GB2153844A - Aluminium tannages - Google Patents

Abstract

Hides and skins are tanned by treating under aqueous conditions with a basic aluminium salt and a polycarboxylic acid of benzene containing three or more carboxylic acid groups, or a water soluble salt or anhydride thereof.

Description

SPECIFICATION Processes for the improvemenf of aluminium tannages The invention relates to processes whereby aluminium tanned leather may be produced having a quality and hydrothermal stability comparable with that of wholly chrome tanned materials.

Application of these processes may advantageously reduce the chrome content of tannary effluent.

Aluminium salts have been used in the leather industry for a long time, particularly for the production of so-called "white-leathers", but due to the poor hydrothermal stability imparted by aluminium salts, their use has been restricted to a considerable extend and aluminium salts have been used only as auxiliary tanning agents. Leather tanned with aluminium salts in the conventional way is not stable and its hydrothermal stability as measured by Method SLP: 1 8 of the Society of Leather Technologists 8 Chemists, U.K., is also reduced considerably on washing with alkaline detergents. Further, this low hydrothermal stability prevents the use of wholly aluminium tanned leather in processes like dyeing where high temperature stability is required.

In recent years polymeric substances like styrene-maleic anhydride copolymer and acrylic resins have been used as pretannage for subsequent aluminium tanning to improve the hydrothermal stability of treated skins, but only marginal improvements have been found in practice. Similarly, use of sodium aluminium silicates as tanning agents for aldehyde pretanned hides have been suggested, but the hydrothermal stability as measured by the shrinkage temperature of the leather was not very high. A maximum shrinkage temperature of 80"C was reported. In our British Patent 1,591,403 we describe a process for the improvement of the hydrothermal stability of chrome tanned leather by treatment with polycarboxylic acids of benzene.We were surprised to find that aluminium tannages could be significantly improved in quality and hydrothermal stability by the application of a similar process, providing leathers comparable with conventional chrome tanned material.

According to the present invention there is provided a process for tanning hides and skins which comprises treating the hide or skin in aqueous conditions with a basic aluminium salt and with a polycarboxylic acid of benzene containing three or more carboxylic acid groups, or a water soluble salt or anhydride thereof.

The treatment with the polycarboxylic acid of benzene or water soluble salt or anhydride thereof may take place simultaneously with treatment with the aluminium salt or subsequent to the aluminium salt treatment, in which case this may be in the same, or in a fresh liquor.

The amount of basic aluminium salt used, (calculated as Awl203) is preferably from 0.5 to 10%, more preferably 0.8 to 4% and the amount of polycarboxylic acid of benzene is preferably from 0.5 to 10%, more preferably 1 to 5%, these percentages being calculated, according to convention, as a percentage on drained pickled pelt weight, or shaved weight of the leather to be treated, as appropriate.

In a further embodiment of the invention, small amounts of conventional chrome tanning agents may be incorporated in the process of the invention. The amount of chrome tanning agent, (calculated as Cr2O3) may be up to 2.0%, preferably 0.5 to 1.0% calculated on the same basis as above.

Examples of basic aluminium salts which may be used in the process of the invention are basic aluminium chloride, aluminium sulphate, aluminium triformate and aluminium acetate.

Examples of polycarboxylic acids of benzene are: hemimellitic acid (benzene-1,2,3-tricarboxylic acid), trimellitic acid (benzene-1,2,4-tricarboxylic acid), trimesic acid (benzene-1,3,5-tricarboxylic acid), prehnitic acid (benzene-1,2,3,4-teracarboxylic acid), mellophanic acid (benzene 1,2,3, 5-tetracarboxylic acid), pyromellitic acid (benzene-l ,2,4-5-tetracarboxylic acid) and mellitic acid (benzene-1,2,3,4,5,6-hexacarboxylic acid).

An example of chrome tanning agent is basic chrome powder or liquor (typically 25% Cr203; 33% basicity).

Leather tanned according to the process of the invention typically has a shrinkage temperature (measured by Method SLP 1 8 of the Society of Leather Technologists and Chemists) of 85-90"C. Incorporation of small amounts of a conventional chrome tanning agent into this process increases the shrinkage temperature, typically to about 1 00 C.

