IMPROVED LEATHER

Abstract: Leather products that are well lubricated, impermeable and water-repellent are produced by impregnating tanned hides or skins under alkaline conditions with an aqueous emulsion of a mixture of alkyl or alkenyl carboxylic acids or anhydrides containing at least 16 carbon atoms, and in particular polyisobutenyl succinic acid or its anhydride containing at least 30 carbon atoms, and fatty acids in specified proportions followed by retaining with basic solutions or with the emulsion which is also covered may additionally contain fatty acids.

Description: Improved Leather In our European Patent Application 89300038.0 we describe well lubricated leather which may also be impermeable, and water-repellent, in addition the leather can have improved fullness. That Application also describes a process for producing such leather which does not significantly change the normal tanning cycle, it also relates to new emulsions which may be used in this process. Products and processes for waterproofing leather have been described for example fluorinated compounds, chromium stearate esters and silicone derivatives have been proposed to impart impermeability to water. However, only exceptionally do such substances have the property of inducing good lubrication of the leather fibre and on no account have they been found to simultaneously impart impermeability, water-repellence and lubrication. Lubrication apart, impermeable leather is not always water-repellent and vice versa, as impermeability is associated with molecular transformation of the water-absorbing loci into water-repellent loci whilst water-repellence is only due to actual depositing (impregnation) of a water repelling agent between the fibres of the skin, without any reaction. Impermeable leather, lacking water-repellent properties, will become considerably wet on the surface when in contact with water before inhibiting penetration of the water. Hitherto, water-repellent properties have been obtained by a hydrophobic coating however, the movement of the leather during use, will displace this coating, with consequent loss of the water-repellent properties. For this reason, water-repellent leathers do not respond well to the I.U.P. 10 dynamic impermeability test. Moreover, it is well known that leathers can lose their impermeability or water repellent properties or lubrication when washed with surfactants or solvents. In the tanning process leather is generally treated with a strong acid such as sulphuric acid and then with a metal tanning agent generally based on chromium or aluminium compounds. This tends to result in the leather retaining a positive charge particularly in the bulk of the leather even if the surface is subsequently neutralised. Previous proposals have been made, for Example in United States Patents 3770372 and 3784400, that leather may be lubricated with emulsions of alkyl or alkenyl succinic acids or anhydrides which may also contribute to the waterproof properties of the leather. These processes would result in a hydrophobic product with no impermeability because the alkenyl succinic acid or anhydride remains only deposited on the surface of the leather (without penetrating the whole leather thickness) which is instead necessary to obtain a good leather impermeability and lubrication. The process of United States Patent 3784400 uses amines (such as morpholine) as emulsifiers for the alkyl or alkenyl succinic anhydride. In United States Patent 3770372, the alkyl or alkenyl group contains an average of 12 to 18 carbon atoms whilst in United States Patent 3784400, the alkenyl group contains from 12 to 24 carbon atoms. In United States Patent 3770372 the materials are applied under acidic conditions to leather without any prior neutralisation. This leads to two problems: (a) there is only a superficial bonding of the alkyl or alkenyl succinic anhydride to the metal tanning agent which is extremely reactive in acidic conditions . This does not result in any good impermeability and lubrication. (b) the alkyl or alkenyl succinic anhydride precipitates in acidic conditions onto the leather surface causing unacceptable staining thereof, as shown in Example 3 of U.S. Patent 3784400. Leather fullness is a very important property. Fullness is the bulkiness of the skin and any loss of fullness leads to a thinner, harder, inflexible and unattractive skin with an undesirable bouch. Fullness is provided by products that, after having fully penetrated the leather bulk, are fixed into the leather structure. According to European Patent Application 89300038.0 if tanned leather is treated with an emulsion of an organic carboxylic acid or anhydride or derivative thereof under alkaline conditions so that reaction of the carboxylic acid or anhydride and the metal ions in the tanned leather is impeded there is greater penetration into the leather by the product. Subsequent acidification ensures an effective bond between the acid and the leather resulting in a significant improvement in the lubrication and fullness of the leather. It is also stated that this is particularly so when the organic carboxylic acid or