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Title:
METHOD AND APPARATUS FOR UNWINDING A BOBBIN OF A HOMOGENIZED TOBACCO SHEET
Document Type and Number:
WIPO Patent Application WO/2018/122356
Kind Code:
A1
Abstract:
The invention relates to a method for unwinding a bobbin (2) of a homogenzied tobacco sheet (3), the method comprising: providing a bobbin (2) of a homogenized tobacco sheet (3), the bobbin (2) comprising an outer surface (4); and heating a portion of the outer surface (4) of the bobbin (2) while unwinding the homogenzied tobacco sheet (3) from the bobbin.

Inventors:
PRESTIA, Ivan (Via Stelloni Levante, 26/6, Calderara di Reno, I-40012, IT)
LA PORTA, Pietro Davide (Via Gino Cervi 21, Bologna, I-40133, IT)
Application Number:
EP2017/084779
Publication Date:
July 05, 2018
Filing Date:
December 28, 2017
Export Citation:
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Assignee:
PHILIP MORRIS PRODUCTS S.A. (Quai Jeanrenaud 3, 2000 Neuch√Ętel, CH-2000, CH)
International Classes:
A24C5/20; B65H16/10
Domestic Patent References:
WO2015193031A12015-12-23
Foreign References:
EP1428644A22004-06-16
EP1695934A22006-08-30
EP0314857A11989-05-10
Other References:
"Gums And Stabilizers For The Food Industry", 1988, IRL PRESS
WHISTLER: "Industrial Gums: Polysaccharides And Their Derivatives", 1973, ACADEMIC PRESS
LAWRENCE: "Natural Gums For Edible Purposes", 1976, NOYES DATA CORP
Attorney, Agent or Firm:
PORTA, CHECCACCI & ASSOCIATI S.P.A. (Via Trebbia 20, Milano, I-20135, IT)
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Claims:
Claims

Method for unwinding a bobbin of a homogenized tobacco sheet, the method comprising: o providing a bobbin of a homogenized tobacco sheet, the bobbin comprising an outer surface; and o heating a portion of the outer surface of the bobbin while unwinding the homogenized tobacco sheet from the bobbin.

Method according to claim 1 , wherein the step of heating a portion of the outer surface of the bobbin while unwinding the homogenized tobacco sheet from the bobbin includes:

o heating a portion of the outer surface of the bobbin to a temperature of at least about 40 degrees Celsius.

Method according to claim 1 or 2, including:

o changing the distance between a heat source used to heat a portion of the outer surface of the bobbin and a center of the bobbin while unwinding. Method according to claim 3, including:

o bringing the heat source nearer to the center of the bobbin while unwinding. Method according to claim 3 or 4, including:

o changing the temperature of the heat source while unwinding.

Method according to claim 5, including:

o reducing the temperature of or the power emitted by the heat source while unwinding.

Method according to one or more of the preceding claims, including:

o heating a portion the outer surface of the bobbin comprising at least half of the outer surface.

Method according to one or more of the preceding claims, including:

o arranging a plurality of heat sources around the outer surface of the bobbin; and

o setting the heating temperature of each heat source of the plurality depending on the position of each heat source with respect to the outer surface of the bobbin.

Method according to one or more of the preceding claims, wherein the homogenized tobacco sheet includes a free portion detaching from the bobbin defining a line of contact between the free portion and the outer surface of the bobbin, and wherein heating a portion of the outer surface of the bobbin while unwinding includes

o bringing the line of contact to a temperature between about 40 degrees Celsius and about 75 degrees Celsius.

10. Method according to one or more of the preceding claims, including:

o measuring a diameter of the bobbin.

11. Method according to claim 10, including:

o changing the distance between a heat source used to heat a portion of the outer surface of the bobbin and the bobbin, or a temperature of or the power emitted by the heat source depending on the diameter of the bobbin.

12. Method according to any of the preceding claims, including:

o measuring a temperature of a portion of the outer surface of the bobbin.

13. Method according to any of the preceding claims, wherein the homogenized tobacco material includes a binder or an aerosol former.

14. Method according to any of the preceding claims, wherein the step of heating a portion of the outer surface of the bobbin includes heating the portion in a contactless

manner.

