NO141690B - PROCEDURE AND MEDICINE FOR CHROME BEARING OF LAWS - Google Patents

Description

For the production of leather, animal hides and skins are tanned

large scale with chrome tanning substances. This results in a residual bath with a relatively high chromium oxide content, e.g. 6-10 g C^O^/l.

Altogether there will be approx. 20-30% of the total amount of chromium oxide unused in the residual baths. In addition to the economic disadvantage, this incomplete utilization presents difficulties for the leather manufacturer when cleaning waste water.

There has therefore been no shortage of attempts to improve the utilization of waste baths. Thus, it is e.g. proposed to

re-apply the remaining bath after tanning after adding powdered chrome tanning substances. This method is laborious and in baths used several times the leather is enriched

fibers and salts to an increasing extent.

By increasing the pH value of the tanning baths, the affinity of the chrome tanning substance to the skin is increased. By thus increasing the baths' pH

values, it is therefore possible to provide a full

constant depletion of the chromium tannins. However, the increased astringency of the chrome tanning substances leads to a contracted grain, i.e. insufficiently smooth leather.

Furthermore, it has been proposed to use so-called network-forming acting dicarboxylic acids, e.g. phthalic acid, when pickling or in chrome tanning. When used in pickel, the rate of penetration of the chrome tanning agent into the skin is slowed down, and it occurs especially with unprepared leather that penetration is difficult.

and an uneven distribution of chromium in the cross-section of the skin. In the chrome tanning itself, the sodium salts of these acids are used together with the chrome tanning substances in solution. Thereby, only amounts up to approx. 1.5 mol per mol C^O-^ usable, since the solutions in the pH and concentration ranges required for chrome tanning when used on a technical scale are only stable for a short time,

after which precipitates are formed (compare e.g. Das Leder, year 1972, page 174, Austrian patent 275,011, German patent 643,088, Journ. of the Internat.Soc. of Leather Trades Chemists, vol. 27 (1943) , page 83) .

The invention relates to a method for chrome tanning by pre-tanning the pickled, cleaned leather hide with chromium (III) salts and tanning with chromium (III) salts, acid binding agents and aliphatic dicarboxylic acids and/or aromatic di- and tricarboxylic acids and/or their salts, the method being characterized in that the tanning takes place with mixtures of chromium (III) salts, acid binders and at least 1.6 mol, preferably 2-3 mol of aliphatic dicarboxylic acids with 4-6 C atoms and/or aromatic di- and /or tricarboxylic acids with 8-13 C atoms and/or their salts per moles of C^O^ of the chromium (III) salts used for tanning, the components being added in powder form, preferably together, so that the total amount of C^O^ consumed amounts to 1.2 to 2%, referred to the weight of cleaned leather skin, especially 1.5

to 1.8%, and that the tanning is carried out with a bath volume of in-

to 100%, referred to leather hide weight, up to a final pH value of the tanning bath which is above 3.6, especially between 3.8 and 4.2.

The invention also relates to a means of execution

of the above method as stated in claim 4.

As chromium (III) salts for the pre-tanning, the usual chromium (III) salts usable for chromium tanning are suitable, especially chromium (III) sulfates, basic chromium (III) sulfates, further with organic acids, e.g. . formic acid, acetic acid, marked chromium (III) salts, self-buffering chromium tanning substances, chromium tanning substances which, in addition to chromium (III) salts, also contain inorganic salts such as sodium sulfate or reaction products of 6-valent chromium compounds with reducing agents, eg.

The mixtures used for tanning contain chromium (III) salts preferably chromium sulphates and basic chromium sulphates. Furthermore, chromium (III) salts, in particular chromium (III) sulphates which suitably have only a small degree of masking, are also usable.

As an acid-binding agent, e.g. dolomite, alkali carbonates and bicarbonates, alkaline earth carbonates and bicarbonates, magnesium oxide and sodium sulphite.

