A process for the use of glyoxylic aromatic condensates as re-tanning agents

Abstract

The present invention provides the use of a re-tanning composition comprising at least one glyoxylic acid aromatic condensate compound in a leather manufacturing process that provides good re-tanning behaviour.

Description

[0001] A PROCESS FOR THE USE OF GLYOXYLIC AROMATIC CONDENSATES AS RE-TANNING AGENTS

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to a novel process for leather manufacturing wherein glyoxylic acid aromatic condensate compounds are used as re-tanning agent.

[0004] BACKGROUND OF THE INVENTION

[0005] 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.

[0006] The present invention relates to the sub-process of tanning, especially the re-tanning part thereof.

[0007] 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.

[0008] 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 sulfate (giving so-called wet-blue leather) or by the use of organic reactive tanning agent as aldehydes, especially glutaraldehyde (resulting in wet-white leather). In rare cases the tanning is carried out with vegetable tanning agents - as traditionally done - or by use of synthetic tanning agents (syntans).

[0009] The product prepared in this sub-process 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. Re-tanning affects the feel of the leather, the dyeability, softness of the leather, fullness of the leather, the fineness of the grain, the stability of grain and other factors such as light and heat 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 more softness and touch. Once re-tannage is complete, the leather is known as “crust”.

[0010] 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 sulfate 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.

[0011] The term syntan refers to the range of synthetic tanning agents. The first syntans were made by condensation of phenol sulfonic acid and formaldehyde (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 1,8418,40 describes the incorporation of urea into the polycondensation of phenol sulfonic acid and formaldehyde, as depicted in Scheme 1, by which such a further development was achieved, enabling obtaining leathers with increased technical requirements like fastness properties concerning light or heat induced ageing.

[0012] R = te po^condensate continues same s&uchse

[0013] Scheme 1: chemistry of synthetic tanning agents

[0014] Because of the wide acceptance of chromium sulfate or glutaraldehyde as tanning agents, syntans are now mainly used in the retanning 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 late 2022, ECHA published a restriction proposal on various bisphenols including bisphenol S and bisphenol F. Limits of 500 ppm bisphenols were proposed for leather chemicals and articles. This restriction proposal was discontinued after a public consultation in August 2023.

[0015] 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 have to provide dispersing properties in order to support the even distribution of vegetable tannins and other leather chemicals like fillers, dyes, and fatliquors (DE 1142173). Given the fact that syntans are still made from oil based and toxic phenol and formaldehyde, the search is ongoing for re-tanning agents made from less toxic starting materials, that can substitute syntans.

[0016] US 9,725,552 describes hydroxymethylfurfural-based phenol formaldehyde resins comprising phosphate ester, phosphate, phosphine oxide, phosphinate ester or phosphinate groups.

[0017] WO2023022595 describes a process to prepare condensates, by condensation of a malonic ester with aromatic aldehydes, optional subsequent transesterification with polyol, and subsequent sulphitation and their use as re-tanning agents.

[0018] WO2023 128758 describes the condensation products of an aldehyde compound, such as glyoxal, and a sulphonated phenolic compound and optionally urea and their use as re-tanning agent.

[0019] A. Nan et al describe in Polym. Chem., 2017, vol 8, pages 3504-3514 a synthesis of polycondensates from phenol, glyoxylic acid and formaldehyde as known chemistry and the aim of the study is directed to synthesis and characterization of highly functionalized organic polymers, which were subsequently converted into magnetic nanostructures.

[0020] W02009 115544 describes a composition comprising a blend of phenol-formaldehyde resin and a phenol- glyoxylate resin wherein the blend has a pH of from 7 to 10 and the mentioned usage is as binder adhesives for mineral wool insulation or in foundry applications.

[0021] W02009 115545 describes a heat curable resin composition comprising phenol- glyoxylate resin and polyol, with intended usage as coatings, adhesives or shaped articles or in the foundry industry.

[0022] EP2189496A describes crosslinking agent made from glyoxylate and a glyoxylic acid ester derivative, which can subsequently react / crosslink with monomers such as ureas, melamine and phenols, with intended usage as crosslinking agent for linear polymers, especially AA-PVA-based resins.

[0023] EP0429830A2 discloses the use of aqueous solutions of condensation products of urea, glyoxylic acid and glyoxal for the re-tanning of chrome- tanned leather treated with acrylic polymer; leather with light fastness and heat-resistance.

[0024] DESCRIPTION OF THE INVENTION

[0025] Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features. It will be further understood that when a particular step of a method is referred to as subsequent to another step, it can directly follow said other step or one or more intermediate steps may be carried out before carrying out the particular step, unless specified otherwise.

[0026] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims.

[0027] It is the aim of the invention to solve above cited problems and provide novel synthans for use as re-tanning agents which are free of toxic compounds such as bisphenol S, F and A and minimize the fraction of formaldehyde while at least maintaining and / or improving the re-tanning properties of the leather. It is a further aim of the invention to avoid the use of sulphuric acid in the synthesis process of synthans for use as re-tanning agents.

[0028] The present invention therefor provides a novel re-tanning composition and its use in a re-tanning process wherein said re-tanning composition solves above state of the art problems and further improves the re-tanning step of leather in a leather manufacturing process. More in particular, the present invention provides an improved re-tanning composition and a re-tanning process wherein glyoxylic acid aromatic condensate compounds are used as re-tanning agent in a leather manufacturing process.

[0029] The glyoxylic acid aromatic condensate compounds according to the invention correspond to compounds comprising the structure of formula [I],

[0030] Wherein R is selected independently from each other from one or more

[0031] OH, a hydrocarbon chain comprising an alkyl, aryl, heteroaryl and / or heteroalkyl group, wherein said alkyl group may be cyclic, linear or branched and is preferably a C1-C5 alkyl group, more preferably a C1-C3 alkyl group and n is an integer, in particular from 1 to 15, preferably from 1 to 10, more preferred from 1 to 5.

