DE69228223T2 - Dishwasher detergent - Google Patents

Description

Technical field

The present invention relates to automatic dishwashing detergents comprising an oxygen-releasing bleaching agent and ingredients commonly used in dishwashing detergents, including optionally other commonly used additives and/or fillers.

State of the art

Typically, machine dishwashing detergents, also referred to in this description as "automatic dishwashing detergents", have been formulated on the basis of chlorine-containing bleaching agents.

In recent years, society and individuals have become increasingly aware of the environmental impact of the high consumption of automatic dishwashing detergents containing chlorine bleach. Consequently, a growing demand for the formulation of alternative automatic dishwashing detergents has developed.

Therefore, the trend in automatic dishwashing detergents is to develop more and more chlorine-free, non-corrosive automatic dishwashing detergents that contain oxygen-releasing bleaching agents.

Examples of such automatic dishwashing detergents include SUN PROGRESS®, which is a powdered, phosphate-free, chlorine-free and non-corrosive automatic dishwashing detergent available from Lever, Germany, and Milde KraftTM, which is also a phosphate-free and chlorine-free, non-corrosive powdered product marketed in Germany by Benckiser.

Such oxygen-releasing bleaches have some disadvantages, especially in connection with silver cutlery, since silver oxidation compounds are formed by corrosion during the dishwashing process, which compounds lead to a discolored yellowish or brownish surface covered by a loose white dust-like layer. This tendency occurs to a greater or lesser extent in all products currently on the market that are based on oxygen-releasing bleaches.

However, this problem is particularly characteristic of automatic dishwasher detergents with a high content of oxygen-releasing bleach. The problem is particularly evident in automatic dishwasher detergents available in tablet form, as a higher content of bleach is required in the tablets compared to powders, due to the lower release of bleach from the tablets.

EP No. 135,226 relates to a peroxide-containing dishwashing detergent with a low chlorine content to prevent tarnishing of silver objects. The publication discloses that the tendency of silver objects to tarnish is related to the presence of chlorine, in particular alkali metal chloride, see page 2, lines 28 to 31 in the publication. The machine dishwashing detergent therefore contains not more than 0.2% by weight of chlorine and preferably not more than 0.1% by weight of chlorine, as it is preferred that the detergent be substantially chlorine-free. A further improvement in reducing the tendency of silver tarnishing can be achieved by adding a small amount of a C₁₂-C₁₈ fatty acid.

The use of automatic dishwashing detergents in the form of tablets is advantageous in itself, as the tablets provide an easy way to ensure a small but still sufficient dosage.

It is therefore desirable to provide a chlorine-free automatic dishwashing detergent that does not corrode silver cutlery during the dishwashing process, even in the case of a high content of an oxygen-releasing bleach.

Brief description of the invention

The present invention relates to an automatic dishwashing detergent comprising an oxygen-releasing bleaching agent and ingredients customary for dishwashing detergents, including other possible customary additives and/or fillers, the automatic dishwashing detergent being characterized in that it comprises a silver corrosion inhibitor consisting of a compound which releases 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 O₂, releasable from the oxygen-releasing bleaching agent.

The automatic dishwashing detergent according to the invention can be used particularly advantageously when a formulation in tablet form is desired, in which the problems of silver corrosion often occur particularly severely.

Examples of useful silver corrosion inhibitors capable of releasing ammonium ions include compounds selected from the group consisting of ammonium chloride, ammonium bromide, ammonium sulfate, diammonium hydrogen citrate, and mixtures thereof.

The automatic dishwashing detergent of the present invention comprises the silver corrosion inhibitor in an amount of at least 1.5 parts by weight of silver corrosion inhibitor, calculated as ammonium chloride, per part by weight of active oxygen, calculated as O₂, releasable from the oxygen-releasing bleach, and preferably not more than 10.5, more preferably not more than 6.5, and most preferably 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-releasing bleaching agent contained in the automatic dishwashing detergent may preferably be a per compound or a perhydrate or mixtures thereof.

