Production of leather

Abstract

In a method of producing leather comprising a plurality of steps, methanesulfonic acid is used in at least one step.

Claims

1. A method of producing soft leather, the process comprising: performing a deliming operation of an animal hide in an aqueous deliming solution having a pH of from 7.5 to 8.5, the deliming solution comprising: from 0.05 to 0.5 wt. % methanesulfonic acid, sodium hydrogensulfite; from 0.5 to 2 wt % of ammonium sulfate, and from 0.6 to 1.0 wt. % of formic acid; for at least 20 minutes to remove calcium ions from the animal hide and increase a free calcium ions concentration in the deliming aqueous solution.

2. The method of claim 1, wherein methanesulfonic acid is used in the form of a mixture comprising a salt and/or another acid and/or an acid derivative.

3. The method of claim 1, wherein the leather is chrome-tanned leather.

4. The method of claim 1, wherein in the deliming operation the methanesulfonic acid is added in the amount of from 0.07 to 0.2 wt. % of the aqueous deliming solution.

5. The method of claim 1, wherein an ammonium salt of a dicarboxylic acid is further added to the aqueous deliming solution in the deliming operation.

6. The method of claim 1, wherein an aliphatic dicarboxylic acid is further added to the aqueous deliming solution in the deliming operation.

7. The method of claim 1, wherein a carboxylic ester is further added to the aqueous deliming solution in the deliming operation.

8. The method of claim 1, wherein the aqueous deliming solution comprises from 0.05 to 0.2 wt % of the methanesulfonic acid, in the deliming operation.

9. The method of claim 1, wherein the deliming operation is performed for 30 minutes to 4 hours.

Description

EXAMPLES

(1) The invention is further explicated by working examples.

(2) Abbreviations Used:

(3) Decaltal® RN: acid-reacting mixture of ammonium salts of inorganic acids and of organic dicarboxylic acids

(4) Decaltal® Pic S: mixture of weak water-soluble aliphatic dicarboxylic acids

(5) Decaltal® ESN: liquid mixture of carboxylic esters

Examples I.1 to I.6

(6) A raw cattlehide was unhaired and fleshed. Unhairing was accomplished by addition of burnt lime and sodium sulfide. For deliming, the leathers were treated with deliming agent as per Examples I.1 to I.6 in order to establish a pH of 8. In the deliming step, the hides were initially treated at room temperature with a mixture A for 20 minutes and then with a mixture B for 60 minutes. The hides were subsequently subjected to tanning and retanning with identical chrome tannage formulations.

Example I.1

(7) mixture A: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite and 0.5 wt % of ammonium sulfate.

(8) mixture B: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite, 0.14 wt % of methanesulfonic acid (70 wt % in water) and 1.5 wt % of an acid-reacting mixture of Decaltal® RN.

Example I.2

(9) mixture A: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite and 0.5 wt % of ammonium sulfate.

(10) mixture B: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite and 0.3 wt % of Decaltal® Pic S and 1.5 wt % of ammonium sulfate.

Example I.3

(11) mixture A: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite and 0.5 wt % of Decaltal® RN.

(12) mixture B: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite, 0.14 wt % of methanesulfonic acid (70 wt % in water) and 1.5 wt % of Decaltal® RN.

Example I.4

(13) mixture A: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite and 0.5 wt % of Decaltal® RN.

(14) mixture B: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite, 0.3 wt % of methanesulfonic acid (70 wt % in water) and 1.5 wt % of Decaltal® RN.

Example I.5

(15) mixture A: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite and 0.14 wt % of methanesulfonic acid (70 wt % in water).

(16) mixture B: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite, 0.14 wt % of methanesulfonic acid (70 wt % in water) and 1.2 wt % of Decaltal® ESN.

Example I.6

(17) mixture A: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite and 0.25 wt % of Decaltal® Pic S.

(18) mixture B: aqueous solution comprising 0.1 wt % of sodium hydrogensulfite, 0.25 wt % of Decaltal® Pic S and 1.2 wt % of Decaltal® ESN.

(19) The use of methanesulfonic acid made it possible to establish the pH within a shorter period and yielded clean and flat rawhides which were not swollen up as much as hides delimed without methanesulfonic acid.

(20) The leathers obtained by using methanesulfonic acid in the deliming step are softer than leathers obtained as per the prior art, and they have attractive, fine and clean grain patterns. The physical properties are comparable or superior to those of leathers obtained as per the prior art.

Example II.1

(21) Four pieces of a raw cattlehide were unhaired and fleshed. Unhairing was accomplished by addition of burnt lime and sodium sulfide. For deliming, the hides were initially washed at room temperature with water for 20 minutes and then admixed with a 1.2 wt % solution of ammonium sulfate initially and then with a 3.5 wt % solution of ammonium sulfate and left to soak for 10 minutes to establish a pH of 8.3 to 8.5.

