GB2201879A - Making cigarette filter rod - Google Patents

Abstract

Apparatus for feeding a non woven ribbon or sliver of polypropylene mixed fibre into a standard filter rod-making apparatus comprises a tensioning roller for maintaining and adjusting the tension in the filtering material upstream of the garniture feed. The tensioning roller is biased toward the feed path to form a V- or U-shaped path diversion arount the roller by a bisecting force that varies from 50 to 200 grams to compensate for variations in mass per unit length of the feed that passes a point upstream of the roller in a given time. The resultant of the force that is exerted as a stretching tension on the feed providing a controlled rate of mass transfer into the garniture and leading to the production of filters with controlled pressure drops and rod densities. <IMAGE>

Description

METHOD AND DEVICE FOR INDEPENDENTLY ADJUSTING ROD DENSITY AND RESISTANCE TO DRAW This invention relates to an improved method for supplying a sliver or a nonwoven ribbon into the garniture of a device for making filter elements to remove particulate matter and tars from cigarette smoke.

Conventional methods for making fiber-based filter rods use crimped textile tow of cellulose acetate, or exceptionally a tow of polyolefins such as polypropylene, that has been produced by well-known yarn "opening" mechanisms using air or steam. Binder formulations are then printed or sprayed onto the opened tow and are absorbed between and into the fibers to adhere them to each other and adjacent fibers.

The tow is then passed into the shaping zone of a filter-rod-making apparatus, which usually includes a garniture "trumpet" and a garniture, where contact is made with "tow wrap' supplied from feed roll. The apparatus includes means within the garniture for drawing in and shaping the fibers to form a filter rod, and a cutting device for cutting the rod into individual filter elements ("plugs").

Cellulose acetate tow can be easily and rapidly processed into cuttable filter rods using such standard commercial filter rod-making equipment. The process is not deleteriously affected by the application of substantial amounts of nonvolatile liquid organic plasticizers such as triacetin, diacetin, citric acid or the like onto a fiber tow before it enters the garniture of the rod making apparatus.

During the many years that filter rods have been made in the conventional way described, the choice of fibers for such filters has remained generally limited to cellulose fiber tow, which filter elements remain popular even though the resulting elements are not as efficient as elements obtained using synthetic fibers of finer denier (such as polyolefins) would be. Cellulose acetate fibers are also weaker (l.0-l.2g./denier) than other available fibers, such as polypropylene fibers. This characteristic limits the amount of tension and crimp that can be applied to a fiber tow prior to introduction into a standard filter rod-making apparatus, which in turn limits the crush resistance, efficiency and "draw" properties of the filter element.

Synthetic polyolefin fiber such as polypropylene, on the other hand, is easily drawn to a much smaller denier that provides improved filter efficiency without loss of the strength needed for crimping and for withstanding the stresses of high speed production.

But polypropylene fibers also have disadvantages. An open or "bloomed" polypropylene fiber tow cannot be readily wet by most cellulose acetate binder formulations, and the known formulations fail to provide the anciliary lubricating properties needed to prevent jamming in conventional high speed equipment unless used in such excessive amounts that filter efficiency and other desirable properties are adversely affected. This is particularly true if one also attempts to incorporate as well as plasticizers, appropriate amounts of modifier components such as humectants, flavors, medicines, absorbents, adsorbents and the like into or onto a fiber tow before the shaping and cutting steps.

Besides the problem involving the use of additives with polypropylene fiber tow, a major unsolved problem involves the relationship between pressure drop (resistance to draw) and dimensional stability or hardness of the resulting filter element. U.S. Patent 4,522,616 (Celanese Corp.), which discloses a high speed process for the preparation of cigarette filter rods from open fiber cellulose acetate tow, recognizes the existence of a complex interrelation between fiber denier, pressure drop and its effect on draw, filter efficiency, and filter hardness (when cellulose acetate tow is used) aThe process of this Celanese patent augments the usual tow-opening steps and so obtains acceptable filter characteristics with cellulose acetate tow by by passing the tow around a tensioning roll mounted at one end of lever arm movable around a fulcrum on a supporting frame between the feed rolls and the rod-making device, the arm being biased in a downward tensioning position by the arm weight distribution, and counterbalanced by adjustable counterweighting.