A particularly advantageous recipe for the automatic dishwashing detergent according to the invention is found within the following limits:

% by weight

oxygen-releasing bleach 3-39

Bleach Activator 1-13

Polycarboxylate 5-21

polyfunctional carboxylic acid 0-30

Sodium silicate 5-10

Surfactants 3-5

Enzymes 1-5

Silver corrosion inhibitor 2-18

Sodium carbonate ad 100

It should be noted that the recipe is based on commercial products and not on 100% active and anhydrous ingredients.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter It is to be understood, however, that the detailed description and specific examples represent preferred embodiments of the invention and are given for purposes of illustration only.

Detailed description of the invention

The essential feature of the present invention is that the discoloration and deposition of dust on silver can be avoided, which is a pronounced problem in connection with a high content of oxygen-releasing bleaching agents. Such a high content of oxygen-releasing bleaching agents is usually necessary in automatic dishwashing detergents in the form of tablets in order to ensure a sufficiently rapid bleaching effect.

Examples of possible oxygen-releasing bleaching agents in question include perhydrates and percompounds and mixtures thereof. The perhydrates preferably include alkali metal compounds of perborates, which can 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 persulfates (e.g. caroates), perbenzoates and peroxycarboxylic acids such as peroxyphthalate, magnesium monoperoxyphthalic acid, diperoxyphthalic acid, 2-octyl-diperoxysuccinic acid, diperoxydodecanedicarboxylic acid, diperoxyazelaic acid, imidoperoxycarboxylic acid, and salts and mixtures thereof. Sodium percarbonate and sodium perborate can be mentioned as particularly preferred bleaching agents.

Regarding the bleaching system, reference is made to P. Kuzel and Th. Lieser, Tenside Surf. Det. 27 (1990) 1, pages 23-28.

The content of oxygen-releasing bleach is usually an amount corresponding to 0.4 to 5.3 parts by weight of active oxygen per 100 parts by weight of dishwashing detergent, which is approximately 3 to 39 parts by weight Sodium percarbonate per 100 parts by weight of dishwashing detergent, in the case of sodium percarbonate it contains 13.5 parts by weight of active oxygen.

Any compound can be used as a silver corrosion inhibitor, provided that this compound releases ammonium ions into the wash water and is active in the formation of stable silver complex salts and at the same time has no adverse effects on the cleaning performance.

The other ingredients of the automatic dishwashing detergent according to the invention can be selected from ingredients conventional for automatic dishwashing detergents, provided that such ingredients are of course compatible with the oxygen-releasing bleach and the silver corrosion inhibitor used. Thus, it is within the general skill of a person skilled in the art to formulate suitable automatic dishwashing detergents by combining an oxygen-releasing bleach and a silver corrosion inhibitor on the basis of the instructions given in the present application and to formulate the remaining ingredients of the automatic dishwashing detergent on the basis of the prior art.

The automatic dishwashing detergent according to the invention is preferably manufactured in the form of tablets to be used at a dosage of, for example, one or two tablets per wash cycle. The manufacture of tablets normally requires the addition of additives, for example in the form of starch, glycerin, polyethylene glycol, preferably in a molar weight of 100 to 10,000, polyvinylpyrrolidone (PVP), polyvinylpolypyrrolidone (PVPP) or a stearate compound such as sodium stearate. Such tablet additives ensure a suitable consistency and granulation.

