DESC:FIELD
The present disclosure relates to a dyeing composition and a process of its preparation. The present disclosure further relates to a process for indigo dyeing of leather and indigo dyed leather.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.
Indigo: The term “indigo” refers to an organic compound dye having the molecular formula C16H10N2O2, with a distinctive blue color, which can be processed using natural or synthetic ingredients or a combination of both. The chemical structure of indigo is as follows:

Wet blue: The term “wet-blue” refers to moist chrome-tanned animal hides which are greyish-blue in color. The hide/leather in this phase is raw and tanned; but neither dried, dyed nor finished.
Re-tanning: The term “re-tanning” as disclosed herein refers to a process of further tanning of an already ‘chrome tanned hide/wet blue’ for improving the feel of the leather, to eventually produce leather of uniform physical properties, to assist in the production of corrected grain leathers.
Setting-out: The term “setting-out” refers to a multi-functional operation, which smooths and stretches hides, while compressing and squeezing out excess moisture from the hide.
Drumming: The term “drumming” also called milling refers to a process wherein the leather is placed in a drum and tumbled to make the leather soft and ensure maximum penetration of the dye throughout the hide.
Fat-liquor: The term “fat liquor” refers to liquor made of an emulsion of soap and fat (castor oil or the like) or sulfonated oil.
Fat-liquoring: The term “fat-liquoring” refers to a process of introducing oil into leather following the tanning process, but before the leather is dried. In fat-liquoring, the oil is introduced into the leather in such a manner that the individual fibres of the hide are uniformly coated with oil.
Acid fixing: The term “acid fixing” is a post-tanning process by which chemicals including dye, fat-liquor and retanning agents are fixed to the fibers of the substrate.
Syntan: The term “syntan” is a class of synthetic tanning materials that are sulfonated condensation products of aromatic compounds with formaldehyde or some other aldehyde.
Staking: The term “staking” refers to a process whereby the fibers of leather are separated to a degree, thus softening the leather and improving its feel and handle.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Leather is used in various applications such as clothing, footwear, handbags, furniture, tools and sports equipment. Generally, due to the increasing demand for products such as leather accessories such as bags, mobile covers, belts, wallets, as well as leather shoes, garments and furniture, the demand for leather is also increasing significantly. As leather products are used extensively in day-to-day life, a variety of hues and designs of these products are the major requirements of the market.
Leather is a material obtained from animal hides followed by chemical treatment. The manufacturing of dyed leather is divided into many steps such as liming, de-liming, chrome tanning, and the like. Further, the dyeing of leather is done with acid dyes after the chrome tanning process. Specifically, after the dyeing process, the finishing of the leather is done with oil and wax.
Further, in the conventional acid dyeing of leather, the dye gives only a solid effect, and it is not possible to get a fading effect, tone variation, and different hues of leather. Alternatively, a pigment may also be utilized for the finishing of leather to improve the quality of leather; but this method is also associated with problems similar to the acid dyeing method. Furthermore, the acid dyes are synthetic which are not eco-friendly and less sustainable.
The indigo dyeing process, which is generally used for a material having cellulosic fibres such as textiles, gives better results at a high pH value of an indigo dye solution. However, at a high pH value the protein structure of the leather may degrade during the indigo dyeing process which is not desirable.
Therefore, there is felt a need to develop a dyeing composition and a method for indigo dyeing of leather and indigo dyed leather articles obtained therefrom that mitigates the drawbacks mentioned hereinabove or at least provides an alternative solution.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide an indigo dyeing composition.
Another object of the present disclosure is to provide a process for the preparation of an indigo dyeing composition.
Yet another object of the present disclosure is to provide a process for indigo dyeing of leather.
Still another object of the present disclosure is to provide a simple and economical process for indigo dyeing of leather.
Yet another object of the present disclosure is to provide a process for indigo dyeing of leather that is not labour intensive.
Still another object of the present disclosure is to provide a process for indigo dyeing of leather which can be performed in less space with minimal equipment.
Yet another object of the present disclosure is to provide a process for the indigo dyeing of leather where both natural and synthetic indigo dyeing can be used.
Yet another object of the present disclosure is to provide a process for the indigo dyeing of leather that provides indigo dyed leather having tone variation and hues.
Still another object of the present disclosure is to provide indigo dyed leather.
Yet another object of the present disclosure is to provide indigo dyed leather which has the desired suppleness, flexibility, fullness and density.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to an indigo dyeing composition comprising water; indigo dye in an amount in the range of 0.01 g/L to 200 g/L of water; surfactant in an amount in the range of 0.01 g/L to 10 g/L of water; pH adjusting agent in an amount in the range of 0.1 g/L to 100 g/L of water; and reducing agent in an amount in the range of 0.5 g/L to 300 g/L of water.
In an embodiment, the dyeing composition comprises water having TDS below 900 ppm; indigo dye in an amount in the range of 1 g/L to 30 g/L of water; surfactant in an amount in the range of 0.05 g/L to 5 g/L of water; pH adjusting agent in an amount in the range of 0.5 g/L to 30 g/L of water; and reducing agent in an amount in the range of 1.5 g/L to 60 g/L of water.
In an embodiment, the surfactant is at least one selected from an anionic surfactant, a non-ionic surfactant and a zwitter-ionic surfactant.
The anionic surfactant can be selected from the group consisting of a salt of phosphoric acid ester, an acrylic copolymer, ammonium lauryl sulfate, sodium laureth sulfate, and sodium lauryl sarcosinate cocamide. The non-ionic surfactant can be selected from cocamide, ethoxylates, and alkoxylates. The zwitter ionic surfactant can be selected from betaines and amino oxides.
The indigo dye can be selected from natural indigo dye, synthetic indigo dye and a combination of natural and synthetic indigo dye.
In an embodiment, the pH adjusting agent is having a pH in the range of neutral pH to 12.5.
In a preferred embodiment, the pH adjusting agent can be selected from the group consisting sodium hydroxide, potassium hydroxide and calcium hydroxide.
The reducing agent can be selected from the group consisting of sodium dithionite, disaccharide, monosaccharide, madder, yeast, ferrous sulphate, thiourea dioxide, bran, sodium borohydride, hydroxyacetone and bacteria.
In a preferred embodiment, the reducing agent is sodium dithionite.
The disaccharide can be selected from lactose and maltose; the monosaccharide can be selected from glucose, fructose and galactose; and the bacteria can be selected from Clostridium isatidis, Amphibacillus and Oceanobacillus.
The dyeing composition of the present disclosure further comprises at least one of a sequestering agent, a binder and a dye other than the indigo dye.
The sequestering agent can be selected from acrylic copolymer, tetrasodium phosphates, sodium hexametaphosphate, tripolysodium phosphate, organophosphonic acid and disodium EDTA; the binder can be selected from acrylic binder and polyurethane based binder; and the dye can be selected from a direct dye, a sulphur dye, a veg dye, an aniline dye and a pigment.
In an embodiment, the direct dye is selected from diamine scarlet, congo red, direct brown and chlorazol dye; the sulfur dye is selected from sulfur blue dye- CI 53235, sulfur brilliant green-CI 53570, sulfur black- CI 53185 and leuco sulfur black 1- CI 53185; the veg dye is selected from a dye extracted from myrobalan fruit, pomegranate rind, sappanwood, turmeric root, chestnut hulls and madder root; the aniline dye is selected from aniline violet, aniline blue and aniline red; and the pigments is selected from mercuric sulfide, lead(II) chromate and iron oxide.
In an embodiment, the dyeing composition of the present disclosure has a pH in the range of 6 to 12.5, preferably in the range of 10 to 11.5.
In a first preferred embodiment, the dyeing composition comprises water; natural indigo dye in an amount of 25 g/L of water; acrylic copolymer (surfactant) in an amount of 5 g/L of water; sodium hydroxide in an amount of 15 g/L of water; and sodium dithionite in an amount of 45 g/L of water.
In a second preferred embodiment, the dyeing composition comprises water; a combination of natural and synthetic indigo dye in an amount of 25 g/L of water; salt of phosphoric acid ester (surfactant) in an amount of 5 g/L of water; sodium hydroxide in an amount of 25 g/L of water; and sodium dithionite in an amount of 50 g/L of water.
In accordance with the second preferred embodiment, an amount of the natural indigo dye is more than 60% with respect to the total amount of the combination of natural and synthetic indigo dye.
In accordance with the second preferred embodiment, a mass ratio of the natural indigo dye to the synthetic indigo dye is 1.5:1.
Further, the present disclosure relates to a process for the preparation of a dyeing composition. The process comprises mixing predetermined amounts of at least one surfactant and indigo dye in water having a predetermined temperature to obtain a first mixture. A predetermined amount of a pH adjusting agent is added to the first mixture followed by adding a predetermined amount of a reducing agent to obtain a second mixture. The second mixture is blended and allowed to stand for a predetermined time period to obtain the dyeing composition.
In an embodiment, the blending of second mixture is carried out in a manner such that oxygen is not introduced into the second mixture during the blending process to prevent oxidation of the components of the second mixture.
The predetermined temperature is in the range of 50 °C to 70 °C.
The predetermined time period is in the range of 30 minutes to 60 minutes.
The process of preparing indigo dyeing composition comprises a step of adjusting pH of the second mixture to be in the range of 6 to 12.5, preferably in the range of 10 to 11.5.
The process of preparing indigo dyeing composition, further comprises a step of adding a sequestering agent, a binder and a dye other than the indigo dye to the second mixture.
