Abstract:
The present invention relates to a method for reactive dyeing of leather, which includes: providing a reactive dye solution including at least one reactive dye and water, and making the reactive dye in the reactive dye solution to act on crust leather at a temperature from 25° C. to 70° C. to form covalent bonds between the reactive dye and the crust leather. Accordingly, the method for reactive dyeing of leather according to the present invention can enhance fastness and levelling property.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a novel method for reactive dyeing of leather and, more particularly, to a method for reactive dyeing of leather, which can enhance fastness and levelling property. 
         [0003]    2. Description of Related Art 
         [0004]    During tanning, dyeing is an important process. In conventional methods for dyeing leather, leather is dyed mainly under acid dyeing condition, such that ionic bonds are formed between dyes and leather. However, ionic bonds between dyes and leather would be broken by alkaline solution, and thereby the dyed leather by acid dyeing methods cannot show excellent washing fastness and perspiration fastness. 
         [0005]    US 2007/0033746 A1 discloses a dyeing method to dye wet blue. In the case of using wet blue to perform a reactive dyeing method, it can be found that leather cannot absorb tannin and fatliquor or leak tannin and fatliquor out, resulting in unleveling dyeing. 
         [0006]    By conventional dyeing methods and the dyeing method disclosed by US 2007/0033746 A1, dyed leather with high washing fastness, perspiration fastness, migration fastness and levelling property cannot be achieved, and thereby the inventors of the present application have devoted themselves to development of a novel method which can enhance washing fastness, perspiration fastness, migration fastness and levelling property of dyed leather. 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the present invention is to provide a novel method for reactive dyeing of leather to obtain dyed leather with improved perspiration fastness, washing fastness, migration fastness, levelling property and colour strength. 
         [0008]    To achieve the object, the present invention provides a method for reactive dyeing of leather, including: providing a reactive dye solution comprising at least one reactive dye and water, and making the reactive dye in the reactive dye solution to act on crust leather at a temperature from 25° C. to 70° C. to form covalent bonds between the reactive dye and the crust leather. 
         [0009]    Accordingly, the dyeing method according to the present invention provides covalent bonds between the reactive dye and the crust leather so as to enhance perspiration fastness, washing fastness and migration fastness, and improve levelling property and feeling due to tannin and fatliquor being absorbed favorably during dyeing process. In comparison with conventional dyeing methods, the dyeing method according to the present invention can be performed at higher temperature, and the dyeing temperature may even be larger than 60° C. and reach 70° C. However, in conventional methods, the temperature is limited and cannot be larger than 60° C. (even 50° C.). 
         [0010]    In the present invention, the reactive dye acts on crust leather preferably at a temperature from 25° C. to 70° C., and more preferably from 55° C. to 70° C. 
         [0011]    In the present invention, the crust leather is not particularly limited in kind, and may be cow crust leather, pig crust leather or goat crust leather. 
         [0012]    In the present invention, the reactive dye may be any conventional reactive dye, and may be a single dye or a mixture of various dyes. In particular, according to the novel dyeing method of the present invention, unleveling dyeing or inconsistent permeability would not occur, and thus various kinds of dyes can be used in a mixture to obtain various color tones. Herein, the reactive dye according to the present invention preferably contains a group of —SO 2 CH═CH 2  or —SO 2 CH 2 CH 2 W, W being a leaving group which is eliminable by a base, such as —Cl, —OSO 3 H, 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and R 1 , R 2  and R 3  each independently being C 1-4  alkyl. 