[0032] The glyoxylic acid aromatic condensate compounds according to the invention may be formed by condensation reaction of glyoxylic acid with aromatic moieties via acidic catalysis (Scheme 2) and obtain water miscible poly-condensates without sulphuric acid, which can subsequently be directly used for aqueous applications. The absence of sulphuric acid is a big advantage, because without sulphuric acid it is not possible to have the undesired formation of Bisphenol S (4,4'-sulfonyldiphenol). A further advantage of the absence of sulphuric acid in the reaction mixture is that no inorganic salt formation can occur, whereas formation of inorganic salts in the final composition could negatively affect the quality of wastewater.

[0033] Scheme 2: General reaction for making glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] according to the invention, with “n” being an integer indicating that the unit within the parenthesis is repeated “n” times.

[0034] According to embodiments, the glyoxylic acid aromatic condensate compound comprising the structure of formula [I] may be a condensation of phenol and glyoxylic acid thereby yielding glyoxylic acid phenolic condensate compounds (see reaction scheme 2a).

[0035] Scheme 2a: General reaction for making glyoxylic acid phenolic condensate compounds according to the invention, with n an integer, in particular from 1 to 15, preferably from 1 to 10, more preferred from 1 to 5.

[0036] Surprisingly, very good results were obtained when the glyoxylic acid aromatic condensates comprising the structure of formula [I] were used in the re-tanning of leather. Tanned leathers treated with these glyoxylic acid aromatic condensates achieved a re-tanning quahty which was similar or superior to leathers re-tanned with syntans, which are conventional retanning agents. It is further demonstrated that these glyoxyhc acid aromatic condensates comprising the structure of formula [I] can be further crosslinked with aldehydes and / or di-aldehydes to achieve cross-linked glyoxyhc acid aromatic condensates in order to further tune the effect on the re-tanned leather (Scheme 3).

[0037] Scheme 3: General reaction sequence for the cross-linking of the glyoxyhc acid aromatic condensate compounds according to formula [I] with aldehyde compounds, with “n”, “m” and “y” indicating that the units within the parenthesis is repeated “n”, “m” or “y” times.

[0038] The cross-linked glyoxylic acid aromatic condensates according to the invention correspond to formula [II],

[0039] Wherein R and R1independently from each other are selected from one or more OH, a hydrocarbon chain comprising an alkyl, aryl, heteroaryl and / or heteroalkyl group, wherein said alkyl group may be cyclic, linear or branched and is preferably a C1-C5 alkyl group, more preferably a C1-C3 alkyl group, n is an integer, in particular from 1 to 15, preferably from 1 to 10, more preferred from 1 to 5, m is an integer, in particular from 1 to 10, more preferred from 1 to 6 and y an integer from 1 to 2. Within the cross-linking reaction step, urea can be optionally added to give organic-bridged cross-linked glyoxylic acid aromatic condensates having the formula shown in Scheme 4 and illustrated by Formula [III] below.

[0040] Scheme 4. General reaction sequence for the cross-linking of the glyoxylic acid aromatic condensate compounds according to formula [I] in the presence of (di)aldehydes and urea thereby yielding organic -bridged cross-linked glyoxylic acid aromatic condensates, wherein “n”, “m”, “k” and “y” are indicating the number of units within the parenthesis are repeated.

[0041] The organic-bridged cross-linked glyoxylic acid aromatic condensates according to the invention correspond to formula [III].

[0042] Wherein R and R1independently from each other are selected from one or more OH, a hydrocarbon chain comprising an alkyl, aryl, heteroaryl and / or heteroalkyl group, wherein said alkyl group may be cyclic, linear or branched and is preferably a C1-C5 alkyl group, more preferably a C1-C3 alkyl group, n is an integer, in particular from 1 to 15, preferably from 1 to 10, more preferred from 1 to 5, m is an integer, in particular from 1 to 10, preferably from 1 to 6, k is an integer, in particular from 0 to 10, preferably from 0 to 6 and y is an integer from 1 to 2.

[0043] The glyoxylic acid aromatic condensate compounds used in the present invention are obtained from the reaction of aromatic moieties and glyoxylic acid which may be further cross-linked through a second reaction step with aldehyde compounds.

[0044] Optionally, the glyoxylic acid aromatic condensate compounds of the invention may be further cross-linked and organic -bridged through a second reaction step with aldehyde compounds further comprising urea compounds thereby yielding the organic-bridged cross-linked glyoxylic acid aromatic condensates. Examples of aromatic moieties that can be employed to prepare glyoxylic acid aromatic condensate compounds used in the present invention are phenol, cresol, naphthol, catechol, resorcinol, hydroquinone, naphthalene, biphenyl, fluorene, anthracene, phenanthrene, phenalene, tetracene, chrysene, triphenylene, pyrene, pentacene, perylene, benzo [a]pyrene, cor annulene, benzo [ghi]perylene, coronene, ovalene, benzo [c]fluorene, orcinol, 3-methylcathecol, 4-methylcathecol, 2- methylbenzene-l,3-diol, 4-methylbenzene-l,3-diol, 2-methylbenzene-l,4- diol, ethylbenzene, mesitylene, durene, 2 -phenylhexane, xylenol, xylene, isopropyl naphthalene, ditolyl ether or any combination thereof. Examples of preferred aromatic moieties include phenol, cresol, naphthalene, naphthol, orcinol and xylenol.

[0045] Examples of aldehydes that can be employed to prepare cross-linked glyoxylic acid aromatic condensate compounds used in the present invention are formaldehyde, furfural, hydroxymethylfurfural, benzaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isovaleraldehyde, cinnamaldehyde, vanillin, tolualdehyde, retinaldehyde, glycolaldehyde. Examples of preferred aldehydes include formaldehyde, furfural, and benzaldehyde.

[0046] Examples of di-aldehydes that can be employed to prepare crosslinked glyoxylic acid aromatic condensate compounds used in the present invention are glyoxal, glutaraldehyde, malondialdehyde, succindialdehyde, phthalaldehyde. Examples of preferred dialdehydes include glyoxal, and glutaraldehyde.

