US 3407822 A
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Description (OCR text may contain errors)
Get. 29, 1968 G p, TQUEY ET AL 3,407,822
TOBACCO SMOKE FILTERS CONTAINING POLYETHYLENE ENCAPSULATED CELLULOSE PARTICLES Filed Feb. 7, 1966 F/LAMENTARY FILTER w/rH POL YE TH YL ENE ENCA PSUL A r50 CELLULOSE ADD/T/VE POL YETHYLE/VE ENCAPSULA TED POLYETHYLE/VE COAT/N6 CELLULOSE PARTICLES CELLULOSE PARTICLE F/L TER F/LA MEN rs y. ro n %o SMOKE GEORGE R TOUEY ROBERT C. MUMPOWER INVEZTORS A TTORNE Y5 United States Patent "ice 3,407,822 TOBACCO SMOKE FILTERS CONTAINING POLYETIIYLENE ENCAPSULATED CEL- LULOSE PARTICLES George P. Touey and Robert C. Mumpower, Kingsport,
Tenn., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Feb. 7, 1966, Ser. No. 525,477 Claims. (Cl. 131-266) ABSTRACT OF THE DISCLOSURE This invention discloses a tobacco smoke filter and a method of manufacture therefor. Said tobacco smoke filter is utilized for the removal of solid and vapor constituents from an efiiuent stream of tobacco smoke and comprises a filamentary carrier material arranged to provide interstices for the passage of smoke in a tortuous manner therethrough and has bonded thereon a finely divided additive of particles of cellulose encased in a polyolefin.
This invention relates to an improved cellulose acetate tow type tobacco smoke filtering material and elements formed thereof which are suitable for use in cigarettes, cigarette holders, pipes, and cigar holders. More particularly this invention relates to cigarette filters made from continuous crimped cellulose acetate filaments in the form of a tow, the tow having as additive fibrous particles of cellulose encased in a film of polymeric material.
As is known, the desirability and advantages to be gained from using a smoke filter on combustible tobacco products have been known for a number of years. As a result a wide variety of fibrous materials including crepe paper, cotton and certain textile fibers have been suggested and tried as tobacco smoke filtering means for removing nicotine, tars and other deleterious components from tobacco smoke. However, most of these materials have certain disadvantages either from the standpoint of their fabrication into filters or their undesirable effect on the taste of the smoke that has limited or totally precluded their use as a tobacco smoke filter. For example, cotton and paper cannot be conveniently processed by conventional cigarette machinery into a form that can be readily cut into filter tips and added to the end of a cigarette. Another disadvantage of tobacco smoke filters made from cotton or paper is that moisture is absorbed quite readily by the filter which makes the smoke too dry.
The use of certain textile fibers, and in particular filaments of cellulose ester, overcomes to a great extent the aforementioned fabrication difficulties encountered with cotton or crepe paper. That is, textile fibers can be manufactored in a form that is easily converted by reasonable conventional cigarette processing equipment into filter tips which can be used for tobacco smoke filtering purposes. Thus, for example, it is possible to orient a large number of cellulose acetate filaments into the form of a continuous band which is commonly known to the trade as a tow. Such tow can be plasticized, cut, and wrapped in cigarette paper to form filter rods on a filter make-up machine at speeds heretofore unknown in the industry. These filter rods are then easily cut into tips of the desired length and placed on the ends of cigarettes.
While, as just mentioned, a tow made of cellulose acetate filaments or like materials has certain advantages for manufacturing tobacco smoke filtering elements, in some instances the resultant filter has not possessed as much tar removal capabilities as desired. This is due in most part to the physical makeup of the filter elements per .se. As is known, these filter elements are prepared 3,407,822 Patented Oct. 29, 1968 from a structurally unitary rod-like mass of filaments with a wrapper encircling the mass, each filament of the mass being substantially coextensive therewith. The filaments as a whole are orientated substantially longitudinally of the mass, but each of the individual filaments having a plurality of short portions thereof crimped into diverging and converging relationship to the main filament axis with a plurality of the filaments having surface solvation bonds to contiguous filaments at random points of contact. Therefore, there is always the possibility in a filter element of this type that tar particles in the smoke will pass between the longitudinally aligned filaments. When this happens obviously these tar particles are not removed by the filter element but pass into the smokers mouth.
