US2765515A - Method of making a filter for tobacco smoke - Google Patents

Description

Get. 9, 1956 H. w. KNUDSON 2,765,515

METHOD OF MAKING A FILTER F OR TOBACCO SMOKE Filed Oct. 7, 1953 HAROLD M KNUDSO/V METHOD OF MAKING A FILTER FOR TOBACCO SMOKE Harold W. Knudson, Norwood, Mass., assignor to H & V

Specialties Co., Inc., East Walpole, Mass, at corporation of Massachusetts, and P. Lorillard Oompany, New York, N. Y., a corporation of New Jersey, jointly Application October 7, 1953, Serial No. 384,673 Claims. (CI. 28-72) This invention relates to the treating or conditioning of tobacco smoke to render it less irritating and less toxic, and pertains more specifically to a filter for removing a selected portion of the smoke particles in fresh tobacco smoke and to a method of making the same.

It appears to be generally agreed that tobacco smoke, particularly when inhaled, is at least potentially harmful, producing undesirable physiological effects, especially in the case of individuals suffering from cardio-vascular disorders, stomach disorders, and the like; and it has been found that even apparently physically sound individuals may show minor blood pressure changes caused by smoking, although in the case of such individuals, irritation of the membranes of the nose and throat is the primary symptom. Despite the potentially harmful effects of smoking on certain individuals, it has been found that substantial reduction or complete cessation of smoking frequently produces even more harmful effects because of shock, both physical and psychological, to the individuals system. This problem is of ever increasing magnitude because of the increasing popularity of cigarette smoking.

It has been found that the smoke particles present in fresh tobacco smoke have for the most part diameters of the order of 0.1 to 0.6 micron and that particles of this size, when inhaled into the lungs, are to a large extent readily exhaled again. However, particles of these small diameters tend to agglomerate into larger particles quite rapidly, even during passage through the body of the cigarette, the rate and extent of agglomeration increasing with the mass concentration of the smoke particles in 'a given volume of gas or air. A substantial proportion of such small particles, in the mass concentration ordinarily present in the mouth of an individual smoking an ordinary cigarette, will agglomerate or condense to larger particles having diameters greater than 0.6 micron in a period of time of the order of a few microseconds. These large particles which are formed in the month before the smoke is inhaled into the lungs may to some extent be condensed upon the tongue and the membranes of the nose and throat by impingement thereagainst, but many survive to be drawn into the lungs, where a substantial proportion are retained by impingement upon the tissues.

Furthermore, when the mass concentration of the smoke particles is high, as is normally the case in smoking ordinary cigarettes, agglomeration and condensation of the small smoke particles continue as these particles are inhaled, larger smoke particles being formed during the period while the smoke is in the trachea, bronchi, and lungs. The large particles thus formed are not completely removed by exhalation but tend to impinge against and be condensed on the tissue of the lungs, bronchi, and trachea. It is the large particles, retained in the lungs, which are believed to be primarily responsible for undesirable physiological changes.

Elimination of all of the smoke particles is undesirable, since that leaves only a colorless and highly unpalatable mixture of combustion gases. However, it has of the smoke particle been found that the present invention is capable of removing not only the large agglomerated smoke particles, but also a substantial proportion of the small particles present in tobacco smoke as it is drawn into the mouth, thus resulting in a greatly reduced mass concentration of smoke particles in the smoke which is inhaled, and greatly reducing the rate of agglomeration or condensation of these particles with each other to form larger smoke particles in situ. As a result, the undesirable physio logical consequences of the accumulation of smoke particles in the lungs and respiratory tract are substantially avoided.

The invention will be described with reference to certain embodiments shown in the appended drawings in which:

Fig. 1 is a schematic representation of the path of a smoke particle past a fiber of large diameter, such as the fibers present in tobacco smoke filters of the prior art;

Fig. 1a is a similar representation of the path of a smoke particle past a fiber of small diameter;

Fig. 2 is a view in elevation, partly broken away and in section, of a filter of the present invention embodied in a cigarette;

Fig. 3 is an end elevation of another embodiment of my invention;

Fig. 4 is a view in elevation, partly broken away and in section, of a smoking pipe embodying the present invention; and

Fig. 5 is a view in elevation, partly broken away and in section, of a cigarette holder embodying the present invention.

