US3400723A - Tobacco smoke filters made of paper - Google Patents

Description

United States PatentQifice 3,400,723 Patented Sept. 10, 1968 3,400,723 TOBACCO SMOKE FILTERS MADE OF PAPER Paul Adolf Miiller, Triesenberg, Liechtenstein, and Erich Barkowski, Aschaffstrasse 69, Aschafienburg, Germany No Drawing. Filed Feb. 20, 1967, Ser. No. 617,084 Claims priority, application Switzerland, Feb. 23, 1966, 2,626/ 66 14 Claims. (Cl. 131-467) ABSTRACT OF THE DISCLOSURE v Tobacco smoke filters, especially for filter-tip cigarettes, which do not impart a so-called paper taste to tobacco smoke passing therethrough in which the paper is substantially free of sulphurous compounds and ismade from a pulp into which is added a sulphur-free metallic compound of an acid from the group comprising acetic acid, propionic acid and formic acid in an amount to achieve a pH value less than 6.0 in the water container of the last screen of the paper-making machine. The compound preferably is aluminum acetate.

The present invention relates to improvements in tobacco smoke filters made of paper, particularly for filtertip cigarettes, in paper for such filters and in methods for producing such filters. More particularly, this invention relates to improving the taste qualities of such filters.

Filters containing paper are known and widely used for filter-tip cigarettes. One method, which is now practiced, for treating paper to make it into an efficient filtering material, i.e., filter paper for filter-tip cigarettes, includes passing a web of smooth raw paper between at least one pair of intermeshing grooving or corrugating rolls provided with axially spaced circumferential ribs. The rolls form in the paper a corresponding number of parallel grooves, i.e. corrugate the paper. During treatment by the rolls, the engagement of the ribs with the paper prevents any substantial transverse shrinking or gathering thereof so that, as a result, the paper web is stretched laterally. Such stretching loosens the fibers of the paper to form fuzzy areas with numerous projecting fiber ends on the surfaces of the grooved web at locations where the fibers are at least partially separated or pulled apart. In some cases the stretching may be to such an extent as to cause haphazardly-located, discontinuous longitudinal tears which have frayed fuzzy edges, although the web for all practical purposes substantially retains its transverse continuity.

This method of treating paper to render it more effective as a tobacco smoke filter is well known, as well as filter paper produced by such treatment, and filter rods or plugs made by laterally gathering such filter paper into an endless string or cord which is wrapped and then cut into filter rods or plugs of any desired length. Such method and products are disclosed, for example, in the following US. patents: Nos. 2,916,039; 2,931,748; 2,995,481; 3,161,557; 3,179,024; 3,226,280.

In accordance with the principal method used to date for grooving and laterally stretching smooth raw paper to the extent needed for efiicient filtering without completely destroying the lateral or transverse continuity of the web it is necessary, prior to the grooving treatment, to make the paper web soft or yielding by a suitable treatment e.g. by moistening with water or any other suitable liquid. As a result, the grooved and laterally stretched web must be dried after the corrugating and stretching treatment before being wound up on spools or bobbins, or before being made directly into filter rods or plugs. This known treatment method includes before, during or after the drying treatment, further deformation or mechanical working of the corrugated and stretched web by any appropriate device, for example, by pinch rolls having smooth or knurled surfaces which partially compress or flatten the corrugations and so minimize the existence of unobstructed through passages in filters made of such paper or greatly restrict such passages. The thus produced filter paper may be wound on spools or bobbins to be fed later to filter rod machines of well known design, or may be fed directly into a filter rod machine. In the abovedescribed known grooving and stretching method, it also is advantageous to heat the grooving and stretching rolls to a temperature up to several hundred F. though cold rolls are by no means insufficient.