[0047] The glyoxylic acid aromatic condensate compounds used in the present invention can be formed under acid catalyzed reaction conditions, or under base catalyzed reaction conditions. Acid catalyzed reaction conditions are preferably achieved by the addition of p -toluene sulfonic acid or benzenesulfonic acid, but also other acids may be employed such as other organic sulfonic acid or sulfonic acid substituted resins or mineral acids like sulphuric acid, hydrochloric acid, or phosphorous acid. Base catalyzed reaction conditions are preferably achieved by the addition of alkali hydroxides.

[0048] The acid catalyzed reaction for the formation of the glyoxylic acid aromatic condensate compounds is executed at a temperature between 30°C and 120°C, preferably between 40°C and 95°C and most preferably between 50°C and 95°C. The reaction is executed for some duration, which is dependent on the reaction temperature and preferably the reaction duration is between 1 and 14 hours, most preferably between 4 and 10 hours, most preferably between 4 and 8 hours.

[0049] The glyoxylic acid aromatic condensate compounds used in the present invention are formed from reacting the components in a molar ratio of the glyoxylic acid and the aromatic moieties which ranges from between 5:1 to 0.5:1, preferably between 4:1 to 0.5:1 and most preferably 3:1 to 0.6:1.

[0050] Optionally, a second reaction step is performed to obtain crosslinked glyoxylic acid aromatic condensate compounds to further tune the properties of the glyoxylic acid aromatic condensate compounds. This second reaction step entails the addition of aldehyde compounds. This second reaction step is executed at a temperature between 30°C and 120°C, preferably between 40°C and 95°C and most preferably between 50°C and 95°C. The reaction time during the second reaction step is dependent on the reaction temperature and preferably the reaction duration is between 1 and 14 hours, most preferably between 4 and 10 hours, most preferably between 4 and 8 hours.

[0051] Also concerning the second (cross-linking) reaction step prior to the addition of the aldehyde the glyoxylic acid aromatic condensate compounds detectable amounts of phenol are preferably removed in order to avoid detectable amounts of unreacted phenol and to avoid the potential formation of Bisphenol F after the second reaction step. The advantage of performing this second reaction step to obtain cross-linked glyoxylic acid aromatic condensate compounds is that leathers treated with the crosslinked glyoxylic acid aromatic condensate compounds of the invention showed similar or better softness, fullness, and lightfastness than leathers treated with non-cross-linked glyoxylic acid aromatic condensate compounds as such.

[0052] When the glyoxylic acid aromatic condensate compounds are (optionally) further reacted with an aldehyde compound or an aldehyde compound and urea then the molar ratio of the aromatic moieties and the aldehyde compound ranges between 8:1 to 1:1 and the molar ratio of the urea and the aldehyde compound ranges between 1:1 to 0.1:1.

[0053] The formation of the glyoxylic acid aromatic condensate compounds and the formation of the (organic -bridged) cross-linked glyoxylic acid aromatic condensate compounds are preferably followed by neutralization with a base to obtain a formulation with a pH between 2 and 7. Preferred bases comprise inorganic bases (such as alkali hydroxides, carbonates, bicarbonates, and oxides) and / or organic bases (such as organic amines or organic hydroxides).

[0054] Optionally, after neutralization, a buffering agent can be added to the glyoxylic acid aromatic condensate compounds. Preferred buffering agents comprise tricarboxylic acids (such as citric acid, isocitric acid, aconitic acid, propane- 1, 2, 3-tricarboxylic acid, agaric acid, trimesic acid), dicarboxylic acids (such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid), monocarboxylic acids (such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid), phosphate salts (such as sodium phosphate dibasic, sodium phosphate monobasic), and any combination thereof. The present invention provides an improved re-tanning composition comprising the glyoxylic acid aromatic condensate compounds and / or crosslinked glyoxyhc acid aromatic condensate compounds and / or organic bridged cross-linked glyoxyhc acid aromatic condensate compounds (further referred to as glyoxyhc acid aromatic condensate compounds comprising the structure of formula [I] which may be further cross-linked or organic bridged).

[0055] Optionally, an antioxidant can be added to re-tanning composition comprising the glyoxylic acid aromatic condensate compound. Preferred antioxidants comprise butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG), tert-butyl hydroquinone (TBHQ), trimethyl phosphate, triphenyl phosphate, trimethylphosphine, phosphoric acid, phosphorous acid, hypophosphorous acid, Irganox L135 and any combination thereof. The advantage of adding an antioxidant to the glyoxyhc acid aromatic condensate compounds is that leather treated with these products provide better lightfastness and improved resistance to aging.

[0056] The re-tanning composition according to the invention comprises between 10 and 80 weight%, preferably between 20 and 60 weight%, more preferably between 30 and 50 weight% of glyoxylic acid aromatic condensate compounds according to the invention comprising the structure of formula [I] and which may be further cross-linked or organic -bridged calculated on the total weight of the composition, and wherein the remaining amount may comprise other re-tanning agents, additives or water or solvents.

[0057] The re-tanning composition comprising the glyoxylic acid aromatic condensate compounds according to the invention comprising the structure of formula [I] and which may be further cross-linked or organic-bridged can also be converted into a solid by removing the water and / or solvents, if present. This conversion process into a solid can be achieved by any means, such as by evaporating the water and solvent, if present, using reduced pressure or increased temperature or a combination thereof, or by spraydrying or by freeze-drying or by any other method, or any of the methods combined. Preferably, if the re-tanning composition according to the invention is used as a solid material, then this is in powder form, which will make the usage as re-tanning agent in solid form more convenient. A retanning composition comprising glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] and which may be further cross-linked or organic-bridged and was further converted into a solid can subsequently also be used to prepare an aqueous re-tanning composition by dissolving or dispersing the solid into water.

[0058] The re-tanning composition according to the invention can be applied on leather, such as via an industry standard procedure, for retanning.

[0059] Surprisingly, it was found that leathers treated with the re-tanning compositions of the invention comprising the glyoxylic acid aromatic condensate compounds according to the invention comprising the structure of formula [I] had similar or better properties on leather than syntans or vegetable tannins have, concerning softness, fullness, and lightfastness, while eliminating the above mentioned toxic compounds such as bisphenol compounds as side products. These compositions represent a novel alternative to oil-based phenol formaldehyde condensates in the leather industry.

