WO2025221146A1

WO2025221146A1 - Use of a composition comprising polycarbodiimide for re-tanning or pre-tanning and/or for tanning leather

Info

Publication number: WO2025221146A1
Application number: PCT/NL2025/050183
Authority: WO
Inventors: Roberta Gamarino; Emanuele MATTIOLO; Silvano SINI
Original assignee: Stahl International BV
Current assignee: Stahl International BV
Priority date: 2024-04-19
Filing date: 2025-04-17
Publication date: 2025-10-23
Anticipated expiration: 2026-10-19
Also published as: NL2037499B1

Abstract

Process for the use of a composition comprising polycarbodiimide for re-tanning or pre-tanning The present invention provides a process for the manufacturing of leather, more in particular improving the re-tanning and/or tanning and/or pre-tanning of leather thereby using a composition comprising at least one polycarbodiimide compound.

Description

Titel:

USE OF A COMPOSITION COMPRISING POLYCARBODIIMIDE FOR RE-TANNING OR PRE-TANNING AND/OR FOR TANNING LEATHER

The present invention relates to a novel process for leather manufacturing wherein polycarbodiimide compounds are used as re-tanning agent or as a component in a re-tanning composition and/or wherein polycarbodiimide compounds are used as a component in a pre-tanning and/or tanning composition.

Leather is a durable, flexible material created via the tanning of animal rawhide and skin. The leather manufacturing process is divided into three fundamental sub-processes: preparatory stages, tanning and crusting.

The present invention relates to the sub-process of tanning, especially the pre-tanning process of leather, such as but not limited for pretanning of wet-white leathers and wet-blue leathers and to the re-tanning process of wet-blue leathers.

In the preparatory stages, hide or skin is prepared for tanning. After trimming, animal skin is soaked to remove salts and other solids, while restoring moisture when the skin was first dried. Then, the flesh side of the wet skin is scraped to remove any remaining traces of flesh or fat, and the skin is optionally dehaired. After an optional bating and pickling step, the skins are subjected to tanning. Other potential steps that may be part of the preparatory stages include preservation, liming, splitting, reliming, deliming, degreasing, frizzing, bleaching and depickling.

Tanning is the process of preserving the skins by converting the protein, via crosslinking the collagen fibres, of the raw hide or skin into a stable material that does not putrefy and provides tanned leathers with satisfactory properties, such as high shrinkage temperatures Ts, suppleness and suitability for subsequent processing such as neutralization, re-tanning, fatliquoring, dyeing, finishing. Tanning is dominantly carried out by treatment of the hides with chromium sulphate (giving so-called wet-blue leather) or by the use of organic reactive tanning agent as aldehydes, especially glutaraldehyde or Granofin® Easy F-90 (an organically based tanning agent, obtainable from Stahl Europe B.V) resulting in wet-white leather. The names of the tanning operations derive from the colour that the leather acquires after having completed the process: wet-white leathers have a whitish colour, whereas wet-blue leathers have a blueish colour.

Prior to the tanning step a pre-treatment can be done in which agents are employed that later on enhance the tanning step. This is part of the pre-tanning operation, and the agents are called pre-tanning agents. Such pre-tanning agents can act as auxiliaries, being their best application as pre-treatment for vegetable tanning. Such auxiliaries by themselves do not provide the tanning characteristics on the leather when used without tanning agents, but they provide enhanced properties compared to when such tanning agents are used without these auxiliaries. By occupying reaction sites in the collagen structure and, consequently, reducing the reaction rate between tannins and collagen, such auxiliaries facilitate penetration, improving the absorption of tannins in the hide.

In rare cases the tanning is carried out with vegetable tanning agents - as traditionally done - or by use of synthetic tanning agents (syntans), or other conventional techniques. The product prepared in this subprocess is an intermediate since it is not sufficient to obtain the desired characteristics specified by the customer. The tanned hides are therefore further treated with various products. This process is called re-tanning. Retanning affects the feel of the leather, the dyeability, fullness of the leather, the fineness of the grain and the stability of grain and other factors such as light fastness, to suit characteristics required for the final leather article - whether for automotive or aviation seating, footwear, garments or bags and leather goods. Re-tanning includes dyeing to give colour and fatliquoring to add softness, fullness and touch. Once re-tannage is complete, the leather is known as “crust”.

Vegetable tanning agents were the first tanning agents. They are now mostly used in the re-tanning, because of the nowadays wide acceptance of chromium sulphate or glutaraldehyde as tanning agents. Common vegetable tanning agents are Mimosa, obtained from the bark of the Acacia tree, and Tara, obtained from the fruit of the Tara bush. They can impose softness and limited filling of the collagen structures to leathers (Hans Herfeld, "Library of Leather; Volume 3: Tanning Agents, Tanning and Retanning", Frankfurt 1985, page 44). Usually, vegetable tanning agents lack fastness properties, such as resistance to light or resistance to heat induced ageing.

The term syntan refers to the range of synthetic tanning agents. The first syntans were made by condensation of phenol sulfonic acid and formaldehyde (E. Stiasny, 1911, Austrian Patent Nr. 58405). While these syntans were initially used as dispersers and auxiliaries for vegetable tannins, they could be applied to replace some or even all vegetable tannins after further development of their chemistry. US 1841840 describes the incorporation of urea into the polycondensation of phenol sulfonic acid and formaldehyde, by which such a further development was achieved, enabling obtaining leathers with increased technical requirements like fastness properties concerning light or heat induced ageing. Because of the wide acceptance of chromium sulphate or glutaraldehyde as tanning agents, syntans are now mainly used in the re-tanning process, where they help to structure and fill the crosslinked collagen fibres. Unfortunately, syntans can contain a residual amount of free formaldehyde or undesired side products as Bisphenol S or F, which means that they should be handled and used with care due to safety reasons.

