PROCESS FOR TANNING LEATHERS, PRE-TANNING PRODUCTS AND USE THEREOF

Abstract

A process for tanning leathers including a pre-tanning step and a tanning step is provided. In the pre-tanning step leathers are treated with a cationic active agent including a quatemized ester of a fatty acid and triethanolamine, or mixtures thereof and, subsequently, with an anionic active agent including tannins vegetable extracts and a natural or synthetic dispersant selected from the group consisting of lignosulfonates, distillation stillages, sulfonated disulfonic polymers, sulfonated naphthalene polymers or mixtures thereof, to obtain leathers with a shrinkage temperature of at least 65° C. The pre-tanning and tanning steps do not include treatment with aldehydes or aldehyde donor compounds and/or with metal salts.

Claims

1. A process for tanning leathers, the process comprising a pre-tanning step and a tanning step, wherein in the pre-tanning step the leathers are treated with a cationic active agent comprising a quaternized ester of a fatty acid and triethanolamine, or mixtures thereof and, subsequently, with an anionic active agent comprising tannins vegetable extracts and a natural or synthetic dispersant selected from the group consisting of lignosulfonates, distillation stillages, sulfonated disulfonic polymers, sulfonated naphthalene polymers or mixtures thereof, to obtain leathers with a shrinkage temperature of at least 65° C., and wherein said pre-tanning and tanning steps do not include a treatment with aldehydes or aldehyde donor compounds and/or with metal salts.

2. The process of claim 1, wherein the tanning step comprises a treatment of pre-tanned leathers with an anionic active agent having a chemical nature corresponding to that used in the pre-tanning step.

3. The process of claim 1, wherein the cationic active agent is a solution comprising a dialkyl ester of triethanolamine methyl sulfate in which alkyl is a linear or branched group having from 12 to 24 carbon atoms.

4. The process of claim 1, wherein the cationic active agent is a compound selected from the group consisting of distearoylethyl hydroxyethylammonium methyl sulfate (Esterquat 75), a mixture of distearoylethyl hydroxyethylammonium methyl sulfate with cetearyl alcohol (Dehyquart F75) and docosanyltrimethylammonium methyl sulfate and mixtures thereof.

5. The process of claim 1, wherein the cationic active agent is a solution comprising a solvent selected from the group consisting of water, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, terbutanol, glycerin, ethoxylated alcohols, propoxylated alcohols, hydroformylation products of alkenes or mixtures thereof and optional dispersing additives selected from the group consisting of sodium lauryl sulfate, ethoxylated castor oil (40 moles) sulphosuccinate, monoesters of C.sub.12-C.sub.14 oxoalcohols or mixtures thereof.

6. The process of claim 1, wherein the anionic active agent comprises hydrolyzable tannins of gallic type.

7. The process of claim 6, wherein the hydrolyzable tannins comprise an extract selected from the group consisting of liquid extract of Tara, liquid extract of Chinese gall, liquid extract of Turkish gall and liquid extract of chestnut or mixtures thereof.

8. The process of claim 1, wherein in the anionic active agent, the dispersant is selected from liquid quebracho sulfited extract and liquid ammonium lignosulfonate.

9. The process of claim 1, wherein in the anionic active agent, the dispersant is selected from “benzene-sulfonic acid, hydroxy-, monosodium salt, reaction products with formaldehyde and sulfonylbis(phenol), sodium salts” (CAS No. 90718-44-3) and “naphthalenesulfonic acids, reaction products with formaldehyde” (CAS No. 97078-68-1) and mixtures thereof.

10. The process of claim 1, wherein the anionic active agent comprises tannins vegetable extracts and dispersants in a ratio of from 1:3 to 1:20, in a polar solvent, said ratio being expressed as a weight ratio between a 45-50% solution of vegetable extract and dispersant.

11. The process of claim 10, wherein the polar solvent is selected from the group consisting of glycerin, monopropylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, methoxylated, ethoxylated or propoxylated derivatives thereof, water and mixtures thereof.

12. The process of claim 1, wherein the tanning step comprises using, as tanning agents, natural tannins, optionally in combination with synthetic tannins and optionally acrylic polymers.

13. A composition of an anionic active agent, for pre-tanning of leathers, comprising a tannin vegetable extract or a mixture thereof and a natural or synthetic dispersant selected from the group consisting of lignosulfonates, distillation stillages, sulfonated disulfonic polymers, sulfonated naphthalene polymers or mixtures thereof.

