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(11) | EP 0 250 806 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method and device for removing nitric oxide from cigarette smoke |
| (57) Method method for making a chemically-treated filter element for cigarettes, to reduce
the concentration of nitrogen oxide by-products in cigarette smoke, by applying a
non-ionic solution or dispersion containing zinc oxide or zinc acetate to the substrate
in the garniture feed, the non-ionic solution or dispersion also containing a polyoxyalkylene
derivative of a sorbitan fatty acid ester, a monoester of a polyhydroxyalcohol, or
a diester of a polyhydroxy alcohol, or containing a mixture of the said dispersants.
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[0001] This invention relates to a method for making a chemically-treated filter element for selective filtration of cigarette smoke.
[0002] Fiber based filter elements are well-known and have been used in the cigarette manufacturing field for at least 40 years. While various synthetic fiber and fiber mixtures have been tried and evaluated in the market place, most cigarette filter elements continue to include cellulose acetate-based fibers.
[0003] Synthetic fibers, particularly fibers of polyolefins such as polypropylene are easily drawn to a much smaller denier than cellulose acetate-based fibers, offering improved filter efficiency without simultaneous loss of strength needed for crimping and high speed production. Such fibers, however, also have disadvantages. These stem mainly from the fact that a substrate, such as an open or bloomed tow is relatively inert and not readily wetted or softened by most adhesive/plasticizer or other hydrophilic-type modifier formulations.
[0004] The incorporation of chemically-active ingredients in order to achieve selective filtration of cigarette smoke has led to various difficulties connected with the substrate characteristics, uneven distribution, as well as interrelationships between filter element efficiency, and the dimensional stability, resiliency and hardness of the resulting filter element. Polyolefin fiber-containing substrates (i.e. tows and slivers) fed into a filter rod-making apparatus have demonstrated a significant negative correlation between pressure drop (resistance to draw) and dimensional stability or hardness of the filter element. In addition, it is often very difficult to avoid jamming of impregnated polyolefin or other synthetic substrates fed at high speed into a conventional filter rod-making apparatus, particularly substantial amounts of modifier components such as adhesives, humectants, flavors, medicines, absorbents, adsorbents, and the like, into or onto the garniture feed. This is due, in part, to an inherent deficiency in lubricating properties of many additive compositions used in the cigarette filter art.
[0005] For instance, U.S. Patent 3,428,056 points out that the addition of water-soluble inorganic salts that effectively remove hydrogen cyanide from cigarette smoke lead to non-uniform powder distribution and poor filtration efficiency. That patent attempts to deal with the problem by using polyolefin powders that have been coated with inorganic salts such as sodium and potassium carbonates, the powders being vibrated onto cellulose acetate tow that has been previously treated with a bonding agent such as glycerol triacetate and that is then compacted and wrapped to form a filter rod.
[0006] U.S. Patent 3,6l8,6l9 deals with the problem of removing by dispersing metal oxides such as zinc oxide, ferric oxide and cuprous oxide in the cellulose acetate solution from which the cellulose acetate tow used in the filters is spun, and then treating the tow with certain organic "activating agents", including glycerol triacetate,to make the tow filaments permeable to hydrogen cyanide.
[0007] U.S. Patent 3,6l8,6l9 discloses the use of a mixture of zinc acetate and other compounds to impregnate a base of aluminum oxide, which is the dispersed in particulate form in filter fibers such as those of cellulose acetate. Many other U.S. patents have defined and attempted to solve the problem of incorporating zinc compounds in cigarette filter material. None of them apparently have addressed the problem of treating polyolefin fiber-containing substrates with such compounds.
[0008] According to the invention, a method for making a chemically-treated filter element for cigarettes in which a cigarette filter element obtained from a conventional filterrod-making apparatus using, as garniture feed, a polyolefin fiber-containing substrate, is treated with a zinc compound, such as zinc oxide or zinc acetate as an active modifier component in order to remove nitrogen oxide and nitrogen oxide by-products from cigarette smoke, characterized in that a non-ionic solution or dispersion containing zinc oxide or zinc acetate is applied to all or part of the substrate in the garniture feed, the non-ionic solution or dispersion also containing as a dispersant a polyoxyalkylene derivative of a sorbitan fatty acid ester, a monoester of a polyhydroxyalcohol, or a diester of a polyhydroxy alcohol, or containing a mixture of the said dispersants.
