NO169663B - DIFFICULT, TIKSOTROP DETERGENT MIXTURE FOR AUTOMATIC DISHWASHERS - Google Patents

Description

The present invention relates to an aqueous, thixotropic detergent mixture for automatic dishwashers. More specifically, the invention relates to detergent mixtures containing potassium polyphosphates and metal salts of long-chain fatty acids as physical stabilizers for thixotropic, aqueous suspensions.

The addition of small effective amounts of potassium polyphosphates and small effective amounts of multivalent metal

salts of long-chain fatty acids significantly improve the physical stability and variations of rheological properties with time in detergent compositions consisting of thixotropic clay-containing aqueous suspensions. The thixotropic properties can be maintained or improved by using lower levels, such as 0.25 - 0.50%, of the thixotropic clay thickener than in the absence of potassium polyphosphates as stabilizer.

The present invention relates in particular to detergent mixtures for automatic dishwashers which have thixo-

tropical properties, improved chemical and physical stability, improved stability against variations in rheological properties over time, and with increased apparent viscosity, and which are easily dispersible in the washing medium so that crockery, glassware, porcelain and the like can be effectively cleaned.

Commercially available detergents for household dishwashers provided in powder form have several disadvantages, e.g. non-uniform composition; expensive operation required in the manufacture; tendency to agglomerate when stored at high humidity, resulting in the formation of clumps that are difficult to disperse; dustiness, a source of particular irritation for users suffering from allergies;

and propensity for clumping in the dishwasher dispenser.

More recent research and development activity has focused

on the gel form or the "thixotropic" form of such mixtures, e.g. scouring agents and products for automatic dishwashers that are characterized as thixotropic pastes. Products for dishwashers provided in this way are primarily unfortunate in that they are insufficiently viscous

to remain "anchored" in the dispenser container in the dishwasher. Ideally, thixotropic cleaning compounds should be highly viscous at rest, Bingham-plastic in nature and have a relatively high yield stress. However, when subjected to shear forces, such as shaking in a container or squeezing through an orifice, they should fluidize rapidly and rapidly return to the high-viscosity/Bingham plastic state upon cessation of the applied shear force. Stability is also of great importance, i.e. there should be no significant evidence of phase separation or leaching after a long standstill.

NO patent application no. 862360 is directed to dishwashing detergent mixtures consisting of thixotropic clay-containing aqueous suspensions containing aluminum stearate as a physical stabilizer. The mixtures according to NO patent application no. 862360 show improvement with regard to physical stability of the detergent mixture and improvement with regard to phase separation compared to the clay-containing mixtures which do not contain aluminum stearate. However, the mixtures according to NO patent application no. 862360 have in some cases encountered difficulties when it comes to achieving stability against variations in rheological properties with time and over large temperature changes, and have generally required a relatively high clay substance content, such as 0.25 - 2, 0%.

The provision of mixtures for automatic dishwashers in gel form with the previously mentioned properties, apart from the improvements described in the above-mentioned application no. 862360 / has so far proven to be problematic, particularly when it comes to mixtures for use in dishwashers in the home. For effective use, it is generally recommended that automatic dishwasher detergent, hereinafter also referred to as ADD, contains (1) sodium tripolyphosphate (NaTPP) to soften water or dissolve minerals in hard water, and to emulsify and/or peptize soil;

(2) sodium silicate to add the necessary alkalinity for effective washing action and to provide protection for glaze and pattern on fine china; (3) sodium carbonate, which is usually considered to be an eventuality, to increase

alkalinity; (4) a chlorine-releasing agent to aid in the removal of soil stains that lead to water staining; and (5) antifoam/surfactant to reduce suds, thereby promoting machine efficiency and providing necessary washing action. See e.g. SDA Detergents in Depth, "Formulations Aspects of Machine Dishwashing", Thomas Oberle (1974). Cleaning agents that come up against the previously described mixtures are mainly liquids or powders. Mixing such ingredients into a gel form that is effective in home machine use has proven difficult. In general, hypochlorite bleaching is avoided in such mixtures as it tends to react with other chemically active ingredients, particularly surfactant. In US Patent No. 4,115,308, thixotropic pastes for automatic dishwashers are thus described which contain a suspending agent, e.g. CMC, synthetic clay substances or the like; inorganic salts including silicates, phosphates and polyphosphates; a small amount of surfactant and an antifoam. Bleach is not described. US Patent No. 4,147,650 is quite similar, possibly including Cl-(hypochlorite) bleach, but no organic surfactant or antifoam. The product is also described as a detergent slurry without any obvious thixotropic properties. US Patent No. 3,985,668 describes scouring agents with 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, which includes low density powdered polymers, expanded perlite, and the like that have a buoyancy thereby stabilizing effect on the mixture in addition to serving as a bulking agent, whereby water that would otherwise be available for undesired supernatant layer formation due to of seepage and phase destabilisation, are replaced. The above mentioned are the essential components. Optional ingredients include hypochlorite bleach, bleach stable surfactant and buffer, e.g. silicates, carbonates and monophosphates. Builders, such as NaTPP may be included as further possible components to add or supplement building function not provided by the buffer, the amount of such builders not exceeding 5% of the total mixture according to the patent. Maintenance of the desired levels of (greater than) pH 10 is achieved by means of the buffer/builder components. High pH is claimed to minimize decomposition of chlorine bleach and unwanted reaction between surfactant and bleach. When NaTPP is present, as mentioned, it is limited to 5%. Defoamer is not described.

