Refrigerative Stereolithography Using Sol-Gel Transformable Photopolymer Resin and Direct Masking
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buried in and held by gel resin. This can extend the range of shapes that can be fabricated and improve fabrication accuracy. PhotopolymetizeALd nl V. aT scan Elevator
S_-
Liquid
(a)Supply liquid resin layer
(d)Lower elevator by layer thickness
Gel
,
,
(b)Cool and solidify layer
(e)Heat, melt and remove
(c) Photopolymerize layer selectively•
(f) Obtain fabcated object
non-photopolymeized resin
Figure1. Rejfigerative StereolithographyProcess * This work was done as a doctoral research
of the second author.
91 Mat. Res. Soc. Symp. Proc. Vol. 625 © 2000 Materials Research Society
Second, additional treatments for layers can easily be introduced. For example, we can draw some mask patterns directly on the surface of the gel layer. In this paper, we discuss and confirm the effectiveness and possibility of using such masks to avoid surplus growth only in the regions where it is unnecessary to improve height direction accuracy and resolution and to solidify the required section shape selectively using a lamp instead of laser scan patterns. SOL-GEL TRANSFORMABLE PHOTOPOLYMER RESIN In our previous study [1], we used a commercially available urethane-acrylate resin for the conventional stereolithography (SCR-500, JSR: Japan Synthetic Rubber Co., Ltd.) and a urethane-acrylate resin (KC 1026-8, JSR) which was specially prepared for obtaining improved temperature-viscosity characteristics. However, we needed to cool the resins SCR-500 and KC1026-8 to -50°C and -10C, respectively, to make them sufficiently solid. The problem with these low temperatures is that they result in inactive photopolymerization reaction, frost on the resin surface, and a large and complex cooling mechanism (e.g., that involving liquid nitrogen). As a resin more suitable for refrigerative stereolithography, a new sol-gel transformable photopolymer resin was composed of urethane-acrylate photopolymer resin and sol-gel transformable resin by Kuraray Co., Ltd. The sol-gel resin consists of iso-PMMA (polymethyl methacrylate) and syn-PMMA molecules. At a low temperature, iso- and syn-PMMA molecules become entangled and the resin is in the gel state. At a high temperature, the entangled molecules separate and the resin becomes a sol. This sol-gel transformation occurs sharply in a rather narrow temperature range and is thermally reversible. By adding this sol-gel transformable resin of 15 weight % to a urethane-acrylate liquid photopolymer resin UV 1214, a sol-gel transformable photopolymer resin (UV1214-15) was prepared by Kuraray Co., Ltd. This composed resin can be photopolymerized both in the sol and gel states. Note that solidification by photopolymerization occurs only by the photopolymer component, and sol-gel resin molecules remain as they are in the photopolymerized resin. 50000
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