DUAL-CURE EPOXY RESINS FOR 3D PRINTING OF HIGH-PERFORMANCE MATERIALS

Abstract

The technology concerns formulations for additive manufacturing including dual-cure materials and multifunctional curing agents.

Claims

1.-62. (canceled)

63. A formulation comprising a dual-cure material being in a form of a monomer or an oligomer, and a multifunctional curing agent, for use in a method of additive manufacturing, wherein the formulation optionally comprises an ink carrier or a carrier suitable for printing.

64. The formulation according to claim 63, wherein the dual-cure material is a polymerizable monomer or oligomer having one or more epoxy functionality and one or more acrylate functionality.

65. The formulation according to claim 63, wherein the dual-cure material is of the structure (I): ##STR00016## wherein the oxirane ring is associated with group R via any of the oxirane carbon atoms or is fused to a group R.

66. The formulation according to claim 65, wherein R is a ring structure or a functionality having a cyclic or an aromatic group, wherein the oxirane ring is fused thereto; or wherein R is a carbon-based group selected from aliphatic groups, aromatic groups, heteroaromatic groups, carbocyclic groups, saturated groups, and unsaturated groups, or wherein R is repeated 1 or more times, wherein each R is an alkylene group having between 1 and 100 carbon atoms, an alkenylene group having between 2 and 100 carbon atoms or an alkynylene group having between 2 and 100 carbon atoms, each of which being optionally substituted, or wherein R is a carbocyclyl group or an aromatic or a heteroaromatic group, that is optionally substituted, or wherein R is an alkylene group comprising 1 to 5 carbon atoms.

67. The formulation according to claim 1, wherein the dual-cure material is of general structure (II): ##STR00017## wherein G is a carbon group comprising between 2 and 50 carbon atoms, and optionally comprising one or more ring structures selected from 4-, 5- and 6-membered carbocyclic, aromatic or heteroaromatic ring systems.

68. The formulation according to claim 67, wherein G is selected from: ##STR00018## wherein the dashed line designates a bond of connectivity to the methylene carbon in structure (II) and wherein the oxirane ring may be substituted on any of the ring positions of the 6-membered ring or is fused to any bond of the 6-membered ring; ##STR00019## wherein the dashed line designates a bond of connectivity to the methylene carbon in a structure (II), said connectivity being through any of the carbon atoms of the 6-membered ring, and wherein the oxirane ring is substituted on any of the ring positions of the 5-membered ring or is fused to any bond of the 5-membered ring; ##STR00020## wherein the dashed line designates a bond of connectivity to the methylene carbon in a structure (II), and wherein the oxirane ring is substituted on any of the ring positions of the 6-membered ring or is fused to any bond of the 6-membered ring; ##STR00021## wherein the dashed line designates a bond of connectivity to the methylene carbon in a structure (II), and wherein the oxirane ring is substituted on any of the ring positions of the 6-membered ring or is fused to any bond of the 6-membered ring.

69. The formulation according to claim 63, wherein the dual-cure material is selected from: ##STR00022##

70. The formulation according to claim 63, wherein the dual-cure material is BAEMA.

71. The formulation according to claim 63, wherein the multifunctional curing agent is selected from methylene dianiline, diethyl aminopropylamine, diethylenetriamine, ethylenediamine, m-phenylenediamine, tris-(dimethylaminomethyl) phenol, triethylenetetramine, dicyandiamide, isopropyl metaphenylenediamine, hexahydrophthalic anhydride, 4,4-methylen-bis-(2-chloraniline), alkylated melamines, cyanate esters, polyphenols and aromatic diisocyanate.

72. The formulation according claim 63, wherein the multifunctional curing agent is selected from melamine and alkylated melamine.

73. The formulation according to claim 63, further comprising an inorganic precursor or a sol gel precursor soluble in the formulation.

74. The formulation according to claim 63, further comprising a photoinitiator suitable for generating an active species capable of inducing polymerization.

75. The formulation according to claim 63, the formulation comprising a dual-cure material, a multifunctional hardener, and/or cyanate esters.

