Customized water-soluble support structures for additive manufacturing

Description

[0001] The present invention relates to a method for producing a plastic component by additive manufacturing, wherein the plastic component to be produced should have a complex geometry that requires the use of a support structure. Furthermore, the present invention relates to a filament, granulate, or powder for use as a support structure in the inventive manufacturing method.

[0002] Various additive manufacturing processes are known in the state of the art for producing plastic components using 3D printing in small series or as prototypes, such as selective laser sintering ( English . selective laser sintering, SLS) or fused layering ( EnglishFused deposition modeling (FDM), also known as strand deposition modeling, is a rapid prototyping manufacturing process with which a component is built layer by layer from a meltable starting material, such as a meltable plastic.

[0003] In order to enable complex geometries, such as overhangs or undercuts, in a plastic component produced using additive manufacturing, the use of a support structure is required. Support structures, which are also synonymously referred to as support constructions, are used wherever the plastic component to be manufactured is to be free-standing or freely suspended, i.e. in all those places that would otherwise be created freely in space, i.e. without support from an already finished subcomponent of the plastic component. The support structure thus provides the necessary support for the plastic melt applied during additive manufacturing, which forms the plastic component after solidification. The principle of the strand deposition process, one of the most frequently used 3D printing processes, is in Fig. 1 illustrated.

[0004] After completion or solidification of the plastic component, it is self-supporting in the areas where the overhangs or undercuts are located. The support structure is now superfluous or, in fact, a hindrance. It must therefore be removed, i.e. separated from the manufactured plastic component. The support structures used in additive manufacturing are often made of the same material as the plastic component to be manufactured. In this case, the support structure must be mechanically removed from the plastic component after completion, usually through time-consuming manual labor. Even complex mechanical post-processing such as grinding and polishing cannot always prevent residues of the support structure from adhering to the plastic component, which negatively affects its external appearance.Mechanical post-processing can also cause scratches on the surface of the plastic component, which also negatively impact its external appearance. If the support structures are removed using excessive force, this can even cause damage to the plastic component.

[0005] Although an improvement has been achieved in this regard by combining different materials for the plastic component and the support structure, which adhere less strongly to one another, this has been shown to be a significant improvement. However, since supporting the plastic component inevitably results in force being transferred to the support structure, adhesion can be reduced but never completely eliminated. Thus, even when using different materials, the problems described above, which previously occurred when removing the support structure, cannot be completely avoided.

[0006] Support structures made of water-soluble polymers, such as polyvinylpyrrolidone, are also known in the state of the art. These can be washed out after the plastic component has been manufactured. However, the polymer chains of the support structure, which are dissolved in water, cannot be removed from wastewater by a conventional sewage treatment plant, and thus ultimately enter the environment. The consequences of this type of environmental pollution on humans and nature have not yet been researched.

[0007] The present invention is therefore based on the object of providing a method which allows the production of a plastic component of complex geometry by additive manufacturing, wherein the support structure used here can be separated from the finished plastic component after completion of the additive manufacturing without leaving any residue or stress, without impairing its external appearance and ideally without damaging the environment.

[0008] This object is achieved by the embodiments of the present invention characterized in the claims.

[0009] In particular, the invention provides a method for producing a plastic component by additive manufacturing, which comprises the following steps (a) and (b): (a) repeatedly depositing a meltable material M 1 , which is formed from at least one thermoplastic K 1 , to construct a plastic component with a predetermined geometry, wherein a support structure made of a meltable material M 2 is used during the construction of the plastic component to enable overhangs or undercuts in the plastic component, and (b) removing the support structure from the plastic component constructed in step (a) after its completion by bringing it into contact with an aqueous solvent, wherein the meltable material M 2 is formed from at least one thermoplastic K 2 which is compounded with at least one salt and one plasticizer, and wherein in the meltable material M 2 , based on 100 parts by mass of the total amount of the at least one thermoplastic K 2 , 100 to 150 parts by mass of the salt and 10 to 50 parts by mass of the plasticizer are present, and wherein the salt compounded together with the at least one thermoplastic K 2 dissolves as soon as it comes into contact with the aqueous solvent, while the at least one thermoplastic K 2 does not go into solution and remains as a porous structure.

