DE69328679T2 - Detergent compositions for dishwashers - Google Patents

Abstract

The present invention relates to a machine dishwashing composition comprising from 1% to 80% by weight of detergent builder compound oxygen-releasing bleaching agent from 0.05% to 2.5% by weight, preferably 0.1% to 1% by weight of paraffin oil, nitrogen-containing corrosion inhibitor compound Most preferably the oxygen-releasing bleaching agent is incorporated such that the level of available oxygen measured according to the method herein is from 0.3 to 1.7, preferably 0.5 to 1.2

Description

The present invention relates to automatic dishwashing detergent compositions that exhibit superior silver anti-tarnish properties.

Detergent compositions intended for use in automatic dishwashers are well known and consequently an attempt has been made by detergent manufacturers to improve the cleaning and/or rinsing action of the composition on tableware and glassware, as reflected in numerous patent publications.

The present invention is concerned with compositions for washing silverware in automatic dishwashing machines, and in particular with the problem of silver tarnishing encountered in current detergent compositions for use in automatic dishwashing machines, such as "compact" granular products based on oxygen bleaching species.

It has been found that the compositions of the present invention can provide excellent silver anti-tarnish properties as well as optimum cleaning/rinsing performance in tableware and glassware. The present compositions are based on oxygen bleaching species and are preferably in a compact form. The optimum silver anti-tarnish and cleaning/rinsing performance is achieved by the combined use of paraffin oil and defined nitrogen-containing corrosion inhibitor compounds, and preferably the control of the oxygen bleaching power.

EP-A-0 150 387 describes machine dishwashing compositions based on chlorine bleach containing a paraffin oil as a foam suppressor; EP-A-0 186 088 describes machine dishwashing compositions based on carbonates and silicates containing paraffin oils as dust-binding agents and water-soluble phosphonates in proportions of 0.5 to 3%. References on corrosion inhibition include FR-A-2 304 667 and FR-A-1 209 904 (on triazoles) and EP-A-541 475 (on ammonium compounds); see also the unpublished WO-9 416 047, WO-9 416 048 and WO-A-9 501 416 for dishwashing compositions containing paraffin oils.

Summary of the invention

Composition for automatic dishwashing, comprising

- 1 to 80 wt.% of a detergent builder compound,

- Oxygen-releasing bleach,

- 0.005 to 2.5% by weight, preferably 0.1 to 0.6% by weight, paraffin oil; and

Nitrogen-containing corrosion inhibitor compound such that the nitrogen is trivalent, and wherein the nitrogen-containing corrosion inhibitor compound is not a benzotriazole compound and not a heavy metal ion complexing agent.

In a highly preferred embodiment of the invention, the oxygen-releasing bleach is incorporated such that the level of available oxygen, measured by the method described herein, is 0.3 to 1.7, preferably 0.5 to 1.2.

The present compositions contain as essential components a detergency builder compound, oxygen releasing bleach species, most preferably with the level of available oxygen controlled, paraffin oil and nitrogen containing corrosion inhibitor compound.

Builders

The first essential component of the automatic dishwashing detergent composition of the present invention is a detergency builder compound which is present in an amount of from 1 to 80%, preferably from 10 to 70%, most preferably from 20 to 60% by weight of the composition.

A suitable detergent builder compound is largely or completely water soluble and may be selected, for example, from monomeric polycarboxylates or their acid forms, homo- or copolymeric polycarboxylic acids or their salts in which the polycarboxylic acid comprises at least two carboxyl radicals separated by not more than two carbon atoms, carbonates, bicarbonates, borates, phosphates, silicates and mixtures of any of the foregoing.

Useful water-soluble, monomeric or oligomeric carboxylate builders can be selected from a wide range of compounds, but such compounds preferably have a first logarithmic carboxylic acid constant (pK1) of less than 9, preferably between 2 and 8.5, more preferably between 4 and 7.5.

The logarithmic acid constant is defined by reference to the equilibrium

H+ + A&supmin; < => HA

where A⊃min; is the fully ionized carboxylate anion of the builder salt.

The equilibrium constant is therefore given for dilute solutions by the expression

and pK&sub1; = log 10 K

For the purposes of this patent specification, the acid constants are defined for 25ºC and for zero ionic strength. Literature values are taken where possible (see Stability Constants of Metal-Ion Complexes, Special Publication No. 25, the Chemical Society, London): where in doubt, they are determined by potentiometric titration using a glass electrode.

The carboxylate or polycarboxylate builders may be of the monomeric or oligomeric type, although monomeric polycarboxylates are generally preferred for cost and performance reasons.

Monomeric and oligomeric builders can be prepared from acyclic, alicyclic, heterocyclic and aromatic carboxylates of the general formulas

or

wherein R₁ is H, C₁₋₃�0 alkyl or alkenyl, optionally substituted by hydroxy, carboxy, sulfo or phosphono groups or linked to a polyethyleneoxy radical containing up to 20 ethyleneoxy groups; R₂ is H, C₁₋₄ alkyl, alkenyl or hydroxyalkyl, or alkaryl, sulfo or phosphono groups; X is a single bond; O; S; SO; SO₂; or NR₁; Y is H; carboxy; hydroxy; carboxymethyloxy; or C₁₋₃�0 alkyl or alkenyl, optionally substituted by hydroxy or carboxy groups;

Z is H; or carboxy;

m is an integer from 1 to 10;

n is an integer from 3 to 6;

p, q are integers from 0 to 6, where p + q is 1 to 6; and where X, Y and Z each have the same or different representations when repeated in a particular molecular formula, and where at least one Y or Z in a molecule contains a carboxyl group.

Suitable carboxylates containing one carboxy group include the water-soluble salts of lactic acid, glycolic acid and ether derivatives thereof as described in Belgian Patent Nos. 831 368, 821 369 and 821 370. Polycarboxylates containing two carboxy groups include the water-soluble salts of succinic acid, malonic acid, (ethylenedioxy)diacetic acid, maleic acid, diglycolic acid, tartaric acid, tartronic acid and fu (Ethylenedioxy)diacetic acid, maleic acid, diglycolic acid, tartaric acid, tartronic acid and fumaric acid, as well as the ether carboxylates described in German Offenlegungsschrift 2 446 686 and 2 446 687 and US Patent No. 3 935 257 and the sulfinyl carboxylates described in Belgian Patent No. 840 623. Polycarboxylates containing three carboxy groups include in particular water-soluble citrates, aconitrates and citraconates, as well as succinate derivatives such as the carboxymethyloxysuccinates described in British Patent No. 1 379 241, the lactoxysuccinates described in British Patent No. 1 389 732 and the aminosuccinates described in Dutch Application 7205873 and the oxypolycarboxylate materials such as 2-oxa-1,1,3-propanetricarboxylates described in British Patent No. 1 387 447.

