Abstract:
An improved smoking article wrapper which significantly reduces sidestream smike using magnesium carbonate in the form of magnesite as a filler. Smoking articles which employ the wrappers exhibit a significant reduction in sidestream smoke without adverse effect on subjective characteristics.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a smoking article wrapper, and in particular, cigarette paper which uses magnesite as a filler composition. Smoking articles which employ the wrappers of the invention exhibit significantly 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 to those near the smoker who are not smoking or do not smoke. 
     Various attempts have been made to reduce sidestream smoke through the use of various cigarette paper fillers such as magnesium hydroxide (Mg(OH) 2 ). See, e.g. U.S. Pat. Nos. 4,881,557, 4,450,847 and 4,433,697. While magnesium hydroxide significantly reduces sidestream smoke, it presents a cigarette with a poor taste and other negative attributes. To overcome this problem, the use of flavoring agents in the paper has been suggested. This suggestion, however, has met with little success. 
     It is an object of this invention to provide a smoking article wrapper which reduces sidestream smoke without adversely affecting the taste of the cigarette. 
     SUMMARY OF THE INVENTION 
     The wrappers of the invention comprise ordinary cigarette paper having magnesite as a filler. The magnesite filler loading is between 15 to 45% by weight of the paper with a preferred loading of between 25 and 35% by weight. Sizing agents such as alkali metal salts of carboxylic acids may be added at an amount equal to between 2 and 15% by weight with the preferred salts being potassium citrate and potassium succinate. 
     The papers of the invention have a basis weight of between 25 and 70 grams per square meter and have a porosity of between about 2 and 15 cubic centimeters per minute per square centimeter as measured by the CORESTA method. The preferred basis weight is about 45 to 65 grams per square meter and the preferred porosity range is between 5 and 7 cubic centimeters per minute per square centimeter of paper (CORESTA Units). 
     DETAILED DESCRIPTION OF THE INVENTION 
     To prepare the wrappers of the invention, conventional cigarette paper manufacturing procedures are used with the substitution of magnesite (MgCO 3 ) for the conventional calcium carbonate filler. Magnesite is distinguished from the magnesium carbonate generally used and taught by others in the art. Magnesium carbonate which is generally available is actually equivalent to the mineral hydromagnesite having the general chemical formula Mg 5  (CO 3 ) 4  (OH) 2 .4H 2  O. This is chemically, physically, and structurally different from magnesite (MgCO 3 ) which is the filler used in this invention. Magnesite is readily distinguished from hydromagnesite by x-ray diffraction analysis, thermogravimetric analysis or elemental analysis. Subjective testing of cigarettes made with hydromagnesite or magnesite has shown that magnesite is preferred. 
     Magnesite can be obtained either from natural sources, such as mineral deposits, or can be made synthetically from such, as for example, hydromagnesite, magnesium hydroxide, or magnesium oxide. 
     It should be appreciated that magnesite is a very specific mineral form of magnesium carbonate and that synthetic magnesite is not a common item of commerce. Although synthetic magnesite can be prepared by hydrothermal procedures, examples of which are disclosed herein, it should further be appreciated that, in addition to hydromagnesite mentioned above, there are other forms of magnesium carbonate. However, the only one which compositionally corresponds to the exact molecular formula of MgCO 3  is magnesite. As such, it is a distinct and unique form of magnesium carbonate. Unless specifically described as magnesite, all other forms of magnesium carbonates (e.g. artinite (Mg 2  (CO 3 )(OH) 2 .3H 2  O), dypingite (Mg 5  (CO 3 ) 4  (OH) 2 .5H 2  O), giorgiosite (Mg 5  (CO 3 ) 4  (OH) 2 .5H 2  O), hydromagnesite (Mg 5  (CO 3 ) 4  (OH) 2 .4H 2  O), lansfordite (MgCO 3 .5H 2  O) and nesquehonite (MgCO 3 .3H 2  O)) are not magnesite and do not correspond chemically to the formula MgCO 3 . Aside from its unique chemical composition, magnesite can be distinguished from other forms of magnesium carbonates by its thermal stability. Magnesite is the most thermally stable form of all the magnesium carbonates, decomposing thermally only when heated above 500° C. All of the other magnesium carbonates decompose at less than 500° C. 
     In the case of naturally occurring magnesite, it is preferable to use magnesite which is free from substances which might present toxicological problems. It is also preferable to use magnesite relatively free of other minerals such as dolomite or calcite. The presence of small amounts of these minerals, however, does not adversely affect the sidestream smoke reduction achieved by using magnesite. One source of natural magnesite is The Baymag Company of British Columbia, Canada. 
     For synthetic magnesite derived from other magnesium compounds, the product of such chemical reactions should be at least about 95% magnesite. Complete conversion of the magnesium precursor is not essential to the practice of the invention. 
     In the practice of the invention, magnesite may be blended with other filler compounds without significant effect on the sidestream smoke reduction achieved by using magnesite. In the case of such blends, at least 50% by weight of the resulting filler should be magnesite. The balance of the filler may comprise one or more of the following: inorganic oxide, inorganic hydroxide or inorganic carbonate. These compounds include magnesium oxide, magnesium hydroxide, calcium carbonate and titanium oxide as well as other fillers known in the art. 
     Included within the scope of this invention is magnesite having a superficial surface area of less than twenty square meters per gram as measured by the BET method. 
     The paper wrappers of this invention may be made from flax, vegetable or other plant fibers. Other than the use of magnesite as a filler, standard cigarette wrapper manufacturing procedures are used to create the wrappers of the invention. In addition, the paper wrappers of this invention may be a conventional one layer construction, a multiwrapped construction or a multilayer single wrap construction. 
     In the preferred embodiment, sizing agents, such as alkali metal salts of carboxylic acids, are used to adjust or control the static burn rate of the resulting smoking article. Particularly good sizing agents include sodium fumarate and potassium salts, namely potassium citrate and potassium succinate. Of these, potassium citrate and potassium succinate are preferred. 
     As used herein the term tobacco includes not only cut tobacco leaf filler usually found in cigarettes, but also includes expanded tobacco, extruded tobacco, reconstituted tobacco, tobacco stems, tobacco substitutes and synthetic tobacco. 
     EXAMPLES 
     The following examples illustrate the practice and beneficial results of this invention. 
     To measure the amount of sidestream smoke generated, burning cigarettes are allowed to free burn while the sidestream smoke travels through a cell through which a light is passed. A photocell detects the transmitted light intensity during the burning of 30 millimeters of the tobacco rod. The measured light intensity over the course of burning is determined and compared to the light intensity when no smoke is present in the cell. The difference between the two values is reported as the extinction coefficient (EC). 
     The tables in the following examples show the percent reduction in visible sidestream smoke as calculated from various extinction coefficients of the test samples versus a control. The control is either a typical 85 or 100 millimeter commercial cigarette having a 25 gram per square meter paper wrapper with a porosity of about 30 CORESTA units and a citrate sizing agent. Test cigarettes were made by hand at comparable packing densities using the same tobacco filler as the control. All test samples were of standard circumference (about 25 millimeters) and 85 or 100 millimeters in length including a 27 millimeter cellulose acetate filter. 
     Static Burn Time (SBT) is the amount of time it takes a cigarette to burn 40 millimeters under static conditions. In other words, it is the rate at which a cigarette smolders in the absence of drafts or puffing action. In the tables below, SBT is expressed in terms of minutes, basis weight is expressed in grams per square meter, porosity is in CORESTA units, and sizing is in weight percent. 
    
