FR2562901A1 - Improved dye composition - Google Patents

Abstract

Dye composition comprising a cake of dyes which are chosen from the group of disperse dyes and of vat dyes, and a dispersing agent consisting of a sulphonated lignin obtained by reacting lignin with an aldehyde and a water-soluble sulphite or bisulphite. The sulphonated lignin employed is prepared by selectively isolating from black liquor lignins which have a molecular weight of more than 5000 and acidifying them to a pH of between 1.5 and 5.0 by washing with sulphuric acid.

Description

Dye composition improves.

The present invention relates to a new improved process for preparing sulfonated lignins and in particular a process for preparing sulfonated lignins of low viscosity, having improved thermal stability.

The dye compositions generally include a dye cake, i.e., disperse dyes or vat dyes and a dispersing agent. These dye compositions are widely used for dyeing both natural and synthetic fibers. In the dye composition, the dispersing agent has three basic functions (1) it facilitates the reduction of the size of the dye particle; (2) it maintains a dispersing medium; and (3) it serves as a diluent.

Dye dispersing agents are generally of one of two main types: sulfonated lignins from sulfite or kraft processes used in the pulp industry, or naphthalene sulfonates from industry petrol.

The use of sulfonated lignins as dispersing agents in dye compositions has advantages based on their intrinsic physical properties, namely good compatibility with many dye systems, characteristics of remarkable dispersion at high and ambient temperatures, and available. However, the use as lignin dispersants, whether they are sulphite lignins or sulphonated kraft lignins, has a number of drawbacks. This concerns the coloring of the fibers, the thermal stability and the viscosity of the lignins used. These negative characteristics have drawbacks for dyers and numerous attempts have been made to eliminate these drawbacks. A number of new methods have thus been developed for modifying sulfonated lignins in order to reduce the negative aspects of the use of these products as dye dispersants without, however, deteriorating the characteristics which make sulfonated lignins desirable as dispersing agents for dyes. The
Patent, US 4,001,202 describes a process for preparing a sulfonated lignin having better fiber coloring characteristics and used as a dye dispersing agent1 by reacting this lignin with an epihalohydrin. In addition, US Patent 4,338,091 proposes to make react a modified lignin with sodium sulfite and an aldehyde. However, lignin is modified by prior treatment with sodium dithionate; thus, the following reaction does not relate to the lignin of the present invention.

Other examples of lignin reactions or modifications to make them more suitable as dye dispersants are cited in the Patents
US 4,184,845, 4,131,564, 3,156,520, 3,094,515, 3,726,850, 2,680 113 and 3,769,272. The purpose of this list is to indicate the state of the art and not all the examples of lignin modifications
Although the processes for treating and preparing sulfonated lignins described above have certain advantages during dyeing, none of them makes it possible to obtain a product exhibiting the improvements obtained by the products according to the claimed process.

It is the general object of the invention to provide a process by which sulfonated lignins or lignosulfonates can be prepared to improve their suitability as dispersants for dyes.

Another object of this invention is to provide a process for reducing the viscosity of sulfonated lignins or lignosulfonates.

Another object of this invention is to provide a process for improving the thermal stability of sulfonated lignins or lignosulfonates.

Other objects, characteristics and advantages of this invention will appear in the following detailed description thereof.

It has been found that the viscosity of sulfonated lignins used as dye dispersing agents in dye compositions can be reduced, while improving the thermal stability of lignin, removing the low molecular weight component of the lignin and making react the lignin thus obtained with sodium sulfite (Na2SO3) and an aldehyde, at a low pH.

Lignin is obtained from used pulp liquors, known as black liquors, from the pulp industry, in which lignocellulosic materials, such as wood, straw, corn stalk, bagasse, etc., are treated to separate cellulose from lignin. The lignins used in the process of this invention are preferably obtained from the kraft process for making paper pulp, in which the natural lignin is present in the form of the sodium salt. In the kraft process, wood is subjected to the effects of a strong base. In this process, lignin forms a soluble sodium salt which is separated from the cellulose and dissolves in the pulping liquor. Lignin is recovered from the liquor. black by acidification.

The acidification of the black liquor containing the lignin salt is carried out by the introduction of carbon dioxide. When carbon dioxide is added to the black liquor, the phenolic hydroxide groups on the lignin molecule, which are in ionized form, are transformed into their phenolic or free acid form.

