Thermally conductive thermoplastics used in filament manufacturing

Abstract

This disclosure relates to filament fabrication and thermally conductive polymers used therein. A method for forming articles using filament fabrication technology is also described.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 119,263, filed November 30, 2020, the entire contents of which are incorporated herein by reference.

[0003] Statement regarding federally funded research or development

[0004] This invention was completed with government support under government contract DE-EE008722. The government holds certain rights to this invention. Technical Field

[0005] This disclosure relates to the manufacture of filaments and the thermally conductive polymers used therein. Background Technology

[0006] Polymers are inherently insulating materials with a thermal conductivity of less than 0.5 W / m / K. One way to increase thermal conductivity is to incorporate conductive fillers, including carbon fibers, graphite, boron nitride, alumina, gold, copper, and graphene, into the polymer matrix. In some cases, this can result in thermal conductivity increases of up to 55 W / m / K. Typically, high concentrations of conductive fillers are required to significantly increase the polymer's base thermal conductivity.

[0007] Fused filament fabrication (FFF) is a rapidly developing 3D printing process that enables the industrial fabrication of complex geometries using a wide variety of polymers. Specifically, FFF is a 3D printing process that uses continuous filaments of thermoplastic materials to print articles. However, thermally conductive polymers have previously been unsuccessful in FFF processes. This is partly due to the high filler concentration in conventional thermally conductive polymers, which increases viscosity and thus makes the process itself stiffer and unable to produce viable final products. The high filler concentration in conventional thermally conductive polymers also leads to poor layer adhesion in FFF processes, which damages the printed articles. Furthermore, the presence of carbon fibers (often used as thermally conductive fillers) in conventional thermally conductive polymers results in poor surface quality of the finished product.

[0008] This disclosure attempts to address these challenges. Summary of the Invention

[0009] In one aspect, methods of forming articles typically include providing a thermally conductive polymer. The polymer comprises spherical nanoparticles and is in the form of filaments. The method further includes extruding the filaments in a filament forming process to produce a 3D-printed article comprising the thermally conductive polymer.

[0010] On the other hand, methods for forming articles typically involve providing a thermally conductive polymer. The polymer is in the form of a filament and has properties at 290°C and 1 second... –1The viscosity at the shear rate is less than about 1.0E+3. The method also includes extruding the filament in a filament forming process to produce a 3D printed article containing the thermally conductive polymer.

[0011] On the other hand, thermally conductive polymers typically comprise a polymer matrix and spherical nanoparticles within the polymer matrix. The thermally conductive polymer exhibits properties at 290°C and 1 second... –1 The viscosity at the shear rate is less than about 1.0E+3, thereby configuring the polymer to have sufficient layer adhesion and sufficient surface quality, making the polymer suitable for filament manufacturing. Detailed Implementation

[0012] This disclosure relates to fused filament fabrication (FFF) printing technology, and more specifically to an FFF process using a thermally conductive polymer. The FFF process of this disclosure utilizes a continuous filament formed from a thermally conductive polymer. The filament is pushed through an extruder to print the desired article. Therefore, the final printed article contains a thermally conductive polymer with sufficient layer adhesion and sufficient surface quality. Thus, the FFF process produces a viable final product formed from a thermally conductive polymer.

[0013] The thermally conductive polymer used in the FFF process for producing filaments comprises a polymer matrix. Specifically, usable polymers include thermoplastic polymers such as acrylonitrile, butadiene, styrene, acrylic acid, cellulose, cellulose acetate, cyclic olefin copolymers, ethylene-vinyl acetate, ethylene-vinyl alcohol, polytetrafluoroethylene, ionomers, liquid crystal polymers, polyoxymethylene, polyacrylates, polyacrylonitrile, polyamides (e.g., polyamide 66 or polyamide 6), polyamide-imide, polyimide, polyaryletherketone, polybutadiene, polybutylene terephthalate, polycaprolactone, polychlorotrifluoroethylene, polyetheretherketone, and polyethylene terephthalate. Esters, polycyclohexamethylene terephthalate, polycarbonate, polyhydroxyalkanoate, polyketone, polyester, polyolefin (e.g., polyethylene, polypropylene, polybutene, etc.), polyetherketoneketone, polyetherimide, polyethersulfone, polysulfone, chlorinated polyethylene, polylactic acid, polymethyl methacrylate, polymethylpentene, polyphenylene oxide, polyphenylene sulfide (PPS), polyphthalamide, polystyrene, polysulfone, polypropylene terephthalate, polyurethane, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, styrene-acrylonitrile, or mixtures thereof. Polyamides and polyphenylene sulfides are particularly preferred.