15. An apparatus for unwinding a bobbin of a homogenized tobacco sheet, comprising:

o a bobbin holder where a bobbin of a homogenized tobacco sheet is placed; and

o a heat source adapted to heat a portion of an outer surface of the bobbin.

16. The apparatus according to claim 15, wherein the heat source is an infrared heater.

17. The apparatus of claim 15 or 16, including a sensor adapted to determine the diameter of the bobbin or to determine the temperature of a portion of the outer surface of the bobbin.

18. The apparatus according to any of claims 15 - 17, including a distance variator adapted to change the distance between the heat source and the bobbin holder.

19. The apparatus according to any of claims 15 - 18, including a temperature variator adapted to change the temperature of or the power emitted by the heat source.

20. The apparatus according to any of claims 15 - 19, including a plurality of heat sources arranged around the bobbin holder.

Description:
METHOD AND APPARATUS FOR UNWINDING A BOBBIN OF A

HOMOGENIZED TOBACCO SHEET

The present invention is related to a method and an apparatus to unwind a bobbin of a homogenized tobacco sheet.

Unwinding bobbins of material can be a difficult task, when the material which is coiled to form a bobbin is at the same time both sticky, so a rather high force need to be applied in order to unwind it, and fragile, so that it can be easily torn apart. Such a material is for example a homogenized tobacco sheet, which can be obtained for example casting a sheet of homogenized tobacco material. The homogenized tobacco sheet, when coiled in bobbins, is difficult to unwind due to its consistency, sensitivity to heat and low tensile strength, all preventing for instance to simply increase the force applied to the sheet to unwind the bobbin.

In current manufacturing process of homogenized tobacco material, unwinding speed has to be lowered sometimes down to about 100 meters per minute in order to prevent as much as possible to tear the homogenized tobacco sheet, which in turn automatically decreases the production speed and hourly production.

In addition to the low tensile strength of the material, some bobbins of homogenized tobacco sheet have quite variable shapes from one to another, so this shape inhomogeneity has to be taken into account in an apparatus and a method to unwind bobbins of homogenized tobacco sheet.

There is therefore a need of a method and an apparatus to unwind bobbins of coiled sheet, in particular of sheets of material having low textile strength or it is "sticky". These method and apparatus should be capable to increase the unwinding speed so that the rest of the production line can increase the overall production rate. Further, the method and the apparatus should minimize ruptures of the sheet while it is unwound from the bobbin.

In a first aspect, the invention relates to a method for unwinding a bobbin of a homogenized tobacco sheet, the method comprising: providing a bobbin of a homogenized tobacco sheet, the bobbin comprising an outer surface; and heating a portion of the outer surface of the bobbin while unwinding the homogenized sheet from the bobbin. According to invention, it is proposed to heat the last layer of the homogenized tobacco sheet in the bobbin, efficiently, to minimize the risk of breaking the sheet during unwinding. The heating may enable to cope with the specific characteristics of the homogenized tobacco sheet, such as a cast leaf sheet, for example its content in binder or aerosol former, to create the adequate conditions to detach the layers of homogenized tobacco sheets without tears. It has been found that the layers of the sheet tend to self-detach from each other if they are brought to a given temperature, for example a temperature within a specific range of temperatures. This given temperature maybe controlled or changed at any time during unwinding of the bobbin, and fine-tuned according to the specific needs.

As used herein, the term "sheet" denotes a laminar element having a width and length substantially greater than the thickness thereof. The width of a sheet is preferably greater than 10 millimeters, more preferably greater than 20 millimeters or 30 millimeters. Even more preferably, the width of the sheet is comprised between about 100 millimeters and 300 millimeters.

Preferably, the sheet is a sheet of homogenized tobacco material.

The most commonly used forms of homogenized tobacco material is reconstituted tobacco sheet and cast leaf. The process to form homogenized tobacco material sheets commonly comprises a step in which tobacco dust and a binder, are mixed to form a slurry. The slurry is then used to create a tobacco web. For example by casting a viscous slurry onto a moving metal belt to produce so called cast leaf. Alternatively, a slurry with low viscosity and high water content can be used to create constituted tobacco in a process that resembles paper- making.

