POLY–(ARYL–ETHER–KETONE) (PAEK) COMPOSITION WITH A LOW CONTENT OF VOLATILE COMPOUNDS AND USE OF SAME IN A SINTERING METHOD

Abstract

The invention relates to a Poly(aryl-ether-ketone) (PAEK) composition, useful in a process for building a three-dimensional object layer by layer by electromagnetic radiation-generated sintering, said composition being characterized in that it has an aromatic ether content comprised between 0 and 0.4% by mass and an aluminium mass content lower than 1000 ppm, preferably lower than 600 ppm and more preferably lower than 500 ppm.

Claims

1. A Poly(aryl-ether-ketone) (PAEK) composition, useful in a process for building a three-dimensional object layer by layer by electromagnetic radiation-generated sintering, said composition being characterized in that it has an aromatic ether content comprised between 0 and 0.4% by mass and an aluminium mass content lower than 1000 ppm, preferably lower than 600 ppm and more preferably lower than 500 ppm.

2. The composition according to claim 1, characterized in that the composition comprises at least polyether-ketone-ketone (PEKK) which represents more than 60% by mass, preferably more than 70% by mass of the composition, bound included.

3. The composition according to claim 1, characterized in that the composition is a Polyether-ketone-ketone (PEKK) composition.

4. The composition according to one of claims 1 to 2, characterized in that the aromatic ether is (1,4-phenoxybenzoyl) benzene.

5. Use of a composition according to one of claims 1 to 4, said composition being in powder form, in a process for building an object layer-by-layer by electromagnetic radiation-generated sintering.

6. A three-dimensional article obtained by the layer-by-layer sintering of a powder using electromagnetic radiation, said powder being characterized in that its composition conforms to one of claims 1 to 4.

7. A process for synthesizing a Poly(aryl-ether-ketone) (PAEK) composition according to one of claims 1 to 4, said process consisting in: bringing one or more aromatic acid chlorides and one or more aromatic ethers into contact in the presence of a Lewis acid in a solvent that dissolves water only at a concentration lower than 0.05% by mass at 25° C. at a temperature comprised between −5 and +25° C. under stirring, completing the polymerization at a temperature comprised between 50 and 120° C., bringing the reaction mixture into contact with water under stirring in the optional presence of acid, separating the poly-aryl-ether-ketone from the liquid effluents, washing the poly-aryl-ether-ketone in the optional presence of acid and separating the liquors, drying the poly-aryl-ether-ketone obtained at a temperature 20° C. above the glass transition temperature Tg, said process being further characterized in that the step of washing the poly-aryl-ether-ketone and of separating the liquors consists in: carrying out a first washing using a water/alcohol mixture and separating the liquors, the water/alcohol mixture comprising proportions of alcohol comprised between 95 and 60% by mass, preferably between 95 and 80% by mass, carrying out at least one further washing with water or acidic water and separating the liquors.

8. The process according to claim 7, characterized in that the alcohol is selected from at least one of the following alcohols: methanol, ethanol or isopropanol.

Description

DESCRIPTION OF THE INVENTION

[0036] By way of preamble, it is specified that the terms “comprised between” and/or “lower than” and/or “above” used within the context of this description must be understood as including the cited bounds.

[0037] The term “build temperature” refers to the temperature at which the powder bed, of a constituent layer of a three-dimensional object being built, is heated during the layer-by-layer sintering process of the powder.

[0038] The PAEK composition according to the invention is synthesized from different combinations of aromatic acid di-chlorides and acid mono-chlorides and aromatic ethers and/or aromatic biphenyls.

[0039] Preferably, the acid chlorides will be selected from terephthaloyl chloride (TCI) and isophthaloyl chloride (ICI) or a mixture thereof, in proportions such that in the final PAEK structure, there is a para-diketophenyl/meta-diketophenyl unit ratio of 100 to 50% and preferably of 85 to 55%% and more particularly of 82 to 60%.

[0040] The acid monochlorides will be selected from benzoyl chloride and benzene sulfonyl chloride.

[0041] Preferably, the following aromatic ethers or aromatic biphenyls will be selected: Diphenyl ether, 1,4-(phenoxybenzoyl) benzene (EKKE), biphenyl, 4-phenoxybenzophenone, 4-chlorobiphenyl, 4-(4-phenoxyphenoxy) benzophenone, and biphenyl 4-benzenesulphonylphenyl phenylether.

