SLA RESINS AND METHODS OF MAKING AND USING THE SAME

Abstract

The present disclosure is directed towards resin compositions and methods of making and using the same, where the resulting resins (e.g. SLA resins) can be utilized in conjunction with additive manufacturing.

Claims

1. A composition, comprising: an epoxy component; a reactive diluent component; a macro dendritic component; and a photo initiator component; configured in an amount to catalyze the epoxy, the reactive diluent, and the macro dendritic component into a resin configured for additive manufacturing an AM component via vat polymerization.

2. The composition of claim 1, further comprising a stabilizer component configured to stabilize the composition and prevent polymerization outside of the vat polymerization process.

3. The composition of claim 1, further comprising a pigment component configured to color the composition.

4. The composition of claim 1, wherein the photo initiator comprises a IN curable photo initiator.

5. The composition of claim 1, wherein the macro dendritic component comprises: a hyperbranched polyester component.

6. The composition of claim 1, wherein the photo initiator component comprises an onium salt solution.

7. The composition of claim 1, wherein the reactive diluent component comprises an oxetane component.

8. A composition, consisting essentially of: an epoxy component; a reactive diluent component including a oxetane; a macro dendritic component having a hyperbranched polyester; and a UV curable photo initiator component; configured in an amount to catalyze the epoxy, the reactive diluent, and the macro dendritic component into an KA resin configured for additively manufacturing an AM green form component via stereolithography.

9. The composition of claim 8, wherein the epoxy component comprises: a 3,4-epoxycyclohexylmethyl 3,4-epoxycyclonexanecarboxylate.

10. A composition, consisting of: at least 65 wt. % to not greater than 85 wt. % an epoxy component; at least 10 wt. % to not greater than 20 wt. % of a dendritic macromolecule component; and at least 0.05 wt. % to not greater than 15 wt. % of a photo initiator component.

11. A composition, consisting of: at least 50 wt. % to not greater than 85 wt. % of an epoxy component; at least 5 wt. % to not greater than 20 wt. % of a dendritic macromolecule component comprising a hyperbranched polyester; not greater than 15. wt. % of a reactive diluent component, wherein at least some reactive diluent component is present; and at least 0.05 wt. % to not greater than 15 wt. % of a photo initiator component.

12. The composition of claim 11, further comprising: at least 0.5 wt. % to not greater than about 5 wt. % of a stabilizer component.

13. The composition of claim 11, further comprising: not greater than about 5 wt. % of a pigment component, wherein at least some pigment component is present.

14. The composition of claim 11, wherein the epoxy component comprises: Uvacure 1500.

15. The composition of claim 11, wherein the photo initiator component comprises an onium salt solution.

16. The composition of claim 11, wherein the reactive diluent component comprises a compound having a four-membered ring.

17. The composition of claim 11, wherein the reactive diluent component comprises oxetane.

18. A method, comprising: componentcomponent componentcomponentdepositing, positioning, spreading, extruding, spraying, rolling, dipping, wiping, casting, and/or combinations thereof, to form a layer of SLA resin on a surface (e.g. substrate or previous AM build surface). componentcomponent componentcomponent, the plurality of AM green form parts including at least a first AM green form part and a second AM green form part;

24. The method of claim 23, wherein the vat polymerization process further comprises stereolithography.

25. The method of claim 23, wherein the AM part comprises a polymeric preform for investment casting.

26. The method of claim 23, wherein the AM part comprises a structural component.

27. The method of claim 23, wherein the AM part comprises a functional component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0124] FIG. 1 is a graph depicting the experimental results of completing a thermogravimetric analysis of the SLA resin in accordance with one or more embodiments of the present disclosure, illustrating the comparative response of the SLA resin to a commercially available SLA resin.

[0125] FIG. 2 depicts a top plan view of two embodiments of AM parts constructed from a formulation of SLA resin in accordance with one or more embodiments of the present disclosure, where the part on the left (overcure 14) was cured after being additively manufactured with a lower overcure than the part on the right (overcure 32). It is observed that the lower overcure (faster laser speed) resulted in a lighter colored part than the part with the higher overcure (slower laser speed), which appears very dark in relation to the image on the left. (Overcure generally refers to the variable on the additive machine that changes the laser speed (length of time that a build portion undergoes polymerization), with an overcure rate of 14 being a lower setting of overcure faster laser speed) than an overcure rate of 32 (e.g. slower laser speed).)

[0126] FIG. 3 is a close-up cut away partial side view of an AM part build in accordance with one or more embodiments of the present disclosure, depicting a border wall (e.g. external wall) and an internal wall/cross-hatched wall (e.g. a plurality depicted, configured such that the AM part has an internal latticed structure in a honeycomb configuration). As depicted, one or more embodiments disclosed herein enable the AM machine to build AM parts with sufficient surface quality, build strength, wall thicknesses, fine features, and/or surface roughness to be utilized in applications including investment castings, molds, and the like, to name a few, in accordance with the present disclosure.