As was pointed out above, smoke drawn into the mouth from an ordinary cigarette contains a predominant proportion of particles of about 0.1 to 0.6 micron diameter. Since the diameter of ordinary paper fibers or textile fibers of the type heretofore employed in tobacco filters is of the order of 10.0 to 25.0 microns, there is present, in the case of the small particles, a situation such as portrayed in Fig. 1 where A is a smoke particle, B is a cross-sectional view of the fiber, C is a slip line representing the flow of the air or gas stream past the fiber, and D is a similar slip line with the Brownian movement of theparticle (denoted by the wavy line F) superimposed thereon. In order for the smoke particle to be removed from the air or gas stream, it must impinge against or collide with the fiber. The possibility of such collision or impingement in the case of such large diameter fibers are remote, because distortion of the slip line around the fiber is sufii-ciently great to overcome the effect of inertia as well as the effect of displacement due to the Brownian movement.

I have found that by employing in such a filter obstructions having a diameter of the order of the diameter of the smoke particles to be removed, that is, having a diameter of the order of 0.1 to 2.0 microns, the smoke particles A do readily impinge against the obstruction indicated by B in Fig. la. The reason for this impingement apparently is that the distortion of theslip stream C around the small diameter obstruction B is not sufficiently great to overcome the inertia of the particle and not greater than the magnitude of'the Brownian movement, as indicated by F, although I do not wish to be bound by this theory. In the case of the large diameter obstruction B of Fig. I, obviously a much higher velocity than is realized with cigarettes in practice would be required to achieve this result.

Accordingly, the filtering medium of the present invention takes the form of a screening or filter member disposed in the path of the tobacco smoke in the form of a stereoreticulate mass including obstructions, such as fibers having for the most part a diameter of 0.1 to 2.0

microns, approaching the diameters of the smoke particles to be removed, theseobstructions being interdispersed and mixed with obstructions, such as fibers, of substantially larger diameter.

The small diameter obstructions prefefably' take the form of fibers. Mineral fibers, suchas asbestos; or glass fibers of the specified diameters have been foundto be particularly satisfactory. However, fibers of a variety of other materials, such as nylon, cellulose acetate, viscose rayon, and polyester fibers; such as Orl'on' and Dacron, are satisfactory provided their diameters are within the specified range.

The obstructions of larger diameter also preferably take the form of fibers, conventional textile fibers, such as cotton, rayon, or other'cellu'losic fibers being preferred. Wool and nylon fibers, as well as fibers of other synthetic textile materials, may also be employed. These fibers normally have diameters of an order of 10.0 to 25.0 microns.

The length of the small diameter fibers or obstructions present in the filter is very small. Opening of asbestos to the extent required to provide fibers of the desired range of diameter inherently results in breaking of the fibers so that they range in length from 0.1 to a' maximum of 3.0 mm. Even when the asbestos is thoroughly opened, there may remain occasional bundles or' sticks of large diameter (over 2.0 microns) ranging in length up toabout 6 mm. However, all of the small diameter fibers (0.1- 2.0 microns) will be no more than 3 mm. in length, and the major proportion will be very much shorter-of the order of 0.1 to 0.3 mm. 1

The length of the larger diameter fibers or obstructions is not critical and may vary upwardly from 3 inch or even less, although they preferably are at least A inch in length and may be of greater lengths up to several inches, although normally such fibers will be no longer than the overall dimensions of the filter.

In order to reduce themass concentration of the smoke particles sufiiciently to have the desired eifec't upon the rate of agglomerationof these particles, and hence upon the extent of retention of smoke particles in the mouth and nose, and particularly in the lungs of the smoker, while at the same time avoiding objectionable impairment of the odor and flavor of the tobacco, it has been found that approximately 40% to 60%" by weight of the smoke particles should preferably be removed from the smoke. Accordingly, the preferred embodiment of the invention is a' filter designed to remove 40% to 60% by weight of the tars and nicotine which form the smoke particles. In order' to achieve this preferred result, the filter should include from 10% to 30% by weight of small diameter obstructions or fibers", the balance being fibers or obstructions of larger diameter.

it will of course be understood that the quantity of the tobacco smoke particles removed is not entirely afunction of the relative weights" of the small diameter and large diameter fibers since the density or compactness of the mixed fibers and the overall dimensions of the filter also affect the result. In order to achieve the desired result with cigarettes, a filter which includes from 10% to 30% by weight of small diameter fibers preferably has a diameter from 0.81 to 0.83 centimeter, a length from 1.0 to 1.2 centimeter, and an apparent specific gravity (weight per unit volume) from 0.1 to 0.23 gram per'cubic centimeter, the ratio of solids to voids by volume being of the order of 1:10 to 1:30, usually about 1:25. It has been found that a filter having these dimensions and the specified apparent specific gravity is capable of removing the desired proportion of smoke particles without objectionable reduction or impairment of the draw or case with which the smoke is drawn through the filter.

