Thermal filler particles, thermal conductive compositions, and assemblies containing them

Abstract

The shaped thermal filler particles have an elongated shape defined by a substantially planar first smooth surface and a second smooth surface contacting the substantially planar first smooth surface along a closed planar path. The closed planar path has a length-to-width ratio of at least 1.5. The shaped thermal filler particles have a maximum linear dimension perpendicular to the planar first smooth surface that is no greater than half the length of the closed path. The thermally conductive composition comprises 1 to 95 volume percent shaped thermal filler particles dispersed in a binder. The assembly includes a heat source, a heat sink, and a thermally conductive composition at least partially sandwiched between the heat source and the heat sink.

Description

[Technical Field]

[0001] This disclosure broadly relates to materials for thermal management and assemblies containing them. [Background technology]

[0002] Thermal interface materials (TIMs) function as pathways for transferring thermal energy from heat-generating devices to the outside. TIMs are used to help transfer thermal energy from devices that need to be kept below a temperature that could impair the device's performance or lifespan. Examples of such devices include batteries (e.g., lithium-ion batteries), electromechanical devices (e.g., motors, generators), and semiconductor electronic devices (e.g., inverters, processors).

[0003] TIMs often take the form of composite materials containing an organic matrix (e.g., organic polymers) and thermal filler particles (e.g., ceramic, carbon, or metal particles). The matrix typically imparts important mechanical properties (e.g., compliance, flexibility, toughness) or interfacial properties (e.g., wet-out, adhesion) to the composite. Thermal filler particles function to increase the thermal conductivity of the composite and can also provide properties such as flame retardancy, endothermic transition, or color. Certain thermal fillers may also play a role in reducing the density of the composite (known in the art as "lightening").

[0004] In order to achieve high thermal conductivity in a polymer matrix composite, particulate thermal fillers are generally included at a high volume percentage (alternatively expressed herein as volume fraction), such as filling above 50 volume percent. Such high filling levels often reduce other properties of the TIM composite (such as elongation at break, compliance), or the processability of the TIM composite. The processing of TIM composites often includes steps where, prior to curing, a fluid dispersion of thermal filler particles in a binder precursor must be transported by flow (such as pumped, dispensed, extruded, coated, squeezed), imposing requirements on the rheological properties of the fluid dispersion. The design of improved TIM composites, including the design of particulate fillers, has been a longstanding challenge due to the trade-off between thermal conductivity and the aforementioned mechanical or rheological properties.

Summary of the Invention

[0005] In thermal management technology, there is a need for improved thermal filler particles that can better balance the thermal conductivity in TIM and the aforementioned rheological properties.

[0006] In a first aspect, the present disclosure provides a shaped thermal filler particle having an elongated shape defined by a first smooth plane surface and a second smooth plane surface that contacts the first smooth plane surface along a closed path, wherein at least a portion of the second smooth plane surface is convex, the closed path has a length-to-width ratio of at least 1.5, and the shaped thermal filler particle has a maximum linear dimension perpendicular to the first smooth plane surface of the plane that is less than or equal to half of the length of the closed path (which may or may not be the thickness of the shaped thermal filler particle).

[0007] In a second aspect, the present disclosure provides a composition comprising 1 to 95 volume percent of the shaped thermal filler particles according to the present disclosure, dispersed in an organic binder.

[0008] In some embodiments, the thermally conductive composition is cured and / or chemically crosslinked.

[0009] In a third aspect, the present disclosure provides an assembly comprising: a heat source, a heat sink, and a thermally conductive composition according to the present disclosure at least partially sandwiched between the heat source and the heat sink.

[0010] As used herein, the term "chemically crosslinked" means crosslinked by covalent bonds between atoms.

[0011] The term "smooth" means, for example, the absence of sharp surface features such as a given sharp point or a steeply sloped protrusion, but small recesses such as, for example, boreholes and / or grooves, and random manufacturing defects such as, for example, slight indentations are tolerated.

[0012] The term "planar" means within a plane (i.e., two-dimensional), but small recesses such as, for example, boreholes and / or grooves, and random manufacturing defects such as, for example, slight indentations are tolerated.

[0013] The term "inorganic" refers to a composition of materials selected from: i) oxides, carbides, nitrides, borides, phosphides, arsenides, chalcogenides, and halides of metals or metalloids; ii) metals or metalloids including elemental metals, alloys, and intermetallic compounds; iii) any of various carbon allotropes including graphite, graphene, carbon nanotubes, and diamond; and iv) combinations thereof.

[0014] The term "formed" means intentionally formed according to a nominal shape (e.g., by a molding or printing process), but a small amount of random or repeated manufacturing defects are tolerated.

[0015] The term "length" refers to the maximum linear dimension of an object.

[0016] The term "width" refers to the maximum linear dimension of an object perpendicular to its length.

[0017] The term "thickness" refers to the maximum straight-line dimension of an object, perpendicular to both its length and width.

[0018] The features and advantages of this disclosure will be further understood by considering the detailed description and the accompanying claims. [Brief explanation of the drawing]

