CA1261227A

CA1261227A - Method for selective adhesive application for manufacturing cigarette fiber filter elements

Info

Publication number: CA1261227A
Application number: CA000500701A
Authority: CA
Inventors: George Jurkiewitsch
Original assignee: Individual
Current assignee: Celanese Acetate LLC
Priority date: 1985-01-31
Filing date: 1986-01-30
Publication date: 1989-09-26
Also published as: FR2576757A1; GB2170391B; CN86101153A; DE3602997A1; FR2576757B1; GB8601984D0; JPS61247368A; BR8600412A; GB2170391A

Abstract

ADHESIVE APPLICATION METHOD
FOR MANUFACTURING
CIGARETTE FILTER ELEMENTS

Abstract of Disclosure A method for making smoke filter rod elements from polyolefin fiber-containing fiber by applying a binding ma-terial formulation onto rod-wrapping sheet material, and offsetting it to the surface of an unbound rod-shaped fiber plug at the wrapping station of a filter rod-making appa-ratus, using the wrapping material as an offset applicator to provide control over the penetration of the binding ma-terial into the rod and the resulting firmness, resilience and drawing properties of the cigarette filter rod.

Description

This inventlon eelates to a method for making filter elements for cigarettes having polypropylene-containing fibers enclosed in a wrapper.
Numerous patents, and particularly U.S. Patent 4,366,826, describe fiber-based filter elements for removing particulate matter and tars from cigarette smoke, particu-larly filter elements made of crimped texti]e tow of cellu-lose acetate or plyolefins such as polypropylene. Such tows are converted into filter rods using well-known processes, such as the processes disclosed in the said U.S. Patent 4,366,826 and U. S. Patent 3,393,635, comprising feeding crimped open fiber tow having a bulk denier of about 40,000 to 60,000 through a yarn opening mechanism using alr 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 or garni-ture of a filter rod-making apparatus, where it is shaped into a continuous cylindrical filter aplug~, cooled or dried if necessary, and optionally wrapped with a plug wrap such as paper or nonwoven material.
In some cases, as disclosed in U.S. Patent 3,144,025, fibers having a lower melting point combined with melting and cooling facilities are used as bonding means.
In all these conventional methods, the amount of the binder or lower-melting fibers and the arrangement of the fiber ~i.e., crimp and fiber orientation etc.) determine, to a great extent, the degree of rigidity (hardness) and resil-iency of the resulting filter element. Since the binder is distributed more or less throughout the fibers, it tends to .. . .

:

'7 reduce the volume of the air passages or voids and inter-feres with the full "draw~ and resiliency associated with unbound soft fiber.
The use of cellulose acetate and the binder formula-tions conventionally used with it have disadvantages notnoted in U.S. Patent 4,366,826. For example, cellul~se acetate fibers are relatively weak compared with synthetic fibers containing polypropylene. This tends to limit the amount of tension and crimp which can be applied to the opened fiber tow before introducing the tow into the garni-ture of a standard filter rod-making apparatus.
Fiber tow or sliver containing polypropylene that is used in cigarette filter elements will be referred to herein generally as ~polypropylene fiber~. The fibers of polypro-.
pylene have the advantage of finer denier, which is generally associated with more efficient filtering properties. Poly-propylene fibers, however, also have disadvantages. An open or bloomed polypropylene fiber tow cannot be readily wet by most cellulose acetate binder formulations, and the known ones fail to provide the anciliary lubricating properties needed in conventional high speed filter manufacturing methods unless used in such excessive amounts that filter efficiency and other desirable properties are adversely affected.
In particular, it has been found that an appropriate degree of firmness in filter rods made of polyolefin fiber tow is likely to interfere with a desirably easy draw in smoking, resulting from the negative correlation in such con-ventional methods between pressure drop ( ~P) or ~draw~ and ~hardness value1 (~F) (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, Grea~ Britain).
According to the invention, a method for making filter elements for cigarettes in which polypropylene-containing tow or sliver is fed into the garniture of a filter rod-making apparatus and shaped to form a fiber plug that is wrapped . ~

with paper or a non-woven material before being cut into filter elements, characterized in that -the fibres in the filter plug are free of bonding material before being wrapped, a po]ypropylene-wetting bonding material is applied to the wrapping material, and by the wrapping the said bonding material is immediately offset to the filter plug whereby the bonding ma-terial impregnates an ou-ter layer of the filter plug, so as to produce a filter element having a hardness value of at least about 80% and not substantially above about 94%, as determined by the equation:

F = D- ~ D X 100%, D

in which F is the hardness value, D is the diameter of the filter element in millimeters, and ~ D is the deflection or decrease in diameter oL the wrapped filter element in hun-dredths of a millimeter after being subjected to a 300 gm load for fifteen seconds.
Preferably, the annular cross-section of the filter plug that is impregnated is from 1 to 20% of the total cross-sectional area of the filter element.
Preferably also, the amount of bonding material thatis applied per unit length of the wrapping material is from 10 to 60% of the weight of the fibers wrapped by that length.
Also according to the invention, a cigarette filter rod ~made by the process according to the invention, has a hardness value of at least about 80%, as determined by the equation:

.

- 3a - 22124-1653 F = D- ~ D X 100%
D

in which F is defined as the hardness value, D is the diameter of the filter plug in millimeters, and ~ D is the deElection or decrease in diameter oE the wrapped filter element in hundredths of a mlllimeter after being subjected to a 300 gm load for Eifteen seconds.
Preferably, to suit the preferences of most users, a smoke filter rod according to the invention will have a hardness 10 value above about 85~, most preferably about 90~, but should not substantially exceed about 94%.
In the process fo.r making a smoke filter rod according to the invention, the appl.ication of the bonding material`
(which can act as a plasticizer as well as an adhesive) occurs substantially simultaneously with the plug-wrapping step, so that the movement of the fibre rod through the machine is not hampered by increased friction caused by the presence of binder or plastici:zer on the surface of the rod . i .

'7 _ 4 _ 22124-1653 or -transfered to the surfaces oE the machine. Most importantly, the offset from a controlled application that is made on the flat surface of the wrap provides a high degree of control over the degree and uniformity of penetration into the filter element, leaving a core of unbonded fibers within the area of bonding.
In mathematical terms, the extent of penetration of the polypropylene-wetting bonding material that is offset to the filter plug, and impregnates its outer layer to the extent of preferably from 1 to 20% of the total cross-sectional area of the filter plug, can be approximately expressed by the equation:

A = dt2R-d) X 100%

wherein "A" is defined as the annular cross-sectional area, in percent of -the total cross-sectional area, that is impregnated by an average depth "d" of penetration of adhesive/plasticizer binder formulation into the wrapped plug in millimeters; and "R" is the outside radius in millimeters of the wrapped plug or filter element (assuming of course that the filter rod has an essentially circular cross-section).

The smoke filter rods according to the invention there-fore provides the "easy draw" that results from an unbound soft fiber core that occupies about 99%-80% and preferably 99%-90%
of the total cross-sectional area of the wrapped filter element or plug, without losing firmness or hardness.
It will be obvious to those skilled in the art that the lower the flexural modulus of the adhesive/plasticizer binder formulation, the higher the value of "A'l that will be required .
. ~ :
~;

.~6~ 7 - 4a - 22124-1653 to achieve a hardness value within the ranye of about 80% to about 94~. Appropriate preferred values of "A" require that the binder should penetrate Erom 150 to 400 microns into the wrapped plug.
The polypropylene Eiber Eilter plugs to be wrapped in the process according -to the invention contain from about 10~ to 100% by weight of polypropylene Eiber tow or sliver, such as 100% polypropylene fiber (which is most preferred) or a mixture of fibers oE polypropylene and another polyolefin ^`r~t3 '' '~"' :

