Low-chromium, low-formaldehyde and low-bisphenol after-tanning wet finishing process

Abstract

The invention relates to a low-chromium, low-formaldehyde and low-bisphenol after-tanning wet finishing process which comprises the following steps: rewetting, retanning and fat liquoring: taking zeolite tanned wet white leather as raw material leather, and carrying out rewetting treatment according to a conventional process; adding a retanning agent, adding carboxymethyl chitosan, adding carboxymethyl chitosan, and adding synthetic oil. White wet leather is tanned by adopting a zeolite tanning agent in a tanning stage, carboxymethyl chitosan is added into a retanning process in tanning wet finishing to replace an original phenolic synthetic tanning agent, the retanning process is adjusted to reduce use of a formaldehyde-containing chemical material, a melamine retanning agent is added to capture free formaldehyde in crust leather, and the content of formaldehyde in the crust leather is reduced. The content of bisphenol and formaldehyde in finished leather is effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of leather manufacturing, in particular to a low-chromium, low-formaldehyde and low-bisphenol post-tanning wet finishing process. Background Art

[0002] Under the background of green and natural leather making, the optimization of leather making process and the reduction of the use of leather making chemicals have become the new development direction of the leather making industry. Chrome tanning has been the most commonly used tanning agent for leather tanning in the past 100 years, and it is highly favored because it can make the finished leather have excellent physical and chemical properties. However, under the development direction of green leather making, the emission of chromium compounds poses potential risks to the environment and health, making low-chrome and chrome-free tanning processes the future development direction.

[0003] Phenolic synthetic tanning agents are frequently used in wet finishing after chrome-free tanning. Common phenolic synthetic tanning agents include sulfomethylated phenol-aldehyde condensation synthetic tanning agents, methyl-bridged phenol-aldehyde condensation synthetic tanning agents, etc. These phenolic synthetic tanning agents have good astringency and can make the retanned leather have a full and soft feel. If the use of phenolic synthetic tanning agents is reduced, the leather after retanning may become stiff, flat, and lack elasticity. However, with the increasing number of substances of very high concern (SVHC) identified by the EU REACH regulation, the export control of various countries has become increasingly strict. Since 2020, the bisphenol content in finished leather has gradually become the focus of the leather industry. This is mainly because when phenolic synthetic tanning agents are used as the main filler in leather production, small molecular phenolic substances will remain in the finished leather, resulting in excessive bisphenol content. Therefore, it is very important to find chemical materials to replace phenolic synthetic tanning agents in the leather making process.

[0004] At the same time, in recent years, as people are pursuing ecological leather products, the issue of formaldehyde content has attracted widespread attention in many countries. Aldehyde chemicals, as a key chemical raw material, are widely used in leather tanning, retanning and finishing. Common aldehyde chemicals include formaldehyde and glutaraldehyde. These aldehyde tanning agents can make the finished leather have a soft and plump feel, and its bending resistance and sweat resistance are better than chrome tanned leather. However, the use of aldehyde chemicals may cause a certain amount of formaldehyde to remain in leather products, making the finished leather have certain safety hazards.

[0005] Based on the above needs, this case came into being. Summary of the invention

[0006] The invention provides a low-chromium, low-formaldehyde and low-bisphenol post-tanning wet finishing process to solve the problem of excessive chromium, formaldehyde or bisphenol in the existing leather tanning.

[0007] The present invention adopts the following technical solution:

[0008] A low-chrome, low-formaldehyde, low-bisphenol post-tanning wet finishing process, comprising the following steps: rewetting → retanning → fatliquoring, wherein:

[0009] Rewetting: Using zeolite tanned white wet leather as raw material, rewetting treatment is carried out according to the conventional process based on the weight of the white wet leather; that is, 180%-200% water is added to the drum, 0.1%-0.2% degreasing agent is added, and the drum is rotated for 40 minutes to drain; 300%-350% water is added, and the drum is rotated for 5 minutes to drain;

[0010] Retanning: add 30%-35% water, add 1%-3% retanning agent, add 1%-2% carboxymethyl chitosan, add 1%-2% organic synthetic tanning agent, add 1%-3% amphoteric acrylic acid, turn for 70min; add 1%-2% acrylic acid, add 1%-2% synthetic oil, turn for 30min; 0.3%-0.5% synthetic tanning agent, add 1%-3% lanolin, turn for 20min; add 1%-3% acrylic acid retanning agent, add 1%-2% acrylic acid retanning agent, turn for 120min; add 1%-2% synthetic tannin, add 1%-2% resin retanning agent, add 1%-2% resin, turn for 150min; add 1%-2% acrylic acid, turn for 90min, then turn for 3min and stop at 27 overnight; add 100% water, temperature 45℃, turn for 10min; 0.1%-0.2% formic acid, turn for 20min; drain;

