METHOD OF LOW TEMPERATURE BLEACHING WITH REDUCED AMOUNTS OF CHLORINE REQUIRING REDUCED BLEACHING INTERVALS

Abstract: A method of bleaching tertile materials in water at lower temperatures and reduced time intervals wherein: a source of bromide ions is added to the water to impart an initial concentration between 1 and 25 ppm; a chlorine ion source is added to the water to yield an initial concentration between 25 and 90 ppm; the wash water and textile materials are agitated for an interval between 30 seconds and 5 minutes; and the bleached textiles are recovered. The process may be carried out at temperatures between 80° and 120°F. Preferred ion donating sources are sodium bromide and sodium hypochlorite. If desired, the sodium bromide may be com­ pounded with conventional detergent formulations.

Description: This invention relates to an improved method of bleaching in aqueous systems such as laundry operations, processing of textile materials, or fabric goods using a mixture of chlorine- and bromine-containing compounds at lower temperatures and shortened time intervals. The use of halogen-releasing agents for bleaching in aqueous solution, as part of the processing or laundering of textile materials, is well known. Traditionally, chlorine-containing bleaching agents have been preferred because of their bleaching ability, relative low cost and acceptable odors. Examples of such chlorine-containing bleaching agents include chlorine gas, alkali metal hypochlorites and organo-chlorine complexes. Most chlorine bleaching agents employed in laundering or processing textile materials require temperatures of approximately 71°C (approximately 160°F) to effect adequate bleaching. Reduction in process temperature is desirable for the associated energy savings. To this end, it has been found that supplementing chlorine bleaching agents with bromine-containing compounds in a highly alkaline solution provides effective bleaching at lower temperatures. To accomplish effective bleaching, low temperature bleaching methods require large concentrations of bromine-chlorine bleaching compounds. The textile material or fabric to be bleached is exposed to high concentrations of halogen ions. Extended periods of contact between aqueous bleaching agents in high concentrations and the textiles to be treated destroys fabric integrity, reduces the useful life of the fabric, and causes discoloration. To date, no bleaching method has been developed which produces effective whitening in shortened bleaching intervals. For example, GB-A-596,192 relates to bleaching cellulose-containing materials by the action of an aqueous hypochlorite vat in the presence of bromide. Also, WO-A-81/02314 proposes the use of positive bromine ions in bleaching textile goods. Bleaching which occurs in highly alkaline aqueous media can have similar detrimental effects on fabric durability and appearance. Thus, a bleaching process in which equivalent cleaning and whitening could be accomplished in shortened time periods requiring less halogenated bleaching agent, is highly desirable. Thus, it would be desirable to provide a method of bleaching fabrics and other materials at or near a solution pH of 7. It is also desirable to provide a bleaching method which can occur at lower process temperatures. The present invention is predicated on the discovery that effective bleaching of textile materials and fabric goods can be accomplished at low temperature and/or at reduced time intervals when the goods are exposed to an aqueous solution which contains a conventional bleaching agent augmented by a bromide ion donor. The present invention, thus, generally, provides a method of bleaching textile goods in which a source of bromide ion is added to the wash solution prior to the addition of a source of chlorine-containing ions. By practising the present invention, bleaching in significantly shortened process times and smaller initial chlorine ion concentrations approximately one-half those employed in present technology is achieved. The present invention provides a method for bleaching textile materials in water comprising contacting the materals with a bleaching solution containing sources of bromide ions and chlorine-containing ions and recovering the textile materials from the water after the termination of the treating period characterised by: (i) adding a source of bromide ions to a wash water containing textile materials to be bleached in an amount sufficient to impart an initial bromide ion concentration between about one and about twenty-five parts per million; (ii) adding a source of chlorine-containing ions in an amount sufficient to yield an initial chlorine-containing ion concentration