NO172293B - GEL-like, thixotropic, watery, liquid detergent AUTOMATIC DISHWASHERS AND USE THEREOF - Google Patents

Abstract

Gel-like, thixotropic, aqueous, liquid automatic dishwashing detergent comprising water, at least one component selected from the group consisting of organic detergent, bleach, detergent builder, sequestering agent, foam inhibitors and mixtures thereof, from 0.5 to 5% of a silica anti- film-forming agent and a sufficient amount of the thixotropic thickener to give a thixotropy index of 2.5 - 10. The detergent reduces film formation. on crockery, glass noise, porcelain and the like, especially in hard water, and remains stable against phase separation.

Description

The present invention relates to a gel-like, thixotropic, aqueous, liquid detergent for automatic dishwashers and the use of the detergent for washing dishes in automatic dishwashers. The washing-up liquid is used for cleaning crockery, glassware, porcelain and the like. The washing-up liquid contains silica as an anti-film forming agent, inorganic building salts, chlorine bleach, bleach-stable detergent and a thixotropic thickener.

The washing-up liquid according to the present invention reduces film formation on tableware, glassware, porcelain and the like, particularly in hard water, and remains stable against phase separation.

The detergents do not require an added rinse aid, are stable when stored, do not form sediments and are easily redispersible and pourable.

The detergent according to the invention constitutes a thixotropic, aqueous suspension with improved physical stability. In the detergent, long-chain fatty acids, metal salts of fatty acids and clay are used as thixotropic agents to form stable, gel-like, liquid suspensions which are suitable for use as liquid detergents for automatic dishwashers.

The present invention relates in particular to aqueous, liquid detergents for automatic dishwashers which have thixotropic properties, improved properties with regard to anti-film formation and physical stability, and which are easily dispersible in the washing medium so that crockery, glassware, porcelain and the like.

Commercially available detergents for household appliances provided in powder form have several disadvantages,

for example, uneven composition, expensive operations necessary in the manufacture, tendency to agglomerate when stored at high humidity, resulting in the formation of lumps which are difficult to disperse, dustiness, a source of particular irritation to users suffering from allergies, and tendency to form lumps in the dishwasher dispenser. However, liquid forms of washing-up detergents can

not used in automatic dishwashers due to high foam levels, unacceptably low viscosities and very high alkalinity.

In addition, the currently used powdered detergents often require a separate step of towel rubbing and drying of crockery, glassware, porcelain and the like in order to avoid leaving unwanted traces or film of precipitated calcium and magnesium salts. The use of liquid detergents presents other problems. The building salts precipitate during storage and are not easily redispersed. The mixtures also often thicken during storage and are not easy to pour.

Recent research and development activity has focused on the gel form or "thixotropic" form of such mixtures, however, such mixtures have generally been found to be insufficiently viscous to remain "anchored" in the dispenser container of the dishwasher, and also produce stain residues on crockery, glassware , porcelain and the like. Ideally, thixotropic cleaning compounds should be highly viscous in a quiescent state, Bingham plastic in nature and have relatively high yield stresses. However, when subjected to shear stress, such as shaking in a container or squeezing through an orifice, they should rapidly fluidize and, upon termination of the applied shear stress, rapidly return to a high viscosity/Bingham plastic state. Stability is also of great importance, i.e. there should be no clear signs of phase separation or leaching after a long standstill.

For effective use, it is generally recommended that the detergent for automatic dishwashers, hereinafter also referred to as ADD, contains (1) sodium tripolyphosphate (NaTPP) to soften or dissolve minerals in hard water, and to emulsify and/or peptize dirt, ( 2) sodium silicate to add the alkalinity necessary for effective washing action, and to provide protection for the glaze and pattern on fine porcelain,

(3) sodium carbonate, generally considered an eventuality, to increase alkalinity, (4) a chlorine release agent to aid in the elimination of dirt stains that lead to water staining, and (5) defoamer/surfactant to reduce foam, thereby machine efficiency is increased and the necessary washing effect is added. See for example SDA Detergents in Depth, "Formulations Aspects of machine Dishwashing", Thomas Oberle

(1974). Detergents that come up against the above-described mixtures are mostly liquids or powders. Generally, in such mixtures, hypochlorite bleach is omitted as it tends to react with other chemical constituents, particularly surfactant, thereby breaking down the suspending or thixotropic agent and weakening its effectiveness.

