METHOD FOR DEHAIRING OF HIDES OR SKINS

Abstract: The method comprises soaking and subsequent dehairing by controlled addition of alkaline proteolytic enzymes and a small amount of Na2S. The hair is removed completely and without environmental harm.

Description: METHOD FOR DEHAIRING OF HIDES OR SKINS The invention comprises a method for dehairing of hides or skins by means of enzymes. The dehairing of hides or skins is an old art, which at least dates back to around the turn of the century. The prior art dehairing methods suffer from the following two drawbacks: 1 ) large quantities of sulfide or other environmentally dangerous chemicals have been necessary during the dehairing, and 2) the entire part of or the major part of the removed hair was dissolved to a point that it could not be put to any useful purpose, and as a consequence - and this is even more important - the BOD 5 is too high from an environmental point of view. Thus, it is the purpose of the invention to provide a method for dehairing of hides or skins by means of enzymes, in relation to which 1) only small quantities of sulfide are necessary, and 2) the hair is removed completely and in an undamaged form useful for further use of the hairs and without environmental harm. The method according to the invention for dehairing of hides or skins by means of enzymes is characterized by the fact that 1 ) the hides or skins are soaked 2) the soaked hides or skins are exhibited to a main soak, and 3) the thus treated hides or skins are dehaired a) by addition of water and exposure to mechanical influence, whereby the water is added in an amount which provides satisfactory rubbing between the individual hides or skins, b) by simultaneous or arbitrarily sequential addition of a base in an amount which is sufficient for raising the pH of the dehairing liquor to between 9.0 and 12.5, and one or more alkaline proteolytic enzymes in an amount corresponding to between 10 and 150 mg of pure enzyme protein / kg of dry hide or skin, preferably between 20 and 50 mg of pure enzyme protein/kg of dry hide or skin, most preferably between 30 and 40 mg of pure enzyme protein/kg of dry hide or skin, and c) by subsequent addition of an easily soluble sulfide in an amount of maximum 0.12% S " in relation to the hide weight or skin weight, before the hairs are immunized by the base, whereby the hairs are removed during the dehairing. It should be noted that the method according to the invention is especially well suited in relation to bovine hides. However, the method for dehairing of hides and skins according to the invention can also be used for hides or skins of other provenance, e.g. sheep skins or goat skins. It is to be understood that the soak in step 1) and the main soak in step 2) are carried out in a conventional way and thus in themselves are not inventive, but that they do form part of the entire invention including the dehairing step 3). Reference can be made to Bibliotek des Leders, Band 2, Arbeiten der Wasserwerkstatt bei der Lederherstellung, 1988, Umschau Verlag, page 26-62. Usually steps 1), 2) and 3) are performed in the same equipment, preferably a beam house drum, but they may be carried out in different pieces of equipment. In regard to the dehairing step 3) it should be noted that an alkaline proteolytic enzyme in this specification with claims is defined as a proteolytic enzyme which according to the CPU activity determination method, in which Hammersten casein is used as a substrate (reference being made to AF 228/1 , obtainable on request from Novo Nordisk A/S), exhibits a pH activity curve with a maximum above pH 7. Examples of these alkaline proteolytic enzymes which can be used in the method according to the invention are the proteases described in WO 92/17576, WO 89/06279, WO 91/00345, and PCT/DK93/00074. Also, in regard to the dehairing step 3) reference should be made to the immunization of the hair as an important aspect of the invention. Reference can be made to Bibliotek des Leders, Band 2, Arbeiten der Wasserwerkstatt bei der Lederherstellung, 1988, Umschau Verlag, page 87-89. Thus, the immunization of the hair is a reaction, wherein the -S-S-bridge is converted to an -S-bridge in alkaline medium, whereby the hair is rendered insoluble in Na 2 S solution. Immunization is a potentially misleading term, which, however, is accepted in this field. Denaturation might be a better term. The aqueous phase