CA2303877A1 - Method for phosphatizing a steel strip - Google Patents
Method for phosphatizing a steel strip Download PDFInfo
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- CA2303877A1 CA2303877A1 CA002303877A CA2303877A CA2303877A1 CA 2303877 A1 CA2303877 A1 CA 2303877A1 CA 002303877 A CA002303877 A CA 002303877A CA 2303877 A CA2303877 A CA 2303877A CA 2303877 A1 CA2303877 A1 CA 2303877A1
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- ions
- phosphating
- zinc
- free
- steel strip
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- 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
- C23C22/07—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 phosphates
- C23C22/08—Orthophosphates
- C23C22/18—Orthophosphates containing manganese cations
- C23C22/182—Orthophosphates containing manganese cations containing also zinc cations
-
- 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
- C23C22/07—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 phosphates
- C23C22/08—Orthophosphates
- C23C22/18—Orthophosphates containing manganese cations
- C23C22/188—Orthophosphates containing manganese cations containing also magnesium cations
-
- 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
- C23C22/34—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 fluorides or complex fluorides
- C23C22/36—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 fluorides or complex fluorides containing also phosphates
- C23C22/368—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 fluorides or complex fluorides containing also phosphates containing magnesium cations
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- Chemical & Material Sciences (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Chemical Treatment Of Metals (AREA)
Abstract
The invention concerns a method for phosphatizing a steel strip or a zinccoated or galvanized steel strip by depositing an alloy on one or two surfaces, by spraying or immersion, for 2 to 20 seconds, with an acid phosphatizing solution, containing zinc, magnesium and manganese, at a temperature of the order of 50 to 70 ~C. Said method is characterised in that the phosphatizing solution does not contain nitrate ions and that it contains: between 1 and 4 g/l of zinc ions, between 1.2 and 4 g/l of manganese ions, between 1 and 4 g/l of magnesium ions, between 10 and 30 g/l of phosphate ions, between 0.1 and 3 g/l of hydroxylamine in free, ionic or combined form. The acid content of said phosphatizing solution ranges between 0.4 and 4 points and its total acid content is of the order of 15 to 45 points.
Description
, ,, CA 02303877 2000-03-17 ..._ ~ ~ i~ Cv "Process for phosphating steel strip" _ This invention relates to a process for the phosphating of steel strip, or of steel strip coated on one or both sides with zinc or zinc alloy, by a spraying or dipping treatment which, depending on the speed of the conveyor belt, takes place over a period of about 2 to about 20 seconds.
Processes for phosphating surfaces of iron, steel, zinc and alloys thereof as well as of aluminum and alloys thereof are long-standing prior art. The phosphating of the above-mentioned surfaces serves to increase the adhesive strength of paint layers and to improve the protection from corrosion. The phosphating is carried out by dipping the metal surfaces into the phosphating solutions and by spraying the metal surfaces with the phosphating solutions. Combined processes are also known. Formed metal parts such as car bodies, may be phosphated, as may also metal strips on high-speed production lines. The present invention is concerned with such a phosphating of strip. Phosphating of strip differs from phosphating of parts in that, because of the high conveyor belt speeds, the phosphating, i.e.
the development of a closed metal phosphate layer, has to take place within a short period of time, for example, within about 2 to about 20 seconds.
Processes for phosphating metal strips, in particular steel strips which have been zinc-coated electrolytically or by hot dipping, are known in the art. For example, WO
describes a process for phosphating steel strip which has been zinc-coated electrolytically and/or by hot dipping; the process involves short-term treatment using acid phosphating solutions which, besides zinc ions and phosphate ions, contain manganese cations and nickel canons, as well as anions of oxygen-containing acids having an accelerating action. The latter term refers, in particular, to nitrate ions. DE-A-35 37 108 likewise describes a process for phosphating electrolytically zinc-coated steel strips by treatment using acid phosphanng solutions which, besides zinc ions, manganese ions and phosphate ions, contain other metal cations, such as nickel ions and/or anions of oxygen-containing acids having an accelerating action, in particular nitrate ions. Here, the zinc cation content is within the relatively low range of 0.1 to 0.8 gll.
. , CA 02303877 2000-03-17 w - _2_ DE-A-39 20 296 describes a process for the production of manganese- and magne~sium-containing zinc phosphate coatings on steel, zinc, aluminum and/or alloys thereof by spraying, spray-dipping and/or dipping using an aqueous solution which contains 0.2 to 1.0 g/1 zinc ions, 0.2 to 2.0 g/1 manganese ions, 0.5 to 2 gll magnesium ions, 10 to 20 g/1 phosphate ions, 0.2 to 10 g/1 nitrate ions and up to 1.0 g/1 fluoride ions.
