PROCESS FOR TREATING A POLYAMIDE-BASED COMPOSITION

Abstract

The present invention relates to a process for treating a polyamide-based composition which is intended to be recycled. More particularly, the present invention relates to a process for treating a composition, typically a powder based on untransformed polyamides during the manufacture of an object in 3D printing. The invention also relates to the use of the recycled composition.

Claims

1. A process for the treatment of a composition (C1) based on polyamides which is intended to be recycled, comprising the following successive stages: (i) a stage of supplying a mixture comprising the composition (C1) based on the polyamides, a polyamide chain-cutting agent, and optionally one or more filler(s) and/or additive(s); (ii) a stage of kneading said mixture in the molten state, whereby a composition (C2) having a targeted inherent viscosity is obtained; (iii) a stage of recovery of the composition (C2).

2. The process as claimed in claim 1, where the composition (C1) is a powder based on polyamides.

3. The process as claimed in claim 1, where the composition (C1) has an inherent viscosity of greater than or equal to 1.50.

4. The process as claimed in claim 1, where the inherent viscosity of the recovered composition (C2) is reduced by at least 10%, with respect to that of the composition (C1).

5. The process as claimed in claim 1, where the chain-cutting agent is chosen from water, a carboxylic acid, an amino acid and/or their mixture.

6. The process as claimed in claim 5, where the chain-cutting agent is a carboxylic acid, chosen from monocarboxylic acids, dicarboxylic acids, metal salts of mono- or dicarboxylic acids, and/or their mixture.

7. The process as claimed in claim 6, where stage (i) is provided with from 0.1% to 2%, by weight of carboxylic acid, with respect to the weight of the composition (C1).

8. The process as claimed in claim 5, where the chain-cutting agent is an amino acid chosen from aminocaproic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and/or their mixture.

9. The process as claimed in claim 8, where stage (i) is provided with from 0.1% to 10%, by weight of amino acid, with respect to the weight of the composition (C1).

10. The process as claimed in claim 1, where a temperature greater by at least 5° C., with respect to the melting point of polyamides, and below 330° C., is applied in the kneading stage (ii).

11. The process as claimed in claim 1 is a batch process.

12. The process as claimed in claim 1 is a continuous process.

13. The process as claimed in claim 1, where the residence time of the mixture in stage (ii) is equal to or less than 10 minutes.

14. The process as claimed in claim 1, where the polyamide is chosen from a homopolyamide, a copolyamide, a copolymer having polyamide blocks and polyether blocks, and their blends.

15. The process as claimed in claim 14, where the polyamide comprises at least one polyamide or one polyamide block chosen 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, 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 their blends.

16. A recycled composition based on polyamides, capable of being obtained by the process as claimed in claim 1, having an inherent viscosity of less than or equal to 1.50.

17. A transformation process comprising the use of the recycled composition as claimed in claim 16 in the form of granules.

18. A manufactured article obtained by the transformation process as claimed in claim 17.

Description

DETAILED DESCRIPTION

Definition

[0078] “Inherent Viscosity”

[0079] The inherent viscosity in solution of the composition based on polyamides is preferably measured according to the standard ISO 307:2007 modified in that the solvent is m-cresol rather than sulfuric acid, in that the concentration is 0.5% by weight and in that the temperature is 20° C.

[0080] Polyamides

[0081] The nomenclature used to define polyamides is described in the standard ISO 1874-1:1992 “Plastics—Polyamide (PA) moulding and extrusion materials—Part 1: Designation”, in particular on page 3 (tables 1 and 2), and is well known to a person skilled in the art.

[0082] The composition (C1) based on polyamides which is intended to be recycled of the present invention can be provided in all its forms in any industrial application, such as powder, granules, filament, resin, fiber, films or pipe.

[0083] The composition (C1) preferably has an inherent viscosity of greater than or equal to 1.50, preferably of greater than or equal to 1.60.

[0084] The polyamide can be aliphatic, semiaromatic and cycloaliphatic.

[0085] The polyamide can be chosen from a homopolyamide, a copolyamide, a copolymer having polyamide blocks and polyether blocks, and their blends.

[0086] 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.

[0087] Within the meaning of the invention, the term “polyamide” is understood to mean the condensation products: [0088] of one or more amino acid monomers, such as aminocaproic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid, or of one or more lactam monomers, such as caprolactam, enantholactam and lauryllactam; [0089] 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.

[0090] 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.

[0091] In the present description of polyamides, the term “monomer” should be taken with the meaning of “repeat unit”. A special case is the case 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.

[0092] 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.

[0093] 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).

[0094] The lactam or amino acid monomers are said to be of “Z” type.

[0095] 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.

[0096] 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.

[0097] According to one embodiment, the polyamide (PA) according to the invention comprises at least one polyamide or one polyamide block chosen 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, 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 their blends.

