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Light-Sensitive Materials: Silver Halide Emulsions, Photoresist, and Photopolymers
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
Sergio Calixto, Daniel J. Lougnot, Izabela Naydenova
Photopolymers are used in the fabrication of three-dimensional (3D) micro- and nano-structures like microoptical components, artificial scaffolds, microfluidic devices and more. Different methods have been used to make the structures, for example Direct Laser Writing (DLW), two-photon photopolymerization (TPP) and structuring to mention but a few. An example of Direct-Write Lithography (DWL) has been mentioned before in the section “Waveguides” [357]. Besides this work, reference [368] describes three methods to make micro-tube arrays. These are Direct Laser Writing (DLW), Optical Vortices (OVs) and Holographic Lithography. A femtosecond laser was used generating 300 fs pulses at 1030 µm (fundamental) and 515 µm (second harmonic). Three different configurations were used, one for each of the writing methods. The material used was hybrid organic–inorganic Zr - containing sol–gel phototoresist SZ 2080. Two types of initiators were used. The photo–polymerization reaction was induced via nonlinear absorption. With these methods, micro-tubes were fabricated with different sizes. Diameter of the micro-tubes was about 10 µm with heights of about several tenths of microns.
A Design Sociotechnical Making of 3D Printing
Published in Steinar Killi, Additive Manufacturing, 2017
The liquid photopolymer used in the fabrication process is sensitive to light and can be highly toxic, requiring special care when preparing the process. Upon contact with a UV laser, a thin layer of liquid is solidified to the fabrication bed (Fig. A.7). Although there are several principles for the fabrication process, they all have in common that the UV laser cures a complete layer before the fabrication bed moves in preparation for the next layer to be fabricated. The object either emerges from the vat of liquid or is gradually submerged into it. Between the curing of each layer, surface tension between the liquid and the solidified polymer is broken by either tilting the vat or sweeping over the most recently fabricated layer with a paddle. Either way, the object that is being made requires a set of support structures that make the parts stick to the fabrication bed, as well as allowing for overhangs to be constructed.
Additive Manufacturing of Polymers for Biomedical Applications
Published in Atul Babbar, Ankit Sharma, Vivek Jain, Dheeraj Gupta, Additive Manufacturing Processes in Biomedical Engineering, 2023
AM parts are increasingly being used in the field of dentistry [61]. Five AM processes are commonly used for 3D printing dental items, and these are vat polymerization technique, digital light processing, polymer jetting, laser stereolithography and FDM [12]. The vat polymerization technique can be utilized in implant dentistry [6]. Vinyl polymers are widely used for dentistry because of their tunable properties. Many of them are biocompatible and nondegradable, which are prerequisites for dental implants. In the 3D printing of dental implants, vinyl polymers are widely used in sintering (e.g., SLS) or photopolymerization (e.g., stereolithography). Photopolymers are composed of a monomer, an oligomer and a photo-initiator. The curing effect of the photopolymer depends on wavelength, the power of light and radiation time [62]. Other polymers used in dental 3D printing are polyesters (such as polycaprolactone, polycarbonate, polylactic acid) and polystyrene (such as polystyrene and acrylonitrile butadiene styrene). The AM of polymers in dental applications can be completed in different ways. Some of the application has been depicted in Figure 6.6. The material selection for AM dental application is crucial. The materials should be biocompatible and mechanically stable with optimum postprocessing requirements [12]. Other applications of 3D-printed polymers in dental fields include the healing of periodontal defects using guided tissue regeneration, prosthodontics crowns and bridges for provisional and fixed dental restoration and the fabrication of removable prostheses, orthodontic mini screws and others [22, 31, 61].
In search for classification and selection of spare parts suitable for additive manufacturing: a literature review
Published in International Journal of Production Research, 2020
Casper Selmer Frandsen, Martin Mathias Nielsen, Atanu Chaudhuri, Jayanth Jayaram, Kannan Govindan
Stereolithography (SLA) and Direct Light Processing (DLP): Vat polymerisation is a process in which a liquid photopolymer in a vat is selectively cured by light activated polymerisation. SLA uses a photosensitive monomer resin as well as a UV laser to build parts layer by layer. It uses mirrors known as galvanometers to rapidly aim a laser beam across a vat. The laser beam solidifies the pattern by tracing the cross-section of the part on the surface on the liquid. After solidification of each layer, the supporting foundation beneath the part is moved down to cover the part with a new layer of resin, where a new layer is solidified by the UV laser. SLA creates a good surface finish, and when the object is complete, supporting materials must be removed manually. Drawbacks of this technology are relatively small build chambers, high cost of the photopolymer, and limited compatible materials. DLP uses a similar method but uses a digital light projector screen to flash a single image of each layer at once. Thus, it can have faster print times compared to SLA. SLA and DLP use thermoset photopolymers to produce the parts. These technologies produce dimensionally accurate parts with high details, intricate features and accurate tolerances. Its primary applications are in jewellery, dental and hearing aids industries. Recent technological development in vat polymerisation is Continuous Direct Light Processing Method which uses a continuous upward motion of the build plate but can work with specific photopolymers (Redwood, Schoffer, and Garrett 2018).
Occupational exposure to gaseous and particulate contaminants originating from additive manufacturing of liquid, powdered, and filament plastic materials and related post-processes
Published in Journal of Occupational and Environmental Hygiene, 2019
Antti J. K. Väisänen, Marko Hyttinen, Sampsa Ylönen, Lauri Alonen
The most common method used in consumer 3D printers is ME, where solid plastic filament is extruded through a heated nozzle layer-by-layer. Filament melts as it is forced through the nozzle, but cools down and hardens quickly, forming the solid printing layer. ME printing does not necessarily require any post-processing other than object removal from the printing platform. In the VP method, photopolymer resin is hardened selectively layer-by-layer with light, usually UV-laser. This method typically requires post-processing where excess photopolymer is dissolved from the object’s surface. In the PBF method, the machine’s powder feeding system spreads thin layers of powder upon each other, which are joined together selectively by laser. Objects must be unloaded from the powder bed and excess powder must be washed from the objects in post-processing. In the MJ method, thin layers of photopolymer resin are selectively jetted layer-by-layer and hardened with UV-light. Like in the VP method, solvents or techniques such as ultrasound treatment must be used to wash away excess material. MJF is a hybrid method, where the machine’s chamber is heated almost up to the melting point of the used powder material. Binding chemical, e.g., ink is jetted selectively on the powder. Binder increases the energy absorption and melts the powder, whereafter a new layer of powder is spread by the feeding system. Like in PBF, MJF manufactured objects must be unloaded and washed in a similar way. Table 1 presents the machine-material combinations used in this study as well as facility descriptions by manufacturing method.
Potential occupational hazards of additive manufacturing
Published in Journal of Occupational and Environmental Hygiene, 2019
Gary A. Roth, Charles L. Geraci, Aleksandr Stefaniak, Vladimir Murashov, John Howard
Potential hazards in these processes emerge from the photopolymer resin itself, which may include volatile or toxic elements and compounds such as antimony, acrylates, and epoxies.[14] Exposures are possible in operation, support processes, and post-processing. Exposures to potentially hazardous chemicals in post processing, such as those used for dissolving support structures, is also possible. Ultraviolet light sources are potentially hazardous as well.[35]