IL34341A - A method of treating webs of fibrous material for making a filter cord - Google Patents

Description

34341/2 lain rnyuiD ¾?is'»a,7 πο1» )3oa an naan o© A method of treating webs of fibrous material for making a filter cord CELFIL COMPANY ESTABLISHMENT, G. 2620 The present invention relates to the manufacture of filtering material in the form of substantially continuous longitudinally grooved fiber-containing webs, especially paper webs, having loosened and exposed fibers, which can be laterally gathered into a bundle. Wrapping this bundle produces an endless filter string or cord which can be divided into filter rods and filter plugs for cigarettes and other tobacco products. Gathering and wrapping of the longitudinally grooved web may be effected directly after its manufacture, or the longitudinally grooved webs may be wound to form rolls, stored and subsequently supplied to the conventional cording machines for the production of a wrapped filter cord and its subdivision into filter rods. he term "crimped paper" normally designates a material which, during production in paper machines, is upset in its direction of travel so tliet irregular transverse ribs are formed and the web possesses a greater weight than corresponding paper webs which are not upset. Such crimped papers were formerly largely employed for the manufacture of cigarette filters, but they are difficult to process since crimping is transverse to the direction of travel of the paper web and, in addition, they retain only insufficiently the solid and liquid particles to be removed from tobacco smoke by the filters.

On the other hand, other longitudinally crimped webs are disclosed in the Israeli patent specification JSo. 9339» in which the crimped grooves run in a direction parallel to the direction of travel of the webs. In the manufacture of such longitudinally crimped webs the paper is assed throu h the n w longitudinal grooving of the paper web is effected at least partly at the expense of the paper thickness* In the process, the web cannot move transversely to the direction of travel so that it is stretched in the transverse direction.

In this process the paper is advantageously rendered ductile prior to longitudinal grooving so that the transverse cohesion of the paper web is not destroyed by strong transverse stretching although such transverse stretching may be increased so a3 to produce discontinuous short longitudinal tears in the paper. After the passage between the intermeshing metal rolls, i.e. the longitudinal crimping unit proper, the web provided with longitudinal grooves is dried. Such longitudinally grooved webs have been found to be useful in the manufacture of filter plugs for cigarettes and are commercially used in a considerable scale.

According to a further equally known development of the aforesaid process, the moistened, virtually inelastic web is also passed through the nip between two heated grooving and stretching rolls provided with narrow intermeshing annular ribs which do not, hpvrever, contact one another so that the web is longitudinally crimped and transversely stretched until fibers are loosened and exposed without fully destroying transverse cohesion of the web, and, after emerging from the nip, the web passes over at least one of the rolls along a given looping angle and is simultaneously partially dried over parallel longitudinal zones, stiffened, and the loosened structur is fixed. Subsequently the web which remains on the roll may be passed between a second nip between this roll and a third identical roll, taken over by the third roll and passes over This improved method, too, has proven to be successful and thanks to the possible deepening of the longitudinal grooves produced in the web in the first nip, where an additional transverse stretching effect occurs, a more frayed web with enhanced filtering efficiency may be produced.

In the process of making longitudinally crimped webs , particularly from thin paper of about 20 to 50 g weight 2 per m , it is necessary to moisten the web of material before it passes through the first nip between intermeshing rolls provided with annular ribs, and consequently afterwards to dry the longitudinally grooved web. These two operations involve difficulties if the travel of the web is accelerated in order to increase hourly production and accordingly to run the machines as efficiently as possible. In so doing, the time available for moistening each centimeter of length of the web becomes ever shorter, and the energy requirements for drying ever greater, as the rate of travel of the web increases. By way of example, if moistening of the web is effected during the passage over 10 cm of travel, the time of dwell of every centimeter of web in the moistening unit is sec reduced to 0.025/at a rate of web travel of about 240 m/min, which no longer suffices even for moistening. Again, the time of dwell in the drying unit becomes correspondingly short, which renders necessary the provision of much space or a corresponding increase of energy for the necessary drying operation.

According to the present invention there is provided a method of treating endless webs of fiber-containing material, the transverse direction and wrapped for the urpose of making an endless filter cord divisible into filter rods, the virtually inelastic web of material being passed through at least one nip between coacting rotating grooving and stretching rolls equipped with close intermeshing annular ribs which do not, however, contact one another, the web of material being clamped by the annular ribs and stretched in a direction transverse to that of travel, the transverse stretching being increased to the point of loosening and exposing fibers without complete destruction of the transverse cohesion of the material, wherein the web of material is treated, prior to its entry into the nip, with a volatile impregnating agent and freed therefrom upon emerging from the nip, the volatile impregnating agent having a boiling temperature lower than that of water and a heat of evaporation of less than 250 kcal/kg.

In the present context the term "volatile impregnating agents" refers to liquids of which the boiling point is below that of water at the prevailing atmospheric pressure, and which have a lower heat of evaporation than water, of less than 250 kcal/kg.