[0010] The manufacturing method according to the invention enables residue-free and stress-free removal of the support structure after completion of the plastic component, without the need for complex mechanical post-processing, such as grinding or polishing. The risk of damage to the plastic component when separating the support structure is thus almost completely minimized. This is achieved by using a support structure made of a meltable material M 2 , which is formed from at least one thermoplastic K 2 compounded with at least one salt and a plasticizer.If, after additive manufacturing, the finished plastic component, including the still-adhering support structure, is brought into contact with an aqueous solvent, in particular water, the salt contained in the meltable material M 2 and compounded together with the at least one thermoplastic K 2 dissolves. The at least one thermoplastic K 2, however, does not dissolve and instead remains as a porous structure. This ultimately disintegrates into fragments with dimensions ranging from a few micrometers to several centimeters. The at least one thermoplastic K 2 thus separates, so to speak, of its own accord after the salt dissolves.The presence of a plasticizer, which is also contained in the meltable material M 2 and compounded with the at least one thermoplastic K 2, also ensures that the brittleness resulting from the addition of the salt is reduced. The meltable material M 2 , which serves to construct the support structure, thus retains sufficient processability.

[0011] According to the present invention, the term "meltable" in connection with the meltable material M 1 or M 2 means that at least the at least one thermoplastic material K 1 or K 2 can be converted into an extrudable state. In this context, one also speaks of plasticizing the meltable material M 1 or M 2 . Other components of the meltable material M 1 or M 2 , however, can remain dispersed as solids in the plastic melt.

[0012] Even if the at least one thermoplastic K2 itself is not water-soluble, the water-soluble support structure can be considered water-soluble due to the water solubility of the salt contained in the meltable material M2. If the at least one thermoplastic K2 is also biodegradable, the support structure can be safely disposed of with wastewater after contact with the aqueous solvent, in particular with water, without causing harmful plastics to enter the environment.

[0013] In the following, the method according to the invention for producing a plastic component by additive manufacturing with steps (a) and (b) is described with reference to Fig. 1 described in more detail, whereby the representation of the manufacturing process according to the invention shown therein is not to be understood as limiting.

[0014] In step (a) of the manufacturing method according to the invention, a meltable material M 1 , which is formed from at least one thermoplastic K 1 , is repeatedly deposited to build up a plastic component with a predetermined geometry.

[0015] The repeated deposition of the meltable material M 1 can, as in Fig. 1shown, with the aid of a (mini-)extruder (7). A plastic wire (1) of the meltable material M 1 , which is also referred to as a plastic filament or just as filament, emerges - after heating above the melting point of the at least one thermoplastic K 1 - in the form of a plastic melt from the nozzle (5) of a 3D printing device suitable for melt layering. By linear application (8) of the plastic melt, the plastic component (6) is gradually built up layer by layer according to the predetermined geometry, wherein during the melt layering, further layers of the meltable material M 1 are created on an already finished, i.e. solidified, subcomponent of the plastic component.

[0016] The linear application of the plastic melt, which is also referred to as a repeated deposition of a melt strand, can be carried out on any build platform (10) suitable for melt layering. For example, on a build platform such as that shown in Fig. 1 As shown, the support structure (9) is located, which enables complex geometries, such as overhangs or undercuts, in the plastic component to be manufactured. However, the support structure can also be located on an already finished subcomponent of the plastic component.

[0017] The manufacturing method according to the invention is not limited to molten layering. In principle, any other form of additive manufacturing can be used to produce a plastic component, as long as it involves the use of a support structure.

[0018] In one embodiment of the manufacturing method defined above, in step (a) during the construction of the plastic component, the support structure is constructed by repeatedly depositing the meltable material M 2. This is particularly useful when multiple support structures are to be used at different positions, which may also only be the case later in the additive manufacturing process. The construction of the plastic component and the construction of the support structure can take place in parallel. A 3D printing device with at least two extruders and nozzles, as described in Fig. 1is shown as an example, wherein the 3D printing device is equipped with both a filament (1) of the meltable material M 1 and a filament (2) of the meltable material M 2, as described in more detail below. Propulsion (3) and contact heating (4) of the 3D printing device are shown in Fig. 1 also shown. Instead of filaments of the meltable material M 1 and the meltable material M 2, corresponding granules or powders thereof can also be used.

