US3032829A - Processing tow - Google Patents

Description

y 1962 w. R. MAHONEY ET AL 3,032,829

PROCESSING TOW Filed Feb. 11, 1958 United States Patent 3,032,829 PROCESSING TOW William R. Mahoney, Richard E. St. Pierre, and Donald T. Dunlap, Charlotte, N.C. assignors to Celanese Corporation of America, New York, N.Y., a corporation of Delaware Filed Feb. 11, 1958, Ser. No. 714,634 26 Claims. (Cl. 19--65) The present invention relates to a novel process for opening a filamentary tow such as is 'used in the formation of cigarette filter plugs, and to apparatus for performing the process.

Cigarette filters are generally formed of a multiplicity of crimped filaments, starting with a :crimped tow or bundle of several thousand continuous filaments. As received from the tow producer, the filaments may be more or less adhered to each other with the crests and Vales of adjacent filaments in registry. The tow is passed through an air spreader to fluff up the bundle, it is fed by driven rolls through a chamber in which plasticizer is applied, and it is thereafter reduced in cross-sectional area to equal approximately the cross-sectional area of a cigarette. The condensed mass is formed into a coherent structure such as by wrapping in paper and/ or curing and is cut into suitable lengths for incorporation into cigarettes.

In commercial operation it has been found that the filters so produced are not all identical in their filtering action. Specifically, it has been found thatthe filters occasionally differ in weight, in filtering efi'iciency and in the ease of draw, i.e. resistance to gas flow. In addition, after smoking many filters show uneven darkening which indicates non-uniform passage of smoke therethrough, the darkened areas identifying zones through which the smoke was preferentially drawn.

It is accordingly an object of the present invention to provide a process for treating tow in a manner which permits formation of uniform cigarette filters.

It is a further object of the invention to process a tow in amanner which provides cigarette filters of improved properties.

Another object of the invention is to provide an apparatus for processing-tow in accordance with .the novel procedures.

Other objects and advantages will be apparent from the following detailed description and claims.

Our investigations have revealed that a major cause of irregularities in the filter tips and their filtration characteristics can be traced to improper opening of the tow. Specifically, in the crimping of the tow all of the filaments are simultaneously acted upon and it will be found that the crimps of adjacent filaments are in registry; if such crimp registration is not done away with there will be channels in the filter through which smoke can pass without contactingany filament surface. In addition, as produced, the ,tow may contain individual filaments or groups of filaments which do not extend longitudinally but rather which extend at an appreciable angle transversely of the tow. In processing, these transversely extending filaments or cross-overs tend to prevent those filaments which they overlie from being spread apart laterally.

If a tow 'hasnot beenevenly crimped initially, failure to open the tow properlywill resultinuneven application of plasticizer and this in turn results in uneven density so thatthere is channelingof smoke through the filter.

In accordance with one aspect of the presentinvention the tow is opened by passage over a ridge which is inclined .to the pathof movement of thetow. Conveniently the towis passed between several pairs of opposed ridges, at least one ridge of each pair being inclined to the path 3,032,829 Patented May 8, 1962 ,of movement of the tow, preferably both being inclined in different directions. This can readily be achieved by passage between a pair ofopposed ridged surfaces, the ridges of one surface being displaced laterally relative to the ridges of the other surface, thereby laterally displacing some of the filaments relative to other of the filaments and thus opening {the tow. Preferably the ridged surfaces are constituted by a pair .of opposed grooved or ridged cylindrical rolls which are positioned close to one another and rotate upon passage of tow therebetween. The surfaces are so formed that the ridges of one surface will not always be inregistry with the grooves of the other surface.

A suitable configuration of ridges is created by forming a helical thread in an elastic, e.g. rubber, or elasticsurfaced cylindrical roll. Advantageously both rolls are threaded in the same direction so that as they rotate in opposite directions the ridges of one roll will .not be in permanent registry with the grooves of the other roll. By way of illustration, at a given time .a point on one ridge of one roll -will contact some point on a ridge of the other roll and as the tow advances-the rolls will rotate and the points on the rolls where they .were previously in contact will be displaced laterally relative to each other.

If the opposed rolls are oppositely threaded, then their pitches, circumferences or rotational speeds'should be different so that there will not be permanent registry be.- tween the ridges and .grooves of the rolls, i.e. so that points on both rolls where they are in contact will be laterally displaced relative to each other.

