GB2030440A - Method for the manufacture of fibrous articles - Google Patents

Abstract

In making articles of type having fibers fused together at points of contiguity thereof, a selection is made of a constituent, for application to the fibers, which has microwave absorptivity in excess of that of the fiber material and in which the fiber material is essentially insoluble. In making self-supporting porous elements, such as cigarette filters, filamentary tow defining the fibers is spread and selectively uncrimped and the selected constituent is applied thereto. The tow is then cylindrically shaped and conducted through a passage in microwave applicator apparatus of type tunable to optimize heating selectivity of the applied constituent whereby such point of contiguity fusion of the fibers is accommodated. Tow issuing from the microwave applicator is subjected to pressurized air and to recovery of vaporized applied constituent. <IMAGE>

Description

SPECIFICATION Method for the manufacture of fibrous articles This invention relates generally to the manufacture of fibrous articles and, more particularly, to making filter elements from continuous filamentary tow.

In current manufacture of cigarette filters, continuous filamentary tow, of material such as cellulose acetate, is withdrawn from a bale and is processed to spread and to controllably uncrimp the filaments. A bonding constituent or plasticizer, such a triacetin, is applied to the spread and selectively uncrimped filaments, and they are then formed into rod configuration and further processed such that the rods attain sufficient structural integrity to retain such configuration in subsequent filter cigarette making operations.

Tow processing up to the juncture of forming plasticizer-impregnated filaments into rod configuration is typically carried out by apparatus of type shown, for example, in U.S. Patent No.3,413,698.

Therein, tow is drawn through a spreading of banding air jet device and then through tensioning rolls to filament separating feed rolls. Another banding jet operates on the tow at this point after which it is led through plasticizer applicator rolls. A funnel receives the plasticizer-impregnated tow and imparts generally cylindrical shape thereto.

Processing practices of the prior art differ at this juncture. In one practice, the rod-shaped plasticizerimpregnated tow is applied to a garniture and thereby enveloped in filter wrap and cut to form filter rods. The rods are then stored for an extended time period during which the plasticizer cures the tow to form a stable structure suited for use in cigarette making operations.

The disadvantages of this practice are enumerated in U.S. Patents No.3,313,306, No.3,111,702 and 3,095,343, all of which relate to the production of filter rods not requiring wrap. As noted in these patents, elimination of wrap while nevertheless providing sufficient handling stablity, enables manufacturing cost reduction, enhances on-line testing and renders rod cutting more convenient.

In the practices of these wrapless filter rod making patents, for example, the '306 patent, the rod-shaped plasticizer-impregnated tow is conveyed by an encircling steam-permeable belt through a station wherein it is subjected to pressurized steam. The steam is said to activate the plasticizer so as to cause instantaneous curing thereof. On issuing from the steam-treatment station, the tow is conveyed to a cooling station wherein pressurized gas is said to deactivate the bonding constituent and remove moisture from the rod. The tow is then conveyed to cutting apparatus to provide rod segments.

To the extent that the practices of such wrapless filter rod making patents may provide tow whose plasticizer is fully cured prior to reaching the cutting apparatus, they would eliminate the extended curing time for segmented rods involved in the firstdiscussed prior art practice and enable direct on-line operation of such apparatus and successive cigarette making equipment. Such practices also would lessen the difficulties involved in cutting at a time prior to full dimensional stability of the tow.

In another aspect, however, the method underlying the foregoing wrapless filter rod making patents, is considered to be at disadvantage in its requirement for introduction of a cure-accelerating medium (steam) undesired in the end product and hence requiring positive removal thereof following cure. Additionally, it is believed that such productextraneous medium may have undesired side effects, e.g., the steam may dilute plasticizer concentration at the points of contiguity of tow filaments and may act further to cause plasticizer flow away from such points of contiguity.

U.S. Patent No.4,003,774 and U.S. application Serial No.743,511, filed on November 1976 copending and commonly-assigned herewith, both disclose the use of microwave-energy in the course of forming cigarette filters. The '511 application delineates a method wherein preselection is made of first and second diverse materials, respectively, constituting a fiber and a plasticizer for the fiber. The second (plasticizer) material is selected to have absorptivity for microwave energy in excess of that of the first material and to have state transition from liquid to vapor on heating thereof. By virtue of such preselection, the plasticizer serves as a medium for absorption of microwave energy and conductive heating of adjacent fibers to effect fusion thereof.

Varieties of such fiber and plasticizer materials, other than the cellulose acetate-tiacetin combination, and meeting the foregoing selection criteria, are set forth in the '511 patent.

