GB1175901A - Apparatus and Process for Producing Tubular Thermoplastic Film - Google Patents

Abstract

1,175,901. Nip rolls for blown tubular film. PETRO-TEX CHEMICAL CORP. 26 Jan., 1967 [26 Jan., 1966], No. 4032/67. Heading B5B. An apparatus for flattening inflated tubular films of thermoplastic polymeric material without creasing the edges of the flattened film comprises a pair of contra-rotating co-operating parallel nip rolls providing between them a centre section which receives and flattens the centre portion of the inflated film, one of the rolls having relieved non-contacting circumferential sections at each end of the centre section or one roll having a relieved section at one end of the centre section and the other roll having a relieved section at the other end of the centre section, such that the edges of the inflated film are also flattened without creasing by forming parallel cushions which are in communication with the interior of the tubular inflated film travelling towards the nip rolls and consequently inflated with the gas inflating the tubular portion of the film. As shown in plan in Fig. 2, a pair of nip rolls according to the invention comprise two cylindrical rolls 21 and 22 of equal diameter fixedly mounted in shafts 27 and 26, the roll 22 being of constant diameter along its length and the roll 22 having two circumferential relieved portions 28 located near the ends of the roll. The diameters of the centre section 29 and the two end sections 31 of the roll 21 are equal to the diameter of the roll 22 which is usually driven, roll 21 being usually an idler roll. The function of the end sections 31 of the roll 21 are to prevent bowing of the roll 21, since the end sections 31 contact, or almost contact, the roll 22. The depth of the relieved sections 28 is generally about 5 to 20 times the wall thickness of the inflated tubular film. The roll 21 may have the shape shown in Fig. 3, the portions 32 of the roll of smaller diameter in this case extending outwardly from the centre section 33 to the ends of the roll. Provided that the length of the centre section 32 is about 85 to 95% the total length of the roll, bowing or bending is not noticeable and the end sections 31 shown in Fig. 1 may be omitted. The film producing apparatus may be provided with means for directing streams of refrigerated air on to the two longitudinal strips of the inflated film which will form the two edges of the flattened film when the film is passed through the nip rolls. The film material may be polymers of alpha olefines or diolefines having the general formula R-CH=CH 2 , wherein R preferably has from one to 12 carbon atoms and is an aliphatic, aromatic or cycloaliphatic saturated or unsaturated radical. The polyolefine used may be butene-1, 4-methylbutene-1, or 5-methylpentene-1.