Liquid additive manufacturing composition

Abstract

To provide surface treated silica-containing particles.SOLUTION: Surface treated silica-containing particles are combined with a resin to form a liquid prepolymer composition for use in additive manufacturing. A surface treatment on the silica containing particles may participate in polymerization of the composition. The silica-containing particles may be colloidal silica or a silica polymer composite particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to methods and compositions for liquid additive manufacturing using silica-based particles to produce printed parts, and the resulting printed parts. [Background technology]

[0002] Stereolithography is a liquid additive manufacturing process that uses light, e.g., an ultraviolet laser or a projection beam, to harden layers of liquid photocurable resin. Reservoirs of curable resin are locally cured to form the layers of the final solid part. After each layer is scanned, the in-process part is moved a small distance, e.g., millimeters, from the light source, and a new layer of photocurable resin is coated on the surface. By repeating the process multiple times, the finished part is gradually built up in shape, layer by layer. In alternative methods, such as continuous liquid interface manufacturing (CLIP) and digital light synthesis (DLS), material is added to the workpiece continuously, rather than layer by layer.

[0003] Photocurable resins typically used in these liquid additive manufacturing processes result in brittle plastics that lack desirable thermal properties or may otherwise not be optimized for the end-use application of the finished product. Therefore, it would be desirable to have additives for photocurable resins that can improve the mechanical properties and thermal stability of the cured polymer, provide other benefits to the finished product, or optimize manufacturing conditions. Summary of the Invention

[0004] In one embodiment, a method of forming a three-dimensional object includes: a) contacting a substrate with a reservoir of a prepolymer composition, the prepolymer composition comprising a resin comprising monomers and oligomers of a polymer selected from acrylate, methacrylate, vinyl polymer, olefin, silicone, and epoxy; and silica-containing particles selected from i) 0.1 to 50 wt % colloidal silica particles having a particle size of 5 nm to 600 nm treated with at least one surface treatment agent, and ii) 0.1 to 50 wt % silica-polymer composite particles comprising colloidal silica particles having a particle size of 10 nm to 3 μm and treated with at least one surface treatment agent, the surface treatment agent comprising an organopolysiloxane, organosiloxane, organosilane, haloorganosilane, or organosilazane, the prepolymer composition being heated at a temperature of 25° C. and 100 s. -1 having a viscosity up to 500 cP greater than the neat resin at a shear rate of; b) imagewise selectively exposing the prepolymer composition to actinic radiation to form a solid polymer on the substrate having a build surface parallel to the substrate, the solid polymer being a continuous portion of a three-dimensional object; c) contacting the build surface with a prepolymer composition; d) selectively exposing the prepolymer composition to actinic radiation to increase the mass of the solid polymer, the additional polymer being a subsequent, continuous portion of the three-dimensional object; and e) repeating steps c) and d) until a three-dimensional object is formed; Includes.

[0005] The surface treatment agent may include a hydroxy-substituted or terminal siloxane oligomer having a 7-14 mer, or a cyclic siloxane having 4 to 14 silicon atoms in the ring, such as a dimethylsiloxane oligomer.

[0006] Alternatively or additionally, the surface treatment agent may be R 1 Si[(OR 2 ) x R 3 3-x], hexamethyldisilazane, or dimethyldichlorosilane; R 1 is C1-C 30 Branched and straight chain alkyls, alkenyls, and C3-C 10 Cycloalkyl, C6-C 10 Aryl, and R 4 Q; R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3 are independently methyl or ethyl, and x is 1, 2, or 3. For example, the surface treatment agent may be 3 3-x (OR 2 ) x ]SiR 4 Q, where n=6 to 10. Alternatively or additionally, the surface treatment agent may comprise [R 3 3-x (OR 2 ) x ]SiR 4 It may contain Q, where Q is an epoxy group or a thiol group.

[0007] Alternatively or additionally, the surface treatment agent contains at least one group [R 3 3-x (OR 2 ) x ]SiR 4 Q may comprise a polysiloxane oligomer or cooligomer, R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3are independently methyl or ethyl, and x is 1, 2, or 3. For example, Q can be a substituted or unsubstituted vinyl group, allyl group, acrylate ester group, or methacrylate ester group, and / or a polysiloxane oligomer or cooligomer having a viscosity of 500 to 3500 cSt.

[0008] Alternatively or additionally, the silica-containing particles are silica-polymer composite particles that may comprise a plurality of silica particles and a polymer matrix, wherein the silica particles are [R 3 3-x (OR 2 ) x ]SiR 4 Surface modified with a first hydrophobizing agent containing Q, 4 Among Q, R 4 is a compound of the general formula C, where n=0-10 n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3 is independently methyl or ethyl, and x is 1, 2, or 3.

[0009] In any of these embodiments, coating the prepolymer composition onto the cross section may include moving the substrate along an axis perpendicular to the cross section. Alternatively or additionally, steps c) and d) may be performed in stages or simultaneously, such that the prepolymer composition is coated onto the cross section while the prepolymer composition is polymerizing.

[0010] The polymer composite can be prepared by any combination of the above embodiments.

[0011] In another embodiment, the method for preparing surface-treated silica particles includes providing an aqueous silica dispersion comprising 5 to 70% colloidal silica particles having an average particle size of 5 to 600 nm, a first BET surface area, and a pH of about 8 to about 11; and dissolving the aqueous silica dispersion in a solution of a compound having the formula [R3 3-x (OR 2 ) x ]SiR 4 Q is 0.4 to 10 molecules / nm 2 (based on first BET surface area) of an alkoxysilane treating agent, or b) 0.5 to 10 R 5 base / nm 2 at least one group R having a viscosity of 4 to 3500 cSt in an amount corresponding to the first BET surface area; 5 Si[(OR 2 ) x R 3 3-x to provide a reaction mixture containing 50 wt % or less of an organic solvent, 5 is C1-C 10 Branched and straight chain alkyls, alkenyls, and C3-C 10 Cycloalkyl, C6-C 10 Aryl, and R 4 Q; R 2 and R 3 are independently methyl or ethyl, x is 1, 2, or 3, and R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n and Q is an alkyl linker having the formula [R 3 3-x (OR 2 ) x ]SiR 4 Alternatively or additionally, R5 is R 4 and / or Q is a substituted or unsubstituted vinyl group, an acrylate ester group, or a methacrylate ester group. The viscosity of the polysiloxane oligomer may be from 500 to 3500 cSt.

[0012] In other embodiments, the particle composition comprises at least one group R 5 Si[(OR 2 ) x R 3 3-x ], and colloidal silica particles surface-treated with a polysiloxane oligomer or cooligomer of R 5 is C1-C 10 Branched and straight chain alkyls, alkenyls, and C3-C 10 Cycloalkyl and C6-C 10 aryl; R 2 and R 3 are independently methyl or ethyl, x is 1, 2, or 3, and R 4 Among Q, R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n and Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group. The polysiloxane oligomer or cooligomer may have a viscosity of 4 to 3500 cSt. Alternatively or additionally, R 5 is R 4 Q, where Q is a substituted or unsubstituted vinyl group, an acrylate ester group, or a methacrylate ester group, and the polysiloxane oligomer has a viscosity of 500 to 3500 cSt. The particulate composition may be in the form of a dry powder.

[0013] In another embodiment, a prepolymer composition for three-dimensional printing via stereolithography, continuous liquid interface manufacturing, or digital photosynthesis comprises a resin including monomers and oligomers of a polymer selected from acrylates, methacrylates, vinyl polymers, olefins, silicones, and epoxies; and silica-containing particles selected from i) 0.1 to 50 wt % colloidal silica particles having a particle size of 5 nm to 600 nm treated with at least one surface treatment agent, and ii) 0.1 to 50 wt % silica-polymer composite particles including colloidal silica particles having a particle size of 10 nm to 3 μm and treated with at least one surface treatment agent, wherein the surface treatment agent comprises an organopolysiloxane, organosiloxane, organosilane, haloorganosilane, or organosilazane, and the prepolymer composition is heated at a temperature of 25° C. and 100 s. -1 It has a viscosity up to 500 cP greater than that of the neat resin at shear rates of 100 psi.

[0014] The surface treatment agent may contain a hydroxy-substituted or -terminated siloxane oligomer having a 7-14 mer or a cyclic siloxane having 4 to 14 silicon atoms in the ring. The siloxane oligomer may be a dimethylsiloxane oligomer.

[0015] Alternatively or additionally, the surface treatment agent may be R 1 Si[(OR 2 ) x R 3 3-x ], hexamethyldisilazane, dimethyldichlorosilane, R 1 is C1-C 30 Branched and straight chain alkyls, alkenyls, and C3-C 10 Cycloalkyl, C6-C 10 Aryl, and R 4 Q; R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2and R 3 are independently methyl or ethyl, and x is 1, 2, or 3. For example, the surface treatment agent may be 3 3-x (OR 2 ) x ]SiR 4 It may contain Q, where n=6 to 10, and / or Q is an epoxy group or a thiol group.

[0016] Alternatively or additionally, the surface treatment agent contains at least one group [R 3 3-x (OR 2 ) x ]SiR 4 Q may comprise a polysiloxane oligomer or cooligomer, R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3 is independently methyl or ethyl, and x is 1, 2, or 3. For example, Q may be a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group, and / or the polysiloxane oligomer or cooligomer may have a viscosity of 500 to 3500 cSt.

[0017] Alternatively or additionally, the silica-containing particles may be silica-polymer composite particles, which may comprise a plurality of silica particles and a polymer matrix, wherein the silica particles are 3 3-x (OR 2 ) x ]SiR 4 Surface modified with a first hydrophobizing agent containing Q, 4 Among Q, R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2nQ is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3 is independently methyl or ethyl, and x is 1, 2, or 3.

[0018] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed.

[0019] The invention will now be described with reference to the several figures of the drawing. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a graph showing the viscosity of silica dispersions in UV-cured acrylic resin at various loadings (x = fumed silica; diamonds = Sample 8-1; triangles = Sample 8-2).

[0021] [Figure 2A] Figures 2A, 2B, 2C, and 2D are scanning electron micrographs of UV-cured acrylic resin containing silica particles surface-treated with 3-methacryloxypropyltrimethoxysilane. In Figures 2A and 2B, the silica was dispersed in the uncured resin as a powder. In Figures 2C and 2D, the silica was dispersed in the uncured resin as a dispersion in an alcohol-based solvent.

[0022] [Figure 2B] Figures 2A, 2B, 2C, and 2D are scanning electron micrographs of UV-cured acrylic resin containing silica particles surface-treated with 3-methacryloxypropyltrimethoxysilane. In Figures 2A and 2B, the silica was dispersed in the uncured resin as a powder. In Figures 2C and 2D, the silica was dispersed in the uncured resin as a dispersion in an alcohol-based solvent.

