EP0697036B1 - Silver-corrosion protection agent (ii) - Google Patents

Abstract

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

Description

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

Even in the mechanical cleaning of silverware occur in practice problems in the form of tarnishing and discoloration of the silver surfaces on. Silver can be found here on sulfur-containing substances in the rinse water are dissolved or dispersed, because when cleaning Dishes in household dishwashers (HGSM) become food waste and with it u. a. also mustard, peas, egg and other sulfur-containing compounds introduced into the washing liquor. Even during machine washing much higher temperatures and the longer contact times with the sulfur-containing food residues favor compared to manual rinsing tarnishing silver. Due to the intensive cleaning process in the Dishwasher will also completely degrease the silver surface and thereby more sensitive to chemical influences.

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

However, the problem of tarnishing silver has become topical again, as an alternative to the active chlorine compounds active oxygen compounds, such as Sodium perborate or sodium percarbonate were used, which to remove bleachable stains, such as Tea stains / tea deposits, coffee residues, vegetable dyes, lipstick residues and the like serve.

These active oxygen compounds are mainly used in modern lower alkaline machine dishwashing detergents of the new generation of cleaners used with bleach activators. These modern means generally exist from the following function blocks: builder component (complexing agent / dispersant), Alkali carrier, bleaching system (bleach + Bleach activator), enzymes and wetting agents (surfactants).

On the changed recipe parameters of the new generation of active chlorine-free cleaners with lowered pH values and activated oxygen bleaching the silver surfaces are generally more sensitive. During the machine dishwashing these agents actually do that in the cleaning cycle bleaching agent free hydrogen peroxide or active oxygen. The bleaching Effect of active oxygen-containing cleaners is through bleach activators reinforced so that a good one even at low temperatures Bleaching effect is achieved. Forms in the presence of these bleach activators peracetic acid as a reactive intermediate. Among these changed Flushing conditions not only form sulfidic in the presence of silver, but through the oxidizing attack of the intermediates Peroxides or the active oxygen preferably oxidic coatings on the Silver surfaces. Chloride can also be present under high salt loads There are deposits. The tarnishing of the silver is also increased due to higher residual water hardness during the cleaning cycle.

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

From the British patent GB 1 131 738 are alkaline dishwashing detergents known as a corrosion inhibitor for silver benzotriazoles contain. In the American patent US 3 549 539 strong alkaline, machine-applicable dishwashing detergent described as an oxidizing agent Perborate with an organic bleach activator can contain. Additives, among other things, are used as anti-tarnish agents. Likewise recommended by benzotriazole and also iron (III) chloride. In doing so pH values of preferably 7-11.5. In the European patent specifications EP 135 226 and EP 135 227 become weakly alkaline, mechanically applicable dishwashing detergent containing peroxy compounds and Activators described as silver protection agents, among others. Benzotriazoles and May contain fatty acids. Finally, is from the German published application DE 41 28 672 discloses that peroxy compounds by addition known organic bleach activators are activated in strong alkaline cleaning agents prevent silver parts from tarnishing.

Surprisingly, it has now been found that organic redox-active substances, especially those commonly used in oxidation dyes not previously described as a silver corrosion inhibitor Coupler and / or developer compounds the corrosion of silver in mechanical Prevent dishwashers effectively.

The invention relates to the use of organic redox-active substances in dishwashing preparations as silver corrosion inhibitors, the organic redox-active substance being a coupler and / or developer compound, selected from the group of the diaminopyridines, aminohydroxypyridines, dihydroxypyridines, heterocyclic hydrazones, aminohydroxypyrimidines, dihydroxypyrimidines, tetraaminopyrimidines, tetraaminopyrimidines, tetraaminopyrimidines, and tetraaminopyrimidines , Diaminodihydroxypyrimidines, dihydroxynaphtalines, naphthols, hydroxyquinolines, aminoquinolines, the primary aromatic amines, the ortho, meta or para position a further free or substituted by C ₁ -C ₄ alkyl or C ₂ -C ₄ hydroxyalkyl groups hydroxy or have amino group, and the di- or trihydroxybenzenes.

The word "corrosion" is in its broadest use in chemistry To interpret meaning, in particular "corrosion" is meant for everyone visually barely noticeable change in a metal surface, here silver stand, be it z. B. a selective discoloration, be it z. B. a large area Start up.

"Organic redox-active substances" are those organic substances accessible to easily reversible oxidation and / or reduction are. Typical complexing agents such as e.g. B. EDTA or hydroxyethane diphosphonic acid and related compounds not under this definition.

The developer used according to the invention to prevent silver corrosion and coupler compounds are common in oxidation colorants substances used from the above groups. Examples for such developer and coupler connections there are e.g. in "Venkataraman, The Chemistry of synthetic dyes, Vol. V, Academic Press New York / London, 1971, pages 478-495 ", as well as in the literature cited there. The developers are particularly suitable for preventing silver corrosion. or coupler compounds selected from the group p-hydroxyphenylglycine, 2,4-diaminophenol, 5-chloro-2,3-pyridinediol, 1- (p-aminophenyl) morpholine, Hydroquinone, pyrocatechol, hydroxyhydroquinone, gallic acid, Phloroglucin, pyrogallol.

The organic redox-active substances are preferably coated, i.e. completely with a waterproof, but at the cleaning temperatures easily soluble material coated for their premature decomposition or To prevent oxidation during storage. Preferred coating materials, those according to known processes, such as the melt coating process according to Sandwik from the food industry, are paraffins, micro waxes, Waxes of natural origin such as carnauba wax, candella wax, Beeswax, higher melting alcohols such as hexadecanol, Soaps or fatty acids. The coating material is solid at room temperature applied to the material to be coated in the molten state, e.g. by finely divided material to be coated in continuous Current through a spray zone of the melted, which is also continuously generated Coating material is thrown. The melting point must be like this be chosen so that the coating material during subsequent use the silver corrosion inhibitor in the dishwasher easily dissolves or melts quickly. The melting point should therefore be for most applications ideally in the range between 45 ° C and 65 ° C and are preferably in the range from 50 ° C. to 60 ° C.

The organic redox-active compounds described above are particularly suitable However, substances to prevent silver corrosion when in lower alkaline Cleaners for machine cleaning of dishes included are. This is all the more surprising than these silver corrosion inhibitors in effect not by the presence of usually in low alkaline cleaners contain oxygen-based bleaches be affected.

Another subject of the invention are 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 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, wherein as a silver corrosion protection agent a coupler and / or developer compounds selected from the group of Diaminopyridines, aminohydroxypyridines, dihydroxypyridines, heterocyclic hydrazones, aminohydroxypyrimidines, dihydroxypyrimidines, tetraaminopyrimidines, triaminohydroxypyrimidines, diaminodihydroxypyrimidines, dihydroxynaphtalines, naphthols, hydroxyquinolines, aminoquinol ine, the primary aromatic amines which have in the ortho, meta or para position a further free or substituted by C ₁ -C ₄ alkyl or C ₂ -C ₄ hydroxyl groups hydroxy or amino group and the di or Trihydroxybenzenes is included.

Preferred dish detergents contain coupler and / or developer compounds selected from the group p-hydroxyphenylglycine, 2,4-diaminophenol, 5-chloro-2,3-pyridine, 1- (p-aminophenyl) morpholine, hydroquinone, Catechol, hydroxyhydroquinone, gallic acid, phloroglucinol, pyrogallol as well as their mixtures.

The organic redox-active substances are preferably in the inventive Average in a total amount of 0.05 to 6 wt .-%, preferably 0.2 to 2.5 wt .-%, based on the total agent.

