NL8900268A - THIXOTROPE AQUEOUS DISHWASHERS FOR AUTOMATIC DISHWASHERS. - Google Patents

Description

i VO 2020

Title: Thixotropic aqueous dishwashing detergents for automatic dishwashers.

Field of the invention:

The present invention relates to scented or unscented liquid dishwashing detergents for automatic dishwashing, with thixotropic properties and improved physical stability and methods for the preparation of these dishwashing detergents.

Background of the_invention:

Recent activities have strongly focused on pasty, gel-like and thixotropic forms of automatic dishwashing liquid dishwashing detergents because of their desirable consumer benefits over conventional powdered detergents. These advantages include the ease with which the detergent is dispensed from its packaging, a lower consumption in volume per batch due to the larger concentrations of active ingredients, and long-term storage without moisture spoilage.

The development of liquid dishwashing detergents for automatic dishwashing has been accompanied by problems due to the requirement that such formulations form a number of ingredients which are generally incompatible, ie that they tend to react with each other prior to use. in the dishwasher. In addition, a liquid automatic dishwashing detergent must also have thixotropic properties, i.e., it must be very viscous in a resting state and it must have relatively high yield values (Bingham Plastic), but when subjected to shear loading, such as e.g. when squeezed through an opening, it must have similar flow properties to a viscous liquid so that it can be easily dispensed into the dishwasher detergent tray or container. Once in the tray or container, it must return quickly to the highly viscous state 89 00 2 * 8. ' - 2 - ("Bingham Plastic state").

Another general problem with liquid dishwashing detergents for automatic dishwashers is that they tend to separate into a substantially solid and a liquid phase during the shelf life of the product. Improvement in phase stability has been accomplished by additives, however, a drawback of this approach is that any addition to the detergent may adversely affect the rheological property of the detergent.

Likewise, the addition of a fragrance to a liquid automatic dishwashing detergent to impart a desirable fragrance to it also posed a problem because of its effect on the complex balance of the ingredients within the mixture, which is necessary to achieve of the desired rheology and other physical properties. For example, e.g. the presence of a chlorine releasing compound is expected to adversely affect an oil type fragrance which is readily oxidized. In addition, the presence of oily fragrances can be expected to adversely affect the phase stability of such mixtures by their tendency to act as anti-foaming agents.

The present invention provides scented or non-scented thi-xotropic liquid dishwashers for automatic dishwashers, with improved physical stability, as well as a new method according to which liquid dishwashers for automatic dishwashers with thixotropic properties can be prepared, which are physically stable and not are subject to separation for long storage times.

The present invention also provides a new method in which air is entrained in a thixotropic liquid dishwashing detergent for automatic dishwashing, in order to maintain stability over long storage times.

A further advantage of the present invention is that it provides a new method according to which a fragrance is introduced into a liquid dishwashing detergent for automatic dishwashing, to impart a pleasant fragrance to the agent without adversely affecting phase stability or rheological properties.

8900268 /

St - 3 -

The present invention provides a liquid automatic dishwashing detergent having thixotropic properties and improved long-term physical stability and a method of preparing these agents.

The invention provides a thixotropic liquid automatic dishwashing detergent comprising a concentrated dispersion of solid particles in a liquid phase, characterized in that air bubbles are entrained in the medium in an amount sufficient to balance the specific gravity of the liquid phase with the total specific gravity of the agent, thereby improving the physical stability of this thixotropic detergent.

The present invention also provides a scented liquid automatic dishwashing detergent having thixotropic properties and improved long-term physical stability. According to the invention, specific perfumed automatic dishwashing liquid detergents may contain all or several of the following ingredients: (1) alkali metal tripolyphosphates for softening or binding minerals from hard water and to emulsify and / or peptize soil; 20 (2) sodium silicate to provide the necessary alkalinity for effective washing and to protect the glaze and fine porcelain pattern; (3) alkali metal carbonate, generally considered optional, to enhance alkalinity; {4) a chlorine releasing agent to promote the removal of dirt stains leading to water stains; (5) a chlorine-bleaching anti-foaming agent to reduce foam to thereby improve machine efficiency and provide additional washing performance; (6) chlorine bleaching surfactant, sometimes referred to as a detergent material, which is compatible with the other ingredients and provides washing performance; (7) thixotropic thickener in an effective amount to give the agent a thixotropic index of about 2.0-10; 35 (8) lye as it is necessary to adjust the pH within 8900268.

* »- 4 - area. From approx. 10 - 14; (9) a salt of a long-chain fatty acid or a long-chain fatty acid as a physical stabilizer, in an effective amount to increase the physical stability of the agent; (10) fragrance in an effective amount to impart a pleasant fragrance to the agent without adversely affecting the stability or thixotropic properties of the agent; (11) water in an effective amount to avoid destruction of the desired thixotropic properties; and 10 (12) air in the form of bubbles with a diameter from about 5 to about

80 µm in an amount of from about 2 to 10 vol%, effective to give the agent a total specific gravity of from about 1.20 to about 1.35 and to improve the physical stability of the agent.

The present invention provides a process for the preparation of liquid automatic dishwashing detergents having a total specific gravity approximately equal to the specific gravity of the liquid phase and having an improved physical stability and improved rheological properties, comprising the following steps: a) forming a pre-dispersion mixture containing water, physical stabilizer, anti-foaming agent and surfactant, (b) forming a pre-mixture of thickener containing the pre-dispersion mixture from step Ca), water and a thixotropic thickener and mixing the thickening premix until the thixotropic thickener is hydrated and desagglomerated, (c) mixing, preferably high shear mixing, the thickening premix from step (b) and additional water with addition of other desired detergent ingredients to form a liquid dishwashing detergent for automatic dishwashing containing about 2 - 10 vol.% air, and 30 (d) homogenizing the liquid automatic dishwashing mixture to balance the total specific gravity and the specific gravity of the liquid phase of the agent to to establish.

The method of the present invention can be carried out under conditions which cause the thixotropic flow to be 89 0026β.

5 - 5 - dishwasher detergent for automatic dishwashing has reached a very stable state. It has been found that this state is achieved when about 2 to about 10% by volume of air is entrained in the agent and the total specific gravity of the agent is approximately equal to the specific gravity of the liquid phase of the agent.

The present invention also provides a method by which a fragrance is added to the liquid automatic dishwashing detergent under such conditions and in an amount that the thixotropic properties or physical stability of the agent is not adversely affected. E.g. a method in which the liquid automatic dishwashing detergent from the above step (d) is first cooled to a maximum temperature below about 29.4 ° C and then the liquid automatic dishwashing detergent and the desired fragrance are introduced into 15 a mixer in which the fragrance is uniformly dispersed in the final liquid dishwashing detergent for automatic dishwashing.

Thus, the present invention provides a method of combining ingredients in such proportions as to provide a liquid automatic dishwashing detergent as a product having improved combinations of properties, particularly thixotropy and phase stability.

Description of the drawing and expressions:

The drawing is a side view of a schematic of the preferred method of the present invention.