    
     EXAMPLE 1 
     Magnesite was prepared hydrothermally from hydromagnesite using the following procedure: 
     Basic magnesium carbonate (hydromagnesite) was slurried in water and added to a pressure reactor. An over-pressure of carbon dioxide of up to 830 psig (as measured at room temperature) was applied and the mixture was heated to 200° C. The reaction pressures can, of course, vary, depending upon the amount of basic magnesium carbonate present and the free volume in the reactor. The pressure rose initially due to the heating and then fell as the reaction progressed. After two days, the mixture was cooled and the excess carbon dioxide vented. The solids were then removed, filtered, washed, and air dried. Analysis of the solids revealed that the basic magnesium carbonate was converted to magnesite having a surface area of 7.0 m 2  /g. 
     The generated magnesite was then used as a filler to make handsheets with basis weights of 45, 55 and 65 grams per square meter. In each case, the filler loading was 30% by weight of magnesite. Potassium citrate was added as a sizing agent at the levels indicated below. The porosity of the sheets ranged from 4.5 to 6.7 cubic centimeters per minute per square centimeter as measured by the CORESTA method. 
     The papers were then used to prepare cigarettes which in turn were evaluated for SBT and EC as well as subjective evaluations for taste and ash appearance. The results of the SBT and EC evaluations are found in Table 1. 
     
