The present invention relates to an aerosol generating material for a smoking article. In particular, the present invention relates to an aerosol generating material for a smoking article comprising particulate sorbent material coated and/or impregnated with diluent, and products comprising the same. The particulate material has a high BET specific surface area, or is calcium carbonate.
It is known to include diluents in smoking articles such as cigarettes. Diluents are compounds that are vapourised during smoking and transfer to the mainstream smoke in aerosol form. They are generally selected such that they transfer to the smoke substantially intact. Other components of the smoke (tobacco-derived components in the case of tobacco-containing smoking articles, or nicotine and/or flavour components in the case of non-tobacco-containing smoking articles) are therefore diluted by this means.
A cigarette can comprise a filter at the mouth end, a tobacco rod comprising smokable filler material, and cigarette paper wrapped around the rod. When diluent is present in the smokable filler material, this may be as a simple mixture with the other ingredients (particularly for diluents in solid form), or the diluent may be carried on one or more of the other ingredients (particularly if the diluent is in liquid form). If incorporated into the filler material as a simple mixture, this may present disadvantages during manufacturing, and the diluent may be easily dislodged from the finished product, especially if it is in fine powder form. Accordingly, it is preferred for the diluent to be held in intimate contact with another ingredient of the filler material.
It has been discovered that, although the diluent is vapourised during smoking in the course of performing its function, vapourisation of the diluent at lower temperatures can cause problems during storage of the cigarettes. Specifically, the diluent can migrate during storage and subsequently be lost to the atmosphere or interact with other parts of the product such as the cigarette paper. This may also lead to staining or marking of the cigarette paper, either by the diluent itself or by compounds released from the diluent interaction. Those in the art have therefore sought to immobilize the diluent until it is required.
US 2008/0110470 describes the immobilization of a diluent in a porous sorbent, which is then incorporated into a tobacco rod. It focuses on silica gel as the sorbent. However, the smoke data disclosed in this document reveals that the use of the silica gels therein caused an increase in the acrolein, B[a]A and B[a]P content of the smoke. Furthermore, the diluent loading capacity for a free-flowing sample is relatively low; for instance, this document states that glycerol can be loaded at about 120% by weight of the silica gel, whereas propylene glycol can be loaded at about 100% by weight of the silica gel.
There is therefore a need in the art to carry diluents on alternative sorbents in a manner that overcomes one or more of the problems outlined above.
Accordingly, the present inventors have devised the invention defined in the claims.
FIG. 1 is a schematic illustration of a precipitated calcium carbonate particle carrying and/or impregnated with a diluent in accordance with an embodiment of the invention, and a similar precipitated calcium carbonate particle additionally coated with a barrier material in accordance with another embodiment of the invention.
FIG. 2 is a schematic illustration of a cigarette containing an aerosol generating material in accordance with another embodiment of the invention.
In the first aspect of the invention, the particulate porous material having a BET specific surface area of at least 1200 m2/g is a sorbent material, preferably an adsorbent material. Such materials are known to the skilled person and, in many cases, commercially available. For instance, examples of sorbent resins having a BET specific surface area of at least 1200 m2/g include the polystyrene-divinylbenzene resin Chromabond® HR-P from Macherey-Nagel GmbH & Co., KG, Düren, Germany and the styrene-based resin Sepabeads from Sorbent Technologies Inc., Atlanta, US.
Preferably, the particulate porous material is a carbon material, a resin or a metal-organic framework, preferably carbon, preferably activated carbon. The activation level can be measured by standard techniques in the art. For instance, activated carbon can be weighed, exposed to carbon tetrachloride (CTC) and then reweighed, and the percentage weight increase determined. In an embodiment, the CTC activation level of the particulate porous material before loading with the diluent is at least 50%, 60%, 70%, 80%, 90%, or 100%.
