WO1994026860A1 - Silver-corrosion protection agent (ii) - Google Patents

Abstract

The invention concerns the use of organic redox compounds, in particular ascorbic acid, indole, methionine, N-(C1-C4 alkyl) glycines, 2-phenylglycine or coupler and/or development compounds selected from the group comprising diaminopyridines, aminohydroxypyridines, dihydroxypyridines, heterocyclic hydrazones, aminohydroxypyrimidines, dihydroxypyrimidines, tetraaminopyrimidines, triaminohydroxypyrimidines, diaminodihydroxypyrimidines, dihydroxynaphthalines, naphthols, pyrazolones, hydroxyquinolines, aminoquinolines, primary aromatic amines which have, in addition, a free hydroxy or amino group, or a hydroxy or amino group substituted with C1-C4 alkyl or C2-C4 hydroxyalkyl groups, at the ortho, meta or para position, and di- or trihydroxybenzenes as silver-corrosion protection agents in dishwasher washing agents, in particular low-alkali dishwaster washing agents.

Description

 "Silver Corrosion Protection Agent II"

It is a well known fact that silver "tarnishes" even when it is not in use. It is only a matter of time before it gets dark, brownish, bluish to bluish-black spots or becomes discolored overall and thus "tarnished" in common usage.

Problems also arise in the form of tarnishing and discoloration of the silver surfaces in machine cleaning of table silver. Silver can react here to sulfur-containing substances, which are dissolved or dispersed in the rinsing water, because when cleaning dishes in household dishwashers (HGSM) food residues and thus u. a. mustard, peas, egg and other sulfur-containing compounds are also introduced into the washing liquor. The much higher temperatures during machine washing and the longer contact times with the sulfur-containing food residues also favor the tarnishing of silver compared to manual washing. Due to the intensive cleaning process in the dishwasher, the silver surface is also completely degreased and therefore more sensitive to chemical influences.

When using active chlorine-containing cleaners, tarnishing can be largely prevented by sulfur-containing compounds, since these compounds are converted into sulfones or sulfates by oxidation of the sulfidic functions in a secondary reaction.

The problem of silver tarnishing, however, became topical again when, as an alternative to the active chlorine compounds, active oxygen compounds, such as sodium perborate or sodium percarbonate, were used, which are used to remove bleachable soiling, for example Tea stains / tea deposits, coffee residues, vegetable dyes, lipstick residues and the like are used.

These active oxygen compounds are mainly used in modern low-alkaline machine dishwashing detergents of the new generation of detergents together with bleach activators. These modern agents generally consist of the following functional components: builder component (complexing agent / dispersant), alkali carrier, bleaching system (bleach + bleach activator), enzymes and wetting agents (surfactants).

The silver surfaces are generally more sensitive to the changed recipe parameters of the new generation of active chlorine-free cleaners with lowered pH values and activated oxygen bleaching. During machine rinsing, these agents release the actual bleaching agent hydrogen peroxide or active oxygen in the cleaning cycle. The bleaching effect of the active oxygen-containing cleaners is enhanced by bleach activators, so that a good bleaching effect is achieved even at low temperatures. In the presence of these bleach activators, peracetic acid forms as a reactive intermediate. Under these changed rinsing conditions, in the presence of silver not only oxidic deposits, but preferably oxidic deposits on the silver surfaces due to the oxidizing attack of the intermediately formed peroxides or the active oxygen substance are formed. If the salt load is high, chloridic deposits can additionally develop. The tarnishing of the silver is also reinforced by higher residual water hardness during the cleaning cycle.

Avoiding silver corrosion, i.e. The formation of sulfidic, oxidic or chloride deposits on silver is the subject of numerous publications. The corrosion of silver is prevented in these descriptions primarily by so-called silver protection agents.

From British patent specification GB 1 131 738, alkaline dishwashing detergents are known which contain benzotriazoles as a corrosion inhibitor for silver. In the American patent US 3 549 539 strong describes alkaline, machine-applicable dishwashing detergents, which can contain, among other things, perborate with an organic bleach activator as the oxidizing agent. Additions of benzotriazole and iron (III) chloride, among others, are recommended as anti-tarnish agents. PH values of preferably 7-11.5 are mentioned. European patent specifications EP 135 226 and EP 135 227 describe weakly alkaline, machine-usable dishwashing detergents containing peroxy compounds and activators, which may contain, among other things, benzotriazoles and fatty acids as silver preservatives. Finally, it is known from German Offenlegungsschrift DE 41 28 672 that peroxy compounds which are activated by addition of known organic bleach activators prevent silver parts from tarnishing in strongly alkaline cleaning agents.

