US3144025A

US3144025A - Tobacco smoke filters

Info

Publication number: US3144025A
Application number: US24328A
Authority: US
Inventors: Victor L Erlich
Original assignee: Reeves Brothers Inc
Current assignee: Reeves Brothers Inc
Priority date: 1960-04-25
Filing date: 1960-04-25
Publication date: 1964-08-11
Anticipated expiration: 1981-08-11
Also published as: GB915783A

Description

Aug. 11, 1964 v. L. ERLICH TOBACCO SMOKE FIL-.Treas Filed April 25, 1960 Inventor l//croe Z. FAM/6H Attorneys United States Patent `O York Filed Apr. 25, 1960, Ser. No. 24,328 20 Claims. (Cl. 131208) The present invention relates to a new and improved cigarette filter and to a process of manufacturing the same. The instant application is a continuation in part of copending application Serial No. 654,462, filed Apr. 23, 1957, now Patent No. 3,049,466 issued Aug. 14, 1962.

Cigarette filters are now common expedients, at least for the purpose of extracting tar, nicotine and other undesirable ingredients from the tobacco smoke. Materials that have been used or suggested for the purpose are cotton, asbestos, cellulose paper and cellulose acetate. These fibrous materials may be used in fiber form to serve as a basic filtering medium, may be subjected to special treatments to render them serviceable, and/ or may serve as a support for filtering agents in granular form, such as activated carbon, and cellulosic powders. Other materials have also been suggested for the purpose, but have not found wide acceptance as yet in the manufacture of popular cigarette brands.

Among the filter materials described, cellulose acetate fibers are at the present time most popular. These fibers, however, require the use of adhesive or solvents for joining the filaments at random points.

Filters made from fibers of poly-alpha-olefins, commonly referred to as polyolefins would meet the requirements of the cigarrete industry. Polyolefins, and especially polyethylenes and/or polypropylene fibers, would be highly desirable as filter mediums for many reasons, one reason because they are almost fully water-repellent, more so than cellulose acetate.

High molecular weight polypropylene having stereospecific molecular structure, and medium and particularly high density polyethylene can be made into fine fibers and in a form similar to that now employed in connection with the cellulose acetate fibers, so that substantially all of the characteristics of cellulose acetate fiber that make it serviceable for cigarette filters can be retained and utilized by the polyolefin fibers. At the same time, a major part of the high speed apparatus now used in the processing of the cellulose acetate fibers to convert them into filtering elements, can be employed in connection with the polyolefin fibers.

Polyolefins in the form of fine fibers have great capabilities as smoke filtering mediums, not only because of the reasons set forth, but also because, especially in the case of polypropylene, the fibers have a tendency to curl and to form teXturized surfaces.

The low specific gravity of the polyolefins compared with cellulose acetate, in addition to the other characteristics of the polyolefins described, makes polyolefin fibers a desirable material for use in connection with cigarette filters. For example, isotactic polypropylene has a specific gravity of 0.90 to 0.91 and the different polyethylenes have specific gravities ranging from 0.92 to 0.96, while cellulose acetate has a specific gravity of 1.32. This means that polyethylene and polypropylene fibers of cross-section area similar to that of cellulose acetate fiber have only about two-thirds the weight of the cellulose acetate liber. This makes the use of polyolen economically interesting.

Cigarette filters manufactured with cellulose acetate fibers are shaped in form of rods which are composed of a multitude of line filaments bonded together into a cylinder of the size of the cigarette. Suchrbonding of 3,l44,025 Patented Aug. 11, 1964 ice Y the fiber tow is necessary to permit handling it in the cigarette making machines and also to inhibit loosening of fiber'parts from the mouthpiece in smoking. However, such bonding must be limited to partial surface contacts so as to provide for sufficient air permeability through the filter above the fiber surface.

Y Whereas such fibrous materials as cellulose acetate can be bonded easily with adhesives and solvents, polyolefins are so chemically inert and so hydrophobic, that ordinary bonding expedients, such as adhesives and solvents, cannot be successfully employed.

