METHOD OF FORMING A MULTI-LAYER COMPOSITE BODY

FIELD OF THE DISCLOSURE

The present disclosure relates to a method of forming a multi-layer composite body including an organic polymer and ceramic particles comprising hexagonal boron nitride (hBN) with a high degree of orientation.

BACKGROUND

Thermally conductive polymer composites play an essential role in a variety of industries with regard to thermal management of electrical devices, as they can significantly lower the operating temperature and prolong the life of a device by dissipating heat to avoid overheating. Typical industries wherein thermally conductive polymer composites play a critical role include consumer electronics (e.g., cell phones, tablets), telecommunication infrastructure (e.g., cell towers), LED lighting, hybrid, and electric vehicles (power modules), data centers (server boards, switches, supervisor modules, and power supplies), and solar cells.

There exists a need to further enhance the variety and efficiency of materials suitable for thermal management.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

FIG. 1A includes a line drawing illustrating a system for forming a multi-layer composite body according to one embodiment.

FIG. 1B includes a line drawing illustrating the layer multiplying procedure of a co-extruded composite body including two layers according to one embodiment.

FIG. 2A includes a line drawing illustrating a platelet type hBN particle contained in the multi-layer composite body illustrated in FIG. 2B.

FIG. 2B includes a line drawing illustrating a side view of a cross-cut of a multi-layer composite body having in-plane oriented hBN particles according to one embodiment.

FIG. 3A includes a graph showing an X-ray spectrum of a multi-layer composite body comprising in-plane oriented hBN particles according to one embodiment.

FIG. 3B includes a graph showing a relationship between r and orientation parameter f according to the March-Dollase method.

DETAILED DESCRIPTION

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 comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such process, method, article, or apparatus.

As used herein, and unless expressly stated to the contrary, “or” refers to an inclusive-or and not to an exclusive-or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

Also, the use of “a” or “an” are employed 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 obvious that it is meant otherwise.

The present disclosure is directed to a method of forming a composite article, wherein the method can comprise: forming a first extrudate and a second extrudate, wherein the first extrudate may comprise an organic polymer and ceramic particles, the ceramic particles including hexagonal boron nitride (hBN) particles; combining the first extrudate and the second extrudate to form a composite body including two layers; and conducting a layer multiplying procedure on the composite body. The layer multiplying procedure can comprise dividing and recombining the composite body to form a multi-layer composite body.

In one embodiment, the layer multiplying procedure can comprise using at least two layer multiplying elements, or at least three layer multiplying elements, or at least four layer multiplying elements, or at least five layer multiplying elements, wherein each layer multiplying element may double an amount of layers in the multi-layer composite body.

In one aspect of the method, the multi-layer composite body can comprise at least at least 16 layers, or at least 32 layers, or at least 64 layers.

In one embodiment, combining the first extrudate and the second extrudate can be conducted by co-extrusion. The method of the present invention is not limited to co-extrusion of two extrudates, but can also comprise co-extrusion of a larger plurality of extrudates, such as at least three extrudates, or at least four extrudates, or at least five extrudates.

An embodiment of a system for conducting co-extrusion followed by layer-multiplying is illustrated in FIG. 1A. The system can comprise a first extruder (11) and a second extruder (12), wherein both extruders can be attached to a co-extrusion block (13). Each extruder can produce an extrudate in form of a liquid stream, herein called first extrudate and second extrudate (not shown). The first extrudate and the second extrudate can be combined in the co-extrusion (13) block to a co-extruded stream containing two layers, herein also called interchangeable composite body (not shown). The layer multiplying may begin after the co-extruded stream is leaving the co-extrusion block (13) and passing a plurality of layer multiplying elements (LME) (14). In each LME, the stream can be divided (sliced) vertically or horizontally to form at least two divided streams. The divided streams can be further compressed and stretched and recombined, which may result in doubling of the amount of layers of the composite body after passing one LEM. Accordingly, with each passing of a LEM, the layers of the composite body can be at least doubled. The system can further contain at the end a die (15); and after passing the die (15), the multi-layer composite body (16) can be obtained.

FIG. 1B illustrates an embodiment how the coextruded stream can be divided, stretched, and recombined to a 4-layer composite body by passing the first layer multiplying element. A further doubling of the amount of layers to 8 layers may be achieved by passing a further LME (total of 2 LMEs), and further multiplication to an amount of 2 (n+1) layers can be achieved by passing n amounts of LMEs.

