Coarse flame retardant

Abstract

The invention relates to a mixture comprising at least one polymer-based material in powder form and at least one halogen-free flame retardant in powder form, the flame retardant in powder form having a particle size distribution in which d50 is in the range of 20 to 80 [mu] m, preferably at least 30 and / or at most 60 [mu] m, and d10 is greater than 10 [mu] m, preferably greater than 15 [mu] m, and also more preferably greater than 20 [mu] m; the present invention relates to a mixture, to a method for preparing such a mixture, to a mixture obtainable by the method, to the use of such a mixture as a building material for additive manufacturing of a three-dimensional object, to a three-dimensional object prepared by curing the mixture, and to a method and system for preparing such a three-dimensional object.

Description

Field of the Invention

[0001] The present invention relates to a mixture comprising at least one polymer-based material in powder form and at least one halogen-free flame retardant in powder form, a method for preparing such a mixture, a mixture obtainable by this method, the use of such a mixture as a construction material for the additive manufacturing of three-dimensional objects, a three-dimensional object prepared by curing the mixture, and a method and system for preparing such a three-dimensional object. Prior Art

[0002] Methods for manufacturing three-dimensional objects by selectively solidifying powdered materials layer by layer are used, for example, in rapid prototyping, rapid tooling, and additive manufacturing, and are known, for example, as "laser sintering" or "selective laser melting". In this case, thin layers of powdered material are repeatedly applied within a build area, and the powdered material in each layer is selectively solidified by selective irradiation with a laser beam, i.e., the powdered material melts or fuses and solidifies at these locations, forming a material composite. A three-dimensional object is produced in this way. In this case, polymer-based materials in powder form, in particular thermoplastic polymers in powder form, are often used as construction materials.

[0003] For the wide range of applications of such three-dimensional objects manufactured using the above methods, it is preferred or even necessary that these three-dimensional objects have a certain degree of flame retardant protection or fire protection. For this purpose, a flame retardant in powder form is usually mixed with a polymer-based material in powder form, and this mixture is used as the construction material for the three-dimensional object.

[0004] The use of such flame retardants, while providing the desired flame retardant protection for the resulting three-dimensional objects, is however accompanied by a number of disadvantages.

[0005] Then the decomposition temperature of the flame retardant additive must be lower than the decomposition temperature of the matrix material. If an economical exposure strategy / energy introduction is used in the laser sintering method, this often results in the formation of thick smoke and at least partial inactivation of the flame retardant additive being processed.

[0006] Furthermore, finely dispersed additives can usually act as crystallization nuclei, so the resulting flame-retardant three-dimensional objects have different degrees of crystallinity and thus have greater distortion or more brittle mechanical properties.

[0007] Equally disadvantageously, the reactivity of the flame retardant additive used also leads to a greater accumulation of molar mass in the unsintered powder or the formation of a highly viscous shell around the polymer particles, and thus prevents flow.

[0008] In the context of the above prior art, there is a need for a mixture comprising at least one polymer-based material in powder form and at least one flame retardant in powder form, which can overcome the above disadvantages attributable to the addition of a flame retardant in powder form.

[0009] The present invention addresses this need. Summary of the Invention

[0010] In the research underlying the present application, it has surprisingly been found that the above disadvantages of the prior art can be overcome. Specifically, by: the mixture according to claim 1, the method for preparing the mixture according to claim 8, the mixture obtainable by the method according to claim 11, the three-dimensional object prepared by curing the mixture according to claim 12, the method and system for curing the mixture according to claims 13 and 14, and the use of the mixture according to claim 16 as a construction material for additive manufacturing of three-dimensional objects, the above disadvantages of the prior art are overcome.

[0011] Regarding the above aspects of the present invention, it should be noted that each preferred embodiment described for one aspect also applies to the preferred embodiments of other aspects, even if the combination is not explicitly described for the sake of clarity. Furthermore, each combination of more or less preferred embodiments of one aspect is considered to be described, as is each combination of more or less preferred embodiments of one aspect with each of the other aspects.

[0012] Regarding the present invention, the term "comprising" or "including" and its grammatical modifications have the following meaning: in one embodiment, other elements may also be included in addition to the said elements. In another embodiment, only the said elements are substantially included. In other words, in a particular embodiment, in addition to their conventional meaning, this term may be used synonymously with the terms "consisting essentially of" or "consisting of".