Surprisingly, it has now been found that organic redox-active substances, in particular the coupler and / or developer compounds which are usually used in oxidation colorants and have not hitherto been described as silver corrosion inhibitors, effectively prevent the corrosion of silver in machine dishwashers.

The invention relates to the use of organic redox-active substances in dishwashing detergent preparations as silver corrosion protection agents.

The word "corrosion" is to be interpreted in its broadest use in chemistry. In particular, "corrosion" should stand for every visually just recognizable change in a metal surface, here silver. B. a selective discoloration, be it z. B. a large area tarnishing.

"Organic redox-active substances" are those organic substances which are accessible to easily reversible oxidation and / or reduction. For example, typical complexing agents such. B. EDTA or hydroxyethane diphosphonic acid and related compounds do not fall under this definition. As typical in the sense of the invention "organic redox-active substances" z. As ascorbic acid (vitamin C), indole, methionine (α-amino-7-methyl-ercaptobutyric acid).

Also suitable are N-mono- (C 1 -C 4 -alkyl) glycines, e.g. N-mono-methyl-glycine and N, N-di- (-C-C4-alkyl) -glycine, e.g. N, N-dimethylglycine and 2-phenylglycine.

Certain coupler and / or developer compounds known from oxidative dyeing are also particularly suitable.

The preferably used organic substances to prevent the corrosion of silver are coupler and / or developer compound chosen from the group of diaminopyridines, aminohydroxypyridines, Dihydroxypyri- dine, heterocyclisehen hydrazones, aminohydroxypyrimidines, Dihydroxypyri i- dine, tetraaminopyrimidines, triaminohydroxypyrimidines, Diaminodihydroxy- pyrimidines Dihydroxynaphtaline, naphthols , Pyrazolones, hydroxyquinolines, aminoquinolines, the primary aromatic amines, which have a further free or substituted with C 1 -C 4 -alkyl or C2-C4 ~ hydroxyalkyl groups in the ortho, meta or para position, and the di or trihydroxybenzenes.

The developer and coupler compounds used according to the invention to prevent silver corrosion are the substances from the abovementioned groups that are usually used in oxidation dyeing agents. Examples of such developer and coupler compounds can be found, for example, in "Venkataraman, The Che istry of synthetic dyes, Vol. V, Academic Press New York / London, 1971, pages 478-495", and in the literature cited there. The developer or coupler compounds selected from the group p-hydroxyphenylglycine, 2,4-diaminophenol, 5-chloro-2,3-pyridinediol, 1- (p-aminophenyl) morpholine are particularly suitable for preventing silver corrosion , Hydroquinone, pyrocatechol, hydroxyhydroquinone, gallic acid, phloroglucin, pyrogallol. The organic redox-active substances are preferably coated, ie completely covered with a waterproof material which is easily soluble at the cleaning temperatures, in order to prevent their premature decomposition or oxidation during storage. Preferred coating materials which are applied by known processes, such as melt coating processes according to Sandwik from the food industry, are paraffins, micro waxes, waxes of natural origin such as carnauba wax, candell law wax, beeswax, higher-melting alcohols such as hexadecanol, soaps or fatty acids. The coating material, which is solid at room temperature, is applied in a molten state to the material to be coated, for example by spinning finely divided material to be coated in a continuous stream through a spray zone of the molten coating material, which is also continuously generated. The melting point must be selected so that the coating material easily dissolves or quickly melts in the dishwasher during the subsequent use of the silver corrosion protection agents. The melting point should therefore ideally be in the range between 45 ° C and 65 ° C and preferably in the range 50 ° C to 60 ° C for most applications.

However, the organic redox-active substances described above are particularly suitable for preventing silver corrosion if they are contained in alkaline cleaners for the automatic cleaning of dishes. This is all the more surprising since the effectiveness of these silver corrosion protection agents is not impaired by the presence of oxygen-based bleaching agents usually present in lower-alkaline cleaners.