An advantage of the co-extrusion process including layer multiplying can be that stresses applied during layer-multiplication can cause the hBN particles to be oriented in the length direction (herein also called in-plane) of the formed sheet-like body with a high alignment. As illustrated in FIG. 2A, when using hBN particles in platelet form, having a greater length (L) in comparison to its thickness (T), an alignment during the layer multiplying processing parallel to the length direction of the formed composite sheet can occur, as also illustrated in FIG. 2B. FIG. 2B illustrates a section of a multi-layer composite body (21) in form of a sheet having four layers (22a, 22b, 22c, 22d), each layer including hBN particles (23) highly oriented in-plane (x-direction) of the sheet and an organic polymer (24).

In a particular aspect, a first composition for forming the first extrudate and a second composition for forming the second extrudate can contain the same ingredients in the same amounts, such that the first extrudate and the second extrudate can have the same material.

In another aspect, the ingredients and concentrations of the first composition and of the second composition may differ. For example, only the first composition can include hBN particles, while the second composition may not contain hBN particles. In another example, the amount of hBN particles and/or the average particles size of the hBN particles may be different between the first and second composition.

In certain further aspects, the first and second compositions can further include additives, for example, surfactants, dies, viscosity regulating agents, or stabilizers.

In one embodiment, the method of the present disclosure can be adapted that an amount of the hBN particles in the formed multi-layer composite body can be at least 10 vol % based on the total volume of the multi-layer composite body, or at least 15 vol %, or at least 20 vol %, or at least 25 vol %, or at least 30 vol %, or at least 35 vol %, or at least 40 vol %, or at least 45 vol %, or at least 50 vol %. In another aspect, the amount of the hBN particles in the multi-layer composite body may be not greater than 70 vol % based on a total volume of the multi-layer composite body, or not greater than 60 vol %, or not greater than 50 vol %, or not greater than 40 vol %, or not greater than 35 vol %.

In a further embodiment, an average particle size (D50) of the hBN particles used for forming the multi-layer composite body 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 another embodiment, the average particle size (D50) of the hBN particles may be not greater than 60 microns, or not greater than 55 microns, or not greater than 50 microns, or not greater than 45 microns, or not greater than 40 microns, or not greater than 35 microns. As used herein, when using platelet shaped hBN particles, the average particle size corresponds to the average length (L), herein also called diameter, of the hBN particles.

In one aspect, 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 aspect, the average aspect ratio of the hBN particles may be not greater than 200, or not greater than 120, or not greater than 100, or not greater than 80, or not greater than 50, or not greater than 40, or not greater than 35, or not greater than 30, or not greater than 20.

In a further aspect, the thickness of the hBN particles can be at least 0.05 microns, or at least 0.1 microns, or at least 1 micron. In another aspect, the thickness may be not greater than 5 microns, or not greater than 3 microns, or not greater than 1 micron.

In a further embodiment, a combination of different sizes of hBN particles can be used. In one aspect, the hBN particles can comprise a first portion of hBN particles having an average particle size between 3 and 7 microns, a second portion of hBN particles having an average particles size between 12 and 20 microns, and a third portion of hBN particles having an average particles size between 25 and 35 microns. A volume ratio of the first portion to the second portion and to the third portion can range from 0.7:1.0:1.3 to 1.3:1.0:0.7, or from 0.8:1.0:1.2 to 1.2:1.0:0.8, or from 0.9:1.0:1.1 to 1.1:1.0:0.9.

Combining the first extrudate and the second extrudate can include co-extrusion at a temperature above a melting temperature of the organic polymer. In one aspect, the temperature during co-extrusion can be at least 15° C. and not greater than 135° C. above a melting temperature of the organic polymer. In a particular aspect, the temperature is maintained after co-extrusion to avoid solidification and the co-extruded stream (herein also called composite body) is subjected to pass a plurality of layer multiplying elements to conduct a layer-multiplying procedure. After passing the layer multiplying elements, the obtained multi-layer composite body can be allowed to solidify by lowering the temperature or subjecting it to the required curing conditions.

In one embodiment, the method of the present disclosure can be adapted of continuously forming the multi-layer composite body.