[0013] According to a first aspect, the present invention thus relates to a mixture comprising at least one polymer-based material in powder form and at least one halogen-free flame retardant in powder form, wherein the flame retardant in powder form has a particle size distribution with a d50 in the range of 20 to 80 μm, preferably at least 30 and / or at most 60 μm, and a d10 greater than 10 μm, preferably greater than 15 μm, more preferably greater than 20 μm.

[0014] The particle size distribution is preferably determined by laser diffraction (according to ISO 13320:2020).

[0015] Alternatively, the particle size distribution can also be determined by dynamic (according to ISO 13322-2:2021) or static (according to ISO 13322-1:2014) image analysis.

[0016] The polymer-based material in powder form is basically not limited, but preferably contains at least one thermoplastic polymer in powder form.

[0017] In one embodiment, the polymer-based material in powder form consists mainly of a polymer. For example, the polymer content in the polymer-based material in powder form is preferably at least 85% by weight, more preferably at least 90% by weight, still more preferably at least 95% by weight, or greater than 99% by weight.

[0018] In one embodiment, the polymer-based material in powder form consists entirely of a polymer.

[0019] In one embodiment, the polymer-based material in powder form has a particle size distribution with a d50 in the range of 5 to 200 μm, preferably 20 to 80 μm, more preferably at least 30 and / or at most 60 μm.

[0020] In one embodiment, the polymer-based material in powder form has a particle size distribution with a d10 greater than 10 μm, preferably greater than 15 μm, more preferably greater than 20 μm.

[0021] In one embodiment, the polymer-based material in powder form has a particle size distribution with a d50 in the range of 20 to 80 μm, preferably at least 30 and / or at most 60 μm, and a d10 greater than 10 μm, preferably greater than 15 μm, more preferably greater than 20 μm.

[0022] The bulk density of the polymer-based material in powder form is preferably 300 to 800 kg / m 3 , especially 400 to 600 kg / m 3 .

[0023] In one embodiment, the flame retardant in powder form has a fine particle fraction determined by the number fraction of particles with a particle size less than 10 μm of less than 10%, preferably less than 8%, particularly preferably less than 5%.

[0024] In one embodiment, the flame retardant in powder form has a particle size distribution with a d90 less than 200 μm, preferably less than 100 μm, more preferably less than 80 μm.

[0025] In one embodiment, the flame retardant in powder form has an absolute distribution width (d90 - d10) of less than 90 μm, preferably less than 60 μm.

[0026] In one embodiment, the flame retardant in powder form has a weighted distribution width ((d90 - d10) / d50) of less than 4.5, preferably less than 3, more preferably less than 2, still more preferably less than 1.

[0027] In one embodiment, the flame retardant in powder form comprises a phosphorus-based flame retardant, in particular a phosphine-containing, phosphine oxide-containing, hypophosphite / ester-containing, phosphonate / ester-containing, phosphite / ester-containing, phosphate / ester-containing, phosphonium-containing and / or polyphosphate / ester-containing flame retardant and / or a red phosphorus-based flame retardant, and / or the flame retardant in powder form comprises a nitrogen-based flame retardant, in particular melamine or isocyanurate, particularly preferably melamine cyanurate, wherein the phosphorus-based flame retardant is particularly preferred.

[0028] Mixtures of the different flame retardants in powder form are also possible.

[0029] Particularly preferred is a hypophosphite-containing flame retardant comprising a compound of general formula I

[0030]

[0031] wherein,

[0032] R1 and R2 are each independently a straight-chain and / or branched C1-C6-alkyl group and / or an aryl group. The groups R1 and R2 may each independently be substituted or unsubstituted.

[0033] M in this case is an alkali metal, alkaline earth metal, transition metal, metal and / or protonated nitrogen-containing base.

[0034] M is preferably selected from Mg, Ca, Al, Sb, Sn, Ge, Ti, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, K and / or ammonium.

[0035] Preferably, R1 and R2 are each an ethyl group.

[0036] Preferably, M is Al.

[0037] The value of m is obtained from the valence of the cation used in each case and is usually 1, 2, 3 or 4. Mixtures of different cations may also be included.

[0038] Particularly preferably, aluminium diethylphosphinate is used as the hypophosphite-containing flame retardant.

[0039] In another embodiment, the flame retardant in powder form is a polyphosphate / ester-containing flame retardant in powder form, in particular ammonium polyphosphate.

[0040] In another embodiment, the flame retardant in powder form is a phosphonate / ester-containing flame retardant in powder form.

