Method for forming a multilayer composite

Abstract

A method of forming a composite can include forming a first extrudate and a second extrudate, where the first extrudate comprises an organic polymer and ceramic particles, where the ceramic particles comprise hexagonal boron nitride (hBN) particles; combining the first extrudate and the second extrudate to form a composite comprising two layers; and performing a layer doubling procedure on the composite, where the layer doubling procedure includes splitting and recombining the composite to form a multi-layer composite.

Description

[Technical Field]

[0001] The present disclosure relates to a method for forming a multilayer composite comprising an organic polymer and ceramic particles comprising highly oriented hexagonal boron nitride (hBN). [Background technology]

[0002] Thermally conductive polymer composites play an important role in various industries in the thermal management of electrical devices, as they can significantly reduce operating temperatures and extend device life by dissipating heat to avoid overheating. Typical industries in which thermally conductive polymer composites play an important role include consumer electronics (e.g., mobile phones, tablets), telecommunications infrastructure (e.g., cell towers), LED lighting, hybrid and electric vehicles (power modules), data centers (server boards, switches, monitoring modules, and power supplies), and solar cells.

[0003] There is a need for greater variety and efficiency of materials suitable for thermal management. [Brief explanation of the drawings]

[0004] The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. [Figure 1A] FIG. 1A includes a diagram illustrating a system for forming a multi-layer composite according to one embodiment. [Figure 1B] FIG. 1B includes a diagram illustrating a layer doubling procedure for a coextruded composite including two layers according to one embodiment. [Figure 2A] FIG. 2A includes a diagram showing platelet-type hBN particles contained in the multilayer composite shown in FIG. 2B. [Figure 2B] FIG. 2B includes a diagram showing a cross-cut side view of a multilayer composite having in-plane oriented hBN grains according to one embodiment. [Figure 3A]FIG. 3A includes a graph showing an X-ray spectrum of a multilayer composite having in-plane oriented hBN grains according to one embodiment. [Figure 3B] FIG. 3B is a diagram including a graph showing the relationship between r and the orientation parameter η according to the March-Dollase method. DETAILED DESCRIPTION OF THE INVENTION

[0005] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of features is not necessarily limited to only those features and may include other features that are not expressly listed or that are inherent to such process, method, article, or apparatus.

[0006] As used herein, unless clearly stated to the contrary, "or" refers to an inclusive or, not an exclusive or. For example, condition A or B can be satisfied by any one of the following: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist).

[0007] Additionally, the use of "a" or "an" is used to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one, and the singular also includes the plural unless it is clear that otherwise is meant.

[0008] The present disclosure is directed to a method of forming a composite article, the method can include forming a first extrudate and a second extrudate, where the first extrudate can include an organic polymer and ceramic particles, where the ceramic particles include hexagonal boron nitride (hBN) particles, combining the first extrudate and the second extrudate to form a composite including two layers, and performing a layer doubling procedure on the composite. The layer doubling procedure can include splitting and recombining the composite to form a multilayer composite.

[0009] In one embodiment, the layer doubling procedure may include using at least two layer doubling elements, or at least three layer doubling elements, or at least four layer doubling elements, or at least five layer doubling elements, where each layer doubling element may double the amount of layers in the multilayer composite.

[0010] In one aspect of the method, the multilayer composite can include at least 16 layers, or at least 32 layers, or at least 64 layers.

[0011] In one embodiment, combining the first and second extrudates can be performed by co-extrusion. The method of the present invention is not limited to the co-extrusion of two extrudates, but can also include the co-extrusion of a greater number of extrudates, such as at least three extrudates, or at least four extrudates, or at least five extrudates.

[0012] One embodiment of a system for coextrusion followed by layer doubling is shown in FIG. 1A. The system can include a first extruder (11) and a second extruder (12), both of which can be attached to a coextrusion block (13). Each extruder can produce an extrudate in the form of a liquid stream, referred to herein as a first extrudate and a second extrudate (not shown). The first extrudate and the second extrudate can be combined in the coextrusion block (13) to form a coextrusion stream containing two layers, also referred to herein as an exchangeable composite (not shown). Layer doubling can begin after the coextrusion stream exits the coextrusion block (13) and passes through multiple layer doubling elements (LMEs) (14). Each LME can split (slice) the stream vertically or horizontally to form at least two separate streams. The split streams can be further compressed, expanded, and recombined, which can result in doubling the amount of layers in the composite after passing through one LME. Thus, each pass through the LEM can at least double the layer of the composite. The system can further include a die (15) at the end, and after passing through the die (15), a multi-layer composite (16) is obtained.

