WO1994003574A1

WO1994003574A1 - Machine dishwashing and rinse aid compositions

Info

Publication number: WO1994003574A1
Application number: PCT/EP1993/001996
Authority: WO
Inventors: Petrus Adrianus J. M. Angevaare; Stuart William Carr; James William Gordon; Kevin Ronald Franklin; Antoine Pierre A. F. Rocourt
Original assignee: Unilever N.V.; Unilever Plc
Priority date: 1992-08-07
Filing date: 1993-07-26
Publication date: 1994-02-17
Also published as: AU4703093A

Abstract

A machine dishwashing or rinse aid composition having improved performance on glass appearance is disclosed comprising an effective level of a hydrotalcite compound having general empirical formula: [Mk+mNn+p(OH)2]Azy-.xH2O, wherein M is any 1+ or 2+ cation or combination thereof; N is any 3+ or 4+ cation or combination thereof; k is the sum of the individual mole fractions of the 1+ cations; m is the sum of the individual mole fractions of the 2+ cations; n is the sum of the individual fractions of the 3+ cations; p is the sum of the individual mole fractions of the 4+ cations; where either but not both of k and m or n and p can be zero and k + m + n + p = 1; Azy- is any anion of charge y- and mole fraction z, or combination of anions of similar or differing y, and k + 2m + 3n + 4p - 2 - zy + 0 and x can range from 1 to 100. Preferred hydrotalcite compounds have the formulas: [Zn¿4?Al2(OH)12](NO3)2.xH2O, and [Mg4Al2(OH)12]Cl2.3H2O.

Description

MACHINE DISHWASHING AND RINSE AID COMPOSITIONS

Field of the invention

This invention relates to machine dish- and warewashing compositions. These compositions are used for the cleaning of housewares such as pots, pans, dishes, cups, saucers, bottles, glassware, crockery, cutlery and other kitchen utensils in automatic-dishwashing and warewashing machines. For brevity sake these compositions are referred to in the description as machine dishwashing compositions.

The invention also relates to rinse aid compositions for use in the final rinse step of the washing machine operation.

Background of the invention

Machine dishwashing compositions usually contain as main components a builder or builder mixture, buffering and/or alkaline agents, a bleaching agent which may-be a chlorine or oxygen bleach, and lately also enzymes. Such machine dishwashing compositions are used in the main wash step of machine dishwashing and in general have a satisfactory -leaning performance.

It is, however, well known in the dishwashing art that the visual appearance of the cleaned article is a critical factor for a dishwashing composition to be satisfactory to the consumer. Frequently after cleaning of an article a film is formed thereon, which results in the article showing a dull surface when dry, or spots are formed on an article upon drying, both phenomena causing the article to have an "unclean" visual appearance.

It is customary to add to the rinsing water a rinse aid composition which causes the articles to dry more evenly and improves the visual appearance of the articles when dry. Although such rinse aid compositions improve said visual appearance in comparison with articles which have not been rinsed with a rinse aid containing rinse liquor, said visual appearance may still need improvement, as, despite the use of a rinse aid, some film- and spot- formation may still occur.

It is known from EP-A-0,139,329, EP-A-0,139,331 and EP-A-0,140,435 that the incorporation of an effective level of a layered clay in machine dishwashing compositions reduces the problem of film and spot formation on the washed articles, thereby improving the so-called "glass appearance". EP-A-0139.330 discloses the incorporation of a layered clay in a rinse aid composition.

Suitable layered clay minerals according to these art references belong to the geological classes of the smectites, the kaolins, the illites, the chlorites, the attapulgites and the mixed layer clays, which may be either naturally occurring or synthetic, preferably the commercial synthetic hectorites ex Laporte Industries Ltd, known under the tradename Laponite®.

Without wishing to be bound by any theory it is believed that the layered clay performs this task by providing a very large surface area in solution which then picks up food fragments, especially proteins and protein/fat complexes, that would otherwise redeposit onto the washed articles, in other words via the mechanism of adsorption.

