Note: Descriptions are shown in the official language in which they were submitted.
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NON-STRINGY GEL TOOTHPASTE COMPRISING KAPPA CARRAGEENAN AND CELLULOSE AS
BINDERS
This invention relates to a gel toothpaste comprising kappa
carrageenan and a cellulose gum. In particular, it relates to a gel
toothpaste comprising a binder containing kappa carrageenan and a
cellulose gum such as carboxymethylcellulose in a formulation so as to
provide a toothpaste having low stringiness. The toothpaste has good
consistency and maintains good physical stability at relatively low
concentrations of binder.
Background
For toothpaste manufacturers, the stringiness of the toothpaste
ribbon has historically been and is today an important parameter of
concern. High volume manufacturers typically package toothpaste in
laminated tubes using high speed filling lines that are capable of filling 80
to
200 tubes per minute. To meet the demands of such production, it is
important that the toothpaste ribbon cuts off sharply from the tube. If
toothpaste remains in the sealing portion of the lamitube, tube sealing could
be faulty resulting in the opening of the tube. Also, toothpaste string
coming out of the tube could cause blackening on the outside portion of the
tube in the sealing area due to burning while it is being sealed. Open and
blackened tubes are rejected during production. On the consumer side,
stringy toothpaste gives a shabby look to the toothpaste nozzle during
usage. These problems are inherent with a toothpaste that tails or is
stringy. To avoid or minimize these problems, a toothpaste formulation is
desired that provides a sharp cut off, i.e., a toothpaste that is not stringy
or
does not tail.
Toothpaste generally contains a polishing agent or abrasive,
humectant, thickener or binder, water, foaming agent and flavoring agents.
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The humectant and water are also referred to collectively as the vehicle. In
addition, agents that provide therapeutic or cosmetic benefits may be
incorporated such as fluoride and tartar control agents. I n seeking to
provide a non-stringy toothpaste, the formulation must maintain other
excellent physical properties to which the consumer is accustomed. For
consumer satisfaction these properties should provide a toothpaste that has
appealing taste, good cleansing effect, is easy to rinse, excellent mouth
feel, and chemical and physical stability. Furthermore, these properties
should be provided in a toothpaste that is cost effective for the consumer.
The formulation properties of a toothpaste will depend on the
inherent properties of the binder, abrasive, humectant, water and other
components of the formulation, and they will also depend on how these
components behave in complex mixtures with each other. In general,
stringiness will be a function of the type and amount of binder and abrasive
used in the toothpaste formulation. To a lesser extent, stringiness will also
be effected by the choice of humectant. Among the commonly used
binders, for example, carboxymethylcellulose (CMC} is known to generally
promote stringiness while carrageenan reduces stringiness. Among the
commonly used abrasives, silica generally enhances stringiness relative to
chalk and dicalcium phosphate (DCP}.
The generic term carrageenan is applied to dozens of similar
polysaccharides derived from seaweed. All carrageenans contain repeating
galactose units joined by alternating (31--> 3 and a1-~ 4 glycosidic linkages
and are partially sulfated. The types of carrageenans may be distinguished,
in part, by their degree of sulfation. Kappa carrageenan has a repeating
unit of D-galactose-4-sulfate-3,6-anhydro-D-galactose providing a sulfate
ester content of about 18 to 25%. Iota carrageenan has a repeating unit of
D-galactose-4-sulfate-3,6-anhydro-D-galactose-2-sulfate providing a sulfate
ester content of about 25 to 34%. Lambda carrageenan has a repeating
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unit of D-galactose-2-sulfate-D-galactose-2,6-Bisulfate providing a sulfate
ester content of about 30 to 40%.
The carrageenans forms gels that are thixotropic. Such gels are
reported to exhibit excellent extrudability, flavor release and rinsability.
