EP1567679A1

EP1567679A1 - Method for producing a leather semi-finished product

Info

Publication number: EP1567679A1
Application number: EP03785657A
Authority: EP
Inventors: Stephan Hüffer; Stefan Schroeder; Jürgen CARLE; Thorsten RÄDLER; Volker Bach; Tilman Lüdecke TAEGER
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2002-11-26
Filing date: 2003-11-25
Publication date: 2005-08-31
Also published as: AU2003294721A1; KR20050085142A; US20060075573A1; BR0315817A; CN1325662C; CN1714158A; AR042044A1; US7753964B2; WO2004048616A1; DE10255095A1

Abstract

The invention relates to a method for producing a leather semi-finished product from the skin of an animal by pretannage using a chromium-free tanning agent and a clay mineral which, after being stirred for 30 minutes in water at 50 °C at a rotational speed of between 5 and 25 m/s, has a number-average particle diameter of less than 2 µm or a bimodal size distribution, a first fine-particle fraction having a number-average particle diameter of less than 0.5 µm and a second, coarser fraction having a number-average particle diameter of less than 5 µm, respectively according to the determination method in accordance with ISO 13320-1, by combined laser light diffraction and light scattering, the proportion of the first, fine-particle fraction amounting to between 10 and 90 wt. %, and then by drying the pretanned animal skin such that it has a water content of between 5 and 45 % in relation to the total weight of the leather semi-finished product.

Description

Process for the manufacture of a semi-finished leather product

The invention relates to a method for producing a semi-finished leather product.

In the leather industry, the perishable raw material, the animal skin, has to be converted into a biologically and mechanically stabilized state in order to be storable and transportable. For this purpose, semi-finished leather products are usually produced by pre-tanning using the following two, fundamentally different processes: firstly, by pre-tanning with chrome-containing tanning agents to form the so-called wet blue semi-finished product, and secondly by chrome-free pre-tanning to the so-called wet white semi-finished product.

Semi-finished leather products can be mixed with biocides in the moist state and then, provided that a maximum temperature of 25 ° C is not exceeded during transport and storage, can be stored for up to approx. 1 year.

Semi-finished wet biue products have the disadvantage that they already contain chromium, i.e. that further processing to a chrome-free leather is not possible and the waste from further processing, for example folding, has to be worked up or deposited in a complex process. In addition, their water content cannot be reduced below a value of around 40 to 80% by weight, since the skin appearance changes irreversibly when drying to lower water contents: wrinkles are fixed, later dyeing attempts lead to an uneven appearance, i.e. the quality is irreversibly deteriorated by drying attempts to lower water contents. Withdrawal is not possible without a reduction in quality.

In contrast, wet white semi-finished products have the advantage that they are not contaminated with the heavy metal chromium, but they are extremely susceptible to attack by microorganisms, in particular mold, and are therefore considered to be practically impossible to transport. In addition, semi-finished wet white products can practically not be dried to a water content below about 40 to 80% by weight, since they dry out like a horn with fiber bonding and reversion is therefore impossible.

Known semi-finished leather products have to be biologically stabilized with the addition of biocides. However, apart from their price, the use of biocides that were previously necessary to stabilize the semi-finished leather products is not without problems, since biocides can also be toxic, sensitizing or allergenic to humans and / or substances that are toxicologically harmful, especially formaldehyde , split off.

The main problem in connection with known semi-finished leather products is therefore that a certain water content must not be undercut if the quality of the leather to be produced in the subsequent process steps is not to be impaired. On the other hand, however, this still relatively high water content leads to correspondingly high transport costs and, in particular, to a limited ability to be transported and stored, since such semi-finished leather products are ideal breeding grounds for microorganisms.

There has been no shortage of attempts to develop processes for the production of semi-finished products which meet these conflicting requirements, i.e. lower the water content to an area where there is no longer any risk of microorganisms, and at the same time the quality of the semi-finished leather is not impaired.

EP-B 0 281 486 describes a process for the biological stabilization of pickled pelts, according to which a residual water content of only about 20% by weight can be achieved by water being selected by a substance from the group of polyalcohols, the condensates of fatty alcohols is replaced with ethylene oxide and the condensates of alkylphenols with ethylene oxide. However, this method has the major disadvantage that substances with surface-active properties are introduced to stabilize the semifinished product, which determine the basic character of the semifinished product and have a negative effect on subsequent tanning steps, for example by influencing the fat distribution. In addition, semi-finished products of this type have a relatively low shrinking temperature in the range of approximately 50 ° C.

