GB1598709A - Tanning composition and process - Google Patents

Description

(54) TANNING COMPOSITIONS AND PROCESS (71) We, MONTEDISON S.p.A.. of Largo Donegani 1/2, 20121 Milano, Italy, an Italian Company, do herebv declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention concerns the chrome tanning of hides.

In the tanning of hides it is well known to use aluminium salts, such as for instance aluminium sulphate or chloride with more or less high basicities. The results of such tannings. however, are not altogether satisfactory due to the poor resistance to water and the low shrinkage temperature of the tanned leather.

The use in the tanning of hides of chromium salts, though it yields good results from the technical point of view, has the drawback of involving considerable shortcomings from the environmental protection point of view. Besides, it must be noted that a shortage of chromium minerals is anticipated in consequence of the continuous growth of the demand for this raw material in the most varied fields.

The invention consists in a bath for tanning hides comprising an aqueous acid mixture containing a neutral or basic aluminium chloride and/or sulphate and a polycarboxylic organic acid complexing agent for the aluminium, together with a chrome tanning agent in an amount not exceeding about 0.7% by weight of the pelt weight of the hides to be tanned, calculated as Cr2O.

It has surprisingly been found that by using the aluminium-organic polycarboxylic acid composition in a normal tanning process, it is possible to lower considerably the quantity of chromium generally required, obtaining results that are altogether similar to or even better than those obtained in a normal chromium tanning operation.

In fact, while in a normal chromium tanning one uses a quantity of basic chromium sulphate which, expressed as Cr203, amounts to about 3% (usually between 2 4%) when referred to the pelt weight of the hide to be tanned, if the composition of this invention is adopted, the consumption of basic Cr-sulphate, still expressed as Cur2031 may be reduced to 0.2% and even less if there are added such amounts of the aluminium - polycarboxylic acid composition that the Al content, expressed as At203, is from 0.6 to 2% referred to the pelt weight. The hides thus tanned show characteristics that are altogether similar to or are even improved in comparison to those derived from a standard chromium tanning; it is thus possible to achieve a finer, more compact grain well adhering to the derma, a particularly soft hide and a uniform glossy dyeing.

The best results are obtained using quantities of basic chromium sulphate, expressed as Cr203, of around 0.7%.

Using the composition according to the invention also affords the advantage that the effluent waters are "cleaner" since the chromium concentration, because of its partial substitution by the easily removable Al, is considerably reduced.

The aluminium-polycarboxylic organic acid composition be used as an aqueous solution but may for convenience be dried and subsequently redissolved in water.

The organic polycarboxylic acid complexing agents may be incorporated as such or as their alkali metal salts. Citric acid is particularly suitable. The amounts giving best results vary according to the nature of the complexing agent itself. If, for instance, as complexing agent for the stabilization of the aluminium salt solutions at a pH of about 4, citric acid is used, at least 50 parts by weight of citric acid monohydrate per 100 parts by weight of Al203 will be needed, while the optimum amounts range from 70 - 80 parts per 100 parts of Air3.

In one convenient method of preparing the aluminium-polycarboxylic organic acid composition, the complexing agent, suitably in aqueous solution, is added, whilst stirring, to an acidic aqueous solution of the aluminium salt or salt mixture. The resulting, generally warm solution, may be allowed to cool until the temperature has fallen to 250 - 30"C, at which point a basic material, suitably an alkali metal or alkaline earth metal hydroxide, carbonate or bicarbonate, may be added to bring the pH to 3.9-4.3.

The concentration of Al in the resulting solution is not critical, although in general mixtures are preferred having a concentration of 3 to 11% by weight of Al expressed as Awl203. Such solutions preferably have a pH of 3.5 - 4.5.

The aforesaid composition may also be made available in the solid state by evaporation of the water.

Other procedures may of course be adopted. Thus the complexing agent may be added to an alkali metal aluminate solution, and subsequently compounded with hydrochloric and/or sulphuric acid or aluminium chloride and/or sulphate, possibly with additional complexing agent, depending on the amount first used. Acid or alkali may be added as required to bring the pH to a desired level.

The invention also consists in a process of tanning hides in which the hides are treated with an acidic solution containing aluminium sulphate and/or chloride and as complexing agent for the aluminium, an organic polycarboxylic acid, especially an organic hydroxy polycarboxylic acid such as citric acid, together with chromium, suitably as basic chromium sulphate, in an amount (expressed as Cr203) not exceeding about 0.7% by weight of the pelt weight. The amount of the aforesaid composition is suitably 0.6 - 2% by weight based on the Al content expressed as Al2O3. The pH of the bath is desirably kept at 3.5 - 4.5, if necessary by periodic adjustment.

