FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL SPECIFICATION
(See Section 10; rule 14)
TITLE OF THE INVENTION
A PROCESS FOR RETANNING LEATHER AND A RETANNING COMPOSITION
APPLICANTS
BASF India Limited, an Indian company
having its registered office at
RBC, Mahindra Towers, 1st Floor, A Wing,
Dr. G.M. Bhosle Marg, Worli,
Mumbai 400 018, Maharashtra India.
INVENTORS
Rasia Banu and Sanjoy Basu both Indian nationals of BASF India Limited,
an Indian company having its registered office at
RBC, Mahindra Towers, 1st Floor, A Wing,
Dr. G.M. Bhosle Marg, Worli,
Mumbai - 400 018, Maharashtra India.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention
and the manner in which it is to be performed.

FIELD OF INVENTION
This invention relates to the process for re-tanning leather with the application of a re-tanning agent wherein the re-tanning agent contains ferrous sulfate or ferrous salts as one of the components. This invention also relates to the process for producing said re-tanning agent.
BACKGROUND OF INVENTION
The treatment of hides and skins for producing leather involves a number of interdependent chemical and mechanical operations. These operations may be divided into a sequence of wet end steps i.e. process steps under wet conditions, followed by a sequence of process steps under dry conditions i.e. typical mechanical operations and a surface treatment called Finishing.
The wet processing of leather involves three major stages: Pre tanning, Tanning and Post tanning.
Pre tanning operations are aimed at removing the non - collagenous materials from raw hides and skins and then conditioning them for the tanning process. In a tanning process, the raw collagen fibers in the hide or skin are converted into a stable product by cross linking it with either mineral salts, vegetable extracts and / or other organic materials like aldehyde etc. Post tanning is understood as meaning the after-treatment of tanned leather in order to optimize the degree of tannage, color, levelness, softness, plumpness and properties with respect to water (hydrophobicity). Since the tanner desires to produce a uniform piece of leather with proper drying characteristics and hence a step known as 'Re-tanning-dyeing-fat liquoring' is often employed.
Re-tanning gives improvements to the fullness of leather, the tightness and smoothness of leather grain, the break, better uniformity in temper or flexibility


and additional stability against water and perspiration. Re-tanning agents are the chemicals that are used in leather processing to achieve the mentioned properties of fullness of leather, the tightness and smoothness of leather grain, the break, better uniformity in temper or flexibility etc.
Re-tanning can be accomplished by using a variety of naturally derived materials including extracts from vegetables or plants like quebracho, wattle, sumac, hemlock, oak and spruce, and synthetic tanning agents such as naphthalene-formaldehyde and phenol-formaldehyde resins etc. The synthetic tanning agents are known as "syntans". The syntans have been used as replacements for natural tannins and are strong dispersants for several other re-tanning chemicals. Cyanamide, dicyandiamide, urea and melamine also react with formaldehyde to yield useful syntans. Acrylic syntans are polymers based on acrylic monomers that can be used as replacement or auxiliary syntans and sometimes as polymeric softeners depending on the composition of the polymer. Recently syntans that are made from hydrolysates of collagen and other proteins are also used as re-tanning agents.
Dyeing is mainly to impart the desired color to the leather surface as well as the cross section. In leather dyeing, acid dyestuffs are predominantly used. Fat liquors are mostly emulsified oils or other fatty materials, which impart softness to the leather by lubricating the inter fibrillary space.
In state-of-the-art practice, the post-tanning operations are done in stages, based on the ionicity of the system. The basic process skeleton consists of re-chroming, neutralization and the crusting step of 're-tanning - dyeing - fat liquoring'.
However, the disadvantage of the state-of the art technique is that it lacks synergistic application of chemicals of different ionicity. Process formulations are done taking into account the individual interaction of the chemicals with the


leather protein; it does not consider the interactions among the chemicals and the leather protein as a system.
In any step viz., re-chroming, neutralization or re-tanning-dyeing-fat liquoring, chemicals are applied in combination or in sequence, to the float in the same process drums. Conventionally, the compatibility of these chemicals is decided in terms of their pH and chemical nature. Accordingly, the applications of mineral salts are restricted only to the cationic process step of re-chroming. Some of the specialty syntans viz., phenol and naphthalene condensate products are used along with these mineral salts in re-chroming, owing to their stability to acid and electrolytes and some amphoteric polymers are used because of their dual charge characters.
Disadvantages of such state-of-the-art practices are the following:
Never the mineral salts are applied in the anionic step of re-tanning-dyeing-fat liquoring due to the expected precipitation of the anionic chemicals in the float itself, which would then hamper their penetration into the cross section. Applying mineral salts in re-chroming step, exploits only their tanning ability. Such applications do not have a significant impact on the fullness, bounciness or the dye depth i.e., characters imparted by re-tanning agents on the final leather. Similarly, the re-tanning step employs re-tanning agents, dyestuffs, fat liquors and other auxiliaries - all of which are having similar chemistries of anionic functional groups. In a float, the leather is offered to react with chemicals of similar charge / ionicity. Particularly in re-tanning float, the syntans, dyes and fat liquors - all have similar reaction mechanisms with the leather protein. This restricts the overall amount of exhaustion and hence increases the effluent load. Since the chemicals fix onto the leather on a competitive mode, there is a lack of synergy in the combined effect produced by them on the leather. Consequently, whenever there is a need for some significant improvement on a particular aspect, the strategy is to increase the


% offer of the particular set of chemicals. This approach proves to be cost ineffective as well as gives only an incremental improvement on the effects. Further, making of certain articles like Jet Black Goat Suede, is rendered impossible because of the lack of synergy - color and fullness goes on in a compromising mode, irrespective of how much ever amount of chemicals is offered.
In re-tanning, the applied chemicals react with the leather protein primarily through ionic interactions ~ major being the cationic amino groups and anionic carboxyl groups. In the re-tanning step, the anionic chemicals fix primarily on the cationic amino groups of collagen chains; the carboxyls remain free and later participate in internal bonding during later steps of drying. The amount of re-tanning chemicals (syntans, dyes, fat liquors) taken up is limited to the levels of the amino groups i.e., due to the competitive reaction mode the level of exhaustion is limited.
The prior art re-tanning agents fix with the cationic amino groups of collagen. Even though certain condensation products or amphoteric polymers are applied in re-chroming, their fixation is with the amino groups ONLY since their reactive groups remain anionic in nature. Collagen contains various side chain groups like amino, carboxyl etc. In conventional processing, we offer chemicals all of which fixes major through amino groups. This restricts the amount of exhaustion as well as leaves the other groups free, which might coalesce on drying. Thus, beyond a certain level, the matrix properties are altered only by filling the macro pore levels; and the process strategy of having synergistic chemical modifications of leather protein is completely missed.
OBJECTS OF INVENTION
Main object of this invention is to provide for a process of re-tanning of leather with the application of a re-tanning agent wherein the said re-tanning agent contains ferrous sulfate or ferrous salts as one of its component.


Another object of the invention is to provide for a process of re-tanning of leather with the application of a re-tanning agent resulting in improved fullness, bounciness and plumpness of the leather.
Yet another object of the invention is to provide for a process of re-tanning of leather with the application of a re-tanning agent resulting in increased dye depth of the leather.
Yet another object of the invention is to provide for a process of producing the said re-tanning agent.
DEFINITIONS
The terms used in the description are defined as follows:
Re-tanning Agent - A chemical or a chemical formulation that is used in leather processing to improve the fullness, bounciness, tightness, smoothness of grain and other organoleptic properties of leather.
Wet Blue - Wet blue is the raw hide that has the flesh, hair and other non-collagenous materials removed and the resultant matrix is stabilized by treatment with tanning agents viz basic chromium sulfate, aluminum salts glutaraldehyde, etc and mild alkali agents.
Float - Float refers to the water in the processing drum in which the wet blue and the chemicals are added and the drum undergoes a circular motion to cause mechanical agitation, which aids the reaction between the chemicals and the wet blue.


Neutralization - Neutralization is the treatment of the wet blue with mild alkaline agents like sodium or ammonium salts of formate, carbonate, acetate etc, which increases the pH of the cross section of the wet blue.
Fat Liquoring - The application of formulations containing emulsified fats, oils, emulsifiers, silicone derivatives etc., to the wet blue during post tanning. These formulations are applied to the re-tanning float, preferably after dyeing.
Penetration of dyestuff - Penetration of dyestuff is checked by cutting a portion of the leather, squeezed heavily to remove water and then is cut into two pieces. The cross section at the cut portions is checked for the color of the dyestuff, which optically indicates the dye penetration.
Shaved weight of wet blue - Prior to post tanning operations, the wet blue is shaved with the aid of a shaving machines i.e., the thickness of the whole area is adjusted to be uniform throughout. After this shaving operation, the weight of the wet blue is noted down and is called "shaved weight of wet blue". In post tanning, all the chemical offers are expressed in terms of a % of this shaved weight.
Running Time - In post tanning, the wet blue is taken in the drum and the process float is added. Then the chemicals are applied to the float in sequence. After addition of each chemical or each set of chemicals, the drum is run for a particular period of time, called "the running time"; this ensures reaction of the chemical in the float with the wet blue fibers and is consequently taken by the wet blue. After this time, the next chemical or set of chemicals is added.
DETAILED DESCRIPTION OF INVENTION WITH PREFERRED EMBODIMENTS
The invention relates to a process of re-tanning leather comprising treating leather with a re-tanning composition containing component A and component


B, wherein component A is selected from a ferrous salt such as ferrous sulfate, ferrous ammonium sulphate, ferrous nitrate or ferrous carbonate in 5% to 95% by weight and component B is selected from polymers based on Phenol sulfonic acids, naphthalene sulfonic acids, formaldehyde, maleic anhydride, urea, melamine, acrylic monomers, nitrogenous acrylic monomers in the presence of conventional additives, fillers, dispersing agents, compatible with components A and B said re-tanning being carried out at a PH of above 4.5
In the preferred embodiment of the invention, in the process of re-tanning of leather, wet blue is neutralized to a pH of above 4.5 to 6 prior to treatment with the re-tanning composition, the ferrous salt selected from ferrous sulphate, ferrous ammonium sulphate, ferrous nitrate or ferrous carbonate in the said composition being in range of 0.5 to 20% by weight of the wet blue at a temperature range of 15 to 60°C for 45 to 120 mins and subsequently dyeing and fat liquoring the treated leather in a known manner followed by acidification in a bath of formic acid and/or sulfamic acid.
In another embodiment of the invention, in the process of re-tanning of leather, wet blue is neutralized with mild alkaline agents like sodium or ammonium salts of formate, carbonate, acetate to a pH from 4.5 to 6.5 prior to treatment with said re-tanning agent.
In another embodiment of the invention, in the process of re-tanning of leather, the neutralization bath is drained and the neutralized wet blue can be washed off with water and drained prior to re-tanning step.
In another embodiment of the invention, the process of re-tanning of leather, wherein the re-tanning agent in accordance with this invention, is applied either alone or in combination with other conventional re-tanning agents such as polymers based on phenol sulfonic acids, naphthalene sulfonic acids, formaldehyde, maleic anhydride, urea, melamine, acrylic monomers,


nitrogenous acrylic monomers, vegetable tanning extracts in powder or extract form, Re-tanning materials based on collagen hydrolysates, protein hydrolysates etc.
In another embodiment of the invention, in the process of re-tanning of leather, the re-tanning is carried out either before or after the dyeing step.
In another embodiment of the invention, in the process of re-tanning of leather, the re-tanned or dyed wet blue is treated with fat liquors, acidified, washed, and mechanically treated.
In another embodiment of the invention, a composition for re-tanning leather comprising at least 70 parts by weight of ferrous salts selected from ferrous sulphate, ferrous ammonium sulphate, ferrous nitrate or ferrous carbonate; and polymer selected from polymers based on phenol sulfonic acids, naphthalene sulfonic acids, formaldehyde, maleic anhydride, urea, melamine, acrylic monomers, nitrogenous acrylic monomers, vegetable tanning extracts in powder or extract form, and conventional additives, dispersants and stabilizers.
In another embodiment of the invention, the process for the preparation of a composition of the retanning agent comprising the step of mixing of,
- ferrous salts selected from ferrous sulphate, ferrous ammonium
sulphate, ferrous nitrate or ferrous carbonate
and
- polymer selected from polymers based on phenol sulfonic acids,
naphthalene sulfonic acids, formaldehyde, maleic anhydride, urea,
melamine, acrylic monomers, nitrogenous acrylic monomers,
vegetable tanning extracts in powder or extract form,
under anhydrous conditions with dispersing agent at 25 to 50 C to form a fine powder.


In another embodiment of the invention, the process for the preparation of the said re-tanning composition wherein the dispersing agent is in 10% by weight of the re-tanning composition.
In another embodiment of the invention, the process for the preparation of the said re-tanning composition, wherein the dispersing agent is a salt of a naphthalene sulfonic acid condensate.
In another embodiment of the invention, a re-tanned leather is formed in accordance with the process mentioned hereinabove.
EXAMPLES
The following Examples are presented to illustrate further various aspects of the present invention, but are not intended to limit the scope of the invention in any respect.
Comparative Trial: In leather field, it is difficult to measure the impact of a particular chemical in an absolute scale. Hence, a comparative scale is adopted where the variant is only the chemical offered whereas all the other parameters are kept constant.
The normal variants involved in the processing are:
The hide itself: Since leather is made from hides & skins, which is of natural origin, each different piece of leather varies from one another in terms of the hide structure. But, in a single hide or skin, the two half pieces with respect to the backbone are symmetric in nature and hence have similar structure. Thus, it is possible to eliminate the differences arising from the hide structure by taking two symmetric pieces of a hide.


The process of comparative pieces of hide, is as follows: One full hide wet blue is taken and is shaved to uniform thickness through the whole area. The hide is then cut into two pieces along the backbone. They are then weighed and if there is any difference, the weight is adjusted to be same on both the sides by slight trimming over the edges. From the set, one is taken for processing as control whereas the other one is taken as experiment.
Process Vessel: Two drums with similar dimensions and similar running speed are used for the trial.
Process Conditions: The amount of float and the time given between successive addition of chemicals are kept equivalent for both the sets of leathers.
Mechanical Operations: After processing, both the set of leathers are piled in similar conditions and for the same length of time. Then, both of them are subjected to the same set of mechanical operations (samming, setting & vacuum drying) with exactly similar operating conditions.
The leathers are then hooked for drying in the same drying chambers. Then, both of them are subjected to the same set of mechanical operations (conditioning, Mollisa staking) with exactly similar operating conditions.
The experimental leather re-tanned according to the process of this invention is found to have better organoleptic properties such as fullness, bounciness and plumpness when compared with the control.
Organoleptic properties are those subjective properties of leather, which are evaluated by persons, having relevant experience in the field.


SEM Analysis: SEM Images indicate better filling and compactness in terms of the experiment leather.
The scanning electron microscope (SEM) is a type of electron microscope that creates various images by focusing a high-energy beam of electrons onto the surface of a sample and detecting signals from the interaction of the incident electrons with the sample's surface.
The following properties are observed in the leather re-tanned with this
composition.
i. Organoleptic Properties: The experimental leather is found to be similar
to control in terms of fullness, bounciness and plumpness,
ii. The dye depth of the experiment leather is marginally higher than the
control. The same is confirmed by the spectral reflectance values in the
table below: