EP1648990A1

EP1648990A1 - Bleaching-action dishwasher detergent with improved yellowing resistance and process for its production

Info

Publication number: EP1648990A1
Application number: EP04763112A
Authority: EP
Inventors: Klaus Zimmermann; Harald Jakob
Original assignee: Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2003-07-30
Filing date: 2004-07-07
Publication date: 2006-04-26
Also published as: WO2005014768A1; DE10334725A1

Abstract

Bleaching-action solid dishwasher detergents comprising a bleaching agent containing active oxygen, a bleaching activator, a silver-anticorrosion agent as well as other conventional constituents, have according to the invention an improved yellowing resistance on storage if they contain particulate bleaching agents and/or particulate bleaching activators in each case in effectively coated form. Preferred detergents, in particular those in tablet form, contain both the bleaching agent as well as the bleaching activator in coated form.

Description

Bleac ing-Action Dishwasher Detergent with Improved Yellowing Resistance and Process for its Production

Description;

The present invention is aimed at bleaching-action dishwasher detergents in powder or granule form or in the form of compressed moulded articles such as tablets, with improved yellowing resistance, in which the detergent contains in substantially homogeneous distribution one or more particulate bleaching agents containing active oxygen, one or more particulate bleaching activators, at least one silver-anticorrosion agent as well as other conventional constituents such as builders, surfactants and enzymes . The invention is also aimed at a process for improving the yellowing resistance of dishwasher detergents .

Conventional dishwasher detergents contain one or more oxygen-based bleaching agents, one or more bleaching activators that in aqueous phase with the bleaching agent are capable of forming an organic peroxycarboxylic acid, inorganic and/or organic builders, and surfactants. Furthermore such detergents may contain one or more constituents from the classes of substances comprising enzymes, silver-anticorrosion agents, complex-forming agents, foam control agents, pH regulators, fragrances and colourants .

A particular problem of dishwasher detergents is that silver cutlery is tarnished to a greater or lesser extent. In order to solve this problem various solutions have been developed. According to DE 41 28 672 Al the tarnishing of silver cutlery can be avoided by using a strongly alkaline detergent without the addition of corrosion inhibitors. The high pH of such detergents is however a disadvantage since glassware and glazes may thereby be attacked.

DE 43 25 039 Al on the other hand discloses a mildly alkaline dishwasher detergent without silver-anticorrosion agent, in which the tarnishing of silver cutlery is avoided by the fact that the bleaching activator is present in an amount above the stoichiometric ratio with respect to^' the bleaching agent. This leads to an increased consumption of activator.

A further possible way of avoiding silver corrosion, i.e. the formation of sulfidic, oxidic or chloridic deposits on silver, consists in the use of silver-anticorrosion agents such as in particular benzotriazole and redox-active organic and/or inorganic substances; reference is made by way of example to DE 43 44 215 Al, WO 95/01416 as well as WO 97/03177.

Although the tarnishing of silver cutlery can be largely avoided by the use of silver-anticorrosion agents in dishwasher detergents containing an oxygen-based bleaching system with an optimised composition of the detergent, a discolouration, generally a yellowing, of these detergents occurs during storage, especially storage under damp and warm conditions, depending on their composition as well as on the form of use of such detergents. Such a discolouration is undesirable since the effectiveness of such detergents that discolour in this way is questioned by the customers. It is assumed that the discolouration is caused by a possible interaction, under the storage conditions, between the bleaching system and the silver- anticorrosion agents . Such an interaction and partial inactivation occurs in particular if the constituents of the detergent are in intimate contact with one another, for example in the form of tablets .

The undesired interaction is avoided in the tablet-type dishwasher detergents according to WO 97/03177 by the fact that the tablet consists of at least two layers, in which the silver-anticorrosion agent is not contained jointly in one layer together with the bleaching agent and the bleaching activator. Instead, in practice a first layer contains the bleaching agent and the silver-anticorrosion agent, and a second layer contains the bleaching activator. The disadvantage of such a formulation is the need to produce a two-layer tablet, which increases the technical complexity of their production.

