Leather chromium-free processing technology

Abstract

The invention discloses a leather chromium-free processing technology which is used for solving the problems that tanning operation in the prior art has great influence on leather performance in the background technology, chrome tanning is a method which is widely applied in the world at present and has a better tanning effect. Leather tanned through the tanning agent has the advantages of being resistant to damp and heat, good in stability, soft and plump in finished leather, good in formability and the like, however, chrome tanning seriously pollutes the environment, a large amount of chrome-containing waste water and chrome leather shavings can be generated in the chrome tanning process, and therefore environmental protection is not facilitated, in addition, the leather obtained through chrome tanning contains chrome, irritation to the skin is large after the leather makes contact with the skin of the human body, and the leather cannot be damaged. The compounds belong to sensitizers; in order to solve the technical problems that the leather is not prone to biodegradation and can pollute the environment after being discarded, the method sequentially comprises the following processing steps of liming, deliming and softening, degreasing and softening, pickling and tanning, chromium-free retanning, neutralizing, filling, dyeing and finishing and finishing. In the pickling and tanning step, a synthetic tanning agent RL and a synthetic tanning agent 806 are used for tanning degreased and softened leather to obtain wet leather, in the chromium-free retanning step, a chromium-free tanning agent TWLZ and a chromium-free tanning agent TWS are used for performing chromium-free tanning on the pickled and tanned leather to obtain wet white leather, and the wet white leather is dyed, finished and coated to obtain finished leather.

Description

Technical Field

[0001] The invention relates to the technical field of leather processing, and in particular to a chromium-free leather processing technology. Background Art

[0002] Leather is a denatured and non-perishable animal skin obtained through physical and chemical processes such as depilation and tanning. It has a history of thousands of years and is widely used in shoes, clothing, bags, furniture and other fields because of its wide variety of patterns and colors, good waterproof performance and relatively low price compared to genuine leather. Chrome-free leather completely eliminates heavy metal chromium pollution in the leather making process from the source, promotes green development and achieves the purpose of environmental protection.

[0003] In leather processing, tanning operations have a great influence on the properties of leather. Chrome tanning is currently the most widely used method in the world and has the best tanning effect. Leather tanned by it has many advantages such as resistance to moisture and heat, good stability, soft and plump leather, and good formability. However, chrome tanning causes great pollution to the environment. The chrome tanning process will produce a large amount of chromium-containing wastewater and chrome leather shavings, which is not conducive to environmental protection. In addition, the leather obtained by chrome tanning contains chromium, which is very irritating to the skin after contact with human skin and is an allergen. Moreover, this type of leather is not easily biodegradable and will pollute the environment after being discarded. Summary of the invention

[0004] The purpose of the present invention is to propose a chrome-free leather processing technology in view of the deficiencies in the prior art, so as to solve the problem that the tanning operation of the prior art mentioned in the background technology has a great influence on the performance of the leather. Chrome tanning is a method that is widely used in the world and has a relatively good tanning effect. The leather tanned by it has many advantages such as resistance to moisture and heat, good stability, soft and plump leather, good formability, etc. However, chrome tanning causes great pollution to the environment. The chrome tanning process will produce a large amount of chrome-containing wastewater and chrome leather scraps, which is not conducive to environmental protection. In addition, the leather obtained by chrome tanning contains chromium, which is highly irritating to the skin after contacting human skin and is an allergen. Moreover, this type of leather is not easy to biodegrade and will cause technical problems such as pollution to the environment after being discarded.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions:

[0006] A chrome-free leather processing technology comprises the following processing steps in sequence: liming, deliming and softening, degreasing and softening, pickling tanning, chrome-free retanning, neutralization, filling, dyeing, finishing and painting. In the pickling tanning step, synthetic tanning agents RL and 806 are used to tan the leather after degreasing and softening to obtain wet leather. In the chrome-free retanning step, chrome-free tanning agents TWLZ and TWS are used to chrome-free tan the leather after pickling tanning to obtain white wet leather. The white wet leather is dyed, finished and painted to obtain finished leather.