                       TABLE 1______________________________________         Coresta  Basis  Poros-   Siz-           EC ×                                       % ECSample Wt     ity      ing  SBT  EC   SBT*  Reduct**______________________________________Control                      8.1 0.73 5.91  --1      45     6.7      6.8  11.2 0.28 3.14  622      45     6.7      8.0   9.9 0.28 2.77  623      45     6.7      8.7  10.6 0.34 3.60  534      55     5.9      6.6  11.2 0.18 2.02  755      55     5.9      8.1  11.3 0.25 2.82  666      65     4.5      6.6  11.1 0.20 2.22  737      65     4.5      7.9  12.2 0.16 1.95  78______________________________________ *Product of the Static Burn Time and the EC. **Percent Reduction in E.C. compared to the Control. Evaluation of samples 1-7 revealed positive subjectives. 
    
     EXAMPLE 2 
     The magnesite prepared above was then used to prepare a series of cigarettes similar to those in Examples 1-7 with the exception that potassium succinate was used as the sizing agent/burn enhancer. The cigarettes and paper were evaluated as above and the results are reported in Table 2. 
     
                       TABLE 2______________________________________         Coresta  Basis  Poros-   Siz-           EC ×                                       % ECSample Wt     ity      ing  SBT  EC   SBT*  Reduct**______________________________________Control                      8.2 0.93 7.63  -- 8     45.4   3.5      8.4  10.2 0.39 3.98  58 9     45.0   8.7      7.0  12.4 0.26 3.22  7210     45.0   8.7      6.6  10.9 0.34 3.71  6311     55.0   6.8      5.7  11.1 0.34 3.77  63______________________________________ *Product of the Static Burn Time and the EC. **Percent reduction in EC compared to the Control. 
    
     EXAMPLE 3 
     A third series of experiments was conducted to examine the effect of sizing agents and levels of sizing agents. The sample papers and cigarettes were prepared as described above with varying levels of potassium citrate or potassium succinate. The papers and cigarettes were evaluated and the results are set forth in Table 3. 
     
                       TABLE 3______________________________________         Coresta  Basis  Poros-   Siz-           EC ×                                       % ECSample Wt     ity      ing  SBT  EC   SBT*  Reduct**______________________________________Control                8.2   0.87 7.13Potassium Citrate (K.sub.3 Cit.)12     45.5   4.7      3.8  11.0 0.42 4.62  5213     45.4   4.5      5.1  10.9 0.40 4.36  5414     45.0   4.7      7.1  10.9 0.36 3.92  5915     45.5   4.0      7.9  10.6 0.37 3.92  5716     45.5   4.0      9.7  10.8 0.36 3.89  59Potassium Succinate (K.sub.2 Succ.)17     46.0   4.0      4.2  11.4 0.36 4.10  5918     46.0   3.7      5.3  10.8 0.39 4.21  5519     45.5   4.0      7.6  10.8 0.37 4.00  5720     45.2   4.0      8.5  10.8 0.41 4.43  5321     45.5   3.6      8.9  10.8 0.37 4.00  57______________________________________ *Product of the Static Burn Time and the EC. **Percent reduction as compared to the Control. 
    
     As seen from these examples, variation in the amount of either of the sizing agents does not appear to cause significant variation in the reduction of sidestream smoke. 
     EXAMPLE 4 
     In the next series, natural magnesite obtained from Baymag was ground to yield particles having a superficial surface area of 10.6 square meters per gram. The natural magnesite was then used to prepare cigarette papers and cigarettes in the manner described above. The magnesite filler loading for Examples 22 through 24 was 30% by weight and for sample 25, the loading was 40% by weight. The cigarettes and papers were then evaluated and the results are set forth in Table 4. 
     
                       TABLE 4______________________________________       CorestaSam- Basis  Poros-                    EC ×                                       % ECple  Wt     ity      Sizing SBT  EC   SBT*  Reduct**______________________________________Con-                        8.5  0.87 7.40trol22   45     4.7      9.9    9.2  0.36 3.31  59                K.sub.3 Cit.23   65     5.5      7.2    8.6  0.45 3.87  48                K.sub.2 Succ.24   65     5.8      7.6    10.1 0.48 4.85  45                Na.sub.2                Fumarate25   45     6.2      9.2    8.5  0.36 3.06  59                K.sub.3 Cit.______________________________________ *Product of the Static Burn Time and the EC. **Percent reduction as compared to the Control. 
    
