US2805671A - Aerosol filters - Google Patents

Description

Sept. 1o, 195i E. J. HAcKNEY ETAL 2,805,671

AEROSOL FILTERS Filed 001'.. '7, 1953 3 Sheets-Sheet l IN VEN TORS EDWARD J. HACKNEY CHARLES D. FAUCETTE BY F REDERIOK R. DARKIS ATTORNEYS f E. J. HACKNEY ETAL AEROSOL FILTERS Filed Oct. 7. 1953 3 Sheets-Sheet 2 S m@ Mzwmrrmm m/ @MEQ v im S mv 4 a .L N m 6% n@ @L wl.-

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INVENTORS l DSJ. HA RICK R.

nABKls ATTORNEYS sept. 1o 1957 Filed 001:. 7,1953

. J. HAcKNEY ETAL AEROSOL FILTERS 3 sheets-sheet 3 www* ATTORNEYS United States Patent 2,805,671 AnRosoL FILTERS Edward J. Hackney, Charles D. Faucette, and Frederick R. Darkis, Durham, N. C., assignors to Liggett & Myers Tobacco Co., New York, N. Y., a corporation of New Jersey Application Qctober 7, 1953, Serial No. 384,684

14 Claims. (Cl. 131-208) This invention relates to aerosol filters, and to a process and machine for making them. While the filter is believed to be useful for the filtration of any kind of aerosol or particulate suspension or dispersion in a gaseous medium, such as smoke, fog and the like, the following description sets forth by way of example a filter according to this invention which is especially adapted to be used in and to form part of a cigarette where the aerosol dispersion to be filtered is smoke produced by the burning of tobacco in the cigarette, being drawn into the mouth of the smoker.

Among the objects of the invention are to provide an aerosol filter which provides a large number of small fibers lying at right angles to the direction of gas movement through the filter, which permits such fibers to be preselected in accordance with the characteristics of the aerosol to be filtered, which permits the pressure drop through the filter to be predetermined, and which is especially effective in absorbing nicotine from tobacco smoke.

Other objects of the invention are to provide a process of making an aerosol filter in which spun textile filamenta-ry material, which is to constitute the matrix of the filter, may be efficiently and conveniently provided with a fuzz-like attachment consisting of short rod-like particles or fibers of microscopic size, in which a'towv of filaments of spun textile material is opened up and spread apart 'oy electrostatic repulsion in order to prepare such filaments for further treatment, in which filaments of such material are passed through an agitated cloud of rod-like particles of microscopic size, while the filaments themselves are charged, in order to cause the rod-like particles to orient themselves as they enter the field of the charged filaments and to become attached thereto in a generally oriented relationship thus forming the fuzz.

Other objects of the invention are to provide machinery or apparatus for making an aerosol filter in which powered rollers having a surface of hard high-dielectric material are adapted to draw a tow of spuntextile filaments through a pair of braked rollers having similar surfaces, whereby electrostatic charge is generated in the filaments of the tow and the tow is thereby opened up and spread apart by the mutual repulsion of the filaments, thus preparing it for further treatment; and in which electrostatically charged filaments of spun textile material are passed through an applicator chamber in which feeder rollers and beater fans maintain in proximity to the moving filaments an agitated cl-oud or suspension of rodlike particles of microscopic size which adhere to the surface of the filaments in oriented manner to form a fuzz-like attachment thereto. p

In the drawings annexed to and forming part hereof-J Fig. l shows a filter-tipped cigarette;

2,805,671 Patented Sept. l0, 1957 ICC Fig. 2 is a longitudinal section through thev filter and adjacent portions of a filter-tipped cigarette;

Fig. 3 is a section in the plane 3 3 of Fig. 2;

Fig. 4 is a perspective of a portion of a cigarette filter 18 according to this invention, somewhat diagrammatic in form.

Fig. 5 is a rsection through one -of the'filam'ents 19, showing attached thereto a few of the oriented rod-like fibers 20, as seen under a microscope;

Fig. 6 is a diagrammatic longitudinal section through a machine according to this invention for making aerosol filters, with some parts in section and other parts in elevation;

Fig. 7 is a vertical section in the plane 7-7 of Fig. 6, showing a portion of the fiber-applicator box 55;

Fig. 8 is a horizontal diagrammatic section, looking downwardly, in the plane 8-8 of Fig. 6, showing the apparatus which stretches and charges the filament, and spreads the tow, thus readying it for further treatment;

Fig. 9 is a vertical section in the plane 9--9 of Fig. 6, showing the air blast which completes the spreading of the filaments in the tow;

Fig. l() is a diagrammatic drawing' to illustrate what is believed to be the mechanism by which the rod-like fibers 20 become oriented as they enter the field of the charged filament 19 in the fiber-applicator box 55; and

Fig. 1l is a section in the plane 11-11 of Fig. 6, showing the means by which the spread tow, after treatment, is gathered into a compact bundle.

