Definitions

• the present invention relates to new protective coatings, in particular for metallic substrates, their production and their applications.
• FR 2 648 822 a technique of grafting amorphous silica onto a ferrous substrate.
• the corresponding treatment consists of an amorphous phosphating which then makes it possible to apply the zinc-rich paint without mechanical treatment of shot blasting.
• this known process does not lead to protective coatings having sufficient adhesion to withstand severe mechanical stresses, in particular repeated folding.
• the kinetics of coating formation are too slow, which implies a minimum duration of 24 hours at room temperature.
• the object of the invention is to remedy the drawbacks presented by the products and methods of the prior art, as they have been briefly recalled above.
• the invention relates to amorphous protective coatings having markedly improved adhesion properties.
• the invention also relates to protective coatings containing zinc at much lower concentrations than in the prior art.
• the invention also relates to protective coatings containing other metallic and / or mineral fillers, such as titanium or aluminum, or based on silica in various forms or on silicate.
• Another advantageous object of the invention is a new process for obtaining protective coatings for metallic substrates, involving chemical attack on the substrate under controlled conditions and requiring no mechanical treatment, the substrate thus treated being able to be and remain perfectly polished.
• the method according to the invention makes it possible to obtain the protective coating, with all the desired qualities thereof, much faster than in the prior art, thanks to the implementation of conditions making it possible to accelerate the kinetics of coating formation.
• the subject of the invention is a protective coating chemically fixed to a metal substrate, comprising an amorphous mineral silicate at least 1 ⁇ m thick and having the following adhesion properties:
• the adhesion test after folding at 180 ° which will be illustrated below, consists in folding over itself a sample of substrate in the form of a plate (or sheet) to which a protective coating has been applied according to the invention . We then stick an adhesive tape on the folding area and remove the tape by peeling. The coating protector passes the adhesion test when the tape practically does not peel off any coating.
• the 160 impact adhesion test with equipment conforming to ISO / TR 6272-1979 implements a test method designed to assess the crack resistance by rapid deformation of an applied coating on a metal support.
• the shock device uses a hemispherical punch with a diameter of 15.87 mm in accordance with ISO / TR 6272-1979 and with an energy value supported by the sample equal to 160 inc-pound or approximately 18 joules.
• the protective coating passes the adhesion test when there is no chipping after the impact of the punch.
• the thermal shock adhesion test involves at least one immersion cycle of the coated sample in liquid nitrogen and then heating to 650 ° C.
• the protective coating passes the adhesion test when no spalling is observed after this thermal shock.
• the protective coating According to an important characteristic of the protective coating, it is purely mineral. After obtaining it, the coating contains only traces of hydrocarbon groups. The coating therefore consists only of one or more amorphous mineral silicates.
• the adhesion of the coating is significantly higher than that which could be obtained until now.
• the new coatings can withstand severe mechanical stresses, consisting for example of repeated folding, while also having a high resistance to thermal shocks.
• the thickness of the protective coating is greater than or equal to 1 ⁇ m and can reach 10 ⁇ m or more without the adhesion properties being altered, whereas with the known coatings, losses of adhesion were noted as soon as that the thickness reached 0.5 ⁇ m, as will be illustrated in the comparative examples below.
• the protective coating additionally contains a filler of at least one metal having a redox potential lower than the potential of the substrate.
• a metal is in particular zinc, titanium or aluminum, alone or as a mixture.
• the protective coating may also contain a mineral filler, alone or in combination with the metal filler previously indicated.
• Said mineral filler can in particular be based on silica or an inorganic silicate, such as a magnesium silicate and / or an aluminum silicate.
• the expression "filler based on silica” means a filler comprising at least partially hydrophobic silica or made hydrophobic by a known prior treatment.
• silica-based mineral filler is combined with a metallic filler, its hydrophobic nature is less important, especially if it is present in a relatively minor amount compared to the metallic filler.
• the invention also relates to protective coatings containing no filler, either metallic or mineral.
