A method of annealing polymeric granules

Abstract

There is provided a method of annealing granules of a polyaryletherketone, PAEK, polymer to obtain annealed granules suitable for use in an additive manufacturing process. The method comprises: a) obtaining precursor granules of the PAEK polymer, wherein the precursor granules have a crystallinity of between about 0% and 20%, as measured by differential scanning calorimetry, DSC; and b) heating the precursor granules to an annealing temperature to thereby obtain annealed granules, wherein the annealing temperature is at least a glass transition temperature, Tg, of the PAEK polymer and at most about 50°C less than a melting temperature, Tm, of the PAEK polymer. following annealing in b), the annealed granules have a crystallinity of between about 15% and 35%, as measured by DSC, and wherein the annealing in b) increases the crystallinity of the precursor granules by at least 2%.

Description

[0001] A Method of Annealing Polymeric Granules

[0002] Technical field

[0003] The present invention relates to annealing polymeric granules by heating, for use in an additive manufacturing process. The invention also concerns granules produced by this annealing process and components made by an additive manufacturing process using granules produced according to this annealing process.

[0004] Background

[0005] Processes that involve the conversion of three-dimensional object geometry, e.g., CAD data, to physical objects or components are known as rapid prototyping. One approach is named additive manufacturing (AM), which concerns the step-wise (often layer-wise) construction of an object from a precursor or feedstock material, which may initially be shapeless or neutral with respect to shape. This may be contrasted with traditional manufacturing by machining, in which material is removed or "subtracted" from a starting blank in order to arrive at a desired component shape. More generally, rapid prototyping or AM methods may be known as 3D- printing, and the terms are used interchangeably in the present specification.

[0006] Typically, a three-dimensional model of an object to be fabricated is provided to an apparatus (e.g. a 3D printer), which then fabricates the object or component by gradually depositing, or otherwise forming, the constituent material in the shape of the object. Successive parts (e.g. layers) of material that represent cross-sections of the object may be deposited or otherwise formed. Generally, the deposited parts / layers of material fuse (or otherwise solidify) to form the final object. Originally, layer-wise additive manufacturing methods were limited to prototyping, but now AM methods are used to directly manufacture components.

[0007] One direct manufacturing technique is fused filament fabrication (FFF), in which a feedstock material, i.e. , a filament, is fed into a heated print head and then extruded in molten or semimolten form to print a portion (e.g., a layer) of a component or object. The stepwise addition of further layers can occur continuously until the desired three-dimensional component has been created. The feedstock material may be in the form of a filament on a reel. There are a number of processes related to FFF that employ slight modifications, for example, melt extrusion manufacturing (MEM) or selective deposition modelling (SOM). The feedstock is then placed in a feedstock hopper and fed through an extruder to a nozzle or printhead and printed as described above. FFF methods themselves have their advantages, though they are by definition restricted to using filaments. This means that the precursor material must be formed before FFF-based 3D-printing can take place. This is often inconvenient since polymeric materials are typically manufactured and sold as granules or pellets. Thus, the granules must be formed into filament precursor to use FFF, thus wasting additional energy and resources. Further pre-processing may also need to be performed on the filaments in order to make them suitable for use in FFF manufacturing processes.

[0008] Recent developments allow 3D printing / AM methods to use granules comprising, or made of, polymeric materials as the immediate precursor. The ability to use granules directly is beneficial because many polymers are manufactured into granules. For the purposes of this specification, the term ‘granules’ includes other terms such as pellets and micropellets. Generally, the term ‘granule’ refers to a small formation, and ‘granules’ refers to a plurality of such small formations whose small size and form factor allows them to be readily packaged into arbitrary-shaped containers, conveyed, and dispensed.

[0009] A wide range of different types of polymeric materials are used in known AM processes. Poly(aryletherketone) polymers, referred to herein as PAEK polymers, have been found to be particularly useful, as components that have been manufactured from PAEK are typically characterised by low flammability, good biocompatibility as well as 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.

[0010] However, some PAEK polymers are more suited to AM production methods than others. For example, PAEK polymers that are predisposed to have a low crystallinity have been observed to form blockages more frequently in AM processes, including in FFF processes using filaments made of PAEKs having low crystallinity. PAEK polymers predisposed with a low crystallinity are referred to as ‘slow-crystallizing PAEK polymers’ in this specification. It would therefore be beneficial to find a suitable pre-treatment for granules made of slow-crystallizing PAEK in order to mitigate blockages and other efficiency problems, so that such granules may be used in granule-fed AM processes. The embodiments described below are provided by way of example only and are not limiting of implementations which solve any or all of the disadvantages of known methods and apparatus which perform the coating of a reinforcement fibre.

[0011] Summary of the Invention

[0012] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description.

[0013] Particular embodiments are outlined in the attached independent claims, with other embodiments in the dependent claims.

[0014] In a first aspect there is provided a method of annealing granules of a polyaryletherketone, PAEK, polymer to obtain annealed granules suitable for use in an additive manufacturing process, the method comprising: a) obtaining precursor granules of the PAEK polymer, wherein the precursor granules have a crystallinity of between about 0% and 20%, as measured by differential scanning calorimetry, DSC; b) heating the precursor granules to an annealing temperature to thereby obtain annealed granules, wherein the annealing temperature is at least a glass transition temperature, Tg, of the PAEK polymer and at most about 50°C less than a melting temperature, Tm, of the PAEK polymer; wherein, following annealing in b), the annealed granules have a crystallinity of between about 15% and 35%, as measured by DSC, and wherein the annealing in b) increases the crystallinity of the precursor granules by at least 2%.

[0015] In a second aspect there is provided a method of forming a component in an additive manufacturing process, the method comprising: a) obtaining a plurality of granules comprising a polyaryletherketone, PAEK, polymer, wherein the PAEK polymer of the precursor granules have a repeat unit of formula

[0016] -O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

[0017] -O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety, and wherein the PAEK polymer of the plurality of granules has a crystallinity of between about 15% and 35% as measured by differential scanning calorimetry, DSC, b) heating and melting the plurality of granules in a pre-extrusion zone to thereby obtain molten PAEK polymer; c) extruding the molten PAEK polymer through an exit orifice of a printing head to form at least part of the component, wherein a temperature of both the pre-extrusion zone in b) and the exit orifice in c) is in the range of about i) the melting temperature, Tm, of the PAEK polymer to about ii) 150 °C above the Tm of the PAEK polymer.

[0018] In a third aspect there is provided a component made by any additive manufacturing process as disclosed herein.

[0019] In a fourth aspect there is provided a plurality of granules comprising a polyaryletherketone, PAEK, polymer, the plurality of granules suitable for use in an additive manufacturing process to make a component, wherein the plurality of granules are annealed granules which have a crystallinity of between about 15% and 35% as measured by differential scanning calorimetry, DSC, wherein the annealed granules have been produced from precursor granules that are substantially amorphous and have a crystallinity of between about 0% and 20%, as measured by DSC, wherein the annealed granules have been produced by an annealing process comprising: heating the precursor granules to an annealing temperature, wherein the annealing temperature is at least a glass transition temperature, Tg, of the PAEK polymer and at most about 50°C less than a melting temperature, Tm, of the PAEK polymer.

[0020] In a fifth aspect there is provided a use of a plurality of granules comprising a polyaryletherketone, PAEK, according to a plurality of granules as disclosed herein, in an additive manufacturing process to form a component.

[0021] In a sixth aspect there is provided a plurality of granules produced according to any of the methods disclosed herein.

[0022] Brief Description of the Figures

[0023] The present disclosure will now be described by way of example with reference to the accompanying drawings, in which:

[0024] Figure 1 shows a cross-sectional view of a direct granule feed printing apparatus and the different regions therein; and

[0025] Figure 2 shows a graph showing the temperature-dependence of the modulus for a nonannealed PAEK polymer and an annealed version of the same PAEK polymer. Figure 3 is a graph showing an example DSC trace used to calculate the crystallinity of polymer samples.

