ARTICLES THEREFROM

BACKGROUND

[0001] Rapid prototyping or rapid manufacturing processes are manufacturing processes which aim to convert available three-dimensional CAD data directly and rapidly into workpieces, as far as possible without manual intervention or use of molds. In rapid prototyping, construction of the part or assembly is usually done in an additive, layer-by-layer fashion. Those techniques that involve fabricating parts or assemblies in an additive or layer-by-layer fashion are termed “additive manufacturing” (AM), as opposed to traditional manufacturing methods which are mostly reductive in nature. Additive manufacturing is commonly referred to by the general public as“3D printing” and“3DP.”

[0002] There are currently several basic AM technologies: powder bed fusion, material extrusion, material jetting, binder jetting, material jetting, vat photopolymerization, sheet lamination, and directed energy deposition. Powder bed fusion techniques include, among others, selective heat sintering (SHS), selective laser melting (SLM), selective laser sintering (SLS), selective absorbing sintering (SAS), high speed sintering (HSS), and selective inhibition sintering (SIS).

SUMMARY

[0003] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0004] In one aspect, embodiments disclosed herein relate to a method for manufacturing an article using an additive manufacturing technique that includes irradiating a layer of polymer powder, a radiation absorption material, and a processing aid with infrared light to sinter the polymer powder together.

[0005] In another aspect, embodiments disclosed herein relate to an article that includes a plurality of printed layers, the plurality of printed layers comprising a polymer, a radiation absorption material, and a processing aid. [0006] In another aspect, embodiments disclosed herein relate to a thermosensitive ink that includes a radiation absorption material; and a processing aid selected from the group consisting of fluoropolymers, boron nitride, metal stearates, hydrocarbon oils, hydrocarbon oligomers, modified silicas, fatty acid amides, fatty acid esters, and combinations thereof.

[0007] In yet another aspect, embodiments disclosed herein relate to a modified polymer powder for high speed sintering that includes a polymer powder; and a processing aid having a lower melting temperature and/or lower melt viscosity than the polymer powder blended with the polymer powder.

[0008] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

DETAILED DESCRIPTION

[0009] In one aspect, embodiments disclosed herein relate to use of processing aids in a powder bed fusion additive manufacturing technique such as high speed sintering. Generally, powder bed fusion techniques apply a layer of powder (such as a polymer powder) that is sintered together prior to depositing the successive layers of powder. In high speed sintering, a radiation absorption material is selectively deposited on the powder layer so that upon the application of radiation to sinter the powder, the powder having the radiation absorption material deposited thereon will be sintered together (while the powder free of radiation absorption material remain as powder). The rapid speed of the high speed sintering is a benefit to provide high through-put of formed parts; however, this speed also serves a challenge to the types of polymer particles that can be used in the printing process. Specifically, the sintering speed is difficult for polymers that have high melt viscosity (or do not flow), such as ultrahigh molecular weight polymers, and cannot or minimally achieve chain diffusion between the particles during the time span at which the radiation passes over the layer of powder. Thus, embodiments of the present disclosure use, in conjunction with the radiation absorption material, a processing aid that provides for better chain diffusion among the high or ultrahigh molecular weight particles.

[0010] “Sintering” as used herein refers to the coalescence of the particles in a printed powder. In this system, the build-up of material strength is associated with sintering. In high speed sintering (HSS), manufacturing occurs by depositing a fine layer of polymeric powder, after which inkjet printheads deposit an infrared (IR) absorbing material (often referred to as inks) directly onto the powder surface where sintering is desired. The entire build area is then irradiated with an IR radiation source such as an infrared lamp, causing the printed fluid to absorb this energy and then melt and sinter the underlying powder. This process is then repeated layer by layer until the build is complete.

[0011] However, the properties, surface finish, and porosity of the completed object depend to a large extent on the size of the powder granules, which are often on the order of 50 microns. Another important factor is the degree of sintering and melt between the particles in each deposited layer. While some polymer materials may be advantageous in terms of mechanical strength, other properties such as viscosity, resistance to melt and coalescence, and chain diffusion may limit the applicability of many polymers in sintering applications where poorly consolidated particles create voids or weak regions in the final product.