US Patent No. 3,985,668 describes abrasive scouring agents of a gel-like consistency which contain (1) ops-si emmingmidde1, preferably smectite and attapulgite types of clay (2) abrasive agent, e.g. silica sand or perlite, and (3) fillers comprising low density powdered polymers, expanded perlite and the like, which have a buoyancy and thereby stabilizing effect on the mixture in addition to serving as a bulking agent, whereby water that would otherwise be available to form undesirable supernatant layer due to leaching and phase destabilisation, is displaced. 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 additional optional ingredients to provide or supplement building function not provided by the buffer, the amount of such builder not exceeding 5% of the entire mixture according to the patent specification. Maintenance of the desired (greater than) pH 10 levels is achieved with the help 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, it is limited to 5%, which. indicated. Antifoam is not described.

In GB patent applications no. 2 116 199A and 2 140 450A liquid ADD mixtures are described with properties which desirably characterize thixotropic gel-type structure and which comprise each of the various components which are necessary for effective washing action in an automatic dishwasher . The normally gel-like, aqueous detergent for automatic dishwashers having 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% chlorine bleach stable, water dispersible, organic detergent active material,

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

(f) chlorine bleach compound in an amount giving approx. 0.2 - 4% available chlorine, (g) thixotropic thickener in a sufficient amount to give the mixture with a thixotropy index of approx. 2.5 - 10, and (h) sodium hydroxide as needed, by adjusting the pH. ADD mixtures composed in this way are low-foaming, easily soluble in the washing medium and most effective at pH values that best contribute to improved washing performance, i.e. pH 10.5 - 13.5. The mixtures normally have a gel consistency, i.e.

a highly viscous,. opaque gel-like material with Bingham-plastic character and thus relatively high yield stresses. Accordingly, a certain shear force is required to initiate or increase flow, which would be achieved in the agitated dispenser container of a powered automatic dishwasher. 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 approaching its former consistency.

US Patent No. 4,511,487 describes a low-foaming detergent paste for dishwashers. The mixture is based on a mixture of finely divided hydrated sodium metasilicate, an active chlorine compound and a thickener which is a shale silicate of the hectorite type. Small amounts of nonionic surfactants and alkali metal carbonates and/or hydroxides may be used.

Reference is also made to the related GB patent document No. 2,185,037. This patent document describes a thixotropic, aqueous detergent for automatic dishwashers which contains a long-chain fatty acid as a thixotropic thickener.

The thixotropic, aqueous, liquid detergents according to the present invention overcome many of the problems within the state of the art associated with powder and liquid detergents. Due to the addition of a small effective amount of silica anti-film forming agent to the mixture, no added rinse aid is required, and no towel rubbing and drying is required to achieve dry, sparkling clean crockery, glasses, cups and cutlery. The thixotropic, aqueous, liquid detergent has the additional advantages of being stable, non-precipitating on storage and easily redispersible. The liquid detergent according to the present invention is easy to pour, easy to measure out and easy to place in the dishwasher.

A further and unexpected advantage of adding silica anti-film forming agents to the detergent mixture is that the silica prevents the formation of brown color in the dishwasher. The brown color is formed by deposition in the dishwasher of iron and/or manganese oxides. The formation of tan is a particularly serious problem in areas with hard water. The silica in the mixture acts on the iron and/or manganese in the washing water so that deposition in the form of iron and/or manganese oxides in the dishwasher is prevented.

It is an object of the present invention to provide a thixotropic, aqueous, liquid detergent for automatic dishwashers which has improved anti-filming properties.