Polycarboxylates containing four carboxy groups include the oxydisuccinates, 1,1,2,2-ethanetetracarboxylates, 1,1,3,3-propanetetracarboxylates and 1,1,2,3-propanetetracarboxylates described in British Patent No. 1,261,829. Polycarboxylates containing sulfo substituents include the sulfosuccinate derivatives described in British Patent Nos. 1,398,421 and 1,398,422 and U.S. Patent No. 3,936,448 and the sulfonated pyrolyzed citrates described in British Patent No. 1,439,000.

Alicyclic and heterocyclic polycarboxylates include cyclopentane cis,cis,cis-tetracarboxylates, cyclopentadienide pentacarboxylates, 2,3,4,5-tetrahydrofuran cis,cis,cis-tetracarboxylates, 2,5-tetrahydrofuran cis-dicarboxylates, 2,2,5,5-tetrahydrofuran tetracarboxylates, 1,2,3,4,5,6-hexane hexacarboxylates and carboxymethyl derivatives of polyhydric alcohols, such as sorbitol, mannitol and xylitol. Aromatic polycarboxylates include mellitic acid, pyromellitic acid and the phthalic acid derivatives described in British Patent No. 1,425,343.

Of the above, the preferred polycarboxylates are hydroxycarboxylates containing up to three carboxy groups per molecule, especially citrates.

The parent acids of the monomeric or oligomeric polycarboxylate chelating agents or mixtures thereof with their salts, e.g. citric acid or citrate/citric acid mixtures, are also contemplated as components of detergent composition builder systems useful in the present invention.

Other useful water-soluble organic salts are the homo- or copolymeric polycarboxylic acids or their salts in which the polycarboxylic acid comprises at least two carboxyl radicals separated by not more than two carbon atoms. Polymers of the latter type are described in GB-A-1 596 756. Examples of such salts are polyacrylates having a MW of 2000-5000 and their copolymers with maleic anhydride, such as copolymers having a molecular weight of 20,000 to 70,000, especially about 40,000. These materials are normally used in proportions of from 0.5 to 10% by weight, more preferably from 0.75 to 8% by weight, most preferably from about 1 to 6% by weight of the composition.

Water-soluble detergent builders include, but are not limited to, the alkali metal, ammonium and alkanolammonium salts of polyphosphates (e.g. Borate builders, as well as builders containing borate-forming materials which can form borate under detergent storage or wash conditions, may also be used, but are not preferred at wash conditions of less than about 50°C, especially less than about 40°C.

Specific examples of phosphate builders are the alkali metal tripolyphosphates, sodium, potassium and ammonium pyrophosphate, sodium and potassium and ammonium pyrophosphate, sodium and potassium orthophosphate, sodium polymetal phosphate in which the degree of polymerization is 6 to 21, and salts of phytic acid.

Suitable silicates include the water-soluble sodium silicates having a SiO₂:Na₂O ratio in the range of 1.0 to 2.8, with ratios of 1.6 to 2.4 being preferred and a ratio of 2.0 being most preferred. The silicates can be in either the anhydrous salt form or in the form of a hydrated salt. Sodium silicate having a SiO₂:Na₂O ratio of 2.0 is the most preferred silicate.

Silicates are preferably present in the detergent compositions for machine dishwashing in the invention in a proportion of 5 to 50% by weight of the composition, more preferably 10 to 40% by weight.

The compositions described herein may also include less water-soluble builders, although their level of incorporation is preferably minimized. Examples of such less water-soluble builders include the crystalline layered silicates and highly water-insoluble aluminosilicates.

Crystalline sodium layered silicates have the general formula

NaMSixOx+1·yH₂Q

wherein M is sodium or hydrogen, x is a number from 1.9 to 4 and y is a number from 0 to 20. Crystalline sodium layered silicates of this type are described in EP-A-0 164 514 and processes for their preparation are described in DE-A-34 17 649 and DE-A-37 42 043. For the purposes of the present invention, x in the general formula above has a value of 2, 3 or 4 and is preferably 2. More preferably M is sodium and y is 0 and preferred examples of this formula include the α-, β-, γ- and δ-forms of Na₂Si₂O₅. These materials are available from Hoechst AG FRG as NaSKS-5, NaSKS-7, NaSKS-11 and NaSKS-6 respectively. The most preferred material is δ-Na₂Si₂O₅, NaSKS-6.

The crystalline sodium layered silicate material is preferably present in granular detergent compositions as particles in intimate admixture with a solid, water-soluble, ionizable material. The solid, water-soluble, ionizable material is selected from organic acids, organic and inorganic acid salts and mixtures thereof. The main requirement is that the material should contain at least one functional acidic group whose pKa should be less than 9, thereby providing the ability to at least partially neutralize the sodium released by the crystalline layered silicate. droxylionen is provided.

The incorporation into the particles of other ingredients in addition to the crystalline layered silicate and the ionizable water-soluble compound may be advantageous, particularly in processing the particles and also in increasing the stability of detergent compositions in which the particles are included. In particular, certain types of agglomerates may require the addition of one or more binders to assist in binding the silicate and the ionizable water-soluble material to produce particles with acceptable physical characteristics. The particle-containing crystalline layered sodium silicate may take a variety of physical forms such as extrudates, marumes, agglomerates, flakes or compacted granules. A preferred method for producing compacted granules comprising crystalline layered silicate and a solid water-soluble ionizable material has been described in jointly assigned, non-prepublished EP-A-0 581 895.

Suitable aluminosilicate zeolites have the unit cell formula Naz[(AlO₂)zSiO₂)y]·XH₂O, where z and y are at least 6; the molar ratio of z to y is 1.0 to 0.5 and x is at least 5, preferably 7.5 to 276, more preferably 10 to 264. The aluminosilicate material is in hydrated form and is preferably crystalline and contains 10% to 28%, more preferably 18% to 22% water in bound form.