[0060] It was also found that the addition of urea in the second crosslinking step to achieve organic-bridged cross-linked glyoxylic acid aromatic condensate compounds provides improved lightfastness as well as resistance to heat induced ageing in the leather treated with these products.

[0061] 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 agent is added followed by further turning of the tanning drum for a certain period of time, 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 composition comprising glyoxylic acid aromatic condensate compounds is added as a re-tanning agent wherein the glyoxylic acid aromatic condensate compounds comprising the structure according to formula [I] (optionally organic -bridged and / or cross-linked) are used in an amount of between 2% and 30 weight%, and preferably in an amount of between 5% and 25 weight%, and most preferably in an amount of between 8% and 20 weight%, wherein the percentages refer to the weight percentage of the non-volatile part of the re-tanning composition of the present invention to the weight of the leather.

[0062] State of the art syntans are made from phenol, sulphuric acid and formaldehyde and as a consequence they can release formaldehyde and can contain free phenol, Bisphenol F, or Bisphenol S. Rest monomer analysis for formaldehyde like ISO 27587 is widely applied in the leather industry. Bisphenols and Phenol can be analyzed with ISO 18218-1 in parallel to alkylphenols.

[0063] The present invention provides a novel re-tanning composition and re-tanning process for use in a leather manufacturing process wherein glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] (optionally organic -bridged and / or crosslinked) are used as retanning agents thereby avoiding and / or eliminating both bisphenol F and Bisphenol S.

[0064] The re-tanning composition and re-tanning process 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 a product 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 woolen skins and furs (e.g. fur-bearing suede leather).

[0065] 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.

[0066] The leathers obtained by the process of the present invention can subsequently be further processed, as is customary in the leather industry, by any of the processes of bleaching, coloring, dyeing, fat liquoring, setting to dry, conditioning, staking, milling, tumbling, buffing, pressing, embossing, ironing, finishing with a coating.

[0067] The novel use of glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] which are optionally further organic- bridged and / or cross-linked represents a novel alternative to using classical oil -based phenol formaldehyde condensates in the leather industry.

[0068] Summarizing, the use of glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] as re-tanning agents are out-performing syntans on leather like properties like softness, fullness, as well as light and heat induced ageing, and in addition enabling for less toxic starting materials.

[0069] It was surprisingly seen that the re-tanning properties of the glyoxylic acid aromatic condensate compounds of the present invention can be further tuned and optimized on leather by cross-linking said glyoxylic acid aromatic condensate compounds with aldehydes and / or organic- bridging them with urea in a second (cross -linking) reaction step.

[0070] For avoidance of doubt, glyoxylic acid aromatic condensate compounds according to the present invention for use in a re-tanning composition of leather comprises the glyoxylic acid aromatic condensate compounds comprising the structure of formula [I], said glyoxylic acid aromatic condensate compounds are also referred herein as polycondensates and encompass also the cross-linked glyoxylic acid aromatic condensate compounds according to formula [II] and which are obtained by cross-linking the glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] with aldehydes as well as the organic-bridged cross-linked glyoxylic acid aromatic condensate compounds according to formula [III] and which are obtained by cross-linking the glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] with aldehydes and urea.

[0071] The present invention will be further elaborated by the following non-limiting working examples.

[0072] Example 1 (glyoxylic acid and phenol)

[0073] In a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, 210 g of glyoxylic acid (50 wt.% in water; 1.42 mole) was added, followed by adding 90 g of phenol (0.96 mole), which was previously melted at 45-50°C. The reaction mass was heated to 80°C, and then 7.6 g of p-toluene sulfonic acid (0.044 mole) was slowly added. The reaction was subsequently stirred at 95-97°C for 4 hours. The reaction was then cooled to 40-45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0074] Example 2 (glyoxylic acid and phenol)

[0075] In a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, 630 g of glyoxylic acid (50 wt.% in water; 4.26 mole) was added, followed by adding 270 g of phenol (2.87 mole), which was previously melted at 45-50°C. The reaction mass was heated to 80°C, and then 16.3 g of p-toluene sulfonic acid (0.95 mole) was slowly added. The reaction was then stirred at 95-97°C for 8 hours. The reaction was then cooled to 40-45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0076] Example 3 (glyoxylic acid and phenol)

[0077] In a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, 295 g of glyoxylic acid (50 wt.% in water; 1.99 mole) was added, followed by adding 75 g of phenol (0.80 mole), which was previously melted at 45-50°C. The reaction mass was heated to 80°C, and then 6.4 g of p-toluene sulfonic acid (0.037 mole) was slowly added. The reaction was then stirred at 95-97°C for 8 hours. The reaction was then cooled to 40-45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0078] Example 4 (glyoxylic acid and phenol)

[0079] In a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, 254 g of glyoxylic acid (50 wt.% in water; 1.72 mole) was added, followed by adding 189 g of phenol (2.01 mole), which was previously melted at 45-50°C. The reaction mass was heated to 80°C, and then 9.4 g of p-toluene sulfonic acid (0.055 mole) was slowly added. The reaction was then stirred at 95-97°C for 8 hours. The reaction was then cooled to 40-45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0080] Example 5 (glyoxylic acid and phenol)

[0081] In a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, 317 g of glyoxylic acid (40 wt.% in water; 1.71 mole) was added, followed by adding 189 g of phenol (2.01 mole), which was previously melted at 45-50 °C. The reaction mass was heated to 80°C, and then 18.9 g of p-toluene sulfonic acid (0.11 mole) was slowly added. The reaction was then stirred at 95-97°C for 15 hours. The reaction was then cooled to 40- 45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0082] Example 6 (glyoxylic acid, phenol and formaldehyde)

[0083] In a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, 317 g of glyoxylic acid (40 wt.% in water; 1.71 mole) was added, followed by adding 189 g of phenol (2.01 mole), which was previously melted at 45-50 °C. The reaction mass was heated to 80°C, and then 9.4 g of p-toluene sulfonic acid (0.055 mole) was slowly added. The reaction was then stirred at 95-97°C for 8 hours. Next, 68.7 g of a 24% aqueous solution of formaldehyde (0.55 mole) was added in a period of 30 minutes and stirring was continued for 4 hours. The reaction was then cooled to 40-45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0084] Example 7 (glyoxylic acid, phenol and formaldehyde)

