WO2017142867A1 - Extrusion additive manufacturing of pellets or filaments of thermosetting resins - Google Patents

Abstract

Method of preparing a three-dimensional structure, the method comprising, i. providing a solid non-crosslinked thermoset resin in the form of pellets or a filament; ii. subjecting a bead of the thermoset resin to curing conditions while extruding the bead of the thermoset resin onto a support to form a first layer, wherein the thermoset resin is partially or fully cured to form a partially or fully cured first polymer layer of a thermoset material; and iii. subjecting a bead of thermoset resin to curing conditions while extruding the bead of the thermoset resin to form a second layer of thermoset material in contact with the cured first polymer layer of a thermoset material, wherein the second layer of thermoset material is partially or fully cured to form a partially or fully cured second polymer layer of thermoset material, and wherein the three-dimensional structure is prepared. The steps of the method can be performed repeatedly to prepare a three-dimensional structure by additive manufacturing processes.

Description

EXTRUSION ADDITIVE MANUFACTURING OF PELLETS OR FILAMENTS OF

THERMOSETTING RESINS

FIELD OF THE INVENTION

The present invention is directed to material extrusion of pellets or filaments comprising a thermosetting resin in additive manufacturing processes to form 3D structures.

BACKGROUND OF THE INVENTION

Additive manufacturing is also known as rapid prototyping and is a manufacturing process that aims to convert digital representations, such as CAD data, directly and rapidly into three-dimensional ("3D") structures, largely without manual intervention or use of molds. Additive manufacturing has been used for many years.

Additive manufacturing systems are used to print or otherwise build 3D parts from digital representations of the 3D parts (e.g., AMF and STL format files) using one or more additive manufacturing techniques. Examples of commercially available additive manufacturing techniques include extrusion -based techniques, jetting, selective laser sintering, powder/binder jetting, electron -beam melting, and stereolithographic processes. For each of these techniques, the digital representation of the 3D part is initially sliced into multiple horizontal layers. For each sliced layer, one or more tool paths are then generated, which provides instructions for the particular additive manufacturing system to print the given layer.

These techniques have varying degrees of geometric complexity, but generally have few restrictions in comparison to conventional machining. Each type of technique has associated with it advantages and disadvantages, particularly with respect to solid state processing, fine grain structures, and mechanical properties.

Material extrusion is another additive manufacturing process that utilizes a fluid resin to build a part layer-by-layer. In this process, a part is formed by the extrusion of beads of a molten thermoplastic material that fuse to each other to form layers of the part. The molten thermoplastic material hardens by cooling below its melting temperature or glass transition temperature after extrusion from a mobile nozzle. Typically, the nozzle heats the thermoplastic material above its glass transition temperature, and for crystalline or semi-crystalline material, above the melting point. The molten material is then deposited by an extrusion head. Examples of thermoplastic materials that are used in material extrusion include, acryonitrile butadiene styrene (ABS), polylactic acid, polycarbonate, polyamides, and polystyrene. Material extrusion was first developed by Stratays, Inc. and is also known under the trademark FUSED DEPOSITION MODELING™.

While material extrusion generally provides an effective process for building a part, it does have some disadvantages. First, prior to adding a successive layer, the previously built layer needs to sufficiently cool and solidify. Second, the part may have lower strength in the Z-direction (e.g., between successive layers) due to poor entanglement of polymer chains between successive layers. In addition, for many thermoplastics, such as ABS, it is necessary to first dry the resin prior to extrusion.

Accordingly, a need still exists for new resins and processes to be used in additive manufacturing. The present disclosure addresses these needs.

BRIEF SUMMARY OF THE INVENTION

In embodiments, the subject matter described herein is directed to a process of material extrusion comprising, heating a non-crosslinked thermoset composition in the form of pellets or a continuous strand and extruding the heated thermoset composition along a tool path to prepare a three-dimensional structure.

In embodiments, the subject matter described herein is directed to a method of preparing a three-dimensional structure, the method comprising: i. providing a solid non-crosslinked thermoset resin in the form of pellets or a filament; ii. subjecting a bead of the thermoset resin to curing conditions while extruding the bead of the thermoset resin onto a support to form a first layer, wherein the thermoset resin is partially or fully cured to form a partially or fully cured first polymer layer of a thermoset material; and iii. subjecting a bead of thermoset resin to curing conditions while extruding the bead of the thermoset resin to form a second layer of thermoset material in contact with the cured first polymer layer of a thermoset material, wherein the second layer of thermoset material is partially or fully cured to form a partially or fully cured second polymer layer of thermoset material, and wherein the three- dimensional structure is prepared.. In embodiments, the subject matter disclosed herein is directed to a pelleted composition comprising a solid non-crosslinked thermoset resin in the form of pellets.

In embodiments, the subject matter disclosed herein is directed to a filament composition comprising a solid non-crosslinked thermoset resin in the form of a strand.

In embodiments, the subject matter described herein is directed to a three- dimensional structure having an engineered shape, wherein the object comprises a cured, crosslinked thermoset resin prepared from pellets or filaments of a non- crosslinked thermoset resin that are subjected to material extrusion in an additive manufacturing process.

These and other aspects of the subject matter are disclosed in more detail in the description of the invention given below.

DETAILED DESCRIPTION OF THE INVENTION

The presently disclosed subject matter will now be described more fully hereinafter. However, many modifications and other embodiments of the presently disclosed subject matter set forth herein will come to mind to one skilled in the art to which the presently disclosed subject matter pertains having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the presently disclosed subject matter is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.

Disclosed herein, are advantageous processes and materials for use in additive manufacturing processes that utilize thermoset resins. In embodiments, the subject matter disclosed herein is directed to extruding or printing a bead of a heated, non- crosslinked thermosetting resin that is fed into the extrusion nozzle as a pellet or filament. Additive manufacturing techniques that involve material extrusion can be made more efficient by using such a solid, non-crosslinked thermoset resin in the form of pellets or a filament strand. As described herein, thermoset resins, even including thermoset resin powders that can be pelleted or made into a filament, can now be used as a stock material for such material extrusion techniques by forming solid pellets or filaments out of the thermoset resin material and feeding the pellets or filament into an extrusion apparatus having a nozzle for dispensing a fluid bead of the thermoset resin material.

Crosslinkable thermoset resins have the potential to solve at least two of the shortcomings of parts made by material extrusion of thermoplastic resins. These shortcomings include (1) build speed and (2) strength in the Z direction. Indeed, many art methods of additive manufacturing, such as those utilizing thermoplastics, require that a preceding layer is sufficiently cool and hardened prior to depositing a subsequent layer. As a result, entanglement of the polymer between adjacent layers is limited, which in return results in lower strength in the z-direction of the manufactured part. As set forth herein, the first shortcoming is addressed because the part does not have to cool from high temperatures before it can be handled, which is a slow step in conventional 3D printing by material extrusion. The second shortcoming is addressed by chemical crosslinking across the boundary between the two applied layers. The thermoset resin pellets and/or filament strands are employed in material extrusion to prepare a 3D object in an additive manufacturing process. The products of these processes comprise the cured or partially cured thermoset resin(s) and they have three-dimensional, engineered shapes.

The use of thermoset resins in the form of pellets or filaments for material extrusion additive manufacturing processes provides several advantages. Ease of handling of the thermoset resin in these physical forms is but one benefit. Additionally, the curing of these resins can be accomplished without the addition of significant heat since the heat applied to extrude the material also provides the energy required for curing the thermoset resin(s). Importantly, because sintering or melting is not required, the three-dimensional structures prepared by these processes are not subjected to the thermal stress generated during typical sintering or melting. As such, the integrity of the three-dimensional structures will not be compromised as a result of such stress.

