Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: TITANIUM DIOXIDE SUSPENSION FOR USE IN FILM COATING
The Back~round of the Invent on
The pigment suspension of the present invention is
used for producing a film coating of such items as
pharmaceutial tablets, confectionary pieces~ and the like. The
pigment suspension is typically stirred into a larger volume of
polymer solution. The resulting film-forming suspension is
used in the coating process. The fil~ coating, in the form of
a very thin film, must be uniform and consistent from one batch
of tablets to the next.
The technique of film coating is generally known in
the prior art. U.S. Patent No. 2,954,323 to Endicott et al.
discloses the increased efficiency and superior coating
properties obtained with film coating in gen~ral as compared to
other processes of coating.
The present invention relates to a pigment suspension
which comprises, as pigment, titanium dioxide. Such pigment
suspensions for use in film coating are preferably sold having
a concentration of titanium dioxide as high as possible.
~owe~er, as the concentration of titanium dioxide increases,
the suspension tends to become more viscous and may reach a
point where it becomes difficult to pour from its container.
Upon aging, a thick suspension of titanium dioxide may harden
to the extent of becoming unusable.
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In developing a high concentration pigment suspension,
it is desirable to obtain a product in which the titanium
dioxide particles form a stable suspension and will not settle
for a prolonged period of time. The need is ~or 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 film coating.
U.S. Patent No. 3,981,984 to Signorino discloses a
pigment suspension which claims to achieve a high concentration
of titanium dioxides in a non-aqueous solvent. This pigment
suspension consists of titanium dioxide particles, a protective
colloid such as hydroxypropyl cellulose, and a non-aqueous
solvent such as ethanol. Signorino teaches that as the
titanium dioxide 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 aqueous
pigment suspensions. However, a high content of titanium
dioxide in water is not normally posssible for use in
film-coating. Although titanium dioxide suspensions in an
aqueous sugar syrup are known, such suspensions are not
generally suitable for use in a film-forming polymer solution.
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The present invention involved a search or a
combination of ingredients which would permit a high content of
titanium dioxide particles in an aqueous suspension useful in
film coating. Due to the fact that the composition may
comprise merely water and a very small amount of xanthan gum,
not requiring the presence of organic solvents, the composition
is very simple, safe and inexpensive to make.
The Objects of the Invention
One object of the present invention is to achieve a
pigment suspension which contains a high titanium dioxide
content.
Another object of the present invention is to achieve
a high concentration pigment suspension in a solvent comprising
a substantial amount of water, for use in film coating.
A further object of the invention is to obtain a high
concentration pigment suspension which pours readily from
containers.
A further object o the invention is to obtain a high
concentration pigment suspension which does not settle upon
aging.
A further object oE the present in~ention is to obtain
a pigment suspension with a high titanium dioxide concentration
which is capable of being transported to customers in
containers, and which may readily be combined with a
film-forming polymer solution by stirring.
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A further object of the present invention is to
produce an aqueous pigment dispension which is inflammable and
non-hazardous during handling and safe for use in edible
products intende~ for human consumption.
The above and other objects of the present invention
will become apparen'c from a reading of the following detailed
description of the invention and the preferred embodiments
thereof.
Detailed- Description o~ the Invention
~ he pigment suspension of the present invention
comprises a mixture of titanium dioxide, xanthan gum, and water.
The titanium dioxide pigment employed in the present
invention is preferably water dispersable titanium dioxide
3328, sold by Whitaker, Clarke & Daniels in South Plainfield,
New Jersey. The pigment is suitable present in an amount by
weight of about 20 to 75 percent, and most preferably in an
amount by weight of about 30 to 60 percent.
Titanium dioxide is a relatively heavy pigment which,
when mixed in a solvent, tends to settle out and form a thick
non-pourable layer of pigment on the bottom of the container.
It has now been found that an excellent aqueous pigment
dispersion can be obtained by the addition of a very small
amount of xanthan gum.