It has been surprisingly observed that the method of the present disclosure can align platelet shaped hBN particles to a high degree of orientation in the in-plane direction of the formed multi-layer composite body. Not being bound to theory, during each layer multiplying step, the liquid stream (herein also called composite body) experiences substantial extensional flow, similar to fluid flow in a converging channel. As a result, the hBN platelet particles are aligned to a high degree in the in-plane direction, as illustrated in FIG. 3A.

In one embodiment, the March-Dollase orientation parameter η of the hBN particles in the in-plane direction of the multi-layer 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 multi-layer composite body. The March Dollase orientation parameter is obtained by conducting X-ray diffractometry and analyzing the X-ray spectrum according to the March-Dollase method (see detailed description in the examples). It was found that the March-Dollase orientation parameter η can be a suitable quantitative expression for characterizing the degree of alignment of the dispersed hBN particles within the multi-layer composite body. A March-Dollase orientation parameter η of 50% or greater corresponds to a high degree of orientation (herein also called alignment) of the hBN particles.

A high degree of alignment can correspond to a high thermal conductivity of the multi-layer composite body. In one aspect, the in-plane thermal conductivity of the multi-layer composite body 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 aspect, the in-plane thermal conductivity of the multi-layer composite body may be not greater than 40 W/mK, or not greater than 30 W/mK, or not greater than 20 W/mK, or not greater than 10 W/mK.

In one embodiment, the organic polymeric material of the first extrudate and the second extrudate can comprises a thermoplastic polymer. The thermoplastic polymer can include a polyethylene, a polypropylene, a polystyrene, a polyurethane, a polyacrylate, a polyester, a polycarbonate, a polyimide, a polybutylene terephthalate (PBT), polymethyl methacrylate (PMMA), a polyethylene terephthalate (PET), a polyamide, a liquid crystalline polymer (LCP), a polyacrylonitrile (PAN), a polyether ether ketone (PEEK), a polyetherketoneketone (PEKK), a polysulfone, a polyethersulfone, a polyphenylene oxide (PPO), a polyetherimide, a thermoplastic elastomer (TPE, olefinic or styrenic), a fluoropolymer such as polyvinylidene fluoride (PVDF), a perfluoroalkoxy alkanes (PFA), a fluorinated ethylene propylene (FEP), or a ethylene tetrafluoroethylene (ETFE), or any copolymer thereof, or any combination thereof.

In another embodiment, the organic polymer can be a polymerizable polymer including functional groups. In this case, the method can be adapted that a major part of the curing of the polymerizable monomer occurs after combining the first and second extrudate and after passing the layer-multiplication elements.

In a particular aspect, the polymerizable polymer can include a silicone polymer, or an acrylate polymer, or an epoxy polymer.

In a certain particular aspect, the polymerizable polymer can be a silicone polymer comprising vinyl groups. In a non-limiting embodiment, the silicone polymer comprising vinyl groups can be polymerized by cross-linking with a cross-linking agent. In a certain aspect, the weight ratio of silicone polymer comprising vinyl groups to cross-linker can be between 0.5 to 5, or 1 to 3, or 1 to 2.

In one embodiment, the hBN particles can be surface functionalized before combining them with the organic polymer. For example, the surface functionalizing of the hBN particles can include an oxygen plasma treatment, or silane surface functionalizing, or fluorine surface functionalizing, or epoxy surface functionalizing, or amine surface functionalizing, or hydroxyl surface functionalizing. The surface functionalization of the hBN particles can be of advantage to obtain a higher solids loading of hBN particles within the organic polymer and to improve the flow-behavior of the extrudates and of the formed composite body for the layer-multiplication. In a particular aspect, before surface functionalization, the hBN particles can be subjected to exfoliation and/or an activation by treatment with OH-introducing compounds.

In a certain particular aspect, the organic polymer can be a silicone, and the hBN particles can be surface functionalized with a silane, or via oxygen plasma treatment, or via fluorine surface functionalization. Non-limiting examples of silane compounds can include SiH₄, or an aminosilane. Examples of fluorine surface functionalization can include plasma treatment with CF4, or CHF3, SF₆, or C₂F₆.

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

In a further aspect, the organic polymer can be a polyethylene, and the hBN particles can be subjected to fluorine surface functionalization, or silane functionalization.

In yet another aspect, the organic polymer can be a thermoplastic polyurethane (TPU) or polybutylene terephthalate (PBT), and the hBN particles can be functionalized with an epoxy compound, an amine, or hydroxyl groups. In certain further aspects, PBT can be also surface functionalized by oxygen plasma treatment, air-plasma treatment, treatment with boric acid/urea combined with thermal treatment, or boric acid/melamine combined with thermal treatment.