The sheet material of tobacco can be referred to as a reconstituted sheet material and formed using particulate tobacco (for example, reconstituted tobacco) or a tobacco particulate blend, a humectant and an aqueous solvent to form the tobacco composition. This tobacco composition is then casted, extruded, rolled or pressed to form a sheet material from the tobacco composition. The sheet of tobacco can be formed utilizing a wet process, where tobacco fines are used to make a paper-like material; or a cast leaf process, where tobacco fines are mixed together with a binder material and cast onto a moving belt to form a sheet.

The sheet of homogenized tobacco material is then rolled in bobbins which needs to be unwound in order to be further processed, to be part for example of an aerosol-forming article, that is to be included in the aerosol-forming substrate of the aerosol-forming article. In a "heat-not-burn" aerosol-generating article, an aerosol-forming substrate is heated to a relatively low temperature, in order to form an aerosol but prevent combustion of the tobacco material. Further, the tobacco present in the homogenized tobacco sheet is typically the only tobacco, or includes the majority of the tobacco, present in the homogenized tobacco material of such a "heat-not-burn" aerosol-generating article. This means that the aerosol composition that is generated by such a "heat-not-burn" aerosol-generating article is substantially only based on the homogenized tobacco material. As used herein, the term "aerosol forming material" denotes a material that is capable of releasing volatile compounds upon heating to generate an aerosol. Tobacco may be classed as an aerosol forming material, particularly a sheet of homogenized tobacco comprising an aerosol former. An aerosol forming substrate may comprise or consist of an aerosol forming material.

The homogenized tobacco sheet generally includes, in addition to the tobacco, a binder and an aerosol-former, such as guar and glycerine. This composition leads to a sheet which is "sticky", that is, it glues to adjacent objects, and at the same time it is rather fragile having a relatively low tensile strength.

The present invention is especially adapted to unwind bobbins made of homogenized tobacco material as defined above, however it can be applied as well in any process wherein a sheet having such characteristics need to be unwound from a bobbin.

The bobbin shape can be any. It can have a substantially cylindrical shape, however an oval or anyhow deformed shape, such as a bobbin with bulges deforming a underlying cylindrical shape, do not hinder the application of the teaching of the invention.

In order to properly unwind the bobbin, keeping in mind its stickiness and fragility and thus minimizing breakage but at the same time keeping a relatively high unwinding speed, the surface of the bobbin is heated, that is, the outer layer of the bobbin is brought to a given temperature. The heating takes place while the bobbin is unwound, for example pulling a free end of the sheet already unwound from the bobbin.

Further, the outer surface of the bobbin, that is, the outer layer of the bobbin, is heated. In this way only a portion of the bobbin is heated and not the whole bobbin, limiting the heating to where it is needed, that is, the heating is limited to the layer which is unwound. Less power is required to heat only a portion of the bobbin than the whole bobbin and, in addition, if the process is interrupted, some layers have not been heated for no purpose.

The outer surface of the bobbin is defined as the substantially cylindrical surface of the bobbin. The outer surface connects the two lateral substantially circular surfaces of the bobbin. The outer surface does not include surfaces of portions of the sheet that may detach from the bobbin. Further, the method is relatively simple to be applied and does not require expensive or complex machinery.

