US3842846A

US3842846A - Microwave expansion of tobacco

Info

Publication number: US3842846A
Application number: US00325594A
Authority: US
Inventors: T Laszlo
Original assignee: Philip Morris USA Inc
Current assignee: Philip Morris USA Inc
Priority date: 1973-01-22
Filing date: 1973-01-22
Publication date: 1974-10-22
Anticipated expiration: 1991-10-22
Also published as: DE2402658A1; NL169676C; AU472845B2; FR2214420B1; CH566728A5; CA1002417A; AU6462374A; SU533322A3; DE2402658B2; JPS49102900A; ES422139A1; GB1431124A; FR2214420A1; NL7400795A; BE810009A; IT1008705B; JPS5238117B2

Abstract

A process for puffing tobacco leaf in whole or cut form is disclosed in which the tobacco is impregnated with a suitable liquid, such as water, and then introduced into a water vapor containing zone wherein the tobacco is subjected to exposure to a microwave field to vaporize the water in the tobacco expanding the cells and thereby puffing the tobacco.

Description

" nited States Patent 1191 Laszlo MICROWAVE EXPANSION OF TOBACCO Tibor S. Laszlo, Richmond, Va.

Philip Morris Incorporated, New York, NY.

Jan. 22, 1973 Inventor:

Assignee:

Filed:

Appl. No.:

us. 01 131/140 P, 131/121 Int. Cl A24b 3/18 Field ofSearch 131/121,140 144 [56] References Cited UNITED STATES PATENTS 5/1952 Sowa 131/140 P 8/1956 Heljo 11/1968 delaBurde ..l3l/l40P 2/1969 Hindetal. 131/121 STE Primary ExaminerMelvin D. Rein Attorney, Agent, or Firm-Watson Leavenworth Kelton & Taggart 5 7 ABSTRACT A process for puffing tobacco leaf in whole or cut form is disclosed in which the tobacco is impregnated with a suitable liquid, such as water, and then introduced into a water vapor containing zone wherein the tobacco is subjected to exposure to a microwave field to vaporize the water in the tobacco expanding the cells and thereby puffing the tobacco. 1

12 Claims, 2 Drawing Figures AM N STEAM OUT WAVE IN WAVE OUT MICROWAVE EXPANSION OF TOBACCO BACKGROUND OF THE INVENTION The desirability of expanding tobacco for use in smoking products is well-known, tobacco in expanded form having, inter alia, for a given weight thereof a greater filling capacity than regular tobacco, and in some instances a lower resistance-to-draw (RTD) as well as other advantageous characteristics. Certain manners of expanding tobacco are well-known. Thus, tobacco has been expanded by impregnating it with certain volatile materials or blowing agents, and then applying heat to cause puffing, the latter being facilitated in some instances by a reduction of the external pressure acting on the tobacco. lmpregnants used in such processes include water, organic solvents, ammonia, carbon dioxide, and combinations of the last two. Of these the simplest and most desirable in terms of cost, availability and absence of need for removal from the product following puffing is water. The use of water to puff tobacco stems in conjunction with applying energy in various forms to cause rapid heating and hence expansion is described in detail in US. Pat. Nos. 3,409,022; 3,409,023 and 3,529,606.

However, the expansion of tobacco leaf, whole or cut, with water impregnant by such means as provided in the patents aforesaid does not provide a commercially optimal puffing procedure for leaf tobacco. It is believed the ready permeability of the leaf structure to water permits escape before substantial puffing can take place. Since the tobacco expansion process is based on generating elevated pressure in the tobacco cell walls at a suitable rate, the rate of vaporization has to be greater than the diffusion of the vapors through the cell walls, but the maximum resulting pressure has to be less then the bursting strength of the cell structural elements. Accordingly, while such known procedures are satisfactory for puffing stems wherein permeability is satisfactorily low, the said known procedures are not effective for puffing leaf tobacco. The alternative procedure of effecting tobacco expansion with water alone, through freeze-drying, while well-known is a comparatively slow and expensive approach.

