DETERGENT COMPOSITIONS CONTAINING SILVER ANTI-TARNISHING AGENTS

Description

FIELD OF THE INVENTION

[0001] This invention relates to bleaching detergent compositions which include silver anti-tarnishing agents. More particularly, the invention relates to detergent compositions based on peroxygen and/or hypohalite bleaching agents and which include one or more particular organic heterocyclic species as a silver anti-tarnishing agent.

BACKGROUND OF THE INVENTION AND PRIOR ART

[0002] Silver is chemically the most reactive element among the noble metals and tarnishes readily on exposure to sulphur bearing atmospheres. Because of its electronic state, silver exhibits a drastically different chemical behaviour from, for instance, copper, although both metals are in the same group of the Periodic Table. Thus, silver tarnishing is very different from corrosion of other metals.

[0003] Tarnishing, sometimes referred to as discolouring, is caused by a silver oxidation process in which sulphide is formed. Food such as onions, mustard and eggs which contain organic sulphur compounds are also known to tarnish silver. See Singh et al., "Silver Tarnishing and its Prevention - A Review" Anti-corrosion Methods and Materials, Vol. 30 (July 1983), pp. 4-8.

[0004] Silver tarnishing is also known to occur when an oxygen bleaching agent used in detergent compositions oxidizes the silver to silver oxide. This oxidation process causes surface-blackening of the silver, leaving undesirable tarnishing of silverware when machine-dishwashed, for example.

[0005] The use of organic compounds to enhance the resistance of a silver surface to tarnishing has been described in Singh et al, supra pp. 5-6. Certain triazoles, particularly benzotriazole and its variations, are useful as corrosion-inhibiting agents in detergent compositions as described in CH 673033 (1990) and U.S. 4,321,166 (Procter & Gamble, 1982).

[0006] U.S. Patents Nos. 2,618,606 (Procter & Gamble) and 2,618,608 (Procter & Gamble) disclose the use of derivatives of triazole, including 1,2,3-triazole, imidazole and pyrazole, as discolouration inhibitors used in detergent compositions for non-ferrous metals, such as copper and brass. The detergents described do not, however, contain a bleaching agent which complicates silver tarnish inhibition. The patents further state that a mixture of copper inhibitors are required to prevent tarnishing over a broad pH range.

[0007] Conventional detergents, particularly automatic machine dishwashing detergents, are generally formulated with chlorine bleaching agents in a high alkaline pH range. During washing, certain such chlorine bleaches (e.g. chloroisocyanurate) react to form isocyanuric acid and thus do not greatly effect silver discolouration.

[0008] Detergent compositions are, however, increasingly being based on peroxygen bleaching agents and are being formulated to be milder to produce more environmentally-friendly products. The problem of tarnishing of silver and silver-plated articles has thus become more severe.

[0009] It is thus a primary object of the present invention to provide a peroxygen and/or hypohalite bleach-based detergent composition containing one or more compounds which prevent or ameliorate the problem of silver tarnishing, particularly in the context of a machine dishwashing environment, especially in an alkaline washing medium.

[0010] It is a further object of the invention to provide an environmentally-friendly detergent composition which prevents or inhibits tarnishing of silver or silver-plated articles.

[0011] Another object of the invention is to provide a method for washing silver or silver-plated articles without discolouring them.

[0012] A further object of the invention is to protect a silver or silver-plated article against tarnishing from organic foodstuffs with which it comes into contact.

[0013] Silver anti-tarnishing bleaching detergent compositions formulated for use in automatic dishwashing machines or fabric washing machines which are stable in a variety of physical forms, including liquid, powder and flakes is another object of the invention.

SUMMARY OF THE INVENTION

[0014] Accordingly, in a first aspect the present invention provides a bleaching detergent composition comprising:

(a) from 1 to 20% by weight of a bleaching agent selected from a peroxygen or peroxygen-yielding compound, a hypohalite or hypohalite-yielding compound, or a salt thereof, or mixtures thereof;

(b) from 0.05 to 10% by weight of an anti-tarnishing agent selected from:

(i) a purine class compound of the following formula (I) or its tautomers :

wherein X¹ is nitrogen or C-R³, Y¹ is nitrogen or C-R⁴, and R¹, R², R³ and R⁴ are each independently hydrogen, hydroxy, alkoxy, amine, straight or branched chain alkyl having 1 to 20 carbon atoms, amido, amidoalkyl, alkylthio, alkenyl or hydroxyalkyl; wherein R¹ may additionally be SH when R² is hydrogen, X¹ is nitrogen, and Y¹ is CH.

(ii) cyanuric acid or isocyanuric acid or a salt thereof;

(iii) a 1,3-N azole compound of the following formula (II);

wherein X² is C-R⁷ or nitrogen provided Y² is also nitrogen, Y² is nitrogen or C-R⁶, and R⁵, R⁶ and R⁷ are each independently hydrogen, amine, amido, straight or branched chain alkyl having from 1 to 20 carbon atoms, an amino- or carboxylic-containing chain, alkoxy, alkylthio, hydroxy, hydroxyalkyl, alkenyl, or R⁵ and R⁶ taken together form an unsubstituted or substituted aryl group; or a salt thereof;

(iv) a mixture of any of the above compounds (i), (ii) or (iii);

(c) optionally from 1 to 75% by weight of a detergency builder; and

(d) optionally, from 0.01 to 40% by weight of a surfactant;

wherein the composition exhibits a pH value in a 1% aqueous solution in the range from 7 to 13, especially from 7 to 11, and wherein the anti-tarnishing agent has a pK_a value at least one unit below the pH value of a 1% aqueous solution of the composition.

[0015] In a second aspect, the invention provides a method of washing a silver or silver-plated article whilst preventing or inhibiting tarnishing thereof during or as a result of the washing process, the method comprising washing the said article with a bleaching detergent composition according to the first aspect of the invention defined above.

[0016] In a third aspect, the invention provides the use of a compound selected from any of (i) to (iv) defined above in accordance with the first aspect of the invention, as a silver anti-tarnishing agent in a peroxygen- and/or hypohalite based bleaching detergent composition having a pH value in a 1% aqueous solution in the range from 7 to 13, and wherein the anti-tarnishing agent has a pK_a value at least 1 unit below the pH value of a 1% aqueous solution of the composition.

[0017] The various aspects of the invention, and preferred embodiments thereof, will now be described in detail.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

Anti-tarnishing agent

[0018] The silver anti-tarnishing agent of compositions of the invention is a compound or a mixture of two or more compounds selected from any of the following:

(i) a purine class compound of the following formula (I) or its tautomers:

wherein X¹ is nitrogen or C-R³, Y¹ is nitrogen or C-R⁴, and R¹, R², R³ and R⁴ are each independently hydrogen, hydroxy, alkoxy, amine, straight or branched chain alkyl having 1 to 20 carbon atoms, amido, amidoalkyl, alkylthio, alkenyl or hydroxyalkyl, wherein R¹ may additionally be SH when R² is hydrogen, X¹ is nitrogen, and Y¹ is CH ;

(ii) cyanuric acid or isocyanuric acid or a salt thereof;

(iii) a 1,3-N azole compound of the following formula (II);

wherein X² is C-R⁷ or nitrogen provided Y² is also nitrogen, Y² is nitrogen or C-R⁶, and R⁵, R⁶ and R⁷ are each independently hydrogen, amine, amido, straight or branched chain alkyl having from 1 to 20 carbon atoms, an amino- or carboxylic-containing chain, alkoxy, alkylthio, hydroxy, hydroxyalkyl, alkenyl, or R⁵ and R⁶ taken together form an unsubstituted or substituted aryl group; or a salt thereof;

with the proviso that the compound(s) have a pK_a value which is at least 1 unit below, preferably at least 2 units below, a pH value of a 1% aqueous solution of the composition in which the compound(s) is/are incorporated.

[0019] Most preferably, the pK_a value of the anti-tarnishing compound(s) is at least 2 and up to 6 units below the pH value of the aqueous solution of the composition.

[0020] As used herein, the term "pK_a" means a pH value at which 50% of the heterocyclic ring moieties of the compound (particularly the five-membered rings in the case of the purine class compounds) are in ionic form.

[0021] As used herein, the term "purine class compound" includes not only compounds of formula (I) above, but also tautomeric forms of these compounds.

[0022] Preferred compounds of formula (I) include those wherein X¹ is nitrogen and Y¹ is C-R⁴ and R¹, R² and R⁴ are each independently hydrogen, hydroxy, alkoxy, alkylthio, amine, amido or lower alkyl having from 1 to 6 carbon atoms, wherein R¹ may additionally be SH when R² is hydrogen, X¹ is nitrogen and Y¹ is CH.

[0023] Especially preferred compounds of formula (I) include purine, adenine, guanine, 6-mercaptopurine, xanthine, hypoxanthine, uric acid, and allopurinol.

[0024] The above purine class compounds are available commercially, for example from Aldrich Chemical Co. of Milwaukee, Wisconsin, USA.

[0025] As used herein, the term "cyanuric acid" means 1,3,5-triazine-2,4,6(1H,3H,5H)-trione, normal cyanuric acid, symtriazinetriol, 2,4,6-trihydroxy-1,3,5-triazine, tricyanic acid or trihydroxycyanidine. Corresponding possibilities apply to the term "isocyanuric acid" as used herein, and within the scope of both terms are salts thereof.

[0026] Preferably, the cyanuric acid or isocyanuric acid, or a salt thereof, as an anti-tarnishing agent in the present invention, is an unsubstituted such species.

[0027] Cyanuric acid is available commercially, for example also from Aldrich Chemical Co. of Milwaukee, Wisconsin, USA.

[0028] Preferred 1,3-N azole compounds of formula (II) above include those wherein X² is C-R⁷, X² is nitrogen provided Y² is nitrogen, Y² is C-R⁶ and R⁵ and R⁶ taken together form an aryl or a substituted aryl group. Other preferred compounds of formula (II) include those wherein Y² is C-R⁶ and R⁵ and R⁶ are each independently hydrogen, amine, amido, straight or branched chain alkyl having from 1 to 6 carbon atoms, alkoxy, alkylthio, hydroxy, alkenyl or an amino- or carboxylic-containing moiety.

