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The present invention relates to thixotropic clay aqueous suspension with
improved physical stability. More specifically the invention relates to
the use of alkali metal fatty acid salts as physical stabilizers for
thixotropic clay aqueous suspensions.
The present invention specifically relates to automatic dishwashing
detergent compositions having thixotropic properties, improved chemical
and physical stability, and with increased apparent viscosity, and which
are readily dispersible in the washing medium to provide effective
cleaning of dishware, glassware, china and the like.
Commercially available household-machine dishwasher detergents provided in
powder form have several disadvantages, e.g. non-uniform composition;
costly operations necessary in their manufacture; tendency to cake in
storage at high humidities, resulting in the formation of lumps which are
difficult to disperse; dustiness, a source of particular irritation to
users who suffer allergies; and tendency to cake in the dishwasher machine
dispenser.
Recent research and development activity has focused on the gel or
"thixotropic" form of such compositions, e.g. scouring cleansers and
automatic-dishwasher products characterized as thixotropic pastes.
Dishwasher products so provided are primarily objectionable in that they
are insufficiently viscous to remain "anchored" in the dispenser cup of
the dishwasher, and moreover yield spotty residues on dishware, glassware,
china and the like. Ideally, thixotropic cleansing compositions should be
highly viscous in a quiescent state, Bingham plastic in nature, and have
relatively high yield values. When subjected to shear stresses, however,
such as being shaken in a container or squeezed through an orifice, they
should quickly fluidize and, upon cessation of the applied shear stress,
quickly revert to the high viscosity/Bingham plastic state. Stability is
likewise of primary importance, i.e. there should be no significant
evidence of phase separation or leaking after long standing.
The U.S. patent application Ser. No. 744,754 filed June 14, 1985, which is
assigned to applicant's assignee, is directed to thixotropic clay aqueous
suspension dishwashing detergent compositions containing polyvalent metal
salts of long chain fatty acids, such as aluminum stearate as physical
stabilizing agents. The application Ser. No. 744,754 compositions show
improvement in the physical stability of the detergent composition and
improvement against phase separation over those clay containing
compositions that do not contain the aluminum stearate. The polyvalent
metal salts of the long chain fatty acids are, however, highly water
repellent and pose special problems requiring certain types of mixing
equipment and stringent process mixing conditions.
The provision of automatic-dishwasher compositions in gel form having the
aforedescribed properties, other than for the improvements described in
the above mentioned application Ser. No. 744,754, has thus far proven
problematical, particularly as regards compositions for use in home
dishwasher machines. For effective use, it is generally recommended that
the automatic dishwashing detergent, hereinafter also designated ADD,
contain (1) sodium tripolyphosphate (NaTPP) to soften or tie up hard-water
minerals and to emulsify and/or peptize soil; (2) sodium silicate to
supply the alkalinity necessary for effective detergency and to provide
protection for fine china glaze and pattern; (3) sodium carbonate,
generally considered to be optional, to enhance alkalinity; (4) a
chlorine-releasing agent to aid in the elmination of soil specks which
lead to water spotting; and (5) defoamer/surfactant to reduce foam,
thereby enhancing machine efficiency and supplying requisite detergency.
See, for example, SDA Detergents in Depth, "Formulations Aspects of
Machine Dishwashing," Thomas Oberle (1974). Cleansers approximating to the
aforedescribed compositions are mostly liquids or powders. Combining such
ingredients in a gel form effective for home-machine use has proved
difficult. Generally, such compositions omit hypochlorite bleach, since it
tneds to react with other chemically active ingredients, particularly
surfactant. Thus, U.S. Pat. No. 4,115,308 discloses thixotropic automatic
dishwasher pastes containing a suspending agent, e.g. CMC, synthetic clays
or the like; inorganic salts including silicates, phosphates and
polyphosphates; a small amount of surfactant and a suds depressor. Bleach
is not disclosed. U.S. Pat. No. 4,147,650 is somewhat similar, optionally
including C1-(hypochlorite) bleach but no organic surfactant or foam
depressent. The product is described, moreover, as a detergent slurry with
no apparent thixotropic properties.
