Manufacture of foamed tobacco-containing articles by extrusion

Abstract

 A wet blend containing tobacco particles and a binder is extruded under conditions such that steam is generated within the material upon extrusion and effects foaming. To minimize the amount of water used, which may subsequently have to be dried off, the binder is pre-hydrated by mixing with water before being mixed with the tobacco particles. To improve the consistency of the hydrated binder a small proportion of tobacco particles can be mixed with the binder before hydration or part of the binder can be mixed dry with the tobacco particles, leaving an excess of water for admixture with the rest of the binder.

Description

[0001] The present invention relates to a method of forming tobacco-containing articles, such as cigarette rods, by extrusion in which the material is foamed as it leaves the extruder as a result of generation of steam within the material.

[0002] European Patent Specification EP-A-0113595 published on 18th July 19R4 and the corresponding U.S. Patent 4,510,950 describe one such method in which a single strand is extruded and is of such a diameter as to be usable as a cigarette rod. The method involves the formation of a dry blend of tobacco particles with a cellulosic binder and optionally a filler material, mixing the dry blend with water to form a wet blend, and extruding the wet blend. The wet blend contains 15% to 50% by weight of water while the extruded article contains 5% to 20% by weight of water.

[0003] European Patent Specification EP-A-0167370 published on 8th January 1986 describes a similar method using a similar wet blend, but in that case the wet blend is extruded as a plurality of strands by using an extrusion nozzle with multiple orifices. The strands are then caused to adhere to one another to form a cigarette rod which has passages extending therethrogh between the strands. EP-A-0167370 additionally describes an improved method of forming the wet blend in which the binder is pre-hydrated by admixture with water before being mixed with the other constituents of the mixture to form the wet blend. That disclosure, however, dates only from the filing date of the European Application 85304645.6, namely 28th June 1985, and not from the priority date of that application.

[0004] The present application is concerned with the pre-hydration step, which is applicable both to the multi-strand extrusion process and to a single strand process. Specific examples of the application of the present invention will be given in the present specification but for detailed disclosure of features of the method in which the present invention is applicable reference is made to the two published European Patent Specifications already referred to, which will be referred to hereafter as "the European Specifications".

[0005] In accordance with the present invention there is provided a method of forming tobacco-containing articles by extrusion of a wet blend containing tobacco particles and a binder in which the material is foamed in the course of extrusion by the generation of steam within the material characterized in that at least a major part of the binder is pre-hydrated by mixing with water before the pre-hydrated binder is mixed with tobacco particles.

[0006] Preferably the wet blend contains 15% to 50% by weight of water and the remainder, on a dry weight basis, comprises 5% to 98% and preferably more than 50% of tobacco particles having a particle size up to 5 mesh (4 mm), from 0% to 60% of a filler having a particle size of not more than 350 m, and from 2% to 40% of the binder.

[0007] Tobacco particles up to an amount of 5% by weight may be added to the binder which is to be pre-hydrated. Alternatively a proportion of the binder may be mixed with the tobacco particles so that the remainder of the binder is pre-hydrated with an excess of water.

[0008] A preferred method in accordance with the invention comprises the steps of (1) dry blending (a) from about 2 to about 98 wt. % of tobacco particles having a particle size of up to about 5 mesh and an 0V value of from about 3 to about 20% with (b) from 0 to about 60 wt. % of a filler having a particle size of up to about 350µm, (2) prehydrating from about 2 to about 40 wt. % cellulosic binder with water or similar solvent to activate the adhesive character of the binder, (3) admixing the dry blend from step (1) with the prehydrated cellulosic binder from step (2) to form a wet blend containing from about 15 to about 50 wt. % of water, then (4) extruding the wet blend from step (3) into various shaped articles under extrusion conditions of temperature and pressure such that as the wet blend is extruded, the moisture in the blend is converted to steam, thereby foaming the article. Alternatively, a portion of the dry blend from step (1) could be prehydrated together with the binder in step (2) or a portion of the binder could be dry blended with the ingredients in step (1). As used herein, the term "extrudate" refers to the wet blend of materials after they have reached the mixing barrel of the extruder.

[0009] Preferably the wet blend is extruded as a single cylindrical strand which after extrusion is sized to a substantially cylindrical shape having a diameter between 2 mm and 35 mm and preferably betwen 4 mm and 25 mm. Alternative cross-sectional configurations may be made with an appropriate die, for example oval or star-shaped. The rods thus formed can be cut to an appropriate length and wrapped to form a cigarette. Alternatively a multistrand extrusion can be formed with the strands adhering to form the cigarette rod.

