Process for producing smoking rod wrapper and smoking rod containing same

A printing ink comprises a liquid vehicle, containing a binder, and a smoke-enhancing additive in the form of particles that are insoluble in the liquid vehicle and that have sizes in the range 5-80 microns, preferably at least 90% of the particles having sizes in the range 10-50 microns. The inks are printed onto the inner surface of a smoking rod wrapper in amounts such that the weight of dry deposits is in the range 20 to 60 mg per wrapper.

The present invention relates to printing inks, especially suitable for 
printing the inner surface of a cigarette wrapper, to wrappers carrying 
dried deposits of the ink and smoking rods made with the wrappers. 
In GB No. 2027326 a web of reconstituted tobacco sheet is printed with a 
non-aqueous ink containing ground tobacco offal to produce markings 
simulating the veins of natural tobacco leaf. The printed web is used as a 
cigar wrapper in place of natural tobacco leaf. One side of the sheet is 
printed and the printed side forms the outer surface of the cigar. The 
sheet is 100-500 micron thick and likely to be non-porous. The amount of 
tobacco offal printed onto the sheet is not mentioned but is likely to be 
small relative to the total amount of tobacco constituting the sheet by 
virtue of the nature of the pattern that is being printed and would thus 
have no effect on the smoking proporties of a cigar made with the 
wrappers. The inks have a low tobacco content (14% for the gravure ink 
exemplified and 30% for the screen printing ink exemplified) so that even 
if it were desired to produce high loadings of ink onto the web a large 
amount of solvent would have to be dried off the printed web and this is 
clearly undesirable. The tobacco is ground to 200 mesh (about 75 microns, 
according to the French equivalent of this citation, FR No. 2431834) which 
will produce an ink that is satisfactory for producing a coarse raised 
pattern on the printed substrate, as is desired in the application 
disclosed. Additives other than ground tobacco and conventional ink 
additives are not mentioned. 
The inks disclosed in GB No. 2027326 would be of no use in printing 
wrappers for cigarettes, which are usually made from porous white paper 
having a thickness of about 40 micron where a reasonably high loading of 
ink additive was required, since the dried deposits would be too coarse 
for instance two or more times the thickness of the paper web, thus 
decreasing the length of printed paper that may be wound on to a roll in 
the production of wrappers. This increases the number of times the printed 
roll needs to be changed and thus decreases the manufacturing rate. Also 
the amount of solvent applied to the web would be undesirably high. 
Evaporating and recovering large amounts of solvent increases the 
manufacturing time and energy. 
We described in, for instance, British Patent Specifications Nos. 2007078 
and No. 2094611 how wrappers for smoking rods could be printed with an ink 
containing a smoke enhancing additive, that is to say an additive which 
will in use, upon approach of the hot burning tip of the smoking rod, be 
transferred and contribute to the main stream smoke drawn through the rod 
to enhance the satisfaction to the smoker. The described inks were aqueous 
inks and, in practice, contained the additive in solution. For instance in 
an example the ink is an aqueous solution of nicotine hydrogen tartrate 
thickened by carboxymethyl cellulose. Although there was reference to the 
inks also containing organic solvent, e.g. ethyl alcohol or isopropyl 
alcohol, it appears that the inks would always have also contained water 
as part of the carrier. 
The maximum amount of additive that could be incorporated in the ink was 
relatively low, for instance 20% or less, because of the need to dissolve 
the additive in a fluid vehicle. High loadings of additive on the 
substrate therefore required the application of large amounts of ink and 
this was often detrimental to the appearance or other properties of the 
substrate. For instance, even quite low amounts of ink tended to be 
visible through the substrate and so spoilt the appearance of the smoking 
rod. This was a particular problem when the additive was a nicotine salt, 
such as nicotine hydrogen tartrate. Another problem was that the printed 
deposits of dissolved additive tended to be tacky. 
These problems of relatively low loadings and spoiling the substrate can be 
reduced, but not eliminated, by formulating an ink from a solution of a 
water soluble salt formed between a polymeric acid, such as a 
polysaccharide, and nicotine or other suitable alkaloid, the salt serving 
as binder and viscosity regulator as disclosed in EP No. 0103969. However 
inks based on these polymeric salts still tend to suffer from tackiness 
and the other disadvantages and, additionally, suffer from the 
disadvantage that it can be difficult to produce the salts, and inks 
containing them, conveniently on a commercial scale. Also they are only of 
value for printing an alkaloid, and in the invention we are concerned with 
printing a wide range of different additives. 
