NO167517B - DIFFICULT, TIKSOTROP, LIQUID CLEANING MIXING FOR AUTOMATIC DISHWASHER AND USING THE CLEANING FOR CLEANING SERVICE. - Google Patents

Description

The present invention relates to an aqueous, thixotropic, liquid cleaning mixture for automatic dishwashers,

as well as using the mixture for cleaning tableware.

The cleaning mixture according to the invention has thixotropic properties, improved chemical and physical stability, and increased apparent viscosity, and is easily dispersible in the washing medium so that it provides effective cleaning of crockery, glassware, porcelain and the like.

Commercially available washing-up agents for household machines which are produced in powder form have several disadvantages, e.g. uneven composition, expensive operations required in the manufacture, tendency to stick together when stored in high humidity leading to the formation of lumps which are difficult to disperse, dust so that they are a source of particular irritation to users suffering from allergies, and tendency for gluing together in the dishwasher's dispenser. However, liquid forms of such mixtures cannot generally be used in automatic dishwashers due to strong foaming, unacceptably low viscosity values and excessively high alkalinity.

More recent research and development activity has focused

on the gel form or the "thixotropic" form of such mixtures, which are insufficiently viscous to remain "anchored" in the dispenser container in the dishwasher, and which also leave stain residues on crockery, glassware, porcelain and the like. Ideally, thixotropic cleaning mixtures should be highly viscous in a quiescent state, Bingham plastic in nature and have relatively high yield stress values. When subjected to shear forces, such as being shaken in a container or squeezed through an opening, however, they should rapidly fluidize and, and upon cessation of the applied shear force, rapidly return to the high-viscosity/Bingham plastic state. Stability is also of great importance, i.e. there should be no significant signs of phase separation or liquefaction after long-term storage.

The provision of mixtures in gel form with the above-mentioned properties for automatic dishwashers has thus far proved problematic, particularly when it comes to mixtures for use in domestic dishwashers. For effective use, it is usually recommended that the detergent for the automatic dishwasher, hereinafter also referred to as ADD, contains (1) sodium tripolyphosphate (NaTPP) to soften or bind minerals in hard water and emulsify and/or peptize dirt, (2) sodium silicate to add the necessary alkalinity for effective washing action and to provide protection for fine porcelain glazes and patterns, (3) sodium carbonate which is usually considered an eventuality, to increase alkalinity, (4) a chlorine releasing agent to aid in the removal of dirt spots that lead to water spotting, and (5) defoamer/surfactant to reduce foam, thereby increasing machine efficiency and adding needed washing power.

See e.g. SDA Detergents in Depth, "Formulations Aspects of Machine Dishwashing", Thomas Oberle (1974). Cleaning agents that come up against the above-described mixtures are usually liquids or powders. It has proven difficult to combine such ingredients in a gel form that is effective when used in a home washing machine. In general, hypochlorite bleach is avoided in such compositions as it tends to react with other chemically active ingredients, particularly surfactant, thereby breaking down the suspending or thixotropic agent and impairing its effectiveness. Thus, US patent document no. 4,115,308 describes thixotropic pastes for automatic dishwashers which contain a suspending agent, e.g. CMC, synthetic clay substances or similar, inorganic salts, including silicates, phosphates and polyphosphates, a small amount of surfactant and a foam suppressant. Bleach is not described. US Patent No. 4,147,650 describes a similar mixture which optionally includes Cl-(hypochlorite) as a bleaching agent, but no organic surface-active agent or any anti-foaming agent. The product is also described as a detergent slurry without any apparent thixotropic properties.

US Patent No. 3,985,668 describes abrasive scouring agents with gel-like consistency containing (1) suspending agent, preferably clay substances of the smectite and attapulgite type, (2) abrasive, e.g. silica sand or perlite, and (3) fillers comprising powdered polymers of low density, expanded perlite and the like, which have a buoyancy and thus stabilizing effect on the mixture in addition to serving as a bulking agent, thereby replacing water which would otherwise would be available for undesired formation of a supernatant layer due to leaching and phase destabilization. The above mentioned are 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 additional optional ingredients to add or supplement a building function not provided by the buffer, the amount of such builder not exceeding 5% of the total mixture according to the patent. Maintenance of the desired pH levels (greater than) 10 is achieved by means of the buffer/builder components. High pH is claimed to minimize decomposition of chlorine bleach and unwanted interaction between surfactant and bleach. When NaTPP is present, it is limited to 5% as indicated. Defoamer is not described.

