US3674540A - Method of making a filter for tobacco smoke - Google Patents

Abstract

A HIGHLY POROUS FILTER FOR TOBACCO SMOKE MADE UP OF A DEMINERALIZED, DEFATTED, GAS-FLUFFED AND BLEACHED WOVEN COTTON FABRIC GAUZE IMPREGNATED WITH A MIXTURE OF WATER SOLUBLE CHLOROPHLL, TANNIC ACID AND GLYCERINE. THE BLEACHED FABRIC IS DEFATTED BY DIPPING IN AN AQUEOUS CAUSTIC SODA SOLUTION FOLLOWED BY RINSING AND DRYING. DEFATTING INCREASES THE POROSITY AND SURFACE AREA OF THE FABRIC, OF THE THREADS THEREOF AND OF THE FIBERS THEMSELVES, THEREBY INCREASING THE AMOUNT OF THE CHLOROPHYLL-TANNIC ACID-GLYCERINE MIXTURE WHICH CAN BE SUBSEQUENTLY ABSORBED AND/OR ADSORBED BY THE FABRIC AND INCREASING THE CAPACITY OF THE FABRIC TO RETAIN, AND THEREBY REMOVE FROM THE TOBACCO SMOKE, THE TOXIC MATERIALS IN SUCH SMOKE. THE DEFATTED FABRIC IS DEMINERALIZED BY DIPPING IN AN AQUEOUS HYDROCHLORIC ACID SOLUTION. DEMINERALIZING FURTHER INCREASES THE POROSITY AND SURFACE AREA OF THE FABRIC, THE THREADS AND THE FIBERS, THEREBY FURTHER INCREASING THE AMOUNT OF THE AFORESAID MIXTURE WHICH CAN BE ABSORBED AND/OR ADSORBED BY THE FABRIC AND THE CAPACITY OF THE FABRIC TO REMOVE THE TOXIC MATERIALS IN THE TOBACCO SMOKE. THE DEFATTED, DEMINERALIZED FABRIC IS GAS-FLUFFED BY DIPPING THE FABRIC, WHILE IT STILL CONTAINS HYDROCHLORIC ACID FROM THE DEMINERALIZING STEP, INTO A SOLUTION OF SODIUM BICARBONATE TO NEUTRALIZE THE HYDROCHLORIC ACID AND GENERATE IN THE INTERSTICES OF THE FABRIC AND THREADS CO2 GAS WHICH THINS OR SPREADS OR DISPERSES AND THEREBY FLUFFS THE FABRIC AND THREADS TO FURTHER INCREASE THE SURFACE AREA AND POROSITY THEREOF, FOLLOWED BY DRYING. THE MIXTURE OF CHLOROPHYLL, TANNIC ACID AND GLYCERINE IS APPLIED TO THE DEFATTED, DEMINERALIZED AND GAS-FLUFFED FABRIC BY DIPPING IN A SOLUTION OF SUCH MIXTURE IN WATER AND ETHYL ALCOHOL FOLLOWED BY DRYING. THE TREATED FABRIC, IS LOOSELY PACKED WITHIN A CONFINED VOLUME TO PROVIDE A HIGHLY EFFICIENT FILTER, WHICH IS EFFECTIVE TO REMOVE AS HIGH AS 85% OF THE TARS PRESENT IN CIGARETTE OR CIGAR SMOKE WITHOUT DELETERIOUSLY AFFECTING DRAW. THE FILTER MAY TAKE THE FORM OF A CIGARETTE OR CIGAR FILTER WHICH MAY BE MANUFACTURED AND SOLD AS PART OF THE CIGARETTE OR CIGAR OR IT MAY BE PACKED IN A CAPSULE FOR INSERTION IN A CIGARETTE OR CIGAR HOLDER OR IT MAY BE PACKED DIRECTLY IN A DISPENSABLE CIGARETTE OR CIGAR HOLDER.

Description

y 4, 1972 s. PERGAMlNOS 3,574,540

METHOD OF MAKING A FILTER FOR TOBACCO SMOKE Filed Aug. 26, 1969 INVENTOR STAVROS PERGAMINOS ATTORNEYS United States Patent 3,674,540 METHOD OF MAKING A FILTER FOR TOBACCO SMOKE Stavros Pergaminos, Pythias St., Athens (809), Greece Filed Aug. 26, 1969, Ser. No. 853,087 Int. Cl. A24c 5/50 US. Cl. 117-56 9 Claims ABSTRACT OF THE DISCLOSURE A highly porous filter for tobacco smoke made up of a demineralized, defatted, gas-fluffed and bleached woven cotton fabric gauze impregnated with a mixture of water soluble chlorophyll, tannic acid and glycerine.