It is another object of the invention to provide a thixotropic, aqueous, liquid detergent which is stable when stored, easily pourable and easily dispersible in the washing-up water. A thixotropic, aqueous, liquid detergent according to the invention in which a separate rinsing aid is not added or required, is used when washing tableware, glassware, porcelain and the like in an automatic dishwasher.

When washing crockery, glassware, porcelain and the like in automatic dishwashers using an aqueous, liquid detergent according to the invention, the crockery, glassware, porcelain and the like are machine dried without leaving traces or a film.

It is a further object of the invention to provide stable aqueous thixotropic liquid compositions, particularly detergents for automatic dishwashers, by incorporating into the aqueous suspension a small effective amount of a silica anti-film forming agent. A small amount of fatty acid, metal salt of a fatty acid and/or a thixotropic clay thickener is also added which effectively prevents precipitation of the suspended particles and prevents phase separation.

These and other objects of the invention, which will be more easily understood from the following detailed description of the invention, and the preferred embodiments thereof, are achieved by incorporating in an aqueous liquid detergent a small but effective amount of an anti-film forming agent of silica. The physical stability of the mixture is improved by the addition of a fatty acid, a metal salt of a fatty acid and/or a thixotropic clay thickener. More specifically, the present invention provides a gel-like detergent for automatic dishwashers in which from 0.5 to 5% of an anti-film forming agent of silica is incorporated. The silica anti-film forming agent has a particle size of 0.1 - 10 µm. Furthermore, a sufficient amount of a thixotropic thickener is added to the mixture to give a thixotropy index of 2.5 - 10, and to prevent precipitation of the suspended particles, such as alkali metal building salts etc.

In accordance with this, the present invention provides a gel-like, thixotropic, aqueous, liquid detergent for automatic dishwashers which is characterized in that it comprises, on a weight basis:

(a) 5 - 35% detergent builder,

(b) 2.5 - 40% sodium silicate,

(c) 0.5 - 5% silica as an anti-film forming agent with a particle size of 0.1 - 10 micrometers,

(d) 0 - 9% alkali metal carbonate,

(e) 0.1 - 5% chlorine bleach stable, water dispersible, organic, detergent active material,

(f) O - 5% chlorine bleach stable defoamer,

(g) chlorine bleach compound in an amount providing 0.2 - 4% available chlorine, (h) a sufficient amount of a thixotropic thickener to provide a thixotropy index of 2.5 - 10,

(i) 0 - 8% sodium hydroxide and

(j) the rest water.

According to the invention, the gel-like, thixotropic, aqueous, liquid detergent is used for washing dishes in an automatic dishwasher with an aqueous wash bath containing an effective amount of the detergent for automatic dishwashers (LADD) as described above. The LADD mixture can be easily poured into the dispenser container of the automatic dishwasher and, within just a few seconds, will instantly thicken to its normal gel-like pasty state so that it remains securely in the dispenser container until shear forces are reapplied, such as by of the water injection from the dishwasher.

The invention will be described in more detail below using specific embodiments thereof.

The LADD products according to, for example, the previous description in the aforementioned GB applications Nos. 2,116,199A and 2,140,450A, exhibit rheological properties evaluated by testing product viscosity as a function of shear rate. The mixtures exhibited higher viscosity at a low shear rate and lower viscosity at a high shear rate, the data indicating effective fluidization and gelation well within the shear rates found in standard dishwashers. In practice, this means improved properties with regard to pouring and processing, as well as less leakage in the machine's dispenser container, compared to previously known liquid or gel ADD products. For applied shear rates corresponding to 3 to 30 ppm, the viscosity (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 speed of 7.4 seconds corresponds to a spindle rpm of approx. 3^ An approximate 10-fold increase in shear speed gives approx. a 3- to 9-fold reduction in viscosity. The mixtures according to the above-mentioned GB patent applications thus exhibit threshold fluidizations at lower shear rates and to a significantly greater extent when it comes to stepwise increases in shear rate in relation to stepwise decreases in viscosity. This characteristic of the LADD products according to the previous invention is summarized by means of a thixotropy index (Tl) which is the ratio between the apparent viscosity at 3 rpm and at 30 rpm. The mixtures according to the earlier invention have a TI of 2 - 10. The LADD mixtures should show substantial and rapid return to the previous consistency in the resting state when the shear force is interrupted.

