Precipitated polyether block amides and thermoplastic polyethylene to enhance the operating window for 3D printing

Abstract

Polymer materials suitable for 3D printing include at least one of polyether block amides, thermoplastic polyurethanes, and thermoplastic olefins. The polymer is a precipitated powder polymer formed by chemical precipitation, the precipitated powder polymer having enhanced operating window characteristics selected from at least one of the following: a wider range than the typical range between melting and recrystallization temperatures, a larger enthalpy at melting, and a lower volume change during recrystallization.

Description

[0001] Divisional application

[0002] This invention is a divisional application of Chinese Patent Application No. 201780078141.7, filed on October 17, 2017, entitled "Precipitated polyether block amide and thermoplastic polyethylene to enhance the operating window for 3D printing". Technical Field

[0003] This invention relates to materials for additive manufacturing and methods for preparing them, and more specifically, to precipitated powdered polyether block amides (PEBA), thermoplastic olefins (TPO), and thermoplastic polyurethanes (TPU) having an extended operating window for additive manufacturing applications. Background Technology

[0004] Additive manufacturing, commonly known as 3D printing, represents a significant advancement not only in printing technology but also in product development, prototyping, and experimentation capabilities. The capabilities of 3D printing include forming physical objects of virtually any geometry. As a non-limiting example, gears, sprockets, toys, models, prototypes, and countless other physical objects can now be built using 3D printers.

[0005] Typically, the object to be built is first created as a 3D digital model image. This model image can be essentially created using general-purpose computer-aided design (CAD) software. The object model is then "sliced" into thin layers, ultimately containing instructions on how to physically build the model using a 3D printer. This virtual "slicing" is necessary because traditional 3D printing methods involve a print head that continuously deposits material into thin layers based on the geometry of the model image, according to printing instructions for each layer. The physical object is then produced by depositing successive layers of material one on top of the other, from bottom to top, according to the layer instructions. The print head can deposit heated material while moving along multiple linear directions, while the base moves in three dimensions. The print head continues to deposit material until it reaches the top or last layer of the object, thus fully forming the object.

[0006] Many powder-based 3D printing methods have been developed. Selective laser sintering (SLS) is a 3D printing technique that uses a laser to melt powder material onto a continuous series of layers, based on the geometry of the 3D model. High-speed sintering (HSS) and multi-jet fusion (MJF) 3D printing employ multiple jets, similarly depositing layers of IR-absorbing ink onto the powder material sequentially, then exposing it to IR energy to selectively melt these powder layers. Electrophotographic 3D printing uses rotating photoconductors to build objects layer by layer from a substrate.

[0007] SLS, MJF, and HSS 3D printing share the same type of free-floating, non-fixed powder bed used to produce objects. Because the free-body diagrams of the attached build objects will apply the same stresses, they share the same material requirements in terms of compatibility with the printing processes, using only different heating mechanisms to obtain the molten phase. The free-body diagram of the 3D printed object can be used to determine the expected residual stresses in the object. This is necessary for successful object construction. If the residual stresses are too high, the object will deform into the printing area and be displaced within the part bed by printing processes such as powder deposition blades or rollers.

[0008] Existing technologies have identified numerous methods for addressing residual stress. Generally, to achieve the lowest possible amount of residual stress in a free-floating powder bed, both the modulus and volume change of the molten phase should be appropriately low. This prevents the selectively molten region from generating sufficiently large residual stresses within the object as it leaves the build plane. The most common approach to addressing residual stress in these powder beds for 3D printers is to use polymers with a sufficiently large operating window between their melting and recrystallization temperatures. Therefore, maintaining a low modulus and non-crystallization in the molten region minimizes large strains until the entire object is built. Unfortunately, few polymers possess a sufficiently wide window between these two phase transitions to allow SLS and MJF processes to build objects with sufficiently low residual stress.

[0009] Therefore, the width of the operating window is an important process parameter when selecting 3D printing materials. Suitable polymer physical characteristics include a melt temperature above its recrystallization temperature and suitability for effective localized melting.