One object of the present invention is to provide a new and improved tobacco smoke filter made essentially of polyolefin fibers.

Another object of the present invention is to provide a new and improved process for converting polyolefin fibers into compact, firm, rod-like segments suitable for cigarette filter elements, without the use of adhesives or solvents.

A further object is to provide a new and improved process for bonding substantially parallelized polyolefin fibers in rod-like coherent form, without the use of adhesives or solvents.

In accordance with certain features of the present invention, a blended tow or sliver of polyolefin fibers of two types, differing in molecular structure, so that they differ in melting points, is heated to the softening point of the fibers of lower melting point, without melting the latter fibers. It is desirable to employ polyolefin fibers having a melting point difference of at least about 20 C. between the two types of fibers in the tow. For instance, it is advantageous to employ as the fibers of higher melting point, polypropylene having a stereospecific molecular structure, i.e., a molecular structure in which the side chains branch out from the linear paraffinic backbone or nucleus into the molecular space in orderly predetermined directions as distinguished from a molecular structure in which the side chains branch out randomly in opposite directions from the linear paraffnic backbone. Such stereospecific polymers are sometimes also designated as isotactic or syndiotactic depending on the specific orderly arrangement of the side chains in one or in alternate directions. In combination with such polypropylene fibers, it is advantageous to employ as the fibers of lower melting point, a polyethylene having a medium to high density, i.e., a specific gravity ranging between 0.93 and 0.95. Also, it is desirable for the fibers of higher melting point to constitute in number the major part of the blended tow, `and to be at least 50% greater in total weight than the fibers of lower melting point. The number of fibers of lower melting point is preferably 10 to 20% of the number of fibers of higher melting point. The polyolefin fibers in the blended tow may be all continuous monofilaments, may be all cut staples ranging in length, desirably from about l cm. to about 5 cm., or may be a combination of continuous monofilaments and cut staples.

The blended tow or sliver is heated as will be described and cooled to partially bond the fibers of the two types at their points of contact, without destroying the fiber structure and without eliminating the voids between and along the fibers to afford the necessary air permeability.

Where the -polyolefin fibers are fully molecularly oriented along the length of the fibers, the dimensions of these fibers are affected by the process described above to which they are subjected. It is, therefore, desirable to use polyolefin fibers in the blended tow, not or only partially molecularly oriented to the point where they will substantially retain dimensional stability up to their softening point to avoid distortion of the fibers during heating. The limit of molecular orientation for that purpose 3 varies according to the type of polyolefin fiber employed, and in the case where the blended tow consists essentially of isotactic polypropylene and high density polyethylene, the molecular orientation of these fibers may be not higher than approximately 25%V of that needed for full orientationof the fibers.

The compact bonded tow in the form of a rod is then wrapped and cut tov formA filter elements or plugs for use in connection with cigarettes in the manner well known in the cigarette making art.

Referring to the more specific aspects of the present invention, the process iscarried out with a blended tow of continuous filaments or a sliver of cut polyolefin fibers having a total denier as required for the formation of the cigarette in its final cylindrical tow. The tow may be composed of between 10,000 and 50,000 individual filaments in continuous or cut form having a size which may vary between 1 and 31/2 denier and molecularly unoriented or oriented only partially to maintain acceptable dimensional stability up to the softening point of the fibers. The bers in the tow need not be ofthe same denier, and it may be advantageous to have the fibers of the lower meltingv point of different denierthan the fibers of the higher melting point, It is also advantageous to impart to the fibers a crimped or textured form to improve the surface effect for filtering efficiency.

