Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR IMPROVING DYE STABILITY IN COLORED ACIDIC RINSE-
AID FORMULATIONS
TECHNICAL FIELD
The present invention relates to acidic rinse aid formulations used in
automatic
dishwashing. More particularly, the invention relates to a method for
improving stability of
a dye used in a colored aqueous acidic rinse aid composition to ambient and
ultra-violet
light radiation of a machine dishwasher rinse aid formulation.
BACKGROUND OF THE INVENTION
The use of rinse aids in commercial and institutional machine dishwashers and
also
in household automatic dishwashers, is well known. In automatic dishwashing,
during the
rinse cycle, a final rinse of fresh water serves to displace pre-final rinse
water and its
attendant detergent and soil residues. Rinse aid formulations are aqueous
solutions
containing a low foam nonionic surfactant. During the rinse cycle, the rinse
aid is injected
into the final fresh water rinse at a concentration of about 100 to about 500
ppm. The
surfactant in the rinse water lowers the surface tension of the rinse water
and improves the
wetting action of the rinse water.
The inventors of the present invention have previously discovered that it is
possible
to formulate an aqueous rinse aid containing a low foam nonionic surfactant
and a low
molecular weight neutralized, partially neutralized, or non-neutralized
polyacrylate polymer
without the use of a compatibilizing high molecular weight polymer or a high
cloud point
co-surfactant, thus providing an acidic, stable aqueous rinse aid dispersion
which reduces
spotting and filming while improving sheeting action and drainage.
One major problem, however, associated with acidic, stable rinse aid
dispersions is
that when a dye is added in the composition to impart a pleasing color,
especially a typical
blue or green dye, such as a FD&C #1 Blue dye for example, there is a tendency
for such
rinse aid compositions to change color upon exposure to ambient and UV light,
for example
sunlight. Frequently, if not inevitably, acidic rinse aid products will be
subjected to UV
light (e.g., sunlight) repeatedly and over extended periods of time prior to
use by the
consumer. The formulations of typical automatic dishwashing (ADW) rinse aid
products
are specifically tailored to a color that has been proven to be aesthetically
pleasing to
consumers. Any change in the target formulation color, especially when clear
or
translucent bottle or other packaging container is used, can negatively impact
the
consumer's perception of the quality of the product.
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Typically, in the past, colored rinse aid compositions have been formulated at
or
near neutral pH, since it has been generally heretofore understood that non-
acidic rinse aid
compositions will not reduce the dye stability to ambient and ultraviolet
light radiation.
The inventors of the present invention have addressed this dye stability issue
in the present
invention and provided an effective solution to this problem. Before the
present invention,
there has been no method or composition known heretofore that addresses this
dye stability
problem in acidic rinse aid compositions.
Accordingly, it has thus been desirable to have a colored acidic rinse aid
product
which is not significantly altered by UV light. Further, despite the above-
mentioned
disclosures in the art, it has been desirable to have an acidic rinse aid
product which has
superior performance in addition to a packaging appearance. It is extremely
desirable that
the packaging appearance (e.g., color) is maintained until the consumer has
disposed of the
product. The present invention overcomes the problems as set forth above.
BACKGROUND ART
U.S. Patent No. 5,254,282, issued on Oct. 19, 1993 to Fusiak, discloses
acidified
paint removal formulations which are stabilized against color formation by
inclusion of a
chelating agent; and
U.S. Patent No. 5,206,006, issued on April 27, 1993 to Frontini et al.
discloses a
composition of the trinder type for detecting hydrogen peroxide evolved in a
solution,
which contains a chelating agent, relevant portions of both of these patents
being
incorporated herein by reference.
SUMMARY OF THE INVENTION
The invention meets the needs above by providing a method and composition for
improving stability of a dye used in a colored aqueous acidic rinse aid
composition to
ambient and ultra-violet light radiation.
In one aspect of the present invention, the method for improving stability of
a dye
used in a colored aqueous acidic rinse aid composition to ambient and ultra-
violet light
radiation includes the step of adding a chelant to an acidic rinse aid
composition. The
chelant is present in an amount of at least 1 ppm by weight of the rinse aid
composition.
