CA2842396A1 - Method for the bleaching of kitchenware in a dishwasher - Google Patents

Abstract

The invention provides a method for bleaching kitchen utensils in a machine dishwasher, comprising the step of in situ activation of a bleach activator by means of a reactive oxygen species, the reactive oxygen species being generated in situ in the dishwasher by electrolysis of an aqueous solution.

Description

, , Method for the bleaching of kitchenware in a dishwasher Description The invention relates to a method for bleaching kitchenware in a dishwasher, and to the combination of a dishwasher with an electrolysis cell located outside of the dishwasher in the inflow line or with a battery-operated electrolysis cell located in the wash chamber.
For the bleaching of kitchenware such as crockery and cutlery, cleaning compositions are usually used which comprise bleaches and/or bleach activators (bleach precursors) in order to remove different types of soiling, in particular tea and coffee stains, from the kitchenware to be cleaned. In this connection, the "actual" bleach, for example singlet oxygen, is only formed in situ from the bleaches and/or bleach activators used.
Examples of bleaches are hydrogen peroxide sources such as sodium percarbonate and sodium perborate, which form hydrogen peroxide in the presence of water, and this in turn decomposes at temperatures above 60 C to give water and singlet oxygen. When using hydrogen peroxide sources, the bleaching action thus only occurs at temperatures above 60 C.
Examples of bleach activators are acyl derivatives such as tetraacetyl-ethylenediamine (TAED) and sodium p-nonanoyloxybenzenesulphonate (NOBS). The acyl derivative bleach activators are used together with a hydrogen peroxide source. Following release of the hydrogen peroxide from the hydrogen peroxide source, the acyl derivative bleach activators react with hydrogen peroxide with the formation of peroxycarboxylic acids.
The peroxycarboxylic acids generally disintegrate even at room temperature, with the formation of the carboxylic acid and singlet oxygen.
Depending on the hydrogen peroxide source used, however, hydrogen peroxide is only released at relatively high temperatures; for example, sodium percarbonate only forms hydrogen peroxide at temperatures above 50 C in the presence of water. Consequently, in the case of the combination acyl derivative bleach activator/hydrogen peroxide source, the bleaching effect also only occurs at relatively high temperatures, depending on the hydrogen peroxide source used.

Hydrogen peroxide and many peroxycarboxylic acids, for example peroxyacetic acid, are unstable and consequently non-storable, and can therefore not be added directly to the dishwashing detergent.
DE10104470 and WO 2007/052064 describe customary cleaning compositions for use in dishwashers which can also comprise bleaches and/or bleach activators.
US 6,387,238 describes a method of producing an antimicrobial solution comprising peroxyacetic acid. This method comprises the electrolytic production of hydrogen peroxide, peroxide ions or peroxide radicals and the reaction of this species with an acetyl donor, with the formation of peroxyacetic acid. Example 1 describes the electrolytic (current strength:
5 A, current density: 100 mA/cm2, voltage: 10 V) production of peroxyacetic acid.
WO 2006/117201 describes a method for cleaning, sterilizing and disinfecting dishes and other kitchenware by means of a washing liquid where, as a result of the direct application of an electrical current to an electrode arranged in the washing liquid, said electrode being a diamond and/or lead/tin electrode, OH radicals are generated in the washing liquid and these permit the cleaning, sterilizing and disinfecting of the dishes and the other kitchenware. The current density at the electrode is between 5 A/d m2 (=500 mA/cm2) to 300 A/dm2 (= 30 A/cm2).
US 2002/023847 describes a method for producing a cleaning solution by means of electrolysis of water, and also an apparatus for the cleaning and sterilizing of objects such as dishes and clothing. The apparatus comprises, for example, an electrolysis chamber with an ion exchange membrane which separates the anode chamber from the cathode chamber. The cathode chamber contains tap water, the anode chamber saltwater. During the electrolysis, an aqueous solution of sodium hydroxide is formed in the cathode chamber, and an aqueous solution of HOCI is formed in the anode chamber. The aqueous solution of sodium hydroxide is pumped from the cathode chamber and the objects to be cleaned are sprayed therewith.

