GB2116199A - Gel-type automatic dishwasher compositions having thixotropic properties - Google Patents

Abstract

An aqueous thixotropic automatic dishwasher composition containing alkali metal tripolyphosphate, sodium silicate, alkali metal carbonate (preferably), bleach-stable surfactant, sodium hypochlorite, mono- or di-(C16-C18) alkyl acid phosphate ester foam suppressor, clay thickener, and sufficient caustic soda to provide a pH of 10.5 to about 13.5

Description

SPECIFICATION Gel-type automatic dishwasher compositions having thixotropic properties The present invention relates to automatic dishwashing detergent compositions having thixotropic properties, improved chemical and physical stability, and which are readily dispersible in the washing medium to provide effective cleaning of dishware, glassware, china and the like.

Commercially available household-machine dishwasher detergent provided in powder form has several disadvantages, e.g. non-uniform composition; costly operations necessary in their manufacture; tendency to cake at high humidities, resulting in the formation of lumps which are difficult to disperse, and dustiness, a source of particular irritation to users who suffer allergies. Liquid forms of such compositions, moreover, generally cannot be used in automatic dishwashers due to high foam levels, unacceptably low viscosities and exceedingly high alkalinity.

Recent research and development activity has focused on the gel or "thixotropic" form of such compositions, e.g. scouring cleansers and automatic-dishwasher products characterised as thixotropic pastes. Dishwasher products so provided are primarily objectionable in that they are insufficiently viscous to remain "anchored" in the dispenser cup of the dishwasher, and moreover yield spotty residues on dishware, glassware, china and the like. Ideally, thixotropic cleansing compositions should be highly viscous in a quiescent state, Bingham plastic in nature, and have relatively high yield values.

When subjected to shear stresses, however, such as being shaken in a container or squeezed through an orifice, they should quickly fluidize and, upon cessation of the applied shear stress, quickly revert to the high viscosity/Bingham plastic state. Stability is likewise of primary importance, i.e. there should be no significant evidence of phase separation or leaking after long standing.

The provision of automatic-dishwasher compositions in gel form having the aforedescribed properties has thus far proved problematical, particularly as regards compositions for use in home dishwasher machines. For effective use, it is generally recommended that the automatic dishwashing detergent, hereinafter also designated ADD, contain (1) sodium tripolyphosphate (NaTPP) to soften or tie up hard-water minerals and to emulsify and/or peptize soil; (2) sodium silicate to supply the alkalinity necessary for effective detergency and to provide protection for fine china glaze and pattern; (3) sodium carbonate, generally considered to be optional, to enhance alkalinity; (4) a chlorine-releasing agent to aid in the elimination of soil specks which lead to water spotting; and (5) defoamer/surfactant to reduce foam, thereby enhancing machine efficiency and supply requisite detergency.See, for example, SDA Detergents in Depth, "Formulations Aspects of Machine Dishwashing," Thomas Oberle (1974).

Cleansers approximating to the aforedescribed composition are mostly liquids or powders. Combining such ingredients in a gel form effective for home-machine use has proved difficult. Generally, such compositions omit hypochlorite bleach, since it tends to react with other chemically active ingredients, particularly surfactant, thereby degrading the suspending or thixotropic agent and impairing its effectiveness. Thus, U.S. Patent No. 4,11 5,308 discloses thixotropic automatic dishwasher pastes containing a suspending agent, e.g. CMC, synthetic clays or the like; inorganic salts including silicates, phosphates, polyphosphates, etc., a small amount of surfactant and a suds depressor. Bleach is not disclosed. U.S. Patent No. 4,147,650 is similar and further includes a hypochlorite bleach.The product is described, however, as a detergent slurry.

