Note: Descriptions are shown in the official language in which they were submitted.
1~71~76
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TITLE: AQUEOUS LARE PIGMENT SUSPENSION
The Background of the Invention
Pigment suspensions are used for producing coating suspensions
for coating such items as pharmaceutial tablets or pills,
confectionary pieces, and the like. The pigment suspension is
typically stirred into a larger volume of solution to produce a
coating suspension which is used in the coating process. One process
of coating is generally known as film coating in which the coating
solution includes a film forming polymer. U.S. Patent No. 2,954,323
to Endicott et al. discloses examples of film coating. Another
techinique, frequently used, with respect to confectionary pieces,
is generally known as sugar coating, in which the pigment suspension
i8 added to a sugar syrup solution of Sugar and water.
Pigment suspensions for use in making coating suspensions are
preferably sold having a concentration of pigment as high as
possible. However, as the concentration of pigment increases, the
suspension becomes more viscous and tends to reach a point where it
becomes difficult to pour from its container. Over time, a thick
suspension of pigment may even harden to the extent of becoming
unusable.
In developing a high concentration pigment suspension, it is
desirable to obtain a product in which the pigment particles form a
stable suspension and will not settle. The need is for a pigment
suspension which will readily pour from its container and will
maintain its uniform properties during both transportation and
storage, until ready for application in a coating suspension.
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U.S. Patent No. 3,981,984 to Signorino discloses a
pigment suspension which claims to achieve a high
concentration of pigment in a non-aqueous solvent. This
pigment suspension consists of pigment particles, a
protective colloid such as hydroxypropyl cellulose, and a
non-aqueous solvent such as ethanol. Signorino discloses
that as the pigment particles are added to the solvent, the
mixture becomes too viscous, and the further addition of
the protective colloid serves to suspend the particles and
reduce the viscosity.
In view of the increasingly strict requirements of
governmental regulating agencies in regard to the use of
organic solvents, it has become desirable to obtain an
aqueous pigment suspension. A high content of pigment is
not normally possible and the present invention involved a
search for a combination of ingredients which would permit
a high content of pigment particles in an aqueous
suspension. However, the invention is also applicable to
suspensions in organic solvents which include a sufficient
amount of water to dissolve what is referred to below as
the viscosity reducing agent.
The Ob~ects of the Invention
One object of the present invention is to achieve a
pigment suspension which may have a high pigment content.
Another object of the present invention is to
achieve a high concentration pigment suspension in an
aqueous solvent or a mixture of water and an organic
solvent.
A further object of the invention is to obtain a
high concentration pigment suspension which pours readily
from its container.
A further object of the invention is to obtain a
high concentration pigment suspension which does not settle
upon standing.
A further object of the present invention is to
obtain a pigment suspension with a high pigment
concentration which is capable of being transported to
customers in containers, and which may readily be combined
with a film-forming polymer solution or sugar solution by
stirring.
The above and other objects of the present
invention will become apparent from a reading of the
following detailed description of the invention and the
preferred embodiments thereof.
Detailed Descri~tion of the Invention
The pigment suspension of the present invention
comprises a mixture of a pigment, at least one of a
polymeric colloid, sugar and an organic solvent, a
viscosity lowering agent, and water.
The pigments suitable for use in the context of the
present invention include FD&C lakes, which are dyes
combined with a metal hydroxide substratum. A variety of
lakes, including lakes incorporating azo, triphenylmethane,
fluorescein, and sulfonated indigo dyes, are suitable in
the present invention. FD&C lakes are suitable for
application in food, drug, and cosmetic products.
Lakes have been developed with a wide range of
strengths. For food and confection applications, the mid-
range dye content lakes
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are the most useful. These lakes are available from several
sources. Suitable lakes are manufactured by Warner-Jenkinson
Manufacturing Company of Saint Louis, Missouri (hereinafter referred
to as NW-Jn), and Crompton & Knowles Corporation of Fairlawn, New
Jersey (hereinafter referred to as "C&Kn). For example, the
following pigments are commercially available from C&K and W-J:
Yellow # 6/40%
Yellow # 5/36%
Blue # 1/11%
Blue # 2/39%
Red #40/40%
Red #27/36%
Red # 3/40%
It has been found that due to variations in the processes
of manufacturing lakes, the properties of a particular brand of
lake, produced by one manufacturer, may not be as satisfactory in
the present invention as that produced by another manufacturer.
