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
  • C23C22/16—Orthophosphates containing zinc cations containing also peroxy-compounds

Definitions

• the present invention relates to phosphating solutions and to the use of these solutions in a process of producing improved phosphate coatings on metallic surfaces.
• a crystalline coating of an inorganic phosphate may be produced on metallic surfaces, particularly ferrous, zinciferous and aluminum surfaces. Such a coating is useful in that a subsequently applied paint film has good adhesion to the metal surface and the corrosion resistance of the painted metal surface is improved.
• the most useful phosphate coatings are normally applied to the metal surface by treatment with an acidic phosphating solution which contains an inorganic phosphate, for example zinc or manganese phosphate and it is common practice to accelerate the coating reaction by including a suitable oxidant in the phosphating solution.
• Oxidants conventionally employed as accelerators are, for example, sodium nitrite (used either alone or in conjunction with, for example, a chlorate or a nitrate), and hydrogen peroxide.
• the crystalline coating is fine and hard in texture.
• the known phosphating solutions with or without those oxidants known to be useful as accelerators and optionally combined with other known phosphating additives it has not been possible to obtain the most desirable fine and hard coatings.
• a conventional phosphating accelerator we mean an oxidant which will by itself effectively accelerate the deposition of a phosphate coating under the normal phosphating conditions, and these accelerators are well known to those skilled in the art.
• oxidants and the preferred conventional accelerators are the alkali metal nitrites and ammonium nitrite and hydrogen peroxide. The nitrites are particularly preferred since they lend themselves to good control of the coating reaction.
• Other less effective oxidants include the alkali metal nitrates and chlorates.
• lt is also known to use these accelerators in combination with other accelerators, for example, the nitrites may be used in combination with the nitrates or chlorates or certain accelerators may be used in combination with certain other additives which may serve to improve the performance of the phosphating process, for example glycerophosphate and fluoride ions. These combinations may be present in the new phosphating solutions.
• the conventional accelerators are to be distinguished from those salts comprising an acid radical derived from peroxy disulphuric acid, peroxy diphosphoric acid, peroxy diboric acid and peroxy dicarbonic acid which are known by those skilled in the art to be ineffective as phosphating accelerators by themselves under the normal phosphating conditions, and more particularly they are quite ineffective when a phosphate coating is to be obtained on a metallic surface in a short space of time by spraying the surface with phosphating solution, e.g., at temperatures in the region of l30-l40 F. for 60 seconds.
• the peroxy acid radicals which are present in the improved phosphating solutions are distinguished from the conventional phosphating accelerators in that they contain the grouping X- O-O-X in which X represents an S, P, C or B atom covalently bonded to other atoms.
• X represents an S, P, C or B atom covalently bonded to other atoms.
• the present invention also provides a process of producing a phosphate coating on a ferrous, zinciferous or aluminum surface in which the surface is treated, preferably by spraying, with an acidic phosphating solution which contains zinc phosphate, an acid radical derived from peroxy disulphuric acid, peroxy diphosphoric acid, peroxy diboric acid or peroxy dicarbonic acid and a conventional accelerator as herein defined for such a period of time and at such a temperature as to produce a phosphate coating.
• an acidic phosphating solution which contains zinc phosphate, an acid radical derived from peroxy disulphuric acid, peroxy diphosphoric acid, peroxy diboric acid or peroxy dicarbonic acid and a conventional accelerator as herein defined for such a period of time and at such a temperature as to produce a phosphate coating.
• the characteristics of a phosphate coating are commonly determined by visual inspection of the coating and of a subsequently applied paint film, and by a simple scratching test, for example with a fingernail. We find that the phosphate coatings obtained using the improved phosphating solutions are more resistant to scratching, e.g., they are less readily marked than are the prior phosphate coatings by a fingernail drawn across the surface, and they yield a smoother and more glossy surface when subsequently coated with paint.
• the hardness, tightness and uniformity of the coatings produced when using the present solutions are particularly valuable when an article is to be painted subsequently by electrodeposition.
• a paint applied by electrodeposition is particularly liable to reflect and even magnify any unevenness of the substrate to which it is applied and the character of the coatings obtained by using the present solutions ensures that the optimum appearance for a given substrate can be achieved.
• weight of phosphate coating deposited on a metallic surface can be readily regulated by the addition of peroxy acid radical and may be progressively decreased depending upon the proportion of peroxy acid radical present.
• the acid radical of the peroxy acids is preferably introduced into the phosphating solution as the alkali metal or ammonium salt of the peroxy acid.
• the acid radical of the peroxy acids is preferably introduced into the phosphating solution as the alkali metal or ammonium salt of the peroxy acid.
• Addition of the peroxy acid salt to the phosphating solution may take place at any suitable time, for example just prior to use in the phosphating process and at suitable times thereafter to maintain the concentration approximately constant and to maintain the desired coating weight on the metal surface.
• the acidity of the phosphating solutions and their content of zinc and phosphate ions are based on the conventional phosphating solutions containing zinc phosphate and are well known to those skilled in the art.
• the proportion of conventional accelerator which is desirably present in the phosphating solution will dependupon the particular accelerator chosen and upon the coating characteristics required. In general this will be known to those skilled in the art but preferably, and particularly in spray application there is employed between 0.005 percent and 0.1 percent of hydrogen peroxide (100 vol.) or nitrite by weight based on the total weight of the solution.
• EXAMPLE 1 An acidic phosphating solution based on zinc phosphate and phosphoric acid was prepared containing 0.2 percent zinc and 0.5 percent phosphate based on the weight of the solution. The solution was divided into four portions (a), (b), (c) and (d) to which were added sodium nitrite and/or ammonium persulphate according to Table 1 below.
• the panels were rinsed with water and dried in a blast of warm air.
• the nature of the resulting phosphate coating is described in Table 1.
• EXAMPLE 2 An acidic aqueous phosphating solution based on zinc phosphate, phosphoric acid and zinc nitrate was prepared containing 0.16 percent zinc, 0.7 percent phosphate and 0.5
• the solution was divided into four portions (a), (b), (c) and (d) to which were added sodium nitrite and/or ammonium persulphate according to the Table 2 .below.
• Example 1 Each of the four portions of phosphating solution were applied to a separate steel panel (cleaned as in Example 1) according to the method of Example 1. The nature of the of the When the panels were subsequently coated by electrodeposition as in Example 1 and stoved, panel (d) showed the best final appearance.
• An acidic aqueous phosphating solution based on zinc phosphate and phosphoric acid was prepared containing 0.2 percent zinc and 1.5 percent phosphate based on the weight of the solution.
• the solution was divided into four portions (a), (b). (c) and (d) to which were added hydrogen peroxide and/or ammonium rsul hate according to Table 3 below.
• An acidic phosphating solution which contains zinc phosphate, an acid radical having the grouping X-O-O-X where X is selected from'the group consisting of S, P, C or B and derived from peroxy disulphuric acid, peroxy diphosphoric acid, peroxy diboric acid or peroxy dicarbonic acid and between 0.005 percent and 0.1 percent, based on the total weight of solution, of a phosphating accelerator selected from the group consisting of alkali metal nitrite, ammonium nitrite and hydrogen peroxide.
• An acidic phosphating solution according to claim 1 which contains an acid radical derived from peroxy disulphuric acid or peroxy diphosphoric acid.
• An acidic phosphating solution according to claim I wherein there is present 0.01 percent to 1.0 percent of peroxy acid radical based on the weight of the phosphating solution.
• a process of forming a phosphate coating on a ferrous, zinciferous or aluminum surface which consists in treating the surface with a phosphating solution according to claim i for such a period of time and at such a temperature as to produce a coating.

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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)
• Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
• Dental Preparations (AREA)

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Citations (6)

• 1968
  • 1968-08-16 GB GB39268/68A patent/GB1272772A/en not_active Expired
• 1969
  • 1969-08-06 IE IE1104/69A patent/IE33514B1/xx unknown
  • 1969-08-08 ZA ZA695701A patent/ZA695701B/xx unknown
  • 1969-08-08 US US848699A patent/US3645806A/en not_active Expired - Lifetime
  • 1969-08-08 CA CA059104A patent/CA924223A/en not_active Expired
  • 1969-08-14 DE DE19691941489 patent/DE1941489B2/de not_active Ceased
  • 1969-08-14 BE BE737556D patent/BE737556A/xx unknown
  • 1969-08-14 FR FR6928133A patent/FR2016961A1/fr not_active Withdrawn
  • 1969-08-15 SE SE6911404A patent/SE349065C/xx unknown
  • 1969-08-16 PL PL1969135402A patent/PL80298B1/pl unknown
  • 1969-08-18 ES ES370579A patent/ES370579A1/es not_active Expired
  • 1969-08-18 CH CH1250369A patent/CH517834A/de not_active IP Right Cessation
  • 1969-08-18 NL NL6912524A patent/NL6912524A/xx unknown

Patent Citations (6)

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