US2830596A - Production of tobacco sheets - Google Patents

Description

United States Patent PRODUCTION OF TOBACCO SHEETS Walter G. Frankenburg, Millersville, and Alfred M. Gottscho, Lancaster, Pa., assignors to General Cigar go klnc, New York, N. Y., a corporation of New or a No Drawing. Application September 23, 1955 Serial No. 536,294

6 Claims. (Cl. 131-140) This application is a continuation-in-part of our copending application Serial No. 378,722, filed September 8, 1953, now U. S. Patent 2,747,583, issued May 29, 1956.

This invention relates to the continuous manufacture of thin tobacco sheets, particularly sheets made of tobaccos used in cigarettes.

Going back over a period of more than fifty years, there have been numerous proposals for the conversion of tobacco into sheets in order to utilize portions of the tobacco plant previously discarded as well as tobacco waste resulting from the processing of tobacco, but these proposals have failed to achieve commercial success because the tobacco sheets produced thereby were not acceptable to smokers. Recently, however, commercial production of tobacco sheets has been established based on the teachings of U. S. Patents 2,592,553 and 2,592,554, issued April 15, 1952 to W. G. Frankenburg and P. W. Garbo. Our copending application discloses apparatus which was developed for the large-scale and economic production of tobacco sheets in accordance with the processes of U. S. Patents 2,592,553 and 2,592,554. As brought out in our copending application, an aqueous paste or suspension of powdered tobacco and a binding agent is applied as a thin coating on a moving belt which passes through a drying zone wherein the wet coating is contacted by a flow of heated and relatively dry air to convert the wet coating into a dry, coherent film or sheet.

The commercial operation pursuant to our copendiug application for the production of tobacco sheets used as binders in the manufacture of cigars and cigarillos has aroused the interest of the cigarette industry in achieving a low-cost and large-scale production of tobacco sheets suitable for use in the manufacture of cigaretes.

Extensive experimentation with the aim of achieving the goal of the cigarette industry has revealed that the types of tobacco and tobacco waste products which would be utilized in the production of tobacco sheets for cigarettes present new problems not encountered with the tobaccos which are used in the manufacture of cigars.

Additionally, the tonnages of tobacco sheets required by the cigarette industry far exceed those of the cigar industry; this difference in tonnages emphasizes the need to use a binding agent which is available in abundant supply and at a low price. The foregoing factors requiring attention for the commercial production of cigarette tobacco sheets are largely independent of still another factor which stems from the lower value of cigarettes as compared with cigars. The latter point involves the need to accelerate the rate of production as much as possible so that large tonnages of cigarette tobacco sheets may be obtained, while avoiding an unreasonably large 'manufacturing plant and high capital cost.

Experimentationhas shown that tobaccos, such as flue- -cured and Turkish tobaccos, which are used in the manufacture of cigarettes, substantially increase the difiicul- -ties of making goodrtobacco sheets. Specifically, ciga- 'ice rette tobaccos tend to yield weaker sheets of greater adhesion to the surface on which they are formed. Because of lower strength and higher adhesion, it is often impossible to remove from the supporting surface the dry tobacco coating as a continuous tobacco sheet. Furthermore, as brought out in our copending application, a very satisfactory tobacco sheet is made by using methyl cellulose of 4000 centipoise type or grade. This is a premium grade of methyl cellulose, and consequently, more expensive than standard grade methyl cellulose, i. e., 400 centipoise type.

Accordingly, a principal object of this invention is to provide a continuous, rapid process for producing large tonnages of cigarette tobacco sheets at an economically attractive cost.

In accordance with this invention, a tobacco sheet suitable for the manufacture of cigarettes is made by dissolving about 2.2% to 2.6% by weight of 400 centipoise grade methyl cellulose in water, admixing the resulting solution with dry-ground tobacco in the proportions of 2.5 to 4.5 parts by weight of the aqueous solution to each part of tobacco, applying the resulting viscous mixture as a thin coating on a metal surface, drying the coating by contact with air heated to a temperature in the range of F. to 160 F., and removing from the metal surface the thus dried coating as the desired tobacco sheet. In accordance with our copending application, the drying operation is preferably conducted in two stages; in the first stage, the wet coating is contacted with air at a temperature in the range of F. to F. and having a relative humidity not exceeding about 25%, while in the second stage, the air is at a temperature about 10 F. to 15 F. lower than that of the first stage but not lower than 110 F. and has a relative humidity in the range of 12% to 25%.

