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
  • C23C22/48—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 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M173/00—Lubricating compositions containing more than 10% water
  • C10M173/02—Lubricating compositions containing more than 10% water not containing mineral or fatty oils
• • 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
  • C23C22/48—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 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
  • C23C22/50—Treatment of iron or alloys based thereon
• • 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
  • C23C22/48—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 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
  • C23C22/53—Treatment of zinc or alloys based thereon
• • 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
  • C23C22/48—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 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
  • C23C22/56—Treatment of aluminium or alloys based thereon

Definitions

• the invention relates to a method for the formation of conversion layers on a metal surface selected from zinc, iron, aluminum, copper, lead and their alloys, as well as galvanized, electrozinced, aluminized, coppered steels. , making it possible to produce at high speed conversion layers formed of very small crystals, from 1 to 20 ⁇ m.
• these metal surface conversion treatments When applied prior to forming the sheet metal, these metal surface conversion treatments generally have at least one of the following effects:
• the conversion layer can be easily removed when it is no longer useful.
• the conversion baths essentially contain anions and cations capable of forming insoluble compounds with the dissolved metal of the surface.
• the main conversion treatments applied to the steels are thus chromating treatments on galvanized steel (by dip galvanizing or electrogalvanizing) or aluminized, phosphating on unalloyed bare steels or coated steels, or even oxalation on alloy steels such as as stainless steels, for example.
• the treated surface After being brought into contact with a conversion bath, the treated surface is generally rinsed to remove unreacted surface and / or treatment solution components, and this surface is dried, particularly to harden the coating layer. conversion and / or to improve its properties.
• the conversion treatment may itself be preceded by a pretreatment, generally consisting of a preliminary degreasing and rinsing of the surface followed by a so-called refining operation using a pretreatment solution adapted to create and / or promote germination sites on the surface to be treated.
• a pretreatment generally consisting of a preliminary degreasing and rinsing of the surface followed by a so-called refining operation using a pretreatment solution adapted to create and / or promote germination sites on the surface to be treated.
• sols or colloidal suspensions of titanium salts which allow the subsequent production of a conversion layer having smaller crystals in a denser layer.
• a post-treatment can be carried out on a conversion layer obtained by phosphatation.
• the object of the invention is to propose treatments by carboxylation of metal surfaces, in particular zinc and zinc alloy layers coating the galvanized and electrogalvanized steel sheets, solving better than the existing treatments the problems that we have just described. to quote.
• the subject of the invention is a conversion process by carboxylation of a metal surface chosen from zinc, iron, aluminum, copper, lead and their alloys, galvanized or electrozinced, aluminized steels. , coppered, under oxidizing conditions with respect to the metal, by contact with an aqueous or hydro-organic bath containing a mixture of organic acids, characterized in that:
• organic acids are saturated linear carboxylic acids containing from 10 to 18 carbon atoms;
• said mixture is a binary or ternary mixture of such acids
• the respective proportions of these acids are such that: for a binary mixture x + 5% - y + 5%, x and y being, in molar percentages, the respective proportions of the two acids in a mixture with the composition of the eutectic;
• the concentration of said mixture in said bath is greater than or equal to 20 g / l.
• the respective proportions of the acids are x + 3% - y + 3%.
• Said oxidizing conditions can be created by the presence in the bath of an oxidizing compound for the metal surface.
• Said oxidizing compound may be hydrogen peroxide.
• Said oxidizing compound may be sodium perborate. Said oxidizing conditions can be created by the bath application of an electric current.
• the bath may be a hydro-organic bath and contain a co-solvent.
• This co-solvent may be chosen from 3-methoxy-3-methylbutan-1-ol, ethanol, n-propanol, dimethylsulfoxide, N-methyl-2-pyrrolidone and 4-hydroxy-4-methyl.
• -2-pentanone diacetone alcohol.
• Said bath may be an aqueous bath and include a surfactant and / or a dispersant.
• Said surfactant may be chosen from alkylpolyglycosides, ethoxylated fatty alcohols, ethoxylated fatty acids, ethoxylated oils, ethoxylated nonylphenols and ethoxylated sorbitan esters.
• Said dispersant may be chosen from high molecular weight polyols, carboxylic acid salts such as (meth) acrylic copolymers, polyamide derivatives such as polyamide waxes.
• Said saturated carboxylic acids may each have an even number of carbon atoms.