EP-A 634 478 and, similarly, WO 95/01416 disclose dishwasher detergents that contain an oxygen-containing bleaching agent system, paraffin oil and at least one nitrogen-containing corrosion inhibitor. The bleaching agent system consists of a bleaching agent such as sodium perborate or sodium percarbonate, and a bleaching activator. Although powders, granules and tablets have been mentioned as application forms, the aforementioned problem of a discolouration of this special detergent during storage has obviously not been recognised. In the two previously mentioned documents it is also stated that, on account of the limited storage stability of sodium percarbonate, this is preferably used in coated form, a coating consisting of for example a mixed salt of sodium sulfate and sodium carbonate and a coating amount of preferably 1 to 10 wt.% being mentioned. Finally, it is also known from these documents that it is possible to spray bleaching agents with a dispersion containing the paraffin oil and/or the silver-anticorrosion agent, and to compact the mixture after drying and then mix it with the remaining constituents of the detergent. The tendency of these detergents to undergo yellowing was possibly reduced or avoided by the presence of the paraffin oil, although doubts exist as regards such a combination, particularly if the paraffin oil is located directly on the sodium percarbonate particles.

From DE-A 100 03 429 a detergent for dishwashers is known that consists of a first measured amount, termed base moulded article, that also contains a silver-anticorrosion agent, and a second measured amount that contains a bleaching system and is coated, inter alia by means of paraffin and/or polyethylene glycols, against premature dissolution. After the bleaching system has been effectively separated from the silver-anticorrosion agent by means of the coating, no yellowing occurs during storage. Although such a dishwasher detergent permits a controlled release of active constituent, nevertheless an increased technical expenditure is necessary for the production of the detergent. This document does not contain any information that the particulate bleaching agent and/or the particulate bleaching activator are used as such in coated form.

The object of the present invention is accordingly to provide a further dishwasher detergent that contains a bleaching agent, a bleaching agent activator and a silver- anticorrosion agent as well as conventional further constituents such as in particular builders and surface active components, that can be stored without yellowing. According to a further object the dishwasher detergent should also be available in the form of compressed moulded articles, such as tablets, in a form resistant to yellowing, in which the aforementioned essential components are present in a single layer.

It has been established that the undesired yellowing of a dishwasher detergent containing bleaching agent, bleaching activator and silver-anticorrosion agent can be partly or completely avoided if the bleaching activators are used in effectively coated form. In principle the yellowing resistance can also be improved by an ef ective coating of the bleaching agent with inorganic coating components, though in this case a coating amount is necessary that is greater than that contained in the currently commercially available products. A particularly good yellowing resistance is obtained if the bleaching activators as well as the bleaching agents are contained in coated form in dishwasher detergents .

The invention accordingly provides a bleaching-action dishwasher detergent in powder or granule form or in the form of compressed moulded articles with improved yellowing resistance during storage, containing in substantially homogeneous distribution one or more particulate bleaching agents containing active oxygen, one or more particulate bleaching activators, at least one silver-anticorrosion agent as well as other conventional constituents, which is characterised in that it contains the particulate bleaching activators and/or the particulate bleaching agents in each case in an effectively coated form, detergents however being excluded that contain bleaching agents coated with paraffin oil in combination with bleaching activators that are not coated or are incompletely coated. The subclaims relate to preferred embodiments of the composition of the dishwasher detergent as well as to the form of use.

The dishwasher detergent according to the invention may exist in powder or granule form or in compressed form, in particular in tablet form. Compressed moulded articles, in particular granules and tablets, are preferred. The mean grain diameter of granules is in this connection preferably in the range from greater than 0.15 mm to less than 2.0 mm. If the detergent is used in tablet form, the dimensioning is preferably such that one tablet is sufficient for one wash cycle; a tablet contains in general 2 to 20g, in particular 5 to lOg of the detergent.

