Device for surface treatment of molded parts

Abstract

Device for treating a surface of at least one molded part (10) produced in a 3D printing process, the device comprising - a pressure-tight container (20) with an interior (21) in which the molded part to be treated is received, - a solvent container (40) for holding a solvent (70), and - a vacuum pump (30) coupled to the pressure-tight container (20) in order to generate a negative pressure, preferably a substantial vacuum, in the interior (21) of the pressure-tight container, - a device for heating the solvent (70) to a predetermined solvent temperature, - a supply line (25) via which the heated solvent (70) can be introduced into the negative-pressure interior space (21) of the pressure-tight container (20), wherein the device is designed such that the temperature of the molded part (10) is lower than the solvent temperature when the solvent (70) is introduced into the interior space (21), and the solvent (70) evaporates or is introduced as solvent vapor when introduced into the interior space (21), the solvent vapor condensing on the surface of the molded part (10).

Description

Field of the invention

[0001] The invention relates to a device for treating a surface of at least one molded part produced in a 3D printing process. Background of the invention

[0002] It is known to produce molded parts using a 3D printing process. 3D printing refers to additive manufacturing processes in which a molded part is built up layer by layer, particularly using a plastic.

[0003] Such additive manufacturing processes have the disadvantage that the resulting molded parts generally do not have a closed surface, i.e., they have a rough surface due to the manufacturing process, which can often negatively impact the user's haptic impression of the molded part. Furthermore, the rough surface of such a molded part tends to become dirty relatively quickly, making cleaning the surface difficult. Furthermore, the surface of such molded parts exhibits a large number of pores due to the manufacturing process.

[0004] To smooth the surfaces of molded parts produced using a 3D printing process, the surfaces can be mechanically processed, for example, by grinding and / or blasting. The disadvantage of this, however, is that some material is removed from the surface of the molded part - albeit a small amount - which is usually above predetermined tolerance values ​​to achieve the desired surface smoothness, so that smoothing the surface is accompanied by an undesirable change in the geometry of the molded part. In addition, grinding does not reach small corners or small recesses, which then remain unprocessed and thus not smoothed. With flexible molded parts, such mechanical processes for smoothing the surface are either impossible or very difficult to apply. In addition, areas of the surface that are extremely concave or have undercuts can only be mechanically smoothed with great effort or not at all.With very delicate surface structures, there is also a risk of damage during grinding or blasting. Furthermore, existing pores on the surface are not adequately closed, even during grinding or blasting.

[0005] Another disadvantage of mechanical surface smoothing is that it is not suitable for series production. Object of the invention

[0006] The object of the present invention is therefore to provide solutions that allow surfaces of molded parts produced in a 3D printing process to be efficiently smoothed or homogenized without causing significant changes to the geometry of the molded parts and that can also be efficiently used for flexible molded parts and for molded parts that have surface sections that are difficult to machine mechanically. Inventive solution

[0007] This object is achieved according to the invention by a device for treating a surface of at least one molded part produced in a 3D printing process according to the independent claim.

[0008] Accordingly, a device is provided for treating a surface of at least one molded part produced in a 3D printing process, wherein the device comprises - a pressure-tight container with an interior in which the molded parts to be treated are accommodated, - a solvent container for holding a solvent, and - a vacuum pump, - the solvent container is coupled to the pressure-tight container via a supply line in order to supply the solvent from the solvent container to the pressure-tight container, - the vacuum pump is coupled to the pressure-tight container in order to generate a negative pressure, preferably a substantial vacuum, in the pressure-tight container.

[0009] In particular, a device is provided for treating a surface of at least one molded part produced in a 3D printing process, the device comprising - a pressure-tight container with an interior in which the molded part to be treated is accommodated, - a solvent container for holding a solvent, and - a vacuum pump coupled to the pressure-tight container to create a negative pressure, preferably a substantial vacuum, in the interior of the pressure-tight container, - a device for heating the solvent to a predetermined solvent temperature, - a supply line via which the heated solvent can be introduced into the negative pressure interior of the pressure-tight container, wherein the device is designed such that the temperature of the molded part is lower than the solvent temperature when the solvent is introduced into the interior, and the solvent evaporates or is introduced as solvent vapor when introduced into the interior, the solvent vapor condensing on the surface of the molded part.

[0010] It may be advantageous if the solvent container has a heating device to heat the solvent contained in the solvent container.

[0011] Furthermore, it may be advantageous if the pressure-tight container has a heating device in order to heat the interior and / or the molded parts accommodated in the interior.

[0012] In one embodiment of the invention, the solvent container can be designed to be pressure-tight.

[0013] In one embodiment of the invention, a vacuum pump can be coupled to the solvent container in order to generate a negative pressure, preferably a substantial vacuum, in the solvent container.

[0014] It may be advantageous if a temperature sensor and / or a pressure sensor is assigned to the solvent container and / or the pressure-tight container.

[0015] The device may comprise a control / regulating device with which - the heating device of the pressure-tight container and the vacuum pump are adjustable and / or controllable in order to adjust the pressure and temperature inside the pressure-tight container, and - the heating device of the solvent container is adjustable and / or controllable in order to adjust the temperature of the solvent.

[0016] The pressure-tight container can be coupled to an extraction device in order to extract solvent vapor and / or solvent condensate present in the pressure-tight container.

[0017] The extraction device can be coupled to the solvent container via a return line in order to return the extracted solvent vapor and / or the extracted solvent condensate to the solvent container.

[0018] The device may comprise a cleaning and / or distillation device adapted to clean and / or distill the extracted solvent vapor and / or the extracted solvent condensate.

[0019] According to one embodiment of the invention, the device can have at least one additional solvent container, which is coupled to the pressure-tight container via at least one additional supply line, in order to supply at least one additional solvent from the at least one additional solvent container to the pressure-tight container. This allows different solvents to be used for treating the surface, for example, a first solvent in a first treatment cycle and a second solvent in a second treatment cycle.

[0020] The solvent container can be pressure-tight. Short description of the characters

[0021] Further details and features of the invention will become apparent from the following description taken in conjunction with the drawing. It shows: Fig. 1 an enlarged view of a section of a surface of a molded part produced by a 3D printing process, which is smoothed after a process for treating the surface; Fig. 2 a flow chart illustrating a method for treating the surface; Fig. 3 shows a first example of a temperature profile of the internal temperature of an interior space of a surface treatment device, wherein a solvent was added to the interior space three times; Fig. 4 shows a second example of a temperature profile of the internal temperature of an interior space of a surface treatment device, wherein a solvent was added to the interior space three times; Fig. 5 shows a third example of a temperature profile of the internal temperature of an interior space of a surface treatment device, in which a solvent was added to the interior space three times; Fig. 6 shows a fourth example of a temperature profile of the internal temperature of an interior space of a surface treatment device, wherein a solvent was added to the interior space three times; Fig. 7 shows a fifth example of a temperature profile of the internal temperature of an interior space of a surface treatment device, wherein a solvent was added to the interior space three times; Fig. 8 a schematic representation of a device according to the invention for treating a surface of at least one molded part produced in a 3D printing process. Detailed description of the invention

[0022] Fig. Figure 1 shows, in Figure (a), an enlarged section of a surface 11 of a molded part 10 produced using a 3D printing process. A powder-based printing process was used to produce the molded part 10. The surface 11 of the molded part 10 exhibits manufacturing-related unevenness, particularly pores, which promote the adhesion of dirt or contaminants to the surface 11 of the molded part 10. The rough or porous surface 11 of the molded part 10 also negatively affects the feel of the molded part 10. The surface shown in Figure (a) has not yet been processed using a surface treatment process.

[0023] The surface 11 of the molded part 10 is smoothed to eliminate or close the unevenness, especially the pores. For this purpose, a solvent in the form of solvent vapor is applied to the surface 11 of the molded part 10, which condenses on the surface of the molded part. The molded part is then dried. A method for treating the surface is described in detail with reference to Fig. 2 to Fig. 6 described.

[0024] The treatment of surface 11 may comprise multiple cycles, with each cycle involving the application of solvent, i.e., solvent vapor, to the surface, followed by drying of the molded part 10. Depending on the material used to produce the molded part in the 3D printing process and the desired surface smoothness, a single cycle may be sufficient. However, multiple cycles are advantageous.

[0025] Figure (b) shows the surface 11 of the molded part 10 after a first treatment cycle, in which solvent was applied to the surface 11 in the form of solvent vapor and then dried. It is clearly visible here that the surface 11 is significantly smoother than the surface shown in Figure (a), in particular, it has almost no pores.

[0026] In order to achieve even further smoothing of the surface, a further processing cycle can be carried out in which solvent in the form of solvent vapor is again applied to the surface 11 of the molded part 10 and the molded part 10 is then dried.

[0027] Figure (c) shows the surface 11 of the molded part 10 after the second treatment cycle. It can be seen that the surface 11 has been further smoothed compared to the surface shown in Figure (b). Furthermore, it is evident that the smoothing process resulted in virtually no change in the geometry of the molded part. In contrast to mechanical surface treatment, almost no material removal occurs here, since the solvent applied to surface 11 only slightly dissolves the surface of the molded parts, thereby removing any unevenness. A significant advantage, however, is that any pores present on the surface are closed.

[0028] The molded parts treated in this way have a particularly high quality in terms of surface smoothness, so that in many cases impregnation of the surface is not necessary.

[0029] Fig. 2 shows a flowchart according to an embodiment of a method for treating the surface.

[0030] To carry out the process, a device is provided that comprises a pressure-tight container with an interior space in which the surface of the molded part is treated, and a container containing a solvent. These two containers are connected via a line, and the supply of solvent to the container in which the molded part is treated is controlled via a valve. The container in which the molded part is treated is designed to be pressure-tight. The container containing the solvent is preferably also designed to be pressure-tight.

[0031] The molded part produced in a 3D printing process is introduced into the interior of the pressure-tight container in step S1.

[0032] Before the molded part is placed in the pressure-tight container, it can be heated to a specific temperature, for example, between 90 and 120°C. How far the molded part can be heated depends essentially on the material or plastic used to produce the molded part in the 3D printing process. Accordingly, depending on the material used, the molded part can be heated to over 120°C or even to a temperature below 90°C. The maximum temperature to which the molded part can be heated must always be set so that the molded part does not deform due to the temperature. Furthermore, the maximum temperature to which the molded part is heated must be set so that in the subsequent processing, the temperature of the molded part can continue to rise due to the solvent vapor flowing into the interior of the pressure-tight container without the molded part becoming deformed.

[0033] As an alternative to heating the molded part before placing it in the pressure-tight container, the molded part can also be heated after placing it in the pressure-tight container, ie heated in the pressure-tight container.

[0034] For this purpose, in a step S0, which is performed before step S1, the interior of the pressure-tight container can be heated to a predetermined temperature, for example, 130°C. The heating of the interior of the pressure-tight container can be carried out using a heating device, for example, heating sleeves. The heating can be monitored by a temperature sensor arranged in the interior of the pressure-tight container.

[0035] Once the interior has reached the predetermined temperature, the molded part can be inserted into the interior of the pressure-tight container (step S1). The inserted molded part is thus heated to a specific temperature, with the interior temperature of the interior simultaneously cooling slightly, as the molded part absorbs a certain amount of thermal energy during heating, and the pressure-tight container releases heat to the environment. For example, the interior of the pressure-tight container can cool to approximately 108°C, and the molded part heats up to approximately 108°C, preferably to a maximum of 108°C.

[0036] The heating device can be used to ensure, if necessary, that the internal temperature does not drop below a certain temperature after the molded part has been inserted into the cavity, or that it does not drop at all. For example, if the cavity is heated to 130°C, it can be ensured that the temperature of the cavity remains at approximately 130°C after the molded part has been inserted, or that it does not drop below, for example, 108°C.

[0037] Alternatively, step S0 can also be performed after step S1. This means that after the molded part has been introduced into the interior of the pressure-tight container, the interior of the pressure-tight container is heated, for example, to approximately 108°C. This also heats the inserted molded part to approximately 108°C.

[0038] After the molded part has been inserted, a negative pressure, preferably a substantial vacuum, is created inside the pressure-tight container. Negative pressure here means a pressure below atmospheric pressure. In the context of the present invention, vacuum means a pressure below 300 mbar.

[0039] It is advantageous if the negative pressure or vacuum is generated in the interior of the pressure-tight container immediately after the molded part has been introduced into the interior in order to prevent yellowing or other discoloration of the molded parts during heating. It has been shown that yellowing of the molded parts during heating can be prevented if they are exposed to no or almost no oxygen. Accordingly, it is advantageous to generate a negative pressure or vacuum in the pressure-tight container immediately after the molded part has been introduced into the pressure-tight container, regardless of whether step S0 is performed before or after step S1.

[0040] In a step S3, the solvent stored in the solvent container is heated to a predetermined solvent temperature, for example, to 130°C. The solvent container is preferably designed to be pressure-tight.

[0041] It has proven particularly advantageous to use several liters of heated solvent, preferably at least 20 liters. This ensures that sufficient solvent is available at the appropriate temperature for the process. This enables a particularly stable and therefore reproducible process, which can be carried out regardless of the number of parts to be processed or their surface, without affecting the smoothing result.

[0042] The heating of the solvent in the solvent container can be done, for example, by means of a sleeve or jacket heater or directly via heating rods.

[0043] For many applications, a solvent temperature above 100°C has proven particularly advantageous, as it ensures a sufficient temperature difference between the parts to be smoothed and the solvent vapor throughout the entire process. This ensures condensation of the solvent on the surface. At the same time, an elevated solvent temperature is crucial for the temperature of the solvent condensate, which in turn significantly influences the solvent's solvency and thus the smoothing result.

[0044] Step S3 can be performed before steps S0 to S2 or in parallel with steps S0 to S2, whereby it must only be ensured that the solvent has reached the predetermined solvent temperature before step S4 is performed. This can be checked using a temperature sensor in the preferably pressure-tight solvent container.

[0045] After the solvent has reached the predetermined solvent temperature and the interior of the pressure-tight container or the molded part introduced into the interior has reached the desired temperature, the heated solvent is introduced into the negatively pressurized interior of the pressure-tight container in step S4. This can be done, for example, by opening a valve that separates the interior of the pressure-tight container from the interior of the solvent container.

[0046] By opening this valve and due to the pressure difference between the interior of the pressure-tight container and the solvent container, a certain amount of solvent enters the gas-free and heated interior of the pressure-tight container, where it evaporates suddenly. Alternatively, solvent vapor can also enter the gas-free and heated interior of the pressure-tight container.

[0047] Whether solvent vapor enters the interior space or whether solvent enters the interior space and suddenly evaporates there ultimately depends on the temperature and pressure conditions in the interior space and in the solvent container. However, it is advantageous if the solvent enters the interior space already as solvent vapor. In this case, it is particularly advantageous if the solvent container also has a negative pressure, particularly preferably a substantial vacuum. This enables the evaporation of higher-boiling solvents at temperatures low enough not to destroy the molded part, for example a molded part made of a polymer with a comparatively low melting point. For benzyl alcohol as a solvent, for example, a pressure in the solvent container of 100 mbar to 150 mbar at a solvent temperature of approximately 140°C has proven advantageous.This allows a vapor temperature suitable for processing molded parts, even with high-boiling solvents, without the molded parts being destroyed by the thermal stress or dissolving or even completely dissolving. The negative pressure in the solvent tank also offers the advantage of a very safe process, as the resulting negative pressure virtually eliminates any solvent leakage, and in the event of a leak, only air would be drawn in. The pressure in the solvent tank can be monitored using a pressure sensor.

[0048] The temperature of the interior of the pressure-tight container, the negative pressure created therein, and the solvent temperature must be coordinated so that the solvent introduced into the interior can evaporate instantly, unless solvent vapor is already introduced into the interior of the pressure-tight container. Pressures in the interior of the pressure-tight container of less than 10 mbar have proven particularly advantageous.

[0049] In the event that the solvent is already evaporated in a pressure-tight solvent container, and in particular in the event that this can only be achieved by generating a negative pressure in the solvent container (if, for example, benzyl alcohol is to be evaporated at a maximum solvent temperature of 140°C), the particularly low pressure of less than 10 mbar in the interior of the pressure-tight container nevertheless results in the technical advantage that there is a sufficiently large pressure gradient (between the interior of the pressure-tight container and the interior of the pressure-tight solvent container) in order to efficiently supply the evaporated solvent to the pressure-tight interior.

[0050] For solvents with a low evaporation temperature, the interior temperature of the pressure-tight container can be selected lower and / or lower negative pressures can be created within the interior of the pressure-tight container. However, it has been shown that very high negative pressures, such as a near-complete vacuum, favor the evaporation of the introduced solvent, especially since a substantial vacuum should be created anyway to prevent yellowing of the molded parts during heating.

[0051] Due to the temperature difference between the molded parts placed inside the pressure-tight container and the solvent vapor introduced into this interior (the molded parts initially have a lower temperature than the introduced solvent), the solvent vapor condenses on the surface of the molded part. The solvent condensing on the surface of the molded part slightly dissolves the surface of the molded part, closing pores on the surface and thus smoothing the surface. The amount of vapor condensing on the surface of the molded part depends essentially on the temperature difference between the molded part and the introduced solvent vapor. In addition, the amount of condensate forming on the surface of the molded part is crucial for the degree of dissolution and thus for the effective smoothing of the surface.

[0052] It is therefore important in surface treatment processes that the correct vapor temperature of the solvent is achieved, since at temperatures that are too low, insufficient vapor is generated, thus only partially dissolving the surface of the molded part. Furthermore, at vapor temperatures that are too low, solvent condensate may settle on the surface of the molded part, but the temperature of the condensate may be too low to ensure initial dissolution of the surface. Therefore, for many molded part material / solvent combinations, it is particularly advantageous to heat the solvent to a temperature above 100 °C.

[0053] Excessively high steam temperatures, on the other hand, can cause excessive dissolution of the molded part's surface, which can lead to a change in the part's geometry or promote the formation of drops or snags. Furthermore, excessive dissolution of the surface can lead to the formation of bubbles on the surface during subsequent vacuum drying.

[0054] On the other hand, the molded parts introduced into the interior must have a certain temperature before the heated solvent is introduced so that the temperature difference between the molded part and the introduced solvent vapor causes the generation of a certain amount of condensate on the surface of the molded part.

[0055] Ultimately, the parameters (internal temperature of the pressure-tight container or temperature of the molded part, solvent temperature and pressure in the pressure-tight container, and, if applicable, pressure in the solvent container) must be coordinated depending on the solvent used and the material of the molded part so that a certain amount of solvent condensate forms on the surface of the molded part to be treated, which achieves the desired smoothing effect. The temperature of the molded part is always lower than the temperature of the solvent or solvent vapor. At the same time, the pressure in the pressure-tight container is lower than the pressure in the solvent container, whereby both can be negative pressure or a near vacuum.

[0056] By introducing the solvent into the negatively pressurized interior of the pressure-tight container and the sudden evaporation of the solvent, or by introducing the solvent vapor into the negatively pressurized interior of the pressure-tight container, the temperature in the interior of the pressure-tight container steadily rises. Condensation of the solvent vapor causes a reduction in pressure in the interior of the pressure-tight container, causing further solvent to be continuously introduced into the interior and subsequently evaporate suddenly, or further solvent vapor to be continuously introduced into the interior.

[0057] The valve remains open until a predetermined temperature is reached inside the pressure-tight container. The desired temperature inside the pressure-tight container (target temperature or predetermined second temperature) is selected so that only enough condensate forms on the surface of the molded part to achieve the desired smoothing effect.

[0058] If the valve is kept open for too long, the temperature inside the pressure-tight container can rise above the desired target temperature, which can lead to excessive condensate on the surface of the molded part and thus to excessive dissolving of the surface of the molded part. Excessive dissolving of the surface of the molded part by the solvent condensate can cause material bubbles to form during the subsequent vacuum drying (step S5), as the solvent-plastic mixture formed on the surface can begin to boil. Bubbles or craters can then form during the simultaneous curing of the surface.

[0059] It has proven advantageous to keep the valve open for a time between 1 s and 600 s. A valve opening time of 5 s to 300 s is particularly advantageous. However, it should be noted that the valve opening time depends on the valve design and may need to be adjusted to the valve diameter.

[0060] It has proven advantageous to rotate the molded parts placed in the pressure-tight container during the vapor deposition phase, or alternatively to rotate the molded parts rigidly arranged in the interior together with the interior or the pressure-tight container. This can significantly reduce droplet formation.

[0061] Alternatively or additionally, the prevention or significant reduction of droplet formation can be achieved by means of a swirling unit, such as a fan, arranged in the interior of the pressure-tight container, which swirls the introduced solvent vapor. Such swirling of the introduced solvent vapor can also be caused or supported by the pressure difference between the interior of the solvent container and the interior of the pressure-tight container.

[0062] After introducing the heated solvent in step S4, the molded parts are dried in step S5. In one embodiment of the invention, the molded parts can be removed from the pressure-tight container for drying.

[0063] In an alternative embodiment of the invention, which has proven advantageous, the molded parts are dried in the negative-pressure interior of the pressure-tight container. This has the advantage that the drying process is considerably faster under negative pressure or vacuum. It is particularly advantageous if, immediately before drying the molded parts, in a step S4.1, the solvent vapor present in the interior of the pressure-tight container and, if applicable, the solvent condensate formed on the inner wall and collected at the bottom of the interior are suctioned off. The solvent can also be suctioned off during the entire drying process. This has the advantage that already condensed solvent can drain off directly and does not have to be evaporated again before being removed from the chamber. This allows the molded part to be dried within a few seconds.

[0064] The extracted solvent vapor or solvent condensate can then be filtered and purified if necessary and then returned to the solvent container. This allows the solvent to be reused in a closed loop. This has the technical advantage that no materials requiring disposal or other waste are generated during the process. This makes the process a resource-saving, efficient method. Furthermore, the extraction of the solvent ensures that the user never comes into direct contact with the solvent.

[0065] Particularly efficient vacuum drying (or negative pressure drying) can be achieved if the generation of the negative pressure / vacuum in the pressure-tight chamber is interrupted by a controlled inflow of a transport gas. In one embodiment of the invention, such a transport gas can be carried out cyclically, i.e. the generation of the negative pressure / vacuum is interrupted cyclically. This has the technical advantage that even vacuum pumps with lower suction power can completely remove the solvent residues from the interior of the pressure-tight container. In order to prevent the solvent from condensing again on the surface of the molded parts due to the pressure increase in the interior of the pressure-tight container caused by the supply of the transport gas, it is particularly advantageous if the inflowing amount of transport gas is controlled and the pressure in the pressure-tight interior does not rise too sharply.Increasing the pressure from 8 mbar to between 50 mbar and 100 mbar, followed by evacuating it again to 8 mbar, has proven particularly advantageous and efficient. If an oxygen-containing gas, such as air, is used as the transport gas, keeping the pressure low (i.e., maintaining the pressure below 100 mbar) also has the technical advantage of preventing the parts from yellowing due to oxidation. This risk would arise if a large amount of oxygen were to enter the chamber during the drying process, as the molded parts would still be at an elevated temperature at this time and would therefore be highly susceptible to oxidation, as is the case with polyamide parts, for example.

[0066] After vacuum drying the molded part, it can be removed from the pressure-tight container in the final step. Before removing the molded part, the interior of the pressure-tight container can optionally be cooled to a specific temperature. Especially in the case of vacuum drying directly before removing the molded parts, the previously described efficient vacuum drying with the addition of a transport gas is preferable to drying without the addition of a transport gas.

[0067] The steps S4, S5 and, if applicable, S4.1 are collectively referred to as a cycle (processing cycle).

[0068] In one embodiment of the invention, this cycle, i.e., steps S4 and S5 and, if appropriate, step S4.1, may be repeated several times. This has proven particularly advantageous when the initial dissolution of the surface, which is caused by the introduction of the solvent vapor in step S4, does not achieve a sufficient smoothing effect. This may be the case, for example, if, due to the molding material and the solvent used, only very short vapor deposition times are possible without damaging the molding.

[0069] After the first cycle, i.e. after the initial steaming and vacuum drying of the molded parts, the temperature of the molded part is higher than at the beginning of the first cycle, since the introduction of the solvent vapor increases the temperature in the interior of the pressure-tight container and thus also the temperature of the molded part. This means that during the next cycle, steam must be supplied to the interior of the pressure-tight container until the interior or the molded part reaches a temperature at which sufficient condensate settles on the surface of the molded part to achieve the desired smoothing effect (for example in Fig. 3). Since the temperature of the molded part is higher at the beginning of the second cycle than at the beginning of the first cycle (unless the molded part is cooled between two cycles), the temperature difference between the temperature of the molded part and the temperature of the solvent is no longer large enough to generate sufficient condensate on the surface of the molded part when the same amount of solvent is added as in the first cycle.

[0070] In principle, this cycle can be repeated any number of times. However, the number of repetitions is limited where the temperature of the molded part reaches a value at which the molded parts would be destroyed. An example temperature profile of the internal temperature of the pressure-tight container is shown with reference to Fig. 3 to Fig. 6 described in more detail.

[0071] In order to compensate for the smaller temperature difference between the molded part and the introduced solvent after each cycle, it may also be provided to further heat the solvent after each cycle in order to achieve the desired temperature difference between the temperature of the molded part and the temperature of the solvent for the next cycle.

[0072] In an alternative embodiment of the method, the temperature of the interior of the pressure-tight container can be lowered before the heated solvent is introduced in the next cycle, preferably until the desired temperature difference between the molded part and the solvent to be introduced is again reached. For example, the temperature of the interior can be lowered to the value at which solvent was introduced into the interior in the first cycle (as in Fig. 4). Cooling can be achieved indirectly through the evaporative cooling during the generation of the negative pressure or vacuum. With this alternative embodiment of the process, the molded part can be vapor-coated as often as desired, i.e., any number of cycles can be repeated. However, it has been shown that, depending on the material of the molded part and the solvent used, between three and six cycles may be sufficient to achieve an optimal smoothing result.

[0073] The surface treatment process is particularly suitable for molded parts produced using the SLS (Selective Laser Sintering), MJF (Multijet Fusion), HSS (High Speed ​​Sintering), FDM (Fused Deposition Modeling), and SLA (Stereolithography) processes. The surface treatment process 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, MJF, or HSS processes, since the surface in these powder-based processes is particularly rough and contains pores.

[0074] Polymers, in particular the following materials, can be used to produce the molded parts, which are particularly suitable for smoothing the surface of the molded parts produced from them: Polyester, PA12 (polyamide 12), PP (polypropylene), TPU (thermoplastic polyurethane), TPE (thermoplastic elastomers), PA11 (polyamide 11), PA6 (polyamide 6), PA6.6 (polyamide 6.6), glass-filled polyamide, ceramic-filled polyamide, PU (polyurethane), ABS (acrylonitrile-butadiene-styrene copolymers), PEK (polyether ketones), PEI (polyetherimides), PPS (polyphenylene sulfides) and PLA (polylactides), cyanate esters, materials based on (meth)acrylates, and combinations thereof.

[0075] However, other materials can also be used, provided they are suitable for a 3D printing process and the surface of the molded parts produced with them can be dissolved using a solvent vapor.

[0076] The following solvents (which also include high boilers for the purposes of the present invention) have proven to be advantageous as solvents, although other solvents not mentioned here can also be used: Acetaldehyde, acetamide, acetone, acetonitrile, acetophenone, acetylene, aliphatic hydrocarbons, in particular cyclohexane, cyclohexene, diisobutylene, hexane, octane, n-pentane and terpinene, alcohols, in particular benzyl alcohol, butylene glycol, butanol, ethanol, ethylene glycol, methanol, allyl alcohol, n-propanol and isopropanol, amyl acetate, aniline, anisole, gasoline, benzaldehyde, benzene, chlorobenzene, decalin, dioxane, dimethylamide, dimethylformamide, diethyl ether, dimethylformamide, dimethyl sulfide, dimethyl sulfoxide, ethylbenzene, ethyl acetate, formaldehyde, formamide, furfural, halogenated hydrocarbons, in particular bromochloromethane, chloroform, ethylene chloride, methylene chloride, perchloroethylene, tetrachloromethane, trichloroethane and trichloroethylene, menthone, Methyl tert-butyl ether, methyl ethylene ketone, nitrobenzene, phenols, phenylethyl alcohol, propanol, pyridine, styrene, tetrahydrofuran, tetrahydronaphthalene, toluene, triethanolamine, and combinations thereof.

[0077] Solvents approved for processing food-grade plastics (for example, according to Commission Regulation (EU) No. 10 / 2011 of January 14, 2011, on plastic materials and articles intended to come into contact with food) have proven particularly advantageous, as these applications particularly benefit from a smoothed surface of the molded parts. Such smoothed surfaces are water-repellent and thus effectively prevent potential microbial growth. Benzyl alcohol, among others, belongs to this class of solvents.

[0078] The use of benzyl alcohol also offers the advantage of preventing the solvent from spreading and, since it is a low-volatility substance, allowing for efficient disposal of any solvent that may leak due to handling errors. Furthermore, benzyl alcohol has a very low odor threshold, meaning that potential solvent contamination can be detected well below the maximum workplace concentration or the level hazardous to health, as well as below the explosion limit.

[0079] Before treating 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. This is particularly advantageous because powder residues would also be dissolved and subsequently harden on the surface. Too much residual powder on the surface can negatively impact the smoothing result.

[0080] In addition, the molded parts can be blasted with plastic beads before or after smoothing to compact the surface. It is advantageous if the plastic beads have a lower hardness than the material of the molded part – this ensures compaction of the surface without damaging it.

[0081] In one embodiment of the invention, the molded parts can be colored before or after smoothing and / or impregnated or painted after smoothing.

[0082] Fig. 3 shows a temperature profile of the interior of the pressure-tight container or of the molded part introduced into this interior during the implementation of the method for treating the surface, in which three cycles (steps S4 to S5) are carried out, wherein after each cycle the temperature of the molded part or the internal temperature of the interior increases.

[0083] A cycle can also include multiple vaporization of the surface with the vaporous solvent, whereby the internal temperature can be adjusted between each vaporization of the surface. Fig. 3, the three cycles shown and described below can also be part of a single cycle. This also applies to the other cycles with reference to Fig. 4 to Fig. 7 shown temperature curves.

[0084] For the Fig. In the example shown in Figure 3, the material PA12 was used to manufacture the molded part. Benzyl alcohol was used as the solvent.

[0085] The interior of the pressure-tight container is initially heated to a first internal temperature of approximately 130°C. At time t1, the molded part is placed inside the interior, the pressure-tight container is sealed pressure-tight, and a largely vacuum is created within the interior. The molded part placed inside the interior is heated by the radiant heat of the interior, causing the first internal temperature to simultaneously drop to a third internal temperature of approximately 108°C. At time t2, the temperature of the molded part largely corresponds to the third internal temperature.

[0086] At time t3, which can occur immediately after time t2, the solvent, heated to 130°C, is added. This solvent evaporates abruptly or enters the interior of the pressure-tight container as solvent vapor. The solvent vapor then condenses on the surface of the molded part, since the temperature difference between the temperature of the molded part and the temperature of the solvent vapor is approximately 22°C.

[0087] By adding the solvent, the internal temperature rises by approximately 2°C to a second internal temperature (here, approximately 110°C). Once this second internal temperature is reached, the solvent supply is stopped, and the molded part is vacuum-dried. Any solvent vapor remaining in the interior can be extracted. Any solvent condensate present on the interior walls or floor of the interior can also be extracted. The drying process then takes just a few seconds.

[0088] After the molded part has dried, solvent is added again at time t4, still at a temperature of approximately 130°C. Since the temperature difference between the molded part and the added solvent is now smaller (here, approximately 20°C) than at time t3, the second internal temperature, and thus the temperature of the molded part, must be increased even further by adding the solvent (here, to approximately 115°C), so that sufficient solvent vapor can condense on the surface of the molded part to achieve the desired smoothing effect. The molded part is then vacuum-dried again.

[0089] At time t5, the third cycle is started, in which solvent heated to 130°C is again added. Since at time t5 the temperature difference between the temperature of the molded part and the added solvent is even smaller (here approximately 15°C) than at time t4, the addition of the solvent must further increase the second internal temperature and thus the temperature of the molded part, in this case to approximately 120°C. This ensures that sufficient solvent vapor can condense on the surface of the molded part for the desired smoothing in the third cycle. The molded part is then vacuum-dried.

[0090] Subsequently, at time t6, cooling of the interior and thus of the molded part is initiated. Once a certain interior temperature is reached, in this case approximately between 105°C and 110°C, the molded part can be removed from the interior. This cooling process is purely optional, meaning the molded parts can be removed immediately after drying. However, the cooling process has the advantage of preventing yellowing of the removed molded parts, since the cooling process takes place under negative pressure or vacuum.

[0091] Of course, the interior of the pressure-tight container must be brought to atmospheric pressure before the molded parts are removed.

[0092] The second internal temperature to be achieved in the second and third cycles can be reduced if the solvent temperature is increased accordingly for the second and third cycles, respectively. For example, an increase in the solvent temperature from 130°C to 135°C in the second cycle may be sufficient for the second internal temperature in the second cycle to only need to be increased from 110°C to 112°C, since in this case, at time t4, the temperature difference between the temperature of the molded part and the temperature of the solvent is approximately the same as at time t3. However, such an increase in the solvent temperature is only possible if the increased solvent temperature does not lead to excessive dissolving or damage to the surface of the molded part.

[0093] Fig. 4 shows a temperature curve of the internal temperature of the interior, whereby after each cycle the internal temperature of the interior and thus the temperature of the molded part are cooled to a certain value.

[0094] PA12 was also used to manufacture the molded part. Benzyl alcohol was also used as the solvent.

[0095] First, the interior of the pressure-tight container is heated to a first internal temperature of approximately 130°C. At time t1, the molded part is placed inside the interior, and the interior is sealed pressure-tight. A substantial vacuum is then created in the interior. The temperature difference between the temperature of the molded part and the first internal temperature causes the first internal temperature to drop to a third internal temperature by time t2, and the temperature of the molded part to rise to this third internal temperature (here, approximately 108°C).

[0096] After this third internal temperature has been reached, at time t3, a solvent heated to 130°C is added. This solvent evaporates abruptly in the interior or enters the interior as solvent vapor. The solvent vapor condenses on the surface of the molded part, thereby achieving the desired smoothing. By adding the solvent, the interior temperature and thus the temperature of the molded part rise from the third internal temperature to the second internal temperature (here, approximately 110°C). As soon as this second internal temperature is reached, the addition of the solvent is stopped. The molded part is then vacuum-dried.

[0097] After the drying process is complete, the interior is cooled, preferably to the third internal temperature, as at time t2 (here, approximately 108°C). This ensures that in the next cycle, the temperature difference between the temperature of the molded part and the temperature of the solvent is the same as at time t3.

[0098] After the interior or the molded part has cooled down, the solvent heated to 130°C is added again at time t4. In contrast to the Fig. According to the temperature profile shown in Figure 3, the second internal temperature to be reached after time t4 in this second cycle does not need to be higher than in the first cycle. It is sufficient to bring the second internal temperature in the second cycle to the second internal temperature as in the first cycle (i.e., to approximately 110°C) by adding the solvent to the internal space. This is because the temperature difference between the temperature of the molded part and the temperature of the solvent at the beginning of the second cycle allows sufficient vapor to condense on the surface of the molded part to achieve the desired smoothing. The molded part is then vacuum-dried again, and the internal temperature of the internal space is lowered again, preferably to the third internal temperature as at time t2.

[0099] The third cycle is identical to the second cycle and is initiated at time t5 by adding the solvent heated to 130°C.

[0100] At time t6, the third cycle is completed and the interior can be cooled to a predetermined temperature. The molded parts can then be removed from the pressure-tight container. This cooling process can also be omitted and the molded parts removed directly after drying. However, the cooling process also has the same effect as with respect to Fig. 3 mentioned advantages.

[0101] Fig. Figure 5 shows a temperature curve of the internal temperature of the interior, whereby after each cycle the internal temperature of the interior and thus the temperature of the molded part are cooled to a certain value.

[0102] PA12 was also used to manufacture the molded part. Benzyl alcohol was also used as the solvent.

[0103] First, the interior of the pressure-tight container is heated to a first internal temperature of approximately 130°C. At time t1, the molded part is placed inside the interior, and the interior is sealed pressure-tight. A substantial vacuum is then created in the interior. The temperature difference between the temperature of the molded part and the first internal temperature causes the first internal temperature to drop to a third internal temperature by time t2, and the temperature of the molded part to rise to this third internal temperature (here, approximately 115°C).

[0104] After this third internal temperature has been reached, at time t3, a solvent heated to 130°C is added, which either suddenly evaporates in the interior or enters the interior as solvent vapor. The solvent vapor condenses on the surface of the molded part, thereby achieving the desired smoothing. By adding the solvent, the internal temperature of the interior and thus also the temperature of the molded part rise from the third internal temperature (here approx. 115°C) to the second internal temperature (here approx. 117.5°C), i.e. by approx. 2.5°C. As soon as this second internal temperature has been reached, the introduction of the solvent is stopped. The molded part is then vacuum-dried.

[0105] After the drying process is complete, the interior is cooled down. Fig. 4, the temperature of the interior was reduced to the temperature at time t2, in the example shown in Fig. In the example shown in Figure 5, the temperature of the interior is lowered to a temperature below the temperature at time t2 (here by approximately 5°C to 112.5°C). This ensures that at the beginning of the next cycle, the temperature difference between the temperature of the molded part and the temperature of the solvent is greater than at the beginning of the previous cycle (at time t3).

[0106] After the interior or the molded part has cooled down, the solvent heated to 130°C is added again at time t4. In contrast to the Fig. 4, the second internal temperature reached after time t4 can be lower in this second cycle (here, approximately 115°C) than in the first cycle. This is because the larger temperature difference between the temperature of the molded part and the temperature of the solvent at time t4 still allows sufficient vapor to condense on the surface of the molded part to achieve the desired smoothing. The molded part is then vacuum-dried again, and the internal temperature of the interior is lowered again (here, to approximately 110°C).

[0107] The third cycle is identical to the second cycle and is initiated at time t5 by adding the solvent heated to 130°C, which increases the second internal temperature to about 112°C.

[0108] At time t6, the third cycle is completed and the interior can be cooled to a predetermined temperature. The molded parts can then be removed from the pressure-tight container. This cooling process can also be omitted and the molded parts removed directly after drying. However, the cooling process also has the same effect as with respect to Fig. 3 mentioned advantages.

[0109] The advantage here is that the continuous cooling reduces the amount of dissolving of the surface of the molded part in each cycle, resulting in a more gentle smoothing process. The higher temperatures in the first cycle have the advantage of achieving a faster initial smoothing.

[0110] It may also be advantageous to reduce the temperature of the solvent after each cycle, for example by 2°C to 5°C. This also applies to the Fig. 3, Fig. 4, Fig. 6 and Fig. 7 variants shown.

[0111] Fig. 6 shows a temperature profile of the interior temperature of the interior, where after each cycle the interior temperature of the interior and thus the temperature of the molded part are cooled to a certain value, in contrast to the Fig. 5, the second internal temperature in each cycle is higher than in the previous cycle.

[0112] PA12 was also used to manufacture the molded part. Benzyl alcohol was also used as the solvent.

[0113] First, the interior of the pressure-tight container is heated to a first internal temperature of approximately 130°C. At time t1, the molded part is placed inside the interior, and the interior is sealed pressure-tight. A substantial vacuum is then created in the interior. The temperature difference between the temperature of the molded part and the first internal temperature causes the first internal temperature to drop to a third internal temperature by time t2, and the temperature of the molded part to rise to this third internal temperature (here, approximately 111°C).

[0114] After this third internal temperature has been reached, at time t3, a solvent heated to 130°C is added, which either evaporates suddenly in the interior or enters the interior as solvent vapor. The solvent vapor condenses on the surface of the molded part, thereby achieving the desired smoothing. By adding the solvent, the internal temperature of the interior and thus also the temperature of the molded part rise from the third internal temperature (here approx. 111°C) to the second internal temperature (here approx. 113°C), i.e., by approx. 2°C. As soon as this second internal temperature has been reached, the addition of the solvent is stopped. The molded part is then vacuum-dried.

[0115] After the drying process is complete, the interior is cooled (here by approximately 2°C to approximately 111°C). This ensures that at the beginning of the next cycle, the temperature difference between the temperature of the molded part and the temperature of the solvent is approximately the same as at the beginning of the previous cycle (at time t3).

[0116] After the interior or the molded part has cooled down, the solvent heated to 130°C is added again at time t4. In contrast to the Fig. According to the temperature curve shown in Figure 5, the second internal temperature reached after time t4 can be higher in this second cycle (here, approximately 115°C) than in the first cycle. Subsequently, the molded part is vacuum-dried again, and the internal temperature of the cavity is lowered again (here, by approximately 2°C to approximately 113°C).

[0117] The third cycle is identical to the second cycle and is initiated at time t5 by adding the solvent heated to 130°C, which increases the second internal temperature to about 117°C.

[0118] At time t6, the third cycle is completed and the interior can be cooled to a predetermined temperature. The molded parts can then be removed from the pressure-tight container. This cooling process can also be omitted and the molded parts removed directly after drying. However, the cooling process also has the same effect as with respect to Fig. 3 mentioned advantages.

[0119] Fig. 7 shows a temperature curve of the internal temperature of the interior, whereby after each cycle the internal temperature of the interior and thus the temperature of the molded part is further heated.

[0120] PA12 was also used to manufacture the molded part. Benzyl alcohol was also used as the solvent.

[0121] First, the interior of the pressure-tight container is heated to a first internal temperature of approximately 130°C. At time t1, the molded part is placed inside the interior, and the interior is sealed pressure-tight. A substantial vacuum is then created in the interior. The temperature difference between the temperature of the molded part and the first internal temperature causes the first internal temperature to drop to a third internal temperature by time t2, and the temperature of the molded part to rise to this third internal temperature (here, approximately 111°C).

[0122] After this third internal temperature has been reached, at time t3, a solvent heated to 130°C is added, which either evaporates suddenly in the interior or enters the interior as solvent vapor. The solvent vapor condenses on the surface of the molded part, thereby achieving the desired smoothing. By adding the solvent, the internal temperature of the interior and thus also the temperature of the molded part rise from the third internal temperature (here approx. 111°C) to the second internal temperature (here approx. 113°C), i.e., by approx. 2°C. As soon as this second internal temperature has been reached, the addition of the solvent is stopped. The molded part is then vacuum-dried.

[0123] After the drying process is completed, the interior (and thus the molded part) is further heated (here by approx. 2°C to approx. 115°C).

[0124] After heating the interior or the molded part, the solvent heated to 130°C is added again at time t4. The second internal temperature thus rises by approximately 3°C to approximately 118°C. The molded part is then vacuum-dried again, and the internal temperature of the interior is further heated (here by approximately 2°C to approximately 120°C).

[0125] The third cycle is identical to the second cycle and is initiated at time t5 by adding the solvent heated to 130°C, which increases the second internal temperature to about 123°C.

[0126] At time t6, the third cycle is completed, and the interior can be cooled to a predetermined temperature. The molded parts can then be removed from the pressure-tight container.

[0127] In the cases relating to Fig. 3 to Fig. For each of the temperature curve examples shown in Figure 7, three cycles (evaporation of the surface followed by drying) were performed. Depending on the desired smoothness and the material of the molded part and the solvent used, more or fewer than three cycles may be performed.

[0128] In the cases relating to Fig. 3 to Fig. In the examples of a temperature profile shown in Figure 7, the internal temperature of the pressure-tight container was first brought to a predetermined first internal temperature (here 130°C) before the (cold) molded part was introduced into the interior (at time t1).

[0129] Alternatively, the molded part can also be placed in the "cold" interior and then the interior can be brought to the desired first interior temperature (e.g. to 130°C). Fig. 3 to Fig. In the examples shown in Figure 7, it would be sufficient to bring the interior (including the cold molded part inserted therein) to a first internal temperature, at which a subsequent lowering to a third internal temperature is no longer necessary. For example, in the example shown in Fig. In the example shown in Figure 3, the interior space with the molded part arranged therein is heated until a temperature of approximately 108°C is reached. The solvent can then be added directly. It is advantageous to heat the interior space and thus the molded part under vacuum.

[0130] In the cases relating to Fig. 3 to Fig. In the examples shown in Figure 7, the same solvent was added in each cycle. Alternatively, a different solvent can be added in at least one cycle than in the others. For example, for molded parts with particularly coarse-pored surfaces, a solvent can be added in the first cycle that causes rapid and / or stronger dissolution of the surface. This can also close larger pores. In subsequent cycles, a solvent can then be added that dissolves the surface only slightly and / or more slowly.

[0131] In the Fig. 3, Fig. 6 and Fig. In the examples shown in Figure 7, the second internal temperature increases successively with each cycle. Fig. In the example shown in Figure 4, the second internal temperature remains constant over several cycles. Fig. In the example shown in Figure 5, the second internal temperature decreases successively with each cycle.

[0132] The Fig. 3 to Fig. The temperature curves shown in Figure 7 can also be combined. This means that the surface treatment process can also be carried out such that the second internal temperature rises or falls in two or more consecutive cycles and falls or rises in cycles following these cycles.

[0133] This allows the temperature profile to be optimally adapted to the desired surface smoothness depending on the materials of the molded parts and the solvent used, especially when two or more different solvents are used.

[0134] The above with reference to Fig. 3 to Fig. 7 described experiments were carried out for - TPU as the material of the molded part and benzyl alcohol as the solvent, and - PA12 as the material of the molded part and methylene chloride as the solvent were repeated.

[0135] Example: TPU as the material of the molded part and benzyl alcohol as the solvent: Since TPU has a lower melting point than PA12, the Fig. 3 to Fig. The temperatures shown in Figure 7 can be reduced by approximately 15°C each.

[0136] Example: PA12 as the material of the molded part and methylene chloride as the solvent: The temperatures in the Fig. 3 to Fig. The temperature curves shown in Figure 7 are approximately between 20°C and 40°C. Specifically, a molded part made of PA12 was tested with the Fig. 3, the temperature profile shown was carried out, with the temperature at time t2 being approximately 20°C, and the second internal temperature at approximately 23°C in the first cycle, approximately 29°C in the second cycle, and approximately 35°C in the third cycle. The pressure inside the pressure-tight container was set to below atmospheric pressure (specifically, approximately 450 hPa). This slight negative pressure is sufficient for methylene chloride to evaporate inside at temperatures as low as approximately 20°C.

[0137] Two further experiments are described below. Attempt 1:

[0138] The molded parts are manufactured using polyamide PA2200 in a 3D printing process.

[0139] The interior 21 of the pressure-tight container is heated to a temperature of 135°C (step S1, first interior temperature).

[0140] The molded parts are introduced into the interior space 21 (step S2), and a substantial vacuum (approximately 7 mbar) is created in the interior space 21. By opening and closing the process chamber while the molded parts are being introduced into the interior space, the interior cools down slightly (to approximately 125°C, the third interior dream temperature).

[0141] The solvent container is filled with benzyl alcohol as the solvent. Before or during steps S1 and S2, the solvent is heated to a temperature of approximately 140°C (step S3), whereby a pressure of 130 mbar is reached in the solvent container. Due to the vapor pressure curve of benzyl alcohol, this causes some of the solvent to evaporate.

[0142] By opening valve 50 for a duration of approximately 16 seconds and maintaining the pressure difference between the interior space 21 and the solvent container 40, solvent flows into the interior space 21 in step S4 and condenses on the molded parts, since these have a lower temperature than the incoming vapor. The pressure in the solvent container 40 drops to approximately 100 mbar, while the pressure in the interior space 21 rises to approximately 80 mbar. At the same time, the temperature in the interior space 21 increases to approximately 126°C (second interior temperature).

[0143] Subsequently, the solvent is vacuumed out of the interior space 21 (step S4.1) and the molded part is dried under vacuum (step S5). Due to the evaporation of the solvent, the temperature in the interior space 21 drops to a temperature below the second interior space temperature (<126 °C), although the temperature may also drop below the third interior space temperature (<125 °C).

[0144] This ensures that the temperature of the solvent vapor is always above the temperature of the interior chamber 21 and thus also above the temperature of the molded parts to be smoothed. This also ensures that solvent condenses on the surface of the molded parts in subsequent vaporization cycles, further smoothing them.

[0145] Steps S4, S4.1 and S5 are then repeated 18 times before the component is finally dried. Attempt 2:

[0146] The molded parts are manufactured using a thermoplastic polyurethane (TPU) in a 3D printing process.

[0147] The interior 21 of the pressure-tight container is heated to a temperature of approximately 130°C (step S1, first interior temperature).

[0148] The molded parts are introduced into the interior space 21 (step S2), and a substantial vacuum (approximately 8 mbar) is created in the interior space 21. By opening and closing the process chamber 20, the interior space 21 cools down slightly during this process step.

[0149] The molded parts then remain in the preheated, evacuated chamber for 30 minutes. This has the advantage of gently heating the molded parts, thus minimizing the thermal stress caused by the inflow of hot solvent vapor. At the same time, it allows for the gentle escape of any water bound in the material and reduces the amount of condensed solvent during subsequent vaporization. This prevents blistering due to boiling of the surface. After this time, the interior 21 has cooled to a temperature of 105°C (3rd interior temperature).

[0150] The solvent container 40 is filled with benzyl alcohol as the solvent. Before or during steps S1 and S2, the solvent is heated to a temperature of approximately 135°C (step S3), whereby a pressure of approximately 120 mbar is reached in the interior space 70. Due to the vapor pressure curve of benzyl alcohol, this causes a portion of the solvent to evaporate.

[0151] By opening valve 50 for a duration of approximately 25 seconds and maintaining the pressure difference between the interior space 21 and the interior space 70, solvent flows into the interior space 21 in step S4 and condenses on the molded parts, since these have a lower temperature than the incoming solvent vapor. The pressure in the solvent container 40 drops to approximately 90 mbar, while the pressure in the interior space 21 rises to approximately 70 mbar. At the same time, the temperature in the interior space 21 increases to approximately 110°C (second interior temperature).

[0152] The solvent is then vacuumed off (step S4.1) and the component is dried under vacuum (step S5). During this process, the temperature in the interior space 21 drops to a temperature below the second interior temperature (<110 °C) due to the evaporation of the solvent.

[0153] Subsequently, the temperature in the interior 21 is reduced, which can be achieved, for example, by briefly opening the container 20 followed by closing the container 20 again and evacuating the interior 21. This achieves a temperature below the second interior temperature, preferably exactly the third interior temperature.

[0154] Steps S4, S4.1 and S5 are then repeated twice before the component is finally dried.

[0155] Fig. 8 shows schematically a device according to the invention for treating a surface of at least one molded part produced in a 3D printing process.

[0156] The device essentially comprises a pressure-tight container 20 into whose interior 21 the molded part to be treated is introduced. The pressure-tight container 20 is designed such that a negative pressure, in particular a substantial vacuum, can be generated in the interior 21.

[0157] Furthermore, the device comprises a solvent container 40 for storing the solvent 70 to be introduced into the interior space 21. The solvent container 40 can also be designed to be pressure-tight, in particular such that a negative pressure can be generated in the interior space 70.

[0158] The solvent container 40 and the pressure-tight container 20 are connected to one another via a supply line 25, wherein a valve 50 can be arranged in the supply line, with which the supply of solvent from the solvent container 40 into the interior 21 of the container 20 can be controlled.

[0159] The pressure-tight container 20 and the solvent container 40 are each designed such that, on the one hand, the interior 21 of the pressure-tight container 20 and, on the other hand, the solvent 70 located in the solvent container 40 can each be heated to a predetermined temperature. For this purpose, for example (in Fig. 8) Heating sleeves or jacket heaters (not shown) can be arranged on the respective container 20, 40. Other heating devices are possible.

[0160] To control the temperatures in the interior and the solvent, appropriate temperature sensors TS can be provided, which are coupled to a control / regulating device 60. Depending on the measured temperature values, the control / regulating device 60 can control the supply of thermal energy for heating the interior 21 or for heating the solvent 70.

[0161] Furthermore, the pressure-tight container 20 can have a pressure sensor DS with which the pressure conditions in the interior 21 can be monitored. This pressure sensor DS is also coupled to the control / regulating device 60.

[0162] The control / regulating device 60 can also control a vacuum pump 30, with which a negative pressure or a vacuum can be generated in the interior 21 of the pressure-tight container 20.

[0163] In addition, the control / regulating device 60 is coupled to the valve 50 so that the control / regulating device 60 can control the valve 50 depending on the temperature in the interior 21.

[0164] In a particular embodiment of the device according to the invention, it can have one or more additional solvent containers 40', each of which is connected to the pressure-tight container 20 via a supply line 25' and which can also be designed to be pressure-tight. The supply lines 25' can each have a valve 50', with which the supply of solvent from the respective solvent container 40' into the interior 21 of the container 20 can be controlled.

[0165] Furthermore, the solvent containers 40, 40' can each have a pressure sensor DS (in Fig. 8 not shown), with which the pressure conditions in the respective interior spaces 70, 70' can be monitored. These pressure sensors DS are also coupled to the control / regulating device 60.

[0166] A different solvent can be stored in each of the solvent containers 40, 40', which is particularly advantageous if a different solvent is to be used for one cycle than for the other cycles.

[0167] However, the same solvent can also be stored in the solvent containers 40, 40'. This is advantageous, for example, if this solvent is to be supplied to the interior space 21 in two different cycles at different temperatures. The solvent in the solvent container 40 can thus be heated to a different temperature than the solvent stored in the solvent container 40'.

[0168] It is particularly advantageous if the pressure-tight container 21 is coupled to a suction device 90, which in turn is coupled to the solvent container 40 via a return line 27. The suction device 90 is adapted to extract the solvent vapor present in the interior 21 and / or the solvent condensate present on the interior walls of the interior and return it to the solvent container 40 via the return line 27. This allows for optimal use of the solvent, which, on the one hand, reduces the costs of smoothing and, on the other hand, protects the environment.

[0169] The extracted solvent vapor or solvent condensate can be processed, in particular purified and / or distilled, before being fed to the solvent container 40. For this purpose, a purification and / or distillation device 80 can be provided in the return line 27. Distilling the extracted solvent vapor or solvent condensate has proven particularly advantageous, so it is particularly advantageous to use distillable solvent.

[0170] For the further solvent containers 40', corresponding return lines with corresponding cleaning and / or distillation devices can also be provided, which are Fig. 8 are not shown.

[0171] The method for treating the surface and the device according to the invention for carrying out the method have the advantage that the smoothing of the surfaces of the molded parts can be carried out particularly time-efficiently, making the method also suitable for surface smoothing on an industrial scale. The vapor deposition in each cycle takes only a few seconds, as this period is sufficient to allow sufficient solvent vapor to flow into the interior of the pressure-tight container, with which the desired smoothing effect is achieved in one cycle. Vacuum drying also only takes a few seconds, especially if the solvent vapor still present in the interior and the solvent condensate formed on the interior walls and floor of the interior are suctioned away. This means that a cycle can be completed within a few seconds.

[0172] In addition, the process for treating the surface is particularly suitable for flexible molded parts whose surfaces cannot be smoothed mechanically or can only be smoothed with considerable effort.

[0173] Tests have shown that the surface treatment process can produce smoothed surfaces that are practically indistinguishable from the surfaces of molded parts produced by the injection molding process.

[0174] A significant advantage of the invention, however, is that the smoothing process results in the molded parts having a highly homogeneous surface, which is particularly advantageous when the molded parts are subsequently colored. The homogeneous surface of the molded parts achieved by the surface treatment process results in colors being absorbed equally well across the entire surface, resulting in a homogeneous color appearance. In particular, spotting is effectively prevented.

[0175] The following describes a method for clarifying the functioning of the device according to the invention, i.e. a method for treating a surface of at least one molded part produced in a 3D printing process, wherein: (a) the molded part is placed in the interior of a pressure-tight container, (b) after the molded part has been introduced into the container, a negative pressure, preferably a substantial vacuum, is created in the interior of the container, (c) a solvent is heated to a predetermined solvent temperature, and (d) after the molded part has been introduced into the interior of the container, the heated solvent is introduced from a solvent container into the interior having the negative pressure, whereby - the temperature of the molded part is lower than the solvent temperature, and - when the solvent is introduced into the interior, the solvent evaporates or the solvent is introduced into the interior as solvent vapor, whereby the solvent vapor condenses on the surface of the molded part.

[0176] It is advantageous if, after the molded part has been placed in the container, a negative pressure of less than 10 mbar is created in the interior of the container.

[0177] The negative pressure or the near-vacuum in the interior of the container ensures that the solvent enters the interior in vapor form and condenses on the surface of the molded part due to the lower temperature of the molded part. By adjusting the temperature difference between the molded part and the solvent vapor, the duration of the solvent supply, and, if necessary, the pressure difference between the solvent container and the interior of the pressure-tight container, the solvent condensate forming on the surface of the molded part can be very precisely controlled, which in turn allows the degree of surface dissolution to be controlled. This cannot be achieved with a solvent bath into which the molded part to be treated is placed.

[0178] It may be advantageous if, before or after step (a), the interior of the pressure-tight container is brought to a predetermined first internal temperature. For this purpose, a temperature sensor can be arranged in the interior of the pressure-tight container.

[0179] By introducing the solvent into the interior space (step (d)), the temperature of the interior space can be brought to a predetermined second internal temperature, which can be lower or higher than the predetermined first internal temperature, wherein - as long as solvent is introduced into the interior until a predetermined second interior temperature is reached, or - solvent is introduced into the interior over a predetermined period of time, whereby the predetermined second interior temperature is reached after the predetermined period of time.

[0180] The first internal temperature and the second internal temperature can be the same.

[0181] The second internal temperature can therefore be higher, equal to, or lower than the first internal temperature. A reduction in temperature can be caused by the natural cooling of the chamber or evaporative cooling, or actively facilitated by a cooling unit.

[0182] In one embodiment, it may be advantageous if solvent is introduced into the interior space over a period of between 1 s and 600 s, preferably between 5 s and 300 s (step (d)).

[0183] It may be advantageous if, after the molded part has been introduced into the interior (step (a)) and before the solvent has been introduced into the interior (step (d)), the temperature of the interior is brought to a third internal temperature.

[0184] The third internal temperature can be lower than the predetermined second internal temperature, thereby bringing the molded part to a part temperature that is lower than the predetermined second internal temperature. In one embodiment of the method, the part temperature can be equal to the third internal temperature.

[0185] In one embodiment, (e) after the solvent has been introduced into the interior, the molded part is dried.

[0186] It is advantageous if the molded part is dried, in particular vacuum dried, in the interior space having the negative pressure.

[0187] It can be advantageous if the molded part is dried in the interior space, whereby a negative pressure, preferably a substantial vacuum, is generated in the interior space for drying the molded part. The generation of the negative pressure is interrupted at least once by supplying a transport gas to the interior space. After the supply of the transport gas, the generation of the negative pressure can be continued. This process can be repeated several times.

[0188] It can be advantageous to supply the transport gas to the interior when the pressure there is less than 50 mbar, whereby the supply of the transport gas increases the pressure in the interior to a value between 50 mbar and 100 mbar. After reaching a pressure between 50 mbar and 100 mbar, the negative pressure can be generated again until the internal pressure is again less than 50 mbar. This process can be repeated several times.

[0189] According to an advantageous embodiment of the method, steps (d) and (e) can be repeated several times.

[0190] It can be advantageous if, when repeating - in step (d), the temperature of the interior space is brought to a second interior temperature which is higher than the second interior temperature in the previous execution of step (d), or - in step (d), the temperature of the interior space is brought to a second interior temperature which is lower than the second interior temperature in the previous execution of step (d), or - in step (d), the temperature of the interior space is brought to a second interior temperature which is the same as the second interior temperature in the previous execution of step (d).

[0191] In a repetition, before performing step (d), the temperature of the interior space may be brought to a temperature which is lower or higher than the second interior temperature in the previous execution of step (d).

[0192] It may be advantageous to reduce the temperature of the solvent after each repetition.

[0193] After step (d), the solvent evaporated in the interior and / or the solvent condensed on the inner wall of the interior can be sucked off.

[0194] The extracted solvent can be processed, in particular purified and distilled, and the processed solvent can be returned to the solvent container. This results in a particularly advantageous embodiment of the invention, a process in which a solvent is used that can be reused in the cycle as often as desired without compromising the quality of the smoothing result, and without generating solvent waste or other products requiring disposal.

[0195] The negative pressure in the interior, the solvent temperature and the interior temperatures can be coordinated so that when the solvent is introduced into the interior, the solvent evaporates in the interior or enters the interior as solvent vapor.

[0196] Due to the pressure difference between the solvent container and the interior of the pressure-tight container, turbulence can occur within the container, allowing for a uniform distribution of the solvent around the component, especially around undercuts, cavities, tubes, and blind holes. This ensures homogeneous smoothing even on hard-to-reach surface areas.

[0197] It has proven advantageous if the inserted molded part is moved, especially rotated, during steps (d) and / or (e). This prevents the formation of drops or snags on the surface of the molded part.

[0198] Optionally, the surface of the molded part can be mechanically treated, in particular by grinding or blasting, before being inserted into the interior.

[0199] Optional, but still advantageous, is when - the molded part is colored before step (a) or after step (d), and / or - the moulded part is freed of residual powder before step (a), if the moulded part was printed using a powder-based process, and / or - the moulded part is matted after step (d), in particular by blasting the surface, and / or ground, and / or - the moulded part is impregnated and / or painted after step (d), and / or - the surface of the moulded part is compacted before step (a) or after step (d), in particular by blasting the surface with plastic balls, and / or - the surface of the moulded part is smoothed, in particular by grinding, before step (a) or after step (d).

[0200] The molded part can be heated before step (a). This is particularly advantageous for materials that tend to absorb water, as they would otherwise be prone to additional blistering during the smoothing process due to the evaporation of the bound water (at high temperatures and / or under negative pressure).

[0201] The solvent (both classic solvents and high boilers) can be selected from the group comprising acetaldehyde, acetamide, acetone, acetonitrile, acetophenone, acetylene, aliphatic hydrocarbons, in particular cyclohexane, cyclohexene, diisobutylene, hexane, octane, n-pentane and terpinene, alcohols, in particular benzyl alcohol, butylene glycol, butanol, ethanol, ethylene glycol, methanol, allyl alcohol, n-propanol and isopropanol, amyl acetate, aniline, anisole, gasoline, benzaldehyde, benzene, chlorobenzene, decalin, dioxane, dimethylamide, dimethylformamide, diethyl ether, dimethylformamide, dimethyl sulfide, dimethyl sulfoxide, ethylbenzene, ethyl acetate, formaldehyde, formamide, furfural, halogenated hydrocarbons, in particular chlorobromomethane, chloroform, ethylene chloride, methylene chloride, perchloroethylene, Tetrachloromethane, trichloroethane and trichlorethylene, menthone, methyl tert-butyl ether, methyl ethylene ketone, nitrobenzene, phenols, phenylethyl alcohol, propanol, pyridine, styrene,Tetrahydrofuran, tetrahydronaphthalene, toluene, triethanolamine, and combinations thereof.

[0202] It is particularly advantageous if the solvent is a distillable solvent.

[0203] For the production (printing) of the molded part, the material of the molded part can be selected from the group comprising polyester, PA12 (polyamide 12), PP (polypropylene), TPU (thermoplastic polyurethane), TPE (thermoplastic elastomers), PA11 (polyamide 11), PA6 (polyamide 6), PA6.6 (polyamide 6.6), glass-filled polyamide, ceramic-filled polyamide, PU (polyurethane), ABS (acrylonitrile-butadiene-styrene copolymers), PEK (polyether ketones), PEI (polyetherimides), PPS (polyphenylene sulfides) and PLA (polylactides), cyanate esters, materials based on (meth)acrylates, and combinations thereof.

[0204] It is advantageous if the molded part is produced using a powder-based 3D printing process, in particular a powder-based layered construction process in which individual layers are fused together, in particular using the SLS process (Selective Laser Sintering), MJF process (Multijet Fusion) or HSS process (High-Speed ​​Sintering).

[0205] It is advantageous if several liters of solvent, preferably at least 20 liters of solvent, are heated to the predetermined solvent temperature.

[0206] It may be advantageous if the solvent is heated to the predetermined solvent temperature, which is above 100°C.

[0207] The solvent container can be designed to be pressure-tight, whereby a negative pressure is generated in the interior of the solvent container before the solvent is introduced from the solvent container into the interior of the pressure-tight container.

[0208] It can be advantageous if a substantial vacuum is created in the interior of the solvent container.

[0209] It is particularly advantageous if the pressure inside the pressure-tight container is lower than the pressure inside the solvent container.

[0210] In one embodiment, it may be advantageous if the pressure difference between the interior of the pressure-tight container and the interior of the solvent container is selected such that the solvent introduced into the interior of the pressure-tight container is swirled due to the pressure difference.

[0211] It has been found to be advantageous to use a food-safe solvent or a solvent approved for processing food-grade plastics. Reference symbol: 10 molded part 11 Surface of the molded part 10 20 pressure-tight container 21 Interior of the pressure-tight container 20 25, 25' supply line 27 Return line 30 vacuum pump 40, 40' solvent container, preferably pressure-tight 50, 50' valve 60 Control / regulating device 70, 70' Solvent or interior of the solvent container 40, 40' 80 Cleaning / distilling facility 90 Extraction device DS pressure sensor S1 - S6 steps of the procedure TS temperature sensor QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 10 / 2011

[0077]

Claims

[1] Device for treating a surface of at least one molded part (10) produced in a 3D printing process, the device comprising - a pressure-tight container (20) with an interior (21) in which the molded part to be treated is received, - a solvent container (40) for holding a solvent (70), and - a vacuum pump (30) coupled to the pressure-tight container (20) in order to generate a negative pressure, preferably a substantial vacuum, in the interior (21) of the pressure-tight container, - a device for heating the solvent (70) to a predetermined solvent temperature, - a supply line (25) via which the heated solvent (70) can be introduced into the negative-pressure interior space (21) of the pressure-tight container (20), wherein the device is designed such that the temperature of the molded part (10) is lower than the solvent temperature when the solvent (70) is introduced into the interior space (21), and the solvent (70) evaporates or is introduced as solvent vapor when introduced into the interior space (21), the solvent vapor condensing on the surface of the molded part (10). [2] Device according to the preceding claim, wherein - the solvent container has a heating device to heat the solvent contained in the solvent container, and / or - the pressure-tight container has a heating device to heat the interior and / or the molded parts accommodated in the interior. [3] Device according to one of the two preceding claims, wherein the solvent container (40) is designed to be pressure-tight. [4] Device according to the preceding claim, wherein a vacuum pump is coupled to the solvent container (40) in order to generate a negative pressure, preferably a substantial vacuum, in the solvent container (40). [5] Device according to one of the preceding claims, wherein a temperature sensor (TS) and / or a pressure sensor (DS) is assigned to the solvent container (40) and / or the pressure-tight container (20). [6] Device according to one of the preceding claims, wherein it comprises a control / regulating device (60) with which - the heating device of the pressure-tight container (20) and the vacuum pump (30) are adjustable and / or controllable in order to adjust the pressure and the temperature in the interior (21) of the pressure-tight container (20), and - the heating device of the solvent container (40) is adjustable and / or controllable in order to adjust the temperature of the solvent. [7] Device according to one of the preceding claims, wherein the pressure-tight container (20) is coupled to a suction device (90) in order to suck out solvent vapor and / or solvent condensate present in the pressure-tight container. [8] Device according to the preceding claim, wherein the suction device (90) is coupled to the solvent container (40) via a return line (27) in order to return the extracted solvent vapor and / or the extracted solvent condensate to the solvent container (40). [9] Device according to the preceding claim, wherein it comprises a cleaning and / or distilling device (80) which is adapted to clean and / or distill the extracted solvent vapor and / or the extracted solvent condensate. [10] Device according to one of the preceding claims, wherein it has at least one further, preferably pressure-tight solvent container (40') which is coupled to the pressure-tight container (20) via at least one further supply line (25') in order to supply at least one further solvent (70') from the at least one further solvent container (40') to the pressure-tight container.

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