[0009] The non-ionic solution or dispersion will be referred to as a non-ionic "spin solution" in acordance with usage in the art. Preferably, the nonionic spin solution contains about 0.l wt%-l0 wt% and preferably 0.5 wt%-l0 wt% of one or more of the surfactants.
[0010] Preferably, the surfactants in the non-ionic spin solution are ethoxylates, carboxylic acid esters, glycerol esters, polyoxyethylene esters, anhydrosorbitol esters, ethoxylated anhydrosorbitol esters, ethoxylated natural fats, oils and waxes, glycol esters of fatty acids, polyoxyethylene fatty acid amides, polyalkylene oxide block copolymers, and poly(oxyethylene-co-oxypropylene).
[0011] Preferably the amount of the modifier components is applied is about l wt%-l0 wt% based on fiber weight.
[0012] The term "substrate", as used herein, denotes a fiber-containing or fibrillated film-containing component suitable for use as garniture feed for a filter rod-making apparatus. Substrates may be (a) open polyolefin-containing fiber tows, (b) open ribbons of a nonwoven polyolefin- containing material or (c) open webs of fibrillated polyolefin films combined with active modifier component.
[0013] When nonwoven fabric is used as substrate component for garniture feed, the open fabric ribbon can comprise up to about l00% and preferably l0% - l00% by weight of polyolefin (mono-, bi-, or tri-component) fiber identified generally as staple polypropylene, or may consist of webs having filaments of mixed denier, or combination of fibers such as (a) polypropylene/polyethylene, polypropylene/polyvinylidene chloride, polypropylene/cellulose acetate, polypropylene/ rayon, polypropylene/nylon, cellulose acetate/polyethylene, plasticized cellulose acetate, polypropylene/paper; or (b) polypropylene/polystyrene/polyethylene, and the like, in a preferred ratio of about (a) l0% - 90%/90% - l0% or (b) l0% - 90%/45% - 5%/45% - 5% by weight of fiber.
[0014] Preferably, the substrate is an open polyolefin fiber web or open tow or nonwoven ribbons of polypropylene or polyethylene.
[0015] Such garniture feeds can usefully include up to about four substrate components, one or more of which have active modifier component applied onto one or both faces, the manner and number of faces treated depending upon the desired filter efficiency, taste, feel, hardness, and draw of the resulting filter element.
[0016] For purposes of the present invention, and because of the nature of the active component, it is generally immaterial whether the garniture feed is fabricated, in situ, (i.e. immediately upstream of the garniture) or produced and stored before use. It is also found useful, for present purposes to use one or more nonwoven fabrics of the same or different fiber composition and denier, particularly when not all of the substrates are used as a carrier or posses different absorbing properties for the active modifier component.
[0017] Preferably, the polyolefin-containing substrate is pretreated by corona or plasma discharge before application of the solution or dispersion of the active modifier component.
[0018] Conventional filter rod-making apparatus, suitable for carrying out the method according to the invention, comprises a tow trumpet, a garniture, shaping means, wrapping means, and cutting means in accordance with well-known components and processes, described, for instance, in U.S.Patents 3,l44,023 and USP 2,794,480. If desired, however, obvious modifications can be made to facilitate in-situ or prior spraying, dipping, printing or other traditional application of modifier components prior to formation of the filter plug.
[0019] Cnventionally, baled substrate can be prepared for use by continuous dip coating or by contact with one or more printing rolls fed from reservoirs of the active components, followed by conventional drying steps effected by nip rolls, heated drying rolls, ovens, and the like, at temperatures generally within the range of about 70°C-l25°C.
[0020] Generally speaking, nonwoven material from fibers within a wide denier range can be obtained using art-recognized techniques. Preferably such material falls within a weight range of about l0-50 grams per m², and a ribbon width of about 4ʺ - l2ʺ will generally assure successful passage through the garniture of a conventional filter rod-making apparatus at production speeds.
