Method for treating the surface of a shaped part manufactured in an additive method

Abstract

The invention relates to a method for treating the surface of a shaped part manufactured in an additive method and to be dyed with a dye, wherein the surface of the shaped part consists at least in sections of a material which has dye binding points, wherein in a homogenisation step, the dye binding points on the surface are at least partially shielded, wherein as a result of the at least partial shielding of the dye binding points, the binding of the dye is at least partially prevented at the at least partially shielded dye binding points. The invention also relates to a dying method in which the surface of the shaped part is treated in accordance with the invention.

Description

[0001] Process for the surface treatment of a molded part produced by an additive process

[0002] Field of the invention

[0003] The invention relates to a method for the surface treatment of a molded part produced by an additive process (3D printing process) and to be colored with a dye.

[0004] Background of the invention

[0005] Molded parts additively manufactured from a plastic, such as polyamide materials, are typically dyed with a desired color during post-processing. Anionic acid dyes can be used for this purpose. In a dyeing process, the pH of a dyeing solution is carefully controlled so that the amino groups present in the polyamide are at least partially protonated, and the acid dyes, which exist as anions at the set pH value, are attracted to them. The protonatable amino groups (or other dye binding sites) are therefore crucial for the success and quality of the dyeing.

[0006] Homogeneous / uniform coloring of additively manufactured molded parts is a desired property. It can happen that the coloring of polyamide molded parts is inhomogeneous, both within a single molded part (crispy or speckled coloring, different coloring of upskin and downskin areas typical / inherent for 3D printing), within a single dyeing process (multiple molded parts dyed simultaneously exhibit different coloring), or even within a dyeing batch (the molded parts from a single printing process are dyed in batches, and although the dyeing conditions are the same, the color of the molded parts varies from batch to batch).

[0007] For example, the varying porosity of the material to be colored on the surface of the molded part, which is a result of the manufacturing process, can influence the uniformity of the coloring. The porosity can be largely homogenized by blasting or compacting the surface, which ensures more even penetration of the dye, which in turn leads to more homogeneous coloring.

[0008] It is known from WO 2015 124 639 A1 that the uniformity of the coloring can be improved by prior blasting of the components.

[0009] From WO 2021 014 004 A1 it is known to improve the uniformity of the dyeing by adding quaternary ammonium salts to the dyeing solution.

[0010] However, it has been shown that uniform coloring cannot always be achieved or cannot be achieved sufficiently by prior blasting of the surface or by adding quaternary ammonium salts to the coloring solution.

[0011] Object of the invention

[0012] The object of the present invention is therefore to provide a method for the surface treatment of a molded part produced by an additive process, which enables a better, in particular more homogeneous, coloring of the surface of the molded part. Solution according to the invention

[0013] This object is achieved by a method for surface treatment and a method for coloring molded parts produced by an additive process according to the independent claims. Advantageous embodiments are specified in the respective dependent claims.

[0014] Accordingly, a method is provided for the surface treatment of a molded part produced in an additive process and to be colored with a dye, wherein the surface of the molded part consists at least in sections of a material which has dye binding sites, wherein in a homogenization step the dye binding sites on the surface are at least partially shielded, wherein the at least partial shielding of the dye binding sites at least partially prevents binding of the dye to the at least partially shielded dye binding sites.

[0015] This means that the dye binding sites are at least partially shielded during staining with the dye.

[0016] It is advantageous if the partial shielding of the dye binding sites causes the dye binding sites to appear more homogeneous on the surface overall, whereby the dye is bound more homogeneously.

[0017] In one embodiment of the invention, the dye binding sites can be at least partially shielded by contacting the surface with a shielding agent, wherein the shielding agent is selected such that it is adapted to at least partially prevent the dye from binding to the dye binding sites. It is advantageous if the shielded dye binding sites are amino groups.

[0018] The shielding agent can be chosen so that it is adapted to at least partially prevent protonation of the free amino groups.

[0019] The shielding agent can be selected such that the bond between the shielding agent and the dye binding sites shielded by the shielding agent is stronger than the bond between the dye and the dye binding sites. The shielding agent is thus selected such that it cannot be displaced by the dye during dyeing.