In one embodiment of the method, the thickness of the multi-layer composite body can be at least 10 microns, or at least 30 microns, or at least 50 microns, or at least 100 microns, or at least at least 150 microns, or at least 200 microns, or at least 250 microns. In another embodiment, the thickness of the multi-layer composite body may be not greater than 2500 microns, or not greater than 1000 microns, or not greater than 500 microns, or not greater than 300 microns, or not greater than 100 microns.

In yet a further embodiment of the method, the thickness of each layer of the multi-layer composite body 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 may be not greater than 20 microns, or not greater than 10 microns, or not greater than 7 microns, or not greater than 5 microns, or not greater than 3 microns, or not greater than 2 microns, or not greater than 1 micron.

In a particular aspect, the thickness of each layer of the multi-layer composite body can be at least the size of the average thickness of the hBN particles and not greater than 2 times of average (D50) size of the hBN particles, or not greater than 5 times, or not greater than 10 times of the average size of the hBN particles.

The multi-layer composite body formed by the present method can have electrically insulating properties. In one aspect, the electric volume resistivity of the multi-layer composite body 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.

In another embodiment, multi-layer composite body can be continuously formed in for of a multi-layer sheet. The multi-layer sheet and can be folded to form a multi-layer stack. In one aspect, the multi-layer 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 multi-layer stack can be subjected to pressing and curing (if needed) to form a composite stack. Curing may not be required if the organic polymer is a thermoplastic polymer and already used as starting material when forming the coextruded melt stream, for example, a thermoplastic polyurethane (TPU). Thereafter, a composite slice can be cut in a height direction (z) of the composite stack, wherein the composite slice may have a thermal conductivity orthogonal (through-plane) to the cutting direction 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.

Many different aspects and embodiments are possible. Some of those aspects and embodiments are described herein. After reading this specification, skilled artisans will appreciate that those aspects and embodiments are only illustrative and do not limit the scope of the present invention. Embodiments may be in accordance with any one or more of the embodiments as listed below.

EMBODIMENTS

Embodiment 1. A method of forming a composite article, comprising: forming a first extrudate and a second extrudate, wherein the first extrudate comprises an organic polymer and ceramic particles, the ceramic particles including hexagonal boron nitride (hBN) particles;

- combining the first extrudate and the second extrudate to form a composite body including two layers;
- conducting a layer multiplying procedure on the composite body, the layer multiplying procedure comprising dividing and recombining the composite body to form a multi-layer composite body.

Embodiment 2. The method of Embodiment 1, wherein the layer multiplying procedure comprising using at least two layer multiplying elements, or at least three layer multiplying elements, or at least four layer multiplying elements, or at least five layer multiplying elements, wherein each layer multiplying element doubles an amount of layers in the multi-layer composite body.

Embodiment 3. The method of any one of the preceding Embodiments, wherein the multi-layer composite body comprises at least at least 16 layers, or at least 32 layers, or at least 64 layers.

Embodiment 4. The method of any one of the preceding Embodiments, wherein the first extrudate and the second extrudate comprise an organic polymeric material and ceramic particles, the ceramic particles including hexagonal boron nitride (hBN) particles.

Embodiment 5. The method of Embodiment 4, wherein a material of the first extrudate and a material of the second extrudate are the same.

Embodiment 6. The method of Embodiment 1, wherein the second extrudate does not include hBN particles.

Embodiment 7. The method of any one of the preceding Embodiments, wherein an amount of the hBN particles in the multi-layer composite body is at least 10 vol % based on the total volume of the multi-layer composite body, or at least 15 vol %, or at least 20 vol %, or at least 25 vol %, or at least 30 vol %, or at least 35 vol %, or at least 40 vol %, or at least 45 vol %, or at least 50 vol %.

Embodiment 8. The method of any one of the preceding Embodiments, wherein an amount of the hBN particles in the multi-layer composite body is not greater than 70 vol % based on a total volume of the multi-layer composite body, or not greater than 60 vol %, or not greater than 50 vol %, or not greater than 40 vol %, or not greater than 35 vol %.

Embodiment 9. The method of any one of the preceding Embodiments, wherein an 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.