It would be desirable to be able to formulate inks easily from readily 
available materials and that have high additive loadings and that can be 
applied in large quantities onto a substrate without detrimentally 
affecting the other properties of the substrate. 
It is known to formulate decorative inks containing particulate pigment 
dispersed in a liquid vehicle. The particulate material always has very 
small particle size, typically 0.2 to 1 micron, and the amounts of these 
particles in the inks are always very low since if the amounts are 
increased significantly the ink becomes a stiff paste that cannot 
conveniently be printed. 
A printing ink according to the invention comprises a liquid vehicle, which 
comprises an ink binder, and a smoke-enhancing additive and is 
characterised in that the smoke-enhancing additive is present in the ink 
in the form of particles that are insoluble in the liquid vehicle and that 
substantially all have sizes in the range 5-80 microns. Preferably at 
least 90% of the particles have sizes in the range 10-50 microns, 
preferably 95% of the particles or more having sizes in the range 10-50 
microns. 
As a result of incorporating the additive in the form of particles in this 
size range, it is possible to increase the amount of additive in the ink 
considerably compared to the amount that can be incorporated if the 
additive is in solution, in conventional sub-micron size particles or as 
particles of ground tobacco as in the inks disclosed in GB No. 2027326. 
Thus the inks preferably contain at least 33% by weight, based on total 
ink, of the smoke-enhancing additive. The amount of the additive is 
usually less than 70% and is most preferably in the range 33-55%. 
According to a second aspect of the invention a process for enhancing the 
smoking properties of a smoking rod comprises providing the inner surface 
of the smoking rod wrapper with dried deposits comprising binder and an 
effective amount of a smoke-enhancing additive, and is characterised in 
that each deposit comprises an impregnated part, that is impregnated into 
the inner surface of the wrapper, and a raised part that is raised above 
the surface of the wrapper, the smoke-enhancing additive being present 
substantially only the raised part. The deposits are generally printed 
deposits and are usually provided by printing an ink according to the 
invention. 
According to a third aspect of the invention, in a process for producing a 
smoking rod wrapper, a web which is less than 100 microns thick is printed 
on one surface with an ink according to the invention. The web is 
generally substantially white in colour. 
As a result of the additive being insoluble in the liquid vehicle the 
appearance of the unprinted surface of the substrate can be substantially 
unchanged even at high additive loadings, whereas in the prior art 
processes, where this type of wrapper was printed, strike through of the 
additive even at low additive loadings tended to spoil the appearance of 
the unprinted surface of the smoking rod wrapper. The particles of smoke 
enhancing additive must be sufficiently large that the ink has appropriate 
rheology despite the high content of smoke enhancing additive and 
therefore substantially all the particles are at least 5 microns in size 
and most preferably at least 10 microns in size. (All references to the 
size of the particles refer to the maximum dimension of the particles.) 
However smaller particles may be present in small amounts, e.g. less than 
10% preferably less than 5% by weight based on the total weight of 
particles, provided they do not soak into the substrate sufficiently to 
spoil its appearance. Preferably there is substantially no strike through 
of ink through the substrate. If the particles are too large it is 
difficult to form appropriate deposits of them, for instance by printing 
or for an adequate loading to be achieved and so the particles should 
substantially all be less than 80 microns in size. 
The substrate web should be sufficiently permeable to allow some 
impregnation of the ink into the substrate, but insufficiently permeable 
to allow particles to strike through the substrate web. Smoking rod 
wrappers are formed from paper that is usually less than 100 microns 
generally 30-50 microns thick and that is porous, often having pores with 
sizes in the range of about 1 micron. In a smoking rod the deposits are 
provided on the inner surface only of the wrapper, the outer surface 
preferably remaining substantially unchanged in appearance. 
The volatilisable smoke enhancing additive may be any additive which will 
volatalise in use, (upon approach of the hot burning tip of the smoking 
rod), and will be transferred to and will contribute to the main stream 
drawn through the rod to enhance the satisfaction to the smoker. 
One type of suitable additive is a compound to improve initial impact, e.g. 
biuret, nicotine, ammonium compounds such as ammonium carbonate, 
carbamate, sulphate and phosphate, and quaternary compounds and urea. 