[0012] In general, higher molecular weight (MW) polyolefins are often preferred for product manufacture in many manufacturing techniques because of their enhanced mechanical properties and durability when compared to low MW polyolefins. However, in sintering processes, higher MW polyolefins exhibit correspondingly higher viscosity under melt conditions, which impacts the sintering performance in powder based fusion methods due to the poor polymer chain diffusion and poor coalescence of the polymer particles. As a result, printed articles prepared from high MW polyolefins often exhibit less mechanical resistance compared to injection molded articles of the same material.

[0013] While a number of factors are involved, the lack of sintering among particles of high MW polyolefin leads to articles having lower mechanical resistance, because the lack of chain diffusion between particles creates weak inter-particle and inter layer adhesions. Methods in accordance with the present disclosure increase chain diffusion among particles by depositing a polymer composition with a processing aid, whereby the processing aid penetrates into the polymer particles and helps transfer the heat absorbed by the radiation absorption material to be transferred to the polymer particles. [0014] It is envisioned that the processing aid is deposited by various routes: 1) as a material that is deposited onto a layer of powder separate from the radiation absorption material, 2) as a material that is applied onto a layer of powder in conjunction with or simultaneous with the radiation absorption material, or 3) blended with the polymer powder prior to the polymer powder being deposited as a layer for sintering. Each of such routes will be discussed in turn.

[0015] In one or more embodiments, the processing aid is deposited onto a layer of polymer powder in a step that is separate from the radiation absorption material. Thus, in such embodiments, a fine layer of polymer powder may be deposited on a printer bed, which may be heated to a temperature lower than the powder melt temperature. Following the polymer powder deposition, a processing aid may be applied onto the surface of the powder, followed by the deposition of a radiation absorption material onto the surface of the polymer powder (which may occur selectively to the pattern of powder that is desired to be sintered together to achieve the three dimensional article to be built). It is envisioned that in such embodiment, it may be advantageous to use separate inkjet printheads, /. _<? ., two printheads, for the separate application of the radiation absorption material and the processing aid. Following the application of the radiation absorption material and the processing aid, the surface is irradiated, such as with an infrared lamp, causing the printed radiation absorption material to absorb the energy and melt and sinter the underlying polymer powder. In this process, the processing aid may penetrate into the polymer particles and may help transfer the IR heat absorbed by the radiation absorption material to the polymer particles. Each of these steps may be repeated until the final article or part is built.

[0016] In one or more other embodiments, the processing aid is deposited with the radiation absorption material, which together may be referred to as a modified ink. Thus, in such embodiments, a fine layer of polymer powder may be deposited on a printer bed, which may be heated to a temperature lower than the powder melt temperature. Following the polymer powder deposition, a modified ink (containing both a radiation absorption material and a processing aid) may be applied onto the surface of the polymer powder (which may occur selectively to the pattern of powder that is desired to be sintered together to achieve the three dimensional article to be built). The surface is then irradiated, such as with an infrared lamp, causing the printed modified ink to absorb the energy and melt and sinter the underlying polymer powder. In this process, the processing aid included in the modified ink may penetrate into the polymer particles and may help transfer the IR heat absorbed by the radiation absorption material to the polymer particles. Each of these steps may be repeated until the final article or part is built.

[0017] In the final route, the processing aid may be combined with the polymer powder prior to the deposition of the polymer powder as a fine layer on a printer bed. In such embodiments, the polymer powder may be blended with a processing aid that has a lower melting temperature and/or lower melt viscosity than the polymer of the polymer powder. During the blending, the processing aid may penetrate or migrate into the porous granules of the polymer powder. A fine layer of polymer powder (blended with a processing aid) may be deposited on a printer bed, which may be heated to a temperature lower than the powder melt temperature. Following the polymer powder deposition, a radiation absorption material may be applied onto the surface of the polymer powder (which may occur selectively to the pattern of powder that is desired to be sintered together to achieve the three dimensional article to be built). The surface is then irradiated, such as with an infrared lamp, causing the printed radiation absorption material to absorb the energy and melt and sinter the underlying polymer powder. In this process, the processing aid included in the polymer powder may penetrate into the polymer particles and may help transfer the IR heat absorbed by the radiation absorption material to the polymer particles. Each of these steps may be repeated until the final article or part is built.