Furthermore, the present disclosure relates to a process for indigo dyeing of leather and indigo dyed leather obtained therefrom. In the process as disclosed herein, the starting material is wet blue. Wet blue is soaked in a soaking solution in a bath for a time period in the range of 30 minutes to 120 minutes to obtain soaked wet blue followed by draining off the excess soaking solution. Thereafter, the soaked wet blue is washed with washing fluid to obtain washed wet blue. The washed wet blue is then re-tanned with a re-tanning composition for a time period in the range of 6 hours to 8 hours to obtain re-tanned wet blue having pH in the range of 3 to 6. The pH of the re-tanned wet blue is adjusted to obtain a pH adjusted wet blue having a pH in the range of 5 to 9. The pH adjusted wet blue is then dyed with a dyeing composition having pH in the range of 6 to 12.5, preferably in the range of 10 to 11.5 for a time period in the range of 5 minutes to 60 minutes to obtain dyed wet blue having pH in the range of 6 to 12.5, preferably in the range of 10 to 11.5. pH of the dyed wet blue is adjusted to obtain pH adjusted dyed wet blue having pH in the range of 4.5 to 5.5. The pH adjusted dyed wet blue is then fat-liquored, followed by acid fixing to obtain conditioned dyed wet blue. Thereafter, the conditioned dyed wet blue is set-out to obtain set dyed wet blue having moisture content in the range of 50% to 60%. Then, the set dyed wet blue is dried to obtain indigo dyed leather having moisture content in the range of 12% to 14%.
In an embodiment, the process includes drumming for a time period in the range of 0.5 hours to 6 hours to obtain indigo dyed leather of a desired flexibility.
The drumming process ensures the penetration of the dye and other agents.
In an embodiment, the process includes at least one of chemical finishing and mechanical finishing of the indigo dyed leather to obtain finished indigo dyed leather.
In an embodiment, the wet blue is obtained by performing beam house processes followed by chrome tanning of a hide selected from buffalo hide, cow hide, goat hide, sheep hide, deer hide, alligator hide, crocodile hide, ostrich hide and camel hide.
In an embodiment, the wet blue has a thickness in the range of 0.4 mm to 10 mm.
In an embodiment, a ratio of wet blue to the soaking solution is in the range of 1:0.9 to 1:1.2.
In an embodiment, the soaking solution comprises water and a surfactant. In an embodiment, the amount of surfactant is in the range of 5 gram per litre (g/L) to 20 gram per litre (g/L).
In an embodiment, the surfactant is at least one selected from the group consisting of an anionic surfactant, a non-ionic surfactant and a zwitter ionic surfactant.
In an embodiment, the washing fluid is water.
In an embodiment, water has total dissolved solids (TDS) less than 900 ppm, pH in the range of 6 to 7, total suspended solids (TSS) in the range of 5 ppm to 6 ppm, total hardness in the range of 100 ppm to 200 ppm and COD in the range of 15 mg/L to 30 mg/L.
In an embodiment, the re-tanning composition comprises grain tightening acrylic syntan in an amount in the range of 3 mass % to 8 mass % with respect to the total mass of the washed wet blue; semi-synthetic fat-liquor in an amount in the range of 2 mass % to 6 mass % with respect to the total mass of the washed wet blue; and q.s. water.
In another embodiment, the re-tanning composition comprises chromium sulphate in an amount in the range of 1 mass % to 5 mass % with respect to the total mass of washed wet blue; sodium formate in an amount in the range of 1 mass % to 2 mass % with respect to the total mass of the washed wet blue; at least one basifying agent in an amount in the range of 0.5 mass % to 1 mass % with respect to the total mass of washed wet blue, optionally, at least one preservative in an amount in the range of 0.2 mass % to 0.5 mass % with respect to the total mass of washed wet blue; optionally, grain tightening acrylic syntan in an amount in the range of 2 mass % to 6 mass % with respect to the total mass of the washed wet blue; optionally, semi-synthetic fat-liquor in an amount in the range of 2 mass % to 6 mass % with respect to the total mass of the washed wet blue, and q.s. water.
In an embodiment, the basifying agent is magnesium oxide (MgO).
In an embodiment, the preservative is a biocide.
In one embodiment, the biocide is selected from 2-thiocyano-methylthiobenzothiazole (TCMTB) and N-octyl-isothiazolinone (N-OITZ).
In another embodiment, the biocide is selected from 2-thiocyano-methylthiobenzothiazole (TCMTB) and N-octyl-isothiazolinone (N-OITZ) along with organosulfur compounds and alkaline organic salt compounds.
In an embodiment, pH of the re-tanned wet blue is adjusted by treating the re-tanned wet blue with at least one weak acid or at least one weak base for a time period in the range of 30 minutes to 45 minutes.
In an embodiment, the weak acid is at least one selected from the group consisting of formic acid, acetic acid and oxalic acid; and the weak base is at least one selected from the group consisting of sodium bi-carbonate, sodium formate and ammonia.
In an embodiment, the weak acid has a concentration in the range of 5 g/L to 15 g/L; and the weak base has a concentration in the range of 5 g/L to 20 g/L.
In an embodiment, pH adjusted wet blue is washed with water having a temperature in the range of 55 °C to 65 °C.
In an embodiment, pH of the dyed wet blue obtained in step (e) is adjusted by using a weak acid selected from acetic acid, formic acid and oxalic acid.
In an embodiment, acetic acid has a concentration in the range of 10 g/L to 30 g/L.
In an embodiment, the fat-liquoring comprises subjecting the pH adjusted dyed wet blue to a fat-liquoring composition for a time period in the range of 60 minutes to 90 minutes.
In an embodiment, the fat-liquoring composition comprises at least one component selected from a synthetic fat-liquor and a semi-synthetic fat-liquor.
In another embodiment, the fat-liquoring composition comprises a synthetic fat-liquor in an amount in the range of 30 g/L to 40 g/L, phenol–naphthalene based syntan in an amount in the range of 30 g/L to 40 g/L, chrome-melamine syntan in an amount in the range of 50 g/L to 60 g/L, and a semi-synthetic fat-liquor in an amount in the range of 50 g/L to 60 g/L.
The synthetic fat-liquor is selected from synthetic esters, synthetic fat-liquor based on phosphate esters, electrolyte stable synthetic softening agents, modified alkane sulphonates and synthetic oils, sulfo-ester derivatives and high molecular weight hydrocarbons.
The semi-synthetic fat-liquor is selected from fat-liquor based on synthetic oils, natural oil containing sulphite, esters of fatty substances and monohydric alcohol.
In an embodiment, the drying in step (i) is air drying, with air having a temperature in the range of 20 °C to 40 °C, and humidity in the range of 10% to 80%.
In an embodiment, the chemical finishing is performed by spraying a finishing medium on the indigo dyed leather, wherein the finishing medium can be selected from
a. the dyeing composition of the present disclosure,
b. a mixture of at least one binder and at least one of dye and pigment, wherein a ratio of the binder to the dye/pigment is in the range of 4:1 to 60:1,
c. at least one binder; and
d. at least one water-repelling agent.
In an embodiment, the binder is at least one selected from the group consisting of an acrylic binder, a polyurethane binder and a polyethylene.
In an embodiment, the dye is selected from indigo dye, a direct dye, a sulphur dye, a veg dye and an aniline dye.
In an embodiment, the pigment is selected from white pigment, mercuric sulfide, lead (II) chromate and iron oxide.
In an embodiment, the water-repelling agent is at least one selected from teflon, polyurethane, silicones, oils, fluoro polymers, fluoro carbons, solvent or water based emulsion of synthetic waxes, solvent-based fluorine-free waterproof agent, solvent-based silicone, cationic silicone emulsion, perfluorocarbon based water repelling agents and blend of paraffin.
In an embodiment, the mechanical finishing comprises at least one process selected from buffing, ironing and printing/ engraving.
The indigo dyed leather obtained by the process of the present disclosure is characterized by having thickness in the range of 0.4 mm to 10 mm; tensile strength in the range of 20 N/mm2 to 40 N/mm2; tear strength selected from single edge tear strength in the range of 40 N to 80 N, and double edge tear strength in the range of 90 N to 260 N.
In an embodiment, the dye of the indigo dyed leather of the present disclosure is stable after 10 washings.
DETAILED DESCRIPTION
The present disclosure relates to a dyeing composition and a process of its preparation. The present disclosure further relates to a process for indigo dyeing of leather and indigo dyed leather.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Leather is used in various applications such as clothing, footwear, handbags, furniture, tools and sports equipment. Generally, due to the increasing demand for products such as leather bags, mobile covers, belts, wallets, and the like, the demand for leather is also increasing significantly. As leather products are used extensively in day-to-day life, a variety of hues and designs of these products are the major requirements of the market.
Leather is a material obtained from animal hides followed by chemical treatment. The manufacturing of the leather is divided into many steps such as liming, de-liming, chrome tanning, and the like. Further, the dyeing of leather is done with acid dye after the chrome tanning process. Specifically, after the dyeing process, the finishing of the leather is done with oil and wax.
Further, in the conventional acid dyeing of the leather, the dye gives only a solid effect, and it is not possible to get a fading effect, tone variation, and different hues of the leather. Alternatively, a pigment may also be utilized for the finishing of the leather to improve the quality of the leather; but this method is also associated with problems similar to the acid dyeing method. Furthermore, the acid dye and the pigment are synthetic colors which are less eco-friendly and less sustainable.
The indigo dyeing process generally gives better results at a high pH value of an indigo dye solution which is generally used for a material having cellulosic fibres such as denim. However, at a high pH value, the protein structure of the leather may degrade during the indigo dyeing process which is not desirable.
