Patent Publication Number: US-2022235224-A1

Title: Laser activated thermoset powder bed printing

Description:
TECHNICAL FIELD 
     This disclosure relates to three-dimensional printing, more particularly with three-dimensional printing using powder beds. 
     BACKGROUND 
     Three-dimensional manufacturing techniques include many different types of manufacturing including 3D printing, selective laser sintering (SLS), etc. Palo Alto Research Center (PARC) has developed a body of work around linked particle networks. These networks typically comprise polymers with functionalized particles directly linked into a linked particle network. This may involve highly loaded particles, such as those that have high contents of graphene. Liquid inks do not generally work well with higher amount of material, making the use of liquid inks prohibitive. Using solid particles may alleviate that issue. 
     In laser sintering applications, such as laser based powder bed printing, thermoplastic materials undergo laser treatment that causes the particles to bond together, but they do not crosslink. 
     SUMMARY 
     According to aspects illustrated here, there is provided a composition of matter including macroparticles comprising particles of one or more continuous phase matrix materials and functionalized microparticles contained at least partially in the one or more matrix material. 
     According to aspects illustrate here, there is provided a method of manufacturing including producing macroparticles comprising a continuous phase thermoset matrix material mixed with a thermal initiator, depositing a layer of the matrix material onto a powder bed, applying a focused heat source to the layer of matrix material to selectively cure portions of the layer, repeating the depositing and applying until a final shape is formed, and removing uncured powder from the final shape. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a diagram of an embodiment of a composition of matter. 
         FIG. 2  shows a diagram of an embodiment of particles with microparticles and filler particles. 
         FIG. 3  shows a diagram of an alternative embodiment of a macroparticle. 
         FIG. 4  shows a flowchart of a method of manufacturing a composite material. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The embodiments here involve a composition of matter and use of that composition in a manufacturing process. As used here, the term “continuous phase” material, or “continuous phase matrix material” means a material that acts as a polymer matrix, with or without particles dispersed within it. The macroparticles may be referred to comprising “one or more” particles, which means that the macroparticles may comprise one or more materials in a mixture of macroparticles, or that the particles themselves may comprise two different materials. 
       FIG. 1  shows an embodiment of a composition of matter. In one embodiment, the composition of matter  10  may comprise particles such as  12  and  14  of two different materials. Each particle of the composition of matter may include at least one type of functionalized microparticles contained at least partially in the one or more matrix material. As used here, “at least partially contained” means that the functionalized microparticles reside within the matrix material or some portion of the functionalized microparticles resides within the matrix material. 
       FIG. 2  shows the particles of the matrix materials that make up the macroparticles. The microparticles, such as  16  and  18 , serve to provide some sort of functionality to the macroparticles, allowing them to form linked particle network bonds to others of the particles, resulting in stronger bonds than just heat cured bonds. Macroparticles  12  and  14  may have different microparticles or combinations of microparticles. 
     The matrix materials making up the macroparticles may be one of several different materials. Referring to  FIG. 1 , the particles  12  may be one material and particles  14  may be of another. One or the other of the differing particles may comprise an initiator that starts the cross linking reaction. The initiator may comprise a thermal initiator, thermal radical initiator, thermal cationic initiator, photo radical initiator, and photo anionic initiator. 
     The matrix materials may comprise one of many materials including amines, epoxies, and solid monomers in combination or not with one of the initiators mentioned above. If the one or more matrix materials comprise a solid monomer and an initiator, the solid monomer may comprise the bulk of the macroparticles, such as up to 95 wt % with the initiator comprising at least 5 wt %. 
     If one of the matrix materials comprises an amine, for example, the functionalized materials may comprise amines, epoxies, and graphene. Similarly, if one or more of the matrix materials comprises an epoxy, the microparticles may comprise an epoxy or functionalized graphene. 
     Examples may include: one or matrix materials comprising an amine and the functionalized microparticles comprise amine functionalized particles; the one or more matrix materials comprises an epoxy and the functionalized particles comprises epoxy functionalized particles; the one or more matrix materials comprise an amine and the functionalized microparticles are functionalized graphene; and the one or more matrix materials comprises an epoxy and the microparticle comprises functionalized graphene. 
     In some embodiments, the one or more matrix materials may comprises two solids that occur in combination. These may include a solid amine and a solid epoxy, solid silicone part A and part B, solid nylon part A and part B, and thermoplastic polyurethane part A and part B. 
     A further example may include a composition of matter where the one or more matrix materials comprise an amine with amine-reacted fluorographene (ARFG) microparticles, and an epoxy. In one embodiment the amine-reacted fluorographene (ARFG) has a wt % of one of either at least twenty percent or at least forty percent. 
     In yet another embodiment, the one or more matrix materials may comprise an epoxy and the microparticles comprise functionalized epoxy reacted flurographene (ERFG). In one embodiment the ERFG has a wt % of either at least twenty percent or at least forty percent. 
     In some embodiments, the composition of matter may include a particle filler. Particle fillers may take many forms, including clay, graphene, and fume silica. These materials may also be used as functionalized microparticles. 
     Using the composition of matter as set out above, one can implement a manufacturing process similar to SLS. Instead of each layer of powder being fused together, the heat or other energy will instead cause the powder particles to form a linked particle network between the particles, creating a stronger finished product. 
     In one embodiment, the continuous phase matrix powder will include a thermal initiator to cause the cross linking between particles. In addition to the thermal initiator, the particles may include one or more of the continuous phase matrix materials. In one embodiment as shown in  FIG. 3 , the macroparticles themselves may be made of at least two different materials,  12  and  14 . In manufacturing using lasers or other energy sources, one of the two materials may be an initiator. 
     In one embodiment, the particles result from a solid being ground into particles and then functionalized. Functionalization of the particles may take many forms. Some methods of functionalizing particles can be found in US Patent Pub. 201901944, “Functionalized Graphene Oxide Curable Formulations,” filed Dec. 21, 2077, US Patent Pub. 202001989, “Composite Materials Comprising Chemically Linked Fluorographite-Derived Nanoparticles,” filed Dec. 19, 2019, incorporated in their entirety herein. The grinding may take the form of cryoscopic grinding of a thermoset material to particles. In one embodiment the particles have a size of less than 100 microns. 
       FIG. 4  shows a flow chart of a manufacturing process. Beginning in the upper left corner, the powder containing the macroparticles  10  is deposited on a powder bed or other substrate to form a layer of powder. The powder bed may be contained in a chamber that is heated, or may itself be heated. In one embodiment the chamber or bed is heated at slightly above the T g  of the macroparticles in the powder, where T g  is the glass transition temperature, the point at which a material begins to alter state from a rigid, glass-like solid, to a more flexible, pliable compound. This keeps the powder ‘sticky’ such that it remains in place during cure. 
     Next, a focused heat source such as  22  then operates on the layer to selectively cure a portion or portions of the layer. The focused heat source will typically comprises a laser. In one embodiment will provide enough energy to convert at least 50% of the selected powder, where conversion means that the molecules at least start to cure. 
     The portion cured  24  represents the object being manufactured. The final design of the object determines which portion or portions of each layer undergo curing. As shown in  FIG. 4 , the object comprises a ‘solid’ object that does not have any separate portions. However, some objects may have portions separate from each other in each layer that undergo curing, to be joined together by later layers that cover all of the portions. The process does not have limit so any particular shape or geometry of any object. One should not infer any limitation. 
     The process then deposits a new layer of powder as show in the upper right. The source  22  again cures the next layer of the powder in accordance with the shape of the object  24 . This process of depositing powder, selectively curing at least a portion, and then repeating continues until the final shape of the object  24  is achieved. 
     Depending upon the process and the materials used, the process may involve reducing the temperature of the powder bed or the chamber below the glass transition temperature to assist with removal of unused powder. Reducing the ‘stickiness’ of the uncured powder particles may allow for easier extraction of the finished object  24 . Again, depending upon the materials and the overall process, the object  24  may be washed in a bath  26  with a solvent  28 . This results in a ‘clean’ finished object  30 . If necessary, the object  30  may also undergo a post-formation cure or sinter at  32 . 
     Other variations and modifications of the process may exist. For example, the macroparticle powder may include a flowability additive to increase the curing of the powder. The particles may also include an absorption additive such as carbon black to increase the energy absorption of the particles when the laser applies heat. Another modification may apply heat from a different source, such as a soldering iron. In some embodiments, the uncured powder may be blown away and no post cure processes are needed. 
     It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.