In GB patent applications No. 2 116 199A and 2 140 250A are

it described liquid ADD mixtures with properties desirably characteristic of gel-type thixotropic structure and comprising each of the various components necessary for effective washing action in an automatic dishwasher. The normally gel-like aqueous detergent mixture for automatic dishwashers with thixotropic properties comprises the following components by weight:

(a) 5 - 35% alkali metal tripolyphosphate,

(b) 2.5 - 20% sodium silicate,

(c) 0-9% alkali metal carbonate,

(d) 0.1 -5% organic detergent active material which

is chlorine bleach stable and water dispersible,

(e) 0-5% antifoam which is stable against 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 give the mixture a thixotropic number of about 2.5; - 10, and. (h) sodium hydroxide as needed to adjust pH. The ADD mixtures formulated in this way are low-foaming, easily soluble in the washing medium and very effective at pH values which are best when it comes to contributing to improved cleaning performance, i.e. pH 10.5 - 13.5. The mixtures usually have a gel consistency, i.e. they are a very viscous,

opaque jelly-like material with Bingham-plastic character and thus relatively high yield stresses. Accordingly, a certain shear force is required to initiate or increase flow, such as would be achieved in the dispensing container with agitation in an automatic dishwasher during operation. Under such conditions, the mixture fluidizes quickly and disperses easily. When the shearing force is interrupted, the fluid mixture rapidly returns to a high-viscosity, Bingham-plastic state close to its previous consistency.

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 rotational viscometer at a spindle speed of 5 revolutions per minute. minute. The mixture 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 amounts of nonionic surfactants and alkali metal carbonates and/or hydroxides may be used.

The formation of organoclays by reaction between clay substances (such as bentonite and hectorite) and 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 described liquid ADD mixtures do not have, or have to a lesser extent, one or more of the above-described deficiencies, it has been found that in practice still further improvements are required with regard to

physical stability to increase the shelf life of the product

thereby making it more acceptable to the consumer.

According to prior art, the physical stability of clay-based thixotropic liquid mixtures is improved by adding small amounts, e.g. from approx. 0.02 to 1% by weight, of a multivalent . metal salt of a long-chain fatty acid, such as aluminum stearate.

Although the combination of clay as a thickener,

and fatty acid salt as a stabilizer, have been found to provide satisfactory long-term stability, such as the absence of phase separation for a period of up to 12 weeks or more, the addition of clay to these mixtures has several disadvantages.

When clay thickeners are used, e.g. the order of addition of the various components and the regulation of the process conditions during the formation of the mixtures are of decisive importance in order to achieve the desired thixotropic properties and low foaming characteristics. In addition, the clay thickeners are expanding materials and can contribute significantly to the price of the final product for the consumer. In some cases, the clay thickeners can actually work

the total cleaning effect.

Accordingly, it is an object of the invention to provide stable, thixotropic, aqueous cleaning agents where the use of clay thickeners is avoided.

It is another object of the invention to provide liquid ADD mixtures with thixotropic properties and with improved physical stability and improved rheological properties.

It is yet another object of the invention to provide thixotropic liquid ADD mixtures with reduced levels of thixotropic thickener without adversely affecting the generally high viscosity values at low shear rates, and low viscosity values at high shear rates, which are characteristic of the desired thixotropic properties.

More generally, it is an object of the invention to provide stable, aqueous, thixotropic, liquid, non-clay-based cleaning compositions for automatic dishwashers, by incorporating into the clay-free aqueous suspension a small amount of a fatty acid which acts to inhibit the sedimentation of slurries particles and prevents phase separation.

These and other objects of the invention, which will be more easily understood from the detailed description below and preferred embodiments thereof, are achieved by incorporating into an aqueous liquid detergent mixture a small, but effective, determined amount of a non-clay-containing, non-polymeric thixotropic agent which is an aliphatic fatty acid. More specifically, according to the invention, a normal gel-like detergent mixture for automatic dishwashers is provided in which from 0.03 to 0.5% by weight of the mixture of an aliphatic fatty acid with 8-22 carbon atoms, dimers or trimers thereof, is incorporated, which acts to inhibit sedimentation of the suspended particles, such as alkali metal building salts, etc., without the need for any clay, polymeric or other thickening agent.

