FILAMENT FOR ADDITIVE MANUFACTURING AND PROCESS FOR MAKING THE SAME

Abstract

A fused filament fabrication filament, method and process, for layer-wise formation of a component, wherein the filament, method and process comprise feedstock material comprising a polyaryletherketone, PAEK and optionally, one or more filler means.

Claims

1. A fused filament fabrication (FFF) filament, for use in layer-wise formation of a component, wherein the filament comprises feedstock material comprising a polyaryletherketone, PAEK and one or more filler means, wherein the PAEK is a copolymer comprising repeat units of formula ##STR00007## and repeat units of formula ##STR00008## wherein 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 60:40 to 80:20; and wherein the PAEK has a shear viscosity, SV, from 100 to 400 Pa.Math.s as measured using capillary rheometry at 400° C. at a shear rate of 1000 s.sup.−1 by extrusion through a tungsten carbide capillary die of 0.5 mm diameter and 8.0 mm length; and wherein the one of more fillers comprises at least 5 wt. % and up to 38 wt. % of the composition.

2. A filament according to claim 1 wherein the SV of the copolymer is from 150 to 300 Pa.Math.s, and more preferably, 180 to 260 Pa.Math.s.

3. A filament according to claim 1 or claim 2 wherein the molar ratio 1:11 of the copolymer is from 70:30 to 80:20.

4. A filament according to any preceding claim, wherein the one of more fillers is selected from a fibrous filler and a non-fibrous filler.

5. A filament according to any preceding claim, wherein the fibrous filler is a continuous fibrous filler or a discontinuous fibrous filler.

6. A filament according to any preceding claim, wherein the one or more fillers is selected from glass fibre, carbon fibre, asbestos fibre, silica fibre, alumina fibre, zirconia fibre, boron nitride fibre, silicon nitride fibre, boron fibre, fluorocarbon resin fibre and potassium titanate fibre, mica, silica, talc, HydroxyApatite (or Hydroxyl Apatite), alumina, kaolin, calcium sulfate, calcium carbonate, titanium oxide, titanium dioxide, zinc sulphide, ferrite, clay, glass powder, zinc oxide, nickel carbonate, iron oxide, quartz powder, magnesium carbonate, fluorocarbon resin, graphite, graphene, carbon powder, nanotubes, nanofibres and/or barium sulphate.

7. A filament according to any preceding claim, wherein the one or more fillers is discontinuous carbon fibre having a nominal length between 50 microns and 300 microns, and more preferably between 100 and 300 micros and even more preferably between 125 microns and 175 microns.

8. A filament according to any preceding claim, wherein the feedstock material further includes a viscosity modifier selected from ethylene-octene copolymer such as Paraloid 3815, buytyl acrylate/PMMA core-shell such as Paraloid 3361, silicone such as Kaneka Kane-Ace MR02, or polyoctohedralsilsesquioxane compounds.

9. A filament according to any preceding claim, wherein the ratio of the copolymer shear viscosity measured at a shear rate of 100 s.sup.−1 to the copolymer shear viscosity measured at a shear rate of 10,000 s.sup.−1 is from 2.0 to 6.0, with the shear viscosity at each shear rate measured using capillary rheometry at 400° C. by extrusion through a tungsten carbide capillary die of 0.5 mm diameter and 8.0 mm length, and more preferably, the ratio of the copolymer shear viscosity measured at a shear rate of 100 s.sup.−1 to the copolymer shear viscosity measured at a shear rate of 10,000 s.sup.−1 is from 3.0 to 5.5, or even more preferably, 3.5 to 5.0, with the shear viscosity at each shear rate measured using capillary rheometry at 400° C. by extrusion through a tungsten carbide capillary die of 0.5 mm diameter and 8.0 mm length.

10. The use of a filament according to any preceding claim, in a process for formation of a component in a layer-wise fashion by sequentially depositing layers of the feedstock material in layers, each layer defining a cross-section of the component.

