CA2169193A1 - Process for treating zinciferous surfaces - Google Patents
Process for treating zinciferous surfacesInfo
- Publication number
- CA2169193A1 CA2169193A1 CA002169193A CA2169193A CA2169193A1 CA 2169193 A1 CA2169193 A1 CA 2169193A1 CA 002169193 A CA002169193 A CA 002169193A CA 2169193 A CA2169193 A CA 2169193A CA 2169193 A1 CA2169193 A1 CA 2169193A1
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- Prior art keywords
- ions
- chromium
- ion
- molar ratio
- process according
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
- C23C22/30—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds containing also trivalent chromium
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/34—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing cold phosphate binders
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
- C23C22/33—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds containing also phosphates
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
- C04B2111/00482—Coating or impregnation materials
- C04B2111/00525—Coating or impregnation materials for metallic surfaces
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Mechanical Engineering (AREA)
- General Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Inorganic Chemistry (AREA)
- Structural Engineering (AREA)
- Chemical Treatment Of Metals (AREA)
- Electroplating Methods And Accessories (AREA)
- Coating With Molten Metal (AREA)
- Other Surface Treatments For Metallic Materials (AREA)
Abstract
A solid 10-200 mg/m2, calculated as chromium metal, film is formed on a zinciferous surface by coating the surface with an acidic aqueous liquid composition that contains hexavalent chromium ions, trivalent chromium ions, at least one of sulfate ions and nitrate ions, and zinc, nickel, cobalt, and/or aluminum ions, in which liquid composition the trivalent chromium ion/hexavalent chromium ion molar ratio is 1/9 to 4/1, the (nitrate + sulfate + phosphate)/(hexavalent chromium ion + trivalent chromium ion) molar ratio is 0.1 to 2.0 and the metal ion/inorganic acid molar ratio is 0.05 to 1, and subsequently drying the applied coating. The chromate film formed has both an excellent resistance to blackening and an excellent resistance to white rust.
Description
WO 9~/OS247 2 1 6 9 1 9 3 PCTIUS94/08318 Desc, iplion PROCESS FOR TREATING ZINCIFEROUS SURFACES
Technical Field The invention relates to a plucess for treating ~incire, uus surfaces to give them an excellent r~sisla"ce to both blackening and white rusting. The process, which uses a one-step chromate treatment that does not require a preliminary 5 flash treal",enl with, e.g., Ni or Co, is particularly useful for the manufacture of ~incirerous-plated steel sheet. As used herein, "~incirerous-plated" refers to eleG
trogalva, li~aliol1, hot-dip zinc plating, hot-dip 5% AlQn plating, hot-dip 55% Al/Zn plating, and the like. The p, ocess is largely des~ ibed below with respect to zin-ciferous-plated steel sheet, but is equally applicable to any other surface with the 10 same chemical composition.
Background Art The use of zinc plating to provide iron and steel with sacrificial corrosion resistance has proven generally to be the most effective and economical ap-proach, and for this r~ason 10 % of Japan's annual raw steel output of 100 mil-5 lion tons, or 10 million tons, is produce~l as galvanized steel sheet. Galvanizedsteel sheet is used in a variety of af)pli~liol)s, for exd",~le, as a construction ma-terial, in automobiles, and for household electrical appliances. The sa~ iricial cor-rosion resislance conrer,ed by zinc is based on the formation of a galvanic cellby bringing two clirrerent metals into co, It~Ct, in this case zinc and steel (or iron).
20 The zinc, as the baser metal, forms an anode and thereby cathodizes the iron.This inhibits corrosion of the steel or iron by preventing the anodic dissolution due to local ceîl formation that occurs in the case of iron by itself. Thus, since the anticorrosion activity ceases when the zinc in co, It~;t with the iron or steel has been consumed, co" osio" of the zinc layer must also be inhibited if its sacri-25 ficial anlicG"~,sio" activity is to be maintained for long periods of time. One coun-te,l,~easure to collosiGn of the zinc layer consisls of the execution of a chro",ate treal",enl after plating.
This ch,ulllaling-based anlico"usion slrateyy is, however, not without its pr~tlc ns. While the ~;h,or"ale ~, ea~",ei It of zinc-plated steel sheet does lead to a s~ ~bst~ntial i, ll ,ibi~ion of white rust dcvelop"~enl it still permits the develop"~enl of ae~thelically Ul ,desirable black rust (also known as blackening) during storage and transport. It has been observed that this blackening phenomenon occurs more readily for steel sheet subjected to a post-galvanization skin pass and forZn/AI-plated (several % Al) steel sheet.
Flash treatment for example with an aqueous solution containing Ni2 and/or Co2t as described in e.g. Japanese Laid Open [Kokai or Unexamined]
Patent A~plic~tion Number Sho 59-177381 [177 381/1984] is currently regarded as a very effective countermeasure for solving this post-cl~ro",dting black rustproblem. Here and below flash l,eal",e,ll is taken to mean the chemical deposi-tion of very small quantities of metal. In its essenlial features the above-refer-enced invention conce, r,s a means for inhibiting black rust through the pre-chro-mating flash treatment of the surface of zinc-plated or zinc alloy-plated steel sheet. In this particular flash treatment the surface of the steel sheet is flash-treated with an ~ueous solution (pH 1 to 4 or 11 to 13.5) that contains Ni2 and/or Co2~ metal ions. This treatment results in the deposition of these metal ions on the plating surface as the metal or oxide. This treatment is followed bya water wash and then the fo""alion of a cl ,romale film.
The I l leol lal lism for black rust il ll ,ibi~ion on zinc-plated or zinc alloy-plated steel sheet that has been flash-treated with Ni and/or Co and then chromated has yet to be clearly eslablished. However according to the report on pages 150 to 151 of Ab~lldcts of the 60th S~ ,c. Itiric Lectùre Con~er~nce of Kinzoku Hyomen Gijutsu Kyokai [Metal Finishing Society of Japan], the na~l ,ed metal is largely de-,~,osiled at the zinc crystal grain boundaries. It is further rq~, led that the chromi-um ~",pounds laid down in a follow-on coating-type ch,o",ale l,eatmenl are like the flashed metal also distributed at the grain boundaries. Based on this it is presumed that some type of inler;~ction which results in adso",lion and immob-ilization of the chro",ium compounds on the flashed metal occurs between the flashed metal and the chromium compounds.
WO 95/05247 ;~ 9 ~ PCT/US94/08318 Disclosure of the Invention Problems to Be Solved by the Invention Zinc black rust like the co"esponding white rust is thought to be a basic zinc ca,bo,)ate (ZnCO3)y - [Zn(OH)2]y; however it differs from white rust in that it s is stoicl ,i~l ,)etrically oxygen dericient. Black rust is Ll ,ere~ore a corrosion product occurring under oxygen-~lericien~ conditions and in particular it is thought that black rust is formed in association with the developn~e"~ of corrosion from the grain boundaries. As a result it can be post~ Pd that the cl "~omium COI npoundsc~ncerlt,dled at the grain bounda, ies by the na-~hed metal COntl ibute to an inhibi-10 tion of black rust development by inhibiting corrosion originating from the grainbou~ Iddl ies. It is in this way that the Ni and/or Co flash tredl" ,enl of zinc-plated steel sheet prior to the chromate lr~al",el ,t thereof is believed to be able very effectively to counter the problem of black rust. However despite its ability to in-hibit black rust this pre~, omdling flash t, t:dtl l lel ll results in the rather facile de-15 velGpl"ent of white rust. It is precisely this problem that the present inventionseeks to solve.
Summarv of the Invention The invention offers a one-step process that consists of only a ~:hro,nale l,~at",e,)l and that does not employ a p,etr~at",e, It, but is able to simultaneously 20 inhibit both blackening and white rust. This one-step process renders unneces-sary the two-step prior art process of a flash treatmènt with Ni and/or Co plus a cl,fomale l,eat,ne"l. This process yields ~i"cirerous-plated steel sheet that ex-hibits a s~ti~r~to~ corrosion resistance blackening resisla"ce and white rust resisla"ce. Moreover being a one-step process it avoids the drawbacks in the 25 prior art due to the use of a two-step l,eal",ent process (pretreatment followed by chr~",ate t(eat",enl). This novel one-step chro",dte lreal"~ent process is the subject of Ja~.anese Patent Application Number Hei 4-164083 [164 083/1992].