The mineral double salt CaCO^- is used as dolomite

MgC03, which has a content of 20-40% CaO, preferably 25-35%

CaO and which has a content of from 10 to 25% MgO, preferably 16

to 24% MgO. The dolomite can be used either alone or in combination with other acid-binding substances, as the dolomite content of the mixture should preferably amount to at least 10% of the total amount of acid-binding agents used.

Particularly suitable are mixtures containing 10-130 parts by weight of dolomite per 100 parts by weight Cr203. The amount of dolomite to be used depends on the basicity of the chromium (III) salts used, further on the basicity to which these chromium (III) compounds are to be brought during tanning, on the basicity and quantity of the chromium (III) used in pre-tanning III) salts and according to the amount of any further acid-binding substances co-used in the mixture.

As aliphatic dicarboxylic acids with 4-6 C atoms

can e.g. succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, aspartic acid, glutamic acid or their mixtures are used. Preferably, glutaric acid and adipic acid or mixtures are used

of these acids, optionally with further other dicarboxylic acids.

Aliphatic dicarboxylic acids with 4-6 C atoms which contain a hydroxy group in the a-position to the carboxyl group and/or the sulphonic acid group should only be co-used up to approx. 1/3 (molar ratio) of the combined amounts of dicarboxylic acid used.

Aromatic dicarboxylic acids and tricarboxylic acids with 8-13 C atoms are those of the benzene and naphthalene series, which, in addition to the carboxyl group, may also contain hydroxy,

amino or nitro groups and/or halogen atoms. Phthalic acid and isophthalic acid are preferably used. Aromatic di- and tricarboxylic acids which, in addition to the carboxyl groups, also contain sulfonic acid groups can only be used together Up to approx. 1/3 (molar ratio) of the combined amounts of carboxylic acid used.

The carboxylic acids can be used both in their form

free acids, in the form of mixtures of the free acids and the salts of such carboxylic acids as also alone in the form of the salts, suitably of the alkali metal salts. Powdered mixtures of free carboxylic acids and their salts are preferably used in molar ratios of 60:40 and 40:60.

To carry out the method according to the invention, decalcified and pickled cleaned leather is used in a manner known per se. The chromium (III) salts used for tanning are preferably used in an amount of at least 0/5% C^O^», preferably of at least 0.8% C^O-^, referred to cleaned leather hide weight. In a preferred embodiment, the pre-tanning is carried out in such a way that the skin is already fully tanned through the overall cross-section.

The tanning takes place conveniently in the same bath by adding the mixture in powder form. Components of the mixture according to the invention can preferably be added simultaneously.

Of these components, only some can also be added together, but also separately. Appropriately, the basic chromium (II) salts are added alone or first together with further components. These chromium (III) salts can also be added together with the chromium (III) salts used for tanning.

The quantities to be used of the mixtures are dimensioned so that the combined total Cr^ O^ quantity in pre-tanning and tanning amounts to 1.2 to 2%, especially 1.5 to 1.8% Cr 2 O 3 , referred to cleaned leather skin weight.

Tanning takes place in a bath of a size equal to or less than 100%, preferably 10 to 50%, referred to the weight of cleaned leather. The tanning thus leads to a pH in the bath at the end of the tanning which is equal to or greater than 3.6, especially 3.8 to 4.2.

The value of the method according to the invention lies in the sum of the mutually coordinated method precautions which lead to a particularly high depletion of the chrome tanning without the leather quality being adversely affected, when the tanning process is carried out on a technical scale. A residual bath is obtained with a C^O^ content below lg per litres.

It could not be predicted that with greater than or equal to 1.6 mol of aliphatic carboxylic acids or aromatic di- and tricarboxylic acids per mol Cr203 of the chromium (III) salts used for tanning, in connection with the additional inventive precautions, tanning can be carried out, preferably short baths, i.e. at higher concentrations on a technical scale without chromium precipitation and through-tanning difficulties occurring and yet high chromium depletions are achieved . Against the use with less than 1.5 mol of aromatic di- and tricarboxylic acids or aliphatic carboxylic acids per mol Cr203, a clearly better depletion of the residual bath is achieved by observing the precautions according to the invention.

