Title of Invention

"PROCESS FOR THE DYEING OF COTTON AND OTHER CELLULOSIC SUBSTRATES WITH LAC DYE"

Abstract

The present invention relates to a process for the dyeing of cotton and other cellulosic substrates in the form of fibres, yarn, fabrics, garments, floor coverings and the like with lac dye which for the first time on a commercial scale is successful in obtaining deep, bright, wash-fast dyeings on such substrates. The process resides in the subjection of such fibres or fabrics before and/or after the dyeing thereof to a unique sequence of treatment steps involving the application of cationic agents and metallic mordants to the substrates. These treatment steps are carried out within carefully regulated temperature ranges and for predetermined periods of time.

Full Text

The present invention relates to a process for the dyeing of cotton and other cellulosic substrates in the form of fibres, yarn, fabrics, garments, floor coverings and the like with lac dye. Other than cotton, examples of cellulosic substrates capable of being dyed by the process of the invention include linen, jute, ramie, and regenerated cellulosic fibres such as rayon and "Tencel". Lac dye is obtained from lac which is the resinous protective secretion of a tiny insect known as the lac insect, genus laccifer, family lacciferidae. The lac insect actually constitutes a pest on a number of plants, both wild and cultivated, chief among which are ber (zizypus mauritiana), kusum (scheichera oleosa) and palas (butea monosperma). The minute red coloured larvae of the insect settle in myriads on young succulent shoots of the host plant and drive their long probosces into the bark in order to draw the nutriment which they need for survival from the sap of the plant. As they feed, these larvae secrete a thick resinous fluid which envelopes their bodies. These secretions from individual insects deposit on the twigs and branches of the host plant where they coalesce into the form of a hard continuous encrustation. After completion of the lac insects' life cycle which coincides approximately to the time of emergence of the next generation of larvae, the twigs of the plant are harvested and the encrustations thereon removed. Conveniently, this removal is effective by scraping the encrustations off the twigs. The removed encrustations are dried. The product resulting from this processing is referred to in the art as "sticklac". Analysis of the sticklac has shown that on a percentage by weight it has the following approximate composition: Resin 70% to 80% Sugars, proteins and soluble salts 2% to 4% Wax 1%to2% • Sand, woody matter, insect bodies and other extraneous matter 8% to 12% The resinous content of sticklac contains a red water-soluble dye and both the resinous secretion of the lac insect and the red colouring matter obtainable therefrom have been known in India since early times. In fact, the lakhera artisans of central India, who employ lac as the main item of their craftsmanship, trace their ancestry back to the ancient Indian epic, the Mahabharat, where one of their ancestors built the infamous "lac house" which, because of the inflammability of the substance, was conceived as a trap in which to encarcerate the Pandavs and burn them to death. In order to extract the dye therefrom, the sticklac is washed with alkaline water and since lac dye is water soluble, the lac dye content of the sticklac is dissolved along with some shellac. The solution thus obtained is filtered and the dye precipitated by the addition thereto of one or more precipitating agents. The precipitated dye is then washed with ordinary water and dried under vacuum. Preferably, the alkaline content of the washed water is provided by sodium carbonate and the precipitating agents are selected from strong mineral acids particularly concentrated sulphuric acid. It has been established that lac dye has an affinity for wool, silk, nylon and other polypeptide and polyamide fibres and excellent results have been obtained when employing lac dye to dye these fibres. Furthermore, it is possible to modify the hue of the dyed material by subjecting the latter to a treatment with mordants such as tannins or certain metal salts of tin, iron, copper, aluminum and the like employed either singly or in combination. The preferred metal salts include sulphates, chlorides and acetates. This treatment can be carried out at any of three stages. It may be effected as a pre-treatment of the material prior to the application of dye thereto. It may be carried out simultaneously with the application of