[0018] In any of the above routes, it is envisioned that following the sintering, unsintered powder may be removed from the built part, and any remaining radiation absorption material and/or processing aid may also be removed from the pores of the printed part, in conjunction with one or more post-treatment processes. As the porous parts printed may have open porosity, such additional post processing step can be performed to "wash" any remaining radiation absorption material and/or processing aid.

[0019] Radiation Absorption Materials [0020] As mentioned above, methods may include the step of applying a radiation absorption material (RAM or an IR absorber) to a deposited polymer powder prior to irradiation with a radiation source. RAM generally contains carbon black which is a strong infrared absorber and it acts to create a substantial difference between the IR absorptivity of the areas with RAM and those without. The areas with RAM will absorb sufficient energy to cause particles to sinter. The amount of RAM deposited on the powder surface will determine the amount of energy absorbed, which will influence the degree of particle melt.

[0021] The radiation absorption materials used in HSS are inks that can absorb in the infrared region. By definition, ink is a liquid or paste that contains pigments or dyes and can be either solutions or suspensions. Dyes can refer to solutions where the material has solubility or can refer to suspension where the material is not soluble. In one or more embodiments, the inks to be used in the claimed processes may be a liquid, and the composition of the dye may be varied in order to improve the capacity of the ink to sinter the polymer powder in an effective way, such as, for example, depending on the type of polymer powder being sintered.

[0022] The absorber may also be in the form of particles such as black toner.

Absorbers may be applied uniformly or selectively, in different amounts. For example, the absorber may be applied as a mixture of absorbers with different absorption maxima, or different absorbers may be applied independently, in an alternating manner, or in a predetermined sequence. In one or more embodiments, IR absorbers may be oil-based absorbers containing carbon particles such as oil- based soot particle ink.

[0023] Processing Aid

[0024] As described above, a processing aid may be added to the polymer powder (by any of the routes described above) to aid in chain diffusion between polymer powder during the sintering step. For example, it is envisioned that the presence of a processing aid may transform the RAM into a thermo sensitive ink in which the processing aid can dissolve the polymer particles above their melting point. In such a manner, it may be possible to perform the HSS process steps (as is conventionally done). When the infrared light turns on, it will heat the new thermo sensitive ink, and the ink carrier may start dissolving the polymer particles surfaces and will allow a much better chain diffusion among the particles.

[0025] In some embodiments, the processing aid may be dissolved in or suspended in the solvent or carrier of the RAM or in a similar solvent or carrier, i.e., be present in a liquid form. In such embodiments, the processing aid can be chosen among a variety of polymer additives and other substances such as fluoropolymers, boron nitride, metal stearates (such as calcium stearate, sodium stearate, etc), hydrocarbon oils, hydrocarbon oligomers, modified silicas, fatty acid amides, fatty acid esters, etc.

[0026] However, as described above, there are also embodiments envisioned where the processing aid is blended with the polymer powder prior to the deposition of the polymer on the print bed. In such instances, polymer powder may be dry blended with an amount (such as less than 10%wt) of a second dry component such as LLDPE, VLDPE, polyolefin oligomers, hydrocarbon oils, fluoropolymers, fatty acid amides, PVA, silicon, polymer plasticizers, etc. In one or more embodiments, this processing aid may be selected to have a lower melting temperature and/or much lower melt viscosity than polymer powder and may act as a“lubricant”, in order to improve the heat transfer between the RAM and the polymer particles.

[0027] Polymer Powder

[0028] Embodiments of the present disclosure may use a polymer powder that includes plastics, such as, for example polyolefin, polyvinyl chloride, acrylonitrile butadiene styrene, or polytetrafluoroethylene.

[0029] Polyolefins

[0030] Polyolefin powders may be selected from polypropylene, polyethylene, propylene copolymer or ethylene copolymers, including for example, ethylene vinyl acetate. Polyolefins may include homopolymers, random copolymers, block copolymers, and multiphasic polymer compositions such as impact copolymers. In some embodiments, polyolefin compositions may include a polymer matrix phase that surrounds other components such as an internal phase polymer and/or other additives. Polyolefins in accordance with the present disclosure may include a combination of one or more polymers or copolymers that may be blended pre- or post-polymerization in a reactor. [0031] Polyolefin compositions in accordance with the present disclosure may be prepared from polymers and copolymers of C2 to C8 olefins such as ethylene, propylene, butene, pentene, hexene, heptene, octene, and the like. In some embodiments, examples of suitable polyolefins include polyethylene, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), ultrahigh molecular weight (UHMWPE), and polypropylene (PP). In some embodiments, polyolefins may be obtained from renewable resources and/or may be post-consumer recycled polyolefin.