In principle, all builders commonly used in machine dishwashing detergents are suitable as water-soluble builder components, eg. B. polymeric alkali phosphates, which may be in the form of their alkaline neutral or acidic sodium or potassium salts. Examples include: tetrasodium diphosphate, disodium dihydrogen diphosphate, pentasodium triphosphate, so-called sodium hexametaphosphate and the corresponding potassium salts or mixtures of sodium hexametaphosphate and the corresponding potassium salts or mixtures of sodium and potassium salts. 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 a co-builder. For example, polyacrylic acids and copolymers of maleic anhydride and acrylic acid and 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 42 28 786.3) 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 hydroxycarboxylic 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. As sodium citrate come anhydrous Trisodium citrate or preferably trisodium citrate dihydrate in Consideration. Trisodium citrate dihydrate can be fine or coarse crystalline Powder can be used. Depending on the ultimately in the pH set according to the invention can also be adjusted to citrate corresponding acids are present.

Sodium perborate mono- and tetrahydrate or sodium percarbonate. The stake Sodium percarbonate has advantages because it is particularly cheap affects the corrosion behavior on glasses. The oxygen-based bleach is therefore preferably a percarbonate salt, in particular Sodium percarbonate. Since active oxygen only at elevated temperatures of only its full effect unfolds to be activated in the Dishwasher so-called bleach activators used. As organic bleach activators serve e.g. PAG (pentaacetyl glucose), DADHT (1,5-diacetyl-2,4-dioxo-hexahydro-1,3,5-triazine) 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 phosphonates, borates or Metaborates and metasilicates as well as magnesium salts such as magnesium sulfate 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 Ibis; 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 Ibis; Lipases such as Lipolase ^(R) 30 T from Novo; Cellulases such as Celluzym (R) 0.7 T from Novo Nordisk. The dishwashing detergents preferably contain proteases and / or amylases.

The agents according to the invention preferably additionally contain the alkali carriers contained in customary low-alkaline machine dishwashing agents, such as, for. B. alkali silicates, alkali carbonates and / or alkali hydrogen carbonates. The alkali carriers usually used include carbonates, hydrogen carbonates and alkali silicates with a molar ratio SiO ₂ / M ₂ O (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, may 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 hydrogen carbonate, preferably sodium carbonate and hydrogen carbonate, in an amount of up to 60% by weight, preferably 10 to 40% by weight, based on the total agent, is included. Depending on which pH value is ultimately desired or set, the ratio of carbonate and bicarbonate used varies; 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 serve to better detach 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. 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 C ₁₂ -C ₁₈ alkyl polyethylene glycol polypropylene glycol ethers, each containing up to 8 moles of ethylene oxide and propylene oxide units in the molecule. But you can also use other, known as low-foam nonionic surfactants, such as. B. C ₁₂ -C ₁₈ alkyl polyethylene glycol polybutylene glycol ether, each with up to 8 moles of ethylene oxide and butylene oxide units in the molecule, end-capped alkyl polyalkylene glycol mixed ethers and the foaming but ecologically attractive C ₈ -C ₁₄ alkyl polyglucosides with a degree of polymerization of about 1 - 4 ( e.g. APG ^(R) 225 and APG ^(R) 600 from Henkel) and / or C ₁₂ -C ₁₄ 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 C ₆ -C ₁₄ ). 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, them up to 6% by weight, preferably about 0.5 to 4% by weight of one foam-suppressing compound, preferably from the group of silicone oils, Mixtures of silicone oil and hydrophobicized silica, paraffin oil / Guerbet alcohols, Paraffins, hydrophobized silica, the bisstearic acid amides and other other well known commercially available defoamers be added. Other optional additives are e.g. B. Perfume oils.

The dishwashing detergents according to the invention are preferably in powder form, granular or tablet-like preparations that are in themselves customary, for example by mixing, granulating, roller compacting and / or can be produced by spray drying.

For the preparation of cleaning agents according to the invention in tablet form, the procedure is preferably such that all constituents are mixed with one another in a mixer and the mixture by means of conventional tablet presses, for example eccentric presses or rotary presses, with pressures in the range from 200 × 10 ⁵ Pa to 1 500 10 ⁵ Pa pressed. In this way, unbreakable tablets are obtained with a flexural strength of normally more than 150 N that are sufficiently quickly soluble under conditions of use. 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 production of machine dishwashing detergents in the form of non-dusting, storage-stable free-flowing powders and / or granules with high Bulk densities in the range from 750 to 1000 g / l are characterized by that in a first stage of the process with the builder components at least a proportion of liquid mixture components while increasing the Bulk density of this premix is mixed and subsequently - if desired after intermediate drying - the other components of the dishwasher detergent, including organic redox-active substances, combined with the premix obtained in this way.

