Thermoplastic polyurethane powder blend for additive manufacturing

Abstract

A thermoplastic polyurethane powder blend for use in producing a recyclable three-dimensional object in an additive manufacturing process. The blend includes a first thermoplastic polyurethane material having a first reactive group and a number average functionality of about 1.8 to about 2.4 and a second thermoplastic polyurethane material having a second reactive group and a number average functionality of about 1.8 to about 2.4, wherein the first reactive group is different from the second reactive group.

Description

THERMOPLASTIC POLYURETHANE POWDER BLEND FOR ADDITIVE MANUFACTURINGFIELD

[0001] The present disclosure generally relates to a thermoplastic polyurethane powder blend for use in producing thermoplastically recyclable three-dimensional objects, e.g., for use in producing thermoplastically recyclable three-dimensional objects in an additive manufacturing process such as selective laser sintering.BACKGROUND

[0002] Additive manufacturing is generally a process for manufacturing a three-dimensional object in an additive manner utilizing a computer model of the object. The basic operation includes slicing a three-dimensional computer model into thin cross sections, translating the result into position data, and feeding the position data to control equipment which manufactures the three-dimensional object in a layer-wise manner using one or more additive manufacturing techniques. Additive manufacturing entails many different approaches to the method of fabrication, including fused deposition modeling, ink jetting, selective laser sintering, multijetfusion, high speed sintering, powder / binder jetting, electron-beam melting, electrophotographic imaging, and stereolithographic processes.

[0003] One process that is especially well suited for the purpose of rapid prototyping or the manufacture of components in small-scale series is selective laser sintering. In this process, plastic powders contained in a chamber are selectively exposed to a laser beam for a short period of time causing the powdery particles hit by the laser beam to melt. The melted particles blend into each other and solidify quickly to form a solid mass. In this process, three-dimensional structures can be produced in a simple and quick way by repeated exposure of continuously applied powder layers.

[0004] Plastic powders made of polyester, polyvinyl chloride, polyacetal, polypropylene, polyethylene, polystyrene, polycarbonate, poly-(N-methylmethacrylamide) (PMMI), polymethylmethacrylate (PMMA) and polyamide or mixtures thereof can be used for selective laser sintering. In particular, powders mainly made of polyamide-12 have been used.

[0005] Furthermore, use of powders made of thermoplastic polyurethanes (TPU) in selective laser sintering can be found in, for example, WO200525839, WO2015197515, W02015109143 and WO2018197392. It has been found TPU powders which have a low melt viscosity tend to produce objects having less physical strength while highly viscous TPU materials tend to exhibit poor sintering due to lower coalescence and poor interlayer bonding. Additionally, the three-dimensional objects tend to have unacceptable strength in the z-direction. Furthermore, known TPU powders are thermoplastically recyclable, but are anisotropic in terms of performance / strength, and thereby are often limited in applicability beyond prototyping. The blending of 2 TPU powders (which are not chemically reactive towards each other) has been done, such as described by EP17167681A, in order to tune the properties of the final three-dimensional object (hardness, elongation), resulting in a thermoplastically recyclable printed part, however still remaining anisotropic in terms of performance / strength. Finally, crosslinking of the TPU material, as described in EP3621812, can cause stress in the resulting object due to shrinkage thus making the objects appear to be warped. The resulting three-dimensional object will also no longer be thermoplastically recyclable (thermoset) and will display significantly reduced elongation (crosslink density), making them less suitable in elastomeric applications.

[0006] Accordingly, it would be desirable to improve upon current TPU powders by providing new TPU powders that are capable of being used in additive manufacturing processes to produce three-dimensional objects that are fully thermoplastically recyclable, having good mechanical strength (for e.g., tensile strength, especially in the z-direction), highly isotropic properties (for e.g. similar tensile strength in the x,y and z-direction), less object deformation and / or no warping.SUMMARY

[0007] The present disclosure describes a thermoplastic polyurethane powder blend for use in producing a thermoplastically recyclable three-dimensional object.

[0008] In one aspect, there is provided a thermoplastic polyurethane powder blend for use in producing a thermoplastically recyclable three-dimensional object, the powder blend comprising a first thermoplastic polyurethane material having a first reactive group and a numberaverage functionality of about 1.8 to about 2.4 and a second thermoplastic polyurethane material having a second reactive group and a number average functionality of about 1.8 to about 2.4, wherein the first reactive group is different from the second reactive group.

[0009] In another aspect, there is provided a method for producing a thermoplastic polyurethane powder blend for use in producing a thermoplastically recyclable three-dimensional object, the method comprising the steps: reacting a first reaction mixture having an isocyanate index greater than 100% to form a first thermoplastic polyurethane material; reacting a second reaction mixture having an isocyanate index less than 100% to form a second thermoplastic polyurethane material; grinding the first and second thermoplastic polyurethane materials separately to form a first thermoplastic polyurethane powder material and a second thermoplastic polyurethane powder material; and blending the first thermoplastic polyurethane powder material and the second thermoplastic polyurethane powder material to form the thermoplastic polyurethane powder blend.

[0010] In another aspect, there is provided a method for producing a thermoplastically recyclable three-dimensional object comprising the steps:(a) depositing a quantity of the thermoplastic polyurethane powder blend as described herein on a support surface to form a layer of the thermoplastic polyurethane powder blend;(b) melting the layer of the thermoplastic polyurethane powder blend to form an integral layer;(c) depositing another quantity of the thermoplastic polyurethane powder blend as described herein on the integral layer to form a layer of the thermoplastic polyurethane powder blend;(d) melting the layer of the thermoplastic polyurethane powder blend formed in step (c) to form an additional layer that is bonded to the adjacent integral layer formed in step (b), wherein the additional layer and the adjacent integral layer combine to form the integral layer; and(e) repeating steps (c) and (d), as required, to form the thermoplastically recyclable three- dimensional object.

[0011] In some embodiments, the melting of the layer of the thermoplastic polyurethane powder blend in steps (b) and / or (d) is performed by directing an energy beam over a predetermined target area on the support surface. In other embodiments, steps (b) and (d) of the method for the producing a three-dimensional object is conducted according to the multijetfusion or high-speed-sintering principle by applying a radiation-absorbing ink to a white powder bed, by means of a print head. Areas not to be printed, on the other hand, are optionally cooled with a second printing fluid, a detailing agent. After the powder bed has been printed, an infrared lamp is used to inject energy into the powder bed to fuse / sinter the desired area.

[0012] In another aspect, there is provided a thermoplastically recyclable three- dimensional object obtainable by the method described herein.

[0013] In a further aspect, there is provided a use of the thermoplastic polyurethane powder blend as described herein in producing a thermoplastically recyclable three-dimensional object.BRIEF DESCRIPTION OF FIGURES

[0014] Figure 1 shows A, D and F-type dogbones used in the Examples.DETAILED DESCRIPTION

[0015] The present disclosure provides a thermoplastic polyurethane powder blend comprising a first thermoplastic polyurethane material having a first reactive group and a number average functionality of about 1.8 to about 2.4 and a second thermoplastic polyurethane material having a second reactive group and a number average functionality of about 1.8 to about 2.4. Inone embodiment, the first reactive group and the second reactive group are capable of reacting with each other to form a covalent bond. It has been surprisingly found the use of a blend of the first thermoplastic polyurethane material having a first reactive group and the second thermoplastic polyurethane material having a second reactive group facilitates chain growth during an additive manufacturing process which leads to an improvement in the physical properties, especially in the z-direction, of the resulting three-dimensional object. In addition, because the first and second thermoplastic polyurethane materials may be easily designed have a similar range in melting temperatures, higher powder bed temperatures may be used during the process which leads to reduced stress in the resulting object and hence less warping. Finally, it has been surprisingly found the use of the thermoplastic polyurethane powder blend of the present disclosure in an additive manufacturing process may produce thermoplastically recyclable three-dimensional objects exhibiting significant improvement in isotropy.

[0016] If appearing herein, the term "comprising" and derivatives thereof are not intended to exclude the presence of any additional component, step, or procedure, whether or not the same is disclosed herein. In order to avoid any doubt, all compositions claimed herein through use of the term "comprising" may include any additional additive, adjuvant, or compound, unless stated to the contrary. In contrast, the term, "consisting essentially of" if appearing herein, excludes from the scope of any succeeding recitation any other component, step, or procedure, except those that are not essential to operability and the term "consisting of", if used, excludes any component, step or procedure not specifically delineated or listed. The terms "or" and "and / or", unless stated otherwise, refer to the listed members individually as well as in any combination. For example, the expression A and / or B refers to A alone, B alone, or to both A and B.

[0017] The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical objects of the article. By way of example, "a polyol" means one polyol or more than one polyol. The phrases "in one embodiment", "according to one embodiment" and the like generally mean the feature, structure, or characteristic following the phrase is included in at least one embodiment of the present disclosure and may be included in more than one embodiment of the present disclosure. Importantly, such phrases do notnecessarily refer to the same embodiment. If the specification states a component or feature "may", "can", "could", or "might" be included or have a characteristic, that component or feature is not required to be included or have the characteristic.

