EP0533011B1 - Process for producing chrome-tanned leather - Google Patents

Description

In the normal production of chrome leathers, the peeling material is tanned after picking with standard chrome (III) salts. After mechanical dewatering and any splitting, the resulting wet blue is folded to the desired thickness.

This results in large quantities of chromium-containing shavings, the disposal of which causes ecological problems today. The same applies to corresponding trimmings.

In order to remedy this problem, it was proposed in US Pat. No. 4,060,384 to pre-tan the bare material chromium-free, so that the shrinking temperature of the skins rises to 77-85 ° C. The correspondingly pre-tanned skin material is then split (in the case of uncleaved pelts) and folded, producing non-chromium-containing, easy-to-dispose shavings. The skin material pretreated in this way is then chrome-tanned in the usual way. In practice, this process is called the Wet White process.

• Aluminiumverbindungen (z.B. Leather Manufacturer 105 (1987) 12, 9-16, Leder- und Häutemarkt (1985) 19, 28-35, JALCA 79 (1984) 6);
• Aluminium-/Titanverbindungen (z.B. EP-A 0 291 165, DE-OS 3 903 499);
• Glutaraldehyd beziehungsweise Glutaraldehydderivate, gegebenenfalls in Kombination mit Harz-/Austauschgerbstoff (z.B. DE-OS 3 935 879, JALCA 78 (1983) 174, LIRI Research Bulletin No. 894 (1985), JALCA 74 (1979) 9, 288-300);
• Austauschgerbstoffe auf Basis von Bis-(4-hydroxyphenyl)- sulfon (z.B. EP-A 428 481, Rev. Tech. Ind. Cuir 77 (1985) 5, 161-165);
• Oxazolidine (z.B. Leather 188 [1986] 4531, 41-43).

In the meantime, the following tanning substances, for example, have also been proposed for the pretanning claimed in US Pat. No. 4,060,384:

• Aluminum compounds (e.g. Leather Manufacturer 105 (1987) 12, 9-16, Leder- und Häutemarkt (1985) 19, 28-35, JALCA 79 (1984) 6);
• Aluminum / titanium compounds (e.g. EP-A 0 291 165, DE-OS 3 903 499);
• Glutaraldehyde or glutaraldehyde derivatives, optionally in combination with resin / exchange tanning agent (for example DE-OS 3 935 879, JALCA 78 (1983) 174, LIRI Research Bulletin No. 894 (1985), JALCA 74 (1979) 9, 288-300);
• Exchange tanning agents based on bis (4-hydroxyphenyl) sulfone (for example EP-A 428 481, Rev. Tech. Ind. Cuir 77 (1985) 5, 161-165);
• Oxazolidines (e.g. Leather 188 [1986] 4531, 41-43).

The chrome leather produced with the help of the substances described above differs in leather character in terms of feel (see, for example, Das Leder 37 (1986) 12, 221-224), fullness, softness and dyeability from conventionally chrome-tanned and folded leather. Experience has shown that such serious deviations in the property profile are not tolerated by the leather manufacturer and / or processor.

In order to avoid such disadvantages in further processing, in the case of aluminum pretreatment, it has been proposed to largely remove the aluminum salts by washing before folding before chrome tanning (see Das Leder 38 (1987) 4, 71-75). However, this additional work step leads to a toxicologically unacceptable contamination of the wastewater with aluminum salts.

It has now surprisingly been found that a pretreatment can also be carried out with special non-tanning condensation products, which gives a substrate that can be machine-dewatered and folded or split or folded without problems. The skin material pretreated in this way can be stored indefinitely after appropriate preservation under normal conditions. The resulting leather after chrome tanning does not differ in its application properties from conventionally chrome-tanned and folded leather.

The invention thus relates to a process for the production of chrome leather, characterized in that the descaled, pickled and pickled skin material in the usual manner in an aqueous liquor with a non-tanning condensation product of (i) aromatic C₆-C₂₄-sulfonic acids which are 0.8 to 3 Contain sulfonic acid groups per molecule, and (ii) formaldehyde pretreated and folded after mechanical dewatering or split (in the case of uncleaved pelt material) and folded and then chrome-tanned with commercially available chromium (III) salts and post-treated as usual. The usual aftertreatment generally includes neutralization, retanning, coloring and oiling.

The pretreatment agents used according to the invention are condensation products of aromatic sulfonic acids which do not contain any phenolic hydroxyl groups, e.g. those of naphthalene or diaryl ethers, e.g. the ditolyl ether, preferably the β-naphthalenesulfonic acid, with formaldehyde. Aromatic sulfonic acids preferred for the condensation contain 1 to 2 sulfonic acid groups per molecule.