JP 2003/211104 A describes a washing station which has a washing water preparation unit which comprises a cathode and an anode, where the surface of at least one of the electrodes has conductive diamond. One example of a washing station is a dishwasher (tableware scrubber). In all cases, the "functional" water has sterilizing properties. Example 3 describes the formation of an aqueous persulphate solution by electrolysis (5 A, 120 cm2, 15 min, 14 V) of a 0.6% strength aqueous sodium sulphate solution using diamond electrodes doped with boron.
WO 2009/067838 describes a method for the cleaning, sanitization, disinfection and odour neutralization of laundry, textiles, dishes, floor surfaces and vehicles with electrolyzed cold or warm water by means of oxidative radicals produced by boron-doped diamond electrodes. The cleaning intensities required for this purpose by means of oxidative radicals can only be achieved with the help of diamond electrodes with 4 volt overvoltage.
EP 1 944 403 describes a method for the work-up of washing water from a cleaning installation, e.g. a washing machine, and for reusing the worked-up washing water in the cleaning installation, where the method provides, inter alia, a step in which the washing water to be worked up is treated electrochemically. In this step, organic constituents of the washing water to be worked up, e.g. surfactants or soiling components are decomposed by means of ozone, hypochlorous acid (HOCI) or other active oxygen species.
During the electrolysis, for example diamond electrodes can be used, and a high voltage is applied so that highly concentrated ozone is formed.
US 2003/0414202 describes the production of electrolytic water by the electrolysis of an alkaline electrolyte solution, where the electrolytic water can be taken for cleaning and disinfection. The alkaline electrolyte is a mixture of at least one electrolyte selected from the group consisting of sodium carbonate, potassium carbonate, phosphorus sodium carbonate and sodium hypochlorite, and also a further electrolyte selected from the group consisting of sodium chloride, potassium chloride, sodium bromide and potassium bromide. Nickel ferrite can be used as anode. The invention can be used in many applications, e.g. for the cleaning and disinfection of warm water in public baths.

DE 103 36 588 A1 describes a method for the removal/decolouring of coloured substances/residues in liquids and from surfaces, in particular in dishwashers and in washing machines. In the method, the liquid circulates continuously through channels between electrodes. In so doing, the coloured molecules are anodically oxidized directly at the electrode surface. In addition, "active" oxygen and "active" chlorine are formed at the electrode surfaces, and their accumulation likewise brings about a removal/decolouring of coloured substances/residues in the liquid and from surfaces. An anode made of titanium which has a layer of titanium oxide, for example, can be used as anode.
DE 10 2006 037 905 describes a dishwasher comprising an electrolysis cell for producing bleaches from the regenerating salt of a water softener.
During the electrolysis, the salt solution produces oxidatively active substances (bleaches), in particular chlorine and sodium chlorite solution or potassium hypochlorite solution, depending on the type of regenerating salt. Hydrogen gas and oxygen gas are formed as by-products. The electrodes consist preferably of corrosion-resistant materials, also with a catalytic coating, e.g. electrodes made of titanium substrate with an oxidative coating of precious metal oxides and precious metal dopings. In addition, however, it is also possible to use other electrode materials such ' as conductive diamond, platinum, tin oxide and stainless steels.
It was the object of the present invention to provide a method for the bleaching of kitchenware in a dishwasher which achieves excellent bleaching results even at temperatures of less than 45 C.
Moreover, the method according to the invention should be technically realizable (no storage of unstable bleaches such as hydrogen peroxide or peroxycarboxylic acids) and economical (low electricity consumption), and also gentle as regards the dishwasher (no corrosion) and the kitchenware (no undesired discolorations).
This object is achieved by the method according to Claim 1, and also by the combinations in Claims 21 and 22.
The method for bleaching kitchenware in a dishwasher of the present invention comprises the step of the in situ activation of a bleach activator .=

