Preparation method of low-odor environment-friendly sofa leather

Abstract

The present invention relates to a preparation method of a low-odor environmentally friendly sofa leather, belonging to the technical field of leather treatment. In the present invention, a branched imidazoline carboxylic acid sulfonic acid alcohol compound containing a large number of carboxyl groups, sulfonic acid groups, phenolic hydroxyl groups and hydroxyl groups at the same time is used as a matrix, and it is subjected to a coordination reaction with an aluminum salt and a zirconium salt. The carboxyl groups, sulfonic acid groups and phenolic hydroxyl groups in the matrix can combine with the aluminum salt and the zirconium salt to obtain a chromium-free tanning agent, which can crosslink with the hide collagen in the leather. Moreover, the quaternary ammonium salt group in the matrix can improve the surface activity of the tanning agent, enhance the contact activity between the hide collagen and the tanning agent, and improve the permeability and tanning effect of the tanning agent. Compared with the traditional chromium tanning agent, the leather tanned with the chromium-free tanning agent of the present invention has a similar shrinkage temperature, a greater thickness and thickening rate, and higher mechanical properties, and can completely replace the traditional chromium tanning agent, avoiding chromium pollution and waste liquid treatment, reducing costs, and improving the environmental friendliness of the leather.

Description

Technical Field

[0001] The present invention relates to a preparation method of low - odor and environment - friendly sofa leather, belonging to the technical field of leather treatment. Background Art

[0002] In recent years, with the increasing improvement of people's living standards, people pursue more comfort and a return to nature, and genuine leather sofas are more and more favored by people. However, at present, due to the advantages of chrome - tanned leather such as high temperature resistance, heat - and - humidity stability, plumpness and softness of the leather body, the manufacturing method of sofa semi - finished leather in the market still mainly uses the chrome - tanning process. However, a large amount of chromium - containing wastewater is generated during the chrome - tanning process, causing environmental pollution and relatively high wastewater treatment costs. At the same time, the heavy metal chromium in the leather also has an adverse effect on the human body. At present, most sofa leather manufacturing enterprises lack chrome - free tanning technology because when using chrome - free tanning agents for tanning, it is impossible to ensure the shrinkage temperature and physical and mechanical properties of the leather, and large - scale production is difficult.

[0003] In addition, after being placed for a certain period of time, the currently manufactured sofa leather generates a putrid smell or an acidic smell due to the unsaturated fats being oxidized and decomposed into volatile small - molecule substances during use and the gradual volatilization of the residual small - molecule acidic substances in the leather, which affects its normal use and endangers human health.

[0004] In order to reduce chromium pollution in the production process of sofa leather and produce green leather, and at the same time reduce the smell of sofa leather, it is necessary to start from the chemical materials and process conditions used in the leather - making process. From raw hides to finished leather, many complex chemical and mechanical treatment processes are required. Among them, the tanning process and the retanning process take the longest time and play a crucial role in the final performance of the leather. Therefore, there is an urgent need to develop a preparation method of low - odor and environment - friendly sofa leather to solve the problems of serious chromium pollution and strong smell in the current production process of sofa leather starting from the tanning process and the retanning process. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of low - odor and environment - friendly sofa leather to solve the problems of serious chromium pollution and strong smell in the current production process of sofa leather.

[0006] The present invention provides a method for preparing a low-odor environmentally friendly sofa leather, comprising the following steps: Immerse pickled cowhide in a pretreatment solution, rotate at room temperature for 30 - 45 min for pretreatment, then add a chromium-free tanning agent, rotate at 35 - 40 °C for 4 - 4.5 h, then adjust the pH of the liquid-phase material in the stainless steel drum to 3.7 - 3.9 with a 0.1% sodium bicarbonate solution, stop rotating, stand for 6 - 8 h, then rotate for another 45 - 60 min, drain the liquid, and wash with water to obtain a semi-finished leather; Then immerse the semi-finished leather in a retanning solution, rotate for 60 - 90 min, and then fix it with a 0.5 - 0.7% formic acid solution, wash with water and stand to obtain the finished sofa leather; The pretreatment solution is prepared by mixing water and sodium chloride with a mass ratio of 100:5 - 7 and adjusting the pH to 3.2 - 3.5 with formic acid; The chromium-free tanning agent is composed of an aluminum salt tanning agent and a zirconium salt tanning agent with a mass ratio of 3:4 - 5, and the mass of the chromium-free tanning agent is 4% - 7% of the mass of water in the pretreatment solution; The aluminum salt tanning agent is prepared by mixing a branched imidazoline carboxylic acid sulfonic acid alcohol compound and aluminum sulfate in water at 25 - 30 °C for 4 - 6 h with a mass ratio of 6:2 - 2.5; The zirconium salt tanning agent is prepared by mixing a branched imidazoline carboxylic acid sulfonic acid alcohol compound and zirconium sulfate in water at 25 - 30 °C for 4 - 6 h with a mass ratio of 6:1.8 - 2.2; The retanning solution is composed of water and a retanning agent, and the retanning agent is prepared by mixing an imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound, acrylic acid, and azodiisopropylimidazoline hydrochloride in water at 45 - 60 °C for 1.5 - 2 h with a mass ratio of 10:15 - 20:0.5 - 0.8; The structure of the branched imidazoline carboxylic acid sulfonic acid alcohol compound is as follows:

[0007] ;

[0008] The structure of the imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound is as follows:

[0009] 。

[0010] Preferably, the preparation method of the imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound is as follows:

[0011] (1) Mix acrylic acid imidazoline and epichlorohydrin at 40 - 45 °C and react for 24 - 30 h to obtain an imidazoline chlorohydrin compound;

[0012] (2) Mix the imidazoline chlorohydrin compound and bromoacetic acid at 60 - 65 °C and react for 24 - 30 h to obtain an imidazoline chlorocarboxylic acid alcohol compound;

[0013] (3) Mix the imidazoline chlorocarboxylic acid alcohol compound and 4-hydroxypyridine-3-sulfonic acid at 75 - 85 °C and react for 24 - 30 h to obtain the imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound.

[0014] Preferably, in step (1) of the preparation method of the imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound, the molar ratio of imidazoline acrylate to epichlorohydrin is 0.23:0.25; epichlorohydrin is added dropwise.

[0015] Preferably, in step (2) of the preparation method of the imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound, the molar ratio of the imidazoline chlorohydrin compound to bromoacetic acid is 75:85; bromoacetic acid is added dropwise.

[0016] Preferably, in step (3) of the preparation method of the imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound, the molar ratio of the imidazoline chlorocarboxylic acid alcohol compound to 4-hydroxypyridine-3-sulfonic acid is 75:82 - 83; 4-hydroxypyridine-3-sulfonic acid is added dropwise in the form of a solution.

[0017] Preferably, the structure of the imidazoline acrylate is as follows:

[0018] 。

[0019] The imidazoline acrylate in the present invention is prepared by reacting acrylic acid with diethylenetriamine.

[0020] Preferably, the preparation method of the branched imidazoline carboxylic acid sulfonic acid alcohol compound is as follows: Mix 3-aminopropionic acid, triethanolamine and the imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound at 70 - 80 °C and react for 3 - 5 h to obtain the branched imidazoline carboxylic acid sulfonic acid alcohol compound.

[0021] Preferably, the molar ratio of 3-aminopropionic acid, triethanolamine and the imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound is 1:1.5 - 2:2.5 - 3.

[0022] Preferably, when preparing the aluminum salt tanning agent, the mass ratio of the branched imidazoline carboxylic acid sulfonic acid alcohol compound, aluminum sulfate and water is 6:2 - 2.5:50 - 60; when preparing the zirconium salt tanning agent, the mass ratio of the branched imidazoline carboxylic acid sulfonic acid alcohol compound, zirconium sulfate and water is 6:1.8 - 2.2:50 - 60.

[0023] Preferably, the standing time is 12 h.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The present invention uses a branched imidazoline carboxylic acid sulfonic acid alcohol compound containing a large number of carboxyl groups, sulfonic acid groups, phenolic hydroxyl groups and hydroxyl groups as the matrix, and coordinates it with aluminum salts and zirconium salts. The carboxyl groups, sulfonic acid groups and phenolic hydroxyl groups in the matrix can combine with the aluminum salts and zirconium salts to obtain an aluminum salt tanning agent and a zirconium salt tanning agent. The aluminum salt tanning agent and the zirconium salt tanning agent are used to tan leather instead of the traditional chromium salt tanning agent. The aluminum salt tanning agent and the zirconium salt tanning agent can crosslink with the hide collagen in the leather, and the quaternary ammonium salt group in the matrix can improve the surface activity of the tanning agent, enhance the contact activity between the hide collagen and the tanning agent, reduce the contact resistance, and improve the permeability and tanning effect of the tanning agent. The experimental results show that compared with the traditional chromium tanning agent, the leather tanned with the chromium-free tanning agent of the present invention has a similar shrinkage temperature, a greater thickness and thickening rate, and higher mechanical properties, and can completely replace the traditional chromium tanning agent, avoid chromium pollution and waste liquid treatment, reduce costs, and improve the environmental protection of leather;

