METHOD FOR THE SELECTIVE SPATIAL SEPARATION OF COMPOSITE MATERIALS IN ADDITIVELY MANUFACTURED MOLDED PARTS

Description

[0001] The invention relates to a method for treating a molded part and an element obtainable from the method.

[0002] It is known that molded parts made of a polymer or thermoplastic polymer can be produced using various printing technologies. Industrially, selective laser sintering (SLS) is a particularly widespread method. The point-by-point and grid-like sintering of the powder with one or more lasers usually results in long process times. Several methods have since been developed to shorten these process times. Infrared radiation-based processes, such as Multi-Jet Fusion (MJF) technology, and High-Speed ​​Sintering (HSS) are particularly noteworthy. The also significantly accelerated Laser Pro-Fusion technology is based on lasers instead of infrared radiation. The common feature of these processes is the addition of energy-absorbing substances to the powder bed. In the MJF and HSS processes, the additives are selectively introduced into the white plastic powder through controllable nozzles.In Laser Pro-Fusion technology, the powder already contains the additive before sintering. Other laser sintering processes also utilize powders with energy-absorbing additives. These additives generally enable faster and more cost-effective processes due to their faster energy input (energy absorption). For example, the use of carbon black as an inexpensive energy-absorbing additive means that molded parts produced using MJF, HSS, or Laser Pro-Fusion are typically gray to black in color. This significantly limits the possibility of coloring these dark parts through subtractive color mixing.

[0003] It is also known to incorporate printing materials with other additives (shredded and long mineral, carbon or glass fibers, color particles, nanoparticles and nanotubes, wood, metals, etc.) or to combine several polymer materials (e.g., ABS and PC) to influence the aesthetic, mechanical, or functional properties of the molded parts. Such composite materials can be printed using Fused Deposition Modeling (FDM) and the aforementioned SLS, HSS, and MJF processes. These printing processes result in the "bonding" of components, thus creating a homogeneous distribution of components within the (polymer) matrix and isotropic properties. However, this can lead to the surface potentially revealing areas that cannot be (stably) colored (e.g., glass fibers or polymers with lower dye affinity).

[0004] WO 2019 / 185756 A1 discloses a method for treating components produced using additive manufacturing. In this context, WO 2019 / 185756 A1 describes how the top layer of a 3D-printed polyamide part can be treated with nitric acid for up to 45 minutes at a temperature of 0°C to 65°C, causing the surface to turn black. After the nitric acid is removed and the surface comes into contact with a liquid solution, such as water, the previously black surface turns whitish to white. A disadvantage of this method is the requirement to use strongly oxidizing HNO₃.

[0005] WO 2019 / 201932 A1 describes the smoothing of the surfaces of 3D-printed molded parts using solvents. The smoothing is achieved through contact of the solvent with the molded part surface by immersion or vapor deposition. All soluble polymers that are soluble in alcohols, tetrahydrofuran, or dichloromethane are compatible with this method.

[0006] WO 2014203254 A1 describes the chemical smoothing of 3D-printed molded parts by immersion in a solvent (any solvent).

[0007] In principle, current state-of-the-art methods involve dyeing gray 3D-printed parts with less bright and vibrant colors in a dye bath. Any existing carbon black particles are visible as black dots after dyeing. Since the surface may also contain other components that cannot be dyed (or dyed well enough), this also affects the color quality. Depending on the printing process, the parts can also be completely dark gray to black, in which case dyeing is no longer possible. Coloring in this case can only be achieved by painting. Modifying other surface properties can also be achieved by applying an extra layer (for example, an additional heat shield between additively manufactured electrical components). The disadvantage here is that applying an additional layer significantly alters the geometry of the component.

[0008] Therefore, there is a need for an improved method for treating molded parts, preferably to create an inhomogeneity on the surface of the intrinsically homogeneous molded parts in order to level out the undesirable surface phenomena caused by fillers / additives without applying substances (e.g. coating) and to synergistically introduce further useful functionality.

[0009] This problem is solved by the features of the independent claims. The features in the dependent claims define specific embodiments.

