EP0632135A1 - Process and agent for the protection of non-tanned animal skins - Google Patents

Abstract

Process and agent for the treatment of untanned skins, in particular pelts, with a view to ensuring a protection of the latter avoiding or reducing the degradation or the loss of their quality. This process consists in placing the substances in contact with an aqueous bath containing, in combination, an electrolyte, silicon oxide and at least one amide-amine, the pH of the bath being adjusted to a value of between 1.5 and 5, in particular between 3.7 and 4.3. The process of the invention provides a reversible treatment allowing the collagen-based substances to be subsequently returned to their initial state by a reverse treatment consisting in raising the pH to a value of at least 5.3.

Description

The invention relates to a method and a reversible treatment agent for untanned hides in order to ensure protection of said hides preventing or reducing their degradation and the loss of their properties. By "reversible treatment process" is meant a process capable of temporarily protecting the skins and making it possible, if necessary, to return them to their initial state. By "skins" is meant both whole skins and pieces of skin. The invention extends to the reverse treatment method for bringing the skins back to their initial state. The invention can in particular be applied to treat tripe skin; it extends to a process for recovering collagen waste from skins which have undergone the treatment of the invention.

In the leather industries, skin protection is traditionally carried out by pre-tanning and tanning treatments using tanning agents (tannins); these treatments aim to make the skin rot-proof and to preserve or improve its mechanical qualities. No known pre-tanning and tanning process is completely reversible: the skin can no longer be returned to its initial state and freed from the tanning agents attached to it. The tanning agents which currently give the best results are agents containing metals (chromium, aluminum, zirconium, titanium, ...) or certain organic compounds (aldehydes) which have the serious defect of leading to polluting bath discharges and toxic (in particular chromium tannins) which must undergo expensive treatments.

In addition, a study was carried out on the combination of conventional tanning and tanning using silica in order to determine which sites fix tannins on collagen ("V. RAMA Nohana Rao et al., Silica Tanning : Part IV Studies on combination tannages and iso-electric point of silica-tanned leather - Central Leather Research Institute, Madras, Leather Science, Vol. 27, 1980, p. 283-290 "). In the tests which are reported in this publication, the treated material is hide powder and silica is used at saturation at very high contents (30 g to 75 g for 100 g of skin); the duration of treatment is 12 hours. This study indicates that the various tannings which have been combined are in competition and that a pre-tanning with a given compound then decreases the fixation of another compound. during tanning, it concludes that the silica binds both on the amino sites of collagen and on the CONH sites thereof, however, these tests carried out on powdered collagen did not lead to any test on whole skins. or in pieces, or a fortiori to any industrial process probably due to the very high contents required and the total absence of results on the quality of the collagen obtained.The publication referred to neither mentions nor suggests any character of reversibility treatment.

Currently, there is therefore no process allowing totally reversible protection of the skins with the aim of temporarily increasing their resistance to mechanical agents and to aging, with the possibility of bringing them back to their initial state. However, reversible protection would be interesting in the skin and leather industries; in fact, the traditional tanning treatments are necessarily carried out, due to their very nature, after various operations for treating the skin in guts (mechanical, physical, chemical, biological treatments ... such as pickling, degreasing, slitting ... ): protecting the skins prior to these operations would allow them to be carried out in better conditions (ability to work at higher temperatures, reduced risk of deterioration, etc.), the skins may or may not be then rid of the protective agents according to the nature of the treatments envisaged; another benefit of protection reversible would reside in the faculty of recovering and recovering the large volumes of collagenic waste to which lead the treatments of skin in tripe: for example, this waste would become usable for animal feed after reverse treatment rid them of the agents of protection.

The invention proposes to provide a reversible treatment process for non-tanned hides, with a view to ensuring their protection avoiding or reducing their degradation and the loss of their properties, in particular during the operations preceding tanning.

An objective of the invention is to provide a completely reversible process when the basic compounds targeted by the invention are applied alone, making it possible to return the skins to their initial state by reverse treatment.

Another objective is to obtain, at the same time, effective protection of the skins and low consumption of the compounds used (relative to the weight of skins).

Another object of the invention is to provide a protection process which does not use pollutants containing heavy metals or aldehydes.