The bleached fabric is defatted by dipping in an aqueous caustic soda solution followed by rinsing and drying. Defatting increases the porosity and surface area of the fabric, of the threads thereof and of the fibers themselves, thereby increasing the amount of the chlorophyll-tannic acid-glycerine mixture which can be subsequently absorbed and/or adsorbed by the fabric and increasing the capacity of the fabric to retain, and thereby remove from the tobacco smoke, the toxic materials in such smoke. The defatted fabric is demineralized by dipping in an aqueous hydrochloric acid solution. Demineralizing further increases the porosity and surface area of the fabric, the threads and the fibers, thereby further increasing the amount of the aforesaid mixture which can be absorbed and/or adsorbed by the fabric and the capacity of the fabric to remove the toxic materials in the tobacco smoke. The defatted, demineralized fabric is gas-fiulfed by dipping the fabric, while it still contains hydrochloric acid from the demineralizing step, into a solution of sodium bicarbonate to neutralize the hydrochloric acid and generate in the interstices of the fabric and threads CO gas which thins or spreads or disperses and thereby fiuffs the fabric and threads to further increase the surface area and porosity thereof, followed by drying.

The mixture of chlorophyll, tannic acid and glycerine is applied to the defatted, demineralized and gas-fluffed fabric by dipping in a solution of such mixture in water and ethyl alcohol followed by drying.

The treated fabric is loosely packed within a confined volume to provide a highly efficient filter, which is effective to remove as high as 85% of the tars present in cigarette or cigar smoke without deleteriously affecting draw. The filter may take the form of a cigarette or cigar filter which may be manufactured and sold as part of the cigarette or cigar or it may be packed in a capsule for insertion in a cigarette or cigar holder or it may be packed directly in a dispensable cigarette or cigar holder.

BRIEF SUMMARY OF THE INVENTION The harmful effect and danger to the health caused by the poisonous and toxic combustion products in tobacco smoke are well known and have been the subject of much research for many years.

Although nicotine, a highly poisonous and toxic substance, has received the most attention, researches have proven that harm is also caused by the tars in the smoke which are saturated with hundreds of by-products re sulting from the pyrolysis of the organic ingredients contained in tobacco leaves.

Numerous filters and filter materials based on mechanical filtering and/or chemical filtering to remove these noxious materials from the smoke have been suggested since the latter part of the nineteenth century.

Cotton, sponge, pumice powder, sand, charcoal, silica gel, metal screws, tannic acid, citric acid, tartaric acid,

3,674,546 Patented July 4, 1972 r3 ce suggested. See US. Pat. Nos. 1,784,566, 2,116,706 2,171,770, 2,203,864, 2,762,375, 134,713, 253,296, 882,913, 712,818, 2,345,676, 2,460,285, 2,716,411,

2,832,351, 2,460,284 and 757,514.

However, the problem is still a serious one and has remained in the main part unsolved.

Part of the problem is not only the limited ability of the filter material to remove these harmful substances from the tobacco smoke but also the limited capacity of the filter material to do so, i.e., although in many cases, it is effective to remove some of the harmful substances, e.g. nicotine, nevertheless a substantial amount still remains in the smoke which enters the mouth of the smoker. Some filter materials will effectively remove some of the harmful substances but not others and even with respect to the particular substances which they will remove, their capacity to do so is limited so that some of even those substances remain in the smoke. This is in part due to the limited amounted of the filter material necessitated by the maximum mass and volume which a filter can practically occupy and to the limited practical time of contact. In this respect, another problem is to remove such substances without increasing the drawing effort by the smoker (by increasing resistance to flow of the smoke) to a point at which it is difficult for him to draw the smoke through the filter. This severely limits maximum contact time and maximum intimacy of contact and also limits the mass and volume of the desired filter material which can be used.

Accordingly, it is a primary object of the present invention to provide a novel filter material and method for making the same, which removes substantially greater amounts and a substantially greater number of the aforesaid harmful and toxic combustion products in tobacco smoke without deleteriously affecting draw.

This is achieved in accordance with the present invention by impregnating a porous defatted and/or demineralized and/ or gas-fluffed (preferably defatted, demineralized and gas-fluffed) cotton fabric gauze, preferably bleached cotton, with a material selected from the group consisting of a hygienic water soluble chlorophyll, such as that which is sold in the form of solid lumps under the name XX Uncoppered Chlorophyll by Chlorophyll Co., Wharf Road, W. D. London, England, and which is copper-free, tannic acid, glycerine and a mixture of two or more of the same, a mixture of the three being preferred.