[0026] Detailed Description

[0027] In a first aspect there is provided a method of annealing granules of a polyaryletherketone, PAEK, polymer to obtain annealed granules suitable for use in an additive manufacturing process, the method comprising: a) obtaining precursor granules of the PAEK polymer, wherein the precursor granules have a crystallinity of between about 0% and 20%, as measured by differential scanning calorimetry, DSC; b) heating the precursor granules to an annealing temperature to thereby obtain annealed granules, wherein the annealing temperature is at least a glass transition temperature, Tg, of the PAEK polymer and at most about 50°C less than a melting temperature, Tm, of the PAEK polymer; wherein, following annealing in b), the annealed granules have a crystallinity of between about 15% and 35%, as measured by DSC, and wherein the annealing in b) increases the crystallinity of the precursor granules by at least 2%.

[0028] Preferably, the annealing in b) increases the crystallinity of the precursor granules by at least 5%, more preferably by at least 10%, and preferably still by at least 15% or at least 20%. Preferably, the crystallinity of the annealed granules is in the range of about 20% and 30%, more preferably between about 23% and 30%. The PAEK polymer preferably comprises a homopolymer and / or a copolymer. In some examples, the some examples the PAEK polymer of the precursor granules have a repeat unit of formula -O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

[0029] -O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety.

[0030] Formula I is referred to in the present disclosure as polyetheretherketone, PEEK, and formula II is referred to as polyetherdiphenyletherketone, PEDEK. Thus, the copolymer formed by a combination of repeat units of formula I and repeat units of formula II is referred to as PEEK- PEDEK, or PEEK-PEDEK copolymer. In other examples, the PAEK polymer comprises a polyetherketoneketone, PEKK, polymer. In additive manufacturing (AM), the layer-wise manufacturing processing and resultant structure of a component produced by AM means that polymer chains may not be homogenously dispersed, and do not traverse the boundaries between subsequent layers well. This is because the new layer is typically added to a cooled, now-solid, layer, which cannot mix with the preceding layer. Advantageously, the applicant has found that this problem can be overcome by using a slow-crystallising polymer, which remains molten for sufficient time after being printed, for example, for the following layer to be printed onto it. This has been shown to improve mixing at the interface between layers, in turn resulting in improved mechanical properties on the component.

[0031] However, granules based on slow-crystallising PAEKs, e.g., PEEK-PEDEK copolymers or PEKK homopolymers can be difficult to feed into melt-extrusion devices, for example, meltextrusion 3D printers. In the present disclosure, a ‘slow crystallising PAEK’ may also be referred to as a PAEK having a low crystallinity. Slow crystallising PAEK polymers tend to be amorphous, e.g., when manufactured using melt-extrusion processes known in the art. Nevertheless, it should be understood that the property of “slow-crystallising” is a property of the polymer composition, i.e., polymer backbone, itself. In other words, the crystallisation rate (i.e. , the rate at which an amorphous polymers forms crystalline regions when heated above Tg) depends on properties of the polymer composition, e.g., the ratio of polymers in a copolymer. The crystallisation rate also depends to a lesser extent on the on the molecular weight of the polymer. However, the degree of crystallinity is in general independent of the polymer composition, and thus any polymer could in principle be amorphous.

[0032] Generally, in this disclosure, a PAEK having low crystallinity, or a slow crystallising PAEK, is considered to have a crystallinity of between about 0% and 15%. This range of crystallinity is referred to as ‘amorphous’ in this specification. Often, the crystallinity of slow crystallising PAEK may be lower than 10%, or lower than 5%, or even lower than about 2%. Specific examples of slow-crystallising PAEK polymers are provided in more detail below.

[0033] One problem with using slow crystallising PAEKs in melt-extrusion devices is that blockages are often observed towards the end part of the hopper, or pre-extrusion zone, of the meltextrusion device. Specifically, the blockages occur at the point where the temperature of the apparatus approaches, and / or exceeds, the Tg of the polymer. This region usually coincides with the start of a screw-assembly used to transport the granules (and subsequently the molten polymer) through the printer. This problem is particularly noticeable in ‘direct granule feed’ printing systems, i.e., 3D printers or other additive manufacturing devices that use granules as the precursor printing material. The inventors have observed that this is because, amongst other things, the granules stick together in the pre-extrusion zone, which often carries residual heat from the melt-extruder portion of the apparatus. The sticking thus impedes the progress of the granules through the extrusion device, resulting in reduced, uneven, and unreliable feed rates. This makes control of the extruder difficult, and thus results in reduced throughput rates. It can also result in adhesion problems during the layer-wise building of the product during the additive manufacturing process, e.g., if the throughput rate is too slow, resulting potentially in products that are more prone to disintegration.

[0034] The problem feed rate in direct granule feed printing systems has been observed in particular for slow crystallising PAEKs. The inventors have established that this is because the glass transition temperature, Tg, of many slow crystallising PAEKs is within the temperature range, or close to the temperature range, of the internal environment of the pre-extrusion zone (e.g., part of the hopper, or the initial part of a screw-assembly), of the printer. The environment of the pre-extrusion zone is often hot, e.g., between about 100 and 200 °C, due to proximity to the melt-extrusion zone of the printer. Thus, when granules comprising, or formed of, slow crystallising PAEK polymer reach a pre-extrusion zone in AM direct granule feed printing systems, the PAEK polymers begin to soften. The softened granules stick to one another and, particularly in gravity-fed systems, start to move more slowly or unpredictably through the hopper.

[0035] Current solutions to mitigate this problem all have disadvantages. For example, one solution is to use flow-aids, e.g., powdered additives comprising for example calcium stearate or talc. However, the addition of flow-aids is sub-optimal because it introduces impurity into the polymer that is extruded, and may be undesirable in the end product. In some cases, it may be critical that the final component contains no additives, for example, in the aerospace industry where the integrity of components is critical and / or the composition of the products is strictly controlled. Another known workaround is to use a different screw design in the direct granule feed printing system. However, a different screw design may introduce other problems, e.g., less effective mixing, or a slower throughput rate. Finally, operators of direct granule feed printing systems may deliberately slow down the throughput of the extruder to ensure that the slow feed rate in the hopper can keep up with the rate of extrusion. It would be desirable to provide a solution to this problem that does not affect the quality or composition of the output of the AM process, and / or that can achieve fast feed rates, e.g., comparable to feed rates achievable with granules made of highly-crystalline PEEK polymers.

[0036] Consequently, the inventors have established that the feed properties of granules formed of slow crystallising PAEK, for (amongst other processes) the purposes of direct granule feed printing systems, may be improved by annealing the granules to increase their crystallinity. The annealing process involves heating the granules to a temperature that is i) greater than or equal to the annealing temperature, and ii) is at least a glass transition temperature, Tg, of the PAEK polymer, to thereby encourage crystallisation. The annealing temperature is also chosen to keep the granules solid, i.e., to avoid the granules becoming semi-molten, deforming, or merging. Consequently, the annealing temperature is chosen to be less than the melting temperature, Tm, of the PAEK polymer by at least 50°C, i.e., the annealing temperature, TA, is chosen such that TA Tm - 50°C.

[0037] Advantageously, once annealed, the resultant crystallinity of the annealed granules persists indefinitely. In other words, the annealed granules obtain an indefinite shelf life during which point the crystallinity does not change or degrade (provided that the granules are stored below the Tg of the polymer). Furthermore, since AM methods melt the polymer, the crystallinity of the feedstock granules has no direct effect on the polymer of the resulting component, i.e., meaning that the advantages described above in respect of using slow-crystallising polymers in AM processes (i.e., improved mechanical properties on the component due to improved layer-wise mixing / adhesion) are obtained equally when using crystalline, annealed, granules.

