US3837928A - Conversion coating on metal - Google Patents

Conversion coating on metal Download PDF

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Publication number
US3837928A
US3837928A US00288338A US28833872A US3837928A US 3837928 A US3837928 A US 3837928A US 00288338 A US00288338 A US 00288338A US 28833872 A US28833872 A US 28833872A US 3837928 A US3837928 A US 3837928A
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United States
Prior art keywords
phosphating
coating
metal
liquid
zinc
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Expired - Lifetime
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US00288338A
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English (en)
Inventor
A Morrison
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Dulux Australia Ltd
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Dulux Australia Ltd
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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
    • C23C22/07—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
    • C23C22/12—Orthophosphates containing zinc cations

Definitions

  • ABSTRACT [30] Foreign Application Priority Data Oct 5 1971 Australia 6526/71
  • Int Cl 7/10 lutIon is Improved by the addItIon thereto of a poly-
  • Fieid I6 15 Z meric additive which is an addition copolymer of an 4 unsaturated carboxylic acid and a selected ethylenic monomer.
  • This invention relates to an improved process for the formation of crystalline zinc phosphate coatings on steel and zinc surfaces and to improved zinc phosphating solutions for use therein.
  • Crystalline zinc phosphate coatings play an important industrial role in up-grading the corrosion resistance and paint adherence properties of ferrous and zinciferous (especially galvanised") surfaces.
  • These coatings which are applied to the metal by subjecting it to the action of acidic aqueous solutions comprising zinc orthophosphates, are believed to consist essentially of interlocking crystals of insoluble tertiary zinc phosphates, which may contain minor amounts of phosphates of other metals, e.g., iron, calcium and manganese and are known in the art by the trivial name conversion coatings.”
  • the nature of the coating deposited from a particular phosphating solution appears to depend, to a substantial degree, on the metallurgical history of the metal to be coated and its physical pretreatment prior to phosphating. For example, if a conversion coating is applied to a cold-rolled steel surface (pre-cleaned with, for example, trichlorethylene) the coating is usually relatively fine-grained and uniform. If, however, the same surface is precleaned with an alkaline aqueous cleaning bath, which for practical reasons is widely used industrially, the coating deposited thereon from the same phosphating solution is commonly much thicker and comprises relatively coarse crystals. These crystals lead to high coating weights and a fluffy deposit, which often exhibits a pronounced dendritic structure. The films of high coating weight are economically undesirable and show inferior mechanical and corrosioninhibiting properties. Consequently there has arisen a technical and economic need to develop processes which will provide a dense conversion coating of low coating weight and can tolerate the customary cleaning processes of the industry.
  • a phosphating solution to produce dense, fine-grained conversion coatings depends on there being present at the surface of the metal to be treated a substantial number of nucleating sites to initiate rapid crystallisation of the phosphate crystals deposited thereon. Suitable sites are said to be, for example, sharp metal edges, points, heterogeneities at crystal junctions and breaks in the metal crystal texture. It is suggested that the effect of alkali cleaning (and of some acidic media) is to inactivate these sites and hence to lead to the growth of coarser phosphate crystals due to the diminished number of available nuclei. The rate of formation of the coating is also correspondingly reduced.
  • the particular polymeric additives to be used in this invention are addition copolymers of monomer (a) and monomer (b) in essentially equimolar ratios wherein monomer (a) is at, least one unsaturated polycarboxylic acid or acid anhydride selected from the group consisting of maleic acid, maleic anhydride, fumaric acid and citraconic acid and monomer (b) is at least one unsaturated monomer selected from the group consisting of ethylene, methyl vinyl ether, ethyl vinyl ether and cyclohexyl vinyl ether.
  • the copolymer must be soluble in the phosphating liquid at the concentration required, which is typically 2 gm per litre maximum.
  • the polymeric additive may be prepared by wellknown convention addition polymerisation techniques. We have found that for ease of processing, copolymers of maleic anhydride are to be desired and hence these are our preferred compositions. These copolymers convert readily, at least in part, to the maleic acid analogues in contact with water. Although the primary characteristic of the polymeric additives we disclose is their molar composition, the solubility requirement imposes certain predictible limitations on their overall nature. For example, it is known that addition polymers of unsaturated monomers are commonly substantially straight-chain polymers in which the molecular weight of the polymer varies with the length of its carboncarbon bonded backbone chain. If the molecular weight of the polymer is too high, it will be insoluble in the phosphating liquid.
  • Polymers of this type are usually prepared by the free-radical initiated polymerisation of the constituent unsaturated monomers and it is known that some degree of branching or even crosslinking of adjacent chains can take place during the polymerisation. This is not objectionable for the performance of the present invention provided the copolymer so-produced is soluble at the required concentration in the phosphating liquid.
  • the minimum effective concentration of polymer in the phosphating liquid is of the order of 0.1 gm per litre, the concentration being adjusted to give a deposited phosphate crystal of the required size and a film of the required coating weight.