[0042] Poly-(aryl-ether-ketones) (PAEKs) consist of units having the following formulae:

(—Ar—X—) and (—Ar.sup.1—Y—)

wherein: [0043] Ar and Art each denote a divalent aromatic radical; [0044] Ar and Ar.sub.1 may preferably be selected from 1,3-phenylene, 1,4-phenylene, 4,4′-biphenylene, 1,4-naphthylene, 1,5-naphthylene and 2,6-naphthylene; [0045] X denotes an electron-withdrawing group; it may preferably be selected from the carbonyl group and the sulfonyl group, [0046] Y denotes a group selected from an oxygen atom, a sulphur atom, an alkylene group, such as —CH.sub.2— and isopropylidene.

[0047] In these units X and Y, at least 50%, preferably at least 70%, and more particularly at least 80% of the groups X are a carbonyl group, and at least 50%, preferably at least 70%, and more particularly at least 80% of the groups Y represent an oxygen atom. According to a preferred embodiment, 100% of the groups X denote a carbonyl group and 100% of the groups Y represent an oxygen atom.

[0048] More preferentially, the poly-arylene-ether-ketone (PAEK) may be selected from: [0049] a poly-ether-ketone-ketone, also called PEKK, comprising units of Formula I A, Formula I B and a mixture thereof:

##STR00001## [0050] a poly-ether-ether-ketone, also called PEEK, comprising units of Formula II:

##STR00002##

The sequences can be totally para (Formula II). Similarly, meta sequences can be introduced, partially or totally, into these structures at the ethers and the ketones according to the two examples of Formulae III and IV below:

##STR00003##

Or ortho sequences according to Formula V:

##STR00004## [0051] a poly-ether-ketone, also called PEK, comprising units of Formula VI:

##STR00005##

Similarly, the sequence may be totally para, but meta sequences can also be partially or totally introduced (Formulae VII and VIII):

##STR00006## [0052] a poly-ether-ether-ketone-ketone, also called PEEKK, comprising units of Formula IX:

##STR00007##

Similarly, meta sequences can be introduced into these structures at the ethers and the ketones. [0053] a poly-ether-ether-ether-ketone, also called PEEEK, comprising units of Formula X:

##STR00008##

Similarly, meta sequences can be introduced into these structures at the ethers and the ketones, but also biphenol sequences according to Formula XI:

##STR00009##

[0054] Other arrangements of the carbonyl group and the oxygen atom are also possible.

[0055] Preferably, the PAEKs used in the invention are selected from PEKKs, PEEK or PEEK-based copolymers, PEK or PEK-based copolymers.

[0056] During the synthesis of these Poly-aryl-ether-ketones, by the preferred electrophilic substitution reaction process, the following Lewis acids are preferably used: Anhydrous aluminium trichloride, anhydrous aluminium tribromide, and more preferably anhydrous aluminium trichloride.

[0057] The solvents used are acid chloride solvents and not polymer solvents and dissolve water at a concentration<0.2% by mass, preferably <0.05% by mass. Preferably, it is orthodichloro-benzene.

[0058] The different phases of the synthesis process can be performed in the same reactor or in a succession of several reactors. A first phase of the reaction is carried out at a temperature between −5° C. and 25° C. under stirring, then the polymerization reaction is completed at a temperature comprised between 50 and 120° C. The PAEK obtained is separated from the liquid effluents after bringing the reaction medium into contact with water in the optional presence of acid. This separation step is followed by a washing step.

[0059] Advantageously, this washing step consists in bringing the synthesized PAEK, for example a PEKK, into contact with a water/alcohol mixture, under stirring between 15 and 60° C., preferably between 25 and 50° C., and in maintaining this stirring for one hour. According to one variant, the water/alcohol mixture can also be added to a reactor after the PAEK has been introduced.

[0060] This washing sequence can be divided into several successive sequences depending on the size of the equipment used.

[0061] The water/alcohol mixture used represents 15 to 50 times the mass of PAEK to be washed. The water can be acidified up to 10% pure hydrochloric acid, preferably 4%.

