PL177936B1 - Agent for protecting silver i against corrosion - 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

The present invention relates to a low-alkaline machine dishwashing agent, in particular used as a silver corrosion protection agent.

177 936

It is generally known that silver "takes" even when not in use. It is only a matter of time before it becomes dark, brown, blue to blue-black, or it changes color in general, so, as we used to say, "will happen".

Even in the case of machine washing of table silver, there are still problems with overlapping and discoloration of the silver surface. Here, silver can react to sulfur-containing substances that are dissolved or dispersed in the rinsing water, because during dishwashing in domestic dishwashers (HGSMHaushaltsgeschirrspulmaschinen), food remains are transferred to the rinsing bath, including mustard, peas, eggs and other sulfur-containing substances. such as mercaptoamic acid. The much higher temperatures used in machine dishwashing and the longer contact times with sulfur-containing food remnants also promote silver accumulation more than in manual dishwashing. The intensive washing process in the dishwasher also completely degreases the silver surface and therefore becomes more sensitive to chemical influences.

When using detergents which contain active chlorine, the silver formation caused by sulfur-containing compounds can be largely prevented, since these compounds are converted into sulfones or sulfates in a secondary reaction by oxidizing the sulfide functions.

However, the problem of silver overlap has become relevant again when, alternatively to compounds containing active chlorine, compounds with active oxygen, such as sodium perborate or sodium percarbonate, are used to remove bleachable disorders such as, for example, tea stains and deposits, coffee residues, vegetable dyes, lipstick residue and the like.

These compounds with active oxygen are used primarily in modern low-alkaline machine dishwashing agents of the new generation of cleaning agents together with bleach activators. These modern agents generally consist of the following functional ingredients, namely builder (complexing agent / dispersing agent), alkali carrier, bleach system (bleach + bleach activator), enzymes and wetting agents (surfactants).

Silver surfaces are generally more sensitive to the altered formulation parameters of a new generation of active chlorine-free, low-pH cleaners with active oxygen bleaching. During machine dishwashing, these agents release a bleaching agent, i.e. hydrogen peroxide or active oxygen, in the cleaning step. The bleaching effect of cleaners containing active oxygen is enhanced by bleach activators, so that a good bleaching effect is obtained even at low temperatures. In the presence of these bleach activators, peracetic acid is formed as a reactive intermediate. Under these altered washing conditions in the presence of silver, not only sulphide deposits but also oxide deposits are formed on the silver surfaces, which is favored by the oxidative attack of the indirectly formed relatively active oxygen peroxides. Chloride deposits may additionally form under high salt loads. The addition of silver is also favored by the higher hardness of the residual water during the cleaning process.

Avoiding silver corrosion, that is, the formation of sulfide, oxide or chloride deposits on silver, is the subject of numerous publications. In these descriptions, corrosion of silver is prevented primarily by the use of so-called silver corrosion protection measures.

GB 1 131 738 discloses alkaline dishwashing agents which contain benzotriazoles as silver corrosion inhibitors. US 3,549,539 describes highly alkaline machine-usable dishwashing agents which may contain as oxidizing agents, inter alia, perborate with an organic bleach activator. Additives, including benzotriazole and also ferric chloride, are recommended as preventive measures. In this process, pH values of 7-11.5 are preferably used. In European patents

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EP 135 226 and EP 135 227 describe slightly alkaline machine dishwashing agents containing peroxygen compounds and activators, which may contain benzotriazoles and fatty acids as silver protection agents, among others. Finally, it is known from DE 41 28 672 that peroxy compounds, which are activated by the addition of known organic bleach activators, prevent the silver articles from overgrowing in highly alkaline cleaning agents.

It has now surprisingly been found that inorganic redox active substances, in particular salts or complexes of certain metals which have not yet been described as silver corrosion protection agents, effectively prevent the corrosion of silver in machine dishwashers.

Inorganic redox active substances are used according to the invention in dishwashing preparations as silver corrosion protection agents.

