EP0411986A1 - Untanned hides biologically stable in wet form - Google Patents

Abstract

Wet hides stripped of colour, biologically stable, untanned, intrinsically insensitive to mildews, containing from 50 to 70% of water, from 5 to 30% of inorganic matter, from 0.5 to 1.5% of Al2O3 and from 85 to 90% of dermic substances. <??>They are obtained by impregnating pickled hides with the aid of a basic aluminium polychloride or polychlorosulphate followed by a basification.

Description

The present invention relates to untanned hides, biologically stable, in wet form, also called B.S.H. ("White Stabilized Wet").

Commercially, skins can come in different forms:
- unprocessed (salted, brined, salted-dry and fresh ...)
- in the pickled state (treatment with a strong acid solution in the presence of salt)
- in the tanned state (notably "wet-blue" chrome treatment)
- in the semi-worked state (stain)
- or in the finished state.

The skins in the raw state present, according to their presentation problems of salt pollution, rewetting .... As for pickled skins, they are fragile because they have not undergone chemical treatment and must be protected against swelling.

The presentation of goods in "wet-blue" is not without drawbacks, particularly from an ecological point of view; Indeed, without the use of additional adjuvants and / or suitable chromium depletion procedures, the effluent solutions rejected have a high concentration of chromium coming from the tanning baths themselves and then from retanning operations (displacement by retanning).

In addition, up to 40% of the chromium baths are lost in the form of solid waste during slitting and deraying operations.

It has been proposed (French Patent No. 2,239,525), in order to reduce the chromium concentration of the effluents, to precede the chrome tanning by a treatment for 10 to 12 hours at a pH of the order of 3 , 9 to 4.2 using basic aluminum polychloride in an amount expressed as Al₂O₃ corresponding to 1 to 4% of the weight of the skin to be treated.

This is a real irreversible pretanning operation because it significantly transforms the collagen molecule.

For the past ten years, the leather industry has been interested in new products constituting an intermediate phase of preconditioning the skins after pickling; these have several advantages:
- they are free of chromium
- they are likely to withstand the operations of slitting and shoring (intended to produce leathers for different markets) before the tanning operations; these ripping and deraying operations carried out on these new products therefore make it possible to avoid the production of chrome-plated solid waste.
- the defects existing in the skins can be detected very early in the leather transformation sector, which allows a better choice and a better orientation of the skins according to their quality and market needs.
- the manufacturing differences that constitute the crusts of too small thickness and all the waste can be revalorized by transformation into industrial gelatin and food collagen, since they do not contain chromium.
- They make it possible to present a skin whose stability character is easily reversible; in fact, after elimination of the stabilization products, these materials are equivalent to the original pickled skin because the collagen becomes again available for conventional tanning operations.
- They have a high shrinkage temperature and stability over time, allowing them to be stored for long periods under difficult conditions (for example transport over long distances for several months).

These new products are called "White Stabilized Humid" (B.S.H.) when wet or "White Stabilized Dry" (B.S.S.) when dry (French Patent No. 2,610,643).

The subject of the present invention is moist, colorless, biologically stable, untanned skins, completely free of chromium, containing from 50 to 70%, preferably from 55 to 65% by weight of water, from 5 to 30%, preferably from 7 to 12%, by weight of total mineral matter relative to dry leather and degreased, from 0.5 to 1.5%, preferably less than 1%, by weight of Al₂O₃ relative to dry and degreased leather and from 85 to 90% by weight of dermal substance relative to dry and degreased leather, wet skin characterized in that it is intrinsically insensitive to mold without the addition of complementary fungistatic and bacteriostatic agents.

The BSHs of the invention can be obtained by impregnation at a pH of the order of 3 to 4, preferably of the order of 3.5 to 3.8, of pickled skins, using a base of basic aluminum polychloride or of basic aluminum polychlorosulfate in an amount corresponding to 0.08 to 0.45%, preferably 0.10 to 0.25% by weight of Al₂O₃ relative to the weight of the skin in guts, then basification to a final pH of the order of 4 to 4.4 and possibly wringing.

The pickled skins used come from various animal species such as sheep, goats, cattle ... and obtained by pickling according to the usual methods of pickling skins that have undergone the classic river operations (revegetation, depilation, deliming, confectionery ).