For example, it has been found that for use in the present
invention, Blue #2/39% pigment as presently manufactured by W-J is
preferable. Similarly, it has been found that for use in the
present invention, Blue #1/11% pigment, as presently manufactured by
C&K, is preferable.
A 50/50 combination of C&K and W-J lakes may be preferable.
In general, it was found that W-J lakes tend to have a higher tint,
but may cause thickening. By using a mixture of W-J and C&K lakes,
both a high tint and non-thickening is more readily obtained. Of
course, developments and changes in the lakes by their manufacturers
may require a reassessment, as would be capable by those skilled in
the art, of the properties of a particular brand in regard to use in
7~i
the present invention.
In each individual case of a particular 12ke, it is
readily determined by trial and error.
The concentration of pigment in the pigment
suspension by weight is in the range of 20% to 75%.
Preferably a range of 25% to 65% is obtained. Most
preferably a range of 30% to 60% is obtained. However, the
amount of pigment achieved in any particular suspension
depends to some degree on the particular pigment used and,
somewhat higher contents of one particular pigment or a
particular brand of pigment may be achieved than with
another.
The polymeric colloid assists in preventing
settling and hardening of the pigment. Gums, both natural
and synthetic, have been found to be suitable polymeric
colloids. Suitable gums include, but are not limited to,
gum arabic, guar gum, agar, xanthan gum, PG alginate,
hydroxypropyl cellulose, gum trag, gelatin 250 Bloom,
citrus pectin, and carragheen. Preferred gums include gum
arabic, xanthan gum and guar gum, the most preferred
polymeric colloid being xanthan gum. In substitution of
gum, such polymeric colloids as corn starch or
polyvinylpyrrolidone may also be employed.
The polymeric colloid is present in the invention
in amounts, by weight, ranging from 0.005 to 5.0 percent.
As is evident, only relatively very small quantities of the
polymeric colloid need be present in the suspension. A
preferred range is 0.01 to 2.0 percent and most preferably
0.05 to 0.50 percent.
The viscosity lowering agent is a salt of an
organic,
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7~i76
carboxyl containing compound and mixtures thereof with the acid
form. Preferred viscosity lowering agents include salts of
compounds having one to three carboxylic groups. In addition, it
has been found that lactones, which are believed to convert to
carboxyl containing compounds in water, are also suitable.
Viscosity lowering agents include, but are not limited to, salts of
adipic acid, benzoic acid, citric acid, fumaric acid, succinic acid,
maleic acid, lactic acid, tartaric acid, and propionic acid and
mixtures with the acid thereof. In addition such lactones as
ascorbic acid and glucono-delta lactone may also be employed.
The viscosity lowering agents should, at least partly, be
in the salt form. A 50/50 combination of the salt and acid is
suitable. For example, sodium citrate, by itself, or a mixture of
sodium citrate and citric acid, produces excellent results. On the
other hand citric acid, by itself, did not work as well. It is
~urmised that the viscosity lowering agent complexes or chelates to
the lake pigment particles. Due to the wide variety of dyes present
in lake pigments, it is further surmised that the metal hydroxide
substrate of the FD&C lakes functions in the complexing of the
viscosity lowering agent. The resulting complex is believed to have
electronic properties such that they repell another such complex,
thereby resulting in dispersed pigment particles which form a thin,
less v scous suspension, preventing thickening and hardening thereof.
The complexing or chelating effect is surmised, based
partly on the fact that a similar effect is not acheived by a mere
~7
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acid. For example, hydrochloric acid does not work, and the acid
form alone of the given viscosity lowering agents are either
inferior or unsatisfactory to the salt form of the viscosity
lowering agents.
The presence of one of the viscosity lowering agents can
result in a dramatic lowering of the viscosity of the suspension.