As a possible alkali carbonate content the alkalinity of the product strongly influenced, the intermediate drying must be carried out so that the Disintegration of sodium bicarbonate to sodium carbonate as low as possible (or at least as constant as possible). An additional through drying The resulting sodium carbonate portion should namely in the formulation of Granulate recipe are taken into account. Low drying temperatures not only counteract sodium bicarbonate decay, but also also increase the solubility of the granulated detergent in the Application. It is therefore advantageous when drying a supply air temperature that on the one hand as low as possible to avoid bicarbonate decay should be and which, on the other hand, must be as high as necessary to produce a product with good storage properties. Drying is preferred an inlet air temperature of approx. 80 ° C. The granules themselves shouldn't be on Temperatures above about 60 ° C are heated. In the first part of the The builder is usually mixed with at least a mixing process another component of the dishwashing detergent with the liquid components acted upon. For example, a preliminary stage can be considered, in which the builder component in admixture with perborate with the liquid non-ionic surfactants and / or the solution of the fragrances and is intimately mixed. Below are the remaining components added and worked through the entire mixture in the mixing device and homogenized. The use of additional amounts of liquid, in particular the use of additional water is here in the Usually not required. The resulting mixture of substances then lies as free-flowing, dust-free powder of the desired high bulk density about in the range of 750 to 1000 g / l.

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

In a particular embodiment, it can be used in the manufacture of fine Granules may be useful by powdering the surface of the formed Granules a further stabilization and leveling adjust. Small amounts of water glass powder are particularly suitable for this or powdered alkali carbonate.

The funds to be used can be found both in household dishwashers as used in commercial dishwashers. The addition takes place by hand or using suitable dosing devices. The Application concentrations in the cleaning liquor are about 2 to 8 g / l, preferably 2 to 5 g / l.

The rinse program is generally followed by some on the cleaning cycle following intermediate rinse cycles with clear water and a rinse cycle with supplemented with a common rinse aid and finished. After drying you don't just get a completely clean and hygienic one flawless crockery, but above all bright silver silver cutlery.

Examples

Silver spoons (type WMF, hotel cutlery, form Berlin) were cleaned with a silver cleaner, degreased with petrol 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 (1) 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 = whole / 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 Tables 1 to 3.

At the same time, the removal of tea stains on porcelain was assessed. Here the rating was between 0 and 10 with 0 = no tea removal and 10 = complete tea removal; Values in the lower right part of Tables 1 to 3. (1) Soiling composition: Ketchup: 25 g Mustard (extra hot) 25 g Gravy: 25 g Potato starch: 5 g Benzoic acid: 1 g Egg yolk: 3 pieces Milk: 1/2 l Margarine: 92 g City water: 608 ml

Production of tea soiling

16 l of cold city water (16 ° d) are briefly heated to boiling in a water treatment boiler. 96 g of black tea are drawn in the nylon net with the lid closed for 5 minutes and the tea is transferred to a diving apparatus with heating and agitator.
60 teacups are dipped into the prepared tea brew 25 times at one-minute intervals at 70 ° C. The cups are then removed and placed on a tray with the opening facing down to dry.

