Process to reduce or suppress cigarette spotting; cigarette and cigarette paper related to the process

Abstract: The invention concerns cigarette spotting. To reduce or suppress cigarette paper spotting, cigarette is equiped with an inner wrapper placed between tobacco and the external enveloppe, this inner wrapper being a paper made of cellulose fibres, with a basis weight at the utmost equal to 30 g/m², presenting pores made during paper manufacture, or perforations made after manufacture in such a way that the air permeability is at least 500 coresta units. This invention applies to all cigarettes and similar smoking products.

Description: The invention concerns a manufactured cigarette according to the preamble of claim 1. Cigarettes are generally wrapped in white cigarette paper. The degree of whiteness of a cigarette is considered as a quality characteristic. Conversely, yellowing or presence of brown spots on cigarette paper is considered by consumers as a sign of poor quality or too long storage. Experts know however that a long storage is not a prerequisite to yellowing or spotting. In fact, when cigarettes are kept under high humidity, spotting may happen within weeks or even days. Spotting is explained by the transfer, at the point of contact between tobacco shreds and cigarette paper, of tobacco colored constituents. Cigarette paper is a highly hydrophilic material, due to (i) the chemical nature of cellulose, with its large number of hydroxyls groups, (ii) the physical structure of the fibers presenting a micro capillarity and (iii) the porous structure of the sheet (see N. Baskevitch, Annales du Tabac (Paris) vol 14, p 33-43 (1976)). Under the influence of a high relative humidity, tobacco constituents transfered to the internal face of cigarette paper migrate through the paper to form visible discrete spots on the outside of the wrapper. No technique exists today which allows to solve a spotting problem when cigarettes are stored in extreme climatic conditions. The object of the invention is to provide a cigarette having reduced spotting. This is achieved, according to the invention, by a cigarette as defined in claim 1. In a preferred way, the air permeability obtained through perforations or macropores is at least 1000, or better above 1500, or even better above 3000 coresta units. Coresta units, as defined by the "Cooperation center for scientific research related to tobacco" (CORESTA) is the flow rate (in cm³/mn) of air passing through 1 cm² area of cigarette paper under a pressure difference of 10 cm water gauge. Results are expressed in cm³/mn/cm² or cm/mn. By producing macropores, a majority of which are comprised between 3 and 15 microns radius, one may advantageously obtain an air permeability in the range of 30 000 to 40 000 cm/m (coresta units). Double wrapped cigarettes are known from prior art, as disclosed for instance in patents US-A-4505282 and US-A-3633589, and publication NL-A-6703935. However, this prior art is not concerned with the spotting problem. Further, publication NL-A-6703935 is not concerned with a manufactured cigarette but is concerned with wrapped cut tobacco from which the user may roll a cigarette. Experts use a method which allows to evaluate the structure of porous papers and to distinguish between structures consisting mainly of micropores or macropores. This method is based on the physical laws describing the flow of air through porous materials. According to Poiseuille law, the air flow (F) through microporous capillaries is a direct function of the pressure differential ( P) between the two faces. Air flow is laminar F = Z x Δ P In contrast, according to the Bernouilli theorem, the air flow through macroporous orifices is a function of the square root of the pressure differential between the two faces. Air flow is turbulent. F = Z x √ Δ P In practice, the nature of the porous structure of paper is evaluated by measuring its air permeability under two pressure differential : 0,5 and 2 cbar, and by calculating the index A index equal to 1,0 characterises a paper whose porous structure is entirely made of micropores. Cigarette papers show generally an index in the range of 0,9 to 1,0. An index below 0,85 characterises a porous structure predominantly made of macropores and orifices. The papers used as inner wrapper in the invention have a R index, as described above, in the range 0,6 to 0,8. It is advantageous to use as inner wrapper a paper with a basis weight as low as possible in order minimize its influence on the taste characteristics, and the tar and carbon monoxide deliveries in the smoke. According to the invention, it is preferable to use as inner wrapper a paper with a basis weight below 20 g/m², and better, below 16 g/m². According to a further characteristics of the invention, the application of a water rapellent treatment to the inner wrapper allows total elimination of cigarette spotting, when needed. The manufacture of cigarette with a double wrap on conventional cigarette maker should cause no special problem to the experts. It is recommended that the inner wrapper has a width corresponding exactly to cigarette circumference, allowing its sides to join without overlap. The width of the outer wrapper will be, in preference, such as allowing an overlap of 2 to 2,5 mm. Examples.- A laboratory test has been developed allowing an accelerated spotting of cigarette paper. This test consists in storing the cigarettes during 72 hours in a climatic chamber (Model HO - Flam and Cie - Neuilly sur Marne - France) working at 80 % relative humidity and at 20°C. A number of other experimental conditions were evaluated. The above conditions were prefered as they allow the simulation of cigarette spotting in a fast, reproducible and discriminatory way. The test result is expressed in number of discrete spots per cigarette, with an indication of the average diameter. All commercial cigarettes experimented under the test conditions were uniformly spotted with brown blots with a diameter above 3 mm. Under same test conditions, cigarettes equipped with papers, according to the invention showed no visible spots at the end of the test. Example 1 (control experiment).- Plain cigarettes, 8 mm in diameter, containing 850 mg of flue cured tobacco, wrapped in a cigarette paper grade Verge 30C (air permeability 30 cm/mn, R index 0,99 ; as combustion salt, sodium and potassium citrate 0,8 %) are subjected to the test conditions. After 72 hours, a large number of spots (more than 250/cig) with an average diameter above 3 mm, is observed. Example 2.- Cigarette with same characteristics as control are wrapped with two layers of the same cigarette paper "Verge 30C". The width of the inner wrapper is 25 mm. The width of the outer wrapper is 27,5 mm. After 72 hours under test conditions, around 100 spots per cigarette, with an average diameter of 3 mm, are observed. Example 3.- Cigarettes with same characteristics as control are double wrapped. The inner wrapper is a paper "65-18" with an air permeability of 6500 coresta units, a R index of 0,62 and a basis weight of 18 g/m². The outer wrapper is a cigarette paper "Verge 30C". The width of the inner wrapper is 25 mm. The width of the outer wrapper is 27,5 mm. After 72 hours under test conditions, around 100 spots per cigarette, with an average diameter of 1 mm, are observed. Example 4.- Cigarettes with same characteristics as control are double wrapped. The inner wrapper is a paper "13 TUC" with an air permeability of 3500 coresta units, a R index of 0,60 and a basis weight of 13 g/m². The outer wrapper is a cigarette paper "VERGE 30". The width of the inner wrapper is 25 mm. The width of the outer wrapper is 27,5 mm. After 72 hours under test conditions, around 50 spots per cigarette, with an average diameter of 1 mm, are observed. Example 5.- Cigarettes with same characteristics as control are double wrapped. The inner wrapper is a paper "15 TUC" with an air permeability of 8000 coresta units, a R index of 0,61 and a basis weight of 15 g/m². The outer wrapper is a cigarette paper "Verge 30C". The width of the inner wrapper is 25 mm. The width of the outer wrapper is 27,5 mm. After 72 hours under test conditions, around 50 spots per cigarette, with an average diameter of 1 mm, are observed. Example 6.- Cigarettes with same characteristics as control are double wrapped. The inner wrapper is a paper "65-18 aqua" with an air permeability of 6500 coresta units which has received a water repellent treatment by addition of 0,5 % of alkyletene dimer (Aquapel TM from Hercules Corp.), its R index of 0,62 and a basis weight of 18 g/m². The outer wrapper is a cigarette paper "Verge 30C". The width of the inner wrapper is 25 mm. The width of the outer wrapper is 27,5 mm. No spotting at all is observed after 72 hours under test conditions. Example 7.- The nature of the tobacco blend has generally little influence on spotting of cigarettes stored under high relative humidity. Most tobaccos offer similar propensity to spotting of cigarettes with a single wrap. Mentholated blends are known to be more prone to generate cigarette spotting. Cigarette papers, whatever their physical (basis weight, thickness) or chemical (fiber composition, filler content) characteristics show generally similar propensity to spotting as climatic conditions become extreme. The presence of combustion salts, like sodium or potassium citrate, incorporated in high concentration to cigarette paper is a worsening factor for spotting. In order to test the invention in the most difficult conditions, an experiment was designed where a mentholated blend has been combined with a cigarette paper containing a high level of potassium citrate. Control.- Control cigarettes, plain, are manufactured (850 mg tobacco, 8 mm diameter) from a mentholated american blend wrapped in a single layer of cigarette paper "80 C7", with an air permeability of 80 coresta units, a R index of 0,98 and as combustion salt, 7 % of potassium citrate. After 72 hours under test conditions, the cigarettes are totally spotted. Experiment.- Cigarettes with same characteristics as control are manufactured from the mentholated blend wrapped in two layers of paper. The inner wrapper is a paper "65-18 aqua" with an air permeability of 6500 coresta units and a R index of 0,62. This paper has received a water repellent treatment by addition of 0,5 % alkyletene dimer. The outer wrapper is a cigarette paper 80 C7 (air permeability 80 coresta, combustion salt : potassium citrate 7 %). After 72 hours in the climatic chamber (80 % relative humidity, 20°C), no spots at all are observed on the cigarette paper. Note : In the examples, the name of papers Vergé 30C, 65-18, 13 TUC, 15 TUC, 65-18 aqua, 80C7 are commercial grades manufactured by PAPETERIES DE MAUDUIT (France). The invention is applicable to all cigarettes