The term "total specific gravity", as used herein, refers to the specific gravity of a homogeneous liquid dishwashing detergent for automatic dishwashing, which includes all the required ingredients. The term "liquid phase specific gravity" as used herein refers to the specific gravity, measured by conventional techniques, of a deaerated liquid which has been centrifuged from the liquid automatic dishwashing detergent, i.e., the total dishwashing detergent.

The term "thixotropity index" is the ratio of the viscosities measured at 3 rpm and 30 rpm at room temperature after 3 minutes using a Brookfield HATDV II Viscometer 83 0026 8.

- 6 - with a spindle No. 4.

Detailed description of the invention:

The present invention is directed to liquid dishwashing detergents for automatic dishwashing with thixotropic properties and long-term phase stability and which may include a fragrance which does not adversely affect the properties of the mixture. The present invention is also directed to a process for the preparation of liquid dishwashers for automatic dishwashing, with thixotropic properties and an improved long-term phase stability, whereby air is entrained in the agent in an amount of about 2 - 10% by volume, in order to establish a state of equilibrium between the total specific gravity and the specific gravity of the liquid phase of the agent. In addition, the present invention is also directed to a method of incorporating a fragrance into liquid automatic dishwashing detergents without adversely affecting the rheological properties or long-term phase stability of the agent.

A preferred example of the present invention pertains to an agent which may be perfumed with fragrance, comprising the following components by weight unless otherwise stated: (a) 5 - 35% alkali metal tripolyphosphate, (b) 2.5 - 20% sodium silicate , (c) 0-9% alkali metal carbonate, (d) 0.1 - 5% chlorine bleach resistant, water dispersible organic material with washing power, (e) 0.01 - 5% chlorine bleach resistant anti-foaming agent, (f ) chlorine bleach compound in an amount to provide about 0.2-4% available chlorine, (g) thixotropic thickener in an amount sufficient to give the agent a thixotropic index of about 2.0-10, (h) alkali metal hydroxide, in the amount necessary to adjust a pH of about 10-14, (i) a long chain fatty acid or its salt as a physical stabilizer in an effective amount to increase the physical stability of the agent, 8900268.

i - 7 - (j) (optional) fragrance in an effective amount to provide an odor and to avoid destruction of the desired thixotropicity and physical stability of the mixture, (k) water in an effective amount to destroy the antlers 5 thixotropic properties to be avoided, and (1) air in an amount of about 2-10% by volume, effective to give the mixture a total specific gravity of about 1.20 to about 1.35.

According to the method of the invention, a phase-stable, thixotropic liquid dishwashing liquid for automatic dishwashing is prepared by entraining air into the medium to achieve an equilibrium state between the specific gravities of the total agent and the liquid phase of to establish the remedy.

It has been found that concentrated dispersions containing both liquid and solid phases, such as the liquid automatic dishwashing detergents, can be stabilized by dispersing an appropriate amount of air in the form of microscopic bubbles throughout the liquid phase of the agent. It has also been found that the air can be dispersed and stabilized in the form of bubbles throughout the liquid phase, using a multi-part stabilizing system comprising two or more components, preferably three, usually categorized as physical stabilizers, suds suppressors or anti-foaming agents and surfactants. While it is not intended to be bound by any theory explaining how the stabilizing system and air interact with each other in the liquid automatic dishwashing detergents, it is believed that the stabilizing ingredients interact to such an extent at the interface between air and Liquid, that the hydrophobic groups of these components are oriented to the air bubbles, while the hydrophilic groups are oriented to the aqueous phase. The hydrophilic groups, in turn, and the solid particles of the slurry interact with each other either through hydrogen bonding or by electrostatic interaction. In other words, the liquid-air interface of the components of the stabilizer. - 8 - lubricating system and solid particles, giving rise to a liquid-crystalline type structure for the interface.

According to the preferred method of the present invention, a three-part stabilizing system provides a very stable liquid dishwashing detergent for automatic dishwashing by stabilizing the microscopic air bubbles throughout the whole such that the total specific gravity of the liquid dishwashing detergent for automatic dishwashing is approximately equal to the specific weight of only the liquid phase in the liquid dishwashing detergent 10 for automatic dishwashing. This is the condition under which the automatic dishwashing liquid detergent exhibits high stability, i.e. there is little or no tendency for phase separation due to density variations in the agent.

In order to effectively disperse air throughout the entire automatic dishwashing liquid detergent, it has been found that the size of the entrained air bubbles should be greater than the size of all dispersed solids. The size of the bubbles may generally range from about 5 to about 80 µm, and preferably from about 20 to about 60 µm. The size of the air bubbles can generally be controlled by varying the speed of the blade trunnion of dispersers or stirrers during the mixing operations. It was also found that entrained air from about 2 to about 10% by volume provided stable phase agents, the preferred range being from about 4.0 to about 9.0% by volume, and the preferred strength range is from about 6.5 to about 8.5% by volume.

As can be seen in the drawing, the method of the present invention can be carried out in a mixing system, comprising a vessel 2 for predispersing, a vessel 4 for premixing, a vessel 6 for the main batch, homogenizers 8, 10, 19 and 21, 30 heat exchanger 12, an in-line mixer 14 and a storage vessel 16. As shown in the drawing, all vessels are in open communication with the atmosphere.

A pre-dispersion mixture comprising the stabilization system is prepared in the pre-dispersion vessel 2, then it is transferred to the pre-mixing vessel 4 via line 18 and homogeneous 8900268.

- Nisator 19 via pump 20, where it is added to a thixotropic thickener to prepare a thickening premix. The thickening premix is then fed to main charge vessel 6 through line 22 and homogenizer 21 through pump 24, into which the remaining 5 automatic dishwashing liquid detergent ingredients are added.

The detergent from vessel 6 is then fed via homogenizers 8 and 10 and then cooled in the heat exchanger 12. if a perfumed detergent is desired, the cooled product is passed through a static mixer 14 incorporated in the pipe, where a fragrance is added. added. The liquid detergent is then fed to vessel 16 where it is stored.

In the preferred process of the present invention, a liquid detergent pre-dispersion mixture is first prepared, 15 of which are included as components of the liquid dishwashing detergent for automatic dishwashing, the selected physical stabilizer, the anti-foaming agent and the surfactant, as well as as part of the water content of the liquid automatic detergent. Depending on the choice of the stabilizing components, one or more of the components may initially be solid, necessitating either the addition of heat to form a melt or the addition of water to form a solution or emulsion. The amount of water added to the predispersion mixture should be limited to maintain a highly viscous mixture. The pre-dispersion mixture is subjected to mixing, preferably high shear mixing, for about 5 minutes, during which time the temperature of the pre-dispersion mixture may exceed 37.8 ° C. High shear mixing, as used herein, is defined in terms of shear rates and is a function of a number of variables, the most important of which is the configuration of the mixing vessel and the tip speed of the blades. For example, e.g. the predispersion mixture

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preferably mixed under high shear in a Myers HSD mixer using about 20 cm blades at a blade speed of about 1372.5 m / min. The "high shear" rate under these conditions is approximately the order of 100 sec *.

89 0016 8.

The pre-dispersion mixing stage can be carried out in other conventional grinding equipment or high shear grinding equipment, e.g. rolling mills, colloid mills and Premier mills.

