DE102023104249A1 - Expandable 3D printing filament and method for its production - Google Patents

Abstract

A method for producing expandable 3D printing filaments is proposed by providing a 3D printing filament made of a thermoplastic polymer or polymer blend and impregnating it with at least one blowing agent below its melting temperature at a pressure higher than ambient pressure. The invention provides 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. The invention further relates to an expandable 3D printing filament obtainable by means of such a method made of a thermoplastic polymer or polymer blend impregnated with at least one blowing agent, as well as to a foamed polymer molding which is produced from at least one expandable 3D printing filament of the aforementioned type by means of 3D printing.

Description

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 higher than 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 which is produced from at least one expandable 3D printing filament of the aforementioned type by means of 3D printing.

The melt layer process, also known as "fused deposition modeling" (FDM) or "fused filament fabrication" (FFF), is used in 3D printers and is a manufacturing process in which a 3D printing filament made of a thermoplastic polymer or a polymer blend of several thermoplastic polymers is plasticized and deposited layer by layer using a nozzle usually provided in the print head of the 3D printer in order to produce the polymer molded part ultimately made up of a large number of such layers. On the one hand, this enables layer-by-layer production of relatively complex molded parts with more or less complex structures that are not or only difficult to produce using conventional thermoplastic processing methods such as injection molding, extrusion, etc., and on the other hand, the melt layer process is increasingly being used for the series production of polymer molded parts, especially with relatively complex structures.

In the melt layer 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 in particular using the well-known methods of computer-aided design (CAD). In addition, using suitable software, such as a so-called slicer program (e.g. Cura™ or the like), the three-dimensional model of the molded part to be produced is broken down into a number of thin layers, whereupon the plasticized polymer of the 3D printing filament is deposited layer by layer using the nozzle of the correspondingly moving 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 droplet form, the solidification process begins, with the deposited plasticized material solidifying, for example, at ambient temperature or with active cooling.

An inherent disadvantage of the melt layer process using 3D printers is that, on the one hand, the density of the printed polymer molding can only be influenced to a small extent, and, on the other hand, the printing times for large-volume polymer moldings are relatively long, since only very thin plastic strands can be deposited layer by layer. In order to reduce the density of the printed polymer molding and at the same time save polymer material, the so-called infill is currently usually reduced, which means the inner filling or the inner support structure of the printed polymer molding that is not visible from the outside, whereby the infill can be between 100% (in the case of a solid or completely compact polymer molding) to almost 0% (in the case of a completely hollow polymer molding). However, the mechanical properties of the polymer molded part deteriorate significantly as the infill decreases, and notch effects that form at the transitions between strands deposited or produced from the printed 3D printing filaments represent another weak point. Alternatively or additionally, attempts have recently been made to reduce the density of the printed polymer molded part by using 3D printing filaments loaded with blowing agents, so that the plasticized strand can be foamed during 3D printing and a foamed polymer molded part is obtained. However, the reduction in density that can be achieved in this way is currently limited, and minimum densities of the polymer molded part of up to around 400 kg/m ³ can be achieved in this way.

The WO 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, whereby 3D printing filaments made of thermoplastic polymers are impregnated with a blowing agent below their melting temperature under increased pressure. Inert gases such as carbon dioxide (CO ₂ ), nitrogen (N ₂ ) or water (H ₂ O) are used as blowing agents on the one hand, and short-chain alkanes such as isobutane, pentane and cyclopentane on the other. A particular disadvantage is the practically non-existent storage capacity of the 3D printing filaments impregnated with the blowing agent, since the blowing agent more or less spontaneously outgasses as soon as the temperature set during the impregnation is reached. Overpressure is used to expand the filaments. The 3D printing filaments must therefore be printed immediately after they have been impregnated. They must first be cooled in the 3D printer before they are heated to their melting temperature in order to foam the plastic and deposit it layer by layer to form the foamed polymer molded part. In addition, the maximum possible density reduction of the foamed polymer molded part is also limited here and amounts to up to around 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 3D printing of foamed polymer moldings from them in accordance with the EP 3 403 806 A1 by impregnating the 3D printing filaments 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 shelf 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 by means of conventional, commercially available 3D printers.

From a process engineering point of view, this object is achieved according to the invention in a process 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.

In terms of product technology, the invention further provides for solving this problem by means of such a process, a 3D printing filament 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, in order to solve this problem, the invention provides, in terms of product technology, a foamed polymer molded part which is 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 give the expandable 3D printing filament a considerably longer shelf life of up to several weeks compared to the prior art, so that the impregnated 3D printing filaments do not have to be processed immediately after impregnation, and can be processed into foamed polymer moldings 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 controlled within wide limits, in particular 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 to about 40 kg/m ^3. It is assumed that the relatively high molecular weight compared to the previously known blowing agents of expandable 3D printing filaments and the relatively high vapor pressures of the blowing agents according to the invention, with a nevertheless sufficiently low boiling or evaporation temperature, play a role. As already mentioned, the expandable 3D printing filaments according to the invention can be processed into foamed polymer molded parts with a predetermined geometry using virtually any known 3D printer by means of melt layers.

