Filter material for smoking article
United States Patent Hill Apr. 29, 1975 1 FILTER MATERIAL FOR SMOKING 3.3021501 2/1967 Greene 131/269 UX ARTICLE 3.336 l74 8/1967 Dyer ct al .1  
  3393.120 8/1968 Touey Mill. 131/269 ux [75] Inventor: Michael Hill, Seaburn, England I [73] Assignee: British Ropes Ltd., Doncaster. Primary E.\&#39;an11&#39;nerMelvin D. Rein England Attorney, Agent, or Firm-Brady, O&#39;Boyle &amp; Gates [22] Filed: Apr. 19, 1973 211 Appl. No.1 352,674 [57] ABSTRACT A filter material, particularly for tobacco-smoke filters. comprises fibrillated polyolefin sheet having main [30] Foreign Appmtanonfnonty Data 7 generally longitudinally-extending strands intercon- Apr. 20, I972 United Kmgdom 18457/72 ncctcd by interconnecting Strands and having a stantial number of free ends formed by severing main [52] U.S. Cl 131/269; 83/2 strands and/or Strands Which would Otherwise h [51 Int. Cl.... A24b 15/02 constituted interconnecting Strands. the Strands having [58] Field of Search l3l/lO.3-l0.9, a thickness in the range 5 micronS to 25 microns and l at least 40 percent (preferably at least 70 percent) of the strands having a width not greater than their thick- [56] References Cited ness UNITED STATES PATENTS 10 Cl 2 D F 3,290.20? 12 1966 Magat Cl 111 .6 131/269 ux rawmg gums FILTER MATERIAL FOR SMOKING ARTICLE This invention is concerned with filter material and particularly, but not exclusively with tobacco-smoke filter material.  
  It is well-known to produce filamentary material by splitting into a plurality of interconnected strands a polyolefin film which has been orientated in a longitudinal direction. The production of the material is known as fibrillation and the material will hereinafter be called fibrillated material of the kind referred to.&#34;  
  It has now been found and provides the basis of the present invention that fibrillated material of the kind referred to is unexpectedly effective as a tobaccosmoke filter material provided that it has certain special structural characteristics. Compared with conventional filamentary tobacco-smoke filter materials, the special fibrillated material provides, tobacco-smoke filters which give better filtration per unit pressure drop, and better filtration and a lower pressure drop are obtainable with a lower weight of material. Also, the material permits of unexpectedly easy production of tobacco-smoke filters, being readily handled by conventional machinery. The same properties which render the material very effective as a tobacco-smoke filter also render it very effective for various other filtration purposes.  
  According to the invention, a filter material comprises fibrillated material of the kind referred to having main generally longitudinally-extending strands interconnected by interconnecting strands and having a substantial number of free ends formed by severing main strands and/or strands which would otherwise have constituted interconnecting strands, the strands having a thickness in the range 5 p. to 25 p. and at least 40 percent (preferably at least 70 percent) of the strands having a width not greater than their thickness.  
  The word thickness as used herein in relation to strands means the dimension in the same direction as the thickness of the film from which the material is produced.  
  The preferred strand thickness is about 14 p. (i.e., 14 microns).  
  The number of severed ends hereinbefore mentioned present in the fibrillated material of the kind referred to may be optimised to improve significantly the filtration efficiency of the filter material whilst retaining sufficient strength for conventional continuous tow afterprocessing. The random disposal of these severed ends throughout the network effectively leads to a maximising of surface area which in turn gives improved filtration efficiencies.  
  The interconnecting strands preferably join the main strands at substantially regular spaced intervals. Thereby, if the material is expanded laterally, a network is produced which appears substantially regular, as distinct from a network in which the network has interconnections which are clearly randomly spaced and openings which randomly vary in size.  
  The polyolefin of which the polyolefin film is made may consist of polypropylene or polyethylene or a mixture of polypropylene and polyethylene or a copolymer of propylene and ethylene (see examples.  
  A whitening agent in the form of a solid material in finely divided form, preferably titanium dioxide, may be incorporated in the polyolefin. it has surprisingly been found that such agents facilitate the production of very narrow strands as hereinbefore referred to.  