[0029] Especially useful compounds of formula (II) include imidazole, benzimidazole, tetrazole, 4-aminotetrazole, 1,2,4-triazole, 3-amino-1,2,4-triazole and histidine. 1,3-N azole compounds of formula (II) above useful in the invention are commercially available, for example also from Aldrich Chemical Co. of Milwaukee, Wisconsin, USA.

[0030] In the above formulae (I) and (II), a group defined as being "alkyl" preferably means a group having from 1 to 20 carbon atoms, more preferably from 1 to 6 carbon atoms, most preferably from 1 to 4 carbon atoms.

[0031] In formulae (I) and (II) above, those defined groups which are substituted alkyl groups preferably have an alkyl chain length of from 1 to 5 carbon atoms, more preferably from 1 to 3 carbon atoms. The term "aryl" includes aryl groups containing one or more heteroatoms such as S, N or O, preferably N. The term "substituted aryl" includes an aryl group substituted with one or more of the following groups: straight or branched chain alkyl having from 1 to 20 carbon atoms, hydroxy, alkoxy or alkenyl.

[0032] In the making of the present invention, it was surprising to discover that the above defined compounds (i) to (iii) provide beneficial anti-tarnishing properties to silver and silver-plated articles in the context of the subject active oxygen- or active halogen-based bleaching detergent compositions. In contrast, compositions containing certain 1-N azoles (e.g. pyrrole), 1,2-N azoles (e.g. indazole, pyrazole) and pyrimidine have been observed to be substantially ineffective in preventing heavy tarnishing of similar silver and silver-plated articles. This observation was particularly surprising in view of the fact that most of the 1-N and 1,2-N azole compounds did prevent copper tarnishing under similar conditions. Without being limited by theory, it is proposed that the compounds used in the present invention form a complex with the silver molecules at the surface of the article to form a protective film which prevents or diminishes its tendency to tarnish in an oxidative environment.

[0033] In the anti-tarnishing bleaching detergent compositions of the invention, the one or more compounds forming the anti-tarnishing agent are present in a (total) amount of from 0.05 to 10% by weight, preferably from 0.25 to 2.5% by weight, most preferably from 0.75 to 2% by weight.

pH

[0034] The pH of a 1% aqueous solution of the compositions in accordance with the invention should be from 7 to 13, more preferably from 7 to 11, most preferably from 7 or 8 to 10.

Peroxy bleaching agent

[0035] Peroxygen or peroxygen-yielding bleaching agents for use in the compositions of the invention include organic peroxy acids and diacylperoxides. Typical monoperoxy acids useful herein include alkyl peroxy acids and aryl peroxy acids such as:

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

(ii) aliphatic and substituted aliphatic monoperoxy acids, e.g., peroxylauric acid, peroxystearic acid, epsilon-phthalimido peroxyhexanoic acid, o-carboxybenzamido peroxyhexanoic acid, N-nonenylamidoperadipic acid and N-nonenylamidopersuccinic acid.

[0036] Typical diperoxy acids useful herein include alkyl diperoxy acids and aryldiperoxy acids, such as:

(iii) 1,12-diperoxydodecanedioic acid

(iv) 1,9-diperoxyazelaic acid

(v) diperoxybrassylic acid; diperoxysebacic acid and diperoxyisophthalic acid

(vi) 2-decyldiperoxybutane-1,4-dioic acid

(vii) N,N-terephthaloyl-di(6-aminopercaproic acid).

[0037] A typical diacylperoxide useful herein includes dibenzoylperoxide.

[0038] Inorganic peroxygen compounds are also suitable for use in the present invention. Examples of such useful materials include salts of monopersulphate, perborate monohydrate, perborate tetrahydrate, and percarbonate.

[0039] Preferred organic oxygen bleaching agents include epsilon-phthalimidoperoxyhexanoic acid, o-carboxybenzamidoperoxy hexanoic acid, and mixtures thereof.

[0040] When an oxygen bleaching agent is used as the bleaching agent in compositions of the invention, it is present therein in an amount from 1 to 20% by weight, preferably from 1 to 15% by weight, most preferably from 2 to 10% by weight.

[0041] The oxygen bleaching agent may be incorporated directly into the formulation or may be encapsulated by any suitable encapsulation technique known in the art to produce stable capsules in alkaline liquid formulations.

[0042] A preferred encapsulation method is described in U.S. Patent No. 5,200,236 (Lang et al). In the patented method, the bleaching agent is encapsulated as a core in a paraffin wax material having a melting point from 40°C to 50°C. The wax coating has a thickness of from 100 to 1500 microns.

[0043] Oxygen bleaching agent systems which may be employed in the present invention may if desired or if necessary employ one or more peroxyacid bleach precursors.

[0044] Suitable peroxygen peracid precursors for peroxy bleach compounds have been amply described in the literature, including United Kingdom Patents Nos. 836,988; 855,735; 907,356; 907,358; 907,950; 1,003,310 and 1,246,339; and U.S. Patents Nos. 3,332,882 and 4,128,494.

[0045] Typical examples of precursors are polyacylated alkylene diamines, such as N,N,N',N'-tetraacetylethylene diamine (TAED) and N,N,N',N'-tetraacetylmethylene diamine (TAMD); acylated glycolurils, such as tetraacetylglycoluril (TAGU); triacetylcyanurate, sodium sulphophyl ethyl carbonic acid ester, sodium acetyloxybenzene sulphonate (SABS), sodium nonanoyloxybenzene sulphonate (SNOBS) and choline sulphophenyl carbonate. Peroxybenzoic acid precursors are known in the art, e.g., as described in GB-A-836,988. Examples of suitable precursors are phenylbenzoate; phenyl p-nitrobenzoate; o-nitrophenyl benzoate; o-carboxyphenyl benzoate; p-bromo-phenylbenzoate; sodium or potassium benzoyloxy benzenesulphonate; and benzoic anhydride.

[0046] Preferred peroxygen bleach precursors are sodium p-benzoyloxybenzene sulphonate, N,N,N',N'-tetraacetylethylene diamine, sodium nonanoyloxybenzene sulphonate and choline sulphophenyl carbonate.

Halogen bleaching agent

[0047] Hypohalite or hypohalite-yielding bleaching agents for use in the compositions of the invention include hypohalite salts per se or compounds which yield hypohalite anions in aqueous alkaline conditions. Such materials are preferably incorporated into compositions of the invention in the form of dry, particulate, water-soluble anhydrous inorganic salts.

[0048] Examples of suitable hypohalite salts for use in the invention include lithium, sodium or calcium hypochlorite and hypobromite, and halogenated (e.g. with chlorine or bromine) trisodium phosphate. Sodium hypochlorite is particularly preferred for liquid compositions in accordance with the invention.

[0049] Hypohalite-yielding compounds suitable for use in the invention include, for example, chloramines, chloramides, chlorimines, chlorosulphonamides, and chlorohydantoins (though preferably not N-chloro imides which are harsher and less environmentally friendly than oxygen bleaching agents and other hypohalite bleaching agents such as those above), and active halogen compounds corresponding to any of these but which contain bromine instead of chlorine, or contain a mixture of chlorine and bromine.

[0050] Also suitable for use in the invention as a bleaching agent are halogenated isocyanuric acids, such as trichloroisocyanuric acid, dichloroisocyanuric acid, and salts thereof, especially the sodium salts. Commercial sources of chlorinated isocyanuric acids include, for example, ACL-59 (trade mark) supplied by Mansanto Company, and Clearon CDB-56 (trade mark) supplied by Olin Corporation.

[0051] When a halogen-based bleaching agent such as those described above is used as the bleaching agent in compositions of the invention, it is present therein in a similar amount to that when an oxygen-based bleaching agent is used, namely in an amount of from about 1 to about 20% by weight, preferably from 1 to 15% by weight, most preferably from 2 to 10% by weight.

[0052] In embodiments where a mixture of oxygen and halogen bleaching agents are optionally employed, each component is used in an appropriate amount, such that the total amount of bleaching agent present also falls within the essential and preferred narrower ranges defined above with respect to each type of bleaching agent separately.

Detergent Builder Materials

[0053] The compositions of this invention may contain all manner of detergent builders commonly taught for use in automatic dishwashing or other cleaning compositions. The builder component can include any of the conventional inorganic and organic water-soluble builder salts or mixtures thereof and, when present, is included in the composition preferably in an amount of from 1 to about 75% by weight, preferably from about 5 to 70% by weight.

[0054] Typical examples of phosphorus-containing inorganic builders include water-soluble (especially alkali metal) pyrophosphates, orthophosphates and polyphosphates. Specific examples of inorganic phosphate builders include sodium and potassium tripolyphosphates, phosphates, pyrophosphates and hexametaphosphates.

[0055] Suitable examples of non-phosphorus-containing inorganic builders include water-soluble (especially alkali metal) carbonates, bicarbonates, sesquicarbonates, borates, silicates, metasilicates, and crystalline and amorphous aluminosilicates. Specific examples include sodium carbonates (with or without calcite seeds), potassium carbonate, sodium and potassium bicarbonates, silicates and zeolites.

[0056] Particularly preferred inorganic builders may be selected from the group consisting of sodium tripolyphosphate, potassium pyrophosphate, sodium carbonate, potassium carbonate, sodium bicarbonate, sodium silicate and mixtures thereof. When present in the compositions of the invention, sodium tripolyphosphate builder concentrations may range from 2 to 40% by weight, preferably from 5 to 30% by weight of the composition. Sodium carbonate and bicarbonate, when present, may range from 5 to 50% by weight, preferably from 10 to 30% by weight of the composition. Sodium tripolyphosphate and potassium pyrophosphate are preferred builders in gel formulations, where they may be used in an amount of from 3 to 30% by weight, preferably from 10 to 20% by weight.

[0057] Organic detergent builders may also be used in the compositions of the invention. Examples of organic builders include alkali metal citrates, succinates, malonates, fatty acid sulphates, fatty acid carboxylates, nitrilotriacetates, phytates, phosphonates, alkanehydroxyphosphonates, oxydisuccinates, alkyl and alkenyl disuccinates, oxydiacetates, carboxymethyloxy succinates, ethylenediamine tetraacetates, tartrate monosuccinates, tartrate disuccinates, tartrate monoacetates, tartrate diacetates, oxidized starches, oxidized heteropolymeric polysaccharides, polyhydroxysulphonates, polycarboxylates such as polyacrylates, polymaleates, polyacetates, polyhydroxyacrylates, polyacrylate/polymaleate and polyacrylate/polymethacrylate copolymers, aminopolycarboxylates and polyacetal carboxylates such as those described in U.S. Patents Nos. 4,144,226 and 4,146,495.