In many applications syntans and vegetable tannins are applied together since the performance of vegetable tannins alone is considered insufficient. The syntans generally have higher fastness properties and beyond that have dispersing properties. This helps to support the even distribution of vegetable tannins and other leather chemicals like fillers, dyes, and fatliquors (DE 1142173).

KR10 1453216-B1 describes a dye composition comprising a carbodiimide compound and a dye, preferably a reactive dye, that introduces a specific functional group capable of covalent bonding with a protein residue of hair, skin, fibre or leather, which composition can continuously impart a semi-permeable dyeing effect without damage to hair, skin, fibres or leather. The carbodiimide is preferably directed to a specific polycarbodiimide made from tetramethylxylene diisocyanate (TMXDI) or to l-ethyl-3-(3- dimethylaminopropyl)carbodiimide, which is a monocarbodiimide, and the dyeing is mainly directed to hair. The amount of carbodiimide compound is between 0.001 and 10 pbw per 100 pbw of dyeing composition and the amount of the dye is between 0.001 and 50 pbw per 100 pbw of dyeing composition. In the examples the amount of dye as well as TMXDI polycarbodiimide is 0.5 wt% on total dyeing composition. The polycarbodiimides were not used as a re-tanning agent.

WO20 19235658-Al and KR20180108266 are similar but describe additionally a requirement for a reaction-promoting additive for forming a peptide bond. This reaction-promoting additive for forming a peptide bond is selected from a group consisting of hydroxysuccinimide, hydroxycarb amide, hydroxytriazole, hydroxybenzotriazole, hydroxypyridinone, hydroxyphenylbenzimidazole, hydroxyindolinone, hydroxybenzotriazine and oxyma, or a water-soluble non-ionic polymer, a bead- or resin-type polymer resin, but most emphasis is given to the various polymer types that may be suitable. In the examples a polybutene is included in an amount of 16 wt%, besides other oily components that may also be considered as non-ionic polymers. In the examples the amount of dye is 0.01 wt% and the amount of TMXDI polycarbodiimide is 0.1 wt% both on total dyeing composition. The polycarbodiimides were not used as a re-tanning agent.

US 2010/174018 describes an aqueous formulation comprising a pigment, a polycarbodiimide and a random polyurethane for coloring textile substrates such as leather. Pigments are being defined as substantially insoluble, dispersed, finely divided, organic or inorganic colorants as defined in DIN 55944. No dye is used. The polycarbodiimides were not used as a retanning agent.

WO 2022098232 describes a dyeing composition suitable for dyeing leather, hides and/or pelts comprising at least one dyeing agent and at least one polycarbodiimide compound, but the polycarbodiimides were not used as a re-tanning agent.

EP 3342395-A2 describes a composition for skin modification or hair modification comprising a carbodiimide-based compound, but the composition is not used for re-tanning, but for antioxidation; conditioning; moisturizing; whitening; blocking ultraviolet rays; imparting fragrance; preventing or improving a wrinkle; keratin care; preventing or improving dandruff/itching; stimulating hair growth; stimulating hair regrowth; preventing acne or inhibiting bacteria; suppressing body odour; atopic dermatitis care; pore care; epilation or fingernail and toenail care. Furthermore, the skin modification is meant to be directed to living skin, e.g. a tissue covering the body including facial skin, the scalp, body skin, fingernails and toenails which are accessory organs of the skin, and the skin modification is not directed to dead skin, such as pelts, crusts or leather. The reaction schemes in EP3342395-A2 indicate that the polycarbodiimide only serves as a coupling agent to have two components with differing functional groups form a covalent bond, for example a peptide bond formed from a carboxylic group and an amine group.

WO 2019006331-Al describes compositions and systems for treating keratinous fibres, comprising a polycarbodiimide compound and a carboxylic acid, and optionally an amine and/or a carboxysilicone polymer in order to improve the quality of the keratinous fibres such as hair. These compositions and systems are not used for re-tanning.

US 3922143A describes the use of specific carbodiimides in the treatment of porous anionically charged collagen fiber matrix, e.g. leather, but these specific carbodiimides contain many fluoro groups and the objective of using these specific fluoro-functional carbodiimides is to obtain dynamic water resistance and not for re-tanning purpose.

CN 10851738 IB describes the use of carbodiimides as a coupling agent between amino-terminated hyperbranched polymer and carboxyl groups of collagen during the tanning process of leather. However, the carbodiimide is not a polycarbodiimide and it is not the tanning agent itself and is used in small amount compared to the amount of the aminoterminated hyperbranched polymer.

US 5417723A describes the use of ester-based polyurethane in the retanning of wetblue leather for the optimization of softness, fullness, color, hydrophobicity and fixation of tanning agents in the leather.

The present invention provides a novel process to improve the pretanning, tanning and/or re-tanning step of leather in a leather manufacturing process. More in particular, the present invention provides an improved retanning process wherein polycarbodiimide compounds are used as re-tanning agent or as a component in a re-tanning composition in a re-tanning step for leather, such as but not limited to the re-tanning of wet-blue leathers in a leather manufacturing process. The present invention also provides an improved pre-tanning process wherein polycarbodiimide compounds are used as a component in a pre-tanning and/or tanning composition in a pre-tanning step for leather, such as but not limited to the pre-tanning of wet-white leathers and wet-white leathers. It was found that the polycarbodiimide compounds according to the invention can be used as re-tanning agent giving improved properties to the obtained leathers and that these polycarbodiimide compounds are thus able to replace syntans or other re-tanning agents in the re-tanning of leather such as but not limited to the re-tanning of wet-blue leathers.