Although the glass appearance benefit of Laponite® clay can indeed be demonstrated, the effect is still far from ideal, especially at higher protein concentrations in the wash liquor.

It is therefore that there is a vivid interest amongst researchers to diligently look for better alternatives, since a good glass appearance is one of the most striking effects observed by consumers for judging the quality of a machine dishwashing product. Object of the invention

It is an object of the invention to provide a machine diεhwasing composition having improved performance on glass appearance, i.e. having improved reduction to form films and spots on the articles cleaned therewith. It is another object of the invention to provide an improved rinse aid composition.

Summary of the invention It has now surprisingly been found that the above object can be achieved by the incorporation in a machine dishwashing composition or in a rinse aid composition of an effective level of a hydrotalcite compound, preferably a Zn/Al or Mg/Al hydrotalcite. The hydrotalcite compound can be used according to the invention as partial or preferably complete replacement for the layered clay of the art.

Description of the invention

The term "hydrotalcite" is used herein to refer to the naturally occurring material as well as to the synthetic forms of the hydrotalcite group of compounds. Use of hydrotalcite-like materials as dye-transfer reducing agent in fabric washing detergent compositions is described in EP-A-0,431,867, and use thereof in oral compositions to combat growth of dental plaque is described in EP-A-0,368,420.

Naturally occurring hydrotalcite is a Mg/Al hydroxy carbonate mineral having a molar composition [Mg₆ Al₂(OH)₁₆]C0₃.4H₂0 and consists of positively charged hydroxide sheets alternating with negatively charged inter- layer sheets. The positive charge on the hydroxide streets arises from isomorphic replacement of approximately one third of magnesium atoms by aluminum creating the necessity for the compound to take up anions in-between the sheets for charge compensation. Thus hydrotalcites are layered compounds with an intracrystalline void space created by the intercalation of anions and water, which is in contrast to clays that have a negatively charged layer also as a result of isomorphic substitutions and, therefore, intercalate cations for charge balance, making them the charge-wise mirror image of hydrotalcites.

By synthesis, various combinations of mono-divalent (e.g. Li⁺ Mg²⁺, Cu²⁺, Zn²⁺, Ni²⁺, Sn²⁺, Ca²⁺, Sr²⁺) and tri- tetravalent cations (e.g. Cr³⁺, Fe³⁺, Al³⁺, Ti⁴⁺, Sn ⁺) and a wide variety of anions (e.g. C0₃ ²~, N0₃ ^", S0₄ ^2~. Cl^") are possible giving rise to an entire family of hydrotalcite compounds with the general empirical formula: ₊m N_n+p (OH)₂ A ^" . X H₂0.

The invention therefore provides a machine dishwashing composition or a rinse aid composition comprising an effective level of a hydrotalcite compound having the general empirical formula:

[M_k+m N_n+p (0H)₂]A₂y- . x H₂0.

where:

M is any 1 + or 2 + cation or combination thereof;

N is any 3 + or 4 + cation or combination thereof; k is the sum of the individual mole fractions of the 1 + cations; m is the sum of the individual mole fractions of the 2 + cations; n is the sum of the individual mole fractions of the 3 + cations; p is the sum of the individual mole fractions of the 4 + cations, where either but not both of k and m or n and p can be zero and k + m + n + p = l ;

A₂~^y is any anion of charge y- and mole fraction z, or combination of anions of similar or differing y, and k + 2m

+ 3n + 4p -2 -zy = 0 and x can range from 1- 100, depending upon and consistent with the molar composition. The above definition of the hydrotalcite compound in the composition of the present invention includes the mixed metal hydroxide compounds disclosed by US-A-5, 015,409 and US-A-5, 154 , 932, both of which documents are incorporated herein for all purposes.

Preferred cations M in the above formula are Mg²⁺, Zn²⁺, Fe²⁺, Cu²⁺, particularly Mg²⁺, Zn²⁺ and Cu²⁺.