The tablets are prepared in a manner known per se. First, a base powder fraction is prepared comprising the solid components of the automatic dishwashing detergent, which, for example, 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 brief stirring for 1 to 5 minutes, the liquid components, usually comprising liquid surfactants, are sprayed onto it, after which one or more tabletting additives can be sprayed on or added, followed by final mixing for 2 to 10 minutes. The powder mixture obtained is pressed into tablets of a diameter of, for example, 32 mm in a tablet press (e.g. Fette Perfecta 4B). The thickness of the tablets produced depends on the desired tablet weight and the formulation, and is usually in the range of 1 3 to 20 mm. Further examples of tablet production 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, in which the automatic dishwashing detergent is in the form of tablets, the automatic dishwashing detergent comprises:

% by weight

oxygen-releasing bleach 21.0

Bleach Activator 7.0

Polycarboxylate 16.0

polyfunctional carboxylic acid 15.0

Sodium carbonate 14.0

Sodium silicate 10.0

Surfactants 4.0

Enzymes 3.0

Silver factor (Silver factor (SF) = silver corrosion inhibitor.) 10.0

A second embodiment of the invention, wherein the automatic dishwashing detergent is in powder form is as follows:

% by weight

oxygen-releasing bleach 15.0

Bleach Activator 5.0

Polycarboxylate 1010

polyfunctional carboxylic acid 15.0

Sodium carbonate 33.0

Sodium silicate 5.0

Surfactants 4.0

Enzymes 3.0

Silver factor 10.0

In the above recipes, the amount of bleach activator is given as TAED. Non-limiting examples of bleach activators include N-acyl compounds and O-acyl compounds such as acylated amines, diamines, amides, acylated glycolurils, N-acylated cyclic hydrazides, triazoles, urazoles, diketopiperazines, sulphurylamides, cyanurates and imidazolines, carboxylic anhydrides, acylated sugar compounds, acylated ester compounds, etc. Particularly preferred compounds are tetraacetylmethylenediamine, tetraacetylethylenediamine (TAED) and higher homologues, tetraacetylglycoluril (TAGU), pentaacetylglucose (PAGE), p-hydroxybenzenesulfonates, sodium nonanoyloxybenzenesulfonate (NOBS) and sodium octanoyloxybenzenesulfonate. TAED is most preferred. TAED is available as granules with an active content of 85 to 95 wt.%.

The bleach activators are described in more detail in GB-PS No. 2,040,983 and GB-PS No. 1,473,201.

Examples of polycarboxylate used include polymers of acrylic acid, hydroxyacrylic acid, maleic acid, itaconic acid, metaconic acid, Aconitic acid, methylenemalonic acid, citraconic acid, etc. as well as copolymers of the carboxylic acids either with each other or with other ethylenically unsaturated compounds, such as ethylene, propylene, isobutylene, vinyl alcohol, vinyl methyl ether, furan, acrolein, vinyl acetate, acrylamide, acrylonitrile, methacrylic acid or crotonic acid.

The molecular weight of the polycarboxylate may range from 1000 to 1,000,000, preferably from 2000 to 100,000, and most preferably from 7000 to 30,000.

With regard to polycarboxylates, reference is made to the publication by J. Perner and H.-W. Neumann, entitled "Polycarboxylate in the cleaning of textile and non-textile substrates", Tenside Surfactants Detergents 24 (1987) 6, pages 334-340.

In the above recipes, the weights given for polyfunctional carboxylic acid refer to anhydrous citric acid. Useful polyfunctional carboxylic acids can be generally defined as those acids which, in addition to the one required carboxylic acid group, additionally contain at least one other functional group selected from carboxyl and hydroxy. Furthermore, nitrogen may also be present in the molecule in some cases. In addition to citric acid, examples of such polyfunctional carboxylic acids include NTA, EDTA and isoserinediacetic acid of the formula (CH2COOH)2N-CH2CHOHCOOH.

The following examples illustrate the preparation of automatic dishwashing detergents according to the invention.

example 1

Tablets weighing 18.0 g, with a diameter of 32.0 mm and a height of 15.0 mm were prepared based on the following recipe. Ammonium chloride was used as silver factor (SF). Recipe 1 (with 10.0 wt.% silver factor)

* SokalanTM PA 40 is a powdered polyacrylate in the form of the sodium salt with a molecular weight of approximately 15,000, available from BASF Germany.

** Hoe 4049, Tetraacetylethylenediamine is available from Hoechst AG, Frankfurt am Main, Germany.

*** PlurafacTM LF 403 is a low foaming non-ionic surfactant in the form of ethoxylated fatty alcohol available from BASF, Germany.

Example 2

Tablets weighing 18.0 g, with a diameter of 32.0 mm and a height of 15.0 mm were prepared based on the following recipe. Ammonium chloride was used as silver factor (SF). Recipe 2 (with 5.0 wt% silver factor)

Example 3

The present example illustrates a comparative test carried out with automatic dishwashing detergents according to the invention in the form of tablets containing 10% and 5% silver factor in the form of ammonium chloride as indicated in Examples 1 and 2, a recipe corresponding to the recipe of Example 1 but without the content of silver factor (recipe A); and a leading powder product on the market "MILDE KRAFT" (recipe B) based on an oxygen-releasing 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

SokalanTM PA 40 G 15,9

TAED 7.0

PlurafacTM LF 403 4.1

Enzymes 3.0

The test was carried out under the following test conditions:

Dishwasher: Cylinda E 1502

Temperature: 55ºC - no pre-wash

Water hardness: 20ºdH and 2ºdH

Dosage: 1 tablet with 18 g

Number of wash cycles: 6

Test objects: Silver spoons with three different types of fineness stamps, all clean.

After the 6 wash cycles, each of the three spoons was visually assessed for brownish/yellowish discoloration and loose dust deposits.

A scale of 0 to 4 was used, where 0 indicates no discoloration or no dust deposition and 4 indicates considerable discoloration or considerable dust deposition.

The results are given in Table 1 below, where the sum of the score of the three different silver spoons rated for brownish/yellowish discoloration or loose dust deposits is given together with the overall score. Thus, the best achievable score is 0 and the worst achievable score is 24.

Table 1

Corrosion of silver spoons after 6 washing cycles tested at 55ºC in hard and soft water.

* The dosage for this product is 25 g and is therefore in the medium range, cf. 20-30 g stated in the consumer information on the packaging.

Based on the dishwashing test, the automatic dishwashing detergents according to the invention appear to be superior, as they have a substantially show reduced corrosion of silver cutlery. An overall rating of 6 to 13 was obtained for the automatic dishwashing detergents according to the invention (recipes 1 and 2) at a water hardness of 20ºdH. MILD POWER (recipe B) represents the best phosphate-free and chlorine-free non-corrosive powder product on the market and when this product is used at a dosage of 25 g, it causes much more corrosion in the form of dust deposits and discoloration, the overall rating being 15. The same applies to recipe A, where the overall rating is also 15.

For the tablet, it seems that the lower the water hardness, the less the problem of discoloration and dust deposits.

Example 4

The present example illustrates a comparative test carried out with automatic dishwashing detergents in tablet form according to the invention on the one hand and with tablets according to recipe A and MILD POWER (recipe B) on the other hand. In the test, the corrosion of the silver spoons as indicated in example 3 was determined, as well as the cleaning performance of steel cutlery and other tableware soiled in accordance with the guidelines established by the IEC (International Electrotechnical Commission).

In Table 2 below, the compositions of recipes 3 to 6 are as follows:

Recipe 3 (with 10% silver factor)

This recipe is the same as Recipe 1 except that anhydrous monosodium citrate was used as a solubilizer instead of citric acid.

Recipe 4 (with 10% silver factor)

This recipe is the same as Recipe 1 except that diammonium hydrogen citrate was used as the silver factor instead of ammonium chloride.

Recipe 5 (with 10% silver factor)

This recipe is the same as Recipe 1 except that ammonium sulphate has been used as the silver factor instead of ammonium chloride and that this recipe uses TAED under the trade name TAED ATC, available from Warwick International Ltd., Mostyn, North Wales instead of TAED supplied by Hoechst.

Recipe 6 (with 10% silver factor)

This recipe is the same as Recipe 1 except that ammonium sulfate was used as the silver factor instead of ammonium chloride.

The determination of cleaning performance was carried out on steel cutlery and other tableware, i.e. cups, plates, glasses, etc., soiled in accordance with the guidelines established by the IEC (International Electrotechnical Commission). Then the steel cutlery and the other tableware were washed together with the silver spoons.

In the washing tests, the evaluations were carried out as follows:

After each wash cycle, each cup, plate, knife, fork, etc. was rated on a scale of 1 to 5 units. The rating was calculated for steel cutlery, various plates and glasses soiled with non-tea stains and for tea cups soiled with tea. The overall rating was also calculated. The rating obtained is shown in Table 2 below, where 100% indicates the maximum cleaning performance available. Table 2 Corrosion of silver spoons after 6 washing cycles tested at 55º in hard and soft water and determination of cleaning performance for silver cutlery and other tableware Table 2 (continued) Corrosion of silver spoons after 6 wash cycles tested at 55º in hard and soft water and determination of cleaning performance for silver cutlery and other tableware

It appears from Table 2 that the automatic dishwashing detergents according to the invention are superior in terms of reduced corrosion of silver cutlery.

It appears that the use of ammonium sulfate as silver factor (Recipes 5 and 6) has a very great ability to prevent loose dust deposits, while the ability to prevent discoloration is less advantageous 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 a solubilizer has no adverse effect on the results obtained, neither in terms of corrosion nor cleaning performance.

In terms of cleaning performance, it appears that at a water hardness of 20ºdH, the automatic dishwashing detergents according to the invention (recipes 1 to 6) and recipe A and recipe B generally show the same performance with regard to stains containing tea. With regard to stains not containing tea and the overall evaluation, no significant difference is shown either. In terms of cleaning performance, the automatic dishwashing detergents according to the invention are therefore satisfactory and comparable with the best products on the market.

The above description of the invention makes it obvious that it may be modified in many respects. Such modifications are intended to be covered by the following claims.

Claims (9)

1. Automatic dishwashing detergent comprising an oxygen-releasing bleach and ingredients commonly used in dishwashing detergents, including other possible common additives and/or fillers, characterized in that it comprises a silver corrosion inhibitor consisting of a compound which releases 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 O₂, which can be released from the oxygen-releasing bleach. 2. Dishwasher detergent according to claim 1, characterized in that it is in the form of a tablet. 3. Machine dishwashing detergent according to claim 1, characterized in that the silver corrosion inhibitor is selected from the group consisting of ammonium chloride, ammonium bromide, ammonium sulfate, diammonium hydrogen citrate and mixtures thereof. 4. Dishwasher detergent according to claim 1, characterized in that it contains 1.5 to 6.5 parts by weight of silver corrosion inhibitor, calculated as ammonium chloride, per part by weight of active oxygen. 5. Dishwasher detergent according to claim 1, characterized in that it contains 1.5 to 5.3 parts by weight of silver corrosion inhibitor, calculated as ammonium chloride, per part by weight of active oxygen. 6. Dishwasher detergent according to one of the preceding claims, characterized in that the oxygen-releasing bleaching agent is selected from per compounds or perhydrates or mixtures thereof. 7. Dishwasher detergent according to one of the preceding claims, characterized in that it comprises: % by weight oxygen-releasing bleach 3-39 Bleach Activator 1-13 Polycarboxylate 5-21 polyfunctional carboxylic acid 0-30 Sodium silicate 5-10 Surfactants 3-5 Enzymes 1-5 Silver corrosion inhibitor 2-18 Sodium carbonate ad 100 8. Use of a composition comprising an oxygen-releasing bleaching agent and ingredients commonly used in machine dishwashing detergents, including other possible common additives and/or fillers, and a compound which releases 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 O2, releasable from the oxygen-releasing bleaching agent, as a machine dishwashing detergent with silver corrosion-inhibiting action. 9. 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.