WO2022002672A1

WO2022002672A1 - Use of a composition as anti-corrosion agent

Info

Publication number: WO2022002672A1
Application number: PCT/EP2021/066866
Authority: WO
Inventors: Alias Younis AL-BAYATI; Rainer MÜLLER-LEIFHEIT; Karlheinz Ulrich Hahn; Torsten Roth; Alexander Wink; Itahisa SUAREZ
Original assignee: Reckitt Benckiser Finish B.V.
Priority date: 2020-07-01
Filing date: 2021-06-21
Publication date: 2022-01-06
Also published as: GB202010074D0

Abstract

The use of a composition comprising elemental tin and zinc for the inhibition of corrosion of wares comprising silver in an automatic dishwashing or rinsing process.

Description

USE OF A COMPOSITION AS ANTI-CORROSION AGENT

The present invention relates to the use of compositions to inhibit silver corrosion, compositions for such a use and method of preparing such a composition.

Silver is chemically the most reactive element among the noble metals and tarnishes readily. Silver discoloration, generally termed tarnishing, is often caused by a silver oxidation process in which compounds are formed on the surface of the material. Food, such as onions, mustard and eggs that contain organic sulphur compounds, are known to tarnish silver.

Silver tarnishing is also known to occur when an oxygen bleaching agent is used in detergent compositions and oxidises silver to silver oxide. This oxidation process causes surface blackening of the silverware when it is washed in a machine. The level of tarnishing observed can range from slight discolouration of the silverware to the formation of a dense black coating on the surface of the silverware, depending on the formulation and, more precisely, the type of bleaching agent. The dual challenge in formulating a product is therefore the optimization of the cleaning of bleachable soils while minimizing the occurrence of tarnishing of silverware components The phenomenon of silver tarnishing therefore increased in automatic dishwashers with the widespread introduction of low-alkaline formulations containing oxygen bleaching agents. As a consequence, the oxidation potentials were shifted to favour the formation of black silver oxide during the cleaning process. To suppress this reaction, the concentration of the bleach system had to be optimized, and anti-tarnishing agents, such as benzotriazole (BTA), had to be added.

However, recent environmental science publications highlighted the alarming biodegradability profile of BTA and some of its derivatives. As a result of their resistance to conventional wastewater treatment procedures, an accumulation of this omnipresent organic micropollutant in the aquatic environment takes place, while it is also a potential endocrine disruptor. Thus, inexpensive, environmentally-friendly yet highly active substitute materials are currently being sought in order to replace the currently used toxic compounds. There is therefore a need to identify a silver corrosion inhibition agent with an efficacy comparable to the currently employed benzotriazoles. Moreover, the potential agent must not have any known risks to the environment or the human health, as well as being easily available on a commercial scale at a reasonable cost.

The present invention addresses this technical problem through the use of a composition comprising elemental tin and zinc for the inhibition of corrosion of wares comprising silver in an automatic dishwashing or rinsing process.

By the term 'corrosion' we hereby include the degradation of the material, as well as the tarnishing and discolouration through the formation of surface compounds, including sulphides, chlorides and oxides of silver. Without wishing to be bound by theory, it is believed that use of the claimed composition forms a protective layer on the surface of the wares in order to inhibit the corrosion.

Preferably, the wares, such as silver cutlery, comprise at least one silver-containing surface.

Advantageously, the composition comprises an alloy of tin and zinc. As both components of such an alloy are well known benign metals, no registration or safety studies are necessary for their introduction into a product for consumer use.

Preferably, the alloy comprises tin in an amount from 10 to 60 wt.%, such as from 15 to 50 wt.%, from 20 to 40 wt.%, from 21 to 39 wt.%, from 22 to 38 wt.%, from 26 to 34 wt.%, or preferably from 27 to 33 wt.%.

Preferably the alloy comprises zinc in an amount of from 60 to 80 wt.%, such as from 61 to 79 wt.%, from 63 to 77 wt.%, from 65 to 75 wt.%, or preferably from 67 to 73 wt.%. Preferably, the alloy comprises less than 1 wt.% of non-tin or zinc metals, such as less than 0.5 wt.% of non-tin or zinc metals. Advantageously, the composition additionally comprises one or more components selected from builders, enzymes, polymers, bleaching agents, nonionic surfactants and alkalising agents. Alternatively, but also preferred, the composition may be used in combination with a secondary composition comprising one or more components selected from builders, enzymes, polymers, bleaching agents, nonionic surfactants and alkalising agents.

