Use of powder to coat a substrate by a powder coating process and powder coating processes

Abstract

The invention relates to the use of a powder for coating a substrate by a powder coating process, said powder comprising particles made of a composition C based on one or more polymers, said composition C comprising at least one polyaryletherketone and having the following characteristics: a melt flow index at 380°C under a 5 kg load being greater than or equal to 1.5 and less than or equal to 33 cm³ / 10 min; and a crystallization rate evaluated by an enthalpy of fusion measured by differential scanning calorimetry in second heating according to the thermal cycle indicated in the description, strictly greater than 0 J / g and less than or equal to 30.0 J / g. The invention also relates to a powder coating process for a substrate, and a coated substrate. Figure for abstract: no figure

Description

Title of the invention: Use of powder to coat a substrate by a powder coating process and powder coating processes technical field

[0001] The invention relates to the field of powders and powder coating processes.

[0002] More specifically, the invention relates to the use of a powder for coating a substrate by a powder coating process, said powder comprising particles made of a composition C based on one or more polymers and comprising at least one polyaryletherketone. The invention also relates to powder coating processes using this powder and to coatings obtained from this powder. Previous art

[0003] It is known from CN107674560, the use of a powder comprising a polyetherketoneketone having a T / I ratio of 55 / 45 and an intrinsic viscosity equal to 0.6 dL / L, and a carbon filler, such as graphene or a carbon nanotube, for coating a steel substrate, by electrostatic deposition.

[0004] The viscosity of polyetherketoneketone corresponds to a fairly fluid grade, typical of a powder coating application.

[0005] The document only addresses the surface appearance, which appears to be correct only for powders in which the carbon filler has been incorporated by compounding. The document provides very little detail on the implementation conditions of the electrostatic deposition coating process. The document does not address the issue of coating adhesion to the metal, nor the issue of coating crystallinity.

[0006] There is currently a need for the use of polyaryletherketone(s)-based powders that provide a coating with a good surface finish and good adhesion to the substrate, particularly for substrates with a metallic surface. Furthermore, the powders must exhibit a degree of adaptability to be used in various powder coating environments, so that the coatings can maintain a good surface finish and good adhesion to the substrate over a wide processing window. Objective of the invention

[0007] The objective of the invention is to propose the use of a powder comprising a polyaryletherketone to coat a substrate by a powder coating process.

[0008] An objective of the invention is, at least according to certain embodiments, to make it possible to obtain a coating having a good surface appearance, that is to say in particular essentially free or free from craters and / or having a smooth appearance (no orange peel).

[0009] An objective of the invention is, at least according to certain embodiments, to enable obtaining a coating having good adhesion to its substrate, in particular to a substrate having a metallic surface.

[0010] An objective of the invention is, at least according to certain embodiments, to allow control of the final crystallinity achieved by the coating.

[0011] An objective of the invention is, at least according to certain embodiments, to propose the use of a powder to coat a substrate by a powder coating process, said process being able to be implemented over a wide process window. Summary of the invention

[0012] The invention relates to the use of a powder for coating a substrate by a powder coating process, said powder comprising particles made up of a composition C based on one or more polymers, said composition C comprising at least one polyaryletherketone and having the following characteristics: a. a melt flow index at 380°C under a 5 kg load being greater than or equal to 1.5 and less than or equal to 33 cm³ / 10 min; and, b. a crystallization rate evaluated by an enthalpy of fusion measured by differential scanning calorimetry in second heating according to the thermal cycle indicated in the definitions, strictly greater than 0 J / g and less than or equal to 30.0 J / g.

[0013] According to certain embodiments, said composition C has a crystallization rate evaluated by an enthalpy of fusion measured by differential scanning calorimetry in second heating greater than or equal to 0.01 J / g and less than or equal to 25.0 J / g, preferably greater than or equal to 0.05 J / g and less than or equal to 10.0 J / g, and extremely preferably greater than or equal to 0.1 J / g and less than or equal to 2.5 J / g.

[0014] According to certain embodiments, said composition C has a melt flow index at 380°C under a 5 kg load being greater than or equal to 2 and less than or equal to 25 cm3 / 10 min and, preferably, being greater than or equal to 2.5 cm3 / 10 min and less than or equal to 20 cm3 / 10 min.

[0015] According to certain embodiments, said composition C is essentially made up of, or made up of, said at least one polyaryletherketone.

[0016] According to certain embodiments, said at least one polyaryletherketone of composition C is a polyetherketone essentially consisting of, or consisting of, an isophthalic repeating unit (I) having the chemical formula:

[0017] [Chem.l]

[0018] and a terephthalic repeating unit (T) having the chemical formula:

[0019] [Chem.2]

[0020] the molar ratio in terephthalic units relative to isophthalic units, denoted ratio T:I, being from 0:100 to 45:55 or from 55:45 to 65:35, and preferably from 55:45 to 65:35. The polyetherketoneketone may in particular be essentially made up of, or made up of, the repeat units T and I, the ratio T:I being from 57:43 to 63:37.

[0021] According to certain embodiments, said powder is essentially made up of, or made up of, said particles of composition C.

[0022] According to certain embodiments, said particles of composition C have a particle diameter distribution such that the median diameter dv50 is from 10 pm to 150 pm, and preferably from 15 pm to 75 pm, as measured by laser diffraction according to ISO 13320:2009.

[0023] The invention also relates to a powder coating process on a substrate comprising:

[0024] iii) a step of applying a layer of powder to the surface of the substrate

[0025] iv) a step where the applied powder layer is melted;

[0026] v) possibly repeating steps iii) and iv) allowing the application of several layers of powder; and,

[0027] vi) a cooling step, to obtain a substantially amorphous coating, the substantially amorphous coating being characterized by an enthalpy of fusion measured by differential scanning calorimetry in first heating with a temperature ramp of 20°C / min, strictly less than 5.0 J / g.

