1. Field of the Invention
This invention relates to cigarettes which go out rapidly or are self-extinguishing, whose tobacco is surrounded by a casing of cigarette paper comprising areas with lesser and greater air permeability in the form of patterned, preferably annular zones.
2. Prior Art
Such cigarettes are already known from DE-OS; 25 59 071 in which the cigarette paper exhibit zones of lesser porosity in a range up to 100 and zones of greater porosity in a zone of 150 to 2000 at an average porosity of 50 to 500 units, which units are determined in cm.sup.3 min.sup.-1 /per 10 cm.sup.2 and at a pressure of 10 cm water column. In these known cigarettes, a controlled burning speed and/or an increased number of puffs should be rendered possible by means of the annular zones of alternating porosity.
Instead of the porosity, the air permeability P is now indicated according to DIN ISO/DIS 2965.2 as the amount of air in cm.sup.3 per minute, per cm.sup.2 and per kiloPascal; it is calculated from the ratio of the volumetric current of air in cm.sup.3/ min which passes through the test specimen to the product of test surface of the test specimen in cm.sup.2 and of the pressure difference between the two surfaces of the test specimen in kPa and was also indicated earlier as the so-called "Coresta value". The ISO/DIS 2965.2 was promulgated by the International Organization for Standardization and is incorporated herein by reference in its entirety.
Accordingly, a cigarette paper is used in accordance with DE-OS 25 59 071 whose areas of lesser porosity correspond to an air permeability value of up to 10 P and preferably 5 P whereas the areas of greater porosity exhibit a value of 15 to 200 P at a total porosity of this cigarette paper of 5 to 50 P. The reduction of the porosity in the areas of lesser porosity can be achieved according to the literature in paper with a high porosity by the application of gel-forming agents such as glue, methyl cellulose, gums or also lacquers and varnishes; the cigarette papers cited in it as being slightly porous with a porosity of approximately 3.6 P can also be perforated electrostatically or by pressure rollers or marking presses in order to achieve zones of greater porosity, in which instance the average porosity is approximately 24 P. The smouldering rates of one of these known cigarettes in e.g. around 3.2 mm/min at a puff number of 9.7 whereas the corresponding reference cigarette with customary paper with an average porosity of approximately 26 P exhibits a higher smouldering or burn rate of 4.2 mm/min and a lower draw number of 7.5.
Furthermore, DE-OS 23 15 613 teaches that the porosity of the paper can be reduced in its thickness by abrading in order to increase the permeability or the porosity of the paper. This purportedly makes it possible to affect the taste of the cigarette in an especially advantageous manner and not to weaken the structure of the cigarette paper by perforations.
Moreover, DE-PS 17 61 500 teaches that compressed areas in the form of a gridlike or wafflelike pattern consisting e.g. of a silicate pulp can be provided and the intersection points can be reinforced with a noncombustible substance in order in particular to prevent the ash from falling off.
Moreover, U.S. Pat. No. 3,911,923 teaches the use of cigarette papers whose porosity is increased in the direction of the mouthpiece in order to shape the supply of smoke in a more uniform manner.
All these known suggestions do result, to the extent that they can be realized technically at all, in certain advantages; however, these advantages are achieved at the expense of other desirable qualities. The increase of the porosity by means of electrostatic perforation raises the puff gradient, that is, the amount of smoke per puff, from the first to the last puff in a disadvantageous manner during smoking. If the porosity is reduced by means of the application of noncombustible substances or gelatins, pyrolysis products or undesirable combustibles are supplied to the smoker.
In addition, none of these suggestions has the result that the incandescent zone of the cigarette goes out by itself after a set time.
As regards the considerable danger of an accident created by cigarettes which have been set down, thrown away or which fell down when the smoker goes to sleep and continue to smoulder, the suggestion was made in the past, e.g. in accordance with U.S. Pat No. 4,061,147, that several separate sections consisting of noncombustible material such as e.g. aluminum foils be provided in a cigarette paper which can be torn off area by area in these areas at a selected breaking point. Aside from the fact that the manufacture of such cigarettes with aluminum foils on a paper base which foils can be torn off is quite expensive, such cigarettes exhibit a completely insufficient draw behavior and a considerable reduction in quality.