Embodiment 10. The method of any one of the preceding Embodiments, wherein the average particle size (D50) of the hBN particles is not greater than 60 microns, or not greater than 55 microns, or not greater than 50 microns, or not greater than 45 microns, or not greater than 40 microns, or not greater than 35 microns.

Embodiment 11. The method of any one of the preceding Embodiments, wherein an average aspect ratio of length to thickness 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.

Embodiment 12. The method of any one of the preceding Embodiments, wherein the average aspect ratio of the hBN particles is not greater than 200, or not greater than 120, or not greater than 80, or not greater than 50, or not greater than 40, or not greater than 35, or not greater than 30, or not greater than 20.

Embodiment 13. The method of Embodiments 11 or 12, wherein the aspect ratio of the hBN particles is at least 5 and not greater than 50, or at least 5 and not greater than 35, or at least 7 and not greater than 20.

Embodiment 14. The method of any one of the preceding Embodiments, wherein a thickness of the hBN particles is at least 0.05 microns, or at least 0.1 microns, or at least 1 micron.

Embodiment 15. The method of any one of the preceding Embodiments, wherein a thickness of the hBN particles is not greater than 5 microns, or not greater than 3 microns, or not greater than 1 micron.

Embodiment 16. The method of any one of the preceding Embodiments, wherein an in-plane thermal conductivity of the multi-layer composite body 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.

Embodiment 17. The method of any one of the preceding Embodiments, wherein an in-plane thermal conductivity of the multi-layer composite body is not greater than 40 W/mK, or not greater than 30 W/mK, or not greater than 20 W/mK, or not greater than 10 W/mK.

Embodiment 18. The method of any one of the preceding Embodiments, wherein the organic polymer comprises a thermoplastic polymer.

Embodiment 19. The method of Embodiment 18, wherein the thermoplastic polymer includes a polyethylene, a polypropylene, a polystyrene, a polyurethane, a polyacrylate, a polyester, a polycarbonate, a polyimide, a polybutylene terephthalate (PBT), polymethyl methacrylate (PMMA), a polyethylene terephthalate (PET), a polyamide, a liquid crystalline polymer (LCP), a polyacrylonitrile (PAN), a polyether ether ketone (PEEK), a polyetherketoneketone (PEKK), a polysulfone, a polyethersulfone, a polyphenylene oxide (PPO), a polyetherimide, a thermoplastic elastomer (TPE, olefinic or styrenic), a fluoropolymer such as polyvinylidene fluoride (PVDF), a perfluoroalkoxy alkanes (PFA), a fluorinated ethylene propylene (FEP), or a ethylene tetrafluoroethylene (ETFE), or any copolymer thereof, or any combination thereof.

Embodiment 20. The method of any one of Embodiments 1-17, wherein the organic polymer is a polymerizable polymer including functional groups.

Embodiment 21. The method of Embodiment 20, wherein the polymerizable polymer includes a silicone polymer, or an acrylate polymer, or an epoxy-polymer.

Embodiment 22. The method of Embodiment 21, wherein the polymerizable polymer is a silicone polymer comprising vinyl groups.

Embodiment 23. The method of any one of the preceding Embodiments, wherein a March-Dollase orientation parameter η of the hBN particles in an in-plane direction of the composite slice is at least 50%, or at least 55%, or at least 60%.

Embodiment 24. The method of any one of the preceding Embodiments, wherein a thickness of the multi-layer composite body is at least 10 microns, or at least 50 microns, or at least 250 microns.

Embodiment 25. The method of any one of the preceding Embodiments, wherein the thickness of the multi-layer composite body is not greater than 2500 microns, or not greater than 1000 microns, or not greater than 500 microns.

Embodiment 26. The method of any one of the preceding Embodiments, wherein a thickness of each layer of the multi-layer composite body 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.

Embodiment 27. The method of any one of the preceding Embodiments, wherein a thickness of each layer of the multi-layer composite body is not greater than 20 microns, or not greater than 10 microns, or not greater than 7 microns, or not greater than 5 microns, or not greater than 2 microns, or not greater than 1 micron.

Embodiment 28. The method of any one of the preceding Embodiments, wherein a thickness of each layer of the multi-layer composite body is not greater than 1 microns, or not greater than 10, microns, or not greater than 20 microns.

Embodiment 29. The method of any one of the preceding Embodiments, wherein a thickness of each layer of the multi-layer composite body is at least a size of an average thickness of the hBN particles and not greater than 10 times of the average (D50) size of the hBN particles, or not greater 5 times, or not greater than 3 times or not greater than 2 times.