in step 3) is identified as the dehairing float in this specification with claims. If the sulfide is added too early after step 3b), i.e. immediately after or shortly after step 3b), the remaining hair, which is still adhering to the hide, will be dissolved, and if the sulfide is added too late, i.e. after completion of the immunization, the hairs cannot longer be removed from the hides. However, the average worker in the art will know when to add the sulfide, on the basis of the instructions indicated in this specification with claims, i.e. as follows. As a guideline a preliminary dehairing experiment can be carried out, according to the invention, and all variable parameters can be noted. Between step 3b) and step 3c) samples can be taken out regularly, and for each sample it can be determined, if the hairs are immunized or not (if immunized, the hairs cannot be removed from the hides by addition of Na 2 S). It will be found that the first samples are not immunized, and that all samples beginning with a critical sample are immunized. The time corresponding to the sample immediately preceding the critical sample will be the ideal time for addition of the sulfide. Usually step 3c) is performed around 4-12 hours after step 3b), depending upon the kind and concentration of the base. Also, a guideline in regard to the time interval between step 3b) and 3c) can be extracted from the following examples. 0.12% of S " , in relation to the dry hide weight or skin weight corresponds to 0.5% of a 60% Na 2 S solution or 0.3% of a 72% NaHS solution, the 0.5% and 0.3% being related to the dry hide weight or skin weight. Surprisingly it has been found that only small quantities of sulfide are necessary, and that the hair is recovered 100% as useful, undamaged hair without any environmental disadvantages, if the method is carried out as indicated above, especially if step 3c) is carried out at the time indicated, i.e. before the hairs are immunized by the base, preferably just before the hairs are immunized by the base. The Novo Nordisk product sheet "Examples of Application of NUE 0.6 MPX for dehairing of hides" (B 533a-GB 2000 Oct. 1989 NHS) describes a prior art dehairing process, in which an amount of 0.36% of S " (related to the dry weight of hides) is recommended. Usually, the process will not work satisfactorily with a smaller concentration of S " . From Bibliotek des Leders, Band 2, Arbeiten der Wasserwerkstatt bei der Lederherstellung, 1988, Umschau Verlag, page 62-63 it appears that one of the classical dehairing methods comprises hair destruction, i.e. dissolution of the hair. This method is very disadvantageous from an environmental point of view. In the process according to the invention the hairs are not dissolved at all. A preferred embodiment of the method according to the invention comprises that a green fleshing is carried out between step 2) and 3). In this embodiment the following advantages are obtained: 1) the enzymatic action during the dehairing is improved due to the reduced amount of fat in the dehairing float and on the hides or skins, 2) the sewage water contains less fat and is thus more acceptable from an environmental point of view, 3) the fat removed during the green fleshing will not be exposed to sulfides and will thus exhibit a better quality, and 4) the necessary amount of S " in step 3c) will be less, in certain cases even 0. A preferred embodiment of the method according to the invention comprises that in step 3a) the amount of water added to the treated hides or skins is between 30 and 200% in relation to the dry weight of the hides or skins, preferably between 75 and 125% thereof. With an amount of water less than 30% the abrasion of the hides or skins will be damaging, and with an amount of water above 200% the mechanical impact will be too low, and also, the consumption of water will be undesirably high. A preferred embodiment of the method according to the invention comprises that in step 3b) the base is Ca(OH) 2 or NaOH. In this manner the BOD 5 is kept relatively low, in contradistinction to the case, when e.g. NH 3 is used as the base. Also, Ca(OH) 2 is even better than NaOH, because Ca(OH) 2 cannot damage the hides if an overdose of Ca(OH) 2 is accidentally used. A preferred embodiment of the method according to the invention comprises that the alkaline proteolytic enzyme is the proteolytic enzyme producible by means of an alcalophilic Bacillus