The blended tow or sliver constitutedv as described is opened up and spread intor a thin ribbon or web form, for instance by means of an air blowing system and this ribbon or webs passed through a heating zone where the ribbon is heated to a temperature necessary to soften the fibers of lower melting point but to 15 C. below the melting point of these fibers. At this temperature, the fibers of higher melting point will not soften. The heated tow in ribbon form is then desirably compacted sidewise to cause the fibers of higher melting point to become embedded into the softened fibersof lower melting point, and the tow while hot is passed through a funnel-like tube where the tow is condensed'and'shaped substantially into the cylindrical rod-like form and size it will have in the final cigarette filter. During this condensing process, the fibers are brought together and integrally bonded together through the softened fibers while the rod-like mass retains the desirable amount of air permeability for easy smokingl draw. The fibers so shaped are then passed through a cooling zone where the bonding is made permanent. From here, the bonded'filter rod is cut into segments and the segments arewrapped to form filter elements for combination with the tobacco holding parts of the cigarette. The latter steps are all well known in the cigarette making art.

A specific example for carrying out the invention is illustratedherein in conjunction with the accompanying drawings, in which FIG. 1 is a flow sheet showing diagrammatically in side elevation an apparatus for carryingout the process of the present invention;

FIG. 2 is a side elevational diagrammatic View of the apparatus; and

FIG. 3 isV an enlarged longitudinal section through a portion of a tipped cigarette assembled with a filter of the invention.

In accordance with a specific example, the filter tow to be used for the cigarette filter has a total denier of 50,000 composed of 20,000 continuous monofilaments of 21/2 denier each. Seventeen thousand (17,000 filaments were isotactic propylene having a melting point of 170 C. and 3000 filaments were of high density polyethylene having a specific gravity of .945 and a melting point of 130 C. These filaments had been melt-extruded from forty (40) spinnerettes, each having 500 orifices, adequately sized to yield individual filaments of 6.25 denier gauge, so that each spinnerette supplied an individual tow of 3125 denier. Thirty-four (34) of these individual tows constituted polypropylene filaments and six (6) of tain fullorientation of the fibers.

these individual tows constituted polyethylene filaments. The six 6) individual polyethylene tows were evenly distributed among the thirty-four (34) individual polypropylene tows to form a blended tow of 125,000 total denier.

The blended tow constituted as described, was then stretched in a conventional tow stretching device in the ratio of 1.0 to 2.75 at avtemperature of C. and relaxed in the ratio of 1.1; toY 1.0, so that total net stretch ratio imparted to the filaments was 1.0 to 2.5. This stretch ratioprovided for partial molecular orientation of the filaments, which inthis case under the conditions described was approximately 25% of that needed to at- The blended tow prior to being collected in bale was conducted through a crimping machine well-known in the art to crimp the filaments.

Referring to the drawings, the crimped blended tow 1f)l constituted as described, ssupplied in the form of a compressed bale 11, from which the tow is taken off at a continuousrspeed of about 300 feet per minute by means of driven Godet rolls 12, these being desirably circumferentially grooved to draw the tow fromthe bale. The tow isthen passed through the field ofV action of a blowing device 13, which is designed to project air jets against the travelling tow to open up the tow, to break up any individual concentration of filaments, within the two and to spread the tow sidewise into the form of a thin fiat ribbon having substantially` uniform distribution of filaments running substantially parallel therealong.

The blowing device 13 may take any form well known in the art of making cigarette filters from filaments, such as those now employed in connection with cellulose acetate filaments. For example, it may take the form of a pair of plates on opposite sides of the course of the tow defining a fiat passageway therebetween through which the tow travels and provided with orifices through which jets of air or other gas under pressure are projected for impingement on opposite faces of the tow.

The tow in ribbon formis taken up by a tow fiattening driven roll system 14, where the tow may be further spread out, and evened out uniformly sidewise, and is then conducted through the field of a heating device 15. This heating device 15 may be in the form of a chamber comprising two heated plates on opposite faces of the ribbon tow for heating the fibers of the tow to the required temperature to soften the fibers of lower melting point without melting the lat-ter fibers or softening the fibers of higher melting point. For that purpose, the ribbon tow is heated in the heating chamber 15 to a temperature maintained between and 120 C. The heat necessary for heating the fibers to this temperature may be supplied by an infra red heating system or by hot air or other gas, the heat being controlled by the speed of the forwardly moving ribbon tow to assure the heating of the tow to the proper temperature.