U.S. Pat. No. 3,985,668 describes abrasive scouring cleaners of gel-like
consistency containing (1) suspending agent, preferably the Smectite and
attapulgite types of clay; (2) abrasive, e.g. silica sand or perlite; and
(3) filler comprising light density powdered polymers, expanded perlite
and the like, which has a bouyancy and thus stabilizing effect on the
composition in addition to serving as a bulking agent, thereby replacing
water otherwise available for undesired supernatant layer formation due to
leaking and phase destabilization. The foregoing are the essential
ingredients. Optional ingredients include hypochlorite bleach, bleach
stable surfactant and buffer, e.g. silicates, carbonates, and
monophosphates. Builders, such as NaTPP, can be included as further
optional ingredients to supply or supplement building function not
provided by the buffer, the amount of such builder not exceeding 5% of the
total composition, according to the patent. Maintenance of the desired
(greater than) pH 10 levels is achieved by the buffer/builder components.
High pH is said to minimize decomposition of chlorine bleach and undesired
interaction between surfactant and bleach. Foam killer is not disclosed.
In U.K. Patent Application GB No. 2,116,199A and GB No. 2,140,450A, both of
which are assigned to Colgate-Palmolive, liquid ADD compositions are
disclosed which have properties desirably characterizing thixotropic,
gel-type structure and which include each of the various ingredients
necessary for effective detergency with an automatic dishwasher. The
normally gel-like aqueous automatic dishwasher detergent composition
having thixotropic properties includes the following ingredients, on a
weight basis:
(a) 5 to 35% alkali metal tripolyphosphate;
(b) 2.5 to 20% sodium silicate;
(c) 0 to 9% alkali metal carbonate;
(d) 0.1 to 5% chlorine bleach stable, water dispersible organic detergent
active material;
(e) 0 to 5% chlorine bleach stable foam depressant;
(f) chlorine bleach compound in an amount to provide about 0.2 to 4% of
available chlorine;
(g) thixotropic thickener in an amount sufficient to provide the
composition with thixotropy index of about 2.5 to 10;
(h) sodium hydroxide, as necessary, to adjust pH; and
(i) balance water.
ADD compositions so formulated are low-foaming; are readily soluble in the
washing medium and most effective at pH values best conducive to improved
cleaning performance, viz, pH 10.5-14. The compositions are normally of
gel consistency, i.e. a highly viscous, opaque jelly-like material having
Bingham plastic character and thus relatively high yield values.
Accordingly, a definite shear force is necessary to initiate or increase
flow, such as would obtain within the agitated dispenser cup of an
energized automatic dishwasher. Under such conditions, the composition is
quickly fluidized and easily dispersed. When the shear force is
discontinued, the fluid composition quickly reverts to a high viscosity,
Bingham plastic state closely approximating its prior consistency.
U.S. Pat. No. 4,511,487 dated Apr. 16, 1985 describes a low-foaming
detergent paste for dishwashers. The patented thixotropic cleaning agent
has a viscosity of at least 30 Pa.s at 20.degree. C. as determined with a
rotational viscometer at a spindle speed of 5 revolutions per minute. The
composition is based on a mixture of finely divided hydrated sodium
metasilicate, an active chlorine compound and a thickening agent which is
a foliated silicate of the hectorite type. Small amount of nonionic
tensides and alkali metal carbonates and/or hydroxides may be used.
The formation of organoclays by the interaction of clays (such as bentonite
and hectorite) with organic compounds such as quaternary ammonium salts,
has also been described (W. S. Mardis, JAOCS, Vol. 61, No. 2, p. 382
(1984)).
While these previously disclosed liquid ADD formulations are not subject or
are subject to a lesser degree to one or more of the above described
deficiencies, it has been found that further improvements in physical
stability at lower costs are desired to increase the shelf-life of the
product and thereby enhance consumer acceptance.
While the combination of clay thickener and polyvalent metal fatty acid
salt stabilizer disclosed in the above mentioned Ser. No. 744,754 has been
found to provide satisfatory long term stability, such as absence of phase
separation for periods of up to 12 weeks and longer, it is desirable to
further improve the stability so as to avoid phase separation for up to
six months or more.
Further, the use of the known stabilizers, e.g. polyvalent metal fatty acid
salt stabilizers and clay thickeners require a specified order of addition
of the various ingredients and the close control of the process conditions
during formulation of the composition is critical to obtain the desired
thixotropic properties and low foam characteristics.
At the same time it would be highly desirable to increase the physical
stability of other clay based thixotropic liquid formulations, such as
scouring cleansers; dental pastes, "liquid" soaps, and the like.
Accordingly, it is an objective of the invention to provide anti-settling
additives for thixotropic clay aqueous suspensions.