In the convection heating or mass transfer (so-called tower" procedures) and radiant transfer (infrared) expansion methods, the energy required for the heating of the liquid to vaporize same is deposited at the outermost surface of the cut "tobacco and only reaches the impregnating liquid by thermal conduction through the tobacco cell walls. Accordingly, the rate of vapor generation is controlled by the rate of energy delivery at the tobacco surface and by the thermal conductance of the cell wall. Generally to effect vaporization at the requisite rate, a high rate of energy delivery at the tobacco surface is required so that in effecting energy transfer in both aforementioned expansion processes, the outer surface of the tobacco reaches an unnecessary, and in many cases, harmfully high temperature.

The principles of application of a microwave field to tobacco for various purposes and with various consequences thereto including a certain resultant puffing are known. The use of a microwave field on moisturecontaining tobacco for the purpose of puffing stems also is known, being described, e.g., in US. Pat. No. 3,409,023. Techniques for puffing as described in the last-mentioned patent as generally known involving microwave field application are not commercially feasible for puffing leaf tobacco principally because they involve prolonged exposure of the tobacco to the microwave field and the degree of expansion achieved with leaf by such known techniques is insufficient to accomplish a satisfactory increase in the filling power of the tobacco.

SUMMARY OF THE PRESENT INVENTION The present invention relates to the application of a microwave field to tobacco leaf containing moisture while the latter is in an environment saturated or nearsaturated with water vapor to therewith cause a significant degree of puffing or expansion of the tobacco. The exposure of the tobacco to such form of energy is very short so that a high through-put is possible thereby providing an effective and commercially optimal manner of expanding tobacco.

In a suitably selected oscillating electromagnetic (microwave) field, the energy coupling (transfer) occurs preferentially between the field and certain liquids in some solids. The solid structure does not heat up at all, or only through conductance from the heated liquid. Under these circumstances, not only will the greater fraction of the invested energy be used for the heating (vaporization) of the liquid but the temperature of the solid will lag considerably behind that of the liquid.

In accordance with the present invention, leaf tobacco in whole leaf or cut filler form is impregnated with a suitable aqueous liquid impregnant such as water alone or a salt solution to provide a' total basis weight of liquid of at least 20 percent and the impregnated tobacco is then introduced into a water vapor containing zone wherein the tobacco is exposed to microwave energy, i.e., a microwave field, to vaporize the water in the tobacco at a rate and pressure which expands the cell walls of the tobacco and causes puffing of the same. Preferably the treatment of the tobacco is effected in a suitable microwave applicator on a continuous basis involving transporting the tobacco through the applicator in a predetermined period of time on a suitable traveling belt. For the purpose of providing a water vapor environment in the microwave applicator, the same can be provided with connection to a source of saturated steam and further it is preferable that the temperature condition in the zone be equilibrated to a temperature in the range of about C. to C. As an incident to the evaporation of liquid from the impregnated tobacco, any condensate consequent therefrom, as well as from the presence of steam in the applicator, can be and preferably is removed.

The achievement of puffing of leaf in the manner provided by the present invention is believed to occur for the following reasons. The competing routes for re lease of pressure resulting from vaporization of moisture within the cell wall are expansion and diffusion to the surroundings. The first is a function of. the overall pressure difference, the latter a function of the water vapor partial pressure difference. To minimize the second route, the external water vapor partial pressure must be substantially increased without increasing the total external pressure as by saturation of the surrounding atmosphere. A desirable lower limit is 40 percent water vapor by volume pressure).

For the purpose of generating a microwave field, a

microwave fringing field applicator of known construction can be employed, being used in conjunction with a thermally resistant glass or low loss factor glass hood enclosure which defines the zone wherein the puffing is effected with suitable connections for inlet and outlet of steam being provided on the hood.

