Title of Invention

A NOVAL PROCESS OF AQUEOUS FINISHING FOR WATERPROOF LEATHERS

Abstract

The present invention relates to a novel process of aqueous finishing for waterproof leathers. The process has enormous potential application in leather processing industry as an eco-friendly option for finishing waterproof leathers. It is envisaged to be a major step towards production of high quality waterproof leathers even by using aqueous system.The process steps are: conditioning post tanned wet leather by known method to get sammed leather having moisture content in the range of 60-80% w/w.,. characterized in that applying aqueous base coat of film forming material, such as acrylate, polyurethane, used either individually or in combination, on the grain side of the sammed leather, as obtained in step (i), by known method, followed by conventional drying at a temperature in the range of 30-45°C and subsequent subjecting of the resulting leather to conventional finishing by known method to get aqueous finished waterproof leather.

Full Text

The present invention relates to a novel process of aqueous finishing for waterproof leathers. The process has enormous potential application in leather processing industry as an eco-friendly option for finishing waterproof leathers. It is envisaged to be a major step towards production of high quality waterproof leathers even by using aqueous system. As reported in the Leather Finishing Manual, Pp 34, prepared by Indofil Chemicals Ltd, finishing is a process of application of film(s) on the surface of crust leathers with an objective of protecting the grain surface from any external damages caused by rubbing, scuffing etc. Moreover, appropriate finishing also helps in covering the natural defects present on leather surface, thereby adding value to it. The protective coat(s), while improving the aesthetic appeal, also imparts the desired colour and level appearance to the leather. A normal finish essentially consists of three coats viz. Base coat Intermediate coat Topcoat It has been a practice among the tanners to apply a base coat on the crust leather to be finished so as to seal the grain surface for controlling the depth of penetration of succeeding pigment coat, so that a leveled and uniform coating is obtained. This coat is also known as sealing coat, which is normally carried out using canonic oil emulsion and ammonia. The intermediate coat is applied over the base coat not only to impart desired colour to leather, but also to ensure necessary covering of surface defects. Since these requirements are primarily fulfilled by using pigments in case of semi aniline or pigment finished leather, this coat is also known as pigment coat This coat may also contain film-forming materials, plasticisers and other finishing auxiliaries like dye solution. The top coat serves the purpose of protecting the finish underneath and of imparting desired properties like appearance, handle, fastness to wet and dry rubbing etc. The nature of topcoat to be used depends on the type of intermediate coat used. While leathers finished with resin binders in the intermediate coat are usually topped by water resistant lacquer coat to result in the water resistance of the final leather, protein finished leathers are more prone to water absorption, which is usually reduced in the trade by using formaldehyde on the top coat. Although finishing of leather may in general be of either aqueous or non-aqueous type depending upon the medium used for dispersing the ingredients, aqueous finishing has been the usual practice for leather finishing throughout the globe primarily because of its ease of application, besides other factors like cost-effectiveness as well as eco-friendliness. This approach of using aqueous finishing has however faced a major problem while finishing waterproof leathers, which have, over the years, gained much demand all over the globe, because of the simple reason that the water based finishing materials used in the aqueous finishing system are not likely to be compatible with waterproof leathers. This has prompted the leather finishers to adopt absolute non-aqueous system for finishing waterproof leathers. The non-aqueous systems involve use of either non-aqueous solvents as such or those with cross linkers based on compounds like aziridines. The major limitation associated with them is that they are prone to result in health hazard. Further, the non-aqueous finish system affects the water vapour permeability , feel and handle of leathers adversely. This is why there has been increased restraint on the use of these hazardous chemicals for the purpose of leather finishing. Attempts are therefore being made to evolve a better option for finishing of waterproof leathers. As reported by Levy and Bagg ( Journal of American Leather Chemists Association^, 118,1995), the major problems associated with the use of aqueous systems for finishing water proof leathers are wetting and adhesion, which are closely interrelated. Use of strong wetting agents, particularly surfactants, can defeat the objective of getting good quality water proof leathers. Normally to improve adhesion, the surface of the leather is abraded before finishing. Such abrasion technique leads to distortion of grain characteristics and impairing of water proofness. Until now, a judicial combination of using surfactants and mechanical abrasion technique is being adopted with certain compromises on functional and physical requirements of waterproof leathers. The main objective of the present invention is to provide a novel process of aqueous finishing for waterproof leathers, which obviates the drawbacks mentioned above. Another objective of the present invention is to use film forming material as the base coat while finishing leather. Accordingly the present invention provides a novel process of aqueous finishing for water proof leathers which comprises i. conditioning post tanned wet leather by known method to get sammed leather having moisture content in the range of 60-80% w/w. ii. characterized in that applying aqueous base coat of film forming material, such as acrylate, polyurethane, used either individually or in combination, on the grain side of the sammed leather, as obtained in step (i), by known method, followed by conventional drying at a temperature in the range of 30-45°C and subsequent subjecting of the resulting leather to conventional finishing by known method to get aqueous finished waterproof leather. In an embodiment of the present invention, the method of conditioning post tanned wet leather used may be such as piling, sammying and / or setting. In another embodiment of the present invention, the acrylate used as film forming material may be such as polymethyl acrylate, poly methyl methacrylate, polyethyl acrylate. In yet another embodiment of the present invention, the concentration of film forming material in the aqueous solution of base coat may be in the range of 50-100% w/w. In still another embodiment of the present invention, the method of drying used may be such as natural air drying, forced hot air drying, vacuum drying. The present invention is described below in detail. Waterproof leathers, obtained after post tanning are conditioned by known method to sammed stage by allowing the moisture content to come down in the range of 60-80% w/w. Aqueous base coat solution of 50-100% w/w, of film forming materials is then applied by known method, on the grain surface of the sammed leather to be finished and the resulting leather is then allowed to dry by known method at a temperature in the range of 30-45°C for a period of 10-12 hrs. The resulting dried leather is subjected to conventional finishing operations by known method to get aqueous finished waterproof leather. The novelty and non-obviousness of the present invention lies in applying aqueous solution of film forming materials on the sammed leather before drying as well as subsequent conventional aqueous finishing, thereby providing a cost effective and eco-friendly method of finishing water proof leathers using aqueous system. The invention is described in detail with reference to the following examples which should not however be construed to limit the scope of the present invention. Example -1 Five drum dyed waterproof cow leathers were piled overnight for sammying by allowing the water to drip out. Next day, the moisture content of the leathers was found to be 70%. 500 gms of polymethacrylate solution was taken in a beaker and one full cross coat of the said solution was sprayed on the grain side of each of the above sammed leathers, which were then allowed to air dry at a temperature of 30°C. After a period of 12 hrs, the leathers were staked, trimmed and buffed. The finishing coat was prepared in a beaker using the following composition. (Table Removed) Three full cross-coats of the above finishing mixture were sprayed on the grain side of the leathers manually with intermittent drying. The leathers were then sprayed manually with topcoat of following composition. (Table Removed) Finally, the leathers were subjected to air drying followed by plain plating at 80°C to get aqueous finished waterproof leathers, which were piled for storing. Two drops of water were placed on each of the leathers, which did not get wet Example - 2 Four drum dyed waterproof buffalo leathers were piled overnight and set in setting machine. The moisture content of the leather was found to be 60%. 