US3560697A - Adding spark-comminuted zinc to tobacco-smoke filters - Google Patents

Abstract

The invention concerns a method and apparatus for improving the filtration properties of fibrous, filamentary and sheet tobacco smoke filtering material. The method consists in treating the said material with a finely divided zinc-containing powder produced by a high-energy comminution process carried out under water. The powder is advantageously a powder produced by electric-spark erosion action between two zinc electrodes submerged in water.

Description

D United States Patent {1113,560,697

[72} inventor Thomas William Charles Tolman [50] Field of Search 2 l9/69M, Southampton, England 69V, 50, 68, 70; l31/9, 10, 88, 196, 207, 261, 264, [2!] Appl No. 750,656 265, 266 [22] Filed Aug. 6, 1968 45 Patented Feb. 2, 1971 1 References Cited [73] Assignee Brown and Williamson Tobacco UNITED STATES PATENTS corporatim 1,564,500 12/ 1925 Van de Voorde i3 l/261UX Louisville, Ky. a corpomfion 0 Delaware Primary ExammerR F. Staubly [32] priority Aug 9, 1967 Attorneyl(ane, Dalsimer, Kane, Sullivan and Kurucz [33] Great Britain [31] 36520/67 ABSTRACT: The invention concerns a method and apparatus [54] ED ZINC To for improving the filtration properties of fibrous, filamentary 7 Claims 2 D and sheet tobacco smoke filtering material. The method conrawmg sists in treating the said material with a finely divided zinc- [52] U.S.Cl....- 219/69, containing powder produced by a high-energy comminution 131/10, 13 1 I26] process carried out under water. The powder is ad- (51] Int. Cl 823p i/08, vantageously a powder produced by electric-spark erosion ac- A24f 25/00 tion between two zinc electrodes submerged in water.

ADDING SPARK-COMMINUTED ZINC TO TOBACCO- SMOKE FILTERS Many forms of filter for tobacco smoke consist of filamenta- 1 ry or sheet material capable of removing the particulate phase by nonnal filter mechanism. Commonly, additional materials are incorporated into such filters to improve their effectiveness by removing a proportion of the vapor phase, or specific substances therefrom. Such materials are usually substances which can remove the less pleasant constituents which are present in the tobacco smoke and which have an adverse effeet on the taste of the filtered smoke. Of these less pleasant constituents of tobacco smoke, the presence of the more volatile acidic compounds may be undesirable, especially hydrogen sulfide and hydrogen cyanide.

An object of the present invention is to provide means whereby hydrogen sulfide and hydrogen cyanide can be largely removed from the smoke of burning tobacco.

According to the invention, fibrous, filamentary or sheet tobacco smoke filtering material is treated with a finely divided zinc-containing powder produced by a high-energy comminution process carried out under water.

Preferably, the powder is produced by electric-spark action between two zinc electrodes submerged in water. In this case, the finely divided zinc-containing powder may be obtained initially as a grey-black suspension in distilled water which, on standing, changes colour to become light grey. This powder may contain about 90 percent zinc.

The powder is applied to the filtering material in the fonn of the aqueous suspension, by dipping, spraying or coating, to give a final increase in weight after drying of up to percent based on the original weight of the said material. Quite small additions are efieetive, but practical difficulties arise if the addition exceeds 10 percent. Preferably, the addition is such as to give an increase in weight of from 2 percent to 5 or 6 percent approximately.

One manner of preparing the aqueous suspension of finely divided zinc-containing powder will now be more fully described by way of illustration. In the accompanying draw- FIG. I is a diagram of a suitable arrangement of spark-erosion apparatus used for preparing the suspension, and

FIG. 2 a circuit diagram for this apparatus.

Referring to FIG. I, the apparatus comprised a stationary zinc electrode I in the form of a large flat disc and a movable zinc electrode 2 in the form of a slender rod clamped to the soft iron core 3 of a solenoid 4. The two electrodes 1, 2 were arranged mutually in contact 2 cm. below the surface of a dish 5 containing distilled water of relatively low conductivity. The movable electrode 2 and core 3 were counterbalanced by an adjustable weight 6 to such an extent that a small attractive force by the solenoid 4 on the core would suffice to separate the two electrodes.

The circuit, FIG. 2, for the electrodes 1, 2 and solenoid 4 was supplied with direct current from a source 7 of alternating current at l40 volts through a full-wave rectifier 8, the electrade 2 being connected to the positive side. An S-microfarad capacitor 9 was connected across the electrodes 1, 2 which were effectively, in series with the said capacitor. For adjustably controlling the current flow through the solenoid 4, a variable-series resistor 10 and variable shunt resistors ll,l2, of 200, I55 and 45 ohms respectively, were provided.

When the circuit was switched on, current flowed by way of the electrodes I, 2 through the solenoid 4. The resultant attraction of the core 3 lifted the movable electrode 2, interrupting contact between the two electrodes. The capacitor 9 rapidly became charged to its discharge potentiaiand, at a critical maximum separation of the electrodes I, 2, discharge across them, causing a spark to be produced. In the meanwhile, due to the separation of the electrodes, the solenoid became substantially deenergized, so that the core 3 was no longer attracted and the electrode 2 returned towards contact with the electrode 1. Discharge from the capacitor 9 ceased and the solenoid was reencrgized and the electrodes 1,2 reseparated, the cycle being repeated continuously and rapidly to produce a continuous rapid succession of erosive sparks between the electrodes.