14. The composition of claim 13, wherein the tannin vegetable extract is an extract selected from the group consisting of liquid extract of Tara, liquid extract of Chinese gall, liquid extract of Turkish gall, liquid extract of chestnut and mixtures thereof.

15. The composition of claim 13, further comprising a synthetic dispersant selected from “benzenesulfonic acid, hydroxy-, monosodium salt, reaction products with formaldehyde and sulfonyl bis(phenol), monosodium salts” and “naphthalenesulfonic acids, reaction products with formaldehyde” or mixtures thereof.

16. The composition of claim 13, wherein said tannin vegetable extract and said dispersant are in a weight ratio from 1:3 to 1:20, said ratio being expressed as a weight ratio of a solution made of 45-50% of vegetable extract and dispersant.

17. A method for tanning leathers, comprising a pre-tanning treatment, wherein a cationic active agent comprising a quaternized ester of a fatty acid and triethanolamine is used in said pre-tanning treatment.

18. Tanned leathers substantially free from aldehydes, aldehyde donor compounds and/or metal salts deriving from tanning or pre-tanning, obtained by the process of claim 1.

Description

DETAILED DESCRIPTION

The Cationic Product

[0028] The cationic product contains an active substance belonging to the family of quaternary ammonium salts, in particular a quatemized ester of a fatty acid and triethanolamine. The quatemizing agent is typically dimethyl sulfate, but other quaternizing agents may be used. Preferably, the cationic product contains a dialkyl ester of triethanolamine methyl sulfate, in which the alkyl is linear or branched and has 12 to 24 carbon atoms, also known as dialkyl dihydroxyethylammonium methyl sulfate or esterquat. Within this family, the following substances are of particular interest: [0029] distearoylethyl hydroxyethylammonium methyl sulfate (also known as distearoylethyl hydroxyethylamonium methosulfate) or (2-hydroxyethyl)methylbis[2-[(1-oxooctadecyl)oxy]ethyl]ammonium methyl sulfate (also commercially known as Esterquat 75); [0030] disteaoroylethyl hydroxyethylammonium methyl sulfate mixed with cetearyl alcohol (also commercially known as Dehyquart F75); and [0031] docosanyltrimethylammonium methyl sulfate (also known as docosyltrimethylammonium methyl sulfate).

[0032] The active substances described are part of a class of non-toxic and plant-derived substances deriving from the fatty acids of vegetable oils, such as rapeseed oil or coconut oil. These substances are typically used as cationic surfactants and conditioning agents in cosmetic products, mainly in shampoos.

[0033] Quaternary ammonium ions with long-chain substituents have characteristics of surfactants and for this reason, depending on the substituents present, they are used as detergents and as biocides. The products of particular interest for use according to the invention are known and generally used as fabric softeners or as hair conditioners.

[0034] The above cationic products may for example be prepared by the process described in U.S. Pat. No. 5,705,663, which relates to a process for the production and use of quatemized esters of fatty acids and triethanolamine, prepared from triethanolamine, fatty acid, fatty acid ester and a quaternizing agent. According to what has been published, the quatemized esters of fatty acids and triethanolamine thus prepared may be used to produce laundry softeners having a high active content, resistant to rinse cycles and particularly stable in viscosity during storage.

[0035] The production process is also reported, for example, in U.S. document 2002/0002298, where a process for the production of esterquats is described in which triglycerides are transesterified with alkanolamines and the resulting alkanolamine esters of fatty acids are subsequently quaternized with alkyl halides or dialkyl sulfates in the presence of solvents, characterized in that the glycerol released during transesterification is continuously removed from the reaction equilibrium.

[0036] As mentioned, these substances are known and used as surfactants and for their softening properties. These are mainly used on fabrics and hair. In some cases, it is known that they may also be used as softeners for finished leathers, but exclusively as touch modifiers for chrome leathers, as products with which to treat leathers after tanning and only to impart softness in the fattening step. In no case have they already been described to prepare the leather for tanning in the pre-tanning step, so that it is more reactive to the products used.

[0037] In order to facilitate its use in the process according to the invention, the cationic active substance product is preferably formulated in a formulation comprising a solvent (for example: water, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, terbutanol, glycerin, ethoxylated alcohols, propoxylated alcohols, hydroformylation products of alkenes or mixtures thereof) and dispersing additives compatible with water (for example: sodium lauryl sulfate, castor oil ethoxylate 40 moles, sulphosuccinate, monoesters of C12-C14 oxoalkols or mixtures thereof). The solvent and the dispersing additives also have the function and the advantage of improving the stability over time, ease of dispersion in water and effectiveness.