In accordance with this, the present invention provides an aqueous, thixotropic, liquid cleaning mixture for automatic dishwashers which is characterized in that it comprises on a weight basis:

(a) 5 - 35% alkali metal tripolyphosphate,

(b) 2.5 - 40% sodium silicate,

(c) 0-9% alkali metal carbonate,

(d) 0.1 - 5% chlorine bleach stable, water dispersible,

organic4 detergent-active material,

(e) 0-5% chlorine bleach stable defoamer,

(f) chlorine bleach compound in an amount which provides

0.2 - 4% available chlorine,

(g) 0.03 - 0.5% of an aliphatic fatty acid with 8-22

carbon atoms, dimers or trimers thereof,

(h) 0-8% sodium hydroxide

(i) the rest water.

In connection with this, the invention also provides a use of the mixture for cleaning crockery in an automatic dishwasher with an aqueous wash bath containing an effective amount of the liquid cleaning mixture for automatic dishwashers (LADD) as described above. In use, the LADD. mixture can be easily poured into the dispenser container in the automatic dishwasher and within just a few seconds will immediately thicken to its normal gel-like or paste-like state so that it is safely retained in the dispenser container until shear forces are applied again, such as by the splash of water from the dishwasher.

The invention will be described in more detail below with the help of specific embodiments and with the help of the following drawing, where the figure is a graphical representation of thixotropic numbers for two different mixtures according to the present invention and a clay-thickened liquid detergent mixture for automatic dishwashers as described in GB patent application no. 2 140 450A.

The LADD products according to the previous disclosures in the above-mentioned GB Patent Applications Nos. 2,116,199A and 2,140,450A, and according to other prior art exhibit improved rheological properties as determined by testing product viscosity as a function of shear rate. The mixtures showed higher viscosity at a low shear rate and lower viscosity at a high shear rate, the data indicating effective fluidization and gel formation well within the shear rates found in standard type dishwashers. In practice, this means improved pouring and impact properties, as well as less leakage in the machine's dispenser container compared to previously known liquid or gel-form ADD products. For added shear speeds corresponding to 3-30 rpm, the viscosity values (Brookfield) varied accordingly from approx. 10,000 - 30,000 eps to approx. 3000 - 7000 eps measured at room temperature using an LVT Brookfield viscometer after 3 minutes using a No. 4 spindle. A shear rate of

7.4 seconds corresponds to a spindle rpm of approx. 3. An approximately 10-fold increase in cutting speed gives approx. 3 to 9 times reduction in viscosity. The mixtures according to the previous invention thus exhibit threshold fluidizations at lower shear rates and a significantly greater extent in terms of stepwise increases in shear rate versus stepwise decreases in viscosity. This characteristic of the LADD products

according to the previous invention is summarized as a thixotropic index (TI) which is the ratio between the apparent viscosity at 3 rpm and at 30 rpm. The prior art compositions have a TI of 2 to 10. The LADD compositions should exhibit substantial and rapid return to the previous consistency in the resting state when the shear force is discontinued.

While the determination of thixotropic index TI as a ratio of apparent viscosity at 3 and at 30 rpm provides a satisfactory measure of product applicability, further research and experience have shown that a more reliable measure of thixotropic index and product applicability as a liquid ADD is obtained by determining the thixotropy as a measure of the area

in the hysteresis loop obtained by plotting, under the conditions described below, of shear stress, S,

as a function of shear rate, i) , when the shear rate is increased from 0 to a maximum value and then returns to 0. The larger the area in the hysteresis loop, the larger the thixotropic index. Expressed as apparent viscosity, it has also been confirmed that as long as the viscosity at room temperature (22 - 1°C) measured in a Brookfield viscometer HATD using a No. 4 spindle at 20 rpm,

is less than approx. 20,000 eps, the mixture can be easily shaken so that a thixotropic mixture can be easily "fluidized" or "liquefied" so that the product can be dispensed through a conventional squeeze bottle or other suitable dispenser.