Another objective is to provide a protection process in which the basic compounds can be combined with certain known non-polluting tannins, with a view to achieving very effective protection of the skins in cases where the completely reversible nature of the process is not essential.

Another objective is to broaden the possibilities of using collagenic waste from treated skin.

• . au moins un électrolyte constitué par un sel en quantité supérieure ou égale à 20 g par litre de bain,
• . de l'oxyde de silicium en proportion pondérale comprise entre 0,04 % et 3 % par rapport au poids de peaux sèches,
• . au moins un amide-amine en proportion pondérale comprise entre 0,04 % et 3 % par rapport au poids de peaux sèches,
• . au moins un acide en teneur adaptée pour ajuster le pH du bain à une valeur comprise entre 1,5 et 5.

The process according to the invention for protecting untanned hides is characterized in that said hides are placed in the presence of an aqueous bath containing, in combination:

• . at least one electrolyte consisting of a salt in an amount greater than or equal to 20 g per liter of bath,
• . silicon oxide in a weight proportion of between 0.04% and 3% relative to the weight of dry skin,
• . at least one amide-amine in a weight proportion of between 0.04% and 3% relative to the weight of dry skin,
• . at least one acid in content suitable for adjusting the pH of the bath to a value between 1.5 and 5.

By "aqueous bath" is meant a bath containing by weight at least 15% of water, this bath being able to be as well a liquid volume in which the skins are immersed as a flow delivered towards the skins making it possible to put them in contact with the treatment liquid. In general, this bath will essentially consist of water, but it can, if necessary, consist of a mixed bath containing one or more organic solvents. By "electrolyte" is meant, in the usual manner in the skin treatment industries, a salt capable of decomposing into ionic species in water, in particular sodium chloride.

The silicon oxide used is advantageously a fumed silica which can be obtained, in a manner known per se, by hydrolysis of silicon tetrachloride in the vapor phase at 1,800 ° C. in the presence of hydrogen and oxygen. The amide-amine used is advantageously urea.

Experiments have shown that the process of the invention, combining, in an acidic aqueous medium, the use of silica, an amide-amine and an electrolyte in the form of a salt, provides remarkable protection. skins avoiding or considerably reducing their degradation and the loss of their properties during subsequent operations. Unexpectedly, this result is obtained by using very small quantities of compounds (from 10 to 1000 times more lower than the quantities of silica used in the RAMA publication already mentioned). In addition, without it being possible to provide an explanation, the combination of base silica / amide-amine / electrolyte used under the conditions of the invention leads to a completely reversible process allowing, as will be seen below, 100% elimination of these basic compounds, the skins being able to be brought back to their initial state.

The process can in particular be applied for the protection of skin in guts: it then makes it possible to work in full bath the skins at temperatures ranging up to 62 ° C to 65 ° C without risk of gelatinization, these temperatures being much higher than those currently accepted for working unprotected tripe skins (around 38 ° C for wet mammal skins); this ability increases the efficiency of these operations, whether mechanical, physical, chemical or biological (degreasing, declutching, slitting, etc.). It should be noted that, in traditional tanning processes, the declutching is carried out after tanning; thanks to the protection which it provides, the process of the invention makes it possible to perform the declutching before tanning and thus ensures a saving in tanning products since the waste (which generally represents around 30% of collagenic materials) does not undergo the tanning treatment. These collagen wastes which contain amine-amine rich in nitrogen and are free of tannins are very suitable for making fertilizers (neutral silica is not a nuisance); the invention extends to a process for recovering said waste which consists in using it for the manufacture of fertilizers.

After having undergone the mechanical, physical, chemical or biological operations mentioned above, the skins or pieces of skin or possibly skin waste can then be brought back to their initial state, by raising their pH in an aqueous medium until reaching a value at less equal to 5.3, in particular of the order of 5.5 to 5.8. This total reversibility is notably interesting when the skins must undergo subsequent treatments which are thwarted by the presence of the above-described compounds providing protection; for example, in the case of leathers tanned using chromium tanning agents, the skins will be treated in reverse before being subjected to chromium tanning in order to free the sites on which these agents are fixed (COOH groups of collagen). Furthermore, the collagen waste from the previous operations carried out on the protected tripe skins may, if necessary, undergo reverse treatment themselves in order to find an intact collagen capable of being recovered.