The present disclosure relates to a dyeing composition and a process of its preparation. Further, the present disclosure relates to a process for indigo dyeing of leather and indigo dyed leather obtained therefrom.
In a first aspect, the present disclosure provides an indigo dyeing composition.
The indigo dyeing composition comprises water; indigo dye in an amount in the range of 0.01 g/L to 200 g/L of water; surfactant in an amount in the range of 0.01 g/L to 10 g/L of water; pH adjusting agent in an amount in the range of 0.1 g/L to 100 g/L of water; and reducing agent in an amount in the range of 0.5 g/L to 300 g/L of water.
In an embodiment of the present disclosure, the dyeing composition comprises water having TDS below 900 ppm; indigo dye in an amount in the range of 1 g/L to 30 g/L of water; surfactant in an amount in the range of 0.5 g/L to 5 g/L of water; pH adjusting agent in an amount in the range of 0.5 g/L to 30 g/L of water; and reducing agent in an amount in the range of 1.5 g/L to 60 g/L of water.
The indigo dye can be selected from natural indigo dye, synthetic indigo dye and a combination of natural and synthetic indigo dye. In an exemplary embodiment of the present disclosure, the indigo dye is natural indigo dye. In another exemplary embodiment of the present disclosure, the indigo dye is synthetic indigo dye. In still another exemplary embodiment of the present disclosure, the indigo dye is a combination of natural indigo dye and synthetic indigo dye.
The pH adjusting agent can be selected from the group consisting sodium hydroxide, potassium hydroxide and calcium hydroxide. In an exemplary embodiment of the present disclosure, the pH adjusting agent is sodium hydroxide.
The reducing agent can be selected from the group consisting of sodium dithionite, disaccharide, monosaccharide, madder, yeast, ferrous sulphate, thiourea dioxide, sodium borohydride, hydroxyacetone and bacteria.
The disaccharide can be selected from lactose and maltose; the monosaccharide can be selected from glucose, fructose and galactose; and the bacteria can be selected from Clostridium isatidis, Amphibacillus and Oceanobacillus.
In an exemplary embodiment of the present disclosure, the reducing agent is sodium dithionite.
In an embodiment, the surfactant can be at least one selected from an anionic surfactant, a non-ionic surfactant and a zwitter-ionic surfactant.
The anionic surfactant can be selected from the group consisting of a salt of phosphoric acid ester, an acrylic copolymer, ammonium lauryl sulfate, sodium laureth sulfate, and sodium lauryl sarcosinate cocamide.
The non-ionic surfactant can be selected from cocamide, ethoxylates, and alkoxylates.
The zwitter ionic surfactant can be selected from betaines and amino oxides.
In an exemplary embodiment of the present disclosure, the surfactant is a salt of phosphoric acid ester in an amount of 5 g/L of water. In another exemplary embodiment of the present disclosure, the surfactant is an acrylic copolymer in an amount of 5 g/L of water.
In an embodiment of the present disclosure, the dyeing composition further comprises at least one of a sequestering agent, a binder and a dye other than indigo dye.
The sequestering agent can be selected from acrylic copolymer, tetrasodium phosphates, sodium hexametaphosphate, tripolysodium phosphate, organophosphonic acid and disodium EDTA. In an exemplary embodiment of the present disclosure, the sequestering agent is acrylic copolymer.
The sequestering agents, also known as chelating agents, are supplementary chemicals that are used to eliminate water hardness and heavy metals. The sequestering agents need to be added depending on properties of water being used.
The binder can be selected from acrylic binder and polyurethane based binder. In an exemplary embodiment of the present disclosure, the binder is styrene acrylic copolymer.
The additional dye can be selected from a direct dye, a sulphur dye, a veg dye, an aniline dye and a pigment.
In an embodiment, the direct dye is selected from diamine scarlet, congo red, direct brown and chlorazol dye; the sulfur dye is selected from sulfur blue dye- CI 53235, sulfur brilliant green-CI 53570, sulfur black- CI 53185 and leuco sulfur black 1- CI 53185; the veg dye is selected from a dye extracted from myrobalan fruit, pomegranate rind, sappanwood, turmeric root, chestnut hulls and madder root; the aniline dye is selected from aniline violet, aniline blue and aniline red; and the pigments is selected from mercuric sulfide, lead(II) chromate and iron oxide.
The pH of the dyeing composition of the present disclosure is in the range of 6 to 12.5. In a preferred embodiment, pH of the dyeing composition of the present disclosure is in the range of 10 to 11.5.
In a first exemplary embodiment of the present disclosure, the dyeing composition comprises water; natural indigo dye in an amount of 25 g/L of water; salt of phosphoric acid ester (surfactant) in an amount of 5 g/L of water; sodium hydroxide in an amount of 15 g/L of water; and sodium dithionite in an amount of 45 g/L of water.
In a second exemplary embodiment of the present disclosure, the dyeing composition comprises water; a combination of synthetic and natural indigo dye in an amount of 25 g/L of water; salt of phosphoric acid ester (surfactant) in an amount of 5 g/L of water; sodium hydroxide in an amount of 25 g/L of water; and sodium dithionite in an amount of 50 g/L of water.
In accordance with the second exemplary embodiment, an amount of the natural indigo dye is more than 60% with respect to the total amount of the combination of natural and synthetic indigo dye.
In accordance with the second exemplary embodiment, a mass ratio of the natural indigo dye to the synthetic indigo dye is 1.5:1.
The organoleptic properties in relation to look, feel and texture of the indigo dyed leather can be varied by varying the combinations of the natural indigo dye and the synthetic indigo dye.
In a second aspect, the present disclosure provides a process for the preparation of a dyeing composition.
The process comprises mixing predetermined amounts of at least one surfactant and an indigo dye in water having a predetermined temperature to obtain a first mixture. A predetermined amount of a pH adjusting agent is added to the first mixture followed by adding a predetermined amount of a reducing agent to obtain a second mixture. The second mixture is blended and allowed to stand for a predetermined time period to obtain the dyeing composition. Care should be taken that oxygen is not introduced into the mixture during the blending process and during the time when it is allowed to stand to prevent oxidation of the components of the second mixture. In an embodiment of the present disclosure, the pH of the second mixture is adjusted to be in the range of 6 to 12.5, preferably in the range of 10 to 11.5.
The predetermined amount of the surfactant is in the range of 0.01 g/L to 10 g/L of water.
In an exemplary embodiment of the present disclosure, the surfactant is salt of phosphoric acid ester in an amount of 5 g/L of water.
The indigo dye can be selected from a natural indigo dye, a synthetic indigo dye and a combination of natural and synthetic indigo dye. The predetermined amount of the indigo dye is in the range of 0.01 g/L to 200 g/L of water.
The preferred range of the amount of the indigo dye is 1 g/L to 30 g/L of water, wherein good result are obtained in terms of dye uniformity, shade reproducibility, shade depth and the like. Further, the workable range of amount of the indigo dye is 0.5 g/L to 200 g/L, however, in this range the dye shade variation and the shade repeatability problem may occur after 30 g/L and below 0.5 g/L, the shade depth is very low and above 200 g/L, the dye particle aggregation will occur which makes it difficult to dye.
The predetermined amount of the pH adjusting agent is in the range of 0.1 g/L to 100 g/L of water. In an exemplary embodiment of the present disclosure, the pH adjusting agent is sodium hydroxide in an amount of 15 g/L of water.
The preferred range of amount of the pH adjusting agent is 0.5 g/L to 30 g/L as in this range the indigo dye solubility in water is good. Further, the workable range is 0.1 g/L to 100 g/L, wherein dyeing is possible but proper dye water solubility is not obtained. Below 0.5 g/L and above 30 g/L of the pH adjusting agent, the leather will start to damage because strong solution of alkaline agent degrades the collagen of the protein in leather.
The predetermined amount of the reducing agent is in the range of 0.5 g/L to 300 g/L of water. In an exemplary embodiment of the present disclosure, the reducing agent is sodium dithionite in an amount of 45 g/L of water.
The preferred range of amount of the reducing agent is 1.5 g/L to 30 g/L, wherein good results are obtained in terms of dye particle dissolution, dye particle solubility, shade reproducibility, shade depth, and the like. Further, the workable range of amount of the reducing agent is 0.5 g/L to 300 g/L, however, below 1.5 g/L and above 30 g/L, the dye shade variation, the shade repeatability problem may occur i.e. below 1.5 g/L, the shade depth is very low and above 300 g/L, the shade may be dull.
The predetermined temperature of water in which the indigo dye is mixed is in the range of 50 °C to 70 °C. In an exemplary embodiment of the present disclosure, the predetermined temperature is 60 °C.
The predetermined time period for which the second mixture is allowed to stand is in the range of 30 minutes to 60 minutes. In an exemplary embodiment of the present disclosure, the predetermined time period is 30 minutes.
The process of the present disclosure further comprises a step of adding a sequestering agent, a binder and a dye other than said indigo dye.
In the leather dyeing process, dyeing is generally done after the re-tanning process but in some practices, dyeing may be carried out immediately after formation of wet blue. In the prior art of dyeing leather mostly acid, basic or direct dyes are used which are water soluble and performed in acid pH or at neutral pH. However, in the present disclosure, the inventors have developed an indigo dyeing composition which can be used for dyeing the leather mostly in an alkaline pH range. Indigo dye is a water insoluble vat dye and to make it water soluble or suitable for dyeing, it is converted into water soluble form using a reducing agent and a pH adjusting agent. The reducing agent converts the indigo dye into leuco acid ester which is neutralized with the pH adjusting agent and gets converted into a sodium salt of leuco ester which is the water soluble form of indigo dye.
In a preferred embodiment, the water used at various steps of making the dyeing composition is soft water.