The preparation of the condensation products to be used according to the invention is described below using the example of β-naphthalenesulfonic acid / formaldehyde:

1.1 to 1.8, preferably 1.4 to 1.5 mol of 100% sulfuric acid can be used per mole of naphthalene. The sulfonation is generally carried out at from 120 to 160, preferably 140 to 150 ° C. it is usually completed within 1 to 3 hours. 0.4 to 0.8, preferably 0.55 to 0.65, mol of formaldehyde are added (mostly in the form of its aqueous solution). The condensation can take place at temperatures from 95 to 120 ° C, preferably from 110 to 120 ° C; it is usually completed within 2 to 5 hours. Finally, the mixture is neutralized to a pH of 5 to 8, preferably 6 to 6.5, with alkali metal hydroxide solution or to a pH of 2 to 5, preferably 3 to 3.5, using ammonia. In a preferred embodiment, these products are adjusted to an acid number (mgKOH / g) of 20 to 60 with 1 to 8, preferably 3 to 4% by weight, based on the condensation product, of C₄-C₈-dicarboxylic acid (eg glutaric acid).

The condensation products used according to the invention do not have a single-gene effect (Bibliothek des Leders, Vol. 3, p. 65, Umschau-Verlag, Frankfurt / Main, 1st ed. 1985) in the sense of a covalent collagen crosslinking, as is the case, for example, with polyfunctional aldehydes and isocyanates or in Collagen cross-linking by hydrogen bonding with phenol-containing exchange / vegetable tannins or in the sense of collagen cross-linking by complex formation of mineral tannins.

By treatment with the condensation products used according to the invention, shrinkage temperatures of less than 65 ° C. are achieved. At the same time, however, they cause extremely strong drainage of the skin material on the wilting machine and enable trouble-free mechanical folding without any signs of burns.

It proves to be particularly advantageous here that the fold thickness of the skin material pretreated in this way corresponds to the thickness of the chrome-tanned finished leather and makes additional folding unnecessary.

Another advantage is that the timing of this wet white process largely corresponds to the production rhythm of conventional chrome leather production.

In the processes according to the invention, the pestle material obtained by customary soaking and liming is descaled in the usual way, pickled and with pH values of organic and / or inorganic acids 2 to 6, preferably 2.5 to 4.5 adjusted (pounded).

The pretreatment is then carried out with 3 to 15, preferably 4 to 8% by weight (based on the pelt weight) of the above-mentioned condensation products, calculated as a solid.

After mechanical dewatering, the hides pretreated in this way can be folded without any problems or, in the case of uncleaved nakedness, split and folded.

The skins are then chrome-tanned with commercially available chromium (III) salts and finished in the usual way.

The finished leather obtained by the process according to the invention has no differences in the property profile compared to conventionally produced chrome leather. The leathers can be dyed brilliantly and are therefore particularly suitable for the production of high-quality aniline leather for processing into furniture, shoe upper and clothing leather.

The shavings obtained by the process according to the invention are chromium-free and offer various options for disposal.

The condensation products used according to the invention can be used in spray-dried form or as an aqueous solution.

• anorganische Aluminium- und/oder Titanverbindungen
• Aldehyde
• Oxazolidine
• phenolische Gruppen enthaltene Verbindungen und Mischungen dieser Substanzen.

The condensation products used according to the invention can also be used in combination with other tanning substances. Examples include:

• inorganic aluminum and / or titanium compounds
• Aldehydes
• Oxazolidines
• compounds and mixtures of these substances containing phenolic groups.

Unless stated otherwise, the percentages in the following examples relate to the weight.

The dilution ratios mentioned in the following examples relate to parts by weight, the larger number in each case meaning the parts of water.

The concentrations of the acids to be diluted correspond to the usual practice: formic acid 85%, sulfuric acid 96%.