The compounds used: silicon oxide, amide-amine, electrolyte can be placed in the bath to the exclusion of any tannin or tanning agent in order to obtain a completely reversible treatment. It is also possible, in particular for the treatment of certain skins, to add to the bath a synthetic tannin, in particular of phenol-sulfone type: this type of tannin is fixed on the phenolic groups (in very large numbers), and its fixation remains satisfactory in the presence of the compounds targeted by the invention; this significantly increases the effectiveness of the protection. However, the presence of such a tannin reduces the reversibility of the treatment and the synthetic tannin will be added if a total reversibility is not sought, for example in the case where it is a question of carrying out an improved and non-polluting tanning. of skins. In practice, the proportion by weight of synthetic tannin added to the bath will be less than 30% of the dry mass of skins.

• . on utilise un acide minéral et/ou de l'acide carboxylique pour ajuster le pH du bain,
• . la teneur d'acide est ajustée de façon que le pH du bain contenant les peaux soit compris entre 3,7 et 4,3,
• . on met les peaux au contact du bain à une température comprise entre 12° C et 35° C pendant une durée comprise entre 10 et 120 minutes,
• . la proportion pondérale d'eau du bain par rapport à la masse sèche de matières collagéniques est ajustée entre 300 % et 1000 %.

The tests show that the optimal conditions for implementing the process of the invention are as follows:

• . a mineral acid and / or carboxylic acid is used to adjust the pH of the bath,
• . the acid content is adjusted so that the pH of the bath containing the skins is between 3.7 and 4.3,
• . the skins are brought into contact with the bath at a temperature of between 12 ° C and 35 ° C for a period of between 10 and 120 minutes,
• . the proportion by weight of bath water relative to the dry mass of collagenic materials is adjusted between 300% and 1000%.

In addition, in a manner known per se, an antiseptic can be added to the bath to increase the shelf life of the skins in the wet state, for example a quaternary ammonium; this antiseptic will be introduced into the bath in a proportion by weight of less than 0.2% of the dry mass of skins.

The method of the invention can be implemented by mixing the various compounds defined above directly in the bath. It is also possible to prepare beforehand an aqueous preparation containing, relative to the silica / amide-amine unit, a weight proportion of silicon oxide of between 20% and 60% and a weight proportion of amide-amine of between 20% and 60%. Preferably, this preparation will contain an acid content such that the pH of the preparation is between 1.5 and 5 so as to avoid a modification of the pH of the bath during mixing. This preparation, which can be stored indefinitely, can be prepared by the chemical industrialist and then delivered to the treatment site: the user will prepare an acidic aqueous bath with a pH between 1.5 and 5 containing the electrolyte, and introduce the skins and mix the above preparation in this bath in an appropriate amount to obtain the desired proportions of compounds in the ranges indicated above.

The invention extends, as a new product, to an agent for protecting untanned skins, in particular tripe skins, characterized in that it comprises a mixture of silicon oxide, in particular pyrogenic silica, and at least one amide-amine, in particular urea. This agent can be in the form of an aqueous preparation containing, referred to the silica / amide-amine group, a weight proportion of silicon oxide of between 20% and 60%, a weight proportion of amide-amine of between 20% and 60%, and an acid content, in particular mineral and / or carboxylic such that the pH of the preparation is between 1.5 and 5. In addition, the weight proportion of water in the preparation is advantageously between 65% and 85%, in order to avoid any risk of gelation of that -this. If necessary, the formulation of the protective agent can be completed by the presence of a synthetic tannin in a weight proportion of less than 80% relative to all of the other active compounds.

The process and the protective agent in accordance with the invention are illustrated by the following examples, which provide, without limitation, formulations of protective agents and methods of carrying out the process for the treatment of skins sheep and cattle.

EXAMPLE 1 Protective agent allowing a completely reversible protective treatment.

• (a) silice pyrogénée sous forme de produit colloïdal de diamètre moyen de particule égale à 10 nanomètres environ en proportion pondérale égale à 7,50 %,
• (b) urée ("urée technique" à 99,45 %) sous forme de granulés sphériques (diamètre moyen : 1,5 mm), en proportion pondérale égale à 6,00 %,
• (c) acide sulfurique en proportion pondérale égale à 0,35 % (ramenée à de l'acide pur),
• (d) eau : 86,15 %.