It is true that random bonds produced between adjacent filaments by the application of plasticizer bonding agents to the tow prior to its conversion into a paper wrapped filter element helps alleviate this condition. Also, it is true that incompleteness of filament orientation and the degree of crimp given to the tow reduces this smoke channeling effect somewhat. Nevertheless, all of these conditions are still not sufficient to make the path of the smoke sufficiently complex or tortuous so that a substantial improvement in the filter elements effectiveness for removing tar and nicotine particles is realized.
One method for making a more effective filter element from a crimped tow of cellulose acetate filaments involves the application of powdered additives to the opened tow during its continual conversion into filter elements. These solid finely divided particles fill in, to a certain extent, the channels that would otherwise exist through the filter element thereby greatly increasing the probability that the heavy smoke components will strike and become impinged upon a portion of the filter. Rice starch, flour, pectin and other like materials are among those finely divided particles that have been proposed for use in spread out crimped cellulose acetate tow fibers prior to their conversion to filter elements. However, even though the incorporation of such finely divided additives onto the surface of the crimped filaments have been successful in improving the filtering efficiencies of these filter elements from the standpoint of increasing its capacity for removing nicotine and tar, it has given rise to other equally bothersome problems. One of the more troublesome of these problems is how to keep the finely-divided additives from sifting out of the filter rod while it is being cut into filter segments, or out of the final filter when it is on the cigarette. As will be apparent this sifting out of the additive not only decreases the efficiency of the filter, but quite often these loose additives get into the smokers mouth thereby creating a condition that will not be tolerated by the smoker.
In an effort to minimize this sifting out of finely-divided additives from a filter tow or element it has been proposed that some steps be taken to bond the additive directly to the tow or element. This approach usually involves the use of an adhesive-like material which not only adds to the expense of manufacturing tobacco smoke filter elements, but also greatly complicates the processing steps necessary for forming a suitable filter element. Furthermore since tobacco smoke filters are usually held in the smokers mouth, of if a holder is employed even then the filter is near the smokers mouth, it is apparent that many materials that are strong adhesive agents cannot be used because of appearance, taste, odor or other similar reasons. Also certain materials that have adhesive properties exhibit such adhesiveness at the onset that they present problems of gumming the filter making equipment and plugging the applicator equipment.
Another method for preventing fall out of powdered additives from a cellulose acetate tow type of filter involves the use of plasticizer type of bonding agents such as triacetin, dimethyl phthalate, and the like. They have the advantage of being oily rather than tacky liquids and therefore they no not cause the filaments of the tow to adhere to the filter fabricating machinery. Also, after the final filter rod has aged for a certain length of time these plasticizers partially dissolve some of the filaments in the filter at random spots and causes a fusing of filaments which gives rigidity to the filter rod. The disadvantage of this type of bonding agent for powdered additives, however, is the fact that as the plasticizer is absorbed by the filaments to cause the fused spots less of it remains on the surface of the filaments to function as a means of keeping the additive particles bound to that surface. As a result much of the powder originally adhering to the filaments can drop out of the filter if it is jarred or tapped.
Therefore, it is apparent that the development of a finely-divided additive material that could be used to improve the filtering properties of a tobacco smoke filter without creating a sifting out problem or requiring the use of an adhesive type bonding material would represent a highly desirable step forward in the tobacco smoke filter art.
After extended investigation it has been found that such a non-sifting, adhesive free finely-divided additive can be produced which, when used in a tobacco smoke filter element, greatly improves the tar and nicotine removal capabilities of a filter element. This novel filter material and element is formed by adding a polyethylene coated cellulose powder as an additive to the cellulose acetate tow and then heating either the tow or the final filter rods formed from the tow to soften the polyethylene coating. The heating step not only bonds the coated cellulose particles to the fibers in the tow at the points of contact, but it also imparts rigidity to the filter. This is because the polyethylene coating softens, when heated properly, and functions as an adhesive.
