Powders, especially for layer-by-layer manufacturing of three-dimensional objects

Abstract

The present invention relates to a powder for use in the layer-by-layer, tool-free manufacturing of three-dimensional objects. The powder comprises a polymer powder characterized by a specific volume fraction of polymer particles having a particle size less than 10.48 μm and a particle size within the range of 10.48 μm to 30.53 μm, as well as a corresponding volume fraction of polymer particles having a particle size of 30.53 μm or greater, such that the total volume of the polymer powder is 100%. The powder has good free-flowing properties, provides a sufficiently large process window, and allows for the production of components characterized by a low tendency to warp. The invention also relates to a process for producing the powder, its uses, and molded bodies produced using the powder.

Description

[Technical Field]

[0001] The present invention relates to a powder, in particular for use in the layer-by-layer tool-free manufacturing of three-dimensional objects. The present invention further relates to a process for manufacturing the powder, a powder bed comprising the powder, uses of the powder, and compacts manufactured using the powder. [Background technology]

[0002] The rapid delivery of prototypes or small batches is a problem that is frequently faced these days, and the process that makes this possible is called rapid prototyping, rapid manufacturing, additive fabrication, or simply 3D printing.

[0003] Particularly suitable processes are those that operate on the basis of powder materials and in which the desired structure is produced tool-free, layer by layer, by selective melting and solidification. The powder bed surrounding the melted area provides sufficient support, so that support structures in the case of overhangs and undercuts can be dispensed with. Subsequent support removal operations are therefore avoided. After cooling and solidification of the previously melted layer-by-layer areas, the compact can be removed from the powder bed. Methods that operate according to these principles are herein encompassed under the umbrella term Powder Bed Fusion (hereinafter also referred to as PBF for short).

[0004] In PBF, selectivity can be achieved, for example, by applying susceptors, absorbers, or inhibitors; by masks; by focused energy input, for example, by a laser beam; through glass fibers; or by selective application of powders. Energy input is typically achieved by electromagnetic radiation. The wavelength of the electromagnetic radiation typically ranges from 100 nm to 10 cm, preferably from 400 nm to 1600 nm or from 800 nm to 1060 nm. The radiation source can be, for example, a microwave generator, a suitable laser, a radiant heater or lamp, or a combination thereof.

[0005] One example of a PBF method particularly suited to rapid prototyping is selective laser sintering, which is described in detail, for example, in U.S. Pat. No. 6,136,948 A and WO 96 / 06881 A2. In this method, polymer powder is selectively and briefly irradiated with a laser beam in a chamber, thus melting the powder particles that are struck by the laser beam. The molten particles coalesce and rapidly resolidify to form a solid mass. By repeatedly irradiating newly added layers in constant succession, this method can be used for the rapid and simple production of three-dimensional objects.

[0006] Other suitable PBF methods are, for example, the SIV method described in WO 01 / 38061 A1, or the methods described in EP 1 015 214 A1 or U.S. Pat. No. 6,531,086 B1. Both methods operate using a two-dimensional infrared heater to melt the powder. Selectivity of melting is achieved in the former method by applying an inhibitor, and in the latter method through a mask. A further method is described in DE 103 11 438 A1. In this method, the energy required for melting is introduced via a microwave generator, and selectivity is achieved by applying a susceptor.

[0007] Further suitable methods include methods that operate with absorbers that are present in powders or that are applied by ink-jet techniques, as described in DE 102004012682 A1, DE 102004012683 A1, DE 102004020452 A1 and WO 2005 / 105412 A1.

[0008] The powder bed of the PBF process can be made of a powder substrate, particularly one composed of polymers. Numerous polymers and copolymers are suitable for this application, including polyester, polyvinyl chloride, polyacetal, polypropylene, polyethylene, polystyrene, polycarbonate, poly(N-methylmethacrylimide) (PMMI), polymethylmethacrylate (PMMA), ionomers, polyamides, or mixtures thereof. For example, German Patent No. 19747309A1 describes powders suitable for use in the PBF process. The polyamide-12 powder disclosed therein is obtained by ring-opening and reprecipitation of a previously prepared polyamide, followed by polycondensation with laurolactam. The polyimide-12 powder thus obtained has a favorable combination of melting temperature, solidification temperature, and melting enthalpy. However, the free-flowing properties of the powder are also crucial for the process procedure and reliability of the PBF process. Furthermore, polyaryletherketones (PAEKs) are also suitable. WO 2020 / 061029 describes a powder composition comprising two fractions of PEAK particles with different parameters and a further fraction comprising a plurality of carbon fibers.

[0009] For example, the free-flowing properties of the powder in the PBF process must allow it to be transported and applied without difficulty during the process. This is not true to a sufficient extent for the polymer powders obtained by the method described in German Patent No. 19747309A1. Therefore, to adjust the free-flowing properties, free-flow aids are typically added to the powders for the PBF process. For example, European Patent No. 1443073A1 discloses a powder composition containing, in addition to the polymer powder, hydrophobized particles or hydrophobic silica or a mixture thereof. According to the teachings of European Patent No. 1443073A1, this allows for good free-flowing properties regardless of storage conditions. German Patent No. 3113392A1 discloses a method for reducing the electrostatic charge of thermoplastic powder polyamides and subsequently reducing their tendency to form agglomerates. Similar to the thermoplastic powder polyamides, the thermoplastic coating powders produced by this method also contain the addition of a small amount of fine inorganic powder, which is coated with an antistatic agent.

[0010] However, the drawback of adding inorganic free-flow additives is that they can lead to problems in processing powder materials in the PBF process. The inorganic particles act as recrystallization seeds, leading to premature solidification of the melt, which in turn leads to warping of the melt layer. The result is "curl," which can lead to the halting of the build process in the PBF process and results from shrinkage during solidification. Furthermore, the manufactured components typically exhibit warping. While these effects can, in principle, be reduced by increasing the energy input and build temperature during the build process, these measures subsequently lead to various problems, such as increased thermal stress on the polymer powder and increased sintering of the powder cake. The effect of inorganic free-flow additives is also due to their role as a separating agent, separating particles from one another. While this is desirable when adding powder layers, it is disadvantageous in the particle-melting operation, as it prevents the particles from melting and sintering.

[0011] It is therefore an object of the present invention to provide a powder with good free-flowing properties for the PBF process that reduces or avoids the above-mentioned drawbacks of the prior art.

[0012] overview Surprisingly, it has been discovered that this objective can be achieved by a powder, particularly for use in powder bed fusion, comprising a polymer powder having a volume fraction of polymer particles less than 10.48 μm in size, 0.5% to 15%, a volume fraction of polymer particles between 10.48 μm and 30.53 μm in size, and a volume fraction of polymer particles greater than 30.53 μm in size, where the volume fractions and particle sizes are determined by the laser diffraction-based method described herein, such that the total volume of the polymer powder equals 100%. The powder may optionally contain one or more inorganic free-flow additives, preferably in an amount less than 0.1 wt. % based on the total weight of the powder.

[0013] In the prior art, it is typically assumed that powders containing a significant proportion of fine polymer particles have relatively poor free-flow properties. Surprisingly, it has been discovered that by adjusting the volume fraction of polymer particles as claimed, it is possible to obtain polymer-based powders characterized by good free-flow properties without the addition of inorganic free-flow additives. This makes it possible to avoid the aforementioned drawbacks associated with the use of inorganic free-flow additives. Therefore, the powders of the present invention have a larger process window than powders containing inorganic free-flow additives. Furthermore, in contrast to powders containing inorganic free-flow additives, the powders of the present invention allow the production of components with a lower tendency to warp. This avoids the occurrence of curling during the PBF process.

[0014] The present invention also relates to a process for producing a powder according to the present invention, wherein the polymer powder is provided by at least combining at least one first powder comprising polymer particles and a second powder comprising polymer particles.

[0015] The present invention further relates to a powder bed, particularly for use in the fusion zone of a powder bed fusion process, the powder bed comprising a powder as disclosed herein, preferably produced by the method described herein.

[0016] Furthermore, the present invention also relates to the use of the powder according to the present invention or the powder bed disclosed herein in powder bed fusion processes.