[0026] (2) The present invention uses a copolymer of an olefin monomer containing a large number of carboxyl groups, sulfonic acid groups, phenolic hydroxyl groups, hydroxyl groups and imidazoline rings and acrylic acid as a retanning agent. The carboxyl groups, sulfonic acid groups, phenolic hydroxyl groups and hydroxyl groups in the retanning agent can endow it with good water solubility and free activity, improve its permeability in leather, and help to fill and thicken the leather; and the quaternary ammonium salt group in the retanning agent can further improve the surface activity of the retanning agent, and improve the permeability and filling ability of the retanning agent. The long fatty chains in the retanning agent can improve the softness and elasticity of the leather, and the rigid imidazoline rings and pyridine rings in the retanning agent can improve the strength of the leather, so that the leather has good flexibility and rigidity at the same time, and improves the wear resistance, friction color fastness and folding resistance of the leather. At the same time, the cyclic imidazoline rings and pyridine rings, as well as the long-chain molecular chains, can be wound and stacked to make the filler have a certain porosity, thereby increasing the water vapor permeability of the leather;

[0027] (3) By treating leather with a tanning agent and a polymer retanning agent containing imidazoline rings and pyridine rings, the above structures can be embedded in the leather. The imidazoline rings and pyridine rings can adsorb acidic volatile substances and volatile corrupt substances that may remain in the leather through nitrogen atoms and lock them in the leather filler, preventing the volatilization of volatile substances, reducing the odor during leather storage, and improving the leather quality. At the same time, the carboxyl groups, sulfonic acid groups, phenolic hydroxyl groups, quaternary ammonium salt groups and imidazoline rings and pyridine rings in the tanning agent and retanning agent can form a composite sterilization and antibacterial system, prevent the growth of bacteria and other microorganisms, and reduce the occurrence of corruption and the emission of corrupt odors;

[0028] (4) By using a chromium-free tanning agent and a polymer retanning agent to treat leather, the present invention can replace the traditional chromium tanning agent, and the finished leather after treatment has good tensile strength, tear strength, elongation at break, light resistance, wear resistance and friction color fastness, and has a low odor, and has good popularization and application value. Description of the Drawings

[0029] Figure 1 1H NMR spectrum of the imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound prepared in step (3) of Example 1 of the present invention;

[0030] Figure 2 1H NMR spectrum of the branched imidazoline carboxylic acid sulfonic acid alcohol compound prepared in step (4) of Example 1 of the present invention. Detailed Description of the Invention

[0031] The following examples are intended to further illustrate the content of the present invention rather than limit the scope of protection of the present invention.

[0032] Example 1. The preparation method of the low-odor and environmentally friendly sofa leather in this example includes the following steps:

[0033] (1) Add 0.23 mol of imidazoline acrylate and 50 mL of methanol into a reaction kettle, and then dropwise add 0.25 mol of epichlorohydrin under stirring. After the addition is completed, heat to 40 °C and stir and reflux for 24 h, and then remove the solvent by rotary evaporation to obtain an imidazoline chlorohydrin compound. Among them, the structure of imidazoline acrylate is as follows:

[0034] ;

[0035] (2) Add 75 mmol of the imidazoline chlorohydrin compound and 60 mL of methanol into a reaction kettle, and then dropwise add 85 mmol of bromoacetic acid under stirring. After the addition is completed, heat to 60 °C and stir and reflux for 24 h, and then remove the solvent and unreacted bromoacetic acid by vacuum distillation to obtain an imidazoline chlorocarboxylic acid alcohol compound,

[0036] (3) Add 75 mmol of the imidazoline chlorocarboxylic acid alcohol compound and 65 mL of ethanol into a reaction kettle, and then dropwise add an ethanol solution (mass fraction 30%) containing 82 mmol of 4-hydroxypyridine-3-sulfonic acid under stirring. After the addition is completed, heat to 75 °C and stir and reflux for 24 h, and then remove the solvent by vacuum distillation to obtain a concentrate. The concentrate is purified by column chromatography (the eluent is chloroform and isopropanol with a volume ratio of 3:4) to remove the unreacted 4-hydroxypyridine-3-sulfonic acid to obtain an imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound (the 1H NMR spectrum of the imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound is as shown in Figure 1 ), and the structural formula is as follows:

[0037] ;

[0038] (4) Add 0.01 mol of 3-aminopropionic acid, 0.015 mol of triethanolamine, and 60 mL of ethanol into a reaction kettle. Then, dropwise add 0.025 mol of imidazoline chloro-pyridinium salt sulfonic acid carboxylic acid alcohol compound under stirring and at 22 °C. After the dropping is completed, stir and react at 70 °C for 5 h. Then, remove the solvent by distillation under reduced pressure to obtain a concentrate. Purify the concentrate by column chromatography (the eluent is dichloromethane and ethanol with a volume ratio of 3:3) to obtain a branched imidazoline carboxylic acid sulfonic acid alcohol compound (the proton nuclear magnetic resonance spectrum of the branched imidazoline carboxylic acid sulfonic acid alcohol compound is as shown in Figure 2 ), and the structural formula is as follows:

[0039] ;