Preferred cations N in the above formula are Al³⁺, Fe³⁺, Ti⁴⁺, Sn⁴⁺, particularly Al³⁺ and Ti⁴⁺.

The anion A may be inorganic or organic. Preferred inorganic anions A are N0₃~, C0₃ ^2-, S0₄ ^2" and Cl~, Br~ and I~. The best results were achieved with the monovalent anions, such as N0₃ ^" and Cl~. Examples of organic anions are carboxylate ions, such as citrate and stearate.

Preferred compounds are those wherein the M/N- ratio does not exceed 5.

Examples of such hydrotalcite compounds include:

(i) the natural hydrocalcite,

(ii) synthetic hydrotalcite,

(iii) Mg/Al hydroxy nitrates, carbonates, sulphates, chlorides,

(iv) Zn/Al hydroxy nitrates, carbonates, sulphates, chlorides,

(v) Li/Al hydroxy nitrates, carbonates, sulphates, chlorides, (vi) Ca/Al hydroxy nitrates, carbonates, sulphates, chlorides,

(vii) Mg/Fe hydroxynitrates, carbonates, sulphates, chlorides,

(viii)Zn/Cr hydroxy nitrates, carbonates, sulphates, chlorides. Specific examples include:

1) [Mg₆Al₂(OH)₁₆]C0₃.4H₂0

2) [Zn₄Al₂(OH)₁₂] (N0₃)₂.xH₂0

3) [Mg₆Al₂(OH)₁₆] (N0₃)₂.xH₂0 4) [Mg₄Al₂(OH)₁₂]C0₃.xH₂0

5) [Mg₈Al₂(OH)₂₀](NO₃)₂.xH₂O

6) [Mg₆Fe₂(OH)₁₆]C0₃.xH₂0

7) [Zn₆Al₂(OH)₁₆] (N0₃)₂.xH₂O

8) [Zn₄Al₂(OH)₁₂] (C0₃) .XH₂0 9) [Zn₄Al₂(OH)₁₂]S0₄.xH₂0

10) [Li₂Al₄(0H)₁₂] (N0₃)₂.XH₂0

11) [Ca₄Al₂(0H)₁₂] (N0₃)₂.xH₂0

12) [Zn₄Cr₂(0H)₁₂] (N0₃)₂.xH₂0

13) [Mg₄Al₂(OH)₁₂](Cl)₁₂.3H₂0

Though any of the above described hydrotalcite compounds is usable within the invention, preferred hydrotalcites are the Zn/Al and Mg/Al hydroxy nitrates and chlorides. A particularly preferred hydrotalcite is Zn/Al hydroxy nitrate of the following molar composition: [Zn₄ Al₂ (OH)₁₂] (N0₃)₂.xH₂0. wherein x is from 2-5.

The effective level of hydrotalcite compound to be included in the machine dishwashing composition of the invention will range from about 0.01 to 40% by weight, usually from 0.1 to 20% by weight, preferably from 0.5 to 10% and most preferably from 0.5 - 5% by weight.

Preferably the hydrotalcite material has a particle size of less than 250 μm, more preferably less than 100 μm, i.e. smaller than the micro-filter mesh size of the dishwashing machine. The crystal platelet size of the hydrotalcite material is preferably less than 0.4 μm, more preferably less than 0.2 μm, for obtaining a good glass appearance performance. The machine dishwashing composition of the invention will normally also contain a builder or builder mixture, buffering and/or alkaline agents, optionally but preferably also a bleaching agent and an enzyme or mixtures of enzymes.

The builder material

Builder materials (phosphates and non-phosphate builder materials) are well-known in the art and many types of organic and inorganic compounds have been described in literature. They are normally used in all sorts of cleaning compositions to provide alkalinity and buffering capacity, prevent flocculation, maintain ionic strength, extract metals from soils and/or remove alkaline-earth metal ions from washing solutions.