Defatting of the cotton fabric is achieved by applying to it, preferably by dipping, an aqueous solution of a strong alkali, such as an alkali metal hydroxide, preferably caustic soda, to saponify the fatty materials and solubilize any other alkali soluble materials in the cotton fabric and thereby remove them. This increases the porosity and surface area (decreases density) of the fabric, the threads and the fibers thereof and thereby increases the amount of the subsequent chlorophyll-tannic acidglycerine mixture and the amount of toxic gaseous, liquid and solid materials in the tobacco smoke which are retained by the fabric. The caustic treated fabric is then rinsed and dried.

Demineralizing of the defatted fabric is achieved by applying to it, preferably by dipping, an aqueous solution of a strong but non-corrosive mineral acid, preferably hydrochloric acid, to solubilize the minerals and other acid soluble materials in the fabric and thereby remove them. This further increases the porosity and surface area (decreases density) of the fabric, the threads and the fibers thereof to further increase their capacity to retain the subsequent chlorophyll-tannic acid-glycerine mixture as well as the gaseous, liquid and solid toxic materials in the tobacco smoke.

Gas flufiing of the defatted and demineralized fabric is achieved by applying to the fibers, preferably by dipping, a solution of a gas forming compound, preferably sodium bicarbonate, which reacts with the residual acid in the fabric to neutralize it and thereby generate in the interstices of the fabric and threads gas bubbles, CO bubbles in the case of sodium bicarbonate, which expand and flow through such interstices to thereby disperse, spread and thin out (open) the fibers and threads of the fabric to fluff and soften them, thereby increasing the porosity and surface area (decreases density) thereof and of the fabric and, accordingly, their capacity to retain the chlorophyll-tannic acid-glycerine mixture, as well as the gaseous, liquid and solid toxic materials in the tobacco smoke. This fluffing or dispersion or thinning of the fabric, its threads and its fibers by generating a gas therein is hereinafter sometimes referred to as gas-fiufling" and the fabric so treated as gas-fiuffed.

It is believed that the CO HCl and caustic treatments condition the fabric in other ways to increase its filtering effect after impregnation with the aforesaid mixture. Because these pretreatments increase the amount of chlorophyll-tannic acid and glycerine which are retained by the fabric and which remove toxic materials from the tobacco smoke chemically as Well as physically, they increase the amount of such toxic materials removed from such smoke. Also, because they increase the porosity and surface area (decrease density) of the fabric and threads and even of the fibers themselves, they increase the amounts of such toxic materials which are physically removed from the smoke by physical absorption or adsorption, i.e., they increase the physical capacity of the fabric to retain such toxic materials. These pretreatments, in addition to increasing porosity and surface area, also appear to make the pretreated exposed fiber surfaces themselves more receptive to the chlorophyll, tannic acid and glycerine and more receptive to the toxic materials in the tobacco smoke. 'It is believed that the removal of the acid soluble and alkali soluble materials in the fibers coupled with the gas flufiing leaves the individual fibers in the form of a highly porous open lacework or latticework skeleton to thereby substantially increase the porosity of the fabric as well as the surface area, i.e. the spaces formerly occuplied by these removed materials become open and unoccupied pores and the CO gas expands these spaces as Well as dispersing the individual fibers and threads. It is believed that many of these pores formed in the fibers and threads are microscopic in size.

After the gas-fiuffing step the fabric is dried.

The impregnation of the pretreated fabric, i.e. pretreated by defatting, demineralizing and gas-fiufiing, with the chlorophyll-tannic acid-glycerine mix is preferably carried out by applying a solution of these three compounds, preferably by dipping the pretreated fabric in such solution. A preferred solution is one in water, which is a solvent for the chlorophyll, and an alcohol solvent, preferably pure hygienic ethyl alcohol, for the tannic acid. Thereafter, the fabric is dried to evaporate the water and alcohol solvent thereby leaving the chlorophyll, tannic acid and glycerine deposited on the surfaces of the fibers and also probably absorbed in the fibers. It is believed that these compounds are deposited on the interior fiber surfaces forming the tiny pores left by the defatting, demineralizing and gas-flulfing steps. However, the resulting fabric is still highly porous. Accordingly, the tobacco smoke can flow freely through it.

