Expandable 3D printing filament and method for the production thereof
Patent Information
- Application Number
- EP2024710022
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-02-21
- Filing Date
- 2024-02-20
- Publication Date
- 2025-12-31
AI Technical Summary
Existing 3D printing methods using thermoplastic polymers have limited control over density of printed parts, leading to long printing times and mechanical property degradation due to high density, and prior expandable filaments with blowing agents have a short shelf life and limited density reduction.
The use of hydrocarbons with up to six carbon atoms, partially substituted with fluorine, as blowing agents in 3D printing filaments, impregnated at increased pressure below the melting temperature, allows for longer shelf life and adjustable density of printed parts from conventional 3D printers.
The solution provides 3D printing filaments with a significantly longer shelf life and the ability to produce foamed polymer moldings with densities as low as 5% of the unfoamed density, maintaining mechanical stability and homogeneous pore structure.
Smart Images
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Abstract
Description
[0001] Expandable 3D printing filament and method for its production The invention relates to a method for producing expandable 3D printing filaments by providing a 3D printing filament made of at least one thermoplastic polymer and impregnating it with at least one blowing agent below its melting temperature at a pressure elevated relative to ambient pressure. The invention further relates to an expandable 3D printing filament made of at least one thermoplastic polymer, which is impregnated with at least one blowing agent, produced in particular by means of such a method, and to a foamed polymer molded part produced from at least one expandable 3D printing filament of the aforementioned type by means of 3D printing.For the production of polymer molded parts, the melt-deposition process, also known as "fused deposition modeling" (FDM) or "fused filament fabrication" (FFF), is used in 3D printers. This process involves plasticizing a 3D printing filament made of a thermoplastic polymer or a polymer blend of several thermoplastic polymers and depositing it layer by layer using a nozzle typically provided in the print head of the 3D printer to ultimately produce the polymer molded part composed of a multitude of such layers. This enables, on the one hand, the layer-by-layer production of relatively complex parts, suitable for prototyping or small series production, for example, using conventional thermoplastic processing methods such as injection molding, extrusion, etc., molded parts that are difficult or impossible to manufacture and have more or less complex structures. On the other hand, the fused deposition process is also increasingly being used for the series production of polymer molded parts, particularly those with relatively complex structures. In the fused deposition process using 3D printing, also known as "additive manufacturing," a three-dimensional model of the molded part to be produced is usually created digitally, which can be done particularly using the well-known methods of computer-aided design (CAD). In addition, suitable software, such as a so-called slicer program (e.g., Cura), is used to create the desired shape. TMor the like), the three-dimensional model of the molded part to be produced is broken down into a plurality of thin layers, whereupon the plasticized polymer of the 3D printing filament is deposited layer by layer using the nozzle of the correspondingly moved print head in order to build up the polymer molded part layer by layer. Immediately after the polymer plasticized material is discharged from the nozzle of the print head in more or less strand- or drop-like form, the solidification process begins, whereby the deposited plasticized material solidifies, for example, at ambient temperature or during active cooling. An inherent disadvantage of the melt layer deposition process using 3D printers is that, on the one hand, the density of the printed polymer molded part can currently only be influenced to a limited extent, and, on the other hand, the printing times for large-volume polymer molded parts are relatively long, since only very thin plasticized strands can be deposited layer by layer.In order to reduce the density of the printed polymer part and simultaneously save polymer material, the so-called infill is currently typically reduced. This refers to the internal filling or internal support structure of the printed polymer part that is not visible from the outside. The infill can range from 100% (in the case of a solid or entirely compact polymer part) to almost 0% (in the case of a completely hollow polymer part). However, the mechanical properties of the polymer part deteriorate significantly with decreasing infill, and notch effects, which form at the transitions between strands deposited or generated from the printed 3D printing filaments, represent a further weak point.Alternatively or additionally, recent attempts have been made to reduce the density of the printed polymer molding by using 3D printing filaments loaded with blowing agents, allowing the plasticized strand to be foamed during 3D printing and resulting in a foamed polymer molding. However, the resulting reduction in density is currently limited, and minimum densities of the polymer molding of up to approximately 400 kg / m³ can be achieved in this way. 3WO 2020 / 043669 A1 describes a process for producing expandable 3D printing filaments and a process for 3D printing foamed polymer moldings from such expandable 3D printing filaments, wherein 3D printing filaments made of thermoplastic polymers are impregnated with a blowing agent below their melting temperature under elevated pressure. The blowing agents used are, on the one