CHEMICAL TREATMENT OF COMPONENTS

Description

[0001] The present invention relates to methods for treating objects produced by an additive manufacturing process, which have a surface formed from or are formed from a polymer with a glass transition temperature of at least 120°C, wherein, in the course of the method, the surface of the object is treated and brought into contact with an organic or inorganic solvent. The present invention further relates to three-dimensional objects produced by such a method and to the use of organic or inorganic solvents to reduce the surface roughness and / or the modulus of elasticity and / or to increase the tensile strength and / or the elongation at break of the object and / or to increase its chemical resistance. State of the art

[0002] Objects manufactured using 3D printing have a comparatively rough surface compared to their injection-molded counterparts, a result of the manufacturing process itself. In injection molding, the roughness of the object is determined by the roughness of the mold used to produce it, making it easy to create very smooth and aesthetically pleasing surfaces. In contrast, 3D-printed objects are manufactured, for example, by spraying successive layers or by selectively melting plastic powder in a powder bed in the areas where the final object is created.While the roughness can be influenced by the layer thickness of individual layers, the visibility or at least tactile perceptibility of the layer structure cannot be completely avoided even with small layer thicknesses, especially since this is limited by the minimum possible processing size of plastic powders or filaments. Furthermore, 3D printing requires a compromise between quality and speed, which places practical limits on avoiding layer structures.

[0003] These and other problems with 3D printing result in parts with a rough, jagged, "pixelated" surface, which is sometimes even porous, often visually or aesthetically undesirable. Furthermore, such surface finishes can be functionally limiting when smooth or impermeable surface properties are a required attribute of the 3D-printed object. Small gaps and crevices on the surface of 3D-printed devices, for example, make sterilization difficult or impossible, as bacteria can colonize these spaces. Additionally, a pronounced layered structure negatively affects the object's mechanical properties perpendicular to the plane in which the layers extend, and the resulting roughness creates points of leverage for forces acting on the object, potentially leading to damage or destruction.Furthermore, the rough to porous surface structure can create an undesirable notch effect, which can negatively affect the achievable maximum strengths and elongations.

[0004] Several methods have been described for smoothing the surface of 3D-printed objects, such as mechanical treatment (e.g., grinding, polishing), chemical treatments (e.g., heated acetone vapor), thermal treatments (e.g., localized IR or other heating), or the application of thicker coatings or lacquers. The effectiveness of such techniques depends heavily on the required surface properties of the resulting surface in terms of time, cost, durability, etc. Such techniques may only serve to smooth the part, which may then necessitate additional steps to enable controlled textures or surface features. In some embodiments, it may be desirable to pretreat the surface before applying a film to provide optimal cosmetic and functional properties.

[0005] Mechanical processing involves removing material from the object's surface, which is not necessarily desirable from a material economy perspective. Furthermore, certain areas of the object may be difficult or even impossible to reach with an abrasive, thus limiting the shapes of objects that can be processed.

[0006] Chemical treatment, for example with acetone vapor, is described for objects made of relatively soft plastics such as PLA or ABS. Here, the surface is softened or brought into a fluid state with the help of the solvent vapor, allowing a smooth surface to form due to the surface forces at work. However, the problem is that only a limited range of materials can be smoothed in this way, and that excessively long exposure or the use of too much solvent can lead to undesirable "bleaching" of the surface or even damage to the object.

[0007] During thermal treatment, the often low thermal conductivity of plastics poses a problem, leading to uneven heating of the object. This can be compensated for by very slow heating, but this significantly increases production time.

[0008] US Patent 9,908,291 B2 describes a method for providing a smooth surface to a three-dimensional plastic object produced by a 3D printing process, in which a larger raw product layer is first created and then, during the printing process, a special filament material is applied to the areas of the surface that are to be smoothed.

[0009] US Patent 10,759,116 B2 describes the application of a curable coating to a three-dimensional object initially created via 3D printing, whereby excess coating material is wiped off by rotating the object before the coating is cured.

[0010] US 2021 / 114304 A1 describes a method for manufacturing medical devices in which an element is first produced via an additive manufacturing process, and this element is then treated with an alcohol in the gas phase or in liquid form.

[0011] In light of the prior art described above, there is a need for a method that allows the surface of a plastic object to be smoothed safely and easily. In particular, there is a need for a method that allows plastic objects produced by 3D printing or additive manufacturing, based on high-temperature-resistant polymers, to be smoothed quickly, cost-effectively, and safely, while simultaneously improving their mechanical properties. The present invention addresses this need. Description of the invention

[0012] In the investigations underlying this invention, it was surprisingly discovered that plastic objects made of a high-temperature-resistant polymer, or at least having a surface formed of such a polymer, can be smoothed by treatment with an organic or inorganic solvent. The solvent is applied to the surface, for example by wetting or vaporizing it, and after a short exposure time is removed from the object by, for example, evaporation or washing. Compared to a grinding process, for example, treatment with the solvent has the advantage that the solvent can reach and act on all surface areas of the object, even those with areas shielded by the surface.Compared to a thermal process, the advantage is that it is not necessary to heat slowly to a very high temperature, which is beneficial from an energy-economic point of view and because of possible damage to the object at high temperatures.