[0013] 1B shows an embodiment of how the coextrusion stream can be split, expanded, and recombined into a four-layer composite by passing it through the first layer multiplication element. Further doubling of the layer quantity to eight layers can be achieved by passing an additional LME (two LMEs total), and further doubling of the quantity to 2(n+1) layers can be achieved by passing n quantities of LMEs.

[0014] An advantage of the coextrusion process involving layer doubling is that the stress applied during layer doubling can orient the hBN particles with high alignment along the length (also referred to herein as in-plane) of the formed sheet. When using platelet-shaped hBN particles with a large length (L) relative to their thickness (T), as shown in Figure 2A, alignment during the layer doubling process parallel to the length of the formed composite sheet can occur, as also shown in Figure 2B. Figure 2B shows a cross-section of a multilayer composite (21) in the form of a sheet with four layers (22a, 22b, 22c, and 22d), each containing hBN particles (23) and an organic polymer (24) that are highly oriented in the plane (x direction) of the sheet.

[0015] In certain embodiments, the first composition for forming the first extrudate and the second composition for forming the second extrudate can contain the same components in the same amounts, such that the first extrudate and the second extrudate can have the same materials.

[0016] In another embodiment, the components and concentrations of the first and second compositions may be different. For example, only the first composition may contain hBN particles, and the second composition may not contain hBN particles. In another example, the amount of hBN particles and / or the average particle size of the hBN particles may differ between the first and second compositions.

[0017] In certain further embodiments, the first and second compositions can further comprise additives, such as surfactants, dyes, viscosity modifiers, or stabilizers.

[0018] In one embodiment, the method of the present disclosure can be adapted so that the amount of hBN particles in the formed multilayer composite can be at least 10% by volume, or at least 15% by volume, or at least 20% by volume, or at least 25% by volume, or at least 30% by volume, or at least 35% by volume, or at least 40% by volume, or at least 45% by volume, or at least 50% by volume, based on the total volume of the multilayer composite. In another aspect, the amount of hBN particles in the multilayer composite can be 70% by volume or less, or 60% by volume or less, or 50% by volume or less, or 40% by volume or less, or 35% by volume or less, based on the total volume of the multilayer composite.

[0019] In further embodiments, the average particle size (D50) of the hBN particles used to form the multilayer composite can be at least 1 micron, or at least 5 microns, or at least 10 microns, or at least 15 microns, or at least 20 microns, or at least 25 microns, or at least 30 microns, or at least 35 microns, or at least 40 microns. In other embodiments, the average particle size (D50) of the hBN particles can be 60 microns or less, or 55 microns or less, or 50 microns or less, or 45 microns or less, or 40 microns or less, or 35 microns or less. As used herein, when platelet-shaped hBN particles are used, average particle size corresponds to the average length (L) of the hBN particles, also referred to herein as the diameter.

[0020] In one embodiment, the average aspect ratio of length (L) to thickness (T) of the hBN particles can be at least 5, or at least 10, or at least 20, or at least 30, or at least 40, or at least 50, or at least 60, or at least 70, or at least 80, or at least 90, or at least 100, or at least 110, or at least 120. In another embodiment, the average aspect ratio of the hBN particles can be 200 or less, or 120 or less, or 100 or less, or 80 or less, or 50 or less, or 40 or less, or 35 or less, or 30 or less, or 20 or less.

[0021] In further embodiments, the thickness of the hBN particles can be at least 0.05 microns, or at least 0.1 microns, or at least 1 micron, hi other embodiments, the thickness can be 5 microns or less, or 3 microns or less, or 1 micron or less.

[0022] In further embodiments, a combination of hBN particles of different sizes can be used. In one aspect, the hBN particles can include a first portion of hBN particles having an average particle size of 3-7 microns, a second portion of hBN particles having an average particle size of 12-20 microns, and a third portion of hBN particles having an average particle size of 25-35 microns. The volume ratio of the first portion to the second and third portions can be in the range of 0.7:1.0:1.3-1.3:1.0:0.7, or 0.8:1.0:1.2-1.2:1.0:0.8, or 0.9:1.0:1.1-1.1:1.0:0.9.