A constant desired back tension (normally measured in grams) is obtained. The tensioning roll is preferably fixed but may be a floating roll such as a "dancer" roll), to determine the tow width and direction and to impart a degree of tension or "drag" that is not however adjustable during operation, and is relaxed before the tow enters the garniture.

The patent points out that the resistance to air flow through the length of the filter rod (RTD) should be uniform, since fiber density influences the resistance to air flow. To ensure more uniformity in cellulose acetate tow, U.S. patent 3,960,345 (Rothmans of pall Mall Canada) discloses similar use of a roller, by providing an "inertialess" roller on a movable shaft that exerts variable braking pressure against the moving tow before it enters the conical entrance of the garniture, in order to compensate for variations in the density of the tow being fed to the blooming apparatus.Through sensing means, the braking pressure is adjusted to compensate for variations in density of the tow after it leaves the feed or drag" rollers and opening nozzles, so as to maintain a constant tension in the moving opened tow as it moves toward the gripping rollers that move the tow toward the garniture. The tension is relaxed before the tow enters the garniture.

Neither patent is of course concerned with the effect of using, instead of an opened cellulose acetate fiber tow of the conventional type, a polypropylene nonwoven or sliver feed (particularly one that contains a variable mixture of fibers and deniers). A feed material of polypropylene sliver or nonwoven material, which has a much greater degree of elasticity than cellulose acetate fiber, would not be expected to behave in the same manner (if usable at all) as an opened cellulose acetate fiber tow.

Nonwoven ribbon or sliver of mixed denier and contain- ing polypropylene, either of which is-one of the least costly form of fiber that might provide the advantage of more efficient filtering properties resulting from finer denier, also eliminate the jamming problem caused by the use of additives with tow. They may include different fiber compositions and as well as different deniers, including a low melting fiber such as polyethylene, combined with other polyolefin fibers or cellulose acetate fibers, and provide filters of varying bonding and liquid absorption properties.

Such mixed denier fibers for use in cigarette filter elements will be referred to herein generally as polypropylene mixed fibers.

To suit the preferences of most users, a smoke filter rod will have a hardness value above about 85%, most preferably about 90%, but should not exceed about 92%. The p?es- sure drop likewise should not exceed about 350 millimeters of water in a conventional water pressure gauge (defined as mm WG) for typical rods weighing between about 535 and and about 580 g per thousand.

It is to be noted that the appropriate degree of firmness in filter rods made of polypropylene fiber tends to increase the pressure drop and thus interfere with the desirable easy "draw" in smoking. In other words, there is a negative correlation between pressure drop-or "draw" (Delta P or mm WG) and "hardness value" (%F). (These values are based on the use of "Filtrona Hardness and Resilience and pressure Drop Testers", Mark V Series, of the type manufactured by Abbey Manufacturing Estates, Wembly Middlesex, Great Britain).

An equally desirable parameter value, which is equally difficult to attain with polypropylene mixed fiber, is "draw" uniformity between filter elements, namely, a low level of variation in pressure drop. In other words, a low percentage coeffficient of variation or "CV", in the order of about 7% or less, is essential for obtaining high quality filters.

Thus the use of polypropylene mixed fiber in a standard filter rod-making apparatus operating at speeds in excess of 100 meters per minute makes it very difficult to combine a desirable degree of firmness, a desirable easy "draw" for the smoker, and an essential level of uniformity in these characteristics.