[0010] Preferably, the operating window should allow the selectively molten polymer to have a sufficiently low modulus to prevent problematic residual stresses in the printed object while cooling to the part bed temperature. Furthermore, no crystal formation is observed at the part bed temperature. Preferably, the window should allow the polymer to melt effectively at a sufficiently low modulus to prevent residual stresses from being introduced into the printed object during cooling. If this is achieved, there is no substantial volume change in the object throughout the recrystallization temperature until the entire object is constructed. If the polymer's operating window is too small, stress accumulation occurs partially because the polymer shrinks during construction.

[0011] Therefore, the gap temperature between the polymer's melting point and recrystallization temperature forms a suitable operating window to better allow polymer printing in SLS, HSS, and MJF 3D printing systems. To expand the range of usable materials in these printing systems, the physical properties of the polymer, as well as processes that may alter these properties and extend the operating window, must be considered.

[0012] Other polymers, such as thermoplastic elastomers (TPEs), can exhibit sufficiently low moduli that, when operated outside the typical operating window, do not result in part build failure but rather in higher-than-desirable porosity. That is, a higher melting point, larger and / or more crystals, and a lower recrystallization temperature are still required. This is because a higher melting point will result in a higher part bed temperature, producing larger and / or more crystals to prevent unwanted growth in the part bed (i.e., when the powder near the selectively melting polymer also melts), and a lower recrystallization temperature. Summary of the Invention

[0013] The disclosed exemplary apparatus, systems, and methods provide an enhanced operating window for 3D printing applications such as SLS, MJF, HSS, and electrophotography, formed by chemical precipitation of powdered polyether block amides, thermoplastic polyurethanes, and / or thermoplastic olefins. One embodiment of the invention enables the provision of a precipitated powdered polymer formed by precipitating the polymer in a solvent, allowing the polymer to crystallize, and then using the precipitated powdered polymer in a powder-based 3D printing process.

[0014] Polymer materials suitable for 3D printing may include at least one polymer selected from the group consisting of polyether block amides, thermoplastic polyurethanes, and thermoplastic olefins. The at least one polymer is chemically precipitated to form a precipitated powder polymer, which is characterized by an enhanced operating window. This characteristic is selected from at least one of the following: a wider range than the typical range between melting and recrystallization temperatures, a larger enthalpy at melting, and a lower volume change during recrystallization.

[0015] In the above and other exemplary embodiments, the polymer material may further include: a granular geometry not formed by grinding (including cryogenic grinding), features of an enhanced operating window for 3D printing applications such as selective laser sintering, multi-jet fusion, or high-speed sintering, a precipitated powdered polymer having a melt temperature above its recrystallization temperature and melt characteristics suitable for effective local melting, sinterable properties ranging from about room temperature to below about 150 degrees Celsius, and a particle size range of about 25 micrometers to about 75 micrometers prepared by chemical precipitation.

[0016] Another exemplary embodiment of the present invention may include a powdered polymer precipitated by one or more of the following: a first precipitation method comprising: mixing one or more of the polymers into a solution of toluene and eicosapentaenoic acid to form a composition; adding a stabilizer to the composition; stirring the composition; heating the composition to boiling; boiling off the eicosapentaenoic acid from the composition; and drying the precipitated polymer powder; a second precipitation method comprising: dissolving one or more of the polymers in ethanol to form a composition; heating the composition; and precipitating the polymer into a crystalline powder; a third precipitation method comprising: melting one or more of the polymers in nitrogen in an autoclave, and heating the contents of the autoclave to a temperature above 200 degrees Celsius; increasing the pressure of the autoclave; and maintaining... The pressure in the autoclave, while heating the contents to above 250 degrees Celsius; reducing the pressure in the autoclave while maintaining nitrogen; and drying any resulting polymer powder; a fourth precipitation method, comprising: adding one or more of the polymers to a container containing ethanol denatured with 2-butanone and about 1% water to form a composition; heating the composition to above 130 degrees Celsius for about 1 hour; cooling the composition; and removing the ethanol by distillation; a fifth precipitation method, comprising: reacting one or more of the polymers with laurolactam, 1,12-dodecanoic acid, water, and an aqueous solution of hypophosphite. The following steps are performed: mixing hypophosphorous acid to form a composition; heating the composition in an autoclave; maintaining the autogenous pressure from the composition in the autoclave; stirring the composition in the autoclave; reducing the pressure of the autoclave to atmospheric pressure; and passing the composition through nitrogen gas; and a sixth precipitation method comprising: adding one or more of the polymers to a tank; heating the polymers to above 140 degrees Celsius; stirring the polymers in the tank; adding ethanol denatured with 2-butanone and water to the tank to form a composition; maintaining the composition at an elevated temperature for a period of time; reducing the heat; removing the ethanol by distillation while stirring the composition; and drying the composition.