During the first few seconds of operation, a brown colloidal solution was formed in the dish 5, which changed during continued operation to a dark grey/black suspension. On subsequent standing, the particles in the suspension changed colour to become light grey. Analysis of these light grey particles showed that they contained 88 percent by weight of zinc. If it is assumed that the colour change is brought about by the formation of zinc hydroxide, this analysis corresponds to a composition for the particles of approximately percent zinc and 25 percent zinc hydroxide. The particles proved to be irregularly shaped aggregates of size ranging from 5 to 50 microns. The components of the aggregates were of size from 0.5 to 1 micron.

The following examples illustrate the effect of the addition of a suspension of zinc-containing particles produced by the spark-erosion process to filters of paper and cellulose acetate.

EXAMPLE I A suspension of light grey particles obtained in the abovedescribed manner was sprayed onto tobacco smoke filtering paper of the kind well-known as "Myria" paper to give a final increase in weight, after drying, of 0.5 percent, calculated on the original weight of the paper.

The treated paper was formed into filter rods of cigarette diameter and cut into filter tips each of i5 mm. length.

EXAMPLE II I The procedure of example I was repeated, except that a quantity of the suspension sufficient to give a final increase in weight of 1 percent was applied.

EXAMPLE m The procedure of example I was repeated except that the suspension was applied so as to give an increase in weight of 2.5 percent.

EXAMPLE IV The procedure of example I was repeated except that the suspension was applied so as to give an increase in weight of 5.0 percent.

EXAMPLE V The procedure of example I was repeated except that the suspension was applied so as to give an increase in weight of 10.0 percent.

Filter tips prepared as in the above examples were attached to cigarettes and smoked, in comparison with cigarettes without filter tips, using an engine which provided one puff per minute of 2 seconds duration and 35 cc. volume. The smoke collected was analyzed and the ascertained amounts of hydrogen sulfide and hydrogen cyanide removed by the treated filters are shown in Table I below.

Filtration ellieiency for 15 Pressure drop, mm. filter, percent em. water gauge (at air [low of Hydrogen Hydrogen Example 1,050 ce./min.) sulphide cyanide EXAMPLE VI A continuous tow of cellulose acetate filaments of filament denier 5 and total denier 72.000 was sprayed with an aqueous suspension of zinc-containing particles prepared on a commercial scale by the spark-erosion process. The particles comprised 20 percent of the total weight of the suspension. The treated tow was fed to a conventional filter-rod making machine. by which it was formed into rods. The rods were dried at 70 F. for 48 hours and conditioned in a cabinet maintained at 70 F. and 60 percent relative humidity.

On analysis, the rods were found to contain 2.3 percent by weight of zinc.

EXAMPLE Vll Filter rods were prepared as in example Vl except that the addition of particles was such that the rods contained 4.6 percent of zinc.

EXAMPLE Vlll TABLE II Filtration eflicieney for Pressure drop, mm. length, percent cm. water gauge (at air flow of Hydrogen Hydrogen Example 1,050 cc./m.in.) sulphide cyanide The flavour of the smoke was not found to be adversely affected by the additions made to the filtering materials in any of examples I to Vlll.

lclaim:

l. A method of improving the filtration properties of tobacco smoke filtering material of the group consisting of fibrous, filamentary and sheet filtering material, comprising treating the said material with a finely divided. zinc-containing powder produced by a high-energy comminution process carried out under water.

2. A method according to claim 1, wherein the powder is produced by electric-spark erosion action between two zinc electrodes submerged in water.

3. A method according to claim 1, wherein the filtering material is treated with the zinc-containing powder in the form of an aqueous suspension and is dried.

4. A method according to claim 1, wherein the filtering material is treated to give a final increase in weight of up to 10 percent with respect to the original weight of the said material.

5. A method according to claim 1, wherein the filtering material is treated to give a final increase in weight of from,2 to 5 percent with respect to the original weight of the said material.

6. A method of improving the filtration properties of tobacco smoke filtering material comprising treating the said material with a minor amount of a finely divided zinc-contain ing powder, said powder being produced by a high energy comminution process carried out under water and then forming a filter element from said treated filtering material whereby said filter element is adapted to be attached to a smoke article.

7. A tobacco smoke filter element made by the methodof claim 6.

Claims (7)

1. A method of improving the filtration properties of tobacco smoke filtering material of the group consisting of fibrous, filamentary and sheet filtering material, comprising treating the said material with a finely divided zinc-containing powder produced by a high-energy comminution process carried out under water.

2. A method according to claim 1, wherein the powder is produced by electric-spark erosion action between two zinc electrodes submerged in water.

3. A method according to claim 1, wherein the filtering material is treated with the zinc-containing powder in the form of an aqueous suspension and is dried.

4. A method according to claim 1, wherein the filtering material is treated to give a final increase in weight of up to 10 percent with respect to the original weight of the said material.

5. A method according to claim 1, wherein the filtering material is treated to give a final increase in weight of from 2 to 5 percent with respect to the original weight of the said material.

6. A method of improving the filtration properties of tobacco smoke filtering material comprising treating the said material with a minor amount of a finely divided zinc-containing powder, said powder being produced by a high energy comminution process carried out under water and then forming a filter element from said treated filtering material whereby said filter element is adapted to be attached to a smoke article.

7. A tobacco smoke filter element made by the method of claim 6.

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