The following, which describes the making of a preferred fo-rm of filter for filter-tippedA cigarettes, is set forth for purposes of `illustration and not to limit the invention, as hereinafter claimed. v

THE FILTER STRUCTURE A filter according to this invention comprises two main elements, which may and usually will forconvenience be made of different materials,.though theycan be of the same material if desired. The first is the supporting matrix composed of long filaments, in most cases as long as the gas path through the filter and disposed generally in a direction parallel to the direction of gas movement. These filaments are not necessarily or usually straightfas wire would be). They are commonly somewhat warped or slightly kinked at regular intervals, resulting naturally or from the spinning operation by which they were made. The second is finely divided material, preferably in the form of short rod-like fibers (which in a cigarette filter will be not more than about 1000 microns in length), adherent to the peripheral surfaces ofthe matrix filaments and oriented inV such manner that the major axis of the rod-like fibers extends generally at right angles to the direction of gas flow through the filter. Normally a very large number of such rod-like fibers are attached to the surfaces of the filaments, forming a sort of fuzz thereon. The filter as a whole consists of a compact package or bundle of matrix filaments extending generally parallel to each other and tothe direction of gas movement through the filter, the surfaces` of these filaments bearing the fuzz above-mentioned, and the entire bundle being enclosed within a wrapper irnpervious to gas at the prevailing pressure, which surrounds the sides of the bundle and leaves the ends open for Ythe entrance and exit of gas. By suitably selecting the diameter and kinkiness of the matrix filaments, the character and density'of the fuzz deposited along their peripheral surfaces, andthe degree of compactness of the bundle when made up into a finished filter structure, this invention enables a filter to be made in which pressure drop `is reproducible and controllable; and which may be manufactured to have predetermined character-V istics for the removal of aerosol particles of differing size distributions and densities according to the nature of the smoke, fog or the like to `be filtered.

In general, thematrix filamentsmaybe ofanykind of spun textile material. LExamplesarethe synthetics isuch as rayons, proteins, nylons, 1vinyls, A"fiber glass and their analogues. "Carded orcombed naturally-occurring fibers may also'be used'inLsome forms-'offfilters AIn general the material of the matrix filament should be one which isnot deleteriouslyaffected .by contactwith thegaseous medium =tolbelfiltered,and Awhich does notrdeleterionsly affect, as by desorption'or'otherwise, the gaseous medium which issuesfromfthe -filter. irspecial requirement-in the case of `.cigarette filters is lthatfthe `lfilament -be non-toxic` and 1mm-injuriousA if taken into the'mouth.

Filamentary diameter and knkiness are important chiefiy for 1he lbearing 'they Yhave upon pressure drop. Y

Pressure drop rdepends, for any given type of material `used'in accordance with'thisinvention, upon the degree of lateral compression to which the bundle of matrix` filaments isisubjccted when it has been assembled into a filter body, the frequency and, degree of kinking and vdiameter of thematrixffilaments, the density, diameter and lengthofthe irappliedrfuzz, the type of gaseous medium to be filtered, the length of the `filter and the ratio of cross-sectional areaof matrix-filaments to thetotal crosssectional area of thefilter. These factors may be `varied at will in usingthe invention and Ait is one ofthe advantages `of lthe invention that pwhen a filter ofdesired 'pressure drop and extractiva power has been made accord-` filaments arecompacte'd into alter Yabout 1%, in diam- Leter, which Lis `'average cigarettesize. 'Under these cir- 'cumstancesithe total cross-sectional area of the matrix filaments occupies about :14%, of the total 'cross-sectional area ofthe filter. i i

The rrod-likefibers which, according to Vthe jpreferred 'form of Vthis invention, tare adherent to .the jperiphera'l surfaces of the'matrix filaments Vandare oriented so as -to extendrinafdireetion generally at .right Vangles to the ldirection of gas vfiow through the filter, may consist of Iany elongated fiber-flike material whosewparticles are of `substantially greater length in `one-axis than Y'in an yaxis at right angles thereto andV preferably `are rod-like in form. For convenience in exposition, `and by way of illustration but not to limit-the invention, these particles `will "be described herein "as if lthey'were short sections of solid rod, circular in crosssection,1v and of length substantially greater than their diameter. They are herein called fibers 'For .high efficiency in filtering ,an` aerosol-containing gas, it is necessary to providein theffilter avery large number of such fibers'disposed at ,right angles to the axisof gas fiow. The rate at which Asuch fibers .capture aerosol `particles suspended `in themoving gas stream depends, among other things, on the diameter of the fiber and the diameter of the particles. i In general, relatively large `fibers have a low'capture-rate for the very `small particles. In cigarette `smoke as its` reaches a cigarette filter the particles range in size from about 0.1 to l5 microns in diameter. In order to provide a satisfactory rate of capture for particles near the smaller end of this range, it is necessary that the diameter of the fibers be less than `about 25 microns. While this is a relative matter, and fibers of larger diameters may be used when less efficient filtration of smaller particles can he tolerated, we have found that fibers of diameter from about 5 to 25 microns are satisfactory for cigarette smoke, although with fibers of this size capture-rate appears to fall ofi in respect to particles smaller in diameter ythan about 0.3 micron. In the preferred form of this invention the diameter of the fibers should not exceed about 40 microns orthe diameter of the matrix filaments whichever is less.

The length of the fibers, onthe other hand, may .be materially grcaterthan their diameter. Where it is desired to compact the matrix filaments very closely together, so that the gas spaces between them are restricted, the desirable length of the rod-like `fibers may be very short, on the order, say, of 15 to 50 microns. Where, however, more space is available between the matrix fila ments, whether because of their crimping or because they vare to be spaced farther apart to avoid excessive pressure. drop, fibers may be employed having a greater length. For example, in making cigarette filters a convenient and desirable fiber-length is about 300 microns. In general, .the upper limit of length for these ,fibers is that at which Vthey no longer exhibit the function of orientation when they enter theelectrostatic field of the filament, as hereinafter disclosed. The rod-like fibers may consist .of any natural or synthetic substance which is not deleteriously `affected by the gaseous medium `to be filtered, and does not deleteriously affect, by desorption or otherwise, the gaseous medium issuing from the filter. 'Other specific requirements may exist in particular cases. For example, in the case of a filter to be used in a cigarette, this substance should be one which is non-toxic and non-injurious if taken into the mouth.