According to the invention, apparatus for feeding cigarette filtering material into a standard filter rod-making apparatus operating at speeds in excess of 200 meters per minute, including a tensioning roller for maintaining tension in the filtering material upstream of the garniture feed and means for cutting the filter rods into filter elements, the amount of tension being adjustable, is characterized in that the cigarette filtering material is a nonwoven ribbon or sliver of polypropylene mixed fiber, and the tensioning roller is biased toward the feed path to form a Vor U-shaped path diversion around the roller by a bisecting force that varies from 50 to 200 grams to compensate for variations in mass per unit length of the feed that passes a point upstream of the roller in a given time, the resultant of that force that is exerted as a stretching tension on the feed providing a controlled rate of mass transfer into the garniture that provides a pressure drop not exceeding about 350 millimeters of water along the length of a filter element having a circumference of about 24.3 mm and weighing between about 535 and 580 g per thousand, a hardness value of the filter element between 84 and 95 and a percentage coeffficient of variation in pressure drop value of not above about 7%.

Also according to the invention, a method for feeding cigarette filtering material into a standard filter rodmaking apparatus operating at speeds in excess of 200 meters per minute and including a tensioning roller for maintaining tension in the garniture feed, the amount of tension being adjustable to control the tension in the feed, is characterized in that the cigarette filtering material is a nonwoven ribbon or sliver of polypropylene mixed fiber, and the tensioning roll is biased toward the feed path to form a V- or U-shaped path diversion around the roller by a force that varies from 50 to 200 grams to compensate for variations in mass per unit length of the feed that passes a point upstream of the roll in a given time, the resultant of that force that is exerted as a stretching tension on the feed providing a controlled rate of mass transfer into the garniture that provides a pressure drop not exceeding about 350 millimeters of water along the length of a filter element having a circumference of about 24.3 mm and weighing between about 535 and 580 g per thousand, a hardness value of the filter element between 84 and 95 and a percentage coeffficient of variation in pressure drop value of not above about 7%.

preferably, the percentage coeffficient of variation in pressure drop value is not above about 4%.

The effect of the tensioning roll in the apparatus and method according to the invention is to establish a uniform and acceptable rate of mass of feed material entering the garniture, which -obviously may require variations from the constant tension on the feed required by the Rothmans U.S.

patent 3,960,345.

Exemplary embodiments of the present invention are further described in the following drawings, in which: Figure 1 is a partial schematic section of a filter rod-making system having feeding means (24), including back tensioning means in the form of a mounted tensioning roll (25) of sufficient width to carry a ribbon of nonwoven material or a sliver (10) and mounted upstream of the garniture (14) of a filter rod-making apparatus (1).

Figure 2 schematically demonstrates a modification of a filter rod-making system, in which additives (43A) are applied, dried, and sandwiched between a plurality of nonwoven ribbons or a ribbon and sliver, and similarly controlled with respect to pressure drop and firmness.

Figure 3 schematically represents a preferred closed loop system for automatic adjustment of the tensioning device shown in Figures 1 and 2, whereby manually adjustable counterweight (34A) of Figure 2 is replaced with a solenoid (32B), or similar device, electronically activated through a micro- processor and switching means (30B), which is, in turn, responsive to one or more sensing means (31B, 33B and 36B) that use conventional measuring means to determine variations in the mass transfer rate, the mass per unit length of the feed that passes a given point in a given time.

Referring to Figure 1 in detail, which illustrates a manually controlled arrangement that demonstrates that acceptable filter elements can be produced according to the invention from a nonwoven ribbon or a sliver of polypropylene mixed fiber by manual adjustment without automatic feed control, a ribbon of nonwoven material of about 4"-12" width or a sliver (10) is fed from a feed reel (not shown) through feed roll (11) and feed and register rolls (12), over guide roll (17) and around tensioning roll (25) rotatably mounted at one end of reciprocally movable lever arm (26) secured at fulcrum (27) to a supporting frame (not shown), the arm being biased is biased toward the feed path by a force of from 25 to 500 grams to form a V- or U-shaped path diversion around the roller in a downward tensioning position by the arm weight distribution, and counterbal danced,' in part, by counterweight (28) and adjustable counterweight (34) threadably secured on tuning stem (35) to the opposite end of the lever arm. A level of desired tension (easily measurable in grams) is obtained by adjusting the counterweight from time to time to compensate for variations in the feed characteristics.

