Method of making a stand-up plastic bag

A method of making a stand-up plastic bag, comprising the steps of:

• (a) supplying a multi-layered film of first and second thermoplastic materials, said first material being heat-sealable at a temperature within a first temperature range and said second material being heat-sealable at a temperature within a second temperature range which is a range of temperatures higher than the temperatures in said first temperature range;
• (b) folding said film to form a pair of front and rear side walls and a pair of front and rear bottom gusset walls disposed between said side walls with said first and second materials being on respective interior and exterior surfaces of said side and gusset walls;
• (c) heat sealing at a temperature within said first temperature range to simultaneously form a first set of heat seals which (1) joins lower end portions of said front and rear bottom gusset walls with corresponding lower end portions of said front and rear side walls at contiguous regions of said first material on said interior surfaces thereof to form a bottom wall of connected upper portions of said front and rear bottom gusset walls which extend between said front and rear side walls, and (2) joins said front and rear side walls with said front and rear bottom gusset walls along opposite longitudinal edges thereof at contiguous portions of said first material on interior surfaces of said longitudinal edges of said walls;
• (d) heat sealing at a temperature within said second temperature range to form a second set of heat seals which joins said front and rear bottom gusset walls together along their opposite longitudinal edges at contiguous portions of said second material on said exterior surfaces thereof;
• and
• (e) separating said film into completed plastic bags by severing said film through at each of said heat seals at each of said longitudinal edges of said walls.