[0040] (5) Add 6 g of the branched imidazoline carboxylic acid sulfonic acid alcohol compound, 2 g of aluminum sulfate, and 50 g of deionized water into a reaction kettle. Stir at 25 °C for 4 h. Then, remove the water by distillation under reduced pressure to obtain an aluminum salt tanning agent,

[0041] (6) Add 6 g of the branched imidazoline carboxylic acid sulfonic acid alcohol compound, 1.8 g of zirconium sulfate, and 50 g of deionized water into a reaction kettle. Stir at 25 °C for 4 h. Then, remove the water by distillation under reduced pressure to obtain a zirconium salt tanning agent,

[0042] (7) Add 10 g of the imidazoline chloro-pyridinium salt sulfonic acid carboxylic acid alcohol compound prepared in step (3), 15 g of acrylic acid, 70 g of deionized water, and 0.5 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride into a reaction kettle. After stirring evenly, heat to 45 °C and stir and react for 1.5 h. Then, remove the water by distillation under reduced pressure to obtain a retanning agent,

[0043] (8) Add deionized water and sodium chloride with a mass ratio of 100:5 into a stainless steel drum. Then, adjust the pH of the material in the stainless steel drum to 3.2 with formic acid to obtain a pretreatment solution. Then, immerse pickled cowhide (cowhide after liming, deliming, softening, and pickling treatments) in the pretreatment solution and rotate at room temperature for 30 min for pretreatment. Then, add a chromium-free tanning agent into the stainless steel drum. The chromium-free tanning agent is composed of the aluminum salt tanning agent prepared in step (5) and the zirconium salt tanning agent prepared in step (6). The mass ratio of the aluminum salt tanning agent to the zirconium salt tanning agent is 3:4. The total mass of the chromium-free tanning agent is 4% of the mass of water in the stainless steel drum. Then, rotate at 35 °C for 4 h. Then, adjust the pH of the liquid phase material in the stainless steel drum to 3.7 with a 0.1% sodium bicarbonate solution. Stop rotating, let it stand for 6 h. Then, rotate for another 45 min, drain the liquid, and wash with water to obtain a wet blue,

[0044] (9) Add the retanning agent prepared in step (7) and water into a stainless steel drum at a mass ratio of 6:100, heat to 40 °C, stir evenly to obtain a retanning solution, then immerse the leather blank prepared in step (8) in the retanning solution, rotate for 60 min, fix with a 0.5% formic acid solution by mass, wash out of the drum with water, and stack and stand for 12 h to obtain the finished sofa leather.

[0045] Example 2. The preparation method of the low-odor and environmentally friendly sofa leather in this example includes the following steps:

[0046] (1) Add 0.23 mol of acrylic imidazoline and 50 mL of methanol into a reaction kettle, then dropwise add 0.25 mol of epichlorohydrin under stirring. After the dropping is completed, heat to 42 °C, stir and reflux for 26 h, then rotary evaporate to remove the solvent to obtain an imidazoline chlorohydrin compound.

[0047] (2) Add 75 mmol of the imidazoline chlorohydrin compound and 60 mL of methanol into a reaction kettle, then dropwise add 85 mmol of bromoacetic acid under stirring. After the dropping is completed, heat to 63 °C, stir and reflux for 28 h, then distill under reduced pressure to remove the solvent and unreacted bromoacetic acid to obtain an imidazoline chlorocarboxylic acid alcohol compound.

[0048] (3) Add 75 mmol of the imidazoline chlorocarboxylic acid alcohol compound and 67 mL of ethanol into a reaction kettle, then dropwise add an ethanol solution (mass fraction 30%) containing 82.5 mmol of 4-hydroxypyridine-3-sulfonic acid under stirring. After the dropping is completed, heat to 80 °C, stir and reflux for 26 h, then distill under reduced pressure to remove the solvent to obtain a concentrate. Purify the concentrate by column chromatography (the eluent is chloroform and isopropanol with a volume ratio of 3:4) to remove the unreacted 4-hydroxypyridine-3-sulfonic acid to obtain an imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound, and the structural formula is as follows:

[0049] ;

[0050] (4) Add 0.01 mol of 3-aminopropionic acid, 0.018 mol of triethanolamine and 60 mL of ethanol into a reaction kettle, then dropwise add 0.027 mol of the imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound under stirring and at 23 °C. After the dropping is completed, stir and react at 75 °C for 4 h, then distill under reduced pressure to remove the solvent to obtain a concentrate. Purify the concentrate by column chromatography (the eluent is dichloromethane and ethanol with a volume ratio of 3:3) to obtain a branched imidazoline carboxylic acid sulfonic acid alcohol compound, and the structural formula is as follows:

[0051] ;

[0052] (5) Add 6 g of branched imidazoline carboxylic acid sulfonic acid alcohol compound, 2.2 g of aluminum sulfate, and 55 g of deionized water into a reaction kettle, stir at 27 °C for 5 h, and then remove water by vacuum distillation to obtain an aluminum salt tanning agent.