In the manufacture of my filter, it is important that the blending of the two classes of fibers be as uniform as possible. In addition, it is important that the small diameter fibers be thoroughly opened, the degree of opening required being much greater than is the case with asbestos fibers which have been commercially available heretofore. The opening of such fibers, which normally contain substantial quantities of sticks (fiber clusters or agglomerates), may be accomplished by a crushing and grinding operation, as on a hammer mill, followed by screening and further opening of the fibers on a mixing picker and carding machine while simultaneously blending the opened fibers with at least a portion of the larger diameter fibers. If the opening. of the small diameter fibers is carried out in the absence of the larger fibers, it has been found that they tend to reagglomer'ate into clusters before they can be interdispersed or blended with the larger diameter fibers. If the small diameter fibers are blended with the total amount of large diam eter fibers in one operation,v the resulting fiber mass is so large and flufiy, due to the extreme mechanical action necessary to completely open the small fibers, that it cannot be accommodated on suitable processing machinery. Best results have been obtained by first blending the small diameter fibers with approximately an equal weight of larger diameter fibers, the remainder of the larger diameter fibers being interdispersed in the mixture in a second step. For example, the small diameter fibers and an equal weight of the larger diameter fibers may be fed together to the mixing picker where they are opened and blended. This blend is then fed with the remaining portion of the large fibers through a second mixing picker for further opening and blending. This blended mass is fed into a breaker carding machine, thence into a finishing carding machine from which it is obtained in the form of a web or roving. Alternatively a mixing picker such as is used in the wool industry may be employed for the formation of a lap of mixed fibers and the lap may be delivered to the feed apron of a wool carding machine.

The two fibers in the desired proportions may also be fed into a hard waste opener which comprises a drum and pins picking from two sets of feed rollers and which provides extreme retting of the fibers. The blend of small diameter fibers with a portion of the large diameter fibers thus prepared is then fed to a mixing picker or to a wool mixing picker together with the balance of the large diameter fibers, and from there to a carding machine.

It has also been found that air-laid webs of the fibers mixture, such as those which are formed on a Rando- Webber machine by feeding the opened and blended fibers into an air blast which then deposits them as a web upon a rotating perforated cylindrical condenser are eminently satisfactory for the purpose of the present invention.

The larger diameter fibers in the fiber mixture serve to maintain the structure sufficiently open to permit ready passage of air and to prevent excessive impairment of draw. In the absence of such large diameter fibers, the density of the filter would be such that it would be virtually impossible to draw smoke through it. In the preferred form of the invention, the resistance of the filter to draw is not substantially greater than an equivalent volume of tobacco as contained in a cigar, cigarette, or pipe, the filter under these conditions effectively removing from 40% to 60% by weight of the tars and nicotine, i. e., of the smoke particles.

However, it should be understood that the range of proportions of small diameter and large diameter fibers is not critical. Even with amounts of small diameter fibers as low as 1% by weight of the mixture, the filter of the present invention shows a distinct improvement over the crepe paper or all cotton filters of the prior art. Normally, however, the filters of the present invention should contain at least 5% by weight of small diameter fibers and in some cases it may be desirable to increase the proportion of small diameter fibers to as much as 30% by weight or more despite the fact that at this point there is definite impairment of taste and flavor of the smoke.

The web of mixed fibers prepared as described above may be formed into a filter in several ways. In some cases I have found it desirable to apply a hinder or bonding material to the fiber mixture in order to bind together the individual fibers or a substantial proportion of them at their intersections to render the filter firm and resilient and to prevent undue compression with consequent impairment of draw. The binder material may be a thermoplastic or thermo-sensitive material if desired, such as a synthetic resinous binder. Among the resins which may be employed are polyethylene, polystyrene, polymers and copolymers of vinyl chloride, vinyl acetate, vinylidene chloride, methyl acrylate, methyl methacrylate, and the like, polyvinyl acetals such as polyvinyl butyral, polyester resins phenol formaldehyde, and the like. Preferably the thermo-sensitive binders have a softening point or activation point between about 150 and 300 F. The binder material may be applied to the fiber mixture in the form of particles of dry solid material or liquids droplets, or a dispersion or emulsion of the binder material in an aqueous or other liquid medium may also be employed. In any event, the binder material may be applied to the fiber mixture by blowing or spraying or by any other suitable means. If the bonding material is applied to the fibers in the form of a solution, care should be taken to coat only the larger diameter fibers, as for example by coating such fibers before they are blended with the fibers of small diameter.