In one convenient method of operation the hides are tanned initially using an aluminium-organic polycarboxylic acid com position, then a chrome tanning agent is incorporated, and subsequently a further amount of the aluminium-polycarboxylic acid composition.

The following examples illustrate how the invention may be carried into effect. The "salt" referred to, unless otherwise speci fied, is sodium chloride.

Example 1 100 kg of an aluminium-based tanning agent were prepared as follows: To 33 kg of "Alpoclar" (a solution containing basic aluminium chloride and basic sulphate - produced by the Applicants) of 11% Al concentration expressed as Al203, and having a pH of 1.7, were added 2.8 kg of citric acid monohydrate dissolved in 11 kg of water.

After gentle stirring, there were added 5.0 kg of 66 BeH2SO4, the gentle stirring being continued. The mixture was then cooled to 25"C, diluted with 16 kg of water and then treated with 27 kg of an aqueous solution containing 5.4 kg of NaOH. It was then checked that the pH was 4.1 - 4.2. The mixture was then made up with water to 100 kg.

For the tanning operation 10 cow hide backs were used with a pelt weight of 230 kg. After standard preparation treatment comprising deliming, bating and pickling, the hides were passed on to the tanning stage, conducted as follows:46 kg of water (20% on the pelt weight), 4.14 kg of sodium chloride and 16.7 kg of the prepared tanning agent, representing 0.26% of Al on the hide weight expressed as Awl203, were made up as a tanning bath.

After a 42 hour tumbling the hides were left to soak in the bath overnight. Thereupon tumbling was resumed for 30 minutes whereafter there were added 5.52 If of basic chromium sulphate having a 25o Cr content expressed as Cr203, that is 0.6% of Cr, expressed as Cr203, based on the hide weight. After a further 50 minutes tumbling and the addition of 0.5% (on the hide weight) of cationic grease, the bath was tumbled for a further 2 hours. 2.07 kg (0.9%) of NaHCO3 were then added and, after tumbling for a further 2t hours the pH of the solution was checked and found to be 3.6. The cationic grease used was LIPAMIN LICKER O.

At this point there were added 46 kg (20% calculated on the hide weight) of the previously prepared tanning agent, representing 0.72% of Al expressed as Al203.

After tumbling for a further 2 > hours, 1.26 kg of NaHCO3 (0.55%) were added; the pH amounted to 3.9. Thereupon the mixture was tumbled for another 2 hours after which it was allowed to stand overnight.

The subsequent processing steps were conventional. The tanned hide showed characteristics altogether similar to those obtainable by conventional chrome tanning.

Example 2 322 kg of aluminium hydroxide with a 57% w/w Al203 content were dissolved in 756 kg of 20.6% w/w HC1 and 293 kg of 98% w/w H2SO4. To the solution thus obtained were added, at 900C, 133 kg of citric acid monohydrate and 510 kg of water.

Thereupon, in the course of two hours and whilst stirring, 1530 kg of a 30% w/w solution of Na2CO3 were fed in, the final temperature amounting to 50"C. Thereby 3350 kg of liquid tanning agent containing 5.5% w/w Al203 were obtained, the product having a pH of 3.9. This liquid was then dried to give 1025 kg of solid tanning agent with an 18% w/w content of Awl203.

For the tanning there were used 8 calf hides, with a pelt weight of 130 kg. After conventional deliming, bating and pickling, the hides were passed to the tanning treatment stage. Referring to the hide weight, a tanning bath was prepared with 25% of water, 2% of salt and 1.5% of the dry tanning agent (corresponding to 0.26% of Al expresses as Al203). Tumbling was conducted for 2 hours, and then 2.8% of basic chromium sulphate (containing 25% of Cr expressed as Cr2O3), corresponding to 0.7% of Cr expressed as Cr203, was incorporated. Tumbling was continued for 2 hours, and then batches of about 0.7% of NaHCO3 were added in several stages until the pH of the solution had reached 3.7 - 3.8.

At this point there were added a further 4% (still referred to the hide weight), of the previously prepared solid tanning agent which corresponds to 0.72% of Al expressed as Al203. After tumbling for 22 hours the bath was treated with NaRCO3 (3-4 times with doses varying from 0.2 to 0.3%) until the solution reached a pH of 3.9-4.

Thereupon the hides were allowed to soak overnight in the stationary paddle tumbler and subsequent processing steps were carried out conventionally. The tanned hides showed characteristics altogether similar to those obtained by standard chrome tanning.