Embodiment 30. The method of any one of the preceding Embodiments, wherein a thickness (T) of the hBN particles is at least 0.05 microns, or at least 0.1 micron, or at least 1 micron.

Embodiment 31. The method of any one of the preceding Embodiments, wherein a thickness (T) of the hBN particles is not greater than 5 microns, or not greater than 3 microns, or not greater than 1 micron.

Embodiment 32. The method of any one of the preceding Embodiments, wherein an electric volume resistivity of the multi-layer composite body is at least 1.0E+12 Ω·m; or at least 1.0E+13 Ω·m, or at least 1.0E+14 Ω·m.

Embodiment 33. The method of any one of the preceding Embodiments, wherein combining the first extrudate and the second extrudate includes coextrusion at a temperature above a melting point of the organic polymer.

Embodiment 34. The method of any one of the preceding Embodiments, wherein the temperature during coextrusion is at least 15° C. and not greater than 135° C. above a melting temperature of the organic polymer.

Embodiment 35. The method of any one of the preceding Embodiments, wherein the method is adapted of continuously forming the multi-layer composite body.

Embodiment 36. The method of any one of the preceding Embodiments, wherein the multi-layer composite body is a multi-layer composite sheet.

Embodiment 37. The method of any one of the preceding Embodiments, further comprising transmitting the multi-layer body through a die under pressure before solidifying or curing the organic polymer.

Embodiment 38. The method of any one of the preceding Embodiments wherein the hBN particles comprise a multi-modal particle distribution.

Embodiment 39. The method of Embodiment 34, wherein the multi-modal particles distribution is bi-modal or tri-modal.

Embodiment 40. The method of Embodiments 34 or 35, wherein the hBN particles include a combination of three different particle size ranges.

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 between 3 and 7 microns, a second portion of hBN particles having an average particles size between 12 and 20 microns, and a third portion of hBN particles having an average particles size between 25 and 35 microns.

Embodiment 42. The method of Embodiment 37, wherein a volume ratio of the first portion to the second portion and to the third portion ranges from 0.7:1.0:1.3 to 1.3:1.0:0.7, or from 0.8:1.0:1.2 to 1.2:1.0:0.8, or from 0.9:1.0:1.1 to 1.1:1.0:0.9.

Embodiment 43. The method of any one of the preceding Embodiments, further comprising surface functionalizing of the hBN particles before forming the first extrudate and the second extrudate.

Embodiment 44. The method of Embodiment 39, wherein surface functionalizing of the hBN particles includes an oxygen plasma treatment, or silane surface functionalizing, or fluorine surface functionalizing, or epoxy surface functionalizing, or amine surface functionalizing, or hydroxyl surface functionalizing.

EXAMPLES

The following non-limiting examples illustrate the present invention.

Example 1

Continuous forming of multi-layered composite body comprising aligned hBN particles.

A set of two extruders (extruder A and extruder B) is used, wherein each extruder contains the same liquid mixture of 37 vol % hBN particles (average particle size 30 microns), dispersed in silicone-gum (AB specialty Indium H110-O) and 2,4-dichlorobenzoyl peroxide (50% in polydimethyl-siloxane) as crosslinking agent. The weight percent ratio of crosslinker to silicone is about 1 to 1.5. The liquid mixture is further including 2-5 wt % of a surfactant or surfactant combination.

A first extrudate is formed with the mixture of extruder A and a second extrudate is formed with the mixture of extruder B and the first extrudate and the second extrudate are combined to a two-layer composite body. While the two-layer composite body is still in form of a fluid stream, it is subjected to a layer multiplying procedure using a combination of five layer multiplying elements. After passing the five layer multiplying elements a multi-layer composite sheet (herein also called multi-layer composite body) is obtained containing 64 layers.

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

The orientation of the hBN particles in the plain direction of the multi-layer composite body is measured via X-ray analysis as described below, and an orientation parameter f is calculated via the March-Dollase method, wherein f is greater than 60%.

Example 2

Example 2 is conducted the same way as Example 1, except that the hBN particles are surface functionalized with a silane. The thermal conductivity and the orientation parameter is being measured and expected to be greater than the thermal conductivity and orientation parameter of the multi-layer composite sheet of Example 1.