[0038] In order to provide granules that do not stick together so readily (i.e., at the temperature of the environment of the hopper / pre-extrusion zone of the printing apparatus), the inventors have established that the crystallinity of the resulting annealed granules should be at least 15%. Preferably, the crystallinity should be at least 20%, more preferably at least about 25%. Advantageously, PAEK polymers that are by nature slow crystallising, when they are annealed to have increased crystallinity, have slightly higher Tg compared to when they are in amorphous form. Thus, PAEK polymers with a crystallinity of above about 15% show a reduced propensity to stick together in direct granule feed printers. This is because the temperature of the PAEK granules in the hopper of the printer remains below the Tg of the granules for longer, and so the granules can be more readily conveyed through the hopper and into the extrusion zone of the printer without sticking.

[0039] The inventors have established that heating the granules to this annealing temperature allows the crystallinity of the granules to increase. In some examples, the crystallinity of the PAEK polymer may be between about 0% and 2%. A significant increase in crystallinity, e.g., more than 15%, would therefore be desirable to improve the thermal properties of the granules. Generally, the inventors have established that an increase in crystallinity of at least 2% should be provided by annealing. For example, it may be desirable to further improve the thermal properties of PAEK granules that already have a crystallinity of about 15%. Thus, the granules could be annealed at an annealing temperature (e.g., Tg, or about 5°C, 10°C, 15°C, or 20°C above the Tg) for period of time (examples of annealing times are provided in more detail below) to increase their crystallinity by 2% or more. Generally, higher crystallinities correlate to increased Tg and therefore to a reduced propensity to stick together. For example, it may be desirable to anneal granules having a crystallinity of about 19% to thereby increase the crystallinity to about 25%.

[0040] By annealing amorphous granules of PAEK polymer in this way for AM processes, the inventors have found that the feed rate of direct granule feed printers can be increased by a factor of up to four, compared to using unannealed amorphous granules (e.g., having low crystallinity of less than 15%).

[0041] Preferably, the Tg of PAEK polymer of the granules is in the range of about 135°C to about 175°C, preferably in the range of about 140°C to about 165 °C, more preferably in the range of about 145°C to about 155 °C. Preferably, the melting temperature, Tm, of the PAEK polymer is in the range of 280°C to about 330°C, preferably in the range of about 290°C to about 310°C.

[0042] Therefore, preferably the annealing temperature is in the range of about 10°C above the Tg to about 40°C above the Tg. The inventors have established that this range is particularly suitable for increasing crystallinity in the granules. Advantageously, by heating the granules to about 10°C above the Tg of the polymer, the crystallinity of the granules readily increases without the need to use more energy heating the granules anywhere near the substantially higher melting temperature.

[0043] The annealing method may also comprise, subsequent to b), cooling the annealed granules to below the Tg of the PAEK polymer. Alternatively, there may be no cooling step: the annealing step b) may form part of an additive manufacturing (AM) process, e.g., the AM apparatus may be configured to anneal granules prior to feeding them through an extrusion part of the apparatus. In this case, it may not be needed to cool the granules to below their Tg.

[0044] Preferably, the annealing temperature is in the range of about 160°C to about 200°C, preferably in the range of about 165°C to about 190°C, more preferably in the range of about 165°C to about 180°C. It can be advantageous to heat the granules at an annealing temperature that is more than 10°C above the Tg. For example, where the Tg of a PAEK polymer forming, or comprised within, the granules is about 150°C, the annealing temperature may be about 165°C, or 170°C, or even 175°C. The advantage of this is that the granules obtain an increased level of crystallinity faster than heating at the Tg. Thus, heating the granules at a temperature in this range can reduce the energy requirements overall. For example, in some cases, an increase in annealing temperature of 5°C (e.g., from 165°C or 170°C) may halve the time taken to increase the crystallinity of granules from 1 % to 20%.

[0045] Preferably, step b) comprises holding the precursor granules at the annealing temperature for between about 1 minute and 2 hours, preferably for between about 3 minutes and 2 hours, and more preferably for between about 10 minutes and 2 hours. It should be appreciated that the residence time (i.e., the residence time being the time held at the annealing temperature) depends at least partly, and in some cases depends significantly, on any one or more of the following factors: i) starting level of crystallinity; ii) final level of crystallinity to be obtained; iii) type of polymer; iv) where polymer is a PAEK copolymer, the ratio of different repeat units; and v) the annealing temperature

[0046] Merely for example, a bulk volume of granules comprising, or formed of, PAEK polymer with a crystallinity of 1% heated at an annealing temperature of 165°C may need 8 hours of heating time (including thermal equilibration) in order to obtain 20% crystallinity. However, heating the same bulk volume of granules may only need to be heated for 4 hours (including thermal equilibration) at an annealing temperature of 170°C to obtain at least 20% crystallinity. It should be appreciated that ‘heating at an annealing temperature’ and ‘holding at an annealing temperature’ are different heating requirements. Heating granules at an annealing temperature, e.g., in an oven that is held at the annealing temperature, may take a significant proportion of time for the granules to thermally equilibrate (i.e., reach the annealing temperature of the oven). By contrast, ‘holding at an annealing temperature’ refers to heating granules at an annealing temperature once already thermally equilibrated. For a large bulk volume of granules, a large proportion of the heating time may involve thermal equilibration of the granules. Thus, the time for which granules need to be held at an annealing temperature, once the matter of the granules has reached the annealing temperature, may be significantly less than the heating times mentioned above. Depending on the type of granules, the actual annealing time (at an annealing temperature of 170°C to obtain at least 20% crystallinity) may be as little as 1 hour, or 30 minutes, or even less than 15 minutes.

[0047] The heating of the precursor granules to an annealing temperature in step b) may comprise heating the granules in an oven. Preferably, the precursor granules are heated in the oven until all granules thermally equilibrate, e.g., when heating in an oven preferably at least 30 minutes is allowed for the granules to reach the Tg and / or the annealing temperature. In general, the residence time in the oven may therefore be at least about 30 minutes greater than the residence time required for an in-line annealing method, e.g., in which granules are conveyed along a conveyor and are better thermally exposed to a heat source. Heating the precursor granules to an annealing temperature in step b) may therefore comprise heating all polymeric material comprised within the granules to at least the annealing temperature.

[0048] Preferably, heating the precursor granules to an annealing temperature in step b) comprises: conveying the precursor granules, via a movable surface, through a heating zone, wherein the annealed granules are obtained after having passed the precursor granules through the heating zone. Advantageously, by conveying the granules along a movable surface, such as a conveyer belt, the granules may be spread out and a greater proportion of their surface area can be exposed. This increased exposure promotes better heat transfer from the heating zone, and so the granules reach the annealing temperature faster. Thus, conveying granules through a heating zone can anneal granules advantageously faster than using a static oven. Preferably, a temperature of the precursor granules immediately after exiting the heating zone is at least the annealing temperature. Preferably, one or more heating elements of the heating zone heat the precursor granules to at least the annealing temperature. Preferably, wherein a residence time of the precursor granules in the heating zone is at least about 5 seconds, preferably at least about 10 seconds, more preferably about 30 seconds, and no more than about 10 minutes, preferably no more than 5 minutes, more preferably still no more than about 3 minutes.

[0049] Preferably, the precursor granules have been produced by melt-processing the PAEK polymer. In one example, the granules have been produced by melt-processing followed by extruding, preferably wherein the extrudate is air-cooled and subsequently formed into granules by a pelletiser or other suitable chopping apparatus.