• alkylsilicate in which the alkyl radical contains from 1 to 5 carbon atoms is used, as will be indicated below.
• the alkylsilicate may be present in the form of a monomer, comprising a single silicon atom, or of an oligomer, the polysiloxane chain of which contains from 2 to 5 silicon atoms.
• the protective coatings according to the invention when they contain a filler of at least one metal, as defined above, provide very good cathodic protection to the coated substrate.
• This parameter can be determined and compared with that of known protective coatings by measuring under standardized conditions the ionic resistance of a sample of coated substrate. The measurements are carried out in an electrochemical cell containing a NaCl solution, the characteristics and use of which will be described later with reference to a drawing. Under the conditions of this test, the coatings according to the invention have an ionic resistance greater than 1 K_ .cm 2 and in particular greater than 2K_.cm 2 after 3000 h of immersion. These values cannot be reached by known coatings. The results of the ion resistance measurements are confirmed by capacity measurements.
• zinc When it is present in the protective coating, zinc can be chosen from any of the products of this kind already used in zinc paints, in the most diverse forms and particle sizes, but, according to an advantageous characteristic of the invention, the zinc charge can be significantly reduced compared to that previously known, without detracting from the anticorrosion characteristics.
• the use of protective coatings with lower zinc charges not only has an advantageous impact on the cost but also ensures better environmental protection, since the production of zinc salts in a corrosive atmosphere is limited. ; this latter factor also has a very favorable influence on the subsequent adhesion of the various finishing coatings which must cover the primary coating according to the invention, since the swelling effect of the latter in a corrosive atmosphere is greatly reduced.
• the zinc contents when it is present in the coating, can be less than 50% by weight and even less than 40% by weight.
• the protective coating contains titanium
• it can also be used in the form of pure Ti ⁇ 2 titanium oxide, in its various allotropic varieties, or else in the known forms of Ti ⁇ 2 coated with aluminum or silicon.
• These Ti ⁇ 2 pigments are known to those skilled in the art who can easily choose the pigments which are most suitable from the various allotropic varieties of Ti ⁇ 2, the so-called aluminized forms of Ti ⁇ 2 or the so-called “coated” forms of Ti ⁇ 2-
• certain precautions must be taken for the conditioning of the coating composition, since aluminum acts as a catalyst during the formation of the coating and therefore exerts an active influence on the polymerization kinetics.
• the protective coating contains a mineral filler
• a mineral filler it is generally present between 1 and 10% by weight, preferably between 3 and 7% by weight. If the mineral filler is combined with a metallic filler, the quantity of mineral filler to be used can be comparatively reduced and go up to 0.1% by weight of the total composition. If it is desired to increase the anti-corrosion properties, it may be advantageous to increase the amount of mineral filler, even beyond 10% by weight of the total composition.
• the mineral fillers can be of synthetic or natural origin and can be used alone or as a mixture. It is possible, for example, to use natural or chemically modified silicas, or natural silicates, such as mica.
• the thickness of the protective coating is not really critical. However, it is not useful to unduly increase the thickness when satisfactory results are already obtained with small thicknesses.
• the thickness varies from 1 to 50 ⁇ m approximately, preferably from 1 to 15 ⁇ m approximately.
• the coating comprises titanium, particularly in Ti ⁇ 2 form, the thickness can vary from 1 to 50 ⁇ m approximately, preferably from 1 to 20 ⁇ m approximately.
• the coating When the coating has no charge, it constitutes an electrically insulating coating. This electrical insulation property can be considerably increased by the addition of charges having recognized dielectric characteristics, for example Ti0 2 .
• the substrates according to the invention are, in a preferred embodiment, iron-based substrates, such as steel and galvanized steel.
• the substrates can also be based on aluminum or its alloys.
• the metallic substrates comprising a protective coating according to the invention can receive wide applications as articles or parts of articles subjected to aggressive environments and / or to mechanical and / or thermal stresses.
• the coatings can be applied inside or outside articles.
• the internal coatings can be used in the packaging or other fields, for example for hydrocarbon storage tanks.