U.S. Patent No. 3,985,668 describes abrasive scouring cleaners of gel-like consistency containing (1) suspending agent, preferably the smectite and attapulgite types of the colloid forming clays; (2) abrasive, e.g. siiica sand or perlite; and (3) filler comprising light density powdered polymers, expanded perlite and the like, which has a buoyancy and thus stabilizing effect on the composition in addition to serving as a bulking agent, thereby replacing water otherwise available for undesired supernatant layer formation due to leaking and phase destabilization. The foregoing are the essential ingredients. Optional ingredients include hypochlorite bleach, bleach stable surfactant and buffer, e.g. silicates, carbonates, and monophosphates.Builders, such as NaTPP, can be included as further optional ingredients to supply or supplement building function not provided by the buffer, the amount of such builder not exceeding 5% of the total composition, according to the patent. Maintenance of the desired pH at levels less than 10 is achieved by the buffer/builder components. High pH is said to minimize decomposition of chlorine bleach and undesired interaction between surfactant and bleach. When present, NaTPP is limited to 5%, as stated. Foam killer is not disclosed.

In accordance with the present invention, it has been discovered that improved detergent compositions particularly adapted for use in automatic dishwashers, particularly those of the type found in the home, are provided having the properties desirably characterizing thixotropic, gel-type structure and including each of the various ingredients necessary for effective detergency within such automatic dishwasher.

The present invention aims to provide a detergent composition having thixotropic properties and beneficially adapted for use in an automatic dishwasher.

The invention also aims to provide such a composition having good physical stability with no significant phase separation being evident after prolonged periods of standing.

The invention also aims to provide such a composition wherein problems associated with undesired interaction of chemically active ingredients are eliminated or at least substantially mitigated.

The invention also aims to provide such a composition having the aforementioned stability under the highly alkaline conditions necessary for effective detergent performance.

The invention also aims to provide such a composition having improved rheological properties exhibiting higher viscosities at low shear rates and lower viscosities at high shear rates - thus being advantageously adapted for use in the dispenser cup of automatic dishwashing machines.

The invention also aims to provide such a composition having low foam characteristics, improved detergency and which is readily dispersible in the washing machine.

According to the broader aspects of the present invention a normally gel-like aqueous automatic dishwasher-detergent composition having thixotropic properties comprises, by weight, from about: (a) 5 to 35% water-soluble alkali metal tripolyphosphate having an average degree of hydration of from about 1 to 5; (b) 2.5 to 20% sodium silicate; (c) O to 9% water-soluble alkali metal carbonate; (d) 0.1 to 5% bleach stable, dispersible organic surfactant; (e) 0.1 to 0.5% of a mono- or di-(C18-C18) alkylester of phosphoric acid as a foam depressor; (f) 320% NaOCI solution of 13% available chlorine content; (g) 1.5 to 10% inorganic, colloid-forming clay thickening agent; and (h) sufficient sodium hydroxide to provide a pH 10.5-13.5, said composition having a thixotropy index of about 2.5 to 10.

ADD compositions so formulated are low-foaming; stable, both chemically and physically; are readily soluble in the washing medium and most effective at pH values best conducive to improved cleaning performance, viz, pH 10.5--13.5. The compositions are normally of gel consistency, i.e. a highly viscous, opaque jelly-like material having Bingham plastic character and thus relatively high yield values. Accordingly a definite shear force is necessary to initiate or increase flow, such as would obtain within the agitated dispenser cup of an energized automatic dishwasher. Under such conditions, the composition is quickly fluidized and easily dispersed. When the shear force is discontinued, the fluid composition quickly reverts to a high viscosity, Bingham plastic state, closely approximating its prior consistency.

Generally, ADD effectiveness is directly related to (a) available chlorine levels; (b) alkalinity; (c) solubility in washing medium; and (d) de-foamer efficacy important herein that the pH of the ADD composition be from about 10.5-13.5 and preferably at least about 11.5. The use of NaOH herein is thus essential, since without NaOH, the ADD pH is below 10.5. At this pH, the ADD product is too viscous, i.e. solid-like, and thus not readily fluidized under the shear-force levels created within the dispenser cup under normal machine-operating conditions. In essence, the composition loses much, if not all, of its thixotropic character. In that case, addition of NaOH is thus essential to increase pH and flowability properties. The presence of carbonate is often needed herein, since it acts as a buffer enabling maintenance of the necessary pH level.Excess carbonate is to be avoided, however since it may cause the formation of needle-like crystals of carbonate, thereby impairing the stability and/or functionality of the ADD product. The caustic soda serves the further vital function of neutralizing the phosphoric acid ester foam depressor.

