3D Printing – Ernst Selbertinger, Frank Achenbach, Bernd Pachaly, Wacker Chemie AG
Abstract for “Method for producing silicone elastomer parts”
“Silicon Elastomer Articles are prepared using a 3-D printing process. Droplets of high-viscosity curable silicon are deposited onto a substrate layer after layer with independently spatially controlled nozzles. Then, the substrate is irradiated with independently spatially adjustable electromagnetic energy.
Background for “Method for producing silicone elastomer parts”
“1. “1.
“The invention is a process that generates shaped bodies from crosslinkable silicon compositions using electromagnetic radiation. This process is characterized by repeating precise placement of small amounts of crosslinkable silica compositions and crosslinking thereof with electromagnetic radiation.
“2. “2.
There are many processing options available for the production of shaped parts made from crosslinkable silicone rubber compounds. The consistency and mechanism for crosslinking the silicone rubber mixture can determine the method of producing shaped parts. This depends on how the mold is made. The properties of the shaped silicone parts (hardness, tensile, extensibility and color, among others) are determined by how they were made. The physical makeup of crosslinkable silicone rubber and the processing conditions (temperature and pressure) determine the properties of the shaped silicone part formed. These processes produce large quantities of shaped silicone parts that are largely isotropic in terms mechanical and optical properties.
The existing processes are becoming increasingly difficult when it comes to shaped silicone parts with complex geometry, different material compositions and/or variable properties. For example, the production of injection molds that are suitable for this purpose is becoming more difficult and costly. These types of requirements are common in the fields of exo-, endoprostheses, and particularly epitheses, such as artificial outer ears, where the softer and more difficult areas (skin and cartilage) blend continuously with one another. Additionally, complex structures such as those discovered from bionics cannot be achieved using conventional processing techniques. In addition, the general trend towards individualization and individual adaptations of commodity articles results in smaller unit numbers which reduces conventional processing’ efficiency. This is also true for the production of prototypes.
“Generative fabrication is becoming increasingly important for the production of shaped parts. Additive Manufacturing and 3D printing processes are two examples of many technologies that share a common feature. They involve an automated additive buildup layer by layer of the shaped part. (A. Gebhardt. Generative Fertigungsverfahren. Carl Hanser Verlag Munich 2013. All generative production methods require the representation of the geometry, and other properties (color, composition, etc.) of the desired shape body in digital 3D data sets. This can be understood as a virtual model. Computer-aided design (or 3D CAD) is a preferred method for modeling. 3D data can also be used to create a 3DCAD model. This could include data resulting from CT measurements (Computer Tomography), or MRT measurements(Magnetic Resonance Tomography). The 3D CAD data must be further enhanced with data specific to the material, process and fabricating unit. This is done by handing the data over via an interface in a suitable format to an additive manufacturing software (e.g. STL, CLI/SLC or PLY, VRML or AMF format). The software then generates virtual individual layers (slices) from the geometric information. It also takes into account the optimal orientation of the component within the construction space and support structures. This data allows for direct driving the machine (3D printer), which is used to perform generative fabrication.
“The software sequence is:
“Generative fabrication is available for many materials and combinations thereof (e.g. metals, plastics or ceramics, glasses).
“Overall it may be stated that the production of shaped rubber-elastic silicone bodies by the stereolithography-like processes above is unsuitable on account of the inadequacies recited. The noncrosslinked material that forms the shaped bodies in the aforementioned generative processes has one thing in common. It is not used in a selective manner on areas of a work surface or as a bath, but is instead present in other regions that do not form part of the shaped bodies. A part of the applied composition or part thereof can only be made a part of a shaped part by selective curing. The stereolithography process differs in that the crosslinkable composition is only placed at the locations where it will become part of the shaped parts. Crosslinking can then be done either selectively (by using a laser for example) or not (by using an areal irradiation lamp for example).
Extrusion is one way to achieve site-selective crosslinking. DE 10 2012 204 494A1 describes how to produce a primary silicone contact material that can be used for wound management. This production is possible using the 3D printing process. The primary contact material is a mesh or lattice that is created analogously to filament 3D printing by continuous extrusion using silicone rubber compositions via a nozzle, and then crosslinking.
“It is evident that none of the processes and apparatuses described in the prior art can produce high-quality, high-quality parts of silicone elastomers using a generative fabrication process.
“The object was to provide a generative manufacturing process and an apparatus that can be used therefor for the efficient production individualized, high quality, shaped silicone rubber parts without any of the drawbacks previously mentioned.”
“FIG. “FIG.
“FIG. “FIG.
“FIG. 3 shows another 3D article created by the inventive process.
“FIG. “FIG.
“DESCRIPTION OF PREFERRED EMBODIMENTS.”