[0028] According to certain embodiments, the layer of powder applied, or where applicable each layer of powder applied, is melted at a temperature of at least 15°C above the melting point of said composition C and less than or equal to 400°C, and preferably at a temperature of at least 25°C above the melting point of said composition C and less than or equal to 390°C.

[0029] According to some embodiments, several layers, preferably at least three layers, and extremely preferably at least four layers of powder are applied.

[0030] According to some embodiments, the substrate has a metallic surface, preferably a surface comprising aluminum or iron.

[0031] According to certain embodiments, said step of applying a layer of powder is carried out by dipping in a fluidized bed of powder, by hot powdering without electrostatic charge of powder, or by electrostatic spraying of powder; and preferably is carried out by electrostatic spraying or hot powdering without electrostatic charge of powder.

[0032] According to some embodiments, the process includes, after said cooling step, an annealing step of the amorphous coating so as to obtain a semi-crystalline coating.

[0033] The invention also relates to a substrate coated with a coating comprising a composition C based on one or more polymers, said composition C comprising at least one polyaryletherketone and having the following characteristics: a. a melt flow index at 380°C under a 5 kg load being greater than or equal to 1.5 and less than or equal to 33 cm³ / 10 min; and, b. a crystallization rate evaluated by an enthalpy of fusion measured by differential scanning calorimetry in second heating according to the thermal cycle indicated in the description, strictly greater than 0 J / g and less than or equal to 30.0 J / g,

[0034] said coating having fewer than 15 defects per square decimeter,

[0035] preferably less than 10 defects per square decimeter,

[0036] and, in an extremely preferred manner, less than 5 defects per square decimeter. Detailed description of the invention Definitions

[0037] The term “powder” means a fractionated state of matter, generally in the form of very small pieces (particles), generally of a hundred micrometers or less.

[0038] The term "dv50" means the value of the powder particle diameter such that the volume-weighted cumulative particle diameter distribution function is equal to 50%. The value of "dv50" is measured by laser diffraction according to the ISO 13320:2009 standard, for example on a Malvern Mastersizer 2000® diffractometer.

[0039] The term "viscosity index" means the measurement taken at 25 °C, in an aqueous solution of 96% by mass sulfuric acid, according to ISO 307:2019, applied to a poly(aryl ether ketone). The viscosity index is expressed in deciliters per gram.

[0040] The term "hot volume melt flow index", otherwise known as MVR, means the measurement taken at 380°C under a 5kg load according to ASTM D1238-10. The hot volume melt flow index is expressed in cubic centimeters of composition per ten minutes (cm3 / 10 min).

[0041] In the present invention, the "crystallization rate of composition C" is evaluated using the enthalpy of fusion on a second heating by differential scanning calorimetry under a nitrogen atmosphere. The enthalpy of fusion for this measurement is expressed in joules per gram of composition (J / g). The thermal cycle for this measurement is as follows: - First heating from 20°C to 380°C, at a speed of 20°C / min; - First cooling from 380°C to 300°C, at a rate of 20°C / min; then from 300°C to 180°C, at a rate of 5°C / min; then from 180°C to 20°C, at a rate of 20°C / min; and, - Second heating 20°C to 380°C, 20°C / min.

[0042] This thermal cycle corresponds to the standard cycle with heating and cooling at 20°C / min, for which the cooling rate has been slowed down to between 300°C and 180°C. This modification is explained by the fact that the invention targets compositions with sufficiently slow crystallization.

[0043] The term "melting point" refers to the melting temperature at which a composition, at least partially crystalline, transitions to a viscous liquid state. In the invention, the melting point is measured by a second heating cycle, following the thermal cycle described above for measuring the enthalpy of fusion in a second heating cycle. More specifically, unless otherwise indicated, this refers to the peak melting temperature, and where applicable, the temperature of the highest peak in the case where several endothermic peaks are present on the thermogram.

[0044] In the present invention, the "crystallism of a coating" is evaluated using the enthalpy of fusion on first heating by differential scanning calorimetry under a nitrogen atmosphere, the first heating being carried out from 20°C to 380°C at a rate of 20°C / min. The enthalpy of fusion for this measurement is expressed in joules per gram of composition. A coating is considered to be in an amorphous state if its enthalpy of fusion on first heating is strictly less than 5.0 J / g. A coating is considered to be in a semi-crystalline state if its enthalpy of fusion in first heating is greater than or equal to 5.0 J / g, and preferably greater than or equal to 10.0 J / g. Composition C

[0045] The powder, the use of which is claimed in the present invention, comprises particles made up of a composition C. Composition C has the following cumulative characteristics: a) a melt flow index at 380°C under a 5 kg load being greater than or equal to 1.5 and less than or equal to 33 cm3 / 10 min, and, b) a crystallization rate evaluated by an enthalpy of fusion measured by differential scanning calorimetry in second heating according to the thermal cycle indicated in the definitions, strictly greater than 0 J / g and less than or equal to 30.0 J / g.

[0046] The inventors have demonstrated that selecting these two characteristics within specific ranges makes it possible to obtain a coating that is virtually free or completely free of defects, over a wide temperature range for the application of the powder coating process. Furthermore, the inventors have demonstrated that selecting these two characteristics within specific ranges makes it possible to obtain a coating with good adhesion to a metallic surface.

