Bleaching agent

Abstract: The invention relates of particles comprising a peroxy compound with capability of releasing hydrogen peroxide or peroxy acids in aqueous solutions, wherein in that the core of the particles contain alkali metal silicate and a chelating agent selected from alkali metal salts or alkaline earth metal salts of a hydroxy carboxylic acid satisfying the formula: RC n H m (OH) n COOH in which R is CH 2 OH or COOH, n is 2-6 and m is 0-n. The invention also relates to a method of preparing such particles.

Description: The present invention relates to particles comprising a peroxy compound with capability of releasing hydrogen peroxide or peroxy acids in aqueous solutions and a chelating agent selected from salts of hydroxy carboxylic acids. The invention also relates to preparation and use of the particles. Further, the invention relates to a composition containing such particles. Powder detergent compositions often contain peroxy compounds as bleaching agents which release hydrogen peroxide or peroxy acids in aqueous solutions. However, many peroxy compounds are not storage stable. Their decomposition is supposed to be catalysed by metal cations moving comparatively freely through the water normally being present in detergents, but is also facilitated by the alkaline pH (normally from about 8 to about 12) and by other components commonly present in detergents, for example zeolites or bleaching activators such as TAED (tetraacetylethylene diamine), TAGU (tetraacetylglucoluril) or PAG (penta acetyl glucose). In order to make environmental friendly detergents, it is desirable to use alkali metal carbonate peroxy hydrate, known as percarbonate, as a bleaching agent. However, the activity of percarbonate in a detergent decreases rapidly through decomposition if the detergent is stored at normal room temperature and humidity. Many attempts to stabilize percarbonate have been done, for example by mixing or coating with stabilizing substances such as borates, silicates or organic substances. Such stabilizing methods are described in the patent literature, for example in GB-A-1575792, EP-A-459625, US-A-3975280 and EP-A-573731. It has also been disclosed to combine percarbonate with chelating agents such as alkali metal citrate (see EP-A-546815) or phosphonic acids (see WO-A-91/15423). CH-A-659082 describes a detergent additive comprising a mixture of a peroxide, an inorganic carbonate and an acid or its salt. The additives facilitate the dissolution of the bleaching agent. US-A-4075116 discloses a method of preparing sodium percarbonate from sodium carbonate and hydrogen peroxide, which method includes adding a compound selected from sodium sulfate, potassium sulfate, sodium pyrophosphate, potassium pyrophosphate, sodium metasilicate, sodium disilicate, sodium citrate, sodium glucoheptonate, sodium perborate, anhydrous sodium carbonate, potassium carbonate and mixed sodium and potassium carbonate. However, the patent is not addressed towards stabilization of previously prepared sodium percarbonate or to the inhibition of the other constituents of detergent mixtures containing percarbonate. JP-A-58074508 relates to a process of producing sodium percarbonate by granulation of percarbonate together with at least one member selected from silicic acid hydrosol, a silicate and an aluminum hydroxide containing hydrosol, and at least one member selected from phosphoric acid, and a salt thereof, ortho- or metaboric acid and a salt thereof, and an organic polycarboxylic acid selected from citric acid, succinic acid, tartaric acid, crotonic acid, lactic acid, malonic acid and malic acid. This invention solves the problem of providing percarbonate particles that are soluble in room temperature. EP-A-0567140 discloses sodium percarbonate particles that are coated with at least one coating agent selected from the group (A) consisting of boric acids, borates and alkali metal silicates, and at least one coating agent selected from the group (B) consisting of carbonates, hydrogen carbonates and alkali metal or alkaline earth metal sulfates. EP-A-550077 relates to a granular bleaching composition comprising an alkali metal salt of percarbonate and a crystalline layered silicate. The main object of the present invention is to provide particles comprising a peroxy compound, particularly alkali metal percarbonate, with improved storage stability, particularly in detergent compositions. It is another object of the invention to provide particles comprising a peroxy compound only containing environmental friendly constituents. Through the present invention, these objects have been fulfilled by providing particles comprising a peroxy compound with capability of releasing hydrogen peroxide or peroxy acids in aqueous solutions, particularly in alkaline solutions, wherein the peroxy compound in the particles is mixed with alkali metal silicate and a chelating agent selected from alkali metal salts or alkaline earth