• the coated substrates according to the invention can also be used widely in industries such as the automobile or aeronautics, for the production of all kinds of parts, for example the exhaust pipes of the automotive industry.
• the coated substrates according to the invention can also be used for the production of cold rooms or oven partitions.
• the protective coatings can confer anti-ultraviolet protection, and can be used as flame retardant coatings, anti-corrosion primers, insulators, anti-graffiti varnish, etc.
• the coated plates can also serve as printed circuits. All the above indications are purely illustrative and in no way limitative insofar as those skilled in the art can use coated metal substrates according to the invention to meet very
• the protective coating is chemically fixed by virtue of the presence of hydroxyl groups on the substrate. These hydroxyl groups can be present on the surface of the substrate itself or on a layer of paint or coating applied to the substrate. If this comprises several layers of paint, the last layer should comprise hydroxyl groups, which promote the adhesion of the protective coating according to the invention.
• An interesting practical application of the invention consists in providing various substrates with an anti-graffiti protective varnish.
• the invention relates to a process for obtaining a substrate comprising a protective coating of the type defined above, said process comprising the following steps: (a) degreasing of the substrate to be coated by conventional means ;
• step (e) heat treatment having the effect of eliminating the organic residues, the chemical attack of step (b) being carried out using an agent capable of being fixed on the substrate while providing hydroxyl groups, ensuring during the final step (e) a controlled reaction of hydrolysis and condensation initiated on the surface of the substrate.
• Step (a) of degreasing is carried out in a manner known to those skilled in the art, for example by treatment of the substrate using methyl ethyl ketone or other component or formulation known for this purpose.
• Steps a) and b) of the process can be carried out separately or simultaneously.
• the two stages can be common by using a potassium hydroxide solution, which degreases and slightly passive the surface.
• step c) just rinse (step c) with hot water (about 60 ° C).
• the degreased substrate is subjected to a chemical attack with specific means and under selected conditions.
• the method of the invention does not include any mechanical treatment step, such as shot blasting or the like.
• the protective coating is fixed to the substrate by a chemical anchor. It is thus possible to use in the invention substrates whose surface is perfectly regular and polished.
• the chemical attack of step (b) must be adapted to the substrate to treat, but in all cases, this attack must allow the formation of the coating through an initiation on the surface of condensation or polymerization.
• the chemical attack is carried out using a reagent or a combination of reagents which reacts on the substrate by fixing on it and by providing hydroxyl groups, from which the reaction of film formation by polymerization can to start.
• the Redox potential of the attacking agent being from 0.5 to 0.8 V / ENH.
• the oxidizing compounds can in particular be metallic nitrates, such as iron nitrate, added with nitrites type regulators, such as sodium nitrite at levels providing a pH of 1 to 4 and a total acidity (AcT) of 4 to 14.
• the invention includes, as a means for carrying out the above process, an aqueous chemical attack composition based on phosphoric acid and comprising at least one oxidizing compound of mineral nature, as mentioned above, in especially iron nitrate added with sodium nitrite as a regulating agent.
• the iron nitrate is preferably present in hydrated form, in particular in the form Fe (N ⁇ 3), 9H2O.
• the contents of the various components of this chemical attack composition can respectively vary according to the following ranges: - phosphoric acid from 2 to 15 g / l
• Such phosphoric acid compositions have been found to be the best for etching ferrous substrates.
• metallic substrates in particular based on zinc, aluminum or their alloys, chromic, oxalic, sulfuric acid and other acids capable of initiating hydroxyl groups on the surface of the substrate can be used.
• the chemical attack treatment in particular of ferrous supports using the phosphating composition described above, is carried out under good conditions by immersing the substrates in a bath at a temperature for example of the order of 60 ° C., but can also be carried out at a higher temperature (80 ° C.) or at ambient temperature, this temperature parameter only influencing the kinetics of carrying out the surface chemical treatment.
• Spray treatment can also be implemented.
• the substrate is subjected to a rinsing intended to remove all the fractions not fixed on the substrate, then to drying.