species. It has been found experimentally that an enzyme of this kind gives rise to a satisfactory dehairing. A preferred embodiment of the method according to the invention comprises that the alkaline proteolytic enzyme exhibits a pH activity curve with a maximum above pH 9, according to the CPU activity determination method. In this manner a very satisfactory removal of the hairs is obtained. A preferred embodiment of the method according to the invention comprises that in step 3b) the base is added before the proteolytic enzyme. In this manner local, extremely high pH values are avoided, which might inactivate the alkaline protease. A preferred embodiment of the method according to the invention comprises that in step 3b) maximum 0.02% S " is added, in relation to the dry hide weight or the dry skin weight. In this embodiment the immunization will be somewhat delayed, and thus the enzymes will be able to influence the hairs over a longer period of time, and thus the dehairing will be more complete. A preferred embodiment of the method according to the invention comprises that in step 3c) the sulfide is Na 2 S or NaHS. Na 2 S or NaHS are the cheapest sulfides on the market, and no other sulfides perform better than Na 2 S or NaHS. A preferred embodiment of the method according to the invention comprises that the sulfide is added as late as possible before the immunization of the hairs. In this manner no hair at all is dissolved, and the maximum amount of hair can be collected. A preferred embodiment of the method according to the invention comprises that the hairs are removed from the dehairing liquor by continuous filtration during the dehairing. If no continuous filtration is carried out the hairs will tend to adhere to the fatty tissue on the back of the hide or skin. In US 3,840,433 a dehairing method with a specially selected group of alkaline proteases is described. The final leather product resulting from this dehairing, however, exhibits a tendency towards grain damage and nubuckisation, in contradistinction to the leather product resulting from the dehairing method according to the invention. The method according to the invention will be illustrated by the following examples. In the examples transportation times are included in the time schedule. Thus, the interval between two consecutive times does not necessarily correspond to the duration of the treatment in question. All percentages are calculated in relation to the dry weight of hide or skin. 5 Both hides are clean. The bull hide is more fresh than the cow hide. The cow hide is more dry on the hair side than the bull hide. The bull hide is more dry on the flesh side than the cow hide. Both hides comprise a relatively small amount of fat. 0 h Soak 10 200% of water with a temperature of approx. 28°C 0.1% of Baymol FD (0.051 kg) (detergent) Start - 5 minutes of operation/5 seconds break (5 rev./minute) 1 h Main soak 200% of water with a temperature of approx. 28°C 15 " 1 ) 0.1 % of Baymol FD (0.051 kg) (detergent) 2) 0.5% of NH 3 added as a 25% solution (0.250 kg) 3) 13 mg of enzyme protein per kg of salted hide. The enzyme is the alkaline proteolytic enzyme described in Example 1 of WO 92/17576. Concentration of salt, mainly NaCI: 3.5 Be 20 1 35 h pH: 9.96 1 5 h Operation of drum set to 10 minutes of operation/20 minutes break (5 rev./minute) 13 h Green fleshing pH: 9.33; temperature: 28°C (measured) 25 Concentration of salt, mainly NaCI: 2.6 Be Weight of fleshed hide: 50.0 kg 15*° h Dehairing 75% of water at 28°C 0.7% of Ca(OH) 2 on hide = 357 g 5 15 45 h 80 mg of enzyme protein per kg of salted hide. The enzyme is the alkaline proteolytic enzyme described in Example 1 of WO 92/17576. Operation of drum set to 5 minutes of operation/6 seconds break (5 rev./minute) pH 12.27 0 Weakly initiative dehairing - pH 11.86 Dehairing proceeding well - pH 11.60 - 11.37 Iδ ∞ h pH 11.16 20°° h pH 10.87 20 45 h Stop - The hides are taken out 5 All hairs are removed from the float Added amount of water: 22.5 litres 1.3% of Ca(OH) 2 on hides = 650 g 0.5% of Na 2 S = 250 g 21 ,s h Operation of drum set to 10 minutes of operation/20 minutes break (5 0 rev./minute) 29 40 h Cow hide: fully dehaired. No stretch marks Bull hide: fully dehaired. No stretch marks Stop, pH 12.20 The hides were not quite as clean as in Example 1. O h Soak 200% of water with a temperature of approx. 