METHOD FOR TANNING AN ANIMAL SKIN WITH DIALDEHYDES

Abstract

A method for tanning an animal skin may include: (a) putting the animal skin in contact with a first tanning bath including at least one dialdehyde of general formula OCH(CH).sub.nHCO, wherein n is 0 or an integer number greater than or equal to 1 and less than or equal to 8, and wherein the first tanning bath has a pH greater than or equal to 1 and less than or equal to 5; (b) bringing the pH of the first tanning bath to a pH greater than 5 and less than 8; and/or (c) repeating one or more times the steps (a) and (b) on the animal skin coming from the step (b) using a second or further tanning bath. The first, second, and further tanning baths may be substantially free of surfactants.

Claims

1. A method for tanning an animal skin, the method comprising: (a) putting the animal skin in contact with a first tanning bath comprising at least one dialdehyde of general formula (I)
OCH(CH).sub.nHCO(I), wherein n is 0 or an integer number greater than or equal to 1 and less than or equal to 8, and wherein the first tanning bath has a pH greater than or equal to 1 and less than or equal to 5; (b) bringing the pH of the first tanning bath to a pH greater than 5 and less than 8; and (c) repeating one or more times the steps (a) and (b) on the animal skin coming from the step (b) using a second or further tanning bath; wherein the first, second, and further tanning baths are substantially free of surfactants.

2. The method of claim 1, wherein the at least one dialdehyde of general formula (I) is present in the first and second tanning baths in an amount greater than or equal to 0.1% by weight and less than or equal to 30% by weight with respect to a pelt weight of the animal skin.

3. The method of claim 1, wherein the pH of the first tanning bath in the step (b) is brought to greater than or equal to 5.5 and less than or equal to 7.5.

4. The method of claim 1, wherein the at least one dialdehyde of general formula (I) is selected from: glyoxal, malonic dialdehyde, succinic dialdehyde, glutardialdehyde, adipinic dialdehyde, pimelic dialdehyde, or mixtures thereof.

5. The method of claim 1, wherein the at least one dialdehyde of general formula (I) is glutardialdehyde.

6. The method of claim 1, wherein the step (a) has duration greater than or equal to 1 hour and less than or equal to 7 hours.

7. The method of claim 1, wherein a weight percentage ratio of the first tanning bath of the step (a) to the animal skin is greater than or equal to 1:5 and less than or equal to 10:1.

8. The method of claim 1, wherein the method does not comprise any tanning treatment with tanning agents different from the at least one dialdehyde of general formula (I).

9. The method of claim 1, wherein the animal skin is selected from: cowhide, sheepskin, goatskin, and reptile skin.

10. The method of claim 1, wherein the animal skin is cowhide.

11. The method of claim 1, wherein the at least one dialdehyde of general formula (I) is present in the first and second tanning baths in an amount greater than or equal to 0.5% by weight and less than or equal to 15% by weight with respect to a pelt weight of the animal skin.

12. The method of claim 1, wherein the at least one dialdehyde of general formula (I) is present in the first tanning bath in an amount greater than or equal to 0.1% by weight and less than or equal to 30% by weight with respect to a pelt weight of the animal skin.

13. The method of claim 1, wherein the at least one dialdehyde of general formula (I) is present in the second tanning bath in an amount greater than or equal to 0.1% by weight and less than or equal to 30% by weight with respect to a pelt weight of the animal skin.

14. The method of claim 1, wherein the at least one dialdehyde of general formula (I) is present in the first tanning bath in an amount greater than or equal to 0.5% by weight and less than or equal to 15% by weight with respect to a pelt weight of the animal skin.

15. The method of claim 1, wherein the at least one dialdehyde of general formula (I) is present in the second tanning bath in an amount greater than or equal to 0.5% by weight and less than or equal to 15% by weight with respect to a pelt weight of the animal skin.

16. The method of claim 1, wherein the pH of the first tanning bath in the step (b) is brought to greater than or equal to 6 and less than or equal to 7.

17. The method of claim 1, wherein the at least one dialdehyde of general formula (I) comprises glutardialdehyde.

18. The method of claim 1, wherein the step (a) has duration greater than or equal to 1.5 hours and less than or equal to 4 hours.

19. The method of claim 1, wherein a weight percentage ratio of the first tanning bath of the step (a) to the animal skin is greater than or equal to 1:2 and less than or equal to 6:1.

20. The method of claim 1, wherein the animal skin is calf skin or baby calf skin.

Description

[0069] In the following examples, reference will be made to the accompanying figures, which illustrate:

[0070] FIG. 1, a photographic image of the surface of a first leather obtained with the tanning method according to the present invention;

[0071] FIG. 2, a photographic image of the surface of a second leather obtained with the tanning method according to the present invention;

[0072] FIG. 3, a photographic image of the surface of a leather obtained with a conventional chrome tanning method.

EXAMPLE 1

[0073] A first Dutch calf rawhide (pickled) included in a batch of weight range 11-13 was subjected to a tanning treatment in accordance with the method of the present invention.

[0074] The first tanning bath had the following composition (percentages by weight referred to the pelt weight of the treated skin): [0075] water, [0076] 1.5% of glutaraldehyde, [0077] pH=3 [0078] 9 B (by addition of sodium chloride).

[0079] The skin was treated in the tanning bath (step a) for 4 hours at 25 C. in a drum. The percentage ratio between the weight of the water of the tanning bath and the pelt weight was equal to 400%.

[0080] At the end of the treatment, sodium carbonate was added to the bath until the pH of the bath was adjusted to a value of approximately 6.5. The skin was maintained in the bath at the aforesaid pH for 1.5 hours to allow fixing the aldehyde tanning agent (step b).

[0081] At the end of the aforesaid steps a and b (first treatment cycle), the exhausted first tanning bath was removed from the drum and replaced with a second tanning bath having the same composition as the first tanning bath. The second tanning bath was used in the same weight ratio with respect to the pelt weight of the treated skin. The steps a and b described above were then repeated once (second treatment cycle).

[0082] At the end of the second treatment cycle, the tanned skin had the following characteristics: [0083] Tc=90 C., [0084] thickness 1.7 mm, [0085] area yield of the process equal to approximately 2.2 ft.sup.2/kg.

[0086] The grain side of the leather had few visible superficial defects as shown in FIG. 1.

EXAMPLE 2

[0087] A second Dutch calf raw hide included in the same batch as the skin of Example 1 was subjected to the same tanning treatment described in Example 1. For this second skin, the same results of Tc, skin thickness and area yield of the process observed in Example 1 were obtained. This demonstrates the reproducibility of the results of the process according to the previous invention.

[0088] The grain side of the leather had few visible superficial defects as shown in FIG. 2.

EXAMPLE 3

[0089] By way of comparison, the Dutch calf raw hide used in Example 1 was subjected to a conventional chrome tanning treatment.

[0090] The chrome tanned skin had the following characteristics: [0091] Tc=100 C., [0092] thickness 1.3 mm, [0093] area yield of the process equal to approximately 1.9 ft.sup.2/kg.

[0094] The grain side of the leather had a higher quantity of visible superficial defects than those of the leather of Examples 1 and 2, as shown in FIG. 3.

[0095] The thickness of the leather obtained with the method according to the present invention (Examples 1 and 2) is approximately 30% greater than the thickness of the leather obtained subjecting the same raw hide to a traditional chrome tanning process.

[0096] Moreover, the area yield of the raw hide treated with the method according to the present invention is approximately 15% greater than the area yield of the chrome tanning method.