The builder material usable herein can be any one or mixture of the various phosphate and preferably non- phosphate builder materials, such as for example the alkalimetal citrates, carbonates and bicarbonates; nitrilotriacetic acid (NTA) ; dipicolinic acid (DPA) ; oxydisuccinic acid (ODS) ; alkyl- and alkenylsuccinates (AKS) ; layered silicate; and zeolites. They may be present in the composition of the invention in an amount of from 10% up to about 90% by weight, preferably from 20% to 80% by weight.

Particularly preferred builders are citrates, alkenylsuccinates, carbonates, bicarbonates, zeolites, and mixtures thereof.

The buffering and/or alkaline agent

This is normally an alkalimetal silicate, preferably sodium silicate at a level of from about 1 to about 70% by weight, preferably from 5 to 40% by weight. This material is employed as a cleaning ingredient, source of alkalinity, metal corrosion inhibitor and protector of glaze on china tableware. Especially effective is sodium silicate having a mol ratio of Si0₂:Na₂0 of from about 1.0 to about 3.3., preferably from about 1.8 to about 2.5, normally referred to as sodium disilicate.

NaOH anά/or KOH are also commonly used to provide alkalinity in compositions for industrial warewashing machines.

The bleaching agent If present the amount of bleaching agent will preferably lie in a range from 1 to 30% by weight. Alkali metal hypochlorite may be incorporated. Other chlorine bleaches are alkali metal salts of di- and tri-chloro and di- and tri-bromo cyanuric acids.

Preferred bleaches are the peroxygen bleaches, such as sodium perborate (tetra- or monohydrate) or sodium percarbonate. These are preferably used in conjunction with a bleach activator which allows the liberation of active oxygen species at a lower temperature. Numerous examples of activators of this type, often also referred to as bleach or peracid precursors, are known in the art. Preferred bleach activators are tetraacetyl ethylene diamine (TAED) , glucose pentaacetate (GPA) and the mono-long chain acyl tetraacetyl glucoses as disclosed in WO 91/10719, but other activators such as choline sulphophenylcarbonate (CSPC) as disclosed in US Patents 4,751,015 and 4,818,426 can be used. The amounts of sodium perborate or percarbonate and bleach activator in the compositions preferably do not exceed 20% and 10% by weight respectively, e.g. from 4-20% and from 2-10% by weight respectively.

Another peroxygen bleach is potassium monopersulphate. Further peroxygen bleaches which may be used are the organic peroxyacids and their metal salts. Typical peroxy- acids include:

(i) peroxybenzoic acid and ring-substituted peroxybenzoic acids, e.g. peroxy-α-naphthoic acid;

(ii) aliphatic and substituted aliphatic monoperoxy acids, e.g. peroxylauric acid and peroxystearic acid;

(iii) 1, 12-diperoxydodecanedioic acid (DPDA) ;

(iv) 1, 9-diperoxyazelaic acid;

(v) diperoxybrassylic acid; diperoxysebacic acid and diperoxyisophthalic acid;

(vi) 2-decyldiperoxybutane-l,4-dioic acid; and

(vii) phthaloylamido peroxycaproic acid (PAP)

Instead of or together with said bleach activators, a bleach catalyst, such as the manganese complexes of EP-A- 458,397 and the sulphonimines of US Patents 5,041,232 and 5,047,163 may also be added.

Enzymes

Amylolytic and/or proteolytic enzymes are normally used. The amylolytic enzymes usable herein can be those derived from bacteria or fungi. Preferred amylolytic enzymes are those prepared and described in GB Patent No. 1,296,839,

cultivated from the strains of Bacillus licheniformis NCIB 8061, NCIB 8059, ATCC 6334, ATCC 6598, ATCC 11945, ATCC 8480 and ATCC 9945 A. Examples of such amylolytic enzymes are those produced and distributed under the Trade-names of SP-95^® and Termamyl^® by Novo Industri A/S, Copenhagen, Denmark. These amylolytic enzymes are generally presented as granules and may have enzyme activities of from about 2 to 10 Maltose units/milligram. They may be present in the composition of the invention in amounts such that the final composition has amylolytic enzyme activity of from 10³ to 10⁶ Maltose Units/Kilogram.

