WO1994026859A1 - Silver-corrosion protection agent (i) - Google Patents

Abstract

The invention concerns the use of inorganic redox compounds, in particular salts and/or complexes of metals selected from the group comprising Mn, Ti, Zr, Hf, V, Co, and Ce, as silver-corrosion protection agents in dishwasher washing-up agents, in particular low-alkali dishwasher washing-up agents.

Description

 "Silver Corrosion Protection Agent I"

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 frequently arise in the form of tarnishing and discoloration of the silver surfaces when machine cleaning 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 such as mercaptoamino acid are also introduced into the washing liquor. The much higher temperatures during machine rinsing and the longer contact times with the sulfur-containing food residues also favor the tarnishing of silver compared to manual rinsing. 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 in a secondary reaction by oxidation of the sulfidic functions.

However, the problem of silver tarnishing became topical again, as an alternative to the active chlorine compounds, active oxygen compounds, such as sodium perborate or sodium percarbonate, which were 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, not only sulfidic but also oxidic deposits are formed on the silver surfaces due to the oxidizing attack of the intermediately formed peroxides or the active oxygen in the presence of silver. 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 the 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 inorganic redox-active substances, in particular the salts or complex compounds of certain metals which have not hitherto been described as silver corrosion inhibitors, effectively prevent the corrosion of silver in automatic dishwashers.

The invention relates to the use of inorganic 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 noticeable change in a metal surface, here silver. B. a selective discoloration, be it z. B. a large area tarnishing.

"Inorganic redox-active substances" are those inorganic substances which are amenable to easy reversible oxidation and / or reduction. For example, the oxides, hydroxides or halides of ammonium salts or of alkali or alkaline earth metals do not fall under this definition. Examples of "inorganic redox-active substances" are the substances Na2S2Ü3 (sodium thiosulfate), Na2S2Ü4 (sodium dithionite) or a2S2Ü5 (sodium disulfite), which are based on various oxidation levels of the sulfur.

However, the salts or complex compounds of certain metals are particularly suitable. It is preferred to use metal salts and / or metal complexes selected from the group consisting of manganese, titanium, zirconium, hafnium, vanadium, cobalt and cerium salts and / or complexes for preventing the Silver corrosion, the metals being in one of the oxidation states II, III, IV, V or VI.

The common definition in chemistry for "oxidation level" is e.g. in "Römpp Chemie Lexikon, Georg Thieme Verlag Stuttgart / New York, 9th edition, 1991, page 3168".

The metal salts or metal complexes used are said to be at least partially soluble in water. The counterions suitable for salt formation include all customary one, two or three times negatively charged inorganic anions, e.g. B. oxide, sulfate, nitrate, fluoride, but also organic anions such. B. stearate.

For the purposes of the invention, metal complexes are compounds which consist of a central atom and one or more ligands. The Zentralato is one of the above metals in one of the above oxidation states. The ligands are neutral molecules or anions that are monodentate or multidentate; the term “ligand” in the sense of the invention is explained in more detail, for example, in “Römpp Chemie Lexikon, Georg Thieme Verlag Stuttgart / New York, 9th edition, 1990, page 2507”. If the charge of the central atom and the charge of the ligand (s) do not add up to zero in a metal complex, then depending on whether there is a cationic or an anionic excess charge, either one or more of the abovementioned anions or one or more Cations, e.g. B. sodium, potassium, ammonium ions for the charge compensation. Suitable complexing agents are, for example, citrate, acetylacetonate or 1-hydroxyethane-l, 1-diphosphonate.

Particularly preferred metal salts and / or metal complexes are selected from the group MnSOj, Mn (II) citrate, Mn (II) stearate, Mn (II) acetylacetonate, Mn (II) - [l-hydroxyethane-l, l -diphosphonate], V2O5, V2O4, VO2, Ti0S04, K2TiFö, K2ZrF6, C0SO4, Co (N03) 2, Ce (N03) 3 and their mixtures. MnSÜ4 is particularly preferred.

These metal salts or metal complexes are generally commercially available substances which can be used for the purpose of the silver corrosion protection according to the invention without prior cleaning. For example, the mixture of pentavalent and tetravalent vanadium (V2O5. VO2, V2O4) known from the S03 production (contact process) is suitable, as is the titanyl sulfate, Ti0S04, formed by diluting a Ti (S04) 2 ~ solution.

The inorganic redox-active substances, in particular metal salts or metal complexes, are preferably coated, ie completely coated 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, for example melt coating processes according to Sandwik from the food industry, are paraffins, microwaxes, waxes of natural origin such as carnauba wax, candella wax, beeswax, higher-melting alcohols such as hexadecanol, soaps or fats acids. The coating material, which is solid at room temperature, is applied in the 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 dissolves easily or quickly melts during the subsequent use of the silver corrosion inhibitor in the dishwasher. The melting point should therefore be for most Applications are ideally in the range between 45 ° C and 65 ° C and preferably in the range 50 ° C to 60 ° C.