[0053] (6) Add 6 g of branched imidazoline carboxylic acid sulfonic acid alcohol compound, 2 g of zirconium sulfate, and 55 g of deionized water into a reaction kettle, stir at 28 °C for 5 h, and then remove water by vacuum distillation to obtain a zirconium salt tanning agent.

[0054] (7) Add 10 g of the imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound prepared in step (3), 17 g of acrylic acid, 80 g of deionized water, and 0.7 g of 2,2'-azobis(isobutyramidine) dihydrochloride into a reaction kettle, stir evenly, heat to 50 °C, stir and react for 1.7 h, and then remove water by vacuum distillation to obtain a retanning agent.

[0055] (8) Add deionized water and sodium chloride with a mass ratio of 100:6 into a stainless steel drum, and then adjust the pH of the material in the stainless steel drum to 3.3 with formic acid to obtain a pretreatment solution. Then immerse pickled cowhide (cowhide after liming, deliming, softening, and pickling treatments) in the pretreatment solution, rotate at room temperature for 40 min for pretreatment. Then add a chromium-free tanning agent into the stainless steel drum. The chromium-free tanning agent is composed of the aluminum salt tanning agent prepared in step (5) and the zirconium salt tanning agent prepared in step (6). The mass ratio of the aluminum salt tanning agent to the zirconium salt tanning agent is 3:4.5. The total mass of the chromium-free tanning agent is 6% of the mass of water in the stainless steel drum. Then rotate at 38 °C for 4.2 h, and then adjust the pH of the liquid phase material in the stainless steel drum to 3.8 with a 0.1% sodium bicarbonate solution, stop rotating, stand for 7 h, then rotate for another 50 min, drain the liquid, and wash with water to obtain wet blue leather.

[0056] (9) Add the retanning agent prepared in step (7) and water into the stainless steel drum according to a mass ratio of 7:100, heat to 43 °C, stir evenly to obtain a retanning solution. Then immerse the wet blue leather prepared in step (8) in the retanning solution, rotate for 70 min, fix with a 0.6% formic acid solution, wash out of the drum, and stack and stand for 12 h to obtain finished sofa leather.

[0057] Example 3. The preparation method of the low-odor and environmentally friendly sofa leather in this example includes the following steps:

[0058] (1) Add 0.23 mol of imidazoline acrylate and 50 mL of methanol into a reaction kettle, and then dropwise add 0.25 mol of epichlorohydrin under stirring. After the addition is completed, heat to 45 °C, stir and reflux for 30 h, and then remove the solvent by rotary evaporation to obtain an imidazoline chloroalcohol compound.

[0059] (2) Add 75 mmol of imidazoline chloroalcohol compound and 60 mL of methanol into a reaction kettle, then dropwise add 85 mmol of bromoacetic acid under stirring. After the addition is completed, heat to 65 °C and stir and reflux for 30 h. Then, remove the solvent and unreacted bromoacetic acid by distillation under reduced pressure to obtain the imidazoline chloro-carboxylic acid alcohol compound.

[0060] (3) Add 75 mmol of imidazoline chloro-carboxylic acid alcohol compound and 70 mL of ethanol into a reaction kettle, then dropwise add an ethanol solution (mass fraction 30%) containing 83 mmol of 4-hydroxypyridine-3-sulfonic acid under stirring. After the addition is completed, heat to 85 °C and stir and reflux for 30 h. Then, remove the solvent by distillation under reduced pressure to obtain a concentrate. Purify the concentrate by column chromatography (the eluent is chloroform and isopropanol with a volume ratio of 3:4) to remove the unreacted 4-hydroxypyridine-3-sulfonic acid, and obtain the imidazoline chloro-pyridinium salt sulfonic acid carboxylic acid alcohol compound, the structural formula of which is as follows:

[0061] ;

[0062] (4) Add 0.01 mol of 3-aminopropionic acid, 0.02 mol of triethanolamine and 60 mL of ethanol into a reaction kettle, then dropwise add 0.03 mol of imidazoline chloro-pyridinium salt sulfonic acid carboxylic acid alcohol compound under stirring and at 25 °C. After the addition is completed, stir and react at 80 °C for 3 h. Then, remove the solvent by distillation under reduced pressure to obtain a concentrate. Purify the concentrate by column chromatography (the eluent is dichloromethane and ethanol with a volume ratio of 3:3) to obtain the branched-chain imidazoline carboxylic acid sulfonic acid alcohol compound, the structural formula of which is as follows:

[0063] ;

[0064] (5) Add 6 g of the branched-chain imidazoline carboxylic acid sulfonic acid alcohol compound, 2.5 g of aluminum sulfate and 60 g of deionized water into a reaction kettle, stir at 30 °C for 6 h, and then remove the water by distillation under reduced pressure to obtain the aluminum salt tanning agent.