[0050] In some examples, the precursor granules comprise a fibrous filler, preferably wherein the fibrous filler is selected from carbon fibre or glass fibre. Optionally, the fibrous filler may be asbestos fibre, silica fibre, alumina fibre, zirconia fibre, boron nitride fibre, silicon nitride fibre, boron fibre, fluorocarbon resin fibre and potassium titanate fibre, mica, nanotubes, and / or nanofibres. The fibrous filler may be continuous or discontinuous. Where the filler is a fibrous filler (e.g., carbon fibre) and is a discontinuous fibre, preferably the fibres have a nominal length between 50 pm and 300 pm, and more preferably between 100 pm and 300 pm and even more preferably between 125 pm and 175 pm. When the fibrous filler is carbon fibre, preferably the D50 length of the fibre in the precursor granules is in the range of about 120 pm to about 200 pm. An amount of filler is preferably in the range of about 1 wt% to about 50 wt% filler, preferably between about 5 wt% and 40 wt%, more preferably between about 20 wt% and 30 wt%. The incorporation of fillers is beneficial because it can reduce the level of shrinkage on solidification of components formed by an AM process. The incorporation of fibrous fillers may also lower the amount of residual and / or internal stress present in the manufactured object.

[0051] In another regard, it is particularly advantageous to be able to use granules with a fibrous filler in a direct granule feed AM process, compared to using filaments with a fibrous filler (e.g., in a fused filament fabrication (FFF) method). A disadvantage of filaments with a fibrous filler is that they are especially rigid, which presents difficulties in spooling the filled filaments onto reels. It also creates difficulties loading the filament into FFF printing apparatuses, e.g., because the pathway for the filament in the printer may contain bends. Thus, filaments having fibrous fillers can obstruct fused filament fabrication printers or generally make extrusion slower or less reliable. Advantageously, these problems are avoided altogether when the feedstock material for the printing process is a granule, as opposed to a filament, since the rigidity of a granule does not affect extrusion rate or locomotion in granule-fed AM devices. In other words, granules having a fibrous filler are readily extrudable and transferable through the hopper and extruder head of a direct granule feed AM apparatus.

[0052] The present disclosure relates to the annealing of PAEK polymers predisposed with a low crystallinity, in other words, polymers that are slow-crystallizing. The crystallisation rate of a polymer depends on various factors, including the polymer composition and the molecular weight. Without being bound by theory, the crystallisation kinetics of the PAEK polymeric material may be modified by modifying the polymer backbone which determines how the PAEK polymeric material solidifies and / or crystallises when cooling form a molten form, e.g., during an additive manufacturing process. Optionally, the polymer backbone is modified by selecting the structure of the repeat units and / or by controlling the ratio of repeat units in the PAEK polymeric material, examples of which are provided above.

[0053] One way to define the crystallisation rate of a polymer is by its isothermal crystallisation halflife. This is an intrinsic property of the composition of the polymer, i.e., the polymer backbone, and does not depend on transient properties such a degree of crystallinity in a solid state. Isothermal crystallisation half-life is defined as the time consumed to reach half of the final crystallinity at a specific isotherm, and is determined by integration of isothermal heat flow measurements. Consequently, it can be advantageous to select a PAEK polymer having a crystallisation half-life within a particular range, as doing so can provide particularly beneficial results (according to the benefits described above) when that selected PAEK polymer is used as part of a direct granule feed additive manufacture system or process. The following example ranges provide the advantages described in the present specification.

[0054] Preferably, the PAEK polymer has an isothermal crystallinity half life, T1 / 2 of greater than about 3 minutes and less than about 20 minutes at a temperature of 280 °C, as measured by Differential Scanning Calorimetry, DSC. More preferably, the isothermal crystallinity half life, T1 / 2 is greater than about 4 minutes and less than about 13 minutes at a temperature of 280 °C.

[0055] Preferably, the PAEK polymer has an isothermal crystallinity half life, T1 / 2 of greater than about 5 seconds and less than about 1 minute at 220 °C. More preferably, the crystallinity half life, T1 / 2, is greater than about 8 seconds and less than about 20 seconds at 220 °C, and yet more preferably greater than about 10 seconds and less than about 16 seconds at 220 °C.

[0056] The isothermal crystallisation half-life can be determined using the following DSC method:

[0057] A dried sample of each polymer was compression moulded into an amorphous film, by heating 7g of polymer in a mould at 400°C under a pressure of 50bar for 2 minutes, then quenching in cold water producing a film of dimensions 120 x120mm, with a thickness in the region of 0.20mm. An 8mg plus or minus 3mg sample of each film was scanned by DSC as follows:

[0058] The sample was first heated to 30°C and allowed to equilibrate for 15 mins. It was then heating to 400°C at 20°C / minute, and held at this temperature for 15 minutes. The sample was then cooled at 20°C / minute to the desired isotherm temperature (typically 270-290°C) and held isothermally for up until 3 hours, until crystallisation was complete. It was then cooled back to ambient temperature at 20°C / minute.

[0059] From the DSC trace resulting from the scan the heat flow data at the isothermal crystallisation temperature were obtained and plotted. Crystallisation half-life was taken to be the time from the start of the isothermal hold (at the crystallisation temperature) to the time when the crystalline level reached one half of its ultimate level.

[0060] To provide a specific example, the isothermal crystallinity half-life, T1 / 2, of a PAEK polymer with the composition in the ratio of PEEK-PEDEK 75:25 is about 12 seconds at 220 °C. The isothermal crystallinity half-life, T1 / 2, of PEEK-PEDEK 75:25 at 280 °C is between about 7 minutes and about 8 minutes. Preferably, the D99 length of granules in the precursor granules is less than about 3 mm, and the D99 diameter or width of granules in the precursor granules is less than about 2 mm. It should be understood that the term diameter refers to average width, since the granules may not be cylindrical.

[0061] The precursor granules may be substantially amorphous. In this disclosure, any polymer having a crystallinity below about 15% may be considered amorphous. Preferably, the PAEK polymer of the precursor granules may have a crystallinity that is significantly below 15%, e.g., below 10%, below 5%, or even below 2%.

[0062] Preferably, the PAEK polymer of the precursor granules has a repeat unit of formula -O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

[0063] -O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety.

[0064] Formula I repeat units may be referred to as polyetheretherketone, PEEK, polymer, and formula II repeat units may be referred to as polyetherdiphenyletherketone, PEDEK, polymer. The copolymer formed of a combination of PEEK and PEDEK is called a PEEK-PEDEK copolymer in this disclosure.

[0065] The PAEK preferably has a shear viscosity from 130 to 430 Pa s, preferably from 145 to 350 Pa s, more preferably from 200 Pa s to 280 Pa s, as measured using capillary rheometry at 400°C at a shear rate of 1000 s-1by extrusion through a circular cross-section tungsten carbide capillary die of 0.5mm diameter and 8.0 mm length. This range of shear viscosity may be used to characterise a PAEK as being a slow-crystallising PAEK.

[0066] Shear viscosity may be 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.

[0067] The repeat unit of formula I may have the structure and said repeat unit of formula II may have the structure:

[0068] In examples, at least 95 mol% of the copolymer repeat units are repeat units of formula I and of formula II. Preferably, the copolymer repeat units of formula I and of formula II are in the molar ratio 1:11 of 55:45 to 95:5, preferably 65:35 to 80:20, and more preferably 65:35 to 75:25. The copolymer may also have end units, which may be the same as the repeat units but may comprise a terminal OH or F group, for example. The process for forming the polymer may include a separate end-capping step at the completion of polymerisation, in which case a separate monomer or reagent may be added as an end-capping agent so that the end units may differ from the repeat units of the polymer. Such end-capping is well-known in the field of nucleophilic polycondensation reactions.

[0069] Preferably, the repeat units I and II are in the relative molar proportions 65:35 to 75:25, and the annealing temperature is in the range of about 165°C to about 200°C, and wherein step b) comprises holding the precursor granules at the annealing temperature for between about 1 minute and about 90 minutes.

[0070] Preferably, when the relative molar proportions of formula I and of formula II are in the molar ratio l:ll of 65:35, the annealing temperature is in the range of about 170°C to about 200°C, and step b) comprises holding the precursor granules at the annealing temperature for between about 1 minute and about 240 minutes, more preferably between about 1 minute and 60 minutes. This annealing temperature and time range would enable the crystallinity in the annealed granule to be at least 20%, preferably at least 24%. It is also possible, in examples, the hold the precursor granules at the annealing temperature for longer than 240 minutes, e.g., which may be done to further increase the crystallinity. Although diminishing returns of crystallinity may be observed for increasingly long annealing times if the granules are held at an annealing temperature of between 170°C to about 200°C for between 90 minutes and 240 minutes, crystallinity above 25% (e.g., 30%, and even approaching 35%) may be achieved.

