Abstract: An internal mandrel for cooling a tubular thin film is disclosed where an air layer is eliminated in the lower side cooler of the internal mandrel, so that the tubular thin film can be continuously and stably produced. In the internal mandrel for directly cooling the tubular thin film while using external circularly shaped cooling tank where the tubular thin film is downwardly extruded through a circular slit of the die, the internal mandrel is characterized in that coolant for cooling a lower most part of the internal mandrel is flown in the countercurrent direction in the internal mandrel to the tubular thin film.

Abstract: The object of the present invention is to provide an internal mandrel for cooling a tubular thin film where air layer is not remaining in the lower side cooler of the internal mandrel, so that the tubular thin film can be continuously and stably produced. In the internal mandrel for directly cooling the tubular thin film while using external circularly shaped cooling tank where the tubular thin film is downwardly extruded through a circular slit of the die, the internal mandrel is characterized in that coolant for cooling a lower most part of the internal mandrel is flown in such a direction as to oppose to the tubular thin film.

Abstract: This invention relates to a tubular stretching method for producing a stretched film by passing a tubular thermoplastic resin film between pairs of nip rolls having mutually different peripheral speeds and by inflating the tubular film with internal pressure under heating and a stretching apparatus to be employed therefor. The pairs of nip rolls include at least three pairs of nip rolls. Pressurized air is admitted into a stretched bubble situated between the first and second rolls through a slit-like air injecting nozzle, and the bubble formed by the supplied pressurized air is inflated and stretched under heating. In this stage, if desired, the amount of injected pressurized air is controlled by manual or automatic control by detecting the diameter of the bubble so as to keep the bubble's diameter constant. After stretching, the tubular film is collapsed and is introduced to the second nip rolls. Both side ends of the collapsed film are cut open with film cutting knives to make two sheets of flat films.

Abstract: A process for producing a porous resin film containing a polyolefin resin as a main component, comprising meltinig a mixture of (A) 100 parts by weight of a polyolefin resin, (B) 0 to 50 parts by weight of a polyester-polyether type thermoplastic elastomer, and (C) a thermoplastic polyester resin having an instrinsic viscosity of not more than 0.5, the amount of the component (C) being from 25 to 90 part by weight per 100 parts of the total amount of the component (A) and the component (B), by heating the mixture at a temperature of not less than the melting temperature of the component (C); kneading the mixture at a shear rate of not less than 200/sec.