Another type is a flavour improver such as menthol borate, tobacco 
extracts and synthetic flavourants. Another type is a material to reduce 
irritancy (harshness reducers) such as glycols and other hydrophilic smoke 
diluents, sugars and organic acids such as citric acid. Another type is a 
burn controllers such as sodium carboxymethyl cellulose. Others are smoke 
producing agents and smoke nucleation agents. Physiologically active 
compounds such as alkaloids generally nicotine, may be used. 
The additive may, if crystalline, be provided as crystals of the desired 
particle size. However if necessary smaller particles may be aggregated to 
form particles of the desired size. 
The invention is particularly useful when the additive comprises particles 
which comprise ethanol-insoluble components of tobacco and ethanol-soluble 
components of tobacco, nicotine being present in an amount of 1-50% by 
weight based on the weight of total tobacco components in the ink. The 
ethanol-soluble components are the components of tobacco that are 
extractable with aqueous ethanol and the ethanol-insoluble components are 
the components that remain after the extraction. 
Extraction of ethanol-soluble components is a standard process and may be 
conducted using solvents other than aqueous ethanol, in which the 
ethanol-soluble components are also soluble, for instance aqueous 
methanol, or ethyl acetate. If the ethanol-soluble components are 
extracted from tobacco before use in the invention they may be chemically 
reacted, for instance to convert nicotine to a nicotine salt, before being 
mixed with the ethanol-insolubles, or they may be used unreacted. If the 
ethanol-soluble components are extracted from the ethanol-insolubles, for 
use in the invention, they may be recombined with insolubles different 
from those from which they were extracted. For instance extracted 
ethanol-solubles from leaf tobacco may be recombined with, for instance, 
stem tobacco, or with extracted leaf or stem tobacco. 
Generally however the ethanol-soluble components, if extracted, are 
recombined with ethanol-insolubles from which they were extracted. Thus 
leaf or other tobacco may be extracted to remove ethanol-solubles, some of 
the ethanol-insolubles may then be discharged, and the ethanol-solubles 
recombined with the remaining ethanol-insolubles to form a product having 
a higher ethanol-solubles content, and therefore a higher nicotine 
content, than the starting tobacco. 
Preferably however the particles are formed by comminution of unextracted 
tobacco leaf, preferably having a nicotine content of 5 to 12%, generally 
6 to 8 or 10% by weight based on the weight of leaf. However by conducting 
the extraction process it is possible for the nicotine content of the 
particles to be much higher, often up to 15 or 20% by weight and even up 
to 50% by weight of the combined weight of ethanol-soluble and 
ethanol-insoluble tobacco components. 
Some components of tobacco may tend to cause undesired staining of the 
wrapper on which they are printed. This can be eliminated by extracting 
nicotine from tobacco leaf, washing the resultant pulp thoroughly to 
remove colour, or bleaching it chemically, (e.g., with hydrogen peroxide), 
and then recombining the nicotine with the pulp. 
These particles can be obtained by comminution of the ethanol-insoluble 
components of tobacco intimately admixed with the soluble components. For 
instance the communication can be in an energy mill, causing dry abrasion 
of the particles, in a dry colloid mill or in a colloid or bead mill that 
causes slurry grinding. One preferred method of comminution involves 
slurry grinding in an organic solvent at a temperature below 0.degree. C. 
For instance the mixture of ethanol-insoluble and ethanol-soluble 
components, which may be tobacco dust, offal, stem or leaf as well as a 
blend of extracted ingredients, may be fed into a ball mill containing 
ethanol as organic solvent and held at a temperature between -10.degree. 
C. and -30.degree. C. during grinding. 
The liquid vehicle of the ink normally comprises a carrier and a binder and 
the smoke enhancing additive must be substantially insoluble in both. Its 
solubility in the vehicle, and also in the carrier, is preferably less 
than 10, most preferably less than 6, grams per 100 grams of the vehicle 
or carrier. Thus there may be a small amount of additive dissolved in the 
liquid phase of the ink. This may be, for instance, ethanol-soluble 
components of tobacco that are also soluble in the ink liquid vehicle. The 
smoke enhancing additives are often soluble in water and so the carrier, 
and the entire vehicle, are preferably non-aqueous. The carrier should be 
sufficiently volatile that deposits of the ink can easily be dried and so 
should have a boiling point generally below 100.degree. C. Suitable 
carriers are organic liquids such as aliphatic alcohols, ketones, esters 
and hydrocarbons and mixtures of these. Ethanol and ethylacetate and 
mixtures are the preferred carrier. 
