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
  • C23C22/34—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
  • C23C22/37—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 hexavalent chromium compounds
  • C23C22/38—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 hexavalent chromium compounds containing also phosphates

Definitions

• This invention relates to the art of producing chemically formed corrosion resistant and paint-base coatings on metallic surfaces from chromate-fiuoride type coating solutions.
• chromate-fluoride type coating solutions which are multi-purpose coating solutions effective in forming entirely satisfactory corrosion resistant and paint-base coatings on widely different metallic surfaces, particularly on surfaces of either aluminum or iron and alloys of each.
• Another important object of the invention is to provide an improved method of treating widely different metallic surfaces to form thereon corrosion resistant and paintbase coatings of increased coating weight.
• condensed phosphate compounds when incorporated in well defined proportions in chromate-fiuoride coating solutions of the type to be described, unexpectedly broaden the range as to the metallic surfaces on which satisfactory corrosion resistant and paintbase coatings can be formed.
• the improved chromatefluoride coating solutions which constitute the subject matter of the present invention contain one or more condensed phosphate compounds and have been found to produce coatings on surfaces of iron and iron alloys in addition to those of aluminum, and even on surfaces of magnesium and magnesium alloys which are commercially acceptable from the standpoint of bare corrosion resistance and receptivity for paint, lacquer, enamel, varnishes and other siccative coatings. It has also been found that the coatings produced from the condensed phosphate compound-containing chromate-fiuoride solutions form particularly good base coatings for various adhesives commercially used for applying plastic sheet film to metal-surfaces.
• condensed phosphate compounds which are additives for the chromate-fiuoride type coating solutions in accordance with the present invention are sometimes referred to as complex or sequestering phosphate compounds but the term condensed phosphate compounds is the one used herein.
• the condensed phosphate compounds that have been found to be useful are those which yield the condensed phosphate radical in solution and which are the alkali metal condensed phosphate salts which term includes the ammonium salts and the condensed phosphoric acids from which such salts are derived. From a standpoint of availability and economy the alkali metal condensed phosphate salts are preferably used.
• condensed phosphoric acids are formed 4 by condensation of phosphoric acid with elimination of the water and the term condensed phosphate compound includes only thosecondensed phosphates of the type just mentioned in which the mole ratio of cationic oxides to anionic oxides is greater than 0 and less than 3. All phosphate compounds can be represented stoichiometrically as combination of oxides.
• the mole ratio of cationic oxides (such as Na O and including H O of composition) to anionic oxides (P 0 defines any given phosphate compound, and as previously indicated, this ratio must be greater than 0 and less than 3 for the condensed phosphate compound usable for the purposes of the present invention.
• the condensed phosphate compounds of the type with which the present invention is concerned generally fall within certain fairly well recognized groups, examples of which in the order from the lower to the higher condensation product are: the ultraphosphates; metaphosphates; polyphosphatcs; and the pyrophosphates.
• Orthophosphate compounds are those in which the mole ratio of cationic oxides to the anionic oxides is 3.
• Condensed phosphate compounds derived from phosphoric acids which in turn are formed by the elimination of approximtely one molecule of water from one molecule of orthophosphoric acid are the metaphosphates and the mole ratio for the metaphosphates is l.
• Condensed phosphate compounds in which the mole ratio of cationic oxides to anionic oxides is less than 1 and greater than 0 are the ultraphosphates.
• Condensed phosphate compounds derived from phosphoric acids which in turn are formed by the elimination of approximately one molecule of water from two molecules of orthophosphoric acid are the pyrophosphates and the mole ratio of cationic to anionic oxides for the pyrophosphates is 2.
• Condensed phosphates in which the mole ratio of cationic oxides to anionic oxides is less than 2 and greater than 1 are the polyphosphates.
• Condensed phosphates in which the mole ratio is less than 3 and greater than 2 are obtainable but do not fall within any recognized group.
• the condensed phosphate radicals are preferably introduced through the alkali metal condensed phosphate compounds.
• specific examples of condensed phosphate compounds that may be employed in the practice of the invention are tetra-sodium pyrophosphate, disodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate, and the respective condensed phosphoric acids from which these salts are derived.
• Potassium and ammonium condensed phosphate salts cor responding to the sodium salts enumerated may likewise be used.