[0019] The present invention also encompasses embodiments in which more than two different meltable materials are used. For example, apart from the meltable material M 2 , two different meltable materials M 1a and M 1b can be used, which are preferably provided from two different extruders and form the plastic component. These two different meltable materials M 1a and M 1b can differ, depending on the purpose, both in the type of the at least one thermoplastic K 1 and in the color or other properties. The meltable material M 2 , from which the support structure is / will be formed, can here, for example, be provided from a third extruder. Further combinations of meltable materials (such as M 1a / M 1b / M 1c / M 2 or M 1 / M 2a / M 2b ) are also conceivable within the meaning of the present invention.

[0020] Since, according to the present invention, the water solubility of the support structure is based on the solubility of the salt compounded with the at least one thermoplastic K 2 , the at least one thermoplastic K 1 of the meltable material M 1 , which serves to construct the plastic component, and the at least one thermoplastic K 2 of the meltable material M 2 , which serves to construct the support structure, can even be identical. Thus, after contact with an aqueous solvent, in particular with water, the support structure remains as a porous structure made of the at least one thermoplastic K 1 = K 2 , which ultimately disintegrates into fragments with dimensions ranging from a few micrometers to a few centimeters.The plastic component constructed from the identical thermoplastic material, however, is not attacked due to the lack of water solubility of the at least one thermoplastic material K 1 = K 2.

[0021] The use of identical thermoplastics naturally ensures compatibility between the plastic component and the support structure. However, for support structures made of water-soluble polymers, such as polyvinylpyrrolidone, which is a conventional, petroleum-based plastic that is also not biodegradable, a different thermoplastic must necessarily be used for the plastic component to be manufactured.

[0022] According to the present invention, the at least one thermoplastic K 1 of the meltable material M 1 used to construct the plastic component is not further restricted. Thus, in principle, any thermoplastic commonly used in the additive manufacturing of plastic components can also be used in the manufacturing process according to the invention.

[0023] In one embodiment of the manufacturing process defined above, the at least one thermoplastic K1 is selected from the group consisting of polyesters, polyamides, polyurethanes, polycarbonates, polyketones, and polyolefins, and is optionally a thermoplastic elastomer. If desired, the at least one thermoplastic K1 can also have elastomeric properties. The at least one thermoplastic K1 can be either homopolymers or copolymers, or corresponding mixtures thereof.In a further embodiment of the above-defined manufacturing process, the at least one thermoplastic K 1 is selected in particular from the group consisting of polylactide (PLA), acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene-acrylate copolymer (ASA), polymethyl methacrylate (PMMA), polyetheretherketone (PEEK), and glycol-modified polyethylene terephthalate (PETG), but is not limited thereto. According to a preferred embodiment of the present invention, the at least one thermoplastic K 1 is PLA or ABS.

[0024] Typically, the at least one thermoplastic K 1 should not exceed a melting temperature of about 250 °C to ensure its processability and handling in additive manufacturing, for example in melt layering.

[0025] If necessary, the at least one thermoplastic material K 1 can be compounded with one or more additives. This allows specific properties to be imparted to the meltable material M 1 , which serves to construct the plastic component. In addition to plasticizers, possible additives include flow aids, impact modifiers, nucleating agents, and fillers, as described in more detail below in connection with the meltable material M 2 . Compounding is also described in more detail below.

[0026] According to the present invention, the at least one thermoplastic K 2 of the meltable material M 2 , which is compounded at least with a salt and a plasticizer and serves to construct the support structure, is not further restricted as long as it is not water-soluble. With the proviso that the at least one thermoplastic K 2 is not water-soluble, in principle any thermoplastic as is usually used in additive manufacturing, for example in melt layering, for support structures can also be used in the production process according to the invention, including the thermoplastics mentioned above in connection with the meltable material M 1. As in the case of the at least one thermoplastic K 1, the at least one thermoplastic K 2 can be both homopolymers and copolymers as well as corresponding mixtures thereof.If at least one of the thermoplastic K 2 materials is biodegradable, as described below, the support structure can be safely disposed of via wastewater after the plastic component has been manufactured.

