US2954036A - Cellulosic sheet and filter, and process therefor - Google Patents

Description

Sept. 27, 1960 M. o. scHuR ETAL 2,954,036

CELLULOSIC SHEET AND FILTER, AND PROCESS THEREFOR Filed June a, 1958 Flew-Z INVENTOR.

O. SCHUR BY JAMES C. RICKARDS M MILTON F le-6 CELLULOSIC SHEET AND FILTER, AND PROCESS THEREFOR Milton 0. Schur', Asheville, and James C. Richards, Brevarrl, N.C., assignors to Olin Mathieson Chemical Corporation, Pisgah Forest, N.C., a corporation of Virginia Filed June 3, 1958, Ser. No. 739,513

11 Claims. (CL 131--208) This invention relates to an improved cellulosic sheet particularly adapted for the mass production of novel filter tips, capableof providing superior filtration of tobacco smoke, as well as to the process for producing the same. I

In this art, numerous previous proposals of a variety of filter tips for cigarettes and other tobacco smoking devices have failed to solve the problems of providing a relatively inexpensive filter which is adapted to mass production methods and thereby consistently yield a product capable of removing a high percentage of the'undesired particulate matter in the smoke without unduly increasing the resistance to the passage of the smoke therethrough.

The main object of this invention has been to provide novel products, and processes therefor, adapted for the consistent production on a large scale of excellent filters for tobacco smoke characterized by high efficiency of removal of particulate matter without high resistance to gas flow. Another object has been the provision of an elongated cellulosic strip which is readily adapted for conversion to improved filter rods and tips. Further objects have included the provision of novel processes as well as additional features which will be apparent from the following description.

, In our copending application, Serial No. 460,355 filed October 5, 1954, we have disclosed that improved filters may be obtained from cellulosic sheets by providing numerous torn areas in the sheet having fuzzy edges, where the fibers have been pulled apart, and then gather- .ing and conforming the so-treated sheets to form filter In a' preferred embodiment, such torn areas in prior to its consolidation into filter rod. Thus, theforegoing objects have been accomplished in providing a controlled compression step after the cellulosic sheet has been grooved, resulting in a grooved and compressed sheet, which in a subsequent consolidation step results in a filter rod of excellent efiiciency and appearance.

Referring to the drawings, a preferred embodiment of suitable apparatus is represented diagrammatically in Fig. 1. Starting cellulosic strip 1 is fed from supply reel 2, and after being moistened, if necessary, by means of water spray 3, the strip passes through grooving or fiuting'rolls 4 and 5.

Preferably, rolls 4 and 5 are mating rolls of steel or other suitable metal and are provided with a plurality of parallel circumferential grooves. As shown in Fig. 2, which is an enlarged fragmentary sectional view along plane 22 of Fig. l, the circumferential grooves 6 of roll 4 mate with the intervening annular projections 7 of roll 5, while the raised rings 7 of roll 4 penetrate the grooves 6 of roll 5. The spacing between the rolls is maintained to produce the desired quality of sheet product, in any convenient manner, for example by connited States Patent 0 Patented Sept. 27, 1960 trolling the relative positions of the roll shaft bearings.

The sheet 1 is held between the complementary grooves ing of the fibers and ruptures of the sheet occur mainly at the paper surface areas contacting the grooves 6. Such areas of the grooved paper, referred to hereinafter as outer ridge surfaces, are fuzzy, being provided with large numbers of projecting fiber ends.

The grooved paper strip is then passed through a dryer 8, where any excess moisture is removed from the sheet by circulating heated gas or by other suitable means as by infra-red lamps.

The grooved and dried strip, containing the desired amount of moisture, is then compressed by passage through the nip of smooth-surfaced pinch rolls 9, made of steel or other metal.

The compressed grooved strip 10 may then be wound to form bobbins 11 by means of conventional spooling equipment. The conversion of strip 10 to filter rod may conveniently be effected by means of the apparatus shown diagrammatically in Fig. 3. Strip 10 from bobbin 11 is fed together with conventional cigarette wrapper paper 12, taken from bobbin 13, on theendless belt 14, passing over rolls 15, through the forming cone 16, as conventionally used in the assembly of cigarette rods. In the cone, the strip 10 is laterally gathered and formed under radial compression into a substantially cylindrical consolidated filter rod and is encircled by wrapper paper 12.

Paste is applied to the upstanding edge 17 of wrapper 12 by applicator 18, the pasted edge 17 then being pressed into firm contact with the portion of the wrapper which it overlaps by means ofcylindrical member 19. Wrapped filter rod 20 emerges and may be cut into convenient lengths.

