Abstrict A pH-indicating material capable of undergoing a clearly visually
detectable color transition at a desired pH, e.g., at a pH at or
below about 5.6 and/or at a pH at or above about 7.6. When the pH-indicating
material is wetted on its surface with liquid animal dross, particularly
animal urine, such as cat urine, the pH-indicating material will
undergo a clearly visible color transition at a urine-problematic
pH, e.g., acidic or alkaline. The pH-indicating material is maintained
on an inert carrier, separate from the cat litter material itself,
so that the cat litter material does not chemically interfere with
the urine pH-induced color transition provided by the dye(s) in
the coating material, and so that the color transition is an exclusive
result of the pH of the contacting animal urine, without pH interference
from the litter material. In a preferred embodiment, the pH-indicating
material is admixed with any cat litter material and has dual indicators
that provide one color transition at a low pH and a different color
transition at a high pH so that acidic or alkaline animal urine
problems can be visibly detected upon contact between the animal
urine and the pH-indicating material.
Claims What is claimed is:
1. A pH-indicating material capable of undergoing a color transition
upon contact with animal urine having an acidic or alkaline pH comprising:
an inert core substrate;
a coating on said substrate formed from an aqueous solution of
a water-soluble polymer and an effective amount, for color transition,
of a water-soluble pH-indicating dye, dried in place on said core
substrate.
2. The pH-indicating material defined in claim 1 wherein the coating
includes two pH-indicating dyes, a first dye undergoing a color
transition at a pH below about 5.4 and a second dye undergoing
a color transition at a pH above of about 7.6; each dye undergoing
a color transition to a color that is different from the pH-neutral
color of the other dye.
3. The pH-indicating material defined in claim 2 wherein the two
dyes are methyl red and bromothymol blue.
4. The pH-indicating material of claim 1 wherein the water-soluble
polymer is selected from the group consisting of polyvinylpyrrolidone;
hydrolyzed polyvinylpyrrolidone; partially hydrolyzed polyvinylpyrrolidone;
N-methylpyrrolidone; N-ethylpyrrolidone; N-vinylpyrrolidone; N-isopropyl-5-methylpyrrolidone;
pyrrolidone-N-acetic acid; N-cyclohexyl-pyrrolidone; hexamethylene-bis(2-pyrrolidone);
metal salts of the foregoing; poly(ethylene oxide); poly(propylene
oxide); poly(vinyl methyl ether); polyoxymethylene; copolymers of
ethylene oxide and propylene oxide; polyacrylic acid; fully or partially
neutralized metal salts of polyacrylic acid; polymethacrylic acid;
fully or partially neutralized metal salts of polymethacrylic acid;
poly(methacrylamide); poly(N,N-dimethylacrylamide); poly(N-isopropylacrylamide);
poly(N-acetamidoacrylamide); poly(N-acetamidomethacrylamide); acrylic
interpolymers of polyacrylic acid and poly(methacrylic acid); acrylic
interpolymers of polyacrylic acid and poly(methacrylamide); acrylic
interpolymers of polyacrylic acid and methacrylic acid; poly(vinyl
alcohol); poly(vinyl acetate); poly(vinylacetate-co-vinyl alcohol);
polyvinyloxazolidone; polyvinylmethyloxazolidone; and mixtures of
any two or more of the foregoing.
5. The pH-indicating material of claim 1 wherein the dye is included
in the aqueous solution in an amount of about 0.01% to about 5%
by weight of the aqueous solution.
6. The pH-indicating material of claim 1 wherein the aqueous solution
includes about 20% to about 60% by weight water, prior to drying.
7. The pH-indicating material of claim 1 wherein the water-soluble
polymer is polyvinylpyrrolidone coated onto said core substrate
in a thickness of about 1 mil to about 25 mils.
8. The pH-indicating material of claim 1 wherein the water-soluble
polymer is polyvinylpyrrolidone coated onto said core substrate
in a thickness of about 3 mils to about 20 mils.
9. The pH-indicating material of claim 1 wherein the water-soluble
polymer is polyvinylpyrrolidone coated onto said core substrate
in a thickness of about 5 mils to about 15 mils.
10. The pH-indicating material of claim 7 wherein the polyvinylpyrrolidone
is partially hydrolyzed.
11. The pH-indicating material of claim 10 wherein the polyvinylpyrrolidone
has at least 50% of its monomer units hydrolyzed.
12. The pH-indicating material of claim 11 wherein the polyvinylpyrrolidone
has at least 75% of its monomer units hydrolyzed.
13. The pH-indicating material of claim 12 wherein the polyvinylpyrrolidone
has about 80% to about 90% of its monomer units hydrolyzed.
14. An animal litter comprising a plurality of water-absorbent
particles containing, in combination therewith, about 2% to about
75% by total litter volume of a plurality of discrete particles
of pH-indicating material, said pH-indicating material comprising
:
an inert core substrate;
a coating on said substrate formed from an aqueous solution of
a water-soluble polymer and an effective amount, for color transition,
of a water-soluble pH-indicating dye, dried in place on said core
substrate.
15. The animal litter of claim 14 wherein the coating includes
two pH-indicating dyes, a first dye undergoing a color transition
at a pH below about 5.4 and a second dye undergoing a color transition
at a pH above of about 7.6; each dye undergoing a color transition
to a color that is different from the pH-neutral color of the other
dye.
16. The animal litter of claim 14 wherein the two dyes are methyl
red and bromothymol blue in a weight ratio of about 3:1 respectively.