[0013] According to a first aspect, the present invention therefore relates to a method for treating a three-dimensional object produced by an additive manufacturing process, comprising bringing the object into contact with an organic or inorganic solvent, wherein at least the surface of the object is formed from a polymer having a glass transition temperature of at least 120°C, wherein the polymer is selected from polyphenylene sulfides (PPS), polyetherimides (PEI), polyimides (PI), polyamide-imides (PAI), polyaryletherketones (PAEK), preferably polyetheretherketones (PEEK), polyetherketones (PEK), polyetherketone ketones (PEKK), polyetherketone-polyetherdiphenyletherketone (PEK-PEDEK), polyesters, polyethers or polycarbonates, and the organic or inorganic solvent is selected from one or more of concentrated and / or dilute mineral acids, concentrated organic acids,and aprotic organic solvents.

[0014] A glass transition temperature of at least 120°C means that the object is designed for high continuous use. Below this temperature, the material is in a glassy state, in which it does not deform during use. Preferably, the polymer from which the object is made has a glass transition temperature of at least 125°C and / or at most 170°C, and particularly preferably at least 130°C and / or at most 160°C.

[0015] The polymer also preferably has a continuous operating temperature, determined as heat resistance according to ISO 75 HDT / A (1.8 MPa), of at least 140°C and particularly preferably at least 150°C.

[0016] In the context of the invention described herein, the "organic or inorganic solvent" is a medium that is liquid at ambient temperature (approximately 20°C) and can interact with the polymer, for example, by dissolving the polymer, etching it (partial decomposition at the surface), or penetrating the polymer by causing it to swell, thereby increasing the mobility of the polymer chains or promoting crystallization of the polymer chains. If the object has a mixture of polymers on its surface, it is sufficient if the solvent interacts with one of these polymers in the manner described. Similarly, in the case of a block copolymer or a copolymer with an inhomogeneous distribution of monomers, interaction in the manner described can occur with only one block of the block copolymer or with the part of the copolymer that is more compatible with the solvent. In these cases, swelling of the polymer usually occurs.

[0017] The described procedure involves the analysis of a three-dimensional object manufactured using an additive manufacturing process. Such an object typically exhibits a significant surface roughness, for example, a roughness of at least 20 µm and preferably at least 25 µm (determined as the mean roughness value according to DIN EN ISO 4287:2010). Furthermore, a three-dimensional object manufactured using an additive manufacturing process can be distinguished from conventionally manufactured objects (e.g., by injection molding) by the fact that, at least upon microscopic examination of cross-sections, it exhibits a recognizable layered structure resulting from the object's "layer-by-layer" construction in the additive manufacturing process.

[0018] The additive manufacturing process used to produce the object is, on the other hand, not relevant to the process. Such objects can be produced, but are not limited to, by selective laser sintering or selective laser melting, where a powdered starting material is used as a powder bed and the areas in the layer to be included in the object are heated and liquefied by the action of electromagnetic radiation. The object is then built up as the material cools, with further material being deposited layer by layer. Alternatively, the object can be produced by fused deposition modeling (FDM), which uses a filament as the starting material and in which molten filament is sprayed onto the areas of the future object using a nozzle.

[0019] Furthermore, the object can be manufactured using a process that employs a plastic powder as the starting material. This powder is solidified by applying an ink (as a "fusing agent") to the portions of the layer where the object is to be created. Subsequent irradiation of the layer's surface with a two-dimensional light source of a wavelength absorbed only by components of the ink solidifies the object. In this way, the ink-marked plastic material is selectively melted and can then solidify into the three-dimensional object. HP commercially markets this process as "Multi Jet Fusion."In a similar process, also known as "binder jetting", a binder is applied to the parts of the layer of a plastic powder bed in which the object is to be produced later, and the object is produced in which the binder solidifies.

[0020] Other methods by which the object can be manufactured include multijet modeling (where a liquid, light-sensitive plastic material is applied to a platform by means of a printhead and cured by means of a radiation source integrated into the printhead), film transfer imaging (by 3D systems), electrophotographic (EP) imaging and deposition (by Evolve Additive solutions), or any other technology described for 3D printing.

[0021] All these processes have in common that objects with a layered structure that is at least microscopically detectable are obtained. The "three-dimensional object produced by an additive manufacturing process" that was manufactured using the process according to the invention accordingly exhibits such a structure.

[0022] In a preferred embodiment, the object brought into contact with the solvent in accordance with the inventive process is formed entirely from the specified polymer, i.e., the object contains only polymer with a glass transition temperature of at least 120°C. However, in addition to the polymer, other components, such as fillers, may also be present.

[0023] As a result of contact between the object and the organic or inorganic solvent, the solvent can interact with the polymer in such a way that the polymer swells or is partially dissolved, while the inner region of the object remains in a plastically stable state and preferably at least partially in a glassy state (object temperature < solvent temperature). The surface of the object thus becomes deformable, with surface tension effects leading to a reduction in roughness and the closure of any existing pores. The resulting smoothed surface further prevents or reduces the penetration of foreign substances into the object.