[0010] Therefore, the invention relates to a method for treating a molded part, comprising the steps: a) Providing a molded part composed of a1) at least one polymer K and a2) at least one material, which preferably differs from the polymer K, b) Contacting the molded part with at least one solvent A, b1) Producing a gel based on the polymer K of the molded part and the solvent A, c) Forming a concentration gradient on the surface of the molded part from the polymer K and the material, wherein the concentration of the polymer K increases towards the surface, d) At least partial component separation, wherein the solvent A causes the polymer K to swell at least partially on the surface, wherein the molded part is manufactured using additive manufacturing and the material is veneered with the polymer K, and wherein the material is selected from electrically conductive organic materials, polymers with a polarity other than the polymer K, ceramics, metals, alloys, glasses, graphite, activated carbon, carbon black, fullerenes, carbon nanotubes, carbon fibers, graphene and graphene derivatives such as graphene nanoplatelets, amorphous carbon or mixtures thereof.

[0011] Preferably, the invention relates to a method for treating a molded part, comprising the steps of: a) Providing a molded part composed of a1) at least one polymer K and a2) at least one material, which is preferably different from the polymer K, b) Contacting the molded part with at least one solvent A, b1) Producing a gel based on the polymer K of the molded part and the solvent A, c) Forming a concentration gradient on the surface of the molded part from the polymer K and the material, wherein the concentration of the polymer K increases towards the surface.

[0012] The described molded parts are composed of two components, polymer K and the material, which have different properties, e.g., regarding their colorability. Preferably, the molded part consists of polymer K and the material. Due to the manufacturing method, these fused components are preferably distributed uniformly throughout the entire molded part. This results in the surface of the molded part being partially composed of a material that cannot be colored (or colored sufficiently) (e.g., carbon black, glass, polymers without reactive groups, such as Teflon).

[0013] Ideally, the concentration gradient ensures that no materials are present in the plane of the molded part's surface, so that the surface is formed by the polymer K. Advantageously, the concentration gradient forms independently of gravity; that is, a body completely in contact with the solvent A forms a corresponding gradient.

[0014] Therefore, a concentration gradient within the meaning of the present invention preferably denotes the change in the concentration of polymer K in the molded part with respect to the material towards the surface of the molded part. The concentration of polymer K increases towards the surface, particularly when compared to the concentration before contact of the molded part with at least one solvent A. Preferably, due to the concentration gradient, the surface of the molded part is free of material.

[0015] One advantage of this invention is that the surface of the molded part can be modified in a single step, without applying additional layers, so that it becomes more easily or even possible to be colored, or acquires other surface properties that are often the opposite of those in the interior of the component, but advantageous for the specific application. For example, by converting gray molded part surfaces to white surfaces, the parts can be colored without restriction. Since no material needs to be removed or added, the dimensions of the molded part remain unchanged, unlike in additive manufacturing processes such as painting.

[0016] Therefore, it is advantageous to convert the surface color of gray 3D-printed parts to a white shade or the natural color of the polymer, regardless of the printing technology used. This eliminates the need to rely on a single printing technology for producing white 3D-printed parts. As a result, a more cost-effective and time-saving printing technology, such as the MJF printing process, can be used to print the parts. Another advantage is that the coloring options are significantly expanded after the 3D-printed parts have been treated with this process. This enables homogeneous coloring (e.g., without black soot spots on the surface) as well as a wider color spectrum (especially coloring with lighter or more vibrant colors). The coloring process, which is optimized for polymers without materials, can be directly adopted.

[0017] It may be advantageous if the molded part is subjected to further processing operations before or after the inventive method, such as unpacking, depowdering, compacting, grinding, smoothing, impregnating, dyeing, coating, covering and / or painting.

[0018] Preferably, the inventive method, in which the molded part comprises a recycled material made of a polymer, allows the original or natural color tone to be restored without the additives that change the color.

[0019] Ideally, different polymer classes can be processed. This allows for the treatment of a wide variety of components, enabling them to be adapted to specific requirements.