The amylolytic activity as referred to herein can be determined by the method as described by P. Bernfeld in "Method of Enzymology" Volume I (1955) page 149. The proteolytic enzymes usable herein are for example the subtilisins which are obtained from particular strains of B. Subtilis and B. licheniformis, such as the commercially available substilisins Maxatase^® supplied by Gist-Brocades NV, Delft, Holland, and Alcalase^®, supplied by NOVO

Industri A/S Copenhagen, Denmark. Particularly suitable are proteases obtained from a strain of Bacillus having maximum activity throughout the pH range of 8-12, being commercially available from NOVO Industri A/S under the Trade names of Esperase^® and Savinase^®. The preparation of these and analogues enzymes is described in GB Patent No. 1,243,784. These enzymes are generally presented as granules, e.g. marumes, prills, T-granulates etc., and may have enzyme activities of from 500 to 1700 Glycine Units/mg. The proteolytic enzyme activity can be determined by the method as described by M.L. Anson in "Journal of General Physiology" Vol. 22 (1938) , page 79 (one Anson unit/gram = 733 Glycine Units/milligram) .

In the compositions of the invention proteolytic enzymes . may be present in amounts such that the final composition has proteolytic enzyme activity of from about 10⁶ to 10⁸ Glycine Units/Kilogram.

Other enzymes, such as lipolytic enzymes may also be incorporated to improve fat removal. Typical examples of commercial lipolytic enzymes are Lipase YL, Amano CE, Wallerstein AW, Lipase My, and Lipolase ex Novo Ind.

Other optional ingredients

Surfactants though not strictly essential may also be present for detergency, soil removal, foam depression and/or as rinse aids. If present they can be used in an amount of up to about 60% by weight depending upon their type and properties. Normally in a properly built or highly built composition as is conventional, only small amounts of low- to non-foaming nonionic surfactant in the order of 0.1-5% by weight are used, preferably from 0.1-4%, to aid detergency and particularly to suppress excessive foaming caused by some protein soil. Higher amounts i.e. 5-60% by weight of highly detersive surfactants, such as the high HLB nonionic surfactants, the anionic sulphate or sulphonate surfactants and the alkyl polyglycoside class of surfactants, may be used in lower builder containing active/enzyme-based compositions. In the context of the present invention a surfactant content from 0 to less than 5% by weight is preferred.

Zinc salts, both soluble and insoluble zinc salts, can also be incorporated as adjuncts for minimizing glass corrosion.

An inert particulate filler especially sodium sulphate may also be incorporated, though in compact powdered composition it should desirably be omitted as practically possible.

The presence of alkali-metal or alkaline earth metal salts of amino polyphosphonic acids such as the sodium or calcium salt of ethylene diamine tetra methylene phosphonic acid, and ethylene hydroxy dimethylene phosphonate may also be preferred because of their stabilizing effect on percompound bleaches and/or their anti-scaling properties. Also polycarboxylate polymeric substances, such as the maleic acid/methacrylic acid copolymers, known under the Trade Name Sokalan CP5^® may be present to aid in the inhibition of scaling. This latter may be preferred for reasons of non-P containing. Other anti-scaling agents, such as polypeptides may also be used.

The products of the present invention can be manufactured and presented in any physical form such as a powder, liquid, paste or solid blocks or tablets, and are *; eferably formulated such that they provide a wash liquor with a pH of between 6 and 13, preferably from 8-11, and more preferably from 9.5-10.5 (measured at a concentration of from 0.1-0.3% by weight in water).

As explained the invention is also applicable to conventional rinse aid compositions, which usually comprise an aqueous solution comprising a low-foaming nonionic surfactant, citric acid or sodium citrate and optionally a hydrotrope such as a lower alcohol or sodium xylene sulphonate.

The invention will now be illustrated by way of the following examples (percentages are by weight unless otherwise stated) .

Example I

Preparation of hydrotalcite compound (2)

[Zn₄Al₂(OH)₁₂] (N0₃)₂.xH₂0.

