Smoking article exhibiting reduced sidestream smoke, and wrapper paper therefor

Abstract: The sidestream smoke associated with a cigarette (10) or cigarette-like smoking article is reduced by wrapping the tobacco (12) in a double layer (18a, 18b) of paper. Each layer includes calcium carbonate and a burn control chemical. The outer layer (18a) also preferably includes monoammonium phosphate and sodium carboxy methyl cellulose. The calcium carbonate employed has a relatively high surface area per unit weight. The porosity of the outer layer is adjusted by electrostatic perforation.

Description: This invention relates to smoking articles such as cigarettes, and more particularly to cigarettes or cigarette-like smoking articles having reduced sidestream smoke. Sidestream smoke is the smoke given off by the burning end of a cigarette or cigarette-like smoking article between puffs. Such smoke may be objectionable those near the smoker who are not smoking or who do not smoke. It has therefore been desired to reduce the amount of sidestream smoke associated with cigarettes or cigarette-like smoking articles. It has also been desired to provide cigarettes or cigarette-like smoking articles having reduced sidestream smoke. EP-A-0 251 254 discloses a cigarette wrapper comprising a single layer of paper having a basis weight of 40g/m², a porosity of from 5 to 30cm/min at a pressure differential of 1 centibar (Coresta method) a filler loading of 30% calcium carbonate having a superficial surface of a least 20m²/g (by the BET method), from 6 to 12% by weight potassium acetate or sodium citrate. The wrapper is said to reduce the sidestream smoke emission of the cigarette. EP-A-0 290 911 discloses a wrapper for a cigarette comprising a single layer of paper of initial porosity between 45 Coresta units, the actual porosity of which is raised by laser, mechanical or electrostatic perforation to form 50 to 250 Coresta units. The paper may also contain filler and burn additives such as potassium citrate or carbonate. Such a wrapper in conjunction with low packing density filler and a low efficiency filter, is said to reduce visible sidestream smoke emission. EP-A-0 375 844, which forms part of the state of the art only by virtue of Art 54(3) EPC, discloses a wrapper for a cigarette comprising two layers of paper. The outer layer has a basis weight of from 20 to 60 g/m², a porosity of from 10 to 250 Coresta units, a filler, such as calcium carbonate, content of from 10 to 60% by weight and up to 50% burn additive. The inner layer has a basis weight of from 6 to 20 g/m², a porosity of up to 12 Coresta units and may contain up to 6% filler such as calcium carbonate and up to 2% burn additive such as sodium acetate. Such a wrapper is said to reduce the sidestream smoke emission of a cigarette employing the wrapper. According to the present invention there is provided a cigarette wrapper for reducing sidestream smoke produced by a cigarette wrapped with the wrapper, the wrapper comprising outer and inner layers of paper, the outer layer of paper having a basis weight of 30 to 70, preferably about 50, grams per square metre, an initial porosity of 2 to 10, preferably about 5 cubic centimetres per minute by the Coresta method, a calcium carbonate filler loading of 30 to 40, preferably about 35, % by weight, the calcium carbonate having a surface area of 20 to 80, preferably about 25, square metres per gram by the BET method, 2 to 10% by weight of a burn chemical, preferably an alkali metal burn chemical such as citrate or succinate, particularly preferably about 5.5% by weight succinate, 0 to 1, preferably about 0.6% by weight monoammonium phosphate, and about 0 to 1, preferably about 0.3, % by weight sodium carboxy methyl cellulose, and being perforated for example by electrostatic perforation to increase its porosity to 50 to 100, preferably about 60, cubic centimetres per minute by the Coresta method, and the inner layer of paper having a basis weight of 15 to 25, preferably about 18, grams per square metre, a porosity of 20 to 40, preferably about 30, cubic centimetres per minute by the Coresta method, a calcium carbonate filler loading of 2 to 15, preferably about 3, % by weight, 0 to 2 % by weight of a burn chemical preferably an alkali metal burn chemical such as citrate or succinate, particularly preferably about 0.6% by weight citrate. The invention also provide a cigarette comprising a wrapper according to the invention. FIG. 1 is a simplified cross sectional view (taken along the line 1-1 in FIG. 2) of an embodiment of a cigarette according to the invention. FIG. 2 is a simplified elevational view of an illustrative