[0041] In order to adjust the particle size distribution of the flame retardant in powder form, the flame retardant in powder form itself can be agglomerated. The size of the individual particles can thereby be increased.

[0042] Alternatively or additionally, the flame retardant in powder form can be agglomerated on a polymer material. The polymer material is preferably used as a binder for the flame retardant in powder form in this case. The polymer material can, for example, include a thermoplastic polymer, a thermosetting polymer and / or an elastomeric polymer. The bonding with the flame retardant in powder form can in this case be carried out, for example, by softening or melting the polymer material. Alternatively, the bonding with the flame retardant in powder form can also be carried out by inclusion and / or crosslinking.

[0043] Preferably, the polymer material is a material which is also used for the polymer-based material in powder form in the mixture.

[0044] The bulk density of the flame retardant in powder form is preferably 20 to 2000 kg / m 3 , especially 300 to 700 kg / m 3 .

[0045] Flame retardants on mineral supports sometimes have a high density and thus a high bulk density. Preferably, the density of the flame retardant (and the bulk density) is similar to that of the polymer powder to avoid segregation effects. However, due to the particle shape of the flame retardant, a low bulk density may exist, for example in the original form; after mixing with the polymer powder and optionally a flow aid, the preferred bulk density can then be achieved.

[0046] In one embodiment, the mixture according to the invention is characterized in that at least one polymer-based material comprises at least one thermoplastic polymer.

[0047] Suitable thermoplastic polymers are preferably selected from the group comprising polyetherimide, polycarbonate, polyphenylene sulfone, polyphenylene ether, polyether sulfone, acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene-acrylate copolymer (ASA), polyvinyl chloride, polyacrylate, polyester, polyamide, polyaryletherketone (PAEK), polyether, polyurethane, polyimide, polyamideimide, polysiloxane, polyolefin and copolymers having at least two different repeating units of the above polymers, and / or at least one polymer blend based on at least two of the aforementioned polymers and / or copolymers.

[0048] In particular, the at least one thermoplastic polymer comprises a polyamide, in particular PA6, PA6,6, PA11, PA12, PA6,13, PA10,12, PA5, PA5,10, a polypropylene-polyethylene copolymer, a thermoplastic polyurethane and / or a thermoplastic polyamide elastomer.

[0049] In one embodiment, the mixture according to the invention is characterized by a bulk density of from 300 to 700 kg / m 3 , preferably from 400 to 600 kg / m 3 , in particular from 450 to 550 kg / m 3 of the mixture.

[0050] In another embodiment, the mixture according to the invention is characterized in that the mixture has a unimodal particle size distribution. This means that the particle size distributions of the polymer-based material in powder form and the flame retardant in powder form, in particular their respective d50s, are substantially the same.

[0051] In an alternative embodiment, the d50 of the polymer-based material in powder form deviates from the d50 of the flame retardant in powder form by no more than 25 μm, particularly preferably no more than 20 μm, especially no more than 10 μm (and vice versa).

[0052] For carrying out the invention, it is sufficient if the mixture comprises at least one polymer-based material in powder form and at least one flame retardant in powder form, each as defined above. However, the mixture may further comprise at least one additional additive.

[0053] Possible additives are preferably selected from the group consisting of: heat stabilizers, UV stabilizers, flow aids, anti-caking agents, discoloration inhibitors, lubricants, nucleating agents, thickeners, antioxidants, antistatic agents, agents for improving biodegradability or biocompatibility, preservatives, colorants, fragrances, hydrolysis stabilizers, fillers, fibers, especially fibers in the form of glass fibers or carbon fibers, and / or plasticizers, absorbers, especially carbon black or graphite, which absorb especially in the wavelength range of the radiation source of the processing system.

[0054] In another aspect, the invention relates to a method for preparing a mixture as described above.

[0055] All the above-described embodiments and definitions apply analogously to the method according to the invention.

[0056] The method according to the invention comprises adjusting a specific particle size distribution in the flame retardant in powder form, with a d50 in the range from 20 to 80 μm, preferably at least 30 and / or at most 60 μm, and a d10 greater than 10 μm, preferably greater than 15 μm, more preferably greater than 20 μm, and mixing the flame retardant in powder form with at least one polymer-based material in powder form.

[0057] Since commercially available flame retardants in powder form usually have an excessive amount of fines and thus an undersized d50, it is relevant to adjust the specific particle size distribution to eliminate the disadvantages of the prior art described at the beginning.