Example II.2

(22) Two pieces of the rawhide from Example II.1 were then admixed with an aqueous solution comprising 0.6 wt % of methanesulfonic acid to establish a pH of 8.3

(23) The aqueous solutions of Examples II.1 and II.2 were measured for their pH and calcium ion content after 10, 20, 40, 80 and 140 minutes. The results are reported in Table 1.

(24) TABLE-US-00001 TABLE 1 pH and calcium ion concentration in ppm in the deliming solution of Examples II.1 and II.2, Ca.sup.2+ concentration determined via atomic emission spectroscopy t [min] 10 20 40 80 140 pH Example II.1 8.4 8.55 8.55 8.45 8.43 pH Example II.2 9.0 8.13 8.38 8.35 8.3 [Ca2+], Example II.1 450 475 525 530 550 [ppm] [Ca2+], Example II.2 415 620 610 700 700 [ppm]

(25) The pH of the deliming solutions in Examples II.1 and II.2 was in both cases between 8.3 and 8.43, and was very similar.

(26) The content level of free calcium ions in the deliming solution of Examples II.1 and II.2 was distinctly higher with addition of methanesulfonic acid than without addition of methanesulfonic acid.

Example II.3

Determination of Calcium Content of Leather

(27) The subsequent method was carried out on different pieces before starting the deliming process and also after concluding the deliming process.

(28) The leathers of Examples II.1 and II.2 were dried before starting and after concluding the deliming, respectively. 0.15 g of leather was placed in a 50 ml conical flask and 4 ml of a mixture of nitric acid and hydrochloric acid (mass ratio 1.3) were added. As soon as the mixture had cooled back down to room temperature, 1 ml of hydrogen peroxide (32 wt % in water) was added thereto. The mixture was heated to 120° C. for 180 min. The mixture was cooled down to room temperature and made up to 50 ml with water. The content level of calcium ions in the leather was determined by determining the concentration of calcium ions in the solution by atomic absorption spectroscopy.

(29) It transpired that the proportion of calcium removed from the leather was 29% on using ammonium sulfate as neutralizing agent and 52% on using ammonium sulfate and methanesulfonic acid.

Example II.4

(30) The leathers of Examples II.1 and II.2 were washed twice with water for 10 minutes. The hides were then subjected to tanning and retanning with identical chrome tannage formulations. The leathers of Example II.2 (with addition of methanesulfonic acid) were less swollen and softer than the leathers of Example II.1 (without methanesulfonic acid).

Example III

(31) Chrome-tanned wet-blue leather (cattle) was cut into pieces 1×1 cm in size and 25 g at a time were introduced into a 250 ml glass flask. In each case 5 g of fatliquoring agent as per Table 2 were added and also in each case sufficient completely ion-free (CIF) water for the amount of liquid in the flask including the fatliquoring agent to be 75 ml. The flasks were heated to 40° C. for three hours.

(32) The mixtures thus obtained were adjusted in accordance with Table 2 to various pH values using formic acid or methanesulfonic acid. The mixtures thus obtained were heated to 40° C. for three hours. Of the mixtures thus obtained, a sample of the supernatant solution was taken and measured by atomic absorption spectroscopy for its content of chromium salts.

(33) The results are reported in Table 2.

(34) TABLE-US-00002 TABLE 2 Chromium content of wastewater from various wet-blue leathers on addition of formic acid or MSA in the fatliquoring step; fatliquoring agents used: SS: sulfonated rapeseed oil, SIM: sulfite fish oil, OSL: sulfite fish oil, SXL/N: combined fatliquoring agent, sulfate/castor oil; amount particulars of acid in wt % relative to leather used. Chromium Chromium Fatliquoring Formic content content agent acid/% pH (mg/L) MSA/% pH (mg/L) SIM 0.6 4.79 37 0.5 4.9 15.6 0.8 4.21 44.4 0.9 4.08 18.7 1.0 3.77 49.7 1.1 3.79 20.4 SXL/N 0.6 4.64 29.2 0.6 4.73 11.2 0.8 4.31 36.2 0.9 3.94 16 1.0 3.87 48.3 1.1 3.66 19.2 SS 0.7 4.89 20 0.8 4.13 10.3 0.9 4.02 21.2 0.9 3.68 13.9 1.1 3.81 25.3 1.1 3.36 14.5 OSL 0.6 4.91 40.9 0.7 4.36 18.1 0.8 4.03 52.5 0.9 3.96 23.6 1.0 3.59 55 1.1 3.7 24.3 sulfated 0.8 4.8 8.6 0.7 4.67 6 castor 1.0 4.24 10.9 1.0 3.97 6.4 oil 1.2 3.9 15.1 1.2 3.66 7 no fat- 0.6 4.94 1.42 0.7 3.89 1.65 liquoring 0.8 4.16 17.79 0.9 3.57 3.33 agent 1.2 3.74 37.03 1.1 3.04 4.94

(35) At the same pH, distinctly less chromium is washed out of leather in the presence of MSA than in the presence of formic acid.