In GB patent applications No. 2 116 199A and 2 140 450A are

the described liquid ADD mixtures that have properties that desirably characterize the thixotropic structure of gel-

type and which includes each of the different components that are necessary for effective washing with an automatic dishwasher. The generally gel-like, aqueous automatic dishwashing detergent compositions with thixotropic properties include the following ingredients on a weight basis:

(a) 5 - 35% alkali metal tripolyphosphate,

(b) 2.5 - 20% sodium silicate

(c) 0-9% alkali metal carbonate,

(d) 0.1 - 5% water dispersible organic detergent active material which is stable to chlorine bleach, (e) 0 - 5% antifoam which is stable to chlorine bleach, (f) chlorine bleach compound in an amount that gives approx.

0.2 - 4% available chlorine,

(g) thixotropic thickener in an amount sufficient to add to the mixture a thixotropic number of approx. 2.5 - 10, (h) sodium hydroxide as needed to adjust pH; and (i) the remainder water.

ADD mixtures designed in this way are low-foaming, easily soluble in the washing medium and most effective at pH values that best contribute to improved cleaning performance,

i.e. pH 10.5 - 14.0. The mixtures usually have a gel consistency, i.e. a rough, opaque jelly-like material with a Bingham plastic character and consequently relatively high yield stresses.

Under such conditions, the mixture fluidizes quickly and disperses easily. When the shearing force is interrupted, the liquid mixture quickly returns to a high-viscosity Bingham plastic state that approaches its former consistency.

NO patent application no. 853170 describes aqueous, thixotropic ADD mixtures with improved stability by incorporating a limited amount of potassium salt, e.g. in the form of potassium tripolyphosphate.

US Patent No. 4,511,487 describes a low-foaming detergent paste for dishwashers. The patented thixotropic cleaning agent has a viscosity of at least 30 Pa.s at 20°C determined with a rotary viscometer with a spindle speed of 5 revolutions per minute. 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 silicate of the hectorite type divided into thin layers. Small amounts of nonionic surfactants and alkali metal carbonates and/or hydroxides may be used.

The formation of organic clay substances by reaction between clay substances (such as bentonite and hectorite) and such organic compounds as quaternary ammonium salts has also been described (W.S. Mardis, JAOCS, Vol. 61, No. 2, p. 382

(1984)).

It is consequently known to use aqueous, thixotropic ADD mixtures containing a potassium salt such as, for example potassium-tripolyph osf at . However, it is not known that it would be possible to achieve a synergistic effect on the stabilization of such mixtures by using both potassium polyphosphate and at least one long-chain fatty acid or a metal salt of a long-chain fatty acid to increase stability while reducing the amount of required clay substance. This synergistic effect is shown in examples 1 and 2, which are discussed later.

Although these previously described liquid ADD compositions do not suffer, or suffer to a lesser degree, from one or more of the above-described deficiencies, it has been found that further improvements in physical stability and stability against variations in rheological properties with time are the desire to increase the shelf life of the product and thereby make the product more acceptable to consumers.

At the same time, it would be highly desirable to increase the physical stability and stability against variations in rheological properties with time in other clay-based thixotropic liquid mixtures, such as scouring agents, toothpastes, "liquid" soaps and the like.

An aim of the invention is to provide liquid ADD mixtures which have thixotropic properties with improved physical stability and improved stability against variations in rheological properties with time.

It is yet another object of the invention to provide thixotropic liquid ADD compositions having reduced levels of thixotropic thickeners without adversely affecting the generally high viscosities at low shear rates, and lower viscosities at high shear rates, which are characteristic of the desired thixotropic properties.

It is yet another object of the invention to improve the stability of aqueous thixotropic clay-based mixtures, in particular liquid detergent pastes or gels for automatic dishwashers, by incorporating into the clay-containing aqueous suspension a smaller amount of potassium polyphosphates and a smaller amount of fatty acid metal salts which effect -tively inhibits the sedimentation of the suspended particles and prevents phase separation.