The word corrosion "should be taken in the broadest sense used in chemistry, and especially" corrosion "is to mean any visually recognizable change in the surface of a metal, in this case silver, whether it is a point change in color, for example, or overlapping a large surface.

"Inorganic redox active substances" are those inorganic substances which are easily oxidized and / or reduced reversibly. Excluded under this definition are, for example, oxides, hydroxides or halides of ammonium salts or of alkali metals or alkaline earth metals.

"Inorganic redox active substances" are, for example, substances based on different degrees of sulfur oxidation such as Na ₂ SO 3 (sodium thiosulphate), Na ₂ S ₂ 04 (sodium dithionite) or Na ₂ S ₂ 0 ₅ (sodium disulphite).

However, the salts or complex compounds of certain metals are particularly suitable. For the prevention of silver corrosion, metal salts and / or metal complex compounds selected from the group consisting of salts and / or complexes of manganese, titanium, zirconium, hffirnium, vanadium, cobalt and cerium are preferably used, the metals having one of the oxidation states II. III, IV, V or VI.

The chemistry definition of "oxidation state" is given, for example, in "Rompp Chemie Lexikon, Georg Thieme Verlag Stuttgart / New York, 9th edition, 1991, page 3168".

The metal salts or metal complex compounds used should be at least partially water-soluble. Suitable counterions for salt formation include all the usual one, two or three negatively charged inorganic anions, e.g. oxide, sulfate, nitrate, fluoride, but also organic anions, e.g. stearate.

The metal complex compounds in the sense of the invention are. compounds that consist of a central atom and one or more ligands. The central atom is one of the above-mentioned metals in one of the above-mentioned oxidation states. The ligands are. neutral molecules or anions that are mono- 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 in the metal complex compound the charge of the central atom and the charge of the ligand / ligands do not complement each other to zero, then depending on whether there is an excess of cationic or ammonium charge, it is necessary to balance the charges with either one or more of the above-mentioned anions or one or more cations , e.g. sodium, potassium or ammonium ions. Suitable complexing agents are, for example, 1-hydroxyethane citrate, acetylacetonate or 1,1-diphosphonate.

Particularly preferred metal salts and / or metal complex compounds are selected from the group such as MnSO4, Mn (II) citrate, Mn (II) stearate, Mn (II) acetylacetonate, Mn (II) - [1-hydroxyethane-1,1- diphosphonate], V2O5, V2O4, vO2, TiOSO4, K ^TiFg, K ^ZrFg, CoSO4, Co (NOj) 2, Ce (NO3) _3, and mixtures thereof. MnSO4 is especially preferred.

These metal salts or metal complex compounds are generally commercially available substances which can be used without prior purification

177 936 for the protection of silver against corrosion according to the invention. Thus, for example, a mixture of five and tetravalent vanadium (V ₂ O ₅ , VO ₂ , V ₂ O4) known from the production of SO ₃ (contact method) is suitable, as is the sulphate formed by dilution of the solution of Ti (SO4) ₂ titanyl, T1OSO4.

Inorganic redox active substances, in particular metal salts or metal complexes, are preferably coated, that is to say coated with a completely watertight but at the wash-off temperature with a readily soluble material in order to prevent premature decomposition or oxidation during storage. Preferred coating materials which are applied by known methods, for example by the alloying method according to Sandwik from the food industry, are paraffins, micro waxes, natural waxes such as carnauba wax, candelilla wax, beeswax, alcohols melting at higher temperatures, such as hexadecanol, for example. , soaps or fatty acids. The coating material to be coated is hereby applied to the coating material which is solid at room temperature in molten state, e.g. by swirling a continuous stream of fine-grained coating material through the also continuously produced mist zone of the molten coating material. The melting point should be selected such that the coating material dissolves readily or melts quickly during the subsequent application of the silver corrosion protection agent in a dishwasher. Therefore, the melting point should be in the range 45-65 ° C for most applications, and preferably in the range 50-60 ° C.

However, the above-described inorganic redox active substances are particularly suitable for preventing the corrosion of silver when they are included in low-alkaline dishwashing detergents. This is all the more unexpected since the effectiveness of these silver corrosion protection agents is not impaired by the presence of oxygen-based bleaching agents normally found in low-alkaline cleaners.

