DEVICE FOR CLEANING COMPONENTS MANUFACTURED BY MEANS OF A LITHOGRAPHIC GENERATIVE MANUFACTURING PROCESS

Description

[0001] The application discloses a method for cleaning components to which unreacted resin adheres, in particular components manufactured using a lithographic additive manufacturing process, comprising a cleaning step in which the components are placed in a cleaning chamber, the components in the cleaning chamber are contacted with a cleaning medium, whereby resin is removed from the components, and the cleaning medium loaded with the removed resin is discharged from the cleaning chamber, and a regeneration step in which the loaded cleaning medium is fed to a distillation unit in which the contaminated cleaning medium is regenerated by distillative separation of the resin.

[0002] The invention relates to a device according to claim 1 for carrying out this method.

[0003] Publication JP H01 258702 A describes a method for cleaning components to which unreacted resin adheres.

[0004] Publication US 5,248,456 A describes a device for cleaning components to which unreacted resin adheres, according to the preamble of claim 1.

[0005] The invention relates to the field of industrial cleaning of additively manufactured three-dimensional structures produced using a radiation-curing process. In radiation-curing additive manufacturing processes, liquid reactive resins are typically exposed to radiation at process temperature, resulting in local and high-resolution curing. The first layer is cured on a build platform or substrate, to which the subsequently cured three-dimensional components can adhere. The layer-by-layer build-up of the components can be carried out in a bottom-up or top-down process. Examples of radiation-curing additive manufacturing processes include stereolithography, digital light processing (DLP), two-photon lithography, inkjet printing, and various combinations thereof. Another method is the hot lithography technology developed by the applicant.Here, highly viscous resins are selectively heated at room temperature, thereby reducing the viscosity until the resins can be processed.

[0006] After successful 3D printing, the geometries are still contaminated with reactive resin. Removal of this unwanted residual resin typically occurs in immersion baths containing volatile and sometimes highly flammable organic solvents (e.g., isopropanol). The solvent dissolves the residual resin adhering to the 3D-printed structures, thus removing it from the cross-linked photopolymer component. These cleaning processes usually take place in an open environment, exposing the user to solvent vapors and solvent residues on the cleaned component surfaces. In many cases, the cleaning performance of the solvent decreases significantly even after a small resin load and can no longer completely remove resin residue from the components. Due to this gradual decline in the solvent's cleaning performance, consistent, reproducible cleaning results cannot be achieved.Therefore, the solvent is often disposed of after only a short time, resulting in enormous amounts of solvent waste.

[0007] Unlike the cleaning of 3D-printed parts manufactured using non-resin-based additive manufacturing technologies (e.g., FDM or powder technologies SLS or SLM), the dissolved radiation-curing resin remains reactive and capable of thermal and radiation-induced curing. Therefore, solvent regeneration proves particularly challenging. Furthermore, the often manual cleaning process leads to inconsistent cleaning results, which can significantly impact component quality and the mechanical properties of the printed material. Special geometries, such as long, thin, resin-encrusted channels, blind holes, and / or undercuts, may not be satisfactorily cleaned using conventional methods.Removing viscous and highly viscous resin residues is particularly difficult, as they must be cleaned at elevated temperatures for effective removal from the component, consequently increasing solvent evaporation and associated hazards such as flash point, exposure, etc.

[0008] During the distillation-based regeneration of the solvent, there is a risk that the highly reactive resin, which accumulates in the distillation sump, will thermally polymerize. Consequently, excluding light from the distillation sump is advisable. However, avoiding the introduction of thermal energy into the distillation sump is difficult in a distillation process. Typical sump temperatures range from 40 to 200°C, depending on the solvent, with 70 to 150°C or 90 to 130°C being preferred. Crosslinking of the dissolved resin in the sump or of volatile monomers in the distillation unit can lead to significant damage to the system, as the polymerized residue, if removable at all, must be mechanically removed, potentially resulting in long downtimes and costly repairs.

[0009] Therefore, a process of the type mentioned above should be improved in such a way as to overcome the disadvantages mentioned above and to avoid polymerization of the resin adhering to the component and subsequently detached from the component during the cleaning and regeneration steps.

[0010] Furthermore, a closed, industrial cleaning process based on liquid cleaning media is to be created that avoids the user's exposure to the cleaning medium, ensures the continuous regeneration of the cleaning medium to avoid solvent waste, and optimizes the cleaning process through a combination of process steps and can be repeated reproducibly.

[0011] To solve this problem, a process of the type mentioned above provides for the addition of at least one inhibitor to the cleaning medium, which delays, suppresses, and / or prevents polymerization of the resin during the cleaning and / or regeneration steps. The use of at least one polymerization inhibitor is particularly advantageous in heated, resin-contaminated areas, such as the distillation sump. Stabilization with inhibitors prevents thermally induced polymerization in the distillation sump, which can lead to solidification of the sump and consequently halt the distillation process. Furthermore, stabilization allows for a higher solvent concentration in the sump and, for example, enables the resin residues to be concentrated before emptying the sump, thus resulting in less solvent loss.The emptying of the sump can be designed in such a way that the residual resin, after concentration, can be pumped directly into an empty chemical container without the user having to come into direct contact with the residual resin.

[0012] According to a preferred embodiment and taking into account the temperatures prevailing in the distillation unit, in particular in the distillation sump, it can be provided that the inhibitor prevents thermally and / or light-induced polymerization of the resin at a temperature of > 70°C, preferably > 100°C.