[0047] According to advantageous embodiments, composition C has a crystallization rate evaluated by an enthalpy of fusion measured by differential scanning calorimetry during a second heating greater than or equal to 0.01 J / g, preferably greater than or equal to 0.05 J / g, and most preferably greater than or equal to 0.1 J / g. This makes it possible, in particular, to crystallize the coating for which the powder is used sufficiently quickly during an optional annealing step as explained later.

[0048] According to advantageous embodiments, composition C has a crystallization rate evaluated by a melting enthalpy measured by differential scanning calorimetry in second heating of less than or equal to 25.0 J / g, preferably less than or equal to 10.0 J / g, and most preferably less than or equal to 2.5 J / g. This makes it possible, in particular, to obtain a coating in amorphous form, at least initially, that is virtually free or free of defects and has good adhesion to a substrate, in particular a substrate having a metallic surface.

[0049] Composition C can therefore have an enthalpy of fusion measured by differential scanning calorimetry in second heating according to the thermal cycle indicated in the definitions, greater than or equal to 0.01 J / g and less than or equal to 25.0 J / g, preferably greater than or equal to 0.05 J / g and less than or equal to 10.0 J / g, and extremely preferably greater than or equal to 0.1 J / g and less than or equal to 2.5 J / g.

[0050] According to advantageous embodiments, composition C has a melt flow index at 380°C under a 5 kg load of greater than or equal to 2 cm3 / 10 min, and preferably of greater than or equal to 2.5 cm3 / 10 min.

[0051] According to advantageous embodiments, composition C has a melt flow index at 380°C under a 5 kg load of less than or equal to 25 cm3 / 10 min and, preferably, of less than or equal to 20 cm3 / 10 min.

[0052] Composition C can therefore have a melt flow index at 380°C under a 5 kg load of 2 or greater and 25 cm³ / 10 min or less, and preferably 2.5 cm³ / 10 min or greater and 20 cm³ / 10 min or less. Such viscosity grades are generally reserved for other applications such as extrusion or calendering. The inventors found, quite surprisingly, that such a range of melt flow indexes at 380°C, selected in combination with a particular range of crystallization rates allowing for an amorphous coating (at least initially), was particularly beneficial with regard to the surface appearance of the coating and its adhesion to the substrate, over a wide range of application temperatures for a powder coating process.

[0053] Composition C is based on one or more polymers and includes at least one polyaryletherketone.

[0054] It generally comprises more than 50% by weight of polymer(s) relative to the total weight of the composition. Preferably, it comprises more than 75% by weight of polymer(s) relative to the total weight of the composition. In particular, it may comprise more than 80% by weight, or more than 85% by weight, or more than 90% by weight, or more than 95% by weight, or more than 98% by weight of the total polymer(s), relative to the weight of the composition.

[0055] According to certain embodiments, as described below, composition C comprises more than 95% by weight of the total polymer(s), relative to the weight of the composition. It is then essentially made up of said one or more polymers.

[0056] According to certain embodiments, composition C consists of said one or more polymers.

[0057] Said at least one polyaryletherketone generally represents more than 50% by weight, relative to the total weight of the polymer(s) of composition C. Said at least one polyaryletherketone may represent more than 60% by weight, or more than 70% by weight, or more than 75% by weight, or more than 80% by weight, or more than 85% by weight, or more than 90% by weight, or more than 95% by weight, or more than 98% by weight, relative to the total weight of the polymer(s) of composition C.

[0058] According to certain embodiments, as described below, said one or more polymers comprise at least 70% by weight of said at least one polyaryletherketone, relative to the total weight of the polymer(s) of composition C.

[0059] According to certain advantageous embodiments, as described below, said one or more polymers comprise at least 95% by weight of said at least one polyaryletherketone, relative to the total weight of the polymer(s) of composition C.

[0060] According to certain advantageous embodiments, as described below, composition C comprises only said at least one polyaryletherketone as polymer(s) in the composition. Polyaryletherketone

[0061] A polyaryletherketone (PAEK) comprises the following formula units:

[0062] (-Ar-X-) and (-Ar^Y-),

[0063] in which:

[0064] - Ar and An each designate a divalent aromatic radical;

[0065] - Ar and An can preferably be chosen from 1,3-phenylene, 1,4- phenylene, 1,1'-biphenylene divalent in positions 3,3', 1,1'-biphenyl divalent in positions 3,4', 1,4-naphthylene, 1,5-naphthylene and 2,6-naphthylene;

[0066] - X designates an electro-attractive group; it can preferably be chosen from among the carbonyl group and sulfonyl group;

[0067] - Y designates a group chosen from an oxygen atom, a sulfur atom, a alkylene group, such as -(CH)2- and isopropylidene.

[0068] In these motifs X and Y, at least 50%, preferably at least 70% and more particularly at least 80% of the X groups are a carbonyl group, and at least 50%, preferably at least 70% and more particularly at least 80% of the Y groups represent an oxygen atom.

[0069] According to a preferred embodiment, 100% of the X groups designate a carbonyl group and 100% of the Y groups represent an oxygen atom.