by means of a reactive oxygen species, where the reactive oxygen species is generated in situ in the dishwasher by electrolysis of an aqueous solution.
5 Dishwasher includes all types of dishwashers, i.e. both dishwashers for private households (domestic dishwashers) and also dishwashers that can be used commercially (industrial and commercial dishwashers).
Kitchenware includes all types of kitchenware, for example crockery, 10 cutlery, pots and glasses.
The reactive oxygen species is usually a reactive oxygen species which has at least one oxygen atom with the oxidation number -1. Examples of reactive oxygen species which have at least one oxygen atom with the 15 oxidation number -1 are hydrogen peroxide, hydrogen peroxide anions, perhydroxyl radicals, hydroxyl radicals, hyperoxide anions and ozone.
Preferably, the reactive oxygen species is selected from the group consisting of hydrogen peroxide, hydrogen peroxide anions, perhydroxyl 20 radicals and hydroxyl radicals. Particularly preferably, the reactive oxygen species is selected from the group consisting of hydrogen peroxide, hydrogen peroxide anions and perhydroxyl radicals.
The reactive oxygen species is preferably generated by electrolysis of the 25 water present in the aqueous solution.
The electrolysis can take place in an electrolysis cell comprising at least one anode/cathode pair. The electrolysis cell can comprise one anode/cathode pair or a plurality of serially connected anode/cathode pairs.
30 Preferably, the electrolysis cell comprises a plurality of serially connected anode/cathode pairs. The connection of the anode/cathode pairs can take place in a monopolar or bipolar manner. A bipolar connection is preferred.
The anode can comprise the following materials: carbon, for example 35 graphite, glass carbon and electrically conductive diamond, precious metals, for example platinum and gold, metal oxides, for example iridium oxide, chromium oxide, lead oxide, palladium oxide and ruthenium oxide, or mixed metal oxides.

. CA 02842396 2014-01-20 ..) Preferably, the anode comprises graphite, electrically conductive diamond or platinum.
5 Particularly preferably, the anode comprises materials with which a high oxygen overvoltage can be achieved, for example electrically conductive diamond or platinum.
The anode very particularly preferably comprises electrically conductive diamond.
Electrically conductive diamond is diamond which is doped with foreign atoms such that the diamond doped with foreign atoms conducts the electrical current. Suitable foreign atoms are, for example, boron or nitrogen.
Preferably, the anode is an anode comprising electrically conductive diamond where the electrically conductive diamond is a diamond doped with boron.
Anodes comprising electrically conductive diamond usually comprise a carrier material, and the electrically conductive diamond.
Suitable as possible carrier materials are niobium, silicon, tungsten, 25 titanium, silicon carbide, tantalum and graphite, and also ceramic carrier materials such as titanium suboxide. Preferred carrier materials are niobium, titanium and silicon. A particularly preferred carrier material is niobium.
30 The cathode can comprise the following materials: carbon, for example graphite, glass carbon and electrically conductive diamond, metals, for example iron and nickel, steel, for example stainless steel, or precious metals, for example platinum.
35 The cathode very particularly preferably comprises electrically conductive diamond or steel.
Preferably, the cathode is a cathode comprising electrically conductive diamond, where the electrically conductive diamond is a diamond doped with boron.
Cathodes comprising electrically conductive diamond usually comprise a carrier material, and the electrically conductive diamond.
Suitable as possible carrier materials are niobium, silicon, tungsten, titanium, silicon carbide, tantalum and graphite, and also ceramic carrier materials such as titanium suboxide. Preferred carrier materials are niobium, titanium and silicon. A particularly preferred carrier material is niobium.
Anodes or cathodes comprising electrically conductive diamond can be prepared by the CVD ("chemical vapour deposition") method. Such diamond electrodes are commercially available, such as for example from Condias GmbH or Adamant-Technologies.
Anodes or cathodes comprising electrically conductive diamond can also be produced by the HTHP ("high temperature high pressure") method. In this method, industrial diamond powder is incorporated mechanically into the surface of a carrier metal sheet. Such diamond electrodes are also commercially available such as, for example, from pro aqua Diamantelektroden Produktion GmbH.
In one embodiment according to the invention, the anode comprises boron-doped diamond, and the dishwasher housing comprising steel, preferably stainless steel, functions as cathode. In this embodiment, the dishwasher is thus part of the electrolysis cell.
Preferably, the dishwasher housing is not part of the electrolysis cell.
In a further, preferred embodiment according to the invention, both the anode and also the cathode comprise boron-doped diamond. This embodiment has the advantage that the electrode polarity can be swapped, and possible deposits on the electrodes can be removed. The electrode polarity can be swapped, for example every 5 seconds to every 200 minutes, or between the individual wash cycles.