Example 3

Example 3 is conducted the same way as Example 1, except that a variety of thermoplastic polymers are used, specifically polyethylene, thermoplastic polyurethane (TPU), polybutylene terephthalate (PBT), and an epoxy-polymer.

Furthermore, in an additional set of experiments, the hBN particles have been surface functionalized. The type of surface functionalization and the corresponding organic polymers are listed in Table 1. The thermal conductivity of the obtained multi-layer sheets is being measured and expected to be greater than the thermal conductivity when using hBN which has not been surface-functionalized.

TABLE 1

Organic Polymer
Surface Functionalization of hBN

polyethylene
CF₄plasma treatment

TPU
allylamine plasma treatment

PBT
oxygen plasma treatment

Epoxy-polymer
allyl glycidyl ether plasma treatment

Example 4

Continuous folding of the multi-layer composite sheet.

The continuously formed multi-layer composite sheet of Example 1 or Example 2 is continuously folded to form a multi-layer stack. The stack is subjected to a compression treatment by applying a pressure, followed by a heat treatment to conduct curing of the organic polymer, if needed.

From the pressed and cured multi-layer stack, a 0.5 mm thick composite slice is cut with a diamond wire. The composite slice is analyzed in its thickness direction (z) for the thermal conductivity. The thermal conductivity throughout the thickness direction (through-plane) of the composite slice is at least 90% the same as the in-plane thermal conductivity of the multi-layer composite bodies obtained in Examples 1 and 2.

Measuring the Thermal Conductivity

The thermal conductivity is measured using a transient plane source device (TPS 2500 S, Hot Disk Instruments). The instrument and measurement are designed by placing a temperature sensor between two samples of the test material, introducing a pulse of heat at the surface of the test sample, measuring the temperature change, and calculating based thereon the thermal conductivity. The temperature sensor is a Paton-insulated Hot Disk® sensor model 5501 (6.4 mm radius). The heat pulse is varied in the range of 60-150 mW for 3-15 seconds to make sure that the conductivity values stay constant independent of the pulse parameters. The measurements is conducted according to the Hot Disk Thermal Constants Analyser Instruction Manual (2015 Apr. 15) from Hot Disk®. For in-plane measurements, the Slab Module is used, and for through-plane values the anisotropic method.

Measuring the March-Dollase Orientation Parameter η

X-ray diffraction analysis is conducted to determine the degree of orientation (also called herein alignment) of the hBN particles within the composite body. In the case of in-plane aligned hBN platelets, the primary plane of interest was the in-plane direction parallel to the surface (such as the (002) plane). First, a 2D XRD spectrum is obtained after spot diffraction of the sample with a Bruker D8 diffractometer using a focused Cu Kα radiation (λ=1.5418 Å) in the step scan mode at angular positions ranging from 10° to 80°. Thereafter, a one-dimensional (1D) XRD spectrum is obtained by integration of the 2D spectrum using built-in capability of EVA software from Bruker. A Rietveld peak fitting methodology is used to compare the (002) peak intensity of the oriented hBN pattern against an un-oriented hBN database pattern to obtain a quantifiable measurement of orientation. An typical XRD spectrum showing the (002) peak is shown in FIG. 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.

The peak fitting of the XRD pattern is performed using the Topas quantification software from Bruker. The Topas software has a built-in refinement functionality to determine the March-Dollase parameter using the March-Dollase function W(α), see equation (1):

$\begin{matrix} W (α) = {(r^{2} \cos^{2} α + \frac{1}{r} \sin^{2} α)}^{- 3 / 2}, & (1) \end{matrix}$

wherein W(α) is the fraction of crystallites oriented in the preferred direction, α is the angle between a crystallite plane (hkl) normal and the preferred orientation direction, and r is the March-Dollase parameter.

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

$\begin{matrix} η = 100 {% [\frac{{(1 - r)}^{3}}{1 - r^{3}}]}^{3 / 2} . & (2) \end{matrix}$

The graph shown in FIG. 2B shows the relationship between the March-Dollase parameter r and the degree of preferred orientation η (r), which is herein also called “March-Dollase orientation parameter η.” The solid line in the graph indicates the actually measured curve and the dashed line is a conversion of the curved line to a simplified linear trend line.

Measuring the Electric Volume Resistivity

The electric resistivity of the samples is determined according to ASTM D257.

In the foregoing specification, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, 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 invention.

METHOD OF FORMING A MULTI-LAYER COMPOSITE BODY

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