94.5 g (1.16 moles) of ZnO were weighed into a 1 litre polypropylene bottle and then slurried in 250 ml of water. 145.1 g (0.39 moles) of A1(N0₃)₃ 9 H₂0 were dissolved in 500 ml of water and then added with stirring to the ZnO- slurry.

The bottle was capped, shaken vigorously and then placed in a ther ostatted oven at 90°C for 6 days. The solid was filtered off, washed thoroughly with water and then freeze- dried. The material was finally equilibrated with water vapour at a water activity of 0.75.

Characterization

Confirmed by XRD to be a layered double hydroxide with a hydrotalcite structure. The basal spacing was 8.8 A, which is characteristic of a nitrate form material. The Zn/Al ratio was found by XRF analysis to be 2.0. IR indicated that nitrate was the only anion present. The water content was determined by thermal analysis and was consistent with the molar composition:

Zn₄Al₂(OH)₁₂(N0₃)₂. 2.9 H₂0 The water was labile and may vary slightly with storage.

TEM shows the crystals to be stacks of hexagonal plates of about 0.2 μm diameter. In the solid state these crystal stacks aggregate to form irregular particles of about 20 to 50 μm diameter.

Example II

The following powdered machine dishwashing composition were prepared:

1) = acrylic acid/maleic acid copolymer ex BASF

2) = N, N, N¹, N¹-tetraacetylethylene diamine bleach activator

3) = a) Laponite XLG ex Laporte Industries Ltd b) Synthetic hydrotalcite, [Mg₆Al₂(OH)₁₆]C0₃.4H₂0 c) Zn/Al hydrotalcite of Example I d) None

4) = Sodium disilicate containing 20% H₂0

Machine dishwashing experiments were carried out with the above formulations (a) , (b) , (c) and (d) at a product dosage of 17 g. per run (= 3.4 g/1) in a Bosch S 510 machine at a water intake of 5 litre (16°FH) . The wash programme consisted of a pre-wash, main wash at 55°C, two intermediate rinses and a final rinse of 65°C. Total washing time 65 minutes. The load per wash consisted of a dummy load together with five milk-glasses and two glass- plates. As in glass appearance terms egg yolk is notoriously known as problem-soil, it is used here as the standard-soil. The machine dishwashing product and egg-yolk soiling (a dispersion in ca. 20 ml water) were added to the wash-liquor at the start of the main wash cycle.

A series of five experiments were carried out for each composition with varying egg-yolk concentrations in the wash-liquor i.e.: 0.05 g/1 0.10 g/1

0.20 g/1 0.30 g/1 0.40 g/1 and the glass-appearance was judged in terms of spot-score according to the following table.

The results are shown in Figure 1.

It can be seen from this figure that hydrotalcites are superior adjuncts in terms of glass appearance as compared with Laponite clay. Whereas with a composition containing Laponite clay an appreciable number of spots were observed already at an egg-yolk concentration of 0.10 g/1, no spot- formation was observed with the formulations containing hydrotalcites. With composition (b) containing syntehtic hydrotalcite a perceptible spot formation started at egg- yolk concentration of 0.15 g/1, and with composition (c) containing Zn/Al hydrotalcite perceptible spot formation only started at egg-yolk concentration of above 0.30 g/1, which undoubtedly is a significant improvement.

Example III

In this Example a comparison was made between Laponite clay and Zn/Al hydrotalcite in Machine dishwashing experiments carried out with a similar formulation as used in Example II, but this tiie the formulation contains a nonionic surfactant.

The same Bosch® S 510 machine, the same wash programme and the same product dosage were used.

* = a) Laponite XLG ex Laporte Industries Ltd b) Zn/Al hydrotalcite of Example I. The soilings used in the experiments were: i) egg-yolk ii) ASTM (20% skimmed milk powder + 80% Blue Band margarine) iii) mixture consisting of: 31% mashed potato

23% pudding 11% spinach 15% milk

In the washing experiments (i) was added in an amount of 0.75 g. ; (ii) was added in an amount of 20 g. ; and (iii) was added in amounts of 4 g. and 20 g.