The builder is advantageously selected from the group consisting of methylglycine diacetic acid (MGDA), N,N-dicarboxymethyl glutamic acid (GLDA), citrate and combinations of two or more thereof. It is to be appreciated that the terms MGDA, GLDA and citrate encompass the free acids as well as salts, esters and derivatives thereof. Preferably, the citrate is trisodium citrate. Other phosphorous-free builders include succinate-based compounds. The terms "succinate- based compound" and "succinic acid-based compound" are used interchangeably herein.

Particular suitable builders include; for example, aspartic acid-N-monoacetic acid (ASMA), aspartic acid-N,N-diacetic acid (ASDA), aspartic acid-N-monopropionic acid (ASMP), iminodisuccinic acid (IDA), N-(2-sulfomethyl) aspartic acid (SMAS), N-(2-sulfoethyl)aspartic acid (SEAS), N-(2-sulfomethyl)glutamic acid (SMGL), N-(2-sulfoethyl)glutamic acid (SEGL), N- methyliminodiacetic acid (MIDA), a-alanine-N,N-diacetic acid (a-ALDA), -alanine-N,N- diacetic acid (b-ALDA), serine-N,N-diacetic acid (SEDA), isoserine-N,N-diacetic acid (ISDA), phenylalanine-N,N-diacetic acid (PHDA), anthranilic acid-N,N-diacetic acid (ANDA), sulfanilic acid-N,N-diacetic acid (SLDA), taurine-N,N-diacetic acid (TUDA) and sulfomethyl-N,N-diacetic acid (SMDA) and alkali metal salts or ammonium salts thereof.

Suitable builders include; for example, aspartic acid-N-monoacetic acid (ASMA), aspartic acid- N,N-diacetic acid (ASDA), aspartic acid-N-monopropionic acid (ASMP), iminodisuccinic acid (IDA), N-(2-sulfomethyl) aspartic acid (SMAS), N-(2-sulfoethyl)aspartic acid (SEAS), N-(2- sulfomethyl)glutamic acid (SMGL), N-(2-sulfoethyl)glutamic acid (SEGL), N- methyliminodiacetic acid (MIDA), a-alanine- N,N-diacetic acid (a-ALDA), -alanine-N,N- diacetic acid (b-ALDA), serine-N,N-diacetic acid (SEDA), isoserine-N,N-diacetic acid (ISDA), phenylalanine-N,N-diacetic acid (PHDA), anthranilic acid-N,N- diacetic acid (ANDA), sulfanilic acid-N,N-diacetic acid (SLDA), taurine-N,N-diacetic acid (TUDA) and sulfomethyl-N,N-diacetic acid (SMDA) and alkali metal salts or ammonium salts thereof.

Further succinate compounds have the formula:

in which R, Rl, independently of one another, denote H or OH; R2, R3, R4, R5, independently of one another, denote a cation, hydrogen, alkali metal ions and ammonium ions, ammonium ions having the general formula R6R7R8R9N+ and R6, R7, R8, R9, independently of one another, denote hydrogen, alkyl radicals having 1 to 12 C atoms or hydroxyl-substituted alkyl radicals having 2 to 3 C atoms.

Examples include tetrasodium imminosuccinate. Iminodisuccinic acid (IDS) and (hydroxy)iminodisuccinic acid (HIDS) and alkali metal salts or ammonium salts thereof are especially preferred succinate-based builder salts. The phosphorous-free co-builder may also or alternatively comprise non-polymeric organic molecules with carboxylic group(s). Builder compounds which are organic molecules containing carboxylic groups include citric acid, fumaric acid, tartaric acid, maleic acid, lactic acid and salts thereof. In particular the alkali or alkaline earth metal salts of these organic compounds may be used, and especially the sodium salts.

Most preferably, however, the builder is a carboxylate, such as citrate, and/or an aminocarboxylate, such as methylglycine diacetic acid. The builder is preferably present in a quantity of from 10 to 50 wt.%, such as from 15 to 45 wt.%, or even from 21 to 37 wt.%.