[0027] In one embodiment of the manufacturing process defined above, the at least one thermoplastic K 2 is selected from the group consisting of polyhydroxyalkanoates (PHA), in particular poly-3-hydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), as well as polycaprolactone (PCL), thermoplastic starch, polybutylene adipate terephthalate (PBAT) and polybutylene succinate (PBS), but is not limited thereto. All of these (bio)polymers have in common that they are biodegradable. While thermoplastic starch and PCL are biodegradable in water, PBAT and PBS are less biodegradable in water but more biodegradable in soil.

[0028] Polyhydroxyalkanoates, also known as polyhydroxy fatty acids, are biodegradable in both water and soil. They are naturally occurring, water-insoluble polyesters that can be degraded aerobically or anaerobically by microorganisms, such as bacteria. The at least one thermoplastic K2 can therefore be a polyhydroxyalkanoate, such as poly(3-hydroxybutyric acid). Poly(3-hydroxybutyric acid), also known as poly(3-hydroxybutyrate), is a structurally simple and naturally occurring polyhydroxyalkanoate. PHB is formed by fermentation, for example, based on sugar or starch, and typically consists of 1,000 to several hundred thousand 3-hydroxybutyric acid units. Naturally occurring poly(3-hydroxybutyric acid) is usually derived from the monomer with the (R) configuration. It is therefore poly-(R)-(3-hydroxybutyrate).In contrast, the monomer with (S) configuration and the corresponding poly-(S)-(3-hydroxybutyrate) play only a minor role, as does the racemic mixture of poly-(R)-(3-hydroxybutyrate) and poly-(S)-(3-hydroxybutyrate). Naturally occurring poly(3-hydroxybutyric acid) has a melting point of approximately 175 °C; decomposition occurs above 200 °C. In some of its properties, poly(3-hydroxybutyric acid) is comparable to polypropylene, particularly with regard to crystallinity, glass transition temperature, and tensile strength. References herein to poly(3-hydroxybutyric acid) refer to any stereoisomer thereof, i.e., regardless of tacticity.In addition to PHB, the copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid, i.e., poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and the copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid, i.e., poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), are particularly suitable thermoplastics for the meltable material M 2. 3-hydroxyvaleric acid and 3-hydroxyhexanoic acid follow 3-hydroxybutyric acid in the homologous series. Thus, they have one or two additional methylene groups, respectively, which increases extensibility and decreases brittleness while maintaining virtually the same biodegradability.

[0029] According to the present invention, the at least one thermoplastic K 2 is compounded, i.e., mixed, with at least one salt and one plasticizer. The salt and the plasticizer are added as additives to the at least one thermoplastic K 2. This applies equally to the additives mentioned below, if provided. For this purpose, all methods can be used as are customary for compounding in plastics technology. Typically, the compounding of the thermoplastic K 2 with the salt and the plasticizer takes place in a twin-screw extruder, whereby a granulate is obtained, as in Fig. 2The twin-screw extruder can be co-rotating or counter-rotating. However, instead of a twin-screw extruder, a planetary roller extruder or a co-kneader can also be used. If necessary, the resulting granulate can be processed into a filament using a single-screw extruder, as shown in Fig. 3 shown.

[0030] In principle, the present invention is not particularly restricted with regard to the salt for compounding with the at least one thermoplastic K 2. For this purpose, salts are expediently used which, in addition to being highly soluble in the aqueous solvent used, in particular in water, do not react with it in an acidic or basic manner, i.e. which leave the pH value of the aqueous solvent, in particular of water, virtually unchanged. Furthermore, the salts used should have only a low hygroscopicity to prevent excessive water absorption during additive manufacturing, which would otherwise adversely affect the stability of the support structure. Ideally, the salts used are neither environmentally hazardous nor otherwise objectionable.

[0031] In one embodiment of the above-defined manufacturing process, the salt with which the at least one thermoplastic K 2 is compounded is selected from the group consisting of, but not limited to, sodium chloride, sodium sulfate, sodium nitrate, potassium chloride, potassium sulfate, and potassium nitrate. The chlorides, sulfates, and nitrates of the light alkali metals sodium and potassium are characterized by their high water solubility. They are also largely ecologically harmless. In principle, however, the corresponding chlorides, sulfates, and nitrates of alkaline earth metals such as magnesium and calcium can also be used for compounding, as can those of other metals, provided they meet the aforementioned criteria.