The nonwoven ribbon or sliver (10) is then led over guide roll (17)-and into garniture trumpet (15) and garniture (14) of filter rod forming apparatus (1), where contact is made with tow wrap (4) separately supplied from wrap feed roll (5) over support rolls (19), both being fed onto continuous garniture belt (3); said garniture belt and wrap feed roll are rotatably activated by an electric motor or similar device, not shown, to carry the ribbon (or sliver) and tow wrap through the garniture section (2).The conventional rod-making apparatus (1) includes, within the garniture section, (a) means for drawing, shaping and containing the ribbon (or sliver) to form a plug, (b) means for wrapping and securing the tow wrap around the plug, and (c) cutting means for cutting the resulting filter rods into individual filter elements (16) of suitable length, which are then transported by packing belt (18) to a receptacle (23).

Figure 2 diagrammatically demonstrates a modification of the arrangement and process demonstrated in Figure 1, whereby spray head (41A) and connecting feed line (40A) from an outside source (not shown) uniformly applies a fog or spray of melt, solution, emulsion or dispersion of one or more modifiers and additives (43A) of appropriate concentration between two nonwoven fabric ribbon(s) or sliver(s) (lOA,B) from feed rolls (39A and 42A), which are dried in register using heated nip rolls (12A) and passed over guide rolls (17A) before passage through garniture (14A) of rodmaking apparatus (1A) to form filter elements (16A) of desired length and characteristics. The remaining components are identically defined by arabic numbers as in Figure 1, except for the suffix "A".

In the preferred apparatus normally used according to the invention and shown in Figure 3, the manually adjustable counterweight (35) of Figure 1 is replaces with an automatic electronically activated mass transfer rate control arrangement shown as a solenoid (32B) the shaft of which is endwise secured to lever (28B) whereby density and draw properties of the filter are determined by sensing, at a suitable point upstream of the garniture (14A), of the mass per unit length of the sliver or nonwoven ribbon feed that passes a given point in a given time, using a combination of conventional optical or other sensing devices, including a micro sensor (31B) and odometer (33B), providing information that is fed into microprocessor (30B) that controls the tension roll positioning by means of an adjustable contact switch or induction coil (36B).The remaining arabic numbers denote components similar to those in Figures 1 and 2.

A relatively high denier range of fiber can be used for making acceptable filter elements, since the conventionally limiting relationship between fiber denier and density and pressure drop can be modified according to the invention by increased control over the nonwoven fabric, or sliver feed component. For instance, a denier -per filament (dpf) range of about 1-40 and a bulk tow denier (composite 9000 m weight value of a filament bundle) of up to about 50 X 103, or higher can be used.

Suitable nonwoven fabrics of filaments can be made in by conventional methods, utilizing circular or "y" cross section fibers, and may include thermal bonded, spun bonded, or needle punched fabrics, the preferred process being a light thermal bonding. They may weigh anywhere within the range of about 5-50 grams/m2 provided they possess sufficient tensile strength to withstand a tension value not exceeding about 500 g. A suitable ribbon (4"-12" width) or sliver may be made up of filaments having a denier within the range of about 1-40 dpf or even higher in the case of nonwoven fabric.

Suitable modifiers, for products obtained in accordance with Figure 2 include, for instance, solutions, emulsions, suspensions or dispersions of one or more humectants gener ally exemplified by various polyhydric alcohols such as glycerols, glycols, etc. flavors and perfumes such as ketoses and polysaccharides, including wintergreen, spearmint, peppermint, cinnamon, fruit flavors, etc., and medicines, such as menthol and decongestants.

For present purposes, both the treated and untreated ribbon is conveniently wrapped with regular plug wrap paper having a weight within a range of about 25-90 g/m.2 of higher, as desired.

While the back tensioning device (i.e. a tensioning roll and counterweight-as shown in Figure 1) is biased by lever arm weight in a downward (positive tension) position with respect to the ribbon or sliver feed, the desired tension can also be obtained by biasing the lever in the reverse (upward) direction and placing an apprpriately heavier counterweight comparable to (35) on the opposite or tension roll end of lever arm (26).

Depending upon the content and form of the desired filter plug, the tensioning wheel is usefully adjusted to run within a tension force of about 100-200 gm (4.5 dfp 1.5" fiber length, 9"-12" width) while a 4.5 dpf continuous fiber sliver requires a tension force between about 50-200 gm to obtain comparable variations in rod density and resistance to draw (RTD). The exact amount, in each case, depends upon the machine being used and the speed of operation.

For exemplary purposes, the relationships between the amount of tension required on a sliver or ribbon to achieve particular filter density, drawing characteristics, and uniformity is further demonstrated in the Examples and tables below.

Example 1 Slivers of a standard polypropylene feed tow (4.5 dpf) having a bulk denier varying from 58.5 to 66.8 x 103, subjected to variations in tensioning force of from 40 (control) to 200 grams, are fed into the garniture of a filter rod-making apparatus, namely a standard type identified as Model MK5, manufactured by Molens PLC, London, England, which was modified as shown in Figure 1 to provide apparatus according to the invention; the resulting changes in filter element pressure drop and firmness are noted and the results reported in Table I.

Example 2 Slivers essentially identical to those described in Example 1 (4.5 dpf) having a bulk denier varying from about 3 59.8-66.8 X 103 are passed through the filter rod-making apparatus of Example 1, and modified with a back tensioning device (a closed loop device) of the type shown schematically in Figure 3. The test results are reported in Table 2 below.

Example 3 Isotactic polypropylene staple fiber (4.5 dpf and 1.5" cut) having a "y" cross-section and a flow rate of 40+ 5g/10 minutes, is carded into a web weighing about 25 gm/m2.

The web is transferred onto a continuous fiberglass belt and lightly thermally bonded using a hot diamond-patterned calender at 140 C/40 psi roll pressure to obtain a nonwoven fabric which is cut into 1288 test ribbon width.

Using the test ribbon as feed for the filter rod-making apparatus of Example 1, it is found that comparable changes in pressure drop and firmness are obtained within the range of about 100-200 gm tension.

Table I FILTER ROD PHYSICAL PROPERTIES VS. CIGARETTE TOW TENSION CONTROL Bulk Pressure Drop Firm Sample Tension Denier Rwt Circ. P CV ness No. (g) x 103 (g/1000) (mm) (mm WG) (%) (% F) 1 (Control) 40 66.8 571 24.17 342 3.9 89.7 2 (Control) 40 66.6 676 24.76 334 3.6 89.4 3 50 66.0 557 24.22 327 4.0 88.7 4 50 66.4 562 24.24 336 4.6 89.3 5 50 63.3 549 24.19 325 4.7 88.0 6 50 65.4 564 24.13 339 4.7 88.5 7 50 65.5 554 24.13 339 4.4 88.7 8 100 62.0 548 24.34 290 4.6 85.9 9 100 63.5 551 24.28 300 4.5 86.3 10 100 64.6 553 24.37 302 5.5 86.2 11 100 62.6 558 24.36 301 3.7 87.1 12 100 63.7 556 24.30 292 3.8 88.7 13 150 63.2 549 24.33 289 - 3.8 85.4 14 150 58.8 534 24.18 284 4.0 85.6 15 150 59.2 529 24.26 280 5.2 86.1 16 150 62.0 534 24.32 279 4.8 85.3 17 150 62.2 522 24.32 278 4.7 85.8 18 200 60.4 537 24.30 278 5.4 85.7 19 200 59.8 534 24.29 283 4.5 85.3 20 200 59.1 534 24.19 288 4.8 85.8 21 200 59.3 536 24.26 275 3.7 84.7 22 200 59.0 531 24.26 272 4.0 84.3 Table II CLOSED LOOP TENSION CONTROL SYSTEM Bulk Pressure Drop Firm Sample Tension Denier Rwt Circ. P CV ness No. (g) x 103 (g/1000) (mm) (mm WG) (%) (% F) l(**control) 25 66.8 580 24.38 355 10.60 89.0 2(**control) 25 66.6 575 24.35 350- 12.75 87.2 3 50 65.3 583 24.37 347 1.03 89.5 4 100 63.6 575 24.35 342 1.29 89.2 5 150 61.0 571 24.32 342 3.32 89.2 6 200 59.8 535 24.35 333 7.78 88.5 **Manual Overfeed Adjustment Example 4 Example 3 is repeated but one nonwoven ribbon is presprayed with a 5% zinc acetate solution for selectively removing low concentrations of cyanide gas. The sprayed ribbon is then dried and a sandwich formed between two ribbons of untreated nonwoven ribbon. Changes in pressure drop and firmness are found to be comparable to those obtained in Example 3 upon varying back tension within the range of 100-200 gm.

Claims (1)

1. Apparatus for feeding cigarette filtering material into a standard filter rod-making apparatus operating at speeds in excess of 200 meters per minute including a tension ing roller for maintaining tension in the filtering material upstream of the garniture feed and means for cutting the filter rods into filter elements, the amount of tension being adjustable, characterized in that the cigarette filtering material is a nonwoven ribbon or sliver of polypropylene mixed fiber, and the tensioning roller is biased toward the feed path to form a V- or U-shaped path diversion around the roller by a bisecting force that varies from 50 to 200 grams to compensate for variations in mass per unit length of the feed that passes a point upstream of the roller in a given time, the resultant of that force that is exerted as a stretching tension on the feed providing a controlled rate of mass transfer into the garniture that provides a pressure drop not exceeding about 350 millimeters of water along the length of a filter element having a circumference of about 24.3 mm and weighing between about 535 and 580 g per thousand, a hardness value of the filter element between 85 and 92 and a percentage coeffficient of variation in pressure drop value of not above about 7%.

2. Apparatus for feeding cigarette filtering material into a filter rod-making apparatus as claimed in claim 1, * characterized in that the percentage coeffficient of variation in pressure drop value is not above about 4% Apparatus for feeding cigarette filtering material into a filter rod-making apparatus as claimed in claim 1 or 2, * characterized in that the tensioning roller is rotatably mounted on at one end of a pivoted counterweighted lever.

4. Apparatus for feeding cigarette filtering material into a filter rod-making apparatus as claimed in claim 1, 2 or 3? * characterized in that the bisecting force is varied by an electronic mass transfer rate control apparatus that senses the mass per unit length of the sliver or nonwoven ribbon feed that passes a given point upstream of the tensioning roller in a given time and adjusts the counterweight on the lever accordingly.

5. A method for feeding cigarette filtering material into a standard filter rod-making apparatus operating at speeds in excess of 200 meters per minute, including the steps of maintaining tension in the filtering material upstream of the garniture feed and cutting the filter rods into filter elements, the amount of tension being adjustable, the amount of tension being adjustable, characterized in that the cigarette filtering material is a nonwoven ribbon or sliver of polypropylene mixed fiber, and the feed path is biased away from its direct path to-form a V- or U-shaped diversion by a roller-applied bisecting force that varies from 50 to 200 grams to compensate for variations in mass per unit length of the feed that passes a point upstream of the diversion in a given time, the resultant of that force that is exerted as a stretching tension on the feed providing a controlled rate of mass transfer into the garniture that provides a pressure drop not exceeding about 350 millimeters of water along the length of a filter element having a circumference of about 24.3 mm and weighing between about 535 and 580 g per thousand, a hardness value of the filter element between 85 and 92 and a percentage coeffficient of variation in pressure drop value of not above about 7%.

6. A method for feeding cigarette filtering material into a filter rod-making apparatus, as claimed in claim 5, * characterized in that the percentage coeffficient of variation in pressure drop value is not above about 4%.

7. Apparatus for feeding cigarette filtering material into a filter rod-making apparatus, substantially as hereinbefore described with reference to any Figure of the accompanying drawings.

8. A method for feeding cigarette filtering material into a filter rod-making apparatus, substantially as hereinbefore described with reference to the accompanying drawings.

9. A method for feeding cigarette filtering material into a filter rod-making apparatus, substantially as described in Example 1, Example 2, Example 3 or Example 4.