[0018] The terms "preferred" and "preferably" refer to embodiments that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the present disclosure.

[0019] The term "about" as used herein can allow for a degree of variability in a value or range, for example, it may be within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

[0020] Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but to also include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range such as from 1 to 6, should be considered to have specifically disclosed sub-ranges, such as, from 1 to 3, from 2 to 4, from 3 to 6, etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0021] The term "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0022] The term "isocyanate index" (or "NCO index" or "index") means the ratio of -NCO groups over isocyanate active hydrogens present in a reaction mixture, given as a percentage:[ CO] x 100R[active h 'yd —rogen T] mIn other words, the isocyanate index expresses the percentage of isocyanate actually used in a reaction mixture with respect to the amount of isocyanate theoretically required for reacting with the amount of isocyanate active hydrogens used in the reaction mixture. It should be observed that the isocyanate index as used herein is not only considered from the point of view of the actual polymerization process preparing the material involving the isocyanate ingredients and the isocyanate-reactive ingredients. Any isocyanate groups consumed in a preliminary step to produce modified polyisocyanates (including such isocyanate-derivatives referred to in the art as prepolymers) or any isocyanate active hydrogens consumed in a preliminary step (for e.g., reacted with isocyanate to produce modified polyols or polyamines) are also taken into account in the calculation of the isocyanate index.

[0023] The term "isocyanate active hydrogens" for the purpose of calculating the isocyanate index refers to the total amount of active hydrogen atoms in hydroxyl and amine groups present in the reaction mixture; this means that for the purpose of calculating the isocyanate index at the actual polymerization process one hydroxyl group is considered to comprise one active hydrogen, one primary amine group is considered to comprise one active hydrogen and one water molecule is considered to comprise two active hydrogens.

[0024] The term "hydroxyl value" refers to the concentration of hydroxyl groups, per unit weight of the polyol, that can react with -NCO groups. The hydroxyl number is reported as mg KOH / g and may be measured according to the standard ASTM D 1638.

[0025] The term "number average functionality" indicates the number of reactive groups per molecule, on average. For example, the average functionality of a polyol indicates the number of OH groups per molecule, on average. The average functionality of an isocyanate refers to the number of -NCO groups per molecule, on average. The term "number average functionality" is applicable to monomer, oligomers and polymer structures.

[0026] The term "thermoplastic" as used herein refers in its broad sense to designate a material that is reprocessable at an elevated temperature whereas "thermoset" designates a material that exhibits high temperature stability without such reprocessability at elevated temperatures.

[0027] The term "polyurethane", as used herein, is not limited to those polymers which include only urethane or polyurethane linkages. It is well understood by those of ordinary skill in the art of preparing polyurethanes that the polyurethane polymers may also include allophanate, carbodiimide, uretidinedione, and other linkages in addition to urethane linkages.

[0028] The term polymer, as used herein, is referring to the OECD definition for a polymer: Molecules must be distributed over a range of molecular weights; The weight percentage of molecules containing three monomer units or above should exceed 50%; The weight percentage of any molecule of the same molecular weight shall not exceed 50%.

[0029] The term "reaction mixture", as used herein, may be used when two or more components of the mixture have been combined, or to refer to all components of the mixture prior to them having been combined, and does not necessarily require that all components are present at all times simultaneously.

[0030] The term "melting temperature" or "melting point" (Tm) refers to the temperature at which the powder melts and is measured using Differential Scanning calorimetry (DSC). Using DSC the temperature increases and the sample eventually reaches its melting temperature (Tm). The melting process results in an endothermic peak in the DSC heating curve which corresponds to Tm. The melting temperature is determined by the onset temperature of the endothermic peak in the DSC curve measured according to ISO 11357 (taking into account only the first heating run) using a heating rate of 10 K / min and is expressed in °C.

[0031] "D5O particle diameter" refers to a particle size (diameter) distribution (also referred to as Mass-Median-Diameter, MMD) at which 50% of a sample's mass is comprised of smaller particles. The particle size is measured according to ISO 13320. In a similar way the "DM particle diameter" and "Dgo particle diameter" expresses the particle diameter at which respectively 10% and 90% of a sample's mass is comprised of smaller particles.

[0032] The term "selective laser sintering" generally refers to an additive manufacturing technique known to those skilled in the art that uses a laser as the power source to sinter powdered (polymeric) material. The laser is automatically aimed at points in space defined by athree dimensional model to melt at least the outer surface of the powder particles thereby fusing the (polymeric) cores to each other and to a previous layer. In comparison, "high-speed sintering" generally refers to an additive manufacturing technique known to those skilled in the art in which a powder (polymeric) material is rapidly heated at a high temperature and sintered by irradiation with electromagnetic waves or sintered by energization with a large pulse current. Finally, "multijet fusion" generally refers to an additive manufacturing technique known to those skilled in the art in which an ink (fusing agent) is dispensed on the powder (polymeric material) to promote the absorption of infrared light. An infrared energy source is then passed over the material to fuse the inked areas.

[0033] Melt Volume Rate (MVR) is the rate of extrusion of a molten resin through a capillary of specified length and diameter under prescribed conditions of temperature and pressure, the rate being determined as the volume extruded over a specified time. MVR is expressed in units of cubic centimetres per 10 min (cm3 / 10 min). Melting behavior is determined via the change in the MVR (melt volume rate) in accordance with ISO 1133, but using 4 minutes preheated time and load mass of 10 kg at a selected temperature.

[0034] Printed part isotropy: The level of isotropy in the 3D printed part can be determined by calculating the isotropic index as shown in formula: 100The isotropic index, presented as a %, can be calculated for Tensile strength (TS) or elongation (E) by filling in the respective values for samples with 2 different orientations in the print bed. An Isotropic index of 100% means XI = X2 (perfectly isotropic) and the closer to 0, the larger the difference between XI and X2 (anisotropic). To take into account a correction for extremely low values (e.g. poorly sintered parts where XI and X2 could have very low values), the term X1+X2 is introduced. The isotropic tensile strength index is thus calculated by taking the absolute value of the difference in tensile strength (for 2 different orientations in the print bed) and dividing it by the sum of the tensile strengths, and then converting it into a percentage. A similar equation can be used to calculate the isotropic index for elongation.

[0035] In one embodiment, the present disclosure provides a thermoplastic polyurethane powder blend including a first thermoplastic polyurethane material having a first reactive group and a number average functionality of about 1.8 to about 2.4 and a second thermoplastic polyurethane material having a second reactive group and a number average functionality of about 1.8 to about 2.4, wherein the first reactive group is different from the second reactive group. The first reactive group being different from the second reactive group means that the reactive groups are different functional groups.

[0036] In one embodiment, the first reactive group and the second reactive group are capable of reacting with each other to form a covalent bond.

[0037] According to an embodiment, the present disclosure provides a thermoplastic polyurethane powder blend including a first thermoplastic polyurethane material having a first reactive group and a second thermoplastic polyurethane material having a second reactive group, wherein the first reactive group is different from the second reactive group. In one embodiment, the first thermoplastic polyurethane material having a first reactive group does not contain any of the second reactive group type, while the second thermoplastic polyurethane material having a second reactive group does not contain any of the first reactive group type.

[0038] According to an embodiment, the first reactive group and the second reactive group may be terminal reactive groups, pendant reactive groups, or a combination of terminal and pendant reactive groups. Non-limiting examples of reactive groups are: carboxylic acid, epoxy, isocyanate, amine, hydroxyl, thiol, (cyclic) carbonate, acid chloride, acid anhydride, and / or other isocyanate-reactive groups. Non-limiting examples of specific combinations of first reactive groups and second reactive groups include: carboxylic acid and epoxy groups; carboxylic acid and amine groups; carboxylic acid and thiol groups; carboxylic acid and hydroxyl groups; isocyanate and primary or secondary amine groups; isocyanate and hydroxyl groups; isocyanate and thiol groups; isocyanate and carboxylic acid groups; isocyanate and epoxy groups; epoxy and primary or secondary amine groups; epoxy and hydroxyl groups; epoxy and thiol groups; (cyclic) carbonate and primary or secondary amine groups; (cyclic) carbonate and hydroxyl groups; and thiol and epoxy groups. Thus, in one embodiment, the first reactive group is selected from an epoxy group,an isocyanate group, and a (cyclic) carbonate group and the second reactive group is selected from a hydroxyl group, a primary amine group, a secondary amine group, a carboxylic acid group and a thiol group.

[0039] According to an embodiment, the first reactive group and the second reactive group are selected in such way that the material is not crosslinked, or in such way that the material remains thermoplastic. According to an embodiment, reactive groups with double bonds are not present in the first and / or second thermoplastic polyurethane material.

[0040] The first thermoplastic polyurethane material has a number average functionality of about 1.8-2.4, or about 1.85-2.2, or about 1.9-2.1, or about 1.95-2.05, or about 1.95-2.02, or about 1.95-2.015, or about 1.95-2.012, or about 1.98-2.01 or even about 1.98-2.005. In other embodiments, the first thermoplastic polyurethane material may have a number average functionality of about 1.85-2.4, or about 1.9-2.4, or about 1.95-2.4 or about 1.98-2.4. In still other embodiments, the first thermoplastic polyurethane material may have a number average functionality of about 1.8-2.3 or about 1.8-2.2 or about 1.8-2.1 or about 1.8-2.05 or about 1.8- 2.01 or about 1.8-2.005.