[0007] The liming step is specifically as follows: adding 150% to 180% of water based on the total weight of the leather, adding 1% to 1.4% of a liming aid based on the total weight of the leather, 0.4 to 0.7% of sodium sulfate, 0.3 to 0.5% of an anionic dispersing wetting agent and 0.8 to 1.3% of calcium hydroxide, placing the leather in a rotating drum and rotating for 20 to 26 hours to complete the liming operation.

[0008] The deliming and softening process adopts a one-bath process, in which ammonia-free deliming agent and ammonia-free softening enzyme are added to perform deliming and softening.

[0009] Furthermore, the deashing and softening in one bath process is as follows: 55-75% of water at 30-35° C. and 1-3% of an ammonia-free deashing agent are added into a rotary drum, and the drum is rotated for 50-65 minutes. The ammonia-free deashing agent can react with the residual ash and impurities in the leather to clean the residual ash and impurities, and the ammonia-free deashing agent can also combine with the mucin-like substances between the collagen fibers of the leather to make them easier to remove, thereby improving the purity and softness of the leather. The softening liquid ratio is controlled to be 140-150%. At 35-40°C, add 0.3-0.5% ammonia-free softening enzyme and 0.1-0.15% sawdust to the total weight of the fur, rotate for 50-55 minutes, drain, wash once, and complete the deliming and softening operation. By adopting the above technical scheme, the ash alkali on the surface of the leather is removed, the leather surface is softened, and the wrinkles of the leather are relaxed; the alkali is converted into soluble salt, and the physically precipitated and chemically combined ash alkali is removed. Through the deliming and softening operation, the leather strength of the fur can be improved and the shaping performance of the leather can be improved.

[0010] The degreasing and softening step is specifically as follows: adding 100-120% water of the total weight of the leather, 8-12% industrial salt of the total weight of the leather, and 0.1-0.3% degreasing agent of the total weight of the leather to the delimed and softened leather, placing the leather in a rotating drum and rotating for 15-25 minutes before draining the water.

[0011] Furthermore, the degreasing agent is specifically Texent610A, which has good degreasing power and penetration performance, and has a special structure of hydrophilic and hydrophobic groups, which can significantly reduce the interfacial tension between oil and water, thereby producing wetting, penetration, emulsification, dispersion, and solubilization effects, converting hydrophobic fat into hydrophilic substances, dispersing them in the liquid phase (aqueous solution), and separating from the cortex to complete the degreasing operation.

[0012] The pickling tanning step is specifically as follows: adding 75-85% of water of the total weight of the leather to the delimed and softened leather, adding 6-9% of industrial salt of the total weight of the leather, adding 1-3% of fish oil of the total weight of the leather, placing the leather in a rotary drum and rotating for 10-15 minutes; adding 0.4-0.6% of sulfuric acid of the total weight of the leather, adding 0.6-0.9% of formic acid of the total weight of the leather, placing the leather in a rotary drum and rotating for 60-80 minutes, then draining the water, adding 45-55% of water of 28-32°C of the total weight of the leather, adding 4-6% of synthetic tanning agent RL of the total weight of the leather, rotating for 60-80 minutes, adding 4-6% of synthetic tanning agent 806 of the total weight of the leather, placing the leather in a rotary drum and rotating for 20-30 minutes, controlling the pH of the leather to be 3-4, taking the leather out of the drum and standing it, and completing the pickling tanning step.

[0013] Furthermore, sulfuric acid can react with proteins in leather to form stable tannates, thereby improving the physical and chemical properties of leather. Formic acid reacts with active groups on leather fibers to form stable chemical bonds or hydrogen bonds, so that leather fibers are appropriately stretched and dispersed, avoiding the leather being too tight and affecting the feel. Synthetic tanning agent RL can improve the physical and chemical properties of leather. It can reduce the adhesion between bare leather fiber bundles, fibers and fibrils, and make the collagen fiber network loose, thereby making the leather softer and more elastic. In addition, synthetic tanning agent RL can also significantly increase the shrinkage temperature and tensile strength of leather, making the leather body plump, the grain fine, and the water resistance, heat resistance and chemical resistance are also improved.