Consequently, good flowability of the suspension is obtained. The
suspension can be readily poured from its container and it neither
unduly thickens nor settles. The viscosity lowering agent is
present in an amount of 0.005 to 5 percent by weight in the
mixture. Preferably, the agent is present in an amount of o.OOS to
2 percent and most preferably about 0.01 to 0.50 percent. In many
cases, even a relatively very small amount of agent can drastically
and favorably effect the properties of the suspension.
The above descirbed components are dispersed in an aqueous
solvent. The amount of water is suitably as high as 60 to 80
percent, depending on the amount of pigment. AB described in
greater detail below, organic solvents may also be included, in
which case the amount of water may suitably be in the range of 5 to
30 percent.
The compositions were tested by what is referred to as an
oven test. An oven test is an accelerated method of assessing the
long-term properties of a pigment suspension. The oven test
typically involved heating the pigment suspension at 1040F for a
period of 96 hours. This acelerated test is believed to be
1~71~7ti
equivalent to 3 to 4 months at 850F. ~he oven test results were
evaluated according to the following rating system.
~ATING SY~TEM
Rating Description
1 A rock hard or very hard settle is obtained. The
suspension fails to redisperse.
2 A paste or semi-hard solid is obtained. The
suspension fails to pour from its container
without force or requires the use of a spatula.
3 A threshold suspension, with some supernatant, is
obtained. After agitation, the suspension is
still thick, but pourable.
4 A suspension with or without supernatant but no
settle is obtained. The consistency is like
thick yogurt or jam. On agitation the suspension
becomes fluid.
A soft, fluid dispersion with no settle is
obtained. It pours from its container with no
agitation and flows freely.
5.5 The suspension has no settle, but is very watery.
6 The suspension is too watery, and is not
acceptable.
The following examples are intended to illustrate the present
invention.
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Exa-mpl~ l
In a blender, the following compOnents were weighed out and
mixed:
Component Percent by We-ight
Distilled Water 69.93
Xanthan Gum 0.02
Tio2 3328 15.00
Yellow #6/40~ 15.00
Sodium Citrate 0.05
After a period of 96 hours at 1040F, the pigment
suspen~ion exhibited a rating of 5Ø
This example, with 0.05~ sodium citrate, was repeated
except with increasing percentages by weight of sodium
citrate. Pigment suspension with 0.10, 0.15, 0.20, and 0.50
of sodium citrate were obtained. The most preferred pigment
suspensions were obtained with 0.05, 0.10, and 0.15 percent
citrate. A rating of 5.0 or 5.5 was exhibited by each of such
suspensions. The solutions with 0.20 and O.S0 percent sodium
citrate tended to be more watery than optimally desirable. For
example, after a period of 96 hours at 1040F, a rating of 6
was exhibited by the suspension having 0.50 percent sodium
citrate.
~.~71~
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Example 2
In a blender, the following components were weighed
out and mixed:
Component Percent by Weight
Distilled Water 69.90
Xanthan Gum CVF 0.50
TiO2 3328 15.00
Yellow #6/40% 15.00
Sodium Citrate 0.05
After 4 days at 1040F, the suspension exhibited a
rating of 5Ø
The above formula was repeated at increasing
percentages of sodium citrate and, rather that 0.05 percent,
percentages of 0.10, 0.15, 0.20, and 0.50 were tested.
The most preferred amounts of sodium citrate in the
above formula were found to be by weight 0.05% and 0.10%, each
exhibiting, respectively, a rating of 5.0 and 5.5. At high
percen ages, a rating of 6 was obtained after 4 days at
1040F. Therefore, increasing the amount of sodium citrate
above an optimal amount of sodium citrate tended to result in a
more watery suspension than desirable.
Further examples shown in Table A to Table G, below
illustrate the effect of changing the amount of gum and sodium
citrate in the pigment suspension.