dye to the material or yet again, it can be effected as a post-treatment step of the already dyed material. Unfortunately, when it comes to the dyeing of cotton or other cellulosic fibres or fabrics with lac dye, the known process faces a severe drawback. This drawback stems chiefly from the fact that lac dye is an acid dye, the major component of which is laccaic acid. Although lac dye produces excellent results on fibres, yarns or fabrics made from synthetics such as polypeptides and polyamides, the very fact that the dye is an acid dye, is the prime reason why it does not evince the same standard of results with respect to yarn, fabrics or other substrates made from cotton or other cellulosic fibres such as rayon. In fact, lac dye does not have any affinity for cotton and like cellulosic fibres or materials. Hence, the need has existed for several years for the development of a process which produces deep, bright, wash-fast dyeings on cotton and other cellulosic based yarn or fabrics employing lac dye. In fact, a number of attempts have been made in the past to achieve such a process. Unfortunately, all the known attempts have been conducted through small scale, pilot projects. None of them have attempted to solve the problems that existed through a successful commercial scale process. What is more, earlier attempts have, almost without exception, approached the problem by focusing on the aspect of increasing the affinity of cotton or cellulosic fibres or fabrics for lac dye by the creation of sites on such fibres which are receptive to the dye and to which the dye can attach itself. This particular approach to the problem has no doubt been influenced by the prior art attempt made by D. M. Lewis and K. A. Mcllory as described in their paper "The Chemical Modification of Cellulosic Fibres to Enhance Dyeability" [Review of Progress in Coloration, Volume 27, 1997, 5]. This approach involves the treatment of cellulosic fibres with certain cationic compounds in order to modify such fibres and alter their affinity towards different types of direct and reactive dyes but not acid dyes. According to the Lewis-Mcllory process, the treatment of the cellulosic fibres with cationic compounds results in the production on the fibres of aminoalkylcelluloses or simply amino polymers. There is a variety of cationic agents capable of being employed for this purpose including Sandene 8425 (Clariant), Hercosett 125 (Hercules), polyepichlorohydrin-dimethyl-amine (PECH-amine). The cellulosic fibres treated in this manner have been found to be capable of being dyed with anionic dyes such as direct dyes and reactive dyes. With the success of the Lewis-Mcllory process in respect of dyeings with synthetic dyes, an attempt was made to apply the same principle to dyeings with lac dye which is a naturally derived acidic dye. Such method is that described in the publication "Utilisation of Lac Dyes Available Naturally" [S. K. Patra, Colourage, March 1998]. According to this prior art method, salts of metals selected from aluminum, copper, iron and tin are deposited on cellulosic fibre such as cotton or fabrics made therefrom. When subsequently lac dye is applied to the thus treated fibre or to fabric, the dye, which has hydroxyl and carbonyl groups at adjacent ortho- positions in the dye molecule, forms a complex with the metal of the salt applied thereto and the complex so formed attaches itself to the fibre. This prior art process also suggests that for even better results, the cellulosic fibre or fabric should be pre-treated with tannin-containing compounds prior to the deposition of the metal salts thereon. However, the Patra prior approach proceeds on the basis of the formation of a metal complex on the fibres and such complex has been found to be unstable. As a result, dyeings on fabrics treated as described by Patra are not fast to washing and deteriorate with time. An alternative modification of this concept of increasing the affinity of cellulosic fibres or fabrics for lac dye involves the treatment of cotton or other cellulosic fibres or fabrics with chitosan in order to provide sites on the fibres or fabrics for the adsorption of lac dye applied subsequently thereto. Chitosan is a natural polymer obtained from fish bones. It is not easily derived and is therefore expensive to employ. The chitosan approach thus suffers from an initial drawback of being financially unviable when employed on a large-scale financial project. Moreover, for reason of the fact that chitosan does not react with cellulose and is only superficially adsorbed