[0017] The present invention also provides molded articles produced using the powders or powder beds described herein, particularly by powder bed fusion processes. DETAILED DESCRIPTION OF THE INVENTION

[0018] Unless otherwise specified, the numerical parameters and ranges set forth in the following description and appended claims are approximate. Thus, unless otherwise specified, all numbers, values, ranges, amounts, or percentages can be read as if they were preceded by the word "about," even if the term is not explicitly preceded by such. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​of the specific examples are reported as precisely as possible. However, all numerical values ​​contain errors necessarily resulting from the standard deviation of the particular measurements.

[0019] Each numerical range recited herein includes all subranges subsumed therein. For example, a range of "1 to 10" is intended to include all subranges between and including the recited minimum value of 1 and the recited maximum value of 10, i.e., all subranges beginning with a minimum value of 1 or greater and ending with a maximum value of 10 or less, and all subranges therebetween, e.g., 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1. The endpoints of all ranges and / or numbers within said ranges are combinable within the context of this disclosure.

[0020] The term "comprising" is used herein to be open-ended and should be understood as not excluding the presence of additional elements, materials, components, or process steps not described or mentioned. The terms "including," "containing," "formed from," and similar terms should be understood as synonyms for "comprising." The term "consisting of," as used herein, excludes the presence of unspecified elements, components, process steps, etc. Although the present disclosure has been described in terms of "including," "consisting of," or "consisting essentially of," these terms are also within the scope of the present disclosure.

[0021] In the context of this disclosure, the expressions "consisting essentially of" and "essentially formed of" a certain material mean that the corresponding component is formed predominantly of the specified material, with other materials present in at most minor amounts. The other materials are generally not intentionally added, but if present, result from, for example, impurities or incomplete separation. The other materials are typically present in such small amounts that they do not significantly affect the properties of the component in question. For example, in this specification, "consisting essentially of" and "essentially formed of" can mean that each component, e.g., each particle, is formed from or consists of the specified material in an amount of 95% by weight or more, preferably 99% by weight or more, even more preferably 99.5% by weight or more, and even more preferably 99.9% by weight or more.

[0022] The singular forms "a" and "the" are used herein to include the plural forms unless the context clearly dictates otherwise.

[0023] Powder bed fusion, or PBF for short, is understood in the context of the present disclosure to mean a method for the layer-by-layer, tool-free production of three-dimensional compacts, in which regions of the respective powder layer are selectively melted, for example by the input of electromagnetic energy, and the resulting compact is obtained by solidification of the molten regions and subsequent removal from the powder bed. A particularly preferred example of a PBF method is, for example, selective laser sintering.

[0024] The term "polymer" as used herein should be understood to include both homopolymers, i.e., polymers derived from one type of monomer, and copolymers, i.e., polymers derived from two or more different types of monomers. Examples of homopolymers are polyamides such as nylon-11 and nylon-12. Examples of copolymers may be copolyamides such as nylon-6,12, nylon-10,12, and nylon-6,13.

[0025] The term "powder" in the context of the present invention should be considered as a term for a solid in the form of a large number of fine particles. These particles can typically move freely relative to each other when the powder is stirred. For example, powders used in the context of the present invention are particularly free-flowing. Powders can be distinguished from other particulate substances, for example, by the size of the particles. Thus, powders typically consist essentially of particles with dimensions in the submillimeter range, such as less than 500 μm, particularly less than 250 μm.

[0026] As already mentioned above, the present invention relates to a powder, particularly for use in powder bed fusion, comprising a polymer powder, the polymer powder having a volume fraction of polymer particles having a particle size less than 10.48 μm of 0.5% to 15% and a volume fraction of polymer particles having a particle size in the range of 10.48 μm to 30.53 μm of 4.0% or less. The volume fractions are based on the total volume of the polymer powder. The volume fractions and particle sizes are based on particle size distribution determined by a laser diffraction-based method, as described further below. The powder may optionally contain one or more inorganic free-flow aids, preferably in a proportion of less than 1 wt. %, more preferably less than 0.1 wt. %, more preferably less than 0.05 wt. %, and even more preferably less than 0.01 wt. %, based on the total weight of the powder. However, the powder is preferably essentially free of inorganic free-flow aids, meaning that inorganic free-flow aids, if any, are present only in minor amounts as impurities. Most preferably, the powder is free of inorganic free-flow aids.

[0027] Polymer powder is understood to mean a powder containing particles formed from a material containing one or more polymers. Such particles are also referred to herein as polymer particles. Suitable polymers are, in particular, thermoplastic polymers. The thermoplastic polymer is preferably selected from the group consisting of polyolefins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polycarbonate, polyoxymethylene, polyimide, polysulfone, poly(N-methylmethacrylimide), polycarbonate (PC)-acrylonitrile-butadiene-styrene (ABS), ionomers, poly(meth)acrylates such as polymethyl methacrylate, polyvinylidene fluoride, polyether ketone, polyarylether ketone, polyamides, and copolymers, mixtures and combinations thereof. The thermoplastic polymer more preferably comprises homopolyamides, copolyamides, or mixtures of homopolyamides and copolyamides. Particularly preferred (co)polyamides here are nylon-12, nylon-11, nylon-6,10, nylon-6,12, nylon-10,12, nylon-6, nylon-6,6, nylon-6,13, or mixtures thereof, with nylon-12 and nylon-6,13 being particularly preferred. Particularly preferred nylon-12 is described, for example, in published specification German Patent No. 19747309A1. Polypropylene is also preferred. In addition to one or more polymers, the polymer particles may also contain one or more non-polymeric materials. Such optional materials may be selected, for example, from non-polymeric organic materials and additive and filler materials, which may be present in the powder according to the invention in addition to the polymer powder, and are further described herein below in the context of optional independent components. For example, particles of the polymer powder having a particle size of less than 10.48 μm, particles having a particle size in the range of 10.48 μm to 30.53 μm, and / or particles of 30.53 μm or more may each be polymer particles that may optionally contain one or more additional materials that are not polymers. However, the polymer content in the material of the particles of the polymer powder typically predominates.Typically, the particles of the polymer powder are formed from one or more polymers to the extent of 70% by weight or more, 80% by weight or more, 85% by weight or more, particularly 90% by weight or more, preferably 95% by weight or more, and more preferably 99% by weight or more. The remaining weight percentage of the particles of the polymer powder can be accounted for by one or more optional materials that are not polymers. The polymer powder preferably comprises essentially only particles formed essentially from one or more polymers. More preferably, the polymer powder comprises only particles formed from one or more polymers. However, the powder according to the present invention may still optionally comprise, in addition to the polymer powder described, further components composed of polymers and / or non-polymeric materials, such as inorganic free-flow aids, fillers, or further additives as further described below.

[0028] As already mentioned, the polymer powder of the powder according to the present invention has a volume fraction of particles having a particle size of less than 10.48 μm of 0.5% to 15%. The polymer powder may, for example, have a volume fraction of particles having a particle size of less than 10.48 μm of at least 0.6%, particularly at least 0.8%, preferably at least 1.0%, more preferably at least 1.5%, and more preferably at least 2.0%. The polymer powder may also have a volume fraction of particles having a particle size of less than 10.48 μm of 12% or less, preferably 10% or less, more preferably 8.0% or less, and more preferably 6.0% or less. The volume fraction of particles having a particle size of less than 10.48 μm may be within a range formed by any combination of the above values. For example, the polymer powder may have a volume fraction of particles having a particle size of less than 10.48 μm of 0.8% to 12%, preferably 1.0% to 10%, more preferably 1.5% to 8.0%, and more preferably 2.0% to 6.0%. The content of particles with a particle size of less than 10.48 μm is limited to the highest extent by a reduction in the minimum ignition energy, which increases the risk of dust explosions and therefore the level of safety precautions required for handling the powder.

[0029] Furthermore, as already mentioned, the polymer powder of the present invention is characterized in that the volume fraction of particles having a particle size in the range of 10.48 μm to less than 30.53 μm is 4.0% or less. For example, the polymer powder may have a volume fraction of particles having a particle size in the range of 10.48 μm to less than 30.53 μm of 3.5% or less, particularly 3.0% or less, preferably 2.5% or less, even more preferably 2.0% or less, and even more preferably 1.6% or less. The polymer powder may have a volume fraction of particles having a particle size in the range of 10.48 μm to less than 30.53 μm of 0% or more, 0.1% or more, or 0.2% or more. The volume fraction of particles having a particle size in the range of 10.48 μm to less than 30.53 μm may be within a range formed by any combination of the above values. For example, the polymer powder may have a volume fraction of particles having a particle size in the range of 10.48 μm or more to less than 30.53 μm of 0% to 3.0%, 0.1% to 2.0%, or 0.2% to 1.6%.

