[0001] The invention relates to polyarylene ether ketones. [0002] More particularly, the invention relates to a composition based on polyarylene ether ketone (PAEK) Stable melt. [Prior art] [0003] The generic polyarylene ether ketone term (PAEK) is a family of high performance polymers at high thermomechanical properties. These polymers are composed of aromatic rings linked by an oxygen atom (ether) and / or a carbonyl group (ketone). Their properties depend mainly on the ether / ketone ratio. In the abbreviations used to name the materials from the family of PAEK, the letter E is an ether and the letter K is a ketone function. In the following description, these abbreviations will be used in place of the use of names for the compounds to which they relate. [0004] The family of PAEK has more particularly poly ether ketone (PEK), poly ether ether ketone (PEEK), poly ether ether ketone ketone (PEEKK), poly-ether ketone-ketone (PEKK), poly ether ketone ketone ether ketone (PEKEKK), poly ether ether ketone ether ketone (PEEKEK), poly-ether-ether-ether-ketone (PEEEK) and poly-ether-diphenyl-ether-ketone (PEDEK). [0005] These polymers are used for demanding applications in temperature and / or mechanical stresses or chemical. These polymers are found in areas as diverse as aerospace, off-shore drilling, medical implants. Depending on their nature and their applications, they can be implemented by various known techniques such as molding, extrusion, compression molding, compounding, injection molding, calendaring, thermoforming, rotational molding, the impregnation, laser sintering or shaping by melt deposition (FDM) for example, at temperatures generally between 320 and 430 ° C. [0006] The PAEK have high melting temperatures, typically above 300 ° C. Therefore, in order to be implemented, they must be melted at high temperature, typically greater than 320 ° C, preferably greater than 350 ° C and more generally at a temperature of the order of 350 to 390 ° C. These temperatures depend course of PAEK structures considered and viscosities. In the prior art, it was considered that the PAEK melt at a temperature at least 20 ° C to the PAEK considered the melting point. [0007] However, implementation of such temperatures, the molten PAEK are not stable vis-à-vis the thermal oxidation if it does not optimize their composition and / or in the absence of additives to to stabilize the structure. We then observe the evolution of the structure or by cleavage mechanisms phenomena and / or elongation chains induced by hook and / or couplings from chain ends or defects. These defects may come from the oxidation reactions under the influence of temperature and oxygen in the atmosphere or already present in the polymer. These structural changes may be up to crosslinking of the polymer and also lead to clearances of compounds including carbon dioxide may be mentioned (CO 2 ), carbon monoxide (CO), phenols and aromatic ethers . These structural changes lead to degradation phenomena of physicochemical properties and / or mechanical properties of the PAEK and a change in viscosity in the molten state. These changes make it more difficult the implementation of these polymers in the molten state, inducing such variations not only in the machine operating parameters used for the processing of polymers, but also in the product appearance and dimensions obtained after processing. [0008] Solutions have been proposed to stabilize the compositions of PAEK melt, but not entirely satisfactory to date. [0009] The document US5 208 278 describes the use of organic bases to stabilize PAEK. The authors of this document, the organic bases used to capture the acidity in the polymer. Examples show better viscosity stability in the melt, but still in confinement, that is to say in the absence of an environment with oxygen. Furthermore, the use of these organic bases is problematic because they can evaporate and / or they generate volatile organic compounds of the PAEK transformation temperatures. [0010] The stabilizers of metal oxide type, such as disclosed in US3925307 or aluminosilicates, such as disclosed in US4593061 are another way to capture the acid but do not allow to sufficiently improve the stability of the polymer melt vis-a-vis the thermal oxidation and can generate their own structural changes. Moreover, to achieve sufficient stability, add very significant amounts of these additives which can then also have a charging action affecting the properties of the polymer and its implementation. [001 1] The documents US5 063 265, US 5,145,894 and WO2013 / 164855 disclose the use of aromatic organophosphorus compounds to stabilize molten PAEK compositions either alone or in synergy with another additive. The US5 063 265 discloses for example the use of a phosphonite, especially [1, 1-biphenyl] -4,4'-diylbisphosphonite tetrakis (2,4-di-ter-butylphenyl), denoted by PEP-Q result, and an organic acid for stabilizing PAEK. Such organophosphorus compounds have a low degree of oxidation. They are typically in an oxidation state of 2 or 3, and therefore play the role of reducing the peroxide groups in the polymer melt. A major drawback of these aromatic