[0032] With regard to the plasticizer for compounding with the at least one thermoplastic K 2, the present invention is also not subject to any particular restrictions. In addition to plasticizers that are soluble in the aqueous solvent used, especially in water, plasticizers that are insoluble in the aqueous solvent used, especially in water, can also be used in this case. Ideally, the plasticizers used are neither environmentally hazardous nor otherwise objectionable.

[0033] In one embodiment of the manufacturing process defined above, the plasticizer is polyethylene glycol (PEG). Naturally, the melting point of PEG increases with increasing chain length. Above a molecular weight of approximately 1,500 g / mol, PEG exists as a waxy solid at room temperature. In addition to polyethylene glycol, which is biodegradable in water, particularly suitable plasticizers include citric acid esters, glycerols and their derivatives such as tributyrin and triacetin, fatty acid esters such as methyl oleate, and epoxidized esters and oils such as epoxidized soybean oil (ESO).

[0034] According to the present invention, the meltable material M 2 contains, based on 100 parts by mass of the total amount of the at least one thermoplastic K 2 , 100 to 150 parts by mass of the salt and 10 to 50 parts by mass of the plasticizer, preferably 115 to 135 parts by mass of the salt and 20 to 35 parts by mass of the plasticizer, for example 125 parts by mass of the salt and 25 parts by mass of the plasticizer. If the proportion of plasticizer is too low in relation to the proportion of salt, the meltable material M 2 is too brittle. The consequence is inadequate processability, which manifests itself, for example, in clogging or wear of the nozzle and in tearing of the melt strand during repeated deposition of the meltable material M 2 to build the support structure. For example, in the strand laying process, if the meltable material M 2 is too brittle, the filament breaks when fed into the extruder.However, if the proportion of plasticizer is too high relative to the proportion of salt, the meltable material M 2 is not stiff enough. As a result, the support structure deforms under the load of the plastic component, which ultimately also leads to deformation of the plastic component.

[0035] If required, the at least one thermoplastic K 2 can be further compounded with one or more additives selected from the group consisting of flow aids, impact modifiers, nucleating agents and fillers. This makes it possible to impart certain properties to the meltable material M 2 , which serves to construct the support structure. Flow aids such as epoxides, peroxides or isocyanates can be used to adjust the viscosity of the meltable material M 2. Impact modifiers can be used to influence the energy absorption capacity of the meltable material M 2. The addition of nucleating agents, which are also referred to as nucleating agents, such as boron nitride, which is already contained in commercially available PHBV, can increase the elongation at break and the toughness of the meltable material M 2.The addition of nucleating agents also prevents subsequent crystallization, which would otherwise lead to warping (. English warping of the support structure. Finally, fillers such as wood flour, coal, graphite, cellulose powder, shell and kernel flour can be used to influence the density, the modulus of elasticity, the hardness, the heat resistance, and the shrinkage tendency of the meltable material M 2.

[0036] In step (b) of the manufacturing process according to the invention, the support structure is removed from the plastic component constructed in step (a) after its completion by bringing it into contact with an aqueous solvent.

[0037] According to the present invention, the aqueous solvent is not particularly limited and includes all solvents having a water content of at least 50 vol.%. Depending on the application, the aqueous solvent may contain portions of organic solvents, such as alcohols, etc., or additives, such as special salts, etc. The aqueous solvent may also contain acids or bases. Due to easier handling and for ecological reasons, the use of an aqueous solvent which consists essentially of water, i.e., at least 95 vol.%, is preferred. According to a specific embodiment of the present invention, the aqueous solvent is water.