The invention is illustrated, by wa of example, in the accompanying drawings in which: Pig. 1 is a diagrammatic side view of a device for the performance of the method according to this invention; Pig. 2 is an enlarged fragmentary section of the intermeshing grooving and stretching rolls of the device according to Pig, 1, seen in the direction of the travelling webj $ Fig. 3 is a side view of the grooving and stretching rolls according to Fig. 2 in the direction of line 3-3 in Fig. 2 ; Pig. 4 is a cross-section of the grooving and stretching rolls according to Pig. 3 along the plane 4-4 in Pig. 3; Fig. 5 is a diagram of the increase of the resistance to pulling in of filter plugs plotted against the amount, in parts by weight, of impregnating agent I and of water W used for moistening; Fig. 6 is a diagram of the swelling property Q of some paper webs when impregnated with various impregnating agents; Fig. 7 is a diagram of the effect of the concentration K of an additive on the tensile resistance Z of filter rods, and Figs. 8 to 10 are diagrammatic views of various devices for the performance of the method according to the present invention.

In the description below it is assumed that the xieb consists of smooth unsized paper of .06 to 0.07 mm thickness and 20 to 50 g weight per square meter, but the method is not limited to the use of such a web. It is essential for the method that the smooth and flat paper web to be processed is treated, prior to being crimped in the longitudinal direction and at the same time stretched in the transverse direction in a grooving and stretching process, with a volatile impregnating agent, such as methyl alcohol which is removed by evaporation after the grooving and stretching The web processed according to this method displays a frayed structure and possesses a plurality of short, discontinuous tears which run preferentially in the longitudinal direction. The mechanical strength of the web in the longitudinal direction is, however, sufficient to ensure that no breakage occurs as it passes through a cording machine for the production of an endless filter cord. In such a web, and especially in those zone3 thereof where the tears occur or the paper has been thinned considerably by the stretching, fibers have become loosened and exposed, This texture enhances the filtering efficiency of filter plugs made from the transversely gathered web.

The longitudinal crimping of such a web not only facilitates the gathering in the transverse direction into a continuous cord as the web passes through the cording machines, but also ensures the desired uniformity of compacting of the cord in the transverse direction. With a longitudinally crimped paper web of the structure indicated, the paper does not undergo undesirably weakenin and shrinking in use as a filter (which would create longitudinal channels in the plug through which the smoke can pass without being filtered), and the elasticity of the filter plugs in the transverse direction is adequate also during smoking, trior to the longitudinal grooving and simultaneous transverse stretching, the web, e.g. a smooth raw paper web made of only slightly ground fibers, must be impregnated with a volatile liquid, e.g. methyl alcohol. This may be effected, for example, by spraying, dipping or other conventional methods but in any case it must be done continuously since the grooving and stretching rocesses have to be erformed at hi h For grooving and stretching the moistened web runs continuously between grooving and stretching rolls which will be described in greater detail below. During the passage of the moistened web through such grooving and stretching rolls, the paper is apparently more or less firmly clamped at a plurality of adjacent points and stretched and elongated in the transverse direction in the zones between the clamping points. This is borne out by the fact that the longitudinally crimped , aper web has clearly recognizable parallel longitudinal sones of different texture. In any case the grooving and stretchin- treatment greatly increases the surface area of the material in certain zones at the expense of the thickness of the material, which is of importance for the enhancement of filtering efficiency. By way of example, it is possible to perform the grooving and stretching processes in such a manner that the longitudinally grooved paper web has virtually the same width as it emerges from the crimping unit as the raw paper web had when entering it so that shrinking in the transverse direction is avoided.

The grooved and stretched moist web has to be subjected to a drying process in order again to stiffen the longitudinally crimped web and to set the loose structure. After complete drying, the web may have a greater width than the smooth, impregnated raw paper supplied to the crimping unit. This is where the present method differs from the known processes in which water is used for moistening. It is well known that in the known manufacture of longitudinally crimped paper webs the webs emerging from the crimping unit possess virtually the same width as the Compared with the width of the raw paper webs,, the so-crlled shrinkage factor of the dried longitudinally crimped paper web may be as high as 30#. The raw paper impregnated not with water but with methyl alcohol, however, behaves quite differently and after complete drying has become wider than the raw paper web by a so-called expansion factor of '50 and more.

By way of example, if a raw paper smooth on one side 2 weighing 38 g per m is employed, which has an average fiber length of 2 to 4 mm and of which the fibers have been only slightly ground or beaten, a string of such paper 10 cm wide will possess, after passage through a crimping station of the design described below with reference to Figs. 2 to 4 and with unmodified setting of the roll engagement depthι - When moistened with water, a width of the longitudinally crimped strip of 9.8 cm in moist condition, 7.0 cm in dry condition.

- V'hen moistened with methyl alcohol, a width of the longitudinally crimped strip of .0 cm in moist condition, 12.8 cm in dry condition.