The water soluble chlorophyll, which may be a water soluble chlorophyllin made by acid or alkaline treatment of water insoluble chlorophyll but which is preferably copper-free, when deposited in and on the cotton fibers in accordance with the invention, has the capacity to absorb large amounts of a large number of combustion by-products in the tobacco smoke resulting from pyrolysis of the tobacco, including carbonic acid. It is not understood whether this is a physical or a chemical phenomenon but it is believed that both are involved.

The tannic acid withholds and precipitates substantially all of the alkaloids and nicotine in the tobacco smoke, converting them into insoluble salts which are retained on the filter fibers.

The glycerine, when deposited on the fiber surfaces of the fabric tissue, increases substantially the aflinity between the harmful gaseous, liquid and solid ingredients in the smoke and such surfaces to thereby increase substantially the removal of such ingredients. It also increases the amounts of tannic acid and chlorophyll which are retained on the fiber surfaces to thereby increase the removal of toxic materials in the smoke in this way. It is believed that it is the molecular water in the glycerine which provides the beneficial effect. In any event, the glycerine keeps the filter in an apparent moist or wet condition without making it Wet to the touch to thereby increase retention of tannic acid and chlorophyll by the fibers and also increase the absorbability and/or adsorbability of the filter to solid and gaseous elements in the tobacco smoke, such as C0, C0 aldehydes, benzopyrene, etc.

Other non-toxigenic, organic polyhydroxy (polyhydric) compounds such as mannitol, propylene glycol, etc. can be used in place of glycerine but pure, hygienic glycerine is by far preferred.

As aforesaid, it is preferred to use a bleached woven cotton fabric gauze since the bleaching removes color bodies and the like from the fibers to thereby increase the porosity thereof and to make the fabric more absorbent during treatment thereof, particularly during the pretreatment stages. A preferred bleaching process is with a sodium perborate solution with or without citric or tartaric acid, egg. by immersion in a sodium perborate aqueous solution. However, calcium hypochlorite or hypochlorous acid can be used. In fact, conventionally bleached, high grade and clean cotton can be used.

It is preferable to avoid applying substantial compression forces on the fabric during the processing thereof since such forces tend to compress the fragile fibers and thereby decrease the porosity thereof by closing the pores. In this respect, as aforesaid, the defatting, demineralizing and gas fluffing steps reduce the individuals fibers and the threads made up thereby to a fragile latticework skeleton which is highly porous. Accordingly, hot cylinders should not be used for drying and cold cylinders should not be used to squeeze the fabric. Any pressure above 3 kilograms per 0.25 m? of fabric is apt to be harmful.

It is also preferred to process the fabric at temperatures not exceeding 35 C. to 45 C. to avoid damaging the fragile fiber structure and to avoid decomposition of the glycerine and chlorophyll. Also, tannic acid and sodium bicarbonate are sensitive to temperatures above 60 C. This is another reason for not using hot cylinders for drying. Room temperature (ZZZ-35 C.) is preferred.

Preferably, contact of the fabric with metal surfaces should be avoided during and after processing since metal is apt to react with the chemicals used to discolor the fabric and reduce filtering effect.

Since the chlorophyll is sensitive to heat and light, it is best not to carry out the dipping step in the cholorophyll mix in direct sunlight and it is best not to expose the finished filter to direct sunlight for sustained periods of time.

Because of the desirability of avoiding elevated temperatures and pressures, it is best to remove excess water or solution from the fabric by letting it drain and to dry the fabric by hanging it in air. Any squeezing should be light.

The porous woven cotton fabric gauze is preferably of clean, high quality, low ash, long cotton fibers.

Retention of the chlorophyll, tannic acid and glycerine mixture and each of them and the beneficial effect thereof in removing toxic materials in the tobacco smoke without excessive incerase in draw is maximized with the use of cotton fabric, as compared for example to paper.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a longitudinal section through a non-disposable cigarette holder containing a disposable filter capsule packed with an embodiment of the filter material of the present invention.

FIG. 2 is a section taken along the line 22 of FIG. 1.

FIG. 3 is an end view of the larger end of the filter capsule of FIG. 1.

FIG. 4 is a longitudinal section through a disposable cigarette holder containing an embodiment of the filter material of the present invention.

FIG. 5 is a second taken along the line 5-5 of FIG. 4.

FIG. 6 is a plan view of the fabric filter of FIGS. 1 t with the fabric laid fiat.

