1. Field of the Invention
This invention relates to filters and filtration material, and in particular, but not exclusively to tobacco smoke filters, and methods of producing same.
2. Brief Description of Related Art
Numerous methods of making filtration material have been proposed. One method previously proposed by the Applicant was disclosed in British Patent Specification No. 2 205 102A, wherein a particulate plastics material, a polysaccharide, optionally a binder, and water are fed to an extruder which is operated under such heat and pressure conditions that upon emergence from the extruder die, the extrudate assumes a cross-section greater than that of the exit orifice of the die. The expanded product may be fed to the garniture of a cigarette filter making machine or shredded and then gathered and formed into a cigarette filter in a garniture of a cigarette filter making machine. A disadvantage with the product obtained by following the teaching in this document was that, although the product was considerably expanded, it was not very suitable for standard filter making product because at low moisture contents the product could be friable and brittle. Thus, the use of such product on a filter tipping machine, where the filter element is rolled to interattach same to the tobacco rod, would be likely to result in the physical breakage thereof. Furthermore, it has been found that polypropylene, and other plastics materials having similar melting points, fuse with itself and/or the polysaccharide expansion medium and will not break down if left in the physical environment without leaving a fused amalgamation of plastics material.