The carrier must include binder and, if necessary, other additives to 
control the rheology of the ink to make it suitable for the chosen method 
of application. The binder may be a synthetic polymer that may be curable 
after application of the ink but preferably is a cellulosic material that 
can dry to bond the particles together in the dry deposits. 
The binder must be soluble in the chosen solvent. It may be a natural, 
modified natural or synthetic polymer. For instance it may be a cellulosic 
binder such as carboxymethyl, methyl, hydroxypropyl or hydroxethyl 
cellulose, a gum such as an alginate or pectinate or a synthetic polymer 
such as EVA or PVA. 
The use of ethyl cellulose as binder, together with ethanol or other 
organic liquid in which it is soluble, is particularly preferred as 
deposits containing it as the sole binder are less tacky, less likely to 
transfer onto the opposite face of a rolled printed web and less likely to 
lose their shape, than deposits containing other binders, when the 
atmosphere is humid. 
The liquid vehicle preferably consists solely of the carrier (generally 
ethanol) and binder (generally ethyl cellulose) but may include other 
additives to control the rheology or other properties of the ink, for 
instance as discussed in British Patent Specifications Nos. 2007078 and 
2094611. The amount of binder is generally 2 to 20%, preferably 5 to 15%, 
by weight of the ink or 5 to 40% preferably 10 to 25% by weight of the 
liquid phase of the ink. 
The particles may be formed outside the liquid vehicle of the ink and then 
combined with the liquid vehicle or, preferably, are comminuted, e.g. by 
grinding in a mill, to the desired size in the liquid vehicle. 
The inks are preferably printed onto the smoking rod wrapper web by known 
processes, for example rotary screen printing or, preferably gravure 
printing. The particle size range of the additives in the inks enable 
screens or gravure cylinders having small holes or shallow cells, 
respectively, to be used. Thus the gravure cells may have a depth of less 
than 100 microns, for example less than 80 microns. Particles larger than 
the desired size range would not be able to enter the cells. It is 
preferred to use gravure plates having shallow cells to maximise the 
proportion of ink released from the cells on to the substrate. Using deep 
cells, a substantial amount of ink remains in the bottom of the cells 
after printing. The particle size range also enables the inks to have the 
required viscosity at the high levels of additive, so that high loadings 
of additive onto the smoking rod wrapper may be achieved without an 
unsatisfactorily large amount of solvent being applied, and thus having to 
be dried. 
The frequency and size of the deposits can be chosen according to the 
desired loading of the additive. For instance, if the additive comprises 
nicotine, generally the density is such that the amount of nicotine 
printed on to a conventional smoking rod wrapper from 50 to 75 mm long is 
from 1 to 2, preferably about 1.6, mg. For other additives the loading may 
be higher or lower. For instance citric acid (harshness reducer) may be 
present at an average amount of about 4.0 mg/cm.sup.2, glycerol (smoke 
producer/harshness reducer) may be present at an average amount of about 
2.8 mg/cm.sup.2 and urea may be present in an average amount of about 0.7 
mg/cm.sup.2. Preferably substantially all of the additive is printed on 
the half of the wrapper distant from the filter or mouth end of the 
smoking rod. For instance the distribution may be approximately as shown 
in FIG. 3 of GB No. 2,094,611. The total weight of printed deposits for 
each smoking rod wrapper is generally in the range 20 to 60, preferably 25 
to 50 mg dry weight. The concentration of additive on the wrapper is 
usually in the range 0.1-5.0 mg/cm.sup.2, preferably about 0.2 to 4.0 
mg/cm.sup.2. Each deposit preferably has a dry height of 20 to 150, 
generally 30 to 50 microns and a wet height (before evaporating the liquid 
carrier) of 40 to 250, preferably 60 to 100, microns. Each printed deposit 
is generally circular or square and may have a maximum transverse 
dimension typically of 0.25 to 3, generally 0.5 to 1.5 mm. 
The following examples illustrate the invention.

EXAMPLE 1 
15 kg of tobacco containing 6% nicotine by weight was added to 33.5 kg of 
ethanol and cooled to -25.degree. C. by addition of solid carbon dioxide. 