The above aluminosilicate ion exchange materials are further characterized by a particle size diameter of from 0.1 to 10 micrometers, preferably from 0.2 to 4 micrometers. The term "particle size diameter" herein means the average particle size diameter of a particular ion exchange material as determined by conventional analytical techniques, such as microscopic determination using a scanning electron microscope or by means of a laser granulometer. The aluminosilicate ion exchange materials are further characterized by their calcium ion exchange capacity, which is at least 200 mg equivalent of CaCO3 water hardness/g aluminosilicate, calculated on an anhydrous basis, and which is generally in the range of from 300 mg-eq/g to 352 mg-eq/g. The aluminosilicate ion exchange materials herein are further characterized by their calcium ion exchange rate which is at least 130 mg equivalent of CaCO3/liter/minute/(g/liter) [2 grains Ca++/gallon/minute/(grams/gallon)] of aluminosilicate (anhydrous basis) and generally in the range of 130 mg equivalent of CaCO3/liter/minute/(grams/liter) [2 grains/gallon/minute(grams/gallon)] to 390 mg equivalent of CaCO3/liter/minute/(grams/liter) [4 grains/gallon/minute (grams/gallon)] based on calcium ion hardness.

Optimum aluminosilicates for builder purposes exhibit a calcium ion exchange rate of at least 260 mg equivalent of CaCO3/liter/minute/(grams/liter) [4 grains/gallon/minute/(grams/gallon)].

Aluminosilicate ion exchange materials may be naturally occurring materials, but are preferably synthetically derived. A process for preparing aluminosilicate ion exchange materials is discussed in U.S. Patent 3,985,669. Synthetic, Crystalline aluminosilicate ion exchange materials are available under the names Zeolite A, Zeolite B, Zeolite P, Zeolite X, Zeolite HS and mixtures thereof. Zeolite A has the formula

Na 12 [(AlO 2 ) 12 (SiO 2 ) 12 ] xH 2 O

wherein x is 20 to 30, especially 27. Zeolite X has the formula Na₈₆ [(AlO₂)₈₆(SiO₂)₁₀₆]·276H₂O has the formula Na₆[(AlO₂)₆(SiO₂)₆]7.5H₂O).

The builder component described herein may also contain carbonate species such as alkali metal carbonates and bicarbonates, preferably at levels of less than 9%, most preferably less than 5% by weight of the total composition, although higher levels may also be used.

Oxygen-releasing bleach

The second essential feature of the invention is oxygen bleach selected from oxygen releasing agents such as inorganic perhydrate salts, peroxyacid bleach precursors, organic peroxyacids and mixtures thereof.

It has been found that for optimum silver antifouling performance, the level of available oxygen in the present compositions should preferably be carefully controlled; the level of available oxygen should therefore be in the range of 0.3 to 1.7, preferably 0.5 to 1.2, as measured by the method described below.

Preferably, the rate of release of available oxygen is also controlled; the rate of release of available oxygen from the compositions described herein should be such that, using the method described below, the available oxygen is not completely released from the composition until after 3.5 minutes.

As will become apparent below, the control of the release rate of available oxygen can be achieved either by selecting the appropriate bleach species which dissolve relatively slowly in water or by applying certain processing or treatment techniques to otherwise rapidly dissolving species. The release rate can also be determined using the procedure now described:

Method for determining the total available oxygen (AvO) content and the release rate in a detergent composition for automatic dishwashing Proceedings

1. A beaker of water (typically 2L) is placed on a stirrer hotplate and the stirrer speed is selected to ensure that the product is evenly dispersed in the solution.

2. The detergent composition (typically 8 g of product sampled from a bulk feed using a Pascal sampler) is added and simultaneously a stop watch is started.

3. The temperature control should be set to maintain a constant temperature of 20º throughout the experiment.

4. Samples are taken from the solution at 2 minute intervals for 20 minutes, beginning after 1 minute, and are titrated by the "Titration Procedure" described below to determine the amount of available oxygen at each point.

Titration procedure

1. An aliquot of the detergent solution (above) and 2 ml of sulfuric acid are added to a stirred beaker.

2. Approximately 0.2 g of ammonium molybdate catalyst (tetrahydrate form) is added.

3. 3 ml of a 10% sodium iodide solution are added.

4. A titration with sodium thiosulfate is carried out to the end point. The end point can be found using one of two procedures. The first procedure is simply to observe that the yellow iodine color fades to a clear or light color. The second and preferred procedure is to add soluble starch as the yellow color fades, turning the solution blue. More titer is added until the end point is reached (the blue starch complex decolorizes).

The AvO fraction for the sample at each time interval corresponds to the titer amount according to the following equation:

The AvO fraction is plotted versus time as follows:

Examples of inorganic perhydrate salts include perborate, percarbonate, perphosphate, persulfate and persilicate salts. The inorganic perhydrate salts are usually the alkali metal salts. The inorganic perhydrate salt can be present as a crystalline solid without additional protection. However, for certain perhydrate salts, preferred embodiments of such granular compositions utilize a coated form of the material which provides better storage stability for the perhydrate salt in the granular product.

It has also been found that the selection of coarse grade particles for the inorganic perhydrate salts provides better control of the release of available oxygen. Accordingly, the average particle size of the perhydrate salt particles herein should be in the range of 400 to 900 micrometers, preferably 600 to 800 micrometers.

Sodium perborate, which is the most preferred perhydrate for inclusion in automatic dishwashing detergent compositions according to the invention, may be in the form of the monohydrate of nominal formula NaBO₂H₂O₂ or the tetrahydrate NaBO₂H₂O₂·3H₂O.

The tetrahydrate species is particularly preferred due to its slow dissolution and therefore due to a better regulated release of available oxygen.

Sodium percarbonate, which is another preferred perhydrate for inclusion in detergent compositions according to the invention, is an addition compound of a formula corresponding to 2Na₂CO₃·3H₂O₂ and is commercially available as a crystalline solid. The percarbonate is most preferably incorporated into such compositions in coated form. The most preferred coating material comprises a mixed salt of an alkali metal sulfate and carbonate. Such coatings together with coating processes were previously described in GB-A-1 466 799, issued to Interox on 9 March 1977. The weight ratio of the mixed salt coating material to percarbonate is in the range of 1:200 to 1:4, more preferably 1:99 to 1:9, and most preferably 1:49 to 1:19. Preferably, the mixed salt consists of sodium sulfate and sodium carbonate having the general formula Na₂SO₄·n·Na₂CO₃, where n is 0.1 to 3, preferably n is 0.3 to 1.0, and most preferably n is 0.2 to 0.5.

Another suitable coating material is sodium silicate having a ratio SiO₂:Na₂O of from 1.6:1 to 3.4:1, preferably 2.8:1, applied as an aqueous solution to give a level of from 2% to 10% (normally from 3% to 5%) of silicate solids based on the weight of percarbonate. Magnesium silicate may also be included in the coating. Other suitable coating materials include the alkali and alkaline earth metal sulfates and carbonates.