The invention in Japanese Patent Application Number Hei 4-164083 re-- lates to a ~., ocess for fa~ri~ti,)g ~i"~Herous-plated steel sheet that has an excel-30 lent resistance to both blackening and white rusting wherein said process is characterized by the for",alion on zinciferous-plated steel sheet of a 10 - 200 mg/m2 (calculated as chromium metal) film by:
Technical Field The invention relates to a plucess for treating ~incire, uus surfaces to give them an excellent r~sisla"ce to both blackening and white rusting. The process, which uses a one-step chromate treatment that does not require a preliminary 5 flash treal",enl with, e.g., Ni or Co, is particularly useful for the manufacture of ~incirerous-plated steel sheet. As used herein, "~incirerous-plated" refers to eleG
trogalva, li~aliol1, hot-dip zinc plating, hot-dip 5% AlQn plating, hot-dip 55% Al/Zn plating, and the like. The p, ocess is largely des~ ibed below with respect to zin-ciferous-plated steel sheet, but is equally applicable to any other surface with the 10 same chemical composition.
Background Art The use of zinc plating to provide iron and steel with sacrificial corrosion resistance has proven generally to be the most effective and economical ap-proach, and for this r~ason 10 % of Japan's annual raw steel output of 100 mil-5 lion tons, or 10 million tons, is produce~l as galvanized steel sheet. Galvanizedsteel sheet is used in a variety of af)pli~liol)s, for exd",~le, as a construction ma-terial, in automobiles, and for household electrical appliances. The sa~ iricial cor-rosion resislance conrer,ed by zinc is based on the formation of a galvanic cellby bringing two clirrerent metals into co, It~Ct, in this case zinc and steel (or iron).
20 The zinc, as the baser metal, forms an anode and thereby cathodizes the iron.This inhibits corrosion of the steel or iron by preventing the anodic dissolution due to local ceîl formation that occurs in the case of iron by itself. Thus, since the anticorrosion activity ceases when the zinc in co, It~;t with the iron or steel has been consumed, co" osio" of the zinc layer must also be inhibited if its sacri-25 ficial anlicG"~,sio" activity is to be maintained for long periods of time. One coun-te,l,~easure to collosiGn of the zinc layer consisls of the execution of a chro",ate treal",enl after plating.
This ch,ulllaling-based anlico"usion slrateyy is, however, not without its pr~tlc ns. While the ~;h,or"ale ~, ea~",ei It of zinc-plated steel sheet does lead to a s~ ~bst~ntial i, ll ,ibi~ion of white rust dcvelop"~enl it still permits the develop"~enl of ae~thelically Ul ,desirable black rust (also known as blackening) during storage and transport. It has been observed that this blackening phenomenon occurs more readily for steel sheet subjected to a post-galvanization skin pass and forZn/AI-plated (several % Al) steel sheet.
Flash treatment for example with an aqueous solution containing Ni2 and/or Co2t as described in e.g. Japanese Laid Open [Kokai or Unexamined]
Patent A~plic~tion Number Sho 59-177381 [177 381/1984] is currently regarded as a very effective countermeasure for solving this post-cl~ro",dting black rustproblem. Here and below flash l,eal",e,ll is taken to mean the chemical deposi-tion of very small quantities of metal. In its essenlial features the above-refer-enced invention conce, r,s a means for inhibiting black rust through the pre-chro-mating flash treatment of the surface of zinc-plated or zinc alloy-plated steel sheet. In this particular flash treatment the surface of the steel sheet is flash-treated with an ~ueous solution (pH 1 to 4 or 11 to 13.5) that contains Ni2 and/or Co2~ metal ions. This treatment results in the deposition of these metal ions on the plating surface as the metal or oxide. This treatment is followed bya water wash and then the fo""alion of a cl ,romale film.
The I l leol lal lism for black rust il ll ,ibi~ion on zinc-plated or zinc alloy-plated steel sheet that has been flash-treated with Ni and/or Co and then chromated has yet to be clearly eslablished. However according to the report on pages 150 to 151 of Ab~lldcts of the 60th S~ ,c. Itiric Lectùre Con~er~nce of Kinzoku Hyomen Gijutsu Kyokai [Metal Finishing Society of Japan], the na~l ,ed metal is largely de-,~,osiled at the zinc crystal grain boundaries. It is further rq~, led that the chromi-um ~",pounds laid down in a follow-on coating-type ch,o",ale l,eatmenl are like the flashed metal also distributed at the grain boundaries. Based on this it is presumed that some type of inler;~ction which results in adso",lion and immob-ilization of the chro",ium compounds on the flashed metal occurs between the flashed metal and the chromium compounds.
WO 95/05247 ;~ 9 ~ PCT/US94/08318 Disclosure of the Invention Problems to Be Solved by the Invention Zinc black rust like the co"esponding white rust is thought to be a basic zinc ca,bo,)ate (ZnCO3)y - [Zn(OH)2]y; however it differs from white rust in that it s is stoicl ,i~l ,)etrically oxygen dericient. Black rust is Ll ,ere~ore a corrosion product occurring under oxygen-~lericien~ conditions and in particular it is thought that black rust is formed in association with the developn~e"~ of corrosion from the grain boundaries. As a result it can be post~ Pd that the cl "~omium COI npoundsc~ncerlt,dled at the grain bounda, ies by the na-~hed metal COntl ibute to an inhibi-10 tion of black rust development by inhibiting corrosion originating from the grainbou~ Iddl ies. It is in this way that the Ni and/or Co flash tredl" ,enl of zinc-plated steel sheet prior to the chromate lr~al",el ,t thereof is believed to be able very effectively to counter the problem of black rust. However despite its ability to in-hibit black rust this pre~, omdling flash t, t:dtl l lel ll results in the rather facile de-15 velGpl"ent of white rust. It is precisely this problem that the present inventionseeks to solve.
Summarv of the Invention The invention offers a one-step process that consists of only a ~:hro,nale l,~at",e,)l and that does not employ a p,etr~at",e, It, but is able to simultaneously 20 inhibit both blackening and white rust. This one-step process renders unneces-sary the two-step prior art process of a flash treatmènt with Ni and/or Co plus a cl,fomale l,eat,ne"l. This process yields ~i"cirerous-plated steel sheet that ex-hibits a s~ti~r~to~ corrosion resistance blackening resisla"ce and white rust resisla"ce. Moreover being a one-step process it avoids the drawbacks in the 25 prior art due to the use of a two-step l,eal",ent process (pretreatment followed by chr~",ate t(eat",enl). This novel one-step chro",dte lreal"~ent process is the subject of Ja~.anese Patent Application Number Hei 4-164083 [164 083/1992].
The invention in Japanese Patent Application Number Hei 4-164083 re-- lates to a ~., ocess for fa~ri~ti,)g ~i"~Herous-plated steel sheet that has an excel-30 lent resistance to both blackening and white rusting wherein said process is characterized by the for",alion on zinciferous-plated steel sheet of a 10 - 200 mg/m2 (calculated as chromium metal) film by:
2 ~ 6 9 ~ 9 3 PCI`/US94/08318 (I) application to zinciferous-plated steel sheet of a ~;hro",ate bath that contains hexavalent chromium ion trivalent chromium ion and inorganic acid comprising at least one selection from nitric acid boric acid and sulfuric acid and in which the trivalent chromium ion/hexavalent s chromium ion weight ratio is 1/9 to 4/1 and the i"or~a"ic acid/total chromi-um ion (hexavalent cl"o",ium ion + trivalent chromium ion) weight ratio is 0.3 to 2.0 and (Il) subsequently drying the applied coating.