The constituents contained in the detergent are present in particulate form wherein however liquid constituents contained in the detergent have been converted into solid particles by contact of the liquid constituents with solid particulate constituents. The detergent may accordingly be composed of particles that in turn have a different composition. The expression "in substantially homogeneous distribution" is understood to mean that the particles contained in the detergent, which in each case may contain one or more constituents of the detergent, are distributed as uniformly as possible. The term "homogeneous" thus refers to the distribution of the particles in the detergent. Multilayer tablets in which the silver- anticorrosion agent is not contained jointly in a layer together with the bleaching agent and the bleaching activator are therefore excluded. In the detergent according to the invention the bleaching activators, or the bleaching agents or the bleaching activators as well as the bleaching agents may have an effective coating. The term "effective" is understood to mean that the choice of the one or more coating components as well as the coating amount are such that the yellowing resistance is significantly increased and under normal storage conditions of the detergent there is no significant yellowing. According to a particularly advantageous embodiment, the particulate bleaching agents as well as the particulate bleaching activators are coated. The person skilled in the art thus has a wide range of possibilities as regards the choice of coating components, as well as the coating amount to be applied to the bleaching activators or to the bleaching agents.

Particularly preferred detergents contain coated sodium percarbonate with a commercially conventional coating and effectively coated bleaching activators, the coating preferably consisting of one or more hydrate-forming salts and the coating amount preferably being less than 10 wt.%.

It was established that detergents that contain commercially conventionally coated sodium percarbonate and uncoated or not effectively coated bleaching activators have an unsatisfactory yellowing resistance. Only by increasing the coating amount on the sodium percarbonate particles to values above 10 wt.%, in practice above 13 wt.% and in particular 15 to 25 wt.%, can the yellowing resistance be improved.

Dishwasher detergents containing silver-anticorrosion agent whose bleach system comprises uncoated or incompletely coated bleaching activators and bleaching agents coated with paraffin oil are excluded from the scope of protection. Among the compounds releasing hydrogen peroxide and serving as bleaching agents, perhydrates such as sodium perborate tetrahydrate, sodium perborate monohydrate and sodium percarbonate are particularly important. However, bleaching agents from the range comprising persilicates, persulfates, peroxophosphates and peroxopyrophosphates of alkali metals, such as in particular sodium, are also suitable. Peracid salts or peracids such as perbenzoates and peroxophthalates that yield H₂0₂ may however also be used as bleaching agents. From the group comprising organic bleaching agents there may also be mentioned diacyl peroxides and aliphatic peroxy acids such as peroxylauric acid, peroxystearic acid, ε-phthalimido- peroxycarboxylic acids and peroxydicarboxylic acids such as 1, 12-diperoxydodecanedioic acid, 1, 9-diperoxyazelaic acid and 2-decyldiperoxybutane-l, 4-dioic acid. Apart from the active oxygen-containing bleaching agents mentioned hereinbefore the dishwasher detergents may in addition include chlorine-containing bleaching agents, such as in particular dichloroisocyanuric acid and its salts.

If one or more bleaching agents in coated form are used, then coating components are preferred that are wholly or largely of an inorganic nature, for example hydrate- forming salts. Examples of such coating components are sulfates, carbonates, hydrogen carbonates, silicates, carbonate/hydrogen carbonate mixed salts and carbonate/sulfate mixed salts of alkali metals and/or magnesium. Among organic coating components there may be mentioned in particular polybasic carboxylic acids and hydroxycarboxylic acids as well as their salts. The amount of the coating components on the particulate bleaching agents that are used is governed depending on whether and in what way the bleaching activators are coated. As indicated hereinbefore, the coating amount on the bleaching agents must generally be significantly greater than 10 wt.%, in particular 15 to 25 wt.%, if the bleaching activators present are not coated or at least not completely coated. In the case of the particularly preferred dishwasher detergents that contain coated bleaching agents as well as coated bleaching activators, the coating amount on the bleaching agents may however be below 10 wt.%, in particular 2 to below 10 wt.%, referred to the coated material .

The bleaching agents are used in dishwasher detergents generally in an amount of 1 to 30 wt.%, preferably 2.5 to 20 wt.% and in particular 5 to 15 wt.%, in each case referred to the detergent.