• - der Alkohole mit einer Hydroxygruppe, insbesondere aus der Gruppe der acyclischen und cyclischen Alkanole, z.B. Methanol, Ethanol, n-Propanol (Propan-1-ol), iso-Propanol (Propan-2-ol), n-Butanol (Butan-1-ol), isoButanol (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.,
• - der Ether, insbesondere aus der Gruppe der acyclischen und cyclischen Alkylether, z.B. Dimethylether (DME), Ethylmethylether, Diethylether, Methyl-n-propylether, Methyl-iso-propylether, Methyl-tert-butylether (MTBE), n-Butylmethylether, Ethyl-n-propylether, Ethyl-iso-propylether, Di-n-propylether, Ethylbutylether, Tetrahydrofuran (Oxacyclopentan), Tetrahydropyran (Oxacyclohexan) etc.,
• - der Carbonsäuren mit einer Carboxylgruppe, insbesondere aus der Gruppe der acyclischen gesättigten Carbonsäuren, z.B. Ameisensäure (Methansäure), Essigsäure (Ethansäure), Propionsäure (Propansäure) etc., und
• - der Ester, insbesondere aus der Gruppe der Carbonsäureester, z.B. Ameisensäuremethylester (Methylformiat), Ameisensäureethylester (Ethylformiat), Ameisensäurepropylester (Propylformiat), Ameisensäure-n- (Butylformiat), -sec- (sec-Butylformiat), oder -tert-butylester (tert-Butylformiat), Ameisensäurepentylester (Pentylformiat), Essigsäuremethylester (Methylacetat), Essigsäuremethylester (Ethylformiat), Essigsäurepropylester (Propylacetat), Essigsäure-n- (Butylacetat), -sec- (sec-Butylacetat), oder -tert-butylester (tert-Butylacetat), Proprionsäuremethylester (Methylpropionat), Propiosäureethylester (Ethylpropionat), Propionsäurepropylester Propylpropionat), Buttersäuremethylester (Methylbutyrat), Buttersäureethylester (Ethylbutyrat), Valeriansäuremethylester (Methylpentanoat) etc.,

gewählt wird. Alternativ oder zusätzlich kann es sich bei den zumindest teilweise mit Fluor substituierten Kohlenwasserstoffe mit bis zu sechs Kohlenstoffatomen, wie sie erfindungsgemäß als Treibmittel der expandierbaren 3D-Druckfilamente eingesetzt werden, vorzugsweise um Hydrofluoralkane (gesättigte Fluorkohlenwasserstoffe, „HFA“) und/oder Hydrofluoralkene (ungesättigte Fluorkohlenwasserstoffe, sogenannte Hydrofluorolefine, „HFO“) handeln, wie z.B. 1,3,3,3-Tetrafluorpropen, 2,3,3,3-Tetrafluorpropen etc.The at least one, eg 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 hydroxy groups (-OH), ether groups (-O-), carboxyl groups (-COOH) or ester groups (-CO-O-). In an advantageous embodiment, it can be provided that the at least one blowing agent from the group

• - alcohols with a hydroxy 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), isobutanol (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.,
• - 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.,
• - 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
• - the 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), methyl propionate (methyl propionate), ethyl propionate (ethyl propionate), propyl propionate (propyl propionate), methyl butyrate (methyl butyrate), ethyl butyrate (ethyl butyrate), methyl valerate (methyl pentanoate) etc.,

is selected. Alternatively or additionally, the hydrocarbons with up to six carbon atoms that are at least partially substituted with fluorine, 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.

• - der Alkohole mit einer Hydroxygruppe, insbesondere aus der Gruppe der acyclischen und cyclischen Alkanole, z.B. Methanol, Ethanol, n-Propanol (Propan-1-ol), iso-Propanol (Propan-2-ol), n-Butanol (Butan-1-ol), isoButanol (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.,
• - der Ether, insbesondere aus der Gruppe der acyclischen und cyclischen Alkylether, z.B. Dimethylether (DME), Ethylmethylether, Diethylether, Methyl-n-propylether, Methyl-iso-propylether, Methyl-tert-butylether (MTBE), n-Butylmethylether, Ethyl-n-propylether, Ethyl-iso-propylether, Di-n-propylether, Ethylbutylether, Tetrahydrofuran (Oxacyclopentan), Tetrahydropyran (Oxacyclohexan) etc.,
• - der Carbonsäuren mit einer Carboxylgruppe, insbesondere aus der Gruppe der acyclischen gesättigten Carbonsäuren, z.B. Ameisensäure (Methansäure), Essigsäure (Ethansäure), Propionsäure (Propansäure) etc.,
• - der Ester, insbesondere aus der Gruppe der Carbonsäureester, z.B. Ameisensäuremethylester (Methylformiat), Ameisensäureethylester (Ethylformiat), Ameisensäurepropylester (Propylformiat), Ameisensäure-n- (Butylformiat), -sec- (sec-Butylformiat), oder -tert-butylester (tert-Butylformiat), Ameisensäurepentylester (Pentylformiat), Essigsäuremethylester (Methylacetat), Essigsäuremethylester (Ethylformiat), Essigsäurepropylester (Propylacetat), Essigsäure-n- (Butylacetat), -sec- (sec-Butylacetat), oder -tert-butylester (tert-Butylacetat), Proprionsäuremethylester (Methylpropionat), Propiosäureethylester (Ethylpropionat), Propionsäurepropylester Propylpropionat), Buttersäuremethylester (Methylbutyrat), Buttersäureethylester (Ethylbutyrat), Valeriansäuremethylester (Methylpentanoat) etc., und
• - Hydrofluoralkane (HFA) und/oder Hydrofluoralkene (HFO), z.B. 1,3,3,3-Tetrafluorpropen, 2,3,3,3-Tetrafluorpropen etc.,