[0014] The chrome-free retanning step is specifically as follows: adding 45-55% of the total weight of the leather, 28-32° C. water, 8-11% of the total weight of the leather, into the leather after pickling tanning, and rotating in a drum for 15-18 minutes; adding chrome-free tanning agent TWS, 2-6% of the total weight of the leather, 1-1.5% of the total weight of the leather, 7-9% of the total weight of the leather, and rotating in a drum for 130-150 minutes; adding a dispersant, 1-1.5% of the total weight of the leather, 9-11% of the total weight of the leather, and rotating in a drum for 110-130 minutes; adding 45-55% of the total weight of the leather, water, and rotating in a drum for 55-65 minutes, controlling the pH of the leather to be 5.0, and standing for 24 hours. After standing, rotating in a drum for 18-22 minutes, and removing from the drum.

[0015] Furthermore, TWS tanning agent contains multiple groups such as amine groups. These groups can form irreversible bonds when reacting with leather collagen fibers, thereby achieving leather tanning. TWS tanning agent reacts with amine groups on leather collagen fibers to form irreversible bonds. This reaction allows the shrinkage temperature of the leather to reach above 80°C, and the finished leather is fuller, firmer and more elastic. 4 to 8% of the total weight of the leather is added with chrome-free tanning agent TWLZ. The oxidized polysaccharides in the TWLZ tanning agent are coordinated with non-chromium metal salts (such as aluminum and zirconium) to form a complex tanning agent. This complex tanning agent can evenly penetrate into all layers of the leather, coordinate with the amino, carboxyl and hydroxyl groups of the leather collagen fibers to form a multi-point cross-linked network structure. This structure not only improves the physical properties of the leather , and also improves its sensory properties, overcomes the problems of rough grain and stiff leather body of traditional non-chrome metal tanned leather, and uses green renewable biomass resources as raw materials to produce TWLZ tanning agent, which has less impact on the environment. By adding raw oil, the fibers inside the leather can be wrapped by lubricating oil or the fiber surface can be affinity with a large number of "oily" molecules. These oil molecules balance the energy of the leather fiber surface, turning it from a high-energy surface to a low-energy surface, thereby increasing the mutual mobility between fibers, preventing the leather from being hardened and cracked, and giving the leather good physical and mechanical properties. Tannin extract is a vegetable tanning agent, which mainly combines with collagen in the leather through the tannic acid in its ingredients to form a stable compound, making the leather soft, elastic and durable.

[0016] The dyeing and finishing step specifically comprises: adding 190-200% of the total weight of the leather with 30-35° C. water to the leather after chrome-free retanning, adding 0.4-0.6% of the total weight of the leather with OXALIC ACID, adding 0.1-0.2% of the total weight of the leather with SAF, placing the leather in a drum for 35-45 minutes, and then draining and washing the leather, adding 190-200% of the total weight of the leather with 30-35° C. water, adding 1.4-1.6% of the total weight of the leather with PAK, placing the leather in a drum for 23-35 minutes, adding 0.4-0.6% of the total weight of the leather with baking soda, placing the leather in a drum for 23-35 minutes, controlling the pH of the leather to be 4-5, and then draining and washing the leather, adding 45-50% of the total weight of the leather with 30-35° C. water, adding 3.5-4.5% of the total weight of the leather with TANIGAN OS, add 3.5-4.5% ATO of the total weight of the leather, add 9-11% CHD of the total weight of the leather, add 1.4-1.6% H50 of the total weight of the leather, place it in a drum and rotate for 55-60 minutes, check the penetration of the leather, add 95-105% water at 30-35°C of the total weight of the leather, place it in a drum and rotate for 18-23 minutes overnight, then drain and wash the leather, add 95-105% water at 30-35°C of the total weight of the leather, add dye, add 95-105% water at 45-55°C of the total weight of the leather, add 3-4% CVL of the total weight of the leather, add 4-6% H50 of the total weight of the leather, add 1-1.2% E123 of the total weight of the leather, place it in a drum and rotate for 35-40 minutes, add 2.5-3.5% INTAN of the total weight of the leather EG, add INTAN EMS which accounts for 2.5-3.5% of the total weight of the leather, put it into a rotating drum and rotate it for 35-40 minutes, add HCOOH which accounts for 1-1.2% of the total weight of the leather, put it into a rotating drum and rotate it for 15-20 minutes, squeeze out the water and vacuum dry the leather naturally after it comes out of the drum.

