EP4225846A2

EP4225846A2 - Easily recyclable pigmented pulverulent composition for coating substrates

Info

Publication number: EP4225846A2
Application number: EP21807166.0A
Authority: EP
Inventors: Jean-Yves Loze; Pierrick ROGER-DALBERT
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2020-10-09
Filing date: 2021-10-08
Publication date: 2023-08-16
Also published as: WO2022074350A3; CN116438238A; JP2023545086A; FR3115043A1; KR20230084549A; WO2022074350A2; FR3115043B1

Abstract

The invention relates mainly to a pigmented pulverulent composition based on polyamide for coating substrates, comprising: (a) 40% to 99% by weight of at least one polyamide; (b) 1% to 30% by weight of at least one pigment; and (c) 0 to 30% by weight of at least one additive, in which the polyamide has an inherent viscosity, as measured using a Ubbelohde tube at 20°C on a solution at 0.5% by weight in m-cresol according to standard ISO 307, except that the measurement temperature is 20°C instead of 25°C, of greater than 0.7 (g/100g)-1, and in which the composition has a volume median diameter Dv50, as measured according to standard ISO 9276 - parts 1 to 6, of from 10 to 200 μm, preferably 30 to 50 μm. It further relates to a method for producing said composition, to the use thereof for coating a metallic substrate, and to an object comprising a metallic substrate coated with a coating obtained with the pigmented pulverulent composition based on polyamide.

Description

DESCRIPTION

TITLE: EASILY RECYCLABLE PIGMENTED PULVERULENT COMPOSITION FOR COATING SUBSTRATES

[Technical area]

This patent application relates to a pigmented powder composition for coating easily recyclable substrates. It also relates to a process for manufacturing such a composition, the use of this composition for coating substrates, in particular metallic ones, as well as the objects coated with a coating that can be obtained.

[prior technique]

It is known to use polymer powders to manufacture substrate coatings, in particular metallic ones. These powders are formulated from a resin, one or more pigments and specific additives such as plasticizers, stabilizers or flow agents.

The pulverulent composition is applied to the substrate in the form of loose powder, for example by electrostatic spraying or by immersion of the substrate in a fluidized bed of powder, and therefore does not require a solvent or binder. The polymers used for the manufacture of powders are usually thermosetting resins, but it is also possible to use thermoplastic polymers.

Polyamides are, due to their high chemical and thermal resistance, the polymers of choice for demanding applications, such as the coating of dishwasher baskets for example.

The powder composition for coating substrates can be manufactured according to various methods.

It is possible to dry mix the pigment(s) and any additives with the polymer powder. However, these powders are not easily recyclable. Indeed, the fraction of powder that does not reach the substrate during spraying, called “overspray”, which it is interesting to recover for recycling, generally does not have the same composition as the powder initially used and the coatings obtained from it therefore do not correspond to it in terms of appearance and properties.

Application WO 2012/034507 A1 describes a process in which the pigments and any additives are pre-mixed and then mixed with the molten polymer. The molten mixture is then cooled, granulated and ground into a powder. This process gives satisfactory results for a variety of polymers. However, the grades of polyamides suitable for obtaining coatings of powder are too ductile to consider grinding them at room temperature. Their grinding at low temperature by cryogenic grinding is possible, but expensive and with low yield. The powders thus obtained are not very rounded and can therefore be more difficult to use, in particular form clouds of inhomogeneous charged particles due to an increase in friction.

It is also known, for example from US Pat. No. 5,932,687, to manufacture a polyamide powder by hot dissolution in a solvent such as ethanol, and precipitation by cooling in powder form. This process requires large amounts of solvent and can produce porous particles. Furthermore, the incorporation of pigments by addition to the solution is only possible for limited contents and can pose difficulties because of their own nucleating effect. Document US Pat. No. 3,476,711 proposes grinding a low-viscosity polyamide and then heating it under inert gas so that its viscosity rises to the desired value. This document is however silent as to the problem of incorporating pigments and additives into the polyamide powder.

[Summary of Invention]

The object of the invention is therefore to propose a process for the manufacture of a powdery pigmented composition based on polyamide for the coating of substrates based on polyamide which has an appearance, in particular in terms of color and gloss, and properties, in particular mechanical, which are not altered even after recycling while being inexpensive.

Indeed, the present invention is based on the finding that a pigmented powder composition based on easily recyclable polyamide can be obtained by incorporating the pigment(s) into the low-viscosity polyamide in the molten state, the mixture then being crushed and then ground. before being subjected to a heat treatment step to reach the target viscosity of the polyamide.

The pulverulent composition thus obtained has a homogeneous distribution of the pigment(s) and additives in each grain. As a result, it is possible to ensure stability of the appearance, in particular of the color, and of the application properties in all circumstances, including after recycling. Also, according to a first aspect, the subject of the invention is a pigmented powder composition based on polyamide for coating substrates, comprising:

(a) 40 to 99% by weight of at least one polyamide;

(b) 1 to 30% by weight of at least one pigment; and

(c) 0 to 30% by weight of at least one additive, in which the polyamide has an inherent viscosity, as measured using an Ubbelohde tube at 20°C on a 0.5% by weight solution in m-cresol according to the ISO 307 standard except that the measurement temperature is 20°C instead of 25°C, greater than 0.7 (g/100g) ¹ , and wherein the composition has a volume median diameter Dv50, as measured according to ISO 9276 standard - parts 1 to 6, of 30 to 200 μm, preferably 30 to 50 μm.