If desired, the binder material itself may take the form of a fibrous material, and may replace a part or all of either the small diameter or the large diameter fibers in the fibrous mixture. In such cases, the fibrous binder material is preferably thermo-sensitive so that a subsequent heating step is required to activate the binder material and cause the fibers to be bonded together at their intersections. It has also been found that the binder material may be applied as a coating on at least a portion of the large diameter fibers, this coating, when the binder material is thermo-sensitive, being activated by a subsequent heating step.

When the binder material is applied to the fiber mixture, care should be taken to avoid providing a continuous coating of binder material for any substantial proportion of the small diameter fibers, since such a coating will tend to increase the diameter of these fibers beyond the effective range. The proportion of binder material to fiber mixture is about 10% to 25% by weight, preferably about 15% by weight.

The web of mixed fibers, which may be of any desired thickness ranging from a few hundredths of an inch upwards, may be formed into a filter unit by several different methods. In one embodiment of the invention, an approximately cylindrical rod shaped roving may be rawn from the web and cut into the lengths desired for the particular filter. In order to achieve the desired apparent density in the finished filter, the roving may be compressed radially as by passing it through a suitable tubular die, the extent of compression depending, of course, upon the initial apparent density of the roving. Normally, the diameter of the compressed roving is from one-half to one-tenth that of the uncompressed roving. If desired, the initial roving may be of relatively small diameter and two or more such rovings may be combined with a light twist. In any event, the small diameter fibers are arranged in random or heterogeneous fashion in the finished filter, but the larger diameter fibers, a substantial proportion of which are oriented longitudinally of the web by the carding operation, are still further oriented when the roving is drawn from the web, so that in the roving the major proportion of the larger diameter fibers extend generally longitudinally of the roving. When a binder material is employed, the binder may suffice to maintain the roving in the desired state of compression either by applying the binder material to the roving while it is maintained in a compressed condition or by activating a previously applied thermo-sensitive binder by heating during this period.

' A textile fabric, either finely woven or of open mesh,

may also be employed, particularly in the case of a filter for a pipe or cigarette holder. Encasement of the roving in the wrapping material may be accomplished by depositing the roving upon an elongated strip of the wrapping material bent into approximately U-shape in transverse section, then passing the assembly through a tubular die so as to compress the roving and simultaneously lap the edges of the wrapping material, which may be bonded together by any suitable means, such as a conventional cigarette paper adhesive applied in a conventional manner. When a wrapping is employed, activation of the thermo-sensitive binder, if present, may be brought about by heating after the wrapping is applied. Any suitable heating means may be employed, followed if necessary by a cooling step. Following encasement of the roving in the wrapping, the resulting elongated cylinder may be severed transversely into lengths desired for the individual filter units.

As shown in Fig. 2 of the drawing, the individual filter element 10 consisting of a roving including Bolivian blue asbestos fibers and cotton fibers is encased within a wrapping 12 which may simulate ivory or cork, for example, to provide a conventional tip on cigarette 14.

In Figs. 4 and 5, a similar roving 10 having somewhat different overall dimensions and encased within suitable wrappings 18 and 20, respectively, is shown as employed for filtering smoke in a pipe or a cigarette holder. Because of the greater efficiency of the filters, they become loaded with tars and nicotine much sooner than conventional filters and accordingly should be changed more often. However, the filter of Fig. 5, for example, even after the smoking of say ten cigarettes, is still upwards of 200% more efficient than a conventional crepe paper or spun viscose filter freshly inserted in the holder.

Additional mechanical strength may be imparted to the roving when necessary or desirable by braiding the roving with another elongated fibrous material, such as cotton thread or yarn or any other suitable textile yarn or thread, following which the braided roving may be encased in a suitable wrapping if desired as described above.

In another embodiment of the invention, the web of mixed fibers may also be formed into a suitable individual filter element by interleaving the web with layers of a denser paper-like material to form the filter illustrated in Fig. 3 wherein the Web of mixed fibers 10 is folded or spirally wrapped along with crepe paper 16, the whole being compressed within an encasing wrapping material 12, such as paper. The efiiciency of such a filter is at least 500% as great as the efliciency of the same structure without the web of fibrous material, assuming a weight ratio as between the fibrous web (comprising 10% to 20% asbestos fibers) and the crepe paper of approximately 1:2.

In forming such an interleaved filter construction, one or more layers of fibrous web may be plied up with one or more layers of crepe paper or the like to form a laminate, and the laminate may be folded or rolled upon itself into an elongated generally cylindrical form which is then encased in the same wrapping as may be employed for the roving. A binder material for the fibers of the web may be employed in this case also and the laminate may be compressed to any desired extent during or after its formation into a cylinder, as by passing the generally cylindrical assembly through a tubular die while encasing it within the wrapping. Following the wrapping, the assembly may be severed transversely into any desired lengths to form the individual filter units.