[0017] Furthermore, OXALIC ACID can react with the collagen in the leather to destroy the cross-linking structure between its molecules, thus making the leather softer. The surfactant in the oil dispersant can form a thin film in the water to cover the pigment and slurry molecules and keep them dispersed. This film helps to maintain the stability of the pigment and slurry and prevent uneven deposition on the leather surface. TANIGAN OS improves the physical and chemical properties of the leather by combining with the collagen in the leather to form stable chemical bonds. E123 can be used as a solvent or solvent component to help dissolve and disperse dyes, pigments and other chemicals so that they can evenly penetrate into the leather fibers to achieve good dyeing and finishing effects. INTAN EMS can react chemically with the protein in the leather to make the leather softer and more elastic, and have good tensile strength and light resistance. Check the leather penetration. HCOOH helps the dye penetrate the leather and enhance the dyeing effect, while protecting the leather from damage by the dye molecules.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The use of chrome-free tanning agents TWLZ and TWS can make the leather tanning fully and evenly and reduce the chromium content of wastewater in the leather tanning process, thereby reducing environmental pollution during the production process. The leather is then chrome-free retanned and fixed by combining synthetic tanning agents RL and 806 with chrome-free tanning agents TWLZ and TWS. The resulting chrome-free tanned leather has both good physical and chemical properties and subsequent processing performance. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below in conjunction with embodiments.

[0021] Liming, deliming and softening, degreasing and softening, pickling tanning, chrome-free retanning, neutralization, filling, dyeing, finishing and painting. In the pickling tanning step, synthetic tanning agents RL and 806 are used to tan the leather after degreasing and softening to obtain wet leather. In the chrome-free retanning step, chrome-free tanning agent TWLZ is used to perform chrome-free tanning on the leather after pickling tanning to obtain white wet leather. The white wet leather is dyed, finished and painted to obtain finished leather.

[0022] The liming step is specifically as follows: adding 150% to 180% of water based on the total weight of the leather, adding 1% to 1.4% of a liming aid based on the total weight of the leather, 0.4 to 0.7% of sodium sulfate, 0.3 to 0.5% of an anionic dispersing wetting agent and 0.8 to 1.3% of calcium hydroxide, placing the leather in a rotating drum and rotating for 20 to 26 hours to complete the liming operation.

[0023] The deliming and softening process adopts a one-bath process, in which ammonia-free deliming agent and ammonia-free softening enzyme are added to perform deliming and softening.

[0024] The degreasing and softening step is specifically as follows: adding 100-120% water of the total weight of the leather, 8-12% industrial salt of the total weight of the leather, and 0.1-0.3% degreasing agent of the total weight of the leather to the delimed and softened leather, placing the leather in a rotating drum and rotating for 15-25 minutes before draining the water.

[0025] The pickling tanning step is specifically as follows: adding 75-85% of water of the total weight of the leather to the delimed and softened leather, adding 6-9% of industrial salt of the total weight of the leather, adding 1-3% of fish oil of the total weight of the leather, placing the leather in a rotary drum and rotating for 10-15 minutes, adding 0.4-0.6% of sulfuric acid of the total weight of the leather, adding 0.6-0.9% of formic acid of the total weight of the leather, placing the leather in a rotary drum and rotating for 60-80 minutes and then draining, adding 45-55% of water of 28-32° C. of the total weight of the leather, adding 4-6% of synthetic tanning agent RL of the total weight of the leather, rotating for 60-80 minutes, adding 4-6% of synthetic tanning agent 806 of the total weight of the leather, placing the leather in a rotary drum and rotating for 20-30 minutes, controlling the pH of the leather to be 3-4, taking the leather out of the drum and standing it, and completing the pickling tanning step.