The present invention is based on the surprising discovery that the same or improved rheological properties and physical stability, i.e. resistance to phase separation, sedimentation, etc., as in the previously known liquid aqueous ADD mixtures, can be achieved at significantly lower cost and without any special processing requirements, by adding a small but effective amount of a long-chain fatty acid to the mixture instead of the thixotropic clay thickener, and optionally also the metal salt of the fatty acid. At the same time, improvements can be achieved with regard to spotting and film formation (ie fewer spots and reduced film formation).

As an example of the improvement in rheological properties over a standard clay-based thixotropic fluid ADD, reference is made to the attached drawing which is a plot of shear stress, S, as a function of shear rate,^ , for a clay-based LADD (3 wt % clay) (curve 1), and for two similar LADD mixtures where the clay is replaced by 0.06 wt% stearic acid (curve 2) or by 0.08 wt% stearic acid (curve 3). Shear stress, S, is measured in a static test using a Haake RV-3 machine equipped with a coaxial container. The sample is placed in the outer container and the inner container is rotated by the machine at progressively increasing shear rates to a maximum of 13 seconds \ and then the shear rate is progressively reduced to 0. The response is automatically measured as shear stress. The experiments were carried out using an MV II sensor system (constant values, A = 3.76 Pa, M = 0.9 sec- ). The area between the resulting curved lines for each sample is a measure of thixotropy, with larger areas indicating higher thixotropy. The pour point of each sample can also be determined from the curves shown in the figure; the yield point is the maximum stress in the shear stress versus shear rate curve. At the same time, the physical stability is such that even after 6 weeks or more, over temperature ranges extending from near freezing to 40°C and more, the mixtures containing the fatty acid thickeners do not undergo any visible phase separation.

The preferred long-chain fatty acids are the higher aliphatic fatty monocarboxylic acids with from 8 to 22 carbon atoms, preferably from 10 to 20 carbon atoms, and particularly preferably from 12 to 18 carbon atoms, including the carbon atom in the carboxyl group of the fatty acid. Polycarboxylic acids can also be used. The aliphatic radical may be saturated or unsaturated, and may be straight chain or branched. It is preferred with straight-chain saturated fatty acids. Mixtures of fatty acids may be used, such as those derived 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 fatty acids that can be used as thickeners in place of the clay or polymer thickeners include, e.g. decanoic acid, lauric acid, dodecanoic acid, palmitic acid, myristic acid, stearic acid, oleic acid, eicosanoic acid, tallow fatty acid, coconut fatty acid, soya fatty acid and mixtures of these acids. In addition, the dimers or trimers of these acids can also be used. Stearic acid and mixed fatty acids, e.g. coconut fatty acid, is preferred.

Within the ranges of carbon chain lengths of the monocarboxylic fatty acids indicated here, the viscosity of the product tends to decrease as the number of carbon atoms in the monocarboxylic fatty acid decreases. No systematic trends are observed for the dimers or trimers or polybasic carboxylic acids.

The amount of fatty acid thickener to achieve the desired values for thixotropy and physical stability will depend on such factors as the properties of the fatty acid, the detergent-active compound, the inorganic salts, especially TPP, the other LADD components, as well as the expected storage and transport conditions .

In general, however, amounts of the thixotropic fatty acid agent are in the range from 0.03 to 0.5%, preferably from 0.03 to 0.2%, particularly preferred. from 0.03 to 0.08%, the long-term stability and absence of phase separation after standing or during transport both at low and elevated temperatures, which is required for a commercially available product.

In general, LADD efficiency is directly related to (a) available chlorine levels, (b) alkalinity, (c) solubility in washing medium, and (d) foam inhibition. It is preferred that the pH in the LADD mixture is at least approx. 9.5, preferably from 10.5 to 13.5 and most preferably at least approx. 11.5. At relatively low pH values, the LADD product is too viscous, i.e. almost solid, and does not fluidize easily below the shear force levels created in the dispenser container under normal operating conditions for the machine. Actually, the mixture loses a lot, if not all,

of its thixotropic character. Addition of NaOH is thus often required to increase the pH to the above-mentioned areas, and to increase the flowability properties. The presence of carbonate is also often required as it acts as a buffer to help maintain the desired pH level. However, excess carbonate must be avoided as it can cause

formation of needle-like crystals of carbonate and thereby disrupt the stability, thixotropy and/or washing effect of the LADD product, as well as disrupt 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. 0.5-3 wt% NaOH and 2-9 wt% sodium carbonate in the LADD mixtures is typical, although it should be noted that sufficient alkalinity can be provided by NaTPP and the sodium silicate.

