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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a detergent composition in gel form useful for a
wide variety of cleaning purposes and of special application for cleaning
dishes in an automatic dishwasher.
2. The Prior Art
Automatic dishwashing detergents for home use have traditionally been in
powder or granulate form. More recently, the marketplace has seen the
advent of liquid forms of automatic dishwashing products. Liquids have
advantages over powders in their convenience of dispensing or dosing,
their enhanced solubility, absence of lump formation or "caking" during
storage, and absence of dustiness associated with the powder form.
Since automatic dishwashing machines contain a dispenser cup normally
intended for powders, chemists have been challenged in formulating a
liquid product of appropriate rheological properties.
Firstly, the composition must be a uniform mixture to deliver an optimum
combination of active ingredients to the wash with each dose. Thus, the
liquid must possess physical stability against syneresis or physical
separation of its active components during storage.
Secondly, a liquid product must be compatible with automatic dishwashing
equipment presently available to the consumer. Home dishwashers are fitted
with a closed cup to house detergent through several cycles preliminary to
the wash cycle. Cups in these machines do not seal tightly and do not
adequately retain liquids of low viscosity. Excessive leakage leads to
underdosing in the wash cycle. Performance may be adversely affected.
Consequently, any liquid product must possess high viscosity to be
effectively retained in the cup and avoid leakage into cycles preceding
that of the wash.
Conversely, there are situations where the product should have low
viscosity. A low viscosity is desirable for easy dispensing of product
from its bottle. Thixotropic liquids address the foregoing dilemma by
maintaining high viscosity for storage but reverting to lower viscosity
under influence of applied shear. Thixotropy is shear thinning behavior
that is time dependent in both its decrease in viscosity under applied
shear and its regain of viscosity after cessation of shearing.
The earliest approaches to these problems involved the use of clays to
modify viscosity. Typical of this technology are the compositions
disclosed in U.S. Pat. Nos. 4,116,849 (Leikhim), 4,431,559 (Ulrich), GB
Nos. 2 116 199A (Julemont et al.) and 2 140 450A (Julemont et al.). Some
patents such as U.S. Pat. Nos. 4,511,487 (Pruhs et al.) and 4,512,908
(Heile) have singled out hectorite as a particularly efficient thickener.
There has also been reported in U.S. Pat. No. 3,558,496 (Zmoda) the
advantage of combining a negatively charged clay such as hectorite with a
positively charged clay such as alumina clay.
GB No. 2 176 495A suggests the use of polyvalent metal salts of long chain
fatty acids, such as aluminum or zinc stearate, as stabilizers against
phase separation in a clay laiden liquid composition. Another method of
improving phase stability in thixotropic liquids is reported in GB No. 2
163 448A. This patent suggests inclusion of a limited amount of a
water-soluble potassium salt to achieve a potassium:sodium weight ratio of
about 0.04 to 0.5. Relatively large crystals are said to be inhibited from
forming when potassium is present thereby resulting in greater stability
against separation on ageing. U.S. Pat. No. 3,720,621 (Smeets) reports a
further useful property of including some potassium salt within a sodium
tripolyphosphate liquid composition. Here the presence of potassium allows
the amount of sodium tripolyphosphate included within the aqueous
detergent to attain a considerably higher solubility than found in the
absence of potassium.
Although generally acceptable, clay structured liquids have a number of
disadvantages. Montmorillonite clays, even in the presence of stabilizing
agents, are sensitive to ionic strength. They lose their liquid
structuring efficiency at the high electrolyte levels normally present in
autodish liquid detergents. Clays tend to collapse onto themselves, or
flocculate under these conditions. If this collapse occurs to any large
extend during prolonged storage, the liquid will lose its physical
stability, suffer syneresis and/or settling of solids. Collection of
solids at the bottom of the container can lead to the formation of
paste-like plugs which are difficult to dispense.
Attapulgite clay particles suspended in liquids tend to scatter light. Any
large amount of these clay particles will thus impart a muddy dull color
to the liquid. Furthermore, clays, being insoluble minerals, can adversely
affect glass appearance. Deposition of clay onto the surface of glassware
has been known to lead to spotting and filming.