[0041] The second thermoplastic polyurethane material has a number average functionality of about 1.8-2.4, or about 1.85-2.2, or about 1.9-2.1, or about 1.95-2.05, or about 1.95-2.02, or about 1.95-2.015, or about 1.95-2.012, or about 1.98-2.01 or even about 1.98-2.005. In other embodiments, the second thermoplastic polyurethane material may have a number average functionality of about 1.85-2.4, or about 1.9-2.4, or about 1.95-2.4 or about 1.98-2.4. In still other embodiments, the second thermoplastic polyurethane material may have a number average functionality of about 1.8-2.3 or about 1.8-2.2 or about 1.8-2.1 or about 1.8-2.05 or about 1.8- 2.01 or about 1.8-2.005.

[0042] In other embodiments the first thermoplastic polyurethane material may have a number average functionality of about 2.0. In other embodiments the second thermoplastic polyurethane material may have a number average functionality of about 2.0. In other embodiments both the first and the second thermoplastic polyurethane material may have a number average functionality of about 2.0.

[0043] In other embodiments, the first thermoplastic polyurethane material may have a number average molecular weight of 500 - 500 000 g / mol as determined by gel permeation chromatography (with a polystyrene standard as a reference). In other embodiments, the first thermoplastic polyurethane material may have a number average molecular weight of 1000 - 500 000 g / mol, or about 5000 - 500000 g / mol, or about 10000 - 500000 g / mol, or about 20 000 - 500 000 g / mol, or about 30 000 - 500 000 g / mol, or about 40 000 - 500 000 g / mol. In other embodiments, the first thermoplastic polyurethane material may have a number average molecular weight of 10000 - 500000 g / mol, or about 10000 - 300000 g / mol, or about 10000 - 150 000 g / mol, or about 10 000 - 100 000 g / mol, or about 10 000 - 90 000 g / mol, or about 10 000 - 80000 g / mol, or about 10000 - 70000 g / mol, or about 10000 - 60000 g / mol.

[0044] In other embodiments, the second thermoplastic polyurethane material may have a number average molecular weight of 500 - 500 000 g / mol as determined by gel permeation chromatography (with a polystyrene standard as a reference). In other embodiments, the second thermoplastic polyurethane material may have a number average molecular weight of 1000 - 500 000 g / mol, or about 5000 - 500000 g / mol, or about 10000 - 500000 g / mol, or about 20 000 - 500 000 g / mol, or about 30 000 - 500 000 g / mol, or about 40 000 - 500 000 g / mol. In other embodiments, the second thermoplastic polyurethane material may have a number average molecular weight of 10000 - 500000 g / mol, or about 10000 - 300000 g / mol, or about 10000 - 150 000 g / mol, or about 10 000 - 100 000 g / mol, or about 10 000 - 90 000 g / mol, or about 10 000 - 80000 g / mol, or about 10000 - 70000 g / mol, or about 10000 - 60000 g / mol.

[0045] In other embodiments, the first thermoplastic polyurethane material and / or the second thermoplastic polyurethane material is a polymer.

[0046] In other embodiments, both the first and / or the second thermoplastic polyurethane material may have a number average molecular weight of 500 - 500000 g / mol as determined by gel permeation chromatography (with a polystyrene standard as a reference). In other embodiments, both the first and the second thermoplastic polyurethane material may have a number average molecular weight of 1000 - 500 000 g / mol, or about 5000 - 500 000 g / mol, or about 10000 - 500000 g / mol, or about 20000 - 500000 g / mol, or about 30000 - 500000 g / mol,or about 40 000 - 500 000 g / mol. In other embodiments, both the first and the second thermoplastic polyurethane material may have a number average molecular weight of 10 000 - 500 000 g / mol, or about 10 000 - 300 000 g / mol, or about 10 000 - 150 000 g / mol, or about 10 000 - 100 000 g / mol, or about 10 000 - 90 000 g / mol, or about 10 000 - 80 000 g / mol, or about 10 000 - 70 000 g / mol, or about 10 000 - 60 000 g / mol.

[0047] In another embodiment at least 2 thermoplastic polyurethane materials are used. In other embodiments at least 3, or at least 4, or at least 5, or at least 6 thermoplastic polyurethane materials are used.

[0048] In another embodiment the first and the second thermoplastic polyurethane material have a difference in melting temperature (determined using differential scanning calorimetry in accordance with ISO 11357, taking only the first heating run into account and using a heating rate of 10 K / min) of less than 100°C, more preferably less than 90°C, more preferably less than 80°C, more preferably less than 70°C, more preferably less than 60°C, more preferably less than 50°C, more preferably less than 45°C, more preferably less than 40°C, more preferably less than 35°C, more preferably less than 30°C, more preferably less than 25°C, more preferably less than 20°C, more preferably less than 15°C, more preferably less than 10°C, most preferably less than 5°C.

[0049] In another embodiment the first and the second thermoplastic polyurethane material have a difference in melt-volume rate (MVR) at a temperature of 210°C using a weight of 10kg expressed in cm3 / 10 min of less than 200, more preferably less than 175, more preferably less than 150, more preferably less than 125, more preferably less than 100, more preferably less than 75, more preferably less than 50, more preferably less than 25.

[0050] In another embodiment the first and the second thermoplastic polyurethane material have a difference in melt-volume rate (MVR) at a temperature of 200°C using a weight of 10kg expressed in cm3 / 10 min of less than 200, more preferably less than 175, more preferably less than 150, more preferably less than 125, more preferably less than 100, more preferably less than 75, more preferably less than 50, more preferably less than 25.

[0051] In another embodiment the first and the second thermoplastic polyurethane material have a difference in melt-volume rate (MVR) at a temperature of 190°C using a weight of 10kg expressed in cm3 / 10 min of less than 200, more preferably less than 175, more preferably less than 150, more preferably less than 125, more preferably less than 100, more preferably less than 75, more preferably less than 50, more preferably less than 25.

[0052] In another embodiment the first and the second thermoplastic polyurethane material have a difference in melt-volume rate (MVR) at a temperature of 180°C using a weight of 10kg expressed in cm3 / 10 min of less than 200, more preferably less than 175, more preferably less than 150, more preferably less than 125, more preferably less than 100, more preferably less than 75, more preferably less than 50, more preferably less than 25.

[0053] In certain embodiments, the first and the second thermoplastic polyurethane material are used in a weight ratio that may range from about 200:1 to about 1:200; or from about 100:1 to about 1:100; or from about 95:5 to about 5:95; or from about 90:10 to about 10:90; or from about 85:15 to about 15:85; or from about 80:20 to about 20:80; or from about 25:75 to about 75:25; or from about 70:30 to about 30:70; or from about 65:35 to about 35:65; or from about 60:40 to about 40:60.

[0054] In certain embodiments, the first thermoplastic polyurethane material and the second thermoplastic polyurethane material are combined in an amount such that that the molar equivalents of the first reactive group and the second reactive group are present in a ratio ranging from about 200:1 to about 1:200; or from about 100:1 to about 1:100; or from about 95:5 to about 5:95; or from about 90:10 to about 10:90; or from about 85:15 to about 15:85; or from about 80:20 to about 20:80; or from about 25:75 to about 75:25; or from about 70:30 to about 30:70; or from about 65:35 to about 35:65; or from about 60:40 to about 40:60; or in a ratio of 50:50.

[0055] In one embodiment, the first thermoplastic polyurethane material is obtained from the reaction of a first reaction mixture having an isocyanate index of greater than 100% and the second thermoplastic polyurethane material is obtained from the reaction of a second reaction mixture having an isocyanate index less than 100%, wherein the first reaction mixture comprises an isocyanate component and an isocyanate reactive component, and wherein the secondreaction mixture is different from the first reaction mixture and comprises an isocyanate component and an isocyanate reactive component.

[0056] In one embodiment, each of the above first and second reaction mixtures, independently, include a polyol (as the isocyanate reactive component) having at least two isocyanate reactive moieties per compound. For example, the polyol or mixture of polyols may be liquid at 25°C, have a molecular weight ranging from 60 Daltons to 10,000 Daltons (for e.g., 300 Daltons to 10,000 Daltons or less than 5,000 Daltons), a nominal hydroxyl functionality of about 2, and a hydroxyl equivalent weight of 30 to 2000 (for e.g., 30 to 1,500 or 30 to 800). Nonlimiting examples of polyols that may be used include polyether polyols, such as those made by addition of alkylene oxides to initiators, containing from 2 to 8 active hydrogen atoms per compound. In some embodiments, the aforementioned initiators include, but are not limited to, glycols, aniline, o-chloro-aniline, or combinations thereof. Suitable alkylene oxides that may be used to form the polyether polyols include ethylene oxide, propylene oxide, and butylene oxide, or combinations thereof.