NaTPP can be used in the LADD mixture in a range from

5 to 35% by weight, preferably 20-30% by weight, and should preferably be free of heavy metal which tends to decompose or inactivate the preferred sodium hypochlorite and other chlorine 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. On the basis of the stability of the hexahydrate, the presence of some water of hydration is actually very effective as it is believed to serve to form crystallization nuclei of the stable hexahydrate which promotes hydration and soluble? removal of the remaining NaTPP particles. If only the hexahydrate is used, the detergent product may be too liquid and may have little, if any, thixotropic character. If, on the other hand, only the anhydrous NaTPP is used, the product may in some cases be too thick and therefore unsuitable. Particularly preferred LADD mixtures are obtained, e.g. when a 0.5:1 to 2:1 weight ratio of anhydrous to hexahydrated NaTPP is used, values of approx. 1:1 is particularly preferred.

Foam inhibition is important to increase the dishwasher's efficiency and minimize destabilizing effects that can occur due to the presence of excess foam in the washing machine during use. Foam can be sufficiently reduced by suitable 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, so that appropriate regulation of the relative amounts 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 chlorine bleach stable defoamer or inhibitor. Particularly effective are the alkylphosphonic acid esters with the formula:

e.g. commercially available as "PCUK-PAE", and in particular the alkyl acid phosphate esters of the formula

e.g. commercially available as "SAP" and "LPKn-158", where one or both R groups in each ester type may independently be a C^2~C20 alkvl<?ruPPe* Mixtures of the two types, or any other chlorine bleach-stable types, or mixtures of mono- and diesters of the same type, can be used. Particularly preferred is a mixture of mono- and di-C^g-C^g alkyl acid phosphate esters, such as mono-stearyl distearyl acid phosphates 1.2/1. When antifoam is used, it is typically with proportions of 0.01-5% by weight, preferably 0.1-5% by weight, especially 0.1-0.5% by weight, in the mixture, the weight ratio between detergent-active compound (d)

and defoamer(s) typically ranges from 10:1 to 1:1, and preferably from 4:1 to. 1:1. Other defoamers that can be used include e.g. the known silicones.

Although any chlorine bleach compound can be used in the compositions according to the invention, such as dichloroisocyanurate, dichlorodimethylhydantoin or chlorinated TSP, it is preferred to use alkali metal hypochlorite, e.g. potassium, lithium, magnesium and especially sodium hypochlorite. The mixture should contain sufficient chlorine bleaching compound to provide 0.2 - 4% by weight available chlorine, e.g. determined by acidifying 100 parts of the mixture with excess hydrochloric acid.

A solution containing 0.2-4% by weight of sodium hypochlorite contains or gives roughly the same percentage of available chlorine. It is particularly preferred with 0.8 - 1.6% by weight of available chlorine. E.g. a sodium hypochlorite solution (NaOCl) with 11 - 13% available chlorine can advantageously be used in amounts from 3 to 20%, preferably 7 - 12%.

The sodium silicate which provides alkalinity and protection of hard surfaces, such as fine porcelain glazes and patterns, is used in an amount varying from 2.5 to 40% by weight, preferably 10 to 35% by weight, in the mixture. At the higher levels indicated here, e.g. at levels higher than approx. 10% by weight, the silicate also provides an increased anti-stain effect. The sodium silicate is generally added in the form of an aqueous solution, preferably with a Na20:SiO2 ratio of 1:2.2-1:2.8, e.g. 1:2,4. Most of the other ingredients in the mixture, particularly NaOH, sodium hypochlorite and anti-foam can also be added in the form of an aqueous dispersion or solution.