The results are depicted in Figure 2 which again shows the superiority of the composition of the invention containing Zn/Al hydrotalcite to composition of the art containing Laponite XLG clay.

Example IV

In this Example a comparison was made between various Zn/Al-nitrate hydrotalcites having different platelet crystal sizes, in order to find the effect of the platelet crystal size of chemically different composed hydrotalcites on the glass appearance improving performance of these hydrotalcites.

For this purpose, machine dishwashing experiments were carried out with the formulation used in Example II, whereby various types of Zn/Al hydrotalcites having the chemical formula as shown in Example I and of Mg/Al hydrotalcites having the chemical formula [Mg₄Al₂(OH)₁₂] (N0₃)₂.xH₂0 were applied as adsorbing material.

The same Bosch® S510 machine, the same wash programme and the same product dosage were used as in Example II. At the start of the main wash cycle, an egg-yolk soiling (being a dispersion in ca. 20 ml water) was added to the wash liquor, to obtain an egg-yolk concentration in the wash liquor of 0.2 g/litre.

A series of experiments were carried out using the above- mentioned hydrotalcite compounds and the glass appearance was judged in terms of the spot-score according to the table shown in Example II.

The results are depicted in Figure 3 showing the effect of platelet crystal size of the hydrotalcite compounds tested. It can be seen that the best results were achieved with materials having a platelet size less than 0.4 μm. Furthermore, it can be noticed that the chemical compos ion of the platelets is less important than their size with regard to the glass appearance performance to be obtained.

Example V

In this Example, various Zn/Al hydrotalcites having different anions (i.e. nitrate, sulphate and carbonate) were compared, in order to find the influence of the type of anion present in the hydrotalcite applied, on the glass appearance improving performance. Furthermore, the performance of the Zn/Al-nitrate hydrotalcite was compared with that of Mg/Al chloride hydrotalcites.

For this purpose, machine dishwashing experiments were carried out with the formulation used in Example II whereby the following hydrotalcite compounds were applied as adsorbing material:

(a) [ Zn₄Al₂ (OH) ₁₂ ] (N0₃) ₂. xH₂0

(b) [ Zn₄Al₂ (OH) ₁₂ ] S0₄. xH₂0

(c) [ Zn₄Al₂ (OH) ₁₂ ] C0₃. xH₂0

(d) Mg/Al hydrotalcite ex Dow Chemicals, having the chemical composition [Mg₄Al₄(0H)_18>65]Cl_{1 35}.xH₂0, wherein the chloride ions and some of the hydroxyl ions ar exchangeable and wherein the mixed metal hydroxide crystals consist of very thin 30-50 n diameter plates, (e) [Mg₄Al₂(OH)₁₂]C1₂.3H₂0. wherein Mg/Al ~ 2 and the mixed metal hydroxide crystals are thin 50 nm diameter hexagonal plates.

The same Bosch® S510 machine, the same wash programme, the same product dosage and the same egg-yolk concentration in the wash liquor were applied as in Example IV.

First, a series of experiments were carried out using the above-indicated Zn/Al hydrotalcite compounds (a) , (b) and (c) , having a platelet size of 0.2 μm, and the glass appearance was judged in terms of the spot score according to the table shown in Example II.

The results are depicted in Figure 4 showing the effect of the anion type contained in the Zn/Al hydrotalcite compounds tested. It can be seen that the best glass appearance performance was found when applying the Zn/Al nitrate hydrotalcite.

Subsequently, a series of experiments were carried out using the above-indicated Zn/Al nitrate and Mg/Al hydrotalcite compounds (c) , (d) and (e) , and the glass appearance was once again judged in terms of the spot score according to the table in Example II. In these experiments, the Zn/Al nitrate hydrotalcite consisted of platelets having a size of 0.1 μm. The results are shown in Figure 5, clearly showing that the Mg/Al chloride hydrotalcite compounds tested delivered performances approaching that of the Zn/Al nitrate hydrotalcite tested.