[0023] Combining the first extrudate and the second extrudate can include coextrusion at a temperature above the melting temperature of the organic polymer. In one embodiment, the temperature during coextrusion can be at least 15°C and no more than 135°C above the melting temperature of the organic polymer. In certain embodiments, the temperature is maintained after coextrusion to avoid solidification, and the coextruded stream (also referred to herein as the composite) is passed through multiple layer multiplication elements to perform a layer multiplication procedure. After passing through the layer multiplication elements, the resulting multilayer composite can be solidified by reducing the temperature or by subjecting it to the required curing conditions.

[0024] In one embodiment, the method of the present disclosure may be adapted to continuously form a multilayer composite.

[0025] It has been surprisingly observed that the disclosed method can align platelet-shaped hBN particles with a high degree of orientation in the in-plane direction of the formed multilayer composite. Without being bound by theory, during each layer-doubling step, the liquid stream (also referred to herein as the composite) experiences a substantially expanding flow similar to fluid flow in a converging channel. As a result, the hBN platelet particles are highly aligned in the in-plane direction, as shown in Figure 3A.

[0026] In one embodiment, the March-Dollase orientation parameter η of the hBN particles in the in-plane direction of the multilayer body can be at least 50%, or at least 53%, or at least 55%, or at least 57%, or at least 60%, or at least 61%, or at least 62%, or at least 63%. As used herein, the March Dollase orientation parameter is a quantitative expression for characterizing the degree of alignment of the hBN particles within the multilayer composite. The March Dollase orientation parameter is obtained by performing X-ray diffraction measurements and analyzing the X-ray spectrum according to the March-Dollase method (see detailed description in the Examples). It has been found that the March Dollase orientation parameter η can be an appropriate quantitative expression for characterizing the degree of alignment of the dispersed hBN particles within the multilayer composite. A March Dollase orientation parameter η of 50% or greater corresponds to a high degree of orientation (also referred to herein as alignment) of the hBN particles.

[0027] A high degree of alignment can correspond to a high thermal conductivity of the multilayer composite. In one embodiment, the in-plane thermal conductivity of the multilayer composite can be at least 2 W / mK, or at least 3 W / mK, or at least 4 W / mK, or at least 5 W / mK, or at least 7 W / mK, or at least 10 W / mK, or at least 15 W / mK, or at least 20 W / mK. In another embodiment, the in-plane thermal conductivity of the multilayer composite can be 40 W / mK or less, or 30 W / mK or less, or 20 W / mK or less, or 10 W / mK or less.

[0028] In one embodiment, the organic polymeric material of the first extrudate and the second extrudate can include a thermoplastic polymer, such as polyethylene, polypropylene, polystyrene, polyurethane, polyacrylate, polyester, polycarbonate, polyimide, polybutylene terephthalate (PBT), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyamide, liquid crystal polymer (LCP), polyacrylonitrile (PAN), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polysulfone, polyethersulfone, polyphenylene oxide (PPO), polyetherimide, thermoplastic elastomer (TPE, olefinic or styrenic), fluoropolymer, such as polyvinylidene fluoride (PVDF), perfluoroalkoxyalkane (PFA), fluorinated ethylenepropylene (FEP), or ethylenetetrafluoroethylene (ETFE), or any copolymer thereof, or any combination thereof.

[0029] In another embodiment, the organic polymer may be a polymerizable polymer containing functional groups, in which case the method may be adapted so that the majority of the curing of the polymerizable monomer occurs after combining the first and second extrudates and passing through the layer multiplication element.

[0030] In certain aspects, the polymerizable polymer can include a silicone polymer, or an acrylate polymer, or an epoxy polymer.

[0031] In a specific embodiment, the polymerizable polymer can be a silicone polymer containing vinyl groups. In a non-limiting embodiment, the silicone polymer containing vinyl groups can be polymerized by crosslinking using a crosslinking agent. In a specific embodiment, the weight ratio of the silicone polymer containing vinyl groups to the crosslinking agent can be 0.5 to 5, or 1 to 3, or 1 to 2.

[0032] In one embodiment, the hBN particles can be surface functionalized before combining them with the organic polymer. For example, the surface functionalization of the hBN particles can include oxygen plasma treatment, silane surface functionalization, fluorine surface functionalization, epoxy surface functionalization, amine surface functionalization, or hydroxyl surface functionalization. Surface functionalization of the hBN particles can be advantageous for achieving higher solids loading of the hBN particles in the organic polymer and for improving the flow behavior of the extrudate and the formed composite for layer multiplication. In certain embodiments, prior to surface functionalization, the hBN particles can be exfoliated and / or activated by treatment with an OH-introducing compound.