It is another object of the invention to provide liquid ADD compositions
having thixotropic properties with improved physical stability and
rheological properties at lower costs by using alkali metal salts of fatty
acids in place of the more expensive polyvalent metal salts of fatty
acids.
It is still another object of the invention to provide thixotropic liquid
ADD compositions having reduced levels of thixotropic thickener without
adversely effecting the generally high viscosities at low shear rates and
lower viscosities at high shear rates which are characteristic of the
desired thixotropic properties.
More broadly, it is an object of this invention to improve the stability of
aqueous thixotropic clay based compositions, especially liquid automatic
diswasher detergent pastes or gels, by incorporating in the clay aqueous
suspension a minor amount of an alkali metal fatty acid salt effective to
increase the apparent viscosity of the formulation and to inhibit the
settling of the suspended particles and to prevent phase separation.
Unlike the polyvalent metal long chain fatty acid salts, the alkali metal
fatty acid salts of the present invention can be easily incorporated in
the product, e.g. either by emulsifying them with the surfactants or by
directly adding them to the batch. The process conditions for formulating
the composition are not critical. The alkali metal fatty acid salts are
easily dispersed in the composition. The addition of the alkali metal
fatty acid salts allows reduction of the amount of clay that would be
required in the absence of the fatty acid metal salts. Further, the
rheological properties of the product can be fine tuned by adjusting the
amount of alkali metal fatty acid salt added to the composition.
These and other objects of the invention which will become more readily
understood from the following detailed description of the invention and
preferred embodiments thereof are achieved by incorporating in a normally
gel-like aqueous liquid composition a small but effective amount of a
physical stabilizer which is an alkali metal fatty acid salt. More
particularly, according to a preferred and specific embodiment of the
invention, there is provided a normally gel-like automatic dishwasher
detergent composition in which is incorporated an amount of an alkali
metal fatty acid salt which is effective to increase the apparent
viscosity of the formulation and to inhibit settling of the suspended
particles, such as detergent builder and thixotropic clay.
In accordance with this particular aspect, the present invention provides a
normally gel-like aqueous automatic dishwasher detergent composition
having thixotropic properties which include, on a weight basis:
(a) 5 to 35% alkali metal tripolyphosphate;
(b) 2.5 to 20% sodium silicate;
(c) 0 to 9% alkali metal carbonate;
(d) 0.1 to 5% chlorine bleach stable, water dispersible organic detergent
active material;
(e) 0 to 5% chlorine bleach stable foam depressant;
(f) chlorine bleach compound in an amount to provide about 0.2 to 4% of
available chlorine;
(g) thixotropic thickener in an amount sufficient to provide the
composition with thixotropy index of about 2.5 to 10; and
(h) 0 to 8% sodium hydroxide;
(i) an alkali metal fatty acid salt in an amount effective to increase
apparent viscosity and the the physical stability of the composition; and
(j) balance water.
Also related to this specific aspect, the invention provides a method for
cleaning dishware in an automatic dishwashing machine with an aqueous wash
bath containing an effective amount of the liquid automatic dishwasher
detergent (LADD) composition as described above. According to this aspect
of the invention, the LADD composition can be readily poured into the
dispensing cup of the automatic dishwashing machine and will, within just
a few seconds, promptly thicken to its normal gel-like or pasty state to
remain securely within the dispensing cup until shear forces are again
applied thereto, such as by the water spray from the dishwashing machine.
The present invention is based upon the surprising and unexpected discovery
that the same or improved rheological properties and physical stability,
i.e. resistance to phase separation, settling, etc., as in the prior
liquid aqueous ADD compositions can be achieved, at lower cost and without
any particular processing requirements, by adding to the composition an
effective stabilizing amount of an alkali metal fatty acid salt in place
of the polyvalent metal fatty acid salt. At the same time, improvements in
spotting and filming performance (i.e. fewer spots and reduced filming)
can be achieved.
Amazingly, formulations prepared with, for example, 0.03 to 0.2% of the
alkali metal fatty acid salt have excellent rheological properties and
have been stable in storage for up to six months.
Generally, LADD effectiveness is directly related to (a) available chlorine
levels; (b) alkalinity; (c) solubility in washing medium; and (d) foam
inhibition. It is preferred herein that the pH of the LADD composition be
at least about 9.5, more preferably from about 10.5 to 14.0 and most
preferably at least about 11.5. The presence of carbonate is also often
needed herein, since it acts as a buffer helping to maintain the desired
pH level. Excess carbonate is to be avoided, however, since it may cause
the formation of needle-like crystals of carbonate, thereby impairing the
stability, as well as impairing the dispensibility of the product from,
for example, squeeze tube bottles. Caustic soda (NaOH) serves the further
function of neutralizing the phosphoric or phosphonic acid ester foam
depressant when present. About 0.5 to 6 wt% of NaOH and about 2 to 9 wt%
of sodium carbonate in the LADD composition are typical, although it
should be noted that sufficient alkalinity may be provided by the NaTPP
and sodium silicate.