[0019] [Figure 1A] This is a perspective view of an exemplary molded heat-filler particle 100. [Figure 1B] This is a top view of the molded heat-filler particles 100. [Figure 1C] This is a side view of the molded heat-filler particles 100. [Figure 1D] This is an end view of molded heat-filler particles 100. [Figure 2A] This is a perspective view of an exemplary molded heat-filler particle 200. [Figure 2B] This is a top view of the molded heat-filler particles 200. [Figure 2C] This is a side view of the molded heat-filler particles 200. [Figure 2D] This is an end view of molded heat-filler particles 200. [Figure 3A] This is a perspective view of an exemplary molded heat-filler particle 300. [Figure 3B] This is a top view of the molded heat-filler particles 300. [Figure 3C] This is a side view of the molded heat-filler particles 300. [Figure 3D] This is an end view of molded heat-filler particles 300. [Figure 4A] This is a perspective view of comparison particle 400. [Figure 4B] This is a top view of the comparison particle 400. [Figure 4C] This is a side view of comparison particle 400. [Figure 4D] This is an end view of comparison particle 400. [Figure 5A] This is a perspective view of Modeling Example 1, which features molded heat-filler particles 100. [Figure 5B] This is an end view of Modeling Example 1, which features molded heat-filler particles 100. [Figure 5C] This is a side view of Modeling Example 1, which features molded heat-filler particles 100. [Figure 6A] This is a perspective view of Modeling Example 4, which features molded heat-filler particles 200. [Figure 6B] This is an end view of Modeling Example 4, which features molded heat-filler particles 200. [Figure 6C] This is a side view of modeling example 4, which features molded heat-filler particles 200. [Figure 7A] This is a perspective view of modeling example 7, which features molded heat-filler particles 300. [Figure 7B] This is an end view of modeling example 7, which features molded heat-filler particles 300. [Figure 7C] This is a side view of modeling example 7, which features molded heat-filler particles 300. [Figure 8] This is a perspective view of modeling example 10, which features molded heat-filler particles 100. [Figure 9] This is a perspective view of modeling example 14, featuring molded heat-filler particles 200. [Figure 10] This is a perspective view of modeling example 18, featuring molded heat-filler particles 300. [Figure 11] This is a perspective view of comparative modeling example A, which features particle 400 of the comparative example. [Figure 12] This is a perspective view of comparative modeling example B, which features particle 400 of the comparative example. [Figure 13] This is a plot of the volume fraction of the effective thermal conductivity along the x-axis for composite materials including oriented array shapes A, B, and C. [Figure 14]This is a plot of the volume fraction of the effective thermal conductivity averaged across the x, y, and z axes for composite materials including oriented array shapes A, B, and C. [Figure 15] This figure shows the effective thermal conductivity as an average along three orthogonal axes (x, y, and z) for composite materials, including shapes A, B, and C, containing arrays of particles equally oriented along one of the x, y, and z axes. [Figure 16] This figure shows the effective thermal conductivity as an average along three orthogonal axes (x, y, and z) for composite materials, including shapes A, C, D, and E, containing arrays of particles equally oriented along one of the x, y, and z axes. [Figure 17] This is a schematic side view of an exemplary assembly 1700 as described herein. [Figure 18] This is a scanning electron microscope image of the molded heat-filler particles produced in Example 1. [Figure 19] This is a scanning electron microscope image of the molded heat-filler particles produced in Example 2. [Figure 20] This is a scanning electron microscope image of the molded heat-filler particles produced in Example 3.

[0020] Where reference letters in the specification and drawings are used repeatedly, they are intended to represent the same or similar features or elements of the present disclosure. Those skilled in the art should understand that many other modifications and embodiments can be devised and that they fall within the scope and spirit of the principles of the present disclosure. The drawings may not be drawn to scale. [Modes for carrying out the invention]

[0021] Referring here to Figures 1A to 1D, the molded heat filler particle 100 has a shape defined by a substantially planar first smooth surface 130 and a second smooth surface 140 that substantially contacts the planar first smooth surface along a loop 150. In this embodiment, the substantially planar loop has two semicircular ends 160a, 160b connected by two parallel line segments 170a, 170b (i.e., a "racetrack ellipse"). The molded heat filler particle 100 has a length 180, a width 182, and a thickness 184. In this embodiment, the thickness 184 is the maximum straight-line dimension perpendicular to the planar first smooth surface.

[0022] In many embodiments, substantially planar cycles have a "dogbone" shape. Examples of such paths include, for example, Cassini oval and similar shapes.

[0023] Referring here to Figures 2A to 2D, the molded heat filler particle 200 also has a shape defined by a substantially planar first smooth surface 230 and a second smooth surface 240 that substantially contacts the planar first smooth surface along the loop 250. In this embodiment, the substantially planar loop has two rounded ends 260a, 260b and a relatively narrow waist 270 positioned between them. The molded heat filler particle 200 has a length 280 (matching the length of the loop 250), a width 282 (matching the width of the loop 250), and a thickness 284. The waist 270 has a waist width 272 and a waist thickness 274. In this embodiment, the thickness 284 is the maximum straight dimension perpendicular to the planar first smooth surface.

[0024] Referring here to Figures 3A to 3D, the molded heat filler particle 300 also has a shape defined by a substantially planar first smooth surface 330 and a second smooth surface 340 that substantially contacts the planar first smooth surface along the loop 350. In this embodiment, the substantially planar loop has two rounded ends 360a, 360b and a relatively narrow waist 370 positioned between them. The molded heat filler particle 300 has a length 380 (coinciding with the length of the loop 350), a width 382 (coinciding with the width of the loop 350), and a thickness 384. The waist 370 has a waist width 372 and a waist thickness 374. In this embodiment, the thickness 384 is the maximum straight dimension perpendicular to the planar first smooth surface.

[0025] In some embodiments, the waist width (272, 372) is 10% to 90% of the particle width (282, 382), in other embodiments 25% to 80%, in yet another 30% to 70%, and in yet another 35% to 50%. The selection of the waist width as a percentage of the particle width depends at least on a complex trade-off between heat transport through the waist (preferably high and decreasing with decreasing waist width), particle mass (preferably low and decreasing with decreasing waist width), and particle bending strength (preferably high and decreasing with decreasing waist width).

[0026] In some embodiments, the waist thickness (274, 374) is 10% to 90% of the particle thickness (284, 384), in other embodiments it is 25% to 80%, in yet another embodiment it is 30% to 70%, and in yet another embodiment it is 35% to 50%. The selection of waist thickness as a percentage of particle thickness depends at least on a complex trade-off between heat transport through the waist (preferably high and decreasing with decreasing waist thickness), particle mass (preferably low and decreasing with decreasing waist thickness), and particle bending strength (preferably high and decreasing with decreasing waist thickness).