         [0013]    The suitable reactive dyes according to the present invention include, but are not limited to: yellow dyes, such as 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and Everzol Yellow ED, Everzol Yellow NPN, Everzol Yellow LX, Everzol Yellow ED-R, Everzol Yellow GRB, Everzol Yellow PFG, Everzol Yellow 4GL, Everzol Yellow C-GL, Everzol Yellow 3GL, Everzol Yellow ED-2G, Everzol Yellow RNL, Everzol Yellow GSP, Everzol Yellow ED-S, Everzol Yellow GR and Everzol Yellow 3RS sold by Everlight Chemical Industrial Corporation; orange dyes, such as 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and Everzol Orange GR, Everzol Orange 2R, Everzol Orange 2GS, Everzol Orange ED-2R, Everzol Scarlet 3GF, Everzol Orange GSP, Everzol Orange ED, Everzol Orange 3R, Everzol Orange ED-G and Everzol Orange ED-R sold by Everlight Chemical Industrial Corporation; red dyes, such as 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and Everzol Red BS, Everzol Red ED-7B, Everzol Red LF-B, Everzol Red ED-2B, Everzol Red ED, Everzol Red F2B, Everzol Red 3BS, Everzol Red ED-S, Everzol Red BB, Everzol Red RBN, Everzol Rubine ED, Everzol Red ED-3R, Everzol Red ED-3B, Everzol Red LX, Everzol Red F3B, Everzol Red LF-2B, Everzol Red C-3B and Everzol Rubine ED-R sold by Everlight Chemical Industrial Corporation; blue dyes, such as 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and Everzol Navy Blue GG, Everzol Navy Blue BRF, Everzol Blue ED, Everzol Navy ED, Everzol Navy Blue FBN, Everzol Blue ED-G, Everzol Dark Blue LF, Everzol Blue LX, Everzol Blue R S/P, Everzol Turquoise Blue G, Everzol Navy LX, Everzol Navy Blue RGB H/C and Everzol Blue BB sold by Everlight Chemical Industrial Corporation; brown dyes, such as Everzol Brown LNS sold by Everlight Chemical Industrial Corporation; black dyes, such as 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and Everzol Black ED-G, Everzol Black GRN, Everzol Black GSP, Everzol Black GR, Everzol Black ED-2R, Everzol Black MW, Everzol Black B, Everzol Black C-RL, Everzol Black ED, Everzol Black ED-R, Everzol Black N, Everzol Black LNS and Everzol Black NR sold by Everlight Chemical Industrial Corporation. The above-mentioned dyes can be used in single or in mixture according to requirement. In particular, various color tones may be obtained by mixing dyes of various colors. 
         [0014]    In the present invention, the reactive dye solution may further include a dispersant. Herein, the dispersant may be any dispersant favorable to level dyeing and desperation, and is preferably a dispersant containing naphthalene sulfonic acid condensate, such as Evertan PL sold by Everlight Chemical Industrial Corporation. 
         [0015]    In the present invention, the reactive dye acts on the crust leather preferably under a pH from 9 to 11. Herein, any suitable alkaline substance or alkaline buffer system, such as sodium carbonate, sodium bicarbonate, sodium hydroxide, ammonia solution, may be used to control pH of the reactive dye solution. 
         [0016]    In the present invention, the time of the reactive dye acting on the crust leather depends on the practical dyeing condition (such as pH and dyeing temperature), and preferably ranges from 100 minutes to 330 minutes. 
         [0017]    In the present invention, the method may further include a step after the reactive dye acting on the crust leather: adding a fixing agent to make the fixing agent to act on the crust leather. Accordingly, the fixation of the reactive dye on the crust leather can be enhanced. Herein, the fixing agent may be any fixing agent capable of fixing dye, and preferably is a fixing agent containing polyamide, such as Evertan WF sold by Everlight Chemical Industrial Corporation. 
         [0018]    In the present invention, the method may further include a step after the reactive dye acting on the crust leather: adding fatliquor to make the fatliquor to act on the crust leather. Herein, the fatliquor may be any fatliquor suitably used in a fatliquoring step, such as animal fats, plant fats, synthetic fats, waterproofing fats, to enhance feeling and full degree of leather. The step (i.e. fatliquoring step) may be performed after the step of adding the fixing agent. 
         [0019]    In the present invention, the method may further include a step after the reactive dye acting on the crust leather: adding tanning agents to make the tanning agents to act on the crust leather. Herein, the tanning agents may be any known suitable tanning agents, and specifically is metal tannate, such as aluminum tannate, to enhance the fixation of dye on leather and full degree. The step for adding tanning agents may be performed after the fatliquoring step. In additional, a step after adding tanning agents may be further included: adding a fixing agent to make the fixing agent to act on the crust leather so as to enhance the fixation of the dye on the crust leather. 
         [0020]    Accordingly, the dyeing method according to the present invention provides covalent bonds between the reactive dye and the crust leather so as to enhance perspiration fastness, washing fastness and migration fastness, and improve levelling property and feeling due to tannin and fatliquor being absorbed favorably during dyeing process. In comparison with conventional dyeing methods, the dyeing method according to the present invention can be performed at higher temperature, and the dyeing temperature may be even larger than 70° C. However, in conventional methods, the temperature is limited and cannot be larger than 60° C. (even 50° C.). 