Although the known treatment method, as described above, requires the paper to be quite moist during the grooving and stretching process, this moistening is not absolutely necessary. Smooth raw paper webs of some types be treated by passing through the nip of a pair of such intermeshing grooving or corrugating rolls without advance moistening. As so treated in the dry the paper web shows less distinctive or no longitudinal grooves but for lower grade demands of filtering qualities and of end face appearance, when made into a cigarette filter, such paper web treatment is commercially applicable and offers the advantage to omit any moistening and drying devices.

It may be pointed out that other means than the above explained pairs of grooving rolls are known for treating a paper web to produce fiber loosening and projecting fiber ends to render it more effective for use as a filtering material. For example, rolls provided with prongs of determined shape are sufficient for producing slot-like openings of desired shapes in a paper web treated with such rolls so that adhering struck out parts of the paper have frayed edges with a multitude of projecting fiber ends, as disclosed in US. Patent 2,847,286. It has been suggested also to produce lacerations haphazard in shape and size by passing a dry paper web through the nip between two intermeshing sets of axially-aligned and axially-spaced toothed discs as well as through the nip between a smooth soft rubber roll and a metal roll provided with axially-spaced circumferential ribs.

All cigarette filters made heretofore from paper webs, irrespective of their treatment to render them a more efficient filtering material, have the disadvantage, especially in cigarettes of light and mild tobacco mixtures, of producing a taste in the smoke which is well known to cigarette manufactures as paper taste. It is believed that this paper taste is not produced by substances given off from the paper filter into the smoke stream passing therethrough but rather by an absorption of smoke components in a different degree from filters of other material, especially cellulose acetate fibers. But the existence of a paper taste accompanying paper filters used with sensitive, i.e. light and mild, tobacco mixtures is a fact which is regarded occasionally by cigarette manufacturers as a deficiency.

While the cause of such paper taste is not known, it has been thought that the above-described moistening and drying steps, and the engagement of the moist paper with the hot metallic grooving and stretching rolls, may possibly be somewhat responsible. Tests have been shown, however, that paper filters made from a paper web treated, when dry, by non-metallic means to render it more effective as a filter for tobacco smoke have met with failure in respect to elimination or minimization of the paper taste.

Additionally, prior to this invention attempts have been made along other lines to reduce or eliminate the socalled paper taste attendant cigarette filters made of paper. Such efforts have included the addition of acid substances to the fluid used to moisten the paper as a preliminary to the grooving and streaching treatment. In

other cases, acid substances have been sprinkled onto the moistened web, either in advance of or subsequent to the grooving treatment, and in some instances have been sprinkled on the grooved web after it has been dried. Such substances have included acetic acid, formic acid, aluminous water and other acidic substances. All such attempts have met with failure, however, because paper webs treated with such substances, have a disagreeable odor and, moreover, tend to corrode metal parts of the grooving or lacerating apparatus or otherwise deleteriously affect its operation. Unsuccessful earlier efforts to reduce or eliminate the paper taste also have included the use of raw paper having a pH value lower than its normal value of 6.1 to 6.3. All such papers heretofore used, however, have not been satisfactory because they frequently have a yellow color, which is most unattractive to smokers, or have a reduced flexibility that renders them somewhat brittle and of a straw-like character. The brittle characteristic makes such paper completely unsatisfactory for a fiber loosening treatment, as aforesaid, so that such paper webs usually are ineffective as a filter material for tobacco smoke and furthermore have no appreciable reduction in the paper taste.

It is, therefore, an object of this invention to provide improved filter paper for use in the filters of filter-tip cigarettes and filter rods or plugs made therefrom, which, when in use, has a greatly reduced or negligible paper taste.

It is another object of this invention to provide a paper web made from a sulphur-free paper pulp into which is added a sulphur-free metallic compound of an acid from the group comprehending acetic acid, propionic acid and formic acid in an amount to achieve a pH-value less than 6.0 in the water container of the last screen of the papermaking machine, and the paper web then is corrugated and/or lacerated in a controlled manner to loosen its fibers, wrapped up, reshaped into an endless paper rope or filter cord of approximative round sectional shape and subdivided into filter portions of desired lengths.