The use of plasticizers -in the practice of the '511 application in effecting fusion of fibers gives rise to nominal limitations on economy of such microwave method in making filters in that a modicum of the plasticizer, e.g., that which has permeated the fibers, is essentially unrecoverable from the end product for reuse. Also, while triacetin is regarded as a flavorant in cigarette filter making, it is desirable in various other instances not to have remnant applied microwave-absorptive constituent in the end product. One exemplary field of endeavor of this type would be fabric making, wherein printing or dyeing of the ultimate fabric might be more controllably achieved in the absence of remnant plasticizer.Indeed, in cigarette filter making-it may be desirable not to have remnant plasticizer where the choice is to eliminate triacetin from the myriad of other variables in isolating control parameters of taste and the like.

The present invention has as its primary object improvements in the manufacture of fibrous articles, such as wrapless filter rods.

In attaining the foregoing and other objects, the invention provides practice wherein preselection is made of first and second materials, respectively, constituting fiber and a constituent applied to the fibers to effect fusion thereof, wherein the second material is chosen both to exhibit microwave absorptivity in excess of that of the first material and to be essentially fully recoverable, i.e., to be a non-solvent/non-plasticizer for the first material.

Typically, the second material also has characteristic state transition, on heating, from liquid to vapor.

With the absence of plasticization, virtually all applied constituent is recoverable from the ultimate fused fibrous article, permitting economy in manufacture and efficiency in post-forming practices, e.g., printing/dyeing in the case of fabrics.

In the case of cigarette filter making, the invention provides for the conveyance of selected constituentimpregnated tow continuously through microwave applicator apparatus defining a predetermined path therethrough and tunable to provide optimal energy transfer to the applied constituent on its deposition in such path. The apparatus is tuned selectively to the applied constituent whereby energy transfer to the tow filaments is by conduction, successive to and dependent upon applied constituent heating.

Forced air treatment of the tow, after such microwave exposure thereof, recovers volatilized applied constituent from the tow for reuse. Practice under the invention provides for attainment of dimensionally stable unwrapped continuous filter rod without remnant applied constituent. In preferred practice in accordance with the invention, use is made of microwave heating apparatus embodying therein a cylindrical tube of material substantially transparent to microwave energy. A tow conveyor situate in such tube and formed cylindrically thereby is comprised of material of like transparency and of type adapted to minimize longitudinal tension differential in tow during its conveyance through the microwave applicator apparatus.

In practice in accordance with the invention, the microwave "lossiness" of the applied constituent is an order of magnitude or more than the lossiness of the tow material. By sucgh preselection of materials, the microwave applicator may be distinctly tuned as above discussed to the applied constituent, which preferably has a boiling point within twenty percent of the melting point of the fiber constituting the tow.

The foregoing and other objects and features of the invention will be further evident from the following detailed description of preferred practices and apparatus and from the drawings wherein like reference numerals identify like parts throughout. In the drawings: Figure 1 is a front elevational view of apparatus for use in practicing the invention.

Figure 2 is a side elevational view of the microwave applicator apparatus of Figure 1 as seen from plane Il-Il thereof.

Figure 3 is a front sectional view of such micro wave applicator apparatus as seen from plane Ill-Ill of Figure 2.

Referring to Figure 1, filter rod making apparatus 10 receives tow 12 from bale 14 and transports the tow upwardly through banding jet 16 over spreading roller 18 to a second banding jet 20. The tow is then passed through successive pairs of pressure rolls 22 and 24 and through constituent applicator unit 26.

Delivery rolls 28 are equipped with drive means of variable character whereby tow tension may be controlled as desired. Funnel 30 shapes the impre gnated tow into substantially cylindrical configura tion. The mechanisms of apparatus 10 thus far discussed are conventional and in widespread cur rent use, being more particularly described in the above-referenced United States patents which are herein incorporated by reference for brevity in defining such mechanisms.

Tow issuing from funnel 30 is applied to garniture belt or tape 32, an endless belt advanced by drive roiler 34 over rolls 36 through 44. Garniture 46 is also of design customarily found in cigarette wrapping machinery serving herein to arrange belt 32 in encircling relation to tow 12. The encircled tow is advanced from garniture 46 into and through microwave applicator unit 48, the structure of which is discussed below in connection with Figures 2 and 3.

Belt 32 is comprised of material substantially transparent to microwave energy and adapted to frictionally engage the tow so as to minimize tension differential during movement thereof through unit 48. Silicone rubber-backed glass cloth is a preferred belt material. Unit 48 issues the tow therefrom to air jet unit 50, belt 32 being separated from tow between units 48 and 50. Cutting apparatus 52, also of known design, segments the continuous tow into finished filter rods.