[0017] Another exemplary embodiment of the present invention provides one or more polymeric materials suitable for 3D printing, comprising at least one or more of the following features: the one or more polymers are one or more of polyether block amides, thermoplastic polyurethanes, and / or thermoplastic olefins; the one or more polymers are any polyether block amides prepared by a polycondensation reaction of a carboxylic acid polyamide and an alcohol-terminated polyether; the one or more polymers are any thermoplastic plastics or thermoplastic polyurethanes comprising linear block polymers; the one or more polymers are any mixture of polyether block amides, thermoplastic polyurethanes, and / or thermoplastic olefins; the one or more polymers are formed by chemical precipitation; the one or more polymers are... The polymer is a precipitated powder; the particle geometry of the one or more polymers is formed by chemical precipitation; the particle geometry of the one or more polymers is not formed by grinding (including cryogenic grinding); the one or more polymers are precipitated powders with an enhanced operating window, suitable for selective laser sintering, multi-jet melting, high-speed sintering, and possibly electrophotographic 3D printing applications; the precipitated powders have an enhanced operating window feature including at least one of the following: a wider range than the typical range between melting and recrystallization temperatures for a given polymer, a larger enthalpy at melting, and a lower volume change during recrystallization; the precipitated powders The precipitated polymer comprises a melting temperature above its recrystallization temperature and melting characteristics suitable for effective local melting; the precipitated powdered polymer includes a feature that allows the operating window to retain a portion of material unmelted and in solid form during 3D printing, when heated by using an IR heater, in the presence of a laser or in the vicinity of selectively deposited melt, so that the unmelted solid material can serve as a support structure for any molten polymer; the precipitated powdered polymer comprises particles that soften at low temperatures but do not fuse together before being directly exposed to a heat source (e.g., a laser or IR heater); the precipitated powdered polymer is capable of sintering at approximately room temperature to approximately 150 degrees Celsius; the precipitated The powdered polymer does not undergo thermal degradation during printing; the precipitated powdered polymer produced through chemical precipitation has more stable and printable particle size and geometry, spherical geometry, less flow agent required, particle size control, and a tighter distribution of particle geometry; the precipitated powdered polymer produced through chemical precipitation has an optimal particle size and geometry range to balance cohesion and object detail; the precipitated powdered polymer produced through chemical precipitation has a particle size range of approximately 25 micrometers to approximately 75 micrometers; the precipitated powdered polymer cools simultaneously during 3D printing when the object is finished printing; the precipitated powdered polymer has a particle size distribution determined by laser scattering.The precipitated powdered polymer has a melting point and enthalpy determined by differential scanning calorimetry; the precipitated powdered polymer has powder flowability measured using Method A of VIN EN ISO 6186; and the precipitated powdered polymer has an elastic modulus and tensile strength determined according to DIN / EN / ISO 527. Attached Figure Description

[0018] Exemplary apparatuses, systems, and methods will now be described with reference to the accompanying drawings, which are given by way of non-limiting example only, wherein:

[0019] Figure 1 It is a differential scanning calorimeter designed for 3D printing without using TPU powder;

[0020] Figure 2 These are example differential scanning calorigraphs of deposited TPU and baseline TPU;