[0038] The salt compounded together with the at least one thermoplastic K 2 dissolves as soon as it comes into contact with the aqueous solvent, in particular with water. What remains is a porous structure of the at least one thermoplastic K 2 , which does not dissolve. Since this porous structure is mechanically unstable, it disintegrates into fragments with dimensions in the range of a few micrometers to a few centimeters, whereby it can be easily separated from the finished plastic component. Therefore, no complex mechanical post-processing is required to remove the support structure from the finished plastic component. Rather, within the scope of the manufacturing method according to the invention, the support structure separates more or less automatically as a result of being brought into contact with the aqueous solvent, in particular with water.Ideally, the support structure disintegrates into sufficiently small fragments during the dissolution of the compounded salt, leaving virtually no residue on the finished plastic component and requiring no further processing. If a non-biodegradable thermoplastic is used for the support structure, the aforementioned fragments of the support structure are expediently filtered out of the aqueous solvent to prevent them from entering the environment. Such filtration is only possible because the at least one thermoplastic K2 itself is not water-soluble.

[0039] If the at least one thermoplastic K 2 is a naturally occurring polymer, as is the case with the biopolymers shown above, for example polyhydroxyalkanoates, such as polyhydroxybutyric acid, microorganisms, fungi and enzymes present in the aqueous solvent, in particular in water, can degrade the fragments of the support structure from the at least one thermoplastic K 2. In addition to the simplified separability of the support structure, which can be attributed to the compounding with the salt and its dissolution from the support structure upon contact with the aqueous solvent, in particular with water, the use of a biodegradable thermoplastic also makes it possible to simplify the disposal of the support structure.Since the fragments of the at least one thermoplastic K 2 have comparatively small dimensions, they can be easily disposed of via the drain. Wastewater in particular contains a large number of microorganisms, such as bacteria, which allow degradation under aerobic or anaerobic conditions under which their growth is possible. The degradation products are essentially carbon dioxide and water. In one embodiment of the manufacturing process defined above, the at least one thermoplastic K 2 is accordingly biodegradable. Filtering the aforementioned fragments of the support structure from the aqueous solvent is therefore not necessary in this case, but may nevertheless be desirable for reasons of sustainability, for example to enable recycling.

[0040] In accordance with the above statements, the at least one thermoplastic material K 2 , which is itself not water-soluble, can for this purpose be selected from the group consisting of polyhydroxyalkanoates, in particular poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), as well as polycaprolactone, thermoplastic starch, polybutylene adipate terephthalate and polybutylene succinate, but without being limited thereto.

[0041] In a further aspect, the present invention relates to a filament, granulate, or powder of the meltable material M2 for use as a support structure, for example, in the manufacturing process according to the invention. For the filament, granulate, or powder according to the invention, all the statements regarding the meltable material M2 as described above in connection with the manufacturing process according to the invention apply in the same way. Without being limited thereto, the filament according to the invention can have a diameter in the range from 1 mm to 4 mm, for example 1.5 mm to 3.5 mm. Commercially available diameters are, for example, 1.75 mm or 2.85 mm. The aforementioned dimensions also apply to the diameter of the granulate according to the invention.

[0042] The present invention allows for simple, residue-free, and stress-free separation of the support structure from a plastic component of complex geometry, which is produced by additive manufacturing, for example, by melt coating. Since no mechanical post-processing is required, the external appearance of the produced plastic component is not impaired. In particular, its surface quality is not negatively affected. This is achieved by using a support structure made of a meltable material M 2 , which is formed from at least one thermoplastic K 2 compounded with at least one salt and one plasticizer.

[0043] Furthermore, the present invention also allows for easy disposal of the support structure, provided that the at least one thermoplastic K 2 is biodegradable. In this case, the aqueous solvent, in particular water, brought into contact with the support structure can, for example, simply be poured down the drain. Microorganisms, fungi, or enzymes contained in the wastewater ultimately degrade the at least one thermoplastic K 2, which has broken down into fragments as a result of contact with the aqueous solvent, in particular water. Since neither acids nor bases need to be used within the scope of the production process according to the invention, the livelihood of microorganisms, such as bacteria, which are sensitive to the pH value of the water, is not disrupted by the disposal of the support structure with the wastewater.