[0013] Preferred examples of suitable inhibitors are antioxidants, such as phenol or quinone derivatives, sterically hindered phenols, phenol, hydroquinone, benzoquinone, 2-(2-hydroxyphenyl)-2H-benzotriazoles, such as 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol] or 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, quinone methides, tert-butylhydroquinone, 4-methoxyphenol (MEHQ), pyrogallol, nitrophenol, 4-tert-butylcatechol, 2,6-di-tert-butylphenol, 6-tert-butyl-2,4-xylenol, 2,6-di-tert-butyl-p-cresol (BHT), 2-tert-butylhydroquinone, 2-tert-Butyl-1,4-benzoquinone, 1,3,5-Tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazinane-2,4,6-trione, tocopherols, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), copper(II) dibutyldithiocarbamate, phenothiazine, Phenothiazine derivatives, bis-(2-hydroxypropyl)amine, N,N-diethylhydroxylamine, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine, p-phenylenediamine, 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxyl (TEMPOL), as well as TEMPO and TEMPOL derivatives, 2,6-di-tert-butylphenol, tris(N-hydroxy-N-nitrosophenylaminato-O,O')aluminium, ammonium 2-oxo-1-phenylhydrazinolate (Kupferrone), sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate and sodium dibutyldithiocarbamate.

[0014] Examples of preferred inhibitors that delay polymerization include Reversible Addition Fragmentation Chain Transfer Polymerization (RAFT) reagents such as dithio esters, dithiocarbamates, trithiocarbonates and xanthates, Atom Transfer Radical Polymerization (ATRP) reagents and Nitroxide-Mediated Polymerization (NMP) reagents.

[0015] Preferred inhibitors can also exist in higher molecular weight, oligomeric, or polymeric form. Examples include 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,3,5-tris[[4-tert-butyl-3-hydroxy-2,6-xylyl]methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, sebacic acid bis(2,2,6,6-tetramethyl-4-piperidyl) ester, and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate).

[0016] The aforementioned preferred inhibitors may preferably also be used as a mixture of at least two of the aforementioned.

[0017] A mixture of an aerobic and an anaerobic inhibitor is particularly effective, for example, a mixture of at least one hydroquinone or phenol derivative with at least one phenothiazine or phenothiazine derivative. Surprisingly, exceptionally high soil stability was achieved, for example, with a mixture of MEHQ and phenothiazine or with a mixture of pyrogallol and phenothiazine.

[0018] Depending on the problem, inhibitors can be added to the cleaning medium in concentrations ranging from 10 ppm to 20 vol%, preferably 500 ppm to 10 vol%, and even more preferably 1000 ppm to 5 vol%. To guarantee optimal stabilization, inhibitors can be mixed together as desired.

[0019] To further inhibit resin polymerization, it is preferably provided that oxygen is introduced into the bottom of the distillation unit, since oxygen, as an inhibitor, can prevent radical polymerization. The oxygen can be supplied, for example, as atmospheric oxygen. A combination with aerobic inhibitors is advantageous in this case.

[0020] Due to the prevention of resin polymerization in the distillation unit, the distillative regeneration of the cleaning medium can be carried out as a continuous process. This allows for the continuous removal of the detached resin from the process, resulting in a lower resin load in the cleaning medium available for the cleaning step and ensuring an efficient cleaning process. The continuous distillative regeneration of the cleaning medium can be performed simultaneously with the cleaning step or at a later time. For distillative regeneration, a portion of the cleaning medium is circulated in a loop containing the distillation unit.In this context, a preferred method provides that the cleaning medium is continuously circulated in a fluid circuit, in which the cleaning medium is carried away from a storage container or the cleaning chamber, passed through the distillation unit and returned to the cleaning chamber or the storage container.

[0021] The storage container can be connected to either the cleaning chamber or the distillation unit. Specifically, the storage container can be integrated into a fluid circuit in which the resin-laden cleaning medium is fed to the distillation unit and the cleaning medium regenerated in the distillation unit is returned to the storage container, or it can be integrated into a fluid circuit in which the cleaning medium is fed from the storage container to the cleaning chamber and the resin-laden cleaning medium in the cleaning chamber is returned to the storage container.

[0022] Preferably, the two fluid circuits can be connected to each other by a connecting line in such a way that used cleaning medium from the cleaning chamber is fed directly to the distillation unit, i.e. without first entering the storage container.

[0023] Preferably, the two fluid circuits can also be connected in such a way that regenerated cleaning medium from the distillation unit is fed directly into the cleaning chamber, i.e. without first entering the storage container.

[0024] The process is preferably carried out as a closed process in which the cleaning medium remains in enclosed spaces during both the cleaning and regeneration steps, thus preventing the escape of the cleaning medium, which is vaporous at elevated temperatures, and the associated hazards such as ignition, exposure, etc. For this purpose, the cleaning chamber is preferably designed as a vapor-tight sealable chamber.

[0025] The loading and unloading of the components to be cleaned preferably takes place via the cleaning chamber. The additively produced, resin-coated components can either be directly adhered to the build platform and thus introduced into the cleaning chamber together with the build platform, or they can be detached from the build platform before being placed in the cleaning chamber, separated, and individually fixed in suitable fluid-permeable containers, such as baskets, nets, or cages, or they can be supplied in bulk. Loading and unloading of the cleaning chamber can be carried out manually, semi-automatically, or fully automatically. Fully automated loading and unloading of the cleaning chamber can be achieved, for example, via a conveyor belt or conveyor rollers.

