Method of making a filter for tobacco smoke

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 2—2 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 to 5 with the fabric laid flat.

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.²(0.5 mm. x 0.5 mm.), a weight of 50 grams/m.² of fabric, a density of 0.125 gram/cc.³ and a total surface area of 1.3 m.² per square meter of fabric. The thickness of the threads was 0.30 mm. and the pore volume was 0.125 cc.² 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 CO₂ 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 to 6 minutes at room temperature in subdued light in the following solution in a non-metallic (porcelain or plastic or glass) container:

Grams

Chemically pure tannic acid________________ 100

Water soluble uncoppered chlorophyll sold by Chlorophyll Co., Wharf Road, W. D. London, England under the name XX 'Uncoppered Chlorophyll _________________________ 150

Ethyl alcohol (95% chemically pure ethyl alcohol and 5% pure water) _______________ 5,000

Chemically pure glycerine___,_______________ 5,000

Distilled water____________________________10,000 made by dissolving the tannic acid in the alcohol in a 15 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 ²⁰ 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 ^2j 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.³ 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 _3g to direct sunlight.

The fabric was cut into strips 10 cm. x 2 cm. in dimension (20 cm.²) and a strip 2 in FIGS. 1-3 was loosely packed in a disposable tapered plastic filter capsule 4 molded from a blue, translucent polystyrene, such cap40 sule 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.². Typical dimensions of the capsule are: length—0.23 m.; internal diameter at big end—.0085 m.; internal diameter at small end—· ⁴⁵ .0075 m.; wall thickness—.001 m.; and volume—1.5 cm.³. 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 ₅_ 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 ₆₀ 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 70 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 75 against the internal periphery of the chamber, particu3,674,540 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 CO₂ 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 χιθ(Λ \20250^X1U /

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% 30 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 35 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 80% to 97.5%, more preferably between 85% 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 95%.

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 4-5% 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 diffusible throughout the fabric, i.e. more capable of spreading throughout the fully porous fabric. In fact, small larly 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 5 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 10 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 cig- 13 arette 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. 20

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 25 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. 1-3.

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.³, more preferably between 0.12 and 0.13 g./cm.³, a unit weight of between 40 and 60 grams/m.^a, more preferably between 48 and 51 g./m.², a thickness of between 0.2 and 0.6 45 mm., a hole size of between 0.15 and 0.35 mm.², a thread thickness of between 0.1 and 0.5 mm., more preferably 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 50 1190, more preferably between 1160 and 1'180 weft or cross threads per m., a total surface area ranging from 0.07 to 2.5, preferably from 1.0 to 2 m.²/m.² of fabric and a pore volume of between 0.100 and 0.150 cm·³/ per gram of fabric. The pore volume of the final fabric 55 filter is preferably between 0.100 and 0.165 cm.³, more preferably between 0.120 and 0.155 cm.³ 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 60 fatty substances in the fabric. Concentrations of from 3 % to 10% by weight are preferred, a more preferred concentration range being from 4 to 7%. The duration of the caustic dip should preferably be sufficient to solubilize the caustic-soluble materials in the fabric. 65

The HC1 concentration in the acid dip should not be so high as to char the cotton fibers but should be sufficient 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 be- 70 ing between 25 and 35%. The duration of the HC1 dip should preferably be sufficient 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 75

3,674,540 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 5 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 10 delicate porous structure of the fabric.

Particularly, after the HC1 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 13 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 HC1 treatment rinsing and complete drying is avoided since the residual 20 HO left on the fabric fibers after getting rid of excess liquid by drainage is relied on to react with the bicarbonate to develop CO₂ bubbles and thereby thin out and fluff the fibers.

If desired, the fabric may or may not be rinsed before 25 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 30 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, 35 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-fluffing steps. 40

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 45 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 ⁵⁰to 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. 55

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 θθ harmful materials in the smoke.

Because of the large surface area afforded 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 efficient. The ⁶⁵high 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 ab- 70 sorbability of the fabric is extremely high by virtue of the fact that the chemical elements used in its preparation create a strong affinity toward any aqueous, oily fluid or gaseous materials in the smoke.

It is not intended that the invention be limited to the 75 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.