Claims: "A manufactured cigarette including an inner and an outer wrapper, wrapped around tobacco, characterised in that the inner wrapper is paper made of cellulose fibers having a basis weight of at the most 30 g/m2 and, for reducing or even suppressing the formation of spots on the outer wrapper, presenting pores of which the majority has a radius between 3 and 15 microns such that the inner wrapper has an index R of air permeability in the range of 0.6 to 0.8, wherein: F 2cbar being the air flow through the wrapper at a pressure differential of 2 cbar and F 0,5cbar the air flow at 0,5 cbar." Cigarette of claim 1, wherein the air permeability of the inner wrapper is superior to 1000, preferably superior to 1500, even better superior to 3000 coresta units. Cigarette of claim 2, wherein the air permeability of the inner wrapper is in the range 30 000 to 40 000 coresta units. Cigarette of any of claims 1 to 3, wherein the inner wrapper has a basis weight under 20 g/m², or even better under 16 g/m². Cigarette of any of claims 1 to 4, wherein the inner wrapper has received a water repellent treatment. Cigarette of claim 5, wherein the inner wrapper has received an addition of alkyletene dimer.

Inventors: BASKEVITCH NICOLAS, LE GARS MARCELLE, BASKEVITCH, NICOLAS, LE GARS, MARCELLE
Applicants: MAUDUIT PAPETERIES, PAPETERIES DE MAUDUIT
Application year: 1990
Main classification: A24D1
IPC codes: D21H27, A24D1