• the amount of condensed phosphate compound as defined above that is added to the chromate-fiuoride coatmg solutions of the type to be described must be controlled within certain critical proportions to effectively coat both surfaces of iron and aluminum and alloys of each.
• concentration of the different ingredients throughout the specification and in the appended claims is expressed in percent w./v., which refers to weight per unit volume, i. e., the specific gravity of the solutions is taken to be 1.0.
• condensed phosphate compounds their concentration is conveniently expressed as percent by weight based on the condensed phosphate of sodium compound
• the differ- 3 ent condensed-phosphateof-sodium compounds are substantially equally effective onastraight weightbasis and where condensed phosphate compounds other than the sodium salt are employed, the amount of these other compounds is adjusted to-produce'the same effect as the amount of condensed phosphate'of sodium compound within the critical ranges hereinafter-set forth.
• the concentration of the condensed"phosphate compound-maybe .as low as that which produces a-beneficial effect "on resistance to corrosion and paint-base qualities-butE-from a commercial standpoint it-has been -found that very -little ;-benefit is produced when the concentration-ofthecondensed phosphate compound-is -below about 0.-l-% based on condensed phosphate of sodium-compound.
• the con-densed phosphate-compound is added in amountsto produce the same effect as that observed-fromsolutions containing about 0.05% by weight-of:condensedphosphate ofsodium compound.
• the coatings on iron and aluminum surfaces range from fair to excellent as faras bare'corrosion resistan'ce and receptivity to siccative coatings are-concerned.
• bare corrosion resistance is meant the .resistance of the coated metalvsurfacesafter treatment in the working baths and does not-refer to -bare, untreated metal surfaces.
• lnmany instances'metal surfaces are employed in the condition in whichthey areremoved from the working baths of the-present .inventionwithout-the sub sequent application of .lac quers paints, or other additional protective coatings.
• the 'chromate-fluoridetypesolutions that are improved by the addition in the-proporticns previouslyset forth of one'-or:more of' -the condensed'phosphate compounds are s aqueous .acidic solutions which contain -hexavalent chromium and the fluoride radical and preferably the fluoborate radical.
• T The concentration -'of "hexavalent chromium in 'the' coatingbaths constitutingthe subject matter of the present invention can-vary-from about 0.08% to about2;5% Ci-O "Preferably-the concentration of hexavalent chromiumis maintained between' 0.3% and 0.6%, .CrO .by weight.
• 'Chromic acid or alkali metal dichromateszincluding ammonium 'dichromate or dichromates. ofzzinc, calcium, cadmium or aluminum can be used to introduce hexavalentchromium.
• concentration .of the fluoride ion can vary substantially andyet produce satisfactoryresults.
• the fluoride whichis-prescut in the solution may be .-presentin the form of 'free fluoride or .as. a complex fluoride of one or more-of the metallic ions which are also present in thesolution.
• the operation-ofthese solutions itis customary.to .analyze the solution for total fluoride and for satisfactory operation, :the total flufiride content may vary between about 0.01% and about 2%,
• the fluoride ion can be introduced into the coating solution by the addition thereto of soluble, simple or complex fluorides such as hydrofluoric acid, hydrofluosilicic acid and the salts thereof, sodium bifiuoride, or the combination of sulfuric acid and sodium fluoride in proportions to produce the desired concentration of fluoride ion.
• fluorborate ions in the solution has been observed to have the effect of broadeningthe range of concentration of the chromate and fluoride ions which may be present in order to obtain satisfactory coatings.
• the preferred solutions of this invention include the fluoborate ion.
• fluoborate When fluoborate is employed,- the quantity -may satisfactorily extend as high as about 1.6% with a preferred range of fluoborate being 0.65%0.70%, all percentages of fluoborate ion being expressed as weight percent of sodium fiuoborate.
• the 'fluoborate ion is preferably introduced through the use of alkali metal fluoborates although fiuoboric acid or the combination of hydrofluoric acid and boric acid and their salts rnay be satisfactorily used.
• the increase in the range of the chromate and fluoride ion contents of working baths containing fluoborate .in comparison to thosecontaining the fluoride and chromate ions only is illustrated by the following. In a bathcontaining 1 gram per liter NaHF and chromic acid, good coatings were obtained at CrO concentrations between 8 and lOgrams/liter. In the presence of 12.5 grams/ liter NaBF and 1 gram/liter NaHF good coatings were obtained at CrO concentrations of 6-12 grams per liter.
• a feature of the invention is the provision of a coating solution which contains in addition to all of the other ingredients previously enumerated within their respective proportions, potassium titanium fluoride and/or potassium zirconium fluoride which solution has effect of eliminating dusty coatings particularly on ferrous metal surfaces at the higher concentrations of ingredients.