on the fibre or fabric, the pre-treatment of the fibres or fabrics with chitosan brings with it a number of shortcomings. First of all, when the treated fibre or fabric is subsequently washed, the applied lac dye washes off to a large extent. Hence, dyeings on chitosan-treated yarn or fabrics exhibit very poor wash fastness. Secondly, because the dye is deposited merely on the surface of the -fibre of fabric, fabrics treated in this manner exhibit poor rub-fastness. Yet again, pre-treatment with chitosan tends to modify adversely the handle and feel of the fabric. Another drawback in respect of dyeing on chitosan-treated fabrics arises from the fact that chitosan has only a limited number of amino groups capable of acting as sites for the adsorption of lac dye. Hence, it is not possible to obtain deep shades with lac dyes on fabrics pre-treated with chitosan. A basic object of the present invention is the provision of a process for the dyeing of fibres, yarns or fabrics of cotton or other cellulosic material which overcomes the prior art drawbacks associated with such processes. A more specific object of the present invention resides in the provision of a process for the dyeing with lac dye of cotton and other cellulosic substrates such as fibres, yarns, fabrics, garments, and floor coverings including carpets made of linen, jute, ramie, and regenerated cellulosic fibres including rayon and Tencel which imparts to the dyed yarn or fabrics improved characteristics of dye-fastness to both washing and light. Yet.another object of the invention is a process which is versatile enough to achieve in the lac-dyed material different tones of red and red-purple. A still further object of the invention is the provision of a process for the dyeing of fibres, yarns or fabrics of cotton or other cellulosic material with lac dyes which is capable of being conducted successfully on a commercial scale with the desired results. Accordingly, the present invention provides a process for the dyeing of cotton and other cellulosic substrates in the form of fibres, yarn, fabrics, garments, floor coverings and the like with lac dye which comprises: 'applying to the cotton or other cellulose substrate one or more cationic agents such as herein described; dyeing the thus treated substrate with lac dye; applying to the treated substrate simultaneously with or subsequent to the application thereto of the lac dye one or more metallic mordants selected from the group consisting of the sulphates, chlorides and acetates of aluminium, copper, iron-and tin; and applying to the dyed and mordant treated substrate a dye-fixing agent in order to fix the dye on the substrate. There is a variety of cationic agents which are suitable for employment in the process of the invention. These include cationic agents available under the brand names Discofix DBA, Saradye EXH, Basolan F and Sandene 8425. The cationic agent is applied to the fibre or fabric as a solution in which the concentration of the cationic agent depends upon the weight of the yarn or fabric. This concentration can vary from 1% to 5% by weight with a particularly preferred concentration being 3.5% based on the weight of material. The treatment of the material of the substrate with cationic agents is preferably carried out in a bath containing the solution or liquor (referred to in the trade as the "long liquor") while maintaining an overall material to liquor ratio in the range of from 1 : 3 to 1 : 40. Where dyeing is effected employing a standard jigger dyeing machine, a material to liquor ratio of approximately 1 : 4 has been found suitable. Where dyeing is effected employing a standard winch dyeing machine, a material to liquor ratio can be maintained between 1 : 20 to 1 : 40. Conveniently, the treatment of the yarn or fabric with cationic agents is effected at a temperature of from 30° C. to 45° C. for a period of from 15 to 30 minutes or until the entire fabric is impregnated with the cationic treating agent. The fibre, yarn or fabric treated with the cationic agent may be subjected to dyeing with lac dye immediately or the treated substrate may first be dried. Preferably, the material is first dried before being dyed since it has been found •that dried material affords better results in terms of sorption of colouring matter and fastness of dye in the dyed material when compared with material which has not first been dried. As a further feature, the treated material may be washed prior to being dried but this is not essential. The actual procedure for dyeing is the same as that employed in