The NaTPP employed in the LADD composition in a range of about 8 to 35 wt%,
preferably about 20 to 30 wt%, should preferably be free of heavy metal
which tends to decompose or inactivate the preferred sodium hypochlorite
and other chlorine bleach compounds. The NaTPP may be anhydrous or
hydrated, including the stable hexahydrate with a degree of hydration of 6
corresponding to about 18% by weight of water or more. Especially
preferred LADD compositions are obtained, for example, when using a 0.5:1
to 2:1 weight ratio of anhydrous to hexahydrated NaTPP, values of about
1:1 being particularly preferred.
Foam inhibition is important to increase dishwasher machine efficiency and
minimize destabilizing effects which might occur due to the presence of
excess foam within the washer during use. Foam may be sufficiently reduced
by suitable selection of the type and/or amount of detergent active
material, the main foam-producing component. The degree of foam is also
somewhat dependent on the hardness of the wash water in the machine
whereby suitable adjustment of the proportions of NaTPP which has a water
softening effect may aid in providing the desired degree of foam
inhibition. However, there may optimally be included a chlorine bleach
stable foam depressant or inhibitor where a low foam LADD is desired.
Particularly effective are the alkyl phosphonic acid esters of the formula
##STR1##
available for example from BASF-Wyandotte (PCUK-PAE), and especially the
alkyl acid phosphate esters of the formula
##STR2##
available, for example, from Hooker (SAP) and Knapsack (LPKn-158), in
which one or both R groups in each type of ester may represent
independently a C.sub.12-20 alkyl group. Mixtures of the two types, or any
other chlorine bleach stable types, or mixtures of mono-and di-esters of
the same type, may be employed. Especially preferred is a mixture of mono-
and di-C.sub.16-18 alkyl acid phosphate esters such as
monostearyl/distearyl acid phosphates 1.2/1 (Knapsack) or 4/1 (UGINE
KULHPLAN). When employed, proportions of 0.1 to 5 wt%, preferably about
0.1 to 0.5 wt%, of foam depressant in the composition is typical, the
weight ratio of detergent active component (d) to foam depressant (e)
generally ranging from about 10:1 to 1:1 and preferably about 5:1 to 1:1.
Other defoamers which may be used include, for example, the known
silicones. In addition, it is an advantageous feature of this invention
that many of the stabilizing alkali metal long chain fatty acid salts,
such as sodium stearate also act as foam killers.
Although any chlorine bleach compound may be employed in the compositions
of this invention, such as dichloro-isocyanurate, dichloro-dimethyl
hydantoin, or chlorinated TSP, alkali metal, e.g. potassium, lithium,
magnesium and especially sodium, hypochlorite is preferred. The
composition should contain sufficient chlorine bleach compound to provide
about 0.2 to 4.0% by weight of available chlorine, as determined, for
example, by acidification of 100 parts of the composition with excess of
hydrochloric acid. A solution containing about 0.2 to 4.0% by weight of
sodium hypochlorite contains or provides roughly the same percentage of
available chlorine. About 0.8 to 1.6% by weight of available chlorine is
especially preferred. For example, sodium hypochlorite (NaOCI) solution of
from about 11 to about 14% available chlorine in amounts of about 3 to
20%, preferably about 7 to 12% by weight, can be advantageously used.
The sodium silicate, which provides alkalinity and protection of hard
surfaces, such as fine china glaze and pattern, is employed in an amount
ranging from about 2.5 to 20 wt%, preferably about 5 to 15 wt%, in the
composition. The sodium silicate is generally added in the form of an
aqueous solution, preferably having an Na.sub.2 O:SiO.sub.2 ratio of about
1:2 to 1:2.8.