The present invention relates to low-alkaline dishwashing agents whose 1% by weight solutions have a pH of 8-11.5, preferably 9-10.5, containing 15-60% by weight, preferably 30-50% by weight of a water-soluble builder, 5 -25 wt.%, Preferably 10-15 wt.% Oxygen-based bleach, 1-10 wt.%, Preferably 2-6 wt.% Of an organic bleach activator containing O- or N- (C _r C ₁₂ ) acyl groups, 0 , 1-5 wt.%, Preferably 0.5-2.5 wt.% Of the enzyme in each case based on the total agent, and a silver corrosion protection agent, wherein an inorganic redox active substance is present as the silver corrosion protection agent. Particularly suitable are metal salts and / or metal complex compounds selected from the group such as the salts of manganese, titanium, zirconium, hafnium, vanadium, cobalt and cerium and / or complex compounds of these metals, the metals having one of the oxidation states II, III. , IV, V or VI in an amount of from 0.05 to 6% by weight of the total agent.

Preferred dishwashing agents contain metal salts or metal complexes selected from the group consisting of MnSO4, Mn (II) citrate, Mn (II) stearate, Mn (II) acetylacetonate, Mn (II) - [1-hydroxyethane-1,11 diphosphonate], V2O ₅ , V ₂ O.4, VO2, TiOSO4, K2TiF ₆ , K2ZrF ₆ , CoSO ₃ , Co (NO ₃ ) 2, Ce (NO3) ₃ and mixtures thereof. MnSO4 is particularly preferred.

The compositions according to the invention preferably contain inorganic redoxactive substances, in particular metal salts and / or metal complex compounds, in a total amount of 0.2-2.5% by weight, based on the total composition.

Organic bleach activators containing O- or NW ^-acyl groups are substances in which at least one CpC ^-acyl group, preferably an acetyl group, is attached to an O or N atom of the substance, and whose exhaustive hydrolysis provides C1 acids -C1 ₂ -alkane peroxy, preferably peracetic acid.

Suitable water-soluble builders are in principle all builders normally used in dishwashing agents.

177,936 vessels, e.g., polymeric alkali metal phosphates, which may be in the form of alkali, neutral or acid sodium or potassium salts. Examples are tetrasodium diphosphate, disodium dihydrogen phosphate, pentasodium triphosphate, so-called sodium hexametaphosphate, and the corresponding potassium salts or mixtures with 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. Preferably, however, the compositions according to the invention are free of such phosphates. Further possible water-soluble builders are, for example, organic polymers of natural or synthetic origin, above all polycarboxylates, which are particularly effective as co-builders in hard water systems. Possible options are, for example, polyacrylic acids and copolymers of maleic anhydride with acrylic acid, and the sodium salts of these polymeric acids. Commercial products are for example 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. Natural polymers include, for example, oxidized starch (e.g. German patent application P 42 28 786.3) and polyamino acids such as poly (glutamic acid) or poly (aspartic acid), e.g. from Cygnus or SRCHEM.

Further possible builders are naturally occurring hydroxycarboxylic acids, such as, for example, mono- and dihydroxy succinic acid, α-hydroxypropionic acid and gluconic acid. The preferred builders are the salts of citric acid, especially sodium citrate. Suitable sodium citrate is anhydrous trisodium citrate or preferably trisodium citrate dihydrate. Trisodium citrate dihydrate can be used as a fine or coarse crystalline powder. Depending on the pH value finally adjusted, acids corresponding to the citrate may also be present in the compositions according to the invention.