The bleaching agent is preferably selected from the group consisting of an oxygen-releasing bleaching agent, a chlorine-releasing bleaching agent and mixtures of two or more thereof. More preferably, the bleaching agent is or comprises an oxygen-releasing bleaching agent.

The bleaching agent may comprise the active bleach species itself or a precursor to that species. Preferably, the bleaching agent is selected from the group consisting of an inorganic peroxide, an organic peracid and mixtures of two or more thereof. The terms "inorganic peroxide" and "organic peracid" encompass salts and derivatives thereof. Inorganic peroxides include percarbonates, perborates, persulphates, hydrogen peroxide and derivatives and salts thereof. The sodium and potassium salts of these inorganic peroxides are suitable, especially the sodium salts. Sodium percarbonate is particularly preferred.

The bleaching agent is preferably present in an amount of from 9 to 21 wt.%, such as from 12 to 19 wt.%, or even from 13 to 18 wt.%.

The composition may comprise one or more bleach activators and/or bleach catalysts. Any suitable bleach activator may be included, for example tetraacetylethylenediamine (TAED), if this is desired for the activation of the bleaching agent. Any suitable bleach catalyst may be used, for example manganese acetate or dinuclear manganese complexes such as those described in EP 1741774 Al.

The composition may include one or more enzymes. It is preferred that the one or more enzymes are selected from proteases, lipases, amylases, cellulases and peroxidases, with proteases and amylases being most preferred. It is most preferred that protease and/or amylase enzymes are included in the compositions according to the invention as such enzymes are especially effective in dishwashing detergent compositions. More than one species may be used. The total quantity of enzymes is preferably from 0.1 to 5% by weight, such as from 0.2 to 2%. The composition may include one or more surfactants. Any of non-ionic, anionic, cationic, amphoteric or zwitterionic surface active agents or suitable mixtures thereof may plausibly be used. In general, bleach-stable surfactants are preferred according to the present invention.

In the case of automatic dishwashing compositions, it is preferred to minimise the amount of anionic surfactant. Accordingly, preferably the composition comprises no more than 2 wt%, no more than 1 wt%, or no, anionic surfactant. Preferably the composition comprises no more than 5 wt%, no more than 1 wt %, or no, ionic surfactant of any type.

The composition preferably comprises a non-ionic surfactant.

Preferably, the non-ionic surfactant is an optionally end capped alkyl alkoxylate. A preferred class of nonionic surfactants is ethoxylated non-ionic surfactants prepared by the reaction of a monohydroxy alkanol or alkyl phenol with 6 to 20 carbon atoms. Preferably the surfactants have at least 12 moles per mole of alcohol or alkyl phenol. Particularly preferred non-ionic surfactants are the non-ionics from a linear chain fatty alcohol with 10-20 carbon atoms and at least 5 moles, of ethylene oxide per mole of alcohol. According to one embodiment of the invention, the non-ionic surfactants additionally may comprise propylene oxide units in the molecule. Preferably these PO units constitute up to 25 % by weight, preferably up to 20 % by weight and still more preferably up to 15 % by weight of the overall molecular weight of the non-ionic surfactant.

Preferably, the one or more nonionic surfactants comprises a mixed alkoxylate fatty alcohol non-ionic surfactant, preferably comprising a greater number of moles of the lower alkoxylate group than of the higher alkoxylate group in the molecule. Preferably the mixed alkoxylate fatty alcohol non-ionic surfactant comprises at least two of EO, PO or BO groups and most preferably only EO and PO groups. By the term 'higher alkoxylate' it is meant the alkoxylate group having the greatest number of carbon atoms in that alkoxylate group. By the term 'lower alkoxylate' it is meant the alkoxylate group having the lowest number of carbon atoms in that alkoxylate group. Thus, for a mixed alkoxylate fatty alcohol com-prising ethoxylate (EO) and propoxylate (PO) groups the EO is the lower alkoxylate and the PO is the higher alkoxylate. Thus, the detergent compositions of the invention comprise mixed alkoxylate fatty alcohols comprising a greater number of EO groups than PO groups. The same applies to other mixed alkoxylates such as those containing EO and butoxylate (BO) or even PO and BO groups.