[0070] Advantageously, the PAEK(s) can / may be chosen from:

[0071] - a polyetherketone-ketone, also called PEKK; a PEKK comprises a / unit(s) of formula: -Ph-O-Ph-C(O)-Ph-C(O)-;

[0072] - a polyetheretherketone, also called PEEK; a PEEK comprises one or more motif(s) of formula: -Ph-O-Ph-O-Ph-C(O)-;

[0073] - a polyetherketone, also known as PEK; a PEK comprises one or more motif(s) of formula: -Ph-O-Ph-C(O)- ;

[0074] - a polyetheretherketoneketone, also called PEEKK; a PEEKK comprises one or more units of formula: -Ph-O-Ph-O-Ph-C(O)- Ph-C(O)-;

[0075] - a polyetheretherketone, also called PEEEK; a PEEEK comprises one or more units of formula: -Ph-O-Ph-O-Ph-O- Ph-C(O)-;

[0076] - a polyetherdiphenyletherketone also known as PEDEK; a PEDEK comprises one or more units of formula: a PEDEK comprises one or more units of formula -Ph-O-Ph-Ph-O-Ph-C(O)-;

[0077] - their mixtures; and,

[0078] - copolymers comprising at least two of the aforementioned motifs,

[0079] in which: Ph represents a phenylene group and -C(O)- a group carbonyl, each of the phenylenes being independently able to be of ortho (1-2), meta (1-3) or para (1-4) type, preferentially being of meta or para type.

[0080] In addition, defects, terminal groups and / or monomers may be incorporated in very small quantities into the polymers as described in the list above, without affecting their performance.

[0081] Preferably, in embodiments where the poly-aryl-ether-ketone is a copolymer, the latter has a homogeneous structure, in particular of statistical type.

[0082] PAEK can be a polyetherketoneketone essentially consisting of, and preferably consisting of: a terephthalic repeating unit and, where applicable, an isophthalic repeating unit, the terephthalic repeating unit (“T motif”) having the formula (1):

[0083] [Chem.3] v O ..____s O ♦..........-L / y— O <, 7 J........4* ' y .........♦ %....... / ....... /

[0084] (1)

[0085] the isophthalic motif (“motif I”) having the formula (2):

[0086] [Chem.4] OO (2)

[0087] The mass proportion of T motifs relative to the sum of T and I motifs can vary from 0% to 85%. In particular, the mass proportion of T motifs relative to the sum of T and I motifs can be from 0% to 5%; or from 5% to 10%; or from 10% to 15%; or from 15% to 20%; or from 15% to 20%; or from 20% to 25%; or from 25% to 30%; or from 30% to 35%; or from 35% to 40%; or from 40% to 45%; or from 45% to 50%; or from 50% to 55%; or from 55% to 60%; or from 60% to 65%; or from 65% to 70%, or from 70% to 75%, or 75% to 80%, or even 80% to 85%. The choice of the molar proportion of T motifs relative to the sum of T and I motifs is one of the factors that allows tuning the crystallization rate properties of polyetherketoneketones. A given molar proportion of T motifs relative to the sum of T and I motifs can be obtained by adjusting the respective concentrations of the reactants during polymerization, in a manner known per se.

[0088] PAEK can be a homopolymer essentially consisting of, or even consisting of, a repeating unit having the formula (3):

[0089] [Chem.5]

[0090] (3)

[0091] Such poly-aryl-ether-ketones are commercially available under the name KetaSpire® from Solvay, under the name VestaKeep® from Evonik and PEEK Victrex® from Victrex.

[0092] According to certain embodiments, PAEK can be a copolymer essentially consisting of, or even consisting of, a repeating unit having formula (3) and a repeating unit having formula (4):

[0093] [Chem.6]

[0094] (4)

[0095] The molar proportion of unit (3) relative to the sum of units (3) and (4) can range from 0% to 99%, preferably from 0% to 95%.

[0096] According to advantageous embodiments, said at least one polyaryletherketone of composition C is a polyetherketoneketone essentially consisting of, or consisting of, one isophthalic repeat unit (I) and one terephthalic repeat unit (T), the molar ratio T:I being from 0:100 to 45:55 or from 55:45 to 65:35, and preferably from 55:45 to 65:35. In these embodiments, composition C may essentially consist of, or consist of, the polyetherketoneketone as a polymer in the composition since the latter satisfies a crystallization rate evaluated by an enthalpy of fusion measured by differential scanning calorimetry in second heating strictly greater than 0 J / g and less than or equal to 30.0 J / g.

[0097] According to particular embodiments, composition C is essentially made up of, or consists of, a polyetherketone essentially made up of, or consisting of an isophthalic repeating unit (I) and a terephthalic repeating unit (T), the molar ratio T:I being from 57:43 to 63:37.

[0098] According to other, less preferred embodiments, composition C may comprise a polyaryletherketone having a crystallization rate, evaluated by an enthalpy of fusion measured by differential scanning calorimetry on second heating, equal to 0 J / g or strictly greater than 30.0 J / g. The composition shall then comprise an additive and / or another polymer enabling adjustment of the crystallization rate of composition C.

[0099] For example, for polyaryletherketones having a crystallization rate evaluated by an enthalpy of fusion measured by differential scanning calorimetry in second heating strictly greater than 30.0 J / g, the composition may include another polymer such as a polyetherimide (PEI), or a polyetherketoneketone having a molar ratio T:I of 0:100 to 45:55 or of 55:45 to 65:35, and preferably of 55:45 to 65:35, to decrease the crystallization rate of the composition.Examples of polyaryletherketones having a crystallization rate evaluated by enthalpy of fusion measured by differential scanning calorimetry on second heating strictly greater than 30.0 J / g include: a polyetherketoneketone having a T / I ratio of 70 / 30 or more, a homopolymer essentially consisting of, or even consisting of, the formula repeating unit (3), copolymers essentially consisting of, or even consisting of, formula repeating units (3) and (4).