[0033] In certain embodiments, the organic polymer can be silicone, and the hBN particles can be surface-functionalized with silane, via oxygen plasma treatment, or via fluorine surface functionalization. Non-limiting examples of silane compounds include SiH or aminosilane. Examples of fluorine surface functionalization include plasma treatment with CF, or CHF, SF, or C2F6.

[0034] In another embodiment, the organic polymer may be an epoxy polymer, and the hBN particles may be surface-functionalized with an epoxy compound, an amine, or a hydroxyl group. Non-limiting examples of introducing an epoxy compound include plasma treatment with glycidyl methacrylate or plasma treatment with allyl glycidyl ether. Examples of amine functionalization include plasma treatment with allylamine or 3-(aminopropyl)triethoxysilane.

[0035] In a further embodiment, the organic polymer may be polyethylene and the hBN particles may be subjected to fluorine surface functionalization or silane functionalization.

[0036] In yet another embodiment, the organic polymer can be thermoplastic polyurethane (TPU) or polybutylene terephthalate (PBT), and the hBN particles can be functionalized with epoxy compounds, amines, or hydroxyl groups. In certain further embodiments, the PBT can also be surface functionalized by oxygen plasma treatment, air plasma treatment, treatment with boric acid / urea in combination with heat treatment, or treatment with boric acid / melamine in combination with heat treatment.

[0037] In one embodiment of the method, the thickness of the multilayer composite can be at least 10 microns, or at least 30 microns, or at least 50 microns, or at least 100 microns, or at least 150 microns, or at least 200 microns, or at least 250 microns. In another embodiment, the thickness of the multilayer composite can be 2500 microns or less, or 1000 microns or less, or 500 microns or less, or 300 microns or less, or 100 microns or less.

[0038] In yet another embodiment of the method, the thickness of each layer of the multilayer composite can be at least 0.5 microns, or at least 1 micron, or at least 3 microns, or at least 5 microns, or at least 8 microns, or at least 10 microns. In another aspect, the thickness of each layer can be 20 microns or less, or 10 microns or less, or 7 microns or less, or 5 microns or less, or 3 microns or less, or 2 microns or less, or 1 micron or less.

[0039] In certain embodiments, the thickness of each layer of the multilayer composite is at least the size of the average thickness of the hBN particles, and can be no more than two times the average (D50) size of the hBN particles, or no more than five times the average size of the hBN particles, or no more than ten times the average size of the hBN particles.

[0040] The multilayer composite formed by the present method can have electrically insulating properties. In one embodiment, the electrical volume resistivity of the multilayer composite can be at least 1.0E+12 Ω m, or at least 1.0E+13 Ω m, or at least 1.0E+14 Ω m.

[0041] In another embodiment, the multilayer composite can be continuously formed in the form of a multilayer sheet. The multilayer sheet can be folded to form a multilayer stack. In one aspect, the multilayer stack can have a height of at least 1 cm, or at least 10 cm, or at least 20 cm, or at least 30 cm. The multilayer stack can be pressed and cured (if necessary) to form the composite stack. If the organic polymer is a thermoplastic polymer and has already been used as a starting material in forming the coextrusion melt stream, for example, thermoplastic polyurethane (TPU), curing may not be required. Composite slices can then be cut along the height direction (z) of the composite stack, and the composite slices can have a thermal conductivity perpendicular to the cutting direction (through-plane) of at least 3 W / mK, or at least 5 W / mK, or at least 7 W / mK, or at least 10 W / mK, or at least 12 W / mK, or at least 14 W / mK, or at least 16 W / mK, or at least 18 W / mK, or at least 20 W / mK.

[0042] Many different aspects and embodiments are possible. Some of these aspects and embodiments are described herein. After reading this specification, those skilled in the art will understand that these aspects and embodiments are merely illustrative and do not limit the scope of the invention. An embodiment may follow any one or more of the embodiments listed below.

[0043] Embodiment Embodiment 1. A method of forming a composite article, comprising: forming a first extrudate and a second extrudate, the first extrudate comprising an organic polymer and ceramic particles, the ceramic particles comprising hexagonal boron nitride (hBN) particles; combining the first extrudate and the second extrudate to form a composite comprising two layers; performing a layer doubling procedure on the composite, the layer doubling procedure including splitting and recombining the composite to form a multi-layer composite.

[0044] Embodiment 2. The method of embodiment 1, wherein the layer doubling step comprises using at least two layer doubling elements, or at least three layer doubling elements, or at least four layer doubling elements, or at least five layer doubling elements, each layer doubling the amount of layers in the multilayer composite.