11. A method for manufacturing a component, the method comprising: (i) selecting a filament, according to claim 1; and (ii) forming the component in a layer-wise fashion by feeding the filament through an extruder nozzle and sequentially depositing layers of feedstock material such that a plurality of layers correspond to respective cross-sections of the component; wherein a first layer of feedstock material forms a base layer of the component; and each subsequently deposited layer of feedstock material forms a subsequent layer of the component and bonds to the respective preceding layer of the component on contact with the preceding layer whereby the component is formed from the mutually bonded portions of the plurality of layers corresponding to respective cross-sections of the component.

12. A process for improving the printability of a fused filament fabrication filament, the process comprising: extruding feedstock material through a die to form a filament wherein the feedstock material comprises a polyaryletherketone, PAEK and optionally, one or more filler means; annealing the filament at a temperature between a glass transition temperature Tg of the feedstock material and a melt temperature Tm of the feedstock material, for a period of time sufficient to increase the temperature of the filament to above the glass transition temperature of the feedstock material.

13. A process according to claim 12, wherein the feedstock material comprises: a copolymer comprising repeat units of formula ##STR00009## and repeat units of formula ##STR00010## wherein 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 60:40 to 80:20; and wherein the PAEK has a shear viscosity, SV, from 100 to 400 Pa.Math.s as measured using capillary rheometry at 400° C. at a shear rate of 1000 s.sup.−1 by extrusion through a tungsten carbide capillary die of 0.5 mm diameter and 8.0 mm length; and wherein the one of more fillers comprises at least 5 wt. % and up to 38 wt. % of the composition.

14. A process according to claim 12 or 13, wherein the annealing step is either carried out by either: a) by passing the filament through an in-line oven, such that each part of the filament is in the oven for a period between 1 second and 5 minutes, wherein the temperature of the in-line oven is from 160° C. and 220° C.; or b) by passing the filament through an in-line oven, such that the temperature of each part of the filament is raised to at least 160° C. and not more than 220° C. for at least 1 second; or c) by placing a reel of up to 1500 m of wound filament in an oven, wherein the oven temperature is 160° C. to 190° C., and the reel of filament in left in the oven for at least 15 minutes to up to 24 hours.

15. A process according to claim 14, wherein the temperature of the oven in c) is set at 180° C., and is heated to 180° C. from room temperature at a heating rate of 10° C. per minute, and the reel is placed in the oven when the oven is at room temperature.

Description

EXAMPLE 1—PREPARATION OF 0.5 MOL POLYETHERETHERKETONE (PEEK)-POLYETHERDIPHENYLETHERKETONE (PEDEK) Copolymer

[0127] 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 (111.06 g, 0.51 mol), 1,4-dihydroxybenzene (41.29 g, 0.375 mol), 4,4′-dihydroxydiphenyl (23.28 g, 0.125 mol) and diphenylsulphone (242.30 g) 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 (53.40 g, 0.5 mol) and potassium carbonate (2.76 g, 0.02 mol), 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 wastewater was <2 μS. The resulting PEEK-PEDEK powder was dried in an air oven for 12 hours at 120° C.

[0128] The resulting polymer had a Shear Viscosity (SV) of 250 Pa.Math.s at a temperature of 400° C. and a shear rate of 1000 s.sup.−1, as measured by capillary rheometry as described below.

EXAMPLE 2—PREPARATION OF 0.5 MOL POLYETHERETHERKETONE (PEEK)-POLYETHERDIPHENYLETHERKETONE (PEDEK) COPOLYMER

[0129] 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 (112.05 g, 0.51 mol), 1,4-dihydroxybenzene (35.79 g, 0.325 mol), 4,4′-dihydroxydiphenyl (32.59 g, 0.175 mol) and diphenylsulphone (246.50 g) 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 (54.98 g, 0.5 mol) and potassium carbonate (0.17 g, 1.23×10.sup.−3 mol), 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 wastewater was <2 μS. The resulting PEEK-PEDEK powder was dried in an air oven for 12 hours at 120° C.

[0130] The resulting polymer had a Shear Viscosity (SV) of 185 Pa.Math.s at a temperature of 400° C. and a shear rate of 1000 s.sup.−1, as measured by capillary rheometry as described below.