metal salts of a hydroxy carboxylic acid satisfying the formula: RC n H m (OH) n COOH in which R is CH 2 OH, n is 2-6 and m is 0-n. Preferably, the particles also have a coating containing a chelating agent selected from alkali metal salts or alkaline earth metal salts of a hydroxy carboxylic acid satisfying the formula: RC n H m (OH) n COOH in which R is CH 2 OH or COOH, n is 2-6, and m is 0-n. It has surprisingly been found that hydroxy carboxylic acids according to the above formula gives superior storage stability compared to conventional chelating agents such as phosphonic acids, citrate or EDTA (ethylene diamine tetra acetic acid), at the same time as they are easily biodegradable and therefore environmental friendly. It is preferred that chelating agents not being so easily degradable, such as phosphonic acids, phosphonates and EDTA, are not included in the particles. The invention is particularly advantageous if the peroxy compound is alkali metal percarbonate, but also other peroxy compounds can be stabilized, for example alkali metal salts of perborates, peroxysulfates, peroxyphosphates or peroxysilicates, peroxycarboxylic acids or peroxycarboxylic acid releasing compounds such as di-acylated di-peroxy carboxylic acids (see WO-A-91/17143). The particles preferably contains from 10 to 99% by weight, most preferably from 50 to 95% by weight of a peroxy compound, and from 0.1 to 20% by weight, most preferably from 0.5 to 15% by weight of a chelating agent. It is particularly preferred that in coated particles the chelating agent in the coating constitutes from 0.1 to 15% by weight, most preferably from 0.5 to 10% by weight of the particle, and that the chelating agent in the core constitutes from 0.1 to 10% by weight, most preferably from 0.2 to 5% by weight of the particle. The alkali metals in the chelating agent are preferably selected from sodium, potassium or mixtures thereof. Alkaline earth metals agent are preferably selected from calcium, magnesium or mixtures thereof. Preferred chelating agent are alkali metal salts of hydroxy carboxylic acids according to the above formula. Preferably R is CH 2 OH also in the coating. It is also preferred that n is 4 or 5. Preferably, m is equal to n or n-2, the carbon chain thus being saturated or containing one double bond. A particularly preferred chelating agent is alkali metal glucoheptonate which is the alkali metal salt of the compound according to the above formula when R is CH 2 OH and n is 5. Other preferred chelating agents are alkali metal gluconate (R is CH 2 OH, n and m are 4) and alkali metal ascorbate (R is CH 2 OH, n is 4 and m is 2). Other useful chelating agents include, for example, salts of trihydroxy glutaric acid, or saccharic acid. It is to be understood that the particles may include two or more different chelating agents of the above formula. The particles may also include other environmentally acceptable chelating agents. It has surprisingly been found that a synergistic effect in respect of storage stability occurs when the particles contains a chelating agent of the above formula and an alkali metal silicate. The stabilizing effect has been found to be particularly good if the molar ratio SiO 2 :M 2 O, M being an alkali metal, is from 1 to 3, especially from 1.5 to 2.5. The alkali metal is preferably sodium, potassium or mixtures thereof. At least the core of the particles contains alkali metal silicate, suitably in an amount from 0.1 to 10% by weight, preferably from 0.5 to 7% by weight of the particle. Thus, the core contains both alkali metal silicate and a chelating agent. Most preferably, also the coating contains alkali metal silicate, suitably in an amount from 0.1 to 10% by weight, preferably from 0.5 to 5% by weight of the particle. The particles may comprise one or several coating layers containing a chelating agent and optionally alkali metal silicate. The particles may also comprise additional layers not containing chelating agents or alkali metal silicate. A synergistic effect in respect cf storage stability has also been found between chelating agents according to the invention and anhydrous alkali metal carbonate. Thus, the stability is improved if the core of the particles contain anhydrous alkali metal carbonate, particularly sodium carbonate, (commonly known as soda ash), suitably in an amount from 1 to 50% by weight, preferably from 5 to 30% by weight of the particle. It is also possible to include other substantially inert substances such as sulfates or phosphates of alkali metals. Suitably, the particles have an average diameter from 50 to 3000 µm, preferably from 100 to 1250 µm. The preferred density is from 600 to 1500 g/l, particularly from 800 to 1100 g/l. It has been found that a high density as well as a high average particle size improves the storage stability. The invention also concerns a method of preparing particles according to the invention, wherein a peroxy compound with capability of