[0058] In particular, the fines cause poor coating during powder application.

[0059] Furthermore, the fines adhere electrostatically or mechanically to the surface of the polymer particles, encapsulating them and thereby preventing the spreading / coalescence of the melt.

[0060] The adjustment of the specific particle size distribution preferably includes the mechanical separation of the particles, or the sorting out of undersized and / or oversized particles.

[0061] In one embodiment, adjusting the specific particle size distribution in a flame retardant in powder form includes removing particles, in particular by classification, preferably by screening, air jet screening, and / or sieving.

[0062] Classification and screening are classical separation methods used in mechanical process engineering. In mechanical process engineering, classification refers to the separation of a dispersed solid mixture into fractions, preferably according to the criterion of particle size.

[0063] In particular, suitable herein are the methods exemplified below.

[0064] Screen classification; in this case, separation is carried out by means of a sieve plate according to the characteristic length or diameter of the particles, in which there are many openings of substantially the same geometry. The screening can be accelerated by applying an air jet (air jet screening).

[0065] Flow classification; in this case, using different settling velocities or trajectories, the particles reach or pass through a fluid under the action of a field force, a fluid force, and an inertial force.

[0066] In particular, when adjusting the particle size distribution of a commercially available flame retardant in powder form, the above methods are applied.

[0067] In one embodiment, the method according to the invention is preferably characterized in that adjusting the specific particle size distribution in a flame retardant in powder form includes a step in which the flame retardant in powder form agglomerates on itself.

[0068] In one embodiment, the method according to the invention is preferably characterized in that adjusting the specific particle size distribution in a flame retardant in powder form includes a step in which the flame retardant in powder form agglomerates on a polymer material.

[0069] In one embodiment, the method according to the invention is preferably characterized in that the flame retardant in powder form is first compounded with at least one polymer material and then micronized to the target particle size.

[0070] In this case, it is preferred to use a polymeric material for agglomeration and / or compounding as a binder for the flame retardant in powder form. The polymeric material may include, for example, thermoplastic polymers, thermosetting polymers, and / or elastomeric polymers.

[0071] The combination with the flame retardant in powder form can be carried out, for example, by softening or melting the polymeric material in this case. Alternatively, the combination with the flame retardant in powder form can also be carried out by inclusion and / or crosslinking.

[0072] Preferably, the polymeric material is a polymeric-based material in powder form that is also used in the mixture.

[0073] In one embodiment, the method according to the invention is preferably characterized in that adjusting the specific particle size distribution in the flame retardant in powder form includes the step of agglomerating the flame retardant in powder form from a dispersion or solution by precipitation or drying.

[0074] A plurality of the above method steps can also be combined.

[0075] On the other hand, the invention relates to a mixture obtainable by the above method.

[0076] All the above-described embodiments and definitions similarly apply to the mixture obtainable by the above method.

[0077] On the other hand, the invention relates to a three-dimensional object prepared by irradiating and curing a powdered construction material at spatial points corresponding to the cross-sections of the three-dimensional object in the respective layers, wherein the mixture described above and / or the mixture obtainable by the method described above is used as the construction material.

[0078] All the above-described embodiments and definitions similarly apply to the three-dimensional object.

[0079] On the other hand, the invention relates to a method for preparing a three-dimensional object, in particular by curing a powdered construction material at points corresponding to the cross-sections of the three-dimensional object in the respective layers, wherein the mixture described above and / or the mixture obtainable by the method described above is used as the construction material, and preferably the construction material is selectively cured by the action of electromagnetic radiation emitted by a radiation source.

[0080] All the above-described embodiments and definitions similarly apply to the method for preparing a three-dimensional object.

[0081] In a preferred embodiment, the method is a conventional laser sintering method using a CO2 laser or a light source emitting short-wave radiation, such as NIR radiation. In this case, the mixture is regularly applied layer by layer to a substrate or a build platform, and the positions where the subsequent object is to be formed are solidified by activating / melting with a laser beam or a set of two or more laser beams.

[0082] In another embodiment, curing is carried out by applying an ink to a part of the layer where the object will subsequently be produced, and then irradiating the surface of the layer with a two-dimensional light source whose wavelength is only absorbed by the components of the ink. In this case, the mixture "marked" with the ink is selectively melted and can then be solidified into a three-dimensional object. This type of method is sold by HP Inc. as "MultiJet Fusion".