“The layer-by-layer manufacturing of shaped silicone rubber parts (8) involves the following steps:
The invention uses microdroplet metering to benefit from the shear-thinning behavior of silicone rubber compositions. Due to the high shear rate in the metering device during the jetting-metering procedure, the viscosity such filler-containing silicone rubber compounds is greatly reduced and allows for the jetting of very fine microdroplets ((6)). The microdrop (6) is placed on the substrate (3) and its shear rate immediately drops. This causes its viscosity to rise again. The deposited drop (6) instantly becomes high viscosity and allows for the precise construction of three-dimensional structures.
“The spatially independent controllability of the jetting apparatus (1), the source and electromagnetic radiation (2), as well as the baseplate (3) is possible. This means that the apparatus in question can be moved site-selectively in all three directions in space, x, y, and z, in other words three-dimensionally.”
“In another embodiment, the drop (6) can be deposited and crosslinked or incipiently crossed (7) in operations that may be coupled or even synchronous.”
“The invention process is performed on a fabricating machine that contains at least these components:
“FIG. “FIG. 1” shows a diagrammatic illustration of a generative fabricating device that is used in the invention to produce silicone elastomer components (8). The reservoir (4) contains the silicone rubber composition that can be crosslinked by electromagnetic radiation. This reservoir is subject to pressure and connected via a line to a measuring nozzle (5). There may be devices that allow multicomponent silicone rubber compositions, or dissolved gases, to be mixed homogeneously and/or evacuated downstream from the reservoir (4). One (1) may have multiple jetting apparatuses (2) that can operate independently. This allows the construction of the shaped part from different silicone rubber compositions.
“The individual metering devices (5) can be placed in x, y, and z directions to allow precisely targeted deposition.
“To prevent or eliminate fouling the meteringnozzles (5), an automated metering-nozzle cleaner station may be added as shown in FIG. 1.”
“The jetting apparatuses (1) may also have temperature-setting units. This is to condition the rheological properties of silicone rubber compositions, and/or to use the reduction in viscosity by using elevated temperatures for jetting.
“If you are trying to make a shaped part ((8)) in which gas inclusions can be avoided, silicone rubber compositions should be degassed prior to being used. This can be done by applying a reduced pressure to the reservoir (4).
The entire unit shown in FIG. 1. may be placed in a vacuum chamber (or inert gas chamber) to eliminate UV-C radiation losses due to oxygen or prevent air inclusions in a shaped part ((8)).
Crosslinking (7) occurs for drops (6) made of deposited silicone rubber compound. It is done by one or more electromagnetic radiation source (2) (e.g. IR lasers. IR lamps. UV-VIS lasers. LED). These also have the ability to traverse in x, y, and z directions. Radiation sources (2) can include beam-widening and scanning systems, shutters, deflection mirrors, beam-widening units, beam-widening devices, beam-widening, beam-focusing, and beam-widening equipment. Crosslinking and deposition must be coordinated. This invention covers all possible options. For example, it may be necessary to first cover the area of the x,y work plane with silicone rubber drops (6), and then wait for leveling (coalescence), before areally irradiating this region and crosslinking it. For contouring, it may be a good idea to first solidify the area in the edges and then to incipiently crosslink the inner region with suitable shading. Individual drops may need to be incipiently or crosslinked after being placed to prevent them from running. In order to achieve complete crosslinking it may be prudent to either expose the entire work area to radiation during shape-part formation or to only briefly. This may allow for incomplete crosslinking (green force) which can in some circumstances lead to better adhesion between the layers. It will be important that the parameters that determine deposition or crosslinking be adjusted to each other as a function the crosslinking system, rheological characteristics and adhesion properties, as well as the materials used.
The silicone rubber compositions preferred in the invention crosslink through hydrosilylation reaction. This is an addition reaction between Si-bonded hydrogen and aliphatically unaturated groups that are preferably located on the silicone polymer. These silicone rubber compositions are well-known to the skilled individual, such as RTV-2 (2 part Room Temperature Vulcanizing), or LSR (Liquid Silicone Rubber) and are described in U.S. Pat. No. 3,884,866. These silicone rubber compositions are typically supplied in two components. One component contains the SiH-functional crosslinker, and the other the platinum catalyst. The platinum-catalyzed reaction occurs spontaneously at room temperature. It is possible to make one-component silicone rubber compositions by using inhibitory additives or specific platinum catalysts that are inert at room temperatures but can be activated thermothermally.
“In the process of the invention, addition-crosslinkable silicone rubber compositions can be activated thermally by IR radiation, by means of an (N)IR laser or an infrared lamp, for example.”
“There are many platinum catalysts that, in the absence light at room temperature, are almost inert but can be activated with UV/VIS radiation. This allows for rapid addition crosslinking at ambient temperature.”
