Automatic dishwashing composition

Abstract: An automatic dishwashing composition comprising an oxygen donating bleach and ingredients conventional for automatic dishwashing compositions including possible further conventional adjuvants and/or fillers and a silver corrosion inhibitor selected among ammonium compounds. The automatic dishwashing compositon is gentle towards silver cutlery and does not cause a yellowish or brownish discolouration or dust deposits on silver cutlery.

Description: Technical Field The present invention relates to a machine dishwashing composition comprising an oxygen donating bleach and ingredients conventional for dishwashing compositions including optionally further conventional adjuvants and/or fillers. Background Art Traditionally, machine dishwashing compositions, in the present specification also termed "automatic dishwashing compositions" have been formulated on the basis of chlorine-containing bleaches. In recent years, society and the individual citizen have become increasingly aware of the environmental consequences of the large consumption of automatic dishwashing compositions containing chlorine bleaches. Consequently, a growing demand for formulation of alternative automatic dishwashing compositions has developed. Thus, the automatic dishwashing compositions tend to develop more and more towards chlorine-free, non-corrosive automatic dishwashing compositions containing oxygen donating bleaches. Examples of such automatic dishwashing compositions include SUN PROGRESS® which is a pulverulent, phosphate-free, chlorine-free and non-corrosive automatic dishwashing composition available from Lever, Germany, and Milde Kraft™ which is also a phosphate-free and chlorine-free, non-corrosive pulverulent product which is marketed in Germany by Benckiser. Such oxygen-donating bleaches are encumbered with some drawbacks especially in connection with silver cutlery, as silver oxidation compounds are formed by corrosion during the dishwashing process, said compounds resulting in a discoloured yellowish or brownish surface covered by a loose white dust-like layer. This tendency is more or less pronounced for all the products presently on the market which are based on oxygen donating bleaches. This problem is, however, especially marked for automatic dishwashing compositions with a high content of oxygen donating bleaches. The problem applies especially to automatic dishwashing compositions available in the form of tablets, as a higher content of bleaches is required in the tablets compared to powders because of a slower release of bleaches from tablets. EP No 135.226 relates to a peroxide containing dishwashing composition with low chloride content in order to avoid tarnishing of silverware. The publication discloses that the tendency of tarnishing of silverware is connected to the presence of chloride, especially alkali metal chloride, cf. page 2, lines 28-31 in the publication. Thus, the machine dishwashing composition contains not more than 0,2 weight % chloride and preferably not more than 0,1 weight % chloride, as it is preferred that the composition in essentials is chloride free. A further improvement in reducing the tendency of silver-tarnishing can be achieved by adding a small amount of a C 12 -C 18 fatty acid. The use of automatic dishwashing compositions in the form of tablets is advantageous per se as the tablets provide an easy way of ensuring a low but still sufficient dosing. It is therefore desired to provide a chlorine-free automatic dishwashing composition which does not corrode silver cutlery during the dishwashing process, even in the case of high contents of oxygen donating bleach. Brief description of the invention The present invention relates to a machine dishwashing composition comprising an oxygen donating bleach and ingredients conventional to automatic dishwashing compositions including possible further conventional adjuvants and/or fillers, said automatic dishwashing composition being characterised in that it comprises a silver corrosion inhibitor consisting of a compound releasing ammonium ions in an amount of 1.5 to 10.5 parts by weight, calculated as ammonium chloride, per part by weight of active oxygen, calculated as O 2 releasable from the oxygen donating bleach. The automatic dishwashing composition according to the invention may particularly advantageously be used when a formulation in the form of a tablet is desired where the problems of silver corrosion are often especially pronounced. Examples of advantageous silver corrosion inhibitors capable of releasing ammonium ions include compounds selected from the group consisting of ammonium chloride, ammonium bromide, ammonium sulphate, diammonium hydrogencitrate and mixtures thereof. The automatic dishwashing composition according to the invention comprises the silver corrosion inhibitor in an amount of at least 1.5 parts by weight of corrosion inhibitor, calculated as ammonium chloride, per part by weight of active oxygen, calculated as O 2 , releasable from the oxygen donating bleach, and advantageously not more than 10.5, particularly preferred not more than 6.5 and most preferred not more than 5.3 parts by weight of silver corrosion inhibitor, calculated as ammonium chloride, per part by weight of active oxygen. The oxygen donating bleach contained in the automatic dishwashing composition may advantageously be a per-compound or a perhydrate or mixtures thereof. A particularly advantageous recipe for the automatic dishwashing compositon according to the invention is found within the following limits: % by weight Oxygen donating bleach 3-39 Bleach activator 1-13 Polycarboxylate 5-21 Polyfunctional carboxylic acid 0-30 Sodium silicate 5-10 Tensides 3- 5 Enzymes 1- 5 Silver corrosion inhibitor 2-18 Sodium carbonate q.s. 100 It should be noted that the recipe is based on trade products and not on 100% active and anhydrous ingredients. The further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only. Detailed Description of the Invention The essential feature of the present invention is that the discolouration and deposit of dust on silver can be avoided, which presents a pronounced problem in connection with a high content of oxygen donating bleaches. Such a high content of oxygen donating bleaches is usually necessary in automatic dishwashing compositions in the form of tablets in order to ensure a sufficiently fast bleaching effect. Examples of possible oxygen donating bleaches in question include perhydrates and per-compounds as well as mixtures thereof. The perhydrates include preferably alkali metal compounds of perborates which may be present in the form of tetra- and monohydrates, perborax, percarbonates, persilicates, citrate perhydrates and perhydrates of urea and melamine compounds. Furthermore, acidic persalts, such as persulphates (e.g. caroates), perbenzoates and peroxycarboxylic acids, such as peroxyphthalate, magnesium monoperoxyphthalic acid, diperoxyphtalic acid, 2-octyl-diperoxysuccinic acid, diperoxydodecane dicarboxylic acid, diperoxyazelaic acid, imidoperoxycarboxylic acid, as well as salts and mixtures of such. Sodium percarbonate and sodium perborate can be mentioned as particularly preferred bleaches. As to the bleach system, reference is made to P. Kuzel and Th. Lieser, Tenside Surf. Det. 27 (1990) 1, pages 23-28. The content of the oxygen donating bleach is usually of an amount corresponding to 0.4 to 5.3 parts by weight of active oxygen per 100 parts by weight of dishwashing compositon, which corresponds to about 3 to 39 parts by weight of sodium percarbonate per 100 parts by weight of the diswashing composition in the case of sodium percarbonate containing 13.5% by weight of active oxygen. Any compound may be used as silver corrosion inhibitor provided said compound releases ammonium ions in the washing liquor and is active in forming stable silver complex salts while at the same time not having a detrimental effect on the cleaning performance. The other ingredients of the automatic dishwashing compositon according to the invention, may be selected among ingredients conventional for automatic dishwashing compositions, under the condition, of course, that such ingredients are compatible with the oxygen donating bleach and the silver corrosion inhibitor used. Thus it is within the routine skills of a person skilled in the art to formulate suitable automatic dishwashing compositions by combining an oxygen donating bleach and a silver corrosion inhibitor on the basis of the instructions given in the present application and to select the remaining ingredients of the automatic dishwashing composition on the basis of the prior art. The automatic dishwashing composition according to the invention is preferably manufactured in the form of tablets to be used in a dosage of, for instance, one or two tablets per wash cycle. The manufacture of tablets usually requires addition of adjuvants, for instance in the form of starch, glycerol, polyethylene glycol, preferably of a molar weight of 100-10,000, polyvinyl pyrrolidone (PVP), polyvinyl polypyrrolidone (PVPP) or a stearate compound, such as sodium stearate. Such tablet adjuvants ensure a suitable consistency and granulation. The tablets are manufactured in a manner known per se. Firstly, a basic powder fraction is prepared, which comprises the solid ingredients of the automatic dishwashig composition, which for instance in the following recipe 1 according to Example 1 comprises bleach, bleach activator, polycarboxylate, polyfunctional carboxylic acid, silicate, enzymes, silver corrosion inhibitor and sodium carbonate. After a brief stirring for 1 to 5 min, the fluid ingredients, usually comprising liquid tensides, are sprayed thereon, whereupon one or more tableting adjuvants can be sprayed on or added followed by a final mixing for 2 to 10 min. The resulting powder mix is compressed to tablets of a diameter of, for instance, 32 mm in a tablet press (e.g. Fette Perfecta 4B). The thickness of the manufactured tablets depends on the desired tablet weight and the formulation and is usually in the range of 13 to 20 mm. Further examples of the manufacturing of tablets are disclosed in DE-PS No. 355,626, US-PS No. 328,880 and DE-PS No. 3,827,895. In a particularly preferred embodiment of the invention where the automatic dishwashing composition is in the form of tablets, the automatic dishwashing composition comprises: % by weight Oxygen donating bleach 21.0 Bleach activator 7.0 Polycarboxylate 16.0 Polyfunctional carboxylic acid 15.0 Sodium carbonate 14.0 Sodium silicate 10.0 Tens ides 4.0 Enzymes 3.0 Silver factor 10.0 A second embodiment of the invention, where the automatic dishwashing composition is in a pulverulent form, is as follows: % by weight Oxygen donating bleach 15.0 Bleach activator 5.0 Polycarboxylate 10.0 Polyfunctional carboxylic acid 15.0 Sodium carbonate 33.0 Sodium silicate 5.0 Tensides 4.0 Enzymes 3.0 Silver factor 10.0 In the above recipes, the amount of bleach activator is stated as TAED. Non-limiting examples of bleach activators include N-acyl compounds and O-acyl compounds, such as acylated amines, diamines, amides, acylated glycoluriles, N-acylated cyclic hydrazides, triazoles, urazoles, diketopiperazines, sulphuryl amides, cyanurates and imidazolines, carboxylic acid anhydrides, acylated sugar compounds, acylated ester compounds etc. Especially preferred compounds are tetraacetyl methylene diamine, tetraacetyl ethylene diamine (TAED) as well as higher homologues, tetraacetyl glycoluril (TAGU), pentaacetyl glucose (PAGE), p-hydroxybenzene sulphonates, sodium nonanoyloxybenzene sulphonate (NOBS) and sodium octanoyloxybenzene sulphonate. TAED is most preferred, TAED being available as a granulate having an active content of 85 to 95% by weight. The bleach activators are described in greater detail in GB-PS No. 2,040,983 and GB-PS No. 1,473,201. Examples of the polycarboxylate used include polymerisates of acrylic acid, hydroxyacrylic acid, maleic acid, itaconic acid, metaconic acid, aconitic acid, methylene malonic acid, citraconic acid etc., as well as copolymerisates of said carboxylic acids either with each other or with other ethylenically unsaturated compounds, such as ethylene, propylene, isobutylene, vinyl alcohol, vinylmethyl ether, furane, acrolein, vinyl acetate, acrylamide, acrylonitrile, methacrylic acid or crotonic acid. The molecular weight of the polycarboxylate may be in the range of 1,000 to 1,000,000, preferably 2,000 to 100,000 and most preferred 7,000 to 30,000. Regarding the polycarboxylates, reference is made to the paper by J. Perner and H.-W. Neumann, entitled "Polycarboxylate bei der Reinigung textiler und nichttextiler Substrate", Tenside Surfactants Detergents 24 (1987) 6, page 334-340. In the above recipes, the weights stated for the polyfunctional carboxylic acid refer to anhydrous citric acid. Usable polyfunctional carboxylic acids may generally be defined as such acids which in addition to the one requisite carboxylic acid group also contain at least one further functional group selected among carboxyl and hydroxy. Moreover, nitrogen may also be incorporated in the molecule in some cases. In addition to citric acid, examples of such polyfunctional carboxylic acids include NTA, EDTA and isoserine diacetic acid of the formula (CH 2 COOH) 2 N-CH 2 CHOHCOOH. The following examples illustrate the manufacture of automatic dishwashing compositons according to the invention. Example 1 Tablets of a weight of 18.0 g, a diameter of 32.0 mm, and a height of 15.0 mm were manufactured on the basis of the following recipe. Ammonium chloride was used as silver factor (SF). Recipe 1 (with 10.0 % by weight of silver factor) % by weight Sodium percarbonate (bleach) 21.0 Sodium carbonate 14.0 Sodium disilicate 10.0 Citric acid, anhydrous 15.0 Sokalan™ PA 40 G (polymer) 15.9 Silver factor 10.0 TAED 7.0 0 Plurafac™ LF 403 (nonionic tenside) 4.1 Enzymes 3.0 100.0 Example 2 Tablets of a weight of 18.0 g, a diameter of 32.0 mm, and a height of 15.0 mm were manufactured on the basis of the following recipe. Ammonium chloride was used as silver factor (SF). Recipe 2 (with 5.0 % by weight of silver factor) % by weight Sodium percarbonate 21.0 Sodium carbonate 19.0 Sodium disilicate 10.0 Citric acid, anhydrous 15.0 Sokalan™ PA 40 G 15.9 Silver factor 5.0 TAED 7.0 Plurafac™ LF 403 4.1 Enzyme 3.0 100.0 Example 3 The present example illustrates a comparison test carried out on automatic dishwashing compositions according to the invention in the form of tablets containing 10% and 5% of silver factor in the form of ammonium chloride as stated in Examples 1 and 2, a recipe corresponding to the recipe given in Example 1, however without the content of silver factor (recipe A); and on a leading pulverulent product on the market "MILDE KRAFT" (recipe B) based on an oxygen donating bleach. The recipe without silver factor is as follows: Recipe A (without silver factor) % by weight Sodium percarbonate 21.0 Sodium carbonate 24.0 Sodium disilicate 10.0 Citric acid, anhydrous 15.0 Sokalan™ PA 40 G 15.9 TAED 7.0 Plurafac™ LF 403 4.1 Enzymes 3.0 The test was carried out under the following test conditions: Dishwashing machine Cylinda E 1502 Temperature 55°C - no prewash Water hardness 20 °dH and 2 °dH Dosing 1 tablet of 18 g Number of wash cycles 6 Test objects 3 different types of hallmarked silver spoons, all clean. After the 6 wash cycles each of the three spoons was evaluated visually for brownish/yellowish discolouration and for loose dust deposits. A scale from 0 to 4 was used, where 0 indicates no discolouration or no dust deposit, respectively, and 4 indicates extensive discolouration and extensive dust deposit, respectively. The results are stated in Table 1 below, where the sum of the score for the three different silver spoons evaluated for brownish/yellowish discolouration and loose dust deposits, respectively, are stated together with the total score thereof. Thus, the best score attainable is 0 and the worst score attainable is 24. Corrosion of silver spoons after 6 wash cycles tested at 55° C in hard and soft water. Recipe Water hardness Score for brownish/yellowish discolouration Score for loose dust deposits Total score B (MILDE KRAFT) 20° dH 3 12 15 A (without SF) 20° dH 12 3 15 2 (5% SF) 20° dH 9 3 12 2 (5% SF) 20° dH 10 3 13 2 (5% SF) 2° dH 3 0 3 1 (10% SF) 20° dH 6 3 9 1 (10% SF) 20° dH 5 1 6 1 (10% SF) 2° dH 1 0 1 As it appears from the dishwashing test, the automatic dishwashing compositions according to the invention are superior in presenting a substantially reduced corrosion of silver cutlery. Thus total scores of from 6 to 13 are obtained for the automatic dishwashing compositions according to the invention (recipe 1 and 2) at a water hardness of 20° dH. MILDE KRAFT (recipe B) represents the best phosphate-free and chlorine-free, non-corrosive pulverulent product on the market, and when used in a dosage of 25 g this product causes a substantially stronger corrosion in form of dust deposits and discolouration, the total score being 15. The same applies to recipe A, where the total score is also 15. It appears furthermore from the table that the lower the water hardness, the less pronounced is the problem of discolouration and dust deposits. Example 4 The present Example illustates a comparison test carried out on automatic dishwashing compositions in the form of tablets according to the invention on the one hand and on tablets according to recipe A and MILDE KRAFT (recipe B) on the other hand. In the test, corrosion of silver spoons was determined as stated in Example 3 as well as the cleaning performance on steel cutlery and other tableware soiled in accordance with the guidelines stipulated by the IEC (International Electrotechnical Commission). In Table 2 below the composition of the recipes 3 to 6 is as follows: Recipe 3 (with 10% silver factor) This recipe corresponds to recipe 1 with the exception that anhydrous monosodiumcitrate has been used as solubilizer instead of citric acid. Recipe 4 (with 10% silver factor) This recipe corresponds to recipe 1 with the exception that diammoniumhydrogen citrate has been used as silver factor instead of ammonium chloride. Recipe 5 (with 10% silver factor) This recipe corresponds to recipe 1 with the exception that ammonium sulphate has been used as silver factor instead of ammonium chloride, and that this recipe uses TAED with the trade name TAED ATC available from the firm of Warwick International Ltd., Mostyn, North Wales instead of TAED supplied by Hoechst. Recipe 6 (with 10% silver factor) This recipe corresponds to recipe 1 with the exception that ammonium sulphate has been used as silver factor instead of ammonium chloride. The determination of the cleaning performance was carried out on steel cutlery and on other tableware, i.e. cups, plates, glasses etc, soiled in accordance with the guidelines stipulated by the IEC (International Electrotechnical Commission). Thus the steel cutlery and the other tableware were washed together with the silver spoons. In the washing tests, scores were given in the following way: After each wash cycle, each cup, plate, knife, fork etc was evaluated on a scale from 1 to 5 scores. The scores were calculated for steel cutlery, various plates and glasses, which had been soiled with non-tea containing smudge and for teacups which had been smudged with tea. Furthermore, a total score was calculated. The scores obtained are given in Table 2 below, where 100% indicates the maximum cleaning performance attainable. As it appears from TABLE 2, the automatic dishwashing compositions according to the invention are superior with respect to a reduced corrosion of the silver cutlery. It appears that the use of ammonium sulphate as silver factor (recipes 5 and 6) entails a very large ability to prevent loose dust deposits while the ability to prevent discolouration is less favourable compared to ammonium chloride (recipe 1). Furthermore, it appears that the use of anhydrous monosodium citrate (recipe 3) instead of citric acid (recipe 1) as solubilizer does not have a decisive effect on the results obtained with respect to neither corrosion nor cleaning performance. As to the cleaning performance, it appears that at a water hardness of 20 °dH, the automatic dishwashing compositions according to the invention (the recipes 1 to 6) and recipe A and recipe B disclose largely the same performance as to tea-containing stains. As to non-tea containing stains and the total score, no significant difference appears either. As regards the cleaning performance, the automatic dishwashing compositions according to the invention are thus satisfactory and comparable with the best products on the market. The above description of the invention renders it obvious that it can be varied in many ways. Such variations are to be considered comprised by the following claims.

Claims: A machine dishwashing composition comprising an oxygen donating bleach and ingredients conventional for dishwashing compositions including possible further conventional adjuvants and/or fillers, characterised in that it comprises a silver corrosion inhibitor consisting of a compound releasing ammonium ions in an amount of 1.5 to 10.5 parts by weight, calculated as ammonium chloride, per part by weight of active oxygen, calculated as O 2 releasable from the oxygen donating bleach. A machine dishwashing composition as claimed in claim 1, characterised by being in the form of a tablet. A machine dishwashing composition as claimed in claim 1, characterised in that the silver corrosion inhibitor is selected from the group consisting of ammonium chloride, ammonium bromide, ammonium sulphate, diammonium hydrogencitrate and mixtures thereof. A machine dishwashing composition as claimed in claim 1, characterised by containing 1.5 to 6.5 parts by weight of silver corrosion inhibitor, calculated as ammonium chloride, per part by weight of active oxygen. A machine dishwashing composition as claimed in claim 1, characterised by containing 1.5 to 5.3 parts by weight of silver corrosion inhibitor, calculated as ammonium chloride, per part by weight of active oxygen. A machine dishwashing composition as claimed in any of the preceding claims, characterised in that the oxygen donating bleach is selected among per-compounds or perhydrates or mixtures thereof. A machine dishwashing composition as claimed in any of the preceding claims, characterised in that it comprises: % by weight Oxygen donating bleach 3-39 Bleach activator 1-13 Polycarboxylate 5-21 Polyfunctional carboxylic acid 0-30 Sodium silicate 5-10 Tensides 3-5 Enzymes 1-5 Silver corrosion inhibitor 2-18 Sodium carbonate q.s. 100 Use of a composition comprising an oxygen donating bleach and ingredients conventional for machine dishwashing compositions including possible further conventional adjuvants and/or fillers, and a compound releasing ammonium ions in an amount of 0.03 to 10.5 parts by weight, calculated as ammonium chloride, per part by weight of active oxygen, calculated as O 2 releasable from the oxygen donating bleach, as a machine dishwashing composition with silver corrosion inhibiting effect. The use according to claim 8, wherein the composition contains 0.7 to 6.5 parts by weight of silver corrosion inhibitor, calculated as ammonium chloride, per part by weight of active oxygen.

Inventors: KRISTENSEN ANDERS BJERRE, PEDERSEN BJARNE SKINDHOJ, KRISTENSEN, ANDERS BJERRE, PEDERSEN, BJARNE SKINDHOJ
Applicants: CLEANTABS AS, CLEANTABS A/S
Application year: 1992
Main classification: C11D3
IPC codes: C11D3, C11D17