MXPA96002181A - Procedure for the preparation of dispersiones de colorante stable to the store - Google Patents

Abstract

The present invention relates to a process for the preparation of dye dispersions stable to the storage of alkali metal salts of azo anionic direct dyes consisting of: a) preparing an aqueous suspension of an alkali metal salt of an azo direct dye, having said salt a solubility in water at 25 ° C of about 0.1 to about 15% by weight, by azo coupling of one or more aromatic diazonium salts with one or more couplers, while maintaining a pH of less about 5 adding a basic alkali metal compound in the absence of a nitrogen-containing base, b) optionally stirring the aqueous suspension at a temperature of 5 ° C to 100 ° C for about six hours, c) optionally adjusting the the aqueous suspension of 5 ° C to 40 ° C, and d) add to the aqueous suspension, without initially isolating the dyes, a viscosity enhancing agent in an amount sufficient to obtain a viscosity, determined at a temperature of from about 20 to about 25 ° C, from 500 to 5000 centipoise and from 0 to 10% by weight, based on the total weight of the dye dispersion, of a humectant, thus forming the stable dye dispersion when stored

Description

PROCEDURE FOR THE PREPARATION OF COLORANT DISPERSIONS STABLE TO STORAGE This application is a Continuation in Part of the application Serial No. 08 / 485,565, filed on June 7, 1995. BACKGROUND OF THE INVENTION This invention relates to the direct preparation of storage-stable dye dispersions based on metal salts alkalines of direct azo dyes stabilized by viscosity enhancing agents. Direct azo dyes are known. For example, "Direct Dyes" in Color Index, Third Edition, Vol. 2 (The Society of Dyers and Colourists, 1971), pages 2005-2006; H. Zollinger, Color Chemistry (VCH Verlagsgesellschaft, 1973), pages 163-167, and H.E. Woodward, "Azo Dyes for Cotton" in The Chemistry of Synthetic Dyes and Pigments, ed. HE HAS. Lubs (Robert E. Krieger Publishing Company, 1955), pages 111-143. Direct azo dyes are anionic dyes containing one or more azo groups and are, by definition, substantive for cellulose when applied from an aqueous bath containing an electrolyte (eg, Color Index, on page 2005), although some direct dyes can also be used to dye or print leather, wool, silk, nylon and yarn fibers. When azo direct dyes are used as dilute aqueous solutions, the counter ion is not critical in general. However, when such dyes are prepared as concentrated aqueous solutions, it is usually necessary to use counterions based on amines (rather than metal ions) and solubilizing agents such as urea to obtain stable solutions of said dyes. Therefore, for economic and environmental reasons, it would be advantageous to avoid using dyes as amine-based salts. Although metal salts of anionic dyes are generally unsuitable for the preparation of concentrated solutions, methods for using metal salts are known. For example, dyes may be formed or their color developed directly on the fiber, thereby avoiding solubility problems. For example, US Patents 913,634 and 1,127,027. However, such methods are not suitable for the preparation of concentrated dye dispersions stable to storage. It is also possible to stabilize dispersions of metal salts of anionic dyes with viscosity enhancing agents, including anionic polysaccharides such as xanthan gum. For example, US Patents 1,719,944, 4,002,603, 4,468,230, 4,545,818, 4,671,691, 4,673,410, 4,726,845 and 5,076,968. However, dispersions are typically prepared by first isolating the metal salt and then only suspending the metal salt in a suitable aqueous medium containing one or more stabilizing additives. Although US Pat. No. 1,719,944 describes the addition of alkylcellulose in various stages during the preparation of low solubility dyes, including the addition immediately after said dyes are formed, the resulting dyes are collected in the form of pastes or solids rather than obtained as stable dispersions. .