[0085] In a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, 647 g of glyoxylic acid (40 wt.% in water; 3.50 mole) was added, followed by adding 385 g of phenol (4.09 mole), which was previously melted at 45-50°C. The reaction mass was heated to 80°C, and then 19.3 g of p-toluene sulfonic acid (0.11 mole) was slowly added. The reaction was then stirred at 95-97°C for 6-8 hours. Next, 144 g of a 24% aqueous solution of formaldehyde (1.15 mole) was added in a period of 30 minutes and stirring was continued for 4 hours. The reaction was then cooled to 40-45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0086] Example 8 (glyoxylic acid, phenol and formaldehyde)

[0087] In a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, 189 g of phenol (2.01 mole) was melted at 45-50°C, and next 9.4 g of p-toluene sulfonic acid (0.055 mole) was added. The reaction mass was then heated to 95-97°C and 317 g of glyoxylic acid (40 wt.% in water; 1.71 mole) was added slowly in a period of 60 minutes. The reaction was then stirred at 95-97°C for 13 hours. Next, 68.7 g a 24% aqueous solution of formaldehyde (0.55 mole) was added in a period of 30 minutes and stirring was continued for 4 hours. The reaction was then cooled to 40-45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0088] Example 9 (glyoxylic acid, phenol and formaldehyde)

[0089] 13.0 g of p-toluene sulfonic acid (65 wt.% in water; 0.049 mole) and 189 g of phenol (2.01 mole), which was previously melted at 45-50°C, were put in a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer. The temperature was raised to 95-97°C, and then 317 g of glyoxylic acid (40 wt.% in water; 1.71 mole) was added to the mixture in a period of 60 minutes. The reaction was then stirred at 95-97 °C for 13 hours. Next, 68.7 g of a 24% aqueous solution of formaldehyde (0.55 mole) was added in a period of 30 minutes and stirring was continued for 4 hours. The reaction was then cooled to 40-45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0090] LC-MS / MS analysis showed that for this sample both bisphenol S and bisphenol F were below the detection limit of 10 ppm.

[0091] The content of unreacted formaldehyde was analyzed by HPLC according to the method ISO 27587:2009 and the content was below the detection limit.

[0092] Example 10 (glyoxylic acid, phenol and formaldehyde, with antioxidant) 13.0 g of p-toluene sulfonic acid (65 wt.% in water; 0.049 mole) and 189 g of phenol (2.01 mole), which was previously melted at 45-50°C, were put in a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer. The temperature was raised to 95-97°C, and then 317 g of glyoxylic acid (40 wt.% in water; 1.71 mole) was added to the mixture in a period of 60 minutes. The reaction was then stirred at 95-97°C for 13 hours. Next, 68.7 g of a 24% aqueous solution of formaldehyde (0.55 mole) was added in a period of 30 minutes and stirring was continued for 4 hours. The reaction was then cooled to 40-45°C and the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50°C. Then, 1.8 g of Irganox L135 (a phenolic antioxidant, obtainable from BASF AG) was added. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0093] Example 11 (glyoxylic acid, phenol, urea and formaldehyde)

[0094] 13.0 g of p-toluene sulfonic acid (65 wt.% in water; 0.049 mole) and 189 g of phenol (2.01 mole), which was previously melted at 45-50°C, were put in a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer. The temperature was raised to 95-97°C, and then 317 g of glyoxylic acid (40 wt.% in water; 1.71 mole) was added to the mixture in a period of 60 minutes. The reaction was then stirred at 95-97°C for 13 hours, then cooled to 55-60°C. Subsequently, 33 g of a 37.5 aqueous solution of urea (0.21 mole) was added, then the mixture was heated to 95-97°C. Next, 68.7 g of a 24% aqueous solution of formaldehyde (0.55 mole) was added in a period of 30 minutes and stirring was continued for 4 hours, the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50 °C. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0095] Example 12 (glyoxylic acid, phenol, urea and formaldehyde; with antioxidant)

[0096] 13.0 g of p-toluene sulfonic acid (65 wt.% in water; 0.049 mole) and 189 g of phenol (2.01 mole), which was previously melted at 45-50°C, were put in a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer. The temperature was raised to 95-97°C, and then 317 g of glyoxylic acid (40 wt.% in water; 1.71 mole) was added to the mixture in a period of 60 minutes. The reaction was then stirred at 95-97°C for 13 hours, then cooled to 55-60°C. Subsequently, 33 g of a 37.5 aqueous solution of urea (0.21 mole) was added, then the mixture was heated to 95-97°C. Next, 68.7 g of a 24% aqueous solution of formaldehyde (0.55 mole) was added in a period of 30 minutes and stirring was continued for 4 hours, the pH was adjusted with 30% aqueous sodium hydroxide to a pH of approximately 4, while maintaining the temperature below 50 °C. Then, 1.8 g of Irganox L135 (a phenolic antioxidant, obtainable from BASF AG) was added. Finally, the solid content of the mixture was adjusted to approximately 40% by adding water.

[0097] The molecular weight average (Mw) of Examples 6-12 were measured by gel permeation chromatography (GPC) analysis, using polystyrene as reference. The results are listed in Table 1. The Mw values measured ranged between 1385 and 1646, indicating that the polycondensates are indeed polymers with a Mw above 1000.

[0098] Table 1. Molecular weight average (Mw) of examples 6-12 as measured by gel permeation chromatography (GPC) analysis using polystyrene as reference.

[0099] Applicative examples

[0100] The novel polycondensates of the present invention were tested as retanning agents on pelt that had been tanned either with chromium sulfate (wet blue) or with a metal free tanning system Granofin® Easy F-90 (an organically based tanning agent, obtainable from Stahl Europe B.V) (wet white). The re-tanning agents have the role to fill the collagen structures and impose characteristics like softness, grain tightness, and fastness properties.

[0101] The resulting leathers were analyzed and compared with leather re-tanned with syntans, which are reference retanning agents.