It is a further object of the invention to improve the stability against variations in rheological properties with time in aqueous thixotropic clay-based compositions, particularly liquid detergent pastes or gels for automatic dishwashers, by incorporating into the clay-containing aqueous suspension a small effective amount of potassium polyphosphates and a small effective amount of a fatty acid metal salt as stabilizing agents.

Incorporation of potassium polyphosphates and metal salt of

a long-chain fatty acid is effective in inhibiting variations in rheological properties with time and effective in inhibiting sedimentation of the slurried particles, such as thixotropic agent and sodium tripolyphosphate building salt.

The present invention thus provides a thixotropic detergent mixture for automatic dishwashers. The detergent mixture is characterized by the fact that, based on weight, it includes:

(a) 5-35% sodium tripolyphosphate,

(b) 2.5-20% sodium silicate,

(c) 0-9% alkali metal carbonate,

(d) 0.1-5% water dispersible organic detergent active material which is stable to chlorine bleach, (e) 0-5% antifoam which is stable to chlorine bleach, (f) chlorine bleach compound in an amount which provides

0.2-4% available chlorine,

(g) thixotropic thickener in an amount sufficient to give the mixture a thixotropic number of 2-10;

(h) 0-8% sodium hydroxide,

(i) an agent that stabilizes physical and rheological properties, comprising 0.5-3% of at least one potassium polyphosphate selected from potassium tripolyphosphate, potassium pyrophosphate and potassium hexametaphosphate, and 0.1-0.5% of a polyvalent metal salt of an aliphatic fatty acid with from 8 to 22 carbon atoms or a mixture of two or more such fatty acids, and

(j) the rest water.

Upon application, the LADD mixture can be easily poured into the dispenser container of the automatic dishwasher and will instantly thicken to its normal gel-like or paste-like state within a few seconds.

In general, LADD efficiency is directly proportional to

(a) level of available chlorine, (b) alkalinity, (c) solubility in washing medium, and (d) foam inhibition. Here, it is preferred that the pH in the LADD mixture is at least approx. 9.5, preferably from approx. 10.5 to 14.0, and preferably at least 11.5. The presence of carbonate is also often required here as it acts as

a buffer that helps to maintain the desired pH

level. However, excess carbonate must be avoided as it causes the formation of needle-like crystals of carbonate and thereby impairs the stability, thixotropy and/or washing effect of the LADD product, as well as impairs the dispensability of the product from e.g. squeeze bottles. Caustic soda (NaOH) serves the additional function of neutralizing phosphoric or phosphonic acid ester defoamers when present. About. 0.5 - 6% by weight NaOH and approx. 2-9 wt% sodium carbonate in the LADD mixture is common, although it should be noted that sufficient alkalinity can be provided by NaTPP and the sodium silicate.

NaTPP used in the LADD mixture in a range from approx.

8 to 35% by weight, preferably approx. 20-30% by weight, should preferably be free of heavy metal which tends to decompose or inactivate the preferred sodium hypochlorite and other chlorine-containing bleach compounds. NaTPP can be anhydrous or hydrated, including the stable hexahydrate with a degree of hydration of 6 which corresponds to approx. 18% water by weight or more. Particularly preferred LADD mixtures are obtained, e.g. when a weight ratio of 0.5:1 to 2:1 between anhydrous and hexahydrated NaTPP is used, values of approx. 1:1 is particularly preferred. Foam inhibition is important to increase dishwasher efficiency and minimize destabilizing effects that can occur due to the presence of too much foam in the washing machine during use. Foam can be satisfactorily reduced by appropriate selection of the type and/or amount of detergent-active material which is the most important foam-producing component. The degree of foaming is also somewhat dependent on the hardness of the washing water in the machine, whereby appropriate regulation of the proportion of NaTPP which has a water softening effect can help to provide the desired degree of foam inhibition. However, it is generally preferred to include a defoamer or inhibitor which is stable against chlorine-containing bleach. Particularly effective are the alkylphosphonic acid esters with the formula that are available under the designation PCUK-PAE, and especially the alkyl acid phosphate esters with the formula

which are available e.g. with the terms SAP and LPKn-158, where one or both of the R groups in each ester type can independently be a C1_2_20 alkyl group. Mixtures of the two types or any other types that are stable against chlorine-containing bleaches, or mixtures of mono- and diesters of the same type, can be used. Particularly preferred is a mixture of mono- and 1~16-18 <a>alkyl acid phosphate esters, such as monostearyl/distearyl acid phosphates, 1,2/1 (Knapsack) or (UGINE KULHPLAN). When antifoam is used,

it is usual with proportions of 0.1 - 5% by weight, preferably approx. 0.1 - 0.5% by weight, in the mixture, the weight ratio between detergent active ingredient (d) and antifoam (e) generally being between 10:1 and 1:1, and preferably between 5:1 and 1:1. Other defoamers that can be used include e.g. the known silicones. In addition, it is an advantageous feature according to the invention that many of the stabilizing salts, such as the stearate salts, e.g. aluminum stearate, are also effective as defoamers.

