This invention relates to a method for manufacturing a tobacco sheet with a top layer of tobacco powder, also referred to as top loaded cigarette filler, wherein a base layer on a basis of a fine fraction of tobacco and cellulose fibres is composed, which base layer is provided on one side with a fraction of coarse tobacco, subsequently the total is submitted to a drying treatment. This invention further relates to a top loaded cigarette filler constituted of a base layer of a fraction of fine tobacco and cellulose fibres and a top load of a fraction of course tobacco.

The method as referred to in the preamble concerning the manufacturing of the base layer is known from U.S. patent 4,306,578. According to the method known therefrom the base layer is obtained from a aqueous slurry with a high solid content, which aqueous slurry contains a fortification agent composed of unrefined short cellulose fibres with an average length of less than 2.0 mm. Such a unrefined short fibre pulp has a lower apparent viscosity than the commonly known soft wood pulp of the same fibre length allowing the use of the unrefined short fibre formulation at a higher solid content. This results in a need to evaporate less water and accordingly the process can be carried out more economically. The fibres applied in such a method have an average length of less than about 2 mm, preferably varying from 0.5 to about 1.5 mm and a width of 5 to 30 µm, and they are commonly obtained from essentialy hardwood species, like oak timber and poplar timber. The application of such wood cellulose fibres is mainly intended to improve the tensile or tear properties of the base layer.

A drawback of the method described above is that the base layer ultimately used in smoking products contains cellulose having no tobacco origin. This drawback could be overcome by e.g. the use of large amounts of high quality binder during the preparation of the base layer. A disadvantage of such a messure is that the end product will contain a lower tobacco content and will furthermore lead to a deteriorated taste. Both effects are undesired. In addition the application of large amounts of high quality binder results in the increase of the price of the final product, which is also commercially undesired.

A method for manufacturing a tobacco sheet is known from the German Offenlegungsschrift 19949983, wherein a aqueous slurry of tobacco stems is obtained by grinding uncooked stems in presence of guar as binder. Furthermore, a solution of particular chemicals is prepared, being guar as binder, humidifier, e.g. glycerol, preservative, e.g. sodium benzoate, additives, e.g. sugar syrup, said chemical solution being first mixed with tobacco powder en then the solution containing tobacco powder is admixed with the aqueous stem slurry. The resulting mixture is spread on a conveyer via a continuous process and dried to a sheet.

GB 1 203 939 relates to a process of manufacturing a coherent tobacco product wherein a refined pulp of cellulosic fibers is combined with comminuted tobacco and a water-insoluble cellulose derivative.

The first object of this invention is to provide a method for manufacturing a base layer wherein substantially no cellulose not originated from tobacco is incorporated.

A second object of this invention is to provide a base layer wherein no large amounts of high quality binders are incorporated and in which the strength of the base layer is maintained and no deteriorated taste results.

The method according to the present invention comprises the steps as disclosed in claim 1.

By the use in the present base layer of cellulose fibres originated for at least 50% from tobacco a base layer is thus obtained which has a small amount of cellulose not originated from tobacco. In a particular embodiment it is preferred that for composing the base layer from a fine fraction of tobacco at least 70%, especially at least 90%, of cellulose fibres originating from tobacco is used. Such percentages of cellulose originating from tobacco provide a base layer which satisfies the desired mechanical properties and in which, in addition, the intended tobacco flavour is maintained. Furthermore large amounts of binders and additives, as used in German Offenlegungsschrift 19949983, can be omitted. It should however be understood that in particular embodiments a certain amount of cellulose fibres from another origin can be used but that the largest part of the cellulose fibres are obtained from tobacco.

It is particularly preferred that the composing of the base layer comprises the steps:

1. i) providing a fine fraction of tobacco,
2. ii) subjecting tobacco leaf veins to a cooking treatment for forming a slurry of cellulose fibres obtained from tobacco,
3. iii) combining and mixing the slurry from step ii) with the fine fraction of tobacco from step i), and
4. iv) dosing the mixture from step iii) on a drying conveyor for forming the base layer.