     EXAMPLE 5 
     A series of cigarettes was prepared from handsheets containing a filler comprising magnesite. The magnesite was prepared by hydrothermally reacting magnesium hydroxide with carbon dioxide in an aqueous slurry at 200° C. for 48 hours. The product was then filtered, washed and air dried. The final product was predominately magnesite with small amounts of magnesium hydroxide present. The residual magnesium hydroxide is believed to be due to the incomplete conversion of the magnesium hydroxide to magnesite, either due to a deficiency in the amount of carbon dioxide taken and/or to reaction time. The papers were sized with potassium succinate. The cigarettes were evaluated as discussed above and the results are recorded in Table 5. 
     
                       TABLE 5______________________________________         Coresta  Basis  Poros-   Siz-           EC ×                                       % ECSample Wt     ity      ing  SBT  EC   SBT*  Reduct**______________________________________Control                     8.3  0.82 6.8126     45.5   3.5      6.4  9.7  0.32 3.10  6127     45.5   2.0      11.5 10.0 0.26 2.60  68______________________________________ *Product of the Static Burn Time and the EC. **Percent reduction as compared to the Control. 
    
     By analysis the filler used in samples 26 and 27 contained 98.5% magnesite and 1.5% magnesium hydroxide. The cigarettes exhibited excellent sidestream smoke reduction. More importantly, these cigarettes exhibited positive subjectives during evaluation. 
     EXAMPLE 6 
     A series of cigarettes was prepared from handsheets containing a filler comprising a mixture of natural magnesite with calcium carbonate. The magnesite had a surface area of 10.6 square meters per gram. The cigarettes both had a filler loading of 30 percent by weight. Sample 28 contained 25% by weight magnesite and 5% by weight Multifex MM calcium carbonate and Sample 29 contained 15% by weight magnesite and 15% by weight Multifex MM calcium carbonate. Potassium succinate was used as the sizing agent for both samples. The cigarettes were evaluated as discussed above and the results are recorded in Table 6. 
     
                       TABLE 6______________________________________         Coresta  Basis  Poros-   Siz-           EC ×                                       % ECSample Wt     ity      ing  SBT  EC   SBT*  Reduct**______________________________________Control                     8.4  0.90 7.5628     45.0   5.7      11.0 10.8 0.31 3.35  6629     45.4   3.3      4.77 8.8  0.5  4.40  44______________________________________ *Product of the Static Burn Time and the EC. **Percent reduction as compared to the Control. 
    
     EXAMPLE 7 
     In this series, cigarettes were made from handsheets having a filler loading of 35% by weight. Sample 30 contained strictly natural magnesite, and Sample 31 contained 30% by weight natural magnesite and 5% by weight Multiflex MM calcium carbonate. Sample 32 contained 25% by weight natural magnesite and 10% Multifex MM calcium carbonate. Potassium citrate was used as a sizing agent. The cigarettes were evaluated as discussed above and the results are recorded in Table 7. 
     
                       TABLE 7______________________________________         Coresta  Basis  Poros-   Siz-           EC ×                                       % ECSample Wt     ity      ing  SBT  EC   SBT*  Reduct**______________________________________Control                     8.7  0.82 7.1330     45     5.2      8.0  9.3  0.27 2.51  6731     45     6.0      7.8  8.7  0.28 2.44  6632     45     5.4      8.6  8.3  0.32 2.66  61______________________________________ *Product of the Static Burn Time and the EC. **Percent reduction as compared to the Control. 
    
     As seen from Examples 6 and 7, magnesite may be combined with up to about equal amounts of traditional fillers such as calcium carbonate and still provide a cigarette with significantly reduced sidestream smoke. The resulting cigarettes also exhibited positive subjective qualities. 
     Thus, it is seen from the foregoing examples that a paper wrapper for a cigarette is provided that results in reduced amounts of sidestream smoke. One skilled in the art will appreciate that the present invention can be practiced by other than the desired embodiments which are presented for purposes of illustration and not of limitation, and the present invention is limited by the claims that follow.