The advantages of thermoset resins over thermoplastic resins is that the hardening step will generally not require removal of heat from the structure. Thus, an advantage of this technology over thermoplastic materials is the excellent dimensional stability in the X, Y and Z direction of the structure particularly with respect to heat distortion. Further, heat will not need to be removed from the part in order to develop the strength of the part thereby allowing the part to be built more quickly because thermoplastic materials are generally poor conductors of heat. Residual, thermal stress leads to the finished part being warped or being weak due to the residual thermal stress. A shortcoming that is experienced when thermoplastics are used is the slow consolidation of the part due to the fact that heat removal is required to solidify the fused section of the part.

Another advantage is the ability to crosslink adjacent layers to each other in the 3D object being built. This provides excellent strength in the Z direction. However, up to now, the use of a thermosetting resin in material extrusion was not available. As described herein, the thermoset resin formed into pellets or a filament strand can be used in place of a thermoplastic resin.

The use the thermosetting resin will employ flow, or alternatively fusion, and curing of the resin to be occurring simultaneously but at different rates. The ability to control the rates of these two processes are provided by the methods described herein. The rate of crosslinking of the resin can be adjusted by the molar density of crosslinkable moieties, the type of catalyst, the amount of catalyst, the molecular weight of the thermosetting resin and the polydispersity, i.e., the degree of branching of the polymeric chains making up the thermosetting resin. The flow or fusion of the thermosetting resin can be adjusted by changing the molecular weight of the thermosetting resin, changing the degree of branching of the polymeric chains making up the thermosetting resin, and adding viscosifiers or viscosity reducers to the thermosetting resin. It is therefore disclosed herein that the flow or fusion and cross- linking can be independently controlled.

Curing of the bead of the thermoset resin is accomplished through the application of curing conditions, that is, exposure to thermal energy, in the additive manufacturing processes. The thermal energy can be from any source such as IR, convection, conduction, etc. The general characteristics of the resin are that, at the conditions of the build tank or chamber being used for the additive manufacturing process, the resin initially printed as a bead undergoes crosslinking reactions that thermoset the polymer. In this way, the layers of the object being built have excellent strength.

As used herein the term "additive manufacturing" refers to any process of joining materials to make objects by depositing layer upon deposited layer. The additive manufacturing techniques that are of particular interest are those that employ a step of material extrusion during printing. Each printed layer will have the desired dimensions and shape such that together the layers form a three-dimensional, engineered structure.

As used herein, the term "thermoset" and "thermosetting" are used interchangeably and each refers to a property of a polymer precursor or polymer made from such precursor where the polymer once crosslinked is irreversibly cured. The cure may be induced by heat above the set temperature, through a chemical reaction that leads to formation of covalent bonds that were not present prior to cure. In addition to heat, some thermoset polymers may be cured via a chemical reaction in which two components chemically react to cure the polymer. Irreversibly cured refers to after thermosetting has taken place, the resin cannot be melted or dissolved without some chemical decomposition taking place first.

As used herein, the terms "thermoset resin" and "thermosetting resin" are used interchangeably and each refers to precursor materials that will form a thermoset polymer also referred to as a thermoset material when induced to crosslink as described herein. Accordingly, the thermoset resin comprises a main component of the build materials and is not present merely as excipients or binders and the like. Thermoset resins are distinguishable from thermoplastic powders and resins, which are known in the art. Thermoset resins are chemically distinct from thermoplastic resins, which are often shaped into the final product form by melting and pressing or injection molding.

As used herein, the term "pellet" refers to granules made using extrusion or compression processes, which is distinct from powders, particles, fines, etc. "Pellets" may have substantially any shape, but typically are small, columnar or cylindrical bodies and may have flat surfaces such as cubes, rectangular parallelepipeds, etc. The pellets are formed from a homogeneous mixture of non-crosslinked thermoset resin(s), which may initially be in the form of a powder before being pelleted. It should be understood that use of the term "pellet" is not meant to imply or require that any particular process be used to prepare the pellet. Rather, pellet is intended to refer to the final solid conglomerated form of the thermoset resin in the form of distinct bodies. In addition to the thermoset resin, the pellets can also be composed of fillers, modifiers and the like. As used herein, the term "filament" encompasses any elongated stock of thermoset resin material suitable for use in additive manufacturing processes. A "filament" may refer to a single strand of material having an elongated, relatively easily bendable shape that can be continuously drawn into the nozzle from which it is to be extruded. The term filament refers to non-crosslinked form of the build materials in the form of a strand. The filament is heated in the printing head and is then extruded through a nozzle to print a 3D object. The filament contains a thermosetting resin, but it may also be possible that filament is composed only to some extent of a thermosetting resin material and is also composed of fillers, modifiers, additives, and the like.

As used herein, the term "curing" refers to the chemical crosslinking within the resin and between different layers of resin. Other chemical changes may be occurring at the same time that crosslinking is occurring. The term "crosslinking" refers to the formation of covalent bonds between thermoset resin monomers, oligomers or polymers and polymers formed therefrom. Such chemical changes are distinguished from a physical change such as melting. In thermoset polymers, unlike thermoplastic polymers, the curing is considered irreversible. Curing and the term "cure" refer to "partial" or "full" curing. As used herein, the term "partial" or "partially" cure, cured or curing refers to an amount of chemical crosslinking within the resin, between different reactive moieties of the thermosetting resin in the same layer and between different reactive moieties in different layers of resin to form covalent bonds between the resin molecules and layers. As used herein, the term "full" or "fully" cure, cured or curing refers to an amount of chemical crosslinking within the resin and between different layers of resin to form covalent bonds between the resin molecules and layers such that subjecting the resin to additional radiation curing does not provide appreciably more of the same type of covalent bonding. Accordingly, the term "fully" does not imply that all of the crosslinking moieties must be covalently bonded. The term "non-crosslinked" refers to a resin that has not yet been subjected to curing conditions such that the resin does not have an appreciable amount of crosslinked polymers.

As used herein, the term "curing conditions" refers to conditions under which the resin cures. Types of curing conditions include thermal energy, humidity, and chemical reactions between multicomponent systems. As used herein, the term "fuse" refers to a transformation process whereby the resin can physically attach to other layers with or without flow occurring. In this way, the layer can be fused with adjacent layers. Layers which contain a thermoplastic resin and a thermoset resin can be partially fused as well as partially cross-linked.

The "viscoelastic" characteristics of the curing polymer refers to the rheology of the polymer(s) when subjected to an energy source as described elsewhere herein. The term "flow" primarily refers to the movement of the heated resin, but can also describe a viscoelastic characteristic of the curing polymer. The flow of the resin can be controlled by the use of flow aids as described elsewhere herein.

A polymer layer that is "cured or fused" refers to a polymer layer that has been fully or partially cured or fused as described herein, but allows for such a layer to have been both cured and fused, for instance, when a blend of stock material that is only partially comprised of a thermoset resin is used and is subjected to curing and fusing. Alternatively, the layer can be cured without being fused and vice versa depending on the parameters utilized in the processes for preparing the three- dimensional structure.

As used herein, the term "fixing" refers to any final drying, hardening, polymerization, crosslinking, binding, etc. to finish the structure.