[0030] The polymer powder may preferably have a volume fraction of particles having a particle size of less than 10.48 μm of 1.0% to 10% and a volume fraction of particles having a particle size in the range of 10.48 μm to less than 30.53 μm of 3.0% or less. For example, the polymer powder may have a volume fraction of particles having a particle size of less than 10.48 μm of 1.5% to 8.0% and a volume fraction of particles having a particle size of 10.48 μm to less than 30.53 μm of 2.0% or less. More preferably, the polymer powder has a volume fraction of particles having a particle size of less than 10.48 μm of 2.0% to 6.0% and a volume fraction of particles having a particle size in the range of 10.48 μm to less than 30.53 μm of 1.6% or less.

[0031] The polymer powders described herein further comprise particles having a particle size of 30.53 μm or greater, together with the volume fraction of particles having a particle size less than 10.48 μm and the volume fraction of particles having a particle size in the range of 10.48 μm to 30.53 μm, in corresponding volume fractions of the polymer powder, such that the total volume of the polymer powder is 100%.

[0032] The powders according to the present invention can be characterized by the process by which the polymer powder particles are produced. Polymer powder particles having a particle size of less than 10.48 μm, particles having a particle size in the range of 10.48 μm to 30.53 μm, and particles having a particle size of 30.53 μm or greater can be produced by the same or different methods. Suitable processes for producing particles having a particle size of less than 10.48 μm, particles having a particle size in the range of 10.48 μm to 30.53 μm, and / or particles having a particle size of 30.53 μm or greater include, for example, grinding, precipitation, polymerization, fiber cutting, or blending a polymer melt in a homogeneously immiscible material. Grinding and precipitation are preferred. Grinding can preferably be carried out as a cryogenic grinding or cryogenic grinding operation. Suitable polymerization methods are all standard polymerization methods for producing polymers, such as cationic, anionic, and free-radical polymerization, with anionic polymerization being particularly preferred. Suitable precipitation methods are presented, for example, in DE 19747309 A1 and EP 1840155 A1.

[0033] The polymer powder particles having a particle size of less than 10.48 μm, the polymer powder particles having a particle size in the range of 10.48 μm to 30.53 μm, and the polymer powder particles having a particle size of 30.53 μm or more may be formed from different materials or the same material. Preferably, the polymer powder particles having a particle size of less than 10.48 μm, the polymer powder particles having a particle size in the range of 10.48 μm to 30.53 μm, and the polymer powder particles having a particle size of 30.53 μm or more are formed from the same material, preferably selected from the thermoplastic polymers mentioned above, in particular nylon-12, nylon-6, 13, and / or polypropylene.

[0034] The polymer powder of the powder according to the present invention can also be described by its D50, D10, and / or D90 particle size. The D50 particle size, also called the median, indicates the particle size below and above which 50% of all particles lie in a volume-based particle size distribution. The D10 particle size, correspondingly, indicates the particle size below which 10% of all particles lie in a volume-based particle size distribution. The D90 particle size, correspondingly, indicates the particle size below which 90% of all particles lie in a volume-based particle size distribution. The D50, D10, and D90 particle sizes each refer to particle size distributions determined by a laser diffraction-based method, as further described in the Examples. The polymer powder of the present invention can have a D50 particle size of, for example, 40 μm to 80 μm, preferably 50 μm to 70 μm. The D10 particle size can be, for example, 30 μm to 50 μm, and / or the D90 particle size can be 75 μm to 120 μm. The polymer powder of the powder according to the present invention may also have any combination of the ranges set out above for the D50, D10 and D90 particle sizes.

[0035] The powder according to the present invention can be characterized by the weight percentage of polymer powder. Thus, the percentage of polymer powder based on the total weight of the powder can be at least 20% by weight, at least 30% by weight, at least 40% by weight, at least 50% by weight, at least 60% by weight, at least 70% by weight, at least 80% by weight, preferably at least 90% by weight, more preferably at least 95% by weight, even more preferably at least 99% by weight, or at least 99.5% by weight. The powder according to the present invention can also be characterized by the volume percentage of polymer powder in the powder. Thus, the percentage of polymer powder based on the total volume of the powder can be at least 70% by volume, at least 80% by volume, preferably at least 90% by volume, more preferably at least 95% by volume, or even more preferably at least 99% by volume. In a preferred embodiment of the present invention, the powder according to the present invention consists essentially of polymer powder. In an equally preferred embodiment of the present invention, the powder according to the present invention consists of polymer powder.

[0036] The powder according to the present invention may optionally contain one or more inorganic free-flow additives. Free-flow additives typically have nanoscale dimensions, for example, 500 nm or less, or 100 nm or less, or 50 nm or less, and are conventionally used to improve the free-flow properties of particulate compositions. They typically act as separating agents, reducing the tendency to form lumps in the powder. The inorganic free-flow additives that may be used can be selected from the group of standard free-flow additives known per se in the prior art. Typical examples include, for example, metal oxides, such as silicon dioxide, aluminum oxide, and mixtures and combinations thereof. Silicon dioxide here can take the form of silica, fumed silica, precipitated silica, colloidal silica, hydrophobized silica, hydrophobic silica, or mixtures thereof. Hydrophobic or hydrophobized silica is preferably obtained by reacting silica with a hydrophobizing agent. Hydrophobization preferably follows precipitation or pyrolysis of the silica and subsequent reaction of the free hydroxyl groups of the silica with, for example, a silane, a silazane, or a siloxane. Preferred hydrophobizing agents are hexadecylsilane, dimethyldichlorosilane, hexamethyldisilazane, octamethylcyclotetrasiloxane, polydimethylsiloxane and methacryloylsilane.Other possible inorganic free-flowing additives are, for example, glass, metal and ceramic particles, such as glass beads, steel balls or metal grit, which can also be added to achieve specific desired mechanical, electrical or magnetic properties.The particles in this paragraph, especially when described in combination with particle size, do not fall under the definition of "particle" used in the present invention for polymer particles.

[0037] However, by controlling the volume fraction of fine particles having a particle size of less than 30.53 μm in the polymer powder as described above, it is typically possible to omit or significantly reduce the addition of inorganic free-flow aids to the powder according to the present invention. The proportion of inorganic free-flow aids is typically less than 1 wt %, more preferably less than 0.1 wt %, more preferably less than 0.05 wt %, and even more preferably less than 0.01 wt %, based on the total weight of the powder. Most preferably, the powder according to the present invention is essentially free of inorganic free-flow aids. This means that one or more inorganic free-flow aids, if present, are present in the powder merely as impurities. Even more preferably, the powder according to the present invention is free of inorganic free-flow aids.

[0038] The powder may optionally further comprise one or more fillers. Fillers are understood herein to mean insoluble additives that, when added in appropriate amounts, affect, for example, the mechanical, electrical, or processing properties of the powder or the molded bodies produced therefrom. Fillers typically have dimensions in the micrometer to millimeter range, e.g., 35 μm to 2 mm, 50 μm to 1 mm, or 75 μm to 500 μm, and therefore differ from free-flow additives. Any of the customarily used fillers can be used. Typical fillers include, for example, fillers composed of organic or inorganic materials, such as organic fillers, amorphous, semi-crystalline, or crystalline fillers, metal powders, carbonates, sulfates, and natural or synthetic silicates, oxides, and hydroxides. Examples include metal oxides, such as magnesium oxide, zinc oxide, and calcium oxide; metal hydroxides, such as magnesium hydroxide and aluminum hydroxide; aluminum powder; barium sulfate; mineral fibers; fumed silica; ground quartz; silica; glass fibers; or glass beads. The powder according to the present invention can be characterized by the weight percentage of filler in the powder. For example, the percentage of filler based on the total weight of the powder can be up to 70 wt%, up to 60 wt%, up to 50 wt%, up to 40 wt%, or up to 30 wt%. The percentage of filler based on the total weight of the powder can be, for example, 5 wt% or more, 10 wt% or more, or 20 wt% or more. The percentage of filler can also be within a range formed by any combination of the above values. The percentage of filler based on the total weight of the powder can be, for example, 0 wt% to 70 wt%, 10 wt% to 60 wt%, or 20 wt% to 50 wt%. In a preferred embodiment of the present invention, the powder according to the present invention is essentially free of fillers. In other words, if fillers are present, they are present only as impurities in the powder. The powder according to the present invention is preferably free of fillers.