Each helical roll will tend to displace the tow laterally in the direction of advance of the helix, considering its direction of rotation, e.g. if a helically grooved roll, on which the thread as viewed from one end advances in clockwise direction, is rotated in counter-clockwise di-. rection atowcontacting the roll will tend to be displaced away from the viewer. Where the other roll is similarly threaded but rotates in opposite direction the tow will tend to be displaced toward the viewer. Both of these simultaneously acting tendencies further aid in opening the tow.

Conveniently, each roll is threaded from one end to its center in one direction, e.g. clockwise, and from its other end to its center in the opposite direction, e.g. counter-clockwise. Two such rolls are assembled with their clockwise-threaded sections opposite each other and with their counter-clockwise-threaded sections opposite each other. One of the .rolls will thus tend to condense laterally a tow fed near its middle while-the other roll will tend to expand the tow laterally. Preferably the expanding roll is on bottom and exerts a greater influence on the tow than the condensing roll so that the tow is wider when it leaves ,the rolls than upon entering therebetween.

The ridged opening surfaces can be incorporated directly into existing apparatus for forming :cigarette filters from tow. Conveniently, the ridged surfaces are positioned just beyond an air spreader to which the tow is led from its bale. After passing between the ridged surfaces the tow is passed between a pair of braking rolls and then between-a pair of driven rolls. The tow is thus tensioned between the driven and braking rolls, the tension temporarily pulling put the crimp and making it more regular upon subsequent relaxation. If desired, the braking rolls may be omitted, their function being performed by the ridged opening surfaces. Following passage between the driven rolls which operate at constant speed, the 'tow is advantageously passed through an air spreader, sprayed in relaxed condition with a plastic-izing/agent and conveyed to conventional condensing equipment to be formed into rods for incorporation into cigarettes as filter plugs.

J In place of two opposed helically ridged cylindrical surfaces, one of the surfaces can be provided with circular or elliptical ridges. Alternatively, both surfaces may be provided with elliptical rings which are either oppositely canted or arranged at different angles relative to their respective axes so that the ridges on one cylinder will not always lie in registry with the grooves of the other cylinder.

A similar effect will be achieved using one cylinder with circular rings and another with elliptical rings.

straight parallel ridges on both opposed fiat surfaces can be employed provided the registry is interrupted as by Oscillating one or both surfaces laterally out of phase with or in opposite direction to the other surface. While circular rings are parallel to the direction of advance of the tow, such oscillation effectively inclines the rings so as to produce the effect of elliptical rings.

The tow is preferably composed of a plurality of crimped continuous filaments of an organic derivative of cellulose, e.g. esters or ethers of cellulose such as cellulose acetate, cellulose propionate, cellulose acetate propionate, highly esterifiedcellulose containing less than 0.20 free hydroxyl groups per anhydroglucose units such as cellulose triacetate, and the like. Other filamentary materials such as rayon (regenerated cellulose), linear supcrpolyamides such as nylon-6 and nylon-66, linear polyesters, acrylonitrile polymers and copolymers, and the like, can also .be employed. I The number of filaments and the total denier can vary within wide limits but, in preparing filters for conventional cigarettes which are 25 to 26 mm. in periphery, the number of filaments generally varies between about 5000 and 33,000 and the total denier ranges from about 60,000 to 160,000, computed on uncrimped tow.

The number of crimps per inch in the tow can range up to about 20 but preferably averages between about 4 and 12. After leaving the driven rolls the tow is still crimped but is about to 200%, and preferably 50 to 150%, longer than initially, i.e. the tow has been stretched so that the distance between the crests of adjacent crimps has been increased and the amplitude reduced. In addition, the crimps are deregistered and more regular than initially.

Because of the openness of the tow the plasticizer attacks all the filaments uniformly so that the density of filters produced therefrom is uniform. The registration of the crimp of-adjacent filaments prevents channeling and makes a firm filter even with a tow of a smaller total denier than normally utilized. In addition, the filtering efiiciency is increased so that a given efficiency can be achieved using less tow and thus with less resistance to draw, i.e. at a lower pressure drop.