[0026] The chrome-free retanning step specifically comprises: adding 45-55% of the total weight of the leather and water at 28-32° C. to the leather after pickling tanning, adding 8-11% of the total weight of the leather and industrial salt, placing the leather in a drum and rotating for 15-18 minutes, adding 2-6% of the total weight of the leather and chrome-free tanning agent TWS, adding 4-8% of the total weight of the leather and chrome-free tanning agent TWLZ, adding 1-1.5% of the total weight of the leather and raw oil, adding 7-9% of the total weight of the leather and Tannin extract is placed in a rotary drum and rotated for 130-150 minutes, 1-1.5% of the total weight of the leather is added with a dispersant, 9-11% of the total weight of the leather is added with tannin extract, and the drum is rotated for 110-130 minutes, 45-55% of the total weight of the leather is added with water, and the drum is rotated for 55-65 minutes, the pH of the leather is controlled to be 5.0, and the leather is allowed to stand for 24 hours. After the standing is completed, the leather is placed in a rotary drum and rotated for 18-22 minutes, and then the leather is taken out of the drum.

[0027] The dyeing and finishing step specifically comprises: adding 190-200% of the total weight of the leather with 30-35° C. water to the leather after chrome-free retanning, adding 0.4-0.6% of the total weight of the leather with OXALIC ACID, adding 0.1-0.2% of the total weight of the leather with SAF, placing the leather in a drum for 35-45 minutes, and then draining and washing the leather, adding 190-200% of the total weight of the leather with 30-35° C. water, adding 1.4-1.6% of the total weight of the leather with PAK, placing the leather in a drum for 23-35 minutes, adding 0.4-0.6% of the total weight of the leather with baking soda, placing the leather in a drum for 23-35 minutes, controlling the pH of the leather to be 4-5, and then draining and washing the leather, adding 45-50% of the total weight of the leather with 30-35° C. water, adding 3.5-4.5% of the total weight of the leather with TANIGAN OS, add 3.5-4.5% ATO of the total weight of the leather, add 9-11% CHD of the total weight of the leather, add 1.4-1.6% H50 of the total weight of the leather, place it in a drum and rotate for 55-60 minutes, check the penetration of the leather, add 95-105% water at 30-35°C of the total weight of the leather, place it in a drum and rotate for 18-23 minutes overnight, then drain and wash the leather, add 95-105% water at 30-35°C of the total weight of the leather, add dye, add 95-105% water at 45-55°C of the total weight of the leather, add 3-4% CVL of the total weight of the leather, add 4-6% H50 of the total weight of the leather, add 1-1.2% E123 of the total weight of the leather, place it in a drum and rotate for 35-40 minutes, add 2.5-3.5% INTAN of the total weight of the leather EG, add INTAN EMS which is 2.5-3.5% of the total weight of the leather, check the penetration of the leather, put it into the drum and rotate it for 35-40 minutes, add HCOOH which is 1-1.2% of the total weight of the leather, put it into the drum and rotate it for 15-20 minutes, squeeze the water out of the leather and dry it naturally in vacuum after it comes out of the drum.

[0028] In the following examples, the method for determining the shrinkage temperature of tanned white wet leather is as follows: the shrinkage temperature of the white wet leather is determined using a shrinkage temperature meter.

[0029] In the following examples, the method for measuring the color difference of tanned white wet leather is as follows: the color difference of white wet leather is measured using a YS4510 leather colorimeter.

[0030] In the following examples, the method for determining the tensile strength of tanned white wet leather is as follows: the tensile strength of the white wet leather is determined using a tensile testing machine.

[0031] In the following examples, the tear strength of tanned white wet leather is determined by using a tensile testing machine to determine the tear strength of the white wet leather.

[0032] In the following examples, the method for determining the hexavalent chromium content of tanned wet white leather is as follows: the hexavalent chromium content of the wet white leather is determined using a hexavalent chromium detector.