Example 3 An aluminium-based tanning agent was prepared generally as described in example 2, except that instead of 133 kg of citric acid monohydrate there were used 186 kg of sodium citrate bihydrate, and the quantity of 30% Na2CO3 concentration was reduced to 1194 kg. After drying the product contained the equivalent of 18% Al203.

For the tanning there were used 25 cow hides with a pelt weight of 100 kg. After normal deliming, bating and pickling treatments, the hides were tanned as follows: Referring to the pelt weight, a tanning bath was prepared using 25% of water, 2% of salt and 1.5% of the dried tanning agent, corresponding to 0.26% of Al expressed as Al203. After tumbling for 2 hours there was added 2.8inc of basic chromium sulphate (25% Cr content expressed as Cr2O3) corresponding to 0.7% of Cr expressed as Cr203. After tumbling for a further 2 hours, there were added about 0.7% of NaHCO3 in each of three or four doses until the pH was 3.7-3.8.

At this point there were added a further 4%, still referred to the pelt weight, of the dried tanning agent, corresponding to 0.72% of Al expressed as Al203.

After tumbling for 2- hours, the bath was treated 3-4 doses of NaHCO3 (varying from 0.2 to 0.3%) until the pH of the solution reached 3.9-4. Thereupon the hides were allowed to soak overnight in the stationary paddle tumbler.

The subsequent processing steps were carried out conventionally. The tanned hides showed characteristics altogether similar to those obtained by conventional chrome tanning.

Example 4 An aluminium-based tanning agent was prepared as follows: 97 kg of a 57% w/w aluminium hydroxide were dissolved in 290 kg of a 31% w/w solution of NaOH and the solution was treated with 40 kg of citric acid -monohy- drate.

The solution thus obtained was gradually added, in the course of 1 hour, and whilst stirring at 500C, to a separate solution containing 40 kg of citric acid monohydrate, 540 kg of crystalline aluminium sulphate (Al2O3 content 17% ssv/w) and 650 kg of water. After stirring for 2 hours at 50 C, there were obtained 1657 kg of a solution containing 8.9% w/w of Al203 and having a pH of 3.9. This- solution was then dried by evaporation to give 590 kg of solid tanning agent of 25% Al203 content.

For tanning there were utilised 100 goat hides with a pelt weight of 106 kg. After conventional deliming, bating and pickling treatments, the hides were transferred to a paddle tumbler containing a tanning bath of composition (by weight on the pelt weight) 25 Rzo of water, 2% of salt and 1.04% of the dry tanning agent, representing 0.26% of Al expressed as Awl203. After tumbling for 2 hours, there were added 2.8% of basic chromium sulphate (containing 25% of Cr expressed as Cr2O3) corresponding to 0.7% of Cr expressed as Cr203. After tumbling for a further 2 hours, 3-4 doses each of about 0.7% of NaHCO3 were added to bring the pH of the solution to 3.7-3.8.

At this point still with reference to the pelt weight, there was added a further 2.8% of the previously prepared solid tanning agents, representing 0.72% of Al expressed as Awl203.

After tumbling of 22 hours the solution was treated 3-4 doses varying from 0.2 to 0.3% of NaHCO3 to bring the pH of the solution to 3.9-4. The hides were then allowed to soak overnight in the stationary tumbler.

Subsequent processing steps were carried out conventionally. The tanned hides showed characteristics altogether similar to those obtained by conventional chrome tanning.

Example 5 An aluminium-based tanning agent was prepared generally a described in example 3, and dried. The product had an 18% Al content expressed as Awl203.

For tanning there were utilized 10 cow hides with a pelt weight of 150 kg. After normal deliming, bating and pickling treatments, the hides were transferred to a paddle tumbler containing a tanning bath made up of (by weight based on the pelt weight) 25% of water, 2% of salt and 1.5% of the tanning agent, corresponding to 0.26% of Al expressed as Awl203. After tumbling for 2 hours, 0.8% of basic chromium sulphate (25% of Cr expressed as Cr203) were added, corresponding to 0.20/0 of Cr expressed as Cr203. After tumbling for a further 2 hours, 3-4 additions were made of about 0.7% of NaHCO3 to bring the pH of the solution to 3.7-3.8.

At this point there were added 6.8%, still referred to the pelt weight, of the dry tanning agent, corresponding to 1.22% of Al expressed as Awl203. After tumbling for a further 22 hours, the solution was treated with three to four additions of NaHCO3 in amounts varying from 0.2 to 0.3% to bring the pH to 3.9 - 4. Thereupon the hides were allowed to soak overnight in the stationary tumbler.