[0039] The powder may optionally contain an organic non-polymeric material, which may be, for example, a lactam.

[0040] The powder may optionally further comprise one or more additives. Additives are understood herein to mean materials added to further modify the powder according to the invention, for example, to color it or to optimize its processing properties and / or the properties of the molded bodies produced with it. The additives used may be additives commonly used in the prior art, such as organic and inorganic pigments, dyes, substances based on supercooled melts, pH adjusters, flame retardants, susceptors, absorbers, stabilizers, processing aids, or mixtures and combinations thereof. Exemplary pigments are titanium dioxide, ferrite, zirconium dioxide, and carbon black. Suitable stabilizers are, for example, phenols, especially sterically hindered phenols. Absorbers are used, for example, to melt the powder by irradiation with electromagnetic energy. Standard absorbers are described, for example, in German Patent No. 102004012683A1 and can be selected, inter alia, from carbon black, copper hydroxide phosphate, chalk, bone charcoal, carbon fiber, graphite, and interference pigments. Additives or a mixture of two or more additives can be present in the powder according to the present invention. Each additive is used in each case in an amount appropriate for the desired end use. Standard amounts are known to those skilled in the art. The amount of additive, based on the total weight of the powder, can be, for example, up to 10% by weight, up to 6% by weight, up to 3% by weight, up to 2% by weight, up to 1% by weight, up to 0.5% by weight, up to 0.25% by weight, up to 0.2% by weight, up to 0.1% by weight, or up to 0.05% by weight. In a preferred embodiment of the present invention, the powder according to the present invention is essentially free of additives. In other words, if additives are present, they are present only as impurities in the powder. In a further preferred embodiment of the present invention, the powder according to the present invention does not contain any additives.

[0041] One way to describe the free-flowing properties of the powders according to the present invention is by measuring the flowability. This can be done, for example, using a "Revolution Powder Analyzer" from Mercury Scientific Inc., as described in the Examples. The parameters obtained here are the "avalanche angle" and the "absolute energy to break," which are measures of the powder's flowability. Higher values ​​of the avalanche angle and absolute energy to break indicate poorer flowability. The powders according to the present invention may in particular have an avalanche angle of less than 50°, preferably less than 45°, and more preferably less than 40°. The powders preferably have an avalanche angle of 20° to 50°, more preferably 30° to 40°. The powders according to the present invention can also be characterized by the absolute energy to break. The powders may have an absolute energy to break of, for example, less than 300 kJ / kg, preferably less than 290 kJ / kg, and more preferably less than 280 kJ / kg. For example, the powder may have an absolute energy to break of 230 kJ / kg to 300 kJ / kg, preferably 240 kJ / kg to 290 kJ / kg, especially 250 kJ / kg to 280 kJ / kg, more preferably 260 kJ / kg to 275 kJ / kg.

[0042] Powders according to the present invention can also be characterized by the width of their process window in Kelvin in the PBF process. The figures given here for the process window relate to the selective laser sintering process as described in the Examples. The process window of a powder is defined as the difference between the lowest necessary lower process temperature and the highest possible upper process temperature. The lowest necessary process temperature is the temperature at which curling, which can stop the build process, no longer occurs. The highest possible process temperature is the temperature at which powder particles in the powder begin to sinter. For example, powders according to the present invention may have a process window in the selective laser sintering process of at least 2 K, preferably at least 3 K, even more preferably at least 4 K, and more preferably at least 5 K. For example, powders according to the present invention may have a process window in the PBF process of 2 K to 15 K, preferably 3 K to 12 K, and more preferably 4 K to 10 K.

[0043] The present invention also relates to a process for producing the aforementioned powder, where the polymer powder is provided by combining at least one first powder containing polymer particles with a second powder containing polymer particles. The first powder and the second powder may independently comprise or consist of one or more materials as described above for the polymer powder. For example, the polymer particles of the first powder and / or the polymer particles of the second powder may independently contain at least one thermoplastic polymer, preferably selected from the thermoplastic polymers described above. In a particularly preferred implementation of the present invention, the particles of the first powder and the particles of the second powder consist essentially of the same material. The particles of the first powder and / or the particles of the second powder can be produced by the above-described methods for producing polymer powders, preferably by cryogenic grinding, cryogenic grinding, and precipitation according to EP 1840155 A1 or DE 19747309 A1.

[0044] The first powder and the second powder are such and / or combined in such proportions that the resulting polymer powder has a volume fraction of polymer particles having a particle size of less than 10.48 μm of 0.5% to 15%, a volume fraction of polymer particles having a particle size in the range of 10.48 μm or more to less than 30.53 μm of 4.0% or less, and a volume fraction of polymer particles having a particle size of 30.53 μm or more such that the total volume of the polymer powder is 100%.

[0045] In a specific variation of the process according to the present invention, the first powder essentially contains particles having a particle size of 30.53 μm or greater. The second powder may essentially contain particles having a particle size less than 10.48 μm. The proportion of particles having a particle size in the range of 10.48 μm to 30.53 μm in the first and second powders is collectively sufficiently low so that the volume fraction of these particles in the polymer powder obtained after combining the first and second powders is 4.0% or less. The mixing ratio of the first and second powders is selected so that the resulting polymer powder contains particles having a particle size less than 10.48 μm in a volume fraction of 0.5% to 15%. In this context, "essentially having a specific particle size" means that the first or second powder contains a very large preponderance of particles of the specified particle size, with only minor amounts of particles of a different particle size present, e.g., less than 5%, 2%, 1%, or 0.5% by volume. Particles of different particle sizes are generally not added intentionally, but if present, they result from, for example, incomplete separation or impurities. Particles of different particle sizes are typically present in such small amounts that they do not significantly affect the properties of the component in question. In particular, this is understood to mean that a first powder essentially consisting of particles having a particle size of 30.53 μm or more has a volume fraction of particles having a particle size of less than 30.53 μm of less than 5%, preferably less than 2%, particularly less than 1%, and more preferably less than 0.5%. A second powder essentially consisting of particles having a particle size of less than 10.48 μm may have a volume fraction of particles having a particle size of less than 10.48 μm of less than 5%, preferably less than 2%, particularly less than 1%, and more preferably less than 0.5%.

[0046] The first powder and / or the second powder can each be obtained by one or more sieving steps. For example, the first powder may comprise a coarse material (i.e., a coarse fraction) obtained by sieving the first primary powder through a 30.53 μm sieve. Here, the first primary powder preferably has a D50 particle size of 40 μm to 120 μm, more preferably 40 μm to 90 μm. The second powder may comprise a fine material (i.e., a fine fraction) obtained by sieving the second primary powder through a 10.48 μm sieve. Here, the second primary powder preferably has a D50 particle size of 1 μm to 20 μm. The first primary powder and the second primary powder may be composed of particles of the same or different materials. Combining the first powder and the second powder results in a powdered polymer powder according to the present invention, which contains corresponding volume fractions of particles having a particle size less than 10.48 μm, particles having a particle size in the range of 10.48 μm or more to less than 30.53 μm, and polymer particles having a particle size of 30.53 μm or more, with the corresponding volume fractions of polymer powder being such that the total volume of the polymer powder is 100%.

[0047] Alternatively, the first and second powders can be obtained by (1) sieving the primary powder through a first sieve at 30.53 μm to obtain the coarse material forming the first powder from the first sieve, and (2) sieving the fine material from the first sieve through a second sieve at 10.48 μm to obtain the fine material forming the second powder from the second sieve. The primary powder preferably has a D50 particle size of 40 μm to 120 μm, more preferably 40 μm to 90 μm. In this way, by combining the first and second powders, a polymer powder according to the present invention can be obtained, which has the above-mentioned volume proportions of particles having a particle size of less than 10.48 μm, particles having a particle size in the range of 10.48 μm to less than 30.53 μm, and a volume proportion of polymer particles having a particle size of 30.53 μm or greater, such that the total volume of the polymer powder is 100%. In this process variant, the particles of the powder according to the invention thus obtained are uniformly formed from essentially the same material.

[0048] The particles of the primary powder can be produced by the methods described above for producing particles of polymer powder, preferably by cryogenic grinding, cryogenic grinding and precipitation according to EP 1840155 A1 or DE 19747309 A1. The materials from which the particles of the primary powder are formed may in particular comprise or consist of the materials described above for the first and second powders and the polymer powder.