[0071] Preferably, when the relative molar proportions of formula I and of formula II are in the molar ratio l:ll of 75:25, the annealing temperature is in the range of about 170°C to about 200°C, and step b) comprises holding the precursor granules at the annealing temperature for between about 1 minute and about 90 minutes, more preferably between about 1 minute and 15 minutes.

[0072] In a second aspect there is provided a method of forming a component in an additive manufacturing process, the method comprising: a) obtaining a plurality of granules comprising a polyaryletherketone, PAEK, polymer, wherein the PAEK polymer of the precursor granules have a repeat unit of formula

[0073] -O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

[0074] -O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety, and wherein the PAEK polymer of the plurality of granules has a crystallinity of between about 15% and 35% as measured by differential scanning calorimetry, DSC, b) heating and melting the plurality of granules in a pre-extrusion zone to thereby obtain molten PAEK polymer; c) extruding the molten PAEK polymer through an exit orifice of a printing head to form at least part of the component, wherein a temperature of both the pre-extrusion zone in b) and the exit orifice in c) is in the range of about i) the melting temperature, Tm, of the PAEK polymer to about ii) 150 °C above the Tm of the PAEK polymer.

[0075] Advantageously, when the PEEK-PEDEK copolymer has a crystallinity of between about 15% and 35%, as measured by DSC, the extrusion rate of the additive manufacturing (AM) process, e.g., which may use a direct granule feed apparatus, is significantly increased. Compared to granules of PEEK-PEDEK copolymer whose crystallinity is below 15%, and typically is much lower, e.g., around 0% to 5% (i.e., substantially amorphous), the extrusion rate is about 4 times faster when using PEEK-PEDEK copolymer has a crystallinity of between about 15% and 35%. Moreover, PEEK-PEDEK copolymer granules with a crystallinity of between about 15% and 35% show a significantly reduced propensity to stick together in the pre-extrusion zone before the granules melt, and so the flow of granules through the additive manufacturing apparatus is steady and predictable, which improves control of the AM process.

[0076] In example implementations, the temperature of both the pre-extrusion zone in b) and the exit orifice in c) is in the range of about 350 °C to about 450 °C. The pre-extrusion zone may comprise a screw, or other suitable locomotion means, to urge the plurality of granules towards the exit orifice of the printing head. Preferably, a temperature of an entry point of the pre- extrusion zone, comprising the screw, is in the range of about 140°C to about 160°C, i.e., close to or above the Tg of the PAEK polymer, but distant from the melting temperature. The entry point of the pre-extrusion zone may comprise the exit region of the hopper containing the granules. Advantageously, the crystallinity of the PAEK polymer in the plurality of granules helps to prevent the granules from sticking together in the pre-extrusion zone even at temperatures in the range of about 140°C to about 160°C, which thus significantly increases the throughput speed of the additive manufacturing process, as mentioned.

[0077] Preferably, the plurality of granules have been annealed (and are thus annealed granules), wherein the annealed granules have been produced from precursor granules that are substantially amorphous and have a crystallinity of between about 0% and 20%, as measured by DSC, wherein the annealed granules have been produced by an annealing process comprising: heating the precursor granules to an annealing temperature, wherein the annealing temperature is at least a glass transition temperature, Tg, of the PAEK polymer and at most about 50°C less than a melting temperature, Tm, of the PAEK polymer, and wherein and wherein the annealing increases the crystallinity of the precursor granules by at least 2%.

[0078] In a third aspect there is provided a component made by an additive manufacturing process disclosed herein. In some cases, components made according to advantageous AM processes, i.e., which use annealed PEEK-PEDEK copolymers and / or PEEK-PEDEK copolymers having a crystallinity of between about 15% and 35%, can produce components of improved integrity (compared to using amorphous PAEK polymers). This is because, as mentioned, the extrusion rate can be significantly improved. Thus, successive layers of polymer laid down by the AM process may adhere better when the extrusion rate is faster, because the residual temperature of the previous layer will be relatively higher, and so will merge more readily with the recently extruded, molten, part. Moreover, since annealed granules feed significantly more consistently through the granule-fed AM devices than nonannealed granules, the risk of defects (such as voids) is reduced. Additionally, this faster extrusion rate is beneficial for printing of larger parts. In large parts, interlayer print time will be longer than for smaller parts, which can cause issues with interlayer adhesion. However, in the present invention, the faster extrusion rate means larger parts can be printed with improved interlayer adhesion. Additionally, if components can be manufactured faster, all parts of the components are more likely to be able to cool at the same rate, thus potentially reducing residual stress in the formed components.

[0079] In a fourth aspect, there is provided a plurality of granules comprising a polyaryletherketone, PAEK, polymer, the plurality of granules suitable for use in an additive manufacturing process to make a component, wherein the plurality of granules are annealed granules which have a crystallinity of between about 15% and 35% as measured by differential scanning calorimetry, DSC, wherein the annealed granules have been produced from precursor granules that are substantially amorphous and have a crystallinity of between about 0% and 20%, as measured by DSC, wherein the annealed granules have been produced by an annealing process comprising: heating the precursor granules to an annealing temperature, wherein the annealing temperature is at least a glass transition temperature, Tg, of the PAEK polymer and at most about 50°C less than a melting temperature, Tm, of the PAEK polymer. Preferably, the PAEK polymer comprising a homopolymer and / or a copolymer.

[0080] The granules may have a diameter in the range of 1.2 mm to 2.5 mm, preferably 1.5 mm to 2.3 mm. The granules may have a mean length in the range of 1.5 mm to 3.5 mm, preferably 1.8 mm to 3.3 mm.

[0081] Preferably, the PAEK polymer of the precursor granules has a repeat unit of formula -O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

[0082] -O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety, preferably wherein the repeat units I and II are in the relative molar proportions 65:35 to 95:5, more preferably 65:35 to 75:25.

[0083] In a fifth aspect, there is provided the use of a plurality of granules comprising a polyaryletherketone, PAEK, according to plurality of granules described above, in an additive manufacturing process to form a component.

[0084] In a sixth aspect, there is provided a plurality of granules produced according to any of the annealing methods disclosed herein. Advantageously, as mentioned, the crystallinity of annealed granules persists once the annealing process has been performed. The shelf-life of annealed granules is therefore arbitrarily long for the purposes of crystallinity.

[0085] The above-described features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the examples described herein. Examples

[0086] Example methods of producing annealed granules according to present embodiments is now disclosed, an example of a direct granule feed additive manufacturing machine (e.g., a granule-fed 3D printer), is now described. Other examples related to the composition of the polymers and annealing details and details are also described.

[0087] Figure 1 illustrates a cross-sectional view of a direct granule feed printing apparatus 100. The apparatus includes a hopper 102, a main barrel 104, and an extruder head, or die 106. The hopper is the entry point for feeding granules into the system. The barrel may also be called an extruder barrel. Usually, the hopper and any granules contained within are at room temperature. The main barrel 104 is heated, and comprises a screw assembly (not shown) that is arranged to urge the granules towards the extruder dye. The screw assembly within the barrel also generates the pressure needed to extrude the granules. The die 106 is usually also heated.

[0088] The apparatus 100 can be notionally divided into four regions: 110, 112, 114, and 116. The first region 100 may be called the hopper zone, or granule entry zone. The first region 100 represents the room-temperature zone, at which point granules move, generally under gravity, towards the entrance to the barrel. The temperature of the hopper, and / or the granules within, may be marginally above room temperature due to the proximity to the heated barrel. However, the temperature of the granules in the entry / hopper zone 110 will be substantially lower than the Tg, and substantially lower than about 100 °C. Thus, granules (annealed or otherwise) do not tend to stick together in the hopper 102 itself.