Accordingly the contraction factor with water is about ~$Qo but the widening factor with methyl alcohol about 28/-.

The longitudinally crimped paper webs made according to this method, however, do not only undergo stretching instead of the shrinking after moistening with water, but the texture of the paper webs so treated is different. Pespite the the crimping rolls, a substantially greater number of tears is apparently produced which are, however, generally short so that the impression of greater fraying is created. /Accordingly, a paper web so produced has a considerably softer touch and appears to possess a velvety fibrous surface.

In order to test the stronger fraying of the paper web treated according to the present method, 24 cm wide strips of the a ove-mentioned raw papers were transformed into corresponding longitudinally crimped webs in a device described in greater detail below with reference to iigs. 1 to 4. '£hese webs were fed directly into a commercial cording machine and filter rods of 8.05 nmi diameter and 90 mm length were produced. \vith the same engagement depth of all rolls, the moistening unit was first filled with water which was then replaced by methyl alcohol. ' e filter rods produced were as usual first tested for their resistance to pulling and then subdivided into six filter plugs, each 15 mm long, which v.'ere mounted on the tobacco cylinder of the sane f lterless cigarette brand and then smoked in a standardized smoking machine; the fraction of liquid and solid particles of tar and nicotine (in milligrams) contained in the smoke behind the filters was determined and the mean value calculated from every 10 such measurements. The following values were obtained: - - Filter rods and filter plugs Made of paper webs Made of paper webs impregnated with impregnated with methyl alcohol water Resistance to pulling (mean value from 10 filter rods) 280 mm WC *) 113 mm WC Quantity of particles in the smoke behind the filter, per cigarette 8 m 18 mg *) water column in the test apparatus.

The difference between the resistance to pulling reveals that the fraying of the paper web, which determines this resistance, is considerably larger on the filter rods made in accordance with this invention. Despite the same quantity of paper in the filter rods compared an increase of the resistance to pulling by about 115^ was found.

The filtering effect of the filter plugs according to the invention was considerably grer ter than that of the plugs made from a water-impregnated web, though both kinds of plug contained the same amount of paper. This shows that the impregnation of the web with methyl alcohol has no detrimental effect on the surface of the fibers contained in the paper and loosened or exposed by the crimping and transverse stretching process. On the contrary it is assumed that the cleansing action of the volatile impregnating agent increases the adsorptive capacity of the fibers for the particles to be separated from the smoke.

The above results of the measurements were achieved with methyl alcohol as a volatile impregnating agent. Instead, other alcohols, such as ethyl alcohol or propyl alcohol, or acetone and other ke e fre- eaos, benzene, light petroleum fractions, or halogenated hydrocarbons such as ethyl chloride, chloroform, carbon tetrachloride and the like, or esters such as ethyl acetate, may be used for the impregnation* Impregnating agents suitable for the present method have boiling temperatures lower than that of water, and a heat of vaporization below 250kcal/kg.

The effect of pure methyl alcohol, pure water and mixtures thereof on the shrinking and stretching factors of longitudinally crimped paper webs in drying is shown by the table below which relates to raw paper strips made of the abovementioned paper quality: Width of the paper Impregnating liquid webs prior to After drying impregnation Pure water 120 mm .90 mm 9 The paper web 1 passes through a moistening station comprising a roll 5 which dips into a volatile liquid 6 and A counter-roll 7 consisting, by way of example, of a resilient material forces the paper web against the roll 5.

Shallower or deeper immersion of the roll 5 in the liquid 6 end regulation of the contact pressure of the roll 7 enables the degree of moistening of the paper web to be adjusted within certain limits, so that on the one hand the paper still possesses adequate tearing strength in its longitudinal direction to pass the downstream stations of the device without breaking, and on the other hand the paper web is impregnated sufficiently to allow corresponding transverse stretching for the desired degree of longitudinal crimping.

Upon leaving the moistening station the web passes into a grooving and stretching station and there first runs into the nip between grooving and stretching rolls 8, 9 which ar both provided with a plurality of closel adjacent annular ribs which intermesh by an adjustable value without contacting one another.

Depending on the type of the volatile impregnating agent employed, it may be advantageous to heot the rolls 8, 9» and also the grooving and stretching roll 10 described below, to a certain temperature which, however, must not be so high that the vapors emerging from the paper web can ignite, to this end, the rolls may be provided with suitable electrical heating elements in their interior which are either stationary and supplied with current through the hollow shafts of the rolls or rotate with the rolls so that power supply must be effected through external slip-rings. Heating may be effected also by ot suitable mesjas, e.g. by hot steam which flows through the hollow rolls. In a y case, temperature control means will be provided the impregnated paper web up to several meters per second.

