FR2670800A1 - SKIN OR LEATHER TREATMENT PROCESS, TANNING AGENTS AND MANUFACTURING PROCESS. - Google Patents

Abstract

A method for processing tawery or tannery articles such as hides and leather whereby loosening of the fibers and internal fat distribution are effected in order to increase the hides' surface area and homogenize their thickness. According to the method, the hides or leather are contacted, during the manufacturing process, with methanesulphonate CH3 SO3<-> ions. In particular, this step may be carried out during the pickling and/or tanning and/or dyeing processes, especially by means of methanesulphonic acid optionally combined with another acid. Said method substantially improves product quality, particularly by allowing a cost-efficient enhancement of inferior quality hides.

Description

SKIN OR LEATHER TREATMENT PROCESS,
TANNING AGENTS AND MANUFACTURING PROCESS
The invention relates to a method of treating tannery or tannery articles made of collagenous tissues such as skins or leathers, with a view to improving the surface qualities thereof (feel, appearance, regularity, unison, etc.) and flexibility. .

Numerous studies have been carried out in an attempt to improve leather manufacturing processes, generally with the aim of limiting the discharge of polluting effluents; these studies aimed to improve certain manufacturing steps such as pickling, tanning, dyeing or finishing operations. Certain existing processes can lead to a certain improvement in the leathers obtained but do not allow the significant improvement of the surface qualities (touch, appearance, unison), especially when the starting skins are skins of so-called inferior quality or having suffered (for example because having undergone a stripping during the heating ...).

Currently, the manufacture of satisfactory quality leathers from certain lower quality hides imposes a very significant additional cost (due to the addition of products, the increased cycle time and the multiplicity of operations) which limits the interest of additional treatments so that these skins generally remain confined to the manufacture of low-end products.

In addition, the existing treatment agents which lead to a certain improvement in leathers are generally specific to such and such an operation (for example acetic acid and adjuvant for the pickling of skins, cationic / anionic products for the nourishment of leathers, etc. ) and cannot be used at any other stage of manufacture.

The problem of improving the surface qualities and suppleness of leather is therefore poorly resolved at the present time, which is explained by the very specific nature of the skins which are made up of collagenic tissues very sensitive to hydrolysis and to skin damage. bacterial agents: most agents degrade these tissues and the number of compatible chemicals is very limited.

The present invention proposes to provide a new process for treating skins or leathers made up of collagenous tissues with a view to improving the surface qualities (feel, appearance, unison) and flexibility thereof.

An objective of the invention is in particular to obtain much more pronounced improvements in quality than in the known processes.

Another objective is to provide a cost-effective process compatible with upgrading hides of inferior quality under good profitability conditions.

Another objective is to provide a process capable of being implemented at different stages in the manufacture of leather (in particular at stages which involve a lowering of the pH).

To this end, the treatment process according to the invention to improve the surface qualities and the flexibility of tannery and tannery articles made up of collagenic tissues such as skins and leather, consists, during manufacture, in putting the skins or leathers in contact with alkanesulfonate ions R 503 or alkanedisulfonates R '(S0 32 - where R or R' is an aliphatic radical containing from 1 to 14 carbons. The best performance is provided by methanesulfonate ions
CH3 S03-. These ions are in particular brought into contact with the skins or leathers in the form of mono or disulphonic alkane acid or in the form of a metal salt of this acid in an aqueous medium or a mixed water / organic solvent medium. (Hereinafter, the term “mixed medium” will denote a medium containing one or more organic solvents and water, even if the latter remains in a very minor proportion). According to the experiments carried out, the minimum quantity of methanesulphonate ions necessary to lead to a significant improvement is of the order of 0.05 mol per kg of dry skins or leathers. (By a "dry skin" weight, the weight of the skin at the start of the treatment is aimed at, after deduction of the weight of bound water).

The invention was born from the fortuitous observation of an unexpected and remarkable phenomenon: when skins or leathers are brought into contact with the aforementioned ions, regardless of the stage of manufacture at which this bringing into contact is carried out, the there is a reproducible, very significant improvement in their surface condition and in their flexibility, without affecting their other physicochemical characteristics which remain at least equivalent. This result is obtained without the need for adjuvants or dopants, the alkanesulfonate ions alone producing the above-mentioned effect. No really convincing explanation can currently be put forward; everything happens as if the alkanesulfonate ion modifies the interactions between the collagen and the skin texture agents, this modification resulting in the aforementioned improvement effect and not a degradation or hydrolysis as is the case for most chemical agents. In addition, all the metal methanesulphonates being very soluble in water, the process of the invention avoids any risk of precipitation of insoluble salts (calcium sulphate for example) liable to be deposited on or in the skin and to cause degradation. of its surface or flexibility qualities.