the dyeing of cotton with direct dyes. The dye concentration used in dyeing step may be anywhere between from 0.1% to 15%, preferably from 0.5% to 10%. The higher the concentration, the lower is the exhaustion. For light shades, it is better to maintain a low dye concentration. The dye gets taken up by the fibre immediately on coming into contact with the material. In order to achieve full exhaustion, the concentrations of the dye and of the cationic agent should be properly balanced. The dyeing may be carried out at any temperature between 30° C. to 100°C., more preferably at a temperature in the range of from 70° C. to 90° C. The time for effecting such dyeing extends from 10 minutes to 2 hours, preferably for a period of 60 minutes. The treatment of the cotton or other cellulose substrate with metallic mordant, either simultaneously with the dyeing step until the dye is exhausted or subsequent thereto, is preferably carried out for a period of from 30 minutes to 60 minutes at a temperature varying between 30° C to 100° C. Particularly preferred metallic mordants include alum, copper sulphate, ferrous sulphate or stannous chloride. It has been found efficacious to maintain the concentration of the metallic mordant to between 0.5% to 2% based on the weight of the material. At higher temperatures of treatment, the reaction between the metal salt and the dye is greater as compared to its reaction at low temperature. The complex formed between the metal ion and the dye is what is responsible for changing the hue of the dyed material. In respect of woven fabric, it is preferable in order to achieve good results in terms of desirable dyeing effects that the material be first desized and scoured or bleached prior to being subjected to treatment with the cationic agents. Scouring and bleaching constitute conventionally accepted procedures in textile technology with respect to fibres, yarns and fabrics of cotton and other cellulosic fibres or material. Scouring involves treating the cotton or other cellulosic material with alkali along with surfactants at high temperature in order to remove impurities naturally occurring therein such as natural wax. Bleaching is generally effected employing hydrogen peroxide in order to remove the natural colouring matter present in cotton. According to a further feature of the invention, the cationic treated, dyed and mordanted material is further subjected to a treatment with a dye-fixing agent commonly employed in the textile industry for fixing direct and/or reactive dyes on cotton. The dye-fixing agent is applied after the steps of dyeing and mordanting are complete. This dye-fixing step may be carried out at any temperature between 30° C to 100° C for a period of from 10 minutes to 60 minutes. This treatment with a dye-fixing agent further improves the wash fastness of the dyed material or the dyed and mordanted material. The process of the invention will now be described in detail in the following example: EXAMPLE 1.5 kg of pre-scoured cotton fibres were treated with 3.5% Discofix DBA at 80° C. for 30 minutes. The thus treated fibres were then removed from the treatment bath and dried. Subsequently, the dried fibres were subjected to dyeing with 5% lac dye along with 1% alum at pH 5 for a period of 45 minutes keeping the temperature at 80°C. Thereafter, the dyed fibres were washed thoroughly, treated with 2% Sandofix WEI for 30 minutes at 50° C to 60° C. and dried. In the Table given hereafter, a comparison is set out between the characteristics of the cotton fibres dyed according to the inventive process described in the Example above and those of fibres dyed in accordance with a prior art process described by S. Saxena, V. Iyer, A. I. Shaikh and V. A. Shenai in their paper "Dyeing of Cotton With Lac Dye" ["Colourage", November 1997, pp. 23 - 28]. According to the Saxena et al. process, cotton fibres were first pre-treated successively with chitosan and dimethyl dihydroxy ethyl urea (DMDHEU) before being dyed. This comparison was made employing in both instances a 5 % dye concentration. TABLE (Table Removed) From the Table shown, it will be observed that the fibres dyed with the process of the present invention evince improved characteristics in terms of light fastness and wash fastness over the fibres dyed by the prior art process and comparable results with respect to dry rub fastness and wet rub fastness. Another significant advantage of the process of the present invention over the Saxena et al. process is that the pre-treatment with chitosan and dimethyl dihydroxy ethyl urea