US3115882A - Tobacco manufacture - Google Patents

Description

United States Patent 3,115,832 TGBACCG MANUFACTURE Corneal I... Domeck, .lru, Prospect, md Charles J. Moll, Jan, Louisville, Ky., assignors to General Cigar Co., Inc New York, N.Y., a corporation of New York No Drawing. Filed Oct. 26, 1962, Ser. No. 233,440 8 Claims. (Cl. 131-17) This invention relates to the manufacture of coherent tobacco products suitable for smoking and more part1cularly to such products in which tobacco has been processed in water to develop a cohesive property in the tobacco itself.

Several processes have been developed for converting tobacco leaves, trimmings and stems into continuous tobacco sheets that may be utilized in the manufacture of cigars and cigarettes. For instance, US. Patent 2,433,877 proposes a process in which all of the tobacco to be converted into a sheet is ground in water for a very long period of time so that the tobacco is largely reduced to colloidal particles. According to the patent, the prolonged wet grinding of tobacco yields an aqueous colloidal suspension of tobacco which may be spread as a coating on a support and the coating then dried to a coherent sheet. While the patent alleges that the aroma and smoke taste of the tobacco remain unaltered by the prolonged and excessive wet grinding, other workers in the tobacco industry have found that tobacco invariably undergoes changes when subjected to such extensive wet grinding.

US. Patent 2,485,670 sets forth an additional proposal as an improvement of the process disclosed in US. Patent 2,433,877. The improvement patent proposes to increase the tensile strength of a tobacco sheet made by wet grinding tobacco by subjecting the aqueous colloidal tobacco suspension to heating at a Water vapor temperature of 250 F. under a pressure of 15 pounds per square inch. This heating step, which lasts from 3 to 6 hours, precedes the spreading and drying of the tobacco suspension to form a sheet. The alleged improvement of tensile strength of the sheet resulting from this interposed step of heating the tobacco suspension to a temperature of 250 F., has not been sufficient to bring the proposal into commercial production. In any event, even though there may be some increase in tensile strength, the heating step certainly does not bring back the losses in aroma and in smoking properties arising when tobacco is reduced to a colloidal suspension by extensive wet grinding. Moreover, tobacco sheets of the prior art have lacked adequate flexibility. In fact, these products are frequently so brittle that in the normal utilization of such tobacco sheets in the manufacture of cigars and cigarettes excessive disintegration occurs. For instance, when such tobacco sheets are shredded by cutting for use in cigarette filler blends, far more fines are formed than when leaf tobacco alone is so shredded.

A primary object of this invention is to convert tobacco in any form such as leaves, shorts, trimmings and stems into a coherent and flexible tobacco product by utilizing a cohesive property developed in the tobacco itself.

Another important object is to make such coherent tobacco products of good flexibility without excessively degrading the tobacco through extensive wet grinding to form an aqueous suspension of colloidal tobacco.

These and other objects and advantages of the invention will be apparent from the description which follows.

In accordance with this invention, tobacco in any form is steeped in Water and kept at a warm temperature for an extended period to develop or activate the substances in the tobacco which give it a cohesive property, the thus Warm-steeped tobacco suspension in water is then subjected to wet grinding to release the cohesive and filmforming substances developed or activated within the cel- "ice lular structure of the warm-steeped tobacco, and the resulting aqueous pulp of processed tobacco is finally converted into a coherent smoking form such as a tobacco sheet made by spreading the aqueous pulp on a stainless steel belt and drying the wet film on the belt to a coherent sheet removable therefrom.

A fundamental feature of the invention is the controlled processing of tobacco to yield coherent smoking bodies which are characterized by good flexibility. As already mentioned, the prior art teaches the wet grinding as well as the heating of aqueous suspensions of tobacco as techniques for forming tobacco sheets and the like but the products of these prior proposals have lacked commercial attractiveness because of their brittleness. It is essential for good flexibility of the final product of this invention that the particle size of the tobacco be carefully controlled both prior to steeping in warm water and after wet grinding the steeped tobacco. Detailed investigation has revealed that when tobacco is reduced to very fine particles prior to steeping in warm water, the final product will have poor flexibility. Accordingly, it was found necessary to start with pieces or particles of tobacco, the major weight portion of which is retained on a 60-mesh screen. Preferably, the major weight proportion of the tobacco should consist of particles coarse enough to be retained on a 40-mesh screen.