[0049] Sieving can be carried out by techniques typically used for this purpose. In a particularly preferred implementation of the present invention, sieving is carried out by water sieving, air sieving, centrifugal sieving, zigzag sieving, or toner sieving, highly preferably by toner sieving. A particularly suitable device for powder sieving is, for example, the TSP 100 manufactured by Hosokawa Alpine AG (Augsburg, Germany). Sieving can be carried out, for example, by the method described below in the Examples. For powder sieving, two or more sieving techniques can be used in succession, or one sieving technique can be used repeatedly. For example, the sieving of primary powders can be carried out by the same sieving technique, the same combination of sieving techniques, or different sieving techniques, or different combinations of sieving techniques. It is conceivable to use a sieving method as an alternative classification method in addition to sieving. However, sieving is less preferred because it is more complicated. Furthermore, suitable sieves for some of the required sieve sizes are not technically available.

[0050] In a preferred embodiment of the present invention, the process according to the present invention comprises mixing a first powder with a second powder. Mixing can be carried out using conventional methods and equipment. In a particularly preferred embodiment of the present invention, mixing is carried out using a high-speed vertical mixer. Another suitable mixing device is the M20 S-FU model manufactured by MTI (Detmold, Germany). The mixing conditions are advantageously adjusted here to achieve a homogeneous mixture. In the above-mentioned mixing device, a homogeneous mixture can be produced, for example, by mixing at 1500 rpm for 3 minutes.

[0051] The process according to the invention may also comprise a step of initially dosing or adding at least one inorganic free-flowing auxiliary to the polymer powder, the at least one inorganic free-flowing auxiliary being preferably homogeneously mixed with the polymer powder, for which purpose it is possible to use conventional mixing techniques, such as those mentioned above.

[0052] The process according to the invention may also include a step of initially adding or adding at least one filler and / or at least one additive to the polymer powder, as described above. The at least one filler and / or at least one additive is preferably homogeneously mixed with the polymer powder. For this purpose, conventional mixing techniques, such as those described above, can be used.

[0053] The use of the powder according to the present invention through the PBF process and in the molded bodies produced by such a process is particularly practical from an economic point of view. The present invention therefore also relates to a powder bed for use in the fusion zone, in particular in a powder bed fusion process, the powder bed comprising the above-described powder according to the present invention, preferably produced by the above-described process. In a preferred implementation of the present invention, the powder bed consists of the powder according to the present invention, or the powder bed is essentially formed from the polymer powder according to the present invention. This means that additional components other than the powder according to the present invention are essentially absent from the powder bed. In the latter case, additional components of the powder bed, if any, result from impurities.

[0054] The present invention therefore also provides the use of a powder or powder bed according to the invention in a powder bed fusion process.

[0055] The present invention also relates to molded articles produced by powder bed fusion using the powder or powder bed according to the present invention. The use of the molded articles according to the present invention is evident in both rapid prototyping and rapid manufacturing. The latter refers to the production of small runs, i.e., two or more identical parts, where production using injection molds or the like is uneconomical, especially when the parts have very complex shapes. Examples are parts for luxury cars and trucks or race or rally vehicles, which are produced in small quantities, or replacement parts for motorsports, where not only the number of parts but also the availability time are important. Industries in which molded articles according to the present invention are used include aerospace, medical technology, mechanical engineering, automobile manufacturing, the sports industry, the household goods industry, the electrical industry, and the lifestyle sector.

[0056] The present invention is therefore particularly directed to the following aspects: 1. A powder, particularly for use in powder bed fusion, comprising a polymer powder, the polymer powder having a volume fraction of polymer particles less than 10.48 μm in size from 0.5% to 15%, a volume fraction of polymer particles having a size in the range of 10.48 μm to 30.53 μm in size from 4.0% to 4.0%, and a volume fraction of polymer particles having a size of 30.53 μm or greater, such that the total volume of the polymer powder equals 100%, the volume fractions and polymer particle size being determined by a laser diffraction method as described herein. 2. Powder according to aspect 1, characterized in that the powder is essentially free of inorganic free-flow aids or the powder comprises at least one inorganic free-flow aid, the proportion of the at least one inorganic free-flow aid being preferably less than 1% by weight, even more preferably less than 0.1% by weight, more preferably less than 0.05% by weight, in particular less than 0.01% by weight, based on the total weight of the powder. 3. The powder according to aspect 2, wherein the at least one inorganic free-flow aid is selected from silicon dioxide and aluminum oxide, and mixtures and combinations thereof. 4. The powder according to any one of aspects 1 to 3, characterized in that the proportion of polymer powder based on the total weight of the powder is at least 30% by weight, at least 50% by weight, preferably at least 70% by weight, even more preferably at least 90% by weight, and even more preferably at least 95% by weight. 5. The powder of any of aspects 1 to 4, having an avalanche angle of less than 50°, preferably less than 45°, more preferably less than 40°, wherein the avalanche angle is determined by a method described herein. 6. The powder according to any of aspects 1 to 5, having an absolute energy to break of less than 300 kJ / kg, preferably less than 290 kJ / kg, more preferably less than 280 kJ / kg, wherein the absolute energy to break is determined by a method described herein. 7. The powder of any one of aspects 1 to 6, having a powder bed fusion process window of at least 2K, preferably at least 3K, and more preferably at least 5K, wherein the powder bed fusion process is carried out by the laser sintering process described herein. 8. The powder according to any one of aspects 1 to 7, wherein the polymer powder has a volume fraction of particles having a particle size of less than 10.48 μm of at least 1.0%, preferably at least 1.5%, more preferably at least 2.0%. 9. A powder according to any one of aspects 1 to 8, characterized in that the volume fraction of particles having a particle size of 10.48 μm or more and less than 30.53 μm in the polymer powder is 3.0% or less, preferably 2.0% or less, and more preferably 1.6% or less. 10. A powder according to any one of aspects 1 to 9, characterized in that the polymer powder has a volume fraction of particles having a particle size of less than 10.48 μm of 10% or less, preferably 10% or less, even more preferably 8.0% or less, and even more preferably 6.0% or less. 11. The powder of any one of aspects 1 to 10, wherein the polymer powder particles having a particle size less than 10.48 μm, the polymer powder particles having a particle size in the range of 10.48 μm to 30.53 μm, and / or the polymer powder particles having a particle size of 30.53 μm or more are produced by grinding, precipitation, polymerization, fiber cutting, or blending a polymer melt in a homogeneously immiscible material, preferably grinding and precipitation. 12. The powder of any one of aspects 1-11, wherein the polymer powder comprises particles formed from a material comprising at least one thermoplastic polymer, the at least one thermoplastic polymer preferably being selected from the group consisting of polyolefins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polycarbonate, polyoxymethylene, polyimide, polysulfone, poly(N-methylmethacrylimide), polycarbonate (PC)-acrylonitrile-butadiene-styrene (ABS), ionomers, polymethyl methacrylate, polyvinylidene fluoride, polyether ketones, polyarylether ketones, polyamides, and copolymers, mixtures and combinations thereof; and wherein the at least one thermoplastic polymer more preferably comprises a homopolyamide, a copolyamide, or a mixture of a homopolyamide and a copolyamide. 13. The powder of any one of the preceding aspects, wherein the polymer powder particles having a particle size less than 10.48 μm, the polymer powder particles having a particle size in the range of 10.48 μm to 30.53 μm, and the polymer powder particles having a particle size of 30.53 μm or greater are formed from the same material, preferably selected from the materials recited in aspect 12. 14. The powder according to any one of aspects 1 to 13, wherein the polymer powder has a D50 particle size of 50 μm to 70 μm, a D10 particle size of 30 to 45 μm, and / or a D90 particle size of 75 to 120 μm. 15. The process for producing a powder according to any of aspects 1-14, wherein the polymer powder is provided by at least combining at least one first powder comprising polymer particles and a second powder comprising polymer particles. 16. The process of embodiment 15, wherein the first powder comprises essentially only particles having a particle size of 30.53 μm or greater, and / or the second powder comprises essentially only particles having a particle size of less than 10.48 μm. 17. The process according to any of aspects 15 and 16, wherein at least the first powder and the second powder are mixed with each other, and the mixing is preferably carried out using a high-speed vertical mixer. 18. The process of any of aspects 15-17, wherein the polymer particles of the first powder and / or the polymer particles of the second powder independently contain at least one thermoplastic polymer, and the at least one thermoplastic polymer is preferably selected from the thermoplastic polymers mentioned in aspect 12. 19. The process of any one of aspects 15-18, wherein the particles of the first powder and the particles of the second powder are formed from essentially the same material. 20. The process according to any of aspects 15 to 19, wherein the first powder and / or the second powder is obtained by one or more sieving steps. 21. The process of any one of aspects 15-20, wherein the first powder comprises a coarse material obtained by sieving the first primary powder at 30.53 μm, and wherein the first primary powder has a D50 particle size preferably between 40 μm and 120 μm, more preferably between 40 μm and 90 μm. 22. The process of any one of aspects 15-21, wherein the second powder comprises fine material obtained by sieving the second primary powder at 10.48 μm, and the second primary powder preferably has a D50 particle size of 1 μm to 20 μm. 23. A first powder and a second powder are - sieving the first primary powder (preferably having a D50 particle size of 40 μm to 120 μm, more preferably 40 μm to 90 μm) through a first sieve at 30.53 μm to obtain from the first sieve a coarse material forming a first powder; and 21. The process according to any of aspects 15 to 20, characterized in that it is obtained by sieving the second primary powder (preferably having a D50 particle size between 1 μm and 20 μm) through a second sieve at 10.48 μm, and obtaining from the second sieve fine material that forms the second powder. 24. A first powder and a second powder are - Passing the primary powder through a first sieve at 30.53 μm to obtain from the first sieve a coarse material forming a first powder; and - obtained by sieving the fine material from the first sieve through a second sieve at 10.48 μm and obtaining from the second sieve the fine material forming the second powder, 21. The process according to any of aspects 15 to 20, wherein the primary powder has a D50 particle size of preferably 40 μm to 120 μm, preferably 40 μm to 90 μm. 25. The process according to any one of aspects 15 to 24, wherein the sieving is carried out by water sieving, air sieving, centrifugal sieving, zigzag sieving, toner sieving or a combination thereof. 26. The process of any one of aspects 15 to 25, comprising the step of initially dosing or adding at least one inorganic free-flowing aid to the polymer powder, wherein the at least one inorganic free-flowing aid is preferably homogeneously mixed with the polymer powder. 27. A powder bed, particularly for use in the fusion zone of a powder bed fusion process, comprising a powder according to any one of aspects 1-14, preferably produced by a process according to any one of aspects 15-26. 28. A compact produced by powder bed fusion using the powder bed according to embodiment 27. 29. Use of a powder according to any one of aspects 1 to 14 or a powder bed according to aspect 27 in a powder bed fusion process, wherein the powder is preferably produced by a method according to any one of aspects 15 to 26.

