Method for enhancing tearing force of cow split suede leather

Abstract

The invention relates to the technical field of leather making, provides a method for enhancing the tearing force of cow split suede leather, and solves the problems of chromium pollution, low compactness and poor leather tearing performance during production of the existing cow split suede leather. Comprising the following steps of rewetting, retanning, neutralizing, dyeing, fat liquoring and fixing. Wherein the retanning comprises the following steps: firstly adding 150-200 parts by weight of water and 0.5-1 part by weight of a fatting agent, adjusting the temperature to 30-35 DEG C, rotating for 20-30 minutes, then adding 0.5-1 part by weight of sodium formate and 1-1.5 parts by weight of baking soda, rotating for 90-120 minutes, finally adding 3 parts by weight of a modified amphoteric polyurethane tanning agent, rotating for 90-120 minutes, and draining water.

Description

Technical Field

[0001] The invention relates to the technical field of sanitary leather, in particular to a method for enhancing the tearing force of cow split suede leather. Background Art

[0002] In the field of leather manufacturing, cow split suede not only inherits the original toughness and durability of cowhide, but also shows a delicate yet rough suede texture through fine processes such as polishing and dyeing. Due to its unique touch and appearance, it is widely used in shoes, luggage, furniture and other fields.

[0003] Chinese patent application No. 202010957076.9 discloses a method for enhancing the tearing force of a two-layer suede leather, comprising the following steps: rewetting, retanning, alkali extraction, neutralization, dyeing, esterification, fixation, addition of aldehyde tanning agent and aluminum tannin, followed by washing, drum discharge, lamination, vacuum drying, softening, grinding, drumming and finishing. The retanning process is as follows: first add 100-130% water and 2-3% salt according to the weight percentage of the two-layer suede leather into the drum, and rotate the drum for 20-30 minutes, then add 0.5-0.7% formic acid, 2-5% aluminum tannin BN, 3-5% chromium powder, 1.5-2.0% WT white tannin, and rotate the drum for 90-100 minutes, and finally add 2-5% GM and rotate the drum for 60-70 minutes. The obtained two-layer suede leather has strong tearing force performance. However, this production method requires the addition of chromium powder, which will produce chromium pollution.

[0004] Chinese patent application No. 201711004774.1 discloses an environmentally friendly, waterproof, chromium-free cow split leather and its production method. The production method is as follows: squeeze the blue wet leather and shave it, then rewet → wash once → tan → wash twice → neutralize → wash three times → fill → dye → wash four times → solid acid → dry → hang to air → soften → grind → thrash to obtain the environmentally friendly, waterproof, chromium-free cow split leather. The cow split leather produced by this method has excellent environmental protection, waterproofness and physical properties; at the same time, the liquid auxiliary chemicals used in each process of the invention are all water-soluble chemicals, which are friendly to the environment and the human body, and will not produce secondary pollution. In addition, each processing process is an acidic environment, which can effectively avoid the conversion of trivalent chromium into hexavalent chromium. However, the cow split leather has the problems of low compactness and poor leather tearing performance. Summary of the invention

[0005] Therefore, in view of the above problems, the present invention provides a method for enhancing the tearing force of cow split suede leather, which solves the problems of chromium pollution, low compactness and poor leather tearing performance caused by the existing cow split suede leather production.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for enhancing the tearing force of cow split suede leather comprises the following steps: rewetting, retanning, neutralization, dyeing, fatliquoring and fixing; wherein the rewetting comprises: adding 100-120 parts of cow split suede leather into a drum, adding 150-200 parts of water, 0.5-1 parts of rewetting agent, 0.5-2 parts of oxalic acid and 0.3-0.5 parts of formic acid by weight, adjusting the pH to 3.0-3.5, rotating for 60-120 minutes, and washing 1-3 times; the retanning comprises: first adding 150-200 parts of water and 0.5-1 parts of fatliquoring agent by weight, adjusting the temperature to 30-35°C, rotating for 20-30 minutes, then adding 0.5-1 parts of sodium formate and 1-1.5 parts of baking soda by weight, rotating for 90-120 minutes, and finally adding 3-4 parts of modified amphoteric polyurethane tanning agent by weight, rotating for 90-120 minutes, and draining;