Therefore an object of this invention is to disclose a new and improved type of additive for increasing the efficiency of a cellulose acetate tow-type filter for removing tars.
Another object is to disclose an additive which, when added to a cellulose acetate tow filter and the combination is heat set, does not fall out of the filter if it is jarred or tapped.
Yet another object is to disclose a powder which, when added to a cellulose acetate tow filter and the combination is heat set, can produce a rigid but porous structure without the application of a plasticizer or any other type of liquid bonding agent. That is, the additive not only improves the elficiency of the filter for removing tars but also serves as a bonding agent for the powder and a hardening agent for the filter rod.
A further object of this invention is to disclose a textile tow type of cigarette filter containing heat set polyethylene coated cellulose particles which show no tendency to sift out of the filter when it is tapped.
These and other objects and advantages of this invention will be more apparent upon reference to the following description, specific working examples, appended claims and drawings wherein:
FIGURE 1 is a greatly enlarged view of a filamentary tobacco smoke filter element having polyethylene encapsulated cellulose particles bonded thereto; and
FIGURE 2 is a perspective view, with portions thereof broken away, of a cigarette having a filter tip made in accordance with this invention.
As mentioned briefly hereinabove, numerous experiments have been conducted and a large group of various finely-divided materials have been tested in an effort to determine which ones are best suited for use as an additive in tobacco smoke filter elements. Many of these tested materials have proven to be beneficial in improving, for example, the tar and nicotine removal capabilities of the filter element. However, all prior known finely-divided additive materials have had one common undesirable characteristic; namely, they tend to sift out of the filter unless an adhesive or bonding agent is applied to the tow for securing them to the fibers of the filter element. Thus, it was a heretofore generally accepted conclusion that no finely-divided filter additive could be added to a cellulose acetate filter tow unless the tow was treated with a bonding or adhesive medium prior to the additive being placed on the tow.
It has been discovered, however, that a finely-divided additive material for cellulose acetate tobacco smoke filter elements can be produced which requires no prior treatment of the filter tow and has no tendency to sift out when the filter element is violently jarred or tapped. This finely-divided additive material consists of cellulose particles that are coated over their outer surface with a thin layer of a polyethylene. It is obvious that various other thermoresponsive polyolefins may be employed with advantage, as for example, polypropylene. The coating can be applied to the fibrous cellulose particles by any convenient means known to the art. One particularly elfective way of accomplishing this is by the slurry method in which the cellulosic material is suspended in a suitable liquid medium such as an organic liquid that does not dissolve or react with either the cellulose or the polymer to be formed. To assure the best possible result it is preferable that an organo-metallic-transition metal catalyst also be added at substantially this point in the process. The slurry of catalyst treated cellulosic material in the organic liquid, after the second component of the catalyst has been added, is placed in a closed reaction vessel and the monomer is fed into the vessel at a suitable rate while maintaining the slurry under agitation. Provisions should be available for controlling the temperature of the reaction vessel, and the reaction should be carried out under reasonably anhydrous conditions. As polymerization proceeds the slurry will become thicker and reaction is stopped at any desirable stage depending upon how much of the polymer is to be formed. The slurry can then be removed from the reaction vessel and simply pressed or filtered to remove the free organic liquid. The resulting polymeric encased cellulose particles can then be washed in water, methanol or other materials which easily dissol-ve out the bulk of the catalyst residue.
By this and similar methods, ethylene is polymerized directly on the surfaces of fibrous cellulose particles and the results are that each individual cellulose particle is substantially encased in a shell of the polyolefin thus producing polyethylene encapsulated cellulose particles. This novel product consisting of individual fibrous cellulose particles having a surface covered with polyethylene is illustrated in FIGURE 1. As can be seen in this final bonded product the additive particles have a rough irregular surface, with the polyolefin wholly encasing the cellulose particle. For use in most cigarette filters the coated fibrous cellulose particles should be capable of passing through a 20 mesh (U.S.S.) screen but not through a 350 mesh screen with the preferred range being between 50 and 250 mesh.