The spreading of the tow into ribbon form to a width of say 40 tot 50 mm. Prior to the heating as described, serves to distribute the filaments of lowerv melting point substantially across the width of the ribbon, and to bring these fibers close to the surface of the ribbon, so that these fibers willbe heated substantially uniformly throughout the cross-section of the ribbon.

As the heated tow moves through the heating chamber, it may be progressively contractedy sidewise by a set of driven Godet rolls 16 on the discharge end of the heating chamber 15 having peripheral grooves forV confining the sides of the tow. The tow is contracted by the rolls 16 to a width of about 16 mm., this contraction causing the fibers of higher melting I:point to be embedded into the softened fibers of lower melting point while still hot and soft, and preventingl the soft fibers from sticking to the rollsurfaces.

The compacted tow is then led directly into a condensing folder 1 7 in the form of a funnel-shape tube, to condense the tow and form it into a compact cylindrical rod a of approximately the desired transverse section having a diameter of about 8 mm. While the rod 10a is passing through the folding tube 17, the fibers of higher melting point lwill become bonded at random points to the fibers of lower melting point which are still soft. The bonding of fibers together in the cylindrical rod 10a is completed by running it through a cooling device 1S of any suitable type, such as one in which cooling air is projected against the rod.

After leaving the cooling device 18, the bonded filter rod 10a will maintain its form without falling apart, will have its fibers distributed substantially uniformly throughout its cross-section, and will retain sufficient air space along the fibers to provide the air permeability necessary to afford easy draw in smoking while affording the necessary fiber surface areas by which the undesirable ingredients of the smoke are extracted by smoke impingement.

The rod i011 formed as described may then be processed by the usual well-known cigarette filter making mechanism to form the filter mouthpieces or plugs for combination with the tobacco holding parts of the cigarettes. For example, the rod 10a may be cut by a cutter 1Z0 into segments and the segments wrapped with sections of cigarette paper by a wrapper folding device 21 to form filter pieces or plugs 22 (FIG. 3). These filter pieces 22 with individual wrappers 23 are then combined with the tobacco holding parts 24 of the cigarettes in their paper Wrapper 25, by overlapping folios 26.

The length bf the filter mouthpieces 22 varies, and may be for instance 17 mm. in a cigarette having a total length of 85 mm.

A good part of the apparatus now employed for malcing cigarette filters, as for example, from cellulose acetate, can be employed at the same high continuous speed in connection with the present invention, so that conversion of the apparatus from the handling of cellulose acetate to the handling of polyolefins is practical from an economic standpoint, and desirable from the standpoint of the character of filter piece produced.

While the invention has been described with particular reference to a specific embodiment, it is to be understood that it is not to be limited thereto, but is to zbe construed broadly and restricted lsolely by the scope of the appended claims.

What is claimed is:

l. The method of producing fibrous rod-like bodies for use in the manufacture of filter elements, which cornprises heating a blended tow of two types of polyolefin fibers having different melting points to the softening point of the fibers of lower melting point but below the melting point of the latter fibers, condensing the tow and shaping it into a rod-like body to cause the fibers to` -be bonded together through the softened fibers, without destroying the fiber structure in the rod-like body and while maintaining sufficient voids in the rod-like body tot afford air permeability therealong, and cooling the rod-like body.

2. The method of 'producing fibrous rod-like bodies for use in the manufacture of filter elements, which comprises heating a blended tow of two types of polyolefin fibers having different melting points to the softening point of the fibers of lower melting point but below the melting point of the latter fibers, While said tow is in flattened ribbon form, shaping and condensing the heated flat ribbon tow into the compact form of a substantially cylindrical rod, to cause the fibers to be bonded together through the softened fibers without destroying the fiber structure while maintaining sufficient voids in the rodlike body to afford permeability therealong, and cooling the cylindrical rod.

3. The method of producing fibrous rod-like bodies as described in claim 1, wherein the polyolefin rfi-bers of lower melting point are polyethylene and the polyolefin fibers of higher melting point are polypropylene of stereospecific molecular structure.