[0098] Preferably, the polyamides (PA) comprise at least one polyamide chosen 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 their blends, in particular chosen from PA 11, PA 12, PA 1010, PA 6, PA 612, and their blends.

[0099] 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.

[0100] It would not be departing from the scope of the invention to replace a portion of the polyamide with a copolymer having polyamide blocks and polyether blocks, that is to say to use a blend comprising at least one of the preceding polyamides and at least one copolymer having polyamide blocks and polyether blocks.

[0101] The copolymers having polyamide blocks and polyether blocks result from the copolycondensation of polyamide blocks having reactive ends with polyether blocks having reactive ends, such as, inter alia:

[0102] 1) polyamide blocks having diamine chain ends with polyoxyalkylene blocks having dicarboxyl chain ends;

[0103] 2) polyamide blocks having dicarboxyl chain ends with polyoxyalkylene blocks having diamine chain ends obtained by cyanoethylation and hydrogenation of α,ω-dihydroxylated aliphatic polyoxyalkylene blocks known as polyether diols;

[0104] 3) polyamide blocks having dicarboxyl chain ends with polyether diols, the products obtained being, in this specific case, polyetheresteramides. These copolymers are advantageously used.

[0105] The polyamide blocks having dicarboxyl chain ends originate, for example, from the condensation of amino acids, lactams or dicarboxylic acids and diamines in the presence of a chain-limiting dicarboxylic acid. The amino acids, the lactams, the diacids and the diamines are those described above.

[0106] The polyether can, for example, be a polytetramethylene glycol (PTMG). The latter is also known as polytetrahydrofuran (PTHF).

[0107] The number-average molar mass of the polyamide blocks is between 300 and 15 000 and preferably between 600 and 5000 g/mol. The molar mass of the polyether blocks is between 100 and 6000 and preferably between 200 and 3000 g/mol.

[0108] The polymers having polyamide blocks and polyether blocks are generally prepared by the simultaneous reaction of the polyether and of the precursors of the polyamide blocks.

[0109] For example, polyether diol, a lactam (or an α,ω-amino acid) and a chain-limiting diacid can be reacted in the presence of a small amount of water. A polymer is obtained having essentially polyether blocks and polyamide blocks of very variable length, but also the various reactants which have reacted randomly, which are distributed randomly along the polymer chain.

[0110] The polyetherdiol blocks are either used as is and copolycondensed with polyamide blocks having carboxyl ends, or they are aminated in order to be converted into polyetherdiamines and condensed with polyamide blocks having carboxyl ends. They can also be mixed with polyamide precursors and a chain limiter in order to make polymers having polyamide blocks and polyether blocks which have randomly distributed units.

[0111] The ratio of the amount of copolymer having polyamide blocks and polyether blocks to the amount of polyamide is advantageously between 1/99 and 15/85 by weight.

[0112] As regards the blend of polyamide and of at least one other polymer, it is provided in the form of a blend having a polyamide matrix and the other polymer(s) form(s) the dispersed phase. Mention may be made, as examples of this other polymer, of polyolefins, polyesters, polycarbonate, PPO (abbreviation for polyphenylene oxide), PPS (abbreviation for polyphenylene sulfide) or elastomers.

[0113] The polyamide, whether or not as a blend with at least one other polymer, can contain fillers, pigments, antioxidants and UV stabilizers.

[0114] Advantageously, the composition (C1) based on polyamides which is intended to be recycled is in a divided form, such as powder or granules.

[0115] According to one embodiment, the composition (C1) based on polyamides is a polyamide-based powder intended for 3D printing, in particular in a sintering process. Preferably, the polyamide results from hydrolytic polycondensation. Hydrolytic polycondensation is induced by water at high temperature. For example, the hydrolytic polycondensation of lactams consists in opening the lactam with water and then in heating under pressure in order to polymerize. Optionally, a catalyst, such as phosphoric acid, can also be employed in the hydrolytic process.

[0116] Fillers and Additives

[0117] The composition (C1) intended to be recycled can comprise fillers. Preferably, these fillers are in the form of a powder or of granules. These fillers can already be present in the composition (C1) before the treatment process according to the invention or be added during the treatment process according to the invention, in order to contribute the mechanical properties (for example modulus, elongation at break, impact strength) to the composition recovered on conclusion of the process. Mention may be made, as examples of pulverulent fillers, of carbonate-comprising inorganic fillers, in particular calcium carbonate, magnesium carbonate, dolomite or calcite, barium sulfate, calcium sulfate, dolomite, alumina hydrate, wollastonite, montmorillonite, zeolite, perlite, nanofillers (fillers of the order of a nanometer), such as nanoclays or carbon nanotubes, glass fibers or carbon fibers.

[0118] The composition (C1) intended to be recycled can also comprise additives. Mention may be made, as examples of additives, of flow agents (e.g. silica), dyes, pigments for coloring, TiO.sub.2, pigments for infrared absorption, fireproofing additives, antioxidants, light stabilizers, UV stabilizers, plasticizers, impact modifiers, antistatic agents, flame retardants and their mixtures. Preferably, these additives can be in the form of a powder or of granules.

[0119] Process

[0120] Use may be made, as installation for carrying out the process of the invention, of any device for the compounding, kneading or extrusion of molten plastics which is known to a person skilled in the art.

[0121] Mention may be made, by way of examples, of internal mixers, open mills, single-screw or counterrotating or corotating twin-screw extruders, continuous co-kneaders or stirred reactors. The kneading device can be one of the abovementioned appliances or their combination, such as, for example, a co-kneader in combination with a take-up single-screw, a corotating twin-screw in combination with a gear pump, a reactor connected to an extruder, and the like. The extrusion appliance is generally configured so as to identify a zone of melting of the polymer, a zone of blending and reaction between the entities present and a zone of pressure reduction/venting to remove the volatile compounds. These different zones can be given material form by the configuration of the screw of the appliance, the use of a restriction zone or the coupling together of appliances. The device can additionally be equipped with a filtration system, which is preferably continuous, and with a strand or underwater granulation system appropriate to the rheology of the polyamide.

[0122] Mention may be made, by way of example, of the Werner 30 or Coperion ZSK30 extruder. Alternatively, use may be made of any suitable kneader, such as a Brabender or Plastograph W50EHT kneader, consisting of a motor, a kneading chamber, two rotors rotating in opposite directions at different speeds to ensure kneading of the material in the molten state, a thermocouple, and data acquisition.

[0123] Preferably, the kneading stage (ii) of the process according to the invention is carried out in an intermeshing corotating twin-screw extruder, which exhibits numerous advantages. For example, the intermeshing corotating twin-screw extruder makes it possible to carry out the process continuously and with a short residence time. Furthermore, the products are less subject to thermal oxidation and in particular are less likely to undergo yellowing.

[0124] The stage of the recovery (iii) consists generally of an extrusion stage, a stage of cooling the composition in the molten state using a water-containing cooling liquid, a stage of cutting the composition in the form of granules, and a stage of separation of the cooling liquid and the cooled composition.

[0125] The extrusion stage can be carried out in a conventional way, in particular through a die. The die is generally placed at the outlet of the reactor containing the mixture, or at the outlet of a transfer line fed with molten composition using a pump, or at the outlet of a kneading device which can generate a pressure greater than atmospheric pressure, generally an extruder. At the die outlet, a material is obtained generally in the form of rods or strips, or directly in the form of granules in the case, for example, of underwater pelletizing, as explained later in the description.

[0126] The cooling stage consists in cooling the material obtained after extrusion, by contact with a water-containing cooling liquid. It can, for example, comprise an alcohol such as ethanol, isopropanol or butanol. Preferably, the cooling liquid comprises only water.

[0127] Suitable cooling devices for such a stage are known to a person skilled in the art, for example a water-spraying device located in the proximity of the device of the die plate or a bath or a stream of water located in the proximity of or in contact with the device of the die plate into which the extruded material is introduced.

[0128] The cutting stage can be carried out in suitable devices known to a person skilled in the art, for example a milling cutter system with teeth or a system comprising knives and a knife block. The device generally comprises a motor for driving the milling cutter or the knife block. The cutting device is usually rotary.

[0129] According to one embodiment, the cutting stage is carried out after the cooling stage and the stage of separation of the cooling liquid. In this case, the cooling liquid, generally water, is separated from the rods or strips of the composition and then the rods or strips are “dry” cut. The separation can be carried out, for example, by departure of the rods or strips from the bath via an entrainment device. The cooling liquid can be removed by using gravity or by sucking the liquid through a screen or any other openwork device over which the rods or strips move. These devices are known to a person skilled in the art.

[0130] According to one embodiment, the cutting and cooling stages start simultaneously. According to this embodiment, the two stages are advantageously carried out using a cutting device positioned immediately at the outlet of the die. Such a granulation device is known to a person skilled in the art. It comprises at least one cutting device which faces the die plate through which the polymer is extruded, and a cooling device. The cutting device generally comprises knives, a knife block and a motor for driving the knife block. The knife block is usually rotary. The cooling device can consist of a device for the spraying or circulation of cooling liquid located in the proximity of the device of the die plate. This is the case with “pelletizing” granulators known to a person skilled in the art. The cutting device and the die plate can also be positioned in a chamber filled with cooling liquid; in this case, it is an “underwater pelletizing” granulator. In this chamber filled with cooling liquid, the cooling liquid is generally in circulation and it provides the cooling and the transportation of the granules of compositions formed at the cutting device toward a separator, where the separation stage is carried out. The separation can be carried out using a centrifuge which separates the cooling liquid and the granules or, for example, using a cycloning device.