Other criteria governing ingredient selection herein and essential to providing a stable, effective ADD product having thixotropic properties are as follows: The NaTPP must be free of heavy metal, since the latter tends to decompose the sodium hypochlorite. On average, the NaTPP contains about 5-1 5% by weight water, corresponding to an average degree of hydration of about 1 to 5. If only the hexahydrate is used, the detergent product is liquid and has little if any thixotropic character. If only the anhydrous NaTPP is used, the product is too thick and therefore unsuitable. Effective compositions are obtained, for example, when using a 0.5:1 to 2:1 weight ratio of anhydrous to hexahydrated NaTPP, values of about 1:1 being particularly preferred.Foam depressor is essential to increase dishwashermachine efficiency and to diminish destabilizing effects which might occur due to the presence of excess foam within the washer during use. Available chlorine levels are supplied herein by sodium hypochlorite rather than, for example, the dichloroisocyanurates used in current powder detergents.

The ADD product exhibits improves rheological properties as evaluated by testing product viscosity as a function of shear rate. Investigation confirms that the compositions exhibit higher viscosity at a low shear rate and lower viscosity at a high shear rate the data indicating efficient fluidization and gellation well within the shear rates extant within the dishwasher machine. In practical terms, this means improved pouring and processing characteristics as well as less leaking in the machinedispenser-cup, compared to current liquid ADD products.For applied shear rates corresponding to 3 to 30 rpm, viscosities (Brookfield) correspondingly range from about 1 5,000-30,000 cps to about 3000-5000 cps, as measured at room temperature by means of an LVT Brookfield viscosimeter after 3 minutes using a No. 4 spindle. A shear rate of 7.4 sec-' corresponds to a spindle rpm of about 3. An approximate ten-fold increase in shear rate produces a six- to seven-fold reduction in viscosity. With current ADD gels, the corresponding reduction in viscosity is only about two-fold. Moreover, with such compositions, the initial viscosity taken at about 3 rpm is only about 2500-2700 cps. The compositions of the present invention thus exhibit threshold fluidizations at lower shear rates and of significantly greater extent in terms of incremental increases in shear rate vs.

incremental decrease in viscosity. This property of the ADD products of the present invention is summarized in terms of a thixotropic index (TI) which is the ratio of the apparent LVT Brookfield viscosity of the sample after 3 minutes at room temperature using a No. 4 spindle a) at 3 rpm and b) at 30 rpm. The present compositions have a TI of from about 2.5 to 10 and preferably 6 to 8. Each of the ADD compositions tested exhibited substantial and quick return to prior quiescent state consistency when the shear force was discontinued.

In preparing the ADD product, one should dissolve or disperse first all the inorganic salts, i.e.

carbonate, silicate and tripolyphosphate, in the aqueous medium. Thickening agent is added last. The phosphoric acid ester foam depressor is preliminarily provided as an aqueous dispersion, as is the thickening agent. The ester dispersion, caustic soda and inorganic salts are first mixed at elevated temperatures in aqueous solution (deionized water) and thereafter cooled, using agitation throughout.

Bleach, surfactant and thickener dispersion at room temperature are thereafter added to the cooled (25-350C) solution. The amount of water used is such as to provide an A.l. concentration in the ADD product of from about 3575%, a range of about 5065% being preferred.

The inorganic salts herein comprise, by weight of total product, about: (a) 5 to 35% and preferably about 20 to 30% NaTPP; (b) 2.5 to 20% and preferably about 10 to 15% sodium silicate having an Na2O : SiO2 ratio of about 0.3 to 0.5%, and (c) 0 to 9%, preferably about 4 to 7%, alkali metal carbonate, preferably sodium carbonate. These salts should provide a total salt concentration of about 20 to 50% and preferably about 35 to 45%.

Bleaching agent comprises sodium hypochlorite (NaOCI) solution of 13% available CI in amounts of about 320%, preferably about 712%.

Caustic soda, as mentioned, should be sufficient to maintain a pH of 10.5 to about 1 3.5 and preferably about 11.5 to about 12.7. Generally these amounts will be about 0.5 to 3%, and in any event at least sufficient to neutralize the foam depressor phosphoric acid ester compound.

The preferred foam depressor comprises mono- and/or di-(C16-C18) alkyl esters of phosphoric acid in a range of about 0.1 to 0.5% and preferably about 0.15 to 0.3%, specific amounts depending in part on the quantity of surfactant present.

Surfactants useful herein must be stable in the presence of hypochlorite bleach and preferably comprise those of the anionic, amine oxide, phosphine oxide, sulphoxide or betaine types, the first mentioned anionics being most preferred. They are used in amounts ranging from about 0.1 to 5% and preferably about 0.3 to 0.8%. To insure adequate foam suppression, it is generally advisable to maintain a surfactant; foam-depressor weight ratio of about 10.1 to 1:1 and preferably about 1.5:1 to 4:1.

Particularly preferred surfactants herein are the linear or branched alkali metal mono- and/or di (CaC14) alkyl diphenyl oxide mono- and/or disulphonates, commercially available for example as DOWFAX (Registered Trade Mark) 3B-2 and DOWFAX 2A-1. In general, the paraffin sulphonates tend to impair, if not destroy thixotropy, having been found to unduly increase viscosity causing severe shearing force problems. In addition, the surfactant should be compatible with the other ingredients of the composition. Other suitable surfactants include the primary alkylsulphates, alkylsulphonates, alkylarylsulphonates and sec.-alkylsulphates.Examples are sodium C10-C18 alkylsulphates such as sodium dodecylsulphate, sodium tallow alcohol-sulphate, sodium C10-C18 alkanesulphonates, such as sodium hexadecyl-1 -sulphonate; sodium C12-C18 alkylbenzenesulphonates such as sodium dodecylbenzenesulphonate, and the corresponding potassium salts.

As other suitable surfactants or detergents, the amine oxide surfactants are typically of the structure R2R1NO, in which each R represents a lower alkyl group, for instance methyl, and R1 represents a long chain alkyl group having from 8 to 22 carbon atoms, for instance a lauryl, myristyl, palmityl or cetyl group. Instead of an amine oxide, a corresponding surfactant phosphine oxide R2R1PO or sulphoxide RR1SO can be employed. Betaine surfactants are typically of the structure R2R1N + R"COO-, in which each R represents a lower alkyl group, R1 represents a long chain alkyl group as above and R" represents an alkylene group having from 1 to 5 carbon atoms.Specific examples of these surfactants are lauryl-dimethylamine oxide, myristyldimethylamine oxide, cocodimethylamine oxide, hardened tallow dimethyl amine oxide, the corresponding phosphine oxides and sulphoxides, and the corresponding betaines including dodecyldimethylammonium acetate, tetradecyl-diethylammonium pentanoate, hexadecyldimethylammonium hexanoate and the like. For biodegradability, the alkyl groups in these surfactants should be linear, and such compounds are preferred.

Surfactants of the foregoing type, all well known in the art are described, for example, in U.S.

Patents 3,985,668 and 4,271 ,Q30.

Thickening or suspending agents useful herein generally comprise the inorganic, colloid-forming clays of smectite and/or attapulgite types, the former being preferred. These materials affect the rheological properties of the composition and are used in amounts of from about 2.5 to 4%, the amount selected being in any event sufficient to confer the desired Bingham plastic character. Smectite clays include montmorillonite (bentonite), the preferred species, hectorite, saponite, and the like. Materials of this type are available under trade names such as Thixogel (Registered Trade Mark) No. 1 and Gelwhite (Registered Trade Mark) GP from Georgia Kaolin Company (both being montmorillonites). Attapulgite clays include the materials commercially available under the trade name Attagel (Registered Trade Mark), i.e. Attagel 40, Attagel 50 and Attagel 1 50 from Engelhard Minerals and Chemicals Corporation.

Mixtures of smectite and attapulgite in weight ratios of 4:1 to 1:5 are useful herein.

Suspending agents of the foregoing type are well known in the art, being described, for example, in U.S. Patent No. 3,985,668 referred to above.

Other ingredients useful in the ADD compositions of the present invention include dyestuffs to provide a pleasantly coloured composition. Particularly preferred are the chlorinated phthalocyanines and polysulphides of aluminosilicate which provide green and blue tints respectively.

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

Percentages herein are by weight and based on total product unless otherwise indicated.

EXAMPLE I A preliminary dispersion of GELWHITE GP (hydration) thickener. 3 g in 17 g water, was prepared alkyl esters of phosphoric acid, 0.16 g, in 6 g water was prepared by mixing at 600C for 30 minutes using a disk impeller. This dispersion is designated Part 1.

A preliminary dispersion of GELWHITE GP (hydrotion) thickener, 3 g in 17 g water, was prepared by mixing at 700C for 10 minutes using a Z-Blade mixer. This dispersion is designated Part 2.

The following ingredients were mixed in a Giusti mixer at 50-600C: % Al% Deionized water 16.9 Part 1 6.16 0.16 Caustic soda solution, 49% NaOH 2.40 1.2 Sodium carbonate 7.00 7.0 Sodium silicate (1:2.4) solution-47.5%solids 13.74 6.5 Sodium TPP (substantially anhydrous i.e. containing 12.00 11.54 0-5%, especially 3%, moisture) Sodium TPP (hexahydrate) 12.00 9.36 The mixture was cooled at 25-300C and agitation maintained throughout, and the following ingredients at room temperature were added thereto:: Sodium hypochlorite solution - (13% available chlorine) 7.615 1.0 Part 2 (dispersed with a high-speed turbine) 20.00 3.0 Dowfax 3B-2 (sodium monodecyl/didecyl disulphonated 0.80 0.36 diphenyl oxide, 45% Al) An opaque composition (about 40% Al) having a gel-like consistency was obtained. The composition was determined to have a TI of about 7, according to the procedure hereinbefore described, based upon apparent viscosity values of 28,000 cps and 4,000 cps at 3 rpm and 30 rpm respectively using a Brookfield viscometer with a No. 4 Spindle. When tested in an automatic dishwasher apparatus provided with a dispenser cup, the above composition provided excellent cleaning performance and was easily and quickly dispensed. The composition was observed to be satisfactorily nonfoaming.Little or no phase separation was observed after prolonged standing in a closed container. The pH of the composition, measured as a 1% solution in water, was 11.6. When conducting the shear-test evaluations, it was observed that the composition quickly reverted to its prior quiescent state consistency, suggesting no appreciable loss of yield value when tested within the limits hereinbefore described, i.e. within shear-force limiting values at least approximating those extant within an energized automatic dishwasher. No discernible differences were observed when the ADD product was dispensed by squeeze tube rather than by dispenser cup.

EXAMPLE 2 Example 1, illustrating a combined polyphosphate carbonate-silicate concentration of about 37% was repeated, but varying the total concentration of such salts within the limits previously given. Best results were obtained at a combined-salt concentration of at least about 30% and particularly when the sodium tripolyphosphate concentration is at least about 20%. Higher silicate concentrations, desirable to protect china glaze and patterns, also impart higher alkalinity which can be compensated for by appropriately reducing the caustic soda concentration and/or adjusting the sodium carbonate (buffer) concentration. The composition appears to be most sensitive, from the point of view of the results to variations in the NaTPP concentration (the higher concentration range is more effective) as well as its degree of hydration.Variations in surfactant concentration generally require corresponding and direct variations in foam-suppressor concentration to achieve the desired low-foam levels.

Decrease of the pH of the composition below about 10.5 is accompanied by significant decrease in composition effectiveness, as well as corresponding decrease of flowability.

EXAMPLE 3 Similar results were obtained when the procedure of Example 1 was repeated, but when certain ingredients were varied namely replacing the Dowfax with an alkyl sulphate surfactant, e.g. sodium coconut alkyl sulphate, the Gel White with an attapulgite clay, e.g. Attagel 50; or a 2 :1 mixture of montmorillonite and Attagel 50.

EXAMPLE 4 The addition of small amounts, e.g. 0.003--0:05% of chlorinated phthalocyanine and aluminosilicate dyes respectively to the Example 1 composition (included with the preliminary thickener dispersion or post-added to the cooled solution) produced pleasantly coloured green and blue compositions respectively.

Claims (14)

1. An aqueous automatic dishwasher composition comprising approximately by weight: (a) 5 to 35% water-soluble alkali metal tripolyphosphate having an average degree of hydration of about 1 to 5; (b) 2.5 to 20% sodium silicate; (c) O to 9% water-soluble alkali metal carbonate; (d) 0.1 to 5% bleach stable, water-dispersible organic surfactant; (e) 0.1 to 0.5% of a mono- or di- or mono- and di (C16-C18) alkyl ester of phosphoric acid as a foam suppressor; (f) 320% of sodium hypochlorite solution containing 13% available chlorine; (g) 1.5 to 10% inorganic, colloid-forming clay thickener; and (h) sufficient sodium hydroxide to provide a pH of 10.5 to about 13.5, the amount of phosphoric acid ester being sufficient to provide low-foaming characteristics, the amount of sodium hydroxide being at least sufficient to neutralize the said phosphoric acid ester, and the composition having a thixotropy index (as defined herein) of about 2.5 to 10.

2. A composition as claimed in Claim 1 in which the weight ratio of surfactant to foam suppressor is about 10 to 1 to 1 to 1.

3. A composition as claimed in Claim 1 or Claim 2 in which the total concentration of tripolyphosphate, silicate and carbonate is at least about 20%.

4. A composition as claimed in Claim 1,2 or 3 in which the concentration of tripolyphosphate is about 20 to 30%.

5. A composition as claimed in Claim 1, 2, 3 or 4 in which the tripolyphosphate comprises a mixture of the substantially anhydrous and the hexahydrate forms thereof in a corresponding weight ratio of about 1:2 to 2:1.

6. A composition as claimed in Claim 5 in which the said weight ratio is about 1:1.

7. A composition as claimed in any one of Claims 1 to 6 further containing an at least tinting amount of dyestuff.

8. A composition as claimed in any one of Claims 1 to 7 in which the said thickener is a smectite or an attapulgite clay or a mixture thereof.

9. A composition as claimed in any one of Claims 1 to 8 in which the said surfactant is an alkali metal Cs to C14 alkyl diphenyl oxide sulphonate.

10. A composition as claimed in any one of Claims 1 to 9 in which the said tripolyphosphate is a sodium tripolyphosphate; the said carbonate is sodium carbonate; the said surfactant is a mixture of mono- and di-(C5 to C14 alkyl) diphenyl oxide disulphonates and the said thickening agent is bentonite.

11. A composition as claimed in any one of Claims 1 to 10 having a pH of 10.5 to about 13.5.

12. A composition as claimed in Claim 11 having a pH of about 11.5 to about 12.7.

1 3. A composition as claimed in any one of Claims 1 to 12 having a thixotropy index of about 6 to 8.

14. A composition as claimed in Claim 1 substantially as specifically described herein with reference to any one of the accompanying Examples.