The grooved and flattened strip may be consolidated to wrapped filter rod as above described by feeding the. strip into the rod-forming mechanism directly without intermediate spooling.

The consecutive steps of grooving a strip and then flattening the corrugations, flutes or pleats improves the suitability of a wide variety of papers for conversion to excellent filters for tobacco smoke. material which is preferred consists of paper made from highly bleached'coniferous kraft wood pulp containing atileast about alpha cellulose, which had been very the paper is much less uniform in formation and strength properties than paper made from well-beaten pulp. When such paper, made from lightly beaten pulp, is stretched, the clotted or clumped fibers tend to pull apart to produce fuzzy or fibrous surfaces.

The starting paper web 1 should desirably contain about 10 to 55% by weight of moisture, preferably about 25%, at the grooving step, as deep grooves can then be formed without excessive tearing or shredding of the sheet.

Excellent grooving or fluting has been accomplished by rolls 4 and 5 constructed as shown in Fig. 2, grooves 6 being 0.30 inch deep and 0.2 inch in width while the annular rings 7 are 0.1 inch in width. While the base The starting sheet of the grooves 6 and the outer surface of rings 7 may be rounded or provided with other suitable contour, the side walls of grooves 6 are preferably in planes transverse to the longitudinal axis of the rolls, or in other equivalent arrangement, so as to substantially avoid the possibility of causing sharp cuts during the grooving operation.

After passing through rolls 4 and 5, the spacing of which is controlled to produce the desired depth of groove, paper web I has a grooved or corrugated strue ture as shown in the enlarged fragmentary sectional view of Fig. 4. The structure may be described as a series of connected ridges, the adjacent ones being faced in opposite directions. The outer surfaces 21 of the ridges are substantially covered by a fuzzy layer of projecting fibers and fiber ends, as contrasted with the inner surfaces 22 of the ridgeswhich have a smooth pressed appearance. The fibrous surface probably results from the stretching and rubbing action on web 1 which is most highly concentrated at the areas of contact between grooves 6 and the paper web. Projecting fibers in the ridge outer surfaces 21 are also in part due to separation of fibers and longitudinal rents which occur most frequently in this portion of the web.

Excellent results have been obtained by the provision of about 25 to 40 grooves per inch, preferably about to 35, with depth of groove ranging from about 0.03 to 0.05 millimeter.

After moisture has been removed by evaporation in dryer 8. the grooved web is passed through pinch rolls 9, which are spaced apart at the proper gap to accomplish the desired compression of the grooved strip. Compression by rolls 9 modify the sheet structure to that shown in the enlarged fragmentary sectional view of Fig. 5. The ridges have been flattened so as to effect a significant increase in the apparent density and, at the same time, to spread the fibrous surfaces 21 laterally, so as to increase substantially the proportion of exposed sheet surface covered by projecting fibers and fiber ends. Likewise, the fiattening pressure accomplishes a further separation of fibers which was initiated during the groov-- ing operation.

The resulting sheet is characterized as having a desirably apparent density, and one whose surface is covered by a multitude of projecting fibers or fiber ends which extend into or across each groove in a haphazard manner, loosely pervading the entire groove.

The increase in the apparent density is of great importance in that a roll of given dimensions contains a significantly greater weight and length of treated paper which is readily handled and transported. Thus, paper strip which has been grooved to a depth of 0.48 to 0.50 mm. displays an apparent density of 0.06 to 0.07 gram per cubic centimeter (3.7 to 4.3 pounds per cubic foot). In contrast, if the same paper strips having grooves 0.48 to 0.50 mm. deep are compressed to ilatten the ridges to final thicknesses of 0.33 to 0.14 mm., the apparent density of the roll of treated paper is increased to a range from about 0.21 to 0.495 gram per cubic centimeter (13.1 to

30.8 pounds per cubic foot).

Filters for tobacco smoke prepared from the grooved and flattened web, for example as described above, display a combination of desirable properties not heretofore attained with cellulosic filters. Especially, such filters display high efficiency in the reduction of particulate content in tobacco smoke, readily accomplishing the removal by a short length of filter tip of over 50% and up to about 60% of the particulate content in the smoke while retaining high permeability to the longitudinal passage of gas.

The filter rods in accordance with this invention likewise display a desirable degree of firmness permitting ease of cutting and handling by high speed automatic machinery, which is essential in the manufacture of cigarettes by modern mass production techniques.

Furthermore, the high filtering efiiciency at desirable ranges of resistance to gas flow are attained by the filter tips of this invention without requiring the use of excessive amounts of filtering material.

