Method for extrusion of tubular films

#1. Field of the Invention

#The present invention relates to the extrusion of thermoplastic tubular films, in particular the employment of a coextrusion process to produce a tubular film laminate which may be employed in, for example, packaging applications. These applications may employ the present films in laminar form or, alternatively, may be employed in a delaminated form as monolayer materials.

#2. Brief Description of the Prior Art

#The following Examples set forth and describe the specific apparatus and production line conditions which were employed to produce certain specific embodiments of the present invention. Accordingly, these Examples should not be construed in a limiting sense and are presented hereinbelow only for purposes of illustration.

#A laminar film having a thickness of about 1.2 mils was produced utilizing conventional tubular coextrusion equipment. One layer of the laminate comprised a high density polyethylene layer blended with about 10% by weight of an ionomer resin. The ionomer resin was identified by the manufacturer as Surlyn-DuPont AD-8231 and the high density polyethylene resin was identified by the manufacturer as DuPont 7810. The Surlyn material was blended with the high density polyethylene to enhance its adhesion characteristics to other polymers. The second layer of the laminate, which constituted about 8% of the overall thickness of the entire laminate, was Nylon-6 and identified by the manufacturer as Allied-8207. Two conventional thermoplastic extruders were employed to supply the respective molten polymers to the tubular coextrusion die. The high density polyethylene-Surlyn blend was fed to the die from a single 21/2 inch extruder with a 20:1 L/D ratio, and the molten nylon was fed to the die with a 11/2 inch, 24:1 L/D extruder. The total output through the die was approximately 88 pounds per hour. The die diameter was about 31/2 inches and the maximum bubble diameter was about 14 inches, resulting in a blow-up ratio of about 4.0:1. The melt temperature was about 480.degree. F. for both of the polymers. A vertical flow air ring was employed immediately adjacent to the die to cool the melt. The frost-line was observed at a point about 1.5 to 2.0 feet from the die. The resultant laminar film was tested for its strength, toughness and tear resistance, and the results thereof are set forth in the following Table I.

#The material produced in accordance with Example 1 was delaminated and the physical characteristics of the high density polyethylene-Surlyn blend layer were tested. The results thereof are set forth in the following Table I.