The method according to the invention shall be explained in more detail by means of the following examples:

Example 1

For the production of aniline leather, 1,000 kg of cleaned cow hide (gap thickness 3 mm) is washed in the usual way in the tanning vat (diameter 2 m, width 2.25 m, rotation speed 12 rpm) in the first row with 150%, referred to hide weight, water of 38°C for 10 minutes. The bath is emptied and the skin is then decalcified with 70% water at 32°C with 3% ammonium chloride and 0.6% sodium bisulphite for 35 minutes and stained for 30 minutes with 0.7% of a commercial enzymatic mordant (bath's pH value 8.0) . The cross-section of the cleaned leather-skin gives no more red coloring with phenolphthalein. It is then rinsed with water at 18°C for 10 minutes and the rinse water is emptied to a residual bath of 30%. 5 minutes after adding 4% table salt pickles with 0.6% formic acid (1:4 dilution) and 0.25% sulfuric acid (1:8 dilution) for 60 minutes (pH 3.6). In the pickle bath, 3.1% of a powdered 33% basic chromium (III) sulfate with a

content of 26% chromium oxide. After an operating time of 1 hour, 5.6% of the tanning mixture mentioned below is subsequently added and further vinified for 7^ hours. The tanning mixture consists of 481 parts by weight powdered 33% basic chromium sulphate, containing 26% chromium oxide, 107 parts by weight dolomite, 163 parts by weight phthalic acid, 249 parts by weight sodium phthalate. The final temperature is 44°C, the final pH is 3.7, the residual bath contains 0.7 g Cr203/litre. After the usual finishing, leather is obtained with a full, gentle grip and very uniform coloring.

In the following examples, parts means parts by weight.

Example 2

100 parts of cleaned cowhide are pre-treated as in example 1, pickled with common salt, sulfuric acid and/or formic acid in the usual way with 20 liters of water in the tanning vat (pH 3.9). In the pickle bath, there are 2 parts of a powdered 50% basic chromium (III) sulphate with a content of 30% chromium oxide and 16% formic acid. After an operating time of X "hours, 5.9 parts of the below-mentioned tanning mixture are added and further washed for 2 hours. The tanning mixture consists of 524 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 61 parts dolomite, 27 parts magnesium oxide, 67 parts

phthalic anhydride, 321 parts of the sodium salt of isophthalic acid. The final temperature is 42°C, the final pH is 4.2, residual

the bath contains 0.3 g Cr203/litre.

Example 3

100 parts of cleaned cowhide pre-treated as in example 1 pickles with common salt, sulfuric acid and/or formic acid in the usual way with 25 parts of water in the tanning vat (pH 4.0). In the pickle bath, 2.3 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide are added. After an operating time of

After 1 hour, add 7.0 parts of the tanning mixture specified below

ding and further sifted for 7 hours. The tanning mixture consists of 552

parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 86 parts dolomite, 44 parts sodium carbonate, 140 parts 3-nitrophthalic acid, 178 parts of the sodium salt of isophthalic acid. The final temperature is 40°C, the final pH is at 40, the residual bath contains 0.7 g of Cr2O3/1.

Example 4

100 parts of cleaned cowhide are pre-treated as in example 1, pickled with common salt, sulfuric acid and/or formic acid

in the usual way with 30 parts water in a tanning vat (pH 3.8). In the pickle bath, 2.1 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide and 5% acetic acid are added. After a residual time of 1 hour, 8 parts of the tanning mixture mentioned below are added and further vinified for 8 hours. The tanning mixture consists of 602 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 74 parts dolomite, 324 parts of the sodium salt of isophthalic acid. The final temperature is 43°C, the final pH is 3.9, the residual bath contains 0.2 g Cr203/1.

Example 5

100 parts of cleaned cowhide pre-treated as in example 1 pickles with common salt, sulfuric acid and/or formic acid in the usual way with 20 liters of water in the tanning vat (pH 4.0). In the pickle bath, 4.4 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide are added. After an operating time of

1 hour later, 6.4 parts of the tanning mixture mentioned below are added and further vinified for 1/ hour. The tanning mixture consists of 420 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide,

88 parts dolomite, 4 92 parts of the sodium salt of 4-chloroisophthalic acid. The final temperature is 45°C, the final pH is 4.2, the residual bath contains 0.4 g Cr203/1.