Also, the ends of the filter tips of this invention have an excellent appearance, characterized particularly by uniformity and by the substantial absence of macroscopic pores, reference being had to the substantial absence of pores which are visible to the normal human eye at the usual reading distance of 10 to 15 inches. Generally, substantially no pores of appreciable size are visible even when an end or transverse section is magnified ten times. The uniform structure is also demonstrated by the even staining of the filter tip after a cigarette has been smoked.

The advantages of filters made from grooved end flattened paper strip in accordance with this invention are illustrated in the following test data obtained using filter rods 102 mm. long and 8 mm. in diameter. The starting paper in each case consisted of sheets 0.07 mm. thick, made from slightly beaten pulp as above described, paper A containing 1% by weight of melamine-formaldehyde wet strength resin, paper B containing 2% by weight of the above resin, and paper C being free of wet-strength resin.

Table I PAPER A: INITIAL W'IDTH, 0 INCHES. GROOVED \VIDTH, 7% INCHES Thickness Filter Column Properties No. Grooved Resist- Filtration Grooved, and Fiat- Density once to softness, Efficimilhtened, (g./ce.) gas flow, millicncy, meter milliinches meter percent meter PAPER B: INITIAL WIDTH 9 INCHES. GROOVED WIDTH,

7% INCHES (s) 0. 53 0. as 0.176 7. a 0. 32 4o. 0 (ii) 53 .20 179 7. 2 54 44. 5 (7) 53 15 178 4. 4 .86 44. 0

PAPER 0: INITIAL WIDTH, 8% INCHES. GROOVED WIDTH, 7 INCHES In contrast with the above, the following test values were obtained on samples of the same paper strips after grooving but omitting any subsequent flattening step.

.In Tables I and II, the paper thickness was measured to the nearest hundredth of a millimeter as the maximum distance between the two surfaces of the sample when subjected to the full pressure, 7 to 9 pounds per square inch, of an E. J. Cady paper caliper measuring instrument.

The rod density values were obtained from measurements of volume and weight of wrapped rod, the weight of wrapper 12 being deducted.

Resistance to gas flow measurements represent the pressure drop in inches of water observed in a filter rod 102 mm. long and 8 mm. in diameter at an air flow rate through the rod of 17.5 cubic centimeters per second.

The softness values were measured by contacting a horizontally disposed filter rod at the seam of the wrapper with the flat end of a vertical cylindrical bar, one-half inch in diameter and supporting a weight of 347.5 grams, and determining to the nearest hundredth of a millimeter the distance of downward movement of the bar in a period of ten seconds. Thus, the softer the filter rod (less resistant to deformation or compression), the higher the measured value of bar travel.

Filtration efficiency values represent the percentage decrease in the amount of solids recovered from smoke collected from filter-tip cigarettes as compared with the amount collected from the smoking of an identical column of tobacco not provided with a filter. The cigarettes for test, selected to have closely agreeing weights, were 85 mm. long including, in the case of the filter-tip samples, a filter-tip 17 mm. long at one end. The cigarettes were smoked in suitable test apparatus at the rate of one 35 cc. puff of two seconds duration per minute until a 62 mm. column of tobacco had been consumed. The smoke from each cigarette was collected in a glass vessel at room temperature and the solids were allowed to settle. The solids were then transferred by use of a solvent to a tared dish and weighed after evaporation of the solvent, drying in an oven at 95 C. for 16 hours, and cooling in a desiccator.

Optimum values of filter rod properties have been found to be as follows:

Resistance to gas flow: 4 to inches of water, and not over 12 inches.

Softness: 0.25 to 0.75 mm., and not over 1.0 mm.

Filtration efficiency: Over 40%, preferably over 50%.

When the filter rod displays values of resistance to gas flow greater than 12 inches of water (or greater than about 2 inches per 17 mm. tip), cigarettes fitted with filter tips consisting of a short length thereof, for example 17 mm. long, are generally unacceptable as requiring unduly high suction in smoking. Resistance values corresponding to a pressure drop of less than 4 inches of water per rod (of sufiicient length to provide six filter tips) are generally indicative of the presence of relatively large pores or channels through the filter leading to poor filtration efliciency and unsatisfactory appearance of the filter end. In accordance with this invention, it is possible to produce filter rods from paper having any desired resistance value between 4 and 12 inches of water, combined with excellent filtration etliciency and highly satisfactory appearance of the filter end.

It has been'found that filter rods, characterized by such low resistance to deformation that the measured values of softness exceed about 1.0 mm., are not well adapted to subdivision and satisfactory handling by automatic machinery operating at the desired high production rates.

The data of Table I show that the present invention enables the production of filter rods of high filtration efliciency, ranging to close to 60%, combined with desirable values of the other essential properties.