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 anionic, amine oxide, phosphine oxide, sulfoxide or betaine types of surface-active aqueous dispersible agents are preferred, the former being anionic most preferred. They are used in amounts varying from 0.1 to 5%, preferably 0.3 to 2.0%. Particularly preferred surfactants are the straight-chain or branched alkali metal mono- and/or -di-(C8-C14)alkyldiphenyl oxide mono- and/or -disulphates, commercially available e.g. such as Dowfax<®> 3B and Dowfax<®> 2A-1. In general, the alkane sulfonates tend to damage, if not destroy, thixotropy, being found to increase viscosity excessively and thereby cause serious shear problems. 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 1 -C 18 -alkyl sulfates, such as sodium dodecyl sulfate and sodium tallow alcohol sulfate, sodium C 2 -C 3 -alkanesulfonates, such as sodium hexadecyl-1-sulfonate, and sodium C 2 -C 3 -alkyl kenzene sulfonate °nates' such as sodium dodecylbenzene sulphonates, the corresponding potassium salts can also be used.

Like other suitable surfactants or detergents, the amine oxide surfactants usually have the structure RR^"SO, where each R is a lower alkyl group, eg, methyl, and R"1" is a long-chain alkyl group of 8-22 carbon atoms, eg a lauryl, myristyl, palmityl or cetyl group. Instead of an amine oxide, a corresponding surfactant of the phosphine oxide type, R9R<1>P0, or sulfoxide type, RR1SO, can be used. Surfactants of the betaine type usually has the structure R2R 1 N - R"COO -, where each R is a lower alkylene group with 1-5 carbon atoms. Specific examples of these surfactants are lauryl dimethylamine oxide, myristyldimethylamine oxide, the corresponding phosphine oxides and sulfoxides, and the corresponding betaines, including dodecyldimethylammonium acetate, tetradecyldiethylammonium pentanoate, hexadecyldimethylammonium hexanoate. For reasons of biological degradability, the alkyl groups 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 e.g. described in US Patent Nos. 3,985,668 and 4,271,030.

The amount of water in these mixtures should, of course, be neither so high that it gives unreasonably low viscosity and fluidity, nor so low that it gives unreasonably high viscosity and low flowability, as thixotropic properties are reduced or destroyed in both cases. The amount is easily determined by routine testing in each particular case, and usually varies from 25 to 75% by weight, preferably from 55 to 65% by weight. The water should also preferably be deionized or softened.

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 cumenesulfonates, preservatives, dyes and pigments and the like, all of which are of course stable against chlorine bleach compounds and

high alkalinity (characteristics of all the components). Particularly preferred for dyeing are the chlorinated phthalocyanines and polysulphides of aluminosilicate, which give attractive green and blue colors respectively. TiG^ can be used to whiten or neutralize unappealing shades.

The liquid ADD mixtures according to the invention are easily used in a known manner for washing crockery, other kitchenware 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 specifically described in connection with its use in liquid detergents for automatic dishwashers, it will be readily understood by those skilled in the art that the advantages of thixotropy and physical stability obtained by the addition of the fatty acid may equally apply to the replacement of clay-containing or polymeric thickeners in other clay or polymer-based thixotropic suspensions, such as the scouring compounds described in

the previously mentioned US Patent No. 3,985,668, dental pastes and the like.

The invention can be practiced in various ways and a number of specific embodiments will be described in the examples below to illustrate the invention.

All amounts and proportions shown herein are based on the weight of the mixture unless otherwise stated.

Example 1

To show the effect of the fatty acid thickener, liquid ADD mixtures were prepared with varying amounts of fatty acid as a thixotropic thickener (experiments 1, 2 and 3), as shown in Table 1. For comparison, a similar mixture (experiment no. 4) corresponding to to the mixture according to example 1 in GB patent application no. 2 140 450A, prepared according to the method described in the example.

A sample of each of the mixtures according to Tests No. 2 and 3 and the clay-based comparative mixture (Test No. 4) was subjected to the shear stress measurement using the Haake RV-3 machine as described above to determine the thixotropic index and the pour point. The results are shown in the figure where curve 1 is based on the sample from trial no. 4, curve 2 is based on the sample from trial no. 2 and curve 3 is

based on the sample from trial no. 3. The value for pour point,

the maximum value of shear stress, S, is shown in Table 2.