[0058] Alkali metal citrates, oxydisuccinates, polyphosphonates and acrylate/maleate copolymers are especially preferred organic builders. When present, they are preferably included in an amount of from 1 to 35% by weight of the composition.

[0059] The foregoing detergent builders are intended to illustrate by way of example only, and not to limit, the types of builders which may be employed in the compositions of the present invention.

Surfactants

[0060] The compositions of this invention may contain one or more surfactant materials. Useful surfactants include anionic, nonionic, cationic, amphoteric and zwitterionic types, and mixtures thereof. Such surfactants are well known in the detergent art and are described at length in "Surface Active Agents and Detergents", Vol. II, by Schwartz, Perry & Birch, Interscience Publishers, Inc. 1959.

[0061] Anionic synthetic detergents can be broadly described as surface-active compounds with one or more negatively charged functional groups. Soaps are included within this category. A soap is a C₈-C₂₂ alkyl fatty acid salt of an alkali metal, alkaline earth metal, ammonium, alkylsubstituted ammonium or alkanolammonium salt. Sodium salts of tallow and coconut fatty acids and mixtures thereof are most common. Another important class of anionic compounds are the water-soluble salts, particularly the alkali metal salts, of organic sulphur reaction products having in their molecular structure an alkyl radical containing from 8 to 22 carbon atoms and a radical selected from the group consisting of sulphonic and sulphuric acid ester radicals. Organic sulphur-based anionic surfactants include the salts of C₁₀-C₁₆ alkylbenzene sulphonates, C₁₀-C₂₂ alkane sulphonates, C₁₀-C₂₂ alkyl ether sulphates, C₁₀-C₂₂ alkyl sulphates, C₄-C₁₀ dialkylsulphosuccinates, C₁₀-C₂₂ acyl isethionates, alkyl diphenyloxide sulphonates, alkyl napthalene sulphonates, and 2-acetamido hexadecane sulphonates. Organic phosphate-based anionic surfactants include organic phosphate esters such as complex mono- or diester phosphates of hydroxyl- terminated alkoxide condensates, or salts thereof. Included in the organic phosphate esters are phosphate ester derivatives of polyoxyalkylated alkylaryl phosphate esters of ethoxylated linear alcohols and ethoxylates of phenol. Also included are nonionic alkoxylates having a sodium alkylenecarboxylate moiety linked to a terminal hydroxyl group of the nonionic through an ether bond. Counterions to the salts of all the foregoing may be those of alkali metal (especially sodium), alkaline earth metal, ammonium, alkanolammonium and alkylammonium types.

[0062] Nonionic surfactants can be broadly defined as surface-active compounds with one or more uncharged hydrophilic substituents. A major class of nonionic surfactants are those compounds produced by the condensation of alkylene oxide groups with an organic hydrophobic material which may be aliphatic or alkyl aromatic in nature. The length of the hydrophilic or polyoxyalkylene radical which is condensed with any particular hydrophobic group can be readily adjusted to yield a water-soluble compound having the desired degree of balance between hydrophilic and hydrophobic elements. Illustrative, but not limiting, examples of various suitable nonionic surfactant types are:

(a) polyoxyethylene or polyoxypropylene condensates of aliphatic carboxylic acids, whether linear- or branched-chain and unsaturated or saturated, containing from 8 to 18 carbon atoms in the aliphatic chain and incorporating from 2 to 50 ethylene oxide and/or propylene oxide units. Suitable carboxylic acids include "coconut" fatty acids (derived from coconut oil) which contain an average of 12 carbon atoms, "tallow" fatty acids (derived from tallow-class fats) which contain an average of 18 carbon atoms, palmitic acid, myristic acid, stearic acid and lauric acid;

(b) polyoxyethylene or polyoxypropylene condensates of aliphatic alcohols, whether linear- or branched-chain and unsaturated or saturated, containing from 6 to 24 carbon atoms and incorporating from 2 to 50 ethylene oxide and/or propylene oxide units. Suitable alcohols include coconut fatty alcohol, tallow fatty alcohol, lauryl alcohol, myristyl alcohol and oleyl alcohol. Particularly preferred nonionic surfactant compounds in this category are the "Neodol"-type products, a registered trademark of the Shell Chemical Company.
Also included within this category are nonionic surfactants having the following formula (III):

wherein R is a linear alkyl hydrocarbon radical having an average of 6 to 18 carbon atoms, R¹ and R² are each linear alkyl hydrocarbons of about 1 to 4 carbon atoms, x is a integer of from 1 to 6, y is an integer of from 4 to 20 and z is an integer from 4 to 25.
One preferred nonionic surfactant of formula I is Poly-Tergent SLF-18 (trade mark), from the Olin Corporation, New Haven, Connecticut, USA, having a composition of the above formula where R is a C₆-C₁₀ linear alkyl mixture, R¹ and R² are methyl, x averages 3, y averages 12 and z averages 16. Also suitable are alkylated nonionics as are described in U.S. Patent No. 4,877,544 (Gabriel et al.).
Another family of nonionic surfactants included within this category are compounds of the following formula (IV):

        R³-(CH₂CH₂O)_aH     (IV)

wherein R³ is a C₆-C₂₄ linear or branched alkyl hydrocarbon radical and q is a number from 2 to 50; more preferably R³ is a C₈-C₁₈ linear alkyl mixture and q is a number from 2 to 15;

(c) polyoxyethylene or polyoxypropylene condensates of alkyl phenols, whether linear- or branched-chain and unsaturated or saturated, containing from about 6 to 12 carbon atoms and incorporating from 2 to 25 moles of ethylene oxide and/or propylene oxide;

(d) polyoxyethylene derivatives of sorbitan mono-, di-, and tri-fatty acid esters wherein the fatty acid component has from 12 to 24 carbon atoms. The preferred polyoxyethylene derivatives are of sorbitan monolaurate, sorbitan trilaurate, sorbitan monopalmitate, sorbitan tripalmitate, sorbitan monostearate, sorbitan monoisostearate, sorbitan tripalmitate, sorbitan monostearate, sorbitan monoisostearate, sorbitan tristearate, sorbitan monooleate, and sorbitan trioleate. The polyoxyethylene chains may contain between 4 and 30 ethylene oxide units, preferably about 20. The sorbitan ester derivatives contain 1, 2 or 3 polyoxyethylene chains dependent upon whether they are mono-, di- or tri-acid esters;

(e) polyoxyethylene-polyoxypropylene block copolymers having the following formula (V):

        HO(CH₂CH₂O)_a(CH(CH₃)CH₂O)_b(CH₂CH₂O)_cH     (V)

or the following formula (VI):

        HO(CH(CH₃)CH₂O)_d(CH₂CH₂O)_e(CHCH₃CH₂O)_fH     (VI)

wherein a, b, c, d, e and f are integers from 1 to 350, reflecting the respective polyethylene oxide and polypropylene oxide blocks of said polymer. The polyoxyethylene component of the block polymer constitutes at least 10% of the block polymer. The material preferably has a molecular weight of between 1,000 and 15,000, more preferably from 1,500 to 6,000. These materials are well known in the art. They are commercially available for example under the trademarks "Pluronic" and "Pluronic R" from BASF corporation;

(f) Alkyl glycosides having the following formula (VII):

        R⁴O(R⁵O)_n(Z¹)_p     (VII)

wherein R⁴ is a monovalent organic radical (e.g., a monovalent saturated aliphatic, unsaturated aliphatic or aromatic radical such as alkyl, hydroxyalkyl, alkenyl, hydroxyalkenyl, aryl, alkylaryl, hydroxyalkylaryl, arylalkyl, alkenylaryl, arylalkenyl, etc.) containing from 6 to 30 (preferably from 8 to 18, more preferably from 9 to 13) carbon atoms; R⁵ is a divalent hydrocarbon radical containing from 2 to 4 carbon atoms such as ethylene, propylene or butylene (most preferably the unit (R⁵O)_n represents repeating units of ethylene oxide, propylene oxide and/or random or block combinations thereof); n is a number having an average value of from 0 to 12; Z¹ represents a moiety derived from a reducing saccharide containing 5 or 6 carbon atoms (most preferably a glucose unit); and p is a number having an average value of from 0.5 to 10, preferably from 0.5 to 5.
Examples of commercially available materials from Henkel Kommanditgesellschaft Aktien of Dusseldorf, Germany include: APG (trade mark) 300, 325 and 350, with R⁴ being C₉-C₁₁, n is 0 and p is 1.3, 1.6 and 1.8-2.2, respectively; APG 500 and 550 with R⁴ is C₁₂-C₁₃, n is 0 and p is 1.3 and 1.8-2.2, respectively; and APG 600 with R⁴ being C₁₂-C₁₄, n is 0 and p is 1.3. Particularly preferred is APG 600;

(g) Amine oxides having the following formula (VIII):

        R⁵R⁶R⁷N = O     (VIII)

wherein R⁵, R⁶ and R⁷ are saturated aliphatic radicals or substituted saturated aliphatic radicals. Preferable amine oxides are those wherein R⁵ is an alkyl chain of 10 to 20 carbon atoms and R⁶ and R⁷ are methyl or ethyl groups or both R⁵ and R⁶ are alkyl chains of 6 to 14 carbon atoms and R⁷ is a methyl or ethyl group.

[0063] Amphoteric synthetic detergents can be broadly described as derivatives of aliphatic and tertiary amines, in which the aliphatic radical may be straight or branched chain and wherein one of the aliphatic substituents contain from 8 to 18 carbons and one contains an anionic water-solubilizing group, i.e., carboxy, sulpho, sulphato, phosphato or phosphono. Examples of compounds falling within this definition are sodium 3-dodecylamino propionate and sodium 2-dodecylamino propane sulphonate.