Another subject of the invention is therefore low-alkaline agents for machine cleaning of dishes, the 1% by weight solutions of which have a pH of 8 to 11.5, preferably 9 to 10.5, containing 15 to 60% by weight, preferably 30 to 50% by weight of a water-soluble builder component, 5 to 25% by weight, preferably 10 to 15% by weight of an oxygen-based bleach, 1 to 10% by weight, preferably 2 to 6% by weight. -% an organic bleach activator, 0.1 to 5% by weight, preferably 0.5 to 2.5% by weight of an enzyme, in each case based on the total agent, and silver corrosion inhibitor, an organic redox-active substance being contained as the silver corrosion inhibitor. In particular, ascorbic acid, indole, methionine, N-mono- (-C-C4-alkyl) -glycine, N, N ^* -Di- (-C-C4-alkyl) -glycine and 2-phenylglycine, but especially coupler and / or developing agents selected from the group of slide inopyri- dine, aminohydroxypyridines, dihydroxypyridines, heterocycTischen hydrazones, aminohydroxypyrimidines, dihydroxypyrimidines, tetraaminopyrimidines, tri- aminohydroxypyrimidines, Diaminodihydroxypyri idine, Dihydroxynaphtaline, naphthols, pyrazolones, hydroxyquinolines, aminoquinolines, primary aro¬ matic amines, which have in the ortho, meta or para position a further free or with C-C4-alkyl or C2-C4-hydroxyalkyl groups substituted hydroxy or amino group and the di- or trihydroxybenzenes.

Preferred dishwashing detergents contain coupler and / or developer compounds selected from the group p-hydroxyphenylglycine, 2,4-diaminophenol, 5-chloro-2,3-pyridine, l- (p-aminophenyl) morpholine, hydroquinone , Pyrocatechol, hydroxyhydroquinone, gallic acid, phloroglucin, pyrogallol and mixtures thereof.

The organic redox-active substances are preferably present in the compositions according to the invention in a total amount of 0.05 to 6% by weight, preferably 0.2 to 2.5% by weight, based on the total composition.

In principle, all builders usually used in machine dishwashing detergents are suitable as water-soluble builder components, eg. B. polymeric alkali metal phosphates, which may be in the form of their alkaline neutral or acidic sodium or potassium salts. Examples include: tetrasodium diphosphate, disodium dihydrogen diphosphate, pentasodium triphosphate, so-called sodium hexametaphosphate and the corresponding potassium salts or mixtures of sodium hexametaphosphate and the corresponding potassium salts or mixtures of sodium and potassium salts. Zen. The amounts of phosphate are in the range of up to about 30% by weight, based on the total agent; however, the agents according to the invention are preferably free of such phosphates. Other possible water-soluble Bu lder components are such. B. organic polymers of native or synthetic origin, especially polycarboxylates, which act in particular in hard water systems as co-builders. For example, polyacrylic acids and copolymers of maleic anhydride and acrylic acid as well as the sodium salts of these polymer acids are suitable. Commercial products include Sokalan ( ^R ) CP 5 and PA 30 from BASF, Alcosperse ( ^R ) 175 or 177 from Alco, LMW ( ^R ) 45 N and SP02 N from Norsohaas. The native polymers include, for example, oxidized starch (eg German patent application P 4228786.3) and polyamino acids such as polyglutanic acid or polyaspartic acid, e.g. B. from the companies Cygnus and SRCHEM.

Other possible builder components are naturally occurring hydroxy carboxylic acids such as. B. mono-, dihydroxysuccinic acid, α-hydroxypropionic acid and gluconic acid. Preferred builder components are the salts of citric acid, especially sodium citrate. Water-free trisodium citrate or preferably trisodium citrate dihydrate are suitable as sodium citrate. Trisodium citrate dihydrate can be used as a fine or coarse crystalline powder. Depending on the pH ultimately set in the agents according to the invention, the acids corresponding to citrate can also be present.

Sodium perborate ono- and tetrahydrate or sodium percarbonate are primarily considered as bleaching agents based on oxygen. The use of sodium percarbonate has advantages because it has a particularly favorable effect on the corrosion behavior on glasses. The oxygen-based bleach is therefore preferably a percarbonate salt, in particular sodium percarbonate. Since active oxygen only develops its full effect on its own at elevated temperatures, so-called bleach activators are used to activate it in the dishwasher. PAG (pentaacetylglucose), DADHT (l, 5-diacetyl-2,4-dioxo-hexahydro-l, 3,5-triazine) and ISA (isato acid) are used as organic bleach activators. reanhydride), but preferably N, N, N ', N'-tetraacetylethylene diamine (TAED). In addition, the addition of small amounts of known bleach stabilizers such as, for example, phosphonates, borates or metaborates and metasilicates and magnesium salts such as magnesium sulfate can also be useful.