This application is a continuation in part of my copending application Serial No. 260,187 filed December 6, 1951.

Although I have herein described specific embodiments of my invention, I do not intend to limit myself solely thereto, but to include all of the obvious variations and modifications within the spirit and scope of the appended claims.

I claim:

1. The method of making a tobacco smoke filter which comprises opening and blending fibers having a diameter of the order of 0.1 to 2.0 microns and fibers of larger diameter, interdispersing said blend with additional hers of said larger diameter to form a web in which the weight of said larger diameter fibers amounts to from 70% to 95% of the total weight of fibers, and compressing said web within a tubular wrapping to an apparent density from 0.1 to 0.23 gram per cubic centimeter.

2. The method of making a tobacco smoke filter which comprises opening and blending a mass of fibers having diameters of the order of 0.1 to 2.0 microns with a mass of fibers of larger diameter, interdispersing said blend with additional fibers of said larger diameter to form a web, forming said web into a roving, encasing the roving in a substantially impervious wrapping, and severing the encased roving transversely into individual filter elements.

3. The method of making a tobacco smoke filter which comprises opening and blending a mass of fibers having diameters of the order of 0.1 to 2.0 microns with a mass of fibers of larger diameter, interdispersing said blend with additional fibers of said larger diameter to form a web, interleaving said web with layers of paper to form a laminate, compressing said laminate into tubular form and encasing it in a substantially impervious wrapping, and severing the encased laminate transversely into individual filter elements.

4. The method as defined in claim 9 wherein at least some of the fibers are thermo-sensitive and including the step of heating the fiber mixture to bond said thermosensitive fibers to other fibers at their intersections.

5. The method of making a tobacco smoke filter which comprises opening and mixing fibers having a diameter of the order of 0.1 to 2.0 microns and fibers of larger diameter, forming the fiber mixture into a web, forming the web into a roving, braiding the roving with another elongated mass of fibrous material to add strength thereto, encasing the braided roving in a substantially impervious wrapping, and severing the encased braided roving transversely into individual filter elements.

6. The method of making a tobacco smoke filter which comprises opening and blending a mass of fibers having diameters of the order of 0.1 to 2.0 microns with a mass of fibers of larger diameter, lnterdispersing said blend with additional fibers of said larger diameter to form a web, applying to said fiber mixture a bonding material adapted to bond the fibers together at their intersections, encasing said fiber mixture in a substantially impervious tubular wrapping, and severing said encased fibers into individual filter units.

7. The method of claim 6 wherein the bonding material is thermo-sensitive and the fiber mixture is heated after application of the bonding material thereto to activate the bonding material and to bond at least some of the fibers together at their intersections.

8. The method of making a tobacco smoke filter which comprises opening and mixing fibers having a diameter of the order of 0.1 to 2.0 microns and fibers of larger diameter. forming the fiber mixture into a web, forming the web into a roving, braiding the roving with another elongated mass of fibrous material to add strength thereto, and severing the braided roving transversely into individual filter elements.

9. The method as defined in claim 8 wherein at least some of the larger diameter fibers are thermosensitive and including the step of heating the fiber mixture to bond said thermosensitive fibers to other fibers at their intersections.

10. The method of making a tobacco smoke filter which comprises opening and blending a mass of fibers having diameters of the order of 0.1 to 2.0 microns with a mass of fibers of larger diameter, interdispersing said blend with additional fibers of said larger diameter to form a web, forming said web into a roving, braiding the roving with another elongated mass of fibrous material to add strength thereto, and severing the braided roving transversely into individual filter elements.

References Cited in the file of this patent UNITED STATES PATENTS 1,572,342 Wiltscy Feb, 9, 1926 2,057,393 Powell Oct. 13, 1936 2,080,759 Chadbourne et al. May 18, 1937 2,132,702 Simpson Oct. 11, 1938 2,152,901 Manning Apr. 4, 1939 2,164,702 Davidson July 4, 1939 2,202,839 Davidson June 4, 1940 2,258,823 Tarrant Oct. 14, 1941 2,311,704 Simison Feb. 23, 1943 2,336,797 Maxwell Dec. 14, 1943 2,438,156 Dodge Mar. 23, 1948 2,507,827 Stafford May 16, 1950 2,658,848 Labino Nov. 10, 1953 2,695,855 Stephens Nov. 30, 1954 FOREIGN PATENTS 437,599 Great Britain Oct. 28, 1935 482,137 Great Britain Mar. 24, 1938

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