The preferred treatment of the starting paper web consists in grooving the web to a suitable depth, generally such that the sheet thickness is increased about four to eight times the original thickness andthen flattening to 6 a thickness amounting to about 30% to 65% of the grooved thickness. The grooved and flattened web then has a structure as shown in Fig. 5 wherein longitudinal ridges 21 consist of flattened loops, the adjacent folds having in transverse section an appearance resembling an hour-glass open at one end.

The outer ridge surfaces 21 are substantially covered by fiber ends loosened from the starting paper structure by the successive steps of grooving and then flattening. The flattening step also spreads the fiber ends laterally to fill the openings of the flattened loops. The fiber ends forming the fuzzy covering over the outer ridges surfaces 21 have been observed to project an average of about 0.25 mm. from the sheet surface where the fibers remain bonded to each other- .As the average fiber length is the preferred starting paper averages close to 1.25 mm.,

the projecting fiber ends are held in place by bonds with surrounding fibers for, on the average, about of the length of the entire fiber. Accordingly, the resulting grooved and flattened sheet is characterized by longitudinal folds connected to one another and consisting of flattened loops, the adjacent ones facing in opposite directions and overlapping each other, each loop having an outer ridge surface which is fuzzy with projecting fiber ends. The resulting strip is further characterized by capability of being spooled to form a compact roll having an apparent density of 0.2 to about 0.5 grams per cubic centimeter.

Grooved and flattened strip as above described is readily formed, as by means of apparatus such as that shown in Fig. 3, into filter rod of highly desirable properties and of excellent end appearance when out into filter rods and tips. The structure is such as to facilitate the consolidation of the strip by means of forming cone 16 into rod of uniform formation and apparent density throughout and displaying end sections of snow-like appearance and substantially free of macroscopic pores. The multitude of passageways for gas or smoke which exist in the flattened loops or between adjacent layers of the consolidated strip, represented in the enlarged fragmentary sectional view shown in Fig. 6, mostly have maximum widths ranging from 0.25 to 0.60 mm., but therefore are substantially filled with the numerous projecting fiber ends existing on both surfaces of strip 10.

Desirable softness values of the above rod, within the above-stated limits of 0.25 to 0.75, result particularly because of the retention of the parallel portions of the web connecting the adjacent ridges 21 which contribute.

significantly to lateral stiffness and resistance to compression.

' The poor filtration efliciency of the rods listed in Table II, made from grooved 'or corrugated but unflattened strip, substantiates the tremendous improvement effected by the addition of a flattening step. The use of initially wider strip, resulting in a higher weight of paper per unit length of rod, brings about a limited but insufiicient improvement at increased cost. Thus, a 102 mm. filter rod of sample 11 requires 0.408 gram more paper than for sample 10, and 0.319 gram more for sample 14 than for sample 13. Also, the appearance of the ends of the rods of Table II is unsatisfactory as many readily visible pores are present. Although some improvement is obtainable in filter rods made from a. more deeply grooved unflattened strip (final thickness of about 0.50 mm.), the filtration efficiency and end appearance remain inadequate.

While best results are obtainable by flattening the 7 extents of flattening, resulting in undesirably high softness values, may however be offset by the use of an initially wider paper strip. Such practice likewise effects an improvement in the appearance of the tip ends in significantly decreasing the number of visible pores which otherwise tend to appear in rods made from strip which has been grooved and was then flattened to such an extent that the loops have been substantially collapsed.

Preferably, the grooved and flattened paper strip of this invention is prepared from paper, as described above, containing about 1% of melamine formaldehyde or other wet-strength resin. Such paper is readily handled, with a minimum of ditliculties, throughout the operations of grooving, drying, flattening and spooling under tension as well as in the steps of consolidating to rod form and further handling thereof. The filter rod and filter tips thus produced are characterized by uniformly excellent appearance and performance. Such desired results are enabled by the novel grooved and flattened strip, in accordance with this invention, characterized by projecting fiber ends substantially uniformly distributed over both surfaces of the strip and anchored thereto.

It will be understood that the described filter may include other ingredients such as activated carbon or other adsorbents for smoke constituents, or agents for modifying tobacco smoke constituents, without departing from the spirit and scope of the invention, as defined in the accompanying claims.

We claim:

1. A filter for tobacco smoke comprising a wrapper and a filling therein, said filling consisting essentially of contacting layers of paper strip material having longitudinally extending connected flattened loops including ridge portions, the adjacent ridges being faced in opposite directions and having a multitude of projecting fiber ends on the outer surface thereof, the adjacent loops partly overlapping each other, and said strip being consolidated to substantially cylindrical form to have an apparent density of about 0.16 to 0.20 gram per cubic centimeter, being readily permeable longitudinally to gases and characterized by end sections substantially free of macroscopic pores.