Tobacco leaf, either in whole or cut filler form treated in accordance with the present invention, has enhanced puffed characteristics on the order of up to 50 percent or more expansion of the puffed product over the raw tobacco, while at the same time such treatment is carried out in shortened time periods on a continuous basis to thereby provide a commercially feasible manner of puffing leaf tobacco with a microwave field.

BRIEF DESCRIPTION OF THE DRAWINGS A fuller understanding of the nature and objects of the present invention will be had from the following detailed description taken in conjunction with the accompanying drawing showing by way of example preferred embodiments of the inventive concept and in which:

FIG. 1 is a diagramatic depiction of the apparatus and process by which leaf tobacco can be expanded in accordance with the principles of the present inventlon.

FIG, 2 is a microwave fringing field applicator which is employed in the apparatus depicted in FIG. 1 for generation of a microwave field.

Throughout the following description, like reference numerals are used to denote like parts in the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is concerned with the puffing of tobacco leaf and while it will be described in embodiments thereof as used for puffing cut tobacco leaf filler, it will be understood that the invention is equally applicable to the puffing of leaf tobacco in whole leaf form.

In accordance with the present invention, the leaf tobacco to be puffed first must be treated with a suitable aqueous liquid to impregnate the tobacco so that it has a moisture content, expressed as oven-volatiles" in the range of about 20 to 60 percent total weight basis. Tobacco contains about 2 percent of volatile matter other than water which is lost in the test for oven volatiles (O.V.), but from a practical standpoint, at moisture levels above l percent in tobacco O.V. may be regarded as substantially equivalent to moisture and is used herein in that context. The O.V. test is used because of its ease and rapidity in preference to water analysis. Preferably the impregnant should amount to about 40 percent of the total basis weight of the tobacco. As impregnants water, as well as salt solutions, are particularly effective. Where salt solutions are used, the same preferably are in the form of a sodium chloride solution in a range of about 0.1 to 0.7 mol NaCl. After the tobacco has been suitably impregnated or moistened to a requisite or desired level, the tobacco is ready for processing in the apparatus depicted in FIG. I, the tobacco in whole leaf or cut filler form being deposited in a feed bin or hopper 12 designed to continuously feed tobacco to the processing apparatus. The apparatus includes a belt conveyor 14 which in one form can be comprised of a resin impregnated woven glass fabric and which transits an endless course through the microwave field applicator depicted generally at 16. Desirably the belt conveyor 14 is made of woven glass fabric impregnated with a polymer of low loss factor, the belt thus being substantially electrically non-conductive and not subject to heating to maximize the amount of thermal energy generated in the tobacco. The microwave applicator unit 16 includes a microwave field generating component 18 known as a fringing field applicator and manufactured by Genesys Systems, Inc., Palo Alto, Calif. The microwave applicator unit 16 further includes the customary cut-off tubes 20 which function to confine the presence of the microwave field to the zone in which the tobacco is to be treated and which zone is defined by a hood like enclosure 22, the hood enclosure 22 being preferably provided in the form of a low loss factor glass hood or enclosure having in association therewith a microwave field reflecting element in the form of a metal cage.

As a preliminary to puffing the tobacco, the microwave applicator unit 16 has the temperature condition in the zone thereof defined by hood enclosure 22 equilibrated to a temperature in the range of about C. to about l50C. Furthermore, the puffing of tobacco in accordance with the present invention involves the provision of a water vapor containing zone inside the microwave applicator and for this purpose as well as for the purpose of equilibrating the temperature therein, saturated steam is introduced into the hood enclosure 22 by way of a suitable

steam line connections

24, 26 there also being provided outlets (not shown) for carry off of any steam condensate as well as water removed from the tobacco. During processing, a certain quantity of excess steam will escape enclosure 22 through cutoff tubes 20.