As a further improvement of this previous invention the subject of this ap-o plication is a process cha~acteri~e~ by the formation on ~incirerous-plated steel sheet of a solid 10 - 200 mg/m2 (calculated as chromium metal) film by:
(I) appli~lion to zinciferous-plated steel sheet so as to form a liquid coating (I ,e, eGn of a ~1 " on ,ale bath that c~" ,prises p, eferably consists essential-ly of or still more preferably consists of:
(A) hexavalent c~"omium ions (B) trivalent chror"ium ions (C) at least one of nitrate ions and sulfate ions and (D) metal ions sele~ed from the group co"sia(i"g of Zn Ni Co and Al ions and mixtures of any two or more thereof and optionally one or more of:
(E) phospl ,a~e ions from an inGrganic acid and (F) colloidal silica in which:
(i) the trivalent ch,u",ium ion/hexavalent chro",ium ion molar ratio is 1/9 to 4/1 (ii) the total of nitrate + sulfate + phosphate ions/total chromium ions (i.e. hexavalent cl~ro",ium ions + trivalent chromium ions) molar ratioisO.1 to2.0 (iii) the total of Zn + Ni + Co + Al ions/the total of nitrate + sulfate +
phospl ,ate ions molar ratio is 0.05 to 1 and (iv) the molar ratio of phospl ,ate ions/total chromium ions does not ex-ceed 0.3; and W O 95/05247 2 1 6 9 1 9 3 PC~rrUS94/08318 -(Il) s~hsequently drying the applied coating.
For the pu, ~uoses of this desc, iplio, I the entire stoicl ,io" ,~t, ic equivalent as phos-phate ions of any pl ,osphoric acid and/or anions produced by ionization thereofthat are added to the cl " o" ,ale bath are counted as pl ,ospl ,ate ions irrespective of the actual degree of io, li~lion of the added acid. Preferably the acid addedis orthophosphoric acid H3P04 but other inorga,)ic pl ,osphoric acids such as HPO3 H4P2O, HsP3O10 may also be used. Also it is to be understood that the constituents specified in ionic form must be acco",panied by counterions so thatthe co,),posilion as a whole is electrically neutral. Such counterions preferably 10 are chose" from other specified constituents of the invention to the extent possi-ble and otherwise may be freely cl ,osen except for avoiding cou"lerions that are detrimental to the purposes of the invention.
Desc, iption of Prefer, ed Embodiments The trivalent chromium ion/hexavalent chrol"ium ion molar ratio in the subject cl "or,)ale treal",enl bath is preferably 1/9 to 411 and more preferably is 1/4 to 7/3. Trivalent chromium ion/hexavalent cl ,ro",ium ion molar ratios below1/9 are u"desi,able be~se such values usually result in excessive chromium ion elution in corrosive enviror""el,ls and thus in pollution of the environment.
When the trivalent chromium ion/hexavalent chromium ion molar ratio exceeds 4/1 the corrosion resistance becomes inadequate.
Sulfate and/or nitrate ions as required for the ~;I,ro",aling treatment ac-cording to the invention are preferably added at least partially in the form of the cor, esponding acids. These anions are added in a quantity that yields values p,~rerably of 0.1 to 2.0 and more pr~ferably of 0.2 to 1.6 for the sulfate + nitrate 25 + ~h osphale anions/total chromium ions molar ratio. The blackening resistance is usually inAdeql lAte when the inorganic anions/total ch~",ium ions molar ratio is less than 0.1. h ,or~anic anions/total chromium ions molar ratios in excess of 2.0 are undesi~ble be~ ~se such values usually result in a degraded corrosion ,~sisla"ce due to a deficient chromium immobi~i~Ation ratio in the resulting chro-30 mate film.
The metal ion/inorga".c anion molar ratio in the subject chromate bath isto be 0.05 to 1. The pH of the ch~",ate bath is too low when the metal ion/inor-W O 95/05247 2 1 6 9 1 9 3 PC~r~US94~08318 ganic anion molar ratio is below 0.0~. As a conse4uence the reaction is too vig-orous when the chro,nate bath and ~ ci~rous-plated steel sheet are brought into conta~ so that there is a whitening of the ~incirerous-plated steel sheet and a deyladed co"usio" r~sisla"ce due to an elevated chromium immobilization ratio in the resulting chromate film. When this ratio has a value in excess of 1 the chromate bath has a red! ~ced stability and precipitation readily occurs.
Any metal ion can be used that is capable of dissolving in the chromate bath of the present invention but Zn Ni Co and Al are particularly preferled.
Alkali metals such as Na and K are undesirable be~ ~se they cause a substan-tial decline in the chromium immobilization ratio of the c;l ,ror"ale film. The addi-tional presence of ~I,ospl,oric acid as inorya,lic acid in the subject chromate lreatment bath fu"~ions to raise the chromium illllllobil;~ ~l;on ratio of the chrom-ate film. When phûsphol ic acid is added it is prere, dL,ly added in a quantity such that the phosphate ions/total chro,nium ions molar ratio does not exceed 0.3.
While phosphate ions/total chromium ions molar ratios above 0.3 do provide an i, lcreased chromium i" "nob ';~ on ratio for the resulting .;I " o" ,ate hlm such val-ues are nevel lheless u"desirable bec~use they cause the ,t:sislance to blacken-ing to deteriorate.
The instant ~I"o",ale treatment bath may of course o~.liûnally contain col-loidal silica as known from the art for example silica sol fumed silica and the like.
The cl " o,ndle film is formed by coating the coaling-type blackening-resist-ant chromate bath prepared as desc, i~ed above on the surface of zinciferous-plated steel sheet followed by drying without a water wash. The film weight pref-erably falls in the range of 10 to 200 mg/m2 calculated as chromium metal. A sat-isrado,y corrosion resistance is not usually obtained when the chromate film weight falls below 10 mg/m2 as chromium metal. At the other extreme the anti-corrosion pe,rol",ance is saturated at cl,ro"~ale film weights in excess of 200 mg/m2 as chromium metal and such values are ll ,erefore uneconomical.
The first essential step in treatment according to the invention begins by applying the lreal",enl bath to the surface of the ~i"cirerous plating e.g. by spraying the lredl"~enl bath on the workpiece or i."" ,e, ~ing the workpiece in the WO 95/05247 2 1 6 9 1 ~ 3 PCT/US94/08318 -treatment bath followed in either case by a roll or air wipe or by applying the lleatlllent bath to the surface of the ~incirerous plating by known coating meth-ods for example by roll coating. After fo""ing a liquid film of substantially uni-form thickness of the ll ed~ ei ,~ bath over the surface being treated the final pro-s tective film is formed by drying the liquid film without any water wash or rinse.
The drying condi~ions should be sufficient to evaporate the water in the coatingand drying is ge"erally carried out at a sheet temperature of 40 C to 100 C.
The function and activity of each of the constituent co",ponents of the in-vention are not known with certainty. However, the sulfate and/or nitrate anionspresenl in the coating-type chro" ,ate ll ea~" ,enl bath appear to suppress blacken-ing by inhibiting the production of basic zinc carbonate (ZnCO3)x [Zn(OH)Jy through the fo""alion of the cor,es~onding salts for example Zn(NO3)2 etc.
between zinc and the inorganic acid.
With regard to the metal ion additive and particularly the Co ion it has been re~G, led (Tetsu to Hagane, Volume 76 pp. 383-390 (1990)) that this addi-tive can inhibit blackening by inhibiting c~tl ,odic rea~io"s on the plating surface and retarcling zinc co~,usion (oxid~tion). The metal ion added in the present in-vention presumably exercises the same effect.
Thus the instant coating-type chrol"ale bath conlaining hexavalent chromium ion trivalent chromium ion inor~a,1ic acid and metal ion is able to pro-vide both a blackening-inhibiting activity (based on the inorganic acid and metal ion) and a white rust-inhibiting activity (based on the hexavalent chromium ion and trivalent chro")ium ion).
The mechanism underlying the white rust-inhibiting activity of chrol"ate 2s films is generally thought to consist of an inhibitor effect in which the hexavalent ;I"o,n.um ion inhibitszincco"osiûn. Another mechanis", as repolled in Zairyo to Kankyo, Volume 41 pp. 244-245 (1992) CGI ,sisls of a self-repair activity exer-cised by hexavalent chromium ion that elutes from the film. In this mechanism the eluted hexavalent ch,o~,ium ion repairs da",aged reg;ons in the film. Accord-ingly when the chromium immobilization ratio is higher than necess~ry the ab-solute amount of hexavalent cl "omium ion available to function as inhibitor will be in~de.~ te. In ~ddition the inhibitor effect cannot be maintained i.e. is not WO 95/05247 2 1 6 9 1 9 3~ PCT/US94/08318 durable when the dhromium i""nobi~ ion ratio is too low. The white rust-inhib-iting activity is in~de~ te in either case. These phenomena make it clear that the c~"o",ium immobilization ratio will have an optimal range.