[0011] Fatliquoring: add 80%-100% water, add 1%-2% carboxymethyl chitosan, add 1%-2% synthetic oil, add 1%-2% amphoteric tannin, add 1%-2% synthetic oil, turn for 30min; add 1%-2% acrylic acid retanning agent, add 1%-2% synthetic tannin, turn for 40min; add 1%-2% resin retanning agent, add 1%-2% acrylic resin, turn for 30min; add 1%-2% amphoteric acrylic acid, turn for 60min; add 50% water, temperature 50℃, add 2.1% formic acid three times, turn for 15min each time; add 0.5% formic acid, turn for 15min; drain; add 300% water, turn for 5min; drain and drum.

[0012] Furthermore, the preparation of the above-mentioned carboxymethyl chitosan comprises the following steps:

[0013] Step 1, take 200g of washed and ground crab shells and put them into a 1L beaker, add 500g of 2%-7% dilute hydrochloric acid and soak for 36h-48h, then take out the solid to obtain acid-treated solid A; Step 2, put solid A into a 500L beaker, add 200L of clean water and wash it for 3 times to obtain washed solid B;

[0014] Step 3, take 100g of solid B and put it into a 500ml beaker, add 200g of sodium hydroxide solution with a mass fraction of 40%-60%, heat to 100℃-120℃, react for 1h-4h to obtain solid C after alkali treatment; Step 4, put solid C into a 500L beaker, add 200L of clean water to wash, repeat 3 times, filter and dry to obtain solid D;

[0015] Step 5, take 20g of solid D and add it to a 2L beaker, add 150ml-200ml of isopropanol, add 200-300ml of a sodium hydroxide solution with a mass fraction of 40%-60%, heat to 60°C-80°C, and react for 60min-90min; add 20g-30g of chloroacetic acid, heat to 60°C-80°C, and react for 5h-8h; add 2%-7% dilute hydrochloric acid to adjust the pH to 6.5-7.0; add 500ml of a 75% ethanol solution to obtain a solid-liquid coexistence A, filter the solid-liquid coexistence A to obtain a solid E;

[0016] Step 6, drying the solid E with a spray dryer to obtain carboxymethyl chitosan.

[0017] Furthermore, the above retanning: add 30% water, add 3% retanning agent, add 2% carboxymethyl chitosan, add 2% organic synthetic tanning agent, add 3% amphoteric acrylic acid, and rotate for 70 minutes; add 2% acrylic acid, add 2% synthetic oil, and rotate for 30 minutes; 0.5% synthetic tanning agent, add 3% lanolin, and rotate for 20 minutes; add 3% acrylic acid retanning agent, add 2% acrylic acid retanning agent, and rotate for 120 minutes; add 2% synthetic tannin, add 1% resin retanning agent, add 2% resin, and rotate for 150 minutes; add 2% acrylic acid, rotate for 90 minutes, then rotate for 3 minutes and stop at 27 overnight; add 100% water, temperature 45°C, rotate for 10 minutes; 0.2% formic acid, rotate for 20 minutes; drain.

[0018] Furthermore, the above-mentioned fatliquoring: adding 80% water, adding 1% carboxymethyl chitosan, adding 1% synthetic oil, adding 1% amphoteric tannin, adding 1% synthetic oil, and rotating for 30 minutes; adding 2% acrylic acid retanning agent, adding 1% synthetic tannin, and rotating for 40 minutes; adding 1% resin retanning agent, adding 1% acrylic resin, and rotating for 30 minutes; adding 2% amphoteric acrylic acid, and rotating for 60 minutes; adding 50% water, the temperature is 50°C, adding 2.1% formic acid in three times, rotating for 15 minutes each time; adding 0.5% formic acid, rotating for 15 minutes; draining; adding 300% water, rotating for 5 minutes; draining and drumming.