Potassium peroxymonopersulfate is another inorganic perhydrate salt of particular utility in machine dishwashing detergent compositions.

The proportion of inorganic perhydrate salt is typically 2 to 15 wt.%, more preferably 3.5 to 10 wt.% of the total composition.

Peroxyacid bleach precursors are preferably used in combination with the above perhydrate salts. The bleach precursors useful herein contain one or more N- or O-acyl groups, with the precursors being selected from a wide range of classes may be chosen. Suitable classes include anhydrides, esters, imides and acylated derivatives of imidazoles and oximes and examples of useful materials within these classes are described in GB-A-1 586 789. The most preferred classes are esters as described in GB-A-836 988, 864 798, 114 871 and 2 143 231 and imides as described in GB-A-855 735 & 1 246 338.

Particularly preferred precursor compounds are the N,N,N',N'-tetraacetylated compounds of the formula

where x can be 0 or an integer between 1 & 6.

Examples include tetraacetylmethylenediamine (TAMD) in which x = 1, tetraacetylethylenediamine (TAED) in which x = 2, and tetraacetylhexylenediamine (TAHD) in which x = 6. These and analogous compounds are described in GB-A-907 356. The most preferred peroxyacid bleach precursor is TAED.

Other preferred classes of peroxyacid bleach activator compounds are the amide substituted compounds of the following general formulas:

or

wherein R¹ is an aryl or alkaryl group having from about 1 to about 14 carbon atoms, R² is an alkylene, arylene and alkarylene group having from about 1 to 14 carbon atoms, and R⁵ is H or an alkyl, aryl or alkaryl group having from 1 to 10 carbon atoms, and L can be virtually any leaving group. R¹ preferably contains about 6 to 12 carbon atoms. R² preferably contains from about 4 to 8 carbon atoms. R¹ can be straight or branched chain alkyl, substituted aryl, or an alkylaryl containing branching, substitution or both, and can be derived from either synthetic sources or natural sources including, for example, tallow fat. Analogous structural variations are permissible for R². Substitution may include alkyl, aryl, halogen, nitrogen, sulfur and other typical substituent groups or organic compounds. R5 is preferably H or methyl. R1 and R5 should not contain more than 18 carbon atoms in total. Amide substituted bleach activator compounds of this type are described in EP-A-0170386.

Other peroxyacid bleach precursor compounds include sodium nonanoyloxybenzenesulfonate, sodium trimethylhexanoyloxybenzenesulfonate, sodium acetoxybenzenesulfonate and sodium benzoyloxybenzenesulfonate, for example as described in EP-A-0341947.

The peroxyacid bleach precursors are normally incorporated in proportions of up to 7% by weight of active material, more preferably from 1 to 5% by weight of active material, based on the total composition.

The bleaching agent species described herein may also contain organic peroxyacids, a particularly preferred class of which are the amide-substituted peroxyacids of the general formula

or

wherein R¹, R² and R⁵ are as defined above for the corresponding amide-substituted peroxyacid bleach activator compounds.

Other organic peroxyacids include diperoxydodecanedioic acid, diperoxytetradecanedioic acid, diperoxyhexadecanedioic acid, mono- and diperazelanic acid, mono- and diperbrassylic acid, monoperoxyphthalic acid, perbenzoic acid and their salts, for example as described in EP-A-0 341 947.

The peroxyacids can be used in proportions of up to 7% by weight, more preferably from 1 to 5% by weight of the composition.

Chlorine bleaches include the alkali metal hypochlorites and chlorinated cyanuric acid salts. The use of chlorine bleaches in the composition of the invention is preferably minimized, and more preferably the present compositions do not contain chlorine bleach.

The paraffin oil

The present compositions must contain from 0.005 to 2.5%, more preferably from 0.05 to 2.5%, most preferably from 0.1 to 1% by weight of the total composition of a paraffin oil, typically a predominantly branched aliphatic hydrocarbon having a number of carbon atoms in the range of 20 to 50; preferably paraffin oil selected from predominantly branched C25-45 species having a ratio of cyclic to non-cyclic hydrocarbons of about 32:68; a paraffin oil meeting these characteristics is sold by Wintershall, Salzbergen, Germany under the trade name WINOG 70.

Nitrogen-containing corrosion inhibitor compound

The detergent compositions of the invention contain as an essential component a nitrogen-containing corrosion inhibitor compound. By nitrogen-containing corrosion inhibitor compound is meant a compound which contains at least one nitrogen atom and which compound acts in a manner to inhibit corrosion of metal, in particular silver, when incorporated in the detergent composition in combination with paraffin oil in the proportions as defined herein and in any mixture of such compounds, wherein the nitrogen-containing corrosion inhibitor compound is not a benzotriazole compound as defined herein and is not a heavy metal ion complexing agent as defined herein.

The nitrogen-containing corrosion inhibitor compound is designed in such a way that the nitrogen is trivalent and therefore has an available lone or free electron pair.

Suitable nitrogen corrosion inhibitor compounds include imidazole and derivatives thereof such as benzimidazole, 2-heptadecylimidazole and the imidazole derivatives described in Czech Patent No. 139,279 and British Patent GB-A-1 137 741, which also describes a process for preparing imidazole compounds.

Also suitable as nitrogen corrosion inhibitor compounds are pyrazole compounds and their derivatives, particularly those where the pyrazole is substituted at any of the 1, 3, 4 or 5 positions by the substituents R1, R3, R4 and R5, where R1 is one of H, CH2OH, CONH3 or COCH3, R3 and R5 are one of C1-C20 alkyl or hydroxyl, and R4 is one of H, NH2 or NO2.

Other suitable nitrogen corrosion inhibitor compounds include 2-mercaptobenzothiazole, thionalide, morpholine, melamine, distearylamine, stearoylstearamide, cyanuric acid, aminotriazole, aminotetrazole and indazole.

Nitrogen corrosion inhibitor compound can be incorporated into the compositions of the invention at a level of 0.005 to 3%, preferably 0.02 to 1%, most preferably 0.05 to 0.5% by weight of the composition.

Optional corrosion inhibitors

The compositions of the invention may also contain optional corrosion inhibitor compounds at a level typically from 0.01 to 3% by weight of the composition. Suitable compounds include mercaptans and diols, particularly mercaptans having from 4 to 20 carbon atoms, including lauryl mercaptan, thiophenol, thionapthol, thionalide and thioanthranol.

Also suitable are the C₁₂-C₂₀ fatty acids or their salts, in particular aluminium tristearate. The C₁₂-C₂₀ hydroxy fatty acids or their salts are also useful.

Phosphonated octadecane and other antioxidants, such as beta-hydroxytoluene (BHT), are also suitable.

