Patent GB-1230991-A (GB)
IPC: B29C48/05
Filed: 1967-05-30
Abstract: 1,230,991. Composite filaments. O.-B. RASMUSSEN. 29 May, 1968 [30 May, 1967], No. 24836/67. Heading B5B. [Also in Division D1] A filament comprises a core of a substantially homogeneous polymer material A and, as a coat, a fine dispersion in the stretched state of at least two mutually incompatible polymer materials B and C, B being compatible with A and bonded to A at the interface of the core and the coat, C being easily removable, and B forming a fibrous structure having an average fibre diameter not exceeding 10Á, the fibres on the average being arranged around the core in a helical orientation. Preferably, component B is in the form of crystal whiskers, has a higher melting range than component A, and has a higher modulus of elasticity than component A. Suitably component A is a copolymer containing a major proportion of the segments from which component B is formed, and thus A may be an elastomeric polyurethane copolymer and component B a compatible polyurethane homopolymer. Alternatively, A may be a polyamide copolymer and B a polyamide homopolymer. The filament is made by extruding a continuous filament of a filament-forming substantially homogeneous polymer material A, applying to the surface of said filament, while it is being extruded, a coating material consisting of a fine dispersion of at least two mutually incompatible polymer materials B and C, B being compatible with A and capable of adhering thereto, C being easily removable, and subjecting said coated filament, while still in a fluid or semi-fluid state, to simultaneous stretching and twisting. B and C may be mixed at random to a fine dispersion, which is extruded through one channel system and A extruded through another channel system, the two polymer streams united in a rotating nozzle designed to apply the dispersion as a coating on a core of A, the coated filament hauled off by means not following the rotation of said nozzle, and the filament solidified by cooling. Thus in Fig. 2, 1 is a rotating nozzle, 2 a static part for feeding a polymer A and 3 a static inlet part for the polymer dispersion (B+C). Polymer A is fed through channel 4, which is connected to one extruder, whereas the polymer dispersion is fed through channel 5 connected to another extruder. Channel 5 widens out to a ring-formed chamber 6, which is in connection with a series of channels 7 arranged in star-form in the rotating part. The dispersion is thus coated upon the core material in the chamber 8. During the passage through channels 5, 6, 7 and 8, the dispersion is strongly drawn and thus acquires a fibre-like structure in the melted state. The filament is hauled off from the nozzle by rollers which do not follow the rotation of 1, and thus the structure of the stretched dispersion is arranged helically. Air cooling is applied to solidify the component B of the dispersion immediately after the extrusion, and the cooling effect is so controlled that the crystallization of B takes place when A has only been stretched to a very small extent, whereas a deep drawdown of the core A is allowed after the crystallization of B. Fig. 1 shows the structure of a filament formed from a composite filament by removal of C, e.g. by dissolution, and shows the fibrous sponge or network formed material B twisted around the core material A. The meshes of the network or sponge formed by B may be very open because of the drawing-down of the core A. In the example, A is a copolymer of polyhexamethylene adipamide and polycaprolactam in a copolymerization ratio of 40/60, B is polycaprolactam homopolymer, and C is polyethylene. The relative proportions of A, B and C are 50: 50:10. B and C are first dry-blended, then mixed in a planetary screw extruder from which the dispersion is fed to the device of Fig. 2. Component A is fed to the die by means of a normal extruder. The diameter of the orifice of the extruder is 0À5 mm., and the filament is drawn-down to a diameter of 0À08 mm., while the copolymer is still molten. The final product has a twist of about 1 rotation per cm.