[0057] The following examples illustrate the manufacturing process of the powder according to the invention and its uses, without limiting the invention thereto.

[0058] Example All amounts given in the examples are based on parts by weight unless otherwise specified.

[0059] Particle size determination: Particle size and particle size distribution are measured by laser diffraction using a Malvern Mastersizer 3000 (Malvern Panalytical GmbH, Kassel, Germany) with model number MAL1176618 and software version 3.63.1709.120. The instrument is equipped with a wet module of type MAL1169873. The optical configuration of the instrument includes a red He-Ne light source with a wavelength of 632.8 nm and a blue LED light source with a wavelength of 470 nm. The optical setup includes an inverse Fourier arrangement of lenses (converging beam paths). The effective focal length is 300 mm. The detector has logarithmically spaced channels with an angular range of 0.015 to 144 degrees.

[0060] The qualification of the equipment and the experiments were carried out in accordance with ISO 13320:2020, with the measurements being carried out as offline measurements and wet measurements. The measurement medium used is degassed, deionized water (approximately 600 ml), which is initially charged into the Hydro LV dispersion unit of the Mastersizer 3000. The measurement medium is at room temperature. An automated background measurement is carried out on the initially charged measurement medium immediately before the addition of the pre-dispersion liquid described below. The measurement time is 10 seconds for the red and blue light sources, respectively.

[0061] To measure powder samples in aqueous media, the sample must be dispersed with sufficient stability. For this purpose, a preliminary dispersion of the powder is first prepared fresh on the day of measurement. Two to three microspatulas of powder sample are introduced into a 50 ml beaker. It is necessary to ensure that the powder to be analyzed is homogeneous at the time of sampling. This can be achieved, for example, by inverting the sample several times in the provided container. Subsequently, 20 ml of a surfactant solution consisting of degassed deionized water, 1.8 wt.% polyoxyethylene-80-sorbitan monooleate, and 0.15 wt.% ethoxylated acetylene surfactant (SURFYNOL® 485 W, Evonik, Essen, Germany) is added. The surfactant solution is also at room temperature. The mixture is then vigorously dispersed at 250 rpm for at least 15 minutes on a laboratory shaker (model KS500, IKA-Labortechnik, Staufen im Breisgau, Germany) to achieve particle dispersion.

[0062] The amount of powder dispersion to be analyzed is taken from the beaker containing the stirred pre-dispersion using a disposable plastic pipette and quickly added manually to the measurement medium in the Hydro LV dispersion unit of the Mastersizer 3000. This is repeated until sufficient shadowing of the two light sources (red and blue) of 7% to 15% is achieved. Bubble formation must be absolutely avoided here. Before the start of the measurement, the sample is dispersed in the measurement medium while degassing for 60 seconds at 100% ultrasonic power (40 W, corresponding to a nominal frequency of 40 kHz) and an agitator speed of 2500 rpm. The ultrasonic probe is then switched off, and the sample is moved from one end of the measurement cell to the other by the agitator operating at 2500 rpm. The sample is analyzed without delay. The sample measurement involves two 10-second measurements with the red light source and two 10-second measurements with the blue light source. The average of the two measurements is used for the evaluation. The following parameters are set in the software: particle type: non-spherical; dry powder mode; refractive index: 1.520; absorption index: 0.100; particle density: 1.00 g / cm3 Dispersion medium: water (refractive index 1.330). Data evaluation is performed by applying the Fraunhofer approximation (software settings: analytical model: universal, Fraunhofer, volume). The Fraunhofer approximation is described in detail, for example, in Annex A of ISO 13320:2020. The evaluation is performed in an automated manner using the parameters set by the above-specified software owned by the instrument. The resulting D50, D10 and P90 particle size values ​​are reported based on the volume distribution.

[0063] Liquidity determination: The analytical evaluation of flowability is achieved using a "Revolution Powder Analyzer" (Rev 2007, software: Revolution Version 5.0) manufactured by Mercury Scientific Inc. (Newtown, USA). The Revolution Powder Analyzer has a rotating cylinder into which the powder to be analyzed is introduced. The end face of the cylinder is transparent, and a digital camera records the behavior of the powder during rotation. The instrument's proprietary software evaluates these recorded images. The obtained values ​​for avalanche angle and absolute energy to break are measures of the powder's flow properties. Higher avalanche angle and absolute energy to break indicate poorer flowability. All powders are dried under vacuum at 70°C for 16 hours before measurement.

[0064] For measurements on the Revolution Powder Analyzer, the "flowability" method is selected with the following parameters: measuring drum diameter 100 mm, roughly poured powder 100 cm 3 Filling with; rotation speed: 0.6 rpm; shooting speed: 10 fps; prep. time: 60 s; avalanche threshold: 0.65%; test stopped after 150 avalanches; camera settings: shutter speed: 7 ms; gain: 8 dB; image analysis: threshold 150; tail correction: on; edge pixels: 30.

[0065] Powder sieve: The sieving of the powders was carried out using a TSP 100 toner sifter manufactured by HosokawaAlpine AG (Augsburg, Germany). The purge gas used was nitrogen. The temperature of the purge gas was 26°C. For sieving at 30.53 μm, a sieve wheel speed of 2000 rpm and a measurement rate of 10 kg / h were selected. The fan was set at 125 m 3 For the 10.48 μm sieve, the sifter wheel speed was 1750 rpm and a measurement speed of 10 kg / h was selected. In this case, the fan was 105 m 3 Driven at / hr.

