Thixotropic Clay Aqueous Suspensions

The present invention relates to thixotropic clay aqueous suspension with improved physical stability. More specifically the invention relates to the use of metal salts of long chain fatty acids 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. Liquid forms of such compositions, however, generally cannot be used in automatic dishwashers.

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. 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 provision of automatic-dishwasher compositions in gel form having the aforedescribed properties 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 elimination 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 tends 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 Cl-(hypochlorite) bleach but no organic surfactant or foam depressant. 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 bluking agent, thereby replacing water otherwise available for undesired supernatant layer formation due to leaking and phase destabilization. The foregoing are the essential ingreadients. 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. When present, NaTPP is limited to 5%, as stated. Foam killer is not disclosed.

In U.K. patent application GB Nos. 2,116,199A and 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) water, balance.

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. 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 in actual practice, still further improvements in physical stability are required to increase the shelf-life of the product and thereby enhance consumer acceptance.

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 object 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.

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 dishwasher detergent pastes or gels, by incorporating in the clay aqueous suspension a minor amount of a fatty acid metal salt effective to inhibit the settling of the suspended particles and to prevent phase separation.

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 a long chain fatty acid metal 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 a metal salt of a long chain fatty acid which is effective to inhibit settling of the suspended particles, such as thixotropic agent and NaTPP.

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 a thixotropy index of about 2.0 to 10;

(h) 0 to 10% sodium hydroxide;

(i) a polyvalent metal salt of a long chain fatty acid in an amount effective to increase 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.

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 and most preferably at least about 12.5. 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 of the LADD product, as well as impairing the dispensability 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 somehwat 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, it is generally preferred to include a chlorine bleach stable foam depressant or inhibitor. 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 Kuhlman). 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 salts, such as the stearate salts, for example, aluminum stearate, are also effective as foam killers.

Although any chlorine bleach compound may be employed in the compositions of this invention, such as dichloroisocyanurate, 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 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 (NaOCl) solution of from about 11 to about 13% available chlorine in amounts of about 3 to 20%, preferably about 7 to 12%, 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 1:2.2 to 1:2.8. At this point, it should be mentioned that most of the other components of this composition, especially NaOH and sodium hypochlorite, are also often added in the form of a preliminary prepared aqueous dispersion or solution.

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, 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, alkylarylsulphonates and sec.-alkylsuphates. 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.fwdarw.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.rarw.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, myristyldimethylamine 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 0.1 to 10, preferably 1 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 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 metal salt fatty acid 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, smectite, saponite, and the like. Montmorillonite clays are preferred and are available under tradenames such as Thixogel (Registered trademark) No. 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 %. 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 UK patent applications GB No. 2,116,199A and GB No. 2,140,450A.

The LADD products of these prior disclosures 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 extant 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 3000-7000 cps, as measured at room temperature by means of an LVT Brookfield viscometer after 3 minutes using a No. 4 spindle after one day. A shear rate of 7.4 sec.sup.31 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 2500-2700 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 these prior liquid aqueous ADD compositions can be significantly improved, without adversely affecting, and in some cases, advantageously affecting, their rheological properties, by adding to the composition a small but effective amount of a metal salt of a long chain 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 of the fatty acid metal salt stabilizer. At the same time, the physical stability may be improved to such an extent that even after twelve weeks or longer, over temperature ranges extending from near freezing to 40.degree. C. and more, the compositions containing the metal salt stabilizers do not undergo any visible phase separation.

The preferred long chain fatty acids are the higher aliphatic fatty acids having from about 8 to about 22 carbon atoms, more preferably from about 10 to 20 carbon atoms, and especially preferably from about 12 to 18 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 from which the polyvalent metal salt stabilizers can be formed include, for example, decanoic acid, dodecanoic acid, palmitic acid, myristic acid, stearic acid, oleic acid, eicosanoic acid, tallow fatty acid, coco fatty acid, soya fatty acid, mixtures of these acids, etc. Stearic acid and mixed fatty acids are preferred.

The preferred metals are the polyvalent metals of Groups IIA, IIB and IIIB, such as magnesium, calcium, aluminum and zinc, although other polyvalent metals, including those of Groups IIIA, IVA, VA, IB, IVB, VB, VIB, VIIB and VIII of the Periodic Table of the Elements can also be used. Specific examples of such other polyvalent metals include Ti, Zr, V, Nb, Mn, Fe, Co, Ni, Cd, Sn, Sb, Bi, etc. Generally, the metals may be present in the divalent to pentavalent state. Preferably, the metal salts are used in their higher oxidation states. 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 metal salt should be selected by taking into consideration the toxicity of the metal. For this purpose, the calcium and magnesium salts are especially higher preferred as generally safe food additives.

Many of these metal salts are commercially available. For example, the aluminum salts are available in the triacid form, e.g. aluminum stearate as aluminum tristearate, Al(C.sub.17 -H.sub.35 COO).sub.3. The monoacid salts, e.g. aluminum monostearate and diacid salts, e.g. aluminum distearate, and mixtures of two or three of the mono-, di- and tri-acid salts can be used for those metals, e.g. Al, with valences of +3, and mixtures of the mono and di-acid salts can be used for those metals, e.g. Zn, with valences of +2. It is most preferred that the diacids of the +2 valent metals and the triacids of the +3 valent metals, the tetraacids of the +4 metals, and the pentacids of the +5 valent metals, be used in predominant amounts.

The metal salts, as mentioned above, are generally commercially available but can be easily produced by, for example, saponification of a fatty acid, e.g. animal fat, stearic acid, etc., or the corresponding fatty acid ester, followed by treatment with an hydroxide or oxide of the polyvalent metal, for example, in the case of the aluminum salt, with alum, alumina, etc., or by reaction of a soluble metal salt with a soluble fatty acid salt.