Therefore, it was an object of the present invention to obtain stable dispersions of metal salts of direct azo dyes which can be prepared without using intermediate isolation steps and used without using special coloring methods. It has now been found that it is possible to obtain stable dispersions to the high quality storage of alkali metal salts of anionic direct azo dyes by adding a viscosity enhancing agent directly to the reaction mixture in which the dye is formed without first isolating the dye . Despite the absence of an isolation step, the dispersions prepared according to the present invention, which do not precipitate on standing, even for prolonged periods, can typically be used as direct substitutes for the corresponding amine-based liquid formulations currently marketed. SUMMARY OF THE INVENTION This invention relates to a process for the preparation of dye dispersions stable to the storage of alkali metal salts of azo anionic direct dyes consisting of: (a) preparing an aqueous suspension of an alkali metal salt of a dye direct azosaid salt having a solubility in water at 25 ° C of about 0.1 to about 15% by weight, by azo coupling of one or more aromatic diazonium salts with one or more couplers, while maintaining a pH of at least about 5 (preferably, a pH of 6 to 9) by adding a basic alkali metal compound (preferably, an alkali metal hydroxide, carbonate or bicarbonate) in the absence of a base containing nitrogen; (b) optionally stirring the aqueous suspension at a temperature of about 5 ° C to about 100 ° C (preferably 50 ° C to 90 ° C, more preferably 70 ° C to 85 ° C), for up to about six hours ( preferably, one to three hours); (c) optionally, adjusting the temperature of the aqueous suspension to about 5 ° C to about 40 ° C (preferably, about 20 ° C to about 40 ° C), and (d) adding a water enhancing agent to the aqueous suspension. viscosity (preferably, an anionic polysaccharide, more preferably, xanthan gum) in an amount sufficient to obtain a viscosity, determined at a temperature of from about 20 to about 25 ° C, from about 500 to about 5000 centipoise (preferably 800 to 1500 centipoise) and 0 to about 10% by weight (preferably, 2 to 5% by weight), based on the total weight of the dye dispersion, of a humectant, thereby forming the stable dye dispersion upon storage. DETAILED DESCRIPTION OF THE INVENTION Suitable azo direct dyes are anionic dyes containing one or more azo groups attached to two aromatic groups or to an aromatic group and an active methylene type coupling and which are substantive for cellulose. Typical azo direct dyes contain four to eleven (or, more typically, four to six) aromatic rings, including heteroaromatic rings, and one to six (or, more typically, one to three) sulfonic acid groups. Some of the aromatic or heteroaromatic rings can be incorporated into fused ring systems, such as naphthalene. The portion of the dye molecule that is derived from the diazonium salt moiety used in the azo coupling process is typically less highly substituted than the portion of the dye that derives from the more electropositive coupling component. Typical coupling components are aromatic compounds, particularly naphthalene derivatives, substituted with hydroxy, amino and sulfonic acid groups. Although less common, the coupling component can also be a β-diketo compound, such as acetoacetates or, preferably, acetoacetamides (eg, an acetoacetanilide), which is coupled through the active methylene group between the β-diketocarbonyl groups. Although one or more azo bonds must be present, the various aromatic moieties may also bridge by other groups, such as urea or amide groups. Preferred direct azo dyes are monoazo direct dyes in which a single azo group is connected to two aromatic groups and the disazo direct dyes in which each of the two azo groups is connected to two aromatic groups (one of which may be , of course, joined to both azo groups). Both monoazo and disazo direct dyes have one or more sulfonic acid groups attached to at least one of the aromatic groups. Examples of suitable colorants include CI. Direct Red 256, Direct Yellow 127, Direct Yellow 147 and Direct Blue 279. Other examples can be found, for example, in the Color Index.

The alkali metal salts of the direct azo dyes are formed during the azo coupling process used to prepare the dyes. In a preferred method, a suitable aromatic amine is converted to the corresponding diazonium salt by known diazotization methods using an alkali metal nitrite salt (preferably sodium nitrite) in an aqueous mineral acid (preferably, hydrochloric acid). The resulting diazonium salt can be isolated by filtration, followed by washing to remove the residual salts and acid or by other known methods, such as centrifugation, which allow the removal of solvent, salts and residual acid. It is also possible, although generally less preferred, to use the diazonium salt directly as prepared or in concentrated form obtained, for example, by membrane separation or decantation methods. The dilution of the diazonium salt is generally not suitable for the preparation of dispersions according to the invention, due to the lower concentration resulting from the final dispersion. The diazonium salt is coupled with a suitable aromatic compound (ie, a "coupling") in a slightly acidic to basic aqueous medium. In a particularly preferred embodiment, the filter cake of the diazonium salt is added to a suspension or solution of an approximately equimolar amount of the coupling (or, alternatively, the coupling is added to a suspension of the diazonium salt in water) and the resulting mixture is adjusted and maintained at a pH of at least about 5 (preferably, a pH of 6 to 9) by the addition of a basic alkali metal compound (preferably, an alkali metal hydroxide, carbonate or bicarbonate, more preferably sodium or potassium hydroxide), thus forming the alkali metal salt in situ. After completion of the coupling reaction, the resulting salts of direct dyes eventually form crystalline precipitates or gels. Although not generally necessary, it may sometimes be desirable to add additional amounts of base before carrying out step (b). The coupling reaction is carried out in the absence of amine bases which are frequently used to obtain dye solutions. As examples of amine bases to be avoided are tertiary amines such as RaRbRcN, where Ra, R and Rc are independently hydrogen, C?-C6 alkyl or C2-C6 hydroxyalkyl, including, for example, triethylamine and triethanolamine. Regardless of the specific preparative method used in step (a), the resulting direct dye salts typically have a solubility in water of about 0.1 to about 15% by weight (preferably 1 to 7% by weight) to 25 ° C, such that the salts can form a dispersion in concentrated form, but, preferably, they can freely dissolve when diluted with water or a mixture of water with a water-miscible organic solvent. In general, salts having a solubility below the specified range would be too insoluble, even when prepared as a dispersion, to be useful as a colorant, whereas it would not be necessary, or even possible, to form dispersions of salts having a higher solubility .