The pre-dispersion mixing step is followed by a second mixing step, during which a thixotropic thickener, e.g. clay, and a further portion of the water content of the total liquid automatic dishwashing detergent is added to the predispersion mixture to form a thickener premix. The thickener premix is preferably subjected to low shear mixing for about 20 minutes, during which time the thickener is hydrated, desagglomerated and dispersed throughout the thickener premix. Low shear mixing, as used herein, is also defined in terms of shear rates and, as described above with respect to high shear, it is a function of a number of variables, including the configuration of the mixing vessel and the tip speed of the blades. Equipment suitable for low shear mixing of the thickener premix includes conventional vane mixers, the average shear rates of the order of about 10 seconds *.

The amount of water added to each of the first two mixing steps is chosen somewhat arbitrarily within the limits of the total water content of the final liquid automatic dishwashing detergent. However, it has been found that the amount of water added to the predispersion mixture should be less than that which forms a mixture with an undesirably low viscosity and high fluidity, since such a state would adversely affect mixing, in particular under high shear mixing conditions.

The second mixing step is followed by a step in which the main batch is mixed and during which the thickener premix, the remainder of the total water content of the liquid dishwashing liquid and other desired liquid components of the liquid dishwashing liquid for automatic washing are mixed, at preferred under high shear conditions to form a main charge. Gedu 89 0026 8. ' During this mixing step, the other liquid ingredients of the detergent are preferably added. Shear rates of the order of 100 sec * are achieved during the main batch mixing stage. The other ingredients of the liquid dishwashing detergent / 5 that may be added include the following: sodium hydroxide, sodium carbonate, silicates, alkali metal tripolyphosphates, chlorine bleaches and other suitable ingredients which form the desired liquid automatic dishwashing detergent.

Devices suitable for high shear mixing operation include roll mills, colloid mills, Premier mills, and Myers BSD.

The main batch mixture from the high shear mixer is then subjected to a series of crude and fine homogenization steps until the solid and liquid phases of the liquid automatic dishwashing detergent are thoroughly homogenized. The homogenization steps are performed under high shear conditions, achieving shear rates of the order of 4 -1 of about 10 seconds. The homogenization step is completed when the total specific gravity of the liquid automatic dishwashing detergent 20 is approximately equal to the specific gravity of the liquid phase of the detergent only. Homogenization of the liquid automatic dishwashing detergent can be carried out in conventional homogenizers, such as one with high speed

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working Dispax, available from IKA-Works, Ine.

According to the invention, the dishwashing detergent is preferably subjected to mixing at a rate and duration which entrain air entrainment in an amount of from about 2 to about 10% by volume, preferably from 4-9% by volume and more particularly 6.5-8.5% by volume, in the detergent. In the preferred embodiment of the invention, air 30 is introduced into the mixture during high shear mixing of the detergent ingredients. However, according to the invention, air can be introduced into the mixture at any time of the process by conventional means to form a phase stable mixture.

35 The existence of a total specific gravity that approximately equals 8 * 00268.

- 12 - depends on the specific gravity of the liquid phase, is indicative of introduced air and a high stability of the product. It has generally been found that specific weights within the range of 1.20-1.35 provide a phase stable liquid dishwashing detergent for automatic dishwashing, with the preferred specific gravity being within the range of from about 1.26 to about 1.32.

According to a more preferred embodiment of the invention, a fragrance is added to the liquid automatic dishwashing detergent after the above-described coarse and fine homogenization steps. In this embodiment, the automatic dishwashing liquid dishwashing liquid is cooled and then this dishwashing liquid and the desired fragrance are mixed, preferably in a static mixer, to form a physically stable and uniformly dispersed liquid dishwashing liquid for automatic dishwashing as a product.

According to an optional embodiment of the invention, the liquid automatic dishwashing detergent is preferably cooled to a temperature below about 29.4 ° C prior to the introduction of a desired fragrance. It has been found that the addition of the desired fragrance prior to cooling has an adverse effect on the specific gravity of the liquid dishwashing detergent, which again affects the phase stability of the mixture. It was also found that the introduction of the fragrance prior to homogenization, ie during the preparation of the main batch, resulted in a product of poor physical stability, ie, the liquid dishwashing detergent for automatic dishwashing begins to separate phase immediately after standing. steps. It has also been found that addition of fragrance in amounts of from about 0.01% to about 0.4% by weight creates a desirable odor without adversely affecting the rheological properties or phase stability of the mixture, with the preferred amount added perfume is about 0.02 to 0.2% by weight.

In a modified embodiment of the present invention, the liquid and solid components of the thixotropic detergent as described above are sequentially added in a high shear mixer 35 with continuous mixing to any desired value.

89 00Z6 8.V

a - 13 positions are included. The detergent is then subjected to high shear mixing for about 15 minutes to form a homogeneous, thixotropic detergent with entrained air. The high shear mixing step is completed when the total specific gravity of the mixture is approximately equal to the specific gravity of the liquid phase.

Although the process of the invention has been described in terms of preferred ingredients and amounts, it will be apparent to those skilled in the art that a very stable thixotropic detergent could be obtained in the absence of one or more of the ingredients by appropriate adjustment of the other ingredients.

For example, it can e.g. possible to formulate a phase stable mixture in the absence of an anti-foaming agent by minimizing the surfactant content and by increasing the amount of physical stabilizer in the mixture.

The liquid detergents for automatic washing prepared according to the method of the present invention are generally formulated with the ingredients in the relative proportions described below.

Any long chain linear, branched, polymer or polybasic, saturated or unsaturated fatty acid can be used as the physical stabilizer of the present invention. The fatty acid is preferably linear and saturated, with about 10 to about 22 carbon atoms, preferably about 10 to 20 carbon atoms, and more particularly about 14 to 18 carbon atoms in the carboxyl group of the fatty acid. Mixtures of fatty acids can be used, such as those from natural sources, such as tallow fatty acid, coconut fatty acid, soy fatty acid, etc., or from synthetic sources derived from industrial manufacturing processes.

Examples of the fatty acids that can be used as physical stabilizers include e.g. decanoic acid, dodecanoic acid, palmitic acid, myristic acid, stearic acid, behenic acid, oleic acid, eicosanoic acid, tallow fatty acid, coconut fatty acid, soy fatty acid, etc. and mixtures of these acids.

Butyric acid, stearic acid and mixed fatty acids are preferred. Liquid dishwashing detergents for automatic dishwashing as well as any other 8900285.

- 14 - fitting in which the means prepared according to this invention come into contact or may come into contact with articles used for the handling, storage or serving of food products or which may otherwise come into contact with or be ingested by humans or animals, 5 the use of the fatty acids as the physical stabilizing agent is of particular advantage because of their known low toxicity. For this reason, stearic acid and behenic acid are particularly preferred. Another clear advantage of using the fatty acids as stabilizers is their lower price compared to the metal salts of fatty acids.

The amount of physical stabilizer required to achieve the desired improvement in physical stability is a function of factors such as the nature of the fatty acid, the nature and amount of thixotropic agents, detergent compounds (surfactants), inorganic salts, in particular tripolyphosphates (TPP) and other liquid components of automatic dishwashing detergents, as well as the expected storage and shipping conditions.