Use of hard water is not recommended as the presence of hardness in the water can cause dye precipitation, and the precipitates can further promote dye aggregations, which results in color specks and loss of depth. Particularly, the calcium and magnesium ions of hard water react with the dye molecules and precipitate the dye. As a result dyestuff is spoilt. Hence, an undesirable depth of dyeing of color is produced.
In a third aspect, the present disclosure provides a process for indigo dyeing of leather.
In the process, wet blue is used as a starting material. The wet blue is soaked in a soaking solution in a bath for a time period in the range of 30 minutes to 120 minutes to obtain soaked wet blue followed by draining off the soaking solution. Thereafter, the soaked wet blue is washed with washing fluid to obtain washed wet blue. The washed wet blue is then re-tanned with a re-tanning composition for a time period in the range of 6 hours to 8 hours to obtain re-tanned wet blue having pH in the range of 3 to 6. The pH of the re-tanned wet blue is adjusted to obtain pH adjusted wet blue having pH in the range of 5 to 9. The pH adjusted wet blue is then dyed with a dyeing composition having pH in the range of 6 to 12.5, preferably in the range of 10 to 11.5 for a time period in the range of 5 minutes to 60 minutes to obtain dyed wet blue having pH in the range of 6 to 12.5, preferably in the range of 10 to 11.5. pH of the dyed wet blue is adjusted to obtain pH adjusted dyed wet blue having a pH in the range of 4.5 to 5.5. The pH adjusted dyed wet blue is then fat-liquored, followed by acid fixing to obtain conditioned dyed wet blue. Thereafter, the conditioned dyed wet blue is set-out to obtain set dyed wet blue having moisture content in the range of 50 % to 60 %. Then, the set dyed wet blue is dried to obtain indigo dyed leather having moisture content in the range of 12 % to 14 %.
In an embodiment, the process includes drumming for a time period in the range of 0.5 hours to 6 hours to obtain indigo dyed leather of a desired flexibility.
The drumming process ensures the penetration of the dye and other agents.
In an embodiment, the process includes at least one of chemical finishing and mechanical finishing of the indigo dyed leather to obtain finished indigo dyed leather.
The method is described in detail hereinbelow:
In a first step, the wet blue is soaked in a soaking solution in a bath for a time period in the range of 30 minutes to 120 minutes to obtain soaked wet blue followed by draining off the soaking solution.
The wet blue is a strong, flexible, and durable material manufactured from one or more conventional beam house processes such as liming, de-liming, and the like, of a raw material such as animal hides. Thereafter, a liming process is performed in which the leather is soaked in an alkali solution. The liming process is performed using a drum and paddle or a pit. After the liming process, a de-fleshing process is performed on the hide followed by a de-liming process, a pickling process, and a chrome tanning process to obtain wet blue.
In accordance with the embodiments of the present disclosure, the wet blue is obtained by performing beam house processes followed by chrome tanning of a hide selected from buffalo hide, cow hide, goat hide, sheep hide, deer hide, alligator hide, crocodile hide, ostrich hide and camel hide. In an exemplary embodiment, the wet blue is obtained by performing beam house processes followed by chrome tanning of buffalo hide. In an exemplary embodiment, the wet blue is obtained by performing beam house processes followed by chrome tanning of goat hide.
After the beam-house operations, the obtained hide is then tanned to obtain a wet blue. Tanning stabilizes the collagen structure of the hide so as to impart durability and stop/ slower the decaying of the hide. It is an imperative step in the process of preparation of the leather. There are different types of tanning processes such as chrome tanning, vegetable tanning, and aldehyde-based chrome free tanning. The process to be used depends upon the further treatment and the desired leather. Generally, in chrome tanning process, the hide is treated with a chrome tanning composition comprising chromium sulphate, sodium formate, chrome stable fat and other components to enhance the durability of the hide. Chrome tanning process is generally performed for a time period in the range of 6 hours to 12 hours.
In accordance with the embodiments of the present disclosure, the wet blue has a thickness in the range of 0.4 mm to 10 mm. In an exemplary embodiment, the wet blue has a thickness of 1.8 mm. In another exemplary embodiment, the wet blue has a thickness of 1.4 mm.
In accordance with the embodiments of the present disclosure, a ratio of wet blue to the soaking solution is in the range of 1:0.9 to 1:1.2. In a preferred embodiment, a ratio of wet blue to the soaking solution is 1:1.
In accordance with the embodiments of the present disclosure, the soaking solution comprises water and a surfactant.
In accordance with the embodiments of the present disclosure, the amount of surfactant is in the range of 5 g/L to 20 g/L. In an exemplary embodiment, the amount of surfactant is 7 g/L.
In accordance with the embodiments of the present disclosure, the surfactant is at least one selected from the group consisting of an anionic surfactant, a non-ionic surfactant and a zwitter ionic surfactant.
The anionic surfactant can be selected from the group consisting of a salt of phosphoric acid ester, an acrylic copolymer, ammonium lauryl sulfate, sodium laureth sulfate, and sodium lauryl sarcosinate cocamide. The non-ionic surfactant can be selected from cocamide, ethoxylates, and alkoxylates. The zwitter ionic surfactant can be selected from betaines and amino oxides.
In a second step, the soaked wet blue is washed with a washing fluid to obtain a washed wet blue.
In accordance with the embodiments of the present disclosure, the washing fluid is water.
In a preferable embodiment, water has total dissolved solids (TDS) less than 900 ppm, pH in the range of 6 to 7, total suspended solids (TSS) in the range of 5 ppm to 6 ppm total hardness in the range of 100 ppm to 200 ppm and COD in the range of 15 mg/L to 30 mg/L.
In a third step, the washed wet blue is then re-tanned with a re-tanning composition for a time period in the range of 6 hours to 8 hours to obtain a re-tanned wet blue having pH in the range of 3 to 6.
A re-tanning process is carried out to ensure further stabilization of the hide collagen, and to obtain the desired strength, fullness, density of the finished leather. Thus, depending upon the animal hide, the thickness of the hide, chromium sulphate is optionally added in the re-tanning composition.
In an embodiment of the present disclosure, the re-tanning composition comprises grain tightening acrylic syntan in an amount in the range of 3 mass % to 8 mass % with respect to the total mass of the washed wet blue; semi-synthetic fat-liquor in an amount in the range of 2 mass % to 6 mass % with respect to the total mass of the washed wet blue; and q.s. water.
In another embodiment, the re-tanning of the washed wet blue is done by using the following re-tanning composition:
• chromium sulphate in an amount in the range of 1 mass % to 5 mass % with respect to the total mass of washed wet blue;
• sodium formate in an amount in the range of 1 mass % to 2 mass % with respect to the total mass of the washed wet blue;
• at least one basifying agent in an amount in the range of 0.5 mass % to 1 mass % with respect to the total mass of the washed wet blue;
• optionally, a preservative in an amount in the range of 0.2 mass % to 0.5 mass % with respect to the total mass of the washed wet blue;
• optionally, grain tightening acrylic syntan in an amount in the range of 2 mass % to 6 mass % with respect to the total mass of the washed wet blue;
• optionally, semi-synthetic fat-liquor in an amount in the range of 2 mass % to 6 mass % with respect to the total mass of the washed wet blue; and
• q.s. water.
Sodium formate generally acts as a pH-neutralizer. Sodium formate is widely used in leather industry, as leather tanning, catalyzer, and disinfector and used as camouflage salt in the chrome tanning. In the chrome tanning process step, sodium formate when used in appropriate quantities, stabilizes the chromium resulting in better leather quality.
In an embodiment, the basifying agent is magnesium oxide (MgO).
In an embodiment, the preservative is a biocide.
In one embodiment, the biocide is selected from 2-thiocyano-methylthiobenzothiazole (TCMTB) and N-octyl-isothiazolinone (N-OITZ).
In another embodiment, the biocide is 2-thiocyano-methylthiobenzothiazole (TCMTB) and N-octyl-isothiazolinone (N-OITZ) along with organosulfur compounds and alkaline organic salt compounds.
In an exemplary embodiment, the preservative is a combination of 2-Thiocyano-methylthiobenzothiazole (TCMTB) with other organosulfur compounds.
Preservatives are used to protect leather from bacteria and fungus/mould infestation. Preservatives may or may not be added during the retanning process but are required during the tanning of leather.
In a fourth step, pH of the re-tanned wet blue is increased to obtain pH adjusted wet blue having pH in the range of 5 to 7.
In accordance with the embodiments of the present disclosure, pH of the re-tanned wet blue is adjusted by treating the wet blue with at least one weak acid or a weak base.
In accordance with a first embodiment of the present disclosure, the weak acid is used to increase the pH of the re-tanned wet blue.
In accordance with a second embodiment of the present disclosure, the weak base is used to increase the pH of the re-tanned wet blue.
The weak acid can be at least one selected from the group consisting of formic acid, acetic acid and oxalic acid.
The weak base can be at least one selected from the group consisting of sodium bi-carbonate, sodium carbonate and ammonia.
In a preferred embodiment, the composition for adjusting the pH of the re-tanned wet blue comprises water, sodium formate in an amount in the range of 5 gram per litre (g/L) to 20 gram per litre (g/L), and sodium bicarbonate in an amount in the range of 5 gram per litre (g/L) to 20 gram per litre (g/L).
In accordance with the embodiments of the present disclosure, the weak base has a concentration in the range of 5 g/L to 20 g/L. In an exemplary embodiment, the weak base is sodium formate and has a concentration of 5 g/L to 20 g/L. In another exemplary embodiment, the weak base is sodium bicarbonate and has a concentration of 5 g/L to 20 g/L.