• Rinsing is advantageously carried out with water, in particular with demineralized water.
• the rinsed substrates are then dried by any conventional means.
• it comprises in the above-mentioned step (d), the application of a binder based on alkyl silicate, the alkyl radical of which contains 1 to 5 carbon atoms .
• a binder essentially based on ethyl silicate.
• the more reactive methyl silicates have the drawback of high toxicity.
• the binder used in step (d) contains a metallic and / or mineral filler, as defined above, if it is desired to obtain a charged protective coating.
• the metal must have a redox potential lower than the potential of the substrate.
• a step of grinding and kneading the loaded binder formulations is strongly recommended.
• the binder is applied either by quenching the substrate in the formulation, or by spraying the latter onto the substrate, or by any other means of application.
• the application of the binder is preferably done at room temperature.
• the process described above is modified in that it does not include the step (b) of chemical attack, thanks to the fact that the substrate itself or the primers present on its surface already contain hydroxyl groups.
• the amount of binder to be used may depend on the treated substrate and is generally chosen to provide coating thicknesses of the order of 1 to 20 ⁇ m, this thickness however being able to range up to approximately 50 ⁇ m when the coating contains zinc.
• step (e) consists of a heat treatment in the temperature range from ambient temperature to approximately 350 ° C., depending on the exact nature of the binder, this treatment allowing accelerate the formation of the protective coating on the surface of the substrate by hydrolysis and condensation (or polymerization) of the silicate-based film.
• this heat treatment the organic residues are mostly removed, to provide a protective coating based on fully amorphous mineral silicate.
• one of the advantageous characteristics of the invention is to allow the production of protective coatings in a period of time significantly less than that required by the products and methods of the prior art. This completion time takes into account the duration of all the steps previously described from a) to e).
• the coating has the qualities required for its handling and storage.
• the optimal properties are only obtained after a period of a few hours at room temperature.
• Fig.1 is a perspective diagram illustrating the adhesion test after folding a sample at 180 °.
• Fig. 2 is an axial section schematically showing the electrochemical cell used for the measurement of the ionic resistance.
• FIG. 1 shows a perspective view of a strip sample 1, for example made of sheet steel provided with a protective coating 1a (magnified) which has been folded at 180 ° on a folding machine, to form a folded strip 2,3.
• a protective coating 1a magnified
• an adhesive tape is fixed.
• the tape has a width of 19 mm and bears the reference 595 TR 1966 from the company 3M. When peeling the tape, the adhesive surface is observed visually to see the presence or absence of flaking coating.
• FIG. 2 shows schematically and in section the electrochemical cell used for the measurement of the ionic resistance.
• Cell 10 is of generally parallelepiped shape. It has a body 11 and a sealed cover 12.
• the cell contains an electrolyte 17 (NaCl solution).
• electrolyte 17 NaCl solution
• the latter is in the form of a plate whose face coated with the protective coating is turned towards the inside of the cell to be in contact with the electrolyte 17.
• the uncoated face of the sample 15 is in contact with the plate 14 during the measurement.
• An O-ring 16 seals the structure.
• the system has three electrodes: the sample 15, acting as working electrode, an electrode 18 for reference to the saturated calomel and a counter-electrode 19 in platinum.
• a coil 20 is provided for a circulation of water in order to regulate the temperature of the electrolyte.
• Cell 10 is made of polymethyl methacrylate. The surface of the sample directly in contact with the electrolyte is 5.75 cm 2 .
• the electrolyte brought to 30 ° C, is a 3% NaCl solution, the pH of which is adjusted to 7.
• the whole study is carried out in a stagnant medium to simulate the natural conditions of use of the coatings.
• sample 15 The potential of sample 15 is continuously measured. To maintain a linear response of sample 15, a sinusoidal voltage of constant amplitude of 10 mV peak to peak, is superimposed on the corrosion potential. The frequencies swept during the measurements range from 10 5 Hz to 10 -2 Hz.
