Rapid prototyping resin compositions
A resin composition suited for rapid prototype is provided comprising an actinic energy radiation-curable silicone composition, an actinic energy radiation-sensitive polymerization initiator, and an actinic energy radiation absorber. The resin composition experiences little viscosity buildup and maintains fluidity during long-term storage at elevated temperature, and is effective in rapid prototyping or shaping by stereolithography using any actinic energy radiation.
This invention relates to a resin composition suitable for use in rapid prototyping or stereolithography technique to form three-dimensional objects having improved rubber physical properties.
Recently, a technique of optically forming a three-dimensional object from a photo-curable liquid resin composition on the basis of data output from a three-dimensional CAD system is on widespread use because the desired three-dimensional object can be manufactured at satisfactory dimensional precision without a need for molds or the like. This technique is broadly referred to as rapid prototyping and specifically as stereolithography. With respect to this technique, JP-A 56-144478 (Kodama) disclosed a method of forming a three-dimensional object by supplying a required amount of optical energy to a photo-curable resin, and JP-A 60-247515 established a practically acceptable method.
A typical method of optically manufacturing a three-dimensional object involves selectively irradiating an ultraviolet laser beam to the surface of liquid photo-curable resin contained in a vat under the control of a computer to harden the photo-curable resin so that a photo-cured resin layer having a predetermined thickness is obtained, then supplying a layer of liquid photo-curable resin onto the cured resin layer and then likewise irradiating an ultraviolet laser beam to the liquid photo-curable resin layer to form a cured resin layer contiguous to the previous one, and repeating the laminating operations until a desired three-dimensional object is obtained. Great attention has recently been paid to this rapid prototyping technique because a three-dimensional object of complex configuration can be formed with ease and within a relatively short time.
To actinic energy radiation-curable resin compositions for use in the rapid prototyping are imposed many requirements including high cure sensitivity to actinic energy radiation, good resolution of a shaped object, high precision of shaping, a minimal volume shrinkage factor upon curing, good mechanical properties of cured product, good self-adherence, good curing properties in an oxygen-containing atmosphere, a low viscosity, resistance to water or moisture, minimal absorption of water or moisture with time, and dimensional stability. Prior art resin compositions known to be used in the rapid prototyping include photo-curable acrylate resin compositions, photo-curable urethane-acrylate resin compositions, photo-curable epoxy resin compositions, photo-curable epoxy-acrylate resin compositions, and photo-curable vinyl ether resin compositions.
There is a need for resins which when processed by the rapid prototyping technique, exhibit “rubber-like property,” that is, the nature that they easily undergo deformation, without rupture, under an applied stress and resume the original shape after the stress is relieved. However, the structures obtained by curing these resins are basically rigid and exhibit the nature that they fail when a stress above a certain level is applied.
A number of materials that exhibit rubber elasticity independently of photo-curing are used in the industry. Typical examples include ethylene-propylene rubber, butadiene rubber, polyurethane rubber, silicone rubber, and fluoro-rubber. However, the resin which cures into a practically acceptable state upon exposure to actinic energy radiation is limited to the silicone rubber.
Although the compositions described in these patents cure upon exposure to actinic energy radiation, their cure rate is yet too slow to apply to the stereolithography so that they could not be used in practical rapid prototyping. Even when they are cured to completion with the time taken therefor being neglected, the resulting rubber model will become embrittled shortly and exhibit no longer rubber elasticity. It would be desirable to have a resin which is amenable to the rapid prototyping or stereolithography and exhibits and maintain rubber elasticity.
An object of the present invention is to provide a rapid prototyping resin composition of the actinic energy radiation cure type, which has improved storage stability and aging stability prior to exposure to actinic energy radiation, experiences little viscosity buildup during long-term storage at elevated temperature, has high cure sensitivity to actinic energy radiation, typically light, and when exposed to actinic energy radiation, produces in a smooth and efficient manner a cured part which has improved dimensional precision, shaping precision, water resistance, and moisture resistance, and exhibits stable rubber elasticity over a long term, especially elastomeric physical properties as demonstrated by an elastic recovery ratio of at least 80% after elongation of at least 100%.
The inventors sought for materials which exhibit rubber physical properties that lend themselves to rapid prototyping or stereolithography. We have found that a silicone resin composition of the actinic energy radiation cure type, especially a silicone rubber (i.e., organopolysiloxane elastomer) based material comprising an alkenyl-containing organopolysiloxane, a mercapto-containing organopolysiloxane, and preferably an alkenyl-containing MQ resin is an effective rapid prototyping resin, and that an actinic energy radiation-curable resin composition obtained by blending therewith an actinic energy radiation-sensitive polymerization initiator (especially radical polymerization initiator) and an actinic energy radiation absorber is amenable to shaping using actinic energy radiation, typically rapid prototyping or stereolithography. Although the resin composition has high cure sensitivity to actinic energy radiation and rapidly cures when exposed to actinic energy radiation, the resin composition is easy to handle in that it has improved storage stability and aging stability, and when stored for a long time, even at elevated temperature, experiences little viscosity buildup and maintains a flowable state compatible with rapid prototyping.
Upon exposure to actinic energy radiation, the resin composition cures into a photo-cured or rapid prototype part which has improved resolution, shaping precision, dimensional precision, mechanical properties and outer appearance, and among the mechanical properties, exhibits improved rubber elasticity as demonstrated by an elastic recovery ratio of at least 80% after elongation of at least 100% which has never been achieved with prior art resins.
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