[0083] As already mentioned, the wavelength of the radiation source is not subject to any relevant limitations as long as it allows selective melting of the desired regions of the layer or the positions of the mixture. In one embodiment, the radiation source is a conventional CO2 laser with a radiation wavelength of 10.6 μm.

[0084] In another embodiment, the radiation source emits electromagnetic radiation with a wavelength in the range of 400 to 1500 nm, preferably one of the wavelength ranges 1,064 ± 8 nm and / or 980 ± 7 nm and / or 940 ± 7 nm and / or 810 ± 7 nm and / or 780 ± 10 nm and / or 640 ± 7 nm, or electromagnetic radiation with a wavelength of about 10.6 μm or in the range of 4.8 to 8.3 μm and preferably about 5 μm.

[0085] The radiation source to be used in the method preferably comprises at least one laser, preferably at least one diode laser.

[0086] On the other hand, the present invention relates to a system for producing a three-dimensional object by curing a powdered build material at positions corresponding to the cross-section of the three-dimensional object in a respective layer, wherein the system comprises at least one radiation source designed to emit electromagnetic radiation; a processing chamber serving as an open container, the processing chamber being designed to have container walls; a support arranged in the processing chamber, wherein the processing chamber and the support are movable relative to each other in the vertical direction, having a storage container and a coater movable in the horizontal direction, wherein the storage container is at least partially filled with the mixture described above and / or a mixture obtainable by the method described above.

[0087] All the embodiments and definitions described above apply analogously to the system for producing a three-dimensional object.

[0088] Conventional systems and methods that can be used within the scope of the present invention are known, for example, from DE 44 10 046, where a three-dimensional object is prepared by repeatedly applying a powder layer, selectively melting (partially or completely) at corresponding positions corresponding to the cross-section of the object, and subsequently solidifying the melt layer by layer according to the "additive manufacturing" principle. By melting the powder layer, the melt combines with the previously melted layer. An example of a laser sintering device having a laser beam and a deflection mirror is shown in Figure 1 in.

[0089] As Figure 1 can be seen in, the device has a container 1 that is open upwards and is defined below by a support 4 for carrying the object 3 to be shaped. The working plane 6 is defined by the upper edge 2 (or its side wall) of the container. The object is located on the upper side of the support 4 and is formed by a plurality of layers of powdery build material that can be cured by electromagnetic radiation and extends parallel to the upper side of the support 4. The support is height-adjustable in the vertical direction, i.e., parallel to the side wall of the container 1. Thus, the position of the support 4 relative to the working plane 6 can be adjusted.

[0090] Above the container 1 or the working plane 6, an application device 10 is provided for applying the powder material 11 to be cured to the build platform 5 or the last cured layer. In addition, an irradiation device in the form of a laser 7 that emits a directed beam 8 is arranged above the working plane 6. The beam is deflected in the direction of the working plane 6 as a deflected beam 8' by a deflection device 9, such as a rotating mirror. This arrangement is common in laser sintering equipment having a CO2 laser. The control unit 40 allows control of the support 4, the application device 10, and the deflection device 9. The elements 1 to 6, 10, and 11 are arranged within a frame 100.

[0091] When preparing the three-dimensional object 3, the powder material 11 is applied layer by layer to the support 4 or the previously cured layer, and is cured with a laser beam 8' at positions corresponding to the object in each powder layer. After each selective curing of a layer, the support is lowered by the thickness of the next powder layer to be applied.

[0092] In the system described above, the radiation source preferably emits electromagnetic radiation with a wavelength in the range of 400 to 1,500 nm, preferably in one of the wavelength ranges 1,064 ± 8 nm and / or 980 ± 7 nm and / or 940 ± 7 nm and / or 810 ± 7 nm and / or 780 ± 10 nm and / or 640 ± 7 nm, or electromagnetic radiation with a wavelength of about 10.6 μm or in the range of 4.8 to 8.3 μm and preferably about 5 μm.

[0093] The radiation source to be used in the system preferably includes at least one laser, preferably at least one diode laser.

[0094] The laser diodes can be arranged in a honeycomb pattern or staggered. Additionally, it is possible for the laser diodes to be arranged in a two-dimensional array. The transmitter can be an edge emitter. Preferably, the emitter is a surface emitter (VCSEL or Philips-VCSEL). By line exposure, a high build speed can be achieved. Additionally, using laser diodes allows for high efficiency and reduced energy costs.