[0057] In certain embodiments, the polyols that are used are polyether polyols that comprise propylene oxide ("PO"), ethylene oxide ("EO"), or a combination of PO and EO groups or moieties in the polymeric structure of the polyols. These PO and EO units may be arranged randomly or in block sections throughout the polymeric structure. In certain embodiments, the EO content of the polyol ranges from 0% to 100% by weight, based on the total weight of the polyol (for e.g., 0% to about 50% by weight, or about 50% to 100% by weight, based on the total weight of the polyol). In some embodiments, the PO content of the polyol ranges from 100% to 0% by weight based on the total weight of the polyol (for e.g., 100% to about 50% by weight or about 50% to 0% by weight, based on the total weight of the polyol). Accordingly, in some embodiments, the EO content of a polyol can range from about 99% to about 33% by weight of the polyol while the PO content can range from about 1% to 67% by weight of the polyol. In other embodiments, the PO content of the polyol can range from about 99% to about 33% by weight and the EO content can range from about 1% to about 67% by weight of the polyol. Moreover, in some embodiments, the EO and / or PO units can either be located terminally on the polymeric structure of the polyol or within the interior sections of the polymeric backbone structure of thepolyol. Suitable polyether polyols include poly(oxyethylene) diols obtained by the addition of ethylene oxide to di-functional initiators known in the art, poly(oxyproplylene) diols obtained by the addition of propylene oxide to di-functional initiators known in the art, and poly(oxyethylene) and poly(oxypropylene) diols obtained by the sequential addition of propylene and ethylene oxides to di-functional initiators that are known in the art.

[0058] The aforementioned polyether polyols also include the reaction products obtained by the polymerization of ethylene oxide with another cyclic oxide (for e.g., propylene oxide) in the presence of polyfunctional initiators such as water and low molecular weight polyols. Suitable low molecular weight polyols include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, cyclohexane dimethanol, resorcinol, bisphenol A, or combinations thereof.

[0059] In certain embodiments, the polyester diol or polyether diol is selected from polyethylene glycol, polypropylene glycol, polysucciniate, polyazealate, polysebbactae, polyadipate, polycarbonate, polycaprolactone, poly(l,3-propanediol) and polytetrahydrofuran (PTHF) or combinations thereof. In certain embodiments copolymers of the mentioned polyols can be used.

[0060] In certain embodiments, the polyols used are having at least two isocyanate reactive moieties per compound. For example, the polyol or mixture of polyols have a molecular weight ranging from 60 Daltons to 10,000 Daltons (for e.g., 300 Daltons to 10,000 Daltons or less than 5,000 Daltons), a nominal hydroxyl functionality of about 2, and a hydroxyl equivalent weight of 30 to 2000 (for e.g., 30 to 1,500 or 30 to 800).

[0061] In another embodiment, the polyol may include a polyester polyol. The polyester polyol includes polyesters having a linear polymeric structure and a number average molecular weight ranging from about 500 Daltons to about 10,000 Daltons (for e.g., preferably from about 700 Daltons to about 5,000 Daltons or about 700 Daltons to about 4,000 Daltons) and an acid number generally less than 1.3 (for e.g., less than 0.8). The molecular weight is determined by assay of the terminal functional groups and is related to the number average molecular weight. The polyester polymers can be produced using techniques known in the art such as: (1) an esterification reaction of one or more glycols with one or more dicarboxylic acids or anhydrides;or (2) a transesterification reaction (i.e., the reaction of one or more glycols with esters of dicarboxylic acids). Mole ratios generally in excess of more than one mole of glycol to acid are preferred so as to obtain linear polymeric chains having terminal hydroxyl groups. Suitable polyester polyols also include various lactones that are typically made from caprolactone and a bifunctional initiator such as diethylene glycol. The dicarboxylic acids of the desired polyester can be aliphatic, cycloaliphatic, aromatic, or combinations thereof. Suitable dicarboxylic acids which can be used alone or in mixtures generally have a total of from 4 to 15 carbon atoms include succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, dodecanedioic, isophthalic, terephthalic, cyclohexane dicarboxylic, or combinations thereof. Anhydrides of the aforementioned dicarboxylic acids (for e.g., phthalic anhydride, tetrahydrophthalic anhydride, or combinations thereof) can also be used. In some embodiments, adipic acid is the preferred acid. The glycols used to form suitable polyester polyols can include aliphatic and aromatic glycols having a total of from 2 to 12 carbon atoms. Examples of such glycols include ethylene glycol, 1,2- propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-l,3-propanediol, 1,4-cyclohexanedimethanol, decamethylene glycol, dodecamethylene glycol, or combinations thereof.

[0062] Further examples of suitable polyols include hydroxyl-terminated polythioethers, polyamides, polyesteramides, polycarbonates (for e.g., those described below), polyacetals, polyolefins, and polysiloxanes. In some embodiments, the polyol may be combined with another isocyanate reactive material such as, without limitation, a polyamine or polythiol.

[0063] In one embodiment, the amount of the polyol present in the first and second reaction mixtures, independently, may be at least about 30% by weight, or at least about 40% by weight, or at least about 50% by weight or at least about 60% by weight or at least about 70% by weight or at least about 80% by weight, based on the total weight of components in the particular reaction mixture above. In other embodiments the amount of polyol present in the particular reaction mixture is within a range of about 50% by weight to 95% by weight, or about 55% by weight to about 90% by weight, or about 60% by weight to about 85% by weight, based on the total weight of components in the particular reaction mixture above. In yet another embodiment, the amount of polyol present in the particular reaction mixture is less than 50% by weight, or lessthan about 45% by weight or less than about 40% by weight, based on the total weight of components in the particular reaction mixture above. In still other embodiments, the polyols in the particular reaction mixture may be the same while in other embodiments they may be different.

[0064] The reaction mixtures having an isocyanate index greater than 100% and less than 100% each, independently, also include a polyisocyanate (or an isocyanate component). Thus, in some embodiments, the polyisocyanate present in the reaction mixture having an isocyanate index greater than 100% and the polyisocyanate present in the reaction mixture having an isocyanate index less than 100% may be the same while in other embodiments they may be different.

[0065] According to one embodiment, the polyisocyanate (or an isocyanate component) is an aliphatic polyisocyanate or an aromatic polyisocyanate. Preferably, the isocyanate component is an aromatic polyisocyanate, preferably diphenylmethane diisocyanate.

[0066] Examples of aliphatic polyisocyanates include, but are not limited to, hexamethylene diisocyanate (HDI), tetraalkyl xylene diisocyanate, cyclohexane diisocyanate, 1,12-dodecane diisocyanate, 1,4-tetramethylene diisocyanate, 1,3- and 1,4-cyclohexane diisocyanate, l-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (isophorone diisocyanate), 4,4'-, 2,2'- and 2,4'-dicyclohexyl-methane diisocyanate, as well as the corresponding isomer mixtures.

[0067] Examples of aromatic polyisocyanates include but are not limited to, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'- or 2,4'- or 2,2'-diphenylmethane diisocyanate (MDI), polymethylene polyphenylene diisocyanate (mixtures of MDI and oligomers thereof known in the art as "crude" or polymeric MDI having an isocyanate functionality of greater than 2), 2,4- and 2,6-toluene diisocyanate (TDI), dianisidine diisocyanate, bitolylene diisocyanate, naphthalene- 1,4-diisocyanate and diphenylene 4,4'-diisocyanate.

[0068] Alternatively, semi-prepolymers or prepolymers formed from the reaction of a polyisocyanate (for e.g., MDI, modified MDI and / or p-MDI) with a polyhydric alcohol may also beemployed as the polyisocyanate. The polyhydric alcohol may be a polyether polyol, a polyester polyol, a polycarbonate polyol, a polycaprolactone polyol or other polyol which may be used either individually or in combinations of two or more. In addition, the polyhydric alcohol may be a copolymer of one or more of a polyether polyol, a polyester polyol, a polycarbonate polyol, a polycaprolactone polyol, or other polyol. In one embodiment, the polyhydric alcohol is a copolymer of a polyester polyol and a polycarbonate polyol.

[0069] Examples of polyether polyols include, but are not limited to, polyethylene glycol, polypropylene glycol, polypropylene glycol-ethylene glycol copolymer, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, and polyether polyols obtained by ring-opening co-polymerization of alkylene oxides, such as ethylene oxide and / or propylene oxide, with isocyanate-reactive initiators of functionality from 2 to 8. The isocyanate-reactive initiators include, but are not limited to, alcohols, glycols or high molecular weight polyether polyols.

[0070] Polyester polyols include, but are not limited to, those which may be obtained by reacting a diol and a polybasic acid. Examples of diols include ethylene glycol, polyethylene glycol, tetramethylene glycol, polytetramethylene glycol, 1,6-hexanediol, 3-methyl-l,5-pentanediol, 1,9- nonanediol and 2-methyl-l,8-octanediol. Examples of polybasic acids include phthalic acid, dimer acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, adipic acid and sebacic acid.