Another problem of suspended solids in prior art liquids is that they are
subject to recrystallization during storage periods. Through a process of
Ostwald ripening, the solids can redistribute themselves in terms of
number and size of crystals. These changes can cause a drastic change in
rheology of the liquid over time. Poor stability and/or cup retention
result.
Many polymers are known for their thickening properties. Within the machine
dishwashing art, polyacrylic acid type polymers have been included as an
important component but not necessarily to function as a thickener. Thus,
U.S. Pat. No. 3,579,455 (Sabatelli et al.) discusses what is evidently a
powdered dishwashing detergent utilizing sodium polyacrylate as an
anti-spotting/streaking agent and hardness precipitator. Polyacrylate has
also been incorporated into thixotropic liquids that have been primarily
thickened with powdered clay. GB Nos. 2 163 447A (Colarusso) and 2 164
350A (Lai et al.) contain such clay-sodium polyacrylate systems and
suggest that the polymer provides improved protection to the overglaze
layer of fine china. Less filming on glassware was also noted.
Use of polymers for gel-formation in liquid detergent compositions was
suggested in U.S. Pat. No. 3,060,124 (Ginn). Apparently, cross-linked
vinyl polymers are primarily suitable. Hydrolyzed polyacrylonitrile
cross-linked with formaldehyde was found particularly effective at
stabilizing the gels against separation. U.S. Pat. No. 4,228,048 (Tesdahl)
illustrates the use of polyallyl sucrose cross-linked polyacrylates,
commercially available under the trademark Carbopol.RTM., as a thickener
for liquid cleaning and bleaching concentrates. Japanese Laid Open Patent
Nos. 59-36198 (Kao Soap) and 59-36200 (Kao Soap) further illustrate the
use of polyacrylate cross-linked with compounds such as allylated
pentaerythritol. These thickened formulas are used to suspend
water-insoluble abrasives such as silicone dioxide and aluminum oxide.
Although the aforementioned polymer systems do provide some measure of
thickening and phase stabilization, they are frequently not fully adequate
at such functions, especially where there is a high level of electrolyte
present. Systems are required exhibiting improved stability against phase
separation at high electrolyte level and having improved rheological
properties. With regard to rheology, the composition must not
substantially leak from the cup of an automatic dishwasher, but at the
same time be sufficiently shearing to allow flow out of its container.
There has also been a search for more aesthetically pleasing product forms.
Clay structurants cream the carrier liquid resulting in an opaque product.
Many polymers also impart opaque properties. Clear compositions would, by
contrast, be more aesthetically pleasing to the consumer.
Liquids including all those of the aforementioned art have another
undesirable characteristic. Subsequent to pouring, the mouth of the
pouring container will retain flow cut-off product droplets. Normally,
these droplets will travel from the lip downward along the outside of the
container. Consumers do not like the resulting mess. Some containers have
been designed with special pour spouts to prevent this problem. The spouts
are, however, quite expensive and not normally used for small-sized
containers. It would therefore be desirable to obtain a product inherently
having non-drip properties.
Accordingly, it is an object of the present invention to obtain a
composition in gel form readily flowable from its container but,
nevertheless, having rigidity when not subjected to shearing forces. With
particular respect to automatic dishwashing compositions, it is an object
of the present invention to provide a gel product that can readily be
dispensed from its bottle but, once placed in a retaining cup of an
automatic dishwasher will have sufficient thickness not to leak from the
cup before dispensing.
Another object of the present invention is to provide a gel that is clear.
A further object of the present invention is to provide a gel cleaning
composition pourable from a container similar to ordinary liquids but
having a recoil elasticity rendering the composition dripless.
A further object of the present invention is to provide an automatic
dishwashing composition in gel form having improved storage stability so
as to avoid phase separation.
A still further object of the present invention is to provide an automatic
dishwashing composition which does not require clay structurants.