As the moistened paper web passes through the nip between the rolls 8 and 9» it is apparently retained somewhat at the spots contacting the ribs so that transverse stretching is particularly pronounced in the zones between these adhering areas of the paper. At all events, after passing through the nip between the rolls 8 and the paper web has parallel, strip-type longitudinal zones of different texture vrhich are clearly visible in the paper web.

For the adjustment of th^ meshing depth of the two rolls 8 and 9 it "is advantageous to make the axis of rotation of the roll 8 adjustable relative to the axis of rotation of the roll 9. '^ is adjustment can be effected, for example, by two jointly driven spindles carrying the shaft of the roll 8 at its front and rear ends so that when the height of this shaft is varied, the shaft remains accurately parallel with the axis of rotation of the roll 9· i'he adjustability of the shaft must be so fine that it is possible to adjust the meshing depth of the annular ribs "between 0 and about 1 mm meshing depth, to fractions of tenth of a millimeter, accurately and reproduceably. The adjusting device is advantageously provided with a calibrated scale and markings so as to ensure that a desired meshing; depth can at any time be re-set if it has been changed for any reason. In addition, the roll 8 can be adjusted on its axle in the axial direction so that the annular ribs of tho roll 9 can be accurately centered relative to the annular ribs of the roll 8. It has also been found that axial displacements of the roll 8 relatively to the roll 9 appear to be capable of changing the The paper web emerging from the nip between the passes rolls 8 and 9 over the roll 9/through a looping angle of about 180°, and then into the nip between roll 9 and a third grooving and stretching roll 10. V.hile the paper web, already grooved and transversely stretched, passes over the surface of the roll 9, the portions of the paper web in contact with the annular ribs of roll 9 are somewhat dried and stiffened so that the loosened texture of the paper produced in the first grooving and stretching zone is fixed and is no longer in danger of being adversely affected by softness and resilience of the paper.

The grooving and stretching roll 10 ie provided with similar annular ribs as are the rolls 8 and 9» and rotates about an axis parallel with that of roll 9. T e shaft of the roll 10 is adjustable in height relatively to that of roll 9, and also slightly in the axial direction similarly as described in connection with roll 8.

As the web, already longitudinally crimped and, to a certain extent transversely stretched, passes through the second nip between the intermeshing rolls 9 and 10, the longitudinal crimping is deepened and the transverse stretching is increased, care being taken that the position of the paper web in the second nip between the rolls 9 and 10 is the same as between the rolls 8 and 9« After emerging from the second nip the paper web, having thus been longitudinally cri:iped and transversely stretched in two steps, passes through a looping angle of 180° on the roll 10 and is drawn off horizontally via a guide roll 11. While the web runs over the roll 10, such portions contact the heated annular ribs as " xvere located between adjacent annular ribs during the passage of the looping angle of the roll 9 and thus did not contact the annular ribs of the roll 9. This ensures that the paper web drawn off the roll 10 is similarly predried and stiffened on it?, upper side and underside.

If desired, the grooving and stretching station ma be covered by a covering hood 14 so that the vapours emerging from the paper web are contained and can escape through a vent 15.

In the course of the longitudinal crimping and transverse stretching steps the web is in most cases completely freed from the moistening liquid by the contact with the rolls 9 and 10. If this drying is still inadequate, the paper web may be fed over the guide rolls 11 and 12 to a further drying device 13 which removes the last traces of liquid, e.g. by electric heating or by hot air. However, with the volatile impregnating agents employed according to the present invention, the additional drying unit 13 can as a rule be omitted since the drying effect of the two heated rolls 9 and 10 suffices fully to dry the web.

As compared with the great energy requirements of the known processes operating with water moistening of the web, the low energy requirements for evaporating the volatile impregnating agents i accordance with the invention constitutes a substantial advantage.

The vapours of the impregnating agent may be reclaimed by means of known devices arranged on the vent of the hood 14.

The device of Fig. 1 may be equipped with a conventional design which winds the longitudinall crim ed paper web may be fed directly into the gathering unit of a cording machine of known design. In this case it is sometimes of advantage that the paper web is completely dried, and the drying is completed after wrapping and subdivision into filter rods. The method according to the invention is advantageous particularly for high-speed cordin machines which may directly be fed with the longitudinally crimped paper webs because the f st removal of the volatile impregnating agent from the web proceeds without difficulty.

Instead of the grooving and stretching station equipped with three intermeshing rolls 8, 9 and 10 according to i'ig. 1, stations of other design may be provided e.g. as described in the Israeli patent specification iio. 9339* The annular ribs of the grooving and stretching rolls have preferably flat flanks normal to the axis of the roll, and a substantially rectangular cross-section with cylindrical faces which preferably form sharp edges with the flanks. By way of example, the annular ribs may advantap;eously be spaced by 0.7 mm and have a thickness of 0»3 mm with a radial flank height of about 1*0 to 1.5 mm. Since the grooving and stretching operation is preferably - but not necessarily - performed with fiber-containing flat material of a thickness below 0.1 iiim, e.g. raw paper with a mean thickness of about 0.07 mm, the web passes through the nip between a pair of rolls having such annular ribs which intermesh to a depth of e.g. 0.5 nun without contacting the side flanks of the ribs if the ribs of one roll extend accurately in the middle of the grooves between the two opposite rolls. With these dimensions the intermeshing annular ribs have lateral distances of 0.2 mm and a a er web assin through this nip will contact the annular ribs only on their cylindrical faces.