[0066] Evaluation of selective laser sintering: In addition to analytical evaluation, selective laser sintering was also performed. For this purpose, powders from the examples were processed in the powder bed of an EOSINT P396 (PSW 3.8) manufactured by Electro Optical Systems (Munich, Germany). Tensile specimens were produced according to DIN EN ISO 527-1:2019-12, type 1B. Mechanical parameters, a layer thickness of 0.15 mm, and a red blade cassette were used to produce the tensile specimens. The process temperature used in each case was 1 K below the temperature at which the powder begins to sinter. The withdrawal chamber temperature was set 40 K below the process temperature. Before starting the exposure of the tensile specimens, a 9 mm empty layer was constructed. The tensile specimens were placed in the center of the plane of the build field, oriented in the X direction. After finishing the exposure of the tensile specimens, another 9 mm empty layer was constructed, and then the cooling process began. After a cooling time of at least 12 hours, the tensile specimens were removed from the powder cake and cleaned by sandblasting. Six tensile specimens were constructed for each powder example.

[0067] The process window results from the difference between the upper and lower process temperatures. The lower process temperature is the lowest possible process temperature at which the tensile specimens described above can be constructed. The upper process temperature is the temperature at which the powder particles in the build field begin to sinter or form sinter necks. This can be confirmed under a microscope by examining a powder sample removed from the center of the build field.

[0068] Tensile specimens are used to assess warpage. Warpage is determined by placing each specimen on a flat base and using a ruler or slide rule to determine the maximum distance of the specimen's top surface from the base. The greater the warpage, the greater the difference observed.

[0069] Example 1: Precipitated nylon-12 powder (not according to the invention) without the addition of free-flowing additives The precipitated nylon-12 powder is produced by the method described in German Patent No. 2906647B1, and the resulting powder has the properties described in German Patent No. 19747309A1.

[0070] The resulting polymer powder has the following indices: [Table 1]

[0071] The powder is processed in an EOSINT P396. The powder can only be measured at room temperature and at the process temperature, which is problematic, making the powder a poor choice for application. The powder has a process window of 8K.

[0072] Example 2: Precipitated nylon-12 powder from Example 1 with inorganic free-flow aid added (not according to the invention) The precipitated nylon-12 powder from Example 1 is mixed with an inorganic free-flow additive (Aerosil® 300, Evonik, Germany) such that the proportion of free-flow additive is 0.2 wt. % based on the total powder weight. The mixture is produced in an M20 S-FU mixer from MTI (Detmold, Germany) at 1500 rpm for 3 minutes.

[0073] The powder obtained has the following indices: [Table 2]

[0074] The powder is processed in an EOSINT P396. The powder can be measured well both at room temperature and at the process temperature, and the application of the powder is good. The powder has only a small process window of 1 K. The components produced show higher warpage than the components of Example 1.

[0075] Example 3: Precipitated nylon-6,13 powder (not according to the invention) without the addition of free-flowing additives The precipitated nylon-6,13 powder is produced according to the method described in German Patent No. 102004020453A1.

[0076] Precipitated nylon-6,13 powder has the following indices: [Table 3]

[0077] The powder is processed in an EOSINT P396. The powder can only be measured at room temperature and at the process temperature, which is problematic, making the powder poorly suited for application. The powder has a process window of 3K.

[0078] Example 4: Precipitated nylon 6,13 powder from Example 3 with inorganic free-flow additive (not according to the invention) The precipitated nylon-6,13 powder from Example 3 is mixed with an inorganic free-flow additive (Aerosil® 90, Evonik, Germany) such that the proportion of free-flow additive is 0.3 wt. % based on the total powder weight. The mixture is produced in an M20 S-FU mixer from MTI (Detmold, Germany) at 1500 rpm for 3 minutes.

[0079] The powder obtained has the following indices: [Table 4]

[0080] The powder is processed in an EOSINT P396. The powder can be measured well both at room temperature and at the process temperature, and the powder application is good. The powder has only one process point, which means that it was possible to produce components, but the powder cake was already quite hard after the process was over. The components produced show a higher warpage than the components of Example 3.

[0081] Example 5: Ground polypropylene powder (not according to the invention) without the addition of free-flow aids Polypropylene granules (type CP360H from Braskem, Rotterdam, The Netherlands) are ground by cold grinding in a pinned disc mill.

[0082] The ground polypropylene powder has the following indices: [Table 5]

[0083] The powder is processed in an EOSINT P396. The powder can only be measured at room temperature and at the process temperature, which is problematic, making the powder poorly suited for application. The powder has a process window of 2K.

[0084] Example 6: Ground polypropylene powder from Example 5 with inorganic free-flow aid added (not according to the invention) The ground polypropylene powder from Example 5 is mixed with an inorganic free-flow additive (Aerosil® R812, Evonik, Germany) in an amount of 0.1 wt. % based on the total weight of the powder. The mixture is produced in an M20 S-FU mixer from MTI (Detmold, Germany) at 1500 rpm for 3 minutes.

[0085] The powder obtained has the following indices: [Table 6]

[0086] The powder is processed in an EOSINT P396. The powder can only be measured at room temperature and at the process temperature, which is problematic, and the application of the powder is poor. The powder has only one process point, which means that it was possible to produce components, but the powder cake was already quite hard after the process was completed. The components produced show a higher warpage than the components of Example 5.

[0087] Example 7: Precipitated nylon-12 powder (according to the present invention) from Example 1, but with an increased proportion of particles having a particle size less than 10.48 μm and a decreased proportion of particles having a particle size between 10.48 μm and less than 30.53 μm. For this purpose, the powder from Example 1 is sieved in a first step to remove particles having a particle size of less than 30.53 μm. This fine fraction is then sieved in a second step to remove particles having a particle size of less than 10.48 μm. The fine fraction from the second step is then mixed with the coarse fraction from the first step. The mixture is produced in an M20 S-FU mixer manufactured by MTI (Detmold, Germany) at 1500 rpm for 3 minutes.

[0088] The powder obtained has the following indices: [Table 7]

[0089] The powder is processed in an EOSINT P396. The powder can be measured both at room temperature and at process temperature, and the application of the powder is good. The powder has a process window of 7 K. The component does not show any warpage compared to Example 1.

[0090] Example 8: Mixtures of precipitated nylon-12 powder from Example 1 with additional precipitated nylon-12 powders having an increased proportion of particles having a particle size less than 10.48 μm and a decreased proportion of particles having a particle size between 10.48 μm and less than 30.53 μm (according to the invention). The precipitated nylon-12 powder from Example 1 is sieved in a first step, where particles having a particle size of less than 30.53 μm are removed.

[0091] The second nylon-12 powder is produced according to the method described in German Patent No. 2906647B1. The second precipitated nylon-12 powder has the following indices: [Table 8]

[0092] This second precipitated nylon-12 powder is sieved to remove particles having a particle size of less than 10.48 μm. The fine material thus obtained from the second precipitated nylon-12 powder is mixed with the coarse fraction from the first precipitated nylon-12 powder. The mixture is produced in an M20 S-FU mixer manufactured by MTI (Detmold, Germany) at 1500 rpm for 3 minutes.

[0093] The powder obtained has the following indices: [Table 9]

[0094] The powder is processed in an EOSINT P396. The powder can be measured both at room temperature and at process temperature, and the application of the powder is good. The powder has a process window of 8 K. The component does not show any warpage compared to Example 1.

[0095] Example 9: Precipitated nylon-6,13 powder (according to the present invention) from Example 3, but with an increased proportion of particles having a particle size less than 10.48 μm and a decreased proportion of particles having a particle size between 10.48 μm and less than 30.53 μm. For this purpose, the precipitated nylon-6,13 powder from Example 3 is sieved in a first step to remove particles having a particle size of less than 30.53 μm. This fine fraction is then sieved in a second step to remove particles having a particle size of less than 10.48 μm. The fine fraction from the second sieving step is then mixed with the coarse fraction from the first sieving step. The mixture is produced in an M20 S-FU mixer manufactured by MTI (Detmold, Germany) at 1500 rpm for 3 minutes.

[0096] The powder obtained has the following indices: [Table 10]

[0097] The powder is processed in an EOSINT P396. The powder can be measured both at room temperature and at process temperature, and the application of the powder is good. The powder has a process window of 5 K. The component does not show any warpage compared to Example 1.

[0098] Example 10: Mixtures of precipitated nylon-12 powder from Example 1 with precipitated nylon-6,13 powder from Example 3 with an increased proportion of particles having a particle size less than 10.48 μm and a decreased proportion of particles having a particle size between 10.48 μm and 30.53 μm (in accordance with the invention). For this purpose, the precipitated nylon-12 powder from Example 1 is sieved to remove particles having a particle size of less than 30.53 μm. Additionally, the precipitated nylon-6,13 powder from Example 3 is sieved to remove particles having a particle size of less than 10.48 μm. The fine material from the precipitated nylon-6,13 powder is then mixed with the coarse fraction from the precipitated nylon-12 powder. The mixture is produced in an M20 S-FU mixer manufactured by MTI (Detmold, Germany) at 1500 rpm for 3 minutes.