According to one embodiment, the polyamide is chosen from PA 9, PA 10, PA 11, PA 12, PA 610, PA 612, PA 614, PA 618, PA 1010, PA 1012. According to one embodiment, the polyamide is a polyamide 11.

According to one embodiment, the pigment is chosen from titanium dioxide, carbon black, cobalt oxide, nickel titanate, molybdenum disulphide, aluminum flakes, iron oxides, zinc oxide, zinc phosphate, and organic pigments, such as phthalocyanine and anthraquinone derivatives.

According to one embodiment, the composition comprises 50 to 95% by weight of at least one polyamide. According to one embodiment, the composition comprises 1 to 30% by weight of at least one additive chosen from anti-crater agents, spreading agents, reducing agents, antioxidants, reinforcing fillers, UV stabilizers, fluidizing agents and corrosion inhibitors.

According to one embodiment, the polyamide has an inherent viscosity, as measured using an Ubbelohde tube at 20° C. on a 0.5% by weight solution in m-cresol according to the ISO 307 standard, except that the measurement temperature is 20°C instead of 25°C, less than 1.0 (g/100g) ¹ .

According to a second aspect, the subject of the invention is a process for the manufacture of such a pigmented powder composition, comprising the steps of:

(i) mixing one or more pigment(s) and optional additives with a polyamide in the molten state, the polyamide having an inherent viscosity of less than 0.6(g/100 g) ¹ ;

(ii) extruding the mixture obtained in step (i) into an extrudate;

(iii) grinding the extrudate obtained in step (ii) into a powdery composition; and

(iv) polycondensation in solid phase of the pulverulent composition obtained in step (iii) until the polyamide in the composition has an inherent viscosity greater than 0.8 (g/100 g) ¹ .

According to one embodiment, the polyamide used in step (i) has an inherent viscosity of less than 0.4 (g/100 g) ¹

According to one embodiment, step (ii) is carried out in a single-screw extruder or a twin-screw extruder.

According to one embodiment, step (Iv) is carried out in a dryer.

According to a third aspect, the subject of the invention is the use of such a composition for coating a substrate, in particular a metal substrate.

According to one embodiment, the coating is produced by electrostatic spraying or hot powdering. Finally, according to a fourth aspect, the subject of the invention is an object comprising a metal substrate coated with a coating obtained with such a pigmented powder composition. According to one embodiment, it is a pipe, an accessory, a pump, or a valve, a splined shaft, a sliding door track or springs, in particular of the truck or car seat shock absorber type, and in particular therefore parts used in automobile construction, or even a dishwasher basket or springs.

[Description of Embodiments]

Definition of terms

The term “inherent viscosity” means the viscosity of a polymer in solution, determined using Ubbelohde tube measurements. The measurement is carried out on a 75 mg sample at a concentration of 0.5% (m/m) in m-cresol. The inherent viscosity, expressed in (g/100 g) ¹ , is calculated according to the following formula: Inherent viscosity = ln(ts/to) x 1/C, with C = m/px 100, in which ts is the time d flow of the solution, to is the flow time of the solvent, m is the mass of the sample whose viscosity is determined and p is the mass of the solvent. This measurement is carried out according to the ISO 307 standard except that the measurement temperature is 20°C instead of 25°C. The viscosity of a composition comprising, in addition to the polymer, any pigments and fillers insoluble in m-cresol is determined by increasing the quantity of the sample so that the solution has a polymer concentration of 0.5% (m /m).

The term "melting temperature" means the temperature at which an at least partially crystalline polymer changes to the viscous liquid state, as measured by differential scanning calorimetry (DSC) according to standard NF EN ISO 11357-3 using a heating rate of 20°C/min.

The term "glass transition temperature" is understood to denote the temperature at which an at least partially amorphous polymer changes from a rubbery state to a glassy state, or vice versa, as measured by differential scanning calorimetry (DSC) according to the standard NF EN ISO 11357-2 using a heating rate of 20°C/min.

The term "polyamide" is understood to denote the polycondensation products of lactam(s), of amino-carboxylic acid(s) or of dicarboxylic acid(s) and diamine(s) and, in general, any polymer formed by units linked together by amide functions.

The term “monomer” within the meaning of the present application must be taken in the sense of “repeating unit”. Indeed, the case where a repeating unit of the polyamide (PA) consists of the association of a diacid with a diamine is particular. It is considered that it is the combination of a diamine and a diacid, that is to say the diamine.diacid pair (in equimolar quantity), which corresponds to the monomer. That is explained by the fact that individually, the diacid or the diamine is only a structural unit, which is not sufficient on its own to polymerize.

In the present application, the expression “based on polyamide” must be understood as meaning “based on one or more polyamides”. The same applies to the other components (for example, the term "a pigment" should be understood as meaning "one or more pigments")•

The term “average diameter by volume” or “Dv” is also understood to mean the average diameter by volume of a pulverulent material, as measured according to standard ISO 9276 - parts 1 to 6: “Representation of data obtained by particle size analysis ". There are different diameters. More specifically, the Dv50 designates the median diameter by volume, that is to say that corresponding to the 50th percentile by volume, and the ^DvlO and Dv90 respectively designate the average diameters by volume below which 10 or 90% are located. in particle volume. The volume-average diameter can be measured in particular by means of a laser particle sizer, for example a laser particle sizer (Malvern System Insitec). Associated software (RT sizer) then makes it possible to obtain the volumetric distribution of a powder and to deduce the Dv10, the Dv50 and the Dv90.

Unless otherwise indicated, all the percentages relating to the quantities mentioned in the present description are understood as mass percentages.

A. Pigmented powder composition

According to a first aspect, the invention relates to a pigmented powder composition based on polyamide intended to form a coating on a substrate.

The polyamide(s) of interest for this pulverulent composition can in principle be chosen from the multitude of polyamides available on the market.

Preferably, however, they are semi-crystalline polyamides, in particular linear aliphatic polyamides, and in particular polyamides derived from monomers comprising 9 or more, preferably 10 or more, carbon atoms.

Among the monomers of the amino acid type, mention may be made of α,β-aminocarboxylic acids, having from 6 to 18 carbon atoms, such as amino-caproic acid, 7-heptanoic acid, amino-9-nonanoic acid, amino- 10-decanoic, amino-ll-undecanoic and amino-12-dodecanoic acid. α,θ-aminocarboxylic acids, having 9 to 18 carbon atoms such as amino-11-undecanoic acid and amino-12-dodecanoic acid are preferred.

Monomers of the “diamine.diacid” type result from the condensation of a dicarboxylic acid with a diamine. By way of example of a dicarboxylic acid, mention may be made of acids having from 6 to 36, in particular those having 8 to 18 and in particular those having 10 to 12 carbon atoms. The diacids can be aliphatic, cycloaliphatic or aromatic diacids. Mention may be made, for example, of adipic acid, azelaic acid, suberic acid, sebacic acid, dodecanedioic acid HOOC-(CH2)IO-COOH, tetradecanedioic acid, isophthalic acid and terephthalic acid. Aliphatic diacids, in particular linear aliphatic diacids such as sebacic acid and dodecanedioic acid are preferred.

By way of example of a diamine, mention may be made of diamines having 2 to 36, preferably 4 to 18 carbon atoms. They can be aromatic, aliphatic or cycloaliphatic. By way of example, mention may be made of 1,4-tetramethylenediamine, 1,6-hexamethylenediamine, 1,8-octamethylenediamine, 1,10-decamethylenediamine and 1,12-dodecamethylenediamine, m-xylylenediamine, bis-p aminocyclohexylmethane and trimethylhexamethylene diamine.

For example diamines. diacids, mention may be made more particularly of those resulting from the condensation of 1,6-hexamethylenediamine or 1,10-decamethylenediamine with sebacic acid or dodecanedioic acid.

In the numeral notation X.Y, X conventionally represents the number of carbon atoms from diamine residues, and Y represents the number of carbon atoms from diacid residues.

According to a particular embodiment, the polyamide is chosen from PA 9, PA 10, PA 11, PA 12, PA 610, PA 612, PA 614, PA 618, PA 1010, PA 1012.

The polyamide in the composition according to the invention preferably has a melting point of less than or equal to 300°C. Preferably, the polyamide has a melting point of less than or equal to 250°C, in particular 200°C, in particular 190°C.

The polyamide in the pigmented powder composition according to the invention has an inherent viscosity greater than or equal to 0.7 (g/100 g) ¹ . Advantageously, the viscosity of the polyamide in the composition is moreover less than or equal to 1.2 (g/100 g) ¹ . Preferably, its inherent viscosity is less than or equal to 1.1 g/100 g) ¹ , in particular 1.0 (g/100 g) ¹ , in particular 0.9 (g/100 g) ¹ , more preferably 0.8 (g/100g) ¹ . Beyond a viscosity of 1.2 g/100 g) ¹ , the composition becomes difficult to apply. A polyamide with a viscosity between 0.8 and 1.0 (g/100 g) ¹ gives coatings with particularly interesting properties.

The median diameter by volume Dv50 of the pigmented powdery composition according to the invention is from 30 to 200 μm, in particular from 30 to 100 μm, and in particular from 30 to 50 μm and even more preferably 32 to 38 μm Dv50 of the pigmented pulverulent composition may be 30 to 50 μm, or 50 to 80 μm, or 80 to 100 μm, or 100 to 130 μm, or 130 to 150 μm, or 150 to 180 μm, or 180 to 200 μm. The polyamide(s) are preferably present in a mass quantity, relative to the total mass of the pulverulent composition, of 40 to 99%, more preferentially of 50 to 95%, even more preferentially of 60 to 90%, for example of 40 to 45%, or 45 to 50%, or 50 to 55%, or 55 to 60%, or 60 to 65%, or 65 to 70%, or 70 to 75%, or 75 to 80%, or from 80 to 85%, or from 85 to 90%, or from 90% to 95%, or even from 95 to 99%.

The pigmented powder composition according to the invention also comprises one or more pigments or dyes. These pigments or dyes are generally found in powder form.

The pigment can in principle be freely chosen from the pigments used in the conventional manner. It can in particular be chosen from mineral pigments such as titanium dioxide, carbon black, cobalt oxide, nickel titanate, molybdenum disulphide, aluminum flakes, iron oxides, zinc, zinc phosphate, and organic pigments, such as phthalocyanine and anthraquinone derivatives.

The dye can also be of any type known to those skilled in the art. Mention may be made in particular of azo dyes, anthraquinone dyes, dyes derived from indigo, triarylmethane dyes, chlorine dyes and polymethine dyes.

The pigments and dyes are preferably present in a quantity by mass, relative to the total mass of the pulverulent composition, of 1 to 30%, more preferentially of 2 to 10%, even more preferentially of 3 to 5%, for example of 0 to 5%, or 5 to 10%, or 10 to 15%, or 15 to 20%, or 20 to 25%, or 25 to 30%.

The pigmented powder composition according to the invention may also comprise, where appropriate, one or more additives chosen from the group consisting of anti-crater agents or spreading agents, reducing agents, antioxidants, reinforcing fillers, UV stabilizers , fluidizing agents, corrosion inhibitors, or mixtures thereof. These additives are advantageously in powder form.

The reinforcing filler can be of any type suitable for the preparation of powders based on polyamides. However, it is preferred that the filler be selected from the group consisting of talc, calcium carbonates, manganese carbonates, potassium silicates, aluminum silicates, dolomite, magnesium carbonates, quartz, boron nitride, kaolin, wollastonite, titanium dioxide, glass beads, mica, carbon black, mixtures of quartz, mica and chlorite, feldspar and dispersed nanoscale fillers such as nanotubes of carbon and silica. It may also be fibers, in particular glass fibers and carbon fibers. Particularly preferably, the filler is calcium carbonate. The anti-crater and/or spreading agent can be of any type known to those skilled in the art. Preferably, the anticrater and/or spreading agent is selected from the group consisting of polyacrylate derivatives.

The UV stabilizer may be of any type known to those skilled in the art. Preferably, the UV stabilizer is selected from the group consisting of resorcinol derivatives, benzotriazoles, phenyltriazines and salicylates.

The antioxidants can be of any type known to those skilled in the art. Preferably, the antioxidants are selected from the group consisting of copper iodide combined with potassium iodide, phenol derivatives and hindered amines.

The fluidizing agent may be of any type known to those skilled in the art. Preferably, the fluidizing agent is selected from the group consisting of aluminas and silicas.

The corrosion inhibitors can be of any type known to those skilled in the art. Preferably, the corrosion inhibitors are selected from the group consisting of phosphosilicates and borosilicates.

Preferably, the composition comprises less than 10% by weight, or even is essentially devoid of matting agent.

These additives are preferably present in a quantity by mass, relative to the total mass of the pulverulent composition, of 0 to 50%, more preferentially of 0 to 30%, even more preferentially of 0 to 5%, for example from 0 to 5%, or 5 to 10%, or 10 to 15%, or 15 to 20%, or 20 to 25%, or 25 to 30%, or 30 to 35%, or 35 to 40% , or 40 to 45%, or 45 to 50%. According to one embodiment, the pigmented powder composition according to the invention essentially consists, or consists, of one or more polyamides, one or more pigments, and optionally one or more additives as described above.

Advantageously, the pigments and/or additives are mixed with the polyamide in the molten state. Such a mixture can be produced for example by compounding, in particular in an extruder. The pigments and/or additives thus added are then found in the form coated with polyamide.

B. Process for manufacturing the powder composition

The invention also relates to a process for the preparation of a pigmented powder composition based on polyamide, comprising the steps of:

(ii) Extrusion of the mixture obtained in step (i) into an extrudate;

(iii) Grinding of the extrudate obtained in step (ii) into a powdery composition; and (iv) Polycondensation in solid phase of the pulverulent composition obtained in step (iii) until the polyamide has an inherent viscosity greater than 0.8 (g/100 g) ¹ -

The polyamide having an inherent viscosity of less than 0.6 (g/100 g) ¹ used in step (i) can be obtained by polycondensation of one or more monomers as described above in the presence of water and the if necessary, a suitable catalyst.

The monomer(s) can be chosen from amino acids such as aminocaproic acid, amino-7-heptanoic, amino-ll-undecanoic, amino-12-dodecanoic, and/or mixtures thereof, preferably l amino-11-undecanoic acid or a mixture thereof.

It can also be a mixture of diamine monomers and diacid monomers, such as a mixture of diamine monomers such as hexamethylenediamine, decanediamine, dodecamethylenediamine, metaxylylenediamine, bis-p aminocyclohexylmethane and trimethylhexamethylenediamine with diacid monomers such as isophthalic, terephthalic, adipic, azelaic, suberic, sebacic, dodecanedioic, tetradecanedioic acids, or a mixture thereof.

According to one embodiment, the water is added in an amount of 10 to 40%, preferably 20 to 30% by weight relative to the total weight of the mixture. Water can be added to the mixture during the supply step, and/or during the polycondensation step.

The catalyst may in particular be an acid based on phosphorus such as phosphoric acid and/or phosphorous acid.

The polyamide synthesis reaction is known per se, and described in particular in the Nylon Plastics Handbook, Ed. Melvin I. Kohan, Hanser Publishers 1995 pages 17 to 27.

The inherent viscosity of the polyamide used in step (i) of the process is less than 0.6 (g/100 g) ¹ and preferably comprised in the range going from 0.25 to 0.55, preferably between 0.3 and 0.4 (g/100g) ¹ .

Advantageously, step (i) is carried out in a mixer under shear such as a single or twin screw extruder.

The pigment(s) as well as any additives can be introduced into the mixer with the polyamide or subsequently. If the pigmented powder composition comprises several pigments, these can be added in the form of a masterbatch in order to facilitate homogenization. The masterbatch can in particular be made from the polyamide used in the composition.

Extrusion step (ii) can be carried out through a pelletizing die to produce pellets. The volume median diameter Dv50 of the granules is advantageously within a range extending from 1 to 10 and in particular from 2 to 4 mm. Alternatively, the extrusion can be carried out through a die to a cooled rolling mill in which the mixture solidifies or using a calender. Then the solidified mixture can be fed to a crusher to produce flakes. These scales typically have an average size of 5x5x1 mm.

Step (iii) is advantageously carried out in a mechanical mill, and at room temperature, in particular in an impact mill such as a hammer mill, a knife mill, a disk mill, or an air jet mill. A grinding aid such as silica, preferably pyrogenic, can be added to the polyamide before grinding.

Advantageously, this step can be carried out in a grinder provided with an integrated selector. In this case, the particle size of the desired composition can be adjusted directly by adjusting the grinding speed, preferably, the adjustment of the grinding speed is made by means of a selector integrated into the grinder.

In general, it may be advantageous to follow step (iii) with a step (iiia) of selecting the powdery composition obtained with a view to adjusting its particle size. The selection can be carried out for example by sieving and/or classification.

It is particularly advantageous to use a grinder equipped with an internal selector. The particle size of the powder composition can be adjusted by adjusting the grinding speed as well as the speed of the selector integrated into the grinder.

Advantageously, the pulverulent composition resulting from stage (iii) if necessary has a median diameter by volume Dv50 of 30 to 200 μm, preferably of 30 to 50 μm in particular of 32 to 38 μm. The Dv50 of the pigmented powder composition can be from 30 to 50 μm, or from 50 to 80 μm, or from 80 to 100 μm, or from 100 to 130 μm, or from 130 to 150 μm, or from 150 to 180 μm, or 180 to 200 pm.

Step (iv) of polycondensation in the solid phase can be carried out at a temperature above the glass transition temperature but below the melting temperature of the polyamide. Advantageously, the reaction is carried out under an inert atmosphere, for example under nitrogen or under vacuum. The reaction time required to reach the expected inherent viscosity depends on the temperature chosen; it can be established by simple routine tests. Advantageously, this step can be carried out in a dryer.

According to the invention, the inherent viscosity of the polyamide in the powdery pigmented composition based on polyamide is greater than 0.7 (g/100 g) ¹ . Advantageously, it is moreover less than 1.2 (g/100 g) ¹ . Preferably, its inherent viscosity is less than or equal to 1.1 g/100 g) ¹ , in particular 1.0 (g/100 g) ¹ , in particular 0.9 (g/100 g) ¹ , still preferred 0, 8 (g/100g) ¹ .

C. Use for coating a substrate The pigmented powder composition based on polyamide according to the invention is especially useful for coating substrates, especially metallic ones.

According to another aspect, the invention therefore relates to the use of the pigmented powder composition based on polyamide as described above for coating a substrate. By "metal substrate" is meant a substrate which comprises, consists essentially of, or consists of, one or more metals. The metal substrate can be of any type. Preferably, the metal substrate is a piece of plain or galvanized steel, aluminum or aluminum alloy.

Before coating, the metal substrate may have undergone one or more of the surface treatments well known to those skilled in the art, such as coarse degreasing, alkaline degreasing, brushing, shot-blasting or sandblasting, fine degreasing, hot rinsing, phosphating degreasing, iron/zinc/tri-cation phosphating, chromating, cold rinsing and chromic rinsing. Thus, the pigmented powder composition can be used for coating treated or untreated metal substrates.

Advantageously, the substrate intended to be coated is made of degreased, smooth or shot-blasted steel, degreased phosphated steel, iron or zinc phosphated steel, Sendzimir galvanized steel, electrogalvanized steel, hot-dip galvanized steel, cataphoresis-treated steel, chromated steel, anodized steel, sandblasted with corundum, degreased aluminum, smooth or shot-blasted aluminum, chromated aluminum, cast iron or any other metal alloy.

The substrate can be coated in whole or in part.

Preferably, the coating formed on the substrate is a film 100 to 550 μm thick, more preferably 100 to 300 μm thick. In embodiments, the film has a thickness of 100 to 150 μm, or 150 to 200 μm, or 200 to 250 μm, or 250 to 300 μm, or 300 to 350 μm, or 350 to 400 μm. pm, or from 400 to 450 pm, or from 450 to 500 pm, or from 500 to 550 pm.

Preferably, the coating on the substrate has an inherent viscosity greater than or equal to 0.7 (g/100 g) ¹ . The inherent viscosity of the coating may be different from that of the powder composition used to form it. In particular, the inherent viscosity of the coating can be higher due to a resumption of polycondensation under the conditions of formation of the coating. In some embodiments, the coating on the substrate has an inherent viscosity greater than or equal to 0.8, greater than or equal to 0.85, or greater than or equal to 0.9, or greater than or equal to 0.95, or greater than or equal to 1.05, or greater than or equal to 1, or greater than or equal to 1.1, or greater than or equal to 1.15, or greater than or equal to 1.2, or greater than or equal to 1.25 , or greater than or equal to 1.3. In the above, the inherent viscosity is expressed in (g/100 g)-1. A subject of the invention is also a process for coating a substrate comprising the following steps: bringing the substrate into contact with the pigmented pulverulent composition based on polyamide as described above; and melting the powder composition under the effect of heat.

The pigmented powder composition can be applied to or brought into contact with a substrate using numerous techniques well known to those skilled in the art. Preferably, the coating is produced by electrostatic spraying or by hot powdering.

Alternatively, the coating can be made by electrostatic spraying.

The step of bringing the substrate into contact with the pigmented pulverulent composition based on polyamide can then comprise the steps of: electrical charging of the pulverulent composition; spraying the electrically charged powder composition onto the substrate; and heating of the substrate to be coated covered with powder composition to a temperature above the melting point of the polyamide.