Preferably, the electrolysis cell has an effective electrode surface (electrode size) of from 0.5 to 1000 cm2, preferably from 1 to 500 cm2 and particularly preferably from 2 to 100 cm2. In this connection, the effective electrode surface refers to the electrode surface of the anode or of the anodes which comes into contact with the aqueous solution during the electrolysis and faces the cathode or the cathodes. If an anode is positioned between two cathodes (in the case of serial connection of a plurality of anode/cathode pairs), then the effective electrode surface of the anode or the anodes arises from the sum of the electrode surfaces facing the cathodes.
In the preferred embodiment according to the invention, in which both the anode and also the cathode comprise boron-doped diamond, the electrodes are preferably of equal size, and therefore when swapping the electrode polarities, the effective electrode surface remains the same.
The distance between the anode and the cathode is preferably 0.1 to mm, preferably 0.5 to 10 mm, particularly preferably 1 to 5 mm.
20 The anode and the cathode are preferably not separated from one another spatially, for example by a membrane.
Electrolysis cells which can be used are electrolysis cell types known to the person skilled in the art such as divided or undivided flow cell, capillary gap cell or stacked-plate cell. A particularly preferred electrolysis cell is the undivided flow cell.
The electrolysis cell can either be a built-in part of the dishwasher or a separate component.
If the electrolysis cell is a built-in part of the dishwasher, then the electrolysis cell can, for example, be incorporated in the flooded area of the washtub, preferably outside of the washing chamber, or the electrolysis cell can be attached in the inflow line within the dishwasher, or the electrolysis cell can be integrated in an additional water circulation within the dishwasher.
A dishwasher which comprises an electrolysis cell, where the electrolysis cell is integrated in an additional water circulation within the dishwasher, also forms part of this invention.
If the electrolysis cell is a separate component, then the electrolysis cell can, for example, be attached in the inflow line outside the dishwasher, for example in the fresh water feed between water tap and dishwasher, or be used as battery-operated electrolysis cell in the washing chamber.
Dishwashers which are commercially available nowadays generally comprise no electrolysis cell as built-in part. It is therefore preferred that the electrolysis cell is used as a separate component. The electrolysis cell is particularly preferably a battery-operated electrolysis cell which is used in the washing chamber of the dishwasher.
A combination of a dishwasher with an electrolysis cell located outside the dishwasher in the inlet line also forms part of this invention.
A combination of a dishwasher with a battery-operated electrolysis cell located in the washing chamber also forms part of this invention.
The electrolysis is carried out preferably at current densities, based on the effective electrode surface, in the range from 0.5 to 1000 mA/cm2, particularly preferably in the range from 1 to 500 mA/cm2, very particularly preferably in the range from 10 to 200 mA/cm2 and most preferably in the range from 50 to 100 mA/cm2.
The electrolysis is preferably carried out at current strengths of from 0.02 to A. A current strength in the range from 0.1 to 16 A is particularly preferred, and very particular preference is given to a current strength in 30 the range from 0.1 to 10 A.
The wash programs of a dishwasher usually include a wash cycle and a rinse cycle. In the wash cycle, the ware is cleaned, while the rinse cycle serves to remove the rinse water and also to dry the ware. The wash cycle can include two or more sub-wash cycles, for example one or more pre-wash cycles and one or more main wash cycles.
The electrolysis can take place over the entire duration of the dishwasher program, but the electrolysis preferably takes place only in one or more time intervals during the dishwashing program. Preferably, the electrolysis takes place here in one or more time intervals before or during the wash cycle. The time intervals in which the electrolysis takes place can be between 5 seconds and 120 minutes, preferably between 5 seconds and 60 minutes, particularly preferably between 1 minute and 30 minutes, and in particular between 5 minutes and 15 minutes. The electrolysis takes place particularly preferably in a plurality of intervals between 1 minute and 30 minutes, preferably between 5 minutes and 15 minutes, before or during the wash cycle.
The method according to the invention can be carried out at temperatures in the range from 10 to 95 C, preferably in the range from 15 to 90 C, particularly preferably in the range from 20 to 65 C and very particularly preferably in the range from 20 to 40 C, for example 30 C.
The method is preferably carried out at a temperature up to 60 C, preferably up to 40 C, particularly preferably up to 30 C.
The aqueous solution is an aqueous solution which comprises electrolytes and thus conducts electrical current. Examples of aqueous solutions which comprise electrolytes and thus conduct an electrical current are aqueous solutions based on tap water.
The aqueous solution can comprise additives when carrying out the electrolysis. However, the additives can also only be added to the aqueous solution while or after carrying out the electrolysis.
Examples of additives are the bleach activator, dishwashing detergents, rinse aids and regenerating salt.
A preferred additive is the bleach activator.
Bleach activators are usually compounds which react with reactive oxygen species, in particular with hydrogen peroxide, hydrogen peroxide anions or perhydroxyl radicals, to give peroxycarboxylic acids or peroxyimino acid.
Both peroxycarboxylic acids and also peroxyimino acid can decompose with the formation of singlet oxygen.