[0019] It can be seen from the above description of the present invention that, compared with the prior art, the present invention has the following advantages:

[0020] 1. The present application adopts zeolite tanning agent to tan wet white leather in the tanning stage, and adopts carboxymethyl chitosan to add to the retanning process in the wet finishing after tanning to replace the original phenolic synthetic tanning agent, and adjusts the retanning process to reduce the use of formaldehyde-containing materials, and adds melamine retanning agent to capture free formaldehyde in the crust leather, thereby effectively reducing the bisphenol and formaldehyde content in the finished leather.

[0021] 2. The present application uses zeolite-tanned white wet leather in the tanning stage, does not use chrome for retanning in the retanning stage, uses other synthetic tanning agents instead, and does not introduce chrome tanning agents in the entire finished leather process; uses carboxymethyl chitosan to replace the use of phenolic synthetic tanning agents in the post-tanning wet finishing stage, optimizes the retanning process, and reduces the use of other chemical materials; uses organic synthetic tanning agents to replace the original glutaraldehyde in the post-tanning wet finishing stage, reducing the introduction of free formaldehyde from the source.

[0022] 3. The carboxymethyl chitosan of the present application is a natural polymer compound obtained by carboxymethylation of chitosan present in the shells of crustaceans, the cell walls of fungi and the cell walls of plants. The raw materials for preparation are green and sustainable, and the carboxymethyl chitosan itself has certain antibacterial properties. Carboxymethyl chitosan has a good dispersing effect and can effectively reduce the amount of other chemical materials. DETAILED DESCRIPTION

[0023] Embodiment 1:

[0024] A low-chromium, low-formaldehyde, low-bisphenol post-tanning wet finishing process comprises the following steps:

[0025] Step 1, rewetting: using zeolite tanned white wet leather as raw material, rewetting treatment is performed according to conventional process; that is, 200% water is added to the drum, 0.2% degreasing agent (W100, Boska (Shangqiu) Chemical Co., Ltd.) is added, and the drum is rotated for 40 minutes to drain; 300% water is added, and the drum is rotated for 5 minutes to drain;

[0026] Step 2, retanning: add 30% water, add 3% retanning agent (GSV, Templer New Materials Jiaxing Co., Ltd.), add 2% carboxymethyl chitosan, add 2% organic synthetic tanning agent (TWS, Sichuan Tingjiang New Materials Co., Ltd.), add 3% amphoteric acrylic acid (TWR5S, Sichuan Tingjiang New Materials Co., Ltd.), turn for 70 minutes; add 2% acrylic acid (A30, Sichuan Dawe Technology Co., Ltd.), add 2% synthetic oil (SK70, Sichuan Desail New Materials Technology Co., Ltd.), turn for 30 minutes; 0.5% synthetic tanning agent (DA, Brother Technology Co., Ltd.), add 3% lanolin (NSL, Templer New Materials Jiaxing Co., Ltd.), turn for 20 minutes; add acrylic acid Retanning agent (R83, Temple New Materials Jiaxing Co., Ltd.) 3%, add acrylic retanning agent (B4, Shanghai Fengzheng Wanwei Leather Chemical Co., Ltd.) 2%, rotate for 120 minutes; add synthetic tannin (R-7898, Sichuan Tingjiang New Materials Co., Ltd.) 2%, add resin retanning agent (R19, Shanghai Fengzheng Wanwei Leather Chemical Co., Ltd.) 1%, add resin (BT4, Suzhou Yichang Chemical Reagent Co., Ltd.) 2%, rotate for 150 minutes; add amphoteric acrylic acid (TWR5S, Sichuan Tingjiang New Materials Co., Ltd.) 2%, rotate for 90 minutes, then rotate for 3 minutes and stop at 27 overnight; add water 100%, temperature 45°C, rotate for 10 minutes; formic acid 0.2%, rotate for 20 minutes; drain.

[0027] Step 3, fatliquoring: add 80% water, add 1% carboxymethyl chitosan, add 1% synthetic oil (30CT, Suzhou Yichang Chemical Reagent Co., Ltd.), add 1% amphoteric tannin (205, Zhejiang Shenghui Chemical Co., Ltd.), add 1% synthetic oil (SK70, Sichuan Desail New Material Technology Co., Ltd.), and turn for 30 minutes; add 2% acrylic acid retanning agent (R83, Temple New Materials Jiaxing Co., Ltd.), add 1% synthetic tannin R-7898, Sichuan Tingjiang New Materials Co., Ltd.), and turn for 40 minutes; add 1% resin retanning agent (R19, Shanghai Fengzheng Wanwei Leather Chemical Co., Ltd.), add 1% acrylic resin (A30, Sichuan Dawei Technology Co., Ltd.), and turn for 30 minutes; add 2% amphoteric acrylic acid (TWR5S, Sichuan Tingjiang New Materials Co., Ltd.), and turn for 60 minutes; add 50% water, the temperature is 50°C, add 2.1% formic acid in three times, and turn for 15 minutes each time; add 0.5% formic acid, and turn for 15 minutes; drain; add 300% water, and turn for 5 minutes; drain and drum.