The molecular weight of the resulting polyethylene coating can vary over a wide range so long as the product is a solid at normal temperatures with a softening point within the range normally encountered with commercial polyethylene (SS-160 (1.). However, the preferred softening point range is 90130 C. since this permits a lower temperature and/or a shorter heating time to be used to soften the polyethylene coating thereby causing it to function as an adhesive for bonding the additive to the filaments and the filaments to one another. The amount of polyethylene coating on the fibrous cellulose particles should be at least 20 percent by weight and should be no greater than 90 percent by weight of the cellulose particles with the preferred range being between 30 and percent.
The polyethylene encapsulated fibrous cellulose particles can be added to the filamentary carrier tow by a variety of known techniques. For example, the opened moving tow on a filter rod making assembly can be passed underan agitated sieve containing the cellulose particles. After the proper amount of additive is spread over the entire width of the tow it is recompacted into the form of a rope or cord and passed through the section of the rod making machine which wraps'the tow with a paper tape having a thickness approximately equal to that of conventional cigarette paper. Another way of adding the polyethylene encapsulated fibrous cellulose particles to a filamentary tow filter is to allow the spread out (bloomed) tow to pass through a fluidized bed of the additive.
The amount of powdered additive required on the crimped cellulose acetate tow to produce a more efiicient filter depends on the number of fibers in the tow, the fineness of the cellulose acetate fibers, and the fineness of the powder. With heavier denier tows (i.e., 8 denier/ filament) more of the powder will be required than with the finer denier tows (i.e., 1 to 5 denier/filament), regardless of the size of the particles in the powder. In general, the amount of powdered additive will be within the range of 1045% by weight; the preferred range is -35% by weight.
As pointed out previously, the heating step required to bond the additive to the cellulose acetate filaments can be performed either during the fabrication of the filter or after the filter rod is made. The amount of heat which should be applied to the tow or the final filter rod can vary depending on the softening point of the polyethylene used to coat the particles of cellulose. Normally a temperature between 90 C. and 250 C. will be sufiicient depending upon the length of time the tow or final filter rod is heated. For example, if a temperature of 90-100 C. is used it will require a heating time of 30 minutes or longer to cause the polyolefin coating on the cellulose particles to soften sufiiciently to function as an adhesive and hardening agent. On the other hand if a temperature of say 250 C. is used it will require only a matter of a few seconds. The preferred temperature is between 150 C. and 200 C. since this gives a firm rod after the treated tow or final filter rod is heated for less than one minute. However, this is assuring that the coating represents at least of the combination of coating and cellulose particle. As will be apparent, this heating step can be carried out in an oven or other suitable heat producing unit to produce a firm highly efiicient cigarette filter of the type illustrated in FIGURE 2.
A further understanding of the invention will be had from a consideration of the following examples that may be used in actual commercial practice and are set forth to illustrate certain preferred embodiments.
Example 1 An 8 denier/filament (D/F) cellulose acetate tow containing 5,000 filaments and having 15 crimps/inch was continuously processed into 90-mm. filter rods mm. circumference) on a commercial filter rod making machine. At one end in the processthe tow was opened to a width of 15 inches and was passed through a bed of polyethylene encapsulated fibrous cellulose particles, the bed being continuously fluidized by means ofa steady flow of nitrogen passing up through it. The encapsulated cellulose particles consisted of 100 mesh fibrous cellulose wherein each particle was coated with enough polyethylene to make the final particle consist of 50% cellulose and 50% polyethylene by weight.
The tow now consisting of 75 parts cellulose acetate and 25 parts additive entered a series of tensioning rolls and was finally drawn into a garniture which compacted it and wrapped it with cigarette paper thereby forming a continuous filter rod with a circumference (25.4 mm.) equal to that of a standard cigarette. The continuous rod was cut into 90-mm. filter rod segments. Before these seg ments were heated it was observed that the powdered additive sifted out of the rods when they were tapped. It was also observed that the rods were soft and difiicult to cut with a knife. However, after the rods were heated at 120 C. for 30 minutes they were quite rigid and easily cut. Also, none of the additive sifted out of the heat-treated rods when they were tapped.