In carrying out the process of the present invention, the alkali metal salt of the azo direct dye is not isolated, but instead is still processed in situ. Although it is possible to obtain a stable dispersion by directly treating the crystalline precipitate or gel form described above with the viscosity enhancing agent (i.e., without adjusting the temperature and sometimes even without stirring the product initially formed from the step (a) )), it is generally necessary to stir (preferably by stirring) the crystalline precipitate or gel before adding the viscosity enhancing agent (i.e., step (b)) at temperatures of up to about 100 ° C (preferably 50 ° C to 90 ° C, more preferably 70 ° C to 85 ° C) for up to about six hours (preferably one to three hours) to promote the conversion of the crystal and give a more stable dispersion. If heated above 40 ° C, the suspension is generally cooled in the eventual stage (c) to a temperature of about 5 ° C to about 40 ° C (preferably about 20 ° C to about 40 ° C) before adding the viscosity enhancing agent of the invention. Even if the suspension does not reach a temperature higher than 40 ° C during stage (a) or eventual stage (b), it may still be advantageous to change the temperature of the suspension to another temperature in the range specified in step (c) before adding the viscosity enhancing agent. Suitable viscosity enhancing agents for use in step (d) of the invention are compounds that increase viscosity and thus help to stabilize the dispersion against settling. Examples of suitable viscosity enhancing agents include natural gums (such as guar gum, alginates and gum arabic), anionic polysaccharides (such as sodium carboxymethylcellulose and xanthan gum), etherified cellulose, various heteropolysaccharides containing side chains of saccharides (such as as mannose and glucuronic acid), polyacrylamides and polymethacrylamides and polyacrylates and polymethacrylates. Preferred viscosity enhancing agents include anionic polysaccharides, particularly xanthan gum (which is generally used as an aqueous solution at 2 to 5% by weight). The viscosity enhancing agent is used in an amount sufficient to obtain the specified viscosities determined at a temperature of about 20 to about 25 ° C using methods known in the art, particularly the rotational method, employing a rotation axis. Although viscosities ranging from 800 to 1500 centipoise are generally preferred, somewhat higher or lower viscosities are often acceptable. For the preferred xanthan gum, suitable viscosities generally can be obtained by using about 0.1 to about 0.5% by weight based on the total weight of the dye dispersion. The final adjustments of color strength and viscosity can be made, in general, if necessary, by adding small amounts of water. In general, known humectants for use with colorants are suitable. Examples of suitable humectants include various glycols, such as propylene glycol and glycerin, glycol ethers, polyglycols, polyglycol ethers, and formamide. If used, the amount of humectant normally varies up to about 10% by weight (preferably, 2 to 5% by weight), based on the total weight of the dye dispersion. Other additives known in the art may also be included. For example, it is generally advantageous to include biocides to inhibit or suppress the growth of molds or bacteria. Examples of suitable biocides include potassium sorbate, sodium pentachlorophenolate, 2,6-dimethyl-1,3-dioxan-4-ol acetate, 1,2-benzisothiazol-3 (2H) -one and condensation of aromatic alcohols and paraformaldehyde (particularly benzyl alcohol and aqueous formaldehyde). The biocides, if used, can typically be used in amounts of up to 3% by weight (preferably from 0.05 to 0.5% by weight). It is also advantageous to include known defoamers, particularly in the coupling step (a). Examples of suitable defoamers include tributyl phosphate, reaction products of an alkylsuccinic acid anhydride and aliphatic alcohols, siloxanes and water immiscible organic liquids (such as mineral oil, chlorinated mineral oil and the like). It is possible to include known inhibitors of corrosion, preferably after completion of the coupling step (a). Examples of suitable corrosion inhibitors include benzotriazole, tolyltriazole and dicyclohexylammonium nitrate.

It is also possible to include known dispersants, such as those described in US Pat. 3,770,371, 4,110,073, 4,468,230 and 4,673,410. Suitable dispersants include compounds in which one part of the molecular structure is hydrophilic (for example, anionic groups such as sulfonate or carboxylate groups) and another part of the molecular structure is hydrophobic and includes sulfonated condensation products of naphthalene and formaldehyde, lignin sulfonates, alkyl sulfonates, polycarboxylic acid ester sulphonates, alkyl benzene sulfonates, sulfonated aliphatic alcohols, sulfuric acid monoesters of condensation products of ethylene oxide with amines, fatty acids, phenols or alcohols. Examples of suitable anionic dispersants include sodium dodecyl sulfonate, sodium lauryl sulfate, sodium dodecylbenzenesulfonate, dibutyl naphthalenesulfonate, sodium dioctyl sulfosuccinate, sulfuric acid monoesters of the condensation products of ethylene oxide with nonylphenol, condensation products of cresol, sodium bisulfite and formaldehyde, condensation products of 2-hydroxynaphthalene-6-sulfonic acid and formaldehyde, sulphonic acids of the condensation products of naphthalene, terphenyl or dithyol ether with formaldehyde and condensation products of cyclohexanone, sodium bisulfite and formaldehyde. In general, sodium or ammonium salts are preferred. Although not generally preferred, it is possible to include additional electrolytes in the dispersions of the invention. Examples of suitable electrolytes include sodium chloride and sodium sulfate.

