Note: Descriptions are shown in the official language in which they were submitted.
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PRINTING PROCESS FOR PATTERNED WRAPPER PAPER
FIELD OF THE DISCLOSURE:
This disclosure relates generally to a process for making cigarette wrapper
paper having an
applied pattern of add-on material. More particularly, the disclosure concerns
a process for making
cigarette wrapper paper with a specially formulated oxidized starch material.
SUMMARY:
A wrapper paper for cigarettes may be fashioned with a pattern of add-on
material to reduce
the ignition propensity characteristics of a smoking article fashioned using
the wrapper. Reduced
ignition propensity characteristics reflect a lowered capability of a smoking
article to cause a
substrate to ignite when a smoldering smoking article is left inadvertently
unattended on a
substrate.
In accordance with this disclosure, a predetermined pattern of add-on material
containing an
aqueous starch solution may be applied to a base web of wrapper paper. The
predetermined
pattern may comprise a plurality of transverse bands, a plurality of
longitudinal bands, a two-
dimensional array of treated regions, or any other suitable pattern.
Preferably, the predetermined
pattern may be applied using a printing technique, such as, for example,
gravure printing, offset
printing, inkjet printing, spraying, die printing, or the like. Most
preferably, gravure printing may be
used.
To improve the ignition propensity characteristics of a smoking article
fashioned from the
wrapper paper, the pattern is preferably applied with a printing solution
containing an oxidized
starch. Preferred printing characteristics may be attained using an aqueous
starch solution having
a room temperature viscosity no greater than about 50mPa.s (centipoise, cP),
and prepared from
particles having a size in the range of about 4 microns to about 40 microns
when dry, and about
90% of the particles having a size in the range of about 10 microns to about
100 microns when wet.
Moreover, it is further desirable that the starch solution be slightly acidic
with a pH in the range of
about 6 to about 6.5. Starch employed for the printing solution preferably may
be mixed with water
to form a printing solution having a starch concentration of about 20% to
about 24% (by weight).
Another desirable characteristic of the printing solution is a relatively high
surface tension, for
example, on the order of 6.5.10-2Nm-1 (65 dynes/centimeter) or more.
If desired, the printing solution may be applied to the base web in two or
more layers.
Those layers may be vertically registered with one another, offset from one
another, have portions
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spaced from one another, and the like. Furthermore, a conventional filler
material, such as calcium
carbonate, may be included in one or more of the layers, as may be desired.
BRIEF DESCRIPTION OF THE DRAWINGS:
Many objects and advantages of this disclosure will be apparent to those
skilled in the art
when this written description is read in conjunction with the accompanying
drawings wherein like
reference numerals are applied to like elements and wherein:
FIG. 1 is a schematic view of a gravure printing process;
FIG. 2 is a schematic view of a wrapper paper having transversely printed
regions;
FIG. 3 is a schematic view of a wrapper paper having longitudinally printed
regions;
FIG. 4 is a schematic view of a wrapper paper having a two-dimensional
pattern;
FIG. 5 is cross-sectional view of a multilayer printed region; and
FIG. 6 is a perspective view of a smoking article having a tobacco rod
constructed with the
wrapper disclosed herein.
DETAILED DESCRIPTION:
Generally, a predetermined pattern of add-on material may be applied to a base
web of a
wrapper paper to obtain improved Ignition Propensity ("IP") characteristics
and also to obtain
improved Self-Extinguishment ("SE") characteristics.
Ignition Propensity is a standard test
zo conducted as set forth in ASTM E 2187-04, "Standard Test Method for
Measuring the Ignition
Strength of Smoking articles".
Ignition propensity measures the probability that a smoking article, when
placed on a substrate, will
generate sufficient heat to maintain static burning of the tobacco rod. Low
values for IP are
desirable as such values correlate with a reduced likelihood that a smoldering
smoking article will
cause combustion in an underlying substrate.
Furthermore, the predetermined pattern of add-on material is typically applied
to a base web
having a permeability lying in the range of about 20 to about 80 CORESTA
units. When dry, the
add-on material often forms a film on the base web that is effective to
locally reduce permeability to
values lying in the range of 0 to about 10 CORESTA units. In some
applications, the add-on
material is applied as an aqueous solution including starch.
