Patent Application
20230061791
The present disclosure relates generally to optical ink compounds. More specifically, it relates to inkjet-printable optical ink compositions suitable for 3D printing of gradient refractive index (GRIN) optical components.
One major advantage to the 3D printing approach is the ability to fabricate non-axially symmetric GRIN optics and the ability to vary the GRIN in both the x,y and z directions broadening the design space of the optical components. While this approach to 3D printing of GRIN optical components has been reduced to practice by Vadient LLC as described in US patent number 20180022950 it is challenging to balance the rheological requirements of 3D inkjet printing and the optical requirements to obtain high quality GRIN optical components. In particular, the addition of dopants to the host matrix greatly increases viscosity and density, impairing the ability to inkjet print the resulting materials. As a result, even with other factors may be resolved, this approach is limited in the optical power that may be obtained using the aforementioned composite materials. Improvements in optical power may be obtained by the use of unique monomers in each ink formulation; however, this approach introduces additional challenges in material compatibility as they are deposited by inkjet printing for form GRIN optical components, resulting in material separation prior to cure obviating the advantages provided by the greater difference in refractive index between the inks.
The present disclosure is directed to optical inks suitable for 3D printing fabrication of gradient refractive index (GRIN) optical components which are composed of one (or more) monomer(s), wherein the ink has a viscosity less than 20 cPoise at the temperature of the printhead (between 20° C. and 80° C.) and is UV curable to form a solid polymer. Two (or more) miscible inks are used in tandem to create an ink set with dissimilar refractive index (>0.02) (specifically phase velocity, the real portion of the refractive index) by varying the composition of the monomers, or the ratio of the monomers in a mixture, between the inks. The monomers are designed/selected such that the resulting polymerized material has a crosslink density greater than 1×10−4 mol/cm3. The most general embodiment, any UV curable monomer can be used within the class of vinyl, acrylate, methacrylate or urethane. In one embodiment, the difference in refractive index is achieved by using two or more monomers with different refractive indices in each ink, and then varying the ratio of the monomers between the two inks. In another embodiment, each ink is composed of a single multifunctional monomer with different refractive index. Ideal embodiments use monomers containing phenyl functionality or hetero-atoms such as sulfur or halogens to raise the refractive index above that which can be achieved by monomers containing only C, O, and H, and monomers containing fluorine to lower the refractive index below that which can be achieved in monomers containing only C, O, and H.
The accompanying drawings, which are incorporated in and constitute a part of the specification, schematically illustrate embodiments of the present disclosure, and together with the general description given above and the detailed description of preferred methods and embodiment given below, serve to explain principles of the present disclosure.
Embodiments of the present disclosure include optical inks suitable for use in fabricating GRIN lenses using 3D printing technology such as standard drop-on-demand inkjet printing. These inks may also be used to fabricate GRIN lenses using other printing techniques such as screen printing, tampo printing, aerosol jet printing, and laser cure printing. Optical inks prepared according to the embodiments of the present disclosure are composed of monomers or blends of monomers with photoinitiators enabling polymerization by UV (or visible light or other ionizing radiation sources) with rheological properties suitable for 3D additive manufacture. Each of the monomer-based inks are placed in adjacent inkjet printheads. The number of inks, and adjacent printheads, is at least two, and other printheads may be used to incorporate additional inks with different optical properties (e.g. varied refractive indices or chromatic dispersions). Drop-on-demand inkjet printing technology is used to create microscopic features on-the-sample in order to precisely control the placement of highly-localized regions of varied refractive index, controlled by the mixture of the relatively high or low refractive index inks. The localized composition in three dimensions is controlled by the placement and number of drops of each ink and the amount of time allowed for diffusion controlled mixing following drop placement before locking the structure in place by polymerization. Each droplet of monomer deposited onto the substrate in order to form a GRIN optical element can be created by varying the desired concentration of high and low index monomers by varying the number of drops, and thus volume, of each of the two (or more) inks being used. The volumetric concentration of each of the inks within a given volume of the optical component determines the effective refractive index of a three-dimensional structure. The creation of precise three-dimensional optical lenses and other optical structures by stereolithography is known to those skilled in the art of GRIN lens design. Embodiments of the present disclosure provide inks suitable for the practical realization of such 3D printable inks for high quality GRIN lens fabrication. These inks provide the ability to control the index of refraction in three dimensions for creating large, localized index changes while maintaining high optical transmission and freedom from deleterious scattering phenomena that arise from feature sizes approaching λ/10, where λ is the wavelength of light that is desired to be manipulated by the optical element. Further these inks provide rapid diffusion of the monomers of varied refractive index, allow for rapid smoothing of features introduced by the relatively large size (dimensions greater than the wavelength of light being focused) of the drops as deposited in order to obtain GRIN optical elements with superior optical properties. This rapid diffusion of the ink components (relative to components found in other optical inks, such as nanoparticles or other inorganic clusters) allows for more rapid fabrication of the GRIN element as diffusion time, required to obtain smooth changes in the refractive index throughout the volume of the GRIN element that result in good optical quality, is greater than the time required for material deposition.
Since drop-on-demand inkjet may utilize multiple printheads with different loading of the index-changing dopant, the inks provided by the present disclosure may be used in various combinations with each other as well as with other optical inks, such as those described in US Patent 20180022950. This type of embodiment has been demonstrated (in the combination of the fluoroacrylate described with the material described in 20180022950.
According to embodiments of the present disclosure, an optical ink is composed of a monomer, or mixture of monomers that is polymerizable by UV/visible light or other ionizing radiation to provide a solid polymer. Preferably, the monomers used are such that UV curing results in a highly crosslinked material. Further, the monomers used in each of the inks used to fabricate the GRIN element are chosen such the shrinking is less than 20% and the relative shrinkage between the various inks is less than 10%, which serves to minimize deformation of the optical structure as well as minimizing stress/strain in the solid part to overcome limits in the dimension of the parts that may be fabricated. The GRIN element, once cured, has a transmittance of at least 80% (preferably >99%) at the wavelengths of interest (e.g., visible spectrum, or infra-red spectrum).
Referring now to the drawings, wherein like components are designated by like reference numerals. Methods of manufacture and various embodiments of the present disclosure are described further herein below.
Referring to
A first multifunctional monomer 6 may also be added to an optical ink matrix 2. The spherical shape of the first multifunctional monomer 6 in
Referring to
where the structure of molecule has fluorine as the functionalized parts 20 and n is a positive integer. The value of n may be controlled during the synthesis or polymerization process to control the viscosity of the optical ink matrix since the size of the molecule affects the viscosity. The multifunctional monomer may also take on another exemplary form:
where X is Oxygen, Sulfur, or Nitrogen, Y is Hydrogen or a Halogen, Z is a Hydrogen, a Halogen, a Phenyl group, or an Alkane, and m is a positive integer.
Referring to
One specific embodiment uses a high index ink comprising Benzyl Acrylate, Tricyclo[5.2.1.02,6]decanedimethanol diacrylate (TCMDA), pentaerythritol tetraacrylate (5.4:1:1 vol.) with 1% Irgacure 184 and 202 ppm BYK-UV-3500, having refractive index of 1.52. The low refractive index ink of this embodiment is ((perfluoroethane-1,2-diyl)bis(oxy))bis(2,2-difluoroethane-2,1-diyl) diacrylate with 3% wt. Irgacure 184, having a refractive index of 1.374. In yet another specific embodiment, the monomers may be used in concert with nanoparticles to further engineer the refractive indices of the resulting GRIN lens. For example, for a high refractive index ink, Neopentylglycol Diacrylate 89% and 11% ZrO2 nanoparticles (vol.) may be used with 1% Iracure 184 and 250 ppm BYK-UV-3500, having a refractive index of 1.53. A low refractive index ink of for this example may use ((perfluoroethane-1,2-diyl)bis(oxy))bis(2,2-difluoroethane-2,1-diyl) diacrylate with 3% wt. Irgacure 184, having a refractive index of 1.374.
Referring to
Referring to
In addition to disclosed compositions and methods of non-axially symmetric GRIN lens, the present disclosure uses diffusion-controlled GRIN fabrication using monomers alone (rather than varying the amount of nanoparticles in a composite material) to achieve greater lens power by increasing the difference in refractive index between high/low index inks and improved optical quality by allowing smaller feature sizes and improving the speed of diffusion and therefore the rate at which GRIN optical components may be fabricated as diffusion time is the limiting bottle-neck in 3D printing of GRIN. However, an example embodiment may also include the use of nanoparticles to further engineer the optical features of the GRIN lens. The formulation of the high refractive index ink in this disclosure may help with compatibility with some monomers including FEGDA, further improving inkjet printability modifying formulations of GRIN ink in order to improve the compatibility of ink pairs while maintaining required rheological properties for inkjet printing.
From the description of the present invention provided herein one skilled in the art can manufacture the apparatus and practice the methods in accordance with the present disclosure. Those skilled in the art to which the present invention pertains will recognize that while above-described embodiments and method of manufacture are exemplified using particular materials, others may be combined using these embodiments without departing from the spirit and scope of the present invention. Although some of the embodiments explained above have certain symmetry one skilled in the art will recognize that such symmetry is not a requirement. In summary, the present invention is described above in terms of particular embodiments. The invention, however, is not limited to the embodiments described and depicted herein. Rather, the invention is limited only by the claims appended hereto.