EXAMPLE 3—PREPARATION OF 0.5 MOL POLYETHERETHERKETONE (PEEK)-POLYETHERDIPHENYLETHERKETONE (PEDEK) COPOLYMER

[0131] 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 (112.05 g, 0.51 mol), 1,4-dihydroxybenzene (35.79 g, 0.325 mol), 4,4′-dihydroxydiphenyl (32.59 g, 0.175 mol) and diphenylsulphone (246.50 g) 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 (54.98 g, 0.5 mol) and potassium carbonate (0.17 g, 1.23×10.sup.−3 mol), 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 wastewater was <2 μS. The resulting PEEK-PEDEK powder was dried in an air oven for 12 hours at 120° C.

[0132] The resulting polymer had a Shear Viscosity (SV) of 239 Pa.Math.s at a temperature of 400° C. and a shear rate of 1000 s.sup.−1, as measured by capillary rheometry as described below.

EXAMPLE 4—PREPARATION OF 0.5 MOL POLYETHERETHERKETONE (PEEK)-POLYETHERDIPHENYLETHERKETONE (PEDEK) COPOLYMER

[0133] 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 (111.72 g, 0.51 mol), 1,4-dihydroxybenzene (41.29 g, 0.375 mol), 4,4′-dihydroxydiphenyl (23.28 g, 0.125 mol) and diphenylsulphone (313.00 g) 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 (53.42 g, 0.5 mol) and potassium carbonate (2.76 g, 0.02 mol), 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.

[0134] After cooling to room temperature, the crude polymer in coarse powder form was then washed with acetone and then with warm water at a temperature of 40-50° C. until the conductivity of the wastewater was <2 μS. The resulting PEEK-PEDEK powder was dried in an air oven for 12 hours at 120° C.

[0135] The resulting polymer had a Shear Viscosity (SV) of 115 Pa.Math.s at a temperature of 400° C. and a shear rate of 1000 s.sup.−1, as measured by capillary rheometry as described below.

[0136] Example 4 is particularly well suited for certain fillers such as fibrous fillers having lengths between around 100 microns and 500 microns. The shear viscosity is tuned to enable a filler weight % of between 10 wt. % and 20 wt. %. The filler contributes to the overall viscosity of the feedstock and this is even more pronounced when using fibrous fillers.

Comparative Examples

[0137] Filament Thermax PEKK-C was obtained from 3DXTECH, 904 36th Street, Suite B, Grand Rapids, Mich. 49508 USA. The SV of the polymeric material was 280 Pa.Math.s at a temperature of 400° C. and a shear rate of 1000 s.sup.−1, as measured by capillary rheometry as described below.

[0138] Filament formed from Victrex PEEK 450G was also used. The SV of 450G was 350 Pa.Math.s.

[0139] Manufacture of Filament

[0140] Filament was formed from the following feedstock material: Victrex 450G and Examples 1, 2, 3, and 4. The selected feedstock was melted and extruded through a die with a 4 mm orifice. The extruder meter pump speed was used to control the final diameter of the filament. A filament having a diameter of 1.77 mm was formed. Once the filament was formed, the filament underwent an annealing step by placing the filament in an oven at room temperature and increasing the temperature of the oven at a rate of 10° C. per minute until the oven was at a temperature of 180° C. The filament was left in the oven for a period of three hours. The final filament had a crystallinity of at least 20%, but typically the crystallinity of the filament was 24%. Crystallinity was measured according to the method below.

[0141] Measurement of Crystallinity—Differential Scanning Calorimetry of the Copolymers of Examples 1 to 4

[0142] Crystallinity may be assessed by several methods for example by density, by IR spectroscopy, by X-ray diffraction or by differential scanning calorimetry (DSC).

[0143] The Glass Transition Temperature (Tg), the Melting Temperature (Tm) and Heat of Fusion of Melting (delta Hm) for the polymers from Examples 1 to 4 were determined using the following DSC method.

[0144] Crystallinity may be assessed by several methods for example by density, by it spectroscopy, by x ray diffraction or by differential scanning calorimetry (DSC). The DSC method has been used to evaluate the crystallinity that developed in the polymers from Examples 1-4 using a Mettler Toledo DSC1 Star system with FRS5 sensor.

