For this purpose, paper roll cores (11) are used as a core material, and the surface of the openings (14) thereof on one side is covered with a porous cover sheet (12) such as a napped cloth, a flocked cloth, or felt, while the surface (15) of the other openings thereof is covered with a sheet (13) which is impermeable to air, such as lead sheeting or a plastic sheet containing iron powder.
Posséde-t-il une lettre, oui ou non, accordant l'appui du gouvernement du Québec?patents-wipo patents-wipo