Patent Application
20170253751
Embodiments of the invention relate to three-dimensional (“3D”) printable inks, based on composite waterborne polymer dispersions.
The 3D printing industry currently faces limitations in the variety of materials that may be printed. Thermoplastic filaments are widely used in fused deposition modeling (“FDM”) and fused filament fabrication (“FFF”) printing, while UV curable resins are dominant in stereolithography (“SLA”) printing.
There is a commercial need for 3D printing of polymer-based inks in electronics, shoe manufacturing, and other industries.
In an aspect, embodiments of the invention relate to a composite waterborne dispersion for 3D printing. The composite waterborne dispersion includes a composition including a first aqueous dispersion of polymer particles, an associative thickener, and a first functional filler including conductive particles. The composition has a yield stress >0 Pa, the yield stress being at least one of a dynamic yield stress and a static yield stress. The composition is film-forming when dried.
One or more of the following features may be included. The composition may have a static yield stress >50 Pa, e.g., >200 Pa. The composition may have a viscosity selected from a range of 10 to 10,000 Pas at shear rate 1/s. The composition may include a non-volatile content selected from a range of 70 wt % to 95 wt %, or greater than 25 volume percent, preferably greater than 40 volume percent. The maximum agglomerate size of the composition may be less than 50 microns, or preferably less than 25 microns. The aqueous dispersion of polymer particles may be self-crosslinking at room temperature. The aqueous dispersion of polymer particles may have a minimum film formation temperature below 22° C. The aqueous dispersion of polymer particles may include at least one of a polyurethane, an acrylic, an alkyd, PVC, styrene butadiene, vinyl acetate, vinyl acetate ethylenes, vinyl maleate, or vinyl versatate. The associative thickener may be selected from the group including a hydrophobically modified ethoxylated urethane (HEUR), a hydrophobically modified alkali swellable emulsion (HASE), a tri-block co-polymer, a hydrophobically modified polyacrylate thickener, a hydrophobically modified polyether thickener, or a hydrophobically modified cellulose ether. The composite waterborne dispersion may include a solid metal precursor and/or a dissolved metal precursor.
The composition may further include a second functional filler. The second functional filler may include a color pigment, and the composition may include 0.1-10 wt % color pigment. The second functional filler may be selected from the group including conductive particles, fumed silica, milled glass fibers, PDMS, a eutectic metal particle, quartz, carbon fiber, thermally insulating particles, thermally conductive particles, ferromagnetic particles, or radar absorbing particles.
At least a portion of the second functional filler may include a coating material that interacts with the associative thickener. The coating material may be selected from the group including an unsaturated hydrocarbon, a fatty acid, an ionic surfactant, a nonionic surfactant, an ionic polymer, or a block copolymer.
The composition may include at least 25 wt % conductive particles. The conductive particles may be selected from the group including silver powder, silver flakes, silver nanowires, silver nanoparticles, silver-coated copper, silver-coated glass, silver-coated aluminum, gold nanowires, gold nanoparticles, gold powder, gold flakes, gold-coated copper, copper nanowires, copper microwires, copper nanoparticles, carbon nanotubes, carbon particles, graphene, copper oxide particles, tungsten particles, aluminum microparticles, nickel microparticles, or microparticles of eutectic metal systems. An average diameter of the polymer particles in the aqueous dispersion may be at least one order of magnitude smaller than an average diameter of the conductive particles of the first functional filler.
The composition may further include a rheological modifier that increases a resting viscosity, yield stress, or pseudoplastic behavior of the composition.
The composition may further include at least one of a defoamer, an antifoam, a coalescent, a dispersant, or an adhesion modifier. The composition may include the defoamer and the defoamer is selected from the group including a silicone-based defoamer, an oil-based defoamer, a powder-based defoamer, a wax-based defoamer, polyethylene glycol-based defoamer, polypropylene glycol-based defoamer, an alkyl-polyacrylate based defoamer, an antifoam, PDMS, polyester-functionalized silicone, or fluorosilicone.
The composition may include a coalescent. The coalescent may be selected from the group including glycol ethers, (3-hydroxy-2,2,4-trimethylpentyl) 2-methylpropanoate (e.g., TEXANOL from Eastman), propylene carbonate, diethyl carbonate, N-Methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF), tetrahydrofuran (THF), dibasic esters, glycols, glycol ether acetates, propylene glycol, ethylene glycol, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (e.g., OPTIFILM enhancer 300), OPTIFILM enhancer 400, 2-ethylhexyl benzoate (e.g., VELATE 368 Coalescent from Eastman), or 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (e.g., VELATE 375 Coalescent from Eastman).
The composition may include the dispersant, and the dispersant may be selected from the group including sorbitan monooleate (e.g., SPAN 80 from Sigma-Aldrich), polyethylene glycol sorbitan monooleate (e.g., TWEEN 80 from Eastman), octylphenol ethoxylate (e.g., TRITON X-100 from Sigma-Aldrich), HYDROPALAT WE 3320 from BASF (Trade Secret: NJTSRN 489909-5554-PC; one component is a type of fatty alcohol alkoxylate), DAPRO W-77 from Elementis Specialties (contains ethylene glycol monobutyl ether, ethyl alcohol, and dioctyl sodium sulfosuccinate), JEFFSPERSE X3503 from Huntsman (proprietary blend of a nonionic polymeric dispersant), DISPERBYK 190 from Byk (solution of a high molecular weight block copolymer with pigment affinic groups), ZETASPERSE 3100 from Air Products (proprietary surface active polymers), RHODOLINE3500 from Solvay, DISPEX Ultra FA 4480 NU from BASF (modified fatty alcohol polyglycol ether), polyacrylic, ionic surfactants, non-ionic surfactants, or comb polymers.
The composition may include the adhesion modifier, and the adhesion modifier may be selected from the group including a silane coupling agent, a secondary polymer, a secondary polymer dispersion, a dissolved polymer, an oligomer, a surfactant, a wetting agent, a chlorinated polyolefins, an epoxy-functionalized compound, or an amino-functional silicone polymer. The adhesion modifier may include the silane coupling agent and the composition may include 0.01-3 wt % silane coupling agent. The adhesion modifier may include the silane coupling agent and the silane coupling agent may be selected from the group including glycidoxypropyltrimethoxysilane, aminopropyltriethoxysilane, aminoethylaminopropyl-trimethoxysilane, 3-methacryloxypropyltrimethoxysilane, cationic vinylbenzyl and amino-functional methoxy-silane, vinyltrimethoxysilane, or aminoethylaminopropyltrialkoxysilane.
The composition may include the adhesion modifier and the adhesion modifier may include at least two different types of silane coupling agents. The adhesion modifier may include a second aqueous dispersion of a second type of polymer particles. The polymer particles of the second aqueous dispersion may be compatible with the polymer particles of the first aqueous dispersion. The adhesion modifier may include a dissolved polymer. The dissolved polymer may be a cellulose derivative, which may be selected from the group including hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropylmethyl cellulose, or sodium carboxy methyl cellulose. The dissolved polymer may be an ionic polymer, which may be selected from the group consisting of polyacrylic acid, alginate, xanthan gum, pectin, carrageenan, or hyaluronic acid. The dissolved polymer may be a nonionic polymer, which may be selected from the group including polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, dextran, guar gum, polyvinyl alcohol, polyacrylamide, or chitosan. The composition may cure or dry at room temperature.
An object may include the composite waterborne dispersion.
The description of elements of the embodiments of other aspects of the invention may be applied to this aspect of the invention as well.
In another aspect, embodiments of the invention relate to a method for three-dimensionally printing an object with a three-dimensional printer including a dispensing system including at least one cartridge adapted to dispense a composite waterborne dispersion through an orifice as a continuous filament, a build surface disposed below the dispensing system, or a robotic control system with at least one axis of movement. The method includes dispensing the composite waterborne dispersion from the cartridge through the orifice to deposit the waterborne dispersion toward the build surface to define at least a portion of the object. The composite waterborne dispersion includes a composition of an aqueous dispersion of polymer particles or associative thickener, and the composition has a yield stress >0 Pa, the yield stress being at least one of a dynamic yield stress and a static yield stress, and the composition is film-forming when dried.
One or more of the following features may be included. The composition may further include a functional filler, which may be selected from the group including a color pigment, conductive particles, fumed silica, milled glass fibers, PDMS, a solder component, quartz, carbon fiber, thermally insulating particles, thermally conductive particles, ferromagnetic particles, barium titonate particles, or radar absorbing particles. The conductive particles may be selected from the group including silver powder, silver flakes, silver nanowires, silver nanoparticles, silver-coated copper, silver-coated glass, silver-coated aluminum, gold nanowires, gold nanoparticles, gold powder, gold flakes, gold-coated copper, copper nanowires, copper microwires, copper nanoparticles, carbon nanotubes, carbon particles, or graphene. The functional filler may include a plurality of particles and an average diameter of the polymer particles may be at least one order of magnitude smaller than an average diameter of the functional filler particles.
A porous substrate may be disposed on the build surface, and a yield stress of the deposited composite waterborne dispersion may allow spanning over gaps in surface pores of the substrate. The porous substrate may include a textile. The textile may be selected from the group consisting of a woven textile or a knit fabric. The substrate may include a non-planar surface.
The method for three-dimensionally printing an object may further include scanning a non-planar surface with at least one of a laser distance sensor, a laser line scanner, or a ccd camera, to obtain a surface map of the topology of the surface, and then using the surface map to control deposition of the waterborne dispersion on the non-planar surface while maintaining a substantially constant standoff.
The waterborne dispersion may be deposited onto a substrate disposed on the build surface. A starting geometry of the printed object may be adapted to shrink into a desired shape, to thereby compensate for shrinkage of the deposited composite waterborne dispersion. The waterborne dispersion may be deposited onto a compliant substrate on the build surface and shrinkage of the deposited composite waterborne dispersion may drive a shape change in the compliant substrate. An object may be formed by the three-dimensionally printing the object with the composite waterborne dispersion.
The description of elements of the embodiments of other aspects of the invention may be applied to this aspect of the invention as well.
In another aspect, embodiments of the invention relate to a composite waterborne dispersion for 3D printing. The composite waterborne dispersion includes a composition including a first aqueous dispersion of polymer particles, an associative thickener, and a first functional filler including fumed silica, milled glass fibers, polydimethylsiloxane (PDMS), eutectic metal particles, carbon fiber, thermally insulating particles, thermally conductive particles, ferromagnetic particles, particles with high acoustic impedance, low-k dielectric particles, or high-k dielectric particles. The composition has a yield stress >0 Pa, the yield stress being at least one of a dynamic yield stress and a static yield stress. The composition is film-forming when dried.
One or more of the following features may be included. The composition may include at least 20 vol % of the first functional filler. The first functional filler may include eutectic metal particles, e.g., tin bismuth, gallium-indium, or indium-silver particles. The first functional filler may include thermally insulating particles, such as foams, aerogels, or hollow spheres. The first functional filler may include thermally conductive particles, e.g., boron nitride particles or diamond particles. The first functional filler may include ferromagnetic particles, such as carbonyl iron, ferrite, or molypermalloy powder. The first functional filler may include particles with high acoustic impedance, such as tungsten, alumina, zirconia, tungsten carbide or lead oxide particles. The first functional filler may include low-k dielectric particles, e.g., polytetrafluoroethylene PTFE, polyimide aerogel particles, and glass. The first functional filler may include high-k dielectric particles, such as titanium dioxide, strontium titanate, barium strontium titanate, barium titanate, or calcium copper titanate. The first functional filler may include fumed silica. The first functional filler may include milled glass fibers. The first functional filler may include polydimethylsiloxane (PDMS). The first functional filler may include an elastomer. The first functional filler may include carbon fiber.
The description of elements of the embodiments of other aspects of the invention may be applied to this aspect of the invention as well.
Printing ink in 3-dimensions places a certain set of demands on the ink rheology. 3D printed inks are designed to have a yield stress and therefore be self-supporting, allowing the ink to remain stable for months in a cartridge without settling or need for remixing. Repeatable extrusion of ink through a small orifice, such as a nozzle tip, demands that the material be highly shear-thinning, so that only a moderate applied pressure is required to extrude the ink through the orifice. Post-extrusion, the material's internal network is temporarily broken apart and viscosity is greatly reduced, requiring a fast recovery to its initial, self-supporting state. For certain applications, extending this recovery time may be advantageous (for example, a slow recovery obscures the appearance of discrete layers), but in general the recovery time is preferably minimal. A material that satisfies the above rheological criteria allows one to span gaps, build in 3D, and print closely spaced deposits of ink without overlap.
Accordingly, certain rheological properties are desired for 3D printing inks: (1) high static yield stress, which is the minimum stress required to initiate flow from a static, solid-like state; (2) pseudoplastic or shear-thinning behavior, which allows the ink to flow easily during extrusion from the nozzle; and (3) minimal thixotropy, meaning quick recovery time. In other words, the ink very quickly recovers the viscosity and yield stress that it had before it was sheared apart.
With the onset of increasingly strict volatile organic compounds (“VOC”) regulations, which limit the commercial usage of organic solvents, the market for waterborne polymer dispersions has flourished. Waterborne polymer dispersions are now used in a variety of applications ranging from paints to shoe manufacturing. Such commercial dispersions include polyurethanes, self-crosslinking polyurethanes, polycarbonate ester polyurethanes, acrylics, styrene acrylics, and self-crosslinking acrylics, just to name a few.
However, waterborne dispersions are low viscosity fluids, generally unsuitable for 3D printing on their own. While every interaction between components of an ink formulation—physical, chemical and/or electrostatic—strongly influences rheology, the list below describes certain ways of optimizing waterborne ink rheology for 3D printing:
The selection of one or more waterborne polymer dispersions depends on the desired application. For example, the formulation for a silver conductive ink requires that a selected polymer dispersion satisfy at least some of the following properties:
For a conductive ink to be successfully incorporated in 3D printed electronics, a number of demands are placed on the ink formulation:
While proper selection of a polymer dispersion is important to the success of a silver conductive ink, a number of other ingredients are typically added to the formulation to improve material properties:
Referring to
Tuning the rheology of conductive ink is important for 3D printing. However, rheology modification requires particular care, because the addition of too much thickener or other additives can cause significant reductions in conductivity:
Referring to
Referring to
Rheological curve fitting software, Trios, may be used to fit a curve to the raw data shown in
τ=τ0+k{dot over (γ)}n
where τ is the shear stress, {dot over (γ)} is the shear rate, τ0 is the dynamic yield stress, k is the consistency index, and n is the flow index. The dynamic yield stress τ0 is the y-intercept of the curve, or the stress level below which the material can no longer flow. The shear rate {dot over (γ)} is the x variable, and the variable that is gradually modulated to study the behavior of the stress with shear rate. The dynamic yield stress is measured as the lowest stress reading recorded during the time period when the rheometer is moving at its lowest shear rate possible, thus causing the material to flow at a very slow rate. The dynamic shear rate is usually recorded through model fitting to rheological models with controlled strain rate (
The Hershel-Bulkley model is frequently used for shear thinning materials with a non-zero yield stress. When the yield stress term, τ0, equals zero and the flow index term, n, equals one, the equation for the Herschel-Bulkley model reduces to Newton's law of viscosity, which may be used to describe a Newtonian fluid like water. Curve fitting analysis demonstrates that the model that best fits the data in
Since the equation shown in
Referring to
Referring to
The ink formulation of an exemplary 3D printable, silver conductive ink is provided in Table 1, and was used for the preparation of the plots in
This exemplary formulation in accordance with embodiments of the invention demonstrated the following material capabilities:
An alternative formulation of 3D printable, silver conductive ink is provided in Table 2:
This alternative formulation yields an ink with good adhesion properties and improved flexibility. For example, experimental data indicated that the adhesion value improved from an initial value of 3, to a value of 5, after incorporating Sancure 12929. This data is based on ASTM D3359—Tape adhesion test, with the adhesion values being unitless grades assigned in accordance with the standards put forth in ASTM D3359.
Referring to
The same conductive ink was also exposed to elevated curing temperatures, and resistivity measurements were taken as shown in
Ink formulations for 3D printing may vary widely. General criteria for 3D printing inks, based on composite waterborne polymer dispersions, are discussed below.
A conductive ink in accordance with some embodiments of the invention is a composite waterborne dispersion for 3D printing, including a composition of a first aqueous dispersion of polymer particles, an associative thickener, and a first functional filler including conductive particles. The composition has a yield stress >0 Pa, the yield stress being at least one of a dynamic yield stress and a static yield stress. In addition, the composition is film-forming when dried. A composition having a non-zero yield stress is advantageous for 3D printing of layers.
As discussed in detail below, in some embodiments of the invention, the first functional filler may be a material other than conductive particles. The following characteristics of the composition are applicable to various embodiments of the invention, including to compositions with fillers other than conductive particles.
The composition may have a static yield stress over 50 Pa, preferably over 100 Pa, and more preferably over 200 Pa, e.g., 240 Pa. The composition may have a dynamic yield stress of over 50 Pa, preferably over 100 Pa, e.g., 160 Pa or more preferably even higher, e.g., greater than 200 Pa. Higher yield stress enables particles to remain suspended in the dispersion for greater periods of time without settling. The high yield stress also allows one to build consecutive layers in printing without the bottom layer sagging from the stress caused by the weight of the layers on top.
The composition may have a viscosity ranging from 10 to 10,000 PA·s at a shear rate of 1/s. For some applications, the viscosity is preferably 100-1000 Pas, and even more preferably 200-500 Pas, e.g., 352 Pas. A higher viscosity allows one to keep fillers suspended for longer periods of time without settling.
The composition may include a non-volatile content of 70 wt % to 95 wt %, e.g., 87.5 wt %. In some embodiments, the composition may include a non-volatile content of greater than 25 volume percent, and more preferably greater than 40 vol % volume percent. A higher non-volatile content reduces shrinkage, due to a smaller volumetric change.
A maximum agglomerate size of the composition may be less than 50 microns. More preferably the maximum agglomerate size is as small as the largest particles present in the system. Preferably, the maximum agglomerate size is less than one-tenth of the diameter of the nozzle through which the waterborne dispersion is extruded, more preferably less than one-hundredth of the nozzle diameter. For example, for applications in which the waterborne dispersion is extruded out of a 250 micron nozzle, a maximum agglomerate size is preferably less than 20 microns. For extrusion of compositions of silver nanoparticles through even smaller nozzles, agglomerate sizes of less than 200 nm may be preferred.
The aqueous dispersion of polymer particles is film-forming at room temperature, i.e., at 22° C. The aqueous dispersion of polymer particles may have a minimum film formation temperature below 22° C. In some embodiments the polymer particles may also be self-crosslinking at room temperature, indicating that they form chemical bonds between particles during the process of coalescence as the water evaporates from the system.
A number of parameters may be considered for selecting appropriate polymer particles for inclusion in the aqueous dispersion. These parameters include mechanical properties suitable for the intended use, cost, compatibility with the chemistry of the functional filler, particle size, and film strength. Accordingly, the aqueous dispersion of polymer particles may include polyurethane, an acrylic, an alkyd, PVC, styrene butadiene, vinyl acetate, vinyl acetate ethylenes, vinyl maleate, and/or vinyl versatate. Examples of suitable acrylics include a styrene acrylic, a vinyl acrylic, a self-crosslinking acrylic, an epoxy-functionalized acrylic, hybrid alkyd-acrylic, and vinyl versatate acrylic. Examples of suitable polyurethanes include a self-crosslinking polyurethane, a polycarbonate ester polyurethane, an epoxy-functionalized polyurethane, and hybrid alkyd-polyurethane.
The associative thickener may be, e.g., a hydrophobically modified ethoxylated urethane (HEUR), an epoxy-functionalized polyurethane, epoxy-functionalized acrylic, an alkyd, a hybrid alkyd-acrylic, an hybrid alkyd-polyurethane, a hydrophobically modified alkali swellable emulsion (HASE), a tri-block co-polymer, a hydrophobically modified polyacrylate thickener, a hydrophobically modified polyether thickener, and a hydrophobically modified cellulose ether.
The composite waterborne dispersion may include a solid metal precursor and/or a dissolved metal precursor. The metal precursor is reduced to a solid metal filler during evaporation of the dispersion. An exemplary composition including silver acetate that functions as a metal precursor is:
When the water evaporates, the amine evaporates from silver complex, and formate complex, the formic acid then reduces the silver precursor into elemental silver. At the same time, the evaporation of the water drives coalescence of the polymeric particles. The composition may include a second functional filler, such as a color pigment, preferably about 0.1-10 wt % color pigment.
In some embodiments, the second functional filler may be conductive particles, fumed silica, milled glass fibers, PDMS, eutectic metal particles, quartz, carbon fiber, thermally insulating particles, thermally conductive particles, thermally insulating particles, polyimide aerogels, ferromagnetic particles, and/or radar absorbing particles.
The second functional filler may include conductive particles of a type different from the conductive particles of the first functional filler, e.g., silver powder, silver flakes, silver nanowires, silver nanoribbons, silver nanoparticles, silver-coated copper, silver-coated glass, silver-coated aluminum, gold nanowires, gold nanoparticles, gold powder, gold flakes, gold-coated copper, copper nanowires, copper microwires, copper nanoparticles, carbon nanotubes, carbon particles, graphene, copper oxide particles, tungsten particles, aluminum microparticles, nickel microparticles, or microparticles of eutectic metal systems. The second functional filler may also be a solder component, i.e., a component of a eutectic system that melts and changes phases when heated.
At least a portion of the second functional filler may include a coating material that interacts with the associative thickener. This interaction between the coating material and the associative thickener is typically a hydrophobic interaction. Associative thickeners for water-based systems almost always have hydrophobic end groups that “modify” the hydrophilic water soluble backbone. This allows the thickener to be soluble in water, but it will also interact with everything that is hydrophobic or hydrophobically-modified, including itself. For example, the conductive particles may also have some hydrophobic functionalization, interacting with the associative thickener and greatly enhancing the thickening effect.
The coating material may be, e.g., an unsaturated hydrocarbon, a fatty acid, an ionic surfactant, a nonionic surfactant, an ionic polymer, and/or a block copolymer. In some embodiments, the composite waterborne dispersion may be uncoated, and the outside may be ionized to electrostatically repel each polymer particle from other polymeric particles, to prevent agglomeration.
The composition may include at least 20 wt % conductive particles. The conductive particles may be, e.g., silver powder, silver flakes, silver nanowires, silver nanoparticles, silver-coated copper, silver-coated glass, silver-coated aluminum, gold nanowires, gold nanoparticles, gold powder, gold flakes, gold-coated copper, copper nanowires, copper microwires, copper nanoparticles, carbon nanotubes, carbon particles, and/or graphene.
In some embodiments, the conductive particles may be silver flakes having a tapped density of 2.7-3.9 g/cm3, a diameter range of 3-10 microns, and a specific surface area of 0.6-1.2 m2/g.
An average diameter of the polymer particles in the aqueous dispersion is preferably at least one order of magnitude smaller than an average diameter of the conductive particles of the first functional filler, although larger particles can be effective in some cases.
The composition may also include a rheological modifier that increases a resting viscosity, yield stress, and pseudoplastic behavior of the composition. Resting viscosity is also referred to as “zero shear viscosity.” Higher yield stress enables particles to remain suspended in the dispersion for greater periods of time without settling. The high yield stress also allows one to build consecutive layers in printing without the bottom layer sagging from the stress caused by the weight of the layers on top.
The composition may further include at least one of a defoamer, an antifoam, a coalescent, a dispersant, and an adhesion modifier.
As used herein, antifoam prevents the formation of foam, and a defoamer eliminates existing foam. The defoamer may be, e.g., a silicone-based defoamer, an oil-based defoamer, a powder-based defoamer, a wax-based defoamer, polyethylene glycol-based defoamer, polypropylene glycol-based defoamer, an alkyl-polyacrylate based defoamer, an antifoam, PDMS, polyester-functionalized silicone, and/or fluorosilicone.
The composition may include the coalescent. The coalescent serves to slow the evaporation rate of solvent in the composite waterborne dispersion, lower the minimum film formation temperature, and aid in the coalescence of polymer particles, thereby improving film formation. The coalescent may be a glycol ether, (3-hydroxy-2,2,4-trimethylpentyl) 2-methylpropanoate (TEXANOL from Eastman), propylene carbonate, diethyl carbonate, N-Methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF), tetrahydrofuran (THF), dibasic esters, glycols, glycol ether acetates, propylene glycol, ethylene glycol, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (OPTIFILM enhancer 300 from Eastman), OPTIFILM enhancer 400, 2-ethylhexyl benzoate (VELATE 368 Coalescent from Eastman) or 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (VELATE 375 Coalescent). Suitable glycol ethers may be dipropylene glycol n-butyl ether, diethylene glycol monomethyl ether, diethylene glycol n-butyl ether, dipropylene glycol monomethyl ether, and 2-butoxyethanol (a glycol ether).
The composition may include the dispersant, and the dispersant may be, e.g., sorbitan monooleate (SPAN 80 from Sigma Aldrich), polyethylene glycol sorbitan monooleate (TWEEN 80), octylphenol ethoxylate triton X-100, HYDROPALAT WE 3320 (from BASF, trade secret: NJTSRN 489909-5554-PC; one component is a type of fatty alcohol alkoxylate), DAPRO W-77 from Elementis Specialties (contains ethylene glycol monobutyl ether, ethyl alcohol, and dioctyl sodium sulfosuccinate), JEFFSPERSE X3503 from Huntsman (proprietary blend), DISPERBYK 190 from BYK (solution of a high molecular weight block copolymer with pigment affinic groups), ZETASPERSE 3100 from Air Products & Chemicals (proprietary surface active polymers), RHODOLINE 3500, DISPEX Ultra FA 4480 NU from BASF (modified fatty alcohol polyglycol ether), ionic surfactants such as sodium stearate or sodium dodecylbenzene sulfonate, a non-ionic surfactant such as polyethylene ethoxylate, or a comb polymer.
The composition may include an adhesion modifier, and the adhesion modifier may be, e.g., a silane coupling agent, a secondary polymer, a secondary polymer dispersion, a dissolved polymer, an oligomer, a surfactant, a wetting agent, a chlorinated polyolefin, an epoxy-functionalized compound, and/or an amino-functional silicone polymer.
The adhesion modifier may include the silane coupling agent and the composition may include 0.01-3 wt % silane coupling agent.
The adhesion modifier may include the silane coupling agent and the silane coupling agent may be, e.g., glycidoxypropyltrimethoxysilane, aminopropyltriethoxysilane, aminoethylaminopropyl-trimethoxysilane, 3-methacryloxypropyltrimethoxysilane, cationic vinylbenzyl and amino-functional methoxy-silane, vinyltrimethoxysilane, or aminoethylaminopropyltrialkoxysilane. In some embodiments, the adhesion modifier may include at least two different types of silane coupling agents.
The adhesion modifier may include a second aqueous dispersion of a second type of polymer particles. The polymer particles of the second aqueous dispersion may be compatible with the polymer particles of the first aqueous dispersion. The particles are compatible in that the second aqueous dispersion does not destabilize the first dispersion or vice versa. Also, the resulting film does not phase separate into two different region e.g., polymer 1 and polymer 2.
The adhesion modifier may include a dissolved polymer. The dissolved polymer may be a cellulose derivative, such as hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropylmethyl cellulose, and/or sodium carboxy methyl cellulose.
Alternatively, the water soluble polymer may be an ionic polymer, such as polyacrylic acid, alginate, polyvinyl alcohol, polyacrylamide, xanthan gum, pectin, carrageenan, and/or hyaluronic acid. In some embodiments, the dissolved polymer may be a nonionic polymer such as polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, dextran, guar gum, and/or chitosan.
The composition may cure and dry at room temperature, i.e., at 22° C. Accordingly, the composition may be used without a heating/curing step.
Instead of (as well as in addition to) the conductive particles included in the conductive inks discussed above, composite waterborne dispersions suitable for 3D printing may include other functional fillers. For example, in an alternative embodiment, an ink is a composite waterborne dispersion for 3D printing, including a composition of a first aqueous dispersion of polymer particles, an associative thickener, and a functional filler. The composition has a yield stress >0 Pa, the yield stress being at least one of a dynamic yield stress and a static yield stress. In addition, the composition is film-forming when dried.
In compositions in accordance with embodiments of the invention, the polymer dispersion is the binder, the associative thickener makes it printable, and the filler carries out the function. Many different polymer dispersions may be used to achieve the same purpose. However, in the case of silver ink, the associative thickener significantly affects the viscosity by interacting with the hydrophobic silver flake. In the case where the functional filler is not hydrophobic, one may choose a polymer dispersion that is more hydrophobic so that the associative thickener provides more thickening without the need for the filler to provide any thickening. In some cases, the filler may contribute to thickening; in such embodiments, the amount of filler may be tuned to accommodate for the thickening.
The functional filler may be selected to provide particular material properties and advantages; the composition may include at least 20 vol % of the functional filler.
The functional filler may be fumed silica, which may increase the mechanical strength and abrasion resistance, as well as improve the rheological properties of the ink for printing.
The functional filler may be milled glass fibers, which may increase the mechanical strength and the stiffness of the cured film.
The functional filler may be polydimethylsiloxane (PDMS), which may make the film more compliant and tough. The addition of PDMS and/or other elastomer particles may also increase the level of acoustic attenuation of the film.
The functional filler may be eutectic metal particles. The inclusion of eutectic particles allows the formulation of an ink that is liquid metal at low temperatures, but quickly solidifies upon cooling. An ink including eutectic particles may be conductive and may be sinterable at low temperatures. Suitable eutectic metal particles may be tin-bismuth, gallium-indium, indium-silver, etc.
The functional filler may be carbon fiber, which increases the mechanical strength and the stiffness of the cured film.
The functional filler may be thermally insulating particles, which shield heat and provide insulation. Suitable thermally insulating particles may be materials containing greater than 30 vol % air, for example, foams, aerogels, hollow spheres, etc., including glass bubbles and polyimide aerogel particles.
The functional filler may be thermally conductive particles, which transmit heat. An ink containing thermally conductive particles may be used to print a heat sink, heat spreader, or matrix for high power carrying conductors. Suitable thermally conductive particles may be particles with thermal conductivities greater than 5 W/mK, for example, boron nitride or diamond.
The functional filler may be ferromagnetic particles. Inks containing ferromagnetic particles may be used to create inductors, motor cores, etc. These ferromagnetic or inducting particles may also be radio frequency (RF) and/or electromagnetic absorbers, which may be used to reduce or stop signal interference and/or noise. Suitable ferromagnetic particles may be carbonyl iron, ferrite, molypermalloy powder, etc.
The functional filler may be particles with high acoustic impedance, which may be used to tune the acoustic impedance of an interface to selectively allow sound or ultrasound to pass through or be reflected by the interface. Suitable particles with high acoustic impedance may be a high density material such as tungsten, alumina, zirconia, tungsten carbide, or lead oxide particles.
The functional filler may be low-k dielectric particles, which may be used to tune the dielectric constant of an ink for RF applications. Low-k dielectric particles may have a dielectric constant less than 2.75. Suitable low-k dielectric particles may be polytetrafluoroethylene (PTFE), polyimide aerogel particles, or glass.
The functional filler may be high-k dielectric particles, which may be used to tune the dielectric constant of an ink for RF applications. Suitable high-k dielectric particles may be barium titanate, strontium titanate, titanium dioxide, barium strontium titanate, or calcium copper titanate.
Generally, any of the previously described aqueous dispersion of polymer particles and associative thickener may be used in combination with these functional fillers, with some customization. For example, the dispersions for the conductive ink indicated above are preferred because they have a small particle size, and are flexible, tough, and self cross-linking. In other situations, another polymer dispersion may be ideal. For example, if high flexibility is desired, a styrene acrylic may be preferred. If low cost is desired, then an acrylic dispersion may be selected. If electrical percolation is not a concern, then a larger particle size polymer dispersion may be chosen for better mechanical properties and greater shelf stability. If bonding to an epoxy matrix is desired, then one may use a dispersion of solid epoxy, such that it can chemically bond to the substrate.