• Working baths were; prepared containing tetrasodiurn py-rophosphate in amounts from 0.05% to 0.5%, together with 0.3% CrO 0.67% sodium fluoborate and 0.075% sodium bifiuoride and were modified by the addition of 0.01%, 0.02%, 0.03%, and 0.04% by weight per volume potassium titanium fluoride.
• the baths in addition contained 0.75% weight per volume nickel sulphate and approximately 0.5% weight per volume ferrous sulphate. A substantial reduction'in the amount of dust produced on hot rolled steel panels processed in' the above modified baths was observed because of the presence of potassium titanium fluoride in the amounts mentioned.
• the range of proportions-0f CrO fluoride and :the condensed phosphate compounds as above set forth operate satisfactorilyin anaqueous acid solution.
• the acidity of the solution is not critical but will necessarily vary with the proportion of chromic acid which is present.
• a Working bath may have a free acid content varying between about 2 /2 points to about 35 points and preferably about 2 /2 toabout 8 points.
• the free acid may be adjusted during operation with nitric acid to obtain the desired level.
• free acid points refers to'the, number of; ml.
• the coating solutions of the present invention are particularly valuable in that they produce satisfactory coatings on widely different metallic surfaces such as iron, steel, nodular iron and iron whichhas been galvanized, and articles of zinc or magnesium and of alloys of each.
• the method of the present invention comprises treating metallic surfaces with chromate-fluoride coating solutions of the type previously indicated which contain one or more of the specified condensed phosphate compounds for a time sufficient to produce thereon corrosion resistant and paint-base coatings.
• the coating solutions of the invention may be applied to the metal surfaces to EXAMPLE I Gms./liter CrO 3.7 NaI-IF 0.75 Condensed phosphate of sodium compound 1.0
• the number is excellent, while the number 5 represents rusting of the panel as far as commercially practical use of the coating is concerned.
• Example I-B Cold rolled steel panels and panels of 3S and 248T aluminum alloy were cleaned, rinsed and processed in the above baths for five minutes. Coatings which were sat- ,isfactory for bare corrosion resistance were produced on both the steel and aluminum surfaces with the coating on the aluminum the lighter in color.
• the bath of Example I-B above was modified in that the concentration of the tetrasodium pyrophosphate was increased in increments. Satisfactory coatings on both aluminum and steel surfaces continued to be produced upon the incremental increases in concentration up to about 0.5% of tetra-sodium pyrophosphate. When this concentration is exceeded, extremely dusty, non-adherent coatings are produced on steel surfaces and aluminum surfaces show no indication of any coating.
• EXAMPLE II Sets of panels of 38 aluminum and aluminum-killed steel were cleaned and processed in the following bath for 5 minutes. Panels of M44H magnesium were similarly cleaned and processed in the same bath for 2 /2 minutes. All of the panels were rinsed in cold water and given a final hot water rinse. The composition of the bath is given below. The chromate radical was introduced by the use of chromic acid.
• the panels of 24 ST aluminum and zinc grip were processed for five minutes and the panels of cold rolled steel and magnesium were processed for 2% minutes and 1 .minute respectively,
• the panels of cold rolled steel, 24 ST aluminum and zinc grip were processed for 5 minutes and the panels of magnesium were processed for one minute.
• Satisfactory coatings generally were produced on all of the panels of a set processed in each of the above baths.
• the baths in each of the abovethree examples were modified by omitting the tetra-sodium pyrophosphate and no coating at all was produced on the cold rolled steel panels while coatings were produced on the aluminum panels.
• Some of the coated panels treate'din' each of the above baths were tested for their bare corrosion'resistance, i. e., their ability to withstand corrosion in their as-processed condition without additional protective coating.
• Others of the coated panels were painted and tested for their paint receptive properties bys'ubjecting't-he painted panels to salt-spray and humidity chambers. The painted panels were also tested for adhesion. The tests conformed to generally accepted standard procedures fordetermining comparative ratings for adhesion, paint-base properties, and corrosion resistance. The results showed that coatings on both the cold rolled steel and aluminum panels were excellent paint-base coatings.
• the bare corrosion resistance on the coated steel panels was satisfactory but not as good generally as on the aluminum panels.
• On the panels of zinc grip and magnesium uniform coatings were formed which tested excellent in adhesion.
• the paint-base characteristics of the coatings on the zinc and magnesium panels ranged from fair to good with some panels considerably poorer than others in this respect.
• EXAMPLE VIII CrO gms./liter 3.7 NaHF gms./liter .75 NaBR; gms./liter 6.7 Disodium' pyrophosph-ate gms./liter 110 Free acid points 5.7