[0027] The closed circuits 150, 250, and 350 include at least some convex portions, for example, portions at the rounded ends (160a, 160b, 260a, 260b, 360a, 360b) in Figures 1A to 1D, 2A to 2D, and 3A to 3D.

[0028] Figures 4A to 4D show comparative particles 400 with a right cylindrical shape defined by a length of 480 and a diameter of 482. With respect to such a right cylindrical shape of particles, the diameter of the cylinder is referred to herein as the width of the cylinder. The aspect ratio of the right cylindrical particle 400 is given by dividing the length by the diameter (or width).

[0029] In some embodiments, the molded heat-filler particles have a length-to-width ratio of at least 1.5 and a length-to-thickness ratio (i.e., aspect ratio) of at least 1.5. In some embodiments, the molded heat-filler particles have a length-to-width ratio (i.e., aspect ratio) of at least 2, at least 2.5, at least 3, at least 3.5, at least 4, at least 5, or even at least 10. In some embodiments, the length-to-width ratio is 1.5 to 10, 2 to 5, or 2.5 to 4.

[0030] In some embodiments of the molded heat filler particles, the loop has a length-to-width ratio of at least 1.5, and the molded heat filler particles have a ratio of at least 1.5 between the length of the loop and the maximum straight dimension perpendicular to the plane. In some embodiments of the molded heat filler particles, the molded heat filler particles have a ratio of at least 2, at least 2.5, at least 3, at least 3.5, at least 4, at least 5, or even at least 10 between the length of the loop and the maximum straight dimension perpendicular to the plane. If the molded heat filler particles have a ratio of at least 2 (2.5, 3, 3.5, 4, 5, 10) between the length of the loop and the maximum straight dimension perpendicular to the plane, it is equivalent to a molded heat filler particle having a maximum straight dimension perpendicular to a first smooth surface of the plane that is less than or equal to half the length of the loop (1 / 2.5, 1 / 3, 1 / 3.5, 1 / 4, 1 / 5, 1 / 10).

[0031] For the filler particles of this disclosure to have a finite volume, their second smooth surfaces (which are substantially in contact with the first smooth surface of the plane along the loop) must extend away from the first smooth surface. The fact that the second smooth surface extends substantially away from the plane of the first smooth surface, when combined with the fact that the second smooth surface is substantially in contact with the first smooth surface of the plane along the loop, results in at least a portion (hereinafter also referred to as a region) of the second smooth surface being convex (hereinafter also referred to as a convex surface portion or surface region). In a preferred embodiment, the regions of the second surface at both ends of the elongated filler particle are smooth and convex. For clarity, in Figures 1C, 2C, and 3C, the convex regions of the second smooth surfaces 140, 240, and 340 at both ends of the elongated filler particle, respectively, are shown as smooth and convex. The filler particles of the present disclosure may also include portions or regions of a second smooth surface having a concave surface (also referred to herein as concave surface portions or surface regions). The filler particles of the present disclosure may also include portions or regions of a second smooth surface having a saddle shape.

[0032] Some preferred embodiments of the heat-filler particles of the present disclosure can be defined in terms of the radius of curvature of the convex surface region of the second smooth surface (for example, the radius of curvature of the smooth, convex region of the second surface at both ends of an elongated filler particle). For example, in some embodiments, the radius of curvature at both ends of a molded heat-filler particle in a plane defined by the length and thickness directions of the particle may be at least 0.11, 0.12, 0.14, 0.17, 0.20, 0.25, 0.33, 0.50, 1, 2, or 4 times the thickness of the molded heat-filler particle. In some embodiments, the radius of curvature at both ends of a molded heat-filler particle in a plane defined by the length and thickness directions of the particle may be 0.10 to 4 times, 0.20 to 2 times, or 0.25 to 1 times the thickness of the molded heat-filler particle. In some embodiments, the radius of curvature at both ends of a molded heat-filler particle in a plane defined by the length and width directions of the particle may be at least 0.11, 0.12, 0.14, 0.17, 0.20, 0.25, 0.33, 0.50, 1, 2, or 4 times the width of the molded heat-filler particle. In some embodiments, the radius of curvature at both ends of a molded heat-filler particle in a plane defined by the length and width directions of the particle may be 0.10 to 4 times, 0.20 to 2 times, 0.25 to 0.75 times, or about 0.5 times the width of the molded heat-filler particle. The radii of curvature described above may be the same or different at both ends of the molded heat-filler particle.

[0033] The first smooth surface is substantially planar. The first smooth surface is nominally planar, except for minor irregularities such as meniscus-related defects, shrinkage-related defects, small voids resulting from mold filling, and / or mold dewetting defects. In a preferred embodiment, the first smooth surface is planar.

[0034] Similar to the first smooth surface, the second smooth surface may have small irregularities such as meniscus-related defects, shrinkage-related defects, small voids due to mold filling, and / or mold dewetting defects. In some embodiments, the second smooth surface is at least substantially convex, for example, completely convex. For clarity, the second smooth surface 140 of the molded heat-filler particle 100 in Figure 1 is shown to be completely convex.

[0035] The molded heat-filler particles may contain inorganic materials.

[0036] Examples of useful molded thermal filler particles include those containing at least one of the following: aluminum oxide (alumina), magnesium oxide, aluminum hydroxide, silicon nitride, zinc oxide, silicon oxide, beryllium oxide, titanium oxide, copper oxide, cuprous oxide, boron nitride, aluminum nitride, silicon carbide, diamond, talc, mica, kaolin, bentonite, magnesite, pyrophyllite, titanium boride, calcium titanate, metals (e.g., copper, aluminum, brass, steel, bronze), graphite, carbon black, graphene, and combinations thereof. Other thermally conductive materials may also be used.