[0102] Applicative Examples 1 - 3, testing Examples 1 - 3, wet blue, neutral

[0103] On 600 g of chrome tanned leather, with shaved weight thickness of 1.1- 1.2 mm, was added into the drum an amount of 1200 g of water, 0.9 g of Eusapon® OC (a degreasing agent; obtainable via Stahl Europe BV), and 3.0 g of oxalic acid and it was run for 30 min at 40°C. Next, the drum was drained. An amount of 1200 g of water at 38°C was added into the drum and it was run for 10 min. Next, the drum was drained. An amount of 900 g of water at 38°C and 30 g of BayChrom FD (a self-basifying organically masked chromium sulfate; obtainable from Lanxess) was added and the drum was run for 120 min, followed by the addition of 12 g of Coralon® NL liq. (a neutralization agent; available via Stahl Europe BV), 12 g of sodium formate. Next, the drum was run for 20 min. Now the pH was between 4.5 and 5.0. Next, 18 g of sodium bicarbonate was added and the drum was run for 60 min, now obtaining a pH between 6.0 and 7.0. Next, the drum was drained. An amount of 1200 g of water at 50°C was added and the drum was run for 10 min, after which the drum was drained. An amount of 900 g of water at 50°C and 60 g of Derminol SO-31 liq. (a synthetic anionic fatliquoring agent, obtainable from Stahl Europe B.V) was added and the drum was run for 60 min, followed by the addition of 4.2 g of formic acid. The drum was run for 20 min and then drained. An amount of 1200 g of water at 20°C was added and the drum was run for 10 min, followed by draining the drum. An amount of 120 g of water at 20°C and 180 g of one of the Examples from 1 to 3 (test product) was added and the drum was run for 120 min. Next, an amount of 900 g of water at 50°C and 6 g of formic acid was added and the drum was stirred for 20 min. Next, an amount of 6 g of formic acid was added and the drum was run for 20 min, followed by draining the drum. Next, an amount of 1200 g of water at 20°C was added and the drum was run for 10 min, followed by draining the drum.

[0104] Applicative Example 4, comparative, wet blue, neutral

[0105] The same process as in Applicative Examples 1-3 was followed, except that 180 g of Tanicor PW liq. (phenol-based retanning agent, reference product; obtainable from Stahl Europe B.V) was used instead 180 g of one of the Examples from 1 to 3 (test product).

[0106] Applicative Examples 5 - 7, testing Examples 1 - 3, wet blue, dyed

[0107] On 600 g of chrome tanned leather, with shaved weight thickness of 1.1- 1.2 mm, was added into the drum an amount of 1200 g of water, 0.9 g of Eusapon® OC, and 3.0 g of oxalic acid and it was run for 30 min at 40°C. Next, the drum was drained. An amount of 1200 g of water at 38°C was added into the drum and it was run for 10 min. Next, the drum was drained. An amount of 900 g of water at 38°C and 30 g of BayChrom® FD was added and the drum was run for 120 min, followed by the addition of 12 g of Coralon® NL liq., 12 g of sodium formate. Next, the drum was run for 20 min. Now the pH was between 4.5 and 5.0. Next, 18 g of sodium bicarbonate was added and the drum was run for 60 min, now obtaining a pH between 6.0 and 7.0. Next, the drum was drained. An amount of 1200 g of water at 50°C was added and the drum was run for 10 min, after which the drum was drained. An amount of 900 g of water at 50°C and 60 g of Derminol® SO-31 liq. was added and the drum was run for 60 min, followed by the addition of 4.2 g of formic acid. The drum was run for 20 min and then drained. An amount of 1200 g of water at 20°C was added and the drum was run for 10 min, followed by draining the drum. An amount of 120 g of water at 20°C and 18 g of Inoderme® Brown Gol (anionic dye metal complex of cobalt; obtainable from Stahl Europe B.V) was added and the drum was run for 20 min. An amount of 180 g of one of the Examples from 1 to 3 (test product) was added and the drum was run for 120 min. Next, an amount of 900 g of water at 50°C and 6 g of formic acid was added and the drum was stirred for 20 min. Next, an amount of 6 g of formic acid was added and the drum was run for 20 min, followed by draining the drum. Next, an amount of 1200 g of water at 20°C was added and the drum was run for 10 min, followed by draining the drum.

[0108] Applicative Example 8, comparative, wet blue, dyed

[0109] The same process as in Applicative Examples 5-7 was followed, except that 180 g of Tanicor® PW liq. (phenol-based retanning agent, reference product) was used instead 180 g of one of the Examples from 1 to 3 (test product).

[0110] Applicative Examples 9 - 17, testing Examples 4 - 12, wet white, dyed

[0111] On 600 g of leather, that was tanned with Granofin® Easy F-90 (an organically based tanning agent, obtainable from Stahl Europe B.V), with shaved weight thickness of 1.1-1.2 mm, was added into the drum an amount of 1200 g of water, 0.9 g of Eusapon® OC, and 0.6 g of oxalic acid and it was run for 30 min at 40°C. Next, the drum was drained. An amount of 1200 g of water at 30°C and 12 g of Densodrin® DP (waterproofing auxiliary agent, obtainable from Stahl Europe B.V) was added into the drum and it was run for 20 min. Next, an amount of 12 g of Coralon® NL liq., 9 g of sodium formate and 108 g of one of the Examples from 4 to 11 (test product) was added and the drum was run for 20 min. Next, an amount of 30 g of Relugan® RV (acrylic polymer retanning agent, obtainable from Stahl Europe B.V) was added and the drum was run for 10 min. Next, an amount of 12 g of Relugan® Soft AP (fatliquoring agent, obtainable from Stahl Europe B.V), 12 g of Lipoderm® Liquor LA (natural fatliquoring agent, obtainable from Stahl Europe B.V) and 18 g of Lipoderm® Liquor E-Al (fatliquoring agent, obtainable from Stahl Europe B.V) was added and the drum was run for 10 min. Then 24 g of Inoderme® Light Brown NG (dyeing agent; obtainable from Stahl Europe B.V) was added and the drum was run for 10 min. Next, 108 g of one of the Examples from 4 to 12 (test product) was added and the drum was run for 20 min. Next, 420 g of water at 50°C and 6 g of formic acid was added and the drum was run for 30 min, followed by draining the drum. Then, an amount of 900 g of water at 35°C was added and the drum was run for 10 min, followed by draining the drum. Next, an amount of 600 g of water at 35°C, 3 g of sodium tripolyphosphate, 90 g of Densotan® A (water repellent, obtainable from Stahl Europe B.V) and 30 g of Relugan® RV (acrylic polymer retanning agent, obtainable from Stahl Europe B.V) was added to the drum and the drum was run for 10 min. Next, an amount of 144 g of one of the Examples from 4 to 12 (test product) was added and the drum was run for 40 min. Next, an amount of 600 g of water at 50°C and 9 g of Catalix®150 liq. (cationic fatliquoring agent, obtainable from Stahl Europe B.V) was added and the drum was run for 20 min. Next, an amount of 36 g of Relugan® Soft AP, 18 g of Lipoderm® Liquor E-Al and 12 g of Lipoderm® liquor LA was added and run for 120 min. Next, an amount 4.2 g of formic acid was added and the drum was stirred for 20 min. Next, an amount of 4.2 g of formic acid was added and the drum was run for 20 min, followed by draining the drum. Next, an amount of 900 g of water at 20°C was added and the drum was run for 10 min, followed by draining the drum.

