Abstract: This invention provides an improvement in a method of slitting and sealing two or more layers of plastic film material in contact with each other. The improvement comprises slitting and sealing the layers with a light beam generated by a laser. The beam intensity is such that the temperature of the beam at the surface of the film is at a point sufficient only to raise the enthalpy of the material to the transition point between the molten and solid states of the material, whereby bead formation is reduced or eliminated at the seal. Methods are also disclosed for slitting a larger single sheet of material into two or more smaller sheets of material as well as for providing microperforations or microporous plastic material by the use of a pulsing beam generated by a laser.

Abstract: This invention provides an improvement in a method of cooling molten extruded tube produced by a blown-tube process. The improvement comprises cooling the tube utilizing the heat of evaporation of moisture in steam. The steam is brought into contact with the molten tube after extrusion of the molten tube from an extrusion die, whereby the steam is permitted to expand prior to, during or subsequent to contact with the molten tube. An apparatus is also provided for carrying out the above-described method.

Abstract: This invention provides an improvement in a method of slitting and sealing two or more layers of plastic film material in contact with each other. The improvement comprises slitting and sealing the layers with a light beam generated by a laser. The beam intensity is such that the temperature of the beam at the surface of the film is at a point sufficient only to raise the enthalpy of the material to the transition point between the molten and solid states of the material, whereby bead formation is reduced or eliminated at the seal. Methods are also disclosed for slitting a larger single sheet of material into two or more smaller sheets of material as well as for providing microperforations or microporous plastic material by the use of a pulsing beam generated by a laser.