The
use of kappa and iota carrageenan as binders in gel toothpaste is known to
also provide a toothpaste that is non-stringy. However, as U.S. Patent
4,604,280 notes a problem associated with compositions made using
carrageenan is that the thickness or viscosity of the composition tends to
decrease when the composition is subjected to mechanical working at a
temperature below the gel-sol temperature. For carrageenan, the gel-sol
temperature is in the range of about 45° to 49°C. Sometimes a
minor
working below this temperature can cause a substantial decrease in
viscosity. To compensate for such loss of viscosity, it is often necessary to
employ additional amounts of carrageenan to the formulation than would
otherwise be necessary. Carrageenan is therefore often employed at a
weight concentration in excess of one percent.
Of the types of carrageenan, iota, kappa and lambda, that have been
used in toothpaste formulations, iota carrageenan is usually preferred. This
preference is due in part to a difference in hardening effect. Relative to
gels based on iota carrageenan, gels based on kappa carrageenan are
reported to harden more readily on the shelf. Toothpastes that harden in
such a manner become difficult to squeeze from the tube. Also, relative to
the iota form, gels based on kappa carrageenan are more likely to have a
syneresis problem; i.e., they will be more likely to have water separate from
the gel. Toothpaste products are deemed unacceptable if they are not
stable against such phase separation. For these reasons, when
carrageenan is employed as a binder in gel toothpaste it is usually the iota
form that is chosen.
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It is an objective of this invention to provide a non-stringy gel
toothpaste which is comprised of kappa carrageenan as a major component
of the binder but without the aforementioned stability problems associated
with kappa carrageenan. It is a further objective to provide such a
toothpaste where the concentration of kappa carrageenan is relatively low.
Summar)r of the Invention
It has now been found that a binder containing kappa carrageenan
and a cellulose gum in toothpaste formulations provides a toothpaste that is
surprisingly non-stringy and exhibits good consistency and physical stability.
The toothpaste may also be formulated to have excellent transparency.
The concentration by weight of binder in the formulation is in the range of
about 0.30 to 0.80%. The weight ratio of kappa carrageenan to cellulose
gum in the binder is in the range of about 25:75 to 75:25. A preferred
concentration of binder is in the range of about 0.45 to 0.65 and a preferred
ratio of kappa carrageenan to cellulose gum is in the range of about 55:45
to 75:25. A preferred cellulose gum is carboxymethylcellulose (CMC).
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Detailed Description of the Invention
This invention pertains to a toothpaste comprised of a binder
containing kappa carrageenan and a cellulose gum in a formulation that is
non-stringy, has good consistency, transparency and exhibits good physical
stability. The invention overcomes the problem of stringiness that is
associated with cellulose gums such as carboxymethylcellulose or CMC and
the problems of syneresis and stability that are associated with kappa
carrageenan. The binder obtained by mixing the cellulose gum and kappa
carrageenan may be used in a standard gel toothpaste formulation to
provide a toothpaste that is non-stringy, is stable to wafer and flavor
separation over extended periods of time, has good Cuban values (has a
good consistency) and does not appreciably harden over extended time
periods. The binder is useful at relatively low concentrations which is
important as a cost consideration.
This invention provides a toothpaste composition which comprises an
orally acceptable vehicle, a polishing agent, a surface active agent and a
binder, the binder containing kappa carrageenan and a cellulose gum, the
percent by weight concentration of binder being in the range of about 0.30
to 0.80%, and the ratio of kappa carrageenan to cellulose gum being in the
range of about 25:75 to 75:25. Important features of this invention are (a)
the percent by weight concentration of the binder and (b) the weight ratio of
kappa carrageenan to cellulose gum in the binder. A preferred
concentration of binder is in the range of about 0.45 to 0.65%. A more
preferred concentration of binder is between about 0.45 to 0.61 %. A
preferred ratio of kappa carrageenan to cellulose gum is in the range of
about 55:45 to 75:25. A more preferred ratio is between about 60:40 to
75:25, and a still more preferred ratio is between about 62:38 to 71:29. The
cellulose gum and kappa carrageenan in the binder may be in the form of a
dry blend mixture or a coprocessed mixture, either of which are suitable.
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Such mixtures may be prepared according to methods that are generally
known in the art.