The silicone rubber compositions that are most preferred for the invention process crosslink via UV-induced or UVVIS-induced addition reaction. The UV- and UV-VIS-induced crosslinking offers many advantages over thermal crosslinking. Because of its low thermal conductivity, the UV- or UV-VIS-induced crosslinking has many advantages. First, the intensity, time and location of UV-VIS radiation exposure can all be precisely sized. Second, the heating of the dropwise-deposited silicone rubber compound (and its subsequent cooling) will always be slowed down. Due to the high intrinsic thermal expansion coefficient of silicones, mechanical stresses that result from thermal crosslinking can adversely affect the dimensional integrity and cause distortions in the shape of the formed part. Another benefit of UV/VIS-induced additive crosslinking is the ability to produce multicomponent shaped pieces, such as hard/soft combinations, which in addition to the silicone elastomer, also contain a thermoplastic that prevents thermally induced warping.
“UV/VIS-induced addition-crosslinking silicone rubber compositions are described for example in DE 10 2008 000 156 A1, DE 10 2008 043 316 A1, DE 10 2009 002 231 A1, DE 10 2009 027 486 A1, DE 10 2010 043 149 A1 and WO 2009/027133 A2. Crosslinking is achieved by UV/VIS-induced activation a photosensitive hydrosilylation catalyst, with platinum complexes being preferred. In the technical literature there are numerous photosensitive platinum catalysts described which are largely inert in the absence of light and which can be converted into room-temperature-active platinum catalysts by irradiation with light having a wavelength of 250-500 nm. Examples thereof are (?-diolefin) (?-aryl)-platinum complexes (EP 0 122 008 A1; EP 0 561 919 B1), Pt (II) -?-diketonate complexes (EP 0 398 701 B1), and (?5-cyclopentadienyl) tri (?-alkyl) platinum( IV) complexes (EP 0 146 307 B1, EP 0 358 452 B1, EP 0 561 893 B1). MeCpPtMe3 is a particularly preferred compound, along with the complexes derived therefrom by substituting the groups on the platinum.
“Compositions that crosslink under UV or UV-VIS induction may be formulated as either one-component or multiple-component systems.”
“The rate at which UV/VIS-induced addition crosslinking occurs is dependent on many factors, including the nature and concentrations of the platinum catalyst, the intensity, wavelength and exposure time for the UV/VIS radiation and the composition of silicone rubber composition.
The platinum catalyst should be used in sufficient catalytic quantities to enable rapid crosslinking at room temperatures. The catalyst is typically used in a range of 0.1-200 ppm, depending on the Pt metal content relative to the entire silicone rubber composition.
The silicone rubber composition that undergoes addition-crosslinking under UV/VIS is cured by using light with wavelengths between 250-500 nm and more preferably 250-400, but more preferably 250-350 nm. To achieve rapid crosslinking, which is defined as a time of crosslinking at room temperature of no more than 20 minutes, preferably not less than 10 minutes, and more preferably 250-400 nm, and also radiation doses of 150 mJ/cm2 to 20,000mJ/cm2, 500 mJ/cm2 to 10,000 mJ/cm2. These output and dose values allow for area-specific radiation times of 2000 s/cm2 and no more than 8 ms/cm2.
“Another subject of the present invention is shaped silicone rubber parts (8), produced by the process.
“For a fabricating device of the invention according to FIG. 1 were commercially available components, which were then modified and harmonised with each other. The generative fabricating unit was a NEO3D printer from German RepRap GmbH (Germany), which was modified and adapted for the purposes of the experiments. To allow dropwise deposition of silicone rubber compositions of various viscosities to the work plate, the original thermoplastic filament metering device was removed from the NEO printer. It was replaced with a Vermes Microdispensing GmbH Otterfing, Germany jettingnozzle.
“Because it was not standardly equipped for the installation jetting nozzles, the NEO printer had to be modified.”
“The VERMES jetting nozzle has been integrated into the printer controller so that the trigger signal (start-stop signal) for the VERMES jetting nozzle could be activated by the G-code control on the NEO printer. A specific signal was saved in the G-code controller for this purpose. “The G-code control of computer switched the VERMES jettingnozzle on and off (start/stop of metering).
“To transmit the start-stop signal, the heating wire of the original filament heating nozzle of NEO printer was disconnected and connected to the Vermes jetting nozzle.”
“The other parameters of metering (metering frequency and rising/falling, etc.) were set by the MDC 3200+ microdispensing control unit.” The MDC 3200+ microdispensing controller unit was used to set the VERMES jetting device.
“The NEO printer could be controlled using a computer. Software:?RepitierHost? These were modified to control the movement of VERMES jetting nozzles in three directions. The trial speed of the modified NEO-printer is 0.01 m/s.
