Patent GB-936535-A (GB)
Title: Improvements in and relating to coating
IPC: B29C48/10
Filed: 1961-05-16
Abstract: <PICT:0936535/III/1> <PICT:0936535/III/2> <PICT:0936535/III/3> <PICT:0936535/III/4> A method for coating a thermoplastic film comprises extruding a molten thermoplastic material in the form of a seamless tubing, maintaining such tubing in an essentially unstretched condition, applying an adherent coating material to the unstretched tubing, regulating the thickness of the said coating and the distribution thereof around the periphery of the tubing by passing the coated tubing through a secondary die peripherally bearing against the coated surface of the tubing and thereafter longitudinally and transversely stretching the coated tubing.  The thermoplastic material may be polyethylene, polycarbonate homo- or copolymer, vinyl resin, e.g. TiO2 pigmented rigid vinyl chloride homopolymer or clear rigid vinyl chloride copolymer, and polystyrene. The coating material which may be applied as a solution, molten liquid or powder by spraying, immersing or fluidized bed techniques, may be a condensation product of a dimerized linolenic acid with a diamine, pentaerythritol ester of rosin, paraffin wax, microcrystalline wax, aluminium paste, polyethylene and mixtures thereof.  A rolling annular bank of coating material is formed around the tubing as it passes through the secondary die.  As shown, a suitable apparatus comprises an extruder 10, a primary die 14 which forms the molten thermoplastic into seamless tubing 16, means for cooling said tubing 16, e.g. air ring 18, means for coating said tubing 16, a secondary die 20 spaced above and coaxial with primary die 14 and bearing peripherally against said tubing 16, means for longitudinally and transversely stretching the coated tubing, a standard collapsing frame 24 and nip rolls 26 which withdraw the tubing 16 and feed it to a windup apparatus (not shown).  The tubing 16 may be stretched by introducing fluid into it via conduit 30.  The air ring 18 and secondary die 20 may be rotated.  A suitable receptacle 44a for containing the coating material is shown in Fig. 2.  It may be provided with heating elements 46 and may also possess a porous bottom to obtain a fluidized bed.  In a modification (Fig. 4) the tubing may be passed through a bed of prewetting compound 44c before being sprayed by air pressure with liquid coating material from applicator ring 50.  In Fig. 5 there is shown an embodiment adapted to coat both inner and outer surfaces of tubing 16 which embodiment comprises an inner doctor blade 54 supported by die pin 34 provided with channels 56 through which the coating material is fed to inner surface 60 of the tubing 16.  The coating compositions containing wax disclosed are: (1) 52,5 parts "Versamid" (Registered Trade Mark, a condensation product of dimerized linolenic acid with a diamine), 42,5 parts "Pentalyn" (Registered Trade Mark, the pentaerythritol ester of rosin) and 5 parts paraffin wax; (2) 30 parts polyethylene, 14 parts microcrystalline wax, 56 parts paraffin wax and 50 parts aluminium paste (i.e. 65% leafing aluminium in mineral spirits); (3) 52,5 parts "Versamid", 42,5 parts "Pentalyn" and 5,0 parts paraffin wax; (4) 30 parts polyethylene, 14 parts microcrystalline wax and 56 parts paraffin wax.  All parts are by weight.ALSO:A method for coating a thermoplastic film comprises extruding a molten thermoplastic material in the form of a seamless tubing, maintaining such tubing in an essentially unstretched condition, applying an adherent coating material to the unstretched tubing, regulating the thickness of the said coating and the distribution thereof around the periphery of the tubing by passing the coated tubing through a secondary die peripherally bearing against the coated surface of the tubing and thereafter longitudinally and transversely stretching the coated tubing.  The thermoplastic material may be polyethylene, polycarbonate homo- or copolymer, vinyl resin, e.g. TiO2 pigmented rigid vinyl chloride homopolymer or clear rigid vinyl chloride copolymer, and polystyrene. As shown, a suitable apparatus comprises an extruder 10, a primary die 14 which forms the molten thermoplastic into seamless tubing 16, means for cooling said tubing 16, e.g. air ring 18, means for coating said tubing 16, a secondary die 20 spaced above and coaxial with primary die 14 and bearing peripherally against said tubing 16, means for longitudinally and transversely stretching the coated tubing, a standard collapsing frame 24 and nip rolls 26 which withdraw the tubing 16 and feed it to a windup apparatus (not shown).  