Suitable oxygen-based bleaching agents are, in particular, sodium perborate mono- and tetrahydrate, or sodium percarbonate. The use of sodium percarbonate has the advantage that it is particularly advantageous with regard to the corrosive behavior of the glasses. Therefore, the oxygen-based bleaching agent is preferably a salt percarbonate, especially sodium percarbonate. Since active oxygen only develops its full effect at elevated temperatures, so-called bleach activators are used to activate it in a dishwasher. Organic bleach activators containing O- or N - C 1-6 acyl groups are used as bleach activators, e.g. PAG (pentaacetyl glucose) DAdHt (1,5-diacetyl-2,4-dioxohexahydro-1,3,5-) triazine) and ISA (isatinic acid anhydride), but preferably N, N, N ', N'-tetraacetylethylenediamine (TAED). Furthermore, it may be expedient to add small amounts of known bleach stabilizers, such as, for example, phosphonates, borates or metaborates and metasilicates, and magnesium salts, such as magnesium sulphate.

In order to better wash off food residues containing protein, fat or starch, the dishwashing agents according to the invention contain enzymes such as proteases, amylases, lipases and cellulases, for example proteases such as BLAP® 140 from Henkel; Optimase® -M-440, Optimase® -M-330, Opticlean® -M-375, Opticlean® -M-250 from Solvay Enzymes; Maxacal® CX 450,000, Maxapem® by Ibis; Savinase® 4.0 T, 6.0 T, 8.0 T from Novo; Esperase® T from Ibis and amylases such as Termamyl® 60 T, 90 T from Novo; Amylase-LT® from Solvay Enzymes or Maxamyl® P 5000, CXT 5000 or CXT 2900 from Ibis; lipases such as Lipolas> e® 30 T from Novo; cellulases such as Celluzym® 0.7 T from Novo Nordisk. The dishwashing detergents preferably contain proteases and / or amylases.

The compositions according to the invention preferably additionally contain alkali carriers contained in the usual low-alkali machine dishwashing agents, such as, for example, alkali metal silicates, alkali metal carbonates and / or alkali metal bicarbonates. Commonly used alkali supports include alkali metal carbonates, bicarbonates and silicates having a SiO2 / M2O molar ratio (M is an alkali metal) of 1.5: 1 to 2.5: 1. The alkali metal silicates can be added in amounts

177,936 to 30% by weight, based on the total agent. The use of highly alkaline metasilicates as alkali carriers is preferably dispensed with. The alkali carrier system used in the compositions according to the invention is a mixture of essentially carbonate and bicarbonate, preferably sodium carbonate and bicarbonate, in an amount of up to 60% by weight, preferably 10-40% by weight, based on the total composition. Depending on what pH is ultimately desired or adjusted, the ratio of the amount of carbonate used and bicarbonate used varies; usually, however, an excess of sodium bicarbonate is used so that the weight ratio between bicarbonate and carbonate is generally 1: 1 to 15: 1.

Optionally, surfactants can also be added to the compositions according to the invention, in particular low-foaming nonionic surfactants, which serve to better wash off fatty food residues, as wetting agents, as granulating aids or as dispersing aids for better homogeneity. spreading the aforementioned silver corrosion protection agents in the rinsing bath and on the silver surface. They are used in an amount of up to 5% by weight, preferably up to 2% by weight. Usually, extremely low-foaming compounds are used. These preferably include C1-C6-alkyl polyethylene glycol and polypropylene glycol ethers with up to 8 moles of ethylene oxide and propylene oxide units in each molecule. But it is also possible to use other surfactants known as low-foaming, e.g. C ₂ -C ₁₈ -alkyl polyethylene glycol ethers of polybutylene glycol with up to 8 moles of ethylene oxide and butylene oxide units in each case, mixed alkyl polyalkylene glycol ethers with closed end groups and, admittedly, foaming are ecologically attractive C 8 -C 6 -alkyl polyglucosides with a degree of polymerization of about 1-4 (e.g. APG ^(R) 225 and APG ^(R ) 600 from Henkel) and / or Cl 2 -C 14 -alkyl polyethylene glycols with 3-8 oxide units ethylene in the molecule. A bleached variety should be used, otherwise a brown granulate is formed. Also suitable are surfactants from the glucoamide family, such as, for example, the alkyl-N-methylglucamides (alkyl = fatty alcohol with a carbon chain length of C 6 -C _M ). It is also partially advantageous to use the described surfactants in the form of a mixture, for example a combination of an alkyl polyglycoside with fatty alcohol ethoxylates or glucoamides with alkyl polyglycosides, etc.

