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LOW BUTENE COMONOMER CONTENT POLYPROPYLENE FOR USE IN BIAXIALLY ORIENTED FILM

IP.com Disclosure Number: IPCOM000128592D
Publication Date: 2005-Sep-16
Document File: 1 page(s) / 26K

Publishing Venue

The IP.com Prior Art Database

Abstract

The present invention concerns a devolatilization device which relies on increased free surface area for volatiles exposure with possibility of using all techniques available to an extruder system such a vacuum and application of stripping agents. The device uses multiple co-rotating or counter-rotating intermeshing, non-intermeshing or partially intermeshing screws in an enclosure with vacuum pulling capability. The screws are (size and number) designed in such a way to operate in a partially filled mode and will use molten polymer supplied by an upstream system (single or twin screw extruder, continuous mixer, etc.). The polymer stream is first spread through a melt manifold in the form of molten strands to maximize free surface area. The strands are then collected by the screws and conveyed downstream for additional surface renewal. For improved devolatilization, a control device can be added to control polymer passage.

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Low Butene Comonomer Content Polypropylene for use in

Biaxially Oriented Film

Film breakage is a major problem in making biaxially oriented polypropylene (BOPP) film.  In order to overcome this problem, polypropylene resins intended for BOPP use are sometimes made with high solubles content, or with low levels of ethylene comonomer.  The use of low butene-1 content random copolymers for BOPP gives advantages in BOPP film making and/or film properties.

Most BOPP (biaxially oriented polypropylene) film lines have a limit of about 50:1 area orientation ratio, which when exceeded, causes numerous web breaks in the tenter oven.  These web breaks can occur 3-4 times in a 24 hour period when line speed is greater than 300 m/min.  New propylene/butene-1 random copolymers have achieved an area orientation ratio as high as 100:1 with xylene solubles varying between 3-5% and butene content varying between 1-3%.  The present preferred formulation is 2% butene content with 4-5% xylene solubles content.

When comparable amounts of ethylene comonomer are added to propylene an improvement is noticed in the area orientation ratio similar to that of the addition of butene, but resultant web has a much narrower operating range in the tenter frame (2-4°C vs 6-8°C for the butene copolymer).  The tensile properties for the 1-2 wt % ethylene comonomer copolymer of propylene are drastically reduced 20-30% and those of the 1-2 wt % butene comonomer copolymer of propylene are reduced about 10-...