[0064] Zwitterionic synthetic detergents can be broadly described as derivatives of aliphatic quaternary ammonium, phosphonium and sulphonium compounds in which the aliphatic radical may be straight or branched chain, and wherein one of the aliphatic substituents contains from 8 to 18 carbon atoms and one contains an anionic water-solubilizing group, e.g., carboxy, sulpho, sulphato, phosphato or phosphono. These compounds are frequently referred to as betaines. Besides alkyl betaines, alkyl amino and alkyl amido betaines are encompassed herewithin.

[0065] The one or more surface active materials forming the surfactant component of compositions of the invention, when present, constitute from 0.01 to 40% by weight of the composition. The amount of surfactant, if present, will generally be within this range, but the actual amount used may depend upon the type of surfactant(s) employed.

[0066] For instance, anionic and/or nonionic surfactants making up the total surfactant concentration may typically be present in an amount of from about 1 to 40% by weight of the composition, more preferably from 2 to 35% by weight, even more preferably from 5 to 30% by weight. Alkyl polyglycosides as the surfactant component, however, may typically be present in lower concentrations, such as in an amount from 0.01 to 20% by weight, preferably from 0.5 to 10% by weight, optimally between 1 and 5% by weight of the composition.

OPTIONAL ADDITIONAL INGREDIENTS

Silicates

[0067] The compositions of this invention may optionally contain sodium or potassium silicate in an amount of from 1 to 40%, preferably from 1 to 20% by weight of the composition. When present, 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 ratio of SiO₂:Na₂O of from 1.0 to 3.3, preferably from 2 to 3.2. Some of the silicate may be in solid form.

Filler

[0068] An inert particulate filler material which is water-soluble may optionally also be present in the compositions of the invention which are in powder form. This material should not precipitate calcium or magnesium ions at the filler use level. Suitable for this purpose are organic or inorganic compounds. Organic fillers include sucrose esters and urea. Representative inorganic fillers include sodium sulphate, sodium chloride and potassium chloride. A preferred filler is sodium sulphate. Its concentration may range from 0 to 60%, preferably from 10 to 30% by weight of the composition.

Thickeners and Stabilizers

[0069] Thickeners are often desirable for inclusion in liquid cleaning compositions of the invention. Thixotropic thickeners such as smectite clays including montmorillonite (bentonite), hectorite and saponite may be used to impart increased viscosity to such liquid bleaching detergent compositions. Silica, silica gel, and aluminosilicate may also be used as thickeners. Salts of polyacrylic acid (of molecular weight of from about 300,000 up to 6 million and higher), including polymers which are cross-linked, may also be used either alone or in combination with other thickeners. Use of clay thickeners for automatic dishwashing compositions is disclosed, for example, in U.S. Patents Nos. 4,431,559; 4,511,487; 4,740,327; and 4,752,409. Commercially available synthetic smectite clays include Laponite (trade mark) supplied by Laporte Industries. Commercially available bentonite clays include Korthix H and VWH ex Combustion Engineering, Inc.; Polargel T ex American Colloid Co.; and Gelwhite clays (particularly Gelwhite GP and H) ex English China Clay Co. Polargel T is preferred as imparting a more intense white appearance to the composition than other clays.

[0070] The amount of clay thickener employed in the compositions, when it is present, is preferably from 0.1 to 10% by weight, preferably from 0.5 to 5% by weight. Use of salts of polymeric carboxylic acids is disclosed, for example, in GB-A-2,164,350, and in U.S. Patents Nos. 4,859,358 and 4,836,948.

[0071] For liquid formulations with a gel appearance and rheology, particularly if a clear gel is desired, a chlorine-stable polymeric thickener is particularly useful. U.S. Patent No. 4,260,528 discloses natural gums and resins for use in clear autodishwashing detergent compositions, which are not chlorine-stable. Cross-linked acrylic acid polymers manufactured by, for example, B.F.Goodrich and sold under the tradename "Carbopol" have been found to be effective for producing clear gels, and Carbopol 940 and 617, having a molecular weight of 4,000,000, are particularly preferred for maintaining high viscosity with excellent chlorine stability over extended periods. Further suitable chlorine-stable polymeric thickeners are described in U.S. Patent No. 4,867,896.

[0072] When it is present, the amount of thickener employed in the compositions of the invention is preferably from 0 to 5% by weight, preferably from 0.5 to 3% by weight.

[0073] Stabilizers and/or co-structurants such as long-chain calcium and sodium soaps and C₁₂ to C₁₈ sulphates which may optionally be incorporated in compositions of the invention are detailed in U.S. Patents Nos. 3,956,158 and 4,271,030 and the use of other metal salts of long-chain soaps is detailed in U.S. Patent No. 4,752,409. Other co-structurants include Laponite (trade mark) and metal oxides and their salts, as described in U.S. 4,933,101.

[0074] The amount of stabilizer which may be used in liquid compositions of the invention is preferably from 0.01 to 5% by weight of the composition, preferably from 0.01 to 2% by weight. Such stabilizers are optional in gel formulations.

[0075] Co-structurants which are found especially suitable for gels include compounds containing trivalent metal ions which may be present in an amount of from 0.01 to 4% by weight of the composition, and Laponite and/or water-soluble structuring chelants, which may be present in an amount of from 1 to 60% by weight. These co-structurants are more fully described in EP-A-0323209.

Defoamer

[0076] Formulations of the cleaning composition of the invention comprising surfactant may further include a defoamer. Suitable defoamers include mono- and distearyl acid phosphate, silicone oil and mineral oil. Even if the composition includes only defoaming surfactant, the defoamer may still assist in the minimizing of foam which food soils can generate. If a defoamer is present, the compositions may include from 0.02 to 2% by weight thereof, more preferably from 0.05 to 1.0% by weight thereof.

Other adjunct ingredients

[0077] Minor amounts of various other optional components may be present in the cleaning compositions of the invention. These include: bleach scavengers including (but not limited to) sodium bisulphite, sodium perborate, reducing sugars, and short-chain alcohols; solvents and hydrotropes such as ethanol, isopropanol and xylene sulphonates; flow control agents (in granular forms of the composition); enzyme-stabilizing agents; soil-suspending agents; antiredeposition agents; anti-tarnish agents; anti-corrosion agents; colourants; other functional additives; perfumes.

[0078] The pH of cleaning compositions of the invention may be adjusted as desired or as necessary by addition of strong acid or base. Such alkalinity or buffering agents include, for example, sodium carbonate and sodium borate.

Enzymes

[0079] Enzymes capable of facilitating the removal of soils from a substrate may also optionally be present in compositions of the invention, preferably in an amount of from 0 to 10% by weight, preferably from 1 to 5% by weight. Such enzymes include proteases (e.g., Alcalase (trade mark), Savinase (trade mark) and Esperase (trade mark) from Novo Industries A/S), amylases (e.g., Termamyl (trade mark) from Novo Industries A/S), lipases (e.g., Lipolase (trade mark) from Novo Industries A/S), oxidases, and mixtures thereof.

[0080] The following examples more fully illustrate the invention in its various aspects and preferred embodiments thereof. All parts, percentages and proportions referred to herein and in the appended claims are by weight unless otherwise indicated.

EXAMPLE 1

[0081] The following seven machine dishwashing compositions were prepared as follows:

Table 1

Ingredient	% by weight
Sodium citrate (2H2O)	30.0
Sodium tetraborate	3.0
Glycerol	6.0
Sokalan CP7 (40%)1	5.0
Sodium hydroxide (50%)	1.6
Bleaching agent2	x
Anti-tarnish agent3	y
Water	to 100

1 An acrylic acid/maleic acid copolymer supplied by BASF Corporation of Parsippany, New Jersey, USA

2 The following different levels of sodium perborate (H2O) and TAED (N,N,N',N'-tetraacetylethylene diamine bleach activator) were used in Example 1:    a. 0.0% sodium perborate (H2O) and 0.0% TAED    b. 0.5% sodium perborate (H2O) and 0.3% TAED    c. 0.7% sodium perborate (H2O) and 0.5% TAED    d. 0.9% sodium perborate (H2O) and 0.6% TAED    e. 1.3% sodium perborate (H2O) and 0.9% TAED    f. 1.7% sodium perborate (H2O) and 1.1% TAED    g. 6.8% sodium perborate (H2O) and 4.3% TAED

3 No anti-tarnish agent was used in Example 1.

[0082] Tarnish-monitoring experiments to determine silver tarnishing were conducted with compositions a, b, c, d, e, f, and g at a product dosage of 40 grams per run in a European dishwasher, Bauknecht GSF 3162, with an intake of of 5 litres deionized water. The wash program consisted of a pre-wash at 40°C, a mainwash at 55°C, two intermediate rinses, and a final rinse at 65°C.

[0083] The mainwash pH with these compositions was typically 8.7. Silver-plated spoons (2 per run) were the monitors used in the test. The spoons were supplied by Oneida Silversmiths, USA. The monitors were washed in a commercially available hand dishwash liquid and rinsed with deionized water and acetone before use. In the dishwasher the monitors were kept apart from each other in the cutlery basket. At the end of a single-run machine program, the monitors were visually analyzed for the presence of colours and the loss of gloss.

[0084] The spoons washed with composition a were unchanged after the dishwashing process, except for a few stain spots. The stain spots were caused by deposition of non-volatile materials during the evaporation of undrained wash solution in the drying step of the machine program and were not related to a tarnishing (i.e. silver oxidation) process of the monitors.

[0085] However, the spoons washed with compositions b, c, d, e, f, and g were increasingly tarnished as the levels of bleaching agent were increased. The spoons washed with composition g were so heavily tarnished that they lost their gloss and were turned brown/black. The set of spoons washed with the compositions a, b, c, d, e, f, and g were ranked from zero to six, respectively. This ranking of spoons was used as a reference scale for all subsequent Examples.

EXAMPLE 2

[0086] Machine dishwashing compositions were prepared as described in Example 1, except that the selected bleaching agent was epsilon-phthalimido peroxyhexanoic acid incorporated at 4% by weight. The compound was supplied by Hoechst AG of Germany. The compositions also contained various anti-tarnish agents incorporated in an amount of 1% by weight, as follows:

Table 2

SAMPLE	ANTI-TARNISHING AGENT (1 wt.%)
A	None
B	Purine
C	Adenine
D	Guanine
E	6-mercaptopurine
F	xanthine
G	uric acid
H	allopurinol

[0087] The anti-tarnishing agents were supplied by Aldrich Chemical Co.