[0065] (6) Add 6 g of the branched-chain imidazoline carboxylic acid sulfonic acid alcohol compound, 2.2 g of zirconium sulfate and 60 g of deionized water into a reaction kettle, stir at 30 °C for 6 h, and then remove the water by distillation under reduced pressure to obtain the zirconium salt tanning agent.

[0066] (7) Add 10 g of the imidazoline chloro-pyridinium salt sulfonic acid carboxylic acid alcohol compound prepared in step (3), 20 g of acrylic acid, 85 g of deionized water and 0.8 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride into a reaction kettle, stir evenly, heat to 60 °C, stir and react for 2 h, and then remove the water by distillation under reduced pressure to obtain the retanning agent.

[0067] (8) Deionized water and sodium chloride with a mass ratio of 100:7 were added to a stainless-steel drum, and then the pH of the material in the stainless-steel drum was adjusted to 3.5 with formic acid to obtain a pretreatment solution. Then, pickled cowhide (cowhide after liming, deliming, bating, and pickling) was immersed in the pretreatment solution, and rotated at room temperature for 45 min for pretreatment. Then, a chrome-free tanning agent was added to the stainless-steel drum. The chrome-free tanning agent was composed of the aluminum salt tanning agent prepared in step (5) and the zirconium salt tanning agent prepared in step (6). The mass ratio of the aluminum salt tanning agent to the zirconium salt tanning agent was 3:5, and the total mass of the chrome-free tanning agent was 7% of the mass of water in the stainless-steel drum. Then, it was rotated at 40 °C for 4.5 h, and then the pH of the liquid-phase material in the stainless-steel drum was adjusted to 3.9 with a 0.1% sodium bicarbonate solution. Rotation was stopped, and it was left standing for 8 h, then rotated for another 60 min, drained, and washed with water to obtain wet blue leather.

[0068] (9) The retanning agent prepared in step (7) and water were added to a stainless-steel drum according to a mass ratio of 8:100, heated to 45 °C, and stirred evenly to obtain a retanning solution. Then, the wet blue leather prepared in step (8) was immersed in the retanning solution, rotated for 90 min, and then fixed with a 0.7% formic acid solution, washed out of the drum, and hung on a horse and left standing for 12 h to obtain finished sofa leather.

[0069] Comparative Example 1

[0070] The difference between the preparation method of the sofa leather in this comparative example and the preparation method of the sofa leather in Example 1 is only that in step (8) of the preparation method of the sofa leather in this comparative example, the chrome-free tanning agent was replaced with a chrome tanning agent, namely basic chromium sulfate.

[0071] Comparative Example 2

[0072] The difference between the preparation method of the sofa leather in this comparative example and the preparation method of the sofa leather in Example 1 is only that in step (5) of the preparation method of the sofa leather in this comparative example, aluminum sulfate was replaced with chromium sulfate.

[0073] Comparative Example 3

[0074] The difference between the preparation method of the sofa leather in this comparative example and the preparation method of the sofa leather in Example 1 is only that in step (5) of the preparation method of the sofa leather in this comparative example, aluminum sulfate was replaced with titanium sulfate.

[0075] Comparative Example 4

[0076] The difference between the preparation method of the sofa leather in this comparative example and the preparation method of the sofa leather in Example 1 is only that in step (6) of the preparation method of the sofa leather in this comparative example, zirconium sulfate was replaced with chromium sulfate.

[0077] Comparative Example 5

[0078] The difference between the preparation method of the sofa leather in this comparative example and that in Example 1 lies only in that in step (6) of the preparation method of the sofa leather in this comparative example, zirconium sulfate is replaced by titanium sulfate.

[0079] Comparative Example 6

[0080] The difference between the preparation method of the sofa leather in this comparative example and that in Example 1 lies only in that in step (8) of the preparation method of the sofa leather in this comparative example, the chromium-free tanning agent is the zirconium salt tanning agent prepared in step (6) of Example 1.

[0081] Comparative Example 7

[0082] The difference between the preparation method of the sofa leather in this comparative example and that in Example 1 lies only in that in step (8) of the preparation method of the sofa leather in this comparative example, the chromium-free tanning agent is the aluminum salt tanning agent prepared in step (5) of Example 1.