The cl,ro",ium immobilization ratio and the Cr3~/CF~ ratio are closely re-5 lated and it is known that the presence of trivalent dhromium ions is essential forinhibiting hexavalent chromium ion elution and raising the chromium immobiliza-tion ratio. However in the case of an ~ eous solution containing only trivalent chromium ions and hexavalent chromium ion the Cr31Cr~ molar ratio must be held below 2/3 in order for Cr3~ ions to remain in the aqueous solution as ions 10 without precipitation. On the other hand Cr/Cr~ ratios in excess of 2/3 are de-sirable in order to improve the white rust-inhibiting activity. The addition of an acid cGI~ponent other than cl "o",ic acid is a tactic that can be considered for the purpose of raising the cr/Cr ratio.
The d~ro",ium immobilization ratio is also ~rrected by the reactivity pre-5 vailing when the cl"o",dle bath and ,incirerous-plated steel sheet are broughtinto contact (abbreviated below as the contact reactivity). The addition of evenvery small quantities of the nitric acid or sulfuric acid that are added to the chromate bath of the prese"t invention G~uses a sharp drop in the pH of the chr(." ,ate bath, whidh inc~eases the conlact reactivity and ultimately results in a 20 higher than "ecess~-y chromium immobilization ratio. Thus the d~rul,,ale bathpH will clearly have an opti,nal range. The following ",ethods can be consideredfor adjusting the pH of a d "~" ,ate bath whose pH has been reduced by the addi-tion of inorgan;c acid: (i) the addition of a metal oxide hydroxide or carbonateto the reduced pH d"~",a(e bath; (ii) in the case of addition of nitric acid or sul-25 furic acid to the d,rol"ale bath the addition of metal salts of these acids.
The inventors carried out det~ile-l investigations into the effects obtained when the specified inorganic anions and metal ions stipulated in the present spedricalion are added to cl ,ro"~ale baths at particular molar ratios relative to the total chromium iûns. These investigations deter")ined that the addition of both 30 inor~anic anions and metal ions as reported below resulted in the same activity as for Ni or Co flash t,eat",enl followed by dhromate treatment. The reasons for- this have yet to be sati~racto~ily resolv0d but it is thought that an anti-blackening WO 95/05247 2 1 6 ~ i 9 3 PCT/US94/08318 activity is produced by the concenl~alion of chromium co",pounds at the grain boundaries of the zinc crystals and by the formation of Zn(NO3)2, etc. An anti-blackening effect also appears to be produced by an inhibition of cathodic reac-tions on the galvanized surface by the metal ion. White rust prevention is s thought to be based on a ~e,~i~lenl or continuing elution of hexavalent chromium ion that is induced by holding the chromium immobilization ratio within an optimal range. Thus, the process of the present invention is able, as described above, to render these two effects or activities compatible.
The presenl invention will be explained in greater detail below through working examples, but these are provided simply to explain the invention and should not be construed as limiting the present invention in any manner.
Exan,ples General Procedure Each sam~le test sheet in the examples and coi"paralive examples was alkaline deyl eased, water washed, and dried as des~, ibed in items (2), (3), and (4) below. The sample test sheet was then subjected to a ch,-o",ate l,ealment using the procedures outlined in items (5) and (6) below. Each sample test sheet, after treatment as specified above, was subjected to accelerated black rust testing and accelcrated white rust testing as described below. The stability of the treatment baths was also tested.
(1 ) sample test sheets:
hot-dip zinc-plated steel sheet hot-dip 5% Al/Zn-plated steel sheet hot-dip 55% Al/Zn-plated steel sheet 25 (2) alkalinedegreasing:
30 second spray at 60 C using a weakly alkaline degreaser (Pal-klinTM 342 from Nihon Parkerizing Kabushiki Kaisha, 2 % aqueous solu-tion) (3) cleaning:
10 second spray with tap water W095/05247 ~ 1 6 9 1 9 3 PCT/US94/08318 (4) drying:
drying in an air current (5) cl,ro",ale treatment:
The cl)ro",ate film weight was controlled through the wet pick-up s in roll coating.
As a further improvement of this previous invention the subject of this ap-o plication is a process cha~acteri~e~ by the formation on ~incirerous-plated steel sheet of a solid 10 - 200 mg/m2 (calculated as chromium metal) film by:
(I) appli~lion to zinciferous-plated steel sheet so as to form a liquid coating (I ,e, eGn of a ~1 " on ,ale bath that c~" ,prises p, eferably consists essential-ly of or still more preferably consists of:
(A) hexavalent c~"omium ions (B) trivalent chror"ium ions (C) at least one of nitrate ions and sulfate ions and (D) metal ions sele~ed from the group co"sia(i"g of Zn Ni Co and Al ions and mixtures of any two or more thereof and optionally one or more of:
(E) phospl ,a~e ions from an inGrganic acid and (F) colloidal silica in which:
(i) the trivalent ch,u",ium ion/hexavalent chro",ium ion molar ratio is 1/9 to 4/1 (ii) the total of nitrate + sulfate + phosphate ions/total chromium ions (i.e. hexavalent cl~ro",ium ions + trivalent chromium ions) molar ratioisO.1 to2.0 (iii) the total of Zn + Ni + Co + Al ions/the total of nitrate + sulfate +
phospl ,ate ions molar ratio is 0.05 to 1 and (iv) the molar ratio of phospl ,ate ions/total chromium ions does not ex-ceed 0.3; and W O 95/05247 2 1 6 9 1 9 3 PC~rrUS94/08318 -(Il) s~hsequently drying the applied coating.
For the pu, ~uoses of this desc, iplio, I the entire stoicl ,io" ,~t, ic equivalent as phos-phate ions of any pl ,osphoric acid and/or anions produced by ionization thereofthat are added to the cl " o" ,ale bath are counted as pl ,ospl ,ate ions irrespective of the actual degree of io, li~lion of the added acid. Preferably the acid addedis orthophosphoric acid H3P04 but other inorga,)ic pl ,osphoric acids such as HPO3 H4P2O, HsP3O10 may also be used. Also it is to be understood that the constituents specified in ionic form must be acco",panied by counterions so thatthe co,),posilion as a whole is electrically neutral. Such counterions preferably 10 are chose" from other specified constituents of the invention to the extent possi-ble and otherwise may be freely cl ,osen except for avoiding cou"lerions that are detrimental to the purposes of the invention.
Desc, iption of Prefer, ed Embodiments The trivalent chromium ion/hexavalent chrol"ium ion molar ratio in the subject cl "or,)ale treal",enl bath is preferably 1/9 to 411 and more preferably is 1/4 to 7/3. Trivalent chromium ion/hexavalent cl ,ro",ium ion molar ratios below1/9 are u"desi,able be~se such values usually result in excessive chromium ion elution in corrosive enviror""el,ls and thus in pollution of the environment.
When the trivalent chromium ion/hexavalent chromium ion molar ratio exceeds 4/1 the corrosion resistance becomes inadequate.
Sulfate and/or nitrate ions as required for the ~;I,ro",aling treatment ac-cording to the invention are preferably added at least partially in the form of the cor, esponding acids. These anions are added in a quantity that yields values p,~rerably of 0.1 to 2.0 and more pr~ferably of 0.2 to 1.6 for the sulfate + nitrate 25 + ~h osphale anions/total chromium ions molar ratio. The blackening resistance is usually inAdeql lAte when the inorganic anions/total ch~",ium ions molar ratio is less than 0.1. h ,or~anic anions/total chromium ions molar ratios in excess of 2.0 are undesi~ble be~ ~se such values usually result in a degraded corrosion ,~sisla"ce due to a deficient chromium immobi~i~Ation ratio in the resulting chro-30 mate film.