76. The formulation according to claim 75, wherein the dual-cure material is BAEMA and wherein the multifunctional hardener is an alkylated melamine, selected from C1-C10 alkylated melamine.

77. A process for forming a 3D object or pattern, the process comprising inducing polymerization of at least one dual-cure material in presence of a multifunctional curing agent and a photoinitiator, to form a crosslinked polymer structure or pattern, wherein the induction of polymerization comprises irradiation of the at least one dual-cure material in presence of the multifunctional curing agent and the photoinitiator by visible or UV or NIR or IR radiation.

78. The process according to claim 77, wherein the process comprises inducing polymerization by visible or UV or NIR or IR light to form in situ crosslinked polymer structures, followed by thermal curing.

79. An object formed of a formulation according to claim 63, the object being a polymeric object, a structure or a pattern having a Tg higher than 180 C.

80. The object according to claim 79, implemented for use in aerospace aviation, automobile industry, electronic packaging, microelectronic insulation, corrosion resistance, films, medical device, and medical implants.

81. An object formed of a process according to claim 79, the object being a polymeric object, a structure or a pattern having a Tg higher than 180 C.

82. The object according to claim 79, characterized by a Tg of 241 C., Young's modulus of 2.43 Gpa and an ultimate tensile strength (UTS) value of 37.5 MPa; or characterized by a Tg value of 283 C., Young's modulus of 2.85 GPa, and UTS value of 44.25 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0155] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0156] FIG. 1 shows examples of dual epoxy-acrylate resins.

[0157] FIG. 2 demonstrates synthesis of the BAEMA dual resin.

[0158] FIG. 3 demonstrates the reaction of alkylated melamine with hydroxyl groups of BAEMA resin.

[0159] FIG. 4 demonstrates reaction of alkylated melamine with epoxide groups of BAEMA resin.

[0160] FIG. 5 presents a SEM micrograph of printed sample containing Cymel NF 2000A and AMTMS as hardeners. The sample was thermal cured @ 275 C.

[0161] FIG. 6 presents an XPS of BAEMA cured by Cymel NF 2000A and AMTMS after thermal curing @ 275 C.

[0162] FIG. 7 shows a photo of printed woodpiles made of ink cured by Cymel NF 2000A without sol-gel precursor after heat curing @ 180 C. The composition is described in table 6.

[0163] FIG. 8 shows printed diamond-lattice shape object and screws made of ink containing Cymel NF 2000A and the sol-gel precursor, (composition is described in table 6) after heat curing @ 180 C.

[0164] FIG. 9 presents a reaction of cyanate ester with epoxide groups of BAEMA resin.

[0165] FIG. 10 presents images of printed woodpiles and a prism object after heat curing.

[0166] FIG. 11 depicts a suggested reaction of phenolic resin with BAEMA.

[0167] FIG. 12 shows printed wheels after heat curing at 275 C. The models are based on formulation 2 in table 10, including hydroquinone (0.0007% based on BAEMA) and Sulfurhodamine B sodium salt (0.0005% base on BAEMA).

DETAILED DESCRIPTION OF THE DRAWING

Methods

[0168] BAEMA (FIG. 1) was synthesized through semi-esterification of the epoxy resins DGEBA with acrylic acid. The synthesized epoxy monoacrylates was characterized via Fourier transforms infrared spectroscopy (FTIR). New absorptions at 1727, and 1406 cm.sup.1 were formed due to the CO and CC ethoxyacrylate stretch of the dual cure oligomer. The absorption peak of the epoxide group at 914 cm.sup.1 decreased in intensity compared with the starting material DGEBA. Proton nuclear magnetic resonance spectroscopy (.sup.1H-NMR) showed characterized chemical shifts of BAEMA at =6.44, 6.19 and 5.89 ppm corresponding the acrylate group (CH.sub.2CH), and peaks at 4.4-3.8 ppm relate to CH.sub.2O and CH.sub.2CHOH groups. The calculated conversion of the epoxy group to acrylate was 53%, and the polymerization degree n=2.2.

