2 was poor and 1 was bad.
As apparent from the Table, the thin tin and zinc plated steel sheet according to the present invention has an excellent weldability and an excellent filiform corrosion resistance.
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Claims (25)
1. A process for producing a thin tin and zinc plated steel sheet having 0.005 - 0.2 g/m2 of zinc and 0.05 - 1.0 g/m2 of tin, which comprises the steps of:
a) electroplating zinc on a substantially clean steel sheet in an aqueous electroplating bath containing zinc ions with or without additives;
b) tinplating the zinc plated sheet of step (a) by immersion or by immersion followed by electroplating in an aqueous, acidic tin plating bath containing stannous ions, said tinplating bath consisting of a stannous sulfate or phe-nolsulfonate bath having a pH below 1.7 or of a stannous halogenide bath having a pH below 4.0, whereby zinc ions from the zinc plated steel sheet replace the stannous ions in the tinplating solution during the immersion tinplating; and c) recycling the resultant solution from step (b), which contains zinc ions, to make up the zinc electroplating bath of step (a).
a) electroplating zinc on a substantially clean steel sheet in an aqueous electroplating bath containing zinc ions with or without additives;
b) tinplating the zinc plated sheet of step (a) by immersion or by immersion followed by electroplating in an aqueous, acidic tin plating bath containing stannous ions, said tinplating bath consisting of a stannous sulfate or phe-nolsulfonate bath having a pH below 1.7 or of a stannous halogenide bath having a pH below 4.0, whereby zinc ions from the zinc plated steel sheet replace the stannous ions in the tinplating solution during the immersion tinplating; and c) recycling the resultant solution from step (b), which contains zinc ions, to make up the zinc electroplating bath of step (a).
2. A process according to claim 1, wherein the source of said stannous ions in the tinplating bath of step (b) is stannous sulfate, stannous phenolsulphonate or stannous halogenide.
3. A process according to claim 1, wherein the tin and zinc plated steel sheet of step (b) is heated at a temperature sufficiently above the melting point of tin for a time sufficient to form an iron-tin alloy.
4, A process according to claim 2, wherein the tin and zinc plated steel sheet of step (b) is heated at a temperature sufficiently above the melting point of tin for a time suffi-cient to form an iron-tin alloy.
5. A process according to claims 1 or 2, wherein the concentration of zinc ions in said recycled solution is supplemented by the dissolution of zinc metal, the addition of zinc hydroxide or the addition of a zinc salt having the same anion as the tinplating bath.
6. A process according to claim 1, wherein the tin-plating solution and zinc electroplating solution contain the same anions and additives.
7. A process according to claim 2, wherein the tin-plating solution and zinc electroplating solution contain the same anions and additives.
8. A process according to claim 1, wherein electro-plating of zinc is carried out in a zinc plating bath con-taining zinc ions and stannous ions at a temperature of 20 - 60°C and a cathodic current density of 0.1 - 100 A/dm2, the concentration of zinc ion in the bath being 10 - 100 g/l, the concentration of stannous ion in the bath being below 1 g/l.
9. A process according to claim 2, wherein electro-plating of zinc is carried out in a zinc plating bath con-taining zinc ions and stannous ions at a temperature of 20 - 60°C and a cathodic current density of 0.1 - 100 A/dm2, the concentration of zinc ion in the bath being 10 - 100 g/l, the concentration of stannous ion in the bath being below 1 g/l.
10. A process according to claim 1, wherein electro-plating of zinc is carried out in a zinc plating bath con-taining zinc ions and stannous ions at a temperature of 20 - 60°C and a cathodic current density of 5 - 70 A/dm2, the concentration of zinc ion in the bath being 10 - 100 g/l, the concentration of stannous ion in the bath being below 1 g/l.
11. A process according to claim 2, wherein electro-plating of zinc is carried out in a zinc plating bath con-taining zinc ions and stannous ions at a temperature of 20 - 60°C and a cathodic current density of 5 - 70 A/dm2, the concentration of zinc ion in the bath being 10 - 100 g/l, the concentration of stannous ion in the bath being below 1 g/l.