The tobacco fibres are obtained from fibre containing plant parts of the tobacco plant, especially from the middle veins of tobacco leaves which are released as residual material in the processing of tobacco leaves. Such middle veins are also called tobacco stems. By means of the cooking treatment used in step ii) a part of the natural binders, e.g. pectin and hemicellulose, goes into solution and the tobacco fibres are rendered lying free. Subsequently in step iii) the slurry subjected to a cooking treatment is admixed with a fraction of fine tobacco and then the thus resulting mixture is dosed on a drying conveyor which is essentially a endless band of steel and subsequently passes through a drying furnace whereby the top load being the fraction of coarse tobacco is spread over the base layer in a regular layer for obtaining the desired end product.

In the present method it is preferred that in a step preceeding step ii) the tobacco leaves veins are crushed and humidified, which decreases the size of the tobacco leaf veins and which promotes the formation of the tobacco leaf veins into a slurry.

The cooking treatment according to step ii) is especially carried out under high pressure, particularly at a temperature in the range of 120-200 °C, especially at a temperature of about 150 °C.

The dry content of the slurry according to step ii) is especially between 4 and 12 %, preferably between 6 and 10 %.

For obtaining optimal properties for the base layer one or more additives selected from the group of plasticizers, binders, diluting agent, fragrances, flavours, preservatives and pH-buffer agents are added to the slurry as obtained in step ii).

For the cellulose fibres to impart a good strength to the ultimate base layer it is preferred that the slurry as obtained in step ii) after the cooking treatment is subjected to a grinding treatment. By thus grinding the cellulose fibres in a refiner under wet conditions the fibres are reduced and fibrils are formed on the fibres. Such fibrils insure the cellulose fibres to entangle whereby the desired fortifying performance is optimally imparted.

To obtain a sufficient strong base layer it is preferred that the cellulose fibre content in the slurry as obtained from step ii) is at least 15 %, calculated on dry material.

As discussed before it is preferred to maintain the amount of cellulose not originated from tobacco in the final base layer at a low level. As appropriate starting material for the present invention a combination of tobacco material can be mentioned. This are generally residual materials from the cigarette industry. Such residual materials are preferably choosen from the group of middle veins of tobacco leaves, tobacco stems, veins with parts of tobacco leaves, tobacco leaf parts and fine dust. The middle veins of tobacco leaves are removed from the leaf in stripperies of tobacco companies to obtain the pure tobacco leaf. This material is often referred to as "tobacco stems". The thus stripped tobaccos are cut in a additional treatment wherein small veins with parts of tobacco leaves are formed which are however not suitable for a direct incorporation into the cigarette. Such small veins with parts of tobacco leaves, also referred to as winnovers, are gravimetrically separated. Furthermore during the overall production process of cigarettes an amount of fine dust is formed, which material is therefore not suitable for direct incorporation into the cigarettes but is suitable however to be used in the present method. The residual materials described above are grinded and screened into two separate fractions being a fine fraction and a coarse fraction whereby the fine fraction is admixed with a slurry of cellulose fibres obtained from tobacco, especially tobacco leaves veins, and dosed on a drying conveyor, additionally provided with a top load of the fraction of course tobacco and subsequently dried for obtaining the desired end product.

The present invention further relates to a top loaded cigarette filler constituted of a base layer of a fraction of fine tobacco and cellulose fibres and a top load of a fraction of coarse tobacco obtained according the method according to the present invention wherein, the cellulose fibres in the base layer are for at least 50 %, preferably at least 75%, especially at least 90 %, originated from tobacco, especially tobacco leaf veins wherein the cellulose fibres are obtained by a slurry method, especially as described above.

The essence of the present invention is the preparation of a base layer wherein substantially no cellulose not originating from tobacco is incorporated as is commonly used according to the prior art. The present invention especially ensures that in the base layer cellulose fibres originating from tobacco, especially from tobacco leaf veins, are used whereby a base layer is thus obtained which comprises a fine fraction of tobacco and cellulose fibres originating from tobacco.