[0100] According to certain embodiments, composition C is essentially composed of, or consists of, a polyaryletherketone selected from: a polyetherketoneketone having a T / I ratio of 70 / 30 or more, a homopolymer essentially composed of, or even composed of, the formula repeating unit (3), a copolymer essentially composed of, or even composed of, formula repeating units (3) and (4); and a polyetherimide, the polyetherimide representing from 5% to 30% by weight, relative to the total weight of polyaryletherketone and polyetherimide in the composition. Powder

[0101] Particles of composition C can be obtained by grinding flakes using techniques known to those skilled in the art. Grinding polymer flakes can be carried out at ambient temperature, i.e. at a temperature that can be, in particular, from 15°C to 35°C, for example 25°C.

[0102] Alternatively, the particles made up of composition C can be obtained by a molten spraying process, as described in patent application EP4408932.

[0103] The particles of composition C have a particle diameter distribution such that the median diameter dv50 is from 10 pm to 150 pm, and preferably 15 pm at 75 pm, as measured by laser diffraction according to ISO 13320:2009. Composition C particles may have a particle diameter distribution such that the median diameter dv50 is from 10 pm to 15 pm, or from 15 pm to 30 pm, or from 30 pm to 45 pm, or from 45 pm to 60 pm, or from 70 pm to 75 pm, or from 75 pm to 100 pm, or from 100 pm to 150 pm. Fillers and additives

[0104] The powder may also comprise one or more fillers. The fillers represent less than 50% by weight, preferably less than 40%, and preferably even less than 30% by weight relative to the total weight of the composition. Examples of fillers include mineral fillers such as carbon black, talc, nanotubes (carbon or non-carbon), and fibers (glass, carbon, etc.), ground or unground.

[0105] According to preferred embodiments, the powder used according to the invention does not include such fillers.

[0106] The powder used according to the invention may also comprise one or more functional additives. The functional additives generally represent less than 5% by weight of the total powder weight. Preferably, the functional additives represent less than 1% by weight of the total powder weight. Examples of functional additives include anti-cratering agents, spreading agents, flow agents, corrosion inhibitors, stabilizing agents (light, in particular UV, and heat), nucleating agents (polymeric or inorganic), optical brighteners, colorants, pigments, and energy-absorbing additives (including UV absorbers).

[0107] According to certain embodiments, the powder comprises a functional additive being a phosphate. The phosphate may, in particular, be a phosphate salt, such as, for example, a salt of H₂PO₄, HPO₄²⁻, or a mixture thereof, preferably having as a counter-ion a sodium ion, a potassium ion, or a calcium ion. The phosphate may be incorporated into composition C in a proportion greater than or equal to 10 ppm, or greater than or equal to 50 ppm, or greater than or equal to 100 ppm. Advantageously, the phosphate is incorporated into the composition in a proportion greater than or equal to 500 ppm, or greater than or equal to 750 ppm, or greater than or equal to 1000 ppm, or greater than or equal to 1500 ppm, or greater than or equal to 2000 ppm, or greater than or equal to 2500 ppm.

[0108] According to other embodiments, the powder does not include phosphate.

[0109] According to some embodiments, the powder may comprise an agent flow agent, for example a hydrophilic or hydrophobic silica. According to these embodiments, the flow agent represents from 0.01 to 0.4% by weight relative to the total weight of powder.

[0110] According to other embodiments, the powder does not include a flow agent.

[0111] According to some embodiments, the powder may comprise a corrosion inhibitor. Examples of corrosion inhibitors include phosphosilicates and borosilicates.

[0112] According to preferred embodiments, the powder does not include an anti-crater agent.

[0113] According to certain embodiments, the powder used according to the invention can consist of said polymer(s) and optionally of one or more functional additives.

[0114] According to certain embodiments, the powder used according to the invention may consist of said at least one polyaryletherketone and optionally of one or more functional additives. Powder coating process

[0115] A powder coating process according to the invention comprises: - i) optionally a surface treatment step of the substrate to be coated; - ii) optionally a preheating step of the substrate, the substrate possibly having undergone a surface treatment; - iii) a step of applying a layer of powder to the surface of the substrate which may have undergone surface treatment and / or may have been preheated; - iv) a step where the applied powder layer is melted; - v) possibly the repetition of steps iii) and iv) allowing the application of several layers of powder; and, - vi) a cooling step, to obtain a substantially amorphous coating.

[0116] The substantially amorphous coating is characterized by an enthalpy of fusion measured by differential scanning calorimetry in first heating with a temperature ramp of 20°C / min, strictly less than 5.0 J / g.

[0117] The optional surface treatment step may include degreasing and / or the application of abrasive particles to a surface of the substrate and / or the application of a chemical treatment to a surface of the substrate.

[0118] The optional surface treatment step may also include the application of a primer layer to the surface of the substrate.

[0119] According to preferred embodiments, the process does not include the application of a primer layer to the surface of the substrate.

[0120] According to some embodiments, the process does not involve the application of abrasive particles to a surface of the substrate.

[0121] According to some embodiments, the process does not include chemical treatment on a surface of the substrate.

[0122] According to certain embodiments, the process only involves degreasing the surface of the substrate to be coated. Indeed, the selection of composition C according to the invention makes it possible to obtain excellent adhesion, particularly on iron (including steel and cast iron) or aluminum surfaces, without any prior surface treatment other than simple degreasing.

[0123] The preheating step is optional according to some methods of application of the powder and mandatory according to other methods of application, as detailed below.

[0124] When a preheating step is implemented, the substrate, possibly having undergone one or more prior surface treatments, is advantageously heated to a temperature at least 15°C above the melting point of composition C. The preheating temperature may be at least 20°C or at least 25°C above the melting point of composition C. The preheating temperature is generally less than 400°C, and preferably less than 390°C.

[0125] The powder layer (step iii) or successive powder layers (steps iii and v) can be applied to or brought into contact with a substrate surface using numerous coating techniques well known to those skilled in the art. Preferably, the application is carried out by a method selected from the group consisting of fluidized bed dipping (preheating required), hot powder coating without electrostatic charge (preheating required), and electrostatic spraying (preheating optional).

[0126] According to advantageous embodiments, the application is carried out by a method selected from the group consisting of hot powder coating without electrostatic charge and electrostatic spraying.

[0127] According to some embodiments, the process comprises the steps of:

[0128] - preheating the surface to a temperature at least 15°C higher than the point of merging of the composition;

[0129] - dipping the surface in a fluidized bed comprising the powder or spraying on the surface of an electrically uncharged powder.

[0130] According to some embodiments, the process comprises the steps of:

[0131] - electrical charge of the powder, and

[0132] - spraying of the electrically charged powder onto the previously prepared surface preheated or not.

[0133] The powder layer or successive powder layers are melted at a temperature at least 15°C above the melting point of said composition C and preferably at a temperature at least 25°C above the melting point of melting of said composition C. The temperature generally remains below 400°C, and preferably below 390°C. The selection of composition C according to the invention has the advantage that a substantially defect-free coating with good adhesion to the substrate can be obtained over a wide temperature range at which the powder layer or successive powder layers are melted.

[0134] According to some preferred embodiments, in particular when several successive layers of powder are applied, the entire coating is remelted at least during the application of the last layer of powder.

[0135] According to certain embodiments, in particular when several successive layers of powder are applied, the entire coating is remelted with each new application of a layer of powder.

[0136] The duration of a step in which a layer of powder is melted, and / or the duration of a step in which the entire coating is melted, generally lasts from 3 minutes to 15 minutes. Too long a duration can lead to thinning, while too short a duration can lead to orange peel defects.

[0137] According to preferred embodiments, several layers of powder are applied. Preferably, at least 3 layers of powder are applied, and extremely preferably at least 4 layers are applied. Generally, no more than 10 layers of powder are applied to form the coating.

[0138] The cooling step is advantageously carried out in ambient air.

[0139] Preferably, the cooling is not implemented by quenching, that is to say by rapidly cooling the coating, at least partially molten. Indeed, such rapid cooling would generate stresses, and therefore brittleness, in the coating.

[0140] In embodiments where several layers are applied, the entire coating is advantageously melted after the application of the last layer of powder and cooled to room temperature.

[0141] The selection of composition C according to the invention thus makes it possible to obtain a substantially amorphous coating characterized by an enthalpy of fusion measured by differential scanning calorimetry during the first heating with a temperature ramp of 20°C / min, strictly less than 5.0 J / g. This coating is essentially free or defect-free and has good adhesion to the substrate.

[0142] An optional annealing step vii) allows the essentially defect-free or defect-free coating to crystallize while maintaining good adhesion to the substrate. The annealing step makes it possible, in particular, to obtain a semi-crystalline coating, preferably a semi-crystalline coating having an enthalpy of melting measured by differential scanning calorimetry in first heating with a temperature ramp equal to 20°C / min, greater than or equal to 10.0 J / g.

[0143] The semi-crystalline coating obtained may have an enthalpy of fusion greater than or equal to 15.0 J / g, or greater than or equal to 20.0 J / g, or greater than or equal to 25.0 J / g.

[0144] The annealing step can be carried out by heating the coating to a temperature at which the coating can crystallize sufficiently rapidly. If the powder consists primarily of polyetherketoneketone particles having a T / I ratio of approximately 60 / 40, the annealing temperature can be from 200°C to 290°C, and preferably from 220°C to 260°C. To avoid thermal shock, a temperature ramp is advantageously used to reach the annealing temperature. For example, a temperature ramp of 0.5°C / min to 3°C / min can be used to increase the temperature of the coating to be annealed from an initial temperature of, for example, 150°C to the annealing temperature. The coating can be left at the annealing temperature for a period of 30 minutes to 3 hours.

[0145] The process according to the invention can be implemented on any type of substrate. In advantageous embodiments, the substrate may have a metallic surface. The metallic surface preferably comprises iron or aluminum. The metallic surface may in particular be selected from degreased steel, smooth or shot-blasted, degreased phosphated steel, iron or zinc phosphated steel, Sendzimir galvanized steel, electro-galvanized steel, hot-dip galvanized steel, cataphoresis-treated steel, chromated steel, anodized steel, corundum-blasted steel, degreased aluminum, smooth or shot-blasted aluminum, chromated aluminum, cast iron, and any other metallic alloy comprising iron and / or aluminum. Coated substrate

[0146] The invention also relates to a coated substrate. The coating comprises, or is essentially made up of, or is made up of composition C. It is capable of being obtained by a powder coating process as described above.

[0147] The coating can be amorphous or semi-crystalline.

[0148] According to some embodiments, the coating is amorphous.

[0149] According to certain embodiments, the coating is semi-crystalline. In these embodiments In its production, it preferably has an enthalpy of fusion measured by differential scanning calorimetry in the first heating with a temperature ramp of 20°C / min, greater than or equal to 10.0 J / g. It may in particular have an enthalpy of fusion greater than or equal to 15.0 J / g, or greater than or equal to 20.0 J / g, or even greater than or equal to 25.0 J / g.

[0150] According to advantageous embodiments, the coating has fewer than 15 defects per square decimeter, preferably fewer than 10 defects per decimeter square, and preferably fewer than 5 defects per square decimeter. The defect count is described in the examples presented below.

[0151] According to some embodiments, the coating has a thickness greater than or equal to 250 micrometers. The coating generally has a thickness less than or equal to 1000 micrometers, and preferably less than or equal to 750 micrometers. Examples

[0152] Polyetherketone ketones from the Kepstan® 6000 range (T:I ratio of 60:40) and Kepstan® 7000 (T:I ratio of 70:30), marketed by Arkema, having different melt flow values ​​at 380°C, were used. Three powders were prepared by grinding PEKK flakes at room temperature to obtain a dv50 of 50 pm.

[0153] Each powder was previously dried at 120°C for 8 hours before use.

[0154] The substrates used were cold-rolled steels (SPCC, 100*50*3 mm). Their surface was simply degreased by cleaning with a cloth soaked in ethanol. No shot blasting was performed. The substrates were preheated before the first coating layer was applied to a preheating temperature (Tpreheat, °C) for a period of 8 minutes (sufficient for the substrates to reach the Tpreheat temperature). This preheating is not essential for applying the coating by electrostatic spraying. However, it does reduce the duration of the first reheating, as described below.

[0155] A layer of powder was then applied by electrostatic spraying (voltage: -40 kV, amperage: 10 pA) onto the substrates (step 1). The substrates coated with this layer of powder were then placed in an oven at temperature Trechauffe (°C) for a period of 4 minutes (step 2). This duration is sufficient to coalesce the powder particles of a layer without the formation of orange peel defects. Steps 1 and 2 were repeated three more times, without substantial cooling of the coated substrates between step 2 of layer n and step 1 of layer n+1, so as to obtain a coating resulting from the deposition of 4 successive layers of powder. The final reheating, that of the fourth layer, advantageously remelts all the successively applied layers.

[0156] Finally, the coated substrates were allowed to cool to room temperature down to 25°C.

[0157] Table 1 below summarizes the various experimental conditions mentioned above, as well as the observations and / or analyses that were carried out on the coated substrates cooled to 25°C. Each experimental condition was performed on two substrates to verify the repeatability of the results. The numerical results correspond to an average value for 2 coatings obtained under given experimental conditions.

[0158] The crystallization rate of each powder was evaluated by measuring the enthalpy of fusion AHv crist, obtained by a second heating according to the thermal cycle indicated in the definitions. The measurement is expressed in joules per gram of polyetherketoneketone.

[0159] The observations and / or analyses include:

[0160] - a visual observation of the general appearance of the visible surface of the coating in order to to determine whether the coating had defects or not and whether the coating was transparent (T) or opaque (O);

[0161] - a count of craters visible to the naked eye per unit area of ​​substrate (nb craters per square decimeter).

[0162] - an evaluation of crystallinity by measurement of the enthalpy of fusion AHcristaiiinity, obtained during the first heating with a temperature ramp of 20°C / min. The measurement is expressed in joules per gram of PEKK.

[0163] [Tables 1] Coated Substrate #1 #2 #3 #4 #5 #6 Invention (I) / Comparison (C) IIICCC Powder PI PI PI P2 P2 P3 Ratio T:I (PEKK) 60:40 60:40 60:40 60:40 60:40 70:30 Viscosity index (dl / g) N / AN / AN / A 0.85 0.85 0.95 At 380°C, under 5kg 12.5 12.5 12.5 71 71 N / A AHv_cnst (J / g) 0.5 0.5 0.5 0.5 0.5 35 Conditions for applying the coating Tpreheat (°C) 340 360 380 340 360 380 Reheating (°C) 340 360 380 340 360 380 Number of layers 4 4 4 4 4 4 Results Observation of defects No Yes Yes Yes Yes Yes Yes Transparent / Opaque Number of defects per dm² 0 2 1 1 15 >20 AH Constancy (J / g) 1 0 1 28 3 32.7

[0164] Table 1

[0165] It is observed that an essentially defect-free amorphous coating is obtained with the PI powder, regardless of the reheating temperature between 340°C and 380°C (#1,#2, #3).

[0166] It is observed that the P2 powder makes it possible to obtain an amorphous coating, but this coating contains many defects (#5). A semi-crystalline coating essentially free of defects is obtained using the P2 powder at a reheating temperature of 360°C (#4).

[0167] It is observed that the P3 powder allows a semi-crystalline coating to be obtained, but this coating includes many defects (#6).

[0168] The coated substrates obtained above (#1-#5) were then annealed. They were initially placed in an oven heated to 150°C for 3 hours to dry. The oven temperature was then increased from 150°C to 240°C at a rate of 1.5°C / min. A temperature plateau of 2 hours was maintained at 240°C. The annealed coated substrates were then removed from the oven and allowed to cool to room temperature.

[0169] Table 2 below summarizes the observations and / or analyses that were carried out on the coated substrates after annealing and cooling to 25°C. These observations and / or analyses include:

[0170] - a visual observation of the general appearance of the coating (Opaque(O) / Transparent (T));

[0171] - an evaluation of crystallinity by measurement of the enthalpy of fusion AHPri obtained during the first heating with a temperature ramp of 20°C / min. The measurement is expressed in joules per gram of PEKK.

[0172] - a qualitative adhesion control test by peeling, according to the principles of the NFT 58-112 standard. According to this qualitative test, adhesion is rated with a whole number from 0 to 4 according to the following scale: • 4: No delamination possible; • 3: Difficult to peel off on at least 50% of the surface of the strip; • 2: The strip can be peeled from the substrate - the force required is high, at the film resistance limit; • 1: The strip is easily removed from the substrate with little resistance; • 0: No membership).

[0173] [Tables2] Coated Substrate #1 #2 #3 #4 #5 Transparent / Opaque 0 0 0 0 0 AHcnstaiiinity (J / g) 29 29 28 35 36 Adhesion Rating 3 3 4 0~l 0~l

[0174] Table 2

[0175] It is observed that the coatings which were amorphous and essentially defect-free before annealing (#1, #2, #3) are semi-crystalline after annealing. Their adhesion to the substrate is good (note 3), or even very good (note 4).

[0176] The coating which was before annealing semi-crystalline and essentially defect-free (#4) has superior post-annealing crystallinity and exhibits very poor adhesion (note 0~l).

Claims

Demands

1. Use of a powder for coating a substrate by a powder coating process, said powder comprising particles made of a composition C based on one or more polymers, said composition C comprising at least one polyaryletherketone and having the following characteristics: a. a melt flow index at 380°C under a 5 kg load being greater than or equal to 1.5 and less than or equal to 33 cm3 / 10 min; and, b) a crystallization rate strictly greater than 0 J / g and less than or equal to 30.0 J / g, evaluated by an enthalpy of fusion measured by differential scanning calorimetry in a second heating according to the following thermal cycle: - First heating from 20°C to 380°C, at a rate of 20°C / min; - First cooling from 380°C to 300°C, at a rate of 20°C / min; then from 300°C to 180°C, at a speed of 5°C / min; then from 180°C to 20°C, at a speed of 20°C / min; and, - Second heating 20°C to 380°C, 20°C / min.

2. Use according to claim 1, wherein said composition C has a crystallization rate evaluated by an enthalpy of fusion measured by differential scanning calorimetry in second heating greater than or equal to 0.01 J / g and less than or equal to 25.0 J / g, preferably greater than or equal to 0.05 J / g and less than or equal to 10.0 J / g, and most preferably greater than or equal to 0.1 J / g and less than or equal to 2.5 J / g.

3. Use according to any one of claims 1 and 2, wherein said composition C has a melt flow index at 380°C under a 5 kg load being greater than or equal to 2 and less than or equal to 25 cm3 / 10 min and, preferably, being greater than or equal to 2.5 cm3 / 10 min and less than or equal to 20 cm3 / 10 min.

4. Use according to any one of claims 1 to 3, wherein said composition C is essentially made up of, or made up of, said at least one polyaryletherketone.

5. Use according to any one of claims 1 to 4, wherein said at least one polyaryletherketone of composition C is a polyetherketoneketone essentially consisting of, or consisting of, an isophthalic repeating unit (I) having the chemical formula: [Chem.7] O O and a terephthalic repeating unit (T) having the chemical formula: [Chem. 8]

6.

7.

8.

9. the molar ratio in terephthalic units relative to isophthalic units, noted ratio T:I, being from 0:100 to 45:55 or from 55:45 to 65:35, and preferably from 55:45 to 65:

35. Use according to claim 5, wherein said at least one polyaryletherketone of composition C is a polyetherketoneketone essentially consisting of, or consisting of, the repeat units T and I, the ratio T:I being from 57:43 to 63:

37. Use according to any one of claims 1 to 6, wherein said powder is essentially made up of, or made up of, said particles of composition C. Use according to any one of claims 1 to 7, wherein said particles of composition C have a particle diameter distribution such that the median diameter dv50 is from 10 pm to 150 pm, and preferably from 15 pm to 75 pm, as measured by laser diffraction according to ISO 13320:2009. A powder coating process on a substrate comprising: iii) a step of applying a layer of powder to the surface of the substrate iv) a step where the applied powder layer is melted; v) optionally the repetition of steps iii) and iv) allowing the application of several powder layers; and, vi) a cooling step, to obtain a substantially amorphous coating, the substantially amorphous coating being characterized by an enthalpy of fusion measured by differential scanning calorimetry in first heating with a temperature ramp of 20°C / min, strictly less than 5.0 J / g.

10. A process according to claim 9, wherein the layer of powder applied, or where applicable each layer of powder applied, is melted at a temperature at least 15°C above the melting point of said composition C and less than or equal to 400°C, and preferably at a temperature at least 25°C above the melting point of said composition C and less than or equal to 390°C.

11. A method according to any one of claims 9 and 10, wherein several layers, preferably at least three layers, and extremely preferably at least four layers of powder are applied.

12. A method according to any one of claims 9 to 11, wherein the substrate has a metallic surface, preferably a surface comprising aluminum or iron.

13. A method according to any one of claims 9 to 12, wherein said step of applying a layer of powder is carried out by dipping in a fluidized bed of powder, by hot powdering electrostatically charged with powder, or by electrostatic spraying of powder; and preferably is carried out by electrostatic spraying or hot powdering not electrostatically charged with powder.

14. A method according to any one of claims 9 to 13 comprising, after said cooling step, an annealing step of the amorphous coating so as to obtain a semi-crystalline coating.

15. Substrate coated with a coating comprising a composition C based on one or more polymers, said composition C comprising at least one polyaryletherketone and having the following characteristics: a. a melt flow index at 380°C under a 5 kg load being greater than or equal to 1.5 and less than or equal to 33 cm³ / 10 min; and, b. a crystallization rate strictly greater than 0 J / g and less than or equal to 30.0 J / g, evaluated by an enthalpy of fusion measured by differential scanning calorimetry in second heating according to the following thermal cycle: - First heating from 20°C to 380°C, at a speed of 20°C / min; - First cooling from 380°C to 300°C, at a rate of 20°C / min; then from 300°C to 180°C, at a rate of 5°C / min; then from 180°C to 20°C, at a rate of 20°C / min; and, - Second heating 20°C to 380°C, 20°C / min; said coating having fewer than 15 defects per square decimeter, preferably fewer than 10 defects per square decimeter, and, in an extremely preferred manner, less than 5 defects per square decimeter.