The Anionic Product

[0038] The anionic product may be in liquid version or powder version. The latter is obtained by removing water from the liquid form, conveniently by a spray-drying process. The anionic product in liquid version should preferably include the following components (parts by weight): [0039] 1 part of tannins vegetable extracts in aqueous solution preferably at 45-50% dry, [0040] 3 to 20 parts of dispersants, and [0041] 0 to 1 part of solvents or stabilizers.

[0042] The tannins vegetable extracts which may be used for the present technology may comprise hydrolyzable or condensed tannins, optionally also in addition to other vegetable tannins, but conveniently they are hydrolyzable type tannins, especially of the gallic type.

[0043] More preferably, the following extracts and their mixtures are used: [0044] liquid extract of Tara, preferably obtained with the following procedure: extract the pods of Peruvian Tara (Caesalpinia spinosa) with ethanol (e.g. 80% Vol.). The extract obtained is removed from the solvent with a stripping process with water. The product obtained is concentrated under vacuum to eliminate the water up to preferably 44-46% of dry matter. The minimum content of tanning substances, according to the ISO14088 method, is preferably between 96 and 98% on a dry basis; [0045] liquid extract of Chinese gall, preferably obtained as the previous one, but by extracting Chinese galls, natural growths produced from the leaves of the Chinese sumac plant (Rhus chinensis), and ground. The minimum content of tanning substances, according to the ISO14088 method, is preferably higher than 98% on a dry basis; [0046] liquid extract of Turkish gall, preferably obtained as the previous one, but extracting Turkish galls, natural growths produced from the bark of the Aleppo oak plant (Quercus infectoria), and ground. The minimum content of tanning substances, according to the ISO14088 method, is preferably higher than 98% on a dry basis; and [0047] liquid chestnut extract, preferably obtained by extracting chestnut wood (Castanea sativa) with hot water and concentrating under vacuum to eliminate the water up to preferably 46-48% dry matter. The minimum content of tanning substances, according to the ISO14088 method, is preferably between 78 and 80% on a dry basis.

[0048] The dispersants are preferably natural and synthetic polyphenols. Among the natural dispersants, lignosulfonates, distillation stillages or mixtures thereof may be mentioned by way of non-limiting example.

[0049] Lignosulfonates derive from the cellulose production process in the paper industry.

[0050] Distillation stillages are residues from the distillation of alcoholic musts deriving from the fermentation processes of various agricultural products which may be grapes, potatoes, cereals, beet molasses or other sugary raw materials, such as those used in bioethanol production processes.

[0051] It is particularly convenient to use liquid quebracho sulfited extract and liquid ammonium lignosulfonate, both in aqueous solution preferably at 45-50% dry. Among the synthetic dispersants it is preferable to use sulfonated disulfonic polymers [also defined as “Benzenesulfonic acid, hydroxy-, monosodium salt, reaction products with formaldehyde and sulfonylbis[phenol], sodium salts” (CAS no. 90218-44-3)], sulfonated naphthalene polymers [also defined as “Naphthalenesulfonic acids, reaction products with formaldehyde” (CAS no. 91078-68-1)] or mixtures thereof. It is particularly convenient to use a liquid sulfonated disulfonic polymer, aqueous solution at 45-50% dry.

[0052] The solvents are preferably polar solvents with a stabilizing effect; non-limiting examples are: glycerin, monopropylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, methoxylated, ethoxylated and propoxylated derivatives of the above, water or mixtures thereof. Particularly suitable is a 50/50 mixture of water and monopropylene glycol.

Embodiment Examples of the Technology

Example 1

[0053] Preparation of the cationic product. In a mixer, load the following percentages by weight in order:

TABLE-US-00001 distearylethyl hydroxyethylammonium methyl sulfate 44% isopropanol  4% oxoalcohols C12-14 2.5%.

[0054] Slowly heat up to 45° C. for 30′, start stirring, then add the following water 4 times:

TABLE-US-00002 water 49.5%.

[0055] Keep stirring for 60 minutes and check for lumps. The appearance of the product at 20° C. and 35° C. is an ivory white paste, at 10% in water it looks like a semi-transparent-semi-milky emulsion. The cationic product thus formulated may be used in a percentage by weight with respect to the weight of the leather in pickle from 0.5 to 7%, preferably from 1 to 4%, conveniently from 2 to 3%.

