Bragg-peak three-dimensional manufacturing with resins

#This invention is in the general area of manufacturing plastic products from organic resins. It is similar to three-dimensional printing, but instead of building up a structure by step-wise or continuously adding two-dimensional layers, this invention envisions building a three-dimensional part inside a resin (e.g., a viscous liquid or solid without support or a fluid liquid with pre-positioned supporting structures) through an application of ion beam technology such as currently used to treat cancer (e.g., proton beam therapy). This invention uses the unique properties of ion beams to deposit most of their energy at a position known as the “Bragg peak,” to initiate polymerization in a small selected volume of space (i.e., a 3-D pixel). These pixels combine to form the new plastic part, which may incorporate prefabricated and pre-positioned sub-parts.

#Currently, three-dimensional plastic parts are typically extruded, cast or machined. Within the last decade, the use of printing technology to build up three-dimensional parts from two-dimensional layers (known as “three-dimensional printing”) has become popular because it offers some flexibility in design and manufacturing, although it is inherently slow because one layer is built as a time. Typically, these printing techniques are used to cure polymer resins. Most commercial resins are cured by UV radiation that induces free radical curing of acrylic compounds (acrylates). Free radical curing systems are readily inhibited by free radical scavengers such as oxygen. Initiation of UV-curing is limited to a shallow depth depending on the absorption and transmission of photons (electromagnetic radiation) by the resin. This factor means that UV curing is normally not efficient for deeper layers of mixtures including opaque solids. Carbon® (Redwood, Calif.) has used these properties to develop a method for continuous liquid interface production (U.S. Pat. No. 9,498,920 B2 CLIP™) and other practitioners have developed less efficient step-wise technologies to create two-dimensional slices of objects that are layered into a three-dimensional part. These technologies are inherently slow (layer-by-layer) and require a moving stage upon which the plastic part is built and are not compatible with the use of solid fillers or reinforcing fibers within the resin.

#I am here disclosing a true “three-dimensional manufacturing” technique, which has much more flexibility than three-dimensional printing. It may also be much faster than 3-D printing because the product is not made up sequentially layer-by-layer. Moreover, the surface shape can be quickly defined and established; followed by curing the interior resin by mass heating after the defined part is removed from the excess resin.

#FIG. 1. This figure demonstrates the principle of Bragg peak activation of resin curing. A particle beam [2] enters a resin mixture [1] and initiates effective curing (polymerization) only at the Bragg peak (i.e., Bragg pixel) [3] where the LET density exceeds the threshold set by suppressing agents and conditions [4]. The concept is illustrated in the graph at the top which shows the typical profile of linear energy transfer (LET) [5] and the threshold for initiation of effective curing (polymerization) [6].

#FIG. 2. This embodiment show use of simultaneously applied ion beams from two sources [7] to fabricate a part [10] in contact with an inert part [8] introduced into the reaction medium [9]. The beams are being scanned independently from different directions to produce Bragg pixels [10] of preselected size of curing resin in a preselected order. This demonstrates the speed and flexibility of this form of “directed energy Three-Dimensional Manufacturing” relative to e.g., continuous liquid interface production (CLIP), casting, milling or extruding.

#FIG. 3. This embodiment shows ion beams from two independent sources [7] building a part [10] within a mesh [11] of (reinforcing) fibers in the reaction mixture [9]. Once, the resin is removed from the excess resin and completely cured, the unwanted fibers can be trimmed.

#The generation and application of ion beams is not within the scope of this invention; it is regarded as a well-developed tool (invented and developed for a different application) that can be adapted to produce protons or other ions of interest, accelerate the ions to very high velocities and guide them into a reaction mixture. It is also known that the depth of penetration of an ion beam into a target (i.e., a human being) or condensed phase (liquid or solid) can be calculated and adjusted by changing the velocity of the ions, or adding high-density or condensed phase shielding to the exterior of the target. The ion beam can be finely adjusted by electromagnetic effects on the beam and gross adjustments can be made by reorienting the target or the beam. Finally, the current electron beam technology includes the ability to quickly scan the beam and adjust the depth of penetration and to program exactly how much energy (actually “energy density” typically measured in Grays, 1 G=1 J/kg) will be delivered into a specifically defined three-dimensional volume (i.e., pixel). This tool is currently being used to selectively kill tumors in human beings while sparing adjacent healthy tissues.

#Here we will only refer to the “ion beam” [2 in FIG. 1] with the understanding that it can be rapidly adjusted and scanned [7 in FIG. 2] according to a pre-determined program to deliver a selected energy density (J/kg) into a pre-determined volume of virtually any shape inside a “reaction medium.” The Bragg peak (i.e., the point of maximum delivered energy density) [3 in FIG. 1] is scanned in three dimensions and each ion (or ion cluster) impact results in what we call a “three-dimensional pixel” [10 in FIG. 2 or 3] where free radical density is created and can initiate a polymerization chain reaction, which radiates outward. The rate and effective distance of spread of the free radical reaction (i.e., curing the resin) is limited by the presence of compounds (inhibitors) that terminate the chain reaction or conditions (e.g., temperature) that suppress the propagation rate. Thus, the size of the three-dimensional pixel of cured resin can be controlled. If the three-dimensional pixels are close enough to overlap, effective macroscopic curing of resins occurs. If these pixels are widely dispersed or very small, effective curing of a resin does not occur.

#The invention of interest here is the application of particle beams to curing resins to manufacture products. The chemistry is not significantly different from the chemistry of resin curing using UV light. What is novel and original is the use of proton beams to selectively polymerize/cure the resins in a three-dimensional pattern deep within the resin reaction mixture [FIG. 1, 2, or 3]. This pattern can be completely independent of a working surface, it can take on any shape, it can be formed in any sequence, it can be formed around inert inclusions [FIGS. 2 and 3], and it can be formed using multiple ions beams currently [FIGS. 2 and 3]. Moreover, ions beams can arrive at the same spot (Bragg peak) from different directions; thus, minimizing the energy density delivered to regions of the reaction mixture that are not intended for curing. This inventive method can be performed while concurrently applying other forms of energy (directed or undirected) to the resin/reaction mixture to facilitate formation/curing of the product.