Although any chlorine-containing bleach compound can be used in the compositions of the invention, such as dichloroisocyanurate, dichloro-dimethyl-hydantoin or chlorinated TSP, alkali metal hypochlorite, e.g. potassium., lithium-. magnesium and especially sodium hypochlorite, preferred. The mixture should contain sufficient chlorine-containing bleaching compound to give 0.2 - 4.0% by weight available chlorine, determined e.g. by acidifying 100 parts of the mixture with an excess of hydrochloric acid. A solution containing approx. 0.2 - 4.0% by weight sodium hypochlorite, contains or provides roughly the same percentage of available chlorine. About. 0.8 - 1.6% by weight available chlorine is particularly preferred. E.g. sodium hypochlorite solution (NaOCl) with from approx. 11 to approx. 13% available chlorine in amounts of approx.

3 - 20%, preferably approx. 7 - 12%.

The sodium silicate, which provides alkalinity and protection of hard surfaces, such as glazes and patterns on fine porcelain, is used in an amount ranging from 2.5 to 20% by weight, preferably 5-15% by weight, in the mixture. The sodium silicate is usually added in the form of an aqueous solution, preferably with a Na 2 O : SiO 2 ratio of 1:2 - 1:2.8.

Detergent-active material that can be used here must be stable in the presence of chlorine bleach, especially hypochlorite bleach, and those belonging to the organic water-dispersible surface-active anion, amine oxide, phosphine oxide, sulfoxide or betaine types are preferred, the former being preferred anionic types are most preferred. They are used in amounts ranging from 0.1 to 5%, preferably 0.3 - 2.0%. Particularly preferred surfactants are the straight-chain or branched alkali metal mono- and/or -di-(Cg_14)-alkyldi-phenyloxide mono- and/or -disulfates or -disulfonates, which are commercially available as "Dowfax 3B-2" and "Dowfax 2A- 1". In addition, the surfactant should be compatible with the other components in the mixture. Other suitable surfactants include the primary alkyl sulfates, alkyl sulfonates, alkyl aryl sulfonates and secondary alkyl sulfates. Examples include sodium C 10 -g alkyl sulfates, such as sodium dodecyl sulfate and sodium tallow alcohol sulfate, sodium C 10 -g alkanesulfonates, such as sodium hexadecyl-1-sulfonate, and sodium C 10 -g alkyl ene sulfonates, such as sodium dodecylbenzene sulfonates. The corresponding potassium salts can also be used.

Like other suitable surfactants or detergents, the amine oxide type surfactants usually have the phoneme P^R^N-O, where R is a lower alkyl group,

e.g. methyl, and R<1> is a long-chain alkyl group with from 8

to 22 carbon atoms, e.g. a lauryl, myristyl, palmityl or cetyl group. Instead of an amine oxide, a corresponding surface-active phosphine oxide R-R^O or sulph-oxide RR 1SO can be used. Surfactant betaine compounds usually have the formula R2R1N-RIC00, where each R is a lower alkylene group with from 1 to 5 carbon atoms. Specific examples of these surfactants are lauryldimethylamine oxide, myristyl dimethylamine oxide, the corresponding phosphine oxides and sulfoxides, and the corresponding betaines, including dodecyldimethylammonium acetate, tetradecyldiethylammonium pentanoate, hexadecyldimethylammonium hexanoate and the like. For reasons of biodegradability, the alkyl group in these surfactants should be straight chain, and such compounds are preferred.