Another object of this invention is to provide a tobacco smoke filter, which is made by subdividing an endless filter rope or cord containing paper in a wrapper and having an approximative round sectional shape, and wherein the paper is free from sulphurous compounds and contains a metallic compound of an acid from the group comprehending acetic acid, propionic acid and formic acid.

Other objects and advantages of the invention will become apparent from the following description.

Known tobacco smoke paper filters are normally made from raw paper, preferably of a weight of from about 20 to about 40 grams per square meter. During manufacture of such raw paper aluminum sulfate is incorporated into the paper pulp in order to increase the tensile strength of the dried paper. Aluminum sulfate has the property of somewhat increasing the coherence or adhesion of the fibers constituting the paper web. When such paper is used as a filter in filter-tip cigarettes containing light and mild tobacco mixtures the undesired so-called paper taste is imparted to the tobacco smoke.

It has been discovered and proved by a multitude of tests that the paper taste normally attendant paper filters is reduced or completely eliminated by this invention. To this end the raw paper web should be produced from a pulp substantially free from sulphuric compounds and containing no aluminum sulfate. To achieve the necessary glueing or adhesion and coherence of the fibers in the paper web other suitable compounds have to be substituted, for aluminum sulfate in the pulp, which possess the same desired property as aluminum sulfate in this regard but which have no sulphurous components. It has been found that aluminum acetate for example, is such a suitable compound when substituted in an amount such that the pH-value of the water in the container of the last screen of the paper-making machine is reduced to a value less than 6.0 or preferably less than 5.8. To accomplish this the aluminum acetate comprises from about 1% to about 2% by weight of the pulp. Such a paper Web, substantially free of sulphurouscompounds and having a higher acid content than normally, can be corrugated or lacerated by a fiber-loosening treatment in dry or moistened conditionto any desired extent and wound up on spools or bobbins which are made up into filter plugs later on, or may be fed directly into a filter rod machine for wrapping and forming in an endless filter rope which is subdivided into filter rods and/ or plugs of desired lengths.

The corrugated and/or lacerated paper webs produced continuously by the above described method can be easily made up into filters which possess mechanical qualities, for example tensile strength and dimensional stability, at least equivalent to the corresponding qualities of filters made of hitherto used paper webs. Also the raw paper embodying this invention has been found to possess mechanical qualities at least equivalent, and possibly better, than corresponding qualities of hitherto used raw paper. The following table compares relevant characteristics of the best quality raw paper used heretofore for making filter paper according to the above-described known process with raw paper embodying this invention.

COMPARISON OF QUALIIIES OF RAW PAPER USED HERE- TOFORE TO MAKE FILTER PLUGS WITH RAW PAPER ACCORDING TO THIS INVENTION It is evident from the foregoing table that raw paper for filters according to this invention has better mechanical qualities than raw paper used heretofore for tobacco smoke filters.

Filter-tip cigarettes have been prepared equipped with filters from longitudinally grooved, mutilated and lacerated paper Webs produced from paper according to this invention and having values according to the above table for socalled blind smoking tests by experts. These tests demonstrated that the paper taste hitherto common to cigarettes having paper filters is noticeable only to a negligible extent or not at all with filters embodying this invention. Further tests have shown that this phenomenon probably results from the fact, that in the paper and its cellulose fibers the aluminum sulfate is replaced by aluminum acetate and at the same time the grooved and/ or lacerated paper web is provided with a higher acid content. Without doubt the described filters provide a' noticeable improvement in taste qualities compared to all other known paper filters for cigarettes.

Other tests have proved that a further reduction of the pH-value below 5.8 to about 5.4 completely removes all eventual existing remainders of the paper taste and is accompanied by a further taste improvement. An increase of the acid content in the paper up to a range of pH values of from about 5.2' to about 5.0 does not produce any taste disadvantage; but the preferred range of pH values with this kind of paper'filter is from about 5.6 to about 5.3.