By employing 400 centipoise type methyl cellulose, not only is the cost of the binding agent reduced as compared with the 4000 centipoise type, but also it has become possible to curtail substantially the amount of water used in preparing the tobacco suspension or paste in order to shorten the drying time. At the restricted aqueous solution-to-tobacco ratios employed in the process of this invention, the higher grades of methyl cellulose yield such viscous and stiff tobacco pastes that r they cannot be applied properly as a thin coating to the surface of a metal belt which conveys the coating to the drying zones. Both for economic and smoking considerations, the cigarette industry requires tobacco sheets with a minimum content of binding'agent; by limiting the content of 400 centipoise grade methyl cellulose in water to the range of about 2.2% to 2.6% by weight, the requirement of the cigarette industry is easily satisfied because at aqueous solution-to-tobacco weight ratios of 2.5 :1 to 4.521 it becomes possible to produce tobacco sheets containing notmore than 10% preferably not more than 8%, of methyl cellulose, based on the Weight of the dry-ground tobacco used in making the sheets. In short, the desired proportion of methyl cellulose to tobacco in the finished tobacco sheet is readily obtained by selecting a concentration of methyl cellulose in water and an aqueous solution-to-tobacco weight ratio, within the 3 when spread on a metal surface and dried, adhere strongly to the surface, making it very difiicult to remove the dried coating as a continuous sheet. Furthermore, cigarette tobaccos tend to give weaker tobacco sheets than do cigar tobaccos used in similar formulations. Often, the cigarette tobacco will yield a tobacco sheet of very dark and disagreeable color, as well as one having a'high cracking propensiy. Correction of the tendency of cigarette tobaccos to form sheets which crack readily and are of disagreeable appearance may be achieved by following the teachings of copending application Serial No. 510,851, filed May 24, 1955, by W. G. Frankenburg and P. H. Waltz. The application of Frankenburg and Waltz discloses that the addition of a minor amount of acid to a paste of powdered tobacco and an aqueous solution of a cellulose derivative like methyl cellulose will prevent the occurrence of the difiiculties previously encountered in the utilization of cigarette tobaccos. While an inorganic acid like phosphoric or boric acid may be used, organic acids, particularly hydroxylated polybasic carboxylic acids, such as citric, malic and tartaric acids, are generally preferred. The amount of acid used in the tobacco paste is generally not more than 5% by weight, based on the tobacco present therein. Frequently, 2% to 3% of acid yields very satisfactory results. The acidified tobacco paste usually has a pH in the range of 3.0 to 5.5.

Methyl cellulose is graded, according to the viscosity, measured in centipoises at a temperature at 25 C., of an aqueous solution containing 2% by weight of the methyl cellulose. Material marketed as 400 centipoise type methyl cellulose commonly embraces methyl eelluloses which in 2% by weight aqueous solutions give viscosities at 25 C. in the range of 300 centipoises to 500 centipoises. Consequently, the aqueous solutions containing from 2.2% to 2.6% by weight of methyl cellulose as prepared in accordance with this invention have viscosities in the range of about 400 centipoises to 1200 centipoises.

It is well to note that while the aqueous solution of methyl cellulose has a viscosity of 400 centipoises to 1200 centipoises at 25 C., the same solution after admixture with the powdered tobacco in the specified proportions will have ,a substantially higher viscosity, i. e., over 6000 centipoises. In order that the tobacco paste may be properly applied as a thin film or coating on a supporting surface, it should have a viscosity not exceeding about 35,000 centipoises; tobacco paste viscosi ties in the range of 12,000 centipoises to 28,000 centipoises are generally preferred. At these viscosities, the

formed generally increases with the total content of carbohydrates, pectins and pentosans of the tobacco used in making the sheets. While the content of these substances in any type of tobaceowill vary with the plant strain, growing conditions, leaf position and similar factors, average values of the total content of carbohydrates, pectins and pentosans for the several types of tobacco fall in thefollowing ranges:

Type of tobacco: Total content Flue-cured 25% to 38% by weight. Turkish 20% to 30% by weight. Burley 16% to 20% by weight. Maryland to 22% by weight.

Cigarette tobacco sheets are distinctly more difiicult to produce when made of flue-cured or Turkish tobaccos (i. e., tobaccos with a total content of carbohydrates,

.pectins and-pentosans of at least%' by weight) than when made of burley or Maryland tobaccos. Cigar tobaccos generally have total contents of carbohydrates, pectins and pentosans below 15% by weight and rarely give the sheet-forming difficulties, like strong adhesion to the supporting surface, high cracking propensity and disagreeable appearance, which are encountered with cigarette tobaccos. While the cracking and color difficulties with cigarette tobacco sheets are substantially overcome by acidifying the tobacco paste before it is spread out as a thin film and dried, the problem of removing the adherent dry film from the supporting surface as a continuous tobacco sheet remains as a serious obstacle to large-scale commercial operation. The latter problem now also vanishes when powdered cigarette tobacco is admixed with an aqueous solution containing 2.2% to 2.6% by weight of 400 centipoise grade methyl cellulose. Cigarette tobacco sheets made with 400 centipoise grade methyl cellulose in accordance with this invention show good tensile strength and are readily stripped from the supporting surfaces on which they are formed, particularly after the dry sheets have been moistened by a fine water mist.