In the filter of a lter-tipped cigarette there is used, according to one form of this invention, particles of alpha cellulose, the preferred form and size being rod-like fibers having an average diameter of about 15 microns and` a length of about 300 microns, with examples of measured diameter from 8 to 24 microns, and of measured length from 70 to 620 microns.

The means `to enclose the sides of the bundle of laments, and thus to complete the filter, may be any material which is substantallyimpervious to gas at the pressureswhich prevail when the filter is in use. A steel container is one example. In the case of a cigarette filter, the enclosing means is preferably a paper tube with overlapped margins adhesively secured together.v

In any case the ends of the .matrix filaments are left free or else in communication with suitable gas passageways. t

Alter-tipped cigarette embodying this invention is shown in Figs. 1 ,to 4. The cigarette 15 comprises a paper wrapper A'16 containing tobacco 17 and a filter plug indicated generally at `18. The filter plug includes `a'bundle of cellulose acetate filaments 19, each filament having a multiplicity of rod-like fibers 20 adherent to its .peripheral surface, the entire bundle of filaments` being enclosed withina paper wrapper 21. Filaments 19 and paper wrapper 21 are of equal length, preferably about a half inch. Cigarette `wrapper 16 fits snugly about plug wrapper 21. The two may be secured together by adhesive if desired. Preferably a mouth-piece `wrapper 22 of .waterproof paperrnaybe wrapped around that end of the cigarette which oontainsplug 18.

The above-described filter may if fdesired, be manu- `factured `by 'first `causing `a towof raw matrix filaments, as drawn from supply, to become electrostaticallycharged; then passing the tow` throughrvan agitated suspension in air of the fibers which are to be adhered to the surface `of` the filaments; and finally assembling the filaments into a bundle which is then suitably enclosed as by-a paper tube. The result of agitating the suspension of fibers in air, usually done by mechanical means such as a fan, is to cause the fibers to acquire electrostatic charges by air friction, and these charges it is believed play a part in the subsequent orientation of the fibers when they enter the electrostatic field surorunding each charged filament. The electrostatic field 23 (see Fig. 10) surrounding each filament 19 as it travels through the cloud of fibers, causes each individual fiber within that field, for example, fiber 24, to be rotated about its center and drawn towards filament 19, to which it strongly adheres (see Fig. 'Thereafter the filaments, having thus acquired a sort of fuzz, are assembled together in a bundle and provided with an enclosure which maintains them in assembled and generally parallel relation. Such a bundle is illustrated by filter plub 18 shown in Figs. 2 and 3. The foregoing process is now covered by our Patent No. 2,774,680, granted December 18, 1956.

In order to explain more fully how this process may be carried out, there is disclosed herein one form of apparatus, now covered by our Patent No. 2,778,403, granted January 22, 1957, suitable for carrying out the process. The apparatus disclosed is primarily intended for the manufacture of filter plugs to be incorporated into cigarettes, but with obvious modifications can be used for the manufacture of filters embodying the invention that are made for other uses. f

APPARATUS FUR MAKING THE FILTER Y threaded clamps 31 and 32, enable the cylindrical faces of rollers 27 and 28 to be moved towards each other and held under compression at their line of contact or bite 33.

Two powered rollers 34 and 35 are mounted upon respective bearings 92 and 93, the bearing 92 being movable towards and from bearing 93 under control of screw-threaded clamps 94 and 95 so that the rollers may be held under predetermined compression at their line of contact or bite 36. Rollers 34 and 3S are driven from a variable speed gear box 37 controlled by lever 37a. The arrangement is such that tow 26, drawn from supply 25, passes between the bite 33 of rollers 27, 28,

then around and in contact with a portion of the peripheral surfaces of each of rollers 28 and 34, and then passes between the bite 36 of powered rollers 34, 3S. Each of rollers 27, 28, 34 and 35 is covered on its peripheral surface with a tread 38 of hard high-dielectric material, for example, hard rubber. When the clamps 31, 32 are tightened to press rollers 27 and 28 into engagement with each other, the effect in coaction with their bearings is that these rollers become braked, and the portion of the tow at 91 passing from the braked rollers 27, 28 to the powered rollers 34, 35 is highly stretched. in order that the stretching action may give rise to high friction between the tow and the surfaces of braked roller 28 and powered roller 34, the tow is arranged in its passage through thel rollers so that it first passesaround and in contact with a portion of the rubberized periphery of one of the braked rollers after leaving the bite between them, and then passes around and in contact with a portion of the rubberized periphery of one of the powered rollers before entering the bite between them. Thus the stretching action of the tow at 91 between bite 33 and bite 36 is accompanied by slippage of the tow under heavy tension against the hard rubber surfaces of rollers 28 and 34. By reason of this slippage 'under heavy tension, each of the several filaments in the tow acquires aV substantial electrostatic charge from one or the other or both of said rubberized surfaces.

Since the several filaments in the tow have, by reason of the above stretching and sliding action received like charges, they become mutually repulsive and as the tow leaves the bite 36 it exhibits a marked tendency to spread laterally (see Fig. 8, at place marked 39).