2. A filter in accordance with claim 1, wherein said paper strip contains interfelted cellulose fibers averaging about 1.25 mm. on length and said fiber ends project an average of about 0.25 mm.

3. A filter in accordance with claim 1, wherein said paper' strip has been grooved to a thickness of about 0.30 to 0.50 mm. and flattened to about 20% to 80% of the grooved thickness.

4. Elongated strip of fibrous cellulosic material, particularly adapted for the formation of filters for tobacco smoke, consisting essentially of paper strip having connected ridges extending longitudinally thereof, the adjacent ridges being faced in opposite directions and having a multitude of projecting fiber ends on the outer surface thereof, said strip having been compressed to have an apparent density of about 0.20 to 0.50 gram per cubic centimeter, and-being characterized by the fact that the said adjacent ridges partly overlap each other with each ridge forming part of a flattened loop.

5. Strip in accordance with claim 4, having a thickness prior to compression of about 0.30 to 0.50 mm. and a final thickness of about 20% to 80% of that prior to compression.

6. Strip in accordance with claim 4, wherein said paper strip contains interfelted cellulose fibers averaging about 1.25 mm. in length and said fiber ends project an average of about 0.25 mm.

7. A grooved and flattened paper sheet provided with substantially parallel grooves including ridge portions, said ridge portions being flattened and having a multitude of fiber ends projecting from the surfaces thereof in haphazard manner, said grooves being about 0.1 to 0.4 mm. in depth and being loosely pervaded by said fiber ends.

8. Process of manufacturing an elongated strip of cellulosic material particularly adapted for the formation of filters for tobacco smoke, comprising the steps of grooving paper strip longitudinally while preventing any substantial transverse shrinkage thereof to provide strip having a thickness of about 0.30 to 0.50 mm. and characterized by a plurality of parallel connected loops each having a ridge portion, the adjacent ridges being faced in opposite directions, and flattening the grooved strip to a thickness of about 20% to of the grooved thickness.

9. Process of manufacturing an elongated rod of cellulosic material adapted for the efficient filtration of tobacco smoke comprising the steps of grooving paper strip longitudinally while preventing any substantial transverse shrinkage thereof to provide a plurality of parallel connected loops each having a ridge portion, the adjacent ridges being faced in opposite directions and having a multitude of projecting fiber ends on the outer surface thereof, compressing the grooved strip to flatten the said loops so that the adjacent fibrous surfaces partly overlap each other, and consolidating said strip to form a substantially cylindrical rod having an apparent density of about 0.16 to 0.20 gram per cubic centimeter and longitudinally permeable to gases.

10. Process of manufacturing an elongated strip of cellulosic material, particularly adapted for the formation of filters for tobacco smoke, comprising the steps of grooving said strip longitudinally while preventing any substantial transverse shrinkage thereof to provide a plurality of parallel connected loops each having a ridge portion, the adjacent ridges being faced in opposite directions and having a multitude of projecting fibers on the outer surface thereof, and compressing the grooved strip to flatten the said loops so that the adjacent fibrous surfaces partly overlap.

11. A filter for tobacco smoke comprising a wrapper and a filling therein, said filling consisting essentially of contacting layers of paper strip material having generally longitudinally extending connected flattened loops including ridge portions, the adjacent ridges facing in opposite directions and having a multitude of projecting fiber ends on the outer surface thereof, the adjacent loops partly overlapping each other, and said strip being consolidated to red form characterized by an apparent density of about 0.16 to 0.20 gram per cubic centimeter, and by generally longitudinal passageways in said loops and between said layers, most of said passageways being 0.25 to 0.60 millimeter in width and being substantially filled with pro jecting fiber ends.

References Cited in the file of this patent UNITED STATES PATENTS 1,208,535 Ford Dec. 12, 1916 2,164,702 Davidson July 4, 1939 2,167,170 Burns July 25, 1939 2,425,207 Rowe Aug. 5, 1947 2,679,887 Doyle et a1. June 1, 1954 2,849,932 Marogg Sept. 2, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2 ,954,036 September 27 1960 Milton 0. Schur et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 71, "0.30" should read 0.03 same line 71 "0 .2" should read 0 02 line 72, "0 .1" should read 0.01 Column 3, line 28, "millimeter" should read inch line 33, "modify" should read modifies lines 43 and 44, "desirably" should read desirable Column 4, line 16, "end" should read and Column 6, line 27, "grams" should read gram Signed and sealed this 2nd day of September 1969.

(SEAL) Attest: v I

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

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