The grooving and stretching operation may also be performed with only two intermeshing rolls provided with annular ribs, but the stress exerted on the paper web is so sudden and violent that the individual fibers may break or tear. This is why crimping station having more than two intermeshing rolls is preferably employed, e.g. as shown in the embodiment according to ig. 1· A preferred embodiment of the grooving and stretching rolls is shown in Figs. 2 to 4 on a Bcale about ten times larger than that of Fig. 1 but with a diameter of the rolls which, for the sake of convenience, is still smaller than in actual practice. The three intermeshing grooving and stretching rolls 8, 9 and 10 are identical in respect of their annular ribs 21 and the annular channels 20 formed therebetween. The annular ribs 21 of the rolls 0 and 10 engage with the associated annular channels 20 of the roll 9. As indicated in Figs. 2 and 3 the paper web 1 passes through the nip between the intermeshing annular ribs. The engagement between the rolls 8 and 9 is preferably less deep (not shown in the drawing) than between the rolls 10 and 9 so that the lower nip has a shallower engagement and the upper nip a deeper one, Sy way of example, engagement of the lower nip may be about 0.3 mm, and that of tjhe upper nip about 0.6 mm. The paper web is thus longitudinally crimped in two steps and at the seme time stretched transversely. Those zones of the paper web which contact the cylindrical faces of the ribs 21 of the roll 9 in the passage through the first nip between the rolls 8 and 9 pass into the second nip between the rolls 9 and 10.

The paper web remains on the roll 9 for a time corresponding to the looping angle of 180°. After the passage through the second nip between the roll 9 and 10, the more deeply crimped and more strongly stretched paper web remains on the roll 10 for a looping angle of again about 180°, and the longitudinal zones of the web contacting the flat faces of the annular ribs 21 of the roll 10 are those which did not contact the annular ribs of the roll 9.

By the two-stage grooving and stretching operation with the rolls as per Figs. 2 to 4, the paper is reliably grooved longit dinally and transversely stretched without excessive stress on the paper even when the rate of web travel is increased. As the rolls 8, 9 and 10 are heated to a desired temperature, those longitudinal strips of the paper which contact the faces of the annular ribs are to a certain extent dried and stiffened, whereby the paper is properly conditioned for the subsequent grooving and stretching operation in the second nip.

The fact that the paper web runs over one of the grooving and crimping rolls throughout a predetermined looping angle is subjected to bending, is advantageous for loosening and exposing individual fibers. In a grooving and crimping station formed of the three rolls 8, 9 and 10, bending of the longitudinally crimped web rf material is effected first in one and then in the other direction, which facilitates the exposure of individual fibers.

As previously mentioned, most of the volatile impregnating agents indicated above cause a widening of the lon itu moistened with water. Accordingly the use of volatile impregnating agents, such as alcohols and ketones, which can be diluted with ¾*ater, enables the width of the longitudinally crimped paper web after drying to be influenced by a greater or lesser addition of water.

By way of example, if a device of the design described for making longitudinally crimped webs of material is employed to provide a paper web of a predetermined width with longitudinal grooves, at the same time stretching it in transverse direction and fraying it so that the paper web can then be directly fed to a commercial cording machine for producing wrapped paper filter rods, the resistance to pulling of the filter rods made may be influenced by the addition of more or less water to the volatile impregnating agent. Byvay of 2 exaaple, a raw paper web 240 mm wide, weighing 35 g per m and 0.06 mm thick was processed in such a device into filter rods of 0.8 mm diameter and 102 mm length, the impregnating agent employed having been a mixture of methyl alcohol and water. The resistance to pulling of the filter rods was determined by the usual standardized method in am water column with the passage of a volume of air of 17e5 cm per second. The result (average of 20 filter rods) is shown by curve A in the diagram of Pig. 5 in which the weights of water W and methyl alcohol T in the impregnating agent are plotte on the abscissa, and the increase Z of the resistance to pulling in against that produced by moistening with pure water (100>5 , o,¾T) on the ordinate. The curve B in the same diagram shows the increase in the resistance to pulling Z when a mixture of acetone T and water W (in parts by weight) "f Where filter rods are employed in machines for making f lter-tipped cigarettes, the mechanical properties, particularly the resistance of the cylindrical filter rods to radial compression, and the complete filling of their diameter are of importance. In filter rode made according to the example described above in conjunction with Fig. 5 it has been found that the resistance to radial pressure remains constant with about i 10 to 15% if the impregnating agent has a water content of 20 to 100 percent by weight.