in an amount between about fifty and about ninety parts per million; (iii) agitating the wash water to provide intimate contact between the textile materials and bleaching agents while the source of bromide ions is added to the wash water prior to the addition of the source of chlorine-containing ions, both sources being added as a liquid bleach; (iv) maintaining the textile materials in the wash water with agitation for a period between about thirty seconds and ten minutes. By this method, the time period required for bleaching of textile materials in water is reduced without sacrificing cleaning efficiency. For a more complete understanding of the present invention reference is made to the following detailed description and accompanying examples. The present invention is predicated on the discovery that the use of bromide ion in solution can accomplish effective bleaching at significantly lower pH levels than previously possible with conventional chlorine bleaches alone. Lower pH levels during bleaching provide better fabric colour retention and reduce fabric damage. It has also been found that the lower pH levels required with bromide-enhanced bleaching lessen the amount of fabric yellowing caused by chlorine retention in the conventionally bleached fabric. The present invention provides a process in which a source of bromide ions is added to a thoroughly mixed wash solution, already containing the textile goods to be bleached. For optimum results, the pH of the wash solution is maintained between about 6.5 and about 10.5 at a maximum 1 percent solution. Reduced pH in the bleach solution permits the use of lower chlorine levels without sacrificing bleaching efficiency. In practising the present invention, the amount of bromide ion material added is such that the initial bromide ion concentration imparted to the solution is between about one and twenty-five ppm. A material which provides a source of chlorine ions or hypochlorous ions is added to the wash solution containing bromide ions to yield an initial total chlorine ion concentration between about twenty-five and about ninety ppm. The resulting wash solution is preferably maintained at a temperature between about 26°C and about 49°C (between about 80°F and about 120°F) and is agitated for an interval between about thirty seconds and ten minutes after which the textile goods are recovered and rinsed and the spent wash solution discarded. If shortened bleaching intervals are desired, larger amounts of chlorine are added to yield an initial chlorine ion concentration of about ninety ppm. The addition of bromide ions enhances the bleaching capability of the solution so that equivalent bleaching is achieved in half the conventional time. By practising the present invention, optical whitening equivalent to a bleaching time of ten minutes or greater is achieved in one half the time. Alternately, if reduction of chlorine concentration is desired the addition of a source of bromide ions will permit effective bleaching in wash solutions in which the chlorine ion concentrations have been reduced by as much as 50 percent. In a solution having an initial bromide ion concentration between about one and about twenty-five ppm maintained at a preferred temperature between about 26°C and about 49°C (between about 80°F and about 120°F) effective bleaching can be achieved in conventional time intervals. The source of bromide ion used herein may be derived from any compound which disassociates to form bromide ions and other radicals and which will not interfere in the bleaching process and any subsequent laundering processes. Inorganic bromide salts such as the alkali or alkaline earth metal bromide salts, e.g., sodium bromide, potassium bromide, magnesium bromide, calcium bromide, and the like, as well as mixtures thereof, can be used. Examples of organic compounds which provide a source of bromide ions suitable for use in this application are organo-N-brominated materials such as N-brominated alkylhydantoins, isocyanurates, melamines, or glycourils, and mixtures thereof. The bromide ion donor may be compounded with any conventionally known organic surfactant. Anionic, non-ionic or amphoteric surfactants or mixtures can be employed. The surfactants can be present alone or can be compounded with builders in detergent compositions. Examples of suitable anionic surfactants are water-soluble salts of higher molecular weight sulfoxy-containing detergents, such as higher alkylbenzene sulfonates, paraffin sulfonates, olefin sulfonates or fatty alcohol sulfates having long hydrophobic chains having 10 to 20 carbon atoms. Among the sulfated and sulfonated aliphatic compounds anticipated are the sulfuric