Also an object of the present invention is to provide an automatic
dishwashing composition having reduced spotting and filming with respect
to glassware.
Finally, another object of the present invention is to provide a cleaning
composition in gel form that may also be utilized in applications other
than automatic dishwashing including those of fabric washing, fabric
softening, bleaching, hard surface cleaning and similar functions.
These and other objects of the present invention will become apparent as
further details are provided in the subsequent discussion and Examples.
SUMMARY OF THE INVENTION
An aqueous cleaning composition is provided in a gel form having a
viscosity on a Haake Rotovisco RV-100 Viscometer at 25.degree. C. under 5
sec.sup.-1 shear of from about 1,000 to 20,000 cps and under 21 sec.sup.-1
shear of from about 200 to 5,000 cps, a pH range from 11 to 13, and a
steady state viscoelastic deformation compliance J.sub.e .degree. greater
than 0.01.
A preferred embodiment of the aforementioned aqueous cleaning gel
composition is a material comprising from 0.1 to 10% of a thickener that
is a cross-linked polycarboxylic polymer. Desirably, there should also be
present from 0.01 to 10% of a trivalent metal containing material.
Aluminum is the most suitable trivalent metal and aluminum oxide is the
preferred material. Moreover, there may be present from 1 to 60% of a
water-soluble structuring chelant selected from the salts of carbonate,
pyrophosphate and mixtures thereof. Potassium carbonate, tetrapotassium
pyrophosphate and mixtures of these salts are best selected as the
structuring chelants. Clear, nearly transparent, properties are retained
by the composition even in the presence of polymer thickener, trivalent
metal containing material, and structuring chelant.
DETAILED DESCRIPTION OF THE INVENTION
The aqueous cleaning compositions of the present invention have several
properties which are unusual and surprising. Unlike known gel
compositions, the present material has an elastic nature rendering the
material non-dripping. When tilting a container upright again after
pouring, the discharging gel exhibits a memory, recoiling back into the
container without leaving any drop of liquid around the container mouth.
The effect is somewhat akin to the action of a yo-yo. Gel elasticity is
believed to arise from strong intermolecular entwinning which does not
seem to occur in other systems. A physical measure of this elasticity or
recoil is J.sub.e .degree., the steady state compliance value. J.sub.e
.degree. is derived from steady state viscoelastic deformation
measurements performed through well known standard techniques (see J.
Ferry, "Viscoelastic Properties of Polymers", Third Edition, John Wiley &
Sons, New York, 1980). J.sub.e .degree. reflects the elastic deformation
and/or energy stored in the elastic components of a fluid during steady
flow. This value identifies the extent to which a fluid rebounds when
stress is removed. Rebounding or recoil is a property associated with
visual perception of elasticity. The J.sub.e .degree. value should be
greater than about 0.01 meters.sup.2 /Newton, preferably greater than
about 0.02 meter.sup.2 /Newton, and optimally between 0.02 and 0.10.
Gel compositions of this invention must also have acceptable flowability
from a container but, when at rest, must be relatively non-flowing. The
non-flowing property is important in such areas such as automatic
dishwashing detergents. When such a detergent is placed in an automatic
dishwashing dispenser cup, the detergent composition should have
sufficient structural integrity not to rapidly flow out of the dispenser
cup. Thus, gel compositions of this invention should possess under the
minimum shear conditions of 5 sec.sup.-1 at 25.degree. C., a viscosity of
from about 1,000 to 20,000 cps, preferably from about 1,500 to 10,000 cps,
optimally between 3,000 and 7,000 cps. Under flow conditions represented
by the shear rate of 21 sec.sup.-1 at 25.degree. C., the viscosity should
range from about 200 to 5,000 cps, preferably from about 800 to 4,000 cps,
optimally from 900 to 2500 cps. The aforementioned viscosities are
measured on a Haake Rotovisco RV-100 Viscometer. A pH range for these
liquids varies from about 11 to 13.