The mixed alkoxylate fatty alcohol non-ionic surfactant preferably has a mole ratio of the lower alkoxylate group to the higher alkoxylate group is at least 1.1:1, most preferably of at least 1.8:1, especially at least 2:1. It is also preferred that the mixed alkoxylate fatty alcohol non-ionic surfactant comprises between 3 to 5 moles of the higher alkoxylate group and between 6 to 10 moles of the higher lower group, preferably 4 or 5 moles of PO and 7 or 8 moles of EO and most preferably 4 moles of PO and 8 moles of EO.

Preferably the mixed alkoxylate fatty alcohol non-ionic surfactant has 12-18 carbon atoms in the alkyl chain.

It is especially preferred that the mixed alkoxylate fatty alcohol nonionic surfactant comprises at least two of EO, PO or BO groups and especially a mixture of EO and PO groups, preferably EO and PO groups only.

It is most preferred that the mole ratio of the lower alkoxylate group to the higher alkoxylate group is at least 1.1:1, more preferably at least 1.5:1, and most preferably at least 1.8:1, such as at least 2:1 or even at least 3:1. An especially preferred mixed alkoxylate fatty alcohol nonionic surfactant according to the present invention comprises between 3 to 5 moles of the higher alkoxylate group and between 6 to 10 moles of the lower group. Especially preferred are mixed alkoxylate fatty alcohol nonionic surfactants having 4 or 5 moles of the higher alkoxylate group and 7 or 8 moles of the lower alkoxylate group. According to one aspect of the invention a mixed alkoxylate fatty alcohol nonionic surfactant having 4 or 5 PO moles and 7 or 8 EO moles is especially preferred and good results have been obtained with for surfactants with 4 PO moles and 8 EO moles. In an especially preferred embodiment, the mixed alkoxylate fatty alcohol nonionic surfactant is C12-15 8EO/4PO. Surfactants of the above type which are ethoxylated mono-hydroxy alkanols or alkylphenols which additionally comprise polyoxyethylene-polyoxypropylene block copolymer units may be used. The alcohol or alkylphenol portion of such surfactants constitutes more than 30%, preferably more than 50%, more preferably more than 70% by weight of the overall molecular weight of the non-ionic surfactant.

The mixed alkoxylate fatty alcohol non-ionic surfactants used in the compositions of the invention may be prepared by the reaction of suitable monohydroxy alkanols or alkylphenols with 6 to 20 carbon atoms. Preferably the surfactants have at least 8 moles, particularly preferred at least 10 moles of alkylene oxide per mole of alcohol or alkylphenol.

Particularly preferred mixed alkoxylate fatty alcohol non-ionic surfactants are those from a linear chain fatty alcohol with 12-18 carbon atoms, preferably 12 to 15 carbon atoms and at least 10 moles, particularly preferred at least 12 moles of alkylene ox-ide per mole of alcohol. When PO units are used, they preferably constitute up to 25% by weight, preferably up to 20% by weight and still more preferably up to 15% by weight of the over-all molecular weight of the non-ionic surfactant.

The mixed alkoxylate fatty alcohol non-ionic surfactants, and especially the C12-15 fatty alcohol 8EO,4PO surfactant exhibit: excellent wetting of plastic, glass, ceramic and stainless steel; excellent temperature stability up to 90 °C for processing; good compatibility with thickeners typically used in the detergent compositions (e.g. PEG); and stability in alkaline conditions. The use of a mixture of any of the aforementioned nonionic surfactants is suitable in compositions of the present invention and are preferably present in an amount from 1 to 9 wt.%, such as from 2 to 7 wt.%, or even 3 to 6 wt.%. Advantageously, the composition comprises less than 0.1 wt.% of one or more triazoles, such as benzotriazole and/or tolytriazoles, more preferably the composition does not contain a triazoles.

Advantageously, the composition is used for multiple dishwashing cycles. By 'multiple' cycles, we mean that the composition is not entirely consumed in the first dishwasher and is present for at least two, preferably from 2 to 20, dishwasher cycles.

Even more advantageously, use of the composition has been found to inhibit silver corrosion for multiple cycles (such as from 1 to 10 cycles) after removal of the composition from the automatic dishwashing machine.