This phosphating solution necessarily also contains 0.02 to 2 g/1 nitrite ions and/or 0.4 to 1 g/1 chlorate ions and/or 0.2 to 1 g/1 of an organic oxidising agent as an accelerator. The nitrate ions essential in this process may, however, in the case of zinc-coated steel surfaces, lead to loss of quality in the phosphate layer as a result of pinholing. In this connection, "pinholes" mean whitish corrosion points on the metal surface which have a crater-like appearance in rnicrographs.
From the phosphating times of more than 2 minutes mentioned in the Examples, it is obvious that this is not a process for the phosphating of strip.
The German Patent Application 196 39 596 attempts to provide a phosphating process which on the one hand solves the problem of pinholing and, on the other hand, also makes it possible, within the short phosphating times usual on production lines, to produce a closed crystalline phosphate layer on steel strips which are not zinc-coated and on the uncoated side of steel strips zinc-coated on one side. According to that document, the object is fulfilled by a process for the phosphating of steel strip, or of steel strip coated on one or both sides with zinc or zinc alloy, by spraying treatment or dipping treatment for a period of 2 to 15 seconds, using an acid phosphating solution containing zinc and manganese, at a temperature of 40 to 70°C, characterised in that the phosphating solution contains:
1 to 4 g/1 zinc ions;
0.8 to 3.5 g/1 manganese ions;
to 30 g/1 phosphate ions;
0.1 to 3 gll hydroxylamine in free, ionic or bound form;
and not more than 1 g/1 nitrate ions; a free acid content of 0.4 to 4 points;
and a total acid content of 12 to 50 points.
The crystalline zinc phosphate layers produced by this process already very adequately meet the standards being set nowadays for a zinc phosphating solution. This is particularly the case when this process is used in an embodiment in which either 0.8 to 3.5 g/1 nickel ions or - _3_ 0.002 to about 0.2 g/1 copper ions are simultaneously present. If the process is carried out without these rations, disadvantages with regard to paint adhesion and protection from corrosion have to be accepted.
For environmental and toxicological reasons, the use of nickel ions in phosphating baths is becoming increasingly less desirable nowadays. For the phosphating of parts, such as the phosphating of car bodies using phosphating times of more than about 2 minutes, phosphating processes have been employed recently in which, instead of the nickel ions, copper ions are used within the low concentration range given above. Processes which function without the use of the toxicologically- and environmentally-disadvantageous nickel ions are also being intensively sought for high-speed production lines with short phosphating times of about 2 to about 20 seconds. For production lines, however, the replacement of the nickel ions by low concentrations of copper ions is not a solution, because for the large area to be phosphated per unit time and with the small bath volume compared with that in the phosphating of parts, the copper content would have to be determined and controlled in time intervals of shorter than 1 minute. There are no suitable measuring and controlling techniques available.
Accordingly, an object of the present invention is to provide a phosphating process for high-speed production lines using phosphating times of about 2 to about 20 seconds, which, on the one hand, is operated free from nickel and which, on the other hand, results in phosphate layers whose quality as regards paint adhesion and protection against corrosion is equal to that of nickel-containing phosphate layers.
This object is fulfilled by a process for the phosphating of steel strip, or of steel strip coated on one or both sides with zinc or zinc alloy, by a spraying or dipping treatment for a period of 2 to 20 seconds, using an acid phosphating solution containing zinc, magnesium and manganese, at a temperature of 50 to 70°C, characterised in that the phosphating solution is free from nitrate ions and in that it contains:
1 to 4 g/1 zinc ions;
1.2 to 4 g/1 manganese ions;
-4_ 1 to 4 g/1 magnesium ions;
to 30 g/1 phosphate ions;
0.1 to 3 g/1 hydroxylamine in free, ionic or bound form;
a free acid content of 0.4 to 4 points; and a total acid content of 15 to 45 points.
In this process, the steel strips may be zinc-coated electrolytically or zinc-coated by hot dipping or coated with zinc alloy. "Coated with zinc alloy" means that the steel surface is coated with an alloy which in addition to zinc contains other metals, such as iron, nickel or aluminum. A zinc alloy coating using a zinc-iron alloy may be carried out, for example, by tempering a zinc-coated steel strip, as a result of which a diffusion of iron atoms into the zinc layer and vice versa takes place. The layer thicknesses of the zinc coating layers are generally within the range of about 5 to about 20 ~cm.