[0008] The preparation method of the modified amphoteric polyurethane tanning agent is as follows:

[0009] I. The weight ratio of polypropylene glycol and isophorone diisocyanate is 2-3:1, and dibutyltin dilaurate is used as a catalyst. The temperature is raised to 60-70° C. and the reaction is carried out for 2-4 hours to obtain a first intermediate reactant;

[0010] II. Add the modifier and 2,2-dimethylolpropionic acid to the first intermediate reactant obtained in step I according to the mass ratio of the modifier, 2,2-dimethylolpropionic acid and the first intermediate reactant of 1:1:2-3, mix well, increase the temperature to 80-85° C., react for 2-4 hours, and obtain a second intermediate reactant;

[0011] III. Add the modified tannin to the second intermediate reactant obtained in step II in a weight ratio of 4-5:1, mix evenly, react for 2-4 hours, lower the temperature to 35-45°C, add a neutralizer to react for 30-45 minutes, then add 10-30 parts by weight of deionized water for emulsification, and treat through a dialysis bag to obtain the modified amphoteric polyurethane tanning agent.

[0012] Furthermore, the preparation method of the modified tannin is:

[0013] S1. Extraction of tannin: drying, crushing and sieving the plant raw material to obtain plant raw material powder, adding the plant raw material powder to the extract in a solid-liquid ratio of 1:20-25, and performing water bath extraction to obtain a tannin extract;

[0014] S2, purification of tannin: adding a macroporous resin to the tannin extract obtained in step I for adsorption treatment, desorbing the macroporous resin after filtration to obtain a desorbed solution, concentrating and drying the desorbed solution to obtain a purified tannin sample;

[0015] S3. Modification of tannin: according to the weight ratio of the purified tannin sample, acetic anhydride and pyridine being 1:5-8:0.01-1, the temperature is raised to 50-60°C in a water bath, and the reaction is stirred for 4-6 hours. After the reaction is completed, the mixture is poured into ice water to obtain a precipitate, and the precipitate is washed with deionized water for 3-5 times, and vacuum dried to obtain the modified tannin.

[0016] Furthermore, the preparation method of the modifier is:

[0017] a. subjecting L-threonine to a substitution reaction under Cl2 illumination to obtain 2-amino-3,4-dihydroxy-carboxybutyric acid, and then adding the 2-amino-3,4-dihydroxy-carboxybutyric acid to 100-200 parts by weight of tetrahydrofuran to dissolve it to obtain a first mixture for standby use;

[0018] b. In an oil bath, add the trichloromethyl carbonate to the first mixture in a molar ratio of 2-amino-3,4-dihydroxy-carboxybutyric acid to trichloromethyl carbonate of 5-6:3, raise the temperature to 60-65° C., react for 1-2 hours, remove excess solvent after the solution becomes clear, and recrystallize to obtain the modifier.

[0019] Furthermore, the rewetting agent is Fit TCA.

[0020] Furthermore, the neutralizing agent is triethylamine.

[0021] Furthermore, the plant raw material is any one of almond peel, pomegranate peel and mulberry peel.

[0022] Furthermore, the water bath extraction is as follows: heating the water bath to 70-90°C, extracting for 2-3 hours, filtering to obtain a filtrate, repeating the extraction 2-3 times, mixing the filtrates to obtain a mixed solution, and concentrating in vacuo; the extract is a 0.1-0.3% NaOH solution.

[0023] Furthermore, the adsorption treatment is carried out in a constant temperature oscillator at a temperature of 25-30° C., oscillation for 20-24 hours, and a rotation speed of 100-120 r / min.

[0024] Furthermore, the desorption is carried out in anhydrous ethanol solution with a solid-liquid ratio of 1:10-20, a temperature of 25-30°C, oscillation for 20-24h, and a rotation speed of 100-120r / min.