Another unusual property that certain embodiments of the present invention
may possess is that of clarity or near transparency. The term "clear" as
used in the specification is intended to connote its usual dictionary
definition. Thus, a clear composition allows ready viewing of objects
behind it. By contrast, a translucent composition although allowing light
to pass through, causes light to be so scattered as by a very small
portion of crystals or insolubles, that it will be impossible to clearly
identify objects behind the translucent material. Within the context of
this invention, the composition is deemed to be clear if the maximum
transmittance of light through a sample 2 cm thick is at least 10%,
preferably at least 20%, optimally greater than 50%. A gel is deemed
translucent if the maximum transmittance of such light through the sample
is between 5% and 10%. Finally, a gel is deemed opaque if the maximum
transmittance of light is below 5%. This transmittance can easily be
measured by placing a sample of the aforestated thickness in the light
path probe of a Brinkmann PC 800, Colorimeter fitted with a 470 nm
filter. Distilled water is considered a baseline for 100% transmittance.
In one embodiment of the present invention, it has been found that a gel
with the aforedescribed unique recoil properties can be obtained by use of
a cross-linked polycarboxylate polymer. Desirably, there should also be
present a trivalent metal containing material. Moreover, there preferably
should be present a structuring chelant.
Polycarboxylic thickening polymers in aqueous media are known to tolerate,
without phase separation, modest electrolyte levels in such products as
liquid automatic dishwashing detergents. Problems of phase separation
will, however, occur when these modest electrolyte levels are
substantially increased by the addition of further salts. Thus, according
to the first embodiment, it has been found that certain cross-linked
polycarboxylic polymers will impart a reasonably high viscosity to liquids
even in the presence of high levels of salts.
Further work has indicated that high viscosity alone is insufficient for
certain product systems. For instance, automatic dishwashing products
require an adequate level of product retention within the cup of a
dishwashing machine. For such product applications, it has been found
desirable to include small amounts of aluminum containing compounds that
will interact with the cross-linked polycarboxylic polymers to
substantially improve product rheology.
Dependent upon the chosen polymer and aluminum containing compound, it may
be desirable to also include a water-soluble structuring chelant. The
matrix formed through the interaction of cross-linked polymer, aluminum
compound and structuring chelant affords a salt tolerant gel unaffected by
the presence of alkaline sources, builder salts and other soluble ionic
species.
By the use of the aforedescribed matrix, it is possible to obtain a clear
gel even in the presence of alkaline salts, builders, surfactants and
other minor ingredients. The system provides for complete solubility of
the foregoing components; the matrix is a highly suspending one. Thereby
is achieved the additional benefit of eliminating suspended solids, and
the attendant settling-separation problems. If desired, significant
amounts of light dispersing solids may nevertheless be included in the
matrix. Translucent or opaque gels would then result.
The polymeric thickener of the first embodiment of the invention is a
polycarboxylic polymer that has been interpolymerized with a multi-vinyl
or multi-allylic functionalized cross-linking agent. Preferably, the
polycarboxylic polymer is interpolymerized with a polyalkenyl polyether of
a polyhydric compound. The polyhydric compound should have at least 4
carbons and 3 hydroxy groups. These thickeners are described in U.S. Pat.
Nos. 2,798,053 and 4,130,501, both of which are herein incorporated by
reference. More specifically the thickeners are water dispersible
copolymers of an alpha-beta monoolefinically unsaturated lower aliphatic
carboxylic acid cross-linked with a polyether of a polyol. The polyol may
be selected from the group consisting of oligosaccharides, reduced
derivatives thereof in which the carbonyl group is converted to an alcohol
group, and pentaerythritol. The hydroxy groups of said polyol are
etherified with allyl groups, said polyol having at least two allyl groups
per polyol molecule. A suitable copolymer is one of acrylic acid with low
percentages (0.71 to 1.5%) poly allyl sucrose.
Molecular weights of the cross-linked polymer may range from about 500,000
up to 10,000,000, preferably between 500,000 and 2,000,000, optimally
about 1,250,000. Examples of commercially available cross-linked polymers
based upon allyl sucrose modified polyacrylic acid are the Carbopol.RTM.
resins manufactured by the B. F. Goodrich Chemical Company. These
materials include Carbopol 941.RTM. (m.w. 1,250,000), Carbopol 934.RTM.