This transformation makes the lignin insoluble in black liquor and as a result it precipitates from it
The lignins present in black liquor exist at various molecular weights. Lignins with a molecular weight less than or equal to 5000 have negative effects on the thermal stability of subsequently sulfonated lignins. In the implementation of the invention, the acidification of the alkaline black liquor containing the lignin salt is carried out at a pH for which an almost negligible quantity of lignins having a molecular weight less than or equal to 5,000 precipitates black liquor with the higher molecular weight lignins, almost all of which therefore remains in solution in the black liquor.

Generally speaking, this selective acidification of black liquor to remove lignins must be carried out at a pH between approximately 9.7 and 11.0 to minimize the amount removed from lignins having molecular weights less than or equal to 5000 Preferably, the acidification should take place at a pH between about 10.0 and 11.0 so that practically no lignin of molecular weight less than or equal to 5000 is removed from the black liquor.

In this precipitation process, the alkaline lignins are usually recovered from the black liquor as water-insoluble products. The lignins obtained from the kraft processes, with sodium hydroxide or any other base, which this invention considers, are not recovered in the form of sulphurated products, but are easily sulphonated by reacting these products with a bisulphite or a sulphite. A sulfonated lignin is any lignin containing at least an effective amount of sulfonated groups to obtain water solubility for solutions with moderately acidic pH and higher.

The next step in the development of a lignin dye dispersing agent is to properly sulfonate lignin. It should be noted that the degree of sulfonation of a lignin is proportional to the solubility of this lignin in an aqueous solution and to the viscosity of this lignin.

One of the conventional methods for sulfonating a lignin is the sulfomethylation of alkaline lignin by reacting this lignin with sodium sulfite and formaldehyde. This process is mentioned by
E.- Adler et al. in US Patent 2,680,113. Sulfomethylation acts on the aromatic nuclei of the lignin molecule in such a way that the -CH2SO3H groups are linked to these nuclei. Said patent indicates that the treatment of lignin with these sulfonating agents is carried out in a temperature range from 50 to 2000C, suitably from 80 to 1700C, and preferably from 100 to 1600C. The amount of sulfite used, calculated as anhydrous sodium sulfite, can vary from about 10 to 100% of the amount of anhydrous lignin and the amount of aldehyde is equivalent to the amount of sulfite, or less, up to about 1%, calculated based on the amount of anhydrous lignin. The treatment is preferably carried out in an alkaline solution.

In the practice of the present invention, the alkaline lignin is mixed with water to form a mud. Sulfomethylating agents, namely sodium sulfite and formaldehyde, are added to this slurry. The ratio of sodium sulfite to formaldehyde is between about 1.1: 0.1 and 2.5: 1.0, the preferred value being about 1.3: 0.8. It has been found that, if an excess of sodium sulfite is added relative to formaldehyde, a sulfonated lignin having a reduced molecular weight is obtained.

When formaldehyde and sodium sulfite are combined in stoichiometric amounts, they almost instantly form a hydroxy methanesulfonate which, in turn, reacts with lignin to form sulfonated lignin derivatives. The intermediate, hydroxymethanesulfonate, exists only 90% in the desired form, while 10% of the reactants are present at all times. The fact that 108 of the reagents are present raises a problem, namely that the formaldehyde is subjected to coupling reactions with lignin during sulfomethylation. It is therefore advantageous that the amount of unreacted formaldehyde in the reaction mixture is as small as possible. This can be achieved by varying the molar ratio of sodium sulfite to formaldehyde; increasing the molar ratio of sodium sulfite to formaldehyde results in the production of a larger amount of the intermediate, l hydroxy methanesulfonate, at the expense of the remaining amounts of unreacted formaldehyde. The increased amounts of sodium sulfite result in a lower degree of polymerization and, consequently, a sulfonated lignin with a lower molecular weight.

In prior methods, sodium sulfite and formaldehyde were added to a lignin solution having an initial pH of about 9.0. Addition of the sulfonating agents raised the pH of the resulting sulfonated lignin solution to an even higher value. In the implementation of the present invention, the precipitated lignin is subjected to an acid wash, preferably with sulfuric acid, and is dried to obtain a lignin having a pH of between approximately 1.5 and 5, 0. Lignin is combined with water to form a slurry with a solids content of about 25%. Lignin exists in precipitated form in this pH range. If the lignin slurry piE is ir.; Below 5, the pH is adjusted to about 5.0 using sodium hydroxide. At this point, sodium sulfite is added to raise the Initial pH of the reaction mixture at a pH between 7.0 and 7.5.

