MXPA03009853A - Improvements in leather processing. - Google Patents

Abstract

The invention relates to improvements in the processing of animal skins to create leather and results in improved leather quality, in terms of softness, and markedly increased area yield. According to the present invention there is provided a process for improving area yield and/or softness of leather which comprises treating chromium (III) or aldehyde tanned skins with an enzyme composition which is a mixture of at least one protease and at least one elastase. The invention applies particularly, although not exclusively, to clothing leather and upholstery leather production.

Description

IMPROVEMENTS IN LEATHER PROCESSING FIELD OF THE INVENTION This invention relates to the processing of animal skins to create leather. The invention generates as a result an improved quality of leather, in terms of smoothness and a markedly increased area performance. The invention applies particularly, although not exclusively, to the production of leather for garments and leather for upholstery. BACKGROUND OF THE INVENTION The area of a piece of leather and, to a lesser extent, its softness is mainly controlled by structural characteristics of the material from which the leather is made, that is, the skin or the skin. This raw material coirprende three main layers, each one contributes with properties to the piece. The flesh layer (or simply flesh) is the part that is closest to the body of the animal. It consists of collagen fibers that have a low and different corrugation angle, which are almost parallel to the skin or skin surfaces. This means that the layer has limited ability to stretch by distorting the waviness horizontally and therefore limits the area of skin or leather. REF: 150894 The dermis (chorion) is the middle section and the thickest part of the original skin. It is composed of a matrix of interconnected collagen fibers; in the raw material the fibers have an average angle of undulation close to 45 °. Waviness allows the skin or leather to adopt a larger area if the angle is relaxed or relaxed, or to adopt a smaller area if the ripple angle is increased during the leather making process, for example at expand the skin without tanning The epidermis layer (or simply epidermis) is the outermost part of the skin. It has an area larger than the dermis and, because it is made up of very fine fibers, it is weaker than the dermis, so that it adopts a convolutional distribution that allows it to be stretched without breaking. The reversibility of the stretching mechanism is made possible by the presence of elastin, a fibrous protein that behaves in a very similar way to an elastic. The area of skin or leather is determined by the undulation angle of the dermis, which in turn is controlled by the area of the skin, if present in the skin, and the area of the epidermis, which is usually present in the leather: of the two control mechanisms, the most important one is the epidermis. In leather with epidermis, the epidermis also limits the softness of the leather, since the presence of elastin has a rigidifying effect.

To increase the area yield and the softness of the leather it has been proposed to degrade elastin. The application of "elastolytic enzymes to raw skins or untanned skins results in the epidermis of desired area, but at the expense of a looseness in the dermis (often unacceptable) .The latter effect is due to the fact that the formulations or products of elastolytic enzymes have predominantly proteolytic activity and this causes considerable degradation of both the dermis itself and the non-structural proteins within the dermis matrix, which contribute to the desired properties of the leather.A solution to the problem would be to degrade elastin by attacking it only However, a source of elastase without an accompanying protease is not known, and the separation of enzymes to purify the elastase is a high cost process, which makes the expensive product prohibitively expensive for industrial production. BRIEF DESCRIPTION OF THE INVENTION The present invention is based on the finding or that mixtures of proteolytic and elastolytic enzymes can be used successfully to improve the softness and performance of leather area when treating skins tanned with chromium (III) salts, or aldehydic tanning agents.

According to the present invention, a process is provided for improving the performance of area or softness of the leather comprising the treatment of skins tanned with chromium (III) or aldehyde with an enzymatic composition which is a mixture of at least one protease and at least one Elastase DETAILED DESCRIPTION OF THE INVENTION Enzyme mixtures containing one or more proteases and one or more elastase are commercially available. They are typically derived from bacterial sources in the form of what is called a microbial protease, which, in the absence of a costly purification process, also contains elastase. The present invention advantageously uses the relatively cheap and unpurified "protease". An example of a commercially available enzyme mixture is NovoCorME AX (available from Novozymes A / S). The process of this invention takes advantage of the difference in the chemistry of collagen and elastin. These differences are established in Table I, which contains. some elements of their amino acid compositions: There is some discrepancy in the literature regarding the precise amino acid composition of these proteins, and therefore the amounts that are presented are indicative, based on the published amounts.

Table I Indicative amino acid compositions of bovine collagen type I and elastin (residues per 1000 residues).