In terms of apparent viscosity, it has 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", enabling the product to be dispensed through a conventional squeeze bottle or other suitable dispenser.

The present invention is based on the surprising discovery that substantially improved anti-film-forming properties can be achieved by adding to the

thixotropic, aqueous, liquid detergents a small effective amount of a silica anti-film forming agent. The physical stability, i.e. resistance to phase separation, sedimentation, etc., can be achieved by adding to the mixture a small effective amount of a thixotropic thickener and stabilizer.

Anti-film forming agents

The anti-film forming agent of silica materials that can be used is evaporated or precipitated synthetic or natural silica. The silica can be amorphous or crystalline.

The silica material used can contain up to 0.1 - 5% alumina (Al2O3), usually up to 0.5 - 3%, and more

usual approx. 1% alumina, based on the weight of silica.

A preferred silica material is Syloid<®> 244 which

is amorphous silica and which has a particle size of approx. 4 micrometers. Another suitable silica material is "Silox" 15 which also has a particle size of approx. 4 micrometers.

Another available silica material is Huber<®>Zeo

49 which is amorphous silica and which contains approx. 1% Alumina (A^O^) • The presence of as little as 1% A^O^ has been found to help reduce the hydrolysis and subsequent solubility of silica in the highly alkaline dishwasher detergent.

The particle size of the silica material used is important when it comes to achieving the desired properties with regard to anti-film formation.

The silica particles used are finely divided and

has a particle size of 0.10 - 10 micrometers, preferably 0.50 - 8 micrometers, and preferably 1.0 - 5.0 micrometers. The silica particles of this size and the quantity used here are not abrasive.

The finely divided particles of silica material in the dishwater act to coagulate proteinaceous particulate dirt and hold them in suspension to prevent them from being deposited on clean glass and crockery.

The amount of silica anti-film forming agent that can be used to achieve the desired improvement in film formation depends on the hardness of the water, the detergent active compound, the inorganic salts and other ADD constituents. The silica anti-film forming agent is particularly effective in hard washing water with, for example, 300 ppm hardness or more.

The amount of silica anti-film former used may be 0.5-5% by weight, preferably 1-4% by weight and most preferably 1.5-3% by weight based on the weight of the entire mixture.

Thixotropic thickeners

The thixotropic thickeners or slurry agents which can be used in accordance with the present invention to give the aqueous medium thixotropic properties can be organic materials, for example fatty acid or polyvalent metal salts of fatty acid or inorganic colloidal clays. The thixotropic thickeners should be stable to high alkalinity and stable to chlorine bleach compounds, such as sodium hypochlorite. The preferred thixotropic thickeners include fatty acid, the polyvalent metal salts of fatty acids and the inorganic, colloid-forming clays of the smectite and/or attapulgite types. The amount of thixotropic thickener used will depend on the particular thickener used, but sufficient thickener is added to the mixture to give it a thixotropy index of 2.5 - 10.

The preferred fatty acid thixotropic thickeners 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. 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.

Examples of the fatty acids that can be used as thickeners thus include, for example, 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. Stearic acid and mixed fatty acids, e.g. coconut fatty acid, is preferred.

The amount of the fatty acid thickener required 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.

The amounts of the fatty acid thickener that can be used, however, are generally in the range from 0.03 to 0.5%, preferably from 0.03 to 0.2%, particularly preferably from 0.05 to 0.15%, which gives the desired long-term stability and absence of phase separation.

The polyvalent metal salts of the above-mentioned fatty acids can also be used in the present invention as thixotropic thickeners. Suitable thixotropic thickeners of metal salts are described in US Patent No. 4,752,409.