Preferably, the step of heating a portion of the outer surface of the bobbin while unwinding the homogenized tobacco sheet from the bobbin includes heating a portion of the outer surface of the bobbin to a temperature of at least about 40 degrees Celsius. It has been found that the temperature to be reached by a portion of the surface of the bobbin for an optimal unwinding is above room temperature and preferably above about 40 degrees Celsius. More preferably, the temperature to be reached by a portion of the outer surface is comprised between about 40 degrees Celsius and about 75 degrees Celsius, even more preferably between about 45 degrees Celsius and about 65 degrees Celsius, most preferably between about 45 degrees Celsius and about 55 degrees Celsius. Within these temperature ranges, it has been found that the outer layer of the bobbin easily detaches from the remaining of the bobbin, so that an easy unwinding is achieved. Preferably, the method includes the step of changing the distance between a heat source used to heat a portion of the outer surface of the bobbin and a center of the bobbin while unwinding. More preferably, it includes bringing the heat source nearer to the center of the bobbin while unwinding. In order to heat the outer surface of the bobbin, at least a heat source is provided. The heat source is movable, that is, the heat source may be moved with respect to the bobbin, changing the distance between the center of the bobbin and the heat source. The distance between the outmost layer of the bobbin and the heat source may be kept constant. The distance between the outmost layer of the bobbin and the heat source may vary. Preferably, while the bobbin unwinds, the heat source is brought closer to the center of the bobbin. In this way a constant heating of the outer surface of the bobbin, for example a heating such that the temperature of a portion of the outer surface of the bobbin at a certain location remains constant, may be achieved, despite the fact that the external diameter of the bobbin decreases during unwinding. Indeed, preferably the temperature of a portion at a specific location of the outer surface of the bobbin is monitored: the material forming the portion changes (because the bobbin unwinds) but a new material moves in the same location which is monitored and preferably that part of the bobbin at such location remains at a given temperature or within a given temperature interval. Without the movement of the heat source, the distance between the outer surface of the bobbin and the heat source would constantly increase due to the fact that during unwinding the diameter of the bobbin decreases. With "center" of the bobbin, the position of the axis of rotation of the bobbin during unwinding is meant.

Preferably, the method includes the step of changing the temperature of the heat source while unwinding. More preferably, the method includes reducing the temperature of or the power emitted by the heat source while unwinding. During unwinding, preferably the temperature of or the power emitted by the heat source is modified, more preferably decreases, to avoid overheating of the layer. For example, if at a distance d1 the temperature of or power emitted by the heat source is T1 , and at a distance d2, where d2

< d1 , the temperature of or the power emitted by the heat source is T2, then preferably T2

< T1 . In case multiple heat sources are present, this is preferably valid for all the heat sources, that is, the closer the heat sources get to the center of the bobbin, the cooler or less powerful they get.

Preferably, the method comprises the step of heating a portion the outer surface of the bobbin comprising at least half of the outer surface. Preferably, not all the outer surface of the bobbin is heated, that is, preferably only a portion of the outer surface of the bobbin is heated. More preferably, this portion includes a location where a free end of the sheet connects to the bobbin. The free end of the homogenized tobacco sheet is the portion of the sheet which is already unwound from the bobbin and a part of it is still in contact with the outer surface of the bobbin itself. A line of contact is defined in the bobbin as a line in the homogenized tobacco sheet connecting the free end of the bobbin and a portion of the outer sheet of the bobbin which is still wound in the bobbin. This line of contact is part of the outer surface of the bobbin. From this line of contact, the free end extends. The surface of the free end detached from the bobbin does not belong to the outer surface of the bobbin, being separated from the bobbin itself. Preferably, the portion of the bobbin which is heated includes the line of contact and a portion of the still wound sheet extending from the line of contact for at least half circumference. This portion of the still wound sheet forms a portion of the outer surface of the bobbin. The heating is performed for example by one or more suitable heat sources.

Preferably, the method comprises the steps of arranging a plurality of heat sources around the outer surface of the bobbin; and setting the heating temperature of each heat source of the plurality depending on the position of each heat source with respect to the outer surface of the bobbin. Each heat source has preferably a specific temperature, and these temperatures of the various heat source can be equal or different one from the others. Preferably, the temperature of each of the heat sources depends on its position with respect to the outer surface of the bobbin. More preferably, its temperature depends on its position with respect to the line of contact of the bobbin. These differences in temperature are present in order to progressively heat the last layer of the bobbin, and to limit the heat transfer to other layers underneath. Preferably, the closer to the line of contact, the higher the temperature of the heat source. For example, in case of 5 heat sources (hs1 ....hs5), positioned one after the other around the outer surface of the bobbin, being hs1 the most remote from the line of contact and hs5 the closest, then the temperatures of the 5 heat sources (Ths1 ... hs5) are preferably as follows: Ths1 < Ths2 < Ths3 < Ths4 < Ths5