       BRIEF DESCRIPTION OF THE DRAWINGS 
       [0021]    None. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    The following examples are used to illustrate the present invention, and many other possible modifications and variations can be made without departing from the spirit of the present invention according to various concepts and applications. The following examples are exemplified for a more concrete description, and the scope of the present invention should not be limited thereto. Without specific explanations, the unit of the parts and percentages used in the examples is calculated by weight, and the temperature is represented by Celsius degrees (° C.). 
       Example 1 
       [0023]    Water of 600 parts, a dispersant (Evertan PL) of 2 parts and a reactive dye (Everzol Red ED) of 5 parts are added into a rotary drum, followed by maintaining the temperature at 60° C. and drumming for 10 minutes. Subsequently, a piece of retanned crust leather of 100 g (thickness: 1.2 to 1.4 mm) is positioned into the rotary drum and drummed for 30 minutes, followed by adding sodium carbonate of 8 parts with drumming for 30 minutes to control pH in a range from 9 to 11. Then, a fixing agent (Evertan WF) of 4 parts is added therein and drummed for 30 minutes to fix the dye. Next, the crust leather is rinsed with water of 600 parts three times for 10 minutes each at 26° C., 40° C. and 50° C. Formic acid of 2 parts is added into water of 600 parts, followed by maintaining the temperature at 50° C. and drumming for 15 minutes. Then, fatliquor (silicon-containing waterproofing fatliquor) of 3 parts is added therein, drummed for 30 minutes and fixed with formic acid of 2.5 parts twice for 15 minutes each at pH 3.0±0.5. After washing with water, formic acid of 1 part is added into 40° C. water of 600 parts and drummed for 5 minutes, followed by adding aluminum tanning agents of 2 parts with drumming for 30 minutes, and then adding a fixing agent (Evertan WF) of 1.5 parts with drumming for 30 minutes. Subsequently, the crust leather is rinsed with 26° C. water of 600 parts and drummed for 10 minutes. Finally, the crust leather is dried and thus a colorful red leather with high colour strength is obtained. 
       Example 2 
       [0024]    Water of 200 parts, a dispersant (Evertan PL) of 2 parts and a reactive dye (Everzol Yellow ED) of 4 parts are added into a rotary drum, followed by maintaining the temperature at 50° C. and drumming for 10 minutes. Subsequently, a piece of retanned crust leather of 100 g (thickness: 1.2 to 1.4 mm) is positioned into the rotary drum and drummed for 30 minutes, followed by adding water of 400 parts with drumming for 10 minutes and then sodium carbonate of 5 parts and sodium hydroxide of 1 part with drumming for 30 minutes to control pH in a range from 9 to 11. Then, a fixing agent (Evertan WF) of 3 parts is added therein and drummed for 30 minutes to fix the dye. Next, the crust leather is rinsed with water of 600 parts three times for 10 minutes each at 30° C., 40° C. and 50° C. Formic acid of 2 parts is added into water of 600 parts, followed by maintaining the temperature at 50° C. and drumming for 15 minutes. Then, fatliquor (silicon-containing waterproofing fatliquor) of 3 parts is added therein, drummed for 30 minutes and fixed with formic acid of 2.5 parts twice for 15 minutes each at pH 3.0+0.5. After washing with water, formic acid of 1 part is added into 40° C. water of 600 parts and drummed for 5 minutes, followed by adding aluminum tanning agents of 2 parts with drumming for 30 minutes, and then adding a fixing agent (Evertan WF) of 1 part with drumming for 30 minutes. Subsequently, the crust leather is rinsed with 26° C. water of 600 parts and drummed for 10 minutes. Finally, the crust leather is dried and thus a colorful yellow leather with high colour strength is obtained. 
       Example 3 