The identity of the plasticizer will of course depend upon the composition of the tow. With cellulose acetate there may be employed triethyl citrate, dimethoxy ethyl phthalate and methyl phthalyl ethyl glycolate but glycerol triacetate (triacetin) is preferred. The proportion of plasticizer applied generally varies from about 2 to 30% by weight of the tow to which it is applied, and preferably from about 4 to The invention will now be described more fully with reference to the accompanying drawing, wherein:

FIG. 1 is a schematic elevation of a tow opening apparatus in accordance with the present invention;

ing apparatus;

FIG. 3 is a lateral elevation of the helically threaded tow opening rolls of FIG. 1;

FIG. 4 is a section through a portion of one of the rolls taken along line 4-4 of FIG. 3;

FIG. 5 is a lateral elevation of another pair of tow opening rolls which can be employed in the practice of the present invention;

FIG. 6 is an elevation of a pair of ridged flat plates which can be substituted for the ridged rolls of FIG. 1; and

FIG. 7 is a plan view of one of the plates of FIG. 6.

Referring now more particularly to the drawing wherein like numerals have reference to the same element, in FIG. 1 there is shown a bale 11 of a multifilament tow 12, which tow is passed through an air spreader 13 comprising a pair of spaced pla-tes provided on their opposed faces with longitudinal slits through which compressed air is directed against the tow.

From the air spreader 13 the tow 12 is drawn between rolls 14, 14 each of which is elastically surfaced as at 15. The rolls 14 have the configuration shown in FIGS. 3 and 4 and described more fully hereinafter. A yoke 16 determines the spacing between the rolls 14 and includes means for oscillating the rolls 14 in opposite directions perpendicular to the plane of the drawing although preferably the rolls are not oscillated but are merely supported for rotation. The tow 12 is then drawn between rubber braking rolls 17 which may be driven or which may be idly mounted for rotation.

The. tow 12 then passes to positively driven rolls 18 which are also elastically surfaced and supply the force necessary to draw the tow along. These rolls 18 operate at a constant speed attuned to the operating speed of the cigarette making machinery. If the braking rolls 17 are positively driven, they are driven at a slower speed than rolls 18 so as to exert a braking action on the tow.

The tow passes through another air spreader 19 and enters a plasticizing chamber 20 wherein there is provided a mist of plasticizer. The plasticized tow upon emerging from chamber 20 is now in condition for passage to rod-forming equipment (not shown) in order to be formed continuously into cigarette filter plugs. Although the tow 12 is now relaxed the spacing between crests of adjacent crimps is greater than it was initially.

Filter rods and plugs formed from the tow are characterized by uniformity in weight, filtering characteristics and density. Smoke passing therethrough isnot channeled as can be seen from the absence of unevenly discolored areas at the end of the filter. The plugs are firm and the paper wrapping does not wrinkle, indicating a tight uniform packing. These advantages are noted even when the original tow was irregularly crimped and contained many cross-overs.

As shown more clearly in FIGS. 3 and 4, the rolls 14 as viewed from the right-hand side are helically threaded for half their lengths in counter-clockwise direction and for the other half in clockwise direction. The base of each groove is V-shaped whereas the tops of the ridges separating adjacent grooves are slightly flattened. In operation, the rolls 14 are moved closer toward each other, the distance being set so that the predetermined speed of driven rolls 18 will result in a tow having the desired percent crimp, i.e. the rolls 18 are driven at the selected v speed and the rolls 14 are moved toward each other until the tow emerging from between rolls 18 has the desired properties. The force of rolls 17 against each other may also be varied to avoid unduly increasing the spacing between rolls 14 which might reduce the opening action. The rolls 14 may also be reciprocated in axial direction to aid in opening.

The rolls 14 rotate in the direction indicated by the arrows and it will be seen that the upper roll will tend to reduce the width of the tow passing therebetween while the lower roll will tend to increase the width of the tow. In practice it has been found that with identical rolls grooved as shown the lower roll apparently exerts a greater influence so that there is a net increase in width of the tow.

The modified apparatus shown in FIG. 2 is identical with that of FIG. 1 except that the braking rolls 17 have been omitted. In this embodiment the grooved rolls 14 take over the braking function to control the stretching of the tow. Control over the uniformity of crimp, i.e., uniformity of tow density in longitudinal direction of the tow, is less exact but if a regularly crimped tow is initially employed the product will be ahnost as uniform as that produced by the apparatus of FIG. 1, whereas the apparatus of FIG. 1 will give excellent results with tows which are regularly crimped, e.g. by toothed gear wheels, as well as with more randomly crimped tow.