Salts of the above fatty acids can also be used as physical stabilizers, e.g. alkali and alkaline earth metal salts and salts of polyvalent metals. The alkali metal salts include sodium, potassium and ammonium salts of the fatty acids. The alkaline earth metal salts include calcium, barium and strontium salts of the fatty acids. Examples of the fatty acids from which the polyvalent 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 and mixtures of these acids. Stearic acid and mixed fatty acids are preferred fatty acids from which polyvalent metal salt stabilizers can be formed.

Preferred polyvalent metals are the metals of groups IIA, IIB and IIIB, in particular magnesium, calcium, aluminum and zinc, although other polyvalent metals, including those of the groups UIA, IVA, VA, IB, IVB, VB, VIB, VUB and VIII of the Periodic Table of the Elements can also be used. Specific examples of these other multivalent metals include Ti, Zr, V, Nb, Mn, Fe, Co, Ni, Cd, Sn, Sb, Bi, etc. As discussed above with regard to choice of safe free fatty acids, the metal salt should also be chosen taking into account its toxicity. For this reason, the calcium and magnesium salts are particularly preferred because they have generally been recognized as safe food additives.

The metal salts described above are generally commercially available, but they can also be readily prepared, e.g. by saponification of fats and oils, e.g. animal fat, or by neutralizing free fatty acids with a hydroxide or oxide of the polyvalent metal, e.g. aluminum oxide, alum, etc. Optionally, metal salts of fatty acids can be prepared by reacting a soluble metal salt with a soluble fatty acid salt.

15 Calcium stearate, i.e. calcium distearate, magnesium stearate, i.e.

magnesium distearate, aluminum stearate, i.e. aluminum monostearate, aluminum distearate, aluminum tristearate and mixtures thereof, and zinc stearate, i.e. zinc distearate, are preferred fatty acid salts of polyvalent metals as stabilizers.

The amount of fatty acid or salt of fatty acid as a stabilizer necessary to achieve the desired improvement in physical stability is a function of factors such as the nature of the fatty acid or its salt, the nature and amount of the thixotropic agent, the detergent compound, the inorganic salts, in particular TPP, and other constituents of liquid dishwashing detergents for automatic dishwashing, as well as the expected storage and shipping conditions.

In general, however, it has been found that long term stability, ie the absence of phase separation at low and high temperatures, is achieved by the addition of free fatty acids or their salts in amounts from about 0.01 to about 1.0 wt%, preferably from about 0.06 to about 0.8 wt% and more particularly from about 0.08 to about

0.4 wt%. Moreover, it has been found that the free fatty acids are preferable to their salts, first of all because of the ease with which they are dispersed.

Optionally, or in addition to the above physical stabilizers, 6900268.

Small but effective amounts of polyacrylic acid polymers and copolymers and their salts can be added to improve the physical stability of the blends. These polymers and their salts are generally commercially available. Suitable polymers are the polyacrylic acids and their sodium salts, which are available from

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Rohm and Haas as ACRYSOL LMW. The relative amounts of polymer can be between 0.01 and 3%, depending on the molecular weight of the polymers, the smaller relative amounts being more suitable for the higher molecular weight polymers.

10 Suppressing foam during the dishwashing cycle is important to maximize the efficiency of the dishwasher and minimize the destabilizing effects that could occur due to the presence of excess foam within the dishwasher. Foam can be sufficiently reduced by appropriate selection of the type and / or amount of active material, the major foam-forming component. The degree of foaming also depends somewhat on the hardness of the washing water in the machine, allowing appropriate adjustment of the relative amounts of water softeners, e.g. alkali metal tripolyphosphate, can provide the desired degree of foam suppression.

According to the invention, however, a chlorine bleach resistant foam suppressant or anti-foaming agent is preferably included as part of the stabilizing system. Effective anti-foaming agents include the alkylphosphonic acid esters of the formula:

O

tl

25 HO - P - R

OR

and the acidic alkyl phosphate esters of the formula:

O

tl

HO - P - OR

30 OR

available e.g. from Hooker (SAP) or from American Hoechst as Knapsack (LPKn-158), where one or both groups R in each ester type may independently have the meaning of a 2Q-alkY10roeP · Mixtures of the two ester types or any other, against chlorine bleaches 35 resistant types, or mixtures of mono- and diesters of the same type, 89 00 26 8.

- 17 - can also be used. The preferred inhibitor of the invention is a mixture of mono and di-C 1-6 alkyl phosphate esters such as 10-Xo monostearyl / distearyl acid phosphates 1.2 / 1 (Knapsack LPKnl58). Moreover, it is a favorable feature of this invention that many of the long-chain stabilizing fatty acids, such as stearic acid and behenic acid, act as additional foam destroyers.

The detergent compositions of the invention generally contain an anti-foaming agent in an amount of from 0 to about 5 wt%, preferably from about 0.01 to about 5.0 wt%, and more particularly from about 0.01 to about 0.5% by weight. In addition, the weight ratio of surfactant to anti-foaming agent is preferably about 10: 1 to about 1: 1, more particularly about 4: 1 to about 1: 1.

The detergent material, i.e., the surfactant selected for use in the liquid automatic dishwashing detergent of the invention must be resistant to chemical decomposition and oxidation by the highly active chlorine bleach which is also present in the liquid automatic dishwashing detergent.

Surfactants useful in the present invention are either of the anionic or nonionic type or combinations of both. Preferred surfactants are mono- or di-anionics containing sulfate, sulfonate or carboxylates as amphiphiles. The most preferred surfactants according to the invention are the linear or branched alkali metal mono- and / or 25-di- (C1-alkyl) diphenyloxy-mono- and / or disulfonates, commercially available

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available from Dow Chemical, e.g. as DOWFAX 3B-2 and DOWFAX 2A-1. In addition, the surfactant must be compatible with the other ingredients of the mixture. Other preferred surfactants include the primary alkyl sulfates, alkyl sulfonates, alkyl aryl sulfonates, sec alkyl sulfates, and olefin sulfonates. Examples include sodium C18 g-alkane sulfonates such as sodium dilauryl sulfonate, sodium hexadecyl-1 sulfonate and sodium C. -C 0 -alkylbenzene-1Z 10 sulfonates such as sodium dodecylbenzene sulfonates. The corresponding potassium salts can also be used.

Other surfactants suitable according to the invention 8900268.

Detergents include the amine oxide surfactants 1 of the formula R 1 R NO where each R has the meaning of a lower alkyl group, e.g. methyl, and R has the meaning of a long chain alkyl group of 8-22 carbon atoms, e.g. a lauryl, myristyl, palmityl or cetyl group. Instead of an amine oxide, use can be made

made of a corresponding surface-active phosphine oxide R R PO

1 1 or sulfoxide RR SO. Betaine surfactants are typically those of the formula R R N-R'COO-, wherein each R has the meaning of a lower alkylene group having 1 to 5 carbon atoms. Specific examples of the amine oxide surfactants are lauryl dimethylamine oxide, myristyl dimethylamine oxide, the corresponding phosphine oxides and sulfoxides, and the corresponding betaines, including dodecyldimethylammonium acetate, tetradecyldiethylamonium pentanoate, and hexadecyldhexanoethylamine.