[0095] Suitable laser diodes typically operate at a power between 0.1 and 500 watts, preferably at least 1.0 watt and / or at most 100 watts. The focus of the laser beam can have a radius between 0.05 mm and 1 mm, preferably at least 0.1 mm and / or at most 0.4 mm.

[0096] The exposure speed, i.e., the speed of the laser focus relative to the build plane, is typically between 10 mm / s and 20,000 mm / s, preferably at least 300 mm / s and / or at most 10,000 mm / s, and particularly preferably at most 6,000 mm / s.

[0097] On the other hand, the present invention relates to the use of the mixtures as described above and / or mixtures obtainable by the methods as described above as construction materials for the additive manufacturing of three-dimensional objects by selectively curing the construction material at cross-sectional points of the three-dimensional object in the respective layer, in particular as described above.

[0098] All the embodiments and definitions described above apply analogously to the use according to the invention. Description of the Drawings

[0099] Figure 1 An example of a conventional laser sintering apparatus for the layer-by-layer preparation of three-dimensional objects is shown.

[0100] The present invention will be described in more detail below with the aid of examples, which, however, are for illustrative purposes only and are not to be understood in any way as limiting the invention described herein. Examples

[0101] Example 1:

[0102] A commercially available phosphonate-based flame retardant of type OP 1400 from Clariant was subjected to air jet sieving using a SLS200 laboratory sieve from Siebtechnik GmbH, followed by classification using a 32 μm sieve and a cyclone separator with a negative pressure of 70 - 90 mbar. OP 1400 type commercially available phosphonate-based flame retardant from Clariant was subjected to air jet sieving using a SLS200 laboratory sieve from Siebtechnik GmbH, followed by classification using a 32 μm sieve and a cyclone separator with a negative pressure of 70 - 90 mbar.

[0103] The following fractions of the flame retardant were obtained:

[0104] F1 describes the unclassified material, F2 describes the sieve residue after sieving, and F3 describes the undersize fraction collected after cyclone separation.

[0105] By air jet sieving, approximately 30 - 40% of the feed material is removed from the feed material as undersize fraction.

[0106] As a comparative example not according to the present invention, use is made of a chemically equivalent flame retardant FN with a significantly smaller particle size obtainable from Clariant under the name OP 930.

[0107] For the materials obtained, by means of laser diffraction, in accordance with ISO 13320:2020, using a CILAS 1064 measuring instrument from Quantachrome Partikelmesstechnik, with a wet dispersion cell, treatment is carried out in water with the addition of a dispersion medium (surfactant). During wet dispersion, the sample is additionally dispersed ultrasonically. The measurement evaluation of the grain size distribution is carried out according to the Fraunhofer model. The particle size distribution is given as d10, d50, and d90, i.e., the 10%, 50%, and 90% quantiles of the volume particle size distribution. Additionally, the fine fraction is given as the fraction of particles with a diameter x < 10 μm. To form a statistical average, multiple measurements are carried out.

[0108] Furthermore, the bulk density is determined in accordance with ISO 60, and the free-flowability is determined in accordance with ISO 6186 for an outlet nozzle diameter of 15 mm.

[0109] The measured data determined are shown in Table 1.

[0110] Table 1: Flame retardants

[0111]

[0112] Thus, the flame retardants F1 and F3 obtained in this way do not have the properties preferred according to the present invention, especially with regard to the content of the fine fraction and the combination of D10 and D50. Only F2 meets these requirements.

[0113] The flame retardant obtained in this way is mixed with a commercially available polyamide 12 fine powder 1125 white from Evonik in a ratio of 25% (mass ratio of the flame retardant relative to the total mixture mass). Additionally, in this case 0.05% (mass ratio of the flow aid relative to the total mixture mass) of Alu C. Mixing was carried out in a laboratory mixer Lab CM 12-MB at room temperature using a short mixing tool. The mixing sequence was 2 minutes at 300 revolutions per minute and then 1 minute at 500 revolutions per minute. The obtained mixture was sieved using a laboratory sieve with a mesh size of 250 μm to remove agglomerates and impurities.

[0114] Hereinafter, the corresponding mixture with flame retardant F1 is referred to as M1, the corresponding mixture with flame retardant F2 is referred to as M2, and the corresponding mixture with flame retardant F3 is referred to as M3.

