Heat-dissipating sheet having high thermal conductivity and its production method

Abstract

A heat-dissipating sheet having a density of 1.9 g/cm 3 or more and an in-plane thermal conductivity of 570 W/mK or more, which comprises carbon black uniformly dispersed among fine graphite particles, a mass ratio of fine graphite particles to carbon black being 75/25 to 95/5, is obtained by repeating plural times a cycle of applying a dispersion of fine graphite particles, carbon black and an organic binder in an organic solvent to a surface of a support plate, and then drying it, to form a resin-containing composite sheet; burning the resin-containing composite sheet to remove the organic binder; and pressing the resultant composite sheet of fine graphite particles and carbon black for densification.

What is claimed is: 
     
         1 . A heat-dissipating sheet having a structure in which carbon black is uniformly dispersed among fine graphite particles, a mass ratio of fine graphite particles to carbon black being 75/25 to 95/5; and said heat-dissipating sheet being obtained by burning and pressing a composite sheet of fine graphite particles, carbon black and an organic binder, so that it has a density of 1.9 g/cm 3  or more and an in-plane thermal conductivity of 570 W/mK or more. 
     
     
         2 . The heat-dissipating sheet according to  claim 1 , which has thickness of 25-150 μm. 
     
     
         3 . The heat-dissipating sheet according to  claim 1 , wherein said fine graphite particles have an average diameter of 3-150 μm and average thickness of 200 nm or more. 
     
     
         4 . The heat-dissipating sheet according to  claim 1 , which is coated with insulating resin layers or insulating plastic films. 
     
     
         5 . A method for producing the heat-dissipating sheet according to  claim 1 , comprising the steps of (1) preparing a dispersion comprising 5-25% by mass in total of fine graphite particles and carbon black, and 0.05-2.5% by mass of an organic binder, in an organic solvent, a mass ratio of said fine graphite particles to said carbon black being 75/25 to 95/5; (2) repeating plural times a cycle of applying said dispersion to a surface of a support plate and then drying it, to form a resin-containing composite sheet comprising said fine graphite particles, said carbon black and said organic binder; (3) burning said resin-containing composite sheet to remove said organic binder; and (4) pressing the resultant composite sheet of fine graphite particles and carbon black for densification. 
     
     
         6 . The method for producing a heat-dissipating sheet according to  claim 5 , wherein a mass ratio of said organic binder to the total amount of said fine graphite particles and said carbon black is 0.01-0.5. 
     
     
         7 . The method for producing a heat-dissipating sheet according to claim  5 , wherein the amount of said dispersion applied by one operation is 5-15 g/m 2  (expressed by the total weight of fine graphite particles and carbon black per 1 m 2 ). 
     
     
         8 . The method for producing a heat-dissipating sheet according to  claim 5 , wherein said organic binder is an acrylic resin, a polystyrene resin or polyvinyl alcohol. 
     
     
         9 . The method for producing a heat-dissipating sheet according to  claim 5 , wherein said organic solvent is at least one selected from the group consisting of ketones, aromatic hydrocarbons and alcohols. 
     
     
         10 . The method for producing a heat-dissipating sheet according to  claim 5 , wherein said dispersion is applied by a spraying method. 
     
     
         11 . The method for producing a heat-dissipating sheet according to  claim 5 , wherein said burning step is conducted at a temperature of 550-700° C. 
     
     
         12 . The method for producing a heat-dissipating sheet according to  claim 5 , wherein cooling after burning is gradually conducted to room temperature over 1 hour or more. 
     
     
         13 . The method for producing a heat-dissipating sheet according to  claim 5 , wherein said pressing step is conducted at pressure of 20 MPa or more. 
     
     
         14 . The method for producing a heat-dissipating sheet according to  claim 5 , wherein said resin-containing composite sheet is pressed in a state sandwiched by a pair of planar die plates in a die plate apparatus. 
     
     
         15 . The method for producing a heat-dissipating sheet according to  claim 14 , wherein said die plate apparatus comprises a lower die plate and an upper die plate; and wherein using said lower die plate as said support plate, said resin-containing composite sheet is formed in a cavity of said lower die plate, burned without being peeled from said lower die plate, and then pressed with said lower die plate combined with said upper die plate. 
     
     
         16 . The method for producing a heat-dissipating sheet according to claim  5 , wherein said composite sheet of fine graphite particles and carbon black is cooled to a temperature equal to or lower than the freezing point of water, and then pressed. 
     
     
         17 . The method for producing a heat-dissipating sheet according to  claim 5 , wherein said pressing step is conducted at a temperature of room temperature to 200° C.