       [0025]    Water of 600 parts and a reactive dye (Everzol Black ED-G) of 8 parts are added into a rotary drum, followed by maintaining the temperature at 70° C. and drumming for 10 minutes. Subsequently, a piece of retanned crust leather of 100 g (thickness: 1.2 to 1.4 mm) is positioned into the rotary drum and drummed for 30 minutes, followed by adding sodium carbonate of 8 parts with drumming for 30 minutes to control pH in a range from 9 to 11. Then, a fixing agent (Evertan WF) of 3 parts is added therein and drummed for 30 minutes to fix the dye. Next, the crust leather is rinsed with water of 600 parts three times for 10 minutes each at 30° C., 40° C. and 50° C. Formic acid of 2 parts is added into water of 600 parts, followed by maintaining the temperature at 50° C. and drumming for 15 minutes. Then, fatliquor (silicon-containing waterproofing fatliquor) of 3 parts is added therein, drummed for 30 minutes and fixed with formic acid of 2.5 parts twice for 15 minutes each at pH 3.0+0.5. After washing with water, formic acid of 1 part is added into 40° C. water of 600 parts and drummed for 5 minutes, followed by adding aluminum tanning agents of 2 parts with drumming for 30 minutes, and then adding a fixing agent (Evertan WF) of 1 part with drumming for 30 minutes. Subsequently, the crust leather is rinsed with 26° C. water of 600 parts and drummed for 10 minutes. Finally, the crust leather is dried and thus a black leather is obtained. 
       Example 4 
       [0026]    Water of 600 parts, a dispersant (Evertan PL) of 2 parts and reactive dyes (Everzol Yellow ED of 2.6 parts, Everzol Red ED of 1.1 parts and Everzol Navy ED of 0.3 part) of 4 parts are added into a rotary drum, followed by maintaining the temperature at 60° C. and drumming for 10 minutes. Subsequently, a piece of retanned crust leather of 100 g (thickness: 1.2 to 1.4 mm) is positioned into the rotary drum and drummed for 30 minutes, followed by adding sodium carbonate of 8 parts with drumming for 30 minutes to control pH in a range from 9 to 11. Then, a fixing agent (Evertan WF) of 3 parts is added therein and drummed for 30 minutes to fix the dye. Next, the crust leather is rinsed with water of 600 parts three times for 10 minutes each at 30° C., 40° C. and 50° C. Formic acid of 2 parts is added into water of 600 parts, followed by maintaining the temperature at 50° C. and drumming for 15 minutes. Then, fatliquor (silicon-containing waterproofing fatliquor) of 3 parts is added therein, drummed for 30 minutes and fixed with formic acid of 2.5 parts twice for 15 minutes each at pH 3.0±0.5. After washing with water, formic acid of 1 part is added into 40° C. water of 600 parts and drummed for 5 minutes, followed by adding aluminum tanning agents of 2 parts with drumming for 30 minutes, and then adding a fixing agent (Evertan WF) of 1 part with drumming for 30 minutes. Subsequently, the crust leather is rinsed with 26° C. water of 600 parts and drummed for 10 minutes. Finally, the crust leather is dried and thus a brown leather with good levelling property and uniform permeability is obtained. 
       Example 5 
       [0027]    Water of 600 parts, a dispersant (Evertan PL) of 2 parts and a reactive dye (Everzol Red ED) of 4 parts are added into a rotary drum, followed by maintaining the temperature at 30° C. and drumming for 10 minutes. Subsequently, a piece of retanned crust leather of 100 g (thickness: 1.2 to 1.4 mm) is positioned into the rotary drum and drummed for 30 minutes, followed by adding sodium carbonate of 8 parts with drumming for 30 minutes to control pH in a range from 9 to 11. Then, a fixing agent (Evertan WF) of 4 parts is added therein and drummed for 30 minutes to fix the dye. Next, the crust leather is rinsed with water of 600 parts three times for 10 minutes each at 26° C., 40° C. and 50° C. Formic acid of 2 parts is added into water of 600 parts, followed by maintaining the temperature at 50° C. and drumming for 15 minutes. Then, fatliquor (silicon-containing waterproofing fatliquor) of 3 parts is added therein, drummed for 30 minutes and fixed with formic acid of 2.5 parts twice for 15 minutes each at pH 3.0±0.5. After washing with water, formic acid of 1 part is added into 40° C. water of 600 parts and drummed for 5 minutes, followed by adding aluminum tanning agents of 2 parts with drumming for 30 minutes, and then adding a fixing agent (Evertan WF) of 1.5 parts with drumming for 30 minutes. Subsequently, the crust leather is rinsed with 26° C. water of 600 parts and drummed for 10 minutes. Finally, the crust leather is dried and thus a colorful red leather with common colour strength is obtained. 
       Example 6 
       [0028]    Water of 600 parts and reactive dyes (Everzol Yellow ED of 1.8 parts, Everzol Red ED of 1.6 parts and Everzol Navy ED of 0.6 part) of 4 parts are added into a rotary drum, followed by maintaining the temperature at 50° C. and drumming for 10 minutes. Subsequently, a piece of retanned crust leather of 100 g (thickness: 1.2 to 1.4 mm) is positioned into the rotary drum and drummed for 30 minutes, followed by adding sodium carbonate of 8 parts with drumming for 30 minutes to control pH in a range from 9 to 11. Then, a fixing agent (Evertan WF) of 3 parts is added therein and drummed for 30 minutes to fix the dye. Next, the crust leather is rinsed with water of 600 parts three times for 10 minutes each at 30° C., 40° C. and 50° C. Formic acid of 2 parts is added into water of 600 parts, followed by maintaining the temperature at 50° C. and drumming for 15 minutes. Then, fatliquor (silicon-containing waterproofing fatliquor) of 3 parts is added therein, drummed for 30 minutes and fixed with formic acid of 2.5 parts twice for 15 minutes each at pH 3.0+0.5. After washing with water, formic acid of 1 part is added into 40° C. water of 600 parts and drummed for 5 minutes, followed by adding aluminum tanning agents of 2 parts with drumming for 30 minutes, and then adding a fixing agent (Evertan WF) of 1 part with drumming for 30 minutes. Subsequently, the crust leather is rinsed with 26° C. water of 600 parts with drumming for 10 minutes. Finally, the crust leather is dried and thus a navy brown leather with good levelling property and uniform permeability is obtained. 
       Example 7 
       [0029]    Water of 600 parts, a dispersant (Evertan PL) of 2 parts and a reactive dye (Everzol Brown LNS) of 4 parts are added into a rotary drum, followed by maintaining the temperature at 60° C. and drumming for 10 minutes. Subsequently, a piece of retanned crust leather of 100 g (thickness: 1.2 to 1.4 mm) is positioned into the rotary drum and drummed for 30 minutes, followed by adding sodium carbonate of 5 parts with drumming for 30 minutes to control pH in a range from 9 to 11. Then, a fixing agent (Evertan WF) of 3 parts is added therein and drummed for 30 minutes to fix the dye. Next, the crust leather is rinsed with water of 600 parts three times for 10 minutes each at 30° C., 40° C. and 50° C. Formic acid of 2 parts is added into water of 600 parts, followed by maintaining the temperature at 50° C. and drumming for 15 minutes. Then, fatliquor (silicon-containing waterproofing fatliquor) of 3 parts is added therein, drummed for 30 minutes and fixed with formic acid of 2.5 parts twice for 15 minutes each at pH 3.0±0.5. After washing with water, formic acid of 1 part is added into 40° C. water of 600 parts and drummed for 5 minutes, followed by adding aluminum tanning agents of 2 parts with drumming for 30 minutes, and then adding a fixing agent (Evertan WF) of 1 part with drumming for 30 minutes. Subsequently, the crust leather is rinsed with 26° C. water of 600 parts and drummed for 10 minutes. Finally, the crust leather is dried and thus a brown leather with good levelling property and uniform permeability is obtained. 
       Example 8 
       [0030]    Water of 600 parts, a dispersant (Evertan PL) of 2 parts and a reactive dye (Everzol Navy ED) of 4 parts are added into a rotary drum, followed by maintaining the temperature at 60° C. and drumming for 10 minutes. Subsequently, a piece of retanned crust leather of 100 g (thickness: 1.2 to 1.4 mm) is positioned into the rotary drum and drummed for 30 minutes, followed by adding sodium carbonate of 4 parts twice with drumming for 15 minutes each to control pH in a range from 9 to 11. Then, a fixing agent (Evertan WF) of 3 parts is added therein and drummed for 30 minutes to fix the dye. Next, the crust leather is rinsed with water of 600 parts three times for 10 minutes each at 30° C., 40° C. and 50° C. Formic acid of 2 parts is added into water of 600 parts, followed by maintaining the temperature at 50° C. and drumming for 15 minutes. Then, fatliquor (silicon-containing waterproofing fatliquor) of 3 parts is added therein, drummed for 30 minutes and fixed with formic acid of 2.5 parts twice for 15 minutes each at pH 3.0+0.5. After washing with water, formic acid of 1 part is added into 40° C. water of 600 parts and drummed for 5 minutes, followed by adding aluminum tanning agents of 2 parts with drumming for 30 minutes, and then adding a fixing agent (Evertan WF) of 1 part with drumming for 30 minutes. Subsequently, the crust leather is rinsed with 26° C. water of 600 parts and drummed for 10 minutes. Finally, the crust leather is dried and thus a blue leather with good levelling property and colour strength is obtained. 
       Comparative Example 1 
       [0031]    Water of 200 parts, a wetting agent of 0.3 part and a piece of wet blue leather of 100 g (its thickness: 1.2 to 1.4 mm) are added into a rotary drum, followed by maintaining the temperature at 40° C. and drumming for 60 minutes. After washing with water, water of 200 parts and chromium powder of 3 parts are added therein and the temperature is maintained at 25° C. with drumming for 60 minutes, followed by adding neutralizing tannin of 2 parts and formic acid of 2 parts with drumming for 20 minutes. Subsequently, soda (sodium bicarbonate) of 0.5 part is added therein with drumming for 50 minutes, and then the wet blue leather is rinsed with water. Water of 150 parts, acrylic tannin of 3 parts, resin tannin of 3 parts and polymer tannin of 3 parts are added therein with maintaining the temperature at 25° C. and drumming for 50 minutes, followed by washing with water. Water of 50 parts, and a leveling agent of 1 part and ammonia solution of 1 part are added therein with maintaining the temperature at 25° C. and drumming for 10 minutes. Subsequently, a reactive dye (Everzol Red ED) of 3 parts is added therein with drumming for 40 minutes, followed by adding fatliquor of 6 parts with drumming for 50 minutes and then water of 150 parts with maintaining the temperature at 50° C. and drumming for 10 minutes. Finally, formic acid of 1.5 parts is added twice with drumming for 20 minutes each, and then the wet blue leather is rinsed with water and dried. 