[0071] Examples of polycarbonate polyols include, but are not limited to, aliphatic polycarbonate diols, for example those based upon alkylene glycols, ether glycols, alicyclic glycols or mixtures thereof. In some embodiments, the alkylene groups for preparing the polycarbonate polyol can comprise from 5 to 10 carbon atoms and can be a straight chain, cycloalkylene or combinations thereof. Non-limiting examples of such alkylene groups include hexylene, octylene, decylene, cyclohexylene and cyclohexyldimethylene. The polycarbonate polyols can be prepared, in non-limiting examples, by reacting the alkylene glycol with a dialkyl carbonate, such as methyl, ethyl, n-propyl or n-butyl carbonate, or diaryl carbonate, such as diphenyl or dinaphthyl carbonate, or by reacting a hydroxy-terminated alkylene diol with phosgene or bischoloroformate, in a manner well known to those skilled in the art.

[0072] Polycaprolactone polyols include, but are not limited to, those prepared by condensing caprolactone in the presence of an initiator such as water, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, dipropylene glycol, 1,3-propylene glycol, polyethylene glycol, polypropylene glycol, poly(oxyethylene-oxypropylene)glycols and similar polyalkylene glycols, either blocked, capped or heteric containing up to about 40 or more alkyleneoxy units in the molecule, 3-methyl-l,5-pentanediol, cyclohexanediol, 4,4'-methylene- bis-cyclohexanol, 4,4'-isopropylidene bis-cyclohexanol, xylenediol, 2-(4- hydroxymethylphenyl)ethanol, 1,4- butanediol, glycerol, trimethylolpropane, 1,2,6-hexanetriol, triethanolamine, triisopropanolamine, erythritol, pentaerythritol and N,N,N',N'-tetrakis-(2- hydroxyethyl)ethylene diamine. The caprolactone reacted with the initiator can be caprolactone itself or a substituted caprolactone as described in US Pat. No. 3169945.

[0073] Examples of other polyols may include ethylene glycol, propanediols, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, cyclohexanedimethanol, polyoxyethylene bisphenol A ether, polyoxypropylene bisphenol A ether, polyoxyethylene bisphenol F ether, and polyoxypropylene bisphenol F ether.

[0074] In one embodiment, the polyisocyanate is a prepolymer having an NCO value from about 8% to about 31% or from about 12% to about 25%, or from about 16% to about 20% that is obtained from MDI, optionally uretonimine-modified and a polypropylene glycol (in some embodiments having a molecular weight from about 1500-2500 Daltons).

[0075] In one embodiment, the polyisocyanate is a prepolymer having an NCO value from about 8% to about 31% or from about 10% to about 25%, or from about 12% to about 20% that is obtained from MDI, optionally uretonimine-modified and a polypropylene glycol (in some embodiments having a molecular weight from about 1500-2500 Daltons).

[0076] In certain embodiments, the first or the second thermoplastic polyurethane material has an NCO value from about 0.001% to about 15% or from about 0.001% to about 10%, or from about 0.001% to about 5%, or from about 0.01% to about 5%, or from about 0.1% to about 5%, or from about 0.2% to about 5%, or from about 0.2% to about 3%, or from about 0.2% to about 1.5%

[0077] In certain embodiments, the first or the second thermoplastic polyurethane material has a hydroxyl value, expressed in mg KOH / g from about 0.1 to about 200, or from about 0.1 to about 100, or from about 0.1 to about 56, or from about 0.1 to about 25, or from about 0.1 to about 10, or from about 0.1 to about 5, or from about 0.2 to about 5, or from about 0.5 to about 5, or from about 1 to about 5, or from about 1.5 to about 5.

[0078] In certain embodiments, the first and / or the second thermoplastic polyurethane material is made using a catalyst. In some embodiments no catalyst is used / required. In some embodiments the level of catalyst is in the range of 0 wt% to 5 wt%. In some embodiment the level of catalyst is in the range of 1 to 10000 ppm, more preferably 20 to 2000 ppm, more preferably 50 to 1000 ppm, most preferably 100 to 600 ppm.

[0079] In some embodiments, the reaction mixtures each may optionally include a chain extender which may be the same or different in the reaction mixtures. Chain extenders are generally grouped as having a functionality equal to 2 and include diols, diamines, and combinations thereof. The chain extender may have a molecular weight of up to about 500 Daltons or up to about 300 Daltons, such as at least about 35-500 Daltons.

[0080] For example, one or more short chain polyols having from 2 to 20, or 2 to 12, or 2 to 10 or 2 to 8 carbon atoms may be used as chain extenders in the reaction mixture(s) to increase the molecular weight of the thermoplastic polyurethane. Examples of chain extenders include, but are not limited to, lower aliphatic polyols and short chain aromatic glycols having molecular weights of less than 500 Daltons or less than 300 Daltons. Suitable chain extenders include organic diols (including glycols) having a total of from 2 to about 20 carbon atoms such as alkane diols, cycloaliphatic diols, alkylaryl diols, and the like. Exemplary alkane diols include ethylene glycol, diethylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, (BDO), 1,5-pentanediol, 2,2-dimethyl-l,3-propanediol, propylene glycol, dipropylene glycol, 1,6-hexanediol, 1,7- heptanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, tripropylene glycol, triethylene glycol, and 3-methyl-l,5-pentanediol. Examples of suitable cycloaliphatic diols include 1,2- cyclopentanediol, and 1,4-cyclohexanedimethanol (CHDM). Examples of suitable aryl and alkylaryl diols include hydroquinone di(l,3-hydroxyethyl)ether (HQEE), 1,2-dihydroxybenzene,1,3-dihydroxybenzene, 1,4-dihydroxybenzene, 1,2,3-trihydroxybenzene, 1,2- di(hydroxymethyl)benzene, l,4-di(hydroxymethyl)benzene, l,3-di(2-hydroxyethyl)benzene, 1,2- di(2-hydroxyethoxy)benzene, l,4-di-(2-hydroxyethoxy)benzene, bisethoxy biphenol, 2,2-di(4- hydroxyphenyl)propane (i.e., bisphenol A), bisphenol A ethoxylates, bisphenol F ethoxylates, 4,4- isopropylidenediphenol, 2,2-di[4-(2-hydroxyethoxy)phenyl]propane (HEPP), and mixtures thereof.

[0081] In one embodiment, the amount of the chain extender present in the reaction mixture(s) may be in the range of about 0.1-20% by weight, based on the total weight of the polyol in the reaction mixture. In another embodiment, the amount of the chain extender present in the reaction mixture(s) may be in a range of about 0.5-12% by weight or about 1-10% by weight, based on the total weight of the polyol in the reaction mixture.

[0082] In still other embodiments, the reaction mixtures, independently, may optionally include one or more conventional auxiliaries, such as organo-metallic compounds (for e.g., organic salts of transition metals such as titanium, iron, nickel), post-transition metals (for e.g., zinc, tin, and bismuth), alkali metals (for e.g., lithium, sodium, and potassium), alkaline earth metals (for e.g., magnesium and calcium), silicates and fumed silicate or combinations thereof, surfactants, silane adhesion promoters, antioxidants, waxes, colorants, flame retardants, microbial inhibitors, fillers, viscosity reducers, carbon black, titanium dioxide, and metal flake infra-red opacifiers, inert and insoluble fluorinated compounds, and perfluorinated cell-size reducing compounds, calcium carbonate fillers, glass fibers and / or ground up foam waste reinforcing agents; zinc stearate, butylated hydroxy toluene antioxidants, dyestuffs and pigments.

[0083] When present, these additional auxiliaries may be used in an amount of about 0.01- 15% by weight, or about 0.1-10% by weight, or about 0.5-5% by weight, based on the total weight of the particular reaction mixture above. These ranges may apply separately to each additional auxiliary present in the reaction mixture or to the total of all additional auxiliaries present.

[0084] In some embodiments, each of the reaction mixtures, independently, may have a hydroxyl value in a range of about 150-700 mg KOH / g or about 200-600 mg KOH / g o about 350- 500 mg KOH / g.

[0085] In another embodiment, the first reaction mixture for producing the first thermoplastic polyurethane material may have an isocyanate index of greater than about 100%, or greater than about 101% or greater than about 105% or greater than about 107% or greater than about 110% or greater than about 115%. In other embodiments, the first reaction mixture for producing the first thermoplastic polyurethane material may have an isocyanate index of less than about 135% or less than about 120%. In still other embodiments, the first reaction mixture for producing the first thermoplastic polyurethane material may have an isocyanate index within a range of about 101-135%, or about 101-120%, or about 101-115%, or about 102-115%, or about 103-115%, or about 104-110%, or about 105-110%.

[0086] In another embodiment, the second reaction mixture for producing the second thermoplastic polyurethane material may have an isocyanate index of less than about 100%, or less than about 99.5%, or less than about 99%, or less than about 98%, or less than about 97% or less than about 95% or less than about 92% or less than about 90%. In still other embodiments, the second reaction mixture for producing the second thermoplastic polyurethane material may have an isocyanate index within a range of greater than about 90% and less than about 99.9% or within a range of about 92-98%. In one embodiment, the second reaction mixture has an isocyanate index within a range of about 90-99.5%, or about 92-99.5%, or about 93-99.5%, or about 94-99.5%, or about 94-99%, or about 94-98%, or about 95-98%.