In place of a pair of rolls 14 which are helically threaded in opposite direction from each end, each roll may be threaded only in one direction. Alternatively, as shown in FIG. 5, one roll 21 may be provided with parallel circular ridges or rings 22 each extending in a plane perpendicular to the axis of the roll 21 while the other roll 23 is provided with parallel elliptical ridges or rings 24 each extending in a plane inclined relative to the axis of roll 23. It is apparent that upon rotation there will be relative lateral movement between the ridges 22 and the ridges 24. This will also be achieved if either roll 21 or 23 is used in conjunction with one roll 14, if two rolls 23 are used with their ridges inclined in opposite directions, if two rolls 21 are used and one is reciprocated laterally relative to the other, etc.

FIG. 6 shows a pair of plates 25 which can be substituted for the rolls 14. In use the plates may be reciprocated laterally but they are preferably stationary. Each plate 25 has a ridged surface and as can be seen in FIG. 6 the surface has the appearance which would result from cutting robber covering 15 of roll 14 parallel to the roll axis and flattening out the covering.

The following example is given to illustrate this invention further.

Example Using the apparatus shown in FIG. 1, an 88,000 denier tow of 11,000 cellulose acetate continuous filaments, averaging 8 crirnps per inch, is passed through air spreader l3 and is subjected to compressed air at 3 p.s.i.g. 'Ilhe tow passes between grooved rolls 14 which are 14 inches long and 5.5 inches in diameter, eighteen helical threads per inch being cut about inch deep into the rubber covering. Next, the tow passes between braking rolls 17, idly mounted for rotation and forced against each other sufliciently hard to require a force of 15 pounds to pull the tow manually therethrough. Driven rolls 18 are rotated at a peripheral speed of 37.25 yards per minute and the tow picks up 20% of its weight of triacetin in chamber 20. The tow leaving the chamber is characterized by derigistered crimps and by uniformity of openness; it has been stretched about 150%, L6. for each 100 feet of tow fed to the apparatus 250 feet emerge.

It is to be understood that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

l. The process which comprises longitudinally advancing a multifilament tow, and contacting one side of said tow with spaced tow engaging zones laterally to displace some of the filaments of said tow relative to other filaments of said row, at least one of said tow engaging zones being inclined at an angle relative to the direction of advance of said tow, whereby said tow is opened.

2. The process which comprises longitudinally advancing a multifilament tow between and in contact with a pair of opposed surfaces, at least one of said surfaces being ridged and tending to shift the tow laterally relative to the other of said surfaces, thereby to displace some of the filaments of said tow relative to other filaments of said tow, whereby said tow is bulked.

3. The process as set forth in claim 2, wherein both surfaces tend to shift the tow laterally in opposite directions.

4. The process which comprises longitudinally advancing a multifilament tow between and in contact with a pair of opposed surfaces, at least one of said surfaces being provided with laterally spaced filament-gripping zones inclined relative to the tow path and tending to shift the tow laterally relative to the other of said surfaces, thereby to displace some of the filaments of said tow relative to other filaments of said tow, whereby said tow is bulked.

5. The process as set forth in claim 4, in which said one surface is ridged, the filament-gripping zones comprising ridges alternated with grooves.

6. The process which comprises longitudinally advancing a multifilarnent tow between and in contact with a pair of opposed ridged surfaces, the ridges of at least one of said surfaces tending to shift the tow lateraily relative to the other of said surfaces, thereby to displace some of the filaments of said tow relative to other filaments of said tow, whereby said tow is bulked.

7. The process which comprises longitudinally advancing a multifilament tow between a pair of opposed ridged surfaces, and laterally displacing the ridges of one of said surfaces relative to the ridges of the other of said surfaces, thereby to displace some of the filaments of said tow relative to other filaments of said tow, whereby said tow is bulked.

8. The process which comprises longitudinally advancing a tow composed of a multiplicity of crimped filaments of an organic acid ester of cellulose between a pair of opposed ridged surfaces, laterally displacing the ridges of one of said surfaces relative to the ridges of the other of said surfaces, thereby to displace some of the filaments of said tow relative to other filaments of said tow, whereby said tow is bulked, drawing said tow away from said ridged surfaces under tension, and applying a plasticizer to said tow.

9. The process as set forth in claim 8, wherein the tension on said tow in being drawn along is sutficient to stretch the tow about 10 to 200% as compared with the initial tow.