Benzotriazole compound

The detergent compositions of the invention may be formulated to contain as a non-essential component a benzotriazole compound in an amount of from 0.005 to 2% by weight, preferably from 0.02 to 1% by weight, and most preferably from 0.05 to 0.5 wt.% of a benzotriazole compound. Benzotriazole compound is a compound of the formula

which is benzotriazole and any derivatives thereof.

Derivatives of benzotriazole include those where the available substitution sites of the aromatic ring are fully or partially substituted. Substituents may include, for example, straight or branched chain alkyl groups containing, for example, one to twenty carbon atoms in the alkyl chain. Other substituents may include -OH-, -SH-, phenyl or halogen groups. Other derivatives include bisbenzotriazoles. British Patent GB-A-1 065 995 describes suitable substituted benzotriazoles of the formula

wherein R is a straight or branched chain alkyl group having two to twenty atoms, and a process for preparing such compounds. British Patent GB-A-1 226 100 describes compositions containing 4,5,6,7-tetrahydrobenzotriazole compounds which are also suitable for inclusion in the compositions of the invention.

British Patent GB-A-1 180 437 describes suitable bisbenzotriazoles of the formula

and

and

wherein X represents a straight chain alkylene group containing one to six carbon atoms in the chain, which is substituted with one or two alkyl groups having one to four carbon atoms, wherein the alkylene group contains only one carbon atom, or which are substituted with one or more alkyl groups having one to four carbon atoms, or which are unsubstituted, wherein the alkylene group contains two or more carbon atoms; a 1:1 residue containing at least five carbon atoms; a carbonyl group; a sulfuryl group, an oxygen atom; or a sulfur atom.

Heavy metal ion complexing agents

The detergent compositions of the invention may be formulated to contain a non-essential component of a heavy metal ion complexing agent incorporated in a proportion of 0.005 to 3%, preferably 0.05 to 1%, most preferably 0.07 to 0.4% by weight of the total composition.

Suitable heavy metal ion chelating agents for use herein include organic phosphonates such as aminoalkylene poly(alkylene phosphonate), alkali metal ethane-1-hydroxydiphosphonates, and nitrilotrimethylene phosphonates.

Preferred among the above species are diethylenetriamine penta(methylenephosphonate), hexamethylenediamine tetra(methylenephosphonate) and hydroxyethylene-1,1-diphosphonate.

The phosphonate compounds can be present either in their acid form or as a complex of either an alkali or alkaline metal ion, the molar ratio of the metal ion to the phosphonate compound being at least 1:1. Such complexes are described in US-A-4,259,200. Preferably, the organic phosphonate compounds are in the form of their magnesium salt.

Other suitable heavy metal ion complexing agents for use herein include nitrilotriacetic acid and polyaminocarboxylic acids such as ethylenediaminotetraacetic acid, ethylenetriaminepentaacetic acid, ethylenediaminedisuccinic acid or the water-soluble alkali metal salts thereof. Particularly preferred is ethylenediamine-N,N'-disuccinic acid (EDDS) or the alkali metal, alkaline earth metal, ammonium or substituted ammonium salts thereof or mixtures thereof. Preferred EDDS compounds are the free acid form and the sodium or magnesium salt or complex thereof. Examples of such preferred sodium salts of EDDS include Na₂EDDS and Na₃EDDS. Examples of such preferred magnesium complexes of EDDS include MgEDDS and Mg₂EDDS. The magnesium complexes are the most preferred for inclusion in compositions according to the invention.

Still other suitable heavy metal ion complexing agents for use as described herein are iminodiacetic acid derivatives such as 2-hydroxyethyldiacetic acid or glyceryl iminodiacetic acid, described in EP-A-317 542 and EP-A-399 133.

The heavy metal ion complexing agent described herein may consist of a mixture of the species described above.

Optional components

In addition to the essential ingredients described above, the compositions of the invention may comprise additional ingredients which are often quite desirable.

A highly preferred component of the machine dishwashing compositions of the invention is a surfactant system comprising a surfactant selected from anionic, cationic, nonionic, ampholytic and zwitterionic surfactants and mixtures thereof. The surfactant system is present at a level of 0.5 to 30%, more preferably 1 to 25%, most preferably 2 to 20% by weight of the compositions.

A typical listing of anionic, nonionic, ampholytic and zwitterionic classes and species of these surfactants is given in US-A-3,929,678, issued to Laughlin and Heuring on December 30, 1975. A list of suitable cationic surfactants is given in US-A-4,259,217, issued to Murphy on March 31, 1981. A listing of surfactants typically included in automatic dishwashing detergent compositions is given in EP-A-0 414 549.

Sulfonate and sulfate surfactants are useful herein. Sulfonates include alkylbenzenesulfonates having 5 to 15 carbon atoms in the alkyl moiety and α-sulfonated methyl fatty acid esters in which the fatty acid is derived from a C6-C18 fatty source. Preferred sulfate surfactants are alkyl sulfates having 6 to 16, preferably 6 to 10 carbon atoms in the alkyl moiety.

A useful surfactant system comprises a mixture of two alkyl sulfate materials, their respective average chain lengths differing from one another. The cation in each case is again an alkali metal, preferably sodium. The alkyl sulfate salts can be derived from natural or synthetic hydrocarbon sources.

The C6-C16 alkyl ethoxysulfate salt comprises a primary alkyl ethoxysulfate derived from the condensation product of a C6-C16 alcohol condensed with an average of one to seven ethylene oxide groups per mole.

Preferred are the C6-C10 alkyl ethoxy sulfate salts with an average of one to five ethoxy groups per mole.

Other anionic surfactants suitable for the purposes of the invention are the alkali metal sarcosinates of the formula

R-CON(R¹)CH₂COOM

wherein R is a linear or branched C₅-C₁₇-alkyl or alkenyl group, R¹ is a C₁-C₄-alkyl group and M is an alkali metal ion. Preferred examples are the lauroyl, co coyl- (C₁₂-C₁₄), myristyl- and oleylmethylsarcosinates in the form of their sodium salts.

Another class of anionic surfactants useful herein are the alkyl ester sulfonate surfactants which include linear esters of C8-C20 carboxylic acids (i.e. fatty acids) sulfonated with gaseous SO3 according to "The Journal of the American Oil Chemists Society", 52 (1975), pages 323-329. Suitable starting materials include natural fatty substances such as derived from tallow, palm oil, etc.