It has further been observed that the paper web is positively widened in drying where the imprejmating agent has a water content between 50 and 0 percent by weight so that it is admissible that the web fed to the cording machine has not been completely dried, during after-drying the paper web inside will expand a little and thus ensure particularly uniform filling of such filter rods.

Examination of the filtering efficiency of filter pl -s uade by cutting the filter rods according to the above examples and attached to cigarettes have confirmed the rule, already known, that the filtering efficiency is proportional to the resistance to pulling. At all events treatment of the raw paper with a volatile impregnating agent has no adverse effect on the absorptive and adsorptive power of the exposed paper fibers. Despite these results, however, it was found that the paper webs moistened with volatile impregnating agents prior to longitudinal crimping differ in respect of their capacit of absorbing water or water vapour from the stream of smoke. ·, It was found that the swelling capacity of paper webs differs de endin on the water on ~t percent was determined by means of measuring instruments of known design for ten superposed raw paper samples of the same origin which were compressed b a cylindrical rasi of 16 ram diameter with a weight of 300 g. The diagrams of Fig. 6 ahov the swelling capacity Q in percent of two 2 2 paper types C (38 g/m ) and D (35 ff/m ) when three different ijapregnatin agents were used for moistening, i.e.: a = pure water b as 50 percent by weight each or water and methyl alcohol c = pure methyl alcohol It can be seen that a difference of about 10:1 in tei-ms of swelling capacity exissts between water and pure methyl alcohol. Similar differences were also noted in respect of the steam absorption capacity from a gas stream. The different behaviour of such longitudinally crimped and highly frayed paper webs regarding water and steam ebsorption, however, is of great importance in their use for cigarette filters since it is undesirable excessively to dry the sinoke because this will adversely affect its taste. It has lon^ since been known that paper filters, despite their good filtering proportion of properties, i.e. retention of a high/tar and nicotine substances from the smoke, produce undesirable modifications of taste ovinn- to excessive moisture absorption and consequent drying of the smoke. Paper webs treated not with water but with volatile impregnating agents according to this invention avoid strong drying of the smoke without reducing the desired high degree of absorption of tar and nicotine substances.

This .improvement may possibly be connected with the fact - - t ^ agents than with paper webs moistened with water in longitudinal crimping and fraying.

As stated previously, it is an advantage of the present method that, in employing volatile impregnating agents, additives can be dissolved in the agent in order to remain in fine dispersion on the paper web when the impregnating agent is evaporated.

By way of example, alcohols as impregnating agents were given additions of tartaric acid, citric acid and similar hydroxy-polycarboxylic acids, and filters were produced which improved the taste of the cigarette smoke. ¼here acetone and other volatile ketones are employed as impregnating agents, cellulose triacetate, cellulose acryl acetate, cellulose nitrate, hydrolysed cellulose and other cellulose compounds, glucose derivatives may be dissolved in the impregnating agent as additives.

These cellulose or glucose derivatives, as well as organic acids and/or polyhydric alcohols such as glycerine and glycol are also suitable as additives for an impregnating agent from the group of organic ethers.

Also suitable for dissolving in the volatile impregnating agents are such additives as cause a chemical reaction, at least on the surface, with the fibers of the xveb.

By way of example alcohols as impregnating agents may contain, as an additive, a hydroxy monoearboxylic acid such as hydroxyformic acid or hydroxyacetic acid. Organic ethers as impregnating agents enable monoearboxylic fatty acids such as formic acid, acetic acid, propionic acid and the like to be added. 4 If in the operation of the device described above the volatile impregnating agents contain such additives, prolonged operation causes the additives in some cases to be deposited on the grooving and stretching rolls, which is undesirable. In such cases it is of advantage to perform the method in two consecutive steps. In the first step the raw paper is treated with an impregnating agent which contains the ueuired substances in solution, and then dried. The web so impregnated is then moistened with a pure, readily volatile impre nating agent, supplied to the possibly heated grooving and stretching rolls and subsequently freed from the impregnating agent. It has been found that no noticeable residues are formed on the grooving and stretching rolls in this two-stage operation even after extended operation.

By way of example, if acetone with a content of a few percent cellulose triacetate is employed, a frayed paper web excellently suited for cigarette filters can be obtained but undesirable deposits form on the grooving and stretching rolls in continued operation. The same paper web, however, can advantageously be produced in two steps. In the first step the raw paper web is impregnated with an acetone in which a small quantity, by way of example 0,2 to 4 percent by weight, of cellulose triacetate is dissolved. Impregnation and subsequent drying take place very rapidly and require only little energy. The raw paper so impregnated is then moistened with a volatile impregnating agent in the manner above described and supplied to the grooving and stretching rolls. It is advantageous to use an alcohol as the volatile impregnating agent in which cellulose triacetate is not case no undesirable residues are produced on the grooving and stretching rolls by a paper so impregnated.