• Some of the coated panels of each set were tested for their bare corrosion resistance and others of the. coated panels of each set were painted and tested for their paint receptive properties by subjecting the. painted panels. to salt spray and humidity chambers and adhesion tests as in the previous examples. Still others. of the panels were used for coating weight determinations.
• the coatings on the aluminum panels were observed to vary in shades from dark grey to golden brown and on the steel panels the coatings were slightly dusty generally with some iridescense.
• the paint-base properties of the coatings ranged from very good to excellent with the coated aluminum panels test ing better generally than the coated steel panels. All of the panels treated showed excellent adhesion of the coating under impact and after visual observation upon scraping the painted panels with a sharp knife edge.
• An aqueous acidic solution for producing corrosionresistant and paint-base coatings on metallic surfaces consisting. essentially of water, at least one compound containing hexavalent chromium, at least one compound containing the fluoride radical, and at least one condensed phosphate compound which yields the condensed phos phate radical in solution and in which the mole ratio of cationic oxides to anionic oxides is greater than 0 and less' than 3, said condensed phosphate compound being present in amounts up to about 0.5% by weight calculated as condensed phosphate of sodium compound.
• An aqueous acidic solution for producing corrosion; resistant and paint-base coatings on metallic surfaces consisting essentially of water, at least one compound containing hexavalent chromium, at least one compound containing the fluoride radical, and at least one alkali metal condensed phosphate compound in which the mole ratio s 9 I of cationic oxides to anionic oxides is greater than and less than 3, said alkali metal condensed phosphate compound being present in amounts up to about 0.5% by weight calculated as condensed phosphate of sodium compound.
• An aqueous acidic solution for producing corrosionresistant and paint-base coatings on metallic surfaces consisting essentially of water, between about 0.08% and 2.5% CrO between about 0.01% and about 2% fluoride expressed as sodium bifluoride, and at least one condensed phosphate compound selected from the group consisting of disodium pyrophosphate, tetrasodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate, said condensed phosphate compound being present in amounts up to about 0.5%.
• An aqueous acidic solution for producing corrosionresistant and paint-base coatings on metallic surfaces consisting essentially of water, between about 0.08% and about 2.5% CrO between about 0.01% and about 2% fluoride expressed as sodium bifluoride, up to about 1.6% fluoborate ion expressed as sodium fluoborate, and at least one condensed phosphate compound selected from the group consisting of disodium pyrophosphate, tetrasodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate, said condensed phosphate compound being present in amounts from between about 0.01% and about 0.5%.
• An aqueous acidic solution for producing corrosion resistant and paint base coatings on metallic surfaces con sisting essentially of water, between about 0.08% and about 2.5% CrO between about 0.01% and about 2% fluoride expressed as sodium bifluoride, between about 0.6% and about 0.7% fluoborate ion expressed as sodium fluoborate, and at least one condensed phosphate compound selected from the group consisting of disodium pyrophosphate, tetrasodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate, said condensed phosphate compound being present in amounts from between about 0.01% and about 0.5
• An aqueous acidic solution for producing corrosion resistant and paint base coatings on metallic surfaces consisting essentially of water, between about 0.3% and about 0.6% CrO between about 0.01% and about 2% fluoride expressed as sodium bifluoride, between about 0.6% and about 0.7% fluoborate ion expressedas sodium fluoborate, and at least one condensed phosphate compound selected from the group consisting of disodium pyrophosphate, tetrasodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaposphate, said condensed phosphate compound being present in amounts from between about 0.01% and about 0.5
• aqueous acidic solution as claimed in claim 4 wherein said solution contains in addition at least one complex fluoride selected from the group consisting of potassium titanium fluoride and potassium zirconium fluoride in a concentration up to about 0.1%
• a method for producing corrosion resistant and paint base coatings on a metallic surface which comprises the steps of contacting the metal surface with an aqueous acidic solution consisting essentially of water, at least one compound containing hexavalent chromium, at least one compound containing the fluoride radical, and at least one condensed phosphate compound which yields the condensed phosphate radical insolution and in which the mole ratio of cationic oxides to anionic oxides is greater than 0 and less than 3, said condensed phosphate compound being present in amounts up to about 0.5% by weight calculated as condensed phosphate of sodium compound, maintaining said solution in contact with said surface for a suflicient time to form said coating.