[0145] The Glass Transition Temperature (Tg), the Cold Crystallisation Temperature (Tn), the Melting Temperature (Tm) and Heat of Fusions of Nucleation (ΔHn) and Melting (ΔHm) for the polymers from Examples 1 to 4 were determined using the following DSC method.

[0146] A dried sample of each polymer was compression moulded into an amorphous film, by heating 7 g of polymer in a mould at 400° C. under a pressure of 50 bar for 2 minutes, then quenching in cold water producing a film of dimensions 120×120 mm, with a thickness in the region of 0.20 mm. An 8 mg plus or minus 3 mg sample of each film was scanned by DSC as follows:

[0147] Step 1 Perform and record a preliminary thermal cycle by heating the sample from 30° C. to 400° C. at 20° C./min.

[0148] Step 2 Hold for 5 minutes.

[0149] Step 3 Cool at 20° C./min to 30° C. and hold for 5 mins.

[0150] Step 4 ΔHm. Re-heat from 30° C. to 400° C. at 20° C./min, recording the Tg, Tn, Tm, ΔHn and

[0151] From the DSC trace resulting from the scan in step 4, the onset of the Tg was obtained as the intersection of the lines drawn along the pre-transition baseline and a line drawn along the greatest slope obtained during the transition. The Tn was the temperature at which the main peak of the cold crystallisation exotherm reaches a maximum. The Tm was the temperature at which the main peak of the melting endotherm reach maximum.

[0152] The Heat of Fusion for melting (ΔHm) was obtained by connecting the two points at which the melting endotherm deviates from the relatively straight baseline. The integrated area under the endotherm as a function of time yields the enthalpy (mJ) of the melting transition: the mass normalised heat of fusion is calculated by dividing the enthalpy by the mass of the specimen (J/g). The level of crystallisation (%) is determined by dividing the Heat of Fusion of the specimen by the Heat of Fusion of a totally crystalline polymer, which for polyetheretherketone is 130 J/g.

[0153] Filaments comprising Examples 1 to 4, had a measured final crystallinity of 24%.

[0154] Measurement of Shear Viscosity

[0155] The shear viscosity, SV, was 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.sup.−1 using a circular cross-section tungsten carbide die, 0.5 mm (capillary diameter)×8 mm (capillary length). The range of SV of the polymeric material selected was from around 100 Pa.Math.s to around 400 Pa.Math.s, at 400° C.

[0156] The results for the rheology shear rate sweeps are shown in FIG. 2. FIG. 2 includes shear rate sweeps for Examples 1, 2 and 3 and Comparative example Filament Thermax PEKK-C. The ratio of the copolymer shear viscosity measured at a shear rate of 100 s.sup.−1 to the copolymer shear viscosity measured at a shear rate of 10,000 s.sup.−1 is from 2.0 to 6.0, with the shear viscosity at each shear rate measured using capillary rheometry at 400° C. by extrusion through a tungsten carbide capillary die of 0.5 mm diameter and 8.0 mm length. The ratio for the comparative example is over 6.0. It has been surprisingly found that filaments made from feedstock made from copolymer having these rheological properties perform very well when printed and produce parts having superior z-strength.

[0157] Improving the low shear rheological properties of filament according to the invention improves certain mechanical and physical properties of components made from the filament in fused filament fabrication as it can aid interlayer adhesion.

[0158] When looking at the mechanical properties of polymer printing using filament fusion fabrication (FFF), it is useful to not only consider test specimens printed horizontally (X and Y directions), but also vertically (Z-direction). This is because Z-strength is a measure of interlayer adhesion, which is required to impart good mechanical strength in real components (as opposed to simple, quasi-2-dimensional test bars).

[0159] For example, test bars printed using the filament made with feedstock comprising the copolymer of Example 1 showed a Z-direction strength of 43 MPa, when printed in a filament fusion fabrication printer with no heated chamber.

[0160] A filament made using feedstock comprising the copolymer made according to Example 2 had a Z-direction of strength of 54 MPa.

[0161] By comparison, a component printed in the same manner but with a conventional PEEK polymer (Victrex 450G for example) has a Z-strength of around 16 MPa.

[0162] Filament according to the present invention provides upwards of almost three times the z-direction strength in a printed component compared to printed components printed with PEEK filaments.

[0163] It has been surprisingly found that components printed with filament according to the present invention comprising feedstock including fillers such as glass, mineral, carbon, or other inorganic fillers may improve mechanical properties above the Tg of the copolymer, including improving stiffness, strength, heat deflection properties, electrical properties such as conductivity or insulation properties, and creep resistance. Such materials are beneficial for use in seal rings and of sealing components, especially in relation to energy applications such as in oil and gas industries. Certain fillers such as glass filler may be used to provide stiffness for structural applications.

[0164] Filament according to the present invention, used to print components for aerospace applications, comprising fillers such as glass, mineral, carbon, or other inorganic fillers may improve mechanical properties above the Tg of the copolymer, including improving stiffness, strength, and creep resistance. Such materials are beneficial for use in system attachments, including but not limited to wire clamps, brackets, straps and other components, especially in relation to aerospace components and parts of aircraft.

[0165] Filament according to the present invention, used to print components for automotive applications, comprising fillers such as glass, mineral, carbon, or other inorganic fillers may improve mechanical properties above the Tg of the copolymer, including improving stiffness, strength, and creep resistance. Such materials are beneficial for use in under-hood engine compartment brackets, cable clamps, and other elevated temperature applications in vehicles.

[0166] Components such as gears, bearings and transmission components made with filament comprising PTFE, carbon fibre and other fillers that minimise friction, wear, and tribological performance of components.

[0167] Components such as bio-reactors and static mixers may be manufactured with filament comprising fillers having catalytic properties, or that improve the adhesion of coatings added to the printed component that impart such properties.

[0168] Electro-static discharge (ESD) performance has been found to be imparted by selecting conductive fillers including short and long carbon fibre, carbon black, and other electrically conductive additives. The benefit of such fillers in filament according to the invention is that components may be printed to support protection from lightning strike and enable grounding to protect sensitive electronics and controls.

[0169] Filament according to the present invention may be used to manufacture medical components such as implants adapted for improved osseointegration using hydroxyapatite.

[0170] In certain examples filament according to the present invention may be overprinting applications whereby filament according to the invention is used to print fine detail onto a moulded part, such as a polyetheretherketone part of a copolymer part where the copolymer is the same copolymer described in the first aspect of the invention. Alternatively, the printed component may form an insert in a moulded component where the over-moulding material has a higher shearing temperature than the copolymer according to the first aspect of the invention.

[0171] In other examples, components such as manifolds and heat exchangers are made with filament according to the present invention. Fillers are selected to improve thermal conductivity to improve the thermal heat exchange, and/or rapid heating/cooling of fluids in manifolds and heat exchangers.

[0172] Fillers such as talc may be used to reduce CTE and post printing shrinkage to enable larger part printing. Other inorganic fillers such as glass and carbon fibre and particles may be used to similarly reduce thermal expansion, including shrink and warp that may occur during the printing process. Filament with fillers such as talc are useful for printed antenna substrates and three-dimensional electronic components.

[0173] Other additive manufacturing processes exist and the feedstock and filament described above are usable in other such processes. Those other processes include but are not limited to extrusion-based processes, powder bed fusion (PBF) processes and three-dimensional composites additive manufacturing processes.

[0174] As such, the feedstock comprising copolymer and filler means described herein may also be applied to other manufacturing processes to impart similar performance benefits in the manufactured components. For example, the feedstock may be used in other form factors (shapes) used as inputs to other melt extrusion additive manufacturing processes, such as thick rods, moulded preform shapes, powders, or granules as inputs to direct extrusion additive manufacturing machines. By extension, the feedstock material described herein may also be used powder based additive manufacturing processes such as selective laser sintering and binder jet high speed sintering processes, wherein the feedstock material is milled into powders suitable for such processes. Beyond additive manufacturing, the feedstock material described herein, when applied to granules, pellets, or powders may also be applied to melt based manufacturing process such as injection moulding, extrusion, or compression moulding.

[0175] 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.