[0021] Figure 3 A flowchart depicting an exemplary method according to the present invention; and

[0022] Figure 4 This is a flowchart describing an exemplary method for preparing a precipitated powdered polymer. Detailed Implementation

[0023] The accompanying drawings and descriptions provided herein have been simplified to illustrate aspects relevant to a clear understanding of the apparatuses, systems, and methods described herein, while other aspects that can be found in typical similar apparatuses, systems, and methods have been excluded for clarity. Therefore, those skilled in the art will recognize additional elements and / or operations that may be desired and / or necessary to implement the apparatuses, systems, and methods described herein. However, because these elements and operations are known in the art and because they do not contribute to a better understanding of the invention, a discussion of these elements and operations may not be provided herein for the sake of brevity. Nevertheless, the disclosure of this invention is considered to include all elements, variations, and modifications of the foregoing aspects known to those skilled in the art.

[0024] Examples are provided throughout this document to ensure that the invention is fully disclosed and that the scope of the embodiments of the invention is fully conveyed to those skilled in the art. Many specific details are set forth, such as examples of particular components, devices, and methods, to provide a thorough understanding of the embodiments of the invention. However, it will be apparent to those skilled in the art that certain specific details disclosed are not necessary, and that embodiments may be embodied in different forms. Therefore, the embodiments should not be construed as limiting the scope of the invention. As mentioned above, in some embodiments, well-known processes, well-known device structures, and well-known techniques may not be described in detail.

[0025] The terminology used in this invention is for the purpose of describing particular embodiments only and is not restrictive. For example, the singular forms “a,” “an,” and “the” (described) may also be intended to include the plural forms, unless the context clearly indicates otherwise. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless specifically identified as a preferred or desired performance order, the steps, processes, and operations described herein should not be construed as requiring them to perform in the specific order discussed or described. It should also be understood that additional or alternative steps may be employed, in place of or in combination with aspects of the invention.

[0026] When an element or layer is referred to as “on,” “above,” “connected to,” or “coupled to” another element or layer, it may be directly on, above, connected to, or coupled to the other element or layer, unless otherwise explicitly stated; intermediate elements or layers may be present. Conversely, when an element or layer is referred to as “directly on,” “directly above,” “directly connected to,” or “directly coupled to” another element or layer, intermediate elements or layers may not be present. Other terms used to describe relationships between elements should be interpreted in a similar manner (e.g., “between” vs. “directly between,” “adjacent” vs. “directly adjacent,” etc.). Furthermore, as used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0027] Furthermore, although the present invention may use terms such as first, second, third, etc., to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by the terms. These terms may be used only to distinguish one element, component, region, layer, or portion from another. Unless the context clearly indicates otherwise, terms such as “first,” “second,” and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or portion discussed below may be referred to as a second element, component, region, layer, or portion without departing from the teachings of the embodiments.

[0028] The disclosure of this invention relates to powdered precipitated polyether block amides (PEBA), thermoplastic polyurethanes (TPU), and thermoplastic olefins (TPO) that have enhanced operating window characteristics, enabling their use in 3D-printing applications such as SLS, MJF, HSS, and possibly electrophotographic. For the purposes of this invention, an "enhanced operating window" includes, for a given TPE, at least one of the following: a wider range than the typical range between melting and recrystallization temperatures, a larger enthalpy at melting, and a lower volume change during recrystallization.

[0029] Exemplary polymers falling within the scope of this invention include, but are not limited to, PEBA, TPO, and TPU compounds. As non-limiting examples, such PEBAs wishing to be within the scope of this invention include PEBAX (Arkema) polyether block amides, Vestamid E (Evonik) polyether block amides, Santoprene (ExxonMobil) block copolymers, Termoton (Termopol Polimer) block copolymers, Arnitel (DSM) block copolymers, Solprene (Dynasol) block copolymers, Engage (Dow) block copolymers, Dryflex (Elasto) block copolymers, Mediprene (Elasto) block copolymers, and Kraton (Kraton polymers). Of course, those skilled in the art will understand from the discussion herein that other PEBAs suitable for obtaining enhanced operating windows for 3D printing using the methods referenced below are considered to be within the scope of this disclosure. PEBAs produced by the polycondensation reaction of carboxylic acid polyamides and alcohol-terminated polyethers are also considered to be within the scope of this disclosure. Similarly, thermoplastic olefins comprising a portion of thermoplastics, elastomers, and fillers can be included within the scope of this invention.

