FIELD OF THE INVENTION

The present invention concerns additive manufacturing resins, methods of making and using the same, and products produced therefrom.

BACKGROUND OF THE INVENTION

A group of additive manufacturing techniques sometimes referred to as “stereolithography” create a three-dimensional object by the sequential polymerization of a light polymerizable resin. Such techniques may be “bottom-up” techniques, where light is projected into the resin onto the bottom of the growing object through a light transmissive window, or “top-down” techniques, where light is projected onto the resin on top of the growing object, which is then immersed downward into the pool of resin.

The recent introduction of a more rapid stereolithography technique known as continuous liquid interface production (CLIP), coupled with the introduction of “dual cure” resins for additive manufacturing, has expanded the usefulness of stereolithography from prototyping to manufacturing (see, e.g., U.S. Pat. Nos. 9,211,678; 9,205,601; and 9,216,546 to DeSimone et al.; and also J. Tumbleston, D. Shirvanyants, N. Ermoshkin et al., Continuous liquid interface production of 3D Objects,Science347, 1349-1352 (2015); see also Rolland et al., U.S. Pat. Nos. 9,676,963, 9,453,142 and 9,598,606). These developments have generated a need for a greater variety of resins with properties appropriate for a greater variety of additively manufactured products.

SUMMARY OF THE INVENTION

Some dual cure additive manufacturing resins contain (meth)acrylate blocked polyurethanes, or “ABPUs,” which are themselves produced with bismuth catalysts. Unfortunately, the bismuth catalysts can cause resins to become hazy over time, as the catalyst interacts with water and (apparently) precipitates.

One solution is to reduce the amount of residual water in the resin. However, reducing residual water to less than 300 parts per million (ppm) is technically difficult and potentially expensive.

Another approach is to switch from a bismuth catalyst to a tin catalyst. However, tin catalysts leave residual tin in resins produced therefrom, and for some uses, tin is unacceptable in the final product. Residual tin in final parts can also result in accelerated ester group hydrolysis over time, decreasing the long-term durability, particularly exterior durability.

Additionally, both bismuth and tin catalysts are known for catalyzing the isocyanate-water reaction, resulting in high molecular weight ABPUs with larger polydispersity indices and is undesired in some circumstances.

A further problem is that the catalyst used to make the ABPU can itself catalyze the reaction of a dual cure resin containing an ABPU with polyols and/or polyamines in the resin (e.g., when “A” and “B” precursor resins are combined), increasing the viscosity of the resin, and consequently decreasing its “printability” during additive manufacturing.

We have unexpectedly found that zirconium catalysts can be used to make an ABPU, which can in turn be used to make precursor resins that have substantially reduced viscosities than those prepared by tin catalysts, even under low water content conditions, resulting in lower dual cure resin viscosities, thus improving handling and printability. Additionally, when the zirconium-based ABPU is combined with a polyol and/or polyamine, the resin maintains a lower viscosity over the time of the printing process, in spite of the residual zirconium catalyst contained therein.

Accordingly, aspects of the present invention include: methods of making ABPUs with zirconium catalysts, dual cure resins containing ABPUs and zirconium catalysts, methods of using the same in additive manufacturing, and products made therefrom.

The foregoing and other objects and aspects of the present invention are explained in greater detail in the drawings herein and the specification set forth below. The disclosures of all United States patent references cited herein are to be incorporated herein by reference.