The tobacco sheets produced in accordance with this invention desirably contain the non-water-swelling siliceous catalysts disclosed in U. S. Patent 2,706,695, granted April 19, 1955 to W. G. Frankenburg. Likewise, it is advisable to include plasticizers like glycerine and the glycols in the formulation of the tobacco sheets in order to increase their flexibility.

By restricting the quantity of aqueous solution of methyl cellulose that is admixed with the powdered tobacco to the range of 2.5 to 4.5 parts by weight for each part of tobacco, the drying time is substantially curtailed. Heretofore, tobacco sheets were produced with a drying time of about 4 minutes, whereas this invention makes it feasible to operate with a drying time of not more than 2 minutes.

For a better understanding of the invention, illustrative embodiments are presented hereinbelow in detail.

Example 1 An aqueous solution containing 2.2% by weight of 400 centipoise grade methyl cellulose is admixed with powdered tobacco consisting on a weight basis of of tobacco dust recovered from the processing of Turkish cigarette tobacco and 20% of dry-ground burley tobacco stems. The methyl cellulose solution is admixed with the powdered tobacco in the weight proportions of 4.1 parts of solution to each part of powdered tobacco; in other words, the methyl cellulose amounts to about 9% by weight based on the tobacco. To the resulting tobacco paste, the following ingredients are added in the proportions indicated:

Citric acid 5% by Weight based on the tobacco.

Diatomaceous earth 7% by weight based on the tobacco.

Triethylene glycol 11% by weight based on the tobacco.

Siliceous catalyst 75% by weight based on the methyl cellulose.

The paste containing all of the ingredients has a viscosity of about 28,000 centipoises at 25 C. and is applied by a reverse roll coater as a thin coating to a stainless steel belt which conveys the coating (approximately 0.01 inch thick) through two drying zones arranged in series. The coating of tobacco paste on the belt is contacted in the first zone for 0.8 minute with air heated to a temperature of 150 F. and having a relative humidity of approximately 15%. The partially dried coating then passes through the second zone wherein it is contacted for another 0.8 minute with air heated to a temperature of F. and having a relative humidity of about 20%. Onleaving the second drying zone, thevisuallydry coating on the conveyor belt is moistened by a fine Water mist so that the coating then has a moisture content of approximately 30% by weight. In this condition, the coating is easily peeled off the supporting belt and is ready for use in the manufacture of cigarettes. The cigarette tobacco sheet thus produced has good tensile strength, is approximately 0.003 inch in thickness and has an attractive tobacco-like appearance.

Example 2 An aqueous solution containing 2.58% by weight of 400 centipoise grade methyl cellulose is admixed with powdered tobacco consisting on a weight basis of 70% of tobacco dust recovered from the processing of mixed cigarette tobaccos predominantly of the flue-cured type and 30% of dry-ground winnower slivers (i. e., small pieces of stems), derived from the cigarette tobaccos. The methyl cellulose solution is admixed with the powdered tobacco in the weight proportions of 2.85 parts of solution to each part of powdered tobacco; in other words, the methyl cellulose amounts to about 7.35% by Weight based on the tobacco. To the resulting tobacco paste, the following ingredients are added in the proportions indicated:

Citric acid 5% by weight based on the tobacco. Diethylene glycol 13% by weight based on the tobacco. Siliceous catalyst 100% by weight based on the methyl cellulose.

The paste containing all of the ingredients has a viscosity of about 22,000 centipoises at 25 C. and is applied by a reverse roll coater as a thin coating to a stainless steel belt which conveys the coating (approximately 0.01 inch thick) through two drying zones arranged in series. The coating of tobacco paste on the belt is contacted in the first zone for 0.7 minute with air heated to a temperature of 145 F. and having a relative humidity of approximately 18%. The partially dried coating then passes through the second zone wherein it is contacted for another 0.7 minute with air heated to a temperature of 133 F. and having a relative humidity of about 16%. On leaving the second drying zone, the visually dry coating on the conveyor belt is moistened by a fine water mist so that the coating then has a moisture content of approximately 32% by weight. In this condition, the coating is easily peeled off the supporting belt and is ready for use in the manufacture of cigarettes. The cigarette tobacco sheet thus produced has good tensile strength, is approximately 0.003 inch in thickness and has an attractive tobacco-like appearance.

Those skilled in the art will visualize several modifications and variations of the invention set forth hereinabove without departing from its spirit and scope. Accordingly, the claims should not be interpreted in any restrictive sense other than that imposed by the limitations recited within the claims.