gewählt ist.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

• - alcohols with a hydroxy 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), isobutanol (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.,
• - 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.,
• - 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.,
• - the 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), methyl propionate (methyl propionate), ethyl propionate (ethyl propionate), propyl propionate (propyl propionate), methyl butyrate (methyl butyrate), ethyl butyrate (ethyl butyrate), methyl valerate (methyl pentanoate) etc., and
• - Hydrofluoroalkanes (HFA) and/or hydrofluoroalkenes (HFO), e.g. 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene etc.,

is selected.

• - bei einem Druck zwischen größer etwa 1 bar und etwa 300 bar, insbesondere zwischen etwa 1,5 bar und etwa 200 bar, vorzugsweise zwischen etwa 2 bar und etwa 100 bar, z.B. zwischen etwa 5 bar und etwa 60 bar, und/oder
• - bei einer Temperatur zwischen etwa 0°C und etwa 200°C, insbesondere zwischen etwa 0°C und etwa 100°C, vorzugsweise zwischen etwa 0°C und etwa 80°C, z.B. zwischen etwa 20°C und etwa 80°C, und/oder
• - über einen Zeitraum zwischen etwa 1 min und etwa 30 h, insbesondere zwischen etwa 5 min und etwa 25 h, vorzugsweise zwischen etwa 10 min und etwa 20 h, z.B. zwischen etwa 30°min und etwa 20 h oder zwischen etwa 1 h und etwa 20 h,

mit dem wenigstens einen Treibmittel imprägniert wird. Dabei kann das Treibmittel während des Imprägniervorgangs durch entsprechende Steuerung von Druck und/oder Temperatur auch verflüssigt werden, oder das 3D-Druckfilament wird über einen entsprechenden Zeitraum dem im gasförmigen Zustand gehaltenen Treibmittel exponiert.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 propellant can be carried out in a manner known per se by feeding the 3D printing filaments, for example, into a pressure vessel, such as an autoclave or the like, after which the pressure vessel is filled with the respective propellant or a mixture of several propellants and, if necessary, tempered. For this purpose, it has proven to be useful, 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 between about 1 minute and about 30 hours, in particular between about 5 minutes and about 25 hours, preferably between about 10 minutes and about 20 hours, e.g. between about 30 minutes and about 20 hours or between about 1 hour and about 20 hours,

with which at least one blowing agent is impregnated. The blowing agent 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 propellant and the thermoplastic polymer(s) of the 3D printing filament, the latter can be impregnated with the at least one propellant, for example, at a temperature in the range of ambient temperature, below ambient temperature or even above it, wherein in the latter case it is preferably cooled after impregnation while maintaining the pressure to a temperature which 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, wherein the impregnation pressure set in the pressure vessel is then preferably suddenly released, whereupon the pressure vessel is opened and the fully impregnated expandable 3D printing filament can be removed from the pressure vessel.

• - der Polyolefine, insbesondere aus der Gruppe Polyethylen (PE), Polypropylen (PP) und Polybutylen (PB), einschließlich deren Copolymeren, insbesondere der Ethylen-Vinylacetat-Copolymeren (EVA) und der Ethylen-Butylacetat-Copolymeren (EBA),
• - der Polyoxymethylene (POM),
• - der Polyalkylenterephthalate, insbesondere aus der Gruppe Polyethylenterephthalat (PET), Polybutylenterephthalat (PBT), Polybutylenadipatterephthalat (PBAT), Bis(2-ethylhexyl)terephthalat und Bis(hydroxyethyl)terephthalat,
• - Polystyrol (PS) einschließlich dessen Copolymeren, insbesondere der Acrylnitril-Butadien-Styrol-Copolymere (ABS),
• - der Polycarbonate (PC),
• - der Polyamide (PA),
• - der Polyimide (PI) einschließlich der Polyetherimide (PEI) und der Polyamidimide (PAI),
• - der Polyhydroxyalkanoate (PHA),
• - der Polysulfone, insbesondere aus der Gruppe Polysulfon (PSU), Polyethersulfon (PES) und Polyphenylensulfon (PPSU),
• - der Polyetheretherketone (PEEK),
• - der Polyphenylensulfide (PPS),
• - der thermoplastischen Polyurethane (TPU),
• - Cellulose einschließlich deren Derivaten, insbesondere aus der Gruppe der Celluloseacetate und -propionate, und
• - der Polylactide (PLA)

einschließlich deren Polymer-Blends gewählt wird bzw. ist.The blowing agents according to the invention are basically suitable for any known thermoplastic polymers, such as those that can be used in 3D printing filaments, in order to foam the 3D printing filament during 3D printing and to produce a foamed polymer molding by means of 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