Extended tests have been made with filters made of paper webs having a complete replacement of thehitherto used aluminum sulfate by aluminumacetate according to the following Examples I and II, respectively.

Example I Into the beater containing paper pulp prepared according to well known methods but without any aluminum sulfate has been passed liquid aluminum acetate Al (OH) (CH COO) in small amounts whilst monitoring the pH value of the water in the container of the last screen of the paper-making machine. The addition of Al (OH) (CH COO) was continued until further addition no longer reduced the pH value, which condition was reached in the range of pH=5.8 to 5.6. A raw paper web of about 32 to 34 grams weight per square meter and with a cloudy" structural appearance was produced from such pulp and Wound up into a raw paper roll.

From this raw paper roll a paper web was continuously wound off with a speed of about 60 to 100 cm. per second, moistened, passed through the nip between a pair of heated rotating steel rolls provided with interfitting axially-spaced circumferential ribs to stretch the paper laterally and then dried by passing a heated dryer.

The treated paper web was provided with narrow longitudinal ridges, intermediate longitudinal grooves, i.e., a corrugated structure, and a multitude of irregularly distributed disconnected longitudinal tears. The web was fed into a filter rod machine of known design, gathered laterally to an endless rope of about 8.3 mm. diameter, wrapped, and subdivided into filter rods of desired length.

The filters produced according to Example I were attached to cigarettes and checked in respect to the nicotine and tars absorption as well as to the taste quality and compared to filters having the same draw resistance made from aluminum sulfate containing raw paper of the same weight treated in the same manner. The filtering effect of the acetate-containing paper filter is at least of the same value and according to many test results even higher than the sulfate-containing paper filter. The taste improvement of this acetate containing paper filter compared to sulfate containing paper filter has been proved beyond any doubt by so-called blind smoking tests of experts.

Example 11 The pulp in the beater was prepared as in Example I and aluminum acetate AI (OH) (CH COO) added up to a pHvalue in the water of the container of the last screen of about 5.8 to 5.6. Then diluted acetic acid CH COOH was admixed with the pulp up to a pH-value of the water from the last screen of about 5.4. The production of paper webs and filters was then carried out as described in Example I.

Filter plugs of 20 mm. length prepared according to Example 11 were attached to a tobacco column of 65 mm. length and tested and compared to filter plugs of the same length and identical draw resistance made from cellulose acetate fibers (Typ ESTRON 3.340) connected to identical tobacco colums. The filter plugs containing cellulose-acetate fibers were prepared in a known manner together with Driacetin as a softening agent whilst the filter plugs according to Example II were used without any additional preparation. The filtering efiiciency of the two filter plu-g types was checked and the following values of components in the smoke stream of one cigarette were found:

Miligrams Milligrams nicotine solid substances Cigarette with filter Example II 0.8 16 Cigarette with cellulose-acetate filter 1. 2 21 plugs.

It may be pointed out that paper webs and filter plugs produced according to Examples I and II are completely odorless and insipid. No trace of an odor exists in closed rooms used for long time storing of raw paper, treated paper webs and filter rods produced according to this invention in contrast to the objectionable odor accompanying filter rods which are made from raw paper impregnated subsequent its production with acid liquids as described above. Also the grooving and lacerating treatment of raw paper produced as described in Examples I and II, by passing between heated metal rolls subsequent to a tmoistening step and followed by a drying step, can be carried out without any odor indicating the presence of acetic compounds or acetic acid added into a pulp. Moreover no corrosion of metallic parts exists whilst raw paper embodying this invention is in contact therewith while' being treated in suitable devices.

A quantitative chemical analysis to ascertain the critical substances in the raw paper or filter rods is rather difficult but suitable methods for a qualitative examination are available. For a detection of aluminum sulfate normally contained in paper filters, but not allowable according to this invention, an examination using chloride of barium is preferred which shows in known manner a deposit of barytes (barium sulfate) if sulfate compounds are contained in the paper. The qualitative detection of acetic compounds in paper filters is more difficult but possible using the known Kadodyl check or the potassium bisulphate check. The first mentioned check is performed by a reaction of arsenic trioxyd and the presence of acetates is indicated by an odor of garlic. The second mentioned check results in a typical acetic acid odor.