Example 2

[0056] Preparation of the anionic product in liquid form. The components indicated below must be conveniently added in the order shown in a mixer suitable for homogenization at room temperature. The percentages are by weight:

Dispersants, Aqueous Solutions at 45-50% Dry:

[0057]

TABLE-US-00003 sulfonated disulfonic polymer 63.3%  sulfonated naphthalene polymer  18% tannins vegetable extracts, aqueous solutions at 45-50% dry: liquid extract of Chinese gall 2.6% liquid extract of Turkish gall 4.4% solvent: water and monopropylene glycol 50/50 11.7%. 

Example 3

[0058] Preparation of the anionic product in powder form.

[0059] Feed the atomizer with the liquid product prepared as described in Example 2. Maintain the feed flow of the liquid product and the temperature of the air entering the atomization chamber so that the temperature of the air leaving is 90±2° C. As an alternative to the atomizer, other types of evaporators may be used, such as freeze dryers, vacuum atomization evaporators, falling film evaporators with solid scraping system. Approximately 2.4 kg of liquid product are required to obtain 1 kg of powder product. The anionic product in powder form thus produced may be conveniently used in a weight percentage with respect to the weight of the leather in pickle from 8 to 25%, preferably from 12 to 20%, reasonably from 15 to 18%.

Example 4

[0060] Below is a recipe for pre-tanning leather in a drum of the experimental tannery using the technology described. The percentages of the products to be used refer to the weight of the leather in pickle loaded into the drum, which also corresponds to the weight of the pelt.

[0061] Load into the drum: [0062] 1) two halves (half cowhides) in pickle, the raw of which was of French origin, thickness from 1.8 to 2.0 mm, total weight of the two halves 17.3 kg, pH of the hides 3.0-3.1, [0063] 2) if necessary, add the waste water from the previous pre-tanning to reduce the COD, run the drum for 30 minutes, drain, [0064] 3) add (50%) 8.65 kg of 8% aqueous solution of NaCl (density 7°Bé), [0065] 4) spin the drum for 20 minutes, [0066] 5) add (2%) 346 g of cationic product described in Example 1, spin for 2 hours, [0067] 6) add (15%) 2.595 kg of anionic product in powder form described in Example 3, spin continuously for 2 hours and in the subsequent 10 hours alternately spin for 10 minutes and wait 30 minutes at room temperature of 20-25° C., then another 2 hours of continuous rotation at 38° C., [0068] 7) add (50%) 8.65 kg of water at 38° C., [0069] 8) spin the drum for 20 minutes, [0070] 9) drain the bath, [0071] 10) wash by adding (200%) 34.6 kg of water at room temperature, [0072] 11) drain the bath and the leathers, [0073] 12) put the leathers to rest on a stand for 24 hours, [0074] 13) the ST is 72° C., [0075] 14) press the pre-tanned leathers to remove excess water, and [0076] 15) shave the leathers up to a thickness of between 1.1 and 1.2 mm.

[0077] The shaved leathers will then be re-tanned with a standard recipe normally used also with leathers pre-tanned with glutaraldehyde. The standard re-tanning includes a variable mixture of natural tannins, such as powdered Tara pod (Caesalpinia spinosa), synthetic tannins such as disulfonic polymers, possibly also with acrylic polymers. In the same re-tanning step, the leathers are also dyed with acid aniline-based dyes. Subsequently, the leathers are then greased using normally natural sulfited greases. After this step, the leathers are dried and moved on to the subsequent finishing and cutting steps.

[0078] The bath drained after the pre-tanning (step 9) may be recovered (possible step 2) more efficiently than what may normally be done after a classic re-tanning in which this step has no particular advantage. In fact, the waste water (step 9), which typically has COD (Chemical Oxygen Demand) values of about 80,000 mg/L, if used in step 2 of the subsequent pre-tanning, since it contains particularly reactive organic substance on the leather in pickle, effectively reduces its COD content and may thus be drained at 12,000-15,000 mg/L of COD. This is an advantageous aspect from the point of view of the environmental impact of the leather tanning process with this technology.

Example 5

[0079] One proceeds as in Example 4, but using 2% of cationic product described in Example 1 and 18% of anionic product in powder form described in Example 3, ST=74° C.

Example 6

[0080] One proceeds as in Example 4, but using 1% of cationic product described in Example 1 and 18% of anionic product in powder form described in Example 3, ST=73° C.

Example 7

[0081] One proceeds as in Example 4, but using 3% of cationic product described in Example 1 and 15% of anionic product in powder form described in Example 3, ST=72° C.

Example 8

[0082] One proceeds as in Example 4, but using 3% of cationic product described in Example 1 and 20% of anionic product in powder form described in Example 3, ST=75° C.