In another aspect of the present invention, a colored acidic rinse aid
composition
exhibiting improved stability of a dye used therein to ambient and ultra-
violet light
radiation includes a low foaming nonionic surfactant present in a range of
from about 2% to
about 80% by weight of the rinse aid composition. The composition also
includes a
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hydrotrope present in a range of from about 0.5% to about 20% by weight of the
rinse aid
composition. The composition further includes a polyacrylate polymer present
in a range of
from about 0.1% to about 15% by weight of the rinse aid composition. The
polymer has a
weight average molecular weight in a range of from about 1000 to about 50,000.
The
composition still further includes a chelant. The chelant is present in an
amount of at least
1 ppm by weight of the rinse aid composition.
DETAILED DESCRIPTION OF THE INVENTION
In the preferred embodiment of the present invention, the method includes the
step
of adding a chelant to an acidic rinse aid composition. The chelant is
desirably present in
an amount of at least 1 ppm, preferably at least 50 ppm, more preferably at
least 100 ppm
and most preferably at least 150 ppm by weight of the rinse aid composition.
Chelants
In the preferred embodiment, the acidic rinse aid composition includes
chelants
selected from the group consisting of amino carboxylates, amino phosphonates,
polyfunctionally-substituted aromatic chelants, and mixtures thereof. Other
useful chelants
include iron and/or manganese chelants. Amino carboxylates useful as optional
chelants
include ethylenediaminetetracetates, N-hydroxyethylethylenediaminetriacetates,
nitrilo-
triacetates, ethylenediamine tetraproprionates, triethylenetetra-amine-
hexacetates,
diethylene-triaminepentaacetates, and ethanoldiglycines, alkali metal,
ammonium, and
substituted ammonium salts therein and mixtures therein.
Polyfunctionally-substituted aromatic chelants include
dihydroxydisulfobenzenes
such as 1,2-dihydroxy-3,5-disulfobenzene, and ethylenediamine disuccinate
("EDDS").
In the preferred embodiment, the chelant is selected from the group consisting
of
ethylene diamine tetra acetic acid carboxylate, diethylene triamine penta
acetic acid
carboxylate , and mixtures thereof. In another preferred embodiment, the
chelants are
selected from polyphosphonate, ethylene diamine tetra acetic acid carboxylate
(EDTA) and
diethylene triamine penta acetic acid carboxylate (DTPA). Most preferably, the
chelant is
ethylene triamine penta phosphoric acid.
Dyes
In the preferred embodiment of the present invention, the dye is selected from
the
group consisting of Pontamine Blue (Copper Phthalocyanine Dyestuff), and
Liquitant
Patent Blue (polymeric colorant) and FD&C Blue #1 (having the molecular
formula
C3~H34N?Na2O9S3), and mixtures thereof. Preferably, the dye has a color
selected from the
group consisting of blue, green, or mixtures thereof. It has been found that
the blue and
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green dyes typically used in rinse aid formulations, such as the FD&C #1, are
unstable to
UV light in acidic conditions unless the rinse aid composition is formulated
with a chelant
according to the present invention. It has been found that even the so-called
"acid stable"
dyes, such as Acid Blue 80, fade quickly when used in acidic rinse aids, i.e.,
the dye is
colorless after an exposure of 1 to 2 days under UV light radiation, unless
the rinse aid is
formulated according to the present invention, with a chelant. Desirably, the
dyes are added
in an amount in a range of from about 0.25% of a 1% solution in water to about
0.5% of a
1 % solution in water.
Dye-Chelant Systems
In the preferred embodiment the dye is selected from the group consisting of
copper
phthalocyanine dyestuff, FD&C #1 colors, polymeric colorants, and mixtures
thereof, and
the chelant is selected from the group consisting of amino carboxylates, amino
phosphonates, polyfunctionally-substituted aromatic chelants, and mixtures
thereof. It has
been found that these "dye-chelant" systems, optimally yield the most
effective dye color
stability to ambient and UV light radiation, when such dyes are used in acidic
rinse aids.