In accordance with the embodiments of the present disclosure, the weak acid has a concentration in the range of 5 g/L to 15 g/L. In an exemplary embodiment, the weak acid is formic acid and has a concentration of 5 g/L to 15 g/L. In another exemplary embodiment, the weak acid is acetic acid and can have a concentration of 5 g/L to 15 g/L.
In accordance with the embodiments of the present disclosure, the pH adjusted wet blue is washed with water having a temperature in the range of 55 °C to 65 °C. In an exemplary embodiment, the pH adjusted wet blue is washed with water having a temperature of 55 °C. In another exemplary embodiment, the pH adjusted wet blue is washed with water having a temperature of 60° C.
In accordance with the embodiments of the present disclosure, a ratio of the amount of the pH adjusted wet blue to the amount of water is in the range of 1:1.3 to 1:1.7. In an exemplary embodiment, the ratio of the amount of pH adjusted wet blue to the amount of water is 1:1.5.
In accordance with the embodiments of the present disclosure, the washing is performed for a time period in the range of 10 minutes to 60 minutes. In an exemplary embodiment, the washing is performed for a time period of 20 minutes. In another exemplary embodiment, the washing is performed for a time period of 40 minutes.
In a fifth step, the pH adjusted wet blue is then dyed with the dyeing composition of the present disclosure having pH in the range of 6 to 12.5, preferably in the range of 10 to 11.5 for a time period in the range of 5 minutes to 60 minutes to obtain dyed wet blue.
In a sixth step, the pH of the dyed wet blue obtained in the fifth step is adjusted to obtain pH adjusted dyed wet blue having a pH in the range of 4.5 to 5.5.
In an embodiment of the present disclosure, pH of the dyed wet blue is adjusted by using a weak acid selected from acetic acid, formic acid and oxalic acid.
In a preferable embodiment, the weak acid has a concentration in the range of 10 g/L to 30 g/L.
In a preferred embodiment, the treatment with the weak acid is performed for a time period in the range of 10 minutes to 30 minutes.
In a seventh step, the pH adjusted dyed wet blue is then subjected to fat-liquoring, followed by acid fixing to obtain conditioned dyed wet blue.
In accordance with the embodiments of the present disclosure, the fat-liquoring comprises subjecting the pH adjusted dyed wet blue to a fat-liquoring composition for a time period in the range of range of 60 minutes to 90 minutes.
In an embodiment, a ratio of the pH adjusted dyed wet blue to the fat liquoring composition is in the range of 1:0.9 to 1:1.2.
In an embodiment, the fat-liquoring composition comprises at least one component selected from a synthetic fat-liquor and a semi-synthetic fat-liquor.
In accordance with the embodiment of the present disclosure, an amount of the synthetic fat-liquor is in the range of 50 g/L to 90 g/L and an amount of the semi-synthetic fat-liquor is in the range of 50 g/L to 90 g/L in the fat-liquoring composition.
In another embodiment, the fat liquoring composition comprises synthetic fat-liquor in an amount in the range of 30 g/L to 40 g/L, phenol–naphthalene based syntan in an amount in the range of 30 g/L to 40 g/L, chrome-melamine syntan in an amount in the range of 50 g/L to 60 g/L, and semi-synthetic fat-liquor in an amount in the range of 50 g/L to 60 g/L.
The synthetic fat-liquor is selected from synthetic esters, synthetic fat-liquor based on phosphate esters, electrolyte stable synthetic softening agents, modified alkane sulphonates and synthetic oils, sulfo-ester derivatives and high molecular weight hydrocarbons;
The semi-synthetic fat-liquor is selected from fat-liquor based on synthetic oils, natural oil containing sulphite, esters of fatty substances and monohydric alcohol.
In an embodiment, acid fixation of the conditioned dyed wet blue is performed with a weak acid solution for a time period in the range of 60 minutes to 90 minutes.
In an embodiment, the weak acid is formic acid.
In an embodiment, the formic acid is used in an amount in the range of 10 g/L to 20 g/L in the acid fixation solution.
In an eighth step, the conditioned dyed wet blue is set-out to obtain set dyed wet blue having moisture content in the range of 50 % to 60 %.
In accordance with the embodiments of the present disclosure, the process step of setting out is performed mechanically, for smoothing and stretching the conditioned dyed wet blue, while compressing and squeezing out excess moisture.
In a ninth step, the set dyed wet blue is dried to obtain indigo dyed leather having moisture content in the range of 12 % to 14 %.
In accordance with the embodiments of the present disclosure, the drying is air drying, with air having a temperature in the range of 20°C to 40 °C, and humidity in the range of 10% to 80%.
In an embodiment, the process includes drumming for a time period in the range of 0.5 to 6 hours to obtain indigo dyed leather of a desired flexibility.
The drumming is performed by rotating the dyed leather in the drum for a time period in the range of 0.5 hours to 6 hours.
The drumming process ensures the penetration of the dye and other agents.
In an embodiment, the process includes at least one of chemical finishing and mechanical finishing of the indigo dyed leather to obtain finished indigo dyed leather.
In accordance with the embodiments of the present disclosure, chemical finishing is performed by spraying a finishing medium on the indigo dyed leather, wherein the finishing medium can be selected from:
a. dyeing composition of the present disclosure,
b. mixture of at least one binder and at least one of dye and pigment, wherein a ratio of the binder to the dye/pigment is in the range of 4:1 to 60:1,
c. at least one binder, and
d. at least one water repelling agent.
In accordance with the embodiments of the present disclosure, the binder is at least one selected from the group consisting of an acrylic binder, a polyurethane binder and a polyethylene.
In an embodiment, the dye is selected from indigo dye, a direct dye, a sulphur dye, a veg dye and an aniline dye.
In an embodiment, the pigment is selected from a white pigment, mercuric sulfide, lead (II) chromate and iron oxide.
In accordance with the embodiments of the present disclosure, the water repelling agent is at least one selected from teflon, polyurethane, silicones, oils, fluoro polymers, fluoro carbons, solvent or water based emulsion of synthetic waxes, solvent-based fluorine-free waterproof agent, solvent-based silicone, cationic silicone emulsion, perfluorocarbon based water repelling agents and blend of paraffin.
In accordance with a first embodiment of the present disclosure, the spray medium composition for chemical finishing of the semi-finished wet blue comprises:
i. acrylic binder in an amount in the range of 12 mass% to 15 mass % with respect to the total amount of the composition (a);
ii. polyurethane binder in an amount in the range of 11 mass% to 15 mass % with respect to the total amount of the composition (a);
iii. wax in an amount in the range of 3 mass% to 5 mass % with respect to the total amount of the composition (a);
iv. filler in an amount in the range of 2 mass% to 5 mass % with respect to the total amount of the composition (a);
v. indigo dye in an amount in the range of 5 mass% to 50 mass % with respect to the total amount of the composition (a);
vi. q. s. water.
In accordance with a second embodiment of the present disclosure, the spray medium composition for chemical finishing of the semi-finished wet blue comprises:
i. acrylic binder in an amount in the range of 5 mass% to 10 mass % with respect to the total amount of the composition (a);
ii. polyurethane binder in an amount in the range of 5 mass% to 8 mass % with respect to the total amount of the composition (a);
wax in an amount in the range of 1 mass% to 2 mass % with respect to the total amount of the composition (a);
iii. filler in an amount in the range of 2 mass% to 3 mass % with respect to the total amount of the composition (a);
iv. indigo dye in an amount in the range of 5 mass% to 50 mass % with respect to the total amount of the composition (a);
v. q. s. water.
In accordance with the embodiments of the present disclosure, the chemically finished indigo dyed leather is provided a top coat having composition which comprises nitrocellulose lacquer in an amount in the range of 30 mass% to 50 mass% with respect to the total amount of the top coat solution, silicone in an amount in the range of 2 mass% to 3 mass% with respect to the total amount of the top coat solution, and q.s. water.
In accordance with the embodiments of the present disclosure, the mechanical finishing comprises at least one process selected from buffing, ironing, printing/ engraving.
In a preferred embodiment, the water used at various steps of indigo dyeing of leather is soft water.
In a fourth aspect, the present disclosure provides indigo dyed leather.
The indigo dyed leather obtained by the process of the present disclosure is characterized by having:
• thickness in the range of 0.4 mm to 10 mm;
• tensile strength in the range 20 N/mm2 to 40 N/mm2, when measured as per BS EN ISO 3376;
• tear strength selected from single edge tear strength in the range of 40 N to 80 N, when measured as per BS EN ISO 3377- 1, and double edge tear strength in the range of 90 N to 260 N, when measured as per BS EN ISO 3377- 2.
BS EN ISO 3376: specifies a method for determining the tensile strength of leather;
BS EN ISO 3377- 1: specifies a method for determining the tear strength of leather using a Single edge tear;
BS EN ISO 3377- 2: specifies a method for determining the tear strength of leather using a Double edge tear.
In accordance with the embodiments of the present disclosure, the color of the indigo dyed leather is stable even after 10 washings.
The indigo dyed leather of the present disclosure can be used for making jackets, bags, footwear, upholstery fabric, and the like.
The foregoing description of the embodiments has been provided for purposes of illustration and is not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
EXPERIMENTAL DETAILS
Experiment 1: Preparation of indigo dyeing composition in accordance with the present disclosure
Example 1: Preparation of indigo dyeing composition by using a natural indigo dye in accordance with the present disclosure
50 g of acrylic copolymer (surfactant) and 250 g of natural indigo dye powder were mixed in 10 L of water having a temperature of 60 °C to obtain a first mixture. 150 g of NaOH was added to the first mixture followed by adding 450 g of sodium dithionite to obtain a second mixture. The second mixture was blended slowly in a manner such that there was no formation of bubbles and no introduction of oxygen in the second mixture. The second mixture was allowed to stand for 30 minutes to obtain the dyeing composition.