The extremely fine sediment of additive produced on the web by the treatment of the latter with the solution of the additive in a volatile liquid is not disturbed by the longitudinal crimping and heavy fraying to which the T.?eb is subjected.

By way of example the raw paper webs C and D described above with reference to the diagram of Jig. 6 were impregnated with a solution of about 1 percent by weight of cellulose triacetate in acetone and then dried. The swelling capacity of the raw paper G after such impregnation i3 indicated at £ in i^ig. 6 and the swelling capacity of the raw paper web D after impregnation at It can be seen that the impregnated paper webs show only an extremely low swelling capacity. On the other hand the svjelling capacity after moistening with methyl alcohol is equal to, or greater than, with the on-impre nated paper webs. This shows that, despite the distribution of the acetone solution containing only 1 cellulose triacetate over the entire surface of the paper web, the cellulose triacetate greatly influences the behaviour of the paper fibers towards water.

Similarly impregnated paper webs 240 mm wide corresponding to the quality indicated for E and F in i?ig. 6 show, after longitudinal crisping and fraying with the use of alcohol as the volatile impregnating agent, subsequent drying and further processing into filter rods or cigarette filters, a substantially different behaviour triacetate in an acetone solution. It was found in several tests that such cigarette filters remove only small quantities of moisture from the smoke and. retain the volatile aromatic substances contained in the smoke to a much lower extent than do corresponding filters made of non-irapregnated paper webs. In any case the detrimental effect of the filters on the taste of the cigarette smoker is eliminated, or nearly so, by the use of filters containing such additives in accordance with the invention The diagram of Fig. 7 shows the influence of the concentration of cellulose triacetate as an additive to acetone used for the impregnation of raw paper webs of the paper quality described in Fig. 6 under D and F.

In the manner described above, filter rods were made from paper webs impregnated with methyl alcohol. The filter rods had a pulling resistance Z of 200 mm water column for a paper web without any impregnation. The changes in the pulling resistance after impregnation with an acetone solution with an increasing percentage K of cellulose triacetate are indicated by curve G which shows that even with as little as 0.5 percent by weight of cellulose triacetate in the acetone solution the resistance to pulling of the filter plugs drops from 200 mm water column to about 125 mm water column. AS the concentration of cellulose triacetate increases above about 2 percent by weight, only a small further drop of the resistance to pulling; is observed. ¾hile curve G' indicates the influence of impregnation of the raw paper web for filter rods made in two successive steps, the curve H plotted in Fig. 7 for comparison shows the influence of the concentration of cellulose acetate in acetone if the solution - - The impregnation in two successive steps may be effected, for example, in a device such as diagrammatically shown in Fig. 8. The raw paper web 1 supplied from the roll 2 is passed over a guide roll 20 and a dipping roll 21 into an impregnating solution 22 in the container 23. The impregnated paper web passes over the guide roll 24 biased by the roll 25 which ma consist of a elastic material so that an' excess of impregnating solution is squeezed off. The impregnated paper web subsequently passes through a drying station 26 in which the solvent of the impregnating solution 22 may be recovered, and is taken up by the supply roll 27 after drying. The paper web so impregnated may be processed into a longitudinally crimped, heavily frayed paper web ty means of the device shown in Fig. 1. Instead of the impregnation method by dipping the paper web into an impregnating solution 22 as shown, impregnation may be effected by any other known method, e.g. by spraying the impregnating solution on one or both sides of the paper web.

Since the impregnating liquid is volatile, the drying of the impregnated paper web proceeds very rapidly.

Accordingly, it is also possible, as diagrammatically shown in Fig. 9» to effect impregnation directly prior to processing the impregnated raw paper by a device according to Fig. 1. The paper web 1 delivered by the supply roll 2 may then pass e.g. between the rolls 30 and 31 and be impregnated by the liquid film taken up by the roll 30 from the impregnsting bath 32 in container 33. A drying station 34 then dries the impregnated paper web which subsequently passes into the moistening device 5 , 6, 7 as previously described with reference to Fig. 1.

Owing to the very fast drying of the longitudinally crimped webs of material, a device according to Fig. 1 can be directly connected to a high-speed cording machine of conventional design as diagraminatically shown in Fig. 10. The longitudinally crimped web 40 largely freed frosi the im eg ati g agent and running over the guide rolls 11 , 12 is directly fed into the inlet funnel 41 of the cording machine along with a wrapping band 48 supplied froti drum 47. rom the funnel 40 the longitudinally crimped web, which is gathered in the transverse direction, em ges as a wrapped cylindrical cord of e.g. 8.0 aim diameter; the projecting edge 42 of the wrapper is provided with a strip of glue in the device 43 , turned over and fastened during its passage through the heated moulding tool 44 so that the wrapped finished filter cord 49 is formed. 'Ho overcome friction, the endless conveyor belt 46 passes arounw. the guide rolls 45 and through the f nnel 41 and the moulding tool 44. 5he finished endless filter cord 49 is then divided in a conventional manner into filter rod3 which usually have a length of 66 to 120 mm corresponding to six times the length of a filter plug.