As long as the cleaners using them. when using a silky seane, up to 6% by weight, preferably about 0.5-4% by weight, of a foam-limiting compound, preferably from the group of silicone oils, mixtures consisting of silicone oil and ornamental silicic acid, mixtures of paraffin oil / guerbefa block oil, paraffins, decorated silicic acid, biistatric acid amides and other known and commercially available anti-thinning agents. Other optional additives are, for example, fragrance oils.

According to the invention, the dishwashing agents are preferably in the form of powder, granule or tablet preparations which can be prepared in principle by known methods, for example by mixing, granulating, roller compaction and / or by annular drying.

For the preparation of the cleaning compositions according to the invention in the form of tablets, a procedure is preferably carried out such that all the components are mixed together in a mixer and the mixture is pressed in conventional tbblets, e.g. eccentric presses or rotary presses, at pressures in the range of 200 105 , 1500 105 pa. Thus, without any problems, tablets which are resistant to breaking are obtained without any problems, yet they dissolve sufficiently quickly under the conditions of use, the flexural strength of which is usually above 150 N. The tablet thus produced preferably has a weight of 15-40 g, in particular 20-30 g, with a diameter of 35-40 mm.

The production of dishwashing agents in the form of non-agile, storage-stable and free-flowing powders and / or granules with high bulk densities in the range of 750-1000 g / l is characterized by the fact that in the first step of the process

Builders are mixed with at least a portion of the liquid components of the mixture to increase the bulk density of this premix, and then, optionally after intermediate drying, further machine dishwashing ingredients, among them inorganic redoxactive substances, are combined with the premix thus obtained.

Since the alkali metal carbonate content strongly influences the alkalinity of the product, intermediate drying must be carried out so that the breakdown of sodium bicarbonate to sodium carbonate is as little or at least as constant as possible. The amount of sodium carbonate additionally formed as a result of drying would have to be taken into account when preparing the granulate recipe. The low drying temperatures not only counteract the disintegration of sodium bicarbonate, but also increase the solubility of the granular cleaning agent when used. It is therefore advantageous during drying to keep the temperature of the feed air as low as possible in order to avoid decomposition of the bicarbonate, and on the other hand to keep the temperature as high as necessary to obtain a product with good storage properties. A feed air temperature of about 80 ° C is preferred during drying, and the granulate itself should not be heated to a temperature above about 60 ° C. In the first step of the mixing process, the builder, as a rule in a mixture with at least one further dishwasher ingredient, is fed with liquid ingredients. This is, for example, a preliminary step in which the builder in a mixture with the perborate is fed with liquid nonionic surfactants and / or a perfume solution and thoroughly mixed. The remaining ingredients are then added and the entire mixture is worked up and homogenized in a mixer. The co-application of additional amounts of liquid, and in particular the use of additional water, is generally not required. The obtained mixture of substances is in the form of a free-flowing, non-dusting powder with the desired high bulk density in the range of about 750-1000 g / l.

The pre-granules are then mixed with the still missing ingredients of the dishwashing detergent, inter alia with inorganic redoxactive substances, and the finished product is thus obtained. The mixing time in all the cases described here, both in the initial thickening step under the influence of the liquid ingredients and in the subsequent final mixing with further ingredients, is several minutes, for example 1-5 minutes.

In a particular embodiment, it may be expedient, during the production of fine grains of granules, to effect a far-reaching stabilization and uniformity by dusting the surface of the formed granulate grain. Small amounts of powdered waterglass or powdered alkali metal carbonate are especially suitable.

The intended agents can be used both in domestic dishwashers and in industrial washing machines. The addition of these agents takes place manually or by means of appropriate dosing devices. The concentrations used in the cleaning bath are about 2-8 g / l, preferably 2-5 g / l.

The washing program is generally completed and completed by several intermediate rinsing steps with clean water following the cleaning step and by a clear rinse step using a conventional clear rinse aid. After drying, not only are the dishes perfectly clean and hygienically impeccable, but also, above all, brightly shining silver parts.

Examples

Silver spoons (WMF type, hotel cutlery, Berlin shape) were cleaned with a silver cleaner, degreased with gasoline and dried. Each time, 3 spoons were placed in the cutlery basket of a domestic dishwasher (HGSM), type Bosch S 712. Then the cleaning program was started (temperature 65 ° C, 16 ° dH) and 50 g of dirt ⁽ 1 and 30 g of cleaning agent were added directly to the After the washing and drying step was completed, the HGSM was opened for 10 minutes, the dishwasher was closed again and washed again in the same manner After the rinsing step 10, the spoons were removed and evaluated.

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The overlap colors of the spoons were assessed on a scale of 0-4, where 0 means no overlap, 1 means quite a slight yellow color, 2 means a stronger yellow color, 3 means a golden to brown color of the entire surface, 4 means a purple to black color of the spoons. ; the values are given in the upper left part of Table 1.

Table

The composition of the dirt ketchup 25 g mustard (very hot) 25 g barbecue sauce 25 g potato starch 5g benzoic acid 1 g egg yolk 3 pieces milk 1/21 margarine 92 g city water 608 ml

At the same time, the removal of tea soiling on porcelain products was assessed. Here, grades ranged from 0-10 with 0 being no tea removal and 10 being complete tea removal; the values are given in the lower right section of Table 1.

Tea soiling

In a kettle for the preparation of water, 16 liters of cold city water (16 ° d) is briefly heated to boiling. 96g of black tea in a nylon net is pulled for 5 minutes under the cover and the tea is transferred to an immersion apparatus with heating and an agitator. 60 tea cups are immersed 25 times with an interval of one minute at 70 ° C in the pre-made sprinkle of tea. The cups are then hung up and placed on the baking tray with the opening facing downwards to dry.

The composition of the cleaning agent

First, the following low-alkali stock was prepared, a 1% by weight solution of which 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% of a mixture of non-ionic surfactants composed of APG 225 (C ₈ -C ₁₀ -alkyl oligoglucoside) and Dehydol® LS2 (Cp-C 1- fatty alcohol ^ EO-ethoxylate) (1: 1)

Various tests have been carried out with this base product with the formula given below. The results are presented in Table 1.

81-86 wt.% Base product. 12 wt.% Sodium percarbonate

0-10% by weight of TAED

0-2 wt% of paraffin coated magnesium sulphate monohydrate 1 wt% protease 1 wt% amylase

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Table 1

Tea scale cleaning / silver corrosion protection Dishwasher: Bosch S 712 Tea: 1 = no cleaning

Dosage: 30 g 10 = optimal cleaning

Program: 65 ° C, universal Silver: 0 = no overlap

Further, machine dishwashing agents were prepared having the following compositions (see Table 2). The compounds A - E were used as silver corrosion protection measures:

A: V2O4 / V ^ O5 B: TiOSO ₄ C: COSO4 D: Ce (NO3) 3 E: Na2S2O3 x 5H2O

Table 2 (all data in% by weight)

1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 11 soda - 27 8 - 26 8 - 26 8 - sodium bicarbonate - - 31 - - thirty - - thirty - sodium disilicate 35 twenty - 35 twenty - 35 twenty - 34 trisodium 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 sodium percarbonate - 10 10 - 10 10 - 10 10 -

177 936 continued, table 2 continued

1 2 3 4 5 6 7 8 9 10 11 sodium percarbonate - 10 10 - 10 10 - 10 10 - sodium perborate monohydrate 7 - - 7 - - 7 - - 7 TAED 2 3 2 2 3 2 2 3 2 2 C12-C14 fatty alcohol ethoxylate (2EO) (Dehydol LS2 from Henkel) 1 0.75 1 1 0.75 1 1 0.75 1 1 C8-C10-alkyl oligoglucoside (APG 225 from Henkel) 1 0.75 1 1 0.75 1 1 0.75 1 1 protease 1.5 1 1 1.5 1 1 1.5 1 1 1.5 amylase 1.5 1 1 1.5 1 1 1.5 1 1 1.5 silver corrosion protection agents (AND) (B) (C) (D) (E) (AND) (B) (C) (D) (E) A-E 1 1 1 1 2 2 2 2 3 3 pH value of a 1% aqueous solution 10.5 11 9.5 10.5 11 9.5 10.5 11 9.5 10.5 11 12 13 14 15 16 17 18 19 twenty soda 26 8 - 25.5 8 - 26 7 - 26 sodium bicarbonate - thirty - - 29 - - 29 - - sodium 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 by BASF) 10 - 10 10 - 10 10 - 9 10 sodium percarbonate 10 10 - 10 10 - 10 10 - 10 sodium perborate monohydrate - - 7 - - 7 - - 7 - TAED 3 2 2 3 2 2 3 2 2 3 Fatty alcohol ethoxylate (Dehydol LS2 from Henkel) 0.75 1 1 0.75 1 1 0.75 1 1 0.75 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 amylase 1 1 1.5 1 1 1.5 1 1 1.5 1 silver corrosion protection agents (AND) (B) (C) (D) (E) (AND) (B) (C) (D) (E) A-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

All silver spoons rated 0-1, that is, "no overlap to very little overlap". In addition, formulations 1-20 against bleachable soils, such as tea, showed excellent cleaning performance.

Identical compositions, but each time without A-D silver corrosion protection agent, performed very well against bleachable stains, but on silver spoons they caused color changes from yellow to purple (rating: 2-4).

Electrochemical measurements

Preparation of samples:

Instead of silver cutlery, silver wire (d = 2 mm, 99.99%) was used as the test material for testing. 10 cm long pieces were cut from this wire, and a part of the sample to be immersed in the measuring solution was ground with SiC sandpaper (grain size 600). The samples were then rinsed well with water twice

Distilled and possibly adhering grinding residues were wiped with a hair-free cloth. This procedure was possibly repeated several times until a sample with a flawless appearance was obtained. After the samples were ground, they were immediately used for measurement to prevent the silver metal from reacting with the laboratory air. The effective surface area of the sample immersed in the solution was 0.70 cm2.

Electrolytes and electrodes:

The experiments were performed in a duran glass cell. The above-mentioned silver wires (A = 0.70 cm2) were used as measuring electrodes. The counter electrode was a gold plate (99.99%) with an area of 1 cm2. A Hg / HgO / 0.1 M NaOH electrode was selected as a comparative electrode based on alkaline electrolyte solutions and connected to the electrolytes via a Haber-Luggin capillary. Measurements were carried out using a 5 g / l detergent solution in 16 ° d hard tap water with a salt load of about 600 mg (dry residue).

When preparing the cleaning solution, the low-alkaline base product (see above) was first dissolved and the solution was heated to a temperature of 65 ° C. The bleach and the bleach activator and / or the silver corrosion protection agent were added immediately prior to measurement. Then the electrochemical measurement was carried out. During the electrochemical experiments, the temperature of the electrolyte solutions was maintained at 65 ° C and flushed with air.

Apparatus and determination of measurement curves:

In order to determine the voltage of the current, the potential of the electrodes was increased at a constant rate, starting from - 0.62 V in relation to the reference hydrogen electrode (SHE). After a total increase of 1.1 V, the potential was then lowered at the same rate. For this, a standard potentiostat was used, consisting of a self-excitation amplifier, a differential amplifier, an adder and an impedance transformer and a function generator (Prodis 16 by Intelligent Controls CLZ GmbH).

Results:

The corrosion properties were characterized on the basis of the current voltage curves. Essential information was obtained from the zero crossing of the current voltage curve (the rest potential, which is also determined by itself without the influence of the external potential) and the slope of the curve at the zero crossing (inverse polarization resistance) E. Heitz, R. Henkhaus, A. Rahmel, "Korrosionskunde im Experiment" Verlag Chemie (1983), page 31 ff; H. Kaesche, "Die Korrosion der Metalle", 2nd edition, Springer Verlag (1979), page 117 et seq. In this case, by adding a silver corrosion protection agent, the zero crossing potential is shifted to lower values and the slope is reduced. As a result of the addition of a silver corrosion protection agent, silver corrosion significantly decreased, which was also confirmed by electrochemical measurements.

177 936

The composition of the cleaning agent Zero crossing position E (mV) (SHE) Zero crossing slope di / DE (mA / V) + + basic product (87%) 12% percarbonate 1% TAED 435 25 + + basic product (87%) 12% percarbonate 1% silver corrosion protection agent 360 0.3 + + + basic product (86.5%) 12% percarbonate 1% TAED 0.5% silver corrosion protection agent 405 7 + + + basic product (86%) 12% percarbonate 1% TAED x) 1% silver corrosion protection agent 375 0.6

^χ ) Silver corrosion protection agent: manganese sulphate monohydrate

177 936

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Claims (12)

Patent claims 1. Low-alkaline machine dishwashing agent, a 1% by weight solution of which has a pH of 8-11.5, preferably 9-10.5, containing 15-60% by weight, preferably 30-50% by weight, of a water-soluble builder. 5-25% by weight, preferably 10-15% by weight of bleaching agent based on oxygen, 1-10% by weight, preferably 2-6% by weight of an organic group containing O or N- (C, -C ₁₂₎ -acyl activator means % of bleaching agent, 0.1-5% by weight, preferably 0.5-2.5% by weight of the enzyme in each case based on the total agent, and a silver corrosion protection agent, characterized in that the silver corrosion protection agent comprises at least partially water-soluble metal salts and / or metal complex compounds selected from the group such as salts and / or complexes of manganese, titanium, zirconium, hafnium, vanadium, cobalt, cerium, the metals of which are in one of the oxidation states II, III, IV, V or VI in an amount from 0.05 to 6% by weight, based on the whole inside it. 2. The agent according to claim The method of claim 1, characterized in that the metal salts and / or metal complex compounds are selected from the group consisting of MnSO4 Mn (II) citrate, Mn (II) stearate, Mn (II) acetylacetonate, Mn (II) - [1-hydroxyethane- 1,1-diphosphonate], V ₂ O5, V ₂ O4, VO ₂ , TiOSO 4, K ₂ TiF ₆ , K.2ZrF ₆ , CoSOa, Co (NC> 3) 2, CeCNCl 2. 3. The agent according to claim The method of claim 1, wherein the metal salt is MnSO4. 4. The agent according to claim 1 2. A method according to any of the preceding claims, characterized in that it contains inorganic redoxactive substances in an amount of 0.2-2.5% by weight, based on the total agent. 5. The agent according to claim 1 The process of claim 1, 2 or 3, characterized in that a salt of citric acid, preferably sodium citrate, is present as the water-soluble builder. 6. The agent according to p. A method as claimed in any one of the preceding claims, characterized in that the oxygen-based bleach is a percarbonate salt, preferably sodium percarbonate. 7. The agent according to p. A method as claimed in any one of the preceding claims, characterized in that the organic, O- or N-C 1-6 acyl bleach activator is N, N, N ', N''tternucetylethylenediamine (TAED). 8. The agent according to claim 1 A process as claimed in any one of the preceding claims, characterized in that the enzyme is amylase and / or protease. 9. The agent according to claim 1 An alkali carrier system consisting essentially of carbonate and bicarbonate, preferably sodium carbonate and sodium bicarbonate, as claimed in any one of the preceding claims, additionally comprising up to 60 wt.%, Preferably 10-40 wt.%, Based on the total agent, of an alkali carrier system. 10. The agent according to claim 1 A method as claimed in any one of the preceding claims, characterized in that it additionally comprises up to 5% by weight, preferably up to 2% by weight, based on the total agent, of surfactants, preferably low-foaming nonionic surfactants. 11. The agent according to claim 1 In the form of tablets. 12. An agent according to claim 1 The formulation of any of the preceding claims, in the form of tablets, powder or granules and having a bulk density of 750-1000 g / l.