WO2023081304A1

WO2023081304A1 - Photopolymer composite formulations compatible with vat polymerization in additive manufacturing

Info

Publication number: WO2023081304A1
Application number: PCT/US2022/048865
Authority: WO
Inventors: Musa Mustafa; Joshua J. MARTIN; Randall M. Erb
Original assignee: 3Dfortify Inc.
Priority date: 2021-11-03
Filing date: 2022-11-03
Publication date: 2023-05-11

Abstract

Formulations of high temperature photopolymer resins filled with CNTs and ceramic particles to achieve electrostatic dissipative parts produced by additive manufacturing are disclosed. The addition of CNT-based pulp enables the formulations disclosed and/or enabled by the present disclosures to reach sufficient electrical conductivity to be electrostatic discharge-safe. The formulations can be modified to tune the electrical resistivity to be either electrostatically dissipative, insulative, or conductive.

Description

Photopolymer Composite Formulations Compatible with Vat Polymerization in Additive Manufacturing

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present disclosure claims priority to and the benefit of U.S. Provisional Application No. 63/275,165, entitled “Photopolymer Composite Formulations Compatible with Vat Polymerization in Additive Manufacturing,” filed on November 3, 2021, and U.S. Provisional Application No. 63/342,061, entitled “Photopolymer Composite Formulations Compatible with Vat Polymerization in Additive Manufacturing,” filed on May 13, 2022, the contents of which are incorporated by reference herein in their entireties.

FIELD

[0002] The present disclosure relates to vat photopolymerization additive manufacturing, including for both stereolithography (SLA) and digital light processing (DLP) style printing, and more particularly relates to photopolymer composite formulations for use in conjunction with the same. The disclosed formulations are able to be used at high temperatures and are also electrostatic discharge-safe.

BACKGROUND

[0003] Electrostatic Discharge (ESD) of small voltages is enough to destroy sensitive electrical components or ignite flammable vapor. Parts made from an ESD-safe material are “static dissipative,” allowing for controlled static discharge with precisely tuned resistivities of approximately 10⁵- 10¹² Q per square. Such resistivities are positioned to deliver ESD-safe performance to industries with explosion and fire hazards, electrostatic protected areas, and/or environments requiring no electrostatic attraction of dust or bioparticles. The current leading solutions are machined from stock materials like sheets of Durapol®. Advantages to Durapol® include its high tolerance, its homogeneity, and its low heat capacity (e.g.., it does not draw heat away from the assemblies in a solder-reflow oven). Disadvantages to Durapol® include that it comes in only standard thicknesses and that it needs to be machined, which limits the geometries of jigs and fixtures. More generally, the issue is that there are no current DLP ESD-safe elastomers available. To the extent ESD-safe elastomers exist in other types of printing, such as fused deposition modeling (FDM) printing, they do not offer high resolution and/or high throughput manufacturing rates.

[0004] There is a need for a 3D-printed ESD-safe material that delivers on the advantages of Durapol® and similar offerings but speaks to the customizable and on-demand geometries not currently available with Durapol® style solutions. There are not many photopolymer solutions on the market that are ESD safe. Most options leverage carbon nanotubes (CNTs) to gain conductivity. Resulting material, however, is typically brittle and weak. There is likewise a need for ESD-safe elastomers that can be produced using 3D printing techniques, such as DLP, that are high resolution and/or can be produced at a high throughput.

SUMMARY

[0005] The present disclosure is directed towards formulations that include high temperature photopolymer resins filled with CNTs and ceramic particles to achieve electrostatic dissipative parts produced by additive manufacturing (also referred to as 3D printing). The resins are formulated to be compatible with vat polymerization in additive manufacturing processes, capable of being used at high temperatures and also being able to be electrostatic discharge-safe. The addition of CNT -based pulp enables the formulations disclosed and/or enabled by the present disclosures to reach sufficient electrical conductivity to comfortably land in the electrostatic dissipative range for surface resistivity. Such formulations address printability issues commonly faced in the additive manufacturing of electrostatic dissipative printable resins, while also exhibiting strong mechanics and high heat deflection temperature (HDT) values for high temperature applications. The formulations provided for and otherwise derivable from the present disclosures can be modified to tune the electrical resistivity to be either electrostatically dissipative, insulative, or conductive.

[0006] One exemplary composite formulation for use in additive manufacturing includes a photopolymer resin and a plurality of carbon nanotubes disposed in the resin. The composite formulation is electrostatic discharge-safe.

[0007] The composite formulation can include a plurality of ceramic particles disposed in the resin. The plurality of ceramic particles can include one or more of aluminum oxide, aluminum nitride, and/or boron nitride in an amount approximately in a range of about 1 vol% to about 10 vol%. In some embodiments, the composite formulation can include one or more additives forming a cross-link between a plurality of strands of the photopolymer resin to create a network of the photopolymer resin.

[0008] A plurality of magnetic particles can be disposed in the resin. In some embodiments, the photopolymer resin can include an elastomeric photoresin. The photopolymer resin can include a high temperature methacrylate resin.

[0009] The plurality of carbon nanotubes can include a carbon nanotube-based pulp. In some embodiments, a volume fraction of the carbon nanotube-based pulp can be approximately in the range of about 0.01 wt% to about 50 wt%.

[0010] In some embodiments, the composite formulation can include a plurality of interconnected pathways configured for electron conduction. The composite formulation can include a granulated structure. The composite formulation can have a Shore Hardness of approximately 70A or softer. The composite formulation can also have a surface resistivity approximately in the range of about 10⁴ per square to about 10⁷ per square. A tear strength of the composite formulation can be approximately 24 KN/M or better. An ultimate tensile strength of the composite formulation can be approximately 1.3 MPa or better. A Young’s Modulus of the composite formulation can be about 10 MPa or better. An elongation at break of the composite formulation can be about 60% or better.

[0011] The composite formulation can be formed into printed circuit board masking boots. In some embodiments, the composite formulation can have a high deflection temperature (HDT) that is approximately in a range of about 150 °C to about 350 °C.

[0012] One exemplary embodiment of a method of printing includes performing an additive manufacturing process to print one or more layers of a printed part using a composite formulation that includes a photopolymer resin and a plurality of carbon nanotubes disposed in the resin, and applying a continuous mixing process to maintain a general homogeneity of the composite formulation as part of the performing action. [0013] In some embodiments, the method can further include tuning a volume fraction of the carbon nanotube-based pulp to approximately in the range of about 0.01 wt% to about 50 wt%. Tuning the volume fraction can include adjusting an amount of the plurality of carbon nanotubes to change a degree of homogeneity of the composite formulation. In some embodiments, the method can further include increasing a time of application of the continuous mixing process to increase the general homogeneity of the composite formulation.

[0014] A plurality of carbon nanotubes can include a carbon nanotube-based pulp. The continuous mixing process can break down the carbon nanotube-based pulp to a viscosity and photokinetic profile of the plurality of carbon nanotubes. In some embodiments, a resistivity of the composite formulation can be proportional to an amount of time that the continuous mixing process is applied.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] This disclosure will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0016] FIG. 1 is a front perspective view of an embodiment of a DLP-printed, ESD-safe elastomeric photoresin of the present embodiments;

[0017] FIG. 2 is a schematic illustration of the composition of the, ESD-safe elastomeric photoresin of FIG. 1;

[0018] FIG. 3 is a side perspective view of DLP-printed surface resistivity samples of a high temperature ESD-safe photoresin;

[0019] FIG, 4 is a prior art schematic illustration of an electrostatic discharge (ESD) range;

[0020] FIG. 5 A is a perspective view of one embodiment of a printing apparatus with which the photoresin formulations of the present disclosure can be used;

[0021] FIG. 5B is a side view of the printing apparatus of FIG. 5 A having a side panel of a housing removed to illustrate components of the printing apparatus disposed within the housing; [0022] FIG. 6 provides three images of a surface of an ESD-safe photoresin of FIG. 1 that illustrate a changing surface resistivity as a factor of time in a continuous kinetic mixer (CKM) module;

[0023] FIG. 7 is a front perspective view of one embodiment of printed circuit board (PCB) masking boots manufactured with the ESD-safe elastomeric photoresin of FIG. 1 disposed on PCB components; and

[0024] FIG. 8 is a table illustrating the results of testing samples of the high temperature ESD- safe photoresin of FIG. 3 using three-dimensional printing techniques at different loading stress levels.

DETAILED DESCRIPTION

[0025] Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure. Terms commonly known to those skilled in the art may be used interchangeably herein. Further, the present disclosure includes some illustrations and descriptions that include prototypes or bench models. A person skilled in the art will recognize how to rely upon the present disclosure to integrate the techniques, systems, devices, and methods provided for into a product in view of the present disclosures.

[0026] The present disclosure generally relates to composite formulations of a high temperature photopolymer resin and one or more fillers to achieve electrostatic dissipative parts produced by additive manufacturing. The one or more fillers can include CNTs and/or ceramic particles that are able to be electrostatic discharge-safe. The addition of these fillers can enable the resin to reside in the electrostatic dissipative range for surface resistivity. An amount of the fillers mixed with the photopolymer resin to create the ESD-safe elastomeric photoresin of the present embodiments can be varied to tune one or more parameters, e.g., temperature, conductivity, and so forth, of the resin.

[0027] FIG. 1 illustrates an exemplary embodiment of a DLP-printed, ESD-safe material 100, e.g. elastomer, printed with the formulation of the present embodiments. In some embodiments, parts made from an ESD-safe material can be “static dissipative,” allowing for controlled static discharge with precisely tuned resistivities of approximately 10⁵- 10¹² Q per square. For example, embodiments of ESD-safe elastomers of the present disclosure can comprise a low durometer resin — having a durometer level lower than any known resin in the industry with a hardness of 70 on the Shore A hardness scale — having electrostatically dissipative properties. Electrostatic Discharge (ESD) of small voltages can be enough to destroy sensitive electrical components or ignite flammable vapor. In at least some embodiments, the ESD-safe elastomers of the present disclosure can have a Shore Hardness of approximately 70A and a surface resistivity approximately in the range of about 10⁴ Q per square to about 10⁷ Q per square. The ESD-safe elastomers of the present disclosure can provide superior protection with arguably the most flexible and/or softest material available on any 3D printing platform. Such resistivities can be positioned to deliver ESD-safe performance to industries with explosion and fire hazards, electrostatic protected areas, and/or environments requiring no electrostatic attraction of dust or bioparticles. Overall, the resulting ESD-elastomer resins can be soft (e.g., Shore Hardness of approximately 70A) and have a higher resolution than FDM materials and/or fused filament fabrication (FFF) materials, among other printing techniques, thus providing the only elastomeric, ESD-safe photoresin in the field.

[0028] FIG. 2 schematically illustrates an exemplary embodiment of the formulation of the ESD-safe elastomeric photoresin 100 of the present embodiments. As shown, the composition of the ESD-safe elastomeric photoresin 100 can include an elastomeric photoresin 102, a conductive filler 104, and/or additives 106. The ESD-safe elastomeric photoresin 100 can have high resolution and enable fast manufacturing and iteration speed to allow for economical production of bespoke elastomeric parts for a variety of applications, including: ESD-safe custom tools, jigs, and/or fixtures; trays for electronics handling/storage; soft grippers and/or contact points; seals, gaskets, boots, and/or plugs; anti-static prototypes and/or end-use components, such as straps; bumpers and/or mounts; and/or vibration absorbers.

[0029] The elastomeric photoresin 102 can include a base photopolymer that is composed of one or more of monomers, oligomers, photoinitiators, UV blockers, dyes, and/or thermoplastic additives. Some non-limiting examples of the base photopolymer can include a high temperature methacrylate resin, high elongation elastomeric resin, and/or high toughness acrylate resin. The use of high temperature compounds in the resin 100 of the present embodiments can contribute to the manufacture of an ESD-safe elastomeric photoresin 100 having a high deflection temperature (HDT) for the ESD formulation that is superior to that of competitors. Moreover, the strength and stiffness of the ESD-safe elastomeric photoresin 100 of the present embodiments can be superior to conventional resins due, at least in part, to the inclusion of the ceramic particles discussed above.

[0030] One or more conductive substances can be added to the photopolymer resin to increase a conductivity of the resin. For example, the electrically conductive filler 104 can be composed of one or more of carbon-based fillers (e.g., carbon nanotubes (CNTs), carbon black, carbon nanotube pulp, carbon fibers, activated carbon, SuperP carbon, graphene, graphite, etc.), metal fillers (e.g., silver, copper, steel, stainless steel, iron, graphene, graphite, boron, aluminum, zinc, cobalt, cadmium, nickel, lithium, platinum, palladium, tin, chromium, selenium, tantalum, niobium, lead, zirconium, titanium, etc.), semiconductor fillers (e.g., silicon), ceramic fillers (e.g., iron oxide, etc. . .), and/or metal-coated fillers (e.g., metal-coated carbon fiber, metal-coated ceramic particles, metal-coated polymeric particles, etc.). Combinations of these particle types are possible and are sometimes synergistic. Volume fractions of these particles can be approximately in the range of about 0.01 wt% to about 50 wt%, and can depend, at least in part, on the desired resistivity in the final part, as discussed in greater detail below.

[0031] In some embodiments, CNTs in the conductive filler of the elastomeric photoresin can include CNT pulp. For example, CNT pulp can be added to the high temperature photopolymer resin to achieve highly conductive composites after polymerization. FIG. 3 illustrates resistivity samples fabricated by using a DLP printing platform approximately one (1) inch wide to test the function of adding CNTs to a photopolymer resin 102. CNT pulp can be easier to mass produce than standard CNTs and is also less expensive. While CNT pulp can have less homogeneity than standard CNTs, CNT pulp can offer at least two distinct advantages over standard CNTs. For example, CNT pulp can create a percolated network having more interconnected pathways for electron conduction at a lower volume fraction than can be achieved with dispersed standard CNTs, allowing conductivity of the resin to be increased while using less CNT product, thereby greatly reducing manufacturing costs. Moreover, the lack of homogeneity, as shown in FIG. 2, can create a granulated structure that exhibits improved thermomechanical properties and provides an aesthetically pleasing granite-like structure of the resin.

[0032] Alternatively, or additionally, in some embodiments, various ceramic particles or platelets can be added to the formulation to aid with thermo-mechanical properties and processability of the material (e.g., CNT aggregation). Some non-limiting examples of the ceramic particles can include aluminum oxide, aluminum nitride, and/or boron nitride. An amount of the ceramic particles can be approximately in a range of about 1 vol% to about 10 vol%, approximately in a range of about 2 vol% to about 8 vol%, approximately in a range of about 3 vol% to about 7 vol%, and/or be about 5 vol%. A size of the ceramic particles can be approximately in a range of about 1 pm to about 50 um, approximately in a range of about 2 um to about 40 pm, approximately in a range of about 3 pm to about 30 um, and/or approximately in a range of about 4 pm to about 20 pm. The addition of ceramic filler can result in manufacture of high resolution 3D printed parts with lesser surface roughness and improved dimensional accuracy. The addition of the ceramic filler can also improve the mechanical properties (e.g., tensile strength, flexural strength) of the formulation, as well as further boosting the measured HDT values.

[0033] An amount of CNT pulp and ceramic particles or platelets used in the elastomeric photoresin can vary. An amount of CNT pulp can be approximately in range of about 0.05 wt% to about 5 wt%, and/or from about 0.01 wt% to about 1 wt% and an amount of the ceramic particles can range from about 1 vol% to about 8 vol%. For example, in some embodiments, the formulation of the present embodiments can be made by combining about 0.1 wt% of CNT pulp and about 5 vol% ceramic platelets, speed mixed in a high HDT methacrylate photopolymer, as discussed in the Example below. [0034] In some embodiments, the CNT pulp of the ESD-safe elastomeric photoresin 100 of the present embodiments can result in an entangled structure that creates better percolated pathways and allow for higher conductivities at lower loadings. The structures provided for herein, or otherwise derivable from the present disclosures, can also create domains of CNT-starved polymer that create pockets of very high mechanical properties that are not typically impacted locally by the presence of CNT. This granulated texturing appears to lead to overall benefits. The slight increase can be variability of the conductivities due to this granular nature, which can be low enough not to provide detriment to ESD-safe applications.

[0035] CNTs can be naturally bonded with sp² bonds exhibiting strong molecular interactions, and can be combined with van der Waals forces that contribute to the inclination for chaining between CNT particles. In some embodiments, additional additives can be added to the photopolymer resin 102 to further facilitate chaining. These additives can include, but are not limited to, monomers, oligomers, photoinitiators, UV blockers, dyes, and/or thermoplastic additives. These additives can effectuate cross-links 106 on the elastomeric photoresin 102, as shown in FIG. 2. The cross-links 106 can be effective to connect the elastomeric photoresin 102 to one another, thereby creating a network of the photoresin within the ESD-safe elastomeric photoresin 100.

[0036] In some embodiments, the ESD-safe elastomeric photoresin 100 of the present disclosure can include a dependency of compression on resistivity. The electrical conductivity can increase upon compression as the conductive particles included in the elastomeric photoresin are driven closer together and can create a more conductive network through the material.

[0037] Table 1 illustrates relevant data collected according to The American Society for Testing and Materials (ASTM) standards that help illustrate the beneficial mechanical properties of the ESD-safe elastomeric photoresin 100 resulting from the present disclosure. The data includes the following: Table 1 CHANICAL PROPERTY

ctrical Resistivity (Q/sq) 10⁴-10⁷

dness Shore A

r Strength (KN/M)

mate Tensile Strength (MPa)

Young’s Modulus (MPa)

Elongation at Break (%)

* 1 M when uncompressed* **Type 5 tensile bars were used**

[0038] Results from the surface resistivity tests of the samples in FIG. 3 demonstrate that the conductivity of the initial formulation can sit in the ESD range shown in FIG. 4. FIG. 4 illustrates the ESD range to measure surface resistivity in greater detail. As shown, electrostatic discharge can be approximately in the range of about IxlO¹ ohms to about 1 x IO²⁰ ohms, with lower surface resistivities corresponding to higher electrical conductivities, and higher values, e.g., 1 x 10¹² ohms and greater, corresponding to higher resistivities. Higher volume fractions can lead to higher electrical conductivities. For instance, adding the electrically conductive particle, e.g., CNT pulp, to the elastomeric photoresin at a sufficient volume fraction can drive bulk electrical conductivity from the insulative regime to the static dissipative regime. By way of non-limiting example, in some embodiments, CNT pulp approximately in the range of about 0.05 wt% to about 5 wt% can be incorporated to the elastomeric photoresin to achieve an electrical resistivity in the static dissipative range. In such embodiments, the elastomeric photoresin can include a surface resistivity approximately in a range of about IxlO⁵ ohms to about I x lO⁸ ohms. In contrast, photoresins without CNT pulp can have surface resistivity values of 1 x 10¹⁰ ohms and greater, thus lacking electrical conduction through the resin, and part(s) produced from the resin. Surface resistivity results in the static dissipative regime can enable the parts printed from the initial ESD formulation to be functional in various industries that utilize ESD-compatible and ESD-safe parts and fixtures, where fabrication of high resolution parts may otherwise be challenging. These industries include, by way of non-limiting examples: semiconductors, medical devices, automotive, electronics, aerospace, healthcare, manufacturing, defense, and/or military.

[0039] Some alternatives to using the resins of the present disclosure can include machining and/or molding a carbon loaded polymer. Durapol® is a common alternative used, for example, in printed circuit board (PCB) assembly and manufacturing as described above. Other alternatives exist, such as ESD-safe fused deposition modeling (FDM) 3D printing, although such techniques may lead to parts that have relatively poor surface finish. Moreover, while, there are alternative providers of ultraviolet (UV)-curable ESD resins, the chemistry used to keep particles in suspension can increase the cost by approximately 100% compared to the solutions provided for herein. Additionally, because the present disclosure uses additional ceramic particles to boost thermo-mechanical properties, the final strength, stiffness, and/or HDT of competitive offerings is typically less than what can be achieved by way of the present disclosure, as discussed above.

[0040] In at least some embodiments, at least some aggregated CNT structure(s) can be maintained, such as those enabled by the CNT pulp, while applying mixing methodologies, such as Continuous Kinetic Mixing™ (CKM), to achieve general homogeneity of the resulting material and/or printed part. The aggregated CNT structure(s) may be beneficial, for example, to enable electron flowing due to, for example, the percolated network that can be created with aggregated pulp-based morphologies. These bigger particle networks, however, may sediment quickly, but methodologies like CKM can help to roughly homogenize without breaking up the smaller percolated networks.

[0041] A person skilled in the art will recognize that the above-mentioned lack of homogeneity of the elastomeric photoresin can be undesirable in some cases. For example, use of CNT pulp can hinder dispersion of the CNT throughout the resin, which can lead to an uneven distribution of conductivity throughout the resin due to a non-uniform distribution of the CNT network therethrough.

[0042] In addition to the unique formulations that result from the present disclosures, printing processes such as those disclosed in International Patent Application Publication No. WO 2020/055870, entitled “Systems and Methods for Mixing Materials for Additive Manufacturing,” and the process of CKM as disclosed in publicly available documentation from 3D Fortify Inc. (at least some of which are incorporated by reference below), allows for the use of cheap CNT- based materials to be used that would otherwise settle out of suspension or agglomerate so badly that the electrical performance is no longer reliable.

[0043] For example, to remedy the heterogeneity of the CNT throughout the resin, the elastomeric resin of the present embodiments can be exposed to a three-dimensional printer. A non-limiting embodiment of a DLP printer is provided with respect to FIGS. 5 A and 5B herein.

[0044] For example, as shown, FIGS. 5 A and 5B illustrate one exemplary embodiment of a FLUX ONE 3D printer 10. The printer 10 includes an outer casing or housing 20 in which various components of the printer 10 are disposed. The FLUX ONE 3D printer is designed to use a bottom-up printing technique, and thus includes a build plate 30 that can be advanced vertically, substantially parallel to a longitudinal axis L of the printer 10 such that the build plate 30 can be moved vertically away from a print reservoir 50 in which resin to be cured to form a desired part, such as resins as provided for above, is disposed. Generally, the build plate 30 can be advanced up and down with respect to a linear rail 32 as desired, the linear rail 32 being substantially colinear with the longitudinal axis L. As a result, the rail 32 can be considered a vertical rail. The build plate 30 can be associated with the linear rail 32 by way or one or more coupling components, such as arm or armatures 34, guides 36, 38, and/or other structures known to those skilled in the art for creating mechanical links that allow one component to move with respect to another.

[0045] As described herein, as the build plate 30 moves away from the print reservoir 50, the resin is cured to the build plate 30 and/or to already cured resin to form the printed part in a layer-by-layer manner as the build plate 30 advances away from the reservoir 50. The resin is cured, for example, by a light source and/or a radiation source, as shown a digital light projector 60. The reservoir 50 can include a glass base 52 to allow the digital light projector 60 to pass light into the reservoir 50 to cure the resin. The glass base 52 can more generally be a transparent platform through which light and/or radiation can pass to selective cure the resin. Resin can be introduced to the printer 10 by way of a materials dock 54 that can be accessible, for example via a drawer 22, formed as part of the housing 20.

[0046] One or more mixers can be included to help keep the resin viscous and homogeneous. More particularly, at least one mixer, as shown an external mixer 80, can be in fluid communication with the print reservoir 50 to allow resin to flow out of the reservoir 50, into the mixer 80 to be mixed, and then flow back into the reservoir 50 after it has been mixed by the mixer 80. The mixer 80 can be accessible, for example, via a front panel door 24 provided as part of the housing 20. At least one heating element 82 can be included for use in conjunction with the mixer 80 such that the treated (i.e., mixed) resin is also heated. In the illustrated embodiment the heating element 82 is disposed proximate to the print reservoir 50, heating the resin after it has been mixed by the mixer 80, although other location are possible, including but not limited to being incorporated with the mixer 80 to heat and mix simultaneously and/or consecutively. The resin can be heated more than once by additional heating elements as well. Resin that travels from the reservoir 50, to the mixer 80, and back to the reservoir 50 can flow through any number of conduits or tubes configured to allow resin to travel therethrough, such as the conduits 84 illustrated in FIG. 5B.

[0047] The resin can also flow through a reservoir manifold 56, which can be disposed above the print reservoir 50. The manifold 56 can serve a variety of purposes, including but not limited to helping to maintain the position of the reservoir 50 during operation, and helping to facilitate mechanical, electrical, and fluid connections between the reservoir and other components of the printer 10. For example, the manifold can be designed to allow resin to be mixed and/or heated to flow out of the reservoir 50, as well as allow mixed and/or heated resin to flow into the reservoir 50 via ports formed therein. Electrical connections to help operate various features associated with the reservoir 50, such as monitoring of a level of resin and/or monitoring an orientation of one or more components disposed and/or otherwise situated with respect to the reservoir 50, can be passed through the manifold 56. The electrical connections may be associated with various electronics and the like housed within the printer 10, for example in an electronics panel 90. Additional details about a reservoir manifold are provided for in International Patent Application No. WO 2021/217102, entitled “Manifold and Related Methods for Use with a Reservoir for Additive Manufacturing,” the contents of which is incorporated by reference herein in its entirety.

[0048] In some embodiments, a magnetic fiber alignment system 92 can be provided for as part of the printer 10. Such a system 92 can help to control aspects of a print job when magnetic functional additives, such as magnetic particles like those described herein, are associated with the resin being printed, such as the resins disclosed herein and/or otherwise derivable from the present disclosures. More specifically, the system 92 can include one or more magnets and/or magnetic field generators that enable the location of the magnetic particle including resin to be controlled by the system 92. Other functional additives that are not necessarily magnetic can also be incorporated with the resin.

[0049] A touch screen 26 or other user interface can be included as part of the housing 20 to allow a user to input various parameters for a print job and/or for instructions, signals, warnings, or other information to be passed along by any systems of the printer 10 to a user. Still further, the housing 20 can include an openable and/or removable hood 28 that enables a printed part, as well as components of the printer 10, to be accessed. The hood 28 can also include a viewing portion, such as a window 29, that allows a user to view a print job being performed. As shown, the build plate 30, and thus a part being printed that will be attached to the build plate 30, can be seen through the window 29. Further, the reservoir 50, manifold 56, and other components of the printer 10 can also be visible through the window 29.

[0050] One of the realized benefits for the ESD materials being developed is the role that the aforementioned CKM system plays in breaking down large aggregate structures of electrically conductive filler and homogenizing the ESD resins. In particular, as mentioned above, the ability of CKM to break down the pulp can allow for use of cheaper and more scaled carbonbased materials like carbon nanotube (CNT) pulp and carbon fiber in manufacturing the ESD- safe photopolymer resin 100 without sacrificing the benefits of filling a photopolymer resin with CNTs. The CKM module can also break down the effective size of carbon fibers, especially pitch carbon fiber, to bring the average particles length to below approximately 100 pm. Larger lengths of carbon fiber (e.g., approximately greater than about 100 pm) can create local hot spots of high electrical conductivity from locally high densities of CNT pulp in a poorly mixed system that may not provide a homogenous material for reliability and safety considerations. The CKM module can break the CNT pulp in approximately a range of about 4 hours to about 8 hours. The ability to break CNT pulp using the above described methods is superior to conventional techniques that cannot tolerate the elevated viscosity and photokinetic profile of the resin having a CNT pulp as the conductive material in a printing process. Moreover, breaking of the CNT pulp can remove the granite-like appearance of the ESD-safe photopolymer resin 100, which can be seen as undesirable in some instances.

[0051] The formulations provided for and otherwise derivable from the present disclosures can be modified to tune the electrical resistivity to be either electrostatically dissipative, insulative, and/or conductive. For example, as mentioned above, the degree of homogeneity of the resin formulation of the present embodiments can depend, at least in part on the amount of time that the elastomeric photoresin filled with CNT pulp is run through the CKM. FIG. 6 illustrates the change in resistivity as a function of time spent in the CKM. As shown, the resistivity of the resin formulation can increase to a value of about 10¹² Q/sq, at which point the resistivity can plateau. Moreover, as shown in FIG. 6, as the time that the elastomeric ESD-safe photoresin spends in the CKM increases, the volume resistivity of the material can be expected to increase from about 10⁶ Q/sq (static dissipative range) to about 10¹² Q/sq, where it plateaus in the insulative range.

[0052] In some embodiments, tuning of the homogeneity can be performed by adjusting a volume fraction of the CNTs added to the resin. For example, tuning the volume fraction by adjusting an amount of the CNTs added to the resin can adjust a volume resistivity, morphology, and/or surface resistivity of the resin to change a degree of the electrical resistivity of the resin, and thus the part(s) produced using the resin. That is, the ESD-safe elastomeric photoresin 100 can be tuned to fall into the conductive range just by increasing the volume fraction. Increasing a volume fraction of the CNT pulp within the resin can contribute to a resin having a higher conductivity while having less CNT filler than conventional CNTs used in resin, which reduces costs of manufacture. A person skilled in the art will recognize that tuning of additional parameters can tune the electrical resistivity of the resin. For example, in some embodiments, magnetic particles, such as those used by Fluxprint, manufactured by 3DFortify Inc. of Boston, MA, can be added to the resin approximately ranging from about 1 vol% to about 8 vol% to tune the resistivity thereof. Additionally, temperature tuning of the resin as part of the CKM module can be used to tune the resistivity of the photopolymer.

[0053] In some embodiments, a control loop can be implemented to provide feedback with respect to one or more parameters of the ESD-safe elastomeric photoresin 100. For example, with respect to the homogeneity of the resin, the resin having CNTs disposed therein that passes through CKM can be compared to a control resin to compare dispersion of the CNT pulp throughout the ESD-safe elastomeric photoresin 100. Resins in which the CNT pulp is not sufficiently dispersed can be run through the CKM until the desired dispersal of the pulp is achieved. Some additional non-limiting examples of parameters of the ESD-safe elastomeric photoresin 100 that can be monitored via the feedback loop can include volume resistivity and/or surface resistivity.

[0054] A person skilled in the art will understand how to apply the principles, techniques, and the like disclosed herein to various additive manufacturing processes and printers. Some nonlimiting examples of DLP printers and techniques with which the present disclosure can be used include those provided for in U.S. Patent No. 10,703,052, entitled “Additive Manufacturing of Discontinuous Fiber Composites Using Magnetic Fields,” U.S. Patent No. 10,732,521, entitled “Systems and Methods for Alignment of Anisotropic Inclusions in Additive Manufacturing Processes,” and the FLUX 3D printer series, including the FLUX ONE 3D printer, manufactured by 3DFortify Inc. of Boston, MA (further details about the FLUX 3D printer series provided for at http://3dfortify.com/ and https://3dfortify.com/tech- talks/?utm_campaign=Press%20Release&utm_medium=email&_hsmi=121056681&_hsenc=p2 ANqtz- 8FkzgrKUqpdmX8htE0mGXDqHASskXxSVI_I_LgnnKsoZ_oCHiruVZLpFcDoACFbnSUDx4 x5Hu06G3 S As9sUij skF2Hl Q&utm_content= 121056681 &utm_source=hs_email, and related web pages), the contents of all, including any videos accessible at such web pages and related web pages, being incorporated by reference herein in their entireties. The videos incorporated by reference at the second provided web page include videos entitled “Fortify’s Product and Services Ecosystem” (length 17 minutes), “CKM: Enabling the Printing of the Highest Performing DLP Materials” (length 9 minutes), “How Fluxprint Enables High Performance Materials for 3D Printing” (length 12 minutes), “Applications Highlight: Fortifying Mold Tools” (length 11 minutes), “Applications Highlight: 3D Printing Low Loss RF Devices” (length 13 minutes), “Tailoring Conductivity in Filled Photopolymers Using Fluxprint and CKM” (9 minutes), and “Innovation Through Collaboration :Fortify’s Material Partnerships” (8 minutes).

[0055] At least some embodiments of the present disclosure provide for ESD-elastomer resin that can be created using the Flux Developer platform for printing, offered by 3DFortify Inc., which can accelerate time to market for new materials formulations. This filled photo-resin can be printed on some of the above-referenced Fortify systems, as well as others known at the time of the present disclosure, including the FLUX CORE printer from 3DFortify Inc. The FLUX CORE printer is a DLP printing platform that can enable high-throughput production of fine- featured parts from heavily loaded materials that are otherwise difficult to process. The FLUX CORE aspect of the printer comes with the aforementioned CKM module that can circulate, heat, and mix loaded materials to maintain particle suspension and ensure even dispersion throughout the printing process. An even dispersion can help ensure that ESD-safe parts as provided for herein have consistent resistivities throughout.

[0056] The present disclosures can be reduced to practice and/or otherwise utilized in a variety of ways. For example, it has been demonstrated that the ESD-elastomer materials of the present disclosure can be used for the specific application of PCB masking boots 110. As shown in FIG. 7, such masking boots can protect sensitive PCB components 112 during PCB transport, PCB production, and/or PCB processing, among other similar components. Such masking boots 110 can also protect sensitive PCB components 112 during field use, including but not limited to mechanical protection and RF shielding. For these end-use implementations of PCB masking boots 110 or equivalents, the elastomeric property can provide cushioning and/or vibration adsorption while the electrically conductive particles can provide RF shielding capabilities, as illustrated in FIG. 7.

[0057] Table 2 illustrates relevant data collected according to The American Society for Testing and Materials (ASTM) standards that help illustrate the beneficial mechanical properties of the high temperature ESD-safe photoresin resulting from the present disclosure. The data includes the following: Table 2

**Type 5 tensile bars were used**

[0058] EXAMPLES

[0059] The present disclosures can be implemented by manufacturing this unique high temperature ESD formulation. The formulation can be made by combination of about 0.1 wt% of CNT pulp and about 5 vol% ceramic platelets, speed mixed in a high HDT methacrylate photopolymer. Other formulations and percentages are possible. A number of techniques can be used to mix and/or otherwise create the formulation, such as speed-mixing material(s) (e.g., CNT pulp from Miralon®) into a neat resin.

[0060] This high temperature ESD formulation can be used, for example, on the Fortify Flux series printers, at least some of which are referenced and incorporated by reference above. Parts printed can be used for high temperature jigs, tools, and/or fixtures, among other uses.

[0061] One instance of reducing the present disclosures to practice included the creation of six HDT samples using 3D printing techniques and then testing the printed samples using a third party testing laboratory (Intertek). The testing was conducted at two different loading stress levels, approximately 0.455 MPa and approximately 1.82 MPa, as outlined by ASTM D648, with the results being shown in FIG. 8 as approximately 284 °C and approximately 165 °C respective to the two load stress levels. The illustrated results include cl ceramic particles , although HDT data without cl ceramic particles is also possible. These high HDT values can be enabled, at least in part, by the base polymeric resin and by the presence of the additional ceramic particles. The HDT of the 3D printed ESD-safe parts in view of the present disclosure can be tunable and can have HDT values approximately in the range of about 150 °C to about 350 °C for the stress level of approximately 1.82 MPa or more, and more specifically, in some embodiments HDT values approximately in the range of about 225 °C to about 325 °C for the stress level of approximately 1.82 MPa.

[0062] One skilled in the art will appreciate further features and advantages of the present disclosure based on the above-described embodiments. Accordingly, the disclosure is not to be limited by what has been particularly shown and described. Further, a person skilled in the art, in view of the present disclosures, will understand how to implement the disclosed systems and methods provided for herein in conjunction with SLA-style and DLP-style additive manufacturing printers. All publications and references cited herein are expressly incorporated herein by reference in their entireties.

[0063] Examples of the above-described embodiments can include the following:

1. A composite formulation for use in additive manufacturing, comprising: a photopolymer resin; and a plurality of carbon nanotubes disposed in the resin, wherein the composite formulation is electrostatic discharge-safe.

2. The composite formulation of example 1, wherein the plurality of carbon nanotubes comprise a carbon nanotube-based pulp.

3. The composite formulation of example 2, wherein a volume fraction of the carbon nanotube-based pulp is approximately in the range of about 0.01 wt% to about 50 wt%.

4. The composite formulation of any of examples 1 to 3, further comprising: a plurality of ceramic particles disposed in the resin. 5. The composite formulation of example 4, wherein the plurality of ceramic particles comprises one or more of aluminum oxide, aluminum nitride, or boron nitride in an amount approximately in a range of about 1 vol% to about 10 vol%.

6. The composite formulation of any of examples 1 to 5, wherein the photopolymer resin comprises an elastomeric photoresin.

7. The composite formulation of any of examples 1 to 6, further comprises one or more additives forming a cross-link between a plurality of strands of the photopolymer resin to create a network of the photopolymer resin.

8. The composite formulation of any of examples 1 to 7, further comprising: a plurality of magnetic particles disposed in the resin.

9. The composite formulation of any of examples 1 to 8, wherein the photopolymer resin comprises a high temperature methacrylate resin.

10. The composite formulation of any of examples 1 to 9, further comprising: a plurality of interconnected pathways configured for electron conduction.