[0088] Tarnish-monitoring experiments as described in Example 1 were conducted with Samples A to H, using two silver-plated spoons as monitors in each of the experiments. The main wash pH in this series of experiments was between 8.8 and 8.5.

[0089] Anti-tarnish scores ranging from 0 to 6 according to the level of tarnishing were obtained for samples A to H as follows:

TABLE 3

Composition	Tarnish Score
A	5
B	0
C	0.5
D	0
E	1
F	0
G	1
H	0

[0090] It was observed that spoons washed with compositions containing anti-tarnish agents (Samples B to H) either remained unchanged or developed a slightly yellowish appearance during the dishwashing process. In contrast, the control sample A, which did not contain an anti-tarnish agent, produced heavy tarnishing.

EXAMPLE 3

[0091] A detergent base was prepared having the following formula:

Table 4

Ingredient	% by weight
Sodium citrate (2H2O)	42
Sodium disilicate 2.0	35
Sodium perborate (H2O)	7
Sokalan CP51	5
TAED2 (80%)	4.2
Amylase	1.7
Protease	1.7
Laponite3	1.7
Nonionic surfactant	1.7

1 An acrylic acid/maleic acid copolymer supplied by BASF, Germany.

2 N,N,N',N'-tetraacetylethylene diamine.

3 A smectite clay supplied by Laporte Industries of Cheshire, England.

[0092] Various amounts of an adenine compound were dosed into 27 gram samples of the foregoing base as follows:

Table 5

SAMPLES	ADENINE (% by weight)
1	0
2	0.05
3	0.1
4	0.25
5	0.5

[0093] As described in Example 1, tarnish monitoring tests were conducted with samples 1 to 5 using two silver-plated spoons as monitors. However, 1 gram/liter of sodium chloride was added to the deionized water used in the experiments. Additionally, 5 grams of egg yolk were dosed in the dishwasher immediately after water intake at the start of the main wash of each experiment. The main wash pH values were typically 9.8.

[0094] Silver-tarnishing scores on a scale of 0 to 6 were observed for samples 1 to 5 as follows:

TABLE 6

Sample	Tarnish Score
1	3
2	1.5
3	1.5
4	0
5	1

[0095] The control sample containing no anti-tarnishing agent gave rise to moderately heavy tarnishing. In contrast, samples 2 to 5 exhibited little to no tarnishing. Optimal anti-tarnishing performance was observed with sample 4 containing 0.25 wt.% adenine.

EXAMPLE 4

[0096] Six machine dishwashing compositions were prepared as described in Example 1, except that the type of bleaching agent and the amount of purine as the anti-tarnish agent were varied as follows:

Table 7

Sample	Bleaching Agent (% by wt)	(% by wt)
A	Peracetic acid1 (4.12%)	0%
B	Peracetic acid1 (4.12%)	1.0%
C	Epsilon-phthalimidoperoxy hexanoic acid2 (4.0%)	0%
D	Epsilon-phthalimidoperoxy hexanoic acid2 (4.0%)	1.0%
E	Sodium hypochlorite3 (8.23%)	0%
F	Sodium hypochlorite3 (8.23%)	1.0%

1 A 32% peracetic acid solution, supplied by Aldrich Corporation of Milwaukee, USA was used.

2 Supplied by Hoechst AG, Germany.

3 An 8.2% active Cl2 solution was used, supplied by Jones Chemicals of Caledonia, NY, USA.

[0097] Tarnishing-monitoring experiments were conducted, using samples A, B, C, D, E, and F at a product dosage of 40 grams per run in a Bauknecht GSF 3162 dishwasher, with an intake of 5 litres water. The mainwash pH values for compositions A and B were adjusted to 7.5; the mainwash pH values for compositions C and D were adjusted to 8.5. Two experiments (each) were conducted, using compositions E and F; the mainwash pH values were adjusted to 9.0 and 10.5, respectively. Silver-plated spoons, knives, and forks (supplied by Oneida Silversmiths, USA), were used as monitors for all experiments. The monitors were washed in a commercially available hand dishwashing liquid and rinsed with deionized water and acetone before use. At the end of the dishwashing machine program, the monitors were visually evaluated for the presence of colours and/or loss of shine, according to the reference scale described in Example 1.

[0098] Each sample containing purine (B, D and F) was observed to reduce the level of tarnishing relative to the samples which did not contain purine (A, C and E). While tarnishing inhibition due to purine occurs through the pH range described above, this effect was observed to be greatest at pH values of 7.5, 8.5 and 9.0. Furthermore, the presence of purine reduced tarnishing regardless of the type of bleaching agent (chlorine or oxygen) present in the samples.

EXAMPLE 5

[0099] The required association of the pK_a value of purine class compounds usable in the invention and the pH of the composition in which they are incorporated to provide effective silver anti-tarnishing was demonstrated and the results are reported below.

[0100] The pK_a of each compound was determined by preparing a 0.001M solution of inhibitor in deionized water. The pH of this solution was adjusted to 3.0 with H₂SO₄. The solution was then titrated with 1N NaOH to pH 11.0. A plot of mls. NaOH vs. pH for each sample was prepared. The pK_a of the compound is that point where the maximum change in pH as a function of mls. NaOH is observed.

[0101] A comparison of anti-tarnishing performance of purine class compounds within the scope of the invention and azole compounds outside the invention was conducted. The selected compounds were incorporated in an amount of 1 wt.% in a machine dishwashing composition containing 4 wt.% epsilon-phthalimido peroxyhexanoic acid as the bleaching agent. The pH values of the compositions were adjusted by the addition of a 50% solution of sodium hydroxide or concentrated sulfuric acid, as necessary.

[0102] Silver plates were then held in each of the compositions for 25 minutes, removed, rinsed with deionized water and evaluated for silver tarnishing, and ranked as described in Example 1. A tarnish score of 3 or less was considered effective as a silver anti-tarnishing compound. The observations were tabulated as presented below:

[0103] It was observed that the compounds used in the invention must exhibit a pK_a of more than 1 unit less than the pH of an aqueous solution of the composition in which they are incorporated. In particular, adenine (pK_a = 7.2) and guanine (pK_a = 6.7) prevented silver tarnishing at pH 8.6, but did not prevent tarnishing at pH 6.9 and 7.0, respectively.

[0104] Azole compounds outside the scope of the invention were tested and the following silver anti-tarnishing results were observed.

[0105] It was observed that compounds having pK_a values greater than the pH values of the compositions in which they were incorporated did not exhibit anti-tarnishing effects.

EXAMPLE 6

[0106] To demonstrate the ineffectiveness of known copper anti-tarnishing compounds on silver plates, machine dishwashing compositions having a pH of both 8.5 and 11 were prepared containing 4% by weight epsilon-phthalimido peroxyhexanoic acid as the bleaching agent and 1% by weight of three copper anti-tarnishing compounds listed below. Samples of the compositions were adjusted to both a pH of 8.5 and 11 by the addition of sodium hydroxide. Copper plates and silver plates were held in each of the compositions for 25 minutes, removed, rinsed with deionized water and evaluated for tarnishing. The following results were observed.

Table 10

Copper Antitarnishing Compounds1	Copper Plates	Silver Plates
6-nitroindazole	+	-
2-phenylimidazole	+	-
pyrazole	+	-

1 Described as effective copper anti-tarnish compounds in US 2,618,608 (Schaeffer)

[0107] It was observed that anti-tarnishing compounds which prevented tarnishing on copper plates had no effect on preventing silver tarnishing. The oxidation behaviour of copper versus silver is very different and compounds which affect one type of metal may be drastically different from those compounds which affect the other. The compounds exhibiting copper anti-tarnishing effects do not possess a structure within the scope of the anti-tarnishing compounds which are useful in the invention.

EXAMPLE 7

[0108] Three machine dishwashing compositions were prepared as described in Example 1, except that a chlorine bleaching agent and cyanuric acid as anti-tarnish agent were combined as follows:

Table 11

Sample	Bleaching agent (% by wt.)	Cyanuric acid3 (% by wt.)
A	Sodium dichloroisocyanurate1 (2.2%)	0%
B	Sodium hypochlorite2 (8.23%)	0%
C	Sodium hypochlorite2 (8.23%)	1%

1 CDB, supplied by Olin Corporation of Stamford, Connecticut, USA

2 An 8.29% active Cl2 solution, supplied by Jones Chemicals of Caledonia, New York, USA

3 Supplied by Aldrich Chemical Co., of Milwaukee, Wisconsin, USA

[0109] Tarnish monitoring experiments as described in Example 1 were conducted with compositions A to C using two silver-plated spoons as monitors in each of the experiments. The mainwash pH in this series of experiments was typically 8.7.

[0110] The influence of the compositions A, B and C on silver tarnishing are shown in the following Table 12. The anti-tarnish scale ranks from 0 to 6, according to the levels of tarnishing obtain with the compositions a to g of Example 1.

TABLE 12

Composition	Tarnish Score
A	1.5
B	5.5
C	O

[0111] It was observed that spoons washed with composition C, containing 1% cyanuric acid, remained unchanged during the dishwashing process. In contrast, composition B, in which hypochlorite was incorporated without cyanuric acid, produced quite heavy tarnishing. Composition A containing sodium dichloroisocyanurate but no anti-tarnishing agent exhibited little silver tarnishing. It is believed that isocyanurate is formed during a wash in which sodium dichloroisocyanurate is used. Isocyanurate can be formed upon dissociation of dicholoroisocyanurate, producing hypochlorite as the active bleaching species. This is also believed to explain why chloroisocyanurate bleach systems generally do not cause many problems in terms of silver tarnishing.