The terms "free acid" and "total acid" are generally known in the field of phosphating. They are determined by titrating a sample from the acid bath using 0.1 N sodium hydroxide solution and measuring the consumption of the latter. The consumption in ml is expressed as a number of points. In the present context, the number of points of the free acid means the consumption in ml of 0.1 N sodium hydroxide solution required to titrate 10 ml of bath solution, which has been diluted to 50 ml using deionised water, to a pH of 4Ø Similarly, the number of points of the total acid gives the consumption in ml to attain a pH of 8.2.
Preferably, the free acid is adjusted to within the range of 1.5 to 2.8 points and the total acid to within the range of 25 to 35 points.
Hydroxylamine may be used as the free base, as a hydroxylamine-abstracting compound, such as hydroxylamine complexes, and as ketoximes or aldoximes, or in the form of hydroxylammonium salts. If free hydroxylamine is added to the phosphating bath or to a phosphating bath concentrate, it will be present largely in the form of hydroxylammonium cations owing to the acid character of these solutions. If it is used in the form of a hydroxyl-ammonium salt, the sulfates and the phosphates are particularly suitable. In the case of the phosphates, the acid salts are preferred owing to the better solubility thereof. In order, on the one hand, to take account of economic aspects and, on the other hand, not to load the phosphating baths with excessive sulfate ions, a combination of free hydroxylamine and _5_ hydroxylammonium sulfate may be used with advantage. Hydroxylamine or derivatives thereof are added to the phosphating bath in quantities such that the calculated concentration of the free hydroxylamine is between about 0.1 and about 3 g/1, preferably between about 0.15 and about 1 g/1.
For the purpose of stating the phosphate concentration, the total phosphorus content of the phosphating bath is regarded as being present in the form of phosphate ions PO43-. In the calculation or determination of the concentration, no consideration is therefore given to the known fact that, at the acidic pH of the phosphanng baths, which is within the range of about 2.0 to about 3.6, only a very small proportion of the phosphate is actually present in the form of the triply negatively charged anions. At these pH values, it is rather to be expected that the phosphate exists chiefly as a singly negatively charged dihydrogen phosphate anion, together with undissociated phosphoric acid and with smaller quantities of doubly negatively charged hydrogen phosphate anions.
No nickel ions are added to the phosphating solution. In the ideal case, this solution is therefore completely free from nickel ions. However, if the phosphating unit is made of specialised steel containing nickel, or if the objects being phosphated are zinc-coated steel strips in which the zinc layer additionally contains nickel, the possibility that low concentrations of nickel ions may enter the solution as a result of attack by the phosphating solution cannot be ruled out. The phosphating solution should nevertheless contain not more than about 0.05 g/1 nickel ions and in particular not more than about 0.015 g/1 nickel ions.
In addition to the above-mentioned layer-forming cations, the phosphating solutions contain alkali metal canons and/or ammonium canons in order to adjust the value of the free acid to within the required range.
The presence of fluoride ions in the phosphating solution is not as a rule necessary for the phosphating of steel which is not zinc-coated. The phosphating of steel strips zinc-coated by hot dipping is, however, facilitated by fluoride ions, and even for the phosphating of electrolytically zinc-coated steel strip, the presence of fluoride ions may be advantageous in forming a uniform layer. Accordingly, another preferred. embodiment of the present invention involves using phosphating solutions which contain up to about 0.8 gll fluoride in free or in complexed form. For example, for phosphating electrolytically zinc-coated steel strip, the preferred fluoride contents are within the range of 0.0 to about 0.5 g/1 and in particular within the range of about 0.1 to 0.2 g/1.
The phosphating solutions are generally prepared in the manner known to those skilled in the art. Phosphate, for example, is introduced into the phosphating solutions in the form of phosphoric acid. The canons are added to the phosphoric acid in the form of acid-soluble compounds, such as the carbonates, the oxides or the hydroxides, so that the acid is partly neutralised. The further neutralisation to within the required pH range is carried out preferably by addition of sodium hydroxide or sodium carbonate. A suitable source of free fluoride anions is, for example, sodium fluoride or potassium fluoride.
Tetrafluoroborate or hexafluorosilicate, for example, may be used as complex fluorides.
A further aspect of the present invention relates to the use of the above phosphating process for the production of phosphate layers having a mass per unit area within the range of about 0.4 to about 2.0 g/m2 on both sides of steel strip or on both sides of steel strip coated on one or both sides with zinc or zinc alloy. Preferably, phosphate layers having a mass per unit area within the range of about 0.9 to about 1.8 g/m2 are produced. The mass per unit area ("layer weight"), as those skilled in the art know, may be determined by weighing a phosphated sample sheet, dissolving the phosphate layer in 5 % chromic acid solution and reweighing the sample sheet. This method is described, for example, in DIN
50942. For the production of phosphate layers having the required mass per unit area, it is preferable to use phosphating solutions wherein the free acid content is within the range of about 1.5 to about 2.8 points and the total acid content is within the range of about 25 to about 35 points. The temperature of the treatment solution is preferably within the range of about 50 to about 70°C
and in particular within the range of about 55 to about 65°C. Preferred treatment times are within the range of about 5 to about 10 seconds. The phosphating solution is preferably sprayed onto the metal surface and rinsed off with water after the required treatment period.
Before the application of the phosphating solution, the metal surface must be completely wettable with water. This is generally catered for in continuously operating production lines.
If the surface of the strip is however to be oiled, the oil should be removed with a suitable cleaner prior to phosphating. The processes for this are common in the industry. Before the phosphating, an activation is generally carried out using activating agents known in the art.
Generally, solutions or suspensions containing titanium phosphates and sodium phosphates are used. The activation is followed by the application of the present phosphating process, which is advantageously followed by a passivating secondary washing. Here an intermediate washing with water generally takes place between phosphating and passivating secondary washing. Treatment baths containing chromic acid are widely used for passivating secondary washing. On grounds of industrial safety and environmental protection and for reasons associated with toxic waste disposal, there is, however, a tendency to replace these chromium-containing passivating baths with chromium-free treatment baths. For this purpose, purely inorganic bath solutions, in particular those based on hexafluorozirconates, or even organic reactive bath solutions, for example, based on substituted poly(vinylphenols) are known. One may also use secondary washing solutions containing 0.001 to 10 g/1 of one or more of the following cations: lithium ions, copper ions, silver ions and/or bismuth ions.
The metal strips phosphated according to the present invention may be coated directly with an organic coating. Even in the initially uncoated state they may, however, after cutting, forming and joining, be assembled to form structural parts, such as car bodies or domestic appliances. The forming processes associated with this are facilitated by the phosphate layer.
If the corrosive stress on the finished structural parts is low as, for example, in the case of domestic appliances, the appliances assembled from the previously phosphated metal may be directly coated. For higher corrosion-prevention standards, such as are set, for example, in automobile construction, it is advantageous for another phosphating treatment to be carried out following the assembly of the car bodies.
The present invention is illustrated in more detail by the Examples below (Table 1).
Phosphating processes according to DE-A-39 20 296 were used as Comparison Examples.
Cleaned sample sheets were activated using an activating agent containing titanium phosphate and were phosphated by spraying. After an intermediate washing, they were post-treated using a post-passivating solution based on chromate and, after having been rinsed with deionised water, were given a grey coating using BASF KTL FT 85-7042. Table 2 shows ._ _g_ results of investigations into corrosion protection by the VDA alternating climate test 621-415 over 10 cycles, together with the stone impact test in accordance with VW
Standard P 1210 (K = 10: worst value, K = l: best value). The creepage of paint was measured along a scribe above the half scribe-width.
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Processes for phosphating surfaces of iron, steel, zinc and alloys thereof as well as of aluminum and alloys thereof are long-standing prior art. The phosphating of the above-mentioned surfaces serves to increase the adhesive strength of paint layers and to improve the protection from corrosion. The phosphating is carried out by dipping the metal surfaces into the phosphating solutions and by spraying the metal surfaces with the phosphating solutions. Combined processes are also known. Formed metal parts such as car bodies, may be phosphated, as may also metal strips on high-speed production lines. The present invention is concerned with such a phosphating of strip. Phosphating of strip differs from phosphating of parts in that, because of the high conveyor belt speeds, the phosphating, i.e.
the development of a closed metal phosphate layer, has to take place within a short period of time, for example, within about 2 to about 20 seconds.
Processes for phosphating metal strips, in particular steel strips which have been zinc-coated electrolytically or by hot dipping, are known in the art. For example, WO
describes a process for phosphating steel strip which has been zinc-coated electrolytically and/or by hot dipping; the process involves short-term treatment using acid phosphating solutions which, besides zinc ions and phosphate ions, contain manganese cations and nickel canons, as well as anions of oxygen-containing acids having an accelerating action. The latter term refers, in particular, to nitrate ions. DE-A-35 37 108 likewise describes a process for phosphating electrolytically zinc-coated steel strips by treatment using acid phosphanng solutions which, besides zinc ions, manganese ions and phosphate ions, contain other metal cations, such as nickel ions and/or anions of oxygen-containing acids having an accelerating action, in particular nitrate ions. Here, the zinc cation content is within the relatively low range of 0.1 to 0.8 gll.