The secondary die 20 is adapted to relieve the greater part of the longitudinal stress exerted by the drawing means on the portion of tubing between the primary and secondary dies to maintain such portion in an essentially unstretched state. The tubing 16 may be stretched by introducing fluid into it via conduit 30.  The air ring 18 and secondary die 20 may be rotated. A suitable receptacle 44a for containing the coating material is shown in Fig. 2.  It may be provided with heating elements 46 and may also possess a porous bottom to obtain a fluidized bed.  In a modification (Fig. 4) the tubing may be passed through a bed of prewetting compound 44#c before being sprayed by air pressure with liquid coating material from applicator ring 50.  In Fig. 5 there is shown an embodiment adapted to coat both inner and outer surfaces of tubing 16 which embodiment comprises an inner doctor blade 54 supported by die pin 34 provided with channels 56 through which the coating material is fed to inner surface 60 of the tubing 16.  The coating compositions disclosed are: (1) 52,5 parts "Versamid" (Registered Trade Mark, a condensation product of dimerized linolenic acid with a diamine), 42,5 parts "Pentalyn" (Registered Trade Mark, the pentaerythritol ester of rosin) and 5 parts paraffin wax; (2) 30 parts polyethylene, 14 parts microcrystalline wax, 56 parts paraffin wax and 50 parts alu <FORM:0936535/IV(a)/1> <FORM:0936535/IV(a)/2> <FORM:0936535/IV(a)/3> <FORM:0936535/IV(a)/4> minium paste (i.e. 65% leafing aluminium in mineral spirits); (3) 52,5 parts "Versamid", 42,5 parts "Pentalyn" and 5,0 parts paraffin wax; (4) 30 parts polyethylene, 14 parts microcrystalline wax and 56 parts paraffin wax.  All parts are by weight.ALSO:A method for coating a thermoplastic film comprises extruding a molten thermoplastic material in the form of a seamless tubing, maintaining such tubing in an essentially unstretched condition, applying an adherent coating material to the unstretched tubing, regulating the thickness of the said coating and the distribution thereof around the periphery of the tubing by passing the coated tubing through a secondary die peripherally bearing against the coated surface of the tubing and thereafter longitudinally and transversely stretching the coated tubing.  The thermoplastic material may be polyethylene, polycarbonate homo- or co-polymer, vinyl resin and polystyrene.  The coating material which may be applied as a solution, molten liquid or powder by spraying, immersing or fluidized bed techniques, may be a condensation product of a dimerised linolenic acid with a diamine, pentaerythritol ester of rosin, paraffin wax, microcrystalline wax, aluminium paste, polyethylene and mixtures thereof.  A rolling annular bank of coating <PICT:0936535/IV(a)/1> <PICT:0936535/IV(a)/2> <PICT:0936535/IV(a)/3> <PICT:0936535/IV(a)/4> material is formed around the tubing as it passes through the secondary die.  As shown, a suitable apparatus comprises an extruder 10, a primary die 14 which forms the molten thermoplastic into seamless tubing 16, means for cooling said tubing 16, e.g. air ring 18, means for coating said tubing 16, a secondary die 20 spaced above and coaxial with primary die 14 and bearing peripherally against said tubing 16, means for longitudinally and transversely stretching the coated tubing, a standard collapsing frame 24 and nip rolle 26 which withdraw the tubing 16 and feed it to a windup apparatus (now shown).  The tubing 16 may be stretched by introducing fluid into it via conduit 30.  The air ring 18 and secondary die 20 may be rotated.  A suitable receptacle 44a for containing the coating material is shown in Fig. 2.  It may be provided with heating elements 46 and may also possess a porous bottom to obtain a fluidized bed.  In a modification (Fig. 4) the tubing may be passed through a bed of prewetting compound 44c before being sprayed by air pressure with liquid coating material from applicator ring 50.  In Fig. 5 there is shown an embodiment adapted to coat both inner and outer surfaces of tubing 16 which embodiment comprises an inner doctor blade 54 supported by die pin 34 provided with channels 56 through which the coating material is fed to inner surface 60 of the tubing 16.