• Said saturated carboxylic acids may be lauric acid and palmitic acid.
• Said metal surface may be a galvanized steel sheet, and the bath may contain an Al 3+ complexing agent .
• said mixture is an eutectic mixture.
• the invention also relates to a method of temporary protection against corrosion of a metal surface, according to which a conversion by carboxylation of said surface is carried out, characterized in that said conversion is carried out by the above method.
• Said metal surface may be selected from zinc, iron, aluminum, copper, lead and their alloys, galvanized steels, aluminas, copper.
• the subject of the invention is also a process for manufacturing a shaped sheet having a metal surface chosen from zinc, iron, aluminum, copper, lead, and their alloys, as well as galvanized, aluminized steels. , copper-coated, in which a carboxylation treatment of said sheet is carried out and shaped, characterized in that said carboxylation treatment is carried out by the above method.
• Said sheet may be steel coated with zinc or a zinc alloy and is shaped by stamping.
• the invention relies on the use, to make up the solution or emulsion carboxylation, a eutectic binary or ternary linear saturated fatty acid Ci 0 - Ci 8, or a mixture having the composition of such a eutectic.
• the acids used are all even-numbered acids of carbon atoms.
• the binary eutectic of C- 12 -C16 acids is particularly preferred.
• the concentration of the eutectic or mixture in the carboxylate bath is greater than or equal to 20 g / l.
• eutectic refers to either a simple mixture with the eutectic composition or a eutectic containing two or three C 10 -C 18 saturated linear fatty acids, is a true eutectic having this composition, obtained by melting the mixture of fatty acids.
• the treatment bath may contain only the eutectic or the mixture of acids in the composition of the eutectic, a surfactant and water, if the necessary oxidizing conditions are obtained by electrochemical means.
• electrochemical means namely by adding an oxidizing compound, such as hydrogen peroxide.
• oxidizing compound such as hydrogen peroxide.
• the minimum concentration of 20 g / l of the eutectic is chosen because, below this limit, the rate of formation of the carboxylated layer is no longer sufficient to obtain an effective conversion layer with a duration of treatment compatible with industrial requirements.
• FIG. 1 which shows schematically the equilibrium diagram of a mixture of two fatty acids A and B as a function of the temperature
• FIG. 2 which represents the binary diagrams of mixtures of linear saturated fatty acids HCi O / HC 12 (FIG. 2a), HC 12 / HCi 6 (FIG. 2b), HC 16 / HC 18 (FIG. HC 1 2 / HC 18 (fig.2d), without being dissolved or diluted in water or in a hydro-organic medium;
• FIG. 3 which shows the evolution of the polarization resistance over time for different eutectics and a reference electrogalvanized sheet, the carboxylation being carried out in a hydro-organic medium;
• FIG. 4 which shows the evolution of the corrosion potential over time, under the same conditions as the tests of FIG. 3
• FIG. 5 which shows the results of tribological tests carried out on a sample of electrozinc plated sheet carboxylated by an HC12 / HC16 eutectic and on a reference sample;
• FIG. 7 which shows the results of tests analogous to those of FIG. 4, carried out in a water + surfactant medium
• FIG. 8 which shows the results of tribological tests carried out on a sample of galvanized dipped-in sheet carboxylated by an HC 12 / HC- 16 eutectic or an HC- 12 / HC 16 mixture and on a reference sample.
• a carboxylation bath contains a linear C n saturated carboxylic acid of general formula (CH 3 (CH 2 ) ⁇ - 2 COOH), with n> 7, denoted HC n , dissolved in water or in a mixture generally equivolumic water-non-aqueous solvent (ethanol, ).
• An oxidant such as hydrogen peroxide or sodium perborate, is added to the bath to produce a sufficient amount of Zn ++ cations at the zinc / solution interface.
• the pH of the bath is close to 5.
• the oxidizing conditions producing the Zn ++ cations are obtained by circulating an electric current between the surface to be protected and a counter electrode immersed in the bath. If the carboxylic acid HC n is noted, the essential formation reaction of the carboxylated layer on the zinc surface is: Zn 2+ + 2 C n " ⁇ Zn (C n) ⁇ 2
• the compounds that can be used in the context of the invention may be derived from products of the green chain, that is to say from agricultural production for non-food use (sunflower, flax, colza ). They advantageously replace the polluting mineral oils used for the lubrication of metal surfaces and the phosphating and chromating solutions used for the protection of these same surfaces against corrosion.