[0037] Molded heat-filler particles can have any thermal conductivity, but when they are incorporated into a binder, the molded heat-filler particles generally have a higher thermal conductivity than the binder. Boron nitride may have any structure, such as c-BN (cubic structure), w-BN (wurtzite structure), h-BN (hexagonal structure), r-BN (rhombohedral structure), and t-BN (random structure). Among these, aluminum oxide, aluminum hydroxide, zinc oxide, boron nitride, and aluminum nitride are often preferred from the viewpoint of thermal conductivity and cost. Aluminum oxide is often more preferred.

[0038] In some embodiments, the shaped thermal particles include thermal filler particles retained in an organic binder. In one common method, a mixture including thermal filler particles and a precursor material for the organic binder (organic binder precursor) is placed within a mold cavity in a manufacturing tool and cured (e.g., by heat, light, and / or an initiator or catalyst) or otherwise cured (e.g., by cooling or drying).

[0039] Examples of suitable organic binder precursors include solvent-based thermoplastics and / or thermosetting resins. Examples of suitable thermoplastics include polyolefins, polyesters, thermoplastic polyurethanes, and polyamides. Examples of thermosetting resins include epoxy resins, urethane resins, ring-opening metathesis polymerization (ROMP) cycloolefin resins, isocyanurate resins, free-radical polymerizable resins (e.g., monofunctional and / or polyfunctional acrylates, methacrylates, acrylamides, vinyl ethers, and / or maleates), phenolic resins, urea-formaldehyde resins, aminoplast resins, silicone resins, and crosslinkable polymer latices.

[0040] Details regarding a common method for forming shaped composite particles having an organic binder matrix can be found, for example, in U.S. Patent No. 5,714,259 (Holmes et al.).

[0041] In some embodiments, the shaped thermal filler particles are at least 1 Wm -1 K -1 (W / mK), at least 2 Wm -1 K -1 , at least 2.5 Wm -1 K -1 , at least 5 Wm -1 K -1 , at least 10 Wm -1 K -1 , at least 15 Wm -1 K -1 , at least 20 Wm -1 K-1 , or at least 30Wm -1 K -1 It has a thermal conductivity of [value], but a lower thermal conductivity may also be used.

[0042] Preferably, the molded filler particles have a narrower particle size distribution. For example, the molded filler particles may have a size distribution with a span of 0.1 or less. The span is the amount (D 90 -D 10 ) / D 50 Defined as, in the formula, D 90 This refers to the particle size in the size distribution, which accounts for up to 90 percent of the total volume of the material in the sample. Similarly, D 50 This refers to the particle size in the size distribution, which accounts for up to 50 percent of the total volume of the material in the sample, and D 10 This is the particle size that contains 10 volume percent of the material below that level. 10 , D 50 and D 90 This may be determined, for example, by laser diffraction or microscopic examination.

[0043] The molded heat-filler particles may have any size, but preferably their length is in the size range of 10 micrometers to 2 millimeters (mm), more preferably 25 micrometers to 1 mm, and more preferably 50 micrometers to 1 mm.

[0044] Molded filler particles can be produced, for example, by a molding process using a production tool on which multiple molded mold cavities are provided on its surface. A precursor material (e.g., a sol-gel, slurry, or other dispersion of thermal filler particles in a suitable binder precursor) is used. Once the precursor material is placed in the mold cavity, it is cured (e.g., by drying (inorganic molded filler particles) or by curing (inorganic filler particles in an organic polymer matrix)), and then optionally, in the case of inorganic molded filler particles, by calcination and / or sintering. General details relating to such processes can be found, for example, in U.S. Patent No. 10,315,289(B2) (Fletcher et al.) and No. 5,714,259 (Holmes et al.), the disclosures of which are incorporated herein by reference.

[0045] The thermally conductive compositions according to this disclosure contain 1 to 95 volume percent, preferably 10 to 50 volume percent, and more preferably 10 to 40 volume percent, molded thermal filler particles dispersed in an organic binder. In some embodiments, the molded thermal filler particles constitute 12 to 36 volume percent of the thermally conductive composition.

[0046] In some embodiments, the thermally conductive composition according to the Disclosure may include both molded thermal filler particles and secondary thermal filler particles. In this case, the molded thermal filler particles may constitute more than or less than half of the total volume of the thermal filler package, i.e., more than 50 volume percent or less than 50 volume percent of the total thermal filler. The secondary thermal filler particles may include inorganic materials. Examples of useful particles include particles containing at least one of the following: aluminum oxide (alumina), magnesium oxide, aluminum hydroxide, silicon nitride, zinc oxide, silicon oxide, beryllium oxide, titanium oxide, copper oxide, cuprous oxide, boron nitride, aluminum nitride, silicon carbide, diamond, talc, mica, kaolin, bentonite, magnesite, pyrophyllite, titanium boride, calcium titanate, metals (e.g., copper, aluminum, brass, steel, bronze), graphite, carbon black, graphene, and combinations thereof. Other thermally conductive materials may also be used. Secondary particles may or may not be formed.

[0047] In some embodiments, the organic binder includes grease, such as silicone grease or hydrocarbon grease.

[0048] In some embodiments, the organic binder is formed by curing a curable organic binder precursor. Exemplary curable organic binder precursors include polymerizable resins, such as epoxy resins, urethane resins, ring-opening metathesis polymerized (ROMP) cycloolefin resins, isocyanurate resins, free-radical polymerizable resins (e.g., monofunctional and / or polyfunctional acrylates, methacrylates, acrylamides, vinyl ethers, and / or maleates), phenolic resins, urea-formaldehyde resins, aminoplast resins, silicone resins, and crosslinkable polymer latexes. Polymerizable resins typically further contain, but are not required, a catalyst, crosslinking agent, and / or initiator (thermal initiator and / or photoinitiator) suitable for inducing polymerization. The selection and amount (e.g., 0.01–10% by weight) of the catalyst, crosslinking agent, and / or initiator will depend on the specific chemical system selected and will be within the capabilities of those skilled in the art.

