Leather tanning process

Abstract: The present invention refers to a new process meant to chrome and/or vegetable leather tanning. The process proposed by the invention comprises the steps of bating, conditioning and chrome and/or vegetable tannage. The conditioning uses hydroxy-butaldehyde which reacts blocking the amines of the collagen and releasing carboxyls. This reaction reduces the isoelectric point to 4.0 - 4.5 making the hide susceptive to the effective chrome tannage, linking the carboxyls, or to tannin, linking through hydrogen bridges. Hydroxy-butaldehyde is used in the conditioning, in a proportion of 2.5 - 3.0 % over the weight of the delimed hide, in a concentration of 40 ± 2 %, and with a pH of 4.2 - 4.4, the reaction time being from 3 to 4 hours.

Description: The present invention refers to a new process relating to chrome and/ or vegetable leather tanning. The conventional processes for leather tanning comprise the following operations: bating, pickle, pre-tanning and tanning. In EP-A-0201054 0.25-2 % of an aldehyde or keto acid is added before tanning. The bating of the hides consists of deliming (removal of lime) and bating the delimed hides with enzymes. The second step is the pickle operation, where the bated hide is submitted to treatment with sulfuric acid and sodium chloride in order to avoid the hide deterioration. Afterwards pre-tannage takes place with chrome or glutaraldehyde, that is the process granting to the hide characteristics of preliminary tannage, already allowing some operations, such as splitting, and afterwards shawing the leather. This phase has as a consequence economy in subsequent steps with the use of a smaller quantity of chemicals. Finally is performed the tanning of the hide with chrome and/or tannins, in accordance with the specifications to be reached. The object of the present invention is an innovative leather tanning process, which through the addition of a specific product, that is hydroxy-butaldehyde, to the bated hide is obtained the conditioning and, later on, chrome and/or vegetable tannage. This process results in the shifting of the isoelectric point that, as the reaction time passes, changes from 3.0 - 3.5 to 4.0 - 4.5 with the pH in the same range. The process proposed by the invention allows a chrome tannage favouring chrome penetration, as the penetration pH range is wide, varying from 4.0 to 6.0, and the optimum point between 4.0 and 6.0 matches with the process of the invention. Advantages of the present invention over the conventional tanning processes are: a. it is autobasifying, the addition of alkalis not being necessary; b. elimination of the pickle and pre-tanning phases with the subsequent removal of sulfuric acid and sodium chloride, but creating a conditioning phase; c. removal of sodium formate and of sodium bicarbonate used in the post-pickle treatment; d. simplification of the effluents treatment due to the reduction of the chrome quantity and the elimination of sodium chloride (main pollution sources of the effluents); e. reduction of the total tanning time, from 24-36 hours to 12 - 14 hours. The tanning process of the present invention comprises the steps of bating, conditioning with hydroxy-butaldehyde and chrome and/or vegetable tannage. The bating of the hides is performed in accordance with the conventional tanning processes. The hydroxy-butaldehyde provides a conditioning on the bated hide, allowing the subsequent tanning and retanning treatments, whenever it is the case. The conditioning is the change of the isoelectric point of the bated hide, as a consequence of the hydroxy-butaldehyde reaction with the amine. The hydroxy-butaldehyde blocks the amines of the collagen (proteins found in greatest number in the hide), releasing the carboxyls and, due to this, it reduces the isoelectric point, making the hide susceptive to the effective chrome tannage (linking the carboxyls) or vegetable tannage (linking through hydrogen bridges). The percent of hydroxy-butaldehyde utilization for the conditioning varies from 2.5 to 3.0% of the delimed hide weight, and the reaction time is approximately 3 to 4 hours. Afterwards, the tanning agent is added in the case of chrome the tanning time being approximately 6 to 7 hours, and for vegetable tanning 12 to 14 hours. Hydroxy-butaldehyde is obtained from the reaction of acetic aldehyde and its structural formula is the following: The characteristics of the product are: mw = 88.0 pH = 4.2 to 4.4 concentration = 40 ± 2 % of hydroxy-butaldehyde.

Claims: A leather tanning process characterized by comprising the steps of bating, conditioning and chrome and/or vegetable tanning, the conditioning using hydroxy-butaldehyde, which reacts by blocking the amines of the collagen and releasing the carboxyls, thereby reducing the isoelectric point to 4.0 - 4.5, making the hide susceptive to chrome effective tannage by linking the carboxyls, or to vegetable tannin by linking through hydrogen bridges. A process in accordance with claim 1, characterized by using hydroxy-butaldehyde in the conditioning step, in a proportion of 2.5 - 3.0 % of the weight of the delimed hide, in a concentration of 40 ± 2 %, and with a pH of 4.2 - 4.4, the reaction time being from 3 to 4 hours.

Inventors: LEUCK CARLOS ALFREDO, LEUCK, CARLOS ALFREDO
Applicants: SETA S A EXTRATIVA TANINO DE A, SETA S.A.-EXTRATIVA TANINO DE ACACIA
Application year: 1997
Main classification: C14C1
IPC codes: C14C1