Cellulose gums that may be used with this invention include those
that are generally suitable as gum thickeners in toothpaste. Examples of
such gums are hydroxyethylcellulose, hydroxypropylcellulose, and
carboxymethylcellulose. As used herein, the term "cellulose gum" refers to
any one or a combination of cellulose gums. A preferred gum is
carboxymethylcellulose.
Toothpastes normally comprise a vehicle, a polishing agent, a binder
and a surface active or detersive agent. In addition, agents that provide
therapeutic or cosmetic benefits may be incorporated such as an enamel
hardening agent, a tartar control agent, a whitening agent, and an
antibacterial agent. One or more sweeteners and flavoring agents are
optionally added for consumer satisfaction. Titanium dioxide may also be
added as an opacifier or a whitening agent where such is desired.
The vehicles of this toothpaste are orally acceptable vehicles
comprised of water and a humectant, such as polyols of three to six
carbons where each carbon is hydroxylated, and mixtures thereof.
Examples of humectants include glycerol, sorbitol, polyethylene glycol,
polyoxyethylene glycol, mannitol, xylitol, and other sugar alcohols. Sorbitol
and glycerol (glycerin) are preferred.
Polishing agents or abrasives that are suitable in the toothpaste of
this invention include finely divided water-insoluble powdered materials
many of which are known to those skilled in the art. These materials have
polishing activity without being overly abrasive. Examples include dicalcium
phosphate, tricalcium phosphate, sodium metaphosphate, crystalline silica,
colloidal silica, complex aluminosilicates, calcium carbonate, magnesium
carbonate, magnesium phosphate, calcium pyrophosphate, bentonite, talc,
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calcium silicate, calcium aluminate, aluminum oxide, silica xerogels. A
preferred abrasive is a silica based abrasive.
The surface active agents (detergents) that may be used in the
toothpaste of this invention are those commonly used to emulsify or
otherwise uniformly disperse toothpaste components. It is generally
preferred that the detergent be anionic or nonionic or a mixture thereof.
Suitable types of anionic detergents include sodium lauryl sulfate, fatty acid
monoglyceride sulfates, fatty alkyl sulfates, higher alkyl aryl sulfonates,
higher alkyl sulfoacetates, higher olefin sulfonates, higher aliphatic
acylamides of lower aliphatic aminocarboxylic acids, higher alkyl poly-lower
alkoxy {of 3 to 100 alkoxy groups) sulfates, and fatty acid soaps. Examples
of these anionic detergents include sodium lauryl sulfate, sodium
hydrogentated coconut oil fatty acids monoglyceride monosulfate, sodium
N-lauroyl sarcoside, and sodium cocate. Suitable types of nonionic
detergents include chains of lower alkyene oxides such as ethylene oxide
and propylene oxide.
Additional materials that are optionally added include flavorings,
enamel hardening agents, and antibacterial compounds. Examples of
flavoring materials include the sweetener saccharin, essential oils such as
spearmint, peppermint, wintergreen, eucalyptus, lemon and lime. Examples
of hardening agents include sodium monofluorophosphate, sodium fluoride
and stannous fluoride. Examples of antibacterials are sodium benzoate,
triclosan, and methyl or ethyl parasept.
Toothpastes of this invention may be prepared as opaque or
translucent. Without the addition of an opacifier the toothpastes have good
transparency. Titanium dioxide is a preferred opacifier that may be added
to provide an opaque toothpaste without otherwise affecting the physical
attributes of the formulation.
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_g_
Toothpaste formulations of the present invention may be prepared in
a manner known to those skilled in the art. An example of a general
procedure performed at ambient temperature is as follows. The binder is
dispersed into sorbitol or glycerin with high speed stirring and the
dispersion
is stirred at that speed for 5 minutes. Water is added and the resulting gum
slurry is stirred for an additional 15 minutes. Separately, a dry blended
mixture is prepared from sodium saccharin and sodium benzoate. If sodium
fluoride, sodium monofluorophosphate, titanium dioxide or any other salts
are to be used, they are added to the mixture at this stage. The mixture is
then dispersed into the gum slurry and stirred at low speed stirring for 10
minutes to form a gel. Color is added and mixed in by stirring for 5
minutes. The gel is then transferred to a Ross~ Mixer. Silica is added and
mixed for 15 minutes under partial vacuum (at least 720 mm Hg). Flavor is
added and mixed for 10 minutes under full vacuum, then sodium lauryl
sulfate is added and mixed for 15 minutes under full vacuum. At this point,
a sample may be withdrawn for testing and the batch discharged for tube
filling.