Xanthan gum is a high molecular weight polysaccharride
produced in a fermentation process by the microorganism
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Xanthomonas campestrisO The gum, which is produced as an
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exocellular coating surrounding the cell wall of the
microorganism, is unique and very specific, and the properties
thereof are constant and reproducable under given conditions.
xanthan gum is known as a suspending or dispersing
agent in various applications. For example, xanthan gum has
been used to suspend solids in ceramic glazes, paints, and
textile print pastes.
The use of xanthan gum to create a high concentration
titanium dioxide pigment suspension for use in a film-forming
process in the food and drug industry is believed to be
entirely new.
A commercially available xanthan gum, suitable in the
,~i3 present invention, is KELTROL~ and especially Keltrol F, a
finely meshed xanthan gum, manufactured by Kelco, a division o
Merk & Co., Incorporated.
The suspension of the present invention differs from
other suspensions in that it can exhibit gel like behavior or
very fluid behavior. Typically, the suspension actually sets
up and only breaks down into a liquid by shearing action, such
as produced by merely shaking the container oE the pigment
suspension, resulting in a readily pourable pigment suspension.
The xanthan gum is present in the invention in
amounts, by weight, ranging from 0.005 to 5.0 percent. As is
evident, typically only relatively very small quantities of the
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xanthan gum need be present in the suspension. A preferred
range is 0.05 to 0.50 percent~
Compositions of the present invention 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, initially, of
96 hours. This acelerated test is believed to be equivalent to
3 to 4 ~onths at 850F. Compositions of the present invention
have withstood heating at 1040F for one month. The oven test
results were evaluated according to the following rating system.
RATING SYSTEM
1.0 A rock hard or very hard settle is obtained. The
suspension fails to redisperse.
.0 A paste or semi-hard solid is obtained. The
suspension fails to pour from its container without
force or requires the use of a spatulaa
3.0 A threshold suspension, with some supernatant, but
stable. After agitation, the suspension is still
thick, but pourable.
4.0 A suspension with or without supernatant but no settle
is obtained. The consistency is like thick yogurt.
On agitation the suspension becomes fluid.
5.0 A soft, fluid dispersion with no settle is obtained.
It pours from its container with no agitation and
flows freely.
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5.5 The suspension has no settle, but is very watery.
6.0 The suspension is too watery, and is not acceptable.
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In a blender, the following components were weighed
out and mixed:
Component Perce~t by-We-ight
Water 69.80%
Xanthan Gum 0.20%
2 30~00%
The xanthan gum was added to the water while mixing at
a moderate speed. Mixing was maintained for about 3 minutes or
until all of the gum had dissolved. The titanium dioxide was
added slowly while the blender was mixin~. The speed was
adjusted to maintain a vortex in the mixture~
An oven test was performed at 104~F for 96 hours. A
rating of 5.5 was obtained. After a further period of 21 days
at 1040F, a rating of 5.5 was obtained, indicating that the
properties of the pigment suspension remained stable~
Xanthan gum has unique properties which permit the
creation of a stable and pourable titanium dioxide pigment
suspension. Other gums or colloids, natural and synthetic, do
not produce a satisfactory product. The following table
illustrates other gums which were tried, but found unacceptable.
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Table_A
Trial/ 1 2 3
Component
Distilled water 49.80 49.80 49.80
Titanium dioxide 50.00 50.00 50.00
Guar gum 0.20
Polyvinylpyrrolidone 0.20
KLUCEL _ - -- 0.20
Rating 1.0 1.0 1.0
As shown in Table A, guar gum, polyvinylpyrrolidone,
3":~ and KLUCEL, a brand of hydroxypropyl cellulose manufactured by
Hercules Co. in Wilmington, Delaware, were unacceptable,
resulting in a suspension that was immediately unusable. Gum
arabic was satisfactory only at high levels such as 15 percent,
too high for commercial practicability.
Conventional additives may be included in the present
composition, as will be understood by those skilled in the
art. For example, about 0.1 percent of an antimicrobial agent
such as methylpropyl paraben or potassium sorbate is suitable.
It is to be understood that the foregoing detailed
description and preEerred embodiment are merely given by way of
illustration, and modifications may be made, within the skill
of the art, without departing ~rom the scope and spirit of the
invention.
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