The most preferred chelants are selected from polyphosphonate ethylene diamine
tetra acetic acid carboxylate (EDTA) and diethylene triamine penta acetic acid
carboxylate
(DTPA) in combination with the most preferred dyes selected from blue dyes
such as
Pontamine Blue (Copper Phthalocyanine Dyestuff), and Liquitant Patent Blue
(polymeric
colorant) and FD&C Blue #1 (for example, an FD&C Blue #1 having the molecular
formula
C37H34NZNaZOgS3). These dye-chelant systems discovered by the inventors, when
formulated in an acidic rinse aid dispersion, all form ambient and UV light
resistant, color
stable systems.
The especially preferred Dye-Chelant systems discovered by the inventors are
listed
below:
Liquitant Patent Blue in combination with CW-Base;
FD&C #1 in combination with CW-Base;
Pontamine Blue in combination with CW-Base;
Liquitant Patent Blue in combination with DTPA;
FD&C #1 in combination with DTPA; and
Liquitant Patent Blue in combination with DTPA.
Carboxylic acids
In the preferred embodiment, the dye stability is further enhanced in the
presence of
carboxylic acids. Especially preferred are polycarboxylic acids, such as
Sokolan PA13PN
manufactured by BASF, Acusol 480, and Acusol 480N, both manufactured by Rohm &
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Haas. These polycarboxylic acids provide multiple benefits, as they help
stabilize the dye
and deliver filming performance benefits in the rinse cycle of automatic
dishwashing.
Desirably, the polycarboxylic acid is present in an amount in a range of from
about 0.25%
to about 10% by weight of the acidic rinse aid composition, and preferably, in
an amount in
a range of from about 1% to about 6% by weight.
In another embodiment of the present invention, the colored acidic rinse aid
composition exhibiting improved stability of a dye used therein to ambient and
ultra-violet
light radiation includes a low foaming nonionic surfactant desirably present
in a range of
from about 2% to about 80% by weight of the rinse aid composition. The
composition also
includes a hydrotrope desirably present in a range of from about 0.5% to about
20% by
weight of the rinse aid composition. The composition further includes a
polyacrylate
polymer desirably present in a range of from about 0.1 % to about 15 % by
weight of the
rinse aid composition. The polymer has a weight average molecular weight in a
range of
from about 1000 to about 50,000. The composition still further includes a
chelant. The
chelant is present in an amount of at least 1 ppm by weight of the rinse aid
composition.
Low Foaming Nonionic Surfactant
The nonionic surfactants useful in the acidic rinse aid dispersion may be any
known
low foaming nonionic surfactant used in machine dishwashing applications.
Typical
suitable nonionic surfactants include the following commercially available
materials: Triton
RTM CF-10 (an alkylaryl polyether) and Triton DF-16 (a modified
polyalkoxylated alcohol)
manufactured by Rohm and Haas Company; Plurafac LF404TM, Plurafac LF400TM
(mixed
linear alcohol alkoxylates), and Pluronic RTM L-62 (a polyoxyethylene-
polyoxypropylene
block copolymer), all manufactured by BASF Wyandotte Corporation, and BASF
RA30
surfactant, manufactured by BASF Corporation. The rinse aid formulation of the
invention
may contain one or a mixture of such low foaming nonionic surfactants.
Essentially any nonionic surfactants useful for detersive purposes can be
included
in the rinse aid compositions. Exemplary, non-limiting classes of useful
nonionic
surfactants are listed below.