It can be seen that elastin has an order of magnitude less acidic and basic groups in the side chains compared to collagen and almost double the amount of apolar side chains. The basis of the invention is that by tanning using chromium (III) salts, chromium (III) binds to the protein in the acid side chains, so that the availability of such groups in the collagen allows tanning to work . Part of the definition of the tanning effect is that the protein acquires resistance to microbial attack. say, resistance to putrefaction by the action of prateolytic enzymes. Therefore, it is known for a long time that it is very difficult to modify the properties of chrome-tanned leather by applying proteolytic enzymes, such as that used in the processes leading to tanning. On the other hand, the lack of acid groups in elastin means that the chromium tanning has little effect on the. elastin, so that it does not confer enzymatic resistance. Therefore, elastin on chromium-tanned skin remains vulnerable to degradation by elastase. As a result, treatment with chromium in leather (leather tanned with chromium (III) salts) with a mixture of enzymes containing an elastase and a protease will result in degradation of elastin but without damage to collagen and other nonstructural tanned proteins. An important feature of the process of this invention is that it is applied to leather tanned with chromium in which the chromium (III) is covalently bound to the protein and therefore does not move in solution; if it moves, the enzymes would be deactivated by the resultant tanning effect applied to them. This could occur, for example, if aluminum (III) or zirconium (IV) was included in the tanning. Typical procedures for tanning with chromium (III) are described in Chem. Soc. Rev. 26 (2), III 1997 (Modern Tanning Chemistry - A.D. Covington). The role of the chromium (III) tanning is also applied to the covalent reaction on the amino groups, that is, by aldehyde tanning reactions, assuming that the bound reagent is not released from a polymeric state by hydrolysis. Suitable aldehyde tanned agents include the aldehydes themselves, monofunctional and difunctional aldehyde derivatives as well as compounds having at least a partial aldehydic function or a reactive hydroxyl function, such as hydroxymethylphosphonium salts, typically sulfate or chloride, and especially oxazolidines. It is recognized that not all potential reticulants are acceptable in the workplace due to toxicity hazards. In addition, all glutaraldehyde derivatives produce leathers which have perceptible colors or shades. Therefore, the preferred crosslinkers are the phosphonium salts with active hydroxyl, which are significantly less toxic than most other reagents and produce white leather. Other tanning reactions that can be used before treatment are probably those that result in an inability to obtain a positive result; such tanneries include vegetable tanning with vegetable polyphenols, tanning with sintan and resin. The reason is that these reactions are labile, that is, reversible and are based in considerable part on the formation of hydrophobic interactions with the protein. The method of the invention is particularly simple, since it only requires that the enzymes are added to the leather during the normal neutralization process before the conventional stage after tanning. Therefore, there is no additional process step involved in the entire treatment of skins to produce leather. This means that process times remain unchanged and, what is more important, there are no capital costs related to its introduction. This means that new processes can be applied in all tanneries. The procedure is remarkably harmless with respect to damage to the leather. The pH of the leather does not need to be high, because the enzyme mixture can be used at a high enough concentration to produce the effect without the need to operate at the optimum pH for the elastase. The collagen resistance is high, although it can be damaged, but not up to the extremely high protease concentration that is used at a significantly elevated temperature, for example 50 ° C. Additional aspects of the safety of the procedure are: The reaction should not be prolonged for penetration by the enzyme, because access to elastin is only a short distance across the surface of the epidermis and elastin does not need to be dissolved completely, it is sufficient that it causes significant degradation, so that its function is eliminated. The new technology has the advantage of not being limited to specific relative activities of elastase and protease in the formulation. The enzymatic reaction can preferably be carried out at a temperature in the range of 35-45 ° C, more preferably of about 40 ° C, a preferable pH in the range of pH 5-8, and more preferably a pH of 6-7, and the reaction time preferably is in the range of 30-180 minutes, more preferably in the range of 60-120 minutes. The enzyme dosage preferably can be in the range of 2 to 10 kg of enzyme product per tonne of rawhide, of rranera will preferably be in the range of 3-5 kg of enzyme product per ton of rawhide. The enzyme product can have an activity measured in units of Lóhlein Volhard (LVU) per gram in the range of 50,000 L / g to 250,000 LVU / g preferably 100,000 LVU / g to 150,000 LVU / g . A unit of Lóhlein-olhard (LVU) is the amount of enzyme which degrades 1. 725 mg of casein under the conditions established here. Proteases degrade casein from an alkaline casein solution under the following standard conditions: temperature 37 ° C, pH 8. 2 and reaction time of 60 minutes. The reaction is stopped by adding HC1 and the non-degraded casein is precipitated with sodium sulfate. The HC1 content of the filtrate which has not been bound to the degraded casein or its degradation products is determined by titration with NaOH. The greater the amount of casein that is degraded and thus not precipitable, the greater the acid in the filtrate. The consumption of NaOH in the retrotitulation therefore serves as a direct measure of the level of proteolytic activity. A remarkable feature of the invention is that softness and area gains can be obtained without loss of leather. This is due to two complementary factors. In the first place, the relaxation of the dermis is limited by the effects of tanning, essentially; fixing the fiber structure in place, so that they retain many of the leather's touch characteristics. Second, the resistance of the protein to the proteolytic attack. it means that the non-structural protein does not separate nor does the collagen dissolve, so that the filling of the fiber structure is maintained. Importantly, the resistance to degradation includes the epidermis-dermal junction, where damage is observed as a loose layer, resulting in a sparse, ie thick, wrinkling of the surface of the epidermis when fold the leather. The maintenance of the "tight" structure is a vital factor in determining the quality of the finished leather. The effectiveness of the invention will become apparent by the treatment of "double-sided" leather, for example, of domestic sheep wool skins from England, followed by drying after chromium tanning. This situation is the worst case, because the flesh is still in place and the presence of wool in the epidermis limits the ability of the epidermis to relax. However, it has surprisingly been found that the leather becomes significantly softer and exhibits an increase in measurable area; see example 1 below. In the case of leather for chrome-tanned upholstery, the profit area can be considerable, up to 10%; see example 2 below. The most noticeable effect in the upholstery leather is due to the fact that the untanned skin is divided before tanning, so that the tanning is applied only to the divided epidermis and the limiting effect of the skin on the ability of the epidermis is eliminated. and dermis to relax. A major impact of the new technology lies in the increased profitability capability of the product. This is exemplified by a tannery processing of approximately 50 tons of skin per day: the annual added benefit of applying this invention would be approximately £ 3 per meter. The following three recipes provide example the proposed use of the enzyme in the neutralization step. Recipe 1: UPHOLSTERY LEATHER WITH NOVOCOR AX Wetblue German bovine, 1.1-1.2 rare All% refers to sheared weight Commercial name of BASF Recipe 2: .-.:. · .- GARMENT LEATHER CLOTHING NOVOCOR AX National English ram skin Flotation ratio: 15L / skin * Trade name of TFL Recipe 3: RECOVERY OF UPHOLSTERY WITH NOVOCOR AX Raw material: Danish vaqas Wet blue, 1.1-1-2 mm All% refers to the sheared weight * Trade name of BASF, ** Trade name of TFL - The invention is further illustrated by the following non-limiting examples. EXAMPLE 1 Again, wool skins (50 pieces) are moistened in cracked and dry condition, adjusted to pH 8.0 with sodium hydrogen carbonate, and then treated with 1.0% by weight? of Pyrase ™ 250 MP (Trade name for a proteolytic / elastolytic enzyme formulation supplied by Novozymes A / S) at 40 ° C for 60 minutes. Pyrase "is a protease produced by submerged fermentation of a genetically modified bacilli After dyeing in the usual way, it is found that the softness has increased, which greatly improves its handling." The area measurement shows that the average area gain of experimental leathers are 3% higher than in normal production.In this production, although the gain of area is commercially important, the most significant result is the improvement and the quality with respect to the softness EXAMPLE 2 In two separate procedures carried out in a tannery, the unique bovine upholstery skins, previously divided in whitewashed and chromium-tanned state, all in the usual manner, are neutralized to pH 7.0, then treated with 1.0% by weight of Pyrase ™ 250 P for 2 hours at 40 ° C. Table II: Average results for tests on skins for upholstery.

