Method and apparatus for making cushioned shipping bags

A method of making a cushioned shipping bag comprising the steps of:

• providing two outer protective layers of tough, durable, flexible sheet material;
• providing a heat-sealable coating on a predetermined surface of each of said outer layers;
• said heat-sealable coating having a melting temperature below the temperature at which said outer layers become damaged;
• positioning said outer layers with their coated surfaces facing inwardly toward each other;
• sandwiching two layers of polypropylene microfoam cushioning material between the coatings on the inner surfaces of said outer layers;
• said polypropylene microfoam material melting at a temperature below the temperature at which said coating melts;
• heat-sealing a region of the bag by applying heat and pressure to the exterior surfaces of said outer layers in said region for feeding heat energy inwardly through said outer layers for burning away and rapidly shrinking back the intervening polypropylene layers and for softening the coatings in said region and for bringing said softened coatings directly together face-to-face in said region for heat sealing said outer layers together in said region;
• said heat and pressure being applied to the exterior surfaces of said outer layers in said region in a manner for facilitating the rapid shrink back of the polypropylene material from between the coatings during its burn away in said region;
• and
• immediately thereafter applying pressure and chilling to the exterior surfaces of said outer layers in said same region thereof for setting said heat seal.