The dispersions prepared according to the present invention typically contain about 10 to about 20% by weight (preferably, 12 to 15% by weight, more preferably about 12% by weight), based on the total weight of the dispersion, of the coloring component. The dispersions according to the present invention are stable in the sense that they do not precipitate on standing, even for prolonged periods of time. The dye dispersions of the present invention can be used to dye a variety of substrates, but are particularly useful for dyeing and printing paper, card and cardboard, as well as other cellulosics. The dye dispersions are preferably used directly undiluted. However, it is also possible to dilute the dispersions before use, thereby forming at least partially dissolved dye mixtures which are useful, for example, for continuous dyeing, such as appliqué applications. Particularly suitable substrates include, for example, bleached, glued or unglued lignin-free paper, for which the starting material may be bleached, unbleached or semi-milled pulps, and recycled and de-inked fibers. Other cellulosic fibers, such as cotton, can also be colored by the dye dispersions of the present invention. The dye dispersions can be applied by any of several methods known in the art, including application to a slurry in aqueous suspension, surface coloration, coating and printing.

Pulp application in an aqueous suspension (also called "internal coloration") can be performed by adding batches to a blender or "hydrodisgregator", which generally provides excellent agitation. The addition of batches is carried out by weighing or volumetrically measuring the colorant in the container containing the pulp. The dye dispersions of the present invention can also be added continuously to a flow of pulp in water by means of a measuring device such as a gear or piston type pump. The dyes can be added in undiluted or diluted form depending on the desired depth of shade and the type of measuring device employed. The surface coloring can be done, for example, in a paper machine with a set of rollers known as "sizing press". These rollers pinch the sheet of paper that travels between them. A pond of sizing press aqueous liquid, which generally contains starch and other additives, as well as the dyes, is measured on both sides of the sheet. The liquid is absorbed in the surface of the leaf, thus imparting a color to the leaf. The surface coloration is frequently used in combination with internal coloring techniques. The coloration by coating can be applied by any of several methods in line or offline with a paper machine. The coating suspensions typically consist of a pigmented filler (such as clay or titanium dioxide), a latex binder, a colorant (such as a dye dispersion according to the present invention) and other known additives to increase the coating performance. The coating mixture is typically applied to the sheet, generally using a roller coated with the coating mixture, and the excess is scraped with a knife. The printing can be carried out using any of several known methods to obtain decorative designs or a bulk surface coating. The dye dispersions of the present invention, for example, can be mixed with other additives, such as binders and lubricants, and applied to the surface of a sheet using any of several known printing techniques, such as flexographic printing. The following examples further illustrate details for the process of this invention. The invention, which is indicated in the foregoing description, is not limited in spirit or scope by means of these examples. Those skilled in the art will readily understand that known variations of the conditions of the following procedures can be used. Unless stated otherwise, all temperatures are degrees Celsius and all percentages are percentages by weight. EXAMPLES The viscosities of the dispersions formed in the following Examples were determined at a temperature from about 20 to about 25 ° C using a Brookfield Viscometer model LTV equipped with a number 3 shaft rotating at 12 rpm. The viscosity in centipoise (cp) of each sample was determined by multiplying the reading of the instrument after twelve revolutions per 100. Example 1 To a stirred suspension of 46.4 g (144 mmol) of 2- (4-aminophenyl) -6-methyl-7-benzothiazolesulfonic acid (also known as dehydrothio-p-toluidine sulfonic acid or "DHTPTSA") in 264 ml of water 12.8 g (160 mmol) of 50% aqueous sodium hydroxide were added. The mixture was stirred at 40 ° C for 15 minutes, after which 25.5 g (148 mmol) of 40% aqueous sodium nitrite was added in one portion. The resulting mixture was added over a period of two hours to a mixture of 1 g of 40% aqueous sodium nitrite in 43.9 g (378 mmol) of hydrochloric acid (20 ° Bé) diluted with approximately 117 ml. of water at 40 ° C. The diazotization mixture was stirred for another two hours, adding small portions of sodium nitrite as necessary to maintain the presence of nitrous acid, after which the reaction was stopped with about 0.2 g of sulfamic acid. The diazonium salt of DHTPTSA was collected and precipitated by filtration and washed with 150 ml of water adjusted to pH 3.5 with hydrochloric acid. The diazonium salt was then stirred with about 125 ml of water to form a suspension having a pH of about 4.0. To the diazonium salt suspension, with stirring, 18.6 g (145 mmol) of barbituric acid was added to form a suspension having a pH of about 