[0028] The preparation of the above-mentioned carboxymethyl chitosan comprises the following steps:

[0029] Step 1, take 200g of washed and ground crab shells and put them into a 1L beaker, add 500g of 2% dilute hydrochloric acid and soak for 36 hours, then take out the solid to obtain acid-treated solid A; Step 2, put solid A into a 500L beaker, add 200L of clean water and wash it for 3 times to obtain washed solid B;

[0030] Step 3, take 100g of solid B and put it into a 500ml beaker, add 200g of 40% sodium hydroxide solution by mass, heat to 100°C, and react for 1h to obtain solid C after alkali treatment;

[0031] Step 4, put solid C into a 500L beaker, add 200L of clean water to wash, repeat 3 times, filter and dry to obtain solid D;

[0032] Step 5, take 20g of solid D and add it to a 2L beaker, add 150ml of isopropanol, add 200ml of 40% sodium hydroxide solution, heat to 60°C, and react for 60min; add 20g of chloroacetic acid, heat to 60°C, and react for 5h; add 2% dilute hydrochloric acid to adjust the pH to 6.5-7.0; add 500ml of 75% ethanol solution to obtain solid-liquid coexistence A, filter the solid-liquid coexistence A to obtain solid E;

[0033] Step 6, drying the solid E with a spray dryer to obtain carboxymethyl chitosan.

[0034] Embodiment 2:

[0035] A low-chromium, low-formaldehyde, low-bisphenol post-tanning wet finishing process comprises the following steps:

[0036] Rewetting: Using zeolite tanned wet leather as raw material, rewetting treatment was carried out according to conventional process; that is, 180% water and 0.2% degreasing agent (W100, Boska (Shangqiu) Chemical Co., Ltd.) were added to the drum, and the drum was rotated for 40 minutes to drain; 350% water was added and the drum was rotated for 5 minutes to drain;

[0037] Retanning: add 35% water, add 1% retanning agent (GSV, Templer New Materials Jiaxing Co., Ltd.), add 2% carboxymethyl chitosan, add 2% organic synthetic tanning agent (TWS, Sichuan Tingjiang New Materials Co., Ltd.), add 1% amphoteric acrylic acid (TWR5S, Sichuan Tingjiang New Materials Co., Ltd.), turn for 70 minutes; add 1% acrylic acid (A30, Sichuan Dawe Technology Co., Ltd.), add 1% synthetic oil (SK70, Sichuan Desail New Materials Technology Co., Ltd.), turn for 30 minutes; 0.3% synthetic tanning agent (DA, Brothers Technology Co., Ltd.), add 1% lanolin (NSL, Templer New Materials Jiaxing Co., Ltd.), turn for 20 minutes; add acrylic acid retanning 1% of the agent (R83, Templer New Materials Jiaxing Co., Ltd.), 1% of the acrylic acid retanning agent (B4, Shanghai Fengzheng Wanwei Leather Chemical Co., Ltd.), and 1% of the reaction mixture, and the mixture was rotated for 120 min; 1% of the synthetic tannin (R-7898, Sichuan Tingjiang New Materials Co., Ltd.), 1% of the resin retanning agent (R19, Shanghai Fengzheng Wanwei Leather Chemical Co., Ltd.), and 1% of the resin (BT4, Suzhou Yichang Chemical Reagent Co., Ltd.), and the mixture was rotated for 150 min; 1% of the amphoteric acrylic acid (TWR5S, Sichuan Tingjiang New Materials Co., Ltd.) was added, and the mixture was rotated for 90 min, then rotated for 3 min and stopped at 27 overnight; 100% of water was added, the temperature was 45°C, and the mixture was rotated for 10 min; 0.1% of formic acid was added, and the mixture was rotated for 20 min; the mixture was drained;

[0038] Step 3, fatliquoring: add 100% water, add 2% carboxymethyl chitosan, add 2% synthetic oil (30CT, Suzhou Yichang Chemical Reagent Co., Ltd.), add 2% amphoteric tannin (205, Zhejiang Shenghui Chemical Co., Ltd.), add 2% synthetic oil (SK70, Sichuan Desail New Materials Technology Co., Ltd.), turn for 30min; add 2% acrylic acid retanning agent (R83, Temple New Materials Jiaxing Co., Ltd.), add 2% synthetic tannin (R-7898, Sichuan Tingjiang New Materials Co., Ltd.), turn for 40min n; add 2% of resin retanning agent (R19, Shanghai Fengzheng Wanwei Leather Chemical Co., Ltd.), add 2% of acrylic resin (A30, Sichuan Dawei Technology Co., Ltd.), and rotate for 30 minutes; add 1% of amphoteric acrylic acid (TWR5S, Sichuan Tingjiang New Materials Co., Ltd.), and rotate for 60 minutes; add 50% of water, the temperature is 50°C, add 2.1% of formic acid in three times, and rotate for 15 minutes each time; add 0.5% of formic acid, and rotate for 15 minutes; drain; add 300% of water, and rotate for 5 minutes; drain and remove from the drum.

[0039] The preparation of the above-mentioned carboxymethyl chitosan comprises the following steps:

[0040] Step 1, take 200g of washed and ground crab shells and put them into a 1L beaker, add 500g of 7% dilute hydrochloric acid and soak for 48h, then take out the solid to obtain acid-treated solid A; Step 2, put solid A into a 500L beaker, add 200L of clean water and wash it for 3 times to obtain washed solid B;

[0041] Step 3, take 100g of solid B and put it into a 500ml beaker, add 200g of 60% sodium hydroxide solution by mass, heat to 120°C, and react for 4h to obtain solid C after alkali treatment;

[0042] Step 4, put solid C into a 500L beaker, add 200L of clean water to wash, repeat 3 times, filter and dry to obtain solid D;

[0043] Step 5, take 20g of solid D and add it to a 2L beaker, add 200ml of isopropanol, add 300ml of 60% sodium hydroxide solution, heat to 80°C, and react for 90min; add 30g of chloroacetic acid, heat to 80°C, and react for 8h; add 7% dilute hydrochloric acid to adjust the pH to 6.5-7.0; add 500ml of 75% ethanol solution to obtain solid-liquid coexistence A, filter the solid-liquid coexistence A to obtain solid E;

[0044] Step 6, drying the solid E with a spray dryer to obtain carboxymethyl chitosan.

[0045] The post-tanning wet finishing process of the present application is compared with the original process, as follows:

[0046] Table 1 Process comparison table

[0047]

[0048]

[0049] The wet blue leather obtained by the post-tanning wet finishing process of the present application was tested as follows:

[0050] Table 1 Comparison of wet blue leather performance

[0051]

[0052] Testing indicators and methods:

[0053] The physical and mechanical properties of leather are measured in accordance with GB / T 39368-39376-2020 Physical and mechanical tests for leather.

[0054] The shrinkage temperature of leather is measured according to QB-T 2713-2005 Determination of shrinkage temperature of leather in physical and mechanical tests.

[0055] The chromium content in leather is measured in accordance with GB / T 22807-2019 Leather and fur chemical tests - Determination of hexavalent chromium content: spectrophotometric method.

[0056] The formaldehyde content is measured in accordance with GB / T 19941--2005 Determination of formaldehyde content of leather and fur.

[0057] Bisphenol content is measured according to the determination of bisphenol compounds in leather and fur chemical test by liquid chromatography.

