ITFI970215A1 - PROCESS FOR THE TREATMENT OF LEATHER WITH VEGETABLE TANNING - Google Patents

Description

"PROCESS FOR THE TREATMENT OF LEATHER WITH VEGETABLE TANNING"

Description

The present invention relates to a process for working leather for the production of footwear, bags, belts and similar products.

More particularly, the present invention relates to a so-called vegetable tanning process.

The so-called vegetable or tannin tanning process is a known process. It can comprise different phases in sequences which can vary according to the final result to be obtained. Typically, however, the vegetable tanning process substantially comprises the following phases:

- soaking of preserved leathers to restore their water content;

- hair removal for the removal of the epidermis and hairs;

- calcination, during which the fats are transformed into calcium salts and the main and secondary bonds of the protein chains constituting the proteins of the skin are broken;

- fleshing for the elimination of meat and fatty parts from the internal surface of the hides;

- split, that is the subdivision in the sense of the thickness of the leather in grain and split;

- deliming, to eliminate the residues of the previous calcination phase;

- maceration, for the elimination of elastin;

- pickling or pickling, involving the acidification of the hides to prepare them for the subsequent tanning phase; - proper tanning, through the use of vegetable or synthetic tannins;

- treatment with oxalic acid to remove excess tannins;

- pressing, i.e. compression of the skin at high pressure for the elimination of excess fluids;

- any operations of fulling, shaving, dyeing, fattening, smoothing and drying.

The leather treatment processes tend to obtain products with high mechanical resistance and high quality characteristics, in particular high softness and pleasantness to the touch. Various variants of the tanning process summarized above have been studied, with the aim of increasing the mechanical and softness characteristics of the leathers. These variants concern both the sequence of operations and the type of products used.

The purpose of the present invention is to propose an innovative leather treatment process which allows to obtain particularly appreciable results both in terms of resistance and softness of the treated leather.

Basically, according to a first aspect of the present invention, it is suggested to insert, between a calcination phase and a deliming and maceration phase, a treatment of the drum hides with an aqueous mixture of hydroxide in a process of leather tanning. lime.

According to a further aspect of the present invention, a process for working leather by vegetable tanning is proposed, comprising at least the following steps:

(a) soaking of the hides according to a per se known technique;

(b) calcination;

(c) treatment in a drum with an aqueous mixture of lime hydroxide;

(d) deliming and maceration;

(e) pickling;

(f) tanning;

(g) pre-fattening with a mixture in water comprising tannins, lecithin, lanolin, oxidized refined sulphited fish oil;

(h) dry fattening.

The phase of treatment with lime hydroxide between the calcination and the subsequent deliming allows to give the leather a particular softness and resistance, not obtainable with traditional processes. In this phase, an aqueous solution of lime hydroxide is used with a weight quantity of lime, with respect to the weight of the hides, for example in the order of 2-9% and preferably between 4 and 6%. In addition to lime hydroxide, a suitable quantity of a sodium salt, for example sodium chloride or sodium sulphate, can be introduced into the drum, preferably in such quantity as to reach a density for example between 2 and 5 ° Bé and preferably between 3 and 4th Well. Particularly appreciable results are obtained with the additional use of a degreaser, for example a product known with the trade name Lauripel 100®, marketed by Cuoiochimica, Italy, or another suitable equivalent product. The degreaser can be added in a variable percentage from 0 to 0.3% by weight in relation to the weight of the hides.

The treatment with lime hydroxide solution is advantageously preceded by a fleshing step and followed by a further fleshing and splitting step.

According to a particularly advantageous embodiment of the present invention, a pre-tanning step is provided between the pickling step and the tanning step, in which paraffin oil and one or more tannins, preferably synthetic, are added to the pickel bath. The pre-tanning is carried out in the drum without having previously discharged the pickling bath. Paraffin oil can be used in any of the commercial forms available, for example Biotan A®, marketed by Prodotti Biokimica, Italy, can be used, which in this case can be used in percentages ranging from 1 to 2% in weight compared to the weight of the skins. Among the synthetic tannins that can be used, Neutropel TS® and Biotan GNW®, by Prodotti Biokimica, Italy, can be mentioned. They can be used in variable percentages, for example from 2 to 4% by weight with respect to the weight of the treated hides. Other suitable tannins can also be used in equivalent percentages.