[0083] Effect Example

[0084] In order to evaluate the comprehensive performance and practical application effect of the finished leather prepared in each example and comparative example, the shrinkage temperature of the wet blue prepared in each example and comparative example was tested respectively, and the thickness of the finished leather, the thickening rate of the wet blue during retanning, tensile strength, tear strength, elongation at break, light fastness, abrasion resistance, rubbing color fastness and odor grade of the finished leather were tested according to the method in Standard GB / T 16799-2008 "Leather for Furniture". Then, the flex resistance was tested according to the method in Standard QB / T 2714-2005, and the water vapor permeability of the finished leather was tested with a water vapor permeability tester. The test results are shown in Table 1-2. Among them, the thickness of the finished leather and the thickening rate of the wet blue during retanning were measured from the back of the cowhide. The light fastness test results were characterized by the color difference of the leather surface before and after the test. During the abrasion resistance test, a CS-10 friction wheel was used, and the load of the friction wheel was 1000 g. The maximum number of friction revolutions when damage, peeling or discoloration occurred in the friction area of the leather was recorded, and the abrasion resistance was characterized by the number of friction revolutions. During the rubbing color fastness test, a felt was used. The felt was a dry felt, a felt soaked in deionized water and a felt soaked in artificial sweat. The corresponding rubbing methods were dry rubbing, wet rubbing and sweat rubbing respectively. After the test, the color difference of the leather surface before and after the test was measured, and the rubbing color fastness was characterized by the color difference. The flex resistance test results were expressed by the maximum number of flexing times when discoloration, fuzzing, cracking, shelling or breaking occurred at the folded part of the leather.

[0085] Table 1 Shrinkage temperature of the wet blue, thickness of the finished leather, thickening rate, tensile strength, tear strength, elongation at break, light fastness and abrasion resistance of the finished leather prepared in each example and comparative example

[0086] 。

[0087] Table 2 Friction Color Fastness, Flex Resistance, Water Vapor Permeability and Odor Grade of the Finished Leather Prepared in Each Example and Comparative Example

[0088] 。

[0089] As can be seen from Table 1-2, since the aluminum salt tanning agent and zirconium salt tanning agent of the present invention contain a large number of carboxyl groups, sulfonic acid groups, phenolic hydroxyl groups and hydroxyl groups, they can crosslink with the skin collagen in the leather, and the quaternary ammonium salt groups therein can improve the surface activity of the tanning agent, improve the contact activity between the skin collagen and the tanning agent, reduce the contact resistance, and improve the permeability and tanning effect of the tanning agent; compared with the traditional chromium tanning agent (Comparative Example 1), the leather tanned with the chromium-free tanning agent of the present invention has a similar shrinkage temperature, a larger thickness and thickening rate, and has higher mechanical properties, and can completely replace the traditional chromium tanning agent, avoiding chromium pollution and waste liquid treatment, reducing costs, and improving the environmental protection of leather. In addition, as can be seen from Example 1 and Comparative Example 1, when the chromium-free tanning agent of the present invention is used in combination with the retanning agent of the present invention, the leather treatment effect can be better improved. This may be because the chromium-free tanning agent and the retanning agent have similar chemical structures. When the two are used in combination, the retanning agent and the chromium-free tanning agent have better affinity, which is conducive to the filling and combination of the acrylic polymer retanning agent, improving the bonding strength and filling effect, and further improving the mechanical properties of the leather. Moreover, the imidazoline ring and pyridine ring embedded in the leather can adsorb the acidic volatile substances that may remain in the leather through nitrogen atoms and lock them in the leather filler, avoiding the overflow of volatile substances, reducing the odor during leather storage, and improving the leather quality; at the same time, the carboxyl groups, sulfonic acid groups, phenolic hydroxyl groups, quaternary ammonium salt groups and imidazoline rings, pyridine rings in the tanning agent and retanning agent can form a composite sterilization and antibacterial system, avoiding the growth of bacteria and other microorganisms, reducing the occurrence of corruption and the emission of corruption odor. As can be seen from Example 1 and Comparative Examples 2-5, when the zirconium salt and aluminum salt corresponding to the branched imidazoline carboxylic acid sulfonic acid alcohol compound based on the present invention are replaced with chromium salt or titanium salt, the corresponding tanning effects are all reduced, indicating that the branched imidazoline carboxylic acid sulfonic acid alcohol compound prepared in the present invention has a better complexing effect with zirconium and aluminum, which helps to form a stable crosslinked structure and improve the tanning effect. As can be seen from Example 1 and Comparative Examples 6-7, when the aluminum salt tanning agent and zirconium salt tanning agent in the present invention are used in combination, they have a good synergistic effect. This may be because the two have different valences, can form different complexing structures and crosslinked structures, and can form a staggered complexing structure when used in combination, improving the complexing utilization rate, and further improving the crosslinking density and compactness, so that the leather has good comprehensive properties.