[0169] The oligomer contains traces of unreacted acrylic acid, which can be further utilized as catalyst for the post printing epoxy curing.

Procedure for Homopolymer Preparation:

[0170] The procedure is based on mixing of BAEMA with the relevant solvent at 50 C., to form a clear solution. Next. TPO, optionally DPI and ITX, added and dissolved in the mixture. Additional mixing by Thinky mixer (2 min) followed by defoaming (2 min) formed a transparent homogenous formulation.

Typical Procedure for Formulation Preparation:

[0171] A typical procedure is based on mixing of BAEMA with the relevant solvent, hardener and optionally a sol gel precursor at 50 C., to form a clear blend. Next, the initiators and catalyst are added and dissolved in the mixture. Finally, water was added to the formulation. Additional mixing by Thinky mixer (2 min) followed by defoaming (2 min) formed a transparent homogenous formulation.

Typical Procedure for Formulations Based on 2 Steps Sol Gel Process:

[0172] Sol gel precursor, buffer solution pH=4 and ethanol were heated and stirred at 50 C. for 3 hours. This solution was mixed with a formulation comprising of BAEMA, hardener and relevant initiators/catalyst, (typical procedure demonstrated above). Additional mixing by Thinky mixer (2 min) followed by defoaming (2 min) formed a transparent homogenous formulation.

[0173] Samples were casted in molds for mechanical properties characterization, assessed by three-point bending dynamic mechanical analysis (DMA).

[0174] Models were printed using an Asiga Max DLP printer with LED wavelength of 385 nm @ 30 mw/cm.sup.2 and layer thickness of 50-200 m. Yet, the same printing process can be performed by other stereolithiography-based printers, including and not limited to, SLA, 2-photons and holographic printers, by proper tailoring the components such as photoinitiators and the printing parameters.

[0175] Dogbones were printed for ultimate tensile strength measurements.

[0176] The length and width of the dog bones are shown, the thickness is 800 m.

[0177] The measurements were performed in an Instron testing machine model 4500.

EXAMPLES

Comparative Example 1: Homopolymerization of BAEMA in the Presence of Inert and Reactive Diluents

[0178] For homopolymerization of the viscous oligomer BAEMA, a diluent was added. In this comparative example, two diluents were used: [0179] 1. A volatile diluent-Methyl ethyl ketone (MEK) [0180] 2. A reactive diluent-1-Phenoxy-2-propanol

[0181] The components of the inks as shown in Table 1 were mixed at 55 C. to form a clear solution, then, the inks were molded to form DMA samples. The first ink was left overnight at room temperature for MEK evaporation before photocuring, while the second ink based on 1-phenoxy-2-propanol was photocured immediately. [0182] Photocuring conditions: 0.5 min/395 nm. [0183] Thermal Curing: 1 h/100 C. followed by 4 h/275 C., heat rate 10 C./min Similar Tg was formed for the two formulations.

TABLE-US-00001 TABLE 1 Tg Ink Component Name % Wt. ( C.) With Epoxy acrylate BAEMA 65.0 112 volatile Diluent MEK 32.0 diluent Photoinitiators TPO 1.3 Ph.sub.2I.sup. PF.sub.6.sup.+ 1.3 Catalyst ITX 0.4 With Epoxy acrylate BAEMA 87.2 117 reactive Diluent 1-phenoxy-2- 8.75 diluent propanol Photoinitiators TPO 1.8 Ph.sub.2I.sup. PF.sub.6.sup.+ 1.8 Catalyst ITX 0.45

Comparative Example 2: Homopolymerization of BAEMA with and without Cationic Photoinitiators

[0184] It was discovered that the presence of traces of acrylic acid in the synthesized oligomer, may enable not using a cationic photoinitiator in the formulation. In this comparative example, BAEMA was homopolymerized in two ways: [0185] 1. By adding a cationic photoinitiator to the formulation [0186] 2. Without cationic photoinitiator