organophosphorus compounds, such as phosphites or phosphonites, for example, lies in the fact that they are susceptible to hydrolysis and thus, it is very difficult to incorporate in aqueous route or during a synthesis process. On the other hand, they are not sufficiently stable at processing temperatures so that they degrade generating the emission of volatile organic compounds. [0012] Now, for example in the field of manufacture of structural composite by impregnation, three main approaches are possible: - or is impregnated by melting the polymer above its melting temperature and often in the presence of air. It is thus understood that the polymer matrix must not be too sensitive to thermal oxidation phenomena. On the other hand, if there is generation of volatile organic compounds, this can lead to defects in level of impregnation, with porosities damaging training for the properties of the final composite material, - a solvent route is used. However, PAEK are only soluble in some organic solvents, generally very acidic, or hot in heavy solvents such as diphenylsulfone. In addition to the difficulty of using this type of solvent, it is very difficult to remove completely, which can cause the same problems as volatile organic compounds. - or finally, one generally uses an aqueous suspension of powder PAEK as described the document "wet impregnation as route to unidirectional carbon fiber reinforced composite thermoplastic manufacturing", KKCHo et al, Plastics, Rubber and Composites, 201 1, Flight . 40, No. 2, p.100- 107. Thus, for example using a PEKK powder suspension and a surfactant which is deposited on carbon fibers or glass for example. The fibers are passed through an oven to evaporate water and then in a high temperature die, typically greater than 400 ° C so that polymer melts and coats the carbon fibers. The prepregs obtained tapes are then used to form composite objects by heating them to high temperature again. [0013] Therefore, the fact that the stabilizer is sensitive to hydrolysis and thermally degrades problematic when incorporated into the polymer melt and / or during the implementation, high temperature, of the polymer. In addition, volatile organic compounds released during the degradation of the stabilizer, are malodorous, harmful to the environment and / or health and create porosity in the composite material in manufacture, resulting in mechanical defects in the finished composite part . Finally, during impregnation of fibers, the emitted volatile organic compounds can further interfere with the coating of the fibers and generate significant mechanical defects in the objects that result. [0014] The WO9001510 discloses a treatment of a polymer powder from the family of PAEK in an aqueous solution of a phosphate salt at high temperature and pressure for 3 hours to reduce the level of impurities. The polymer thus treated is then filtered and washed with water three times and then dried for 16 hours. There is no indication in this document that the phosphate salt, which is soluble in water, is actually retained in the polymer powder. In addition, treatment described is cumbersome and time to implement and is very different from an additive. Finally, nothing is said in this document, it is effective against thermal oxidation phenomenon since stability is evaluated in a confined environment. The phosphate salts are indeed known to be used in other polymer matrices, such as polysulfones, chlorides or vinyl for example, to capture the acidity and the chlorides contained in the polymer. Such uses are described for example in documents US3 794 615 or EP0933 395 or US2013 / 0281587 but again it is not described of stabilizing action in the presence of air. [Technical problem] [0015] The invention therefore aims to remedy at least one of the disadvantages of the prior art. In particular, the invention aims to provide a composition based on PAEK, which is stable in the molten state vis-à-vis the thermo-oxidation, and that does not generate the emission of volatile organic compounds. [Brief description of the invention] [0016] Surprisingly, it was found that a composition based on poly-arylene-ether ketone (PAEK), characterized in that it comprises an organometallic phosphate salt, or a mixture of organometallic phosphate salts has a very high stability in the molten state vis-à-vis the thermal oxidation, even in the presence of air, without releasing volatile organic compounds, the stabilizer used is very stable at high temperature, typically greater than 350 ° C, and insensitive to hydrolysis. organometallic salts of phosphate (s) is predominantly soluble in water incorporation into the PAEK-based composition is facilitated. [0017] According to other optional features of the composition: - Ie (s) salt (s) of organometallic phosphate (s) have the following formula: O II R'O— P-OR I G i PS wherein R is different or not R ', R and R' being formed by one or more aromatic moieties unsubstituted or substituted with one or more groups having 1 to 9 carbons, R and R 'may be directly bound to each other or separated by at least one group selected from the following group: -CH2-; -C (CH3) 2-; -C (CF3) 