PASTE COMPOSITION FOR MICRO POROUS LAYER FORMATION AND MANUFACTURING METHOD THEREOF

PROBLEM TO BE SOLVED: To provide a paste composition for micro porous layer formation and its manufacturing method which are arranged so as to prevent the occurrence of permeation of paste into a base material, thereby preventing the interference with gas diffusion and the reduction of an output under the condition of a high load, and which allow easy control of pores of a micro porous layer and the prevention of occurrence of crack.SOLUTION: The paste composition for micro porous layer formation comprises carbon black, PTFE resin, a water-soluble resin and water, and forms a paste for a micro porous layer formation without surfactant. The paste has a large surface tension, and is used to form a diffusion layer 14. The paste applied to a base material 16 never permeates thereinto. The ratio of the water-soluble resin to the carbon black is arranged in a range of 0.05-1% by weight in terms of a specific surface area (m/g) of the carbon black. Thus, the water-soluble resin makes a binder operable to link carbon particles to each other and necessary pores can be formed in the micro porous layer. In addition, the carbon particles linked to each other relax a contraction stress produced in forming the layer, whereby the occurrence of crack in the micro porous layer can be prevented. Since the paste never permeates into the base material, no interference with gas diffusion is caused, and a superior characteristic under the condition of a high load is achieved.