Polymerization-Stereolithography

Rapid Prototyping Model of Power Saw Cabinet Part as seen in Figures 6 and 7. Using the Stereolithography technique the part was modelled from a polymere. 

As an example stereolithography is a 3-D rapid process that produces automatically simple to very complex shaped models in plastic. Basically it is a method of building successive layers across sections of pho-topolymerized plastics on top of each other until all the thin printed layers can be joined together to form a whole product. The chemical key to the process, photopolymerization, is a well established technology in which a photo initiator absorbs UV energy to form free radicals that then initiate the polymerization of the liquid monomers. The degree... 

Rapid prototyping (or stereolithography or 3D object curing) is a photochemical process used to produce solid 3D objects such as models, masters or patterns of any shape, directly from a design generated on a computer. The computer is used to control the illumination system that builds up the object, usually by a rapid polymerization process. An important part of the design is that the object is sectioned... 

Stereolithography is simple in concept and it provides great economies for the design lab as well as for the modeling process. It also provides previously unrecognized challenges for the polymer photochemist, for it is entirely a laser-initiated technology, and the polymerization reactions take place to depths below a finitely thin surface layer. 

In stereolithography the positions of polymerization x and y are controlled by a mirrored scanner which reflects the laser onto the surface of the to-be-polymerized monomer at a point x,y and the z dimension is determined by the position of the elevator, as shown in Figure 5. During the polymerization z, the depth to which reaction occurs, is held constant through the use of a UV photoinitiator that bleaches either not at all or very slowly, relative to the rate of polymerization. 

Our use of bleachable photoinitiators to carry out polymerization at depth opens the possibility of controlling the vertical dimension photochemically rather than mechanically. We have used the photoreduction of Eosin by triethanolamine to sensitize the polymerization of multifunctional acrylates to demonstrate the principle. Irradiation is carried out at 514 nm with an Ar+ laser having a beam diameter of 1.4 mm. The volume of sample irradiated is a small fraction of the total, simulating the conditions found in stereolithography. Because of bleaching of the photoinitiator, the irradiation generates... 

Although, in contrast to free radical polymerizations, cationic polymerizations are unaffected by O2, their importance is somewhat limited by the scarcity of appropriate macromolecules and suitable photoinitiators [3]. However, this does not apply to the photopolymerization of low molar mass epoxides (see Section 10.3). In this context, applications of photo-cross-linked epoxides in various fields such as stereolithography, volume holography, and surface coating are notable [16]. 

Laser patterning is another writing technique whereby a laser is used to directly expose or polymerize a material. A common application is stereolithography where a reservoir of UV-curable polymer is selectively exposed to a UV laser to fabricate complex three-dimensional (3D) structures in a layer-by-layer fashion. For each layer, the laser beam traces a cross section of the part on the surface of the UV-curable polymer. Exposure to UV laser solidifies the pattern traced on the resin and adheres it to the layer below. 

The low polymerization shrinkage of cycloolefins which is typically <5% (e.g. ca. 4% for DCPD polymerization), compared with >10% for acrylate and methacrylate polymerization, makes PROMP systems attractive for stereolithography or dental applications. Indeed we could formulate stereolithographic resins, which were laser cured by PROMP. However, the lack of an appropriate quenching mechanism (once initiated, the polymerization continues even in the absence of light and leads finally to... 

Finally, it is also worth noting that the polymerization of FA to PFA can be achieved using UV radiation. The UV-photopolymerization of FA has been investigated for its potential appUcation as a resin for stereolithography [69, 70]. As with conventional RIM, UV-RIM requires low viscosity precursors, and hence FA, which is a clear Uquid of low viscosity at room temperature, lends itself to this appUcation. 

Stereolithography (SL) uses a semp similar to SLS, it, a computer-assisted laser source over a platform. In SL, though, the laser is used to induce curing of a liquid layer of polymer resin via photopolymerization. The platform then moves downward together with the first cured layer, allowing for fresh liquid resin to flow over the first cured layer. The process then repeats, with each new layer cured onto the previous layer. Once the SL process is complete, the scaffold is rinsed in solvent to remove the uncured resin. Then, the scaffold can be postcured to increase the degree of polymerization and the mechanical properties. ... 

Optical fabrication processes snch as stereolithography (SLA) employ light energy for photocrosslinking the prepolymers. Different optical-based AM techniques used for various cells encapsulation are shown in Table 8.4. SLA is a typical one photon polymerization (IPP) process where an initiator absorbs a photon with a short wavelength through linear absorption [3, 97, 98]. This in turn initiates polymerization process near the surface of a photocurable polymer. Thus, IPP is a planar process... 

FDM, fused deposition modeling SLA, stereolithography pSLA, micro streolithography SLS, selective laser sintering 1PP/2PP, one/ two photon polymerization. 

Zhang X, Jiang XN, Sun C. Micro-stereolithography of polymeric and ceramic microstructures. Sensors Actuators A Phys 1999 77 149-156. 

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