From Table 2, after drying in the usual way, the experimental skins are at an average .9.0% larger area compared to untreated control skins, comparing the cracked area with the wet blue area. In addition, skins treated with Pyrase are almost twice as strong, measured by tear strength test and tensile strength. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (8)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A process for improving the softness or performance of leather area, characterized by comprising providing skins of animals tanned with chromium (III) salts or an aldehyde tanning agent, and treating the tanned skins with a mixture of enzymes comprising a protease and an elastase.
2. 2. The method according to claim 1, characterized in that the enzyme mixture is a microbial protease with an elastase component.
3. 3. The process according to claim 1 or 2, characterized in that the enzyme mixture is added to the neutralization bath that precedes the post-tanning treatment.
4. 4. The process according to any of the preceding claims, characterized in that the enzymatic treatment is carried out at a temperature in the range of 35-45 ° C, more preferably at about 400 ° C.
5. 5. The process according to any of the preceding claims, characterized in that the enzymatic treatment is carried out at a pH in the range of pH 5-8, preferably pH 6.7.
6. 6. The method according to any of the preceding claims, characterized in that the enzymatic treatment is carried out in a reaction time in the range of 30-180 minutes, preferably in the range of 60-120 minutes. Process according to any of the preceding claims, characterized in that the enzyme dosage is in the range of 2-10 kg of enzyme product per tonne of rawhide, preferably in the range of 3-5 kg of enzyme product per ton of rawhide 8. The method according to claim 1, characterized in that it is substantially as described herein, in examples 1 or 2.