. , CA 02303877 2000-03-17 w - _2_ DE-A-39 20 296 describes a process for the production of manganese- and magne~sium-containing zinc phosphate coatings on steel, zinc, aluminum and/or alloys thereof by spraying, spray-dipping and/or dipping using an aqueous solution which contains 0.2 to 1.0 g/1 zinc ions, 0.2 to 2.0 g/1 manganese ions, 0.5 to 2 gll magnesium ions, 10 to 20 g/1 phosphate ions, 0.2 to 10 g/1 nitrate ions and up to 1.0 g/1 fluoride ions.
This phosphating solution necessarily also contains 0.02 to 2 g/1 nitrite ions and/or 0.4 to 1 g/1 chlorate ions and/or 0.2 to 1 g/1 of an organic oxidising agent as an accelerator. The nitrate ions essential in this process may, however, in the case of zinc-coated steel surfaces, lead to loss of quality in the phosphate layer as a result of pinholing. In this connection, "pinholes" mean whitish corrosion points on the metal surface which have a crater-like appearance in rnicrographs.
From the phosphating times of more than 2 minutes mentioned in the Examples, it is obvious that this is not a process for the phosphating of strip.
The German Patent Application 196 39 596 attempts to provide a phosphating process which on the one hand solves the problem of pinholing and, on the other hand, also makes it possible, within the short phosphating times usual on production lines, to produce a closed crystalline phosphate layer on steel strips which are not zinc-coated and on the uncoated side of steel strips zinc-coated on one side. According to that document, the object is fulfilled by a process for the phosphating of steel strip, or of steel strip coated on one or both sides with zinc or zinc alloy, by spraying treatment or dipping treatment for a period of 2 to 15 seconds, using an acid phosphating solution containing zinc and manganese, at a temperature of 40 to 70°C, characterised in that the phosphating solution contains:
1 to 4 g/1 zinc ions;
0.8 to 3.5 g/1 manganese ions;
to 30 g/1 phosphate ions;
0.1 to 3 gll hydroxylamine in free, ionic or bound form;
and not more than 1 g/1 nitrate ions; a free acid content of 0.4 to 4 points;
and a total acid content of 12 to 50 points.
The crystalline zinc phosphate layers produced by this process already very adequately meet the standards being set nowadays for a zinc phosphating solution. This is particularly the case when this process is used in an embodiment in which either 0.8 to 3.5 g/1 nickel ions or - _3_ 0.002 to about 0.2 g/1 copper ions are simultaneously present. If the process is carried out without these rations, disadvantages with regard to paint adhesion and protection from corrosion have to be accepted.
For environmental and toxicological reasons, the use of nickel ions in phosphating baths is becoming increasingly less desirable nowadays. For the phosphating of parts, such as the phosphating of car bodies using phosphating times of more than about 2 minutes, phosphating processes have been employed recently in which, instead of the nickel ions, copper ions are used within the low concentration range given above. Processes which function without the use of the toxicologically- and environmentally-disadvantageous nickel ions are also being intensively sought for high-speed production lines with short phosphating times of about 2 to about 20 seconds. For production lines, however, the replacement of the nickel ions by low concentrations of copper ions is not a solution, because for the large area to be phosphated per unit time and with the small bath volume compared with that in the phosphating of parts, the copper content would have to be determined and controlled in time intervals of shorter than 1 minute. There are no suitable measuring and controlling techniques available.
Accordingly, an object of the present invention is to provide a phosphating process for high-speed production lines using phosphating times of about 2 to about 20 seconds, which, on the one hand, is operated free from nickel and which, on the other hand, results in phosphate layers whose quality as regards paint adhesion and protection against corrosion is equal to that of nickel-containing phosphate layers.
This object is fulfilled by a process for the phosphating of steel strip, or of steel strip coated on one or both sides with zinc or zinc alloy, by a spraying or dipping treatment for a period of 2 to 20 seconds, using an acid phosphating solution containing zinc, magnesium and manganese, at a temperature of 50 to 70°C, characterised in that the phosphating solution is free from nitrate ions and in that it contains:
1 to 4 g/1 zinc ions;
1.2 to 4 g/1 manganese ions;
-4_ 1 to 4 g/1 magnesium ions;
to 30 g/1 phosphate ions;
0.1 to 3 g/1 hydroxylamine in free, ionic or bound form;
a free acid content of 0.4 to 4 points; and a total acid content of 15 to 45 points.
In this process, the steel strips may be zinc-coated electrolytically or zinc-coated by hot dipping or coated with zinc alloy. "Coated with zinc alloy" means that the steel surface is coated with an alloy which in addition to zinc contains other metals, such as iron, nickel or aluminum. A zinc alloy coating using a zinc-iron alloy may be carried out, for example, by tempering a zinc-coated steel strip, as a result of which a diffusion of iron atoms into the zinc layer and vice versa takes place. The layer thicknesses of the zinc coating layers are generally within the range of about 5 to about 20 ~cm.