Detergent active material useful herein must be stable in the presence of
chlorine bleach, especially hypochlorite bleach, and those of the organic
anionic, amine oxide, phosphine oxide, sulphoxide or betaine water
dispersible surfactant types are preferred, the first mentioned anionics
being most preferred. They are used in amounts ranging from about 0.1 to
5%, preferably about 0.3 to 2.0%. Particularly preferred surfactants
herein are the linear or branched alkali metal mono- and/or
di-(C.sub.8-14) alkyl diphenyl oxide mono and/or disulphates or
disulfonates, commercially available for example as DOWFAX (Registered
Trademark) 3B-2 and DOWFAX 2A-1. In addition, the surfactant should be
compatible with the other ingredients of the composition. Other suitable
surfactants include the primary alkylsulphates, alkylsulphonates,
alkylaryl-sulphonates and sec.-alkylsulphates. Examples include sodium
C.sub.10 -C.sub.18 alkylsulphates such as sodium dodecylsulphate and
sodium tallow alcoholsulphate; sodium C.sub.10 -C.sub.18 alkanesulphonates
such as sodium hexadecyl-1-sulphonate and sodium C.sub.12 -C.sub.18
alkylbenzenesulphonates such as sodium dodecylbenzenesulphonates. The
corresponding potassium salts may also be employed.
As other suitable surfactants or detergents, the amine oxide surfactants
are typically of the structure R.sub.2 R.sup.1 N--O, in which each R
represents a lower alkyl group, for instance, methyl, and R.sup.1
represents a long chain alkyl group having from 8 to 22 carbon atoms, for
instance a lauryl, myristyl, palmityl or cetyl group. Instead of an amine
oxide, a corresponding surfactant phosphine oxide R.sub.2 R.sup.1 PO or
sulphoxide RR.sup.1 SO can be employed. Betaine surfactants are typically
of the structure R.sub.2 R.sup.1 N --R'COO.sup.-, in which each R
represents a lower alkylene group having from 1 to 5 carbon atoms.
Specific examples of these surfactants are lauryl-dimethylamine oxide,
myristyldimetylamine oxide, the corresponding phosphine oxides and
sulphoxides, and the corresponding betaines, including
dodecyldimethylammonium acetate, tetradecyldiethylammonium pentanoate,
hexadecyldimethylammonium hexanoate and the like. For biodegradability,
the alkyl groups in these surfactants should be linear, and such compounds
are preferred.
Surfactants of the foregoing type, all well known in the art, are
described, for example, in U.S. Pat. Nos. 3,985,668 and 4,271,030.
Thixotropic thickeners, i.e. thickeners or suspending agents which provide
an aqueous medium with thixotropic properties, are known in the art and
may be organic or inorganic water soluble, water dispersible or
colloid-forming, and monomeric or polymeric, and should of course be
stable in these compositions, e.g. stable to high alkalinity and chlorine
bleach compounds, such as sodium hypochlorite. Those especially preferred
generally comprise the inorganic, colloid-forming clays of smectite and/or
attapulgite types. These materials were generally used in amounts of about
1.0 to 10, preferably 1.2 to 5 wt%, to confer the desired thixotropic
properties and Bingham plastic character in the assignee's prior disclosed
LADD formulations of the aforementioned GB No. 2,116,199A and GB No.
2,140,450A. It is one of the advantages of the LADD formulations of the
present invention that the desired thixotropic properties and Bingham
plastic character can be obtained in the presence of the alkali metal
fatty acid salt stabilizers with lesser amounts of the thixotropic
thickeners. For example, amounts of the inorganic colloid-forming clays of
the smectite and/or attapulgite types in the range of from about 0.1 to
3%, preferably 0.1 to 2.5%, especially 0.1 to 2%, are generally sufficient
to achieve the desired thixotropic properties and Bingham plastic
character when used in combination with the physical stabilizer.
Smectite clays include montmorillonite (bentonite), hectorite, attapulgite,
smectite, saponite, and the like. Montmorillonite clays are preferred and
are available under tradenames such as Thixogel (Registered trademark) No.
[b 1 and Gelwhite (Registered Trademark) GP, H, etc., from Georgia Kaolin
Company; and ECCAGUM (Registered Trademark) GP, H, etc., from Luthern Clay
Products. Attapulgite clays include the materials commercially available
under the tradename Attagel (Registered Trademark), i.e. Attagel 40,
Attagel 50 and Attagel 150 from Engelhard Minerals and Chemicals
Corporation. Mixtures of smectite and attapulgite types in weight ratios
of 4:1 to 1:5 are also useful herein. Thickening or suspending agents of
the foregoing types are well known in the art, being described, for
example, in U.S. Pat. No. 3,985,668 referred to above. Abrasives or
polishing agents should be avoided in the LADD compositions as they may
mar the surface of fine dishware, crystal and the like.
The amount of water contained in these compositions should, of course, be
neither so high as to produce unduly low viscosity and fluidity, nor so
low as to produce unduly high viscosity and low flowability, thixotropic
properties in either case being diminished or destroyed. Such amount is
readily determined by routine experimentation in any particular instance,
generally ranging from about 30 to 75 wt%, preferably about 35 to 65 wt%
and more preferably from about 35 to 45%. The water should also be
preferably deionized or softened.
So far, the description of the LADD product, except as otherwise noted,
conforms to the compositions as disclosed in the aforementioned U.K.
Patent Applications GB No. 2,116,199A and GB No. 2,140,450A, which are
assigned to applicants' assignee.
The LADD products of the prior U.K. Patent Application GB No. 2,116,199A
and GB No. 2,140,450 exhibit improved rheological properties as evaluated
by testing product viscosity as a function of shear rate. The compositions
exhibited higher viscosity at a low shear rate and lower viscosity at a
high shear rate, the data indicating efficient fluidization and gellation
well within the shear rates extent within the standard dishwasher machine.
In practical terms, this means improved pouring and processing
characteristics as well as less leaking in the machine dispenser-cup,
compared to prior liquid or gel ADD products. For applied shear rates
corresponding to 3 to 30 rpm, viscosities (Brookfield) correspondingly
ranged from about 10,000 to 30,000 cps to about 3,000 to 7,000 cps, as
measured at room temperature by means of an LVT Brookfield viscometer
after 3 minutes using a No. 4 spindle. A shear rate of 7.4 sec.sup.-1
corresponds to a spindle rpm of about 3. An approximate ten-fold increase
in shear rate produces about a 3- to 9-fold reduction in viscosity. With
prior ADD gels, the corresponding reduction in viscosity was only about
two-fold. Moreover, with such compositions, the initial viscosity taken at
about 3 rpm was only about 2,500 to 2,700 cps. The compositions of the
assignee's prior invention thus exhibit threshold fluidizations at lower
shear rates and of significantly greater extent in terms of incremental
increases in shear rate versus incremental decrease in viscosity. This
property of the LADD products of the prior invention is summarized in
terms of a thixotropic index (TI) which is the ratio of the apparent
viscosity at 3 rpm and at 30 rpm. The prior compositions have a TI of from
2 to 10. The LADD compositions tested exhibited substantial and quick
return to prior quiescent state consistency when the shear force was
discontinued.
The present invention is based upon the discovery that the physical
stability, i.e. resistance to phase separation, settling, etc., of the
U.K. Patent Applications GB No. 2,116,199A and GB No. 2,140,450 and the
U.S. patent application Ser. No. 744,754 liquid aqueous ADD compositions
can be significantly improved or not adversely affected while at the same
time significantly increasing the apparent viscosity and improving the
physical stability of the formulations and at lower cost, by adding to the
composition a small but effective amount of an alkali metal salt fatty
acid.
As an example of the improvement in rheological properties, it has been
found that the viscosities at low shear rates, e.g. at a spindle rpm of
about 3, apparent viscosities may often be increased from two- to
three-fold with the incorporation of as little as 0.2% or less, e.g.
0.15%, of the alkali metal fatty acid salt stabilizer. At the same time,
the physical stability may be improved to such an extent that even after a
long time, e.g. 6 months aging at 20.degree. C. (RT), the compositions
containing the alkali metal fatty acid salt stabilizers do not undergo any
visible phase separation.
DETAILED DESCRIPTION OF STABILIZING AGENTS
The preferred alkali metal fatty acid salts are the higher aliphatic fatty
acids having from about 8 to about 24 carbon atoms, more preferably from
about 10 to 24 carbon atoms, and especially preferably from about 12 to 22
carbon atoms, inclusive of the carbon atom of the carboxyl group of the
fatty acid. The aliphatic radical may be saturated or unsaturated and may
be straight or branched. Straight chain saturated fatty acids are
preferred. Mixtures of fatty acids may be used, such as those derived from
natural sources, such as tallow fatty acid, coco fatty acid, soya fatty
acid, etc., or from synthetic sources available from industrial
manufacturing processes.
Thus, examples of the fatty acids which can be used as stabilizers include,
for example, decanoic acid, dodecanoic acid, palmitic acid, myristic acid,
stearic acid, behenic acid, oleic acid, eicosanoic acid, tallow fatty
acid, coco fatty acid, soya fatty acid, mixtures of these acids, etc.
Behenic acid, stearic acid and mixed fatty acids are preferred, with
behenic acid being the most preferred.
The alkali metals that can be used are selected from the Group IA metals of
the Periodic Table Of The Elements. These metals are Li, Na, K, Rb, Cs and
Fr. The Na and K are preferred with the Na being the most preferred.
There may also be used as an alkali metal the NH.sub.4 ammonium cation. The
chlorine bleach compounds are, however, not to be used with the ammonium
fatty acid salt stabilizers, since they are not compatible with chlorine
bleach compounds. In the formulations in which the ammonium fatty acid
stabilizers are used, the chlorine bleach can be omitted or an oxydizing
enzyme can be substituted for the chlorine bleach.
The redox enzymes, also known as oxidoreductase enzymes, can be used in the
present invention. These enzymes catalyze chemical reductions and
oxidations and are involved in the chemical breakdown of foods remaining
on the dishware and utensils that are to be cleaned. Suitable enzymes that
can be used are glucose oxidase, catalase and lipoxidase enzymes.
There can also be used in the formulations of the present invention
proteolytic and amylolytic enzymes and mixtures thereof. The proteolylic
enzymes suitable for use include liquid, powder or slurry enzyme
preparations. Suitable liquid enzyme preparations include "Alcalase" and
"Esperase" sold by Novo Industries, Copenhagen, Denmark. Liquid protease
and liquid amylase enzymes can be used. Suitable alpha-amylase liquid
enzyme preparations are those sold by Novo Industries and Gist-Brocades
under the tradenames "Termamyl" and "Maxamyl", respectively.
The enzymes can be used in amounts of about 0.5 to 3%, preferably about 0.5
to 2.0% and more preferably about 0.5 to 1.5%.
Naturally, for LADD compositions, as well as any other applications where
the invention composition will or may come into contact with articles used
for the handling, storage or serving of food products or which otherwise
may come into contact with or be consumed by people or animals, the use of
the alkali metal fatty acid salts, particularly the Na and K, and the
NH.sub.4 salts as the stabilizing agent are of particular advantage
because of their known low toxicity. For this purpose, the Na and K
stearates are especially preferred as generally safe food additives.
Another distinct advantage of the use of the alkali metal fatty acid salts
as stabilizers is their lower cost as compared to the polyvalent fatty
acid metal salts.
Many of the alkali metal fatty acid salts are commercially available for
example, the sodium stearate is readily available.
Mixed fatty acids, such as the naturally occurring acids, e.g. coco acid,
as well as mixed fatty acids resulting from the commercial manufacturing
process are also advantageously used as an inexpensive but effective
source of fatty acids for use in forming the alkali metal salts.
The amount of the alkali metal fatty acid and ammonium salt stabilizers
used to achieve the desired enhancement of physical stability and apparent
viscosity increase will depend on such factors as the nature of the alkali
metal fatty acid salt, the nature and amount of the thixotropic agent,
detergent active compound, inorganic salts, especially TPP, other LADD
ingredients, as well as the anticipated storage and shipping conditions.
Generally, however, amounts of the alkali metal and ammonium fatty acid
salt stabilizing agents in the range of from about 0.001 to 1%, preferably
from about 0.01 to 0.2%, for example 0.01 to 0.5%, and especially
preferably from about 0.05 to 0.2%, provide the increase in apparent
viscosity and the long term stability and absence of phase separation upon
standing or during transport at both low and elevated temperatures as are
required for a commercially acceptable product.
From the examples to be given below, it will be seen that, depending on the
amounts, proportions and types of physical stabilizers and thixotropic
agents, the addition of the alkali metal fatty acid salts not only
increases physical stability but also provides a simultaneous increase in
apparent viscosity.
The method of formulating the compositions is not critical.
1. According to one method of making these compositions, one should
dissolve or disperse first all the inorganic salts, i.e. carbonate (when
employed), silicate and tripolyphosphate, in the aqueous medium,
Thickening agent is added last. The foam depressor (when employed) is
preliminarily provided as an aqueous dispersion, as is the thickening
agent. The foam depressant dispersion, caustic soda (when employed) and
inorganic salts are first mixed at elevated temperatures in aqueous
solution (deionized water) and, thereafter, cooled, using agitation
throughout. Bleach, surfactant, alkali metal fatty acid salt stabilizer
and thickener dispersion at room temperature are thereafter added to the
cooled (25.degree.-35.degree. C.) solution. Excluding the chlorine bleach
compound, total salt concentration (NaTPP, sodium silicate and carbonate)
is generally about 20 to 50 weight percent, preferably about 30 to 40
weight percent in the composition.