Sulfonation occurs when formaldehyde is added, which raises the pH of the sludge to between about 8.0 and 9.2. The sludge is then brought to a temperature of between approximately 130 and 1750C, the preferred temperature being approximately 1400C. The temperature is maintained for a period of between approximately 30 minutes and 12 hours, and preferably for approximately 2 hours.

The use of a low pH and a low temperature has two advantages. On the other hand, lignin is less likely to decompose under these conditions than under normal reaction conditions. The fact that sulfonation occurs at a low pH means that li gnine. resulting sulfonde will have a pH lower than what could otherwise be obtained.

When sulfonated lignins are used as color dispersants, it is preferred that the pH of this lignin is between about 4 and 8. If a lignin is sulfonated at a high pH, the resulting sulfonated lignin will have a high pH. In order for a dyer to use such a sulfonated lignin as a dispersing agent, it is necessary to add an acid to this lignin to lower the pH, which translates into additional expense. By sulfonating lignin at a low pH, a sulfonated lignin is obtained which does not require the use of an acid to make it suitable as a dye dispersing agent.

An additional advantage is that it is no longer necessary to use an acid to lower the pH of a sulfonated lignin in order to use it as a dispersing agent. Using an acid to lower the pH results in the normal production of an electrolyte. The presence of an electrolyte in the sulfonated lignin tends to negatively affect the thermal stability of certain coloring products which contain this lignin as a dispersing agent. The fact that there is no need to add acid to the sulfonated lignin eliminates the problems associated with the presence of electrolytes.

The sulfonated lignins prepared according to the present invention can be used as dispersing agents in dye compositions. The amount of dispersing agent required varies depending on the particular dye cake, the product to be dyed and the effect desired. Up to 75% dispersing agent can be used, based on the weight of the dry cake. The most important factor in determining the correct amount of dispersing agent composition to be used to prepare the dye is the particular dye cake used. In general, this amount varies from one dye to another.

We will now give a few examples, which should not be considered as limiting the invention.

Example 1
Lignin is isolated from black liquors from the kraft process for preparing paper pulp by acidification of pulping liquors under various pH conditions, as shown in Table 1. The isolated lignin is washed with sulfuric acid up to a pH of about 5.0. A 25% solids lignin slurry is prepared by mixing the recovered lignin with water. Sodium sulfite is added to the mud at a pH of about 5.0. The addition of formaldehyde follows very closely the addition of sodium sulfite. After the addition of these two sulfomethylation ingredients, the pH of the reaction mixture is 8.6 to 9.2 and the temperature is adjusted to 700 C. After one hour, the temperature is raised to 1400C and is maintained at this value for 2 hours.

The viscosities of the sulfonated lignin obtained are determined from each of the samples and they are reported in Table 1. The thermal stability characteristics of the sulfonated lignins resulting from each of the samples are also determined and they are reported in Table 1.

The viscosity is measured by heating the sulphonated lignin solution to approximately 700C and slowly adding glacial acetic acid until a pH of 8 is obtained. The solid concentration is adjusted to 25%. A Brookfield viscometer (LVT model) is used for all measurements. The measurements are made at 250C.

Thermal stability is determined by preparing a dye composition containing the sulfonated lignin.

The dye composition is prepared by mixing 50 grams of red I, 35 grams of sulfonated lignin, 125 milliliters of water and 5 drops of EDTA (ethyeleleliamino tetraacetic acid) (1% solids at a pH between 8.6 and 9.2). The pH is adjusted to 8 with acetic acid or sulfuric acid. The dye composition is ground in a ball mill until the filter dye dispersed test is passed.

Thermal stability is measured by adding 1 gram of the solid dye composition to 250 milliliters of water. The solution is boiled for 15 minutes and is then filtered through a N 2 calibrated Whatman filter paper over an N04 (under vacuum) as specified in the standard thermal stability test of the "American Association of Textile
Chemists and Colorists "(AATCC). The filter paper is dried and the residual dye remaining on the filter is calculated.

The data in Table 1 clearly indicate that the pH at which lignin is isolated from black liquor has a significant influence on sulfonated lignins produced subsequently. When the pH at which the black liquor is isolated is raised, significant improvements are observed in the viscosity and thermal stability of the sulfonated lignins.