The use of volatile impregnating agents according to the invention is particularly suitable for adding flavoring substances to the impregnating agents, which is at times desirable. 34341/3

Claims (25)

1. A method of treating endless webs of fiber-containing material, particularly paper, to make it suitable for being gathered in a transverse direction and wrapped for the purpose of making an endless filter cord divisible into filter rods, the virtually inelastic web of material being passed through at least one nip between coacting rotating grooving and stretching rolls equipped with close intermeshing annular ribs which do not, however, contact one another, the web of material being clamped by the nnnular ribs and stretched in a direction transverse to that of travel, the transverse stretching being increased to the point of loosening and exposing fibers without complete destruction of the transverse cohesion of the material, wherein the web of material is treated, prior to its entry into the nip, with a volatile impregnating agent and freed therefrom upon emerging from the nip, the volatile impregnating agent having a boiling temperature lower than that of water and a heat of evaporation of less than 250 kcal/kg.

2. A method according to Claim 1, wherein the volatile impregnating agent is an alcohol such as methyl alcohol, ethyl alcohol or propyl alcohol.

3. A method according to Claim 1, wherein the volatile impregnating agent is a volatile ketone such as acetone..

4. A method according to Claim 1, wherein the volatile impregnating agent is an ether such as diethyl ether, or a thioether. 34341/5 - 30 -

5. A method according to Claim 1, wherein the volatile impregnating agent is an aromatic hydrocarbon such as benzene, toluono or jcylo o t light petroleum or a fraction.

6. A method according to Claim 1, wherein the volatile impregnating agent is a halogenated hydrocarbon such as ethyl chloride, chloroform, or carbon tetrachloride.

7. Δ method according to Claim 1, wherein the volatile impregnating agent is an ester such as ethyl acetate.

8. A method according to any preceding Claim, wherein additives are dissolved in the impregnating agent for forming a deposit on the web after the removal of the impregnating agent .

9. A method according to Claims 2 and 8, wherein the additive is hydroxy-polycarboxylic acid such as tartaric acid or citric acid.

10. A method according to Claims 3 and 8, wherein the additive is cellulose triacetate, cellulose acryl acetate, cellulose nitrate, hydrolysed cellulose and/or another cellulose compound ,

11. A method according to Claims 4 and 8, wherein the additive is cellulose triacetate, cellulose acryl acetate, cellulose nitrate, hydrolysed cellulose, another cellulose compound, and/or a polyhydric alcohol such as glycerine or glycol.

12. A method according to Claim 8, wherein the additive substance is such as to cause a chemical reaction on at least the surface of the fibers of the web of materials.

13. A method according to Claim 12, wherein the impreg a ing agent is an alcohol and the additive is a hydroxy-monocarhoxylic acid such as hydroxyformic acid or hydroxyscetic acid.

14. A method according to Claim 12, wherein the additive is a monocarboxylic fatty acid such as formic acid, acetic acid or propionic acid.

15. A method according to any one of Claims 1 to 7, wherein the web is impregnated , prior to processing with the volatile impregnating agent, with a liquid according to any one of Claims 8 to 14.

16. A method according to any preceding Claim, wherein 2 the paper web has a weight of between 20 and 50 g. per m .

17. A method according to any preceding Claim, wherein the volatile impregnating agent employed is such as exercise a cleansing action on the surface of the loosened and exposed fibers of the longitudinally crimped paper web.

18. A method according to any preceding .Claiia, wherein the volatile impregnating agent employed is such as to cause a reduction of the swelling capacity and/or a reduction in the rate of absorption of moisture and/or a reduction of the amount of absorption of steam from a stream of smoke by the web of material.

19. A method according to any preceding Claim, wherein the impregnating agent employed is such as to cause exposure of the fibers of the web of material from the web plane during passage of the web between the grooving and stretching rolls.

20. A method according to any preceding Claim, wherein the im re natin a ent is 34341/3 - 32 -

21. A method according to any preceding Claim, wherein the impregnating agent is diluted in water, the width of the dried longitudinally crimped web of material being adjusted by varying; the degree of dilution.

22. A method according to Claim 21, wherein the web of material is supplied, after its passage between the grooving and stretching rolls, to a rod making machine in which it is transversely gathered into a cylindrical cord, provided with a wrapper and made into filter rods of a certain lengt and prescribed, diameter by subdivision, the resistance to pulling of the filter rods being adjusted to a desired value by varying the degree of dilution of the volatile impregnating agent.

23. A method of treating endless webs of fiber-containing material according to Claim 1 substantially as hereinbefore described with reference to the accompanying drawings.

24. Webs treated by the method of any one of the preceding Claims.

25. Filter rods formed from webs according to Claim 24· ΑίΦ PARTNERS C:CB