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~;~71~76
-18 -
As is clear from Table A, in a combination of distilled
water, gum xanthan, Tio2~ Yellow #6/40, and sodium citrate, it was
found that with 0.10 percent gum, higher than the 0.02 of previous
example 1, an optimal amount of sodium citrate is 0.15 percent. In
Table A, this is represented by trial 2. When xanthan gum in the
amount o 0.50 percent is added to the pigment suspension, as
evidenced by trials 5 and 10, then the results are relatively poor,
and it is apparent that the optimal amount of gum, regardless of the
amount of sodium citrate, has been overreached.
In Table B, a different brand of lake has been tested,
Yellow #6/40 AC 5617. It is apparent that the optimal composition
contains gum in the amount of 0.02 to 0.10 percent weight and sodium
citrate in the amount of 0.50 percent. This shows that the
particular lake used will effect the precise optimal percentages of
both gum and sodium citrate. The precise affect of a particular
pigment i8 not predictable and must be determined empirically. It
is desirable to determine, for each particular pigment, the optimal
percent of each component by experiments such as shown in the above
Tables. By varying the amount of gum while controlling the amount
of sodium citrate, and vice-versa, optimal amounts can be determined.
Such experimentation, in view of the guidelines and many examples
given herein, can be readily determined by those of ordinary skill
in the art.
The dependence of the properties of a suspension on the
particular pigment employed is further evidenced by Table C. In the
'7tj
--19--
event that the pigment is not an equal mixture of Yellow ~6/40 and
titanium dioxide, but rather entirely Yellow #6/40, then new optimal
percentages need to be ascertained. In table D, an optimal percent
amount of sodium citrate appears to be 0.50, whether the gum is at
0.05, 0.10 or 0.20 percent. Higher amounts of gum, however, appear
to give less satisfactory results regardless of the amount of sodium
citrate.
Various blue dyes were tested. An equal mixture of Blue
#1/11% and TiO2 was tested. Blue #1/11% alone, without TiO2,
was al~o tested. The results are shown in Tables E and F. It is
evident the optimal results were obtained with the percentages
represented by trial 23 in Table F and trial 18 in Table F. For a
pigment suspension containing about 70% distilled water, and 30% of
an equal mixture of Blue #2/39 and TiO2, optimal amounts of gum
xanthan and sodium citrate were, respectively, 0.05 and 0.50, as
shown in Table G.
In confectionary applications, a very good pigment
~uspension is achieved using a sugar solution as a solvent. The
following is exemplary of a sugar based pigment suspension
obtainable with all lakes:
Example 6
The following components were weighted out and mixed:
~omponent Percent-by We igh t
Sugar solution 58.80
Sodium Citrate 0.20
Red #40/40% 40.00
1 ~ 7~ 6
-20-
The sugar solution comprised a mixture of water and sucrose
in a ratio of about 4 : 6. The resulting suspension exhibited
excellent properties. The suspension was readily pourable and did
not thicken over time.
It has also been found that the presence of a substantial
amount of an organic solvent in the suspension eliminates the
absolute need for a polymeric colloid, athough the results are
generally not as good as with a polymeric colloid. The suspension
apparently requires an effective amount of water which will dissolve
the viscosity lowering agent and therefore, if desired, a small
amount of water, for example, in an alcohol or propylene glycol
based dispersion, is sufficient. Suspensions with 10~ or less of
water have worked satisfactorily. The following example illustrates
a satisfactory pigment suspension.
Example-7
The following components were weighted out and mixed:
~omponent Percent by Weight
Distilled Water 49.80
Propylene Glycol 20.00
Sodium Citrate 0.20
Yellow ~6/40~ 30.00
This suspension exhibited satisfactory viscosity and
non-settling properties. In place of propylene glycol, other
organic 601vents such as glycerin, polyethylene glycol, or the like
may be employed. Pigments employed satisfactory included Yellow
,.. " ' , .
71~l7~:;
-21-
#6/17%, Blue #2/21%, Red #40/40%, Red ~3/40%, and mixtures thereof
with titanium dioxide.
The suspensions of the instant invention may also contain
conventional preservatives in small amounts, in order to prevent the
occurence of mold, fungi, or other microbiological contaminants.
For example, suitable preservatives approved for application in
products intended for human consumption are potassium sorbate and
methyl paraben. These preservatives may be employed in amounts less
than 0.2 percent.