DETAILED DESCRIPTION Clean, high quality, bleached long fiber, Greek (from the Kopais Lake region) cotton thread of low ash content and of high purity were woven into a gauze-like fabric 0.4 mm. thick and having 1660 warp threads per m., 1170 weft or cross threads per m., a hole area of 0.25 mm. (0.5 mm. x 0.5 mm.), a weight of 50 grams/m. of fabric, a density of 0.125 gram/cc. and a total surface area of 1.3 m? per square meter of fabric. The thickness of the threads was 0.30 mm. and the pore volume was 0.125 cc. per gram of fabric.

The fabric was cut into pieces between one and two square meters. These pieces were immersed in a 5% aqueous caustic soda solution for twelve hours in a nonmetallic, caustic-resistant (porcelain or plastic or glass) container after which they were removed and rinsed thoroughly with fresh water until their surfaces became neutral to heliotrope or litmus paper either by running tap water on them or immersing them in a non-metallic container of tap water into which fresh water was continuously flowed to continuously replace the Water in the container.

The fabric pieces were then hung over a hemp or plastic (not metal) rope in air at room temperature to drain and dry. If desired, excess water can be squeezed out of the fabric pieces by squeezing them gently by hand or with non-metallic, e.g. wood, tools.

After the fabric pieces were completely dry to the touch they were immersed in a 35% aqueous hydrochloric acid solution in a non-metallic, acid-resistant (porcelain or plastic or glass) container at room temperature for forty eight hours after which the fabric pieces were removed and again hung over a hemp or plastic (not metal) rope in air at room temperature to drain the excess solution from the fabric. If desired such excess solution can be removed by squeezing gently by hand or with wooden, but not metallic, tools.

Before the pieces were dry, i.e. while they were still moist and contained residual hydrochloric acid, they were dipped in a 12% aqueous solution of sodium bicarbonate in a non-metallic (porcelain or plastic or glass) container at room temperature until the fabric was rendered neutral to heliotrope or litmus paper. The sodium bicarbonate neutralized the residual hydrochloric acid in the fabric to generate CO bubbles which can be observed. If necessary, sodium bicarbonate may be added as required to neutralize the fabric.

After the fabric pieces had a neutral pH they were removed and hung over a hemp or plastic (not metallic) rope to drain and dry until they were dry to the touch.

After the tissues were dry they were immersed from 5 Chlorophyll 150 Ethyl alcohol chemically pure ethyl alcohol and 5% pure water) 5,000 Chemically pure glycerine v 5,000

Distilled water 10,000

made by dissolving the tannic acid in the alcohol in a porcelain or plastic or glass container and the chlorophyll in the water in a porcelain or plastic or glass container followed by mixing the two solutions together in a porcelain or plastic or glass container followed by mixing the glycerine into the resulting mixture of solutions until the mixture is homogeneous.

The fabric pieces were then removed and hung on a hemp or plastic (not metallic) rope to drain and dry in the shade and in air at room temperature. If desired excess solution can be removed by squeezing gently by hand or by non-metallic tools, e.g. wood, until no streaks of liquid appear on the surfaces, followed by drying.

The pore volume of the final treated and dried fabric was 0.125 cm. per gram of fabric.

Any of the aforesaid drying steps can be carried out in a vacuum if desired.

The treated fabric has now become a filter. Exposure of it to direct sunlight should be avoided or kept to a minimum because of the sensitivity of the chlorophyll to direct sunlight.

The fabric was cut into strips 10 cm. x 2 cm. in dimension (20 cm?) and a strip 2 in FIGS. l-3 was loosely packed in a disposable tapered plastic filter capsule 4 molded from a blue, translucent polystyrene, such capsule having four triangular shaped apertures 6 at its smaller end and four triangular shaped apertures Sat its larger end, the total cross sectional area of the four apertures at each end being 6 mm Typical dimensions of the capsule are: length0.23 m.; internal diameter at big end-@0085 m.; internal diameter at small end .0075 m.; wall thickness.001 m.; and volumel.5 cmfi. The large end of the capsule is in the form of a removable cap 10 which is removed from the capsule to pack the fabric strip in the capsule followed by replacing the cap on the capsule, the fit between the cap and capsule being a snug one. The shape and arrangement of the apertures at the small end are the same as those at the large end disclosed in FIG. 3.

The capsule was then placed in the chamber 12 formed in the cigarette holder 14, as shown. The cigarette holder is made up of a mouth piece 16 and a cigarette holding piece 18, the two pieces being threaded together by the externally threaded metal insert 20 pressed into the end of the mouth piece opposite from the tip. A threaded portion of the insert 20 protrudes from the end 22 of the mouth piece as shown and is threaded into the internally threaded end 24 of the cigarette holding piece opposite from the cigarette receiving end 26. The mouth piece 16 and cigarette holding piece 18 each has an internal shoulder 23 and 25, respectively, forming the open end walls of the capsule receiving chamber 12, such chamber being located in part in the end 22 of the mouth piece and in part in the end 24 of the cigarette holding piece. The capsule is received in the chamber with the large end located in the cigarette holding piece and the small end in the mouth piece so that smoke passes through the capsule from large end to small end.

The internal periphery of the chamber 12 is contoured so that the external periphery of the capsule fits snugly against the internal periphery of the chamber, particularly that portion formed by the metal insert and the portion adjacent the wide end of the capsule to form a seal and to hold the capsule firmly so that smoke cannot flow around the capsule but must pass through the interior of the capsule and hence through the packed treated fabric before passing to the tip of the mouth piece. Actually, the tapered capsule is wedged into the metal insert to hold it firmly. Note also in FIG. 1 that the end walls of the chamber are designed so that they do not block the apertures at the ends of the capsule when the capsule is so held.

Tests showed that the filter capsule shown in FIGS. 1-3 removed between 75 and 85% of the tars in the cigarette smoke without deleteriously reducing draw. In fact, reduction in draw was not noticeable when the cigarette holder was used without and then with the filter capsule.

Tar removal dropped off rapidly after ten to twelve cigarettes because the filter pores became loaded and plugged with the large amount of tars removed.

A strip of the fabric filter described above may also be packed in a confining cylindrical container (e.g. of paper or cork) of the type conventionally used to make cigarette filter tips and of the same diameter as the cigarette and secured to the end of the cigarette in conventional manner to form a cigarette filter tip. The tar removal achieved when the filter fabric is used in this way about the same as with the filter capsule of FIGS. l-3.

The strips of fabric filter described above may also be used with a disposable plastic (e.g. polystyrene) cigarette holder 27, as shown in FIGS. 4 and 5, shaped at one end 28 to form a tip and having pressed in the other end 30 thereof a cup 32, e.g. of metal, for receiving the cigarette end and the bottom of which is apertured at 34 for passage of smoke. A strip 2 of fabric filter made as aforesaid was loosely packed within the hollow length of the holder between insert 32 and tip 28. With such an arrangement, sixty five to seventy five percent of all the tars in the cigarette smoke was removed from ten cigarettes.

Preferably, the bleached fabric before treatment has a density of between 0.1 and 0.15 gram/cm. more preferably between 0.12 and 0.13 g./crn. a unit weight of between 40 and 60 grams/m more preferably between 48 and 51 g./m. a thickness of between 0.2 and 0.6 mm., a hole size of between 0.15 and 0.35 mmfl, a

thread thickness of between 0.1 and 0.5 mm., morepreferably between 0.2 and 0.4 mm., a thread density between 1640 and 1680, more preferably between 1650 and 1670, warp threads per m. and between 1150 and 1190, more preferably between 1160 and M80 Weft or cross threads per m., a total sun-face area ranging from 0.07 to 2.5, preferably from 1.0 to 2 n'r /m. of fabric and a pore volume of between 0.100 and 0.150 cm. per gram of fabric. The pore volume of the final fabric filter is preferably between 0.100 and 0.165 cm. more preferably between 0.120 and 0.155 cm. per gram.

The concentration of caustic soda in the caustic dip should not be so great that charring of the cotton occurs but should be sufficient to saponify at least most of the fatty substances in the fabric. Concentrations of from 3% to by weight are preferred, a more preferred concentration range being from 4 to 7%. The duration of the caustic dip should preferably be sufiicient to solubilize the caustic-soluble materials in the fabric.

The HCl concentration in the acid dip should not be so high as to char the cotton fibers but should be sufiicient to solubilize at least most of the minerals and other acidsoluble materials in the fabric. Concentrations from 10 to 40% by weight are preferred, a more preferred range being between and The duration of the HCl dip should preferably be sufiicient to solubilize the acid-soluble materials in the fabric.

The concentration of sodium bicarbonate in the sodium bicarbonate dip may vary and is not critical so long as there is enough provided to neutralize the residual hydrochloric acid. However, the higher it is the better since the higher it is the more violent is the gasifying action. However, the concentration should preferably not be greater than that which can be dissolved in order to avoid the fabric picking up solid sodium bicarbonate particles. A preferred concentration is between 5% by weight and a saturated solution. The duration of this dip is the time it takes to neutralize the residual acid in the fabric.

After treatment with the sodium bicarbonate, squeezing or compression of the fabric should particularly be avoided since it may disturb and compress the CO dispersed and thinned fibers.

The concentration of solutes or active ingredients, i.e. tannic acid, chlorophyll and glycerine, in the final dip of the example is about 25% by weight Concentrations from 15 to 40% are preferred, the maximum being dictated by the maximum amount of the solutes which can be dissolved in a free flowing solution. Of course, the less the concentration, the less is the amount of these solutes retained on the fibers.

The amount of chlorophyll should preferably be greater than the amount of tannic acid and the amount of glycerine should preferably be substantially greater than either or both of the other two.

In the example, the tannic acid constituted about 2% by weight of the tannic acid-chlorophyll-glycerine, the chlorophyll constituted 2.86% by weight thereof and the glycerine constituted 95.14% by weight thereof.

The maximum amounts of the tannic acid, chlorophyll and glycerine are dictated by the solubility thereof in the solution system.

The concentration of tannic acid preferably ranges between 1 and 10.5%, more preferably between 1.50% and 5.00%, by weight of the tannic acid, chlorophyll and glycerine.

The concentration of chlorophyll preferably ranges between 1.5 and 10%, more preferably between 2.50% and 3.0%, by weight of the tannic acid, chlorophyll and glycerine.

The concentration of glycerine preferably ranges from to 97.5%, more preferably between and 96%, by weight of the tannic acid, chlorophyll and glycerine.

The aforesaid percentages of each of these three compounds based on the total weight of all three are about the same in the solution thereof and in the final fabric filter.

In the example, the amount of tannic acid, chlorophyll and glycerine retained in the final dried fabric filter, was 102.5% of the weight of the fabric. This amount may vary considerably depending upon conditions. Preferably, it ranges from 85 to 105%, more preferably from 85 to The duration of the final dip is not particularly critical. Two or three minutes are usually adequate and there is no particular advantage in more than six or seven minutes.

Where the fabric is not purchased from the textile manufacturer in bleached condition, it may be bleached by immersion at room temperature into a 45% aqueous sodium perborate solution (50 grams sodium perborate dissolved in 950 grams of water) for twelve hours followed by addition of 1% of citric or tartaric acid. Calcium hypochlorite or hypochlorous acid may also be used.

Although the ethyl alcohol is evaporated, nevertheless, it is believed that it not only functions as a solvent for the tannic acid but it also has a beneficial effect on the cotton fabric and/or the chlorophyll and/or the glycerine and/ or the tannic acid to increase the amount of the mixture and the tobacco smoke tars which are retained by the fabric. It makes the chlorophyll-tannic acid-glycerine mix more diifusible throughout the fabric, i.e. more capable of spreading throughout the fully porous fabric. In fact, small amounts of the ethyl alcohol may be retained by virtue of the other materials in the mixture or by the small micropores in the fibers. To the extent that any of this alcohol remains in the fabric, it forms insoluble salts with the alkaloids, e.g. morphine, atropine, nicotine, etc., in the tobacco smoke.

Drying can be carried out in an oven but in such case the oven temperature should preferably not be greater than 45 C. and the fabric should be moved therethrough carefully in a delicate manner so as not to disturb the delicate porous structure of the fabric.

Particularly, after the HCl treatment, the fabric is a highly delicate and sensitive tissue and should not be subjected to intense heat or pressure or roughly handled. As aforesaid, high temperatures may impair the molecular structure, particularly if accompanied by pressure, or decompose the chlorophyll and glycerine.

After the caustic soda treatment, rinsing is used to eliminate residual caustic soda but after the HCl treatment rinsing and complete drying is avoided since the residual HCl left on the fabric fibers after getting rid of excess liquid by drainage is relied on to react with the bicarbonate to develop CO bubbles and thereby thin out and fluff the fibers.

If desired, the fabric may or may not be rinsed before drying after the sodium bicarbonate treatment.

The mixing of the final dip is carried out with slow stirring. It is pointed out that tannic acid, when brought in contact with metal, will turn blackish-green, which may adversely affect taste so that the use of metal should be particularly avoided in mixing and using the final dip. Porcelain, plastic or glass may be used. Also preferably the final dry fabric filter should not be brought into contact with metal.

When squeezing is used, other than by hand, special, non-metallic tools should be used such as plaques of wood with a screw carefully propelled by hand to avoid excessive pressure on the fabric which will close the pores which have been dilated by the previous demineralizing, defatting and gas-fiufiing steps.

The capsules may be made of plastic other than polystyrene or of other materials, e.g. Bakelite, polyvinyls, polyethylene, cardboard, etc. However, polystyrene and Bakelite are preferred. Both are strong and flexible and hard to break. Preferably, the capsule should not be made of metal.

Each capsule contains one of the fabric filter strips carefully packed loosely and uniformly therein. Packing should not be too tight since this may increase draw too much as well as exert excessive pressure on the fabric tending I to close the pores thereof.

In the final fabric filter, the fibers and molecules constitute a chemico-mechanical collector of the alkaloids and other by-products in the tars resulting from the burning tobacco.

It will be readily understood that the physical structure of the packed fabric filter is such as to provide excellent mechanical filtering. The tortuous path and changes in direction of the cigarette smoke through the packed fabric filter will themselves mechanically remove many of the harmful materials in the smoke.

Because of the large surface area aiforded by the pores of the packed fabric and because the smoke is forced to come into contact with such large surface areas, removal of tar and other toxic materials is extremely efiicient. The high porosity of the loosely packed fabric because of its closely woven threads and as a result of the chemical processing not only provide excellent removal of tars but also permits the smoke to be drawn through the filter without effort so that the draw is excellent; also the absorbability of the fabric is extremely high by virtue of the fact that the chemical elements used in its preparation create a strong afiinity toward any aqueous, oily fluid or gaseous materials in the smoke.

It is not intended that the invention be limited to the 10 aforesaid example or to the aforesaid conditions, which have been provided by way of example, or by any theory set forth above, but only to the products and methods cliamed in the following claims and their equivalents.

I claim:

1. A method of making a filter for tobacco smoke comprising applying to a porous cotton fabric a strong alkali soltuion to defat the fabric followed by ringing and drying said defatted fabric, applying to the defatted fabric a strong mineral acid solution to remove acid soluble materials in said fabric, and while said fabric contains said acid applying thereto sodium bicarbonate to react with said acid to neutralize the acid and generate CO gas bubbles within the fabric interstices to thereby fluff the fabric followed by drying the fiuffed fabric.

2. A method of making a filter for tobacco smoke comprising pretreating a porous cotton fabric by applying to said fabric a solution of caustic soda, rinsing and drying said caustic soda-treated fabric to remove excess caustic soda, applying to the caustic soda treated fabric a solution of hydrochloric acid and applying to the fabric while it still contains hydrochloric acid, sodium bicarbonate to neutralize said hydrochloric acid and generate CO bubbles within the fabric interstices to thereby fluff the fabric, drying the fluffed fabric and impregnating the pretreated fabric with water soluble chlorophyll, tannic acid, a polyhydric alcohol or a mixture thereof and drying the impregnated fabric.

3. A method according to claim 2, wherein the pretreated fabric is impregnated with a mixture of said chlorophyll, tannic acid and glycerine.

4. A method according to claim 2, said fabric being a woven bleached fabric.

5. A method according to claim 2, wherein said solution of caustic is applied by dipping said fabric into a caustic soda solution, said hydrochloric acid is applied by dipping said fabric into said solution of hydrochloric acid, said sodium bicarbonate is applied by dipping said fabric into a solution of sodium bicarbonate until the hydrochloric acid contained therein has been neutralized and said impregnating with said mixture comprises dipping the pretreated fabric into a bath containing said chlorophyll, tannic acid and glycerine in water and ethyl alcohol.

6. A method according to claim 5, said fabric being dipped in said impregnating bath and dried without exposure to strong sunlight.

7. A mthod according to claim 2 carried out at a maximum temperature of 45 C.

8. A method according to claim 2 carried out without contacting the fabric with metal.

9. A method according to claim 2 carried out without subjecting the fabric to a pressure in excess of 3 kilograms per 0.25 m? of fabric surface.

References Cited UNITED STATES PATENTS 61,267 1/1867 Schmidt 117-56 1,546,211 7/1925 Dreyfus 117-56 2,050,197 8/1936 Sebrell 117-143 R 2,433,370 12/1947 Kauffman et al. 117-56 2,774,354 12/1956 Florman 131-267 2,841,529 7/1958 Schmidt et al. 117-143 R 3,110,315 11/1963 Lendvai 131-267 X 3,417,759 12/1968 Touey et al. 131-267 3,489,827 1/1970 Mueller et al 131-267 X WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner US. Cl. X.R.

8-138, 139; 28-76 R; ll7- 65.2, 98, 143 R, DIG 9; l3l-266, 267

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