The term "structure" or "three-dimensional structure" and the like as used herein refer generally to intended or actually fabricated three-dimensional configurations, objects, or parts that are fabricated and intended to be used for a particular purpose. Such structures, etc. may, for example, be designed with the aid of a three-dimensional CAD system. The shapes may be engineered, meaning that they are particular shapes designed and manufactured according to specification in the desired shape as contrasted with random shapes. Alternatively shapes may be scanned from existing objects whether natural or engineered. The structures will be comprised of layers as described herein. In contrast, structures formed from other methods, such as molding, will not contain such layers. A "plurality" of structures refers to two or more of such structures that are substantially identical. As used herein, the term "substantially" implies that the structures are identical in all respects but are allowed to have minor topological imperfections.

As used herein a "single layer" of resin can be any amount of material applied in any fashion that is exposed to radiation to cure the material prior to the addition of any new material (the next layer) proximate to the cured material. Therefore, in embodiments, a single layer may be defined by multiple individual layers of material if all those layers are exposed to the radiation together. Typically, a single layer of material is provided in a bead proximate to a substrate or cured material; the material is cured to become a part being produced and the uncured material is replaced or supplemented with another single layer of uncured material to define the next single layer of cured material.

As used herein, the term "contacting" includes extruding, beading, applying, spreading, filling dumping, dropping and the like such that the thermoset resins are in position for the processes described herein to proceed.

As used herein, the term "bead" refers to a stream or line of resin that is deposited on a surface by at least one extrusion nozzle. The bead may have a variety of cross-sections including circular, elliptical, rectilinear, trapezoidal or other shapes. A bead can be a continuous stream or line for the entire print layer, or a bead can be discontinuous, such that a single print layer can be made up of more than one bead.

The term "providing", when recited in the claims, is not intended to require any particular delivery or receipt of the provided item. Rather, the term "providing" is merely used to recite items that will be referred to in subsequent elements of the claim(s), for purposes of clarity and ease of readability.

Forms of Thermosetting Resins

Solid thermosetting resins that are suitable for material extrusion are provided in the forms of pellets or filaments. Pellets of thermosetting resins can be made and either fed as pellets to a material extruding 3D printer designed to convey pellets or extruded into a filament and then fed as a filament to a material extruding 3D printer designed to convey filaments. Such apparatuses are known in the art. To prepare the pellets and filaments, an appropriate thermoset resin is subjected to pelleting processes or extrusion into a filament strand. To form the pellets and filaments, the starting material can be any thermoset resin(s) that are amenable to forming into pellets and filaments. As such, the starting material can be compressed into its final form, or heated, generally above and near the T_g and without curing, to a molten state for forming into pellets or filaments. In a particular embodiment, the non-crosslinked thermosetting resin is in the form of pellets. The pellets can comprise a single non-crosslinked thermoset resin or can comprise a "blend" of two or more different non-crosslinked thermoset resins.

Pellets have the added benefit of ease of handling the thermosetting resin prior to it being crosslinked. Pelleting also provides ease of handling more than one component. For example, when the thermosetting resin has two components, a part A and a part B, then the two components can be mixed prior to pelletization or a blend of pellets can be made where pellets made from part A are blended with pellets from part B. This blend of pellets is then fed to a material extruding 3D printer designed to convey pellets. Though not applicable to material extrusion or additive manufacturing, pelletization of thermosetting resins are described in US Patent 5,942,170, US Patent 4,737,407 and US Patent 4,454,089. US Patent Application 20150183159 describes a working material provided in pelletized form, but specifically mentions acrylonitrile-butadiene-styrene (ABS), polycarbonate, polyphenylene sulfone (PPSF and PPSU), all of which are thermoplastics. US Patent Application 20150291833 describes a supply of polymer working material in a pelletized state but specifically calls for the working material to be a polymer that is partially crosslinked prior to being deposited.

In embodiments, in order to form pellets, a thermosetting resin(s) stock material, which can include powders, along with any fillers, modifiers, additives, etc., is pressed through a die extruder to form strands, which are then formed into pellets. In a preferred embodiment for making the pellets, the powdered thermosetting resin and any powdered additive are dry blended to form a homogeneous powder blend. The powder blend then is fed to a suitable pellet mill at a rate that achieves an acceptable pellet yield. As used herein, the term "pellet yield" refers to the wt. % yield of pellets having the acceptable specifications, such as monodispersity, PDI, etc.

Persons of ordinary skill in the art recognize that a variety of factors affect pelleting, including but not necessarily limited to powder composition, rotor speed, feed rate, solvent, type of pellet mill, etc. Another factor is the "aspect ratio" is the ratio of the diameter to the length of the holes in the die plate.

Examples of pelleting equipment suitable for adaptation and use in the present invention include, but are not necessarily limited to those described in the following U.S. Patents, which are incorporated herein by reference: U.S. Pat. Nos. 4,446,086; 4,670,181; 4,902,210; 5,292,461.

The size of the pellet may be varied to suit the particular situation. Typically, the size of the pellet is sufficient to allow it to be easily used in the equipment for additive manufacturing. For example, pellets can be from about 0.1 to about 10 mm in cross-section, and from about 0.1 to about 10 mm in length. The shapes of the pellets can be tailored to suit the particular situation. The pellets can have an aspect ratio (cross-section (mm) divided by length (mm)) of from about 0.1 to less than 10.

The pellets may be monodisperse, which refers to a collection of pellets that have similar shape to each other. For example, a collection of pellets is called uniform or monodisperse if the pellets in the collection have the same size, shape, or mass. The dispersity of the pellets can be calculated by known methods. The pellets can have a poly dispersion index (i.e., normalized size distribution) of between about 0.80 and about 1.20, between about 0.90 and about 1.10, between about 0.95 and about 1.05, between about 0.99 and about 1.01, between about 0.999 and about 1.001, combinations thereof, and the like. The dispersity is calculated by averaging a dimension of the particles. The dispersity can be based on, for example, surface area, length, width, height, mass, volume, porosity, combinations thereof, and the like.

In embodiments, thermosetting resin(s) as described herein is in the form of a filament strand or ribbon. The filament can be a "cylindrical filament," which has a cross-sectional profile that is circular. Alternatively, the filament can be "non- cylindrical," which refers to a cross-sectional profile that is non-circular (e.g., a rectangular or arcuate cross-sectional profile).

The filaments may also be provided in a variety of sizes. For example, a continuous or semi-continuous filament can have a cross-section that is about 0.1 to about 10 mm. Particular mention is made of cross-sectional widths of from about 1 mm to about 5 mm. In some embodiments, it is also desirable that the filament includes a substantially constant cross-section size along its length. The length of the filament can range from about 10 mm to several or hundreds of meters or can be a continuous strand. Particular mention is made of lengths that include 10 mm to about 50 mm. The filaments can have an aspect ratio of greater than about 10. In embodiments, the filament is a rod-like shape of about 10-30 mm in length and 1-3 mm in cross-section. An advantage of such a shape and size is the use in hand-held extrusion devices for 3D printing.

Depending on the particular embodiment, different smoothnesses and tolerances with regards to the filament outer diameter may be used. A constant outer diameter may help to provide constant material flow rate and uniform properties in the final part. It may also assist in winding the filament on a spool for ease of handling. As used herein, the term "continuous" refers to a strand that is generated and fed into the apparatus constantly or it refers to a strand that is simply not segmented, for example, a continuous filament can be a strand that is wound in a non- segmented manner onto a spool.