(i) Nonionic polyhydroxy fatty acid amide surfactant
Polyhydroxy fatty acid amides suitable for use herein are those having the
structural
formula RZCONR~Z wherein: Rl is H, CI -C4 hydrocarbyl, 2-hydroxy ethyl, 2-
hydroxy
propyl, or a mixture thereof, preferable C,-C4 alkyl, more preferably Cl or CZ
alkyl, most
preferably Cl alkyl (i.e., methyl); and RZ is a CS -C31 hydrocarbyl,
preferably straight-chain
CS -C19 alkyl or alkenyl, more preferably straight-chain C9-C,~ alkyl or
alkenyl, most
preferably straight-chain Cn-Cm alkyl or alkenyl, or mixture thereof; and Z is
a
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polyhydroxyhydrocarbyl having a linear hydrocarbyl chain with at least 3
hydroxyls
directly connected to the chain, or an alkoxylated derivative (preferably
ethoxylated or
propoxylated) thereof. Z preferably will be derived from a reducing sugar in a
reductive
amination reaction; more preferably Z is a glycityl.
(ii) Nonionic condensates of alkyl hp enols
The polyethylene, polypropylene, and polybutylene oxide condensates of alkyl
phenols are
suitable for use herein. In general, the polyethylene oxide condensates are
preferred. These
compounds include the condensation products of alkyl phenols having an alkyl
group
containing from about 6 to about 18 carbon atoms in either a straight chain or
branched
chain configuration with the alkylene oxide.
(iii) Nonionic ethoxylated alcohol surfactant
The alkyl ethoxylate condensation products of aliphatic alcohols with from
about 1 to about
25 moles of ethylene oxide are suitable for use herein. The alkyl chain of the
aliphatic
alcohol can either be straight or branched, primary or secondary, and
generally contains
from 6 to 22 carbon atoms. Particularly preferred are the condensation
products of alcohols
having an alkyl group containing from 8 to 20 carbon atoms with from about 2
to about 10
moles of ethylene oxide per mole of alcohol.
(iv) Nonionic ethoxylated/propoxylated fatty alcohol surfactant
The ethoxylated C~-Clg fatty alcohols and C~ -Clg mixed
ethoxylated/propoxylated fatty
alcohols are highly preferred surfactants for use herein, particularly where
water soluble.
Preferably the ethoxylated fatty alcohols are the CIO -Clg ethoxylated fatty
alcohols with a
degree of ethoxylation of from 3 to 50, most preferably these are the Cia -Cl8
ethoxylated
fatty alcohols with a degree of ethoxylation from 3 to 40. Preferably the
mixed
ethoxylated/propoxylated fatty alcohols have an alkyl chain length of from 10
to 18 carbon
atoms, a degree of ethoxylation of from 3 to 30 and a degree of propoxylation
of from 1 to
10.
(v) Nonionic EO/PO condensates with prop le~,alycol
The condensation products of ethylene oxide with a hydrophobic base formed by
the
condensation of propylene oxide with propylene glycol are suitable for use
herein. The
hydrophobic portion of these compounds preferably has a molecular weight of
from about
1500 to about 1800 and exhibits water insolubility. Examples of compounds of
this type
include certain of the commercially-available PluronicTM. surfactants,
marketed by BASF.
(vi) Nonionic EO condensation products with propylene oxide/ethylene diamine
adducts
The condensation products of ethylene oxide with the product resulting from
the reaction of
propylene oxide and ethylenediamine are suitable for use herein. The
hydrophobic moiety
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of these products consists of the reaction product of ethylenediamine and
excess propylene
oxide, and generally has a molecular weight of from about 2500 to about 3000.
Examples
of this type of nonionic surfactant include certain of the commercially
available TetronicTM
compounds, marketed by BASF.
(vii) Nonionic alkylpolysaccharide surfactant
Suitable alkylpolysaccharides for use herein are disclosed in U.S. Pat. No.
4,565,647,
Llenado, issued Jan. 21, 1986, having a hydrophobic group containing from
about 6 to
about 30 carbon atoms, preferably from about 10 to about 16 carbon atoms and a
polysaccharide, e.g., a polyglycoside, hydrophilic group containing from about
1.3 to about
10, preferably from about 1.3 to about 3, most preferably from about 1.3 to
about 2.7
saccharide units. Any reducing saccharide containing 5 or 6 carbon atoms can
be used, e.g.,
glucose, galactose and galactosyl moieties can be substituted for the glucosyl
moieties.