[0025] By adopting the above technical solution, the beneficial effects of the present invention are:

[0026] The polyurethane prepolymer is prepared from polypropylene glycol and isophorone diisocyanate as raw materials, i.e. the first intermediate reactant, and the modifier The polyurethane prepolymer is modified, and 2,2-dihydroxymethyl propionic acid is used as a chain extender to prepare an amphoteric polyurethane prepolymer, i.e., the second intermediate reactant. The amphoteric polyurethane prepolymer is then modified with modified tannin to finally obtain a modified amphoteric polyurethane tanning agent.

[0027] The modifier is prepared with natural amino acid (L-threonine) as raw material, contains two alcoholic hydroxyl groups, and can give the retanning agent higher hydrophilicity, thereby improving the water solubility of the retanning agent and making it easy for the retanning agent to penetrate into the leather and cross-link with the leather.

[0028] Modified tannins are obtained by extraction, purification and modification of plant raw materials, including any one of almond peel, pomegranate peel and mulberry peel. Plant raw material tannins contain a large number of phenolic hydroxyl groups and carbonyl groups. During the tanning process, they can produce multi-point hydrogen bond cross-linking with the amino groups of leather collagen fibers, thereby improving the mechanical properties of the leather. However, this hydrogen bond cross-linking force is weak and the spatial structure is relatively unstable. Therefore, acetic anhydride and pyridine are used as acylating agents and catalysts respectively to complete the modification. On the basis of retaining the original active groups, a large number of aldehyde groups are introduced into the plant raw material tannins to achieve tannin acylation. The amino groups of leather collagen fibers can undergo aldehyde-amine condensation reaction with aldehyde groups to form a stable Schiff base structure. The modified amphoteric polyurethane tanning agent prepared in this way has the structural characteristics of modified tannins. Leather collagen fibers contain a large number of peptide bonds, hydroxyl groups and carboxyl groups. The -NH- group in the peptide bond can form hydrogen bonds with the phenolic carboxyl and phenolic hydroxyl groups of the modified tannins on the modified amphoteric polyurethane tanning agent. The group can form hydrogen bonds with the phenolic hydroxyl groups in tannin; the hydroxyl groups can form hydrogen bonds with the phenolic carboxyl groups and phenolic hydroxyl groups in tannin; the carboxyl groups can form hydrogen bonds with the carbonyl groups and phenolic hydroxyl groups in tannin, and the charged carboxylate ions can form electrostatic bonds with tannin. In the tanning process of leather making, there are both hydrogen bonds between the modified tannin and the leather collagen fibers, and there are also chemical bonds formed by the chemical reaction between the aldehyde groups in the modified tannin structure and the amino groups of the collagen fiber molecules. Under the combined action of the two forces, the leather material is soft, plump, and firm, and the mechanical properties of the leather are significantly improved. The modified amphoteric polyurethane tanning agent of the present invention is an organic chrome-free tanning agent, which is biodegradable, green, environmentally friendly and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the organic synthesis diagram of the amphoteric polyurethane tanning agent in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] Example 1

[0031] refer to Figure 1 A method for enhancing the tearing strength of cow split suede leather comprises the following steps:

[0032] (1) Rehumidification

[0033] Add the cow split suede leather into a drum, add 150 parts of water, 0.5 parts of rewetting agent Fit TCA, 0.5 parts of oxalic acid, and 0.3 parts of formic acid by weight, adjust the pH to 3.0, rotate for 60 minutes, and wash once;

[0034] (2) Retanning

[0035] First, add 150 parts by weight of water and 0.5 parts by weight of fatliquor, adjust the temperature to 30°C, rotate for 20 minutes, then add 0.5 parts by weight of sodium formate and 1 part by weight of baking soda, rotate for 90 minutes, and finally add 3 parts by weight of modified amphoteric polyurethane tanning agent, rotate for 90 minutes, and drain;

[0036] (2-1) Preparation of Modifier

[0037] a. subjecting L-threonine to a substitution reaction under Cl2 illumination to obtain 2-amino-3,4-dihydroxy-carboxybutyric acid, and then adding the 2-amino-3,4-dihydroxy-carboxybutyric acid to 100 parts by weight of tetrahydrofuran to dissolve it to obtain a first mixture for standby use;

