EP0876465A1

EP0876465A1 - Dishwasher detergent

Info

Publication number: EP0876465A1
Application number: EP96934751A
Authority: EP
Inventors: Rainer Sorg; Willi Buchmeier; Peter Jeschke; Jürgen Härer; Christian Nitsch
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1995-10-27
Filing date: 1996-10-18
Publication date: 1998-11-11
Anticipated expiration: 2016-10-18
Also published as: ES2146417T3; DE19540087A1; DE59604975D1; EP0876465B1; WO1997016520A1

Abstract

When water-soluble inorganic redox-active metal compounds are used as silver corrosion protection agents in dishwasher detergents, it is necessary to prevent discoloration of decorative patterns and plastic parts. This has been achieved by using water-soluble inorganic ionic fluorine compounds.

Description

"Dishwashing liquid"

The invention is in the field of machine dishwashing detergents and relates to the use of an active ingredient combination for preventing tarnishing of silver or silver-plated washware.

In the mechanical cleaning of silverware, problems repeatedly arise in the form of tarnishing and discoloration of the silver surfaces. Silver can react here to sulfur-containing substances that 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 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. Furthermore, active chlorine-containing cleaners, due to their generally high pH of more than 12, cause less tarnishing of silver due to electrochemical reasons because of a passivation of the silver surface.

However, the problem of silver tarnishing became a topical issue when active oxygen compounds, such as sodium perborate or sodium percarbonate, were used as an alternative to the active chlorine compounds. which serve to remove bleachable soiling, such as, for example, tea stains / tea deposits, coffee residues, dyes from vegetables, lipstick residues and the like.

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. In particular, the low pH value results in a significantly lower passivation of the silver surface. During machine rinsing, these agents release 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 the actual bleaching agent per (acetic) acid is formed even at low temperatures, thus achieving a good bleaching effect. Under these changed rinsing conditions, not only sulfidic deposits, but preferably oxidic deposits on the silver surfaces due to the oxidizing attack of the intermediately formed peroxides or the active oxygen, are formed in the presence of silver. Chloride deposits can also form under high salt loads. The tarnishing of the silver is also reinforced by higher residual water hardness during the cleaning cycle.

Avoiding silver corrosion, i. H. 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. Additives such as benzotriazole and iron (III) chloride are recommended as tarnish preventers. 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.

In WO94 / 26859, which goes back to the applicant, it is proposed to add inorganic redox-active substances, in particular salts or complex compounds, of certain metals among their manganese to prevent silver corrosion. The agents produced in this way are notable for their outstanding effectiveness and have proven themselves in practice. Under unfavorable conditions, however, certain color decorations, such as those used on drinking glasses, or even plastic objects that are frequently rinsed, can be changed in color or deposits can be applied. At least when using manganese sulfate, such deposits are colored brown and are therefore not accepted by the consumer.

From European patent application 288812 it is known that the corrosion of silicate surfaces which have arisen from molten silicates can be largely prevented by using fluorine compounds which are at least slightly soluble in the aqueous medium. Alkali or ammonium fluorides or aluminum hexafluoride or tin tetrafluoride are mentioned, but also fluorosilicates and fluorophosphate. Contrary to common usage, corrosion in the sense of this citation should be understood to mean the build-up of SiO 2 -containing deposits from silicate-rich detergents on such surfaces. Surprisingly, it has now been found that such compounds counteract the deposits and decor discoloration mentioned when they are used together with the redox-active inorganic substances described in WO94 / 26859.

The invention therefore relates to the use of a combination of water-soluble, inorganic redox-active metal compounds and inorganic, water-soluble fluorine compounds in machine dishwashing detergents to prevent silver corrosion and discoloration of the decor.

The word "corrosion" is to be interpreted in its broadest meaning in chemistry. In particular, "corrosion" should stand for every visually just noticeable change in a metal surface, here silver, be it for example a selective discoloration, be it e.g. B. a large start-up. In the context of this application, corrosion relates only to the corrosion of metals, not to the corrosion of surfaces which have arisen from molten silicates. Such areas are generally not attacked by lower alkaline agents.

"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.

However, the salts or complex compounds of certain metals are particularly suitable. The use of metal salts and / or metal complexes is preferably selected from the group of transition elements of the periodic table, in particular manganese, titanium, zirconium, hafnium, vanadium, cobalt and cerium salts and / or complexes to prevent silver corrosion, the metals being in one of the oxidation states II, III, IV, V or VI. The common definition for "oxidation level" in chemistry is given, for example, 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 central atom is one of the above Metals in one of the above Oxidation levels. The ligands are neutral molecules or anions that are monodentate or multidentate; the term "ligand" in the sense of the invention is e.g. in "Römpp Chemie Lexikon, Georg Thieme Verlag Stuttgart / New York, 9th edition, 1990, page 2507" explained in more detail. 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 e.g. Citrate, acetylacetonate or 1-hydroxyethane-1,1-diphosphonate.