embodiment of a cigarette according to the invention. As shown in FIGS. 1 and 2, a cigarette 10 constructed in accordance with this invention includes tobacco rod 12 and filter 14. Tobacco rod 12 has a filling of tobacco 16 surrounded by two layers of paper 18a and 18b. Outer layer 18a is preferably slightly wider than inner layer 18b to ensure that the inner layer is completely covered by the outer layer in the finished cigarette. Filter 14 is entirely optional and can be omitted if desired. Outer paper 18a has a basis weight of about 30-70 (preferably about 50) grams per square meter. It has an initial porosity of about 2-10 (preferably about 5) cubic centimeters of air per minute as determined by the industry-standard Coresta method. Outer paper 18a is made with a calcium carbonate filler loading of about 30-40% (preferably about 35%) by weight. The calcium carbonate used has a surface area of about 20-80 (preferably about 25) square meters per gram by the well-known BET method (see, for example, F.M. Nelson et al., "Determination of Surface Area", Analytical Chemistry , Vol. 30, No. 8, August 1958, pp. 1387-90, for a description of the BET method). This is a relatively high surface area for a filler in a cigarette paper. A typical surface area would be about 7-10 square meters per gram. To help control or determine the puff count of the cigarette, outer paper 18a also includes about 2-10% by weight of a burn chemical such as succinate, citrate, or any other alkali metal burn chemical known to those in the industry. The preferred burn chemical additive is about 5.5% by weight succinate. In addition to helping to control or determine the burn rate of the paper, the burn chemical is believed to act as a fluxing or dispersing agent for the calcium carbonate and to combine with the calcium carbonate to help make a relatively air- and smoke-impervious ash. The imperviousness of the ash (which is also promoted by the high surface area of the calcium carbonate) is believed to contribute significantly to the reduction of sidestream smoke. Outer paper 18a also includes about 0-1% (preferably about .6%) by weight monoammonium phosphate. This chemical tends to reduce unattractive streaking of the outer paper due to condensation on the inside of the paper following puffs. The tendency of the paper to streak in this manner is increased because the porosity of the paper has been reduced to reduce sidestream smoke. Monoammonium phosphate is used to eliminate this possible cosmetic problem. Outer paper 18a further includes about 0-1% (preferably about .3%) by weight sodium carboxy methyl cellulose. This chemical, which acts as a film former, contributes to the imperviousness of the ash, which, as has been mentioned, helps to reduce sidestream smoke. Sodium carboxy methyl cellulose is also believed to act as a carrying agent to help get the burning agent (e.g., succinate) into the paper. Outer paper 18a is perforated (e.g., by conventional electrostatic perforation) to increase its porosity to about 50-100 (preferably about 60) cubic centimeters of air per minute by the Coresta method. Perforation of outer paper 18a in this manner improves the mechanical feel of the cigarette. It also provides some pressure relief for the cigarette in order to reduce the amount of smoke coming out of the proximal end of the filter or any perforations in the tipping overwrap between puffs. The inner paper 18b discussed in detail below minimizes the visible smoke escaping through the perforations in the outer paper. Inner paper 18b adds another layer to the paper ash to increase its imperviousness and to thereby help reduce sidestream smoke. Inner paper 18b also adds strength to the cigarette and improves its overall appearance. Inner paper 18b has a basis weight of about 15-25 (preferably about 18) grams per square meter. It has a porosity of about 20-40 (preferably about 30) cubic centimeters of air per minute (Coresta). Because of this relatively high porosity, inner paper 18a does not require electrostatic perforation. Inner paper 18b is made with a calcium carbonate filler loading of about 2-15% (preferably about 3%) by weight. This relatively low calcium carbonate loading helps to slow down the burn rate of the inner paper and contributes to reducing the amount of visible smoke that would otherwise come out the perforations in the outer paper. To help control or determine the burn rate of the paper, inner paper 18b also includes about 0-2% by weight of a burn chemical such as succinate, citrate, or any other alkali metal burn chemical known to those in the industry. The preferred burn chemical additive is about .6% by weight citrate.