renders the prior art procedure very expensive added to which there is the fact that the substances employed by it are not eco-friendly. WE CLAIM: 1. A process for the dyeing of cotton and other cellulosic substrates in the form of fibres, yarn, fabrics, garments, floor coverings and the like with lac dye which comprises: applying to the cotton or other cellulose substrate one or more cationic agents such as herein described; dyeing the thus treated substrate with lac dye; applying to the treated substrate simultaneously with or subsequent to the application thereto of the lac dye one or more metallic mordants selected from the group consisting of the sulphates, chlorides and acetates of aluminium, copper, iron and tin; and applying to the dyed and mordant treated substrate a known dye-fixing agent in order to fix the dye on the substrate. 2. A process as claimed in claim 1 wherein said cationic agents are selected from the group consisting of Discofix DBA, Saradye EXH, Basolan F and Sandene 8425. 3. A process as claimed in claim 1 or 2 wherein said cationic agent is applied to the fibre or fabric as a solution in a concentration of from 1% to 5% by weight based on the weight of the material. «*• 4. A process as claimed in claim 3 wherein said cationic agent is applied to the fibre or fabric as a solution in a concentration of approximately 3.5% based on the weight of material. 5. A process as claimed in claim 3 or 4 wherein the treatment of said substrate with cationic agents is carried out in a bath containing said solution or liquor having an overall material to liquor ratio of from 1 : 3 to 1 : 40. 6. A process as claimed in claim 5 wherein said solution or liquor has a material to liquor ratio of 1 : 20 to 1 : 40, more preferably of 1 : 4. 7. A process as claimed in any of claims 1 to 6 wherein said treatment of the yarn or fabric with cationic agents is effected at a temperature of from 30° C. to 45° C. for a period of from 15 to 30 minutes or until the entire fabric is impregnated with the cationic treating agent. 8. A process as claimed in any of claims 1 to 6 wherein the substrate treated with cationic agent is first dried before being dyed. x 9. A process as claimed in claim 8 wherein the substrate treated with cationic agent is first washed before being dried. 10. A process as claimed in any of claims 1 to 7 wherein the dye concentration of the dye employed in said dyeing step is from 0.1% to 15%, preferably from 0.5% to 10%. 11. A process as claimed in any of claims 1 to 10 wherein the dyeing of the substrate with lac dye is carried out at a temperature of from 30°C. to 110° C.. 12. A process as claimed in claim 11 wherein the dyeing of the substrate with lac dye is carried out at a temperature of from 70° C. to 90° C. 13. A process as claimed in any of claims 1 to 12 wherein the dyeing of the substrate with lac dye is carried out for a period of from 10 minutes to 2 hours, preferably for a period of 60 minutes. 14 A process of any of claims 1 to 13 wherein the treatment of the cotton or other cellulose substrate with metallic mordant, either simultaneously with the dyeing step until the dye is exhausted or subsequent thereto, is carried out for a period of from 30 minutes to 60 minutes at a temperature varying between 30° C to 100° C. 15. A process as claimed in any of claims 1 to 14 wherein the metallic mordant is selected from alum, copper sulphate, ferrous sulphate or stannous chloride. 16. A process as claimed in any of claims 1 to 15 wherein said metallic mordant is applied to treated substrate in a solution in a concentration between 0.5% to 2%in solvent based on the weight of the material. ' 17. A process as claimed in any of claims 1 to 16 wherein the cotton or other cellulose substrate is first desized and scoured or bleached prior to being subjected to treatment with said cationic agents. 18. A process as claimed in any of claims 1 to 17 wherein said dye-fixing step is carried out at a temperature between 30° C to 100° C for a period of from 10 minutes to 60 minutes. 19. A process for the dyeing of cotton and other cellulosic substrates substrates in the form of fibres, yarn, fabrics, garments, floor coverings and the like with lac dye substantially as herein described.

Documents:

669-del-2000-abstract.pdf

669-del-2000-claims.pdf

669-del-2000-correspondence-others.pdf

669-del-2000-correspondence-po.pdf

669-del-2000-description (complete).pdf

669-del-2000-form-1.pdf

669-del-2000-form-19.pdf

669-del-2000-form-2.pdf

669-del-2000-form-3.pdf

669-del-2000-form-4.pdf

669-del-2000-gpa.pdf