[0044] Due to their comparatively small dimensions, the fragments of the at least one thermoplastic K 2 emerging from the support structure have a high specific surface area, which further accelerates the biological degradation process. Indirectly, no residues of the at least one thermoplastic K 2 originating from the support structure remain in the environment. In contrast, in the case of a support structure made of water-soluble but non-biodegradable thermoplastics, there is only a physical dissolution of the polymer chains, i.e. the polymer chains remain intact. If the ambient conditions change, for example temperature, mineral content or pH value, the at least one thermoplastic K 2 can precipitate again and then remain in the environment as microplastics, for example in the form of individual polymer chains. This ultimately enters the food chain via soil or water.The manufacturing process according to the invention and the filament, granulate or powder according to the invention do not have all these problems, in particular if the at least one thermoplastic K 2 used for the support structure is biodegradable. Figures

[0045] Fig. 1 This diagram schematically shows the repeated deposition of a melt strand during melt layering, including the support structure used. This is used to create plastic components with complex geometries, such as overhangs or undercuts. Fig. 2 shows schematically the compounding of the thermoplastic K 2 with the salt and the plasticizer in a twin-screw extruder, whereby a granulate is obtained. Fig. 3 shows schematically the processing of the granulate into a filament using a single-screw extruder. Fig. 4shows photographs of (a) support structures and (b) plastic components finished with them for various meltable materials M 2 . Fig. 5 shows the results of an impact test for various meltable materials M 2 . Reference symbols:

[0046] 1Plastic wire / filament of the meltable material M 1 for the plastic component 2Plastic wire / filament of the meltable material M 2 for the support structure 3Propulsion 4Contact heater 5Nozzle 6Plastic component 7Extruder 8Linear application 9Support structure 10Build platform 1'Dryblend (thermoplastic K 2 and plasticizer) 2'Salt 3'Dosing units 4'Twin-screw extruder 5'Extruded compound 6'Conveyor belt 7'Fans 8'Granulator 9'Granules 10'Collecting container 1"Single-screw extruder 2"Positioning rollers 3"Filament 4"Water bath 5"Scraper cloth 6"Laser measurement of the filaments 7"Take-off rollers 8"Filament spool Examples

[0047] The following examples serve to further illustrate the present invention, but are not limited thereto. Component production using 3D printing equipment

[0048] Using a commercially available 3D printing device, plastic components were manufactured that required the use of a support structure due to their overhang. Two different meltable materials M2 were used to construct the support structure, referred to below as Material A and Material B. The composition of the corresponding compounds (in parts by mass of the respective components) is shown in Table 1 below: Table 1 Mass parts PHBV Mass parts PEG Mass parts NaCl Material A 100 50 100 Material B 100 25 125

[0049] The support structures were then constructed by strand deposition at a deposition speed of 36 mm / s, a die temperature of 190 °C, a platform temperature of 75 °C, and a relative flow rate of approximately 105%. Photographs of the support structures constructed in this way are shown in Fig. 4(a) shown, on the left for material A and on the right for material B. From top to bottom, three consecutive images of the construction process of the support structure are shown. It can be seen that the support structure made of material A had a more inhomogeneous surface structure compared to that made of material B. This can be explained by the lower viscosity in the case of material A, due to the higher proportion of plasticizer in the composition. As can be seen from the photographs from Fig. 4(b)As can be seen, the surface structure was ultimately transferred into the plastic component to be manufactured. Despite the more inhomogeneous surface structure, satisfactory results could still be achieved with the support structure made of material A. Mechanical properties

[0050] To further investigate the mechanical properties of the support structure, the impact strength was determined as a function of the composition of the meltable material. Four different meltable materials M2 were used, referred to below as Material C, Material D, Material E, and Material F. The composition of the corresponding compounds (in parts by mass of the respective components) is shown in Table 2 below: Table 2 Mass parts PHBV Mass parts PEG Mass parts NaCl Material C 100 40 60 Material D 100 00 42,86 Material E 100 50 100 Material F 100 00 66,67

[0051] The results are in Fig. 5illustrated. In the case of materials D and F, which did not contain a plasticizer, a comparatively low impact energy was determined. In contrast, a comparatively high impact energy was determined for materials C and E. In contrast to the support structures made of materials D and F, the support structures made of materials C and E only fractured at a significantly higher energy input. This is due to the presence of the plasticizer, which led to a reduction in brittleness. Solubility in water