(Optionally the hydrophobic group is attached at the 2-, 3-, 4-, etc.
positions thus giving a
glucose or galactose as opposed to a glucoside or galactoside.) The
intersaccharide bonds
can be, e.g., between the one position of the additional saccharide units and
the 2-, 3-, 4-,
and/or 6- positions on the preceding saccharide units.
The preferred alkylpolyglycosides have the formula:
RZ O(C" HZnO)t(glycosyl)X
wherein RZ is selected from the group consisting of alkyl, alkylphenyl,
hydroxyalkyl,
hydroxyalkylphenyl, and mixtures thereof in which the alkyl groups contain
from 10 to 18,
preferably from 12 to 14, carbon atoms; n is 2 or 3, preferably from about 1.3
to about 3,
most preferably from about 1.3 to about 2.7. The glycosyl is preferably
derived from
glucose.
(viii) Nonionic fatty acid amide surfactant
Fatty acid amide surfactants suitable for use herein are those having the
formula:
O
R6-C-N(R')2
wherein R6 is an alkyl group containing from 7 to 21, preferably from 9 to 17
carbon atoms
and each R' is selected from the group consisting of hydrogen, Cl-C4 alkyl, Cl-
C4
hydroxyalkyl, and --(CZ Ha O)x H, where x is in the range of from 1 to 3.
The hydrotrope useful in the present rinse aid dispersion is selected from the
group
consisting of sodium cumene sulfonate, sodium xylene sulfonate, sodium
toluenesulfonate,
dioctyl sodium sulfosuccinate, alkyl naphthalene sulfonate and dihexyl sodium
sulfosuccinate. Preferably, the hydrotrope is sodium cumene sulfonate.
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Polyacr. l~~olymer
The low molecular weight polyacrylate polymer useful in the present acidic
rinse
aid dispersion is selected from the group consisting of polyacrylate
homopolymer,
polyacrylate copolymer, polyacrylate terpolymer, and mixtures thereof.
Preferably, the
polyacrylate polymer is a partially neutralized or non-neutralized
polyacrylate polymer
having a pH in a range of from about 2.0 to about 4Ø In the preferred
embodiment, the
polyacrylate polymer is desirably at least about 75% non-neutralized.
Alternatively, the
polyacrylate polymer is non-neutralized. Still alternatively, a neutralized
polyacrylate
polymer, which is more than 25% neutralized may also be used, but an acid must
be added
in an amount sufficient ~to bring the pH value of the resultant rinse aid
dispersion within a
range of from about 2 to about 6.
Typically the polyacrylate polymer is a homopolymer of acrylic or methacrylic
acid, or a copolymer formed from at least about 50 weight percent acrylic
acid. The
polyacrylate polymer is a low molecular weight polymer or its alkali metal or
ammonium
salt, having a weight average molecular weight ranging from about 1,000 to
about 40,000.
Acid
When adding an acid to the rinse aid dispersion, any acid may be used although
organic acids are more desirable and the preferred organic acid is citric
acid.
It has been discovered that even in the absence of a compatibilizing high
molecular
weight polymer, but with the addition of a hydrotrope and in acidic
conditions, the stable
rinse aid dispersion does not phase separate upon storage for a reasonable
time or under
actual use conditions and permits each component to effectively reduce
spotting and
filming and improve sheeting action without interfering with the foaming and
defoaming
action of the surfactant.
In the preferred embodiment, the rinse aid formulation of the invention is an
aqueous dispersion at a pH of from about 2 to about 6. Preferably, the pH
ranges from
about 3 to about 5.
The rinse aid dispersion of the present invention is preferably prepared by
stirring
the desired amount of the surfactant into an aqueous solution of the low
molecular weight
non-neutralized or only partially neutralized (no more than 25 % neutralized)
polyacrylic
acid followed by the gradual addition of the hydrotrope and if necessary,
citric acid to bring
the dispersion to within the desired pH range.