[0049] Examples of curable organic binder precursors also include solvent-based thermoplastic polymers, molten polymers (e.g., molten hot-melt adhesives), and non-crosslinked latex (e.g., acrylic latex). The thermally conductive compositions and / or cured sheets obtained therefrom according to this disclosure are useful, for example, in electronic equipment applications as gap fillers between electronic components (heat sources) and heat sinks.

[0050] In some embodiments, the thermally conductive composition may be provided as a cured sheet, or more typically as a fluid curable composition, which is applied (e.g., using a nozzle dispenser) to at least one of an electronic component or a heat sink, which are then bonded together with the thermally conductive composition provided between them. The thermally conductive composition is then cured to yield a cured thermally conductive composition.

[0051] The thermally conductive compositions according to this disclosure are useful, for example, for conducting thermal energy from a heat source to a heat sink. Referring here to Figure 17, an exemplary assembly 1700 according to this disclosure includes a heat source 1710, a heat sink 1730, and a thermally conductive composition 1720, as described herein, at least partially sandwiched between the heat source and the heat sink.

[0052] Molded heat filler particles can be present in any arrangement within a heat-conductive composition. The term arrangement (or arranged) refers to the position and orientation of the molded heat filler particles. In this specification, molded heat filler particles in a heat-conductive composition are described as aligned if they are located at least substantially along a line. In this specification, molded heat filler particles in a heat-conductive composition are described as oriented if their longitudinal directions are substantially parallel to each other. In some embodiments, molded heat filler particles in a heat-conductive composition sandwiched between a heat source and a heat sink in an assembly are arranged at least substantially aligned with respect to the heat transport direction. In other embodiments, molded heat filler particles in a heat-conductive composition sandwiched between a heat source and a heat sink in an assembly are arranged such that their longitudinal directions are oriented at least substantially parallel to the heat transport direction. In yet another embodiment, molded heat filler particles in a heat-conductive composition sandwiched between a heat source and a heat sink in an assembly are arranged at least substantially aligned with respect to the heat transport direction and such that their longitudinal directions are oriented at least substantially parallel to the heat transport direction. In some embodiments, for ease of processing, the molded heat filler particles are preferably randomly arranged in the thermally conductive composition, but this is not a requirement. In some embodiments, for ease of processing, the molded heat filler particles are preferably randomly positioned in the thermally conductive composition, but this is not a requirement. In some embodiments, for ease of processing, the molded heat filler particles are preferably randomly oriented in the thermally conductive composition, but this is not a requirement. Conveniently, randomly oriented molded particles according to this disclosure have now been found to be unexpectedly effective in improving the important trade-off between thermal energy transfer (quantified, for example, by effective thermal conductivity or composite thermal conductivity) and other properties (e.g., density) compared with known particle shapes such as right cylindrical shapes. However, if desired, the molded heat filler particles may be oriented toward each other or toward the direction of heat transport, as described above.

[0053] Examples of heat sources include semiconductor devices (e.g., diodes, integrated circuits, transistors), resistors, inductors, motors, generators, batteries, and transformers.

[0054] Heat sinks are formed from a thermally conductive material (e.g., metal) that is known in the art and often has a considerable thermal mass relative to the component to be cooled. Often, heat sinks include cooling fins and / or cooling posts. Alternatively, some heat sinks may include integrated channels for the passage of a cooling fluid (e.g., water).

[0055] The purposes and merits of this disclosure are further illustrated by the following non-limiting embodiments, but the specific materials and their quantities, as well as other conditions and details, referenced in these embodiments should not be construed as unduly limiting this disclosure. [Examples]

[0056] Unless otherwise stated, all parts, percentages, ratios, etc., in the examples and elsewhere in this specification are based on weight.

[0057] General Modeling Procedures The particles (shapes A, B, and C) defined in Table 1 and shown in Figures 1A-1D, 2A-2D, and 3A-3D, respectively, were modeled using the CAD software SOLIDWORKS (Dassault Systemes SolidWorks Corporation (Waltham, Massachusetts)). Next, composite materials of these particles, arranged within a bounding box, were generated with various relative particle volumes. Orthogonal cylinders (shapes D and E), defined in Table 1 and schematically shown in Figures 4A-4D, were also modeled as comparative modeling examples, selected to match the volume and length-to-width ratio of particles of shapes A and C, respectively. These CAD assemblies were then loaded into ANSYS v19.1 finite element analysis software (ANSYS, Inc. (Canonsburg, Pennsylvania)), and the effective thermal conductivity of each representative volume was calculated using the steady-state thermal module. For each representative volume, the particle size was calculated to 35 Wm². -1 K -1 The particles are assigned to have a thermal conductivity of 0.16 Wm³. -1 K -1 It was assigned to have the following thermal conductivity:

[0058] To calculate the effective thermal conductivity of a typical volume along a given axis, the boundary box surface is kept at a constant temperature of 273K while 100W / m 2 A constant heat flux was applied to opposing surfaces of the box. All other surfaces were perfectly adiabatic. The average temperature of the opposing surfaces of the box was then examined under steady-state conditions, and from this, the effective thermal conductivity could be calculated using Fourier's law (q = -k∇T), where q is the heat flux, k is the thermal conductivity, and ∇T is the temperature difference across the sample. In this way, the effective thermal conductivity between any opposing surfaces was determined. The effective thermal conductivity as a function of volume fraction or theoretical composite density was compared between particle shapes along different axes. To compare composite densities, 3.95 g / cm³ was used for the particles. 3 Assign a density of 1 g / cm³ to the surrounding volume. 3 We assigned a density to it.

[0059] For modeling examples 1-9, the CAD shapes were constructed by creating 3x3x3 arrays of particles having shapes A, B, or C, with their major axes oriented parallel to the x-axis. The particle spacing in each of the three principal directions (x, y, z) was defined as d. For shapes A, B, or C, a bounding box was superimposed on this array such that the distance between each outer particle and the nearest face of the box was d / 2, as shown in Figures 5, 6, or 7, respectively. Therefore, the dimensions of the bounding box are determined by the particle dimensions and d. The volume fraction of the composite material was changed by varying the value of d while keeping the particle dimensions fixed. The variation in the volume fraction of the composite material arises from the variation in volume between particle designs.