[0038] b. In an oil bath, the trichloromethyl carbonate is added to the first mixture in a molar ratio of 2-amino-3,4-dihydroxy-carboxybutyric acid to trichloromethyl carbonate of 5:3, the temperature is raised to 60° C., the reaction is performed for 1 hour, and after the solution is clarified, the excess solvent is removed, and the modifier is obtained by recrystallization;

[0039] (2-2) Preparation of modified tannin

[0040] S1. Extraction of tannin: drying almond peel, crushing and sieving to obtain plant raw material powder, adding the plant raw material powder to 0.1% NaOH solution at a solid-liquid ratio of 1:20, extracting in a water bath, heating the water bath to 70° C., extracting for 2 h, filtering to obtain a filtrate, repeating the extraction twice, mixing the filtrates to obtain a mixed solution, and concentrating in vacuo to obtain a tannin extract;

[0041] S2, purification of tannin: adding macroporous resin to the tannin extract obtained in step I, performing adsorption treatment in a constant temperature oscillator at a temperature of 25° C., oscillating for 24 hours, and a rotation speed of 100 r / min, desorbing the macroporous resin in anhydrous ethanol solution after filtration, at a solid-liquid ratio of 1:10, at a temperature of 25° C., oscillating for 24 hours, and a rotation speed of 100 r / min, to obtain a desorbed solution, and concentrating and drying the desorbed solution to obtain a purified tannin sample;

[0042] S3, modification of tannin: according to the weight ratio of the purified tannin sample, acetic anhydride and pyridine being 1:5:0.01, the temperature was raised to 50° C. in a water bath, and the mixture was stirred for reaction for 4 hours. After the reaction, the mixture was poured into ice water to obtain a precipitate, and the precipitate was washed with deionized water for 3 times, and vacuum dried to obtain the modified tannin;

[0043] (2-3) The preparation method of the amphoteric polyurethane tanning agent is:

[0044] I. polypropylene glycol and isophorone diisocyanate in a weight ratio of 2:1, dibutyltin dilaurate as a catalyst, raising the temperature to 60° C., reacting for 2 hours to obtain a first intermediate reactant;

[0045] II. Add the modifier and 2,2-dimethylolpropionic acid to the first intermediate reactant obtained in step I according to the mass ratio of the modifier, 2,2-dimethylolpropionic acid and the first intermediate reactant of 1:1:2, mix well, increase the temperature to 80° C., react for 2 hours, and obtain a second intermediate reactant;

[0046] III. Add the modified tannin to the second intermediate reactant obtained in step II at a weight ratio of 4:1, mix well, react for 2 hours, lower the temperature to 35° C., add triethylamine and react for 30 minutes, then add 10 parts by weight of deionized water for emulsification, and treat through a dialysis bag to obtain the modified amphoteric polyurethane tanning agent;

[0047] (3) Neutralization

[0048] Add 150 parts of water, 1 part of sodium acetate, and 0.2 parts of NaHCO3 to the drum by weight, adjust the pH to 4.5-, and rotate for 60 minutes;

[0049] (4) Dyeing

[0050] Add 1 part of disperse tannin YHN dye, 0.08 part of dyeing auxiliary PENETRATOR 7312, 3 parts of chestnut tannin extract TCR, 1 part of NaHCO3, 100 parts of water, and 1 part of formic acid into the drum by weight, adjust the pH to 4, add formic acid three times, rotate for 20 minutes after each addition, and finally drain and wash;

[0051] (5) Fat addition

[0052] Add 100 parts of water, 2 parts of animal fat YMZ, 0.1 parts of triglycerol monooleate, and 0.01 parts of naphthalenesulfonic acid formaldehyde condensate sodium salt to the drum by weight, raise the temperature to 40°C, and rotate for 30 minutes;

[0053] (6) Fixed

[0054] 100 parts of water and 0.3 parts of formic acid were added to the drum by weight, the pH was adjusted to 3.5, and the drum was rotated for 30 minutes.