'~ '' . :

such as polyethylene (which is also preferred), or mixtures of polypropylene with polyvinylidene chloride, cellulose acetate, rayon, nylon, polystyrene, or paper. Such suitable combinations of fibers are described in U. S. Patent 3,393,685.
Any conventional, commercially obtainable plug wrap such as the nonporous wrap paper sold under the registered trade-mark Ecusta and trade designation 646 can be used as the tow plug wrap that in effect serves as an offset applicator me-dium according to the present invention. It will be obviousto those skilled in the art that a nonwoven fabric web with sufficient abrasion resistance, tensile strength and surface adhesion properties can also be used as a fiber plug wrapping.
For instance, suitable paper tow wrap will have a weig~t range between about 7.5-23 g/m2 (30_90 g./yd.2) while cor-responding nonwoven tow wrap material can have a weight range of about 2.50 10.2/yd.2 (10-40 g./yd.2). The latter type of tow wrap may be produced by commercial wet or dry pro-cesses, using thermal bonding, spun bonding, needle punching or other known methods, provided (if no overwrap is used) that contact of such materlal with tongue or lips is not irri-tating or otherwise unacceptable.
The smoke filter rod and process for making it according to the invention are further illustrated diagrammatically in the drawings, in which:
Figure 1 represents a side elevational view of a stan-dard cigarette filter rod-ma~ing apparatus providing for off-set peripheral print application of adhesive/plasticizer binder formulation onto a fiber plug in accordance with the invention;
Figure 2 is an enlarged cutaway longitudinal section of a formulation-treated fiber filter element showing peripheral bonding and tow wrapping; and Figure 3 is a side elevational view of a modification of the apparatus shown in Figure 1, in which the adhesive/
plasticizer binder formulation is applied from a spray head onto plug wrap as the offset applicator medium before delivery at a wrapping station (not shown).

:.
.
, Figure l demonstrates a single continuous ribbon of fiber tow or sliver (10), fed from a roll or bale (ll), past feed and register rolls (12) and guide rolls tl7) into a garniture trumpet (15) and garniture (14) of a standard cigarette filter rod manufacturing apparatus (5), having means for (a) shaping, (b) wrapping, (c) cooling or clrying and (d) cutting the re-sulting filter rod within garniture section (6), using plug wrap (7) fed from feed reel (8), in a dual function as a tow wrap, and as a medium for transferring adhesive/plasticizer (24) formulation onto a plug tow (not shown) at a wrapping station (not shown) within garniture section (6). ~ransfer is carried out by initial contact of the applicator medium (7) with one or more wetting rolls, represented by heated wetting roll (l9) which is placed in receivable contact with the bi~d-ing material (24) stored in well (20), in heated or unheatedstate (depending on whether it is a hot melt, a liquid, or a semi-liquid dispersion or solution), the wrap/applicator me-dium (7) and binder (24) being fed by guide roll (13) to a continuous garniture belt (9), which transports the coated medium into the garniture section (6).
The amount of binder (24) applied to and carrried by the wrapping material and applied to the tow plug at the wrapping station depends largely upon the wettability of the fiber tow, the wettability of the printing surface of roll (19), and the viscosity and wetting chara~teristics of the binder formula-tion itself, and, in the case of the arrangement discussed below and in Figure 3 on the pressure and spray si~e.
As noted above, conventional means for cooling or dry-ing the treated fiber plug (not shown), and means for cutting the resulting wrapped fiber plug (not shown) to obtain a fil-ter element are conveniently arranged downstream of the wrap-ping station. The resulting cut fiber filter elements (16) are then fed to feed chute (18) and packed in container (23).
Figure 2 is a partial cutaway diagrammatic longitudinal section of a bound and wrapped rod-shaped fiber tow filter element (l) having an unbound internal fiber -ore (2), periph-eral binding ~ones (3) comprising fibers (3B) and hardened . . .

