Method of forming a flexible graphite sheet with decreased anisotropy

Method for making flexible graphite sheet having decreased electrical resistivity through the thickness and improved sealability perpendicular to the thickness of the sheet ("c" direction) comprising:

• (i) providing a first batch of relatively large size natural graphite flake sized at least 80% by weight 20.times.50 mesh;
• (ii) providing a second batch of smaller sized natural graphite flake sized at least 80% by weight 50.times.80 mesh;
• (iii) blending said first batch and said second batch to provide a blended mixture containing from about 25 to 75 percent by weight of the smaller sized natural graphite flake of said second batch;
• (iv) treating said blended mixture with an intercalating solution to obtain a heat expandable, intercalated graphite flake mixture;
• (v) exposing the intercalated natural graphite flake mixture of step (iii) to an elevated temperature to exfoliate said intercalated natural graphite flake into a mixture of relatively large size and smaller size expanded vermicular worm shaped particles of graphite;
• and
• (vi) passing the blended mixture of step (v) through pressure rolls to form a coherent, roll pressed, compressed sheet formed of said blended mixture of pre-determined thickness, the electrical resistivity through the thickness of the compressed sheet decreasing with increasing amounts in the blended mixture of step (iii) of the smaller sized natural graphite flake of step (ii).