In addition, it was found that the polycarbodiimide compounds according to the invention can be used as auxiliary to enhance the pre-tanning and tanning of leather, such as but not limited to the pre-tanning for wet white leathers and wet-blue leathers.

The inventors discovered that polycarbodiimide can be applied on leather, such as via an industry standard procedure, for re-tanning. Surprisingly, it was found that leathers treated with polycarbodiimide, gave similar or better properties to the leather than syntans or vegetable tannins, concerning softness, fullness, tightness and smoothness, while creating no bisphenol or formaldehyde problem. Further surprisingly, it was found that leathers treated with polycarbodiimide, gave better tightness and smoothness properties to the leather than syntans or vegetable tannins. An analysis of toxic formaldehyde or bisphenols is usually not even required for these retanning compositions, because none of the ingredients contains or could release formaldehyde or could form bisphenols. The use of polycarbodiimide represents a novel non-toxic, alternative re-tanning agent free of phenol, formaldehyde, bisphenols, metals, compared to conventional re-tanning agents in the leather industry.

A re-tanning composition I pre-tanning composition comprising the polycarbodiimide compounds according to the invention may also comprise other components, such as natural re-tanning agents as lignin, starch, chitin, kaolin, Tara, or proteins or derivates of them or conventional re-tanning agents. The re-tanning composition I pre-tanning composition can also be prepared immediately before use. Preferably, the re-tanning composition / pre-tanning composition comprising the polycarbodiimide compounds of the present invention is a liquid composition, more preferably an aqueous composition which comprises the polycarbodiimide compounds according to the invention in an amount of between 20 and 100 weight%, preferably between 25 and 100 weight%, more preferably between 30 and 100 weight%, most preferably between 35 and 100 weight% of polycarbodiimide compounds calculated on the total weight of the retanning (pre-tanning) composition, and wherein the remaining amount may comprise other re-tanning agents (pre-tanning agents) or water or solvents.

The polycarbodiimide compounds of the present invention may also be used in combination with other additives or conventional products used in previous or following steps of the leather treatment process.

In a preferred embodiment, the polycarbodiimide compounds of the present invention used as component in a re-tanning composition I pretanning composition is liquid at ambient conditions (atmospheric pressure and a temperature of 25°C), wherein the polycarbodiimide compounds of the present invention may be in the form of a solution of polycarbodiimide compounds in a solvent or water or in the form of a dispersion of polycarbodiimide compounds in water. In instances that the polycarbodiimide compound is a solution in a solvent or water or a dispersion in water, it is preferred that the concentration of the polycarbodiimide compounds in the solution or dispersion is above 20 weight%, more preferably above 30 weight% calculated on the total weight of the solution/dispersion. A typical amount of polycarbodiimide compounds in an aqueous dispersion suitable for use in a re-tanning composition I pre-tanning composition according to the invention is 30% to 50% weight%, preferably around 40 weight% polycarbodiimide compounds calculated on the total weight of the dispersion. A typical amount of polycarbodiimide compounds in solvent suitable for use in a re-tanning composition / pre-tanning composition according to the invention is 50% to 70% weight% polycarbodiimide compounds calculated on the total weight of the solvent composition.

In a more preferred embodiment, the total re-tanning composition I pre-tanning composition is liquid at ambient conditions.

Preferably, the amount of polycarbodiimide compounds used is between 3 and 50 weight%, preferably between 5 and 40 weight% and most preferably in between 6 and 30 weight%, relative to the weight of the leather and taking into account only the non-volatile components. In the context of the present invention non-volatile components are those components that do not evaporate into air due to their low vapour pressure and can be defined as any component that has an initial boiling point above 250°C measured at a standard pressure of 101.3 kPa.

The polycarbodiimide compounds in the re-tanning compositions I pre-tanning composition of the present invention are selected from the group of polycarbodiimides that are known as polycarbodiimide crosslinker in the leather finishing industry or in the coatings industry. These polycarbodiimides compounds contain more than one carbodiimide group (- N=C=N-) in their polymer chain or oligomer chain, preferably these polycarbodiimide compounds contain from 2 to 10, preferably from 2 to 6 carbodiimide groups on average. These polycarbodiimide compounds have an average molecular weight of 800 Dalton or higher, preferably 1000 Dalton or higher. These polycarbodiimide compounds are supplied in liquid form, either because the polycarbodiimide non-volatile component is liquid or because the polycarbodiimide non-volatile component is dissolved in a solvent or in water or is dispersed in water. These polycarbodiimide compounds are generally linear polymers, synthesized from di-isocyanates and optionally monoisocyanates, wherein some other functional groups such as hydrophilic components may have been incorporated so that the polycarbodiimide compounds are miscible in aqueous mixtures. This type of products has been described in Progress in Organic Coatings, volume 55, pages 142-148, 2006. Examples of such polycarbodiimide compounds are XR-5592 (a waterborne polycarbodiimide with about 40% non-volatiles), XR-5570 (a solventborne ‘multifunctional’ polycarbodiimide with about 50% non-volatiles, wherein ‘multifunctional’ indicates that beside carbodiimide also other reactive functional groups are present), XR-5517 (a solventborne polycarbodiimide with about 50% non-volatiles in methoxypropyl acetate), XR- 13-554 (‘multifunctional’ polycarbodiimide with about 100% non-volatiles, wherein ‘multifunctional’ indicates that beside carbodiimide also other reactive functional groups are present), XR-5508 (a waterborne polycarbodiimide with about 40% non-volatiles), XR-55-200 (a ‘multifunctional’ polycarbodiimide with about 100% non-volatiles, wherein ‘multifunctional’ indicates that beside carbodiimide also other reactive functional groups are present), XR- 55-250 (a solventborne ‘multifunctional’ polycarbodiimide with about 50% non-volatiles, wherein ‘multifunctional’ indicates that beside carbodiimide also other reactive functional groups are present), all obtainable from Stahl Europe BV, or Zoldine XL-29SE (a solventborne polycarbodiimide with about 50% non-volatiles in methoxypropyl acetate) obtainable from Angus Chemical Company. Especially preferred polycarbodiimide compounds are those polycarbodiimide compounds that are supplied in water or as 100% nonvolatile, so without volatile organic solvents. Preferably the polycarbodiimide used in the present invention was synthesized from isophorone diisocyanate (IPDI) or from 4,4'-methylene dicyclohexyldiisocyanate (H12MDI). The polycarbodiimide used in the present invention is preferably not based on tetramethylxylene diisocyanate (TMXDI), which has a relatively low reactivity compared to polycarbodiimides made from IPDI or H12MDI. Preparation of TMXDI based polycarbodiimides also requires a higher reaction temperature, or a longer reaction time or more catalyst, compared to synthesizing polycarbodiimides made from IPDI or H12MDI. An industry standard procedure for re-tanning comprises treating a tanned leather, such as wet blue, with water, sodium formate and sodium bicarbonate for a period of time resulting in a float with a pH of below neutral, after which the re-tanning composition is added followed by further turning of the tanning drum for a certain period of time, followed by fixation with an acid, such as, but not limited to formic acid, followed by discharging the float and washing with water. Afterwards the leather is dried, such as by hang drying at room temperature without vacuum, or in a vacuum chamber. The re-tanning composition is added in an amount of between 2% and 20%, and preferably in an amount of between 4% and 18%, and most preferably in an amount of between 6% and 15%, wherein the percentages refer to the weight percentage of the non-volatile part of the re-tanning composition compared to the weight of the leather.

In the context of the invention, the term “improved tanning of leather” refers to improved (better) softness, fullness, tightness and/or smoothness properties of the leather after applying a leather treatment process (meaning a pre-tanning, tanning or re-tanning process) with the polycarbodiimide compounds of the present invention.

Fullness is an aesthetic quality parameter, organoleptical characteristic, defined by the spacing between the fibres, suggesting (by the tactile sense) a larger or smaller amount of fibres per area. It is the result of a good filling of the interfibrillar spaces and an adequate lubrication of the fibres avoiding their agglomeration. In colloquial words: a full leather is the one that is round to the touch and an empty leather (contrary to full) is a flat, thin leather. Fullness of re-tanned leathers is dominantly determined via haptics.

Tightness is an aesthetic quality parameter, organoleptical characteristic, defined by the amount of wrinkling or creasing when the leather is flexed grain-inwards (by visual assessment), result of a good or bad adherence between the Grain layer to the underlying Dermis. Tightness can be influenced since the from the breed of the animal to the end of the retanning, passing by distribution of the products, mechanical action, drying, etc... and is desirable for all the articles, even than those which will be milled. The challenge is to keep the layers together without hardening the leather (Hard leathers = normally tight grain). The smoother the layer remains upon bending, the tighter the bended leather is. The more wrinkles observed, the lower the tightness.

Softness, fullness and tightness of re-tanned leathers are determined via haptics and are generally graded with a number, wherein a lower number is better.

The re-tanning composition I pre-tanning composition comprising the polycarbodiimide compounds of the present invention can be used to prepare leathers for all applications, for example shoe, furniture, car, clothing and bag leathers.

Any kind of leather which is conventionally treated is suitable to be treated by using the re-tanning composition I pre-tanning composition comprising the polycarbodiimide compounds of the present invention, particularly grain leather (e.g. nappa from sheep, goat or cow and box-leather from calf or cow), suede leather (e.g. velours from sheep, goat or calf and hunting leather), split velours (e.g. from cow or calf skin), buckskin and nubuck leather; further also woollen skins and furs (e.g. fur -bearing suede leather).

The leathers can be of various thicknesses, such as from 0.5 mm to 8 mm, thus, thin leathers, are suitable for garment leather or glove-leather (nappa); leather of medium thickness, is suitable for shoe upper leather, and handbags, or also thick leathers, are for shoe-sole leather, furniture leather, leather for suitcases, for belts and for sport articles; hair-bearing leathers and furs may also be used.

The leathers obtained by treating with a re-tanning composition comprising the polycarbodiimide compounds of the invention can subsequently be further processed, as is customary in the leather industry, by any of the processes of bleaching, colouring, dyeing, fatliquoring, hang drying, vacuum drying, toggling, conditioning, staking, milling, tumbling, buffing, pressing, embossing, ironing, finishing with a wax or a coating.

The re-tanning compositions comprising the polycarbodiimide compounds of the invention represent a novel non-toxic, alternative for state of the art re-tanning agents.

The re-tanning compositions comprising the polycarbodiimide compounds of the invention can be used as re-tanning agents for the treatment of leather giving softness, fullness and tightness that is similar or better as when using reference re-tanning agents, while polycarbodiimide is a material that is easy to use.

The step in the leather process before re-tanning is tanning and pre-tanning. It was found that polycarbodiimide compounds according to the present invention can be used as auxiliary to enhance the pre-tanning of leather, more in particular of wet-white leathers and wet-blue leathers.

The polycarbodiimide compounds as described above in the retanning compositions may also be used as auxiliary to enhance the properties of the leathers obtained in chrome-free tanning process, also known as wet white leathers. Using such polycarbodiimide compounds in the pre-tanning process, later followed by a tanning step employing a chrome-free tanning agent, resulted in leathers that have a lighter colour, better scud cleanness and better distention of the belly draw. Furthermore, subsequent further treatment in a re-tanning process yields leathers that have better fullness, flufhness, uniformity, shade and better performance concerning wrinkles (resulting in less visible wrinkles after the tanning), compared to leathers that were tanned without the use of polycarbodiimide compounds as auxiliary.

Belly Draw indicates the visual evaluation on growth wrinkles in the belly area of the animal, which are more marked with the age of the animal. It is best these growth marks are less visible after the tanning/pre- tanning. More distension is preferred and better.

Scud Cleanness is a visual evaluation of the grain side of the hides: of the hair and epidermis remained on the grain. A cleaner grain is better.

Wrinkles is a crease or pucker in the skin, as any of those caused by aging. Wrinkles naturally occur in skins/hides and are more marked in specific areas of the animal (like neck and belly).

Using the polycarbodiimide compounds of the invention as auxiliary compounds to enhance the tanning can be monitored by measuring the shrinkage temperature Ts, wherein it was observed that treatment with only the polycarbodiimide compounds of the invention resulted in only a modest increase of the shrinkage temperature. Upon subsequent treatment with a chrome-free tanning agent the shrinkage temperature increased to values that are considered sufficient. Using a treatment with a chrome-free tanning agent only, and thus without the polycarbodiimide compounds of the invention as pre-tanning auxiliary, yields similar sufficient shrinkage temperature, but other properties, such as scud cleanness and better distention of the belly draw, are better when the polycarbodiimide compounds of the invention as pre-tanning auxiliary was used. The shrinkage temperature of pelt or leather is a measurement of the hydrothermal stability of leather. The principle of the method is to suspend the test piece in water, in the form of a strip and heat the water at a rate of 2°C/min. The shrinkage temperature is noted when the sample visibly shrinks.

The present invention will be further elaborated by the following non-limiting working examples. Examples

All percentages mentioned are weight percentages based on leather weight before processing. This is true for all percentages in all examples, unless stated otherwise.

All the polycarbodiimide compounds used in the following examples are commercial products (from Stahl Europe BV).

Examples 1-10: Re-tanning process

Re-tanning agents were tested on pelt that had been chrome tanned and was shaven to a thickness of 1.1- 1.2 mm. The re-tanning agents have the role to fill the collagen structures and impose characteristics like softness, grain tightness, and fastness properties.

Re-tanning was carried out starting with a wash of 200% of water and 0.15% of Eusapon® OC (a degreasing agent; obtainable via Stahl Europe BV) and 0.5% oxalic acid for 30 minutes at 40°C. After draining, a next wash with 200% of water was done. After draining, thereafter the re-tanning process is initiated by adding 150% of water of 38°C to the drum, together with 5% of Baychrom F-D (a self-basifying organically masked chromium sulfate; obtainable from Lanxess) and the drum was run for 120 minutes. Hereafter 2% of sodium formate and 2.0% of Coralon® NL liq. (a neutralization agent; available via Stahl Europe BV) were added. After 20 minutes of turning the drum, with pH at 4.7 and amount of 3% of sodium bicarbonate was added and the drum was run for 60 min, giving a pH of now 6.8. The drum was drained. 200% of water of 50°C was added and the drum was run for 10 min and then the drum was drained. 150% of water of 50°C and 10% of Derminol SO-31 liq. (a synthetic anionic fatliquoring agent, available via Stahl Europe BV) were added and the drum was run for 50 min. An amount of 0.7% formic acid was added and the drum was drained after running for 20 min. 200% of water of 20°C was added and the drum was run for 10 min, followed by draining the drum. Next, 20% of water of 20°C, X% of Inoderme Brown Gol (anionic dye metal complex of cobalt; available via Stahl Europe BV) was added, the pH was adjusted to a value of 5.5 and Y% of ReTanning agent was added, followed by running the drum for 120 min. Next, 150% of water of 50°C and 1% of formic acid were added, followed by running the drum for 20 min, then adding 1% of formic acid and running the drum for 20 min, and then adding yet another 1% of formic acid followed by running the drum for 20 minutes, followed by draining the drum. The leathers were washed with 200% of water of 20° for 10 minutes. Afterwards the leathers were set out and vacuum dried at 50°C for 180 seconds. Thereafter the leathers were hung to complete the drying process. Various Re-Tanning agents were used in combination with a dye or without a dye. Also, comparative Examples are included in Table 1, being Example 5 to 10. The Examples 1 to 10 are listed in Table 1.

Table 1: Examples 1 to 10, as indicated by the specific Re-Tanning agent, and its amount (Y%), and the amount of dye (X%).

XR-5592 is a transparent aqueous polycarbodiimide composition with 40 weight% of polycarbodiimide in water (calculated on the total weight of composition). XR-5508 is a milky-white aqueous polycarbodiimide composition with 40 weight% of polycarbodiimide in water (calculated on the total weight of composition). Tergotan EF Liq is a dark -brown re-tanning composition based on polypeptides and aromatic sulphonates, with 47 weight% of active matter in water (calculated on the total weight of composition). Tanicor SLN is a yellowish powder re-tanning agent based on condensation product of aromatic sulfonic acids. All four products can be obtained via Stahl Europe BV.

Example 11: Evaluation

Leather specimens obtained from Examples 1 to 10 were subjected to various evaluation test. The evaluation results are collected in Tables 2 and Table 3.

The tightness of the grain is an evaluation of the top layer of the leather once it is bent with two hands. The smoother the layer remains the tighter is the bent leather. The more wrinkles observed, the lower the tightness. Lower numbers indicate better tightness.

The smoothness I fineness of the surface was evaluated, in which levelness is considered as very good.

The softness of leathers was determined via haptics and are generally graded with a number, wherein a lower number is better.

Fullness of re-tanned leathers was determined via haptics. Lower numbers indicate better fullness.

The handle I touch of the re-tanned leathers is considered as very good if the superficial touch it is not greasy or too dry, and a silky touch is considered as perfect.