2. A preferred method for mixing the ingredients of the LADD formulations
involves first forming a mixture of the water, foam suppressor (when
employed), detergent, alkali metal fatty acid salt physical stabilizer and
thixotropic agent, e.g. clay. These ingredients are mixed together under
high shear conditions, preferably starting at room temperature, to form a
uniform dispersion. To this premixed portion, the remaining ingredients
are introduced under low shear mixing conditions. For instance, the
required amount of the premix is introduced into a low shear mixer and
thereafter the remaining ingredients are added, with mixing, either
sequentially or simultaneously. Preferably, the ingredients are added
sequentially, although it is not necessary to complete the addition of all
of one ingredient before beginning to add the next ingredient.
Furthermore, one or more of the ingredients can be divided into portions
and added at different times. Good results have been obtained by adding
the remaining ingredients in the following sequence: sodium hydroxide,
alkali metal carbonate, sodium silicate, alkali metal tripolyphosphate
(hydrated), alkali metal tripolyphosphate (anhydrous or up to 5% water),
bleach (preferably, sodium hypochlorite) and sodium hydroxide.
3. In accordance with another method of carrying out the present invention
the ingredients are simply added together in the order listed below with
gentle stirring.
______________________________________
Weight
%
______________________________________
Deionized Water 34-45
Color 1-3
Clay .2-4
Alkali Metal or Ammonium Fatty Acid Salt Stabilizer
.01 to 0.2
Organic Detergent Active Material
0.1-5
Antifoam Agent 0.1-5
NaOH 0.5-6
Sodium Carbonate (Soda Ash) 2-9
Sodium Silicate 5-15
Sodium Tripolyphosphate 20-30
Sodium Hypochlorite (13% available chlorine)
0.2-4
______________________________________
The particular order of adding the ingredients is not critical.
In each of the above three methods specific alkali metal fatty acid salts
can be used and/or mixtures of the alkali metal fatty acid salts can be
used.
Other conventional ingredients may be included in these compositions in
small amounts, generally less than about 3 weight percent, such as
perfume, hydrotropic agents such as the sodium benzene, toluene, zylene
and cumene sulphonates, preservatives, dyestuffs and pigments and the
like, all of course being stable to chlorine bleach compound and high
alkalinity (properties of all the components). In formulations containing
an ammonium fatty acid salt stabilizer, enzymes such as glucose oxidase,
catalase, lipoxidase, proteolytic and amylolytic enzymes can be used in
place of the chlorine bleach. Especially preferred for colouring are the
chlorinated phthalocyanines and polysulphides of aluminosilicate which
provide, respectively, pleasing green and blue tints. TiO.sub.2 may be
employed for whitening or neutralizing off-shades.
The liquid ADD compositions of this invention are readily employed in known
manner for washing dishes, other kitchen utensils and the like in an
automatic dishwasher, provided with a suitable detergent dispenser, in an
aqueous wash bath containing an effective amount of the composition.
While the invention has been particularly described in connection with its
application to liquid automatic dishwasher detergents it will be readily
understood by one of ordinary skill in the art that the benefits which are
obtained by the addition of the alkali metal and ammonium salt fatty
acids, namely increased apparent viscosity and increased physical
stability of the clay based thixotropic suspension, will apply equally
well to other clay based thixotropic suspensions, such as the scouring
paste formulations described in the aforementioned U.S. Pat. No. [b
3,985,668.
The invention may be put into practice in various ways and a number of
specific embodiments will be described to illustrate the invention with
reference to the accompanying examples.
All amounts and proportions referred to herein are by weight of the
composition unless otherwise indicated.
EXAMPLE 1
In order to demonstrate the effect of the alkali metal fatty acid salt
stabilizer, e.g. sodium stearate, a liquid ADD formulation is prepared as
follows.
______________________________________
Percent
______________________________________
Deionized water 41.10
Caustic soda solution
2.20
(50% NaOH)
Sodium carbonate, 5.00
anhydrous
Sodium silicate, 47.5%
15.74
solution of Na.sub.2 O:SiO.sub.2
ratio of 1:2.4
Sodium TPP (substantially
12.00
anhydrous-i.e. 0-5%,
especially 3%, moisture)
(Thermphos NW)
Sodium TPP (hexahydrate)
12.00
(The | | |
