Photohardenable compositions and methods for forming an object in a volume of a photohardenable composition
Photohardenable compositions comprising a photohardenable component and a photoswitchable photoinitiator, wherein the photoswitchable photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable component, and wherein the photohardenable composition displays non-Newtonian rheological behavior are disclosed. Methods including such photohardenable compositions for printing one or more objects are also disclosed.
1 . A photohardenable composition for use in forming an object in a volume of the photohardenable composition, the photohardenable composition comprising a photohardenable component and a photoswitchable photoinitiator, wherein the photoswitchable photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable component, wherein the first and second wavelengths are different, wherein the photohardenable composition displays non-Newtonian rheological behavior for forming the object in the photohardenable composition at a fixed position or with minimal displacement in the photohardenable composition during formation, wherein non-Newtonian rheological behavior is imparted to the photohardenable composition by further including an effective amount of a non-reactive thixotrope additive in the photohardenable composition.
2 . The photohardenable composition of claim 1 wherein exposure of the photoswitchable photoinitiator to light having the first wavelength generates a second form of the photoswitchable photoinitiator, which second form, upon exposure to light having the second wavelength, generates an excited species that can induce a crosslinking or polymerization reaction in the photohardenable component, to at least partially harden the photohardenable composition.
3 . The photohardenable composition of claim 1 wherein exposure of the photoswitchable photoinitiator to light having the first wavelength generates a second form of the photoswitchable photoinitiator, which second form, upon exposure to light having the second wavelength, generates a non-emissive or substantially non-emissive excited species that can induce hardening of the photohardenable component.
4 . The photohardenable composition of claim 1 further comprising one or more coinitiators and/or one or more sensitizers.
5 . The photohardenable composition of claim 1 wherein the non-Newtonian rheological behavior comprises pseudoplastic behavior.
6 . The photohardenable composition of claim 4 wherein the non-Newtonian rheological behavior comprises pseudoplastic behavior.
7 . The photohardenable composition of claim 4 wherein the non-Newtonian rheological behavior comprises Bingham plastic behavior.
8 . The photohardenable composition of claim 4 wherein the non-Newtonian rheological behavior comprises Bingham pseudoplastic behavior.
9 . The photohardenable composition of claim 4 wherein the one or more coinitiators comprise a tertiary amine or a borate salt.
10 . The photohardenable composition of claim 4 wherein the photohardenable component comprises a urethane acrylate or a urethane methacrylate.
11 . The photohardenable composition of claim 4 wherein the one or more coinitiators comprise a tertiary amine and an iodonium salt.
12 . The photohardenable composition of claim 1 wherein the non-Newtonian rheological behavior comprises Bingham plastic behavior.
13 . The photohardenable composition of claim 1 wherein the non-Newtonian rheological behavior comprises Bingham pseudoplastic behavior.
14 . The photohardenable composition of claim 1 wherein the photohardenable component comprises a urethane acrylate or a urethane methacrylate.
15 . A method of printing an object comprising:
(a) providing a volume including a photohardenable composition comprising a photohardenable component and a photoswitchable photoinitiator, wherein the photoswitchable photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable component, wherein the first and second wavelengths are different, wherein the photopolymerizable composition displays non-Newtonian rheological behavior,
(b) simultaneously or sequentially irradiating one or more selected locations within the volume of the photohardenable composition with light having a first wavelength and light having a second wavelength, wherein light having the first wavelength and light having the second wavelength activate the photoswitchable photoinitiator at the one or more selected locations and at least partially harden the photohardenable composition at the one or more selected locations within the volume to at least partially form the object, wherein the object at least partially formed in the photohardenable composition remains at a fixed position or is minimally displaced in the unhardened photohardenable composition during formation, wherein the first and second wavelengths are different; and
(c) optionally repeating step b, irradiating the photohardenable composition at one or more of the same or different locations in the volume until the object is partially or fully formed.
16 . The method of claim 15 wherein the photopolymerizable composition further comprises one or more coinitiators and/or one or more sensitizers.
17 . The method of claim 15 wherein the first wavelength is in a range from about 300 to about 450 nm (inclusive) and the second wavelength is in a range from about 450 to about 1000 nm (inclusive), preferably from about 450 nm to about 850 nm (inclusive).
18 . The method of claim 15 wherein the amount of time during which one or more selected locations within the volume are simultaneously or sequentially exposed to the first wavelength light and the second wavelength light to induce hardening of the photohardenable composition at the one or more selected locations is insufficient to cause hardening of the photohardenable composition when only one of the first and second wavelengths is present.