600 gms of Toluene-di-isocyanate and polyether adduct (Polyurethane) was dissolved in 600 cc. water and one full cross coat of the solution was sprayed on the grain side of the sammed leather. The leather was then allowed to dry at a temperature of 45°C in a hot air room. After a period of 10 hrs, the leathers were staked, trimmed and buffed. The finishing coat was prepared in a beaker using the following composition. (Table Removed) Two full cross-coats of the above finishing mixture were sprayed on the grain side of the leather manually on the leather with intermittent drying. (Table Removed) Finally, the leathers were subjected to air-drying followed by plain plating at 100°C to get aqueous finished waterproof leather. Two drops of water were placed on each of the cut pieces, which did not get wet. Example - 3 Five drum dyed waterproof cow leathers were piled overnight to allow the water to drip out Next day, the moisture content of the leather was found to be 80%. 750gms of poly methyl methacrylate solution was mixed with 250 gms of water and the solution was sprayed on the grain side of the sammed leather. The leather was then allowed to dry at a temperature of 40°C in hot air drying chamber. After a period of 10 hrs, the leather was staked, trimmed and buffed. The finishing coat was prepared in a beaker using the following composition. (Table Removed) Three full cross-coats of the above finishing mixture were sprayed on the grain side of the leather manually on the leather with intermittent drying. The leathers were then sprayed manually with topcoat of following composition. (Table Removed) Finally, the leathers were subjected to air-drying followed by plain plating at 75°C to get aqueous finished waterproof leather. Two drops of water were placed on each of the cut pieces, which did not get wet Example - 4 Five drum dyed waterproof buffalo leathers were piled overnight. Nextday the leathers were sammed and set in machine. The moisture content of the leathers was found to be 60%. 600 gms of polyethylacrylate solution was taken in a beaker and one full cross coat of the said solution was sprayed on the grain side of each of the above sammed leathers, which were then allowed to air dry at a temperature of 45°C. After a period of 10 hrs, the leathers were staked, trimmed and buffed. The finishing coat was prepared in a beaker using the following composition. (Table Removed) Three full cross-coats of the above finishing mixture were sprayed on the grain side of the leathers manually with intermittent drying. The leathers were then sprayed manually with topcoat of following composition. (Table Removed) Finally, the leathers were subjected to air drying followed by plain plating at 80°C to get aqueous finished waterproof leathers, which were piled for storing. Two drops of water were placed on each of the leathers, which did not get wet The advantages of the present invention are the following. 1. The process provides an eco-friendly option of finishing waterproof leather. 2. The water proofness of the leather is not hindered by the application of finishing system 3. The physical and chemical requirements of the leathers are not impaired 4. The process of the present invention provides a method of upgrading leathers in an eco-friendly manner 5. The process is cost effective and can be practiced by all scales of tanners, as it does not call for use of any sophisticated equipment or special chemical input We Claim: 1. A novel process of aqueous finishing for water proof leathers which comprises 1. conditioning post tanned wet leather by known method to get sammed leather having moisture content in the range of 60-80% w/w., ii. characterized in that applying aqueous base coat of film forming material, such as acrylate, polyurethane, used either individually or in combination, on the grain side of the sammed leather, as obtained in step (i), by known method, followed by conventional drying at a temperature in the range of 30-45°C and subsequent subjecting of the resulting leather to conventional finishing by known method to get aqueous finished waterproof leather. 2. A novel process, as claimed in claim 1, wherein the method of conditioning the post tanned wet leather used is such as piling, sammying and/or setting. 3. A novel process, as claimed in claims 1 and 2, wherein the acrylate used as film forming material is selected from polymethyl acrylate, poly methyl methacrylate, polyethyl acrylate. 4. A novel process, as claimed in claims 1 to 3, wherein the concentration of film forming material in the aqueous solution of base coat is in the range of 50-100% w/w. 5. A novel process, as claimed in claims 1 to 4, wherein the method of drying used is such as natural air-drying, forced hot air drying, and vacuum drying. 6. A novel process of aqueous finishing for waterproof leathers, substantially as herein described with reference to the examples.

Documents:

221-del-2001-abstract.pdf

221-del-2001-claims.pdf

221-del-2001-correspondence-others.pdf

221-del-2001-correspondence-po.pdf

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

221-del-2001-form-1.pdf

221-del-2001-form-19.pdf

221-del-2001-form-2.pdf

221-del-2001-form-3.pdf