Yield-optimized method for producing a polyamide powder composition

Abstract

The present invention relates to a process for preparing a powder composition based on polyamide(s) with an optimized yield. The process includes a step of recycling a composition based on a polyamide prepolymer having a lower Dv50, by polycondensation of a mixture comprising said composition and one or more monomers in the presence of water. The invention also relates to the powder composition obtained and to the use thereof, especially for coating metal substrates by fluidized bed dip-coating.

Claims

1. A process for preparing a powder composition based on polyamide(s) (composition PA) having an inherent viscosity of greater than or equal to 0.65 (g/100 g).sup.−1 and less than or equal to 1.40 (g/100 g).sup.−1, comprising: (i) providing a composition (i) based on polyamide prepolymer having a maximum inherent viscosity of 0.60 (g/100 g).sup.−1, which composition is, where appropriate, bulk additized; (ii) grinding the composition (i) to obtain a powder composition (ii); (iii) separating the composition (ii) into at least two compositions, pre-PA0 and pre-PA, which, where appropriate, are bulk additized, such that the Dv50 of pre-PA0 is less than the Dv50 of composition (ii) and that the Dv50 of pre-PA is greater than the Dv50 of composition (ii); (iv) recycling the composition pre-PA0 which, where appropriate, is bulk additized, for the preparation of a powder composition based on polyamide(s) (composition PA1) having an inherent viscosity of greater than or equal to 0.65 (g/100 g).sup.−1 and less than or equal to 1.40 (g/100 g).sup.−1.

2. The process as claimed in claim 1, wherein the step of recycling the composition pre-PA0 comprises: (iv-1) a step of providing a mixture comprising: from 15 to 99.9% by weight relative to the total weight of the mixture, of one or more monomer(s), from 0.1 to 85% by weight relative to the total weight of the mixture, of the composition pre-PA0, which, where appropriate, is bulk additized, having an inherent viscosity of less than 0.60 (g/100 g).sup.−1, optionally, a catalyst; and optionally one or more filler(s) and/or additive(s); (iv-2) a step of polycondensation of said mixture in the presence of water, by means of which a polycondensation product (“composition pre-PA1”) is obtained.

3. The process as claimed in claim 2, wherein water is added in an amount of 10 to 40% by weight relative to the total weight of the mixture.

4. The process as claimed in claim 1, wherein the composition pre-PA0 consists of polyamide prepolymer or comprises at least 50% polyamide prepolymer(s) and one or more additives.

5. The process as claimed in claim 1, wherein the inherent viscosity of the polyamide prepolymer(s) in the composition pre-PA0 and in the composition pre-PA1 is less than 0.60 (g/100 g).sup.−1, typically within the range extending from 0.25 to 0.55 (g/100 g).sup.−1.

6. The process as claimed in claim 1, wherein the composition pre-PA0 is a composition based on prepolymer PA 11, PA 12, PA 1010, PA 1012, PA 6, PA 610, PA 612, PA 614, PA 618, PA 8, PA 9, PA 10, PA 13, PA 14 prepolymers and mixtures thereof.

7. The process as claimed in claim 1, wherein the one or more monomers are selected from amino acids, lactams, aminocaproic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 10-aminodecanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, 13-aminotridecanoic acid, 14-aminotetradecanoic acid and/or mixtures thereof, a mixture of diamine monomers and diacid monomers, hexamethylenediamine, decanediamine, dodecamethylenediamine, meta-xylylenediamine, bis-p-aminocyclohexylmethane and trimethylhexamethylenediamine with diacid monomers and/or mixtures thereof.

8. The process as claimed in claim 1, wherein step (iv) comprises all or at least one of the following steps, in succession: (iv-3) a step of cooling the composition pre-PA1; (iv-4) optionally, a step of mixing in the melt state so as to add additives such as pigments and antioxidants into the composition pre-PA1, by means of which the bulk-additized composition pre-PA1 is obtained; (iv-5) a step of grinding and optionally selecting the cooled composition pre-PA1 which, where appropriate, is bulk additized.

9. The process as claimed in claim 2, comprising: (v) a step of increasing the viscosity of the composition pre-PA1, optionally mixed with the composition pre-PA, until the final desired viscosity for the powder composition based on polyamide(s); (vi) optionally, a step of dry mixing the powder composition based on polyamide(s) with additives, such as pigments and antioxidants.

10. The process as claimed in claim 1, wherein the recycling step (iv) comprises a step of mixing in the melt state of the composition pre-PA0 which, where appropriate, is bulk additized, optionally mixed with a composition of polyamide prepolymers and/or additives, under conditions such that melt-phase polycondensation during this step is limited, by means of which a bulk-additized composition based on prepolymer(s) (composition pre-PA1′) is obtained.

11. The process as claimed in claim 10, wherein step (iv) comprises a step of grinding and optionally selecting the cooled composition pre-PA1′.

12. The process as claimed in claim 10 or 11, comprising: (v) a step of increasing the viscosity of the composition pre-PA1′, optionally mixed with the composition pre-PA, until the final desired viscosity for the powder composition based on polyamide(s); (vi) optionally, a step of dry mixing the powder composition based on polyamide(s) with additives, such as pigments and antioxidants.

13. A powder composition based on polyamide(s) (composition PA), entirely or partially resulting from a process as claimed in claim 1, wherein the polyamide has an inherent viscosity of 0.65 to 1.40 (g/100 g).sup.−1.

14. The composition as claimed in claim 13, comprising additives.

15. The use of the composition as claimed in claim 13 in a process for coating metal substrates by fluidized-bed dip-coating.

16. The use of the powder composition as claimed in claim 13 in paints, corrosion-resistant compositions, paper additives, powder agglomeration technologies using radiation-induced fusion or sintering to manufacture objects, electrophoresis gels, multilayer composite materials, the packaging industry, toys, textiles, the automotive industry and/or the electronics industry.

Description

DETAILED DESCRIPTION

Definition

[0087] The term “prepolymer” refers to a prepolymer for which the inherent viscosity is less than 0.60 (g/100 g).sup.−1.

[0088] The term “inherent viscosity” refers to the viscosity of a polymer in solution, determined via measurements in an Ubbelohde tube. 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).sup.−1, is calculated according to the following formula: Inherent viscosity=ln(ts/to)×1/C, with C=m/p×100, in which ts is the flow time of the solution, to is the flow time of the solvent, m is the mass of the sample whose viscosity is being determined, and p is the mass of the solvent. This measurement is carried out according to standard ISO 307 but with a measuring temperature of 20° C. rather than 25° C. The viscosity of a composition comprising the polymer plus any additives insoluble in m-cresol is determined by increasing the sample quantity so that the solution has a polymer concentration of 0.5% (m/m).

[0089] The term “melting point” is intended to denote 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 the standard NF EN ISO 11 357-3 using a heating rate of 20° C./min.

[0090] The term “glass transition temperature” is intended 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 11 357-2 using a heating rate of 20° C./min.

[0091] Furthermore, the term “volume-average diameter” or “Dv” is intended to refer to the volume-average diameter of a pulverulent substance, as measured according to standard ISO 9276—parts 1 to 6: “Representation of results of particle size analysis”. Various diameters are differentiated. More specifically, the Dv50 denotes the volume-median diameter, i.e. that which corresponds to the 50.sup.th volume percentile, and the Dv10 and Dv90 denote respectively the volume-average diameters below which are 10% or 90% by volume of the particles. The volume-average diameter may be measured especially by means of a laser particle size analyzer, for example a laser particle size analyzer (Sypmatec Helos). Software (Fraunhofer) can then be used to obtain the volumetric distribution of a powder and deduce the Dv10, Dv50 and Dv90 therefrom.

“Polyamide”

[0092] The nomenclature used to define polyamides is described in the standard ISO 1874-1:1992 “Plastics—Polyamide moulding and extrusion materials—Part 1: Designation”, in particular on page 3 (tables 1 and 2), and is well known to those skilled in the art.

[0093] The polyamide can be aliphatic, semiaromatic and cycloaliphatic.

[0094] The polyamide can be selected from a homopolyamide, a copolyamide, and mixtures thereof.