Detergent composition

56,0 %

Trinatriumcitrat-dihydrat

36,1 %

Natriumhydrogencarbonat

6,1 %

Natriumcarbonat, wasserfrei

1,8 %

Gemisch nichtionischer Tenside aus APG 225 (C₈-C₁₀-Alkyloligoglucosid) und Dehydol^(R) LS2 (C₁₂-C₁₄-Fettalkohol-2EO-ethoxylat) (1:1)

The following low-alkaline base product was first prepared, whose 1% by weight solution in distilled water gave 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 (C ₈ -C ₁₀ alkyl oligoglucoside) and dehydol ^(R) LS2 (C ₁₂ -C ₁₄ fatty alcohol 2EO ethoxylate) (1: 1)

81 - 86 Gew.-%

Grundprodukt

12 Gew.-%

Natriumpercarbonat

0 - 10 Gew.-%

TAED

0 - 3 Gew.-%

Brenzcatechin, Gallussäure oder Hydrochinon

1 Gew.-%

Protease

1 Gew.-%

Amylase

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

81 - 86% by weight

Basic product

12% by weight

Sodium percarbonate

0 - 10% by weight

TAED

0 - 3% by weight

Pyrocatechol, gallic acid or hydroquinone

1% by weight

Protease

1% by weight

Amylase

A: p-Hydroxyphenylglycin

B: 2,4-Diaminophenol

C: 5-Chlor-2,3-pyridindiol

D: 1-(p-Aminophenyl)-morpholin

E: 2-Hydroxy-4-aminopyrimidin

F: 2,4-Dihydroxy-5-methylpyrimidin

Machine dishwashing detergents of the following compositions were also prepared (see Table 4). The compounds A - F were used as silver corrosion protection agents:

A: p-Hydroxyphenylglycine

B: 2,4-diaminophenol

C: 5-chloro-2,3-pyridinediol

D: 1- (p-aminophenyl) morpholine

E: 2-hydroxy-4-aminopyrimidine

F: 2,4-dihydroxy-5-methylpyrimidine

The silver spoons were consistently rated 0 to 1, i.e. "no to very weak Tarnish ", rated. Identical compositions, however each without silver corrosion inhibitor A - D caused on silver spoons Yellow to violet colors (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 ground with SiC abrasive paper (600 grit). The samples were then rinsed well with double-distilled water and any adhering grinding residues were wiped off with a lint-free cloth. This process was repeated several times, if necessary, until the sample optically left a perfect impression. After grinding the samples, they were used immediately for the measurement in order to pre-empt a reaction of the metallic silver with the laboratory air. The effective sample surface immersed in the solution was 0.70 cm ² .

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 counter electrode consisted of a gold plate (99.99%) with an area of 1 cm ² . A Hg / Hg0 / 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 / l cleaner in tap water of 16 ° d and a salt load of approx. 600 mg (dry residue).

When preparing the cleaning solutions, the lower alkaline solution was used first Base product (see above) dissolved and the solution heated to 65 ° C. Directly Before the measurement, the bleach and the bleach activator and / or the silver anticorrosive agent is added. Then the electrochemical measurement. During the electrochemical experiments the electrolyte solutions are heated to 65 ° C and flushed with air.

Equipment and recording of the measurement curves:

The electrode potential was used to record the current-voltage curves from - 0.62, V based on the standard hydrogen electrode (SHE), increased at a constant speed. After a total increase The potential then became 1.1 V at the same speed degraded. A standard potentiostat consisting of positive feedback amplifier was used for this, Differential amplifier, adder and impedance converter, as well a function generator (Prodis 16 from Intelligent Controls CLZ GmbH).

Results:

The corrosion behavior was characterized using 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 an 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. Silver corrosion is also significantly reduced by the addition of silver corrosion protection agents, which can be measured electrochemically. Composition cleaner Position zero crossing E (mV) (SHE) Slope at zero crossing di / dE (mA / V) Basic product (86%)
+ 12% percarbonate + 2% hydroquinone 319 0.5

Claims (13)

1. The use of organic redox-active substances in dishwashing detergents as corrosion inhibitors for silver, characterized in that the organic redox-active substance is a primary and/or secondary intermediate selected from the group of diaminopyridines, aminohydroxypyridines, dihydroxypyridines, heterocyclic hydrazones, aminohydroxypyrimidines, dihydroxypyrimidines, tetraaminopyrimidines, triaminohydroxypyrimidines, diaminodihydroxypyrimidines, dihydroxynaphthalenes, naphthols, hydroxyquinolines, aminoquinolines, primary aromatic amines with another free or C_1-4-alkyl- or C_2-4-hydroxyalkyl-substituted hydroxy or amino group in the ortho, meta or para position and di- or trihydroxybenzenes.
2. The use claimed in claim 1, characterized in that the primary or secondary intermediate is selected from the group consisting of p-hydroxyphenylglycine, 2,4-diaminophenol, 5-chloro-2,3-pyridinediol, 1-(p-aminophenyl)-morpholine, hydroquinone, pyrocatechol, hydroxyhydroquinone, gallic acid, phloroglucinol, pyrogallol.
3. A low-alkali machine dishwashing detergent of which 1% by weight solutions have a pH value of 8 to 11.5 and preferably 9 to 10.5 and which contain 15 to 60% by weight and preferably 30 to 50% by weight of a watersoluble builder component, 5 to 25% by weight and preferably 10 to 15% by weight of an oxygen-based bleaching agent, 1 to 10% by weight and preferably 2 to 6% by weight of an organic bleach activator, 0.1 to 5% by weight and preferably 0.5 to 2.5% by weight of an enzyme, based on the detergent as a whole, and silver corrosion inhibitors, characterized in that a primary and/or secondary intermediate selected from the group of diaminopyridines, aminohydroxypyridines, dihydroxypyridines, heterocyclic hydrazones, aminohydroxypyrimidines, dihydroxypyrimidines, tetraaminopyrimidines, triaminohydroxypyrimidines, diaminodihydroxypyrimidines, dihydroxynaphthalenes, naphthols, hydroxyquinolines, aminoquinolines, primary aromatic amines with another free or C_1-4-alkyl- or C_2-4-hydroxyalkyl-substituted hydroxy or amino group in the ortho, meta or para position and di- or trihydroxybenzenes is present as the silver corrosion inhibitor.
4. A detergent as claimed in claim 3, characterized in that the primary or secondary intermediate is selected from the group consisting of p-hydroxyphenylglycine, 2,4-diaminophenol, 5-chloro-2,3-pyridinediol, 1-(p-aminophenyl)-morpholine, hydroquinone, pyrocatechol, hydroxyhydroquinone, gallic acid, phloroglucinol, pyrogallol.
5. A detergent as claimed in claims 3 to 4, characterized in that the organic redox-active substances are present in a quantity of 0.05 to 6% by weight and preferably in a quantity of 0.2 to 2.5% by weight, based on the detergent as a whole.
6. A detergent as claimed in claims 3 to 5, characterized in that the watersoluble builder component is a salt of citric acid, preferably sodium citrate.
7. A detergent as claimed in claims 3 to 6, characterized in that the oxygen-based bleaching agent is a percarbonate salt, preferably sodium percarbonate.
8. A detergent as claimed in claims 3 to 7, characterized in that the organic bleach activator is N,N,N',N'-tetraacetyl ethylenediamine (TAED).
9. A detergent as claimed in claims 3 to 8, characterized in that the enzyme is an amylase and/or protease.
10. A detergent as claimed in claims 3 to 9, characterized in that it additionally contains up to 60% by weight and preferably 10 to 40% by weight, based on the detergent as a whole, of an alkali carrier system consisting essentially of carbonate and hydrogen carbonate, preferably sodium carbonate and sodium hydrogen carbonate.
11. A detergent as claimed in claims 3 to 10, characterized in that it additionally contains up to 5% by weight and preferably up to 2% by weight, based on the detergent as a whole, of surfactants, preferably low-foaming nonionic surfactants.
12. A detergent as claimed in claims 3 to 11, characterized in that it is present in tablet form and is obtainable by mixing all its ingredients in a mixer and tabletting the resulting mixture in a tabletting press under pressures of 2·10⁷ Pa to 1.5·10⁸ Pa.
13. A detergent as claimed in claims 3 to 12, characterized in that it is present in the form of a powder or granules and has an apparent density of 750 g/l to 1000 g/l.