[0045] Embodiment 3. The method of embodiment 1 or 2, wherein the multilayer composite comprises at least 16 layers, or at least 32 layers, or at least 64 layers.

[0046] Embodiment 4. The method of any one of embodiments 1-3, wherein the first extrudate and the second extrudate comprise an organic polymeric material and ceramic particles, and the ceramic particles comprise hexagonal boron nitride (hBN) particles.

[0047] Embodiment 5. The method of embodiment 4, wherein the material of the first extrudate and the material of the second extrudate are the same.

[0048] Embodiment 6. The method of embodiment 1, wherein the second extrudate does not contain hBN particles.

[0049] Embodiment 7. The method of any one of embodiments 1-6, wherein the amount of hBN particles in the multilayer composite is at least 10% by volume, or at least 15% by volume, or at least 20% by volume, or at least 25% by volume, or at least 30% by volume, or at least 35% by volume, or at least 40% by volume, or at least 45% by volume, or at least 50% by volume, based on the total volume of the multilayer composite.

[0050] Embodiment 8. The method of any one of embodiments 1-7, wherein the amount of hBN particles in the multilayer composite is 70% by volume or less, or 60% by volume or less, or 50% by volume or less, or 40% by volume or less, or 35% by volume or less, based on the total volume of the multilayer composite.

[0051] Embodiment 9. The method of any one of embodiments 1-8, wherein the average particle size (D50) of the hBN particles is at least 1 micron, or at least 5 microns, or at least 10 microns, or at least 15 microns, or at least 20 microns, or at least 25 microns, or at least 30 microns, or at least 35 microns, or at least 40 microns.

[0052] Embodiment 10. The method of any one of embodiments 1-9, wherein the average particle size (D50) of the hBN particles is 60 microns or less, or 55 microns or less, or 50 microns or less, or 45 microns or less, or 40 microns or less, or 35 microns or less.

[0053] Embodiment 11. The method of any one of embodiments 1-10, wherein the average length-to-thickness aspect ratio of the hBN particles is at least 5, or at least 10, or at least 20, or at least 30, or at least 40, or at least 50, or at least 60, or at least 70, or at least 80, or at least 90, or at least 100, or at least 110, or at least 120.

[0054] Embodiment 12. The method of any one of embodiments 1-11, wherein the average aspect ratio of the hBN particles is 200 or less, or 120 or less, or 80 or less, or 50 or less, or 40 or less, or 35 or less, or 30 or less, or 20 or less.

[0055] Embodiment 13. The method of embodiment 11 or 12, wherein the aspect ratio of the hBN particles is at least 5 and no more than 50, or at least 5 and no more than 35, or at least 7 and no more than 20.

[0056] Embodiment 14. The method of any one of embodiments 1-13, wherein the thickness of the hBN particles is at least 0.05 microns, or at least 0.1 microns, or at least 1 micron.

[0057] Embodiment 15. The method of any one of embodiments 1-14, wherein the thickness of the hBN particles is 5 microns or less, or 3 microns or less, or 1 micron or less.

[0058] Embodiment 16. The method of any one of embodiments 1 to 15, wherein the in-plane thermal conductivity of the multilayer composite is at least 2 W / mK, or at least 3 W / mK, or at least 4 W / mK, or at least 5 W / mK, or at least 7 W / mK, or at least 10 W / mK.

[0059] Embodiment 17. The method of any one of embodiments 1-16, wherein the in-plane thermal conductivity of the multilayer composite is 40 W / mK or less, or 30 W / mK or less, or 20 W / mK or less, or 10 W / mK or less.

[0060] Embodiment 18. The method of any one of embodiments 1 to 17, wherein the organic polymer comprises a thermoplastic polymer.

[0061] Embodiment 19. The method of embodiment 18, wherein the thermoplastic polymer comprises polyethylene, polypropylene, polystyrene, polyurethane, polyacrylate, polyester, polycarbonate, polyimide, polybutylene terephthalate (PBT), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyamide, liquid crystal polymer (LCP), polyacrylonitrile (PAN), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polysulfone, polyethersulfone, polyphenylene oxide (PPO), polyetherimide, thermoplastic elastomer (TPE, olefin-based or styrenic), fluoropolymer such as polyvinylidene fluoride (PVDF), perfluoroalkoxyalkane (PFA), fluorinated ethylenepropylene (FEP), or ethylenetetrafluoroethylene (ETFE), or any copolymer thereof, or any combination thereof.