[0095] It can also be a blend of polyamide and of at least one other polymer, the polyamide forming the matrix and the other polymer(s) forming the dispersed phase.

[0096] Within the meaning of the invention, the term “polyamide” is understood to mean the condensation products: [0097] of one or more amino acid monomers, such as aminocaproic acid, aminocaproic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 10-aminodecanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, 13-aminotridecanoic acid, 14-aminotetradecanoic acid and one or more lactam monomers such as caprolactam, enantholactam and lauryllactam; [0098] of one or more salts or mixtures of diamine monomers, such as hexamethylenediamine, decanediamine, dodecamethylenediamine, meta-xylylenediamine, bis(p-aminocyclohexyl)methane and trimethylhexamethylenediamine, with diacids, such as isophthalic acid, terephthalic acid, adipic acid, azelaic acid, suberic acid, sebacic acid, dodecanedioic acid and tetradecanedioic acid.

[0099] The polyamide can be a copolyamide. Mention may be made of copolyamides resulting from the condensation of at least two different monomers, for example of at least two different α,ω-aminocarboxylic acids or of two different lactams or of a lactam and of an α,ω-aminocarboxylic acid with a different carbon number. Mention may also be made of copolyamides resulting from the condensation of at least one α,ω-aminocarboxylic acid (or one lactam), at least one diamine and at least one dicarboxylic acid. Mention may also be made of copolyamides resulting from the condensation of an aliphatic diamine with an aliphatic dicarboxylic acid and at least one other monomer chosen from aliphatic diamines other than the preceding one and aliphatic diacids other than the preceding one.

[0100] In the present description, the term “monomer” should be taken as meaning “repeat unit”. A special case is where a repeat unit of the polyamide consists of the combination of a diacid with a diamine. It is considered that it is the combination of a diamine and of a diacid, that is to say the “diamine-diacid” pair, also referred to as “XY” pair, in equimolar amounts, which corresponds to the monomer. This is explained by the fact that, individually, the diacid or the diamine is only a structural unit, which is not sufficient by itself alone to form a polymer.

[0101] Mention may be made, by way of example of diamine X, of aliphatic diamines having from 6 to 12 atoms, it also being possible for the diamine X to be aryl and/or saturated cyclic. Mention may be made, by way of examples, of hexamethylenediamine, piperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, polyol diamines, isophoronediamine (IPD), methylpentamethylenediamine (MPMD), bis(aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), meta-xylylenediamine, bis(p-aminocyclohexyl)methane and trimethylhexamethylenediamine.

[0102] Mention may be made, by way of example of diacid (or dicarboxylic acid) Y, of acids having between 4 and 18 carbon atoms. Mention may be made, for example, of adipic acid, sebacic acid, azelaic acid, suberic acid, dodecanedioic acid, tetradecanedioic acid, isophthalic acid, butanedioic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, the sodium or lithium salt of 5-sulfoisophthalic acid or dimerized fatty acids (these dimerized fatty acids have a dimer content of at least 98% and are preferably hydrogenated).

[0103] The lactam or amino acid monomers are said to be of “Z” type.

[0104] Mention may be made, by way of example of lactams, of those having from 3 to 12 carbon atoms on the main ring and which can be substituted. Mention may be made, for example, of β,β-dimethylpropiolactam, α,α-dimethylpropiolactam, amylolactam, caprolactam, capryllactam, enantholactam, 2-pyrrolidone and lauryllactam.

[0105] Mention may be made, by way of example of amino acid, of α,ω-amino acids, such as aminocaproic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid, n-heptyl-11-aminoundecanoic acid and 12-aminododecanoic acid.

[0106] According to one embodiment, the polyamide (PA) according to the invention comprises at least one polyamide or one polyamide block selected from polyamides and copolyamides comprising at least one of the following monomers: 46, 4T, 54, 59, 510, 512, 513, 514, 516, 518, 536, 6, 64, 66, 69, 610, 612, 613, 614, 616, 618, 636, 6T, 9, 10, 104, 109, 1010, 1012, 1013, 1014, 1016, 1018, 1036, 10T, 11, 12, 124, 129, 1210, 1212, 1213, 1214, 1216, 1218, 1236, 12T, MXD6, MXD10, MXD12, MXD14, and mixtures thereof.