The uniformity of colour is about the dyeing levelness, in which a uniform dyeing coverage on the surface is considered good.

The shade is also a colour property and is considered good if the dyeing does not result in any shade on the surface. In this case the dyestuffs are penetrated, but the colour that the re-tanning agents has, affects the colour that the dyestuffs should bring to the leather. In the case of a white retanning agent, there is generally no influence on the shade, while some dark vegetable re-tanning agent may have a negative effect on the shade.

The degree of bleaching is also a colour property, in which a darker colour is considered as bad, and a lighter colour is considered as good. The darker colour is a result of re-tanning agents blocking the pores of the leather due to which the dyestuffs cannot penetrate the leather properly.

The degree of colouring in a cross section takes into account whether the dyestuffs are completely penetrated, so whether colouring is at the surface only or also deeper inside the leather, in which a full cross section colouring is considered as best.

Table 2: Evaluation results on leather specimens from Examples 1, 3, 5, 7 and 9: the specimens which were not dyed. The scale goes from 1.0 (very good), 2.0 (good), 3.0 (average), 4.0 (below average), 5.0 (poor) to 6.0 (fail). A difference of 0.5 means a marginal difference which will need technical experience to differentiate, but a 1.0 difference means an obvious difference.

Table 3: Evaluation results on leather specimens from Examples 2, 4, 6, 8 and 10: the specimens which were dyed. The scale goes from 1.0 (very good), 2.0 (good), 3.0 (average), 4.0 (below average), 5.0 (poor) to 6.0 (fail). A difference of 0.5 means a marginal difference which will need technical experience to differentiate, but a 1.0 difference means an obvious difference.

As can be seen in Tables 2 and 3, the leathers re-tanned using a polycarbodiimide gave an average score that was slightly better than the scores obtained with the reference re-tanning agents Tergotan EF Liq and Tanicor SLN. Not surprising was that the average scores were poorest for the leathers that were prepared without a Re-Tanning agent, the Examples 9 and 10. The leathers from Innovative Examples 1 to 4 showed excellent tightness and smoothness/fineness, which was much better than obtained for leather re-tanned with reference re-tanning agents Tergotan EF Liq and Tanicor SLN.

Although the leathers from Innovative Examples 1 to 4 appeared to be not very full and spongy, the grain was completely well adhered even in the hollowest areas such as the sides. The leathers from Comparative Examples 5 and 6 presented multiple non-uniformities and the dye was not very well distributed and the leathers lacked in filling and levelling performances. The leathers from Comparative Examples 7 and 8 were very spongy and with little fullness, and despite the high sponginess, the leathers were not very suitable for automotive and footwear applications. The leathers from Comparative Examples 9 and 10 proved to be very poor concerning the tightness, fullness and roundness, and furthermore, also the penetration of the dye in section was not complete. It has thus been demonstrated that re-tanning using a polycarbodiimide gives overall slightly better properties to the leather as retanning using reference materials and better performance concerning tightness and smoothness/fineness compared to reference re-tanning agents.

Example 12: re-tanning process and evaluation

The same re-tanning process as in Examples 1 and 3 was done, with as the only difference that the pH was adjusted to 8.0 with sodium bicarbonate instead of adjusting the pH to a value of 5.5, before the addition of Y% of re-tanning agents XR-5592 or XR-5508. Evaluation of the resulting leather specimens, in the manner as described in Example 11, did not show differences in the results obtained versus the results obtained with corresponding leather specimens from Example 1 or 3.

In both conditions, with adjusting the pH to either 8.8 or 5.5 before the addition of Y% of polycarbodiimides XR-5592 or XR-5508 as re-tanning agent, a very good exhaustion of the bath was noticed, meaning that the leather has absorbed the re-tanning agents very well and that thus only a low amount of re-tanning agents remained in the liquid.

Example 13: Pre-tanning and tanning process for wet-white leather with polycarbodiimides as pre-tanning auxiliary

Hides were used that had been treated with a standard beamhouse process.

Pre-tanning was carried out starting with addition of 10% of water at 25°C and 10% of XR-5592 (a transparent aqueous polycarbodiimide with 40 weight% of polycarbodiimide in water, obtainable from Stahl Europe B.V) and the drum was run for 120 min obtaining a pH of 8.5 and the leather had a shrinkage temperature of 61°C. Another 10% of XR-5592 was added and the drum was run for 300 min. Now, the shrinkage temperature was 61°C. Next, 10% of Granofin® Easy F-90 (an organically based tanning agent, obtainable from Stahl Europe B.V) was added to the drum and the drum was run at 35°C for 120 min and then let run slowly over night. The pH was measured at 5.4 and the shrinkage temperature of the leather was 71°C.

Then 0.25% of Preventol U TEC-G (a biocide for preserving tanned hides, obtainable from Lanxess AG) was added and the drum was run for 30 min followed by addition of 100% of water at 40°C and 2% of Tanicor® AS (a sulphone tanning agent, obtainable from Stahl Europe B.V). The drum was run for 120 min, and the pH was measured at 6.0. Next, the leather was washed with 200% of water of 20° for 10 minutes. The pre-tanned and tanned leather was then summed out and shaved with a thickness 1.0 - 1.1 mm.

Comparative Example 14: Pre-tanning and tanning process for wetwhite leather

Hides were used that had been treated with a standard beamhouse process.

Tanning was carried out starting with addition of 10% of water at 25°C and 10% of Granofin® Easy F-90 (an organically based tanning agent, obtainable from Stahl Europe B.V) and the drum was run at 35°C for 120 min and then let run slowly over night, obtaining a pH of 5,0 and the leather had a shrinkage temperature was 73°C.