[0127] FIG. 4 depicts a graphical analysis of hardness(H) experimental data obtained from completing a nano-indentation analysis on an embodiment of man SLA resin in accordance with the present disclosure, as compared to a commercially available resin additively manufactured into an AM part with two different AM energy source parameters (EC/DP values). It is readily observable from FIG. 4 that the SLA resin of the present disclosure has a much higher hardness as compared to the commercially available SLA resin (at either AM laser build parameter).

[0128] FIG. 5 depicts a graphical analysis of Reduced Modulus (Er) experimental data obtained from completing a nano-indentation analysis on an embodiment of an SLA resin in accordance with the present disclosure, as compared to a commercially available resin additively manufactured into an AM part with two different AM energy source parameters (EC/DP values). It is readily observable from FIG. 5 that the SLA resin of the present disclosure has a much higher reduced modulus as compared to the commercially available SLA resin (at either AM laser build parameter).

DETAILED DESCRIPTION

[0129] Reference will now be made in detail to the accompanying drawings and Examples, which at least assist in illustrating various pertinent embodiments of the present invention.

Example: SLA Resin Composition Comparison

[0130] Utilizing the above-procedure, three formulations having different 3 comparative runs to show what did not cure, what cured but did not produce a good green form, and what produced a good green form. For the runs, the epoxy was UVA cure 1500 (supplied by UCB), the oxetane was trimethylolopropate oxetane (supplied by Perstorp), the polyester was Bolton TM H2004 (supplier Perstorp) and the photo initiator was PF6CPI6992 (Supplied by Aceto Corp).

[0131] The above components were mixed, stirred, and directed into a form and photocured. Non-limiting examples of photo cure include: a UV bulb illuminating a stage with conveyor belt or an energy source (e.g. laser) in an additive manufacturing machine (e.g. SLA machine). The photo cure included: directing a sufficient amount of light (e.g. at a particular wavelength or band of wavelengths) for a sufficient time to cure the SLA formulation/composition into the SLA preform (e.g. SLA green form).

[0132] After photocuring, the SLA green form was postcured in a chamber for a sufficient time to provide the final SLA product.

[0133] Three formulations were evaluated, and based on 100 g sample, the values of the constituents in each formulation are provided in the below table, in wt. %:

TABLE-US-00001 Photo SLA initiator Formulation Epoxy Oxetane Polyester (solution) # (±2) (±1) (±1) (±0.5) Notes 1 75.09 15 9.01 0.90 Did not cure 2 74.40 14.9 8.9 1.8 Cured, did not provide sufficient AM build 3 68.8 13.7 8.3 9.2 Cured, produced AM part

[0134] Without being bound by a particular mechanism or theory, it is believed that an SLA composition having an epoxy, an oxetane, and a hyperbranched polymer in combination with greater than 0.9 wt. % photo initiator can be utilized in an AM process to form a suitable AM part (capable of curing in the AM build via the energy source/laser to form a suitable AM green form and also capable of post curing to provide appropriate strength to the AM part). After this experiment, it was determined that the 1.8 wt. % photo initiator run may not have cured due to some processing parameters and AM machine components/configurations that were remedied.

Example: Thermogravimetric Analysis of SLA Resin

[0135] FIG. 1 is a graph depicting the experimental results of completing a thermogravitnetric analysis of the SLA resin in accordance with one or more embodiments of the present disclosure, illustrating the comparative response of the SLA resin to a commercially available SLA resin.

[0136] The resins were each cured under three different conditions using a Fusion UV System with a UVA bulb and a 480 V Light Hammer power system (CR1: SL7800 cured at 5 ft/min@100% UV; CR2: SL7800 cured at 10 ft/min@100% UV, and CR1: SL7800 cured at 24 ft/min@100% UV). Thermal gravimetric analysis (TGA) was used to determine the thermal properties of the resulting cured resins, with the included graph depicting the response of the different runs as weight percent vs. temperature. It was observable that the SLA resin had a comparable TGA response in terms of weight loss profile to the commercially available resin at three different cure preparations. Additional differential scanning calorimetry testing showed. that the glass transition temperature of the resin is above 50 degrees C.

Example: Analytical Assessment of Remains after Burnout

[0137] The table below illustrates the measurement data obtained for the ash residue and trace of the SLA resin sample after burnout.

TABLE-US-00002 Elements Results Pb <10 ppm Bi <0.5 ppm  Ag <10 ppm Sb   15 ppm Zn   20 ppm Sn  <5 ppm Fe <0.01%

[0138] It was also observed that the SLA resin (approximately 100 g sample size) provided a very low ash content upon burn-off (<0.005%).

Example: Analytical Assessment of Viscosity

[0139] In order to understand any differences in application in an end use application (e.g. additive manufacturing), viscosity measurements were obtained on an embodiment of the SLA resin as described herein, compared to a commercially available SLA resin.

[0140] The viscosity measurements were obtained using a Brookfield Viscometer DVT DVII (Spindle #7). The SLA resin in accordance with the present disclosure was observed to remain stable/have no measurable impact to viscosity after several months on the shelf.

[0141] Moreover, the SLA. resins of the present disclosure have a lower viscosity than the commercially available SL7800 SLA resin. It is noted that the SLA resin has comparable results ranging from 140-180 CPS while the SL7800 resin was different in both color and viscosity and appeared to have more turbidity during evaluation, with the viscosity ranging from 180-220 CPS.

Example: Additive Manufacturing Description

[0142] During an additive manufacturing process, the energy source (e.g. laser) polymerizes the SLA resin in successive layers in an AM build to form an AM green form or AM preform. When a layer is completed, a leveling blade (configured as part of the AM machine) is moved across the surface (which includes the most recent build layer and uncured SLA resin (in locations that are not part of the designated build) in order to smooth the surface it before the next layer of AM feedstock material (e.g. SLA resin) is deposited. After the blade smooths the surface, the platform is lowered by a distance equal to the layer thickness of a build layer. Then the energy source again tracks the build pattern and cures the SLA resin in designated areas, adding another build layer onto the AM build. This process of tracing (with energy source) and smoothing (with leveling blade) is repeated until the AM build is complete, forming the AM preform or AM green form part. After the AM build is completed, then the AM preform undergoes a post-cure step to finish the green state parts into an AM part (e.g. configured with sufficient hardness and/or other properties for end-use applications).

[0143] In order to additively build a part, the energy source (e.g. UV laser) traces out successive cross-sections of a three-dimensional object in a vat of liquid photosensitive polymer (e.g. including border/edges and interior walls). The resin crosslinks to form a thermoset polymer, while the excess resin remains liquid resin adjacent to the AM build. Once the AM build is completed, the AM build is elevated (e.g. raised out of the vat) and drained to remove excess SLA resin. Once the draining is completed, the final cure is completed by placing the part (or parts) into a UV oven or conveyor, and subjecting the AM parts to a sufficient amount of light for a sufficient amount of time to cure the thermoset polymer.

Prophetic Example: AM Through Investment Casting-Utilizing SLA Resin

[0144] An SLA resin composition is prepared according to the above procedure. Optionally, the SLA resin is degassed (e.g. vacuum/negative pressure pulled across a container housing the resin to evacuate gases from the resin and/or vapor space of the container). The SLA resin is configured into an additive machine configured to utilize SLA resin as the AM build material. An AM green form (preform) is configured from SLA resin, by successively depositing SLA resin, layer by layer, onto a build substrate (e.g. via a sweeper arm) and then curing in place the resin into a predetermined build shape with an energy source (e.g. laser beam configured at an appropriate wavelength to cure the SLA resin).

[0145] After the AM build is complete, an AM green form is provided, where the AM green form is configured with a green strength sufficient to be handled and/or further processed to form an AM part.

[0146] The excess SLA resin (liquid AM feedstock, not part of the AM green form) is removed from the surface and interstices/lattice structure of the AM green form (e.g. configured with vents and drains). For example, the AM green form can be rinsed with a solvent, liquid, and/or diluent to remove excess SLA resin from the AM green form. As another example, the AM green form is wiped (e.g. with alcohol or other diluent, organic solvent, and/or solvent) to remove excess SLA resin from the AM green form. As still another example, the SLA resin is placed in a spinner and centrifugally spun to remove the excess SLA resin from the surfaces and/or interstices of the AM green form. In some embodiments, one or more combinations of rinsing, wiping, and/or spinning can be combined to remove excess SLA resin from the AM green form.

[0147] After the excess SLA resin is removed from the AM green form, the AM green form is configured into an AM part via a post cure step. In some embodiments, the post cure step provides/exposes the entire AM green form to a cure process in order to thoroughly cure the entire AM green form and provide an AM part, where the AM part has a strength higher than the strength (green form strength) of the AM green form. In instances where the SLA resin includes a photo initiator, the post cure step includes exposing the AM green form to a sufficient wavelength for a sufficient time (e.g. optionally at an elevated temperature) to cure and form an AM part.

[0148] In order to post cure the AM parts referenced in the examples section, the post cure step is configured with a UVA bulb cure, for a sufficient time (e.g. AM green forms configured on a conveyor belt that passed under a UVA bulb to cure, for 1-2 passes at a rate of 5 ft./min, where the cure zone was configured with a length of approximately 12-18″).

[0149] In other embodiments, a closed post cure chamber (e.g. UV oven) is configured to cure the AM green form while the AM green form is exposed to UVA wavelength fight for a sufficient duration and at a sufficient wavelength to form an AM part. In some embodiments, the AM part in the chamber is configured to rotate on a stage within the chamber and/or may contain a heating element.

[0150] In some embodiments, a surface finishing step (either automated or by hand) is completed on the AM part in order to configure the surface roughness of the AM part for the end use application (e.g. investment casting).

[0151] Next, a plurality of AM parts formed from the above step having specified dimensions and characteristics are configured and attached to form an AM part assembly. In order to attach the AM parts to one another, the SLA resin can be utilized (and cured via UV wand). Alternatively, the AM parts can be glued together with an epoxy glue, utilizing a UV wand. The assembly is sealed (e.g. to close the vents and drains in the individual AM parts) and placed into successive layers of ceramic slurry (and dried between layers) to coat the sealed assembly configured from AM performs made from the SLA resin, such that a ceramic shell is formed over the sealed assembly of AM parts. Optionally, configure the ceramic shell with ports and/or features to enable material addition into the ceramic shell.

[0152] Next, the AM assembly is burned out from the ceramic shell by exposing the ceramic shell and AM assembly to a temperature sufficient to burn out the SLA resin but not so high as to sinter the ceramic shell. The resulting ceramic shell (empty) is sintered at an appropriate temperature to sinter the ceramic material, and the sintered ceramic shell is filled with molten metal to form a casted part with an identical configuration as the original AM part assembly. The ceramic shell is removed to provide the metal cast part.

Example: Proxy for Cure on SLA Machine

[0153] The overcure process for the samples made in accordance with the examples section were provided on a UVA bulb cure assembly that included a UVA bulb and a conveyor belt that conveyed samples (AM green forms) under the UVA light at a rate for a sufficient length of time to cure the AM green forms into an AM part. More specifically, using a Fusion UV system the curing conditions that were used to make the SLA resin samples with the white light source are as follows: sample is passed through the chamber at 5 ft./min at a light intensity of 100% (UVA bulb); with an energy density of roughly 5578 mJ/cm.sup.2 and an intensity of roughly 3048 mW/'cm.sup.2. In some instances, the sample temperature was increased up to 38° C. during the coring (overcure) process. In some instances, multiple passes were completed on samples in order to effect cure in a component.

Evaluation of Proxy Cure vs. SLA Machine Cure

[0154] The same material (Renshape SL78000 Resin) was prepared and cured: one cure occurred on an SLA machine, while the other cure occurred on the Fusion UV system outlined above. The cure was confirmed to be complete and comparable on both the SLA machine and the Fusion UV system.

Evaluation of SLA resin vs. Commercial SLA Resin

[0155] In order to evaluate the SLA resin in comparison with a commercially available resin for an investment casting application, four large patterns were additively manufactured. The pattern was selected to include several right angles, changes in dimension, and at least one drainage hole and vent. The SLA resin included an epoxy, a hyperbranched polyester, a reactive diluent (e.g. oxetane), and a photo initiator in weight percentages consistent with the ranges previously described herein. The AM printing parameters were the same for each run, including the cure, recoating, energy source (laser beam) spot size, and other printing parameters. After printing, the post printing parameters, including draining time, solvent wash, and post cure in a UV chamber (e.g. to transform the AM preform into the AM part) were the same.

[0156] Next, each AM part was surface prepared for ceramic slurry application (as previously described above). Each AM part was also vacuum/pressure checked to ensure there were no leaks prior to ceramic slurry application. In order to enable inspection, each mold was reinforced and braced with wire mesh, which was configured to create a hinge such that the inside of the molds could be accessed after burnout of the SEA resins for ash evaluation.

[0157] Each AM part underwent multiple dips in the ceramic slurry and the assembly was allowed to dry. The resulting resin (retained inside the ceramic shell) was subsequently burned out during a heating step.

[0158] Upon accessing the inner chamber of the ceramic shells (where the SLA resin AM part was retained), it was qualitatively observed (e.g. visual inspection) there were no apparent mold related cracks or surface quality issues on the internal shell walls; as compared to the prior art resin, the SLA resin produced a smaller amount of ash that was easily removed and did not leave any raised blemishes on the interior of the ceramic shell. Overall, it was observed that the tested resin performed as well or better than the current (prior art) resin in terms of burnout performance.

[0159] While various embodiments of the present invention have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.