[0062] Embodiment 20. The method of any one of embodiments 1 to 17, wherein the organic polymer is a polymerizable polymer comprising a functional group.

[0063] Embodiment 21. The method of embodiment 20, wherein the polymerizable polymer comprises a silicone polymer, or an acrylate polymer, or an epoxy polymer.

[0064] Embodiment 22. The method of embodiment 21, wherein the polymerizable polymer is a silicone polymer containing vinyl groups.

[0065] Embodiment 23. The method of any one of embodiments 1 to 22, wherein the March-Dollase orientation parameter η of the hBN grains in the in-plane direction of the composite slice is at least 50%, or at least 55%, or at least 60%.

[0066] Embodiment 24. The method of any one of embodiments 1 to 23, wherein the thickness of the multilayer composite is at least 10 microns, or at least 50 microns, or at least 250 microns.

[0067] Embodiment 25. The method of any one of embodiments 1-24, wherein the thickness of the multilayer composite is 2500 microns or less, or 1000 microns or less, or 500 microns or less.

[0068] Embodiment 26. The method of any one of embodiments 1 to 25, wherein the thickness of each layer of the multilayer composite is at least 0.5 microns, or at least 1 micron, or at least 3 microns, or at least 5 microns, or at least 8 microns, or at least 10 microns.

[0069] Embodiment 27. The method of any one of embodiments 1-26, wherein the thickness of each layer of the multilayer composite is 20 microns or less, or 10 microns or less, or 7 microns or less, or 5 microns or less, or 2 microns or less, or 1 micron or less.

[0070] Embodiment 28. The method of any one of embodiments 1 to 27, wherein the thickness of each layer of the multilayer composite is 1 micron or less, or 10 microns or less, or 20 microns or less.

[0071] Embodiment 29. The method of any one of embodiments 1 to 28, wherein the thickness of each layer of the multilayer composite is at least the size of the average thickness of the hBN particles and is no more than 10 times the average (D50) size of the hBN particles, or no more than 5 times the average size of the hBN particles, or no more than 3 times, or no more than 2 times.

[0072] Embodiment 30. The method of any one of embodiments 1 to 29, wherein the thickness (T) of the hBN particles is at least 0.05 microns, or at least 0.1 microns, or at least 1 micron.

[0073] Embodiment 31. The method of any one of embodiments 1 to 30, wherein the thickness (T) of the hBN particles is 5 microns or less, or 3 microns or less, or 1 micron or less.

[0074] Embodiment 32. The method of any one of embodiments 1 to 31, wherein the electrical volume resistivity of the multilayer composite is at least 1.0E+12 Ω·m, or at least 1.0E+13 Ω·m, or at least 1.0E+14 Ω·m.

[0075] Embodiment 33. The method of any one of embodiments 1 to 32, wherein combining the first extrudate and the second extrudate comprises coextrusion at a temperature above the melting point of the organic polymer.

[0076] Embodiment 34. The method of any one of embodiments 1 to 33, wherein the temperature during coextrusion is at least 15°C and no more than 135°C above the melting temperature of the organic polymer.

[0077] Embodiment 35. The method of any one of embodiments 1 to 34, wherein the method is adapted to continuously form a multilayer composite.

[0078] Embodiment 36. The method of any one of embodiments 1 to 35, wherein the multilayer composite is a multilayer composite sheet.

[0079] Embodiment 37. The method of any one of embodiments 1 to 36, further comprising forcing the multi-layer body through a die under pressure before solidifying or curing the organic polymer.

[0080] Embodiment 38 The method of any one of embodiments 1 to 37, wherein the hBN particles comprise a multimodal particle distribution.

[0081] Embodiment 39. The method of embodiment 34, wherein the multimodal particle distribution is bimodal or trimodal.

[0082] Embodiment 40 The method of embodiment 34 or 35, wherein the hBN particles comprise a combination of three different particle size ranges.

[0083] Embodiment 41. The method of any one of embodiments 34-36, wherein the hBN particles comprise a first portion of hBN particles having an average particle size of 3-7 microns, a second portion of hBN particles having an average particle size of 12-20 microns, and a third portion of hBN particles having an average particle size of 25-35 microns.

[0084] Embodiment 42. The method of embodiment 37, wherein the volume ratio of the first part to the second part to the third part is in the range of 0.7:1.0:1.3 to 1.3:1.0:0.7, or 0.8:1.0:1.2 to 1.2:1.0:0.8, or 0.9:1.0:1.1 to 1.1:1.0:0.9.