[0030] Desired types of thermoplastic polyurethanes in this invention include, exemplarily, Texin (Bayer) thermoplastic polyurethane, Elastollan (BASF) thermoplastic polyurethane, Doesmopan (Covestro) thermoplastic polyurethane, Estane (Lubrizol) thermoplastic polyurethane, Irogran (Huntsman) thermoplastic polyurethane, Avalon (Huntsman) thermoplastic polyurethane, Isothane (Greco) thermoplastic polyurethane, Zythane (Alliance) thermoplastic polyurethane, Tekron (Teknor) thermoplastic elastomer, and Elexar (Teknor) thermoplastic elastomer. Based on the content of this invention, it should also be understood that any thermoplastic plastic including linear block polymers, and in particular thermoplastic polyurethanes, is within the scope of the embodiments.

[0031] It is further anticipated that blends of one or more of the aforementioned polymers may be included within the scope of this invention. Furthermore, those skilled in the art will understand from the discussion of the embodiments herein that flow agents and fillers may be incorporated, and / or individually, into the methods of this invention to produce the precipitated powdered polymer of this invention.

[0032] As mentioned, embodiments of the present invention provide for the enhanced use of precipitated powders of thermoplastic elastomers (including polyether block amides) and thermoplastic polyurethanes with enhanced operating window characteristics, for example, in SLS, MJF, HSS, and possibly electrophotographic 3D printing applications. The physical characteristics of suitable precipitated powdered polymers each include a melt temperature above their recrystallization temperature and melt characteristics suitable for effective local melting. These characteristics allow the operating window to remain in an unmelted solid form, for example, during 3D printing, even in the presence of a laser or the use of an IR heater. These unmelted solid materials can then be used as a support structure for the molten polymer.

[0033] For the purposes of this invention, the enhanced operating window includes at least one of the following characteristics: a wider range than the typical range between melting and recrystallization temperatures, a larger enthalpy at melting, and a lower volume change during recrystallization. By altering the characteristics of the polymer, its particles can soften at lower temperatures but will not fuse together before being directly exposed to a heat source (e.g., a laser). It should be understood that these polymers are sinterable from about room temperature to below 150 degrees Celsius. Utilizing these glass transition temperature (Tg) and sintering temperature ranges, the polymer is less likely to suffer thermal degradation during printing, among other advantages.

[0034] Powder-based 3D printing involves a part bed and a feed bed. The part bed is typically at a stable temperature before being exposed to an energy source. The temperature of the energy source is increased until the melting temperature is reached. Material is placed on the feed bed at the initial temperature. During operation, additional material is placed on top of the cold, reheated original material. Growth occurs when the polymer does not have sufficiently large crystals or sufficient mass within the crystals to absorb excess energy and remain crystallized, and if too much heat causes the feed bed material to begin melting, resulting in unwanted melting of the polymer. It is preferable to melt only the portion of the polymer directly exposed to energy, rather than the surrounding polymer. Larger crystals and higher melting temperatures require more energy to melt those crystals, meaning less growth from the feed bed material. Precipitating the polymer produces even larger crystals, thus limiting this growth.

[0035] A common existing approach to improving these polymers to achieve some of the aforementioned advantages is through grinding, such as cryogenic grinding. However, compared to grinding, chemical precipitation enhances the polymer's operating window and additional printable features significantly. Chemically precipitated polymers also offer more stable and printable grain sizes and geometries. For 3D printing applications using SLS, HSS, and MJF, there is often an optimal range of grain sizes and geometries to balance cohesion and object detail. If the polymer grain size is too small, it becomes too powdery and tends to clump during printing. Conversely, if the polymer grain size is too large, fine features and details on the printed object are lost.