[0115] As a reference, the polymer powder without addition 1125 white is listed under the name M0. In the context of this example, the mixture of FN and polyamide powder was not further considered because preliminary tests with the corresponding mixture showed that the powder could not be metered or applied with the laser sintering system EOS P 396. In addition, mixtures M1 and M3 can be considered not to be within the scope of the embodiments of the present invention because they do not contain all the preferred embodiments.

[0116] The mixtures were also analyzed according to the measurement method described above. The analysis data are shown in Table 2.

[0117] Table 2: Mixtures

[0118]

[0119] Of particular note is the increase in the outflow duration when determining the free-flowability of M3, which contains the highest fine particle fraction. This is evidenced by the poor flow behavior of the material, which negatively affects powder feeding, metering, and application when processing powder mixtures in powder-based additive manufacturing methods.

[0120] Mixtures M1, M2, and M3 were processed on a modified laser sintering system EOS P 396. The modification in this case was limited to reducing the build volume to a build space of 125 mm x 110 mm x 85 mm, which was installed in the center of the original build area. Therefore, the heating elements were adapted to a uniform temperature distribution in the build area. The metering container and the coater with a top scraper (EOS Klinge III) were used accordingly, so that the powder was applied only in the corresponding build area. At a layer thickness of 120 μm and 0.26 J / mm 3Processing is carried out under exposure parameters of volume-related energy input, divided into two exposures, with half of the energy input for each exposure. The laser power used is 18.5 W and the scanning speed is 6 m / s. The processing chamber temperature is 179 °C (measured by a modified temperature measurement system, with a typical deviation of about 10 °C observed relative to the unmodified system), and the extraction chamber temperature is 150 °C. To determine the mechanical properties, 1BA type tensile test bars are manufactured with a nominal thickness of 2.5 mm according to ISO 527-2 in the horizontal component force orientation (XYZ). A23 type tensile test bars are manufactured with a nominal thickness of 2.0 mm according to ISO 20753 in the vertical component force orientation (ZXY). The specimens thus manufactured are tested on a Zwick / Roell Z005 tensile testing machine equipped with strain gauges.

[0121] The determined characteristic values are shown in Table 3.

[0122] Table 3: Mechanical properties

[0123]

[0124] In particular, it is evident for components in the ZXY component force orientation that only material M2 can achieve a high elongation at break. Due to the deteriorated powder application behavior of other powders and the partial deterioration of the flow of molten polymer particles caused by the shielding effect of fine flame retardant particles, the coalescence of the melt is reduced, especially the coalescence between layers. Therefore, in particular, an overall reduction in the mechanical properties of specimens made of M3 is also obtained.

Claims

1. A mixture comprising at least one polymer-based material in powder form and at least one halogen-free flame retardant in powder form, characterized in that, The flame retardant in powder form has a particle size distribution with a d50 in the range of 20 to 80 μm, preferably at least 30 and / or at most 60 μm, and a d10 greater than 10 μm, preferably greater than 15 μm, still more preferably greater than 20 μm.

2. The mixture according to claim 1, characterized in that, The flame retardant in powder form has a fines fraction of less than 10%, preferably less than 8%, particularly preferably less than 5%, determined as the number fraction of particles with a particle size of less than 10 μm.

3. The mixture according to any one of the preceding claims, characterized in that, The flame retardant in powder form has a particle size distribution with a d90 of less than 100 μm, particularly preferably less than 80 μm.

4. The mixture according to any one of the preceding claims, characterized in that, The flame retardants in powder form include phosphorus-based flame retardants, in particular phosphine-containing, phosphine oxide-containing, phosphinate-containing, phosphonate-containing, phosphite-containing, phosphate-containing, phosphonium-containing and / or polyphosphate-containing flame retardants and / or flame retardants based on elemental red phosphorus, and / or the flame retardants in powder form contain nitrogen-based flame retardants, in particular melamine or isocyanurate, particularly preferably melamine cyanurate.

5. The mixture according to claim 4, characterized in that, The powdered flame retardant includes a powdered flame retardant containing phosphinate / ester, especially a flame retardant containing phosphinate containing a compound of formula I in, R1 and R2 are independently of one another straight-chain and / or branched C1-C6-alkyl and / or aryl groups, preferably ethyl groups, and M is an alkali metal, an alkaline earth metal, a transition metal, a metal and / or a protonated nitrogen-containing base, preferably selected from Mg, Ca, Al, Sb, Sn, Ge, Ti, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, K and / or ammonium, especially Al, and / or characterized in that the powdered flame retardant comprises a powdered polyphosphate-containing flame retardant, especially ammonium polyphosphate.