Preferably, the method comprises the steps of arranging a plurality of heat sources around the outer surface of the bobbin, wherein the distance between each heat source of the plurality and the outer surface of the bobbin is the same. Preferably, the homogenized tobacco sheet includes a free portion detaching from the bobbin defining a line of contact between the free portion and the outer surface of the bobbin, and wherein heating a portion of the outer surface of the bobbin while unwinding includes bringing the line of contact to a temperature between about 40 degrees Celsius and about 75 degrees Celsius. Preferably, the portion of the outer surface which is heated includes the portion where the outer sheet detaches from the bobbin. The free end of the sheet detaching from the bobbin is the portion of the sheet at higher risk of tear and therefore it is included in the portion which is preferably heated to a temperature comprised between about 40 degrees Celsius and about 75 degrees Celsius, even more preferably between about 45 degrees Celsius and about 65 degrees Celsius, most preferably between about 45 degrees Celsius and about 55 degrees Celsius. Within these temperature ranges, it has been found that the outer layer of the bobbin easily detaches from the remaining of the bobbin, so that an easy unwinding is achieved.

Preferably, the method includes the step of measuring a diameter of the bobbin. More preferably, the method includes the step of changing the distance between a heat source used to heat a portion of the outer surface of the bobbin and the bobbin, or a temperature of or the power emitted by the heat source depending on the diameter of the bobbin. Preferably, the diameter of the bobbin is measured, so that the position of the outer surface of the bobbin is substantially known and a distance between the heat source heating the bobbin and the outer surface of the bobbin can be selected. Preferably, measuring the diameter allows to change the position of the heat source so that it can heat the outer substrate in a suitable way. Preferably, the position of the outer surface (which depends on the diameter of the bobbin) may influence also the temperature of or the power emitted by the heat source. Preferably, the diameter of the bobbin may be measured by a proximity sensor, so that the measurement is contactless, or by a contact roll. Preferably, the method includes measuring a temperature of a portion of the outer surface of the bobbin. The portion is preferably the line of contact of the homogenized tobacco sheet. The monitoring of the temperature may be performed contactless. For example, the heat source itself may include a temperature sensor in order to determine the effect of its heating on the outer surface of the bobbin. Preferably, the homogenized tobacco sheet is a cast sheet of homogenized tobacco material. More preferably, the cast sheet of homogenized tobacco material includes a binder or an aerosol former. Preferably, the homogenized tobacco sheet comprises a binder to the tobacco in an amount between about 1 percent and about 10 percent in dry weight basis of the homogenized tobacco material. It is advantageous to add a binder, such as any of the gums or pectins described herein, to ensure that the tobacco powder remains substantially dispersed throughout the homogenized tobacco web. For a descriptive review of gums, see Gums And Stabilizers For The Food Industry, IRL Press (G.O. Phillip et al. eds. 1988); Whistler, Industrial Gums: Polysaccharides And Their Derivatives, Academic Press (2d ed. 1973); and Lawrence, Natural Gums For Edible Purposes, Noyes Data Corp. (1976).

Although any binder may be employed, preferred binders are natural pectins, such as fruit, citrus or tobacco pectins; guar gums, such as hydroxyethyl guar and hydroxypropyl guar; locust bean gums, such as hydroxyethyl and hydroxypropyl locust bean gum; alginate; starches, such as modified or derivitized starches; celluloses, such as methyl, ethyl, ethylhydroxymethyl and carboxymethyl cellulose; tamarind gum; dextran; pullalon; konjac flour; xanthan gum and the like. The particularly preferred binder for use in the present invention is guar.

Advantageously, the homogenized tobacco sheet comprises an aerosol-former, preferably in an amount comprised between about 5 percent and about 30 percent dry weight of the slurry.

Suitable aerosol-formers for inclusion in slurry for webs of homogenised tobacco material are known in the art and include, but are not limited to: monohydric alcohols like menthol, polyhydric alcohols, such as triethylene glycol, 1 ,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono- , di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate.

For example, where the homogenized tobacco material according to the specification is intended for use as aerosol-forming substrates in heated aerosol-generating articles, webs of homogenised tobacco material may have an aerosol former or humectant content of between about 5 percent and about 30 percent by weight on a dry weight basis, preferably between about 15 percent and about 20 percent. Homogenized tobacco material intended for use in electrically-operated aerosol-generating system having a heating element may preferably include an aerosol former of greater than 5 percent to about 30 percent. For homogenized tobacco material intended for use in electrically-operated aerosol-generating system having a heating element, the aerosol former may preferably be glycerol.