[0036] The optimal particle size range provided by the embodiments of the invention is from about 25 micrometers to about 75 micrometers. Deviations downwards from this range by about 8 to about 10 micrometers increase the risk of clumping problems, depending on the required printing environment. On the other hand, if the particle size deviates significantly upwards from the aforementioned range, the polymer may no longer have the ability to produce fine details on the object. Therefore, the average particle size produced by the chemical precipitation aspect of the present invention is in the optimal range of 25 to 75 micrometers. Conventional particle sizes can vary over a wider range, for example from 5 micrometers to 500 micrometers.

[0037] Milling polymers in known techniques also produce particles with geometries that can degrade 3D printing performance, such as particles with serrated and broken edges. This is partly because milling does not provide rounded grinding action, but rather more shear grinding. In contrast, the chemical precipitation technique for polymers of the present invention provides particles with more spherical geometries. This translates to stability in particle size and physical characteristics, reduced need for flow agents or additives, and better particle size control in polymer blends. The precipitated polymers of the present invention also have a tighter particle geometry distribution, which may be advantageous for their physical characteristics in SLS and MJF 3D printing applications.

[0038] A differential scanning calorimetry (DSC) illustration of the phase transition of an exemplary, unused TPU specifically designed for 3D printing is shown in [image / image / description]. Figure 1 The existing TPU has been corrected for non-thermal flow, resulting in a flat curve. It shows several different melting peaks and several different crystallization patterns available in the range of about 60°C to about 150°C and about 210°C. It has a recrystallization temperature starting from about 90°C.

[0039] Precipitation methods can also produce powdered polymers with melt temperature and enthalpy that are appropriate for obtaining the powder melting characteristics during 3D printing of SLS, HSS and MJF. Figure 2 The DSC plots of the baseline TPU and the exemplary precipitated TPU are shown. The baseline TPU, labeled 1.1 and 1.3 in the plot, is an off-the-shelf TPU not specifically designed for 3D printing. The precipitated TPU, also not specifically designed for 3D printing, is labeled 2.1 and 2.3 in the plot. During melting, the precipitated TPU 2.1 exhibits greater crystallinity than the base polymer 1.1. The baseline appears to have a melting enthalpy of approximately 1 joule per gram, while the precipitated TPU produces crystals with two different types of melting enthalpies of approximately 5 joules and approximately 7 joules per gram, respectively. Regarding recrystallization temperature, the baseline TPU 1.3 appears to have a recrystallization temperature of approximately 105 degrees Celsius. Recrystallization of the precipitated polymer was not observed at approximately 90 degrees Celsius. A change in recrystallization temperature was unexpectedly found. Furthermore, since there is no spike on the 2.3 line like on the 1.3 line, it appears that recrystallization may have slowed down.

[0040] Various methods for chemically precipitating the polymers described above can be used. Based on the exemplary methods described below, those skilled in the art will understand that other precipitation methods can be employed in the embodiments, although they are not explicitly disclosed herein.

[0041] As those skilled in the art will further understand, based on the discussion and embodiments herein, exemplary embodiments may provide the addition of a polymer to a solvent and its precipitation to allow the polymer to form larger, thicker crystals, which produces the aforementioned operating window for powder-based 3D printing. Figure 3This is an exemplary flowchart depicting such an embodiment of the invention. The method includes, at reference numeral 32, placing a polymer in a solvent for use with that solvent. At reference numeral 34, the polymer is precipitated to form larger crystals, which are believed to provide the desired characteristics of higher melting temperatures and wider operating windows based on the desired precipitate size. It is further believed that solvent-based precipitation of the polymer produces a more ordered crystal structure because the polymer chains have greater mobility in the process to unify and form crystals. The precipitated polymer is then used for powder-based 3D printing (i.e., SL, HSS, and MJF printing), as shown in reference numeral 36.

