ARTICLES CONTAINING A HEAT SOURCE AND A HEAT SPREADER
This invention is related to articles containing a heat source and a heat spreader to conduct heat from the heat source. The heat spreader comprises a core of one or more drawn UHMWPE sheets. The sheets are planar, i.e., have dimensions in two directions that are considerably greater than that of the third dimension. No solvent is used during the drawing process. The draw ratio is typically 100 to 150. The density of a sheet is less than 0.90 g/cm 3 . A sheet has good thermal conductivity k ∥ the direction of the draw. k ∥ is at least 30 W/mK. The thermal conductivity perpendicular to the plane of the sheet k ⊥ is greatly reduced. k ⊥ is less than. 0.20 W/mK.
1 . An article comprising,
a) a heat source; and
b) a heat spreader in direct contact with the heat source, the heat spreader comprising a core of one or more UHMWPE sheets drawn in the absence of a solvent, each UHMWPE sheet having a density ρ less than 0.90 g/cm 3 , a thermal conductivity in the drawn direction, k ∥ , of at least 30 W/mK, a thermal conductivity perpendicular to the plane of the sheet, k ⊥ , of less than 0.20 W/mK and a ratio of k ∥ /k ⊥ greater than 200.
2 . The article of claim 1 , wherein the density ρ is less than 0.85 g/cm 3 .
3 . The article of claim 1 , wherein k ⊥ is less than 0.15 W/mK.
4 . The article of claim 1 , wherein k ∥ is at least 40 W/mK.
5 . The article of claim 1 , wherein the ratio of k ∥ /k ⊥ is greater than 250.
6 . The article of claim 1 , wherein the density ρ is less than 0.85 g/cm 3 , k ⊥ is less than 0.15 W/mK, k ∥ is at least 40 W/mK and the ratio of k ∥ /k ⊥ is greater than 250.
7 . The article of claim 1 , wherein the core of the heat spreader is comprised of two or more sheets and the two or more sheets are arranged in a layer structure with the drawn direction of each sheet aligned with the drawn direction of every other sheet in the core.
8 . The article of claim 1 , wherein the core of the heat spreader is comprised of two or more sheets and the two or more sheets are divided into two sets with the sheets arranged alternately in a layer structure with the drawn direction of one set perpendicular to the drawn direction of the second set to provide thermal conduction in two directions.
9 . The article of claim 1 , wherein an adhesive with a thermal conductivity of at least 0.2 W/mk is coated on one or both sides of the UHMWPE core and is adhered to the heat source.
10 . The article of claim 9 , wherein the adhesive is an acrylic adhesive with a thermal conductivity of at least 0.5 W/mk.
11 . The article of claim 1 , wherein the heat source is a battery and the heat spreader conducts heat away from the battery to maintain an operable battery temperature.
12 . The article of claim 11 , wherein the battery contains a series of cells and the heat spreader is in thermal contact with the cells.
13 . The article of claim 12 , wherein the battery is a lithium battery.
14 . The article of claim 1 , wherein the article is an antenna.
15 . The article of claim 1 , wherein the article is a display panel.
16 . The article of claim 1 , wherein the heat source is a resistive heat generating film or circuit.
17 . The article of claim 16 , wherein the heat spreader conducts heat from the heat source to a battery to heat the battery to optimal battery operating temperature.
18 . The article of claim 1 , wherein the article contains multiple heat sources and a heat spreader conducts heat between them.