• - polyolefins, in particular from the group polyethylene (PE), polypropylene (PP) and polybutylene (PB), including their copolymers, in particular ethylene-vinyl acetate copolymers (EVA) and ethylene-butyl acetate copolymers (EBA),
• - polyoxymethylenes (POM),
• - 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),
• - the polyhydroxyalkanoates (PHA),
• - polysulfones, in particular from the group polysulfone (PSU), polyethersulfone (PES) and polyphenylenesulfone (PPSU),
• - the polyetheretherketone (PEEK),
• - polyphenylene sulfide (PPS),
• - thermoplastic polyurethanes (TPU),
• - Cellulose including its derivatives, in particular from the group of cellulose acetates and propionates, and
• - 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 was found that a polymer blend with at least one predominantly amorphous thermoplastic polymer and at least one partially 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 assumed that 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 partially crystalline polylactide - it has proven to be particularly advantageous in this context if 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.

In an expandable 3D printing filament according to the invention, it can therefore advantageously be provided that it has a polymer blend of at least two thermoplastic polymers of different crystallinity, wherein the expandable 3D printing filament can preferably have a polymer blend which contains at least one, in particular at least two polylactides of different crystallinity, in particular at least one predominantly amorphous polylactide and at least one partially crystalline polylactide.

Examples of implementation:

1. [1] Acrylnitril-Butadien-Styrol-Copolymer (ABS) des Typs „PA-707“ (CHIMEI Corporation);
2. [2] Cellulosepropionat (CP) des Typs „Cellidor CP 400-12“ (MOCOM Compounds GmbH & Co. KG);
3. [3] 3D-Druckfilament aus Polylactid (PLA), teilkristallin, des Typs „eco-PLA“ (colorFabb B.V.);
4. [4] 3D-Druckfilament aus Polylactid (PLA), teilkristallin, des Typs „tough PLA“ (colorFabb B.V.);
5. [5] Polylactid (PLA), teilkristallin, hohe Kristallinität, des Typs „Luminy L175“ (Total Corbion PLA B.V.);
6. [6] Polymer-Blend aus:
   • - 50 Mass.-% PLA, teilkristallin, hohe Kristallinität, des Typs „Luminy L175“ (Total Corbion PLA B.V.), und
   • - 50 Mass.-% PLA, amorph, des Typs „Luminy LX975“ (Total Corbion PLA B.V.);
7. [7] Polylactid (PLA), teilkristallin, geringe Kristallinität, des Typs „Luminy LX175“ (Total Corbion PLA B.V.);
8. [8] Polymer-Blend aus:
   • - 50 Mass.-% PLA, teilkristallin, geringe Kristallinität, des Typs „Luminy LX175“ (Total Corbion PLA B.V.), und
   • - 50 Mass.-% PLA, amorph, des Typs „Luminy LX975“ (Total Corbion PLA B.V.);
9. [9] Polylactid (PLA), amorph, des Typs „Luminy LX975“ (Total Corbion PLA B.V.);
10. [10] Polylactid (PLA) aus Recyclingmaterial;
11. [11] Polycarbonat (PC) des Typs „Calibre 201-10“ (Trinseo S.A.); und
12. [12] Polyhydroxybutyrat (PHBV) des Typs „Enmat Y1000P“ (TianAn Biologic Materials Co., Ltd.).

On the one hand, (compact) 3D printing filaments were produced from various thermoplastic polymer materials using a twin-screw extruder with melt pump, cooling bath, take-off and winding device (examples [1], [2] and [5] ff), 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. [1] Acrylonitrile-butadiene-styrene copolymer (ABS) type “PA-707” (CHIMEI Corporation);
2. [2] Cellulose propionate (CP) of the type “Cellidor CP 400-12” (MOCOM Compounds GmbH & Co. KG);
3. [3] 3D printing filament made of polylactide (PLA), semi-crystalline, of the type “eco-PLA” (colorFabb BV);
4. [4] 3D printing filament made of polylactide (PLA), semi-crystalline, of the type “tough PLA” (colorFabb BV);
5. [5] Polylactide (PLA), semi-crystalline, high crystallinity, of the type “Luminy L175” (Total Corbion PLA BV);
6. [6] Polymer blend of:
   • - 50 mass% PLA, semi-crystalline, high crystallinity, of the type “Luminy L175” (Total Corbion PLA BV), and
   • - 50% by mass PLA, amorphous, type “Luminy LX975” (Total Corbion PLA BV);
7. [7] Polylactide (PLA), semi-crystalline, low crystallinity, of the type “Luminy LX175” (Total Corbion PLA BV);
8. [8] Polymer blend of:
   • - 50 mass% PLA, semi-crystalline, low crystallinity, of the type “Luminy LX175” (Total Corbion PLA BV), and
   • - 50% by mass PLA, amorphous, type “Luminy LX975” (Total Corbion PLA BV);
9. [9] Polylactide (PLA), amorphous, type “Luminy LX975” (Total Corbion PLA BV);
10. [10] Polylactide (PLA) from recycled material;
11. [11] Polycarbonate (PC) of the type ‘Calibre 201-10’ (Trinseo SA); and
12. [12] Polyhydroxybutyrate (PHBV) of the type “Enmat Y1000P” (TianAn Biologic Materials Co., Ltd.).

The (compact) 3D printing filaments according to the above examples 1 to 12 were fed in the form of strand bundles into a pressure vessel in the form of a pressure and temperature-adjustable autoclave with a capacity of 15 l and a blowing agent supply and impregnated with various blowing agents, with dimethyl ether (DME) or 1,3,3,3-tetrafluoropropene (TFP) being used as the blowing agent in the present embodiments. During the impregnation, the autoclave was heated to an impregnation temperature (T _I ) in order to generate a suitable impregnation pressure and in this way an essentially constant impregnation pressure (p _I ) was set, these conditions being maintained over a certain impregnation period (t _I ). The autoclave was then cooled to ambient temperature of about 20°C while maintaining the impregnation pressure (p _I ) 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.

The following Table 1 lists the impregnation parameters and the blowing agent content of the 3D printing filaments obtained after impregnation according to the above examples 1 to 12: 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. Example Propellant T _I P _I t _I Propellant content Type Quantity [g] [°C] [bear] [h] [Mass%] [1] TFP 750 71 11.0 18 1.2 [2] DMEA 500 93 14.4 18 10.2 [3] DMEA 400 25 6.9 18 11.0 [4] DMEA 400 25 6.9 18 9.3 [5] DMEA 400 25 6.9 18 9.9 [6] TFP 750 25 6.0 18 16.0 [7] DMEA 400 25 6.9 18 11.7 [8] TFP 750 23 5.9 18 18.5 [9] TFP 750 27 6.2 5 26.77 [10] TFP 750 100 13.2 18 9.2 [11] TFP 750 71 11.0 18 0.9 [12] TFP 750 71 11.5 5 1.7

Foamed polymer moldings were printed from the expandable 3D printing filaments according to Examples 1 to 12, 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 out of the polymer matrix and foams the plasticized strand. As explained in more detail below, the degree of foaming can be varied to a wide extent by adjusting the process parameters accordingly, in particular the feed or printing speed and the nozzle temperature. Control limits so that foamed polymer moldings can be printed directly and, due to the variable foaming levels, polymer moldings graded in terms of their density can be obtained with full (or partial) infill.

Table 2 below shows exemplary printing parameters in the form of the nozzle diameter (d _D ) and the nozzle temperature (T _D ) of the 3D printer as well as the feed rate (F) of the 3D printing filament, including the densities of a foamed polymer molding achieved thereby, as obtained by printing the expandable 3D printing filaments according to Examples 1 to 12. Table 2: Printing parameters and densities of the printed foamed polymer moldings. Example Printing parameters Moulded part density T _D [°C] F [mm/min] d _D [mm] [kg/ ^m3 ] [1] 270 300 0.6 650 [2] 185 175 0.4 58 [3] 180 350 0.6 381 [4] 180 350 0.6 331 [5] 170 250 0.6 183 [6] 180 350 0.6 107 [7] 160 350 0.6 101 [8] 145 500 0.6 42 [9] [no pressure tests performed] - [10] 220 350 0.8 429 [11] 270 250 0.6 807 [12] 245 300 0.8 829

• 1 ein Schaubild mit rasterelektronenmikroskopischen Querschnittsansichten von anlässlich 3D-Druckens aufgeschäumten Strängen eines expandierbaren 3D-Druckfilamentes aus einem mit einem Treibmittel in Form von 1,3,3,3-Tetrafluorpropen (TFP) imprägnierten thermoplastischen Polymer-Blend aus 50 Mass.-% eines teilkristallinen Polylactids (PLA) mit geringer Kristallinität des Typs „Luminy LX175“ (siehe oben) und 50 Mass.-% eines amorphen Polylactids (PLA) des Typs „Luminy LX975“ (siehe oben) zur Veranschaulichung der Möglichkeiten einer Steuerung des Aufschäumgrades durch die Druckparameter Extrusionsgeschwindigkeit (F) und Düsentemperatur (T_D) des 3D-Druckers;
• 2 ein Schaubild der mittels 3D-Druckens erhaltenen Dichten (ρ) von aufgeschäumten Strängen eines mit dem Treibmittel Dimethylether (DME) imprägnierten expandierbaren 3D-Druckfilamentes aus einem teilkristallinen Polylactid (PLA) mit geringer Kristallinität des Typs „Luminy LX175“ (siehe oben) in Abhängigkeit der Extrusionsgeschwindigkeit (F) und der Düsentemperatur (T_D) des 3D-Druckers;
• 3 ein der 2 entsprechendes Schaubild für ein expandierbares 3D-Druckfilament aus einem mit demselben Treibmittel Dimethylether (DME) imprägnierten teilkristallinen Polylactid (PLA) mit hoher Kristallinität des Typs „Luminy L175“ (siehe oben);
• 4 ein Schaubild der mittels 3D-Druckens erhaltenen Dichten (ρ) von aufgeschäumten Strängen eines mit dem Treibmittel 1,3,3,3-Tetrafluorpropen (TFP) imprägnierten expandierbaren 3D-Druckfilamentes aus einem teilkristallinen Polylactid (PLA) mit geringer Kristallinität des Typs „Luminy LX175“ (siehe oben) in Abhängigkeit der Extrusionsgeschwindigkeit (F) und der Düsentemperatur (T_D) des 3D-Druckers;
• 5 ein der 4 entsprechendes Schaubild für ein expandierbares 3D-Druckfilament aus einem mit demselben Treibmittel 1,3,3,3-Tetrafluorpropen (TFP) imprägnierten teilkristallinen Polylactid (PLA) mit hoher Kristallinität des Typs „Luminy L175“ (siehe oben);
• 6 ein Schaubild der mittels 3D-Druckens erhaltenen Dichten (ρ) von aufgeschäumten Strängen eines mit dem Treibmittel 1,3,3,3-Tetrafluorpropen (TFP) imprägnierten expandierbaren 3D-Druckfilamentes aus einem Polymer-Blend aus einerseits 50 Mass.-% eines teilkristallinen Polylactids (PLA) mit geringer Kristallinität des Typs „Luminy LX175“ (siehe oben) und andererseits 50 Mass.-% eines amorphen Polylactids (PLA) des Typs „Luminy LX975“ (siehe oben) in Abhängigkeit der Extrusionsgeschwindigkeit (F) und der Düsentemperatur (T_D) des 3D-Druckers;
• 7 ein der 6 entsprechendes Schaubild für ein expandierbares 3D-Druckfilament aus einem mit demselben Treibmittel 1,3,3,3-Tetrafluorpropen (TFP) imprägnierten Polymer-Blend aus einerseits 65 Mass.-% des teilkristallinen Polylactids (PLA) mit geringer Kristallinität des Typs „Luminy LX175“ (siehe oben) und andererseits 35 Mass.-% des amorphen Polylactids (PLA) des Typs „Luminy LX975“ (siehe oben);
• 8 ein den 6 und 7 entsprechendes Schaubild für ein expandierbares 3D-Druckfilament aus einem mit demselben Treibmittel 1,3,3,3-Tetrafluorpropen (TFP) imprägnierten Polymer-Blend aus einerseits 85 Mass.-% des teilkristallinen Polylactids (PLA) mit geringer Kristallinität des Typs „Luminy LX175“ (siehe oben) und andererseits 15 Mass.-% des amorphen Polylactids (PLA) des Typs „Luminy LX975“ (siehe oben); und
• 9 ein Schaubild zur Veranschaulichung der Lagerfähigkeit eines expandierbaren 3D-Druckfilamentes aus einem mit dem Treibmittel 1,3,3,3-Tetrafluorpropen (TFP) imprägnierten Polymer-Blend aus einerseits 50 Mass.-% eines teilkristallinen Polylactids (PLA) mit geringer Kristallinität des Typs „Luminy LX175“ (siehe oben) und andererseits 50 Mass.-% eines amorphen Polylactids (PLA) des Typs „Luminy LX975“ (siehe oben) entsprechend der 6 mit dem Anteil an Treibmittel (TFP) in Abhängigkeit von der Lagerzeit (t) bei verschiedenen Lagertemperaturen.

Further features and advantages of the invention will become apparent from the following description of embodiments with reference to the drawings, in which:

• 1 a diagram with scanning electron microscopic cross-sectional views of strands of an expandable 3D printing filament made of a thermoplastic polymer blend impregnated with a blowing agent in the form of 1,3,3,3-tetrafluoropropene (TFP) consisting of 50% by mass of a semi-crystalline polylactide (PLA) with low crystallinity of the type “Luminy LX175” (see above) and 50% by mass of an amorphous polylactide (PLA) of the type “Luminy LX975” (see above) to illustrate the possibilities of controlling the degree of foaming by the printing parameters extrusion speed (F) and nozzle temperature (T _D ) of the 3D printer;
• 2 a graph 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” (see above) impregnated with the blowing agent dimethyl ether (DME) as a function of the extrusion speed (F) and the nozzle temperature (T _D ) of the 3D printer;
• 3 one of the 2 corresponding diagram for an expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with high crystallinity of the type “Luminy L175” (see above) impregnated with the same blowing agent dimethyl ether (DME);
• 4 a graph 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” (see above) impregnated with the blowing agent 1,3,3,3-tetrafluoropropene (TFP) as a function of the extrusion speed (F) and the nozzle temperature (T _D ) of the 3D printer;
• 5 one of the 4 corresponding diagram for an expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with high crystallinity of the type “Luminy L175” (see above) impregnated with the same blowing agent 1,3,3,3-tetrafluoropropene (TFP);
• 6 a diagram 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;
• 7 one of the 6 corresponding diagram 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% by mass of the semi-crystalline polylactide (PLA) with low crystallinity of the type “Luminy LX175” (see above) and, on the other hand, 35% by mass of the amorphous polylactide (PLA) of the type “Luminy LX975” (see above);
• 8 a the 6 and 7 corresponding diagram for an expandable 3D printing filament made of a polymer blend impregnated with the same blowing agent 1,3,3,3-tetrafluoropropene (TFP) consisting of, on the one hand, 85% by mass of the semi-crystalline polylactide (PLA) with low crystallinity of the type “Luminy LX175” (see above) and, on the other hand, 15% by mass of the amorphous polylactide (PLA) of the type “Luminy LX975” (see above); and
• 9 a diagram to illustrate 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) according to the 6 with the proportion of propellant (TFP) depending on the storage time (t) at different storage temperatures.

In the 1 is a diagram with scanning electron microscopic cross-sectional views of strands of an expandable 3D printing filament made of a polymer blend impregnated with a blowing agent in the form of 1,3,3,3-tetrafluoropropene (TFP) and consisting of 50% by mass of a semi-crystalline polylactide (PLA) with low crystallinity of the type “Luminy LX175” (see above) and 50% by mass of an amorphous polylactide (PLA) of the type “Luminy LX975” (see above) is shown. The 1 The enlarged image sections that can be seen 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 if it is only partially shown in one of the photographic views. On the one hand, a very homogeneous foam structure can be seen throughout with pores that are evenly distributed over the cross-section of the strand and have 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 controlled in a simple manner by varying the printing parameters extrusion speed (F) and nozzle temperature (T _D ) of the 3D printer, 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 polylactide blend loaded with TFP - and/or the lower the nozzle temperature (T _D ) - here: between 140°C and 200°C for the polylactide blend loaded with TFP - of the 3D printer is selected.

The 2 The test results discussed below were all obtained by printing expandable 3D printing filaments made of different polymer materials - here: different polylactides (PLA) with different crystallinity - which were impregnated with different 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". The 2 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 low crystallinity of the type “Luminy LX175” (see above) impregnated with dimethyl ether (DME) 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 simple control of the density of the deposited foamed strand by varying the printing parameters extrusion speed (F) and nozzle temperature (T _D ), whereby the lowest density of 101 kg/m ³ , which corresponds to about 8% of the density of the compact (unfoamed) polymer, was achieved in the present case at an extrusion speed (F) of 350 mm/min and a nozzle temperature (T _D ) of 160°C.

In the 3 is an exemplary diagram of the densities (ρ) obtained by 3D printing of foamed strands of a dimethyl ether (DME)-impregnated expandable 3D printing filament made of a semi-crystalline polylactide (PLA) with high crystallinity of the type “Luminy L175” (see above) in Dependence 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 - is shown. 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 ), whereby the lowest density of 183 kg/m ³ , which corresponds to approximately 14% of the density of the compact (unfoamed) polymer, was achieved in the present case at an extrusion speed (F) of 250 mm/min and a nozzle temperature (T _D ) of 170°C.

The 4 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 low crystallinity of the type “Luminy LX175” (see above) impregnated with 1,3,3,3-tetrafluoropropene (TFP) 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 simply controlling the density of the deposited foamed strand by varying the printing parameters extrusion speed (F) and nozzle temperature (T _D ), whereby the lowest density of 141 kg/m ³ , which corresponds to about 11% of the density of the compact (unfoamed) polymer, was achieved in the present case at an extrusion speed (F) of 350 mm/min and a nozzle temperature (T _D ) of 180°C.

In the 5 is 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 1,3,3,3-tetrafluoropropene (TFP) 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 simply controlling the density of the deposited foamed strand by varying the printing parameters extrusion speed (F) and nozzle temperature (T _D ), whereby the lowest density of 214 kg/m ³ , which corresponds to about 16% of the density of the compact (unfoamed) polymer, was achieved in the present case at an extrusion speed (F) of 250 mm/min and a nozzle temperature (T _D ) of 200°C.

The 6 to 8 show a diagram 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 semi-crystalline polylactide (PLA) with low crystallinity of the type “Luminy LX175” (see above) and 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 ( 6 ), 140°C ( 6 and 7 ), 150°C, 160°C, 170°C, 180°C, 190°C ( 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 the 6 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 7 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 8 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 “Luminy LX975”.

• - von beispielsweise etwa 54 kg/m³ (hier: im Falle des PLA-Blends mit 50 Mass.-% „LX175“ und 50 Mass.-% „LX975“ bei einer Extrusionsgeschwindigkeit (F) von 350 mm/min und einer Düsentemperatur (T_D) von 140°C; 6), bzw.
• - von z.B. etwa 56 kg/m³ (hier: im Falle des PLA-Blends mit 65 Mass.-% „LX175“ und 35 Mass.-% „LX975“ bei einer Extrusionsgeschwindigkeit (F) von 350 mm/min und einer Düsentemperatur (T_D) von 140°C; 7), bzw.
• - von z.B. etwa 167 kg/m³ (hier: im Falle des PLA-Blends mit 85 Mass.-% „LX175“ und 15 Mass.-% „LX975“ bei einer Extrusionsgeschwindigkeit (F) von 250 mm/min und einer Düsentemperatur (T_D) von 180°C; 8),

entsprechend etwa 4% bis etwa 6% der Dichte des kompakten (ungeschäumten) Polymer-Blends, erhältlich sind. Darüber hinaus kann sich ein solcher Polymer-Blend mit Blend-Partnern unterschiedlicher Kristallinität insoweit als vorteilhaft erweisen, als hierdurch sowohl sehr hohe Beladungsgrade an Treibmittel als auch eine sichere Handhabung unter Vermeidung eines unzeitigen bzw. ungewollten Aufschäumens des 3D-Druckfilamentes sichergestellt werden können, wobei die vornehmlich kristalline Phase das mit Treibmittel imprägnierte 3D-Druckfilament zu stabilisieren (d.h. vor einem unzeitigen Aufschäumen zu bewahren) vermag, während die vornehmlich amorphe Phase bei sehr hohen Beladungsgraden an Treibmittel ein gutes und gezieltes Aufschäumverhalten gewährleistet.It can be seen that in addition to controlling the degree of foaming or the resulting density of the printed strand by means of the feed rate (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 blowing agent with otherwise identical printing parameters. It is also noticeable that very large density differences can be generated here, with extremely low densities

• - of, for example, about 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; 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; 7 ), or
• - of e.g. about 167 kg/m ³ (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; 8 ),

corresponding to about 4% to about 6% of the density of the compact (unfoamed) polymer blend. In addition, such a polymer blend with blend partners of different crystallinity can prove to be 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 the 9 Finally, a diagram is shown to illustrate 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) according to the 6 with the proportion of blowing agent (TFP in [mass .-%]) as a function of the storage time (t in [h]) at different 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). It can be seen that a very long durability of the impregnated 3D printing filaments is guaranteed at all storage temperatures including room temperature, whereby the proportion of blowing agent (here: TFP) decreases within the first few days due to diffusion, but 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 proportion of about 15 mass .-% being maintained at low temperatures and a blowing agent proportion of about 8 mass .-% being maintained at room temperature.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• WO 2020043669 A1 [0005]
• EP 3403806 A1 [0006]

Claims (12)

Process 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 increased compared 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. Procedure according to Claim 1 , characterized in that the at least one propellant is selected from the group - of alcohols with a hydroxy group, in particular from the group of acyclic and cyclic alkanols, - of ethers, in particular from the group of acyclic and cyclic alkyl ethers, - of carboxylic acids with a carboxyl group, in particular from the group of acyclic saturated carboxylic acids, - of esters, in particular from the group of carboxylic acid esters, and - hydrofluoroalkanes and/or hydrofluoroalkenes. Procedure 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, is impregnated with the at least one propellant. Method according to one of the Claims 1 until 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 ethylene-vinyl acetate copolymers (EVA) and 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 polyurethanes (TPU), - cellulose including its derivatives, in particular from the group of cellulose acetates and propionates, and - polylactides (PLA) including their polymer blends. Procedure according to one of the Claims 1 until 4 , characterized in that a 3D printing filament made of a polymer blend containing at least two thermoplastic polymers of different crystallinity is used. Procedure 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. Expandable 3D printing filament made of at least one thermoplastic polymer which is impregnated with at least one blowing agent, in particular produced by means of a process according to one of the preceding claims, 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. Expandable 3D printing filament Claim 7 , characterized in that the at least one propellant is selected from the group - of alcohols with a hydroxy group, in particular from the group of acyclic and cyclic alkanols, - of ethers, in particular from the group of acyclic and cyclic alkyl ethers, - of carboxylic acids with a carboxyl group, in particular from the group of acyclic saturated carboxylic acids, - of esters, in particular from the group of carboxylic acid esters, and - hydrofluoroalkanes and/or hydrofluoroalkenes. Expandable 3D printing filament according to Claim 7 or 8 , 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 ethylene-vinyl acetate copolymers (EVA) and 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 polyurethanes (TPU), - cellulose including its derivatives, in particular from the group of cellulose acetates and propionates, and - polylactides (PLA) including their polymer blends. Expandable 3D printing filament based on one of the Claims 7 until 9 , characterized in that the 3D printing filament comprises a polymer blend of at least two thermoplastic polymers of different crystallinity. Expandable 3D printing filament according to Claim 10 , characterized in that the 3D printing filament comprises a polymer blend which contains at least two polylactides of different crystallinity, in particular at least one predominantly amorphous polylactide and at least one partially crystalline polylactide. A foamed polymer molded part consisting of at least one expandable 3D printing filament according to one of the Claims 7 until 11 manufactured using 3D printing.