acid esters of polyhydric alcohols which are partially esterified with higher fatty acids, e.g., coconut oil monoglyceride monosulfate, tallow diglyceride monosulfate; long chain pure or mixed alkyl sulphates e.g., lauryl sulfate, cetyl sulfate; hydroxy sulfonated higher fatty acid esters, e.g. higher fatty acid esters of low molecular weight alkylol sulfonic acids, e.g. fatty acid esters of isothionic acid; the fatty acid ethanol-amide sulfates; the fatty acid amides of amino alkyl sulfonic acids, e.g., lauric amide of taurine, and the like. Other suitable synthetic anionic detergents include water-soluble soaps of higher fatty acids such as the sodium soap of a 75:25 mixture of tallow and coconut oil fatty acids. Examples of suitable cationic surfactants which may be used include long chain alkyl quarternary ammonium compounds such as cetyl quarternary ammonium salts. Within this group are included cetyl trimethyl ammonium chloride and cetyl pyridinium chloride. Nonionic surfactants which can be used in the present invention include the polyoxyethylene ethers of alkyl aromatic hydroxy bodies (e.g., the alkylated polyoxyethylene phenols), the polyoxyethylene ethers of long chain aliphatic alcohols and the polyoxyethylene ethers of hydrophobic propylene oxide polymers, e.g., the condensate of ethylene oxide with polypropylene glycol which condensate contains 80 percent ethylene oxide and has a molecular weight of about 1700, and iso-octylphenoxy polyoxyethylene ethanol having about 8.5 ethanoxy groups per molecule, and the like. Alkyl amine oxide detergents such as lauryl or myristal dimethyl amine oxides may be present. The anionic and cationic surface active agents are commonly used in the form of their water-soluble salts. For the synthetic anionic compounds, the alkali metal (e.g. sodium, potassium) salts are preferred, though other salts such as ammonium, amine, alkylolamine, and alkaline earth metals (e.g. calcium, magnesium) salts may be used if desired. For the cationic agents chloride, sulfate, acetate, or like salts may be employed satisfactorily. Amphoteric surfactants also are contemplated for use in the present invention. Examples of these include the salts of higher alkyl beta amino propionic acids, e.g., sodium N-lauryl beta alanine, the higher alkyl substituted betaines such as lauryldimethylammonium acetic acid; and the imidazoline type exemplified by the disodium salt of 1-(2-hydroxyethyl)-1-(carboxy-methyl)-2-(hexadecyl)-4,5-dihydroimidazolinium hydroxide. Likewise, the present invention is extremely efficacious in augmenting the liquid detergent disclosed in GB-A-2,154,599. In practicing the present invention, a liquid bleach is employed. After the bromide ion source has been added to the wash solution and thoroughly mixed, a source of chlorine, which is present as the hypochlorous ion, is added and thoroughly mixed with the wash solution to yield an initial concentration of hypochlorous ions of between about twenty-five and ninety ppm. Any organic or inorganic salt, which disassociates freely to form the hypochlorous ion may be employed in the process of the present invention. Suitable compounds are the alkali and alkaline earth metal hypochlorites such as sodium hypochlorite, lithium hypochlorite or calcium hypochlorite. Other useful hypochlorite-liberating agents include trichloromelamine, N,N-dichlorobenzolene, and N,N-dichloro-p-toluene sulfonamide. Mixtures of the hypochlorite sources may be used. Alternately, water-soluble dry solid materials which generate chlorine on contact with, or dissolution in water can be used. Examples of these are heterocyclic N-chloroimides such as the trichloroisocyanuric acid, and dichloroisocyanuric acid and salts thereof such as sodium dichloroisocyanurate and potassium dichloroisocyanurate. Other imides which may be used include N-chlorosuccinimide, N-chloromalonimide, N-chlorophthalimide and N-chloronaphthalimide, and mixtures thereof. Additional suitable compounds are hydantoins such as 1,3-dichloro 5,5 dimethyl hydantoin; N-monochloro-5,5-dimethylhydantoin; methylene-bis (N-chloro-5,5-dimethylhydantoin); 1,3-dichloro-5-methyl-t-amylhydantoin, and the like. In the preferred embodiment, commercial aqueous sodium hypochlorite (5¼ to 15 percent by volume NaOCl) is added to bromide-containing wash water in sufficient amounts to yield an initial hypochlorite ion concentration between about twenty-five and about ninety ppm. The solution containing textile materials is then agitated for a period of about 30 seconds and five minutes to provide intimate contact between the textile materials and the bleaching agent. When bleaching is completed, the bleached textile materials