Claims

1. A method for preparing low-odor environmentally friendly sofa leather, characterized in that: The following steps are involved: The pickled cowhide is immersed in the pretreatment liquid, rotated at room temperature for 30-45 minutes for pretreatment, and then a chrome-free tanning agent is added, and the drum is rotated at 35-40°C for 4-4.5 hours, and then the pH of the liquid phase material in the stainless steel drum is adjusted to 3.7-3.9 with a sodium bicarbonate solution with a mass fraction of 0.1%, the drum is stopped, and the drum is allowed to stand for 6-8 hours, and then rotated for another 45-60 minutes, the liquid is drained, and the drum is washed with water to obtain a crust leather; then the crust leather is immersed in the retanning liquid, rotated for 60-90 minutes, and then fixed with a formic acid solution with a mass fraction of 0.5-0.7%, and the finished sofa leather is obtained after washing and standing; the pretreatment liquid is prepared by mixing water and sodium chloride in a mass ratio of 100:5-7 and then adjusting the pH to 3.2-3.5 with formic acid; the chrome-free tanning agent is composed of an aluminum salt tanning agent and a tanning agent in a mass ratio of 3:4-5. The zirconium salt tanning agent is composed of a zirconium salt tanning agent, the mass of the chrome-free tanning agent is 4% to 7% of the mass of the water in the pretreatment liquid; the aluminum salt tanning agent is prepared by mixing a branched imidazoline carboxylic acid sulfonic alcohol compound and aluminum sulfate in a mass ratio of 6:2 to 2.5 in water at 25 to 30°C for 4 to 6 hours; the zirconium salt tanning agent is prepared by mixing a branched imidazoline carboxylic acid sulfonic alcohol compound and zirconium sulfate in a mass ratio of 6:1.8 to 2.2 in water at 25 to 30°C for 4 to 6 hours; the retanning liquid is composed of water and a retanning agent, and the retanning agent is prepared by mixing an imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound, acrylic acid and azodiisopropylimidazoline hydrochloride in a mass ratio of 10:15 to 20:0.5 to 0.8 in water at 45 to 60°C for 1.5 to 2 hours; the structure of the branched imidazoline carboxylic acid sulfonic alcohol compound is as follows: ; The structure of the imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound is as follows: 。 2. The method for preparing low-odor environmentally friendly sofa leather according to claim 1, characterized in that: The preparation method of the imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound is as follows: (1) mixing imidazoline acrylate and epichlorohydrin at 40-45°C for 24-30 hours to obtain an imidazoline chlorohydrin compound; (2) mixing the imidazoline chlorohydrin compound and bromoacetic acid at 60-65° C. for 24-30 hours to obtain an imidazoline chlorocarboxylic acid alcohol compound; (3) The imidazoline chlorocarboxylic acid alcohol compound and 4-hydroxypyridine-3-sulfonic acid are mixed and reacted at 75-85° C. for 24-30 hours to obtain the imidazoline chloropyridine salt sulfonic acid carboxylic acid alcohol compound.

3. The method for preparing low-odor environmentally friendly sofa leather according to claim 2, characterized in that: In step (1) of the method for preparing the imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound, the molar ratio of acrylic acid imidazoline to epichlorohydrin is 0.23:0.25; epichlorohydrin is added dropwise.

4. The method for preparing low-odor environmentally friendly sofa leather according to claim 2, characterized in that: In step (2) of the method for preparing the imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound, the molar ratio of the imidazoline chlorohydrin compound to bromoacetic acid is 75:85; bromoacetic acid is added dropwise.

5. The method for preparing low-odor environmentally friendly sofa leather according to claim 2, characterized in that: In step (3) of the method for preparing the imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound, the molar ratio of the imidazoline chlorocarboxylic acid alcohol compound to 4-hydroxypyridine-3-sulfonic acid is 75:82-83; and 4-hydroxypyridine-3-sulfonic acid is added in a solution dropwise manner.

6. The method for preparing low-odor environmentally friendly sofa leather according to claim 2, characterized in that: The structure of the acrylic acid imidazoline is as follows: 。 7. The method for preparing low-odor environmentally friendly sofa leather according to claim 1, characterized in that: The preparation method of the branched imidazoline carboxylic acid sulfonic alcohol compound is as follows: 3-aminopropionic acid, triethanolamine and imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound are mixed and reacted at 70-80° C. for 3-5 hours to obtain the branched imidazoline carboxylic acid sulfonic alcohol compound.

8. The method for preparing low-odor environmentally friendly sofa leather according to claim 7, characterized in that: The molar ratio of the 3-aminopropionic acid, triethanolamine and imidazoline chloropyridinium salt sulfonic acid carboxylic acid alcohol compound is 1:1.5-2:2.5-3.

9. The method for preparing low-odor environmentally friendly sofa leather according to claim 1, characterized in that: When preparing the aluminum salt tanning agent, the mass ratio of the branched imidazoline carboxylic acid sulfonic alcohol compound, aluminum sulfate and water is 6:2~2.5:50~60; when preparing the zirconium salt tanning agent, the mass ratio of the branched imidazoline carboxylic acid sulfonic alcohol compound, zirconium sulfate and water is 6:1.8~2.2:50~60.

10. The method for preparing low-odor environmentally friendly sofa leather according to claim 1, characterized in that: The standing time is 12 hours.

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