2.0. To this suspension was then added 10% aqueous sodium hydroxide (approximately 60 ml) to maintain a pH of about 5.0 to 5.5. The suspension was then adjusted to pH 7.0 using approximately 6 ml of 10% aqueous sodium hydroxide and gradually heated to 80 ° C over a period of one hour. The mixture was allowed to cool to room temperature and was stirred for two hours. To the resulting suspension was added, with stirring, 40.0 g of a 2.5% aqueous solution of xanthan gum (available as Keltrol from Kelco) and 12.0 g of glycerin. The mixture was stirred rapidly for two hours, after which 1.2 g of Giv-Gard DXN (a preservative containing 2,6-dimethyl-1,3-dioxan-4-ol acetate) was added and obtainable from Givaudan Corp.) and 0.8 g of Proxel GXL (a preservative containing 1,2-benzisothiazol-3 (2H) -one and obtainable from ICI Americas). The mixture was diluted to approximately 475 ml with water to form a dispersion containing 13.9% of the monosodium salt of 2- [4- [(hexahydro-2,4,6-trioxo-5-pyrimidinyl) azo] phenyl] -6-methyl-7-benzothiazolesulfonic acid (solubility of 1.2 g / 100 g of water), as well as approximately 0.2% of sodium chloride, with a viscosity of 800 to 1200 cp and a? -, x 413 nm. Example 2 To a solution of 0.735 moles of p-cresidine-o-sulfonic acid dissolved in 1000 ml of sodium hydroxide, M, 174 ml (1.03 eq.) Of a 4.35 M aqueous solution (0.300 g / ml) of nitrite was added. of sodium. The resulting fine suspension was introduced over a period of 30 minutes at room temperature in a stirred mixture of 190 ml (2.5 equiv.) Of 30% hydrochloric acid and 1 ml of a 4.35M aqueous solution of nitrite of sodium in 200 ml of water. After 30 minutes, a small amount of sulfamic acid was added to destroy the excess nitrous acid. The resulting diazonium salt solution was then added over a period of 30 minutes to a stirred solution of 202 g (0.368 equiv.) Of 7,7 '- (carbonyldiimino) -bis [4-hydroxy-2- naphthalenesulfonic acid] ("J-acidic urea") in 800 ml of water, to which 10% sodium hydroxide portions were added to maintain a pH of 6.0, thus giving an easily stirred dark red suspension. More 10% sodium hydroxide was added to bring the pH to 7.0. The solution was then treated with 280 g of 2.5% aqueous xanthan gum, 75 g of glycerin as a humectant and 7.6 g of Giv-Gard DXN and 5.0 g of Proxel GXL as preservatives to form a dispersion containing approximately 12.3% of the tetrasodium salt of 7,7 '- (carbonyldiimino) -bis [4-hydroxy-3- [(2-methoxy-5-methyl-4-sulfophenyl) azo] -2-naphthalenesulfonic acid] (solubility of about 2.6 g / 100 g of water), as well as about 2.3% of sodium chloride, with a viscosity of about 1000 cp and a? max of 503 nm.

Example 3 To a stirred suspension of 75 g (20.3 mmol) of 4,4'-diaminostilben-2,2'-disulfonic acid (also known as flavonic acid) in 470 ml of water was added 31.3 g (39 mmol) of 50% aqueous sodium hydroxide. To the resulting dark brown solution was added 120 g (105 mmol) of hydrochloric acid (20 ° Bé) with high speed stirring over a period of two hours. After adjusting the temperature of the resulting suspension to 30 ° C, 72.3 g (41.9 mmol) of 40% aqueous sodium nitrite was added over a period of four hours. The diazotization mixture was stirred at about 33 ° C for another 1.5 hours, adding small portions of sodium nitrite as necessary to maintain the presence of nitrous acid, after which the reaction was then stopped with about 0.6 g. of sulfamic acid. The diazonium salt which precipitated by filtration was collected. To a suspension of 129 g (40 m ol) of 4-hydroxy-5-aminonaphthalen-2,7-disulfonic acid ("H acid") in 400 ml of water was added 36.4 g (45.5 mmol) of 50% aqueous sodium hydroxide to dissolve the acid H and adjust the resulting solution to pH 8.0. The diazonium salt was added over a period of 30 minutes, during which time a pH of about 7.5 to 8.0 was maintained by adding portions of aqueous sodium hydroxide and maintaining a temperature of 25 to 30 °. C by adding ice as necessary. The reaction mixture was heated at 80 ° C for three hours, cooled to less than 35 ° C with approximately 75 g of ice and treated with 1 g of Giv-Gard DXN. The dye dispersion was diluted with 160 g of water, 12.7 g of 4.7% aqueous xanthan gum and 54 g of glycerin to form a dispersion containing approximately 21% of the 3, 3 'hexasodium salt. - [1-ethenediylbis [(3-sulfo-4,1-phenylene) azo]] -bis [5-amino-4-hydroxy-2,7-naphthalenedisulfonic acid] (solubility of 13.5 g / 100 g of water) with a viscosity of approximately 1230 cp and a Example 4 To a stirred suspension of 92.7 g (289 mmol) of DHTPTSA in 533 ml of water was added 25 g (313 mmol) of 50% aqueous sodium hydroxide. The resulting solution was heated to 40 ° C, after which 53 g (307 mmol) of 40% aqueous sodium nitrite was added in one portion. The resulting mixture was added over a period of two hours at 40 ° C to a mixture of 1 g of 40% aqueous sodium nitrite in 80 g (approximately 680 moles) of hydrochloric acid (20 ° Bé) diluted with approximately 67 mi of water. The diazotization mixture was stirred for another two hours, adding small portions of sodium nitrite as necessary to maintain the nitrous acid, after which the reaction was stopped with about 0.2 g of sulfamic acid. The resulting precipitate was collected by filtration and washed with water until neutral. The resulting diazonium salt of the DHTPTSA was stirred with about 450 ml of water to form a suspension, to which 13.3 g of glycerin and 28.5 g (290 mmol) of 3-methyl were then added with stirring. 