The following Examples illustrate but do not limit the invention.
EXAMPLES
Comparisons were made among a number of formulations with
varying amounts of kappa carrageenan and CMC. To evaluate the effect of
the binder on stringiness, Cuban values, and stability, components other
than the kappa carrageenan and CMC binder were kept constant. Table 1
shows the ingredients that were kept constant in one set of comparisons.
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Table 1. Components other than Binder
Percent
Sorbitol 70% 68.00
Saccharin 0.20
Sodium benzoate 0.20
Silica (precipitated) 7.00
Silica (abrasive) 11.00
Flavor 1.00
Sodium lauryl sulfate 2.00
Water 9.80-10.15
Table 2 illustrates some of the formulations containing the ingredients
in Table 1 and varying amounts of kappa carrageenan and CMC.
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Table 2. Representative Test Formulations
Kappa Iota
Number Carrageenan CMC Carrageenan* Xanthan
1 0.38 0.23 - -
S 2 0.32 0.13 - -
3 0.30 0.15 - -
4 0.34 0.21 - -
5 0.31 0.19 - -
6 0.50 0.30 - -
7 0.30 0.20 - -
8 0.31 0.29 - -
9 0.25 - 0.05 -
10 0.20 - 0.10 -
11 0.15 - 0.15 -
1 S 12 0.10 - 0.20 -
13 0.15 - 0.20 -
14 0.20 - 0.20 -
15 0.20 - - 0.50
16 0.40 - - 0.40
17 - - 0.45 -
18 - - 0.35 -
19 - 0.50 - -
20 - 0.70 - -
21 - - - 0.50
22 - - - 0.75
*lota carrageenan content rom a 0 o 0 0.
is out to
1
Formulations prepared with in 0.03%
iota carrageenan conta
potassium chloride.
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Test Results
For each of the formulations prepared, stringiness, Cuban values,
and physical stability were measured.
The stringiness of the formulation was measured using a texture
analyzer. The texture analyzer is fitted with a plunger that moves
downward and touches a sample of toothpaste. The plunger remains on
the sample for a stipulated time and then starts moving upward bringing
with it a string of toothpaste. After the plunger reaches a particular height
or distance on its upward ascent, the toothpaste string will break. The test
is stopped as soon as the string breaks and the distance travelled in
millimeters by the plunger is the measure of stringiness. The following is a
detailed procedure that was used to measure stringiness for this invention.
A two gram sample of toothpaste was placed at the center of the lower
plate of a texture analyzer. The force of the plunger was set at 200 g, and
the pretest speed of the plunger was set at 1 mmlsec. Pretest speed is the
speed that the plunger will travel down before starting the test. The sample
holding time for the plunger was set at two seconds. This allows the
plunger to touch the sample on the holding plate and remain there for two
seconds before traveling upward. The post test time was set at 1 mmlsec.
This is the speed at which the plunger travels upward. The test was
stopped as soon as the string broke and the distance travelled in
millimeters by the plunger was measured.
Cuban test values are directly related to the viscosity of the
toothpaste. In the Cuban test (also termed the "Rack" test), the paste is
squeezed from a tube through a fixed orifice across a grid of parallel rods,
increasingly spaced apart. The test results are expressed as the greatest
space number (numbers are from 1-12) which represents the longest
distance between rods that support the dentrifice ribbon without having it
break. The rack is about 300 millimeters (mm) long and about 100 mm
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wide. The stainless steel rods are spaced at increasing distances apart
starting at 3 mm between rods 1 and 2 (space number 1 ) and the distance
between rods increases by 3 mm from rod to rod. Thus the distance
between rods 2 and 3 is 6 mm, and the distance between the twelfth and
thirteenth rod (space number 12) is 39 mm. Ratings of 1-2 and 9-12 are
not acceptable, 3 and 8 are acceptable, 4-7 are good.