[0055] Example 2

[0056] A method for enhancing the tearing strength of cow split suede leather comprises the following steps:

[0057] (1) Rehumidification

[0058] Add the cow split suede leather into a drum, add 150 parts of water, 0.8 parts of rewetting agent Fit TCA, 1 part of oxalic acid, and 0.4 parts of formic acid by weight, adjust the pH to 3.2, rotate for 90 minutes, and wash twice;

[0059] (2) Retanning

[0060] First, add 180 parts by weight of water and 0.8 parts by weight of fatliquor, adjust the temperature to 30°C, rotate for 20 minutes, then add 0.8 parts by weight of sodium formate and 1.2 parts by weight of baking soda, rotate for 90 minutes, and finally add 4 parts by weight of modified amphoteric polyurethane tanning agent, rotate for 90 minutes, and drain;

[0061] (2-1) Preparation of Modifier

[0062] a. subjecting L-threonine to a substitution reaction under Cl2 illumination to obtain 2-amino-3,4-dihydroxy-carboxybutyric acid, and then adding the 2-amino-3,4-dihydroxy-carboxybutyric acid to 150 parts by weight of tetrahydrofuran to dissolve it to obtain a first mixture for standby use;

[0063] b. In an oil bath, the trichloromethyl carbonate is added to the first mixture in a molar ratio of 5.5:3 between the 2-amino-3,4-dihydroxy-carboxybutyric acid and trichloromethyl carbonate, the temperature is raised to 65° C., the reaction is performed for 1.5 hours, and after the solution is clarified, the excess solvent is removed, and the modifier is obtained by recrystallization;

[0064] (2-2) Preparation of modified tannin

[0065] S1. Extraction of tannin: drying almond skin, crushing and sieving to obtain plant raw material powder, adding the plant raw material powder to 0.2% NaOH solution in a solid-liquid ratio of 1:22, extracting in a water bath, heating the water bath to 80° C., extracting for 2.5 hours, filtering to obtain a filtrate, repeating the extraction three times, mixing the filtrates to obtain a mixed solution, and concentrating in vacuo to obtain a tannin extract;

[0066] S2, purification of tannin: adding macroporous resin to the tannin extract obtained in step I, and performing adsorption treatment in a constant temperature oscillator, the temperature is 25°C, the oscillation is 24h, the rotation speed is 110r / min, after filtering, the macroporous resin is desorbed in anhydrous ethanol solution, the solid-liquid ratio is 1:15, the temperature is 25°C, the oscillation is 24h, the rotation speed is 110r / min, and a desorbed solution is obtained, and the desorbed solution is concentrated and dried to obtain a purified tannin sample;

[0067] S3, modification of tannin: according to the weight ratio of the purified tannin sample, acetic anhydride and pyridine being 1:5-8:0.1, the temperature was raised to 60°C in a water bath, and the reaction was stirred for 5 hours. After the reaction was completed, the mixture was poured into ice water to obtain a precipitate, and the precipitate was washed with deionized water for 3 times, and vacuum dried to obtain the modified tannin;

[0068] (2-3) The preparation method of the amphoteric polyurethane tanning agent is:

[0069] I. The weight ratio of polypropylene glycol and isophorone diisocyanate is 2.5:1, and dibutyltin dilaurate is used as a catalyst. The temperature is raised to 65° C. and the reaction is carried out for 3 hours to obtain a first intermediate reactant;

[0070] II. Add the modifier and 2,2-dimethylolpropionic acid to the first intermediate reactant obtained in step I according to the mass ratio of the modifier, 2,2-dimethylolpropionic acid and the first intermediate reactant of 1:1:2.5 respectively, mix well, increase the temperature to 80° C., react for 3 hours, and obtain a second intermediate reactant;

[0071] III. Add the modified tannin to the second intermediate reactant obtained in step II at a weight ratio of 4.5:1, mix well, react for 3 hours, lower the temperature to 40° C., add triethylamine and react for 40 minutes, then add 20 parts by weight of deionized water for emulsification, and treat through a dialysis bag to obtain the modified amphoteric polyurethane tanning agent;

[0072] (3) Neutralization

[0073] Add 120 parts of water, 1.5 parts of sodium acetate, and 0.4 parts of NaHCO3 to the drum by weight, adjust the pH to 4.8, and rotate for 90 minutes;