28°C 0.1% of Baymol FD (0.052 kg) (detergent) Start - 5 minutes of operation/5 seconds break (5 rev./minute) Concentration of salt, mainly NaCI: 5 Be ( h Main soak 200% of water with a temperature of approx. 28°C Order of addition: 1) 0.1% of Baymol FD (0.052 kg) (detergent) 2) 0.5% of Ca(OH) 2 = 0.156 kg 3) 13 mg of enzyme protein per kg of salted hide. The enzyme is the alkaline proteolytic enzyme described in Example 1 of WO 92/17576. 0 35 Concentration of salt, mainly NaCI: 0.8 Be pH: 11.83 Operation of drum set to 15 minutes of operation/15 minutes break (5 rev./minute) 9 ,5 h Green fleshing Concentration of salt, mainly NaCI: 4.2 Be pH: 9.95 Temperature: 24°C Weight of fleshed hide: 50 kg h Dehairing 75% of water with a temperature of approx. 28°C 0.5% of Ca(OH) 2 on hide (salted) = 262.5 g 1"° h 80 mg of enzyme protein per kg of salted hide. The enzyme is the alkaline proteolytic enzyme described in Example 1 of WO 92/17576. Operation of drum set to 5 minutes of operation/5 seconds break (5 rev./minute) Stop - The hides are taken out All hairs are removed from the float Added amount of water: 25 litres (28°C) 0.2% of Ca(OH) 2 on hide = 105 g 4* h Operation of drum set to 5 minutes of operation/25 minutes break (5 rev./minute) pH 11.94 - 5 minutes after the pH was 11.86 s6 h pH 11.27; concentration of salt, mainly NaCI: 1.6 Be Cow hide and bull hide fully dehaired Concentration of salt, mainly NaCI: 1.8 Be Stop 5 Both hides look good. 0 h Soak 200% of water with a temperature of approx. 28°C 0.1 % of Baymol FD (0.049 kg) (detergent) Start - 5 minutes of operation/5 seconds break (5 rev./minute) 10 1 00 h Main soak 200% of water with a temperature of approx. 28°C Order of addition: 1) 0.1% of Baymol FD (0.049 kg) (detergent) 2) 0.3% of Ca(OH) 2 = 0.147 kg 15 3) 13 mg of enzyme protein per kg of salted hide. The enzyme is the alkaline proteolytic enzyme described in Example 1 of WO 92/17576. 1 ,5 h pH: 12.0 Operation of drum set to 15 minutes of operation/5 seconds break (5 rev./minute) 0 δ ∞ h pH 10.0 The soak is stopped. Both hides have small spots showing initiative dehairing 5 " " h Dehairing 75% of water with a temperature of approx. 28°C 0.5% of Ca(OH) 2 on hide (salted) = 246 g 5 50 h 80 mg of enzyme protein per kg of salted hide. The enzyme is the 5 alkaline proteolytic enzyme described in Example 1 of WO 92/17576. Operation of drum set to 5 minutes of operation/5 seconds break (5 rev./minute) pH 12.5 β∞ h pH 11.4 10 Operation of drum set to 5 minutes of operation/5 minutes break (5 rev./minute) 12? h pH 10.1 Stop - The hides are taken out All hairs are removed from the float 15 14 20 h Added amount of water: 12 litres (28°C) 2% of Ca(OH) 2 on hide = 984 g 0.5% of Na 2 S on hide = 246 g pH > 12 Operation of drum set to 2 minutes of operation/4 minutes break (5 20 rev./minute) 21 " h pH value not measured Cow hide fully dehaired Bull hide fully dehaired Stop Both hides look good. O h Soak 200% of water with a temperature of approx. 24°C 0.1% of Baymol FD (detergent) 0.01 % of Arazit KF (preservative) 5 minutes of operation/5 seconds break (9 rev./minute) 1°° h Main soak 200% of water with a temperature of approx. 26°C Order of addition: 1 ) 0.3% of Na 2 CO 3 .10H 2 O 2) 0.1% of Baymol FD (detergent) 3) 0.01 % of Arazit KF (preservative) 1 s h 4) 13 mg of enzyme protein per kg of salted hide. The enzyme is the alkaline proteolytic enzyme described in Example 1 of WO 92/17576. pH: 9.1 Operation of drum set to 5 minutes of operation/5 seconds break (6 rev./minute) 6*° h pH: 8.2 The soak is stopped 6 s6 h Dehairing 75% of water with a temperature of approx. 26°C 0.5% of Ca(OH) 2 7 06 h 80 mg of enzyme protein per kg of salted hide. The enzyme is the 5 alkaline proteolytic enzyme described in Example 1 of WO 92/17576. ^ h pH 10.2 Stop - the hides are taken out All hairs are removed and the float is changed 14 00 h 100% of water with a temperature of 26°C 10 0.5% Na 2 S 14 ,0 h 2% of Ca(OH) 2 l^ h pH: 12.25 Operation of drum set to 3 minutes of operation/30 minutes break (6 rev./minute) I5 24°° h Stop EXAMPLE 5 505 kg salted cow hide Total 505 kg 0 h Soak 5 200% of water with a temperature of approx. 25°C 0.1 % of Baymol AN (0.505 kg) (detergent) 0.01% of Arazit KF (0.0505 kg) (preservative) Start - 5 minutes of operation/5 seconds break (5 rev./minute) 1 00 h Main soak 10 200% of water with a temperature of approx. 