[0112] Applicative Example 18, comparative, wet white, dyed

[0113] The same process as in Examples 9-17 was followed, except that Tanicor® PW liq. (phenol-based retanning agent, reference product) was used instead of one of the Examples from 4 to 12 (test product).

[0114] Example 19: evaluation of leather specimens Fullness, softness, fluffiness and handle or touch of re-tanned leathers were determined via haptics. Smoothness and fineness of the grain were determined via haptics. The tightness of the grain is an evaluation of the top layer of the leather once it is bended with two hands. The smoother the layer remains the tighter is the leather. The more wrinkles observed the lower the tightness. In all cases: lower numbers indicate better performance.

[0115] Aspects like uniformity of the dye, shades of the dye, bleaching effects or dye penetration can be evaluated after the dyeing of leathers. The uniformity of the dye, shades of the dye, bleaching effects were evaluated by optical appearance with numbers from one to six, with lower numbers indicating better appearance. The dye penetration was evaluated by cutting the leather with a knife and evaluating the completeness of the dye penetration optically. If the inner section of the leather had the same colour as the outer layer a value of 100% dye penetration was assigned. If the dye penetration was incomplete, the extent was reflected in a percent value. Results are collected in Table 2 and Table 3.

[0116] The leather specimens were also used for measuring the light fastness. The leathers were exposed to light in a sun tester for 24 hours according to ISO 105-B02, also known as the Xenotest. Leather samples were, after exposure to light, evaluated according to blue scale with numbers from 1 to 8. Larger number indicate less colour change and therefore more resistance to light induced ageing.

[0117] The leather specimens were also used for measuring the resistance to heat. The leathers were exposed to heat at 80°C for 72 h, according to ISO 105- A02. Leather samples were, after exposure to heat, evaluated according to the grey scale with numbers from 1 to 5. Larger numbers indicate more stability against.

[0118] The results of heat fastness and light fastness are collected in Table 4. Table 2. Scores of Applicative Examples 1 to 8 for various properties. 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.

[0119] The results obtained from specimens using Examples 1 to 3 showed better tightness and fullness than obtained with Comparative Example 4, wherein the specimen from Example 1 showed the best tightness. Examples 1 and 2 showed improved fluffiness. The results obtained from specimens from Applicative Examples 5 to 7 showed improved tightness and fullness, which is useful for structured leathers, compared with Comparative Example 8. Applicative Example 6 showed an uncomplete penetration, while Applicative Example 7 gave similar results as obtained with the Comparative Example. Table 3. Scores of Applicative Examples 9 to 18 for various properties. 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.

[0120] The results obtained from specimens from Applicative Examples 9 to 17 showed generally better scores for shade and bleaching than obtained with Comparative Example 18. Moreover, the leather specimens from Applicative Examples 9 to 17 were softer than obtained with Comparative Example 18.

[0121] Table 4. Heat induced ageing and lightfastness tests conducted on Examples 9, 10 and 11.

[0122] Light fastness is measured according to the blue wool scale which goes from 1 (fail) to 8 (very good). Heat induced ageing is evaluated according to the grey scale which goes to 1 (fail) to 5 (very good). 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.

[0123] Example 9 was made from glyoxylic acid, phenol and formaldehyde. Example 10 was made from glyoxylic acid, phenol and formaldehyde and contained anti-oxidant. Example 11 was made from glyoxylic acid, phenol, urea and formaldehyde. The results obtained from specimens showed improved lightfastness and heat stability for leather re-tanned with Examples 10 and 11 compared to that re-tanned with Example 9, demonstrating that the addition of anti-oxidant or the incorporation of urea in the polycondensates has beneficial effect on light fastness and on resistance to heat ageing.

Claims

CLAIMS1. Use of a composition for re-tanning leather in a leather manufacturing process, said composition comprising at least one glyoxyhc acid aromatic condensate compound comprising the structure of formula [I]wherein R is selected independently from each other from one or more OH, a hydrocarbon chain comprising an alkyl, aryl, heteroaryl and / or heteroalkyl group, wherein said alkyl group may be cyclic, linear or branched and is preferably a C1-C5 alkyl group, more preferably a C1-C3 alkyl group and n is an integer, in particular from 1 to 15, preferably from 1 to 10, more preferred from 1 to 5, and wherein the composition comprises between 10 and 100 weight% of glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] and wherein the amount of said compounds is calculated on the total weight of the composition, and wherein the remaining amount comprises other retanning agents, water and / or solvents and optional additives.

2. Use according to claim 1 wherein the composition comprises between 20 and 60 weight%, preferably between 30 and 50 weight% of glyoxyhc acid aromatic condensate compounds comprising the structure of formula [I] and wherein the amount of said compounds is calculated on the total weight of the composition, and wherein the remaining amount comprises other re-tanning agents, water and / or solvents and optional additives.