EXAMPLE 8

[0112] Six machine dishwashing compositions were prepared as described in Example 1, except that the bleaching agent and anti-tarnish agent were varied as follows:

Table 13

Composition	Bleaching Agent (% by wt.)	Cyanuric Acid4
A	Peracetic acid1 (4.12%)	0%
B	Peracetic acid1 (4.12%)	1.0%
C	Epsilon-phthalimidoperoxyhexanoic acid2 (4.0%)	0%
D	Epsilon-phthalimidoperoxyhexanoic acid2 (4.0%)	1.0%
E	Sodium hypochlorite3 (8.23%)	0%
F	Sodium hypochlorite3 (8.23%)	1.0%

1 A 32% peracetic acid solution supplied by Aldrich Corp. of Milwaukee, Wisconsin, USA

2 Supplied by Hoechst AG of Germany

3 A 8.2% active Cl2 solution supplied by Jones Chemicals of Caledonia, New York, USA

4 Supplied by Aldrich Corp.

[0113] Tarnish monitoring experiments were conducted using compositions A, B, C, D E and F at a product dosage of 40 grams per run in a Bauknecht GSF 3162 dishwasher, with an intake of 5 litres water. The mainwash pH values for compositions A and B were adjusted to 7.5; the mainwash pH values for compositions C and D were adjusted to 8.5. Two experiments (each) were conducted using compositions E and F; the mainwash pH values were adjusted to 9.0 and 10.5, respectively. Silver-plated spoons, knives, and forks (supplied by Oneida Silversmiths, USA), were used as monitors for all experiments. The monitors were washed in a commercially available dishwashing liquid and rinsed with deionized water and acetone before use. At the end of the dishwashing machine program, the monitors were visually evaluated for the presence of colours and/or loss of shine, according to the reference scale described in Example 1.

[0114] In each case, the presence of cyanuric acid reduced the level of tarnishing relative to the case where no anti-tarnish agent was present. While tarnishing inhibition due to cyanuric acid occurred throughout the pH range described above, this effect was greater at higher alkalinity. At pH 7.5, the introduction of cyanuric acid led to a reduction of 1.5 units of tarnishing; at pH 10.5 the reduction in tarnishing was 3.0 units. Furthermore, cyanuric acid reduced tarnishing irrespective of the type of bleaching agent present in the composition; inhibition was noted for both chlorine and oxygen bleaches.

EXAMPLE 9

[0115] Five machine dishwashing compositions were prepared as described in Example 1, except that epsilon-phthalimidoperoxyhexanoic acid was used as a peroxygen bleaching agent and cyanuric acid was used at five different amounts as follows:

TABLE 14

Composition	Epsilon-phthalimidoperoxy hexanoic acid1 (% wt)	Cyanuric Acid2 (% wt)
A	4.0%	0%
B	4.0%	0.25%
C	4.0%	0.75%
D	4.0%	1.0%
E	4.0%	2.5%

1 Supplied by Hoechst AG, Germany

2 Supplied by Aldrich Co.

[0116] As described in Example 1, tarnish monitoring tests were conducted with compositions A to E using two silver-plated spoons as monitors in each of the experiments. The mainwash pH in this series of experiments was typically between 8.8 and 8.5.

[0117] The effects of compositions A to E on silver tarnishing are shown in Table 15 below. The anti-tarnish scale ranks from 0 to 6, according to the levels of tarnishing obtained with the compositions a to g of Example 1.

TABLE 15

Composition	Tarnish Score
A	5
B	4.5
C	3
D	0.5
E	0.8

[0118] It can be seen from this table that the level of cyanuric acid which gives optimum anti-tarnish performance is about 1%. The monitors had a slightly yellow appearance after using cyanuric acid at a 2.5% level.

EXAMPLE 10

[0119] The following machine dishwashing compositions were prepared according to Example 1, except that 4% by weight of epsilon-phthalimidoperoxyhexanoic acid was incorporated as the bleaching agent and various azole-compound anti-tarnishing agents (both within and outside the scope of the definition of the 1,3-N azole compounds characteristic of the present invention) were incorporated in an amount of 1% by weight, as follows:

TABLE 16

Sample	1% wt Agent1
A	None
B	Pyrrole
C	Indazole
D	Pyrazole
E	Benzimidazole
F	Imidazole
G	1,2,3-triazole
H	Benzotriazole
I	1,2,4-triazole
J	Pyrimidine
K	Histidine

1 Compounds supplied by Aldrich Chemical Co. of Milwaukee, Wisconsin, USA

[0120] Tarnish monitoring experiments were conducted as described in Example 1, using two silver-plated spoons as monitors in each of the experiments. The main wash pH in the experiments was between 8.8 and 8.5.

[0121] The control composition (Sample A) produced heavy tarnishing on the spoons. Samples E, F and K (within the scope of the invention) exhibited only a slightly tarnished appearance on the washed spoons. Compositions G and H also exhibited only a slightly tarnished appearance on the washed spoons. In contrast, compositions B, C, D and J (outside the scope of the invention) exhibited heavy tarnishing on the washed spoons.

EXAMPLE 11

[0122] Six machine dishwashing compositions were prepared as described in Example 1, except that the type of bleaching agent and the amount of 1,2,4-triazole as anti-tarnishing agent were varied as follows:

TABLE 17

Sample	Bleaching Agent (% by weight)	1,2,4-Triazole
A	Peracetic acid1 (4.12%)	0%
B	Peracetic acid1 (4.12%)	1.0%
C	Epsilon-phthalimidoperoxyhexanoic acid2 (4.0%)	0%
D	Epsilon-phthalimidoperoxyhexanoic acid2 (4.0%)	1.0%
E	Sodium hypochlorite3 (8.23%)	0%
F	Sodium hypochlorite3 (8.23%)	1.0%

1 A 32% peracetic acid solution, supplied by Aldrich Corporation of Milwaukee, Wisconsin, USA was used.

2 Supplied by Hoechst AG, Germany.

3 A 8.2% active Cl2 solution was used, supplied by Jones Chemicals of Caledonia, New York, USA.

[0123] Tarnish monitoring experiments were conducted using compositions A, B, C, D, E and F at a product dosage of 40 grams per run in a Bauknecht GSF 3162 dishwasher, with an intake of 5 litres water. The mainwash pH values for compositions A and B were adjusted to 7.5; the mainwash pH values for compositions C and D were adjusted to 8.5. Two experiments (each) were conducted using compositions E and F; the mainwash pH values were adjusted to 9.0 and 10.5. respectively. Silver-plated spoons, knives and forks (supplied by Oneida Silversmiths, USA), were used as monitors for all experiments. The monitors were washed in a commercially available dishwashing liquid and rinsed with deionized water and acetone before use. At the end of the dishwashing machine program, the monitors were visually evaluated for the presence of colours and/or loss of shine, according to the reference scale described in Example 1.

[0124] In each case, the presence of 1,2,4-triazole reduced the level of tarnishing relative to the case where no anti-tarnishing agent was present. While tarnishing, inhibition due to 1,2,4-triazole occurred throughout the pH range described above, this effect was greater at higher alkalinity. At pH 7.5, the introduction of 1,2,4-triazole led to a reduction of 1.5 units of tarnishing; at pH 10.5 the reduction in tarnishing was 3.0 units. Furthermore, 1,2,4-triazole reduced tarnishing irrespective of the type of bleaching agent present in the composition; inhibition was noted for both chlorine and oxygen bleaches.

EXAMPLE 12

[0125] The following machine dishwashing compositions were prepared as described in Example 1, except that epsilon-phthalimido peroxyhexanoic acid was included as the bleaching agent at a level of 4% by weight and various levels of 1,2,4-triazole as anti-tarnish agent were incorporated as follows:

TABLE 18

Sample	1,2,4-Triazole (Wt. %)
A	none
B	0.05
C	0.25
D	0.75
E	1.0

[0126] As described in Example 1, anti-tarnish monitoring tests were conducted using two silver-plated spoons as monitors. The main wash pH in these experiments was between 8.8 and 8.5.

[0127] The effect of samples A to E on silver tarnishing was observed and is shown in Table 19 below:

TABLE 19

Sample	Tarnish Score
A	5.0
B	0.5
C	0.5
D	0.5
E	0

[0128] It was thus observed that at amounts of 0.05 % by weight, the anti-tarnish agent 1,2,4-triazole effectively reduced silver tarnishing. Optimum performance of the agent was achieved at levels of 1 % by weight.

EXAMPLE 13

[0129] The required association of the pK_a value of 1,3-N azole compounds usable in the invention and the pH of the composition in which they are incorporated to provide effective silver anti-tarnishing was demonstrated and the results are reported below.

[0130] A comparison of anti-tarnishing performance of 1,3-N azole compounds within the scope of the invention and azole compounds outside the invention was conducted. The selected compounds were incorporated in an amount of 1 wt.% in a machine dishwashing composition containing 4 wt.% epsilon-phthalimido peroxyhexanoic acid as the bleaching agent. The pH values of the compositions were adjusted by the addition of a 50% solution of sodium hydroxide or concentrated sulfuric acid, as necessary.

[0131] The pK_a of each compound was determined by preparing a 0.001M solution of inhibitor in deionized water. The pH of this solution was adjusted to 3.0 with H₂SO₄. The solution was then titrated with 1N NaOH to pH 11.0. A plot of mls. NaOH vs. pH for each sample was prepared. The pK_a of the compound is that point where the maximum change in pH as a function of mls. NaOH is observed.

[0132] Silver plates were then held in each of the compositions for 25 minutes, removed, rinsed with deionized water and evaluated for silver tarnishing, and ranked as described in Example 1. A tarnish score of 3 or less was considered effective as a silver anti-tarnishing compound. The observations were tabulated as presented below:

[0133] It was observed that tetrazole was not effective as a silver anti-tarnishing at a pH of 8.5 but was effective at a pH of 9.5 and greater. Tetrazole with a pK_a of 8.4 is effective only in compositions having a pH of greater than 9.4. 5-aminotetrazole having a pK_a of 8.1 was not effective at a pH of 8.8. The other compounds exhibited effective anti-tarnishing effects because their pK_a values were more than 1 unit less than the pH of an aqueous solution of the composition in which they were incorporated.

[0134] Azole compounds outside the scope of the invention were tested and the following silver anti-tarnishing results were observed.

[0135] It was observed that compounds having pK_a values greater than the pH values of the compositions in which they were incorporated did not exhibit anti-tarnishing effects. 2-Phenylimidazole did not prevent silver tarnishing at a pH 11.0, possibly because of hindrance from the phenyl group attached to the imidazole ring.