The bleach activators which react with hydrogen peroxide to give peroxycarboxylic acids can are preferably acyl derivatives.
The acyl radical of the acyl derivatives can have the following formula:
(1) where R1 is C1_20-alkyl or C6_10-aryl, or (2) where LI is C1_20-alkylene or C6_10-arylene.
Preferably, R1 is C1_10-alkyl or phenyl, particularly preferably R1 is C1_3-alkyl.
Very particularly preferably, R1 is methyl.
Preferably, L1 is phenylene or naphthylene, particularly preferably Ll is phenylene. Preferably, formula (2) has the following formula o 40 (2a) Acyl derivatives in which the acyl radical has formula (1) are preferred over acyl derivatives in which the acyl radical has formula (2).
Examples of Ci_3-alkyl are methyl, ethyl, n-propyl and isopropyl. Ci_io-alkyl can be unbranched or branched. Examples of Ci_io-alkyl are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl and n-decyl, n-undecyl, n-dodecyl. C1_20-alkyl can be unbranched or branched. Examples of C1.20-alkyl are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl and n-eicosyl (C20).
C6_10-aryl can be phenyl or naphthyl.
C1_20-alkylene can be unbranched or branched. Examples of C1_20-alkylene are methylene, ethylene, propylene, isopropylene, butylene, sec-butylene, isobutylene, tert-butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, undecylene, dodecylene, tridecylene, tetradecylene, 2-decylbutylene, pentadecylene, hexadecylene, heptadecylene, octadecylene, nonadecylene and eicosylene (C20).
Examples of C6_10-arylene are phenylene and naphthalene.
Examples of acyl derivative bleach activators are poly-O-acylated polyols, 0-acylated phenol derivatives, carboxylic anhydrides, 0-acylated hydroxylamines, 0-acylated cyanuric acid derivatives, poly-N-acylated polyamines, N-acylated aniline derivatives, poly-N-acylated heterocycles comprising at least one nitrogen, N-acylated urea derivatives, N-acylated amides, N-acylated imides and N-acylated sulphonamides.
Examples of poly-O-acylated polyols are diacetyl glycol and triacetin, and also poly-O-acetylated sugar alcohols and sugars, for example hexaacetylsorbitol, hexaacetylmannitol, pentaacetylglucose, tetraacetylxylose and octaacetyllactose, and also tetraacetylgluconolactone.
Examples of 0-acylated phenol derivatives are sodium p-nonanoyloxybenzenesulphonate (NOBS), sodium p-isononanoyloxy-benzenesulphonate, sodium p-benzoyloxybenzenesulphonate, sodium p-nonanoyloxybenzoate, and sodium p-decanoyloxybenzoate.
Examples of carboxylic anhydrides are phthalic anhydride and benzoic anhydride.

=

Examples of 0-acylated hydroxylamines are 0-benzoyl-N,N-succinylhydroxylamine, 0-acetyl-N,N-succinylhydroxylamine and 0,N,N-triacetylhydroxylamine.
5 Examples of 0-acylated cyanuric acid derivatives are triacetylcyanuric acid and tribenzoylcyanuric acid.
Examples of poly-N-acylated polyamines are tetraacetylmethylenediamine, tetraacetylethylenediamine (TAED) and tetraacetylhexylenediamine.
One example of a N-acylated aniline derivative is N,N-diacetylaniline.
Examples of poly-N-acylated heterocycles comprising at least one nitrogen are 1,3-diacety1-5,5-dimethylhydantoin, tetraacetylglucoluril, 1,5-diacetyl-2,2-dioxo-hexahydro-1,3,5-triazine, 1,5-diacety1-2,4-dioxohexahydro-1,3,5-triazine, 1,5-diacety1-2,4-dioxohexahydro-1,3,5-triazine, 1,4-diacety1-2,5-diketopiperazine, 1,3-diacety1-4,5-diacetoxyimidazoline and monoacetylmaleic acid hydrazide.
One example of an N-acylated urea derivative is tetraacetylpropylenediurea.
One example of an N-acylated amide is benzoylcaprolactam.
25 One example of an N-acylated imide is N-nonanoylsuccinimide.
Examples of N-acylated sulphonamides are N-methyl-N-mesylacetamide, N-methyl-N-mesylbenzamide, N,N'-dimethyl-N,N'-diacetylsulphurylamide and N,N'-diethyl-N,N'-dipropanoylsulphurylamide.
Bleach activators which react with hydrogen peroxide to give peroxyimino acid can be ammonium nitriles, for example N-methylmorpholinium acetonitrile hydrogen sulphate, trimethylammonium acetonitrile hydrogen sulphate.
Bleach activators which react with hydrogen peroxide to give peroxycarboxylic acids are preferred. Particularly preferred bleach activators are acyl derivative bleach activators. Very particularly preferred , P