[0085] Embodiment 43. The method of any one of embodiments 1 to 42, further comprising surface functionalizing the hBN particles prior to forming the first extrudate and the second extrudate.

[0086] Embodiment 44. The method of embodiment 39, wherein the surface functionalization of the hBN particles comprises oxygen plasma treatment, or silane surface functionalization, or fluorine surface functionalization, or epoxy surface functionalization, or amine surface functionalization, or hydroxyl surface functionalization. [Example]

[0087] The following non-limiting examples illustrate the present invention.

[0088] Example 1 Successive formation of multilayer composites containing aligned hBN particles.

[0089] Two sets of extruders (Extruder A and Extruder B) are used, each containing the same liquid mixture of 37% by volume of hBN particles (average particle size 30 microns) dispersed in silicone rubber (AB specialty Indium H110-O) and 2,4-dichlorobenzoyl peroxide (50% in polydimethylsiloxane) as the crosslinker, with a crosslinker to silicone weight percent ratio of approximately 1 to 1.5. The liquid mixture further contains 2-5% by weight of a surfactant or surfactant combination.

[0090] The mixture from Extruder A is used to form a first extrudate, and the mixture from Extruder B is used to form a second extrudate, and the first and second extrudates are combined into a two-layer composite. While the two-layer composite is still in the form of a fluid stream, it is subjected to a layer doubling procedure using a combination of five layer doubling elements. After passing through the five layer doubling elements, a multilayer composite sheet (also referred to herein as a multilayer composite) containing 64 layers is obtained.

[0091] Each layer of the successively formed hBN composite sheet has a thickness of about 3.0 microns, for a total thickness of the sheet of about 190 microns. The thermal conductivity of the sheet is at least 5 W / mK.

[0092] The orientation of the hBN grains in the planar direction of the multilayer composite was measured via X-ray analysis as described below, and the orientation parameter η was calculated via the March-Dollase method, where η is greater than 60%.

[0093] Example 2 Example 2 is carried out in the same manner as Example 1, except that the hBN particles are surface functionalized with silane. The thermal conductivity and orientation parameter have been measured and are expected to be greater than those of the multilayer composite sheet of Example 1.

[0094] Example 3 Example 3 is carried out in the same manner as Example 1, except that various thermoplastic polymers are used, specifically polyethylene, thermoplastic polyurethane (TPU), polybutylene terephthalate (PBT), and epoxy polymer.

[0095] Furthermore, in an additional series of experiments, hBN particles were surface functionalized. The types of surface functionalization and the corresponding organic polymers are listed in Table 1. The thermal conductivity of the resulting multilayer sheets was measured and is expected to be greater than that obtained using non-surface-functionalized hBN.

[0096] [Table 1]

[0097] Example 4 Continuous folding of multi-layer composite sheets.

[0098] The successively formed multi-layer composite sheets of Example 1 or Example 2 are successively folded to form a multi-layer stack, which is subjected to compression treatment under pressure and then optionally heat treated to cure the organic polymer.

[0099] Composite slices 0.5 mm thick are cut from the pressed and cured multilayer stack with a diamond wire. The composite slices are analyzed for thermal conductivity through their thickness (z). The thermal conductivity across the thickness (through-plane) of the composite slice is at least 90% the same as the in-plane thermal conductivity of the multilayer composite obtained in Examples 1 and 2.

[0100] Thermal conductivity measurement Thermal conductivity is measured using a transient plane source device (TPS 2500 S, Hot Disk Instruments). The instrument and measurements are designed by placing a temperature sensor between two samples of the test material, introducing a heat pulse to the surface of the test sample, measuring the temperature change, and calculating the thermal conductivity based on that. The temperature sensor is a Paton-insulated Hot Disk® sensor model 5501 (radius 6.4 mm). The heat pulse is varied from 60 to 150 mW for 3 to 15 seconds to ensure that the conductivity value remains constant regardless of the pulse parameters. Measurements are performed in accordance with the Hot Disk® Hot Disk Thermal Constants Analyser Instruction Manual (2015-04-15). The Slab Module is used for in-plane measurements, and the anisotropic method is used for through-plane values.