The mixture was then ground to a particle size of less than 50 microns 
using a colloid mill. A low viscosity grade ethyl cellulose binder (3 kg) 
was then added to the slurry and left to gell. 
The ink had a typical viscosity of 15-20 poise at 20.degree. C. 
The ink was applied wrapper by deep cell gravure printing to give a solids 
loading of 32 mg/cm.sup.2 over an area of 8cm.sup.2. The nicotine loading 
per cigarette wrapper was 1.6 mg. 
EXAMPLE 2 
10 kg of urea was suspended in 15.9 kg of ethanol and ground in a colloid 
mill to give a suspension with the majority of crystals in size range 
20-80 .mu.m. The grind was transferred to a mixing tank and 1.5 kg of 
ECN50 ethylcellulose added. The mixture was stirred till gelling of the 
ethyl cellulose was complete. The ink was suitable for gravure printing 
and had a viscosity of 20 poise at 20.degree. C. and a content of about 
36% by weight urea. 
The ink was printed by gravure onto cigarette paper wrapper at a wet 
loading of 1.80 mg/cm.sup.2 as deposits each substantially 1 mm in 
diameter. The loading of urea was 0.67 mg/cm.sup.2. 
After drying by convection each dot was observed to consist of a portion 
soaked into the surface of the paper and consisting substantially only of 
ethyl cellulose and a raised portion consisting of particles of the 
additive bonded with ethyl cellulose. Despite the high additive and wet 
loadings the reverse side of the cigarette wrapper was unchanged in 
appearance. The dots were non-tacky and had no tendency to transfer to 
other sheets. 
Similar satisfactory results were obtained when the urea was replaced by 
nicotine dihydrogen tartrate or by dinicotine tritartrate. 
EXAMPLE 3 
1 kg of ethyl stearate (smoke producer) was suspended in 2 litres of 
ethanol and the slurry ground in a water cooled ball mill to give a 
suspension with the majority of crystals in the size range 15-50 microns. 
The grind was transferred to a mixing tank and 200 g of low viscosity 
hydroxypropyl cellulose added. The mixture was stirred till a constant 
viscosity (35 poise) was attained. 
The ink was rotary screen printed onto cigarette paper at a wet loading of 
7.2 mg cm.sup.-2. The dry solids loading on the printed wrapper was 2.4 mg 
cm.sup.-2. 
EXAMPLE 4 
1 kg of menthol borate (flavour) was suspended in 2 litres of ethyl acetate 
and the slurry ground in a colloid mill to give a suspension with the 
majority of particles in the size range 20-80 microns. The ethyl cellulose 
200 g (grade ECN 7) supplied by Hercules was added to the suspension and 
mixture left till the ethyl cellulose had completely gelled. The ink was 
suitable for gravure printing and had a viscosity of 5 poise at 20.degree. 
C. Printed ink had a menthol content of 75% by weight of dry solids on the 
wrapper. 
EXAMPLE 5 
5 kg of citric acid monohydrate (harshness reducer) was suspended 7.5 kg of 
ethyl acetate and ground in a colloid mill until the majority of 
crystalline particles lay in the size range 20-80 microns. 
0.5 kg of ethyl cellulose (Hercules grade ECN 100) was added to the slurry 
which was stirred till the cellulose had completely gelled, the printing 
composition had a viscosity of 45 poise at 20.degree. C. 
The ink was gravure printed onto cigarette paper in a manner such that the 
maximum concentration of acid was at the tipped end of the cigarette 
wrapper. The wrapper had a citric acid loading of 4.0 mg cm.sup.-2. 
EXAMPLE 6 
5.0 kg of glycerol (harshness reducer/smoke producer) were added to 2.5 kg 
of absorbent silica in 7.5 kg of ethyl acetate. The slurry was mixed till 
disaggregation of the silica was complete, particles having a size greater 
than 20 microns were not observed. 1.0 kg of a low viscosity grade 
hydroxypropyl cellulose (Klucel EF, Hercules) was added to the slurry 
which was stirred until a constant viscosity (80 poise) was attained. 
The ink was rotary screen printed onto cigarette wrapper to give a solids 
loading of 4.8 mg cm.sup.-2, the glycerol loading was shown by analysis to 
be 2.8 mg cm.sup.-2.