4. The method of producing fibrous rod-like bodies for use in the `manufacture of filter elements as described in claim l, wherein the fibers are free from molecular orientation above a degree where the fibers are dimensionally affected during heating of the tow.

5. The method of producing rod-like bodies for use in the manufacture of filters as described in claim l, wherein the tow is formed by a sliver of cut filaments, the individual staple fibers ranging in length from l and 5 cm. and between approximately l tto .3l/2 denier in size.

6. The method of producing rod-like bodies for use in the manufacture of filters as described in claim l, wherein the tow consists partially of continuous and partially of cut filaments wherein the size of the filaments and of the staple fibers ranges approximately from l to 31/2 denier.

7. The method of producing filter mouthpieces for cigarettes, which includes the steps of continuously advancing lengthwise a blended tow comprising fibers of polyethylene and fibers of isotactic polypropylene, the fibers of polyethylene having a melting point lower than that of polypropylene, the fibers being free of such a degree of molecular orientation as would impart to the fibers dimensional instability at the softening point of the polyethylene fibers, spreading and opening up the tow into the form `of a flat ribbon, heating the advancing ribbon tow to the point Where the polyethylene fibers become softened but do not melt, shaping and condensing the advancing ribbon tow into substantially a cylindrical rod-like body, cooling the rod-like body to bond the softened fibers to the other fibers without destroying the fiber structures and while maintaining sufficient voids in the rod-like body to afford air permeability along the rod-like body, and severing the advancing rod-like bonded body into segments in preparation for combination with the tobacco holding parts of the cigarettes.

8. The method of producing filter mouthpieces for cigarettes, which includes the steps of continuously advancing lengthwise a tow of between 10,000 and 50,000 fibers consisting essentially a blend of polyethylene fibers and isotactic polypropylene fibers, the fibers of polyethylene having a meltiny point lower than that of the polypropylene, the fibers being molecularly oriented not higher than approximately 25% of that needed for full orientation of the fibers, the fibers having a size ranging from l to 3'1/2 denier, spreading and opening up to the tow into the form of a flat ribbon, heating the advancing ribbon tow to the point where the polyethylene fibers become softened but do not melt, shaping and condensing the advancing tow into a substantially cylindrical rod-like body having a diameter of about 8 mm, cooling the rod-like body to bond the softened fibers to the other fibers without destroying the fiber structures and while maintaining sufficient voids in the rod-like body to afford air permeability along the rod-like body, and severing the advancing rod-like bonded body into segments in preparation for combination with the tobacco holding parts of the cigarettes.

9. The method of producing a fibrous rod-like body for use in the manufacture of filter elements, which comprises forming a blend of polyolefin fibers extending substantially parallel and a divided polyolefin material of lower melting point mixed therewith, heating the blend to the softening point of the polyolefin material but below the melting point of the fibers, shaping and condensing the fibers into rod-like form, and cooling the heated blend while in compact rod-like form with the fibers extending therealong to cause the fibers to be bonded together through said polyolefin material into a coherent rod-like body while maintaining sufficient voids in the body to afford air permeability therealong,

10. The method of producing fibrous rod-like bodies for use in the manufacture of filter elements, which comprises heating a blended tow of two types of polyolen fibers having different melting points to the softening point of the fibers of lower melting but below the melting point ofthe latter fibers, the fibers of higher melting point constituting in number the major bulk of the fibers in the tow, and being at least 50% greater in weight than the fibers of lower melting point, condensing the tow and shaping it into a rod-like body to cause the fibers tobe bonded together through the softened fibers without destroying the fiber structure in the rod-like body and While maintaining sufficient voids in the rod-like body to afford air permeability therealong, and cooling the rodlike body.

11. The method of producing fibrous rod-like bodies for use in the manufacture of filter elements, which comprises heating a blend tow of two types of polyolefin fibers having different melting points to the softening point of the fibers of lower melting point but below the melting point of the latter bers, the tow consisting of a bundle of continuous filaments in sizes ranging approximately from 1 to 31/2 denier, condensing the tow and shaping it into a rod-like body to cause the fibers to be bonded together through the softened fibers, without destroying the fiber structure in the rod-like body and while maintaining sufiicient voids in the rod-like body tol afford air permeability therealong, and cooling the rodlike body.