5-pyrazolone. To this reaction mixture was added 50% aqueous sodium hydroxide (approximately 112 g) to maintain a pH of about 6. The solution obtained after the completion of the coupling was heated from 70 to 75 ° C, during which time the dye precipitated to form a thick suspension. (Foaming could be controlled by adding a defoamer). After three hours, the mixture was allowed to cool to room temperature. To the resulting fluid suspension (which had a relative color strength of 112% and a viscosity of 260 cp), with stirring, 45 g of a 4.7% aqueous solution of xanthan gum, 0.18 g of Giv were added. -Gard DXN and 0.04 g of Proxel GXL. The mixture was diluted with approximately 220 ml of water to form a dispersion containing approximately 12% of the monosodium salt of 2- [4- [(4,5-dihydro-3-methyl-5-oxo-1H-pyrazole)] -4-yl) azo] phenyl] -6-methyl-7-benzothiazolesulfonic acid with a viscosity of approximately 1800 cp, a?, -X of 444 nm and a spectroscopic color strength of about 98% relative to a corresponding Direct Yellow 127 dye solution available as PONTAMINE Golden Yellow RB Liquid from Bayer Corporation. Performance parameters Performance parameters were obtained for the dye dispersions of Examples 1-3 using acid and alkaline stains (for coloristic properties, bleachability and substantivity) and dilute aqueous solutions (for the propensity to foam and dilute stability ). Acid stains Pulp mixtures were prepared by stirring 3 g (dry weight) of coniferous kraft pulp bleached in 100 ml of artificially hardened water at 200 ppm with calcium chloride. To the pulp suspension was added 1.0% (based on the dry weight of the fiber) of an appropriate standard dye or an equivalent amount (as determined by the spectral transmission method described below) of a dye dispersion of testing. The stained pulp mixture was stirred for two minutes, after which 4.0 ml of a 0.88% solution of Pexol rosin sizing solution was added. After stirring the suspension for another five minutes, 10.0 ml of a 1.5% aluminum sulfate solution was added to the suspension. The dye pulp mixture was stirred for twenty minutes, then diluted again with 100 ml of artificially hardened water and poured into a TAPPI laminar mold half full of deionized water. A sheet of paper was formed as the water was drained from the mold through the forming screen located at the bottom of the TAPPI mold. The resulting sheet was pressed between blotters, placed on a chromium counterplate and placed in a drying ring to dry in an oven at about 90 ° C. The dried leaves are then compared in terms of color strength and hue difference. Alkaline stains Pulp mixtures were prepared by stirring 3 g (dry weight) of coniferous kraft pulp bleached in 100 ml of artificially hardened water at 200 ppm with calcium chloride. A suspension of 3% calcium carbonate (10 ml) was added to the pulp mixture, then allowed to mix for five minutes. To this pulp suspension was added 1.0% (based on the dry weight of fiber) of an appropriate standard dye or an equivalent amount (determined by the spectral transmission method described below) of a test dye dispersion. The pulp suspension was stained for fifteen minutes, after which 2 ml of a 0.3% solution of alkyl ketene dimer sizing agent (available as Hercules 70 from Hercules) was added to the pulp mixture. After stirring the mixture for another five minutes, the suspension was again diluted with 100 ml of hardened water, stirred for another two minutes and poured into a TAPPI laminar mold half filled with deionized water. A sheet of paper was formed as the water was drained from the mold through the forming screen located at the bottom of the TAPPI mold. The resulting sheet was pressed between blotters, placed on a chromium counterplate and placed in a drying ring to dry in an oven at about 90 ° C. The dried leaves were then compared for color strength and hue difference. The performance parameters for the dye dispersions prepared according to Examples 1-3 were determined using the following patterns as a solution: Standard A: C.I. Direct Yellow 147 (available as PONTAMINE Bond Yellow 303 Liquid from Bayer Corporation) Standard B: CI Direct Red 256 (laboratory prepared solution) Standard C: CI Direct Blue 279 (available as PONTAMINE Blue SPN Liquid from Bayer Corporation). The relative color strengths of the dye dispersions of Examples 1-3 and the standard dyes were used to compare their color properties., the absorbances relative to the absorption maximum (? max) of each dye and standard dispersion were compared to determine the relative amounts of each dye dispersion and corresponding pattern that would have to be applied to the paper samples to obtain samples dyed with strength of similar reflectance. Sample sheets of bleached kraft paper dyed as described above were prepared using 1% solutions of appropriate dye standards and the indicated amounts of the dye dispersions of Examples 1-3 (for which the amounts were adjusted as appropriate). previously described to account for the difference in relative light absorbances of the dye mixtures). The sheets of stained paper were compared to determine the reflectance color strengths (by visual evaluation and instrumental measurements), the hue (by visual evaluation and instrumental measurements), the bleachability and the substantivity using the methods described below. Color strength of