[0023] [Figure 2C]Figures 2A, 2B, 2C, and 2D are scanning electron micrographs of UV-cured acrylic resin containing silica particles surface-treated with 3-methacryloxypropyltrimethoxysilane. In Figures 2A and 2B, the silica was dispersed in the uncured resin as a powder. In Figures 2C and 2D, the silica was dispersed in the uncured resin as a dispersion in an alcohol-based solvent.

[0024] [Figure 2D] Figures 2A, 2B, 2C, and 2D are scanning electron micrographs of UV-cured acrylic resin containing silica particles surface-treated with 3-methacryloxypropyltrimethoxysilane. In Figures 2A and 2B, the silica was dispersed in the uncured resin as a powder. In Figures 2C and 2D, the silica was dispersed in the uncured resin as a dispersion in an alcohol-based solvent.

[0025] [Figure 3A] Figures 3A, 3B, 3C, and 3D are scanning electron micrographs of acrylic resin containing silica particles surface-treated with 8-methacryloxyoctyltrimethoxysilane (Figures 3A and 3B) and 3-methacryloxypropyltrimethoxysilane (Figures 3C and 3D).

[0026] [Figure 3B] Figures 3A, 3B, 3C, and 3D are scanning electron micrographs of acrylic resin containing silica particles surface-treated with 8-methacryloxyoctyltrimethoxysilane (Figures 3A and 3B) and 3-methacryloxypropyltrimethoxysilane (Figures 3C and 3D).

[0027] [Figure 3C] Figures 3A, 3B, 3C, and 3D are scanning electron micrographs of acrylic resin containing silica particles surface-treated with 8-methacryloxyoctyltrimethoxysilane (Figures 3A and 3B) and 3-methacryloxypropyltrimethoxysilane (Figures 3C and 3D).

[0028] [Figure 3D]Figures 3A, 3B, 3C, and 3D are scanning electron micrographs of acrylic resin containing silica particles surface-treated with 8-methacryloxyoctyltrimethoxysilane (Figures 3A and 3B) and 3-methacryloxypropyltrimethoxysilane (Figures 3C and 3D). DETAILED DESCRIPTION OF THE INVENTION

[0029] In one embodiment, the prepolymer composition comprises a resin comprising polymeric monomers and oligomers selected from acrylate, methacrylate, vinyl, allyl, silicone, and epoxy, and 0.1 to 50 wt % colloidal silica particles having a particle size of 5 nm to 600 nm that have been surface-treated with a silane agent comprising a group capable of copolymerizing with at least a portion of the monomers and oligomers, and the prepolymer composition is heated at a temperature of 25° C. and 100 S. -1 The colloidal silica particles have a viscosity at a shear rate of up to 500 cP greater than the viscosity of the neat resin, e.g., up to 450 cP greater, or up to 350 cP greater. For example, the colloidal silica particles may be surface treated with methacryloxypropyltrimethoxysilane (MPS). Alternatively or additionally, the colloidal silica particles may be surface treated with a monofunctional silane agent, which results in hydrophobic functional groups attached to the surface, but which do not necessarily copolymerize with the monomer or oligomer.

[0030] The use of such particles can increase one or more of the tensile modulus, tensile strength, tensile elongation, and / or flexural modulus of printed parts produced by liquid additive manufacturing processes compared to neat resin. Such benefits can be realized independently of the orientation of the workpiece relative to the axis along which the polymer is deposited during manufacturing. Other mechanical properties that may be affected include, but are not limited to, flexural modulus, Young's modulus, and low-temperature brittleness.

[0031] Colloidal silica can be produced by a sol-gel process. Colloidal silica particles are often non-aggregated, discrete (primary) particles that are typically spherical or nearly spherical in shape, but can have other shapes (e.g., shapes with roughly elliptical, square, or rectangular cross sections). Preferably, non-aggregated colloidal silica is used in the embodiments provided herein. Colloidal silica is commercially available or can be prepared by known methods from various starting materials (e.g., wet-process silica). Colloidal silica particles are typically made in a similar manner to precipitated silica particles (i.e., precipitated silica particles are coagulated from an aqueous medium), but remain dispersed in a liquid medium (often water alone or with cosolvents and / or stabilizers). Silica particles can be prepared, for example, from silicic acid obtained from an alkaline silicate solution having a pH of about 9 to about 11, where the silicate anions undergo polymerization to produce discrete silica particles having the desired average particle size in the form of an aqueous dispersion. Typically, colloidal silica is available as a sol, which is a dispersion of colloidal silica in a suitable solvent, most often water alone or in combination with a cosolvent and / or stabilizer, as described, for example, in Stoeber et al., "Controlled Growth of Monodisperse Silica Spheres in the Micron Size Range," Journal of Colloid and Interface Science, 26, 1968, pp. 62-69; Akitoshi Yoshida, "Silica Nucleation, Polymerization, and Growth Preparation of Monodispersed Sols," Colloidal Silica Fundamentals and Applications, pp. 47-56 (H.E. Bergna & W.O. Roberts, eds., CRC Press: Boca Raton, Florida, 2006); and Iler, R.K., "The Chemistry of Silica," p. 866, John Wiley & Sons: New York, 1979).Non-limiting examples of commercially available colloidal silica suitable for use in liquid additive manufacturing include SNOWTEX® products available from Nissan Chemical, LUDOX® products available from W.R. Grace & Co., BINDZIL® products available from AkzoNobel, KLEBOSOL® products available from Merck KGaA, and NexSil® A available from Nyacol Nanotechnologies, Inc. TM Series product, Quartron available from Fuso Chemical Industries TM products available from AkzoNobel, and Levasil® products available from AkzoNobel.

[0032] Colloidal silica particles may have an average primary particle size of about 5 nm to about 500-600 nm. Primary particle size can be measured by transmission electron microscopy of at least 2,000 particles or by disc centrifuge sedimentation for non-agglomerated particles. Silica having an average primary particle size of up to about 20-40 nm, e.g., about 5-15 nm, about 10-20 nm, about 15-25 nm, or about 25-35 nm, is considered preferred in embodiments where transparency is desired. Larger silica-based particles, e.g., about 5-200 nm, about 20-150 nm, or about 50-100 nm, may be used to provide mechanical reinforcement and enhance properties such as tensile and flexural strength and tensile modulus. Even larger particles may be used to impart stiffness and / or hardness to printed parts. Particle size can be measured by dynamic light scattering. Generally, the colloidal silica particles are non-agglomerated, but the colloidal silica particles may be low-structure aggregates having less than 5, preferably only 2 or 3, primary particles.

[0033] As used herein, the term "colloidal dispersion" refers to a dispersion of colloidal particles (e.g., particles having an average primary particle size of about 600 nm or less). The colloidal stability of such dispersions prevents the majority of colloidal particles from irreversibly agglomerating. Particle aggregation can be detected by an increase in the overall average particle size. In this regard, colloidal dispersions can be stabilized or unstabilized. As used herein, the term "stabilize" refers to the addition of a stabilizing component, e.g., an acid, base, or other stabilizer known in the art, in an amount sufficient to increase the stability of the dispersion. Methods for stabilizing colloidal dispersions are known in the art. Whether stabilized or not, colloidal dispersions used with the present invention preferably have a degree of colloidal stability such that the overall average particle size of the colloidal particles, as measured by DLS, remains unchanged for a period of 3 weeks or more (e.g., 4 weeks or more, or 5 weeks or more), more preferably 6 weeks or more (e.g., 7 weeks or more, or 8 weeks or more), and most preferably 10 weeks or more (e.g., 12 weeks or more, or 16 weeks or more). Aqueous colloidal silica dispersions are generally commercially available at a slightly basic pH (eg, about 9-10), but are also available as neutral and acidic dispersions.

[0034] Colloidal silica particles may be surface-treated with a surface treatment agent. Exemplary treatment methods are described in US Pat. No. 7,811,540, US Pat. No. 1,040,7571, and US Pat. No. 8,435,474, the entire contents of all of which are incorporated herein by reference. The surface treatment agent, in whole or in part, changes the surface chemistry of the silica from silanol groups to a chemical nature provided by the surface treatment agent. Without wishing to be bound by any particular theory, it is believed that the surface treatment agent reacts with surface hydroxy groups on the surface of the colloidal particles, effectively replacing the hydrophilic groups with other chemical groups. The type and degree of charge imparted to the silica particles varies depending on the type and amount of treatment agent used, which can vary depending on the type of resin used for liquid additive manufacturing. In some embodiments, the surface treatment agent has a density of 0.4 to 10 molecules / nm. 2 , for example, 0.1 to 6 molecules / nm2 or 2 to 5 molecules / nm 2 The surface area is present at a level of 0.05 (surface area measured by the Brunauer-Emmett-Teller (BET) method). The number of molecules on the surface may be calculated from the amount of carbon in the surface-treated particles or by CP / MAS NMR, as described in detail below. Many surface treatment groups impart hydrophobicity to the surface by replacing surface silanols with other, more hydrophobic groups. The hydrophobicity, as measured by the methanol wetting number, may be 0 to 85, for example, less than 50 or less than 40.

[0035] Surface treatment of colloidal silica produces various patterns of substituted silicon atoms attached to the surface of the silica particles or indirectly attached to the surface of the silica particles. These substitution patterns are referred to in the literature as M-sites, D-sites, T-sites, and Q-sites. See, for example, Sindorf, Dean William, "Silicon-29 and Carbon-13 CP / MAS NMR Studies of Silica Gel and Bonded Silane Phases," Department of Chemistry, Colorado State University, Fort Collins, Colo., 1982. CP / MAS 29 The correlation between the resonance signals in Si NMR spectra and the M, D, T, and Q sites has been discussed in Maciel, G., Sindorf, DW, J. Am. Chem. Soc. 102:7607-7608 (1980), Sindorf, DW, Maciel, G., J. Phys. Chem., 86:5208-5219 (1982), and Sindorf, DW, Maciel, G., J. Am. Chem. Soc., 105:3767-3776 (1983).

[0036] As used herein, the T1 site refers to a silicon atom derived from an alkoxysilane compound, at least one of which is located on the surface of a metal oxide particle and has one bond to an oxygen atom further bonded to the silicon atom, two bonds to oxygen atoms containing silanol (Si-OH) groups, and one bond to a carbon atom. The T2 site is represented by the formula (I): R 1 -Si(OH)2-(OSi-P 1 ) and the group R 1 is as defined herein for alkoxysilane compounds, and P 1 represents a bond to a silicon atom on the particle surface and / or a bond to a silicon atom of another silicon-containing molecule. The Si atom corresponding to the T1 site is determined by CP / MAS 29 Correlate resonance signals with chemical shifts in the range of -40 ppm to -50 ppm in the Si NMR spectrum; chemical shifts in ppm are measured relative to standard tetramethylsilane.

[0037] As used herein, the T2 site refers to a silicon atom derived from an alkoxysilane compound, at least one of which is on the surface of a metal oxide particle, and which has two bonds to oxygen atoms further bonded to the silicon atom, one bond to an oxygen atom containing a silanol (Si—OH) group, and one bond to a carbon atom. The T2 site is represented by the formula (I): R 1 -Si(OH)-(OSi-P 1 )(OSiP 2 ) and the group R 1 is as defined herein for alkoxysilane compounds, and P 1 and P 2 represents the bond to the silicon atom on the particle surface and / or the bond to the silicon atom of other silicon-containing molecules, respectively. The Si atom corresponding to the T2 site is determined by CP / MAS 29 Correlate with resonance signals with chemical shifts ranging from -56 ppm to -59 ppm in the Si NMR spectrum; chemical shifts in ppm are measured relative to standard tetramethylsilane.

[0038] As used herein, a T3 site refers to a silicon atom derived from an alkoxysilane compound having three bonds to an oxygen atom further bonded to the silicon atom, at least one of which is a silicon atom on a particle. The site has the formula (II): R 1 -Si(OSi-P 1 )(OSi-P 2 )(OSi-P 3 ) and the group R 1 is as defined herein for alkoxysilane compounds, and P 1 , P 2 and P 3 represents the bond to the silicon atom on the particle surface and / or the bond to the silicon atom of other silicon-containing molecules, respectively. The Si atom corresponding to the T3 site is determined by CP / MAS 29 Correlate with resonance signals with chemical shifts ranging from -65 ppm to -69 ppm in the Si NMR spectrum; chemical shifts in ppm are measured relative to standard tetramethylsilane.

[0039] As used herein, the M site refers to a silicon atom derived from a silazane compound having three bonds to carbon atoms and one bond to an oxygen atom that is further bonded to a silicon atom that is bonded to a surface functional group of the silica particle through reaction with the surface of the silica particle. The M site is represented by formula (III): R'R''R'''-Si-OP, where R', R'', and R''' are C1-C2 atoms bonded to the silicon atom of the silazane compound. 10 The Si atom corresponding to the M site is 29 Correlate with resonance signals with chemical shifts ranging from +7 ppm to +18 ppm in the Si NMR spectrum; chemical shifts in ppm are measured relative to standard tetramethylsilane.

[0040] As defined herein, T2 is a CP / MAS 29 T3 is the integrated intensity of peaks with chemical shifts centered in the range of -56 ppm to -59 ppm in the Si NMR spectrum. 29The total T is the integrated intensity of peaks with chemical shifts centered within the range of -65 ppm to -69 ppm in the Si NMR spectrum. 29 The integrated intensity of the Si NMR spectrum from -40 ppm to -70 ppm. M is the CP / MAS 29 The integrated intensity of peaks with chemical shifts centered within the range of +7 ppm to +18 ppm in a Si NMR spectrum. The intensity of a peak refers to the maximum peak height of the signal at its approximate location or the area of ​​the peak occurring within the recited range, calculated using standard calculation methods well known to those skilled in the art.

[0041] Suitable surface treatment agents include organopolysiloxanes, organosiloxanes, organosilanes, haloorganosilanes, organosilazanes and other agents that react with and / or substitute for silanol groups on the surface of the silica particles. For example, a compound of the formula R 1 Si[(OR 2 ) x R 3 3-x ] may be used, and R 1 is C1-C 30 Branched and straight chain alkyls, alkenyls, and C3-C 10 Cycloalkyl, C6-C 10 Aryl, and R 4 Q; R 2 and R 3 are independently methyl or ethyl, and x is 1, 2, or 3. Preferred alkoxysilanes include trialkoxysilanes such as octyltrimethoxysilane and octyltriethoxysilane. Alternative surface treatment agents include hexamethyldisilazane, dimethyldichlorosilane, and hydroxy-substituted or terminated polysiloxanes, particularly siloxane oligomers having 7-14 mers including monohydroxy- or dihydroxy-terminated oligomers, or cyclic siloxanes having 4-14 silicon atoms in the ring.

[0042] Preferably, or in addition to other treatment agents, the surface treatment agent can be reacted with the monomer or oligomer of the liquid resin. For example, a compound of the formula [R 3 3-x (OR 2 ) x ]SiR 4 Q (i.e., R 1 =R 4 For alkoxysilanes having R 2 , R 3 and x is defined above, R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2nwhere Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group. Alkoxysilanes in which n=6-10, such as 8-methacryloxyoctyltrimethoxysilane (MOS) or 8-methacryloxyoctyltriethoxysilane, can provide greater benefits to the mechanical strength of printed parts than alkoxysilanes in which n=0-5, because the longer linger group can promote dispersion of treated particles of resin. Exemplary alkoxysilanes include (3-acryloxypropyl)trimethoxysilane, (3-acryloxypropyl)triethoxysilane, 3-methacryloxypropyltrimethoxysilane (MPS), methacryloxypropyltriethoxysilane, 8-methacryloxyoctyltrimethoxysilane (MOS), 8-methacryloxyoctyltriethoxysilane, methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane, (3-acryloxypropyl)methyldimethoxysilane, methacryloxypropylmethyldimethoxysilane, methacryloxypropyldimethylethoxysilane, 3-butenyltrimethoxysilane, 3-butenyltrimethoxysilane, 3-butenyltriethoxy ... Examples of suitable alkoxysilanes include, but are not limited to, 4-pentenyltriethoxysilane, 4-pentenyltriethoxysilane, 4-pentenyltrimethoxysilane, 5-hexenetrimethoxysilane, 5-hexenemethyldimethoxysilane, allyltrimethoxysilane, trimethoxy(7-octen-1-yl)silane, 3-(trimethoxysilyl)propyl acrylate, (3-glycidoxypropyl)trimethoxysilane, trimethoxyoxy[2-(7-oxabicyclo[4.1.0]hept-3-yl)ethyl]silane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-methacryloxypropyldimethylmethoxysilane. Alternatively or additionally, short-chain polysiloxane oligomers and cooligomers of any of these alkoxysilanes may be used, such as those having a viscosity of 4 to 3500 cSt, e.g., 4 to 10 cSt, 4 to 20 cSt. Such oligomers have multiple alkoxy side chains that can serve as attachment points to the silica surface.Particularly suitable oligomers and cooligomers are R. 5 Si[(OR 2 ) x R 3 3-x ] can be prepared using R 5 is C1-C 30 Branched and straight chain alkyls, alkenyls, and C3-C 10 Cycloalkyl and C6-C 10 aryl; R 2 and R 3 are independently methyl or ethyl, x is 1, 2, or 3, and R 4 For Q, R 4 and Q are defined above, preferably Q is vinyl, acrylate ester, or methacrylate ester. Exemplary polysiloxane oligomers include oligomeric hydrosylates of vinyltrimethoxysilane, (3-acryloxypropyl)trimethoxysilane, vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, octyltriethoxysilane, methyltrimethoxysilane, propyltriethoxysilane, and copolymers of any of these, commercially available from Gelest. In one embodiment, the polysiloxane oligomer is an oligomeric hydrosylate of methacryloxypropyltrimethoxysilane having a viscosity of 500 to 3500 cSt. When polysiloxane oligomers are used, they contain 0.4 to 10 groups R 5 / nm 2 , for example, 1 to 6 groups R 5 / nm 2 Or 2 to 5 R 5 / nm 2 can be present on the surface in an amount sufficient to provide

[0043] An exemplary method for surface treating colloidal silica with an alkoxysilane or polysiloxane oligomer having a Q group, as described above, is carried out by an aqueous reaction mixture. The reaction mixture is incubated with an appropriate amount of Q-containing alkoxysilane or oligomer and dried. The amount of Q-containing alkoxysilane or oligomer is about 0.4 to 10 Q groups / nm. 2 In the case of alkoxysilane monomers, the density is 0.4 to 10 molecules / nm. 2 This corresponds to about 5 to 70 wt% of silica. The amount of silica in the aqueous reaction mixture is about 5 to 70 wt%, based on the total weight of the reaction mixture. Typically, the amount of silica in the reaction mixture is about 20 wt% or more (e.g., about 25 wt% or more), or about 35 wt% or more (e.g., about 40 wt% or more). Thus, the amount of silica in the reaction mixture can be about 10 to 65 wt% (e.g., about 15 to 60 wt%), or about 20 to 50 wt% (e.g., about 25 to 45 wt%).

[0044] The reaction mixture contains about 50 wt% or less of an organic solvent, for example, about 20 wt% or less of an organic solvent. Suitable organic solvents include water-miscible organic solvents, preferably those in which the alkoxysilane is at least partially soluble. Non-limiting examples of water-miscible organic solvents include alcohols (e.g., methanol, ethanol, isopropanol, etc.), tetrahydrofuran, acetone, and similar solvents. The reaction mixture is typically basic, preferably having a pH of 8 to 11, for example, 8.5 to 10, or 9 to 9.5. Alternatively, the reaction mixture can be acidic, for example, having a pH of 2 to 6, or 4 to 5.5.

[0045] The aqueous colloidal silica dispersion and the Q-containing alkoxysilane or oligomer can be combined to provide a reaction mixture by any suitable method. In one embodiment, the Q-containing alkoxysilane or oligomer and the aqueous colloidal silica dispersion are combined with mixing or stirring to promote contact between the silica particles and the treating agent. Mixing or stirring can be achieved by methods such as using a mixing or stirring device. Examples of suitable devices include paddle stirrers, radial or axial flow impellers, homogenizers, ball mills, and similar devices. The Q-containing alkoxysilane or oligomer can be added all at once, or in two or more portions, each of which can be allowed to react separately.

[0046] The reaction mixture can be maintained at a temperature that allows the Q-containing alkoxysilane or oligomeric treating agent to react with the colloidal silica (e.g., react with silanol groups on the surface of the silica particles). Without wishing to be bound by theory, it is hypothesized that under the reaction conditions, the alkoxysilane groups hydrolyze to form silanols, which then condense with silanols on the surface of the silica and / or other molecules of the hydrolyzed treating agent. As a result, the surface of the silica may contain hydrolyzed oligomers and polymers of alkoxysilane or siloxane oligomers in addition to single molecules attached to the surface. Generally, the reaction mixture is maintained at a temperature of about 5°C to 100°C, such as about 15°C to 80°C, or about 20°C to 70°C, for about 5 minutes or more (e.g., about 30 minutes or more), or about 60 minutes or more (e.g., about 120 minutes or more, or about 180 minutes or more). Longer reaction times (e.g., 5-10 hours, 10-20 hours, or even greater than 20 hours, e.g., 20-30 hours) may be required depending on the particular reaction conditions used (e.g., temperature and concentrations of reagents).