• a spray paint is then applied to the chemically treated support at room temperature and in an uncontrolled atmospheric medium.
• the spray paint consists of the mixture of a solution and powder of titanium oxide.
• This solution itself is made up in% by mass: of 50% of ethyl silicate oligomers of number average molecular mass (determined by tonometry) equal to 610, in an amount equivalent to 20-22% by mass of the solution in Si ⁇ 2; these oligomers can be obtained in known manner by hydrolysis of tetraethoxysilane Si (OC2H5) 4 using hydrochloric acid (or other mineral acid: H3PO4, HNO3 .7) - 31% methoxy-1, propanol-2 - 13% ethanol
• the paint is ground up to a maximum particle size of 5 ⁇ m.
• the polymerization of the film is then carried out thanks to a heat treatment in an infrared oven: three exposures of 10 seconds (100 ° C).
• the sample is then subjected to an impedancemetry test in the cell of FIG. 2, the conditions of the measurement being those set out above.
• the film loaded with Ti ⁇ 2 obtained according to the invention therefore constitutes a remarkable barrier to diffusion. It will be noted that below 300 hours of immersion, this system behaves like a perfect capacitor: completely insulating film, and whose electrical resistivity is difficult to measure conventionally. It has good adhesion and homogeneous cohesion. It passes all the adhesion tests described above.
• Such a plate is perfectly suitable for the manufacture of insulating sheets, for example.
• Example 1 A steel plate identical to that of Example 1 is subjected to the same chemical treatment as in Example 1. The plate is then rinsed with water and then dried. On this plate is then applied according to the technique used in Example 1 a paint consisting of a solution of zinc powder and mica (phyllosilicate).
• the ethyl silicate solution used in Example 1 contains oligomers with 4-5 silicon atoms on average.
• tetraethoxysilane in hydroethanolic solution is used as starting monomer.
• zinc dust of the lamellar type average size of the zinc particles close to 25 ⁇ m
• mica mica
• the mixing is carried out through a grinding-kneading step until a maximum particle size of 20 ⁇ m is obtained.
• the plate is subjected to a heat treatment as described in Example 1. A dry film with a thickness of 25 + 5 ⁇ m is obtained, having good adhesion and homogeneous cohesion.
• Example 2 The sample is then subjected to electrochemical tests as in Example 1. After 800 hours of immersion in the 3% NaCl electrolyte, the ionic resistance of the film amounts to 59 k_.cm 2 ; no rusting is observed visually.
• the dry film thus obtained with an average thickness of 9O ⁇ m, only offers an ionic resistance of 450 _.cm2 after 800 hours of immersion in the 3% NaCl electrolyte.
• the production of zinc salts is extremely important and leads to swelling of the coating, contrary to what can be observed by following the process according to the invention described above.
• the results of the electrochemical tests (potentiometry and impedancemetry) in the NaCl electrolyte (3% by mass) have been detailed below.
• the duration of the cathodic protection phase with zinc can be evaluated by potentiometry, and corresponds to the duration of immersion during which the equilibrium potential of the sample (coated substrate) is close to that of a zinc electrode. (approximately -1000 mV / DHW).
• the ionic resistance Ri and the capacity C of the coatings are evaluated by impedancemetry as in Example 1 at immersion times greater than the duration of the cathodic protection phase.
• the values Ri and C characterize a second protection mechanism: the anti-diffusion barrier by clogging of the pores due to the zinc corrosion salts (salts derived mainly from cathodic protection by zinc).
• the results are collated in Table I below.
• the sheet thus treated is then rinsed with hot water (60 ° C.) to remove the hydroxides formed, then rinsed with cold demineralized water.
• the sheet is dried in an oven at 120 ° C for 15 seconds.
• a coating solution is then applied to the treated galvanized steel. This solution has the following composition (in% by mass):
• the liquid film deposited is dried by double convection cooking in an oven for 30 seconds at around 120 ° C.
• the thickness of the dry film varies from 3 to 5 ⁇ m. It is necessary to wait 24 hours before obtaining the final properties of the coating.