[0087] In another embodiment, the present disclosure also provides a method for producing the thermoplastic polyurethane powder blend for use in producing a thermoplastically recyclable three-dimensional object, the method including the steps: providing the first and second thermoplastic polyurethane materials having first and second reactive groups; grinding, crushing, chopping, jet milling or any combination thereof the first and second thermoplastic polyurethane materials separately to form a first thermoplastic polyurethane powder material and a second thermoplastic polyurethane powder material, and blending the first thermoplastic polyurethane powder material with the second thermoplastic polyurethane powder material to form the thermoplastic polyurethane powder blend.

[0088] In one particular embodiment, the method includes: reacting the first reaction mixture having an isocyanate index greater than 100% to form a first thermoplastic polyurethane material; reacting the second reaction mixture having an isocyanate index less than 100% to form a second thermoplastic polyurethane material; grinding, crushing, chopping, jet milling or any combination thereof the first and second thermoplastic polyurethane materials separately to form a first thermoplastic polyurethane powder material and a second thermoplastic polyurethane powder material; and blending the first thermoplastic polyurethane powder material and the second thermoplastic polyurethane powder material to form the thermoplastic polyurethane powder blend. In one embodiment, the first reaction mixture comprises an isocyanate component and an isocyanate reactive component, and the second reaction mixture is different from the first reaction mixture and comprises an isocyanate component and an isocyanate reactive component. Note in the context of the present disclosure the term "grinding" includes grinding, crushing, chopping, jet milling or any combination thereof.

[0089] The above-mentioned first and second thermoplastic polyurethane materials are usually in pellet form after they have been produced and may be further processed separately (or in alternative embodiments together), such as by pulverization, preferably mechanically, at very low temperature (cryogenic comminution). For example, the first and second thermoplastic polyurethane materials may be produced (for e.g., in the form of blocks) and converted to pellets which may then be deep-frozen by use of liquid nitrogen or liquid air and ground in pin mills. The desired particle size may be set by means of a sieving machine arranged downstream of the mill. In some embodiments, the first thermoplastic polyurethane powder material may have a D5o particle diameter of less than about 100 pm or less than about 90 pm or less than about 85 pm or less than about 80 pm. In another embodiment, the second thermoplastic polyurethane powder material may have a D5o particle diameter of less than about 100 pm or less than about 90 pm or less than about 80 pm or less than about 70 pm.

[0090] In still another embodiment, the first thermoplastic polyurethane powder material may have a melting temperature of between about 90°-190°C or between about 95°-180°C. In another embodiment, the second thermoplastic polyurethane powder material may have a melting temperature of between about 170°-210°C or between about 175°-205°C.

[0091] As described above, the first and second polyurethane powder materials are combined to form the blend. The powder materials may be combined using mechanical mixing, pneumatic mixing, or any other suitable mixing technique. In one embodiment, the first and second thermoplastic polyurethane powder materials may be combined at a weight ratio (first thermoplastic polyurethane powder materiaksecond thermoplastic polyurethane powder material) of about 10:90 to about 90:10, or about 20:80 to about 80:20, or about 30:70 to about 70:30 or about 40:60 to about 60:40 or about 50:50. In still other embodiments, the first and second thermoplastic polyurethane powder materials may be combined at a weight ratio (first thermoplastic polyurethane powder materiaksecond thermoplastic polyurethane powder material) of about 50:50 to about 90:10. In other embodiments, the first and second thermoplastic polyurethane powder materials may be combined at a weight ratio (first thermoplastic polyurethane powder materiaksecond thermoplastic polyurethane powder material) of about 50:50 to about 10:90.

[0092] The thermoplastic polyurethane powder blend of the present disclosure may optionally contain a flow agent. In particular, the thermoplastic polyurethane powder blend of the present disclosure may contain 0% by weight, or about 0.05% by weight to about 5% by weight, or about 0.075% by weight to about 1% by weight of the thermoplastic polyurethane powder blend, of a flow agent. In other embodiments, the thermoplastic polyurethane powder blend may contain about 0.1% by weight to about 0.25% by weight, based on the total weight of the thermoplastic polyurethane powder blend, of a flow agent. The flow agent preferably is present in an amount sufficient to allow the blend to flow and level on a build surface of a laser sintering device.

[0093] The optional flow agent included in the thermoplastic polyurethane powder blend may be a particulate inorganic material and may have a median particle size of 10 microns or less. Preferred flow agents may be selected from hydrated silicon dioxides, hydrophobicized pyrogenic silicas, amorphous aluminum oxide, vitreous silicon dioxides, vitreous phosphates, vitreous borates, vitreous oxides, titanium dioxide, talc, mica, pyrogenic silicon dioxides, kaolin, attapulgite, calcium silicates, calcium stearates, aluminum oxide, magnesium silicates and combinations thereof. The preferred flow agent is a fumed silica.

[0094] The thermoplastic polyurethane powder blend may also contain other optional ingredients. These ingredients may be particulate materials and include organic and inorganic materials, such as fillers, pigments and coloring agents. An ingredient may be present in a sufficient amount to perform its intended function, without adversely affecting the blend or a three-dimensional object prepared therefrom. Optional ingredients may have a particle size in the range of the particle sizes of the first and second thermoplastic polyurethane powder materials and / or optional flow agent. Each optional ingredient may be milled, if necessary, to the desired particle size or particle size distribution.

[0095] Each individual optional ingredient, if present at all, is typically added to the thermoplastic polyurethane powder blend in an amount of about 0.1% by weight to about 30% by weight, based on the total weight of the thermoplastic polyurethane powder blend. The total amount of optional ingredients in the thermoplastic polyurethane powder blend may range from 0% by weight up to about 30% by weight, based on the total weight of the thermoplastic polyurethane powder blend.

[0096] The optional flow agent and ingredient(s) may be blended with the blend of the first and second thermoplastic polyurethane powder materials, in any order, using mechanical mixing, pneumatic mixing, or any other suitable mixing technique until a uniform blend containing discrete particles of each component present results. After blending, the resulting thermoplastic polyurethane powder blend may be sieved to provide a desired particle size.

[0097] Furthermore, it should be noted that each component described above of the thermoplastic polyurethane powder blend may be dry, i.e., contains a minimal amount of moisture, typically 2%, by weight, or less, or 1.5% by weight or less, or 1% by weight or less, based on the total weight of the component.

[0098] The thermoplastic polyurethane powder blend of the present disclosure may be used to form a variety of three-dimensional objects for use in a variety of applications, including, for example, rapid prototyping and rapid manufacturing. Some examples of rapid manufacturing applications include small production run products (for e.g., where production by means of an injection mold is not economical or technically feasible) such as, for example, parts for high-specification cars of which only small numbers are produced, replacement parts for motorsports or aerospace industries, and high-specification fashion items such as spectacle frames; and production of similar but individual components manufactured in relatively large numbers such as, for example, hearing aid components. Examples of industrial sectors that may benefit from objects of the present disclosure include the aerospace industry, medical technology, mechanical engineering, automobile construction, the sports industry, the household goods industry, the electrical industry, the packaging industry, and lifestyle products.

[0099] In some embodiments, the thermoplastic polyurethane powder blends of the present disclosure are capable of forming three-dimensional objects that can withstand elevated temperature environments while still exhibiting one or more suitable mechanical properties. Examples of three-dimensional objects that may require such properties include automotive parts (for e.g., engine parts and other parts in close proximity to an engine); fuel system parts; household appliance parts that require heat resistance (for e.g., dishwasher parts and oven parts); molds for forming molded articles from heated materials; hydraulic parts for contacting heated liquids; intake manifolds (for e.g., hot air intakes and aspiration ducts); lighting system parts; and parts or articles in other applications that may be required to perform in elevated temperature environments (for e.g., aerospace, motorsport, design, electronics, industrial, and packaging applications).

[0100] Any additive process may be used to produce three-dimensional objects from the thermoplastic polyurethane powder blend including, but not limited to, selective laser sintering, high-speed sintering and multijet fusion.

[0101] Thus, in another embodiment, there is provided a process for the producing a three- dimensional object including the steps of:(a) depositing a quantity of the thermoplastic polyurethane powder blend on a support surface to form a layer of the thermoplastic polyurethane powder blend;(b) melting the layer of the thermoplastic polyurethane powder blend to form an integral layer;(c) depositing another quantity of the thermoplastic polyurethane powder blend on the integral layer to form a layer of the thermoplastic polyurethane powder blend;(d) melting the layer of the thermoplastic polyurethane powder blend formed in step (c) to form an additional layer that is bonded to the adjacent integral layer formed in step (b), wherein the additional layer and the adjacent integral layer combine to form the integral layer; and(e) repeating steps (c) and (d), as required, to form the thermoplastically recyclable three- dimensional object.

[0102] In one embodiment, the melting of the layer of the thermoplastic polyurethane powder blend in steps (b) and / or (d) is performed by directing an energy beam over a predetermined target area on the support surface.