In particular, however, the inorganic redox-active substances described above are 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 of an organic, 0- or N- (-C ~ Ci2) acyl group-containing bleach activator, 0.1 to 5 wt .-%, preferably 0.5 to 2.5 wt .-% of an enzyme, each based on the total agent, and silver corrosion ¬ protectant, which contains an inorganic redox-active substance as a silver corrosion inhibitor. Metal salts and / or metal complexes selected from the group consisting of manganese, titanium, zirconium, hafnium, vanadium, cobalt, cerium salts and / or complexes are particularly suitable, the metals being in one of the oxidation states II, III , IV, V or VI are present.

Preferred dish detergents contain metal salts or metal complexes selected from the group nS04, Mn (II) citrate, Mn (II) stearate, Mn (II) acetylacetonate, Mn (II) - [l-hydroxyethane-l, 1- diphosphonate], V2O5, V2O4, VO2, T1OSO4, K2TiF6, K2ZrF6, C0SO4, Co (N03) 2, Ce (NÜ3) 3, and their mixtures. MnS04 is particularly preferred. The inorganic redox-active substances, in particular metal salts and / or metal complexes, are preferably present in the agents 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 agent , contain.

Organic, 0- or N- (-C-Ci2 -) - acyl group-containing bleach activators are substances in which at least one Cj-C ^ -acyl group, preferably the acetyl group, is attached to a 0- or N- Ato is bound, and their perhydrolysis C 1 -C 2 -alkanoic acids, preferably peracetic acid, provides.

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 of these are: 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. 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 builder components are e.g. 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 (e.g. German patent application P 4228786.3) and polyamino acids such as polyglutamic 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 mono- and tetrahydrate or sodium percarbonate are primarily considered as oxygen-based bleaches. 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. Organic bleach activators containing 0- or N- (C 1 -C 12) -acyl groups serve as bleach activators, e.g. PAG (pentaacetylglucose), DADHT (1,5-diacetyl-2,4-dioxo-hexahydro-1,3,5-triazine) and ISA (isatoic acid anhydride), but preferably N, N, N ', N'-tetraacetylethylenediamine (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, Opticlean ( ^R ) -M-375, Opticlean ( ^R ) -M-250 from Solvay Enzy es; 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 the company Ibis and amylases such as Termamyl ( ^R ) 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 commonly used include carbonates, bicarbonates and alkali silicates with a SiO 2 / 2O molar ratio (M = alkali atom) of 1.5: 1 to 2.5: 1. Alkali silicates can be obtained in amounts of up to 30% by weight on the whole 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 entire remedy is included. The ratio of the carbonate used and the hydrogen carbonate used varies depending on which pH value is ultimately desired or set; 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 include preferably Ci2 ~ ^_ CL8 alkyl polyethylene glycol polypropylene glycol ethers containing up-to 8 mol 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. Ci2-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 Hen¬ kel) 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 partially advantageous if the surfactants described are used as mixtures, for. 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, hydrophobicized silica, the bisstearic acid and other known 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.

To produce 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 to ^{10 5} Pa to 1 500 ^• 10 ^ Pa pressed. you thus easily obtains unbreakable tablets which, however, dissolve sufficiently quickly under conditions of use 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 of 35 mm to 40 mm.

The manufacture 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 are mixed while increasing the bulk density of this premix and subsequently - if desired after an intermediate drying - the further components of the dishwasher, including the inorganic redox-active substances, are 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 taken into account when formulating the granule formulation. 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. Here, for example, a precursor comes into consideration, in which the builder component in admixture with perborate with the liquid nonionic surfactants and / or the solution of the fragrances is applied and intimately mixed. 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 missing components of the dishwashing detergent, including inorganic redox-active substances, to give 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 special embodiment, it may be expedient in the production of fine granules to set further stabilization and leveling by powdering the surface of the granules formed. Small amounts 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. Examples

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) has now been started and 50 g of soiling ( ^{• ■} •) and 30 g of the detergent have been dosed 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, the spoons were removed and evaluated. For this purpose, the tarnishing colors were rated in the range from 0 to 4:

(0 = no tarnishing, 1 = very / light yellow coloring, 2 = stronger yellow coloring, 3 • = all-over gold to brown coloring, 4 = violet to black coloring of the spoons; values in the upper left part of table 1).

(1) Composition of the soiling:

Ketchup: 25 g

Mustard (extra hot) 25 g

Gravy: 25 g

Potato starch: 5 g

Benzoic acid: i g

Egg yolk: 3 pieces

Milk: 1/2 1

Margarine: 92 g

City water: 608 ml

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 table 1. 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.

Cleaner composition

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 bicarbonate 6.1% sodium carbonate, anhydrous

1.8% mixture of nonionic surfactants from APG 225 (C8-Cιo-alkyl oligoglu-coside) and dehydol () 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 Table 1.

81-86% by weight of base product

12% by weight sodium percarbonate

0-10% by weight TAED

0 - 2 wt% manganese sulfate monohydrate coated with paraffin

1% by weight of protease 1% by weight of a ylase Table 1 Tea cleaning / 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 Furthermore, automatic dishwashing detergents of the following compositions were produced (see Table 2). Compounds A - E were used as silver corrosion inhibitors:

V2O4 / V2O5 TiOSθ4 C0SO4 Ce (N0 ₃ ) ₃ Na2S2θ3 x 5H2O

Continuation of table 2 (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 lase 1 1 1.5 1 1 1.5 1 1 1.5 1

Silver corrosion protection agent AE (A) (B) (C) (D) (E) (A) (B) (C) (D) (E) 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

Table 2 (all data in% by weight)

The silver spoons were consistently rated 0 to 1, i.e. "no to very weak tarnishing", rated. In addition, the compositions showed 1 to 20 against bleachable stains such. B. Tea excellent cleaning performance.

Identical compositions, but each without silver corrosion protection agent A - D, also worked very well against bleachable soiling, but 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 cm2.

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%) with an area of 1 cm. A Hg / HgO / 0.1 m NaOH electrode was chosen as the reference electrode due to the alkaline electrolyte solutions, 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 and / or the silver corrosion inhibitor were added directly before the measurement. 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 location zero crossing slope in

Cleaner E (mV) (SHE) zero crossing di / dE (mA / V)

Base product (87%) 435 25

+ 12% percarbonate

+ 1% TAED

Base product (87%) 360 0.3

+ 12% percarbonate

+ 1% silver corrosion protection agent *)

Base product (86.5%) 405 7

+ 12% percarbonate

+ 1% TAED

+ 0.5% silver corrosion protection agent *)

Base product (86%) 375 0.6

+ 12% percarbonate

+ 1% TAED

+ 1% silver corrosion protection agent *)

) Anti-corrosion agent: Manganese sulfate monohydrate

Claims

Patent claims 1. Use of inorganic redox-active substances in dishwashing detergent preparations as silver corrosion inhibitors. 2. Use according to claim 1, characterized in that the inorganic redox-active substance is a metal salt and / or metal complex selected from the group consisting of manganese, titanium, zirconium, hafnium, Va nadium, cobalt and Cerium salts and / or complexes and the metals are in one of the oxidation states II, III, IV, V or VI. 3. Use according to claim 2, characterized in that the metal salts and / or metal complexes are selected from the group MnSθ4, Mn (II) citrate, Mn (II) stearate, Mn (II) acetylacetonate, Mn (II ) - [l-hydroxyethane-l, l-diphosphonate], V2O5, V2O4, VO2, TiOSθ4, ^ TiFß, ^ ZrF, C0SO4, Co (N0 ₃ ) ₂ , Ce (N0 ₃ ) ₃ . 4. Use according to claim 3, characterized in that the metal salt is MnSθ4. 5. 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 to 10% by weight, preferably 2 to 6% by weight of one organic, 0- or N- (-C-Ci2) -acyl group-containing bleach activator, 0.1 to 5 wt .-%, preferably 0.5 to 2.5 wt .-% of an enzyme, each based on the total agent, and silver corrosion inhibitor , characterized ge indicates that an inorganic redox-active substance is contained as silver corrosion protection agent. 6. Low alkaline agent for machine cleaning of dishes according to claim 5, characterized in that as a silver corrosion protection medium metal salts and / or metal complexes selected from the group consisting of manganese, titanium, zirconium, hafnium, vanadium, cobalt, cerium salts and / or complexes and that the metals in one of the oxidation stages II, III , IV, V or VI are present. 7. Composition according to claim 6, characterized in that the metal salts and / or metal complexes are selected from the group MnSÜ4, Mn (II) - citrate, Mn (II) stearate, Mn (II) acetylacetonate, Mn (II) - [l-hydroxyethane-l, l-diphosphonate], V2O5, V2O4, VO2, Ti0S04, - ^ TiFe, K2ZrF6, C0SO4, Co (N0 ₃ ) ₂ , Ce (N0 ₃ ) ₃ . 8. Composition according to claim 6, characterized in that the metal salt is MnS04 » 9. Composition according to claim 5 to 8, characterized in that the inorganic redox-active substances in an amount of 0.05 to 6 wt .-%, preferably 0.2 to 2.5 wt .-%, based on the total Means are included. 10. Composition according to claim 5 to 9, characterized in that the water-soluble builder component is a salt of citric acid, preferably sodium citrate. 11. A composition according to claim 5 to 10, characterized in that the oxygen-based bleach is a percarbonate salt, preferably sodium percarbonate. 12. Composition according to claim 5 to 11, characterized in that the organic, 0- or N- (-C-Ci2) acyl group-containing bleach activator is N.N.N'.N'-tetracetylethylenediamine (TAED). 13. Composition according to claim 5 to 12, characterized in that the enzyme is an amylase and / or a protease. 14. Composition according to claim 5 to 13, characterized in that it additional Lich up to 60 wt .-%, preferably 10 to 40 wt .-% based on the total agent, an alkali carrier system consisting essentially of carbonate and hydrogen carbonate, preferably Sodium carbonate and sodium hydrogen carbonate, contains 11. 15. Composition according to claim 5 to 14, 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. 16. Composition according to claim 5 to 15, 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 pressing pressures of 2 ^• 10? Pa up to 1.5 • 10 ^ Pa is available. 17. Composition according to claim 5 to 15, 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.