12. A process according to claims 8 or 9, wherein electroplating of zinc is carried out in a zinc sulfate bath or zinc phenolsulfonate bath with the pH of the bath being below 1.7.
13. A process according to claims 10 or 11, wherein electroplating of zinc is carried out in a zinc sulfate bath or zinc phenolsulfonate bath with the pH of the bath being below 1.7.
14. A process according to claims 8 or 9, wherein electroplating of zinc is carried out in a zinc halogenide bath with the pH of the bath being below 4Ø
15. A process according to claims 10 or 11, wherein electroplating of zinc is carried out in a zinc halogenide bath with the pH of the bath being below 4Ø
16. A process according to claims 1 or 2, wherein tinplating is carried out in a stannous sulfate bath or a stannous phenolsulfonate bath at a temperature of 20 - 60°C
and the immersion time in said tinplating bath being 0.1 - 5 seconds, the concentration of stannous ion being 2 - 70 g/l, the pH of the bath being below 1.7.
and the immersion time in said tinplating bath being 0.1 - 5 seconds, the concentration of stannous ion being 2 - 70 g/l, the pH of the bath being below 1.7.
17. A process according to claims 1 or 2, wherein tinplating is carried out in a stannous halogenide bath at a temperature of 20 - 60°C and the immersion time in said tinplating bath being 0.1 - 5 seconds, the concentration of stannous ion being 2 - 70 g/l, the pH of the bath being below 4Ø
18. A process according to claims 1 or 2, wherein tinplating is carried out by an electroplating under a cathodic current density of 5 - 50 A/dm2 after an immersion for 0.1 - 5 seconds into a stannous sulfate bath or a stannous phenolsulfonate bath at a temperature of 20 - 60°C, the concentration of stannous ion being 2 - 70 g/l, the pH of the bath being below 1.7.
19. A process according to claims 1,or 2, wherein tin-plating is carried out by an electroplating under a cathodic current density of 5 - 50 A/dm2 after an immersion for 0.1 -5 seconds into a stannous halogenide bath at a temperature of 20 - 60°C, the concentration of stannous ion being 2 - 70 g/l, the pH of the bath being below 4Ø
20. A process according to claims 1 or 2, wherein 0.05 - 1.0 g/m2 of tin is plated by immersion or by electro-plating after immersion of the zinc plated steel sheet of step (a) having 0.032 - 0.42 g/m2 of zinc, into said tinplating bath.
21. A process according to claims 3 or 4, wherein heating said tin and zinc plated steel sheet is carried out at a temperature of 232 - 400°C for 0.5 - 10 seconds.
22. A process according to claims 1 or 2, wherein the zinc plated steel sheet of step (a) is washed with water before being treated in step (b).
23. A process according to claims 1 or 2, wherein the stannous ions in said tinplating solution are substan-tially exhausted before said solution is recycled to step (a).
24. A process according to claims 3 or 4, wherein the stannous ions in said tinplating solution are substan-tially exhausted before said solution is recycled to step (a).
25. A process according to claims 6 or 7, wherein the stannous ions in said tinplating solution are substan-tially exhausted before said solution is recycled to step (a).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000412070A CA1211407A (en) | 1982-09-23 | 1982-09-23 | Process for producing a thin tin and zinc plated steel sheet |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000412070A CA1211407A (en) | 1982-09-23 | 1982-09-23 | Process for producing a thin tin and zinc plated steel sheet |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1211407A true CA1211407A (en) | 1986-09-16 |
Family
ID=4123652
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000412070A Expired CA1211407A (en) | 1982-09-23 | 1982-09-23 | Process for producing a thin tin and zinc plated steel sheet |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1211407A (en) |
-
1982
- 1982-09-23 CA CA000412070A patent/CA1211407A/en not_active Expired
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