[0074] (4) Dyeing

[0075] Add 2 parts of disperse tannin YHN dye, 0.1 parts of dyeing auxiliary PENETRATOR 7312, 5 parts of chestnut tannin extract TCR, 2 parts of NaHCO3, 150 parts of water, and 1.2 parts of formic acid to the drum by weight, adjust the pH to 4.2, add formic acid three times, rotate for 25 minutes after each addition, and finally drain and wash;

[0076] (5) Fat addition

[0077] Add 120 parts of water, 3 parts of animal fat YMZ, 0.15 parts of triglycerol monooleate, and 0.05 parts of naphthalenesulfonic acid formaldehyde condensate sodium salt to the drum by weight, raise the temperature to 45°C, and rotate for 45 minutes;

[0078] (6) Fixed

[0079] 120 parts of water and 2 parts of formic acid were added to the drum by weight, the pH was adjusted to 3.5, and the drum was rotated for 45 minutes.

[0080] Example 3

[0081] A method for enhancing the tearing strength of cow split suede leather comprises the following steps:

[0082] (1) Rehumidification

[0083] Add the cow split suede leather into a drum, add 200 parts of water, 1 part of rewetting agent Fit TCA, 2 parts of oxalic acid, and 0.5 parts of formic acid by weight, adjust the pH to 3.5, rotate for 120 minutes, and wash twice;

[0084] (2) Retanning

[0085] First, add 200 parts by weight of water and 1 part by weight of fatliquor, adjust the temperature to 35°C, rotate for 30 minutes, then add 1 part by weight of sodium formate and 1.5 parts by weight of baking soda, rotate for 120 minutes, and finally add 4 parts by weight of modified amphoteric polyurethane tanning agent, rotate for 120 minutes, and drain;

[0086] (2-1) Preparation of Modifier

[0087] a. subjecting L-threonine to a substitution reaction under Cl2 illumination to obtain 2-amino-3,4-dihydroxy-carboxybutyric acid, and then adding the 2-amino-3,4-dihydroxy-carboxybutyric acid to 200 parts by weight of tetrahydrofuran to dissolve it to obtain a first mixture for standby use;

[0088] b. In an oil bath, the trichloromethyl carbonate is added to the first mixture in a molar ratio of 2:1 between the 2-amino-3,4-dihydroxy-carboxybutyric acid and trichloromethyl carbonate, the temperature is raised to 65° C., the reaction is carried out for 2 h, and after the solution is clarified, the excess solvent is removed, and the modifier is obtained by recrystallization;

[0089] (2-2) Preparation of modified tannin

[0090] S1. Extraction of tannin: drying almond peel, crushing and sieving to obtain plant raw material powder, adding the plant raw material powder to 0.3% NaOH solution at a solid-liquid ratio of 1:25, extracting in a water bath, heating the water bath to 90° C., extracting for 3 hours, filtering to obtain a filtrate, repeating the extraction for 3 times, mixing the filtrates to obtain a mixed solution, and concentrating in vacuo to obtain a tannin extract;

[0091] S2, purification of tannin: adding macroporous resin to the tannin extract obtained in step I, performing adsorption treatment in a constant temperature oscillator at a temperature of 30° C., oscillating for 24 hours, and a rotation speed of 120 r / min, desorbing the macroporous resin in anhydrous ethanol solution after filtration, at a solid-liquid ratio of 1:20, at a temperature of 30° C., oscillating for 24 hours, and a rotation speed of 120 r / min, to obtain a desorbed solution, and concentrating and drying the desorbed solution to obtain a purified tannin sample;

[0092] S3, modification of tannin: according to the weight ratio of the purified tannin sample, acetic anhydride and pyridine being 1:5-8:1, the temperature is raised to 60°C in a water bath, and the reaction is stirred for 6 hours. After the reaction is completed, the mixture is poured into ice water to obtain a precipitate, and the precipitate is washed with deionized water for 5 times, and vacuum dried to obtain the modified tannin;

[0093] (2-3) The preparation method of the amphoteric polyurethane tanning agent is:

[0094] I. The weight ratio of polypropylene glycol and isophorone diisocyanate is 2-3:1, and dibutyltin dilaurate is used as a catalyst. The temperature is raised to 60-70° C. and the reaction is carried out for 2-4 hours to obtain a first intermediate reactant;

[0095] II. Add the modifier and 2,2-dimethylolpropionic acid to the first intermediate reactant obtained in step I according to the mass ratio of the modifier, 2,2-dimethylolpropionic acid and the first intermediate reactant of 1:1:3, mix well, increase the temperature to 85° C., react for 4 hours, and obtain a second intermediate reactant;

[0096] III. Add the modified tannin to the second intermediate reactant obtained in step II at a weight ratio of 5:1, mix well, react for 4 hours, lower the temperature to 45° C., add triethylamine and react for 45 minutes, then add 30 parts by weight of deionized water for emulsification, and treat through a dialysis bag to obtain the modified amphoteric polyurethane tanning agent;

[0097] (3) Neutralization

[0098] Add 200 parts of water, 2 parts of sodium acetate, and 0.6 parts of NaHCO3 to the drum by weight, adjust the pH to 5.0, and rotate for 90 minutes;

[0099] (4) Dyeing

[0100] Add 3 parts of disperse tannin YHN dye, 0.12 parts of dyeing auxiliary PENETRATOR 7312, 6 parts of chestnut tannin extract TCR, 3 parts of NaHCO3, 150 parts of water, and 1.5 parts of formic acid into the drum by weight, adjust the pH to 4.5, add formic acid three times, rotate for 30 minutes after each addition, and finally drain and wash;

[0101] (5) Fat addition

[0102] Add 150 parts of water, 5 parts of animal fat YMZ, 0.2 parts of triglycerol monooleate, and 0.1 parts of naphthalenesulfonic acid formaldehyde condensate sodium salt to the drum by weight, raise the temperature to 45°C, and rotate for 60 minutes;

[0103] (6) Fixed

[0104] 150 parts of water and 5 parts of formic acid were added to the drum by weight, the pH was adjusted to 3.8, and the drum was rotated for 60 minutes.

[0105] Comparative Example 1

[0106] The difference from Example 1 is that the modified amphoteric polyurethane tanning agent prepared by the present invention is not used in the retanning stage, but commercially known 4% retanning agent MB-1, 3% retanning agent RTD, and 2% melamine resin type synthetic retanning agent are used. Other technical schemes are the same as those in Example 1.

[0107] Table 1 is the test data of the products of Example 1, Example 2, Example 3 and Comparative Example 1.

[0108] Table 1

[0109]

[0110] The hexavalent chromium content of the retanning effluent in Table 1 was tested according to the "Water Pollutant Discharge Standard for Leather and Fur Processing Industry" (GB30486-2013).

[0111] It can be seen from Table 1 that the leather prepared by the present technical solution is fuller and firmer; the hexavalent chromium content of the retanning drainage is ND (less than 0.2 mg / L), indicating that it is not detected; and the products of Example 1, Example 2 and Example 3 all have good mechanical properties.

[0112] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes may be made to the present invention in form and details without departing from the spirit and scope of the present invention as defined by the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. A method for enhancing the tearing strength of cow split suede leather, characterized in that: The following steps are involved: Rewetting, retanning, neutralization, dyeing, fatliquoring and fixing; wherein, the rewetting is as follows: 100-120 parts of cow split suede leather are added into a drum, 150-200 parts of water, 0.5-1 parts of rewetting agent, 0.5-2 parts of oxalic acid, 0.3-0.5 parts of formic acid are added by weight, pH is adjusted to 3.0-3.5, rotating for 60-120 minutes, and washing 1-3 times; the retanning is as follows: 150-200 parts of water and 0.5-1 parts of fatliquoring agent are first added, the temperature is adjusted to 30-35°C, rotating for 20-30 minutes, then 0.5-1 parts of sodium formate and 1-1.5 parts of baking soda are added, rotating for 90-120 minutes, and finally 3-4 parts of modified amphoteric polyurethane tanning agent are added, rotating for 90-120 minutes, and draining; The preparation method of the modified amphoteric polyurethane tanning agent is as follows: I. The weight ratio of polypropylene glycol and isophorone diisocyanate is 2-3:1, and dibutyltin dilaurate is used as a catalyst. The temperature is raised to 60-70° C. and the reaction is carried out for 2-4 hours to obtain a first intermediate reactant; II. Add the modifier and 2,2-dimethylolpropionic acid to the first intermediate reactant obtained in step I according to the mass ratio of the modifier, 2,2-dimethylolpropionic acid and the first intermediate reactant of 1:1:2-3, mix well, increase the temperature to 80-85° C., react for 2-4 hours, and obtain a second intermediate reactant; III. Add the modified tannin to the second intermediate reactant obtained in step II in a weight ratio of 4-5:1, mix evenly, react for 2-4 hours, lower the temperature to 35-45°C, add a neutralizer to react for 30-45 minutes, then add 10-30 parts by weight of deionized water for emulsification, and treat through a dialysis bag to obtain the modified amphoteric polyurethane tanning agent.