What is claimed is:

1. A process for producing a tobacco sheet from cigarette tobacco having a content of carbohydrates, pectins and pentosans totaling at least 15% by weight, which comprises dissolving about 2.2% to 2.6% by weight of 400 centipoise grade methyl cellulose in water, admixing the resulting solution with said cigarette tobacco in powdered form in the proportions of 2.5 to 4.5 parts by weight of said solution to each part of said cigarette tobacco to yield a viscous mixture containing not more than parts by weight of said methyl cellulose for each parts of said cigarette tobacco, applying said viscous mixture as a thin coating on a met-a1 surface, drying said coating by contact with air heated to a temper ature in the range of to 160 F., moistening the dried coating with atomized water, and peeling the moistened coating from said metal surface as a tobacco sheet.

2. The process of claim 1 wherein the viscous mixture applied as a thin coating has a viscosity in the range of about 12,000 centipoises to 28,000 centipoises at a temperature of 25 C.

3. A process for producing a cigarette tobacco sheet which comprises dissolving about 2.2% to 2.6% by weight of methyl cellulose in water to produce a solution having a viscosity in the range of 400 centipoises to 1200 centipoises at a temperature of 25 C., admixing said solution with dry-ground cigarette tobacco having a con tent of carbohydrates, pectins and pentosans totaling at least 15% by weight in the proportions of 2.5 to 4.5 parts by weight of said solution to each part of said cigarette tobacco to yield a viscous mixture containing not more than 8 parts by weight of said methyl cellulose for each 100 parts of said cigarette tobacco, applying said viscous mixture as a thin coating on a metal surface, drying said coating by contact with air heated to a temperature in the range of F. to F., moistening the dried coating wtih atomized water, and peeling the moistened coating from said metal surface as a cigarette tobacco sheet.

4. The process of claim 3 wherein the cigarette tobacco is flue-cured tobacco and the viscous mixture applied as a thin coating has a viscosity in the range of about 12,000 centipoises to 28,000 centipoises at a temperature of 25 C.

5. The process of claim 3 wherein the cigarette tobacco has a content of carbohydrates, pectins and pentosans totaling at least 20% by weight and the viscous mixture is acidified to a pH in the range of 3.0 to 5.5 before being applied as a thin coating.

6. In a process for producing a tobacco sheet by admixing powdered tobacco with an aqueous solution of methyl cellulose and by drying the resulting aqueous tobacco suspension in the form of a film deposited on a supporting surface, the improvement of accelerating the drying of said film to yield a tobacco sheet that is readily stripped from said supporting surface, which comprises dissolving about 2.2% to 2.6% by weight of methyl cellulose in water to produce a solution having a viscosity in the range of 400 centipoises to 1200 centipoises at a temperature of 25 C., admixing not more than 4.5 parts by weight of said solution with each part of powdered tobacco to yield a viscous mixture having a viscosity in the range of 6000 centipoises to 35,000 centipoises at a temperature of 25 C., applying said viscous mixture as a film approximately 0.01 inch thick on a supporting surface, and drying said film in not more than 2 minutes by contact with air heated to a temperature of not more than F.

References Cited in the file of this patent UNITED STATES PATENTS 2,433,877 Wells et al Jan. 6, 1948 2,534,113 Egger Dec. 12, 1950 2,592,553 Frankenburg et a1 Apr. 15, 1952 2,613,673 Sartoretto et al. Oct. 14, 1952 FOREIGN PATENTS 1,026,418 France Feb. 4, 1953

Claims (1)

1. A PROCESS FOR PRODUCING A TOBACCO SHEET FROM CIGARETTE TOBACCO HAVING A CONTENT OF CARBOHYDRATES, PECTINS AND PENTASONS TOTALING AT LEAST 15% BY WEIGHT, WHICH COMPRISES DISSOLVING ABOUT 2.2% TO 2.6% BY WEIGHT OF 400 CENTIPOISE GRADE METHYL CELLULOSE IN WATER, ADMIXING THE RESULTING SOLUTION WITH SAID CIGARETTE TOBACCO IN POWDERED FORM IN THE PROPORTIONS OF 2.5 TO 4.5 PARTS BY WEIGHT OF SAID SOLUTION TO EACH PART OF SAID CIGARETTE TABACCO TO YIELD A VISCOUS MIXTURE CONTAINING NOT MORE THAN 10 PARTS BY WEIGHT OF SAID METHYL CELLULOSE FOR EACH 100 PARTS OF SAID CIGARETTE TOBACCO, APPLYING SAID VISCOUS MIXTURE AS A THIN COATING ON A METAL SURFACE, DRYING SAID COATING BY CONTACT WITH AIR HEATED TO A TEMPERATURE IN THE RANGE OF 110*F. TO 160*F., MOISTENING THE DRIED COATING WITH ATOMIZED WATER, AND PEELING THE MOISTENED COATING FROM SAID METAL SURFACE AS A TOBACCO SHEET.