17. The animal litter of claim 14 wherein the water-soluble polymer
is selected from the group consisting of polyvinylpyrrolidone; hydrolyzed
polyvinylpyrrolidone; partially hydrolyzed polyvinylpyrrolidone;
N-methylpyrrolidone; N-ethylpyrrolidone; N-vinylpyrrolidone; N-isopropyl-5-methylpyrrolidone;
pyrrolidone-N-acetic acid; N-cyclohexyl-pyrrolidone; hexamethylene-bis(2-pyrrolidone);
metal salts of the foregoing; poly(ethylene oxide); poly(propylene
oxide); poly(vinyl methyl ether); polyoxymethylene; copolymers of
ethylene oxide and propylene oxide; polyacrylic acid; fully or partially
neutralized metal salts of polyacrylic acid; polymethacrylic acid;
fully or partially neutralized metal salts of polymethacrylic acid;
poly(methacrylamide); poly(N,N-dimethylacrylamide); poly(N-isopropylacrylamide);
poly(N-acetamidoacrylamide); poly(N-acetamidomethacrylamide); acrylic
interpolymers of polyacrylic acid and poly(methacrylic acid); acrylic
interpolymers of polyacrylic acid and poly(methacrylamide); acrylic
interpolymers of polyacrylic acid and methacrylic acid; poly(vinyl
alcohol); poly(vinyl acetate); poly(vinylacetate-co-vinyl alcohol);
polyvinyloxazolidone; polyvinylmethyloxazolidone; and mixtures of
any two or more of the foregoing.
18. The animal litter of claim 14 wherein the dye is included
in the aqueous coating solution in an amount of about 0.01% to about
5% by weight of the aqueous solution.
19. The animal litter of claim 14 wherein the aqueous solution
includes about 20% to about 60% by weight water, prior to drying.
20. The animal litter of claim 14 wherein the water-soluble polymer
is polyvinylpyrrolidone coated onto said core substrate in a thickness
of about 1 mil to about 25 mils, and the pH-indicating material
is included in the animal litter in an amount of about 5% to about
20% based on the total combined volume of animal litter.
21. The animal litter of claim 20 wherein the polyvinylpyrrolidone
is partially hydrolyzed.
22. The animal litter of claim 21 wherein the polyvinylpyrrolidone
has at least 50% of its monomer units hydrolyzed.
23. The animal litter of claim 22 wherein the polyvinylpyrrolidone
has at least 75% of its monomer units hydrolyzed.
24. The animal litter of claim 23 wherein the polyvinylpyrrolidone
has about 80% to about 90% of its monomer units hydrolyzed.
25. The animal litter of claim 14 wherein the water-absorbent
particles comprise bentonite clay.
26. The animal litter of claim 14 wherein the water-absorbent
particles comprise attapulgite clay.
27. The animal litter of claim 14 wherein the water-absorbent
particles comprise Fullers Earth.
28. A method of manufacturing a pH-indicating material comprising
coating an inert solid substrate with an aqueous solution of a film-forming
amount of a water-soluble polymer, and an effective amount of a
water-soluble pH-indicating dye; and drying the coating on said
inert substrate to bind the dye to the substrate, within the water-soluble
polymer.
29. The method of claim 28 wherein the substrate is a solid mineral;
the water-soluble polymer is a partially hydrolyzed metal salt of
polyvinylpyrrolidone; the aqueous coating composition includes about
40% to about 80% by weight polymer; and the coating composition
contains a combination of methyl red and bromothymol blue.
30. In a method of detecting feline urologic syndrome including
adding a pH-indicating material, having a color transition at a
pH above about 7.6 to a cat litter in an amount sufficient for
contact with urine when a cat urinates in said cat litter, and visually
reading the pH-indicating material within about 24 hours of cat
urine contact to determine if a color transition has occurred in
the pH-indicating material, the improvement comprising the pH-indicating
material comprising:
an inert core substrate;
a coating on said substrate formed from an aqueous solution of
a water-soluble polymer and an effective amount, for color transition,
of a water-soluble pH-indicating dye, dried in place on said core
substrate.
Description FIELD OF THE INVENTION
The present invention is directed to a pH-indicating material formed
from an inert carrier coated with a water-soluble polymer film containing
one or more pH-indicating dyes. More particularly, the present invention
is directed to an inert carrier material having a dried film of
a water-soluble polymer containing one or more pH-indicating dyes,
particularly two pH-indicating dyes, one dye undergoing a visibly
detectable color transition below about pH 5.6 and the other dye
undergoing a visibly detectable color transition at a pH of about
7.4 particularly useful as an additive for cat litter as an indication
of cat urine having an acidic pH (below about pH 5.6) or an indication
of feline urologic syndrome (FUS) at a cat urine pH of about 7.4
and above.
BACKGROUND OF THE INVENTION AND PRIOR ART
The commercial cat litter industry has undergone substantial change
since the introduction of clumping bentonite clay cat litters as
disclosed in the Hughes U.S. Pat. No. 5000115 hereby incorporated
by reference. As disclosed in the Hughes '115 patent, bentonite
clay cat litter that is wetted with cat urine will agglomerate into
a clump having sufficient structural integrity so that the agglomerated
clump can be removed from a cat litter box, thereby removing the
cat urine, as well as feces, with a slotted scoop. The remainder
of the unsoiled cat litter material can remain in the litter box
for reuse without generation of odor over substantial periods of
time of one year or more.
Some of the patents that disclose the use of clay as an absorbent
pet litter material are as follows: Crampton, et al. U.S. Pat. No.
4657881; Stuart U.S. Pat. No. 4685420; McFadden U.S. Pat. No.
3286691; Japanese published patent applications J5 8009-626 J6
3044-823-A; J6 0094-043-A; J6 3185-323-A, J6 2239-932-A, and JO
1191-626-A; German DE 3620-447-A; Ducharme, et al. U.S. Pat. No.