The metal ion/inorga".c anion molar ratio in the subject chromate bath isto be 0.05 to 1. The pH of the ch~",ate bath is too low when the metal ion/inor-W O 95/05247 2 1 6 9 1 9 3 PC~r~US94~08318 ganic anion molar ratio is below 0.0~. As a conse4uence the reaction is too vig-orous when the chro,nate bath and ~ ci~rous-plated steel sheet are brought into conta~ so that there is a whitening of the ~incirerous-plated steel sheet and a deyladed co"usio" r~sisla"ce due to an elevated chromium immobilization ratio in the resulting chromate film. When this ratio has a value in excess of 1 the chromate bath has a red! ~ced stability and precipitation readily occurs.
Any metal ion can be used that is capable of dissolving in the chromate bath of the present invention but Zn Ni Co and Al are particularly preferled.
Alkali metals such as Na and K are undesirable be~ ~se they cause a substan-tial decline in the chromium immobilization ratio of the c;l ,ror"ale film. The addi-tional presence of ~I,ospl,oric acid as inorya,lic acid in the subject chromate lreatment bath fu"~ions to raise the chromium illllllobil;~ ~l;on ratio of the chrom-ate film. When phûsphol ic acid is added it is prere, dL,ly added in a quantity such that the phosphate ions/total chro,nium ions molar ratio does not exceed 0.3.
While phosphate ions/total chromium ions molar ratios above 0.3 do provide an i, lcreased chromium i" "nob ';~ on ratio for the resulting .;I " o" ,ate hlm such val-ues are nevel lheless u"desirable bec~use they cause the ,t:sislance to blacken-ing to deteriorate.
The instant ~I"o",ale treatment bath may of course o~.liûnally contain col-loidal silica as known from the art for example silica sol fumed silica and the like.
The cl " o,ndle film is formed by coating the coaling-type blackening-resist-ant chromate bath prepared as desc, i~ed above on the surface of zinciferous-plated steel sheet followed by drying without a water wash. The film weight pref-erably falls in the range of 10 to 200 mg/m2 calculated as chromium metal. A sat-isrado,y corrosion resistance is not usually obtained when the chromate film weight falls below 10 mg/m2 as chromium metal. At the other extreme the anti-corrosion pe,rol",ance is saturated at cl,ro"~ale film weights in excess of 200 mg/m2 as chromium metal and such values are ll ,erefore uneconomical.
The first essential step in treatment according to the invention begins by applying the lreal",enl bath to the surface of the ~i"cirerous plating e.g. by spraying the lredl"~enl bath on the workpiece or i."" ,e, ~ing the workpiece in the WO 95/05247 2 1 6 9 1 ~ 3 PCT/US94/08318 -treatment bath followed in either case by a roll or air wipe or by applying the lleatlllent bath to the surface of the ~incirerous plating by known coating meth-ods for example by roll coating. After fo""ing a liquid film of substantially uni-form thickness of the ll ed~ ei ,~ bath over the surface being treated the final pro-s tective film is formed by drying the liquid film without any water wash or rinse.
The drying condi~ions should be sufficient to evaporate the water in the coatingand drying is ge"erally carried out at a sheet temperature of 40 C to 100 C.
The function and activity of each of the constituent co",ponents of the in-vention are not known with certainty. However, the sulfate and/or nitrate anionspresenl in the coating-type chro" ,ate ll ea~" ,enl bath appear to suppress blacken-ing by inhibiting the production of basic zinc carbonate (ZnCO3)x [Zn(OH)Jy through the fo""alion of the cor,es~onding salts for example Zn(NO3)2 etc.
between zinc and the inorganic acid.
With regard to the metal ion additive and particularly the Co ion it has been re~G, led (Tetsu to Hagane, Volume 76 pp. 383-390 (1990)) that this addi-tive can inhibit blackening by inhibiting c~tl ,odic rea~io"s on the plating surface and retarcling zinc co~,usion (oxid~tion). The metal ion added in the present in-vention presumably exercises the same effect.
Thus the instant coating-type chrol"ale bath conlaining hexavalent chromium ion trivalent chromium ion inor~a,1ic acid and metal ion is able to pro-vide both a blackening-inhibiting activity (based on the inorganic acid and metal ion) and a white rust-inhibiting activity (based on the hexavalent chromium ion and trivalent chro")ium ion).
The mechanism underlying the white rust-inhibiting activity of chrol"ate 2s films is generally thought to consist of an inhibitor effect in which the hexavalent ;I"o,n.um ion inhibitszincco"osiûn. Another mechanis", as repolled in Zairyo to Kankyo, Volume 41 pp. 244-245 (1992) CGI ,sisls of a self-repair activity exer-cised by hexavalent chromium ion that elutes from the film. In this mechanism the eluted hexavalent ch,o~,ium ion repairs da",aged reg;ons in the film. Accord-ingly when the chromium immobilization ratio is higher than necess~ry the ab-solute amount of hexavalent cl "omium ion available to function as inhibitor will be in~de.~ te. In ~ddition the inhibitor effect cannot be maintained i.e. is not WO 95/05247 2 1 6 9 1 9 3~ PCT/US94/08318 durable when the dhromium i""nobi~ ion ratio is too low. The white rust-inhib-iting activity is in~de~ te in either case. These phenomena make it clear that the c~"o",ium immobilization ratio will have an optimal range.
The cl,ro",ium immobilization ratio and the Cr3~/CF~ ratio are closely re-5 lated and it is known that the presence of trivalent dhromium ions is essential forinhibiting hexavalent chromium ion elution and raising the chromium immobiliza-tion ratio. However in the case of an ~ eous solution containing only trivalent chromium ions and hexavalent chromium ion the Cr31Cr~ molar ratio must be held below 2/3 in order for Cr3~ ions to remain in the aqueous solution as ions 10 without precipitation. On the other hand Cr/Cr~ ratios in excess of 2/3 are de-sirable in order to improve the white rust-inhibiting activity. The addition of an acid cGI~ponent other than cl "o",ic acid is a tactic that can be considered for the purpose of raising the cr/Cr ratio.
The d~ro",ium immobilization ratio is also ~rrected by the reactivity pre-5 vailing when the cl"o",dle bath and ,incirerous-plated steel sheet are broughtinto contact (abbreviated below as the contact reactivity). The addition of evenvery small quantities of the nitric acid or sulfuric acid that are added to the chromate bath of the prese"t invention G~uses a sharp drop in the pH of the chr(." ,ate bath, whidh inc~eases the conlact reactivity and ultimately results in a 20 higher than "ecess~-y chromium immobilization ratio. Thus the d~rul,,ale bathpH will clearly have an opti,nal range. The following ",ethods can be consideredfor adjusting the pH of a d "~" ,ate bath whose pH has been reduced by the addi-tion of inorgan;c acid: (i) the addition of a metal oxide hydroxide or carbonateto the reduced pH d"~",a(e bath; (ii) in the case of addition of nitric acid or sul-25 furic acid to the d,rol"ale bath the addition of metal salts of these acids.
The inventors carried out det~ile-l investigations into the effects obtained when the specified inorganic anions and metal ions stipulated in the present spedricalion are added to cl ,ro"~ale baths at particular molar ratios relative to the total chromium iûns. These investigations deter")ined that the addition of both 30 inor~anic anions and metal ions as reported below resulted in the same activity as for Ni or Co flash t,eat",enl followed by dhromate treatment. The reasons for- this have yet to be sati~racto~ily resolv0d but it is thought that an anti-blackening WO 95/05247 2 1 6 ~ i 9 3 PCT/US94/08318 activity is produced by the concenl~alion of chromium co",pounds at the grain boundaries of the zinc crystals and by the formation of Zn(NO3)2, etc. An anti-blackening effect also appears to be produced by an inhibition of cathodic reac-tions on the galvanized surface by the metal ion. White rust prevention is s thought to be based on a ~e,~i~lenl or continuing elution of hexavalent chromium ion that is induced by holding the chromium immobilization ratio within an optimal range. Thus, the process of the present invention is able, as described above, to render these two effects or activities compatible.
The presenl invention will be explained in greater detail below through working examples, but these are provided simply to explain the invention and should not be construed as limiting the present invention in any manner.