The formulation may also contain other additives including sequestants
such as NTA, EDTA, or sodium citrate and water miscible solvents such as
ethanol,
isopropanol and propylene glycol. Ethanol is the preferred solvent, present
desirably in a
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range of from about 0.1 % to about 10% by weight of the rinse aid dispersion
and preferably
in a range of from about 2% to about 8% by weight.
H dy rotrope
In the preferred embodiment, the hydrotrope is selected from the group
consisting
of sodium cumene sulfonate, sodium xylene sulfonate, sodium toluenesulfonate,
dioctyl
sodium sulfosuccinate, alkyl naphthalene sulfonate and dihexyl sodium
sulfosuccinate.
Preferably, the hydrotrope is sodium cumene sulfonate, and the partially-
neutralized
polyacrylate polymer is a polyacrylate copolymer which is about 20%
neutralized. In the
preferred embodiment, the stable aqueous rinse aid dispersion is essentially
free of a high
molecular weight compatibilizing polymer and is also free of an additional
nonionic
surfactant having a cloud point of at least 70 degrees C.
The following examples are intended to illustrate the invention.
EXAMPLE 1
A rinse aid dispersion according to the present invention is made as follows,
from the
following composition, by weight percent:
Low foam nonionic surfactant 20.0%
Sodium cumene sulfonate hydrotrope 7.0%
Polyacrylate copolymer (20% neutralized) 4.5%
Ethanol 6.0%
Chelant (DTPA) 0.015%
Liquitant Patent Blue 0.25%
Water 62.235 %
This dye has ambient and LTV light radiation stability and its color is
unchanged after
exposure to L1V radiation for 1-2 days.
EXAMPLE 2
Another rinse aid dispersion according to the present invention is made as
follows, from the
following composition, by weight percent:
Low foam nonionic surfactant 35.0%
Sodium cumene sulfonate hydrotrope 4.0%
Polyacrylate copolymer (20% neutralized) 4.0%
Citric acid 1.6%
Ethanol 6.0%
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Chelant (polyphosphonate) 0.015%
FD&C Blue #1 0.25%
Water 49.135%
This dye has ambient and LTV light radiation stability and its color is
unchanged after
exposure to UV radiation for 1-2 days.
EXAMPLE 3
Another rinse aid dispersion according to the present invention is made as
follows, from the
following composition, by weight percent:
Low foam nonionic surfactant 12.0%
Sodium cumene sulfonate hydrotrope 4.0%
Polyacrylate copolymer (20% neutralized) 1.0%
Citric acid 1.6%
Ethanol 5.0%
Chelant (polyphosphonate) 0.015%
FD&C Blue #1 0.25%
Water 76.135 %
This dye has ambient and ITV light radiation stability and its color is
unchanged after
exposure to LTV radiation for 1-2 days.
The above rinse aid formulations are prepared by the following procedure:
appropriate amounts of: a low foaming nonionic surfactant (Plurafac LF 404TM),
a 45%
active sodium cumene sulfonate hydrotrope (45% active SCS), a 50% active
polyacrylate
copolymer (Acusol 480TM, made by Rohm & Haas), a 50% active citric acid,
ethanol and
deionized water are added to a beaker and stirred sequentially. Also added is
a chelant in
an amount of 0.015 weight% (150 ppm by weight) and a color dye as indicated.
The
resulting mixture obtained is a blue or green colored, single-phase acidic
dispersion and is
stable, with no phase separation occurring after the resulting mixture is kept
undisturbed in
a closed container for a period of 2 weeks at a temperature of 50 degrees C.
Further, the
resulting mixture exhibits no more than about a 30% dye discoloration when
exposed to
ambient light for 6 months, and no more than about a 30% dye discoloration
when exposed
to LTV light for 2 days.
Accordingly, having thus described the invention in detail, it will be obvious
to
those skilled in the art that various changes may be made without departing
from the scope
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of the invention and the invention is not to be considered limited to what is
described in the
specification.