[0062] The alcohol is preferably selected from at least one of the following alcohols: methanol, ethanol or isopropanol. It acts as solvent and complexing agent for the aluminium and thus promotes its removal.

[0063] However, the proportions of alcohol in the mixture should not be so high as to cause side reactions. Neither must they be too low to allow sufficient removal of the aluminium.

[0064] Therefore, a compromise must be reached on the proportions of alcohol. Thus, the mass proportions of alcohol in the water/methanol mixture are preferably comprised between 95 and 60%, preferably between 95 and 80%.

[0065] After said washing, the reaction mixture is separated from the majority of the liquors by a suitable separator.

[0066] The liquors are subjected to appropriate treatments, decantation, neutralization, distillation and resin treatment allowing them to be recovered or recycled in the process.

[0067] The polymer is then subjected to several further steps of washing with water or acidic water, then separation.

[0068] Finally, a step of drying the polymer is carried out at a temperature 20° C. above the glass transition temperature Tg under 30 mbar.

[0069] The product obtained has an aromatic ether content comprised between 0 and 0.4% by mass. Preferably this content is comprised between 0 and 0.3% by mass, and more preferably it is comprised between 0 and 0.2% by mass. Aromatic ether means compounds having a molar mass lower than 500 g.Math.mol.sup.−1, such as EKKE whose molar mass is 470 g/mol. The Al mass content in the product obtained is lower than 1000 ppm, preferably lower than 600 ppm, and more preferably lower than 500 ppm.

[0070] Such a composition can be used in powder form in a process for building an object using electromagnetic radiation, notably laser radiation, consisting in irradiating the powder layer by layer, following a predetermined path, in order to locally melt the poly-aryl ether-ketone and obtain said object.

[0071] The composition comprises at least polyether-ketone-ketone (PEKK) which represents more than 60% by mass, preferably more than 70% by mass of the composition, bound included. The remaining 30 to 40% by mass may for example consist of other polymers belonging to the PAEK family, and/or fibres, such as carbon fibres, glass fibres for example, and/or fillers such as mineral fillers, glass beads or carbon blacks, graphites, graphenes, carbon nanotubes.

[0072] The PAEK composition is preferably a Polyether-ketone-ketone (PEKK) composition, and the aromatic ether is (1,4-phenoxybenzoyl) benzene (EKKE).

[0073] The composition is in powder form, ready for use in an electromagnetic radiation-generated sintering process to produce three-dimensional objects layer by layer.

[0074] Finally, the invention relates to a three-dimensional article obtained by sintering a powder layer by layer using electromagnetic radiation, said powder being a PAEK powder having a composition in which the aromatic ether content is comprised between 0 and 0.4% by mass. Furthermore, the aluminium mass content in the composition is lower than 1000 ppm, preferably lower than 600 ppm, and more preferably lower than 500 ppm. Such a powder generates very little or no vapour, so that the lens of the sintering equipment does not become fouled and the three-dimensional articles fabricated with such a powder have mechanical properties that are satisfactory and constant over time.

EXAMPLES

1. Comparison of Lens Condition as a Function of EKKE Content Measured on Various PEKK Samples

[0075] Protocol for Measuring the Aromatic Ether Content:

[0076] The samples are dissolved in a BTF/HFIP mixture in the presence of an internal standard.

[0077] All analyses were performed on a VARIAN® 3800 GC equipped with a 1041 on-column injector and a FID. [0078] Column: MXT 500 Sim Dist 6 m/320 μm/ef=0.15 μm [0079] Temperature Det (FID)=400° C. [0080] 1041 injector temperature=set at T≤40° C. [0081] Column flow rate (constant flow)=3 ml/min, [0082] Oven programming=40° C. (2 min).fwdarw.150° C. to 8° C./min [0083] 150° C. (0 min).fwdarw.330° C. (0 min) at 15° C./min [0084] 330° C. (0 min).fwdarw.360° C. (5 min) at 25° C./min [0085] Carrier gas=helium [0086] Injection mode: in the column with the injection point located in the part regulated by the oven [0087] Injection volume=0.5 μl

[0088] Sintering tests were performed on three PEKK samples. A first product A, synthesized and marketed by OPM with the product designation OxPEKK, has an EKKE mass content, measured by GC, of 1.13%. A product B, a PEKK marketed by Arkema with the product designation Kepstan 6000 and synthesized according to the process described in document WO2014013202, with washing exclusively with water, has an EKKE content, measured by GC, of 0.45%. A third product C, a Kepstan 6000 PEKK synthesized according to the same process as for product B, but whose first washing step is carried out with a water/methanol mixture whose mass proportions of alcohol are comprised between 95 and 60%, preferably between 95 and 80%, has an EKKE content, measured by GC, of 0.25% by mass.