2-; -SO2-; -S-, -CO-; -O- and M represents an element of Group IA or MA of the periodic table, - the organometallic phosphate salt is sodium phosphate 2,2'-methylene-bis- (4,6-di-tert-butylphenyl) - the proportions of organometallic phosphate salt (s) in the composition is between 10 ppm and 50000 ppm, preferably between 100 and 5000 ppm, - the base of PAEK composition is more particularly to a composition based on one of the following polymers: PEKK, PEEK, PEEKK, PEKEKK, PEEEK or PEDEK, - the base of PAEK composition is more particularly a poly ether ketone ketone (PEKK), - the base of PAEK composition is more particularly to a composition based on PEKK, and includes, in addition to the PEKK, at least one of the following polymers: PEK, PEEKEK, PEEK, PEEKK, PEKEKK, PEEEK, PEDEK, with content of less than 50% by weight of the composition, preferably less than or equal to 30% by weight of the composition. - the composition further comprises at least one filler and / or at least one further additive, - the composition is stable in the molten state, - the organometallic salt of phosphate, or mixture of organometallic phosphate salts, also acts as nucleating within said composition. [0018] The invention also relates to an object made by a technology selected from the laser sintering, the molding by melt deposition, casting, injection, extrusion, thermoforming, rotational molding, compounding, compression molding or impregnation from a composition as described above. [0019] Finally, the invention relates to use of an organic metal phosphate salt for stabilizing a composition based on poly-arylene-ether ketone (PAEK) melt. [0020] Other advantages and features of the invention appear on reading the following description given by way of illustrative and nonlimiting example, with reference to the appended figures which represent: • Figure 1, a plot of complex viscosity as measured by an oscillatory rheometer versus time, a non-stabilized reference product under nitrogen, · Figure 2 is a thermogravimetric curve in function of temperature of a stabilizer of reference used for comparison. [Description of the invention] [0021] The poly-arylene-ether ketones (PAEK) used in the invention include the following units of formulas: (- Ar - X -) and (- An - Y -) in which : Ar and An are each a divalent aromatic radical; Ar and An can be chosen, preferably, among the 1, 3-phenylene, 1, 4-phenylene, 4,4'-biphenylene, 1, 4-naphthylene, 1, 5-naphthylene and 2,6 -naphthylène; X is an electron withdrawing group; it may be chosen preferably from the carbonyl group and the sulfonyl group, Y denotes a group selected from an oxygen atom, a sulfur atom, an alkylene, such as -CH 2 - and isopropylidene. In these units X and Y, at least 50%, preferably at least 70% and more particularly at least 80% of the X groups are a carbonyl group, and at least 50%, preferably at least 70% and more particularly at least 80% of the Y groups represent an oxygen atom. According to a preferred embodiment, 100% of the groups X denote a carbonyl group and 100% of the Y groups represent an oxygen atom. [0022] More preferably, the poly-arylene-ether ketone (PAEK) may be selected from: - also a poly ether ketone ketone PEKK appointed comprising units of formula IA of formula IB and their mixture: - a polyether-ether ketone also called PEEK comprising units of formula MA: formula MA Similarly one can introduce para linkages in these structures at the ethers and ketones of formula MB: formula MB The sequence can be totally para but it may also introduce sequences meta partially or completely: Formula Or : formula IV Or ortho linkages according to the formula V: In Formula - poly ether ketone PEK also known consisting of units of the formula VI: Formule VI Similarly, the sequence can be totally para but it may also introduce sequences meta partially or totally (the formulas VII and VIII): Or - poly ether ketone ether ketone also named PEEKK comprising units of formulas IX: formula IX Similarly linkage can be introduced in these structures meta level ethers and ketones. - a polyether-ether ether ketone also named PEEEK consisting of X units of formulas: formula X Similarly linkage can be introduced in these structures meta level ethers and ketones as well as biphenols sequences according to formula XI: O ■ o -o - ★ Formule XI [0023] Other arrangements of the carbonyl group and the oxygen atom are also possible. [0024] The composition object of the invention is based on PAEK. More particularly, the composition is a composition based on poly ether ketone ketone (PEKK). [0025] According to an alternative embodiment, the PAEK-based composition may also be a composition based on one of the following polymers: PEEK, PEEKK, PEKEKK, PEEEK or PEDEK. [0026] The PAEK-based composition may also be a composition based on a mixture of polymers of the family of PAEK. Thus, the composition may be based on PEKK and include, in addition of the PEKK, at least one of the following polymers: PEK, PEEKEK, PEEK, PEEKK, PEKEKK, PEEEK, PEDEK, with a content of less than 50% by mass of the composition, preferably less than or equal to 30% by weight of the composition. [0027] Advantageously, the