anhydride, is a polyalkenyl preferably, a polyisobutenyl succinic anhydride containing at least 30 preferably at least 40 carbon atoms in the polyalkene chain. After this treatment the leather is not yet impermeable. Impermeability is obtained only after retanning with metal tanning agents such as chromium or aluminium salts, which may take place after any dyeing or colouration step. In European Patent Application 893000380.0 we also described the treatment of leather with blends of the alkyl or alkenyl succinic anhydride and fatty acids. In the development of this technology we have found that in order to obtain optimum surface finish for .the leather the ratio of the alkyl or alkenyl succinic anhydride to the fatty acids is important and should be higher than that disclosed in EP 89300038.0. In addition this permits a reduction in the amount of emulsifier, which leads to improved water repellancy of the leather. The use of higher amounts of fatty acids can also overcome some surface cracking problems particularly with thick leather. We have also found that, by using the techniques of the present invention, the bonds between the acid or anhydride and the leather and the retanning agent are sufficiently strong that the improved properties of the final leather are retained over many cycles of washing with solvents and surfactants. Thus, according to one aspect of the present invention, tanned leather is treated with an aqueous emulsion of a mixture of an alkyl or alkenyl carboxylic acid or anhydride or derivative thereof whose alkyl or alkenyl group contains at least 16 carbon atoms from 15% to 60% by weight fatty acids under alkaline conditions of a PH from 9 to 10 and, after treatment such as vegetable or synthetic resins secondary retanning and any colouring, the system is acidified to enable bonding of the acid or anhydride to the leather or the tanning agents contained therein. This process of the invention is not simply an impregnation but a full penetration into the hide followed by a chemical reaction between the dermic material and/or the tanning agent and the carboxylic acid or anhydride. In a preferred aspect of the process of the invention the leather obtained by the process described above is further retanned with metal salts to achieve water-repellent and water proofing properties. In another aspect the invention provides tanned leather impregnated with a " mixture of a polyalkenyl succinic acid or anhydride or derivative thereof particularly a polyisobutenyl succinic anhydride in which the polyalkenyl group contains at least 25 preferably at least 30 carbon atoms and fatty acids, said mixture containing from 15 to 60% by weight of fatty acids. Also provided is such impregnated leather which has been retanned with the metal salts. In another aspect, the invention provides the use of an emulsion of a mixture of alkyl or alkenyl carboxylic acid or anhydride or derivative thereof in which the alkyl or alkenyl group contains at least 16 carbon atoms and from 15% to 60% by weight based on the weight of the mixture of fatty acids in the treatment of leather under alkaline conditions. The alkyl or alkenyl carboxylic acids or anhydrides used in the present invention are preferably alkyl or alkenyl derivatives of dicarbox lic acids or anhydrides the preferred materials being alkyl or alkenyl succinic acids or anhydrides whose alkyl or alkenyl group contains at least 16 carbon atoms. We have found that polypropenyl or polybutenyl succinic acids containing at least 30 especially at least 60 carbon atoms in the polypropenyl or polybutenyl group are particularly useful. The materials may be acids or anhydrides or their derivatives such as the sulphonated derivative thereof. Where dicarboxylic products are used it is believed t at once the product has fully penetrated the hide, the subsequent acidification enables one carboxyl group to bond with the metal tanning agents in the leather leaving free carboxyl ^ groups. These may partake in subsequent reactions such as final retanning with metal salts which has been found to give such a significant improvement in waterproofing and water repellanc . Saturated and unsaturated monocarboxylic acids may also be used but it is preferred that they be used in combination with an aldehyde such as formaldehyde, acetaldehyde, or glutaraldehyde to enable subsequent Mannich reaction between the naturally occurring amino groups in the leather and the methyl groups of the acid or a double bond in an unsaturated acid, so again providing free carboxyl groups for further reactions after penetration and acidification. Examples of suitable fatty acids useful in the mixtures of this invention are mono-carboxylic acids such as stearic, oleic, palmitic acids and tall oil fatty acids or mixtures thereof. Mixtures of mono and di-carboxylic acids may also be used and we have found a mixture of Cg to C19 mono and di-carboxylic acids to be particularly useful. The acid mixtures of this invention are applied to the leather as aqueous emulsions and any suitable non-ionic, cationic or anionic emulsifier may be used. We prefer to use a non-ionic emulsifier and have found that