[0021] As above-indicated, the garniture feed may usefully comprise one and up to about 4 or even more substrate components of identical or different weight, dimensions, bonding, absorption, fiber composition, and denier, and such substrate can be introduced with the components wholly or partly in register. For best results, however, one relatively lightly thermally bonded open fabric, tow, or fibrillated film in register with one, or between two nonwoven fabrics is found to offer a high degree of flexibility for adapting the resulting filter element to a variety of market needs, including cost, filter draw, and hardness parameters.
[0022] The inclusion of an additional low melting fiber such as polyethylene, combined with other polyolefin fiber as garniture feed is also found useful (although not mandatory) for obtaining tow plugs of widely varying bonding and liquid absorption or adsorption properties.
[0023] Cost-wise, open fiber tows and nonwoven ribbons are found especially useful since they permit the use of relatively cheap polyolefin webs of mixed denier and type, and simplifying the precise distribution of modifier components within a filter element without the need for abandoning the above-listed art-recognized techniques and equipment such as printing rolls and spray heads for coating one or more nonwovens, before forming a filter plug.
[0024] Supplemental components, in addition to the above-defined active modifier components, can also be employed as, for instance, solutions, emulsions, suspensions or dispersions of one or more humectants generally exemplified by polyhydric alcohols such as glycerols, gylcols, etc.; flavors and perfumes such as ketoses and polysaccharides, including wintergreen, spearmint, peppermint, cinnamon, fruit flavors, etc., and additives as otherwise found in USP 4,485,828; medicines, such as menthol and decongestants, etc.
[0025] In order to maintain precise control over such additives, however, it is found useful if each treated substrate is dried to a moisture content of less than about 3% before conversion into filter elements. In addition, the filter element and its active additive components can be usefully shielded, as desired, from direct contact with the lips by applying the active component onto a tow or nonwoven fabric which is, in turn, sandwiched within two or more untreated nonwoven fabrics of lesser permeability (Ref. Fig. 3). In addition, the resulting filter element can be externally coated with cork or similar inert heat-insulating material (not shown). The amount and effectiveness of modifier(s) applied to filter elements in this way is determined substantially by the substrate width and number of substrates which are fed simultaneously into a garniture, as well as the amount of treated surface exposed to cigarette smoke in the filter element.
[0026] For present purposes, both treated and untreated fabric ribbon can be usefully wrapped using regular plug wrap paper having a weight within a range of about 25-90 g/m² or higher, as desired.
[0027] The instant invention is further illustrated in Figures l-3, wherein Figure l diagrammatically represents a conven tional cigarette filter rod-making apparatus modified to convert substrates prepared in accordance with the instant invention into filter elements, and Figures 2-4 diagrammatically represent further modifications and improvements within the instant invention, whereby one or more tows or ribbons of a nonwoven in register or partial register, are easily impregnated with one or more active modifier components by spraying or dipping and the use of multiple substrates favors increased filter element bulk and improved crush resistance, or hardness.
[0028] Referring to Figure l for further detail, a single continuous substrate such as open fiber tow, fibrillated film or ribbon of nonwoven fabric (l0) is fed from feed reel (ll) or a bale (not shown) through spray heads (20) feedably connected to feed lines (2l) from outside sources (not shown) to apply active modifier component(s) (22). The treated substrate is then dried by heated air drying rolls (l2) and means (not shown) to obtain a desired degree of dryness, and then led by guide rolls (l7) into a garniture trumpet (l5) and garniture (l4) of a cigarette filter rod manufacturing apparatus (l) comprised of a garniture section (2) including (but not showing) means for shaping and retaining the substrate feed, wrapping means, and cutting means for converting the wrapped plug or rod into filter element (l6); the wrapping means is conveniently supplied with tow wrap from wrap feed reel (5) supported by support rolls (l9) and moved onto continuous garniture belt (3) for introduction into the apparatus.
[0029] The apparatus, as described, comprises conventional means for sealing the tow wrap around a filter plug (not shown), the later being cut by cutting means (not shown) into cylindrical filter elements (l6) of desired length (normally 90 mm), before removal by filter chute (l8) (shown in fragment) for packing in container (23).
[0030] Figure 2 diagrammatically demonstrates a further suitable arrangement for separately applying active modifier component(s) onto two open substrates of the same or different type whereby spray heads (20A) fed by connecting feed lines (2lA) apply active modifier component(s) (22A) (identical or otherwise) onto substrates (l0A, l0B), fed in register and dried using air and heated rolls (l2A) before passage through garniture (l4A) of rod-making apparatus (lA), to form filter elements (l6A) as before. Substrates (l0A and l0B), are fed from feed rolls (llA) and (llB) or bales (not shown) and conveniently brought into register at heated nip rolls (l2A), then guided by guide rolls (l7A) into garniture (l4A), the garniture feed or substrate components shown being similarly defined by arabic numbers in each of Figures l-3.
[0031] Figure 3 diagrammatically demonstrates a still further modification of the equipment and process of Figures l and 2, whereby several substrates of the same or different types (l0C, l0D, and l0E) from reels or boxes (not shown) are fed through a nip created by heated rolls (l2B), depending upon the degree of filtration desired, the middle substrate (l0D) can be varied in width and preferably posses higher absorption or adsorption properties then external untreated substrates (l0C and l0E). As shown, substrate (l0D) is sprayed on both sides to fully expose it to one or more active modifier components (22B) by spray heads (20B) fed from feedlines (2lB), substrate (l0E) preferably being widest and arranged so as to catch surplus drip or misdirected active modifier not captured by ribbon (l0D), all three substrates are then air dried by passing in register through heated nip rolls (l2B), as before, and directed by guide rolls (not shown) into the garniture of a filter rod apparatus in the manner of Figures l and 2.
[0032] Figure 4 is a diagrammatic representation of a further modification in which one or more substrates (not shown) can be separately fed from a bale or box (24C), passed over guide rolls (l7C), and dipped into a reservoir (25C) containing active modifier component (22C), then passed through nip rolls (26C), through a heating oven (27C), through drawer rolls (28C) and a three step drying oven (29C), to garniture (l4C) of a cigarette rod manufacturing apparatus in the manner of Figures l-3, supra or boxed for future use.
[0033] Where a continuous fiber tow is used as a substrate component, preparation of the tow is conveniently carried out in the usual way by drawing the fiber from one or more creels through a fluid bulking or texturing jet and then handled as noted above.
[0034] Substrates which are employed in the above manner can usefully be of a variety of synthetic filaments as noted above. Thus, it is possible to use polyesters, polyamides, acrylics, as well as polypropylene or cellulose acetate materials. Due to its relatively low density, compared to other synthetic fiber-forming material and excellent spin properties, combinations of filament-forming copolymers of propylene with ethylene or other lower olefins monomers are preferred tow, ribbon and fibrillated film material.
[0035] The bulk denier of a tow for carrying out the present invention can conveniently fall between about 2,000 and l0,000. As noted above, this substrate can be supplied as a crimped fiber from a single creel or bale, or a composite of several creels or bales combined and passed through a fluid jet simultaneously. For best performance as cigarette filters, however, it is preferred that at least some of the tow be substantially untwisted and untexturized prior to entering a fluid jet.
Example l
[0037]
(A). Isotactic polypropylene staple fiber (4.5 dpf and l.5" cut) having a "Y" cross section and a flow rate of 40± 5g/l0 min., is carded into an open web weighing about 0.l8 grams per yd.². The web is transferred onto a continuous fiber-glass belt and lightly thermally bonded using a hot diamond-patterned calender at l40°C./40 psi roll pressure to obtain a nonwoven fabric which is die cut into l2 inch width test ribbon substrate hereafter identified as TS-l.
(B). Spun drawn 2.5 denier cellulose acetate yarn (circular cross section) obtained under conventional commer cial spin conditions is unwound in parallel from a roll off creel under 0.0lg/denier tension and combined to form a fiber tow . The tow is then fed through a bulking jet using steam at 70 psi (l07-ll0°C), the resulting open tow substrate being hereafter identified as TS-2.
(C). Spun drawn 4.5 denier bulked polyproplene yarn ("Y" cross section) is obtained in the manner of (B) supra, the resulting polypropylene bulk tow substrate being hereafter identified as TS-3.