The preferred metals are the polyvalent metals, such as magnesium, calcium, aluminum and zinc.

In general, the metals may be present in the divalent to pentavalent state. The metal salts are preferably used in their higher oxidation states. For the LADD mixtures, as well as for all other applications where the mixture according to the invention will or may come into contact with objects used for the handling, storage or serving of food products, or which may otherwise come into contact with or be consumed by people or animals, it naturally applies that the metal salt should be selected by 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. For example, the aluminum salts are available in the triacid form, e.g. aluminum stearate as aluminum tristearate, Al (C-^-H^COO) ^ • The monoacid salts, e.g. aluminum monostearate, Al(OH)2(<C>17<H>35<C>OO) and the diacid salts, e.g. aluminum distearate, Al (OH^C-^H-^COO) 2 , and mixtures of two or three of the mono-, di- and tri-acid salts, can be used for those metals, e.g. Al, which has valences of +3, and mixtures of the mono- and diacid salts can be used for these metals, e.g. Zn, which has valences of +2. It is more preferred to use in predominant amounts the acid salts of the metals with valence +2 and the triacid salts of metals with valence +3, the tetraacid salts of metals with valence +4 and pentaacid salts of the metals with valence +5. For example, at least 30%, preferably at least 50%, particularly preferably from 80 to 100%, of the total content of 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.

The metal salts are, as mentioned above, generally commercially available, and can be easily produced, for example by wood

saponification of 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, e.g. with alum, alumina, etc. in the case of the aluminum 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. coconut acid, like the mixed fatty acids that emerge from the commercial manufacturing process, is also used with advantage as a cheap but effective source of the long-chain fatty acid.

The amount of the fatty acid salt stabilizers which

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

Amounts of the polyvalent metal fatty acid salt as stabilizer in the range from approx. 0.02 to 1%, preferably from 0.06 to 0.8%, particularly preferred from 0.08 to 0.4

%, however, generally provides the long-term stability and the absence of phase separation after standing or during transport both at low and elevated temperatures, which is required for a commercially acceptable product.

In the present invention, the conventional inorganic thixotropic clay thickeners can also be used. The thickeners of clay can be used in small quantities in admixture with the thickeners of fatty acids or in admixture with the thickeners of polyvalent metal salts of fatty acids. The clay thickeners can, however, be used in themselves as the thixotropic thickeners.

The preferred clay thickeners include the inorganic, colloid-forming clays of the smectite and/or atta-pulgite types.

The smectite clays include montmorillonite (bentonite), hectorite, attapulgite, smectite, saponite and the like. Montmorillonite clays are preferred and are available under such trade names 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 smectite and attapulgite types in weight ratios from 4:1 to 1:5 can also be used here. Thickening or slurrying agents of the above-mentioned types are well known in the art, as it is described for example in US patent no. 3,985,668. Abrasive or polishing agents should be avoided in the LADD mixtures as they can scratch the surface of fine crockery, crystal and the like.

When used in combination with the fatty acids or the polyvalent metal salts of the fatty acids, the thixotropic thickeners of clays are used in amounts of 0.1 - 3%, preferably 0.1 - 2.5% and most preferably in amounts of 0.1 - 2% .

When the thixotropic thickeners of clay are used alone as the thixotropic thickener, they can be used in amounts of 1.5-8% by weight, preferably 2-5% by weight, of the mixture.

In general, LADD efficiency is directly related to (a) amounts of available chlorine, (b) alkalinity, (c) solubility in liquid media, and (d) foam inhibition. It is here preferred that the pH in the LADD mixture is at least 9.5, more preferably from 10.5 to 13.5 and preferably at least 11.5. At the relatively lower pH values, the LADD product is too viscous, i.e. solid-like, and is thus not easily fluidized under the shear force levels created in the dispenser container under normal operating conditions for the machine. Addition of NaOH is therefore often required to increase the pH to within the above-mentioned ranges, and to increase fluidity 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 the formation of needle-like crystals of carbonate, and thereby impair the stability, thixotropy and/or washing effect of the LADD product, as well as impair the dispensability of the product from, for example, squeeze bottles. Caustic soda (NaOH) serves the additional function of neutralizing the defoamer of the phosphoric or phosphonic acid ester when one is present. It is typically with 0.5-3 wt% NaOH and 2-9 wt% sodium carbonate in the LADD mixture, although it should be noted that sufficient alkalinity can be provided by NaTPP and sodium silicate.