For biodegradability reasons, the alkyl groups in these surfactants are preferably linear. Detergents according to the invention may contain from 0 to about 5% by weight surfactant, preferably from about 0.1 to about 5% by weight, and more particularly from about 0.3% to 2.0% by weight.

Thixotropic agents, which are thickeners or suspending agents, which impart thixotropic properties to an aqueous environment are known in the art. These thixotropic agents are water-soluble, water-dispersible or colloid-forming, organic or inorganic and monomer or polymer. They must be stable in the detergent compositions of the invention, i.e., resistant to strong alkalinity and chlorine bleaches, such as sodium hypochlorite. Preferred thixotropic agents are the inorganic colloid-forming clays of the smectite and / or attapulgite type. These agents are generally used in amounts from about 0.1 to about 10% by weight, to impart the desired thixotropic properties or plastic behavior according to Bingham to the liquid automatic dishwashing detergents. Other suitable thixotropic agents include small but effective amounts of a long chain aliphatic fatty acid having 8-22 carbon atoms or their dimers or trimers. This 8900268.

Agents are generally used in amounts of 0.02-0.5 wt%. An advantage of the liquid automatic dishwashing detergents of the invention is that the desired thixotropic properties or plastic behavior according to Bingham can be obtained in the presence of the aforementioned physical stabilization system with smaller amounts of the thixotropic thickeners. For example, e.g. the addition of colloid-forming clays of the smectite and / or attapulgite type to the liquid dishwashing detergents for automatic dishwashing according to the invention in an amount of about 0 - 3% by weight, preferably 0.2 - 2.5% by weight , more particularly 0.5-2.2 wt%, generally sufficient to achieve the desired thixotropic properties and Bingham Plastic character when used in combination with the physical stabilization system.

The smectite clays include montmorillonite (bentonite), hec-torite, saponite, and the like. Montmorillonite clays have front

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label and these are available under trademarks such as Thixogel Nö.1

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and Gel White GP, H, etc., from Georgia Kaolin Company and ECCAGüM GPj H, etc. from Luthem Clay Products. Attapulgite clays include the

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commercially available materials under the Attagel trademark,

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20 i.e. Attagel 40, Attagel 50 and Attagel 150 from Engelhard Minerals and Chemicals Corporation. Mixtures of smectite and attapulgite types in weight ratios of 4: 1 to 1: 5 are also useful according to the invention. Thickeners or suspending agents of the aforementioned types are known in the art and are described e.g. in US-A-3,985,668. Abrasives or polishes should be avoided in the liquid dishwashing detergents for automatic dishwashing, as they can damage the surface of fine crockery, crystal and the like.

As an alternative to the above thixotropic thickeners, small but effective amounts of high molecular weight polyacrylic acid polymers and copolymers and their salts can be added to improve the rheological properties as well as the physical stability of the blends. These polymers and their salts are usually commercially available and have the formula: 89 00 268.

- 20 - fl 2 c - c - R 3 coom 5 in which R 2, R 2 and R 2 may be the same or different and may have the meaning of hydrogen, C 1 -C 2 -lower alkyl or combinations thereof . The value of n is 5-2000, preferably 10-1500 and more especially 20-1000. M has the meaning of hydrogen or an alkali metal such as sodium or potassium, the preferred substituent being sodium. Preferred groups R 1, R 1, and R 1 are hydrogen, methyl, ethyl, and propyl. Preferred acrylic acid monomer represents R 1 to R 2 hydrogen, such as e.g. in acrylic acid, either R 1 and R 1 represent hydrogen and R 2 represents methyl, e.g. with methyl acrylic acid monomer. Polyacrylic acid copolymers can include: copolymers of e.g. acrylic acid or methacrylic acid and polycarboxylic anhydride or acid such as succinic anhydride, succinic acid, maleic acid, maleic anhydride, citric acid and the like.

Specific polyacrylic acid polymers and their salts which can be used include ACRYSOL acrylic acid polymers from Rohm and Haas,

TM

20 ALCOPERSE 110 from Alco or CARBOPOL from B.F. Goodrich. To polyacrylic

TM

acid copolymer that can be used is SOKALAN CP5, available from BASF.

The relative amounts of the polymer used in the detergent compositions can be about 0-3%, depending on the presence and amount of other stabilizing components.

The detergent compositions of the present invention may also contain various inorganic wash strength enhancing materials, such as alkali metal tripolyphosphates and silicates.

A preferred washing power booster or builder material 30 is sodium tripolyphosphate (NaTPP) that softens hard water minerals and emulsifies and / or peptizes dirt. The amount of NaTPP used in the liquid automatic dishwashing detergent according to the invention is in the range of from about 5 to about 35% by weight, preferably from about 20 to about 30% by weight. The NaTPP should preferably be free of heavy metals, which tend to be the preferred sodium hypochlorite 89 00 26 8.

- 21 -

and decompose or deactivate other chlorine bleaches. The NaTPP

can be anhydrous or hydrated, including the stable hexahydrate with a degree of hydration of 6 corresponding to about 22% by weight of water or more. The NaTPP is commercially available in the anhydrous or hydrated TM.

5 dated form under the trademarks THERMPHOS NW resp. THERMPHOS NH

Preferred liquid dishwashing detergents for automatic dishwashing have been used e.g. obtained using a weight ratio of anhydrous NaTPP to NaTPP hexahydrate in the range of about 0.5: 1 to about 2: 1, preferably about 1: 1.

In detergents in which no or a low phosphate content is desired, other functionally equivalent builder materials can be used instead of NaTPP. For example, e.g. 5 - 35% aluminosilicate zeolite are used in the agents of the present invention when the sodium silicate content is increased to 25% or more.

Preferably, the automatic dishwashing liquid dishwashing compositions of the present invention make an alkali metal silicate, e.g. sodium silicate, part, to ensure the alkalinity of the agent as well as to protect hard surfaces such as glazes and fine porcelain cartridges. The silicate component is present in the liquid dishwashing detergents for automatic dishwashing in an amount of from 0 to about 50 wt%, preferably from about 2.5 to 20 wt% and more particularly from about 5.0 to about 15.0 wt%. The silicate is usually added in the form of an aqueous solution, preferably at a ratio of about 0: S102 from about 1: 2.2 to 1: 2.8.

A chlorine bleach can be used in the automatic dishwashing liquid dishwashing preparations prepared in accordance with the method of the present invention. The source of the chlorine compound is preferably an alkali metal hypochlorite, e.g. potassium hypochlorite, lithium hypochlorite, calcium hypochlorite, magnesium hypochlorite and more particularly sodium hypochlorite. Other sources of bleached chlorine compounds include dichloroisocyanurate, dichlorodimethylhydantoin, and chlorinated PSP. The liquid automatic dishwashing detergents of the invention should contain sufficient chlorine compounds to provide about 0.2-4.0 wt%, preferably about 0.8-1.6 wt% available chlorine, determined e.g. by 89 00268.