For better detachment of food residues containing protein, fat or starch, the dishwashing detergents according to the invention contain enzymes such as proteases, amylases, lipases and cellulases, for example proteases such as BLAP ( ^R ) 140 from Henkel; 0ptimase ( ^R ) -M-440, 0ptimase ( ^R ) -M-330, 0ρticlean ( ^R ) -M-375, 0pticlean ( ^R ) -M-250 from Solvay Enzymes; Maxacal ( ^R ) CX 450,000, Maxapem ( ^R ) from Ibis; Savinase ( ^R ) 4.0 T, 6.0 T, 8.0 T from Novo; Esperase ( ^R ) T from Ibis and amylases such as TermamyH) 60 T, 90 T from Novo; Amylase-LT ( ^R ) from Solvay Enzymes or Maxamyl ( ^R ) P 5000, CXT 5000 or CXT 2900 from Ibis; Lipases such as Lipolase ( ^R ) 30 T from Novo; Cellulases such as Celluzym ( ^R ) 0.7 T from Novo Nordisk. The dishwashing agents preferably contain proteases and / or amylases.

The agents according to the invention preferably additionally contain the alkali carriers contained in conventional low-alkaline machine dishwashing detergents, such as. B. alkali silicates, alkali carbonates and / or alkali hydrogen carbonates. The alkali carriers usually used include carbonates, bicarbonates and alkali silicates with a SiÜ2 / M2O molar ratio (M = alkali atom) of 1.5: 1 to 2.5: 1. Alkali silicates can be present in amounts of up to 30% by weight all the means. The use of the highly alkaline metasilicates as alkali carriers is preferably dispensed with. The alkali carrier system preferably used in the agents according to the invention is a mixture of essentially carbonate and hydrogen carbonate, preferably sodium carbonate and hydrogen carbonate, in an amount of up to 60% by weight, preferably 10 to 40% by weight, based on the total Means, is included. Depending on which pH is ultimately desired or set, the ratio of carbonate and hydrocarbon used varies. gene carbonate; Usually, however, an excess of sodium hydrogen carbonate is used, so that the weight ratio between hydrogen carbonate and carbonate is generally 1: 1 to 15: 1.

If appropriate, surfactants, in particular low-foaming nonionic surfactants, can also be added to the agents according to the invention, which improve the detachment of fatty food residues, as wetting agents, as granulating aids or as dispersing aids for better, homogeneous distribution of the aforementioned silver corrosion inhibitors in the washing liquor and on the Silver surfaces serve. Their amount is then up to 5% by weight, preferably up to 2% by weight. Extremely low-foam connections are usually used. These preferably include Ci2-Cl8 ^_ alkyl polyethylene glycol polypropylene glycol ether, each containing up to 8 moles of ethylene oxide and propylene oxide units in the molecule. However, it is also possible to use other nonionic surfactants known as low-foam, such as. B. Cχ2-Ci8-alkylpolyethylene glycol-polybutylene glycol ether, each with up to 8 moles of ethylene oxide and butylene oxide units in the molecule, end-capped alkylpolyalkylene glycol mixed ethers and the foaming but ecologically attractive C8-Ci4-alkylpolyglucosides with a degree of polymerization of about 1 - 4 ( eg APG ( ^R ) 225 and APG ( ^R ) 600 from Henkel) and / or Ci2-Ci4-alkyl polyethylene glycols with 3 - 8 ethylene oxide units in the molecule. Bleached quality should be used, otherwise brown granules will result. Also suitable are surfactants from the family of glucamides, such as, for example, alkyl-N-methyl-glucamides (alkyl = fatty alcohol with the C chain length C6-C14). It is advantageous in some cases if the surfactants described are used as mixtures, e.g. B. the combination of alkyl polyglycoside with fatty alcohol ethoxylates or glucamides with alkyl polyglycosides etc.

If the cleaning agents foam too much during use, they can still contain up to 6% by weight, preferably about 0.5 to 4% by weight, of a foam-suppressing compound, preferably from the group of silicone oils, mixtures of silicone oil and hydrophobized silica, Paraffin oil / Guerbet alcohols, paraffins, hydrophobized silica, the bisstearic acid amides and other other known commercially available defoamers can be added. Other optional additives are e.g. B. Perfume oils.

The dishwashing detergents according to the invention are preferably in the form of powdery, granular or tablet-like preparations which can be prepared in a conventional manner, for example by mixing, granulating, roller compacting and / or by spray drying.

For the preparation of cleaning agents according to the invention in tablet form, the procedure is preferably such that all constituents are mixed with one another in a mixer and the mixture is used by means of conventional tablet presses, for example eccentric presses or rotary presses, with pressures in the range from 200 ^• 10-5 Pa to 1 500 • 10 ^ Pa pressed. In this way, unbreakable tablets are obtained which, under application conditions, dissolve sufficiently quickly and have a flexural strength of normally more than 150 N. A tablet produced in this way preferably has a weight of 15 g to 40 g, in particular 20 g to 30 g, with a diameter from 35 mm to 40 mm.