[0024] Depending on the exposure time, the solvent can also improve the bonding of the layers within the object, resulting in improved mechanical properties compared to the object before treatment. Furthermore, the solvent can also cause microscopic changes in the layer structure or arrangement of the polymer chains, which can, for example, promote increased polymer crystallization. This can then manifest macroscopically as increased strength and / or chemical resistance of the object.

[0025] In the process described here, the object is preferably brought into contact for a period suitable for reducing the surface roughness Ra, determined as the mean roughness value according to DIN EN ISO 4287:2010, by at least 5% and preferably at least 10% compared to the object's surface roughness before treatment. It should be noted that the change in surface roughness depends strongly on parameters such as temperature, the polymer, and the solvent used to treat the object, making it difficult to specify meaningful timeframes. However, a person skilled in the art can determine a suitable period for a given set of parameters including temperature, polymer, and solvent through a simple series of tests.As an example, in a series of tests, a reduction of more than 10% in the surface roughness of the object before treatment was achieved for an object made of PEKK by treatment with concentrated H 2 SO 4 at 23°C for less than 1 minute, by treatment with THF at 23°C for more than 30 minutes and by treatment with N-methylpyrrolidone at 23°C for at least 5 minutes.

[0026] Alternatively or additionally, it is preferred that the contact is carried out for a period sufficient to increase the tensile strength and / or the elongation at break, determined according to DIN ISO 527-1, by at least 5% and preferably at least 10% compared to the object before treatment, and / or to reduce the modulus of elasticity by at least 5% compared to the object before treatment. Since, in this case as well, the period depends on the underlying polymer, the solvent, and the temperature, a suitable period for each set of these parameters can be determined by a person skilled in the art based on a simple series of tests.

[0027] In some cases, treatment with the solvent may also lead to an increase in the Young's modulus, for example, by inducing stronger crystallization of the polymer. In such cases, it is preferred if the contact is carried out for a period sufficient to increase the Young's modulus, determined according to DIN ISO 527-1, by at least 2% and preferably at least 5% compared to the object before treatment.

[0028] Despite the aforementioned dependency, it is preferred that the contact period be at least 10 seconds and / or at most 240 minutes, and preferably at least 30 seconds and / or at most 180 minutes. If a mineral acid is used as the solvent, the period can be relatively short, e.g., 40 seconds to a maximum of 20 minutes, and preferably at least 60 seconds and / or at most 15 minutes. If an organic aprotic solvent is used, a longer treatment time is usually required to achieve the desired smoothing and / or to modify the tensile strength and / or elongation at break and / or the modulus of elasticity, e.g., a period of 3 to 180 minutes, and preferably at least 5 minutes and / or at most 60 minutes.

[0029] The object can be brought into contact with the solvent at any temperature at which the solvent is in liquid or gaseous form, provided that the temperature does not exceed the melting point and preferably not the glass transition temperature of the polymer in order to avoid deformation of the object (except for the desired surface smoothing). A suitable temperature range for bringing the object into contact is 15°C to 220°C, preferably at least 20°C and / or at most 180°C.

[0030] In a preferred embodiment, contact is initiated at ambient temperature (approximately 20°C). In another preferred embodiment, contact is initiated at elevated temperature, for example, at a temperature in the range of 30 to 220°C, and preferably at least 60°C and / or at most 180°C. Solvents with which temperatures above 100°C can be achieved include, for example, N-methylpyrrolidone (boiling point 202°C) and dimethylacetamide (boiling point 165°C). With these or other solvents, treatment with liquid solvent at temperatures above the boiling point at normal pressure is also possible by carrying out the treatment at elevated pressure.

[0031] When treating objects at the aforementioned temperatures, care must be taken to ensure that the treatment temperature does not exceed the glass transition temperature (Tg) of the polymer. It is preferred that the treatment temperature be at least 10°C and particularly preferably at least 15°C lower than the glass transition temperature (Tg) of the polymer. For polymer blends or block copolymers that have several phases with different glass transition temperatures, the lowest glass transition temperature should be used to determine the treatment temperature.

[0032] Contact is established at normal pressure (1013 hPa) or elevated pressure (> 1013 hPa). If contact is established at elevated pressure, the

[0033] The pressure should not exceed 250 bar and preferably should be a maximum of 50 bar, and particularly a maximum of 5 bar. Contacting is preferably carried out at atmospheric pressure. Alternatively, contacting can also be carried out at a pressure below 1013 hPa, such as a pressure in the range of 100 to 800 hPa.

[0034] In a preferred embodiment, contact is brought into contact at ambient temperature by immersion at normal pressure or increased pressure, and preferably at normal pressure.

[0035] In another preferred embodiment, contact is brought into contact at elevated temperature by immersion at normal or elevated pressure, wherein the temperature is lower than the boiling point of the solvent and the melting point of the polymer. Preferably, in this embodiment, contact is brought into contact at normal pressure.

[0036] In a further preferred embodiment, contact is brought into contact at elevated temperature in the presence of a vaporous solvent at normal or elevated pressure. For this embodiment as well, it is preferred that contact is brought into contact at normal pressure. This embodiment can be produced, for example, by vaporizing the object with the solvent, whereby the solvent can be thermally evaporated or vaporized or nebulized under the influence of ultrasound.