[0042] Therefore, the characteristics of powder-precipitated polymers do not result in large volumetric changes during 3D printing of SLS, HSS, and MJF before the entire object is built. When 3D printing an object, it is detrimental to crystallization occurring in the plastic before the object is finished. The entire object should be at an isothermal or approximately the same temperature so that crystallization does not occur. Otherwise, irregular moments of crystallization may occur during printing, which can lead to catastrophic stress or strain. Similarly, if one part of the object crystallizes before another, irregular moments can cause deformation of the object.

[0043] An exemplary method for preparing a precipitated powdered polymer includes a mixture of a polymer, toluene, eicosapentaenoic acid (EPA), and water. An exemplary flowchart depicting this exemplary method 40 is shown in [the diagram]. Figure 4 The method involves first mixing any of the aforementioned polymers into a solution of toluene and EPA, as shown at 42. Water is added and the composition is heated, as shown at 44, and stirred at 46. A stabilizer may be added at 44 to stabilize the toluene. The composition is continued to be heated until boiling, as shown at 48. Continued boiling causes the EPA to boil off at 50, leaving a precipitated polymer powder, which is then dried at 52. It should be noted that this process is intended to form a powder with controllable particle size.

[0044] Particle size distribution can be determined by laser scattering. Melting point and enthalpy can be determined by DSC. Powder flowability can be measured using Method A of VIN EN ISO 6186. Elastic modulus and tensile strength can be determined according to DIN / EN / ISO 527.

[0045] It should be understood that polymers can be mixed in different proportions and particle sizes. This can have the effect of altering or controlling the properties of the resulting powdered polymer.

[0046] It is further anticipated that the aforementioned polymers can be produced in powder form through other chemical precipitation methods. Other such examples include dissolving the polymer or polymer group in ethanol and precipitating the polymer(s) into a crystalline powder.

[0047] An alternative method for the chemical precipitation of one or more of the above polymers may include melting one or more of the polymers in nitrogen at a temperature above 200 degrees Celsius. The composition is placed in an autoclave, where the internal pressure is increased. The pressure is maintained while heating to above 250 degrees Celsius. The autoclave is then depressurized while maintaining nitrogen. The resulting material is then dried.

[0048] Another method for chemically precipitating the polymer may include adding one or more of the aforementioned polymers to a container containing ethanol denatured with 2-butanone and about 1% water. The composition is then heated to above 130 degrees Celsius for about 1 hour. The composition is then cooled and the ethanol is removed by distillation. The polymer precipitates during the cooling process.

[0049] In another embodiment, laurolactam is mixed with 1,12-dodecanedioic acid, water, and an aqueous solution of hypophosphite. The composition is heated, stirred, and maintained under autogenous pressure in an autoclave. The heat and pressure are maintained for a first period of time. The composition is then depressurized to atmospheric pressure, and nitrogen is passed through it for a second period of time to form the polymer.

[0050] In another embodiment, the polymer or polymer group can be heated to above 140 degrees Celsius and stirred in a tank. Ethanol, denatured with 2-butanone and water, is added to the tank. The composition is maintained at the elevated temperature for a period of time while stirring. Then, while stirring the composition, the heat is reduced and the ethanol is removed by distillation. Once precipitation begins, the distillation rate is increased until the internal temperature of the composition decreases. The composition is then dried, and any remaining ethanol is removed by further distillation.

[0051] It should be understood that these polymers can also be redeprecipitated using one or more of the methods described above. It should also be understood that different temperatures, pressures, times, and stirring rates can be applied to these precipitation methods to alter various characteristics of the polymers.

[0052] In conjunction with the use of the polymers described above, another exemplary embodiment includes adding a flow agent to the powdered polymer. Exemplarily, the flow agent may include one or more of the following substances: calcined silica, calcium silicate, alumina, amorphous alumina, magnesium silicate, glassy silica, hydrated silica, kaolin, attapulgite, glassy phosphate, glassy borate, glassy oxide, titanium dioxide, talc, pigment, or mica. These flow agents may have a particle size of about 10 micrometers or less. Furthermore, they are included only to the extent that they enhance the flowability of the polymer material. In an exemplary embodiment, the flow agent may be blended with the powdered precipitated polymer(s). It should be understood that the amount of flow agent used should not significantly alter the Tg of the polymer(s). Exemplarily, the amount of flow agent present is less than 5% by weight of the composition.