  The present invention also provides a tobacco smoke filter, and a cigarette having a tobacco-smoke filter, wherein the filter comprises a body of filter material as hereinbefore defined contained in a tubular outer sheet. Preferably, said main strands extend axially (i.e.,  
 longitudinally) along the filter. Preferably, in accordance with known practice, a binding agent is incorporated in the material, e.g., by spraying the agent on to the material.  
  The present invention also provides a method of making filter material as hereinbefore defined wherein said material is produced by passing said film over a roller having projecting pins thereon. The pin arrangement, the arc of contact between the film and the roller, and the relative speed of the film and the roller are such as to produce a fibrillated material having the characteristics defined above.  
  Advantageously, a plurality of superimposed films are passed simultaneously over the roller so that fibrillation of all of the films occurs.  
  The requirements can be determined by calculation and/or routine experiment by an experienced worker in the field of fibrillation. In order to obtain a substantial number of free ends as hereinbefore mentioned, it is desirable for the fibrillation ration (i.e., the ratio of the surface speed of the roller to the film speed) to be within the range 1.05:1 to 3:1 and preferably 2:1 to 2.5:1.  
  In order to produce the preferred structure in which the interconnecting strands join the main strand at substantially regular intervals, pins are preferably arranged on the roller in parallel rows and in spaced staggered relationships, for example as specified in British Pat. No. 1,073,741. Thereby, on rotation of the roller the paths of travel of the pins in each row are different (i.e., laterally spaced from) the paths of travel of the pins in immediately adjacent rows.  
  To facilitate the production of the &#39;narrow strands. preferably each row of pins extends across the roller on a line which is inclined to a line parallel to the roller axis. Each row may be ona sinusoidal line which extends across the roller in a direction parallel to the roller axis. Alternatively, the pins may be arranged in pairs of parallel rows extending across the roller on lines inclined to lines parallel to the roller axis, immediately adjacent pairs of rows being oppositely inclined.  
  The following is an example of a method of producing tobacco-smoke filter material in accordance with the invention.  
 EXAMPLE 1 A copolymer of propylene and ethylene of Melt Index 0.8 containing approximately 20 percent by weight of copolymerised ethylene was extruded using a known blown film technique into a film of nominal 25 a thickness. The film so produced was slit to required width (e.g., 1] inches) and the slit film was passed through a standard heating and stretching (orientating) system where it was longitudinally orientated with a stretch ratio of 7:1 to produce a film of 14 p. thickness. The orientated film was passed round part of the periphery of a pinned fibrillating roller. The physical data of the roller and the operating conditions were as follows:  
 Fibrillator roller diameter 8 inches Pins in spaced staggered relation ship In parallel sinusoidal rows each extending across the roller in a direction parallel to the roller axis Number of rows of pins 90 Pin density in each row 40 pins per inch Angle of rake of pins (angle of pins to tangent to roller in opposite direction to that of roller rotation) 60 Pin projection 1 mm Pin diameter 0.0145 inch Arc of contact of film with roller 60 Film input speed 150 ft/min Surface speed of i.e. Fibrillation fihrillator roller 300 ft/min Ratio of 2:1  
  The fibrillated film, which constituted filter material in accordance with the invention, was collected direct from the fibrillating stage by conventional means. Finally a number of (e.g., three) of the fibrillated films were combined to give the required final runnage (i.e., length per unit weight.)  
  The fibrillated film so produced was then submitted to a crimping process for example involving passage of the film through a stuffer box crimper in a conventional known manner. Other conventional means of crimping, for example gear tooth&#34; crimping, false-twist crimping, etc., may also be used for inducing crimp in the fibrillated film.  
  The accompanying drawing in FIG. 1 shows a piece of the fibrillated film in accordance with the invention expanded laterally to show the network formation before the crimping operation was carried out. In FIG. 1, reference numeral 1 indicates main strands, 2 indicates interconnecting strands and 3 indicates free-ends. FIG. 2 shows a cigarette 4 having a filter tip 5 made from filter material 6 in accordance with the invention in a tubular outer cover 7.  
 , TEST 1 Tobacco smoke filters were made from fibrillated film in accordance with the invention made by the method hereinbefore described. The fibrillated film which had a runnage of 182 feet per pound (8,175 tex), was converted into filter rods using a conventional filter rod making machine. The filter rods were cut into filter tips of 15 mm length. Each filter tip contained 103 mg of fibrillated film. The pressure drop of the filter was 5.6 cm of water gauge at an airflow of 1,050 ml per minute.  