The invention provides a process for the production of aluminium tanned white leathers of good hydrothermal stability. By the incorporation of small amounts of conventional chrome tanning agents into the process, the hydrothermal stability is further enhanced giving leathers equal to the best chrome tanned materials yet with significantly reduced chrome content to the waste liquors.

In a preferred process, the polycarboxylic acid of benzene, its water soluble salts or anhydride, are applied to aluminium tanned leather in an aqueous system at a temperature from 0 C to 60"C, preferably 35 to 50"C for times of up to 10 hours, preferably 60 to 90 minutes.

Aluminium tanned leather, so treated according to the process of the invention, has a shrinkage temperature around 85"C to 90"C and therefore may be dyed under the conditions normally used for chrome tanned leather (i.e. in the temperture range of 40-60"C), or washed with alkaline detergent at 40-60"C without any appreciable shrinkage and/or deterioration in the quality of the leather.

As an example of a further process of the invention, pickled sheepskins are tanned with 0.5% to 2% Al203 as aluminium triformate, preferably 0.8 to 1% Al203, and 0.3% to 1% Cr203 as basic chrome powder or liquid (33% basicity), preferably 0.5% to 0.8% Cr203, and 1.0 to 4.0%, preferably 2.0 to 3.0%, sodium salt of pyromellitic acid, (percentages calculated on drained pickled weight of the skins), to obtain leather which withstands boiling for 2 minutes.

The leather obtained according to this process has similar properties to leather obtained from a conventional chrome tanning system using 3% Cr203 as basic chrome powder or liquid (33% basicity). This will be evident from the data submitted under Example 2. This novel system considerably reduces the chrome effluent from the tannery as only a fraction of the chrome tanning agent normally employed in the conventional system is needed for the production of satisfactory leather.

In another example of the process of the invention, pickled wool skin, which under conventional chrome tanning system would be tanned with 20 g/l chrome powder (25% Cr203; 33% basicity) at a float of 1:10, may be tanned at the same float with only 2 g/l. Al203 as aluminium triformate, 0.5 g/l Cr203, (i.e. 2 g/l chrome powder (25/33)) and 3 g/l ammonium salts of a polycarboxylic acid of benzene to obtain leather with shrinkage temperature of 90-92"C. The wool skin obtained according to this process can be dyed under the conditions normally used for futl chrome tanned leather (i.e. in the temperature range of 40-60"C) with no appreciable shrinkage and/or deterioration of the quality of the skin.According to this novel process, considerable reduction of chrome effluent in the exhaust can be achieved as the amount of original chrome offered in the process is only 1 /10to of the amount required in the conventional process for this type of wool skin tannage. The process has the advantage also of reducing the chrome stain on the wool.

The present invention is illustrated, although not restricted by, the following examples. These relate to the use of sodium or ammonium salts of polycarboxylic acids of benzene containing four carboxylic acid groups, but it is to be understood that this is purely by way of example only and the other carboxylic acids, salts or anhydrides described in this invention may be used in an analogous manner. Except where stated otherwise, the percentages given in the following examples are percentages by weight based on the weight of hides and skins or leather to be tanned.

EXAMPLE 1 Two pickled wool skins were taken and cut through the backbone to obtain 2 matched pairs.

After weighing, each set comprised of two sides, was placed in separate tanning drums. Brine (4% solution) was added to obtain a float ratio of 1:10. All chemicals were calculated on the basis of this float. The sides were then depickled with 2 g/l sodium bicarbonate to a bath pH of 4.0. 10 g/l of a liquid phenolic replacement syntan (Paralene WG) was added and after running for 60 minutes, 3 g/l Altos in the form of aluminium triformate solution was added to the bath, and the drums run for 3 hours. Samples were taken from the skins and the shrinkage temperature of the leather thus obtained was measured according to the method SLP:1 8 of the Society of Leather Technologists 8 Chemists, U.K.Keeping one set as control, 3 g/l ammonium salt of a polycarboxylic acid of benzene containing 4 carboxylic acid groups was added to the other set. Both drums were run for another 2 hours, samples taken from the skins for shrinkage tests and the remainder allowed to stand overnight. Next day, the shrinkage temperature of the leather was re-measured.