releasing hydrogen peroxide or peroxy acids in aqueous solutions, alkali metal silicate and a chelating agent selected from alkali metal salts or alkaline earth metal salts of a hydroxy carboxylic acid satisfying the formula: RC n H m (OH) n COOH in which R is CH 2 OH, n is 2-6 and m is 0-n, are mixed and granulated to form particles. According to the method, particles may for example be prepared from fine particles mainly consisting of a peroxy compound, preferably with a particle diameter less than 200 µm, adding the chelating agent and alkali metal silicate and/or optional ingredients, and granulating the mixture to obtain particles of a suitable size. Granulation may be performed by conventional methods well known among those skilled in the art, such as compacting, extruding, agglomeration in drum or disk, fluid-bed granulation, prilling or in different kinds of mixers. Also the coating may performed by conventional methods such as spraying in drums or fluidized beds. A particularly preferred method also comprises a step of applying a coating on particles prepared according to the invention, which coating contains a chelating agent selected from alkali metal salts or alkaline earth metal salts of a hydroxy carboxylic acid satisfying the formula: RC n H m (OH) n COOH in which R is CH 2 OH or COOH, n is 2-6 and m is 0-n. Preferably, the coating also contains alkali metal silicate. Alkali metal silicate is preferably added in the form of an aqueous solution, and the chelating agent is preferably mixed therein before addition to the peroxy compound. Regarding preferred peroxy compounds, chelating agents, alkali metal silicate and other components, as well as suitable amounts thereof, the above description of the particles according to the invention is referred to. The invention further concerns use of the described particles comprising a peroxy compound and a chelating agent as a bleaching agent, preferably in connection with washing of textiles or dishwashing. The washing water may be supplied with particles according to the invention being included in a detergent composition or being in the form of a separate bleaching powder. Preferably, washing water is supplied with particles in an amount so to obtain from 0.001 to 1 gram active oxygen per litre, which for example corresponds to from 0.01 to 6 grams sodium percarbonate. Finally, the invention concerns a composition containing an inert filler, and/or one or several substances active at washing, which composition further contains particles comprising a peroxy compound and a chelating agent according to the invention, for example in an amount from 1 to almost 100% by weight. The composition may comprise a mixture of particles containing different kinds of peroxy compounds. The substances active at washing may include detergent builders, surfactants, alkali generating substances, bleaching activators, or any other substances commonly used in detergents. The detergent builder may for example be selected from phosphates, zeolites, polycarboxylates, citrates, crystalline disilicates, amorphous disilicates (e.g. Britesil™), or mixtures thereof. The surfactants are preferably selected from anionic surfactants, nonionic surfactants, soaps or mixtures thereof. Anionic surfactants may for example be selected from linear alkylbenzene sulfonates, secondary alkane sulfonates, alcohol-ethoxysulfates or alpha-olefine sulfonates. Nonionic surfactants may for example be selected from alkoxylated compounds such as fatty alcohols, alkylphenols and alkylamines. Soaps may for example be selected from sodium or potassium salts of tallow. Also cationic surfactants such as quaternary ammonium compounds or imidazolinium salts, as well as amphoteric surfactants might be used. Alkali generating substances may for example be selected from carbonates, silicates, phosphates or mixtures thereof. The bleaching activators may for example be selected from TAED, TAGU, SNOBS (sodium nonanoyl benzene sulfonate), PAG (penta acetyl glucose) or diacylated diperoxy carboxylic acids (see WO-A-91/17143). The filler may include any inert substance such as sodium sulfate. The composition may constitute a complete detergent or a bleaching powder to be added separately at washing. A complete detergent for washing of textiles suitably contains from 1 to 30% by weight, preferably from 10 to 20% by weight of particles according to the invention. Further, the detergent suitably contains a detergent builder, for example from 5 to 50% by weight, surfactants, for example from 5 to 35% by weight and an alkali generating substance, for example from 5 to 20% by weight. Preferably, the detergent contains from 5 to 20% by weight of anionic surfactants, from 2 to 15% by weight of nonionic surfactants, and from 0.1 to 5% by weight of soaps. The detergent may also contain bleaching activators, for example from 1 to 10% by weight, and fillers such as sodium sulfate, for example from 5 to 50% by weight. Although