Polymeric material, manufacture and use

Abstract

Polyaryletherketone, PAEK, in the form of particles, is provided for use in component formation by powder bed sintering (PBS). The PAEK is a polyetheretherketone- polyetherdiphenyletherketone (PEEK-P

Description

The invention relates to polymeric materials, in the form of particles, which are suitable for use in the formation of components by selective sintering and melt-bonding of sequentially deposited layers of powder comprising the particles. The invention also relates to processes for making the polymeric particles, their use in powder bed sintering, and methods for component formation from the particles. Methods in which rapid manufacturing of components is carried out from construction data under computer control are sometimes referred to as rapid prototyping methods. In prior art methods the component to be manufactured is built layer-wise from a building material. In some prior art methods, the building material is in powder (i.e. solid particulate) form, with the uppermost layer of powder selectively sintered, for instance by selective heating with a laser, in order to melt-bond powder particles together, and to melt bond them to the layer on which they are deposited, in order to form a melt-bonded cross sectional layer of the component. Such methods were, for example, known under the names 3D laser sintering, 3D laser melting or 3D printing. Metals, ceramics and plastics may be used as powdered building materials. For instance, the patent US 5,730,925 describes a laser sintering method, in which layers of a powder are applied onto a support that can be vertically repositioned and in which the layers are selectively sintered at the positions corresponding to the cross-section of the object to be manufactured by means of a laser. Originally, such methods were limited to prototyping, but now the methods are used for component manufacture. In this specification, such methods will be referred to by the term additive layer manufacturing (ALM), indicating that 3D parts are constructed by the build-up of successive layers. A term used to describe such a method of component manufacture, where the powder particles in each layer are selectively sintered using electromagnetic radiation in order to melt-bond the particles to each other and to the underlying layer, is powder bed sintering (PBS). This may be contrasted with traditional manufacturing by milling, in which material is removed or "subtracted" from a starting blank in order to arrive at a desired component shape. Powder bed sintering apparatus for manufacture of components from polymeric powders using laser sintering is described in patent application publications such as WO00 / 21736 A1, with apparatus now commercially available from manufacturers such as EOS GmbH. Typically, a laser sintering device is employed by means of which layer-wise manufacturing of a three-dimensional object may be performed using selective fusion of layers of a powder bed. Instead of using a scanning or rastering laser beam and / or a focussed high energy light beam, other systems to selectively deliver electromagnetic radiation could be used, such as mask exposure systems or the like. A wide range of different types of polymeric materials has been proposed for use as building materials using PBS. Poly(aryletherketone) polymers, referred to herein as PAEK polymers, have been found to be particularly useful, as components that have been manufactured from PAEK powder or PAEK granulates are typically characterized by a low flammability, good biocompatibility as well as a high resistance against hydrolysis and radiation. It is the thermal resistance also at elevated temperatures as well as the chemical resistance that distinguishes PAEK powders from conventional polymer powders such as polyamides, polyesters and the like. The high-performance characteristics of PAEK polymers, combined with their low density, make them of use in the aerospace industry, in the automotive industry, in the electronic industry and in the medical industry. US patent publication US7847057B2 discloses the use of tempering to improve the properties of PAEK powders, as ALM / PBS building materials, in order to improve uniformity and evenness of applied layers of powders in order to improve accuracy of manufacturing of parts by laser sintering. The publication refers to polyaryletherketones and makes reference to the group consisting of polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetherketone (PEK), polyetheretherketoneketone (PEEKK) and polyetherketoneetherketoneketone (PEKEKK). PEEK is the polymer used in the Examples of this patent. European patent application publication EP2123430A1 seeks to address the problem of providing an improved process for producing an object by selective sintering which leads to improved mechanical properties. The problem is said to be solved by producing objects having a final crystallinity of 80% or less, preferably within the specific range 5 to 45%. The publication states: “the advantages of the invention are particularly feasible when polyaryletherketone polymer or a polyaryletherketone copolymer, or when a polyamide polymer or a polyamide copolymer is appropriately used as a polymer material of the polymer powder". Also disclosed is use of a polymer in powder form wherein the polymer is preselected for lowering the crystallinity of the manufactured three-dimensional object. Assuming a given molecular weight of a selected polymer such as PAEK as a reference, it was found by the inventors that already a relatively slight increase in molecular weight of the