In order to assist the separating or spreading tendency of the tow, it may then if desired be run over a table 41 beneath an air blast device 40 fed with air from a pump 42 and having side guide walls 96 and 97. The tow leaving the air blast device at 4S is at its maximum separation. For example, a tow comprising about 5000 filaments of 16 ldenier and intended to form the filter plug for a cigarette, will at 45 be in the form of a fiattened ribbon from 41/2 to 6 inches in width and of a thickness preferably not greatly exceeding the thickness of one or two filaments. At this point, and until the tow is finally condensed in funnel 83, the individual filaments are generallyat such distance from each other as to show visual separation at least of the major groups, but most filaments remain within the electrostatic field of their neighboring filaments whereby the tow is kept in its spread condition.

Powered roller 46 receives the flattened tow coming from the air blast device, and directs it in an upward direction into an adhesive applicator box 47 through which the tow passes while in flattened condition. The application of adhesive is not necessary to the realization of the advantages of this invention, but is desirable in the manufacture of filterswhich are intended for use in cigarettes. The reason is that the adhesive, when hardened, promotes cross-linking between matrix filaments and thus gives to the filter body the added degree of strength which seemsto be necessary to enable the finished filter plug to withstand the action of cutting knives without distortion.

Adhesive may conveniently be applied in applicator box 47 through vspray nozzles 48, 49 fed by pump 50 from a source 51 and atomized by air supplied by pump 98. Since the openings 52 and 53 through which the flattened tow enters and leaves applicator box 47 would permit escape of adhesive spray, means' is provided to e maintain a negative pressure within box 47. This may conveniently take the form of a pump 54 adapted to draw adhesive spray or mist from the interior of box 47 and to return it to source 51, through a separator (not shown) if desired.

From adhesive applicator box 47 the flattened ribbon of tow passes to the fiber applicator box 55 having openings 56 and 57 through which the tow enters and leaves the box. Applicator box 55 consists of a hopper portion 58 and an agitation chamber 59. A door 60 permits finely-divided fiber material to be introduced into hopper 58.

Positioned in the lower part of hopper 58 are a pair of powered fluted feed rollers 61, 62, positioned respectively adjacent the inwardly sloping side walls 63, 64 of hopper 58. Between rollers 61 and 62 are mounted, a pair of` walls 99, forming a vchannel 65 through which the tow is adapted to pass. Each of walls 99 and 100 is provided at its lower end with a curved shoe 102, 103, concentric respectively with the cylindrical surface of revolution described by the outer edges of the flutes of the rollers 61 and 62 and closely adjacent thereto. Thus each fiuted roller and its shoe forms a feeder of predetermined .size for delivering fiber particles from hopper 58 to agitation chamber 59.

In the agitation chamber 59 of box 55 are suitably journaled'and positioned a pair, and preferably two pairs, of agitator fans 67, 68 powered to rotate at high speed, for example 1800 R. P. M., by motors 67a and 68a respectively. ySuch fans maybe made as follows: Upon `a shaft 69 are secured two fiat circular plates 70 and through which `thecharged filamentspass and in which they attract `large `numbers `of fiber particles.

To aid rollers 61, 6,2 in `feeding finely-divided material `to agitationchamber 59, it is desirable tosecure a ,pair of `powered uvibrators 101, `102 (see Fig. 7)" to the outer walls of hopper 58. To prevent the escape of fiber'particles -through openings 56 and 57, apump 73 is'arranged to drawfairfrombox 55-and to-discharge itiinto aseparator 76 containing a cloth bag 74, an air escapevent 75` and a removablecover 77. Finely-divided material recovered in bag 74may`bereturned to the-sys tem through door60.

After passing over'rollers 80 and'81 and leaving Abox through opening 57 the tow at'78 isinthe form of a flattened ribbon consisting of a plurality of vfilaments each having on its surface a layer 79 of adhesive material and also having adherent thereto a large number of particles of finely-divided fibers (see Fig. 5). This 'tow after -passing around the powered Aroller 82 enters condensing funnel `83. At point -f84 (see Fig. l1) the tow is about Vto be gathered linto a bundle of desired external-configuration. At point 85, where it emerges from funnel 83,y thetow has been Igatheredinto a bundle posi sessing the desired-cross-sectional configuration which,in the case Iof `filters made to be incorporated in cigarettes, is substantially circular in outlineand about W16" indiameter. It is then ready to be enclosed in a suitable wrapper.

In the case Vof fltersgmade to Vbe incorporated in cigarettes, the wrapper Iis a paper tube. Preferably the bundle formed `in 4funnel 83 `is advanced into a forming tube 86 (see Fig. 6) 'where it is continuously wrapped in a strip of paper 87` drawn from a sourceB.Y The ma# chine for wrapping the Abundle of filaments 85 in a tube of `paper 87, and cutting the lsame off into tubes of deircd lengthby'means of knife 89, is essentiallythe same as the known machinery `forthe manufacture of ciga-` rettes. Such machines are well Vknown vand will `not be describedfin detail here.

In manufacturing 'filter-tipped cigarettes as shown in Figs. 1 4, it ispreferable to form an intermediate pro`d- 'uct 90 lconsisting yof a continuous bundle of `cellulose 'acetate filaments, Vwith adherent finely-'divided fibers, Whichis about 3 inchesilongand-is contained'ina paper tube of the same length. Such intermediate product is afterwardssevered into :appropriate 'half-inch lengths lforinsertion in individual cigarettes. This maybe done t automatically inknown machines which'neednot be here described.

If 4the nature ofthe adhesive requires the subsequent application of heat in order toset or bake it,interme'diate product 9th-handled inthe same manner as cigarettes, may be introduced into low-temperature `baking ovens for the -requiredlength of time.

.PROCESSOF MAKING THE FILTER IThe processof manufacture `according to this invention may now be more fullytdescribed, lhavingreference Y vto .the aforementioned apparatus,` by away lof .example only. `For'illustration the :process -to be set forth ypertains `to `the manufacture -.of cigarettefilters.

`Applying tlzetelectrostatic charger-Preferablythe elec- .trostatic charge .is applied'tota tow-of spun textileflarmentssuch rasicellulose 4acetate by .friction `with ahard,`

8 high-dielectric solid. 1f adesired, however, .the charge mayzbelapplied .in other known ways, as for example-.by friction with ,-gas molecules such as ta-hotair blast, -by corona discharge, or by administration of a direct electrical charge. .In the preferred form of the process the tow `is drawnvfrom a `source of supply through the `bite of a-pairof braked rollers having hard rubber surfaces by means of a pair of i powered `rollers having similar surfaces. Thetow may be threaded through the rollers in such manner rthat-'it-passes around a portion ofoneof the braked rollers `after leaving the bite ybetweenthem, and around a portion of one of the powered rollers before entering the bite between them. Thus apronounced stretch is introduced into the filaments of the tow, by `reason of the resistance of the braked rollers, and the individual filaments of the tow are broughtinto hard slipping engagement withithe surface of the rollers, thus acquiring a strong electrostatic charge. The existence-of this charge is made evident by the tendency of the tow to spread as it leaves the powered rollers, the

- individual filaments at this point being similarly charged t and mutually repulsive.

'Further spreading the-tow by air blast.-if desired or necessary, `the 'individual filaments of the tow may be further separated and spread `apart by suitable air blast applied thereto after the tou/.leaves the powered rollers abovementioned. Such a device is indicated at 40.

When the tow has been flattened into a ribbon ofsubstantial width and a thickness preferably not much more than that'of oneor two filaments, and each filament bears a strong electrostatic charge, it is then ready for application oftfinelydivi`ded fibers. Such application may take place immediately, or may be preceded if desired by application to the tow filaments of a layer of adhesive material. Atthis time and during the subsequent stages of treatment, each or most of the individual charged filaments continues to be within the electrostatic field'of at least its neighboring filaments, and thus under the inliuence of a force tending to keep thevfilamentsseparated Vone from another.

Applying the adhesiva-The application of adhesive to the filaments'is by no means necessary to secure firm adherence of the fibers thereto. Electrostatic attraction is sufficient to assure a permanent attachment between the fibers and the peripheral surfaces of the supporting filaments, and such attractionwill' last indefinitely even after the filter has been incorporated in a cigarette. (See filter No. 3 in the table which follows near the end of this specification.) The use of an adhesive is, however, desirable Vin `the manufacture of filters for use in cigarettes, in order to give the filter plug as a whole the necessary degree of rigidity and resistance to compres sion which lwill `permit it to be cut without deformation by theknives of a cigarette-making machine. For this purposeit is preferred vto coat the peripheral surfaces of the filaments beforethey pass to the ber applicator'box, withV alayer of a substance which is a solvent for the particularjfilament used. Then, when the surface of the filament has been wetted with such solvent and a soft solid solution has formed, contacting filaments will tend to stick together and thus give the entire filter bundle greater internal strength. It is usually desirable to heat the filter plugs, after the manufacture of the intermediate product `is completed, in order to harden or dry the surface of the filament, particularly if the same is to be used immediately in cigarette manufacture.

It is also desirable, when making a cigarette filter, to -use an adhesive which will not give any noticeable taste to the smoke issuing from the filter into the mouth of the smoker. In` making cigarette filters in which the filaments are madeV of cellulose acetate, the preferred `adhesive is triethylcitrate. After the intermediate products f90have been made, they `may be heated for about .two hours `at .175 F. in order to bring the setting of the adhesive to a prompt completion. However, the hardening of the adhesive occurs spontneously at a slow rate and ultimately the desired degree of firmness can be achieved without heating, if a sufficient length of time is available.

Applying the fibers- Whether or not the filaments have been coated with adhesive, the next step of the process is to move the ribbon-like flattened band of charged filaments into a zone where they pass in intimate contact with an agitated suspension or cloud of finelydivided fibers which, as above stated, may be of any material of appropriate size and non-deleterious material, but preferably consist of small rod-like particles of alpha cellulose having a diameter from about 8 to 24 microns (average and a length of from about 70 to 620 microns (average 300). Each fibrous particle of microscopically small size, such as the alpha cellulose just described, has the property when it has entered the field surrounding a charged lament, of rotating in space till its end oppositely charged from that -of the filament is nearest to the filament, and as thus oriented it is drawn towards the surface of the filament until it makes contact therewith. This end of the fiber is then strongly held in contact with the filamentary surface while the yopposite end of the fiber is repelled thereby. The result is that, in general, the fibers which become attached to the peripheral surfaces of the charged filaments stand out therefrom in a manner which might be characterized as resembling a fuzz, although under a microscope the fuzz does not appear particularly dense.

The quantity of fibers picked up by the filaments can be controlled by regulating the speed at which the filaments pass through the cloud and the density of the cloud. The greater the speed, or the less the density, or both, the less will be the pick-up of fuzz.

Assembling and wrapping the bundle-After the tow of spread and charged filaments has been passed through an agitated cloud of fiber particles, as described, the tow is then passed to a funnel or the like where it is gathered into a compact bundle preferably of circular outline as seen in cross-section, and thence fed directly to a place where it is automatically and continuously wrapped in a paper tube.

Examples Five cigarettes, each containing a filter plug, were made and tested for weight of material removed by the filter per puff of smoke. The plugs were made from cellulose acetate tow in which the individual filaments were 16 denier and the total denier of the tow was 117,000 before stretching. The individual filaments contained on the average 9 crimps per inch before stretching. During stretching the denier of the tow was reduced to about 92,000. This did not result in any measurable reduction in the average diameter of the individual filaments which, by measurement, was 43.3 microns. The stretching did however reduce the number of crimps to about 5 or 6 to the inch.

The fibers attached to the filaments (except in filter No. 1 where no fibers were used) consisted of alpha cellulose in the form of rod-like particles which, by measurement, were found to be from 8 to 24 microns in diameter (average 15 microns) and from,70 to 620 microns in length (average 300 microns).

The adhesive material was triethyl citrate. In each case about 5,000 cellulose filaments, comprising an aggregate cross-sectional area calculated to be 0.01135 sq. in., was formed into a bundle one half inch long and wrapped in a paper tube to form a plug having a total cross-sectional area of 0.0822 sq. in. Thus the aggregate crosssectional area of the filaments, by calculation, was 13.8% of the total cross-sectional area of the plug. This however does not take into account cross-linking between filaments caused by the adhesive nor the area occupied by the alpha cellulose fibers.

FILTRATION EFFECTIVENESS OF FIVE CIGARETTE FILTERS MADE AS ABOVE-DESCRIBED AND DIFFERING FROMVEACH OTHER AS SHOWN IN THIS TABLE.

As a percent of Total Weight in the Filter Milligrams ot Filter No. Smoke Cellulose Alpha Removed Acetate Adhe- Cellulose per Puffl Filasive Particles ments 1 "Puff" means the passage of 31 cc. of air into a lighted cigarette for a period of 2 seconds, repeated once every minute.

The foregoing shows that a bundle of cellulose acetate filaments free of adherent alpha cellulose fibers pos-A that the presence of alpha cellulose particles, attached to the peripheral surfaces of the cellulose acetate filaments in the manner herein disclosed, substantially increases the total weight of material removed from the gas stream. The effectiveness of the filter in removing such material increases with increase in the quantity of alpha cellulose particles present, until the number thereof causes too great a pressure drop for comfortable smoking.

While the above invention has been described primarily with reference to filters and their manufacture for incorporation in and as part of a cigarette, which said filters are of relatively small diameter and short gas path, it is intended that this invention shall include filters and their manufacture for other applications such as for use in gas masks, air purification systems, ventilation, industrial smoke and dust control, dehydration of vapors, and the like. This invention is not limited to the specific means or steps or apparatus herein shown and described but extends to and includes all equivalents thereof which, in the combinations recited in the subjoined claims, operate in the same or similar manner to achieve the results therein set forth.

While the spun textile filaments are here described for illustration as being disposed generally parallel to the direction of gas-flow through the filter, and no twisting is produced in condensing funnel 83 as here shown, a filter may be made in accordance with this invention in which the filaments, after the fuzz has been applied and the tow gathered into round form, are then twisted together so that they occupy helical paths in the filter. Such twisting will, of course, cause the path of gas-flow to be correspondingly twisted, but the filaments will nevertheless continue to be generally parallel to the direction ofgas-fiow. Such twisting may be employed to assist in keeping the bundle compact, or as a further control in assuring a desired degree of pressure drop.

While the rod-like fibers are herein described for illustration as being at right angles, or generally at right angles, to the direction of gas flow through the filter or to the axis of the filter plug, in practice such fibers may be disposed in a somewhat heterogeneous angular relationship thereto. It is believed that the most efficient use of the fibers is made when a majority of them are substantially at right angles, as stated, but this is not essential to the invention since the only effect of having a majority ofthe fibers at an angle other than a right angle is to make a less efficient use of the available material.'` The effective length of a fiberV for filtering pur- ".11 posesis, of course, aprojection of .the `fiber ina plane. at right angles tothedirectiono'f gasflow.

In the apparatus.: herein shownztheeveral; movingparts may all `be powered from-a common source, which may be the motor which drivesl the..forming and cutting mechanism 86, 89. Powerfromthis motormay be communicated (by means not sh'own) to'a shaft 103. `Fromrshaft 103power may" be .delivered to=vaiable speed gear box 37`for drivingrollerskiiand 3'5. 'lFrom shaft 103 power may also-be delivered to shaft `104,`on which roller 46 is mounted, thence'to shaft 105, on which 'roller82 is mounted, and thence to shaft `106 from `which fluted rollers 61 and 62 may be driven inopposite directions at suitable low speed. Forfconvenience, fans "67 `and x68, which require high speed rotation, are here shown as beingseparately powered.

Preferably condensing ifunnel (S31-'should be of'fiattened configuratiomas shown:in Figs. .6.and .1.1. This shape appears to produce `a .more 4satisfactory rdistribution of alpha cellulose yfuzz throughout Athe cross-sectional area of thel filter.

'What is claimed is:`

l. 4Anaerosol tobacco smoke `filtercomprising ,a compact bundle of-textile filamentsdisposedA generally parallel to `thedirectionof gas-ow through the filter, a multiplicityf-ofrod-like .fibers-of diameter not exceedingabout40 microns orthe diameter of theffilaments whichever is less,

each thereof being secured adjacent one of its ends to a peripheralsurfaceof one of said filaments `with its other end extending .generally at right angles to the direction of `gas-dow Ythrough the filter, said filaments being .in proximate contiguousV relation having ,gas-flow passage spacestherebetween in longitudinalrelation with andgenerally paralleling said filaments .andisaid 4rod-lilcefibers extending across said passage spaces inmultiple spaced relation along the Ylongitudinal extent of said passage` spaces,.and means .to enclose the `sides of the bundle.

2.4 `Au aerosol filter comprising a compact bundle of textile .filaments disposed `generally parallel Ato the,V direction Aof gas-ow through the ffilter, a multiplicity-of particles `of alpha cellulose not exceeding. 4along their minor axes the diameter .ofthe filaments, each thereof being .securedadjacent one of Aits ends to `a .peripheral surface of one of said 'filaments with its other end extending generaly at right angles to `the direction ofgas-flow throughthe filter, said filaments being inproximate .contiguous -relation ihaving Vgas-flow passage spaces therebetween inv longitudinal relation `with and, generallyil paralleling saidfilaments and said particles extending across saidrpassage spaces in multiple spaced relation-,along the longitudinal extent of said passage means, and means to J.enclose "thesidesofthe bundle.

3. An aerosol tobacco smoke filter comprising a compact bundle of cellulose acetate filaments disposed generally parallel to the direction of gas-flowfthrough the filter, a multiplicity of rod-like fibers ofdiameter not exceeding about 40 microns or the diameter of the vfilaments whichever is less, each thereof being secured adajcent one of its ends to a peripheral 'surface `of one of said fila-` ments .with its other endextending generally at right angles to the direction of gas-dow through the filter, said filaments beingin proximate contiguous relation having gas-flow passage spaces therebetween in longitudinal relation withl and generally paralleling said filaments and said rod-like fibers extending across said passage spaces in multiple spaced relation along the longitudinal extent of said passage spaces, and means to enclose the sides'of the bundle.

'4. An aerosoliilter comprisinga compactlbundle of cellulose acetate filamensdisposed.generally parallel -to the direction of gas-flow through the. filter, .a multiplicity of iparticlesof alpha cellulosenot" exceeding along their minor axes the diameter of the-filamentneach .thereof being secured adjacent--one ofitsendsto ya peripheral surface` of `one :of `@said `filaments `:with .its :.other end` .ex-

tending generally atrightfangles ,to the .direction-,of gastlow through thetilter, saidtfilaments being in proximate contiguoussrelation'having gas-flow passage spaces therebetween `in longitudinal relation wit-h and generally paralleling said Vfilaments and said particles extending across saidpassago spaces in multiple spacedrelation along `the longitudinal extentof said passage means, and means to enclose the sides of the bundle.

`5..-'A `tobacco Asmoke ,filter v.plug suitable `for `use .in filter-tipped cigarettes comprising a compact bundle `of textile filaments disposed generally parallel to the major axis of the plug, a multipicity of rod-like fibers of diameternot exceeding about "40 microns or the diameter of the'filaments whichever is less, each thereof being secured adjacent .one of its ends to a peripheral surface of one of saidfilaments wit-h its other end extending generally at right'angles tothe axis of the plug, said filamentsbeing in proximate contiguous relation having gas-flow passage spaces therebetween in longitudinal relation with and generally'paralleling said filaments and said rod-like fibers extending across saidpassage spaces in multiple spaced relati'onalongithe longitudinal extent of said passage spaces, and a'papertube enclosing the bundle.

6. Afilter'plug suitable for use in filter-tipped cigarettes comprising a compact bundle of textile filaments disposed generallyparallel vto the major axis of the plug, a multiplicity of particles of alpha cellulose of sizes not exceeding about'lOOO microns along their major axes and about the diameter'of the filaments along their minor axeseaclr thereof being secured adjacent one of its ends to a peripheral surface of one of said filaments withits other en'dextending generally at right agnlesto the'axis of the plugysaid'filaments being in proximate contiguous relation havinggas-fiow'passage spaces therebetween in longitudinal relation with and generally paralleling said filaments and said particles extending across said passage spaces in multiple spaced 'relation along the longitudinal `extentofsad passage means, and a paper tube yenclosing the bundle.

y7. A filter lplug suitable for use infiltrer-tipped cigarettes comprising a compact bundle of cellulose Aacetate filaments disposed generally parallel to the major axis of the plug, a multiplicity of rod-like fibers of diameter` not exceeding about 40 microns or the diameter of the fila f ments whichever is less, each thereof being secured adjacent one of its ends to `a peripheral surface of oneof saidfilamentsfwithlits other end extending Ygenerally at right angles' tothe axisof the plug, said filaments being in'iproximate' contiguous relation having gas-fiow passage spaces therebetween in longitudinal relation with .and generallyparallelingsaid` filaments `and said rod-like fibers extending across saidpassage spaces in multiple spaced relation along the longitudinal extent of said passage spacesgand a; paper tube enclosing the bundle.

8. iAffilterplug suitable for use 'in filter-tipped cigarettes comprising aecompact bundle of `cellulose acetate `filaments disposedfgenerallyparallel to the majoraxis of the -plugfa multiplicity of particles of alpha cellulose f sizes not exceeding about 1000 microns along their-major axes and aboutf the Ndiameter of the filaments along their minor axes, `each thereof being secured adjacent one of its ends `to-a peripheral surface of"A one of said filaments with :its other vend extending generally `at right Aangles to the axis ofthe plug, said filaments being in proximate contiguous relation having gas-flow passage spaces therebetween in longitudinal relation, with and generally paralleling =saidilaments -and said particles extending across4 saidvpassage spaces in multiple spaced relation along the' longitudinalextent of -saidpassage means, and apaper tube enclosing the zbundle.

,9..1A filter-.plug-suitable for use in filter-tipped cigarettes comprising a :compact bundle of cellulose acetate 'filamentslhavingadiameter of about 35 to 55 microns dispovseclz-generallyl parallel'to the major axis ofthe plug,`a multiplicityfof 4rod-like vfibers of :diameter notexceeding the diameter of the filaments andI of length not exceeding about 1000 microns, each thereof being secured adjacent one of its ends to Ia peripheral surface of one of said filaments wit-h its other end extending generally at right angles to the axis of the plug, and a paper tube enclosing the bundle, said filaments lbeing in proximate contiguous relation having gas-liow passage spaces therebetween in longitudinal rel-ation with and generally paralleling said filaments and said rod-like fibers extending across said passage spaces in multiple spaced relation along the longitudinal extent of said passage spaces, the rod-like fibers comprising from about 10% to 20% the weight of the plug.

10. A filter plug suitable for use in filter-tipped cigarettes comprising -a compact bundle of cellulose acetate filaments having a diameter of about 35 to 55 microns disposed generally parallel to the major axis of the plug, a multiplicity of particles of alpha cellulose of sizes about 8 to 24 microns along their minor axes and 70 to 620 microns along their major axes, each thereof being secured adjacent one of its ends to a peripheral surface of one of said filaments with its other end extending generally at right angles to the axis of the plug, said filaments ybeing in proximate contiguous relation having gas-flow passages spaces therebetween in longitudinal relation with and generally paralleling said filaments and said particles extending across said passage spaces in multiple spaced relation along the longitudinal extent of said passage means, and a paper tube enclosing the bundle, the alpha cellulose comprising from about 10% to 20% the weight of the plug.

11. A filter plug suitable for use in filter-tipped cigarettes comprising a compact bundle of textile filaments having a diameter of about 43.3 microns and to 6 crimps to the inch disposed generally parallel to the major axis of the plug, a multiplicity of particles of alpha cellulose of sizes about 8 to 24 microns along their minor axes and 70 to 620 microns along their major axes, eac'h thereof being secured adjacent one of its ends to a peripheral surface of one of said filaments with its other end extending generally at right angles to the axis of the plug, said filaments being in proximate contiguous relation having gas-How passage spaces therebetween in longitudinal relation with and general paralleling said filaments and said particles extending across said passage spaces in multiple spaced relation along the longitudinal extent of said passage means, Iand a paper tube wrapped about the bundle of suc-h diameter that the aggregate cross-sectional area fof the filaments is about 13.8% of the cross-sectional area of the tube.

12. A filter plug suitable for use in filter-tipped cigarettes comprising a compact bundle of cellulose acetate filaments having a diameter of about 43.3 microns and 5 to 6 crimps to the inch disposed generally parallel ot the major axis of the plug, a multiplicity of particles of alpha cellulose of sizes about 8 to 24 microns along their minor axes and 70 to 620 microns along their major axes, each thereof being secured adjacent one of its ends to a peripheral surface of one of said filaments with its other end extending generally at right angles to the axis of the plug, said filaments being in proximate contiguous relation having gas-iiow passage spaces therebetween in l 13. A filter plug suitable for us in a filter-tipped ciga-v rette comprising a compact bundle of textile filaments disposed generally parallel to the direction of flow of smoke throughv the filter, a multiplicity of elongated particles of alpha cellulose not exceeding about 1,000 microns in greatest dimension secured to the peripheral surfaces of said filaments and extending generally at right angles to said direction of flow of smoke, the filaments forming gas-flow passage spaces between and parallel to themselves, and the said particles extending across said gas-flow passage spaces in multiplespaced relation along the longitudinal extent thereof, and a paper tube enclosing the bundle.

14. A filter plug suitable for use in a filter-tipped cigarette comprising a compact bundle of cellulose acetate filaments disposed generally parallel to the direction of liow of smoke through the filter, a multiplicity of elongated particles of alpha cellulose not exceeding about 1,000 microns in greatest dimension secured to the peripheral surfaces of said filaments and extending generally at right angles to said direction of liow of smoke, the filaments forming gas-flow passage spaces between and parallel to themselves and the said particles extending across Asaid gas-flow passage spaces in multiple spaced relation along the longitudinal extent thereof, and a paper tube enclosing the bundle.

References Cited in the file of this patent UNITED STATES PATENTS 413,036 Demuth Oct. 15, 1889 729,680 Schwartz June 2, 1903 945,917 Cottrell Ian. 11, 1910 1,854,475 Littlefield Apr. 19, 1932 1,876,251 Lehman Sept. 6, 1932 1,952,502 Kinkead Mar. 27, 1934 2,058,620 Petitmerment Oct. 27, 1936 2,126,422 Tarrant Aug. 9, 1938 2,221,443 Davidson Nov. 12, 1940 2,358,227 Hiers Sept. 12, 1944 2,372,437 Lathrop et al. Mar. 27, 1945 2,447,374 Smyser Aug. 17, 1948 2,573,964 Green et al. Nov. 6, 1951 2,615,477 Crawley Oct. 28, 1952 2,688,380 MacHenry Sept. 7, 1954 2,707,308 Taylor et al. May 3, 1955 2,740,184 Thomas Apr. 3, 1956 FOREIGN PATENTS 413,694 Great Britain July 20, 1934 665,278 Great Britain Ian. 23, 1952

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