The following compounds are mixed to form a white milky preparation:

• (a) fumed silica in the form of a colloidal product with an average particle diameter of approximately 10 nanometers in a weight proportion equal to 7.50%,
• (b) urea ("technical urea" at 99.45%) in the form of spherical granules (average diameter: 1.5 mm), in a weight proportion equal to 6.00%,
• (c) sulfuric acid in a weight proportion equal to 0.35% (reduced to pure acid),
• (d) water: 86.15%.

The mixing is carried out at 35 ° C. by first introducing urea in water, then silica, then acid.

In this product, the weight proportion of silica (a) relative to all of the active compounds a, b, c (assumed to be pure) is 54.15%, while the weight proportion of urea (b) is 43.32%. The pH of the product is 2.2.

EXAMPLE 2 Protective agent allowing a partially irreversible treatment.

• (a') silice identique à la précédente, en proportion pondérale égale à 7,5 %,
• (b') urée identique au précédent, en proportion pondérale égale à 6 %,
• (e) tannin de synthèse constitué par un phénol-sulfone (vendu par la Société "Procalp" sous la marque déposée "PROTAN" type 175 P) en proportion pondérale égale à 10 %,
• (c') acide sulfurique identique au précédent en proportion pondérale égale à 0,35 %,
• (d') eau : 76,15 %.

The formulation of this preparation is as follows:

• (a ') silica identical to the previous one, in a weight proportion equal to 7.5%,
• (b ') urea identical to the previous one, in a weight proportion equal to 6%,
• (e) synthetic tannin consisting of a phenol sulfone (sold by the company "Procalp" under the registered trademark "PROTAN" type 175 P) in a weight proportion equal to 10%,
• (c ') sulfuric acid identical to the previous one in a weight proportion equal to 0.35%,
• (of) water: 76.15%.

The mixing is carried out at 35 ° C. by first introducing urea in water, then synthetic tannin, then silica, finally acid.

In this preparation, the weight proportion of synthetic tannin relative to all of the other active compounds (a ', b', c ') is equal to 41.93%. The pH of the product is 2.6.

EXAMPLE 3 Reversible treatment of bovine hides

The skins treated in this example are bull skins each weighing approximately 50 kg gross; the skins have previously undergone the classic river work (quenching, pelanage, fleshing, deliming, jamming) and are in the form of tripe skins with a pH of the order of 7.5 to 7.8 and a rate of approximately 80% hydration; their shrink temperature is 37 ° - 38 ° C.

The skins are introduced into a bath consisting of water placed in a rotary tannery drum at room temperature (20 ° C.) at the rate of 600% of water relative to the mass of dry matter. An electrolyte consisting of sodium chloride is introduced into this bath. sodium to reach 8 ° Baumé corresponding to 87 g of salt per liter of bath. A mixture of acids (acetic acid, formic acid, sulfuric acid) is added to the bath so as to stabilize the pH of the bath and of the skins at a value between 4 and 4.2.

• 1,01 % d'oxyde de silicium rapporté à la masse sèche de peaux,
• 0,81 % d'urée rapporté à la masse sèche de peaux.

The preparation of Example 1 is then added to the bath in a proportion by weight of 13.5% of preparation relative to the dry mass of skins, which corresponds by weight to:

• 1.01% silicon oxide based on the dry mass of skins,
• 0.81% urea based on the dry mass of skins.

The pH of the bath is between 4 and 4.2. The fuller is made to rotate for 40 minutes at 20 ° C.

The antiseptic sold by the company "Procalp" is then introduced under the designation "AQUARTYL" at a rate of 0.15% relative to the dry mass of skins.

The fuller is again rotated for 20 minutes so that the total treatment time is 60 minutes in this example.

The retraction temperature of the skins is then controlled, which has gone from 38 ° C. to 60 ° C. which characterizes an excellent effectiveness of the protection obtained.

The skins are removed from the fuller, established, left to drain for 48 hours, wrung to bring them back to a hydration rate of 35% water relative to the mass of dry matter. The skins are wrung out easily and are white.

The skins are then subjected to the following conventional mechanical operations: slitting, declutching, resizing. These operations take place under more favorable conditions than for skins pre-tanned using an aluminum and / or aldehyde tannin: less viscous skin (due, in particular, to more efficient spinning resulting in better regularity in thicknesses), absence of skin burns by the blades saw.

It should be noted that the precision of the slitting (made possible by the depth protection obtained) makes it possible to stretch the skins more during this operation and therefore to obtain a higher surface yield in finish. It should also be emphasized that the effluents from the treatment of the invention are free of heavy metals and aldehydes and have a very high biodegradability character.

Slag and re-cutting waste are obtained which can be used as it is, as raw materials for organic fertilizers. If necessary, this waste can be subjected to the reverse treatment described in Example 6 with a view to using collagens as a raw material in various industrial sectors (in particular food, cosmetology, etc.).

EXAMPLE 4 Partially Reversible Treatment of Sheep Skin

• peaux : peaux de moutons confitées picklés d'Australie de pH de l'ordre de 2,5, de taux d'hydratation de 60 % environ, ayant une température de rétraction de 38° C (choix ridé II, c'est-à-dire qualité très médiocre),
• opération avant le traitement de l'invention (réhydratation au moyen d'un mouillant, écharnage) conduisant à une peau nettoyée sur chair de taux d'hydratation d'environ 70 %,
• traitement : même bain qu'à l'exemple 3 (87 g d'électrolyte par litre d'eau), mais la préparation ajoutée est celle de l'exemple 2 en proportion pondérale de 10 % de préparation par rapport à la masse sèche de peaux, ce qui correspond en poids à :
  • . 0,75 % d'oxyde de silicium rapporté à la masse sèche,
  • . 0,60 % d'urée,
  • . 1 % de tannin de synthèse.

This example is implemented in a manner analogous to Example 3 with the following characteristics:

• skins: Australian pickled confit sheep skins with a pH of around 2.5, hydration rate of around 60%, with a shrinkage temperature of 38 ° C (wrinkled choice II, i.e. - say very poor quality),
• operation before the treatment of the invention (rehydration by means of a wetting agent, fleshing) leading to cleansed skin on flesh with a hydration rate of approximately 70%,
• treatment: same bath as in Example 3 (87 g of electrolyte per liter of water), but the preparation added is that of Example 2 in proportion by weight of 10% of preparation relative to the dry mass of skins, which corresponds by weight to:
  • . 0.75% silicon oxide based on the dry mass,
  • . 0.60% urea,
  • . 1% synthetic tannin.

The pH of the bath is between 4 and 4.2. The fuller is made to rotate for 40 minutes at 20 ° C.

The shrink temperature then increased to 62 ° C.

Some skins have been spun (hydration rate reduced to 40% water) and declutching. The same results as above are observed. It is observed in particular that, on these skins of poor quality (wrinkled II), the disengagement of the protected skins makes it possible to flatten the wrinkles and make them disappear, therefore considerably improving the choice of skins.

Other skins have undergone hot degreasing using a biodegradable degreaser distributed by "Procalp" under the registered trademark "CALCIFORT" at a temperature of 52 ° C for 20 minutes. This degreasing at such a temperature is extremely effective and does not lead to any degradation of the skins: this ability to work at a higher temperature is a considerable practical advantage of the invention.

EXAMPLE 5 Treatment of Skins of Unconfirmed Cattle

• peaux : peaux de taureaux de même caractéristique qu'à l'exemple 3 ayant subi les opérations de rivière classiques à l'exception du confitage,
• traitement de l'invention : identique à l'exemple 3.

This example is implemented in a manner analogous to Example 3, with the following characteristics:

• skins: bull skins with the same characteristics as in Example 3 having undergone conventional river operations, with the exception of confection,
• processing of the invention: identical to example 3.

The same results are obtained. After the reverse treatment referred to in Example 6, the skins regain their properties of tripe skins and are brought to undergo the conventional jamming operation (digestion of elastic yellow fibers); such an operation can be adapted to the layer concerned obtained after slitting: flower or crust (unlike traditional methods where the jam is made before slitting, the flower and the crust being therefore treated in the same way); in the invention, the flower can undergo a deeper jam and the crust a lighter jam. The protection according to the invention which makes it possible to perform under good conditions a slitting of non-candied skins, thus confers the considerable advantage of allowing a jamming of the slit skins, perfectly adapted to the layer concerned.