Example 15: evaluation of pre-tanned and tanned leathers

Pre-tanned leather specimens obtained from Examples 13 and 14 were subjected to various evaluation test. The evaluation results are collected in Table 4. Neck Draw refers to the visual evaluation of the neck area of the animal with specific evaluation of how much the natural wrinkles, due to the animal's growth, have been softened by the effect of the pre-tanning/tanning agent. More distension is preferred and better.

Belly Draw refers to the visual evaluation of the belly area of the animal with specific evaluation of how much the natural wrinkles, due to the animal's growth, have been softened by the effect of the pre-tanning/tanning agent. More distension is preferred and better.

Growth Marks indicates the visual evaluation on growth wrinkles in the overall areas of the animal, which are more marked with the age of the animal. It is best these growth marks are less visible after the tanning/pre- tanning. More distension is preferred and better.

Veins indicates the visual evaluation on the visibility of veins after the tanning/pre-tanning. Less visible is better.

Through tanning (%) indicates the part, in percentage, in which tanning has occurred through the hides through hides. This is made visible by using a universal pH indicator. A value of 100% is best.

The shrinkage temperature of pelt or leather is a measurement of the hydrothermal stability of leather. The principle of the method is to suspend the test piece in water, in the form of a strip and heat the water at a rate of 2°C/min. The shrinkage temperature is noted when the sample visibly shrinks.

Shaving behavior indicates the mechanical resistance I attitude of the hides to be shaved: dry is better and sticky is not good, because then the hides is difficult to shave.

Aspect, fullness is determined via haptics. Lower numbers indicate better fullness. It is a general evaluation of the fullness of the hides. Aspect, touch is determined via haptics. The handle I touch of the tanned/p re -tanned hides is considered as very good if the superficial touch is not greasy and not too dry, and a silky touch is considered as best.

Table 4: Evaluation results on pre-tanned leather specimens from Examples 13 and 14: the scale goes from 1.0 (very good), 2.0 (good), 3.0 (average), 4.0 (below average), 5.0 (poor) to 6.0 (fail). A difference of 0.5 means a marginal difference which will need technical experience to differentiate, but a 1.0 difference means an obvious difference.

The leather specimen obtained from Example 13 shows a good behaviour in the pre-tanning and tanning. It shows a good general appearance especially for the distention of the belly draw, neck draw and growth marks. The leather specimen obtained from Example 13 shows a whiter colour than obtained with comparative Example 14. Overall, the leather obtained from Example 13 behaved slightly better than comparative Example 14.

Example 16 and 17: Re-tanning process of wet-white leathers obtained from Examples 13 and 14.

The pre-tanned and tanned leathers from Example 13 and 14 were processed according to the following re-tanning procedure to obtain a final Automotive article. All percentages mentioned are based on leather weight shaved of thickness 1.0 - 1.1 mm before processing. Re-tanning was carried out starting with addition of 200% of water at 35°C and 0.5% of Tergolix® SL-01 (biodegradable, non-ionic wetting and degreasing agent, obtainable from Stahl Europe B.V). The drum was run for 10 min and 3.0% of sodium bicarbonate was added and the drum was run for 60 min, resulting in a pH of 7.4. The drum was drained and the leathers were washed with 150% of water at 35°C for 10 min, after which the drum was drained again. 60% of water at 35°C was added followed by 6% of Granofin® Easy F-90 (an organically based tanning agent, obtainable from Stahl Europe B.V) and the drum was run for 180 min. Next, 3% of Relugan® Soft AP (fatliquoring agent, obtainable from Stahl Europe B.V) and 3% of Densodrin® DP (waterproofing auxihary agent, obtainable from Stahl Europe B.V) were added and the drum was run for 20 min, followed by the addition of 6% of Relugan® SE (acrylic polymer retanning agent, obtainable from Stahl Europe B.V) and 10% of Granofin® TA (vegetable tanning agent, obtainable from Stahl Europe B.V). Next, the drum was run for 10 min and 7% of Lipoderm Licker Al New (natural fatliquoring agent, obtainable from Stahl Europe B.V) was added, followed by 2% of Lipoderm Licker LA (natural fatliquoring agent, obtainable from Stahl Europe B.V) and the drum was run for 10 min. Next, 10% of Tanicor® DLE (aromatic sulfonic retanning agent, obtainable from Stahl Europe B.V) was added followed by the addition of 0.5% of Trilon B (a chelating agent, obtainable from BASF AG). The drum was run for 90 min giving a pH of 5.2. The drum was run slowly overnight. Next, 100% of water at 50°C was added and the drum was run for 10 min, followed by the addition of 1% of formic acid and the drum was run for 30 min, giving a pH of 4.2. Next, 0.8% Dermafix OK hq. (dye auxiliary agent, obtained from Stahl Europe B.V.) was added and the drum was run for 10 min, then 1.5% of formic acid was added and the drum was run for 30 min giving a pH of 3.9. The drum was drained and the leather washed with 150% of water at 20°C, and the drum was run for 10 min and drained again. Next, 100% of water at 20°C and 0.5% of Coriagen® Or II New (neutralization agent, obtainable from Stahl Europe B.V) were added, after which the drum was run for 10 min giving a pH of above 4.5. Next, 6% of Relugan RV (acrylic polymer retanning agent, obtainable from Stahl Europe B.V) was added and the drum was run for 10 min. Next, 1% of Coralon M (anionic dispersing agent to speed up the penetration and distribution of retanning vegetables and dyestuffs, obtainable from Stahl Europe B.V), 2.6% of Melioderm® HF brown R (anionic dyestuff giving brown colour, obtainable from Stahl Europe B.V), 1.5% of Melioderm® HF red brown W (anionic dyestuff giving red brown colour, obtainable from Stahl Europe B.V), 0.5% of Melioderm® HF dark brown R (anionic dyestuff giving dark brown colour, obtainable from Stahl Europe B.V), 6% of Tanicor® VX-IT (retanning agent, obtainable from Stahl Europe B.V) and 6% of Tanicor® MLB (retanning agent, obtainable from Stahl Europe B.V) were added and the drum was run for 60 min. Then 100% of water at 50°C, 10% of Lipoderm Liquor Al New, 3% of Lipoderm Liquor LA, 3% of Relugan® soft AP, 0.5% Lipoderm N (natural fatliquoring agent, obtainable from Stahl Europe B.V) were added and the drum was run for 60 min. Next, 6% of Tanicor® VX-IT was added and the drum was run for 60 min, followed by the addition of 1.5% of formic acid and the drum was run for other 30 min. Next, 1.5% of formic acid was added and the drum was run for 30 min followed by the addition of 0.5% of Dermafix OK liq. and the drum was run for 30 min giving a pH of 3.5. The drum was drained and 150% of water at 50°C was added, followed by the addition of 1% of Coralon M, 1.3% of Melioderm® HF brown R, 0.7% of Melioderm® HF red brown W and 0.2% of Melioderm® HF dark brown R and the drum was run for 15 min. Next, 2% of formic acid was added and the drum was run for 30 min. The drum was drained and the leather was washed with 150% of water at 20°C for 10 min. The drum was drained and 200% of water was added, followed by 0.5% of formic acid and the drum was run for 10 min, then 1% of Dermafix P (dye auxiliary agent, obtained from Stahl Europe B.V.) was added and the drum was run for 40 min. Afterwards the leathers were set out and vacuum dried at 42 °C for 4 minutes. Thereafter the leathers were hung to complete the drying process. Pre-tanned leather from Example 13 resulted in Example 16.