An exemplary formulation for a 3D printable polyamide aerogel ink is given in Table 3.
This exemplary formulation has a low dielectric constant and is thermally insulating.
3D Printing of Composite Waterborne Dispersions
Any of the composite waterborne dispersions discussed herein may be used in three-dimensional printing e.g., direct-write. Broadly, an object may be three-dimensionally printed by a three-dimensional printer that includes (i) a dispensing system having at least one cartridge adapted to dispense a composite waterborne dispersion through an orifice as a continuous filament, (ii) a build surface disposed below the dispensing system, and (iii) a robotic control system. An example of a suitable three-dimensional printer is the Voxel8 Developer's Kit, available from Voxel8, Inc., Somerville, Mass. The composite waterborne dispersion is dispensed from the cartridge through the orifice to deposit the waterborne dispersion onto the build surface to define at least a portion of the object. The composite waterborne dispersion includes a composition of an aqueous dispersion of polymer particles and an associative thickener. The composition has a yield stress >0 Pa, the yield stress being at least one of a dynamic yield stress and a static yield stress. The composition is film-forming when dried.
Referring to
Referring to
The composition may also include a functional filler, such as a color pigment, conductive particles, fumed silica, milled glass fibers, PDMS, a solder component, quartz, carbon fiber, thermally insulating particles, thermally conductive particles, ferromagnetic particles, and/or radar absorbing particles.
Exemplary suitable conductive particles are silver powder, silver flakes, silver nanowires, silver nanoparticles, silver-coated copper, silver-coated glass, silver-coated aluminum, gold nanowires, gold nanoparticles, gold powder, gold flakes, gold-coated copper, copper nanowires, copper microwires, copper nanoparticles, carbon nanotubes, carbon particles, and graphene.
The functional filler may include a plurality of particles, such that an average diameter of the polymer particles is at least one order of magnitude smaller than an average diameter of the functional filler particles. This size difference allows silver flakes to lay flat without being perturbed by large polymeric particles.
A porous substrate may be disposed on the build surface, or act as the build surface itself, and a yield stress of the deposited composite waterborne dispersion allows spanning over gaps in surface pores of the substrate. The porous substrate may be a textile, e.g., a woven textile or a knit fabric. The substrate may have a non-planar surface, such as a shoe upper.
The non-planar surface may be scanned with a laser distance sensor, a laser line scanner, and/or a ccd camera, to obtain a surface map of the topology of the surface. Then surface map may then be used to control deposition of the waterborne dispersion on the 3D surface while maintaining the nozzle at approximately a constant distance or standoff from the 3D surface.
In some embodiments, the waterborne dispersion may be deposited onto a substrate that is disposed on the build surface. A starting geometry of the printed object may be adapted to compensate for shrinkage of the deposited composite waterborne dispersion. For example, if a cube shape was directly printed onto a rigid substrate, then the shrinkage from drying would cause the cube to shrink, but it would still be constrained by the substrate, causing the desired cube to turn into a trapezoidal prism like geometry with a base that has a larger area than the top surface. If the forces caused by shrinkage are modeled, then the starting geometry can be adjusted such that the dried and deformed shape resembles the initially desired form. For example, a trapezoidal prism with a base having a smaller area than the top surface could be printed, such that after shrinking, a cube is left. In some embodiments, the unavoidable shrinkage forces can be taken advantage of to drive a desired shape change. In particular, the waterborne dispersion may be deposited onto a compliant substrate on the build surface, and shrinkage of the deposited composite waterborne dispersion drives a shape change in the compliant substrate.
A particular application for 3D printing of composite waterborne dispersions lies in athletic shoe manufacturing, for which the yarn upper knit shoes includes polymer dispersions that were cast into a mold and hot-pressed onto the woven or knit surface. The polymer film serves as a stretchable, tough and breathable coating, satisfying the high demands of athletic wear. Although the rheological demands for 3D printing shoe uppers are substantially similar to 3D printing conductive traces in electrical circuits, certain requirements are unique:
An exemplary formulation for optically clear ink for shoe uppers is listed in Table 4.
An alternative embodiment of an optically clear ink for textile coating is shown in Table 5.
An alternative embodiment of a black ink for textile coating is shown in Table 6.
The above embodiments of inks for textile coating are capable of spanning large gaps and may be used in applications such as coating porous athletic shoes.
Referring to
Having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive. Various combinations and permutations of the materials and properties of the embodiments disclosed herein are considered to be taught, as well.
This application claims priority to U.S. Provisional Patent Application Ser. No. 62/286,067, filed Jan. 22, 2016, the entire contents of which are incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 62286067 | Jan 2016 | US |