In the preferred case of methanesulfonate ions, the methanesulfonic acid which leads to these ions in an aqueous medium is a strong organic acid, known per se. US Pat. No. 2,297,722 describes a method of manufacturing it. It is currently used mainly as a fluoroboric acid substitute in electroplating baths, as a trapping agent for heavy metals in petroleum derivatives, as a corrosion inhibitor with regard to magnesium alloys, or as a catalyst for certain reactions ( esterification, alkylation, olefin polymerization ...).

It should be noted that compounds of close families (metal sulphates) have been used for a long time in the tanning operations of skins and leathers without leading to the surface qualities and flexibility provided by the ions targeted by the invention.

In addition, it has been observed that the above-mentioned improvement provided by the mono or disulfonate alkane ions and in particular methanesulfonates occurs regardless of the stage of manufacture at which they were introduced.

The cycle of manufacturing leather from raw hides generally includes a pickling operation consisting in acidifying these hides. The bringing into contact of the raw or tripe hides with the alkanesulphonate ions can be carried out during this pickling operation using an alkanesulphonic acid optionally combined with another acid (in particular sulfuric acid).

The manufacturing cycle also includes a tanning operation. The contacting can be carried out during this operation by introducing the alkanesulphonate ions into the tanning bath. The tanning agent for this bath can be of any known type, mineral, vegetable and / or synthetic, and the bath then contains a mixture of this agent and of an alkanesulfonic acid or of a salt of this acid.

It is also possible to carry out chromium tanning with a specific agent consisting of chromium methanesulphonate in an aqueous or mixed medium. This compound releases both the metal ions ensuring the tanning and the methanesulfonate ions improving the surface qualities and the flexibility of the skins or leathers.

The leather manufacturing cycle also includes a dyeing operation, contacting the dye generally being ensured at a pH close to neutrality and fixing of the latter at a lower pH. The contacting of the alkanesulphonate ions can be carried out during this operation by using an alkanesulphonic acid optionally combined with another organic acid (in particular formic acid or acetic acid).

If necessary, the skins can be brought into contact with the alkanesulphonate ions several times and in particular at the three aforementioned stages of manufacture: pickling, tanning and dyeing. This mode of implementation leads in particular to the following practical advantage: to obtain a given quality, the concentration of alkanesulphonate ions is lower at each operation (compared to a single contacting), which avoids too much reduction. of the pH, which could be detrimental to the quality of the skins.

According to the tests carried out, the optimum total quantity of methanesulphonate ions, which should be brought into contact with the skins one or more times during the manufacturing cycle in order to obtain a marked improvement in their qualities without wasting product , seems to be between 0.1 and 2.0 moles per kg of dry skins or leathers.

The invention extends, as such, to the products used for carrying out the process defined above: tanning agent for skins or leathers containing alkane mono or disulfonate ions, in particular methanesulfonate ions, tanning agent based on chromium methanesulfonate.

It should be noted that the manufacture of a metal methanesulfonate is known per se. The publication "RC PAUL et al, Indian Journ. Of Chem., Vol. 12, August 74, pages 825-826" describes in particular a manufacturing process from methanesulfonic acid which consists in reacting this acid with a chloride metallic at 1700 C and under high vacuum. However, these severe conditions affect the price of the product obtained, especially since it is then difficult to isolate.

The present invention also relates to a new process for manufacturing chromium methanesulfonate making it possible to obtain this compound at a considerably reduced cost.

This process consists of reacting methanesulfonic acid with a barium salt, then reacting the barium methanesulfonate obtained with chromium sulfate and removing the precipitate by filtration in order to isolate the chromium methanesulfonate in solution. This process can be carried out at ambient temperature and at atmospheric pressure. By precipitating, the barium sulphate shifts the equilibrium and leads to chromium methanesulphonate without particular precaution.

The invention is illustrated in the examples of implementation which follow.

Example 1: Use of chromium methanesulfonate for tanning hides
a) Manufacture of chromium methanesulfonate
The manufacturing process requires two steps
- preparation of barium methanesulfonate
To a solution of 200 g of barium hydroxide octohydrate dissolved in 280 ml of deionized water, 170 ml of 70 ml methanesulfonic acid are added dropwise.

After stirring for 1 hour 30 minutes at 55 ° C., the water is evaporated off under vacuum until precipitation of the barium methanesulfonate, which is isolated in the form of white crystals by a succession of filtration and washing with ethyl alcohol.

- manufacture of chromium methanesulfonate
To a solution of 110 g of chromium sulphate dissolved in 350 ml of deionized water, 176 g of barium methanesulphonate, obtained during the first step, are added.

After 30 minutes of stirring at room temperature, the barium sulphate precipitate formed is removed by centrifugation (1 h at 4000 rev / min.)
The chromium content of the chromium methanesulphonate solution thus prepared is determined by atomic absorption: 35 g Cr / l.

This solution can be used directly in tanning or else the chromium salt can be isolated in crystalline form by precipitation with acetone.

b) Tanning
The quantities of products added are expressed as a weight percentage of the weight of the pickled skins.

Four skins (2800 g) of Nouvelle lambs
Wet Zealand. degreased and pickled are placed in
for 250% brine bath at 8 Baumé (i.e. 88.24 g / l of NaCl) / 15 minutes.

1728 ml of chromium methanesulphonate solution obtained previously, ie 60.5 g of Cr, is introduced all at once (quantity of CH 3 SO 3 ions equal to 3.56 moles relative to 1 kg of dry skin). After stirring for one hour, gradually basified by adding 1% sodium formate, then 4% sodium hydrogencarbonate every hour for 4 hours. The pH at the end of tanning is 3.9.

The skins are removed from the tanning bath and left to stand for 48 hours (skins stretched out stacked on top of each other).

The tanned skins obtained are subjected to a visual analysis: the chromium is uniformly distributed and fixed; the skins have a shrinkage temperature greater than 1000 C, which characterizes good tanning quality.

These skins then undergo a traditional supply of food, dyeing and drying.

These finished leathers have been appreciated by a panel of leather professionals and characterized as follows: very good tanning, very good flexibility, excellent silky, slightly waxy feel. These qualities were significantly better than those of similar skins treated under the same conditions, but with chromium sulfate.
Example 2: Use of methanesulfonic acid for pickling hides
The quantities of products added are given as a weight percentage of the weight of the skins in tripe.

5 skins of New Zealand lambs (lower quality) defatted, hurnid, are divided into two parts lengthwise in order to better appreciate the quality improvements brought about by the invention.

a) 6 dec D waters are Dicklated in a NaUl) and traditional way (50% brine bath at 80 Baumé (i.e. 88.24 9/1 of! 2% formic acid) and tanned in a conventional way, after one night stirring in the pickling bath.

b) G half-skins are pickled according to the invention, that is to say by adding 1: c of 70% methanesulfonic acid in two batches for one hour, then 1.5% formic acid in three times for 1 hour 30 (quantity of CH3 303 ions equal to G, 36 mole relative to 1 kg of dry skin).

After stirring overnight in the pickling bath, these skins are tanned in a conventional manner.

After 48 hours of rest, the two batches of skins a) and b) are fed, then dyed in a conventional manner.

The leathers thus finished were appreciated by a panel of professionals who classified them into two categories.
- the first (a) corresponding to the batch pickled with formic acid has the usual characteristics of chrome-tanned hides: good thermal and tear resistance, good flexibility, but very average surface qualities.

- the second (b) corresponding to the batch treated with methanesulfonic acid has the same characteristics of thermal resistance and tearing, accompanied by increased flexibility, a feeling of "full" and a particularly silky touch of the flower side as on the flesh side.

Example 3: Addition of methanesulfonic acid during tanning
The quantities of products added are expressed as a weight percentage of the weight of the pickled skins.

2 skins of country lambs (very good quality) and 2 skins from New Zealand (medium quality) defatted and pickled (3600 g) are placed in 100% acid brine bath at 8 Baumé (i.e. 88.24 g / l of NaCl), to which is added 2.5% / 70% methanesulfonic acid in five times in one hour (quantity of CH3 SO3 ions equal to 0.52 mole relative to 1 kg of dry skin).

Then added to the bath 8% of chromium sulphate (basicity 330, chromium content: 26 i) operation which is followed by the addition, after one hour, of 1% of sodium formate, then of 14% of hydrogen carbonate. sodium in four times in three hours; the pH at the end of tanning is 4.1. Still in the tanning bath, the skins are heated for one hour at 500 C.