[0014] Compared to conventional thermoplastic materials used in the FFF process, the thermally conductive polymers used in the FFF process described herein exhibit reduced brittleness through the incorporation of spherical nanoparticles. In one embodiment, the brittleness of the extruded filaments is reduced by a factor of three through the incorporation of spherical nanoparticles. The nanoparticles can also contribute to reduced viscosity and enhanced nanocomposites. In one embodiment, the viscosity of the thermally conductive polymer is [value missing] at 290°C and 1S [value missing].–1 The shear rate is less than about 1.0E+3. However, this value can vary depending on the characteristics of the polymer groups, as will be readily understood by those skilled in the art. Spherical nanoparticles include, but are not limited to, nanodiamond, pyrolytic silica, nanoalumina, pyrolytic alumina, or combinations thereof. The nanoparticles may be contained in the polymer matrix at a concentration of at least about 0.1 wt%, at least about 0.5 wt%, at least about 1 wt%, at least about 1.5 wt%, or at least about 2 wt%. For example, the nanoparticle concentration can be from about 0.1 wt% to about 2 wt%.

[0015] The thermally conductive polymers used in the FFF process of this invention also typically have a cold crystallization initiation temperature below about 220°C, which allows for better layer adhesion and surface quality. The cold crystallization temperature can be below about 210°C, below about 200°C, below about 190°C, below about 180°C, below about 170°C, below about 160°C, below about 150°C, below about 140°C, below about 130°C, below about 120°C, below about 110°C, or below about 100°C.

[0016] The thermally conductive polymers used in the FFF process also have reduced crystallinity to reduce warping and deformation of the printed parts. For example, the crystallinity can be less than about 10%, less than about 9%, less than about 8%, less than about 7%, less than about 6%, less than about 5%, less than about 4%, or less than about 3%.

[0017] The thermally conductive filler used in the thermally conductive polymer in the FFF process can include any filler known in the art to have thermal conductivity. The filler can have high thermal conductivity (e.g., up to about 900 W / m / K or greater than about 10 W / m / K), intermediate thermal conductivity (e.g., about 5 W / m / K to about 10 W / m / K), or low thermal conductivity (less than about 5 W / m / K). Generally, fillers with high and intermediate thermal conductivity are preferred when primarily used as thermally conductive fillers.

[0018] As an example, thermally conductive fillers may include carbon black, alumina, boron nitride, silicon dioxide, carbon fibers, graphene, graphene oxide, graphite (such as, for example, expanded graphite, synthetic graphite, low-temperature expanded graphite, etc.), aluminum nitride, silicon nitride, metal oxides (such as, for example, zinc oxide, magnesium oxide, beryllium oxide, titanium oxide, zirconium oxide, yttrium oxide, etc.), carbon nanotubes, calcium carbonate, talc, mica, wollastonite, clay (including flaky clay), metal powders (such as, for example, aluminum, copper, bronze, brass, etc.) or mixtures thereof.

[0019] The thermally conductive polymers described herein are specifically designed for 3D printing processes, particularly for filament fabrication. That is, the thermally conductive polymers described herein can be extruded in a 3D printer. Therefore, this paper provides a method for forming an article of art, comprising: providing a thermally conductive polymer in the form of a continuous filament; and extruding the thermally conductive polymer via a 3D printer. Typically, the thermally conductive polymer is extruded in layers, thereby forming the printed article from bottom to top. Specifically, the filament process involves feeding a filament of thermally conductive polymer material from a spool through a moving, heated printer extruder head and depositing the material onto the grown workpiece. The print head is operatively connected to a controller programmed to print the desired shape of the thermally conductive polymer material. The print head can move in two dimensions to deposit one horizontal plane or layer at a time. The print head can then be moved vertically in small increments to begin a new layer.