4844010; Kumar U.S. Pat. No. 4343751; and Jaffee, et al. U.S.
Pat. No. 4459368. The following U.S. patents teach pet litters
that include additives, e.g., polymers for clumping, or odor control
additives: U.S. Pat. No. Lang U.S. Pat. No. 4736706; Smith U.S.
Pat. No. 4671208; Stuart U.S. Pat. No. 4685420 Sowle, et al.
U.S. Pat. No. 5014650; and Nelson U.S. Pat. No. 5062383.
In addition to a good portion of the cat litter industry moving
toward the use of clumping bentonite clay cat litters, others have
attempted to provide additional improvements to cat litter material
for the purpose of providing a home diagnostic means and/or a home
animal health monitoring means to quickly monitor the health of
a cat at home, by the use of feline urine screening tests. One of
these home feline urine screening tests presently is marketed under
the trademark CATSCAN.TM.--a finely divided solid substance that
is sprinkled from a package onto the surface of the cat litter from
one of four different packages, each having an indicator dye indicative
of one of: blood, pH, protein or glucose contained in the cat urine.
Another commercial cat litter product, called FUSSY CAT D, is a
clumping, clay cat litter material that includes a pH-indicating
dye bound to the clay material during manufacture of the cat litter
and having a color transition at an a alkaline pH indicative of
feline urologic syndrome.
U.S. patents uncovered that disclose the use of a pH indicator
in connection with an absorbent product or a polymeric substance
include Seidenberger U.S. Pat. No. 3994821; Rohowetz U.S. Pat.
No. 4179397; Tratnyek U.S. Pat. No. 4407960; and Marsoner, et
al. U.S. Pat. No. 4587101. Mandel, et al. U.S. Pat. No. 4865761
discloses mineral-based, clay-containing absorbent material for
absorbing hazardous, acidic spills. Hamm, et al. U.S. Pat. No. 4925826
discloses a mineral-based absorbent material for the absorption
of animal excrement. Gruss U.S. Pat. No. 4326481 discloses a granular
material useful in taking a urine sample from a cat; Nugent U.S.
Pat. No. 4827944 and Seidler, et al. U.S. Pat. No. 3774455 disclose
urine collection and testing devices.
One of the problems associated with combining one or more pH-indicating
dyes with a clay-based cat litter material is that clay litter materials
include a number of exchangeable metallic cations and other chemical
species that, when in contact with cat urine, may alter the pH of
the cat urine, or otherwise interfere with the color transition
of indicator dyes within the pH range that a color transition should
be indicated, thereby providing false urine pH information. Further,
attempts to provide pH indicators as a coating material onto the
surface of clay cat litter material during manufacture have not
been entirely successful since the dyes, particularly the water-soluble
dyes that are indicative of pH of cat urine within a desired pH
range, are substantially absorbed into the interior of the clay
particles and, therefore, any color transition that occurs within
the interior of a clay cat litter particle is difficult if not impossible
to perceive visually, particularly for the water-swellable bentonite
clays.
The pH-indicating materials and the cat litter material containing
the pH-indicating materials of the present invention overcome the
deficiencies of the pH-indicating cat litter materials of the prior
art by providing the pH indicator(s) within a dried film of water-soluble
polymer dried onto a solid, inert carrier material. In this manner,
when the film coating on the inert carrier material is wetted with
cat urine, the urine penetrates the polymeric film and the water-soluble
pH-indicating dye(s) are solubilized within the cat urine to provide
an easily detectable color transition on the surface of the inert
carrier material without interference from any pH interaction or
dye interaction from the cat litter material itself.
SUMMARY OF THE INVENTION
In brief, the present invention is directed to a pH-indicating
material capable of undergoing a clearly visually detectable color
transition at a desired pH, e.g., at a pH at or below about 5.6
and/or at a pH at or above about 7.4. When the pH-indicating material
is wetted on its surface with liquid animal dross, particularly
animal urine, such as cat urine, the pH-indicating material will
undergo a clearly visible color transition at a urine-problematic
pH, e.g., acidic or alkaline. The pH-indicating material is maintained
on an inert carrier, separate from the cat litter material itself,
so that the cat litter material does not chemically interfere with
the urine pH-induced color transition provided by the dye(s) in
the coating material, and so that the color transition is an exclusive
result of the pH of the contacting that animal urine, without pH
interference from the litter material.
The pH-indicating material of the present invention is manufactured
such that the pH-indicating dyes are bound to a water-penetrable
(water-soluble) polymer and the dye(s) and polymer are coated over
an inert, preferably non-water-absorbent carrier material. In this
manner, the pH-indicating dye(s) are held on a surface of the inert
carrier material within a dried film of the water-soluble polymer.
In a preferred embodiment, the pH-indicating material of the present
invention is admixed with any cat litter material and has dual indicators
that provide one color transition at a low pH and a different color
transition at a high pH so that acidic or alkaline animal urine
problems can be visibly detected when the animal urine contacts
the pH-indicating material of the present invention. In the preferred
embodiment, the pH-indicating material of the present invention
is admixed with any cat litter material in an amount of about 5%
to about 20% by volume, preferably about 10% to about 15% by volume,
based on the total volume of the litter material containing the
pH-indicating material.
Accordingly, one aspect of the present invention is to provide
a dye-coated inert carrier material capable of undergoing a visually
detectable color transition when wetted with an aqueous solution,
e.g, cat urine, at a pH of about 5.6 or below.
Another aspect of the present invention is to provide a dye-coated
inert carrier material including a pH-indicating dye coated on an
exterior surface of the inert carrier material within a water-soluble
polymeric binder and capable of undergoing a visually detectable
color transition at a pH of about 7.6 or above.