[0047] The surface-treated silica particles can be isolated from the reaction mixture and dried. As used herein, the terms "dry" and "dried" with respect to the surface-treated silica particles mean substantially or completely free of liquid components of the reaction mixture, including water and other liquid-phase solvents, reactants, by-products, and other liquid components that may be present. Similarly, as used herein, the term "drying" refers to the process of removing the liquid components of the reaction mixture from the surface-treated silica particles.

[0048] The surface-treated silica particles can be isolated from the reaction mixture before drying, or the surface-treated silica particles can be dried directly from the reaction mixture. Any suitable method can be used to isolate the surface-treated silica particles from the reaction mixture. Suitable methods include filtration, centrifugation, and other methods known to those skilled in the art. The particles can be purified by diafiltration or dialysis. Alternatively, the surface-treated silica particles can be used in the form of a dispersion. For example, the surface-treated silica particles can be solvent-exchanged into an organic solvent such as an alcohol using an azeotropic distillation technique.

[0049] The surface-treated silica particles can be dried after isolation from the reaction mixture or directly from the reaction mixture by evaporating the volatile components of the reaction mixture from the surface-treated silica particles. Evaporation of the volatile components of the reaction mixture can be achieved using heat and / or reduced pressure. When heat is used, the surface-treated silica particles can be heated to a suitable drying temperature using, for example, an oven or other similar device. The selected drying temperature will depend, at least in part, on the specific components of the reaction mixture that require evaporation. Typically, the drying temperature is about 40°C or higher (e.g., about 50°C or higher), such as about 70°C or higher (e.g., about 80°C or higher), or about 120°C or higher (e.g., about 130°C or higher). Thus, the drying temperature generally falls within the range of about 40°C to 250°C (e.g., about 50°C to 200°C), such as about 60°C to 200°C (e.g., about 70°C to 175°C), or about 80°C to 150°C (e.g., about 90°C to 130°C).

[0050] The surface-treated silica particles can be dried at a pressure that provides a useful evaporation rate. When using a drying temperature of about 120°C or higher (e.g., about 120°C to about 150°C), a drying pressure of about 125 kPa or less (e.g., about 75 kPa to about 125 kPa) is appropriate. At drying temperatures below about 120°C (e.g., about 40°C to 120°C), a drying pressure of about 100 kPa or less (e.g., about 75 kPa or less) is useful. Of course, reduced pressure (e.g., a pressure of about 100 kPa or less, 75 kPa or less, or 50 kPa or less) can be used as the only method for evaporating volatile components of the reaction mixture.

[0051] The surface-treated silica particles can also be dried by other methods. For example, the surface-treated silica particles can be dried using spray drying. Spray drying involves spraying the reaction mixture containing the surface-treated silica particles, or a portion thereof, into a drying chamber as a fine mist, and then contacting the fine mist with hot air to cause evaporation of the volatile components of the reaction mixture. Alternatively, the surface-treated silica particles can be dried by freeze-drying, in which the liquid components of the reaction mixture are converted to a solid phase (i.e., frozen) and then converted to a gas phase by applying a vacuum. For example, the reaction mixture containing the surface-treated silica particles can be brought to a suitable temperature (e.g., about -20°C or below, or about -10°C or below, or -5°C or below) to freeze the liquid components of the reaction mixture, and a vacuum can be applied to evaporate the liquid components of the reaction mixture to provide dry hydrophobic silica particles.

[0052] Alternatively or additionally, the colloidal silica particles may be modified with siloxane surface treatments as described in U.S. Pat. No. 8,895,145 and / or U.S. Pat. No. 6,830,811, the entire contents of both of which are incorporated herein by reference, or may be modified with other siloxanes using methods known to those skilled in the art.

[0053] Alternatively or additionally, the silica-polymer composite particles may be used in prepolymer compositions for liquid additive manufacturing. Exemplary silica-polymer composite particles include those described in US9568847, US2010160491, US20190264127, the entire contents of which are incorporated herein by reference, and other methods known to those skilled in the art that result in silica-polymer composite particles having exposed silica on at least a portion of the surface of the silica-polymer composite particles.

[0054] For example, in US9586847, silica-polymer composite particles are produced by combining a first hydrophobizing agent with a colloidal silica dispersion. Any of the colloidal silicas described herein for hydrophobization and subsequent use in liquid additive manufacturing processes can be used to produce the silica-polymer composite particles. For liquid additive manufacturing applications, the first hydrophobizing agent preferably has the formula [R 3 3-x (OR 2 ) x ]SiR 4 Q and R 2 , R 3 , R 4 , Q and x are defined above. Suitable primary hydrophobizing agents include those described above as [R 3 3-x (OR 2 ) x ]SiR 4 Exemplary alkoxysilanes include those listed in connection with the description of Q and others known to those skilled in the art. Silica particles are incubated with a first hydrophobizing agent, which is then polymerized by the addition of a suitable initiator. The resulting silica-polymer composite particles have groups Q on their surfaces. Alternatively or additionally, the silica particles may be surface-treated with a surface treatment agent using any of the surface treatment agents described above, either prior to the first hydrophobizing agent or, for silane treating agents, simultaneously with the first hydrophobizing agent.

[0055] The silica-polymer composite particles may be surface-treated using any of the surface treatment agents described above. For example, the silica-polymer composite particles may be surface-treated with the surface treatment agents described above for colloidal silica. Preferred surface treatment agents for the silica-polymer composite particles are those having a group Q as described above, such as a methacryloxy group, an acryloxy group, or a vinyl group.

[0056] The particle composition can be formulated as a dry particle composition (e.g., a dry powder) or as a dispersion containing silica-based (colloidal silica or silica-polymer composite) particles. The dispersion can include a suitable solvent, such as water alone, or water with cosolvents, treating agents, or any type of additive commonly used in dispersions of treated silica particles. Alternatively or additionally, the dispersion can include silica-based particles dispersed in an oligomer of a resin used in a liquid additive manufacturing process, or in a suitable diluent for the resin. As shown in the examples, combining a solvent dispersion of silica-based particles with a liquid additive manufacturing resin promotes the quality of the dispersion. Without being bound by theory, it is believed that mixing a well-dispersed solvent dispersion into the resin reduces or avoids the shear required to completely disperse the powdered silica-based particles in the resin. Any suitable solvent can be used. Preferably, the solvent is also a good solvent for the resin used in the liquid additive manufacturing process. Exemplary solvents include polar solvents such as alcohols (eg, methanol, ethanol, isopropanol, etc.), tetrahydrofuran, and acetone.

[0057] The resin may be any resin suitable for stereolithography, CLIP, DLS, or other liquid additive manufacturing processes. Typical types of resins include free-radical curable resins such as methacrylate resins, epoxy resins, and oxetane resins, as well as reactive resins such as hydroxy-containing resins, such as hydroxy-terminated polyethers, polyesters, and polyurethanes. Alternatively, the reactive resin may be terminated with vinyl, acrylate, or methacrylate groups (e.g., methacrylic-terminated polyurethanes). These resins may be used alone or in any combination with each other. Silicone resins may also be used.

[0058] The prepolymer composition may further include an initiator, such as a cationic initiator or a free radical initiator, or both, depending on the type of resin. Sensitizers may also be used to increase light yield during polymerization. One skilled in the art will readily select an appropriate initiator for use with the resin of the prepolymer composition. Suitable resins and initiators for use with the silica and silica-polymer composite particles (collectively "silica-based particles") described herein include those described in U.S. Pat. No. 5,972,563 and U.S. Pat. No. 9,457,515, the entire contents of both of which are incorporated herein by reference.

[0059] Additional components that may be useful in prepolymer compositions for liquid additive manufacturing include impact modifiers, rheology modifiers, dyes, pigments, antioxidants, wetting agents, free radical chain transfer agents, leveling agents, defoamers, surfactants, additional fillers other than the silica-based particles provided herein, and other additives known to those skilled in the art.

[0060] Additive manufacturing has long been used to produce complex-shaped polymeric molded articles. Important properties of the resulting articles vary depending on the end-use application, but may include mechanical properties such as tensile, compressive, or shear strength, chemical resistance, and thermal properties. Furthermore, the uncured resin systems used in liquid additive manufacturing have unique performance requirements. For example, in stereolithography, the viscosity of the uncured resin must be low enough so that a new resin layer can quickly flow under the workpiece after each layer is deposited. Similar low or even lower viscosities are required for continuous processes. The resin must be adequately cured for addition to the workpiece, preferably without significantly distorting its shape. The silica-based particles provided herein can promote these and other desirable properties in prepolymer systems for liquid additive manufacturing.

[0061] In one embodiment, the silica-based particles can participate in the crosslinking of the prepolymer composition during polymerization. For example, the silica-based particles can have groups Q, such as acrylate and other double bond-containing groups, on their surfaces that can participate in polymerization. This provides covalent interactions between the particles and the surrounding polymer. Triacrylate and other multifunctional groups can also promote crosslinking. Such crosslinking can provide additional mechanical strength beyond that provided by particles that do not have reactive groups present on their surfaces.

[0062] Alternatively or additionally, the group Q may participate in a reaction that occurs after additive manufacturing. For example, a prepolymer composition may have two or more different monomers or oligomers that polymerize via different mechanisms. A first monomer or oligomer may be polymerized during stereolithography, CLIP, DLS, or a similar method, for example, using a photoinitiator. A second monomer or oligomer may be polymerized during a post-deposition step, for example, using a thermally activated initiator. The group Q may be polymerized in this second polymerization step. Exemplary groups Q for this step include epoxy groups, isocyanate groups, and hydroxy groups.

[0063] Alternatively or additionally, the group Q may provide additional comonomers to the prepolymer composition that might otherwise have poor solubility or miscibility with the other components of the prepolymer composition. Even if different monomers and oligomers are miscible, the cured polymers may not be miscible, and silica may act as a surfactant to prevent phase separation during polymerization.

[0064] Alternatively or additionally, the silica-based particles may be surface-treated with reactive species that provide other functionality to the processed article besides participating in polymerization. For example, if the prepolymer composition undergoes condensation polymerization, the silica-based particles may be surface-treated with species that would otherwise promote the reverse (depolymerization) reaction. Such particles can promote the high-temperature stability of the finished article by retarding resin degradation or corrosion.

[0065] Alternatively or additionally, silica-based particles may help prevent thermal degradation of printed parts by simply absorbing heat. Such applications can benefit from higher particle loadings to provide additional thermal capacity. Non-aggregated colloidal silica, either by itself or in silica-polymer composites, contributes less to viscosity increase than fumed or pyrogenic silica particles, even with similar surface treatments. The additional reinforcement or rigidity provided by higher loadings can also help the finished product resist deformation at high temperatures.

[0066] The use of silica-based particles described herein can also provide mechanical reinforcement to polymeric resins. Silica-based particles can be incorporated at loading levels of 0.1 to 50 wt%, e.g., 1 to 40%, 2 to 30%, or 5 to 25%. Such reinforcement can improve properties such as tensile and / or flexural modulus, tensile and / or flexural strength, and elongation at break. For example, the use of surface-treated colloidal silica particles at a 5% loading level can improve the tensile modulus of a part made with an acrylic resin by at least 7%, e.g., 7% to 10%, or 7% to 15%, relative to a part made without such particles. Similarly, the flexural modulus can be improved by at least 3.5%, e.g., 3.5% to 5%, or 3.5% to 8%. The use of silica-polymer composite particles at a 5% loading level can increase the tensile elongation at break by at least 20%, e.g., 20% to 30%, or 25% to 35%, or 40%, relative to an acrylic resin without such particles. The interaction between silica-based particles and polymers can be tailored by the selection of polymer and the surface treatment of the silica. Chemical interactions between the Q group of the silica-based particles and the polymer can crosslink the polymer. Depending on the frequency and concentration of such interactions, the particles can provide additional crosslinks to the resin in combination with conventional reinforcement. For example, even in the absence of crosslinks, the particles can improve fracture toughness and impact resistance by interrupting crack propagation. In some embodiments, the additional crosslinks provided by the selection of reactive groups for Q can improve tensile properties in manufactured parts. Furthermore, because the particles alter the dynamics of the polymer chains, silica-based particles can be used to tailor thermal properties such as glass transition temperature, low-temperature brittleness, coefficient of thermal expansion, or melting point, or to improve thermal deflection performance. Surface treatments that can interact with the polymer matrix can improve the reinforcing effect of silica-based particles compared to untreated particles. In some embodiments, surface treatments using a Q group where n is 6 to 10 provide improved mechanical properties relative to surface treatments without a Q group or with a Q group where n is 5 or less.

[0067] Nevertheless, silica preferably does not dramatically increase the viscosity of the uncured resin, which can make the resin more difficult to process using SLA, CLIP, or similar methods. In certain embodiments, the use of silica does not increase the viscosity of the resin by more than 500 cP, e.g., 450 cP or 350 cP, relative to unfilled resin.

[0068] Alternatively or additionally, the surface treatment agent can improve the affinity and / or dispersibility of the silica-based particles with the resin, the prepolymer, or both. This can help the silica-based particles influence the surface appearance and other properties of the processed object. The reinforcement provided by the silica-based particles can improve the scratch resistance of printed parts. Altering the flow properties of the prepolymer composition can also enable a smoother surface finish and reduce variations between individual polymer layers.

[0069] Surface treatments can also improve other properties. For example, hydrophobized silica-based particles can retard moisture migration into the finished part, reducing swelling in humid environments. Surface chemistry can also be tailored to provide chemical resistance, for example, by selecting a surface treatment that is immiscible or has limited miscibility or solubility with chemicals expected to come into contact with the printed part. Alternatively or additionally, silica-based particles can be used at sufficiently high loadings to impart a surface roughness or matte finish to the finished part.

[0070] Silica-based particles can also promote leveling of the prepolymer composition. The rheological control provided by the silica-based particles allows for the rapid formation of a smooth layer of prepolymer under the workpiece. This improves processability by reducing the time it takes for additional prepolymer composition to flow under the workpiece after a layer has been deposited. By allowing thinner layers of polymer to be deposited, higher resolution features can also be formed. In continuous processes, improved leveling improves processability and resolution by preventing defects in the final product due to uneven flow of the prepolymer composition.

[0071] Silica-based particles can also be used to disperse different components of a prepolymer formulation. For example, colloidal silica may be used to stabilize mixtures of different monomers or oligomers that might otherwise be immiscible, for example, by forming a particle-stabilized emulsion. Alternatively or additionally, silica-based particles may be used to stabilize the dispersion of other solid additives in the prepolymer composition. For example, the silica-based particles may have a surface treatment that reduces the interfacial energy between the solid additive and the monomers and / or oligomers of the prepolymer composition, thereby acting as a dispersant. Such additives may include glass fillers, ceramics such as alumina, zirconia, titania, lead zirconate titanate, silicon carbide, silicon nitride, aluminum nitride, tin oxide, magnesium sulfate, metal fillers, polymer fibers, clay, cellulose, and other additives known to those skilled in the art. Such additives may be in the form of relatively equiaxed particles or whiskers. Larger silica particles, such as Admatechs' ADMAFINE products, are available as powders and are also suitable for use in the liquid additive manufacturing processes described herein.

[0072] Silica-based particles may be used to engineer the microstructure of the cured prepolymer composition. For example, silica-based particles may be surface-treated with groups such as amines that trap initiators. This concentrates the initiator on the particle and changes the molecular weight of the cured polymer as a function of distance from the particle. In some embodiments, the molecular weight near the surface may be significantly lower than the bulk of the material, providing a core-shell morphology in the finished product. Alternatively, the same chemistry may be used to improve the shelf life of components for liquid additive manufacturing. For example, if initiator-containing silica is mixed with the remaining components of the prepolymer composition immediately before use, the liquid component may be more resistant to polymerization during storage.

[0073] The silica-based particles can be used in combination with other components typically used in liquid additive manufacturing processes. For example, one or more of the additives described above can be used even if dispersed by a mechanism other than the silica-based particles provided herein. Alternatively or additionally, the prepolymer can include a leveling agent, a surfactant, a plasticizer, or another polymer.

[0074] Silica-based particles can be used in prepolymer compositions suitable for use in stereolithography, CLIP, or DLS. These processes are different but operate on similar principles. A substrate is contacted with the prepolymer composition, e.g., placed in a reservoir, and the prepolymer composition is polymerized imagewise by exposure to actinic radiation to initiate a workpiece by forming a layer of solid polymer on the substrate with a surface parallel to the substrate. The radiation can be emitted by a light source such as a laser that is rastered in a linear or two-dimensional pattern across the surface of the workpiece. In a layer-by-layer process such as SLA, the workpiece is then removed from the reservoir. Additional prepolymer composition is filled into the reservoir, the workpiece is replaced into the reservoir, and the build surface is brought into contact with the prepolymer composition. The prepolymer composition is again imagewise cured, depositing additional solid polymer on the workpiece. The surface of the solidified prepolymer defines the build surface of the workpiece and the final 3D-printed part, which is built by building sequential layers along an axis transverse to the cross section. Each iteration of the process deposits successive portions of the three-dimensional object onto the workpiece. In a continuous process, the workpiece does not need to be removed from the reservoir until the three-dimensional object is formed. Rather, the prepolymer composition is imagewise cured simultaneously with the resupply of new prepolymer composition to the reservoir. The workpiece is moved away from the reservoir along an axis transverse to the substrate and cross-section. Thus, the liquid prepolymer composition is always in contact with the workpiece, even as each subsequent successive portion of the three-dimensional object is formed by polymerization of the composition. As a result, new prepolymer composition contacts the exposed build surface simultaneously as the prepolymer composition polymerizes to form a solid. The workpiece is built in a sequential manner, but individual "layers" are indistinguishable. Exemplary methods for additive manufacturing are described in US10589512, US10792855, US5015424, US5151813, and US9034236, the entire contents of both of which are incorporated herein by reference.

[0075] The present invention is further clarified by the following examples, which are intended to be merely exemplary in nature. [Example]

[0076] Example 1 In this example, the colloidal silica was surface treated with an alkoxysilane having a methacrylate group.

[0077] A three-neck flask was charged with 547 g of colloidal silica dispersion (115 nm diameter, pH 9.3, 40% solids), 469 g of deionized water, and 573 mL of isopropyl alcohol, followed by 2.7 g of 3-methacryloxypropyltrimethoxysilane (MPS). The mixture was stirred at 200-250 rpm at ambient temperature for 4 hours. The mixture was then heated to 60°C over 45 minutes and maintained with stirring for 1 hour and 45 minutes. After this, an additional 10.9 g of MPS was added, and the mixture was incubated at 60°C for an additional 6 hours. The mixture was cooled overnight, transferred to a large crystallizing dish, and the entire contents of the flask were removed with additional isopropyl alcohol. The mixture was heated on a hot plate at 120°C for several hours with occasional manual stirring, and then dried overnight at 90°C without further stirring. Further drying was performed in an oven at 120°C for 6 hours. The resulting white powder was ground in an IKA M20 Universal Mill (IKA Works, Inc., Wilmington, NC).

[0078] Example 2 In this example, the performance of various colloidal silica and silica polymer mixtures was evaluated in a commercial SLA process.

[0079] To form 5 wt% samples, 7.5 g of TG-C191 octyltrimethoxysilane-treated colloidal silica (110-115 nm diameter, Cabot Corporation), TG-C110 hexamethyldisilazane (HMDZ)-treated colloidal silica (110-115 nm diameter, Cabot Corporation), the MPS-treated colloidal silica of Example 1 (which has a particle size of 80 nm and is silica-polymer composite particles manufactured according to U.S. Pat. No. 9,568,847, in which MPS is used as a first hydrophobizing agent and no second hydrophobizing agent is used), and Atlas100 silica-polymer composite particles with HMDZ surface treatment (Cabot Corporation) were dispersed in separate 142.5 g samples of clear acrylic resin for stereolithography (Formlabs, clear resin LPGPCL04) using a Cole-Parmer ultrasonic processor at 30% amplitude, 2 s pulse interval, and 5 s pulse time. To improve dispersion quality, the silica-based sample was added to the resin in small increments at approximately 5-minute intervals until all of the silica-based powder was incorporated. The mixture was allowed to cool for approximately 15 minutes before being transferred to the resin tank of a stereolithography 3D printer (Formlabs Form2). A 25 wt% sample was prepared in a similar manner using 37.5 g of silica-based particles and 112.5 g of resin. Similarly, neat resin samples were also prepared by filling the 3D printer tank with at least 150 g of resin. Dogbone- and bar-shaped samples, approximately 12 mm–13 mm thick and 6.4 mm–7 mm long, were prepared with the printing axis perpendicular to the sample strain angle and in the plane of the sample.

[0080] The sample loaded with 5 wt% composite particles was translucent, while the sample prepared with 5% colloidal silica was opaque. However, the particles appeared well dispersed to the naked eye in both samples. Similarly, good dispersion was observed in the sample loaded with 25 wt% colloidal silica. Although the silica-polymer composite particles were not fully dispersed at 25 wt% loading, additional ultrasonic treatment may improve dispersion.

[0081] Dogbone specimens underwent tensile testing and showed brittle fracture with smooth fracture surfaces. The addition of colloidal silica and HMDZ-treated silica-polymer composite particles increased tensile strength and modulus, but elongation at break generally decreased. Furthermore, the use of colloidal silica and silica-polymer composite particles increased flexural modulus, respectively. These results were observed at both 5% and 25% loadings of colloidal silica and 5% loading of composite particles. At 5% loading, MPS-treated colloidal particles provided superior elongation at break, tensile modulus, and tensile strength compared to octyltrimethylsilane-treated colloidal particles. It is hypothesized that poor dispersion of the composite particles at 25% loading affected mechanical performance.

[0082] It was found that the use of colloidal silica and silica-polymer composite particles had little effect on the Shore A hardness.

[0083] Example 3 In this example, colloidal silica is modified with mercaptopropyltrimethoxysilane.

[0084] Mercaptopropyltrimethoxysilane (7.07 g) was added to 177.8 g (45% solids) of Ludox CL-X colloidal silica dispersion (110–115 ml). 2 The resulting white powder is added to a stirred mixture of 1000 mg of PEG-400 (1 / g, available from Sigma-Aldrich), 64 g of water, and 160 g of methanol. The mixture is then heated at 50°C for 90 hours. The mixture is cooled to room temperature and dried under nitrogen without stirring at 90°C overnight. Further drying is carried out in an oven under nitrogen at 120°C for 6 hours. The resulting white powder is ground in an IKA M20 Universal Mill (IKA Works, Inc., Wilmington, NC).

[0085] Example 4 In this example, colloidal silica is modified with an alkoxysilane bearing a methacrylate group.

[0086] A three-neck flask is charged with 547 g of colloidal silica dispersion (100 nm diameter, pH 9.3-9.6, 40% solids), 469 g of deionized water, and 573 g of isopropyl alcohol, followed by 2.7 g of 3-methacryloxypropyltrimethoxysilane (MPS). The mixture is stirred at 200-250 rpm at ambient temperature for 4 hours. The temperature is then increased to 60°C over 45 minutes and maintained with stirring for 1 hour 45 minutes. After this, an additional 10.9 g of MPS is added and the mixture is incubated at 60°C for an additional 6 hours. The mixture is cooled overnight, transferred to a large crystallizing dish, and the entire contents of the flask are removed with additional isopropyl alcohol. The mixture is heated on a hot plate at 120°C for several hours with occasional manual stirring, and then dried overnight at 90°C without further stirring. Further drying is carried out in an oven at 120°C for 6 hours. The resulting white powder is ground in an IKA M20 Universal Mill (IKA Works, Inc., Wilmington, NC).

[0087] Example 5 In this example, the colloidal silica was surface treated with an alkoxysilane having a methacrylate group.

[0088] A three-neck flask was charged with 500 g of colloidal silica dispersion (50 nm diameter, pH 9.3–9.6, 44% solids), 516.5 mL of deionized water, and 573 mL of isopropyl alcohol, followed by 3.6 g of 3-methacryloxypropyltrimethoxysilane (MPS). The mixture was stirred at 200–250 rpm at ambient temperature for 4 hours. The mixture was then heated to 60°C over 45 minutes and maintained with stirring for 1 hour and 45 minutes. After this, an additional 14.6 g of MPS was added via syringe at 1 mL / min, and the mixture was incubated at 60°C for an additional 6 hours. The mixture was cooled overnight, transferred to a large crystallizing dish, and the entire contents of the flask were removed with additional isopropyl alcohol. The mixture was heated on a hot plate at 120°C for several hours with occasional manual stirring, and then dried overnight at 90°C without further stirring. Further drying was performed in an oven at 110°C for 6 hours. The resulting white powder was ground in an IKA M20 Universal Mill (IKA Works, Inc., Wilmington, NC).

[0089] Example 6 In this example, the colloidal silica was surface treated with an alkoxysilane having a methacrylate group.

[0090] A three-neck flask was charged with 851 g of colloidal silica dispersion (115 nm diameter, pH 9.3, 40% solids) and 470 mL of isopropyl alcohol, followed by 2.5 g of 3-methacryloxypropyltrimethoxysilane (MPS). The mixture was stirred at 200-250 rpm at ambient temperature for 4 hours. The mixture was then heated to 60°C over 45 minutes and held with stirring for 1 hour 45 minutes, after which an additional 9.7 g of MPS was added over 5 minutes and the mixture was incubated at 60°C for an additional 6 hours. The mixture was spray dried to yield a powder with a carbon content of 1.1 wt% (Leco C-200 Carbon Analyzer).

[0091] Example 7 In this example, a stereolithography resin was filled with silica-based particles to form a mechanical test part.

[0092] To form a 25 wt% masterbatch, 11 g of each of the MPS-treated colloidal silica from Example 1 and 80 nm silica-polymer composite particles with a particle size of 80 nm, manufactured according to U.S. Patent No. 9,568,847, using MPS as the first hydrophobizing agent but no second hydrophobizing agent, were dispersed into separate 33 g samples of a clear acrylic resin for stereolithography (Formlabs, FLGPCL04 clear resin) by manually adding a small amount of the particles to the resin, followed by approximately 45 minutes of additional manual mixing. The mixture was then treated using a Cole-Parmer ultrasonic processor at 30% amplitude, 2 seconds between pulses, and 5 seconds for the pulse time, followed by 2 minutes of manual mixing. This ultrasonic + manual mixing sequence was repeated five times. A letdown containing 5% silica-based particles was prepared by combining 36 g of the masterbatch's sufficient neat resin to create a 180 g mixture, followed by manual mixing for at least 20 minutes. The ultrasonic treatment used for the masterbatch was then repeated on the letdown. The composition was then transferred to the resin tank of a stereolithography 3D printer (Formlabs Form2, 100 μm resolution). Similarly, neat resin samples were also prepared by filling the 3D printer tank with at least 150 g of resin. Bar-shaped samples measuring 64.00 mm x 12.80 mm x 6.40 mm were prepared for flexural testing with their long axis parallel to the printing axis. Dogbone-shaped samples measuring 57.15 mm x 9.53 mm x 2.03 mm were prepared with their long axis tilted approximately 45° relative to the printing axis, with the sample itself in the plane of the printing axis. The sample containing MPS-treated colloidal silica exhibited improved tensile modulus (1900 MPa) compared to the neat resin (1760 MPa) and improved flexural modulus (43,433 MPa) compared to the neat resin (41,685 MPa). The samples containing silica-polymer composite particles showed improved tensile elongation at break (6.4%) compared to the neat resin (5.0%). Flexural strength, flexural elongation, and tensile strength did not show significant changes for any of the experimental samples.

[0093] Example 8 Aqueous dispersions of colloidal silica with particle sizes of 23 nm, 115 nm, and 330 nm were used (Table 1). A three-neck flask was charged with the colloidal silica dispersion, deionized water, ammonium hydroxide, and isopropyl alcohol, in that order, as specified in Table 2, followed by a first treating agent (TA) charge of either 3-methacryloxypropyltrimethoxysilane (MPS) or 8-methacryloxyoctyltrimethoxysilane (MOS) (see Table 3). The mixture was stirred at 200-250 rpm at ambient temperature for 4 hours. The mixture was then heated to 60°C over 30 minutes and maintained with stirring for 1 hour and 30 minutes. After that, a second TA charge, as specified in Table 2, was added, and the mixture was incubated at 60°C for an additional 6 hours. The total amount of treating agent added was 100% to 120% of the total silica surface area. 2 This corresponds to four molecules of TA per 1000 ml of silica. The mixture was cooled overnight, transferred to a large crystallizing dish, and the entire contents of the flask were removed with additional isopropyl alcohol. For Samples 8-1, 8-2, and 8-5, the mixture was heated on a hot plate at 120°C for several hours with occasional manual stirring, and then dried overnight at 90°C without further stirring. The resulting white solid was ground in an IKA M20 Universal Mill (IKA Works, Inc., Wilmington, NC). For Samples 8-3 and 8-4, the sample was repeatedly concentrated from multiple additions of IPA (150 mL each), each time allowing the azeotropic removal of water to bring the sample to a wet paste before adding the next portion of IPA. This was done a total of six times, resulting in a nearly water-free IPA dispersion after the final IPA addition. The silica concentrations in the resulting dispersions are shown in Table 2. [Table 1] [Table 2] [Table 3]

[0094] Samples 8-1 through 8-5 were combined with photocurable resin as follows: For Samples 8-1, 8-2, and 8-5, 30 g of silica was combined with 570 g of Formlabs V4 Clear Light Resin in a FlackTek DAC600 Speedmixer equipped with vacuum until visual inspection of a small sample dropped onto a glass slide using an optical microscope revealed the sample was dispersed. Specifically, six 15 mm yttria-stabilized zirconia grinding media (FlackTek), 85 g of resin, and 5 g of silica were loaded into a Max250 cup. The cup was capped and mixed at 800 rpm for 30 seconds, after which any material that had accumulated along the sides of the cup was washed and returned to the resin. The 30-second / 800 rpm / wash sequence was repeated, and the resin mixture was then mixed for three 2-minute cycles at 2300 rpm, with a 2-minute cooling period after each mixing cycle. The resin mixture was then degassed under 30 mBar or maximum vacuum for two cycles at 1500 rpm for 30 seconds and 1000 rpm for 7 minutes. After each 1000 rpm cycle, the resin mixture was allowed to cool for 2 minutes. A 125 μm paint screen was used to remove the ceramic media, and sufficient resin was added to dilute the mixture to 5% silica. The letdown was mixed at 1500 rpm for 30 seconds, followed by 1000 rpm for 7 minutes. This procedure was repeated to obtain a 5% silica / resin mixture sufficient for additive manufacturing by SLA. For Examples 8-4 and 8-5, 570 g of Formlabs V4 Clear Light resin was loaded into a large crystallizing dish, to which sufficient silica dispersion was added to provide a 5% solids loading in the final IPA-free resin composition. The mixture was magnetically stirred and maintained at 60°C overnight, protected from light, with a slight nitrogen sweep over the top of the crystallizing dish.

[0095] A 5 wt% dispersion in acrylic resin was prepared using MPS-treated fumed silica (Aerosil R711 silica, Evonik Industries). 30 g of silica was combined with 570 g of Formlabs V4 Clear Light resin in a vacuum-equipped FlackTek DAC600 Speedmixer until visual inspection of a small sample dropped onto a glass slide under an optical microscope revealed the sample was dispersed. Specifically, 95 g of resin and 5 g of silica were loaded into a Max250 cup. The cup was capped and mixed at 1500 rpm for 30 seconds, after which the material that had accumulated along the sides of the cup was washed and returned to the resin. The 30 s / 1500 rpm / wash procedure was repeated. Once the silica was completely wetted out, six 15 mm yttria-stabilized zirconia grinding media (FlackTek) were added to the dispersion. The resin mixture was further mixed for three 2-minute cycles at 2300 rpm, with a 2-minute cooling period after each mixing cycle. Finally, the ceramic media was removed using a 125 μm paint screen. This procedure was repeated until approximately 600 g of a 5% silica / resin mixture was obtained, sufficient for additive manufacturing by SLA.

[0096] The viscosity characteristics of the uncured resin mixture were measured using an AR2000ex rheometer (TA Instruments) with a 40 mm 2° cone at 25°C and 35°C, ranging from 0.01 to 1000 s -1The shear strengths were measured at shear rates of 100 sq. m / s and are shown in Table 4. Resin mixtures were printed on a Form3 SLA 3D printer (Formlabs) according to the manufacturer's instructions to create the shapes required for mechanical testing according to ASTM D638-14 (tensile and elongation tests), ASTM D790-03 (flexural properties), and ASTM D256-04 (Izod impact). Five dogbone-shaped specimens measuring 165 mm (gauge length 50 mm) in length (z-axis as manufactured), 13 mm in width, and 3.2 mm in thickness were prepared for tensile testing. Three rectangular specimens (length = 127 mm, width = 12.7 mm, thickness = 3.2 mm) were prepared for flexural testing. Ten rectangular specimens (length = 63.5 mm, width = 12.7 mm, thickness = 6 mm) were prepared for Izod impact testing. For Izod impact testing, the prints were printed with notches of the size specified by ASTM standards to improve reproducibility, and the prints were unnotched. The printed parts were washed with isopropyl alcohol in a Form Wash device (Formlabs) for 10–15 minutes until the printed parts were tack-free. After air drying for 30 minutes, the printed parts were post-cured in a Form Cure device (Formlabs) at 65°C for 30 minutes, followed by additional irradiation with 405 nm light. [Table 4]

[0097] The data in Table 4 show that the use of surface-treated colloidal silica generally improved the mechanical performance of printed parts without significantly adversely affecting resin viscosity. In contrast, MPS-treated fumed silica dramatically increased the resin's viscosity at room temperature. MOS surface treatment of colloidal silica outperformed MPS in improving impact resistance for 23 nm and 115 nm core silica particles. Flexural modulus increased with decreasing particle size (increasing surface area), with MOS outperforming MPS for 115 nm core silica. Tensile modulus increased for all silica samples relative to the clear resin.

[0098] Using the above method, additional dispersions were prepared with 10% and 15% loadings of Samples 8-1 and 8-2 and MPS-treated fumed silica, with the amount of resin adjusted appropriately. These dispersions were then heated at 25°C and a shear rate of 100 s -1 The viscosities at 800 kJ / min are shown in Figure 1 (x = fumed silica, diamonds = Sample 8-1, triangles = Sample 8-2), demonstrating a dramatic increase in viscosity with increasing loading due to the thixotropic effect of fumed silica, while the colloidal silica resin dispersions show relatively little change in viscosity with loading. Additional dispersions containing 20% ​​loading of Sample 8-1 were prepared using the same method as above, but on a smaller scale, and showed a similarly low viscosity of approximately 1250 cP.

[0099] The quality of the resin's silica dispersion was evaluated by SEM imaging of printed 3D sections. The samples were sectioned to expose a cross section, then embedded and cured in SPI PON812 epoxy. The cut surface was polished to a final finish of 50 nm using a series of silicon carbide abrasive discs (Ted Pella, Inc.) and alumina polishing slurry (for a finish quality of 5 μm or better) (Pace Technologies). The samples were bath sonicated and washed in running water to remove polishing residue. After a final rinse in isopropanol and drying, the surface was sputter-coated with sufficient platinum to provide conductivity during SEM imaging using a Denton Desk V sputter coater. In-lens secondary electron SEM images were taken using a Zeiss UltraPlus Field Emission SEM at 1 kV with a 30 μm aperture and a working distance of ~3-3.5 mm. Images were saved in TIFF format at a resolution of 1024 × 768 pixels. Low-magnification images (1000X) were collected using the SEM's Line Integration setting with a scan speed of 6 and an N=30 scan size to eliminate noise. 5K and 25K images were taken with the Frame Integration setting, a scan speed of 3, and an N=50 scan size. This shortened pixel dwell time and reduced the charging effects and beam damage / contamination deposition seen with line integration. Resins prepared from IPA dispersions of MPS-treated colloidal silica (Sample 8-3) exhibited very well-dispersed single particles with essentially no agglomeration (Figures 2A and 2B). Dispersion of dry silica (e.g., Sample 8-1) into resin required intense mechanical high-shear mixing to achieve good dispersion, although some agglomerates could still be found in cured parts (Figures 2C and 2D). MOS-treated 115 nm particles (Figures 3A and 3B) dispersed more readily in resin than the corresponding MPS-treated 115 nm particles (Figures 3C and 3D) (Samples 8-3 and 4).

[0100] Example 9 The colloidal silica and TG-C110 silica from Sample 8-1 were combined with Formlabs Flexible 80A resin in the same manner and proportions as used to combine the silica and V4 resin in Example 8. The viscosity of the uncured resin was measured at 100 s at 25°C and 35°C as described in Example 8. -1 and 1000s -1 (Table 5). 3D printed samples were fabricated as described in Example 8. [Table 5]

[0101] Adding silica to flexible resins increases viscosity, but the increase is not so great that the resin becomes unprintable. The resulting 3D printed parts exhibit increased stiffness (elastic modulus) relative to parts printed with neat resin as a result of silica reinforcement (approximately 6.1 to 6.2 MPa with colloidal silica vs. 4.9 MPa without), but printed parts containing Sample 8-1 exhibited higher tensile strength than parts containing TG-C110 silica.

[0102] Example 10 In this example, the colloidal silica was surface treated with an alkoxysilane hydrolysate having a methacrylate group.

[0103] A three-neck flask was charged with 382 g of colloidal silica dispersion (115 nm diameter, pH 2.5, 31.4% solids), 10 g of deionized water, and then 3.12 g of 5N NH4OH. The final pH was 9.5-9.8. To this stirred mixture, 196 mL of isopropyl alcohol was added, followed by 6 g of methacryloxypropyltrimethoxysilane, oligomer hydrolyzate (H-MPS, 1000-3000 cSt, Gelest). The mixture was stirred at 200-250 rpm at ambient temperature for 4 hours. It was then heated to 60°C over 45 minutes and maintained with stirring for 7 hours and 30 minutes. The mixture was cooled overnight, transferred to a large crystallizing dish, and the entire contents of the flask were removed with additional isopropyl alcohol to ensure complete removal. The mixture was heated on a hot plate at 120°C for several hours with occasional manual stirring, and then dried overnight at 120°C without further stirring. The resulting white powder was milled in an IKA M20 Universal Mill (IKA Works, Inc., Wilmington, NC) to produce approximately 125 g of fine white powder.

[0104] Example 11 In this example, colloidal silica was surface treated with an alkoxysilane bearing a methacrylate group at low pH.

[0105] A three-neck flask was charged with 382 g of ion-exchanged colloidal silica dispersion (115 nm diameter, pH 2, 31.4% solids), 10 g of deionized water, and 196 mL of isopropyl alcohol, followed by 4.7 g of 3-methacryloxypropyltrimethoxysilane (MPS). The mixture was stirred at 200-250 rpm at ambient temperature for 4 hours. The temperature was then increased to 60°C over 45 minutes and maintained with stirring for 7 hours and 30 minutes. The mixture was cooled overnight, transferred to a large crystallizing dish, and the entire contents of the flask were removed with additional isopropyl alcohol to ensure removal. The mixture was heated on a hot plate at 120°C for several hours with occasional manual stirring, and then dried overnight at 120°C without further stirring. The resulting white powder was milled in an IKA M20 Universal Mill (IKA Works, Inc., Wilmington, NC).

[0106] Example 12 The solid state of the samples as shown in Table 6 29 Si cross-polarized electromagnetic angle spinning (CP / MAS) NMR spectra were obtained at 9.4 T ( 29 79.49MHz and 1 Recordings were made at a frequency of 400.19 MHz for H. A linear ramp of 70% to 100% proton channel RF amplitude was used during the cross-polarized contact time to obtain good and stable Hartmann-Hahn matching conditions at a magic angle spinning rate of 8 kHz. 29 The Si RF field is 49KHz. 29 The contact time for the Si CP / MAS measurements was set to 10 ms. During the data acquisition period, multiple pulse proton decoupling (TPPM) with a field strength of 42 kHz was applied. Typically, 2000 repeated scans were performed with a recycle delay of 3 seconds to acquire the data. All NMR measurements were performed at room temperature. 29Si chemical shifts are referenced to tetramethylsilane using an external standard of tris(trimethylsilyl)silane. Results in Table 6 (units = 1 nm of silica surface) 2 The (molecule of treatment chemical per 1000) indicates that the surface treatment agent is covalently bonded to the silica via a siloxane bond. [Table 6]

[0107] The foregoing description of preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described to explain the principles of the invention and its practical application so that those skilled in the art may utilize the invention in various embodiments and with various modifications as suited to the particular uses envisioned. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