After the temperature condition of the microwave applicator has been properly equilibrated, tobacco is delivered from the hopper 12 onto the traveling conveyor belt 14 and is transported through the microwave applicator wherein the tobacco is exposed to the microwave field and the liquid impregnant is evaporated with the pressure thereof and the rate of evaporation ex panding the tobacco cell walls and thus puffing the tobacco. As indicated earlier the present invention provides that the puffing of the tobacco can be effected in a very short period of time and without unduly heating the tobacco by employing a microwave field. Accordingly, the conveyor belt 14 is designed to operate at a speed to transport the tobacco through the oven so that the total time exposure of the tobacco to the microwave energy is within the range of about 0.05 to about 5.0 minutes, but preferably in a time in the range of 0.05 to 0.15 minutes. In conjunction with such exposure periods, the power density of the microwave applicator is preferably in the range of about 0.01 to about 2.5 kw but preferably 2.0 to about 2.5 kw.

As those skilled in the art will discern, the microwave field frequency can be any one of the four bands available for the commercial purposes of treating vegetable material as provided under existing FCC regulations, such frequencies being 22,000; 5800; 2,450 and 915 MH although it will be understood that any frequency within the range of 915-22,000 MH would be suitable for the practice of the present invention with frequencies at the higher end of the range being preferred. The maintenance of a water vapor containing zone wherein puffing takes place is an important part of the present invention and as has already been indicated the saturation of the zone defined by the hood enclosure 22 preferably is effected by using saturated steam. The degree of water vapor saturation within the zone should be such as to provide a relative humidity therein in the range of 40-100 percent, relative humidities of somewhat higher values being preferred.

The fringing field applicator 30 depicted in FIG. 2 is as indicated a conventional type manufactured by the Genesys Systems, Inc., Palo Alto, Calif, and is connected to a microwave power source at the wave-in connection 32 and at the wave-out end to a dummy load connection 34.

For the purposes of providing continuous uniform delivery of tobacco to the microwave applicator unit, the tobacco from hopper I2 can be levelled on the conveyor belt 14 in known manner, as for example per use of a rotary brush mechanism, to provide a smooth bed of uniform thickness. Following the puffing of the tobacco in the microwave applicator, the product as it reaches the end of the conveyor belt travel at the right end of FIG. 1 can be removed for further processing in known manner. For example, the same can be blended with regular cut tobacco leaf filler for cigarette filler purposes or it can be used in its entirety as a cigarette filler. Further and since the puffing of the tobacco results in reduction of the moisture content of the tobacco below a desired level, it may be desirable to reestablish a particular desired moisture content in the puffed tobacco, as for example to provide a tobacco moisture content of about 8 to 15 percent.

The following examples serve to illustrate the present invention:

EXAMPLE 1 A cut, bright filler tobacco containing 40 percent O.V. was fed to the conveyor belt. after the apparatus of FIG. 1 had been brought to equilibrium temperature condition with steam. Three runs with varying parameters gave the results shown in Table I below.

Table l Tobacco Power density feed rate Exposure time kw g./min. sec. 7! Expansion The degree of expansion was determined by measuring the apparent density of filler at -11 percent O.V. before and after treatment and dividing the first by the second. Apparent density was measured by the standard weight-loss method on immersion in acetone.

EXAMPLE 2 Table II Microwave Control Treated Change Rod wt.. g. 0.870 0.766 12 Rod firmness, 35.5 35.5 0 Rod resistance to draw, 2.9 2.8

in water Total particulate matter, 26.l 22.6 l3

mgJcig. Nicotine, mg./cig. l.79 L48 1? Water, mg./cig. 2.8 2.3 l8 Puff count 9.5 8.5 II

Filler containing 20 percent O.V. was similarly treated. Expansion was about 15 percent.

EXAMPLE 3 Ten pounds of cut filler tobacco containing approximately 60 percent O.V. was fed to the conveyor belt and passed through the apparatus (already brought to temperature with steam) at rates to give exposure varying from 2 to 15 seconds, at power density from 2.0 to 2.5 kw. Expansion of the product compared at about 11 percent O.V. is 30 to 50 percent.

