Note: Descriptions are shown in the official language in which they were submitted.
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POST-TREATMENT OF HUMIC ACID-DYED PAPER
Technical Field
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; The invention relates to improved methods for staining
papers suitable for use as wrappers for smoking articles
wherein alkali humates are utilized. The humates are rendered
insoluble on the paper using solutions of magnesium sulfate.
Background of the Prior Art
The use of humic acid and fractions thereof as dyes is
!,, well known. ("Recent Progress in the Chemistry of Natural and
' 10 Synthetic Coloring Matters," T.S. Gore et al. eds., Academic
Press, N.Y. 1962, pps. 99-112.) Recently, a variety of cigar-
ettes manufactured with brown paper wrappers have enjoyed
increased popularity among smokers, and some of these cigarettes
are fabricated using brown wrappers stained with humic acid.
; Processes for staining cigarette paper brown have included the
; use of dyes such as synthetic azo dyes, dyes produced from
walnut shells, caramel, tannic acid and the like. However,
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the aforementioned stains or dyes are undesirable for a variety
of reasons. First, the azo dyes, which contain large amounts
of nitrogen, may produce undesirable pyrolysis products and,
therefore, could be unsuitable for use in smoking articles.
Secondly, the amount of caramel required to produce the
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desired intensity of brown color considerably inhibits the
burn rate of the paper. The use of such stains as tannlc
acid may provide the desired brown color; however, treatment
of this type simultaneously reduces the porosity of the paper
thereby also reducing the rate of combustion. In addition,
adverse affects on the gas phase composition are also noted
(see Austrian Patent 175,148).
By definition, humic acids are allomelanins found in
soil, peat, and low-rank coal. They are generally alkali
soluble and precipitated in the presence of acids. From a
chemical standpoint, hu~ic acids generally consist of a mixture
of complex macro-molecules characterized as having polymeric
phenolic structures with the ability to chelate with metals.
In addition, humic acids have a strong base-binding power,
and thision-exchange capability can be used advantageously in
their use as dyes. There are many variations of humic acid
depending upon differences in the plant remains from which
they originate as well as the soil, climate, microflora,
drainage, etc.
Humic acids, by nature, are intensely chocolate brown in
color; and because of their natural origin, they are particular
ly preferred over synthetic dyes as staining pigments for
producing brown wrappers or papers for smoking products.
Generally, an a~lkaline solution is prepared by mixing the
powdery humic acid with an alkali metal hydroxide, i.e.,
sodium hydroxide, to form a soluble humate salt. This solution
is used to impregnate the paper on one or both sides, and this
is followed by a fixing step, generally with salts such as
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aluminum, calcium, iron, and the like. In essence, sodium
ions are partially exchanged for alkaline earth or metal ions
in the fixing process, thus leaving a water insoluble humate
salt on the paper.
Hennig in Allgemeine Papier-Rundschau, No. 31:1027 (21
August 1967) describes methods for staining paper, and espec-
ially paper suitable for cigarette wrappers, with Sap Brown
( also termed "nut stain" or humates) at about neutral pH.
The Sap Brown may be rendered insoluble on the paper by fixing
with aluminum or iron sulfate. We have found that certain
disadvantages are encountered when utilizing the foregoing
method of Hennig. For instance, when aluminum sulfate is
employed as the fixing agent, an undesirable masking of the
rich brown color is observed.
Others have suggested various cations that are useful
for precipitating humates, and they include chromium, magnesium,
; lead, copper, calcium, potassium, and the like. However, none
have suggested that any one of the cations listed above would
be suitable for use as a fixing agent when staining paper for
ultimate use in smoking articles. Moreover, no suggestion
has been made to indicate that one of these cations, when used
as a fixing agent, might be preferable for use in smoking
articles due to improved smoking characteristics, improved
appearance, or lowered gas phase constituents on smoking.
Analy~ cal studies using humic acid-treated brown wrap-
pers have indicated in some instances a tendency toward
increased gas phase constituents. Various attempts have been
made to reduce constituents, such as carbon monoxide, by
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using more efficient filter elements, by increasing the
degree of ventilation in filters, or by increasing the poros-
ity of the paper or wrapper, etc. However, none of these
me1:hods have proven to be entirely satisfactory.
Brief Summary of the Invention
This invention concerns the improvement of humic acid-
treated paper or sheet material in which tobacco or any other
smoking product is rolled for the fabrication of cigarettes,
cigars, or the like.
The invention relates specifically to a process for
treating humic acid-dyed brown paper suitable for use as
wrappers for smoking articles wherein some of the products of
pyrolysis are substantially reduced. In studies with cigar-
ettesmade with commercially available humic acid-stained
papers, it was observed that on pyrolysis the burning papers
produced more carbon monoxide than conventional white cigarette
wrappers. In an effort to identify the cause, experiments were
designed to study a number of parameters related to dyeing
with humic acid. The concentration and composition of humic
acid was varied as well as the pH of the staining solution;
and in addition, a variety of cations (fixing agents) that
render the humic acid insoluble and colorfast on the paper,
were utilized in an attempt to reduce gas phase delivery.
