Patent ID: 7255354

Claim:
A gas-permeable plug for inserting into an insertion hole formed through a part of a casing in an inward-outward direction of the casing, the gas-permeable plug comprising: a plug body; and a gas-permeable and liquid impermeable sheet including therein a plurality of minute permeable pores having irregular shapes and directed in irregular directions and/or a plurality of fine permeable gaps having irregular shapes and directed in irregular directions, wherein: the plug body comprises a material having rubber-like elasticity; the plug body has a vent hole formed at a center portion of the plug body in the inward-outward direction of the casing; the plug body has a sheet bonding portion formed outside of the vent hole; the plug body has a substantially ring shape or a substantially tubular shape having an outer shape slightly larger than an inner shape of the insertion hole; the gas-permeable and liquid impermeable sheet is integrally bonded with the sheet bonding portion by mechanical engagement during formation of the plug body such that at least a portion of the minute permeable pores and/or the fine permeable gaps of the gas-permeable and liquid impermeable sheet at the sheet bonding portion has the material of the plug body solidified in irregular shapes and irregular directions therein; and a portion of the gas-permeable and liquid impermeable sheet is compressed in a thickness direction over a full area of the sheet bonding portion of the plug body and is thinner than an original thickness of the gas-permeable and liquid impermeable sheet, wherein the gas-permeable and liquid impermeable sheet has an annular compressed portion located inside of the portion of the gas-permeable and liquid impermeable sheet at the sheet bonding portion, the annular compressed portion being compressed in the thickness direction and being thinner than the original thickness of the gas-permeable and liquid impermeable sheet.