[0038] Active modifier compositions within the definition of C-l, C-2 and C-3 (Table I) are applied as finish compositions to substrates TS-l, TS-2 and TS-3 in the manner indicated in the following Examples.
EXAMPLE II
[0039]
A. One of two twelve inch (l2ʺ) wide open ribbons of continuous nonwoven polypropylene
material (TS-l) from Example I is roll dipped for 30 seconds in a bath containing
C-l finish in the manner shown schematically in Figure 4, then passed through heated
nip rolls, oven dried, hand rolled to form a filter rod of standard width, which is
cut into a 27mm filter length elements (0.l8 g and 24.35mm circum- ference) identified
as F-l for testing purposes.
A second untreated (undipped) ribbon of TS-l but otherwise identically prepared is
used as a control (FC-l). The two filters (F-l and FC-l) are tested and reported as
described in Example III and Table II below.
B. Four samples of 4.5 dpf bulked polypropylene substrate (TS-3) as described in Example I C., are treated as follows: (l) two samples are roll dipped respectively in C-2 and C-3 finish, heated, dried and rolled as in II A. to obtain test filters F-3 and F-3A; (2) the remaining two samples are identically processed but without the roll dipping step, as controls, to obtain control test filters FC-3 and FC-3A.
C. Two samples of TS-2 as described from Example I B. are treated as follows: (l) one sample is roll dipped in C-l finish, heated, dried and rolled to obtain test filter F-2,; and (2) the second sample is identically processed as a control but without the roll dipping step, to obtain control test filter FC-2.
Example III
[0040] The test filters described in Examples I and II as F-l, FC-l, F-2 and FC-2 are tested on a filter testing device comprising a valved constant pressure NO/N₂ gas source flowably secured on the downstream side by glass and Tygon tubing to a plastic filter holder which is connected, on its downstream side, to a Drager Tube(*3) prepacked with Cr(VI) catalyst and p,p-diamino, m,m-dimethly biphenyl as a color indicator for detecting nitrous oxide (NO).
*3. National Drager Inc., Pittsburgh, Pennsylvania.
[0041] The test gas contains l00 ppm NO in nitrogen gas, and the filter is exposed for thirty (30) minutes at a 50 ml/minute flow rate. Test results are reported in Table II below.
Example IV
[0042] The test filters described in Examples I and II as F-3, FC-3, F-3A, FC-3A are taped to Camel light tobacco rods and smoked on a Borg-Waldt smoking machine at a rate of eight (8) two second 35 ml puffs with a 58 second period between puffs. The machine exhaust is connected directly to a Chem Lot UK nitric oxide analyzer (using chemilumenescence properties for detecting NO concentration using a 50, l00 and l,000 ppm NO/N₂ calibration standard. Test results are reported in Table II below.
1. A method for making a chemically-treated filter element for cigarettes in which
a cigarette filter element obtained from a conventional filter-rod-making apparatus
using, as garniture feed, a polyolefin fiber-containing substrate, is treated with
a zinc compound, such as zinc oxide or zinc acetate as an active modifier component,
characterized in that a non-ionic solution or dispersion containing zinc oxide or
zinc acetate is applied to all or part of the substrate in the garniture feed, the
non-ionic solution or dispersion also containing as a dispersant a polyoxyalkylene
derivative of a sorbitan fatty acid ester, a monoester of a polyhydroxyalcohol, or
a diester of a polyhydroxy alcohol, or containing a mixture of the said dispersants.
2. A method for making a chemically-treated filter element as claimed in claim l,
further characterized in that the nonionic solution or dispersion contains about 0.l
wt%-l0 wt% and preferably 0.5 wt%-l0 wt% of one or more of the surfactants.
3. A method for making a chemically-treated filter element as claimed in claim l or
2, further characterized in that the amount of the active modifier component contained
in the non-ionic solution or dispersion is about l wt%-l0 wt% based on the fiber weight.
4. A method for making a chemically-treated filter element as claimed in claim l or
2, further characterized in that the the nonionic solution or dispersion is applied
to separate substrate surfaces comprising an open polyolefin fiber web or open tow
or nonwoven ribbons of polypropylene or polyethylene.
5. The method of claim l wherein polyolefin-containing substrate is pretreated by
corona or plasma discharge before application of active modifier component.