  • the most useful range of concentration of polymer in the phosphating liquid is from about 0.25 to 0.5 gm per litre.
  • the use of the copolymers we have described to control deposited conversion coating weights imposes no unusual requirements on the composition of the actual phosphating liquid. That is, the liquid of the invention is arrived at by simply dissolving a polymer as hereinabove defined in a conventional zinc phosphating liquid at the required concentration and then using the liquid to deposit a conversion coating on ferrous or zinciferous metal in the known manner.
  • the non-gassing phosphating liquids to which this invention relates consist essentially of solutions in water of zinc orthophosphates and a source of hydrogen ions, commonly phosphoric acid.
  • the liquids as used commercially comprise in addition the appropriate strong oxidising agents, e.gl sodium nitrite and hydrogen peroxide, and are well known and recognisable in the art by terms such as chlorate-nitrite type, which refer to auxiliary features of their mode of functioning.
  • chlorate-nitrite type which refer to auxiliary features of their mode of functioning.
  • the present invention provided they are essentially acidic zinc phosphating liquids with a pH of about 2 3.5 which deposit tertiary phosphates on the metal to which they are applied, without a significant evolution of hydrogen. we draw no distinction be tween them.
  • the treatment of ferrous or zinciferous metals to produce a zinc phosphate coating thereon most commonly involves the following sequence of steps; alkali cleaning, water rinse, activating and grain-refining rinse, water rinse, zinc phosphating, water rinse and final passivating rinse.
  • the metals treated were cold rolled steel strip and a similar metal which had been hot dip galvanised.
  • the grade used was known as minimised spangle but not passivated.”
  • the control phosphating liquid was a conventional aqueous zinc phosphating solution and while its composition is not critical within the permitted limitations known to the art, the actual liquid used was prepared according to Formula No. 2 of US. Pat. No. 3,33 3,988.
  • the phosphating liquid according to the invention (hereinunder referred to as the test' liquid) consisted of the above liquid in which was dissolved 0.25 gm per litre of a copolymer of methyl vinyl ether and maleic anhydride in essentially equimolar proportions.
  • the copolymer had a viscosity of 200 centipoise at 25C when tested as a 4 percent by weight solution in water adjusted to pH 9 with sodium hydroxide.
  • the testing procedure used was to clean the test panels by immersion in an aqueous alkaline cleaning bath of pH about 9, wash thoroughly with water and then treat the cleaned metal surface by spraying it with phosphating liquid at a temperature of 54C for one minute. The panels were then given a further water wash and the coating weight determined by the method of Australian Standard No. SK-9 Part VI i968, Appendix A2 in which the coating is stripped from a weighed panel using chromic acid under standard conditions and the panel re-weighed.
  • the conversion coatings deposited from the test phosphating liquid were visually denser and more finely crystalline than those from the control phosphating liquid and as the above data show their coating weights were substantially lower.
  • a conventional zinc phosphating liquid as described in example l were modified by adding to each of them one of the following water-soluble materials at a concentration of 0.25 gm per litre; poly (vinyl alcohol), hydroxyethyl cellulose, poly (vinyl pyrrolidone), sodium poly (acrylate), carboxymethyl cellulose, poly(styrene/maleic acid) and sucrose.
  • the sodium poly (acrylate) carboxymethyl cellulose and the poly (styrene/maleic anhydride) were insoluble in the liquid and these mixtures were not tested further.
  • EXAMPLE 3 Additive Nature 1 Maleic anhydride/ethylene copolymer (approx. l:l molar ratios) of essentially linear structure and viscosity of 2.0 centipoise as a 2% by wt. solution in water.
  • the phosphating liquids so-prepared were tested on cold rolled steel plate by the general method described in example 1 save that instead of spraying the phosphating liquid onto the panels, they were immersed in a bath of the liquid held at 667 1C for 3 minutes.
  • Thecoating weight in the absence of any additive was approximately 600 mg per sq. ft. of treated metal serface.
  • Liquids comprising additives Nos. 1-4 and 7, which are compositions according to the invention, effectively reduced the coating weight at concentrations as low as 0.5 gm per litre.
  • the coatings so-produced were dense, uniform and of very fine crystal structure.
  • additives Nos. 5, 6, 8 and 9, which are not compositions according to the invention were spot-checked at an intermediate concentration range in the above series.
  • Additives 5 and 6 had no significant effect on the nature of the coating at a concentration of 0.25 gm per litre and while additives 8 and 9 did have a measurable effect at a concentration of 0.5 gm per litre, their usefulness was considerably less than that of the compositions according to the invention and it was even less than that of additives 1-4 when they were used at one tenth of that concentration.
  • a further feature of practical significance in using these compositions can be seen by reference to the test results using additives 1-3.
  • the three additives are basically the same materials but of ascending molecular weights, as indicated by their solution viscosities.
  • the data in the table show that at least for this particular series of resins there is a drop in coating weight with increasing molecular weight of the additive.
  • the results at a concentration of 2.0 gm per litre show, while there may be some advantage (in terms of materials consumed for a given coating weight) if the molecular weight of the resin is too high, an excessive concentration in the phosphating liquid can lead to complete failure to deposit a phosphate coating on the metal.
  • the obvious remedy is to use less additive or to select a lower molecular weight analogue.