[0033] Embodiment 1:

[0034] The pickled cowhide obtained by conventional process is placed in a drum, 60wt% of pickling solution and 5wt% of chrome-free organic tanning agent TWS are added based on the weight of the limed bare hide, and the drum is rotated for 3h. After the alkali is extracted to pH 7.7 with sodium carbonate and sodium bicarbonate, 150wt% of hot water based on the weight of the limed bare hide is added, and the bath temperature is maintained at 42°C. The drum is rotated for 2h, and the drum is stopped overnight. After rotating for 0.5h the next day, the liquid is drained; 30wt% of conventional tanning agent based on the weight of the limed bare hide is added to the drum. Warm water and 2.5wt% sodium lignin sulfonate, rotate for 1.2h, adjust the pH of the bath liquid to 3.8 with formic acid, add 4wt% of chrome-free metal tanning agent TWLZ based on the weight of the limed bare hide, continue to rotate for 4h, use automatic alkali extracting agent MGO to increase the alkali to pH 4.0, add 200wt% of hot water based on the weight of the limed bare hide, keep the bath temperature at 38°C, rotate for 4h, stop the drum overnight, rotate for 0.5h the next day, take out the drum, and obtain ecological chrome-free tanned white wet leather.

[0035] It was determined that the pH value of the ecological chrome-free tanned white wet leather was 4.3, the shrinkage temperature was 81±1℃, the color difference was 16.5±1.5, the tensile strength was 12±1.5, and the tear strength was 65.5±1. The test results are shown in Table 1.

[0036] Embodiment 2:

[0037] The difference between Example 2 and Example 1 is that: 100wt% of pickling solution and 3wt% of chrome-free organic tanning agent TWS are added based on the weight of the limed bare skin, the mixture is rotated for 4h, alkali is extracted with sodium carbonate and sodium bicarbonate to a pH of 8.5, and then 200wt% of hot water based on the weight of the limed bare skin is added, the bath temperature is maintained at 35°C, the mixture is rotated for 1h, the drum is stopped overnight, and the mixture is drained after rotating for 0.5h the next day; 60wt% of the weight of the limed bare skin is added to the drum; % normal temperature water and 1wt% sodium lignin sulfonate, rotate for 2h, adjust the pH value of the bath liquid to 4.5 with formic acid, add 6wt% of chromium-free metal tanning agent TWLZ based on the weight of the limed bare hide, continue to rotate for 1h, use sodium bicarbonate to extract the alkali to pH 4.5, add 100wt% hot water based on the weight of the limed bare hide, keep the bath temperature at 42°C, rotate for 1h, stop the drum overnight, rotate for 0.5h the next day, take out the drum, and obtain ecological chrome-free tanned white wet leather.

[0038] It was determined that the pH value of the ecological chrome-free tanned white wet leather was 4.5, the shrinkage temperature was 70±1°C, the color difference was 12.5±1.5, the tensile strength was 8±1.5, and the tear strength was 50.5±1. The test results are shown in Table 1.

[0039] Example 3

[0040] The difference between Example 3 and Example 2 is that: 30wt% of pickling solution and 1wt% of chrome-free organic tanning agent TWS are added to the drum, the drum is rotated for 2h, alkali is extracted with sodium carbonate and sodium bicarbonate to pH 7.0, hot water is added to the drum to 100wt% of the weight of the limed skin, the bath temperature is maintained at 38°C, the drum is rotated for 3h, the drum is stopped overnight, and the drum is rotated for 0.5h the next day, and the liquid is drained; 100wt% of ordinary limed skin is added to the drum to make it dry; Warm water and 4wt% sodium lignin sulfonate, rotate for 0.5h, adjust the pH of the bath liquid to 3.0 with formic acid, add 2wt% of chromium-free metal tanning agent TWLZ based on the weight of the limed bare skin, continue to rotate for 2.5h, use sodium carbonate to extract the alkali to pH 3.5, add 150wt% of hot water based on the weight of the limed bare skin, keep the bath temperature at 35°C, rotate for 2.5h, stop the drum overnight, rotate for 0.5h the next day, take out the drum, and obtain ecological chrome-free tanned white wet leather.