The production of machine dishwashing detergents in the form of non-dusting, storage-stable, free-flowing powders and / or granules with high bulk densities in the range from 750 to 1000 g / l is characterized in that in a first process stage, the builder components are at least partially liquid Mixing components mixed with increasing the bulk density of this premix and subsequently - if desired after an intermediate drying - the further components of the dishwasher detergent, including organic redox-active substances, combined with the premix obtained in this way.

Since a possible alkali carbonate content strongly influences the alkalinity of the product, the intermediate drying must be carried out so that the decomposition of the sodium bicarbonate to sodium carbonate is as low as possible (or at least as constant as possible). An additional sodium carbonate portion resulting from the drying would have to be in the formulation of Granulate recipe are taken into account. Low drying temperatures not only counteract sodium bicarbonate decay, but also increase the solubility of the granulated detergent during use. It is therefore advantageous for drying to have a supply air temperature which, on the one hand, should be as low as possible to avoid bicarbonate decomposition and, on the other hand, must be as high as necessary in order to obtain a product with good storage properties. A supply air temperature of approximately 80 ° C. is preferred during drying. The granules themselves should not be heated to temperatures above about 60 ° C. In the first sub-stage of the mixing process, the builder is generally charged with the liquid components in admixture with at least one further component of the dishwashing detergent. For example, a precursor may be considered in which the builder component, mixed with perborate, is acted upon by the liquid nonionic surfactants and / or the solution of the fragrances and mixed intimately. The remaining components are then added and the entire mixture is worked through and homogenized in the mixing device. The use of additional amounts of liquid, in particular the use of additional water, is generally not necessary here. The mixture of substances obtained is then in the form of a free-flowing, dust-free powder of the desired high bulk density in the range from 750 to 1000 g / l.

The pre-granules are then mixed with the still missing components of the dishwashing detergent, including organic redox-active substances, to form the finished product. In all the cases shown here, the mixing time is both in the preliminary stage of the compacting mixture under the influence of liquid components and in the subsequent final mixture with the other components in the range of a few minutes, for example in the range of 1 to 5 minutes.

In a particular embodiment, it may be expedient in the production of fine granules to further stabilize and level out by powdering the surface of the granules formed adjust. Small portions of water glass powder or powdered alkali carbonate are particularly suitable for this purpose.

The agents to be used can be used both in household dishwashers and in commercial dishwashers. They are added by hand or using suitable dosing devices. The application concentrations in the cleaning liquor are about 2 to 8 g / 1, preferably 2 to 5 g / 1.

The rinse program is generally supplemented and ended with a few intermediate rinse cycles with clear water and a rinse cycle with a common rinse aid following the cleaning cycle. After drying, not only are completely clean dishes which are impeccable from a hygienic point of view, but above all also bright silver silver cutlery.

B e i s p e l e

Silver spoons (type WMF, hotel cutlery, form Berlin) were cleaned with a silver cleaner, degreased with gasoline and dried. Three spoons each were then placed in the cutlery basket of a Bosch S 712 household dishwasher (HGSM). The cleaning program (65 ° C, 16 ° dH) was now started and 50 g of a soiling (-0 and 30 g of the detergent) were metered directly into the machine. After the rinsing and drying process had ended, the HGSM were opened for 10 minutes, The machine was closed again and rinsed again in the same way. After the 10th rinse cycle, the spoons were removed and evaluated.

0 = no tarnishing, 1 = whole / slight yellowing, 2 = stronger yellowing, 3 = all-over gold to brown coloring, 4 = violet to black coloring of the spoons; Values in the upper left part of Tables 1 to 3.

At the same time, the removal of tea stains on porcelain was assessed. Here the rating was between 0 and 10 with 0 = no tea removal and 10 = complete tea removal; Values in the lower right part of Tables 1 to 3.

(1) Composition of the protection

Ketchup: 25 g

Mustard (extra hot) 25 g

Gravy: 25 g

Potato starch: 5 g

Benzoic acid: 1 9

Egg yolk: 3 pieces

Milk: 1/2 1

Margarine: 92 g

City water: 608 ml Production of tea soiling

16 l of cold city water (16 ° d) are briefly heated to boiling in a water treatment boiler. 96 g of black tea are left to draw in the nylon net with the lid closed for 5 minutes and the tea is transferred to a dipping apparatus with heating and stirrer.