Particularly preferred dishwasher detergents with sodium percarbonate as bleaching agent contain the latter in coated form, the coating amount being 2 to 10 wt.%, in particular 3 to 7 wt.%, referred to the coated sodium percarbonate. Among the coating components there may be mentioned especially hydrate-forming inorganic salts such as in particular sodium sulfate, sodium carbonate, sodium hydrogen carbonate, sodium borates and magnesium sulfate, and mixed salts of sodium sulfate and sodium carbonate or sodium carbonate and sodium hydrogen carbonate. If the sodium percarbonate that is used is to have a delayed release behaviour, this can be achieved by a further coating layer comprising essentially sodium silicates. The bleaching-action dishwasher detergents according to the invention contain, apart from at least one bleaching agent, preferably a coated bleaching agent, at least one bleaching activator, preferably a coated bleaching activator, which is able to support the action of the at least one bleaching agent. Known bleaching activators are compounds that contain one or more N-acyl or O-acyl groups capable of perhydrolysis. In particular substances from the following classes of substances are suitable: anhydrides, esters, N-acylated amines and N-acylated i ides, N-acylated imidazoles and O-acylated oxiraes . As bleaching activators there may in particular be used compounds that under perhydrolysis conditions yield aliphatic peroxycarboxylic acids with preferably 1 to 12 C atoms, in particular 2 to 4 C atoms, or aromatic peroxycarboxylic acids such as perbenzoic acid and substituted perbenzoic acids. Examples of suitable bleaching activators are multiply acylated alkylenedia ines, such as in particular tetraacetylethylenediamine (TAED) , acylated triazine derivates, in particular 1, 5-diacetyl-2, 4-dioxohexahydro- 1,3,5-triazine (DADHT) , acylated glycoluriles, in particular tetraacetylglycolurile (TAGU) , N-acylimides, in particular N-nonanoylsuccinimide (NOSI) , acylated phenolsulfonates, in particular n-nonanoyl- or iso- nonanoyloxybenzenesulfonate (n- or iso-NOBS) , carboxylic acid anhydrides such as phthalic anhydride, acylated polyhydric alcohols such as ethylene glycol diacetate, 2, 5-diacetoxy-2, 5-dihydrofuran, enol esters, acetylated sorbitol and mannitol (SOR, MAN) , acylated sugars such as pentaacetylglucoses, N-acylated lactams, in particular N-acylcaprolactam and N-acylvalerolactam. According to particularly preferred embodiments the detergents contain a bleaching activator from the range comprising TAED, TAGO, n- and iso-NOBS and NOSI. Preferred embodiments of the dishwasher detergent according to the invention contain the bleaching activator or activators in effectively coated form. The coating materials may be of an organic and/or inorganic nature. Inorganic coating components preferably include water- soluble hydrate-forming inorganic salts from the list comprising sulfates, carbonates, hydrogen carbonates, silicates, borates, carbonate/hydrogen carbonate mixed salts and carbonate/sulfate mixed salts of alkali metals, in particular sodium and/or magnesium.

Effective organic coating components for bleaching activators include polybasic carboxylic acids and their salts, carboxyl group-containing polymers and their salts, hydroxycarboxylic acids in monomeric and polymeric form, as well as salts of these substances, in particular sodium citrate. There may also be used polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, fatty acid esters, fatty acid alcohols, fatty amides, alkoxylated compounds of fatty alcohols and fatty amides, paraffin oils and natural and synthetic waxes with a melting point in the range of the dishwasher washing temperature, in particular therefore from 40 to 70°C.

The yellowing resistance increases with increasing amount of the one or more coating components on the bleaching activators contained in the detergent. If the bleaching agents themselves are not coated or are only incompletely coated, then the person skilled in the art will use more highly coated bleaching activators in order to achieve an effective yellowing resistance.

The necessary coating amount is also governed by the selected coating components as well as the coating method that is employed. The coated bleaching activators can be produced particularly advantageously using the fluidised bed technology. In this, at least one solution containing one or more coating components is sprayed onto a particulate bleaching activator contained in a fluidised bed and at the same time the solvent is evaporated. If desired, a granulation of the bleaching activator with further constituents of the dishwasher detergent may be carried out beforehand or simultaneously. The so-called melt coating procedure is also suitable for coating with coating materials that melt above 30°C, in particular in the range from 40° to 70°C.

The coating amount applied to the bleaching activators is generally in the range from 0.5 to 20 wt.%, in particular 1 to 15 wt.%, preferably 1 to 10 wt.% and particularly preferably 2 to 7 wt.%, referred to the coated bleaching activator.

According to a further embodiment the coating of the bleaching activator contains a surface-active agent, in particular a non-ionic surfactant, or a coating component that increases the release time. In order to delay the release of the bleaching activator there are conveniently used those coating components that have a relatively hydrophobic nature. Apart from the possibility described in connection with the bleaching agents, of increasing the dissolution time by the application of alkali metal silicates, this object may also be achieved in the bleaching activators by using hydrophobic substances such as fatty alcohols, fatty amides, paraffin oil, or natural and synthetic waxes . The amount of bleaching activators used in the dishwasher detergents according to the invention is in the range from 0.1 to 25 wt.%, preferably 0.25 to 15 wt.% and particularly preferably 1 to 10 wt.%. Conventional bleach-intensifying transition metal complexes may in addition be present in the usual amount.

Silver-anticorrosion agents are an essential constituent of the dishwasher detergents according to the invention. This term includes agents that prevent or reduce the tarnishing of non-ferrous metal, in particular silver. Particularly preferred silver-anticorrosion agents are those from the list comprising triazoles, benzotriazoles, bisbenzotriazoles, aminotriazoles and alkylaminotriazoles, in which the aforementioned classes of substances may also have substituents. Suitable substituents are linear or branched alkyl groups with 1 to 20 C atoms, vinyl, hydroxy, thio, fluorine, chlorine, bromine and iodine. Tolyltriazole is a particularly preferred triazole.

Suitable bisbenzotriazoles are those in which the two benzotriazole groups are in each case joined in the 6 position via a group X, in which X may be a bond, a straight-chain alkylene group with preferably 1 to 6 carbon atoms and optionally substituted with one or more Ci- to C₄-alkyl groups, or a cycloalkyl radical with at least 5 carbon atoms, a carbonyl group, a sulfonyl group, or an oxygen atom or sulfur atom. The aromatic rings of the bisbenzotriazole may be substituted as defined hereinbefore for benzotriazole.

A further class of silver-anticorrosion agents are redox- active substances, for example ascorbic acid, methionine, n-alkylglycine, diaminopyridine, aminohydroxypyrimidines, dihydroxypyrimidines, hydroxyquinolines, aminoquinolines, dihydroxybenzenes and trihydroxybenzenes . With regard to the aforementioned classes of substances, reference is made to WO 94/26860.

Inorganic redox-active substances are furthermore suitable as silver-anticorrosion agent. These are in particular metal salts and/or metal complexes from the group comprising manganese, titanium, zirconium, vanadium, cobalt and cerium salts and/or complexes. Selected examples include manganese(II) stearate, manganese (II) - 1-hydroxyethane-l, 1-diphosphonate, titanyl sulfate and cobalt (III) nitrate.

Suitable silver-anticorrosion agents are also paraffin oils with 20 to 50 C atoms, with a ratio of cyclic to non- cyclic hydrocarbons in the range from 1:10 to 2:1.

The amount of silver-anticorrosion agents used in the dishwasher detergents according to the invention is in the range from 0.01 to 5 wt.%, particularly preferably 0.1 to 3 wt.%, referred to the detergent.

Apart from the classes of substances already mentioned, the dishwasher detergent according to the invention contains conventional constituents such as in particular detergent builders and in most cases also surface-active agents. Further constituents may be selected from the classes comprising heavy metal complex-forming agents, enzymes, pH regulators, fragrances and foam regulators. Suitable as detergent builders, also simply termed builders, in dishwasher detergents are homopolymeric and copolymeric polycarboxylic acids as well as their partially or fully neutralised salts, monomeric polycarboxylic acids and hydroxycarboxylic acids and their salts, carbonates and bicarbonates of alkali metals, borates, phosphates, silicates, as well as mixtures of such substances. Suitable as silicates are in particular sodium silicates such as sodium disilicates and sodium metasilicates, crystalline layer silicates and sodium aluminium silicates, in particular those with a zeolite structure.

If the use of phosphate builders shall not be avoided, then these substances are orthophosphates, pyrophosphates and polymeric metaphosphates, in particular of sodium and potassium, and in some cases also ammonium. Alkali metal dihydrogen phosphates may furthermore be used.

Further builder substances may be typical alkali carriers, such as alkali metal carbonates, alkali metal hydrogen carbonates, alkali metal sesquicarbonates and alkali metal silicates.

Preferred builder systems contain tripolyphosphates and sodium carbonate or tripolyphosphate, sodium carbonate and sodium disilicate.