Claims: A cigarette wrapper for reducing sidestream smoke produced by a cigarette wrapped with the wrapper, the wrapper comprising an outer (18a) and inner (18b) layers of paper, the outer layer of paper having a basis weight of 30 to 70 grams per square meter, an initial porosity of 2 to 10 cubic centimeters per minute by the Coresta method, a calcium carbonate filler loading of 30 to 40% by weight, the calcium carbonate having a surface area of 20 to 80 square meters per gram by the BET method, 2 to 10% by weight of a burn chemical, about 0-1% by weight monoammonium phosphate, and 0 to 1% by weight of sodium carboxy methyl cellulose, the paper being perforated to increase its porosity to 50 to 100 cubic centimeters per minute by the Coresta method, and the inner layer of paper having a basis weight of 15 to 25 grams per square meter, a porosity of 20 to 40 cubic centimeters per minute by the Coresta method, a calcium carbonate filler loading of 2 to 15% by weight, and 0 to 2% by weight of a burn chemical. A wrapper according to claim 1 in which the basis weight of the outer layer (18a) of paper is about 50 grams per square meter. A wrapper according to claim 1 or 2 in which the initial porosity of the outer layer (18a) of paper is about 5 cubic centimeters per minute by the Coresta method. A wrapper according to claim 1, 2 or 3 in which the calcium carbonate filler loading of the outer layer (18a) of paper is about 35% by weight. A wrapper according to any preceding claim in which the calcium carbonate of the outer layer (18a) of paper has a surface area of about 25 square meters per gram by the BET method. A wrapper according to any preceding claim in which the burn chemical in the outer layer (18a) of paper is an alkali metal burn chemical, such as succinate or citrate. A wrapper according to any preceding claim in which the burn chemical the outer layer (18a) of paper is succinate in an amount of about 5.5% by weight. A wrapper according to any preceding claim in which the the outer layer (18a) of paper contains about 0.6% by weight monoammonium phosphate. A wrapper according to any preceding claim in which the the outer layer (18a) of paper contains about 0.3% by weight sodium carboxy methyl cellulose. A wrapper according to any preceding claim in which the porosity of the outer layer (18a) of paper is increased to about 60 cubic centimeters per minute by the Coresta method. A wrapper according to any preceding claim in which the porosity of the outer layer (18a) of paper is increased by electrostatic perforation. A wrapper according to any preceding claim in which the basis weight of the inner layer (18b) of paper is about 18 grams per square meter. A wrapper according to any preceding claim in which the porosity of the inner layer (18b) of paper is about 30 cubic centimeters per minute by the Coresta method. A wrapper according to any preceding claim in which the calcium carbonate filler loading of the inner layer (18b) of paper is about 3% by weight. A wrapper according to any preceding claim in which the burn chemical in the inner layer (18b) of paper is an alkali metal burn chemicals, such as succinate or citrate. A wrapper according to any preceding claimin which the inner layer (18b) of paper contains about 0.6% by weight citrate as the burn chemical. A cigarette (10) comprising a wrapper according to any preceding claim.

Inventors: GOODMAN BARBRO L, HOUCK WILLIE GRAY JR, GOODMAN, BARBRO L., HOUCK, WILLIE GRAY, JR.
Applicants: PHILIP MORRIS PROD, PHILIP MORRIS PRODUCTS INC.
Application year: 1990
Main classification: A24D1
IPC codes: D21H27, A24D1