The terms "free acid" and "total acid" are generally known in the field of phosphating. They are determined by titrating a sample from the acid bath using 0.1 N sodium hydroxide solution and measuring the consumption of the latter. The consumption in ml is expressed as a number of points. In the present context, the number of points of the free acid means the consumption in ml of 0.1 N sodium hydroxide solution required to titrate 10 ml of bath solution, which has been diluted to 50 ml using deionised water, to a pH of 4Ø Similarly, the number of points of the total acid gives the consumption in ml to attain a pH of 8.2.
Preferably, the free acid is adjusted to within the range of 1.5 to 2.8 points and the total acid to within the range of 25 to 35 points.
Hydroxylamine may be used as the free base, as a hydroxylamine-abstracting compound, such as hydroxylamine complexes, and as ketoximes or aldoximes, or in the form of hydroxylammonium salts. If free hydroxylamine is added to the phosphating bath or to a phosphating bath concentrate, it will be present largely in the form of hydroxylammonium cations owing to the acid character of these solutions. If it is used in the form of a hydroxyl-ammonium salt, the sulfates and the phosphates are particularly suitable. In the case of the phosphates, the acid salts are preferred owing to the better solubility thereof. In order, on the one hand, to take account of economic aspects and, on the other hand, not to load the phosphating baths with excessive sulfate ions, a combination of free hydroxylamine and _5_ hydroxylammonium sulfate may be used with advantage. Hydroxylamine or derivatives thereof are added to the phosphating bath in quantities such that the calculated concentration of the free hydroxylamine is between about 0.1 and about 3 g/1, preferably between about 0.15 and about 1 g/1.
For the purpose of stating the phosphate concentration, the total phosphorus content of the phosphating bath is regarded as being present in the form of phosphate ions PO43-. In the calculation or determination of the concentration, no consideration is therefore given to the known fact that, at the acidic pH of the phosphanng baths, which is within the range of about 2.0 to about 3.6, only a very small proportion of the phosphate is actually present in the form of the triply negatively charged anions. At these pH values, it is rather to be expected that the phosphate exists chiefly as a singly negatively charged dihydrogen phosphate anion, together with undissociated phosphoric acid and with smaller quantities of doubly negatively charged hydrogen phosphate anions.
No nickel ions are added to the phosphating solution. In the ideal case, this solution is therefore completely free from nickel ions. However, if the phosphating unit is made of specialised steel containing nickel, or if the objects being phosphated are zinc-coated steel strips in which the zinc layer additionally contains nickel, the possibility that low concentrations of nickel ions may enter the solution as a result of attack by the phosphating solution cannot be ruled out. The phosphating solution should nevertheless contain not more than about 0.05 g/1 nickel ions and in particular not more than about 0.015 g/1 nickel ions.
In addition to the above-mentioned layer-forming cations, the phosphating solutions contain alkali metal canons and/or ammonium canons in order to adjust the value of the free acid to within the required range.
The presence of fluoride ions in the phosphating solution is not as a rule necessary for the phosphating of steel which is not zinc-coated. The phosphating of steel strips zinc-coated by hot dipping is, however, facilitated by fluoride ions, and even for the phosphating of electrolytically zinc-coated steel strip, the presence of fluoride ions may be advantageous in forming a uniform layer. Accordingly, another preferred. embodiment of the present invention involves using phosphating solutions which contain up to about 0.8 gll fluoride in free or in complexed form. For example, for phosphating electrolytically zinc-coated steel strip, the preferred fluoride contents are within the range of 0.0 to about 0.5 g/1 and in particular within the range of about 0.1 to 0.2 g/1.
The phosphating solutions are generally prepared in the manner known to those skilled in the art. Phosphate, for example, is introduced into the phosphating solutions in the form of phosphoric acid. The canons are added to the phosphoric acid in the form of acid-soluble compounds, such as the carbonates, the oxides or the hydroxides, so that the acid is partly neutralised. The further neutralisation to within the required pH range is carried out preferably by addition of sodium hydroxide or sodium carbonate. A suitable source of free fluoride anions is, for example, sodium fluoride or potassium fluoride.
Tetrafluoroborate or hexafluorosilicate, for example, may be used as complex fluorides.