[0053] Because the polymer powders of this invention are precipitated rather than ground, they have a greater proportion of particles with spherical geometries. This means less flow agent or additive is needed. If a flow agent is added, much less is required than for ground powders. For precipitated polymers, the flow agent is only needed to help the powdered polymer remain level when poured into a container. It should also be understood that the flow agent is introduced only into the dry powder polymer and mixed only to the extent that the agent is adequately distributed. If overmixed, static electricity may accumulate in the powder, which could limit the powder's ability to remain level when poured into a container.

[0054] Another exemplary embodiment of the invention may include adding a compatible filler to a powdered polymer. These fillers may be organic or inorganic. Such fillers may include pigments, glass, ceramics, or metals in the form of particles or beads. In this exemplary embodiment, the filler should have a particle size equal to or smaller than the average particle size of the corresponding powdered polymer. Additionally, the filler may constitute up to about 25% of the total weight of the powder blend.

[0055] Furthermore, the description of the invention is provided to enable any person skilled in the art to make or use the embodiments of the invention. Various modifications to the invention will be apparent to those skilled in the art, and the general principles defined herein can be applied to other variations without departing from the spirit or scope of the invention. Therefore, the invention is not intended to be limited to the examples and designs described herein, but is consistent with the widest scope of the principles and novel features disclosed herein.

Claims

1. Application of polymer materials in improving residual stress in 3D printed objects, among which, Polymer materials include: at least one polymer selected from the group consisting of polyether block amides and thermoplastic polyurethanes; In this process, at least one or more polymers are formed by chemical precipitation to form a precipitated powdered polymer; The precipitated powdered polymer prepared by chemical precipitation has a particle size range of 25 micrometers to 75 micrometers. The precipitated powdered polymer is formed by precipitating the polymer in a solvent and causing the polymer to crystallize. The precipitated powdered polymer is formed from one or more of the following: The first precipitation method includes: One or more of the polymers are mixed into a solution of toluene and eicosapentaenoic acid to form a composition; Add a stabilizer to the composition; Stir the composition; Heat the composition to boiling; Eicosapentaenoic acid is extracted from the composition; and, Dry precipitated polymer powder; The second precipitation method includes: One or more of the polymers are dissolved in ethanol to form a composition; Heating the composition; and The polymer is precipitated into a crystalline powder; The third precipitation method includes: One or more of the polymers are melted in nitrogen in an autoclave, and the contents of the autoclave are heated to a temperature above 200 degrees Celsius. Increase the pressure of the autoclave; Maintain the pressure in the autoclave while heating the contents to above 250 degrees Celsius; While maintaining nitrogen gas, the pressure vessel is reduced; and, Dry any resulting polymer powder; The fourth precipitation method includes: One or more of the polymers are added to a container containing ethanol denatured with 2-butanone and 1% water to form a composition; Heat the composition to above 130 degrees Celsius for 1 hour; Cooling the composition; and, The ethanol is removed by distillation; The fifth precipitation method includes: One or more of the polymers are mixed with laurolactam, 1,12-dodecanoic acid, water, and an aqueous solution of hypophosphite to form a composition; The composition is heated in an autoclave; Maintain the autogenous pressure from the composition within the autoclave; The composition is stirred in the autoclave; The pressure of the autoclave is reduced to atmospheric pressure; and, Nitrogen gas is passed through the composition; and, The sixth precipitation method includes: Add one or more of the polymers to the tank; The polymer is heated to above 140 degrees Celsius; Stir the polymer in the tank; Ethanol denatured with 2-butanone and water was added to the tank to form a composition; The composition is kept at an elevated temperature for a period of time; Reduce calories; The ethanol was removed by distillation while the composition was being stirred; and, Dry the composition; The at least one or more polymers have a particle geometry that is not formed by grinding, including cryogenic grinding.

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