Surfactants of the above-mentioned type, all of which are well known in the art, are described e.g. in US Patent 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 can be organic or inorganic water-soluble, water-dispersible or colloid-forming, and monomeric or polymeric, and should of course be stable in these mixtures , e.g. stable against high alkalinity and chlorine-containing bleaching compounds, such as sodium hypochlorite. Those which are particularly preferred generally comprise the inorganic colloid-forming clay substances of the smectite and/or attapulgite types. These materials were generally used in amounts of 1.5 - 10, preferably 2 - 5% by weight, to provide the desired thixotropic properties and Bingham plastic character in the previously described LADD mixtures

1 the previously mentioned GB patent applications No. 2 116 199A and

2 140 450A. It is one of the advantages of the LADD mixtures according to the present invention that the desired thixotropic properties and Bingham plastic character can be achieved in the presence of the potassium polyphosphates and the metal salt fatty acid stabilizers according to the present invention with smaller amounts of the thixotropic thickeners. E.g. quantities of the inorganic colloid-forming clay substances are usually sufficient

of the smectite and/or attapulgite types in the range from 0.1

to 0.5%, preferably 0.2 - 0.4%, especially 0.25 - 0.30%,

to achieve the desired thixotropic properties and the desired Bingham plastic character when used in combination with the potassium polyphosphates and the fatty acid metal salts as physical stabilizers.

Smectite clays include montomorillonite (bentonite), hectorite, attapulgite, smectite, saponite and the like. Montmorillonite clays are preferred and are available under such trademarks as "Thixogel No. 1" and "Gelwhite GP, H", etc. and "Eccagum GP, H" etc. Attapulgite clays include those materials commercially available under the trade name " Attagel", i.e. "Attagel 40", Attagel 50" and "Attagel 150". Mixtures of the smectite and attapulgite type in a weight ratio of 4:1 - 1:5 can also be used. Thickening or suspending agents of the above-mentioned types is well known in the art, and is described, for example, in the above-referenced US Patent No. 3 9 85 66 8. Abrasives and polishing agents should be avoided in the LADD mixtures as they can mar the surface of fine tableware, crystal and such.

The amount of water in these mixtures should of course not be so high that it gives unreasonably low viscosity and fluidity, or so low that it gives unreasonably high viscosity and low flowability, as thixotropic properties are reduced or destroyed in both cases. Such an amount is easily determined by means of routine tests in any particular case, and usually varies from 30 to 75% by weight, preferably 30 - 65% by weight. The water should also preferably be deionized or softened.

So far, the description of the LADD product, except where otherwise indicated, is consistent with the compositions as described in the previously mentioned GB Patent Applications Nos. 2,116,199A and 2,140,450A.

The LADD products of GB Patent Applications Nos. 2,116,199A and 2,140,450A exhibit improved rheological properties as evaluated by testing product viscosity as a function of shear rate. The mixtures exhibited higher viscosity at a lower shear rate, and lower viscosity at a high shear rate, the data indicating effective fluidization and gelation well within the shear rates found in a standard dishwasher. In practice, this means improved pouring and processing properties as well as less leakage in the machine's dispenser container compared to previously known liquid or gel-like ADD products. For applied shear rates corresponding to 3-30 rpm, the viscosities (Brookfield) varied accordingly from approx. 10,000 - 30,000 eps to approx. 2000 - 6000 eps, measured at room temperature using an LVT Brookfield viscometer after 3 minutes using spindle #4 1 day after manufacture. A cutting speed of 7.4 sec<-1> corresponds to a spindle rpm of approx. 3. An approximate 10-fold increase in cutting speed gives approx. 3 to 9 times reduction in viscosity. With previously known ADD gels, it was a corresponding reduction

in viscosity only approx. 2 times more. In such mixtures, the original viscosity was also measured at approx. 3 rpm only approx. 2500 - 2700 eps. The previously known mixtures thus exhibit the threshold fluidization at lower shear rates and to a significantly greater extent when it comes to incrementally increasing increases in shear rate in relation to incrementally increasing reductions in viscosity. This property of previously known LADD products is summarized by means of a thixotropic number (TI) which is the ratio between the apparent viscosity at 3 rpm and at 30 rpm. The previously known mixtures have a TI of 2 - 10. The tested LADD mixtures showed substantial and rapid return to the previous consistency 1 resting state when the shear force was interrupted.

The present invention is based on the discovery that the physical stability, i.e. resistance to phase separation, sedimentation, etc., according to GB patent applications no. 2 116 199A and 2 140 450A, and according to NO patent application no. 862360 liquid aqueous ADD mixtures can be significant improved or not adversely affected while the stability against variations in rheological properties with time and temperature is significantly improved by the addition of the mixture of a small but effective amount of potassium polyphosphates and small effective amounts 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 approx. 3, apparent viscosities can often be increased from 2 to 3 times by the incorporation of as little as 1-2% or less of the potassium polyphosphates, and as little as 0.25-0.50% of the fatty acid metal salt stabilizer. At the same time, the physical stability can be improved to such an extent that even after 12 weeks or more, over temperature ranges extending from near freezing to 40°C and above, the compositions containing the potassium polyphosphates and metal salt stabilizers are stable against variations in rheological properties with time and the temperature, and does not undergo any visible phase separation.