Example 6

100 parts of cleaned cowhide pre-treated as in example 1 pickles with common salt, sulfuric acid and/or formic acid in the usual way with 20 liters of water in the tanning vat (pH 5.0). In the pickler bath, 3.4 parts of potassium chrome alum with a content of 15% chromium oxide are added. After an operating time of 1 hour, 5.5 parts of the below-mentioned tanning mixture are added and further vinified for 1 hour. The tanning mixture consists of 559 parts powdered 33% basic chromium sulfate containing 26% chromium oxide, 50 parts dolomite, 29 parts magnesium oxide, 362 parts of the sodium salt of terephthalic acid. The final temperature is 40°C, the final pH is 4.3, the residual bath contains 0.1 g Cr203/litre.

Example 7

100 parts of cleaned cowhide are pretreated as in example 1, pickled with common salt, sulfuric acid and/or formic acid in the usual way with 30 parts of water in a tanning vat (pH 3.8). In the pickle bath, 4 parts of a powdered 50% basic chromium (III) sulphate with a content of 30% chromium oxide and 16% formic acid are added. After an operating time of 1 hour, 8.3 parts of the tanning mixture mentioned below are added and further vinified for 8 hours. The tanning mixture consists of 372 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 48 parts dolomite, 34 parts sodium bicarbonate, 107 parts 3-nitrophthalic acid, 439 parts sodium shiltet of benzene, 1,3,5-tricarboxylic acid. The final temperature is 42°C, the final pH is 4.0, the residual bath contains 0.4 g Cr203/1.

Example 8

100 parts of cleaned cattle hide are pretreated as in example 1, pickled with common salt, sulfuric acid and/or formic acid in the usual way with 25 parts of water in a tanning vat (pH 3.9). In pickle

5 parts of a powdered 33% basic chromium (III) sulphate with a content of 26% chromium oxide are added to the bath. After an operating time of 1 hour, 5.1 parts of the tanning mixture mentioned below are subsequently added and further macerated for 7 hours. The tanning mixture consists of 377 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 30 parts dolomite, 30 parts sodium carbonate, 554 parts of the sodium salt of 5-amino-isophthalic acid. The final temperature is 45°C, the final pH is 3.9, the residual bath contains 0.1 g Cr203/1.

Example 9

100 parts of cleaned cowhide are pre-treated as in example 1, pickled with common salt, sulfuric acid and/or formic acid in the usual way with 20 parts of water in the tanning vat (pH 3.8). In the pickle bath, 6.2 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide and 5% acetic acid are added.

After an operating time of 1 hour, 7.3 parts of the tanning mixture mentioned below are added and further vinified for 1 hour. The tanning mixture consists of 210 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 25 parts dolomite, 150 parts 3-nitrophthalic acid, 615 parts of the sodium salt of 5-amino-isophthalic acid. The final temperature is 42°C, the final pH is 3.9, the residual bath contains 0.7 g Cr203/1.

Example 10

Roughly 8 x 30 cm in size, corresponding to example 1, up to and including decalcification, pre-treated cattle hides are pickled and chrome-tanned comparatively as described by E. Komarek and G. Mauthe in "Das Leder" (1961), pages 285 to 289, especially page 287 .

100 parts of cleaned bovine hide from a piece of A pickles with 3 parts of common salt, 0.7 parts of formic acid and 0.4 parts of sulfuric acid in the usual way with 11 parts of water in a milking machine (pH 3.7).

In the pickle bath, 3.1 parts of a powdered 33% basic chromium (II) sulphate with a content of 26% are added. chromium oxide. After an operating time of 1 hour, add 5.6 parts of the tanning mixture mentioned below. The tanning mixture consists of 481 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 163 parts phthalic acid and 249 parts sodium phthalate and 107 parts dolomite.