NaTPP can be used in the LADD mixture in a range from 8 to 35% by weight, preferably 20-30% by weight, and should preferably be free of heavy metals which tend 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 corresponding to approx. 18% water by weight or more.

On the basis of the stability of the hexahydrate, the presence of some hydrate water is actually very effective, as it is believed to serve to form crystals of the stable hexahydrate which accelerates hydration and solubilization of the remaining NaTPP particles. If only the hexahydrate is used, the detergent product may become too liquid. If only the anhydrous NaTPP is used, the product can conversely in some cases/be too thick and therefore unsuitable. Particularly preferred LADD mixtures are obtained, for example, 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 the stabilizing effects that can occur due to the presence of excessive foam in the washing machine during use. Foam can be sufficiently 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 suds is also somewhat dependent on the hardness of the washing water in the machine, whereby appropriate regulation of the proportions of NaTPP which have a water-softening effect can help to provide the desired degree of suds inhibition. However, it is generally preferred to include a chlorine bleach-stable defoamer or inhibitor. Particularly effective are the alkyl esters of phosphonic acid with the formula which are for example available as PCUK-PAE, and especially the acidic alkyl esters of phosphoric acid with the formula

which are for example available as SAP and LPKN-158, where one or both of the R groups in each type of ester

can be a C^2_2ø~aHcyl group. Mixtures of the two types, or all other chlorine bleach stable types, or mixtures of mono- and diesters of the same type, can be used. Particularly preferred is a mixture of acidic mono- and di-C 2 -C 2 -alkyl esters of phosphoric acid, such as acidic monostearyl/distearyl phosphates in a ratio of 1.2/1. When antifoam is used, it is typically in proportions of 0.01 - 5% by weight, preferably 0.1 - 5% by weight, especially 0.1 - 0.5% by weight, in the mixture, as the weight ratio between detergent active ingredient and antifoam generally varies from 10:1 to 1:1, and preferably from 4:1 to 1:1. Other defoamers that can be used include, for example, the known silicones.

Although any chlorine bleach compound may be used in the compositions of the invention, such as dichloroisocyanurate, dichlorodimethylhydantoin or chlorinated-. TSP, it is preferred with alkali metal, e.g. potassium, lithium, magnesium and especially sodium hypochlorite. The mixture contains sufficient chlorine bleach compound to provide 0.2 - 4.0% by weight available chlorine, determined for example by releasing 100 parts of the mixture with excess hydrochloric acid. A solution containing 0.2 - 4.0% by weight of sodium hypochlorite contains or provides roughly the same percentage of available chlorine. A solution containing 0.8-1.6 wt% sodium hypochlorite contains 0.8-1.6 wt% available chlorine and is particularly preferred. For example, sodium hypochlorite solution (NaOCl) can advantageously be used with from 11 to 13% available chlorine in amounts of 3 - 20%, preferably 7 - 12%.

The sodium silicate, which provides alkalinity and protection of hard surfaces, such as glaze patterns on porcelain, is used in an amount varying from 2.5 to 40% by weight, preferably 10 to 35% by weight, in the mixture. The sodium silicate also protects the washing machine against corrosion. In the larger quantities indicated here, e.g. in quantities greater than approx. 10% by weight, the silicate also provides an increased effect against staining. The sodium silicate is generally added in the form of an aqueous solution, preferably with a Na2O:SiC3 ratio of 1:2.2 - 1:2.8, for example 1:2.4. Most of the other ingredients in the mixture, especially NaOH, sodium hypochlorite and defoamer can also be added in the form of an aqueous dispersion or solution.