not preferred from an environmental point of view, it is possible to include chelating agents such as phosphonates or EDTA, for example in an amount from 0.1 to 1% by weight. Additionally, the detergent may contain conventional components such as water glass, carboxy methyl cellulose, enzymes, foam regulators, perfumes, colouring agents, optical brighteners and water. The detergent can be prepared with conventional methods such as dry mixing, agglomeration or spray drying. If the preparation involves spray drying, any heat sensible component such as particles comprising peroxy compounds, enzymes and perfumes should be added to the dried material. A separate bleaching powder may comprise up to almost 100% by weight of particles containing peroxy compounds according to the invention, but preferably the content is from 5 to 90% by weight. The bleaching powder may comprise only one peroxy compound or a mixture of particles containing different kinds of peroxy compounds. It is advantageous if a hydrogen peroxide generating substance such as percarbonate, for example from 10 to 75% by weight, is used in combination with a bleaching activator such as TAED or TAGU, for example from 2 to 25% by weight. Also other bleaching activators such as a diacylated dipercarboxylic acid may be used, for example in an amount from 2 to 25% by weight. A bleaching powder may also contain detergent builders, for example from 5 to 90% by weight, surfactants, for example up to about 10% by weight, enzymes, for example up to 2% by weight, or fillers, for example from 5 to 90% by weight. A preferred bleaching powder consists essentially of from 30 to 75% by weight of particles containing percarbonate, from 10 to 25% by weight of a bleaching activator, the balance preferably substantially being detergent builders, fillers, surfactants, water or mixtures thereof. A detergent for dishwashing may be in the form of a low alkaline detergent (pH of washing water intended to be about 10-11) suitably containing from 2 to 15% by weight of a bleaching agent comprising particles according to the invention, such as sodium percarbonate, from 5 to 50% by weight of alkali metal disilicate, from 0 to 40% by weight of alkali metal carbonate, from 15 to 50% by weight of builders such as sodium citrate and polycarboxylates or sodium tri polyphosphate (STPP), from 0.5 to 5% by weight of low foaming nonionic surfactants, from 0.5 to 5% by weight of enzymes and from 1 to 6% by weight of bleaching activators such as TAED. A dishwasher detergent may also be high alkaline (pH of washing water intended to be about 11-12) having a similar composition as the low alkaline detergent, the disilicate however being replaced with from 20 to 80% by weight of alkali metal meta silicate and the builder preferably substantially consisting of STPP. The present invention makes it possible to prepare stable bleaching agents comprising peroxy compounds, particularly percarbonate, which may be used in detergents including zeolites such as zeolite 4A. The invention also makes it possible to decrease or exclude the use of other chelating agents in detergents, such as the commonly used EDTA or phosphonates which are less suitable from an environmental point of view. The invention will now be described through the following examples which, however, not are intended to limit the scope of the invention. If not otherwise stated, all contents an percentages refer to content and percent by weight. EXAMPLE 1 (not within the scope of the invention): Sodium percarbonate particles with a diameter of about 315-1250 µm and a density of about 1000 g/l were coated with different chelating agents and optionally with aqueous sodium disilicate solution by spraying in a rotating drum and drying in a fluidized bed. Particles according to the invention were prepared by coating with sodium glucoheptonate and sodium gluconate. Particles for comparison were prepared by coating with sodium citrate, Dequest® 2016 (1-hydroxyethylidene (1,1-diphosphonic acid) tetra sodium salt) and disodium EDTA. In order to test the storage stability of the percarbonate, the prepared particles as well as uncoated particles were included in a standard detergent IEC-Z (Henkel) consisting of 9.7% linear alkyl benzenesulfonate (C average 11.5), 5.2% ethoxylated C 12-18 alcohol (EO 7 ), 3.6% sodium-soap, 32.5% zeolite A, 13.0% sodium carbonate, 5.2% sodium salt of copolymerisate of acrylic- and maleic acid (CP 5 ), 3.9% sodium waterglass (ratio 3.3), 1.3% carboxy methyl cellulose, 0.3% EDTA, 0.3% optical brightener (stilbene type), 24.4% sodium sulfate, water and foam regulator, 0.6% enzyme prills protease (activity 300.00). Samples were prepared from 64 grams IEC-Z, 12 grams percarbonate particles and 4 grams TAED. A Quick Stability Index (QSI) was determined for each sample by measuring the amount of oxygen formed during 24 hours storage at 40°C and dividing the amount oxygen liberated by the relative content (%) of