Other properties are also shown in Table 2, including the apparent viscosity, f), measured on a 24 hour old sample using a Brookfield HATD viscometer using a #4 spindle at 20 rpm (T = 221°C); density; capillary drainage rate; stability and centrifugation. Capillary drainage rate (CDR) is a measure of stability, with higher values indicating higher stability. CDR measurements were made using the following procedure: Whatman No. 1 filter paper with a marked circle of diameter 6.4 cm was placed on a flat glass plate, 10 cm x 10 cm. A 6.4 cm long plastic tube with a 3.4 cm diameter was placed in an upright position in the middle of the circle. The tube was filled with the sample of liquid ADD mixture (after standing for 1 day). The time required for the solvent to seep out of the tube and reach the marked circle was measured. The time was measured on three sides of the circle and the average value calculated. Shorter times mean that the gel does not hold back the solvent (water) successfully, so that this can seep into the filter paper. Time periods that are greater than approx. 7 minutes (all samples), is acceptable. The stability measurement was made by placing the sample in a glass bottle which was kept at room temperature, and observing the percentage separation at the end of a period of 4 weeks. The centrifugation test is also a measure of stability. Glass centrifuge tubes were filled with equal volumes of each sample and centrifuged vertically, i.e. in a plane parallel to the substrate, in a Sorwall centrifuge for 25 minutes at 500 rpm. Then the volume of the clear liquid was measured. The results are expressed as the ratio of the height of clear liquid to the total height of the sample multiplied by 100, i.e.

Lower numbers indicate greater stability.

The data in Table 2 clearly show the superior phase separation stability of the stearic acid based compositions compared to the clay based composition. These results, together with the thixotropy properties indicated by means of the graphical representations in the figure, further show the superiority of the preparations according to the invention in terms of leaching from the container in the dishwasher.

Example 2

Each of the compositions from Trials 1-4 of Example 1 was tested to compare cleaning performance (buildup of stains and films on glassware) using a Kenmore dishwasher using tap water with a temperature of 54°C and a hardness of 120 ppm. The test procedure is described in ASTM D3566-79, except that only four cleaning cycles were used. The film formation and staining were assessed according to the following scales:

Scale for judging film formation

1. Best, apparently no movie.

2. Slight film formation, which becomes visible.

3. Noticeable film formation, increasing.

4. Steady increase of significant film formation.

5. The film formation becomes strong.

6. Strong film formation, strong build-up.

7. Steady increase of heavy film formation.

Scale for judging spots

A. Best, no stains.

B. Very few visible spots.

C. Distinctly.

D. Substantial coverage, about 50%.

The results are shown in table 3.

Example 3

Similar results to those described above were obtained if the stearic acid was replaced with isostearic acid, myristic acid, palmitic acid, lauric acid, Emphol<®> dimer acid, Emphol<®> trimer acid or Emphol<®> 1052 polybasic acid.

In addition to the excellent physical stability, thixotropy and cleaning effect, the compositions according to the invention have the further significant advantage that they do not require any specific order of addition of the respective components. All the ingredients can be added in any order or at the same time to a single container, mixer, etc. and stirred until a uniform homogenous mixture is obtained. Mixing can be carried out at room temperature or at an elevated temperature. It is not necessary to premix any of the components or to use different shear conditions during mixing.

Claims (7)

1. Aqueous, thixotropic, liquid cleaning mixture for automatic dishwashers, characterized in that it comprises: (a) 5-35% by weight alkali metal tripolyphosphate, (b) 2.5-40% by weight sodium silicate, (c) 0-9% by weight alkali metal carbonate, (d) 0.1-5% by weight chlorine bleach stable, water dispersible, organic, detergent active material, (e) 0-5% by weight chlorine bleach stable antifoam, (f) chlorine bleach compound in an amount providing 0.2-4% by weight available chlorine, (g) 0.03 - 0.5% by weight of an aliphatic fatty acid with 8 - 22 carbon atoms, dimers thereof or trimers thereof (h) 0-8% by weight sodium hydroxide and (i) the remainder water. 2. Mixture according to claim 1, characterized in that the aliphatic fatty acid (g) contains from 10 to 20 carbon atoms. 3. Mixture according to claim 2, characterized in that the fatty acid contains from 12 to 18 carbon atoms. 4. Mixture according to claim 3, characterized in that the fatty acid is stearic acid. 5. Mixture according to claims 1-4, characterized in that the fatty acid is present in an amount from 0.03 to 0.2% by weight. 6. Mixture according to claim 5, characterized in that the fatty acid is present in an amount from 0.03 to 0.08% by weight. 7. Use of the mixture according to claim 1 for cleaning crockery.