In a practical embodiment, the pickel bath is partially discharged before the addition of the paraffin oil and the tannins, to proceed with the pre-tanning. Before proceeding with the partial discharge of the pickel bath, according to a possible embodiment of the process according to the invention, it is envisaged to add a certain quantity of an aldehyde, in particular glutaric aldehyde, to the pickel bath. This can be used in one of the commercial forms available, for example in the form of Relugan GT-50®, manufactured by BASF, Germany. In this case, a suitable percentage of product can vary from 0.2 to 1% and preferably from 0.5 to 1% by weight of Relugan GT-50® with respect to the weight of the treated leathers.

The aldehyde added in this phase gives the leather a particular mechanical resistance and rubbery consistency, thus improving the characteristics of the final product.

According to a further improvement of the process according to the invention, after the tanning step the hides are kept at rest in the pile for about 5-10 days. This allows the skin to take on a characteristic of softness and resistance distributed evenly over the entire skin.

The pre-fattening phase is carried out for example with a mixture in water of synthetic tannins, lecithin, lanolin and refined oxidized oil of sulphited fish with the function of softening the skin. In a quantity of water, for example, approximately equal to 50% by weight with respect to the weight of the treated leather, variable quantities (expressed in percentages by weight with respect to the weight of the treated leather) are added from 1 to 2% of synthetic tannin, for example Biotah A®, from the 1! 2% Nutrexoil 195® (marketed by Houghton, Ita-

lia), from 1 to 2% of Likersol NG® (marketed by Biokimica products, Italy) and from 2 to 4% of Sulfinex S / 12® (marketed by Houghton, Italy).

The subsequent dry fattening treatment can be carried out after medium pressure pressing (60/80 atmospheres in a rotary press), placing the leather in the drum with the addition of a mixture of fatty substances in quantities from 10 to 13% by weight of the hides placed in the drum. The drum is rotated until a temperature of 38-40 ° C is reached.

The mixture of fatty substances used in the dry fattening phase can comprise, in percentages by weight of the total mixture:

- 20 to 30% of unrefined bovine tallow

- from 20 to 30% of refined bovine tallow

- from 1 to 3% of fungicide

- from 4 to 7% of Nutrexoil 195® or an equivalent quantity of other compounds based on lecithin;

- from 4 to 7% of Bioxoil BS® (marketed by Prodotti Biokimica) or an equivalent quantity of other compounds based on synthetic sulphonated oil;

- from 1 to 3% of Deterpon SC / 3® (marketed by Prodotti Biokimica) or an equivalent quantity of another emulsifier;

- from 20 to 25% of non oxidized fish oil;

- 8 to 15% oxidized fish oil.

An example of implementation of the complete process is described below. It must be understood that the process described below has an exclusively exemplary and non-limiting nature of the invention, which is vice versa defined in its generality in the foregoing and in the attached claims.

EXAMPLE

The percentages indicated below refer to the weight of the leather unless otherwise specified.

Greening phase:

The hides are placed in the drum with the addition of 150% of water at 30-37 ° C and 0.1% of sodium sulphide. The drum is rotated for 60 minutes and the bath is subsequently discharged. Then water is introduced in the ratio of 150% at a variable temperature from 30 to 37 ° C and a rotation is carried out for about 15 minutes followed by the discharge of the bath.

Subsequently a mixture is introduced into the drum comprising:

70% water at 29-34 ° C

0.3% Ecovit 90® (marketed by Prodotti Biokimica)

0.2% Cuoiodase K® (marketed by Cuoiochimica, Italy)

0.3% Surfax 510® (marketed by Houghton)

0,4 Cuoiocal SP® (marketed by Cuoiochimica) After a rotation of 3-4 hours with a barrel temperature of about 29-30 ° C, 70% of water is added at 26-27 ° C and 0.2% of Lauripel 100® to reach a density of about 3-3.5 ° Bé. The rotation is continued for about 15 minutes at a barrel temperature of 26/28 ° C. Calcination and fleshing

The following is added to the bathroom as defined above:

0.7% Cuoiocal SP®

1% Lime hydroxide

0.2% R / 69® (marketed by Cuoiochimica).

The drum is rotated for 10 minutes and then added:

4% Lime hydroxide

3.2% Sodium sulfide

0.5% Sodium sulfhydrate

and a cycle of rotations in two phases of 45 minutes in one direction and 45 minutes in the opposite direction is performed for one night.

The bath is then unloaded and after a dry rotation of about 20 minutes the hides are unloaded and subjected to a first fleshing.

Lime milk bath, subsequent fleshing and splitting

A mixture is prepared in the drum comprising:

150% of water at 25-26 ° C

4% lime hydroxide

0.1% Lauripel 100®

sodium sulphate up to a density of 3 ° Bé.

The drum is rotated for 10 minutes, then the skinned hides are added. A rotation of 10 minutes follows and then a cycle of 14 hours with a rotation of 2 minutes every hour. The bath is then unloaded and the skins again fleshed out and split.

Deliming and maceration

A mixture is prepared in the drum comprising: 120% of water at 36-37 ° C

0.3% sodium bisulfite

0.1% ammonium sulfate

The drum is rotated for 5 minutes, then the skins are added, rotated for 15 minutes and the bath is drained. Subsequently, 120% of water at 30-33 ° C is introduced, a rotation of 5 minutes is carried out and then the drain is carried out. The following blend is then prepared in the drum:

70% water 32-33 ° C

0.8% leathercal VS / T ® (marketed by Cuoiochimica)

0.3% sodium bisulfite

After a rotation of 15 minutes it is added

0.8% leathercal VS / T® (marketed by Cuoiochimica)

0.2 Lauripel 100®

A rotation of 20-30 minutes is carried out and then 0.05% of Biosint TR / Conc® (marketed by Biokimica) is added and a rotation of about 20 minutes is carried out at the end of which the bath is drained and a washing in running water for 15-20 minutes and then the residual bath is drained.

Picklaggio

The pickel is made with a mixture of

60% cold water

7% sodium sulfate

0.2% Biokal KL® (marketed by Prodotti Biokimica)

After a rotation of about 10 minutes, 1% of formic acid with a dilution of 1:10 is added. After a further rotation of about 30 minutes, 1.4% of sulfuric acid with a dilution of 1:20 is added and then a rotation cycle of two hours is carried out for one night, at the end of which the pH of the bath has reached the value of 3-3.2.

Pre-tanning

Without draining the pickling bath 0.5% of Relugan GT-50® is added and then a rotation of about 45 minutes is performed followed by a 2/3 discharge of the pickel bath. Are added:

1% Biotan A®

2% Neutropel TS®

2% Biotan GNW®

and a further 45 minute rotation is performed. Tanning

Without draining, the following 7% Quebracho tannins are added

2% Tara extract

1% Biotan A®.

The drum is rotated for about two hours and then the following is added:

3% chestnut

16% quebracho

0.5% Biotan A®

A rotation of 6/8 hours is then carried out up to a temperature of 36-37 ° C and then a continuous automatic rotation is carried out with possible inversions of the direction of rotation every 2 hours for one night.

Stacking

The skins are then unloaded and left to rest on the pile for about seven days.

Pressing, fulling and shaving

The tanned hides are subjected to a pressure of about 280-300 atmospheres in a flat press, then dry milled for about 30 minutes in the drum and then shaved to the desired thickness.

Oxalic acid treatment

The shaved hides are placed in a drum with a mixture of

150% cold water

1% oxalic acid

and rotate for about 50 minutes. The bath is then drained and washed with cold running water up to pH 4-4.2.

Subsequently in the drum are placed:

30% cold water

1% Neutropel TS®

rotate for 30 minutes and add

150% water 40 °

formic acid

The bath is drained after a rotation of approximately 25 minutes.

Pre-fattening

The following are immersed in the drum:

50% water at 40 ° C

1% Biotan A®

1% Nutrexoil 195®

1% Likeresol NG®

2% Sulfimex S / 12®

After a rotation of about 70 minutes, 150% of cold water is added and rotated for 5 minutes. Subsequently the bath is drained and the hides are stacked for about 24 hours.

Dry fattening

After stacking, the hides are subjected to pressing with a rotary machine at a pressure of 60-80 atmospheres.

The following operations are then carried out:

the hides are placed in a drum with spigots, rotated dry for about 35 minutes. 11% of a mixture of fatty substances based on natural and synthetic fats is then added to the drum. The mixture is made up in percentages by weight of the total mixture, by:

25% unrefined bovine tallow

25% refined bovine tallow

2% antifungal

5% Nutrexoil 195®

5% Bioxoil BS®

3% Deterpon SC / 3®

25% straw yellow oil

5% pure moellon

5% ruby oil

The drum is rotated until it reaches a temperature of 38-40 ° C. The hides are then removed from the drum and stacked for about 48 hours before undergoing flattening, drying and finishing.

It is understood that the drawing shows only an exemplification given only as a practical demonstration of the invention, since it can be found to vary in the forms and arrangements without however departing from the scope of the concept that informs the invention itself.

Claims (14)

CLAIMS 1. A process of working leather by vegetable tanning, comprising, between a calcination step and a deliming and maceration step, a treatment of the skins in a drum with an aqueous mixture of lime hydroxide. 2. Process according to claim 1, comprising at least the following steps: (a) soaking of hides; (b) calcination; (c) treatment in a drum with an aqueous mixture of lime hydroxide; (d) deliming and maceration; (e) pickling; (f) tanning; (g) pre-fattening with a mixture in water comprising tannins, lecithin, lanolin, oxidized refined sulphited fish oil; (h) dry fattening. 3. Process according to claim 1 or 2, in which the treatment in the drum with aqueous mixture of lime hydroxide (phase c) is carried out with a percentage from 2 to 9% and preferably from 4 to 6% by weight with respect to the weight of the leather put into the drum, of lime hydroxide. 4. Process according to claim 1, 2 or 3, in which a degreaser is added to the aqueous solution of lime hydroxide. 5. Process as per claim 1, 2, 3 or 4, in which a sodium salt is added to the lime hydroxide mixture until a density of 2-5 ° Bé is reached. 6. Process according to claim 5, wherein said sodium salt is sodium chloride or sodium sulfate. 7. Process according to at least claim 2, further comprising, between the pickling step and the tanning step, a pre-tanning step in which paraffin oil and one or more tannins are added to the pickel bath. 8. Process according to claim 7, in which said tannins added to the pickel bath are synthetic tannins. 9. Process according to claim 7 or 8, in which the pickel bath is partially discharged before the addition of said paraffin oil and said tannins. 10. Process according to claim 7, in which said pre-tanning step comprises: an initial addition of an aldehyde to the pickel bath; partial discharge of the pickel bath; the addition of said paraffin oil and said tannins. 11. Process according to claim 10, in which said aldehyde is glutaric aldehyde. 12. Process according to at least claim 2, in which after the tanning step the hides are kept at rest in the pile for about 5-10 days and preferably for about 7 days. 13. Process according to at least claim 2, wherein said dry fattening comprises the following steps: - pressing in a rotary machine at 60/80 atmospheres of the hides to be greased; - place the hides in the drum with the addition of a mixture of fatty substances in quantities from 10 to 13% by weight of the hides placed in the drum; - rotate until reaching a temperature of 38-40 ° C. 14. Process as per claim 13, wherein said mixture of fatty substances comprises, in percentages by weight of the total mixture: - 20 to 30% of unrefined bovine tallow - 20 to 30% of refined bovine tallow - from 1 to 3% of fungicide - from 4 to 7% of Nutrexoil 195® or an equivalent quantity of other compounds based on lecithin; - from 4 to 7% of Bioxoil BS® or an equivalent quantity of other compounds based on synthetic sulphonated oil; - from 1 to 3% of Deterpon SC / 3® or an equivalent quantity of another emulsifier; - 20 to 25% of non-oxidized fish oil - 8 to 15% oxidized fish oil.