. ~

. . : : ;"
"
. ~

adhesive/plasticizer formulation (3C) arranged between and among the fibers to form a lattice which is, in turn, exter-nally bounded by the tow wrap (7B).
Figure 3 demonstrates a modification of Figure 1 in which wetting roll (19) and formulation well (20) are re-placed by a spray head (21A) f-.ed by spray feed line (22A) for supplying hot melt or other convenient adhesive/ plasticizer binding formulation from a source (not shown) onto the offset formulation applicator medium (7A). As shown, similar compo-nents in each Figure are identified by the same arabic num-bers.
While adhesive/plasticizer binding formulations suitable for use in the present invention are not limited other than with respect to polypropylene-fiber wetting characteristics~
and to conventional melting, setting or other characteristics well-known to those skilled in the art, it is found that the following general classes of binders are particularly suit-able:
I. Butadiene/styrene-based rubber of a nonionic or anionic type, in ~he form of emulsions having a weight ratio of about 95-65/55-35, or ethylene/vinylacetate-based copolymers with rosin esters of a type which are obtainable commercially from Union Oil of California under the trademark AMSCO-RES , par-ticularly AMSCO-RES-4125, and including the corresponding hot melts such as AMSCO-MELTTM 204;
II. Butylacrylate or butylmethacrylate-containing polymers with hydrocarbon resin additives of the type obtainable com-mercially from Rohm and Haas Company under the trademark RhoplexR, particularly Rhoplex 621, 631 and P-376; and III. Alpha-methylstyrene copolymer hydrocarbon resins obtain-able from Hercules Incorporated under the trademark KRISTALEX
particularly KRISTALEX 3100, including aqueous ~ispersions or emulsions.
Other binding formulations suitable for use in the pres-ent invention are ethylene/vinylacetate based copolymers ofthe type obtainable commercially from Eastman Kodak Company under the trademark EastobondR, including the ~A~ series - : - :

. . - ~ , '~ :
:

thereof such as Eastobond A-381, and Eormulations that may be described as comprising ~X~ and ~A components, the ratio of (X)-to-lY) being about 5-30 to 95-70 parts by weight, in which the (X) component is defined as a rosin ester modifier in the form of an emulsion of a hard resinous solid, the resin moiety of which is preferably about 45% to about 100% hydrogenated.
In these latter formulati.ons the ester modifier may in-clude about 5-25 weight percent resin ester having an abietic acid concentration of up to about 5%, with a drop softening point within the range of about 60C.-95C. J and not exceeding a weight average molecular wei.ght of about 2000. The ~X~ com-ponent is obtainable commercially in the solid form or, in some cases, as an aqueous dispersion of a product sold com-mercially under the trademark ForalR* 85 or 105 (glycerin and pentaerythritol ester of highly hydrogenated rosin Av.
MW 600-1000); Hercolyn DR (hydrogenated rosin methyl ester);
Piccolyte A 115 resin (polyterpene); Staybelite Ester 10 (glycerin ester of hydrogenated rosin, Av. MW 600-1000);
PentalynR H (pentaerythritol ester of hydrogenated rosin, Av. MW 600-1000) or Piccotex resin (copolymers of methyl-styrene and vinyltoluene).
The corresponding (Y) component of these formulations may be made by (a) by polymerization of monomers such as vinyl acetate alone or in admixture with a comonomer such as ethylene, or (b) by polymerization of monomers such as acrylic acid, methacrylic acid, ethyl acrylate, butyl acry-late, methyl methacrylate, etc., or mixtures thereof with co-monomers such as styrene, ethylene, propylene, butadiene andthe like. Suitable copolymer lattices of the above type are described, for instance, in British Patent No. 1,514,217 or obtainable commercially, for instance, under the trademark Vinac 881 (a homopolymer of vinyl acetate~, or Airflex 405 (a copolymer of vinyl acetate 90/ethylene 10).
The bulk denier of fiber tow or slivers suitable for use in carrying out the present invention can usefully vary between about 6,000 to 60,000 total denier, and can be supplied from a ,.. .

-, ~, . .
~::
-;. - . .

.

single creel or from a composite of several creels with the use of fluid texturizing jets. ~or best performance, however, it is preferred that fiber tow be used in a substantially un-twisted and untextured state.
Fluid jets are optional for purposes of the present in-vention and may be of conventional design. Also found useful are guide tubes for the purpose of confining tow or yarn as it enters the garniture, such as the trumpet 15 in Figure 1.
The high degree of texturization imparted to the yarn and the turbulence around the exit of the jet can cause the yarn to lose its structural integrity and become undesirably entangled if it is not confined in this area.
The invention is further illustrated by the following Ex-amples, in which parts and percentages are by weight unless~
otherwise specified.
EXAMPLE I
Two continuous 4.5 denier per filament (dpf) polypropy-lene staple fiber tows having a ~Y~ cross-section are opened into a thin ribbon about 30 to 36 cm wide (12-14 inches) and drawn through the garniture of a standard filter rod-forming apparatus modified to operate in the general manner of Figure 3, to form a fiber filter plug, which is wrapped and bonded using a paper tow wrap having a weight of 29.0 gm/m2, upon which is coated a binder by spraying the paper tow wrap under slight tension with a multi-jet spray producing six uniformly spaced parallel lines of the indicated adhesive formulation at amounts identified as ~(% Add On)~ and based on the result-ing increase in weight of the filter plug. The binder formu-lations used were those already described as obtainable under the trademarks (a) Rhoplex 631, (b) Rhoplex P376, (c) XRISTA-~EXR 3100* and (d) AMSCO-RESR 4125. The coated, wrapped, and cut test filter elements, having a length of 90mm and a cir-cumference of 24.35mm, are then tested, using the standard Filtrona cigarette testing equipment already referred to, and microscopic examination to estimate the approximate extent of penetration ~d~ of the binding material. The res~ ~ are re-ported in the Table below as Samples T-l through ; ' '`
' L~612Z7 CONTROL EXAMPLE I-B

Example I is repeated using identical 4.5 dpf opened fiber tow but without applying any binder to the fiber tow. A small amount of tow wrap adhesive was app:Lied to the tow wrap to secure it. The test results are reported in Table I below as sample C-IA.

TABLE I
Samples Add On %F ~ P d(mic) A% Formulation T-l 14.4 85.0 431 600 28.554 RHOPLEX 631 T-2 14.0 85.4 440 600 28.554 RHOPLEX P376 T-3 38.5 93.6 421 1000 44.930 KRISTALEX 3100 T-4 54.4 94.4 510 2000 76.556 KRISTALEX 3100 T-5 44.7 91.5 474 1500 62.406 KRISTALEX 3100 C-IA 0 79.6 384 (Control) . :.. ,.. ,.. ,,, .. . -

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for making filter elements for cigarettes in which polypropylene-containing tow or sliver is fed into the garniture of a filter rod-making apparatus and shaped to form a fiber plug that is wrapped with paper or a non-woven material before being cut into filter elements, characterized in that the fibers in the filter plug are free of bonding material before being wrapped, a polypropylene-wetting bonding material is applied to the wrapping material, and by the wrapping the said bonding material is immediately offset to the filter plug whereby the bonding material impregnates an outer layer of the filter plug, so as to produce a filter element having a hardness value of at least about 80% and not substantially above about 94%, as determined by the equation:

x 100% , in which F is the hardness value, D is the diameter of the filter element in millimeters, and .DELTA.D is the deflection or decrease in diameter of the wrapped filter element in hundredths of a millimeter after being subjected to a 300 gm load for fifteen seconds.

2. A process for making filter elements as claimed in claim 1, wherein the bonding material impregnates an outer layer of the filter plug that has an annular cross-section that is from 1 to about 20% of the total cross-sectional area of the filter element.

3. A process for making filter elements as claimed in claim 2, further characterized in that the annular cross-section of the filter plug that is impregnated is from 1 to 10% of the total cross-sectional area of the filter element.

4. A process for making filter elements as claimed in claim 1, 2 or 3, wherein said hardness value is above about 85% but not substantially above about 94%.

5. A process for making filter elements as claimed in claim 1, 2 or 3, further characterized in that the amount of bonding material that is applied to the wrapping material is from about 10 to about 60% of the weight of the filter plug wrapped by that length.

6. A filter element as claimed in claim 1, 2 or 3, further characterized in that the polypropylene containing tow in the filter plug is substantially entirely composed of polypropylene or polypropylene and another polyolefin.

7. A filter element as claimed in claim 1, 2 or 3, further characterized in that the polypropylene containing tow in the filter plug is substantially entirely composed of polypropylene.