Example 2: Preparation of indigo dyeing composition by using a combination of natural and synthetic indigo dye in accordance with the present disclosure
50 g of salt of phosphoric acid ester (surfactant) and 100 g of synthetic indigo dye powder and 150 g of natural indigo dye powder were mixed in 10 L of water having a temperature of 60 °C to obtain a first mixture. 250 g of NaOH was added to the first mixture followed by adding 500 g of sodium dithionite to obtain a second mixture. The second mixture was blended slowly in a manner such that there was no formation of bubbles and no introduction of oxygen in the second mixture. The second mixture was allowed to stand for 30 minutes to obtain the dyeing composition.
Experiment 1 was repeated several times by varying the temperature of the water at various temperatures between 50 °C to 70 °C for obtaining the first mixture, varying the pH adjusting agent by using KOH and calcium hydroxide, and various reducing agents including lactose, maltose, glucose, fructose, galactose, and ferrous sulphate, thiourea dioxide, sodium borohydride, hydroxyacetone, and appropriate indigo dyeing compositions were obtained that could be used in the further processes.
Instead of natural indigo dye, synthetic indigo dye was also used in similar quantities. The dyeing composition obtained using synthetic indigo dye was found to have similar properties as that of the composition made using natural indigo. The indigo dyed leather obtained by using the dyeing composition comprising the synthetic indigo dye was found to have higher colour saturation and flatter colouring as compared to that obtained by using the natural indigo dye composition.
Experiment 2: Preparation of indigo dyed leather, in accordance with the present disclosure:
Example 1: Preparation of indigo dyed leather, in accordance with the present disclosure
6 kg of wet blue was used as a starting material. The wet blue was soaked in a soaking solution (10 g/L of salt of phosphoric acid ester in water) for 40 minutes to obtain a soaked wet blue followed by draining the soaking solution. Thereafter, the soaked wet blue was washed with water to obtain a washed wet blue. The washed wet blue was then re-tanned with a re-tanning composition (Water – 100% with respect to the weight of washed wet blue + 3% basic chromium sulphate + 0.7% MgO + 1.5% sodium formate) for 7 hours to obtain a re-tanned wet blue having pH 5. The pH of the re-tanned wet blue was increased using sodium carbonate to obtain a treated wet blue having pH 8. The treated wet blue was then dyed with a dyeing composition of Experiments 1, Example 1 for 20 minutes to obtain dyed wet blue having pH 11.5. The pH of the dyed wet blue was adjusted by using acetic acid to obtain pH adjusted dyed wet blue having pH 5.
The pH adjusted dyed wet blue was then fat-liquored using a synthetic fat-liquor based on phosphate esters (80 g/L), followed by acid fixing using formic acid (15 g/L) to obtain conditioned wet blue. Thereafter, the conditioned wet blue was set-out using mechanical operation to obtain a set wet blue having a moisture content of 50 %. Then, the set wet blue was dried at a temperature of 35° C and relative humidity 60% to obtain indigo dyed leather having a moisture content of 12%. Thereafter, the indigo dyed leather was drummed for 3 hours to increase the pliability and softness of the indigo dyed leather. The soft and pliable indigo dyed leather was chemically finished using a chemical treatment of polyurethane binder 200 parts and indigo powder 50 parts to obtain finished indigo dyed leather.
Example 2: Preparation of indigo dyed leather, in accordance with the present disclosure
10 kg of wet blue was used as a starting material. The wet blue was soaked in a soaking solution (15 g/L of salt of phosphoric acid ester in water) for 50 minutes to obtain a soaked wet blue followed by draining the soaking solution. Thereafter, the soaked wet blue was washed with water to obtain a washed wet blue. The washed wet blue was then re-tanned with a re-tanning composition (Water – 100% with respect to the weight of washed wet blue + 2% basic chromium sulphate + 40 g/L grain tightening acrylic syntan + 0.5% MgO + 1% sodium formate + 35 g/L Fat-liquor based on synthetic oils + 0.1% TCMTB with other organosulfur compounds) for 8 hours to obtain a re-tanned wet blue having pH 4.5. The pH of the re-tanned wet blue was increased using sodium bicarbonate to obtain a treated wet blue having pH 8.5. The treated wet blue was then dyed with a dyeing composition of Experiments 1, Example 1 for 15 minutes to obtain dyed wet blue having pH 11. The pH of the dyed wet blue was adjusted by using acetic acid to obtain pH adjusted dyed wet blue having pH 5.5.
The pH adjusted dyed wet blue was then fat-liquored using a semi-synthetic fat-liquor (90 g/L monohydric alcohol), followed by acid fixing using 12 g/L formic acid to obtain conditioned wet blue. Thereafter, the conditioned wet blue was set-out mechanically to obtain a set wet blue having a moisture content of 55%. Then, the set wet blue was dried at a temperature of 35° C and relative humidity 65% to obtain indigo dyed leather having a moisture content of 14%. Thereafter, the indigo dyed leather was drummed for 3 hours to increase the pliability and softness of the indigo dyed leather. After drumming, the soft and pliable indigo dyed leather was subjected to mechanical finishing of staking and printing. Thereafter, the indigo dyed leather was chemical-finished using a mixture of acrylic binder 50 parts, polyurethane binder 150 parts and white pigment 40 parts to obtain finished indigo dyed leather.
Example 3: Preparation of indigo dyed leather, in accordance with the present disclosure
8 kg of wet blue was used as a starting material. The wet blue was soaked in a soaking solution (12 g/L of salt of phosphoric acid ester in water) for 30 minutes to obtain a soaked wet blue followed by draining the soaking solution. Thereafter, the soaked wet blue was washed with water to obtain a washed wet blue. The washed wet blue was then re-tanned with re-tanning composition (Water – 100% with respect to the weight of washed wet blue + 50 g/L Synthetic re-tanning agent grain tightening acrylic syntan + 40 g/L Fat-liquor based on synthetic oils) for 6 hours to obtain a re-tanned wet blue having pH 5.5. The pH of the re-tanned wet blue was increased using ammonia to obtain a treated wet blue having pH 9. The treated wet blue was then dyed with a dyeing composition of Example 1 of Experiment 1, for 40 minutes to obtain dyed wet blue having pH 10.5. The pH of the dyed wet blue was adjusted by using acetic acid to obtain pH adjusted dyed wet blue having pH 5.2.
The pH adjusted dyed wet blue was then fat-liquored using a semi-synthetic fat-liquor (85 g/L esters of fatty substances), followed by acid fixing using 20 g/L formic acid to obtain conditioned wet blue. Thereafter, the conditioned wet blue was set-out to obtain a set wet blue having a moisture content of 60%. Then, the set wet blue was dried at a temperature of 40° C and relative humidity 55% to obtain indigo dyed leather having a moisture content of 13%. Thereafter, the indigo dyed leather was drummed for 2 hours and then subject to a mechanical buffing. The indigo dyed leather was then chemical-finished using a mixture of an acrylic binder 150 parts and direct dye 30 parts to obtain finished indigo dyed leather.
Example 4: Preparation of indigo dyed leather, in accordance with the present disclosure
5 kg of wet blue was used as a starting material. The wet blue was soaked in a soaking solution (8 g/L of salt of phosphoric acid ester in water) for 30 minutes to obtain a soaked wet blue followed by draining the soaking solution. Thereafter, the soaked wet blue was washed with water to obtain a washed wet blue. The washed wet blue was then re-tanned with re-tanning composition (Water – 100% with respect to the weight of washed wet blue + 2.5% basic chromium sulphate + 35 g/L grain tightening acrylic syntan + 0.4% MgO + 1.2% sodium formate + 35 g/L Fat-liquor based on synthetic oils) for 450 minutes to obtain a re-tanned wet blue having pH 5.3. The pH of the re-tanned wet blue was increased using ammonia to obtain a treated wet blue having pH 8.5. The treated wet blue was then dyed with a dyeing composition of Experiment 1, Example 2 for 40 minutes to obtain dyed wet blue having pH 11. The pH of the dyed wet blue was adjusted by using acetic acid to obtain pH adjusted dyed wet blue having pHv 5.3.
The pH adjusted dyed wet blue was then fat-liquored using a fatliquoring composition (40 g/L synthetic fat-liquor based on phosphate esters + 40 g/L esters of fatty substances), followed by acid fixing using 18 g/L formic acid to obtain conditioned wet blue. Thereafter, the conditioned wet blue was set-out to obtain a set wet blue having a moisture content of 55%. Then, the set wet blue was dried at a temperature of 40° C and relative humidity 50% to obtain indigo dyed leather having a moisture content of 14%. Thereafter, the indigo dyed leather was drummed for 2 hours and then subject to a mechanical buffing.
Various tests were performed on the indigo dyed leather obtained in accordance with the procedure as disclosed in Examples 1-4 of Experiment 2. The details of these tests, including results, are as disclosed in Table 2. The color fastness rating details are provided in Table 1.