[0089] The second region 112 represents the start of the screw-feed assembly. This region is referred to as the pre-extrusion zone 112 in this specification. The screw (not shown) extends through at least a portion of the extruder barrel 104. This region is not typically heated, though it is close in proximity to the heated part of the main barrel. Thus, the temperature of the start of the screw-feed assembly 112, in use, can be in the region of about 150 °C to about 200 °C. The heat of this region causes slow-crystallising (e.g., amorphous) PAEK polymers to soften because the temperature of this region 112 is roughly equal to, or slightly above, the Tg of the PAEK polymer.

[0090] The region at the start of the screw-assembly 112 is therefore problematic, in known granule- fed devices, for non-annealed slow-crystallising PAEK granules. This is because the locomotion of the granules within this region is significantly hindered by sticky granules. In otherwords, the granules tend to stick together and / or form blockages in this region 112, rather than being steadily transferred by the screw assembly along the barrel towards the extruder 106.

[0091] The third region barrel 114 is heated, and in use has a temperature of about 350 °C to about 450 °C. Preferably, in use, the extruder barrel operates at about 400 °C. Thus, the temperature of this region is intended to be at least the melting temperature, Tm, of the PAEK polymer comprised within the granules. The granules become molten in this third region 114. In use, the molten PAEK polymer is transported along the barrel towards the extruder die 106. By this point, since the granules are molten, the locomotion of the PAEK polymer is, in theory, the same irrespective of whether the granules have been annealed. However, due to the timing bottle-neck at the start of the screw-assembly 112, in known direct granule feed apparatus that use slow-crystallising PAEKs the speed of the screw may have to be reduced to accommodate the slow progress through region 112. The advantage of annealed granules formed of slow-crystallising PAEK is that, as established by the inventors, the annealed granules flow into the screw-feed section 112 of the extruder much more readily than nonannealed granules. This can improve the overall extrusion rate from the extruder die by a factor of up to 4.

[0092] The fourth region is the extrusion zone 116 itself, containing the extruder die. This region may be directly heated, or may simply be heated via proximity to the heated barrel. The temperature range of the extrusion zone itself is about the same as in region 114, i.e., about 350 °C to about 450 °C. Generally, the temperature of this region 116 is also intended to be at least the melting temperature, Tm, of the PAEK polymer comprised within the granules.

[0093] Figure 2 is a graph 200 that plots the temperature 206 (in °C) versus the storage modulus (in MPa) of two slow-crystallising PAEK polymers having two different crystallinities. The storage modulus, G’, depends (amongst other things) on the crystallinity of the polymer. The graph 200 in Figure 2 was plotted using dynamic mechanical thermal analysis (DMTA). To produce the data for the graph 200, a Tritec 2000 DMTA apparatus was used. The DMTA measurements were performed in heating mode with a heating rate of 4 °C per minute, and using a 3-point bend geometry.

[0094] The upper line 202 represents crystalline slow-crystallising PAEK (where the crystallinity is [25%), and the lower line represents substantially amorphous slow-crystallising PAEK (where the crystallinity is 5%). The composition of the slow-crystallising PAEK in Figure 2 is the same in both cases, i.e., a PEEK-PEDEK copolymer having a molar ratio of formula I of formula II 75:25, wherein the repeat unit of formula I has the structure and the repeat unit of formula II has the structure:

[0095] The Tg of the PEEK-PEDEK copolymer referenced in figure 2 is 151 °C (measured according to the “Measurement of Crystallinity” example below), and the Tm is 303 °C (measured according to the " Measurement of Crystallinity’ example below, i.e., taken as the point that main peak of the melting endotherm reaches maximum).

[0096] The storage modulus provides an indication of the ability of a material to store elastic energy, in other words, an provides an indication of the solidity character of a polymer. A high storage modulus represents that it is more difficult to break down the polymer. A higher storage modulus also makes it more difficult to force a polymer through an extruder nozzle. The inventors have surprisingly established that, in direct granule feed AM processes, it is advantageous to maintain a higher storage modulus at a certain point in the process, as this reduces the ‘stickiness’ of the granules and thus promotes steady and fast flow through the direct granule feed printer.

[0097] The graph thus serves as a proxy for indicating how sticky the polymer is dependent on temperature. The temperature of the entry region of the screw-assembly 112 is indicated on the graph, in order to indicate the temperature range at which the problematic stickiness of non-annealed granules is observed in direct granule feed printers.

[0098] At 150 °C, the graph shows that the storage modulus of the crystalline PAEK 202 is about 1500 MPa (data point 210), whereas the storage modulus of the amorphous PAEK 204 is only about 20 MPa (data point 212, between 0 and 50 MPa) at 150 °C. This illustrates that, when amorphous granules of slow-crystallising PAEK enter the screw assembly, which reaches a temperature of about 150 °C or slightly more, they rapidly lose their rigidity and thus have a propensity to stick together and / or clog the screw assembly. This slows the progress of the granules through the printer 100. By contrast, the crystalline (e.g., annealed) granules - formed of exactly the same PAEK polymer - maintain a significantly higher storage modulus, thus indicating that the granules maintain a higher degree of solidity and thus are not as likely to deform or stick together at the entry point to the screw assembly 112. The graph 200 therefore demonstrates the surprising advantage of using annealed granules, which have a substantially higher storage modulus at about the Tg temperature of the polymer, in an AM or 3D printing process that is granule-fed.

[0099] Annealing of Granules

[0100] The following tables provide indications of the annealing time taken to achieve a particular level of crystallinity at a particular temperature for PEEK-PEDEK copolymer formed into granules as described above. In the following examples, the PAEK polymer is a PEEK-PEDEK copolymer of the precursor granules, which has a repeat unit of formula -O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula -O-Ph-Ph-O-Ph-CO-Ph- II in which the repeat unit of formula I has the structure and the repeat unit of formula II has the structure:

[0101] Annealing conditions for two different PEEK-PEDEK copolymers are provided below. Those two polymers are as follows: Table 1

[0102] The following two tables indicate annealing times based on holding the granules of the polymers at different annealing temperatures. The annealing time here is taken to be the total time spent at the annealing temperature, i.e., the time spent annealing once the granules have reached the referenced annealing temperature. The following tables therefore indicate suitable annealing times for an in-line annealing method, e.g., in which the granules are immediately annealed following melt-extrusion.

[0103] The following tables also indicate suitable annealing times for an annealing process in which the granules are conveyed through a heating chamber, e.g., spread out over a conveyor belt, wherein the annealing time in the tables corresponds to a ‘residence time’ in the heating chamber. It is presumed, due to the good exposure of the surface area of the granules to the heating elements of the chamber, that the granules reach the annealing chamber almost immediately, e.g., within 20 seconds, or within 10 seconds.

[0104] The following tables also indicate suitable annealing times for an oven-based method, though, in this case, the times are representative of the annealing time once granules have reached the annealing temperature. The total heating time for an oven-based method may therefore be obtained by adding about 30 minutes to the values in the tables.

[0105] Table 2 represents the time taken for substantially amorphous granules (e.g., having a crystallinity of about 0% to about 5%) to reach a crystallinity of at least about 24%, for a series of different annealing temperatures. Table 3 represents the time take for substantially amorphous granules (e.g., having a crystallinity of about 0% to about 5%) to reach a crystallinity of at least about 30%. Table 2

[0106] Table 3

[0107] The tables indicate that higher annealing temperatures generally shorten the annealing times, sometimes substantially. For example, for PEEK-PEDEK 75:25, to achieve 24% crystallinity, annealing at 170°C takes 12 minutes, and increasing the annealing temperature by only 10°C (to 180°C) reduces the annealing time by a factor of four, i.e. , to 3 minutes.

[0108] It should be understood that the annealing times provided here apply also to filled granules, e.g., granules filled with fibrous filler such as chopped carbon fibre (CF), including where the filler is in the range of about 1 wt% to about 50 wt% filler, preferably between about 5 wt% and 40 wt%. Some particular examples CF filled polymers that provide the advantages of annealed slow-crystalline PAEK for use in direct granule feed AM processes as disclosed herein are PEEK-PEDEK 65:35 with 30 wt% chopped CF, and PEEK-PEDEK 75:25 with 20 wt% CF or 30 wt% CF. In these particular examples, the D50 (post melt-extrusion) of the fibre in the PEEK-PEDEK 75:2530 wt% CF compound after extrusion was about 143pm, and for the 20% CF compound was about 179pm.

[0109] Annealing of Bulk Polymer

[0110] The following tables provide experimental annealing results of a bulk volume of PEEK-PEDEK. The bulk form of the PEEK-PEDEK polymer in these examples is a spool of polymer (i.e., polymer that has been melt extruded but not pelletised into granules). The annealing times are nonetheless representative, or at least indicative, of the annealing temperatures and relative timescales that can be used to anneal slow-crystallising PAEK polymers to obtain crystalline PAEK. In the following examples, the PAEK polymer is a PEEK-PEDEK copolymer having repeated formulas I and II as in the above example, and with the structure of formula III and IV in the above examples.

[0111] It should be noted in these examples that the “heating time” in column 2 of the tables is not the annealing time, but rather the total time spent heating the bulk polymer. The corresponding annealing time would be substantially lower. Furthermore, the corresponding annealing time when applied to granules, as opposed to bulk polymer, would be substantially lower still, e.g., more consistent with the shorter annealing times in tables 2 and 3.

[0112] In both Tables 4 and 5, the second column entitled “Tm Peak Crystallisation (%)” represents the enthalpy of the melting transition during a DSC measurement, and is indicative of a degree of crystallinity. The third column entitled “Anneal Peak Crystallisation (%)” and the fourth column entitled “Cold Crystallization Peak” represents the same part of the DSC trace, i.e., the enthalpy of the transition that occurs just above the glass transition temperature and is indicative of an extent to which the polymer crystallises during the DSC scan. The “Anneal Peak Crystallisation (%)” represents an endothermic region and is this indicative of a degree of crystallinity in the original sample. The fourth column, entitled “Cold Crystallisation Peak (%) (Amorphous)”, represents an exothermic region and this is indicative of the extent to which the original sample is amorphous. The overall level of crystallinity is obtained by summing the values of the second and third columns (i.e., representing crystallinity in the sample) and subtracting the value of the fourth column (i.e., representing a degree to which the sample annealed / crystallised during the DSC heating scan).

[0113] For example, in the last entry in Table 4, the overall crystallinity is above about 25% and the cold crystallisation peak is 0, which indicates that substantially no further crystallisation occurs during the heating past the glass transition temperature, i.e., the original polymer sample is substantially not amorphous. More details on the overall crystallinity can be calculated as described in the “Measurement of Crystallinity” example below. Table 4

[0114] Table 5 As with tables 2 and 3, tables 4 and 5 generally indicate that higher annealing temperatures generally shorten the annealing times, sometimes substantially. It is further observed that annealing at higher temperature, in some cases, enables a higher degree of crystallinity to be obtained. For example, heating PEEK-PEDEK 65:35 at 165 °C for 8 hours yields a crystallinity of 20.06%, which may not substantially increase based on further annealing at that temperature. Beneficially, however, heating PEEK-PEDEK 65:35 at 170 °C for only 4 hours yields a higher crystallinity of 25.84%. Figure 3 is a graph 300 showing an example DSC trace used to calculate the crystallinity of polymer samples. The X-axis represents temperature (°C), and the Y-axis represents normalised heat flow (in units of W / g). The negative (i.e., downward) direction on the Y-axis represents exothermic transitions. This graph 300 shows the DSC trace used to calculate the crystallinity for the fifth entry in Table 4, i.e., where the annealing temperature is 165 °C and the heating time is 8 hours. The DCS trace shows the ‘Tm Peak Crystallisation’ peak 306 (relating to the second column in Table 4), the ‘Anneal Peak Crystallisation’ peak 302 (relating to the third column in Table 4), and the ‘Cold Crystallisation Peak’ peak 304 (relating to the fourth column in Table 4). In this example, the peak temperature value of the ‘Tm Peak Crystallisation’ 306 is 316 °C, the peak temperature value of the ‘Anneal Peak Crystallisation’ 302 is 182 °C, and the peak temperature value of the ‘Cold Crystallisation Peak’ 304 is 185 °C.

[0115] The areas under each peak, relative to a straight baseline (shown in Figure 3), are also indicated as: region 308 under the ‘Anneal Peak Crystallisation’, region 310 under the ‘Cold Crystallisation Peak’, and region 312 under the ‘Tm Peak Crystallisation’ 306. The areas of each of these regions are used to calculate the percentage values for each of the columns in Table. It can be seen that the small region 308 representative of the Anneal Peak Crystallisation is endothermic, i.e., representative of some crystallinity in the original sample. As indicated in Table 4, this area 308 corresponds to an ‘Anneal Peak Crystallisation (%)’ of 0.25 %. The Cold Crystallisation Peak region 310 (representing an exothermic transition) is also small (1.93 %). The small size of this region 310 indicates that little further annealing took place during this portion of the DSC scan, and thus indicating that the original sample was substantially crystalline. The endothermic Tm Peak Crystallisation region 312 is large (21.74%), which is representative of a high degree of crystallinity in the sample. The total crystallinity of the original sample is thus calculated in this example by the following summation: 21.74 (%) + 0.25 (%) - 1.93 (%) = 20.06 %.

[0116] Direct Granule Feed Experiment

[0117] In an experiment to compare the relative extrusion times of annealed versus non-annealed slow-crystallising PAEK polymers, two different granules were fed into a direct granule feed AM printer. The first set of granules were comprised of PEEK-PEDEK 65:35 that were not annealed and had a crystallinity of about 5%. The second set of granules were comprised of PEEK-PEDEK 65:35 that were annealed and had a crystallinity of about 25%. In both cases, the polymer material were a carbon-fibre filled blend, comprising 70% by weight PEEK-PEDEK 65:35 co-polymer (with shear viscosity, SV, equal to 150 Pa s) and 30 % by weight of chopped carbon fibre, CF, (SGL C30). The printer was a CEAD AM Flexbot.

[0118] The observation from the operators, during the experiment, was that the granule feed was much smoother , i.e. , more consistent, with annealed granules compared to the non-annealed granules. There operators also measured an approximate 4-fold increase in the maximum granule feed rate.

[0119] The results of the extrusion experiment are shown below. The rate of extrusion is shown in arbitrary units, and is representative of the mass per unit time of molten polymer that is extruded from the exit die of the direct granule feed AM printer.

[0120] Table 6

[0121] As indicated in the table, the rate of extrusion is substantially improved by using annealed granules of this type of slow-crystallising PAEK.

[0122] Measurement of Crystallinity

[0123] The Glass Transition Temperature (Tg), the Melting Temperature (Tm) and Heat of Fusion of Melting (delta Hm) for the polymers disclosed herein may be determined using the following Differential scanning calorimetry (DSC) method.

[0124] Crystallinity may be assessed by several methods for example by density, by IR spectroscopy, by x-ray diffraction or by differential scanning calorimetry (DSC). A suitable DSC method that can used to evaluate the crystallinity that develops in the polymers described herein uses a Mettler Toledo DSC1 Star system with FRSS sensor.

[0125] The Glass Transition Temperature (Tg), the Cold Crystallisation Temperature (Tn), the Melting Temperature (Tm) and Heat of Fusions of Nucleation (AHn) and Melting (AHm) for the polymers disclosed herein may be determined using a DSC method consistent with ISO11357-1 : 2023

[0126] A sample of polymer in granule form (approximately 8mg) was placed in an aluminium DSC pan and the lid attached before being placed in the DSC instrument. It was then analysed by heating from 30 to 400°C at20°C / min. Tg (onset), Tn, Tm, AHn and AHm were recorded. Peak areas were determined relative to a straight baseline (e.g., as indicated in Figure 3).