[0041] It was determined that the pH value of the ecological chrome-free tanned white wet leather was 3.5, the shrinkage temperature was 90±1℃, the color difference was 19.5±1.5, the tensile strength was 17±1.5, and the tear strength was 75.5±1. The test results are shown in Table 1.

[0042] Table 1 Test results

[0043] Example 1 Example 2 Example 3 pH 4.3 4.5 3.5 Shrinkage Temperature 81±1℃ 70±1℃ 90±1℃ Chromatic Aberration 16.5±1.5 12.5±1.5 19.5±1.5 Tensile Strength 12±1.5 8±1.5 17±1.5 Tear Strength 65.5±1 50.5±1 75.5±1 Hexavalent chromium content (mg / kg) Not detected Not detected Not detected

[0044] The test results in Table 1 show that no hexavalent chromium content was detected in the leather obtained in the present application. Compared with Example 1, Example 2 can reduce the color difference value and shrinkage temperature of the leather by increasing the content of chromium-free organic tanning agent TWS and reducing the content of sodium lignin sulfonate. However, compared with Example 1, the tensile strength and tear strength of the leather itself in Example 2 are reduced.

[0045] The test results in Table 1 show that no hexavalent chromium content was detected in the leather obtained in the present application. Compared with Example 1, Example 3 can improve the tensile strength and tear strength of the leather by reducing the content of chromium-free organic tanning agent TWS and increasing the content of sodium lignin sulfonate. However, compared with Example 1, the shrinkage temperature and color difference of the leather itself in Example 3 are lower.

[0046] The test results in Table 1 show that no hexavalent chromium content was detected in the leather obtained in the present application. Compared with Example 2, Example 3 can improve the tensile strength and tear strength of the leather by reducing the content of chromium-free organic tanning agent TWS and increasing the content of sodium lignin sulfonate. However, compared with Example 2, the shrinkage temperature and color difference of the leather itself in Example 3 are lower.

[0047] The test results in Table 1 show that the tear strength and tensile strength of the leather obtained in the present application are 49.5-76.5σ and 6.5-18.5N respectively, having high mechanical properties, the color difference value of the leather is 11-21ΔE, and the leather does not shrink at a temperature of 70°C, and the hexavalent chromium content is not detected, having high comprehensive performance.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be covered by the scope of the claims of the present invention.

Claims

1. A chrome-free leather processing process, characterized in that: The method comprises the following processing steps in sequence: liming, deliming and softening, degreasing and softening, pickling tanning, chrome-free retanning, neutralization, filling, dyeing, finishing and painting. In the pickling tanning step, synthetic tanning agents RL and 806 are used to tan the leather after degreasing and softening to obtain wet leather. In the chrome-free retanning step, chrome-free tanning agents TWLZ and TWS are used to chrome-free tan the leather after pickling tanning to obtain white wet leather. The white wet leather is dyed, finished and painted to obtain finished leather.

2. The chrome-free leather processing technology according to claim 1, characterized in that: The liming step is specifically as follows: adding 150% to 180% of water based on the total weight of the leather, adding 1% to 1.4% of a liming aid based on the total weight of the leather, 0.4 to 0.7% of sodium sulfate, 0.3 to 0.5% of an anionic dispersing wetting agent and 0.8 to 1.3% of calcium hydroxide, placing the leather in a rotating drum and rotating for 20 to 26 hours to complete the liming operation.

3. The chrome-free leather processing technology according to claim 1, characterized in that: The deliming and softening process adopts a one-bath process, in which ammonia-free deliming agent and ammonia-free softening enzyme are added to perform deliming and softening.

4. The chrome-free leather processing technology according to claim 1, characterized in that: The degreasing and softening step is specifically as follows: adding 100-120% water of the total weight of the leather, 8-12% industrial salt of the total weight of the leather, and 0.1-0.3% degreasing agent of the total weight of the leather to the delimed and softened leather, placing the leather in a rotating drum and rotating for 15-25 minutes before draining the water.