Examples Production of the condensation product to be used according to the invention

1 mol of naphthalene is sulfonated with 1.43 mol of 100% sulfuric acid at 145 ° C for 3 hours. The sulfonation mixture is allowed to cool somewhat and is condensed for 3 hours at 115-117 ° C. with 0.64 mol of formaldehyde, which is used in the form of its 30% strength aqueous solution. The reaction mixture is then allowed to cool to 80 ° C. and aqueous ammonia is then added to a pH of 3.5. 4%, based on the resulting ammonium salt of the condensation product, of glutaric acid is added to this solution and an acid number of 35 is thus obtained. The product is preferably spray-dried, but can also be used as a 40-60% strength aqueous solution.

example 1 Manufacture of furniture leather a) after the Wet White process

To produce furniture leather, washed 800 kg of beef pelts (split by 2 mm) in the tanning drum are first washed with 100% (based on pelt weight; like all the following% data) water at 35 ° C. for 15 minutes. The fleet is drained and then is without liquor, decalcified with 1.3% ammonium chloride and 0.4% citric acid for 45 minutes, 80% water at 35 ° C added and pickled with 0.2% of a commercially available pickling agent (with 1500 tryptic units) for 120 minutes (pH value of the liquor 7.7). The cross-section of the nakedness no longer gives a red color with phenolphthalein. Then it is washed with 100% water at 25 ° C. and the liquor is drained apart from a remaining liquor of approx. 50%. 5 minutes after the addition of 8% sodium chloride, 0.4% formic acid (diluted 1:10 with water) and after a further 10 minutes 0.6% sulfuric acid (diluted 1:10 with water) are added and pickled for 180 minutes (pimple pH Value 3.4).

5% of the condensation product to be used according to the invention is now added to the pickling liquor. After one hour, 1% of a commercially available synthetic fat is added and the process is continued for 10 hours. The final pH is 3.4 and the final temperature is 31 ° C.

After draining the remaining liquor, the wet whites are unloaded, wilted and, if necessary, folded to 1.0 mm thickness after 24 hours of intermediate storage. About 30 kg of chromium- free shavings are obtained per 100 kg of bare material used.

300 kg of folded wet whites were mixed in 1% of a commercially available synthetic fat in 250% (based on fold weight; like all the following% data) water of 35 ° C. and drummed for 15 minutes. Then 0.5% formic acid (diluted 1:10 with water), after 45 minutes 11.5% of a commercially available, weakly organic mask Chromium (III) sulfate solution with 15% chromium (III) oxide and 40% basicity (according to Schorlemmer), and after a further 15 minutes 3% fat (see above) was added. After a running time of 60 minutes, 0.9% sodium bicarbonate is added in 3 installments of 30 minutes each and run for 120 minutes (pH = 3.4). The liquor is heated to 38 ° C. and 4% of a commercially available chromium-syntan complex (commercially available chromium-containing synthetic retanning agent with 12% chromium (III) oxide) is added, after 15 minutes running time 6% of a fat mixture of natural and synthetic fats added and tanned for 8 hours. The remaining liquor has a chromium (III) oxide content of 1.8 g / l, a final pH of 3.3 and a final temperature of 35 ° C. The mixture is then neutralized to pH 6.5 in the usual way, greased and finished by intermediate drying.

b) after usual chrome tanning

The descaled, pickled and pickled pelts (slit thickness 2 mm) in Example 1a) are mixed in the pickling liquor with 2.3% (based on pelt weight, like all the following% data) of a commercially available synthetic fat, and after 15 minutes 9% a commercially available, slightly organically masked chromium (III) sulfate solution with 15% chromium (III) oxide and 40% basicity (according to Schorlemmer) was added. After a running time of 90 minutes, 0.35% magnesium oxide is added and the process is continued for 10 hours. The final pH is 3.8 and the final temperature is 38 ° C. The chromium oxide (III) content of the remaining liquor is 5.9 g / l.

The resulting wet blues (with approx. 3.8% chromium (III) oxide, based on anhydrous wet blue) are wilted and folded to a thickness of 1.0 mm. The folded wet blues have the same chromium (III) oxide content as that in example 1a) after the chrome-tanned wet whites have been folded. About 28 kg of chrome shavings with about 3.8% chromium (III) oxide, based on anhydrous chrome shavings, are obtained per 100 kg of bare material used. The mixture is then neutralized to pH 6.5 in the usual way, greased and finished by intermediate drying.

The table below compares the chromium emissions of the two processes.

Example 2 Manufacture of furniture leather

To produce furniture leather, the wet white leather produced in example 1a) is wilted and folded. 100 kg of folded wet whites in 250% water (based on fold weight; like all the following% data) are mixed with 1.5% of a commercially available, synthetic fat and drummed for 15 minutes. Then 0.4% formic acid (diluted 1:10 with water) and after 45 minutes 7% of a commercially available chrome tanning agent with 26% chromium (III) oxide and 33% basicity (according to Schorlemmer) are added. After a further 15 minutes of running time, 3% fat is added (see above). After 60 minutes, 3% of a commercially available, self-dulling chromium-syntan complex with 11% chromium (III) oxide are added and the mixture is left to run for 150 minutes (pH = 3.7). The liquor is heated to 38 ° C., 3% of a commercially available chromium-syntan complex with 12% chromium (III) oxide and, after 15 minutes, 6% of a fat mixture of natural and synthetic fats are added and tanned for 8 hours. The remaining liquor has a chromium (III) oxide content of 0.9 g / l, a final pH of 3.6 and a final temperature of 36 ° C.

The mixture is then neutralized to pH 6.5 in the usual way, greased and finished by intermediate drying.

Example 3 Manufacture of furniture leather

To produce furniture leather, ashed, decalcified and pickled pelts are washed in 50% liquor as in Example 1a) after addition of 8% sodium chloride with 0.5% formic acid (diluted 1:10 with water) and 0.3% sulfuric acid (1:10 diluted with water) and pickled for 120 minutes (pimple pH 3.7).

10% of an aqueous solution (50%) of the condensation product to be used according to the invention are now added to the pickling liquor. After one hour, 1.5% of a commercially available synthetic fat is added and the process is continued for 10 hours. The final pH is 3.7 and the final temperature is 32 ° C. The remaining fleet is chrome-free. The wet whites are further processed analogously to example 1a).

Example 4 Manufacture of furniture leather from unsplit pelts

To produce furniture leather, 100 kg of beef pestle, unsplit, washed in the usual manner is first washed in the tanning drum with 150% (based on pelt weight, like all the following% data) water of 38 ° C. twice for 15 minutes. The liquor is drained and then decalcification without liquor with 2.5% ammonium sulfate, 0.3% sodium bisulfite and with 0.4% formic acid (diluted 1:10 with water) for 60 minutes, 40% water added at 35 ° C and pickled with 0.5% of a commercial pickling agent (with 1500 tryptic units) for 50 minutes (pH of the liquor 7.5). The cross-section of the nakedness no longer gives a red color with phenolphthalein.

Then it is washed twice with 150% water at 20 ° C. and the liquor is drained apart from a remaining liquor of approx. 30%. 5 minutes after the addition of 6% sodium chloride, 0.5% formic acid (diluted 1:10 with water) and after a further 10 minutes 0.7% sulfuric acid (diluted 1:10 with water) are added and the mixture is pickled for 180 minutes (pimple pH Value 3.1).

8% of the condensation product to be used according to the invention are then added to the pickling liquor and further tumbled for 10 hours. The final pH is 3.1 and the final temperature is 32 ° C.

After draining the remaining fleet, the wet whites are unloaded, wilted and split to 2 mm. About 400 g of chromium-free pelt gap is obtained per kg of pelt.

After 24 hours, the wet whites are folded to a thickness of 1 mm and processed as in Example 1a). However, care must be taken to ensure that the pH in the chrome tanning is increased to approximately 3.5 by adding 1.1% (instead of 0.9%) of sodium bicarbonate.

Example 5

100 kg of beef peat pretreated as in Example 4 are mixed with 0.5% formic acid (1:10 with water) and 0.6% sulfuric acid (1:10 diluted with water) pickled (pimple pH 3.2). The pretreatment is carried out with 17% of an aqueous solution (50%) of the condensation product to be used according to the invention. The wet whites are then wilted, split and folded as in Example 4 and processed as in Example 2.

Example 6 Manufacture of upper leather

For the production of upper leather, washed 1000 kg beef pelts (split approx. 3.5 mm) in the tanning drum are washed in the usual way with 150% (based on pelvis weight; like all the following% data) water of 38 ° C for 10 minutes. The liquor is drained and then descaled with 30% water at 35 ° C with 2% ammonium sulfate, 0.2% sodium bisulfite and 0.2% formic acid (diluted 1:10 with water) for 30 minutes and with 0.5% of a commercially available Pickling agent (with 1500 tryptic units) pickled for 30 minutes (pH of the liquor 8.3). The cross-section of the nakedness no longer gives a red color with phenolphthalein. Then it is washed twice with 150% water at 20 ° C. and the liquor is drained down to a remaining liquor of approx. 20%. 5 minutes after the addition of 5% sodium chloride, 0.5% formic acid (diluted 1:10 with water) and after 10 minutes 0.7% sulfuric acid (diluted 1:10 with water) are added and the mixture is pecked for 60 minutes (pimple pH value 3.1).

6% of the condensation product to be used according to the invention and 0.1% are now added to the pickling liquor Sodium bisulfite (for H₂S elimination) added. After one hour, 1% of a commercially available natural fat (oil product) is added and the product is tumbled on for 12 hours.

The final pH is 3.2 and the final temperature is 31 ° C. After draining off the remaining liquor, the wet whites are unloaded, wilted and, if necessary, folded to 1.8 mm thickness after 24 hours of intermediate storage. Approx. 36 kg of chrome-free shavings are obtained per 100 kg of bare material used.

100 kg of folded wet whites are mixed in 150% (based on fold weight; like all the following% data) water at 35 ° C with 12% of a commercially available, slightly organically masked chromium sulfate solution with 15% chromium (III) oxide and 40% basicity ( according to Schorlemmer), added (pH = 3.1). After 2 hours, 3% of a commercially available, self-dulling chromium-syntan complex with 11% chromium (III) oxide are added and after 2 hours (pH = 3.6) heated to 39 ° C.

After a running time of 12 hours, the liquor is drained, 100% water at 50 ° C. is added and 1.5% of a commercially available chrome tanning agent with 26% chromium (III) oxide and 33% basicity (according to Schorlemmer) and 2% of the above-mentioned chromium -Syntan complex post-chromed over 60 minutes (pH = 4.1). The mixture is then neutralized to pH 4.7 with 1.5% of a commercially available neutralizing tanning agent and 0.5% sodium bicarbonate, and the liquor is drained off after 45 minutes. The neutralized Chrome leather is retanned in the usual way (with a combination of exchange, resin or polymer and vegetable tannins), dyed and greased.

Example 7 Manufacture of upper leather

For the production of upper leather, ashed, decalcified and pickled 100 kg of beef pelts (split approx. 3.5 mm) in 20% (based on pelt weight, like all the following% data) are left in a liquor after addition of 5% sodium chloride with 0 , 5% formic acid (1:10 diluted with water) and 0.7% sulfuric acid (1:10 diluted with water) for 60 minutes (pimple pH 3.1).

11% of an aqueous solution (50%) of the condensation product to be used according to the invention and 0.1% of sodium bisulfite are now added to the pickling liquor. Then, as in Example 6, greasing, tumbling, unloading, wilting and folding are carried out.

50 kg of folded wet whites in 150% (based on fold weight: like all the following% data) water of 35 ° C with 7% of a commercially available chrome tanning agent with 26% chromium (III) oxide and 33% basicity (according to Schorlemmer) (pH = 3.0). After 2 hours, 30% of a commercially available chromium-syntan complex with 15% chromium (III) oxide are added and the solution is truncated to pH 3.6 with 0.8% sodium bicarbonate. After 2 hours, the mixture is heated to 39 ° C. The leather is processed and finished as in Example 6.

Example 8 Manufacture of furniture leather

To produce furniture leather, decalcified and pickled 800 kg of beef pelts (split 2.1 mm) are tanned in 50% (based on pelt weight; like all the following% data) residual liquor after addition of 7.5% sodium chloride and addition of 0.4% formic acid (1:10 diluted with water) after 5 minutes and 0.5% sulfuric acid after a further 10 minutes total 180 minutes (pimple pH 3.5).

4% of the condensation product to be used according to the invention is added to the pickling liquor. After 30 minutes, 0.5% of a commercially available synthetic exchange tanning agent based on bis (4-hydroxyphenyl) sulfone is added. After a further 60 minutes, 1.5% of a commercially available synthetic fat is added and the process is continued for 12 hours.

The final pH is 3.5 and the final temperature is 33 ° C.

After draining off the remaining fleet, the wet whites are unloaded, withered and folded, chrome-tanned and finished as in Example 1.

Claims (6)

1. Process for producing chrome leather, characterized in that the hide material delimed, bated and pickled in the conventional manner is pretreated in an aqueous liquor with a condensation product not having a tanning action and consisting of (i) aromatic C₆-C₂₄-sulphonic acids, which contain 0.8 to 3 sulphonic acid groups per molecule, and (ii) formaldehyde, and, after mechanical dewatering, is shaved or (in the case of unsplit pelt material) split and shaved and then chrome-tanned with commercially available chromium(III) salts and after-treated in the usual way.
2. Process according to Claim 1, characterized in that sulphonation products of naphthalene or diaryl ethers are used as the sulphonated aromatic compounds.
3. Process according to Claim 1, characterized in that pelt material split after liming is used.
4. Process according to Claim 1, characterized in that the split pelt material is pretreated with 3-15% by weight, relative to pelt material, of the condensation product, calculated as solids.
5. Process according to Claim 1, characterized in that the condensation product is used in combination with a tanning substance.
6. Process according to Claim 5, characterized in that aluminium compounds and/or titanium compounds, aldehydes, oxazolidines or compounds containing phenolic groups, optionally in combination with one another, are used as tanning substances.