Another aspect of the present invention is to provide a pH-indicating
additive material capable of incorporation into any powdered or
granular material and capable of undergoing a visually detectable
color transition when wetted with an aqueous acidic liquid, e.g.,
having a pH below about 6.0; and also capable of undergoing a different,
visually detectable color transition when wetted with an aqueous
alkaline liquid, e.g., having a pH above about 7.5.
Still another aspect of the present invention is to provide an
inert carrier material that includes one or more pH-indicating dyes
bound to the surface of the inert carrier within a film of water-penetratable
or water-soluble polymer such that the dyes are sufficiently adhered
to the inert carrier material such that upon wetting with liquid
animal dross, the dye(s) will not be washed away from the carrier
material but will maintain in contact with the carrier material
so that the color transition in the pH-indicating dye will be easily
visually detectable and will remain concentrated on the surface
of the inert carrier material.
The above and other aspects and advantages of the present invention
will become more apparent from the following detailed description
of the preferred embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The pH-indicating material, cat litter material and methods of
the present invention are provided by coating a carrier material,
preferably non-water-absorbent, with a film or coating of a aqueous
solution of one or more water-soluble pH-indicating dyes and one
or more water-soluble polymers and drying the coating material to
secure the pH-indicating dye(s) to an exterior surface of the inert
coating material When the dye-coated inert carrier material is wetted
with a liquid animal dross, e.g., cat urine, the water-soluble polymer
is at least partially solubilized, together with the dye(s), to
provide a visually detectable color transition if the pH of the
liquid animal dross is above a predetermined value, e.g., 7.6 and/or
below a predetermined value, e.g., 5.6 without the pH of the cat
urine being falsely changed by interaction with the cat litter surrounding
the pH-indicating material, and without undesirable interactions
between the cat litter and the indicating dye(s).
The inert carrier material or substrate that forms a core of the
pH-indicating material of the present invention can be any material
that, when wetted with water, does not liberate acid or base ions
which would interfere with the pH of animal urine. Any resulting
color transition is thereby effected only by the contact of the
animal urine with the dissolved pH-indicating dye within the coating
layer applied over the inert carrier, as will be described in more
detail hereinafter. Accordingly, a wide variety of inert carrier
substrates can be provided in accordance with the features of the
present invention.
It is preferred that the inert carrier material have a light color
(reflective color) so that the inert carrier does not interfere
with the visual detection of color transition taking place in the
dyes contained in the polymeric coating, as seen on the surface
of the material through a transparent or translucent water-soluble
polymeric binder. Accordingly, it is preferred that the inert carrier
material have a reflective surface, such as white calcium carbonate
chips, as obtained from the cutting to size of calcium carbonate
marble slabs. Preferably, the inert substrate has a light reflectance
of at least 20%, preferably at least 50% for easier detection of
color transition. Calcium carbonate marble chips are inert to the
extent that they do not materially alter the pH point at which a
pH-indicating dye coating will undergo a color transition, when
wetted with an acidic or alkaline animal urine. It is preferred
that the inert carrier substrate is non-water-absorbent so that
the inert carrier substrate can be more easily coated with a water-soluble
polymer/dye composition while maintaining the dye on the exterior
surface of the inert carrier. However, water-absorbent inert carrier
materials also can be used with some waste of water-soluble polymer/water-soluble
dye composition since some of the aqueous polymer/dye solution will
be absorbed into the interior of an absorbent inert carrier substrate.
Another example of suitable inert carrier substrates includes beads
of water-insoluble polymer material, such as highly cross-linked
sodium polyacrylate; beads of polyethylene, polypropylene, polystyrene,
and the like. Any other granite chips and other wood chips, cereal
grains and the like, also are suitable as the core substrate in
forming the pH-indicating material of the present invention.
The size and shape of the inert carrier material are not particularly
important in accordance with the principles of the present invention.
However, in the preferred embodiment, the pH-indicating materials
of the present invention are added to clumping cat litter material,
as disclosed in Hughes U.S. Pat. No. 5000115 and, accordingly,
for this preferred cat litter material, the size of the finished
pH-indicating material additive of the present invention should
be within the range of the preferred cat litter particle size, or
about 50 microns to about 3350 microns. Other sizes for the inert
carrier material can be used so long as some of this pH-indicating
material remains near a surface of the cat litter material so that
it can be wetted by liquid animal dross, e.g., cat litter urine,
each time the animal urinates onto the surface of the litter material.
If the pH-indicating material of the present invention is hand-sprinkled
onto the surface of a cat litter material, as is contemplated in
accordance with the principles of the present invention, the only
consideration in terms of size and shape of the inert carrier material
is that a sufficient amount of the pH-indicating material of the
present invention is distributed over the surface of the cat litter
material so that urine contact will be made each time the animal
urinates in the litter material.
In accordance with an important feature of the present invention,
at least one and preferably two pH-indicating dyes are coated over
a surface of the inert carrier substrate and sealed to the substrate
surface within a water-soluble polymer coating material that is
applied from aqueous solution and then is dried onto the inert substrate
surface to secure the dye(s) in place. The water-soluble polymer/water-soluble
dye aqueous solution conveniently is prepared by dissolving the
water-soluble polymer(s) into water heated to at least the solubilization
temperature of the water-soluble polymer, and thereafter adding
one or more water-soluble dyes to the aqueous polymer solution.
Alternatively, the dye(s) can be dissolved in water first, and thereafter
the aqueous dye solution can be heated to at least the solubilization
temperature of the polymer(s) to dissolve the polymer(s) into the
aqueous dye solution. It is preferred to incorporate only a small
excess of water into the coating composition, enough to assure complete
solubilization of the water-soluble polymer(s) and complete solubilization
of the water-soluble dye(s) while minimizing the amount of drying
necessary after coating the inert substrate material with the aqueous
polymer/dye composition.