5. The chrome-free leather processing technology according to claim 1, characterized in that: The pickling tanning step is specifically as follows: adding 75-85% of water of the total weight of the leather to the delimed and softened leather, adding 6-9% of industrial salt of the total weight of the leather, adding 1-3% of fish oil of the total weight of the leather, placing the leather in a rotary drum and rotating for 10-15 minutes, adding 0.4-0.6% of sulfuric acid of the total weight of the leather, adding 0.6-0.9% of formic acid of the total weight of the leather, placing the leather in a rotary drum and rotating for 60-80 minutes and then draining, adding 45-55% of water of 28-32° C. of the total weight of the leather, adding 4-6% of synthetic tanning agent RL of the total weight of the leather, rotating for 60-80 minutes, adding 4-6% of synthetic tanning agent 806 of the total weight of the leather, placing the leather in a rotary drum and rotating for 20-30 minutes, controlling the pH of the leather to be 3-4, taking the leather out of the drum and standing it, and completing the pickling tanning step.

6. The chrome-free leather processing technology according to claim 1, characterized in that: The chrome-free retanning step specifically comprises: adding 45-55% of the total weight of the leather and water at 28-32° C. to the leather after pickling tanning, adding 8-11% of the total weight of the leather and industrial salt, placing the leather in a drum and rotating for 15-18 minutes, adding 2-6% of the total weight of the leather and chrome-free tanning agent TWS, adding 4-8% of the total weight of the leather and chrome-free tanning agent TWLZ, adding 1-1.5% of the total weight of the leather and raw oil, adding 7-9% of the total weight of the leather and Tannin extract is placed in a rotary drum and rotated for 130-150 minutes, 1-1.5% of the total weight of the leather is added with a dispersant, 9-11% of the total weight of the leather is added with tannin extract, and the drum is rotated for 110-130 minutes, 45-55% of the total weight of the leather is added with water, and the drum is rotated for 55-65 minutes, the pH of the leather is controlled to be 5.0, and the leather is allowed to stand for 24 hours. After the standing is completed, the leather is placed in a rotary drum and rotated for 18-22 minutes, and then the leather is taken out of the drum.

7. The chrome-free leather processing technology according to claim 1, characterized in that: The dyeing and finishing step specifically comprises: adding 190-200% of the total weight of the leather with 30-35° C. water to the leather after chrome-free retanning, adding 0.4-0.6% of the total weight of the leather with OXALIC ACID, adding 0.1-0.2% of the total weight of the leather with SAF, placing the leather in a drum for 35-45 minutes, and then draining and washing the leather, adding 190-200% of the total weight of the leather with 30-35° C. water, adding 1.4-1.6% of the total weight of the leather with PAK, placing the leather in a drum for 23-35 minutes, adding 0.4-0.6% of the total weight of the leather with baking soda, placing the leather in a drum for 23-35 minutes, controlling the pH of the leather to be 4-5, and then draining and washing the leather, adding 45-50% of the total weight of the leather with 30-35° C. water, adding 3.5-4.5% of the total weight of the leather with TANIGAN OS, add 3.5-4.5% ATO of the total weight of the leather, add 9-11% CHD of the total weight of the leather, add 1.4-1.6% H50 of the total weight of the leather, place it in a drum and rotate for 55-60 minutes, check the penetration of the leather, add 95-105% water at 30-35°C of the total weight of the leather, place it in a drum and rotate for 18-23 minutes overnight, then drain and wash the leather, add 95-105% water at 30-35°C of the total weight of the leather, add dye, add 95-105% water at 45-55°C of the total weight of the leather, add 3-4% CVL of the total weight of the leather, add 4-6% H50 of the total weight of the leather, add 1-1.2% E123 of the total weight of the leather, place it in a drum and rotate for 35-40 minutes, add 2.5-3.5% INTAN of the total weight of the leather EG, add INTAN EMS which is 2.5-3.5% of the total weight of the leather, check the penetration of the leather, put it into the drum and rotate it for 35-40 minutes, add HCOOH which is 1-1.2% of the total weight of the leather, put it into the drum and rotate it for 15-20 minutes, squeeze the water out of the leather and dry it naturally in vacuum after it comes out of the drum.