Detergent-active material that is applicable here must be stable in the presence of chlorine bleach, especially hypochlorite bleach, and those belonging to the organic anionic, water-dispersible surfactants of the amine oxide, phosphine oxide, sulfoxide or betaine types, the former anionic surfactants being preferred is most preferred. They are used in amounts varying from 0.1 to 5%, preferably 0.3 - 2.0%. Particularly preferred surfactants are the straight-chain or branched, alkali metal mono- and/or disulfonates of mono- and/or di-(Cg_^4)<->alkyl diphenyl oxide, commercially available for example 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^Q_^g-alkyl sulfates, such as sodium dodecyl sulfate and sodium tallow alcohol sulfate, sodium C^Q_^g-alkanesulfonates, such as sodium hexadecyl-1-sulfonate and sodium C^2_;i_<g>~<a> lkylbenzenesulfonates, s^-^ soxa sodium dodecylbenzenesulfonates. The corresponding potassium salts can also be used.

Like other suitable surfactants or detergents, the amine oxide surfactants usually have the formula R-R^NO, where each R is a lower alkyl group,

for example methyl, and R is a long-chain alkyl group of 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 PO or sulfoxide RR SO can be used. Surfactants of the betaine type usually have the formula R2R<1>N - R"COO~, where R" is a lower alkylene group with from 1 to 5 carbon atoms. Certain examples of these surfactants are lauryldimethylamine oxide, myristyldimethylamine oxide, the corresponding phosphine oxides and sulfoxides, and the corresponding betaines, including dodecyldimethylammonium acetate, tetradecyldiethylammonium pentanoate, hexadecyldimethylammonium hexanoate and the like. For biodegradability, 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 described, for example, 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. Such an amount is readily determined by routine experimentation in any particular case, and generally ranges from 25 to 75% by weight, preferably 50 to 65% by weight. The water should also preferably be deionized or softened. These amounts of water in the mixture include the water added as part of the liquid solutions of other ingredients, but do not include bound water, such as that in NaTPP hexahydrate.

Other common ingredients may be included in these mixtures in small amounts, generally less than 3% by weight, such as perfume, hydrotropic agents, such as sodium benzene, sodium toluene, sodium xylene and sodium cumenesulfonates, preservatives, dyes and pigments and the like, all of which are of course stable to chlorine bleach compounds and high alkalinity ■ (properties of all the components). Particularly preferred for dyeing are the chlorinated phthalocyanines and polysulphides of aluminum silicate, which give the accused green and blue colors respectively.

The liquid ADD mixtures according to the invention are easily used in a known manner for washing crockery, glasses, cups, cutlery 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.

In a preferred embodiment of the invention, the aqueous, liquid detergent is put together using the below-mentioned components.

The thixotropic, aqueous, liquid detergents for automatic dishwashers according to the present invention may contain common additives for detergents. The mixtures can be prepared by commercially available solid builders in powder form, and/or the components can be mixed and the mixtures ground to a desired particle size.

The invention can be practiced in various ways, and certain specific embodiments will be described to illustrate the invention in the accompanying examples.

All quantities and proportions shown are percentages by weight of the mixture unless otherwise stated.

The present invention is further illustrated by means of the examples below.

Example 1

A thixotropic, aqueous, liquid detergent for automatic dishwashers is made from the following ingredients in the indicated amounts.

(1) Mixture of mono- and distearyl (C^g-C^g) alkyl esters of phosphoric acid, molar ratio 1:1.3. (2) Silica Syloid<®> 244 has a particle size of approx. 4 micrometers. (3) Na mono- and didecyl diphenyl ether disulfonate (45% solution)

The stearic acid is melted and the ingredients are added to the water generally in the order indicated and stirred gently until a homogeneous mixture is obtained. The mixture is tested by washing glassware and crockery at a temperature of 54°C in hard water (300 ppm hardness) in an automatic dishwasher, and the clean and dried washed items are found to have no visible film.

Example 2

To demonstrate the effect of adding silica as an anti-filming agent, the mixture is prepared with and without silica as an anti-filming agent and compared with a commercially available powder detergent.

The mixtures are made so that they contain the following components.

The stearic acid is melted and the ingredients are added to the water generally in the order indicated and stirred until a homogeneous mixture is obtained. The mixture is tested by washing glassware at 54° C in hard water (300 ppm hardness).

The two compositions (A) and (B) above were tested and compared to a commercially available powder detergent for automatic dishwashers C. The compositions were tested in a Kenmore automatic dishwasher using the procedure described in ASTMD 3566-79, except that only four wash cycles was used. The film formation and staining were judged according to the following scales:

Rating scale for film formation

1. Best, no visible film

2. Slight film formation, starting to become visible

3. Noticeable film, increasing

4. Continued increase of significant film

5. Film formation begins to become severe

6. High film formation, strong build-up

7. Continued increase of heavy film.

Rating scale for spotting

A. Best, no stains

B. Very few spots visible

C. Distinctly

D. Substantial coverage, approximately 50%.

The results obtained in the fourth cycle are set out in Table 1 below.

Example 3

Thixotropic, aqueous, liquid detergents for automatic dishwashers are made from the following ingredients in the indicated amounts.

The stearic acid is melted and the ingredients are added to the water generally in the order indicated and stirred until a homogeneous mixture is obtained. The mixtures are tested by washing glassware at 54° C in hard water (300 ppm hardness).

The two blends were tested and compared to a commercial automatic dishwasher powder detergent F. The blends were tested in a Kenmore automatic dishwasher using the procedure described in ASTMD 3566-79, except that only four wash cycles were used. Staining and film formation were assessed as in Example 2, and the results obtained in the fourth cycle are reproduced below in Table 2.

Example 4

A thixotropic, aqueous, liquid detergent for automatic dishwashers is made from the following ingredients in the amounts indicated.

The components are mixed in the usual way or mixed by following the method according to US patent document no. 4,752,409.

The mixture is tested by washing glassware at 54° C in hard water (300 ppm hardness) in an automatic dishwasher. The clean and dried glassware is found to be free of film.

The thixotropic, aqueous, liquid detergents for automatic dishwashers according to the present invention provide improved film properties.

Claims (7)

1. Gel-like, thixotropic, aqueous, liquid detergent for automatic dishwashers, characterized in that, based on weight, it comprises: (a) 5 - 35% detergent builder, (b) 2.5 - 40% sodium silicate, (c) 0.5 - 5% silica as an anti-film forming agent with a particle size of 0.1 - 10 micrometers, (d) 0 - 9% alkali metal carbonate, (e) 0.1 - 5% chlorine bleach stable, water dispersible, organic, detergent active material, (f) 0 - 5% chlorine bleach stable antifoam, (g) chlorine bleach compound in an amount which gives 0.2-4% available chlorine, (h) a sufficient amount of a thixotropic thickener to give a thixotropy index of 2.5-10, (i) 0-8% sodium hydroxide and (j) the balance water. 2. Detergent according to claim 1, characterized in that the thixotropic thickener comprises a fatty acid with 8-22 carbon atoms in an amount of 0.03-0.5%. 3. Detergent according to claim 1, characterized in that the thixotropic thickener comprises a polyvalent metal salt of a fatty acid with 8-22 carbon atoms in an amount of 0.02-1.0%. 4. Detergent according to claim 2, characterized in that it additionally comprises a clay as a thixotropic thickener in an amount of 0.1 - 3.0%. 5. Detergent according to claim 3, characterized in that it additionally comprises a clay as a thixotropic thickener in an amount of 0.1 - 3.0%. 6. Detergent according to claim 1, characterized in that the anti-film forming agent consisting of silica has a particle size of 0.5 - 8.0 micrometres. 7. Use of a gel-like, thixotropic, aqueous, liquid detergent according to claim 1 for washing dishes in automatic dishwashers.