[0089] These sintering tests were conducted at a build temperature of 285° C. These tests revealed that the first two products, A and B, generate a significant release of vapours during the test (see Table I below). These vapours condense on the lens. Analysis of a sample of this condensate shows the presence of EKKE. In addition to fouling the machine, this lens deposit changes the energy received by the PEKK powder, which does not sinter properly, and the resulting three-dimensional object thus has mechanical properties that decrease over time.

TABLE-US-00001 TABLE I EKKE content (%) Lens condition Product A 1.13% Deposit Product B 0.45% Deposit Product C 0.25% No deposit

2. Comparison of Lens Condition as a Function of Al Content

[0090] Method for Determining the Aluminium Content

Mineralization:

[0091] Weigh 0.5 g of the sample in a digitube. [0092] Add 10 mL of 67% nitric acid [0093] Heat 2 hours at 99° C. in a heating block [0094] Filter on a Whatman filter (589/1 diam 125 mm) [0095] Make up to the mark with a final volume of 25 mL with Milly Q water

Quantification:

[0096] By the optical ICP/AES technique (Vista Pro ICP, Varian) [0097] Standard is run before and after the sample to control drift [0098] Working wavelength: 396.15 nm for the element aluminium

[0099] Two samples of product B (samples numbered 5 and 6 in Table II below) and four samples of product C (samples numbered 1 to 4 in Table II below) from Example 1 were compared. The aluminium mass content of each sample was measured by the method described above. Product B, corresponding to a PEKK of the prior art, has an aluminium content comprised between 1900 and 2000 ppm depending on the samples. Product C, in conformity with the invention, has an aluminium content that varies from 8 ppm, 9 ppm to 800 ppm depending on the samples.

[0100] Thermogravimetric analyses (TGA) were performed with a Netzsch TG209F1 device. This device consists of two main components: a highly sensitive microbalance coupled with a temperature-controlled oven. The microbalance is capable of detecting a variation of 0.1 mg for a maximum capacity of 1.3 g. The sample is placed in a platinum crucible and the beam keeps the platform in balance via a current proportional to the supported mass. The temperature is set between 30° C. and 1000° C. with temperature increases up to 200° C.min.sup.−1. A thermocouple near the sample is used to monitor the temperature and regulate the heat output. Calibration was performed with Indium and Zinc with Curie points of 157° C. and 420° C., respectively.

[0101] All TGA on the samples were performed isothermally, under nitrogen, at a temperature of 285° C., corresponding to the laser sintering build temperature, for one hour. The measured mass losses are shown in Table II below.

TABLE-US-00002 TABLE II Isothermal TGA 1 h at 285° C. under N2 Isothermal mass Samples losses in % m Al content 1-Product C 0   8 ppm 2-Product C 0   9 ppm 3-Product C 0  200 ppm 4-Product C 0  800 ppm 5-Product B 0.3 1900 ppm 6-Product B 0.2 2000 ppm

[0102] These TGA mass-loss measurements show that there is a correlation between the thermal stability of the PEKK sample and its aluminium content. For example, at aluminium contents below 1000 ppm, the PEKK composition is thermally stable.

[0103] The results obtained by TGA show that the aluminium in samples 5 and 6 of product B of the prior art forms complexes likely to generate vapours under the effect of temperature, which generate vapours sufficient to foul the lens of the sintering equipment. Product C according to the invention contains aluminium contents low enough not to generate vapours, no loss of mass being detected. The lens of the sintering equipment is thus not fouled when sintering the PEKK powder according to the invention.

[0104] The PAEK composition according to the invention thus makes it possible to preserve the sintering equipment and to obtain three-dimensional sintered objects with mechanical properties that are satisfactory and constant over time.