TECHNICAL FIELD

This invention relates to machine dishwashing compositions including compositions for machine warewashing, which contain low levels of phosphate salts or which are completely phosphate-free.

BACKGROUND AND PRIOR ART In the general detergent art it has been well established that, although for ecological reasons it is desirable to formulate compositions containing low or zero-phosphate contents, alternative compounds capable of matching all the properties of phosphate salts are difficult to find. Over the last two decades numerous well-known alternatives have been proposed, including zeolites, sodium nitrilotriacetate, citrates and carbonates, to be employed either alone or in various combinations with each other.

Because of their ability to sequester calcium-ions from solution, zeolites have found widespread use as main builder component to replace phosphates in detergent compositions for the textile and fabric washing.

Zeolite is a crystalline alkalimetal aluminosilicate material having calcium binding capacity functioning by ion- exchange. Although many crystal forms of zeolite are known, the preferred zeolite for detergents use has always been zeolite A. Other zeolites such as X or P(B) have not found favour because their calcium ion uptake is either inadequate or too slow. Zeolite A has the advantage of being a "maximum aluminium" structure containing maximum possible proportion of aluminium to silicon - or the theoretical minimum Si: Al ratio of 1.0 - so that its capacity for taking up calcium ions from aqueous solution is intrinsically greater than

those of zeolite X and P which generally contain a lower proportion of aluminium (or a higher Si: Al ratio) .

Despite this good calcium ion uptake, zeolites in general, and zeolite A in particular, have not found their utilization in machine dishwashing products. Here, the weaker builders, particularly citrates and carbonates, are more commonly used as phosphate replacements. The main reason therefor is that zeolite, being a water-insoluble particulate material, tend to cause problems of sedimentation during the wash and leaving visible residues on the washed articles, which in machine dishwashing are unacceptable.

Still, for both cost and performance reasons, the use of zeolite in machine dishwashing compositions would have been preferred instead of or to at least partially replace citrate and/or carbonate.

It has now been found that an effective zeolite built machine dishwashing composition can be formulated with a significantly less or substantially no tendency to cause sedimentation and residue problems by using a finely divided zeolite having a particle size smaller than 6 μm, preferably smaller than 5 μm, and most preferably smaller than 4 μm.

SUMMARY OF THE INVENTION

The present invention provides a low phosphate to phosphate- free machine dishwashing composition comprising finely divided zeolite having a particle size smaller than 6 μm, preferably smaller than 5 μm and most preferably smaller than 4 μm as determined by the method described hereinafter.

DETAILED DESCRIPTION OF THE INVENTION According to the invention there is provided a low phosphate to phosphate-free machine dishwashing composition comprising a zeolite builder, characterized in that the zeolite is a finely divided material having a particle size smaller than 6 μm, preferably smaller than 5 μm, and most preferably

smaller than 4 μm, as determined according to the Fraunhofer laser-diffraction method using a HELOS ^® apparatus ex Sympatic.

It is of note that for the purpose of the invention the upper limit of the particle size is important and should be sharply defined. It is furthermore of importance that the material contains an as high as possible percentage of smaller particles i.e. the smaller the better with no limitation in the lower end of the particle size other than that as determined by constraints in preparing the material. It is thus not sufficient for the purpose of the invention to define the particle size in terms of average particle size, average particle diameter or d values. _

The analysis of the particle size as defined herein is carried out according to the Fraunhofer laser-diffraction method using a HELOS® apparatus ex Sympatic. For the purpose of the present invention volume distributions are measured with 32 channels within the range of 0.18 μm to 35 μm. The samples are dispersed in a diluted standard silicate solution consisting of 1.3 g/1 of sodium disilicate (Si0 ₂ : Na ₂ 0 = 2.0) and 0.3 g/1 KOH in de ineralised water; in all cases an ultrasonic pretreatment of 120 seconds is applied with the HELOS®.

By using this technigue the particle size is determined as particle size distribution expressed in cumulative volume %.

In a more specific embodiment of the invention the zeolites should preferably have the following particle size distributions:

Particle size

The amount of zeolite usable in the composition of the invention may vary from about 5% to about 60% by weight, preferably from about 10% to about 50% by weight of the composition.

A still further improvement to the effect that substantially no deposit on glasses is observed can be obtained if all particles of the zeolite used are of a size smaller than 2 μm.

Zeolites as commercially available though after sonication generally have particle size d ₈₀ of about 50 μm appeared to contain substantial amounts of particles > 6 μm, and are not suitable for use in the present invention. In order to be usable they have to be milled or preferably manufactured to the required particle size as defined hereinbefore and hereinafter.

When commercial zeolite 4A, ex Degussa which upon analysis has particle size distribution (carried out with a HELOS ^® equipment ex Sympatic according to the Fraunhofer laser- diffraction method) of: < 10 μm = 100%

was milled to a particle size distribution of:

< 6 μm = 100%

< 5 μm = 100%

< 4 μm = 100% < 3 μm = 99%

< 2 μm = 93%

it was found that the milled fine 4A material indeed gave much less tendency to sedimentation and residue formation.