[0032] In one or more embodiments, polyolefins may include a polypropylene polymer have a percent by weight (wt%) of a C2 to C8 polyolefin comonomer that ranges from a lower limit selected from 0.5, 1, or 5 wt%, to an upper limit selected from 2.5, 5, or 10 wt%, where any lower limit may be combined with any upper limit.

[0033] Polyolefins in accordance with the present disclosure may be formulated as a polymer powder having an average particle diameter in a range having a lower limit selected from 1 pm, 2 pm, 5 pm, and 10 pm, to an upper limit selected from 50 pm, 100 pm, 500 pm, and 1000 pm, where any lower limit may be paired with any upper limit.

[0034] In one or more embodiments, the strength of the adhesions created during melting and sintering may be modified by tuning the porosity of a polymer powder, which governs the concentration of the processing aid available at the powder particle surface.

[0035] Polyolefins in accordance with the present disclosure may be formulated as a polymer powder having a porosity in a range having a lower limit selected from 0.1 cm ³ /g, 0.2 cm ³ /g, and 0.5 cm ³ /g, to an upper limit selected from 0.5 cm ³ /g, 0.20 cm ³ /g, and 0.30 cm ³ /g, where any lower limit may be paired with any upper limit.

[0036] Internal Rubber Phase

[0037] In one or more embodiments, polyolefin compositions in accordance with the present disclosure include multiphasic polymer compositions having an internal rubber phase dispersed in a polyolefin matrix phase. In some embodiments, polymer compositions may include polymer compositions classified as impact copolymers (ICP). [0038] In one or more embodiments, rubbers suitable for use as an internal rubber phase include homopolymers and copolymers having one or more monomers. In some embodiments, rubbers may include including graft copolymers such as maleated ethylene-propylene copolymers, and terpolymers of ethylene and propylene with nonconjugated dienes such as 5-ethylidene-2-norbornene, 1,8 octadiene, 1,4 hexadiene cyclopentadiene, and the like. Other polymers may include low density polyethylene, ethylene propylene rubber, poly(ethylene-methyl acrylate), poly(ethylene-acrylate), ethylene propylene diene rubber (EPDM), vinyl silicone rubber (VMQ), fluorosilicone (FVMQ), nitrile rubber (NBR), acrylonitrile-butadiene- styrene (ABS), styrene butadiene rubber (SBR), styrene-ethylene rubber, styrene- butadiene-styrene block copolymers (SBS and SEBS), polybutadiene rubber (BR), styrene-isoprene-styrene block copolymers (SIS), partially hydrogenated acrylonitrile butadiene (HNBR), natural rubber (NR), synthetic polyisoprene rubber (IR), neoprene rubber (CR), polychloropropene, bromobutyl rubber, chlorobutyl rubber, polyurethane, elastomer polyolefins as ethylene-octene copolymer, and combinations thereof.

[0039] In some embodiments, the internal rubber phase may be an ethylene -propylene rubber (EPR), which may include EPRs having one or more comonomers in addition to ethylene and propylene. Other comonomers may include, for example, a-olefins such as 1 -butene, 1-pentene, 1 -hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1- undecene, 1-dodecene, and the like.

[0040] In one or more embodiments, polyolefin compositions may include a multiphasic polymer having a polyolefin matrix phase and internal rubber phase present at a percent by weight (wt%) of the composition that ranges from a lower limit selected from any of 2, 3, 5, and 10 wt%, to an upper limit selected from any of 50, 60, 70, and 75 wt%, where any lower limit may be paired with any upper limit.

[0041] In one or more embodiments, polyolefin compositions may include a multiphasic polymer having an internal rubber phase prepared from ethylene and a C3 to C8 polyolefin comonomer, where the ethylene is present at a percent by weight (wt%) of the internal rubber phase that ranges from a lower limit selected from any of 5, 10, 15, and 20 wt%, to an upper limit selected from any of 50, 60, 70, and 75 wt%, where any lower limit may be paired with any upper limit.