6. The mixture according to any one of the preceding claims, characterized in that, The flame retardant in powder form itself is agglomerated and / or the polymer material is agglomerated.

7. The mixture according to any one of the preceding claims, characterized in that, At least one polymer-based material comprises at least one thermoplastic polymer, wherein the thermoplastic polymer is preferably selected from the group consisting of polyetherimide, polycarbonate, polyphenylene sulfone, polyphenylene ether, polyether sulfone, acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene-acrylate copolymer (ASA), polyvinyl chloride, polyacrylate, polyester, polyamide, polyaryletherketone (PAEK), polyether, polyurethane, polyimide, polyamideimide, polysiloxane, polyolefin and copolymers having at least two different repeating units of the above polymers, and / or at least one polymer blend based on at least two of the aforementioned polymers and / or copolymers, wherein the at least one thermoplastic polymer preferably comprises polyamide, in particular PA6, PA6,6, PA11, PA12, PA6,13, PA10,12, PA5, PA5,10, polypropylene-polyethylene copolymers, thermoplastic polyurethanes and / or thermoplastic polyamide elastomers.

8. A method for preparing the mixture according to any one of claims 1 to 7, comprising adjusting a specific particle size distribution in a flame retardant in powder form, wherein d50 is in the range of 20 to 80 μm, preferably at least 30 and / or at most 60 μm, and d10 is greater than 10 μm, preferably greater than 15 μm, more preferably greater than 20 μm, and mixing the flame retardant in powder form with at least one polymer-based material in powder form.

9. The method according to claim 8, characterized in that, Adjusting the specific particle size distribution in the flame retardant in powder form includes removing particles, especially by classification, preferably by screening, air jet screening, and / or sieving.

10. The method according to any one of claims 8 or 9, characterized in that, Adjusting the specific particle size distribution in the flame retardant in powder form includes the following steps, wherein - the flame retardant in powder form agglomerates on its own, - the flame retardant in powder form agglomerates on the polymer material, - agglomerating the flame retardant in powder form from a dispersion or solution by precipitation or drying, and / or wherein - the flame retardant in powder form is first compounded with at least one polymer material and then micronized to the target particle size.

11. A mixture obtainable by a method according to at least one of claims 8 to 10.

12. A three-dimensional object prepared by irradiating and curing a powdered building material at spatial points corresponding to cross-sections of the three-dimensional object in respective layers, wherein a mixture according to any one of the preceding claims 1 to 7 and / or a mixture according to claim 11 is used as the building material.

13. A method for preparing a three-dimensional object, especially by curing a powdered building material at points corresponding to cross-sections of the three-dimensional object in respective layers, wherein a mixture according to any one of the preceding claims 1 to 7 and / or a mixture according to claim 11 is used as the building material, and preferably the building material is selectively cured by the action of electromagnetic radiation emitted by a radiation source.

14. A system for preparing a three-dimensional object by curing a powdered building material at positions corresponding to cross-sections of the three-dimensional object in respective layers, wherein the system includes at least one radiation source designed to emit electromagnetic radiation; a processing chamber serving as an open container, the processing chamber being designed to have container walls; a support arranged in the processing chamber, wherein the processing chamber and the support are movable relative to each other in a vertical direction; a storage container and a coater movable in a horizontal direction, wherein the storage container is at least partially filled with a mixture according to any one of the preceding claims 1 to 7 and / or a mixture according to claim 11.

15. The method according to claim 13 or the system according to claim 14, wherein the radiation source emits electromagnetic radiation having a wavelength in the range of 400 to 1,500 nm, preferably electromagnetic radiation in one of the wavelength ranges 1,064 ± 8 nm and / or 980 ± 7 nm and / or 940 ± 7 nm and / or 810 ± 7 nm and / or 780 ± 10 nm and / or 640 ± 7 nm, or electromagnetic radiation having a wavelength of about 10.6 μm or in the range of 4.8 to 8.3 μm and preferably about 5 μm, wherein the radiation source includes at least one laser, preferably at least one diode laser.

16. Use of a mixture according to any one of the preceding claims 1 to 7 and / or a mixture according to claim 11 as a construction material for additive manufacturing of a three-dimensional object by selectively curing the construction material at cross-section points of the three-dimensional object in a respective layer, in particular according to claim 13 or 15.

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