EP0551785B1 - Application of silica sols for obtaining a skin called "blanc picklé stabilisé" or "blanc stabilisé" - Google Patents

Abstract

Use of an aqueous silica sol to obtain a blanc picklé stabilisé or blanc stabilisé from a skin, especially by treating a skin at a pH of between 1 and 8, at ambient temperature, in an aqueous or brine bath with a density of between 1.014 and 1.09, with an aqueous silica sol containing, by weight, from 10 to 50 % silica in the form of discrete particles not bonded together by siloxane bonds and exhibiting a mean diameter of between 3 and 100 nm, and process for obtaining a blanc picklé.

Description

The present invention relates to the application of silica soils to obtain a so-called stabilized pickled white or stabilized white skin.

Today, in the hides and skins industry, there is a search for a reliable and economical process for obtaining a skin which has undergone certain operations of the leather transformation cycle, having a long shelf life and capable of being oriented quickly. , according to customer demand, towards the desired tanning and finishing.

Until now, according to demand, the tanner hires after manual selection, a raw hide in the tanning process, in order to obtain the requested article. This procedure requires a large stock of raw hide and leads to long delivery times because the transformation of raw hide into leather generally requires more than a month. Consequently, the tanner wishes to have at his disposal hides in the state of technological intermediaries, in particular in the state of stabilized pickled white or stabilized white, capable of being quickly and reliably transformed into the desired article.

It is known to prepare stabilized whites by pre-tanning the skins using mineral salts of certain metals, such as aluminum, titanium, magnesium, which do not color the skins and which raise their shrinkage temperature sufficiently. to be able to carry out without burns the conventional mechanical operations of setting to the thickness, then the tanning, and the desired finishes (see FR-A-2.650.293). However, pre-tanning with the aforementioned mineral salts gives the skins properties specific to the tanning agent used. In some very rare cases, they can be favorable, but generally they are annoying and oblige the tanner to generally carry out a elimination by rinsing or an appropriate breakdown before carrying out the tanning necessary for the confection of the desired article. It was also recommended to prepare a stabilized blank with aldehyde tanning or with low molecular weight silicic monomers or polymers; these processes have led to serious setbacks during tanning and / or finishing treatments: only superficial tanning, brittle leather ....

Furthermore, it is known to use aqueous silica soils to either skin the hides (US Pat. No. 5,215,542), or split the hides (EP-A-0 437 997), or combination with a compound capable of forming hydrogen bonds such as ketones, alcohols, for the tanning of hides (US-A-2 276 315), but to the knowledge of the applicant aqueous silica soils have never been proposed to obtain a stabilized white or pickled white stabilizes.

In order to overcome these drawbacks, the Applicant has discovered that the use of an aqueous silica sol makes it possible to obtain a pickled white having excellent stability, physical-mechanical and thermal properties capable of subjecting it without damage conventional mechanical operations allowing a choice in quality and thickness at this stage of the preparation and that said use did not give the skin any coloring by tanning, nor any significant modification.

The present invention makes it possible to obtain, from a pickled or unpicked skin, depilated or not, skinned or not, a technological intermediate having not only excellent stability but also better reactivity towards tanning agents and a temperature gelatinization, hereinafter referred to as TG, sufficient to protect the skin against possible overheating.

This is why the subject of the present application is the use of a silica sol, in particular an aqueous silica sol, particularly an aqueous silica sol containing by weight from 10 to 50% of silica in the state of discrete particles, not linked together by siloxane bonds and having an average diameter of between 3 and 100 nm, for obtaining a stabilized pickled white or stabilized white from a skin. As already indicated, the starting skin can be pickled or not, shaved or not, skinned or not.

The term skin can denote, for example, the skin of sheep, goats, pigs, cattle, horses, fish, reptiles such as boa, and more generally of a terrestrial or marine mammal such as sheep, kid, pork, goat, foal, heifer, cow, beef, horse, reindeer, antelope, seal.