hand, inert gases such as carbon dioxide (CO2), nitrogen (N2), or water (H2O), and, on the other hand, short-chain alkanes such as isobutane, pentane, and cyclopentane. A particular disadvantage is the virtually non-existent storage life of the 3D printing filaments impregnated with the blowing agent, since the blowing agent outgasses more or less spontaneously as soon as the overpressure established during impregnation is expanded.The 3D printing filaments must therefore be printed immediately after impregnation. They must first be cooled in the 3D printer before being heated to their melting temperature to foam the plasticized material and deposit it layer by layer to form the foamed polymer molded part. Furthermore, the maximum possible density reduction of the foamed polymer molded part is limited here as well, amounting to up to approximately 45% compared to a corresponding compact (unfoamed) molded part. The same applies to a large extent to another process for producing expandable 3D printing filaments in the immediate run-up to the 3D printing of foamed polymer molded parts therefrom according to EP 3403 806 A1, in which the 3D printing filaments are impregnated below their melting temperature with blowing agents in the form of supercritical inert gases, such as carbon dioxide in particular.The invention is based on the object of developing a method for producing expandable 3D printing filaments of the type mentioned at the outset, as well as a 3D printing filament that can be produced in this way, and a foamed polymer molded part produced therefrom by means of 3D printing, while at least largely avoiding the aforementioned disadvantages in a simple and cost-effective manner, such that the expandable 3D printing filament has a longer storage life than the prior art and can be processed by means of 3D printing to form foamed polymer molded parts with a lower density, wherein the expandable 3D printing filament should be able to be printed in particular using conventional, commercially available 3D printers.From a process engineering perspective, this object is achieved according to the invention in a method of the type mentioned at the outset in that the at least one blowing agent is selected from the group of hydrocarbons having at least one functional group and / or at least partially substituted with fluorine and having up to six carbon atoms. From a product engineering perspective, the invention further provides for the solution of this object by a 3D printing filament producible by means of such a method and made of at least one thermoplastic polymer which is impregnated with at least one blowing agent, wherein the at least one blowing agent is selected from the group of hydrocarbons having at least one functional group and / or at least partially substituted with fluorine and having up to six carbon atoms.Furthermore, to achieve this object, the invention provides, from a product-technical perspective, a foamed polymer molded part made from at least one expandable 3D printing filament of the aforementioned type. Surprisingly, it was found that the blowing agents according to the invention impart a considerably longer storage life of up to several weeks to the expandable 3D printing filament compared to the prior art, so that the impregnated 3D printing filaments, on the one hand, do not have to be processed immediately after impregnation, and, on the other hand, can be processed into foamed polymer molded parts using conventional 3D printers. The foamed plastic proves to be very stable and has a very homogeneous pore structure that does not collapse during the solidification of the plastic strands.The density of a foamed polymer molded part printed in this way can be varied within wide limits, particularly by varying the nozzle temperature and the extrusion speed of the 3D printer, down to very low densities of the polymer molded part of less than 5% of the density of a corresponding compact (unfoamed) polymer molded part or up to densities in the order of about 30 kg / m. 3 up to about 40 kg / m 3It is suspected that, in particular, the relatively high molecular weight and the relatively high vapor pressures of the blowing agents according to the invention, compared to the previously known blowing agents for expandable 3D printing filaments, play a role, coupled with a sufficiently low boiling or evaporation temperature. As already mentioned, the expandable 3D printing filaments according to the invention can be processed into foamed polymer moldings with a predetermined geometry using virtually any known 3D printer by means of melt layers. The at least one, e.g., exactly one, functional group of the hydrocarbons with up to six carbon atoms, as used according to the invention as blowing agents for the expandable 3D printing filaments, can preferably be hydroxyl groups (-OH), ether groups (-O-), ketone groups (-CO-),Carboxyl groups (-COOH) or ester groups (-CO-O-). Thus, in an advantageous embodiment, it can be provided that the at least one propellant from the group of - alcohols with a hydroxyl group, in particular from the group of acyclic and cyclic alkanols, e.g. methanol, ethanol, n-propanol (propan-1-ol), iso-propanol (propan-2-ol), n-butanol (butan-1-ol), iso-butanol (2-methyl-1-butanol), sec-butanol (2-butanol), tert-butanol (2-methyl-2-butanol), n-pentanol (pentan-1-ol), 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol etc., - the ether, in particular from the group of acyclic and cyclic alkyl ethers, e.g. dimethyl ether (DME), ethyl methyl ether, diethyl ether, Methyl n-propyl ether, methyl iso-propyl ether, methyl tert-butyl ether (MTBE), n-butyl methyl ether, ethyl n-propyl ether, ethyl iso-propyl ether, di-n-propyl ether, ethyl butyl ether, tetrahydrofuran (oxacyclopentane), tetrahydropyran (oxacyclohexane) etc., - the ketones,preferably with a maximum of 4 carbon atoms, such as in particular dimethyl ketone (acetone) or methyl ethyl ketone (butanone), diethyl ketone (3-pentanone), methyl propyl ketone (2-pentanone), etc., - carboxylic acids with a carboxyl group, in particular from the group of acyclic saturated carboxylic acids, e.g. formic acid (methanoic acid), acetic acid (ethanoic acid), propionic acid (propanoic acid), etc., and - esters, in particular from the group of carboxylic acid esters, e.g. methyl formate (methyl formate), ethyl formate (ethyl formate), propyl formate (propyl formate), n-formate (butyl formate), sec-formate (sec-butyl formate), or tert-butyl formate (tert-butyl formate), pentyl formate (pentyl formate), Methyl acetate, methyl acetate (ethyl formate), propyl acetate, n-butyl acetate, sec-butyl acetate, or tert-butyl acetate,Propionic acid methyl ester (methyl propionate), propionic acid ethyl ester (ethyl propionate), propionic acid propyl ester (propyl propionate), butyric acid methyl ester (methyl butyrate), butyric acid ethyl ester (ethyl butyrate), valeric acid methyl ester (methyl pentanoate), etc. Alternatively or additionally, the at least partially fluorine-substituted hydrocarbons having up to six carbon atoms, as used according to the invention as blowing agents for the expandable 3D printing filaments, can preferably be hydrofluoroalkanes (saturated fluorocarbons, "HFA") and / or hydrofluoroalkenes (unsaturated fluorocarbons, so-called hydrofluoroolefins, "HFO"), such as 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene, etc. In an expandable 3D printing filament according to the invention, it can therefore preferably be provided that the at least one blowing agent is selected from the group of - alcohols having a hydroxyl group,in particular from the group of acyclic and cyclic alkanols, e.g. methanol, ethanol, n-propanol (propan-1-ol), iso-propanol (propan-2-ol), n-butanol (butan-1-ol), iso-butanol (2-methyl-1-butanol), sec-butanol (2-butanol), tert-butanol (2-methyl-2-butanol), n-pentanol (pentan-1-ol), 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol etc., - the ethers, in particular from the group of acyclic and cyclic alkyl ethers, e.g. dimethyl ether (DME), ethyl methyl ether, diethyl ether, methyl n-propyl ether, methyl isopropyl ether, methyl tert-butyl ether (MTBE), n-butyl methyl ether, ethyl n-propyl ether, ethyl isopropyl ether, di-n-propyl ether, ethyl butyl ether, tetrahydrofuran (oxacyclopentane), tetrahydropyran (oxacyclohexane), etc., - ketones, preferably with a maximum of 4 carbon atoms, such as in particular dimethyl ketone (acetone) or methyl ethyl ketone (butanone), diethyl ketone (3-pentanone), methyl propyl ketone (2-pentanone), etc.,- carboxylic acids with a carboxyl group, in particular from the group of acyclic saturated carboxylic acids, e.g. formic acid (methanoic acid), acetic acid (ethanoic acid), propionic acid (propanoic acid), etc., - esters, in particular from the group of carboxylic acid esters, e.g. methyl formate (methyl formate), ethyl formate (ethyl formate), propyl formate (propyl formate), n-formate (butyl formate), sec-formate (sec-butyl formate), or tert-butyl formate (tert-butyl formate), pentyl formate (pentyl formate), methyl acetate (methyl acetate), methyl acetate (ethyl formate), propyl acetate (propyl acetate), n-formate (butyl acetate), sec-formate (sec-butyl acetate), or tert-butyl acetate (tert-butyl acetate), propionic acid methyl ester (methyl propionate), propionic acid ethyl ester (ethyl propionate), propionic acid propyl ester (propyl propionate), butyric acid methyl ester (methyl butyrate), butyric acid ethyl ester (ethyl butyrate),Valeric acid methyl ester (methyl pentanoate) etc., and - hydrofluoroalkanes (HFA) and / or hydrofluoroalkenes (HFO), e.g. 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene etc. The impregnation of the 3D printing filaments made of at least one thermoplastic polymer below its melting temperature at a pressure higher than ambient pressure with the at least one blowing agent can be carried out in a manner known per se by placing the 3D printing filaments, e.g., in a pressure vessel such as an autoclave or the like, after which the pressure vessel is pressurized with the respective blowing agent or a mixture of several blowing agents and, if necessary, tempered. For this purpose, it has proven to be expedient, for example, if the 3D printing filament - at a pressure between greater than about 1 bar and about 300 bar, in particular between about 1.5 bar and about 200 bar, preferably between about 2 bar and about 100 bar,e.g., between about 5 bar and about 60 bar, and / or - at a temperature between about 0°C and about 200°C, in particular between about 0°C and about 100°C, preferably between about 0°C and about 80°C, e.g., between about 20°C and about 80°C, and / or - over a period of time between about 1 min and about 30 h, in particular between about 5 min and about 25 h, preferably between about 10 min and about 20 h, e.g., between about 30 min and about 20 h or between about 1 h and about 20 h, with the at least one propellant. The propellant can also be liquefied during the impregnation process by appropriate control of pressure and / or temperature.or the 3D printing filament is exposed to the blowing agent kept in the gaseous state for a corresponding period of time. Depending on the selected blowing agent and the thermoplastic polymer(s) of the 3D printing filament, the latter can be impregnated with the at least one blowing agent, for example, at a temperature close to, below, or above ambient temperature. In the latter case, it is preferably cooled after impregnation while maintaining the pressure to a temperature that corresponds at most to ambient temperature. In this way, any unwanted foaming of the 3D printing filament at the end of the impregnation can be prevented, with the impregnation pressure set in the pressure vessel then preferably being released abruptly.The pressure vessel is then opened and the fully impregnated expandable 3D printing filament can be removed from the pressure vessel. The blowing agents according to the invention are generally suitable for any known thermoplastic polymers that can be used in 3D printing filaments to foam the 3D printing filament during 3D printing and produce a foamed polymer molding using melt layers. For example, it can be provided that the at least one thermoplastic polymer of the expandable 3D printing filament is selected from the group of - polyolefins, in particular from the group of polyethylene (PE), polypropylene (PP) and polybutylene (PB), including their copolymers, in particular the ethylene-vinyl acetate copolymers (EVA) and the ethylene-butyl acetate copolymers (EBA), - polyoxymethylenes (POM), - polyalkylene terephthalates, in particular from the group of polyethylene terephthalate (PET), polybutylene terephthalate (PBT),Polybutylene adipate terephthalate (PBAT), bis(2-ethylhexyl)terephthalate and bis(hydroxyethyl)terephthalate, - polystyrene (PS) including its copolymers, in particular acrylonitrile-butadiene-styrene copolymers (ABS), - polycarbonates (PC), - polyamides (PA), - polyimides (PI) including polyetherimides (PEI) and polyamideimides (PAI), - polyhydroxyalkanoates (PHA), - polysulfones, in particular from the group polysulfone (PSU), polyethersulfone (PES) and polyphenylenesulfone (PPSU), - polyetheretherketones (PEEK), - polyphenylene sulfides (PPS), - thermoplastic elastomers (TPE), in particular from the group of polyether block amides (PEBA), - thermoplastic polyurethanes (TPU), - cellulose including its derivatives, in particular from the Group of cellulose acetates and propionates,and - the polylactide (PLA), including their polymer blends, is or is selected. In an advantageous embodiment of the method according to the invention, it can be provided that a 3D printing filament made of a polymer blend containing at least two thermoplastic polymers of different crystallinity is used. In this context, it has been found that a polymer blend with at least one predominantly amorphous thermoplastic polymer and at least one semi-crystalline thermoplastic polymer ensures both very high loading levels with the blowing agents according to the invention and the resulting very low densities of a foamed polymer molded part printed from such an expandable 3D printing filament, as well as very reliable handling of the 3D printing process, whereby uncontrolled or premature foaming of the 3D printing filament is prevented. It is assumedthat the semi-crystalline phase of the thermoplastic polymer blend stabilizes the expandable 3D printing filament impregnated with the blowing agents according to the invention, while the amorphous phase of the polymer blend ensures good foaming and welding behavior with regard to a low density and a homogeneous cell morphology of a stable polymer foam. While preferably at least one polylactide (PLA) can be used as a blend component of such a polymer blend - be it a predominantly amorphous polylactide or a predominantly semi-crystalline polylactide - it has proven particularly advantageous in this context if a 3D printing filament made of a polymer blend is used which comprises at least two polylactides of different crystallinity, in particular at least one predominantly amorphous polylactide and at least one semi-crystalline polylactide.In an expandable 3D printing filament according to the invention, it can therefore advantageously be provided that it comprises a polymer blend of at least two thermoplastic polymers of different crystallinity, wherein the expandable 3D printing filament can preferably comprise a polymer blend containing at least one, in particular at least two, polylactides of different crystallinity, in particular at least one predominantly amorphous polylactide and at least one semi-crystalline polylactide. Embodiments: On the one hand, (compact) 3D printing filaments were produced from various thermoplastic polymer materials using a twin-screw extruder with a melt pump, cooling bath, take-off and winding device (Examples [1], [2] and [5] et seq.).On the other hand, commercially available (compact) 3D printing filaments were provided (examples [3] and [4]). The following polymer materials were used as examples: [1] Acrylonitrile-butadiene-styrene copolymer (ABS) of the type "PA-707" (CHIMEI Corporation); [2] Cellulose propionate (CP) of the type "Cellidor CP 400-12" (MOCOM Compounds GmbH & Co. KG); [3] 3D printing filament made of polylactide (PLA), semi-crystalline, of the type "eco-PLA" (colorFabb BV); [4] 3D printing filament made of polylactide (PLA), semi-crystalline, of the type "tough PLA" (colorFabb BV); [5] Polylactide (PLA), semi-crystalline, high crystallinity, of the type "Luminy L175" (Total Corbion PLA BV); [6] Polymer blend of: - 50 mass% PLA, semi-crystalline, high crystallinity, of the type "Luminy L175" (Total Corbion PLA BV), and - 50 mass% PLA, amorphous, of the type "Luminy LX975" (Total Corbion PLA BV); [7] Polylactide (PLA), semi-crystalline, low crystallinity,of the type "Luminy LX175" (Total Corbion PLA BV); [8] Polymer blend of: - 50 mass% PLA, semi-crystalline, low crystallinity, of the type "Luminy LX175" (Total Corbion PLA BV), and - 50 mass% PLA, amorphous, of the type "Luminy LX975" (Total Corbion PLA BV); [9] Polylactide (PLA), amorphous, of the type "Luminy LX975" (Total Corbion PLA BV);
[0010] Polylactide (PLA) from recycled material;
[0011] Polycarbonate (PC) of the type "Calibre 201-10" (Trinseo SA);
[0012] Polyhydroxybutyrate (PHBV) of the type "Enmat Y1000P" (TianAn Biologic Materials Co., Ltd.);
[0013] Amorphous polyetherimide (PEI) of the type "Ultem 1000" (SABIC);
[0014] Thermoplastic elastomer (TPE) in the form of a polyether block amide of the type "Pebax 3533 SP01" (Arkema SA);
[0015] Thermoplastic polyolefin (TPO) in the form of an ethylene-propylene copolymer of the type "Versify 3401" (Dow,Inc.);
[0016] Low-density polyethylene (LDPE) of the type "2501 NO" (SABIC); and
[0017] Thermoplastic polyolefin (TPO) in the form of a propylene-ethylene random copolymer of the type "ISPLEN PR 264 G1F" (Repsol SA). The (compact) 3D printing filaments according to the above examples 1 to 17 were fed in the form of strand bundles into a pressure vessel in the form of a pressure- and temperature-controllable autoclave with a 15 l capacity and blowing agent supply and impregnated with various blowing agents, wherein in the present embodiments, dimethyl ether (DME), 1,3,3,3-tetrafluoropropene (TFP) or dimethyl ketone (acetone) were used as blowing agents. During the impregnation, the autoclave was heated to an impregnation temperature (T, I ) and in this way an essentially constant impregnation pressure (p I), whereby these conditions are maintained over a certain impregnation period (t I ) were maintained. The autoclave was then closed while maintaining the impregnation pressure (p I) was cooled to ambient temperature of approximately 20°C to prevent any foaming of the blowing agent during impregnation. The pressure was then suddenly released and the autoclave opened to remove the expandable 3D printing filaments and determine the respective blowing agent content gravimetrically. In the case of Example 13, the loading with the blowing agent acetone took place in a sealed bag, which withstands the vapor pressure of acetone. The following Table 1 lists the impregnation parameters and the blowing agent content obtained after impregnation of the 3D printing filaments according to the above Examples 1 to 17: Table 1: Impregnation of the 3D printing filaments with the blowing agent dimethyl ether (DME) or 1,3,3,3-tetrafluoropropene (TFP) and the blowing agent contents achieved thereby. Foamed polymer moldings were printed from the expandable 3D printing filaments according to Examples 1 to 17, which had been impregnated with the respective blowing agent in the manner described above, using a conventional, commercially available 3D printer of the type "SOVOL SV-03". For this purpose, the expandable 3D printing filaments were introduced into the 3D printer and plasticized by applying heat in the print head in order to print them. As the thermoplastic polymer softens, the blowing agent precipitates from the polymer matrix and foams the plasticized strand. As explained in more detail below, the degree of foaming can be adjusted by appropriately adjusting the process parameters, in particular the feed rate and / orPrint speed and nozzle temperature can be controlled within wide limits, so that foamed polymer moldings can be printed directly and, due to the variable foaming levels, polymer moldings with graded density can be obtained while still being fully (or partially) infilled. Table 2 below shows exemplary printing parameters in the form of nozzle diameter (i.e. D ) and the nozzle temperature (T D ) of the 3D printer and the feed rate (F) of the 3D printing filament, including the resulting densities of a foamed polymer molded part, as obtained by printing the expandable 3D printing filaments according to Examples 1 to 17. Table 2: Printing parameters and densities of the printed foamed polymer molded parts. Further features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the drawings. In the drawings: Fig. 1 shows a diagram with scanning electron microscopic cross-sectional views of strands of an expandable 3D printing filament foamed during 3D printing, made of a thermoplastic polymer blend impregnated with a blowing agent in the form of 1,3,3,3-tetrafluoropropene (TFP), consisting of 50 mass% of a semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) and 50 mass% of an amorphous polylactide (PLA) of the type "Luminy LX975" (see above), to illustrate the possibilities of controlling the degree of foaming by means of the printing parameters extrusion speed (F) and nozzle temperature (T D) of the 3D printer; Fig. 2 shows a graph of the densities (ρ) of foamed strands of an expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) obtained by 3D printing as a function of the extrusion speed (F) and the nozzle temperature (T D) of the 3D printer; Fig. 3 is a diagram corresponding to Fig. 2 for an expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with high crystallinity of the type "Luminy L175" impregnated with the same blowing agent dimethyl ether (DME) (see above); Fig. 4 is a diagram of the densities (ρ) obtained by 3D printing of foamed strands of an expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" impregnated with the blowing agent 1,3,3,3-tetrafluoropropene (TFP) (see above) as a function of the extrusion speed (F) and the nozzle temperature (T D) of the 3D printer; Fig. 5 shows a diagram corresponding to Fig. 4 for an expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with high crystallinity of the type "Luminy L175" impregnated with the same blowing agent 1,3,3,3-tetrafluoropropene (TFP) (see above); Fig. 6 is a graph of the densities (ρ) obtained by 3D printing of foamed strands of an expandable 3D printing filament impregnated with the blowing agent 1,3,3,3-tetrafluoropropene (TFP) made of a polymer blend of, on the one hand, 50 mass% of a semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) and, on the other hand, 50 mass% of an amorphous polylactide (PLA) of the type "Luminy LX975" (see above) as a function of the extrusion speed (F) and the nozzle temperature (T D) of the 3D printer; Fig. 7 is a diagram corresponding to Fig. 6 for an expandable 3D printing filament made of a polymer blend impregnated with the same blowing agent 1,3,3,3-tetrafluoropropene (TFP), consisting, on the one hand, of 65 mass% of the semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) and, on the other hand, of 35 mass% of the amorphous polylactide (PLA) of the type "Luminy LX975" (see above); Fig. 8 shows a diagram corresponding to Figs. 6 and 7 for an expandable 3D printing filament made of a polymer blend impregnated with the same blowing agent 1,3,3,3-tetrafluoropropene (TFP) and consisting, on the one hand, of 85 mass% of the semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) and, on the other hand, of 15 mass% of the amorphous polylactide (PLA) of the type "Luminy LX975" (see above); and Fig.9 a diagram illustrating the storage life of an expandable 3D printing filament made of a polymer blend impregnated with the blowing agent 1,3,3,3-tetrafluoropropene (TFP) consisting, on the one hand, of 50 mass% of a semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) and, on the other hand, 50 mass% of an amorphous polylactide (PLA) of the type "Luminy LX975" (see above) according to Fig. 6 with the proportion of blowing agent (TFP) as a function of the storage time (t) at different storage temperatures. Fig. 1 shows a diagram with scanning electron microscopic cross-sectional views of strands of an expandable 3D printing filament made of a 50 mass polymer blend impregnated with a blowing agent in the form of 1,3,3,3-tetrafluoropropene (TFP) foamed during 3D printing with a commercially available 3D printer of the type "SOVOL SV-03".-% of a semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) and 50 mass% of an amorphous polylactide (PLA) of the type "Luminy LX975" (see above). The enlarged image sections visible in Fig. 1 have an original size of 2 mm x 2 mm, which means that the diameter of a foamed rod shown is larger than 2 mm, provided it is only partially depicted in one of the photographic views. On the one hand, a very homogeneous foam structure can be seen throughout, with pores evenly distributed across the cross-section of the strand, with an essentially spherical shape and constant size. Furthermore, it is clear that the degree of foaming and thus the density of the strand can be easily controlled by varying the printing parameters of extrusion speed (F) and nozzle temperature (T). D) of the 3D printer is possible, whereby the degree of foaming is greater - or the density is lower - the higher the extrusion speed (F) - here: between 50 mm / min and 350 mm / min for the TFP-loaded polylactide blend - and / or the lower the nozzle temperature (T D) – here: between 140°C and 200°C for the TFP-loaded polylactide blend – of the 3D printer. The test results discussed in Fig. 2 ff. were all also obtained by printing expandable 3D printing filaments made of various polymer materials – here: various polylactides (PLA) with different crystallinities – which were impregnated with various blowing agents – here: on the one hand, dimethyl ether (DME) and on the other hand, 1,3,3,3-tetrafluoropropene (TFP) – using a commercially available 3D printer of the type "SOVOL SV-03". Fig.Figure 2 shows an exemplary diagram of the densities (ρ) of foamed strands of an expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) obtained by 3D printing as a function of the extrusion speed (F) - here: at 50 mm / min, 150 mm / min, 250 mm / min and 350 mm / min - and the nozzle temperature (T). D ) of the 3D printer - here: at 160°C, 180°C, 200°C and 220°C. One can again see the possibility of easily controlling the density of the deposited foamed strand by varying the printing parameters extrusion speed (F) and nozzle temperature (T D ), with the lowest density of 101 kg / m 3 , which corresponds to approximately 8% of the density of the compact (unfoamed) polymer, in this case at an extrusion speed (F) of 350 mm / min and a die temperature (T D) of 160°C has been reached. Fig. 3 shows an exemplary diagram of the densities (ρ) obtained by 3D printing of foamed strands of an expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with high crystallinity of the type "Luminy L175" (see above) impregnated with dimethyl ether (DME) as a function of the extrusion speed (F) - here again at 50 mm / min, 150 mm / min, 250 mm / min and 350 mm / min - and the nozzle temperature (T D ) of the 3D printer - here: at 170°C, 180°C, 200°C and 220°C. Here, too, one can see the possibility of easily controlling the density of the deposited foamed strand by varying the printing parameters extrusion speed (F) and nozzle temperature (T D ), with the lowest density of 183 kg / m 3, which corresponds to approximately 14% of the density of the compact (unfoamed) polymer, in this case at an extrusion speed (F) of 250 mm / min and a die temperature (T D ) of 170°C has been reached. Fig. 4 shows an exemplary diagram of the densities (ρ) obtained by 3D printing of foamed strands of a 1,3,3,3-tetrafluoropropene (TFP)-impregnated expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) as a function of the extrusion speed (F) - here: again at 50 mm / min, 150 mm / min, 250 mm / min and 350 mm / min - and the nozzle temperature (T D ) of the 3D printer - here: at 180°C, 200°C, 220°C, 240°C and 260°C. Here, too, one can see the possibility of easily controlling the density of the deposited foamed strand by varying the printing parameters extrusion speed (F) and nozzle temperature (TD ), with the lowest density of 141 kg / m 3 , which corresponds to approximately 11% of the density of the compact (unfoamed) polymer, in this case at an extrusion speed (F) of 350 mm / min and a die temperature (T D ) of 180°C has been reached. Fig. 5 shows an exemplary diagram of the densities (ρ) obtained by 3D printing of foamed strands of a 1,3,3,3-tetrafluoropropene (TFP)-impregnated expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with high crystallinity of the type "Luminy L175" (see above) as a function of the extrusion speed (F) - here again at 50 mm / min, 150 mm / min, 250 mm / min and 350 mm / min - and the nozzle temperature (T D) of the 3D printer - here: at 180°C, 200°C, 220°C, 240°C, 260°C and 270°C. Here, too, one can see the possibility of easily controlling the density of the deposited foamed strand by varying the printing parameters extrusion speed (F) and nozzle temperature (T D ), with the lowest density of 214 kg / m 3 , which corresponds to approximately 16% of the density of the compact (unfoamed) polymer, in this case at an extrusion speed (F) of 250 mm / min and a die temperature (T D) of 200°C has been reached. Figs. 6 to 8 each show a graph of the densities (ρ) obtained by 3D printing of foamed strands of expandable 3D printing filaments impregnated with the blowing agent 1,3,3,3-tetrafluoropropene (TFP) made of a polymer blend of, on the one hand, semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) and, on the other hand, an amorphous polylactide (PLA) of the type "Luminy LX975" (see above) as a function of the extrusion speed (F) - here: again at 50 mm / min, 150 mm / min, 250 mm / min, and 350 mm / min - and the nozzle temperature (T D) - here: at 130°C (Fig. 6), 140°C (Fig. 6 and 7), 150°C, 160°C, 170°C, 180°C, 190°C (Fig. 7 and 8), 200°C, 220°C and 240°C - of the 3D printer. The diagrams differ only in the proportion of the two blend partners, which in the case of Fig. 6 is 50 mass% of the semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" and 50 mass% of the amorphous polylactide (PLA) of the type "Luminy LX975", in the case of Fig. 7 is 65 mass% of the semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" and 35 mass% of the amorphous polylactide (PLA) of the type "Luminy LX975" and in the case of Fig. 8 is 85 mass% of the semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" and 15 mass% of the amorphous polylactide (PLA) of the type "Lu- miny LX975". It can be seen that in addition to controlling the degree of foaming orthe resulting density of the printed strand by means of the feed speed (F) and the nozzle temperature (T. D ) of the 3D printer, it is possible to control the density of the printed rod by changing the recipe of a blend with identical blend partners and identical propellant, with otherwise identical printing parameters. It is also noticeable that very large density differences can be generated, with extremely low densities – for example, around 54 kg / m 3 (here: in the case of the PLA blend with 50 mass% "LX175" and 50 mass% "LX975" at an extrusion speed (F) of 350 mm / min and a nozzle temperature (T D ) of 140°C; Fig. 6), or - of e.g. about 56 kg / m 3 (here: in the case of the PLA blend with 65 mass% "LX175" and 35 mass% "LX975" at an extrusion speed (F) of 350 mm / min and a nozzle temperature (T D ) of 140°C; Fig. 7), or - of e.g. about 167 kg / m3 (here: in the case of the PLA blend with 85 mass% "LX175" and 15 mass% "LX975" at an extrusion speed (F) of 250 mm / min and a nozzle temperature (T D) of 180°C; Fig. 8), corresponding to approximately 4% to approximately 6% of the density of the compact (unfoamed) polymer blend. Furthermore, such a polymer blend with blend partners of different crystallinity can prove advantageous in that it can ensure both very high loading levels of blowing agent and safe handling while avoiding untimely or unwanted foaming of the 3D printing filament, whereby the predominantly crystalline phase is able to stabilize the 3D printing filament impregnated with blowing agent (i.e., to protect it from untimely foaming), while the predominantly amorphous phase ensures good and targeted foaming behavior at very high loading levels of blowing agent. In Fig.Finally, Figure 9 is a graph illustrating the storage life of an expandable 3D printing filament made of a polymer blend impregnated with the blowing agent 1,3,3,3-tetrafluoropropene (TFP) consisting of, on the one hand, 50 mass% of a semi-crystalline polylactide (PLA) with low crystallinity of the type "Luminy LX175" (see above) and, on the other hand, 50 mass% of an amorphous polylactide (PLA) of the type "Luminy LX975" (see above) corresponding to Figure 6, with the proportion of blowing agent (TFP in [mass%]) as a function of the storage time (t in [h]) at various storage temperatures of -22°C (upper curve marked with squares), at 5°C (middle curve marked with circles), and at room temperature of 20°C (lower curve marked with triangles). reproduced.It can be seen that a very long durability of the impregnated 3D printing filaments is guaranteed at all storage temperatures, including room temperature. Although the proportion of blowing agent (here: TFP) decreases within the first few days due to diffusion, it remains essentially constant from a storage time of about 400 h (about 2 weeks) up to more than 1600 h (about 2 months), with a blowing agent content of about 15 mass% being maintained at low temperatures and a blowing agent content of about 8 mass% being maintained at room temperature.
Claims
Patent claims 1. A method for producing expandable 3D printing filaments, in which a 3D printing filament is provided from at least one thermoplastic polymer and impregnated with at least one blowing agent below its melting temperature at a pressure elevated relative to ambient pressure, characterized in that the at least one blowing agent is selected from the group of hydrocarbons having at least one functional group and / or at least partially substituted with fluorine and having up to six carbon atoms. 2.Method according to claim 1, characterized in that the at least one blowing agent is selected from the group of - alcohols with a hydroxyl group, in particular from the group of acyclic and cyclic alkanols, - ethers, in particular from the group of acyclic and cyclic alkyl ethers, - ketones, in particular dimethyl ketone (acetone), - carboxylic acids with a carboxyl group, in particular from the group of acyclic saturated carboxylic acids, - esters, in particular from the group of carboxylic acid esters, and - hydrofluoroalkanes and / or hydrofluoroalkenes.
3. Method according to claim 1 or 2, characterized in that the 3D printing filament - at a pressure between greater than 1 bar and 300 bar,. in particular between 1.5 bar and 200 bar, preferably between 2 bar and 100 bar, and / or - at a temperature between 0°C and 200°C, in particular between 0°C and 100°C, preferably between 0°C and 80°C, and / or - over a period of time between 1 min and 30 h, in particular between 5 min and 25 h, preferably between 10 min and 20 h, with the at least one blowing agent.
4. The method according to one of claims 1 to 3, characterized in that the at least one thermoplastic polymer of the 3D printing filament is selected from the group of - polyolefins, in particular from the group of polyethylene (PE), polypropylene (PP) and polybutylene (PB), including their copolymers, in particular the ethylene-vinyl acetate copolymers (EVA) and the ethylene-butyl acetate copolymers (EBA), - polyoxymethylenes (POM), - polyalkylene terephthalates, in particular from the group of polyethylene terephthalate (PET), polybutylene terephthalate (PBT),Polybutylene adipate terephthalate (PBAT), bis(2-ethylhexyl)terephthalate and bis(hydroxyethyl)terephthalate, - polystyrene (PS) including its copolymers, in particular acrylonitrile-butadiene-styrene copolymers (ABS), - polycarbonates (PC), - polyamides (PA), - polyimides (PI) including polyetherimides (PEI) and polyamideimides (PAI), - polyhydroxyalkanoates (PHA), - polysulfones, in particular from the group poly-, sulfone (PSU), polyethersulfone (PES), and polyphenylenesulfone (PPSU), - polyetheretherketones (PEEK), - polyphenylene sulfides (PPS), - thermoplastic elastomers (TPE), in particular from the group of polyether block amides (PEBA), - thermoplastic polyurethanes (TPU), - cellulose including its derivatives, in particular from the group of cellulose acetates and propionates, and - polylactides (PLA), including their polymer blends.
5. The method according to one of claims 1 to 4, characterized in that a 3D printing filament made of a polymer blend containing at least two thermoplastic polymers of different crystallinity is used. 6.A method according to claim 5, characterized in that a 3D printing filament made of a polymer blend is used which contains at least two polylactides of different crystallinity, in particular at least one predominantly amorphous polylactide and at least one partially crystalline polylactide.
7. Expandable 3D printing filament made of at least one thermoplastic polymer which is impregnated with at least one blowing agent, in particular produced by a method according to one of the preceding claims, characterized in that the at least one blowing agent is selected from the group consisting of polymers having at least one functional group and / or at least. partially fluorine-substituted hydrocarbons having up to six carbon atoms.
8. Expandable 3D printing filament according to claim 7, characterized in that the at least one blowing agent is selected from the group of - alcohols with a hydroxy group, in particular from the group of acyclic and cyclic alkanols, - ethers, in particular from the group of acyclic and cyclic alkyl ethers, - ketones, in particular dimethyl ketone (acetone), - carboxylic acids with a carboxyl group, in particular from the group of acyclic saturated carboxylic acids, - esters, in particular from the group of carboxylic acid esters, and - hydrofluoroalkanes and / or hydrofluoroalkenes. 9.Expandable 3D printing filament according to claim 7 or 8, characterized in that the at least one thermoplastic polymer of the 3D printing filament from the group - of polyolefins, in particular from the group polyethylene (PE), polypropylene (PP) and polybutylene (PB), including their copolymers, in particular the ethylene-vinyl acetate copolymers (EVA) and the ethylene-butyl acetate copolymers (EBA), - of polyoxymethylenes (POM), - of polyalkylene terephthalates, in particular from the group polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylene adipate terephthalate. (PBAT), bis(2-ethylhexyl)terephthalate and bis(hydroxyethyl)terephthalate, - polystyrene (PS) including its copolymers, in particular acrylonitrile-butadiene-styrene copolymers (ABS), - polycarbonates (PC), - polyamides (PA), - polyimides (PI) including polyetherimides (PEI) and polyamideimides (PAI), - polyhydroxyalkanoates (PHA), - polysulfones, in particular from the group polysulfone (PSU), polyethersulfone (PES) and polyphenylenesulfone (PPSU), - polyetheretherketones (PEEK), - polyphenylene sulfides (PPS), - thermoplastic elastomers (TPE), in particular from the group of polyether block amides (PEBA), - thermoplastic polyurethanes (TPU), - cellulose including its derivatives, in particular selected from the group of cellulose acetates and propionates, and - polylactides (PLA) including their polymer blends. 10.Expandable 3D printing filament according to one of claims 7 to 9, characterized in that the 3D printing filament comprises a polymer blend of at least two thermoplastic polymers of different crystallinity.
11. Expandable 3D printing filament according to claim 10, characterized in that the 3D printing filament comprises a polymer blend which comprises at least two polylac-. tides of different crystallinity, in particular at least one predominantly amorphous polylactide and at least one semi-crystalline polylactide.
12. A foamed polymer molded part produced from at least one expandable 3D printing filament according to one of claims 7 to 11 by means of 3D printing.