“Metering system”: The metering device used to measure the silicone rubber compositions was the MDV3200A microdispensing metering unit from Vermes Microdispensing GmbH. Otterfing (Germany), hereafter referred to as VERMES metering. It connected to the PC control unit and, via movable cable, to the nozzle. This allowed for setting the jetting metering parameters (rising/falling, open time, needle lift delay, open time, voxel size, air admission pressure at cartridge), distance, voxel dimension, nozzle diameter, nozzle, nozzle, nozzle. There are VERMES jetting devices with diameters up to 50, 100, 150 and 200?m. It was possible to place ultrafine silicone rubber dropslets in the nanoliter range, at any desired x or y position on the baseplate. The standard Vermes valve nozzle insert was a 200?m nozzle (nozzle insert No11-200).
“Reservoir vessels for silicone rubber composition were vertical 30ml Luerlock cartridges that were attached to the dispensing device to prevent liquid leakage and were then compressed with compressed air.
“The modified NEO printer was controlled by a PC and the VERMES system was metering using a?Repitier?Host? open-source software.”
“Radiation Sources:”
The BLUEPOINT irradiation device, which is based upon a 150 W high pressure mercury lamp, allows a UV-A intensity of approximately 13,200 mW/cm2 when set at 80%. It also has a timer setting range from 0.1 to 999.9 seconds.”
“The Omnicure R-200 radiometer was used to calibrate the BLUEPOINT radiation system. The BLUEPOINT irradiation systems have a maximum irradiation output output of 80%. This resulted in an irradiation output output of 13.200 mW/cm2.
“UV Chamber with Osram UV lamp”
“For off-line UV radiation of components, a UV chamber was used. It had a reflective interior finish and the following dimensions:
“Length 50 cm\nHeight 19 cm\nWidth 33 cm”
“The distance between fluorescent UV lamps and substrate was 16 cm.”
“Radiation source: UV lamp producing 36 watts of electrical output.”
“Osram Puritec L 36 W 2G11”
“Osram GmbH, Augsburg, Germany.”
“IR Radiation Source”
“For the IR (thermal) crosslinking, a short wave infrared module called IR-Spot from OPTRON GmbH Garbsen/Hannover (power consumption 150W) was used. The IR spot operates in the short-wave IR spectrum and has the advantage of a deep penetration by radiant energy. A focal spot with a diameter of 10mm is produced at the focal point, which has a focal length 50mm. The IR-Spot has an output adjuster that allows for online output adjustment during the printing process.
“EXAMPLES”
“The following examples serve to illustrate the invention, without limiting it.” The invention’s converted fabricating unit was used in all the cases.
“Conditioning the silicone rubber compounds: All silicone rubber compositions were devolatilized prior to processing. 100g of the composition was stored in an open PE container in a desiccator for three hours at 10 mbar pressure and room temperature. The composition was then dispersed in air-free mode into a 30ml cartridge with bayonet closing, and sealed using an appropriate sized plastic ejector piston. The Luerlock cartridge was then secured into the Vermes metering device’s vertical cartridge holder. This prevented liquid escape. A pressure piston applied compressed air at 3-8 bars to the upper cartridge side. The cartridge’s ejector piston prevents the air from entering the previously evacuated silicone rubber mixture.
All UV-sensitive silicone compositions were manufactured under yellow light (except light below 700nm), and devolatilized in the same way. Then, they were dispensed into light impervious Semco cartridges.
Table 2 shows the viscosity of silicone rubber compositions used to make the examples.
“Raw Materials and Silicone rubber Compositions Used:
“R1”: Vinyl-functional MQ silicon resin powder containing M, Mvinyl and Q units in anM:Mvinyl:Q ratio of 0.72 to 0.09: 1. It has a molecular mass Mw=5300g/mol, Mn=2400g/mol, and a vinyl content 70 mmol per 100g of silicone resin.
“R5: Methylhydrosiloxane-dimethylsiloxane copolymer having a molecular weight of Mn=1900-2000 g/mol and a methylhydrogensiloxy content of 25-30 mol %, available from Gelest, Inc. (65933 Frankfurt am Main, Germany) under the product name HMS-301.”
“R6: Methylhydrosiloxane-dimethylsiloxane copolymer having a molecular weight of Mn=900-1200 g/mol and a methylhydrogensiloxy content of 50-55 mol %, available from Gelest, Inc. (65933 Frankfurt am Main, Germany) under the product name HMS-501.”
“R11: (3-Glycidoxypropyl)trimethoxysilane, 98%, available from ABCR GmbH, Karlsruhe, Germany, CAS No. [2530-83-8].”
“Example 1”
“Example 2”
“A silicone composition was prepared”
“Subsequently in the absence of Light”
“were added to the mixture and devolatilized according to above. The mixture was then dispensed into light-impervious 30ml cartridges.”
“Example 3”
“A silicone composition was prepared”
“Subsequently in the absence of Light”
“were added to the mixture and devolatilized according to above. The mixture was then dispensed into light-impervious 30ml cartridges.”
Summary for “Method for producing silicone elastomer parts”
“1. “1.
“The invention is a process that generates shaped bodies from crosslinkable silicon compositions using electromagnetic radiation. This process is characterized by repeating precise placement of small amounts of crosslinkable silica compositions and crosslinking thereof with electromagnetic radiation.
“2. “2.
There are many processing options available for the production of shaped parts made from crosslinkable silicone rubber compounds. The consistency and mechanism for crosslinking the silicone rubber mixture can determine the method of producing shaped parts. This depends on how the mold is made. The properties of the shaped silicone parts (hardness, tensile, extensibility and color, among others) are determined by how they were made. The physical makeup of crosslinkable silicone rubber and the processing conditions (temperature and pressure) determine the properties of the shaped silicone part formed. These processes produce large quantities of shaped silicone parts that are largely isotropic in terms mechanical and optical properties.
The existing processes are becoming increasingly difficult when it comes to shaped silicone parts with complex geometry, different material compositions and/or variable properties. For example, the production of injection molds that are suitable for this purpose is becoming more difficult and costly. These types of requirements are common in the fields of exo-, endoprostheses, and particularly epitheses, such as artificial outer ears, where the softer and more difficult areas (skin and cartilage) blend continuously with one another. Additionally, complex structures such as those discovered from bionics cannot be achieved using conventional processing techniques. In addition, the general trend towards individualization and individual adaptations of commodity articles results in smaller unit numbers which reduces conventional processing’ efficiency. This is also true for the production of prototypes.
“Generative fabrication is becoming increasingly important for the production of shaped parts. Additive Manufacturing and 3D printing processes are two examples of many technologies that share a common feature. They involve an automated additive buildup layer by layer of the shaped part. (A. Gebhardt. Generative Fertigungsverfahren. Carl Hanser Verlag Munich 2013. All generative production methods require the representation of the geometry, and other properties (color, composition, etc.) of the desired shape body in digital 3D data sets. This can be understood as a virtual model. Computer-aided design (or 3D CAD) is a preferred method for modeling. 3D data can also be used to create a 3DCAD model. This could include data resulting from CT measurements (Computer Tomography), or MRT measurements(Magnetic Resonance Tomography). The 3D CAD data must be further enhanced with data specific to the material, process and fabricating unit. This is done by handing the data over via an interface in a suitable format to an additive manufacturing software (e.g. STL, CLI/SLC or PLY, VRML or AMF format). The software then generates virtual individual layers (slices) from the geometric information. It also takes into account the optimal orientation of the component within the construction space and support structures. This data allows for direct driving the machine (3D printer), which is used to perform generative fabrication.
“The software sequence is:
“Generative fabrication is available for many materials and combinations thereof (e.g. metals, plastics or ceramics, glasses).
“Overall it may be stated that the production of shaped rubber-elastic silicone bodies by the stereolithography-like processes above is unsuitable on account of the inadequacies recited. The noncrosslinked material that forms the shaped bodies in the aforementioned generative processes has one thing in common. It is not used in a selective manner on areas of a work surface or as a bath, but is instead present in other regions that do not form part of the shaped bodies. A part of the applied composition or part thereof can only be made a part of a shaped part by selective curing. The stereolithography process differs in that the crosslinkable composition is only placed at the locations where it will become part of the shaped parts. Crosslinking can then be done either selectively (by using a laser for example) or not (by using an areal irradiation lamp for example).
Extrusion is one way to achieve site-selective crosslinking. DE 10 2012 204 494A1 describes how to produce a primary silicone contact material that can be used for wound management. This production is possible using the 3D printing process. The primary contact material is a mesh or lattice that is created analogously to filament 3D printing by continuous extrusion using silicone rubber compositions via a nozzle, and then crosslinking.
“It is evident that none of the processes and apparatuses described in the prior art can produce high-quality, high-quality parts of silicone elastomers using a generative fabrication process.
“The object was to provide a generative manufacturing process and an apparatus that can be used therefor for the efficient production individualized, high quality, shaped silicone rubber parts without any of the drawbacks previously mentioned.”
“FIG. “FIG.
“FIG. “FIG.
“FIG. 3 shows another 3D article created by the inventive process.
“FIG. “FIG.
“DESCRIPTION OF PREFERRED EMBODIMENTS.”