A further aspect of the present invention relates to the use of the above phosphating process for the production of phosphate layers having a mass per unit area within the range of about 0.4 to about 2.0 g/m2 on both sides of steel strip or on both sides of steel strip coated on one or both sides with zinc or zinc alloy. Preferably, phosphate layers having a mass per unit area within the range of about 0.9 to about 1.8 g/m2 are produced. The mass per unit area ("layer weight"), as those skilled in the art know, may be determined by weighing a phosphated sample sheet, dissolving the phosphate layer in 5 % chromic acid solution and reweighing the sample sheet. This method is described, for example, in DIN
50942. For the production of phosphate layers having the required mass per unit area, it is preferable to use phosphating solutions wherein the free acid content is within the range of about 1.5 to about 2.8 points and the total acid content is within the range of about 25 to about 35 points. The temperature of the treatment solution is preferably within the range of about 50 to about 70°C
and in particular within the range of about 55 to about 65°C. Preferred treatment times are within the range of about 5 to about 10 seconds. The phosphating solution is preferably sprayed onto the metal surface and rinsed off with water after the required treatment period.
Before the application of the phosphating solution, the metal surface must be completely wettable with water. This is generally catered for in continuously operating production lines.
If the surface of the strip is however to be oiled, the oil should be removed with a suitable cleaner prior to phosphating. The processes for this are common in the industry. Before the phosphating, an activation is generally carried out using activating agents known in the art.
Generally, solutions or suspensions containing titanium phosphates and sodium phosphates are used. The activation is followed by the application of the present phosphating process, which is advantageously followed by a passivating secondary washing. Here an intermediate washing with water generally takes place between phosphating and passivating secondary washing. Treatment baths containing chromic acid are widely used for passivating secondary washing. On grounds of industrial safety and environmental protection and for reasons associated with toxic waste disposal, there is, however, a tendency to replace these chromium-containing passivating baths with chromium-free treatment baths. For this purpose, purely inorganic bath solutions, in particular those based on hexafluorozirconates, or even organic reactive bath solutions, for example, based on substituted poly(vinylphenols) are known. One may also use secondary washing solutions containing 0.001 to 10 g/1 of one or more of the following cations: lithium ions, copper ions, silver ions and/or bismuth ions.
The metal strips phosphated according to the present invention may be coated directly with an organic coating. Even in the initially uncoated state they may, however, after cutting, forming and joining, be assembled to form structural parts, such as car bodies or domestic appliances. The forming processes associated with this are facilitated by the phosphate layer.
If the corrosive stress on the finished structural parts is low as, for example, in the case of domestic appliances, the appliances assembled from the previously phosphated metal may be directly coated. For higher corrosion-prevention standards, such as are set, for example, in automobile construction, it is advantageous for another phosphating treatment to be carried out following the assembly of the car bodies.
The present invention is illustrated in more detail by the Examples below (Table 1).
Phosphating processes according to DE-A-39 20 296 were used as Comparison Examples.
Cleaned sample sheets were activated using an activating agent containing titanium phosphate and were phosphated by spraying. After an intermediate washing, they were post-treated using a post-passivating solution based on chromate and, after having been rinsed with deionised water, were given a grey coating using BASF KTL FT 85-7042. Table 2 shows ._ _g_ results of investigations into corrosion protection by the VDA alternating climate test 621-415 over 10 cycles, together with the stone impact test in accordance with VW
Standard P 1210 (K = 10: worst value, K = l: best value). The creepage of paint was measured along a scribe above the half scribe-width.
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Claims (5)
1. A process for phosphating steel strip or steel strip galvanized or alloy-galvanized on one or both sides by spraying for 2 to 20 seconds with or dipping in for the same period in an acidic zinc-, magnesium- and manganese-containing phosphating solution with a temperature in the range from 50 to 70°C, characterized in that the phosphating solution is free from nitrate and copper ions and contains no more than 0.05 g/l nickel ions and in that it contains 1 to 4 g/l zinc ions, 1.2 to 4 g/l manganese ions, 1 to 4 g/l magnesium ions, 10 to 30 g/l phosphate ions and 0.1 to 3 g/l hydroxylamine in free, ionic or bound form and has a free acid content of 0.4 to 4 points and a total acid content of 15 to 45 points.
2. A process as claimed in claim 1, characterized in that the phosphating solution contains up to 0.8 g/l fluoride in free or complexed form.
3. A process as claimed in one or both of claims 1 and 2, characterized in that the phosphating solution contains 0.15 to 1 g/l hydroxylamine in free, ionic or bound form.
4. A process as claimed in one or more of claims 1 to 3, characterized in that the phosphating solution has a free acid content of 1.5 to 2.8 points and a total acid content of 25 to 35 points.