The preferred alkyl ester sulfonate surfactants have the structural formula

wherein R3 is C8-C20 hydrocarbyl, preferably alkyl, or a combination thereof, R4 is C1-C6 hydrocarbyl, preferably alkyl, or a combination thereof, and M is a cation which forms a water-soluble salt with the alkyl ester sulfonate. Suitable salt-forming cations include metals such as sodium, potassium and lithium and substituted or unsubstituted ammonium cations such as monoethanolamine, diethanolamine and triethanolamine. Preferably R3 is C10-C16 alkyl and R4 is methyl, ethyl or isopropyl. Particularly preferred are the methyl ester sulfonates wherein R3 is C10-C16 alkyl.

One class of nonionic surfactants useful in the present invention includes the water-soluble C6-C16 ethoxylated fatty alcohols and the mixed ethoxylated/propoxylated C6-C16 fatty alcohols and mixtures thereof. Preferably, the ethoxylated fatty alcohols are the ethoxylated C₁₀-C₁₆ fatty alcohols with a degree of ethoxylation of 3 to 50, most preferably these are the ethoxylated C₁₂-C₁₆ fatty alcohols with a degree of ethoxylation of 3 to 40. Preferably, the mixed ethoxylated/propoxylated fatty alcohols have an alkyl chain length of 10 to 16 carbon atoms, a degree of ethoxylation of 3 to 30 and a degree of propoxylation of 1 to 10.

Thus, C6-C16 alcohol itself can be obtained from natural or synthetic sources. Thus, C6-C16 alcohols derived from natural fats, or Ziegler olefin buildup, or OXO synthesis can form suitable sources for the alkyl group. Examples of synthetically derived materials include Dobanol 25 (RTM) sold by Shell Chemicals (UK) Ltd. which is a mixture of C₁₂-C₁₅ alcohols, Ethyl 24 sold by Ethyl Corporation which is a mixture of C₁₂-C₁₅ alcohols, Ethyl 24 sold by Ethyl Corporation which is a mixture of C₁₃-C₁₅ alcohols in the ratio 67% C₁₃, 33% C₁₅ sold under the trade name Lutensol by BASF GmbH and Synperonic (RTM) by ICI Ltd. and Lial 125 sold by Liquichimica Italiana. Examples of naturally occurring materials from which the alcohols can be derived are coconut oil and palm kernel oil and the corresponding fatty acids.

Another class of nonionic surfactants includes alkyl polyglucoside compounds of the general formula

RO(CnH₂nO)tZx

wherein Z is a residue derived from glucose; R is a saturated hydrophobic alkyl group containing 6 to 16 carbon atoms, preferably 6 to 14 carbon atoms; t is 0 to 10 and n is 2 or 3; x is 1.1 to 4, the compounds including less than 10% unreacted fatty alcohol and less than 50% short chain alkyl polyglucosides. Compounds of this type and their use in detergent compositions are described in EP-B-0 070 074, 0 070 077, 0 075 996 and 0 094 118.

Another preferred nonionic surfactant is a polyhydroxy fatty acid amide surfactant compound of the structural formula

wherein R1 is H, C1-C4 hydrocarbyl, 2-hydroxyethyl, 2-hydroxypropyl or a mixture thereof, preferably C1-C4 alkyl, more preferably C1 or C2 alkyl, most preferably C1 alkyl (i.e. methyl) and R2 is a C5-C15 hydrocarbyl, preferably a straight chain C5-C13 alkyl or alkenyl, more preferably a straight chain C5-C11 alkyl or alkenyl, most preferably a straight chain C5-C9 alkyl or alkenyl, or a mixture thereof: and Z is a polyhydroxyhydrocarbyl having a linear hydrocarbyl chain with at least 3 hydroxyl groups directly connected to the chain, or an alkoxylated (preferably ethoxylated or propoxylated) derivative thereof. Z is preferably derived from a reducing sugar in a reductive amination reaction; more preferably Z is glycityl. Suitable reducing sugars include glucose, fructose, maltose, lactose, galactose, mannose and xylose. As raw materials, high dextrose corn syrup, high fructose corn syrup and high maltose corn syrup as well as the individual sugars listed above can be used. These corn syrups can provide a mixture of sugar components for Z. It is to be understood that in no way is it intended to exclude other suitable raw materials. Z is preferably selected from the group comprising - CH₂-(CHOH)n-CH₂OH, -CH(CH₂OH)-(CHOH)n-1--CH₂OH, -CH₂- (CHOH)₂(CHOR')(CHOH)-CH₂OH, where n is an integer from 3 to 5 (inclusive) and R' is H or a cyclic or aliphatic monosaccharide and alkoxylated derivatives thereof. Most preferred are glycityls in which n is 4, especially -CH₂-(CHOH)₄CH₂OH.

In the formula (I), R¹ can e.g. B. N-methyl, N-ethyl, N-propyl, N-isopropyl, N-butyl, N-2-hydroxyethyl or N-2-hydroxypropyl.

R₂-CO-N< can be, for example, cocamide, stearamide, oleamide, lauramide, myristamide, capricamide, palmitamide or tallowamide.

Z can be 1-deoxyglucityl, 2-deoxyfructityl, 1-deoxymaltityl, 1-deoxylactityl, 1- deoxygalactityl or 1-deoxymannityl or 1-deoxymaltotriotityl. Preferred compounds are N-methyl-N-1-deoxyglucityl-C₁₄-C₁₈-fatty acid amides.

Another class of surfactants are the semipolar surfactants, such as amine oxides. Suitable amine oxides are mono-C6-C20, preferably C6-C10 N-alkyl or alkenylamine oxides and propylene-1,3-diamine dioxides, in which the remaining N-positions are substituted by methyl, hydroxyethyl or hydroxypropyl groups.

Cationic surfactants may also be used in the detergent compositions described herein and suitable quaternary ammonium surfactants are selected from mono-C6-C16, preferably C6-C10 N-alkyl or alkenyl ammonium surfactants wherein the remaining N-positions are substituted by methyl, hydroxyethyl or hydroxypropyl groups.

Another optional ingredient useful in detergent compositions is one or more enzymes.

Preferred enzymatic materials include amylases, neutral and alkaline proteases, lipases and esterases conventionally incorporated into detergent compositions. Suitable enzymes are illustrated in U.S. Patents 3,519,570 and 3,533,139.

Preferred commercially available protease enzymes include those sold under the trade names Alcalase and Savinase by Novo Industries A/S (Denmark) and Maxatase by International Bio-Synthetics, Inc. (Netherlands). Protease enzyme can be incorporated into the compositions according to the invention in a proportion of 0.005 to 2% by weight of active enzyme of the composition.