EXAMPLE 6 Reverse Processing

The skins treated in Examples 3, 4 and 5 are treated in the following manner at the end of the operations described in these examples.

These skins with a pH of approximately 4 - 4.2 are immersed in a neutral bath containing water and sodium chloride (8 ° Baumé, density = 1.058 g / cm³). The skins and the bath are stirred and a buffered deacidification agent consisting of the product distributed by the company "Procalp" under the registered trademark "KELAT" type 112 is introduced, until a stabilized pH of 5 is obtained, 5.

A water rinse is then carried out. The shrinking temperature returned to 38 ° C for the skins of Examples 3 and 5, which characterizes a total elimination of the protection, and to 40 ° C for the skins of Example 4, which characterizes a elimination of the protection. about 95% protection. After reverse treatment, the skin is equivalent to a tripe skin and can undergo without disadvantage all the subsequent operations of this type of skin, and in particular a tanning of the conventional type of any kind.

Claims (17)

Process for the reversible treatment of untanned skins with a view to ensuring protection of said skins avoiding or reducing their degradation and the loss of their properties, characterized in that said skins are placed in the presence of an aqueous bath containing, in combination: . at least one electrolyte consisting of a salt in an amount greater than or equal to 20 g per liter of bath, . silicon oxide in a weight proportion of between 0.04% and 3% relative to the weight of dry skin, . at least one amide-amine in a weight proportion of between 0.04% and 3% relative to the weight of dry skin, . at least one acid in content suitable for adjusting the pH of the bath to a value between 1.5 and 5. Treatment method according to claim 1, characterized in that the silicon oxide used is fumed silica. Treatment method according to one of claims 1 or 2, characterized in that the amide-amine used is urea. Treatment method according to one of claims 1, 2, or 3, wherein the electrolyte used is sodium chloride. Treatment method according to one of claims 1, 2, 3, or 4, characterized in that the pH of the bath and the skins is adjusted to a value between 3.7 and 4.3. Treatment process according to claim 5, in which a mineral acid and / or a carboxylic acid is added to the bath to adjust the pH of the bath and the skins. Treatment method according to one of claims 1, 2, 3, 4, 5, or 6 in which the skins are brought into contact with the bath at a temperature comprised between 12 ° C and 35 ° C for a period of between 10 and 120 minutes. Treatment method according to one of the preceding claims, in which the proportion by weight of bath water relative to the weight of dry skin is adjusted to a value between 300% and 1000%. Method according to one of claims 1 to 8, characterized in that a synthetic tannin is added to the bath in a weight proportion of less than 30% of the weight of dry skin. Treatment method according to one of the preceding claims, in which an antiseptic is added to the bath in a weight proportion of less than 0.2% by weight of dry skin. Treatment method according to one of the preceding claims, characterized in that: an aqueous preparation is prepared beforehand containing, relative to all the active compounds, a weight proportion of silicon oxide of between 20% and 60%, a weight proportion of amide-amine of between 20% and 60%, and an acid content such that the pH of said solution is between 1.5 and 5, - an acidic aqueous bath of pH between 1.5 and 5 containing the electrolyte is prepared, and the skins are introduced therein, - Mixing the aqueous preparation with the above bath. Reversible protective agent for untanned skins, characterized in that it comprises between 20% and 60% by weight of silicon oxide and between 20% and 60% of amide-amine. Protective agent according to claim 12, characterized in that it consists of an aqueous preparation having an acid content such that its pH is between 1.5 and 5. Protective agent according to claim 13, having a weight proportion of water of between 65% and 85%. Protective agent according to one of claims 12, 13 or 14, comprising a synthetic tannin in a weight proportion of less than 80% relative to all of the other active compounds. Process for the reverse treatment of skins or waste skins having undergone a protective treatment according to one of claims 1 to 11, characterized in that the pH of said skins is raised in an aqueous medium until reaching a value at least equal to 5.3. The reverse treatment method according to claim 21, wherein the pH rise is produced in the presence of an electrolyte.