Table 1: Color fastness rating details:
All colorfastness rating based on Grey scale (grade 1-5 rating)
Color change All colorfastness rating based on Grey scale (grade 1-5 rating)
Color stain/ self-staining
5 Negligible Or No Change 5 Negligible Or No Staining
4 Slightly Changed 4 Slightly Stained
3 Noticeably Changed 3 Noticeably Stained
2 Considerably Changed 2 Considerably Stained
1 Much Changed 1 Heavily Stained
Table 2: Test properties and testing results:
Test Property Test Results Maximum Test Method
Colorfastness to Water Spotting No color changes observed NA BS EN ISO 15700
Colorfastness To Water 3 to 5 5 BS EN ISO 11642
Colorfastness To Perspiration 4 to 5 5 BS EN ISO 11641
Colorfastness To Rubbing 3 to 5 5 BS EN ISO 11640
Colorfastness To Circular Rubbing 3 to 5 5 BS EN ISO 17700
Colorfastness To Crocking 3 to 5 5 BS EN ISO 105-x12
Colorfastness To Light 2 to 4 8 BS EN ISO 105 B02
Tensile Strength 20 to 40 N/mm2 NA BS EN ISO 3376
Tear Strength (Single Edge) 40 to 80 N NA BS EN ISO 3377- 1
Tear Strength (Double Edge) 90 TO 260 N NA BS EN ISO 3377- 2
Flexing Resistance (Bally Flex) No crack / no damage observed NA ISO 5402-1
Flex Resistance (Vamp Flex) No crack / no damage observed NA EN ISO 5402-2
Abrasion Resistance No abrasion / discoloration observed at the edges of the specimen NA BS EN ISO 13250
Chemical determination of hexavalent Chromium (chrome VI, Cr VI) content in Leather Not detected NA BS EN ISO 17075-1
From the above test results, it is observed that the indigo dyed leather of the present disclosure has improved mechanical properties such as tensile strength, tear strength (single edge), tear strength (double edge), flexing resistance and abrasion resistance. Further, the indigo dyed leather of the present disclosure has improved and unique aesthetics including tone variation and hues.
TECHNICAL ADVANCEMENTS
The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of;
? a dyeing composition that:
• can provide a wide range of blue shades to the leather; and
• can provide unique depth, tone and shade on leather;
? a process for the preparation of a indigo dyeing composition that:
• is simple, economic and environmentally friendly;
? a process for the indigo dyeing of leather that:
• is time effective; and
• is cost-effective; and
? an indigo dyed leather that
• has improved mechanical properties; and
• has improved and unique aesthetics including tone variation and hues.
The indigo dyed leather of the present disclosure can be used to make a variety of items, including clothing, footwear, handbags, furniture, tools, sports equipment, and the like.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising, will be understood to imply the inclusion of a stated element, integer or step,” or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
The economy significance details requirement may be called during the examination. Only after filing of this Patent application, the applicant can work publically related to present disclosure product/process/method. The applicant will disclose all the details related to the economic significance contribution after the protection of invention.
,CLAIMS:WE CLAIM:
1. A dyeing composition comprising:
a. water;
b. indigo dye in an amount in the range of 0.01 g/L to 200 g/L of water;
c. surfactant in an amount in the range of 0.01 g/L to 10 g/L of water;
d. pH adjusting agent in an amount in the range of 0.1 g/L to 100 g/L of water; and
e. reducing agent in an amount in the range of 0.5 g/L to 300 g/L of water.
2. The dyeing composition as claimed in claim 1 comprising,
a. water having TDS below 900 ppm;
b. indigo dye in an amount in the range of 1 g/L to 30 g/L of water;
c. surfactant in an amount in the range of 0.5 g/L to 5 g/L of water;
d. pH adjusting agent in an amount in the range of 0.5 g/L to 30 g/L of water; and
e. reducing agent in an amount in the range of 1.5 g/L to 60 g/L of water.
3. The dyeing composition as claimed in claim 1, wherein said indigo dye is selected from natural indigo dye, synthetic indigo dye and a combination of natural and synthetic indigo dye.
4. The dyeing composition as claimed in claim 1, wherein said pH adjusting agent is having a pH in the range of neutral pH to 12.5.
5. The dyeing composition as claimed in claim 1, wherein said pH adjusting agent is selected from the group consisting sodium hydroxide, potassium hydroxide and calcium hydroxide.
6. The dyeing composition as claimed in claim 1, wherein said reducing agent is selected from the group consisting of sodium dithionite, disaccharide, monosaccharide, madder, yeast, ferrous sulphate, thiourea dioxide, bran, sodium borohydride, hydroxyacetone and bacteria.
7. The dyeing composition as claimed in claim 6, wherein said disaccharide is selected from lactose and maltose; said monosaccharide is selected from glucose, fructose and galactose; and said bacteria is selected from Clostridium isatidis, Amphibacillus and Oceanobacillus.
8. The dyeing composition as claimed in claim 1, wherein said reducing agent is sodium dithionite.
9. The dyeing composition as claimed in claim 1, wherein said surfactant is at least one selected from an anionic surfactant, a non-ionic surfactant and a zwitter-ionic surfactant.
10. The dyeing composition as claimed in claim 9, wherein
• said anionic surfactant is selected from the group consisting of a salt of phosphoric acid ester, an acrylic copolymer, ammonium lauryl sulfate, sodium laureth sulfate, and sodium lauryl sarcosinate cocamide;
• said non-ionic surfactant is selected from cocamide, ethoxylates, and alkoxylates; and
• said zwitter ionic surfactant is selected from betaines and amino oxides.
11. The dyeing composition as claimed in claim 1 further comprises at least one of a sequestering agent, a binder and a dye other than indigo dye.
12. The dyeing composition as claimed in claim 11, wherein
• said sequestering agent is selected from acrylic copolymer, tetrasodium phosphates, sodium hexametaphosphate, tripolysodium phosphate, organophosphonic acid and disodium EDTA;
• said binder is selected from acrylic binder and polyurethane based binder; and
• said dye is selected from a direct dye, a sulphur dye, a veg dye, an aniline dye and a pigment.
13. The dyeing composition as claimed in claim 12, wherein
• said direct dye is selected from diamine scarlet, congo red, direct brown and chlorazol dye;
• said sulfur dye is selected from sulfur blue dye, sulfur brilliant green, sulfur black and leuco sulfur black;
• said veg dye is selected from a dye extracted from myrobalan fruit, pomegranate rind, sappanwood, turmeric root, chestnut hulls and madder root;
• said aniline dye is selected from aniline violet, aniline blue and aniline red; and
• said pigment is selected from mercuric sulfide, lead(II) chromate and iron oxide.
14. The dyeing composition as claimed in claim 1 comprising,
a. water
b. natural indigo dye in an amount of 25 g/L of water;
c. acrylic copolymer in an amount of 5 g/L of water;
d. sodium hydroxide in an amount of 15 g/L of water; and
e. sodium dithionite in an amount of 45 g/L of water.
15. The dyeing composition as claimed in claim 1 comprising,
a. water
b. a combination of natural and synthetic indigo dye in an amount of 25 g/L of water;
c. salt of phosphoric acid ester in an amount of 5 g/L of water;
d. sodium hydroxide in an amount of 25 g/L of water; and
e. sodium dithionite in an amount of 50 g/L of water.
16. The dyeing composition as claimed in claim 15, wherein an amount of said natural indigo dye is more than 60% with respect to the total amount of said combination of natural and synthetic indigo dye.
17. The dyeing composition as claimed in claim 15, wherein a mass ratio of said said natural indigo dye to said synthetic indigo dye is 1.5:1.
18. The dyeing composition as claimed in claim 1, having pH in the range of 6 to 12.5, preferably in the range of 10 to 11.5.
19. A process for the preparation of a dyeing composition, said process comprising the following steps:
(i) mixing predetermined amounts of at least one surfactant and indigo dye in water having a predetermined temperature to obtain a first mixture;
(ii) adding a predetermined amount of a pH adjusting agent to said first mixture followed by adding a predetermined amount of a reducing agent to obtain a second mixture; and
(iii) blending said second mixture and allowing it to stand for a predetermined time period to obtain said dyeing composition.
20. The process as claimed in claim 19, wherein said blending is carried out in a manner such that oxygen is not introduced into said second mixture during said blending process to prevent oxidation of the components of the second mixture.
21. The process as claimed in claim 19, wherein said predetermined temperature is in the range of 50 °C to 70 °C; and said predetermined time period is in the range of 30 minutes to 60 minutes.
22. The process as claimed in claim 19, comprises a step of adjusting pH of said second mixture to be in the range of 6 to 12.5, preferably in the range of 10 to 11.5.
23. The process as claimed in claim 19, further comprises a step of adding a sequestering agent, a binder and a dye other than said indigo dye to said second mixture.
24. A process for indigo dyeing of leather, said process comprising the following steps:
a. soaking wet blue in a soaking solution in a bath for a time period in the range of 30 minutes to 120 minutes to obtain soaked wet blue followed by draining off said soaking solution;
b. washing said soaked wet blue with a washing fluid to obtain washed wet blue;
c. re-tanning said washed wet blue with a re-tanning composition for a time period in the range of 6 hours to 8 hours to obtain re-tanned wet blue having a pH in the range of 3 to 6;
d. adjusting the pH of said re-tanned wet blue to obtain pH adjusted wet blue having a pH in the range of 5 to 9;
e. dyeing said pH adjusted wet blue with a dyeing composition having pH in the range of 6 to 12.5, preferably in the range of 10 to 11.5 for a time period in the range of 5 minutes to 60 minutes to obtain dyed wet blue having pH in the range of 6 to 12.5, preferably in the range of 10 to 11.5;
f. adjusting pH of said dyed wet blue to obtain pH adjusted dyed wet blue having a pH in the range of 4.5 to 5.5;
g. fat-liquoring said pH adjusted dyed wet blue followed by acid fixing to obtain conditioned dyed wet blue;
h. setting out said conditioned dyed wet blue to obtain set dyed wet blue having moisture content in the range of 50% to 60%; and
i. drying said set dyed wet blue to obtain indigo dyed leather having moisture content in the range of 12% to 14%.