[0020] Therefore, polymer K is preferably selected from the group consisting of thermoplastic elastomers, polyoxymethylenes, polyethylene terephthalates, polyethylene terephthalate glycols, polyether block amides, polyethylene furanoates, polyurethanes, acrylonitrile butadiene styrenes, thermoplastic polyamides, photopolymers, triblock polymers of polystyrene and poly(ethylene oxide) blocks, polyamides, polyesters, polyolefins, polyacrylates, polyvinylamines, polyacrylamides, polymethyl (meth)acrylates, polyethers, polycarbonates, polylactides, polyethersulfones, polysulfones, polyphenylsulfones, polyimides, polyetherimides, polyketones, polyetherketones, styrene polymers, styrene block polymers, acrylonitrile styrene acrylates, or copolymers, blends, or mixtures of the aforementioned polymer types.

[0021] Depending on the polymer types mentioned above, the molded part, which is made of polymer K, needs to be in contact with solvent A for varying lengths of time. The size of the molded part, its surface properties (such as porosity), and the presence of cavities can be taken into account accordingly.

[0022] The inventive method for treating a molded part comprises the steps of providing a molded part composed of at least one polymer K and at least one material, followed by step b), contacting the molded part with at least one solvent A.

[0023] Preferably, step b) is carried out for 5 seconds to 20 hours, particularly preferably for 1 minute to 5 hours, and especially for 1 minute to 5 minutes. This time period advantageously allows the solvent to dissolve or swell the polymer.

[0024] Preferably, step b) is carried out at atmospheric pressure.

[0025] According to the invention, the solvent A causes at least partial swelling of the polymer K at the surface.

[0026] The solvent A is particularly favorably able to cause the polymer K to swell across the entire surface with which the polymer K is in contact.

[0027] The resulting source layer is preferably in the range between 5-500 µm, particularly preferably in the range between 10-200 µm.

[0028] Preferably, the molded part is contacted by immersion, vapor deposition, or spraying. This can be achieved using, among other things, autoclaves, immersion baths, dripping devices, spraying, immersion, flood, and steam cleaning systems, steam smoothing systems, misting nozzles, atomizers, and other spraying devices.

[0029] In order for swelling or dissolution to occur, the solvent A should advantageously have a similar polarity to the polymer K.

[0030] Preferably, solvent A is selected from the group consisting of ketones, aldehydes, lactones, lactams, nitriles, nitro compounds, tertiary carboxylic acid amides, urea derivatives, sulfoxides, sulfones, carbonic acid esters, water, alcohols, amines, carboxylic acids, primary amides, secondary amides, halogenated hydrocarbons, or mixtures thereof. The polar solvents mentioned above are particularly suitable for dissolving or swelling polar polymers.

[0031] Preferably, solvent A is also selected from the group consisting of hydrocarbons, petroleum, aromatics, carboxylic acids, esters, ethers, or mixtures thereof. The aforementioned nonpolar solvents are particularly suitable for dissolving or swelling polymers that are less polar or not less polar.

[0032] The principle of near-surface separation through the swelling process of components generally works for all systems in which only one component is soluble in a chosen solvent. A suitable solvent can therefore be selected for each component (e.g., polymer type) and for each intended application.

[0033] Preferred examples of relevant polymer-particle systems are carbon black-filled polyamide 12, carbon black-filled polyamide 11, carbon black-filled polypropylene, and / or carbon black-filled TPU (thermoplastic polyurethane). Suitable solvents for polyamides include, for example, benzyl alcohol, N-methyl-2-pyrrolidone (NMP), N-butyl-2-pyrrolidone (NBP), propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, ethyl methyl carbonate, γ-butyrolactone (GBL), mixtures of dichloromethane and formic acid, and other polar solvents. Suitable solvents for polypropylene include, for example, alkylbenzenes, limonene, diethylbenzene, and other nonpolar solvents. Suitable solvents for TPU (thermoplastic polyurethanes) include, for example, benzyl alcohol and dimethyl sulfoxide.

[0034] The process according to the invention can be applied not only to particle-filled polymers (i.e., polymer and material) but is also capable of separating other homogeneous multi-component mixtures. For example, plastics colored with pigments and dyes can be lightened. A general requirement is that one component has a different solubility (or no solubility) than the other component in the selected solvent. The process according to the invention is advantageously applicable not only to 3D-printed parts but also to all plastic parts containing additives.