[0037] According to the invention, the polymer is selected from homo- or copolymers or polyblends comprising one or more selected from polysulfones (PSU), preferably polyarylene sulfones (PAS), polyarylethersulfones (PAES), polyethersulfones (PES), polyarylene sulfides, preferably polyphenylene sulfides (PPS), polyetherimides (PEI), polyimides (PI), polyamideimides (PAI), polyaryletherketones (PAEK), preferably polyetheretherketones (PEEK), polyetherketones (PEK), polyetherketone ketones (PEKK), polyetherketone-polyetherdiphenyletherketone (PEK-PEDEK), polyesters, polyethers or polycarbonates. A particularly preferred polymer is polyetheretherketone (PEEK) and polyetherimide (PEI); it is correspondingly preferred if the polymer of the three-dimensional object contains more than 50 wt.% (based on the total amount of polymer) of PEKK or PEI, and it is particularly preferred if the polymer of the three-dimensional object contains only PEKK or PEI as the polymer.

[0038] In addition to the polymer, the three-dimensional object may contain other components commonly found in objects produced by additive manufacturing, such as flow agents, anti-agglomerating agents, reflective particles, and / or pigments. A suitable type of reflective particle includes, for example, TiO₂. A suitable flow agent and / or anti-agglomerating agent is, for example, carbon black or fumed silica. A particularly preferred type of additive that can be used to impart absorption properties at wavelengths where the polymer materials do not absorb light are IR- or NIR-absorbing materials, such as the types of carbon black described in WO 2020 / 099236 A1. Furthermore, the three-dimensional object may contain typical stabilizers found in engineering polymers (e.g., antioxidants and UV stabilizers), chain growth limiters, and / or other additives for controlling the polymerization reaction (e.g.,acidic buffer systems), functional additives (e.g. flame retardants) and / or intentional or unintentional impurities from polymerization or pulverization processes (e.g. catalysts, compatibilizers, processing aids).

[0039] Furthermore, the three-dimensional object can contain fillers, e.g., in the form of fibers (especially carbon fibers), glass spheres, which may optionally be hollow, or metal and especially aluminum particles. Such fillers can be present in the object in an amount of up to 60 wt.% or in the range of 30 wt.% to 55 wt.%. In this case, the polymer content in the three-dimensional object is preferably at least 85 wt.%, more preferably at least 90 wt.%, and even more preferably at least 95 wt.% of the proportion of materials from which the object is formed that is not provided by fillers.

[0040] The inorganic or organic solvent in the process according to the invention is a dilute or concentrated mineral acid, a concentrated organic acid, or an aprotic organic solvent. Preferred mineral acids are, for example, sulfuric acid or nitric acid. Preferred organic acids are, in particular, acids with a pKa of 4.8 or less, and preferably acids with a pKa of 2 or less. A suitable acid with a pKa of 4.8 or less is, for example, acetic acid. Suitable acids with a pKa of 2 or less are, for example, fluorinated carboxylic acids such as, in particular, trifluoroacetic acid or trifluoromethanesulfonic acid. Acids as solvents are particularly preferred in combination with acid-sensitive polymers such as polyethers, polyesters, or polyamides.

[0041] In a particularly preferred embodiment, the solvent is sulfuric acid with a concentration of at least 70% and the polymer is or contains one of PEKK, PEK, PEEK or PEI.

[0042] In another preferred embodiment, a concentrated or diluted alkali, e.g. in the form of sodium hydroxide or potassium hydroxide, is included in the process as a solvent.

[0043] In a further preferred embodiment, an aprotic organic solvent is used as the solvent in the process according to the invention, which advantageously has a Hildebrand solubility parameter δ in the range of 18 to 24. Particularly suitable solvents that meet this requirement are tetrahydrofuran (THF), dichloromethane, N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), or dibromomethane. A particularly preferred aprotic organic solvent is THF. Solvents with a Hildebrand solubility parameter δ of 18 to 24 are particularly advantageous in combination with polyether polymers such as PEK, PEKK, or PEEK, which have a similar Hildebrand solubility parameter and thus a similar polarity to the solvent.

[0044] The process can be made particularly advantageous by treating the object in several stages with different solvents. A treatment in a first stage, in which the surface of the object is smoothed with a concentrated or diluted mineral acid, and a subsequent second stage, in which a crystallizing organic solvent is used, is particularly preferred.

[0045] A crystallizing effect of the organic solvent on the polymer of the object can generally be deduced from the Young's modulus, which increases due to a higher crystalline polymer content compared to the object before treatment. Alternatively, a "crystallizing effect" of a solvent on a polymer can be determined using DSC or WAXS, in which higher crystallinity is indicated by more pronounced melting transitions (peaks). Examples of solvents with a crystallizing effect include tetrahydrofuran, dichloromethane, and dibromomethane.

[0046] To remove unwanted solvent residues from the treated object after contact, it is advisable to wash the three-dimensional object with water and, if necessary, a water-miscible organic solvent with a boiling point below 100°C. Suitable solvents for washing include, in particular, lower alcohols (C1-C6), preferably ethanol, and lower ketones (C1-C6), especially acetone. The object can then be dried. Depending on the solvent used in the treatment, residues can also be removed by treatment under reduced pressure / vacuum. Removing the solvent ensures that the solvent cannot have a plasticizing effect on the object, thus preserving optimal mechanical properties.Furthermore, this prevents the solvent from being released during later use of the object, where it could cause unpleasant odors.