Stability tests were conducted by filling tubes with the sample paste.
The tubes were capped and stored flat for 12 weeks at room temperature
and at 50~ C. After the twelve week exposure, a toothpaste ribbon of about
5 cm in length was squeezed from the tube and examined. The tubes were
then slit open and the contents evaluated for flavor and phase separation
(syneresis). The separation of the flavoring and water phase at the tip of
the toothpaste tube may be noted as "wet cap". Flavor separation was
rated as 1 = slight, 2 = moderate and 3 = severe. Stability was rated as
"not ok", "ok", and "good". To be rated "not ok," the sample readily
exhibited some undesirable properties such as flavor separation, syneresis,
being very hard in the tube, or having unacceptable Cuban values. To be
rated "ok," the sample did not separate but could be somewhat grainy and
lacking in good sheen. To be rated "good," the sample exhibited no
separation of any sort and the sample was superior in subtle details such
as fine texture or not grainy and had superior sheen or gloss. Table 3
shows the results of the Cuban and stability testing for the formulations
described above in Tables 1 and 2.
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Table 3. Test Results
Stability
Number Cuban value RT 50~ C
1 5 good good
2 5 good good
3 3 good ~ good
4 5 ok ok
5 5 ok ok
6 9 thick thick
7 5 slighty slighty
thick thick
8 5 ok ok
9 10 ok flavor sep.
10 9 ok flavor sep.
11 9 ok flavor sep.
12 5 ok flavor sep.
13 8 thick ok
14 9 thick flavor sep.
15 3 ok ok
16 4 ok ok
Entries 1-8 in Table 3 are kappa carrageenan I CMC formulations
where the ratio of kappa carrageenan to CMC is in the range of 52:48 to
71:29. As can be seen from Table 3, the Cuban values for the kappa
carrageenan I CMC formulations (entries 1-8) are good when the percent by
weight concentration of kappa carrageenan was greater than 0.30% and
less than 0.50%. At the higher concentration of kappa carrageenan,
thickening also becomes a problem over the extended time period.
Entries 9-14 of Table 3 are representative of the attempts to prepare
a suitable binder by mixing kappa and iota carrageenan. As can be seen
from the Cuban values andlor the stability results, these formulations were
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generally unacceptable. Entry 15 of Table 3 is representative of an
unsuccessful attempt to prepare a suitable binder by mixing kappa
carrageenan and xanthan.
In addition to providing a kappa carrageenan-based gel toothpaste
having good viscosity and stability, a further objective was to provide such a
toothpaste that is also non-stringy. As used herein, the term "non-stringy"
refers to a toothpaste having low stringiness (below about 20 mm). It was
found that certain gel toothpastes comprised of a binder containing kappa
carrageenan and CMC exhibited surprisingly iow stringiness. To provide a
toothpaste having low stringiness, a preferred percent by weight
concentration of binder is in the range of about 0.45 to 0.61 %. Within this
range, a preferred ratio of kappa carrageenan to CMC is in the range of
about 62:38 to 71:29. Table 4 shows how some representative toothpastes
of this invention compare with other toothpaste formulations, including some
commercial brands which are widely used. The formulations for entries 1-
22 are described above in Tables 1 and 2.
Table 4. Comparison of Stringiness
Number Stringiness (mm)
1 15.0
2 11.9
17 22.7
18 22.9
19 20.2
20 26.1
21 19.4
22 22.7
Brand A 18.7
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Brand B 19.2
Brand C 18.2
Brand D 13.6
The toothpastes of this invention (represented in Table 4 by entries 1
and 2) have very low stringiness. The stringiness of these toothpastes is
substantially lower than three of the four commercial toothpastes tested and
certain toothpastes of this invention are significantly less stringy than the
best commercial product tested. The low stringiness was achieved with
formulations that employed relatively low amounts of kappa carrageenan in
gels that exhibited good consistency and stability.