Particularly preferred metal salts and / or metal complexes are selected from the group MnSO 4, Mn (II) citrate, Mn (II) stearate, Mn (II) acetylacetonate, Mn (II) - [l-hydroxyethane-l, l diphosphonate], salts of acids of vanadium, based on V2O5, V2O4, VO2 (here: called vanadates), Ti0S04, C0SO4, Co (N03) 2, Ce (N03) 3 and mixtures thereof. MnS04 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 S03 production (contact process) is suitable, as well as the titanyl sulfate, T1OSO4, formed by diluting a Ti (Sθ4) 2 * solution.

The inorganic redox-active substances, in particular metal salts or metal complexes, are preferably coated, i.e. 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 to the material to be coated in a molten state, e.g. by throwing finely divided material to be coated in a continuous stream through a likewise continuously generated spray zone of the molten coating material. 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 ideally be in the range between 45 ° C. and 65 ° C. and preferably in the range 50 ° C. to 60 ° C. for most applications.

Inorganic, water-soluble, ionic fluorine compounds from the class of salts or complex salts which release fluoride ions under the conditions of automatic dishwashing can be used as fluorine compounds. Salts of hydrofluoric acid or hexafluorosilicic acid or mono-, di- or pentafluorophosphoric acid are particularly suitable.

These are, in particular, the fluorides of the alkali salts such as sodium or potassium, ammonium fluoride, magnesium fluoride and complex fluorides such as magnesium hexafluorosilicate, sodium hexafluorosilicate, potassium hexafluorosilicate, sodium hexafluorosilicate, ammonium hexafluorosilicate. Fluorophosphates of alkali metals or ammonium are also suitable. Preferred among these compounds are the hexafluorosilicate, in particular sodium or magnesium hexafluorosilicate. It is also possible Use of aluminum hexafluoride or tin tetrafluoride. However, these are

Substances not preferred. The fluorine compounds mentioned are in

Quantities of 0.1 to 6% by weight are used, preferably 0.1 to 5 and in particular 0.2 to 2.5% by weight, based on the total mixture.

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- (Cj-Ci2) acyl group-containing bleach activator, 0.1 to 5 wt .-%, preferably 0.5 to 2.5 wt .-% of an enzyme, in each case based on the total agent, and Silver corrosion protection agent, an inorganic redox-active substance being contained as the silver corrosion protection agent. Particularly suitable are metal salts and / or metal complexes selected from the group consisting of manganese, titanium, zirconium, hafnium, vanadium, cobalt, cerium salts and / or complexes, the metals being in one of the oxidation states II, III , IV, V or VI are present.

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 -C-Ci2 acyl group, preferably the acetyl group, to which a 0 or N atom contained in the substance is bound, and the perhydrolysis of which gives C 1 -C 2 -alkanoic acids, preferably peracetic acid.

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 and NTA and their derivatives.

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, citric acid may also be present. Sodium perborate mono- and tetrahydrate or sodium percarbonate are primarily considered as oxygen-based bleaches. The oxygen-based bleach is therefore preferably a percarbonate salt, especially 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, 0- or N- (-C-Ci2) acyl group-containing bleach activators, such as PAG (pentaacetylglucose), DADHT (1,5-diacetyl-2,4-dioxo-hexa- hydro-l, 3,5-triazine) are used as bleach activators ) and ISA (isatoic anhydride), 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; Optimase ( ^R ) -M-440, Optimase ( ^R ) -M-330, Opticlean ( ^R ) -M-375, Opticlean ( ^R ) -M-250 from Solvay Enzymes; Maxacal ( ^R )

CX 450,000, Maxapem ( ^R ) from Gist Brocades; Savinase ( ^R ) 4.0 T, 6.0 T, 8.0 T from Novo; Esperase ( ^R ) T from 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 Gist Brocades; 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.

If desired, the agents according to the invention additionally contain the alkali carriers contained in customary low-alkaline machine dishwashing detergents, such as. B. alkali silicates, alkali carbonates and / or alkali hydrogen carbonates. The alkali carriers commonly used include carbonates, hydrogen carbonates and alkali silicates with a SiO 2 / M2O molar ratio (M = alkali atom) of 1.5: 1 to 2.5: 1. Alkali silicates can be used in amounts of up to 30% by weight. -%, based on the total Means to be included. The use of the highly alkaline metasilicates as alkali carriers is preferably avoided. The alkali carrier system preferably used in the agents 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 to 40% by weight. , based on the total agent, 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 preferably include C12-C18 alkyl polyethylene glycol polypropylene glycol ethers, 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. 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 Cβ-C ^ -alkylpolyglucosides with a degree of polymerization of about 1 - 4 (e.g. 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. A bleached quality should be used, since otherwise brown granules are formed. 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, 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 the inventive cleaning compositions in tablet form is preferably such procedure is to shear-mixing all ingredients in a Mi¬ together and the mixture using conventional Tablet¬ tenpressen, for example eccentric presses or rotary presses with press pressures in the range of 200 ^• 10 * - * Pa up 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 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 constituents of the dishwasher detergent, 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 Decay 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. 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 inorganic 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 special embodiment, it may be expedient in the production of fine granules to further stabilize and level by powdering the surface of the granules formed adjust. 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 3 to 6 g / 1.