[0060] For modeling examples 10-21, and comparative modeling examples A and B, CAD shapes were constructed consisting of particles with equal distributions, whose major axes are oriented parallel to each of the principal directions (x, y, z). Particle arrays were constructed by aligning either the center of a flat surface (shapes A, B, and C) or the center of volume (shapes D and E) with the coordinates provided in Table 2 (units are unit cell length a), the direction of the major axis, and the surface normal of the flat surface (where applicable).

[0061] Next, a 2a×2a×2a bounding box with the origin at (0,0,0) was superimposed on the array. Then, the volume of all particles outside the box was truncated by the box's surface for shapes A, B, C, D, or E, as shown in Figures 8, 9, 10, 11, or 12, respectively. The particle spacing, and therefore the volume fraction of the particles, was adjusted by changing the unit cell length a. The value of a was chosen so that the particles would not intersect.

[0062] Modeling Example 1 Following a general modeling procedure, shape A was modeled with dimensions of 1.314 × 0.720 × 0.510 mm. 3 The particles were arranged in a 3x3x3 array with uniform spacing within the bounding box, with a particle content of 12.5 volume percent and 1.37 g / cm³. 3 The density was obtained. The particle spacing d was 0.100 mm.

[0063] Modeling Example 2 Following a general modeling procedure, shape A is modeled with dimensions of 1.164 × 0.570 × 0.360 mm. 3 The particles were arranged in a 3x3x3 array with uniform spacing within the bounding box, with a particle content of 25.3 volume percent and 1.75 g / cm³. 3 The density was obtained. The particle spacing d was 0.050 mm.

[0064] Modeling Example 3 Following a general modeling procedure, shape A is modeled with dimensions of 1.044 × 0.450 × 0.240 mm. 3 The particles were arranged in a 3x3x3 array with uniform spacing within the bounding box, with a particle content of 53.7 volume percent and 2.58 g / cm³. 3 The density was obtained. The particle spacing d was 0.010 mm.

[0065] Modeling Example 4 Following a general modeling procedure, shape B was modeled with dimensions of 1.314 × 0.720 × 0.510 mm. 3 The particles are arranged in a 3x3x3 array with uniform spacing within the bounding box, with a particle content of 10.0 volume percent and 1.30 g / cm³. 3 The density was obtained. The particle spacing d was 0.100 mm.

[0066] Modeling Example 5 Following a general modeling procedure, shape B was modeled with dimensions of 1.164 × 0.570 × 0.360 mm. 3 The particles were arranged in a 3x3x3 array with uniform spacing within the bounding box, with a particle content of 20.2 volume percent and 1.60 g / cm³. 3 The density was obtained. The particle spacing d was 0.050 mm.

[0067] Modeling Example 6 Following a general modeling procedure, shape B was modeled with dimensions of 1.044 × 0.450 × 0.240 mm. 3 The particles were arranged in a 3x3x3 array with uniform spacing within the bounding box, with a particle content of 42.8 volume percent and 2.26 g / cm³.3 The density was obtained. The particle spacing d was 0.010 mm.

[0068] Modeling Example 7 Following a general modeling procedure, shape C was modeled with dimensions of 1.314 × 0.720 × 0.510 mm. 3 The particles were arranged in a 3x3x3 array with uniform spacing within the bounding box, with a particle content of 8.7 volume percent and 1.26 g / cm³. 3 The density was obtained. The particle spacing d was 0.100 mm.

[0069] Modeling Example 8 Following a general modeling procedure, shape C was modeled with dimensions of 1.164 × 0.570 × 0.360 mm. 3 The particles were arranged in a 3x3x3 array with uniform spacing within the bounding box, with a particle content of 17.6 volume percent and 1.52 g / cm³. 3 The density was obtained. The particle spacing d was 0.050 mm.

[0070] Modeling Example 9 Following a general modeling procedure, shape C was modeled with dimensions of 1.044 × 0.450 × 0.240 mm. 3 The particles were arranged in a 3x3x3 array with uniform spacing within the bounding box, with a particle content of 37.2 volume percent and 2.10 g / cm³. 3 The density was obtained. The particle spacing d was 0.010 mm.

[0071] Modeling Example 10 Following a general modeling procedure, shape A was distributed in an array within a bounding box described by a unit dimension a of 0.582 mm at the positions shown in Table 2, resulting in a particle content of 10.2 volume percent and a density of 1.30 g / cm³.

[0072] Modeling Example 11 Following a general modeling procedure, shape A is distributed within a bounding box described by a unit dimension a of 0.500 mm at the positions listed in Table 2 and arranged in an array, with a particle content of 16.1 volume percent and 1.48 g / cm³. 3The density was obtained.

[0073] Modeling Example 12 Following a general modeling procedure, shape A is distributed within a bounding box described by a unit dimension a of 0.436 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 24.3 volume percent and 1.72 g / cm³. 3 The density was obtained.

[0074] Modeling Example 13 Following a general modeling procedure, shape A is distributed within a bounding box described by a unit dimension a of 0.386 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 35.1 volume percent and 2.04 g / cm³. 3 The density was obtained.

[0075] Modeling Example 14 Following a general modeling procedure, shape B is distributed within a bounding box described by a unit dimension a of 0.582 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 8.2 volume percent and 1.24 g / cm³. 3 The density was obtained.

[0076] Modeling Example 15 Following a general modeling procedure, shape B is distributed within a bounding box described by a unit dimension a of 0.500 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 12.9 volume percent and 1.38 g / cm³. 3 The density was obtained.

[0077] Modeling Example 16 Following a general modeling procedure, shape B is distributed within a bounding box described by a unit dimension a of 0.436 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 19.4 volume percent and 1.57 g / cm³. 3 The density was obtained.