• Such a eutectic or mixture provides a significant improvement of the corrosion protection compared with coatings obtained with a single acid or a mixture of acids of composition not close to a eutectic. Also, the lubricating properties of these coatings according to the invention are excellent. They make it possible to do without an oiling of the coated product during its shaping.
• saturated fatty acids those containing an even number of carbon atoms are preferred.
• saturated fatty acids with an even number of carbon atoms that can be used in the context of the invention are:
• FIG. 1 shows the equilibrium diagram of mixtures of fatty acids A and B as a function of temperature.
• the minimum e indicates the formation of a eutectic and the change of slope at point u is due, in general, to the existence of a defined molecular compound c of formula A m B n (m and n denote the molar fractions of A and B respectively).
• the eutexte point e as well as the point of inflection u corresponding to the complex, do not appear respectively at 25 and 50%, as is the case with acid mixtures whose chain lengths differ only by two carbon atoms (Fig.2a for HC 10 / HC 12 and Fig.2c for HCi 6 / HCi 8 ). Eutectic is shifted to higher molar concentrations of the shortest fatty acid.
• the shape of the binary diagram and the positions of the points u and e are a function of the more or less limited stability of the complex. The form depends on the difference between the chain lengths of the constituents, and more exactly, the difference between the melting points of these two fatty acids.
• Table 1 shows the compositions of the eutectics e of various binary mixtures and their melting points T f (e).
• the eutectic compositions given in Table 1 are approximate. According to the publications, they can vary from a few percent. These differences are due to the purity of the fatty acids used.
• the sheets were degreased in an alkaline degreasing bath, similar to those used in industrial alkaline phosphating. They were then rinsed. Then the carboxylation treatment took place chemically (presence of an oxidant in the bath, such as hydrogen peroxide or a sodium perborate tetrahydrate) or electrochemical.
• an oxidant in the bath such as hydrogen peroxide or a sodium perborate tetrahydrate
• the oxidizing conditions allow a fast reaction between Zn 2+ and C n " , providing fine crystals of Zn carboxylate.
• the concentration of H 2 O 2 in the solution is, for example, from 2 to 15 g / l. Below 2 g / l the medium is generally not enough oxidizing to form enough Zn 2+ in solution. The duration of the reaction may not be compatible with industrial requirements. Above 15 g / l, the medium is generally too oxidizing and the crystals are poorly formed. The optimum concentration is about 8 to 12 g / l H 2 O 2 in the solution.
• Co ⁇ preferred solvent is 3-methoxy-3-methylbutan-1-ol (MMB). It is a green and biodegradable solvent. In addition, its flash point, which is the temperature from which it becomes flammable, is 71 0 C, compared for example with that of ethanol which is 12 0 C. The MMB therefore provides security conditions better than ethanol. It is also possible to use ethanol, n-propanol, dimethylsulfoxide, N-methyl-2-pyrrolidone, 4-hydroxy-4-methyl-2-pentanone or diacetone alcohol.
• a first advantage is the lowering of the melting temperature compared to the use of a single fatty acid, as is apparent from Figure 2. This allows to maintain the bath of carboxylation at a relatively low temperature, of about 45 ° C in many cases, especially if using a hydro-organic medium.
• Eutectic is prepared by melting for several hours the mixture of fatty acids component. The mixture is then slowly cooled to room temperature.
• electrogalvanized steel sheets (thickness of the Zn layer: 7.5 ⁇ m) were treated to obtain a weight of carboxylated layer of between 1 and 2 g / m 2 , of which experience shows that it provides a maximum coverage rate of the sheet.
• the weight of the carboxylate layer is evaluated by measuring the difference in mass between the carboxylate substrate and the substrate etched with dichloroethane under ultrasound, which treatment causes the dissolution of the carboxylate layer.
• the aqueous corrosion resistance of the test samples was tested in a conventional three-electrode electrochemical cell, by monitoring the corrosion potential and measuring the polarization resistance.
• the electrolyte used is water according to the ASTM D1384-87 standard (148 mg / l of Na 2 SO 4 , 138 mg / l of NaHCO 3 , 165 mg / l of NaCl, pH 7.8). This corrosive solution is usually used to evaluate the effectiveness of corrosion inhibitors in the laboratory.