[0020] It is advantageous if the shielding agent is selected from the group comprising ketones, aldehydes, lactones, lactams, nitriles, isonitriles, nitro compounds, carboxylic acids and carboxylic acid derivatives, urea and urea derivatives, sulfoxides, sulfones, sulfonic acids, carbonic acid esters, inorganic acids, anhydrides of inorganic acids, alcohols, amines, amides, acetals, hemiacetals, and combinations and mixtures thereof.

[0021] The shielding agent can further be selected from the group comprising amino group-reactive compounds, preferably carboxylic acid anhydrides, most preferably acetic anhydride.

[0022] In one embodiment of the invention, the shielding means can be heated to a predetermined temperature and brought into contact with the surface for a predetermined time.

[0023] An additive, in particular a solvent, a catalyst, a base, or an activating agent, can be added to the shielding agent. Shielding the dye binding sites can involve thermally treating at least the portions of the molded part's surface containing the material.

[0024] The thermal treatment may comprise controlled heating and controlled cooling of the sections of the surface of the molded part comprising the material, whereby more dye binding sites are present in the crystalline regions of the surface than before, and / or the dye binding sites are distributed more homogeneously on the surface overall.

[0025] The controlled heating may comprise heating for a predetermined time to a material-dependent predetermined temperature, preferably between recrystallization temperature and maximum melting temperature, and the controlled cooling may comprise a defined cooling rate and / or reaching a material-dependent predetermined temperature, preferably below the recrystallization temperature.

[0026] The material may comprise a plastic, in particular a polymer.

[0027] In one embodiment of the invention, the thermal treatment of the surface can be carried out before and / or after bringing the surface into contact with a shielding agent.

[0028] Furthermore, a dyeing method is provided, comprising the following steps: providing a molded part produced in an additive process, wherein the surface of the molded part consists at least in sections of a material containing dye binding sites;

[0029] Carrying out a surface treatment step for treating the surface of the molded part according to the above-mentioned method; carrying out a coloring step for coloring at least the surface of the molded part treated in the surface treatment step with one or more dyes.

[0030] The surface treatment step and the dyeing step can be carried out immediately one after the other.

[0031] Short description of the characters

[0032] Further details and features of the invention will become apparent from the following description taken in conjunction with the drawing. It shows:

[0033] Fig. 1 is a sketch to explain the chemical shielding; and

[0034] Fig. 2 a sketch to explain the physical shielding

[0035] Detailed description of the invention

[0036] The core of the invention is to at least partially shield free dye binding sites on the surface of the molded part to be colored that are accessible to the dye. Dye binding sites can be chemical in nature (functional groups such as amino groups or acid groups, or surface sections such as aliphatic chains) and / or physical in nature (cavities, pores). Shielding in the sense of the present invention means reducing the affinity of the dye for the dye binding site or making the dye binding site less accessible to the dye. By partially shielding the free dye binding sites, binding of the dye to the shielded dye binding sites is at least partially prevented. The shielding has the effect that all dye binding sites are preferably equally well orare equally difficult to access for the dye. The dye binding sites appear more homogeneous on the surface of the molded part, whereby the dye is bound more homogeneously, which leads to a significantly more chromatic coloring of the molded part.

[0037] Surprisingly, the inventors discovered that by partially shielding the free dye binding sites responsible for the coloration, the homogeneity of the coloration can be significantly improved.

[0038] The inventors have discovered that partial shielding of the free dye binding sites can be achieved both chemically and physically. Both chemical and physical shielding are based on the same core idea of ​​the invention, namely, making free dye binding sites on the surface of the molded part at least partially inaccessible to the dye.

[0039] The inventive method described below is particularly suitable for additively manufactured molded parts produced using the SLS (Selective Laser Sintering) process, the MJF (MultiJet Fusion) process, the HSS (High-Speed ​​Sintering) process, the SAF (Selective Absorption Fusion) process, the FDM (Fused Deposition Modeling) process, and the SLA (Stereolithography) process. The inventive method is particularly advantageous for molded parts produced using a powder-based layered construction process in which individual layers are fused together, such as the SLS process. In these powder-based processes, the components are often exposed to uncontrollable thermal stress. Thus, the number and distribution of the dye binding sites are uncontrollably altered, leading to inhomogeneous coloring.For the production of the molded part in the additive process, the material of the molded part can be selected from the group comprising aliphatic, semi-aromatic and aromatic polyamides, in particular polyamide 6 (PA6), polyamide 6.6 (PA6.6), polyamide 11 (PAI 1), polyamide 12 (PA12), polyamide 4.6 (PA4.6), polyamide 6.12 (PA6.12), polyphthalamides (PPA), thermoplastic co-polyamides, thermoplastic polyether polyamides (TPA) and other polyamide-based block polymers, as well as copolymers, blends and mixtures of polyamides with other materials, for example with metal powders (alumides) and / or with other particles (for example with glass, ceramics) and / or additives (for example with antioxidants, antistatic agents, flow agents, brighteners).