  The filters were attached to cigarettes and were smoked using a smoking machine which took a puff of 35 ml volume and 2 seconds duration every minute. A comparison of the weights of Total Particulate Matter (TPM) delivered from cigarettes having the filters with those from cigarettes without filter showed that the filter removed 40 percent of the TPM.  
 TEST 2 A 15 mm length of a commonly used cigarette filter Example 1, the filter pressure drop was 5.5 cm of water gauge, and the filter removed 35 percent of the TPM.  
 TEST 3 Filters were made and tested as in Example 1, but in this case the fibrillated film did not contain severed ends. The filter contained 103 mg of fibrillated film and the pressure drop was 4.8 cm W.G. at a flow rate of 1,050 ml per minute. The filtration efficiency for Total Particulate Matter was 35 percent.  
  The following is a further example of a method of producing tobacco-smoke filter material in accordance with the invention.  
 EXAMPLE 2 A copolymer of propylene and ethylene of melt index 0.8 (containing 20 percent copolymerised ethylene) was formed by a known blown film technique using an oscillating die into a film of 28 p. thickness. The doublelayer of the film so produced was slit to required width (e.g., 6.4 inches). Three such widths of the doublelayer of the film were superimposed and passed through a standard heating and stretching (orientating) system where they were longitudinally orientated with a stretch ratio of 7:1 to produce films of 14 M thickness. The orientated films were passed round part of the periphery of a pinned fibrillating roller. the physical data of the roller and the operating conditions were as follows:  
 Fibrillator roller diameter 8 inches Pins in spaced staggered relationships in pairs of parallel rows extending across the roller on lines inclined to lines parallel to the roller axis. immediately adjacent pairs of rows being oppositely inclined.  
 Number of rows of pins Pin density in each row 25 pins per inch Angle of rake of pins (angle of pins to tangent to roller in opposite direction to that of roller rotation) 60 Pin projection 1 mm Pin diameter 0.0145 inch Arc of contact of film with roller 45 Film input speed 210 ft/min Surface speed of Fibrillation TEST 4 The texturising process was followed by a decrimping operation, producing a bloomed fiocculent mass, the crimp characteristics of which were typically 16 crimps per inch.  
  On making up this material into a filter rod as described in Test 1, each filter rod 15 mm in length) was found to contain 72 mg of fibrillated film. The pressure drop of the filter was 4.2 of water gauge at an airflow of 1,050 ml per minute.  
 I claim:  
  1. A filter material for a smoking article comprising fibrillated material in the form of filamentary material produced by splitting into a plurality of interconnected strands a polyolefin film which has been oriented in a longitudinal direction, said fibrillated material having main generally longitudinally-extending strands, interconnecting strands interconnecting the main strands, and a substantial number of free ends formed by severing main strands and/or strands which would otherwise have constituted interconnecting strands, the strands having a thickness in the range of 5 p. to ,u. and at least 40 percent of the strands having a width not greater than their thickness, the said material being shaped to conform to the smoke passageway of said article.  
  2. A filter material according to claim 1 in which at least 70 percent of the strands have a width not greater than their thickness.  
  3. A filter material according to claim-l which the strand thickness is approximately 14 microns.  
  4. A filter material according to claim 1 in which the interconnecting strands join the main strands at substantially regularly spaced intervals.  
  5. A filter material according to claim 1 in which the polyolefin of which the material is made is selected from the group consisting of polypropylene, polyethylene, a mixture of polypropylene and polyethylene, and a copolymer of propylene and ethylene.  
  6. A filter material according to claim 1 in which a whitening agent in the form of a solid material in finely divided form is incorporated in the polyolefin of which the material is made.  
  7. A filter material according to claim 6 in which the whitening agent is titanium dioxide.  
  8. A filter material according too claim 1 made from a plurality of superimposed polyolefin films which have been subjected to fibrillation while superimposed.  
  9. A tobacco-smoke filter comprising a body of filter material according to claim 1.  
  10. A filter according to claim 9 in which said main strands extend axially (i.e., longitudinally) along the filter.