Preferably, the homogenized tobacco sheet comprises a binder and an aerosol former.

Preferably, the step of heating a portion of the outer surface of the bobbin includes heating the portion in a contactless manner. In order to improve the unwinding of bobbins of homogenized tobacco sheet, for example to avoid breakage of sheet during unwinding, mechanical apparatus in contact with the sheet material of the bobbin, such as blades to separate the unwinding sheet external layer from the previous layer as well as rolls to create the same effect may pose problems. Such solutions are may cause some mechanical stress through mechanical contact. In the present invention, preferably, the characteristics of the sheet material, and its compound, to create the most favorable conditions to enable the progressive self-detachment of the layers of the sheet from the bobbins during unwinding are used. Due to a contactless heating, there is no invasive extra mechanical contact and mechanical stress to try to detach/separate the sheets in layers in the bobbins, as well as no change the unwinding system that has physical contact with the bobbins or sheets.

According to a further aspect, the invention relates to an apparatus for unwinding a bobbin of a homogenized tobacco sheet, the apparatus comprising: a bobbin holder where a bobbin of a homogenized tobacco sheet is placed; and a heat source adapted to heat a portion of an outer surface of the bobbin. The advantages of this aspect have been already outlined with regard to the first aspect and therefore are not repeated in the following.

The following characteristics can be applicable also to the first aspect of the invention.

Preferably, the heat source is an infrared heater. The IR (infrared) sources are known as heaters and are relatively cheap. The IR sources are preferably ceramic cells, supplying mainly IR rays, which do not present issues with environmental, health and safety regulations.

Preferably, the apparatus includes a sensor adapted to determine the diameter of the bobbin or to determine the temperature of a portion of the outer surface of the bobbin. The sensor may include a contact roll or a proximity sensor. It may be embedded in the heat source as well. Control of the temperatures may be done through known available technologies, for example by the temperature control embedded in the heat source and its control unit, as well as directly measuring the effective temperature in the surface of the homogenized tobacco sheet, for example using a contactless temperature reading device as existing in the market, which interfaces with the system's control unit.

Preferably, the apparatus includes a distance variator adapted to change the distance between the heat source and the bobbin holder. Preferably, the heat source, such as an IR source, is moveable with respect to the bobbin. In order to make such movements, the distance variator may be attached to sliders or pivoting arms to "follow" the external or outer surface of the bobbin.

Preferably, the apparatus includes a temperature variator adapted to change the temperature of or the power emitted by the heat source. In this way, the temperature or power can be optimized depending on the sheet of material, e.g. its composition or physical or chemical characteristics. Further, the temperature or power may be optimized depending on the distance between the outer surface and the heat source.

Preferably, the apparatus includes a plurality of heat sources arranged around the bobbin holder. In initial condition, that is, when the bobbin is still complete and not unwound yet, the heat sources are preferably spaced from each other, so that there are heat losses. In final condition, when the bobbin has been unwound almost to the end, the heat sources, approaching the center of the bobbin due to the fact that the bobbin is reducing its diameter, are closed together, thereby limiting the heat losses. Heat power can then be decreased during unwinding process. Preferably, a plurality of heat sources, such as IR heaters, more preferably moveable towards and away from the bobbin, follow the external layer of the bobbin, and each of the heat sources has its temperature which may be different from other heat sources. This difference allows to provide a progressive heating of the last outmost layer of the sheet, and a constant heating despite the decrease in the external diameter of the bobbin. Preferably, the apparatus include a crimper. In order to further process the homogenized tobacco sheet, for example for the production of an aerosol forming article, the sheet needs to be crimped. The sheet is crimped downstream the unwinding station.

The invention further relates to a method for unwinding a bobbin of a coiled sheet, the method comprising: providing a bobbin of a coiled sheet, the bobbin comprising an outer surface; and heating a portion of the outer surface of the bobbin while unwinding the coiled sheet from the bobbin. According to a further aspect, the invention relates to an apparatus for unwinding a bobbin of a coiled sheet, the apparatus comprising: a bobbin holder where a bobbin of a coiled sheet is placed; and a heat source adapted to heat a portion of an outer surface of the bobbin. The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a simplified schematic lateral view of a bobbin to be unwound according to the invention;

Figure 2 is a schematic side view of a unwinding station according to the invention in a first operative position; and

Figure 3 is a schematic side view of the unwinding of figure 1 in a second operative position.