The preferred water-soluble polymer is polyvinylpyrrolidone (PVP)
having a monomeric structure as follows: ##STR1## The water-solubility
of PVP can be adjusted according to (1) the degree of hydrolysis
of the polyvinylpyrrolidone to take into account different thicknesses
of PVP/dye films applied over the inert substrate, and (2) by forming
a metal salt of PVP, such as sodium or potassium. It is preferred
that at least 50% of the PVP monomeric units are hydrolyzed to the
structure: ##STR2## and that the PVP be used in the salt form, e.g.,
sodium or potassium polyvinylpyrrolidone and that the polymer/dye
aqueous composition is coated over the inert substrate in a thickness
of about 5 mils to about 25 mils, preferably about 10 mils to about
20 mils. Such PVP coatings provide immediate partial solubility
of the polymer when wetted with animal urine while maintaining the
interaction of the animal urine and dye on the surface of the inert
substrate. The color transition, concentrated on the surface of
the inert substrate, provides surprisingly spectacular color development
and intensity over a few hours to a few days with improved color
resolution and differentiation on the surface of the inert substrate.
The molecular weight of the PVP polymer is not critical so long
as the PVP is water-soluble. Excellent results can be obtained with
PVP having weight average molecular weights in the range of about
225 to about 1000000 or more, preferably about 2000 to about
100000.
Other PVP derivatives that are water-soluble and function well
as the binding polymer for binding one or more water-soluble dyes
to the surface of an inert substrate include the following: N-Methylpyrrolidone
(NMP); N-Ethylpyrrolidone (NEP); and N-Vinylpyrrolidone, having
the structures: ##STR3##
Other substituted water-soluble pyrrolidones useful in accordance
with the present invention include: N-isopropyl-5-methylpyrrolidone;
pyrrolidone-N-acetic acid; N-cyclohexyl-pyrrolidone; and hexamethylene-bis(2-pyrrolidone).
It appears that best results for polyvinylpyrrolidone and its derivatives
are achieved when the PVP has about 80% to about 90% of its monomer
units hydrolyzed.
Other water-soluble polymers useful as binders in the aqueous polymer/dye
coating composition include poly(ethylene oxide) having monomer
units; ##STR4## hereinafter PEO; available as PLURACOL E from Wyandote,
and POLYOX WSR or CARBOWAX from Union Carbide--water-soluble even
at the very high molecular weights, e.g., 1000000 or more; poly(propylene
oxide), having monomer units: ##STR5## water-soluble only in the
oligomer form, having weight average molecular weights from about
100 to about 1000 preferably about 100 to about 500; poly(vinyl
methyl ether), having monomer units: ##STR6## and their hydrolysis
product derivatives. Poly(vinyl methyl ether) is water-soluble and
available commercially as GANTREZ M from GAF Corporation and is
water-soluble, like PEO, at room temperature, at very high molecular
weights, e.g., from about 120 to about 1000000 and more. Another
suitable water-soluble polymer is polyoxymethylene (POM), having
monomer units ##STR7## which are water-soluble in the very short
oligomer form, i.e., poly(formaldehyde) and having a melting point
of about 180.degree. C., and weight average molecular weights from
about 40 to about 400. Oxide copolymers also are suitable as the
water-insoluble binding polymer, including random and block copolymers
of poly(ethylene oxide) with a variety of monomers, including propylene
oxide and/or poly(propylene oxide). One particularly useful copolymer
is sold as PLURONIC F68 having a poly(propylene oxide) core molecular
weight of about 1800 and including 80% w/w ethylene oxide units,
giving a combined molecular weight for the two outer poly(ethylene
oxide) sections of 6600--for a combined weight average molecular
weight of 8400.
The polyacrylic acid polymers are also suitable, having monomer
units: ##STR8## and are commercially available as CARBOPOL resins
from B. F. Goodrich and PRIMAL resins from Rohm & Haas. Light
cross-linking will slightly hinder the water-solubility for better
adherence of the polymer and dyes to the inert substrate.
Other, water-soluble derivatives of, and substituted, polyacrylic
acid also are useful in accordance with the present invention, such
as poly(methacrylic acid), (PMAA), having a monomeric structure:
##STR9##
Similar water-soluble polymers that are suitable in accordance
with the present invention include poly(methacrylamide), or PMAAm,
having the general monomeric structure: ##STR10##
Poly(N,N-Dimethylacrylamide), having the general monomeric structure:
##STR11##
Poly(N-Isopropylacrylamide), or PIPAAm, having the monomeric structure:
##STR12##
Poly(N-acetamidoacrylamide), having a monomeric structure: ##STR13##
and Poly(N-acetmidomethacrylamide), having a monomeric structure:
##STR14##
Water-soluble copolymers including any one or more of the above-described
acrylic polymers also are useful in accordance with the principles
of the present inventions, including the acrylic interpolymers of
polyacrylic acid and poly(methacrylic acid); polyacrylic acid with
poly(methacrylamide); and polyacrylic acid with methacrylic acid.
suitable water-soluble vinyl polymers include poly(vinyl alcohol):
##STR15## poly(vinyl acetate): ##STR16## and their copolymers, e.g.,
poly(vinylacetate-co-vinyl alcohol): ##STR17## also known as partially
hydrolyzed poly(vinylacetate) or partially acetylated poly(vinyl
alcohol), available commercially from DuPont as ELVANOL and from
Airco Chemical as VINOL.