bleach activators are poly-N-acylated polyamines. A particularly preferred bleach activator is tetraacetylethylenediamine (TAED).
The concentration of the bleach activator in the aqueous solution can be 5 0.001 to 10% by weight, preferably 0.01 to 5% by weight, particularly preferably 0.02 to 1% by weight, based on the weight of the aqueous solution.
The bleach activator can be part of the dishwashing detergent.
The dishwashing detergent can comprise the constituents customary for a dishwashing detergent, for example water softeners, bleaches, bleach activators, bleach catalysts, bleach stabilizers, surfactants and enzymes.
Moreover, the dishwashing detergent can also comprise foam inhibitors, 15 corrosion inhibitors and fillers.
Examples of water softeners are pentasodium triphosphate, sodium carbonate, sodium hydrogencarbonate, soap, zeolites, and complexing agents such as ethylenediaminetetraacetic acid (EDTA). Pentasodium 20 triphosphate or zeolite are the preferred water softeners.
Examples of bleaches are "oxygen-based" bleaches, and also "chlorine-based" bleaches.
25 Customary "oxygen-based" bleaches are hydrogen peroxide sources.
Examples of hydrogen peroxide sources are alkali metal perborates, for example sodium perborate and alkali metal percarbonates, for example sodium percarbonate, alkali metal persulphates, for example potassium monopersulphate, alkali metal persilicates and alkali metal perphosphates.
One example of a "chlorine-based" bleach is sodium hypochlorite.
"Oxygen-based" bleaches are preferred, in particular sodium perborate and sodium percarbonate. The most preferred bleach is sodium percarbonate.
Examples of bleach stabilizers are phosphonates.
Examples of surfactants are anionic surfactants, for example linear alkylbenzenesulphonates, secondary alkanesulphonates, fatty alcohol sulphates and methyl ester sulphates, and non-ionic surfactants, for example fatty alcohol polyglycol ethers and sugar surfactants.
Examples of enzymes are amylases, lipases and proteases.
Examples of foam inhibitors are silicone oils and paraffin oils.
One example of a corrosion inhibitor is sodium metasilicate.
One example of a filler is sodium sulphate.
The regenerating salt is sodium chloride.
Particularly preferred additives are water softeners, bleach activator, surfactants and enzymes.
The pH of the aqueous solution is preferably in the range from 2 to 13, particularly preferably in the range from 3 to 12, and very particularly preferably in the range from 6 to 11.
Preferably, for the method according to the invention, a degree of soil removal for bleachable soilings, for example tea, of at least 20%, preferably at least 50%, is achieved.
The degree of soil removal is determined as follows:
The determination takes place by soiling a white melamine resin reference substrate firstly under standard conditions (the following were used: DM 11 Tea Serie 096, 2.4 cm x 3.9 cm) and subjecting it to a reflection measurement at 460 nm before and after carrying out the treatment with the aqueous solution. The soil removal is calculated in % from the reflectance values R before and after carrying out the method and also the reflectance value of a white melamine resin reference substrate according to the following formula:
R (after cleaning) - R (before cleaning) Degree of soil removal [%] -x100 R (white melamine resin) - R (before cleaning) p All of the measurements here are carried out five times and the average is given. The following values were measured for the white melamine resin reference substrate and the standardized melamine substrate DM11:
R (white reference): 0.81 5 R (DM11 Tea Serie 096): 0.47 The reflectance measurements are carried out using a spectrophotometer, make Gretag Macbeth, model Spectrolino, under the following conditions:
observation angle 10 , type of light D65, UV filter.
The method according to the invention is characterized in that it is exceptionally suitable for the bleaching of kitchenware in a dishwasher, where the method has a very good bleaching effect even at temperatures of less than 45 C.
The method according to the invention is also technically realizable (no storage of unstable bleaches such as hydrogen peroxide or peroxycarboxylic acids) and economical (low electricity consumption) and also gentle with regard to the dishwasher (no corrosion) and the 20 kitchenware (no undesired decolourations).
Furthermore, the method can exhibit positive accompanying effects, such as the decolouring of the aqueous solution and also disinfection, cleaning and odour neutralization of the kitchenware to be bleached.
Figure 1 shows the schematic representation of the experimental apparatus used in the examples.
Examples Experimental set-up The experiments are carried out in a 1000 ml jacketed vessel made of glass with mechanical stirrer (IKA stirrer motor with glass stirrer and movable PTFE stirrer blade) and liquid circulation (lwaki magnetic pump MD6-230GS01, 80-901/h) and an electrolysis cell with boron-doped diamond electrodes (Adamant miniDiaCell, diamond on silicon, 12.5 cm2 electrode area). Figure 1 shows a schematic representation of the experimental apparatus.