25°C Order of addition: 1 ) 0.1 % of Baymol AN (0.505 kg) (detergent) 2) 0.3% of Na 2 C0 3 = 1.515 kg 3) 0.01 % of Arazit KF (0.0505 kg) (preservative) 15 4) 6 mg of enzyme protein per kg of salted hide. The enzyme is the alkaline proteolytic enzyme described in Example 1 of WO 92/17576. 2 00 h pH: 8.8 Operation of drum set to 10 minutes of operation/5 seconds break (5 rev./minute). 0.2% of Na 2 C0 3 (1.01 kg) was added. 20 4 00 h pH = 8.8 0.2% of Na 2 C0 3 (1.01 kg) was added. 7°° h pH 8.9 The soak is stopped. 7°° h Dehairing 100% of water with a temperature of approx. 25.5°C 0.5% of Ca(OH) 2 (2.525 kg) 0.2% of Na 2 S (1.010 kg) 5 7°° h 37 mg of enzyme protein per kg of salted hide. The enzyme is the alkaline proteolytic enzyme described in Example 1 of WO 89/06279. Operation of drum set to 5 minutes of operation/5 seconds break (5 rev./minute) pH 12 10 8*° h pH 11.2 0.2% of Ca(OH) 2 (1.01 kg) 11 15 h pH 11.6 0.2% of Ca(OH) 2 (1.01 kg) Operation of drum: 10 minutes of operation/hour 15 14 ∞ h pH 11.5 0.1 % Ca(OH) 2 (0.505 kg) 21°° h pH 10.8 Stop - The hide is taken out All hairs are removed from the float 20 21 00 h Added amount of water: 250 litres (15°C) 2% of Ca(OH) 2 = 10 kg 0.5% of Na 2 S = 2.5 kg pH > 12 Operation of drum set to 5 minutes of operation/5 seconds break (5 rev./minute) 21 30 h Added amount of water of 15°C: 50% (250 litres) 23 ,s h Rinsing with 200% of water (1010 kg) of 25°C 5 23 30 h Fleshing For a somewhat more detailed description of Example 5, reference is made to the below indicated table. With pH electrode. The figures in paranthesis are measured with indicator paper The protease is the protease preparation described in Example 1 in WO 89/06279 With pH electrode. The figures in paranthesis are measured with indicator paper The protease is the protease preparation described in Example 1 in WO 89/06279 With pH electrode

Claims: CLAIMS 1. Method for dehairing of hides or skins by means of enzymes, wherein 1) the hides or skins are soaked 2) the soaked hides or skins are exhibited to a main soak, and 3) the thus treated hides or skins are dehaired a) by addition of water and exposure to mechanical influence, whereby the water is added in an amount which provides satisfactory rubbing between the individual hides or skins, b) by simultaneous or arbitrarily sequential addition of a base in an amount which is sufficient for raising the pH of the dehairing liquor to between 9.0 and 12.5, and one or more alkaline proteolytic enzymes in an amount corresponding to between 10 and 150 mg of pure enzyme protein / kg of dry hide or skin, preferably between 20 and 50 mg of pure enzyme protein/kg of dry hide or skin, most preferably between 30 and 40 mg of pure enzyme protein/kg of dry hide or skin, and c) by subsequent addition of an easily soluble sulfide in an amount of maximum 0.12% S ~~ in relation to the hide weight or skin weight, before the hairs are immunized by the base, whereby the hairs are removed during the dehairing. 2. Method according to Claim 1 , wherein a green fleshing is carried out between step 2) and 3). 3. Method according to Claim 1 - 2, wherein in step 3a) the amount of water added to the treated hides or skins is between 30 and 200% in relation to the dry weight of the bovine hides, preferably between 75 and 125% thereof. 4. Method according to Claims 1 - 3, wherein in step 3b) the base is Ca(OH) 2 or NaOH. 5. Method according to Claims 1 - 4, wherein the alkaline proteolytic enzyme is the proteolytic enzyme producible by means of an alcalophilic Bacillus 5 species. 6. Method according to Claims 1 - 5, wherein the alkaline proteolytic enzyme exhibits a pH activity curve with a maximum above pH 9, according to the CPU activity determination method. 7. Method according to Claims 1 - 6, wherein in step 3b) the base is 10 added before the proteolytic enzyme. 8. Method according to Claims 1 - 7, wherein in step 3b) also maximum 0.02% S " is added, in relation to the dry hide weight or the dry skin weight. 9. Method according to Claims 1 - 8, wherein in step 3c) the sulfide is Na 2 S or NaHS. 15 10. Method according to Claims 1 - 9, wherein the sulfide is added as late as possible before the immunization of the hairs. 11. Method according to Claims 1 - 10, wherein the hairs are removed from the dehairing liquor by continuous filtration during the dehairing.

Inventors: ANDERSEN LARS PETER, ANDERSEN, LARS, PETER
Applicants: ANDERSEN LARS PETER, NOVONORDISK AS, NOVO NORDISK A/S
Application year: 1993
Main classification: C14C1
IPC codes: C14C1