• a method for producing corrosion resistant and paint base coatings on a metallic surface which comprises the steps of contacting the metal surface with an aqueous acidic solution consisting essentially of water, at least gne compound containing hexavalent chromium, at least one compound containing the fluoride radical, and at least one alkali metal condensed phosphate compound in which the mole ratio of cationic oxides to anionic oxides is greater than 0 and less than 3, said alkali metal condensed phosphate compound being present in amounts up to about 0.5% by weight calculated as condensed phosphate of sodium compound, maintaining said solution in contact with said surface for a suflicient time to form said coating.
• a method for producing corrosion resistant and paint base coatings on a metallic surface which comprises the steps of contacting the metal surface with an aqueous acidic solution consisting essentially of water, between about 0.08% and 2.5% CrO between about 0.01% and about 2% fluoride expressed as sodium bifluoride, and at least one condensed phosphate compound selected from the group consisting of disodium pyrophosphate, tetrasodiumv pyrophosphate, sodium tripolyphopshate, and sodium hexametaphosphate, said condensed phosphate compound being present in amounts up to about 0.5%,
• a method for producing corrosion resistant and paint base coatings on a metallic surface which comprises the steps of contacting the metal surface with an aqueous acidic solution consisting essentially of water, between about 0.08% and about 2.5% CrO between about 0.01% and about 2% fluoride expressed as sodium bifluoride, up to about 1.6% fluoborate ion expressed as sodium fluoborate, and at least one condensed phosphate compound selected from the group consisting of disodium pyrophosphate, tetrasodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate, said condensed phosphate compound being present in amounts from between about 0.01% and about 0.5%, maintaining said solution in contact with said surface for a suflicient time to form said coating.
• a method for producing corrosion resistant and paint base coatings on a metallic surface which comprises the steps of contacting the metal surface with an aqueous acidic solution consisting essentially of water, between about 0.08% and about 2.5 CrO between about 0.01% and about 2% fluoride expressed as sodium bifluoride, between about 0.6% and about 0.7% fluoborate ion expressed as sodium fluoborate, and at least one condensed phosphate compound selected from the group consisting of disodium pyrophosphate, tetrasodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate, said condensed phosphate compound being present in amounts from between about 0.01% and about 0.5 maintaining said solution in contact with said surface for a sufficient time to form said coating.
• a method for producing corrosion resistant and paint base coatings on a metallic surface which comprises the steps of contacting the metal surface with an aqueous acidic solution consisting essentially of water, between about 0.3% and about 0.6% CrO between about 0.01% and about 2% flouride expressed as sodium bifluoride, between about 0.6% and about 0.7% fluoborate ion expressed as sodium fluoborate, and at least one condensed phosphate compound selected from the group consisting of disodium pyrophosphate, tetrasodium pyrophosphate,
• said condensed phosphate compound being present in amounts from between about 0.01% and about 0.5%, maintaining said solution in contact with said surface for a sufficient time to form said coating.
• a method for producing corrosion resistant and paint base coatings on a metallic surface which comprises the steps of contacting the metal surface with an aqueous acidic solution consisting essentially of water, between about 0.08% and about 2.5% CrO between about 0.01% and about 2% fluoride expressed as sodium bifluoride, up to about 1.6% fluoborate ion expressed as sodium fluoborate, at least one complex fluoride selected 11 from the group consisting of potassium titaniumfluoride and potassium zirconiu n'fiuoridetin a concentration up to about '0.1'%,tand at ileast one condensed phosphate compound selected "from 'the,gr,oup consisting of fdisodium pyrop'hosphate, tetrasodium pyrophosphate, sodium .tfipolyphosphate, and sodium hexametaphosphate, saidcondensed phosphate compound being ,present in amounts from between about 0.01 and about 0.5%, maintaining said solution in contact iwit

Landscapes

• 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)

Priority Applications (8)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24555550

Family Applications (1)

Country Status (7)

Cited By (7)

Families Citing this family (2)

Citations (3)

• 0
  • BE BE563956D patent/BE563956A/xx unknown
  • NL NL107091D patent/NL107091C/xx active
  • NL NL224487D patent/NL224487A/xx unknown
• 1957
  • 1957-01-31 US US637350A patent/US2868682A/en not_active Expired - Lifetime
  • 1957-11-05 FR FR1190562D patent/FR1190562A/fr not_active Expired
  • 1957-12-19 CH CH5399257A patent/CH373616A/fr unknown
• 1958
  • 1958-01-16 DE DEM36422A patent/DE1096153B/de active Pending
  • 1958-01-31 GB GB3300/58A patent/GB830632A/en not_active Expired

Patent Citations (3)

Also Published As

Similar Documents

Legal Events