• the resistance to atmospheric corrosion of 50 cm 2 samples was studied according to DIN 50017 using a climatic chamber where the samples were placed vertically and subjected to cycles of 24 h, each with successive exposure. 8 hours at a humidity of 100% (bipermuted water at 40 ° C.) and then at ambient air for 16 hours.
• the degradation of the coating was estimated by visual observation and X-ray diffraction.
• Dusting of the samples was evaluated by measuring the mass difference of the substrate before and after successive passes between two squeezing rollers.
• the loss of mass thus measured can be related to the dusting tendency of the coating.
• Tribological tests were carried out to evaluate the lubricating properties of the coating during stamping. They were carried out on a plane / plane tribometer with control of the clamping force, by scrolling the sample of tight plate at a speed of 1 to 100 mm / s, and by measuring revolution of the distance between the flat tools ensuring the tightening of the sample. It is thus possible to determine the coefficient of friction as a function of the clamping pressure.
• compositions of the baths were as follows:
• Figure 3 shows the evolution over time of the polarization resistance R p of the coatings
• Figure 4 shows this same trend for the corrosion potential E cor r in corrosive water, for the three coatings tested previously defined and , by way of reference, for an electrogalvanized EG non-carboxylate coating.
• the coatings according to the invention have much better performances than coatings resulting from simple electrogalging.
• the polarization resistance is of the order of 2 k ⁇ .cm 2
• the carboxylation coatings usually made with water-solvent solutions based on a single fatty acid provide only one relatively weak improvement of this value (up to 15 k ⁇ .cm 2 ).
• the coatings according to the invention provide values of the order of 5 to 15 times higher than those observed for coatings electrozinced alone.
• the coatings obtained with HCi 2 / HCi 6 in the first place, and thanks to HCi 2 / HCis second, provide the best results in absolute value and stability over time.
• those of the coatings according to the invention are 80 to 140 mV higher than the values obtained for the electrogalvanized coating.
• the HCi 2 / HCi 6 again gives the best result.
• Coatings obtained using a single fatty acid in a water-solvent medium usually provide corrosion potentials of the order of -1020 to -1080 mV, and therefore less favorable than those of the coatings according to the invention.
• the resistance to atmospheric corrosion was also estimated by observing the percentage of the surface of the corroded sample after 20 cycles of exposure, as defined above.
• this coating is not very subject to dusting. After 20 passes on stripper rolls, a layer weight loss of 0.2 g / m 2 was measured, against 0.4 g / m 2 for a steel coated with a Zn (Cv) 2 conversion layer.
• the carboxylation coatings obtained with the aid of binary mixtures of fatty acids with the composition of the eutectic have performance at least equal, and often superior to all points of view, to those coatings obtained with the aid of single fatty acids in water-solvent medium. Overall, the HCi 2 / HC 16 mixture is the most satisfactory of those tested.
• Another method is to prepare the surface before carboxylation by removing the I 2 O 3 layer:
• alkaline degreasing NaOH, surfactants, complexing agents
• alkaline oxidation NaOH, iron and cobalt salts, complexing agents
• H 2 SO 4 acid attack
• composition difference (in mol%) with respect to the eutectic x% - y% should not exceed x + 5% - y + 5% and preferably x + 3% - y + 3%, for binary eutectics or x + 3%, y + 3% - z + 3% for ternary eutectics.
• surfactants a wide variety of compounds have been used, generally chosen from nonionic surfactants and especially:
• alkylpolyglycosides such as Agrimul PG 215 CS VP and Glucopon 225 DK / HH from the company COGNIS; these surfactants are sugar-based, non-toxic and have exceptional resistance to alkalis and salts;
• ethoxylated fatty alcohols such as Brij 58 from ACROS
• dispersants it is possible to use especially high molecular weight polyols, carboxylic acid salts such as (meth) acrylic copolymers, polyamide derivatives such as polyamide waxes. Under these conditions, the optimum for the oxygenated water concentration is between 2 and 8 g / l. With single fatty acids, carboxylation without an organic solvent by means of a simple aqueous emulsion does not provide optimal coatings for corrosion protection because the weight of the carboxylate layer is relatively low. It has therefore been verified whether the use of eutectic fatty acids under these conditions could be more satisfactory.
• carboxylation emulsions containing water, the surfactant APG 215 mentioned above and the eutectic HCl 2 / HCl 6 81/19% were prepared.