12. A rod-like coherent filter body comprising a plurality of polyolefin fibers of two types extending along the body, one type having a melting point lower than that of the other type, the fibers of the two types being mixed for substantial uniform distribution of the fibers of one type among the fibers of the other type, the fibers of lower melting point being bonded to the fibers of higher melting point by the compacting of the body while the fibers of lower melting point are soft and the fibers of higher melting point are unsoftened, and by the cooling of the compacted body, said body having voids therein imparting to the body an air permeability in the direction of its length.

13. A rod-like coherent filter body as described in claim 12, wherein the differences in melting point between the two types of polyolefin fibers is at least 20 C.

14. A rod-like coherent filter body as described in claim 12, wherein the body is substantially cylindrical in shape and of a diameter to adapt it for use in making cigarette mouthpieces.

15. A rod-like coherent fiber body as described in claim 8 12, wherein the body consists essentially of a blend of polyethylene fibers and of polypropylene fibers of stereo-specific molecular structure, and wherein the polyethylene fibers have the lower melting point.

16. A rod-like coherent filter body as described in claim 12, wherein the fibers are molecular oriented only partially to impart dimensional stability to the fibers up to their respective softening points.

17. A rod-like coherent filter body as described in claim l2, wherein the fibers of higher melting point constitute in number the major bulk of the fibers in the tow, and are at least greater in weight than the fibers of lower melting point.

18. A rod-like coherent claim 12, wherein the fibers to 31/2 denier.

19. A rod-like coherent filter body as described in claim 12, wherein the body is substantially cylindrical in shape and of a diameter to adapt it for use in making cigarette mouthpieces, the body consists essentially of a blend of polyethylene fibers and isotactic polypropylene fibers, the fibers have a number between 10,000 and 50,000 and a size ranging from 1 to 3%. denier, and the fibers are molecularly oriented only partially to impart dimensional stability to the fibers up to their respective melting points.

20. A rod-like coherent filter body comprising a plurality of polyolefin bers extending therealong and bonded together through a polyolefin material of lower melting point distributed throughout the mass of fibers.

References Cited in the file of this patent UNTTED STATES PATENTS filter body as described in have a size ranging from 1 2,500,282 Francis Mar. 14, 1950 2,707,308 Taylor et al. May 3, 1955 2,794,480 Crawford et al. June 4, 1957 2,812,767 MacHenry Nov. 12, 1957 2,812,796 MacHenry Nov. 12, 1957 2,818,868 Rivers Jan. 7, 1958 3,836,576 Piccard et al May 27, 1958 2,933,154 Lauterbach Apr. 19, 1960 2,966,157 Touey et al Dec. 27, 1960 FOREIGN PATENTS 752,600 Great Britain July ll, 1956

Claims

12. A ROD-LIKE COHERENT FILTER BODY COMPRISING A PLURALITY OF POLYOLEFIN FIBERS OF TWO TYPES EXTENDING ALONG THE BODY, ONE TYPE HAVING A MELTING POINT LOWER THAN THAT OF THE OTHER TYPE, THE FIBERS OF THE TWO TYPES BEING MIXED FOR SUBSTANTIAL UNIFORM DISTRIBUTION OF THE FIBERS OF ONE TYPE AMONG THE FIBERS OF THE OTHER TYPE, THE FIBERS OF LOWER MELGINT POINT BEING BONDED TO THE FIBERS OF HIGHER MELTING POINT BY THE COMPACTING OF THE BODY WHILE THE FIBERS OF LOWER MELTING POINT ARE SOFT AND THE FIBERS OF HIGHER MELTING POINT ARE UNSOFTENED, SAND BY THE COOLING OF THE COMPACTED BODY, SAID BODY HAVING VOIDS THEREIN IMPARTING TO THE BODY AS AIR PERNEABILITY IN THE DIRECTION OF ITS LENGTH.