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EP-4508098-B1 - METHOD OF FORMING AN OBJECT

EP4508098B1EP 4508098 B1EP4508098 B1EP 4508098B1EP-4508098-B1

Inventors

  • SANDERS, Samuel, N.
  • ARNDT, Emily, M.
  • KUMARASAMY, Elango
  • KIEL, Gavin, R.

Dates

Publication Date
20260506
Application Date
20230513

Claims (15)

  1. A method of forming an object, the method comprising: (a) providing a volume of a photohardenable composition comprising a photohardenable resin component, a first photoinitiator that is activatable by exposure to light at a first wavelength and light at a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable composition, and a second photoinitiator that is activatable by exposure to light at a third wavelength, wherein the first, second, and third wavelengths are not the same and the third wavelength is shorter than the first wavelength and the second wavelength, and wherein the first photoinitiator comprises a photoswitchable photoinitiator, or the second photoinitiator comprises a free-radical photoinitiator, or both; (b) selectively irradiating the photohardenable composition at a series of selected locations in the volume with light at the first wavelength and light at the second wavelength to form a partially hardened object in the volume of the photohardenable composition; and (c) irradiating the partially hardened object with light at a third wavelength to further harden the object.
  2. The method of claim 1 further comprising removing or separating the partially hardened object from the volume, and optionally further washing the removed or separated partially hardened object, prior to step (c).
  3. The method of claim 1 or 2, wherein: the photohardenable composition is comprised in a hardenable resin composition, which further comprises a resin component that is hardenable by a thermally driven reaction or mechanism, the resin component comprising a monomer, an oligomer, a pre-polymer, a polymer, or a mixture including at least one of the foregoing; the first photoinitiator is a photoswitchable photoinitiator; and step (b) comprises forming an initial print from the hardenable resin composition, wherein formation of the initial print comprises: (i) simultaneously or sequentially irradiating the selected locations within the volume of the hardenable resin 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 selected locations to induce a crosslinking or polymerization reaction in the photohardenable composition at the intersection of the first and second wavelengths at the selected locations within the volume to partially harden the hardenable composition at the selected locations to at least partially form the initial print; and (ii) optionally, repeating step (i) at one or more of the same or different selected locations within the volume of the hardenable resin composition until the initial print is formed; and step (c) comprises irradiating the initial print with light at a third wavelength to further harden the initial print.
  4. The method of claim 3, wherein the hardenable resin composition further includes a thermally activated initiator, and/or wherein the method further comprises heating the initial print before, during or after irradiation with light at the third wavelength to further harden the object.
  5. The method of any one of the preceding claims, wherein the first photoinitiator comprises a photoswitchable photoinitiator.
  6. The method of any one of the preceding claims, wherein the first wavelength is in a range from 300 nm to 550 nm, preferably is in a range from 375 nm to 455 nm, and/or wherein the second wavelength is in a range from 450 nm to 700 nm.
  7. The method of any one of the preceding claims, wherein the second photoinitiator comprises 1-hydroxycyclohexyl phenyl ketone.
  8. The method of any one of the preceding claims, wherein the object is suspended in the volume during irradiation with the light at the first wavelength and the light at the second wavelength.
  9. The method of any one of the preceding claims, wherein light at the first wavelength and light at the second wavelengths are separately directed into the volume.
  10. The method of any one of the preceding claims, wherein the light at the first wavelength is directed into the volume as a light sheet and/or the light at the second wavelength is directed into the volume as an optical image, wherein the optical image is preferably perpendicular to the direction in which it is directed into the volume.
  11. The method of any one of the preceding claims, wherein the light at the first wavelength is directed into the volume along a first illumination axis and the light including the second wavelength is directed into the volume along a second illumination axis orthogonal to the first illumination axis.
  12. The method of any one of the preceding claims, wherein the third wavelength is not directed into the volume during irradiation with the light at the first wavelength and light at the second wavelength.
  13. The method of any one of the preceding claims, wherein the second photoinitiator is not activatable or appreciably activatable by the first or second wavelengths.
  14. The method of any one of the preceding claims, wherein the first photoinitiator is included in the photohardenable composition in an amount in a range from 0.0001 to 0.5 weight percent, preferably in an amount in a range from 0.0001 to 0.009 weight percent, more preferably in an amount in a range from 0.0001 to 0.005 weight percent.
  15. The method of any one of the preceding claims, wherein the first wavelength is in a range from 300 nm to 550 nm, the second wavelength is in a range from 450 nm to 700 nm, the third wavelength is in a range from 240 nm to 400 nm, wherein preferably the first wavelength is in a range from 375 nm to 455 nm, the second wavelength is in a range from 450 nm to 700 nm, the third wavelength is in a range from 240 nm to 400 nm, and wherein the third wavelength is shorter than the first wavelength which in turn is shorter than the second wavelength.

Description

CLAIM OF PRIORITY This application claims priority to U.S. Provisional Patent Application No. 63/341,594 filed on May 13, 2022 and U.S. Provisional Patent Application No. 63/438,280 filed on January 11, 2023. TECHNICAL FIELD OF THE INVENTION The present invention relates to the technical field of three-dimensional printing and related methods WO2020/245456 A1, US2022/007005 A1 and DE10 2019129868 A1 are documents that illustrate relevant concepts known in the field. BRIEF SUMMARY OF THE INVENTION The present invention includes a method of forming an object applying a photohardenable composition as defined in claim 1. The photohardenable composition of the method includes a photohardenable resin component, a first photoinitiator that is activatable by exposure to light at a first wavelength and light at a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable composition, and a second photoinitiator that is activatable by exposure to light at a third wavelength, wherein the first, second, and third wavelengths are not the same, and the third wavelength is shorter than the first wavelength and the second wavelength, and wherein the first photoinitiator comprises a photoswitchable photoinitiator, or the second photoinitiator comprises a free-radical photoinitiator, or both. Preferably the second photoinitiator comprises a free-radical photoinitiator. The method of the present invention also includes hardenable resin compositions including a photohardenable resin component, a first photoinitiator that is activatable by exposure to light at a first wavelength and light at a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable composition, a second photoinitiator that is activatable by exposure to light at a third wavelength, wherein the first, second, and third wavelengths are not the same and the third wavelength is shorter than the first wavelength and the second wavelength, and a resin component that is hardenable by a thermally driven reaction or mechanism, the resin component comprising a monomer, an oligomer, a pre-polymer, a polymer, or a mixture including at least one of the foregoing. Achieving a maximum possible degree of conversion of reactive species to a polymer or cross-linked state in 3D printing is desirable for producing parts (also referred to herein as objects) with reduced leaching of reactive species and/or one or more improved physical properties, such, for example, increased hardness, flexural modulus, tensile strength, scratch resistance, tear resistance, etc. Advantageously, inclusion of a second photoinitiator that is activatable by exposure to light at a third wavelength in a photohardenable composition including photohardenable resin component and a first photoinitiator that is activatable by exposure to light at a first wavelength and light at a second wavelength can facilitate achieving a higher degree of conversion without requiring use of the first photoinitiator in amounts for achieving a sufficiently hardened object, which can disadvantageously result in attenuation of the passage of the first wavelength through the photohardenable composition due to increased absorption of first wavelength light by the higher amounts of the first photoinitiator. Such attenuation can result, for example, in non-uniform printing across the volume. Inclusion of a second photoinitiator that is activatable by exposure to light at a third wavelength in a photohardenable resin component in addition to the first photoinitiator, and subsequent exposure of an initial print of an object formed via photoactivation of the first photoinitiator to the third wavelength for activating the second photoinitiator, can facilitate achieving a higher degree of conversion of reactive species to a polymer or cross-linked state in the printed object without increased amount of the first photoinitiator. By including a second photoinitiator with a shorter wavelength of activation than the wavelengths for activating the first photoinitiator, the printing process is not affected by the presence of the second photoinitiator and can facilitate faster and more complete post-cure of the initial print in a post-curing step including exposure to light at a third wavelength. As used herein, "initial print" refers to an object that is not fully hardened that results from selective exposure of the photohardenable composition to the first and second wavelengths. An initial print can preferably have the same shape as, or a shape to be imparted to, the desired object being printed. In the present invention, there is applied a photohardenable composition comprising a photohardenable resin component, a first photoinitiator that is activatable by exposure to light at a first wavelength and light at a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable composition, and a second photoinitiator that is activatable by exposur