Other suitable water-soluble polymers include polyvinyloxazolidone
(PVO) and polyvinylmethyloxazolidone (PVMO), having the monomeric
structures: ##STR18##
It has been found that any pH-indicator dye can be used in the
method of the present invention, provided that if two dyes are combined,
one is capable of interacting with cat urine over an acid pH range,
with the other changing color over an alkaline pH range to undergo
a sufficient and contrasting color transition over the different
pH ranges.
The pH-indicating dye(s) used with the binder polymer can be any
indicating dye(s) and are chosen for the particular pH range in
which a color transition is desired. For use in detecting animal
health problems associated with acidic gastrointestinal symptoms
that result in incomplete assimilation of nutrients and vitamins,
methyl red has been found to provide the best, most distinct color
transition from yellow (neutral) to red (acid), with the transition
from yellow to red at the problematic pH, occurring from pH 6.3
to about 4.2. When combined with another indicating dye for color
transition within another pH range, e.g., alkaline, each dye should
be capable of undergoing a distinctly different, visually detectable
color transition. Each of the pH-indicator dyes utilized in the
composition should undergo a distinctly different color transition
at different pH ranges.
In accordance with the method of the present invention, if only
one dye is used, the aqueous polymer/dye solution can be buffered
to a pH value slightly above or below the pH range wherein the dye
changes color, in order for each dye to undergo its maximum color
transition, and therefore most appreciably improve color resolution
and most substantially increase color transition sensitivity. The
quantity of buffer is usually between about 100 millimolar (mM)
and about 500 millimolar.
Finally, if two dyes are incorporated into the aqueous polymer/dye
coating composition, the dyes employed in the composition should
undergo color transitions that do not mutually interfere with one
another. For example, the benefits of improved color resolution
and increased color sensitivity can be defeated or minimized if
a first dye undergoes a color transition to match the original color
of a second dye; or if the second dye undergoes a color transition
to match the original color of the first dye. For example, if at
a constant pH the first dye is red in color and the second dye is
colorless; then upon interaction with animal urine, the first dye
undergoes a color transition from red to colorless and the second
dye undergoes a color transition from colorless to red, the benefits
of improved color resolution and sensitivity are diminished or negated.
The relative amounts of combined dyes are not important.
It should be understood that optional ingredients, such as surfactants,
that do not materially alter the nature and the function of the
indicator dyes and that do not interfere with the pH of the contacting
urine, also can be included in the aqueous polymer/dye coating composition.
Likewise, other such non-essential ingredients include nonactive
background dyes, polymers and plasticizers.
In accordance with an important feature of the present invention,
TABLE I lists representative pH-indicator dyes, and their pH color
transition ranges, and preparations that can be used, singularly
or in admixture, in the aqueous polymer/dye coating compositions
of the present invention. The combination of methyl red and bromothymol
blue provide exceptional results for a fast and long-lasting indication
of acidic or alkaline cat urine. Methyl red has a red color about
pH 6.0 and changes from red to yellow through the pH range 6.0 to
4.8. Bromothymol blue has a yellow color below pH 6.0 and changes
from yellow to blue through the pH range 6.0 to 7.6.
A combination of methyl red and bromothymol blue will appear orange
when viewed through the transparent or translucent polymeric binder.
When animal urine has a problematic acidic pH, below about 6.0
e.g., 5.0 the methyl red will change from yellow to red (the same
as the bromothymol blue). Accordingly, a red appearance indicates
a problematic acidic urine. When animal urine has a problematic
alkaline pH, indicative of feline urologic syndrome, e.g., pH 7.5
to 8.0 the bromothymol blue will change from yellow to blue or
purple and, combined with the yellow colored methyl red, the combination
of pH-indicators will appear green to violet colored. Surprisingly,
once the color changes on the surface of the inert core substrate,
the color change remains for days for viewing by the pet owner,
although methyl red is easily reduced and, when not bound by the
polymers of the present invention, quickly loses its color necessitating
prompt readings. It is theorized that the water-soluble polymer
binders stabilize or lock the pH-indicating dyes against chemical
degradation and, upon polymer solubilization, permit dye color change
while wet and the polymer will quickly dry to again stabilize the
dyes, in their new color, against chemical degradation.