are removed and rinsed. The spent wash water is also discarded. For a more complete understanding of the present invention, reference is made to the following examples. The examples are to be construed as illustrative and not limitative of the present invention. EXAMPLE I The cleaning capability of various liquid detergent compositions was determined for ten minute wash intervals. The total detergent concentration was varied, as was the solution temperature, to determine optimum temperatures and concentrations. The detergent compositions at the various temperatures and concentrations were also tested for increased cleaning ability in the presence of chlorine. Three typical competitive liquid detergents were selected for purposes of comparison. An analysis of the composition of these three liquid detergents is set forth in Table I. The fourth detergent tested was fortified with sodium bromide. The components of this fourth detergent designated OPL Liquid E are set forth in Table II. To determine cleaning efficiency a swatch of Empa 115 Bleach Cloth having initial reflectance of 29.5 as determined by a Hunter Reflectometer was agitated in solutions at 49°C (120°F) containing 0.06 weight percent, 0.12 weight percent or 0.24 weight percent of the various detergents and 100 ppm chlorine. Similar swatches were treated in identical detergent solutions having no added chlorine. After treatment the optical reflectance of each swatch was measured. The increase in optical reflectance over the initial sample indicates soil removal (ΔSR). The results are shown in Table III. COMPOSITION OF TEST LIQUID DETERGENTS ASSAY Alkalinity as Na₂O COMPETITIVE A COMPETITIVE B COMPETITIVE C Total 5.84 11.42 23.6 Active 2.42 9.60 26.0 pH of 1% Solution 10.7 12.53 12.7 % Non-volatile 45.0 46-51 67.0 % Phosphate as P₂O₅ 10.96 4.1 0.9 % Anionic as LAS - 5.5 - % Nonionic 6.65 3.35 14.7 % Other Surfactant 7.33 (Unknown) 10.50 (Unknown) 2.2 (Fatty Acids) % Silicates as SiO₂ 1.60 Not Detected Citrates - - Present 10 Minute Agitation at 49°C (120°F) Detergent Concentration (wt.%) ΔSR 100 ppm Chlorine Added ΔSR No Chlorine Added Competitive A 0.06 50.50 1.01 0.12 51.34 1.46 0.24 50.10 1.04 Competitive B 0.06 46.82 0.95 0.12 44.07 0.85 0.24 39.51 0.92 Competitive C 0.06 39.88 2.96 0.12 38.03 1.80 0.24 35.15 3.16 OPL Liquid E 0.06 51.50 1.46 0.12 51.34 1.63 0.24 50.10 1.54 EXAMPLE II The procedure outlined in Example I was repeated on new swatches at solution temperatures of 38°C (100°F). The results are shown in Table IV. 10 Minute Agitation at 38°C (100°F) Detergent Concentration (wt.%) ΔSR 100 ppm Chlorine Added ΔSR No Chlorine Added Competitive A 0.06 46.93 0.81 0.12 45.80 0.95 0.24 45.56 1.01 Competitive B 0.06 37.86 0.58 0.12 36.09 1.14 0.24 30.85 1.02 Competitive C 0.06 34.90 1.16 0.12 27.23 1.16 0.24 26.16 1.27 OPL Liquid E 0.06 48.84 1.17 0.12 48.45 1.03 0.24 48.78 0.92 EXAMPLE III The procedure outlined in Example I was repeated with new swatches at solution temperature of 26°C (80°F). The results are shown in Table V. 10 Minute Agitation at Detergent Concentration (wt.%) ΔSR 100 ppm Chlorine Added ΔSR No Chlorine Added Competitive A 0.06 0.12 0.24 41.01 0.45 41.37 1.27 39.90 1.43 Competitive B 0.06 0.12 0.24 26.95 0.57 21.39 0.71 20.52 0.70 Competitive C 0.06 0.12 0.24 23.34 1.99 18.14 0.86 15.68 0.68 OPL Liquid E 0.06 0.12 0.24 45.49 1.67 45.46 1.17 44.84 0.88 EXAMPLE IV The procedure outlined in Example I was repeated using 50 ppm and 100 ppm chlorine concentrations. The wash interval wash was shortened to five minutes. The results are shown in Table VI. By comparing the results of Tables III and VI, it can be seen that reduction of the agitation time from 10 to 5 minutes with 100 ppm chlorine concentrations does not reduce the bleaching effectiveness of OPL Liquid E as dramatically as the non-bromide ion containing compositions. OPL Liquid E combined with 100 ppm chlorine provides effective bleaching in washing intervals which are one-half the conventional periods. 5 Minute Agitation at 49°C (120°F) Detergent Concentration (wt.%) ΔSR 50 ppm Chlorine Added ΔSR 100 ppm Chlorine Added Competitive A 0.06 0.12 0.24 17.9 24.0 16.4 23.6 16.0 25.0 Competitive B 0.06 0.12 0.24 9.5 15.0 7.6 12.8 6.0 11.4 Competitive C 0.06 0.12 0.24 8.8 3.8 7.7 12.0 7.1 11.5 OPL Liquid E 0.06 0.12 0.24 29.5 34.0 32.3 36.3 33.4 38.0 EXAMPLE V The procedure outlined in Example II was repeated using 50 ppm and 100 ppm chlorine concentrations. The wash interval was shortened to five minutes. The results are shown in Table VII. As can be seen from a comparison of Tables VI and VII, the bleaching capability at 38°C (100°F) of the OPL liquid containing a source of bromide ions and either 50 ppm or 100 ppm chlorine is affected less by the decrease in wash intervals than the other non-bromide ion-containing bleaching compositions. 