Pre-tanned leather from Example 14 resulted in Example 17.

Example 18: evaluation of Examples 16 and 17

Leathers obtained in the Examples from 16 and 17 were subjected to various evaluation test. The evaluation results are collected in Table 5.

Wrinkles: a crease or pucker in the skin, as any of those caused by aging. Wrinkles naturally occur in skins/hides and are more marked in specific areas of the animal (like neck and belly).

Milling pattern: Milled leather is the product of a leather after it has undergone milling. The process is run in a leather milling machine made up of large cylinders rotating along the axis, in which the hides are vigorously tumbled and softened mechanically in an environment with controlled humidity and temperature. The process naturally intensifies the fine lines the leather may possess. Milling pattern is the grain typical and specific of the surface of the milled leather.

Table 5: Evaluation results on leather specimens from Examples 16 and 17: the scale goes from 1.0 (very good), 2.0 (good), 3.0 (average), 4.0 (below average), 5.0 (poor) to 6.0 (fail). A difference of 0.5 means a marginal difference which will need technical experience to differentiate, but a 1.0 difference means an obvious difference.

The leather of Example 16 (using pre-tanned and tanned leather obtained by Example 13) responded well to the re-tanning process. The product XR-5592 imparted a uniform filling effect with a soft round handle. In comparison to Example 17, the leather in Example 16 was tighter and with a good covering power by improving the dyeability and the colour uniformity between grain and flesh side. Also fullness, fluffiness and wrinkles were better for Example 16 than obtained with comparative Example 17, as demonstrated by the overall better score of 2.1 for Example 16 versus a score of 2.8 for Comparative Example 17.

Claims

1. Use of a composition comprising at least one polycarbodiimide compound in a leather manufacturing process for re-tanning of tanned wetblue leather, pre-tanning of leather before tanning and/or for tanning leather.

2. Use according to claim 1 wherein the composition comprising at least one polycarbodiimide compound is used in a leather manufacturing process for pre-tanning of wet-white leather and wet-blue leather.

3. Use according to claim 1 or 2, wherein the composition comprises between 20 and 100 weight%, preferably between 25 and 100 weight%, more preferably between 30 and 100 weight%, most preferably between 35 and 100 weight% of polycarbodiimide compounds calculated on the total weight of the composition, and wherein the remaining amount may comprise other pretanning, tanning and/or re-tanning agents or water or solvents.

4. Use according to any of foregoing claims, wherein the composition comprising at least one polycarbodiimide compound is liquid at ambient conditions (atmospheric pressure and a temperature of 25°C), preferably said composition is an aqueous compositions or a liquid composition containing no volatile components.

5. Use according to any of foregoing claims wherein the polycarbodiimide compound contains on average from 2 to 10, preferably from 2 to 6 carbodiimide groups (-N=C=N-) in its polymer chain or oligomer chain.

6. Use according to any of foregoing claims, wherein the polycarbodiimide compound has an average molecular weight of 800 Dalton or higher, preferably 1000 Dalton or higher.

7. Use according to any of foregoing claims, wherein the polycarbodiimide compound was synthesized from isophorone diisocyanate (IPDI) or from 4,4'-methylene dicyclohexyldiisocyanate (H12MDI).

8. Use according to any of foregoing claims, wherein between 3 and 50 weight%, preferably between 5 and 40 weight% and most preferably in between 6 and 30 weight%, relative to the weight of the hides/leather of polycarbodiimide compounds, taking into account only the non-volatile components, is used.

9. Use of the composition according to any of foregoing claims as a retanning composition in a re-tanning step for leather in a leather manufacturing process for improving the tightness, smoothness, fineness and/or softness of tanned leather.

10. Use of the composition according to any of foregoing claims as a pre-tanning composition in a pre-tanning step for leather in a leather manufacturing process for enhancing the tanning in a subsequent tanning process and/or for improving the cleanness, tightness, fluffiness, uniformity and/or fullness of the leather before tanning the leather.

11. Leather obtained using the composition according to any of foregoing claims 1-8 in a re-tanning process according to claim 9 and/or a pre-tanning process according to claim 10.