The filament can be wound onto a material dispenser that can be a spool, wherein the filament is wound around the core. The wound-up roll of filament can be stored and applied subsequently as print in any conventional extrusion-based 3D printer for the application of filaments as print.

During printing, the pellets and/or filaments of non-crosslinked thermoset resin(s) are fed through a heated deposition head, such as conduit nozzle. As the pellets and/or filaments are fed through the conduit nozzle it is heated to a preselected deposition temperature. This temperature may be selected to effect any number of resulting properties including, but not limited to, viscosity of the deposited material, bonding of the deposited material to the underlying layers, and the resulting surface finish. While the deposition temperature may be any appropriate temperature, in one embodiment, the deposition temperature is greater than the melting temperature of the resin, but is less than the curing temperature of the resin. Any suitable heater may be employed to heat the deposition head, such as a band heater or coil heater.

The thermosetting resins may contain a variety of additives including fillers, fibers, impact modifiers, anti-oxidants, colorants, and others. These can be added as a dry material to the pellets or filaments just before being conveyed to the material extruder. Alternatively, they can be mixed or compounded with the resin prior to pelletization or extrusion into a filament.

Particular embodiments include: pellets or filaments of a non-crosslinked thermoset acrylic copolymer comprising acrylate and methacrylate, for example 1 mol % glycidyl methacrylate and 1 mol % β-carboxyethyl acrylate; pellets or filaments comprising a non-crosslinked thermoset phenol -formaldehyde resin; and pellets or filaments comprising a non-crosslinked thermoset bisphenolA-based epoxy resin. These pellets or filaments are particularly useful as they allow for the use of a thermoset resin in material extrusion additive manufacturing processes.

Additive Manufacturing Processes and Devices

Additive manufacturing is defined by the American Society for Testing and

Materials (ASTM) as the "process of joining materials to make objects from 3D model data, usually deposit layer upon deposit layer, as opposed to subtractive manufacturing methodologies, such as traditional machining and casting." As referred herein as "additive manufacturing," there are a number of processes for creating a digital model and producing a three-dimensional solid object of virtually any shape from that model. These processes are named 3D printing, rapid prototyping, fused-filament, additive manufacturing, and the like. Additive manufacturing is, therefore, a set of methods for forming three-dimensional articles through successive fusion of chosen parts of layers resting on a substrate.

Particular mention is made to additive manufacturing techniques that employ an extrusion-based digital manufacturing system. These systems are used to build a 3D model from a digital representation of the 3D model in a layer-by-layer manner by extruding a flowable modeling material. The modeling material is extruded through an extrusion tip carried by an extrusion head, and is deposited as a sequence of beads or roads on a tool path on a substrate in an x-y plane. In general, the extruded modeling material fuses to previously deposited modeling material, and solidifies upon a drop in temperature. However, as described elsewhere herein, the thermosetting resin also crosslinks adjacent layers. The position of the extrusion head relative to the substrate is then incremented along a z-axis (perpendicular to the x-y plane), and the process is then repeated to form a 3D model resembling the digital representation. Material extrusion with a crosslinkable polymer is described in US Patent Application Pub. No. 20150291833. This application describes controlling the viscosity of the melt at temperature by controlling the degree of crosslinking. The degree of crosslinking will be changing throughout the process and is, therefore, difficult to control.

As disclosed herein, the usefulness of extrusion-based additive manufacturing technology to provide low cost product assembly and the building of any number of products with engineered, complex shapes/geometries, complex material compositions and designed property gradients has been expanded to thermoset resins as the material for the build.

In an additive-manufacturing process, a model, such as a design model, of the component may be defined in any suitable manner. For example, the model may be designed with computer aided design (CAD) software. The model may include 3D numeric coordinates of the entire configuration of the component including both external and internal surfaces of an airfoil, platform and dovetail. The model may include a number of successive 2D cross-sectional slices that together form the 3D component.

There is typically a relatively high cost of operation and expertise is required to operate 3D printers. 3D design files can be created using Computer Assisted Design (CAD) software, such as SolidWorks™, to generate a digital representation of a 3D object. The STL (Standard Tessellation Language) file format is a commonly used format for storing such CAD files. This CAD file, in other words the digital representation of the 3D object, is subsequently converted into a series of contiguous 2D cross sections, representing sequential cross-sectional slices of the 3D object. These 2D cross sections are commonly referred to as 2D contour data. The 2D contour data can be directly input into a 3D printer in order for the printer to print the 3D object. Conversion of a 3D design file into 2D cross-sectional data is often carried out by dedicated software.

As such, additive manufacturing systems are used to print or otherwise build three-dimensional ("3D") parts from digital representations of the 3D parts (e.g., AMF and STL format files) using one or more additive manufacturing techniques. In the present invention, the additive manufacturing techniques described herein are directed to an extrusion-based process in which a thermoset resin is deposited and cured in successive layers to form a 3D part.

At an initial stage, the digital representation of the 3D part is sliced into multiple horizontal layers. For each sliced layer, a tool path is then generated, which provides instructions for the additive manufacturing system to print the given layer.

A three-dimensional structure of the present invention may be built using, for example, a three-dimensional printing system similar to embodiments described in U.S. Patent Nos. 5, 121,329, and 6,658,314. An exemplary three-dimensional extrusion system may generally include one or more extrusion nozzles, and at least dispenser from which the thermoset resin is extruded. The system will may also include a pump, piston or similar device to apply external shear stress to the thermoset resin and thereby cause the resin to flow from the dispenser to an associated extrusion nozzle. The thermosetting resin may be supplied to the extrusion nozzle as a single component system, or alternatively, may include two or more components that are only mixed prior to extrusion. A static mixing tube is one device that is designed to intimately mix two components immediately prior to extrusion.

In one embodiment, the extrusion system may include at least two extrusion nozzles. For example, a first extrusion nozzle may be connected to a first dispenser that is used to dispense a first thermoset resin, and a second extrusion nozzle may be connected to a second dispenser that is used to dispense a second thermoset resin or a thermoplastic polymer.

The build platform may comprise a work table, substrate or the like, which may be a releasable substrate, on which the three-dimensional article is to be formed.

The three-dimensional extrusion system further includes a controller, a Computer Aided Design (CAD) system, optional curing device, and optionally a positioning apparatus. The controller is coupled to the CAD system, curing unit, positioning apparatus, extrusion nozzle(s) and dispensers containing the thermoset resin. Control may be effected by other units than, such as one or more separate units. The three-dimensional structure is built in layers, the depth of each layer typically being controllable by selectively adjusting the output from each extrusion nozzle.

Depending on the nature of the thermoset resin and the desired curing mechanism, the curing device may be integral to the three-dimensional extrusion system, or may comprise a separate and stand-alone device. For example, the curing device may comprise an energy source for delivering thermal energy (e.g., radiant heat) to the deposited resin whereby curing of the thermoset resin takes place, heating element, oven, high relative humidity chamber, or the like.

In one embodiment, the extrusion nozzle may be heated to liquefy the pellets or filaments for depositing as a bead. The heating can be adjusted higher to initiate curing of the thermoset resin as it is deposited onto the build platform. The systems employed in the embodiments described herein are generally used for manufacturing three-dimensional structures from a curable thermoset resin and for manufacturing an engineered three-dimensional structure comprised of the cured thermoset resin. This manufacturing can be employed for rapid prototyping. A device comprising a source of curing energy (such as a C0₂ laser, IR lamp, oven, etc.) can provide the necessary curing conditions to effect curing of the resin.

A three-dimensional structure is formed through consecutive deposition and crosslinking of consecutively formed cross sections of layers, successively laid down by the extrusion nozzle. Systems for depositing a layer containing or more beads of the thermoset resin may comprise any known means for laying out a bead of flowable resin material. Examples of devices suitable for performing additive manufacturing processes include any commercially available device for such purpose.

The devices utilize a computing system which implements design tools and/or topology optimization according to desired design aspects. The system includes a memory. The memory may store data. The memory may store executable instructions used to implement the topology optimization according to the desired design. The executable instructions may be stored or organized in any manner and at any level of abstraction, such as in connection with one or more processes, routines, procedures, methods, etc.

The instructions stored in the memory may be executed by one or more processors. The processor may be coupled to one or more input/output (I/O) devices. In some embodiments, the I/O device(s) may include one or more of a keyboard or keypad, a touchscreen or touch panel, a display screen, a microphone, a speaker, a mouse, a button, a remote control, a joystick, a printer, a telephone or mobile device (e-g-, a smartphone), a sensor, etc. The I/O device(s) may be configured to provide an interface to allow a user to interact with the system in the generation of a specification according to the desired build.

The specification is transferred to an additive manufacturing device which performs the additive manufacturing techniques according to the specification in order to create the 3D structure. While not required in all aspects, the additive manufacturing device can include processors that interpret the specification, and control other elements which apply the materials using robots, nozzles, lasers or the like to add the materials as layers or coatings to produce the 3D structure. The following discussion is provided as an example of how a three-dimension structure can be built in accordance with embodiments of the present invention. It should be recognized that other systems and processes can be used to build three dimensional structures using the thermoset resins described herein.

In an initial step, the thermoset resin is subjected to sufficient conditions to cause the resin to flow from a dispenser to an associated nozzle. The resin is then deposited as a bead onto the build platform. In one embodiment, the nozzle may make multiple passes, with each pass taking place in a controlled pattern as dictated by the computer software to form a single layer.

Curing of the thermoset resin may be initiated while the resin is being deposited, or initiated after one or more of the deposition of a bead, multiple beads, a single layer, multiple layers, or combination thereof is completed. In some embodiments, the thermoset resin may be subjected to curing after each layer or after two or more layers successive layers have been deposited.

Generally, the computer and related software programs determine when the extrusion nozzle is on and off based on the digital computer model. The machine controller controls the operation of the extrusion nozzle along the "X," "Y," and "Z" axes via a plurality of drive motors. Each of these motors may be operating separately, or one or more of them may be operating simultaneously, depending upon the shape of the structure to be formed. Circular patterns for each layer can be generated by controlled movement along the "X" and "Y" axes of the build platform.

The extrusion nozzle may be initially positioned a predetermined height above the build platform to form the first layer of the three dimensional structure. The height of each subsequent layer is then closely controlled. Typically, thinner layers provide result in the surface of the structure having an overall smoother surface.

Thicker layers generally increase the speed at which the structure is built. Layers as thin as 0.0001 inches may be formed. The layers can be formed horizontally, vertically, or in any 360° orientation to the horizontal. Depositing of the resin may take place along any of the three axes. The dispensing of the resin may take place along only the "X" - "Y" plane, until it is advantageous to deposit in the "X" "Z" plane or the "Z" "Y" plane. Normally, the extrusion nozzle will be mounted along the "Z" axis generally perpendicular to the build platform, and thus perpendicular to the "X" - "Y" plane of build platform. When forming and building up multiple layers, one or more beads of the thermoset resin are deposited to form a first layer. The first layer may take any shape dictated by the computer program. The first layer may then be subjected to an energy source to initiate curing of the resin. A second and each subsequent layer may take slightly different shapes, as dictated by the particular cross section for each layer from the computer program and layering software. In the pattern situation for each layer wherein each layer is formed only in a horizontal "X" - "Y" plane. A motor supporting the extrusion nozzle may be selectively actuated after each layer is formed to raise the nozzle incrementally along the "Z" axis a closely controlled,

predetermined distance to control the gap between layers and thus the thickness of each layer.

After the extrusion nozzle is thus raised, the next layer is dispensed and formed along a controlled path, also referred to as a "tool path." In some instances, the extrusion nozzle may be moving in a direction along the "Z" axis as the layer is formed, such as when forming a spiral pattern, and the software program will control the location of the extrusion nozzle at the end of each layer. Thus, when at the start position for the next layer, the extrusion nozzle may have already been raised a distance along the "Z" axis above the corresponding point on the previously-formed layer. In such a situation, the extrusion nozzle may not have to be elevated at all at the commencement of the next layer, or it may be elevated incrementally a very small distance to form the desired gap between layers, and thus the predetermined layer thickness.

The multiple layers may be of uniform thickness, or the layers may vary in thickness, as necessary and appropriate for the forming of a particular structure. Also, the layers may each vary in thickness across the height of each layer.

Additive manufacturing systems build the solid part one layer at a time. Typical layer thicknesses range from about 0.001-10.00 mm. However, depending on the build design, the layer may be thicker or thinner as practicable. The thickness can be adjusted depending on the process parameters, including the average height of the bead in the layer, the total number of layers that make up the structure, and the speed in which the structure is being built.

The device may operate generally according to a method comprising the following steps: (i) depositing on the build platform one or more beads of the thermoset resin prepared from non-crosslinked thermoset resin pellets or filaments; (ii) curing the layer by subjecting the deposited layer of thermoset resin to radiation (e.g., thermal energy), (iii) laying out one or more successive beads on top of the previous layer; (iv) curing the successive layer to form the next cross-sectional layer; (v) repeating steps (iii) and (iv) until the three-dimensional structure is built. In some embodiments, it may be desirable to first deposit multiple successive layers prior to initiating a step of curing the thermoset resin.

Energy Sources

Curing of the thermoset resins may be accomplished in a variety of different ways depending on the thermoset resin. In one embodiment, curing is accomplished by subjecting the resin to irradiation that thermally heats the resin to effect curing. In preferred embodiment, thermal energy is used for curing. Curing temperatures may typically range from 25° C to 125° C.

The electromagnetic radiation may include actinic radiation, visible or invisible light, UV-radiation, IR-radiation, electron beam radiation, X-ray radiation, laser radiation, or the like. Moreover, while each type of electromagnetic radiation in the electromagnetic spectrum may be discussed generally, the disclosure is not limited to the specific examples provided. Those of skill in the art are aware that variations on the type of electromagnetic radiation and the methods of generating the electromagnetic radiation may be readily determined. Methods to cure the structure further include holding the part at elevated temperature or irradiation with high intensity ultraviolet (UV) lamps to achieve desirable mechanical properties without subjecting the object to unnecessary thermal stress.

Thermosetting Resins

Useful thermosetting resins are described below. The physical form of the resin employed in the methods is a pellet or filament as described elsewhere herein. Thermosetting resins in the form of pellets and filaments can be prepared from known thermosetting resins, including powders. Useful thermoset resins for use in embodiments disclosed herein are any known thermoset resins that can be made into the form of a pellet or filament. Such pellets and filaments can be obtained by the methods described herein.

Useful resins are thermoset resin selected from the group consisting of thermoset phenolic resins; thermoset lignin resins; thermoset tannin resins; thermoset amino resins; thermoset polyimide resins; thermoset isocyanate resins; thermoset Maillard reactants or Maillard resins, thermoset vinylic resins; thermoset styrenic resins; thermoset polyester resins; thermoset melamine resins; thermoset vinylester resins; thermoset acrylate resins; thermoset maleimide resins; epoxy resins; polyamidoamine resins; and mixtures thereof.

In embodiments, the thermoset resin is selected from the group consisting of thermoset phenolic resins and thermoset amino resins. In embodiments, the thermoset resin is one of the phenolic resins known as drop resole resins. More preferred thermoset phenolic resins are those selected from the group consisting of a phenolic resin having a mole ratio of formaldehyde to phenol of about 2: 1 to about 3 : 1, and a phenolic resin having a crosslinker and a 0.6 to 0.9 ratio of formaldehyde to phenol. More preferred thermoset amino resins are those having a mole ratio of formaldehyde to urea from about 2.2: 1 to about 3.8: 1.

Thermoset phenolic resins are useful. These include phenol-formaldehyde resins. The resin can be tailored for a specific application by controlling the mole ratio of the precursor, the pH of the precursor and the relationship of solids and viscosity for the aqueous solution or dispersion of the precursor. A phenolic, curable precursor resin can range in mole ratio of formaldehyde to phenol from 2: 1 to 2.95: 1. A more preferred range is from 2: 1 to 2.65 : 1. The pH of a phenolic, curable precursor resin can range from 7.1 to 13.9. A more preferred range is from 8.5 to 12.9. A phenolic, curable precursor resin at 50 wt% solids in an aqueous medium can range in viscosity from 60 to 60,000 cps at room temperature. A more preferred range for the phenolic, curable precursor resin at 50 wt% solids in an aqueous medium is from 100 cps to 2000 cps.

Another type of commercially available thermosetting phenolic resins are known as Novolacs. An example is phenolic novolac with the addition of bis phenol A diglycidyl ether as cross linker. The material will cure with the application of heat into a thermoset material. The mole ratio for this class of polymer is in the 0.6 to 0.9 ratio of formaldehyde to phenol. Another class of thermosetting phenolic is a drop resole, manufactured by Plenco of Sheboygan, WI.

Another class of thermosetting phenolic resin is benzoxazine such as those sold by Huntsman Inc. Another class of thermosetting resin is bismaleimide such as those sold by Hexion Inc.

Another category of thermosetting resin is an amino resin, including urea- formaldehyde resins. The mole ratio of formaldehyde to urea for the precursor resin can range from 2.2: 1 to 3.8: 1. A more preferred range is from 2.6: 1 to 3.6: 1. The viscosity of the amino precursor resin can range from 60 to 60,000 cps at room temperature at 50 wt% solids in an aqueous medium. A more preferred range for the amino precursor resin is 100 to 2000 cps at 50 wt% solids in an aqueous medium at room temperature. The pH of the precursor amino resin can range from 2.1 to 6.9. A more preferred range is from 2.6 to 4.6.

Yet another category of thermosetting resin is thermoset epoxy resins. An example of this resin is bisphenolA-based epoxy resins.

The resins that have been named are intended to be examples of classes without limiting the range of materials that may be used. Precursors that include resorcinol, tannin, lignin, epoxies, urethanes, polyesters, or melamine are also encompassed.

The pellets and filaments made from the resins described herein can contain additives such as a catalyst. The type of catalyst will be chosen based on the crosslinking moieties on the thermosetting resin and is well within the skill of those in this field. Non-limiting examples include the following. For example, the crosslinking of isocyanate moieties can be catalyzed with dibutyl tin oxide or dibutyl tin dilaurate. The crosslinking of resole phenol formaldehyde resins can be catalyzed with sodium hydroxide, potassium hydroxide or salts of ethylenediamine-sulfonic acid. The crosslinking of novolac phenol formaldehyde resins can be catalyzed with boric acid, oxalic acid or sulfamic acid. Thermosetting epoxy resins can be catalyzed with tributylamine, cis-5-Norbornene-endo-2,3-dicarboxylic anhydride, or oxalic acid. Certain resins that are composed of polycarboxic acid with polyols, crosslink by esterification reactions and these esterification reactions can be catalyzed with sodium hypophosphite.

As mentioned before, the flow or fusion of the thermosetting resin can be adjusted by changing the molecular weight of the thermosetting resin, changing the degree of branching of the polymeric chains making up the thermosetting resin, and adding viscosifiers or viscosity reducers to the thermosetting resin. The following non-limiting examples describe such components. Examples of additives that may be used to formulate the pellets or filaments to increase the viscosity under curing conditions include fumed silica, alkylammonium montmorillonite, wollastonite, calcium carbonate, magnesium oxide, hydroxyethylcellulose, cellulose acetate butyrate and poly(ethylene oxide). Examples of some additives that may be used to formulate the pellets or filaments to reduce the viscosity include dioctylphthalate, dioctyladipate, triphenylphosphate, Bisphenol-A, low molecular weight polyvinyl acetates and low molecular weight polyvinyl butyrates. Utilizing known viscosifiers and viscosity reducers and adjusting the above-mentioned parameters is well within the skill of those in this field. Examples of additives to reinforce the final part after cure are glass fiber and carbon fiber. Examples of additives to increase the durability of the final part after cure are elastomers and rubbers such as amino-terminated butyl rubber and carboxy-terminated butyl rubber.

Thermoplastic polymers that are chemically and physically distinct from thermoset resins include nylons, polyethylene, polypropylene, polystyrene, poly (methyl methacrylate), poly (vinyl chloride), poly (vinyl acetate), polycarbonate, polycaprolactone, poly (ethylene oxide), poly (vinyl alcohol), poly (ethylene terephthalate), poly (ether sulphone), poly (butyl terephthalate), poly (ethyl methacrylate), ultrahigh molecular weight polyethylene; polyaryletherketones such as polyetherketone or polyetheretherketone, polyvinylchlorides, polycaprolactones, styrene-vinyl acetate diblock copolymers, acrylonitrile-butadiene-styrene terpolymer, polyolefins such as polypropylene or polyethylene, and olefin-based copolymers. Those of skill in the art are well aware of the physical and chemical distinctions and therefore can easily distinguish between the classes.

The thermoset resin pellets and filaments disclosed herein can comprise blends of materials. As used herein, a "blend" is a mixture containing a thermoset resin and further comprising a thermoplastic resin. The blends can be from about 1 : 1 thermoset to thermoplastic; from about 0.5 to about 1 thermoset to thermoplastic; from about 0.1 to about 1 thermoset to thermoplastic; from about 0.01 to about 1 thermoset to thermoplastic; from about 1 to about 0.5 thermoset to thermoplastic; from about 0.1 to about 1 thermoset to thermoplastic; or from about 1 to about 0.01 thermoset to thermoplastic;. Useful "blends" described herein are those that cure under the conditions described herein to form the layers of the engineered structures. The blends may also consist of two distinct thermosetting resins. For example, polyamines can be blended with polyol and crosslinked with polycarboxylates. Another example is a resole phenol-formaldehyde resin blended with a novolac phenol-formaldehyde resin.

Using the methods described herein, the 3D structures prepared will comprise a layer of cured thermoset resin in an engineered pattern having desired dimensions and shape. The steps may be repeated successively as many times as desired to produce an engineered, three-dimensional structure in an additive manufacturing technique. As described herein therefore, the process can include independently selecting any type of resin in any successive step to prepare a structure having the desired composition.

The thermoset resins comprise the major component of the build materials in the processes and in the fabricated parts or structures. Accordingly, thermoset resins are present in amounts of at least 30% of the weight of all the build materials in the processes and in the fabricated parts or structures. In embodiments, thermoset resins are present in amounts of at least 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% or more of the weight of all the build materials in the processes and in the fabricated parts or structures.

In practicing the disclosed methods, the first layer of thermoset resin can be the same type of resin as the second layer of thermoset resin. As a non-limiting example, both layers can be the same species of thermoset phenolic resin. Alternatively, the first layer of thermoset resin can be a different type of resin than the second layer of thermoset resin. As a non-limiting example, one layer can be a thermoset phenolic resin and the second layer can be an epoxy thermoset resin; or one layer can be a thermoset phenolic resin and the second layer can be a thermoset amino resin; or one layer can be a phenolic resin species and the other layer a different species of phenolic resin. Accordingly, successive layers in the structure can be composed of the same or different materials.

Alternatively, in embodiments, one layer can comprise or consist essentially of a thermosetting resin and another layer can comprise or consist essentially of a thermoplastic resin. Such layers may or may not be adjacent in the structure. Also as a non-limiting example, both layers can be the same composition of a blend of thermoset phenolic resin with a thermoplastic resin, such as a nylon. However, in embodiments, the thermoset resins in the form of pellets or filaments can contain organic or inorganic particles such as wood flour, ceramics, metals and wax. Yet another example is the combination of a thermosetting phenolic resin, thermoplastic resin and other organic or inorganic particles. Preferably, the amount of particles present provides a desirable characteristic to the pellets, filament or the finished part made therefrom. In this aspect, the amount of organic or inorganic particles present can be from about 0.001% wt/wt to about 50% wt/wt, or from about 0.001%) wt/wt to about 25%> wt/wt or less.

In embodiments, the present subject matter is directed to a structure comprising, a cured thermoset resin having an engineered three-dimensional shape. The structure will comprise one or more layers of a cured thermoset resin. Accordingly, in embodiments, the structure can contain from 2 to an unlimited number of engineered layers; from 2 to about 10,000 layers; from 2 to about 5,000 layers; from 2 to about 1,000 layers; from 2 to about 500 layers; from 2 to about 250 layers; from 2 to about 100 layers; from 10 to about 500 layers; from 50 to about 500 layers; from 100 to about 500 layers; or from 250 to about 500 layers. Each layer may be of the same or different type of resin. Each layer may be the same or different dimensions. There is almost no limit to the shapes that can be prepared by additive manufacturing. The shapes will be designed and engineered to a specification. The methods described herein can prepare the structures according to the specification. In embodiments, the structure is an engineered three-dimensional shape designed using computer-aided design. Almost unlimited substantially identical copies of the structures can be prepared by the methods. In aspects of this embodiment, the present subject matter is directed to a plurality of monodisperse three-dimensional structures comprising, two or more discrete structures, each comprising or consisting essentially of a cured thermoset resin having an engineered three-dimensional shape, wherein each structure of the plurality is substantially identical. In this embodiment, the material distinction is that the structure is fabricated using essentially only the thermoset resin.

The structures may contain other components. For example, the structures can comprise a layer of thermosetting resin and an adjacent layer being inorganic or organic in nature. Organic layers include those prepared from a hydrocarbon, lipid or wax. For example, one role of these other, adjacent layers may be to support portions of the part that might not support itself until nearly fully cured.

Structures can be carbonized thermally after the part has been nearly fully cured.

The subject matter described herein is directed to the following embodiments:

1. A method of preparing a three-dimensional structure, the method comprising:

i. providing a solid non-crosslinked thermoset resin in the form of pellets or a filament;

ii. subjecting a bead of the thermoset resin to curing conditions while extruding the bead of the thermoset resin onto a support to form a first layer, wherein the thermoset resin is partially or fully cured to form a partially or fully cured first polymer layer of a thermoset material; and

iii. subjecting a bead of the thermoset resin to curing conditions while extruding the bead of the thermoset resin to form a second layer of thermoset material in contact with the cured first polymer layer,

wherein the second layer of thermoset material is partially or fully cured to form a partially or fully cured second polymer layer of thermoset material, and wherein the three-dimensional structure is prepared. In embodiments, each successive layer is crosslinked to each adjacent layer. The steps above can be repeated to form a three- dimensional object having tens, hundreds or thousands of layers, and in each one, the polymers can be crosslinked or entangled with the polymers in the two adjacent layers. The polymers can be crosslinked or entangled in fewer than each of the layers depending on the nature of a particular layer and its two adjacent layers.

2. The method of embodiment 1, wherein the thermoset resin is a solid selected from the group consisting of thermoset phenolic resins; thermoset lignin resins; thermoset tannin resins; thermoset amino resins; thermoset polyimide resins; thermoset isocyanate resins; thermoset Maillard reactants or Maillard resins, thermoset vinylic resins; thermoset styrenic resins; thermoset polyester resins; thermoset melamine resins; thermoset vinylester resins; thermoset maleimide resins; thermoset epoxy resins; thermoset acrylate resins, polyamidoamine resins; and mixtures thereof.

3. The method of any above embodiments, wherein the thermoset resin is selected from the group consisting of thermoset phenolic resins, thermoset amino resins, thermoset epoxy resins, thermoset isocyanate resins, and thermoset acrylate resins. 4. The method of any above embodiments, wherein the first cured polymer layer is cross-linked with the second cured polymer layer.

5. The method of any above embodiments, wherein said step of subjecting the bead to curing conditions comprises irradiating the bead with thermal energy.

6. The method of any above embodiments, wherein said first layer comprising a thermoset resin is the same type of resin as the second layer comprising a thermoset resin.

7. The method of any above embodiments, wherein said first layer comprising a thermoset resin is a different type of resin as the second layer comprising a thermoset resin.

8. The method of any above embodiments, wherein the thermoset resin is extruded through a heated nozzle.

9. The method of any above embodiments, wherein the thermoset resin material is in the form of pellets.

10. The method of any above embodiments, wherein said pellets are monodisperse.

11. The method of any above embodiments, wherein the pellets comprise a thermoset phenol resin that is a phenol-formaldehyde resin.

12. The method of any above embodiments, wherein the pellets comprise a thermoset epoxy resin.

13. The method of any above embodiments, wherein the pellets comprise a thermoset acrylic copolymer resin.

14. The method of any above embodiments, wherein the pellets comprise two or more different types of pellets.

15. The method of any above embodiments, wherein the pellets comprise a first pellet comprising a thermoset phenol-formaldehyde resin, and a second pellet comprising a thermoset epoxy resin.

16. The method of any above embodiments, wherein the first pellet and the second pellet are present in a particular ratio.

17. The method of any above embodiments, wherein the phenolic OH group on the thermoset phenol-formaldehyde resin is equimolar to the oxirane group of the thermoset epoxy resin.

18. The method of any above embodiments, wherein the thermoset resin material is in the form of a filament. 19. The method of any above embodiments, wherein the filament is a continuous strand.

20. The method of any above embodiments, wherein the strand is wound on a spool.

21. The method of any above embodiments, wherein the filament is rod-like and from about 10 mm to about 30 mm in length.

22. The method of any above embodiments, wherein the thermoset resin is a thermoset phenolic resin.

23. The method of any above embodiments, wherein the thermoset phenolic resin is a drop resole resin.

24. The method of any above embodiments, wherein the thermoset resin is a thermoset epoxy resin.

25. The method of any above embodiments, wherein the thermoset resin is a thermoset acrylic copolymer resin.

26. The method of any above embodiments, wherein the thermoset phenolic resin is a phenol-formaldehyde resin having a mole ratio of formaldehyde to phenol of about

1.1 : 1 to about 3 : 1.

27. The method of any above embodiments, wherein the thermoset phenolic resin has a crosslinker and a 0.6 to 0.9 ratio of formaldehyde to phenol.

28. The method of any above embodiments, wherein the thermoset amino resins are resins having a mole ratio of formaldehyde to urea from about 2.21.1 : 1 to about 3.8: 1.

29. The method of any above embodiments, wherein subjecting the thermoset resin to irradiation comprises subjecting said thermoset resin to UV-radiation or laser radiation.

30. The method of any above embodiments, further comprising a layer comprising a thermoplastic resin.

31. The method of any above embodiments, further comprising successively repeating steps i. through iii. to form a three-dimensional structure having three or more layers.

32. A composition in the form of a pellet or filament comprising a resin selected from the group consisting of: non-crosslinked thermoset acrylic copolymer comprising acrylate and methacrylate, such as, 1 mol % glycidyl methacrylate and 1 mol % β- carboxyethyl acrylate; non-crosslinked thermoset phenol-formaldehyde resin; and non-crosslinked thermoset bisphenolA-based epoxy resin. The following examples are offered by way of illustration and not by way of limitation.

EXAMPLES Example 1

Pelletized Thermosetting Resin for Material Extrusion An acrylic copolymer is made with acrylate and methacrylate monomers to a molecular weight of 41,000 daltons via a known process that is solvent-free. The composition is 1 mol% glycidyl methacrylate and 1 mol% β-carboxyethyl acrylate. The Tg of the composition is 45°C measured by differential scanning calorimetry.

The molten acrylic polymer is pelletized as it is discharged from the reactor. The pellets are then conveyed to a material extrusion 3D printer with a temperature profile controlled so that crosslinking only begins at the tip of the extruder. The conveying mechanism is a conical twin-screw extruder that applies sufficient force of the pellets to push the fused material out of the extruder tip.

A three dimensional object is printed with this printer under computer control.

Example 2

Filament Strand of Thermosetting Resin for Material Extrusion An acrylic copolymer is made with acrylate and methacrylate monomers to a molecular weight of 41,000 daltons via a known process that is solvent-free. The composition is 1 mol% glycidyl methacrylate and 1 mol% β-carboxyethyl acrylate. The Tg of the composition is 45°C measured by differential scanning calorimetry.

The molten acrylic polymer is discharged from the reactor as a filament and collected on a spool.

The filament is then conveyed to a material extrusion 3D printer with a temperature profile controlled so that crosslinking only begins at the tip of the extruder. The conveying mechanism feeds the filament to the extruder tip with sufficient force to push the fused material out of the extruder tip.

A three dimensional object is printed with this printer under computer control.

Example 3 Material Extrusion of Two Types of Thermoset Resin Pellets in Additive

Manufacturing of a 3D Structure

One novolac resin suitable for this invention is GP 2074 which has a weight average molecular weight of about 3300 Daltons and equivalent weight of 104 grams per mole of hydroxyl groups. GP 2074 has a glass transition temperature at about 60°C. Pellets of Novolac phenol-formaldehyde resin and pellets of bisphenolA-based epoxy are obtained by the process of Example 1. The two types of pellets are blended at a ratio such that the phenolic OH group is equimolar to the oxirane group. This pellet blend is conveyed and extruded under computer control in an additive manufacturing process to prepare a three dimensional structure.

It is to be noted that the term "a" or "an" entity refers to one or more of that entity; for example, "a nanoparticle" is understood to represent one or more nanoparticles. As such, the terms "a" (or "an"), "one or more," and "at least one" can be used interchangeably herein.

Throughout this specification and the claims, the words "comprise," "comprises," and "comprising" are used in a non-exclusive sense, except where the context requires otherwise.

As used herein, the term "about," when referring to a value is meant to encompass variations of, in some embodiments ± 20%, in some embodiments ± 10%, in some embodiments ± 5%, in some embodiments ± 1%, in some embodiments ± 0.5%), and in some embodiments ± 0.1%> from the specified amount, as such variations are appropriate to perform the disclosed methods or employ the disclosed compositions.

Further, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the presently disclosed subject matter be limited to the specific values recited when defining a range. All publications and patent applications mentioned in the specification are indicative of the level of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the foregoing list of embodiments and appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

THAT WHICH IS CLAIMED:

1. A method of preparing a three-dimensional structure, the method comprising:

i. providing a solid non-crosslinked thermoset resin in the form of pellets or a filament;

ii. subjecting a bead of the thermoset resin to curing conditions while extruding the bead of the thermoset resin onto a support to form a first layer, wherein the thermoset resin is partially or fully cured to form a partially or fully cured first polymer layer of a thermoset material; and iii. subjecting a bead of thermoset resin to curing conditions while

extruding the bead of the thermoset resin to form a second layer of thermoset material in contact with the cured first polymer layer of a thermoset material, wherein the second layer of thermoset material is partially or fully cured to form a partially or fully cured second polymer layer of thermoset material,

wherein the three-dimensional structure is prepared.

2. The method of claim 1, wherein said thermoset resin is selected from the group consisting of thermoset phenolic resins; thermoset lignin resins; thermoset tannin resins; thermoset amino resins; thermoset polyimide resins; thermoset isocyanate resins; thermoset Maillard reactants or Maillard resins, thermoset vinylic resins; thermoset styrenic resins; thermoset polyester resins; thermoset melamine resins; thermoset vinylester resins; thermoset maleimide resins; thermoset epoxy resins; thermoset acrylate resins, and polyamidoamine resins; and mixtures thereof.

3. The method of claim 2, wherein said thermoset resin is selected from the group consisting of thermoset phenolic resins, thermoset amino resins, thermoset epoxy resins, thermoset isocyanate resins, and thermoset acrylate resins.

4. The method of claim 1, wherein the first cured polymer layer is cross- linked with the second cured polymer layer.

5. The method of claim 1, wherein said step of subjecting the bead to curing conditions comprises irradiating the bead with thermal energy.

6. The method of claim 1, wherein said first layer comprising a thermoset resin is the same type of resin as the second layer comprising a thermoset resin.

7. The method of claim 1, wherein said first layer comprising a thermoset resin is a different type of resin as the second layer comprising a thermoset resin.

8. The method of claim 1, wherein the thermoset resin is extruded through a heated nozzle.

9. The method of claim 1, wherein the thermoset resin is in the form of pellets.

10. The method of claim 9, wherein said pellets are monodisperse.

11. The method of claim 9, wherein the pellets comprise a thermoset phenol resin that is a phenol-formaldehyde resin.

12. The method of claim 9, wherein the pellets comprise a thermoset epoxy resin.

13. The method of claim 9, wherein the pellets comprise a thermoset acrylic copolymer resin.

14. The method of claim 9, wherein the pellets comprise two or more different types of pellets.

15. The method of claim 14, wherein the pellets comprise a first pellet comprising a thermoset phenol-formaldehyde resin, and a second pellet comprising a thermoset epoxy resin.

16. The method of claim 15, wherein the first pellet and the second pellet are present in a particular ratio.

17. The method of claim 16, wherein the phenolic OH group on the thermoset phenol-formaldehyde resin is equimolar to the oxirane group of the thermoset epoxy resin.

18. The method of claim 1, wherein the thermoset resin is in the form of a filament.

19. The method of claim 11, wherein the filament is a continuous strand.

20. The method of claim 11, wherein the filament is rod-like and from about 10 mm to about 30 mm in length.