Unexpectedly, it has been found that certain characteristics of the starch
material give rise
to predetermined patterns that yield very low Ignition Propensity values when
the patterned base
paper is formed into smoking articles. Even more surprising has been the
realization that within the
standard specifications for some well-known starch materials, batch-to-batch
variations in material
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properties can affect the Ignition Propensity of the resulting smoking
articles. By way of example,
the specifications of an oxidized tapioca starch commercially offered by
National Starch & Chemical
Co. as Flo-Max 8 indicate a pH in a 1% solution lying in the range of 4.5 to
6.5, with particles
having molecular weights in excess of 10,000. Surprisingly, when a
predetermined pattern was
applied to a base web with a batch of Flo-Max 8 having a pH in the range of
about 6 to about 6.5,
Ignition Propensity has been found to be much improved when compared to other
batches of Flo-
Max 8 for which the pH was less than about 6 but still within the
manufacturer's specifications.
Various balances or trade-offs need to be made in selection of starch
parameters for use in
applying films to wrapper paper. For example, while high molecular weight
starch may give rise to
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effective permeability reduction, such high molecular weight starches must be
used in low
concentrations, resulting in a solution having a very high water content. But
high-water-content
films are much more difficult to effectively dry on porous wrapper paper.
Moreover, it has been
found that surface tension of the starch solution affects the retention of
small bubbles of air -- low
surface tension allows smaller bubbles to remain in the solution, whereas high
surface tension
causes bubbles to agglomerate and separate out of the solution giving a more
uniform and
consistent material for application to the wrapper paper.
Although not fully understood, the preferred pH range of the oxidized starch
is believed to
reflect a lower degree ¨ or less complete oxidation of the starch polymer
chains giving more,
longer polymer chains than the more acidic (i.e., lower pH) starches.
Furthermore, longer polymer chains yield a solution having a higher viscosity.
Higher
viscosity for the starch solution translates to better control when applied to
a wrapper paper in a
printing process.
Based on these understandings, it has been found that marked improvement in
the Ignition
Propensity of patterned wrapper paper results for starch solutions having
particular, and improved,
characteristics. Those characteristics for an aqueous solution including
oxidized starch include a
pH in the range of about 6 to about 6.5; a surface tension of at least about
6.5.10-2Nm-1
(65 dynes/centimeter); a room temperature viscosity of no greater than about
50 mPa=s; and a
particle size distribution in the range of about 4 microns to about 40 microns
for dry particles, with
about 90% also being in the range of about 10 microns to about 100 microns
when wet.
Furthermore, the particles preferably have a molecular weight such that the
solution can have
starch concentrations in the range of about 20% to about 24%. Preferably, the
starch comprises an
oxidized tapioca starch.
The aqueous starch solutions used for application to the base web or wrapper
paper are
typically prepared by making a starch/water mixture by first mixing the
desired weight of dry starch
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powder with the desired weight of room temperature water (i.e., at about 15 C
to about 25 C) to
obtain a starch/water mixture having the preselected concentration. For
example, to prepare a
starch/water solution with a preselected concentration of 20%, 20 parts by
weight of starch are
mixed with 80 parts by weight of water. The starch/water solution is then
heated to an elevated
sub-boiling temperature in the range of about 90 C to about 95 C ¨ i.e., below
the boiling
temperature. The starch/water solution is held at the elevated temperature for
about 20 to about 30
minutes for thermal soaking. Then, the starch/water solution is cooled to room
temperature. That
cooling step can occur by passively, such as by naturally occurring heat
transfer processes; or the
cooling step can be active (or forced) such as by immersion in a cooling bath
or by use of a
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conventional mechanical cooling system. Throughout the mixing step, the
heating step, the thermal
soaking step, and the cooling step, the starch/water mixture is stirred. The
stirring can be
continuous or substantially continuous. If additional constituents, such as
calcium carbonate, are to
be incorporated into the starch/water solution, those constituents should be
added after the
starch/water solution returns to room temperature following the thermal
soaking step.