TABLE I p11 of insulation pH report pH Viscosity Stability of the final initial molar lignin for the thermal pH of the liquor Na2SO3 / CH203 at 25% (residue on black solids the filter = mg)
9.2 1.3 / 0.8 8.7 8.90 8,500 128.0
9.7 1.3 / 0.8 8.7 8.95 117.5 60.0
10.1 1.3 / 0.8 8.6 8.63 27.0 18.5
Example 2
Lignin is isolated from black liquors from the kraft pulp preparation process by acidification of pulping liquors to a pH of about 9.8. The isolated lignin is washed with sulfuric acid to obtain a pH of about 5.0.

A 25% solids lignin mud is prepared by mixing the recovered lignin with water. Sodium sulfite is added to the mud at a pH of about 5.0.

The addition of formaldehyde follows very closely the addition of sodium sulfite. After the addition of the two sulfomethylation ingredients, the pH of the reaction mixture is adjusted to various levels indicated in the table. He. The temperature of the reaction mixture is adjusted to 700C and maintained at this value for 1 hour, after which the temperature is raised to 1400C and is maintained there for 2 hours.

The viscosity of the resulting sulfonated lignin is determined for each of the samples and this value is reported in Table II. The viscosity is measured according to the procedure indicated in Example 1.

The thermal stability of the sulfonated lignin resulting from each of the samples is determined and it is reported in Table II. The thermal stability is measured according to the procedure indicated in Example 1.

The data in Table II clearly indicate that the pH at which sulfonation of lignin takes place in conjunction with the molar ratio of sulfonating agents has a notable effect on the sulfonated lignins subsequently produced. The improvements in viscosity and thermal stability of sulfonated lignins are notable.

TABLE II
Molar ratio pH pH Viscosity for Stability Na2S03 / C, initial H203 final pH at 25% thermal (residue
solids on the filter = mg) 10.3 10.3 10.40 400,000 38.0 *
1.0 / 1.0 9.9 10.65 400,000 18.5
1.3 / 0.8 8.6 8.70 27 18.0
1.4 / 0.7 8.9 9.25 23 26.7
1.5 / 0.5 9.0 9.40 22 103.0
2.0 / 1.15 9.6 9.80 24 302.0 * Lignin is produced at 100 C instead of 1400C.

Although the preceding examples have illustrated an embodiment of the invention, it is understood that other variants and modifications can be made while remaining within the scope of the appended claims.

Claims (10)

Claims 1. Coposition of dye improving carprenant a cake of dyes chosen from the group comprising disperse dyes and cwe dyes, and a dispersing agent consisting of a sulfonated lignin prepared by reacting lignin with an - aldehyde and a sulfite, chosen from the group comprising sulphites and bisulphites soluble in water, characterized in that the improvement defers the following stages: (a) the lignin is selectively isolated from the alkaline black liquor by reducing the pH of the black liquor so that almost all of the lignins with a molecular weight less than or equal to 5000 remain in solution in the black liquor, (b) the lignin is acidified to a pH between about 1.5 and 5.0 by washing with sulfuric acid, after which a strip is added to the lignin to form a mud containing approximately 25% of solids, (c) the sulphite and the aldehyde are added to the lignin mud with a molar ratio of sulphite to aldehyde com taken between about 1.1: 0.1 and 2.5: 1.0, this addition producing an initial reaction pH of about 8.0 to 9.2, and (d) raising the reaction temperature of the room temperature at around 130 to 1750C for a period between 0.5 and 12 hours. 2. Composition according to claim 1. characterized in that ia lignin is isold of black liquor at a pH between about 9.7 and 11.0. 3. Conposition according to claim 2, characterized in that the pH range is from 10.0 to 11.0. 4. Composition according to claim 1, characterized in that the water-soluble sulfite is sodium sulfite and that the aldehyde is formaldehyde. 5. Coosition according to claim 4, characterized in that the molar ratio of sodium sulfite to formaldehyde is about 1.3: 0.8. 6. CoitQsition according to claim 1, characterized in that the initial reaction pH is approximately 8.6. 7. Composition according to claim 1, characterized in that the addition of aldehyde follows the addition of sulfite. 8. Composition according to claim 1, characterized in that the reaction temperature is firstly raised to 700C for one hour after the stage (c) and before stage (d). 9. Composition according to claim 8, characterized in that the reaction temperature of stage (d) is 1400C and that this temperature is maintained for 2 hours. 10. Composition according to claim 1. characterized in that the pH of the lignin mud, if it is less than 5.0, is raised to 5.0 by addition of sodium hydroxide.