The potassium polyphosphates which can be used are generally commercially available. Specific examples of potassium polyphosphates are potassium tripolyphosphate (TPP), potassium pyrophosphate and potassium hexametaphosphate. The potassium tripolyphosphate (TPP) is preferred.

The amount of potassium polyphosphates needed to reach

the desired improvement in physical stability will depend on such factors as the properties of the fatty acid salt, the amount of and the properties of the thixotropic agent, detergent active. compound, inorganic salts, sodium TPP, other LADD constituents as well as the expected storage and transport conditions-.

The amounts of potassium polyphosphates as stabilizers (50% AI) which can be used are in the range from 0.5 to 3.0%, preferably 0.8 - 2.0%, particularly preferably 1.0 - 1.8%.

The preferred long-chain fatty acids are the higher aliphatic fatty acids with from 8 to 22 carbon atoms, preferably 10 - 20 carbon atoms and particularly preferably 12 - 18 carbon atoms, including the atom in the carboxyl group of the fatty acid. The aliphatic radical may be saturated or unsaturated, and may be straight chain or branched. Straight-chain saturated fatty acids are preferred. Mixtures of fatty acids that can be used such as those extracted from natural sources, such as tallow fatty acid, coconut fatty acid, soy fatty acid, etc., or from synthetic sources available from industrial manufacturing processes.

Examples of the fatty acids from which the multivalent metal salt stabilizers can be formed include e.g. decanoic acid, dodecanoic acid, palmitic acid, myristic acid, stearic acid, oleic acid, eicosanoic acid, tallow fatty acid, coconut fatty acid, soy 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 IIID, such as magnesium, calcium, aluminum and zinc, although other polyvalent metals, including those from groups 11 IA, IVA, VA, VIA, VHA, IB, IVB, VB, VIB, VIIB and VIII in the periodic table for the elements can also be used. Certain examples of such other multivalent metals include Ti, Zr, V, Nb, Mn, Fe, Co, Ni, Cd, Sn, Sb, Bi, etc. In general, the metals may be present in the divalent to the pentavalent state. The metal salts are preferably used in their higher oxidation states. As is natural for LADD mixtures, as well as for any other applications where the mixture according to the invention will or may come into contact with articles used in the handling, storage or serving of food products, which may otherwise come into contact with or be consumed by people or animals, the metal salt should be chosen taking into account the toxicity of the metal. For this purpose, the calcium and magnesium salts are particularly highly preferred as generally safe food additives.

Many of these metal salts are commercially available. E.g. are the aluminum salts available in the triacid form, e.g. aluminum stearate such as aluminum tristearate, Al (C^-H^COO) ^ • The monoacid salts, e.g. aluminum monostearate, Al (OH) 2 (C^H-^COO) and the diacid salts, e.g. aluminum distearate, Al(OH)C17H35COO)2, and mixtures of two or three of mono-,

The di- and tri-acid salts can be used for the metals with a valence of +3, e.g. Al, and mixtures of the mono- and diacid salts can be used for the metals with a valence of +2, e.g. Zn. It is most preferred that the diacids of the metals with valence +2 and the triacids of the metals with valence +3, the tetraacids of the metals with valence +4 and the pentaacids of the metals with valence +5, are used in dominant amounts. E.g. at least 30%, preferably at least at least 50%, particularly preferably from 80 to 100%, of the total metal salt should be in the highest possible oxidation state, i.e. that each of the possible valence sites is occupied by a fatty acid residue.

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

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. coconut acid, as well as mixed fatty acids resulting from the commercial manufacturing process, are also used with advantage as a cheap but effective source of the long-chain fatty acid.

The amount of the potassium polyphosphates and fatty acid salt stabilizers required to achieve the desired increase in physical stability will also depend on such factors as the properties of the fatty acid salt, the properties and amount of the thixotropic agent, detergent active compound, inorganic salts, NaTPP, other LADD -components as well as the expected storage and transport conditions.

In general, however, quantities of the fatty acid stabilizers with multivalent metal are used in the range from 0.10 to 0.5%, preferably from 0.2 to 0.4%, particularly preferably from 0.25 to 0.30%. The use of the potassium polyphosphates together with the polyvalent metal salts of fatty acids as stabilizers provides the long-term physical stability, stability against variations in rheological properties with time and temperature, and the absence of phase separation after standing or during transport, both at low and high temperatures, as required for a commercially acceptable product.

In another embodiment of the invention, the fatty acid itself can be used as a stabilizing agent instead of the fatty acid metal salts described above.

