Title of Invention	A NOVAL PROCESS FOR PRPARATION OF MULTI TONED DYED LEATHER
Abstract	A novel process is provided for regulating uptake of dyes selectively resulting in the formation of more than one tone on leather surface in a consistent, uniform and reproducible manner ensuring an economic option for enhancing aesthetic value of final leather.

Full Text

The present invention relates to a novel process for preparation of multi toned dyed leather . More particularly the invention relates to a process for producing multi-tone dyeing on leather in the dye-yard of a tannery. It is envisaged to have enormous potential application in tanning industry not only for producing leather for fancy articles , but also for upgrading lower grade leathers , thereby resulting in substantial value addition.In leather manufacture the aesthetic appearance of the leather is improved to a great extent by a process called dyeing . Conventionally tanned leathers are dyed in a drum by treating with synthetic coal tar or natural dyestuffs followed by fixing and optional topping depending upon the end use of the resulting leather. This process results in conventional unicolour leather. However, the increasing demand of fancy leather articles has over the years resulted in the requirement for leather with two-tone or even multitone effect which has also eventually paved the way for upgradation of lower ends. Creating two-tone effect on leather has thus been an established practice for upgrading lower grade leathers for reasons of enhancement of unit value realization, aesthetic appearance etc. The tie and dye process has been a popular technique among the tanners to dye leather in two different tones in the dye yard of a tannery. As reported by Khanna etal. (Fancy, split, and speciality leathers, CLRI publication, pp98,1975) this involves folding the leather in concentric circles or designs and keeping them in position by tying with strings and subsequently dyeing in a pit or tub, wherein only untied or exposed portions get coloured. The knots are systematically untied to dye folded portions in contrast colour so as to produce a two tone or multicolour effect. While the technology is simple and does not involve use of any sophisticated equipment or chemical, the process is associated with the following major limitations. 1. Being manual system, the consistency and uniformity of the design suffers to a large extent. 2. The methodology limits application to very thin and soft leathers only. 3. The work involves special skills which restricts wider adoption of the system. 4. The system is labour intensive, which limits higher productivity. Most of these limitations associated with tie and dye technique are overcome by adopting screen and block printing technique in the finishing yard. It has been a very popular practice among the leather finishers for producing various multitone designs on leather with the help of screen or block using dye as reported by Gupta etal, (Fancy, split, and speciality leathers, CLRI publication, pp91, 1975) or pigment as reported by Venkatachalapathy etal . (Fancy, split, and speciality leathers, CLRI publication, pp87, 1975) in the form of a paste. While this technique enables a finisher to command a control over the type of required dye or design, it is in fact a manual technique requiring skilled manpower, thereby limiting the productivity. The other major limitations associated with this process are the following.Application of the process is limited to firm and flat leathers. 1. The feel and the handle of the leathers are often likely to be adversely i affected. 3. Fixation of the dyes is likely to pose a problem, thereby resulting in poor fastness characteristics of leathers. The main objective of the present invention is to provide a novel process for preparation of dyed leather in more than one tone which obviates the limitations stated above. Another objective of the present invention is to provide a process for selective blocking of surface in respect of conventional aqueous dyeing to facilitate creation of mutitones on leather surface. Yet another objective of the present invention is to provide applicable to leathers of varying degrees of softness and thickness. Yet another objective of the present invention is to produce more than one tone on leather surface consistently. Accordingly the present invention provides a novel process for preparation of multi toned dyed leather which comprises : i) effecting temporary indentations on the surface of the dyed or undyed leather by conventional methods as herein described, ii) applying coat of water repellent/ waterproof non film forming materials selected from Fluoro carbon , poly siloxanes, emulsion of phosphated oil having chain length in the range of C17 - C25, alkyl acrylate of molecular weight in the range of 8000 - 10000, diluted to maximum of 50% w/v, on the surface of leather as formed in step (i), followed by topping the said surface with 5 - 20% w/v, of aqueous solution of chloride or sulphate salt of trivalent metal such as herein described and subsequent drying at a temperature 50°C by conventional manner, iii) dyeing the resulting leather by conventional manner with aqueous dye to get leather in more than one toneiv) repeating steps (i), (ii) and (iii), with different indentations, for n times, wherein n refers to a positive integer, to produce desired multi toned dyed leather. In an embodiment of the present invention the method for effecting indentation on leather surface may be such as printing embossing, stamping. In another embodiment of the present invention, the length of the Carbon chain of the alkyl group of the alkyl acrylate used may be in the range of 15-25. In yet another embodiment of the present invention, the amount of water repellent/ water proof material used for coating leather surface may be in the range of 6 - 10 gms per sq. ft. of leather. In still another embodiment of the present invention, the trivalent metal used may be such as aluminium, iron, chromium. In yet another embodiment of the present invention, the known method used for coating leather surface may be such as spraying , padding, roller coating, brushing. In still another embodiment of the present invention the amount of metal salt used may be minimum 1 gm per sq. ft. of leather. In yet another embodiment of the present invention the method used for drying of leathers may be such as natural air drying, forced hot air drying. The process is described below in detail. The surface of the leather to be dyed in more than one tone is subjected to temporary indentation by known method, while ensuring non-uniform projections on the surface. The leather surface is then coated by using 6-10 gms of water repellent/ waterproof non film forming material, diluted to a maximum of 50%w/v, per sq. ft. of leather, by known method. The resulting surface is then topped by 5-20% w/v, of aqueous solution of chloride or sulphate salt of bivalent metal by known method, the amount of salt used being minimum 1 gm per sq. ft. of leather. The leather is then dried at a temperature not exceeding 50°C by conventional method. The dried leather is then conventionally drum dyed to get leather of more than one tone. The process of effecting indentations on leather surface and subsequent coating of water repellent/ waterproof material followed by metal salt topping and subsequent drying are optionally repeated for n times, each time effecting different indentations, for getting (n+2) tones on the final dyed leather.The novelty and non-obviousness of the present invention lies in subjecting the leather surface to temporary indentation of different projections followed by applying water repellent /waterproof coating thereon, thereby ensuring blocking of projected portion of the surface during subsequent aqueous dyeing, resulting in multitone formation on leather surface in a consistent, uniform and reproducible manner ensuring an economic option for enhancing aesthetic value of the final leather. The invention is described in detail with reference to the examples given below which should not however be construed to limit the scope of the present invention.100 sq.ft. of white goat crust leathers were printed with seal grain print. 800 gms of poly siloxane dissolved in 400 cc water was coated on the projected portions of the printed leather using a roller coating machine. 100 gm of basic aluminum sulfate was dissolved in 1000 cc of water and sprayed on the leathers. The leathers were then dried at 35°C. Then they were wet back using 20 litres of water, 60gms of wetting agent and 60 gms of ammonia by drumming for a period of 20 minutes and then leaving in the medium overnight. Next day, the leathers were washed by drumming with 12 litres of water for a period of 20 minutes.The resulting leathers were then dyed with 120 gms of anionic violet colour dye using 20 litres of water as the medium, by drumming for 20 minutes. The dye was fixed using 120 gms of formic acid, added to the drum in 3 instalments of 10 minutes interval. Finally, the leathers were washed in 12 litres of water and dried to produce white and violet coloured two-tone leathers.200 sq.ft. of yellow colour dyed cow crust leathers were embossed with crocodile print. . 1200 gms of aqueous emulsion of fluorocarbon was sprayed on projected portions using angular spraying technique. 400 gm of ferric chloride dissolved in 8000 cc of water was sprayed on the leathers. The leathers were then dried at 50°C in a hot air chamber. Then they were wet back using 120 litres of water, 400gms of wetting agent and 400 gms of ammonia by drumming for a period of 20 minutes and then leaving in the medium overnight Next day, the leathers were washed by drumming with 80 Itrs of water for a period of 20 minutes.The resulting leathers were then dyed with 1200 gms. of anionic red dye using 120 Itrs of water as the medium by drumming for a period of 20 minutes. The dye was fixed using 1200 gms of formic acid, added to the drum in 3 instalments of 10 minutes interval. Finally, the leathers were washed in 80 litres of water and dried to produce yellow and red two-tone leathers.50 sq.ft. of white sheep crust leathers were stamped with zug grain print SOOgms of phosphated oil was padded on the projected portions of the leather. 100 gms of Basic Chromium Sulphate was dissolved in 1000 cc of water and sprayed on the leathers. The leathers were then dried at 40°C. Then they were wet back using 10 litres of water, 30gms of wetting agent and 30 gms of ammonia by drumming for a period of 20 minutes and then leaving in the medium overnight. Next day, the leathers were washed by drumming with 12 litres of water for a period of 20 minutes. The resulting leathers were then dyed with 90 gms of direct yellow dye using 20 litres of water as the medium, by drumming for 20 minutes. The dye was fixed using 90 gms of formic acid, added to the drum in 3 instalments of 10 minutes interval. The leathers were then washed in 12 litres of water and dried. The dried leathers were staked to soften and printed with seal grain print. 500 gms of phosphated oil was coated on the projected portions of the printed leather using a roller coating machine. 100 gms of Basic Chromium Sulphate was dissolved in 1000 cc of water and sprayed on the leathers. The leathers were then dried at 40°C. Then they were wet back using 10 litres of water, 30gms of wetting agent and 30 gms of ammonia by drumming for a period of 20 minutes and then leaving in the medium overnight. Next day, the leathers were washed by drumming with 12 litres of water for a period of 20 minutes. The resulting leathers were then dyed with 90 gms of acid blue dye using 20 litres of water as the medium, by drumming for 20 minutes. The dye was fixed using 90 gms of formic acid, added to the drum in 3 instalments of 10 minutes interval. The leathers were then washed in 12 litres of water and dried to produce, leathers having white, yellow and green tones. Example - 4 200 sq.ft. of white colour dyed buffalo crust leathers were printed with crocodile print. 1200 gms of Alkyl acrylate of molecular weight 10000, was brushed on projected portions. 400 gm of ferric chloride dissolved in 2000 cc of water was sprayed on the leathers. The leathers were then dried at 50°C in a hot air chamber. Then they were wet back using 120 litres of water, 400gms of wetting agent and 400 gms of ammonia by drumming for a period of 20 minutes and then leaving in the medium overnight. Next day, the leathers were washed by drumming with 80 Itrs of water for a period of 20 minutes. The resulting leathers were then dyed with 1200 gms. of metal complex grey dye using 120 Itrs of water as the medium by drumming for a period of 20 minutes. The dye was fixed using 1200 gms of formic acid, added to the drum in 3 instalments of 10 minutes interval. Finally, the leathers were washed in 80 litres of water and dried to produce white and grey two-tone leathers. The advantages of the present invention are the following. 1. It is a versatile process applicable to leathers of varying thickness and softness. 2. The process produces more than one tone on leather surface uniformly and consistently. 3. Unlike the hitherto known methods, the present process does not require any specialized skills. 4. The effect improves the surface characteristics of the leathers significantly. We Claim: 1. A novel process for preparation of multi toned dyed leather which comprises i) Effecting temporary indentations on the surface of the dyed or undyed leather by conventional methods as herein described, ii) applying coat of water repellent/ waterproof non film forming materials selected from Fluoro carbon , poly siloxanes, emulsion of phosphated oil having chain length in the range of C17 - C25, alkyl acrylate of molecular weight in the range of 8000 - 10000, diluted to maximum of 50% w/v, on the surface of leather as formed in step (i), followed by topping the said surface with 5 - 20% w/v, of aqueous solution of chloride or sulphate salt of trivalent metal such as herein described and subsequent drying at a temperature 50°C by conventional manner, iii) dyeing the resulting leather by conventional manner with aqueous dye to get leather in more than one tone. iv) repeating steps (i), (ii) and (iii), with different indentations, for n times, wherein n refers to a positive integer, to produce desired multi toned dyed leather. 2. A novel process, as claimed in claim 1, wherein indentation on surface of leather may be effected by methods selected from printing, embossing, stamping. 3. A novel process, as claimed in claims 1 and 2, wherein the length of the carbon chain of the alkyl group of the alkyl acrylate used is in the range of 15-25. 4. A novel process, as claimed in claims 1 - 3, wherein the amount of water repellent or water proof material used for coating leather surface is in the range of 6 - 10 gm per sq. ft. of leather. 5. A novel process, as claimed in claims 1 to 4, wherein the trivalent metal used is selected from aluminium, iron, chromium. 6. A novel process , as claimed in claims 1 to 5, wherein the coating of leather surface is effected by method selected from spraying, padding, roller coating, brushing. 7. A novel process, as claimed in claims 1 to 6, wherein the amount of metal salt used is 1 gm per sq. ft. of leather. 8. A novel process ,as claimed in claims 1 to 7, wherein the method used for drying of leathers is effected by methods selected from natural air drying, forced hot air drying. 9. A novel process for preparation of multi toned dyed leather, substantially as herein described with reference to the examples.

Documents:

363-del-2001-abstract.pdf

363-del-2001-claims.pdf

363-del-2001-correspondence-others.pdf

363-del-2001-correspondence-po.pdf

363-del-2001-description (complete).pdf

363-del-2001-form-1.pdf

363-del-2001-form-18.pdf

363-del-2001-form-2.pdf

363-del-2001-form-3.pdf