Exan,ples General Procedure Each sam~le test sheet in the examples and coi"paralive examples was alkaline deyl eased, water washed, and dried as des~, ibed in items (2), (3), and (4) below. The sample test sheet was then subjected to a ch,-o",ate l,ealment using the procedures outlined in items (5) and (6) below. Each sample test sheet, after treatment as specified above, was subjected to accelerated black rust testing and accelcrated white rust testing as described below. The stability of the treatment baths was also tested.
(1 ) sample test sheets:
hot-dip zinc-plated steel sheet hot-dip 5% Al/Zn-plated steel sheet hot-dip 55% Al/Zn-plated steel sheet 25 (2) alkalinedegreasing:
30 second spray at 60 C using a weakly alkaline degreaser (Pal-klinTM 342 from Nihon Parkerizing Kabushiki Kaisha, 2 % aqueous solu-tion) (3) cleaning:
10 second spray with tap water W095/05247 ~ 1 6 9 1 9 3 PCT/US94/08318 (4) drying:
drying in an air current (5) cl,ro",ale treatment:
The cl)ro",ate film weight was controlled through the wet pick-up s in roll coating.
(6) drying:
maximum attained sheet temperature = 100 C drying time = 5 seconds (7) chro",ium immobilization ratio:
The cl"or"ate-treated zincirerous-plated steel sheet was alkali-washed under the conditions given below and the chromium add-on in mg/m2 was measured using an X-ray fluorescence analyzer both before and after this alkali wash. The chromium immobilization ratio was then calculated from the equation given below (a higher percentage indicates a higher cl"c""ium immobilization ratio).
Chromium i",mobilization ratio = (A/Ao) x 100 (%) where:
A : chromium film weight after the alkali wash in mg/m2 Ao : ~;hro",ium film weight before the alkali wash in mg/m2 The alkali wash co, Isisled of a 2 minute spray at 60 C with a 2 %
~queolJs solution of a sodium silicate-based alkaline degreaser (PalklinTM
N364S from Nihon Parkerizing Kabushiki Kaisha).
maximum attained sheet temperature = 100 C drying time = 5 seconds (7) chro",ium immobilization ratio:
The cl"or"ate-treated zincirerous-plated steel sheet was alkali-washed under the conditions given below and the chromium add-on in mg/m2 was measured using an X-ray fluorescence analyzer both before and after this alkali wash. The chromium immobilization ratio was then calculated from the equation given below (a higher percentage indicates a higher cl"c""ium immobilization ratio).
Chromium i",mobilization ratio = (A/Ao) x 100 (%) where:
A : chromium film weight after the alkali wash in mg/m2 Ao : ~;hro",ium film weight before the alkali wash in mg/m2 The alkali wash co, Isisled of a 2 minute spray at 60 C with a 2 %
~queolJs solution of a sodium silicate-based alkaline degreaser (PalklinTM
N364S from Nihon Parkerizing Kabushiki Kaisha).
(8) accelerated black rust testing ("ABRr ):
Multiple 70 x 150 mm test coupons were cut from each sample test sheet. The test surfaces of two test coupons were laid against each other 2s to give a pair and 5 to 10 pairs were stacked. The stack was wrapped with vinyl-coated paper the four corners were li,JI ,tel ~ed down with bolts and a 0.67 kgf cm load was applied with a torque wrench. This assembly was held in a hu~l ,iJislat for 240 hours at 70 C/RH 80 %. After removal blackening of the coUI)tel rac;ng areas was visually evaluated. The evalu-ation standards are given below.
WO 95/05247 2 1 6 9 1 9 3 PCT/US94tO8318 5: no blackening 4: very slight graying 3: less than 25 % blackening 2: blackening from 25 % to less than 50 %
1: 50 % or more blackening.
Multiple 70 x 150 mm test coupons were cut from each sample test sheet. The test surfaces of two test coupons were laid against each other 2s to give a pair and 5 to 10 pairs were stacked. The stack was wrapped with vinyl-coated paper the four corners were li,JI ,tel ~ed down with bolts and a 0.67 kgf cm load was applied with a torque wrench. This assembly was held in a hu~l ,iJislat for 240 hours at 70 C/RH 80 %. After removal blackening of the coUI)tel rac;ng areas was visually evaluated. The evalu-ation standards are given below.
WO 95/05247 2 1 6 9 1 9 3 PCT/US94tO8318 5: no blackening 4: very slight graying 3: less than 25 % blackening 2: blackening from 25 % to less than 50 %
1: 50 % or more blackening.
(9) accelerated white rust testing ( AWRr ):
A 70 x 150 mm test coupon was cut from each sample test sheet and submitted to salt-spray testing as specified in JIS Z371. The area of white rust develop",ent was visually inspected after 72 hours for the hot-dip zinc-plated steel sheet after 240 hours for the 5 % Al/Zn-plated steel sheet and after 600 hours for the 55 % Al/Zn-plated steel sheet.
The evaluation sla,)dards are given below.
5: no white rust 4: less than 5 % area of white rust development 3: area of white rust development from 5 % to less than 25 %
2: area of white rust dcvelop" ,en~ from 25 % to less than 50 %
1: area of white rust development of 50 % or more.
Tables 1 - 4 report the co" ,position of the chromale treatment baths the co" "~onent ratios for the treatment baths the pH the film weight the chromium 20 j~YIIIIObj~ jGn ratio and the results of accelerated black rust testing and acceler-ated white rust testing.
WO 95/05247 2 1 6 ~ 1 9 3 PCT/US94108318 Table 1: RESULTS FOR HOT-DIP ZINC-PLATED STEEL SHEETS
6E~ample or Comparison FilmMass, Chromium E~ample No. Milligrams/ Immobiliza- ABRT AWRT
for the Chro- Square Meter tion Ratio, %
mating Bath 0 Ex. 1 12 70.2 5 5 Ex.2 13 75.3 5 5 Ex. 3 12 77.2 5 5 Ex. 4 50 65.9 5 5 Ex. 5 23 67.4 5 5 Ex. 6 12 83.5 5 5 Ex. 7 11 78.4 5 5 C. Ex. 1 12 26.7 2 C.Ex.2 12 98.1 4 C.Ex.3 13 86.0 1 5 20C.Ex.4 12 92.5 2 4 Notes for Table 1 "AWRT" = Accelerated White Rust Testing; "ABRT" = Accelerated Black Rust Testing; "Ex." = Exarnple; "C. Ex. = CG111PaliSOn EX~mrle.
The compositions of the cl-rol..~ p. l~ baths are given in Table 4.
2s The wet pick-up mass ofthe ~le~ l bath was about 1.2 millilit~rs/meter2.
The film mass was measured as its stoi~hiometric equivalent as chromium metal.
WO 95/05247 2 1 6 ~ t 9 ~ PCT/US94108318 -Table 2 sRESULTS FOR HOT-DIP 5 % ALUMINUM/ZINC-PLATED STEEL SHEETS
Example or Comparison FilmMass, Chromium Esample No. Milligrams/ Immobiliza- ABRT AWRT
for the Chro- Square Meter tion Ratio, %
mating Bath Ex. 1 2S 73.4 5 5 Ex. 2 26 76.7 5 5 Ex. 3 24 75.5 5 5 Ex. 4 110 62.1 5 5 Ex. 5 54 65.0 5 5 Ex. 6 25 80.1 5 5 Ex. 7 23 85.5 5 5 C. Ex. 1 26 26.0 2 C.Ex.2 25 99.0 4 C. Ex. 3 28 90.0 1 5 C.Ex.4 25 91.5 1 4 Notes for Table 2 The wet pick-up mass ofthe tleAl....;..l bath was about 2.5 milliliters/meter2.
2s Other notes are the same as for Table 1.