5 Minute Agitation at 38°C (100°F) Detergent Concentration (wt.%) ΔSR 50 ppm Chlorine Added ΔSR 100 ppm Chlorine Added Competitive A 0.06 0.12 0.24 12.4 16.7 9.7 16.9 9.8 16.1 Competitive B 0.06 0.12 0.24 6.1 11.3 5.3 9.7 4.0 6.5 Competitive C 0.06 0.12 0.24 6.1 8.4 5.5 7.0 4.8 6.2 OPL Liquid E 0.06 0.12 0.24 25.1 28.2 29.1 31.2 29.9 34.6 EXAMPLE VI The procedure outlined in Example III was repeated using 50 ppm and 100 ppm chlorine concentration. The wash interval was decreased to five minutes. The results are shown in Table VIII. As can be seen from a comparison of Tables V and VIII the bleaching capability of the OPL liquid and either 50 ppm or 100 ppm chlorine is largely unaffected by the reduction in the wash interval. 5 Minute Agitation at 26°C (80°F) Detergent Concentration (wt.%) ΔSR 50 ppm Chlorine Added ΔSR 100 ppm Chlorine Added Competitive A 0.06 6.3 9.8 0.12 7.6 9.5 0.24 7.3 12.0 Competitive B 0.06 4.2 6.9 0.12 3.3 5.4 0.24 0.9 4.2 Competitive C 0.06 2.8 4.8 0.12 3.3 3.7 0.24 2.4 2.8 OPL Liquid E 0.06 21.2 23.4 0.12 24.0 26.2 0.24 24.3 27.5 It can be seen from the data that detergent enhanced with bromide ion provides more effective and efficient cleaning at 100 ppm chlorine concentration at temperatures between about 26°C and 49°C (between about 80°F and 120°F). Furthermore, bromide ion-enhanced detergent provides cleaning efficiency at 50 ppm chlorine approximately equivalent conventional detergents at 100 ppm chlorine.

Claims: A method for bleaching textile materials in water comprising contacting the materals with a bleaching solution containing sources of bromide ions and chlorine-containing ions and recovering the textile materials from the water after the termination of the treating period characterised by: (i) adding a source of bromide ions to a wash water containing textile materials to be bleached in an amount sufficient to impart an initial bromide ion concentration between about one and about twenty-five parts per million; (ii) adding a source of chlorine-containing ions in an amount sufficient to yield an initial chlorine-containing ion concentration in an amount between about fifty and about ninety parts per million; (iii) agitating the wash water to provide intimate contact between the textile materials and bleaching agents while the source of bromide ions is added to the wash water prior to the addition of the source of chlorine-containing ions, both sources being added as a liquid bleach; (iv) maintaining the textile materials in the wash water with agitation for a period between about thirty seconds and ten minutes. A method as claimed in claim 1 wherein the bromide ion source is a compound selected from alkali or alkaline earth metal bromide salts, or mixtures thereof. A method as claimed in claim 2 wherein the source of bromide ions is sodium bromide. A method as claimed in claim 1 wherein the bromide ion source is a compound selected from N-brominated alkylhydantoins, isocyanurates, melamines, glycourils and mixtures thereof. A method as claimed in any of claims 1 to 4 wherein the source of bromide ions is in admixture with an organic surfactant. A method as claimed in claim 5 wherein the surfactant is present in a detergent composition, the detergent composition consisting essentially of up to about one hundred weight percent of the organic surfactant. A method as claimed in claim 6 wherein the detergent composition further comprises a water-soluble builder salt in an amount at least two-thirds of the amount of the surfactant and about one-eigth to one percent, by weight, alkali metal bromide. A method as claimed in any of claims 1 to 7 wherein the source of chlorine-containing ions is a compound selected from alkali metal hypochlorites, alkaline earth metal hypochlorites, trichloromelamine, N,N-dichlorobenzolene, N,N-dichloro- p -toluene sulfonamide, heterocyclic-N-chloroimides, chlorinated alkyl hydantoins and mixtures thereof. A method as claimed in claim 8 wherein the source of chlorine-containing ions is an alkali metal hypochlorite. A method as claimed in claim 9 wherein the source of chlorine-containing ions is sodium hypochlorite. A method as claimed in any of claims 1 to 10 wherein the wash water is maintained at a temperature in the range of from about 26 to 49°C (from about 80 to 120°F). A method as claimed in any of claims 1 to 11 wherein the pH of the wash water is maintained between about 6.5 and about 10.5.

Inventors: CORTE, GEORGE E.
Applicants: DIVERSEY CORPORATION
Application year: 1986
Main classification: D06L3
IPC codes: D06L3, C11D3