Turning to Figures 2 and 3, microwave applicator unit 48 includes a waveguide 54 closed at its lower end and connected at its upper opposite end to a source of microwave energy 55. Tuning stubs 56, 58 and 60 are separately movable into the waveguide, for purposes discussed below, stub 58 being shown in inserted disposition in Figure 2. Sidewall 62 of waveguide 54 has an opening 64 therein with a cut-off waveguide 66 arranged in juxtaposition with such opening. Sidewall 68 of waveguide 54 includes an opening 70 whereby energy can be fed from waveguide 54 into resonant cavity 72. Cavity 72 includes a sidewall 74 having an opening 76 therein with cut-off waveguide 78 juxtaposed therewith.

Upper outerwall 80 of cavity 72 supports a tuning control element 82 vertically movable relative to the outer wall 80 and supporting an inner cavity closure member 84. In the same fashion, cavity lower outer wall 86 supports tuning control element 88 therein which in turn is secured to inner cavity closure member 90. An elongate cylindrical tube 92 traverses both cavity 72 and waveguides 54, 68 and 70 and is comprised of a material substantially transparent to microwave energy, such poiytetraf luoroethylene, polypropylene, polysulfone, fused silica and alumina. Tube 92 is shown broken away in the vicinity of waveguide sidewall 68 to better illustrate an apertured element 94 which is suitably removable secured to sidewall 68, for purposes discussed below.

In practice in accordance with the invention, microwave energy selected from one of the four covernmentally assigned frequencies, or otherwise, where permitted, within a range of from 915 megacycles to 22,000 megacycles, is applied to waveguide 54 by source 55 with apertured control element 94 and other elements in position indicated in Figure 3.

Constituent-impregnated filter tow is not garniturefed by belt 32 (Figure 1) into and through tube 92 at a constant tow speed. By reference to measuring devices (not shown), customarily employed in electromagnetic energy studies for respectively indicating the power generated by the microwave source and power reflected thereto from waveguide 54, tuning stubs 56-60 are separately inserted in the waveguide until reflected power is minimized. Such tuning elements are mutually spaced apart by one-quarter wavelength measured at the frequency of the microwave energy furnished to the waveguide by source 55. Next, cavity tuning control elements 82 and 88 are adjusted until such reflected power is further minimized.

By the foregoing tuning procedures, locations of maximum energy intensity both in waveguide 54 and in cavity 72 are conformed to the location of the passage defined therethrough by tube 92. Further, since the applied constituent is selected to have substantially greater absorption for microwave energy, i.e., is substantially lossierthan cellulose acetate at electromagnetic radiation frequencies in the microwave range, the heating apparatus is further tuned to the applied constituent for heating thereof. Heating apparatus in the general form of unit 48, comprising a tunable high-Q cavity, is available commercially from Gerling Moore, Inc., Palo Alto, California, United States of America.Plural aperturedefining members 94 are provided and the foregoing tuning procedure is repeatedly carried out with different aperture-defining members in unit 48 to determine which member provides the greatest ratio of power generated by source 55 to reflected power, this condition defining maximum transfer of generated power to the applied constituent for heating thereof.

As is known in the art, cut-off waveguides 66 and 78 are of dimensions designed for a given operating frequency such that they function as a waveguide for, i.e. transmit, only energies propagated at frequencies exceeding the operating frequency, namely, the frequency of radiant energy supplied by source 55. Accordingly, such cut-off waveguides define non-leakage access ports through which tube 92 can enter and exit unit 48.

The phenomenon of extremely rapid fusing of tow fibers at contiguous locations is believed to be attributable in part to the capillary effect tending to cause the applied liquid constituent to migrate along the fibers to the points of contiguity of the fibers and there thicken and concentrate. On exposure to microwave energy in the described tunable high-Q cavity, the liquid is heated very rapidly to high temperature levels and consequently heats adjacent fiber sections through conduction. In an immediately following sequence, the liquid vaporizes.

While the foregoing disclosure and the ensuing examples are specific to the use of cellulose acetate as the tow material, various other materials may be selected in place of the specified fiber material, for example, polypropyiene, polyethylene, and the like.

Typical applied constituents for cellulose acetate include propylene glycol, glycerol, ethylene glycol, diethylene glycol, triethylene glycol and mixtures thereof. Benzyl alcohol and methyl benzoate are suitable applied constituents for polyethylene fibers.