WO 95/05247 2 1 6 9 1 9 ~ PCT/US94/08318 Table 3 5 RESULTS FOR HOT-DIP 55 % ALUMINUMQINC-PLATED STEEL SHEETS
Example or Comparison Film Mass, Chromium E~ample No. Milligrams/ Immobiliza- ABRT AWRT
for the Chro- Square Meter tion Ratio, %
mating Bath Ex. 1 40 69.7 5 5 Ex. 2 41 70.4 5 5 Ex. 3 40 71.5 5 5 Ex. 4 165 60.1 5 5 Ex. 5 124 62.2 5 5 Ex. 6 42 75.0 5 5 Ex. 7 41 85.8 5 5 C.Ex.1 41 24.9 3 20 C. Ex. 2 42 95.0 4 C.Ex.3 40 90.5 1 5 C.Ex.4 40 96.0 2 4 Notes for Table 3 The wet pick-up mass ofthe llc~ bath was about 4 millilit~rs/meter2.
25Other notes are the same as for Table 1.
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WO95/05247 2 1 69. 1 9 3 PCT/US94/08318 As reported in Tables 1 to 3 execution of a chromate lreat",ent of the p,esenL invention on gah,ani e-J steel sheet is able to improve the chromium im-mobilization ratio blackening resistance and white rust resistance of various types of hot-dip galva"i ad steel sheet. Moreover this is achieved even without 5 the use of a metal flash treatment and a good balance is also obtained among the aforesaid prope, lies. Thus the process of the invention makes possible a one-step treatment which consists of only a cl,ro"~a~e treal",enl that can re-place the two-step process of a pretreatment followed by a chromate treatment.
This clearly has i""~o, lal ,~ industrial effects for example providing an efficient .0 continuous oper~lion. In cGnlras~ to this while the co,nposition of Comparative Example 2 does provide an anti-black rust activity white rust resistance is poor.
Co"",arati~/e Examples 3 and 4 produce a moderate activity with regard to the chromium i"""obi~ on ratio and white rust resistance but they lack any anti-black rust activity. The cclllposilion in Com,uarali~/e Example 1 pel ror",s poorly s in all areas (chromium i""~obilization ratio anti-black rust activity and anti-white rust activity) Benefits of the Invention As has been rliscussed in detail above the cl)ro",dle llaatlllellt process of the ~ ,asent invention offers very substantial practical results for i"cirarous-20 plated steel sheet. Not only does the invention process improve both the resist-ance to black rust and the resislance to white rust it also stabilizes and improves the chromium immobilization ratio and the appearance of the chromate film.
A 70 x 150 mm test coupon was cut from each sample test sheet and submitted to salt-spray testing as specified in JIS Z371. The area of white rust develop",ent was visually inspected after 72 hours for the hot-dip zinc-plated steel sheet after 240 hours for the 5 % Al/Zn-plated steel sheet and after 600 hours for the 55 % Al/Zn-plated steel sheet.
The evaluation sla,)dards are given below.
5: no white rust 4: less than 5 % area of white rust development 3: area of white rust development from 5 % to less than 25 %
2: area of white rust dcvelop" ,en~ from 25 % to less than 50 %
1: area of white rust development of 50 % or more.
Tables 1 - 4 report the co" ,position of the chromale treatment baths the co" "~onent ratios for the treatment baths the pH the film weight the chromium 20 j~YIIIIObj~ jGn ratio and the results of accelerated black rust testing and acceler-ated white rust testing.
WO 95/05247 2 1 6 ~ 1 9 3 PCT/US94108318 Table 1: RESULTS FOR HOT-DIP ZINC-PLATED STEEL SHEETS
6E~ample or Comparison FilmMass, Chromium E~ample No. Milligrams/ Immobiliza- ABRT AWRT
for the Chro- Square Meter tion Ratio, %
mating Bath 0 Ex. 1 12 70.2 5 5 Ex.2 13 75.3 5 5 Ex. 3 12 77.2 5 5 Ex. 4 50 65.9 5 5 Ex. 5 23 67.4 5 5 Ex. 6 12 83.5 5 5 Ex. 7 11 78.4 5 5 C. Ex. 1 12 26.7 2 C.Ex.2 12 98.1 4 C.Ex.3 13 86.0 1 5 20C.Ex.4 12 92.5 2 4 Notes for Table 1 "AWRT" = Accelerated White Rust Testing; "ABRT" = Accelerated Black Rust Testing; "Ex." = Exarnple; "C. Ex. = CG111PaliSOn EX~mrle.
The compositions of the cl-rol..~ p. l~ baths are given in Table 4.
2s The wet pick-up mass ofthe ~le~ l bath was about 1.2 millilit~rs/meter2.
The film mass was measured as its stoi~hiometric equivalent as chromium metal.
WO 95/05247 2 1 6 ~ t 9 ~ PCT/US94108318 -Table 2 sRESULTS FOR HOT-DIP 5 % ALUMINUM/ZINC-PLATED STEEL SHEETS
Example or Comparison FilmMass, Chromium Esample No. Milligrams/ Immobiliza- ABRT AWRT
for the Chro- Square Meter tion Ratio, %
mating Bath Ex. 1 2S 73.4 5 5 Ex. 2 26 76.7 5 5 Ex. 3 24 75.5 5 5 Ex. 4 110 62.1 5 5 Ex. 5 54 65.0 5 5 Ex. 6 25 80.1 5 5 Ex. 7 23 85.5 5 5 C. Ex. 1 26 26.0 2 C.Ex.2 25 99.0 4 C. Ex. 3 28 90.0 1 5 C.Ex.4 25 91.5 1 4 Notes for Table 2 The wet pick-up mass ofthe tleAl....;..l bath was about 2.5 milliliters/meter2.
2s Other notes are the same as for Table 1.
WO 95/05247 2 1 6 9 1 9 ~ PCT/US94/08318 Table 3 5 RESULTS FOR HOT-DIP 55 % ALUMINUMQINC-PLATED STEEL SHEETS
Example or Comparison Film Mass, Chromium E~ample No. Milligrams/ Immobiliza- ABRT AWRT
for the Chro- Square Meter tion Ratio, %
mating Bath Ex. 1 40 69.7 5 5 Ex. 2 41 70.4 5 5 Ex. 3 40 71.5 5 5 Ex. 4 165 60.1 5 5 Ex. 5 124 62.2 5 5 Ex. 6 42 75.0 5 5 Ex. 7 41 85.8 5 5 C.Ex.1 41 24.9 3 20 C. Ex. 2 42 95.0 4 C.Ex.3 40 90.5 1 5 C.Ex.4 40 96.0 2 4 Notes for Table 3 The wet pick-up mass ofthe llc~ bath was about 4 millilit~rs/meter2.
25Other notes are the same as for Table 1.
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.W ~ X Z-~ W
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Z s ~ o ~ O Uo~W
WO95/05247 2 1 69. 1 9 3 PCT/US94/08318 As reported in Tables 1 to 3 execution of a chromate lreat",ent of the p,esenL invention on gah,ani e-J steel sheet is able to improve the chromium im-mobilization ratio blackening resistance and white rust resistance of various types of hot-dip galva"i ad steel sheet. Moreover this is achieved even without 5 the use of a metal flash treatment and a good balance is also obtained among the aforesaid prope, lies. Thus the process of the invention makes possible a one-step treatment which consists of only a cl,ro"~a~e treal",enl that can re-place the two-step process of a pretreatment followed by a chromate treatment.
This clearly has i""~o, lal ,~ industrial effects for example providing an efficient .0 continuous oper~lion. In cGnlras~ to this while the co,nposition of Comparative Example 2 does provide an anti-black rust activity white rust resistance is poor.
Co"",arati~/e Examples 3 and 4 produce a moderate activity with regard to the chromium i"""obi~ on ratio and white rust resistance but they lack any anti-black rust activity. The cclllposilion in Com,uarali~/e Example 1 pel ror",s poorly s in all areas (chromium i""~obilization ratio anti-black rust activity and anti-white rust activity) Benefits of the Invention As has been rliscussed in detail above the cl)ro",dle llaatlllellt process of the ~ ,asent invention offers very substantial practical results for i"cirarous-20 plated steel sheet. Not only does the invention process improve both the resist-ance to black rust and the resislance to white rust it also stabilizes and improves the chromium immobilization ratio and the appearance of the chromate film.