[0026] If the components are still on their respective build platforms, the platform(s) can be movably mounted within the cleaning chamber. To catch any components that might detach from the build platform during the cleaning process, it is advantageous to provide cage-like or basket-like structures around the platform(s). The axis of rotation of the basket, cage, build platform, etc., can be in any direction, but preferably vertical and horizontal, or even just in one of these two directions.

[0027] Cleaning the construction platform(s) in fluid-permeable containers, such as baskets, griddled containers, or surrounding the construction platform(s) with nets has the advantage that components that may detach during the cleaning process remain in the container and are not freely swirled around in the cleaning chamber, which could, for example, lead to blockages of pipes and filters.

[0028] In the cleaning chamber, the components are cleaned in batches, preferably in a closed process. For this purpose, cleaning medium at different temperatures can be introduced into the cleaning chamber from the preheated or precooled reservoir(s). The cleaning chamber can be completely filled (flooded) with the cleaning medium. By means of movements, such as rocking or rotating motions, the components can be moved at different speeds within the cleaning medium. This results in turbulent relative motion of the components with respect to the cleaning medium, thus increasing the cleaning efficiency. Furthermore, cleaning medium, air, and / or compressed air can be introduced into the cleaning chamber via valves and nozzles to create turbulent flow.

[0029] Cleaning in the cleaning chamber can be further enhanced by ultrasound or vacuum-assisted ultrasound, for which, for example, plates or rod ultrasound generators can be used. Typical frequency ranges for ultrasound are between 1 and 400 kHz.

[0030] The components can also be cleaned using spraying and aeration processes. For example, spraying and / or aeration cleaning via nozzles and directed inlet valves and inlet geometries into the cleaning chamber is possible. Another option is the application of pressure cycling. These processes, through changing pressure conditions, shift the boiling point of the cleaning medium. This causes the cleaning medium to boil and condense on the components, which can significantly improve the cleaning effect. Applying overpressure in the cleaning chamber can also lead to improved cleaning.

[0031] The steam generated in the distillation unit from the cleaning medium can also be fed directly into the cleaning chamber. An additional cleaning effect can be achieved by steaming the components with hot steam. Another option is to apply a vacuum to the cleaning chamber to evaporate any remaining cleaning medium on the components. For this purpose, the pressure in the cleaning chamber can be reduced to a few millibars (< 20 mbar) or even below 1 mbar. This step can serve as a drying step, but also as an additional process step to extract resin residues from small cavities, blind holes, and / or pores for subsequent rinsing or spraying.

[0032] Additionally, the contaminated components can be heated in the cleaning chamber with infrared radiation or hot air to reduce the viscosity of the residual resin adhering to the components. The advantage of infrared heating is that, in the event of a final vacuum drying of the 3D printed components, it can increase the intrinsic energy of the photopolymers and thus promote evaporation.

[0033] Components can be dried using hot air, infrared radiation, or in a vacuum. Particularly good drying results are achieved with a combination of vacuum and infrared radiation.

[0034] The aforementioned advantageous steps in the cleaning chamber can, where practical and physically feasible, be partially performed simultaneously. In any case, the components can be set in motion during each step, for example, by rotational or rocking movements.

[0035] The steps mentioned above in the cleaning chamber can be repeated as often as desired in any order until the desired cleaning result is achieved.

[0036] In principle, all fluids and liquids capable of removing or dissolving resin residues are suitable cleaning media for use in the cleaning chamber. Typical cleaning media that can be used in the cleaning chamber include water, all types of aqueous solutions, acids, bases, surfactant solutions, salt solutions, and all organic solvents such as glycols, linear, branched, and modified alcohols, hydrocarbons, aromatic, cycloaliphatic, linear, and branched hydrocarbons, alkenes, alkynes, ethers, esters, amides, amines, ketones, lactones, lactams, nitriles, nitro compounds, sulfones, sulfoxides, urea derivatives, carbonates, acetates, malonates, morpholine derivatives, amino alcohols, halogenated solvents, fluorinated solvents, and many more. Various solvent mixtures can also be used.

[0037] Cleaning media with flash points above 50°C are particularly suitable for use in the cleaning chamber, preferably flash points above 60°C, since the use of cleaning media with lower flash points would require additional complex, structural safety measures regarding explosion protection.

[0038] Typical cleaning agents with higher flash points include dimethyl sulfoxide, dimethylformamide, benzyl alcohol, benzyl acetate, propyl glycol, butyl glycol, ethyl glycol acetate, 1-butoxypropan-2-ol, 1-propoxypropan-2-ol, 1,2-propanediol, butyl lactate, hexan-1-ol, triethylene glycol, 1,3-propanediol, propylene carbonate, 1-aminopropan-2-ol, diisopropanolamine, 3-butoxypropan-2-ol (RG Cleaner 63, DOWANOL™< PnB), linear, branched and cyclic hydrocarbons, 1,5-dimethyl glutarate, 1,6-dimethyl adipate and 1,4-dimethyl succinate, 2-(2-butoxyethoxy)ethanol, hexanols, 2-pyrrolidone, dipropylene glycol, dipropylene glycol-n-propyl ether. Dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, diethylene glycol monoethyl ether acetate, 2-ethylhexanol, diethylene glycol monohexyl ether, ethyl 3-(2,4-dimethyl-1,3-dioxolan-2-yl) propanoate, diethylene glycol monobutyl ether, ethylene glycol monohexyl ether, anisole, methylanisole, phenetol, tetrahydrofurfuryl alcohol and 2,2-dimethyl-1,3-dioxolane-4-methanol,as well as mixtures of the aforementioned.