[0101] Measurement of the March-Dollase orientation parameter η X-ray diffraction analysis is performed to determine the degree of orientation (also referred to herein as alignment) of the hBN particles within the composite. For in-plane aligned hBN platelets, the primary plane of interest was the in-plane direction parallel to the surface (e.g., the (002) plane). First, a 2D XRD spectrum is obtained after spot diffraction of the sample with a Bruker D8 diffractometer using focused Cu Kα radiation (λ = 1.5418 Å) in step-scan mode at angular positions ranging from 10° to 80°. One-dimensional (1D) XRD spectra are then obtained by integration of the 2D spectrum using the built-in capabilities of the EVA software from Bruker. Using the Rietveld peak fitting method, the (002) peak intensity of the oriented hBN pattern is compared to a database pattern of unoriented hBN to obtain a quantifiable measure of orientation. A typical XRD spectrum showing the (002) peak is shown in Figure 2A. As more (002) hBN planes align parallel to the surface, the relative intensity of the (002) experimental peak increases compared to the database peak.

[0102] Peak fitting of the XRD patterns is performed using Peak Topas quantification software from Bruker. The Topas software has a built-in refinement function to determine the March-Dollase parameters using the March-Dollase function W(α), see equation (1).

[0103]

number

[0104] The degree of preferred orientation η(r) as a function of the March-Dollase parameter r is calculated according to equation (2) below:

[0105]

number

[0106] The graph shown in Figure 2B illustrates the relationship between the March-Dollase parameter r and the degree of preferred orientation η(r), also referred to herein as the "March-Dollase orientation parameter η." The solid line in the graph represents the actual measured curve, while the dashed line represents the curve converted to a simplified linear trend line.

[0107] Measurement of electrical volume resistivity The electrical resistivity of the samples is determined according to ASTM D257.

[0108] In the foregoing specification, the concepts have been described with reference to specific embodiments. However, those skilled in the art will recognize that various modifications and changes can be made without departing from the scope of the invention as set forth in the following claims. Therefore, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention.

Claims

1. 1. A method of forming a composite article, comprising: forming a first extrudate and a second extrudate, the first extrudate comprising an organic polymer containing hexagonal boron nitride (hBN) particles, and the second extrudate comprising an organic polymer and hBN particles; combining the first extrudate and the second extrudate to form a composite comprising two layers; performing a layer doubling procedure on the composite, the layer doubling procedure comprising splitting and recombining the composite to form a multi-layer composite; Including, 10. A method according to claim 1, wherein the amount of hBN particles is at least 10% by volume and no more than 40% by volume, based on the total volume of the multilayer composite, the multilayer composite being in the form of a sheet, and the hexagonal boron nitride particles being oriented in a plane within the sheet.

2. 10. The method of claim 1, wherein the layer doubling procedure includes using at least two layer doubling elements, or at least three layer doubling elements, or at least four layer doubling elements, or at least five layer doubling elements, each layer doubling the amount of layers in the multilayer composite.

3. The method of claim 2 wherein the multilayer composite comprises at least 16 layers.

4. 4. The method of claim 1, wherein the amount of hBN particles in the multilayer composite is at least 20% by volume, based on the total volume of the multilayer composite.

5. 4. The method of any one of claims 1 to 3, wherein the hBN particles have an average particle size (D50) of at least 1 micron and no more than 60 microns.

6. 4. The method of claim 1, wherein the hBN particles have an average length-to-thickness aspect ratio of at least 5.

7. A method according to any one of claims 1 to 3, wherein the multilayer composite has an in-plane thermal conductivity of at least 3 W / mK.

8. The method of any one of claims 1 to 3, wherein the organic polymer comprises a thermoplastic polymer.

9. 9. The method of claim 8, wherein the thermoplastic polymer comprises polyethylene, polypropylene, polystyrene, polyurethane, polyacrylate, polyester, polycarbonate, polyimide, polybutylene terephthalate (PBT), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyamide, liquid crystal polymer (LCP), polyacrylonitrile (PAN), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polysulfone, polyethersulfone, polyphenylene oxide (PPO), polyetherimide, thermoplastic elastomer (TPE, olefinic or styrenic), fluoropolymer, or any combination thereof.

10. The method of any one of claims 1 to 3, wherein the organic polymer comprises a polymerizable polymer containing a functional group.

11. The method of claim 10, wherein the polymerizable polymer is a silicone polymer containing vinyl groups.

12. 4. The method of claim 1, wherein the March-Dollase orientation parameter η of the hBN grains in the in-plane direction of the multilayer composite is at least 50%.

13. The method of any one of claims 1 to 3, wherein the multilayer composite has a thickness of at least 10 microns.

14. 4. The method of any one of claims 1 to 3, wherein the multilayer composite has an electrical volume resistivity of at least 1.0E+12 Ω·m.

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