In the dishwasher detergents according to the invention organic co-builders may preferably also be present. Suitable co-builders are acyclic, alicyclic, heteroaromatic and aromatic polycarboxylic acids with at least two carboxyl groups . Examples include succinic acid, tartaric acid, citric acid, polymethacrylic acid and methacrylic acid copolymers. The dishwasher detergents according to the invention generally contain between 40 and 90 wt.% of builder substances, preferably 60 to 80 wt.%.

The detergents according to the invention as a rule also contain one or more surface-active agents from the list comprising anionic, cationic, non-ionic and zwitterionic surfactants and mixtures thereof. A large number of substances from the aforementioned classes are known to those active in this field. Suitable compounds for dishwasher detergents are for example those mentioned in WO 95/01416. Particularly preferred are non-ionic surfactants, including ethoxylated and ethoxylated/ propoxylated fatty alcohols with 6 to 18 C atoms, in particular 12 to 18 C atoms. Examples are ethoxylates of coconut butter alcohol, palm oil alcohol, tallow fat alcohol or oleyl alcohol with 2 to 8 EO groups per mole of alcohol . Further classes of non-ionic surface-active agents include polyhydroxy fatty acid amides with the structural element R²-C(0) -NR¹Z, where R² is an hydrocarbon radical with 5 to 50 C atoms, R¹ is H, alkyl, 2-hydroxyethyl or 2-hydroxypropyl, and Z is a polyhydroxycarbyl group, for example a sugar residue.

The dishwasher detergents according to the invention generally contain 0.5 to 30 wt.%, preferably 1 to 25 wt.% and particularly preferably 1 to 10 wt.% of one or more surface-active substances . The dishwasher detergents according to the invention may furthermore contain one or more conventionally used enzymes from the list comprising proteases, amylases, upases and esterases. The enzymes may in this connection be adsorbed on carrier substances or embedded in coating substances, in order to protect them against decomposition. The proportion of the enzymes or enzyme mixtures in enzyme-containing detergents according to the invention is generally in the range from 0.1 to 10 wt.%, in particular 0.1 to 5 wt.%.

A further class of constituents that may be present in dishwasher detergents according to the invention are complex-forming agents for heavy metals. Examples of such agents are organic phosphonates such as diethylenetriamine penta(methylenephosphonate) , hexamethylenediamine tetra(methylenephosphonate) and 2-hydroxyethylene- 1, 1-diphosphonate. Known aminopolycarboxylates such as EDTA and NTA, methylglycinediacetic acid and polyaspartates may also be used. If such complex-forming agents are contained in the detergent, the amount used is in the range from 0.01 to 10 wt.%, in particular 0.1 to 2 wt.%.

The invention is also directed to a process for increasing the yellowing resistance of dishwasher detergents in powder or granule form or in the form of compressed moulded articles such as tablets, containing in substantially homogeneous distribution one or more particulate bleaching agents containing active oxygen, one or more particulate bleaching activators, at least one silver-anticorrosion agent as well as other conventional constituents, said process comprising mixing the particulate substances, in which connection these may contain one or more constituents including liquid constituents of the detergent adsorbed on solid constituents, and if necessary granulating or compressing the mixture into moulded articles, which process is characterised in that the one or more particulate bleaching activators and/or the one or more particulate bleaching agents are used in effectively coated form, the use of bleaching agents coated with paraffin oil in conjunction with uncoated or incompletely coated bleaching activators being excluded.

For the production the individual constituents of the dishwasher detergent are accordingly mixed and if necessary granulated or compressed in a conventional way. The individual constituents may in this connection be used in powder and/or granule form as such or as pre-mixtures and/or optionally granules of at least two substances. Such mixtures exist in particular if the detergent contains a liquid constituent such as a liquid surface- active agent. In this case the liquid agent is converted into a particulate material by contacting it with a pulverulent constituent. The particulate constituents to be mixed preferably have a similar grain spectrum in order to avoid demixing phenomena.