The successive processing steps were carried out conventionally and the tanned hides showed good characteristics.

WHAT WE CLAIM IS: 1. A bath for tanning hides, comprising an aqueous acid mixture containing a neutral or basic aluminium chloride and/or sulphate and a polycarboxylic acid complexing agent for the aluminium, together with a chrome tanning agent in an amount not exceeding about 0.7% by weight of the pelt weight of the hides to be tanned.

2. A bath according to Claim 1, in which the polycarboxylic acid is citric acid.

3. A bath according to Claims 1 or 2 having a pH of 3.5-4.5.

4. A bath according to Claim 3 in which the pH is 3.9-4.3.

5. A bath according to Claim 3 or 4, in which the aluminium content of the solution, expressed as Al203, is from 3 to 11% by weight.

6. A method for tanning hides in which there is used a bath according to any of the foregoing claims.

7. A method according to Claim 6, in which the bath contains from 0.6 to 2% by weight of aluminium, expressed as Al203 and calculated on the pelt weight of the hide being tanned.

8. A method according to Claim 6 or 7 in which the pH of the tanning bath is periodically adjusted, as necessary, to be from 3.5 - 4.5.

9. A method according to Claim 6, 7 or 8, in which the hides are tanned initially with a bath containing an aluminiumorganic polycarboxylic acid composition, then a chrome tanning agent is incorporated in an amount not exceeding about 0.7% by weight of the pelt weight, and subsequently a further amount of aluminium-organic polycarboxylic acid composition is incorporated.

10. A method of tanning hides according to Claim 6 and substantially as described in any of the foregoing examples.

11. Hides when tanned by a method according to any of Claims 6-10.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. those obtained by conventional chrome tanning. Example 5 An aluminium-based tanning agent was prepared generally a described in example 3, and dried. The product had an 18% Al content expressed as Awl203. For tanning there were utilized 10 cow hides with a pelt weight of 150 kg. After normal deliming, bating and pickling treatments, the hides were transferred to a paddle tumbler containing a tanning bath made up of (by weight based on the pelt weight) 25% of water, 2% of salt and 1.5% of the tanning agent, corresponding to 0.26% of Al expressed as Awl203. After tumbling for 2 hours, 0.8% of basic chromium sulphate (25% of Cr expressed as Cr203) were added, corresponding to 0.20/0 of Cr expressed as Cr203. After tumbling for a further 2 hours, 3-4 additions were made of about 0.7% of NaHCO3 to bring the pH of the solution to 3.7-3.8. At this point there were added 6.8%, still referred to the pelt weight, of the dry tanning agent, corresponding to 1.22% of Al expressed as Awl203. After tumbling for a further 22 hours, the solution was treated with three to four additions of NaHCO3 in amounts varying from 0.2 to 0.3% to bring the pH to 3.9 - 4. Thereupon the hides were allowed to soak overnight in the stationary tumbler. The successive processing steps were carried out conventionally and the tanned hides showed good characteristics. WHAT WE CLAIM IS:

1. A bath for tanning hides, comprising an aqueous acid mixture containing a neutral or basic aluminium chloride and/or sulphate and a polycarboxylic acid complexing agent for the aluminium, together with a chrome tanning agent in an amount not exceeding about 0.7% by weight of the pelt weight of the hides to be tanned.

2. A bath according to Claim 1, in which the polycarboxylic acid is citric acid.

3. A bath according to Claims 1 or 2 having a pH of 3.5-4.5.

4. A bath according to Claim 3 in which the pH is 3.9-4.3.

5. A bath according to Claim 3 or 4, in which the aluminium content of the solution, expressed as Al203, is from 3 to 11% by weight.

6. A method for tanning hides in which there is used a bath according to any of the foregoing claims.

7. A method according to Claim 6, in which the bath contains from 0.6 to 2% by weight of aluminium, expressed as Al203 and calculated on the pelt weight of the hide being tanned.

8. A method according to Claim 6 or 7 in which the pH of the tanning bath is periodically adjusted, as necessary, to be from 3.5 - 4.5.

9. A method according to Claim 6, 7 or 8, in which the hides are tanned initially with a bath containing an aluminiumorganic polycarboxylic acid composition, then a chrome tanning agent is incorporated in an amount not exceeding about 0.7% by weight of the pelt weight, and subsequently a further amount of aluminium-organic polycarboxylic acid composition is incorporated.

10. A method of tanning hides according to Claim 6 and substantially as described in any of the foregoing examples.

11. Hides when tanned by a method according to any of Claims 6-10.