[0039] In addition to resin stabilization through inhibitors, additives can be added to the solvent to extend its shelf life and improve process control in the plant. Examples include pH regulators such as amines (e.g., triethylamine or aminopropanol), morpholine and morpholine derivatives, lubricating oils, petroleum distillates, antifoaming agents to prevent foaming, non-volatile substances that act as thinners, corrosion inhibitors, silicates, polyphosphates, sulfonates, organic nitrogenous acids, zinc salts, and complexing agents (e.g., calcium salts of carboxylic acids and / or calcium alkylnaphthalenesulfonate).

[0040] Photoresins typically consist of (end-group modified, reactive) oligomers, low-molecular-weight mono- and / or multifunctional reactive diluents, fillers, additives, and / or at least one photoinitiator. Examples of (end-group modified, reactive) oligomers include virtually all polymers, polyaddition and polycondensation products such as polyethers, polyesters, polyurethanes, polycarbonates, polyamides, polythioethers, polythioesters, silicones, etc. In most cases, the reactive components possess at least one or more reactive end group(s) which, upon exposure to radiation of a suitable wavelength, cure by decomposing at least one photoinitiator, forming a solid, cross-linked polymer. Examples of reactive end groups include unsaturated double bonds, vinyl, acrylates, methacrylates, acrylamides, allyl compounds, norbornenes, vinyl ethers, epoxides, oxetanes, maleimides, and thiols, to name just a few.Typical photoinitiators form radicals, cations, anions or other active species upon decomposition or activation, which trigger polymerization upon irradiation with certain wavelengths and usually lead to a cross-linked photopolymer.

[0041] Photoresins can also contain a high proportion of organic, inorganic, ceramic, and / or metallic fillers, resulting in hybrid materials after polymerization. Fillers can also be oligomers, prepolymers, and / or polymers. Typical filler content ranges from 1 to 95%. After purification, photopolymers filled with inorganic, ceramic, or metallic materials, for example, can be further processed into ceramics or metals using debinding and sintering processes. Furthermore, these photopolymers can also consist of dual-cure systems, where an initial crosslinking occurs during the 3D printing process for shaping, and a second crosslinking is triggered thermally in subsequent processes.

[0042] A limiting factor for classic lithography-based additive manufacturing processes is resin viscosity. These processes, often carried out in immersion baths, require low-viscosity resins with a viscosity typically less than 2 Pa·s at room temperature. Newer processes, such as hot lithography, are now heatable and can process photoresin systems that, at room temperature, can exhibit medium-viscosity resins with a viscosity of 5 to 30 Pa·s, high-viscosity resins with a viscosity of 30 to several hundred pascals, and very high-viscosity resins of 1,000 Pa·s and above. However, at elevated process temperatures between 40 and 150 °C, the viscosity of these resins decreases, making them processable. Cleaning is difficult with high-viscosity resin systems because the resin residues adhering to the component are harder to remove due to their high viscosity.Consequently, the cleaning medium must also be heated during the cleaning process, typically to 40 to 100°C, to achieve the desired cleaning result. This, in turn, leads to increased evaporation of the cleaning media used and increases the user's exposure. For this reason, a closed process is preferable or even necessary for cleaning components made of highly viscous resins.

[0043] In light of the aforementioned circumstances, a preferred embodiment of the method provides that the resin adhering to the components has a viscosity of > 2 Pa·s, preferably > 30 Pa·s, at 20°C. Rheological data were obtained in connection with the present invention using an Anton Paar MCR 102 rheometer. For determining the rheological properties, the rheometer was operated in rotational mode (PP-25, shear rate 50 s⁻¹, temperature range 20°C to 70°C with a heating rate of 0.5 K / min, measuring gap 1 mm).

[0044] The major advantage of this cleaning process lies in the continuous processing of the cleaning medium in the distillation unit. The cleaning medium, contaminated with reactive resin, is collected in the sump and, if necessary, converted into the vapor phase by applying heat and a vacuum. While the resin residues remain in the sump, the pure steam of the cleaning medium rises in the distillation unit and, after condensation, is stored as a processed cleaning medium in the temperature-controlled storage tank. If desired, the hot steam can also be directed into the cleaning chamber for steam cleaning of the components.

[0045] The cleaning process can be integrated into a conventional manufacturing process for the additive layer-by-layer lithographic production of components, the steps of which are schematically described in Fig. 1The manufacturing process includes a digital preparation step in which the three-dimensional components to be produced are digitally prepared. The components are then printed using a lithography-based additive manufacturing process. This may be followed by one or more optional pre-cleaning steps. The components are then cleaned according to the cleaning procedure, and finally, the final three-dimensional component is obtained in one or more downstream processes.

[0046] In the digital preparation step, existing 3D data of a component is optimized and prepared for the printing process according to the specifications of the subsequent additive manufacturing process. These processing steps on the 3D model can include, among other things, data error analysis and possible data repair, scaling, placement of the 3D models on the digital build platform, geometric compensation for overpolymerization (e.g., that occurring in radiation-curing processes), creation of support geometries, and generation of layer information. All sub-steps can be performed manually, semi-automatically, or fully automatically. Alternatively, the print data can also be created directly in CAD software according to process-specific design guidelines, including all sub-steps.

[0047] Printing certain geometries requires corresponding support structures, which are built up during the photopolymerization process. These support structures enable, for example, the construction of extreme overhangs. Methods for removing such support structures after successful printing include mechanical methods using tweezers, grippers, blades, milling machines, drills, brushes, and grinding devices, as well as directed fluid jets such as gas jets, compressed air, liquid jets, and water jets, and solid-material methods such as dry ice blasting, snow blasting, and / or sandblasting. Support structures can also be removed by controlled explosions, in which reactive gases such as hydrogen or methane can be detonated. The aforementioned methods for removing support structures can be performed manually, semi-automatically, and fully automatically, and as often as desired and in any sequence.

[0048] Another option for removing support structures is the use of soluble or meltable support structures. These soluble support structures can be dissolved in the cleaning system's solvent, for example, if the component itself does not dissolve in the cleaning medium, but the support structure does. Alternatively, cleaning chambers / systems with two or more different solvents can be used, where the first solvent cleans the supported components and the second dissolves the support structures (e.g., water-soluble support structures), or vice versa.

[0049] In connection with such post-processing of the components, it may preferably also be provided that at least one further processing step is carried out to remove support structures from the components, to color the components, to chemically modify component surfaces and / or volumes of the components and / or to impregnate the components.

[0050] In photopolymerization-based printing processes, the photoresins are irradiated locally and with high resolution using a lithography-based method, causing the irradiated areas to harden into a solid. The process is carried out in stages or continuously, and the previously prepared three-dimensional structures are built up. The components are typically located on a build platform. After the 3D printing process is complete, the produced 3D components are contaminated with resin.

[0051] The optional pre-cleaning process can comprise one or more steps, which can be performed any number of times in any order. During this process step, the printed 3D parts can either remain on the build platform or be removed and separated. This removal process can be manual, semi-automated, or fully automated. One example of a pre-cleaning process is allowing residual resin to drip off the parts. This process can be accelerated by temperature and assisted by rotation. Other options include pre-cleaning with a liquid spray to remove coarse resin residue. Pre-cleaning can also be achieved through rapid rotation of the parts or parts on the build platform(s), for example, by centrifugation.The cleaning effect of the centrifuge can be enhanced by increasing the temperature, introducing spray mist, and varying the orientation of the components to be cleaned or the build platform relative to the axis of rotation, as well as by using a movable, mounted build platform. If appropriate, the pre-cleaning process can also include the removal of any necessary support structures.

[0052] After cleaning, according to Fig. 1Typically, one or more downstream processes are required to produce the final 3D component. Typical downstream processes include drying, post-curing, coating with materials such as metals, semi-metals, ceramics, and / or plastic coatings, mechanical post-processing of the 3D components, removal of any support structures, component placement, application of conductive traces, insertion of contact pins, coloring of the components, and much more. Drying steps can be carried out in air or other atmospheres, such as nitrogen or argon, at room temperature, at elevated temperatures (e.g., in ovens or belt ovens), using various compressed air technologies, and / or directed hot air. Post-curing can be a thermal and / or radiation-induced process (e.g., UV light sources).However, other downstream processes suitable for manufacturing the final product can also be used. The described thermal processes can take place at temperatures between 40 and 400°C. In the case of debinding and sintering processes, the thermal processes can also take place at several hundred degrees and up to over 1,000°C. Thermal exposure can be carried out batchwise or continuously, for example in a belt furnace. The same applies to radiation curing, which can also be carried out batchwise or continuously, for example in radiation belt furnaces. The described curing steps can be performed in any sequence and as often as necessary to obtain the final properties of the 3D component.

[0053] Ultimately, a final 3D component is obtained. Examples of such 3D components include medical, dental, and orthodontic applications such as intraoral devices like braces, aligners, splints, or attachments; electronic components such as connectors, plugs, or housings; 3D-printed shoe soles; parts for the aerospace industry; military applications; consumer goods applications; mobility, automotive, and electromobility applications; 3D-printed parts for use in the energy sector; sports applications such as shoe soles or cushioning elements; and printed electronics applications, to name just a few.

[0054] The invention relates to a device for carrying out the cleaning process described above, comprising a cleaning chamber, at least two storage containers for a cleaning medium connectable to the cleaning chamber, and a distillation unit, the inflow of which can be connected to the cleaning chamber or the storage containers via a first line and the outflow of which can be connected to the cleaning chamber or the storage containers via a second line, in order to supply resin-loaded cleaning medium from the cleaning chamber or the storage containers to the distillation unit and simultaneously return regenerated cleaning medium from the distillation unit to the cleaning chamber or the storage containers.

[0055] According to the invention, the storage containers are each connected to the cleaning chamber via an inlet line and an outlet line in order to circulate the cleaning medium.

[0056] Each of the two storage containers is connected to the cleaning chamber via an inlet pipe and an outlet pipe.

[0057] It goes without saying that the strategies described here are not limited to additively manufactured components. Rather, the described stabilization strategies can also be applied to all other conceivable resin systems. Examples include, in any case, unsaturated polyester resins, alkyd resins, adhesives, and / or coatings of any kind.

[0058] The invention is explained in more detail below using exemplary embodiments. Fig. 1 shows the steps of a lithographic additive manufacturing process, Fig. 2 shows a first embodiment of a device not according to the invention, Fig. 3 shows an embodiment of a device according to the invention, Figs. 4a and 4b show a fluid-permeable container for arrangement in the cleaning chamber, Figs. 5a-5fshow different arrangements of the components to be cleaned in the fluid-permeable container and Fig. 6 shows a further embodiment of a device according to the invention.

[0059] In Fig. 1 The sequence of process steps of a typical lithographic additive manufacturing process is shown schematically. As already explained in more detail above, the process steps include a digital preparation step for the printing process, the photopolymerization-based printing process, an optional pre-cleaning step, and then the cleaning of the printed component according to the invention to remove any unreacted resin adhering to the component. The cleaned components are then subjected to downstream processes, and finally the final component is obtained.

[0060] Fig. 2Figure 1 shows a non-inventive embodiment of a device for carrying out such a process. The device comprises a cleaning chamber 1, a reservoir 2 for cleaning medium, a vacuum pump 3 connected to the cleaning chamber, and a distillation unit 4. The components to be cleaned are first placed in the cleaning chamber 1. Cleaning medium stored in the reservoir 2 can then be introduced into the cleaning chamber 1 and returned to the reservoir 2 in a closed loop, or it can be purified directly in the distillation unit 4 and returned to the reservoir 2 as a liquid by condensation. Direct introduction of superheated steam from the distillation unit 4 into the cleaning chamber 1 is also possible. A vacuum pump 3 connected to the cleaning chamber 1 enables the implementation of a pressure swing process as well as vacuum drying.

[0061] Fig. 3shows an embodiment of the device according to the invention, which differs from the embodiment according to Fig. 2 The system is characterized by the arrangement of two reservoirs, 2 and 5. The presence of two or more reservoirs, 2 and 5, allows cleaning processes to be carried out with cleaning media containing varying concentrations. For example, the cleaning medium with a higher resin concentration in reservoir 2 could be used for initial coarse cleaning, while the subsequent fine cleaning would be performed with a cleaning medium of higher purity from reservoir 5. Such a process can improve the cleaning result. The throughput of components to be cleaned can be increased, for example, by adding a second or further cleaning chamber (not shown).

[0062] Fig. 6 shows a similar structure to in Fig. 3, however, the supply of the freshly distilled solvent only takes place in the storage container 2 and the storage container 5 is filled by overflow from the storage container 2.

[0063] The in Fig. 2, 3 and 6The sketched cleaning chambers are kept simple for clarity. Of course, any number of additional cleaning chambers, pipelines, circuits, auxiliary tanks, oil separators, water separators, various valves, heat exchangers, columns, hoppers, filters, shut-off valves, mixing valves, pumps, compressors, vacuum pumps, insulation, dryers, evaporators, coolers, fans, membranes, controllers, ultrasonic sources, condensers, infrared sources, compressed air supplies, heaters, hot air supplies, and other process engineering components can be added to these cleaning chambers to guarantee their smooth operation. Furthermore, they can be equipped with a wide variety of measuring and control equipment for manual, semi-automated, and fully automated process monitoring and control.

[0064] Fig. 4aFigure 1 schematically shows a fluid-permeable container 6, designed as a cuboid basket, a grid, or a mesh. The container 6 can be made of metal and / or plastic and can have different mesh sizes. The basket geometry can be chosen arbitrarily, for example, rectangular, square, round, or oval, to name just a few. The basket openings can have different geometries, for example, rectangular, square, round, oval, or other special geometries.

[0065] Fig. 4b shows the construction platform 7 arranged in container 6 with components 8 arranged on it.

[0066] The Figs. 5a-5f show various possibilities for arranging and securing the construction platforms 7 inside the container 6. In the variant according to Fig. 5a Four construction platforms 7 are arranged in cross-section in the form of a square, rotated by 45° relative to the container 6. In the variant according to Fig. 5b Two construction platforms 7 lie with their backs against each other and, viewed in cross-section, are arranged along a diagonal of the container 6. In the variant according to Fig. 5c Two construction platforms 7 are also positioned with their backs against each other, but are arranged along a horizontal central plane in the container 6.

[0067] As in Fig. 5d As can be seen, the construction platforms 7 can also form a triangle in cross-section. Alternatively, the construction platforms 7 can be arranged as shown in Fig. 5e shown, arranged on the walls of container 6. Based on the Fig. 5f It has been shown that the container 6 can also be cylindrical.

[0068] To make the cleaning process more efficient, ideally several build platforms 7 can be introduced into the cleaning chamber 1 simultaneously. Furthermore, positioning the build platforms 7 facing outwards, i.e., towards the inside of the container surface, is advantageous for cleaning. EXAMPLES

[0069] The following examples are given to illustrate various possible embodiments of the invention and are not intended to limit the disclosed invention in any way. The examples of the described methods are to be understood as representative and exemplary. Example 1:

[0070] Example 1 describes the cleaning of simple structures with large surface areas. This example describes cleaning in a device that conforms to the apparatus. Fig. 2This process is similar. In this example, 20 dental plastic aligners are digitally prepared and printed from a low-viscosity resin using a stereolithography-based process. After printing, the resin-cured aligners are removed from the build platform and placed in a basket, which is automatically inserted into the cleaning chamber. In the first cleaning step, the chamber is evacuated, and the aligners are exposed to hot steam for initial cleaning. Next, a 55°C hot solvent (2-butoxyethanol) is sprayed onto the aligners from the reservoir while the basket is slowly rotated. The used solvent is then returned to the reservoir. The cleaning chamber is then flooded with solvent, and the basket is subjected to ultrasound for two minutes while the basket is slowly rotated vertically. Finally, the chamber is emptied and evacuated.In a final cleaning step, the cleaning chamber is flooded, and turbulent flow is created by introducing first compressed air and then targeted jets of solvent. This removes any remaining resin, and the contaminated solvent is directed into the distillation sump, which is stabilized with inhibitors. Final cleaning is achieved by introducing hot steam from the vacuum distillation unit into the cleaning chamber. This heats the components, causing the solvent to condense on them, ensuring thorough cleaning. In the final vacuum drying step, the remaining solvent is then removed from the components. After the washing chamber is ventilated, the dried aligners are automatically removed and post-cured in a UV curing system to achieve the final product. Example 2:

[0071] Example 2 describes the cleaning of complex structures with thin channels and narrow blind holes. This example describes cleaning in a device similar to that of Fig. 3The process is similar. In this example, micronozzles measuring 30 mm in length, 5 mm in width, and 8 mm in height with a double row of through holes are produced. 500 of these micronozzles are digitally prepared and additively manufactured from high-viscosity resin using a high-temperature lithographic 3D printing process (hot lithography). The resin-coated micronozzles are then transferred to a centrifuge on the build platform and centrifuged. After pre-cleaning, the micronozzles and build platform are fed into the cleaning chamber of the device, which is then evacuated. Hot steam from the distillation unit is then introduced directly into the cleaning chamber to remove coarse contaminants and warm the components. Finally, 70 °C hot 2-butoxyethanol is sprayed into the cleaning chamber from the first reservoir while the build platform is rotated at 6 revolutions per minute.The solvent with a higher resin content from the first storage container is circulated from the cleaning chamber back into the first storage container.

[0072] In the second process step, the cleaning chamber is flooded with tempered solvent from the first reservoir and subjected to ultrasound for one minute while slowly rotating. The heavily contaminated solvent is then transferred to the sump of the inhibitor-stabilized distillation unit for regeneration. After the initial cleaning is complete, the cleaning chamber is evacuated for one minute to remove residual resin from the still-sealed component channels and blind holes. Immediately afterward, 70°C hot, pure solvent from the second reservoir is introduced into the cleaning chamber, and the micronozzles on the build platform are subjected to ultrasound for one minute while slowly rotating. Finally, the components are steam-cleaned with hot steam from the distillation unit for fine cleaning before being dried under vacuum.After ventilation of the cleaning chamber, the cleaned and dried micronozzles are further processed into the final product in the downstream thermal oven process. Example 3:

[0073] Example 3 describes the efficiency of vacuum drying of solvent-cleaned, photoresin-based 3D components. Since photopolymers have low intrinsic heat capacity, insufficient drying is assumed because it is an endothermic process.

[0074] Rectangular, resin-coated connectors made of "Evolution" material from Cubicure (Vienna, Austria), measuring 35.5 mm in length, 11.8 mm in width, and 14.8 mm in height, with a double row of seven through holes, are cleaned in an ultrasonic bath with the solvents described in Table 1 for a specific time at a specific temperature (Table 1: Solvent Exposure). Cleaning the components in an ultrasonic bath is preferred over simple stirring because the ultrasound effectively removes the resin residue adhering to the component and within its holes. A combination of ultrasound and slow stirring is particularly effective. Following cleaning, the wet components are evacuated to below 10 mbar in a vacuum drying chamber for a specific time at a defined temperature (Table 1: Vacuum Drying).After removing the connectors from the vacuum oven, the components are inspected for solvent residues and the result of the vacuum drying is determined (Table 1: Results). As can be seen in Table 1, all connectors were successfully dried in the vacuum without leaving any solvent traces on the component surface, although in some cases a slight, non-disturbing solvent odor was still perceptible despite the dry surface. Consequently, the vacuum drying of photopolymer-based 3D printed plastic components can be surprisingly fast and efficient. Table 1: Overview of vacuum drying of photopolymer-based 3D molded parts after solvent cleaning solvent Solvent exposure Vacuum drying Result Isopropanol 12 min at 45°C 3 minutes at 23°C Dry acetic acid n-butyl ester 15 min at 45°C 4 minutes at 23°C Dry 2-Ethoxyethanol 10 min at 45°C 4 minutes at 23°C Dry DMSO 10 min at 60°C 5 min at 70°C Dry Tripropylene glycol monomethyl ether 5 min at 60°C 5 min at 70°C Dry RG Cleaner 63 5 min at 60°C 5 min at 70°C Dry Example 4:

[0075] Example 4 illustrates the cleaning effect of steam purging photopolymers. An uncleaned photopolymer-based 3D molded part made of the photopolymer resin "Evolution" from Cubicure (Vienna, Austria) was placed in the distillation head of a microdistillation system. Isopropanol, stored in the distillation sump, was used as the solvent. The oil bath for heating the sump was heated to approximately 80°C, and a slight vacuum of 600 mbar was applied to the system to generate steam. The resulting steam rose in the steam tube, heated the component, and eventually condensed on it. The condensate detached resin residues from the component and carried them back into the sump. Meanwhile, some of the solvent vapor condensed in the condenser of the distillation apparatus and was collected in a receiving flask. After approximately...After 20 minutes, the experiment is stopped and the cleaned component is removed from the distillation apparatus. A visual inspection reveals a well-cleaned part that no longer shows any resin residue on the exposed surfaces. Consequently, steam treatment of resin-coated photopolymer-based 3D molded parts can be classified as an efficient cleaning method for removing resin residue from surfaces. Example 5:

[0076] Photopolymer-based 3D molded parts are typically built up layer by layer from a radiation-curing resin. The component surface is still contaminated with residual resin, which must be removed by washing processes with fluids. As illustrated in this example, inhibitors are used to regenerate the cleaning medium, which is sometimes loaded with highly reactive resin.

[0077] To simulate a solvent cleaning system, a 100 mL amber glass round-bottom flask with a Soxhlet attachment (capacity 30 mL) and reflux condenser was set up. In this experiment, the round-bottom flask represents the distillation sump, in which the solvent and residual resin are heated for distillative regeneration under magnetic stirring. The Soxhlet attachment itself simulates a cleaning chamber in which a resin-coated connector component is placed. The solvent vapor generated in the round-bottom flask can rise through the vapor tube of the Soxhlet attachment into the reflux condenser, where it condenses and drips into the Soxhlet attachment as warm / hot solvent. Over time, the Soxhlet chamber fills with solvent, which cleans the component.Once the rising liquid level in the Soxhlet attachment reaches the height of the drain pipe, the solvent, now loaded with resin, empties into the sump and can be regenerated again by distillation, with the removed residual resin remaining in the sump.

[0078] To represent the widest possible range of potential photoresin impurities in the distillation sump, a mixture of reactive diluents, reactive and unreactive oligomers, initiators, additives, and fillers was prepared. The mixture included, for example, the following mono- and / or multifunctional compounds: vinyl compounds, methacrylates, acrylates, acrylamides, epoxides, oxetanes, thiols, radical and cationic photoinitiators, thermal initiators, maleimides, tertiary, secondary, and primary amines, divinyl ethers, allyl compounds, silicones, polyesters, polyurethanes, polyethers, polycarbonates, organic and inorganic fillers, and many more. The total mass of the viscous photoresin mixture in the sump was 41.5 g. This was placed in the sump and mixed with 60 mL (~52.8 g) of the modified alcohol RG Cleaner 63 (3-butoxy-2-propanol). The experiment was conducted in the sump under dark conditions.

[0079] An uncleaned component made of "Evolution" material from Cubicure (Vienna, Austria) was placed in the Soxhlet condenser, and the unstabilized mixture was heated to 100°C while stirring. The apparatus was then carefully vacuum-sealed until a final pressure of 40 mbar was reached. Shortly thereafter, vapor was generated, which then dripped from the condenser into the Soxhlet chamber, slowly filling it. One hour after the start of the experiment, it was observed that no more solvent was condensing in the reflux condenser. Inspection of the sump revealed a fully polymerized, highly cross-linked resin, which could no longer be removed from the flask despite considerable effort.

[0080] In the second experiment, the same photoresin composition was dissolved in the same amount of modified alcohol in the distillation sum, and a resin-coated component was placed in the Soxhlet attachment. This time, 4.8 wt% each of MEHQ and phenothiazine were added to the distillation sum as inhibitors. Surprisingly, the combination of MEHQ and phenothiazine was able to keep the sum stable for a total of 5 days after increasing the temperature to 100°C at 40 mbar pressure, without the resin polymerizing in the single-necked round-bottom flask. During this time, a total of ten components made of the "Evolution" photopolymer resin were successfully cleaned, with the washed-off resin becoming concentrated in the sum. Due to the temporary concentration of the pure solvent in the Soxhlet attachment, the resin concentration in the sum fluctuated between 44 and 67 wt%. These significant concentration changes in the sum underscore the high stability achieved through the addition of inhibitors.

[0081] The inventive stabilization of the distillation sump with inhibitors is therefore a basic requirement for successfully cleaning resin-based 3D printed molded parts in a cleaning device with continuous distillation. Example 6:

[0082] To further highlight the novel stabilization of the distillation sump of the cleaning apparatus, the experiment from Example 5 was repeated. This time, however, butyl lactate (65.6 g) was used as the solvent. A mixture of highly viscous photoreactive resin products (35.2 g) from Cubicure (Vienna, Austria) was dissolved in the solvent. In the first attempt, an unstabilized solution was heated to a sump temperature of 130°C at 50 mbar pressure, which polymerized completely after approximately two hours. Subsequently, the same quantity of resin mixture and solvent was stabilized with an additional 2.5 wt% each of pyrogallol and phenothiazine. As described in Example 5, three resin-coated components were again cleaned in the Soxhlet apparatus. After 24 hours, the inhibited sump was still liquid and thus stable, whereupon the successful experiment was terminated.The resin concentration in the sump varied between 35 and 49 wt% during this time, confirming the high efficacy of the inhibitor. As in Example 5, the inventive stabilization of the solvent contaminated with stereolithography resin in the purification apparatus was confirmed.

Claims

1. Device for cleaning components manufactured by means of a lithographic additive manufacturing process, comprising at least one cleaning chamber (1), at least two storage containers (2, 5) for a cleaning medium connectable to the cleaning chamber (1), and a distillation unit (4), whose inlet is connectable via a first line to the cleaning chamber (1) or to the storage containers (2, 5) and whose outlet is connectable via a second line to the cleaning chamber (1) or to the storage containers (2, 5), in order to supply resin-laden cleaning medium from the cleaning chamber (1) or the storage containers (2, 5) to the distillation unit (4) and simultaneously return regenerated cleaning medium from the distillation unit (4) to the cleaning chamber (1) or the storage containers (2), characterized in that the two storage containers (2, 5) are each connected to the cleaning chamber (1) via an inlet line and an outlet line to circulate the cleaning medium.

2. Device according to claim 1, characterized in that an overflow is provided from a first storage container (2) to a second storage container (5) and optionally an overflow is provided from the second storage container (2) to the distillation unit (4).

3. Device according to claim 1 or 2, characterized in that a vacuum pump (3) is connected to the cleaning chamber (1).

4. Device according to any one of claims 1 to 3, characterized in that one storage container (2) containing cleaning medium with higher resin concentration is arranged for coarse cleaning and another storage container (5) is arranged for fine cleaning with cleaning medium of higher purity.