The washing program of a household dishwasher is generally supplemented and ended by a few intermediate rinsing cycles with clear water and a rinsing cycle with a common rinse aid following the cleaning cycle. After drying you get not only a completely clean and hygienically perfect tableware, but above all also bright silver cutlery items.

example

A) Preparation of the cleaner

A low-alkaline cleaner for household dishwashers was produced, the weight percent solution of which in distilled water has a pH of 9.5. They were used for this

56.0% by weight of trisodium citrate dihydrate

36.1% by weight sodium bicarbonate 6.1% by weight sodium carbonate, anhydrous

1.8 wt .-% of a mixture of nonionic surfactants from Cβ- to Cir _j -Alkyloligo- glucoside and Cj2- to Ci4 fatty alcohol 2E0 ethoxylate in a ratio of 1: 1.

The base product obtained in this way was disassembled into a dishwashing detergent in the following manner: 81% by weight base product 12% by weight sodium percarbonate

4% by weight bleach activator TAED

2% by weight of manganese sulfate monohydrate coated with paraffin (1.5% by weight of manganese salt, based on the recipe) remainder enzymes, especially protease and amylase.

With the product obtained in this way, rinsing tests were carried out in a Bosch SMS 7082 machine at 65 ° C. (universal program) at a dosage of 30 g per washing program. The machine was fed with water of approx. 16 ° dH.

Decorative glasses were used as washware, which were printed on the one hand with high-bleach, low-melting colors or on the other hand with lead-free colors based on bismuth. The print showed red, blue, yellow, green and white color patches.

After 25 rinsing cycles, there were already strong brown discolorations in the white field.

The rinsing experiments were repeated using a second agent to which 3% by weight of magnesium hexafluorosilicate had been added. After 25 rinsing cycles, even white areas showed at most little discoloration.

Claims

claims

1. Use a combination of

- Water-soluble, inorganic redox-active metal compounds and

- Inorganic, water-soluble fluorine compounds in machine dishwashing detergents to prevent silver corrosion and discoloration of decor.

2. Embodiment according to claim 1, characterized in that the metal salts and / or metal complexes are selected from the group MnS04, Mn (II) citrate, Mn (II) stearate, Mn (II) acetylacetonate, Mn (II ) - [l-Hydroxyethane-l, l-diphosphonate].

3. Embodiment according to claims 1 and 2, characterized in that the inorganic, water-soluble, ionic fluorine compounds used are salts or complex salts which release fluoride ions under the conditions of automatic dishwashing, in particular aluminum or ammonium salts of hydrofluoric acid, hexafluorosilicic acid, of mono-, di- or pentafluorophosphoric acid.

4. Embodiment according to claims 1 to 3, characterized in that the inorganic, water-soluble, ionic fluorine compounds are used in amounts of 0.1 to 6 wt .-%.

5. Embodiment according to claims 1 to 4, characterized in that manganese sulfate is used as the water-soluble, inorganic, redox-active metal compounds.

6. Low-alkaline agent for machine cleaning of dishes, the weight percent solution of which has 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 one organic bleach activator containing 0- or N- (Cj-Ci2) acyl groups, 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 protection agents, characterized in that an inorganic, water-soluble redox-active metal compound is used as the silver corrosion protection agent and an inorganic, water-soluble, ionic fluorine compound is used to prevent decor discoloration.

7. The composition according to claim 6, characterized in that the metal salt ^is MnSθ4 *

8. Composition according to claims 5 to 7, characterized in that salts of hydrofluoric acid, hexafluorosilicic acid or fluorophosphoric acids with the alkali metals, ammonium or magnesium are used as fluorine compounds.

9. Composition according to claims 5 to 9, 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 ¬ tel, are included and that the inorganic, water-soluble, ionic fluorine compounds in amounts of 0.1 to 5 wt .-%, preferably in amounts of 0.2 to 2.5 wt .-%, are used.

10. Composition according to claims 5 to 9, characterized in that the water-soluble builder component is a salt of citric acid, preferably trisodium citrate and / or its dihydrate.

11. Agent according to claims 5 to 10, characterized in that the oxygen-based bleach is a percarbonate salt, preferably sodium percarbonate.

12. Composition according to claims 5 to 11, characterized in that the organic, 0- or N- (-C-Ci2) acyl group-containing bleach activator is N, N, N ', N'-tetraacetylethylenediamine (TAED).

13. Composition according to claims 5 to 12, characterized in that enzymes, in particular amylases, proteases and / or lipases, are used.