Electrostatic spray coating consists of depositing electrostatically charged powder particles on a substrate, in particular at room temperature. The powdery composition may be electrostatically charged as it passes through the nozzle of spray equipment. The composition thus charged can then be sprayed onto the substrate to be coated which is connected to a zero potential. The coated substrate can then be placed in an oven at a temperature to fuse the composition into a film.

The powder projection equipment can be of any type, for example an electrostatic gun which charges the powder by Corona effect and/or by triboelectrification. Preferably, the nozzle is brought to a high potential of between ten and a hundred kilovolts, of negative or positive polarity.

Preferably, the flow rate of powder in the projection equipment is 10 to 200 g/min, and more preferably, 50 to 120 g/min. Preferably, the temperature of electrostatic application of the powder is from 15 to 25°C. Preferably, the residence time of the substrate in the oven is 3 to 15 minutes. The heating temperature of the powder-coated substrate can be at least 30°C higher, preferably 30 to 60°C higher than the melting temperature of the polyamide. The substrate can then be cooled, for example, to room temperature.

According to another embodiment, the coating of the substrate is carried out by hot powdering. The step of bringing the substrate into contact with the pigmented powder composition then comprises the steps of: heating the substrate to a temperature above the melting temperature of the polyamide; spraying the pigmented powder composition onto the substrate.

The substrate heating temperature may be as described above in connection with fluidized bed dip coating. The substrate can then be cooled, for example, to room temperature. The sprayed composition may or may not be electrostatically charged.

D. Obtainable Coated Items

According to another aspect, the invention relates to an object comprising a substrate covered with a coating capable of being obtained by melting the powder composition as described above. Indeed, the coating gives the object effective anti-corrosion and anti-abrasive protection.

This object is preferably intended: for the transfer of fluids, in particular in the form of piping, accessories, pumps or valves; automotive, in particular in the form of a splined shaft, sliding door rail or springs, in particular of the truck shock absorber type or automobile seats; wire articles, in particular in the form of dishwasher baskets or springs.

[Brief description of figures]

The invention will be better understood with regard to the following description and the figures, which show:

[Fig. 1] represents a diagram of the process for recycling the powder of examples 1 to 4 used to manufacture films;

[Fig. 2] represents a semi-logarithmic diagram of the particle size distribution by volume (fraction of volume as a function of size) of a powder according to example 1, measured using a Malvern Insitec laser particle sizer (solid line: virgin powder ; -o-: powder recycled once; -□- powder recycled twice; -0- powder recycled three times);

[Fig. 3] represents a semi-logarithmic diagram of the particle size distribution by volume (fraction of volume as a function of size) of a powder according to example 2, measured by means of a Malvern Insitec laser particle sizer (solid line: virgin powder ; -o-: powder recycled once; -□- powder recycled twice; -0- powder recycled three times);

[Fig. 4] represents a semi-logarithmic diagram of the particle size distribution by volume (fraction of volume as a function of size) of a powder according to example 3, measured by means of a Malvern Insitec laser particle sizer (solid line: virgin powder; -o-: powder recycled once; powder recycled twice; -0- powder recycled three times); and

[Fig. 5] represents a semi-logarithmic diagram of the particle size distribution by volume (fraction of volume as a function of size) of a powder according to Example 4, measured using a Malvern Insitec laser particle sizer (solid line: virgin powder -o-: powder recycled once; powder recycled twice; -0- powder recycled three times).

[EXAMPLES]

EXAMPLE 1

A pigmented powdery composition based on polyamide was manufactured according to the following process.

First, a low viscosity polyamide 11 was synthesized, called in the following

"prepolymer", from 1.2 kg of amino-ll-undecanoic acid in the presence of 0.5 kg of water, 5 g of hypophosphorous acid and 9.8 g of phosphoric acid. The mixture is heated to a temperature of 190° C. in 2 hours with stirring as soon as the temperature reaches 160° C. or the pressure exceeds 8.5 bars. During the synthesis, the water initially charged with amino-ll-undecanoic acid is eliminated by evaporation at constant pressure (P=10 bars). After having drawn off a quantity of water of 430 g, the molten prepolymer is extruded by means of a twin-screw extruder. The mixture is then cooled using two steel rollers with circulation of cold water to be solidified, cooled and crushed into scales.

The prepolymer thus obtained, having a viscosity of 0.35, and is mixed in a suitable container with a formulation of additives comprising antioxidants and spreading agents and a white pigment based on titanium dioxide in the proportions indicated. in Table 1 below.

This mixture is introduced into a twin-screw extruder to be melted and intimately mixed and then extruded. The mixture is then cooled using two steel rollers with circulation of cold water to be solidified and cooled and then crushed into scales.

The pigmented and additive prepolymer recovered in the form of flakes is then ground in a hammer mill equipped with an internal selector until a powder with a volume median diameter Dv50 is obtained, as measured according to ISO 9276 - parts 1 at 6, from 35pm.

The ground powder is then subjected to solid phase polycondensation in a dryer at 140-152° C. under vacuum in order to increase the viscosity of the polyamide to 0.93 (g/100 g) ¹ . ^Table 1]

Composition of pigmented powder compositions

EXAMPLE 2 (Example for comparison to EXAMPLE 1)

By way of comparison, a pigmented powdery composition based on polyamide was manufactured according to the following process.

The prepolymer obtained according to the process indicated in Example 1 in the form of scales is ground in a hammer mill equipped with an internal selector until a powder is obtained having a median diameter by volume Dv50, as measured according to the standard ISO 9276 - parts 1 to 6, from 35pm.