[0108] The contents described in the claims are as follows: Examples of embodiments of the present invention are listed in the following items [Aspect 1] to [Aspect 36]. [Aspect 1] 1. A method of forming a three-dimensional object, comprising: a) contacting a substrate with a reservoir of a prepolymer composition, the prepolymer composition comprising a resin comprising monomers and oligomers of a polymer selected from acrylate, methacrylate, vinyl polymer, olefin, silicone, and epoxy; and silica-containing particles selected from i) 0.1 to 50 wt % colloidal silica particles having a particle size of 5 nm to 600 nm treated with at least one surface treatment agent, and ii) 0.1 to 50 wt % silica-polymer composite particles comprising colloidal silica particles having a particle size of 10 nm to 3 μm treated with at least one surface treatment agent, the surface treatment agent comprising an organopolysiloxane, organosiloxane, organosilane, haloorganosilane, or organosilazane, the prepolymer composition being heated at a temperature of 25° C. and 100 s. -1 having a viscosity up to 500 cP greater than the neat resin at a shear rate of; b) imagewise selectively exposing the prepolymer composition to actinic radiation to form a solid polymer in the substrate having a build surface parallel to the substrate, the solid polymer being a continuous portion of the three-dimensional object; c) contacting the build surface with the prepolymer composition; d) selectively exposing the prepolymer composition to actinic radiation to increase the mass of the solid polymer, wherein the additional polymer is a subsequent, continuous portion of the three-dimensional object; and e) repeating steps c) and d) until the three-dimensional object is formed; A method comprising: [Aspect 2] 2. The method of claim 1, wherein the surface treatment agent comprises a hydroxy-substituted or terminal siloxane oligomer having a 7-14 mer, or a cyclic siloxane having 4 to 14 silicon atoms in the ring. [Aspect 3] 3. The method of claim 2, wherein the siloxane oligomer is a dimethyl siloxane oligomer. [Aspect 4] The surface treatment agent is R 1 Si[(OR 2 ) x R 3 3-x ], hexamethyldisilazane, or dimethyldichlorosilane, R 1 is C 1 -C 30 Branched and straight chain alkyls, alkenyls, and C 3 -C 10 Cycloalkyl, C 6 -C 10 Aryl, and R 4 Q; R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3 The method of any one of aspects 1-3, wherein x is independently methyl or ethyl; and x is 1, 2, or 3. [Aspect 5] The surface treatment agent is [R 3 3-x (OR 2 ) x ]SiR 4 Q, and n=6 to 10. [Aspect 6] The surface treatment agent is [R 3 3-x (OR 2 ) x ]SiR 4 6. The method of any one of claims 4 to 5, comprising Q, wherein Q is an epoxy group or a thiol group. [Aspect 7] The surface treatment agent has at least one group [R 3 3-x (OR 2 ) x ]SiR 4 Q, and R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3 is independently methyl or ethyl; and x is 1, 2, or 3. [Aspect 8] Aspect 8. The method of aspect 7, wherein Q is a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group. [Aspect 9] 9. The method of any one of claims 7 to 8, wherein the polysiloxane oligomer or cooligomer has a viscosity of 500 to 3500 cSt. [Aspect 10] 2. The method of embodiment 1, wherein the silica-containing particles are silica-polymer composite particles. [Aspect 11] The silica-polymer composite particles include a plurality of silica particles and a polymer matrix, and the silica particles are 3 3-x (OR 2 ) x ]SiR 4 Surface modified with a first hydrophobizing agent containing Q, 4 Among Q, R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3 is independently methyl or ethyl; and x is 1, 2, or 3. [Aspect 12]

[0023] Aspect 12. The method of any one of aspects 1-11, wherein coating the prepolymer composition onto a cross section comprises moving the substrate along an axis perpendicular to the cross section. [Aspect 13] 13. The method of any one of aspects 1-12, wherein steps c) and d) are performed stepwise. [Aspect 14] Aspect 13. The method of any one of aspects 1-12, wherein steps c) and d) are performed in a stepwise or simultaneous manner such that the prepolymer composition is coated on the cross section while the prepolymer composition is polymerizing. [Aspect 15] A polymer conjugate prepared by the method of any one of embodiments 1-14. [Aspect 16] 1. A method for preparing surface-treated silica particles, comprising: providing an aqueous silica dispersion comprising 5 to 70% colloidal silica particles having an average particle size of 5 to 600 nm and a first BET surface area, and having a pH of about 8 to about 11; The aqueous silica dispersion is dissolved in a solvent containing a compound having the formula [R 3 3-x (OR 2 ) x ]SiR 4 Q is 0.4 to 10 molecules / nm 2 (based on the first BET surface area) of an alkoxysilane treating agent, or b) 0.5 to 10 R 5 base / nm2 at least one group R having a viscosity of 4 to 3500 cSt in an amount corresponding to said first BET surface area; 5 Si[(OR 2 ) x R 3 3-x to provide a reaction mixture containing 50 wt % or less of an organic solvent, 5 is C 1 -C 10 Branched and straight chain alkyls, alkenyls, and C 3 -C 10 Cycloalkyl, C 6 -C 10 Aryl, and R 4 Q; R 2 and R 3 are independently methyl or ethyl, x is 1, 2, or 3, and R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n and Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; and a) drying the surface-treated silica particles directly from the reaction mixture to form a powder, or b) solvent-exchanging the surface-treated silica particles into a solvent comprising a mixture of an organic solvent and water, wherein the amount of water is no more than the amount of water present in an azeotropic mixture of the organic solvent and water. A method comprising: [Aspect 17] 17. The method of embodiment 16, wherein the reaction mixture has a pH of about 8 or greater. [Aspect 18] The alkoxysilane treating agent is a compound represented by the formula [R 3 3-x (OR 2 ) x ]SiR 4 18. The method of claim 16 or 17, wherein Q is an epoxy group or a thiol group, or both. [Aspect 19] R 5 R 4 Q. [Aspect 20] Aspect 20. The method of any one of aspects 16-19, wherein Q is a substituted or unsubstituted vinyl group, an acrylate ester group, or a methacrylate ester group. [Aspect 21] Aspect 22. The method of any one of aspects 16-21, wherein the viscosity of the polysiloxane oligomer is 500 to 3500 cSt. [Aspect 22] At least one group R 5 Si[(OR2 ) x R 3 3-x ], and colloidal silica particles surface-treated with a polysiloxane oligomer or cooligomer of R 5 is C 1 -C 10 Branched and straight chain alkyls, alkenyls, and C 3 -C 10 Cycloalkyl, and C 6 -C 10 aryl; R 2 and R 3 are independently methyl or ethyl, x is 1, 2, or 3, and R 4 Among Q, R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n and Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group. [Aspect 23] 23. The particulate composition of embodiment 22, wherein the polysiloxane oligomer or cooligomer has a viscosity of 4 to 3500 cSt. [Aspect 24] R 5 R 4 24. The particle composition of any one of claims 22 to 23, wherein Q is a substituted or unsubstituted vinyl group, an acrylate ester group, or a methacrylate ester group; and the polysiloxane oligomer has a viscosity of 500 to 3500 cSt. [Aspect 25] Aspect 26. The particle composition of any one of aspects 22-25, wherein the particle composition is in the form of a dry powder. [Aspect 26] 1. A prepolymer composition for three-dimensional printing via stereolithography, continuous liquid interface manufacturing, or digital photosynthesis, comprising: a resin comprising polymeric monomers and oligomers selected from acrylates, methacrylates, vinyl polymers, olefins, silicones, and epoxies; and i) 0.1 to 50 wt% colloidal silica particles having a particle size of 5 nm to 600 nm treated with at least one surface treatment agent, and ii) 0.1 to 50 wt% silica-polymer composite particles having a particle diameter of 10 nm to 3 μm and containing colloidal silica particles treated with at least one surface treatment agent. and silica-containing particles selected from The surface treatment agent comprises an organopolysiloxane, an organosiloxane, an organosilane, a haloorganosilane, or an organosilazane, and the prepolymer composition is heated at a temperature of 25° C. and 100 s -1 A prepolymer composition having a viscosity up to 500 cP greater than the neat resin at a shear rate of 100 psi. [Aspect 27] 27. The prepolymer composition of embodiment 26, wherein the surface treatment agent comprises a hydroxy-substituted or terminal siloxane oligomer having a 7-14 mer or a cyclic siloxane having 4 to 14 silicon atoms in the ring. [Aspect 28] 28. The prepolymer composition of embodiment 27, wherein the siloxane oligomer is a dimethyl siloxane oligomer. [Aspect 29] The surface treatment agent is R 1 Si[(OR2 ) x R 3 3-x ], hexamethyldisilazane, dimethyldichlorosilane, R 1 is C 1 -C 30 Branched and straight chain alkyls, alkenyls, and C 3 -C 10 Cycloalkyl, C 6 -C 10 Aryl, and R 4 Q; R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3 is independently methyl or ethyl; and x is 1, 2, or 3. [Aspect 30] The surface treatment agent is [R 3 3-x (OR 2 ) x ]SiR 4 30. The prepolymer composition of embodiment 29, comprising Q, wherein n=6-10. [Aspect 31] The surface treatment agent is [R 3 3-x (OR 2 ) x ]SiR 4 31. The prepolymer composition of any one of claims 29 to 30, comprising Q, wherein Q is an epoxy group or a thiol group. [Aspect 32] The surface treatment agent has at least one group [R 3 3-x (OR 2 ) x ]SiR 4 Q, and R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R3 is independently methyl or ethyl; and x is 1, 2, or 3. [Aspect 33] Aspect 33. The prepolymer composition of aspect 32, wherein Q is a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group. [Aspect 34] 34. The prepolymer composition of claim 32 or 33, wherein the polysiloxane oligomer or cooligomer has a viscosity of from 500 to 3500 cSt. [Aspect 35] Aspect 35. The prepolymer composition of any one of aspects 26-34, wherein the silica-containing particles are silica-polymer composite particles. [Aspect 36] The silica-polymer composite particles include a plurality of silica particles and a polymer matrix, and the silica particles are 3 3-x (OR 2 ) x ]SiR 4 It is surface-modified with a first hydrophobizing agent containing Q, and R 4 Among Q, R 4 is a compound represented by the general formula C, where n=0 to 10. n H 2n Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; R 2 and R 3 is independently methyl or ethyl; and x is 1, 2, or 3.

Claims

1. 1. A method for preparing surface-treated silica particles, comprising: providing an aqueous silica dispersion comprising 5 to 70 wt. % colloidal silica particles having an average particle size of 5 to 600 nm and a first BET surface area, and having a pH of about 8 to about 11; The aqueous silica dispersion is dissolved in a solvent containing a compound of the formula [R ３ ３－ｘ (OR ２ ) ｘ ]SiR ４ 0.4 to 10 molecules / nm with Q ２ (based on said first BET surface area) of an alkoxysilane treating agent, or b) 0.5 to 10 R ５ group / nm ２ at least one group R having a viscosity of 4 to 3500 cSt in an amount corresponding to said first BET surface area; ５ Si[(OR ２ ) ｘ R ３ ３－ｘ to provide a reaction mixture containing 50 wt % or less of an organic solvent, ５ is C １ -C １０ Branched and straight chain alkyl, alkenyl, C ３ -C １０ Cycloalkyl, C ６ -C １０ Aryl, and R ４ Q; R ２ and R ３ are independently methyl or ethyl, x is 1, 2, or 3, and R ４ is a compound of the general formula C, where n=1 to 10. ｎ H ２ｎ and Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group; and a) drying the surface-treated silica particles directly from the reaction mixture to form a powder, or b) solvent-exchanging the surface-treated silica particles into a solvent comprising a mixture of an organic solvent and water, wherein the amount of water is no more than the amount of water present in an azeotropic mixture of the organic solvent and water. A method comprising:

2. At least one group R ５ Si[(OR ２ ) ｘ R ３ ３－ｘ The polysiloxane oligomer or cooligomer has a viscosity of 4 to 3500 cSt, and R ５ is C １ -C １０ Branched and straight chain alkyl, alkenyl, C ３ -C １０ Cycloalkyl, C ６ -C １０ Aryl, and R ４ Q; R ２ and R ３ are independently methyl or ethyl, x is 1, 2, or 3, and R ４ is a compound of the general formula C, where n=1 to 10. ｎ H ２ｎ and Q is an epoxy group, a thiol group, or a substituted or unsubstituted vinyl group, an allyl group, an acrylate ester group, or a methacrylate ester group, in the form of a dry powder.

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