[0099] The powder obtained has the following indices: [Table 11]

[0100] The powder is processed in an EOSINT P396. The powder can be measured both at room temperature and at process temperature, and the application of the powder is good. The powder has a process window of 8 K. The component does not show any warpage compared to Example 1.

[0101] Example 11: Milled polypropylene powder (according to the invention) from Example 5, but with an increased proportion of particles having a particle size of less than 10.48 μm and a decreased proportion of particles having a particle size of between 10.48 μm and less than 30.53 μm. For this purpose, the ground polypropylene powder from Example 5 is sieved in a first step to remove particles having a particle size of less than 30.53 μm. This fine fraction is sieved in a second step to remove particles having a particle size of less than 10.48 μm. The fine fraction from the second sieving step is then mixed with the coarse fraction from the first sieving step. The mixture is produced in an M20 S-FU mixer manufactured by MTI (Detmold, Germany) at 1500 rpm for 3 minutes.

[0102] The powder obtained has the following indices: [Table 12]

[0103] The powder is processed in an EOSINT P396. The powder can be measured both at room temperature and at process temperature, and the application of the powder is good. The powder has a process window of 5 K. The component does not show any warpage compared to Example 1.

[0104] Example 12: Mixtures of ground polypropylene powder from Example 5 with further ground polypropylene powder having an increased proportion of particles having a particle size of less than 10.48 μm and a decreased proportion of particles having a particle size of between 10.48 μm and 30.53 μm (according to the invention). For this purpose, the ground polypropylene powder from Example 5 is sieved in a first step so that particles having a particle size of less than 30.53 μm are removed.

[0105] To produce the second ground polypropylene powder, polypropylene granules (type CP360H from Braskem, Rotterdam, The Netherlands) are ground by cold grinding in a pinned disc mill. The second ground polypropylene powder has the following indices: [Table 13]

[0106] The second ground polypropylene powder is sieved to remove particles having a particle size of less than 10.48 μm. The fine material from the second ground polypropylene powder is mixed with the coarse fraction from the ground polypropylene powder from Example 5. The mixture is produced in an M20 S-FU mixer manufactured by MTI (Detmold, Germany) at 1500 rpm for 3 minutes.

[0107] The powder obtained has the following indices: [Table 14]

[0108] The powder is processed in an EOSINT P396. The powder can be measured both at room temperature and at process temperature, and the application of the powder is good. The powder has a process window of 5 K. The component does not show any warpage compared to Example 1.

[0109] Non-inventive Examples 1, 3, and 5, which do not contain a free-flow additive, exhibit poor flowability. The addition of an inorganic free-flow additive can clearly improve flowability, but the process window is reduced and the resulting parts exhibit a higher tendency to warp (non-inventive Examples 2, 4, and 6). In contrast, inventive Examples 7 to 12 show a clear improvement in powder flowability within the same process window. The components thus additionally obtained also do not exhibit an increased tendency to warp.

Claims

1. 1. A powder, particularly for use in powder bed fusion, comprising a polymer powder, the polymer powder having a volume fraction of polymer particles having a particle size less than 10.48 μm of 0.5% to 15%, a volume fraction of polymer particles having a particle size in the range of 10.48 μm or more to less than 30.53 μm of 4.0% or less, and a volume fraction of polymer particles having a particle size of 30.53 μm or more, the volume fractions of the polymer powder corresponding to a total volume of the polymer powder of 100%, wherein the volume fractions and the polymer particle size are determined by a laser diffraction-based method as described herein.

2. 2. The powder according to claim 1, characterized in that the powder is essentially free of inorganic free-flow aids or that the powder comprises at least one inorganic free-flow aid, the proportion of the at least one inorganic free-flow aid, based on the total weight of the powder, being preferably less than 1% by weight, even more preferably less than 0.1% by weight, more preferably less than 0.05% by weight, in particular less than 0.01% by weight.

3. 3. Powder according to any of claims 1 to 2, characterized in that the proportion of the polymer powder based on the total weight of the powder is at least 30% by weight, at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight, even more preferably at least 95% by weight.

4. The polymer powder the volume fraction of polymer particles having a particle size of less than −10.48 μm is at least 1.0%, preferably at least 1.5%, more preferably at least 2.0%, and / or the volume fraction of polymer particles having a particle size of less than −10.48 μm is 10% or less, preferably 10% or less, even more preferably 8.0% or less, and even more preferably 6.0% or less; and / or The polymer powder has a volume fraction of polymer particles having a particle size in the range of 10.48 μm or more to less than 30.53 μm of 3.0% or less, preferably 2.0% or less, more preferably 1.6% or less. The powder according to any one of claims 1 to 3.

5. 5. Powder according to any of claims 1 to 4, characterized in that the polymer particles of the polymer powder having a particle size of less than 10.48 μm, the polymer particles of the polymer powder having a particle size in the range of ≧10.48 μm to ≦30.53 μm, and / or the polymer particles of the polymer powder having a particle size of ≧30.53 μm are produced by grinding, precipitation, polymerization, fiber cutting or blending of a polymer melt in a homogeneously immiscible material, preferably grinding and precipitation.

6. 6. The powder according to any one of claims 1 to 5, characterized in that the polymer powder comprises polymer particles formed from a material comprising at least one thermoplastic polymer, the at least one thermoplastic polymer being preferably selected from the group consisting of polyolefins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polycarbonate, polyoxymethylene, polyimide, polysulfone, poly(N-methylmethacrylimide), polycarbonate (PC)-acrylonitrile-butadiene-styrene (ABS), ionomers, polymethylmethacrylate, polyvinylidene fluoride, polyetherketones, polyaryletherketones, polyamides and copolymers, mixtures and combinations thereof, the at least one thermoplastic polymer more preferably comprising a homopolyamide, a copolyamide or a mixture of a homopolyamide and a copolyamide.

7. 7. The powder according to any one of claims 1 to 6, characterized in that the polymer particles of the polymer powder having a particle size of less than 10.48 μm, the polymer particles of the polymer powder having a particle size in the range of ≧10.48 μm to ≦30.53 μm, and the polymer particles of the polymer powder having a particle size of ≧30.53 μm are formed from the same material, said material preferably being selected from the materials mentioned in claim 6.

8. 8. The process for producing a powder according to any one of claims 1 to 7, wherein the polymer powder is provided by at least combining at least one first powder comprising polymer particles and a second powder comprising polymer particles.

9. 9. The process of claim 8, wherein the first powder comprises essentially only polymer particles having a particle size of 30.53 μm or greater, and / or the second powder comprises essentially only polymer particles having a particle size of less than 10.48 μm, and / or the polymer particles of the first powder and the particles of the second powder are formed from essentially the same material.

10. 10. The process according to claim 8 or 9, characterized in that the first powder and / or the second powder are obtained by one or more sieving steps.

11. - the first powder comprises the coarse material obtained by sieving a first primary powder at 30.53 μm, the first primary powder preferably having a D50 particle size of 40 μm to 120 μm, more preferably 40 μm to 90 μm; and / or - said second powder comprises said fine material obtained by sieving a second primary powder at 10.48 μm, said second primary powder preferably having a D50 particle size of between 1 μm and 20 μm; The process according to any one of claims 8 to 10, characterized in that

12. The first powder and the second powder are - sieving the primary powder through a first sieve at 30.53 μm to obtain from said first sieve said coarse material forming said first powder; - by sieving the fine material from the first sieve through a second sieve at 10.48 μm and obtaining from the second sieve the fine material forming the second powder; The primary powder preferably has a D50 particle size of 40 μm to 120 μm, preferably 40 μm to 90 μm. The process according to any one of claims 8 to 10, characterized in that

13. A powder bed, in particular for use in the fusion zone of a powder bed fusion process, comprising a powder according to any one of claims 1 to 7, preferably produced by a process according to any one of claims 8 to 12.

14. 14. A compact produced by powder bed fusion using the powder bed of claim 13.

15. Use of a powder according to any one of claims 1 to 7 or a powder bed according to claim 13 in a powder bed fusion process, wherein said powder is preferably produced by a method according to any one of claims 8 to 12.

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