11. The composite formulation of any of examples 1 to 10, further comprising: a granulated structure.

12. The composite formulation of any of examples 1 to 11, wherein the composite formulation has a Shore Hardness of approximately 70A or softer.

13. The composite formulation of any of examples 1 to 12, wherein the composite formulation has a surface resistivity approximately in the range of about 10⁴ per square to about 10⁷ per square.

14. The composite formulation of any of examples 1 to 13, wherein the composite formulation has a tear strength of approximately 24 KN/M or better.

15. The composite formulation of any of examples 1 to 14, wherein the composite formulation has an ultimate tensile strength of approximately 1.3 MPa or better. 16. The composite formulation of any of examples 1 to 15, wherein the composite formulation has a Young’s Modulus of about 10 MPa or better.

17. The composite formulation of any of examples 1 to 16, wherein the composite formulation has an elongation at break of about 60% or better.

18. The composite formulation of any of examples 1 to 17, wherein the composite formulation is formed into printed circuit board masking boots.

19. The composite formulation of any of examples 1 to 18, wherein the composite formulation has a high deflection temperature (HDT) is approximately in a range of about 150 °C to about 350 °C.

20. A method of printing, comprising: performing an additive manufacturing process to print one or more layers of a printed part using a composite formulation comprising a photopolymer resin and a plurality of carbon nanotubes disposed in the resin; and applying a continuous mixing process to maintain a general homogeneity of the composite formulation as part of the performing action.

21. The method of example 20, wherein the plurality of carbon nanotubes comprise a carbon nanotube-based pulp.

22. The method of example 21, wherein the continuous mixing process breaks down the carbon nanotube-based pulp to a viscosity and photokinetic profile of the plurality of carbon nanotubes.

23. The method of printing of example 20 or example 21, further comprising tuning a volume fraction of the carbon nanotube-based pulp to approximately in the range of about 0.01 wt% to about 50 wt%.

24. The method of printing of any of examples 20 to 23, wherein tuning the volume fraction comprises adjusting an amount of the plurality of carbon nanotubes to change a degree of homogeneity of the composite formulation. 25. The method of any of examples 20 to 24, further comprising increasing a time of application of the continuous mixing process to increase the general homogeneity of the composite formulation.

26. The method of any of examples 20 to 25, wherein a resistivity of the composite formulation is proportional to an amount of time that the continuous mixing process is applied.

[0064] Some non-limiting claims are provided below.

Claims

23 What is claimed is:

2. The composite formulation of claim 1, wherein the plurality of carbon nanotubes comprise a carbon nanotube-based pulp.

3. The composite formulation of claim 2, wherein a volume fraction of the carbon nanotubebased pulp is approximately in the range of about 0.01 wt% to about 50 wt%.

4. The composite formulation of claim 1, further comprising: a plurality of ceramic particles disposed in the resin.

5. The composite formulation of claim 4, wherein the plurality of ceramic particles comprises one or more of aluminum oxide, aluminum nitride, or boron nitride in an amount approximately in a range of about 1 vol% to about 10 vol%.

6. The composite formulation of claim 1, wherein the photopolymer resin comprises an elastomeric photoresin.

7. The composite formulation of claim 1, further comprises one or more additives forming a cross-link between a plurality of strands of the photopolymer resin to create a network of the photopolymer resin.

8. The composite formulation of claim 1, further comprising: a plurality of magnetic particles disposed in the resin.

9. The composite formulation of claim 1, wherein the photopolymer resin comprises a high temperature methacrylate resin.

10. The composite formulation of claim 1, further comprising: a plurality of interconnected pathways configured for electron conduction.

11. The composite formulation of claim 1, further comprising: a granulated structure.

12. The composite formulation of claim 1, wherein the composite formulation has a Shore Hardness of approximately 70A or softer.

13. The composite formulation of claim 1, wherein the composite formulation has a surface resistivity approximately in the range of about 10⁴ per square to about 10⁷ per square.

14. The composite formulation of claim 1, wherein the composite formulation has a tear strength of approximately 24 KN/M or better.

15. The composite formulation of claim 1, wherein the composite formulation has an ultimate tensile strength of approximately 1.3 MPa or better.

16. The composite formulation of claim 1, wherein the composite formulation has a Young’s Modulus of about 10 MPa or better.

17. The composite formulation of claim 1, wherein the composite formulation has an elongation at break of about 60% or better.

18. The composite formulation of claim 1, wherein the composite formulation is formed into printed circuit board masking boots.

19. The composite formulation of claim 1, wherein the composite formulation has a high deflection temperature (HDT) is approximately in a range of about 150 °C to about 350 °C.

21. The method of claim 20, wherein the plurality of carbon nanotubes comprise a carbon nanotube-based pulp.

22. The method of claim 21, wherein the continuous mixing process breaks down the carbon nanotube-based pulp to a viscosity and photokinetic profile of the plurality of carbon nanotubes.

23. The method of printing of claim 20, further comprising tuning a volume fraction of the carbon nanotube-based pulp to approximately in the range of about 0.01 wt% to about 50 wt%.

24. The method of printing of claim 20, wherein tuning the volume fraction comprises adjusting an amount of the plurality of carbon nanotubes to change a degree of homogeneity of the composite formulation.

25. The method of claim 20, further comprising increasing a time of application of the continuous mixing process to increase the general homogeneity of the composite formulation.

26. The method of claim 20, wherein a resistivity of the composite formulation is proportional to an amount of time that the continuous mixing process is applied.