After 48 hours of rest, they are fed, tinted and dried. The leathers obtained are subjected to a visual analysis: the dye is uniformly distributed, as is the chromium, as evidenced by a shrinkage temperature greater than 1000 C.

Their qualities are then evaluated by a panel of professionals: very good flexibility, lots of fullness and excellent silky, slightly waxy feel.

It should be noted that after treatment with this process, there is hardly any difference (flexibility, feel) between skins of very different initial qualities, which is a remarkable result and highlights the considerable interest of the process. the invention to treat and enhance low-end skin.

Example 4: Use of methanesulfonic acid during the dyeing of tanned hides
The quantities of products added are given as a weight percentage of the weight of the dry tanned hides.

To 2 tanned, nourished and dried skins, placed in 100% water at 550 ° C., 14 anionic-cationic food are added.

After one hour of stirring, 6% of brown acid dye is introduced. The dye is fixed one hour later by acidification with 2% formic acid and 2% 70% methanesulfonic acid in 2 times in 2 hours (0.14 mol per kg of dry tanned hides).

The tinted skins are then put in the wind and dried.

The evaluation of their qualities by a panel of professionals gives the same results as in the previous examples: very good flexibility, excellent touch, silky slightly waxy. A comparative test carried out in the absence of methanesulfonic acid (4% formic acid) leads to inferior qualities of flexibility and feel.

Example 5: Use of methanesulfonate acid at the end of vegetable tanning
The quantities of products added are given as a weight percentage of the weight of the pickled skins.

3 skins (2000 g) of defatted and pickled lambs are placed in 200% brine bath at 80
Baumé, (i.e. 88.24 g / l of NaCl).

After depicklage (adjustment of the pH to a value between 5.5 and 6), the skins are placed in a water bath (250%) to which are added 30 g of extract of quebracho in 3 times over 2 hours. The skins are left in the bath with stirring overnight, then rinsed, bleached and nourished.

For a skin, bleaching and nourishment are carried out in a conventional way: it is placed in a bath of 200% water at 50 C to which is added 1% oxalic acid, then 3% sodium thiosulphate, and finally 3 g of food.

The other two skins undergo the same treatment completed by the addition of 1% of 70 methanesulfonic acid in two stages, after the action of oxalic acid (0.21 mole of CH3 S03- ion per kg of dry skin) .

The three dry skins have a shrinkage temperature of 80-85 C, characteristic of good vegetable tanning and are, as before, subject to the judgment of professionals.

The two skins treated with methanesulfonic acid exhibit greater flexibility and above all a particularly silky feel, compared to skin treated conventionally.

Example 6: Successive use of methanesulfonic acid during pickling and during dyeing
Lamb skins in tripe are pickled with methanesulfonic acid according to Example 2, tanned with chromium in the traditional way, then dyed with fixation of the dye with methanesulfonic acid according to Example 4.

The panel of professionals consulted judged these skins to be even softer and to have an even silkier feel than skins treated with methanesulfonic acid in a single step (pickling or dyeing).

Example 7: Use of chromium methanesulfonate in a mixed medium
The quantities of products added are expressed as a percentage by weight relative to the weight of the pickled skins.

Two skins (1000 g) of defatted and pickled lambs are placed in 400% brine bath at 80 Baumé, ie 88.24 g / l of Nazi) for one hour; by draining, the humidity of the skins is reduced to 200% water relative to the dry weight.

These skins are then placed in a bath of 250% of 1,1,2-trichloro-1,2,2-trifluoroethane to which is added 308 ml of the chromium methanesulfonate solution described in Example 1 (i.e. 10.8 g Cr) (amount of ions
CH3 S03 equal to 1.78 mole relative to 1 kg of dry skin overall quantity of water equal to 3000 g relative to 1 kg of dry skin).

After stirring for one hour, gradually basified by successively adding 1% sodium formate, 4% sodium phthalate and 3.58 sodium hydrogencarbonate, in small fractions over 8 hours. The pH at the end of tanning is 4.3.

It should be noted that the chromium content of the waste bath is zero.

After 48 hours of rest, the skins are nourished and dried in the traditional way.

The dry tanned hides are subjected to a visual analysis: the chromium is uniformly distributed and fixed; the skins have a shrinkage temperature greater than 1000 ° C., characteristic of good tanning.

They are then appreciated by a panel of professionals who once again underlined their great flexibility and their very good silky feel.

Example 8: Use of ethanesulfonic acid during tanning
The quantities of products added are expressed as a weight percentage of the weight of the pickled skins.

2 lamb skins (1700 g), defatted and pickled, are placed in a 200% brine bath at 80
Baumé (88.24 g / l of Nazi), to which 1% ethanesulfonic acid is added
CH3 CH2 SO3H. 12% chromium sulphate (basicity 330, chromium content 26%) is then added to the bath, an operation which is followed by a gradual basification by successive additions of 1% sodium formate and 5% sodium hydrogencarbonate. in 4 times in 6 hours; the end of tanning pH is 4.5. Still in the tanning bath, the skins are heated for one hour at 500 C.

After 48 hours of rest, they are fed and dried.

Visual analysis shows that the chromium is evenly distributed and fixed, as evidenced by a shrinkage temperature above 2000 C.

These skins were evaluated by a panel of professionals, who judged their qualities of flexibility and touch better than skins tanned in a conventional way, the improvement of these qualities being however less pronounced than when using methanesulfonic acid. .

Claims (13)

1 / - Process for the treatment of tannery or tannery articles made of collagenous tissues such as skins and leathers, with a view to improving the surface qualities and flexibility thereof, characterized in that, during manufacture, the the skins or leathers are brought into contact with alkanesulfonate ions R S03 or alkanedisulfonates R '(S03) 2- where R or R' is an aliphatic radical containing between 1 and 4 carbons, the quantity of alkane ions mono or disulfonates used being at least equal to 0.05 mol per kg of dry skins or leathers. 2 / - Method according to claim 1, characterized in that one uses methanesulfonate ions CH3 S03-. 3 / - Method according to one of claims 1 or 2, characterized in that the alkane mono or disulfonate ions are brought into contact with the skins or leathers in the form of an alkanesulfonic acid in aqueous medium or mixed medium water / organic solvent. 4 / - Method according to one of claims 1 or 2, characterized in that the alkane mono or disulfonate ions are brought into contact with the skins or leathers in the form of a metal salt of an alkanesulfonic acid in aqueous medium or mixed medium water / organic solvent. 5 / - Method according to one of claims 1 to 4 for the manufacture of leathers from raw hides, wherein, during the manufacturing cycle, the raw hides are subjected to a pickling operation, characterized in that the the skin is brought into contact with the alkanesulphonate ions during the pickling operation, using an alkanesulphonic acid optionally combined with another acid. 6 / - Method according to one of claims 1 to 4 for the manufacture of leathers from skins, wherein, during the manufacturing cycle, the skins are subjected to a tanning operation, characterized in that the setting contact of the alkanesulfonate ions is combined with the tanning operation, by introducing said ions into the tanning bath. 7 / - A method of manufacturing leathers according to claim 6, characterized in that one uses a tanning bath containing a rièlange, on the one hand, of at least one mineral, vegetable and / or synthetic tanning agent, on the other hand, an alkanesulfonic acid or a salt thereof. & - A method of manufacturing leather according to claim 6, characterized in that one uses an aqueous or mixed tanning bath containing chromium methanesulfonate. 9 / - Method according to one of claims 1 to 4 for the manufacture of leathers from tan skins, wherein, during the manufacturing cycle, the tanned skins are subjected to a dyeing operation with contacting the dye at pE close to neutrality, then fixing thereof at lower pH, characterized in that the contacting of the alkanesulphonate ions is carried out during the dyeing operation, using an alkanesulphonic acid optionally combined with another acid. 10 / - A method of manufacturing leathers according to claims 5, 6 and 9 taken together, characterized in that the skins are brought into contact with the alkanesulphonate ions at least three times: during pickling, during tanning in the bath of tanning and during the dyeing operation. 11 / - A method of manufacturing leather according to one of claims 5 to 1C, characterized in that the skins are brought into contact with methanesulfonate ions so that the total amount of these ions is corrpr4se between 0.1 and 2.0 moles per kg of dry skin. 12 / - Tanning additive characterized in that it contains alkanesulfonate ions n SO3- or alkanedisulfonates R '(SO3) 2- where R or, t is an aliphatic radical containing between 1 and 4 carbons, in particular CH3 radical. 13 / - Tanning agent, characterized in that it is based on chromium me-thanesulfonate. 14 / - A method of manufacturing a tanning agent according to claim 13, characterized in that it consists in reacting methanesulfonic acid with a barium salt, then in reacting the barium methanesulfonate obtained with chromium sulfate and G. filter the precipitate to isolate the chromium riethanesulfonate in solution.