60 teacups are immersed 25 times in one-minute intervals at 70 ° C in the prepared tea infusion. The cups are then removed and placed on a tray with the opening facing down to dry.

Reiniqerzusammmensetzuno

First the following low alkaline base product was produced, the

1% by weight solution in distilled water had a pH of 9.5:

56.0% trisodium citrate dihydrate

36.1% sodium hydrogen carbonate 6.1% sodium carbonate, anhydrous

1.8% mixture of non-ionic surfactants from APG 225 (Cs-Cio-alkyl oligoglu-coside) and dehydol ( ^R ) LS2 (Ci2-Ci4-fatty alcohol-2E0-ethoxylate) (1: 1)

The test variations specified with the following recipe were carried out with this basic product. The results are shown in Tables 1 to 3.

81-86% by weight of base product

12% by weight sodium percarbonate

0-10% by weight TAED

0 - 3% by weight catechol, gallic acid or hydroquinone

1 wt% protease

1 wt% amylase Table 1 Teereiniouno / silver corrosion protection

Machine: Bosch S 712 tea: 1 no cleaning

Dosage: 30 g 10 optimal cleaning

Program: 65 ° C Universal Silver: 0 no start

Water hardness: 16 ° dH 4 strong start

TAED Table 2 Teereiniouno / silage corrosion protection

Machine: Bosch S 712 tea: 1 no cleaning dosage: 30 g 10 optimal cleaning program: 65 ° C universal silver: 0 no start water hardness: 16 ^β dH 4 strong start

TAED Table 3 Teereiniouno / silver corrosion protection

Machine: Bosch S 712 Tee: 1 = no cleaning

Dosage: 30 g 10 = optimal cleaning

Program: 65 ^β C Universal Silver: 0 • = no start

Water hardness: 16 ° dH 4 «strong start

TAED Machine dishwashing detergents of the following compositions were also prepared (see Table 4). The compounds A - M were used as silver corrosion inhibitors: A: p-hydroxyphenylglycine B: 2,4-diaminophenol C: 5-chloro-2,3-pyridinediol D: 1- (p-aminophenyl) morpholine E: ascorbic acid F: N-monomethylglycine G: N, N-dimethylglycine H: 2-hydroxy-4-aminopyrimidine I: 2,4-dihydroxy-5-methylpyrimidine K: indole L: methionine M: 2-phenylglycine

Table 4 (all data in% by weight)

1 2 3 4 5 6 7 8 9 10

Soda - 27 8 - 26 8 - 26 8 -

Na hydrogen carbonate - - 31 - - 30 - - 30 -

Na disilicate 35 20 - 35 20 - 35 20 - 34

Trinatriu citrate dihydrate 40 25.5 44 40 25.5 44 39 25.5 43 39

Polycarboxylate

(Sokalan CP5 from BASF) 10 10-10 10-10 10-10

Na percarbonate - 10 10 - 10 10 - 10 10 -

Na perborate onohydrate 7 - - 7 - - 7 - - 7

TAED 2 3 2 2 3 2 2 3 2 2

Ci2-Ci4-fatty alcohol ethoxylate (2E0) (Dehydol LS2 from Henkel) 1 0.75 1 1 0.75 1 1 0.75 1

Cn-Cin-alkyl oligoglucoside (APG 225 from Henkel) 1 0.75 1 1 0.75 1 1 0.75 1

Protease 1.5 1 1 1.5 1 1 1.5 1 1.5

Amylase 1.5 1 1 1.5 1 1 1.5 1 1.5

Silver corrosion inhibitor AM (A) (B) (C) (0) (E) (F) (G) (H) (I) (K) 1 1 1 1 2 2 2 2 3 pH value of a 1% aqueous 10 , 5 11 9.5 10.5 11 9.5 10.5 11 9.5 10.5 solution

Continuation of table 4 (all figures in% by weight)

'11 12 13 14 15 16 17 18 19 20

Soda 26 8 - 25.5 8 - 26 7 - 26

Na hydrogen carbonate - 30 - - 29 - - 29 - -

Na disilicate 19.5 - 34 19 - 34 18.5 - 34 18.5

Trisodium citrate dihydrate 25 43 38 25 43 38 24 43 38 24

Polycarboxylate

(Sokalan CP5 from BASF) 10 - 10 10 - 10 10 - 9 10

Na percarbonate 10 10 - 10 10 - 10 10 - 10

Na perborate monohydrate - - 7 - - 7 - - 7 -

TAED 3 2 2 3 2 2 3 2 2 3

Fatty alcohol ethoxylate 0.75 1 1 0.75 1 1 0.75 1 1 0.75 (Dehydol LS2 from Henkel)

Alkyl oligoglucoside

(APG 225 from Henkel) 0.75 1 1 0.75 1 1 0.75 1 1 0.75

Protease 1 1 1.5 1 1 1.5 1 1 1.5 1

A ylase 1 1 1.5 1 1 1.5 1 1 1.5 1

Silver corrosion protection agent AM (L) (M) (A) (B (C) (D) (E) (F) (G) (H) 3 3 4 4 4 4 5 5 5 5 pH value of a 1% aqueous solution 11 9.5 10.5 11 9.5 10.5 11 9.5 10.5 11 solution

The silver spoons were consistently rated 0 to 1, i.e. "no to very weak tarnishing", rated. Identical compositions, but without silver corrosion inhibitor A - D in each case caused yellow to violet colors on silver spoons (rating: 2 to 4).

Electrochemical measurements

Sample preparation:

For the investigations, silver wire (d = 2 mm, 99.99%) was used as the sample material instead of silver cutlery. Approximately 10 cm long pieces were cut from this silver wire and the part of the sample immersed in the measuring solution was sanded with SiC sandpaper (600 grit). The samples were then rinsed well with bidistilled water and any adhering grinding residues were wiped off with a lint-free cloth. This process was repeated several times, if necessary, until the sample optically left a perfect impression. After grinding the samples, they were used immediately for the measurement in order to pre-empt a reaction of the metallic silver with the laboratory air. The effective sample surface immersed in the solution was 0.70 cm ^.

Electrolytes and electrodes:

The experiments were carried out in a Duran glass cell. The silver wires mentioned (A = 0.70 cm 2) served as measuring electrodes. The counterelectrode consisted of a gold plate (99.99% pure) with an area of 1 cm ^. On the basis of the alkaline electrolyte solutions, a Hg / Hg0 / 0.1 m NaOH electrode was chosen as the reference electrode, which was connected to the electrolytes via a Haber-Luggin capillary. The measurements were carried out with 5 g / 1 cleaner in tap water of 16 ° d and a salt load of approx. 600 mg (dry residue).

When preparing the cleaning solutions, the low-alkaline basic product (see above) was first dissolved and the solution heated to 65 ° C. The bleach and the bleach activator were used immediately before the measurement and / or the silver anticorrosive agent is added. The electrochemical measurement was then carried out. During the electrochemical experiments, the electrolyte solutions were heated to 65 ° C and flushed with air.

Equipment and recording of the measurement curves:

In order to record the current-voltage curves, the electrode potential was increased at a constant speed starting from -0.62, V based on the standard hydrogen electrode (SHE). After a total increase of 1.1 V, the potential was subsequently lowered at the same rate. A standard potentiostat consisting of a positive feedback amplifier, differential amplifier, adder and impedance converter and a function generator (Prodis 16 from Intelligent Controls CLZ GmbH) were used for this purpose.

Results:

The corrosion behavior was characterized on the basis of current-voltage curves. Essential information comes from the zero crossing of the current voltage curve (rest potential, which arises automatically even without external influence on the potential) and the slope of the curve at the zero crossing (reciprocal polarization resistance) E. Heitz, R. Henkhaus, A. Rahmel, "Corrosion Science in Experiment "Verlag Chemie (1983), pages 31 ff; H. Kaesche, "The Corrosion of Metals", 2nd edition, Springer Verlag (1979), pages 117 ff. The addition of the silver corrosion inhibitor shifts the potential for zero crossing to lower values and the slope decreases. The silver corrosion is thus also considerably reduced by the addition of the silver corrosion protection agents.

Composition position zero crossing slope in the cleaner E (mV) (SHE) zero crossing di / dE (mA / V)

Base product (86%) 319 0.5 + 12% percarbonate + 2% hydroquinone

Claims

Patent claims 1. Use of organic redox-active substances in dishwashing preparations as silver corrosion inhibitors. 2. Use according to claim 1, characterized in that the organic redox-active substance is ascorbic acid, indole or methionine. 3. Use according to claim 1, characterized in that the organic redox-active substance is an N-mono- (-C-C4-alkyl) -glycine, an N, N-di- (-C-C4 ~ alkyl) -glycine or 2-phenylglycine is. 4. Use according to claim 1, characterized in that the organic redox-active substance is a coupler and / or developer compound is selected from the group of the diaminopyridines, aminohydroxypyridines, dihydroxypyridines, heterocyclic hydrazones, aminohydroxypyrimidines, dihydroxypyrimidines, tetraaminopyridines, triaminohydroxypyrimidines, diaminodihydroxyne, diaminodihydroxyne, diaminodihydroxyne Naphtols, pyrazolones, hydroxyquinolines, aminoquinolines, the primary aromatic amines, which have a further free or substituted by C1-C4-alkyl or C2-C4-hydroxyalkyl groups in the ortho, meta or para position and the di - or trihydroxybenzenes. 5. Use according to claim 4, characterized in that the coupler or developer compound is selected from the group p-hydroxyphenylglycine, 2,4-diaminophenol, 5-chloro-2,3-pyridinediol, l- (p-amino - phenyl) morpholine, hydroquinone, pyrocatechol, hydroxyhydroquinone, gallic acid, phloroglucin, pyrogallol. 6. Low-alkaline agent for machine cleaning of dishes, whose 1% by weight solution has a pH of 8 to 11.5, preferably 9 to 10.5, containing 15 to 60% by weight, preferably 30 50% by weight of a water-soluble builder component, 5 to 25% by weight, preferably 10 to 15% by weight of an oxygen-based bleach, 1 up to 10% by weight, preferably 2 to 6% by weight of an organic bleach activator, 0.1 to 5% by weight, preferably 0.5 to 2.5% by weight of an enzyme, based in each case on the Entire agent and silver corrosion protection agent, characterized in that an organic redox-active substance is contained as silver corrosion protection agent. 7. Low alkaline agent for machine cleaning of dishes according to claim 6, characterized in that ascorbic acid, indole or methionine is contained as Silberkorrosionschutz¬. 8. Lower alkaline agent according to claim 6, characterized in that an N-mono- (-C-C4-alkyl) -glycine, an N-N-di- (-C-C4-alkyl) -glycine or 2-phenylglycine is contained as the silver corrosion inhibitor. 9. A low alkaline agent for machine cleaning of dishes according to claim 6, characterized in that as a Silberkorrosionschutzmit¬ tel a coupler and / or developer compound selected from the group of diaminopyridines, aminohydroxypyridines, dihydroxypyridines, heterocyclic hydrazones, aminohydroxypyrimidines, dihydroxypyrimidines, tetraaminopyrimidines, Tria inohydroxypyrimidines, diaminodi- hydroxypyrimidines, dihydroxynaphtalins, naphthols, pyrazolones, hydroxyquinolines, aminoquinolines, the primary aromatic amines, which are in the ortho, meta or para position, a further free or with Cj-C4-alkyl or C2-C4-hydroxyalkyl groups have substituted hydroxy or amino groups, and which contains di- or trihydroxybenzenes. 10. Composition according to claim 9, characterized in that the coupler or developer compound is selected from the group p-hydroxyphenylglycine, 2,4-diaminophenol, 5-chloro-2,3-pyridinediol, l- (p-aminophenyl ) - morpholine, hydroquinone, pyrocatechol, hydroxyhydroquinone, gallic acid, phloroglucinol, pyrogallol. 11. Composition according to claim 6 to 10, characterized in that the organic redox-active substances in an amount of 0.05 to 6 wt .-%, preferably 02, to 2.5 wt .-%, based on the total agent are included. 12. Composition according to claim 6 to 11, characterized in that the water-soluble builder component is a salt of citric acid, preferably sodium citrate. 13. Composition according to claim 6 to 12, characterized in that the oxygen-based bleach is a percarbonate salt, preferably sodium percarbonate. 14. Composition according to claim 6 to 13, characterized in that the organic bleach activator is N, N, N'N'-tetraacetylethylene diamine (TAED). 15. Composition according to claim 6 to 14, characterized in that the enzyme is an amylase and / or a protease. 16. Composition according to claim 6 to 15, characterized in that it additional Lich up to 60 wt .-%, preferably 10 to 40 wt .-%, based on the total agent, of an alkali carrier system consisting essentially of carbonate and hydrogen carbonate, preferably sodium carbonate and sodium hydrogen carbonate. 17. Composition according to claim 6 to 16, characterized in that it additionally contains up to 5% by weight, preferably up to 2% by weight, based on the total composition, of surfactants, preferably low-foaming nonionic surfactants. 18. Composition according to claim 6 to 17, characterized in that it is in tablet form and by mixing all of its constituents in a mixer and pressing the mixture by means of a tablet press at compression pressures of 2 ^• 10? Pa up to 1.5 • 10 * Pa is available. 19. Composition according to claim 6 to 17, characterized in that it is in the form of powder or granules and has a bulk density of 750 g / 1 to 1000 g / 1.