[0035] By contacting the molded part with at least one solvent A, preferably by immersing the molded part in a suitable solvent, by spraying the molded part with a suitable solvent or by vaporizing the molded part with a suitable solvent, the soluble component, the polymer K, is spatially separated from the component insoluble in this solvent, the material.

[0036] Advantageously, the selective spatial separation of components and subsequent encapsulation of the non-colorable material with a colorable polymer K, as described in steps b) and c), allows for unrestricted coloring of the components. This enables on-demand coloring without sacrificing the superior properties of multi-component polymer blends. Often, it is also desirable to have different properties on the surface and in the interior of the molded part.

[0037] This spatial separation allows for different surface properties of the molded part. For example, it can result in a different feel.

[0038] According to the invention, the method comprises the step: b1) Production of a gel based on the polymer K of the molded part and the solvent A.

[0039] The polymer K-solvent A-gel preferably surrounds and covers the insoluble components (material). The temperature, pressure, duration of contact with the solvent, and other factors influencing solvent diffusion determine the extent of the dissolution or swelling process.

[0040] According to the invention, the method further comprises the step: d) at least partial component separation. The gel swells and surrounds the less soluble components. Partial component separation (polymer K and material) preferably allows for the achievement of different surface properties. For example, not all areas can have the same properties. Similarly, areas can be produced that are white and contain colorable groups and can be treated with a dye, while other areas remain unchanged. Preferably, the molded part has only the gel on its surface.

[0041] Preferably, the process also includes the step: e) drying the molded part at atmospheric pressure and a temperature in the range of 10°C to 140°C, most preferably at 20°C to 80°C. Or alternatively, drying in a vacuum (0-900 mbar) at temperatures between 10°C and 140°C, most preferably between 20°C and 80°C.

[0042] The temperature and pressure are preferably selected such that the temperature is below the melting point of polymer K, and particularly preferably below the softening point of polymer K, and that the combination of pressure and temperature allows the solvent to escape from the gel within a realistic timeframe. This temperature range during drying does not result in a large energy input into the molded part. This has the advantage that, firstly, thermoplastic molded parts in particular do not change their shape, and secondly, that no high energy costs are incurred. This enables, for example, mass production or high throughput when treating a molded part with the process according to the invention. For a solvent with a boiling point of approximately 200°C, drying at 20 mbar and 80°C is suitable, for example.

[0043] After drying step e), the polymer K on the surface of the molded part exhibits a different crystallinity than before the process. The surface crystallinity can be influenced by the selected temperature and pressure in the drying process e) as well as the duration of contact between the molded part and the solvent A in step b).

[0044] The altered crystallinity at the surface of the molded part can be monitored by density measurement, differential scanning calorimetry, X-ray diffraction, IR spectroscopy or NMR spectroscopy.

[0045] The process can be used to create a surface of a molded part that has chemical and / or physical properties that differ from the interior of the molded part.

[0046] The molded part is manufactured according to the invention by means of additive manufacturing in a process selected from the group consisting of powder bed processes, such as (selective) laser sintering (SLS), binder jetting, multijet fusion technologies (MJF), high-speed sintering (HSS), cold metal fusion or laser melting processes; light-curing processes, such as stereolithography (SLA or STL), digital light production (DLP), continuous light interface production (CLIP), polyjet processes (PJM), dual-cure processes, hot lithography and extrusion processes such as fused deposition modeling (FDM), fused filament fabrication (FFF), multijet modeling (MJM), layer plastic deposition, selective thermoplastic electrophotographic process (STEP).

[0047] The molded parts produced using these methods are preferably made of plastic and may optionally contain other materials. Plastics are characterized by their diverse properties and can be adapted to the respective areas of application.

[0048] According to the invention, the material is veneered with the polymer K. In this context, veneering can mean fusing, blending, subsequent introduction of a material into the surface (e.g., by blasting with glass, sand, or ceramic particles), as well as physical mixing of the polymer K with the material.

[0049] Preferably, the method comprises the step: f) coloring the molded part with a dye. The coloring is preferably carried out in a dye solution.

[0050] Preferably, the dye solution consists of at least one dye dissolved in a solvent. The dye may be selected from, but is not limited to, acid dyes, disperse dyes, direct dyes, reactive dyes, metal complex dyes, vat dyes, developing dyes, and cationic dyes.

[0051] According to the invention, the material is preferably selected from electrically conductive organic materials, polymers with a polarity other than polymer K, ceramics, metals, alloys or glasses, graphite, activated carbon, carbon black, fullerenes, carbon nanotubes, carbon fibers, graphene and graphene derivatives such as graphene nanoplatelets, amorphous carbon or mixtures thereof.

[0052] The electrical and thermal conductivity of the molded part can also be altered by this surface modification. Therefore, spatial separation can be used to modify not only colorability but also other properties on the surface compared to the interior of the component. For example, the surface could be electrically insulated by spatially separating the conductive and insulating components, with the insulating component, polymer K, surrounding the conductive component, the base material. Materials that are electrically and / or thermally conductive are particularly suitable for this purpose.

[0053] Here too, the advantage of converting the existing material is that no material needs to be removed or added. Unlike additive processes such as painting, the dimensions of the molded part are preserved.

[0054] Therefore, the material selected from the group consisting of graphite, activated carbon, carbon black, fullerenes, carbon nanotubes, carbon fibers, graphene and graphene derivatives such as graphene nanoplatelets, amorphous carbon or mixtures thereof is particularly preferred.

[0055] Another object of the invention is an element obtainable from the inventive method.

[0056] Particularly preferred is an element obtainable from a process for treating a molded part, comprising the steps: a) Providing a molded part composed of a1) at least one polymer K, wherein the polymer K is selected from the group consisting of thermoplastic elastomers, polyoxymethylenes, polyethylene terephthalates, polyethylene terephthalate glycols, polyether block amides, polyethylene furanoates, polyurethanes, acrylonitrile butadiene styrenes, thermoplastic polyamides, photopolymers, triblock polymers of polystyrene and poly(ethylene oxide) blocks, polyamides, polyesters, polyolefins, polyacrylates, polyvinylamines, polyacrylamides, polymethyl methacrylates, polyethers, polycarbonates, polylactides, polyethersulfones, polysulfones, polyphenylsulfones, polyimides, polyetherimides, polyketones, polyetherketones, styrene polymers, styrene block polymers, acrylonitrile styrene acrylates or copolymers, blends or mixtures of the aforementioned polymer types therefrom, and a2) at least one material,wherein the material is selected from electrically conductive organic materials or polymers with a polarity other than polymer K, ceramics, metals, alloys or glasses, or graphite, activated carbon, carbon black, fullerenes, carbon nanotubes, carbon fibers, graphene and graphene derivatives such as graphene nanoplatelets, amorphous carbon or mixtures thereof, b) contacting the molded part with at least one solvent A, wherein the solvent is selected from the group consisting of ketones, aldehydes, lactones, lactams, nitriles, nitro compounds, tertiary carboxylic acid amides, urea derivatives, sulfoxides, sulfones, carbonic acid esters, water, alcohols, amines, carboxylic acids, primary amides, secondary amides, halogenated hydrocarbons or mixtures thereof, or hydrocarbons, petroleum, aromatics, carboxylic acids, esters, ethers or mixtures thereof,c) Formation of a concentration gradient at the surface of the molded part between the polymer K and the material, wherein the concentration of polymer K increases towards the surface.

[0057] Preferably, an element is available from a process for treating a molded part, comprising the steps of: a) Providing a molded part composed of a1) at least one polymer K, wherein the polymer K is selected from the group consisting of thermoplastic elastomers, polyoxymethylenes, polyethylene terephthalates, polyethylene terephthalate glycols, polyether block amides, polyethylene furanoates, polyurethanes, acrylonitrile butadiene styrenes, thermoplastic polyamides, photopolymers, triblock polymers of polystyrene and poly(ethylene oxide) blocks, polyamides, polyesters, polyolefins, polyacrylates, polyvinylamines, polyacrylamides, polymethyl methacrylates, polyethers, polycarbonates, polylactides, polyethersulfones, polysulfones, polyphenylsulfones, polyimides, polyetherimides, polyketones, polyetherketones, styrene polymers, styrene block polymers, acrylonitrile styrene acrylates or copolymers, blends or mixtures of the aforementioned polymer types therefrom, and a2) at least one material,wherein the material is selected from electrically conductive organic materials or polymers with a polarity other than polymer K, ceramics, metals, alloys or glasses, or graphite, activated carbon, carbon black, fullerenes, carbon nanotubes, carbon fibers, graphene and graphene derivatives such as graphene nanoplatelets, amorphous carbon or mixtures thereof, b) contacting the molded part with at least one solvent A, wherein the solvent is selected from the group consisting of ketones, aldehydes, lactones, lactams, nitriles, nitro compounds, tertiary carboxylic acid amides, urea derivatives, sulfoxides, sulfones, carbonic acid esters, water, alcohols, amines, carboxylic acids, primary amides, secondary amides, halogenated hydrocarbons or mixtures thereof, or hydrocarbons, petroleum, aromatics, carboxylic acids, esters, ethers or mixtures thereof,b1) Production of a gel based on the polymer K of the molded part and the solvent A, c) Formation of a concentration gradient on the surface of the molded part from the polymer K and the material, wherein the concentration of the polymer K increases towards the surface. Brief character description

[0058] Figure 1 : In the Figure 1 The schematic top view illustrates the surface of a molded part made of polymer K (black) and the material (grey) that have been fused together. This is illustrated by the blurred transitions. Figure 2 : In the Figure 2a The schematic shows that a polymer K-solvent gel has formed. This is illustrated by the textured area. The material is partially obscured by the swelling of the gel ( Figure 2b ). Figure 3 : In the Figure 3aThe schematic shows how the polymer K completely envelops the material, and in the top view only the polymer K is visible, which solidifies again after evaporation of the solvent (at room temperature, by heat or by vacuum). Figure 3b ) Figure 4: Figure 4 Figure 1 illustrates a cross-section of the molded part after it has been subjected to the inventive process. It can be seen that the material (grey) is contained within the polymer matrix of polymer K (black) and no longer appears on the surface. Detailed description of the figures

[0059] Figure 1This shows that the polymer K and the material are present on the surface of the molded part. The black areas represent the polymer K, and the gray areas represent the material. After the molded part is contacted with a solvent (in vapor or liquid form) that causes the polymer K to swell, a polymer K-solvent gel is formed (see Figure 2 , Figure 3a(textured areas). After a defined period (e.g., 2 minutes), the molded part is separated from the vapor or solution. After evaporation of the solvent (at room temperature, by heat, or by vacuum), the soluble component solidifies or recrystallizes on the surface. Now, no materials are present on the surface of the molded part, so that the surface is preferably formed exclusively by polymer K. After the drying step, the surface of the molded part exhibits a different crystallinity and / or density than before the process. The surface now shows a crystallinity that differs from that of the interior of the molded part. This altered crystallinity was confirmed by X-ray diffraction. Therefore, following the process, the solidified surface of the molded part exhibits chemical and / or physical properties that differ from those of the interior.In the case of carbon black-filled components, the new polymer layer on the surface no longer contains any fillers (materials) (this is described in the . Figures 3b and 4(illustrated by way of example) and thus appears in its natural color, which is colorless in most polymers. The color of the newly formed polymer layer is strongly dependent on the crystallinity of the polymer. Partially crystalline or crystalline regions of the polymer, in particular, are highly refractive and result in a white appearance. In the context of the present invention, this white appearance includes a visually perceptible brightening. In one embodiment of the invention, the brightening can be so pronounced that it is perceived as a white coloration. The curing rate, and thus the crystallinity and density of the material, can be influenced by the speed, temperature, and boiling points of the solvent (mixture). This also allows for the influence of the material's density and color. The white polymer surface can be colored without restriction using established methods. Examples: Example 1

[0060] Carbon black-filled polar polymers such as HP 3D HR PA12 and HP 3D HR PA11 (which are polyamides based on PA12 / 11 with graphite) were immersed in hot NMP. After evaporation of the solvent, a white polymer layer remained. The surface of the polar polymers exhibited altered crystallinity after the process. The white layer was successfully colored in an immersion bath with an aqueous dye solution. The white layer could then be further treated by processing in a solvent vapor deposition unit, resulting in a scratch-resistant white surface. Example 2

[0061] HP Ultrasint polypropylene molded parts were immersed in hot toluene, limonene, and dichlorobenzene. This resulted in a pronounced lightening of the surface, attributable to the leaching of polymer. The surface of the molded parts exhibited altered crystallinity after the process. Example 3

[0062] A molded part made of HP 3D HR PA12 was immersed in hot benzyl alcohol (120°C) and left in the bath for 45 seconds. The part was then removed, and the solvent was slowly evaporated at room temperature. After the process, the surface of the part exhibited altered crystallinity. The dried surface is white after evaporation and can be colored. The carbon black particles typical of MJF are no longer visible. Example 4

[0063] A commercially purchased, purple-colored injection-molded polypropylene part was immersed in hot petroleum. Upon exposure to air, the part turned completely white. The surface of the part exhibited altered crystallinity after the process. Example 5

[0064] The molded parts made of the carbon black-filled polar polymers HP 3D HR PA12 and HP 3D HR PA11 were immersed in a solvent mixture of formic acid and dichloromethane in a 1:1 ratio at room temperature for 30–60 seconds, removed, and allowed to dry. Upon exposure to air, the molded parts quickly turned completely white. After the process, the surface of the molded parts exhibited altered crystallinity and density. Example 6

[0065] The molded part, made of glass bead-filled polyamide 12 (e.g., PA 3200 GF, PA12-GB), was coated with a solvent in a vapor deposition system. With longer vapor deposition and exposure times, the components separate spatially. The polymer matrix deposits over the insoluble glass beads, resulting in a homogeneous surface after the process. The surface of the molded part exhibited altered crystallinity after the process. Example 7

[0066] Carbon black-filled polar polymers such as HP 3D HR PA12 and HP 3D HR PA11 (which are polyamides based on PA12 / 11 with graphite) were immersed in hot γ-butyrolactone (GBL) at atmospheric pressure. The molded parts were then removed, and the solvent was slowly evaporated at room temperature and atmospheric pressure. After this process, the surface of the polar polymers exhibited altered crystallinity. The dried surface is white after evaporation and can be colored. Example 8

[0067] Carbon black-filled polar polymers such as HP 3D HR PA12 and HP 3D HR PA11 (which are polyamides based on PA12 and PA11, respectively, with graphite) were immersed in hot N-butyl-2-pyrrolidone (NBP) at atmospheric pressure. After evaporation of the solvent at room temperature and atmospheric pressure, a white polymer layer remained. The surface of the polar polymers exhibited altered crystallinity after the process. The white layer was successfully dyed in an immersion bath with an aqueous dye solution.

[0068] Since the mixture of polymer and filler, or of two polymers, is only spatially separated in the described process in the examples above, no geometric change occurs. Whitening the molded parts using methods known from the prior art, such as dip-coating or spray-coating, inevitably leads to material deposition and thus to a change in dimensions.

[0069] The process according to the invention not only preserves the dimensions but also avoids the introduction of foreign materials (e.g., TiO2, polymers, etc.). In addition, compared to WO 2019 / 185756 A1, the process according to the invention is a gentler method for brightening gray parts. Unlike nitric acid, the solvents used in the process according to the invention are significantly less aggressive, potentially more environmentally friendly, and preserve the molecular structure of the polymers. Nitric acid is a strong oxidizing agent that can also attack polymers and fillers. Dissolving the polymeric component with solvents does not attack the molecular structure and thus preserves the properties of the molded part. Furthermore, compared to WO 2019 / 185756 A1, the process according to the invention is reduced to only one treatment step, thus representing an improvement in terms of technical effort and process time.

Claims

1. Method for treating a molded part, comprising the steps: a) providing a molded part constructed from a1) at least one polymer K and a2) at least one material, b) contacting the molded part with at least one solvent A, characterized by: b1) preparing a gel based on the polymer K of the molded part and the solvent A, c) forming a concentration gradient on the surface of the molded part from the polymer K and the material, wherein the concentration of the polymer K increases towards the surface, d) at least partial separation of components, wherein the solvent A causes the polymer K to swell at least partially at the surface, wherein the molded part is produced by additive manufacturing and the material is bonded to the polymer K, and wherein the material is selected from electrically conductive organic materials, polymers with a different polarity than polymer K, ceramics, metals, alloys, glasses, graphite, activated carbon, carbon black, fullerenes, carbon nanotubes, carbon fibers, graphene, and graphene derivatives such as graphene nanoplatelets, amorphous carbon, or mixtures thereof.

2. Method according to claim 1, wherein step b) is carried out for 5 seconds to 20 hours, particularly preferably for 1 minute to 5 hours.

3. Method according to one of claims 1 to 2, comprising the step: e) Drying the molded part at atmospheric pressure and a temperature in the range from 10°C to 140°C or, alternatively, drying in a vacuum (0-900 mbar) at temperatures between 10°C and 140°C.

4. Method according to one of claims 1 to 3, wherein the polymer K on the surface of the molded part after the drying step e) has a different crystallinity than before the method, wherein the different crystallinity manifests itself in a changed refraction of light on the surface of the molded part, and wherein the changed refraction of light leads to a white appearance of the molded part.

5. Method according to claim 4, wherein the altered crystallinity on the surface of the molded part can be influenced by the selected temperature and pressure in drying method e) and the duration of contact between the molded part and solvent A.

6. Method according to one of the preceding claims, wherein the intensity of the swelling process on the surface of the polymer K can be influenced by temperature, pressure, or duration of step b).

7. Method according to one of the preceding claims, wherein steps b) - d) are carried out at atmospheric pressure.

8. Method according to one of the preceding claims, wherein in drying step e) the temperature is below the melting temperature of polymer K, particularly preferably below the softening temperature of polymer K, and the combination of selected pressure and temperature allows the solvent to escape from the gel formed in step b1).

9. Method according to one of the preceding claims, comprising the step: f) coloring the molded part with a dye.

10. Method according to one of the preceding claims, wherein the polymer K consists of a non-conductive material and the material K consists of a conductive material, and the surface of the molded part exhibits a changed electrical conductivity after the drying step f).

11. Method according to one of claims 1 to 10, wherein the polymer K is selected from the group consisting of thermoplastic elastomers, polyoxymethylenes, polyethylene terephthalates, polyethylene terephthalate glycols, polyether block amides, polyethylene furanoates, polyurethanes, acrylonitrile-butadiene-styrenes, thermoplastic polyamides, photopolymers, triblock polymers made from polystyrene and poly(ethylene oxide) blocks, polyamides, polyesters, polyolefins, polyacrylates, polyvinylamines, polyacrylamides, polymethyl methacrylates, polyethers, polycarbonates, polylactides, polyethersulfones, polysulfones, polyphenylsulfones, polyimides, polyetherimides, polyketones, polyetherketones, styrene polymers, styrene block polymers, acrylonitrile styrene acrylates or copolymers, blends or mixtures of the aforementioned polymer types.

12. Method according to one of claims 1 to 11, wherein the molding is contacted by immersion, vapor deposition, or spraying.

13. Method according to one of claims 1 to 12, wherein solvent A is selected from the group consisting of ketones, aldehydes, lactones, lactams, nitriles, nitro compounds, tertiary carboxylic acid amides, urea derivatives, sulfoxides, sulfones, carbonic acid esters, water, alcohols, amines, carboxylic acids, primary amides, secondary amides, halogenated hydrocarbons, or mixtures thereof.

14. Method according to one of claims 1 to 13, wherein the solvent A is selected from the group consisting of carbonic acid esters, lactones, lactams, sulfoxides, or mixtures thereof.

15. Element obtainable from the process according to any one of claims 1 to 14.