[0058] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A low-chromium, low-formaldehyde, low-bisphenol post-tanning wet finishing process, characterized in that: The process comprises the following steps: rewetting → retanning → fatliquoring, wherein: Rewetting: Using zeolite tanned wet leather as raw material, rewetting treatment is carried out according to conventional process; that is, add 180%-200% water to the drum, add 0.1%-0.2% degreasing agent, rotate for 40 minutes and drain; add 300%-350% water, rotate for 5 minutes and drain; Retanning: add 30%-35% water, add 1%-3% retanning agent, add 1%-2% carboxymethyl chitosan, add 1%-2% organic synthetic tanning agent, add 1%-3% amphoteric acrylic acid, turn for 70min; add 1%-2% acrylic acid, add 1%-2% synthetic oil, turn for 30min; 0.3%-0.5% synthetic tanning agent, add 1%-3% lanolin, turn for 20min; add 1%-3% acrylic acid retanning agent, add 1%-2% acrylic acid retanning agent, turn for 120min; add 1%-2% synthetic tannin, add 1%-2% resin retanning agent, add 1%-2% resin, turn for 150min; add 1%-2% acrylic acid, turn for 90min, then turn for 3min and stop at 27 overnight; add 100% water, temperature 45℃, turn for 10min; 0.1%-0.2% formic acid, turn for 20min; drain; Fatliquoring: add 80%-100% water, add 1%-2% carboxymethyl chitosan, add 1%-2% synthetic oil, add 1%-2% amphoteric tannin, add 1%-2% synthetic oil, turn for 30min; add 1%-2% acrylic acid retanning agent, add 1%-2% synthetic tannin, turn for 40min; add 1%-2% resin retanning agent, add 1%-2% acrylic resin, turn for 30min; add 1%-2% amphoteric acrylic acid, turn for 60min; add 50% water, temperature 50℃, add 2.1% formic acid three times, turn for 15min each time; add 0.5% formic acid, turn for 15min; drain; add 300% water, turn for 5min; drain and drum.

2. A low chromium, low formaldehyde, low bisphenol post-tanning wet finishing process as claimed in claim 1, characterized in that: The preparation of the carboxymethyl chitosan comprises the following steps: Step 1, taking 200 g of sea crab shells washed and ground with water and adding them into a 1L beaker, adding 500 g of dilute hydrochloric acid with a concentration of 2%-7%, soaking for 36h-48h, and then taking out the solid to obtain acid-treated solid A; Step 2, put solid A into a 500L beaker, add 200L of clean water and wash it 3 times to obtain washed solid B; Step 3, take 100g of solid B and put it into a 500ml beaker, add 200g of 40%-60% sodium hydroxide solution by mass, heat to 100°C-120°C, and react for 1h-4h to obtain solid C after alkali treatment; Step 4, put solid C into a 500L beaker, add 200L of clean water to wash, repeat 3 times, filter and dry to obtain solid D; Step 5, take 20g of solid D and add it to a 2L beaker, add 150ml-200ml of isopropanol, add 200-300ml of a sodium hydroxide solution with a mass fraction of 40%-60%, heat to 60°C-80°C, and react for 60min-90min; add 20g-30g of chloroacetic acid, heat to 60°C-80°C, and react for 5h-8h; add 2%-7% dilute hydrochloric acid to adjust the pH to 6.5-7.0; add 500ml of a 75% ethanol solution to obtain a solid-liquid coexistence A, filter the solid-liquid coexistence A to obtain a solid E; Step 6, drying the solid E with a spray dryer to obtain carboxymethyl chitosan.

3. A low chromium, low formaldehyde, low bisphenol post-tanning wet finishing process as claimed in claim 1, characterized in that: The retanning process comprises the following steps: adding 30% water, 3% retanning agent, 2% carboxymethyl chitosan, 2% organic synthetic tanning agent, 3% amphoteric acrylic acid, and rotating for 70 minutes; adding 2% acrylic acid, 2% synthetic oil, and rotating for 30 minutes; adding 0.5% synthetic tanning agent, 3% lanolin, and rotating for 20 minutes; adding 3% acrylic acid retanning agent, adding 2% acrylic acid retanning agent, and rotating for 120 minutes; adding 2% synthetic tannin, 1% resin retanning agent, adding 2% resin, and rotating for 150 minutes; adding 2% acrylic acid, rotating for 90 minutes, then rotating for 3 minutes, and stopping for 27 hours overnight; adding 100% water, heating at 45°C, and rotating for 10 minutes; adding 0.2% formic acid, and rotating for 20 minutes; and draining.

4. A low chromium, low formaldehyde, low bisphenol post-tanning wet finishing process as claimed in claim 1, characterized in that: The fatliquoring comprises the following steps: adding 80% water, 1% carboxymethyl chitosan, 1% synthetic oil, 1% amphoteric tannin, 1% synthetic oil, and rotating for 30 minutes; adding 2% acrylic acid retanning agent, 1% synthetic tannin, and rotating for 40 minutes; adding 1% resin retanning agent, 1% acrylic resin, and rotating for 30 minutes; adding 2% amphoteric acrylic acid, and rotating for 60 minutes; adding 50% water, the temperature is 50°C, adding 2.1% formic acid in three times, and rotating for 15 minutes each time; adding 0.5% formic acid, and rotating for 15 minutes; draining the water; Add 300% water and rotate for 5 minutes; drain and remove the drum.

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