Some of the heat-treated filter rods were cut into 17- mm. segments. These were attached to standard cigarettes which were shortened to 68 mm. to compensate for the length of the filters. These filter cigarettes were smoked to 35-mm. butt lengths on an automatic smoking machine. The percentage of smoke solids (tars) removed.
by the filters is shown in Table 1. This method of automatically smoking filter cigarettes and determining the efficiency of the filters in terms of the percent tars removed is described by W. V. McConnell, R. C. Mumpower, and G. P. Touey in Tobacco Science, vol. 4, pp. 55-61 (1960). The 17-mrn. filters were also measured for pressure drop (resistance to draw) before they were placed on the cigarettes. The average pressure drop of the filters is also shown in Table 1. The method used for determining pressure drop in inches of water at an air flow rate of 17.5 ml./sec. is described by G. P. Touey in Analytical Chemistry, vol. 27, pp. 17881790 (1955).
Example 2 A 5 denier/filament cellulose acetate tow containing 10,000 filaments and having 12 crimps/inch was continuously processed into filter rods on a commercial rod making machine. At one point in the process the tow was opened to a width of 15 inches and drawn under a vibrating box having a screened (10 mesh) bottom. The box contained polyethylene encapsulated fibrous cellulose particles coating-20% cellulose by weight) capable of passing through a 20 mesh screen but incapable of pass: ing through an 80 mesh screen. After this treatment, which produced a combination of 80 parts cellulose acetate fibers and 20 parts additive, the opened tow was drawn through a heating chamber maintained at 180 C. During this 10 second exposure time the coating on the cellulose particles softened thereby bonding the particles firmly to the cellulose acetate fibers. Then the tow was drawn through the rest of the filter rod making equipment which compacted it into the form of a rope and wrapped it with cigarette paper to give filter rods of 25.4-mm. circumference. These rods were quite firm and there was no tendency for the additive to sift out of them when they were tapped. On the other hand, similar rods prepared without the heat treatment were not firm and did not exhibit this nonsifting characteristic unless they were heated as discussed in Example 1.
The rods from the heat-treated tow containing the additive were cut into 17-mrn. segments which were tested for pressure drop and for filter efficiency as described in Example 1. The results are shown in Table 1.
Example 3 A 3 denier/filament cellulose acetate tow containing 9,000 filaments and having 15 crimps/inch was continuously processed into filter rods on a commercial rod making machine. At one point in the process the spread out tow passed through a dusting chamber which added a fine powder of polyethylene encapsulated cellulose particles (200 mesh and finer) to the surface of the cellulose acetate fibers. Each particle of the additive consisted of 40 parts polyethylene and 60 parts cellulose; the dusted tow contained cellulose acetate fibers and 15% additive. The dusted tow was then drawn through the remaining parts of the machine which converted it into cigarette paper wrapped filter rods that were mm. in length and 25.4 mm. in circumference. These rods were very soft and there was a strong tendency for the powdered additive to fall out of them when theywere held in a vertical position and gently tapped. However, after they were heated at 150 C. for 20 minutes the rods were firm and easily cut. Also this heat treatment eliminated the tendency of the additive to fall out of the filters. The heattreated rods were cut into l7-mm. segments which were tested for pressure drop and for filter efficiency as described in Example 1. The results are shown in Table 1.
Example 4 The following filter tows were processed into paper wrapped rods on a commercial filter rod making machine without any devices to heat the tow or to apply an additive.
Denier/Filament Total No. of Fila- Orimps/Ineh ments in Tow In each of these cases the total number of fibers in the crimped tow represents the maximum amount of tow which can be compressed into a circumference of 25.4 mm. without bursting the paper wrapper. Filters 17 mm. in length were cut from these soft rods and tested for tar removal and pressure drop in the manner described in Example 1. The results of these tests are listed in Table 2.