[0187] Components of the inks as shown in Table 2 were mixed at 55 C. to form a clear solution, then, molded to form DMA samples. [0188] Photocuring conditions: 0.5 min/295 nm. [0189] Thermal Curing: 1 h/100 C. followed by 4 h/275 C., heat rate 10 C./min

TABLE-US-00002 TABLE 2 Tg Ink Component Name % Wt. ( C.) With cationic Epoxy acrylate BAEMA 65.0 112 Photoinitiator Diluent MEK 32.0 Photoinitiators TPO 1.3 Ph.sub.2I.sup. PF.sub.6.sup.+ 1.3 Catalyst ITX 0.4 Without Epoxy acrylate BAEMA 65.0 134 cationic Diluent MEK 33.7 Photoinitiator Photoinitiator TPO 1.3

[0190] The resulting Tg shows that due to the presence of acid in the oligomer, a heat curing of the epoxide occurs without a cationic photocatalyst. This result has a significant impact on the overall cost reduction of the printing formulation.

[0191] Dogbones were printed from both inks (table 2) and tested by the Instron testing machine. The results of the mechanical properties are attached in Table 3.

TABLE-US-00003 TABLE 3 Tensile Ultimate Tough- Young's Yield Yield tensile Max ness modulus Strength Strain strength Strain (MJ/ (MPa) (MPa) (%) (MPa) (%) m{circumflex over ()}3) With cationic 2062 26.01 1.2 41.85 2.5 2430 Photoinitiator Without 1772 11.42 0.6 20.14 2.2 1436 cationic Photoinitiator

[0192] It can be concluded from table 3 that additional cationic photoinitiator may be required to obtain a homopolymer with higher mechanical properties.

Example 3: Formulation with a Hardener Alkylated Melamine

[0193] When alkylated melamine is heated with the oligomer, it reacts with the OH groups of BAEMA to form urethane linkages (FIG. 3). Reaction with the epoxide functional groups forms N-substituted carbamate and oxazolidone crosslinks (FIG. 4). This process increases the rigidity of the final polymer.

[0194] This example shows the effect of adding a hardener on the mechanical and thermal properties of the resulting polymer, while evaluating the hardener:oligomer ratio. All inks presented here as examples are based on: BAEMA:Cymel NF 2000A as a hardener, and the photoinitiator TPO (2% wt of BAEMA) (see Table 4). The samples were photocured 0.5 min/395 nm, then heated 1 h/100 C. followed by 4 h/275 C. with a heat rate of 10 C./min.

TABLE-US-00004 TABLE 4 BAEMA:alkylated Curing Tg Ink melamine (% wt) conditions ( C.) 1 1:0 1 h/100 C. + 134 4 h/275 C. 2 1:1 1 h/100 C. + 241 4 h/275 C. 3 2:1 1 h/100 C. + 187 4 h/275 C. 4 3.2:1.sup. 1 h/100 C. + 147, 190 4 h/275 C.

[0195] As clearly indicated in table 4, the addition of a melamine-based hardener increases the Tg dramatically from 134 C. for the homopolymer up to 241 C.

Example 4: Effect of Curing Temperature

[0196] In this example, the effect of heat curing temperature on the mechanical properties of the final polymer was evaluated. All samples are based on ink 2 shown in Table 4, containing BAEMA:Cymel NF 2000A:TPO 49:49:2 (wt %). The samples were photocured 0.5 min/395 nm. Tg and mechanical tests results are shown in Table 5.

TABLE-US-00005 TABLE 5 Ultimate Young's Yield Yield tensile Max Tensile Curing Tg modulus Strength Strain strength Strain Toughness conditions ( C.) (MPa) (MPa) (%) (MPa) (%) (MJ/m{circumflex over ()}3) 1 h/100 C., 152 Not Detected 2 h/180 C. 1 h/100 C., 187 2239 11.55 0.5 35.23 1.7 1675 4 h/240 C. 1 h/100 C., 241 2439 15.96 0.6 37.46 2.8 3713 4 h/275 C.