[0010] The optimal amount of prehydrated cellulosic binder present in the admixed wet blend will vary with the specific cellulosic binder used. For example, when hydroxypropyl cellulose is used as the only cellulosic binder, an optimal amount is at least about 8 wt. %. When hydroxypropyl cellulose is not included, an optimal amount of another cellulosic binder is at least about 10 wt. %. When hydroxypropyl cellulose is used in combination with another cellulosic binder, an optimal amount of hydroxypropyl cellylose is at least 1 wt. % in combination with at least 2 wt. % of the other cellulose binder(s) for a total amount within the range of from 3 to about 40 wt. X.

[0011] The binder may be selected from the materials described in European Specification 0167370 which include those referred to as "the compounds" in European Specification 0113595. Optional materials included in the wet blend are fillers, alcohols and stiffening agents all as described in the European Specifications. The stiffening agent is preferably added during the dry blending step but may alternatively be added during the pre-hydration step or the admixing step or immediately subsequent thereto.

[0012] The binder is pre-hydrated by blending the binder with sufficient water so that the wet blend resulting after step (3) contains from about 15 to about 50X water. The prehydrating step provides the water directly to the binder materials where it is best utilized for activating the adhesive character of the binder efficiently, for forming the foamed extruded smoking article. The tobacco particles, being relatively more hygroscopic than the binder, tend to absorb more of the water than the binder when the binder and tobacco are dry blended together first, and water added second. This provides a wet extrudate having a significant amount of binder that is not activated and incompletely utilized. Consequently, either a larger than necessary amount of binder or an excessive amount of water, or both must be added to a dry blend of tobacco and binder to activate enough binder to form the product. The extrudate must be dried significantly, to reduce the water content to the desired level of between about 5 and 20 wt. % water for the smoking article.

[0013] Prehydrating the binder reduces the amount of water necessary to extrude the wet blended materials, resulting in a dryer and firmer extrudate. The tobacco does not absorb large amounts of water, that must later be removed by drying because the binder has already used most of the water. This also eliminates the need for special handling equipment required for the wetter non-prehydrated extrudate. Prehydration also reduces the amount of energy needed to dry the resulting extrudate to the desired moisture content because of its overall lower moisture content.

[0014] Prehydrating the binder also provides for a stronger extrudate than when a binder is not prehydrated. Because significantly more of the prehydrated binder is activated, there is a proportionately greater amount of adhesive activity which results in more binding and a more rigid product. By prehydrating the binder, a lesser amount of binder is needed to perform the binding function than the amount of binder required in the nonprehydrated blend. Reducing the amount of binder is not only more economical but greatly improves the subjective quality factors of the resulting smoking article, for example, taste, feel, aroma, colour, and quality of smoke.

[0015] Prehydrated binder is a viscous dough-like material. Because in some cases the viscosity may be too high for the conventional mixing apparatus at hand, it may be advantageous to add some of the dry blended materials of step (1) to the binder during the prehydrating step. Although the added dry blend of up to about half (preferably no more than 5X) of the total tobacco weight will absorb some of the water, it will neither significantly interfere with prehydration of the binder nor raise the overall moisture content of the mass, but it will act as a lubricant to keep the dough-like mass within a workable, blendable, and extrudable viscosity range. Alternatively, some of the cellulosic binder materials in an unhydrated condition may be added to the mixture to be dry blended in step (1) with the balance of the binder being prehydrated. This too, will result in a relatively lower viscosity for the prehydrated binder as there will be some excess water in the prehydrated binder mass. Then, upon admixing the dry blend and prehydrated binder, the excess water is taken up by both the non-prehydrated binder and the tobacco present in the dry blend. In this alternative, most of the binder will be prehydrated so that any water absorbed by the tobacco is not significant compared to the resulting extrudate moisture content, and the admixed mass has a viscosity that can be extruded readily.

[0016] The prehydration of the binder, with or without a small portion of dry blend from step (1), is carried out in a conventional mixing device. The amount of water present in the wet blend is critical in that if the water content is reduced to less than about 15 wt. %, shear at the die of the extruder increases to the point that the surface of the extruded product becomes porous and rough, which results in a less than desirable degree of foaming. At water contents in excess of about 50 wt. %, without alteration of temperature, insufficient energy is supplied to the formulation to generate foam formation as the product exits the die.

