Method and device for manufacturing a laminated material

A plate assembly for applying high pressing force uniformly over a plate material such as a stack of sheet material to be pressed together to become a laminate plate material, comprising a base plate member formed with a shallow chamber space at a central portion thereof while an annular peripheral portion thereof being left to provide an annular land portion surrounding said shallow chamber space, an annular seal member placed in said shallow chamber space so as to extend along and adjacent said annular land portion, a cover plate member mounted in said shallow chamber space with an annular peripheral portion thereof being placed to extend along and adjacent an inner peripheral portion of said annular land portion in continuous sealing engagement with said annular seal member, thereby confining a thin pressure chamber in said shallow chamber space as peripherally blocked by said annular seal member, an annular retainer member having an annular outside half portion engaged with said land portion of said base plate member and an annular inside half portion engaged with an annular peripheral portion of said cover plate member, and means for fastening said annular retainer member to said annular land portion of said base plate member, said thin pressure chamber being adapted to be filled with oil.