It was an object of the invention to provide a method for producing a biologically stable semi-finished leather product which is environmentally friendly, the quality of the Semi-finished products and end products made from them are not affected and there are no restrictions on further processing.

The object is achieved by a process for producing a semi-finished leather product from an animal skin by pretanning with a chromium-free tanning agent, which is characterized in that a clay mineral is additionally used for the pretanning, which after stirring for 30 minutes in water at 50 ° C. a rotor speed in the range of 5 to 25 m / s, a number average particle diameter of less than 2 μm or a bimodal size distribution with a first, finely divided fraction, the number average particle diameter of which is less than 0.5 μm, and a second, coarser fraction, the number average particle diameter is less than 5 μm, in each case according to the determination method according to ISO 13320-1, by combined laser light diffraction and light scattering, the proportion of the first, finely divided fraction being between 10 and 90% by weight, and that the pretanned animal skin is applied to one Water content of 5 to 45%, based on the total weight of the L eder semi-finished products, dries.

It has surprisingly been found that semi-finished leather products, using finely divided clay minerals, are pre-tanned with the particle diameters defined above, dry loosely, fiber-insulated and, after drying, can be easily receded with pure water without additives.

Clay minerals that, after stirring for 30 minutes in water at 50 ° C with a rotor speed in the range of 5 to 25 m / s, have a number average particle diameter of less than 2 μm or a bimodal size distribution with a first, finely divided fraction, the number average particle diameter of which is less than 0.5 μm and a second, coarser fraction, whose number-average particle diameter is less than 5 μm, the proportion of the first, finely divided fraction being between 10 and 90% by weight, are used as tanning agents or for the production of tanning agents from the not previously published German patent application DE 102 37 259 known.

Clay minerals with the particle sizes defined above form stable formulations for use in chrome-free or chrome tanning, which ensure improved properties of the leather obtained therewith.

For the delamination to determine the number-average particle diameter, treatment with a sufficient amount, usually about 950 ml of water, is necessary 50 g of the clay mineral at 50 ° C. and vigorous stirring, with a rotor circulation speed in the range from 5 to 25 m / s, preferably from 10 to 20 m / s, are required for 30 minutes, the clay mineral being dispersed in the water. For example, a rotor-stator-Ultraturrax ^® mixer from LKA can be used for this. This treatment is intended to ensure that the clay mineral is delaminated until the particle size no longer changes.

The particle sizes and particle size distribution were determined in accordance with ISO 13320-1 by combined laser light diffraction and light scattering using an analysis device from Malvern, type Malvern 2000.

It is believed that the interaction of the clay minerals with the particle sizes defined above is essential for their interaction with the collagen chains of the skin. This interaction is possible, for example, via hydrogen bonds between collagen and the surface hydroxyl groups of the clay minerals. It was surprisingly found that clay minerals with the defined particle sizes are irreversibly embedded in the skin.

Clay minerals are weathering products made from primary aluminosilicates, i.e. from compounds with different proportions of aluminum oxide and silicon dioxide. Silicon is tetrahedrally surrounded by four oxygen atoms, while aluminum is in octahedral coordination. Clay minerals predominantly belong to the phyllosilicates also known as layered silicates or leaf silicates, but in some cases also to the band silicates (cf. Römpp Chemie Lexikon, 9th edition, 1995, pages 4651 and 4652).

For the formulations according to the invention, it is particularly advantageous if the clay mineral is a phyllosilicate. The phyllosilicate can preferably be a kaolinite, muscovite, montmorillonite, smectite, saponite, vermiculite, hallosit or bentonite, in particular a hectorite or an organically modified variant thereof.

Particularly good results are achieved if, before or during the use of the clay minerals as tanning agents, the substances are mixed with substances that, due to their chemical structure, are able to form strong hydrogen bonds with the clay mineral, in particular with urea or urea derivatives, alcohols, polyols, propylene carbonate organic amides Urethanes, saccharides or derivatives of saccharides, especially nitrocellulose, sulfite cellulose or ethylhexyl cellulose. This treatment supports, among other things, the delamination of the clay mineral, especially layered silicate.

In addition to the clay mineral, a chrome-free tanning agent is used for the pretanning, preferably an aldehyde tanning agent, an isocyanate, an aluminum salt, an oxazolidine or tetrakishydroxymethylphosphonium chloride.

Clay minerals with a number average particle diameter of less than 1 μm are preferably used.

In the process according to the invention, the animal skins pretanned using a finely divided clay mineral are dried to a water content of 5 to 45%, based on the total weight of the semi-finished leather product, preferably to a water content in the range from 15 to 35% by weight, based on the total weight of the semi-finished leather.

By setting the water content to a value below 45% by weight, preferably below 35% by weight, a state of the pretanned animal skin is achieved which is largely biologically stable and can nevertheless be re-soaked without problems, without impairing the quality of the end products made from it.

The drying step is fundamentally not restricted with regard to the process conditions: drying can be carried out at ambient temperature and pressure, under vacuum and / or at elevated temperature, preferably by stretch drying. Tension drying results in largely flat, easily stackable semi-finished products.

The method according to the invention preferably has the further processing step of drying the semi-finished leather product by treating it with water or the aqueous solution of a tannery auxiliary, in particular an amphoteric or cationic polymer, preferably by spraying, to a water content in the range from 50 to 80% by weight, based on the total weight of the semi-finished leather, recedes.

Another advantage of the method according to the invention is due to the absorbency of the largely dried semi-finished leather product: for example, aqueous solutions of tanning agents with a low affinity for the skin are physically absorbed and uniformly inner skin areas transported and distributed, which has so far led to unsatisfactory results due to the comparatively low chemical potential when working in an aqueous liquor. The semifinished leather product produced by the process according to the invention can thus be moistened in a further processing step with the aqueous solution of a tannery auxiliary which is absorbed into the semifinished leather product by physical forces, in particular osmosis, preferably mostly aqueous solutions of proteins, in particular Protein hydrolyzates or polymers. This can advantageously be carried out simultaneously with the step of retreating by spraying or dipping.

According to the invention, a semi-finished leather product is thus made available which is completely open with regard to further processing into end products. Chrome-free work can be carried out up to the stage of the semi-finished leather product, with further processing being possible both chrome-free and chrome tanning. The semi-finished leather product can be folded before drying as well as after receding, always producing chrome-free shavings. The waste during folding, which can amount to up to 30% of the material fed to the folding, is unproblematic because it is chromium-free, so it does not have to be disposed of as special waste, but on the contrary can be recycled as fertilizer.

A further advantage is that skin defects or abnormalities of the skin which impair the quality of the dried semifinished products can be better observed in the sense of the error detection and thus the sorting with regard to the skin quality can be carried out more easily, more quickly and with improved reproducibility. Another advantage is the reduced water content, which leads to obvious economic advantages in terms of transportation and storage.

The invention is explained in more detail below with the aid of examples.

Comparative example V0 and examples B1 to B5

The trade types listed below under their brand names are products from BASF AG, Ludwigshafen. Comparative example VO:

Core pieces of pickled beef halves split to a thickness of 3 mm were in succession at a pH of 2.8-3.0 and room temperature with 3% Relugan ^® GT 24, a glutardialdehyde solution, for 60 minutes and then with 3% of a 50 % liquid sulfon tannin treated. 1 mixture of Tamol ^® NA and sodium formate at pH 3.8 to 4.0 blunted: After a milling time of 90 minutes, with a second

Examples B 1 to B5:

Deviating from the pre-tanning described under V0, 2% by weight, based on the weight of the pimples, of the clay minerals listed below were added to the liquors together with the glutardialdehyde solution or immediately after the addition.

The morphological parameters are listed in Table 1 below. The average particle size of the clay minerals was determined by laser diffraction / light scattering on freshly prepared suspensions with a solids content of 5% in each case according to ISO 13320-1.

Fleet consumption and foldability were assessed visually on a scale from 1 to 5. The shrink temperature was determined in accordance with DIN 53336, which was modified in the following points as follows:

Point 4.1: The test pieces had the dimensions 3 cm • 1 cm, the thickness was not determined; Point 4.2: only one instead of two samples per leather sample was tested;

Point 6 was dropped;

Point 7 the drying in the vacuum desiccator was omitted and point 8 when the pointer fell the shrinkage temperature was read. Table 1:

The table shows mainly improved values in liquor consumption, foldability and shrinking temperature for examples B1 to B5, based on comparative example V0.

The semi-finished products obtained according to V0 or B1 to B5 were dried and then retanned. For this purpose, the skins obtained according to Comparative Example V0 and Examples B1 to B5 were rolled, folded to 1.5 to 1.7 mm and cut into four strips of the same size, each about 1 kg.

In the comparative experiments marked with the letter a below, one strip was left in the moist state, i.e. placed on trestle overnight and then further processed with the other strips of the corresponding test series.

1h in each of the experiments marked with the letter b, a strip was dried in air at 25 ° C, in the experiments marked with the letter c a strip was clamped or clamped on a frame and dried at 45 ° C in an air stream , Finally, in the examples marked with the letter d, a strip was placed in a vacuum dryer for 10 minutes 45 ° C and 80 mbar dried. The remaining water was measured with a moisture meter type Aqua-Boy ^® LMDI of Messrs. Schröder testing machines KG, Weinheim.

To assess the quality of the dried semi-finished products, they were subjected to retanning in the direction of furniture leather.

The pre-tanned and dried skin strips were drummed for 3 minutes in a barrel together with, based on the dry weight, 300% water. The receding behavior was assessed on a scale from 1 to 5, with good marks indicating that supple, absorbent skin was obtained without further mechanical treatment. Grade 5 indicates an irreversible cornification of the tissue.

The fiber appearance of the meat side was rated on a scale from 1 to 5. Grade 5 also stands for an inhomogeneous fiber morphology with a high proportion of fiber bonds.

For retanning, 20% Relugan ^® SI was dosed and drummed at 30 ° C for 10 minutes, followed by 20% Densodrin ^® PS, which was left to act for a further 90 minutes. 8% Basyntan ^® SW and 4% Luganil ^® Braun NGB were also used. This was followed by acidification to pH 3.6 with 3% formic acid over 30 minutes. The test strips of the a-series were mixed with about 50% reduced amounts of chemicals in tanning aids.

The leathers were washed twice with 500% water, wilted, air-dried and stabled. The leather was evaluated with regard to the quality properties of fullness, levelness and grain strength on a scale from 1 to 5. The tensile strength was determined in accordance with DIN 53328.

Table 2:

The results in Table 2 show that in the comparative experiments VOb to VOd the drying leads to an extreme deterioration in the quality of the fibers on the hot side and led to fiber bonding during the retraction. No leather end products could be obtained from the dried test strips of the VO series.

The comparison of the a-series (without drying) with the dried test strips of the series b to d shows mainly an improvement in the quality features of fullness, levelness, grain strength and tensile strength of the retanned end products.

Examples 6 to 9: retanning with chrome-containing tanning agents in the direction of shoe leather

Four pickled cattle halves with a gap thickness of 3.0 mm were converted into the corresponding semi-finished product according to the wet white standard method described above under Comparative Example V0.

In comparative example V6, the tanning liquor contained no clay mineral, whereas in examples 7 to 9 2.5% montmorillonite powder, corresponding to example B5, was used.

The pre-tanned skins were folded to 1.6 to 1.8 mm after wilting. The skins from Examples B8 and B9 were dried overnight on a stenter at 45 ° C. and the skins from Comparative Example V6 and Example B7, on the other hand, were protected from drying out until further processing.

In Example B8, the receding was carried out by dipping with water (150%) in a corresponding tub. In example B9, the skin was softened by spraying with a 20% solution of a protein hydrolyzate obtained from leather waste and then placed over bock for 2 hours.

The further processing of the halves in each followed by a barrel along with 150% of water, based on the shaved weight, about 0.3% formic acid, to a pH of 3.2 to 3.5, and 5% Chromitan ^® B, wherein the leather were drummed at 30 ° C for 90 minutes in a barrel. Subsequently, after the change of the liquor (100%) at 25 to 35 ° C 1% of the dye Luganil ^® Braun was blunted with sodium bicarbonate to pH 3.9 to 4.1, were added and drummed for 10 minutes. Thereafter, 3% Relugan RV polymer tanning agent, 5% Basyntan DLX sulfon tanning agent and 2% Relugan ^® DLF resin tanning agent were added and the drum was drummed again at 10 revolutions per minute for 20 minutes. In addition, the skin over 40 minutes with 3% of vegetable Mimosa ^®, followed by a further 2% of the dye Mimosa ® over 40 minutes was treated.

It was acidified to pH 3.6 to 3.8 with formic acid. After 20 minutes the liquor was drained and washed with 200% water. Finally, 5% Lipodermlicker ^® CMG and 2% Lipodermlicker ^® PN were dosed in 100% water at 50 ° C. After a milling time of 45 minutes, the mixture was acidified with 1% formic acid.

The washed leathers were wilted, dried and stalled and assessed according to the quality characteristics listed in Table 3 below.

The chrome consumption rate (in%) relates to the amount of chrome offered. The chromium concentration of the fleets was determined by titration. The Hotten exhaustion relates to substances that are used in further retanning steps, in particular resin tanning agents, fatliquoring agents or dyes, samples being taken after each coloring and fatliquoring and assessed visually.

Table 3:

The table shows that in examples B7 to B9 all leather properties are improved compared to comparative example V6 and, furthermore, the hotten consumption is also improved.

Claims

claims

1. A process for producing a leather semi-finished product from an animal skin by pretanning with a chromium-free tanning agent, characterized in that a clay mineral is additionally used for the pretanning, which after stirring for 30 minutes in water at 50 ° C. with a rotor circulation speed in the range of 5 up to 25 m / s a number-average particle diameter of less than 2 μm or a bimodal size distribution with a first, finely divided fraction whose number-average particle diameter is less than 0.5 μm and a second, coarser fraction whose number-average particle diameter is less than 5 μm, in each case according to the determination method according to ISO 13320-1, by combined laser light diffraction and light scattering, the proportion of the first, finely divided fraction being between 10 and 90% by weight, and that the pretanned animal skin has a water content of 5 to 45% , based on the

Total weight of the semi-finished leather, dries.

2. The method according spoke 1, characterized in that one selects the chromium-free tanning agent for the pretanning from the list below: aldehyde tanning agents, in particular glutaraldehyde, isocyanates, aluminum salts,

Oxazolidine or tetrakishydroxymethylphosphonium chloride.

3. The method according to claim 1 or 2, characterized in that drying the pretanned animal skin to a water content of 15 to 35%, based on the total weight of the semi-finished leather product.

4. The method according to any one of claims 1 to 3, characterized in that one uses a clay mineral with a number average particle diameter of less than 1 micron.

5. The method according to any one of claims 1 to 4, characterized in that before or during use of the clay mineral in the pre-tanning with substances that are able due to their chemical structure to form strong hydrogen bonds with the clay mineral, in particular with Urea or urea derivatives, alcohols, polyols, propylene carbonate, organic amides, urethanes, saccharides or derivatives of saccharides, in particular nitrocellulose, sulfite cellulose or ethylhexyl cellulose.

6. The method according to any one of claims 1 to 5, characterized in that the clay mineral is a phyllosilicate.

7. The method according spoke 6, characterized in that the phyllosilicate is a kaolinite, muscovite, montmorillonite, smectite, saponite, vermiculite, hallosit or bentonite, in particular a hectorite, or an organically modified variant thereof.

8. The method according to any one of claims 1 to 7, characterized in that the drying is carried out at ambient temperature and pressure, under vacuum and / or elevated temperature, preferably by stretch drying.

9. The method according to any one of claims 1 to 8, characterized in that it has the further process step that the leather semi-finished product is moistened with the aqueous solution of a tannery aid, the physical

Forces, in particular osmosis, are absorbed into the semi-finished leather product, preferably with the aqueous solution of a protein hydrolyzate.

10. The method according to any one of claims 1 to 9, characterized in that it has the further processing step that the dried leather semi-finished product by treatment with water or with the aqueous solution or suspension of a tannery aid, for example an amphoteric or cationic polymer , preferably by spraying, to a water content in the range of 50 to 80%, based on the total weight of the semi-finished leather product.