[0017] Optionally, in step (1), in step (2), in step (3), or in step (4) a foaming agent may be added to the blend. The foaming agent is preferably selected from the group consisting of air, nitrogen, carbon dioxide, ammonium carbonate, ammonium carbamate, an azide, a hydrazide, pentane, hexane, heptane, a halogenated fluorocarbon, pyrrole, acetone, ethanol, a peroxide, and azodicarbonamide. Some of these foaming agents may require the addition of an acid or a base for decomposition. The foaming agent will supplement the foaming effect of the water in the wet blend and may allow the use of lower amounts of water.

[0018] Preferred extruders include twin screw extruders having a positive displacement action, optionally having a plurality of multiple product feed ports along the length of the mixing chamber so that the prehydration of step (2) can occur in one segment of the mixing chamber, followed by the admixing of step (3) in the adjacent segment, followed by extrusion and foaming. A twin screw extruder because the positive displacement action is capable of processing more viscous masses. Screw tolerances and kneading blocks or forward and reversing paddles can be adjusted to select the net force pushing the material down the extrusion tube. The net force must be controlled to prevent overworking or cooking of the mixture, resulting in a dark coloured product that will not foam properly, or underworking the mixture which results in an incompletely mixed and insufficiently foamed product. It is important that the tobacco particles and any preferred additional ingredients be mixed to form a homogenous mixture prior to introduction into the feeding bin or in-feed port of an extruder.

[0019] The feeding bin is a starting point common to many single screw extruder systems and is typically lcoated near the extruder with its purpose being to provide a continuous source of raw ingredients. The feeding bin receives material from a conventional mixer/surge system and it typically discharges into a variable speed metering/feeding device. A simple gravity bin with a bottom discharge may suffice for the ingredients employed in the step (3). Some feed assist means may be preferred depending on the viscosity of the mass.

[0020] A variable speed metering/feeding device is typically employed to take the wet blend away from the feeding bin and to transport it toward the extruder. This variable speed feeding device is a key link in theoutput of the extruder and sets the extrusion rate. Vibratory feeders and variable speed screw feeders are two commonly used metering/feeding devices.

[0021] An intermediary processing device may be utilized to prehydrate the binder, adding water, binder, and any other desired materials to form the dough-like viscous mass. This mass is then added to a second intermediary processing device to admix the prehydrated binder with the dry blend from step (1) in step (3). Continuous mixing of the dry blend with the prehydrated binder is accomplished in the processing device from which the wet blend is then fed directly into the extruder barrel.

[0022] When a twin screw extruder having multiple feed ports is used, typically one intermediary processing device will mix the binder materials together and feed it to a first feed port and a second materials together and feed it to a first feed port and a second intermediary processing device will mix the tobacco and other materials and feed it to a second port downstream of the first port. The respective feed rates are to be controlled to drive the desired proportions of binder to tobacco, to filler, etc., and water is added as needed, first to prehydrate the binder, and second maintain the moisture content above the 15% OV minimum, along the extruder barrel, as mixing and homogenizing occurs up until extrusion occurs.

[0023] Sensors for detecting the pressure of the extrudate within the barrel may be placed along the extruder barrel. Corresponding water input feeds may also be arranged along the barrel to add water when necessary to control the moisture level, for example, above the 15% or other desired minimum level to prevent the mixture from cooking or too high shear extrusion.

[0024] When a single feed port extruder is available, the binder could be first prehydrated in an intermediary processing device. Then the tobacco, filler, and other materials, having first been dry blended in a separate device are introduced to the intermediary processor for admixture, and the resulting wet blend then fed directly to the extruder barrel.

[0025] The method of the invention is illustrated by the following examples:-

Example I

[0026] This concerns a multi-strand extrusion and compares results obtained by Method B, which is the pre-hydration method of the present invention, with those of Method A in which the binder and tobacco particles are mixed before adding water. It uses a Baker-Perkins twin screw extruder, Model MPF-50D, having a 1263.6 mm long extrusion chamber, wherein the two screws had the same assemblage of components, as follows:

[0027] The screws were rotated so as to be 90° out of phase to prevent interfering with each other and to provide a tolerance between the screws of about 50/64 mm. The Baker-Perkins extruder has multiple feed ports along its length so auxiliary mixing equipment was not required. The binder was added at a distance 15:1 length:diameter ("L/D") screw length measured from the extrusion end (die), the water used to prehydrate the binder was added at a distance 12:1 (L/D) from the die, and the tobacco dust was added at a distance 10:1 (L/D) from the die. The binder mixture used consisted of the following blend:

[0028] 

The results of the various extrusions are set forth in Table I below.