Aqueous starch solutions having the characteristics specified above and
prepared in the
manner described above can be applied to a base web using any of a multitude
of printing
techniques including, by way of example and without limitation, the group
consisting of gravure
printing, offset printing, inkjet printing, spraying, and die printing. Other
printing processes may also
be suitable and are intended to lie within the teachings of this
specification. Preferably, however,
gravure printing may be used to apply the starch solution to a base web to
obtain a patterned
wrapper paper.
For example, (see FIG. 1), a base web of wrapper paper 10 may be fed from a
bobbin 12
into a gravure printing system 14 where a predetermined pattern of starch
solution prepared in
accord with the foregoing specification is applied to the base web 10. The
base web 10, with the
newly applied predetermined pattern is collected on a collection bobbin 16. In
otherwise
conventional steps, the bobbin 16 of patterned wrapper paper may be used to
fashion tobacco rods
for use in making smoking articles, such as cigarettes.
The gravure printing system 14 may include one, two, three, or more printer
operations 14a,
14b, 14c. As these operations are essentially the same, it will suffice to
describe details of one with
the understanding that the others have corresponding details. The starch
solution described above
may be furnished to a reservoir 20 from which it is pumped or otherwise
supplied to a gravure roll
22 having a patterned surface. That roll 22 rotates in a bath of the starch
solution. As the gravure
roll 22 rotates, the starch solution is wiped from the roll surface by a
doctor blade assembly 23 so
that, as the gravure roll 22 contacts the base web 10 at the nip between the
gravure roll 22 and the
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resiliently faced backing roll 24, the starch solution transfers to the base
web with the pattern on the
surface of the gravure roll 22.
After suitable drying, the base web 10 may advance to one or more other print
operations
14b, 14c where one or more additional layers of starch material in the same or
different
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predetermined patterns may be applied to the base web 10. If desired, the
starch material in other
print operations may include other constituents, for example, calcium
carbonate. Furthermore, if
desired, the starch solution having calcium carbonate could be applied in the
first printing operation
14a, while the starch solution without calcium carbonate may be applied in the
second or
successive printing operation 14b, 14c.
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The base web 10 (see FIG. 2) typically has a transverse or cross-web direction
(shown by
the arrow 30) as well as a longitudinal direction (shown by the arrow 32). The
predetermined
pattern of add-on material may comprise a plurality of transversely oriented,
generally parallel,
regions or bands 34. These bands may be uniformly spaced along the length of
the base web 10,
or may be arranged at recurrent spacing patterns related to tobacco rod length
and finished
cigarette fabrication.
Alternatively, the base web 10 may include a predetermined pattern such as one
or more
longitudinally extending regions or stripes 36 (see FIG. 3) of add-on
material. If desired, the
predetermined pattern may also comprise a two-dimensional array of regions 38
(see FIG. 4) of
add-on material spaced along and/or transversely of the base web 10.
Furthermore, as noted above, the add-on material can be applied in two or more
layers 40,
42 (see FIG. 5). The layers can be fully registered and co-extensive with one
another if so desired.
Alternatively, the upper layer 42 may be split or slit into two portions 42a,
42b, each of which is
superposed on the first or lower layer 40 such that a space exists between the
two portions 42a,
42b. That space may extend either longitudinally or transversely on the base
web 10. In a further
alternative, the upper layer 42 may be superposed on the lower layer 40, but
not co-extensive
therewith.
A smoking article (see FIG. 6) comprises a tobacco rod 205 and a filter 207,
which are
attached to one another with a tipping paper 209. The tobacco rod 205 includes
a wrapper 210 that
is constructed in accordance with the teachings herein.
When the word "about" is used in this specification in connection with a
numerical value, it is
intended that the associated numerical value include a tolerance of 10%
around the stated
numerical value. Moreover, when reference is made to percentages in this
specification, it is
intended that those percentages are based on weight, i.e., weight percentages.
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It will now be apparent that a new, improved, and nonobvious process for
making patterned
wrapper paper has been described in this specification with sufficient
particularity as to be
understood by one of ordinary skill in the art. Moreover, it will be apparent
to those skilled in the art
that numerous modifications, variations, substitutions, and equivalents exist
for features of the
invention which do not materially depart from the scope of
the invention. Accordingly, it is
expressly intended that all such modifications, variations, substitutions, and
equivalents which fall
within the
scope of the invention as defined by the appended claims shall be embraced
by the appended claims.