Although any zeolite types e.g. A, X and P (B) , can be used, a preferred zeolite for use in the present invention is a novel zeolite P having a silicon to aluminium ratio not greater than 1.33, preferably not greater than 1.15, as described in EP-A-0, 384,070. This type of zeolite can be defined as maximum aluminium zeolite P, which will hereinafter also be referred to as "zeolite MAP".

The zeolite MAP as preferably used herein is described and claimed in EP-A-0,384,070 (Unilever) .It is defined as an alkalimetal aluminosilicate of the zeolite P type having a silicon to aluminium ratio (Si: Al) not greater than 1.33, preferably within the range of 0.9 to 1.33, and more preferably within the range of 0.9 to 1.2.

Of especial interest for use in the present invention is zeolite MAP having a silicon to aluminium ratio not greater than 1.15 and having a tetragonally distorted cubic crystal structure.

Zeolite MAP generally has a calcium binding capacity of at least 150 mg CaO per gram of anhydrous alumino-silicate.

The advantage of zeolite MAP is that, unlike most other known zeolite types of the art e.g. zeolite 4A, its calcium binding capacity is independent of particle size, and is substantially unaffected by size reduction.

The zeolite can be used as the sole builder or, if desired, may be used in conjunction with other inorganic or organic builder materials. Builder materials that may be present include the phosphate salts, such as sodium triphosphate; sodium carbonate and/or sodium bicarbonate; alkalimetal citrates, especially sodium citrate; nitrilotriacetate (NTA) ; dipicolinic acid; oxydisuccinic acid (ODS) ; alkenylsuccinates (AKS) ; the poly carboxylate polymers such as poly-acrylates, acrylic/maleic copolymers and acrylic phosphonates; and the various organic polyphosphonates such as ethylene diamine tetra-methylene phosphonates, ethylene hydroxy diphosphonates, known under the Dequest ^® Trade mark series. Each of these supplementary builder may be used alone or in various combinations thereof and may be present in amounts of from 1% to about 25% by weight.

Phosphate builders if present, should be used in only small amounts e.g. up to about 12% by weight, preferably up to 10% by weight.

Preferably however the composition of the invention should be entirely phosphate-free.

The composition of the invention may and preferably further contains one or more of the following specialized components for specific purposes during the multi-step wash cycle typical for machine dishwashing composition.

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 55% 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 preferably used, to aid detergency and particularly to suppress excessive foaming caused by some protein soil. Higher amounts i.e. 5 - 55% by weight of highly detersive surfactants, such as the high HLB nonionic

surfactants, the anionic sulphates and sulphonate surfactants, and the alkyl polyglycoside class of surfactant, may be used in lower builder containing active- based composition.

Alkalimetal silicate - Preferably sodium silicate at a level of from about 1 to about 40% by weight, preferably from 5 to 35% 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 Si0 ₂ :Na ₂ 0 of from about 1.0 to about 3.3., preferably from about 1.8 to about 2.5, normally referred to as sodium disilicate.

Bleach system - If present the amount will preferably lie in a range from 1 to 30% by weight. Alkali metal hypochlorite may be incorporated in liquid compositions. Other chlorine bleaches which may be incorporated 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.

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) l, 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 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 lichenifor is 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 Ter anyl ^® 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 10 ³ to 10 ⁶ 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. maru es, 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 10 ⁶ to 10 ⁸ 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 that can be further included in minor amounts are clay minerals, particularly the layered clay minerals to reduce film- and spot formation on washed articles. Typical and particularly preferred commercial clay products are the synthetic hectorites manufactured and supplied by Laporte Industries Ltd, England as Laponite ^® clays e.g. Laponite S, Laponite XLS, Laponite RD and Laponite RDS. 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 composition of the invention should be formulated such that they provide in the wash liquor a pH in the range of from about 7 to 12.0, preferably of from 9-11.5 at a use concentration of about 3 gram/liter in water.

The composition can be in any product-form, such as in powder, gel, aqueous and non-aqueous liquids.

As hitherto it has not been possible to formulate a commercially viable phosphate-free liquid machine dishwashing product with adequate building capacity, the use of zeolite, particularly zeolite MAP according to the invention can be of special importance to machine dishwashing products in an aqueous liquid form.

The invention will now be further illustrated by way of the following non-limited Examples.

Examples I - IV

The following compositions in powder form are within the purview of the present invention:

Composition(% b wei ht II III IV

A prototype zeolite MAP liquid machine dishwashing product.

^* The zeolite MAP used in Examples I-V was zeolite P of Example 2 of EP-A-0,384, 070 and had the following particle size distribution:

Zeolite deposits on inverted standard wine glasses were determined in washing machine appraisal tests using the prototype liquid formulation of Example V containing zeolite MAP and commercial zeolite 4A ex Degussa respectively.

The results show that with zeolite MAP the amount of deposit on all glasses were less than 10 mg/glass (65% < 2 mg; 85% < 5 mg and 15% between 5-10 mg) and with zeolite 4A heavy deposits of more than 10 mg to more than 15 mg per glass are observed on 40% of the washed glasses.