EXAMPLE 14

[0136] To demonstrate the ineffectiveness of known copper anti-tarnishing compounds on silver plates, machine dishwashing compositions having a pH of both 8.5 and 11 were prepared containing 4% by weight epsilon-phthalimido peroxyhexanoic acid as the bleaching agent and 1% by weight of three copper anti-tarnishing compounds listed below. Samples of the compositions were adjusted to both a pH of 8.5 and 11 by the addition of sodium hydroxide. Copper plates and silver plates were held in each of the compositions for 25 minutes, removed, rinsed with deionized water and evaluated for tarnishing. The following results were observed.

Table 22

Copper Antitarnishing Compounds1	Copper Plates	Silver Plates
6-nitroindazole	+	-
2-phenylimidazole	+	-
pyrazole	+	-

1 Described as effective copper anti-tarnish compounds in US 2,618,608 (Schaeffer)

[0137] It was observed that anti-tarnishing compounds which prevented tarnishing on copper plates had no effect on preventing silver tarnishing. The oxidation behavior of copper versus silver is very different and compounds which affect one type of metal may be drastically different from those compounds which affect the other. The compounds exhibiting copper anti-tarnishing effects do not possess a structure within the scope of the anti-tarnishing compounds which are useful in the invention.

Claims

1. A bleaching detergent composition comprising:

(a) from 1 to 20% by weight of a bleaching agent selected from a peroxygen or peroxygen-yielding compound, a hypohalite or hypohalite-yielding compound, or a salt thereof, or mixtures thereof;

(b) from 0.05 to 10% by weight of an anti-tarnishing agent selected from:

(i) a purine class compound of the following formula (I) or its tautomers:

wherein X¹ is nitrogen or C-R³, Y¹ is nitrogen or C-R⁴, and R¹, R², R³ and R⁴ are each independently hydrogen, hydroxy, alkoxy, amine, straight or branched chain alkyl having 1 to 20 carbon atoms, amido, amidoalkyl, alkylthio, alkenyl or hydroxyalkyl, wherein R¹ may additionally be SH when R² is hydrogen, X¹ is nitrogen, and Y¹ is CH;

(ii) cyanuric acid or isocyanuric acid or a salt thereof;

(iii) a 1,3-N azole compound of the following formula (II);

wherein X² is C-R⁷ or nitrogen provided Y² is also nitrogen, Y² is nitrogen or C-R⁶, and R⁵, R⁶ and R⁷ are each independently hydrogen, amine, amido, straight or branched chain alkyl having from 1 to 20 carbon atoms, an amino- or carboxylic-containing chain, alkoxy, alkylthio, hydroxy, hydroxyalkyl, alkenyl, or R⁵ and R⁶ taken together form an unsubstituted or substituted aryl group; or a salt thereof;

(iv) a mixture of any of the above compounds (i), (ii) or (iii);

(c) optionally from 1 to 75% by weight of a detergency builder; and

(d) optionally, from 0.01 to 40% by weight of a surfactant;

wherein the composition exhibits a pH value in a 1% aqueous solution in the range from 7 to 13, and wherein the anti-tarnishing agent has a pK_a value at least 1 unit below the pH value of a 1% aqueous solution of the composition.

2. A composition according to claim 1, wherein the anti-tarnishing agent has a pK_a value from 2 to 6 units below the pH value of a 1% aqueous solution of the composition.

3. A.composition according to claim 1 or claim 2, wherein the anti-tarnishing agent comprises a compound of formula (I) wherein X¹ is nitrogen and Y¹ is C-R⁴ and R¹, R² and R⁴ are each independently hydrogen, hydroxy, alkoxy, alkylthio, amine, amido or lower alkyl having from 1 to 6 carbon atoms, wherein R¹ may additionally be SH, when R² is hydrogen, X¹ is nitrogen, and Y¹ is CH.

4. A composition according to claim 1 or claim 2, wherein the compound of formula (I) is selected from purine, adenine, guanine, 6-mercaptopurine, xanthine, hypoxanthine, uric acid, and allopurinol.

5. A composition according to claim 1 or claim 2, wherein the anti-tarnishing agent comprises a 1,3-N azole compound of formula (II) wherein X² is C-R⁷, X² is nitrogen provided Y² is nitrogen, Y² is C-R⁶ and R⁵ and R⁶ taken together form an aryl or a substituted aryl group, or a 1,3-N azole compound of formula (II) wherein Y² is C-R⁶ and R⁵ and R⁶ are each independently hydrogen, amine, amido, straight or branched chain alkyl having from 1 to 6 carbon atoms, alkoxy, alkylthio, hydroxy, alkenyl or an amino- or carboxylic-containing moiety.

6. A composition according to claim 1 or claim 2, wherein the anti-tarnishing agent is selected from imidazole, benzimidazole, 1,2,3,5-tetrazole, 4-amino-1,2,3,5-tetrazole, 1,2,4-triazole, 3-amino-1,2,4-triazole and histidine.

7. A composition according to any preceding claim, which has a pH value in a 1% aqueous solution of from 7 to 11.

8. A composition according to any preceding claim, wherein the bleaching agent comprises a peroxy compound selected from the group consisting of: organic mono- and di-peroxyacids; organic diacylperoxides; and inorganic peroxy-containing salts.

9. A composition according to any preceding claim, wherein the bleaching agent comprises a peroxyacid bleach precursor.

10. A composition according to any preceding claim, wherein the bleaching agent comprises a halogen-containing compound selected from the group consisting of: hypohalite salts; active halogen-containing compounds which yield hypohalite anions in aqueous alkaline solution; and halogenated isocyanuric acids.

11. A composition according to any preceding claim, which further comprises one or more additional ingredients selected from the group consisting of: silicates; filler materials; thickeners; stabilizers and/or co-structurants; defoaming agents; and enzymes.

12. A method of washing a silver or silver-plated article whilst preventing or inhibiting tarnishing thereof during or as a result of the washing process, the method comprising washing the said article with a bleaching detergent composition according to any one of claims 1 to 11.

13. Use of a compound selected from any of (i) to (iv) defined in claim 1 as a silver anti-tarnishing agent in a peroxygen- and/or hypohalite-based bleaching detergent composition having a pH value in a 1% aqueous solution in the range of from 7 to 13, wherein the anti-tarnishing agent has a pK_a value at least one unit below the pH value of a 1% aqueous solution of the composition.

Ansprüche

1. Bleichende Waschmittelzusammensetzung, umfassend:

(a) 1 bis 20 Gew.-% eines Bleichmittels, ausgewählt aus einer Persauerstoff- oder Persauerstoff-ergebenden Verbindung, einer Hypohalogenit- oder Hypohalogenic-ergebenden Verbindung, oder einem Salz davon, oder Gemischen davon;

(b) 0,05 bis 10 Gew.-% eines Mittels zur Verhinderung von Anlaufen, ausgewählt aus:

(i) einer Verbindung der Purinklasse der nachstehenden Formel (I) oder ihren Tautomeren:

   worin X¹ Stickstoft oder C-R³ darstellt, Y¹ Stickstoff oder C-R⁴ darstellt und R¹, R², R³ und R⁴ jeweils unabhängig Wasserstoff, Hydroxy, Alkoxy, Amin, gerad- oder verzweigtkettiges Alkyl mit 1 bis 20 Kohlenstoffatomen. Amido. Amidoalkyl. Alkylthio, Alkenyl oder Hydroxyalkyl darstellen, wobei R¹ zusätzlich SH sein kann, wenn R² Wasserstoff darstellt, X¹ Stickstoff darstellt und Y¹ CH darstellt;

(ii) cyanursäure oder Isocyanursäure oder einem Salz davon;

(iii) einer 1,3-N-Azolverbindung der nachstehenden Formel (II):

   worin X² C-R⁷ ist oder Stickstoff mit der Maßgabe darstellt. daß Y² ebenfalls Stickstoff darstellt. Y² Stickstoff oder C-R⁶ darstellt und R⁵, R⁶ und R⁷ jeweils unabhängig wasserstoff, Amin. Amido, eine gerad- oder verzweigtkettige Alkylgruppe mit 1 - 20 Kohlenstoffatomen, eine Amino-oder Carboxyl-enthaltende Kette. Alkoxy, Alkylchio, Hydroxy, Hydroxyalkyl, Alkenyl darstellen oder R⁵ und R⁶ zusammen-genommen eine unsubstituierte oder substituierte Arylgruppe bilden oder einem Salz davon;

(iv) einem Gemisch einer der vorstehenden Verbindungen (i), (ii) oder (iii).

(c) gegebenenfalls 1 bis 75 Gew.-% eines Waschmittelbuilders; und

(d) gegebenenfalls 0.01 bis 40 Gew.-% eines Tensids: wobei die Zusammensetzung einen pH-Wert in einer 1%-igen wässerigen Lösung im Bereich von 7 bis 13 zeigt, und wobei das Mittel zur Verhinderung von Anlaufen einen pKa-Wert von mindestens einer Einheit unterhalb des pH-Werts einer 1%-igen wässerigen Lösung der Zusammensetzung aufweist.

2. Zusammensetzung nach Anspruch 1, wobei das Mittel zur Verhinderung von Anlaufen einen pKa-Wert von 2 bis 6 Einheiten unterhalb des pH-Werts einer 1%-igen wässerigen Lösung der Zusammensetzung aufweist.

3. Zusammensetzung nach Anspruch 1 oder Anspruch 2, wobei das Mittel zur Verhinderung von Anlaufen eine Verbindung der Formel (T¹, worin X¹ Stickstoff darstellt und Y¹ C^- R⁴ darstellt und R¹, R² und R⁴ jeweils unabhängig Wasserstoff, Hydroxy, Alkoxy, Alkylthio, Amin. Amido oder Niederalkyl mit 1 bis 6 Kohlenstoffatomen darstellen, wobei R¹ zusätzlich SH sein kann, wenn R² wasserstoff darstellt, X¹ stickstoff darstellt und Y¹ CH darstellt, umfaßt.

4. Zusammensetzung nach Anspruch 1 oder Anspruch 2, wobei die Verbindung der Formel (I) ausgewählt ist aus Purin. Adenin, Guanin, 6-Mercaptopurin. Xanthin Hypoxanthin, Harnsäure und Allopurinol.