In a second aspect of the invention, there is provided a dishwashing additive composition comprising elemental tin and zinc. A dishwashing additive as used in the present application means a material, ingredient, compound or product that provides an additional consumer benefit, such as rinse aids, bleach booster, cleaning performance booster, shine performance improver, material care product, antimicrobial agents, and malodour control agents, where the additive is to be used in combination with an automatic dishwashing detergent.

In a third aspect of the invention, there is provided an automatic dishwashing detergent composition comprising elemental tin and zinc as described herein.

Preferably, the additive and/or detergent composition comprises an alloy of tin and zinc.

In a fourth aspect of the invention, there is provided a method of preparing a composition as described herein.

The invention is illustrated in the following non-limiting Examples. Examples

The properties of elemental tin and zinc for use in automatic dishwashing were tested on silver cutlery placed in the basket of an automatic dishwasher.

In separate experiments, elemental tin (Sn, in the form of a foil), elemental zinc (Zn, in the form of a granulate), and a tin-zinc alloy (SnZn, in the form of a wire and with the chemical composition defined below) were each added in a quantity of 27 g to an automatic dishwasher and remained present for the specified number of wash cycles without modification.

In conjunction, a base detergent composition without any silver corrosion inhibitors, as defined in Table 1, was prepared and one tablet of said composition was dosed per wash cycle. Subsequently, the uncleaned machine of the SnZn alloy test was re-tested with the base composition in the absence of any metal.

The methodology is set out below and the results presented in Table 2. SnZn alloy wire composition Zn: 29-31 wt.%

Sn: 69-71 wt.%

Base detergent composition Table 1

Methodology

Machine: Miele G'1222 SC GSL Program: 65 °C Water hardness: <l°dH Rinse Aid: None

Evaluators: Two trained evaluators

Scoring 5 = no discolouration/shine loss

4 = minor discolouration/shine loss

5 = discolouration/shine loss visible 2 = strong discolouration/shine loss

1 = very strong discolouration/shine loss

Results Table 2

* Average weight loss from the SnZn alloy was found to be 13 mg per cycle It was therefore conclusively demonstrated that inclusion of tin and zinc in the dishwashing process improved the corrosion protection of silver items in a dishwasher and that the corrosion protection benefit occurred over multiple wash cycles. It is also evident that neither Sn (2) nor Zn (3) by itself achieves the high degree of silver corrosion protection of the SnZn alloy (4). Remarkably, when "Base composition...(5)" was re-tested directly after concluding tests with the SnZn alloy (4) it demonstrated that the SnZn alloy (4) results in long-lasting corrosion protection that were exhibited in cycles even in the absence of the SnZn alloy. The invention is defined by the claims.

Claims

1. The use of a composition comprising elemental tin and zinc for the inhibition of corrosion of wares comprising silver in an automatic dishwashing or rinsing process.

2. The use according to claim 1, wherein the wares comprise at least one silver- containing surface.

3. The use according to claim 1, wherein the composition comprises an alloy of tin and zinc.

4. The use according to 2, wherein the alloy comprises tin in an amount from 20 to 40 wt.%.

5. The use according to claim 2 or 3, wherein the alloy comprises zinc in an amount of from 60 to 80 wt.%.

6. The use according to any of claims 2 to 4, wherein the alloy comprises less than 1 wt.% of non-tin or zinc metals.

7. The use according to any of the preceding claims, wherein the composition comprises one or more components selected from builders, enzymes, polymers, bleaching agents, nonionic surfactants and alkalising agents.

8. The use according to any of claims 1 to 5, wherein the composition is used in combination with a secondary composition comprising one or more components selected from builders, enzymes, polymers, bleaching agents, nonionic surfactants and alkalising agents.

9. The use according to any of the preceding claims, wherein the composition does not contain one or more benzotriazoles.

10. The use according to any of the preceding claims, wherein the composition is present for multiple dishwashing cycles.

11. A dishwashing additive composition comprising elemental tin and zinc.

12. An automatic dishwashing detergent composition comprising elemental tin and zinc.

IB. A composition according to claim 11 or 12, wherein the composition comprises an alloy of tin and zinc.

14. A method of preparing a composition according to claim 11 to 13.