Decyl alcohol can be used as the applied constituent for polypropylene fibers. Applied constituent selection for these and other materials is made in accordance with the practice under the invention such that the applied constituent have sufficiently greater heatability by microwaves than the selected tow material to permit maximization of microwave energy absorption by the former material and to permit tuning of the microwave energy applicator unit selectively to the applied constituent. Addition ally, the applied constituent is characterized as matter in which the selected fiber material is essen tially insoluble. Preferably, the applied constituent exhibits state transition, on heating, from liquid or solid to vapor to facilitate recovery.In this preferred aspect, choice is made of applied constituent having a boiling point within twenty percent of the melting point of the fiber material. In the specific case of cellulose acetate fiber material, having a melting point of 220"C, ethylene glycol is appropriate with its boiling point of 197"C. Triethylene glycol (boiling point - 276"C) is desirably used jointly with a lesser boiling point medium, for example, ethylene glycol (197"C), in working cellulose acetate fibers. Aqueous solutions of applied constituent may be employed and the ratio of liquids to solids, i.e., applied constituent to tow material, is in the range of about eight percent to twenty-five percent and preferably twelve percent.Particulate additives may be applied to the tow prior to its conveyance to the microwave energy applicator, such additives being of materials having capability for selectively absorbing or adsorbing certain constituents of smoke. The subse quent radiative heating of the applied constituent and consequent fusion of tow filaments will provide a a fibrillar matrix wherein infusable additive particles are maintained by mechanical entrapment within the matrix or wherein fusible additive particles are bonded therein. The invention further contemplates introducing a solid particulate constituent, such as a low melting point powder to microwave energy, in the tow in lieu of or additional to liquid applied constituent.

The following listed examples are further descrip tive of practices in accordance with the invention.

Example 1 Cellulose acetate tow of type 3.4 denier/36,000 total denier is processed as above discussed into rod configuration with ethylene glycol applied to the spread tow in amount equal to 12 percent of the weight of such rod. The rod is advanced into and through microwave applicator unit 48 at a speed of 150 feet per minute, the path of travel of the rod within unit 48 being six inches. Unit 48 is energized by energy source 55 such that the power absorbed by the rod is 2.25 Kw at 2450 megacycles as measured by the difference between the power generated by source 55 and power reflected thereto from waveguide 54. On completion of its travel through unit 48, the rod is a dimensionally stable and self-supporting porous structure.

Example 2 Cellulose acetate tow of 3.4 denier/38,000 total denier is processed as above discussed into rod configuration with 50 percent triethylene glycol - 50 percent ethylene glycol applied to the spread tow in amount equal to 15 percent of the weight of such rod. The rod is advanced into and through microwave applicator unit 48 at a speed of 180 feet per minute, the path of travel of the rod within unit 48 being six inches. Unit 48 is energized by energy source 55 such that the power absorbed by the rod is 2.3 Kw at 2450 megacycles as measured by the difference between the power generated by source 55 and power reflected thereto from waveguide 54.

On completion of its travel through unit 48, the rod is a dimensionally stable and self-supporting porous structure.

In the foregoing examples, the rod achieves such dimensional stability following travel through unit 48 upon being subjected to pressurized air. Forthis purpose, a nozzle having an orifice of one-quarter inch diameter, supplied air pressureized at from five to fifty pounds per square inch, preferably twentyfive pounds per square inch, directs air at tow issuing from unit 48. Such dimensional stability is alternately achieved, without need for application of pressurized air to the tow, by decreasing tow speed to seventy-five feet per minute. In experimental analysis, nominal ethylene glycol remnant in a dimensionally stable and self-supporting cellulose acetate rod made as above noted was chemically extracted and the extraction verified by weight comparison. Firmness testing of the rods before and after extraction indicated substantially identical firmness.

In practice under the invention, recovery of vaporized applied constituent may be accommodated by introducing vacuum recovery ducts in communica- tion both with the microwave applicator unit and with a suitable recovery hood disposed in encircling relation to the exit of tube 92.

Claims (8)

1. A method for making a fibrous article comprising the steps of: (a) preselecting fibers of a first material and a constituent for application to said fibers of a second material, said second material having absorptivity for microwave energy in excess of said first material, said first material being essentially insoluble in said second material; then (b) applying said constituent to said fibers; then (c) forming said fibers into predetermined shape configuration wherein adjacent fibers have points of contiguity with one another; and then (d) subjecting such formed fibers to microwave energy for heating such applied constituent and thereby fuse said fibers one to another at said points of contiguity thereof.

2. A method according to claim 1 wherein said step (d) is practiced by defining a passage for conveyance of said formed fibers through a volume excited with microwave energy and conforming locations of maximum microwave energy intensity in said volume to said passage while said formed fibers are situated in said passage.

3. A method according to claim 1 or 2 wherein said step (a) is practiced further by selecting said second material to exhibit state transition to vapor on heating thereof.

4. A method according to claim 1,2 or 3 wherein said step (b) is practiced by applying said constituent in liquid phase to said fibers.

5. A method according to any one of claims 1 to 4 wherein said step (a) is practiced further by selecting said second material to have a boiling point within twenty percent of the melting point of said first material.

6. A method according to any one of the preceding claims including the further step of recovering such applied constituent from said fibers on practice of said step (d).

7. A method according to claim 1 substantially as described with reference to Example 1 or 2.

8. Use of an article produced by a method as claimed in any one of the preceding claims as a filter element.