3. Use according to claim 1 or 2, wherein the glyoxyhc acid aromatic condensate compounds are obtained from the reaction of aromatic moieties with glyoxylic acid, preferably by acid catalyzed condensation, in a molar ratio of the glyoxyhc acid to the aromatic moieties between 5:1 to 0.5:1, preferably between 4:1 to 0.5:1 and most preferably 3:1 to 0.6:1.

4. Use according to any of foregoing claims wherein the composition is solid, preferably a powder.

5. Use according to any of foregoing claims 1-3 wherein the composition is liquid at ambient conditions (atmospheric pressure and a temperature of 25°C), preferably said composition is an aqueous composition.

6. Use according to any of foregoing claims, wherein between 2% and 30 weight%, and preferably in an amount of between 5% and 25 weight%, and most preferably in an amount of between 8% and 20 weight%, relative to the weight of the hides / leather, of glyoxylic acid aromatic condensate compounds comprising the structure of formula [I], taking into account only the non-volatile components, is used.

7. Use according to any of foregoing claims wherein the composition comprises glyoxylic acid aromatic condensate compounds which are crosslinked glyoxylic acid aromatic condensate compounds according to formula [II] and which are obtained by cross-linking the glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] with aldehydeswherein R and R1independently from each other are selected from one or more OH, a hydrocarbon chain comprising an alkyl, aryl, heteroaryl and / or heteroalkyl group, wherein said alkyl group may be cyclic, linear or branched and is preferably a C1-C5 alkyl group, more preferably a C1-C3 alkyl group, n is an integer, in particular from 1 to 15, m is an integer, in particular from 1 to 10, preferably from 1 to 6 and y is an integer from 1 to 2.

8. Use according to any of foregoing claims wherein the composition comprises glyoxylic acid aromatic condensate compounds which are organic - bridged cross-linked glyoxylic acid aromatic condensate compounds according to formula [III] and which are obtained by cross-linking the glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] with aldehydes combined with urea compoundswherein R and R1independently from each other are selected from one or more OH, a hydrocarbon chain comprising an alkyl, aryl, heteroaryl and / or heteroalkyl group, wherein said alkyl group may be cyclic, linear orbranched and is preferably a C1-C5 alkyl group, more preferably a C1-C3 alkyl group, n is an integer, in particular from 1 to 15, preferably from 1 to 10, more preferred from 1 to 5, m is an integer, in particular from 1 to 10, preferably from 1 to 6, k is an integer, in particular from 0 to 10, preferably from 0 to 6 and y is an integer from 1 to 2.

9. Use according to any of foregoing claims wherein the glyoxylic acid aromatic condensate compounds comprising the structure of formula [I] are obtained by reaction glyoxylic acid and aromatic moieties wherein the reaction temperature is between 40°C and 120°C, and wherein the aromatic moieties are selected form the list consisting of phenol, cresol, naphthol, cathecol, resorcinol, hydroquinone, naphthalene, biphenyl, fluorene, anthracene, phenanthrene, phenalene, tetracene, chrysene, triphenylene, pyrene, pentacene, perylene, benzo [a]pyrene, corannulene, benzo[ghi]perylene, coronene, ovalene, benzo [c]fluorene, orcinol, 3- methylcathecol, 4-methylcathecol, 2-methylbenzene-l,3-diol, 4- methylbenzene-l,3-diol, 2-methylbenzene-l,4-diol, ethylbenzene, mesitylene, durene, 2 -phenylhexane, xylenol, xylene, isopropyl naphthalene, ditolyl ether or any combination thereof.

10. Use according to any of foregoing claims wherein the cross-linked glyoxylic acid aromatic condensate compounds according to formula [II] and / or organic -bridged cross-linked glyoxylic acid aromatic condensate compounds according to formula [III] are obtained from reacting the glyoxylic acid aromatic condensate compounds having the structure according to formula [I] with an aldehyde compound or an aldehyde compound and urea and wherein the reaction temperature is between 40°C and 120°C, and wherein the aldehyde compound is selected form the list consisting of formaldehyde, furfural, hydroxymethylfurfural, benzaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isovaleraldehyde,cinnamaldehyde, vanillin, tolualdehyde, retinaldehyde, glycolaldehyde, glyoxal, glutaraldehyde, malondialdehyde, succindialdehyde, phthalaldehyde or any combination thereof.

11. Use according to any of foregoing claims wherein the cross-linked glyoxylic acid aromatic condensate compounds according to formula [II] and / or organic-bridged cross-linked glyoxylic acid aromatic condensate compounds according to formula [III] are obtained by cross-linking and / or organic bridging the glyoxylic acid aromatic condensate compounds having the structure according to formula [I] with an aldehyde compound or an aldehyde compound and urea and wherein the molar ratio of the aromatic moieties and the aldehyde compound ranges between 8:1 to 1:1 and the molar ratio of the urea and the aldehyde compound ranges between 1:1 to 0.1:1.

12. Use according to any of foregoing claims wherein the glyoxylic acid aromatic condensate compounds having the structure according to formula [I] are obtained by acid catalyzed condensation of glyoxylic acid and aromatic moieties, optionally followed by a cross-linking reaction with aldehydes or aldehydes combined with urea and wherein the aromatic moiety is phenol and the aldehyde, when present, is formaldehyde.

13. Use of the re-tanning composition according to any of foregoing claims as a re-tanning composition in a re-tanning step for leather in a leather manufacturing process for improving the fluffiness, shade, bleaching and / or softness of tanned leather.

14. Use according to claim 13 wherein the glyoxylic acid aromatic condensate compounds comprising the structure according to formula [I] and optionally organic -bridged and / or cross-linked are used in an amount ofbetween 2% and 30 weight%, and preferably in an amount of between 5% and 25 weight%, and most preferably in an amount of between 8% and 20 weight% relative to the weight of leather and wherein the percentages refer to the weight percentage of the non-volatile part of the re-tanning composition.

15. Leather obtained after using the re-tanning composition according to any of claims 1-14.

16. Use of the leather obtained after using the re-tanning composition according to claims 1-14.

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