E.g. are long-chain fatty acids that can be used, aliphatic fatty acids with from 8 to 22 carbon atoms, preferably from 10 to 20 carbon atoms, and most preferably from 12 to 18 carbon atoms, including the carbon atom of the fatty acid's carboxyl group. The aliphatic radical may be saturated or unsaturated, and may be straight chain or branched. Straight-chain saturated fatty acids are preferred. Mixtures of fatty acids may be used, such as those obtained from natural sources, such as tallow fatty acid, coconut fatty acid, soy fatty acid, etc., or from synthetic sources available from industrial manufacturing processes.

Thus, examples of the fatty acids that can be used as stabilizers include, e.g. decanoic acid, dodecanoic acid, palmitic acid, yristic acid, stearic acid, behenic acid, eicosanoic acid, tallow fatty acid, coconut fatty acid, soya fatty acid, mixtures of these acids, etc. Behenic acid, stearic acid and mixed fatty acids can be used.

Many of the fatty acids are commercially available. E.g. stearic acid and behenic acid are readily available. Mixed fatty acids, such as the naturally occurring acids, e.g. coconut acid, as well as mixed fatty acids resulting from the commercial manufacturing process, are also used with advantage as a cheap but effective source of long-chain fatty acids. The sodium and potassium salts of the fatty acids can also be used as stabilizers.

The amount of the fatty acid stabilizers, and/or the sodium or potassium salts thereof, which can be used, is in the same range as the above-mentioned metal salts.

From the examples below it will be seen that, depending

of the amount, proportion and types of physical stabilizer and thixotropic agents, the addition of the potassium polyphosphates and fatty acid salts not only increases physical stability, but also in some cases provides a simultaneous increase in apparent viscosity and provides stability against variations in rheological properties with time and/or temperature .

The physical stabilizers are added just before adding the clay material thickener. Disregarding the chlorine bleach compound, the total salt concentration (NaTPP, sodium silicate and carbonate) is usually

20 - 50% by weight, preferably 30 - 40% in the mixture.

A useful method for mixing the components in the LADD mixtures first comprises forming a mixture of the water, the anti-foam, the detergent, the physical stabilizers (potassium tripolyphosphate and fatty acid salt) and the thixotropic agent, e.g. clay material. These ingredients are mixed together under high shear conditions, preferably starting at room temperature, so that a uniform dispersion is formed. To this premixed part, the remaining components are introduced under mixing conditions at a low shear rate. For example, the required amount of the premix is introduced into a mixer at a low shear rate and then the remaining ingredients are added during mixing, either one after the other or simultaneously. Preferably, the components are added one after the other, although it is not necessary to complete the addition of all of one component before starting to add the next component. Furthermore, one or more of the components can be divided into portions and added at different times. Results have been obtained by adding the remaining ingredients in the following order: sodium hydroxide, alkali metal carbonate, sodium silicate, sodium tripolyphosphate (hydrated), sodium tripolyphosphate (anhydrous or up to 5% water), bleach (preferably sodium hypochlorite) and sodium hydroxide.

Other conventional ingredients may be included

in these mixtures in small amounts, usually less than approx.

3% by weight, such as perfume, hydrotropic agents, such as the sodium benzene, toluene, xylene and cumene sulphonates, preservatives, dyes and pigments and the like, all of which are of course stable against chlorine-containing compounds and high alkalinity (the properties of the constituents). Particularly preferred for dyeing are the chlorinated phthalocyanines and polysulphides of aluminum silicate, which give appealing green and blue hues, respectively. TiC^ can be used for whitening or neutralizing discolourations.

The liquid ADD mixtures according to the invention are easily used in a known manner for washing crockery, other kitchen equipment and the like in an automatic dishwasher which is equipped with a suitable detergent dispenser, in an aqueous washing bath containing an effective amount of the mixture.

Although the invention has been particularly described in connection with its application to liquid detergents for automatic dishwashers, it will be readily understood by those skilled in the art that the advantages obtained by the addition of the potassium tripolyphosphate and the long-chain fatty acid metal salt, namely increased physical stability for the clay-based thixotropic suspension and stability against variations in rheological properties with time, will apply equally well to other clay-based thixotropic suspensions, such as the pasty scouring agents described in the previously mentioned US patent no. 4,985,668.

The invention can be put into practice in various ways and a number of specific embodiments will be described to illustrate the invention in the accompanying examples.

All quantities and proportions referred to herein are based on the weight of the mixture unless otherwise stated.

Example 1

To show the effect of the potassium tripolyphosphate and the metal salt stabilizers, liquid ADD mixtures were prepared with different amounts of the potassium tripolyphosphate and the fatty acid stabilizers and thixotropic clay thickener, as follows:

THIXOTROPIC CLAY MIXTURES

These products were mixed under high shear at room temperature and the following ingredients were then added at room temperature.