Preferred amylases include, for example, amylases obtained from a particular strain of B. licheniforms as described in more detail in GB-1 269 839 (Novo). Preferred commercially available amylases include, for example, Rapidase, sold by International Bio-Synthetics Inc., and Termamyl, sold by Novo Industries A/S. The invention contains a level of from 0.001% to 2% active enzyme by weight of the composition.

A preferred lipase is derived from Pseudomonas pseudoalcaligenes, which is described in the granted European patent EP-B-0 218 272.

A further optional component of the machine dishwashing or rinsing detergent compositions of the invention is a silicone foam control agent present in amounts of from 0.01 to 5%, more preferably from 0.05 to 3%, most preferably from 0.05 to 1% by weight of the composition.

Another lipase described herein is obtained by cloning the gene from Humicola lanuginosa and expressing the gene from Aspergillus oryza as a host, as described in European Patent Application EP-A-0 258 068, which is commercially available from Novo Industries A/S, Bagsvaerd, Denmark, under the trade name Lipolase. This lipase is also described in U.S. Patent 4,810,414, Huge-Jensen et al., issued March 7, 1989.

Another optional ingredient is a lime soap dispersant compound present in an amount of 0.05 to 40%, more preferably 0.1 to 20%, most preferably 0.25 to 10% by weight of the compositions.

A lime soap dispersant is a material which prevents the precipitation of alkali metal, ammonium or amine salts of fatty acids by calcium or magnesium ions. Preferred lime soap dispersants include ethoxylated C13-15 alcohol sulfates having an average degree of ethoxylation of 3.

By silicone foam control agent is meant any foam control agent comprising a silicone antifoam compound. Thus, silicone foam control agents include agents containing silicone-silica mixtures and particles in which the silicone or silicone-silica mixture is incorporated in a water-soluble or water-dispersible carrier material. Alternatively, the silicone foam control agents may comprise silicone or silicone-silica mixtures dissolved or dispersed in a liquid carrier and applied by spraying to one or more of the other components of the detergent composition.

In industrial practice, the term "silicone" has become a collective term, which includes a variety of polymers with relatively high molecular weight, containing siloxane units and hydrocarbyl groups of various types.

In general, the silicone antifoam compounds can be described as siloxanes of the general formula

where R can independently be an alkyl or an aryl radical. Examples of such substituents are methyl, ethyl, propyl, isobutyl and phenyl. Preferred polydiorganosiloxanes are polydimethylsiloxanes having trimethylsilyl endblocking units and having a viscosity at 25°C of 5 x 10-5 m2/s to 0.1 m2/s, i.e. a value of n in the range of 40 to 1500. These are preferred due to their ready availability and their relatively low cost.

A preferred type of silicone foam control agent useful in the compositions described herein comprises a mixture of an alkylated siloxane of the type described above and solid silica.

The solid silica may be a silica powder, a precipitated silica or a silica prepared by a gelation technique. The suitable silica particles have an average particle size of 0.1 to 50 micrometers, preferably 1 to 20 micrometers, and a surface area of at least 50 m²/g. These silica particles may be Treating with dialkylsilyl groups and/or trialkylsilyl groups which are either directly linked to the silica or by means of a silicone resin. It is preferred to use a silica whose particles have been made hydrophobic with dimethyl and/or trimethylsilyl groups. The foam control agents for inclusion in the detergent compositions according to the invention suitably contain such an amount of silica that the weight ratio of silica to silicone is in the range 1:100 to 3:10, preferably 1:50 to 1:7.

A preferred silicone foam control agent is represented by a hydrophobic silanated (most preferably trimethylsilanated) silica having a particle size in the range of 10 nanometers to 20 nanometers and a specific surface area of above 50 m²/g intimately mixed with dimethyl silicone fluid having a molecular weight in the range of about 500 to about 200,000 in a weight ratio of silicone to silanated silica of about 1:1 to about 1:2.

Another preferred silicone foam control agent is described in Bartolotta et al., U.S. Patent 3,933,672. Other particularly useful foam suppressors are the self-emulsifying silicone foam suppressors described in German Patent Application DTOS 2 646 126, published April 28, 1977. An example of such a compound is DC0544, commercially available from Dow Corning, which is a siloxane/glycol copolymer.

A highly preferred silicone foam control agent is particles of the type described in EP-A-0 210 731 comprising a silicone antifoam agent and an organic material having a melting point in the range 50° to 85°C, the organic material comprising a monoester of glycerol and a fatty acid having a carbon chain of 12 to 20 carbon atoms. EP-A-0 210 721 describes similar particulate foam control agents but in which the organic material is a fatty acid or an alcohol having a carbon chain of 12 to 20 carbon atoms or a mixture thereof, having a melting point of 45° to 80°C.

Other highly preferred silicone foam control agents are described in copending European application 91870007.1 in the name of Procter and Gamble Company, which describes granular foam suppressors comprising a silicone antifoam compound, a carrier material, an organic coating material and glycerol in a weight ratio of glycerol:silicone antifoam compound of 1:2 to 3:1. Copending European application 91201342.0 also describes highly preferred granular foam control agents comprising a silicone antifoam compound, a carrier material, an organic coating material and crystalline or amorphous aluminosilicate in a weight ratio of aluminosilicate:silicone antifoam compound of 1:3 to 3:1. The preferred carrier material in the two highly preferred granular foam control agents described above is starch.

The preferred methods for incorporating the silicone foam control agents involve either applying the silicone foam control agent in liquid form by spraying it onto one or more of the major components of the composition or alternatively forming the silicone foam control agent into discrete particles which can then be mixed with the other solid components of the composition. The incorporation of the foam control agents as discrete particles also allows the inclusion therein of other foam control materials such as C20-C24 fatty acids, microcrystalline waxes and high molecular weight copolymers of ethylene oxide and propylene oxide which would otherwise adversely affect the dispersibility of the matrix. Techniques for forming such foam control particles are described in the aforementioned U.S. Patent No. 3,933,672 to Bartolotta et al.

Other optional ingredients suitable for inclusion in the compositions of the invention include anti-redeposition and soil suspending agents, perfumes, colors and filler salts, with sodium sulfate being a preferred filler salt.

Form of compositions

The automatic dishwashing compositions of the invention may be formulated in any desired form, such as powders, granules, pastes, liquids, gels and tablets, with granular forms being preferred.

The bulk density of the granular detergent compositions according to the present invention is typically at least 650 g/litre, more usually at least 700 g/litre, and more preferably from 800 g/litre to 1200 g/litre.