The test substrates are made of melamine resin (DM 11 Tea Serie 096, 2.4 cm X 3.9 cm).
The following aqueous solutions are used:
Aqueous solution A: 700 g of demin. water, 10 g of NaHCO3 Aqueous solution B: 700 g of demin. water, 10 g of NaHCO3, 0.18 g of TAED
Aqueous solution C: 700 g of demin. water, 10 g of NaHCO3, 0.18 g of TAED, 0.32 g of H202 solution (30% of H202 in water).
TAED stands for tetraacetylethylenediamine. Demin. water stands for demineralized and completely deionized water.
'15 The selected concentration of TAED in the aqueous solutions B and C
corresponds to that of standard commercial dishwashing detergents. In the aqueous solution C, the molar ratio of H202/TAED is 4:1.
Comparative Examples C1 to C3 The aqueous solutions A (C1), B (C2), and C (C3) are provided in the experimental apparatus. The test substrates are introduced into the jacketed vessel such that they immerse completely into the aqueous solution and are wetted by it. The aqueous solutions are circulated by pumping for 30 minutes at 40 C without electrolysis. The test substrates are removed from the experimental apparatus, rinsed thoroughly with demin. water and dried with the exclusion of light.
Example 1 The aqueous solution B is provided in the experimental apparatus. The test substrate is introduced into the jacketed vessel such that it immerses completely into the aqueous solution and is wetted by it. The aqueous solution B is circulated in the experimental apparatus by pumping for 30 minutes at 40 C with electrolysis (1.2 A). The test substrate is removed from the experimental apparatus, rinsed thoroughly with demin. water and dried with the exclusion of light.
Example 2 The aqueous solution B is provided in the experimental apparatus. The test substrate is introduced into the jacketed vessel such that it immerses completely into the aqueous solution and is wetted by it. The aqueous solution B is circulated in the experimental apparatus by pumping for 30 minutes at 60 C with electrolysis (1.2 A). The test substrate is removed from the experimental apparatus, rinsed thoroughly with demin. water and dried with the exclusion of light.
Example 3 The aqueous solution A is circulated in the experimental apparatus by pumping at 40 C with electrolysis (1.2A) for 10 minutes without test substrate. The current source is switched off. 0.18 g of TAED and the test substrate are added and the resulting aqueous solution is circulated by pumping at 40 C for a further 30 minutes without the application of current.
The test substrate is removed from the experimental apparatus, rinsed thoroughly with demin. water and dried with the exclusion of light.
Example 4 The aqueous solution A is circulated in the experimental apparatus by pumping at 60 C with electrolysis (1.2A) for 10 minutes without test substrate. The current source is switched off. 0.18 g of TAED and the test substrate are added and the resulting aqueous solution is circulated by pumping at 60 C for a further 30 minutes without the application of current.
The test substrate is removed from the experimental apparatus, rinsed thoroughly with demin. water and dried with the exclusion of light.
Determination of the degree of soil removal The soil removal is determined by subjecting the test substrate made of melamine resin to a reflection measurement at 460 nm before and after the treatment with the aqueous solution. The soil removal was calculated in %
from the reflectance values R before and after the treatment, and also the reflectance value of a white reference substrate made of melamine resin according to the following formula:
R (after cleaning) - R (before cleaning) Soil removal [%] = x100 R (white substrate) - R (before cleaning) The reflectance measurements are carried out using a spectrophotometer, make Gretag Macbeth, model Spectrolino, under the following conditions:

, r observation angle 100, type of light D65, UV filter.
The test substrates of the Comparative Examples C1 to C3, and also of Examples 1 to 4 have the following degree of soil removal following the treatment:
Example Temperature [ C] Soil removal [%]

Table 1 The pure washing effect of aqueous solution A brings about a soil removal of 21% (C1). The addition of TAED (C2) leads, as expected, only to a slight improvement in the soil removal to 25%. Likewise as expected, as a result of adding H202 (C3), the bleach precursor (TAED) is activated, such that a soil removal of 48% is achieved.
Example 1 shows that, at 40 C and with the same amount of TAED, using the method according to the invention a higher soil removal (60%) can be achieved than with the comparative method C3 (48%). Example 2 shows that the soil removal increases to 67% as a result of increasing the temperature to 60 C.
Examples 3 and 4 show that it is also possible to first activate the aqueous solution electrolytically for 10 minutes, and then to add TAED. It is thus possible to achieve a very good soil removal with a lower current input.

Claims (22)

1. A method for bleaching kitchenware in a dishwasher, comprising the step of the in situ activation of a bleach activator by means of a reactive oxygen species, where the reactive oxygen species is generated in situ in the dishwasher by electrolysis of an aqueous solution.

2. The method according to Claim 1, where the reactive oxygen species is a reactive oxygen species which has at least one oxygen atom with the oxidation number -1.

3. The method according to Claim 2, where the reactive oxygen species is selected from the group consisting of hydrogen peroxide, hydrogen peroxide anions, perhydroxyl radicals and hydroxyl radicals.

4. The method according to any one of Claims 1 to 3, where the electrolysis takes place in an electrolysis cell comprising at least one anode/cathode pair.

5. The method according to Claim 4, where the anode comprises electrically conductive diamond.

6. The method according to Claim 5, where the anode comprises diamond doped with boron.

7. The method according to any one of Claims 4 to 6, where the cathode comprises diamond doped with boron.

8. The method according to any one of Claims 4 to 7, where the electrolysis cell is a built-in part of the dishwasher.

9. The method according to any one of Claims 4 to 7, where the electrolysis cell is a component separate from the dishwasher.

10. The method according to Claim 9, where the electrolysis cell is attached in the inflow line outside of the dishwasher, or is used as battery-operated electrolysis cell in the wash chamber.

11. The method according to any one of Claims 1 to 10, where the electrolysis is carried out at current densities in the range from 10 to 200 mA/cm2, preferably in the range from 50 to 100 mA/cm2.

12. The method according to any one of Claims 1 to 11, where the electrolysis is carried out at current densities in the range from 0.1 to 16 A, preferably in the range from 0.1 to 10 A.

13. The method according to any one of Claims 1 to 12, where the electrolysis takes place in one or more time intervals from 1 minute to 30 minutes, preferably from 5 minutes to 15 minutes, before or during the wash cycle.

14. The method according to any one of Claims 1 to 13, where the method is carried out at temperatures in the range from 20 to 65°C, preferably in the range from 20 to 40°C.

15. The method according to any one of Claims 1 to 14, where the aqueous solution comprises additives while carrying out the electrolysis, or additive are added to the aqueous solution after carrying out the electrolysis.

16. The method according to Claim 15 where the bleach activator is one of the additives.

17. The method according to any one of Claims 1 to 16, where the bleach activator is an acyl derivative, the acyl radical of which has the following formula:
where R1 is C1-20-alkyl or C6-10-aryl, or where L1 is C1-20-alkylene or C6-10-arylene.

18. The method according to any one of Claims 1 to 17, where the bleach activator is a poly-N-acylated polyamine.

19. The method according to any one of Claims 1 to 18, where the bleach activator is tetraacetylethylenediamine (TAED).

20. The method according to any one of Claims 1 to 19, where the pH of the aqueous solution is in the range from 3 to 12, preferably in the range from 6 to 11.

21. A combination of a dishwasher with an electrolysis cell located outside of the dishwasher in the inflow line.

22. A combination of a dishwasher with a battery-operated electrolysis cell located in the wash chamber.