[0020] The unique structure of thermally conductive polymers facilitates their use in filament fabrication processes. For example, the use of nanoparticles in thermally conductive polymers reduces polymer viscosity and improves the layer adhesion of printed layers, thereby forming viable printed articles.

[0021] The thermally conductive polymers and methods described herein can be used to prepare articles known to those skilled in the art. Suitable applications include a variety of heat sink applications, such as electronic devices, printed electronic devices and housings, or automotive parts, including inverters, on-board chargers (OBCs), and power distribution units (PDUs).

[0022] The invention has been described in detail, and it will be apparent that modifications and variations may be made without departing from the scope of the invention as defined in the appended claims.

[0023] When describing elements of the invention or its preferred embodiments, the articles “a,” “an,” “the,” and “the” are intended to indicate the presence of one or more elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that other elements besides those listed may be present.

[0024] In view of the above, it can be seen that several objectives of this disclosure have been achieved and other favorable results have been obtained.

[0025] Various changes can be made to the above components and methods without departing from the scope of the invention. All contents contained in the above specification should be understood as illustrative and not restrictive.

Claims

1. A method for forming an article, the method comprising: A thermally conductive polymer is provided, wherein the polymer comprises spherical nanoparticles and is in the form of filaments; as well as The filament is extruded in a filament forming process to produce a 3D printed article containing the thermally conductive polymer. The spherical nanoparticles include at least one of pyrolytic silica, nano-alumina, pyrolytic alumina, or combinations thereof.

2. The method according to claim 1, wherein the thermally conductive polymer has a cold crystallization temperature below about 220°C.

3. The method according to claim 1, wherein the thermally conductive polymer has a crystallinity of less than about 5%.

4. The method according to claim 1, wherein the thermally conductive polymer has a temperature of 290°C and 1 second... -1 Viscosity less than approximately 1.0E+3 at the shear rate.

5. The method of claim 1, wherein the filament is extruded in layers.

6. The method of claim 1, wherein the spherical nanoparticles are present in the thermally conductive polymer at a concentration of about 0.1% to about 2% by weight.

7. The method of claim 1, wherein the thermally conductive polymer comprises a polymer matrix comprising at least one polymer selected from the group consisting of polyphenylene sulfide, polyamide, polyketone, polyolefin, and mixtures thereof.

8. The method of claim 1, wherein the thermally conductive polymer comprises a thermally conductive filler in the polymer matrix.

9. The method of claim 8, wherein the thermally conductive filler comprises at least one of boron nitride, carbon fiber, graphite, carbon nanotubes, or mixtures thereof.

10. A method of forming an article, the method comprising: Provide a thermally conductive polymer, wherein the polymer is in the form of a filament and has properties at 290°C and 1 second. -1 Viscosities less than approximately 1.0E+3 at the shear rate; and The filament is extruded in a filament forming process to produce a 3D printed article containing the thermally conductive polymer. The thermally conductive polymer comprises spherical nanoparticles, which include at least one of pyrolytic silica, nano-alumina, pyrolytic alumina, or combinations thereof.

11. The method of claim 10, wherein the filament is extruded in layers.

12. The method of claim 10, wherein the spherical nanoparticles are present in the thermally conductive polymer at a concentration of about 0.1% to about 2% by weight.

13. The method of claim 10, wherein the thermally conductive polymer comprises a polymer matrix comprising at least one polymer selected from the group consisting of polyphenylene sulfide, polyamide, polyketone, polyolefin, and mixtures thereof.

14. The method of claim 13, wherein the thermally conductive polymer comprises a thermally conductive filler in the polymer matrix.

15. The method of claim 14, wherein the thermally conductive filler comprises at least one of boron nitride, carbon fiber, graphite, carbon nanotubes, or mixtures thereof.

16. A thermally conductive polymer, comprising: Polymer matrix; and The spherical nanoparticles in the polymer matrix; The thermally conductive polymer described herein has properties at 290°C and 1 second. -1 The viscosity at the shear rate is less than about 1.0E+3, thereby configuring the polymer with sufficient layer adhesion and sufficient surface quality, making the polymer suitable for filament manufacturing. The spherical nanoparticles include at least one of pyrolytic silica, nano-alumina, pyrolytic alumina, or combinations thereof.

17. The polymer of claim 16, further comprising a thermally conductive filler in the polymer matrix.