Bulk density is measured using a simple funnel and cup device consisting of a conical funnel rigidly formed or fixed to a base and fitted with a flap valve at its lower extremity to allow emptying of the contents of the funnel into an axially aligned cylindrical cup provided below the funnel. The funnel measures 130 mm and 40 mm at its upper and lower extremities respectively. It is fitted so that the lower extremity is 140 mm above the upper surface of the base. The cup has an overall height of 90 mm, an internal height of 87 mm and an internal diameter of 84 mm. Its nominal volume is 500 ml.

To make a measurement, the funnel is filled with powder by hand pouring, the flap valve is opened and powder is poured into the cup until it overflows. The filled cup is removed from the frame and excess powder is removed from the cup by running a smooth-edged tool, such as a knife, across the top of the cup. The filled cup is then weighed and the value obtained for the weight of the powder is doubled to obtain the bulk density in g/litre. Repeat measurements are made as required.

The particle size of the components of granular compositions according to the invention should preferably be such that not more than 5% of the particles are larger than 1.4 mm in diameter and not more than 5% of the particles are less than 0.15 mm in diameter.

Generally, when machine dishwashing or rinsing detergent compositions are in liquid form, the liquid should be thixotropic (i.e., exhibit a high viscosity when subjected to a low load and a lower viscosity when subjected to a high load), or at least have a very high viscosity, for example 1,000 to 10,000,000 centipoise. In many cases, it is desirable to include a viscosity controlling agent or a thixotropic agent to provide a suitable liquid product form. Suitable thixotropic or viscosity controlling agents include methylcellulose, carboxymethylcellulose, starch, polyvinyl, pyrrolidone, gelatin, colloidal silica, and natural or synthetic clay minerals.

Paste compositions according to the invention generally have viscosities of about 5000 centipoise and up to several hundred million centipoise. To provide satisfactory paste compositions, a small amount of a solvent or solubilizing agent or a gelling agent may be included. Water is most commonly used in this context and forms the continuous phase of a concentrated dispersion. Certain nonionic surfactants in high proportions form a gel in the presence of a small amount of water and other solvents. Such gelled compositions are also contemplated in the present invention.

pH value of the compositions

The pH of a 1% solution of the present compositions is preferably 7.5 to 12, more preferably 9 to 11.5, most preferably 10 to 11.

Method of preparation of the compositions described herein

A preferred method of preparation for the compositions described herein comprises premixing the paraffin oil with a dispersant, the resulting intimate premix being sprayed onto the remainder of the composition. The dispersant may advantageously consist of a nonionic surfactant as described above, which therefore performs two functions in the present composition.

A preferred dispersant is Plurafac LF404, sold by BASF.

An alternative route is to spray the intimate mixture of paraffin oil and dispersant onto the particles of a bleach, which leads to a reduction in the dissolution rate of the bleach in water and thus to a control of the release rate of available oxygen. The coated particles of a bleaching agent are then dry-mixed with the rest of the composition.

In an embodiment of another method described herein, the particles of bleaching agents are compacted prior to dry blending with the rest of the composition. This technique slows the rate of dissolution in water and is therefore advantageously applied to otherwise rapidly dissolving species such as perborate monohydrate.

In this embodiment, the paraffin oil is typically compacted together with the bleaching species and optionally with other ingredients such as sodium sulfate and/or binders. The resulting particles are then dry blended with the remainder of the ingredients.

Examples

The following examples illustrate the present invention.

In the detergent compositions below, the abbreviated names have the following meanings:

Citrate: Trisodium citrate dihydrate

Phosphate: Sodium tripolyphosphate

MA/AA: Copolymers with 1:4 maleic acid/acrylic acid, an average molecular weight of about 80,000

Silicate: Amorphous sodium silicate (SiO2:Na2O ratio usually follows)

Protease: Proteolytic enzyme sold under the trade name Savinase by Novo Industries A/S

Amylase: Amylolytic enzyme, sold under the trade name Termamyl by Novo Industries A/S

Non-ionic ingredient: mixed ethoxylated/propoxylated C₁₃-C₁₅ fatty alcohol with an average degree of ethoxylation of 3.8 and an average degree of propoxylation of 4.5, sold under the trade name Plurafac LF404 by BASF GmbH.

Anionic component: C₆-C₁₀-alkyl ethoxy sulfate with 1-5 ethoxy groups per mole

Sulfate: Anhydrous sodium sulfate

TAED: Tetraacetylethylenediamine

DTPMP: Diethylenetriaminepenta(methylenephosphonic acid)

EDDS: Ethylenediamine-N,N-disuccinic acid

The following detergents for machine dishwashing are prepared according to the invention (parts by weight):

(1) Pre-compacted before installation

(2) WINOG 70 from Wintershall

(3) Premixed with the paraffin oil before introduction

(4) Lutensol AO12 from BASF

Claims (10)

1. A composition for automatic dishwashing, comprising - 1 to 80 wt.% of a detergent builder compound, - Oxygen-releasing bleach, - 0.005 to 2.5% by weight paraffin oil, and - Nitrogen-containing corrosion inhibitor compound, such that the nitrogen is trivalent, and wherein the nitrogen-containing corrosion inhibitor compound is not a benzotriazole compound and not a heavy metal ion complexing agent. 2. The automatic dishwashing composition of claim 1, wherein the nitrogen-containing corrosion inhibitor compound is incorporated in an amount of 0.005 to 3% by weight of the composition. 3. A machine dishwashing composition according to claims 1-2, wherein the oxygen-releasing bleach is incorporated such that the proportion of available oxygen in the composition, measured according to the method described herein, is 0.3 to 1.7. 4. Composition according to claims 1-3, wherein the paraffin oil is present in a proportion of 0.1 to 1% by weight. 5. Composition according to claims 1-4, wherein the paraffin oil is selected from predominantly branched aliphatic hydrocarbons having 20 to 50, preferably 25 to 45 carbon atoms, with a ratio of cyclic to noncyclic hydrocarbons of about 32:68. 6. Composition according to claims 2-5, wherein the nitrogen-containing corrosion inhibitor compound is imidazole or a derivative thereof. 7. Composition according to claims 2-6, wherein the proportion of available oxygen is 0.5 to 1.2. 8. A composition according to claims 1-7, wherein the release rate of available oxygen is such that the available oxygen is not completely released from the composition until after 3.5 minutes, using the test procedure specified in this description. 9. A composition according to claim 8, wherein the bleaching agent consists of perborate tetrahydrate and an activator therefor. 10. Composition according to claims 1-9, which is in granular form, has a bulk density of more than 650 g/litre and a pH, measured as a 1% solution thereof, in the range of 7.5 to 12.