The expression pickled skin or not, depilated or not, skinned or not, may denote, for example, a skin of hairs, a skin of pickled hairs, a skin of hair that is sparse and not picked, a skin of hairs that is sparse and picked, a skin of tripe not picked, a skin of tripe , a pickled and split gut skin, a non-pickled and split gut skin.

By "stability" is meant in the present application a physico-chemical and biological stability with respect to microbial and / or fungal agents. Furthermore, it has been observed with astonishment that the use of the silica soils according to the present invention causes on the treated skins a significant reduction in the activity of the water, hereinafter referred to as Aw (cf. Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd edition, volume 11, page 173 - John WILEY and SONS, New-York 1980), and, as a result, decreased the development of microorganisms on treated skin, allowing their storage without alteration for several months .

The aqueous silica soils containing from 10 to 50% by weight of silica in the form of discrete particles not linked to one another by siloxane bonds, having an average diameter of 3 to 100 nm, are today commercial products sold in particular by the Applicant under the generic designation of "KLEBOSOL" ^R.

The application described above can in particular be implemented as follows: a skin is treated, before or after pickling, before or after depilation, before or after fleshing, before or after slitting, at a temperature below 35 ° C., preferably at room temperature, at a pH between 1 and 10, preferably at a pH between 1 and 9 and more particularly at a pH between 1 and 8, in an aqueous bath or in a brine of density between 1.01 and 1.10, especially between 1.014 and 1.09, with an aqueous silica sol.

By brine is preferably meant an aqueous solution of sodium chloride or other salts such than sodium sulfate or calcium chloride.

Under preferential conditions for implementing the invention, the treatment described above is carried out with an aqueous silica sol containing, by weight, from 10 to 50% of silica in the form of discrete particles, of an average diameter included. between 3 and 100 nm, in particular between 5 and 50 nm, preferably between 7 and 50 nm and more preferably between 9 and 50 nm, not linked to each other by siloxane bonds.

The stabilized pickled whites or stabilized whites obtained according to the invention have, in the working environment, a gelatinization temperature of 65 ± 1 ° C. This considerable elevation of TG is particularly advantageous during mechanical sawing, skinning, or declutching operations, it also makes it possible to work serenely and quickly without fear of burns, all the more so since the coefficient of friction of the skin is very noticeably increased, thus improving machine handling.

The use according to the invention also gives treated skins a better reactivity towards tanning agents. We do not know the exact reasons, but we find that the tanning is carried out in better conditions; good penetration of the tanning agent throughout the thickness of the leather, uniform tanning both on the flower side and on the flesh side, less consumption of tanning agent, resulting ipso facto in a reduction in its rate in the waste water.

Among the tanning agents, mention may be made of vegetable tannins, mineral tannins, organic tannins such as those extracted from oak wood, chestnut wood, sumac leaves, mirobolan pods, pine bark, quebracho wood, cane roots , chromium derivatives such as chromium III sulfate, zirconium salts, aluminum salts such as aluminum sulfate, formaldehyde, polyphenols.

When submitting a stabilized blank obtained according to the present invention to a conventional tanning with a usual chromium tanning agent such as chromium III sulfate, basic chromium III sulfate, a chromium salt masked with organic acids, a self-buffering or basifying chromium tannin, the amounts of residual chromium in the bath at the end of the tanning are always less than 100 mg of chromium expressed as Cr₂O₃ per liter of bath.

The use according to the present invention is implemented very simply and very quickly, for example in a fuller for 1 to 24 hours, depending on the choice of methods and application parameters: pH, temperature, pressure, length of bath.

The doses of aqueous silica sol can vary widely, but usually 0.3 to 3% by weight, expressed as SiO₂, is used relative to the weight of the skins used. Depending on the doses used, the Aw of the treated skins can vary from 0.92 to 0.8.