       Comparative Example 2 
       [0032]    A piece of wet blue leather (its thickness after shaved: 1.1 mm) of 100 g is washed at 30° C. for 20 minutes in a rotary drum filled with water of 200 parts, followed by using water of 150 parts, a disperant (Evertan PL) of 2 parts and a reactive dye (Everzol Red ED) of 5 parts to dye the wet blue leather at pH 4.4 and 30° C. for 60 minutes. At 50° C., 15% sodium carbonate aqueous solution of 100 parts is added in batches to fix the dye in the course of 60 minutes of drumming at pH 10.0, followed by washing with water of 200 parts four times for 10 minutes each at 40° C. The pH value is adjusted to 4.7 by adding water of 200 parts and formic acid of 0.7 part. Next, the dyed leather is retanned in a freshly set float composed of water of 100 parts, a polymeric tanning material of 2 parts and a naturally based fatliquor of 2 parts at 35° C. for 30 minutes. The float is then admixed with a liquid synthetic tanning material of 15 parts, a polymeric tanning material of 6 parts and Tara vehetable tanning material of 10 parts and drummed for 20 minutes. The leather is subsequently fatliquored in the same float with a fishoil-based fatliquor of 8 parts and a lecithin-based fatliquor of 2 parts at 35° C. by drumming for 2 hours. Finally, the leather is acidified to pH 3.6 with concentrated formic acid of 2 parts and drummed twice for 10 minutes and once for 30 minutes. The dyed, retanned and fatliquored leather is additionally rinsed with cold water at 15° C. for 10 minutes and then dried. 
       Test Example 
       [0033]    The dyed leathers prepared by Comparative Examples 1-2 and Examples 1-8 according to the present invention are compared in perspiration fastness, washing fastness, levelling property, feeling and colour strength, and the results are shown in Table 1. Herein, washing fastness is tested according to IUF 423, and perspiration fastness is tested according to the following method. 
         [0034]    First, a saline solution (salt of 2 g being dissolved in distilled water of 100 mL) is prepared and positioned in a beaker of 250 mL, while another distilled water of 100 mL is positioned in another beaker of 250 mL. Subsequently, the dyed leather is cut into a specimen of 50.8×50.8 mm in size, and positioned between fiber fabrics (50.8×50.8 mm) to obtain two sandwich-like samples (i.e. a first sample and a second sample). Next, the first sample is immersed into the prepared saline solution until being wetted thoroughly and then squeezed to remove redundant liquid, followed by placing the first sample on a base plate of a perspiration tester. Then, the first sample is covered with clean plastic plates or glass plates. According to the above-mentioned steps, the second sample is immersed into the prepared distilled water and stacked on the plastic plates or the glass plates over the first sample. Subsequently, all plastic plates or glass plates are homed, and weights of 3.6 kg are placed on the perspiration tester with samples disposed thereon, followed by tightening screws of the perspiration tester to orientate the plate and then removing the weights. The perspiration tester is placed into a resealable plastic bag (33×38 cm), and disposed into an oven preheat to 38° C., therewith the bag being unsealed. Then, distilled water of 50 mL is placed into a beaker of 100 mL and disposed in the above-mentioned plastic bag, followed by sealing the bag and placing the sealed plastic bag into the oven for 24 hours or more. Then, the beaker is removed and the perspiration tester is taken out of the oven. The samples are taken from the plate of the perspiration tester and placed on a nonabsorbent material until the samples are thoroughly dry. During drying, the specimen cannot separate from the fiber fabrics. After drying, the distilled water and saline solution are observed for color bleeding to compare perspiration fastness of dyed leathers. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Kind of 
                 perspiration 
                 washing 
                 levelling 
                   
                 colour 
               
               
                 Entry 
                 Color 
                 leather 
                 fastness 
                 fastness 
                 property 
                 feeling 
                 strength 
               
               
                   
               
             
             
               
                 Example 1 
                 Red 
                 cow grain 
                 excellent 
                 excellent 
                 excellent 
                 excellent 
                 good 
               
               
                   
                   
                 crust 
               
               
                   
                   
                 leather 
               
               
                 Example 2 
                 Yellow 
                 cow split 
                 excellent 
                 excellent 
                 excellent 
                 excellent 
                 good 
               
               
                   
                   
                 crust 
               
               
                   
                   
                 leather 
               
               
                 Example 3 
                 Black 
                 cow split 
                 excellent 
                 excellent 
                 excellent 
                 excellent 
                 good 
               
               
                   
                   
                 crust 
               
               
                   
                   
                 leather 
               
               
                 Example 4 
                 Brown 
                 cow split 
                 excellent 
                 excellent 
                 excellent 
                 excellent 
                 good 
               
               
                   
                   
                 crust 
               
               
                   
                   
                 leather 
               
               
                 Example 5 
                 Red 
                 cow split 
                 excellent 
                 excellent 
                 excellent 
                 excellent 
                 common 
               
               
                   
                   
                 crust 
               
               
                   
                   
                 leather 
               
               
                 Example 6 
                 Brown 
                 cow split 
                 excellent 
                 excellent 
                 excellent 
                 excellent 
                 good 
               
               
                   
                   
                 crust 
               
               
                   
                   
                 leather 
               
               
                 Example 7 
                 Brown 
                 cow split 
                 excellent 
                 excellent 
                 excellent 
                 excellent 
                 good 
               
               
                   
                   
                 crust 
               
               
                   
                   
                 leather 
               
               
                 Example 8 
                 Blue 
                 cow split 
                 excellent 
                 excellent 
                 excellent 
                 excellent 
                 good 
               
               
                   
                   
                 crust 
               
               
                   
                   
                 leather 
               
               
                 Comparative 
                 Red 
                 cow grain 
                 bad 
                 bad 
                 good 
                 excellent 
                 common 
               
               
                 Example 1 
                   
                 wet blue 
               
               
                   
                   
                 leather 
               
               
                 Comparative 
                 Red 
                 cow grain 
                 good 
                 good 
                 bad 
                 bad 
                 excellent 
               
               
                 Example 2 
                   
                 wet blue 
               
               
                   
                   
                 leather 
               
               
                   
               
             
          
         
       
     
         [0035]    From the above-mentioned test examples, it can be found that the leathers prepared by Examples 1 to 8 of the present invention exhibit good permeability and levelling property, and excellent washing fastness and perspiration fastness. In comparison with the dyed leather according to Comparative Example 1, dyed leathers prepared by the dyeing method according to the present invent exhibit improved color tone, better stability of color strength, excellent washing fastness, perspiration fastness and levelling property. In addition, Comparative Example 2 uses wet blue leather to perform reactive dyeing, and the resultant dyed leather exhibits bad levelling property and feeling due to that leather cannot absorb tannin and fatliquor or leaks tannin and fatliquor out of it. On the contrary, Examples 1 to 8 according to the present invention use crust leather to perform a dyeing process, and thus the absorption of tennin can be improved and the leakage of fatliquor from the leather can be inhibited, resulting in dyed leathers with improved levelling property and feeling. Also, the dyed leathers prepared by Examples 1 to 8 of the present invention have better perspiration fastness and washing fastness than that prepared by Comparative Example 2. 
         [0036]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.