[0029] The products of runs c, d, and e, made in accordance with Method B prehydration of binder technique, were much stronger and better in appearance than the product made by the non-prehydrated Method A, run a, even though they contained a significantly lesser amount of binder. In addition, using Method B and prehydrating the binder allowed for the extrusion of a drier extrudate by using a lesser amount of water. Run "a", made in accordance with Method A, could not produce a satisfactory product with a lesser amount of water or a lesser amount of binder than used in the example.

Example II

[0030] This concerns single strand extrusion using a Baker-Perkins twin screw extruder, model MPF-50D having a 755.65 mm long extrusion chamber wherein the two screws had the same assemblage of components as follows:

[0031] The screws were rotated so as to be 90° out of phase to prevent interfering with eachg other and to provide a tolerance between the screws of about 50/64 mm.

[0032] The binder comprised 2 parts hydroxypropyl cellulose (Klucel HF), a part carboxymethyl cellulose (CMC HF), and 1 part cereal binder (a pre-gelatinized corn starch). The binder material had a moisture content of 6.3% OV and a commercial tobacco blend dust was used. The Baker-Perkins extruder has multiple feed ports along its length, so auxiliary mixing equipment was not required as it was in the Wenger extruder. The binder was added at a distance 679.45 mm from the die, the water used to prehydrate the binder was added at a distance 615.95 mm from the die, and the tobacco dust was added at a distance 425.45 mm from the die. The L:D ratio is 15:1 where the binder is added and 10:1 where the tobacco dust is added. The following runs were made at the extrusion conditions set forth in Table II.

Example III

[0033] The following examples were extruded in the Baker-Perkins extruder under the following extrusion conditions.

[0034] The same feed port arrangement and L:D ratios as used in Example II were used here. The binder mixture was selected from one of the three blends comprising:

[0035] The results of the various extrusions are set forth in Table III below:

[0036] These results show that Runs IIc. IId and IIIb, when compared to the control, had a lower OV content in the mixing barrel and as extruded, and a greater weight per unit length. The results of Example II show generally that the prehydrated binder blends have somewhat higher resistance to draw with about the same rod circumference for the same amount of binder as the control. In general, the resulting product from prehydrated binders were stronger and had less moisture than non-prehydrated binders, thus requiring less amount of binder overall and less time to dry the extrudate. Compare Run IIIc having 8 wt. % binder to the control having 10 wt. % binder where it appears that using less binder in a prehydrated state results in having about the same moisture content, a comparable resistance to draw, a larger rod circumference, and a greater weight, mass rate, and velocity of extrusion. The product also had a lighter colour, probably because the prehydration prevented the tobacco from absorbing much water which probably resulted from not overcooking the extrudate.

Claims

1. A method of forming tobacco-containing articles by extrusion of a wet blend containing tobacco particles and a binder in which the blend is foamed in the course of extrusion by the generation of steam within the blend characterized in that at least a major part of the binder is pre-hydrated by mixing with water before the pre- hydrated binder is mixed with the tobacco particles.

2. A method as claimed in claim 1 in which a proportion of the binder is mixed with the tobacco particles so that the rest of the binder is pre-hydrated with an excess of water.

3. A method as claimed in claim 1 or 2 in which tobacco particles . amounting to up to 5% by weight of the blend of a dry weight basis are added to the binder which is pre-hydrated.

4. A method as claimed in any of claims 1 to 3 in which the wet blend contains 15% to 50% by weight of water and the remainder, on a dry weight basis, comprises 5% to 98% of tobacco particles having a particle size up to 4 mesh (4 mm), from 0% to 60% of a filler having a particle size of not more than 350µm, and from 2% to 40% of the binder.

5. A method as claimed in any of claims 1 to 4 in which the binder is a cellulosic binder.

6. A method as claimed in any of the preceding claims in which the tobacco particles, together with any filler which is used, are initially mixed with an alcohol and/or a stiffening agent before mixing with the pre-hydrated binder.

7. A method as claimed in any of the preceding claims in which the wet blend is extruded as a single strand and the foamed strand is sized to a cylindrical shape with a diameter of from 2 to 35 mm.

8. A method as claimed in claim 7 in which the diameter is from 4 to 25 mm.

9. A method as claimed in any of the preceding claims in which from 01 to 15% by weight of a polyfunctional acid such as citric acid is added to the tobacco particles before mixing with the pre- hydrated binder.

10. A method as claimed in any of the preceding claims in which the wet blend contains 15% to 35% of water.

11. A method as claimed in any of the preceding claims in which the moisture content of the extrudate is below 25% OV.