[0107] Preferably, the polyamides (PA) comprise at least one polyamide selected from polyamides and copolyamides comprising at least one of the following XY or Z monomers: 59, 510, 512, 514, 6, 69, 610, 612, 614, 109, 1010, 1012, 1014, 10T, 11, 12, 129, 1210, 1212, 1214, 12T, MXD6, MXD10, MXD12, MXD14, and mixtures thereof; in particular selected from PA 11, PA 12, PA 1010, PA 1012, PA 6, PA 610, PA 612, PA 614, PA 618 and mixtures thereof.

[0108] Mention may be made, by way of examples of copolyamides, of PA 6/12, PA 6/66, PA 6/12/66, PA 6/69/11/12, PA 6/66/11/12, PA 69/12 or PA 11/10T.

Fillers and Additives

Additives

[0109] Mention may be made, by way of examples of additives, of one or more pigments or dyes.

[0110] The pigment may in principle be freely selected from conventionally used pigments. It may especially be selected from inorganic pigments such as titanium dioxide, carbon black, cobalt oxide, nickel titanate, molybdenum bisulfide, aluminum flakes, iron oxides, zinc oxide, zinc phosphate, and organic pigments, such as phthalocyanine and anthraquinone derivatives.

[0111] The dye may also be of any type known to those skilled in the art. Mention may be made in particular of azo dyes, anthraquinonoid dyes, indigo-derived dyes, triarylmethane dyes, chlorine dyes and polymethine dyes.

[0112] Mention may also be made of one or more additives selected from the group consisting of anti-crater agents or spreading agents, reducing agents, antioxidants, reinforcing fillers, UV stabilizers, fluidizing agents and corrosion inhibitors, or mixtures thereof.

[0113] The anti-crater agent and/or spreading agent may be of any type known to those skilled in the art. Preferably, the anti-crater agent and/or spreading agent is selected from the group consisting of polyacrylate derivatives.

[0114] 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.

[0115] The antioxidants may 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.

[0116] 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.

[0117] The corrosion inhibitors may 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.

[0118] The additives are preferably present in a quantity by mass, relative to the total mass of the composition, of 1 to 30%, more preferentially from 2 to 10%, even more preferentially from 3 to 5%, for example from 0 to 5%, or from 5 to 10%, or from 10 to 15%, or from 15 to 20%, or from 20 to 25%, or from 25 to 30%.

Fillers

[0119] The reinforcing filler may be of any type that is suitable for preparing polyamide-based powders. However, it is preferable for the filler to 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 nanometric fillers such as carbon nanotubes and silica. The filler is particularly preferably calcium carbonate.

[0120] The fillers are preferably present in a quantity by mass, relative to the total mass of the composition, of 0 to 50%, more preferentially from 0 to 10%, even more preferentially from 0 to 5%, for example from 0 to 5%, or from 5 to 10%, or from 10 to 15%, or from 15 to 20%, or from 20 to 25%, or from 25 to 30%.

EXAMPLES

[0121] The following examples illustrate the invention without limiting it.

Example 1

[0122] 1.1 70% by weight of 11-aminoundecanoic acid and 30% by weight of a fine (Dv50=32 μm) polyamide 11 prepolymer powder (referred to as “powder pre-PA0”), the inherent viscosity of which is 0.40, are loaded into an autoclave with 30% water by weight relative to the mixture of 11-aminoundecanoic acid and the prepolymer powder, with addition of phosphoric acid. The mixture is heated a temperature of approximately 190° C. under a pressure of 10 bar. The water is distilled and the reactor is degassed. The vapor taken off is recondensed and weighed. The amount of vapor removed is monitored until a certain amount of vapor has been removed, which corresponds to the viscosity desired for the prepolymer. The prepolymer having a viscosity of 0.40 is then drained. At the draining valve, the prepolymer is still molten, then it cools when in contact between two cold metal rollers, and is solidified. The solidified prepolymer is then passed into a pelletizer or a grinding mill, which reduces it to a coarse powder having a mean diameter of less than 5 mm. The experiment was repeated 3 times to obtain prepolymers having viscosities of 0.39/0.42/0.40 (g/100 g).sup.−1.