[0047] In a further aspect, the present invention relates to a method for producing a three-dimensional object comprising i) producing the three-dimensional object by selectively solidifying a powdered build-up material at the locations corresponding to the cross-section of the three-dimensional object in the respective layer by applying electromagnetic radiation, wherein the build-up material is a plastic powder based on a polymer with a glass transition temperature of at least 120°C, or producing the three-dimensional object from a filament as a starting material, wherein molten filament of such a polymer is sprayed to the locations of the subsequent object using a nozzle, and ii) subsequently treating the object by bringing it into contact with an organic or inorganic solvent, wherein the three-dimensional object is produced from a polymer.the compound is selected from polyphenylene sulfides (PPS), polyetherimides (PEI), polyimides (PI), polyamideimides (PAI), polyaryletherketones (PAEK), preferably polyetheretherketones (PEEK), polyetherketones (PEK), polyetherketoneketones (PEKK), polyetherketone-polyetherdiphenyletherketone (PEK-PEDEK), polyesters, polyethers, or polycarbonates, and the organic or inorganic solvent is selected from one or more of concentrated and / or dilute mineral acids, concentrated organic acids, and aprotic organic solvents. For preferred embodiments of step ii), reference is made to the preceding descriptions of preferred embodiments of the process according to the first aspect.

[0048] A method for producing the three-dimensional object by selectively solidifying a powdered build-up material, which can be used in step i), is, for example, a method such as that known from DE 44 10 046. In such a method, a three-dimensional object is produced layer by layer – according to the principle of additive manufacturing – by applying layers of powder and bonding these layers together by selectively solidifying the powder at the locations corresponding to the cross-sections of the object. Other suitable methods for producing the three-dimensional object by selectively solidifying a powdered build-up material are those specified above.

[0049] In a further aspect, the present invention relates to a three-dimensional object produced according to a method as described above. Such an object can be distinguished from conventionally produced objects by its inhomogeneous layered structure, which is still microscopically discernible in cross-section at a greater distance from the object's surface, while it may no longer be perceptible at the object's surface due to the action of the solvent.

[0050] Preferably, according to this aspect of the invention, the object has a surface roughness Ra according to DIN EN ISO 4287:2010 of less than 20 µm, preferably less than 15 µm, more preferably less than 10 µm, even more preferably less than 8 µm, and even more preferably less than 5 µm. Since the surface roughness is highly dependent on manufacturing processes, material properties, process parameters, and component orientations, this value is to be determined based on the usual parameters for objects manufactured by powder bed fusion (PBF) for Z-oriented (i.e., perpendicular to the build plane) surfaces with standard processing parameters (layer thicknesses, exposure parameters, etc.). Other additive manufacturing processes (e.g., material extrusion processes) and modified process parameters (in particular, smaller layer thicknesses, exposure parameters, etc.)Due to the inherent characteristics of the manufacturing process, significantly higher or lower surface roughness values ​​can be achieved. Accordingly, the achievable surface roughness values ​​after treatment can also differ considerably. Nevertheless, the mode of action and effect on the component properties is preferred according to this invention.

[0051] In a further aspect, the present invention relates to the use of a treatment in which a three-dimensional object produced by an additive manufacturing process is brought into contact with an organic or inorganic solvent to reduce the surface roughness and / or the modulus of elasticity and / or to increase the tensile strength and / or the elongation at break of the object and / or to increase its chemical resistance, wherein the object has a surface formed from a polymer having a glass transition temperature of at least 120°C, wherein the three-dimensional object is formed from a polymer selected from polyphenylene sulfides (PPS), polyetherimides (PEI), polyimides (PI), polyamideimides (PAI), polyaryletherketones (PAEK), preferably polyetheretherketones (PEEK), polyetherketones (PEK), polyetherketoneketones (PEKK), polyetherketone-polyetherdiphenyletherketone (PEK-PEDEK), polyesters, polyethers, or polycarbonates.and the organic or inorganic solvent is selected from one or more concentrated and / or dilute mineral acids, concentrated organic acids, and aprotic organic solvents, and preferably from such a polymer, optionally including further non-polymeric components. Improved chemical resistance can be determined, for example, according to DIN EN ISO 175, whereby the change in mass, dimensions, extent, and surface changes after storage of the object in the chemical for a period of 24 hours is determined. Alternatively, better chemical resistance correlates with a higher degree of crystallinity in the polymer or at least in the polymer at the surface of the object, which can be determined using DSC or WAXS. The surface roughness and mechanical properties are to be determined in each case using the test methods specified above.

[0052] In connection with the above aspects, it should be noted that each preferred embodiment described above for one aspect is equally described as a preferred embodiment of the other aspects, even if the combination is not explicitly stated above for reasons of brevity. Furthermore, any combination of more or less preferred embodiments of one aspect, as well as any combination of more or less preferred embodiments of one aspect with any other aspect, as described above, is considered to be described according to the invention.