TABLE I __________________________________________________________________________
APPROXI- MATE COLOR- INDICATOR pH RANGE CHANGE PREPARATION __________________________________________________________________________
Methyl Violet 0.0-1.6 yel to bl 0.01-0.05% in water Crystal Violet
0.0-1.8 yel to bl 0.02% in water Ethyl Violet 0.0-2.4 yel to bl
0.1 g in 50 ml of MeOH + 50 ml in water Malachite Green 0.2-1.8
yel to water bl grn Methyl Green 0.2-1.8 yel to bl 0.1% in water
2-(p-dimethylamino- 0.2-1.8 yel to bl 0.1% in EtOH phenylazo)pyridine
4.4-5.6 red to yel o-Cresolsulfone- 0.4-1.8 yel to red 0.1 g in
26.2 ml 0.01N phthalein 7.0-8.8 yel to red NaOH + 223.8 ml water
(Cresol Red) Quinaldine Red 1.0-2.2 col to red 1% in EtOH p-(p-dimethylamino-
1.0-3.0 red to yel EtOH phenylazo)-benzoic acid, Na-salt (Paramethyl
Red) m-(p-anilnophenylazo) 1.2-2.4 red to yel 0.01% in water benzene
sulfonic acid, Na-salt (Metanil Yellow) 4-Phenylazodiphenyl- 1.2-2.6
red to yel 0.01 g in 1 ml 1N amine HCl + 50 ml EtOH + 49 ml water
Thymolsulfonephthalein 1.2-2.8 red to yel 0.1 g in 21.5 ml 0.01N
(Thymol Blue) 8.0-9.6 yel to bl NaOH + 229.5 ml water m-Cresolsulfone-
1.2-2.8 red to yel 0.1 g in 26.2 mol 0.01N phthalein 7.4-9.0 yel
to purp NaOH + 223.8 ml water (Metacresol Purple) p-(p-anilinophenylazo)
1.4-2.8 red to yel 0.01% in water benzenesulfonic acid, Na-Salt
(Orange IV) 4-o-Tolylazo-o- 1.4-2.8 or to yel water toluidine Erythrosine,
disodium 2.2-3.6 or to red 0.1% in water salt Benzopurpurine 48
2.2-4.2 vt to red 0.1% in water N,N-dimethyl-p-(m- 2.6-4.8 red to
yel 0.1% in water tolylazo)aniline 44'-Bix(2-amino-1- 3.0-4.0 purp
to red 0.1 g in 5.9 ml 0.05N naphthylazo)22'-stil- NaOH + 94.1
ml water benedisulfonic acid Tetrabromophenol- 3.0-4.2 yel to bl
0.1% in EtOH phthaleinethyl ester, K-salt 3',3",5',5"-tetrabromo-
3.0-4.6 yel to bl 0.1 g in 14.9 ml 0.01N phenolsulfonephthalein
NaOH + 235.1 ml water (Bromophenol Blue) 24-Dinitrophenol 2.8-4.0
col to yel saturated water solution N,N-Dimethyl-p-phenyl- 2.8-4.4
red to yel 0.1 g in 90 ml in azoaniline EtOH + 10 ml water (p-Dimethylamino-
azobenzene) Congo Red 3.0-5.0 blue to red 0.1% in water Methyl Orange-Xylene
3.2-4.2 purp to grn ready solution Cyanole solution Methyl Orange
3.2-4.4 red to yel 0.01% in water Ethyl Orange 3.4-4.8 red to yel
0.05-0.2% in water or aqueous EtOH 4-(4-Dimethylamino-1- 3.5-4.8
vt to yel 0.1% in 60% EtOH naphthylazo)-3-meth- oxybenzenesulfonic
acid 3',3",5',5"-Tetrabromo- 3.8-5.4 yel to blue 0.1 g
in 14.3 ml 0.01N m-cresolsulfone- NaOH + 235.7 ml water phthalein
(Bromocresol Green) Resazurin 3.8-6.4 or to vt water 4-Phenylazo-1-
4.0-5.6 red to yel 0.1% in EtOH naphthylamine Ethyl Red 4.0-5.8
col to red 0.1 g in 50 ml MeOH + 50 ml water 2-(p-Dimethylamino-
0.2-1.8 yel to red 0.1% in EtOH phenylazo)-pyridine 4.4-5.6 red
to yel 4-(p-ethoxyphenylazo)- 4.4-5.8 or to yel 0.1% in water m-phenylenediamine
monohydrochloride Lacmoid 4.4-6.2 red to bl 0.2% in EtOH Alizarin
Red S 4.6-6.0 yel to red dilute solution in water Methyl Red 4.8-6.0
red to yel 0.02 g in 60 ml EtOH + 40 ml water Propyl Red 4.8- 6.6
red to yel EtOH 5',5"-Dibromo-o- 5.2-6.8 yel to purp 0.1 g
in 18.5 ml 0.01N cresolsulfone-phthalein NaOH + 231.5 ml water (Bromocresol
Purple) 3',3"-Dichlorophenol- 5.2-6.8 yel to red 0.1 g in 23.6
ml 0.01N sulfonephthalein NaOH + 226.4 ml water (Chlorophenol Red)
p-Nitrophenol 5.4-6.6 col to yel 0.1% in water Alizarin 5.6-7.2
yel to red 0.1% in MeOH 11.0-12.4 red to purp 2-(24- 6.0-7.0 yel
to bl 0.1% in water Dinitrophenylazo)-1- naphthol-36-disulfonic
acid, di-Na salt 3',3"-Dibromothyl- 6.0-7.6 yel to bl 0.1 g
in 16 ml 0.01N molsulfonephthalein NaOH + 234 ml water (Bromothymol
Blue) 68-Dinitro-24- 6.4-80 col to yel 25 g in 115 ml M (1H)quinazolinedione
NaOH + 50 ml boiling (m-Dinitrobenzoylene water urea) 0.292 g of
NaCl in 100 ml water
Brilliant Yellow 6.6-7.8 yel to or 1% in water Phenolsulfonephthalein
6.6-8.0 yel to red 0.1 g in 28.2 ml 0.01N (Phenol Red) NaOH + 221.8
ml water Neutral Red 6.8-8.0 red to amb 0.01 g in 50 ml EtOH + 50
ml water m-Nitrophenol 6.8-8.6 col to yel 0.3% in water o-Cresolsulfone-
0.0-1.0 red to yel 0.1 g in 26.2 ml 0.01N phthalein 7.0-8.8 yel
to red NaOH + 223.8 ml water (Cresol Red) Curcumin 7.4-8.6 yel to
red EtOH 10.2-11.8 m-Cresolsulfone- 1.2-2.8 red to yel 0.1 g in
26.2 ml 0.01N phthalein 7.4-9.0 yel to purp NaOH + 223.8 ml water
(Metacresol Purple) 44'-Bis(4-amino-1- 8.0-9.0 bl to red 0.1 g
in 5.9 ml 0.05 N naphthylazo) NaOH + 94.1 ml water 22' stilbene
disulfonic acid Thymolsulfonephthalein 1.2-2.8 red to yel 0.1 g
in 21.5 ml 0.01N (Thymol Blue) 8.0-9.6 NaOH + 228.5 ml water o-Cresolphthalein
8.2-9.8 col to red 0.04% in EtOH p-Naphtholbenzene 8.2-10.0 or to
bl 1% in dil. alkali Phenolphthalein 8.2-10.0 col to pink 0.05 g
in 50 ml EtOH + 50 ml water Ethyl-bis(24-dimethyl- 8.4-9.6 col
to bl saturated solution in phenyl)acetate 50% acetone alcohol Thymolphthalein
9.4-10.6 col to bl 0.04 g in 50 ml EtOH + 50 ml water 5-(p-Nitrophenylazo)
10.1-12.0 yel to red 0.01% in water salicylic acid, Na-salt (Alizarin
Yellow R) p-(24- 11.4-12.6 yel to or 0.1% in water Dihydroxyphenylazo)
benzenesulfonic acid, Na-salt 55'-Indigodisulfonic 11.4-13.0 bl
to yel water acid, di-Na-salt 246-Trinitrotoluene 11.5-13.0 col
to or 0.1-0.5% in EtOH 135-Trinitrobenzene 12.0-14.0 col to or
0.1-0.5% in EtOH Clayton Yellow 12.2-13.2 yel to amb 0.1% in water
__________________________________________________________________________
Other indicator dyes, capable of undergoing a color transition
either in the acidic or in the neutral to alkaline pH range, also
can be combined to yield a dual indicator reagent composition to
afford improved color resolutions and differentiation and increased
color sensitivity. However, each indicator dye of a combination
of dyes must undergo sufficiently different color transitions over
different pH ranges. In addition, several other suitable pH-indicator
dyes are available commercially from numerous manufacturers and
distributors.