reflectance a. Visual. The stained sheets were visualized under a standard light source (MacBeth light cabinet equipped with a D65 light source). The observed strength of each test dye dispersion is given in relation to a standard (indicated in each table as parts). b. Instrumental. The stained sheets were analyzed using a color measuring device (Data Color Systems, ACS model CS-5). The instrument measures the absorbance a? - ^ x for each sheet and (using the Kubelka-Munk K / S equation) automatically calculates the difference in color strength between the sheets stained with a test dye dispersion and those dyed with a Pattern. The results appear in each table as parts. Tint a. Visual. The stained sheets were visually examined under the same conditions as those described above for visual color strength. Any difference in hue is given using the standard terms of color difference used to describe hue and brightness / lack of brightness. The terms of difference are based on the AATCC Grays Scale and are given as follows: Yellow dyes Trace red Trace green Light red Light green Differentiated green Differentiated green Considerable red Considerable green Very red Very green Faded green Faded green Blue dyes Trace red Trace green Light red Light green Differentiated green Differentiated green Considerable red Considerable green Very red Very green Fading red Faded green Red dyes Trace yellow Trace blue Light yellow Light blue Differentiated yellow Differentiated yellow Considerable yellow Considerable blue Very yellow Very blue Faded yellow Faded blue Descriptive terms similar to brightness and lack of brightness apply. b. Instrumental. The color measurement device described above for the reflectance color strength gave color readings in the CIÉ CMC system (2: 1) for sheets of dyed paper. In the CIÉ CMC system (2: 1), the term L * refers to clarity, for which a higher value is a lighter color and a lower value is a darker color; the term C * refers to chromaticity, an indication of color saturation, and H * refers to tone. The results are given in terms of the difference (ie, delta values) between the corresponding values L *, C * and H * of sheets stained with the test dye dispersions and with the corresponding values of the standards. Blanchability Blanchability tests were used to determine the amount of color removed from the stained paper using sodium hypochlorite. For each test, sample leaves were reconverted into pulp by mixing vigorously in water. The pulp was collected in a sieve and suspended in a vessel using sufficient water to form a 4% slurry of pulp. Samples were separately treated at 60 ° C for 30 minutes with 4% sodium hypochlorite (or the equivalent necessary to provide 2% available chlorine) at about pH 10. The bleached pulp samples were then poured into a laminar mold TAPPI half full of deionized water. The sheet of paper formed as the water was drained from the mold was pressed through the forming screen located at the bottom of the sheet mold between blotting papers and dried at about 93 ° C in a drum-type electric desiccator. The resulting dyed sheets were compared to unbleached sheets of paper in terms of color strength. Samples that had less color remains are considered more bleachable. In the tables the results are given as a percentage of the rest of the color in relation to the stained unbleached samples. Substantivity Substantivity was measured for each dye dispersion and an appropriate standard dye solution during the acid staining procedure. As the sheet of paper formed in the TAPPI mold, a small portion of the effluent water was placed in a transparent glass container. The containers for each test sample and for the corresponding pattern were placed next to each other in front of a sheet of white blotting paper. The relative color strengths were compared visually and evaluated using the same scales as those described above (ie, trace, slightly, differentiated entity, considerably or much more or less color strength or equal color strength). A sample of effluent water that contains more color indicates that a colorant is less substantive to the fiber. The propensities for foaming and dilute stabilities of the dye dispersions of Examples 1-3 and standard dyes were obtained by the following methods. Progression to foam formation A 2.5 g sample of each dye dispersion and an appropriate standard dye solution was diluted to approximately 500 ml with deionized water in a mixing cup. The test solutions were mixed at high speed for 60 seconds in a Waring blender. The height of the foam was measured immediately after stopping the mixer and after one minute. Diluted Stability Samples of each dye dispersion and an appropriate standard dye solution were independently mixed with about 200 to about 500 ml of deionized water at about 25 ° C to a concentration of about 0 ° C.,3%. The containers were covered to prevent evaporation and allowed to stand at approximately 20 ° C. The resulting solutions were observed for evidence of precipitation or turbidity after a given period of time. An "equal" rating indicates that there was no precipitation of the test solution. The performance parameters for the dye dispersion of Example 1 are summarized in Tables la and Ib, the performance parameters for the dye dispersion of Example 2 are summarized in Tables 2a and 2b and the performance parameters for the dispersion of dye of Example 3 are summarized in Tables 3a and 3b.