composition of PAEK according to the invention is stable in the molten state through the incorporation of a phosphate salt in the composition. [0028] In the present description, the term "stable melt polymer" means a polymer whose structure changes little when melted, so that its physicochemical properties, especially the viscosity, vary only within a limited range. More specifically, it is considered as a polymer stable to melting under nitrogen state when the change in its viscosity in the molten state in 30 minutes, measured with an oscillatory rheometer under nitrogen and with an oscillation frequency of 1 Hz , 380 ° C or 20 ° C above its melting temperature when it exceeds 370 ° C, is less than 100%, especially less than 50%, in particular less than 20%, especially between -20% and + 20%. Similarly, it will be considered as a polymer stable in air under molten state when the change in its viscosity in the molten state in 30 minutes when measured as described above but under air and with an oscillation frequency of 0 , 1 Hz is less than 150%, in particular less than 100%, particularly preferred less than 50% and most preferably between -20% and + 50%. [0029] Alternatively, the stabilizer incorporated into the composition may be a mixture of phosphate salts. [0030] It has in fact been found that such a phosphate salt is used to stabilize a composition of PAEK in a molten state as well as nitrogen as in air. This PAEK stabilizing effect in the melt in air is very surprising and it was not at all intuitive for a skilled person to choose to incorporate a phosphate salt to stabilize a PAEK melt vis- in respect of a phenomenon of thermal oxidation. Indeed presents a phosphate salt maximum oxidation state so that it is not known to be an antioxidant. However, in the presence of oxygen from the air, it happens to stabilize the polymer in the molten state vis-à-vis the thermoxidation phenomenon. Is obtained in fact a viscosity of the composition melt, more stable compared to the same composition without phosphate salt, which means that the elongation phenomena chains using branching phenomena among others, are more limited. [0031] The phosphate salt presents itself as an active stabilizer compositions of PAEK in a molten state even in the presence of air, with as high efficiency as an aromatic organophosphorus compound. However, it also has a considerable advantage over an aromatic organophosphorus compound because it does not hydrolyze and does not generate volatile organic compound emission. Only water can be generated in some cases where the phosphate salt is in a hydrated form or when dimerized phosphate salt. [0032] Advantageously, one or more salt (s) of phosphate may (can) be incorporated (s) in the composition based on PAEK. The phosphate salt is preferably selected from (of) salt (s) of ammonium phosphate, sodium, calcium, zinc, aluminum, potassium, magnesium, zirconium, barium, lithium, or rare earths. Preferably, the (s) salt (s) of phosphate is (are) one (or more) salt (s) of organometallic phosphate. [0033] The one or more salt (s) of organometallic phosphate (s) (s) used has (have) the following formula: G I I 'O-P- OR wherein R is different or not R ', R and R' being formed by one or more aromatic moieties unsubstituted or substituted with one or more groups having 1 to 9 carbons, R and R 'may be directly linked together or separated by at least one group selected from the following group: -CH2-; -C (CH3) 2-; -C (CF3) 2-; -SO2-; -S-, -CO-; -O- and M represents an element of group IA or MA of the periodic table. [0034] More preferably, the organometallic phosphate salt is sodium phosphate 2,2'-methylene-bis- (4,6-di-tert-butylphenyl). [0035] Preferably, the phosphate salt, or mixture of phosphate salts, is incorporated into the PAEK-based composition in an amount ranging between 10 ppm and 50000ppm and, even more preferably between 100 and 5000ppm. [0036] Another surprising effect related to the incorporation of the phosphate salt in the composition based on PAEK lies in the fact that it allows to act as a nucleating agent. Increase the crystallization kinetics into a crystallizable product under standard processing conditions or for example by laser sintering, and so have a semi-crystalline PEKK is advantageous for certain properties such as chemical resistance. In addition, such a nucleating agent allows to control the crystal morphology of the polymer, and in particular the size of the crystalline areas (or spherulites), to ensure constancy in the mechanical properties of the polymer and this, whatever the conditions of out of the polymer. [0037] The invention further relates to a process for stabilizing the melt, of a composition based on PAEK, said method comprising a step of incorporating a stabilizing agent vis-à-vis phenomena thermo-oxidation, said method being characterized in that the stabilizing agent is incorporated a phosphate salt, or a mixture of phosphate salts. [0038] The incorporation of the phosphate salt in the PAEK-based composition may be accomplished by one of the following techniques: dry blending (also known as the Anglo-Saxon terminology "dry blend"), compounding, wet