While any solid material can be used for the core of the pH-indicating
material of the present invention, it has been found that solid
mineral matter, such as marble chips or granite chips, crushed stones,
and the like, preferably less than about 1/2 inch in every dimension,
functions best as the core or substrate that is coated with the
aqueous polymer/dye solutions. It is preferred that the solid, mineral
core material is not a clay material because of the potential for
interaction between the clay and the pH-indicator dyes. The solid
mineral material can be chosen to have a specific gravity approximating
(.+-.25%, preferably .+-.10%) the specific gravity of an absorbent
cat litter material with which the pH-indicating material is admixed
to prevent substantial separation of the pH-indicating material
from the litter material.
For clumping bentonite clay cat litter, granite chips or marble
chips are preferred so that the polymer/dye-coated chips can be
admixed with the bentonite clay particles, usually having a size
from about 50 microns to about 4000 microns, preferably about 50
microns to about 3350 microns, and homogeneously blended with the
bentonite clay particles. Storage, transportation and handling of
the homogeneously blended bentonite clay/pH-indicating material
composition of the present invention will not cause substantial
separation of the coated mineral chips from the bentonite clay animal
litter material so that the coated chips are available for animal
urine contact simply by pouring the blended material into a litter
box, or other area where the animal urinates.
Best results are achieved by coating a solid mineral-based core
substrate, preferably CaCO.sub.3 marble chips, with an aqueous solution
containing about 20% to about 60%, preferably about 30% to about
50%, e.g., about 40% by weight water and approximately 58% by weight
sodium polyvinylpyrrolidone that has 80% to 90% of its monomer units
hydrolyzed, with about 2% by weight sodium dodecyl sulfate surfactant
added for better adhesion of the polymer/dye composition to the
exterior of the marble chips. The preferred indicator dyes are a
combination of methyl red and bromothylmol blue in a weight ratio
of about 3:1. Concentrations of each dye are not critical and can
be provided in the concentration indicated in Table I. Preferably,
the aqueous composition contains about 0.01% to about 1%, e.g.,
about 0.05% by weight of a sodium phosphate buffer. The solution
can be sprayed onto the surface of the marble chips, or the chips
can be dipped into the solution. The coated chips then are heated
to about 170.degree. C. to 180.degree. C. (above the melting point
of the water-soluble polymer) for about 10 minutes to dry the polymer,
protect and hold the dye on the surface of the marble chips, and
cure the polymer coating while maintaining water-solubility of the
polymer. Higher temperatures above the melting point of the polymer
may be used for a shorter time period to achieve drying.
Upon complete drying, the chips are cooled slowly, in a confined
chamber, to room temperature, over the course of one to five hours.
The coating preferably is applied in a thickness of about 10 to
30 mils. Water-soluble polymers having a high degree of hydrolysis,
e.g., 100% hydrolyzed polyvinylpyrrolidone, can be provided in thicker
coatings, e.g., 20 mils to 40 mils, and cured at higher temperatures,
e.g., 200.degree. C., for drying and curing in a reasonable amount
of time. Water-soluble polymers that are less water-soluble, e.g.,
a partially cross-linked sodium polyacrylate, preferably are provided
in a thinner coating, e.g., 5 mils to 10 mils thick, and dried at
a lower temperature, e.g., 120.degree. C. to 140.degree. C. Preferably,
the water-soluble polymer film will have sufficient resistance to
solubilization that the polymer will not be completely washed away
from the surface of the substrate or core when doused with cat urine.
Degree of cross-linking, if any, degree of hydrolysis, curing temperatures
and the like can be varied to vary the ease of solubilization of
the polymer film coating.
Numerous modifications and alternative embodiments of the invention
will be apparent to those skiled in the art in view of the foregoing
description. Accordingly, this description is to be construed as
illustrative only and is for the purpose of teaching those skilled
in the art the best mode of carrying out the invention. The details
of the composition may be varied substantially without departing
from the spirit of the invention, and the exclusive use of all modifications
which come within the scope of the appended claims is reserved. |