Composite structure and process for producing the same

A method of manufacturing a composite structure comprising a first polytetrafluoroethylene (PTFE) porous layer, a second PTFE porous layer, and a framework structural member having a plurality of gaps or openings, wherein the method includes the following Steps 1 through 3:

• Step 1 for preparing an intermediate composite material which is formed by arranging the first PTFE porous layer, the framework structural member, and the second PTFE porous layer in this order and placing on and around a circumferencial surface of a mandrel
• Step 2 for applying pressure at least from one outside of the first and second PTFE porous layers through a mass of fine particles so that the first and second PTFE porous layers can be adhered not only with each other through the gaps or openings of the framework structural member, but also with the framework structural member closely along the surfaces of the respective elements of the framework structural member in such a manner as to wrap the respective elements;
• and
• Step 3 for uniting the respective adhered parts by heating at a temperature lower than the pyrolysis temperature of polytetrafluoroethylene in a state where pressure is applied, wherein:
• in the Step 1, the framework structural member is sandwiched through fluoroplastics between the first and second PTFE porous layers, and thereby, in the Step 3, the first and second PTFE porous layers are united with the framework structural member through fluoroplastics closely along the surfaces of respective constituent elements of the framework structural member,
• the mandrel is made by lapping a plate spirally into a tubular form,
• a diameter of fine particles is 5 to 500 μm,
• the fine particles are at least one selected from the group consisting of aluminum oxide, calcium carbonate, silica, kaolin, clay, titanium oxide, zinc oxide, barium sulfate, magnesium hydrate, sodium chloride, or potassium chloride, and
• in the Step 1, a dispersion of the fluoroplastics is applied on a bonding surface of at least one of the first and second PTFE porous layers so that a nonporous layer having a thickness of 10 μm or less is formed.