Preferably, the particulate porous material has a BET specific surface area of at least 1300 m2/g, preferably at least 1400, 1500, 1600, 1700 or 1800 m2/g. In general, the greater the BET specific surface area, the greater the amount of diluent that can be carried by the particles. However, the brittleness can increase if the surface area is too high. Preferably, the BET specific surface area is 3000 m2/g or less, preferably 2500 m2/g or less, preferably 2000 m2/g or less.
In an embodiment, the particles of the porous material have an average particle size in the range 3-45 μm, preferably 5-30 μm, preferably 6-20 μm, preferably 8-15 μm.
In an embodiment, the pore volume of the porous material is at least 0.5 cc/g, preferably at least 0.6, 0.7 or 0.8 cc/g.
In the second aspect of the invention in which the aerosol generating material comprises particulate calcium carbonate carrying and/or impregnated with a diluent, any suitable calcium carbonate particles may be used. The calcium carbonate is preferably precipitated calcium carbonate, which is crystalline.
Preferably, the particles have a surface morphology with a plurality of indentations and/or protrusions, in or between which a substantial quantity of the diluent can reside. For example, each particle may be an agglomeration of scalenohedral calcite and/or acicular aragonite crystals. FIG. 1 illustrates one suitable structure schematically: a precipitated calcium carbonate particle (1) formed by an agglomeration of scalenohedral calcite crystals has crystalline protrusions (2) on its surface. Although not wishing to be limited by theory, it is thought that, upon exposure to the diluent, the diluent (3) may become trapped between these protrusions, in addition to entering the pores of the material. A further advantage of this type of structure is that the protrusions may interlock effectively in the aerosol generating material of the invention to form a strongly bound entity.
In an embodiment, the calcium carbonate has an average particle size in the range 0.05-200 μm, preferably 0.5-50 μm, 1-45 μm, 1.5-30 μm, 1.8-20 or 2-10 μm.
In both these aspects of the invention, application of the diluent to the sorbent is by any suitable method known to the skilled person or described herein. The diluent may be applied in pure form or in a vehicle of, or mixture with, one or more other materials, which may include a barrier material as described below but, in an embodiment, do not include a barrier material.
In an embodiment, the diluent is comprised in a liquid in which the sorbent is washed or soaked. Alternatively, the sorbent can be sprayed with the diluent in a liquid or gel format. For instance, diluents that are solid at room temperature may be melted, or incorporated into a liquid vehicle such as methanol or ethanol, and those that are liquid at room temperature may be applied in pure form or dissolved or emulsified with another liquid. Simple admixture may also be suitable, for instance admixture of the liquid with the sorbent, allowing the liquid to seep into the pores of the material. Further processing steps may be employed such as curing or pressure treatment.
When using calcium carbonate, such methods may result in a surface covering of the diluent, and/or the diluent may seep into its pores. When using the material specified in the first aspect of the invention, however, it is required for the diluent to enter the pores of the particulate porous material to take advantage of the high BET surface area of the particles, thereby allowing a higher loading of the diluent.
The diluent is at least one aerosol forming agent which may be, for instance, a polyol aerosol generator or a non-polyol aerosol generator, preferably a non-polyol aerosol generator. It may be a solid or liquid at room temperature, but preferably is a liquid at room temperature. Suitable polyols include sorbitol, glycerol, and glycols like propylene glycol or triethylene glycol. Suitable non-polyols include monohydric alcohols, high boiling point hydrocarbons, acids such as lactic acid, and esters such as diacetin, triacetin, triethyl citrate or isopropyl myristate. A combination of diluents may be used, in equal or differing proportions. Triacetin, triethyl citrate and isopropyl myristate are particularly preferred.
There may be several factors influencing the stability and migration of diluents under ambient conditions. These factors may include hydrophobicity or hydrophilicity, viscosity, saturated vapour pressure at room temperature, boiling point, molecular structure (such as hydrogen bonding or Van der Waals forces) and the absorptive/adsorptive interaction between diluent and the substrate. Some diluents will suffer from migration problems to a greater extent than others; for instance, it has been found that triacetin, isopropyl myristate and triethyl citrate particularly benefit from immobilisation as in the present invention.