Among the basic aluminum polychlorides and basic aluminum polychlorosulfates, mention may be made of those of formula:
- Al _n (OH) _m Cl _3n-m (I)
where n and m are any positive integers with 3n-m positive
- Al (OH) _m Cl _3-m-2n (SO4) _n (II)
where m is between 1.1 and 2.1; n between 0.12 and 0.18; its basicity is between 0.37 and 0.70.
This product is described in French patent No. 2,239,525
- Al _n (OH) _m Cl _3n-m-2k (SO4) _k (III)
where k, m and n are positive integers with 3n> m + 2 k and k / n = 0.01 to 0.3; its basicity m / 3n is between 0.3 and 0.7.
This product is described in US Patent No. 3,929,666.
- [Al _n (OH) _3n-m-2p Cl _m (SO4) _p ] z (IV)
where (3n-m-2p) / 3n = 0.4 to 0.7; p = 0.04 to 0.25n; m / p = 8 to 35, m, n and p being whole numbers and z is equal to at least 1.
This product is described in English Patent No. 2,128,977.
- Al _n (OH) _m (SO4) _k Cl _3n-m-2k (V)
where the basicity m / 3n is between 0.40 and 0.65, the equivalent Al / equivalent Cl ratio is between 2.8 and 5, the weight average molecular weight M _w ranging from 10,000 to 500,000, preferably from 10,000 to 300,000, the actual hydrodynamic diameters 0̸Z and 0̸W having the following values:
0̸Z (A) from 90 to 450,
0̸W (A) from 50 to 300.
This product is described in European application No. 218.487. The basic polychlorides or the basic aluminum polychlorosulphates can be used in the form of aqueous solutions at 4-20% by weight of active material expressed as Al₂O₃ or in the form of a pulverulent solid.

The impregnation operation can be carried out at ordinary temperature (10 to 35 ° C. for example) in a fulling drum with adjustable speed of rotation with the possibility of reheating the impregnation bath.

The basification operation is then carried out for example using bicarbonate or sodium carbonate, magnesium oxide, dolomites ... in sufficient quantity to obtain a pH of the bath of the order of 4 to 4 , 4.

It is noted that, surprisingly, the product obtained is not very sensitive to molds, without the addition of fungistatic or bacteriostatic agents. So after 7 weeks of storage at 35 ° C, the B.S.H. of the invention still do not exhibit mold.

A refinement of the impregnation operation, making it possible to prevent any accidental phenomenon of mold, consists in introducing into the treatment bath from 0.5 to 5% by weight relative to the weight of tripe of a vinyl acid such as methacrylic. , allylic and in particular acrylic and / or 0.02 to 1.25% by weight (expressed as oxide) relative to the tripe weight of one of their metal salts (rare earths of the lanthanum, cerium type; zinc, nickel ...) and in particular lanthanum acrylate.

The Applicant has finally found that these vinyl acids or their metal salts reinforce the antifungal activity of the treatment bath based on polychloride or basic aluminum polychlorosulfate.

These vinyl acids or their salts can be eliminated or transformed for the subsequent use of waste, by polymerization using an oxidation-reduction couple, X-rays, etc.

Although not necessary, the usual antifungal agents in the treatment of skin can also be introduced into the impregnation bath (derivatives of chlorinated phenols, benzothiazoles, isothiazolones).

The B.S.H. of the invention have particularly good rewettability properties, which make it possible in particular in the case of small skins (goats, sheep) not to use a rewetting agent (surfactants of the sulfonate type, amines, amine salts. ..) for their transformation into BSS dry stabilized skin The B.S.H. of the invention are simply introduced for rewetting in a fuller in the presence of water with minimum mechanical work so as not to damage the skins by abrasion.

The B.S.H. of the invention is easily reversible; in fact, it can be transformed back into raw skin by acid treatment in a fuller (for example using an aqueous solution of hydrochloric, sulfuric acid, etc.) in order to remove the aluminum salts.

The B.S.H. subject of the invention have a minimum shrinkage temperature of at least 60 ° C, generally of the order of 64 to 68 ° C, fully compatible with slitting and derayage operations.

The B.S.H. can then undergo the conventional tanning operations: chrome tanning with better exhaustion of the chromium bath since the B.S.H. contains aluminum salts; synthetic tanning; vegetable tanning or combinations of these different types of tanning.

The following examples are given for information only and cannot be considered as limiting the scope and spirit of the invention.

Example 1

Half-croupons of cows having undergone river operations (re-greening, depilation, deliming, jamming) are subjected to the pickling and stabilization operations according to the invention.
The device used is an 800 liter wooden fuller with adjustable speed. The percentages mentioned are by weight and calculated on the weight of tripe unless otherwise indicated.

• 1)- eau froide (18-20°C) : 25 %
  - sel marin : 5 %
  - rotation : 5 mn
  - densité du bain : 1,04 à 1,07 g/cm³
• 2) ajout de 1,5 % d'acide sulfurique sous forme d'une solution aqueuse à 10 %
  - rotation : 30 mn
• 3) ajout de 0,7 % de formiate de sodium sous forme d'une solution aqueuse à 10 %
  - rotation : 3 heures

Picklage : rotation speed from 6 to 8 revolutions / min. We treat the croupons in the following baths:

• 1) - cold water (18-20 ° C): 25%
  - sea salt: 5%
  - rotation: 5 min
  - bath density: 1.04 to 1.07 g / cm³
• 2) addition of 1.5% sulfuric acid in the form of a 10% aqueous solution
  - rotation: 30 min
• 3) addition of 0.7% sodium formate in the form of a 10% aqueous solution
  - rotation: 3 hours

The pH of the bath obtained is 3.4.

Impregnation : rotation speed 6 to 8 rpm
2% (ie 0.16% expressed as Al₂O₃) of aqueous aluminum polychlorosulfate solution having a basicity of 55%, a desulfation rate of 82% and an Al₂ O₃ content of 8.3% obtained are added to the bath. according to the process described in European patent application No. 218,487.
The medium is rotated for 2 hours
The pH of the bath obtained is 3.6.

Basification

0.6% of sodium bicarbonate is added to the bath in the form of a 10% aqueous solution.
The medium is rotated for 1 h 30 min.
The pH of the bath is 4.1.
The BSH skin thus obtained is wrung under low pressure (5 x 10⁵ Pa).

The BSH wringed contains
- 60% of its weight of water
- 10% of its weight (relative to the dry matter according to standard NF-G 52 202) of mineral matter.
- 0.80% of its weight (relative to the dry matter) of Al₂O₃
- 85% of its weight (relative to the dry matter) of dermal substances.

Its shrinkage temperature measured according to standard NF-G 52 012 is 67 ° C.
After storage at 32/35 ° C and 80-85% relative humidity for 7 weeks, there is no mold.

Transformation into wet-blue

The percentages mentioned below are by weight and calculated on the weight of BSH wrung x x 1.5 (to obtain a% equivalent to that expressed relative to the tripe).
The BSH half-rips wrung and stored are then shifted to 1.8 mm without any problem and undergo rewetting, acidification, tanning and basification operations in a fuller similar to that described above.
. rewetting : rotation speed from 6 to 8 rpm
- cold water (16-18 ° C) = 10%
- rotation: 10 min then draining.
. acidification : rotation speed of 6 to 8 revolutions / min
- cold water (16-18 ° C) = 40%
- NaCl = 4%
- rotation: 10 min
- pH of the bath = 4.0 density of the bath: 1.04 to 1.07 g / cm³
Then addition of 0.5% sulfuric acid in the form of a 10% aqueous solution
rotation: 20 min
The pH of the bath obtained is 3.2.

Tanning : rotation speed from 8 to 10 rpm
8% chromium sulphate is added to the bath in the form of a 25% aqueous solution
- rotation: 6 hours
The pH of the bath obtained is from 3.2 to 3.3.

Basification : rotation speed 8 to 10 rpm
We add to the bath:
. 0.5% sodium bicarbonate in the form of a 10% aqueous solution.
rotation: 15 min, the pH obtained is 3.6
. then again 0.5% sodium bicarbonate in the form of a 10% aqueous solution
rotation: 60 min, the pH obtained is 3.9.

The wet-blue obtained are unloaded and placed on an easel.

Transformation of wet-blue into stain

The percentages mentioned below are calculated based on the weight of blue.

The half-croupons ex BSH chrome tanned in the previous operation undergo the following operations:
. washing : rotation speed 8 to 10 rpm
- cold water (16-18 ° C): 150%
- rotation: 5 min then draining
. retanning-neutralization : rotation speed 8 to 10 rpm
- water at 35 ° C: 100%
- SYNEKTAN NCR (organometallic tannin marketed by ICI): 4%
- 30 min rotation

Then addition of 2% of NEUTRAKTAN D (neutralization agent marketed by ICI)
- 1 hour rotation
The pH of the bath obtained is 5.4

After draining the product is washed with 100% water at 40 ° C - 5 min rotation

Retanning : rotation speed 8 to 10 rpm
- water at 40 ° C: 50%
- ALBATAN SF (synthetic tannin marketed by Rhône-Poulenc): 8%
- 45 min rotation then draining

Food : rotation speed 8 to 10 rpm
- water at 60 ° C: 50%
- Lipoderm-licker PK (sulphited oil of animal origin marketed by BASF): 6%
- 45 min rotation

The stains obtained are unloaded and placed on the easel for 24 hours.

After spinning and drying, it is found that the product obtained contains 0.132% of fixed Al₂O₃ (expressed relative to the dry matter).

The B.S.H. contained 0.80% of Al₂O₃ expressed in relation to the dry matter.

It is therefore found that most of the Al₂O₃ has been removed by displacement by the tanning agents during the transformation into wet-blue and stain; this is due to the reversibility property of the B.S.H.

Example 2

The pickling, impregnation and basification operations described in Example 1 are repeated, carrying out the impregnation operation using 2.2% aqueous solution of basic aluminum polychlorosulfate.

After 2 hours of rotation, 1.1% expressed relative to the weight of tripe of acrylic acid is added.

After 2 hours of rotation the medium is basified as above until pH4.

After storage at 32/35 ° C and 80.85% relative humidity for 11 weeks, there is no mold.

Claims (8)

1 - Wet skins devoid of coloring, biologically stable, not tanned, completely free of chromium, containing 50 to 70% by weight of water, 5 to 30% by weight of total mineral matters compared to dry and degreased leather, from 0.5 to 1.5% by weight of Al₂O₃ relative to dry and defatted leather and from 85 to 90% by weight of dermal substance relative to dry and defatted leather, wet skins characterized in that they are intrinsically insensitive to mold without the addition of complementary fungistatic and bacteriostatic agents. 2 - Wet skin according to claim 1) characterized in that they contain 55 to 65% by weight of water, 7 to 12% by weight of total mineral matter and less than 1% by weight of Al₂O₃ 3 - Process for the preparation of wet skins subject of claims 1 and 2 by impregnation at a pH of the order of 3 to 4 of pickled skins, using a bath based on basic aluminum polychloride or of a basic aluminum polychlorosulfate in an amount corresponding to 0.08 to 0.45% by weight of Al₂O₃ relative to the weight of the skin in guts, then basification to a final pH of the order of 4 at 4.4 and possibly spin. 4 - Process according to claim 3) characterized in that the pH is of the order of 3.5 to 3.8 and the amount of Al₂O₃ of the order of 0.10 to 0.25% 5 - Process according to claim 3 or 4 characterized in that the basic polychloride or polychlorosulfate of aluminum has the formula.
- Al _n (OH) _m Cl _3n-m (I)
where n and m are any positive integers with 3n-m positive
- Al (OH) _m Cl _3-m-2n (SO4) _n (II)
where m is between 1.1 and 2.1; n between 0.12 and 0.18; its basicity is between 0.37 and 0.70.
- Al _n (OH) _m Cl _3n-m-2k (SO4) _k (III)
where k, m and n are positive integers with 3n> m + 2 k and k / n = 0.01 to 0.3; its basicity m / 3n is between 0.3 and 0.7.
- [Al _n (OH) 3 _nm-2p Cl _m (SO4) _p ] z (IV)
where (3n-m-2p) / 3n = 0.4 to 0.7; p = 0.04 to 0.25 n; m / p = 8 to 35, m, n and p being whole numbers and z is equal to at least 1.
- Al _n (OH) _m (SO4) _k Cl _3n-m-2k (V)
where the basicity m / 3n is between 0.40 and 0.65, the equivalent Al / equivalent Cl ratio is between 2.8 and 5, the weight average molecular mass M _w ranging from 10,000 to 500,000 diameters ØZ and ØW real hydrodynamics with the following values:
ØZ (Å) from 90 to 450,
ØW (Å) from 50 to 300, 6 - Method according to any one of claims 3 to 5) characterized in that the bath also contains 0.5 to 5% by weight relative to the weight of tripe of a vinyl acid and / or 0.02 1.25% by weight relative to the weight of tripe of a vinyl salt of rare earth. 7 - Process according to claim 5) characterized in that the vinyl acid is acrylic acid and the rare earth salt of lanthanum acrylate. 8 - Use of wet skins subject of claim 1 or 2 for the preparation of skins in the tanned state, in the semi-worked state or in the finished state.