[0052] Finally, the solubility of the support structure in water was further investigated. Five different meltable materials M2 were used, referred to below as Material G, Material H, Material I, Material J, and Material K. The composition of the corresponding compounds (in parts by mass of the respective components) is shown in Table 3 below: Table 3 Mass parts PHBV Mass parts PEG Mass parts NaCl Material G 100 50 100 Material H 100 40 60 Material I 100 25 125 Material J 100 11,11 111,11 Material K 100 24 76

[0053] The respective support structures were immersed in demineralized water and kept for a total of four hours at a temperature of 70 °C while stirring at 100 rpm. Evaluation was performed by weighing after drying at room temperature. Table 4 below shows the results: Table 4 M previously in g m later in g m soluble in g m dissolved in g m dissolved / m soluble Material G 6,2 3,5 3,7 2,7 73% Material H 5,8 3,8 2,9 2,0 69% Material I 7,3 4,1 4,4 3,2 73% Material J 7,2 4,4 4,0 2,8 70% Material K 7,2 5,6 3,6 1,6 44%

[0054] The soluble fraction is determined from the total amount of plasticizer and salt. It is shown that in all cases, a significant portion of the support structure was dissolved in water after four hours.

[0055] In summary, the presence of the plasticizer in the meltable material M 2 can reduce the brittleness of the support structure resulting from the addition of the salt without adversely affecting the functioning of the support structure.

Claims

1. A method for producing a plastic component by additive manufacturing, comprising the following steps (a) and (b): (a) repeatedly depositing a meltable material M1 formed from at least one thermoplastic K1 for building up a plastic component having a predetermined geometry, wherein a support structure made of a meltable material M2 is used during the build-up of the plastic component enabling overhangs and / or undercuts in the plastic component, and (b) removing the support structure from the plastic component built up in step (a) after its completion by bringing it into contact with an aqueous solvent, wherein the meltable material M2 is formed from at least one thermoplastic K2 compounded with at least a salt and a plasticizer, wherein in the meltable material M2, 100 to 150 parts by mass of the salt and 10 to 50 parts by mass of the plasticizer are present based on 100 parts by mass of the total amount of the at least one thermoplastic K2, and wherein the salt compounded with the at least one thermoplastic K2 dissolves as soon as it comes into contact with the aqueous solvent, whereas the at least one thermoplastic K2 does not dissolve and remains as a porous structure.

2. The method according to claim 1, wherein the support structure is built up in step (a) during the build-up of the plastic component by repeatedly depositing the meltable material M2.

3. The method according to claim 2, wherein a 3D printing device having at least two extruders and nozzles is used for the build-up of the plastic component and the support structure, wherein the 3D printing device is provided both with a filament, granulate or powder of the meltable material M1 and with a filament, granulate or powder of the meltable material M2.

4. The method according to any one of claims 1 to 3, wherein the at least one thermoplastic K1 and the at least one thermoplastic K2 are identical.

5. The method according to any one of claims 1 to 4, wherein the at least one thermoplastic K1 is selected from the group consisting of polyesters, polyamides, polyurethanes, polycarbonates, polyketones and polyolefins, and is optionally a thermoplastic elastomer.

6. The method according to claim 5, wherein the at least one thermoplastic K1 is selected from the group consisting of polylactide, acrylonitrile butadiene styrene, acrylonitrile styrene acrylate, poly(methyl methacrylate), polyether ether ketone and glycol-modified poly(ethylene terephthalate).

7. The method according to any one of claims 1 to 6, wherein the at least one thermoplastic K2 is selected from the group consisting of polyhydroxyalkanoates, in particular poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), as well as polycaprolactone, thermoplastic starch, polybutylene adipate terephthalate and polybutylene succinate.

8. The method according to any one of claims 1 to 7, wherein the salt is selected from the group consisting of sodium chloride, sodium sulfate, sodium nitrate, potassium chloride, potassium sulfate and potassium nitrate.

9. The method according to any one of claims 1 to 8, wherein the plasticizer is polyethylene glycol.

10. The method according to any one of claims 1 to 9, wherein the at least one thermoplastic K2 is further compounded with one or more additives selected from the group consisting of flow aids, impact modifiers, nucleating agents and fillers.

11. The method according to any one of claims 1 to 10, wherein the at least one thermoplastic K2 is biodegradable.

12. A filament, granulate or powder of the meltable material M2 for use as a support structure in the method according to any one of claims 1 to 11.