[0078] Modeling Example 17 Following a general modeling procedure, shape B is distributed within a bounding box described by a unit dimension a of 0.386 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 28.0 volume percent and 1.83 g / cm³. 3 The density was obtained.

[0079] Modeling Example 18 Following a general modeling procedure, shape C is distributed within a bounding box described by a unit dimension a of 0.582 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 7.1 volume percent and 1.21 g / cm³. 3 The density was obtained.

[0080] Modeling Example 19 Following a general modeling procedure, shape C is distributed within a bounding box described by a unit dimension a of 0.500 mm at the positions listed in Table 2 and arranged in an array, with a particle content of 11.2 volume percent and 1.33 g / cm³. 3 The density was obtained.

[0081] Modeling Example 20 Following a general modeling procedure, shape C is distributed within a bounding box described by a unit dimension a of 0.436 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 16.9 volume percent and 1.50 g / cm³. 3 The density was obtained.

[0082] Modeling Example 21 Following a general modeling procedure, shape C is distributed within a bounding box described by a unit dimension a of 0.386 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 24.3 volume percent and 1.72 g / cm³. 3 The density was obtained.

[0083] In Table 1 below, the length and width are determined based on the closed loops defining the intersection points of the plane and the smooth surface, and the thickness is measured as the length of a vector perpendicular to the plane. Radius 1 is the radius of curvature of the closed loop along the edge of the plane at the end of the length of the shape. Radius 2 is the radius of curvature along the closed loop from the plane to the maximum thickness along the major axis of the shape. Radius 3 is the radius of curvature along the maximum width of the particle from one plane to the other. Radius 4 is the radius of curvature along the edge of the plane defining the constricted region at the waist. Particles B and C have waist widths of 70% and 41.4% of their particle width, respectively. Particles B and C have waist thicknesses of 70% and 41.4% of their particle thickness, respectively. [Table 1]

[0084] Comparative Modeling Example A Following a general modeling procedure, shape D is distributed within a bounding box described by a unit dimension a of 0.436 mm, at the positions listed in Table 2, and arranged in an array with a particle content of 16.1 volume percent and 1.48 g / cm³. 3 The density was obtained.

[0085] Comparative Modeling Example B Following a general modeling procedure, shape E was distributed in an array within a bounding box described by a unit dimension a of 0.386 mm at the positions shown in Table 2, resulting in a particle content of 11.2 volume percent and a density of 1.33 g / cm³. [Table 2-1] [Table 2-2] [Table 2-3]

[0086] Table 3 below reports the calculated volume percentage, theoretical density, effective thermal conductivity along the x-axis, and averaged effective thermal conductivity across the x, y, and z axes for Modeling Examples 1-21 and Comparative Examples A and B. [Table 3]

[0087] Figure 13 shows the effective thermal conductivity along the x-axis for composites containing oriented arrays of shapes A, B, and C. The volume fraction of particles required to obtain equivalent effective thermal conductivity is lower for the composite containing shape C than for the composite containing shape B, and even lower for the composite containing shape A. Assuming that the material used to construct the particles of shapes A, B, and C, and the volume surrounding the particles, are the same for all composites, this difference results in the composite containing shape C having the lowest density and the composite containing shape A having the highest density, while achieving equivalent thermal conductivity.

[0088] Figure 14 shows the effective thermal conductivity as the average of three orthogonal axes (x, y, and z) for composites containing oriented array shapes A, B, and C. The volume fraction of particles required to obtain equivalent effective thermal conductivity is lower for the composite containing shape C than for the composite containing shape B, and even lower than for the composite containing shape A.

[0089] Figure 15 shows the effective thermal conductivity as an average along three orthogonal axes (x, y, and z) for composite materials including shapes A, B, and C, for arrays containing particles equally oriented along the x, y, and z axes, as reported in Table 2.

[0090] Typical arrangements of this particular array for shapes A, B, or C are shown in Figures 8, 9, or 10, respectively. Note that the overall orientation of the particles within the array is not biased towards any of the three principal directions, so the effective thermal conductivity is the same regardless of which of the three pairs of opposing faces of the bounding box is measured along. The volume fraction of particles required to obtain equivalent effective thermal conductivity is lower for composites containing shape C than for composites containing shape B, and this is even lower than for composites containing shape A.

[0091] Figure 16 shows the effective thermal conductivity as an average along three orthogonal axes (x, y, and z) for composite materials including shapes A, C, D, and E, with arrays containing particles equally oriented along one of the x, y, and z axes. Representative arrangements of these particular arrays for shapes A, C, D, or E are shown in Figures 8, 10, 11, or 12, respectively. Note that the aspect ratios of shapes D and E are the same as those of shapes A and C, respectively. Thus, composite materials containing particles of the shapes described herein (shapes A and C) have higher effective thermal conductivity than comparative shapes D and E for a given volume fraction.

[0092] Example 1 Molded alumina particles were produced from an aqueous suspension of alumina in water containing a binder and dispersant, using the components and amounts reported in Table 4 below. [Table 4]

[0093] The molded alumina particles were produced by preparing an aqueous suspension of alumina in water containing a binder and a dispersant.

[0094] First, cellulose gum was added very slowly to water and completely dissolved by aggressive high-shear mixing. Next, a solution of polymethacrylate was added, followed by the addition of alumina. After 30 minutes of high-shear mixing, the mixture was transferred to a 1.8 L ball mill (obtained as ROALAX from USStoneware (East Palestine, Ohio)), half-filled with 1 cm cylindrical alumina medium (obtained as BURUNDUM from USStoneware), and a homogeneous suspension was prepared over 24 hours at 175 revolutions per minute. Molding precursor green particles were prepared from the suspension as generally described in U.S. Patent No. 8,701,441 (Kramlich et al.), incorporated herein by reference. The mold used had the dimensions specified for shape A in Table 1. Figure 18 shows the obtained molding precursor particles.