[0131] The process of the invention can be followed by a grinding stage in order to obtain the composition (C2) in the form of granules, flakes or coarse powders. According to one embodiment, the process according to the invention comprises a grinding stage where the composition (C2) is ground in order to obtain a composition in the form of granules, flakes or coarse powders.

[0132] The grinding stage can be carried out in a pin mill, a hammer mill or a whirl mill.

[0133] The process can additionally comprise a sieving stage. The sieving can be carried out on a sieve.

[0134] Alternatively, after grinding, the process can comprise a selection stage in order to obtain the desired particle size profile. Typically, the powders can be dispersed by a selection wheel and transported by classification air. The dust entrained in the air is conveyed through a support wheel and discharged via a first outlet. The coarse product is rejected by a classifying wheel and transported to a second outlet. The selector can comprise several successive wheels working in parallel.

[0135] According to a specific embodiment, the composition (C2) is ground, sieved and/or selected in order to obtain a powder with a volume-median diameter (D50) within the range from 5 to 200 μm, preferably in the form of a powder with a D50 within the range from 10 to 150 μm. These powders can be used as starting material in a 3D printing process using powders (e.g., 3D printing by sintering).

[0136] The invention will be further explained in a nonlimiting way with the help of the Examples which follow.

Examples

[0137] For each example, the starting materials listed in table 1, including the PA11 powder with an inherent viscosity of 1.94, dried to a moisture content of 0.05%, are introduced under flushing with nitrogen into a Micro15 microcompounder of the DSM brand, preheated to 260° C. The speed of the screws is 100 rpm and the extruder is placed in recirculation mode for the 3 minutes corresponding to the duration of the test. Throughout the test, an estimative monitoring of the melt viscosity of the material can be carried out by measuring the Normal Force (NF). This normal force increases as the inherent viscosity and the melt viscosity increase. Samples are withdrawn at chosen intervals and their inherent viscosity is evaluated (Table 1).

TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 PA11 powder 18 g 17.91 g 17.82 g 17.1 g 17.64 g 17.1 g 17.1 g 11- — — — —  0.36 g  0.9 g — Aminoundecanoic acid Adipic acid — — — — — — 0.09 g Distilled water —  0.09 g  0.18 g  0.9 g — — — Result Negative— Drop in Drop in Drop in Drop in Drop in Drop in the screws NF NF NF NF NF NF lock (excessively high NF) NF minimum — 3 3 3 3 3 — (min) NF after 3 min — 1100 1000 1000 700 400 600 (N) Inherent viscosity — 1.20 1.18 1.17 1.07 0.99 1.04 after 3 min (at the NF minimum)

[0138] In the absence of any additive (example 1), it is not possible to melt the PA11 powder. Due to its excessively high inherent viscosity, the Force required to set the screws in motion is too high and the screws automatically lock to prevent damage to the machine.

[0139] On adding water to the PA11 powder (examples 2 to 4), it is observed that melting becomes possible and that the Normal Force decreases. This phenomenon is accompanied by a drop in the inherent viscosity. At a minimum, a PA with an inherent viscosity of less than 1.20 is easily achieved.

[0140] On adding an aminocarboxylic acid (examples 5 and 6), a drop in the Normal Force and in the inherent viscosity is observed. At a minimum, a PA11 with an inherent viscosity of less than 1.1 is easily achieved, and even than 1.0 if the content of 11-aminoundecanoic acid is adjusted.

[0141] On adding a carboxylic acid (example 7), a drop in the Normal Force and in the inherent viscosity, with an inherent viscosity of less than 1.10 being easily obtained, is observed.

[0142] Thus, an inherent viscosity of less than 1.50 can be easily achieved by employing the chain-cutting agent.

[0143] The tests were carried out under the same conditions for a period of time of 10 minutes. The results were measured (Table 2). A drop in viscosity after 3 minutes, as observed in Table 1, and then a rise in viscosity in the cases of examples 2 to 6 and a steady drop for example 7 are observed.

TABLE-US-00002 TABLE 2 Example 1 2 3 4 5 6 7 NF after 10 — 2700 3200 3500 2000 1500 500 min (N) Inherent — 1.72 1.85 1.95 1.55 1.35 1.01 viscosity after 10 min

[0144] The examples above show that a desired inherent viscosity can be easily achieved by adjusting the chain-cutting agent employed and its amount and by controlling the reaction time. Typically, if a subsequent rise in viscosity is desired, a chain-cutting agent of the amino acid type can be chosen.