[0123] 1.2 A test was carried out following the same protocols in example 1.1, where the mixture of 11-aminoundecanoic acid and the powder pre-PA0 was replaced by 100% by weight of 11-aminoundecanoic acid monomers. The experiment was repeated 3 times to obtain prepolymers having viscosities of 0.40/0.39/0.41 (g/100 g).sup.−1.

[0124] Inherent viscosity analyses show that the two products of examples 1.1 and 1.2 have a virtually identical viscosity.

[0125] Gel permeation chromatography (GPC) analyses were carried out. It was observed that, in addition to identical prepolymer viscosities, the chain length distribution with (example 1.1) or without (example 1.2) recycling the fine powders is similar. In addition, there are no bi-populations of molecular weight. This is reflected by an Mn (number-average molecular weight), an Mw (weight-average molecular weight) and a PI (polydispersity index: Mw/Mn) that are identical.

[0126] This demonstrates that a prepolymer produced from the recycling of prepolymers is identical to the prepolymer produced from monomers.

Example 2

[0127] 2.1 The coarse powder obtained in example 1.1 is ground in a hammer mill provided with an internal classifier. The crude ground powder thus obtained is separated in a cyclone classifier, making it possible to obtain 2 powders: [0128] a powder (“powder pre-PA0a”), having Dv50=32 μm (˜8% by weight of the crude powder), [0129] a powder (“powder pre-PA”), having Dv50=111 μm (˜92% by weight of the crude powder).

[0130] 2.2 A Powder Obtained by Cryogenically Grinding Granules of Polyamide 11 (Cryogenically Ground Powder)

[0131] The particle sizes of the powder pre-PA (powder according to the invention) and the cryogenically ground powder are presented in FIG. 1.

[0132] The cryogenically ground powder has a proportion of fine particles having a size of less than 50 μm that is much greater than the powder of the present invention—approximately 5% for the cryogenically ground powder, as opposed to less than 0.3% for the powder of the present invention.

[0133] The cryogenically ground powder also has a proportion of large particles having a size of greater than 300 μm that is much greater—approximately 8% for the cryogenically ground powder, as opposed to approximately 1% for the powder of the present invention.

[0134] Thus, the powder of the present invention has two main advantages for use in fluidized-bed dip-coating: [0135] The low proportion of particles >250 μm makes it possible to reduce the fluidization rate (see example 4), [0136] The low proportion of fines <50 μm, as well as a low fluidization rate, makes it possible to limit flyaway of fines.

[0137] Consequently, while a cryogenically ground powder loses up to 5% of its material during fluidization, the powder of the present invention makes it possible to limit this loss to less than 0.1%.

[0138] This also makes it possible to maintain a constant quality of application.

[0139] FIG. 2 shows changes in particle size caused by fluidization:

[0140] The change in the particle size of a cryogenically ground powder is significant, whereas the powder of the present invention is stable. Consequently, the quality of application of the present invention is stable.

[0141] This stability in the quality of application of the product makes it possible to reuse the powder of the present invention after numerous dip-coating operations, while cryogenically ground powder would have to be refreshed with virgin powder. The present invention makes it possible to reduce the amount of waste generated by this refreshing of product by approximately 5%.

Example 3

[0142] FIG. 3 presents the delta P profile as a function of the air speed for a powder bed. When an increase in the air speed does not cause an increase in the pressure loss (delta P), this means that the powder is fluidized.

[0143] The “virgin” cryogenically ground powder, i.e. powder for a first fluidization, shows that the minimum fluidization rate is approximately 1.8 m/s, while the powder of the present invention requires 1.0 m/s for fluidization thereof.

[0144] This difference is due to the narrower particle size distribution and especially the lower proportion of particles >250 μm.

[0145] This lower rate makes it possible in particular to reduce losses due to the flyaway of fines (5% losses) and consequently to stabilize the quality of the product which does not require refreshing (reduction of 5% in losses).