polymer comprised in the powder readily leads to a surprisingly marked decrease of the crystallinity in the manufactured object, which in turn transforms into a significant improvement of certain, very advantageous mechanical properties of the manufactured object. It is disclosed that preselecting a PEEK polymer material having a relatively high molecular weight of typically Mn=32,000 and Mw=99,000 rather than having a molecular weight of typically Mn=23,000 and Mw=68,000 assists in lowering the crystallinity of the manufactured object to below 50%. The melt viscosity of the polymer is disclosed as correlating with the molecular weight of the polymer or copolymer in that the higher the molecular weight of a polymer or copolymer, the higher is also its melt viscosity. Therefore, for PAEK polymers or copolymers, melt viscosities in the range 0.2-0.45 kN.s / m2 are particularly preferred according to EP2123430A1 (melt viscosity determined according to US Patent application publication US2006 / 0251878A1 in a capillary viscosimeter with a tungsten carbide nozzle at 400°C and a shear rate of 1000 s-1). European patent application publication EP2145913A1 seeks to improve mechanical properties of objects manufactured by laser sintering of a polymer or copolymer by use of a polymer or copolymer modified by incorporation of branching groups in the polymeric backbone, modification of end groups, incorporation of bulky groups or providing “at least one aromatic group non-linearly linking the backbone chain”. The publication includes a wide-ranging generic disclosure, but its examples only describe a very small number of specific materials - e.g. “a structurally modified PAEK” (Example 1), a modified PEEK / PEK copolymer (Example 2), a powder based on polyamide PA6-3-T (Example 3), structurally modified polyethylene PE-LLD (Example 4), structurally modified polyethylene PE-HD (Example 5) and thermally treated PEEK (Examples 6 &7). US patent application publication US2006134419A1 discloses a polymer powder containing polyaryletherketone. The wide-ranging generic disclosure focuses on polyaryletherketones selected from PEEK, PEK, PEKK and PEEKK but the only polymer specifically exemplified is PEEK. International patent application publication WO2014207458A1 discloses PEEK / PEDEK copolymers, which have repeat units EEK = -O-Ph-O-Ph-CO-Ph- and EDEK = -O-Ph-Ph-O-Ph-CO-Ph- in molar proportions from 55:45 to 95:5 and with melt viscosity (MV) measured at 340°C and 1000s-1 shear rate of at least 0.25 and less than 1.2 kNsm-2. The copolymers are recommended as polymers with high performance, similar to PEEK but with reduced melt temperature, high glass transition temperature and high crystallinity. The tensile strength of the polymeric material in conventionally moulded form is said to be preferably at least 80MPa. International patent application WO2015124903A1 discloses the use of PEEK / PEDEK copolymer as a polymeric powder building material for ALM / PBS, with an EEK / EDEK molar ratio from 55:45 to 95:5 and an MV of at least 0.25 kNsm-2 and less than 1.2 measured at 340°C and at 1000s-1 shear rate. In the Examples of WO 2015124903A1 the PEEK / PEDEK is prepared having an MV of 0.26 kNsm-2, measured at 340°C and at 1000s-1 shear rate, using a nucleophilic process employing 0.628 kg of diphenylsulfone as aromatic sulfone solvent per mole of the mixture of benzene-1,4-diol and 4,4'-biphenol. The MV for such a polymer measured at the higher temperature of 400°C and 1000 s-1 would be lower, with a value of about 0.13 kNsm-2. International patent application publication WO2020141329A1 discloses a PAEK, in the form of particles, which is a PEEK / PEDEK copolymer of molar ratio 55:45 to 80:20 for PEEK:PEDEK. The copolymer has a melt viscosity, MV, from 0.35 to 0.55 kNsm-2 at 400°C and a shear rate of 1000s-1. The copolymer is disclosed to be of use in formation of components having high elongation at break when formed by selective sintering and melt-bonding of sequentially deposited layers of powder comprising the copolymer as particles. International patent application publication WO2020141329A1 discloses polyaryletherketone PAEK polymeric material suitable for use in an additive manufacturing process to make an object. The PAEK polymeric material has a shear viscosity, SV, of at least 145 Pa.s and less than 350 Pa.s, measured using capillary rheometry operating at 400°C at a shear rate of 1000s-1. The PAEK polymeric material is required to have an isothermal crystallinity half-life, T1 / 2, of greater than 12 minutes at a temperature of 280 °C, measured by Differential Scanning Calorimetry, DSC. Components made by PBS using PAEK polymer particles as building material are typically lower in strength and higher in porosity than components made by injection moulding of the same PAEK. Moreover, the PAEKs which provide components with greater mechanical strength typically have a high melting point, making their use in PBS by selective laser sintering more difficult than for building materials with lower melting points. It is an object of the invention to address one or more of the above described problems. One aim of the invention, amongst others, is to provide polymeric particles of PAEK which can be used as building materials (feedstock) in PBS to generate components which have improved mechanical properties compared to prior art PAEK, for instance having greater elongation at break and / or a greater tensile strength. It is further aim of the invention to provide polymeric particles which are flowable at low shear rates when molten so that efficient melt-bonding between the particles may be achieved. It is further aim of the invention to provide polymeric particles which have a high bulk density and which have good powder flow characteristics. Another aim of the invention is to provide PAEK powders having particle sizes which are suitable as feedstock for PBS but which can be readily prepared by comminution of conventional PAEK powder (e.g. coarse powder) or flakes resulting from the polymerisation reaction used to generate the PAEK. The inventors have found that for components made by PBS of PAEK powders, good mechanical properties, and in particular good tensile strength and high values for extension at break, can be provided through the use of polymers which crystallise with a half-life within a certain range under the operating conditions necessary for powder bed sintering. Moreover, these particles can be prepared readily ,by mechanical comminution, in a form having a high bulk density and with good powder flow behaviour. Patent application publication EP2123430A1 linked low final crystallinity with good mechanical properties for a polymer component made by PBS. It will be understood that reduced crystallisation rate is likely to lead to lower final values of crystallinity for powders with the same glass transition temperature, Tg, and cooled to a temperature below Tg at the same rate. EP2123430A1 recommended the use of high molecular weight polymers (high MV or SV polymers), which have long T1 / 2 values as they are slow to crystallise, to achieve better interlayer bonding in order to improve mechanical properties for the resulting component. For conventional moulding of PAEK polymers (such as injection moulding) it is known that high molecular weight PAEKs, such as high molecular weight PEEK, crystallise more slowly than low molecular weight versions of the same polymer type, and so give greater total crystallinity and better mechanical properties when allowed to crystallise isothermally. Surprisingly, the inventors have found that certain low MV / SV (low molecular weight) polymers can be tailored to exhibit slower crystallisation behaviour under PBS manufacturing conditions than their higher MV / SV equivalents, and that crystallisation rate for these polymers can be tailored to provide improved mechanical properties for components formed from such polymers by PBS. It is also the case that high molecular weight (high MV / higher SV) PAEK polymers are difficult to convert into the fine powders necessary for PBS. Such powders are typically required to have a mean diameter of say 60pm and a narrow particle size distribution about the mean. It is usually necessary to use high solvent levels during the nucleophilic polycondensation used for synthesis of the high MV PAEK polymers intended for use in PBS in order to enable the resulting granules or flakes to be friable enough to be comminuted into powders of a suitable size. This, in turn, can lead to low bulk density for the resulting powder because of the large volumes of intraparticle pores arising from the high solvent levels used in synthesis and the subsequent removal of the solvent which leaves a high pore volume within the resulting milled particles. This can also consequently lead to the mechanical properties for components made from such powders by PBS being poorer than would be the case if the powder particles making up the component were less porous. Moreover, such powders typically have poor flowability, which again can result in low bulk density. The inventors have found that by use of a specific range for the ratio of EEK (-O-Ph-O-Ph-CO-Ph-) to EDEK (-O-Ph-Ph-O-Ph-CO-Ph-) repeat units, in a PEEK / PEDEK copolymer with 1,4 para linking, combined with a narrow, low melt viscosity, MV, range for the copolymer, particles of the selected copolymer, when used as a building material for PBS, can be tailored to have half-lives to provide crystallisation at an optimal rate, after sintering, under the conditions present during PBS manufacture. Moreover, the low SV of the selected polymers allows them to be easily comminuted to a suitable particle size for use in PBS without the need for employment of high solvent levels when synthesising the polymers through nucleophilic polycondensation. Hence, the intraparticle pore volume of the polymer powder may be reduced, leading to further improvement in density and mechanical properties for components made from the polymer powders by PBS. In particular, the polymers of the invention result in formation of components which have improved tensile toughness and tensile strength, in particular with improved extension at break. The milled polymer particles have low intraparticle pore volumes, which leads to higher bulk densities for the particles and improved flowability, and components made from them by PBS have reduced porosity arising from these effects. The polymers of the invention, as copolymers of PEEK and PEDEK, also have a lower melting point than the conventional homopolymers such as PEK and PEEK used for PBS, which is advantageous for reduction in energy requirements and lower powder bed temperatures. This in turn means there is less thermal degradation of the unsintered powder particles in the powder bed which in turn permits for ease of reuse of unsintered powder in subsequent PBS operations (i.e. recycling of powder which is unsintered after a first PBS operation to make a first component for use in a second PBS operation to make a second component - either as sole powder or in combination with virgin powder). A first aspect of the invention provides a polyaryletherketone, PAEK, in the form of particles, for use in layer-wise formation of a component by selective sintering with electromagnetic radiation, wherein the PAEK is a copolymer comprising repeat units of formula I; and repeat units of formula wherein at least 95 mol% of the copolymer repeat units are repeat units of formula I and of formula II. The repeat units I and II have a molar ratio l:ll from 69:31 to 73:27. The PAEK has a shear viscosity, SV, from 160 to 280 Pa.sas measured using capillary rheometry at 400°C at a shear rate of 1000s'1. The SV is suitably measured by capillary rheometry as described herein. The isothermal crystallinity half-life, T1 / 2, is from 5 to 11 minutes. The isothermal crystallinity half-life, T1 / 2, is measured by differential scanning calorimetry as described herein at a temperature of 270°C. Preferably, the selective sintering with electromagnetic radiation is carried out with a laser. The copolymer, also referred to as a PEEK-PEDEK copolymer, is preferably a random copolymer prepared by nucleophilic polycondensation as described herein. The PAEK particles preferably have a bulk density of 350 kg / m3 or more. Bulk density may be measured in accordance with ASTM D 1895 method B (2017). A second aspect of the invention provides the use of the PAEK particles according to the first aspect of the invention in a process for formation of a component in a layerwise fashion by sequentially depositing and selectively sintering, with electromagnetic radiation, a plurality of layers comprising the PAEK particles. Preferably the sintering with electromagnetic radiation is carried out with a laser. A third aspect of the invention provides a method of manufacturing a component, the method comprising: (i) selecting PAEK particles according to the first aspect of the invention, (ii) forming the component in a layer-wise fashion by sequentially depositing and selectively sintering, with electromagnetic radiation, a plurality of layers comprising the PAEK particles; wherein a first layer comprising the deposited PAEK particles is selectively sintered to melt-bond particles of the first layer to other particles of the first layer to form a base layer of the component; and each subsequently layer comprising the PAEK particles is selectively sintered to meltbond particles of the subsequently deposited layer to the respective preceding layer, and to other particles of the subsequently deposited layer, prior to deposition of a next deposited layer comprising the PAEK particles; whereby the component is formed from the selectively sintered and mutually melt-bonded portions of the plurality of layers corresponding to respective cross-sections of the component. Preferably the sintering with electromagnetic radiation is carried out with a laser. A fourth aspect of the invention provides a process of forming a polyaryletherketone, PAEK, in the form of particles, for use in a method for layer-wise formation of a component, wherein the PAEK is a copolymer comprising repeat units of formula I; and repeat units of formula wherein Ph represents a phenylene moiety; and wherein the isothermal crystallinity half-life, T1 / 2, of the PAEK is from 5 to 11 minutes at 270°C; The process comprises: a) nucleophilic polycondensation of a mixture of benzene-1,4-diol and 4,4'-biphenol in a molar ratio of benzene-1,4-diol:4,4'-biphenol from 69:31 to 73:27, with 4,4'-difluorobenzophenone, in a reaction mixture comprising sodium carbonate and potassium carbonate in an aromatic sulfone solvent, at a reaction temperature rising to a temperature from 280°C to 330°C; b) cooling of the resulting reaction mixture and recovery of the PAEK copolymer resulting from step from the reaction mixture; and c) forming the recovered PAEK copolymer into particles by comminution and classification. In step a of the process: i the molar ratio of sodium carbonate to the mixture of benzene-1,4-diol and 4,4'-biphenol is from 0.95 to 1.15; ii the molar ratio of potassium carbonate to sodium carbonate is from 0.002 to 0.05; iii the molar ratio of the 4,4'-dihalobenzophenone to the mixture of benzene-1,4-diol and 4,4'-biphenol is from 1.01 to 1.03; iv the aromatic sulfone solvent is present in the reaction mixture as 0.27 to 1.02 kg / mole of the mixture of benzene-1,4-diol and 4,4'-biphenol; and v the polycondensation in step a is continued for sufficient time to ensure that the resulting PAEK recovered from step a has a shear viscosity, SV, from 160 to 280 Pa.s as measured using capillary rheometry at 400°C at a shear rate of 1000s'1. As explained below, the molar ratio for potassium carbonate / sodium carbonate used during the nucleophilic polycondensation reaction of this aspect of the invention can be used to influence the crystallisation behaviour, with higher ratio of potassium carbonate resulting in a polymer that crystallises more rapidly and so has a shorter crystallisation half-life T1 / 2 than the same polymer with the same SV and a lower ratio of potassium carbonate. This can be used to tailor the T1 / 2 values of the PAEK (PEEK-PEDEK) copolymers of the invention to fall within the desired range whilst also having an SV in the required range. Preferably, the aromatic sulfone solvent is present in the reaction mixture as 0.27 to 0.39 kg / mole of the mixture of benzene-1,4-diol and 4,4'-biphenol, and more preferably, the aromatic sulfone solvent comprises at least 95% by weight of diphenylsulfone, preferably consisting essentially of or consisting of diphenylsulfone. This relatively low proportion of aromatic sulfone solvent is thought to provide a low pore volume for the copolymer particles produced by the process, which in turn yields a high bulk density and reduces weaknesses linked to such pores in components formed from the copolymer particles by powder bed sintering (PBS). The comminution of step (c) is preferably carried out in one or more mills selected from the group consisting of a ball mill an impact grinding mill and an air jet mill. The impact grinding mill may be a hammer mill, a needle mill or a disc mill. More preferably, an air jet mill is used for the comminution step (c). A fifth aspect of the invention provides a method of preparing a polyaryletherketone, PAEK, in the form of particles for use in layer-wise formation of a component by selective sintering with electromagnetic radiation. The method comprises: i) selecting a PAEK which is a copolymer comprising repeat units of formula I; and repeat units of formula wherein at least 95 mol% of the copolymer repeat units are repeat units of formula I and of formula II. The repeat units I and II have a molar ratio l:ll from 69:31 to 73:27; and ii) comminuting and classifying the PAEK to generate the particles. The PAEK has a shear viscosity, SV, from 160 to 280 Pa.s as measured using capillary rheometry at 400°C at a shear rate of 1000s'1. The isothermal crystallinity half-life, T1 / 2, of the PAEK is from 5 to 11 minutes at270°C. Preferably, the selective sintering with electromagnetic radiation is carried out with a laser. The comminution in step (ii) is preferably carried out in one or more mills selected from the group consisting of a ball mill an impact grinding mill and an air jet mill. The impact grinding mill may be a hammer mill, a needle mill or a disc mill. More preferably, an air jet mill is used for the comminution step (c). Specific embodiments of the invention will now be described by reference to the following Examples. Example 1- Preparation of polyetheretherketone (PEEK) polyetherdiphenyletherketone (PEDEK) copolymer at 69:31 A 0.5 litre flanged flask fitted with a ground glass lid, stirrer / stirrer guide, nitrogen inlet and outlet was charged with 4,4'-difluorobenzophenone (111.06g, 0.51 mol), 1 ,4-dihydroxybenzene (37.99g, 0.345mol), 4,4'-dihydroxydiphenyl (28.86g, 0.155mol) and diphenylsulphone (242.30g) and purged with nitrogen for 1 hour. The contents were then heated under a nitrogen blanket to 160°C to form an almost colourless solution. While maintaining a nitrogen blanket, dried sodium carbonate (53.40g, 0.5mol) and potassium carbonate (2.76g, 0.02mol), both sieved through a screen with a mesh size of 500 micrometres, were added. The temperature was raised to 185°C at 1 °C / min and held for 100 minutes. The temperature was raised to 205°C at 1 °C / min and held for 20 minutes. The temperature was raised to 305°C at 1 °C / min and held for approximately 60 minutes or until the desired SV was reached as indicated by the torque rise on the stirrer. The required torque rise was determined from a calibration graph of torque rise versus SV. The reaction mixture was then poured into a foil tray, allowed to cool, milled and washed with 2 litres of acetone and then with warm water at a temperature of 40 - 50°C until the conductivity of the waste water was <2pe. The resulting PEEK-PEDEK powder was dried in an air oven for 12 hours at 120°C. The resulting polymer had a shear viscosity (SV) of 254 Pa.s at a temperature of 400°C and a shear rate of 1000 s’1, as measured by capillary rheometry. Example 2 (PEEK-PEDEK 70:30 copolymer) This Example was prepared in the same way as Example 1, with the exception that the quantity of 1,4-dihydroxybenzene was 38.50g (0.35 mol) and the quantity of 4,4’-dihydroxydiphenyl was 27.9g (0.15 mol). The quantity of potassium carbonate used was 1.04 g (0.0075 mol). The resulting copolymer had a shear viscosity (SV) of 265 Pa.s measured at a temperature of 400°C, and at a shear rate of 1000 s’1, by capillary rheometry. Example 3 (PEEK-PEDEK 71:29 copolymer) This copolymer was prepared in the same way as Example 1, with the exception that the quantity of 1,4-dihydroxybenzene was 39.09g (0.355 mol) and the quantity of 4,4’-dihydroxydiphenyl was 27.0g (0.145 mol). The resulting polymer had a shear viscosity (SV) of 232 Pa.s at a temperature of 400°C and a shear rate of 1000 s’1, as measured by capillary rheometry. Example 4 (PEEK-PEDEK 69:31 copolymer) A 0.5 litre flanged flask fitted with a ground glass lid, stirrer / stirrer guide, nitrogen inlet and outlet was charged with 4,4'-difluorobenzophenone (111.06g, 0.51 mol), 1 ,4-dihydroxybenzene (37.99g, 0.345mol), 4,4'-dihydroxydiphenyl (28.86g, 0.155mol) and diphenylsulphone (242.30g) and purged with nitrogen for 1 hour. The contents were then heated under a nitrogen blanket to 160°C to form an almost colourless solution. While maintaining a nitrogen blanket, dried sodium carbonate (53.40g, 0.5mol) and potassium carbonate (0.35g, 0.003mol), both sieved through a screen with a mesh size of 500 micrometres, were added. The temperature was raised to 185°C at 1 °C / min and held for 100 minutes. The temperature was raised to 205°C at 1 °C / min and held for 20 minutes. The temperature was raised to 305°C at 1 °C / min and held for approximately 60 minutes or until the desired SV was reached as indicated by the torque rise on the stirrer. The required torque rise was determined from a calibration graph of torque rise versus SV. The reaction mixture was then poured into a foil tray, allowed to cool, milled and washed with 2 litres of acetone and then with warm water at a temperature of 40 -50°C until the conductivity of the waste water was <2pe. The resulting PEEK-PEDEK powder was dried in an air oven for 12 hours at 120°C. The resulting polymer had a shear viscosity (SV) of 189 Pa.s at a temperature of 400°C and a shear rate of 1000 s’1, as measured by capillary rheometry. Examples 5 to 9 These were prepared using the same method as Example 4, with the quantities of 1,4-dihydroxybenzene and 4,4’-dihydroxydiphenyl adjusted to provide PEEK-PEDEK ratios as shown in table 1 below. The SV values are also set out in Table 1. Comparative Example 10 - Preparation of polyetheretherketone (PEEK) polyetherdiphenyletherketone (PEDEK) copolymer at molar ratio 75:25 A 0.5 litre flanged flask fitted with a ground glass lid, stirrer / stirrer guide, nitrogen inlet and outlet was charged with 4,4'-difluorobenzophenone (111.06g, 0.51 mol), 1 ,4-dihydroxybenzene (41.29g, 0.375mol), 4,4'-dihydroxydiphenyl (23.28g, 0.125mol) and diphenylsulphone (242.30g) and purged with nitrogen for 1 hour. The contents were then heated under a nitrogen blanket to 160°C to form an almost colourless solution. While maintaining a nitrogen blanket, dried sodium carbonate (53.40g, 0.5mol) and potassium carbonate (2.76g, 0.02mol), both sieved through a screen with a mesh size of 500 micrometres, were added. The temperature was raised to 185°C at 1 °C / min and held for 100 minutes. The temperature was raised to 205°C at 1 °C / min and held for 20 minutes. The temperature was raised to 305°C at 1 °C / min and held for approximately 60 minutes or until the desired MV was reached as indicated by the torque rise on the stirrer. The required torque rise was determined from a calibration graph of torque rise versus MV. The reaction mixture was then poured into a foil tray, allowed to cool, milled and washed with 2 litres of acetone and then with warm water at a temperature of 40 -50°C until the conductivity of the waste water was <2pe. The resulting PEEK-PEDEK powder was dried in an air oven for 12 hours at 120°C. The resulting polymer had a shear viscosity (SV) of 276 Pa.s at a temperature of 400°C and a shear rate of 1000 s’1, as measured by capillary rheometry. Comparative Example 11 Preparation of polyetheretherketone (PEEK) polyetherdiphenyletherketone (PEDEK) copolymer at molar ratio 75:25 The same conditions as Comparative Example 10 were used, with the exception that polymerisation was allowed to continue for longer until a SV of 340 Pas (measured at 400°C and a shear rate of 1000 s-1) was achieved. Capillary Rheometry Shear viscosity (SV) is measured in accordance with the principles set out in ASTM D3835 and ISO 11443. The term shear viscosity is used herein to avoid confusion with extensional or elongational viscosity. The shear viscosity of the PAEK copolymer is suitably measured by capillary rheometry using an RH10 capillary rheometer (Netzsch RH10 capillary rheometer), fitted with a tungsten carbide die (die diameter: 0.5mm ± 0.005mm, die length: 8mm). The die is mounted at the bottom of the barrel bore, and its dimensions define the applied shear field. A melt pressure transducer is mounted in the barrel to measure the resultant pressure at the die entrance as the material is extruded. Approximately 35 grams of PAEK is placed into an aluminium dish and dried in an air circulating oven for a minimum of 3 hours at 130°C ± 5 °C. The extruder is allowed to equilibrate to 400°C and the die is tightened to 37Nm after allowing heat expansion for 5 minutes. The RH10 transducers are then calibrated and zeroed using the "Flowmaster® "software. The dried polymer is loaded into the heated barrel of the extruder. The test is started by selecting ‘Run Test’ in the software. After an initial 6 minute pre-heat stage, force is applied to the sample according to the test method and the molten polymer is extruded through the die to form a thin fibre. In the ‘Analysis Tab’ of the software, the shear viscosity (Pa.s) is reported at the specified shear rate (1000 s-1 in this case). Isothermal DSC Measurements DSC Measurements were performed on a Mettler Toledo DSC 1. Approximately 8mg of pressed polymer film prepared from each example was first heated to 50°C and allowed to equilibrate for 15 mins. It was then heated to 400°C at 50°C / minute and held at this temperature for 15 minutes. The sample was then cooled at 50°C / minute to the desired isotherm temperature (270°C) and held isothermally for up until 3 hours, until crystallisation was complete. The sample was then cooled back to ambient temperature at 50°C / minute. The crystallisation curve (i.e. heat flow used to maintain temperature of the sample as a function of time as isothermal crystallisation proceeds) obtained from the DSC was integrated with respect to time, and used to output a running integral of a(t) from 0 to 1, where a(t) represents the degree of crystallisation a (alpha) versus time t with a=1 representing the crystallinity at the time when no further crystallisation-related heat flow is detected. The T1 / 2 value was taken as the time taken from the start of the isothermal period to reach the value of 0.5 for a on the curve. Table 1 Example PEEK:PEDEK ratio Type (1 or 2) T1 / 2 (s - 270°C) SV(Pa.s - 400°C) 1 69:31 1 304 254 2 70:30 1 316 265 3 71:29 1 306 232 4 69:31 2 388 189 5 71:29 2 354 180 6 73:27 2 303 174 7 69:31 2 627 213 8 71:29 2 403 220 9 73:27 2 426 214 10 (Comparative) 75:25 1 282 276 11 (Comparative) 75:25 1 376 340 As can be seen from Table 1, each of Examples 1-9 has a longer crystallisation half-life than that of the comparative example 10. Comparative Example 10 is a copolymer that has an SV which is low enough to potentially be useful for PBS. However, the copolymer crystallises too rapidly (half-life less than 5 minutes). This effect is thought to arise from the higher PEEK-PEDEK ratio compared to examples 1 to 9. Such a material provides brittle components when used as the feedstock powder for PBS manufacture of the components. Comparative Example 11 is a copolymer that provides strong, non-brittle components by PBS as a result of its favourable crystallisation half-life T1 / 2. However, the high SV value for the copolymer results in difficulties in comminuting the copolymer into a fine powder having a particle size distribution suitable for the PBS manufacturing process. Essentially, the high SV needed to provide a T1 / 2 value in the optimal range has to be traded off against a low throughput rate in comminution, in turn increasing manufacturing complexity and cost. It should also be noted that in Table 1, some polymers are indicated as type 1 and others as type 2. This relates to the molar ratio of potassium carbonate to sodium carbonate used during the polymerisation reaction, as discussed below. It is known, in the field of polymers generally, and for PAEKs in particular, that for polymers having the same repeat units, a lower molecular weight linear polymer will crystallise more rapidly than the same polymer, but of higher molecular weight, thought to be due to shorter polymer chains being more readily organised into a crystalline structure. It is also well known that SV is used as a measure of molecular weight, with higher SV corresponding to higher molecular weight. This effect can be seen through comparison of Example 4 with 7, 5 with 8, and 6 with 9 where, for polymers with the same PEEK-PEDEK ratio and the same potassium carbonate / sodium carbonate molar ratio used during polymerisation, the polymer of lower SV has a shorter T1 / 2, in each case, than the equivalent polymer of higher SV. However, the level of potassium carbonate used, in proportion to sodium carbonate, during the polymerisation reaction described in the examples (nucleophilic polycondensation) also has an effect on the crystallisation behaviour. Use of a higher a proportion of potassium carbonate (type 1) results in a copolymer that crystallises more quickly and so has a shorter crystallisation half-life T1 / 2 compared to a copolymer prepared with the same PEEK:PEDEK molar ratio and the same SV but prepared using a lower proportion of potassium carbonate (type 2). In the Examples, the molar ratio for potassium carbonate / sodium carbonate used during the nucleophilic polycondensation reaction was 0.04 or 0.05 (Ex. 2) for the type 1 Examples and 0.006 for the type 2 Examples. For Example 1, with an SV of 254 the T1 / 2 was 304s. Example 1 was type 1 For Example 4 which has the same PEEK-PEDEK ratio of 69:71 as Example 1, the SV was 232 Pa.s. Example 3 was type 2. This resulted in a longer T1 / 2 of 388s for Example 3 compared to T1 / 2 of 304s for Example 1, even though Example 3 has a lower SV. The same effect is seen for Example 3, which has a shorter half-life than Example 5, despite Example 5 having the same molar ratio of PEEK-PEDEK but a lower SV than Example 3. Essentially, the molar ratio for potassium carbonate / sodium carbonate used during the nucleophilic polycondensation reaction can be used to influence the crystallisation behaviour, with higher ratio of potassium carbonate resulting in a polymer that crystallises more rapidly and so has a shorter crystallisation half-life T1 / 2 than the same polymer with the same SV and a lower ratio of potassium carbonate. This can be used to tailor the T1 / 2 values of the PEEK-PEDEK copolymers of the invention to fall within the desired range whilst also having an SV low enough to permit ease of comminution. It is also important, for PBS, that the previously printed layer of an component formed by PBS does not fully crystallise before the next layer of the component is deposited. This provides good interlayer adhesion. Polymeric materials which crystallise too rapidly fail to achieve sufficient adhesion between subsequent layers of the printed object and this will result in poor elongation-at-break properties. Polymeric materials which crystallise too slowly will fail to achieve high final crystallinity levels, resulting in sub-optimal mechanical and chemical resistance for the resulting component. The PEEK-PEDEK copolymers of the invention have a favourable combination of properties that allows them to crystallise slowly enough to give excellent interlayer adhesion whilst still developing the high crystalline level that is desirable for components prepared from high performance PAEKs by PBS. It will be appreciated that numerous modifications to the above-described embodiments may be made without departing from the scope of the invention as defined in the appended claims. In summary, the invention provides polyaryletherketone, PAEK, in the form of particles, for use in component formation by powder bed sintering (PBS). The PAEK is a polyetheretherketone-polyetherdiphenyletherketone (PEEK-PEDEK) copolymer with PEEK:PEDEK molar ratio from 69:31 to 73:27, a shear viscosity, SV, from 160 to 280 Pa.sas 400°C (shear rate of 1000s'1). The isothermal crystallinity half-life of the PAEK is from 5 to 11 minutes. Also provided by the invention are: a use of the PAEK particles for component manufacture by PBS, a method for making components with the PAEK particles by PBS, a process of forming the PAEK, involving nucleophilic polycondensation and a method of comminuting the PAEK to prepare particles for use in PBS. The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as “preferable”, “preferably”, “preferred” or “more preferred” in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim.

Claims

1. A polyaryletherketone, PAEK, in the form of particles, for use in layer-wise formation of a component by selective sintering with electromagnetic radiation, wherein the PAEK is a copolymer comprising repeat units of formularepeat units of formulawherein at least 95 mol% of the copolymer repeat units are repeat units of formula I and of formula II;wherein the repeat units I and II have a molar ratio l:ll from 69:31 to 73:27;wherein the PAEK has a shear viscosity, SV, from 160 to 280 Pa.sas measured using capillary rheometry at 400°C at a shear rate of 1000s-1; andwherein the isothermal crystallinity half-life, T1 / 2, is from 5 to 11 minutes at270°C.

2. The PAEK particles according to claim 1, wherein the PAEK particles have a bulk density of 350 kg / m3 or more.

3. The use of the PAEK particles according to claim 1 or claim 2, in a process for formation of a component in a layer-wise fashion by sequentially depositing and selectively sintering, with electromagnetic radiation, a plurality of layers comprising the PAEK particles.

4. A method of manufacturing a component, the method comprising:(i) selecting PAEK particles according to claim 1,(ii) forming the component in a layer-wise fashion by sequentially depositing and selectively sintering, with electromagnetic radiation, a plurality of layers comprising the PAEK particles;wherein a first layer comprising the deposited PAEK particles is selectively sintered to melt-bond particles of the first layer to other particles of the first layer to form a base layer of the component; andeach subsequently layer comprising the PAEK particles is selectively sintered to meltbond particles of the subsequently deposited layer to the respective preceding layer, and to other particles of the subsequently deposited layer, prior to deposition of a next deposited layer comprising the PAEK particles;whereby the component is formed from the selectively sintered and mutually melt-bonded portions of the plurality of layers corresponding to respective cross-sections of the component.

5. A process of forming a polyaryletherketone, PAEK, in the form of particles, for use in a method for layer-wise formation of a component, wherein the PAEK is a copolymer comprising repeat units of formulaI; andrepeat units of formulaII;wherein Ph represents a phenylene moiety; andwherein the isothermal crystallinity half-life, T1 / 2, of the PAEK is from 5 to 11 minutes at 270°C;the process comprising:a) nucleophilic polycondensation of a mixture of benzene-1,4-diol and 4,4'-biphenol in a molar ratio of benzene-1,4-diol:4,4'-biphenol from 69:31 to 73:27, with 4,4'-difluorobenzophenone, in a reaction mixture comprising sodium carbonate and potassium carbonate in an aromatic sulfone solvent, at a reaction temperature rising to a temperature from 280°C to 330°C;b) cooling of the resulting reaction mixture and recovery of the PAEK copolymer resulting from step from the reaction mixture;c) forming the recovered PAEK copolymer into particles by comminution and classification;wherein in step a of the process:i the molar ratio of sodium carbonate to the mixture of benzene-1,4-diol and 4,4'-biphenol is from 0.95 to 1.15;ii the molar ratio of potassium carbonate to sodium carbonate is from 0.002 to 0.05;iii the molar ratio of the 4,4'-dihalobenzophenone to the mixture of benzene-1,4-diol and 4,4'-biphenol is from 1.01 to 1.03;iv the aromatic sulfone solvent is present in the reaction mixture as 0.27 to 1.02 kg / mole of the mixture of benzene-1,4-diol and 4,4'-biphenol; andv the polycondensation in step a is continued for sufficient time to ensure that the resulting PAEK recovered from step a has a shear viscosity, SV, from 160 to 280 Pa.s as measured using capillary rheometry at 400°C at a shear rate of 1000s'1.

6. The process according to claim 6 wherein the aromatic sulfone solvent is present in the reaction mixture as 0.27 to 0.39 kg / mole of the mixture of benzene-1,4-diol and 4,4'-biphenol.

7. The process according to claim 5 or claim 6 wherein the aromatic sulfone solvent comprises at least 95% by weight of diphenylsulfone, preferably consisting essentially of diphenylsulfone.

8. The process according to any one of claims 5 to 7 wherein the comminution is carried out in one or more mills selected from the group consisting of a ball mill an impact grinding mill and an air jet mill.

9. The method according to claim 8 wherein the comminution is carried out in an air jet mill.

10. A method of preparing a polyaryletherketone, PAEK, in the form of particles for use in layer-wise formation of a component by selective sintering with electromagnetic radiation, the method comprising:i) selecting a PAEK which is a copolymer comprising repeat units of formularepeat units of formulawherein at least 95 mol% of the copolymer repeat units are repeat units of formula I and of formula II;wherein the repeat units I and II have a molar ratio 1:11 from 69:31 to 73:27; andwherein the PAEK has a shear viscosity, SV, from 160 to 280 Pa.s as measured using capillary rheometry at 400°C at a shear rate of 1000s-1;5wherein the isothermal crystallinity half-life, T1 / 2, of the PAEK is from 5 to 11 minutes at 270°C; andii) comminuting and classifying the PAEK to generate the particles.1011. The method according to claim 10 wherein the comminution is carried out in one or more mills selected from the group consisting of a ball mill an impact grinding mill and an air jet mill.15 12. The method according to claim 11 wherein comminution is carried out in an air jetmill.A