The results in Tables 1 and 2 clearly illustrate that for any given tow a substantial improvement in filtering efficiency is realized by substituting the polyethylene encapsulated cellulose additive for part of the tow filaments. The filtering results obtained using filters without an additive show that a similar increase in efficiency cannot be obtained simply by adding more filaments to the tow. Finally, the results show that this improvement in filter efficiency for tars can surpass that obtained with the finest filaments (1.6 denier/filament) of cellulose acetate commercially available.
For convenience all of the data included in the examples given hereinabove is based on crimped tows of cellulose acetate. However, it is obvious that similar results could be obtained with crimped textile tows of other filaments such as regenerated cellulose filaments, polyamide filaments, polyester filaments and the like. Also it is obvious that crimped tows of filaments from other cellulose esters can be used as the carrier for the additives of this invention. Hence tows fabricated from filaments of cellulose diacetate, cellulose triacetate, cellulose acetate propionate, etc., could be employed in practicing this invention.
From the foregoing description it is readily apparent that the additive containing tobacco smoke tow and filter of this invention offers numerous advantages over those filters previously known and used in the cigarette industry. For example, not only does the use of the polyethylene encapsulated cellulose additive give a filament type tobacco smoke filter that can remove appreciably larger quantities of the solid particulates found in cigarette smoke, but no adhesive or binding agent need be added to the filaments to prevent the additive from sifting out of the filter. Thus, since no bonding material is required for holding the polyethylene encapsulated cellulose additive in the filter tow, these additives can be easily dis persed throughout a tow without the use of expensive equipment. Therefore, this elimination of all separately added bonding materials and special applicator equipment for placing or holding the encapsulated additive in a filament type filter tow permits the overall expense of producing the end product to be reduced to an absolute minimum. Furthermore, the heated filter rods or elements formed by using the encapsulated additive are rigid and do not need a plasticizer bonding agent.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove.
What is claimed and desired to be secured by th United States Letters Patent is: Y
1. As a new article of manufacture, a tobacco smoke filter rod for removing solid and vapor constituents from an effluent stream of tobacco smoke comprising a filamentary carrier material arranged to provide interstices for the passage of smoke in a tortuous manner therethrough and having bonded thereon an additive of finely divided particles, said particles each having an irregular exterior surface, each said additive particle consisting of a cellulose particle wholly encased in a polyolefin, wherein said polyolefin bonds the additive particles to the carrier material and hardens the filter rod while still wholly encasing said cellulose particles.
2. As a new article of manufacture, a tobacco smoke lter according to claim 1 wherein the amount of polyolefin on the cellulose particles is between 20 and 90 percent by weight.
3. As a new article of manufacture, a tobacco smoke filter according to claim 1 wherein the amount of polyolefin on the cellulose particles is between 30 and percent by weight.
4. As a new article of manufacture, a tobacco smoke filter according to claim 1 wherein the polyolefin on the cellulose particles has a softening point range between C. and 160 C.
5. As a new article of manufacture, a tobacco smoke filter according to claim 1 wherein the polyolefin on the cellulose particles has a softening point range between C. and C.
6. As a new article of manufacture, a tobacco smoke filter according to claim 1 wherein the amount of finely divided encased particles bonded to the filamentary carrier material is between 10 and 45 percent by weight.
7. As a new article of manufacture, a tobacco smoke filter according to claim 1 wherein the amount of finely divided encased particles bonded to the filamentary carrier material is between 15 and 35 percent by weight.
8. As a new article of manufacture, a tobacco smoke filter according to claim 1 wherein the finely divided encased particles are between 20 and 350 mesh in size.
9. As a new article of manufacture, a tobacco smoke filter according to claim 1 wherein the finely divided encased particles are between 50 and 250 mesh in size UNITED STATES PATENTS 2,765,5l5 10/1956 Knudson 131-266 X 3,039,908
SAMUEL KOREN, Primary Examiner.
D. J. DONOHUE, Assistant Examiner.
6/1962 Parmele 131266 X- 3,364,938 1/1968 Mumpower et al. 131-269 X