Claims (9)
1. A process for treating a zinciferous surface to increase the resistance of the surface to both black and white rusting, wherein a solid surface layer that has from 10 - 200 mg/m2, calculated as chromium metal, is formed on the zinciferous surface by:
(I) coating on the zinciferous surface a layer of an aqueous liquid chromate bath composition that consists essentially of water and:
(A) hexavalent chromium ions, (B) trivalent chromium ions, (C) at least one of nittate ions and sulfate ions, and (D) metal ions selected from the group consisting of Zn, Ni, Co, and Al ions and mixtures of any two or more thereof, and, optionally, one or more of:
(E) phosphate ions from an inorganic acid and (F) colloidal silica, and in which:
(i) the trivalent chromium ion/hexavalent chromium ion molar ratio is 1/9 to 4/1, (ii) the total of nitrate + sulfate + phosphate ions/total chromium ions (i.e., hexavalent chromium ions + trivalent chromium ions) molar ratio is 0.1 to 2.0, (iii) the total of Zn + Ni + Co + Al ions/the total of nitrate + sulfate +
phosphate ions molar ratio is 0.05 to 1, and (iv) the molar ratio of phosphate ions to total chromium ions does not exceed 0.3; and (II) subsequently drying into place on the zinciferous surface the coating formed in step (I).
(I) coating on the zinciferous surface a layer of an aqueous liquid chromate bath composition that consists essentially of water and:
(A) hexavalent chromium ions, (B) trivalent chromium ions, (C) at least one of nittate ions and sulfate ions, and (D) metal ions selected from the group consisting of Zn, Ni, Co, and Al ions and mixtures of any two or more thereof, and, optionally, one or more of:
(E) phosphate ions from an inorganic acid and (F) colloidal silica, and in which:
(i) the trivalent chromium ion/hexavalent chromium ion molar ratio is 1/9 to 4/1, (ii) the total of nitrate + sulfate + phosphate ions/total chromium ions (i.e., hexavalent chromium ions + trivalent chromium ions) molar ratio is 0.1 to 2.0, (iii) the total of Zn + Ni + Co + Al ions/the total of nitrate + sulfate +
phosphate ions molar ratio is 0.05 to 1, and (iv) the molar ratio of phosphate ions to total chromium ions does not exceed 0.3; and (II) subsequently drying into place on the zinciferous surface the coating formed in step (I).
2. A process according to claim 1, wherein (i) the trivalent chromium ion/
hexavalent chromium ion molar ratio is 1/4 to 7/3 and (ii) the total of nitrate +
sulfate + phosphate ions/total chromium ions molar ratio is 0.2 to 1.6.
hexavalent chromium ion molar ratio is 1/4 to 7/3 and (ii) the total of nitrate +
sulfate + phosphate ions/total chromium ions molar ratio is 0.2 to 1.6.
3. A process according to claim 2, wherein the aqueous liquid chromate bath composition contains phosphate ions.
4. A process according to claim 1, wherein the aqueous liquid chromate bath composition contains phosphate ions.
5. A process according to claim 4, wherein step (II) is performed at a treated surface temperature from 40 to 100°C.
6. A process according to claim 3, wherein step (II) is performed at a treated surface temperature from 40 to 100°C.
7. A process according to claim 2, wherein step (II) is performed at a treated surface temperature from 40 to 100°C.
8. A process according to claim 1, wherein step (II) is performed at a treated surface temperature from 40 to 100°C.
9. A process according to any one of claims 1 - 8, wherein the zinciferous surface treated is that of zinciferous-plated steel sheet.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP22222993A JP3288152B2 (en) | 1993-08-14 | 1993-08-14 | Method for producing galvanized steel sheet with excellent resistance to blackening and white rust |
| JP5/222229 | 1993-08-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2169193A1 true CA2169193A1 (en) | 1995-02-23 |
Family
ID=16779146
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002169193A Abandoned CA2169193A1 (en) | 1993-08-14 | 1994-08-11 | Process for treating zinciferous surfaces |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0724488A4 (en) |
| JP (1) | JP3288152B2 (en) |
| KR (1) | KR100311062B1 (en) |
| CN (1) | CN1102442A (en) |
| AU (1) | AU7714194A (en) |
| CA (1) | CA2169193A1 (en) |
| TW (1) | TW247321B (en) |
| WO (1) | WO1995005247A1 (en) |
| ZA (1) | ZA946049B (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BR9706566A (en) * | 1996-07-02 | 1999-07-20 | Nippon Kokan Kk | Manufacturing process on galvanized steel sheet containing lead coated with chromate with black anti-patina property and white anti-rust property |
| US6461449B1 (en) | 1997-10-07 | 2002-10-08 | Henkel Corporation | Conversion coating zinciferous surfaces to resist blackening and white rust |
| CN1062030C (en) * | 1998-08-28 | 2001-02-14 | 宝山钢铁(集团)公司 | Method for producing electrogalvanizing steel plate with high anti-black property |
| KR100436913B1 (en) * | 1999-11-09 | 2004-06-23 | 주식회사 포스코 | Chromate treatment solution and method for manufacturing chromate treated steel |
| KR101560947B1 (en) | 2013-12-24 | 2015-10-15 | 주식회사 포스코 | SURFACE TREATMENT COMPOSITION HAVING EXCELLENT CORROSION RESISTANCE AND BLACKENING RESISTANCE AND METHOD FOR PREPARING SURFACE TREATED Zn-Al-Mg ALLOY PLATED STEEL SHEET USING THE SAME |
| CN106010088A (en) * | 2016-05-20 | 2016-10-12 | 江苏固格澜栅防护设施有限公司 | Zinc steel fence and method for manufacturing same |
| KR101786358B1 (en) * | 2016-06-14 | 2017-10-18 | 주식회사 포스코 | Solution composition for surface treating of steel sheet, zinc-based metal plated steel sheet using the same, and manufacturing method of the same |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4683157A (en) * | 1982-11-15 | 1987-07-28 | Mosser Mark F | Thixotropic coating compositions and methods |
| JPS62278298A (en) * | 1985-08-28 | 1987-12-03 | Kawasaki Steel Corp | Chromated zn or zn alloy plated steel sheet and its production |
| JPS6256580A (en) * | 1985-09-05 | 1987-03-12 | Nippon Parkerizing Co Ltd | Chromating solution for galvanized steel sheet |
| JPS63171685A (en) * | 1986-12-30 | 1988-07-15 | Nippon Steel Corp | Formation of anticorrosive white chromate film |
| CN1039915C (en) * | 1989-07-05 | 1998-09-23 | 新日本制铁株式会社 | Production of grain-oriented silicon steel sheets having insulating film formed thereon |
| JP2839111B2 (en) * | 1990-08-28 | 1998-12-16 | 日本パーカライジング株式会社 | Chromate treatment method for galvanized steel sheet |
| JP3105322B2 (en) * | 1991-12-27 | 2000-10-30 | 日産自動車株式会社 | Method for forming colorless chromate film on glittering aluminum wheels |
-
1993
- 1993-08-14 JP JP22222993A patent/JP3288152B2/en not_active Expired - Lifetime
-
1994
- 1994-08-05 TW TW083107191A patent/TW247321B/zh active
- 1994-08-11 ZA ZA946049A patent/ZA946049B/en unknown
- 1994-08-11 EP EP94927906A patent/EP0724488A4/en not_active Withdrawn
- 1994-08-11 CA CA002169193A patent/CA2169193A1/en not_active Abandoned
- 1994-08-11 WO PCT/US1994/008318 patent/WO1995005247A1/en not_active Application Discontinuation
- 1994-08-11 AU AU77141/94A patent/AU7714194A/en not_active Abandoned
- 1994-08-13 CN CN94109436A patent/CN1102442A/en active Pending
- 1994-08-13 KR KR1019940020005A patent/KR100311062B1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0724488A1 (en) | 1996-08-07 |
| JP3288152B2 (en) | 2002-06-04 |
| AU7714194A (en) | 1995-03-14 |
| WO1995005247A1 (en) | 1995-02-23 |
| JPH0754156A (en) | 1995-02-28 |
| TW247321B (en) | 1995-05-11 |
| KR100311062B1 (en) | 2001-12-15 |
| KR950006022A (en) | 1995-03-20 |
| EP0724488A4 (en) | 1997-01-08 |
| ZA946049B (en) | 1995-06-29 |
| CN1102442A (en) | 1995-05-10 |
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