THERMALLY CONDUCTIVE PLASTIC COMPOSITIONS, EXTRUSION APPARATUS AND METHODS FOR MAKING THERMALLY CONDUCTIVE PLASTICS
A thermally conductive plastic composition and a system and method for forming such compositions. The thermally conductive composition comprises a polymer material and a thermally conductive filler, such as boron nitride, and exhibits good in-plane thermal conductivity, through-plane conductivity, or both. The system for forming thermally conductive plastic compositions comprises an extruder and an extruder screw comprising fractional mixing elements. The extruder can also comprise a screw with shovel elements located in a region of the system for introducing a thermally conductive filler into the extruder. The system and method allow for the processing of thermally conductive plastic compositions comprising boron nitride and can allow for the processing of boron nitride agglomerates such that the agglomerates remain sufficiently in tact to provide a composition exhibiting both excellent in-plane and through-plane conductivity.
1 . A method of manufacturing a thermally conductive composition comprising:
introducing a polymeric material into an extruder;
introducing a thermally conductive filler material into the extruder;
forming a melt blend comprising the polymeric material and the thermally conductive filler material; and
extruding the melt to form an extrudate, wherein the extruder comprises an inlet for introducing material into the extruder and an extruder screw, the extruder screw comprising a section of kneading elements located downstream of the inlet, and a section of fractional mixing elements, screw mixing elements, turbine mixing elements, stirrer elements, or a combination of two or more thereof downstream of the kneading elements.
2 . The method of claim 1 , comprising introducing the polymeric material and the thermally conductive material into the extruder via the inlet.
3 . The method of claim 1 , wherein the extruder screw comprises shovel elements at a section of the screw adjacent to the inlet, and the fractional kneading elements, screw mixing elements, turbine mixing elements, or stirrer elements are located downstream of the shovel elements.
4 . The method of claim 1 wherein the extruder screw comprises screw mixing elements, turbine mixing elements, neutral kneading blocks, fractional kneading blocks, or a combination of two or more thereof, downstream of the fractional mixing elements.
5 . The method of claim 1 , wherein the screw has a length L, and the section of kneading elements has a length of about 10% to about 20% of the screw length L.
6 . The method of claim 1 , comprising introducing the thermally conductive material into the extruder via a side feeder, the side feeder being located downstream of the inlet and the section of kneading block elements.
7 . The method of claim 6 , wherein the side feeder comprises a screw comprising shovel elements.
8 . The method of claim 6 , wherein the side feeder is upstream of the fractional mixing elements.
9 . The method of claim 6 , wherein the thermally conductive filler comprises boron nitride agglomerates.
10 . The method of claim 1 , wherein the thermally conductive filler comprises a filler having a density that is 33% or less of the material's theoretical density.
11 . The method of claim 1 , wherein the thermally conductive filler comprises boron nitride.
12 . The method of claim 11 , wherein the boron nitride is chosen from boron nitride particles, boron nitride agglomerates, or a combination thereof.
13 . The method of claim 1 , wherein the resulting composition has a through-plane thermal conductivity of about 0.9 W/mK or greater.
14 . The method of claim 1 , wherein the resulting composition has a ratio of in-plane thermal conductivity to through-plane thermal conductivity of about 3.5:1 or less.
15 . The method of claim 13 , wherein the composition has a total filler loading of about 43 wt. % or less.
16 . The method of claim 1 wherein the resulting composition has a through-plane conductivity of 1.5 W/mK or greater.
17 . The method of claim 16 , wherein the composition has a total filler loading is about 51 wt. % or less.
18 . The method to make the composition of claim 1 comprising adding a silane to the composition, where the silane is added (a) in-situ to the extruder, (b) to a filler prior to introducing the filler into the extruder, or (c) both (a) and (b).
19 . A shaped article formed by the method of claim 1 .
20 . A thermal management assembly comprising the shaped article of claim 19 .
21 . A thermally conductive composition comprising:
a polymer material; and
a thermally conductive filler dispersed in the polymer material, wherein the composition has an in-plane thermal conductivity of about 2 W/mK or greater, a through-plane thermal conductivity of about 0.9 W/mK or greater, or both.
22 . The composition of claim 21 having an in-plane thermal conductivity of 3.5 W/mK or greater.
23 . The composition of claim 21 where the thermally conductive fillers comprise hexagonal boron nitride, zinc oxide, glass fiber, glass flake, clays, exfoliated clays, calcium carbonate, talc, mica, wollastonite, clays, exfoliated clays, alumina, aluminum nitride, graphite, metallic powders or flakes of aluminum, copper, bronze, or brass, or a combination of two or more thereof, fibers or whiskers of aluminum, copper, bronze, brass, silicon carbide, silicon nitride, aluminum nitride, alumina, zinc oxide, yttrium oxide, or a combination of two or more thereof, carbon nanotubes, graphene, boron nitride nanotubes, boron nitride nanosheets, zinc oxide nanotubes, or a combination of two or more thereof.
24 . The composition of claim 21 comprising a total thermally conductive filler concentration of about 80% by weight or less of the total weight of the composition.
25 . The composition of claim 21 having a total thermally conductive filler content of about 40% or less by volume (v/v) of the composition.
26 . The composition of claim 21 comprising boron nitride chosen from a boron nitride platelet, a boron nitride agglomerate, or a combination thereof.
27 . The composition of claim 26 , comprising a boron nitride concentration of about 45 wt. % or less of the composition.
28 . The composition of claim 26 , wherein the total filler volume fraction is about 40 percent or less by volume of the total composition.
29 . The composition of claim 26 , wherein the aspect ratio of the boron nitride filler is at least 20.
30 . The composition of claim 21 comprising glass fiber and/or glass flakes.
31 . The composition of claim 30 wherein the glass fiber aspect ratio is at least 20.
32 . The composition of claim 30 wherein the aspect ratio of the glass flake used is at least 40.
33 . The composition of claim 21 comprising exfoliated clay.
34 . The composition of claim 33 wherein the aspect ratio of the exfoliated clay used is at least 50.
35 . The composition of claim 21 comprising a silane chosen from an acryloxy silane, a vinyl silane, a halosilane, a mercapto silane, a blocked mercaptosilane, or a combination of two or more thereof.
36 . The composition of claim 35 , wherein the silane is present in an amount of from about 0.1 wt. % to about 6 wt. % of the composition.
37 . The composition of claim 21 , wherein the composition has an in-plane thermal conductivity to through-plane conductivity ratio of about 3.5:1 or less.
38 . The composition of claim 21 , wherein the in-plane thermal conductivity is at least 10 W/mK.
39 . The composition of claim 21 having a notched Izod impact value of 20 J/m or greater.
40 . The composition of claim 21 having a tensile strength value of 7000 psi or greater.
41 . The composition of claim 21 having a strain at break value of 0.8% or greater.
42 . The composition of claim 21 , wherein the filler has a color on the L*, a*, b* scale with L* greater than 90, a* of −1.3 to 1.3, and b* of −2.5 to 2.5.
43 . The composition of claim 21 , wherein the filler comprises a blend of a boron nitride and a silane, wherein the silane is condensed on the surface of the boron nitride and the metal oxide.
44 . The composition of claim 43 , wherein the filler further comprises a metal oxide in the blend, and the silane is condensed on the surface of the blend of the boron nitride and the metal oxide.
45 . The composition of claim 21 with a dielectric strength of 250 V/mil or higher.
46 . The composition of claim 21 with a volume resistivity of 10 12 Ohm-cm or higher.
47 . The composition of claim 21 with a density of 1.7 g/cc or less.