Likewise, to achieve high flexibility in the final tobacco product, it is necessary to avoid excessive Wet grinding of the warm-steeped tobacco. It has been determined that the wet-ground tobacco suspension should have at least 9%, on a dry weight basis, of tobacco particles retained on a -mesh screen when the tobacco suspension is passed through a Clark Classifier. On the other hand, if the fraction of tobacco particles retained on the 100- mesh screen of a Clark Classifier exceeds 17% by weight, it becomes diflicult to form a coherent tobacco product and the physical properties of the product, including flexibility, are quite poor. Preferably, the fraction of wetground tobacco particles retained on the 100-mesh screen of a Clark Classifier should not exceed 15% by weight. A further useful guide to the controlled wet-grinding of the warm-steeped tobacco suspension to obtain a coherent tobacco product of high flexibility lies in the fraction of tobacco particles finer than 100-mesh and coarser than ISO-mesh and the fraction finer than ISO-mesh and coarser than ZOO-mesh. Experience has shown that when the 100- to ISO-mesh fraction of the wet-ground tobacco suspension amounts to about 2% by weight as determined with a Clark Classifier and the to ZOO-mesh fraction is about 2 to 3 /2 times as large as the approximately 2% by weight coarser fraction, the tobacco sheet or like coherent body formed from such wet-ground tobacco suspension will have a very desirable flexibility.

The other pnincipal variables of the process of this lnvention are the temperature at which the tobacco is steeped in water and the duration of the steeping operation. To effect the activation of the cohesive substances in tobacco, the steeping operation must be carried out at a temperature of at least 140 F. However, temperatures in excess of 200 F. must be avoided to prevent such degradation of the substances in the tobacco that the final coherent product not only lacks adequate flexi bility but also has poor smoking qualtiy. In most cases, the tobacco is preferably steeped in water maintained at aggegnlperature in the range of about F. to about The period of steeping the tobacco in warm water is dependent not only on the tobacco used but also on the temperature at which the steeped tobacco is maintained. For any given type of tobacco, the higher the temperature of the tobacco steeping operation is, the shorter will be its duration. However, even at the maximum steeping temperature of 200 F. a minimum period of at least 2 hours is required. Conversely, at the lowest steeping temperature of 140 F. the period will generally not exceed 30 hours. For the preferred temperature range of 160 to 180 F., an adequate steeping period will with most tobaccos fall in the range of 4 to 20 hours.

As already indicated, the character of the specific tobacco used in the process of this invention will dictate the temperature and duration of steeping to bring out the cohesiveness of that tobacco. Thus, as a general rule, 'fiu-cured and Turkish types of cigarette tobacco are among those tobaccos that are most readily responsive to the steeping operation; hence, with such tobacco types a high steeping temperature is not required and the steeping time may be made comparatively short. On the other hand, Wisconsin and Pennsylvania types of cigar tobacco generally are illustrative of tobaccos less responsive to steeping. In such cases, higher steeping temperature and longer periods are advisable.

The wet-grinding of the .tobacco following the steeping operation may be carried out with any of the known devices such as a wet hammer mill, a Waring Blendor and a homogenizer. In terms of economy of operation, a wet hammer mill like the Rietz distintegrator is preferred. Of the *homoge'nizers, the valve-type homogenizer is favored. As is known, in a valve-type homogenizer, the aqueous suspension is pressurized to a pressure of the order of at least 2000 pounds per square inch gauge and passed through a controlled microscopic clearance between the homogenizing valve and valve seat so that intensive shearing homogenization is effected. Regardless of the equipment employed to wet-grind the aqueous suspension of tobacco after the steeping period, the extent of wet-grinding must be carefiuily controlled to preserve in the final tobacco suspension from 9 to 17% by weight, on a dry basis, of tobacco particles retained on the 100-mesh screen of a Clark Classifier. Also, for optimum results, the final tobacco suspension should have an approximately 2% by weight fraction of particles that pass through the 100-rnesh screen but are "retained on the l'50 mesh screen of a Clark Classifier and about 2 to 3 /2 times as large a fraction of particles pass through the 150-mesh screen but are retained :on

the ZOO-mesh screen of the Clark Classifier.

To prevent undue erosion of the mechanical compo 'nents of the'equipment used in the process -of this invenltion, especially the wet-grinding devices, the tobacco should first be desanded by any of the known techniques '-with the tobacco in either the dry or the wet state.

As known in the tobacco art, humectants and plasticizers such as glycerol, sorbitol and various glycols are used in tobacco smoking products to avoid excessive drying and embrittlement of the tobacco prior to smoking. Humectants and plasticizers are desirable incorporated in the products of this invention at any point in the process. Humectants and plasticizers in an amount usually not exceeding about 10% by weight and frequently not exceeding about by weight of the tobacco content are preferably added to the pulp of treated tobacco. Humectants and plasticizers may be even added to the final product of the invention by apply- "ing such materials, usually in aqueous solution, as a coating or spray on the final product.

The composite of treated tobacco pulp and any dryground tobacco that may be added thereto may be converted by a continuous tobacco sheet on a stainless steel conveyor belt equipped with a film applicator such as a reverse roll coater and with dry hoods, all as shown in US. Patent 2,747,583. In making tobacco: sheets pursuant to this invention, it has been found particularly advantageous to heat the film or coating applied on the top side of the stainless steel belt by condensing steam on the bottom side. Such techniques is illustrated in US. Patent 2,155,453. In this way, a very high drying speed is attained without impairment of the final pro-duct.

In most instances, the layer of tobacco coating on the conveyor belt is dried to an adherent film that is more readily removable from the belt after reordering, i.e., conditioning with moisture. U.S. Patent 2,747,583 demonstrates reordering of the adherent film with a fine Water mist from a spray nozzle which may desirably be enclosed by a humidifilcation chamber as illustrated in US. Patent 2,867,220. Other methods of reordering the dry tobacco film to facilitate its removal from the conveyor belt are known.

The reordered tobacco film is then removed or peeled from the conveyor belt and wound up as a roll of continuous tobacco sheet as shown in US. Patent 2,747,583. Often, a doctor blade is used to facilitate parting of the tobacco sheet from the surface of the belt. Where the tobacco sheet is ultimately shredded for use in the manufacture of cigarettes or pipe tobacco, the sheet may be cut into pieces, such as squares with sides measuring 2 or 3 inches, as it is removed from the conveyor belt so that these pieces which are collected in suitable bins may subsequently be easily blended, prior to shredding, with tobacco leaves going into the cigarette or pipe tobacco.

For a'bettcr understanding of the invention and its scope, illustrative embodiments are presented hereinbelow in detail. In the examples, proportions are given in parts by weight unless otherwise specified.

Example 1 Tobacco shorts or rejects from cigarette manufacturing and redrying operations, about 60% by weight of which were particles retained on a 20-mesh screen, were desanded in the dry state. These shorts were .a blend of approximately 50% by weight of flue-cured, 35% of Burley and 15% of a mixture of equal parts of'Maryland and Turkish'tobaccos. To 1300 parts of water, parts of the tobacco shorts having a moisture content of 5% by weight were added. The aqueous suspension of tobacco Was brought to a temperature of 180 F. in aheated 'tank and with mild agitation held at that temperature for 16 hours. At the end of this steeping period, 5.4 parts of glycerol were added to the tobacco suspension.

The tobacco suspension was then passed four times through a Rietz disintegrator to reduce the fraction of particles retained on the IOO-mesh screen of a Clark Classifier to about 12.5% by Weight on a dry basis. For the first passage, the Rietz disintegrator was equipped with a 40 conidure screen (0.016 inch openings) and for readily removed from the belt.

'Measurements showed this product had a thickness of 0.0052 inch, a tensile strength of 170 grams per square millimeter, and an outstanding flexibility of an average of 18,086 flexes as determined on five samples, each measuring 1.5 centimeters wide and 15 centimeters long. The flex test was made with the M .I.T. Folding Endurance Paper Testing Machine in a room maintained at a temperature of 70 F. and at a relative humidity of 60%. 'The clear span between the jaws holding the sample was 10 centimeters and after the upper jaw was closed on the sample, the beam from which it hangs was balanced. With the tobacco sheet sample in place, a IOO-gram weight was set on the balance pan so that the sample was continuously under a tension load of gramsduring the shredded tobacco sheet.

Example 2 Burley tobacco stems were threshed into pieces of about A to inch in length and desanded by sieving and air classification. These stems with a moisture content of by weight were mixed with water in the ratio of 540 parts of stems to 2300 parts of water. The mixture was heated to a temperature of 310 F. in a sealed pressure vessel through which the water circulated at a rapid rate to promote extraction of the stems. After minutes at the temperature of 310 F., the liquid was discarded and the residual stern material was washed four times with 2700 parts of water each time.

The thus extracted stems amounting to 220 parts on a dry basis were mixed with 1100 parts of water to form a total of 3320 parts of aqueous stern slurry. This stem slurry was passed once through a Rietz disintegrator equipped with a conidure screen. The aqueous ex- .traction of the Burley stems followed the teachings of U.S.

Patent 3,043,723.

On a dry basis, 580 parts of the tobacco shorts used in Example 1 were mixed with 80 parts of winnowings and combined with the prepared slurry of extracted stems. The total mixture was heated to a temperature of 180 F. and held at that temperature for 4 hours with mild agitation. Then, 53 parts of glycerol were added and more water was introduced into the aqueous slurry to adjust the final consistency to 7% by weight of dry solids.

The adjusted tobacco slurry was passed four times through a Rietz disintegrator equipped with a 100 conidure screen, a 150 conidure screen and a 200 conidure screen for the successive passages of the slurry which was put through the last screen twice.

The wet-ground tobacco suspension was deaerated, cast on a belt and dried to a sheet which was reordered and removed from the belt as in Example 1. This tobacco sheet had a tensile strength of 365 grams per square millimeter and a thickness of 0.006 inch. By the flex test described in Example 1, this tobacco sheet withstood an average of 21,300 flexes. Cigarettes made with this tobacco sheet and evaluated in smoking tests in the manner set forth in Example 1 were found to have satisfactory taste and aroma.

A repetition of all the steps of this example except the step of heating the tobacco and stem slurry to a temperature of 180 F. for 4 hours yielded a tobacco sheet with a tensile strength of 145 grams per square millimeter. In the flex test, this tobacco sheet failed at an average of 200 flexes.

It is evident from the two runs in this example that the step of warming an aqueous suspension of tobacco for a prolonged period is an essential part of this invention because without it the tobacco sheet produced is much Weaker and very poor in flexibility.

Example 3 To examine the influence of the steeping period on the flexibility of the tobacco sheet produced, 120 parts of the tobacco shorts used in Example 1 were mixed with 1880 parts of water and 7.2 parts of glycerol. The aqueous suspension was heated to a temperature of 180 F. and portions were withdrawn at intervals While the suspension was maintained at that temperature. A portion of the suspension had also been set aside prior to raising the temperature to 180 F.

Each of the withdrawn portions of aqueous siispension was passed five times through a Rietz disintegrator equipped with a 40, 100, 150 and 200 conidure screen for each successive passage of the tobacco suspension which was put through the last screen twice. A sample of each Withdrawn portion after being wet-ground was tested in the Clark Classifier and the remainder of that portion was deaerated, cast, dried, reordered and removed from the stainless steel belt as set out in Example 1. The physical properties of the resulting tobacco sheets as well as the measurements made on the corresponding tobacco suspensions with the Clark Classifier are tabulated below.

Tobacco Suspension, Clark Tobacco Sheet Classifier Fractions steeping Hours at 180 F. +100 100 to 150 to Tensile mesh, +150 +200 Strength Average percent mesh, mesh, gmJmm. Flexes percent percent The tabulated results reveal that with less than 6 hours of steeping the tobacco at a temperature of 180 F. the suspension was not sufl'iciently amenable to wet grinding and the resulting tobacco sheet was weak and lacked satisfactory flexibility. Between 6 and 18 hours of warmsteeping, the tobacco sheet produced had an improved tensile strength and good flexibility. After 22 hours of warmsteeping, the tobacco suspension was too easily wetground so that the Clark Classifier [fraction of particles retained on the 100-mesh screen dropped to 8.7% by weight and the 150 to +200-mesh fraction was more than 3 /2 times as large as the 100 to +150-mesh fraction; in turn, the tobacco sheet so made was again poor in flexibility.

Example 4 Burley tobacco shorts, approximately by weight of which were particles retained on a 40-mesh screen, were mixed with 14 parts of water per part of dry tobacco. The steeped tobacco was held at a temperature of 180 F. for 16 hours and, after adding thereto 6% of glycerol based on the dry weight of tobacco, was passed three times through a Rietz disintegrator equipped with a 40, and conidure screen for the successive passages of the tobacco suspension therethrough.

The resulting wet-ground creamy pulp was deaerated, cast, dried, reordered and removed as a tobacco sheet having a tensile strength of 412 grams per square mi1li meter. The flex test showed that this product withstood an average of 3959 flexes.

A portion of the Warm-steeped tobacco with the added glycerol was passed through a valve-type homogenizer instead of the Rietz disintegrator. A single passage of the aqueous tobacco suspension through the valve-type homogenizer operating at a pressure of 5000' pounds per square inch gauge yielded a creamy pulp that was converted into a tobacco sheet of somewhat higher tensile strength and flexibility when compared with the tobacco sheet made from the same warm-steeped tobacco but Wetgrouncl three times in the Rietz disintegrator.

It is well to note that tobacco sheets made in accordance with this invention are characterized by high flexibility which, when measured with the M.I.T. Folding Endurance Paper Testing Machine as hereinbefore set forth, in general corresponds to more than 2000 average flexes before rupture of the tobacco sheet. Such high flexibility permits the use of the tobacco sheet in conventional manufacturing operations without excessive formation of fine particles or dust. For instance, in the manufacture of cigarettes, a tobacco sheet of this invention may be cut to fine shreds for use in the cigarette filler blend without excessive disintegration of the tobacco sheet to fine particles or dust which is very undesirable in cigarettes.

The screens used herein to measure the percentage of comminuted tobacco that is retained on a specified mesh size before the tobacco is steeped in warm water, as well as the screens used in the Clark Classifier, are screens of the US. Sieve Series.

The screens used with the Rietz disintegrator are those supplied by Cross Perforated Metals Division, National- Standard Company, in Carbondale, Pennsylvania. The simple identification of the 40, 100, 150 or 200 conidure screen used in this specification corresponds to the manufacturers designation as a fine hole perforated 0.016, 0.006, 0.004 or 0.003 inch conidure screen, respectively.

Many variations and modifications of the invention hereinabove disclosed will be visualized by those skilled in the art 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. The improved process of manufacturing a coherent tobacco product adapted for smoking, which comprises steeping tobacco in water, the major portion by weight of said tobacco being retained on a 60-mesh screen, maintaining the aqueous suspension of tobacco at a temperature in the range of about 140 to 200 F. for a period of at least 2 hours, wet-grinding the thus treated aqueous suspension of tobacco until the particles thereof retained on a IOO-mesh screen of a Clark Classifier are not more than 17% by weight but not less than 9% by Weight of the tobacco on a dry basis, and converting the resulting wet-ground tobacco pulp into said coherent tobacco product.

2. The process of claim 1 wherein the temperature of the aqueous suspension of tobacco is maintained in the range of about 160 to 180 F. for a period of about 4 to 20 "hours.

3. The process of claim 1 wherein the major portion by weight of the tobacco is retained on a 40-mesh screen,

and the particles of the wet-ground tobacco pulp which are retained on a IOO-mesh screen of a Clark Classifier are not more than 15% by weight of the tobacco on a dry basis.

4. The improved process of manufacturing a highly flexible tobacco sheet adapted for smoking, which comprises steeping tobacco in water, the major portion by weight of said tobacco being retained on a -1nesh screen, maintaining the aqueous suspension of tobacco at a temperature in the range of about 160 to 180 F. for a period of 4 to 20 hours, wet-grinding the thus treated aqueous suspension of tobacco so that the particles thereof retained on a -mesh screen of a Clark Classifier are not more than 15% by Weight but not less than 9% by weight of the tobacco on a dry basis, and converting the resulting wet-ground tobacco pulp into said highly flexible tobacco sheet.

5. The process of claim 4 wherein the tobacco is a blend of cigarette tobaccos including a substantial portion of flue-cured tobacco.

6. The process of claim 4 wherein the particles of the wet-ground tobacco pulp which pass through a 100-mesh screen but are retained on a -mesh screen of a Clark Classifier are approximately 2% by weight of the tobacco on a dry basis, and the particles of said pulp which pass through said 150-mesh screen but are retained on a ZOO-mesh screen of said Classifier total about 2 to 3 /2 times said approximately 2% fraction of coarser particles.

7. A highly flexible tobacco sheet made in accordance with claim 4 and containing a humectant as the sole additive.

8. A highly flexible tobacco sheet made in accordance with claim 5 and containing a humectant as the sole additive.

References Cited in the file of this patent UNITED STATES PATENTS 2,485,670 Siowa et a1. Oct. 25, 1949 2,897,103 Gottscho July 28, 1959 3,020,179 Hess ;Feb. 6, 1962 3,053,259 Parmele et al. Sept. 11, 1962

Claims (1)

1. THE IMPROVED PROCESS OF MANUFACTURING A COHERENT TOBACCO PRODUCT ADATPED FOR SMOKING, WHICH COMPRISES STEEPING TOBACCO IN WATER, THE MAJOR PORTION BY WEIGHT OF SAID TOBACCO BEING RETAINED ON A 60-MESH SCREEN, MAINTAINING THE AQUEOUS SUSPENSION OF TOBACCO AT A TEMPERATURE IN THE RANGE OF ABOUT 140 TO 200*F. FOR A PERIOD OF AT LEAST 2 HOURS, WET-GRINDING THE THUS TREATED AQUEOUS SUSPENSION OF TOBACCO UNTIL THE PARTICLES THEREOF RETAINED ON A 100-MESH SCREEN OF A CLARK CLASSIFIER ARE NOT MORE THAN 17% BY WEIGHT BUT NOT LESS THAN 9% BY WEIGHT OF THE TOBACCO ON A DRY BASIS, AND CONVERTING THE RESULTING WET-GROUND TOBACCO PULP INTO SAID COHERENT TOBACCO PRODUCT.