Patent GB-1167631-A (GB)
Title: Process and apparatus for the fibrillation of thermoplastic films
Inventor: DEKKER JAN
IPC: D01D5/42
Filed: 1967-03-20
Abstract: 1,167,631. Film fibrillation. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 8 March, 1968 [20 March, 1967], No. 12967/67. Heading B5B. A film is fibrillated by passing a strip thereof having substantially uniaxial molecular orientation in its longitudinal dimension, over a moving body having rows of cutting projections, the rows of cutting projections circulating in a closed path and hitting the film strip and cutting or scratching it in the direction of motion of the film strip, the film strip having contact with at most two successive rows of cutting projections at a time, and preferably with only one row at a time. The moving body may be a rotating cylinder or prism, and the rows of cutting projections the cogged edges of knives, which may be heated. In the preferred embodiment, between the cutting projections of each row of cutting projections sharp rims are present perpendicular to the direction of motion of the film strip or forming a sharp angle with said direction, the rims having a crimping effect upon the fibrillating material, and part of the surface of the moving body between the row of cutting projections which has just lost contact with the fibrillated film strip and the row of cutting projections which is just about to hit the film strip, is in contact with the fibrillating material. The velocity of the film strip is suitably between 2 and 200 m./min., and the velocity of the cutting projections between 10 and 1500 m./min., but always larger than that of the film strip. The film strip may be treated on one or both sides; a laminate comprising two layers the stresselongation curves of which do not coincide, may be used as the film strip. Specified thermoplastic materials include polymers and copolymers of olefins, e.g. polyethylene and polypropylene, polyamides, polyesters, e.g. polyethylene glycol terephthalate, and polymers of pivalolactone, polyvinyl chloride and polyvinylidene chloride. Apparatus as shown comprises an assembly of parallel rows 2 (Fig. III) a plurality of separate cutting projections, e.g. cogs or pins. The knife may be a strip which is rectangular or triangular in a cross-section perpendicular to the direction of the cogged edge a, as in Figs. I, 1 and 2. Figs. I, 3 and I, 4 show alternative forms. The knife may have several cogged edges, as in Figs. I, 5-8, which are cross-sections perpendicular to the cogged edges, the latter being shown at a, b, c and d. A cogged edge is provided with a sequence of cogs or teeth, generally alternating with notches, grooves or incisions. Fig. II shows various cogs and notches in cross-section and in plan view, 1 showing pyramidal and 2, prismoidal cogs. The notches in II, 1 and 2 are of triangular cross-section; Fig. II, 3, shows pyramidal cogs of triangular cross-section and notches of trapezoid cross-section; Fig. II, 4, shows pointed cogs and notches of semicircular cross-section. If the bottom of notches as shown in Figs, II, 3, and II, 4, contains a sharp rim perpendicular to the direction of motion of the film strip, or forming a sharp angle therewith, this rim causes a crimping or curling of the fibrillated material; hence fibrillation and crimping may be achieved simultaneously. Fig. IV shows, in cross-section, a typical arrangement of knives 3 and guide rolls 1, 2, the knife cross-section being as in Fig. I, 3. Fig. V shows different shapes of cogs, in cross-section in a plane through the tops of the cogs and the centre of the axis of rotation. Examples are given, relating to the fibrillation of polypropylene.