100 parts of cleaned bovine leather of the equivalent

piece B pickles with 3 parts table salt, 2.3 parts phthalic acid (equivalent amount, of phthalic acid and sodium phthalate used when tanning comparison pieces A) in the usual way with 11 parts water in a pickling machine (pH 4.0). In the pickle bath, 3.1 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide are added. After an operating time of 1 hour, add 3.3 parts of the tanning mixture mentioned below. The tanning mixture consists of 820 parts powdered 33% basic chromium sulphate, containing 26% chromium oxide and 180 parts dolomite.

In order to examine the through-tanning speed, the tanning on the rolling machine is interrupted and the comparable pieces of leather A and B are cut. The piece A pickled without phthalic acid shows, compared to the piece B pickled with phthalic acid, a clearly faster through-tanning at the same pH values of the residual bath.

Example 11

100 parts cleaned cowhide pre-treated as in example 1 pickles with common salt, sulfuric acid and/or formic acid in the usual way with 20 parts water in a tanning vat (pH 3.6). In the pickle bath, 3.1 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide are added. After an operating time of 1 hour, 8.3 parts of the tanning mixture mentioned below are added and further vinified for 8 hours. The tanning mixture consists of 419 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 65 parts dolomite, 107 parts phthalic acid, 409 parts of the sodium salt of 1,8-naphthalene dicarboxylic acid. The final temperature is 43°C, the final pH is 4.1, the residual bath contains 0.8 g Cr203/litre.

Example 12

100 parts of cleaned cowhide are pre-treated as in example 1, pickled with common salt, sulfuric acid and/or formic acid in the usual way with 20 parts of water in the tanning vat (pH 3.9). In the pickle bath, there are 6 parts of a powdered 33% basic chromium (III) sulphate with a content of 26% chromium oxide. After an operating time of one hour, 0.7 parts sodium carbonate (1:10 dissolved in water) is added continuously over the course of one hour. After a further operating time of 3 hours, a mixture of 1.3 parts of phthalic acid and 1.8 parts of sodium phthalate is added and further leached for 4 hours. The final temperature is 45°C, the final pH is 3.7, the residual bath contains 0.6 g C^O^/litre.

Example 13

For the production of aniline leather, 1,000 kg of cleaned cow hide (gap thickness 3 mm) is washed in the usual way in a tanning vat (diameter 2 m, width 2.25 m, rotation speed: 12 rpm) in the first row at 150%, referred to hide weight, water of 38°C for 10 minutes. The bath is drained and then decalcified with 70% water at 32°C with 3% ammonium chloride and 0.6% sodium bisulphite for 35 minutes and stained for 30 minutes with 0.7% of a commercially available enzymatic mordant (bath's pH value 8.0). The cross-section of the leather does not give more red color with phenolphthalein. Then rinse with water at 18°C for 10 minutes and drain the rinse water until there is a residual bath of 30%. 5 minutes after adding 4% common salt pickles with 0.6% formic acid (diluted 1:4) and 0.25% sulfuric acid (diluted: 1:8) for 60 minutes (pH 3.6). The pickle bath has 2.6% of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide. After an operating time of 1 hour, 5.8% of the tanning mixture mentioned below is subsequently added and further vinified for 1/ hour.

The tanning mixture consists of 520 parts by weight of powdered 33% basic chromium sulphate, containing 26% chromium oxide, 115 parts by weight of dolomite, 140 parts by weight of glutaric acid, 225 parts by weight of sodium glutarate. The final temperature is 45°C, the final pH is 4.0, the residual bath contains 0.5 g Cr203/litre. After the usual finishing, leather is obtained with a full, gentle grip and very even colouring. ;Example 14 ;100 parts of cleaned cowhide pretreated as in example 13 pickles with common salt, sulfuric acid and/or formic acid in the usual way with 20 parts of water in the tanning vat (pH 3.7). In the pickle bath, there are 2.6 parts of a powdered 50% basic chromium (III) sulfate with a content of 30% chromium oxide and 16% formic acid. After an operating time of one hour, 6.9 parts of the tanning mixture mentioned below are subsequently added and further macerated for 8 hours. The tanning mixture consists of 512 parts powdered 33% basic chromium sulphate, containing 26% chromium oxide, 113 parts dolomite, 153 parts adipic acid, 222 parts sodium glutarate. The final temperature is 40°C, the final pH is 4.2, the residual bath contains 0.4 g Cr203/litre. ;Example 15 ;100 parts of cleaned cowhide pre-treated as in example 13 pickles with common salt, sulfuric acid and/or formic acid ;in the usual way with 30 parts of water in the tanning vat (pH 3.9). In the pickle bath, there are 5 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide. After an operating time of ;1 hour, 3.45 parts of the tanning mixture mentioned below are subsequently added and further macerated for 7 hours. The tanning mixture consists of 290 parts powdered 33% basic chromium sulphate, containing 26% chromium oxide, 15 parts dolomite, 695 parts sodium glutarate. The final temperature is 42°C, the final pH is 3.9, the residual bath contains 0.2 g Cr203/litre. ;Example 16 ;100 parts of cleaned cowhide pre-treated as in ./ .. ;Example 13 pickles with sodium chloride, sulfuric acid and/or formic acid in the usual way with 20 parts of water in the tanning vat (pH 3.9). In the pickle bath, there are 2.3 parts of a powdered 33% basic chromium (II) sulfate with a content of 26% chromium oxide. After an operating time of 1 hour, 7.0 parts of the tanning mixture mentioned below are subsequently added and further macerated for 7 hours. The tanning mixture consists of 548 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 230 parts dolomite, 222 parts glutaric acid. The final temperature is 42°C, the final pH is 4.3, the residual bath contains 0.7 g Cr203/litre. ;Example 17 |$^' ;100 parts of cleaned cowhide pre-treated as in example 13 pickles with common salt, sulfuric acid and/or formic acid in the usual way with 25 parts of water in the tanning vat (pH- 4,Oi In the pickle bath there are 2.0 parts of a powdered 33% basic chromium (III)-sulfate with a content of 26% chromium oxide. After an operating time of ;1 hour, 6.3 parts of the tanning mixture mentioned below are added and further washed for 1\ hour. The tanning mixture consists of 476 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, ;74 parts dolomite, 31 parts sodium bicarbonate, 156 parts glutamic acid and 263 parts sodium adipinate. The final temperature is 45°C, the final pH is 4.2, the residual bath contains 0.5 g Cr203/ litres. ;Example 18 ;100 parts of cleaned cowhide pre-treated as in example 13 pickles with table salt, sulfuric acid and/or formic acid in the usual way with 20 parts of water in the tanning vat for 15 minutes (pH 4.1). In the pickle bath there are 4.0 parts of potassium chromalum with a content of ;15% chromium oxide After an operating time of After 1 3/4 hours, 6.2 parts of the tanning mixture mentioned below are added and further macerated for 8 hours. The tanning mixture consists of 485 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 89 parts dolomite, 38 parts magnesium oxide, 175 parts glutaric acid and 213 parts of the sodium salt of fumaric acid. The final temperature is 43°C, the final pH is 4.2, the residual bath contains 0.3 g Cr203/litre. ;Example 19 ;,,.-i"*^100 parts cleaned cowhide pre-treated as in example 13 pickles with common salt, sulfuric acid and/or formic acid in the usual way with 20 parts water in the tanning vat (pH 3.9). In the pickle bath has 3.5 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide. After an operating time of

1 hour later, add 9.1 parts of the tanning mixture mentioned below

ding and further sifted for 8 hours. The tanning mixture consists of 4 24 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 55 parts dolomite, 22 parts sodium carbonate, 126 parts aspartic acid and 373 parts sodium adipinate. The final temperature is 42°C, the final pH is 4.2, the residual bath contains 0.6 g Cr203/litre.

Example 2 0

Approximately 8 x 30 cm in size, corresponding to example 13, including decalcification pre-treated cleaned cowhide pieces pickled and chrome-tanned comparing a balking machine discussed by E. Komarek and G. Mauthe in "Das Leder" 12, (1961), pages 285 to 289 , especially page 287.

100 parts of cleaned cowhide from a piece of A

pickles with 3 parts table salt, 0.7 parts formic acid and 0.4 parts sulfuric acid in the usual way with 11 parts water in the pickling machine (pH 3.7). In the pickle bath, there are 3 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% chromium oxide. After an operating time of 1 hour, add 5.8 parts of the tanning mixture mentioned below. The tanning mixture consists of 520 parts powdered 33% basic chromium sulfate, containing 26% chromium oxide, 140 parts glutaric acid and 225 parts sodium glutarate, and 115 parts dolomite.

100 parts of cleaned cowhide of corresponding piece B pickles with 3 parts of common salt, 1.8 parts of glutaric acid (equivalent amount, referred to glutaric acid and sodium glutarate used in tanning the comparison piece A) and 0.2 parts of sulfuric acid in the usual way with 11 parts of water the milking machine (pH 4.0).

In the pickle bath, there are 3 parts of a powdered 33% basic chromium (III) sulphate with a content of 26% chromium oxide. After an operating time of 1 hour, add 3.8 parts of the tanning mixture mentioned below. The tanning mixture consists of 820 parts powdered 33% basic chromium sulphate, containing 26% chromium oxide and 180 parts dolomite.

To investigate the through-tanning speed, the tanning on the rolling machine is interrupted and the comparable pieces of leather A and B are cut. The piece A pickled without glutaric acid shows, compared to the piece B pickled with glutaric acid, a clearly faster through-tanning at the same pH values of the residual bath.

Example 21

100 parts cleaned cowhide pre-treated as in example 13 pickles with common salt, sulfuric acid and/or formic acid in the usual way with 20 parts water in the tanning vat (pH 3.9). In the pickle bath, there are 6 parts of a powdered 33% basic chromium (III) sulfate with a content of 26% Cr203. After an operating time of one hour, 0.6 parts of sodium carbonate (1:10 dissolved in water) are continuously added over the course of one hour. After a further operating time of 3 hours, 1 part glutaric acid and 1.6 parts sodium glutarate are subsequently added and further washed for 4 hours. The final temperature is 45°C, final pH

lies at 3.8, the residual bath contains 0.3 g C^O^/litre.

Claims (3)

1. Process for chromium tanning by pretanning the pickled, cleaned leather hide with chromium (III) salts and tanning with chromium (III) salts, acid binding agents and aliphatic dicarboxylic acids and/or aromatic di- and tricarboxylic acids and/or their salts , characterized in that the tanning takes place with mixtures of chromium (III) salts, acid binding agents and at least 1.6 mol, preferably 2 to 3 mol of aliphatic dicarboxylic acids with 4-6 C atoms and/or aromatic di- and/or tricarboxylic acids with 8-13 C atoms and/or their salts per mol Cr203 of the chromium (III) salts used for tanning, the components being added in powder form, preferably together, so that the total amount of C^O-^ amounts to 1.2 to 2%, referred to cleaned leather skin weight, especially 1, 5 to 1.8%, and that the tanning is carried out at a bath quantity of up to 100%, referred to the weight of leather, up to a final pH value of the tanning bath, which is above 3.6, especially between 3.8 and 4.2. 2. Method according to claim 1, characterized in that dolomite is used as an acid-binding agent, possibly in a mixture with other acid-binding agents.. - in "fe 3. Method according to claim 1 or 2, characterized in that the necessary amount of the chromium (III) salts to cover both pre-tanning and un-tanning is added all at once. 4- Tanning mixture for carrying out the method according to claim 1-3/consisting of chromium (III) salts, acid binding agents as well as aromatic di- and/or tricarboxylic acids with 8-13 C atoms or aliphatic dicarboxylic acids with 4-6 C atoms, and/or their alphas, characterized by a content of at least 1.6 mol of aromatic di- and /or tricarboxylic acids per mol Cr203, or at least 1.6 mol aliphatic dicarboxylic acids per moles of Cr2O3.