active oxygen in the original percarbonate. Thus, a low QSI-value means high stability. The results appear in the table below, in which the contents of the different constituents refer to % by weight based on the entire particle. The following abbreviations are used: PC = sodium percarbonate; SI = sodium disilicate; C = sodium citrate; D = Dequest® 2016; E = disodium EDTA; GH = sodium glucoheptonate; G = sodium gluconate; AO = active oxygen; QSI = quick stability index. PC SI C D E GH G AO QSI 100 0 0 0 0 0 0 14.8 3.1 95 0 5 0 0 0 0 13.9 1.5 95 0 0 0 0 0 5 14.1 0.9 95 0 0 0 0 5 0 13.9 0.8 93 2 0 5 0 0 0 14.1 0.9 93 2 0 0 5 0 0 14.1 1.2 93 2 0 0 0 5 0 13.8 0.3 91 2 0 0 0 7 0 13.5 0.2 95 5 0 0 0 0 0 14.0 1.4 95 0 0 0 0 5 0 13.9 0.8 93 2 0 0 0 5 0 13.8 0.3 EXAMPLE 2 : Sodium percarbonate particles with a diameter of about 315-1250 µm and a density of about 900 g/l were prepared by granulation from fine percarbonate particles in a rotating Eirich drum together with aqueous sodium disilicate solution and/or sodium glucoheptonate and/or anhydrous sodium carbonate (soda ash) . The particles were subsequently dried in a fluidized bed and were then optionally coated with sodium glucoheptonate and/or aqueous sodium disilicate solution in the same way as in Example 1. All additives were premixed before addition to the percarbonate. The stability of the percarbonate in a standard detergent was determined in the same way as in Example 1. The results appear in the table below. In the case the content of an ingredient is indicated with two numbers, the first one refers to the content in the core and the second one to the content in the coating. As in Example 1, all contents are given in % by weight based on the total weight of the particle. The same abbreviation as in Example 1 are used. Additionally, S stands for soda ash. PC S SI GH AO QSI 76 15 2+2 0+5 11.0 0.1 78 15 2+0 5+0 10.9 1.1 93 0 2+2 0+3 13.1 1.1 95 0 2+0 3+0 13.5 1.8 89 0 2+2 0+7 12.8 0.5 74 15 2+2 0+7 10.7 <0.1 91 0 2+2 0+5 13.1 1.1 76 15 2+2 0+5 11.0 <0.1 83 15 2+0 0 12.0 2.5 91 0 2+2 1+4 13.0 0.6 91 0 2+2 0+5 13.1 1.1 89 0 2+2 1+6 12.7 <0.1 89 0 2+2 0+7 12.8 0.5

Claims: Particles comprising a peroxy compound with capability of releasing hydrogen peroxide or peroxy acids in aqueous solutions, characterised in that the peroxy compound in the particles is mixed with alkali metal silicate and a chelating agent selected from alkali metal salts or alkaline earth metal salts of a hydroxy carboxylic acid satisfying the formula: RC n H m (OH) n COOH in which R is CH 2 OH, n is 2-6 and m is 0-n. Particles as claimed in claim 1, characterised in that they contain from 0.1 to 10% by weight of alkali metal silicate and from 0.1 to 10 % by weight of the chelating agent. Particles as claimed in anyone of the claims 1-2, characterised in that the chelating agent is an alkali metal salt of the hydroxy carboxylic acid. Particles as claimed in anyone of the claims 1-3, characterised in that n is 4 or 5. Particles as claimed in anyone of the claims 1-4, characterised in that m is equal to n or n-2. Particles as claimed in anyone of the claims 1-5, characterised in that the chelating agent is an alkali metal glucoheptonate. Particles as claimed in claim 6, characterised in that the chelating agent is sodium glucoheptonate. Particles as claimed in anyone of the claims 1-7, characterised in that the peroxy compound is sodium percarbonate. Method of preparing particles according to anyone of the claims 1-8, characterised in that a peroxy compound with capability of releasing hydrogen peroxide or peroxy acids in aqueous solutions, alkali metal silicate and a chelating agent selected from alkali metal salts or alkaline earth metal salts of a hydroxy carboxylic acid satisfying the formula: RC n H m (OH) n COOH in which R is CH 2 OH, n is 2-6 and m is 0-n, are mixed and granulated to form particles. Method as claimed in claim 9, characterised in that the chelating agent is an alkali metal salt of the hydroxy carboxylic acid. Method as claimed in any one of the claims 9-10, characterised in that n is 4 or 5. Method as claimed in any one of the claims 9-11, characterised in that m is equal to n or n-2. Method as claimed in any one of the claims 9-12, characterised in that the chelating agent is an alkali metal glucoheptonate. Method as claimed in claim 13, characterised in that the chelating agent is sodium glucoheptonate. Method as claimed in anyone of the claims 9-14, characterised in that the peroxy compound is sodium percarbonate. Use of particles according to anyone of the claims 1-8 as a bleaching agent. Composition containing an inert filler, and/or one or several substances active at washing, characterised in that the composition also contains particles according to anyone of the claims 1-8.

Inventors: JIGSTAM MONICA, LAGNEMO HANS, JIGSTAM, MONICA, LAGNEMO, HANS
Applicants: EKA CHEMICALS AB
Application year: 1995
Main classification: C11D3
IPC codes: C01B15, C11D3, C11D17