[0095] Molding precursor particles were placed in an alumina combustion boat (obtained as AL-5020 from AdValue Technology (Tucson, Arizona)), and the boat containing the particles was placed in a rapid heating furnace (obtained as 1708 BL from CM Furnaces, Inc. (Bloomfield, New Jersey)). The furnace temperature was increased at a rate of 10°C per minute to a set point of 1400°C, maintained at that temperature for 6 hours, and then decreased at a rate of 10°C per minute to room temperature.

[0096] Example 2 Molded heat-filler particles were prepared in the same manner as in Example 1, except that shape B was used instead of shape A. Figure 19 shows the obtained molded precursor particles.

[0097] Example 3 Molded heat-filler particles were prepared in the same manner as in Example 1, except that shape C was used instead of shape A. Figure 20 shows the obtained molded precursor particles.

[0098] The foregoing statements are intended to enable those skilled in the art to practice the disclosures set forth in the claims and should not be construed as limiting the scope of this disclosure, which is defined by the claims and all their equivalents. In the event of any inconsistency or contradiction between any portion of the incorporated references and this application, the information in this application shall prevail. The following are exemplary embodiments. [Item 1] A molded heat filler particle having an elongated shape defined by a first smooth surface on a plane and a second smooth surface that contacts the first smooth surface on the plane along a loop, wherein at least a portion of the second smooth surface is convex, the loop has a length-to-width ratio of at least 1.5, and the molded heat filler particle has a maximum straight dimension perpendicular to the first smooth surface on the plane, which is no more than half the length of the loop. [Item 2] The molded heat-filler particle according to item 1, wherein the closed section has two rounded ends and a relatively narrow waist positioned between the ends. [Item 3] The closed loop has two semicircular ends connected by two parallel line segments, the molded heat-filler particle according to item 1. [Item 4] The molded heat-filler particle described in item 1, wherein the second smooth surface is completely convex. [Item 5] The molded heat-filler particles have at least 1 Wm -1 K -1 Molded heat-filler particles according to any one of items 1 to 4, having the thermal conductivity of the specified value. [Item 6] The molded heat-filler particles according to any one of items 1 to 5, wherein the molded heat-filler particles comprise at least one of aluminum oxide, magnesium oxide, aluminum hydroxide, zinc oxide, boron nitride, or aluminum nitride. [Item 7] The molded heat-filler particles described in any one of items 1 to 6 are inorganic. [Item 8] The molded heat-filler particles described in item 7 are ceramic. [Item 9] The molded heat-filler particles are molded heat-filler particles according to any one of items 1 to 8, having a homogeneous composition. [Item 10] A thermally conductive composition comprising 1 to 95 volume percent of molded thermal filler particles according to any one of items 1 to 9, dispersed in an organic binder. [Item 11] The thermal conductive composition described in item 10, wherein the thermal conductive composition is cured. [Item 12] The thermal conductive composition according to item 10 or 11, wherein the thermal conductive composition is chemically crosslinked. [Item 13] The thermal conductive composition according to item 10, wherein the thermal conductive composition comprises grease. [Item 14] A thermally conductive composition according to any one of items 10 to 13, further comprising secondary thermally conductive particles. [Item 15] The thermally conductive composition contains at least 1 Wm -1 K -1 A thermally conductive composition according to any one of items 10 to 14, having the thermal conductivity of the following: [Item 16] A thermally conductive composition according to any one of items 10 to 15, wherein the molded thermally conductive particles are randomly oriented. [Item 17] Heat source and heatsink and A thermally conductive composition according to any one of items 11 to 16 is sandwiched at least partially between the heat source and the heat sink, An assembly that includes this.

Claims

1. Molded heat filler particles having an elongated shape defined by a first smooth surface on a plane and a second smooth surface in contact with the first smooth surface on the plane along a loop, wherein at least a portion of the second smooth surface is convex, the loop has a length-to-width ratio of at least 1.5, the molded heat filler particles have a maximum straight dimension perpendicular to the first smooth surface on the plane that is less than or equal to half the length of the loop, and the molded heat filler particles have a thermal conductivity of at least 2 Wm⁻¹ K⁻¹.

2. The molded heat-filler particle according to claim 1, wherein the closed section has two rounded ends and a waist portion positioned between the ends, the width of the waist portion being smaller than the width of each of the two ends, the width being defined in a direction perpendicular to the major axis in a top view of the molded heat-filler particle with the first smooth surface as the bottom surface.

3. The molded heat-filler particle according to claim 1, wherein the closed loop has two semicircular ends connected by two parallel line segments.

4. The molded heat-filler particle according to claim 1, wherein the second smooth surface is completely convex.

5. The molded heat-filler particles according to claim 1, wherein the molded heat-filler particles include at least one of aluminum oxide, magnesium oxide, aluminum hydroxide, zinc oxide, boron nitride, or aluminum nitride.

6. The molded heat-filler particles according to claim 1, wherein the molded heat-filler particles are inorganic.

7. The molded heat-filler particles according to claim 6, wherein the molded heat-filler particles are ceramic.

8. The molded heat-filler particles according to claim 1, wherein the molded heat-filler particles have a homogeneous composition.

9. A thermally conductive composition comprising 1 to 95 volume percent of molded thermal filler particles according to any one of claims 1 to 8, dispersed in an organic binder.

10. The thermal conductive composition according to claim 9, wherein the thermal conductive composition is cured or chemically crosslinked.

11. The thermal conductive composition according to claim 9, wherein the thermal conductive composition comprises grease.

12. A thermally conductive composition according to any one of claims 9 to 11, further comprising secondary thermally conductive particles.

13. The thermal conductive composition according to claim 9, wherein the molded thermal conductive particles are randomly oriented.

14. Heat source and heatsink and A thermally conductive composition according to claim 10, which is at least partially sandwiched between the heat source and the heat sink, An assembly that includes this.

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