[0053] Within the scope of the present invention, the terms "comprising" or "containing" and their grammatical modifications have the following meanings: In one embodiment, additional elements may be included besides those mentioned. In another embodiment, essentially only the mentioned elements are included. In other words, in addition to their conventional meaning, the terms may, in a particular embodiment, be synonymous with the terms "essentially consisting of" or "consisting of".

[0054] The present invention is illustrated in more detail below by means of some exemplary embodiments, which, however, are not to be considered in any way as limiting the scope of protection of the application. Example 1:

[0055] Standard test specimens (according to ASTM D638-14, Type I) in ZXY orientation, produced by 3D printing with an EOS P810 laser sintering system from carbon fiber reinforced PEKK (trade name ALM HT-23), were treated with the solvents specified in Table 1 for the time specified therein at room temperature. Excess solvent was then removed, the specimens were washed with water and (in the case of NMP and DMAc, additionally with acetone), and the specimens were dried under an air atmosphere for > 12 hours at room temperature.

[0056] For the specimens treated in this way, the roughness (determined as mean roughness Ra according to DIN EN ISO 4287:2010), the modulus of elasticity, the tensile strength (UTS), and the elongation at break (each according to ASTM D638-14) were determined. The results of these measurements are also given in Table 1. Specimen 1 is a comparison example that was not subjected to any solvent treatment. Table 1: sample Treatment product Treatment time [min] Roughness [µm] E-modulus [MPa] UTS [MPa] Elongation at break [%] 1 - - 25,1 5820 63 1,12 2 H₂SO₄ 1 5,4 5740 70 1,32 3 H₂SO₄ 5 5,4 5480 72,5 1,48 4 H₂SO₄ 10 3,8 5460 74,6 1,53 5 THF 15 24,5 5900 60 1,1 6 THF 60 22,3 4950 65,5 1,42 7 NMP 5 22,3 5760 67 1,28 8 NMP 60 23,2 5660 64 1,18 9 NMP 180 22,9 5800 63,5 1,15 10 DMAc 15 23,4 5500 66,5 1,30

[0057] As can be seen from Table 1, treatment with concentrated sulfuric acid (H₂SO₄) can significantly reduce the roughness of the object. After treatment, improved mechanical properties are also observed, including increased tensile strength and elongation at break, and a reduced modulus of elasticity. Samples treated with THF (tetrahydrofuran) showed a smaller improvement in roughness, but with a longer treatment time (60 min), increased tensile strength and elongation at break. Similarly, samples treated with NMP showed a slight improvement in roughness, and with a shorter treatment time, an increase in elongation at break and tensile strength. Example 2:

[0058] Tensile bars according to DIN EN ISO 527-2, type 1BA, made of polyetherketoneketone powder (PEKK, based on the Kepstan 6000 series from Arkema) or carbon fiber-filled PEKK powder (PEKK-CF, trade name: ALM HT-23) were produced by layer-by-layer, regioselective solidification on an EOS P810 laser sintering system in ZXY orientation. Additionally, cuboid test specimens were produced to determine the surface roughness, also in ZXY orientation.

[0059] The components were treated in concentrated sulfuric acid (96% or 80%) at room temperature (RT, ~23°C) or elevated temperature (60°C) for 1, 5, 10, and 15 minutes, respectively, at ambient pressure, by immersion and continuous stirring. After the treatment time, the test specimens were rinsed in water and then stored in water for at least 12 hours to extract as much of the remaining acid residue as possible. Subsequently, the test specimens were dried for at least 12 hours in a vacuum oven at 120°C with a flow of dry nitrogen at an absolute pressure of 220 to 280 mbar.

[0060] The tensile bars were tested according to DIN EN ISO 527-1. Each measured value was determined as the average of five individual measurements.

[0061] The surface roughness Ra was determined before and after treatment on the respective test specimen using a Keyence VR-3200 digital macroscope with measurement software version 2.5.0.236. For this purpose, a 3D model of the surface under consideration was first created using various exposure settings, from which the mean line roughness Ra was calculated from several individual lines in the Z-orientation.

[0062] The method used to determine Ra is based on the standards ISO 4287 and ISO 4288 with filtering according to ISO 11562 with λc = 2.5 mm and without λs (noise filtering) using a Keyence VR-3200 digital macroscope with measurement software version 2.5.0.236, as per the manufacturer's instructions. Reference is also made to the Keyence VR-3000 user manual (April 2016), and in particular to chapters 11 and 12. For the determination, end-effect correction was activated, the double Gaussian filter was deactivated, the number of measurement sections was 3, and the number of profiles was 31. The respective images were acquired with the 40x zoom microcamera and evaluated using suitable software.

[0063] The development of the mechanical properties (tensile strength and elongation at break) for the various PEKK samples and the corresponding treatment conditions in comparison to the reference (untreated sample) is exemplified in Figure 1 shown.