Shrinkage Temperature of Aluminium Tanned Leather Time after adding Treated with benzene Aluminium salt Control Polycarboxylic acid 3 hours 68-694 5 hours 69-70 C 81-82"C Overnight 75-76"C 88-89"C All the pieces were crusted out following a conventional fatliquoring and drying process and their quality assessed. The sides treated with an aluminium salt and a polycarboxylic acid of benzene were considerably better in handle and overall feel, than the control sides which had not received treatment with the benzene polycarboxylic acid.The sides which received the full treatment according to the invention, (with both aluminium salt and benzene polycarboxylic acid), remained stable without any appreciable shrinkage and/or deterioration of quality when washed repeatedly in an alkaline detergent.

EXAMPLE 2 Three domestic pickled and degreased sheep-skins were taken and cut through the backbone to obtain 3 matched pairs of skins. One side from each skin was taken as a control and tanned with 10% chrome powder (25% Cr2O3 and 33% basicity), according to the normal conventional art of chrome tanning. The other 3 sides were depickled to pH 4.0 with 3% disodium phthalate in a brine (4% solution) bath for 60 minutes. These pieces were then tanned as follows: Add 50% water at 25"C 1% Al2O3 as aluminium triformate Drum for 60 minutes Add 2% chrome powder (25% Cr203; 33% basicity Drum for a further 90 minutes. Check pH = 3.5 Add 2% sodium salt of pyromellitic acid Drum for a further 2 hours.Check pH = 3.7 (At this point a sample of tanned skin was taken and found to withstand a 2 minute boil).

Stand overnight.

Next day, these pieces, along with the 3 control pieces, were piled-up for 48 hours. After that the pieces were sammed, shaved and finally crusted out all following the same conventional process of neutralisat on, dyeing and fatliquoring. On assessment of the quality of these leathers, matched pair by matched pair, it was found that in all cases the aluminium + polycarboxylic acid treatment gave the best quality leather in respect of fullness, softness, and general handle. Colour and penetration of dyes on the aluminium/polycarboxylic acid tanned leather was brighter than on the control. The results of shrinkage temperature measurements were as follows: Shrinkage qemperatures, C Control (Chrome Aluminium /polycarboxylic Tannage) acid Tannage After After After After Tanning Ageing Tanning Ageing Set 1 (i.e.Skin -1) 104 105 104 106 Set 2 (i.e. Skin 2) 109 114 106 109 Set 3 (ire. Skin 3) 106 113 106 110 The tear and tensile strength of these leathers was measured by cutting out pieces from exactly similar matched locations, as per the methods SLP:7 and SLP:6 respectively of the Society of Leather Technologists 8 Chemists, U.K. The results, as given in the following tables, indicate that the aluminium/polycarboxylic acid tannage of the invention gave similar results to the conventional chrome tannage.

TEAR STRENCTH OF SHEEPSKIN (Absolute values in Kg) Novel ConventionaI Aluminium/polyearboxylic acid Chrome Tanning Tannage Breaking Average Breaking Average Load Load Set 1 3.33 4.31 3.14 3.00 3.92 3.68 2.55 3.33 3.14 Set 2 5.29 5.48 4.51 4.31 4.51 4.60 4.11 .4.31 3.33 4.11 Set 3 5.29 5.29 4.90 4.35 4.51 4.11 3.33 3.53 3.92 3.14 TENSILE STRENGHT OF SHEEPSKIN Conventional Chrome Tannage Novel Aluminium/polycarboxylic acid Tannage Breaking Average Tensile Average Breaking Average Tensile Average Load (kg) Strength Load (kg) Strength (kg) (kg/mm) (kg/mm) Set 1 22.53 2.25 22.14 2.22 19.79 2.32 19.79 2.15 18.56 2.13 19.74 2.15 16.07 2.00 19.00 2.10 15.87 1.98 18.02 2.12 Set 2 32.53 2.96 34.68 3.15 30.57 2.78 33.12 3.01 27.85 2.64 29.54 2.75 26.18 2.62 29.59 2.82 22.14 2.21 20.77 1.97 Set 3 32.14 2.92 41.76 3.79 28.60 2.86 28.72 3.14 27.97 2.83 27.15 2.86 26.26 2.76 20.38 2.76 24.88 2.76 18.22 2.27 EXAMPLE 3 Two pickled wool skins were taken and cut through the backbone to obtain 2 matched pairs of skins. After weighing, each set comprised of two sides was placed in separate drums. Brine (4% solutions) was added to obtain float ratio 1:10. All chemicals were then calculted on the basis of this float. One set was treated as a control, following a conventional chrome tanning process with 20 g/l basic chrome powder (25% Cr203, 33% basicity) over 24 hours, after initial masking with 2 g/l Disodium phthalate for 30 minutes and starting the tannage at pH 4.0.The second set was masked with 10 g/l liquid phenolic replacement syntan (Paralene WG) for an hour. 2 g/l Al203 as aluminium triformate was added and after running for 2 hours, 4 g/l basic chrome powder (25% Cur203, 33% basicity) and 4 g/l cationic fatliquor + 1 g/l raw neatsfoot oil were added and tanning continued for 2 hours. Finally, 3 g/l sodium salt of pyromellitic acid were added and tanning completed over 24 hours, exactly in the same manner as the control.

Both tannages were finished at pH 3.8. The shrinkage temperature of the wet leather was measured as per the method SLP:18 of the Society of Leather Technologists 8 Chemists, U.K.

and were found to be in the range of 98-100"C for both sets of leather. All these pieces were then crusted out following a conventional drying process. On assessment, it was found that the aluminium/polycarboxylic acid tanned leather was considerably fuller, softer and tighter than the control and the wool was brighter and free from any chrome staining. This process reduced the chrome in the effluent considerably as only 1 /5th of the chrome tanning agent normally used in the conventional chrome tannage was employed.

EXAMPLE 4 Two limed hides were taken, and cut through the backbone to obtain two matched pairs. One set, selected as a control, was tanned after de-liming and pickling in the conventional manner of chrome tanning with 2% chrome powder (25% Cr2O3, 33% basicity) for 1 hour, and then with 7% chrome powder (25% Cr203; 50% basicity) for 7 hours, finally basifying to a pH of 3.7 with sodium bicarbonate. The other set was de-limed and pickled in the same way, treated with 2% disodium phthalate for 30 minutes in a drum and then tanned with 1 % Al203 as aluminium triformate solution for one hour. 3% chrome powder (25% Cr203, 33% basicity) was then added and drumming continued for 3 hours. 2% sodium salt of a benzene tetracarboxylic acid was added and run for 2 hours, and finally the pH adjusted to 3.7 with sodium bicarbonate as with the control.The shrinkage temperatures of these leathers were measured at each stage of the process following method SLP:1 8 of the Society of Leather Technologists 8 Chemists, U.K.

All these sides gave comparable results. They were then processed as shoe upper leather. On assessment it was found that the aluminium and polycarboxylic acid treated leather gave similar results to the conventional chrome tannage, both in respect of fullness and overall handle.

EXAMPLE 5 Pickled sheepskin was placed in a drum. After depickling to pH 4.0 with 3% disodium phthalate, 3% Al2O3 as basic aluminium chloride was added. The drum was run for 2 hours and then 2% sodium salt of pyromellitic acid was added. After drumming for a further 2 hours, it was left standing overnight. Next day, the drum was run for a further 30 minutes and the leather taken out. The shrinkage temperature of this leather when measured as per the method SLP:1 8 of the Society of Leather Technologists 8 Chemists, U.K. was found to be 90"C. The leather was then washed, neutralised, fatliquored with 4-5% lightfast fatliquors and finally bleached with 4% sulphone syntan (Paralene PCV), and crusted out following a conventional drying process for such white leather. Very satisfacotry white leather was obtained.

EXAMPLE 6 Two pickled domestic sheepskins were taken and cut through the backbone to obtain two matched pairs. One set was tanned with 10% chrome tanning powder (25% Cr203, 33% basicity) following a conventional chrome tanning process, finishing the tannage at pH 3.7-3.8.

The other set was tanned with 2% chrome tanning powder (25% Cr203, 33% basicity) for 2 hours and basified to pH 3.5-3.6 with sodium bicarbonate. In a fresh bath, this leather was then tanned with 1.5% AI2O3 as aluminium triformate for 2 hours after which 2% sodium salt of pyromellitic acid was added and run for a further 1 hour. The leather was kept overnight in the bath. Next day, it was rinsed and horsed up. The two sets of leather were then processed as usual up to the drying stage to compare their quality. Very satisfactory leather was obtained.

The grain and overall handle of the aluminium/polycarboxylic acid tanned leather was comparatively superior to the conventional chrome tanned leather.

Claims (11)

1. A process for tanning hides and skins which comprises treating the hide or skin in aqueous conditions with a basic aluminium salt and with a polycarboxylic acid of benzene containg three or more carboxylic acid groups, or a water soluble salt or anhydride thereof.

2. A process as claimed in claim 1, in which the basic aluminium salt is used in an amount of 0.5 to 10% by weight based on drained pickled pelt weight or shaved weight of leather.

3. A process as claimed in claim 2, in which the basic aluminium salt is used in an amount of 0.8 to 4% by weight, based on drained pickled pelt weight or shaved weight of leather.

4. A process as claimed in any of claims 1 to 3, in which the polycarboxylic acid or watersoluble salt or anhydride thereof is used in an amount of 0.5 to 10% by weight, based on drained pickled pelt weight or shaved weight of leather, the water-soluble salt or an hydride weights being calculated as the free acid.

5. A process as claimed in claim 4, in which the polycarboxylic acid or water-soluble salt or anhydride thereof is used in an amount of 1 to 5% by weight, based on drained pickled pelt weight or shaved weight of leather, the water-soluble salt or anhydride weights being calculated as the free acid.

6. A process as claimed in any of claims 1 to 5, in which up to 2.0% of chrome tanning agent (calculated as Cr203), by weight based on drained pickled pelt weight or shaved weight of leather, is incorporated.

7. A process as claimed in claim 6, in which the chrome tanning agent is used in an amount of 0.5 to 1.0% (calculated as Cr203) by weight, based on drained pickled pelt weight or shaved weight of leather.

8. A process as claimed in any of claims 1 to 7, in which the basic aluminium salt is basic aluminium chloride, aluminium sulphate, aluminium triformate or aluminium acetate.

9. A process as claimed in any of claims 1 to 7, in which the polycarboxylic acid of benzene is hemimellitic acid (benzene-1,2,3-tricarboxylic acid), trimellitic acid (benzene-1 ,2,4-tricarboxylic acid), trimesic acid (benzene-1 ,3,5-tricarboxylic acid), prehnitic acid (benzene-1 2,3,4-tetracar- boxylic acid), mellophanic acid (benzene-1 ,2,3,5-tetracarboxylic acid), pyromellitic acid (ben zene-1,2,4,5-tetracarboxylic acid) or mellitic acid (benzene-1,2,3,4,5 6-hexacarboxylic acid).

10. A process as claimed in any of claims 1 to 9, in which the polycarboxylic acid, its salt or anhydride is applied to aluminium tanned leather at 0 C to 60"C.

11. A process as claimed in claim 10, in which the polycarboxylic acid, its salt or anhydride is applied to aluminium tanned leather at 35"C to 50"C.

1 2. A process as claimed in any of claims 1 to 11, in which the polycarboxylic acid, its salt or anhydride is applied to aluminium tanned leather for up to 10 hours.

1 3. A process as claimed in claim 12, in which the polycarboxylic acid, its salt or anhydride is applied to aluminium tanned leather for 60 to 90 minutes.

1 4. A process for tanning hides and skins substantially as hereinbefore described with particular reference to any of the foregoing Examples.

1 5. Hides and skins whenever tanned by a process as herein described and claimed.