Another relevant factor is the loading level of the diluent. For instance, if a diluent such as glycerol is included in a large amount, migration problems can still be significant.
The diluent loading level in the present invention may depend upon the specific diluent. In an embodiment of the first aspect of the invention, however, the particulate porous material is loaded with up to 500% by weight of the diluent, preferably 80-450%, 130-400%, 140-350%, 150-300% or 160-250% by weight of the diluent, preferably triacetin. In an embodiment of the second aspect of the invention, the calcium carbonate is loaded with 20-100%, preferably 30-95% or 50-90%, by weight of the diluent.
The particulate sorbent material, once impregnated and/or loaded with diluent, may be encapsulated in a barrier material, which provides further hindrance to migration of the diluent during storage of the smoking article but allows release of the diluent during smoking of the smoking article. This is particularly advantageous for the second aspect of the invention, since calcium carbonate tends to bind diluents relatively weakly. FIG. 1 shows the barrier material (4) encapsulating a calcium carbonate particle loaded with diluent. Use of a barrier material also assists in hindering dislodging of powder in the finished cigarette.
The barrier material may be one that melts, decomposes, reacts, degrades, swells or deforms to release the diluent at a temperature above room temperature but at or below the temperature reached inside a smoking article during smoking. For instance, the physical expansion occurring with vapourisation of sufficient levels of diluent may break down the structure of the barrier material. In embodiments of the invention, the barrier material releases substantial amounts of the diluent above 50° C., preferably above 60° C., 70° C., 80° C. or 90° C.
The barrier material may be, for example, a polysaccharide or cellulosic barrier material, a gelatin, a gum, a gel or a mixture thereof. Suitable polysaccharides include an alginate, dextran, maltodextrin, cyclodextrin and pectin. Suitable cellulosic materials include methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and cellulose ethers. Suitable gums include gum Arabic, gum ghatti, gum tragacanth, Karaya, locust bean, acacia, guar, quince seed and xanthan gums. Suitable gels include agar, agarose, carrageenans, furoidan and furcellaran.
In a preferred embodiment of the invention, the barrier material comprises a polysaccharide. An alginate is especially preferred, due to its encapsulation properties. The alginate may be, for instance, a salt of alginic acid, an esterified alginate or glyceryl alginate. Salts of alginic acid include ammonium alginate, triethanolamine alginate, and group I or II metal ion alginates like sodium, potassium, calcium and magnesium alginate. Esterified alginates include propylene glycol alginate and glyceryl alginate.
In an embodiment, the barrier material is sodium alginate and/or calcium alginate. Calcium alginate provides a greater inhibition of migration of the diluent at ambient temperature than sodium alginate, but also may release the diluent at a higher temperature than the latter.
Application of the barrier material to the particulate sorbent material carrying the diluent is by any suitable method known to the skilled person or described herein, which does not cause complete loss of the diluent in the process. Preferably, substantially no diluent is lost due to the step of applying the barrier material. In an embodiment, the barrier material or a precursor thereto is sprayed onto the particulate sorbent material.
For instance, the particulate sorbent material carrying the diluent can be sprayed with an aqueous sodium alginate solution and dried to form a water-soluble film of sodium alginate on the surface. Alternatively, the particulate material can be sprayed with sodium alginate and then treated with a source of calcium ions, to form a water-insoluble film or gel covering of calcium alginate.
In the resulting product of the invention, individual diluent-carrying particles are surrounded by barrier material and migration of the diluent is further hindered under ambient conditions. This should be contrasted with a comparative situation in which the diluent is combined with “barrier” material before application to the sorbent, such that in the resulting product the barrier material resides only in homogeneous admixture with the diluent, or the diluent has been pre-encapsulated with the barrier material before application to the sorbent (and so is not in intimate contact with the sorbent).