25. The process as claimed in claim 24, wherein said process includes drumming for a time period in the range of 0.5 hours to 6 hours to obtain indigo dyed leather of a desired flexibility.
26. The process as claimed in claim 24, wherein said process includes at least one of chemical finishing and mechanical finishing of said indigo dyed leather to obtain finished indigo dyed leather.
27. The process as claimed in claim 24, wherein said wet blue is obtained by performing beam house processes followed by chrome tanning of a hide selected from buffalo hide, cow hide, goat hide, sheep hide, deer hide, alligator hide, crocodile hide, ostrich hide and camel hide.
28. The process as claimed in claim 24, wherein said wet blue has a thickness in the range of 0.4 mm to 10 mm.
29. The process as claimed in claim 24, wherein said soaking solution comprises water and a surfactant, wherein the amount of said surfactant is in the range of 5 g/L to 20 g/L; wherein said surfactant is at least one selected from the group consisting of an anionic surfactant, a non-ionic surfactant and a zwitter-ionic surfactant.
30. The process as claimed in claim 29, wherein
• said anionic surfactant is selected from the group consisting of a salt of phosphoric acid ester, an acrylic copolymer, ammonium lauryl sulfate, sodium laureth sulfate, and sodium lauryl sarcosinate cocamide;
• said non-ionic surfactant is selected from cocamide, ethoxylates, and alkoxylates; and
• said zwitter ionic surfactant is selected from betaines and amino oxides.
31. The process as claimed in claim 24, wherein said washing fluid is water.
32. The process as claimed in claim 31, wherein water has:
• total dissolved solids (TDS) less than 900 ppm;
• pH in the range of 6 to 7;
• total suspended solids (TSS) in the range of 5 ppm to 6 ppm;
• total hardness in the range of 100 ppm to 200 ppm; and
• COD in the range of 15 mg/L to 30 mg/L.
33. The process as claimed in claim 24, wherein said re-tanning composition comprises
• grain tightening acrylic syntan in an amount in the range of 3 mass % to 8 mass % with respect to the total mass of said washed wet blue;
• semi-synthetic fat-liquor in an amount in the range of 2 mass % to 6 mass % with respect to the total mass of said washed wet blue,
wherein said semi-synthetic fat-liquor is selected from fat-liquor based on synthetic oils, natural oil containing sulphite, esters of fatty substances and monohydric alcohol; and
• q.s. water
34. The process as claimed in claim 24, wherein said re-tanning composition comprises:
• chromium sulphate in an amount in the range of 1 mass % to 5 mass % with respect to the total mass of said washed wet blue;
• sodium formate in an amount in the range of 1 mass % to 2 mass % with respect to the total mass of said washed wet blue;
• at least one basifying agent in an amount in the range of 0.5 mass % to 1 mass % with respect to the total mass of said washed wet blue;
• optionally, at least one preservative in an amount in the range of 0.05 mass % to 0.5 mass % with respect to the total mass of said washed wet blue;
• optionally, grain tightening acrylic syntan in an amount in the range of 2 mass % to 6 mass % with respect to the total mass of said washed wet blue;
• optionally, semi-synthetic fat-liquor in an amount in the range of 2 mass % to 6 mass % with respect to the total mass of said washed wet blue,
wherein said semi-synthetic fat-liquor is selected from fat-liquor based on synthetic oils, natural oil containing sulphite, esters of fatty substances and monohydric alcohol; and
• q.s. water.
35. The process as claimed in claim 34, wherein said basifying agent is magnesium oxide (MgO); and said preservative is a biocide, wherein said biocide is selected from 2-thiocyano-methylthiobenzothiazole(TCMTB), N-octyl-isothiazolinone(N-OITZ), other organosulfur compounds and alkaline organic salt compounds.
36. The process as claimed in claim 24, wherein pH of said re-tanned wet blue is adjusted by treating said re-tanned wet blue with at least one weak acid or at least one weak base for a time period in the range of 30 minutes to 45 minutes.
37. The process as claimed in claim 36, wherein said weak acid is at least one selected from the group consisting of formic acid, acetic acid and oxalic acid.
38. The process as claimed in claim 36, wherein said weak base is at least one selected from the group consisting of sodium bi-carbonate, sodium formate and ammonia.
39. The process as claimed in claim 36, wherein said weak acid has a concentration in the range of 5 g/L to 15 g/L; and said weak base has a concentration in the range of 5 g/L to 20 g/L.
40. The process as claimed in claim 24, wherein said pH adjusted wet blue obtained in step (d) is washed with water having a temperature in the range of 55 ° C to 65 °C.
41. The process as claimed in claim 24, wherein said dyeing composition comprises:
a. water;
b. indigo dye selected from natural indigo dye and synthetic indigo dye in an amount in the range of 0.01 g/L to 200 g/L of water;
c. surfactant selected from an anionic surfactant, a non-ionic surfactant and a zwitter-ionic surfactant in an amount in the range of 0.01 g/L to 10 g/L of water;
d. pH adjusting agent selected from the group consisting sodium hydroxide, potassium hydroxide and calcium hydroxide in an amount in the range of 0.1 g/L to 100 g/L of water; and
e. reducing agent selected from the group consisting of sodium dithionite, disaccharide, monosaccharide, madder, yeast, ferrous sulphate, thiourea dioxide, sodium borohydride, hydroxyacetone and bacteria in an amount in the range of 0.5 g/L to 300 g/L of water,
wherein pH of said dyeing composition is in the range of 6 to 12.5, preferably in the range of 10 to 11.5.
42. The process as claimed in claim 41, wherein
• said anionic surfactant is selected from the group consisting of a salt of phosphoric acid ester, an acrylic copolymer, ammonium lauryl sulfate, sodium laureth sulfate, and sodium lauryl sarcosinate cocamide;
• said non-ionic surfactant is selected from cocamide, ethoxylates, and alkoxylates; and
• said zwitter ionic surfactant is selected from betaines and amino oxides.
43. The process as claimed in claim 41, wherein said dyeing composition further comprises at least one of a sequestering agent, a binder and a dye other than indigo dye.
44. The process as claimed in claim 43, wherein
• said sequestering agent is selected from acrylic copolymer, tetrasodium phosphates, sodium hexametaphosphate, tripolysodium phosphate, organophosphonic acid and disodium EDTA;
• said binder is selected from acrylic binder and polyurethane based binder; and
• said dye is selected from a direct dye, a sulphur dye, a veg dye, an aniline dye and a pigment.
45. The process as claimed in claim 24, wherein pH of said dyed wet blue is adjusted by using a weak acid selected from acetic acid, formic acid and oxalic acid.
46. The process as claimed in claim 45, wherein said weak acid has a concentration in the range of 10 g/L to 30 g/L.
47. The process as claimed in claim 24, wherein said fat-liquoring comprises subjecting said pH adjusted dyed wet blue to a fat-liquoring composition for a time period in the range of 60 minutes to 90 minutes.
48. The process as claimed in claim 47, wherein said fat-liquoring composition comprises at least one component selected from a synthetic fat-liquor and a semi-synthetic fat-liquor.
49. The process as claimed in claim 48, wherein
• said synthetic fat-liquor is selected from synthetic esters, synthetic fat-liquor based on phosphate esters, electrolyte stable synthetic softening agents, modified alkane sulphonates and synthetic oils, sulfo-ester derivatives and high molecular weight hydrocarbons; and
• said semi-synthetic fat-liquor is selected from fat-liquor based on synthetic oils, natural oil containing sulphite, esters of fatty substances and monohydric alcohol.
50. The process as claimed in claim 24, wherein said drying in step (i) is air drying with air having a temperature in the range of 20 °C to 40 °C, and humidity in the range of 10% to 80%.
51. The process as claimed in claim 26, wherein said chemical finishing is performed by spraying a finishing medium on said indigo dyed leather, wherein said finishing medium is selected from:
a. said dyeing composition used in step (e),
b. a mixture of at least one binder and at least one of dye and pigment, wherein a ratio of said binder to said dye/pigment is in the range of 4:1 to 60:1,
c. at least one binder, and
d. at least one water repelling agent.
52. The process as claimed in claim 51, wherein
• said binder is at least one selected from the group consisting of an acrylic binder, a polyurethane binder, and a polyethylene;
• said dye is selected from indigo dye, a direct dye, a sulphur dye, a veg dye and an aniline dye;
• said pigment is selected from a white pigment, mercuric sulfide, lead(II) chromate and iron oxide; and
• said water repelling agent is at least one selected from teflon, polyurethane, silicones, oils, fluoro polymers, fluoro carbons, solvent or water based emulsion of synthetic waxes, solvent-based fluorine-free waterproof agent, solvent-based silicone, cationic silicone emulsion, perfluorocarbon based water repelling agents and blend of paraffin.
53. The process as claimed in claim 26, wherein said mechanical finishing comprises at least one process selected from buffing, ironing and printing/ engraving.
54. An indigo dyed leather obtained by a process as claimed in claim 24, characterised by having:
a. thickness in the range of 0.4 mm to 10 mm;
b. tensile strength in the range of 20 N/mm2 to 40 N/mm2; and
c. tear strength selected from single edge tear strength in the range of 40 N to 80 N and double edge tear strength in the range of 90 N to 260 N.
55. The leather as claimed in claim 54, wherein the dye is stable after 10 washings.

Dated this 23rd day of June, 2023

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
of R.K.DEWAN & CO.
Authorized Agent of Applicant

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI