Title of Invention

AN IMPROVED PROCESS FOR PRODUCING LEATHERS IN MORE THAN ONE TONE

Abstract

A novel process is provided for the preparation of multi tone leathers by selective removal of colour from dyed leathers. The invention is directed to the selective blocking of the surface to the bleaching action of ozone with the help of coating of film forming materials leading to multitone formation on leather in a consistent and uniform manner ensuring an economic option for enhancing aesthetic value of the final leather.

Full Text

FIELD OF THE INVENTION The present invention relates to an improved process for producing leathers in more than one tone. More particularly the invention relates to an improved process for producing multi-tone effect in leather. It is envisaged to have enormous application potential in tanning industry not only for producing leathers for fancy articles, but also for upgrading lower grade leathers, thereby resulting in substantial value addition. BACKGROUND OF THE INVENTION Conventionally tanned leathers are dyed in drum by treating with synthetic coal tar or natural dyestuffs followed by fixing it with formic acid. This process results in producing conventional unishade 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 grade leathers. Creating multitone and 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. There are several methods to produce two tone or multi tone leathers. The tie and dye process has been a popular technique among the tanners to dye leathers in two different tones. As reported by Khanna etal. (Fancy split, and specialty leathers, CLRI publication, pp. 98, 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 in contrast colour so as to produce two tone or multicolor 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 involved limits the application thereof to very thin and soft leathers only. 3 The work involves special skill 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 techniques 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 et al. (Fancy, split, and specialty leathers, CLRI publication, pp. 91,1975) or using pigment in the form of a paste as reported by Venkatachalapathy et al. (Fancy, split, and specialty leathers, CLRI publication, pp. 87, 1975). While this technique enables the finisher 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. 1 Application of the process is limited to firm and flat leathers. 2 The feel and the handle of the leathers are often likely to be adversely affected. 3. Fixation of the dyes is likely to pose a problem, thereby resulting in poor fastness characteristics of leathers. Our co-pending patent application number 363 DEL 2001 provides a method for producing leather in more than one tone, wherein the uptake of dye is regulated selectively. This method however calls for use of machinery like hydraulic press or roller coating machine and hence limits wider application. Discharge printing of materials is a known method to ornament dyed materials (Patent No. 478/MAS2000 Anna University, Chennai). By this method, a foam printing paste is prepared with water, foaming agent and foam stabilizer. The dyed material to be discharge printed is printed with the above mentioned foam printing paste using printing machine and then the material is subjected to ozone-oxygen gas mixture in an apparatus wherein colour discharge takes place only in the coated areas. However, the limitations associated with this process are the following: • This process is developed for textiles and extended to leather whereby the coating of the leather with specialty chemicals often adversely affect the feel and handle of the leather. • Use of foam based compounds; often adversely affect subsequent finishing operation and fastness properties of suede leathers. • Use of foam based compounds leads to ecological and treatability issues. • Unless the flow properties of the printing paste are properly regulated, consistency of the printing cannot be ensured in the aforesaid system. Therefore, keeping in purview the limitations of the hitherto reported prior art, the inventors have realized that there exists a dire need to develop a process which regulates the production of multi-tone in leather by selective inhibition of ozone action for colour removal from dyed leathers. OBJECTS OF THE INVENTION The main object of present invention is to develop an improved process for producing leathers in more than one tone, which obviates the limitations stated above. Another objective of the present invention is to provide a process applicable to both grain finished and suede leathers. Still another object of the present invention is to provide a process whereby leathers in more than one tone are produced by selective removal of colour from dyed leathers. Yet another object of the present invention is to provide a process which is applicable to both unidyed and contrast dyed leathers. A further object of the present invention is to produce more than one tone on leather surface consistently. SUMMARY OF THE INVENTION Accordingly, the present invention provides an improved process for producing leathers in more than one tone, which comprises the steps of: [a] applying a coat of film forming materials at concentration ranging from 1.6 to 10% w/v, selectively on the surface of the dyed leather followed by drying at a temperature ranging from 30 to 50 degree C, to obtain selectively coated leather; [b] exposing the coated leather, as obtained in step (a) to ozone treatment in a closed chamber, at ozone quantity ranging from 0.56 to 1.12 g/m2 for a period of 30 to 50 minutes, to obtain leathers with more than one tone. In an embodiment of the present invention, the method of coating the leather surface may be such as spraying, padding, roller coating, brushing. In another embodiment of the present invention, the method of drying of leathers may be natural air drying, forced hot air drying. In still another embodiment of the present invention, the concentration of the film forming material is preferably 10% w/v. In yet another embodiment of the present invention, drying is done preferably at a temperature of 30 degree C. In a further embodiment of the present invention, the quantity of ozone used is preferably 0.56 g/m2 of the leather for a period of 30 minutes. DETAILED DESCRIPTION OF THE INVENTION The surface of the leather is coated with film forming materials such as starch or carboxy methyl cellulose (CMC) after placing a stencil having slotted design on the leather. The concentration of the film forming material ranges from 1.6 to 10% by weight based on solution volume. The surface coating of the leather is followed by drying at a temperature in the range of 30 to 50 degree C, to obtain selectively coated leather and exposing the leather to ozone in a closed chamber at quantity ranging from 0.56 to 1.12 g/m2 for a period of 30 to 50 minutes wherein the uncoated areas lose surface colour to produce leather of more than one tone. The novelty and non-obviousness of the present invention lies in selective blocking of the surface to the bleaching action of ozone with the help of coating of film forming materials leading to multitone formation on leather in a consistent and uniform 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. Example -1 0.9 m2 of blue dyed (Navy I5RE (C.I. No. Acid blue 113)) full chrome sheep nappa leather sprayed with 60 g of CMC dissolved in 1L of water to block the surface selectively using a stencil having slotted design. The leathers were then dried at 30°C by open air drying. Then the leathers were exposed to 0.56 g ozone in a closed chamber for 30 minutes to get leathers with blue and white tones. Example - 2 09 m2 of Red dyed (Acid Red (C.I. Acid Red 119)) semi chrome Goat suede leather top dyed with yellow (Yellow 5GN (C. I. Yellow 110)) was coated with brush with 16 g of CMC dissolved in 1L of water to block the surface selectively using a stencil having slotted design. The leathers were then dried at 40°C in hot air chamber. Then the leathers were exposed to 1.12 g ozone in a closed chamber for 40 minutes to get leathers with red and yellow tones. Example - 3 0.9 m2 of yellow dyed (Yellow 5GN (C. I. Yellow 110)) and then top dyed with Navy I5RE (Acid Blue (C. I. Acid Blue 113)) full chrome buff upper leather was coated with 100 g of CMC dissolved in 1L of water using roller coater to block the surface selectively using a stencil having design. The leathers were then dried at 50°C in hot air chamber. Then the leathers were exposed to 0.8 g ozone in a closed chamber for a period of 50 minutes to get leathers with blue and yellow tones. ADVANTAGES: The present invention has the following advantages: 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, or any special equipment. We claim: 1. An improved process for producing leathers in more than one tone, which comprises the steps of: [a] applying a coat of film forming materials at concentration ranging from 1.6 to 10% w/v, selectively on the surface of the dyed leather followed by drying at a temperature ranging from 30 to 50 degree C, to obtain selectively coated leather; [b] exposing the coated leather, as obtained in step (a) to ozone treatment in a closed chamber, at quantity ranging from 0.56 to 1.12 g/m2 for a period of 30 to 50 minutes, to obtain leathers with more than one tone. 2. A process as claimed in claim 1, wherein the film forming materials are preferably starch, carboxy methyl cellulose [CMC]. 3. A process as claimed in claim 1, wherein the concentration of the film forming material is preferably 10% w/v. 4. A process as claimed in claim 1, wherein drying is done preferably at a temperature of 30 degree C. 5. A process as claimed in claim 1, wherein the quantity of ozone used is preferably 0.56 g/m2 of the leather for a period of 30 minutes. 6. A process as claimed in claim 1, wherein the method of coating the leather surface is preferably spraying, padding, roller coating, brushing. 7. A process as claimed in claim 1, wherein the method of drying is preferably natural air drying, forced hot air drying. 8. An improved process for producing leathers in more than one tone substantially as herein described with reference to the foregoing examples.

Documents:

1764-del-2006-abstract.pdf

1764-del-2006-Claims-(28-03-2014).pdf

1764-del-2006-claims.pdf

1764-del-2006-Correspondence Others-(29-07-2013).pdf

1764-del-2006-Correspondence-Others-(28-03-2014).pdf

1764-del-2006-correspondence-others.pdf

1764-del-2006-Description (Complete)-(28-03-2014).pdf

1764-del-2006-dsecription (complete).pdf

1764-del-2006-form-1.pdf

1764-del-2006-form-2.pdf

1764-del-2006-Form-3-(29-07-2013).pdf

1764-del-2006-form-3.pdf

1764-del-2006-form-5.pdf