[0042] Physical properties [0043] In one or more embodiments, polymers used in the polymer powders may have a melting temperature that ranges from 90 to 170°C. In one or more embodiments, polymers used in the polymer powders may have an initial melt flow index (MFI) at 190 °C and 2.16 kg as determined according to ASTM D1238 in a range having a lower limit selected from any of 1 g/lOmin, 5 g/lOmin, 10 g/lOmin, and 15 g/lOmin, to an upper limit selected from any of 50 g/lOmin, 100 g/lOmin, 500 g/lOmin, and 600 g/10min, where any lower limit may be paired with any upper limit. In some embodiments, the polyolefin may be a polypropylene having an initial MFI in the range of 5 to 500 g/10min. In some embodiments, the polyolefin may be a polyethylene having an initial MFI in the range of 1 to 50 g/lOmin.

[0044] Further, it is also envisioned that the embodiments may have particular applicability to ultrahigh molecular weights, such as a number average molecular weight (Mn) that is at least 350,000 g/mol, or at least 500,000 g/mol, or at least 1,000,000 g/mol, or at least 5,000,000 g/mol, or at least 8,000,000 g/mol. For example, it is envisioned that the present embodiments may enable the use of polymers such as UHMWPE in an HSS process, which was not otherwise feasible due to the high melting viscosity and low or non-flowability of UHMWPE and the short sintering times of HSS. Examples of the properties of two UHMWPE samples are shown below in Table 1.

[0045] Table 1 - Molecular Characterization of UHMWPE samples

[0046] Despite such properties, incorporation of a processing aid, as described herein, may allow for chain diffusion between polymer particles, thereby allowing the particles to sinter together. Further, while the present embodiments may have particular applicability to higher molecular weights (and low melt viscosities), it is envisioned that the incorporation of the claimed processing aid may provide improved chain diffusion between any polymer particles in a powder fusion bed additive manufacturing technique. [0047] Additives

[0048] Polymeric compositions in accordance with the present disclosure may include additives that modify various physical and chemical properties when added to the polymeric composition during blending that include one or more polymer additives such as coupling agents, flow lubricants, antistatic agents, clarifying agents, nucleating agents, beta-nucleating agents, slippage agents, antioxidants, antacids, light stabilizers such as HALS, IR absorbers, silica, titanium dioxide, silicon dioxide, organic dyes, organic pigments, inorganic dyes, and inorganic pigments.

[0049] Applications

[0050] In one or more embodiments, articles in accordance with the present disclosure may be formed using an additive manufacturing system that prints, builds, or otherwise produces 3D parts and/or support structures. The additive manufacturing system may be a stand-alone unit, a sub-unit of a larger system or production line, and/or may include other non-additive manufacturing features, such as subtractive- manufacturing features, pick-and-place features, two-dimensional printing features, and the like.

[0051] Articles that may be formed, include, for example, packaging, rigid and flexible containers, household appliances, molded articles such as caps, bottles, cups, pouches, labels, pipes, tanks, drums, water tanks, medical devices, shelving units, and the like. Specifically, any article conventionally made from the polymer compositions of the present disclosure (using conventional manufacturing techniques) may instead be manufactured from additive manufacturing.

[0052] The use of polymer compositions in accordance with the present disclosure may provide greater flexibility in the products produced by the additive manufacturing methods. Specifically, for example, the articles produced by additive manufacturing may have a lower flexural modulus and excellent fatigue resistance as compared to PLA or ABS.

[0053] Radiation Sources

[0054] Methods in accordance with the present disclosure may incorporate one or more radiation sources to generate ionizing radiation at intensities that induce heating in polymer compositions. In some embodiments, radiation sources may have variable intensity that may span from intensity suitable to initiate melting of a polymer composition to intensity suitable to heat the polymer composition.

[0055] Radiation sources may include sources used in commercial additive manufacturing applications and include lamps and lasers that operate in across spectra such as infrared (IR), ultraviolet (UV), gamma, and xray, electron beams, and the like. In one or more embodiments, radiation sources may be focused on a powder bed during melting and/or sintering, and the radiation source may be stationary or mobile.

[0056] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus- function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words‘means for’ together with an associated function.