At the end of treatment, the skins are generally dropped, then placed in a pile and stored. They can also be wrung out and dried. In this case, they are treated with an agent allowing their rewetting and avoiding the crystallization of mineral salts.

The stabilized whites obtained according to the present invention can also be immediately engaged in the tanning process: the unpeeled stabilized whites can be depilated, the unharvested stabilized whites can be skinned, the guts stabilized whites can be split and / or loose or they can be tanned using a conventional tanning process. The present invention thus offers the tanner a large choice of possibilities and great flexibility of execution in order to obtain the quality of the leather which he desires.

Another advantage of the use according to the present invention is the recovery of waste. In fact, the various wastes from mechanical operations are not not soiled with metals and / or tanning agents, they contain, in addition to the natural products present in the original skin, only silica. Therefore, this waste can be easily used in other fields, such as the preparation of animal and human foodstuffs.

According to a variant of the present invention, it is possible to combine the use according to the invention, with a pre-tanning with an aldehyde acid such as, and preferably, glyoxylic acid or one of its water-soluble salts. This pretanning can be carried out either before or after the treatment of the pickled skin or not, depilated or not, skinned or not, with the silica sol, but preferably this pretanning is carried out after the treatment with the silica sol.

If this pre-tanning is carried out before, the desired amount of glyoxylic acid or one of the water-soluble salts and then the other acids chosen for pickling are placed in the brine used before the introduction of the aqueous silica sol and finally, the aqueous silica soil. This gives a stabilized pickled white pre-tanned with glyoxylic acid or the like.

In the case where this pre-tanning is carried out afterwards, it is then carried out in a conventional manner in an aqueous bath containing the necessary quantities of sodium chloride and glyoxylic acid, at an acidic pH in the presence of mineral and organic acids. It can in particular be carried out according to the method described in the patent of United States of America No. 4,978,361.

The present invention also relates to a process for obtaining a stabilized pickled white or stabilized white from a pickled skin or not, depilated or not, skinned or not, characterized in that the skin is treated at a temperature below 35 ° C, preferably at room temperature, at a pH between 1 and 10, preferably at a pH between 1 and 9 and more particularly at a pH between 1 and 8, in an aqueous or brine bath with a density between 1.01 and 1.1, preferably between 1.014 and 1.09, with an aqueous silica sol containing by weight from 10 to 50 % silica in the form of discrete particles, not linked to one another by siloxane bonds and having an average diameter of between 3 and 100 nm, preferably between 7 and 50 nm.

The method described above can be implemented on the skins defined above, in particular a skin of hairs, a skin of pickled hairs, a skin of plucked and non-pickled hairs, a skin of plucked and pickled hairs, a skin in non-pickled tripe, a pickled tripe skin, a pickled and split tripe skin, a non-pickled and split tripe skin.

The above process is notably characterized by the fact that the silica particles in the aqueous silica sol have an average diameter of between 9 and 50 nm. Preferably, 0.3 to 3% of silica is used by weight relative to the weight of the tripe skins used.

It is also advantageous to combine the above process with a pretanning with an aldehyde acid or one of its water-soluble salts.

The present invention also relates to the use of stabilized pickled white prepared by the process of the invention, for obtaining commercial hides or skins. The stabilized pickled white or stabilized white, resulting from the process of the present invention makes it possible in particular to obtain a finished leather of good presentation, of excellent hold of flower, presenting no stain, no defect, no burning and uniform coloring even when the finished item is colored in pastel or light colors.

The following examples illustrate the present invention without, however, limiting it.

EXAMPLE 1

• 240 Kg d'un sol de silice commercial contenant pondéralement 30 % de silice sous forme de particules discrètes, non liées entre elles par des liaisons siloxane, d'un diamètre moyen de 50 nm, soit environ 72 Kg de silice (2 % en poids par rapport au poids des peaux).