[0103] In other embodiments, the three-dimensional objects from the thermoplastic polyurethane powder blend may have an isotropic index of the x / z and / or y / z for tensile strength and / or elongation which is larger than 30%, more preferably larger than 35%, more preferably larger than 40%, more preferably larger than 45%, more preferably larger than 50%, more preferably larger than 55%, more preferably larger than 60%, more preferably larger than 65%, more preferably larger than 70%, more preferably larger than 75%, more preferably larger than 80%, more preferably larger than 85%, more preferably larger than 87%, more preferably larger than 90%, more preferably larger than 92%, more preferably larger than 95%. The tensile strength (TS) or elongation (E) is measured according to DIN 53504 with a test speed of 100 mm / min using an S2-dogbone. The isotropic index, as calculated in the formula below, is presented as a %, can be calculated for Tensile strength (TS) or elongation (E) by filling in the respective values for samples with 2 different orientations in the print bed (e.g. for the x and z direction and / or for the y and z direction). 100

[0104] There is no specific limit to the support surface the thermoplastic polyurethane powder blend can be placed on. The support surface can be selected for a particular application. For example, the support surface may initially be a board or a base plate and subsequent layers of deposited blend. The surface on which the thermoplastic polyurethane powder blend is placed can be smooth, coarse, plane, or a curved plane.

[0105] The deposited thermoplastic polyurethane powder blend can be cured upon application of an energy beam, such as a laser beam or electron beam. Thus, during the process, the thermoplastic polyurethane powder blend (i.e., the top layer) may be deposited on a thin layered cured material (i.e., the bottom layer). The energy beam is applied over a predetermined target area to again cure the top layer. This curing occurs not only to the top layer but also to the interface with the bottom layer.

[0106] In a typical process, after one implementation of the steps (a) - (b) the support surface is lowered, and a new layer is deposited. A typical process uses layer-by-layer melting and hardening of the powder particles (sintering) to produce the integrally bonded layers of three- dimensional object.

[0107] Examples of devices suitable for selective laser sintering and for related additive manufacturing processes are Formiga P 110, EOS P 396, EOSINT P 760 and EOSINT P 800 (EOS GmbH), 251P and 402P (Hunan Farsoon High-tech Co., Ltd), ProX SLS 500, sPro 140, sPro 230 and sPro 60 (3D Systems Corporation), M3 (Blueprinter) and Jet Fusion 3D (Hewlett Packard Inc.), SnowWhite printer (Sharebot SRL) and the Fuse series printers (Formlabs Inc.). In the case of the M3 (Blueprinter) and Jet Fusion 3D (Hewlett Packard Inc.) devices, the localized melting is achieved with the aid of infrared radiation.

[0108] Non-limiting embodiments:

[0109] In one embodiment, there is provided a thermoplastic polyurethane powder blend for use in producing a thermoplastically recyclable three-dimensional object, the powder blend comprising a first thermoplastic polyurethane material having a first reactive group and a number average functionality of about 1.8 to about 2.4 and a second thermoplastic polyurethane materialhaving a second reactive group and a number average functionality of about 1.8 to about 2.4, wherein the first reactive group is different from the second reactive group, and wherein the first reactive group and the second reactive group are capable of chemically reacting with each other to form a covalent bond.

[0110] In one embodiment, there is provided a thermoplastic polyurethane powder blend for use in producing a thermoplastically recyclable three-dimensional object, the powder blend comprising a first thermoplastic polyurethane material having a first reactive group and a number average functionality of about 1.8 to about 2.4 and a second thermoplastic polyurethane material having a second reactive group and a number average functionality of about 1.8 to about 2.4, wherein the first reactive group is different from the second reactive group, wherein the first thermoplastic polyurethane material is obtained from the reaction of a first reaction mixture having an isocyanate index of greater than 100% and the second thermoplastic polyurethane material is obtained from the reaction of a second reaction mixture having an isocyanate index less than 100%, wherein the first reaction mixture comprises an isocyanate component and an isocyanate reactive component, and wherein the second reaction mixture is different from the first reaction mixture and comprises an isocyanate component and an isocyanate reactive component.

[0111] In one embodiment, there is provided a thermoplastic polyurethane powder blend for use in producing a thermoplastically recyclable three-dimensional object, the powder blend comprising a first thermoplastic polyurethane material having a first reactive group and a number average functionality of about 1.8 to about 2.4 and a second thermoplastic polyurethane material having a second reactive group and a number average functionality of about 1.8 to about 2.4, wherein the first reactive group is different from the second reactive group, wherein the first thermoplastic polyurethane material is obtained from the reaction of a first reaction mixture having an isocyanate index of greater than 100% and the second thermoplastic polyurethane material is obtained from the reaction of a second reaction mixture having an isocyanate index less than 100%, wherein the first reaction mixture comprises an isocyanate component and an isocyanate reactive component, and wherein the second reaction mixture is different from the first reaction mixture and comprises an isocyanate component and an isocyanate reactivecomponent, and wherein the first reactive group is an isocyanate group and the second reactive group is an isocyanate reactive group, preferably wherein the isocyanate reactive group is a hydroxyl group.ExamplesTable 1 - Chemicals used

[0112] A polyol pre-blend is prepared by the addition of 83 pbw Irophen® 28-50, 16 pbw butanediol and 1 pbw Irganox® 1010 and mixing them at 85°C.

[0113] All TPUs are produced on a Kraus-Maffei Extruder ZE 25 extruder with a diameter of 25 mm. The temperatures used on the extruder are set between 170-210°C for the different heating zones. The water bath temperature after the extruder is set to 25°C. The catalyst mixture is dosed separately at a level of for example 0.6 w% based on the full TPU composition to obtain a level of 600 ppm of active catalyst ingredient. The level of catalyst is adjusted based on the reactivity of the mixture and should be taken into account during the production.

[0114] TPU1 is prepared by mixing the polyol pre-blend (containing Irophen® 28-50, butanediol and Irganox® 1010) together with Suprasec® 1308 and the described catalyst level at an index of 100%. TPU2 is prepared similarly at an index of 112 %, while TPU3 is prepared at an index of 99 %. The indexes of the different TPU materials are based on the theoretically calculated index using the measured isocyanate value (NCOv) and hydroxyl-value (OHv) of the specific material batches used in the experiment. The number average functionality of each of TPU1, TPU2 and TPU3 is 2.

[0115] The molecular weight of the different TPUs is measured on a Waters gel permeation chromatograph (GPC) equipped with Model 2414 refractive index detector held at 40°C. The GPC conditions may be a temperature of 40°C, a column set of Phenogel Guard + 2x mixed D (5u), 300 x 7.5 mm, a mobile phase of tetrahydrofuran (THF) stabilized with 250 ppm butylated hydroxytoluene, a flow rate of 1.0 ml / min, an injection volume of 50 ml, sample concentration about 0.12%, and data acquisition using Waters Empower Pro Software. A small amount, typically approximately 0.05 gram of polymer, is dissolved in 20 ml of stabilized HPLC-grade THF, filtered through a 0.45-micron polytetrafluoroethylene disposable filter (Whatman), and injected into the GPC. The molecular weight calibration curve may be established with EasiCal® polystyrene standards from Polymer Laboratories.

[0116] The melting temperature of the different TPUs is determined by the onset temperature of the endothermic peak in using differential scanning calorimetry (DSC) in accordance with ISO 11357 (taking only the first heating run into account and using a heating rate of 10 K / min) and is expressed in °C.

[0117] The cryogenic grinding of the different TPU materials is performed using a pin mill equipped with a 100 pm screen using liquid nitrogen to cool down the TPU pellets. The grinding yield / speed is determined in kg / h and an overall efficiency is presented (low-medium-high). The particle size distribution of the obtained TPU powders is determined using a Malvern Mastersizer 3000 Laser Diffraction Spectrometer.Table 2 - TPU materials with properties and their respective powder particle size:

[0118] Before the TPU powder is used in the 3D powder printer, a flow additive is added to improve the powder flow. The flow additive, fumed silica AEROSIL® 200 (obtained from Evonik), is added to the respective TPU powder at a 0.1 w% concentration and is thoroughly homogenized with the TPU powder.Table 3 - Examples and their TPU powder composition

[0119] 3D printing procedure: The test specimens were printed using a Sharebot SnowWhite SLS printer ("SnowWhite") which is equipped with a 14-watt CO2 laser to sinter thermoplastic powder layer by layer. The laser selectively melts the powder material in a layer- by-layer fashion to obtain the desired object which was initially designed by a computer-aided- design (CAD) model. After the scanning or melting of the first layer, the print bed is lowered (by the required layer height) and a recoater (via roll / scraper) brings in a new layer of powder which can be molten by the laser.Table 4 - SnowWhite SLS printer settings

[0120] During the 3D printing the achieved powder temperature is about 136°C and the printer is exposed to standard air (no gas purging used). The hatching distance between two laser scanned lines is set at 0.1 mm using slic3r slicing software.