(m.w. 3,000,000) and Carbopol 940.RTM. (m.w. 4,000,000). Most preferred is
Carbopol 941.RTM. which gives the best structuring and clarity.
The polymeric thickener of this invention may be present in an amount from
about 0.1 to about 10%, preferably from about 0.5 to 2% optimally between
about 0.7 and 1.5% by weight of the composition.
In conjunction with the polymeric thickener, there may be present a
co-structurant such as a trivalent metal containing material. Most
effective are those materials containing aluminum, especially aluminum
salts or aluminum oxides. Among the inorganic aluminum salts that have
been found useful are those with counterions selected from sulfate,
chloride, phosphate, nitrate, chlorhydroxide, bromide, carbonate and
fluoroborate. Alumina is however the most effective source of aluminum. A
most preferred form of this material is boehmite, a crystalline phase of
aluminum oxyhydroxide. Especially desirable is a semi-crystalline phase
commonly referred to as pseudoboehmite. Aluminosilicates were found not to
be effective co-structurants and, for purposes of this invention, are
excluded as the trivalent metal ion source. Of course, aluminosilicates
(e.g. zeolites) might be present for other purposes, such as for calcium
hardness sequestration, in the gel compositions, especially where clarity
of the fully formulated product is unnecessary.
Trivalent metal containing material may be present in an amount from 0.01
up to 10%, preferably from about 0.1 to about 4%, optimally from about 0.1
to 2% by weight of the composition.
A third desirable element of the gel composition is a water-soluble
structuring chelant. Particularly suitable are salts of carbonate,
pyrophosphate and mixtures of these two materials. For purposes of product
clarity, it is preferable to select potassium as the counterion to the
carbonate and/or pyrophosphate. Small amounts of sodium may, however, be
tolerated. Thus, the molar ratio of potassium to sodium ion should
preferably be greater than 1:1, and optimally greater than 4:1. Under
situations where potassium carbonate and potassium pyrophosphate are both
present, the relative ratio of these chelants will be from 1:10 to 10:1,
preferably from 1:4 to 4:1, optimally about 1:4 to 1:1.5. The amount of
chelant may range anywhere from about 1% up to about 60%, preferably
between about 15 and 35%, optimally between about 25 and 30% by weight of
the composition.
When the gel composition is used as an automatic dishwashing formulation,
it will normally also contain an oxidizing agent. Traditionally, liquid
dishwashing compositions have for this purpose utilized sodium
hypochlorite because it is inexpensive. Other oxidizing agents may,
however, be employed. For instance, it is also possible to utilize
heterocyclic N-bromo and N-chloro imides such as trichlorocyanuric,
tribromocyanuric, dibromo and dichlorocyanuric acids, and salts thereof
with water solubilizing cations such as potassium and sodium. An example
of a hydrated dichlorocyanurate acid is Clearon CDB 56, a product
manufactured by the Olin Corporation. The oxidizing material will be
present in the mixture from about 0.1 to 10%, with the most preferred
range being from 0.1 to 2% by weight. Preferred concentrations will
provide about 0.2 to about 1.5 weight % available chlorine.
Automatic dishwashing detergent compositions based upon this invention will
also contain sodium or potassium silicate. This material is employed as a
cleaning ingredient, source of alkalinity, metal corrosion inhibitor, and
protector of glaze on china tableware. Especially effective is sodium
silicate having a ratio of SiO.sub.2 :Na.sub.2 O from about 1.0 to about
3.3, preferably from about 2 to about 3.2. The silicate may be used in the
form of an aqueous liquor or a solid. It will be present from about 0.1 to
25%, more preferably from about 5 to 10% by weight of the composition.
Surfactants are desirably part of the aforementioned compositions. These
surfactants should be of the low-foaming type; foam interferes with the
dishwasher cleaning action. Suitable surfactants may be selected from
nonionic, anionic and amphoteric types and mixtures thereof. Nonionic
surfactants can be broadly defined as compounds produced by the
condensation of alkylene oxide groups with an organic hydrophobic material
which may be aliphatic or alkyl aromatic in nature. The length of the
hydrophilic or polyoxyalkylene radical which is condensed with any
particular hydrophobic group can be readily adjusted to yield a
water-soluble compound having the desired degree of balance between
hydrophilic and hydrophobic elements. Illustrative, but not limiting
examples, of the various chemical types as suitable nonionic surfactants
include:
(a) polyoxyethylene or polyoxypropylene condensates of aliphatic carboxylic
acids, whether linear- or branched-chain and unsaturated or saturated,
containing from about 8 to about 18 carbon atoms in the aliphatic chain
and incorporating from 5 to about 50 ethylene oxide and/or propylene oxide
units. Suitable carboxylic acids include "coconut" fatty acids (derived
from coconut oil) which contain an average of about 12 carbon atoms,
"tallow" fatty acids (derived from tallow-class fats) which contain an
average of about 18 carbon atoms, palmitic acid, myristic acid, stearic
acid and lauric acid.
(b) polyoxyethylene or polyoxypropylene condensates of aliphatic alcohols,
whether linear- or branched-chain and unsaturated or saturated, containing
from about 6 to about 24 carbon atoms and incorporating from about 5 to
about 50 ethylene oxide and/or propylene oxide units. Suitable alcohols
include the "coconut" fatty alcohol, "tallow" fatty alcohol, lauryl
alcohol, myristyl alcohol and oleyl alcohol. Particularly preferred
nonionic surfactant compounds in this category are the "Neodol" type
products, a registered trademark of the Shell Chemical Company.
Included within this category are nonionic surfactants having the formula:
##STR1##
wherein R is a linear, alkyl hydrocarbon having an average of 6 to 10
carbon atoms, R' and R" are each linear alkyl hydrocarbons of about 1 to 4
carbon atoms, x is an integer from 1 to 6, y is an integer from 4 to 15
and z is an integer from 4 to 25. A particularly preferred example of this
category is Poly-Tergent SLF-18, a registered trademark of the Olin
Corporation, New Haven, Conn. Poly-Tergent SLF-18 has a composition of the
above formula where R is a C.sub.6 -C.sub.10 linear alkyl mixture, R' and
R" are methyl, x averages 3, y averages 12, and z averages 16.
(c) polyoxyethylene or polyoxypropylene condensates of alkyl phenols,
whether linear- or branched-chain and unsaturated or saturated, containing
from about 6 to about 12 carbon atoms and incorporating from about 5 to
about 25 moles of ethylene oxide and/or propylene oxide.
(d) polyoxyethylene derivatives of sorbitan mono-, di-, and tri-fatty acid
esters wherein the fatty acid component has between 12 and 24 carbon
atoms. The preferred polyoxyethylene derivatives are of sorbitan
monolaurate, sorbitan trilaurate, sorbitan monopalmitate, sorbitan
tripalmitate, sorbitan monostearate, sorbitan monoisostearate, sorbitan
tristearate, sorbitan monooleate, and sorbitan trioleate. The
polyoxyethylene chains may contain between about 4 and 30 ethylene oxide
units, preferably about 20. The sorbitan ester derivatives contain 1, 2 or
3 polyoxyethylene chains dependent upon whether they are mono-, di- or
tri-acid esters.
(e) polyoxyethylene-polyoxypropylene block copolymers having the formula:
HO(CH.sub.2 CH.sub.2 O).sub.a (CH(CH.sub.3)CH.sub.2 O).sub.b (CH.sub.2
CH.sub.2 O).sub.c H
wherein a, b and c are integers reflecting the respective polyethylene
oxide and polypropylene oxide blocks of said polymer. The polyoxyethylene
component of the block polymer constitutes at least about 40% of the block
polymer. The material preferably has a molecular weight of | | |