5. Zusammensetzung nach Anspruch 1 oder Anspruch 2. wobei das Mittel zur Verhinderung von Anlaufen eine 1.3-N-Azolverbindung der Formel (II), worin X² C-R⁷ darstellt, X² Stickstoff darstellt, mit der Maßgabe, daß Y² stickstoff darstellt, Y² C-R⁶ darstellt und R⁵ und R⁶ zusammengenommen eine Aryl- oder eine substituierte Arylgruppe bilden. oder eine 1,3-N-Azolverbindung der Formel (II), worin Y² C-R⁶ darstellt und R⁵ und R⁶ jeweils unabhangig Wasserstoff, Amin, Amido. eine gerad- oder verzweigtkettige Alkylgruppe mit 1 bis 6 Kohlenstoffatomen, Alkoxy, Alkylthio, Hydroxy, Alkenyl oder einen Amino- oder Carboxyl-enthaltenden Rest darstellen, umfaßt.

6. Zusammensetzung nach Anspruch 1 oder Anspruch 2, wobei das Mittel zur Verhinderung von Anlaufen ausgewählt ist aus Imidazol, Benzimidazol, 1,2,3,5-Tetrazol, 4-Amino-1,2,3,5-tetrazol, 1.2,4-Triazol, 3-Amino-1,2,4-triazol und Histidin.

7. Zusammensetzung nach einem vorangehenden Anspruch, die einen pH-Wert in einer 1%-igen wässerigen Lösung von 7 bis 11 aufweist.

8. Zusammensetzung nach einem vorangehenden Anspruch, wobei das Bleichmittel eine Peroxyverbindung, ausgewählt aus der Gruppe, bestehend aus: organischen Mono- und Diperoxysäuren, organischen Diacylperoxiden und anorganischen Peroxy-enthaltenden Salzen, umfaßt.

9. Zusammensetzung nach einem vorangehenden Anspruch, wobei das Bleichmittel eine Peroxysäurebleichmittelvorstufe umfaßt.

10. Zusammensetzung nach einem vorangehenden Anspruch, wobei das Bleichmittel eine Halogen-enthaltende Verbindung, ausgewählt aus der Gruppe, bestehend aus: Hypohalo-genitsalzen : aktives Halogen-enthaltenden Verbindungen, die in wässeriger alkalischer Lösung Hypohalogenitanionen ergeben; und halogenierten Isocyanursäuren, umfaßt.

11. Zusammensetzung nach einem vorangehenden Anspruch, die weiterhin einen oder mehrere zusätzliche Bestandteile, ausgewählt aus der Gruppe, bestehend aus: Silicaten, Füllstoffen, Verdickungsmitteln. Stabilisatoren und/oder Costrukturierungsmitteln, Entschäumungsmittel und Enzymen, umfaßt.

12. Verfahren zum Waschen eines Silber- oder Silberbelegten Gegenstands unter Verhindern oder Inhibieren von Anlaufen davon während des Waschverfahrens oder als Ergebnis davon, wobei das Verfahren Waschen des Gegenstands mit einer bleichenden Waschmittelzusammensetzung nach einem der Ansprüche 1 bis 11 umfaßt.

13. Verwendung einer Verbindung, ausgewählt aus beliebigen von (i) bis (iv) gemäß Anspruch 1, als Mittel zur Verhinderung des Anlaufens von Silber in einer bleichenden Waschmittelzusammnnsetzung auf der Basis von Persauerstoff und/oder Hypohalogenit mit einem pH-Wert in einer 1%-igen wässerigen Lösung im Bereich von 7 bis 13, wobei das Mittel zur Verhinderung von Anlaufen einen pKa-Wert von mindestens einer Einheit unterhalb des pH-Werts einer 1%-igen wässerigen Lösung der Zusammensetzung aufweist.

Revendications

1. Composition détergente de blanchiment comprenant:

(a) de 1 à 20 pourcent en poids d'un agent de blanchiment choisi parmi un composé peroxygéné ou un composé produisant un composé peroxygéné, un hypohalite ou un composé produisant un hypohalite, ou un sel de ceux-ci, ou leurs mélanges;

(b) de 0,05 à 10% en poids d'un agent anti-ternissement choisi parmi:

(i) un composé de la classe purine des formules (I) suivante et ses tautomères:

   dans laquelle X¹ représente un atome d'azote ou un groupe C-R³, Y¹ représente un atome d'azote ou un groupe C-R⁴, et R¹, R², R³ et R⁴ représentent indépendamment un atome d'hydrogène, un groupe hydroxy, alcoxy, amine, alkyle à chaîne droite ou ramifiée possédant 1 à 20 atomes de carbone, amido, amidoalkyle, alkylthio, alcényle ou hydroxry-alkyle dans laquelle R¹ peut de plus représenter SH lorsque R² représente un atome d'hydrogène, X¹ représente un atome d'azote, et Y¹ représente un groupe CH

(ii) de l'acide cyanurique ou de l'acide isocyanurique ou un sel de ceux-ci;

(iii) un composé 1,3-N-azole de formule (II) suivante:

   dans laquelle X² représente un groupe C-R⁷ ou un atome d'azote à condition que Y² soit également un atome d'azote, Y² représente un atome d'azote ou un groupe C-R⁶, et R⁵, R⁶ et R⁷ représentent chacun indépendamment un atome d'hydrogène, un groupe amine, amido, alkyle à chaîne droite ou ramifiée possédant 1 à 20 atomes de carbone, une chaîne contenant un groupe amino ou carboxylique, alcoxy, alkylthio, hydroxy, hydroxyalkyle, alcényle, ou R⁵ et R⁶ pris ensemble forment un groupe aryle substitué ou non substitué; ou un sel de ceux-ci;

(iv) un mélange de l'un quelconque des groupes (i), (ii), ou (iii);

(c) éventuellement de 1 à 75% en poids d'un adjuvant de détergence; et

(d) éventuellement, de 0,01 à 40% en poids d'un tensio-actif;

dans lequel la composition présente une valeur de pH dans une solution aqueuse à 1% dans la gamme de 7 à 13, et dans laquelle l'agent anti-ternissement possède une valeur de pK_a inférieure d'au moins une unité à la valeur du pH d'une solution aqueuse à 1% de la composition.

2. Composition selon la revendication 1, dans laquelle l'agent anti-ternissement possède une valeur pK_a inférieure de 2 à 6 unités à la valeur du pH d'une solution aqueuse à 1% de la composition.

3. Composition selon la revendication 1 ou 2, dans laquelle l'agent anti-ternissement comprend un composé de formule (I) dans laquelle X¹ représente un atome d'azote et Y¹ représente un groupe C-R⁴ et R¹, R² et R⁴ représentent chacun indépendamment un atome d'hydrogène, un groupe hydroxy, alcoxy, alkylthio, amine, amido, un groupe alkyle inférieur possédant de 1 à 6 atomes de carbone, dans laquelle R¹ peut de plus représenter SH, lorsque R² représente un atome d'hydrogène, X¹ représente un atome d'azote et Y¹ représente CH.

4. Composition selon la revendication 1 ou la revendication 2, dans laquelle le composé de formule (I) est choisi parmi la purine, l'adenine, la guanine, la 6-mercapto-purine, la xanthine, l'hypoxanthine, l'acide urique, et l'allopurinol.

5. Composition selon la revendication 1 ou la revendication 2, dans laquelle l'agent anti-ternissement comprend un composé 1,3-N-azole de formule (II) dans lequel X² représente un groupe C-R⁷, X² représente un atome d'azote à condition que Y² représente un atome d'azote, Y² représente un groupe C-R⁶, et R⁵ et R⁶ pris ensembles forment un groupe aryle ou un groupe aryle substitué, ou un composé 1,3-N-azole de formule (II) dans lequel Y² représente un groupe CR⁶ et R⁵ et R⁶ représentent chacun indépendamment un atome d'hydrogène, un groupe amine, amido, alkyle à chaîne droite ou ramifiée possédant de 1 à 6 atomes de carbone, alcoxy, alkylthio, hydroxy, alcényle ou une fraction contenant un groupe amino ou carboxylique.

6. Composition selon la revendication 1 ou la revendication 2, dans laquelle l'agent anti-ternissement est choisi parmi l'imidazole, le benzimidazole, le 1,2,3,5-tetra-zole, le 4-amino-1,2,3,5-tétrazole, le 1,2,4-triazole, le 3-amino-1,2,4-triazole et l'histidine.

7. Composition selon l'une quelconque des revendications précédentes, qui possède une valeur de pH de 7 à 11 en solution aqueuse à 1%.

8. Composition selon l'une quelconque des revendications précédentes, dans laquelle l'agent de blanchiment comprend un composé peroxy choisi dans le groupe formé par: les mono- et di-peracides organiques; les diacylperoxydes organiques; et les sels inorganiques contenant un peroxy.

9. Composition selon l'une quelconque des revendications précédentes, dans laquelle l'agent de blanchiment comprend un précurseur de blanchiment à base de peroxyacide.

10. Composition selon l'une quelconque des revendications précédentes, dans laquelle l'agent de blanchiment comprend un composé contenant un halogène choisi dans le groupe formé par: les sels d'hypohalite: les composés contenant un halogène actif qui produisent des anions hypohalite dans des solutions alcalines aqueuses, et des acides isocyanuriques halogénés.

11. Composition selon l'une quelconque des revendications précédentes, qui comprend de plus un ou plusieurs ingrédients supplémentaires choisis dans le groupe formé par les silicates; les matériaux de charge; les épaississants; les stabilisants et/ou les co-structurants; les agents anti-mousse, et les enzymes.

12. Procédé de lavage d'un article en argent ou en plaqué argent tout en empêchant ou en inhibant son ternissement au cours ou en résultats du procédé de lavage, le procédé comprenant le lavage dudit article avec une composition détergente de blanchiment selon l'une quelconque des revendications 1 à 11.

13. Utilisation d'un composé choisi parmi l'un quelconque de (i) à (iv) définis dans la revendication 1 en tant qu'agent anti-ternissement de l'argent dans un détergent de blanchiment à base de peroxygène et/ou hypohalite ayant une valeur de pH en solution aqueuse à 1% comprise entre 7 et 13, dans laquelle l'agent anti-ternissement possède une valeur de pKa inférieure d'au moins une unité à la valeur de pH d'une solution aqueuse à 1% de la composition.