• a handy product, resistant to solvents (methyl ethyl ketone, indelible felt), with a high gloss and very good adhesion to the support is obtained. No scale is observed even after 40 days of aging of the film.
• the sample is a GALFAN galvanized steel identical to that of Example 3. It is treated as in Example 3, but the duration of the treatment with potassium hydroxide is increased from 10 seconds to 30 seconds in order to take account of the presence of alumina on the surface, more resistant to bases than zinc oxide.
• EXAMPLE 5 The sample studied is a GALFAN galvanized steel identical to that of Example 3, which is treated as in Example 4. However, the tetraethoxysilane solution, described in Example 3, is added with colloidal silica (5% by mass in the solution). The silica charge is dispersed using a mechanical stirrer. This silica can be treated or not, so as to reduce the gloss of the dry coating. Table II below brings together the characteristics of different coatings obtained with the addition of 5% silica, depending on the types of silica used.
• a steel plate identical to that of Example 1 is degreased in a methyl ethyl ketone bath and it is subjected to a crystalline zinc-calcium phosphating treatment, a surface treatment commonly used before painting the steel. .
• the phosphating is carried out by immersion in a very dilute aqueous solution of orthophosphoric acid (at 0.01 g / l of H3PO4 of density 1.7) to which Zn (N ⁇ 3) 2.6H2 ⁇ (21 g / l) have been added , Ca (N03) 2,
• the sample thus treated is rinsed with demineralized water, then dried in an oven at 50 ° C.
• the sample is treated either thermally as in Example 1, or left to polymerize in an ambient medium with different relative humidity levels (from 20 to 70% RH) for 24 hours.
• a ferrous steel substrate identical to that of Example 1 is degreased in a methyl ethyl ketone bath.
• the plate thus degreased is then directly coated in a K HAND COATER device with K BAR threaded rods of a solution of the same composition as that used in Example 2, but containing neither lamellar zinc nor mica.
• the plate After depositing the liquid film, the plate is heat treated in an infrared oven for 1 minute.
• the thickness of the dry coating is 1 ⁇ m.
• a preliminary dilution in ethanol of the coating solution on the one hand, and the use of threaded rods of various sizes on the other hand allow the development of coatings of thicknesses ⁇ 1 ⁇ m.
• the adhesion of the various coatings is then tested by folding on cylinders with a diameter of 10, 20 and 30 mm with the application of adhesive tape. The results are reported in Table III below.
• the tetraethoxysilane solution can be applied to degreased steel only, but the main drawback of this method lies in its inability to form acceptable coatings of thickness greater than 1 ⁇ m.
• the process of the invention which consists of a chemical pretreatment of the substrate under precise conditions makes it possible to obtain coatings of much greater thickness (up to 10 ⁇ m when the coating is unloaded) without measurable alteration of their physicomechanical qualities. .
• the sample is a galvanized steel coated with a layer of 5 ⁇ m of primer and 20 ⁇ m of a polyester / melamine finish layer pigmented in titanium oxide at a pigment / binder ratio of 1.
• a coating solution of the same composition as that of Example 3 is applied to this sample.
• the liquid film deposited is dried by double convection cooking in an oven for 30 seconds at approximately 50 ° C.
• the thickness of the film varies from 3 to 5 ⁇ m.
• a product resistant to solvents is obtained, in particular to indelible felts which can be cleaned with denatured ethyl alcohol even after a waiting time of 48 hours.
• the coating retains its initial shine even after several indelible felt-tip writing cycles.
• This example illustrates the variant embodiment of the method of the invention which does not include a step of chemical attack on the substrate.
• Shot steel sample (DS 2.5) phosphated steel 90% by mass of zinc 90% in zinc 40% in zinc thickness 90 ⁇ m 40 ⁇ m 40 ⁇ m duration of cathodic protection 550 hours 1100 hours 2200 hours

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• 1996
  • 1996-08-29 EP EP96929381A patent/EP0922074A1/de not_active Withdrawn

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