impregnation or during the polymer synthesis process PAEK. [0039] The method of synthesis of a PAEK usually consists of a polycondensation. The synthesis can be done in two ways: a nucleophilically, wherein ether linkages formed during the polymerization step, or electrophilically, wherein the carbonyl bridges are formed during the polymerization step. PEKK for example, results of a Friedel-Crafts polycondensation reaction between the DPE (diphenyl ether) and a téréphthaloyl chloride and / or isophthaloyl chloride, for example. [0040] Advantageously, the stabilized composition based PAEK can be obtained in granular form by compounding on a tool known to those skilled in the art, such as an extruder twin-screw, a cokneader, or an internal mixer . [0041] The composition thus prepared, can then be transformed for use or further processing known to those skilled in the art using tools such as an injection molding machine, an extruder, laser sintering equipment etc .... [0042] The method of preparing the composition according to the invention may also be used a twin-screw extruder feeding, without intermediate granulation, an injection molding machine or an extruder according to an implementation device known by those skilled in the art. [0043] The stabilized composition based PAEK can also be obtained in powder form, by dry mixing, for example (more commonly known as the Anglo-Saxon terminology "Dry Blend"). [0044] From the composition obtained, which can be either in granular form or powder form, it is possible to manufacture different objects by a laser sintering technique, injection or extrusion, thermoforming, rotomolding , compression molding, or impregnation, for example. [0045] The wet impregnation for example, for making pre-impregnated composite tapes, still referred to under their English terminology "tape", consists in depositing on carbon or glass fibers for example, an aqueous dispersion a powder of PAEK and salt (s) of phosphate. More particularly, the dispersion may for example comprise powder of PEKK and salt (s) of phosphate and a surfactant in aqueous solution. The fibers thus coated with the aqueous dispersion are then passed through an oven to evaporate the water. Then they are passed through a die at high temperature, typically greater than 370 ° C, to melt the polymer PEKK stabilized and it can coat the fibers properly. After cooling, there are obtained "tapes" or pre-impregnated tapes which are then used by assembling and / or by superimposing them, and to remelt form composite objects. [0046] A great advantage of the phosphate salts is the fact that even heated to very high temperature, greater than or equal to 350 ° C for example, they do not generate the emission of volatile organic compounds but they simply lose the water in the form of steam. Therefore, phosphate salts present no risk to the environment and / or health and they do not create porosities may hinder coating the fibers and / or generate the appearance of defects in the final object made, may then lead to a degradation of mechanical properties. [0047] The composition based on PAEK and salt (s) of phosphate as defined above, may be prepared by any known method, for obtaining a homogeneous mixture containing the composition according to the invention and optionally other additives, fillers, other polymers. Such a method may be selected from the techniques of dry blend (or dry mixing using for example a roller mixer), an extruder at melt compounding, or wet impregnation or during the process of polymer synthesis. [0048] More particularly, the composition according to the invention may be prepared by mixing in the melt of its components, particularly in a process called live. [0049] Compounding, for example, is a process which allows to mix by melting the plastic and / or additives and / or fillers. To manufacture the composition, raw materials, in the form of granules, are arranged in a co-rotating twin-screw extruder. [0050] The following examples illustrate without limitation the scope of the invention: Example 1 under nitrogen viscosity measurements [0051] Several compositions PEKK were prepared. A Cj control composition of PEKK having no stabilizer was prepared by a conventional synthesis method by a polycondensation reaction. [0052] A second composition based on PEKK, referenced C1, was prepared by wet impregnation, wherein the PEP-Q ([1, 1-biphenyl] -4,4'-diylbisphosphonite tetrakis (2,4-di -ter-butylphenyl) phosphite) of formula (1) below, was incorporated up to 1000ppm. This phosphite is used as a comparative example to stabilize the composition of PEKK. [0053] A third composition based PEKK, referenced C2 was prepared by aqueous impregnation, wherein anhydrous sodium dihydrogen phosphate (NaH 2 PO 4 ), also called sodium dihydrogen phosphate of the formula (2) below was built up to 1000ppm. O I I O. (2) HO" \ O" Na OH [0054] A fourth composition based PEKK, referenced C3, was prepared in the same manner as the second and third compositions, aqueous impregnation, wherein sodium trimetaphosphate (NasPsOg), also called anhydrous trisodium phosphate of the formula (3) below, was incorporated at the OOOppm. QQ - Na +