10. The process as set forth in claim 8, wherein said tow is composed of cellulose acetate continuous filaments.

11. The process as set forth in claim 8, wherein said opposed ridged surfaces comprise cylinders having ridges inclined to the direction of advance of said tow, the ridges of opposed portions of the two cylinders being inclined in the same direction, relative lateral displacement between the ridges of the cylinders being effected by rotation of the cylinders in opposite directions.

12. The process as set forth in claim 11, wherein said opposed ridged cylinders comprise helically threaded cylinders.

13. The process which comprises longitudinally advancing a multifilament tow between and in contact with a pair of opposed surfaces, at least one of said surfaces rotating upon advance of said tow and having ridges inclined to the direction of advance of said tow, thereby to displace some of the filaments of said tow relative to other filaments of said tow, whereby said tow is bulked.

14. The process as set forth in claim 13, wherein both surfaces are ridged and tend to shift the tow laterally in opposite directions.

15. A tow opening apparatus comprising, in combination, means for advancing a multifilament tow in longi tudinal direction, and means for contacting both surfaces of said tow, at least one of said means including spaced tow engaging zones for laterally displacing some of the filaments of said tow relative to other filaments of said tow.

16. A tow opening apparatus comprising, in combination, means for advancing a multifilament tow in longitudinal direction, and a pair of rolls between which said tow advances, said rolls having parallel axes and at least one of said rolls having means for laterally displacing some of the filaments of said tow relative to other filaments of said tow.

17. A tow opening apparatus comprising, in combination, means for advancing a multifilament tow in longitudinal direction, and a pair of opposed ridged surfaces contacting said tow during its advance, the ridges of one of said surfaces being laterally displaced relative to the ridges of the other of said surfaces upon advance of said tow therebetween, said lateral displacement producing lateral displacement of some of the filaments of said tow relative to other filaments of said tow.

18. A tow opening apparatus as set forth in claim 17, wherein said opposed ridged surfaces are ridged cylinders supported for rotation.

19. A tow opening apparatus as set forth in claim 18, wherein the ridges of at least one of said ridged cylinders are formed by a helical thread.

20. A tow opening apparatus as set forth in claim 18, wherein the ridges of both of said ridged cylinders are formed by helical threads, the helical threads on each of said cylinders extending in opposite directions from both ends of that cylinder, the threads of opposed portions of the two cylinders being in the same direction.

21. A tow opening apparatus as set forth in claim 18, wherein the ridges of at least one of said ridged cylinders comprise a plurality of separate rings which encircle their respective cylinder.

22. A tow conditioning apparatus comprising, in combination, means for advancing a multifilament tow in longitudinal direction, a pair of opposed ridged surfaces contacting said tow during its advance, the ridges of one of said surfaces being laterally displaced relative to the ridges of the other of said surfaces upon advance of said tow therebetween, said lateral displacement pro- 3 ducing lateral displacement of some of the filaments of said tow relative to other filaments of said tow, and means for applying a plasticizer to said tow.

23. A ,tow conditioning apparatus comprising, in combination, a pair of rotatably mounted opposed ridged cylinders, means for drawing a multifilament tow in its longitudinal direction between said ridged cylinders, said cylinders rotating during passage of said tow therebetween, the ridges of one cylinder being laterally displaced relative to the ridges of the other cylinder upon rotation, said lateral displacement producing lateral displacement of some of the filaments of said tow relative to other filaments of said tow, and means for applying a plasticizer to said tow.

24. A tow conditioning apparatus as set forth in claim 23, including an air spreader positioned in ad Vance of said plasticizer applying means.

25. A tow conditioning apparatus as set forth in claim 23, including a pair of braking rolls through which said tow passes in travelling from said ridged cylinder to said drawing means.

26. A tow conditioning apparatus as set forth in claim 23, wherein the ridges of said ridged cylinders are formed by helical threads, the threads of opposed portions of the ridged cylinders being in the same direction.

References Cited in the file of this patent UNITED STATES PATENTS 1,347,714 Rowley July 27, 1920 2,215,112 Van Beck et al. Sept. 17, 1940 2,657,433 Merrirnan Nov. 3, 1953 2,806,694 Penman Sept. 17, 1957 2,843,881 Bishop et al. July 22, 1958 2,897,549 Paterson Aug. 4, 1959 FOREIGN PATENTS 573,407 Great Britain Nov. 20, 1945 694,789 Great Britain July 29, 1953

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