The liquid ADD mixtures 1 to 9 were prepared and were measured for density, apparent viscosity at 3 and 30 rpm, and physical stability (phase separation) after standing and in a transport test. The results obtained are shown in tables I and II below.

From the data presented in Tables I and II, the following conclusions were drawn: The incorporation of 0.1% aluminum stearate into a mixture containing 1.25% "Pharmagel H", experiment 2 (control), leads to an increase in the physical stability without changing the apparent viscosity compared to test 1 (control).

The incorporation of 0.4% aluminum stearate in a mixture containing 0.25% "Pharmagel H", experiment 3 (control), compared to experiments 1 (control ) and 3 (control), leads to an increase of the physical stability and of the apparent viscosity. The use of the higher aluminum stearate level of 0.4%, trial 3 (control), also enables the reduction of the clay content level from 1.25%, trial 2 (control), to 0.25%, trial 3 ( control), while maintaining the physical stability of the mixture.

The data in Table I also show that a simultaneous application of approx. 1.6% potassium TPP in a mixture containing 0.5% or 0.3% "Pharmagel H", trials 4 and 6, does not adversely affect the physical stability of the mixtures, while allowing stabilization of the variations in a rheological capacity over time.

Notes to Table I

(1) Measured with spindle 4 after 3 minutes on 24-hour-old samples.

(2) At altitude (RT=room temperature=20<±>2°C).

(3) By weight (RT=room temperature=20<±>2°C).

(4) Liquid separation measured after 6 weeks and 2000 km in a private car (by weight in a plastic bottle).

Example 2

To determine the variations in rheological properties with time, the apparent viscosities in runs 2 - 7 of Example 1 were measured at 3 rpm and 30 rpm after 1 day, 2 weeks, 4 weeks, 6 weeks and 12 weeks, and the data obtained are reproduced in Table II below.

The data in Table II show that the addition of 1.6%

(experiments 4, 6 and 7) leads to a strong stabilization of the variations in the rheological properties over time, without the physical stabilities of the mixtures changing at clay-substance f contents of "Pharmagel H" of 0.3 and 0.5% , compared to experiments 3 (control) and 5 (control) which exhibit be-. clear variations with time in apparent viscosity.

Example 3

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

It may also add smaller amounts of perfume, color, etc. to the mixture.

The mixture was found to have good thixotropic properties, good stability against phase separation and good variation of rheological properties with time.

Example 4

A gel-like thixotropic liquid ADD was prepared as in Example 3, with the change that 1.6% (50% AI) of potassium pyrophosphate was used instead of potassium TPP. Similar results were obtained as according to Example 3.

Example 5

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

Smaller amounts of perfume, dye, etc. can also be added to the mixture.

Example 6

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

Smaller amounts of perfume, colour, etc. can also be added to the mixture.

Claims (7)

1. Aqueous, thixotropic detergent mixture for automatic dishwashers, characterized in that, based on weight, it comprises: (a) 5-35% sodium tripolyphosphate, (b) 2.5-20% sodium silicate, (c) 0-9% alkali metal carbonate, (d) 0.1-5% water-dispersible organic detergent active material stable to chlorine bleach, (e) 0-5% defoamer stable to chlorine bleach, (f) chlorine-bleach compound in an amount giving 0.2-4% available chlorine. (g) thixotropic thickener in an amount sufficient to give the mixture a thixotropic number of 2-10, (h) 0-8% sodium hydroxide, (i) an agent that stabilizes physical and rheological properties, comprising 0.5-3% of at least one potassium polyphosphate selected from potassium tripolyphosphate, potassium pyrophosphate and potassium hexametaphosphate, and 0.1-0.5% of a polyvalent metal salt of an aliphatic fatty acid having from 8 to 22 carbon atoms or a mixture of two or more such fatty acids, and (j) the balance water . 2. Mixture according to claim 1, characterized in that the multivalent metal salt comprises a metal from group II, III or IV in the periodic table. 3. Mixture according to claims 1-2, characterized in that the multivalent metal salt is an aluminium, zinc, calcium or magnesium salt. 4. Mixture according to claims 1-3, characterized in that the multivalent metal salt is aluminum stearate, calcium stearate, zinc stearate or magnesium stearate. o 5. Mixture according to claim 1, characterized in that the fatty acid contains from 12 to 18 carbon atoms. 6. Mixture according to claim 1, characterized in that the thixotropic thickener (g) is an inorganic colloid-forming clay substance f. 7. Mixture according to claims 1 and 6, characterized in that it contains 0.2-0.4% by weight clay substance, 0.8-2.0% by weight potassium polyphosphate and 0.2-0.4% by weight fatty acid metal salt.