In figure 1 a bobbin 2 to be unwound by the apparatus and according to the method of the invention is indicated. The bobbin is formed by a sheet 3 of homogenized tobacco material. The bobbin 2 is substantially cylindrical and defines an outer surface 4, part of the outmost layer of the sheet 3. Further, the bobbin 2 defines a free end 10 which is a portion of the coiled sheet 3 detaching from the bobbin 2 and a line of contact 1 1 , representing the line in which the free end 10 connects to the remaining of the sheet wound in the bobbin. The bobbin has a diameter 13 which is reduced during unwinding. In figures 2 and 3, an unwinding station to unwind the bobbin 2 of coiled sheet 3 is represented and globally indicated with 1 .

The unwinding station 1 includes a bobbin holder 5 where the bobbin 2 is positioned in order to be unwound. The bobbin holder 5 is adapted to rotate around a rotational axis X which is preferably coinciding with an axis of the bobbin 2. On this common axis, a center of the bobbin 2 is defined.

The unwinding station 1 further comprises a plurality of heat sources, in the present embodiment in the number of 5, indicated with 21 , 22, 23, 24 and 25. The heat sources 21 - 25 are disposed contactless in proximity of the outer surface 4 of the bobbin 2 and preferably their distance 90 from the center or axis of the bobbin is the same for all heat sources. Further, preferably the heat sources are angularly positioned at regular intervals around the outer surface of the bobbin. The heat sources 21 - 25 surrounds at least half of the outer surface 4 of the bobbin 2. Heat sources 21 - 25 are preferably infrared ceramic heat sources.

The temperature of each heat source 21 - 25 is controlled independently and can be varied during the unwinding. The unwinding station 1 further comprises a variator 30 to change the distance 90 between the heat sources 21 - 25 and the center of the bobbin 2 or bobbin holder 5. Preferably, the distance 90 between each heat sources and the bobbin holder 5 is independently changed.

The unwinding station 1 also comprises a temperature sensor 40 to determine the temperature of a portion of the outer surface of the bobbin 2, preferably of the line of contact 1 1 , and a diameter sensor to determine the diameter 13 of the bobbin 2. Preferably temperature sensor 40 and diameter sensor 50 are contactless sensors, determining temperature and diameter without contact with the bobbin 2.

The unwinding station 1 operates as follows.

In use, the bobbin 2 is placed on the bobbin holder 5 and the distance 90 between heat sources 21 - 25 and the outer surface 4 of the bobbin is set. Further, a temperature T of the heat sources is selected, so that the closer is the heater to the line of contact 1 1 of the bobbin, the higher its temperature is. In the depicted embodiment T21 < T22 < T23 < T24 < T25. The temperature can be for example selected selecting the power emitted by the heat sources. The temperature and/or power is so selected that the temperature of the outer surface of the bobbin at the line of contact 1 1 is above 40 degrees Celsius. This temperature is determined and monitored by the temperature sensor 40.

The heating of the heat sources 21 - 25 starts and the bobbin 2 is unwound, by pulling the free end 10 of the bobbin along the arrow 60 depicted in figures 2 and 3. At the beginning of the unwinding, the diameter 13 of the bobbin 2 is relatively large, as shown in figure 2. During unwinding, the diameter 13 of the bobbin is reduced because more and more layers of sheet 3 are removed from it. This reduced diameter configuration is shown in figure 3.

In order to ensure a constant heating, the heat sources 21 - 25 during unwinding are moved towards the bobbin holder 5. The diameter sensor 50 detects the variations of the diameter 13 of the bobbin and the distance 90 between the bobbin holder 5 and the heat sources 21 - 25 is varied accordingly. The heat sources are moved closer to the bobbin holder 5 during unwinding. Further, the temperature of the heat sources 21 - 25 may be varied as well depending on the size of the diameter 13. Preferably, the temperature of the heat sources is decreased during unwinding to avoid overheating.