ethoxylated and propoxylated emulsifiers are particularly useful, especially polymers and copolymers of ethylene oxide and propylene oxides, propoxylated emulsifiers being preferred due to their biodegradability. Compounds such as alcohols, glycols and acids such as citric or tartaric acid may be used, glutaraldehyde is another preferred, emulsifier, examples of other emulsifiers are the cationic sulphonates, and the anionic amine sulphonates. Care must be taken in the manufacture of the emulsion, it is preferred to use a system containing as little emulsifier as possible since many emulsifiers are hydrophilic and although the leather is washed after treatment some emulsifier remains in the leather which reduces the ' waterproofness. We have found that the fatty acids used in the present invention act also as co-emulsifiers and not only reduce the need for traditional emulsifiers but if used in the proportions of this invention allow a better product penetration which contributes significantly to improve the surface finish of the leather. In a preferred process, the polyalkenyl succinic acid or anhydride emulsion is prepared by mixing water, emulsifier (preferably an alkoxy emulsifier) and ammonium hydroxide at typically 60°-80°C for from 5-20 minutes and blending this ( emulsion with a component obtained by mixing water, fatty acids and ammonium typically at 40°C for from 5-20 minutes. A preferred emulsion contains for 1000 parts by weight of the alkyl or alkenyl carboxylic acid or anhydride or derivative thereof from 150 to 600 parts by weight of fatty acids, from 300 to 1000 parts by weight of water, from 50 to 200 parts by weight of emulsifier and sufficient base, preferably ammonia, to ensure the PH is in the range 9 to 10. The treatment by the aqueous emulsion may be carried out using the typical drumming techniques used for leather treatment. In the leather treatment typically the tanned leather is in a drum in water at about 50°-60°C at a pH from 5-6. According to this invention, the pH in the drum is raised to about 9 to 10 preferably by the addition of aqueous, ammonia although other bases such as amines, inorganic hydroxides, carbonates and bicarbonates may be used or a mixture of them may be used. Generally from 5-15 wt% of the formulation of this invention based on the weight of the tanned, shaved skins is used. The secondary retanning is a conventional process to provide reactive fillers to increase the thickness and fullness of the leather. Suitable materials are vegetable tanning (e.g. wattle, chestnust, quebracho) or synthetic retanners or resins. The process of the present invention produces well lubricated leather, furthermore when the polyalkenyl materials containing more than 30 carbon atoms the lubricated leather has notably improved fullness. However, the well lubricated leather is water absorbing owing to the presence of free carboxylic groups. If a sulphonated carboxylic acid has been used the sulphonic group which is not coupled can also have an influence on the water- absorbing properties of the material. A further final tanning treatment (after dyeing and retanning with synthetic or vegetable tanning or resins) with metal salts such as chromium or aluminium basic salts block these groups and produce leather which, after appropriate washing and drying, is impermeable as well as well lubricated and extremely full. The retanning with chromium or aluminium salts may not, however, impart the ultimate water-repellent characteristics because the treated leather may contain some residual carboxylic acid or carboxylic acid metal salt complex within the body of the leather. These are often bonded to the leather by hydrogen bonding and water repellancy may be further improved by a treatment to destroy the hydrogen bonding which encourages migration to the surface of the leather to impart water repellency. For example treatment with methylene chloride optionally together with water is very effective. Alternatively the leather retanned with metal salts may be treated with a surfactant, followed by contact with a basic ammonia solution for approximately 15 minutes . Thus to summarise treatment of tanned leather under alkaline conditions prevents the chromium or any other tanning metal bonding with the acids, anhydrides or their derivatives and therefore, in contrast to what is described by other authors, mixtures of alkyl or alkenyl carboxylic acids from Cig, in particular polyalkyl succinic acids or anhydrides or their derivatives, and fatty acids in the right proportions can penetrate deep into the structure of the skin. When this has been achieved the acid may be fixed to the metal tanning agent by final acidification, which can also fix the dyes and the organic re-tanning agents used during the treatment. Treatment of the leather under alkaline conditions according to this invention enables the use of aqueous emulsions of the acids anhydrides or derivatives of emulsifier:acid ratios of 1:50. Choice of suitable surfactants also makes it possible to operate in baths having the same and even a greater dilution than that usually used in the leather dyeing, re-tanning