The ground prepolymer is then subjected to polycondensation in the solid phase at 140-152° C. under vacuum in order to increase the viscosity of the polyamide up to 0.93 (g/100 g) ¹ .

Finally, the pulverulent polyamide 11 is mixed in a rapid mixer of the Henschel type for 120 seconds at 1800 rpm, at room temperature (between 15 and 50° C.) with the formulation of additives and a white pigment based on carbon dioxide. titanium in the proportions indicated in Table 1 above.

EXAMPLE 3

First, a low viscosity polyamide 11 was synthesized, called in the following

"prepolymer", from 1.2 kg of amino-ll-undecanoic acid in the presence of 0.5 kg of water and 9.5 g of hypophosphorous acid. The mixture is heated to a temperature of 190° C. in 2 hours with stirring as soon as the temperature reaches 160° C. or the pressure exceeds 8.5 bars. During the synthesis, the water initially loaded with amino-ll-undecanoic acid is eliminated by evaporation at constant pressure (P=10 bars). After having drawn off a quantity of water of 430 g, the molten prepolymer is extruded by means of a twin-screw extruder. The mixture is then cooled using two steel rollers with circulation of cold water to be solidified, cooled and crushed into scales. The prepolymer thus obtained is mixed in a suitable container with a formulation of additives: a white pigment based on titanium dioxide, a blue pigment based on cobalt salt and a black pigment of the carbon black type in the proportions indicated in the table 1 above.

The ground powder is then subjected to solid phase polycondensation in a dryer at 140-152° C. under vacuum in order to increase the viscosity of the polyamide to 0.93 (g/100 g) ¹ .

EXAMPLE 4 (Example for comparison to EXAMPLE 3)

Finally, the pulverulent polyamide 11 is mixed in a rapid mixer of the Henschel type for 120 seconds at 1800 rpm, at ambient temperature (between 15 and 50° C.) with a formulation of additives, a white pigment based on carbon dioxide titanium, a blue pigment based on cobalt salt and a black pigment of the carbon black type in the proportions indicated in Table 1 above.

Production of coatings

In order to compare the applicative properties of the pigmented powder compositions as they were recycled, the virgin powder prepared in the previous examples was used to manufacture a first film (virgin film), then the excess powder was recovered three times. successively to manufacture recycling films, according to the procedure detailed in FIG.

1.

First, the virgin and recycled powders were characterized by measuring the particle size by volume (see Fig. 2 to 5) and the DvlO, Dv50 and Dv90, as measured according to ISO 9276 standard - parts 1 to 6, using a laser particle sizer (Malvern System Insitec) and the associated software (RT sizer). The particle size distributions obtained for the powders are illustrated in Figs. 2 to Fig. 5. The Dv10, Dv50 and Dv90 values recorded on these curves are collated in Table 2 below.

From these results, a moderate change in the particle size of the powders is observed as they are recycled. Indeed, the extraction of air in the spray booth entrains some of the fine particles of the powder. It is further noted that the Dv90 of the powder of Example 2 increases markedly more than that of the powder of Example 1 and that the Dv90 of the powder of Example 4 increases markedly more than that of the powder of 1 example 3.

The particle size curves (Fig. 2 to Fig. 5) also show that the maximum diameters of the powders of Examples 1 and 3 remain essentially stable around 200 μm, whereas they increase for the powders of Examples 2 and 4 to more 300 µm at the third recycle, indicative of particle agglomeration. However, because of their weight, the large particles have a greater tendency to detach from the metal support before passing through the oven, which makes the application of the powders of examples 2 and 4 more difficult. Moreover, the coalescence of these particles is longer and therefore affects the film formation.

^Table 2] Evolution of the particle size of the powder composition

The films were manufactured by applying the powder by means of an electrostatic gun (Corona positive, +35 to + 45 kV, 10 to 30 pA) on 3 mm thick steel metal plates treated with an anti-corona treatment. -adherent (silicone type coating), facilitating the subsequent detachment of the coating films. The metal plates thus coated with powder were then heat-treated (oven at 220° C. for 10 minutes), in order to melt the powder and obtain a film. The films are then peeled off from the substrates to be characterized in terms of appearance and mechanical properties.

The films were characterized by the color of the films on an Insitec spectrophotometer from Malvern by means of their coordinates L*, a*, b* and the difference in tint dE*, according to the ISO 18314 standard. In addition, their gloss at 60° was determined using a Byk micro-Tri-Gloss glossmeter according to the ISO 2813 standard. Finally, the appearance of the films was visually inspected, to classify them as follows: (+) = homogeneous appearance and bright ; (-) = heterogeneous and satin aspect, some craters; (--) = heterogeneous and satin aspect, numerous craters.

The results of these measurements and evaluations are collated in Table 3 below.

It is noted that even before any recycling, the appearance of the film resulting from the powder of example 1 is much more homogeneous and shiny than that of example 2. The same is true for the film resulting from the powder of example 3 which is also much more homogeneous and shiny than that of example 3. After recycling, the films obtained from the powder of example 1 and those obtained from the powder of example 3 exhibit high and virtually unchanged gloss regardless of the number of recyclings. In contrast, the films obtained from the powder from Example 2 and the films obtained from the powder from Example 4 see their gloss decrease as recycling progresses, which reflects a roughness of higher surface area and poorer film formation. This observation can be related to the presence of large particles, whose coalescence would be less perfect. A change in the number of craters is also observed as recycling proceeds for the powders of Examples 2 and 4, unlike the powders of Examples 1 and 3.

The films were manufactured by applying the powder by means of an electrostatic gun (Corona positive, +35 to + 45 kV, 10 to 30 pA) on 3 mm thick steel metal plates treated with an anti-corona treatment. -adherent (silicone type coating), facilitating the subsequent detachment of the coating films. The metal plates thus coated with powder were then heat-treated (oven at 220° C. for 10 minutes), in order to melt the powder and obtain a film. The films are then peeled off from the substrates to be characterized in terms of appearance and mechanical properties. The results of these measurements and evaluations are collated in Table 3 below.

Furthermore, it is noted that as the recycling progresses, the variation in shade dE* is higher for the films obtained with the powder of Examples 2 and 4 compared respectively to those obtained with the powders of Examples 1 and 3. This observation is considered to reflect better color retention of the powders of Examples 1 and 3, in which the pigments are encapsulated. Finally, the mechanical properties of the films obtained were evaluated by means of the elongation at break, using a Zwick BZ1 dynamometer from Instron according to standard ISO 527-3.

In order to facilitate the comparison of the results, the relative elongation at break A _rei was calculated resulting from the ratio of the elongation at break of the coating evaluated A _test t to that of the coating obtained from the powder of the example 1 A _ref : [Math 1]

The results of these measurements are collated in Table 4 below.

It can be seen that the films obtained with the powder of examples 1 and 3 have higher and more stable elongations at break as the recycling progresses compared to those obtained from the powders of examples 2 and 4. The initial elongation at break between the two types of film therefore increases with the number of recyclings. A better elongation at break is considered to reflect a better dispersion of the additives and pigments in the powder. The powders of Examples 1 and 3 therefore make it possible to obtain more homogeneous and more flexible films.

^Table 3]

Appearance of the films obtained in terms of color, gloss and visual appearance ^Table 4]

Elongation at break of the films obtained

The tests carried out clearly demonstrate that the recycling of a powder in which the pigments are encapsulated in the polyamide is possible. Indeed, this powder, even recycled, makes it possible to obtain films whose optical and mechanical properties vary little, unlike a powder in which the pigments and additives are simply mixed dry.

[List of cited documents]

WO 2012/034507 Al US 5,932,687

US 3,476,711

Claims

1. Pigmented powder composition based on polyamide for coating substrates, comprising:

(a) 40 to 99% by weight of at least one polyamide;

(b) 1 to 30% by weight of at least one pigment; and

(c) 0 to 30% by weight of at least one additive, wherein the pigment and optional additive are added to the polyamide in the molten state, the polyamide has an inherent viscosity, as measured using 'an Ubbelohde tube at 20°C on a 0.5% by weight solution in m-cresol according to the ISO 307 standard except that the measurement temperature is 20°C instead of 25°C, higher than 0.7 ( g/100g) ¹ , and in which the composition has a median diameter by volume Dv50, as measured according to standard ISO 9276 - parts 1 to 6, of 30 to 200 μm, preferably 30 to 50 μm.

2. Composition according to claim 1, in which the polyamide is chosen from PA 9, PA 10, PA 11, PA 12, PA 610, PA 612, PA 614, PA 618, PA 1010 and PA 1012.

3. Composition according to claim 1 or 2, in which the polyamide is a polyamide 11.

4. Composition according to any one of claims 1 to 3, in which the pigment is chosen from titanium dioxide, carbon black, cobalt oxide, nickel titanate, molybdenum disulphide, flakes of aluminum, iron oxides, zinc oxide, zinc phosphate, and organic pigments, such as phthalocyanine and anthraquinone derivatives.

5. Composition according to any one of claims 1 to 4, comprising 50 to 95% by weight of at least one polyamide.

6. Composition according to any one of claims 1 to 5, comprising 1 to 30% by weight of at least one additive chosen from anti-crater agents, spreading agents, reducing agents, antioxidants, reinforcing fillers , UV stabilizers, fluidizing agents and corrosion inhibitors.

7. Composition according to any one of claims 1 to 6, in which the polyamide has an inherent viscosity, as measured using an Ubbelohde tube at 20° C. on a solution at 0.5% by weight in m -cresol according to the ISO 307 standard except that the measurement temperature is 20° C. instead of 25° C., less than 1.0 (g/100 g) ¹ .

8. A method of manufacturing a pigmented powder composition according to one of claims 1 to 7, comprising the steps of:

(i) mixing one or more pigment(s) and optional additives with a polyamide in the molten state, the polyamide having an inherent viscosity of less than 0.6 (g/100 g) ¹ ;

22 (ii) extruding the mixture obtained in step (i) into an extrudate;

(iii) grinding the extrudate obtained in step (ii) into a powder composition; and

9. Process according to claim 8, in which the polyamide used in step (i) has an inherent viscosity of less than 0.4 (g/100 g) ¹ .

10. Process according to claim 8 or 9, in which step (ii) is carried out in a single-screw extruder or a twin-screw extruder.

11. Method according to any one of claims 8 to 10, in which step (Iv) is carried out in a dryer.

12. Use of the pigmented powder composition according to any one of claims 1 to 7 for coating a substrate, in particular a metallic substrate.

13. Use according to claim 12, characterized in that the coating is produced by electrostatic spraying or hot powdering.

14. Object comprising a metal substrate coated with a coating obtained with the pigmented powder composition according to any one of claims 1 to 7.

15. Object according to claim 14, characterized in that it is a pipe, an accessory, a pump, or a valve, a splined shaft, a rail sliding door or springs, in particular of the truck or car seat shock absorber type, or even a dishwasher basket or springs.