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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)
  • Application Of Or Painting With Fluid Materials (AREA)
  • Luminescent Compositions (AREA)
  • Laminated Bodies (AREA)
US00288338A 1971-10-05 1972-09-12 Conversion coating on metal Expired - Lifetime US3837928A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AUPA652671 1971-10-05

Publications (1)

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US (1) US3837928A (enrdf_load_stackoverflow)
JP (1) JPS5217504B2 (enrdf_load_stackoverflow)
AR (1) AR193760A1 (enrdf_load_stackoverflow)
BE (1) BE789631A (enrdf_load_stackoverflow)
BR (1) BR7206935D0 (enrdf_load_stackoverflow)
CA (1) CA963778A (enrdf_load_stackoverflow)
DE (1) DE2248867A1 (enrdf_load_stackoverflow)
FR (1) FR2156045B1 (enrdf_load_stackoverflow)
GB (1) GB1410176A (enrdf_load_stackoverflow)
IE (1) IE36693B1 (enrdf_load_stackoverflow)
IT (1) IT967512B (enrdf_load_stackoverflow)
NL (1) NL7213483A (enrdf_load_stackoverflow)
ZA (1) ZA726226B (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4705703A (en) * 1986-06-30 1987-11-10 Nalco Chemical Company Method of preventing corrosion of uncoated aluminum sheet or beverage cans in a brewery pasteurizer water system
WO1997017480A1 (en) * 1995-11-07 1997-05-15 Henkel Corporation Finely crystalline and/or fast phosphate conversion coating composition and process
US6730409B1 (en) * 1999-05-27 2004-05-04 International Business Machines Corporation Promoting adhesion between a polymer and a metallic substrate
US6743302B2 (en) 2000-01-28 2004-06-01 Henkel Corporation Dry-in-place zinc phosphating compositions including adhesion-promoting polymers
US20190105686A1 (en) * 2017-10-05 2019-04-11 Héctor Delgado Morales Process for the polymer coating of non-ferrous metal surfaces
CN115522191A (zh) * 2022-10-11 2022-12-27 山东商业职业技术学院 一种用于金属表面处理的磷化液及其制备方法与应用

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1549856A (en) * 1975-06-20 1979-08-08 Ici Ltd Phosphating process
DE3418359A1 (de) * 1983-05-23 1984-11-29 Shipley Co., Inc., Newton, Mass. Loesung zur bildung schwarzer oxidschichten und verfahren zur herstellung von laminaten

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3728163A (en) * 1970-05-25 1973-04-17 Balm Paints Ltd Alkaline liquids for cleaning metals

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3728163A (en) * 1970-05-25 1973-04-17 Balm Paints Ltd Alkaline liquids for cleaning metals

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4705703A (en) * 1986-06-30 1987-11-10 Nalco Chemical Company Method of preventing corrosion of uncoated aluminum sheet or beverage cans in a brewery pasteurizer water system
WO1997017480A1 (en) * 1995-11-07 1997-05-15 Henkel Corporation Finely crystalline and/or fast phosphate conversion coating composition and process
US6730409B1 (en) * 1999-05-27 2004-05-04 International Business Machines Corporation Promoting adhesion between a polymer and a metallic substrate
US20040166438A1 (en) * 1999-05-27 2004-08-26 International Business Machines Corporation Promoting adhesion between a polymer and a metallic substrate
US6908684B2 (en) 1999-05-27 2005-06-21 International Business Machines Corporation Promoting adhesion between a polymer and a metallic substrate
US6743302B2 (en) 2000-01-28 2004-06-01 Henkel Corporation Dry-in-place zinc phosphating compositions including adhesion-promoting polymers
US20190105686A1 (en) * 2017-10-05 2019-04-11 Héctor Delgado Morales Process for the polymer coating of non-ferrous metal surfaces
CN115522191A (zh) * 2022-10-11 2022-12-27 山东商业职业技术学院 一种用于金属表面处理的磷化液及其制备方法与应用
CN115522191B (zh) * 2022-10-11 2024-06-07 山东商业职业技术学院 一种用于金属表面处理的磷化液及其制备方法与应用

Also Published As

Publication number Publication date
CA963778A (en) 1975-03-04
DE2248867A1 (de) 1973-04-12
IE36693B1 (en) 1977-02-02
FR2156045A1 (enrdf_load_stackoverflow) 1973-05-25
BE789631A (fr) 1973-02-01
JPS4872045A (enrdf_load_stackoverflow) 1973-09-28
NL7213483A (enrdf_load_stackoverflow) 1973-04-09
JPS5217504B2 (enrdf_load_stackoverflow) 1977-05-16
ZA726226B (en) 1973-05-30
AR193760A1 (es) 1973-05-22
IT967512B (it) 1974-03-11
IE36693L (en) 1973-04-05
GB1410176A (en) 1975-10-15
BR7206935D0 (pt) 1973-08-23
FR2156045B1 (enrdf_load_stackoverflow) 1976-10-29

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