“The layer-by-layer manufacturing of shaped silicone rubber parts (8) involves the following steps:
The invention uses microdroplet metering to benefit from the shear-thinning behavior of silicone rubber compositions. Due to the high shear rate in the metering device during the jetting-metering procedure, the viscosity such filler-containing silicone rubber compounds is greatly reduced and allows for the jetting of very fine microdroplets ((6)). The microdrop (6) is placed on the substrate (3) and its shear rate immediately drops. This causes its viscosity to rise again. The deposited drop (6) instantly becomes high viscosity and allows for the precise construction of three-dimensional structures.
“The spatially independent controllability of the jetting apparatus (1), the source and electromagnetic radiation (2), as well as the baseplate (3) is possible. This means that the apparatus in question can be moved site-selectively in all three directions in space, x, y, and z, in other words three-dimensionally.”
“In another embodiment, the drop (6) can be deposited and crosslinked or incipiently crossed (7) in operations that may be coupled or even synchronous.”
“The invention process is performed on a fabricating machine that contains at least these components:
“FIG. “FIG. 1” shows a diagrammatic illustration of a generative fabricating device that is used in the invention to produce silicone elastomer components (8). The reservoir (4) contains the silicone rubber composition that can be crosslinked by electromagnetic radiation. This reservoir is subject to pressure and connected via a line to a measuring nozzle (5). There may be devices that allow multicomponent silicone rubber compositions, or dissolved gases, to be mixed homogeneously and/or evacuated downstream from the reservoir (4). One (1) may have multiple jetting apparatuses (2) that can operate independently. This allows the construction of the shaped part from different silicone rubber compositions.
“The individual metering devices (5) can be placed in x, y, and z directions to allow precisely targeted deposition.
“To prevent or eliminate fouling the meteringnozzles (5), an automated metering-nozzle cleaner station may be added as shown in FIG. 1.”
“The jetting apparatuses (1) may also have temperature-setting units. This is to condition the rheological properties of silicone rubber compositions, and/or to use the reduction in viscosity by using elevated temperatures for jetting.
“If you are trying to make a shaped part ((8)) in which gas inclusions can be avoided, silicone rubber compositions should be degassed prior to being used. This can be done by applying a reduced pressure to the reservoir (4).
The entire unit shown in FIG. 1. may be placed in a vacuum chamber (or inert gas chamber) to eliminate UV-C radiation losses due to oxygen or prevent air inclusions in a shaped part ((8)).
Crosslinking (7) occurs for drops (6) made of deposited silicone rubber compound. It is done by one or more electromagnetic radiation source (2) (e.g. IR lasers. IR lamps. UV-VIS lasers. LED). These also have the ability to traverse in x, y, and z directions. Radiation sources (2) can include beam-widening and scanning systems, shutters, deflection mirrors, beam-widening units, beam-widening devices, beam-widening, beam-focusing, and beam-widening equipment. Crosslinking and deposition must be coordinated. This invention covers all possible options. For example, it may be necessary to first cover the area of the x,y work plane with silicone rubber drops (6), and then wait for leveling (coalescence), before areally irradiating this region and crosslinking it. For contouring, it may be a good idea to first solidify the area in the edges and then to incipiently crosslink the inner region with suitable shading. Individual drops may need to be incipiently or crosslinked after being placed to prevent them from running. In order to achieve complete crosslinking it may be prudent to either expose the entire work area to radiation during shape-part formation or to only briefly. This may allow for incomplete crosslinking (green force) which can in some circumstances lead to better adhesion between the layers. It will be important that the parameters that determine deposition or crosslinking be adjusted to each other as a function the crosslinking system, rheological characteristics and adhesion properties, as well as the materials used.
The silicone rubber compositions preferred in the invention crosslink through hydrosilylation reaction. This is an addition reaction between Si-bonded hydrogen and aliphatically unaturated groups that are preferably located on the silicone polymer. These silicone rubber compositions are well-known to the skilled individual, such as RTV-2 (2 part Room Temperature Vulcanizing), or LSR (Liquid Silicone Rubber) and are described in U.S. Pat. No. 3,884,866. These silicone rubber compositions are typically supplied in two components. One component contains the SiH-functional crosslinker, and the other the platinum catalyst. The platinum-catalyzed reaction occurs spontaneously at room temperature. It is possible to make one-component silicone rubber compositions by using inhibitory additives or specific platinum catalysts that are inert at room temperatures but can be activated thermothermally.
“In the process of the invention, addition-crosslinkable silicone rubber compositions can be activated thermally by IR radiation, by means of an (N)IR laser or an infrared lamp, for example.”
“There are many platinum catalysts that, in the absence light at room temperature, are almost inert but can be activated with UV/VIS radiation. This allows for rapid addition crosslinking at ambient temperature.”