- 22 - acidify 100 din of the agent with excess hydrochloric acid. An about 0.2 to about 4.0 wt% sodium hypochlorite-containing solution contains or provides about the same percentage of available chlorine.

As an alternative to the chlorine bleach, a stabilized enzyme system can be used to provide the dishwashing detergents with the cleaning action of proteolytic and amylolytic enzymes. The stabilized system preferably contains 0.5-2.0 wt% enzyme, 1-4 wt% of a water-dispersible proteinaceous material selected from the group consisting of casein and collagen, 0.75-2 wt% of a boron compound and 1.5-4% by weight of an Ot-hydroxycarboxylic acid.

Preferably, the pH of the automatic dishwashing liquid dishwashing preparations prepared according to the method of the present invention is measured to be at least 9.5, preferably about 10-14.0 and more particularly about 11.0-11.5 in a 1% aqueous solution. The liquid automatic dishwashing detergents are adjusted to the desired alkali content by the addition of an alkali metal hydroxide, e.g. sodium hydroxide. Typical sodium hydroxide concentrations in the liquid automatic dishwashing detergent compositions are from about 0 to about 6% by weight, preferably from 0 to 3.0% by weight. The presence of sodium hydroxide performs the additional function of neutralizing the phosphate or the phosphonic acid ester.

An alkali metal carbonate, e.g. sodium carbonate, can also be used in the liquid dishwashing detergents prepared according to the method of the present invention for automatic dishwashing. The carbonate serves as a buffer to maintain the desired pH value. Typical sodium carbonate concentrations in the liquid dishwashing detergents for automatic dishwashing are about 0-9.0 wt%, preferably 2-9.0 wt%.

Fragrances useful in the present invention must be resistant to chemical decomposition and oxidation by the highly active chlorine bleach also present in the blends. Fragrances useful according to the present invention, which come from natural sources, such as extracts of vegetable material, e.g. essential oils, or from synthetic sources available from industrial manufacturing processes. Examples of against bleach 8900268.

Detergent agents useful for imparting a fragrance to the detergent include p-cresol methyl ether, di-hydrolimone epoxide, dodecene-1,2-epoxide and n-undecyl nitrile. Other examples of suitable bleach-resistant fragrances are described in US-A-3,876,551. It will be understood that the chosen fragrance must be fairly stable in a bleaching environment, i.e. it must not be easily oxidized by the hypochlorite in the detergent. This is important for two reasons: first, the loss of hypochlorite would exceed the limits of acceptability in a dishwashing product, and second, the oxidation of the fragrance would reduce the aromatic character of the product and in some cases it would result may be an unpleasant odor. It has been found that addition of fragrance to the detergents in an amount of about 0.01-0.40 wt%, preferably 0.02-0.2 wt%, gives a desirable odor without affecting theological properties or physical stability of the detergent.

The amount of water present in these dishwashing detergents must, of course, be sufficient to obtain the desired viscosity and fluidity without adversely affecting the thixotropic properties of the detergent. The amount of water required is easily determined by routine testing in any given case, and generally it is about 30-75 wt%, preferably about 35-65 wt%. In addition, the water is preferably de-ionized or softened.

In addition to the ingredients described above, the detergent compositions prepared according to the method of the present invention may contain small amounts of further ingredients, usually less than 3% by weight, such as hydrotropic agents such as sodium benzene, toluene, xylene and cumene sulfonates. , preservatives, dyes and pigments and enzymes, all of which must be resistant to chlorine bleaches and strong alkalinity. Chlorinated phthalocyanines and polysulphides of aluminum minosilicate which have a pleasant green resp. give blue tint. TiOj can be used for bleaching or neutralizing discolorations.

Particular preference for eliminating or minimizing 8900268.

Film and staining on glass emanates to low molecular weight polyacrylic acid polymers and their salts with molecular weights in the range 2000 - 10,000, preferably 4,000 - 6,000. Specific polymers that can be used are the low molecular weight polyacrylic acids and their corresponding sodium salts, available from e.g. Rohm

TM

and Haas as ACRYSOL LMW.

The liquid automatic dishwashing detergents according to the invention can be easily used in a known manner for washing dishes, kitchen utensils and the like in an automatic dishwashing machine provided with a suitable detergent dispenser and in an aqueous washing bath containing a effective amount of detergent. Although the invention has been described in particular in connection with its application to liquid automatic dishwashing detergents and methods for their preparation, it will be readily apparent to those skilled in the art that the benefits obtained by incorporating air in a three-part stabilizing system, i.e., an increased physical stability of the thixotropic suspension, applies equally to other thixotropic suspensions.

The invention can be practiced in various ways and the preferred embodiment is described to illustrate the invention with reference to the accompanying examples. t Example 1

A scented thixotropic liquid dishwashing detergent for automatic dishwashing, having the composition described below, was prepared using the preferred method of the present invention, as shown in the accompanying drawing.

Step_ Component wt% water (softened) 41.44 30 PRE-DISPERSION mono- and di-C._ to C.-phosphate ester 8.84 lo 18 (anti-foaming agent) (I) Al-stearate (physical stabilizer) 5.52 sodium- mono- and -didecyl-disulfonated diphenyloxide (surfactant) 44.20 35 Total 100.00 8900268.

- 25 - PREMIXTURE water (softened) 82.37 (II) pre-dispersion (I) 10.43 montmorillonite clay 7.20 total 100.00 5 MAIN CHARGE water (softened) 25.69 (III) premix (II) 17.53 sodium hydroxide ( 50% AB) 2.42 sodium carbonate 5.05 sodium silicate (43.5% AB) 17.42 10 NaTPP hydrate 12.12

NaTPP anhydrous 12.12 sodium hypochlorite (13% A.B.) 7.48 subtotal 99.83 HOMOGENIZATION, 15 COOLING AND PERFUME 0.17 MIXING total 100.00 (IV)

According to the preferred method according to the invention, a predispersion mixture was prepared in a vessel (2) equipped with a rapid

IM

Rotating dispersing element, e.g. Myers HSD. The amount of water introduced into the predispersion vessel was limited, so that the mixture remained viscous and sensitive to high shear dispersion. High-shear dispersion was carried out for about 5-10 minutes, after which the pre-dispersion mixture was pumped through a homogenizer (19) to a pre-mixing vessel (4) where the clay thickener and water were added to the pre-dispersion mixture under weak shear conditions. A blade type mixer, e.g. a baffled crutcher was used in the premix vessel, which mechanically disagglomerated the clay as it was hydrated. The preparation of the premix usually takes about 20 minutes depending on the speed of the mixer. The resulting premix was removed and homogenized in homogenizer (21), then it was charged with water into the main batch vessel (6) where it was subjected to high shear dispersion under

TM

35 using a Myers HSD. During mixing under strong fumes.

The remaining liquid and solid components were added successively into the main batch vessel (6).

When the further ingredients, in particular the solid ingredients, were added, the mixture became more viscous and the high speed disperser ground the particles to a fine particle size, which in turn increased in temperature, to about 52-66 ° C, caused. Continuous high shear dispersion also resulted in entraining a significant relative amount of atmospheric air into the vessel (6) for the main 10 batch, which is in open communication with the atmosphere. High shear dispersion continued for a total of about 20 minutes during which time visible clumps of solid material disappeared and the particle size of the undissolved particles was reduced to form a phase stable dispersion.

The main batch material was then fed through a series of coarse and fine homogenizers (8 and 10), where the material was milled at high speeds for relatively short periods of time to further desagglomerate any remaining solid particles. The resulting product was a stable, thixotropic liquid dishwashing detergent for automatic dishwashing, including entrained bubbles of atmospheric air with diameters in the range of 5 - 80 µm.

If one wishes to add a fragrance to the dishwashing detergent, as in the present example, the material of the main batch is cooled in the heat exchanger (12) of the temperature of the main batch, which is usually higher than 37.8 ° C, typically 44 - 52 ° C, to a temperature of about 29 ° C or less. The cooled main batch material was then passed through a series of in-line static mixers (14) and the resulting product was a stable, perfumed, thixotropic liquid dishwashing detergent for automatic dishwashing.

It has been found that the addition of fragrance to the detergent composition by this method avoids an adverse effect on the rheological properties of the detergent composition or on the long-term phase stability of the detergent composition. The specific gravity of the perfumed detergent was measured (Example 1A). For comparison, a sample of the main batch material (Example 1B) was removed for analysis 8900268.

- 27 - prior to the addition of the fragrance. Measurements of the specific gravity of the total material and the liquid phase were carried out using conventional techniques known in the art.

For example, e.g. the specific gravity of the total detergent is determined by weighing a known volume of the total detergent and an identical volume of water. The ratio of the weight of the total agent to the weight of the water is referred to as "total specific gravity".

The specific gravity of the liquid phase was determined by first sampling a sample of the liquid dishwashing detergent in a conventional centrifuge, e.g. Ivan Sorvall centrifuge, and then spin the centrifuge at a speed of approximately 2000 rpm to remove a sufficient amount of top liquid (clear deaerated liquid phase) to be weighed.

The centrifugation stage requires about 1 - 1 hour to separate a sufficient amount of top liquid layer for different measurements. Then, the specific gravity of the top liquid layer was calculated by dividing the weight of an ampoule with 8 ml of the top liquid layer by the weight of an identical volume of water, which ratio is defined as "liquid phase specific gravity" .

The viscosity of the detergents was measured using a Brookfield HATDV II Model II viscometer with a No. 4 spindle (Brookfield Labs, Stoughton, Mass.). Viscosity was observed after the detergents were sheared for 90 seconds at a shear rate of 20 rpm. The results are summarized below:

Example 1

Property IA 1B

30 specific gravity (TOTAL) 1.28 1.28 specific gravity (LIQUID) 1.28 1.28 viscosity (cP) - 1 day after preparation 5060 4760 viscosity (cP) - 12 weeks after preparation 5150 6350 separation (%) - 12 weeks after preparation 00 35 From the above data it appears that the process according to & 9 0ΘΖ68.

The present invention provides a thixotropic liquid dishwashing liquid for automatic dishwashing which is very stable and not subject to phase separation after long storage periods.

Example 2 The following liquid automatic dishwashing detergents with the compositions described in Table I were prepared in a single open mixer according to an alternative embodiment of the method of the invention.

TABLE I

10 Component Example 2A Example 2B

water 36.90 36.15 mono- and di-C 1 to C 14 -alkyl phosphate ester (anti-foaming agent), 5% 3.20 3.20 sodium mono- and dodecyl disulfonated diphenyloxide (surfactant) 0.80 0.80 stearic acid (physical stabilizer) 0.10 0.10 montmorillonite clay 1.25 0 caustic soda (50% AB) 2.40 2.40 20 sodium carbonate 5.00 5.00 silicate (45% AB) 17.34 17.34

NaTPP hydrate 12.00 12.00

NaTPP anhydrous 12.00 12.00 bleach (11% A.B.) 9.00 9.00 acrylic acid polymer 0 2.00 air (REST) _ 0.01 0.01 TOTAL 100.00 100.00

TM

All of the above ingredients were mixed in a Premier

Mill Mixer at room temperature. In the examples, a 5% aqueous anti-foaming agent (LPKn) dispersion is first prepared by heating and mixing the anti-foaming agent in water until it is dispersed.

TM

Similarly, the surfactant (Dowfax) and a physical stabilizer (stearic acid) are heated to form an emulsion prior to and during introduction into the mixer.

35 After the addition of the surfactant and the physical 89 00268.

The stabilizer is allowed to cool the mixture and the other ingredients are added sequentially in the order shown in Table I while the mixture is subjected to continuous high shear mixing in the presence of atmospheric air.

After addition of the last ingredient, typically a bleaching compound, the mixture is subjected to further high shear mixing to atmospheric air in an amount of ca.

2% to about 10% is entrained in the thixotropic detergent in the form of innumerable bubbles with a diameter in the range of 5-8 µm, 10 balancing the total specific gravity of the product with the specific gravity of the deaerated liquid phase.

As can be seen from the above examples, a three-component air stabilization system, i.e., a physical stabilizer, foam suppressant (anti-foaming agent) and surfactant is used with each mixture.

In each of the resulting liquid detergents, the specific gravity, aeration and phase stability, i.e., phase separation, were measured after standing. The degree of aeration is calculated as follows: density of the deaerated product. , .. density of the aerated product. ΛΛ aeration rate,% =.,. -r ~ z -—> - rv - ^ - ΤΤΊ. - x 100 density of the vented product

The density of the deaerated product is determined by centrifuging the mixture to remove all entrained air, after which the density of the centrifuged mixture is measured by conventional means. The results obtained are summarized below.

Example 2

Property 2A 2B

30 specific gravity (total) 1.28 1.28 specific gravity (liquid) 1.28 1.28 aeration (%) 7.91 7.20 type of separation 0.00 * 0.00 * * 8 weeks after the preparation of the sample.

From the above data it can be seen that liquid detergents 89 00268.

Containing a three-component stabilization system of the present invention have excellent stability.

As can be seen, the air-stabilized agent of Example 2A has a total specific gravity (1.28 g / cm3) which is equal to the specific gravity (1.28 g / cm3) of the detergent. Under these conditions, the detergent has excellent phase stability.

Substantially identical results were obtained with the detergent of Example B in the absence of a thixotropic thickener, e.g. clay, achieving a total specific gravity of 1.29 g / cm3, substantially equal to the specific gravity of the liquid phase of the detergent composition. Example 2B shows that clay is not required to prepare an acceptable stabilized detergent. Such a detergent is further beneficial in that all of its ingredients are completely water-soluble, resulting in superior staining and film-forming performance, compared to thixotropic clay-based detergents.

The invention in its broader aspects is not limited to the specifically described embodiments or examples, and one can depart from it without departing from the principles of the invention and without sacrificing its main advantages.

8900268.

Claims (37)

A thixotropic automatic dishwashing detergent comprising a concentrated dispersion of solid particles in a liquid phase, characterized in that air bubbles are entrained in the dishwashing liquid in an amount sufficient to balance the specific gravity of the liquid phase with the specific weight of the total detergent, thereby improving the physical stability of the thi-xotropic detergent. Dishwashing detergent according to claim 1, wherein the concentrated dispersion forms a washing power booster, an organic material with washing power, a physical stabilizer and a thickening agent. Dishwashing detergent according to claim 2, wherein the concentrated dispersion further comprises a foam-suppressing agent. Dishwashing detergent according to claim 1, wherein the air constitutes 2-10% by volume of the dishwashing detergent. Dishwashing detergent according to claim 1, wherein the air constitutes 4-9% by volume of the dishwashing detergent. Dishwashing detergent according to claim 1, wherein the air constitutes 6.5 - 8.5% by volume of the dishwashing detergent. Dishwasher detergent according to claim 1, wherein the specific gravity of the liquid phase is equal to the specific gravity of the total phases. Dishwashing detergent according to claim 4, wherein the total specific gravity is about 1.20 to about 1.35. Dishwasher detergent according to claim 1, wherein the total specific gravity is about 1.26 to about 1.32. Dishwasher detergent according to claim 1, wherein the air bubbles are bubbles of microscopic size. Dishwashing detergent according to claim 1, wherein the air bubbles are stabilized by a three-component system 30 comprising a surfactant, an anti-foaming agent and a physical stabilizer. Dishwashing detergent according to claim 4, wherein the air bubbles are larger than the solid particles. Dishwashing detergent according to claim 8, wherein the air bubbles have a diameter of about 5 to 80 µm. Dishwasher detergent according to claim 1, wherein the air bubbles have a diameter of about 20-60 µm. Dishwashing detergent according to claim 9, wherein the concentrated dispersion comprises: (a) 5 - 35% alkali metal tripolyphosphate; (b) 0-50% sodium silicate; (C) 0-9% alkali metal carbonate; (d) 0-5% chlorine bleach resistant, water dispersible, organic, detergent active material; (e) 0-5% chlorine bleach resistant foam suppressant; (F) a bleaching chlorine compound in an amount to provide about 0.2-4% available chlorine; (g) a long chain fatty acid or its salt in an effective amount to increase the physical stability of the detergent composition, · 20 (h) air in an amount of about 2-10% by volume; (i) thixotropic thickener in an effective amount to give the detergent a thixotropicity index of about 2.0 to about 10.0; and (j) water in an amount effective to avoid loss of the desired thixotropic properties. Dishwashing detergent according to claim 15, wherein the material with washing power is a compound selected from the group consisting of branched alkali metal mono- and di-CQ-4-alkyl diphenyl oxide mono- and disulfonates and linear alkali metal mono- and di-C 8 -alkyldiphenyloxyde mono- and disulfonates. Dishwashing detergent according to claim 16, wherein the suds suppressant is selected from the group consisting of alkyl phosphonic acid esters and acidic alkyl phosphate esters. 18. Aqueous thixotropic automatic dishwashing detergent comprising 35% by weight: 8900268. - 33 - (a) 5 -35% alkali metal tripolyphosphate; (b) 2.5-20% sodium silicate; (c) 0-9% alkali metal carbonate; (d) 0.1-5% chlorine bleach resistant, water dispersible organic material with washing power; (e) 0.01-5% chlorine bleach resistant foam suppressant; (f) a bleaching chlorine compound in an amount to provide about 0.2-4% available chlorine; (G) a long chain fatty acid or its salt in an amount effective to increase the physical stability of the detergent; (h) stabilized air bubbles in an amount of from about 2 to 10% by volume with dimensions of 5 - 80 µm; (I) a thixotropic thickener in an amount effective to give the dishwashing detergent a thixotropicity index of about 2.0-10.0; and (j) water in an amount effective to avoid the loss of the desired thixotropic properties. Dishwashing detergent according to claim 18, wherein the air (h) is present in an amount such that the total specific gravity of the detergent is approximately equal to the specific gravity of the liquid phase of the detergent. Dishwasher detergent according to claim 19 with a specific gravity of from about 1.20 to about 1.35. Dishwashing detergent according to claim 18, wherein the thickening agent (i) is a sodium salt of a polyacrylic acid. Dishwasher detergent according to claim 19, wherein the physical stabilizer (g) is stearic acid or a salt thereof and is present in an amount from about 0.01 to about 1.0%. Dishwashing detergent according to claim 19, wherein the physical stabilizer (g) is a long chain aliphatic fatty acid or its metal salt. Dishwashing detergent according to claim 19, wherein the thixotropic thickener (i) is present in an amount of about 0.1 to about 10%. 8900268. A dishwashing detergent according to claim 19, wherein the suds suppressant is selected from the group consisting of alkyl phosphonic acid esters and acidic alkyl phosphate esters. 26. A method of preparing a thixotropic automatic dishwashing detergent comprising the steps of preparing a concentrated dispersion of solid particles in a liquid phase, and entraining air bubbles of microscopic size into the detergent in an amount sufficient to balance the specific gravity of the liquid phase with the total specific gravity of the detergent to improve stability. 27. A method of preparing a thixotropic automatic dishwashing detergent having improved phase stability, comprising a concentrated dispersion of solid particles in a liquid phase, characterized in that stabilizing air bubbles are entrained in the detergent in an amount sufficient to specifically to balance the weight of the liquid phase with the total specific gravity of the dishwashing detergent, comprising the following steps: (a) mixing a surfactant, a physical stabilizer and water to form a substantially smooth pre-dispersion, (b) forming a thickener premix containing the pre-dispersion from step (a), a thixotropic thickener and water, and mixing the premix so that the thickener is substantially hydrated, desagglomerated and dispersed throughout the premix, (c) mixing a master batch containing the foregoing mixture from step (b) and water while adding other ingredients, (d) entraining air in an amount of about 2% to about 10% by volume in the detergent, and (e) homogenizing the dishwashing detergent to desagglomerate any solid particles to thus prepare a smooth, thixotropic automatic dishwashing detergent. The method of claim 27, wherein the predispersion (a) further comprises a foam suppressant. The method of claim 27, wherein the pre-dispersion (a) 8900268. is subjected to high shear mixing. The method of claim 28, wherein the premix (b) is subjected to low shear mixing. 31. The method of claim 27, wherein about 4 to about 9% by volume of air is entrained in the dishwashing detergent. The method of claim 28, wherein about 6.5 to about 8.5% by volume of air is entrained in the dishwashing detergent. 33. The method of claim 28, wherein the dishwashing detergent contains at least about 0.1% of a bleach-resistant surfactant. The method of claim 28, wherein the detergent contains at least about 0.01 of a bleach resistant foam suppressant. The method of claim 28, wherein the dishwashing detergent contains at least about 0.01% of a physical stabilizer selected from the group consisting of long chain fatty acids and their salts. The method of claim 28, wherein the dishwashing detergent contains about 0.1 to about 3% thixotropic thickener. 37. The method of claim 28, wherein the thixotropic thickener consists of a high molecular weight polyacrylic acid polymer or copolymer or their salts. The method of claim 28, wherein the air entrained in the dishwashing detergent is in the form of bubbles measuring from about 5 to about 80 µm. 25 8900268.