[0127] The degree of crystallinity (from the melt and nucleation peaks) was determined by dividing either AHm or AHn by the reference value for fully crystalline PAEK of 130 J / g. This reference value of 130 J / g is suitable for use as a reference value for this measurement, and is suitable even when carried out on other PAEK polymers, including PEEK / PEDEK copolymers. The reference value of 130 J / g may therefore be taken as a suitable Heat of Fusion for totally crystalline polymers for the purposes of determining the level of crystallisation in PAEK polymers in general.

[0128] Typically, for PEEK / PEDEK copolymer, the Tm value is about 300 °C to 310°C and the Tg value is about 145 to 165°C.

[0129] Measurement of shear viscosity

[0130] The shear viscosity, SV, may be measured according to a Standard method as defined in ISO11443:2014 using capillary rheometry operating at 400°C at a shear rate of 1000 s-1using a circular cross-section tungsten carbide die, 0.5 mm (capillary diameter) x 8 mm (capillary length). The range of SV of the polymeric material selected was from around 100 Pa s to around 400 Pa s, at 400 °C.

[0131] In more detail, the shear viscosity of PAEK copolymers (such a PEEK-PEDEK) 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"8"' 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’1in this case).

Claims

CLAIMS1 . A method of annealing granules of a polyaryletherketone, PAEK, polymer to obtain annealed granules suitable for use in an additive manufacturing process, the method comprising: a) obtaining precursor granules of the PAEK polymer, wherein the precursor granules have a crystallinity of between about 0% and 20%, as measured by differential scanning calorimetry, DSC; b) heating the precursor granules to an annealing temperature to thereby obtain annealed granules, wherein the annealing temperature is at least a glass transition temperature, Tg, of the PAEK polymer and at most about 50°C less than a melting temperature, Tm, of the PAEK polymer; wherein, following annealing in b), the annealed granules have a crystallinity of between about 15% and 35%, as measured by DSC, and wherein the annealing in b) increases the crystallinity of the precursor granules by at least 2%.

2. The method of claim 1 , wherein the Tg of PAEK polymer is in the range of about 135°C to about 175°C, preferably in the range of about 140°C to about 165 °C, more preferably in the range of about 145°C to about 155 °C.

3. The method of claim 1 or 2, wherein the Tm of the PAEK polymer is in the range of about 280°C to about 330°C, preferably in the range of about 290°C to about 310°C .

4. The method of any preceding claim, wherein the annealing temperature is in the range of about 10°C above the Tg to about 40°C above the Tg.

5. The method of any preceding claim, wherein the annealing temperature is in the range of about 160°C to about 200°C, preferably in the range of about 165°C to about 180°C.

6. The method of any preceding claim, wherein step b) comprises holding the precursor granules at the annealing temperature for between about 1 minute and 5 hours, preferably for between about 2 minutes and 4 hours, more preferably between 3 minutes and 2 hours, more preferably still for between about 20 minutes and 2 hours.

7. The method of any preceding claim, wherein heating the precursor granules to an annealing temperature in step b) comprises heating the granules in an oven.

8. The method of any preceding claim, wherein heating the precursor granules to an annealing temperature in step b) comprises: conveying the precursor granules, via a movable surface, through a heating zone, wherein the annealed granules are obtained after having passed the precursor granules through the heating zone.

9. The method of any preceding claim, wherein the precursor granules have been produced by melt-processing the PAEK polymer.

10. The method of any preceding claim, wherein the precursor granules comprise a fibrous filler, preferably wherein the fibrous filler is selected from carbon fibre or glass fibre.

11. The method of any preceding claim, wherein the PAEK polymer has an isothermal crystallinity half-life, T1 / 2, of greater than about 3 minutes and less than about 20 minutes at a temperature of 280 °C, as measured by Differential Scanning Calorimetry, DSC.

12. The method of any preceding claim, wherein the PAEK polymer has an isothermal crystallinity half-life, T1 / 2, of greater than about 5 seconds and less than about 1 minute at 220°C, as measured by Differential Scanning Calorimetry, DSC.

13. The method of any preceding claim, wherein the PAEK polymer of the precursor granules has a repeat unit of formula-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety.

14. The method of claim 13, wherein the PAEK polymer of the precursor granules has a shear viscosity from, preferably from 145 to 350 Pa s, as measured using capillary rheometry at 400°C at a shear rate of 1000 s'1by extrusion through a circular cross-section tungsten carbide capillary die of 0.5mm diameter and 8.0 mm length.

15. The method of claim 13 or 14, wherein the repeat unit of formula I has the structuresaid repeat unit of formula II has the structure:

16. The method of any of claims 13 or 15, wherein the repeat units I and II are in the relative molar proportions 55:45 to 95:5, preferably 65:35 to 80:20, and more preferably 65:35 to 75:2517. The method of claim 16, wherein the repeat units I and II are in the relative molar proportions 65:35 to 75:25, and wherein the annealing temperature is in the range of about 165°C to about 200°C, and wherein step b) comprises holding the precursor granules at the annealing temperature for between about 1 minute and about 90 minutes.

18. A method of forming a component in an additive manufacturing process, the method comprising: a) obtaining a plurality of granules comprising a polyaryletherketone, PAEK, polymer, wherein the PAEK polymer of the precursor granules have a repeat unit of formula-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety, and wherein the PAEK polymer of the plurality of granules has a crystallinity of between about 15% and 35% as measured by differential scanning calorimetry, DSC, b) heating and melting the plurality of granules in a pre-extrusion zone to thereby obtain molten PAEK polymer; c) extruding the molten PAEK polymer through an exit orifice of a printing head to form at least part of the component, wherein a temperature of both the pre-extrusion zone in b) and the exit orifice in c) is in the range of about i) the melting temperature, Tm, of the PAEK polymer to about ii) 150 °C above the Tm of the PAEK polymer.

19. The method of claim 18, wherein the plurality of granules have been annealed, wherein the annealed granules have been produced from precursor granules that are substantiallyamorphous and have a crystallinity of between about 0% and 20%, as measured by DSC, wherein the annealed granules have been produced by an annealing process comprising: heating the precursor granules to an annealing temperature, wherein the annealing temperature is at least a glass transition temperature, Tg, of the PAEK polymer and at most about 50°C less than a melting temperature, Tm, of the PAEK polymer, and wherein and wherein the annealing increases the crystallinity of the precursor granules by at least 2%.

20. A component made by an additive manufacturing process according to claim 18 or 19.

21. A plurality of granules comprising a polyaryletherketone, PAEK, polymer, the plurality of granules suitable for use in an additive manufacturing process to make a component, wherein the plurality of granules are annealed granules which have a crystallinity of between about 15% and 35% as measured by differential scanning calorimetry, DSC, wherein the annealed granules have been produced from precursor granules that are substantially amorphous and have a crystallinity of between about 0% and 20%, as measured by DSC, wherein the annealed granules have been produced by an annealing process comprising: heating the precursor granules to an annealing temperature, wherein the annealing temperature is at least a glass transition temperature, Tg, of the PAEK polymer and at most about 50°C less than a melting temperature, Tm, of the PAEK polymer.

22. The granules of claim 21, wherein the PAEK polymer of the precursor granules have a repeat unit of formula-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety, preferably wherein the repeat units I and II are in the relative molar proportions 55:45 to 95:5, preferably 65:35 to 80:20, and more preferably 65:35 to 75:2523. The use of a plurality of granules comprising a polyaryletherketone, PAEK, according to claim 21 or 22, in an additive manufacturing process to form a component.

24. A component made by the additive manufacturing process of claim 23.

25. A plurality of granules produced according to the method of any of claims 1 to 17.

Images