[0064] Tables 2 and 3 show the relative changes in the measured values ​​due to the treatment. The values ​​are presented as a dimensionless quotient of the measured value after treatment relative to the measured value before treatment (for the mean line roughness Ra) or relative to the untreated reference specimens (for the tensile properties), rounded to two decimal places. Accordingly, a measured value less than 1 indicates a decrease, and a measured value greater than 1 indicates an increase in the respective measured value due to the treatment. Deviations of 3–5% are within the range of the standard deviation. Table 2: Certain properties of PEKK after treatment (relative values) solvents temperature Length of time [min] E-module Tensile strength Elongation at break Roughness H₂SO₄, 96% RT 1 1,06 1,04 0,99 0,46 5 1,03 1,07 1,06 0,41 10 1,02 1,11 1,11 0,60 15 0,99 1,03 1,02 0,46 60°C 1 1,06 1,20 1,14 0,36 5 0,95 1,04 1,10 0,63 10 0,90 1,02 1,14 0,85 15 0,87 0,99 1,16 H₂SO₄, 80% RT 1 1,04 1,06 1,02 0,79 5 1,06 1,11 1,06 0,36 10 1,04 1,12 1,09 0,37 15 1,04 1,09 1,05 0,54 60°C 1 1,04 1,04 0,97 0,50 5 1,06 1,10 1,05 0,40 10 1,08 1,10 1,02 0,27 15 1,06 1,05 0,96 0,30 Table 3: PEKK-CF results after treatment (relative values) solvents temperature Length of time [min] E-module Tensile strength Elongation at break Roughness H₂SO₄, 96% RT 1 1,00 1,04 1,05 0,45 5 0,99 1,06 1,09 0,35 10 0,95 1,01 1,09 0,32 15 0,94 1,00 1,09 0,40 H₂SO₄, 80% RT 1 0,98 1,02 1,03 0,96 5 1,00 0,98 1,00 0,81 10 1,00 0,99 1,05 0,97 15 0,99 0,97 1,00 1,08

[0065] The results in Tables 2 and 3 show a significant smoothing effect for concentrated sulfuric acid (96%), which is also accompanied by an improvement in mechanical properties, in particular an increase in elongation at break of approximately 10%. Since this effect occurs essentially independently of any change in the tensile modulus, it is assumed that the effect is due to the reduced notch effect caused by the smoothing.

[0066] At elevated temperatures, a change in the tensile modulus can also be observed for PEKK, which indicates an effect of the solvent also inside the component.

[0067] The beneficial effects are still visible even with sulfuric acid diluted to 80%, but sometimes require a longer exposure time. Example 3:

[0068] Tensile bars according to DIN EN ISO 527-2, type 1BA, made of polyetherimide powder (PEI, based on the Ultem 5000 series from Sabic) were manufactured using layer-by-layer, regioselective solidification on a modified EOS P810 laser sintering system in XYZ orientation. One specimen at a time was immersed in a solvent (purity >99%) according to Table 4 for 180 minutes at room temperature and ambient pressure. Subsequently, the specimens were washed with ethanol and immersed in ethanol for at least 12 hours to extract as much solvent residue as possible. Finally, the specimens were dried for at least 12 hours in a vacuum oven at 120°C with a flow of dry nitrogen at an absolute pressure of 220 to 280 mbar.

[0069] The individual tension bars were subjected to a tensile test in accordance with DIN EN ISO 527-1. Additionally, a set of five untreated tension bars was tested as a reference.

[0070] Following tensile testing, the components were subjected to differential thermal calorimetry according to DIN EN ISO 11357. For this purpose, a sample of approximately 5 mg was taken from each component and evaluated using a measuring system (DSC 823e, Mettler Toledo, evaluation via "STARe Software", version 16.30) under nitrogen 5.0 (purity >99.999% nitrogen). The sample was first conditioned at 0°C for 5 minutes and then heated to 400°C at a constant heating rate of 20 K / min. After conditioning at 400°C for 5 minutes, the sample was cooled to 0°C at a cooling rate of 20 K / min and then, after conditioning at this temperature for another 5 minutes, heated again to 400°C at a constant heating rate of 20 K / min. The glass transition temperature Tg, the melting point Tm and the specific enthalpy of fusion ΔHm were determined for various samples from DSC measurements in accordance with DIN EN ISO 11357.Table 4 lists the corresponding values ​​determined during the first heating run. Here, the glass transition temperature Tg corresponds to the midpoint of the stage according to the standard, the melting temperature Tm corresponds to the peak maximum of the melting peak, and the enthalpy of fusion ΔHm describes the integral of the peak normalized to the sample mass. Table 4: solvents Tg [°C] Tm [°C] ΔHm [J / g] comment reference 224 -- -- Translucent component N,N'-Dimethylacetamide 224 -- -- No visual change Tetrahydrofuran 225 295 1,5 No visual change Dibromomethane 223 282 8 Component opaque, partial cracking on the surface Dichloromethane 223 281 17 Component opaque, with partial cracking on the surface

[0071] The results show that suitable solvents can induce crystallization, whereas the component produced in the manufacturing process (reference) is amorphous. However, the result and its effects are highly dependent on the solvent. Increased crystallinity is expected to result in higher mechanical strength (e.g., in the form of an increased tensile modulus). Furthermore, the increased crystallinity (higher enthalpy of fusion) is expected to provide better resistance to chemical attack.

[0072] By optimizing the treatment conditions (e.g. solvent, method and duration of exposure), further optimization of the desired properties can be expected; for example, improved chemical resistance can be achieved through crystallization of the surface layer limited in depth and (through partial dissolution or swelling) a smoother surface, while avoiding a reduction in elongation at break.

Claims

1. Method for the treatment of a three-dimensional object produced according to an additive manufacturing method, comprising bringing the object into contact with an organic or inorganic solvent, wherein at least one surface of the object is formed from a polymer having a glass transition temperature, measured according to DIN EN ISO 11357, of at least 120°C, wherein the polymer is selected from polyphenylene sulfides (PPS), polyether imides (PEI), polyimides (PI), polyamide imides (PAI), polyaryl ether ketones (PAEK), preferably polyether ether ketones (PEEK), polyether ketone-polyether diphenyl ether ketone (PEK-PEDEK), polyesters, polyethers, or polycarbonates and the organic or inorganic solvent is selected from one or more of concentrated and / or diluted mineral acids, concentrated organic acids, and aprotic organic solvents.

2. Method as claimed in claim 1, wherein the bringing into contact takes place for a period of time which is sufficient to reduce the surface roughness Ra, defined as the average roughness value according to DIN EN ISO 4287:2010, by at least 5% and preferably at least 10% in relation to the surface roughness of the object before the treatment.

3. Method as claimed in claim 1 or 2, wherein the bringing into contact takes place for a period of time which is sufficient to increase the tensile strength and / or the elongation of fracture, determined according to DIN ISO 527-1, by at least 5% and preferably at least 10% in relation to the object before the treatment and / or to reduce the modulus of elasticity by at least 5% in relation to the object before the treatment.

4. Method as claimed in any one of claims 1 to 3, wherein the bringing into contact of the object is carried out by immersing the object in the solvent or by vapor deposition of the object.

5. Method as claimed in any one of the preceding claims, wherein the bringing into contact takes place at a temperature in the range of 15°C to 220°C, and preferably 60°C to 180°C.

6. Method as claimed in any one of the preceding claims, wherein the organic or inorganic solvent is selected from sulfuric acid or nitric acid, and aprotic organic solvents having a Hildebrand solubility parameter δ in the range of 18 to 24, preferably selected from the group comprising THF, dichloromethane, N-methyl pyrrolidone, and dimethyl acetamide.

7. Method as claimed in any one of the preceding claims, wherein the treatment of the three-dimensional object takes place in multiple steps using various solvents, particularly preferably for smoothing the surface by means of a concentrated or diluted mineral acid in a first step and treatment using an organic solvent having a crystallizing effect in a following second step.

8. Method as claimed in any one of the preceding claims, wherein the three-dimensional object is washed, after the treatment using the organic or inorganic solvent, using water and optionally a water-miscible organic solvent having a boiling point of less than 100°C and subsequently dried.

9. Method for producing a three-dimensional object comprising i) producing the three-dimensional object by selectively solidifying a powdered construction material at points corresponding to the cross-section of the three-dimensional object in the respective layer by the action of electromagnetic radiation, wherein a plastic powder is used as construction material, which is based on a polymer having a glass transition temperature of at least 120°C, or producing the three-dimensional object from a filament as starting material, wherein molten filament of such a polymer is sprayed with the aid of a nozzle at the points of the later object, and ii) subsequently treating the object by bringing the object into contact with an organic or inorganic solvent, wherein the three-dimensional object is produced from a polymer selected from polyphenylene sulfides (PPS), polyether imides (PEI), polyimides (PI), polyamide imides (PAI), polyaryl ether ketones (PAEK), preferably polyether ether ketones (PEEK), polyether ketones (PEK), polyether ketone ketones (PEKK), polyether ketone-polyether diphenyl ether ketone (PEK-PEDEK), polyesters, polyethers, or polycarbonates and the organic or inorganic solvent is selected from one or more of concentrated and / or diluted mineral acids, concentrated organic acids, and aprotic organic solvents.

10. Three-dimensional object produced according to a method as claimed in any one of claims 1 to 9.

11. Three-dimensional object as claimed in claim 10, wherein the object has a surface roughness Ra, determined as mean roughness value according to DIN EN ISO 4287:2010, of less than 20 µm, preferably less than 15 µm, and particularly preferably less than 10 µm.

12. Use of a treatment, in which a three-dimensional object produced via an additive manufacturing method is brought into contact with an organic or inorganic solvent, for reducing the surface roughness and / or the modulus of elasticity and / or for increasing the tensile strength and / or the elongation of fracture of the object and / or for increasing the chemical resistance, wherein the object preferably has a surface formed from a polymer having a glass transition temperature of at least 120°C, wherein the three-dimensional object is formed from a polymer selected from polyphenylene sulfides (PPS), polyether imides (PEI), polyimides (PI), polyamide imides (PAI), polyaryl ether ketones (PAEK), preferably polyether ether ketones (PEEK), polyether ketones (PEK), polyether ketone ketones (PEKK), polyether ketone-polyether diphenyl ether ketone (PEK-PEDEK), polyesters, polyethers, or polycarbonates and the organic or inorganic solvent is selected from one or more of concentrated and / or diluted mineral acids, concentrated organic acids, and aprotic organic solvents.