Process for production of a bag having linear ribs

A process for production of a bag having linear ribs comprising:

• (a) providing first and second material sheets, said first and second material sheets being formed from a multi-layer resin film having a surface layer of a heat adhesive resin with a low melting point;
• forming linear ribs on said first and second material sheets by providing a plate shaped mold having an upper face and a lower face, the upper face and the lower face of the plate shaped mold each having linear protrusions, and introducing the first of the material sheets into a space between the upper face of the plate shaped mold and an upper female mold disposed at the upper face of the plate shaped mold and introducing the second of the material sheets into a space between the lower face of the plate shaped mold and a lower female mold disposed at the lower face of the plate shaped mold, the layers of the heat adhesive resin having a low melting point which face the plate shaped mold;
• the upper female mold and the lower female mold have penetrated linear cavities at positions corresponding to the linear protrusions on the upper and lower faces of the plate shaped mold, said cavities exposing portions of the material sheets, and the upper female mold and the lower female mold being capable of opening or closing, an upper heating panel being disposed at an upper side of the upper female mold and a lower heating panel being disposed at a lower side of the lower female mold, the heating panels providing heat to the linear cavities and to said exposed portions of the material sheets;
• the heating panels being capable of opening and closing;
• pushing the material sheets at the exposed portions over or below the linear protrusions on both faces of the plate shaped mold into the linear cavities of the female molds by pressing the upper female mold and the lower female mold toward the plate shaped mold with a driving mechanism of the female molds or by moving the upper heating panel and the lower heating panel toward the plate shaped mold from outside of the female molds with a driving mechanism of the heating panels, the heating panels being heated to a temperature of or above the softening point of the heat adhesive resin, thereby forming linear ribs on the sheets;
• (b) heat sealing the material sheets of the multi-layer resin film having linear ribs at portions thereof corresponding to peripheral parts of the bag to be produced including a bottom and side edges;
• and
• (c) cutting off and separating the heat sealed parts from the material sheets to produce the bag.