[0197] It can be concluded from Table 5 that increasing the temperature improves epoxide curing. As a result, the Tg and the mechanical properties of the final polymer improved dramatically. The modulus of a cured polymer @ 275 C. reached the value of 2439 MPa and the toughness was doubled compared to curing @ 180 C. It should be noted that heat curing at this high temperature leads to objects having a dark brown color.

Example 5: Addition of a Sol Gel Precursor with Melamine

[0198] This example presents inks based on alkylated melamine as a hardener, with and without the addition of a sol-gel precursor (Table 6). [0199] The ratio BAEMA:hardener1:1. [0200] Photocuring conditions: 0.5 min/395 nm. [0201] Thermal Curing: 1 h/100 C. followed by 4 h/275 C., heat rate 10 C./min.

[0202] Printed models are shown in FIG. 7 and FIG. 8, indicating that both inks are printable.

TABLE-US-00006 TABLE 6 Tg Ink Component Name % Wt. ( C.) Without Sol- Epoxy acrylate BAEMA 49.0 241 Gel precursor Hardener Cymel NF 49.0 2000A Photoinitiator TPO 2.0 With Epoxy acrylate BAEMA 48 280 Sol-Gel Hardener Cymel NF 47.5 precursor 2000A Photoinitiator TPO 1.0 Sol-Gel Acryloxymethyl 2.5 precursor trimethoxysilane (AMTMS) Sol-Gel Water 1.0 precursor additive

[0203] The results in Table 6 show the high Tg of polymer cured by alkylated melamine. Clearly, the addition of a soluble sol-gel precursor at a very low concentration to the formulation increased significantly the Tg from 241 up to 280 C.

TABLE-US-00007 TABLE 7 Ultimate Young's Yield Yield tensile Max Tensile modulus Strength Strain strength Strain Toughness (MPa) (MPa) (%) (MPa) (%) (MJ/m{circumflex over ()}3) Without 2439 15.96 0.6 37.46 2.8 3713 Sol-Gel precursor With 2492 27.63 1.0 44.25 2.3 2878 Sol-Gel precursor

[0204] The measured tensile properties in Table 7 indicate that the strength and modulus increase when the sol-gel precursor is added. However, the toughness of the polymer decreases from 3713 to 2878 MJ/m{circumflex over ()}3. This is possibly resulted by lowering of the crosslinking density of the epoxide-melamine system.

[0205] SEM was used to observe the microstructure of the printed samples after thermal curing. The sample containing alkylated melamine as a hardener has a homogeneous smooth surface. However, sample cured by alkylated melamine and AMTMS has amorphous silicates, with a size range of few to tens microns, that were detected by SEM ESD analysis (FIG. 5).

[0206] The presence of silicon oxide and silane in the polymer was also detected by X-Ray Photoelectron Spectroscopy (XPS). The survey scan shows that the polymer contains carbon (78.35%), nitrogen (5.38%), oxygen (13.21%) and silicone (3.06% atomic concentration) (FIG. 6). A peak at 102.5 eV (2, spin 3/2) corresponds to the binding energy of silanes and silicates, indicating that the AMTMS that was chemically bonded to the epoxy network, did not fully hydrolyze and polymerize to silicon oxide. The second peak at 103.294 eV (3, spin 3/2) refers to SiO.sub.2. Each one of these two peaks has another peak shifted with 0.6 eV (2, 3). According to the ratio between the two doublets, it was found that 15% of the Silicon precursor was fully converted to SiO.sub.2.

[0207] FIG. 7 shows printed woodpiles made of ink cured by Cymel NF 2000A without sol-gel precursor after heat curing @ 180 C. The composition is described in table 6.

[0208] For printing purposes, the formulation presented in table 6 included hydroquinone (0.004% based on BAEMA) and Sulfurhodamine B sodium salt (0.0005% base on BAEMA), for achieving a good resolution.

[0209] FIG. 8 below shows printed diamond-lattice shape object and screws made of ink containing Cymel NF 2000A and the sol-gel precursor, (composition is described in table 6) after heat curing @ 180 C. For printing purposes, the formulation presented in table 6 includes hydroquinone (0.004% based on BAEMA) and Sulfurhodamine B sodium salt (0.0005% base on BAEMA), for addressing optimal printability.

[0210] Samples shown in FIG. 7 and FIG. 8 were printed by Asiga Max DLP printer. The build parameters are the following: [0211] slice thickness: 0.2 mm, [0212] heat temp: 50 C. (actual temp 32.6 C.), [0213] light intensity: 29.28 mW/cm.sup.1, [0214] exposure time burn in: 10 sec, [0215] exposure time other layers: 3 sec, [0216] separation velocity: 5 mm/sec, [0217] separation distance: 5 mm, [0218] approach velocity: 0.5 mm/s, [0219] wait time (after exposure): 2 sec, [0220] wait time (after separation): 2 sec, [0221] wait time (after approach): 2 sec.

[0222] The printed models were washed in a solution of 10% Cymel NF 2000A/CH.sub.2Cl.sub.2 in order to remove the access ink. The solvent was evaporated at room temperature overnight, then the model was heated to 70 C. under vacuum for 1 h. After cooling, the printed models in FIG. 8 were thermally Cured: 1 h/100 C. followed by 4 h/180 C. (in order to avoid dark brown samples).

[0223] Unlike the common approach of blending epoxy and acrylate monomers to enable both photopolymerization and thermal curing, here we present the formation and application of a bifunctional oligomer, having both acrylate and epoxy groups within the same molecule. This oligomer is combined with unique multifunctional hardeners, alkylated melamine (Cymel), and silica precursor (AMTMS). The fabrication process is composed of DLP printing, thus forming the required object by photopolymerization of the oligomer, followed by heat curing the epoxides with Cymel. This specific hardener led to the formation of a highly crosslinked, high-performance polymer characterized by superior properties: excellent Tg (241 C.) with Young's modulus of 2.43 Gpa and UTS value of 37.5 MPa.

[0224] Further addition of the sol-gel dual precursor AMTMS provided a unique multifunction: photopolymerization, crosslinking, and forming silica particles. The combination of all three led to the extremely high Tg value of 283 C., excellent Young's modulus of 2.85 GPa, and UTS value of 44.25 MPa.

Example 6: Cyanate Ester as a Hardener

[0225] Cyanate ester may react with epoxide groups of BAEMA in two routes, to form a highly crosslinked polymers, based on oxazolidinone and triazine rings (FIG. 9).

[0226] In this example, the hardener is with a ratio of 1:1 to BAEMA (Table 8). The Tg of the cured polymer is 208 C., which is much higher than that of the homopolymer only (described in table 1).

TABLE-US-00008 TABLE 8 Tg Component Name % Wt. ( C.) Epoxy acrylate BAEMA 48.0 208 Hardener 1,1-Bis(4-cyanatophenyl) 48.4 ethane [47073-92-7]* Photoinitiator TPO 2.0 Catalyst Zinc acetylacetonate 1.6 hydrate in isobornyl acrylate *AroCy L-10 cyanate ester supplied by Huntsman [0227] Photocuring conditions: 0.5 min/395 nm. [0228] Thermal Curing: 1 h/120 C., 2 h/180 C., 1 h/220 C., 1 h/240 C., heat rate 10 C./min.

[0229] Dogbones were printed from the ink (table 8) and tested by the Instron testing machine. The results of the mechanical properties are attached in Table 9.

TABLE-US-00009 TABLE 9 Young's Yield Yield Ultimate tensile Max Tensile modulus Strength Strain strength Strain Toughness (MPa) (MPa) (%) (MPa) (%) (MJ/m{circumflex over ()}3) 1767 30.16 1.6 85.35 5.7 1335

[0230] Based on the results in table 9, it can conclude that this specific cyanate ester hardener forms a polymer with relatively low mechanical properties, compared with the alkylated melamine hardener.

[0231] Printed woodpiles and a prism object after heat curing are shown in FIG. 10. For printing purposes, the formulation presented in Table 8 includes hydroquinone (0.0007% based on BAEMA) and Sulfurhodamine B sodium salt (0.0005% based on BAEMA).

[0232] The build printing parameters are the following: [0233] slice thickness: 0.2 mm, [0234] heat temp: 50 C. (actual temp 35.0 C.), [0235] light intensity: 29.19 mW/cm.sup.1, [0236] exposure time burn in: 20 sec, [0237] exposure time other layers: 6 sec, [0238] separation velocity: 0.5 mm/sec, [0239] separation distance: 5 mm, [0240] approach velocity: 0.5 mm/s, [0241] wait time (after exposure): 2 sec, [0242] wait time (after separation): 2 sec, [0243] wait time (after approach): 2 sec.

[0244] The models were washed in acetone before heat curing.

Example 7: Phenolic Resin as a Hardener

[0245] The phenolic resin used reacts with the epoxide groups of BAEMA during the thermal curing. The process requires a catalyst, and the result is a crosslinked polymer (FIG. 11).

[0246] A comparative example of inks based on a phenolic resin as a hardener, with and without sol gel precursor is presented in Table 10. The ratio BAEMA:hardener is 1:1. In this example, ink 2 includes additional acrylate monomer for printing improvement.

TABLE-US-00010 TABLE 10 Approx. Tg Ink Component Name % Wt. ( C.) 1 Epoxy acrylate BAEMA 49.0 125, Hardener Phenolic 49.0 230 resin* Photoinitiator TPO 2.0 2 Epoxy acrylate BAEMA 45.0 167, Hardener Phenolic resin 45.0 255 (Phenodur PR 401/72B) Photoinitiator TPO 1.0 Sol-Gel AMTMS 2.5 precursor Printing Isobornyl 6.5 additive acrylate *phenolic resin = Phenodur PR 401/72B [0247] Photocuring conditions: 0.5 min/295 nm. [0248] Thermal Curing: 1 h/100 C. followed by 4 h/275 C., heat rate 10 C./min.

[0249] In both inks, no catalyst for the epoxide-hydroxyl reaction is needed. This is probably due to the presence of residues of acrylic acid in the oligomer, which makes the external addition of acid catalyst unnecessary.

[0250] In both inks, the cured polymer has a major Tg peak and a shoulder with a higher Tg. This can be explained by the potential existence of two phases formed in the final polymers. Comparison between the two inks indicates a significant increase of the Tg due to the addition of AMTMS sol-gel precursor.

[0251] The results of the mechanical properties of printed dog bones are presented in Table 11.

TABLE-US-00011 TABLE 11 Ultimate Young's Yield Yield tensile Max Tensile modulus Strength Strain strength Strain Toughness (MPa) (MPa) (%) (MPa) (%) (MJ/m{circumflex over ()}3) Without 1327 7.02 0.3 26.1 3.6 3576 Sol-Gel Precursor With 2172 21.62 1.0 50.6 2.5 3269 Sol-Gel Precursor

[0252] The measured mechanical properties in Table 11 indicates that the strength and modulus improved significantly with addition of the sol gel precursor. In addition, this phenolic resin reacts with BAEMA to forms polymers with a high tensile toughness.

[0253] FIG. 12 shows printed wheels after heat curing at 275 C. The models are based on formulation 2 in table 10, including hydroquinone (0.0007% based on BAEMA) and Sulfurhodamine B sodium salt (0.0005% base on BAEMA).

[0254] The build printing parameters are the following: [0255] slice thickness: 0.2 mm, [0256] heat temp: 50 C. (actual temp 32.0 C.), [0257] light intensity: 20.0 mW/cm.sup.1, [0258] exposure time burn in: 10 sec, [0259] exposure time other layers: 5 sec, [0260] separation velocity: 0.5 mm/sec, [0261] separation distance: 5 mm, [0262] approach velocity: 0.5 mm/s, [0263] wait time (after exposure): 2 sec, [0264] wait time (after separation): 2 sec, [0265] wait time (after approach): 2 sec.

[0266] The models were washed in MEK followed by isopropanol, before heat curing.