In a fuller of 3 m in diameter, 4 m wide, rotating at a speed of 4 revolutions per minute, 1500 skins of veal are placed in guts, of less than 4 kg gross weight having undergone the classic operations of soaking, liming , deliming and jamming, or approximately 3600 Kg, in 85% of the bath by volume (approximately 3000 L) of brine at d = 1.055 (ie water containing approximately 7.5% of sodium chloride), to which 1% is added by weight of concentrated sulfuric acid (36 Kg) and 0.5% by weight of formic acid (18 Kg). The final pH of the bath is 2.5. The mixture is stirred for 3 hours at room temperature, then the following is introduced into the fuller:

• 240 Kg of a commercial silica sol containing 30% by weight of silica in the form of discrete particles, not linked together by siloxane bonds, with an average diameter of 50 nm, or approximately 72 Kg of silica (2% by weight relative to the weight of the skins).

Then stirred as before for 30 minutes and then the skins are dropped, put in a pile or wrung out. This gives stabilized pickled white calf skins with good stability, a shrinking temperature in the working bath of 66.2 ° C (pH = 2.5) and an electrovalent reactivity index of 3.8.

EXAMPLE 2

In a 2 m diameter and 3.6 m long bender, whose turnstile rotates at a speed of 60 revolutions per minute, 4000 kg of sodium chloride brine are placed at d = 1.075 then 1200 lamb skins in guts each weighing approximately 1 Kg. The mixture is then stirred for 3 hours at room temperature and then 60 kg of concentrated sulfuric acid diluted in 500 kg of water are introduced into the bath. Stirring is continued until a homogeneous pH of the skin portion is obtained. At this stage, the stirring is continued for another hour and then 80 kg of an aqueous silica sol containing 30% silica are introduced in the form of discrete particles which are not bonded together by siloxane bonds, a average diameter of 9 nm, or 2% of pure silica relative to the weight of the skins. Stirring is continued for one hour, then the skins are placed in piles and finally drained for 48 hours and pressed before being packaged and shipped. Upon receipt, they are rewetted for 2 to 3 hours in a brine bath at d = 1.043, then they are skinned. It is found that this operation is easily and perfectly carried out with complete separation of the meaty and fatty part which detaches from the skin in one piece, like a film.

EXAMPLE 3

• 25 Kg de chlorure de sodium,
• 500 g d'acide orthoborique,
• 525 g d'une solution aqueuse d'hypochlorite de sodium à 3,5 % de chlore actif,
• 100 Kg d'eau.

In a plastic tank, we place:

• 25 Kg of sodium chloride,
• 500 g of orthoboric acid,
• 525 g of an aqueous solution of sodium hypochlorite with 3.5% active chlorine,
• 100 Kg of water.

The reaction medium is then stirred, then 13.3 kg of an aqueous silica sol containing 30% by weight of silica are introduced in the form of discrete particles with an average diameter of 50 nm, and finally 200 kg of crocodile skins partially skinned, and salted, wound on themselves, in the form of cylinders of suitable diameter and size. The reaction medium is left under stirring at room temperature until penetration into the heart of the bath. The skins are then taken out of the bath, resalated, and sent to the user for their final transformation into tanned skin. It is noted that the presence of colloidal silica on the surface of the flesh allows the reception factories to perform a good fleshing, conducive to degreasing and to a tanning of excellent quality avoiding the surface stains noted on badly skinned skins.

EXAMPLE 4

In a fulling drum, rotating at the speed of 12 revolutions per minute, 7.5 kg of sodium chloride are dissolved in 142.5 kg of water, then 8 skins of dechaled and candied calves are introduced, ie approximately 100 kg. After 30 minutes of stirring, the pH of the bath is 8. 3 kg of an aqueous silica sol containing 30% by weight of silica are introduced, the discrete particles of which have an average diameter of 9 nm, diluted in 12 kg of water. Stirring is continued for 150 minutes at room temperature, then the bath is acidified to pH = 2.8 with dilute sulfuric acid and with dilute formic acid, then stirring is continued for 90 minutes. The skins are then drained and established on easels. The Aw value of the pickled skin is 0.920. The weight of the skins after draining and spinning is 69 kg. The hides are then sawn to a thickness of 1.5 mm, then chipped to 1.3 mm in order to obtain, after tanning, a thickness of 1.5 to 1.6 mm. The weight of the skins is 2.5 kg and the weight of the crusts is 21 kg.

The skins are then treated in a bath consisting of 70 kg of water and 3.5 kg of sodium chloride. After 30 minutes of stirring, 140 g of concentrated sulfuric acid and 700 g of an aqueous solution of glyoxylic acid at 40% by weight are introduced into the bath, so as to obtain a pH of the bath of 2.6. Stirring is continued for 1 hour and then the chromium salts necessary for carrying out a conventional chromium tanning are introduced. At the end of tanning, the chromium salt content of the bath is 0.035 g / l expressed as Cr⁺⁺⁺.

EXAMPLE 5

In a barrel 1 m wide and 2 m in diameter, 720 kg are placed, i.e. 60 tripe skins, skinned, leveled, dechaled and candied, the edge of which remains white in the phenolphthalein test (the pH of the last bath rinse on confit was 7.8), then 220 kg of water and 28.8 kg of sodium chloride. The mixture is stirred for 30 minutes at room temperature. At this stage, the bath pH is 8.2, its density 4 ° Baumé (d = 1.0285). Then introduced into the bath, 21.6 kg of a silica sol at 30% by weight of silica in the form of discrete particles with an average diameter of 9 nm, then left to stir for 150 min. The silica content of the bath decreases very quickly, from 30 g / l it decreases to 8.6 g / l after 45 minutes of stirring, then to 3 g / l after 90 minutes to reach 1.5 g / l after 150 minutes of agitation. The bath is then acidified to pH = 2.8 by addition of dilute sulfuric acid, then the skins are left for 1 hour with stirring and 16 hours of rest. The skins are then taken out of the bath, placed on pallets and drained for 24 hours. The Aw value of the pickled skin is 0.943. They are then spun and drawn in two batches. The first batch of 30 skins is derailed at 1.8 mm; 200 kg of skins and 40 kg of spines are thus obtained. The second batch of 30 skins is offset at 2 mm; 220 kg of skins and 20 kg of spines are thus obtained. These 60 kg of skins are suitable for use in the food industry. The first batch is chrome tanned with a pre-tanning process using glyoxylic acid. To do this, place the 30 skins (200 kg) in a bath containing 40 kg of water, 10 kg of sodium chloride, 400 g of concentrated sulfuric acid and 1.6 kg of an aqueous acid solution glyoxylic 40% by weight. After 30 minutes of stirring at room temperature, 7.6 kg of chromium III salts at 33 ° from Schorlemmer (chromium sulfate with a basicity index of 33%) are introduced into the bath, followed by stirring for 90 minutes. at room temperature and finally 3 kg of basifying salts (magnesium oxide) are introduced. Agitation is carried out for 6 hours then the skins are left for 16 hours with agitation for 10 minutes every two hours. Then introduced 100 kg of water at 70 ° C, stirred for one hour while maintaining the temperature at 45 ° C. We then take out the tanned hides and measure the residual chromium in the tanning. There is 0.0125 g / l of chromium expressed as Cr⁺⁺⁺.

The second batch is tanned with a vegetable tannin. To do this, the 30 skins (220 kg) are placed in a bath containing 110 kg of water and 14 kg of sodium chloride. After dissolution of the salt, about 1.1 kg of sodium hyposulfite is introduced into the bath so as to obtain a pH of 3 and then 11 kg of a replacement tannin dissolved in 110 kg of water. The mixture is stirred for one hour and then 5.5 kg of a neutralizing agent are introduced before adding the powdered vegetable tannin.

Both by chrome tanning and by vegetable tanning, perfectly tanned hides are obtained which meet the requirements of the user.

EXAMPLE 6

In a fulling drum, 3 tonnes of dechaled and candied cowhide skins are placed, the edge of the skins no longer showing any phenolphthalein coloring, 1116 liters of an aqueous solution at 12% by weight of sodium chloride and 1500 kg of water. The mixture is stirred for 30 minutes at 20 ° C. Then introduced 90 kg of silica sol containing 30% by weight of silica in the form of discrete particles with an average diameter of 9 nm in the bath having a density of 1.030. The mixture is stirred for 150 minutes, then the reaction medium is acidified with dilute sulfuric acid and formic acid. The agitation is continued for 3 hours; at this stage the pH of the bath is 2.7. It is left for 16 hours at room temperature with stirring for 10 minutes every 2 hours, then the skins have fallen, established on pallets then, 48 hours later, wrung, sawn, chipped and finally split into strips. The Aw value of the pickled skin is 0.925. The split skins are then pretanned with glyoxylic acid and then tanned with chromium as in Example 5. At the end of the tanning, a bath containing 0.07 g / l of chromium expressed as Cr⁺⁺⁺ is obtained.

EXAMPLE 7

In a fuller, 1,020 kg are placed, ie 350 delhaled and candied calf skins with an ionic equilibrium point of 5.6 and a colorless slice in the phenolphthalein test and whose last rinsing bath after jamming had a pH of 8.

Then introduced into the fuller 510 liters of an aqueous solution of sodium chloride at 20% by weight, then stirred 45 minutes. At this stage, the pH of the bath is 8.1 and its density of 1.06. The reaction medium is acidified to pH = 4.5 by addition of approximately 13 kg of acetic acid, then stirred for 45 minutes and then 20.4 kg of silica sol 30% by weight of silica are introduced. the state of discrete particles with an average diameter of 9 nm and 40.8 kg of water. Abandoned with stirring for 3 hours and then introduced in 40 minutes 17.3 kg of concentrated sulfuric acid. One hour left with stirring and then 16 hours at rest; the pH of the bath is 2.4. The skins are then taken out of the bath, established on pallets and left for 48 hours. The Aw value of the pickled skin is 0.836. At this stage, the skins have a water content of 4% lower than that found in skins of the same origin and having undergone the same treatment without silica sol. The skins are then skinned and derailed. The skinning and cutting operations are carried out very well and the flesh is smooth and shiny. The skinned and husked skins are then tanned in a fuller in a conventional manner with 5% by weight relative to the weight of the skins of a chromium III salt at 33 ° from Schorlemmer (chromium sulfate with a basicity index of 33%) and at 25% by weight of Cr₂O₃ followed after two hours of stirring with the addition of 0.5% by weight relative to the weight of the dolomite skins (dolomite). The skins are then left for 4 hours with stirring and then 16 hours with intermittent stirring for 5 minutes every hour. The pH of the final bath is 3.6 and its chromium salt content, expressed as Cr⁺⁺⁺ is 0.13 g / l. The skins contain 4.1% of Cr₂O₃ expressed on the dry weight.

EXAMPLE 8

In a fuller, 500 l (525.5 kg) of an aqueous solution of sodium chloride with a density of 1.051 and 1000 kg are placed, that is to say 80 skins, of heavy calf, skinned, equalized, de-stalked and candied.

After two hours of stirring at 10 revolutions / minute, at room temperature, 60 kg of an aqueous solution containing 10 kg of 98% concentrated sulfuric acid are introduced, then stirring is continued for 30 minutes, the pH of the bath is 2.2. Then introduced 20 kg of a silica sol containing 30% by weight of silica in the form of discrete particles with an average diameter of 50 nm. After 30 minutes of stirring, the silica content of the bath is 0.2 g / l, which indicates almost complete adsorption of the silica by the skins. At this stage, a solution consisting of 8 kg of an aqueous solution of glyoxylic acid at 40% by weight in 20 kg of water is introduced, then stirring is continued for 30 minutes. The pH of the bath is 2.4. 38 kg of a powdered chromium salt are then introduced, the mixture is stirred for 2 hours and then 15 kg of a self-basifying chromium salt is introduced.

After 6 hours of stirring, the reaction medium is left overnight with stirring for 5 minutes per hour. The following day, into the reaction medium, which is at the temperature of 38 ° C., 500 kg of water are introduced at 75 ° C., the mixture is stirred for 1 hour and the temperature of the medium is 45 ° C. The skins are removed from the bath, they have a very fine flower, they are relaxed, the wrinkle is not marked, the vein is not visible.

The bath contains 0.02 g / l of chromium in the Cr⁺⁺⁺ state and after filtration, it is recycled for a new operation.

The finished leather has excellent grain adhesion and a 3% increase in surface area, a full hand, exceptional grain fineness, a load-bearing side which significantly reduces the need for cutting.

Claims (20)

1. Use of an aqueous silica sol for obtaining a stabilized pickled white or a stabilized white from a hide.
2. Use according to claim 1, characterized by the fact that the hide is a non-pickled hide.
3. Use according to claim 1, characterized by the fact that the hide is a pickled hide.
4. Use according to any one of claims 2 and 3, characterized by the fact that the hide is a fell.
5. Use according to any one of claims 2 and 3, characterized by the fact the hide is a dehaired hide.
6. Use according to claim 4, characterized by the fact that the fell is not fleshed.
7. Use according to claim 5, characterized by the fact that the dehaired hide is fleshed.
8. Use according to any one of claims 4 to 7, characterized by the fact the dehaired or haired, fleshed or unfleshed, pickled or unpickled hide is a pared hide.
9. Use according to any one of claims 1 to 8, characterized by the fact that a hide is treated at a pH between 1 and 9, at a temperature below 35°C, in an aqueous or brine bath with a density between 1.014 and 1.09, with an aqueous silica sol containing by weight 10 to 50% silica in the form of discrete particles, not linked together by siloxane bonds and having an average diameter between 3 and 100 nm.
10. Use according to claim 9, characterized by the fact that the pH is between 1 and 8.
11. Use according to any one of claims 9 and 10, characterized by the fact the hide is treated at ambient temperature.
12. Use according to any one of claims 9 to 11, characterized by the fact that the silica particles of the aqueous silica sol have an average diameter between 7 and 50 nm.
13. Use according to claim 12, characterized by the fact that the silica particles of the aqueous silica sol have a diameter between 9 and 50 nm.
14. Use according to any one of claims 1 to 13, characterized by the fact that 0.3 to 3 % of silica by weight is used relative to the weight of the hide employed.
15. Use according to any one of claims 1 to 14, characterized by the fact that it is combined with a pretanning with an aldehyde acid or one of its water-soluble salts.
16. Process for obtaining a stabilized pickled white or a stabilized white from a pickled or non-pickled, haired or dehaired, fleshed or unfleshed hide, characterized by the fact that the hide is treated at a pH between 1 and 9, at ambient temperature, in an aqueous or brine bath with a density between 1.014 and 1.09, with an aqueous silica sol containing by weight 10 to 50% silica in the form of discrete particles not linked together by siloxane bonds and having an average diameter between 3 and 100 nm.
17. Process according to claim 16, characterized by the fact that the silica particles of the aqueous silica sol have an average diameter between 7 and 50 nm.
18. Process according to any one of claims 16 and 17, characterized by the fact that 0.3 to 3% by weight of silica is used relative to the weight of pelts employed.
19. Process according to any one of claims 16 to 18, characterized by the fact that it is implemented at a pH between 1 and 8.
20. Process according to any one of claims 16 to 19, characterized by the fact that it is combined with a pretanning with an aldehyde acid or one of its water-soluble salts.