It could not have been foreseen that the yellowing resistance of the generic dishwasher detergents could be reliably improved by coating the bleaching activators with a coating material that may be varied in multifarious ways. A further advantage of the invention is that, due to the use of coated bleaching activators, a wider selection of bleaching agents, bleaching activators, and silver-anticorrosion agents is possible without the occurrence of undesirable interactions of components of the bleaching system with the silver-anticorrosion agent. A high yellowing resistance is achieved by the presence of coated bleaching activators in the detergents according to the invention. A particularly high yellowing resistance is then obtained if the bleaching activators as well as the bleaching agents are present in coated form in the dishwasher detergent. A thin coating layer of both the bleaching activators and also the bleaching agents is more effective than a thick coat layer just on the bleaching agent or the bleaching activator.

The invention is illustrated with the aid of the following examples .

Example 1: Coating of tetraacetylethylenedia ine (TAED) with 6 wt.% sodium sulfate

940 g of a TAED spray granulated material were added to a Strea 1 coater from the Aeromatic company. The material was maintained in a fluidised bed by feeding in hot air at a temperature of 90°C and a feed rate of 70 m³/h. 300 g of a 20% solution of sodium sulfate in water were sprayed by means of a two-component nozzle within 15 minutes into the fluidised bed. The mixture was then dried for a further 30 minutes at a feed air temperature of 100°C. The product was removed and weighed. Weighed yield: 798 g.

Example 2: Coating of TAED with 6 wt.% sodium sulfate and 0.75 wt.% sodium water glass

466 g of a TAED spray granulated material were added to a Strea 1 coater from the Aeromatic company. The material was maintained in a fluidised bed by feeding in hot air at a temperature of 90°C and a feed rate of 70 m³/h. 150 g of a 20% solution of sodium sulfate in water were sprayed by means of a two-component nozzle within 15 minutes into the fluidised bed. After a 5-minute drying phase 38 g of a 10% sodium water glass solution, modulus 3.3, were sprayed in within 10 minutes. The mixture was then dried for 30 minutes at a feed air temperature of 100°C. The product was removed and weighed. Weighed yield: 404 g.

The product thereby obtained has a delayed dissolution rate compared to that of Example 1.

Example 3 : Compressing dishwasher detergent tablets and yellowing test

In a 50 ml plastic bottle 1.80 g of coated sodium percarbonate (coated with 6 wt.% sodium sulfate) were added to 13.20 g of dishwasher detergent of the basic formulation R/A, R/B and R/C. The formulation R/A contained benzotriazole as silver-anticorrosion agent, but no bleaching activator. The formulation R/B also contained benzotriazole, and was prepared by adding 1.5 parts by weight of TAED (quality the same as the starting substance in Examples 1 and 2) to 98.5 parts by weight of R/A. The formulation R/C was prepared similarly to R/B, but with the use of the TAED coated with sodium sulfate according to Example 1.

The respective mixture was thoroughly mixed for 20 minutes in a turbular mixer and the mixture was stored for four days at room temperature. The mixture was compressed into tablets in a tablet press at a pressure of 50 kN for 15 seconds and the tablets were stored for 14 days at 50°C in a drying cabinet. The degree of yellowing of the tablets after storage was determined by using a diffuse reflection measuring remission instrument. Example No. Formulation Diffuse Reflection (%)

Comparison Example (A) R/A 79.96

Comparison Example (B) R/B 72.92

Invention (C) R/C 80.17

A comparison of the yellowing of the dishwasher detergent (C) according to the invention with that of the comparison example (B) shows that the yellowing can be reduced to a value that is found in the TAED-free detergent (A) by coating the bleaching activator TAED with sodium sulfate.

Claims

Patent Claims

1. Bleaching-action dishwasher detergent in powder or granule form or in the form of compressed moulded articles with improved yellowing resistance on storage, containing in substantially homogeneous distribution one or more particulate bleaching agents containing active oxygen, one or more particulate bleaching activators, at least one silver- anticorrosion agent as well as other conventional constituents, characterised in that it contains the particulate bleaching activators and/or the particulate bleaching agent in each case in effectively coated form, in which detergents are excluded that contain bleaching agents coated with paraffin oil in combination with uncoated or incompletely coated bleaching activators .

2. Dishwasher detergent according to claim 1, characterised in that it is present in the form of compressed moulded articles, in particular tablet form.

3. Dishwasher detergent according to claim 1 or 2, characterised in that it contains the bleaching activators as well as the bleaching agents in the form of substantially completely coated particles.

4. Dishwasher detergent according to one of claims 1 to 3, characterised in that it contains as bleaching activator at least one O-acylated or N-acylated compound from the list comprising anhydrides, esters, imides, acylated imidazoles and oximes capable of undergoing perhydrolysis.

5. Dishwasher detergent according to one of claims 1 to 4, characterised in that it contains overall 0.1 to 25 wt.%, preferably 0.25 to 15 wt.% and particularly preferably 1 to 10 wt.% of bleaching activators, and 1 to 30 wt.%, preferably 1 to 20 wt.% of bleaching agents.

6. Dishwasher detergent according to one of claims 1 to 5, characterised in that it contains the bleaching activator or activators in coated form, wherein the coating comprises one or more organic and/or inorganic coating components and the coating amount is 0.5 to 20 wt.%, in particular 1 to 10 wt.%, referred to the coated bleaching activators.

7. Dishwasher detergent according to one of claims 1 to 6, characterised in that it contains one or more coated bleaching activators whose coating contains one or more water-soluble hydrate-forming inorganic salts from the list comprising sulfates, carbonates, hydrogen carbonates, borates, silicates, carbonate/ hydrogen carbonate and carbonate/sulfate mixed salts of alkali metals and/or magnesium and/or salts of polybasic carboxylic acids .

8. Dishwasher detergent according to one of claims 1 to 7, characterised in that it contains one or more coated bleaching activators whose coating contains one or more salts from the list comprising sodium sulfate, sodium carbonate, sodium hydrogen carbonate, mixed salts of these salts and/or sodium citrate, in a total amount of 2 to 10 wt.% referred to the coated bleaching activators .

9. Dishwasher detergent according to one of claims 1 to 8, characterised in that it contains as bleaching agent a peroxo compound from the list comprising sodium perborate monohydrate, sodium perborate tetrahydrate, sodium percarbonate, sodium persilicates, persulfates, peroxophosphates and peroxopyrophosphates .

10. Dishwasher detergent according to one of claims 1 to 8, characterised in that it contains one or more coated bleaching agents, in particular coated sodium percarbonate, wherein the coating contains one or more hydrate-forming inorganic salts in an amount of 2 to 10 wt.%, referred to the coated sodium percarbonate.

11. Dishwasher detergent according to one of claims 1 to 10, characterised in that it contains one or more silver-anticorrosion agents from the list comprising triazoles, benzotriazoles, bisbenzotriazoles, aminotriazoles, alkylaminotriazoles and transition metal complexes of the aforementioned triazoles in a total amount in the range from 0.01 to 5 wt.%.

12. Dishwasher detergent according to claim 1 or 2, characterised in that it contains as conventional other constituents one or more substances from one or more classes of substances from the list comprising inorganic builder materials, surface-active agents, heavy metal complex-forming agents, enzymes, pH regulators, fragrances and foam regulators.

13. Dishwasher detergent according to claim 1 or 2 , characterised in that the bleaching agent is a single-layer or multilayer coated sodium percarbonate, in which the coating comprises more than 10 wt.%, in particular more than 13 wt.% of one or more inorganic hydrate-forming salts, referred to the coated sodium percarbonate, and the bleaching activator is uncoated or incompletely coated.

14. Process for improving the yellowing resistance of dishwasher detergents in powder or granule form or in the form of compressed moulded articles, containing in substantially homogeneous distribution one or more particulate bleaching agents containing active oxygen, one or more particulate bleaching activators, at least one silver-anticorrosion agent as well as other conventional constituents, comprising mixing the particulate substances, wherein these may contain one or more constituents of the detergent including liquid constituents adsorbed on solid constituents, and if necessary granulating or compressing the mixture into moulded articles, characterised in that the particulate bleaching activators and/or the particulate bleaching agents are used in effectively coated form, wherein the use of bleaching agents coated with paraffin oil in conjunction with uncoated or incompletely coated bleaching activators is excluded.

15. Dishwasher detergent according to claim 10, characterised in that it contains coated sodium percarbonate as the bleaching agent which in addition to a coating comprising one or more hydrate-forming inorganic salts has a further coating layer comprising essentially sodium silicates.