[0121] The file printed during the test is shown in figure 1 and contains a series of differentS2-type dogbones for tensile testing (according to DIN 53504) which are oriented in different directions. Dogbone types A, D and F are shown in figure 1.Table 5 - Description of 3D print specimen orientation

[0122] The different dogbones are digitally labelled on the printed part (A, D, F type) to ensure that they are correctly identified after unpacking the printed parts from the powder bed. Five S-2 type dogbones are tested using an Instron equipment according to DIN 53504 with a test speed of 100 mm / min. The actual printed dimensions of the S-2 type dogbones are taken into account to ensure the tensile strength of the printed part is not over or underestimated versus the digital print file (3D design dimensions). The average of the result of the tensile strength (kPa) and elongation (%) of the tested material is presented in table 6. The level of isotropy in the 3D printed part can be determined by calculating the isotropic index. The isotropic tensile strength index is calculated by taking the ratio of tensile strength of dogbones from the A-type / F-type and D-type / F-type as presented in the table. Similarly the isotropic elongation index is calculated by taking the ratio of elongation of dogbones from the A-type / F-type and D-type / F-type as presented in table 6.

[0123] The level of isotropy in the 3D printed part can be determined by calculating the isotropic index as shown in formula: 100

[0124] The isotropic index, presented as a %, can be calculated for Tensile strength (TS) or elongation (E) by filling in the respective values for samples with 2 different orientations in the print bed, e.g. x, y or z (XI and X2 are both values of TS or both values of E). An Isotropic index of 100% means XI = X2 (perfectly isotropic) and the closer to 0, the larger the difference between XI and X2 (anisotropic). To take into account a correction for extremely low values (e.g. poorly sintered parts where XI and X2 could have very low values), the term X1+X2 is introduced. The isotropic tensile strength index is thus calculated by taking the absolute value of the difference in tensile strength (e.g. between A-type / F-type or D-type / F-type dogbone) and dividing it by the sum of the tensile strengths, and then converting it into a percentage. A similar equation can be used to calculate the isotropic index for elongation. The calculated isotropic TS index and EL index is calculated for both the A-type / F-type and the D-type / F-type as presented in table 6.Table 6 - Material performance for different specimen orientations

[0125] Results clearly show that materials CE-1, CE-2, and CE-3 are anisotropic, with at least one of the isotropic TS and EL indexes below 65% (CE1 and CE-2) or even below 35% (CE3). The materials according to the invention show a remarkably high isotropy, with all the isotropic TS and EL indexes above 75% (E-2) or even above 90% (E-l). Additionally the elongation of all the A, D and F type dogbones is > 200% for examples E-l and E-2, an incredibly useful feature for elastomeric applications. Surprisingly, it has also been found that the TPU base materials according to the invention (TPU2 and TPU3, used to make E-l and E-2) have a significantly higher grinding yield / speed compared to TPU1 which was used to made CE-1 (shown in table 2). The invention thus enables to combine features of high isotropy, high performance, and high grinding productivity (during the powderization step).

[0126] The good thermoplastic recyclability of the 3D printed parts made from all examples (CE-1, CE-2, CE-3, El and E-2) was confirmed via compression moulding using a Fontijne Lab-press TP400 at a temperature of 180°C for 3 x 3 minutes using a pressure of 50 kN. This demonstrates that the prepared material remains thermoplastic and can be recycled and re-used in an identical application (after grinding, re-using the powder for 3D powder printing) or in different applications (full dense, foam, thin film, injection moulding, or extrusion).

[0127] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

Claims:

1. A thermoplastic polyurethane powder blend for use in producing a thermoplastically recyclable three-dimensional object, the powder blend comprising a first thermoplastic polyurethane material having a first reactive group and a number average functionality of about 1.8 to about 2.4 and a second thermoplastic polyurethane material having a second reactive group and a number average functionality of about 1.8 to about 2.4, wherein the first reactive group is different from the second reactive group.

2. The thermoplastic polyurethane powder blend of claim 1, wherein the first reactive group and the second reactive group are capable of chemically reacting with each other to form a covalent bond.

3. The thermoplastic polyurethane powder blend of claim 1 or claim 2, wherein the first reactive group is selected from an epoxy group, an isocyanate group, carboxylic acid group and a (cyclic) carbonate group, and the second reactive group is selected from a hydroxyl group, a primary amine group, a secondary amine group, a carboxylic acid group and a thiol group.

4. The thermoplastic polyurethane powder blend of any preceding claim, wherein first reactive group is an isocyanate group and the second reactive group is an isocyanate reactive group, preferably wherein the isocyanate reactive group is selected from a hydroxyl group, a primary amine group, a secondary amine group, a carboxylic acid group and a thiol group, most preferably wherein the isocyanate reactive group is a hydroxyl group.

5. The thermoplastic polyurethane powder blend of any preceding claim, wherein the first thermoplastic polyurethane material and / or second thermoplastic polyurethane material has a number average functionality of about 1.85 to about 2.2, preferably about 1.95 to about 2.02.

6. The thermoplastic polyurethane powder blend of any preceding claim, wherein the first thermoplastic polyurethane material and / or the second thermoplastic polyurethane material has a number average molecular weight of about 500 to about 500 000 g / mol as determined by gel permeation chromatography with a polystyrene standard as a reference, preferably about 10 000 to about 100 000 g / mol, and / or wherein the first thermoplastic polyurethane material and the second thermoplastic polyurethane material have a difference in melting temperature, as determined using differential scanningcalorimetry in accordance with ISO 11357 taking only the first heating run into account and using a heating rate of 10 K / min, of less than about 100°C, preferably less than about 20°C.

7. The thermoplastic polyurethane powder blend of any preceding claim, wherein the first thermoplastic polyurethane material and the second thermoplastic polyurethane material are used in a weight ratio that ranges from about 200:1 to about 1:200, preferably from about 95:5 to about 5:95.

8. The thermoplastic polyurethane powder blend of any preceding claim, wherein the first thermoplastic polyurethane material and the second thermoplastic polyurethane material are combined in an amount such that that the molar equivalents of the first reactive group and the second reactive group are present in a ratio ranging from about 200:1 to about 1:200, preferably from about 80:20 to about 20:80.

9. The thermoplastic polyurethane powder blend of any preceding claim, wherein the first thermoplastic polyurethane material is obtained from the reaction of a first reaction mixture having an isocyanate index of greater than 100% and the second thermoplastic polyurethane material is obtained from the reaction of a second reaction mixture having an isocyanate index less than 100%, wherein the first reaction mixture comprises an isocyanate component and an isocyanate reactive component, and wherein the second reaction mixture is different from the first reaction mixture and comprises an isocyanate component and an isocyanate reactive component.

10. The thermoplastic polyurethane powder blend of claim 9, wherein the first reaction mixture has an isocyanate index within a range of about 101-135%, preferably about 101-115%, and / or wherein the second reaction mixture has an isocyanate index within a range of about 90-99.5%, preferably about 94-99%.

11. The thermoplastic polyurethane powder blend of claim 9 or claim 10, wherein the isocyanate component in both the first and second reaction mixtures is independently selected from an aliphatic polyisocyanate, an aromatic polyisocyanate and a mixture thereof.

12. A method for producing a thermoplastic polyurethane powder blend for use in producing a thermoplastically recyclable three-dimensional object, the method comprising the steps: reacting a first reaction mixture having an isocyanate index greater than 100% to form a first thermoplastic polyurethane material;reacting a second reaction mixture having an isocyanate index less than 100% to form a second thermoplastic polyurethane material; grinding the first and second thermoplastic polyurethane materials separately to form a first thermoplastic polyurethane powder material and a second thermoplastic polyurethane powder material; and blending the first thermoplastic polyurethane powder material and the second thermoplastic polyurethane powder material to form the thermoplastic polyurethane powder blend, preferably wherein the first reaction mixture comprises an isocyanate component and an isocyanate reactive component, and wherein the second reaction mixture is different from the first reaction mixture and comprises an isocyanate component and an isocyanate reactive component.

13. A method for producing a thermoplastically recyclable three-dimensional object comprising the steps:(a) depositing a quantity of the thermoplastic polyurethane powder blend of any of claims 1- 11 on a support surface to form a layer of the thermoplastic polyurethane powder blend;(b) melting the layer of the thermoplastic polyurethane powder blend to form an integral layer;(c) depositing another quantity of the thermoplastic polyurethane powder blend of any of claims 1-11 on the integral layer to form a layer of the thermoplastic polyurethane powder blend;(d) melting the layer of the thermoplastic polyurethane powder blend formed in step (c) to form an additional layer that is bonded to the adjacent integral layer formed in step (b), wherein the additional layer and the adjacent integral layer combine to form the integral layer; and(e) repeating steps (c) and (d), as required, to form the thermoplastically recyclable three- dimensional object, preferably wherein the melting of the layer of the thermoplastic polyurethane powder blend in steps (b) and / or (d) is performed by directing an energy beam over a predetermined target area on the support surface.

14. A thermoplastically recyclable three-dimensional object produced according to the method of claim 13.

15. Use of the thermoplastic polyurethane powder blend as defined in Claims 1-11 in producing a thermoplastically recyclable three-dimensional object.

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