[0040] However, other materials can also be used, provided they are suitable for a 3D printing process and have dye binding sites that can be shielded according to the invention, for example methacrylates with free amino groups in the substituent.

[0041] The dye is selected from the group comprising metal complex dyes, acid dyes, reactive dyes, azo dyes, disperse dyes, and mixtures thereof.

[0042] Partial chemical shielding of the free dye binding sites:

[0043] In chemical shielding, the free dye binding sites are at least partially shielded by contacting the surface of the molded part with a chemical shielding agent. The shielding agent is selected such that it is adapted to at least partially prevent the dye from binding to the dye binding sites. This can occur either covalently or through non-covalent (e.g., ionic or van der Waals) bonds. An advantageous shielding agent is therefore preferably selected from the group comprising dye-binding site-reactive compounds. The dye binding sites can comprise amino groups, which are at least partially shielded with the shielding agent.

[0044] For example, the surface of a molded part made of polyamide can be brought into contact with acetic anhydride. The amino groups are at least partially acetylated. This at least partially prevents protonation of the free amino groups during the dyeing step, making them inaccessible to the dye. The qualitative ninhydrin test was performed on molded part surfaces modified in this way, indicating a reduced number of amino groups.

[0045] The molded parts treated in this way could then be dyed without restriction using known dyeing processes, whereby a greatly improved homogeneity of the dyeing could be achieved compared to untreated molded parts (not treated according to the process according to the invention).

[0046] It may be advantageous if the shielding agent is selected such that the bond of the shielding agent to the dye binding sites shielded with the shielding agent is stronger than that of the dye to the dye binding sites.

[0047] Suitable shielding agents are shielding agents selected from the group comprising ketones, aldehydes, lactones, lactams, nitriles, isonitriles, nitro compounds, carboxylic acids and carboxylic acid derivatives, urea and urea derivatives, sulfoxides, sulfones, sulfonic acids, carbonic acid esters, inorganic acids, anhydrides of inorganic acids, alcohols, amines, amides, acetals, hemiacetals, isocyanates, and combinations thereof. Polymers and polymer-like compounds containing functional groups that are reactive with dye binding moieties (e.g., sulfonated polymers) can also be used as shielding agents.

[0048] Suitable shielding agents also include shielding agents from the group of polymerization chain terminators (for polyamides, for example, from the group comprising acids and lactones) as well as compounds that can attach protective groups to the respective dye binding site. Such protective groups attached to the dye binding sites can then be removed again after dyeing using suitable deprotection methods, if necessary, to expose the dye binding sites again, e.g., to make them accessible for further functionalization.

[0049] Alternatively, a shielding agent can also be generated in-situ or activated with an activating agent, for example, an activated acid can be generated in-situ with a carbodiimide-based activating agent (dicyclohexylcarbodiimide or diisopropylcarbodiimide).

[0050] An advantageous shielding agent for polyamides is selected from the group comprising amino-reactive compounds, preferably carboxylic anhydrides. Particularly advantageous shielding agents are acetic anhydride and propionic anhydride.

[0051] Fig. 1 shows a highly schematic representation of the mode of operation of the method according to the invention, which involves the partial chemical shielding of the free dye binding sites.

[0052] The manufacturing-related accumulation of free dye binding sites or free amino groups (left) on the surface of the molded part leads to darker colored areas and to a clearly visible contrast (i.e., to a clear inhomogeneity of the coloration) compared to a "smaller" accumulation of free dye binding sites or free amino groups (right) on the surface of the molded part.