Consequently the lack of sulfates and the presence of acetates in a paper web and in paper filter plugs can be positively substantiated and constitute material features of the products with satisfactory distinctness.

The above described examples and embodiments of the present method as well as the products thereof relate to a replacement of aluminum sulfate normally contained in paper webs by aluminum acetate with or without additional acetic acid. It may be pointed out, however, that the present method and the products thereof are not restricted to the mentioned replacement substances. An improvement of paper filter taste qualities can be achieved also by replacing aluminum sulfate in paper webs by other aluminum compounds of sulphur-free monovalent organic carbon acids as for example formic acid HCOOI-I or propionic acid C H COOH. The taste qualities of paper filters are also improved when aluminum sulfate is replaced by calcium acetate or magnesium acetate or other calcium or magnesium compounds of sulphur-free monovalent organic carbon acids, but such a replacement also influences mechanical and other properties of the paper.

We claim:

1. A tobacco smoke filter, especially for filter tip cigarettes, generally in the shape of a cylindrical plug longitudinally permeable to gases and a consisting essentially of paper, characterized in that the paper is substantially free of sulphurous compounds and contains aluminum acetate as a substitute for aluminum sulfate sizing agent.

2. A tobacco smoke filter according to claim 1, characterized in that the paper contains the aluminum acetate in a small percentage of the paper weight not exceeding about 2% by weight.

3. A tobacco smoke filter according to claim 1, characterized in that the pH-value of the paper is less than 6.0.

4. A tobacco smoke filter according to claim 1, characterized in that the pH-value of the paper is less than 5.8.

5. A tobacco smoke filter according to claim 1, characterized in that the pH-value of the paper is in the range of from about 5.6 to about 5.3.

6. A tobacco smoke filter according to claim 1, characterized in that the paper has a weight of from about 20 to about 40 grams per square meter.

7. A tobacco smoke filter according to claim 1, characterized in that the fibers of the paper are loosened and at least partly pulled apart and the paper is covered by projecting fiber ends.

8. A tobacco filter plug according to claim 1, characterized in that the paper comprises a transversely gathered sheet having a corrugated structure in transverse section.

9. Tobacco smoke filter fibrous sheet material consisting essentially of porous, smoke permeable paper substantially free of sulphurous compounds and containing aluminum acetate as a substitute for aluminum sulfate sizing agent.

10. Fibrous sheet material according to claim 9 characterized in that the paper contains the aluminum acetate in a small percentage not exceeding about 2% by weight of the pulp from which the paper was made.

11. Fibrous sheet material according to claim 9 characterized in that the pH-value of the paper is less than 6.0, as measured by the water in the container for the last screen of the machine on which the paper was made.

12. Fibrous sheet material according to claim 9 characterized in that the pH-value of the paper is less than 5.8, as measured by the water in the container for the last screen of the machine on which the paper was made.

13. Fibrous sheet material according to claim 9 characterized in that the pH-value of the paper is in the range of from about 5.6 to 5.3, as measured by the water in the container for the last screen of'the machine on which the paper was made.

14. Fibrous sheet material according to claim 9 characterized in that the paper has a weight of from about 20 to about 40 grams per square meter.

References Cited UNITED STATES PATENTS 1,808,068 6/1931 Rafton 162181 2,711,371 6/1955 Lurie 162-181'X 2,847,086 8/1958 Muller 131--216 X 2,995,481 8/1961 Muller 131261 X 3,049,468 8/1962 Hinton et a1 162181 X 3,128,223 4/1964 Rosenberg et al 1 62-181 FOREIGN PATENTS 1,022,513 1/ 1958 Germany.

745,245 2/1956 Great Britain.

SAMUEL KOREN, Primary Examiner.

D. J. DONOHUE, Assistant Examiner.