Table the Test results for acid and alkaline stains based on Example 1 Acid stains Alkaline Stains Pattern Color A Example 1 Pattern A Example 1 Strength of 100 125 100 125 colorant (parts) Quantity of 1.0 1.2 1.0 1 2 dye (%) Visual Force (parts) 100 100 100 100 Same hue Same equal substantivity Reflectance Strength (parts) 100.0 98.9 100.0 101.7 Hue (CMC (2: 1))? L * -0.01 -0.01? C * +0.10 -0.10? H * 0.00 -0.05 Whitening 2.2 2.3 (% of color remaining) Table Ib Physical properties for the dye dispersion of Example 1 Standard A Example 1 Propensity to foam formation Initial foam (mm) After 60 sec. (mm) Transparent diluted stability > 6 days (slightly cloudy) Table 2a Assay results for acid and alkaline stains based on Example 2 Acid stains Alkaline stains Dye Pattern B Example 2 Pattern B Example 2 Strength of 100 155 100 155 dye (parts) Amount of 1.0 1.6 1.0 1 6 dye (%) Visual Force (parts) 100 97 100 100 Matte light light blue, blue traces matte Equal substantivity Reflectance Strength (parts) 100.0 98.4 100.0 99.2 Hue (CMC (2: 1))? L * - -0.24 -0.11? C * - -0.05 -0.02 ? H * - -0.69 -0.30 Bleachability 9.1 6.2 (% of color remaining) Table 2b Physical properties for the dye dispersion of Example 2 Standard B Example 2 Propensity for foaming Initial foam (mm) < 1 < 1 After 60 sec. (mm) < 1 < 1 Transparent transparent stability equal Table 3a Test results for acid and alkaline stains based on Example 3 Acid stains Alkaline stains Pattern Color C Example 3 Pattern C Example 3 Strength of 100 186 100 186 colorant (parts) Amount of 1.0 9.3 1.0 9 3 dye (%) Visual Force (parts) 100 100 100 100 Tint light red light red to red differentiated Equal substantivity Reflectance Strength (parts) 100.0 99.1 100.0 99.1 Hue (CMC (2: 1))? L * - -0.13 -0.08? C * - +0.13 0.00? H * - +0.81 +0.35 Bleachability 0.9 0.7 (% of color remaining) Table 3b Physical properties for the dye dispersion of Example 3 Standard C Example 3 Propensity to foam formation Initial foam (mm) < 1 1 After 60 sec. (mm) < eleven Transparent transparent stability equal

Claims (15)

1. CLAIMS 1. A process for the preparation of dye dispersions stable to the storage of alkali metal salts of azo anionic direct dyes consisting of (a) preparing an aqueous suspension of an alkali metal salt of an azo direct dye, said salt having a solubility in water at 25 ° C from about 0.1 to about 15% by weight, by azo coupling of one or more aromatic diazonium salts with one or more couplers, while maintaining a pH of at least about 5. adding a basic alkali metal compound in the absence of a nitrogen-containing base; (b) optionally stirring the aqueous suspension at a temperature of 5 ° C to 100 ° C for up to about six hours; (c) optionally, adjusting the temperature of the aqueous suspension from 5 ° C to 40 ° C, and (d) adding a viscosity enhancing agent to the aqueous suspension in an amount sufficient to obtain a viscosity, determined at a temperature of about 20 to about 25 ° C, 500 to 5000 centipoise and from 0 to 10% by weight, based on the total weight of the dye dispersion, of a humectant, thus forming the stable dye dispersion upon storage.
2. 2. A process according to Claim 1, wherein the coupling is an aromatic coupling.
3. 3. A process according to Claim 1, wherein the azo coupling is carried out at a pH of from 6 to 9.
4. 4. A process according to Claim 1, wherein the basic alkali metal compound is an alkali metal hydroxide, carbonate or bicarbonate.
5. 5. A process according to Claim 1, wherein the basic alkali metal compound is sodium or potassium hydroxide.
6. 6. A process according to Claim 1, wherein the aqueous suspension is stirred in step (b) at a temperature of 50 ° C to 90 ° C for one to three hours.
7. 7. A process according to Claim 1, wherein in step (c) the temperature of the aqueous suspension is adjusted from 20 to 40 ° C.
8. 8. A process according to Claim 1, wherein the viscosity enhancing agent is an anionic polysaccharide.
9. 9. A process according to Claim 1, wherein the viscosity enhancing agent is xanthan gum.
10. A process according to Claim 1, wherein the viscosity enhancing agent is added in an amount sufficient to obtain a dye dispersion with a viscosity, determined at a temperature of from about 20 to about 25 ° C, from 800 to 1500 centipoise .
11. 11. A process according to Claim 1, wherein from 2 to 5% by weight, based on the total weight of the dye dispersion, of a humectant is added in step (b).
12. 12. A process according to Claim 1, which additionally consists of a biocide, a defoamer, a corrosion inhibitor, a dispersant or a mixture thereof.
13. 13. A process according to Claim 1, wherein the direct anionic azo dye is a direct monoazo or disazo dye.
14. 14. A process according to Claim 1, wherein the direct anionic azo dye is selected from the group consisting of compounds having the formulas
15. 15. A storage stable dye dispersion prepared by the method of Claim 1.