2. The method for enhancing the tearing strength of cow split suede leather according to claim 1, characterized in that: The preparation method of the modified tannin is: S1. Extraction of tannin: drying, crushing and sieving the plant raw material to obtain plant raw material powder, adding the plant raw material powder to the extract in a solid-liquid ratio of 1:20-25, and performing water bath extraction to obtain a tannin extract; S2, purification of tannin: adding a macroporous resin to the tannin extract obtained in step I for adsorption treatment, desorbing the macroporous resin after filtration to obtain a desorbed solution, concentrating and drying the desorbed solution to obtain a purified tannin sample; S3. Modification of tannin: according to the weight ratio of the purified tannin sample, acetic anhydride and pyridine being 1:5-8:0.01-1, the temperature is raised to 50-60°C in a water bath, and the reaction is stirred for 4-6 hours. After the reaction is completed, the mixture is poured into ice water to obtain a precipitate, and the precipitate is washed with deionized water for 3-5 times, and vacuum dried to obtain the modified tannin.

3. The method for enhancing the tearing strength of cow split suede leather according to claim 1, characterized in that: The preparation method of the modifier is: a. subjecting L-threonine to a substitution reaction under Cl2 illumination to obtain 2-amino-3,4-dihydroxy-carboxybutyric acid, and then adding the 2-amino-3,4-dihydroxy-carboxybutyric acid to 100-200 parts by weight of tetrahydrofuran to dissolve it to obtain a first mixture for standby use; b. In an oil bath, add the trichloromethyl carbonate to the first mixture in a molar ratio of 2-amino-3,4-dihydroxy-carboxybutyric acid to trichloromethyl carbonate of 5-6:3, raise the temperature to 60-65° C., react for 1-2 hours, remove excess solvent after the solution becomes clear, and recrystallize to obtain the modifier.

4. The method for enhancing the tearing strength of cow split suede leather according to claim 1, characterized in that: The rewetting agent is Fit TCA.

5. The method for enhancing the tearing strength of cow split suede leather according to claim 1, characterized in that: The neutralizing agent is triethylamine.

6. The method for enhancing the tearing strength of cow split suede leather according to claim 2, characterized in that: The plant raw material is any one of almond peel, pomegranate peel and mulberry peel.

7. The method for enhancing the tearing strength of cow split suede leather according to claim 2, characterized in that: The water bath extraction is as follows: the water bath is heated to 70-90° C., extracted for 2-3 hours, filtered to obtain a filtrate, the filtrates are mixed after repeated extraction for 2-3 times to obtain a mixed solution, and vacuum concentrated; the extract is a 0.1-0.3% NaOH solution.

8. The method for enhancing the tearing strength of cow split suede leather according to claim 2, characterized in that: The adsorption treatment is carried out in a constant temperature oscillator at a temperature of 25-30° C., oscillation for 20-24 hours, and a rotation speed of 100-120 r / min.

9. The method for enhancing the tearing strength of cow split suede leather according to claim 2, characterized in that: The desorption is carried out in anhydrous ethanol solution with a solid-liquid ratio of 1:10-20, a temperature of 25-30° C., oscillation for 20-24 hours, and a rotation speed of 100-120 r / min.

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