From the results obtained, a total system for coating cigar-
ette wrappe~s having reduced gas phase constituents has been
; developed an~ will be described in detail hereinbelow.
Thus, it is an object of this invention to provide a
; method for producing a humic acid-coated paper or smoking
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wrapper whereby smoking articles produced from said paper can
be materially improved.
It is a further object of this invention to provide
methods and means that individually operate to provide a more
desirable brown paper or wrapper from the standpoint of gas
phase delivery whereby such ~as phase consitituents, such as
carbon monoxide, are subtantially reduced.
It is yet a further object of this invention to provide a
method for fixing humates on paper whereby a desirable color
intensity is obtained with a concomitant reduction in gas phase
constituents such as carbon monoxide.
Other objects and advantages will be discussed and des-
cribed in detail hereinbelow.
Detailed Description of the Invention
In the practice of the present invention, commercially
available humic acid is suspended in water with stirring. The
mixture is then centrifuged to recover the insoluble humic
acid, and the acid-soluble materials are discarded. Experiment-
ation indicates that the acid-soluble fraction is undesirable
in that at certain concentrations there is a tendency towards
gel formation, and, in addition~ this fraction does not apprec-
iably improve color depth or intensity of the final staining
solution.
The acid-insoluble humic acid fraction is generally dried,
weighed, and then suspended in water. The pH of the suspension
is adjusted with a base such as sodium, potassium, or ammonium
hydroxide, with sodium hydroxide being preferred. The final
pH of the staining solution should be between about 7 and 8
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for optimum results. There appears to be a tendency towards
increased carbon monoxide delivery as the pH of the staining
solution is increased over about a pH of 8. Stabilization of
the pH of the solution may require about 8 to about 20 hours
with continual stirring.
Just prior to the actual staining or dyeing of the paper,
the alkaline humate solution may be centrifuged to remove any
remaining insoluble materials. The insoluble materials are
dried and weighed. The staining solution containing the alkali
humate is adjusted by the addition of water to give a final
concentrationofabout 12 to 16~ humate and preferably about
14~ humate by weight.
The actual staining process may be carried out utilizing
a conventional size press wherein standard bobbins of cigarette
paper are passed through a staining bath containing the alkali
humate at a predetermined speed to insure that the desired
amount of staining solution is retained on the paper. The
paper may be stained on one or both sides depending on the
desired effect to be achieved.
In an alternate approach, sodium humate is added to a
slurry of purified cellulose pulp, and the slurry is used as a
furnish in a conventional papermaking machineto produce a brown
paper suitable for use in the fabrication of smoking products.
In a preferred embodiment of the present invention, the
alkali humate is fixed on the paper by treatment with a dilute
solution of magnesium sulfate. This salt post-treatment is
preferably carried out after the paper has been stained and
dried by conventional methods. Although calcium salts are
well known fixing agents for alkali humates, we have found
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magnesium sulfate unexpectedly superior for use as a fixing
agent when preparing paper for ultimate use in smoking articles.
Magnesium sulfate at a concentration of about l to 3%, and
preferably about 2% by weight, provided consistently lower
carbon monoxide delivery when compared to calcium chloride or
magnesium acetate. Tests were conducted using aluminum sulfate
as a fixing agent; and although carbon monoxide deliveries
were acceptable, it was noted that at even the lowest concent-
ration possible for fixing the alkali humate, the aluminum salt
caused an unacceptable while film on the paper.
Following the fixing step the paper may be washed with
water to remove excess magnesium sulfate or alkali sulfate salts,
i.e., sodium sulfate, which is formed during fixing. If a
post-washing step is employed, it is necessary to use a more
concentrated solution of magnesium sulfate for fixing, for
; example, a 3 to 5% solution of magnesium sulfate would be
acceptable. This washing step is preferably carried out using
a conventional size press as previously described. The insol-
uble magnesium humate remains on the paper and, after drying,
is color fast and provides an acceptable paper for use in
smoking articles. An acceptably intense brown color is obtained
using the salt post-treatment of the presnet invention while
maintaining a lowered carbon monoxide delivery.
The following examples are illustrative but are not
intended to be limitive thereof.
Example 1
Experiments were conducted to compare different salts for
use in fixing sodium humate stained papers. Conventional white
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cigarette paper was stained with a sodium humate solution
having a pH of 12.7. The stained paper was dried and separate
pieces were treated with one of the following solutions: 5.0%
calcium chloride, 4.~% magnesium acetate, or 5.5% magnesium
sulfate. Increased concentrations of fixing solutions were
used to assure that some of the sodium ions would be displaced
or exchanged by either magnesium or calcium ions. The humate-
stained papers were fixed by immersion in the fixing solution
using a conventional size press.
Eollowing the fixing step withthe above-named solutions,
the stained and fixed papers were dried. Cigarettes containing
a typical blend of tobacco were fabricated at 85 mm lengths
and 120 mm lengths using the treated paper. All of the cigar-
ettes had conventional cellulose acetate filters attached there-
to.
The cigarettes were smo]~ed under controlled laborator~
conditions and the gas phase that passed through the filters
was trapped and analyzed for carbon monoxide using known infra-
red spectroscopy techniques. Cigarettes fabricated from paper
that had not been treated by fixing with a calcium or magnesium
salt served as controls. The results are tabulated in Table 1
below.
~!~,. Table 1
SALT POST-TREATMENT
Na Humate Salt P.C.* CO/cig.(mg.)
pH 12.7 control 9.0 30.3
(A) 85 mm pH 12.7 5.0% CaC12 9.3 28.8
cigarettes pH 12.7 4.9% MgAc 9.0 31.0
pH 12.7 5.5% MgSO4 9.3 24.6
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pH 12.7 control 12 31.4
(B) 120 mm pH 12.7 5.0% CaC12 13 29.3
cigarettes pH 12.7 4.9% MgAc 12 34.7
pH 12.7 5-5% MgSO4 13 22.7
*PC = puff count
The data indicates that the papers treated with 5.5%
magnesium sulfate resulted in reduced carbon monoxide delivery
when compared to the untreated control or to other salts known
to render sodium humate insoluble on paper.
Example 2
Cigarette Paper was stained with sodium humate having a
pH of 10Ø The paper was dried and fixed with one of the
of the following solutions: 5% CaC12, 5.5% MgSO4, and 10% HCl.
Cigarettes were fabricated as in Example 1 and smoked under
controlled laboratory conditions. The gas phase was trapped
and analyzed according to the method previously disclosed.
The results are as follows:
Table 2
SALT POST-TREATMENT
85 mm Cigarettes
Na Humate, pH 10
Salt PC* CO/Cigt. (mg)
control - no salt 8.5 20.5
5% CaC12 9.8 25.0
5.5% MgSO 8.5 20.4
10% HCl 4 10.0 32.0
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*PC = puff count
Although the salts shown above are acceptable in render-
ing the sodium humate insoluble, use of magnesium sulfate as
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the fixing agent results in a more acceptable carbon mon-
oxide delivery rate.
Example 3
The sodium salt of sap brown, obtained from Abbey Chemi-
cal Company, was dissolved in water to give a final concentrat-
ion of 20% by weight. Conventional white cigarette paper was
stained with the sap brown solution and dried. Separate pieces
of the dried paper were fixed using either a 5~ sol~tion of
calcium chloride or a 5.5% solution of magnesium sulfate.
Cigarettes (85mm) were fabricated using the prepared
papers. Control cigarettes were prepared using stained but
unfixed paper. Cellulose acetate filters were attached and
the cigarettes were smoked and the gas phase analyzed as in
Example 1. The results are tabulated in Table 3 below.
Table 3
Paper PC*CO/cigt. (mg)
Control 8.6 26.8
CaCl -- fixed 8.8 23.6
; MgSO4 -- fixed 9.7 21.9
*PC = puff count
Example 4
Technical grade humic acid (Aldridge Chemical Company)
was washed extensively with tap water until the supernatant
uid became clear. Approximately 4% of the acid soluble
material was removed. The humic acid was then treated with 1%
by weight sodium hydroxide. The pH of the mixture was 5Ø
Extensive washing resulted in a 20% weight loss, which repres-
ented additional acid soluble materials.
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The washed humic acid weighing 350 g was then treated
with 21 g sodium hydroxide in three steps. At each step, the
solution having a pH of 7-8 was centrifuged, and the supernat-
ant liquid was decanted,dried at 50 C, and weighed. The
separated sodium humate was combined with an additional wash of
the insoluble residue and dried to yield about 160 g. This
represented approximately 32% of the starting material.
The dried sodium humate was dissolved in water to give a
final concentration of 15% (W/V). Following centrifugation to
remove insolubles, the humate solution was 13.7% (W/V). The
solution was coated on conventional cigarette paper by means of
a size press. The paper was dried and post treated with a
2%(W/V) solution of magnesium sulfate. Unstained white cigar-
ette paper was also treated in a similar manner with 2% magnes-
ium sulfate.
Cigarettes, (120 mm) fabricated using a conventionalblend of tobaccos, were wrapped with the treated papers.
Cellulose acetate filters were attached to the cigarettes.
Cigarette A was wrapped with untreated white paper; Cigarette B
was unstained paper treated with magnesium sulfate; Cigarette C
was stained with humic acid; and Cigarette D was stained with
humic acid and post-treated with magnesium sulfate.
The cigarettes were smoked under controlled laboratory
conditions and analyzed as described in Example 1. The results
are as follows:
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Table 4
PC* CO/cigt. (mg) CO/Puff
Cigarette A
control 11.7 13.5 1.13
Cigarette B
control + MgS04 11.7 14.6 1.24
Cigarette C
humate stained 13.2 24.4 1.82
Cigarette D
humate + MgS04 13.2 22.6 1.66
*PC = puff count
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