5. A process as claimed in one or more of claims 1 to 4 for the production of phosphate coatings with a weight per unit area of 0.4 to 2.0 g/m2 on both sides of steel strip or steel strip galvanized or alloy-galvanized on one or both sides.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE1997140953 DE19740953A1 (en) | 1997-09-17 | 1997-09-17 | High speed spray or dip phosphating of steel strip |
| DE19740953.9 | 1997-09-17 | ||
| PCT/EP1998/005634 WO1999014397A1 (en) | 1997-09-17 | 1998-09-05 | Method for phosphatizing a steel strip |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2303877A1 true CA2303877A1 (en) | 1999-03-25 |
Family
ID=7842689
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002303877A Abandoned CA2303877A1 (en) | 1997-09-17 | 1998-09-05 | Method for phosphatizing a steel strip |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1019564A1 (en) |
| CA (1) | CA2303877A1 (en) |
| DE (1) | DE19740953A1 (en) |
| WO (1) | WO1999014397A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19808755A1 (en) | 1998-03-02 | 1999-09-09 | Henkel Kgaa | Layer weight control for strip phosphating |
| KR100496221B1 (en) | 1999-05-27 | 2005-06-21 | 신닛뽄세이테쯔 카부시키카이샤 | Phosphate-treated electrogalvanized steel sheet excellent in corrosion resistance and coating suitability |
| TW475002B (en) | 1999-07-08 | 2002-02-01 | Kawasaki Steel Co | Perforative corrosion resistant galvanized steel sheet |
| CN1244715C (en) * | 1999-08-09 | 2006-03-08 | 新日本制铁株式会社 | Zinc-based metal plated steel sheet treated with phosphate being excellent in formability and method for production thereof |
| DE10110833B4 (en) * | 2001-03-06 | 2005-03-24 | Chemetall Gmbh | Process for applying a phosphate coating and use of the thus phosphated metal parts |
| DE102006035779B4 (en) * | 2006-08-01 | 2017-01-12 | Schaeffler Technologies AG & Co. KG | Process for producing a running disk of a belt drive |
| WO2013160566A1 (en) | 2012-04-25 | 2013-10-31 | Arcelormittal Investigacion Y Desarrollo, S.L. | Method for producing a metal sheet having oiled zn-al-mg coatings, and corresponding metal sheet |
| DE102019134298A1 (en) | 2019-12-13 | 2021-06-17 | Thyssenkrupp Steel Europe Ag | Method for producing a flat steel product with a metallic protective layer based on zinc and a phosphate layer produced on a surface of the metallic protective layer and such a flat steel product |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3920296A1 (en) * | 1989-06-21 | 1991-01-10 | Henkel Kgaa | METHOD FOR PRODUCING ZINC PHOSPHATE CONTAINING MANGANE AND MAGNESIUM |
| DE4013483A1 (en) * | 1990-04-27 | 1991-10-31 | Metallgesellschaft Ag | METHOD FOR PHOSPHATING METAL SURFACES |
| US5328526A (en) * | 1992-04-03 | 1994-07-12 | Nippon Paint Co., Ltd. | Method for zinc-phosphating metal surface |
| JPH05287549A (en) * | 1992-04-03 | 1993-11-02 | Nippon Paint Co Ltd | Zinc phosphate treatment on metallic surface for cation type electrodeposition coating |
| CA2150545A1 (en) * | 1992-12-22 | 1994-07-07 | Robert W. Miller | Substantially nickel-free phosphate conversion coating composition and process |
| DE4341041A1 (en) * | 1993-12-02 | 1995-06-08 | Henkel Kgaa | Phosphating solns contg hydroxylamine and/or nitrobenzene sulphonate |
| DE19538778A1 (en) * | 1995-10-18 | 1997-04-24 | Henkel Kgaa | Layer weight control in hydroxylamine-accelerated phosphating systems |
| DE19621184A1 (en) * | 1996-05-28 | 1997-12-04 | Henkel Kgaa | Zinc phosphating with integrated post-passivation |
| DE19639596A1 (en) * | 1996-09-26 | 1998-04-02 | Henkel Kgaa | Process for phosphating steel strips |
-
1997
- 1997-09-17 DE DE1997140953 patent/DE19740953A1/en not_active Withdrawn
-
1998
- 1998-09-05 CA CA002303877A patent/CA2303877A1/en not_active Abandoned
- 1998-09-05 EP EP98949988A patent/EP1019564A1/en not_active Ceased
- 1998-09-05 WO PCT/EP1998/005634 patent/WO1999014397A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP1019564A1 (en) | 2000-07-19 |
| WO1999014397A1 (en) | 1999-03-25 |
| DE19740953A1 (en) | 1999-03-18 |
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