It can also be noticed that a somewhat worse glass appearance performance was found when using Zn/Al nitrate consisting of 0.1 μm platelets than with Zn/Al nitrate having a platelet size of 0.2 μm (see Figure 4) . The reason is likely to be a somewhat different egg-yolk composition applied during the two test series. It is noted in this respect that these tests were performed for obtaining relative rather than absolute information about the effect of the type of anion present in the hydrotalcite.

Miyata [Clays and Clay Minerals 31 (1983) 305] found that hydrotalcites have a lower ion exchange selectivity for monovalent anions such as nitrate, chloride and bromide, than for divalent anions, such as sulphate and carbonate, and that the monovalent anions can therefore be more readily replaced in ion exchange reactions. Taking this into account, it can be concluded from the results shown in Figures 4 and 5 that the ability of the hydrotalcites of the present invention to readily undergo ion exchange is beneficial for the glass appearance performance and that hydrotalcites with monovalent anions, such as nitrate and chloride, are preferred compounds in this respect.

Claims

1. A machine dishwashing composition comprising a builder or builder mixture, buffering and/or alkaline agent, characterized in that it further comprises an effective level of a hydrotalcite compound having the general empirical formula:

_[M_k+mNn+p(°^H)_2.A2 ^y--_XH₂0 where

M is any 1 + or 2 + cation or combination thereof;

N is any 3 + or 4 + cation or combination thereof; k is the sum of the individual mole fractions of the 1

+ cations; m is the sum of the individual mole fractions of the 2

+ cations n is the sum of the individual fractions of the 3 + cations; p is the sum of the individual mole fractions of the

4+ cations, where either but not both of k and m or n and p can be zero and k + m + n + p = 1 ;

A_z ^y~ is any anion of charge y- and mole fraction z, or combination of anions of similar or differing y, and k

+ 2m + 3n + 4p - 2 - zy = 0 and x can range from 1 to

100.

2. A composition according to claim 1, characterized in that said hydrotalcite compound is used as adjunct for improving glass appearance.

3. A composition according to claim 1 or 2 , characterized in that M is selected from Mg²⁺, Zn²⁺ and Cu²⁺ and mixtures thereof; N is selected from Al³⁺ and Ti⁴⁺ and mixtures thereof; and A^y~ is selected from C0₃ ^2~, N0₃ ^~ ,C1^", Br^", I^" and S0₄ ^2~.

4. A composition according to claim 3, characterised in that M is selected from Mg²⁺, Zn²⁺ and mixtures thereof; N is Al³⁺; and A^y" is selected from N0₃ ^~ and Cl^".

5. A composition according to claim 1, 2 or 3, characterized in that it comprises from 0.01 to 40% by weight of said hydrotalcite compound.

6. A composition according to claim 1, 2, 3 or 4, characterized in that the hydrotalcite compound is selected from the group of compounds having the formula:

(a) [Mg₆Al₂(OH)₁₆]C0₃.4H₂0

(b) [Mg₄Al₂(OH)₁₂]Cl₂.3H₂0;

(c) [Zn₄Al₂(OH)₁₂] (N0₃)₂.xH₂0; and

(d) [Mg₄Al₄(0H)_18>65]Cl_1>35.xH₂0 , wherein x is from 2-5.

7. A composition according to any of the preceding claims 1-6, characterized in that it further comprises a bleaching agent.

8. A composition according to any of the preceding claims 1-7, characterized in that it further comprises from 0.1 to 5% by weight of a nonionic surfactant.

9. A composition according to any of the preceding claims 1-7, characterized in that it further comprises an enzyme.

10. A composition according to claim 9, characterized in that said enzyme is an amylolytic enzyme.

11. A composition according to claim 9, characterized in that said enzyme is a proteolytic enzyme.

12. A rinse aid composition suitable for use in an aqueous rinse liquor, characterized in that it comprises a hydrotalcite compound as defined in claims 1-6.