[0053] A simplified example: Suppose there are 500 free amino groups at a "densely populated" site and 50 free amino groups at a "sparsely populated" site (left image in Fig. 1). The high contrast (and thus the visible inhomogeneity) is due to the difference in the number of free amino groups (in this example, the difference is 450 free amino groups). If, for example, 60% of the free amino groups are shielded (right image in Fig. 1), 200 free amino groups at the "densely populated" site and 20 free amino groups at the "sparsely populated" site remain for staining. Partially shielding the free amino groups reduces the contrast to only 180 free amino groups compared to 450 free amino groups before shielding, thus enabling significantly more homogeneous staining.

[0054] A significant advantage of the process according to the invention is that, by partially shielding the free dye binding sites or free amino groups, the molded parts have a highly homogeneous surface, which enables highly homogeneous coloring in a subsequent dyeing step.

[0055] In one embodiment of the invention, the partial shielding of the free dye binding sites or free amino groups can also be carried out immediately before the dyeing step, preferably in the same device, for example in the same bath. For example, the component can be brought into contact with a shielding agent according to the method according to the invention, whereupon the dye, including additives, is dosed directly into the shielding agent. It is advantageous if the dye is soluble in the shielding agent or in the solution of the shielding agent. If the dye is poorly soluble, solubilizers can be added. This means that the method according to the invention ensures that the dyes are absorbed equally well over the entire surface.

[0056] Tests have shown that molded parts treated with the process according to the invention and colored molded parts have a more homogeneous color than untreated molded parts or molded parts treated with the processes described above:

[0057] - A highly homogeneous coloring is achieved within the component (significantly less crispy, color balance between upskin and downskin areas).

[0058] - Within a dyeing process, the color differences between several components dyed at the same time are significantly smaller.

[0059] - Within a dyeing series, the color differences between the components produced in one printing process but dyed in several successive portions are significantly smaller.

[0060] The problem of the different colorability of the upskin and downskin areas is typical and unique for the field of 3D printing.

[0061] Tests have also shown that the process according to the invention can be used to produce and color homogenized surfaces that are practically indistinguishable from surfaces of molded parts produced by injection molding.

[0062] For the purposes of the present invention, contacting the molded part with the shielding agent can mean bringing part or all of the molded part into contact with the shielding agent. "Contacting" means that the shielding agent can be present in different aggregate states. Advantageously, the shielding agent is in a liquid state. Preferably, contacting the molded part with the shielding agent occurs by immersion, vapor deposition, or spraying. For this purpose, autoclaves, immersion baths, drip devices, spraying, immersion, flood, and steam smoothing systems, atomizing nozzles, atomizers, and other spraying devices can be used.

[0063] An increased temperature can advantageously accelerate the shielding reaction.

[0064] Alternatively, the shielding agent can be dissolved in a suitable solvent. Alternatively, the shielding agent can be added to the solvent (dropwise), e.g., if the molded parts are already immersed in the solvent. Alternatively, other auxiliaries can be dissolved in the shielding agent and / or the solvent, such as acid scavengers (e.g., a strong inorganic base such as sodium hydroxide).

[0065] If the shielding agent is gaseous or if the shielding agent is used at a temperature above the boiling point of the shielding agent, it can also be mixed with a suitable carrier gas, for example nitrogen or argon.

[0066] After the homogenization step, the surface of the molded part is preferably completely freed of excess shielding agent. For this purpose, the molded part is preferably washed and dried. Drying can take place in air or by means of an air stream / gas stream. Elevated temperature and / or reduced pressure / vacuum can accelerate drying. Chemical shielding can thus be combined with physical shielding if necessary, provided that drying is achieved by heating after chemical shielding. The process conditions for shielding can be adapted depending on the specific molded part, the dye used, or the desired color.

[0067] Example 1 :

[0068] Additively manufactured PA2200 platelets were placed in a beaker and mixed with 25 ml of acetic anhydride. Then, 0.5 g of NaOH dissolved in 3 ml of deionized water was added. The platelets were incubated with stirring at 50°C for 3 h and then thoroughly washed with water. To monitor the reaction, the ninhydrin test was carried out on a "sacrificial platelet" (a drop of fresh 0.5% (w / w) ninhydrin solution in i-propanol was added to a platelet heated to 90°C and treated and incubated for 10 min at 90°C – the absence of a blue color indicated the extensive deactivation or shielding of the amino groups). The treated platelets were then dyed together with untreated platelets (not treated according to the inventive method) with an aqueous dye solution (red dye) in an immersion bath.The resulting color effect of the treated plates was demonstrated by a significantly less crackly and significantly more homogeneously colored surface compared to the untreated plates.