• the tested emulsions had the following compositions:
• emulsion A with a low concentration of APG 215 makes it possible to release the fatty acids more rapidly.
• a coat weight of 1.2 g / m 2 is reached in 5 s, while 10 s are needed to achieve a layer weight comparable with other emulsions.
• contents of APG 215 of 1 to 3% no marked effect of surfactant concentration is observed.
• the oxidant concentration also has no very appreciable effect in the explored range.
• the size of the crystals does not seem to be related to the composition of the emulsion.
• the product of the carboxylation is not well crystallized, and its composition is close to ZnC 12 Ci ⁇ .
• Polarization resistance and corrosion potential measurements were made under the same conditions as above, and compared to those obtained on an electrogalvanized coating EG. The results are illustrated in Figures 6 and 7 respectively. It appears that in aqueous corrosion, all the coatings provide a higher polarization resistance than the electrogalvanized coating alone during the first minutes of immersion, then stabilize at values equal to or slightly greater than that of the electrogalvanized coating. Emulsions that are less rich in surfactant provide the best results. For the corrosion potential, the different coatings have comparable behavior and provide a more favorable corrosion potential than that of electrogalvanized sheet.
• a mixture HCl 2 / HCl 6 was also prepared in respective molar proportions of 77 and 23% (thus deviating slightly from the eutectic 81-19% but remaining in accordance with the invention) in a water / solvent medium ( MMB). This mixture was put in the form of a melt eutectic as previously indicated, and two carboxylation solutions were made using this eutectic mixture.
• solution 1 50% water + 50% solvent by volume, to which 4% of the eutectic in mass + 0.095 g / l of phosphate of AI + 0, 105 g / l of oxalic acid + 5 g / l is added of H 2 O 2 .
• Solution 2 50% water + 50% solvent by volume, to which 4% of the eutectic is added in mass + 0.1 g / l of oxalate of AI + 5g / l of H 2 O 2 .
• the carboxylated sheets according to the invention have friction coefficients of up to 0.05 ⁇ , and still very significantly lower, at equal contact pressure, than those of the reference sheets. It is also seen that the replacement of the phosphate mixture of AI + oxalic acid
• solution 1 with AI oxalate (solution 2) has no significant influence on the tribological properties.
• all solutions 1 to 4 provided a covering and homogeneous deposit.
• the weight of the layer formed reaches 1.2 g / m 2 after 3 to 7 s in all cases.
• the performance of carboxylation coatings formed from eutectics or mixtures with the composition of the eutectic in a water / organic solvent medium are generally greater than those of similar coatings formed by emulsions in water / surfactant medium.
• the performance of the coatings formed without organic solvent are considered sufficient, for example because the coated products are not intended to remain long in a corrosive atmosphere, it is advantageous to use them because the toxicological risks are less for the manipulators and for the environment.
• their implementation does not require or little control and post-treatment of the effluents.
• the oxidizing conditions have been obtained using hydrogen peroxide. But, as is known, they could have been obtained with other oxidants, or by the application to the carboxylation bath of an electrical current of the order of intensity, for example, from 10 to 25 mA / cm. 2 .
• Ci O -C 8 would be used, as these acids each have an even or odd number of carbon atoms. Eutectics of ternary mixtures of such fatty acids can also be used.
• even-numbered carbon atoms which is the preferred mode of implementation of the invention.
• These even fatty acids are of plant origin and are generally derived from the green products sector, from renewable sources. Odd fatty acids do not exist in nature and must be synthesized. In addition, odd fatty acid eutectics require chemical treatments for their preparation.
• the conversion baths may optionally contain:
• pH regulating agents or buffering agents for regulating the conditions of formation of the conversion layer on the surface
• additives facilitating the implementation of the treatment and the distribution of the bath on the surface to be treated such as surfactants (it being understood that the presence of a surfactant is obligatory when the bath is an aqueous emulsion); additives which make it possible to increase the life of the bath, such as, for example, chelating agents for retarding the precipitation of others; compounds that are desired in the conversion layer, or bactericidal agents;
• additives allowing the dispersion of fatty acids in an aqueous medium.
• the conversion treatments according to the invention are applicable to other metal surfaces than galvanized steels. They may concern any metal surface capable of undergoing carboxylation, namely zinc, iron, aluminum, copper, lead and their alloys, aluminized or copper-coated steels.

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