EXAMPLE 4 Cut bright filler containing 40 percent O.V. was treated according to the process of Example 1, with particular attention being given to keeping the stream of filler uniform. Power density was 2.0 kw., feed rate 20g/min., exposure time 4.5 sec. Expansion was found to be 43 percent.

Other forms of microwave energy generation may be used in the process of the present invention.

As indicated earlier, salt solutions can be employed as the impregnant. Water-soluble salts in general will give improved microwave coupling efficiency and thus somewhat better expansion than water. The salts must be chosen with regard to their effect on smoking characteristics since they will remain in the tobacco. Acceptable salts include Na, K, Ca, or Mg citrates, acetates, sulfates and the like. Aqueous ammonia though not a salt also could be used.

The description of the present invention has been given herein in terms of an ambient pressure in the microwave applicator unit, e.g., one atmosphere, although an overpressure also may be used effectively.

What is claimed is:

1. A process for puffing tobacco which comprises treating tobacco leaf with a water impregnant to provide said tobacco leaf with a moisture content, in the range of about 20 percent to about 60 percent by weight of the total weight of the impregnated tobacco leaf, introducing said impregnated tobacco leaf into a treating zone, flowing steam through said treating zone to saturate said zone with water vapor to give a partial pressure of at least 40 percent and subjecting said tobacco while in said zone to a microwave field to vaporize the water in said tobacco leaf at a rate and pressure which expands the cell walls of said tobacco causing puffing of the same.

2. The process of claim 1 wherein the water impreg: nant is that present in a salt solution.

3. The process of claim 2 wherein the salt in said salt solution is sodium chloride and is present in the range of 0.1 to 0.7 mol.

4. The process of claim 1 wherein the water impregnant comprises about 40 percent by weight of the total weight of the impregnated tobacco leaf.

5. The process of claim 1 wherein said tobacco is exposed to said microwave field for a time between about 0.05 minutes to about 5.0 minutes.

6. The process of claim 5 wherein said tobacco is exposed to said microwave field for a time between about 0.05 minutes to about 0.15 minutes.

7. The process of claim 1 wherein said microwave field is generated at a frequency between about 915 MH and about 22,000 MH and is of a power density of between about 0.1 kw to about 2.5 kw.

8. The process of claim 7 wherein said microwave field is of a power density of between about 2.0 kw to is in cut filler form.

l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,842,846 Dated October 22, 1974 Inventor(s) 'I'j bgr Laszlo It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 8, cancel lines 2 4.

Signed arid sealed this 29th day of April 1975 (SEAL) Attest:

' C. MARSHALL DANN RUTH C. MASON Conunissioner of Patents Attesting Officer and Trademarks

Claims

1. A process for puffing tobacco which comprises treating tobacco leaf with a water impregnant to provide said tobacco leaf with a moisture content in the range of about 20 percent to about 60 percent by weight of the total weight of the impregnated tobacco leaf, introducing said impregnated tobacco leaf into a treating zone, flowing steam through said treating zone to saturate said zone with water vapor to give a partial pressure of at least 40 percent and subjecting said tobacco while in said zone to a microwave field to vaporize the water in said tobacco leaf at a rate and pressure which expands the cell walls of said tobacco causing puffing of the same.

2. The process of claim 1 wherein the water impregnant is that present in a salt solution.

7. The process of claim 1 wherein said microwave field is generated at a frequency between about 915 MHZ and about 22,000 MHZ and is of a power density of between about 0.1 kw to about 2.5 kw.

8. The process of claim 7 wherein said microwave field is of a power density of between about 2.0 kw to about 2.5 kw.

9. The process of claim 1 wherein said zone is saturated with water vapor by flowing saturated steam therethrough.

10. The process of claim 7 wherein said zone is maintained at an equilibrated temperature condition in the range of between about 75C. and 150C., and any steam condensate present therein is continuously removed therefrom.

11. The process of claim 7 wherein the temperature condition in said zone is equilibrated before introducing said tobacco leaf into said zone.

12. The process of claim 1 wherein said tobacco leaf is in cut filler form.