[0069] Example 2:

[0070] Several platelets printed in the so-called "sweet spot" (each made of PA2200) were placed in a beaker with 25 ml of acetic anhydride. Then, 0.5 g of NaOH dissolved in 3 ml of deionized water was added. The platelets were incubated with stirring at 50°C for 3 h and then thoroughly washed with water. The treated platelets were then dyed with an aqueous dye solution (brown dye) in an immersion bath, along with untreated platelets printed in the "sweet spot" (not treated according to the process according to the invention). Both the treated and untreated platelets showed slight color differences, with the treated platelets exhibiting an even more homogeneous color. This means that even the surface of the sweet spot platelets, which were already printed under relatively good thermal control, could be further homogenized using the process according to the invention.

[0071] Surprisingly, the partial chemical shielding of the free dye binding sites not only increases the homogeneity of the coloration but also provides effective protection against yellowing. Thus, molded parts treated with the process according to the invention yellow significantly less than untreated molded parts. This effect can be enhanced by using a deactivating agent that also contains UV-absorbing groups (for example, phenyl groups in mellitic acid). This effect is particularly advantageous for molded parts that are chemically smoothed before coloring, because experience has shown that chemically smoothed molded parts yellow more quickly than non-chemically smoothed molded parts. The durability of both undyed and colored molded parts is thereby advantageously increased.This eliminates the need for vacuum packaging and storage under light rejection, which are typically necessary for long-term storage of additively manufactured molded parts.

[0072] Accordingly, a method is also provided for the surface treatment of a molded part produced in an additive process, wherein the surface of the molded part consists at least in sections of a material which contains dye binding sites, wherein in a homogenization step the dye binding sites on the surface are at least partially shielded, wherein the at least partial shielding of the dye binding sites at least partially prevents yellowing of the surface of the molded part.

[0073] Partial physical shielding of the free dye binding sites: Alternatively or in addition to the chemical shielding described above, the dye binding sites on the surface of the molded parts can also be at least partially physically shielded. For this purpose, the surface of the molded part is thermally treated according to the invention and thus thermally homogenized, which also leads to a significantly more homogeneous coloration of the surface in a subsequent coloring step.

[0074] Fig. 2 shows a highly schematic representation of the mode of operation of the method according to the invention, which involves the partial physical shielding of the free dye binding sites.

[0075] It has been shown that the crystallinity of the molded part's surface influences its colorability. If the degree of crystallinity is consistent and the lateral distribution of the crystalline regions is homogeneous (right-hand image of Fig. 2), homogeneous coloring is possible. The process according to the invention achieves a largely consistent degree of crystallinity and a homogeneous distribution of crystallinity on the surface of the molded part, which enables more homogeneous surface coloring.

[0076] For this purpose, the molded part or its surface is heated and then cooled (thermally treated), resulting in more dye binding sites in the crystalline areas of the surface than before the thermal treatment, or in a more homogeneous distribution of the dye binding sites across the surface. Thermal treatment preferentially decreases the ratio of amorphous to crystalline components.

[0077] Preferably, the surface is heated and cooled in a controlled manner.

[0078] Heating is carried out for a predetermined time at a predetermined material-dependent temperature, which preferably lies between the recrystallization temperature and the melting temperature of the material of the molded part. In one embodiment of the invention, heating is carried out for a predetermined time at a predetermined material-dependent temperature, which preferably lies between the glass transition temperature and the melting temperature of the material of the molded part.

[0079] The heating rate can be constant or vary over time. For example, the heating rate can range from 0.5°C / min to approximately 100°C / min.

[0080] The appropriate temperature can be derived from the DSC curve of the powder used.

[0081] Preferably, the component is heated at least until the component is continuously heated to the predetermined material-dependent temperature.

[0082] Cooling takes place at a predetermined cooling rate and / or until a material-dependent predetermined temperature is reached, which is preferably below the recrystallization temperature / recrystallization range.

[0083] In one embodiment of the invention, cooling occurs at a predetermined cooling rate and / or until a material-dependent predetermined temperature is reached, which is preferably below the glass transition temperature. The cooling rate can be constant or vary over time. For example, the cooling rate can range from 0.5°C / min to approximately 100°C / min.

[0084] In one embodiment of the invention, the heating and cooling rates, as well as the temperatures reached, can also be selected such that the proportion of amorphous to crystalline material increases. Even a more homogeneously amorphous component can be colored more homogeneously. Additively manufactured platelets made of PA2200 were kept at 160°C for 8 hours (heating rate 1°C / min) and then cooled at 0°C for 5 minutes. The treated platelets were then colored together with untreated platelets (not treated according to the process according to the invention) using an aqueous dye solution (red dye) in an immersion bath. The resulting color effect of the treated platelets was demonstrated by a significantly less crackly and significantly more homogeneously colored surface compared to the untreated platelets.

[0085] In the context of the present invention, heating the molded part may mean that part or all of the molded part is heated.

[0086] Advantageously, the molded part is heated in an inert environment (e.g., in a vacuum, a protective gas atmosphere, or in an inert silicone oil). Heating can be performed either contact-free or indirectly (e.g., via microwaves) or directly (e.g., via a heat transfer medium).

[0087] For this purpose, autoclaves, immersion baths (with oil, silicone, glycerin as heat transfer medium), hot plates, heating lamps, heated air and gas streams, drying cabinets, ovens, vacuum ovens, induction ovens and induction plates, IR radiators, microwave systems, hair dryers and blowers can be used.

[0088] The heating methods can be combined, e.g. carried out simultaneously or sequentially.

[0089] If there is a risk that the geometry of the molded part will be changed by heating, means can also be used to counteract the change in geometry (e.g. the support structures, the supporting heat transfer medium, the reversibly gelling gel, which can act as a heat transfer medium).

[0090] Cooling is preferably carried out using an ice bath. Alternatively, refrigerators and other chillers and heat sinks, air / gas streams, hair dryers and fans, cooling mixtures and cooling media (especially liquid nitrogen), and Peltier elements can be used. The molded part can also be cooled without external intervention through the thermodynamically favored radiation of heat.

[0091] Before the inventive treatment of the surface of a molded part produced using a 3D printing process, the molded part can be mechanically prepared, for example, by blasting to remove excess powder. Furthermore, the molded parts can be blasted, preferably with plastic beads, before or after the inventive treatment to thereby compact the surface. It is advantageous if the plastic beads have a similar or even lower degree of hardness than the material of the molded part – this ensures compaction of the surface without damaging it.

[0092] In one embodiment of the invention, the molded parts can be smoothed before or after the treatment according to the invention, in particular chemically and / or by grinding. The treatment according to the invention after chemical smoothing can significantly reduce or prevent yellowing of the surface.

[0093] In one embodiment of the invention, the molded parts can be heated outside or inside a polishing chamber prior to chemical polishing, preferably in a controlled manner (i.e., determined by material properties, geometric data, and / or in-situ by heat measurement). This is followed by chemical polishing, followed by physical shielding / post-drying (combined with the drying step to remove any residual solvent remaining in the molded parts), and subsequent dyeing. Post-drying is preferably carried out below the melting point of the molded part, preferably at 160°C for PA12, and can be carried out outside or inside the polishing chamber. The amount of residual solvent can be monitored and measured in such a process, and thus the process control (e.g., time, temperature, heating rate) of the combined "drying and physical shielding" step can be controlled and optimized.The sequence of steps of preheating, smoothing, physical shielding / post-drying, and dyeing can both shorten the overall post-processing time and significantly improve the quality of the subsequent dyeing. In this embodiment of the invention, any residual solvent can act as a plasticizer, thereby facilitating physical shielding. The surface of the molded part is evenly melted and then cooled homogeneously, allowing the crystalline phase to form evenly on the surface.

[0094] In one embodiment of the invention, the molded parts can be impregnated and / or painted after the treatment according to the invention.

[0095] In one embodiment of the invention, the molded parts can be matted, in particular by blasting the surface.

[0096] In one embodiment of the invention, the molded parts can be functionalized before, during or after the treatment according to the invention in order to impart useful functional properties to the surface, for example ESD safety or improved mechanical properties.

[0097] Optionally, the surface of the molded part can be heated in an oven or a vacuum oven before and / or after the treatment according to the invention.

[0098] Optionally, the molded part can be cleaned in a cleaning bath at a predetermined temperature before and / or after the treatment according to the invention.

[0099] According to the invention, the optional pre- and post-treatment steps can be combined in any order.

Claims

Claims 1. A method for the surface treatment of a molded part produced in an additive process and to be colored with a dye, wherein the surface of the molded part consists at least in sections of a material which has dye binding sites, wherein in a homogenization step the dye binding sites on the surface are at least partially shielded, wherein the at least partial shielding of the dye binding sites at least partially prevents binding of the dye to the at least partially shielded dye binding sites.

2. The method according to claim 1, wherein the partial shielding of the dye binding sites causes the dye binding sites to appear more homogeneous on the surface overall, whereby the dye is bound more homogeneously.

3. The method of claim 1, wherein the dye binding sites are at least partially shielded by contacting the surface with a shielding agent, wherein the shielding agent is selected such that it is adapted to at least partially prevent the binding of the dye to the dye binding sites.

4. A method according to any one of the preceding claims, wherein the shielded dye binding sites are amino groups.

5. A method according to any one of the preceding claims 3 to 4, wherein the shielding agent is selected so that it is adapted to at least partially prevent protonation of the free amino groups.

6. The method according to any one of the preceding claims 3 to 5, wherein the shielding agent is selected such that the binding of the shielding agent to the dye binding sites shielded by the shielding agent is stronger than that of the dye to the dye binding sites.

7. The method according to any one of the preceding claims 3 to 6, wherein the shielding agent is selected from the group comprising ketones, aldehydes, lactones, lactams, nitriles, isonitriles, nitro compounds, carboxylic acids and carboxylic acid derivatives, urea and urea derivatives, sulfoxides, sulfones, sulfonic acids, carbonic acid esters, inorganic acids, anhydrides of inorganic acids, alcohols, amines, amides, acetals, hemiacetals, and combinations and mixtures thereof.

8. The method according to any one of the preceding claims 3 to 7, wherein the shielding agent is selected from the group comprising amino group-reactive compounds, preferably carboxylic acid anhydrides, most preferably acetic anhydride.

9. The method of claim 3, wherein the shielding agent is heated to a predetermined temperature and brought into contact with the surface for a predetermined time.

10. The method according to claim 3, wherein an additive, in particular a solvent, a catalyst, a base or an activating agent, is added to the shielding agent.

11. The method according to any one of the preceding claims, wherein shielding the dye binding sites comprises thermally treating at least the portions of the surface of the molded part comprising the material.

12. The method according to the preceding claim, wherein the thermal treatment comprises heating and cooling the portions of the surface of the molded part comprising the material in a controlled manner, whereby more dye binding sites are present in the crystalline regions of the surface than before, and / or the dye binding sites are distributed more homogeneously on the surface overall.

13. Method according to the preceding claim, wherein the controlled heating comprises heating for a predetermined time to a material-dependent predetermined temperature, preferably between recrystallization temperature and maximum melting temperature, and wherein the controlled cooling comprises a defined cooling rate and / or reaching a material-dependent predetermined temperature, preferably below the recrystallization temperature.

14. Method according to one of the preceding claims, wherein the material comprises a plastic, in particular a polymer.

15. The method according to any one of claims 3 to 10 and any one of claims 11 to 14, wherein the thermal treatment of the surface is carried out before and / or after bringing the surface into contact with a shielding agent.

16. Dyeing process comprising the following steps: Providing a molded part produced in an additive process, wherein the surface of the molded part consists at least in sections of a material containing dye binding sites; - carrying out a surface treatment step for treating the surface of the molded part according to the method according to any one of claims 1 to 15; - carrying out a dyeing step for dyeing at least the surface of the molded part treated in the surface treatment step with one or more dyes.

17. A dyeing process according to the preceding claim, wherein the surface treatment step and the dyeing step are carried out immediately one after the other, wherein the surface treatment step is carried out according to the process according to any one of claims 1 to 10.

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