and oiling process. The invention also enables the production of leathers which are well lubricated, impermeable and water-repellent having improved fullness and touch at low cost, in contrast with existing agents, such as those used to impart impermeability and water-repellent properties to leather, whose cost is often extremely high. In addition the invention enables the production of lubricated, impermeable and water-repellent leathers which do not lose these properties after washing or dry cleaning and ageing. The following Examples use a polyisobutylene succinic anhydride from Exxon Chemical whose polyisobutylene group contained an average of 96 carbon atoms. Example 1 An alkaline solution of 45 g of sodium carbonate or corresponding equivalent amount of ammonia and 100 g of a mixture of ethylene oxide and propylene oxide dissolved in 450 ml of water was added to 1 kg of the polyisobutenyl succinic anhydride. The compound which is made alkaline by the addition of ammonia (pH 9.5 to 10.5) was found to be perfectly emulsifiable in water up to a ratio of 1:50. 800 grams of a mixture of mono and di-carboxylic fatty acids ranging from Cς - C19 is added. slowly under agitation to an aqueous solution containing 1000 ml of ammonium hydroxide at 50°C until pH 9.5 to 10.5 is attained. These two systems were then mixed. Chrome leather which had not been neutralized, is treated at a pH 9 to 10 in a revolving drum with 200 wt% based on weight of leather of an alkaline solution containing 20- 25g/litre of ammonium hydroxide. The drum is allowed to revolve for 20-30 minutes and then 5 to 15 wt% based on the drum content of the emulsion of the mixture of alkyl succinic acid and fatty acids is added. The drum is allowed to revolve from 40 minutes to 2 hours depending on the thickness of the hides or skins, then the pH is brought to 7-7.5 by the addition of formic acid and the required quantity of dye is added. This is followed by re-tanning with organic compounds and treatment with formic acid until a pH value of 3-3.5 is reached. The bath is discarded and the leather is re-tanned with 8-10% of chromium salt in 80% of water. The drum is allowed to revolve for approximately 40 minutes to 1 hour and 30 minutes depending on the thickness of the hides or skins. Basification is carried out to pH 5 with a dilute solution of sodium bicarbonate. The bath is discarded and the hides or skins are washed continuously for approximately 20 minutes to wash out the water-absorbing substances being present on the surface of the leather. The hides or skins are dried and then re-finished in the usual manner. The wet hides or skins can be treated with a mixture of 10% water and 5% methylene chloride for approximately 20 minutes to further improve impermeability.

Claims: CLAIMS 1 A process comprising treating tanned hides or skins with an aqueous emulsion of a mixture of an alkyl or alkenyl carboxylic acid or anhydride or derivative thereof containing at least 16 carbon atoms in the alkyl or alkenyl group and from 15% to 60% by weight of fatty acids in which the treatment is carried out at a pH from 9 to 10 and subsequently acidifying the treated hides or skins. 2 A process according to claim, 1. in which the alkyl or alkenyl carboxylic acid or anhydride is a dicarboxylic acid or anhydride. 3 A process according to claim 1 in which the carboxylic acid is monocarboxylic acid and is used in combination with an aldehyde. 4 A process according to any of the preceding claims in which the aqueous emulsion comprises water, the carboxylic acid, anhydride or derivative thereof, the fatty acids and an emulsifier. 5 A process according to any of the preceding claims in which the treated hides or skins is retanned with metal salts to fix the acids used in the treatment as well as dyes and organic retanning agents. 6 A process according to claim 5 in which the treated hides or skins is finally retanned with chromium or aluminium salts. 7 A process according to claims 5 or 6 in which subsequent to retanning the retanned hides or skins is treated with an agent to destroy the hydrogen bonding between the carboxylic acid or anhydride or any derivative thereof and the leather. A process according to claim 7 in which the agent is methylene chloride. Treated hides or skins whenever produced by a process according to any of the preceding claims . Tanned hides or skins impregnated with a mixture of a polyalkenyl succinic acid or anhydride or derivative thereof in which the polyalkenyl group contains at least 16 carbon atoms and from 15% to 60% by weight of fatty acids.. The retanned hides or skins of claim 10. The use in the treatment of tanned hides or skins under alkaline conditions of an emulsion of a mixture of a polyalkenyl succinic acid or anhydride or derivative thereof in which the polyalkenyl group contains at least 16 carbon atoms and from 15% to 60% by weight of fatty acids. The use according to claim 12 in combination with fatty acids.

Inventors: MANZO GIOVANNI, MANZO, GIOVANNI
Applicants: EXXON CHEMICAL PATENTS INC, MANZO GIOVANNI, EXXON CHEMICAL PATENTS INC.
Application year: 1993
Main classification: C14C9
IPC codes: C14C9