The silicone rubber compositions that are most preferred for the invention process crosslink via UV-induced or UVVIS-induced addition reaction. The UV- and UV-VIS-induced crosslinking offers many advantages over thermal crosslinking. Because of its low thermal conductivity, the UV- or UV-VIS-induced crosslinking has many advantages. First, the intensity, time and location of UV-VIS radiation exposure can all be precisely sized. Second, the heating of the dropwise-deposited silicone rubber compound (and its subsequent cooling) will always be slowed down. Due to the high intrinsic thermal expansion coefficient of silicones, mechanical stresses that result from thermal crosslinking can adversely affect the dimensional integrity and cause distortions in the shape of the formed part. Another benefit of UV/VIS-induced additive crosslinking is the ability to produce multicomponent shaped pieces, such as hard/soft combinations, which in addition to the silicone elastomer, also contain a thermoplastic that prevents thermally induced warping.
“UV/VIS-induced addition-crosslinking silicone rubber compositions are described for example in DE 10 2008 000 156 A1, DE 10 2008 043 316 A1, DE 10 2009 002 231 A1, DE 10 2009 027 486 A1, DE 10 2010 043 149 A1 and WO 2009/027133 A2. Crosslinking is achieved by UV/VIS-induced activation a photosensitive hydrosilylation catalyst, with platinum complexes being preferred. In the technical literature there are numerous photosensitive platinum catalysts described which are largely inert in the absence of light and which can be converted into room-temperature-active platinum catalysts by irradiation with light having a wavelength of 250-500 nm. Examples thereof are (?-diolefin) (?-aryl)-platinum complexes (EP 0 122 008 A1; EP 0 561 919 B1), Pt (II) -?-diketonate complexes (EP 0 398 701 B1), and (?5-cyclopentadienyl) tri (?-alkyl) platinum( IV) complexes (EP 0 146 307 B1, EP 0 358 452 B1, EP 0 561 893 B1). MeCpPtMe3 is a particularly preferred compound, along with the complexes derived therefrom by substituting the groups on the platinum.
“Compositions that crosslink under UV or UV-VIS induction may be formulated as either one-component or multiple-component systems.”
“The rate at which UV/VIS-induced addition crosslinking occurs is dependent on many factors, including the nature and concentrations of the platinum catalyst, the intensity, wavelength and exposure time for the UV/VIS radiation and the composition of silicone rubber composition.
The platinum catalyst should be used in sufficient catalytic quantities to enable rapid crosslinking at room temperatures. The catalyst is typically used in a range of 0.1-200 ppm, depending on the Pt metal content relative to the entire silicone rubber composition.
The silicone rubber composition that undergoes addition-crosslinking under UV/VIS is cured by using light with wavelengths between 250-500 nm and more preferably 250-400, but more preferably 250-350 nm. To achieve rapid crosslinking, which is defined as a time of crosslinking at room temperature of no more than 20 minutes, preferably not less than 10 minutes, and more preferably 250-400 nm, and also radiation doses of 150 mJ/cm2 to 20,000mJ/cm2, 500 mJ/cm2 to 10,000 mJ/cm2. These output and dose values allow for area-specific radiation times of 2000 s/cm2 and no more than 8 ms/cm2.
“Another subject of the present invention is shaped silicone rubber parts (8), produced by the process.
“For a fabricating device of the invention according to FIG. 1 were commercially available components, which were then modified and harmonised with each other. The generative fabricating unit was a NEO3D printer from German RepRap GmbH (Germany), which was modified and adapted for the purposes of the experiments. To allow dropwise deposition of silicone rubber compositions of various viscosities to the work plate, the original thermoplastic filament metering device was removed from the NEO printer. It was replaced with a Vermes Microdispensing GmbH Otterfing, Germany jettingnozzle.
“Because it was not standardly equipped for the installation jetting nozzles, the NEO printer had to be modified.”
“The VERMES jetting nozzle has been integrated into the printer controller so that the trigger signal (start-stop signal) for the VERMES jetting nozzle could be activated by the G-code control on the NEO printer. A specific signal was saved in the G-code controller for this purpose. “The G-code control of computer switched the VERMES jettingnozzle on and off (start/stop of metering).
“To transmit the start-stop signal, the heating wire of the original filament heating nozzle of NEO printer was disconnected and connected to the Vermes jetting nozzle.”
“The other parameters of metering (metering frequency and rising/falling, etc.) were set by the MDC 3200+ microdispensing control unit.” The MDC 3200+ microdispensing controller unit was used to set the VERMES jetting device.
“The NEO printer could be controlled using a computer. Software:?RepitierHost? These were modified to control the movement of VERMES jetting nozzles in three directions. The trial speed of the modified NEO-printer is 0.01 m/s.
“Metering system”: The metering device used to measure the silicone rubber compositions was the MDV3200A microdispensing metering unit from Vermes Microdispensing GmbH. Otterfing (Germany), hereafter referred to as VERMES metering. It connected to the PC control unit and, via movable cable, to the nozzle. This allowed for setting the jetting metering parameters (rising/falling, open time, needle lift delay, open time, voxel size, air admission pressure at cartridge), distance, voxel dimension, nozzle diameter, nozzle, nozzle, nozzle. There are VERMES jetting devices with diameters up to 50, 100, 150 and 200?m. It was possible to place ultrafine silicone rubber dropslets in the nanoliter range, at any desired x or y position on the baseplate. The standard Vermes valve nozzle insert was a 200?m nozzle (nozzle insert No11-200).
“Reservoir vessels for silicone rubber composition were vertical 30ml Luerlock cartridges that were attached to the dispensing device to prevent liquid leakage and were then compressed with compressed air.
“The modified NEO printer was controlled by a PC and the VERMES system was metering using a?Repitier?Host? open-source software.”
“Radiation Sources:”
The BLUEPOINT irradiation device, which is based upon a 150 W high pressure mercury lamp, allows a UV-A intensity of approximately 13,200 mW/cm2 when set at 80%. It also has a timer setting range from 0.1 to 999.9 seconds.”
“The Omnicure R-200 radiometer was used to calibrate the BLUEPOINT radiation system. The BLUEPOINT irradiation systems have a maximum irradiation output output of 80%. This resulted in an irradiation output output of 13.200 mW/cm2.
“UV Chamber with Osram UV lamp”
“For off-line UV radiation of components, a UV chamber was used. It had a reflective interior finish and the following dimensions:
“Length 50 cm\nHeight 19 cm\nWidth 33 cm”
“The distance between fluorescent UV lamps and substrate was 16 cm.”
“Radiation source: UV lamp producing 36 watts of electrical output.”
“Osram Puritec L 36 W 2G11”
“Osram GmbH, Augsburg, Germany.”
“IR Radiation Source”
“For the IR (thermal) crosslinking, a short wave infrared module called IR-Spot from OPTRON GmbH Garbsen/Hannover (power consumption 150W) was used. The IR spot operates in the short-wave IR spectrum and has the advantage of a deep penetration by radiant energy. A focal spot with a diameter of 10mm is produced at the focal point, which has a focal length 50mm. The IR-Spot has an output adjuster that allows for online output adjustment during the printing process.
“EXAMPLES”
“The following examples serve to illustrate the invention, without limiting it.” The invention’s converted fabricating unit was used in all the cases.
“Conditioning the silicone rubber compounds: All silicone rubber compositions were devolatilized prior to processing. 100g of the composition was stored in an open PE container in a desiccator for three hours at 10 mbar pressure and room temperature. The composition was then dispersed in air-free mode into a 30ml cartridge with bayonet closing, and sealed using an appropriate sized plastic ejector piston. The Luerlock cartridge was then secured into the Vermes metering device’s vertical cartridge holder. This prevented liquid escape. A pressure piston applied compressed air at 3-8 bars to the upper cartridge side. The cartridge’s ejector piston prevents the air from entering the previously evacuated silicone rubber mixture.
All UV-sensitive silicone compositions were manufactured under yellow light (except light below 700nm), and devolatilized in the same way. Then, they were dispensed into light impervious Semco cartridges.
Table 2 shows the viscosity of silicone rubber compositions used to make the examples.
“Raw Materials and Silicone rubber Compositions Used:
“R1”: Vinyl-functional MQ silicon resin powder containing M, Mvinyl and Q units in anM:Mvinyl:Q ratio of 0.72 to 0.09: 1. It has a molecular mass Mw=5300g/mol, Mn=2400g/mol, and a vinyl content 70 mmol per 100g of silicone resin.
“R5: Methylhydrosiloxane-dimethylsiloxane copolymer having a molecular weight of Mn=1900-2000 g/mol and a methylhydrogensiloxy content of 25-30 mol %, available from Gelest, Inc. (65933 Frankfurt am Main, Germany) under the product name HMS-301.”
“R6: Methylhydrosiloxane-dimethylsiloxane copolymer having a molecular weight of Mn=900-1200 g/mol and a methylhydrogensiloxy content of 50-55 mol %, available from Gelest, Inc. (65933 Frankfurt am Main, Germany) under the product name HMS-501.”
“R11: (3-Glycidoxypropyl)trimethoxysilane, 98%, available from ABCR GmbH, Karlsruhe, Germany, CAS No. [2530-83-8].”
“Example 1”
“Example 2”
“A silicone composition was prepared”
“Subsequently in the absence of Light”
“were added to the mixture and devolatilized according to above. The mixture was then dispensed into light-impervious 30ml cartridges.”
“Example 3”
“A silicone composition was prepared”
“Subsequently in the absence of Light”
“were added to the mixture and devolatilized according to above. The mixture was then dispensed into light-impervious 30ml cartridges.”
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