Calcium stearate, i.e. calcium distearate, magnesium stearate, i.e. magnesium distearate, aluminum stearate, i.e. aluminum tristearate, and zinc stearate, i.e. zinc distearate, are the preferred polyvalent fatty acid salt stabilizers. Mixed fatty acid metal salts, 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 the long chain fatty acid.

The amount of the fatty acid salt stabilizers to achieve the desired enhancement of physical stability will depend on such factors as the nature of the 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 polyvalent metal fatty acid salt stabilizing agents in the range of from about 0.02 to 1%, preferably from about 0.06 to 0.8%, especially preferably from about 0.08 to 0.4%, provide 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 fatty acid salt not only increases physical stability but also provides a simultaneous increase in apparent viscosity. Ratios of fatty acid salt to thixotropic agent in the range of from about 0.08-0.4 weight percent fatty acid salt and from about 1-2.5 weight percent thixotropic agent are usually sufficient to provide these simultaneous benefits and, therefore, the use of these ingredients in these ratios is most preferred.

According to one preferred 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, fatty acid metal 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 wt %, preferably about 30 to 40 wt % in the composition.

Another highly preferred method for mixing the ingredients of the LADD formulations involves first forming a mixture of the water, foam suppressor, detergent, physical stabilizer (fatty acid salt) 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.

Other conventional ingredients may be included in these compositions in small amounts, generally less than about 3 wt %, such as perfume, hydrotropic agents such as the sodium benzene, toluene, xylene 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). 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 long chain fatty acid metal salt, namely 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. 3,985,668.

Although not wishing to be bound by any particular theory as to the mode of operation of the fatty acid metal salt stabilizers, it is hypothesized that these stabilizers, which are anionic salts, interact with the surface of the cationic clay particles used as the thickening/thixotropic agent whereby the fatty acid moieties help to maintain the clay particles in suspension.

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.

In order to demonstrate the effect of the metal salt stabilizer liquid ADD formulations are prepared with varying amounts of stabilizer and thixotropic thickener,

The mixture is cooled at 25.degree.-30.degree. C. and agitation maintained throughout, and the following ingredients at room temperature are added thereto:

The monostearyl phosphate foam depressant and Dowfax 3B-2 detergent active compound are added to the mixture just before the aluminum tristearate or zinc distearate stabilizer or right before the Gel White H thickener.

Each of the resulting liquid ADD formulations as shown in Table I are measured for density, apparent viscosity at 3 and 30 rpm, and physical stability (phase separation) on standing and in a shipping test. The results are also shown in Table I.

From the data reported in Table I the following conclusions are reached:

The incorporation of 0.2% Al stearate in a 1.5% Gel White H containing formula, as well as the incorporation of 0.1% Al stearate or of 0.1% zinc stearate in a 2% Gel White H containing formula leads to a simultaneous increase of the physical stability and of the apparent viscosity (Table I, Runs 1 (control), 2, 6, and 9.

Similar results are observed with 0.1% calcium distearate or 0.1% Radiastar 1100 incorporated with 2% Pharmagel H (a bentonite clay) (Runs 12 (control), 13 and 14).

The incorporation of 0.1% or 0.2% Al stearate in a 1% Gel White H containing formula, of 0.2% Al stearate in a 0.5% Gel Wbite H containing formula, and of 0.3 to 0.4% Al stearate in a 0.25% Gel White H containing formula leads to an increase of the physical stability without any drastic viscosity increase (Table I, Runs 1 (control), 3, 4, 7, 10 and 11).

For the combination of 0.1% Al stearate and 0.5% Gel White H (Run 8) the apparent viscosity values remain acceptable but no significant improvement in physical stability is obtained.

The polyvalent metal salts of short chain fatty acids do not provide or in fact impair physical stability (Runs 15 and 16).

Using the same composition and preparation method as in Example 1 except that in place of Gel White H as the thixotropic thickener, 2% of Attagel 50 (an attapulgite clay) or 0.4% of Bentone EW (a specially processed Hectorite clay) was used with (Runs 2 and 4) or without (control Runs 1 and 3) aluminum tristearate. The apparent viscosities and physical stabilities were measured in the same manner as described for Example 1. The results are shown in Table II.

From the results shown in Table II, it can be seen that small amounts of aluminum stearate are equally effective in increasing the physical stability of attapulgite clay and hectorite clay based liquid thixotropic automatic dishwasher detergent compositions, with the degree of physical stability increase again being depended on the amounts of stabilizer and thickening agent.

This example shows that inorganic aluminum and zinc salts, including Al.sub.2 O.sub.3, ZnSO.sub.4 and Al.sub.2 (SO.sub.4).sub.3 and sodium stearate do not provide improved physical stability to the liquid thixotropic ADD compositions. Using the same formulation as in Run 6 of Example 1, 0.1% of each of Al.sub.2 O.sub.3, ZnSO.sub.4, Al.sub.2 (SO.sub.4).sub.3 or sodium stearate was used in place of 0.1% aluminum stearate. The results of the measurement of apparent viscosity and physical stability are shown in Table III.

The following gel-like thixotropic liquid ADD is prepared following the same general procedures as in Example 1:

Minor amounts of perfume, color, etc. can also be added to formulation.

This example shows the preparation of liquid ADD formulations using a different preparation technique. The following formulation is prepared using a high shear mixer:

The premix, in the required amount, is transferred into a low shear mixer. The following ingredients are then added sequentially, while stirring, to Part I.